Natural Clay Modified with ZnO/TiO2 to Enhance Pollutant Removal from Water

Raw clays, extracted from Bana, west Cameroon, were modified with semiconductors (TiO2 and ZnO) in order to improve their depollution properties with the addition of photocatalytic properties. Cu2+ ions were also added to the clay by ionic exchange to increase the specific surface area. This insertion of Cu was confirmed by ICP-AES. The presence of TiO2 and ZnO was confirmed by the detection of anatase and wurzite, respectively, using X-ray diffraction. The composite clays showed increased specific surface areas. The adsorption property of the raw clays was evaluated on two pollutants, i.e., fluorescein (FL) and p-nitrophenol (PNP). The experiments showed that the raw clays can adsorb FL but are not efficient for PNP. To demonstrate the photocatalytic property given by the added semiconductors, photocatalytic experiments were performed under UVA light on PNP. These experiments showed degradation up to 90% after 8 h of exposure with the best ZnO-modified clay. The proposed treatment of raw clays seems promising to treat pollutants, especially in developing countries

Comportement electrochimique de l'electrode de zinc en milieu basique concentre : applications aux accumulateurs alcalins

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Ionothermal carbonization in [Bmim][FeCl 4 ]: an opportunity for the valorization of raw lignocellulosic agrowastes into advanced porous carbons for CO 2 capture

International audienceIn this study, we investigated the ionothermal carbonization (ITC) in 1-butyl-3methylimidazolium tetrachloroferrate, [Bmim][FeCl 4 ], of cocoa bean shells, a raw lignocellulosic agrowaste. The beneficial inputs of this ITC approach towards mass yield, carbon yield and specific surface area of the solid chars (namely, ionochars) were clearly evidenced. The coordination of [FeCl 4 ]anions to the oxygen atoms of lignocellulosic materials and ionochars seems to stabilize carbon oxygenated groupsaccounting for enhanced mass and carbon yieldsand to favor the generation of micropores. We showed that the use of wet starting agrowastes in the ITC process might be advantageous for the production of highly porous ionochars. Importantly, the contributions of lignin and cellulose were highlighted and the recyclability of [Bmim][FeCl 4 ] was clearly evidenced, proving the sustainability of ITC and making this process easily applicable to other raw lignocellulosic agrowastes. The subsequent activation of the as-obtained ionochars under CO 2-rich atmosphere allowed producing activated carbons with specific surface area superior to 2000 m 2 .g-1 and remarkable CO 2 uptake as high as 4.4 mmol.g-1 at 25°C and 1 bar. This value is the highest post-combustion CO 2 uptake reported to date in literature for CO 2 activated biomassderived carbons

Removal of Cu(II) from aqueous solution using a composite made from cocoa cortex and sodium alginate

International audienceThe aim of this work was to prepare a composite material based on cocoa cortex and sodium alginate and test it to remove Cu(II) ions in aqueous solution in batch conditions. The composite was characterized using elemental analysis, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA/DTG), and point of zero charge. The highest amount of adsorbed Cu(II) for the composite was 19.54 mg/g, i.e., 95.32% of an initial concentration of 100 mg/L. Under the same conditions, the cocoa cortex untreated exhibited extremely low adsorption, while when it was treated with hot soda, it adsorbed 13.67 mg/g. Adsorption by the composite reached the equilibrium after 220 min. Kinetic data analysis suggested that the process was governed by adsorption (pseudo-second-order model) and diffusion through macropores and/or mesopores (intra-particle model). The adsorption isotherm that best described the system was Langmuir’s. The maximum adsorption capacity of Cu(II) was 76.92 mg/g. The values of the thermodynamic parameters indicated that the process was spontaneous, with ΔG° values between (− 7.886 and − 9.458 kJ/mol) and endothermic, with ΔH° = 7.728 kJ/mol

