Preparation and characterization of the semiconductor CuMnO2 by sol-gel route

Nano crystallites of the crednerite CuMnO2 are prepared by sol–gel method with two-step annealing process. The powder heated at 450°C under air flow shows a mixture of CuO, Mn2O3 and CuxMn3−xO4. However, when calcined at 900°C under N2 atmosphere, the crednerite CuMnO2 with a monoclinic structure (space group: C2/m) is obtained. The Raman spectrum shows a single peak at 679cm−1 assigned to A1g mode whereas the infrared analysis confirms the linearity of CuO23− units. The optical transition at 1.70eV, determined from the diffuse reflectance is attributed to the inter-band d-d transition of Cu+ ion. The oxide exhibits semiconducting properties with an activation energy of 0.21eV. The photo-electrochemical measurement shows p-type conduction due to O2− insertion in the two dimensional lattice. The flat band potential (+0.12 VSCE), indicates a cationic character of both valence and conduction bands deriving from Cu+: 3d orbital

Sol–gel synthesis and characterization of the delafossite CuAlO2

Nanocrystalline CuAlO2 is synthesized by sol–gel method using ethylene glycol as solvent. The stages of formation are followed by thermal analysis. The X-ray diffraction pattern of the powder heat-treated at 1100 °C shows a single phase, indexed in a rhombohedral symmetry (R 3¯¯¯ m). The apparent crystallite size (57 ± 8 nm) is determined from the Williamson–Hall plot. The direct optical transition (=3.69 eV), evaluated from the diffuse reflectance spectrum, is attributed to the charge transfer (O2−: 2p → Cu+: 4s). The oxide is p-type semiconductor, and the conduction occurs predominantly by small polaron hopping between mixed valences Cu2+/+, due to oxygen insertion in the layered crystal. The photoelectrochemical characterization gives a flat band of 0.20 VSCE and a hole density of 1.13 × 1018 cm−3. The semicircle centered on the real axis, in the electrochemical impedance spectroscopy (EIS), is due to the absence of constant phase element with a pure capacitive behavior. The straight line at 35° at low frequencies is attributed to the diffusion in the layered structure

Mass transfer process in the removal of Congo Red (CR) onto Natural Clay (NC): Kinetic, isotherm modeling, and thermodynamic study

Industrial growth and technological advancement have led to the worldwide introduction of pollutants of diverse nature into water bodies including pollutants such as dyes and organic contaminants. Their presence in industrial effluents or drinking water is a public health problem. The aim of this study was to evaluate the adsorption of Congo Red (CR) onto Natural Clay (NC) realized in a batch system. The effects of contact time, initial pH, stirring speed, temperature, adsorbent dose, and initial CR concentration on the adsorption capacity were investigated. The NC was characterized by the FTIR, DRX, BET, and point of zero charge. The experimental isotherm data follow well the Langmuir equation, providing a better fit of the equilibrium adsorption data. Under optimized conditions, up to 212.766 mg/g at 25 °C is removed from the solution. The adsorptions kinetics were found to follow rather a pseudo second-order kinetic model with a determination coefficient (R2) of 0.999. The adsorption isotherms at different temperatures have been used for the determination of thermodynamic parameters, i.e., the negative free energy ΔG0 (10.081 to 1.087 kJ/mol), positive enthalpy change ΔH0 Q5 (64 = 175 kJ/mol) values indicate that the overall CR adsorption is spontaneous and endothermic in nature. HIGHLIGHTS The aim of this study was to evaluate the adsorption of Congo Red onto Natural Clay (NC).; The effects of parameters were investigated graphically.; Under optimized conditions, up to 212.766 mg/g at 25 °C is removed from the solution.; The adsorption kinetics were found to follow rather a pseudo-second-order kinetic model.; The thermodynamic parameters indicate the adsorption is spontaneous and endothermic in nature.

Removal of gentian violet in aqueous solution by activated carbon equilibrium, kinetics, and thermodynamic study

The quantitative kinetic and equilibrium adsorption parameters for chlorure de méthylrosaniline (gentian violet, crystal violet) removed by commercial activated carbon were studied by UV–visible spectroscopy.Activated carbon with a high specific surface area 1250 m 2 /g was characterized by the Brunauer, Emmett et Teller (BET) method and the zero charge point pH ( pzc) . The adsorption properties of both activated carbon with gentian violet were conducted at variable stirring speed 100–700 trs/min, adsorbent dose 1–8 g/l, solution pH 1–14, initial gentian violet concentration 5–15 mg/l, contact time 0–50 min, and temperature 299–323 K using batch mode operation to find the optimal conditions for a maximum adsorption. The adsorption mechanism of gentian violet was studied using the pseudo-first-order, pseudo-second-order, and Elovich kinetic models. The adsorption kinetics was found to follow a pseudo-second-order kinetic model with a determination coefficient (R 2 ) of 0.999. The Weber–Morris diffusion model was applied for the adsorption mechanism. The equilibrium adsorption data of gentian violet were analyzed by the Langmuir, Freundlich, Elovich, and Temkin models. The results indicate that the Langmuir model provides the best correlation ( q max  = 22.727, 32.258 mg/g at 26 and 40°C, respectively). The adsorption isotherms at different temperatures have been used for the determination of thermodynamic parameters, i.e. free energy (Δ G ° = − 2.30 to −5.34 kJ/mol), enthalpy (Δ H ° = 36.966 kJ/mol), entropy (Δ S ° = 0.131 kJ/mol K), and activation energy ( Ea ) 40.208 kJ/mol of gentian violet adsorption. The negative Δ G ° and positive Δ H ° indicate that the overall adsorption is spontaneous and endothermic in nature