Pseudo-second Order Kinetic Model Research Articles

Plantain peel adsorbent: Simple preparation, and adsorption at phosphate concentrations similar to those of water sources at risk of eutrophication

There are several investigations on the use of food waste to remove contaminants by adsorption. However, a simple route, without chemical activation reagents, is needed for the development of adsorbents. The aim of this study was to develop an adsorbent from plantain peel, using a simple procedure, and to evaluate its capacity to remove phosphate from aqueous solutions at phosphate concentrations similar to those of water sources at risk of eutrophication (0.30 mg/L). The simple pyrolysis method was used in an electric muffle, without chemical activation, using plantain peel as precursor. The variables evaluated were pyrolysis temperature and solution pH. The specific surface area BET, zero loading point of the developed treatments, was determined. Phosphate adsorption was studied in a batch experiment in the presence of calcium ions in solution. Phosphate adsorption was favorable at all three pyrolysis temperature levels (500, 600 and 700 °C) and two solution pH levels (pH 7 and 10). the pseudo-second order kinetic model was the best fit for the experimental data to describe the adsorption mechanism. The best fit to the experimental equilibrium data was obtained with the Langmuir isotherm model. It was found that a 1 g/L dose of the adsorbent was able to reduce 92% of phosphate in water, with a removal capacity 0.14 mg/g at pH 10 and pyrolysis temperature of 700 °C. This study lays the groundwork for future research on the use of this type of adsorbent in water treatment to facilitate access to clean water for rural populations.

Exploring use of titania–bentonite composite for adsorptive detoxification of crystal violet dye in eco-friendly way

In this work, we explored the adsorptive detoxification potential of titania–bentonite clay composite for removing a cationic dye (crystal violet) from aqueous medium. Fresh clay composite sample were prepared by impregnated method, followed by spectroscopic characterization by SEM, FTIR, and EDX. After that, in batch studies dye removal were examined. The results under optimum conditions showed that this composite material has a 96% elimination capacity. Maximum removal of crystal violet was 49.26 mg/g, following Pseudo-second order kinetic model occurred at pH 8, at 125 rpm and 25 ppm initial concentration at 45 °C. Kinetics of reactions and isotherm models were investigated. Adsorption data showing the presence of monolayer adsorption were fitted using the Langmuir isotherm model. Chemisorption was shown to prevail according to Temkin isotherm criteria. Pseudo-second-order kinetics was followed in this case. For removing dye from industrial effluents, this titania–bentonite composite serves as a nonbiodegradable, low-cost, reliable, and ecologically safe adsorbent.

Molecular-level investigation on removal mechanisms of aqueous hexavalent chromium by pine needle biochar

Pine needle biochar produced via oxygen-limited pyrolysis at 800 °C for 2 h was used for removing aqueous hexavalent chromium [Cr(VI)] from water. The optimality of the pseudo-second order kinetic model indicated the chemisorption dominated the removal process. Strong acid environment (pH = 2.0) was more conductive to Cr(VI) removal. The functional groups (C–O, O–C–O, C = O) on biochar contributed to Cr(VI) elimination from aqueous solution. The governing removal mechanisms involved electrostatic attraction, reduction, and complexation. Especially, confocal micro-X-ray fluorescence (μ-XRF) mapping indicated that Cr ions and functional groups were primarily distributed on the surface of biochar. This study firstly provided a deep interpretation of Cr speciation and spatial distribution on pine needle biochar, which provided important information on removal mechanisms of Cr(VI) by pine needle biochar.

Statistically optimised sequestration of mefenamic acid from polluted water by acacia gum phthalate/pectin hydrogel: A novel multifunctional adsorbent material synthesised via microwave-assisted process

