Preparation and Characterization of Activated Carbons from Asparagus Palm (Laccosperma robustum) Bark by Chemical Activation with H3PO4 and KOH

The present work deals with the preparation and characterization of activated carbons from the bark of the asparagus palm (Laccosperma robustum) by chemical activation with phosphoric acid and potassium hydroxide. The process was optimized on the basis of the analysis of the iodine number, methylene blue number and activated carbons yield as a function of the preparation parameters (concentration of the activating agents and the pyrolysis temperature). It emerges that the pyrolysis temperature and the concentration of activating agents influence the activated carbons preparation process. Their values were 500°C and 20% respectively for activated carbon with H3PO4 (ACP) and 700°C and 1.5% for activated carbon with KOH (ACK). The iodine numbers obtained were 850.26 mg/g for ACP and 865.49 mg/g for ACK. The methylene blue numbers obtained were 149.35 mg/g for ACP and 149.25 mg/g for ACK. The activated carbons yields obtained were 25% for ACP and 5.9% for ACK. The activated carbons prepared under optimal conditions have shown the pH of zero-point charge (pHzpc) of 4.4 and 7.0 for ACP for ACK respectively. The determination of the surface functions revealed that ACP had a strong acidic character while ACK had neutral character. The Fourier transformed infrared spectroscopy also showed the presence of different functional groups on the surface of the precursor and activated carbons.

Effect of Zirconium and Cerium Loadings on Aerogel Pd-Based Catalysts for Methane Combustion

Aerogel Pd/(Ce0.33Zr0.66O2)SiO2 catalysts (CeZry) were prepared with variable Ce and Zr loadings (molar ratio Ce/Zr = 1/2) by combining sol-gel and impregnation methods. First, N2-physisorption was used to investigate the texture evolution. Then, H2-chimisorption and TEM were performed to study the effect on particle dispersion. After, TPR was used to determine the catalyst reducibility. Furthermore, XPS characterization was done to identify the palladium oxidation state and to evaluate the Pd-support interaction. Finally, the prepared catalysts were tested in methane combustion to assess their catalytic activity. The obtained results showed that, when the Zr and Ce loadings are varied between 0% and 8% and between 0% and 6% respectively, the BET surface area was increased from 615 to 744 m2/g, the porosity diameter from 45.7 to 83.6 Å, the Pd particle diameter from 5.2 to 7.0 nm, the CeO2 and ZrO2 particle size from 0 to 68 nm, the reduction temperature shift reached 16°C, the Pd binding energy shift attained 0.6 eV, but an optimum amounts of Zr (4 wt.%) and Ce (3 wt.%) are needed to maximize the PdO reducibility and to enhance the catalytic activity. In effect, 100% conversion of methane was reached at around 415°C on the CeZr4 catalyst.

Anaerobic Digestion of Olive Oil Mill Wastewater Pre-Treated with Catalytic Wet Peroxide Photo-Oxidation Using Copper Supported Pillared Clay Catalysts

Because phenolic compounds are toxic for methanogenic bacteria many problems concerning the high toxicity and biodegradability of the olive oil mill wastewater (OMW) have been encountered during anaerobic treatments of this effluent. In this work, we try to develop a new catalytic process for the degradation of phenolic compounds, producing less toxic OMW for methanogenic bacteria, facilitating the anaerobic digestion. This process consists of an oxidative reaction using copper supported on alumina pillared clay in presence of a photocatalytic system (H2O2 with UV light). Preliminary results showed that the use of the copper supported catalyst in presence of 0.88% H2O2 (v/v) allows after 2 h colour reduction (25%), significant abatement of total organic carbon (40%), and important removal of polyphenolic compounds (63%) especially those of high molecular mass and subsequently decreases the OMW toxicity from 100% to 70%. This catalytic pre-treatment process of OMW was efficient for anaerobic digestion.

Synthesis, Crystal Structure and Infrared Characterization of Bis(4-dimethylamino-pyridinium) Tetrachlorocuprate

The chemical preparation, crystal structure and spectroscopic characterization of a novel organic-inorganic hybrid material, bis(4-dimethylaminopyridinium) tetrachlorocuprate, have been reported. This compound crystallizes in the monoclinic system in space group C2/c and cell parameters a = 12.4356 (18), b = 12.0901 (17), c = 14.094 (2) Å, β = 115.303 (2)°, Z = 4 and V = 1915.8 (5) Å3. In the title salt, (C7H11N2)2CuCl4, both 4-dimethylaminopyridinium cations are protonated at their pyridine N atoms. The geometry of the CuCl2-4 ions is intermediate between tetrahedral and square planar. The atomic arrangement can be described by an alternation of inorganic layers built up by tetrachlorocuprate anions and organic layers formed by 4-dimethylaminopyridinium cations. The organic layers are located in sandwich between the inorganic layers. The anionic and cationic layers are held together by N-H···Cl and C-H···Cl hydrogen bonds into a three-dimensional network. The individual cations are π-π stacked with their neighbors at a distance of 3.7622 (5) Å. The vibrational absorption bands were identified by infrared spectroscopy and DFT calculations allowed their attribution.

Crystal Structure of ZnCl₃(Methyl-(2-Pyridin-2-yl-Ethyl)-Ammonium)

A new Zn(II) complex with the monodentate ligand methyl-(2-pyridin-2-yl-ethyl)-ammonium, ZnCl3C8H13N2, has been prepared and characterized by single crystal X-ray diffraction. The Zn(II) ion is tetracoordinated by one nitrogen atom of organic ligand and three chlorine ligands. In the atomic arrangement, the ZnNCl3 tetrahedra form corrugated chains extending along the b-axis. The organic entities are located between these chains through N-H···Cl, C-H···Cl and C-H···N hydrogen bonds to form layers parallel to (b, c) plan. Among these hydrogen bonds two are bifurcated.

