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Herein, we report the optimization of Pb(II) ions removal from soil by electrokinetic remediation, using the response surface methodology (RSM) based on central composite design (CCD) describing individual and interactive effects of three chosen variables: the current intensity (I), electrolyte concentration (C) and remediation time (t). Sulfuric acid was selected as the electrolyte medium. The physicochemical properties of the soil were well characterized. The electrokinetic remediation (EKR) experiments were performed in galvanostatic mode, at constant current intensity. The lead Pb(II) content was measured using the atomic absorption spectrophotometer (AAS). Designing and modeling of the experimental runs were done using the Design Expert software. The results establish that the quadratic polynomial model matches the experimental data between the removal efficiency (η %) and the influencing factors. The obtained p-values (<0.05) through ANOVA analysis reveal a significant term, suggesting that the model was satisfactory. The significance of influencing factors increases is in that order: I < C (H2SO4) < t; increasing the remediation time translates into higher removal efficiencies. The statistical optimization strategy used in this study was successful in attaining the maximal lead removal of 86.79% using current intensity of 0.05 A, H2SO4 concentration of 0.05 M, and remediation time of 24 h 38 min. Ultimately, besides the great potential of the electrokinetic remediation for efficient removal of Pb(II) species, the RSM-based CCD is a promising and valuable tool for modeling and optimizing their elimination from contaminated soils. [ABSTRACT FROM AUTHOR]

Context and results: In this study, the heterojunction Cu2O/TiO2 is used for the degradation of a cationic dye, Rhodamine B, under solar light irradiation over a wide pH range. The physical and optical properties of both semiconductors Cu2O and TiO2 are correlated with the photo-electrochemical characterization to establish the energy diagram of the heterojunction Cu2O/TiO2. X-ray diffraction, UV–visible, SEM, EDX, and BET analyses are conducted for both photocatalysts. The band gap (Eg) of 3.26 eV is obtained for TiO2 with an indirect optical transition. In the case of Cu2O, the transition is directly allowed at 2.05 eV. According to the BET analysis, the specific surface area of TiO2 particles is higher (82.65 m2 g−1) than that of Cu2O (29.81 m2 g−1). The flat band potentials, determined from the Mott-Schottky plots, are 0.3 and − 0.32 VSCE for TiO2 and Cu2O, respectively. The photocatalytic activity is directly proportional to the mass ratio, and the best result is obtained for the mass ratio 1:1 of Cu2O/TiO2. Computational and theoretical techniques: Furthermore, a theoretical study is conducted by using density functional theory to optimize the structure, reactivity sites of the RhB molecule, and physical parameters like the energy of the frontier molecular orbitals and electronegativity and to predict the proposed mechanism of RhB degradation as well as its intermediates. Also, molecular dynamics simulation is used to determine the adsorption behavior of RhB on TiO2 (101) and Cu2O (111) surfaces. The ecotoxicity evaluation showed that degradation products have significantly lower acute toxicity than RhB. [ABSTRACT FROM AUTHOR]

Using the hetero-junction Fe2O3/WO3, a significant rate of photocatalytic activity was obtained for the degradation of Ponceau S Red dye (PSR) under solar irradiation. The mass ratio of Fe2O3 / WO3 was studied. Similarly, the experimental conditions leading to the total degradation of Ponceau S Red dye were optimized. The physical and optical properties of both semiconductors Fe2O3 and WO3 were correlated with the photo-electrochemical characterization to establish the energy diagram of the hetero-junction Fe2O3/WO3/electrolyte. The XRD, UV–visible and BET analyses were performed for both prepared compounds. Fe2O3 and WO3 have the band gap values of 2.18 and 2.66 eV, respectively and their optical transition is directly allowed. The flat band potentials, determined from the capacitance−2 – potential (C−2–E) plots are found to be − 0.16 and 0.47 VSCE, respectively. The absorption of visible light produces a transfer of electrons from the conduction band of Fe2O3 (− 0.61 VSCE) toward low trapping of WO3–CB energy sites (0.04 VSCE), which promotes the separation of charge carriers and therefore accelerates the PSR degradation. Under solar light illumination and the following conditions: pH ∼ 8, T ∼ 25 °C, and a catalyst dose of 1 mg/mL, total degradation of 10 mg/L of PSR is obtained. The chemical oxygen demand test confirms that most of Ponceau S Red dye was completely mineralized by photocatalytic process. [ABSTRACT FROM AUTHOR]