Pharmaceuticals and personal care products (PPCPs) are an emerging class of perilous pollutants due to their potential inimicalimpacts on ecosystems necessitating their abatement.Herein, an environmentally-affable and multifunctional acacia gum phthalate/ pectin hydrogel (AGP/PEC) was innovatively synthesised by microwave-assisted free-radical polymerisation for subsequent mefenamic acid (MFA) decontamination from synthetic wastewater. The physicochemical characteristics of AGP/PEC was studied through FTIR, XRD, BET, TEM, SEM-EDX and XPS characterisation techniques showing the existence of –OH and –COOH functionalities, rough surface with good surface area (18.95 m2/g) and porosity that contributed to high MFA uptake (93.45%) via hydrogen-bonding, electrostatic, pore-filling, π−π, and n−π interactions. The independent and interactive influences of operative variables on the adsorption capacity of AGP/PEC was statistically evaluated via central composite design of response surface methodology. The most-effective MFA uptake was attained at optimal operating conditions: initial solution pH (5.9), dosage (0.4 g/L), and time (28.5 min). Langmuir isotherm with Qm = 103.43 mg MFA/g and pseudo-second order kinetic models best-correlated the corresponding data. The Qm increased with temperature specifying an endothermic process, which was authenticated by positive ΔH⁰ (= 7.75 kJ/mol). The parameter, bT = 0.16 kJ/mol and ED = 2.12 kJ/mol, calculated from Temkin and Dubinin−Radushkevich isotherm models, respectively specified physisorption. The better adsorptive competence in real water along with an excellent reusable potential (87.1%) up to fifth cycle designated AGP/PEC as a potent adsorbent for practical purposes. These findings accentuated that AGP/PEC could be gainfully implemented as green and advanced multifunctional adsorbent material for removing residual MFA from wastewater.

Synthesis of novel magnetic activated carbon for effective Cr(VI) removal via synergistic adsorption and chemical reduction

The removal of a toxic contaminant like Cr(VI) from the water via green adsorbents like biochar and activated carbon is an eco-friendly technique. In this paper, using commercial activated carbon as a raw material, magnetic ferric oxide/activated carbon (Fe3O4@AC) was prepared by the chemical co-precipitation method, and Cr(VI) adsorption in water was applied. The synthesized materials were characterized by advanced characterization techniques including XRD, BET, FT-IR, and XPS. The effects of initial Cr(VI) concentration, temperature, and adsorption time on the adsorption effect of Cr(VI) were evaluated. Results illustrated that the maximum Cr(VI) adsorption achieved by Fe3O4@AC was 45.3 mg/g, with a removal rate of 88.8% at the optimum pH of 2.0 and an adsorption time of 12 h. Under these conditions, Cr(VI) adsorption by Fe3O4@AC fits the pseudo-second-order kinetic model (PSO) and Langmuir isotherm model and is a spontaneous, endothermic, and irreversible process. The results of BET, XRD, FT-IR, and XPS characterization analysis of Cr(VI) before and after adsorption suggested that the adsorption mechanism of Fe3O4@AC is mainly based on chemisorption, supplemented by physical adsorption, accompanied by electrostatic attraction and complexation.

Adsorption treatment of fibre-cement industry effluent by activated gossweilerodendron caesalpinoideae stem waste: kinetic and thermodynamic studies

This investigation is on the treatment of a fibre-cement industry effluent (FCIE) using activated carbon (AC) adsorbent prepared by chemical activation (60% phosphoric acid) of Gossweilerodendron caesalpinoideae (GC) stem waste. The GCAC adsorbent was characterized by determination of the proximate and functional properties. The chemical groups, morphology and mineral phases of the GC stem waste and GCAC were studied by FTIR, SEM, and XRD methods, respectively. Kinetic and thermodynamic studies were carried out using total dissolved solids (TDS) as evaluating parameter. Effects of adsorbent dosage (5-40 g/L), contact time (0-60 min), and temperature (20-40 °C) on the effluent decontamination were investigated. Results from the characterized supernatant showed up to 97% removal of the contaminants using 40 g/L of GC adsorbent at effluent pH 7.4. The concentrations of TDS obtained by U-V spectrophotometric analysis were fitted to pseudo-first and pseudo-second order, Elovich and intraparticle kinetic models. The adsorption followed the pseudo-second order rate equation. Obtained free energy and enthalpy of adsorption values indicated non-spontaneous and endothermic adsorption. The study affirmed that the bioadsorbent, GCAC can be used for FCIE treatment.

