Lifting removal of cationic dye (methylene blue) from wastewater by improving Zr-MOFs via second metal Al coordination

Introduction

Despite government regulations, ensuring environmental compliance with established terms of wastewater release and chemical handling is difficult [1]. Today, dye contaminants have become one of the most important environmental problems in the world. Effluent with organic dyes discarded into natural watercourses endanger living creatures and the environment because of their toxicity and carcinogenic effects [2]. In addition, dye content in water prevents sunlight penetration which decreases plant photosynthesis [1].

Significant amounts of dyes are employed in a wide range of industries involved in producing paper, textile, leather, pharmaceutics, food, cosmetics, print products, iron-steel products, coke, petroleum, pesticides, paints, solvents, wood-preserving chemicals. Further, their manufacturing plants consume large volumes of water that in turn generate large volumes of wastewater [3]. Almost 100,000 dyes and pigments have been tabulated to exist, consisting of 7000 kinds of chemical structures, that are used to produce 7 × 105 tonnes per year worldwide [4-7]. The majority of these dyes are resistant to biodegradation and oxidation processes [8]. About 10–15% of the dyes is discharged into the effluent during the dyeing process [9,10]. Recently, studies have reported that around 12% of synthetic dyes are wasted through colouring processes and operations [11]; 20% of lost dyes enter industrial wastewaters [12,13].

Dyes can be divided into two main groups, anionic (acidic) and cationic (basic) colour dyes. Methylene blue (MB) is a basic dye that is a focus of this study. Although MB is used in some medical applications, it is also widely used in colouring paper, dyed cottons, wools, coating for paper stocks, etc. Though MB is not strongly hazardous, it has some harmful effects. Acute exposure to MB will cause increased heart rate, vomiting, shock, Heinz body formation, cyanosis, jaundice, quadriplegia and tissue necrosis in humans [14].

Environmentally, it is essential to remove dyes from industrial wastewater because of their toxicity and high visibility [6,15-17]. Consequently, there is a continuous urgent need to ensure the removal these pollutants from industrial effluent and to comply with government legislation [18]. Many techniques have been attempted to discolour industrial discharge that involve chemical, biological and physical removal methods; however, most are unsuccessful because of their limitations and disadvantages [19].

Adsorption is a well-known and favourite technique because of its feasibility, simplicity and efficiency in the removal of such contaminants [20]. Many adsorbents have been employed to treat industrial wastewater containing dye. They include activated carbon derived from different sources of raw materials [21-30], agricultural solid waste [31-44], biosorbents [16,17,45-57], zeolites [58-63], industrial solid wastes [14,64-71], natural clay minerals [72-80], resins [81-84], metal oxides [85,86], metal organic frameworks (MOFs) [2,87-90].

Activated carbon from various sources has been the most investigated adsorbent in laboratories and most used by industries to remove basic dyes from their wastewaters [84,91-94]. However, its cost has limited its commercial use as a sorbent. As a result, many studies have been undertaken in the last decade to identify a cost-effective sorbent [43].

MOF [95-102], or hybrid inorganic and organic framework [103], is a 21st century material with tuneable options, organic functionality, open metal sites in its skeleton, large-sized pores, high surface areas (1000 to 10,000 m2/g) as well as high thermal, water, chemical, architectural and mechanical stability [2,104]. It is a class of ultra-high porous material constructed with secondary building units (SBUs) [105] and synthesised by reticular chemistry [106,107] that connect the inorganic part with the metal ion to the organic part with polytopic carboxylate group to form vertices and linkers with strong bonds [108]. The variety of geometry, size and functionality of the constituents of MOFs has enabled scientists around the world to synthesise more than 84,185 MOF structures [98]. Their variety and multiplicity, as well as permanent porosity, make them favourable materials in many applications, such as CO2 capture, hydrogen and methane storage, sensors, photocatalysis, drug delivery, catalysis applications and the adsorptive removal of contaminants from aqueous solutions [87,105,108-112].

The objective of the present study is to describe the synthesis and characterisation of single-metal Zr-MOF (UiO-66) and bimetal Zr-MOFs (UiO-66-10%Al and UiO-66-30%Al), and examine their potential as sorbents to remove MB, a cationic basic dye, in wastewater. The kinetics and equilibrium of the adsorption process were fitted to kinetics models and equilibrium theoretical models. Further, the mechanism that limits the rate of sorption reaction was investigated using an intraparticle diffusion method to improve understanding of the dynamics in the adsorption process.

Materials and Methods Synthesis and activation

All chemicals were supplied by Sigma-Aldrich (Australia) without further purifications. A scaled-up procedure of a previously reported method [56] of synthesising Zr-MOF was successfully undertaken, using a modified ratio of ZrCl4:BDC:DMF (2.27 mmol ZrCl4, 2.27 mmol 1,4-benzenedicarboxylic acid [BDC]). The abovementioned chemicals were mixed with continuous agitation with 405.38 mmol N, N-dimethylformamide (DMF) solvothermally. The resulting mixture was placed in an autoclave at 393 K for 1 d. The product Zr-MOF was filtered, dried and immersed in chloroform for 5 d. After activation by chloroform was completed, the solid was filtered and dried using vacuum and heated at 463 K for 48 h. The following method was used to synthesise UiO-66-10%Al. Terephthalic acid (1.1 g, 98%; Sigma-Aldrich) and DMF (73 mL, 99%; Sigma-Aldrich) were mixed together and stirred until the acid dissolved. Within 10 min of the clear solution forming, ZrCl4 (1.5 g; Sigma-Aldrich, 99%) was added to the solution with continued stirring for another 5 min. Al (NO3)3.9H2O (0.15 g) was then added, along with 2 mL of H2O, to the mixture and stirred for another 15 min. The solution was transferred to a 125-mL Teflon-lined autoclave, which was tightly sealed and then placed in a preheated oven at 132 °C for 24h. The white powder product of UiO-66-10% Al was collected using a centrifuge machine and washed in DMF three times. The resultant product was dried in an oven and activated by immersing it in absolute methanol (100%; Sigma-Aldrich) for 5 d. Before using the MOF as an adsorbent, it was filtered, dried and heated in vacuum at 473K overnight. To synthesise UiO-66-30%Al, ZrCl4 (1.5 g) was mixed with terephthalic acid (1.3 g) in DMF (60.2 mL). After mixing for 15 min, Al (NO3)3.9H2O (0.45 g) was added and then 5 mL of H2O was added to the mixture. The solution was mixed for approximately 30 min. It was then moved to a 125-mL Teflon-lined autoclave, which was tightly sealed and then placed in a preheated oven at 157°C for 1d. The white powder product of UiO-66-10% Al was collected using a centrifuge machine and washed in DMF three times. The resultant product was dried in an oven and activated by immersing in absolute methanol (100%; Sigma-Aldrich) for 5d. Before using the MOF as an adsorbent, it was filtered, dried and heated in a vacuum at 473K overnight.

 Characterisation

Thermogravimetric analysis (TGA) of the single-metal and bimetal Zr-MOFs was done using a TGA instrument (TGA/DSC1 STARe system; Mettler-Toledo). All MOF samples were placed in crucibles and transferred to the machine and heated at a rate of 5K/min until 1173K when the air gas flow rate was maintained at 10 mL/min. The stability of the functional groups on the organic linkers were assessed using Fourier transform infrared spectroscopy (FTIR; Spectrum 100 FT-IR spectrometer, PerkinElmer). A scanning process was undertaken by an attenuated total reflectance technique to obtain the FTIR spectra range 600 to 4000 cm−1 with a resolution of 4 cm−1. To check the integrity of the MOF structure, X-ray powder diffraction patterns were obtained using an X-ray diffractometer (D8 Advance, Bruker AXS) with Cu Kα radiation (λ = 1.5406 Å), accelerating voltage 40 kV and current 40 mA. N2 adsorption/desorption isotherms were performed using a Quantachrome instrument (Autosorb-1), and textural properties of the Zr-MOFs were determined, such as pore size, pore volume and surface area. All MOFs were prepared by heat and vacuum for 1 d before loading to the machine to determine their adsorption properties.

 Adsorption process

An aqueous stock solution of MO (1000 ppm) was prepared by dissolving MB (C16H18ClN3S, molecular weight 319.85 g.mol–1; Sigma-Aldrich) in deionised water. Aqueous solutions with different concentrations of MB (5–100 ppm) were prepared by successive dilution of the stock solution with water, and MB concentrations were determined using absorbance at 668 nm wavelength of the solution after obtaining the UV spectra of the solution with a spectrophotometer (UV spectrophotometer). A calibration curve was obtained from spectra of the standard solutions (5–100 ppm). Prior to adsorption, the adsorbents were dried overnight in a vacuum at 373 K. Several glass containers were cleaned, dried and filled to 20 mL with MB of different concentrations ranging from 5 to 50 ppm. Following this, an exact amount of an MOF adsorbent (20 mg) was put in each glass container.

The dye solutions containing the adsorbents were mixed well by a magnetic stirrer and maintained for 5 min to 24h at 298K. The samples for analysis were collected by syringe filter at different sampling intervals. A UV spectrometer was used to investigate the dye content in the supernatant.

 Adsorption study

The adsorption mechanism and rate of diffusion were estimated using three kinetic models: are pseudo second-order [113], pseudo first-order [114] and intraparticle diffusion models [115]. Adsorption behaviours were simulated using the Langmuir [116] and Freundlich [117] adsorption isotherms.

Kinetics study

Batch adsorption laboratory techniques were used to design the experiments. All practical kinetics experiments were conducted by preparing the specified initial concentrations (5–50 mg/L) and adding a predetermined dose of the adsorbent into a definite volume of MB solution at room temperature. Agitation was performed with a magnetic stirrer machine at 200 rpm to optimise mass transfer and contact with the interfacial area for a predetermined time interval. MB concentration was measured using the supernatant at each predetermined time interval using a UV spectroscopy machine.

The amount of MB adsorbed onto UiO-66, UiO-66-10%Al and UiO-66-30%Al MOFs at any time was calculated using Equation 1 [118]. However, the percentage removal of MB was computed by Equation 2 [119].

\begin{equation}\tag{1} \end{equation}

\begin{equation}\tag{2} \end{equation}

Where:

\(\): the amount of MB adsorbed per unit weight of MOF at any time t (mg/g)

\(\): initial concentration of the MB solution at time zero (mg/L)

\(\): the concentration of MB solution at time t (mg/L)

\(\): volume of the MB solution in the batch adsorption process (L)

\(\): percentage removal of MB

\(\): MOF mass used in the adsorption batch process (g).