Thermal Conductivity of Compressed Earth Bricks Strengthening by Shea Butter Wastes with Cement

Currently, in a context of sustainable development, the economic and environmental challenges incite, to valorize local materials such as clays and agro-industrial waste. It is in this approach that a new category of compressed earth bricks (BTC) stabilized with shea meal (TK) and cement was proposed. The purpose of this paper is to investigate the effect of shea meal rate on the thermal conductivity properties of cement stabilized earth bricks. A lateritic clay (Lat) mainly composed of kaolinite (38.44%), quartz (24.94%), goethite (12.28%), hematite (4.44%) and illite (19.9%) was used to make bricks. Different mix designs made up of lateritic clay and 5% cement were studied. The shea meal is added as a partial lateritic clay replacement in different proportions. The thermal conductivity was determined by hot disk method and correlated to both porosity and density of elaborated materials. The results obtained show that the thermal conductivity and density of bricks decrease respectively from 0.72 W·m-1·K-1 to 0.52 W·m-1·K-1 and from 2.77 g·cm-3 to 2.52 g·cm-3. The presence of shea meal within the material generates pore formation, which may partly explain the improvement of the thermal insulation properties. A positive correlation was noted between density and thermal conductivity of these materials.

Adsorption of Copper (II) Ions in Aqueous Solution by a Natural Mouka Smectite and an Activated Carbon Prepared from Kola Nut Shells by Chemical Activation with Zinc Chloride (ZnCl₂)

The aim of this work was to test the adsorption efficiency of copper (II) ions in an aqueous solution on Natural Smectite (NS) and Activated Carbon (AC). The experiments carried out in batch mode made it possible to determine the stirring time, the adsorbent mass, the pH, the initial concentration of copper (II) ions, the isotherms and the adsorption kinetics. It appears that the stirring time was 15 minutes for the AC and 20 minutes for the NS. The adsorption was at maximum for the two adsorbents at optimum pH of 3.5 for a mass of 0.05 g each. The quantity of copper (II) ions adsorbed was 26.6 mg/L for NS and 36.6 mg/g for AC of a concentration of 600 mg/L each. The Langmuir isotherm was the one that best described the adsorption process for the two adsorbents. The adsorption kinetics obtained was that of the pseudo second-order for our two adsorbents. The results obtained showed that these two adsorbents were effective for the adsorption of copper (II) ions in an aqueous solution.

Chemical Composition Assessment by Wavelength Dispersive X-Ray Fluorescence of Agricultural Soils in the Mining Town of Moanda, Gabon

This work focuses on the analysis of the chemical composition of soils dedicated to agriculture in order to assess the impacts of manganese mining activity in the city of Moanda in South-East Gabon. The result of the analysis obtained using wavelength dispersive X-ray fluorescence revealed the presence of twenty-seven elements in the seventeen soil samples collected namely: Na, K, Rb, Mg, Ca, Sr, Ba, Ti, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Cr, Mn, Al, O, C, P, S, Si, I, Ac and Th. Iron (Fe), aluminum (Al) and manganese (Mn) were respectively higher. The practice of agriculture near mining sites is not without risks for the quality of agricultural products and the health of the population.

Optical, Photoelectrochemical, and Electrochemical Impedance Studies on Photoactive Organic/Inorganic/Interface Assemblies of Poly 2,2 Bithiophene/Poly 3-(2-Thienyl) Aniline (PThA)/TiO₂

Particles of TiO2 modified with poly 3-(2-thienyl) aniline (PThA) and occluded in poly 2,2 bithiophene (PBTh), were subjected to optical, electrochemical impedance spectroscopic (EIS) and photoelectrochemical (PEC) investigation in aqueous, acetate, citrate, and phosphate electrolytes. EIS studies revealed that the assembly film of TiO2/PThA/PBTh possess porous-type structure. They also confirmed the approximate value of Ef obtained from electrochemical studies. Both EIS and optical studies indicated that ac conductivity is much greater than dc conductivity. Guided by the properties of PBTh, no large changes in the energy band structure occurred due to occlusion of TiO2 in PBTh films. Occlusion of TiO2/PThA into the network structure of PBTh inhibits the energy dissipation process and impeded charge polarization process of the material. Photoelectrochemical outcome suggested possible band alignments between the organic film and TiO2 and formation of hybrid sub-bands. Inclusion of TiO2 in the thiophene-based polymers enhanced the charge separation and consequently charge transfer processes and widen the absorption in visible light range.

TiO_2 nanotubes as solid-phase extraction adsorbent for the determination of polycyclic aromatic hydrocarbons in environmental water samples

An analytical method based on TiO2 nanotubes solid-phase extraction （SPE） combined with gas chromatography （GC） was established for the analysis of seven polycyclic aromatic hydrocarbons （PAHs）： acenaphtylene, acenaphthene, anthracene, fluorene, phenanthrene, fluoranthene and pyrene. Factors affecting the extraction efficiency including the eluent type and its volume, adsorbent amount, sample volume, sample pH and sample flow rate were optimized. The characteristic data of analytical performance were determined to investigate the sensitivity and precision of the method. Under the optimized extraction conditions, the method showed good linearity in the range of 0.01-0.8 μg/mL, repeatability of the extraction （RSD were between 6.7% and 13.5%, n = 5） and satisfactory detection limits （0.017-0.059 μg/mL）. The developed method was successfully applied to the analysis of surface water （tap, river and dam） samples. The recoveries of PAHs spiked in environmental water samples ranged from 90% to 100%. All the results indicated the potential application of titanate nanotubes as solid-phase extraction adsorbents to pre-treat water samples.