BENTONITE/CHITOSAN BIOCOMPOSITE AS AN ADSORBENT FOR HEXAVALENT CHROMIUM FROM AQUEOUS SOLUTIONS

The present work focuses on the study of the application of abundant and less expensive materials such as chitosan and bentonite/chitosan biocomposite in the removal of hexavalent chromium. Spectroscopic analysis like techniques FTIR, XRD and BET have been used to characterize the adsorbents. The data indicate that the adsorption of chromium proceeds kinetically according to a pseudo-second order model on both samples and the apparent activation energy (Ea) have been measured to be 22.9 kJ.mol−1 and 84.4 kJ.mol−1 for chitosan and 5%Bt/CS, respectively. The adsorption isotherm experiments show that the adsorption capacity depends on the studied chromium adsorption temperature. It has been found that the data could be well described by the Langmuir as well as the Freundlich models. Thermodynamic parameters (i.e., change in the free energy (DG°), the enthalpy (DH°), and the entropy (DS°) have been also, evaluated

Study of the Paranitrophenol Adsorption on the Commercial Bentonite

This work focuses on the study of the behavior of commercial yellow bentonite (BTJ) vis-a-vis paranitrophenol (PNP). Before beginning the study of adsorption, we realized the physiquo-chemical characterization of clay by FTIR, BET and XRD technical. The surface area of the bentonite is calculated by BET 35 m2/g. The adsorption of para-nitrophenol is carried out at room temperature and at a controlled pH. The kinetic study showed that the equilibrium time is 5h. The kinetic model was a pseudo second order. Adsorption isotherm was the Langmuir model. The adsorption capacity was about 0.37 mg / g. Keywords: Yelow bentonite, paranitorphénol, adsorption, optimisation

Hydrogenation d'especes carbonees, adsorbees sur un catalyseur au fer: experimentation et modelisation cinetique

SIGLEINIST T 74831 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Reac Kinet Mech Cat

Herein we report the performance of cheaper, more efficient and eco-friendlier chitin (CN) and chitosan (CS) biopolymers supported Cu nanoparticles (Cu NPs) catalysts (1.5 wt% Cu/CN) and (4.5 wt% Cu/CS) in the reaction model of para-nitrophenol (p-NP) reduction to para-aminophenol (p-AP) by NaBH4. The catalysts were synthetized with impregnation method and CN was extracted from local shrimp shells wastes, while CS was obtained by the deacetylation of CN. It was found that the activity of 1.5 wt% Cu/CN, with a lower Cu loading, is better than that of 4.5 wt% Cu/CS, which achieved 100% p-NP conversion to p-AP in short reaction times at all studied reaction temperatures. The activity of each catalyst was found to depend on the interaction modes of Cu NPs with the functional groups of CN and CS, which affects the textural parameters of the catalysts and the dispersion of Cu NPs, as revealed by various characterization techniques used. Kinetic of p-NP reduction was found to follows the pseudo-first order with respect to p-NP concentration. The apparent rate constants at T = 25 °C were calculated to be kapp = 0.854 min−1 and 0.350 min−1 for 1.5 wt% Cu/CN and 4.5 wt% Cu/CS catalysts, respectively, which increased with the reaction temperature. Kinetics data of p-NP reduction at T = 25 °C, obtained for various concentrations of reagents, were successfully modeled using the Langmuir–Hinshelwood mechanism. The related kinetic parameters such as the adsorption equilibrium constants K(p-NP), K(BH−4) and the surface rate constant, k, were calculated. The competitive adsorption between p-NP and BH−4 was shown to control the rate of p-NP reduction to p-AP

Catalytic reduction of nitro-phenolic compounds over Ag, Ni and Co nanoparticles catalysts supported on γ-Al2O3

