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Excessive discharge of hazardous azo dyes into the aquatic ecosystem is a global environmental concern. Here, we develop a green approach to remediate dye pollutions in water by fabricating an easy-separable bio-nanocomposite, based on whey protein concentrate, its nanofibrils, and montmorillonite nano-clay. To characterize the nanocomposite, we used SEM, FT-IR, XRD, and BET techniques. Nanofibrils lead to a uniform dispersion of montmorillonite in the whey protein matrix and also reinforce the nanocomposite. The adsorption efficacy was monitored in a batch system, using cationic dyes (Chrysoidine-G, Bismarck brown-R), reactive dyes (reactive black-5, reactive orange-16), acid dyes (acid red-88, acid red-114), and direct dyes (direct violet-51, Congo red). This nanocomposite adsorbed different dye classes, cationic dyes quicker (> 82%, after 4 h), and reactive dyes slower. Then, the effect of initial dye concentration, pH, contact time, adsorbent dose, and temperature on Chrysoidine-G adsorption was explored. The adsorbent showed a high removal (>93%) for a wide concentration range of Chrysoidine-G, also acidic pH and higher temperature are more favorable for the process. Equilibrium adsorption parameters were reasonably fitted with a linear (Nernst) isotherm model. The results indicated the existence of an unlimited number of absorption sites,i.e.no saturation was achieved under our experimental conditions (qmax(Exp)= 731 mg/g). Kinetic data were fitted with pseudo-second-order and intra-particle diffusion models. We conclude that this nanocomposite is a green adsorbent with potential use for wastewater treatment and related purposes.HighlightsWe produced an easy-separable bio-nanocomposite using whey nanofibrils and MMT, with high adsorption capacityNanofibrils help disperse MMT particles uniformly in the WP matrixThe adsorbent’s performance was compared to the adsorbents in absence of MMT and nanofibrilsThis composite adsorbs cationic, anionic, direct and reactive azo dyes with different kineticsAdsorption isotherms and kinetics are studied in detail

We reports the preparation of hierarchical activated carbon (HAC) obtained by CO2 activation of coal gasification residue (CGR) produced from two-stage acid leaching (TSAL). The performance of HAC on removing methylene blue (MB) from aqueous solution was investigated. The obtained HAC was characterized by N2 adsorption-desorption isotherm, Fourier transform infrared spectroscopy (FTIRS), and scanning electron microscopy (SEM). The results show that HAC exhibits hierarchical pore structure with high BET surface area (SBET = 862.76 m2 g-1) and total volume (Vtotal = 0.684 cm3 g-1). SEM images indicated a hierarchical pore texture, and FTIRS results reveal the presence of abundant organic functional groups. Adsorption studies were carried out and experimental data were fitted to 4 non-linear isotherm models and 4 kinetic models. The adsorption experimental equilibrium data of MB onto HAC were best fitted to the Redlich-Peterson (R-P). The kinetic data show that the pseudo-first-order (PFO) model is more suitable at low MB concentration, while the advantages of the pseudo-second-order (PSO) model and the Elovich model are more obvious as the concentration increases. Furthermore, according to the thermodynamic parameters, the HAC-MB adsorption process is spontaneous and endothermic.

Activated carbon from cashew nut shell via a potassium hydroxide (KOH) at 600 °C in an N