 Pseudo first-order model

The MOF removal of MB from simulated wastewater can be represented by a linear pseudo first-order model of adsorption [114,120] expressed below:

\begin{equation}\tag{3} \end{equation}

Where:

\(\): the amount of MB adsorbed per unit weight of MOF at equilibrium (mg/g),

\(\): the amount of MB adsorbed per unit weight of MOF at any time t (mg/g)

\(\): pseudo first-order rate constant (min–1)

\(\): time (min)

The linear relationship between values of \(\) and \(\) can be plotted as a straight line, from which qe and k1 can be found easily from the intercept and slope, respectively.

 Pseudo second-order model

The sorption kinetics of the MOF/MB system may also be described by a linearised form of the pseudo second-order model [113], based on adsorption equilibrium capacity expressed in the following form:

\begin{equation}\tag{4} \end{equation}

Where:

\(\): the amount of MB adsorbed per unit weight of MOF at equilibrium (mg/g)

\(\): the amount of MB adsorbed per unit weight of MOF at any time t (mg/g)

\(\): time (min)

\(\): pseudo second-order rate constant (g/mg min).

The values of \(\) are linearly correlated with \(\), and the plot of \(\) against t should be a straight line. The determination of \(\) and \(\) can be done from the slope and intercept, respectively.

 Elovich kinetic model

The Elovich equation is generally used for chemisorption applications and can be written as follows:

\begin{equation} \tag{5} \end{equation}

Where:

\(\): the amount of MB adsorbed per unit weight of MOF at any time t (mg/g)

\(\): a constant representing the initial rate of adsorption

\(\): constant during any one experiment

\(\): time (min)

It appears that the initial adsorption rate at the beginning of contact time is not controlled by exponential law because when \(\) approaches zero, \(\) equals \(\) [121]. Integrating Equation 5 by assuming \(\) at \(\), the result will be:

\begin{equation} \tag{6} \end{equation}

if \( 1]]>\), the simple form of Equation 6 can be expressed as follows:

\begin{equation}\tag{7} \end{equation}

In a plot of the straight-line equation of \(\) as a function of \(\), the slope and intercept will be \(\) and \(\), respectively.

Equation 7 can facilitate the determination of the applicability of the Elovich kinetic equation on MOF/MB systems [122].

 Intraparticle diffusion model

The intraparticle diffusion–based model is commonly used to test the mechanism of adsorption of pollutants onto a sorbent. This model is employed to identify the adsorption mechanism of MB onto MOF, and can be written as follows:

\begin{equation} \tag{8} \end{equation}

Where:

\(\): the amount of MB adsorbed per unit weight of MOF at any time t (mg/g)

\(\): intraparticle diffusion rate constant (mg/ g min0.5)

\(\): time (min)

\(\): intercept.

Based on this model, which is a linear relationship, the loading capacity is proportional to \(\) as well as the intraparticle diffusion rate constant \(\); \(\) and \(\) can be determined from the slope and intercept of the intraparticle diffusion equation plot, respectively.

 Equilibrium studies

Equilibrium studies were also performed in the same experiments carried out for kinetics studies. Agitation was done using a magnetic stirrer machine at 200 rpm until the process reached equilibrium. The amount of MB adsorbed onto UiO-66, UiO-66-10%Al and UiO-66-30%Al MOFs at equilibrium can be expressed by Equation (2)[123]:

\begin{equation}\tag{9} \end{equation}

Where:

\(\): the amount of MB adsorbed per unit weight of MOF at equilibrium (mg/g)

\(\): initial concentration of MB solution at time zero (mg/L)

\(\): concentration of MB solution at equilibrium (mg/L)

\(\): volume of MB solution in batch adsorption process (L)

\(\): MOF mass used in the adsorption batch process (g).

 Isotherm models

Identifying an adsorption isotherm is essential for describing the interaction of the pollutant (MB) with the adsorbent (MOF), so that the adsorbent can be optimised [36]. The two common isotherms are the Langmuir [124] and the Freundlich [117] isotherms.

 The Langmuir model

A nonlinear form of the Langmuir isotherm model can be expressed as:

\begin{equation} \tag{10} \end{equation}

It is possible to linearise the Langmuir isotherm equation to give the following:

\begin{equation} \tag{11} \end{equation}

Where:

\(\): Langmuir maximum loading capacity (mg/g)

\(\): Langmuir constant related to the energy of adsorption and affinity of binding sites (L/mg)

\(\): the equilibrium concentration of adsorbate (mg/L)

\(\): adsorption capacity at equilibrium (mg/g).

A plot of \( \) versus \( \) should obtain a linear relationship. Therefore, \(\) and \(\) can be determined from the slope and intercept of the plot.

The dimensionless constant separation factor \( \) is an important characteristic of the Langmuir isotherm that can be represented by the following equation [91,93,125,126]:

\begin{equation}\tag{12} \end{equation}

Where:

\( \): initial concentration of MB (mg/L)

\( \): Langmuir constant (L/mg).

The value of \(\) plays a very important role in the shape of the isotherm because it indicates the adsorption process is:

· unfavourable (\( 1]]>\))

· linear (\(\))

· favourable (\(\))

· irreversible (\(\)).

 The Freundlich model

The nonlinear model of the Freundlich isotherm [117] can be expressed as:

\begin{equation}\tag{13} \end{equation}

The linear equation of the Freundlich isotherm can be expressed as [14,127] :

\begin{equation} \tag{14} \end{equation}

Where:

\(\): the calculated Freundlich equilibrium constant ([mg/g] [L/mg]1/n) as an indicator of adsorption capacity

\(\): a measure of the deviation from linearity of adsorption (g/L).

A plot of \(\) versus \(\) should obtain a linear relationship; therefore, \(\) and \(\) can be determined from the slope and intercept of the plot.

If the value of \( 1]]>\), it is good indication that the adsorption process is favourable.

 Results and Discussion Characterisation

As shown in Figure 1(a), the XRD pattern for the modified bimetal Zr-MOF (UiO-66-10%Al and UiO-66-30%Al), in contrast to the parent single-metal Zr-MOF (UiO-66) before and after use, verify the phase purity and structural integrity of the MOF samples. Therefore, they are good signs of successful synthesis and activation of MOFs with pores free of oxide contaminants. Furthermore, Figure 1(a) show also the XRD patterns of the same above-mentioned MOFs after use in adsorption process.

Figure 1. Characterisation of metal organic framework samples: (a) PXRD patterns, (b) FTIR spectra and (c) TGA profiles of pristine and modified UiO-66 samples

Figure 1(b) illustrates FTIR spectra of parent (UiO-66) and modified bimetal Zr-MOF (UiO-66-10%Al and UiO-66-30%Al) before and after use. According to FTIR spectra of the three Zr-MOFs (single-metal and bimetal samples) shown in Figure 1(b), the application of the same vibration bands resulted in a slight deviation in the position of some peaks for the bimetal samples, with broader peaks verifying a difference in the dipole between ground state and excited state of bimetal Zr- MOFs due to incorporation of the second metal centre [128,129]. The extension of the vibration bands of bimetal MOFs was 1590 to 1525 cm–1; it was originally in the range 1615 to 1580 cm–1 because of C=C-C stretching in the aromatic ring of terephthalate salts [130]. In addition, the FTIR spectrum shows the stretching vibration of symmetric COO– and asymmetric COO– in organic linkers at bands 1500 and 1390 cm–1. However, bands at 881, 812 and 785 cm–1 were assigned to Zr-O stretching. In addition, stretching vibration of C-H at 730 cm–1 was attributed to the out-of-plane bending of aromatic ring of UiO-66, in comparison with that at 744 cm–1 attributed to the spectrum of bimetal Zr-MOF [129,131] and the stretching vibration of C-H at 1017 cm–1 to Zr-MOF.

Thermal stability of UiO-66, UiO66-10%Al and UiO66-30%Al was investigated using a TGA machine (TGA/DSC1 STARe system; Mettler-Toledo). The results of thermogravimetric analysis of all Zr-MOFs (single-metal and bimetal) are shown in Figure 1(c). They validate the thermal stability and structural robustness up to 725 K with a continuous mass loss of 15% and 25% for bimetal and single-metal MOFs, respectively. However, the variation in the weight loss of the samples is due to pre-treatment (dehydrated and hydrated) and solvent molecules in the pore interior of the material [132].

Measurements of N2 adsorption/desorption isotherms, pore size and surface area of Zr-MOFs (single-metal and bimetal) were obtained (Autosorb-1, Quantachrome Instruments). The isotherms of UiO-66-Al and UiO-66 are illustrated in Figure 2(a) and (b). According to Figure 2(a), the parent UiO-66 MOF exhibits the analogous of type IV adsorption–desorption isotherm, which is proof of a typical mesoporous network. Moreover, hysteresis from 0.1–1.0 relative pressure indicates a homogeneous pore size distribution [2].

Figure 2. N2 adsorption/desorption isotherm of UiO-66 (a), N2 adsorption/desorption isotherms of UiO-66-Al samples (b), micropore distribution (b)and mesopore distribution (c) of. UiO-66, UiO-66-10% Al and UiO-66-30% Al.

On the other hand, Figure 2(b) shows hysteresis in the desorption isotherm of UiO-66-10%Al and rapid increase in adsorption at approximate relative pressure equal to 0.999, indicating improving mesopore and macropore size. Based on the N2 adsorption–desorption isotherms, the values for the surface area, pore volume and pore size (textural properties) of Zr-MOF were calculated and listed in Table 1. These values indicate decreases in the specific surface area (SBET) with increases in the percentage of the second metal. That is, the SBET gradually decreased from 1585.5 m2g–1 in UiO-66 to become 1145.953 m2g–1 in UiO-66-10%Al, and reached 769.011 m2g–1 in UiO-66-30%Al.