Enhanced adsorptive removal of thiophenic sulfur compounds by nitrogen-doped surfactant modified mesoporous templated carbons

Adsorptive desulfurization is a greenway for sulfur removal from fossil fuels due to its ambient operating conditions and easy recyclable usage of spent adsorbent. This paper studied the effect of nitrogen doping in mesoporous templated carbon for the adsorptive removal of sulfur compounds from model fuel. The undoped and nitrogen-doped templated carbons were synthesized using alumina and surfactant-modified alumina as templates via the chemical vapor deposition method. Modification by nitrogen enhanced both the surface area and pore volume of templated carbon. The nitrogen-doped surfactant-modified alumina templated carbon, AS-N, showed the highest surface area of 1373 m2/g and pore volume of 1.15 cm3/g. The AS-N showed adsorptive removal of sulfur compounds (thiophene 92.15%, benzothiophene 82.90% and dibenzothiophene 82.38%) at 70 °C. This may be attributed to the highest surface area and presence of nitrogen (8.2 wt%), which improved the adsorption capability by increasing the π-π interaction between the sulfur compounds and carbon matrix. Further increase in nitrogen content in templated carbon enhanced the π-π interaction resulting in higher removal capacity. The AS-N-U adsorbent prepared in the presence of urea had 15.2 wt% nitrogen and showed enhanced removal of thiophene 97.7%, benzothiophene 92.4%, and dibenzothiophene 89.3%. The adsorptive desulfurization over AS-N-U for all sulfur compounds were best fitted to pseudo-second order kinetic model and Langmuir adsorption isotherm model. The templated carbon was regenerated successfully using the thermal regeneration process. After five adsorption-regeneration cycles, the removal efficiency was lowered only by 4–10% for all sulfur compounds.

Eco-Friendly Semi-Interpenetrating Polymer Network Hydrogels of Sodium Carboxymethyl Cellulose/Gelatin for Methylene Blue Removal.

The present work describes the potential application of environmentally friendly sodium carboxymethylcellulose/gelatin (CMC/Gel) semi-interpenetrating hydrogels prepared by citric acid as a nontoxic cross-linking agent to adsorb dyes. The prepared hydrogels were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA/DTG), and swelling study. The adsorption performance of CMC/Gel2 (C/G2) hydrogel on methylene blue (MB) was investigated. The results showed the better adsorption conditions: adsorption time of 300 min, initial MB concentration of 500 mg/L, adsorbent dosage of 1.2 g/L, solution pH of 7, and temperature of 30 °C. The adsorption kinetics fit the pseudo-second order kinetics model, and the adsorption isotherm fit the Langmuir isotherm model. The maximum adsorption capacity reached 943.40 mg/g. The adsorption process is a spontaneous exothermic process. After three adsorption-desorption cycles, the removal rate of MB by hydrogel still reached 85%, with good reusability. Consequently, the hydrogel can be used as an environmentally friendly, stable, and efficient adsorbent for dyes in wastewater treatment.

Highly efficient removal of ionic dyes in aqueous solutions using magnetic 3D reduced graphene oxide aerogel supported nano zero-valent iron

This study aims to develop three-dimension reduced graphene oxide aerogel supported nano zero-valent iron (rGOA-nZVI) by hydrothermal and liquid phase reduction approach and applies it to the removal of two typical dyes, methylene blue (MB) and methyl orange (MO) from aqueous solutions. The obtained magnetic rGOA-nZVI composites were characterized by scanning electron microscopy (SEM), atomic force microscopy, Brunauer-Emmett-Teller, X-ray diffraction and Fourier transform infrared spectroscopy, and its removal efficiencies for MB and MO from aqueous solutions were evaluated. The removal processes of MB and MO could be completed within 30 min, which were well described by the pseudo-second order kinetic model. The rGOA-nZVI nanocomposites exhibited remarkable performance for the removal of MB (the maximum adsorption amount, <i>q</i><sub>max</sub> = 3918 mg/g) and MO (<i>q</i><sub>max</sub> = 667 mg/g) in a wide pH range (pH 1.0-10.0). Furthermore, rGOA-nZVI is stable and recyclable with high dye removal efficiencies (> 90%) after five cycles. The removal mechanisms were demonstrated with SEM and XRD analyses before and after MB and MO removal. This study showed that rGOA acts as an excellent carrier for nZVI, and the rGOA-nZVI nanocomposites are efficient materials for the advanced treatment of dye wastewater over a wide pH range.

