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In the present study, the removal of both As(III) and As(V) from aqueous solutions using synthesized ZnO nanomaterials was achieved. The ZnO nanomaterial was synthesized using a precipitation technique and characterized using XRD, SEM, and Raman spectroscopy. XRD confirmed the ZnO nanoparticles were present in the hexagonal wurtzite structure. SEM of the particles showed they were aggregates of triangular and spherical particles. The average nanoparticle size was determined to be 62.03 ± 4.06 nm using Scherrer’s analysis of the three largest diffraction peaks. Raman spectroscopy of the ZnO nanoparticles showed only ZnO peaks, whereas the after-reaction samples indicated that As(V) was present in both As(V)- and As(III)-reacted samples. The adsorption of the ions was determined to be pH-independent, and a binding pH of 4 was selected as the pH for reaction. Batch isotherm studies showed the highest binding capacities occurred at 4 °C with 5.83 mg/g and 14.68 mg/g for As(III) and As(V), respectively. Thermodynamic studies indicated an exothermic reaction occurred and the binding of both As(III) and As(VI) took place through chemisorption, which was determined by the ΔH values of −47.29 and −63.4 kJ/mol for As(V) and As(III), respectively. In addition, the change in Gibbs free energy, ΔG, for the reaction confirmed the exothermic nature of the reaction; the spontaneity of the reaction decreased with increasing temperature. Results from batch time dependency studies showed the reaction occurred within the first 60 min of contact time. 

Electrochemical oxidation of water and electrolyte ions is a sustainable method for producing energy carriers and valuable chemicals. Among known materials for catalyzing oxidation reactions, titanium dioxide (TiO 2 ) offers excellent electrochemical stability but is less active than many other metal oxides. Herein, we used density functional theory calculations to predict an increase in catalytic activity by doping anatase TiO 2 with manganese atoms (Mn). We synthesized Mn-doped TiO 2 and then utilized X-ray absorption spectroscopy to study the chemical environment around the Mn site in the TiO 2 crystal structure. Our electrochemical experiments confirmed that TiO 2 , with the optimal amount of Mn, reduces the onset potential by 260 mV in a 2 M KHCO 3 (pH = ∼8) electrolyte and 370 mV in a 0.5 M H 2 SO 4 (pH = ∼0.5) electrolyte. Moreover, in 0.5 M H 2 SO 4 , we observed that the amount of Mn doping greatly impacts the selectivity towards oxygen production versus peroxysulfate formation. In 2 M KHCO 3 , the Mn doping of TiO 2 slightly decreases the selectivity towards oxygen production and increases the hydrogen peroxide formation. The Mn-doped TiO 2 shows good electrochemical stability for over 24 hours in both electrolytes.