Table 1. Textural properties of adsorbents based on N2 adsorption/isotherms

Adsorbents Specific surface area (SBET) (m2g–1) Pore volume (cc g–1) Pore diameter (nm)
UiO-66 1585.5 0.82 1.04
UiO-66-10% Al 1145.953 1.34 2.33
UiO-66-30% Al 769.011 0.39 1.01

In contrast, the pore volume and diameter were enlarged in UiO-66-10%Al, at 1.34 cc g–1 and 2.33 nm, respectively. The reason for such augmentation is attributable to the replacement of methanol molecules by the second metal in the first activation process involving solvent exchange and discarding it in the second activation process by heating and vacuum.

 Kinetic studies

Studies of kinetics are an essential part of a sorption process to enable the researchers to determine the rate and mechanism of adsorption [133]. To investigate the adsorption mechanism, including the mass transfer and chemical reaction [2], experimental data were examined using pseudo first-order, pseudo second-order and Elovich models. All the information and parameters relating to mechanism of adsorption can be obtained via adsorption kinetics, which are vital in treatment of aqueous effluent [134].

The adsorption process of the three solid /liquid (MOF/MB) systems were examined using pseudo first-order, pseudo second order [135-137] and Elovich models [122,133,138]. The key feature of these equations is the ease with which adsorption properties (e.g., adsorption capacity, rate constant) can be assigned, and the initial adsorption rate can be easily found from the linear equations of these models without previous knowledge of any parameter.

Figure 3. Fitting of experimental data using Elovich and second-order kinetics models of MB adsorption MB onto UiO-66 (a, b), UiO-66-10%Al (c, d) and UiO-66-30%Al (e, f).

Table 2. Calculated kinetics constant (k2) and correlation coefficient (R2) of the pseudo second-order model for Ci = 5, 15, 30 and 50 mg/L.

Adsorbent Adsorbate Pseudo second-order kinetics constant k2 (g/[mg.min])
5 ppm 15 ppm 30 ppm 50 ppm
k2 R2 k2 R2 k2 R2 k2 R2
UiO-66 MB 0.01050 0.9989 0.00546 0.9992 0.00273 0.9992 0.00147 0.9990
UiO-66-10% Al MB 1.34913 0.9999 0.01560 0.9997 0.00653 0.9995 0.00158 0.9953
UiO-66-30% Al MB 0.00520 0.9977 0.00212 0.9984 0.00060 0.9975 0.00074 0.9990

Table 3. Calculated kinetics constants (α and β) and correlation coefficient (R2) of Elovich model for Ci = 5, 15, 30 and 50 mg/L

Adsorbent Adsorbate Pseudo first-order kinetics constant k1 (min–1)
5 ppm 15 ppm 30 ppm 50 ppm
α β R2 α β R2 α β R2 α β R2
UiO-66 MB 0.102294 1.9857 0.9903 0.372103 0.7922 0.9738 0.619666 0.4416 0.9925 0.708909 0.2908 0.9986
UiO-66-10% Al MB 19160.34 2.5654 0.9242 2375.29 0.9349 0.9752 166.6202 0.3296 0.9843 198.8533 0.2332 0.9367
UiO-66-30% Al MB 0.275313 0.8190 0.9839 1.53989 0.4659 0.9626 1.530019 0.3055 0.9861 3.477099 0.2610 0.9884

As adsorption processes involve chemisorption, they can be described by pseudo second-order rate expression [135-137] and Elovich model [122,133,138]. Moreover, the pseudo second-order model showed the highest linear correlation coefficient (R2) and therefore, the highest agreement with the kinetics experimental data than did the Elovich model, for all MB/Zr-MOF systems.

The pseudo first-order equation did not fit well for the entire range of reactions in all MOF/MB systems. In general, the equation was only applicable to the first 20 or 30 min of the adsorption interaction process this is consistent with the reported literature [139-152]. Consequently, the MOF/MB systems did not fit the pseudo first-order equation for the whole range of contact time.

Kinetics adsorption studies are crucial indicators of a criteria of adsorbent efficiency (i.e., the rate of adsorption) and provide a clear picture of the mechanism of adsorption. Figure 3 below explains the variation in the amount of adsorbate on adsorbent (qt) as a function of contact time. The rate of MB adsorption was high at the beginning of the sorption process before slowing as the reaction progressed until reaching an equilibrium saturation. That the rate of adsorption was faster at the start may be due to the accessibility of adsorptive sites of the MOFs [153,154]. The adsorption of MB by UiO-66-10%Al took less time than by the other two MOFs, which indicate that the rate of dye sorption by UiO-66-10%Al was the quickest among the three MOFs examined.

Figure 3 also illustrates the dependency of MB uptake on contact time given different initial concentrations of MB. It confirms that higher initial concentrations of MB lead to increases in adsorption capacity for MB dye. Consequently, MB uptake per unit mass of MOF, or adsorption density, also increases. Specifically, higher initial concentrations of MB may reduce accessibility of adsorption sites, which can increase the amount of adsorbate on adsorbent [155]. The increase in adsorption density or capacity with higher initial concentrations of MB is generally due to the availability of unsaturated adsorption sites on the surface of MOFs during the sorption batch process [156,157].

To analyse the adsorption kinetics of the dye/MOF system, pseudo first-order [120], pseudo second-order [113] and Elovich equations [121] were examined. Table 2 and Table 3 present the resultant values of the parameters fitted to the pseudo second order and Elovich models, respectively.

There pseudo first-order equation was not a good fit for the entire range of reactions in all MOF/MB systems; however, it can be generally applied to the first 20 or 30 min of the adsorption interaction process. This is consistent with the reported literature [139]. Consequently, the MOF/MB systems did not obey the equation during the whole of the contact time through the equation was mostly valid for the initial stage of the sorption process. In addition, the experimental \(\) values, which can be obtained from the intercept of the linear relationship between \(\) and time, did not agree with the computed values. These results are proof that the adsorption of MB onto Zr-MOFs (single-metal and bimetal) is not based on first-order kinetics [91].

The obtained experimental data were further fitted to the pseudo second-order equation. The values for \(\) and \(\) were obtained from the slope and intercept of the linear plots of \(\) versus \(\), respectively, and listed in Table 2. Figure 3(b), (d) and (f) show that MB uptake by Zr-MOF increased with increases in contact time for each of the different initial MB concentrations, as well as at higher initial MB concentrations. The correlation coefficients of the plots showed that the pseudo second-order equation had the best fit with the experimental data, with the range of R2 values (0.9953–0.9999) listed in Table 2. These results verify the agreement of this kinetic model and the second-order behaviour of the adsorption process of MB by Zr-MOFs. Based on the linear regression correlation coefficient values (R2), the nature of the sorption process over the whole range of contact time for all solid/liquid systems in this study can be considered a chemisorption mechanism, as the rate-controlling step related to valence forces of sharing or exchanging electrons between Zr-MOFs and MB.

The results of the correlational analysis of the amount of dye adsorbed (mg/g) against contact time for four initial MB concentrations (5, 15, 30 and 50 ppm) are shown in Figure 3. The results indicate that the amount of dye loading, \(\) (mg/g), increased with contact time for each concentration separately.

The Elovich model can be applied to the chemisorption reaction; it is a model reasonably employed in chemisorption processes and to a wide range of slow adsorption processes. Specifically, this model may facilitate those systems for which the adsorption surface is heterogeneous. Experimental data of MOF/MB batch adsorption systems were incorrectly described using the pseudo first-order model. Further, these systems can be represented by a combination of two or three sequential and instantaneous pseudo first-order reactions. The basic form of the Elovich equation described the experimental data well; however, the Elovich equation can be easily fitted to the experimental data using one straight line to describe the whole progress of contact time [122].

The experimental data were also examined with respect to the Elovich model, with the values of all parameters derived and the slope and intercept of the linear relationship indicating the constants \(\) and \(\) , respectively. In addition, these constants can be comparison parameters of reaction rates of MB adsorption in the various kinds of Zr-MOF; the values of \(\) and \(\) , derived from the linear plots of \(\) versus \(\), are listed in Table 3. According to the Elovich model, the increase in α and/or the decrease in β should increase the adsorption rate, which in turn increases MB uptake. Therefore, the relative loading of the three Zr-MOFs are UiO-66-10%Al > UiO-66-30%Al > UiO-66 [122].

Figure 3(a), (c) and (e) illustrate the changes in Zr-MOFs capacities at different initial MB concentrations with time. Loading capacities are increased with increasing contact time at each initial concentration, and with higher initial MB concentrations. Based on the values of the correlation coefficient (R2) and the fact that higher R2 values reflect better bit with the adsorption kinetics model, the best fit for the experimental data was exhibited by the Elovich equation model for all MB/MOF systems (single-metal and bimetal). The range of R2 values (0.9242–0.9986) is listed in Table 3. These results indicate and emphasise that all the investigated sorption systems obey chemisorption kinetics.

Intraparticle diffusion studies

In addition, the intraparticle diffusion model suggested by Weber and Morris [115] was utilise to recognise the diffusion mechanism. Based on this model, the loading \(\) against the square root of the contact time varies almost proportionally. Further, intraparticle diffusion models are vital to identifying the steps involved in the adsorption process to facilitate understanding of the adsorption mechanism [38].

The lack of descriptions of the adsorption mechanism and rate-controlling step of the adsorption process are some of the limitations of the pseudo first-order, pseudo second order and Elovich kinetic models. In response to these limitations, Weber and Morris created the intraparticle diffusion model [119]. The migration of the pollutant (MB) from bulk phase to the surface of the sorbent (Zr-MOFs) can be either by film or external diffusion, pore diffusion, surface diffusion and adsorption on the pore surface, or a combination of more than one of these steps [158].

Figure 4. Fitting of experimental data using intraparticle diffusion models of MB adsorption onto UiO-66 (a), UiO-66-10%Al (b) and UiO-66-30%Al (c).

Figure 4 plots the \(\) against \(\) rather than \(\), for the various initial MB concentrations. Linear variations in uptake with \(\) is gained for a certain initial fraction of the reaction. The straight-line plot of qt versus \(\) may provide the values of the intraparticle diffusion rate constant \(\); \(\) and \(\) can be found from the slope and intercept of the model, respectively. Table 4 lists these values as well as the correlation coefficients (R2) for the initial MB concentrations 5, 15, 30 and 50 mg/L. The focus of the intraparticle diffusion model is on the second linear portion of the plot, in which the slope characterises the rate constant (\(\)) while the intercept (\(\)) is related to the thickness of the boundary layer [14].

