Adsorptive Potential of 2-Mercaptobenzimidazole-Immobilized Organophilic Hydrotalcite for Mercury(II) Ions from Aqueous Phase and Its Kinetic and Equilibrium Profiles

An organophilic calcined hydrotalcite (OHTC) was prepared by treating calcined hydrotalcite (HTC) with sodium dodecylbenzene sulphonate (an anionic surfactant) to achieve a high loading of thiol functionality through the immobilization of 2-mercaptobenzimidazole (MBI) as a chelating agent. The adsorbent (MBI-OHTC) obtained was characterized using XRD, FTIR, SEM, TG/DTG, surface area analysis and potentiometric titration. The adsorption of MBI-OHTC to remove Hg(II) ions from aqueous solutions was studied as a function of pH, contact time, metal ion concentration, ionic strength and adsorbent dose. The optimum pH range for the maximum removal of Hg(II) was 6.0–8.0. The maximum value of Hg(II) adsorption was found to be 11.63 and 21.52 mg g^?1 for an initial concentration of 25 and 50 mg l^?1, respectively at pH 8.0. The equilibrium conditions were achieved within 3 h under the mixing conditions employed. A reversible pseudo-first-order used to test the adsorption kinetics. The adsorption mechanism consisted of external diffusion and intraparticle diffusion and the intraparticle mass transfer diffusion was predominated after 20 min of experiment. Extent of adsorption decreased with increase of ionic strength. The experimental isotherm was analyzed with two parameters (Langmuir and Freundlich) and three parameters (Redlich–Peterson) equations. The isotherm data were best modeled by the Freundlich isotherm equation. Complete removal (≈100%) of Hg(II) from 1.0 l of chlor-alkali industry wastewater containing 9.86 mg Hg(II) ions, was possible with 3 g of the adsorbent dose at pH 8.0. About 95.0% of Hg(II) can be recovered from the spent adsorbent using 0.1 M HCl.     

Comparison of Activated Carbon and Physic Seed Hull for the Removal of Malachite Green Dye from Aqueous Solution

In the present work, the effectiveness of physic seed hull, PSH (Jatropha curcas L.), as an alternative low-cost adsorbent for the removal of malachite green (MG) dye from simulated wastewater has been studied. It has been observed that PSH has remarkable adsorption capacity compared to granular activated carbon. The PSH adsorbent was characterized by SEM-EDX, BET, CHNS, zeta potential, and FTIR techniques. The adsorption behaviors such as adsorption kinetics, adsorption dynamics, and adsorption isotherms of PSH for the removal of MG dye from aqueous solution were studied in detail. The kinetic data fitted well with the pseudo second-order kinetic model for MG adsorption. Langmuir isotherm was found to be the model best fitted to describe the adsorption process.     

A Novel Pretreatment Method of Lignocellulosic Material as Adsorbent and Kinetic Study of Dye Waste Adsorption

Sulphuric acid-modified bagasse has been used as low-cost adsorbent for the removal of methylene blue (MB) dye from aqueous solution. In order to remove organic compounds that contribute to chemical oxygen demand (COD), pretreatment with thorough washing of adsorbent using boiling distilled water was performed instead of conventional washing using distilled water at room temperature only. This has resulted in the highest efficiency of color removal of 99.45% and COD reduction of 99.36% for MB dye solution at pH 9. Effects of initial pH, dye concentration, adsorbent dosage, temperature, and contact time have been studied. The adsorption of MB dye was pH dependent. Langmuir and Freundlich isotherm models were tested on the adsorption data. The kinetic experimental data were analyzed using pseudo-first order, pseudo-second order, and the intraparticle diffusion model in order to examine the adsorption mechanisms. The adsorption process followed the Langmuir isotherm as well as the Freundlich isotherm and pseudo-second-order kinetic model. The process was found to be endothermic in nature.     

