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

Adsorption of Hexavalent Chromium and phenol onto Bentonite Modified With HexaDecylTriMethylAmmonium Bromide (HDTMABr)

The efficiencies of Hexadecyltrimethylammonium bromide (HDTMABr) modified bentonite (HDTMABt) for phenol and chromium removal from aqueous solutions were studied in batch experiments at pH = 9 and pH = 2 values, respectively. FTIR, SEM, XRD and BET analyses indicated that the HDTMABr molecules were intercalated in the interlayer and at the external surface of initially Na-bentonite (NaBt). Adsorption experiments showed that the HDTMABt was more efficient than the initial NaBt for the removal of phenol and chromium, simultaneously, the extent of the enhancement differed among these pollutants depending on their affinity towards these samples. The kinetic study revealed a rapid adsorption onto HDTMABt of the pollutants during the initial stage (teq < 1h). The pseudo-second-order equation fitted well to the experimental data. Phenol adsorption on NaBt and HDTMABt could be described by a linear Freundlich equation while Langmuir and Freundlich models were the most suitable for Cr(VI) adsorption on both samples.Â

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

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

Characterization of ceramic pieces shaped from clay intended for the development of filtration membranes

This research work is focused in study of the dilation/retreat properties of ceramic membranes and its characterization. The clay used in this work is collected in the region of Midelt in Morocco. This raw material has been characterized by XRD, FTIR, TGA/DTA and X-ray fluorescence. These analyzes show that this clay consists essentially of Quartz and Kaolinite. Then, the clay pastes containing different proportions of the organic additive are aged and used to develop rods and bricks of known geometric dimensions. However, the pastilles were developed by dry process. After drying in the open air with a different percentage of the organic matter (0–15%), the parts are treated at different temperatures (700, 800, 900, 1000 and 1050 °C) according to a suitable heating program, taking into account the initial mineralogical composition and the TGA/DTA thermograms of the samples. The dilation/retreat properties of the processed samples are discussed according to the variation of predetermined parameters such as weight loss, length, height and diameter. The evolution of the porosity, the mechanical and chemical resistance of the samples is determined. It has been found that the organic additive increases the porosity of the parts prepared by its degradation by the heat treatment and the results obtained show that the prepared materials have a high mechanical strength and chemical resistance and they have improved porosity. Indeed, the clay studied will be used to develop tubular membranes intended for the tangential filtration of wastewater, which will be the subject of the second part of this study

Structural, Optical and Photocatalytic Properties of Mn Doped ZnO Nanoparticles Used as Photocatalysts for Azo-Dye Degradation under Visible Light

Doping ZnO with appropriate foreign metal and/or non-metal ions is one of the most promising ways to improve both the extension of ZnO photosensitization to the visible region and the separation of charge carriers. Herein, Mn-doped ZnO nanoparticles were synthesized using a precipitation method. The effect of the Mn amount on the physico-chemical properties of these nanomaterials was investigated using X-ray diffraction, Fourier-transform infrared spectroscopy, UV–visible diffuse reflectance spectroscopy, photoluminescence spectroscopy and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The photocatalytic properties of the synthesized nanomaterials were assessed through methyl orange (MO) under visible light. The obtained results showed that the structural and optical properties of the synthesized Mn-ZnO nanomaterials depended greatly on the Mn amount. It was found that the substitution of Zn2+ by Mn2+/Mn3+ within the lattice of ZnO occurred. The photocatalytic experiments revealed that the sample containing 10 wt% exhibited the best MO conversion. For this sample, the discoloration reached 96%, while the chemical oxygen demand reached 1% after 820 min of visible illumination. The enhanced photocatalytic activity was attributed to the efficient separation of charge carriers. The active species quenching experiments showed that the holes are the main active species in MO degradation under visible light in the presence of 10%Mn-ZnO

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

Structural, Optical and Photocatalytic Properties of Mn Doped ZnO Nanoparticles Used as Photocatalysts for Azo-Dye Degradation under Visible Light

Doping ZnO with appropriate foreign metal and/or non-metal ions is one of the most promising ways to improve both the extension of ZnO photosensitization to the visible region and the separation of charge carriers. Herein, Mn-doped ZnO nanoparticles were synthesized using a precipitation method. The effect of the Mn amount on the physico-chemical properties of these nanomaterials was investigated using X-ray diffraction, Fourier-transform infrared spectroscopy, UV–visible diffuse reflectance spectroscopy, photoluminescence spectroscopy and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The photocatalytic properties of the synthesized nanomaterials were assessed through methyl orange (MO) under visible light. The obtained results showed that the structural and optical properties of the synthesized Mn-ZnO nanomaterials depended greatly on the Mn amount. It was found that the substitution of Zn2+ by Mn2+/Mn3+ within the lattice of ZnO occurred. The photocatalytic experiments revealed that the sample containing 10 wt% exhibited the best MO conversion. For this sample, the discoloration reached 96%, while the chemical oxygen demand reached 1% after 820 min of visible illumination. The enhanced photocatalytic activity was attributed to the efficient separation of charge carriers. The active species quenching experiments showed that the holes are the main active species in MO degradation under visible light in the presence of 10%Mn-ZnO