Zero-valent FeNPs was prepared by using ascorbic acid and Fe(NO)3 redox system in presence of cetyltrimethylammonium bromide (CTAB). The morphology of the FeNPs was determined by SEM, TEM, EDX, FT-IR, XRD, and BET of FeNPs. The batch experiments were carried out to determine the effects of adsorbent dosage, contact time, pH, initial concentration of acid orange 7 and temperature. The mean of free energy pre molecule of adsorbent and heat adsorption showed that the physisorption and chemisorption both involved during the adsorption. Langmuir monolayer adsorption capacity Q0max(= 66.6 mg/g) is better than Dubinin-Radushkevich qDR (44.25 mg/g). The optimum pH for the adsorption was obtained at pH 4.0 for [acid orange 7] = 100 mg/L, amount of adsorbent = 0.05 g, and temperature = 298 K. Gibb's free energy (−0.72 to −3.8 kJ/mol), enthalpy (16.1 to 19.3 kJ/mol), and entropy changes (56.4 to 70.1 J/K/mol) on the chemisorption of orange 7, indicate endothermic, spontaneous, and feasibility nature of the adsorption process. The results showed that the Langmuir isotherm and pseudo-second-order kinetic models fitted the experimental data better than other isotherm and kinetic models. The kinetic studies suggest that the adsorption follow an involvement of film diffusion and intraparticle diffusion mechanism. The as prepared FeNPs can be an alternative for more costly nano-adsorbents used for toxic dye removal from aqueous solution.

The study focuses on evaluation of three mesoporous adsorbents: unmodified Algerian montmorillonite (Mt), unmodified lemon peel waste (LP) and activated carbon (AC) in elimination of brilliant green (BG) textile dye from wastewater. The three adsorbents were characterized by the elementary analysis, the infrared spectroscopy, X-ray diffraction, N2-BET analysis and point of zero charge (pHPZC). The operational conditions of BG adsorption as initial dye concentration, contact time, pH of BG solution and temperature were evaluated in batch mode. Results revealed that BG adsorption kinetics onto Mt, LP and AC are best described by the pseudo-second order model. BG adsorption onto adsorbents follows well Langmuir model indicating that the BG molecule's adsorption is uniform; having the same adsorption energy and a monolayer adsorption takes place. The adsorbed amounts of BG onto prepared adsorbents Mt, LP, and AC are of 229, 150, and 826 mg/g respectively. Activated carbon has the higher adsorption capacity, but it is of a very high cost. Compared to the AC, Montmorillonite and lemon peels were very low-cost and very effectiveness adsorbents in the elimination of cationic dyes from wastewater.

A comparison of linear and non-linear regression method for predicting the optimum isotherm was made using the experimental adsorption equilibrium data of Cu(II) onto treated Martil sand (TMS). For this, six error analysis methods were used: the coefficient of determination r2, the sum of the squares of the errors, the sum of the absolute errors, the average relative error, the hybrid fractional error function and the Marquardt's percent standard deviation. The error values indicated that non-linear method is a better way to obtain the isotherm parameters describing the Cu(II) adsorption onto TMS. The comparison between different models such as Langmuir, Freundlich, Dubinin-Radushkevich, Temkin, Redlich-Peterson, Koble-Corrigan and Fritz-Schlunder showed that Fritz-Schlunder model was more suitable to describe the equilibrium data. Based on this result and in order to optimize the equilibrium model results for more accurate parameters values, the Fritz-Schlunder equation was modified and called modified Fritz-Schlunder model. As a comparison of such developed modified model to existing mentioned ones, the results showed that the adsorption equilibrium of Cu(II) onto TMS was better described by the modified Fritz-Schlunder model than by others.

The aim of present study was to determine the efficacy of polyacrylic acid-based and chitosan-based hydrogels (synthesized via chemical crosslinking) for the adsorption and removal of cadmium contained in aqueous solutions. Reactive functional groups involved in the adsorption of cadmium were confirmed by Fourier-transform infrared spectroscopy and cadmium adsorbed to the hydrogel surface was confirmed by scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy. The cadmium adsorption mechanism was evaluated using non-linear Langmuir, Freundlich, Redlich-Peterson and Sips isotherms, with the best fits found using the non-linear Sips and Redlich-Peterson isotherms for adsorption to polyacrylic acid-based and chitosan-based hydrogels, respectively. Maximum cadmium adsorption capacities of the polyacrylic acid-based and chitosan-based hydrogels were respectively 197.92 and 234.84 mg of metal per g of dried hydrogel at pH 6.0 and 343.0 ± 1.0 K. The best kinetic fit for adsorption to the chitosan-based hydrogel was found with the pseudo-second order kinetic model, whereas the best kinetic fit for adsorption to the polyacrylic acid-based hydrogel was found with the pseudo-first order kinetic model. The thermodynamic results indicated that the adsorption of cadmium to both hydrogels is a favorable, spontaneous process. The desorption studies suggested the formation of reversible chemical bonds between cadmium and active groups in the hydrogel network.