Removal of Plant Pathogen Propagules from Irrigation Runoff using Slow Filtration Systems: Quantifying Physical and Biological Components

A novel high-capacity phosphate removal adsorbent of graphene nanosheets (GNS) supported lanthanum hydroxide (LaOH) is prepared. The phosphate adsorption performance for GNS-LaOH is examined by a batch adsorption method from aqueous solutions. The Freundlich and Langmuir models are used to simulate the sorption equilibrium, which reveal that the Langmuir model has a better correlation with the experimental data. The maximum adsorption capacity is calculated to be 41.96 mg/g. The kinetic data from the adsorption of phosphate is suggested as the pseudo-second-order model, and the multi-linearity adsorption process is observed in the intraparticle diffusion model, indicating that a chemisorption process is dominant in the adsorption of phosphate. The phosphate adsorption mechanism is explored by analyzing the Fourier transform infrared spectroscopy (FT-IR) and the relationship between the adsorption amount and the pH value of phosphate solution. Ligand exchange and electrostatic and Lewis acid–base interactions are determined to be three main factors for phosphate adsorption.     

Immobilization of Green Synthesized Silver Nanoparticles onto Amino-Functionalized Silica and Their Application for Indigo Carmine Dye Removal

In the present work, we have applied a green method for the synthesis of silver nanoparticles (AgNPs) onto amino-functionalized silica using Nigella sativa (black seed) aqueous extract as an eco-friendly and efficient reducing agent. The factors influencing the functionalization of silica and AgNPs loading have been considered. The samples were characterized by elemental analysis, FTIR, XRD, TGA, SEM, and EDX and used for the removal of indigo carmine (IC) dye from aqueous solution. The mean particle size of immobilized AgNPs was calculated from the XRD pattern using the Scherrer equation and is equal to about 26 nm. Adsorption experiments were carried out as batch studies at different contact times, temperature, adsorbent dosage, and initial dye concentrations. The IC adsorption equilibrium was attained after about 20 min of contact time. The equilibrium data shows that the Langmuir model was more reasonable to depict the IC adsorption, and the maximum adsorption capacity of IC is 73.05 mg/g. Based on the kinetic analysis, the adsorption process follows a pseudo-second-order equation. The estimation of the thermodynamic parameters such as the Gibbs free energy, entropy, and enthalpy changes of the adsorption process indicated the feasibility and endothermic nature of IC adsorption. The modified surface was found to be extremely stable in the aqueous medium, and no significant leaching of AgNPs was observed. Thus, immobilization of AgNPs may advance reuse, reduce environmental risks associated with leaching of AgNPs, and enhance cost-effectiveness.     

Biosorption of Methylene Blue from Aqueous Solutions by Hazelnut Shells: Equilibrium, Parameters and Isotherms

This paper presents a study on the batch adsorption of a basic dye, methylene blue (MB), from aqueous solution onto ground hazelnut shell in order to explore its potential use as a low-cost adsorbent for wastewater dye removal. A contact time of 24 h was required to reach equilibrium. Batch adsorption studies were carried out by varying initial dye concentration, initial pH value (3–9), ionic strength (0.0–0.1 mol L^?1), particle size (0–200 μm) and temperature (25–55°C). The extent of the MB removal increased with increasing in the solution pH, ionic strength and temperature but decreased with increase in the particle size. The equilibrium data were analysed using the Langmuir and Freundlich isotherms. The characteristic parameters for each isotherm were determined. By considering the experimental results and adsorption models applied in this study, it can be concluded that equilibrium data were represented well by Langmuir isotherm equation. The maximum adsorption capacities for MB were 2.14?×?10^?4, 2.17?×?10^?4, 2.20?×?10^?4 and 2.31?×?10^?4 mol g^?1 at temperature of 25, 35, 45 and 55°C, respectively. Adsorption heat revealed that the adsorption of MB is endothermic in nature. The results indicated that the MB strongly interacts with the hazelnut shell powder.     

Flexible Alumina-Silica Nanofibrous Membrane and Its High Adaptability in Reactive Red-120 Dye Removal from Water

Flexible and self-standing membrane composed of ultrafine alumina-silica nanofibers (NFs) has been successfully fabricated by the electrospinning method, and further used as an adsorbent for the adsorptive decolorization of Reactive Red-120 (RR-120) dye from an aqueous system. Effects of pH, adsorbent dosage, and contact time on adsorption have been studied. The adsorption of RR-120 on the NFs was found to be highly pH dependent and the optimum pH was found to be 3. The adsorption equilibrium data was explained well with the Langmuir isotherm model, and the maximum sorption capacity was found to be 884.95 mg/g, which was several folds higher than the adsorption capacity of a number of recently studied potential adsorbents. After adsorption, the NF mat could be separated from the liquid phase conveniently and reused. The sorption kinetics was found to follow an intraparticle diffusion model. The high adsorption performance, excellent flexibility, easy recovery, and reuse characteristic of the alumina-silica NF membrane all favor its practical application in environmental remediation.     