Methyl Orange Absorption Using Chitosan from Shrimp Skin as an Adsorbent

In the coloring process, the textile industry generally uses synthetic (artificial) dyes, methyl orange (MO). In this study, the adsorption of methyl orange (MO) dye with chitosan was investigated in a series of batch laboratory studies. The adsorption equilibrium study used a MO solution with a concentration of 10 to 50 mg/L with an adsorbent weight of 3 g put into an Erlenmeyer and shaken until the adsorption reached an equilibrium condition. Meanwhile, the adsorption kinetics used a MO solution with an initial concentration of 10 and 20 mg/L with a volume of 100 mL with an adsorbent weight of 3 g and the solution was adjusted to pH 2. Effective operating parameters such as pH, initial concentration of dye (C0) and contact time at adsorption has been investigated. The results showed that the adsorption capacity of methyl orange (MO) dye from chitosan increased with an increasing acid content, and it was found that a solution of pH 2 was the optimal pH value for MO adsorption. The adsorption parameters for the Langmuir and Freundlich isotherms were determined by nonlinear regression and the equilibrium data were best explained by the Langmuir isotherm model, this was indicated by the high value of the correlation coefficient (R2), which was 0.9595. The maximum adsorption capacity was 0.1297 mg/g. Adsorption kinetics can be successfully applied to pseudo second-order kinetic models. The pseudo second-order model results show that the adsorption process is controlled by chemical sorption (chemisorption).

Adsorption of naproxen pharmaceutical micropollutant from aqueous solutions on superior activated carbon synthesized from sheep manure: Kinetics, thermodynamics, and mechanism

The performance of a new method for synthesizing super activated carbon derived from sheep manure in the adsorption of naproxen micropollutant from an aqueous solution was investigated in this research. Chemical activation employing ZnCl2 as an activator was used to produce activated carbon. The effects of several parameters such as the rate of impregnation, temperature of activation, and duration of activation on the synthesis of activated carbon were examined. FTIR, SEM, and BET measurements were used to characterize the produced activated carbons. The surface area of the manufactured activated carbon was determined to be 2170 m2 g−1. On naproxen adsorption, the effects of solution initial pH, solution initial concentration, and amount of activated carbon were examined. When the pH of the solution was 4, the adsorption capacity was found to be greater. The pseudo-second order kinetic model was found to fit the adsorption kinetics. The data on adsorption equilibrium was found to be consistent with the Langmuir and Freundlich isotherm. According to Langmuir isotherm adsorbent capacity qm was found 7790 mg g−1. ΔG0, ΔS0, and ΔH0, among other thermodynamic parameters, were estimated. The thermodynamics of the naproxen–Activated Carbon combination show that the reaction is endothermic and favourable. This high surface area and adsorption capacity showed that the material is innovatively important.

Triphasic CoFe2O4/ ZnFe2O4 / CuFe2O4 nanocomposite for water treatment applications