Polyaniline/Activated carbon composite was synthesized using in-situ oxidative chemical polymerization technique. The optimized composite (POAC) was applied for the removal of methyl orange (MO) from aqueous solution. Several studies such as changing the concentration of MO solution, contact time and adsorbent dosage were performed batch wise at optimum pH of 6.5. Within 2 h of the experiment 70% of MO was removed. A maximum monolayer adsorption capacity Q of 285 (mg/g) was obtained with Langmuir isotherm model. Pseudo second-order kinetic model explained the experimental data better than Pseudo-first order model and intra particle diffusion model. Saturation concentration of 62.92 (mg/L) obtained by utilizing Brunauer–Emmett–Teller (BET) parameters matched well with the assumed value 63 (mg/L). this work demonstrates that POAC is a potential and effective adsorbent.

The preparation of cost-effective potentially efficient adsorbents of metal pollutants by activated carbons from the natural sources is the challenging research to the scientific community. In the present study, the characteristic features of highly potential activated carbon synthesized from various natural sources are reported. Among the synthesized activated carbons, the best one by its surface area is applied for the analysis of its kinetics and isotherms for copper (II) adsorption. Four different seeds and three leaves were used as the precursors in a chemical activation (three-step) process composed of the impregnation, carbonization and subsequent activation to produce the activated carbons. As per present investigation, Indian gooseberry seeds mixed with their shells showed the highest BET surface area of 1360 m2/g. The maximum adsorptivity of the activated carbon was found to be 66.79 mg/g at 60 °C. The adsorption followed pseudo-second-order and Elovich model kinetics with the Langmuir and Dubinin–Radushkevich (D–R) adsorption isotherms and was spontaneous and endothermic in nature. This AC could be used as a suitable cost-effective copper (II) adsorbent in water purification processes. Moreover, the ACs could be reused after regeneration with high removal efficiency.

Copper is a heavy metal. When its content is low, it is good to the health of biological body. However, when its content is high, it has the toxic effect on biological body. At this time, removal of the toxicity of copper is very important. SBA-15 molecular sieve was prepared by hydrothermal synthesis method. The sample was characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, 77 K adsorption-desorption isotherm of nitrogen. The fibrous particles with a diameter of 333 ± 10 nm were obtained. Nano mesoporous SBA-15 with Brunner-Emmett-Teller specific surface area 503 m2 g−1 was used as an adsorbent to adsorb Cu(II) from solution. The effects of acidity, temperature, contact time, amount of adsorbent and initial concentration of Cu(II) on the adsorption were studied. Under the optimized adsorption conditions, the maximum adsorption rate of Cu(II) by nano-mesoporous SBA-15 was 89.0% and the maximum adsorption capacity was 11.39 mg/g. By studying kinetics, it was found that the adsorption belongs to the quasi-second-order kinetic model, simultaneously belonging to the Freundlich adsorption isotherm. The results of adsorption thermodynamics showed that when temperature is 25–55 °C, △G°

