Search

The adsorption property of the costless green cellulose acetate (CA) was boosted by the dual modifications: inner modification by incorporating carboxylated graphene oxide (COOH-GO) into the CA spheres and outer modification by the surface modification of the COOH-GO@CA spheres by iminodiacetic acid (IDA) for removing Pb(II). The adsorption experiments of the Pb(II) proceeded in a batch mode to evaluate the adsorption property of the COOH-GO@CA@IDA spheres. The maximal Pb(II) adsorption capacity attained 613.30 mg/g within 90 min at pH = 5. The removal of Pb(II) reached its equilibrium within 20 min, and the removal % was almost 100% after 30 min at the low Pb(II) concentration. The Pb(II) adsorption mechanism was proposed according to the kinetics and isotherms studies; in addition, the zeta potential (ZP) measurements and X-ray Photoelectron Spectroscopy (XPS) analysis defined the adsorption pathways. By comparing the XPS spectra of the authentic and used COOH-GO@CA@IDA, it was deduced that the contributed chemical adsorption pathways are Lewis acid–base, precipitation, and complexation. The zeta potential (ZP) measurements demonstrated the electrostatic interaction participation in adsorbing the cationic Pb(II) species onto the negatively charged spheres (ZP = 14.2 mV at pH = 5). The unique channel-like pores of the COOH-GO@CA@IDA spheres suggested the pore-filling mechanism of Pb(II). The promising adsorption results and the superb recyclability character of COOH-GO@CA@IDA enable it to extend of the bench scale to the industrial scale. [ABSTRACT FROM AUTHOR]

In this study, a comparison was conducted involving novel chitosan/polyvinyl alcohol-based membranes comprising carbon nanotubes and molybdenum trioxide nanoparticles. This comparison's primary focus was to assess synthesized membranes' effectiveness in removing methyl red from aqueous solutions. The Fourier transform infrared spectroscopy and scanning electron microscopy confirmed the presence of specific functional groups and homogeneous dispersion of carbon nanotubes and molybdenum trioxide nanoparticles within the membranes, respectively. The membranes underwent additional characterization using various swelling parameters to assess mechanical strength and cross-linking. These parameters included swelling over time in water, swelling in electrolyte solutions, and different pH solutions and gel fraction analysis. Furthermore, the diffusion of water adhered Fickian diffusion principle. Various adsorption parameters were employed, including batch studies, isotherm studies at different pH levels, and temperature studies. The results of the batch study highlighted that chitosan/polyvinyl alcohol/carbon nanotubes membrane exhibited the highest adsorption, reaching approximately 9.7 mM/g (98%) and achieving equilibrium within 60 min. The maximum adsorption of methyl red was observed at pH 7 and decreased with increasing temperature. Moreover, the experimental data were simulated using kinetic models (pseudo-first-order, pseudo-second-order, Elovich model, and diffusion model) and isothermal models (Freundlich, Langmuir, and Langmuir Freundlich). Data indicated that pseudo-first order was the best-fitted model, which confirms physisorption. Among the isothermal models, Langmuir exhibited the most suitable fit, confirming that single-layer adsorption had taken place on the adsorbent surface. Thermodynamic parameters were studied, ensuring the adsorption process was exothermic and spontaneous. [ABSTRACT FROM AUTHOR]

A laboratory study was conducted to understand the kinetics and mechanism of adsorption of micronutrients and S onto Lantana sp., Pinus sp. and wheat straw biochars pyrolyzed at 300 °C and 450 °C. Adsorption kinetics of these nutrients onto phyto-biochars conformed well to pseudo-first-order kinetics and intra-particle diffusion model. Boyd's plots revealed the involvement of other adsorption mechanisms besides intra-particle diffusion. Simple correlation analysis revealed that higher contents of N and humin-like C fraction but lower content of alcoholic-OH groups in phyto-biochars increased the equilibrium adsorption coefficient (qe) and intra-particle diffusion rate coefficient (kid) of Fe while higher contents of total acidity and phenolic-OH groups decreased qe and kid of Zn, Cu and Mn. Higher S content in phyto-biochars increased the initial adsorption (c) for Zn and Mn adsorption. Higher cation exchange capacity of phyto-biochars increased qe and kid of B which indicated the cation bridging of B onto phyto-biochars. A significant positive correlation between the pseudo-first-order rate constant (k01) of B and the contents of H, total acidity and phenolic-OH group but a negative correlation with pH, P and water-soluble C content in biochars showed the involvement of ligand exchange mechanism for B adsorption. Higher contents of total acidity and phenolic-OH groups in phyto-biochars increased c for S adsorption. Thus, the adsorption kinetics of micronutrients and S onto phyto-biochars followed the pseudo-first-order kinetics and intra-particle diffusion process and the properties of phyto-biochars have an important bearing on the progress of the adsorption reaction of these nutrients. [ABSTRACT FROM AUTHOR]