Table 4. Calculated kinetics constant (kp), C and correlation coefficient (R2) for Ci = 5, 15, 30 and 50 ppm.

Adsorbent Initial concentration of MB solution (mg L–1) kp (mg g–1min–(1/2)) C (mg g–1) R2
UiO-66 5 0.0991 0.5017 0.9999
15 0.22 2.1455 0.9918
30 0.3955 3.5763 0.9884
50 0.638 3.8144 0.9959
UiO-66-10%Al 5 0.4314 3.8489 0.9850
15 0.5717 7.9333 0.9552
30 1.011 15.226 0.9797
50 1.1428 24.123 0.9720
UiO-66-30%Al 5 0.2536 1.0889 0.9994
15 0.2958 5.8863 0.9947
30 0.4446 7.9245 0.9901
50 0.4402 15.395 0.9775

Figure 4 illustrates the three stages of the adsorption mechanism, which are represented by the three linear relationships. The first part of the plot is inclined sharply, indicating rapid sorption or external surface adsorption. The second part represents the rate-controlling step which is intraparticle diffusion, the slowest stage of adsorption [159]. The last part is the equilibrium where the processes of adsorption of MB onto Zr-MOFs reach a plateau because either the active adsorptive sites on MOFs have been occupied or the concentration of MB in the solution is extremely low [92]. Specifically,Figure 4 shows that the second straight line does not pass through the origin or initial point of adsorption because of variations in mass-transfer rate between the saturation and equilibrium steps of sorption [160-163]. In addition, this kind of deviation from the origin is proof that pore diffusion is not the only rate-limiting factor [164].

 Equilibrium studies

A set of batch experiments was conducted with various initial MB concentrations: 5, 15, 30 and 50 mg/L. The one factor allowed us to vary concentrations of MB while maintaining other process factors like MOF dose, stirrer speed, volume of the solution and temperature unchanged. Data from the equilibrium experiments were investigated using Langmuir [124] and Freundlich [117] isotherms.

The assumption of the Langmuir isotherm theory is described as monolayer coverage of adsorbate (MB) onto a homogenous adsorbent (Zr-MOFs) surface [124]. Hence, its basic assumption is that sorption takes place at specific homogeneous sites on the adsorbent. As soon as an adsorbent site is occupied by an MB molecule, no additional adsorption can occur at that site again.

Figure 5. Fitting of experimental data using Langmuir and Freundlich models of MB adsorption onto UiO-66 (a), UiO-66-10%Al (b) and UiO-66-30%Al (c).

Table 5. Calculated equilibrium constants (k<sub id="subscript-1">L</sub>, k<sub id="subscript-2">F</sub>, q<sub id="subscript-3">m</sub>, n and correlation coefficient (R<sup id="superscript-1">2</sup>)) of MB adsorption onto UiO-66, UiO-66-10%Al and UiO-66-30%Al for C<sub id="subscript-4">i</sub> = 5, 15, 30 and 50 mg/L.

Adsorbent Adsorption isotherm model Parameter Value R2
UiO-66 Langmuir qm (mg/g) 14.52 0.9889
KL (L/mg) 0.02447
Freundlich KF ([mg/g] [L/mg]1/n) 0.98157 0.9979
n (g/L) 1.2918
UiO-66-10%Al Langmuir qm (mg/g) 49.26 0.9396
KL (L/mg) 29
Freundlich KF ([mg/g] [L/mg]1/n) 53.53 0.9711
n (g/L) 4.05
UiO-66-30%Al Langmuir qm (mg/g) 27.85 0.9777
KL (L/mg) 1.10
Freundlich KF ([mg/g] [L/mg]1/n) 16.71 0.9888
n (g/L) 7.52

The equilibrium data were examined using a Langmuir model. The values of the parameters and constants, together with the R2 values, were obtained from the slope and intercept of the linear plot and listed in Table 5. Figure 5 (a), (b) and (c) illustrate the experimental equilibrium data and the predicted theoretical Langmuir isotherm for the adsorption process of MB onto Zr-MOF (single-metal and bimetal).

The fundamental characteristics of the Langmuir model can be expressed in terms of a dimensionless constant separation factor, RL, or Equation 12 [125]. The value of RL is an indication of the shape of the isotherm. Basically, the RL value determines the favourability of the adsorption process, which can be either unfavourable (RL > 1), linear (RL = 1), favourable (0 < RL < 1) or irreversible (RL = 0). The equilibrium analysis revealed that the RL values were between 0 and 1, indicating a favourable adsorption process for all MB/ Zr-MOF (single-metal and bimetal) systems.

The Freundlich model [117] is an empirical equation that assumes the adsorption process can occur on heterogeneous surfaces and that the adsorption capacity depends on the concentration of MB. According to Equation 13, equilibrium adsorption properties such as kF and (1/n) are rough indicators of the adsorption capacity and the adsorption intensity, respectively. The favourability of the adsorption process can be determined from the magnitude of the exponent (1/n); the criterion for a favourable adsorption is that the values of n must be greater than one [165].

The equilibrium data were further tested by the Freundlich isotherm model. Freundlich isotherm constants and correlation coefficient (R2) values are tabulated in Table 5. As shown in Table 5, the correlation coefficient of the Freundlich isotherm for all MB/MOF systems were higher than those based on the Langmuir model, proving strong linearity. The analysis verified that the values of n for all systems were greater than one, as tabulated in Table 5. Such a result is solid confirmation of favourable adsorption and easy loading of MB onto Zr-MOFs from aqueous solutions [166].

Table 6. Comparison of monolayer equilibrium capacity for methylene blue onto different sorbents.

Adsorbent Condition qm (mg/g) Reference
UiO-66-10%Al Normal 49.26 This study
UiO-66-30%Al 27.85 This study
UiO-66 14.52 This study
Tobacco stem ash Normal 35.70 [167]
Oak sawdust Normal 29.94 [168]
ZnCl2 activated POME sludge Normal 22.40 [169]
Salvadora persica stem ash Normal 22.78 [170]
Activated fly-ash Normal 14.28 [171]
Fly-ash A Normal 6.0 [69]
Coir pith carbon Normal 5.87 [172]
Neem sawdust Normal 3.62 [173]

The maximum Langmuir adsorption capacity was exhibited by UiO-66-10%Al, with qm of 49.26 mg/g. Furthermore, the comparative adsorption capacity of Zr-MOFs for MB in this study, relative to that of other adsorbents reported in the literature, is provided in Table 6.

 Conclusion

The results of the present examination of the three Zr-MOFs (single-metal and bimetal) show that these MOFs are favourable adsorbents of the basic (cationic) dye MB from aqueous solutions at a wide range of MB concentrations. The characterisation of Zr-MOFs reflected the integrity of their structures, the stability of the functional groups on the organic linkers, the suitability of their textural properties and thermal stability. Such characterisation was performed using XRD patterns, FTIR spectrum, N2 adsorption/desorption isotherm and TGA profiles of the UiO-66 samples.

The most efficient adsorbent among the three Ze-MOFs was UiO-66-10%Al, with the largest pore volume (1.34 cc. g–1) and pore diameter (2.33 nm), verifying that the addition of up to 10% Al enhanced the textural properties of the prototype Zr-MOF. For all MB/MOF systems, high initial concentrations of MB were found to facilitate adsorption capacity.

It can be concluded that the pseudo first-order model does not fit the experimental data well. While it can be generally applied to the initial period of the first step of the adsorption consistent with reports of most sorption studies in the literature the applicability of pseudo first-order mechanisms are restricted to a limited fraction of the beginning of the contact time [139]. The Elovich and pseudo second-order models showed the highest correlation in all MOF/MB systems studied over a longer period of adsorption. Besides, adsorption kinetics obeyed the pseudo second order kinetics model nicely, based on the fact that the highest correlation coefficients (R2) were achieved with this model.

Equilibrium data were tested using the Langmuir and Freundlich models, and were found to be best defined by the Freundlich isotherm. The maximum adsorption capacity of the most efficient adsorbent was 49.26 mg/g for UiO-66-10%Al. This performance was compared with that of other porous adsorbents in previous studies.

The gained parameters from this study support the design and lay the foundations for establishing a continuous treatment process that removes MB from wastewater.