Monitoring pollutants in water samples is a challenge to analysts. So, the removal of Napthol blue black (NBB) and Erichrome blue black R (EBBR) from aqueous solutions was investigated using magnetic chelated silica particles. Magnetic solids are widely used in detection and analytical systems because of the performance advantages they offer compared to similar solids that lack magnetic properties. In this context, a fast, simple and clean method for modification of magnetic particles (Fe3O4) with silica gel was developed using microwave technique to introduce silica gel coated magnetic particles (SG-MPs) sorbent. The magnetic sorbent was characterized by the FT-IR, X-ray diffraction (XRD), and scan electron microscope (SEM) analyses. The effects of pH, time, weight of sorbent and initial concentration of dye were evaluated. It was interesting to find from results that SG-MPs exhibits high percentage extraction of the studied dyes (100% for NBB and 98.75% for EBBR) from aqueous solutions. The Freundlich isotherm with r2 = 0.973 and 0.962 and Langmuir isotherms with r2 = 0.993 and 0.988 for NBB and EBBR, respectively were used to describe adsorption equilibrium. Also, adsorption kinetic experiments have been carried out and the data have been well fitted by a pseudo-second-order equation r2 = 1.0 for NBB and 0.999 for EBBR. The prepared sorbent with rapid adsorption rate and separation convenience was applied for removal of NBB and EBBR pollutants from natural water samples with good precision (RSD% = 0.05–0.3%).

Experimental data of the adsorption of reactive dyestuffs onto Filtrasorb 400 activated carbon (FS400) were determined in an equilibrium isotherm study. As most industrial wastewater contains more than one pollutant, an investigation into the effect of multisolute systems (using the unhydrolysed form of the reactive dyes) on the adsorption capacity was undertaken. Equilibrium isotherm models were employed to describe the adsorption capacities of single, binary and ternary dye solutions. The results of these analyses showed that adsorption of reactive dyes from single and multisolute systems can be successfully described by Langmuir, and Redlich–Peterson equilibrium isotherm models. Experimental data indicated that competitive adsorption for active sites on the carbon surface results in a reduction in the overall uptake capacity of the reactive dyes investigated.

This study was to evaluate the adsorption capability of clay minerals of bentonite, kaolin and zeolite to remove Congo Red from aqueous solution. The experiments were carried out in a batch system to optimise operation variables: adsorbent dosage, Congo Red concentration, pH and temperature. Adsorption kinetic and equilibrium isotherm of the clay materials were studied using pseudo-first order and second order kinetic equations, and Freundlich and Langmuir models. The equilibrium data of kaolin was found to best fit to the Langmuir model, while bentonite and zeolite were best explained by the Freundlich model. The adsorption kinetic followed the pseudo-second order equation for the three adsorbents. Intra-particle diffusion studies revealed that the adsorption rates were not solely controlled by the diffusion step. Further thermodynamic investigations showed that the adsorption is an exothermic and spontaneous process. Sodium bentonite demonstrated the best adsorptive capacity followed by kaolin clay, and they can be employed as low-cost alternatives for recalcitrant dye removal from industrial wastewater.

The biosorption of food dyes FDC red no. 40 and acid blue 9 onto Spirulina platensis nanoparticles was studied at different conditions of pH and temperature. Four isotherm models were used to evaluate the biosorption equilibrium and the thermodynamic parameters were estimated. Infra red analysis (FT-IR) and energy dispersive X-ray spectroscopy (EDS) were used to verify the biosorption behavior. The maximum biosorption capacities of FDC red no. 40 and acid blue 9 were found at pH 4 and 298 K, and the values were 468.7 mg g(-1) and 1619.4 mg g(-1), respectively. The Sips model was more adequate to fit the equilibrium experimental data (R20.99 and ARE5%). Thermodynamic study showed that the biosorption was exothermic, spontaneous and favorable. FT-IR and EDS analysis suggested that at pH 4 and 298 K, the biosorption of both dyes onto nanoparticles occurred by chemisorption.