Adsorption of Cadmium on Bed Sediments of River Hindon: Adsorption Models and Kinetics

The adsorption characteristics of cadmium on bed sediments ofriver Hindon in western Uttar Pradesh (India) have been studied.The effect of various operating variables, viz., initial concentration, solution pH, sediment dose, contact time, particlesize and temperature has been studied. The optimum equilibrationtime was found to be 60 min, which was independent of initialconcentration of cadmium ions. The adsorption curves were smoothand continuous leading to saturation, suggesting the possible monolayer coverage of cadmium ions on the surface of the adsorbent. The adsorption of cadmium increased with an increasein pH. Furthermore the adsorption of cadmium increased with increasing adsorbent concentration and decreased with adsorbentparticle size. The important geochemical phases, iron and manganese oxide, support the adsorption of cadmium ions. The adsorption data were analysed using the Langmuir and Freundlichadsorption models to determine the mechanistic parameters relatedto the adsorption process. Thermodynamic parameters, viz., freeenergy change, enthalpy change and entropy change, were alsodetermined. The negative values of free energy change (ΔG°) indicated the spontaneous nature ofthe adsorption and positive values of enthalpy change (ΔG°) suggested the endothermic nature ofthe adsorption process. The intraparticle diffusion of cadmium through pores in the adsorbent was found be the main rate-limiting step.     

Equilibrium and Kinetic Studies on Biosorption of Heavy Metals by Leaf Powder of Paper Mulberry (Broussonetia papyrifera)

Paper mulberry (Broussonetia papyrifera) leaf powder was used to remove heavy metal ions from aqueous solutions. The specific uptakes of Cu (II), Pb (II), and Cd (II) by the leaf powder were 43.40?±?0.2, 43.9?±?0.5, and 30.65?±?0.9 mg g^?1, respectively, when 500 mg L^?1 of the metal solutions were used. The data fitted well to the Langmuir isotherm. The process followed the pseudo-second-order kinetic equation and intraparticle diffusion played an important role in the adsorption process. On the basis of the calculated thermodynamic parameters such as standard enthalpy (??H°), entropy (??S°) and free energy change (??G°), it was inferred that the sorption process was endothermic and spontaneous in nature. The surface properties of the leaf powder (revealed by scanning electron microscopic observations) were suitable for the metal adsorption process. Energy dispersive X-ray fluorescence analysis confirmed the sequestration of the metal ions by the leaf powder. Fourier transform infrared spectroscopy implicated that different functional groups on the leaf powder were involved in the metal adsorption process. The results obtained from this study implicated that the B. papyrifera leaf powder was a good choice as a metal adsorbent. This abundantly available natural and eco-friendly biosorbent could be effectively used to develop a technology in the future.     

Equilibrium, Kinetics, and Thermodynamics of Methylene Blue Adsorption by Pine Tree Leaves

The adsorption capacity of pine tree leaves for removal of methylene blue (MB) from aqueous solution was investigated in a batch system. The effects of the process variables, such as solution pH, contact time, initial dye concentration, amount of adsorbent, agitation speed, salt concentration, and system temperature on the adsorption process were studied. The extent of methylene blue dye adsorption increased with increase in initial dye concentration, contact time, agitation speed, temperature, and solution pH but decreased with increased in amount of adsorbent and salt concentration. Equilibrium data were best described by both Langmuir isotherm and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine tree leaves biomass was 126.58?mg/g at 30?°C. The value of separation factor, R _L , from Langmuir equation and Freundlich constant, n, both give an indication of favorable adsorption. The intrapartical diffusion model, liquid film diffusion model, double exponential model, pseudo-first and second order model were used to describe the kinetic and mechanism of adsorption process. A single stage bath adsorber design for the MB adsorption onto pine tree leaves has been presented based on the Langmuir isotherm model equation. Thermodynamic parameters such as standard Gibbs free energy (??G ⁰), standard enthalpy (??H ⁰), and standard entropy (??S ⁰) were calculated.     