Two approximate analytical expressions based on third degree polynomial and Akbari–Ganji's method (AGM) were derived for the reaction/diffusion controlled kinetics of an immobilized enzyme ( IE ) systems. The approximation methods predict substrate concentration profile and effectiveness factor (η ) in a porous spherical particle. The reaction is assumed to follow reverse Michaelis–Menten ( rMM ) kinetics. The approximate methods predictions were comparable to that of numerical solution (using the Matlab finite difference function, b v p 4 c ) at wide range of ϕ 2 and y o especially at low ϕ 2 and high y o (polynomial equation) and low ϕ 2 and low y o (AGM equation). Although the approximate solution was derived for rMM kinetics, the results can be used to describe other important enzymatic reaction kinetics such as simple Michaelis–Menten ( M M) kinetics and MM with competitive product inhibition kinetics. A necessary design equation should be satisfied when using polynomial or AGM approximation for different enzyme kinetic equations. In this work, two examples of enzymatic reactions of industrial interest were studied, namely glucose-fructose isomerization follows rMM kinetics and hydrolysis of lactose follows Michaelis–Menten ( MM ) equation with competitive product (galactose) inhibition. Predictions of the developed third degree polynomial and AGM approximation equations agree with that of numerical solution, the percentage relative error for the effectiveness factor was less than 11 in comparison with the numerical solution. Good agreement between approximate and numerical estimations demonstrates the validity of these approximation methods. [ABSTRACT FROM AUTHOR]

NaP zeolite crystals were synthesized and used as templating support species for the purpose of hosting and the confinement of silver nanoparticles. This was being adapted primarily by introducing trace amounts of alkyl dimethyl hydroxyethyl ammonium chloride (ADHA) ranging from 50 to 200 ppm into the zeolite (Ag/ADH-NaP). For comparison purposes, ADHA/NaP and Ag/NaP were also prepared under the same conditions. These solids have been examined by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV-Vis spectroscopy as well as surface texture measurements. By increasing the concentration of ADHA and under the effect of UV radiation, the XRD analysis of Ag/ADHA-NaP has shown increase in unit cell parameters of the zeolite along with new peaks attributed to silver nanoparticles (AgNPs) were observed at d values of 2.370 and 2.047 Å. This was confirmed by XPS peaks corresponding to Ag 3d at 368.7 and 374.7 eV. Upon addition of aqueous Cr(VI) to the Ag/ADHA-NaP sample, adsorbed species on the silver surface such as CrO and Cr(OH) produced Raman scattering at 853 and 664 cm, respectively. The latter sample was able to adsorb the Cr(VI) completely, but unlike the other samples, at an initial concentration of 20 ppm. The high effective surface area of AgNPs shows enhanced adsorption and photreduction of Cr(VI) to Cr(III), in compatible with the evaluation of optical band gaps. The adsorption process of Cr(VI) was thought to result from a surface uptake and intra-particle diffusion which operate simultaneously through the interaction between Cr(VI)ions and Ag/ADHA-NaP. [ABSTRACT FROM AUTHOR]

In the present research work Saw palmetto spent (SPS) was used to remove Methylene blue (MB) from aqueous solution economically. SEM and FTIR Studies were made to understand the Morphological properties of the adsorbent. Various parameters of adsorption such as, initial dye concentration, contact time, pH and temperature were studied. Langmuir, Freundlich and Temkin isotherm models were used to explain the adsorption behaviour. Pseudo-first order, pseudo-second order kinetic models and Intra-particle diffusion model were used to study adsorption kinetics. The maximum adsorption capacity value ( q = 90.9 mg g) for Langmuir isotherm was near to the experimental value ( q = 71.00 mg g). Thermodynamics of adsorption was studied and the values obtained indicate that the process is endothermic and spontaneous. It is confirmed that, SPS is an efficient adsorbent for removal of MB from aqueous solution. [ABSTRACT FROM AUTHOR]