In this work, 1 wt.%Ag/gamma-Al2O3, 1 wt.%Ni/gamma-Al2O3 and 1 wt.%Co/gamma-Al2O3 supported catalysts have been prepared using impregnation method. Their activities were investigated toward the reduction of the nitro-phenolic compounds (NPCs) (ortho-, metha- and para-nitrophenol, respectively, o-NP, m-NP and p-NP) to their corresponding aminophenol compounds (APCs), in the presence of excess of NaBH4 as a reducing agent. Characterization techniques such as (FTIR), (XRD), (SEM/EDX), (UV-vis), (MES/EDS/TEM) and BET textural analysis showed that the metallic nanoparticles of Ag, Ni and Co were well dispersed on gamma-Al2O3 support. The results demonstrated that the unreduced catalysts (fresh and calcined in air) exhibited a good catalytic activities and stabilities for the reduction of NPCs (> 85%) even after 8 catalytic cycles. The catalytic activity of calcined catalysts at T = 450 degrees C, was in the order of 1 wt.%Ag/gamma-Al2O3 > 1 wt.%Ni/gamma-Al2O3 > 1 wt.%Co/gamma-Al2O3 and that of fresh catalysts in the order of 1 wt.%Ag/gamma-Al2O3 > 1 wt.%Co/gamma-Al2O3 > 1 wt.%Ni/gamma-Al2O3. The kinetics of the reduction of the NPCs isomers were studied at T = 25, 35 and 45 degrees C, and were found to follow the kinetics of pseudo-first order and Arrhenius equation. Their reactivities over each catalyst followed the order of p-NP > o-NP > m-NP, except for calcined 1 wt.%Co/gamma-Al2O3. Based on our results and the literature data, a mechanism of catalytic reduction reaction of NPCs has been proposed

Study of the Effectiveness of Alumina and HDTMA/Alumina Composite in the Removal of Para-Nitrophenol and the Deactivation of Bacterial Effect of Listeria monocytogenes and Salmonella spp.

Removal of para-nitrophenol (p-NP) from an aqueous solution was studied under various batch adsorption experiments, using alumina (Al2O3) and its composite hexadecyltrimethylammonium bromide (HDTMA+-Br−) as adsorbents. These were later characterized, before and after adsorption of p-NP, by thermal analysis (DSC-TG), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and UV/Visible spectroscopies. The results show that HDTMA+/Al2O3 adsorbents have a greater affinity toward p-NP than Al2O3 alone. Linear and non-linear forms of kinetics and isotherms were used to analyze the experimental data obtained at different concentrations and temperatures. The results indicate that the pseudo-second order kinetic model provided the best fit to the experimental data for the adsorption of p-NP on both adsorbents, and that the intra-particle diffusion was not only the rate controlling step. Both the Langmuir and Redlich-Peterson (R-P) models were found to fit the sorption isotherm data well, but the Langmuir model was better. Physical adsorption of p-NP onto the adsorbents proved to be an endothermic and spontaneous process at high temperatures, which mainly involves a hydrogen bonding mechanism of interactions between p-NP and functional groups of adsorbents. The antibacterial activity of Al2O3, HDTMA+-Br− and HDTMA+/Al2O3 were evaluated against Listeria monocytogenes and Salmonella spp. strains using both disc diffusion and broth microdilution methods. The HDTMA+-Br− and HDTMA+/Al2O3 displayed a bacteriostatic effect against all tested strains of Listeria monocytogenes and Salmonella spp., while Al2O3 exhibited no bacterial effect against all bacterial strains tested

Towards an in-depth experimental and theoretical understanding of the cadmium uptake mechanism on a synthesized chitin biopolymer

This work analyzes the adsorption of cadmium, a potentially toxic pollutant, on biopolymers synthesized from shrimp shells, as a promising new adsorbent. Spectroscopic analysis, such as FTIR, ATD/ATG, XRD, and SEM/EDX techniques, were used to characterize chitin before it was exposed to cadmium ions. Experimental data indicate that Cd(II) adsorption proceeds with pseudo-second-order model kinetics and is influenced by increasing temperature. In the equilibrium, the maximum adsorption capacity obtained was 58.82 mg g−1 at a temperature of 308 K. Experiments to obtain adsorption data were performed at T = 298–318 K. The saturated adsorption capacities of Cd(II) range from 57.40 to 59.90 mg g−1. The application of the physics-statistics model indicates that the Cd(II) atoms are adsorbed on the surface of the chitosan forming a monolayer. In addition to that, the results also show that the adsorption affinity increases with the system temperature, resulting in higher affinity and an increase of 30% in the adsorption capacity. The adsorption energy was found to be around 2.5 kJ mol−1, indicating that the adsorption is physical and endothermic. The entropy was found to quickly increases (reaching a maximum value of 6 × 10−22 kJ mol−1 K−1) at low concentrations followed by the equilibrium after the 40 mg L−1, indicating that the equilibrium is quickly reached. The Gibbs free energy indicates that the process is spontaneous (ranging from −1.364 to −1.451 kJ mol−1) and that the energy tends to remain constant after 15 mg L−1. Last, the results indicate that the Cd(II) is adsorbed due to dipole–dipole interactions and possible coordination bounds. The results of tests on the adsorption of cadmium by chitin showed that this biopolymer could replace other more expensive adsorbents