Intraparticle diffusion process occurring during adsorption of dyestuffs

The adsorption of a dyestuff, Telon Blue (Acid Blue 25) on Fuller's earth and Astrazone Blue onto fired clay has been studied. An intraparticle diffusion rate parameter has been defined characteristic of the rate of diffusion after the early stages of the adsorption. The rate parameter has been determined for a number of variables including adsorbent mass, initial dye concentration, and particle size.     

Removal of Zn2+ from Aqueous Solution using Castor Seed Hull

The effects of various experimental parameters on adsorption of Zn²⁺ metal ion from its aqueous solution by castor seed hull and also by activated carbon have been investigated using batch adsorption experiments. It has been found that the amount of zinc adsorbed per unit mass of the hull increases with the initial metal ion concentration, contact time, solution pH and with the amount of the adsorbent. Kinetic experiments clearly indicate that adsorption of zinc on both castor hull and activated carbon is a three-step process??a rapid adsorption of the metal ion, a transition phase, and an almost flat plateau. This has also been confirmed by the intraparticle diffusion model. It has also been found that the zinc adsorption process followed pseudo-second order kinetics. The kinetic parameters including rate constants have been determined at different initial metal ion concentration, pH, amount, and type of adsorbent, respectively. The Langmuir and Freundlich adsorption isotherm models have been used to interpret the equilibrium adsorption data. The Langmuir model yields better correlation coefficients. The monolayer adsorption capacities (q _m ) of castor hull and activated carbon have been compared with those for others reported in the literature. The value of separation factor (R _L ) derived from the Langmuir model gives an indication of favorable adsorption. Finally, from comparative studies, it has been found that castor hull is a potentially attractive adsorbent as compared to commercial activated carbon for the removal of zinc from aqueus effluents.     

Assessment on the Removal of Methylene Blue Dye using Tamarind Fruit Shell as Biosorbent

Tamarind fruit shell was used as a low-cost biosorbent for the removal of methylene blue from aqueous solution. The various factors affecting adsorption, such as agitation, pH, initial dye concentration, contact time, and temperature, were investigated. The dye adsorption capacity was strongly dependent on solution pH as well as temperature. The Langmuir isotherm model showed good fit to the equilibrium adsorption data, and the maximum adsorption capacity obtained was 1.72 mg g^?1 at 303 K. The kinetics of adsorption followed the pseudo-second-order model and the rate constant increased with increase in temperature, indicating endothermic nature of adsorption. The Arrhenius equation was used to obtain the activation energy (E _a) for the adsorption system. The activation energy was estimated to be 19.65 kJ mol^?1. Thermodynamic parameters such as Gibbs free energy (ΔG ⁰), enthalpy (ΔH ⁰), and entropy (ΔS ⁰) were also investigated. Results suggested that adsorption of methylene blue onto tamarind fruit shell was a spontaneous and endothermic process. The present investigation suggests that tamarind fruit shell may be utilized as a low-cost adsorbent for methylene blue removal from aqueous solution.     

Changes in Mercury Deposition in a Mining and Smelting Region as Recorded in Tree Rings

The adsorption of lead onto date palm fibers (palm fibers) and leaf base of palm (petiole) has been examined in aqueous solution by considering the influence of various parameters such as contact time, solution pH, adsorbent dosage, particle sizes, ionic strength, and temperature. The adsorption of Pb(II) increased with an increase of contact time. The optimal range of pH for Pb(II) adsorption is 3.0?C4.5. The linear Langmuir and Freundlich models were applied to describe the equilibrium isotherms, and both models fitted well. The monolayer adsorption capacity of Pb(II) on palm fibers and petiole was found as 18.622 and 20.040 mg/g, respectively, at pH 4.5 and 25°C. Dubinin-Radushkevich (D-R) isotherm model was also applied to equilibrium data. The mean free energy of adsorption (2.397 and 4.082 kJ/mol) onto palm fibers and petiole, respectively, may be carried out via physisorption mechanism. Pseudo-first-order rate equation and pseudo-second-order rate equation were applied to study the adsorption kinetics. In comparison to first-order kinetic model, pseudo-second-order model described well the adsorption kinetics of Pb(II) onto palm fibers and petiole from aqueous solution. From the results of the thermodynamic analysis, Gibbs free energy ??G, enthalpy change ??H, and entropy ??S were determined. The positive value of ??H suggests that interaction of Pb(II) adsorbed by palm fibers is endothermic. In contrast, the negative value of ??H indicates that interaction of Pb(II) ions by petiole is exothermic. The negative value of ??G indicates that the adsorption of Pb(II) ions on both palm fibers and petiole is a spontaneous process.     