Sugar beet pulp (SBP) is a well known adsorbent, however the use of sugar beet pulp as an adsorbent for removal of cationic dyes was not reported in the literature, so far. Batch adsorption experiments were conducted to study the effects of contact time, initial concentration (20–50 mg/L) and pH (2–8) on the removal of methylene blue (MB) from aqueous solution by SBP. Freundlich and Langmuir isotherm models were found to be suitable for description of MB adsorption on SBP. The SBP was found to have a Langmuir monolayers adsorption capacity of 714.29 mg/g at pH 8 and 25 °C. The results showed that the pseudo-second-order kinetic model best described the absorption process (R2 ≥ 0.9999). The extent of MB adsorption on SBP increased along with an increase of initial pH of the solution and initial MB concentration. The results demonstrated that the SBP is a promising adsorbent for removal of MB from aqueous solutions.

The main objective of this work was to investigate the biosorption performance of unmodified and Cetylpyridinium chloride (CPC)-modified biomass of Penicillium YW 01 for Acid Blue 25 (AB 25). Maximum biosorption capacity of AB 25 onto CPC-modified biosorbent was 118.48 mg g −1 under phosphoric–phosphate buffer with initial dye concentration of 200 mg L −1 at 30 °C. The biosorption pattern of AB 25 onto unmodified biosorbent in aqueous solution and phosphoric–phosphate buffer was well fitted with both Langmuir and Freundlich isotherm models. While the equilibrium data of CPC-modified biosorbent in aqueous solution and phosphoric–phosphate buffer failed to fit the Freundlich isotherm model, indicating the monolayer biosorption formed onto CPC-modified biosorbent. The values of initial biosorption rate of biosorbent in phosphoric–phosphate buffer were found to be higher than that of corresponding values in aqueous solution, indicating phosphoric–phosphate buffer enhanced the initial biosorption rate of biosorption process. Weber–Morris model analysis indicated that the boundary layer effect had more influence on the biosorption process in phosphoric–phosphate buffer. The BET surface area of CPC-modified biosorbent (0.5761 m 2 g −1 ) was larger than that of unmodified biomass (0.3081 m 2 g −1 ). Possible dye–biosorbent interactions were confirmed by Fourier transform infrared spectroscopy.

This paper describes the adsorption capacity of ion exchange Indion NSSR resin for removal of nitrates from aqueous solution. Adsorption capacity of resin was investigated under different conditions viz variations in adsorbent dose, initial concentrations of nitrate and pH. The fitting of the Freundlich, Langmuir and Dubinin–Radushkevich adsorption models to the equilibrium data was investigated. The equilibrium data obtained in this study were found to follow the Langmuir adsorption isotherm. The maximum sorption capacity was 119 mg/g as per Langmuir isotherm at 35 °C under this particular study. The rate parameters for the intra particle diffusion have been estimated for different initial concentrations. In batch adsorption processes, the adsorbate molecules diffuse in porous adsorbent and rate process usually depends on t0.5 rather than the contact time. The nitrate adsorption on Indion NSSR resin from aqueous solution follows first order reversible model. The nitrate adsorption capacity of ca 77 mg/g was observed for the Indion NSSR resin from the column study with specific conditions of operation.

Cashew nut shell (CNS) — a novel, low cost adsorbent prepared from agricultural waste has been utilized as the adsorbent for the removal of Congo red (CR) dye from an aqueous solution. The effect of pH, adsorbent dose, initial dye concentration, time and temperature on adsorption was studied. The results indicate that CNS can be employed as a low cost alternative compared to other commercial adsorbents in the removal of dyes from wastewater. The experimental data were analyzed by Langmuir, Freundlich, Redlich–Peterson, Koble–Corrigan, Sips, Toth, Temkin and Dubinin–Radushkevich adsorption isotherms. The characteristic parameters for each isotherm and related correlation coefficients have been determined using MATLAB 7.1. Thermodynamic parameters such as ∆Go, ∆Ho and ∆So have also been evaluated and it has been found that the sorption process was feasible, spontaneous and exothermic in nature. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were used to fit the experimental data. Kinetic parameters, rate constants, equilibrium sorption capacities and related correlation coefficients, for each kinetic model were calculated and discussed. It was shown that the adsorption of CR could be described by the pseudo-second-order equation, suggesting that the adsorption process is a presumably chemisorption.