In the recent years, ferrites have been extending their application niche from the traditional field of soft magnetics to various other fields, including catalysis, gas sensors, energy, biomedicine, and water decontamination. Most of these applications are geared toward single-phase ferrites and their mixtures are rarely investigated. Here, we report on the first study of a triphasic spinel ferrite nanocomposite containing CoFe2O4, ZnFe2O4 and CuFe2O4 and synthesized using citrate auto-combustion. Detailed characterization of the composite in comparison with its three constitutive ferrites is provided. Interestingly, many of the physical properties of the triphasic nanocomposite are more conducive to adsorption of heavy metals than those of any of the three individual ferrites. These properties include experimental density, surface area and roughness, and microstrain, which were all highest in the nanocomposite. For example, the triphasic nanocomposite displayed a twice higher surface roughness and three times higher surface area than those of CuFe2O4. Further, due to heterogeneous structuring of grain boundaries, the band gap of the nanocomposite was at 2.21 eV lower than that of any individual ferrites comprising it (2.31 – 2.62 eV). Consequently, at 6 × 1010 S-1, the maximum of the optical conductivity versus photon energy dependence was higher and the dielectric constant was lower for the nanocomposite than for any of its constitutive ferrites. The suitability of the nanocomposite to act as an adsorbent of toxic heavy metals was tested on the lead ion. The adsorption of lead increased with pH due to the effects on terminal group configuration, dispersion stability and metal ion speciation. The sorption also increased with the contact time, reaching saturation at 89% of the removal efficiency after 50 min. Adsorption isotherm fitting demonstrated that the ions adsorbed as monolayers on the surface of the nanocomposite. The adsorption process also followed the pseudo-second order kinetic model, with chemisorption as the dominant form of surface binding. The study confirms the potential of the triphasic ferrite nanocomposite to serve as an adsorbent material, given the promising removal efficiencies exhibited under the ambient conditions. This opens the door to a wide range of applications, not restricted to wastewater treatments alone, but also extending to the fields of antimicrobials, dye removal, and photocatalysis.

Sorption Characteristics and Site Energy Distribution Theory of Typical Estrogens on Microplastics

Microplastics (MPs) and estrogens are high-profile emerging contaminants at present, and MPs might become the carrier of estrogens in the environment and induce combined pollution. To study the adsorption behavior of polyethylene (PE) microplastics to typical estrogens, the adsorption isothermal properties of the six estrogens[estrone (E1), 17α-estradiol (17α-E2), 17β-estradiol (17β-E2), estriol (E3), diethylstilbestrol (DES), and ethinylestradiol (17α-EE2)] in single-solute and mixed-solute systems were studied through batch equilibrium adsorption experiments, in which the PE microplastics before and after adsorption were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Then, the site energy distribution theory of the adsorption of six estrogens on PE microplastics was further analyzed based on the Freundlich model. The results showed that the adsorption process of selected estrogens with two concentrations (100 μg·L-1 and 1000 μg·L-1) on PE were more consistent with the pseudo-second order kinetic model. The increase in initial concentration reduced the equilibrium time of adsorption and increased the adsorbing capacity of estrogens on PE. In the single system (one estrogen) or mixed system (six estrogens) with different concentrations (10 μg·L-1-2000 μg·L-1), the Freundlich model showed the best fitting effect for the adsorption isotherm data (R2>0.94). The results of isothermal adsorption experiments and XPS and FTIR spectra showed that the adsorption of estrogens on PE in the two systems was heterogeneous adsorption, and hydrophobic distribution and van der Waals forces were the principal factors in the process of adsorption. The occurrence of C-O-C (in only the DES and 17α-EE2 systems) and O-C[FY=,1]O (in only the 17α-EE2 system) indicated that the adsorption of synthetic estrogens on PE was affected slightly by chemical bonding function, but no obvious effects were observed for natural estrogens. The results of site energy distribution analysis showed that, compared with the single system, the adsorption site energy of each estrogen shifted to the high-energy region in its entirety in the mixed system, and the site energy increased by 2.15%-40.98%. The energy change in DES was the most significant among all of the estrogens, indicating its competitive advantage in the mixed system. The above results of this study can provide some reference for the study of adsorption behavior, mechanism of action, and environmental risks under the coexisting condition of organic pollutants and MPs.

Interactions between titanium dioxide nanoparticles and polyethylene microplastics: Adsorption kinetics, photocatalytic properties, and ecotoxicity

The present study investigated the adsorption mechanism of titanium dioxide nanoparticles (nTiO2) on polyethylene microplastics (MPs) and the resulting photocatalytic properties. This effort was supported by ecotoxicological assessments of MPs with adsorbed nTiO2 on the immobility and behaviour of Daphnia magna in presence and absence of UV irradiation. The results showed that nTiO2 were rapidly adsorbed on the surface of MPs (72% of nTiO2 in 9 h). The experimental data fit well with the pseudo-second order kinetic model. Both suspended nTiO2 and nTiO2 immobilized on MPs exhibited comparable photocatalytic properties, with the latter showing a lower effect on Daphnia mobility. A likely explanation is that the suspended nTiO2 acted as a homogeneous catalyst under UV irradiation and generated hydroxyl radicals throughout the test vessel, whereas the nTiO2 adsorbed on MPs acted as a heterogeneous catalyst and generated hydroxyl radicals only locally and thus near the air-water interface. Consequently, Daphnia, which were hiding at the bottom of the test vessel, actively avoided exposure to hydroxyl radicals. These results suggest that the presence of MPs can modulate the phototoxicity of nTiO2 – at least the location at which it is active – under the studied conditions.