The Vigna Subterranean (L.) Verdc hull's (VSVH) potential to remove Cr(VI) ions from aqueous solutions was investigated. The biosorbent was characterised by FTIR, SEM-EDX and XRF before and after exposure to Cr(VI). The surface comprised of phenolic, carboxylate, sulphonate, carboxyl, ammines, silica, silanol, phosphite esters, alkyl and hydroxyl functional groups responsible for Cr(VI) removal. Batch experiments were carried out in erlenmeyer flasks to optimize pH, contact time, biosorbent dosage and initial concentration of Cr(VI) ions. Reutilization of biosorbent was investigated using predetermined and optimized 0.14 M H2SO4. The initial and residual total chromium concentrations were estimated by FAAS. The optimum pH, contact time and biosorbent dosage were found to be 2, 180 minutes and 3 g/L respectively. The data generated from the effect of contact time and initial Cr(VI) concentration was subjected to kinetics and isotherm modelling respectively. The kinetic data fitted the pseudo first order model (R2 = 0.9334) and the sorption mechanism was diffusion controlled with both film and intra particle diffusion involved in the rate limiting step. The isotherm study confirmed favourable monolayer sorption best described by Langmuir model (R2 = 0.9986) with a very high monolayer sorption capacity of 232.5581 ± 0.9 mg/g. The Temkin model confirmed the endothermicity and weak ion-exchange nature of the Cr(VI)-biosorbent interactions that are important for biosorbent reuse. The biosorbent was recycled three times without significant loss of sorptiondesorption capability. VSVH powder provides a renewable and reusable alternative for simple and effective Cr(VI) removal from wastewaters worth exploring for commercial-industrial application. [ABSTRACT FROM AUTHOR]

The adsorption of erbium (Er) ions on activated charcoal (AC) is investigated at temperatures 10-40 °C from aqueous solutions to understand the kinetics behavior. The intra-particle diffusion, the pseudo-first order kinetic and pseudo-second order kinetic models were used to describe the kinetic data. Results shows that the adsorption of Er ions on AC occurs in two stages and the surface adsorption and diffusion phenomena are operative in the adsorption process. The result also reveals that intra-particle diffusion is not only the main rate determining step through out the adsorption process, but the boundary layer diffusion also play significant role in rate determination. Values of the intra-particle diffusion rate constant and the extent of the boundary layer diffusion were calculated. A comparison of the kinetics models on the overall adsorption rate indicates that the Er/AC system is best described by the pseudo-second order kinetic model than the pseudo-first order model, and the overall rate of the Er ions adsorption on AC appears to be controlled by more than one step, i.e., external mass transfer and diffusion mechanism. [ABSTRACT FROM AUTHOR]

Heterogeneous catalysis is of paramount importance in many areas of gas conversion and processing in chemical engineering industries. In porous pellets, the catalytic reactions may be affected by diffusional limitations such that the global rate can be different from the intrinsic reaction rate. In the literature, a number of multicomponent diffusion flux closures have been applied to characterize the diffusion process within different units in chemical process plants. The main purpose of this paper is to outline the derivation of the different diffusion flux models: the rigorous Maxwell-Stefan and dusty gas models, and the simpler Wilke and Wilke-Bosanquet models. Usually the diffusion fluxes are derived and presented with respect to the molar average velocity definition. In this study, also the diffusion flux closures with respect to the mass average velocity definition is outlined. Thus, if the temperature equation and the momentum equation are used in the pellet model, a consistently closed set of pellet equations is obtained on mass basis holding only the mass average velocity. On the other hand, for the closed set of pellet equations on molar basis, the component balances hold the molar averaged velocity whereas the temperature and momentum equations hold the mass average velocity due to the physical laws applied deriving these fundamental balances. Nevertheless, the Maxwell-Stefan and dusty gas models are manipulated and put on the convenient Fickian form. The second purpose of this article is the evaluation of the diffusion flux closures derived. For this purpose, a transient model is developed to describe the evolution of the species composition, pressure, velocity, temperature, total concentration, and fluxes within a spherical pellet. The catalyst problem has been simulated for the methanol dehydration process producing dimethyl ether (DME), with computed efficiency factor values in the range 0.06-0.6 for pellet pore diameters of 0.1-100 nm. Identical results are expected for the mole and mass based pellet equations. However, deviations are obtained in the component fractions comparing the mass and mole based pellet model formulations where the mass fluxes were described according to the Wilke and Wilke-Bosanquet models. On the other hand, the rigorous Maxwell-Stefan and dusty gas models gave identical results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Among various environmental pollutants, dyes have been reported to contaminate a large quantity of surface water. Rhodamine B, a widely applicable basic dye, is known for its hazardous impact on environment. The present study proposes the application of readily available waste banana peels for the remediation of water contaminated with Rhodamine B. The potential of prepared material to decontaminate Rhodamine B was examined as the function of various parameters. Variation in adsorption time, dose of adsorbent, pH value, and initial concentration has been observed under the influence of diverse condition. Quantitative adsorption was observed at a contact time of 60 min with an adsorbent dose of 12 mg. An increase in the initial dye concentration resulted in the enhancement of adsorption capacity of adsorbent. The value of enthalpy change was observed to be − 8.95 kJ mol−1. The negative value indicates the exothermic removal of Rhodamine B from water. Various models were applied to explain thermodynamics and kinetics of the process. Adsorption kinetics was better explained with pseudo-second-order model, whereas adsorption mechanism by intra-particle diffusion model reveals that pore diffusion was not only the rate-controlling step. [ABSTRACT FROM AUTHOR]