The removal of Pb(II) and Pb(II)-citric acid (Pb(II)-CA) from aqueous solutions by sawdust activated carbon (SDAC) was investigated. The higher adsorptive removal of Pb(II) from aqueous solutions containing Pb(II)-CA than Pb(II) only was observed due to the presence of CA in the former system. The mechanism of adsorption process was studied by conducting pH as well as kinetic studies. Batch adsorption experiments were conducted to study the effect of adsorbent dose, initial concentration and temperature for the removal of Pb(II) from Pb(II) only and Pb(II)-CA aqueous systems. The adsorption was maximum for the initial pH in the range of 6.5-8.0 and 2.0-5.0 for Pb(II) and Pb(II)-CA, respectively. The solution pH, zero point charge (pH(zpc)) and species distribution of Pb(II) and Pb(II)-CA were found to play an important role in the adsorption of Pb(II) and Pb(II)-CA onto SDAC from water and wastewaters. SDAC exhibited very high adsorption potential for Pb(II) ions in presence of CA than when Pb(II) ions alone were present. The kinetic and equilibrium adsorption data were well modeled using pseudo-first-order kinetics and Langmuir isotherm model, respectively.

The removal efficiency of Viscum album L. from lead containing aqueous solutions was investigated. The effect of adsorbent mass, pH of solution, initial Pb(II) concentration and temperature was investigated using a batch adsorption technique. The optimum pH for Pb(II) adsorption was found as 3.0 for Viscum album L. Results were analyzed by the Langmuir, Freundlich, Temkin and Harkins–Jura, equation using linearized correlation coefficient at different temperature. The characteristic parameters for each isotherm have been determined. The Langmuir model agrees very well with experimental data than the other models. According to Langmuir isoterm, the monolayer saturation capacity (Qo) is 769.23 mg/g at 25 °C. Models and the isotherm constant were evaluated depending on temperature. Thermodynamic parameters such as ΔHo, ΔSo and ΔGo were calculated. The adsorption process was found to be endothermic and spontaneous. The experimental data were analyzed using the first- and the second-order kinetic models. The rate constants of adsorption for both kinetics models have been calculated. The second-order model provides the best correlation of the data.

In the study, bagasse fly ash (BFA) (generated as waste material from sugar mill), was used as an adsorbent for the removal of Orange-G (OG), and Methyl Violet (MV), from aqueous solution. Batch studies were performed to address various experimental parameters like pH, contact time, adsorbent dose and initial concentration for the removal of these dyes. Effective pH for OG and MV removal were 4 and 9, respectively. Greater percentage of dye was removed with decrease in the initial concentration of dyes, and increase in amount of adsorbent used. Kinetic study showed that the adsorption of dyes on BFA was a gradual process. Quasi-equilibrium reached in 4 h. Pseudo-first-order, pseudo-second-order, Bangham and intra-particle particle diffusion models were used to fit the experimental data. Pseudo-second-order rate equation was able to provide realistic description of adsorption kinetics. Equilibrium isotherms were analysed by Freundlich, Langmuir, Redlich–Peterson, Dubnin–Radushkevich, and Tempkin isotherm equations using correlation coefficients and five different error functions. Freundlich equation is found to best represent the equilibrium data for OG-BFA system while Redlich–Peterson equation better fits the data for MV-BFA system. Thermodynamic study showed that adsorption of MV on BFA (with a more negative Gibbs free energy value) is more favoured among the dyes studied. BFA which was used without any pretreatment showed high surface area, pore volume and pore size exhibiting its potential to be used as an adsorbent for the removal of OG and MV.