1 01 129-138 39 2005 10.1016/j.watres.2004.09.011 Wang Shaobin Boyjoo Y. Choueib A. Zhu Z.H. Water Research Removal of dyes from aqueous solution using fly ash and red mud 07 27-34 193 2014 10.1016/j.micromeso.2014.03.004 Lin Shuang Song Zhilong Che Guangbo Ren Ao Li Ping Liu Chunbo Zhang Jishuang Microporous and Mesoporous Materials Adsorption behavior of metal–organic frameworks for methylene blue from aqueous solution 3-4 03 997-1026 40 2005 10.1016/j.procbio.2004.04.008 Aksu Zümriye Process Biochemistry Application of biosorption for the removal of organic pollutants: a review 1 07 1-10 62 2004 10.1016/j.dyepig.2003.10.016 Garg V.K Kumar Rakesh Gupta Renuka Dyes and Pigments Removal of malachite green dye from aqueous solution by adsorption using agro-industry waste: a case study of Prosopis cineraria Boca Raton, FL, USA CRC Press, Inc. 1988 0849348498 Chakrabarti T. Subrahmanyam P. V. R. Sundaresan B. B. Wise D.L. Biotreatment systems, Volume II Biodegradation of recalcitrant industrial wastes Berlin Springer 3 1980 978-3-540-38522-6 10.1007/978-3-540-38522-6_7 Clarke E. A. Anliker R. Anthropogenic Compounds. The Handbook of Environmental Chemistry Organic Dyes and Pigments US2744027A 1956 Struve William S Reidinger Albert D Azo pigment production 1990 Pitter P. Chudoba J. Journal of American Chemical Society Biodegradability of organic substance in the aquatic environment 5 05 1187-1193 31 1997 10.1016/s0043-1354(96)00380-6 Young L Water Research Ligninase-catalysed decolorization of synthetic dyes 1 01 126-131 161 2009 10.1016/j.jhazmat.2008.03.063 Lian Lili Guo Liping Guo Chunjing Journal of Hazardous Materials Adsorption of Congo red from aqueous solutions onto Ca-bentonite 2 04 171-180 83 2007 10.1016/j.jenvman.2006.02.012 Hessel C. Allegre C. Maisseu M. Charbit F. Moulin P. Journal of Environmental Management Guidelines and legislation for dye house effluents 1 10-17 2 2007 Hema M. Arivoli S. International Journal of Physical Sciences Comparative study on the adsorption kinetics and thermodynamics of dyes onto acid activated low cost carbon 2-3 09 547-552 157 2008 10.1016/j.jhazmat.2008.01.072 Essawy Amr A. Ali A. El-Hag Abdel-Mottaleb M.S.A. Journal of Hazardous Materials Application of novel copolymer-TiO2 membranes for some textile dyes adsorptive removal from aqueous solution and photocatalytic decolorization 1 04 14-21 284 2005 10.1016/j.jcis.2004.09.063 Kumar K. Vasanth Ramamurthi V. Sivanesan S. Journal of Colloid and Interface Science Modeling the mechanism involved during the sorption of methylene blue onto fly ash 1 01 69-84 60 2004 10.1016/s0143-7208(03)00140-2 Chiou Ming-Shen Ho Pang-Yen Li Hsing-Ya Dyes and Pigments Adsorption of anionic dyes in acid solutions using chemically cross-linked chitosan beads 3 09 251-262 79 2001 10.1016/s0960-8524(01)00028-1 Fu Yuzhu Viraraghavan T Bioresource Technology Fungal decolorization of dye wastewaters: a review 3 12 217-227 58 1996 10.1016/s0960-8524(96)00113-7 Banat Ibrahim M. Nigam Poonam Singh Datel Marchant Roger Bioresource Technology Microbial decolorization of textile-dyecontaining effluents: A review 3 01 196-203 69 2006 10.1016/j.dyepig.2005.03.008 Lee Jae-Wook Choi Seung-Phil Thiruvenkatachari Ramesh Shim Wang-Geun Moon Hee Dyes and Pigments Evaluation of the performance of adsorption and coagulation processes for the maximum removal of reactive dyes 13 09 2590-2598 98 2007 10.1016/j.biortech.2006.09.010 SULAK M DEMIRBAS E KOBYA M Bioresource Technology Removal of Astrazon Yellow 7GL from aqueous solutions by adsorption onto wheat bran 1-3 02 217-223 293 2007 10.1016/j.colsurfa.2006.07.035 Qadeer Riaz Colloids and Surfaces A: Physicochemical and Engineering Aspects Adsorption behavior of ruthenium ions on activated charcoal from nirtic acid medium 1-2 05 31-52 116 1992 10.1016/0048-9697(92)90363-w Pollard S.J.T. Fowler G.D. Sollars C.J. Perry R. Science of The Total Environment Low-cost adsorbents for waste and wastewater treatment: a review 5 08 493-501 56 2004 10.1016/j.chemosphere.2004.04.004 Valix M. Cheung W.H. McKay G. Chemosphere Preparation of activated carbon using low temperature carbonisation and physical activation of high ash raw bagasse for acid dye adsorption 1 07 47-58 54 2002 10.1016/s0143-7208(02)00025-6 Namasivayam C. Kavitha D. Dyes and Pigments Removal of Congo Red from water by adsorption onto activated carbon prepared from coir pith, an agricultural solid waste 1 04 77-79 64 1998 10.1016/s0960-8524(97)86722-3 Namasivayam C. Prabha D. Kumutha M. Bioresource Technology Removal of direct red and acid brilliant blue by adsorption on to banana pith 1-2 05 709-717 153 2008 10.1016/j.jhazmat.2007.09.014 Tan I.A.W. Ahmad A.L. Hameed B.H. Journal of Hazardous Materials Preparation of activated carbon from coconut husk: Optimization study on removal of 2,4,6-trichlorophenol using response surface methodology 1-3 03 191-199 201 2002 10.1016/s0927-7757(01)01004-4 Juang Ruey-Shin Wu Feng-Chin Tseng Ru-Ling Colloids and Surfaces A: Physicochemical and Engineering Aspects Characterization and use of activated carbons prepared from bagasses for liquid-phase adsorption 1 04 28-34 272 2004 10.1016/j.jcis.2003.08.071 Mohamed Mohamed Mokhtar Journal of Colloid and Interface Science Acid dye removal: comparison of surfactant-modified mesoporous FSM-16 with activated carbon derived from rice husk 2-3 12 189-195 66 2003 10.1016/j.micromeso.2003.08.028 Aygün A Yenisoy-Karakaş S Duman I Microporous and Mesoporous Materials Production of granular activated carbon from fruit stones and nutshells and evaluation of their physical, chemical and adsorption properties 3 487-495 41 2003 10.1016/s0008-6223(02)00367-6 Tseng Ru-Ling Wu Feng-Chin Juang Ruey-Shin Carbon Liquid-phase adsorption of dyes and phenols using pinewood-based activated carbons 3 03 239-249 56 2003 10.1016/s0143-7208(02)00159-6 Malik P.K. Dyes and Pigments Use of activated carbons prepared from sawdust and rice-husk for adsorption of acid dyes: a case study of Acid Yellow 36 1 10 417-424 170 2009 10.1016/j.jhazmat.2009.04.080 Weng Chih-Huang Lin Yao-Tung Tzeng Tai-Wei Journal of Hazardous Materials Removal of methylene blue from aqueous solution by adsorption onto pineapple leaf powder 1 01 208-213 250 2010 10.1016/j.desal.2008.07.030 El-Halwany M.M. Desalination Study of adsorption isotherms and kinetic models for Methylene Blue adsorption on activated carbon developed from Egyptian rice hull (Part II) 2 02 912-920 90 2009 10.1016/j.jenvman.2008.02.005 Leechart Piyawan Nakbanpote Woranan Thiravetyan Paitip Journal of Environmental Management Application of ‘waste’ wood-shaving bottom ash for adsorption of azo reactive dye 423–438 114 1999 10.1023/A:1005197308228 McKay G. Porter J. F. Prasad G. R. Water, Air, and Soil Pollution The Removal of Dye Colours from Aqueous Solutions by Adsorption on Low-cost Materials 1 07 233-238 166 2009 10.1016/j.jhazmat.2008.11.019 Hameed B.H. Journal of Hazardous Materials Grass waste: A novel sorbent for the removal of basic dye from aqueous solution 2-3 03 939-944 162 2009 10.1016/j.jhazmat.2008.05.120 Hameed B.H. Journal of Hazardous Materials Evaluation of papaya seeds as a novel non-conventional low-cost adsorbent for removal of methylene blue 1-3 03 78-84 316 2008 10.1016/j.colsurfa.2007.08.033 Hameed B.H. Mahmoud D.K. Ahmad A.L. Colloids and Surfaces A: Physicochemical and Engineering Aspects Sorption of basic dye from aqueous solution by pomelo (Citrus grandis) peel in a batch system 21 1 03 276-286 152 2008 10.1016/j.jhazmat.2007.06.107 Ponnusami V. Vikram S. Srivastava S.N. Journal of Hazardous Materials Guava (Psidium guajava) leaf powder: Novel adsorbent for removal of methylene blue from aqueous solutions 1 02 344-350 162 2009 10.1016/j.jhazmat.2008.05.045 Hameed B.H. Journal of Hazardous Materials Removal of cationic dye from aqueous solution using jackfruit peel as non-conventional low-cost adsorbent 30 2-3 10 499-506 158 2008 10.1016/j.jhazmat.2008.01.098 Hameed B.H. Mahmoud D.K. Ahmad A.L. Journal of Hazardous Materials Sorption equilibrium and kinetics of basic dye from aqueous solution using banana stalk waste 1 02 35-43 126 2007 10.1016/j.cej.2006.08.022 Ofomaja Augustine E. Chemical Engineering Journal Sorption dynamics and isotherm studies of methylene blue uptake on to palm kernel fibre 3 01 332-337 73 2007 10.1016/j.dyepig.2006.01.037 Gong Renmin Jin Youbin Chen Jian Hu Yun Sun Jin Dyes and Pigments Removal of basic dyes from aqueous solution by sorption on phosphoric acid modified rice straw 1-3 06 639-648 154 2008 10.1016/j.jhazmat.2007.10.081 Hameed B.H. El-Khaiary M.I. Journal of Hazardous Materials Sorption kinetics and isotherm studies of a cationic dye using agricultural waste: Broad bean peels 1-3 09 119-127 169 2009 10.1016/j.jhazmat.2009.03.066 Ponnusami V. Gunasekar V. Srivastava S.N. Journal of Hazardous Materials Kinetics of methylene blue removal from aqueous solution using gulmohar (Delonix regia) plant leaf powder: Multivariate regression analysis 5 12 431-439 36 2000 10.1016/s0032-9592(00)00233-8 Aksu Zümriye Tezer Sevilay Process Biochemistry Equilibrium and kinetic modelling of biosorption of Remazol Black B by Rhizopus arrhizus in a batch system: effect of temperature 6 01 595-600 37 2002 10.1016/s0032-9592(01)00234-5 Chu H.C Chen K.M Process Biochemistry Reuse of activated sludge biomass: I. Removal of basic dyes from wastewater by biomass 1 11 239-247 7 2002 10.1016/s1093-0191(01)00123-x Fu Yuzhu Viraraghavan T. Advances in Environmental Research Removal of Congo Red from an aqueous solution by fungus Aspergillus niger 8 01 695-702 21 2001 10.1016/s0956-053x(01)00006-x Aksu Zümriye Yener Jülide Waste Management A comparative adsorption/biosorption study of mono-chlorinated phenols onto various sorbents 4 01 613-622 9 1991 10.1016/0734-9750(91)90734-d Mou Duen-Gang Lim Kim Kee Shen Hwei Ping Biotechnology Advances Microbial agents for decolorization of dye wastewater 10 34 1996 10.1016/s0273-1223(96)00701-9 Hu Tai-Lee Water Science and Technology Removal of reactive dyes from aqueous solution by different bacterial genera 2 04 139-145 82 2002 10.1016/s0960-8524(01)00172-9 Fu Yuzhu Viraraghavan T Bioresource Technology Dye biosorption sites in Aspergillus niger 9 04 1311-1316 38 2003 10.1016/s0032-9592(02)00327-8 Basibuyuk M. Forster C.F. Process Biochemistry An examination of the adsorption characteristics of a basic dye (Maxilon Red BL-N) on to live activated sludge system 1 01 13-20 30 1996 10.1016/0043-1354(95)00108-w Jacobsen Bo Neergaard Arvin Erik Reinders Math Water Research Factors affecting sorption of pentachlorophenol to suspended microbial biomass 7 09 1271-1282 37 1998 10.1016/s0045-6535(98)00125-8 Benoit Pierre Barriuso Enrique Calvet Raoul Chemosphere Biosorption characterization of herbicides, 2,4-D and atrazine, and two chlorophenols on fungal mycelium 1-2 11 87-99 21 2000 10.1016/s1383-5866(00)00194-5 Aksu Z Akpınar D Separation and Purification Technology Modelling of simultaneous biosorption of phenol and nickel(II) onto dried aerobic activated sludge 5 01 599-613 39 2004 10.1016/s0032-9592(03)00132-8 Aksu Zümriye Gönen Ferda Process Biochemistry Biosorption of phenol by immobilized activated sludge in a continuous packed bed: prediction of breakthrough curves 12 12 3601-3606 32 1998 10.1016/s0043-1354(98)00132-8 Lièvremont Didier Seigle-murandi Francoise Benoit-guyod Jean-louis Water Research Removal of PCNB from aqueous solution by a fungal adsorption process 1 02 213-220 151 2008 10.1016/j.jhazmat.2007.05.071 Alpat Sibel Kılınç Özbayrak Özge Alpat Şenol Akçay Hüsamettin Journal of Hazardous Materials The adsorption kinetics and removal of cationic dye, Toluidine Blue O, from aqueous solution with Turkish zeolite 1-2 06 331-335 145 2007 10.1016/j.jhazmat.2006.12.027 Han Runping Wang Yi Zou Weihua Wang Yuanfeng Shi Jie Journal of Hazardous Materials Comparison of linear and nonlinear analysis in estimating the Thomas model parameters for methylene blue adsorption onto natural zeolite in fixed-bed column 25 3 08 946-952 136 2006 10.1016/j.jhazmat.2006.01.038 Wang S Zhu Z Journal of Hazardous Materials Characterisation and environmental application of an Australian natural zeolite for basic dye removal from aqueous solution 1 03 71-78 295 2006 10.1016/j.jcis.2005.08.006 Wang Shaobin Li Huiting Xu Longya Journal of Colloid and Interface Science Application of zeolite MCM-22 for basic dye removal from wastewater 03 344-352 23 2015 10.1016/j.jiec.2014.08.038 Li Changxin Zhong Hong Wang Shuai Xue Jianrong Zhang Zhenyu Journal of Industrial and Engineering Chemistry Removal of basic dye (methylene blue) from aqueous solution using zeolite synthesized from electrolytic manganese residue 29 6 03 845-850 85 2010 10.1002/jctb.2377 Sun Zhi Li Chunjie Wu Deyi Journal of Chemical Technology & Biotechnology Removal of methylene blue from aqueous solution by adsorption onto zeolite synthesized from coal fly ash and its thermal regeneration 20 3 05 183-188 108 2004 10.1016/j.jhazmat.2004.02.012 Gulnaz O Journal of Hazardous Materials Sorption of basic dyes from aqueous solution by activated sludge 7 1740–1747 43 2004 10.1021/ie034218g Gupta V. K. Suhas Suhas Ali Imran Saini V. K. Industrial & Engineering Chemistry Research Removal of Rhodamine B, Fast Green, and Methylene Blue from Wastewater Using Red Mud, an Aluminum Industry Waste 1 07 59-68 15 2003 10.1016/s1369-703x(02)00177-8 Otero M Rozada F Calvo L.F Garcı́a A.I Morán A Biochemical Engineering Journal Kinetic and equilibrium modelling of the methylene blue removal from solution by adsorbent materials produced from sewage sludges 10 09 1401-1407 60 2005 10.1016/j.chemosphere.2005.01.091 Wang Shaobin Boyjoo Y. Choueib A. Chemosphere A comparative study of dye removal using fly ash treated by different methods 15-16 11 3469-3473 87 2008 10.1016/j.fuel.2008.05.022 Wang Shaobin Ma Qing Zhu Z.H. Fuel Characteristics of coal fly ash and adsorption application 20 12 4938-4944 37 2003 10.1016/j.watres.2003.08.011 Janos P Water Research Sorption of dyes from aqueous solutions onto fly ash 1 04 193-200 87 2008 10.1016/j.jenvman.2007.01.001 Lin J.X. Zhan S.L. Fang M.H. Qian X.Q. Yang H. Journal of Environmental Management Adsorption of basic dye from aqueous solution onto fly ash 1-3 09 335-342 181 2010 10.1016/j.jhazmat.2010.05.015 Sun Deshuai Zhang Xiaodong Wu Yude Liu Xin Journal of Hazardous Materials Adsorption of anionic dyes from aqueous solution on fly ash 6 02 295-300 20 2002 10.1016/s0169-1317(01)00081-3 Ghosh Dipa Bhattacharyya Krishna G Applied Clay Science Adsorption of methylene blue on kaolinite 1 05 32-39 261 2003 10.1016/s0021-9797(03)00059-6 Atun G. Hisarli G. Sheldrick W.S. Muhler M. Journal of Colloid and Interface Science Adsorptive removal of methylene blue from colored effluents on fuller's earth 15 1-3 08 630-633 167 2009 10.1016/j.jhazmat.2009.01.014 Hong Song Wen Cheng He Jing Gan Fuxing Ho Yuh-Shan Journal of Hazardous Materials Adsorption thermodynamics of Methylene Blue onto bentonite 2 01 310-314 269 2004 10.1016/j.jcis.2003.09.004 Gürses A Karaca S Doğar Ç Bayrak R Açıkyıldız M Yalçın M Journal of Colloid and Interface Science Determination of adsorptive properties of clay/water system: methylene blue sorption 1-2 11 111-120 24 2003 10.1016/s0169-1317(03)00154-6 Shawabkeh R Applied Clay Science Experimental study and modeling of basic dye sorption by diatomaceous clay 31 1-3 07 188-192 135 2006 10.1016/j.jhazmat.2005.11.048 Hajjaji M Alami A Bouadili A Journal of Hazardous Materials Removal of methylene blue from aqueous solution by fibrous clay minerals 1-3 08 327-342 214 2007 10.1016/j.desal.2006.10.024 Al-Futaisi Ahmed Jamrah Ahmad Al-Hanai Rashid Desalination Aspects of cationic dye molecule adsorption to palygorskite 3 11 229-238 69 2003 10.1016/j.jenvman.2003.09.005 Al-Ghouti M.A. Khraisheh M.A.M. Allen S.J. Ahmad M.N. Journal of Environmental Management The removal of dyes from textile wastewater: a study of the physical characteristics and adsorption mechanisms of diatomaceous earth 1-2 06 355-362 144 2007 10.1016/j.jhazmat.2006.09.097 Weng Chih-Huang Pan Yi-Fong Journal of Hazardous Materials Adsorption of a cationic dye (methylene blue) onto spent activated clay 11-12 928-931 17 2006 10.1002/pat.837 Senkal Bahire Filiz Yavuz Erdem Polymers for Advanced Technologies Preparation of poly(vinyl pyrrolidone) grafted sulfonamide based polystyrene resin and its use for the removal of dye from water 12 12 1471-1477 67 2007 10.1016/j.reactfunctpolym.2007.07.042 Senkal Bahire Filiz Bildik Fatih Yavuz Erdem Sarac Ayfer Reactive and Functional Polymers Preparation of poly(glycidyl methacrylate) grafted sulfonamide based polystyrene resin with tertiary amine for the removal of dye from water 3 01 425-430 54 2004 10.1016/s0045-6535(03)00654-4 Yu Ying Zhuang Yuan-Yi Wang Zhong-Hua Qiu Ming-Qiang Chemosphere Adsorption of water-soluble dyes onto modified resin 02 414-425 217 2013 10.1016/j.cej.2012.11.119 Wawrzkiewicz Monika Chemical Engineering Journal Removal of C.I. Basic Blue 3 dye by sorption onto cation exchange resin, functionalized and non-functionalized polymeric sorbents from aqueous solutions and wastewaters 09 125-136 246 2013 10.1016/j.powtec.2013.05.017 Kumar K. Yogesh Muralidhara H.B. Nayaka Y. Arthoba Balasubramanyam J. Hanumanthappa H. Powder Technology Low-cost synthesis of metal oxide nanoparticles and their application in adsorption of commercial dye and heavy metal ion in aqueous solution 1-3 02 398-403 174 2010 10.1016/j.jhazmat.2009.09.066 Afkhami Abbas Moosavi Razieh Journal of Hazardous Materials Adsorptive removal of Congo red, a carcinogenic textile dye, from aqueous solutions by maghemite nanoparticles 1 01 507-511 185 2011 10.1016/j.jhazmat.2010.09.035 Haque Enamul Jun Jong Won Jhung Sung Hwa Journal of Hazardous Materials Adsorptive removal of methyl orange and methylene blue from aqueous solution with a metal-organic framework