Removal of Cesium and Strontium Ions from Aqueous Solutions by Thermally Treated Natural Zeolite.

The radionuclides of cesium (Cs) and strontium (Sr) are dangerous products of nuclear fission that can be accidentally released into wastewater. In the present work, the capacity of thermally treated natural zeolite (NZ) from Macicasu (Romania) to remove Cs+ and Sr2+ ions from aqueous solutions in batch mode was investigated by contacting different zeolite quantities (0.5, 1, and 2 g) of 0.5-1.25 mm (NZ1) and 0.1-0.5 mm (NZ2) particle size fractions with 50 mL working solutions of Cs+ and Sr2+ (10, 50, and 100 mg L-1 initial concentrations) for 180 min. The concentration of Cs in the aqueous solutions was determined by inductively coupled plasma mass spectrometry (ICP-MS), whereas the Sr concentration was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The removal efficiency of Cs+ varied between 62.8 and 99.3%, whereas Sr2+ ranged between 51.3 and 94.5%, depending on the initial concentrations, the contact time, the amount, and particle size of the adsorbent material. The sorption of Cs+ and Sr2+ was analyzed using the nonlinear form of Langmuir and Freundlich isotherm models and pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models. The results indicated that the sorption kinetics of Cs+ and Sr2+ on thermally treated natural zeolite was described by the PSO kinetic model. Chemisorption dominates the retention of both Cs+ and Sr2+ by strong coordinate bonds with an aluminosilicate zeolite skeleton.

Effective adsorption of Orange G dye using chitosan cross-linked by glutaraldehyde and reinforced with quartz sand

In this study, quartz sand (QS) incorporated into a crosslinked chitosan-glutaraldehyde matrix (QS@Ch-Glu) was prepared and employed as an efficient adsorbent for the elimination of Orange G (OG) dye from water. The sorption process is adequately described by the pseudo-second order kinetic model and the Langmuir isotherm model with maximum adsorption capacities of 172.65, 188.18, and 206.65mg/g at 25, 35, and 45°C, respectively. A statistical physics model was adopted to elucidate the adsorption mechanism of OG on QS@Ch-Glu. Calculated thermodynamic factors revealed that the adsorption of OG is endothermic, spontaneous, and occurs via physical interactions. Overall, the proposed adsorption mechanism was based on electrostatic attractions, n-π stacking interaction, hydrogen bonding interaction, and Yoshida hydrogen bonding. The adsorption rate of QS@Ch-Glu was still above 95% even after 6 cycles of adsorption and desorption. Furthermore, QS@Ch-Glu demonstrated high efficiency in real water samples. All these findings demonstrate that QS@Ch-Glu is qualified for practical applications.

Contribution of zeolite to remove malachite green in aqueous solution by adsorption processes: Kinetics, isotherms and thermodynamic studies