Removal of Cu(II) Ions from Aqueous Solution by Magnetic Chitosan-Tripolyphosphate Modified Silica-Coated Adsorbent: Characterization and Mechanisms

A magnetic chitosan-modified Fe₃O₄@SiO₂ with sodium tripolyphosphate adsorbent (MTPCS) was synthesized by surface modification of Fe₃O₄@SiO₂ with chitosan using sodium tripolyphosphate (STPP) as the cross-linker in buffer solution for the adsorption of Cu(II) ions from aqueous solution. The structure and morphology of this magnetic nanoadsorbent were examined by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), BET surface area measurements, Fourier transform infrared spectrometer (FTIR), and X-ray photoelectron spectroscopy (XPS). The effects of initial pH, adsorbent amount, and initial concentration of heavy metal ions were investigated by batch experiments. Moreover, adsorption isotherms, kinetics, and thermodynamics were studied to understand the mechanism of adsorbing metal ions by synthesized MTPCS. The results revealed that adsorption kinetics was best depicted by the pseudo-second-order rate mode and intraparticle-diffusion models. The adsorption isotherm fitted well to the Langmuir model. Moreover, thermodynamic study verified the adsorption process was endothermic and spontaneous in nature. The maximum adsorption occurred at pH 5 ± 0.1, and the adsorbent could be used as a reusable adsorbent with convenient conditions.     

Removal of As(III) from Aqueous Solution Using Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles: Process Modeling and Optimization Using Statistical Design

In this study, Extran (biodegradable surfactant) was used for the preparation of Fe₃O₄ nanoparticles by microemulsion process to improve removal efficiency of As(III) from aqueous solution. Fe₃O₄ nanoparticles were characterized by XRD, FTIR, FESEM, TEM, HRTEM, and VSM instrumental techniques. The effect of different parameters such as adsorbent dose, initial As(III) concentration, and solution pH were studied by response surface methodology (RSM) based on Box-Behnken design (BBD). The optimized condition for adsorption of As(III) from aqueous solution was obtained as adsorbent dose of 0.70 mg/g, solution pH of 7.7, and initial As(III) concentration of 33.32 mg/L. In this optimum condition, about 90.5% of As(III) was removed from the aqueous solution. Isotherm studies have been done at optimal condition, and it was observed that the Langmuir isotherm models were fitted well with experimental data having a high correlation coefficient of 0.993. From the Langmuir isotherm data, the maximum adsorption capacity of Fe₃O₄ nanoparticles was found to be 7.18 mg/g at pH 7.7 in room temperature. This study revealed that Fe₃O₄ nanoparticles can be used as an efficient, eco-friendly, and effective material for the adsorptive removal of As(III) from aqueous system.     

Comparison of Cadmium Ion Adsorption on Various ACTIVATED CARBONS

Studies on the removal of cadmium(II) ions from aqueous solutions by adsorption on various activated carbons [commercial activated carbon (CAC) and chemically prepared activated carbons (CPACs) from raw materials such as straw, saw dust and datesnut] have been carried out with an aim to obtain information on treating effluents containing Cd(II) ions. Factors influencing the adsorption of Cd(II) ions from aqueous solution by ACs have been investigated by following a batch adsorption technique at 30± 1 ^°C. The percentage removal increased with decrease in initial concentration and particle size of CPACs and an increase in contact time, dose and initial pH of the solution. Adsorption process was inhibited by the added electrolytes. The adsorption data were fitted with the Langmuir, Dubinim–Radushkevich and Freundlich isotherms and first-order kinetic equations viz., first-order, Lagergren and Bhattacharya–Venkobachar equations and intra-particle diffusion model. The kinetics of adsorption is first order with intra-particle diffusion as one of the rate determining steps. Thermodynamic parameters were obtained from equilibrium constants measured at 30, 35 and 40 ^°C (Error = ± 1 ^°C). Results of the studies on adsorption of Cd²⁺ ions from simulated wastewater were compared with that of CAC and Tulsion CXO-9(H), a commercial ion exchange resin/cationic resin (CR). Straw carbon showed the maximum adsorption capacity towards Cd²⁺ ions and a high value of rate constant of adsorption. Straw carbon is an alternative low-cost adsorbent to CAC.     