Hybrid clay-based materials for organic dyes and pesticides elimination in water

peer reviewedNatural clay, extracted from Cameroon, was modified by ion exchange to produce 4 different clays. These latter were modified with photocatalytic semiconductor like ZnO to produce efficient hybrid materials for pollutant removal in water. ZnO was synthesized by the soft sol-gel chemistry method. The results showed that the clay belonged to the smectite family and was composed of different crystalline phases. When the hybrid materials were produced, mix crystalline patterns were obtained with both smectite and ZnO wurtzite phases. The ICP-AES analysis showed that similar ratio between ZnO and clay were obtained for the 4 hybrid materials (30 wt% of ZnO and 70 wt% of clay). The SEM observation of the samples had shown that the hybrid materials had the clay structure as skeletal structure (sheet like structure) with the ZnO spherical materials grafted at the surface, giving a good exposure to light to maintain photocatalytic property. Then, the pollutant removal property of the samples was evaluated on three different model pollutants: p-nitrophenol (PNP), Malachite green (MG) and Diamant brilliant violet (DBV). On PNP, no adsorption was observed, and photocatalytic property was necessary to eliminate this molecule. With the best hybrid material (Clay/Cu 2+ /ZnO), 80% of PNP degradation was observed after 6 h of illumination. On MG and DBV, similar behavior was observed. Indeed, the clays and three out of four hybrid materials adsorbed completely both pollutant after 2 h of contact. Only pure ZnO and Clay/ZnO needed illumination to degrade completely both molecules. This study showed the possibility to obtain very efficient hybrid materials for pollutant removal in water with the use of inexpensive natural clay modified with a low amount of photocatalytic material (ZnO around 30 wt.%)

Silane modified clay for enhanced dye pollution adsorption in water

A natural clay from Bakotcha in Cameroon was modified with two silanes, tetramethoxysilane (TMOS) and [3-(2-aminoethyl)aminopropyl]trimethoxysilane (EDAS) to increase its adsorption properties. The modified clay is intended to be used as an efficient adsorbent for organic pollutant removal from water. Three Clay/TMOS and two Clay/EDAS samples with different [silane]/[clay] ratios were produced and characterized by X-ray diffraction, N2 adsorption-desorption measurements, Inductively Coupled Plasma–Atomic Emission Spectroscopy and Scanning Electron Microscopy. Their adsorption properties were evaluated on three organic model pollutants (i.e. fluorescein, malachite green and brilliant violet diamond). A dilution of the montmorillonite structure of the raw clay is observed when it is modified with TMOS while its original crystalline structure is preserved with EDAS. The morphologies depended on the used silane: (i) with TMOS, highly porous materials with the formation of silica particles at the surface of the clay; (ii) with EDAS, a similar morphology as raw clay with EDAS grafted at the surface of the clay. Both morphologies give two different adsorption behaviors on the 3 pollutants. For the raw clay and the TMOS modified clays, similar adsorption properties are obtained with a better adsorption when the specific surface increases (when TMOS content increases). When clay is modified with EDAS, the adsorption properties change as the surface groups are different, these EDAS modified samples have less affinity with fluorescein and malachite green reducing the adsorption capacity for this kind of pollutants. The tuning of the raw clay with silane opens the way for the development of highly efficient adsorbent for pollutants in water from natural and inexpensive materials

functional agrowaste for CO2 capture

International audienceThis paper presents for the first time surface functionalization of cocoa shells (CS) through the covalent grafting of 3-aminopropyltriethoxysilane (APTES) followed by the substitution of poly(dimethylsiloxane) (PDMS) and in situ generation/insertion of cobalt nanoparticles (Co-NP). The immobilization and stability of APTES–PDMS on cocoa shell were confirmed by Fourier transform infrared spectroscopy and differential scanning calorimetry. Morphological analyses by scanning electron microscopy demonstrated that Co-NPs successfully grew on the surface of CS–APTES–PDMS. The CO2-adsorption capacity of these new materials was examined at ambient conditions. Both CS–APTES–PDMS and CS–APTES–PDMS–Co showed increased CO2 adsorption capacities as compared to unmodified cocoa shell. This enhancement was explained by the synergetic behavior of the silane derivate, PDMS grafting, and Co-NP incorporation for CO2 adsorption. This work represents a new step toward using cocoa shell as an excellent low-cost candidate for a variety of environmental applications such as CO2 storage at ambient temperature

Chemical modification of the cocoa shell surface using diazonium salts

International audienceThe outer portion of the cocoa bean, also known as cocoa husk or cocoa shell (CS), is an agrowaste material from the cocoa industry. Even though raw CS is used as food additive, garden mulch, and soil conditioner or even burnt for fuel, this biomass material has hardly ever been investigated for further modification. This article proposes a strategy of chemical modification of cocoa shell to add value to this natural material. The study investigates the grafting of aryl diazonium salt on cocoa shell. Different diazonium salts were grafted on the shell surface and characterized by infrared spectroscopy and scanning electronic microscopy imaging. Strategies were developed to demonstrate the spontaneous grafting of aryl diazonium salt on cocoa shell and to elucidate that lignin is mainly involved in immobilizing the phenyl layer