material, iron terephthalate (MOF-235) 02 329-339 283 2015 10.1016/j.jhazmat.2014.09.046 Hasan Zubair Jhung Sung Hwa Journal of Hazardous Materials Removal of hazardous organics from water using metal-organic frameworks (MOFs): Plausible mechanisms for selective adsorptions 1-3 09 535-542 181 2010 10.1016/j.jhazmat.2010.05.047 Haque Enamul Lee Ji Eun Jang In Tae Hwang Young Kyu Chang Jong-San Jegal Jonggeon Jhung Sung Hwa Journal of Hazardous Materials Adsorptive removal of methyl orange from aqueous solution with metal-organic frameworks, porous chromium-benzenedicarboxylates 1-3 06 945-951 190 2011 10.1016/j.jhazmat.2011.04.029 Du Jing-Jing Yuan Yu-Peng Sun Jia-Xin Peng Fu-Min Jiang Xia Qiu Ling-Guang Xie An-Jian Shen Yu-Hua Zhu Jun-Fa Journal of Hazardous Materials New photocatalysts based on MIL-53 metal–organic frameworks for the decolorization of methylene blue dye 22 3 03 819-825 141 2007 10.1016/j.jhazmat.2006.07.049 Hameed B Din A Ahmad A Journal of Hazardous Materials Adsorption of methylene blue onto bamboo-based activated carbon: Kinetics and equilibrium studies 1-3 03 111-119 127 2007 10.1016/j.cej.2006.09.010 Tan I.A.W. Hameed B.H. Ahmad A.L. Chemical Engineering Journal Equilibrium and kinetic studies on basic dye adsorption by oil palm fibre activated carbon 1 01 143-149 75 2007 10.1016/j.dyepig.2006.05.039 Hameed B.H. Ahmad A.L. Latiff K.N.A. Dyes and Pigments Adsorption of basic dye (methylene blue) onto activated carbon prepared from rattan sawdust 15 3 04 462-470 137 2008 10.1016/j.cej.2007.04.031 Tan I Ahmad A Hameed B Chemical Engineering Journal Optimization of preparation conditions for activated carbons from coconut husk using response surface methodology 6759 11 276-279 402 1999 10.1038/46248 Li Hailian Eddaoudi Mohamed O'Keeffe M. Yaghi O. M. Nature Design and synthesis of an exceptionally stable and highly porous metal-organic framework 1 191-214 37 2008 10.1039/b618320b Férey Gérard Chem. Soc. Rev. Hybrid porous solids: past, present, future 23 9 11 695-704 1 2009 10.1038/nchem.444 Horike Satoshi Shimomura Satoru Kitagawa Susumu Nature Chemistry Soft porous crystals 28 7 03 2618-2625 29 2017 10.1021/acs.chemmater.7b00441 Moghadam Peyman Z. Li Aurelia Wiggin Seth B. Tao Andi Maloney Andrew G. P. Wood Peter A. Ward Suzanna C. Fairen-Jimenez David Chemistry of Materials Development of a Cambridge Structural Database Subset: A Collection of Metal–Organic Frameworks for Past, Present, and Future 23-24 12 3042-3066 253 2009 10.1016/j.ccr.2009.05.019 Kuppler Ryan J. Timmons Daren J. Fang Qian-Rong Li Jian-Rong Makal Trevor A. Young Mark D. Yuan Daqiang Zhao Dan Zhuang Wenjuan Zhou Hong-Cai Coordination Chemistry Reviews Potential applications of metal-organic frameworks 33 08 8571-8572 120 1998 10.1021/ja981669x Li Hailian Eddaoudi Mohamed Groy Thomas L. Yaghi O. M. Journal of the American Chemical Society Establishing Microporosity in Open Metal−Organic Frameworks: Gas Sorption Isotherms for Zn(BDC) (BDC = 1,4-Benzenedicarboxylate) 06 2 10 869-932 112 2011 10.1021/cr200190s Li Jian-Rong Sculley Julian Zhou Hong-Cai Chemical Reviews Metal–Organic Frameworks for Separations 21 14 03 7245-7250 24 2008 10.1021/la800227x Llewellyn Philip L. Bourrelly Sandrine Serre Christian Vimont Alexandre Daturi Marco Hamon Lomig De Weireld Guy Chang Jong-San Hong Do-Young Kyu Hwang Young Hwa Jhung Sung Férey Gérard Langmuir High Uptakes of CO2 and CH4 in Mesoporous Metal—Organic Frameworks MIL-100 and MIL-101 08 7 06 2969-2970 9 2009 10.1021/cg801381p Biradha Kumar Ramanan Arunachalam Vittal Jagadese J. Crystal Growth & Design Coordination Polymers Versus Metal−Organic Frameworks https://www.youtube.com/watch?v=m6sRQjKFssk Yaghi Omar Chemical and Biological Defense Science and Technology (CBD S&T) Conference Keynote Speaker: Dr. Omar Yaghi 6941 06 705-714 423 2003 10.1038/nature01650 Yaghi Omar M. O'Keeffe Michael Ockwig Nathan W. Chae Hee K. Eddaoudi Mohamed Kim Jaheon Nature Reticular synthesis and the design of new materials 04 12 10 1782-1789 41 2008 10.1021/ar800124u O’Keeffe Michael Peskov Maxim A. Ramsden Stuart J. Yaghi Omar M. Accounts of Chemical Research The Reticular Chemistry Structure Resource (RCSR) Database of, and Symbols for, Crystal Nets 19 3 01 176-182 38 2005 10.1021/ar020022l Ockwig Nathan W. Delgado-Friedrichs Olaf O'Keeffe Michael Yaghi Omar M. Accounts of Chemical Research Reticular Chemistry: Occurrence and Taxonomy of Nets and Grammar for the Design of Frameworks 29 6149 08 1230444 341 2013 10.1126/science.1230444 Furukawa Hiroyasu Cordova Kyle E. O’Keeffe Michael Yaghi Omar M. Science The Chemistry and Applications of Metal-Organic Frameworks 18 5554 01 469-472 295 2002 10.1126/science.1067208 Eddaoudi M. Science Systematic Design of Pore Size and Functionality in Isoreticular MOFs and Their Application in Methane Storage 11 3843 21 2011 10.1039/c0jm01770a Ke Fei Yuan Yu-Peng Qiu Ling-Guang Shen Yu-Hua Xie An-Jian Zhu Jun-Fa Tian Xing-You Zhang Li-De Journal of Materials Chemistry Facile fabrication of magnetic metal–organic framework nanocomposites for potential targeted drug delivery 5 626-630 38 2010 Dai Wei Zhuang H.-T. Lu X.-Q. Han M.-M. Zheng Y. Journal of Fuel Chemistry and Technology Adsorptive separation of thiophene derivatives via metal organic framework material MOF-5 02 60-67 183 2012 10.1016/j.cej.2011.12.021 Chen Chen Zhang Meng Guan Qingxin Li Wei Chemical Engineering Journal Kinetic and thermodynamic studies on the adsorption of xylenol orange onto MIL-101(Cr) 5 07 451-465 34 1999 10.1016/s0032-9592(98)00112-5 Ho Y.S McKay G Process Biochemistry Pseudo-second order model for sorption processes 1-39 24 1898 Lagergren S. Sven. Vetenskapsakad. Handingarl About the Theory of so Called Adsorption of Soluble Substances 2 04 31-59 89 1963 10.1061/jsedai.0000430 Weber Walter J. Morris J. Carrell Journal of the Sanitary Engineering Division Kinetics of Adsorption on Carbon from Solution 9 09 1848-1906 39 1917 10.1021/ja02254a006 Langmuir Irving Journal of the American Chemical Society The Constitution and Fundamental Properties of Solids and Liquids. II. Liquids 01 1 10 385-470 57U 1907 10.1515/zpch-1907-5723 Freundlich Herbert Zeitschrift für Physikalische Chemie Über die Adsorption in Lösungen 2-3 12 576-581 160 2008 10.1016/j.jhazmat.2008.03.028 Hameed B.H. Rahman A.A. Journal of Hazardous Materials Removal of phenol from aqueous solutions by adsorption onto activated carbon prepared from biomass material 2-3 01 753-759 161 2009 10.1016/j.jhazmat.2008.04.019 Hameed B.H. Journal of Hazardous Materials Spent tea leaves: A new non-conventional and low-cost adsorbent for removal of basic dye from aqueous solutions 1 07 15-15 2 1907 10.1007/bf01501332 Lagergreen S. Zeitschrift für Chemie und Industrie der Kolloide Zur Theorie der sogenannten Adsorption gelöster Stoffe 01 3 06 267-312 60 1960 10.1021/cr60205a003 Low M. J. D. Chemical Reviews Kinetics of Chemisorption of Gases on Solids. 2 03 265-268 44 1980 10.2136/sssaj1980.03615995004400020013x Chien S. H. Clayton W. R. Soil Science Society of America Journal Application of Elovich Equation to the Kinetics of Phosphate Release and Sorption in Soils 10 05 3474-3483 101 2010 10.1016/j.biortech.2010.01.002 Kushwaha Jai Prakash Srivastava Vimal Chandra Mall Indra Deo Bioresource Technology Treatment of dairy wastewater by commercial activated carbon and bagasse fly ash: Parametric, kinetic and equilibrium modelling, disposal studies 11 11 2221-2295 38 1916 10.1021/ja02268a002 Langmuir Irving Journal of the American Chemical Society The Constitution and Fundamental Properties of Solids and Liquids. Part I. Solids 2 05 212-223 5 1966 10.1021/i160018a011 Hall K. R. Eagleton L. C. Acrivos Andreas Vermeulen Theodore Industrial & Engineering Chemistry Fundamentals Pore- and Solid-Diffusion Kinetics in Fixed-Bed Adsorption under Constant-Pattern Conditions 1-2 01 37 1988 10.1007/bf00226476 Gupta G.S. Prasad G. Panday K.K. Singh V.N. Water, Air, and Soil Pollution Removal of chrome dye from aqueous solutions by fly ash 3 02 207-215 74 2005 10.1016/j.jenvman.2004.08.016 Namasivayam C. Sumithra S. Journal of Environmental Management Removal of direct red 12B and methylene blue from water by adsorption onto Fe (III)/Cr (III) hydroxide, an industrial solid waste 7 07 823-830 58 2004 10.1366/0003702041389283 Di Marino Antonio Mendicuti Francisco Applied Spectroscopy Thermodynamics of Complexation of Dimethyl Esters of Tere-, Iso-, and Phthalic Acids with α- and β-Cyclodextrins 05 6 02 3295-3304 120 2016 10.1021/acs.jpcc.5b10123 Dhumal Nilesh R. Singh Manish P. Anderson James A. Kiefer Johannes Kim Hyung J. The Journal of Physical Chemistry C Molecular Interactions of a Cu-Based Metal–Organic Framework with a Confined Imidazolium-Based Ionic Liquid: A Combined Density Functional Theory and Experimental Vibrational Spectroscopy Study 2006 10.1002/9780470027318.a5606 Coates John Infrared Spectroscopy Interpretation of Infrared Spectra, A Practical