Equilibrium, Kinetics and Mechanism of Removal of Methylene Blue from Aqueous Solution by Adsorption onto Pine Cone Biomass of Pinus radiata

The kinetics and mechanism of methylene blue adsorption onto raw pine cone biomass (Pinus radiata) was investigated under various physicochemical parameters. The extent of the methylene blue dye adsorption increased with increases in initial dye concentration, contact time and solution pH but decreases with the amount of adsorbent, salt concentration and temperature of the system. Overall the kinetic studies showed that the methylene blue adsorption process followed pseudo-second-order kinetics among various kinetic models tested. The different kinetic parameters including rate constant, half-adsorption time and diffusion coefficient are determined at different physicochemical conditions. Equilibrium data were best represented by Langmuir isotherm among Langmuir and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine cone biomass was 109.89 mg/g at 30°C. The value of separation factor, R _L, from Langmuir equation and Freundlich constant, n, both give an indication of favourable adsorption. Thermodynamic parameters such as standard Gibbs free energy (?G ⁰), standard enthalpy (?H ⁰), standard entropy (?S ⁰) and the activation energy (A) were calculated. A single-stage batch absorber design for the methylene blue adsorption onto pine cone biomass has been presented based on the Langmuir isotherm model equation.     

Copper Ions Adsorption from Aqueous Medium Using the Biosorbent Sugarcane Bagasse In Natura and Chemically Modified

This study evaluated the copper ion adsorption capacity of sugarcane bagasse in natura and chemically modified with citric acid and sodium hydroxide. Adsorption analyses in batch system were carried out in function of contact time with the adsorbent and adsorbate concentration. Flame atomic absorption spectrometry was used to determine the copper concentrations. Adsorption experimental data were fitted to Langmuir and Freundlich linear models, and the maximum adsorption capacity was estimated for copper ions in function of modifications. The chemical modifications were confirmed at 1,730 cm^?1 peak in infrared spectra, referring to the carboxylate groups. The required time for the adsorption to reach equilibrium was 24 h and the kinetics follows the behavior described by the pseudo-second order equation. Besides, a significant improvement of the copper adsorption has been observed after the bagasse treatment, where the maximum adsorption capacity was 31.53 mg g^?1 for copper using modified bagasse with nitric acid according to Langmuir isotherm linear model. The high uptake of copper ions from aqueous medium verified by chemically modified sugarcane bagasse makes this material an attractive alternative for effluent treatment and avoids environmental contamination.     

Kinetic and Removal Mechanisms of Ethylbenzene from Contaminated Solutions by Chitin and Chitosan

In this study, the efficiency of chitin and chitosan toward the removal of ethylbenzene from aqueous solutions was investigated. Batch adsorption experiments of ethylbenzene-contaminated waters (5?C200 mg/L) were carried out to evaluate the removal performance. Ethylbenzene uptake was determined from the changes in concentration, as the residual concentration was measured by gas chromatography with mass spectroscopy. The results indicated that the adsorption of ethylbenzene by chitin and chitosan were in agreement with the Langmuir isotherm, for two parameters model, and Redlich?CPeterson isotherm, for three parameters model. A maximum removal percentage of 65% of ethylbenzene can be achieved using chitosan as adsorbent material. The adsorption capacity of ethylbenzene followed the order chitosan?>?chitin. The pseudo-second order rate model described best the adsorption kinetics of ethylbenzene for the two selected adsorbents. The kinetic studies also revealed that the pore diffusion is not the only rate controlling step in the removal of ethylbenzene. Overall, the study demonstrated that chitosan is a potential adsorbent for the removal of ethylbenzene at concentrations as high as 200 mg/L.