The textile industry produces huge amounts of wastewaters containing synthetic dyes. In the textile industry, acid, basic, reactive, dispersed chemicals are widely used for dyeing. The aim of this study was to evaluate the adsorption of malachite green onto zeolite from aqueous solutions was realized in batch system. The adsorbent was characterized by the Fourier transform infrared spectroscopy, X-ray analysis, and zero point charge (pHzpc = 10.42). However, some examined factors were found to have significant impacts on the adsorption capacity of zeolite such as the initial malachite green concentration (Co), solution pH, adsorbent dose, agitation speed, particles size, and temperature. The best capacity was found at pH 8 with an adsorbent dose 0.2 g/l, an agitation speed 200 rpm and a contact time of 40 min. The kinetic adsorptions were found to follow rather a pseudo-second order kinetic model with a determination coefficient (R2) of 0.999. The equilibrium adsorption data for the malachite green adsorption onto the zeolite were analyzed by the Langmuir, Freundlich, Elovich, and Temkin models. The results indicate that the Langmuir model provides the best correlation with a capacity qmax of 83.33 mg/g at 25°C. The adsorption isotherms at different temperatures have been used for the determination of thermodynamic parameters, namely the free energy (ΔG°); enthalpy (ΔH°) and entropy (ΔS°) to predict the nature of adsorption. The positive values of ΔG° and ΔH° indicate that the overall adsorption is not spontaneous and endothermic with a physisorption process. The adsorbent elaborated from the zeolite was found to be efficient and suitable for the elimination of reactive dyes from aqueous solutions, due to its availability of adsorption sites, low cost preparation, and good uptake capacity.

Biosorption of Hexavalent Chromium (Cr(VI)) from contaminated water using charred tea waste

The goal of this study is to develop charred tea waste (CTW) via chemical process for the removal of Cr(VI) from contaminated water. Batch adsorption experiments were conducted as a function of pH, initial concentration, contact time and adsorbent dosage. Characterization of the adsorbent was analyzed by FT-IR and XRD. Maximum adsorption capacity (qm) of the CTW was found to be 85.32 mg/g at optimum pH 2 in 120 minutes. The adsorption on CTW was well fitted to the Langmuir isotherm and the kinetic data is consistent with the pseudo-second order kinetic model. The findings suggest that CTW could be an efficient and promising adsorbent for the removing Cr(VI) from aqueous solution.

Multilayer adsorption of lead (Pb) and fulvic acid by Chlorella pyrenoidosa: Mechanism and impact of environmental factors

When the multilayer adsorption of lead (Pb) and fulvic acid (FA) occurs on algal surface, the adsorption capacity of Pb on the algae will increase dramatically, thus increasing the environmental risk of Pb. However, the corresponding mechanism and the influence of environmental factors on the multilayer adsorption remain unclear. Here, microscopic observation methods and batch adsorption experiments were exactly designed to investigate the adsorption behavior of multilayer adsorption of Pb and FA on algal surface. The results of Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed that carboxyl groups were the major functional groups responsible for the binding of Pb ions in multilayer adsorption, and its number was more than that in monolayer adsorption. The solution pH, with an optimal pH of 7, was a critical factor influencing the occurrence of multilayer adsorption because it influences the protonation of the involved functional groups and determines the concentration of Pb2+ and Pb-FA in the solution. Increasing the temperature was beneficial for multilayer adsorption, with ΔH for Pb and FA varied from +17.12 to +47.68 kJ/mol and +16.19 to +57.74 kJ/mol, respectively. The multilayer adsorption of Pb and FA onto algal surface also followed the pseudo-second order kinetic model, but was extremely slower than the monolayer adsorption of Pb and FA by 30 times and 15 orders of magnitude, respectively. Therefore, the adsorption of Pb and FA in the ternary system had a different adsorption behavior than that in the binary system, which verified the presence of multilayer adsorption of Pb and FA and further support the multilayer adsorption mechanism. This work is important to provide data support for water ecological risk prevention and control of heavy metals.

Bio-Based Polyurethane Foams for the Removal of Petroleum-Derived Pollutants: Sorption in Batch and in Continuous-Flow.

In this paper, we evaluated the potential of two synthesized bio-based polyurethane foams, PU1 and PU2, for the removal of diesel and gasoline from water mixtures. We started the investigation with the experiment in batch. The total sorption capacity S (g/g) for the diesel/water system was slightly higher with respect to gasoline/water, with a value of 62 g/g for PU1 and 65 g/g for PU2. We found that the sorption follows a pseudo second-order kinetic model for both the materials. The experimental data showed that the best isotherm models were obtained with Langmuir and Redlich-Peterson models. In addition, to provide an idea of the process scalability for future industrial applications, we tested the sorption capacity of the foams using a continuous-flow of the same oil/water mixtures and we obtained performances even better with respect to the batch test. The regeneration can be performed up to 50 times by centrifuge, without losing efficacy.