Approach 1 6 2013 Aroke U O Abdulkarim A Ogubunka R O ATBU Journal of Environmental Technology Fourier-transform Infrared Characterization of Kaolin, Granite, Bentonite and Barite 1-2 08 81-88 73 2004 10.1016/j.micromeso.2003.12.027 Schlichte Klaus Kratzke Tobias Kaskel Stefan Microporous and Mesoporous Materials Improved synthesis, thermal stability and catalytic properties of the metal-organic framework compound Cu3(BTC)2 05 S3381-S3393 10 2017 10.1016/j.arabjc.2014.01.020 Aljeboree Aseel M. Alshirifi Abbas N. Alkaim Ayad F. Arabian Journal of Chemistry Kinetics and equilibrium study for the adsorption of textile dyes on coconut shell activated carbon 1 07 10-20 378 2012 10.1016/j.jcis.2012.04.021 de Menezes Eliana W. Lima Eder C. Royer Betina de Souza Felipe E. dos Santos Bruna D. Gregório José R. Costa Tania M.H. Gushikem Yoshitaka Benvenutti Edilson V. Journal of Colloid and Interface Science Ionic silica based hybrid material containing the pyridinium group used as an adsorbent for textile dye 1 01 119-125 40 2006 10.1016/j.watres.2005.10.040 Ho Yuh-Shan Water Research Second-order kinetic model for the sorption of cadmium onto tree fern: A comparison of linear and non-linear methods Birmingham University of Birmingham 1995 Ho Yuh-Shan Absorption of heavy metals from waste streams by peat 3-4 03 171-193 25 1999 10.1016/s0921-3449(98)00053-6 Ho Y.S McKay G Resources, Conservation and Recycling A kinetic study of dye sorption by biosorbent waste product pith 4 251-263 31 2007 Badmus M A O Audu T. O. K. Anyata B U Turkish Journal of Engineering and Environmental Sciences Removal of Lead Ion from Industrial Wastewaters by Activated Carbon Prepared from Periwinkle Shells (Typanotonus fuscatus) 4 11 332-340 76 1998 10.1205/095758298529696 Ho Y.S. McKay G. Process Safety and Environmental Protection A Comparison of Chemisorption Kinetic Models Applied to Pollutant Removal on Various Sorbents 11 12 1691-1705 25 1992 10.1016/0045-6535(92)90316-j Namasivayam C. Kanchana N. Chemosphere Waste banana pith as adsorbent for color removal from wastewaters 24 2 04 153-157 53 2007 10.1002/jctb.280530208 Namasivayam C. Yamuna R. T. Journal of Chemical Technology & Biotechnology Removal of congo red from aqueous solutions by biogas waste slurry 1-2 10 101-109 65 1992 10.1007/bf00482752 Namasivayam C. Yamuna R. T. Water, Air, & Soil Pollution Removal of Rhodamine-B by biogas waste slurry from aqueous solution 3-4 09 131-143 38 1993 10.1080/02772249309357884 Yamuna R. T. Namasivayam C. Toxicological & Environmental Chemistry Color removal from aqueous solution by biogas residual slurry 11 11 1663-1668 27 1993 10.1016/0043-1354(93)90130-a Namasivayam C. Periasamy K. Water Research Bicarbonate-treated peanut hull carbon for mercury (II) removal from aqueous solution 3 255-261 82 1993 10.1016/0269-7491(93)90127-a Namasivayam C. Ranganathan K. Environmental Pollution Waste Fe(III)/Cr(III) hydroxide as adsorbent for the removal of Cr(VI) from aqueous solution and chromium plating industry wastewater 1 05 7-12 41 1994 10.1002/ps.2780410103 Namasivayam Chinnaiya Thamaraiselvi Kaliannan Yamuna Rangaiya T. Pesticide Science Removal of paraquat by adsorption on ‘waste’ Fe(III)/Cr(III) hydroxide: Adsorption rates and equilibrium studies 1 09 57-65 61 1994 10.1002/jctb.280610109 Singh Binay K. Rawat Narendra S. Journal of Chemical Technology AND Biotechnology Comparative sorption kinetic studies of phenolic compounds on fly ash and impregnated fly ash 9 09 1023-1028 17 1996 10.1080/09593331708616471 Lee C. K. Low K. S. Chow S. W. Environmental Technology Chrome Sludge as an Adsorbent for Colour Removal 2 01 183-189 54 1995 10.1016/0960-8524(95)00130-1 Lee C.K. Low K.S. Kek K.L. Bioresource Technology Removal of chromium from aqueous solution 1 01 79-83 52 1995 10.1016/0960-8524(95)00007-2 Low K.S. Lee C.K. Tan K.K. Bioresource Technology Biosorption of basic dyes by water hyacinth roots 10 34 1996 10.1016/s0273-1223(96)00700-7 Water Science and Technology Biosorption of cationic dyes by dead macro fungus fomitopsis carnea: batch studies 1 07 37-43 57 1996 10.1016/0960-8524(96)00044-2 Namasivayam C. Muniasamy N. Gayatri K. Rani M. Ranganathan K. Bioresource Technology Removal of dyes from aqueous solutions by cellulosic waste orange peel 1-2 05 397-403 189 2011 10.1016/j.jhazmat.2011.02.051 Kilic Murat Apaydin-Varol Esin Pütün Ayşe E. Journal of Hazardous Materials Adsorptive removal of phenol from aqueous solutions on activated carbon prepared from tobacco residues: Equilibrium, kinetics and thermodynamics 01 113-121 215-216 2013 10.1016/j.cej.2012.10.100 Shi Yun Kong Xiangzhen Zhang Caimeng Chen Yeming Hua Yufei Chemical Engineering Journal Adsorption of soy isoflavones by activated carbon: Kinetics, thermodynamics and influence of soy oligosaccharides 05 S2225-S2233 10 2017 10.1016/j.arabjc.2013.07.058 Shahul Hameed K. Muthirulan P. Meenakshi Sundaram M. Arabian Journal of Chemistry Adsorption of chromotrope dye onto activated carbons obtained from the seeds of various plants: Equilibrium and kinetics studies 9 01 1129-1138 27 2007 10.1016/j.wasman.2006.06.009 Malik R. Ramteke D.S. Wate S.R. Waste Management Adsorption of malachite green on groundnut shell waste based powdered activated carbon 2 02 255-264 294 2006 10.1016/j.jcis.2005.07.040 Yener Julide Kopac Turkan Dogu Gulsen Dogu Timur Journal of Colloid and Interface Science Adsorption of Basic Yellow 28 from aqueous solutions with clinoptilolite and amberlite 15 1 05 48-55 139 2008 10.1016/j.cej.2007.07.089 Hameed B Daud F Chemical Engineering Journal Adsorption studies of basic dye on activated carbon derived from agricultural waste: Hevea brasiliensis seed coat 1 39-50 56 1989 10.1016/0269-7491(89)90120-6 Allen S.J. McKay G. Khader K.Y.H. Environmental Pollution Intraparticle diffusion of a basic dye during adsorption onto sphagnum peat 1-2 12 121-131 115 2005 10.1016/j.cej.2005.09.016 Mohanty Kaustubha Das D. Biswas M.N. Chemical Engineering Journal Adsorption of phenol from aqueous solutions using activated carbons prepared from Tectona grandis sawdust by ZnCl2 activation 11 4128–4138 44 2005 10.1021/ie050162+ Mohanty Kaustubha Jha Mousam Meikap B. C. Biswas M. N. Industrial and Engineering Chemistry Research Preparation and Characterization of Activated Carbons from Terminalia Arjuna Nut with Zinc Chloride Activation for the Removal of Phenol from Wastewater 1-12 01 547-554 7 1986 10.1080/09593338609384444 Panday K. K. Prasad G. Singh V. N. Environmental Technology Letters Mixed adsorbents for Cu(II) removal from aqueous solutions 11 06 3049-3059 60 2005 10.1016/j.ces.2004.12.049 Mohanty Kaustubha Jha Mousam Meikap B.C. Biswas M.N. Chemical Engineering Science Removal of chromium (VI) from dilute aqueous solutions by activated carbon developed from Terminalia arjuna nuts activated with zinc chloride 5 926-935 50 1978 Poots V. J. P. McKay G. Healy J. J. Water Pollution Control Federation Removal of Basic Dye from Effluent Using Wood as an Adsorbent 11 428-434 321 2017 10.1016/j.powtec.2017.08.023 Marrakchi F. Auta M. Khanday W.A. Hameed B.H. Powder Technology High-surface-area and nitrogen-rich mesoporous carbon material from fishery waste for effective adsorption of methylene blue 12 237-244 203 2017 10.1016/j.jenvman.2017.07.029 Islam Md. Azharul Ahmed M.J. Khanday W.A. Asif M. Hameed B.H. Journal of Environmental Management Mesoporous activated coconut shell-derived hydrochar prepared via hydrothermal carbonization-NaOH activation for methylene blue adsorption 05 6 05 224 2013 10.1007/s11270-013-1582-5 Ghosh Rakesh Kumar Reddy D. Damodar Water, Air, & Soil Pollution Tobacco Stem Ash as an Adsorbent for Removal of Methylene Blue from Aqueous Solution: Equilibrium, Kinetics, and Mechanism of Adsorption 1-2 04 144-152 142 2007 10.1016/j.jhazmat.2006.07.072 Ferrero F. Journal of Hazardous Materials Dye removal by low cost adsorbents: Hazelnut shells in comparison with wood sawdust 08 388-398 229 2013 10.1016/j.cej.2013.06.005 Sapawe N. Jalil A.A. Triwahyono S. Shah M.I.A. Jusoh R. Salleh N.F.M. Hameed B.H. Karim A.H. Chemical Engineering Journal Cost-effective microwave rapid synthesis of zeolite NaA for removal of methylene blue 101 16661-16668 11 2012 Edris Bazrafshan Ferdos Kord Mostafapour Mohammad Ali Zazouli Methylene blue (cationic dye) adsorption into Salvadora persica stems ash 3 09 1870-1880 2 2014 10.1016/j.jece.2014.06.020 Banerjee Sushmita Sharma Gopesh C. Chattopadhyaya M.C. Sharma Yogesh Chandra Journal of Environmental Chemical Engineering Kinetic and equilibrium modeling for the adsorptive removal of methylene blue from aqueous solutions on of activated fly ash (AFSH) 1 01 14-21 98 2007 10.1016/j.biortech.2005.12.008 Kavitha D Namasivayam C Bioresource Technology Experimental and kinetic studies on methylene blue adsorption by coir pith carbon 283–294 120 2000 10.1023/A:1005207803041 Khattri S. D. Singh M. K. Colour Removal from Synthetic Dye Wastewater Using a Bioadsorbent