Viewpoints on the applicability of the equilibrium isotherm equations in coagulation–flocculation (CF) process are presented herein to stem the tide of the misuse. The two widely used equilibrium isotherm equations (Langmuir and Freundlich equilibrium isotherm equations) have been erroneously used to elucidate the CF mechanism, using plant-based coagulants, without a tenable theoretical basis. This erroneous use of equilibrium isotherm equations in CF process was based on the assumption that adsorption process is the rate determining step in the mechanism of CF process, using plant-based coagulants. This is in contrary to the fact that the rate determining step is a kinetic process, which is different from the equilibrium state.

Adsorption of malachite green (MG) was studied using three adsorbents namely, bagasse fly ash (BFA), a sugar industry waste, and activated carbons commercial grade (ACC) and laboratory grade (ACL). Batch adsorption studies were conducted to evaluate the effect of various parameters such as pH, adsorbent dose, contact time and initial MG concentration on the removal of MG. The initial pH of the dye solution strongly affected the chemistry of both the dye molecules and adsorbents in an aqueous solution. The effective pH was 7.0 for adsorption of MG by the three adsorbents. Equilibrium reached in about 4 h contact time. Optimum BFA, ACC and ACL dosages were found to be 1, 20 and 4 g l−1, respectively. The adsorption followed pseudo-second-order kinetics. Equilibrium adsorption data on BFA, ACC and ACL were analyzed by Freundlich, Langmuir, Dubnin–Radushkevich, Redlich–Peterson and Temkin isotherm equations using regression analysis. Non-linear error analysis showed that the Freundlich isotherm best-fits the equilibrium data for adsorptive removal of MG by BFA and ACC and Redlich–Peterson best follows the equilibrium data for ACL. Thermodynamic study showed that MG adsorption on BFA was comparable to that obtained with ACC or ACL.

Nonionic organic contaminants (NOCs) such as benzene, toluene, and phenol from contaminated wastewater can be effectively adsorbed by organo-zeolites. Organo-zeolites were prepared from synthetic ZSM-5 and natural zeolites, by exchanging the quaternary amines, i.e. hexadecyltrimethylammonium (HDTMA) bromide and n-cetylpyridinium bromide (CPB). The maximum adsorption of CPB onto these zeolites is in the order of clinoptilolite>ZSM-5-88 (SiO2/Al2O3=88)>ZSM-5-31 (SiO2/Al2O3=31) which is mainly dependent on the external cation exchange capacity (ECEC) of each zeolite. Batch adsorption experiment was carried out to remove benzene, toluene, and phenol from aqueous solution using the above-mentioned organo-zeolites. In addition, as-synthesized MCM-41 molecular sieve was employed for removal of organic contaminants from aqueous solution. The experimental results were fitted to the Langmuir, Freundlich, Redlich–Peterson and linear equation isotherms to obtain the characteristic parameters of each model. Our resultant data showed that nonlinear form of Langmuir, the Freundlich and Redlich–Peterson could be fitted well with sorption data in most cases. According to the evaluation using the Langmuir equation, the maximum organics adsorption by synthesized MCM-41 was much greater than that of the natural clinoptilolite and ZSM-5 zeolites.

The ability of chitosan, derived from deacetylated crab shell chitin, to remove acid dyes from effluent solution by adsorption has been studied. Equilibrium isotherms for the adsorption of five acid dyes, Acid Green 25 (AG25), Acid Orange 10 (AO10), Acid Orange 12 (AO12), Acid Red 18 (AR18) and Acid Red 73 (AR73), on chitosan were measured experimentally. Results were analysed by the Langmuir, Freundlich and Redlich–Peterson (R–P) equation using a linearised correlation coefficient. The Langmuir isotherm gave the best correlation for the adsorption of AG25, AR18, AR73 and AO12 while the composite Freundlich isotherm gave excellent correlation for AO10. The equilibrium data were then analysed using five different non-linear error analysis methods and two significant findings were obtained. Firstly, the order of isotherm selection was changed showing that the R–P equation had the lowest error values for all five acid dye-chitosan isotherms. Secondly, the values of the individual isotherm constants changed with the error methodology selected.