In this study, SiO2 nano-particles were prepared according to Stöber method, where titanium dioxide was grown on the surface of the silicon dioxide core via the sol-gel approach to fabricate the core-shell structured photocatalysts. In order to improve the catalytic activity of the as-synthesized photocatalyst, Pd was doped to enhance the photocatalytic effectiveness of titanium dioxide photocatalyst. Simultaneously, sodium hydroxide was employed to remove the silicon dioxide template and to obtain hollow titanium dioxide microspheres. In the further experiment, the as-prepared catalyst was found to have core-shell and porous structure analyzed by SEM and TEM. The specific surface area of PTS and PHT are 52.167 and 71.412 m2/g and pore sizes are about 3.3 nm (mesoporous). After XRD analysis, TiO2 was determined as an anatase crystalline form. After FTIR analysis, Si-O-Ti bound was found at 969.1 cm-1 and photoelectric characteristics was examine by PL and EIS that 0.25 wt% Pd doped had the smallest electron hole recombination rate and the smallest resistance value. In addition, oxidation ability of TiO2/SiO2 (TS), Hollow TiO2 (HT), Pd/TiO2/SiO2(PTS), and Pd/H-TiO2 (PHT) photocatalsyts as synthesized was performed towards the oxidation of methyl orange dye wastewater, where 0.25 wt% Pd/H-TiO2showed the best result among all as-synthesized photocatalysts. Since the reduction of nitrate is the main topic of this study, we have focused on promoting the reduction ability of these photocatalysts combined with the UV light at the wavelength of 254 nm. The initial concentration of nitrate sample was kept at 439.3 mg/L and the catalysis by UV-254 light source was performed for two hours. According to the experimental results, the concentration of nitrate, nitrite, and ammonium was discovered to be significantly altered by using 0.25wt% PdO/H-TiO2. The photocatalyst could completely remove the nitrate within 100 minutes, where a very small amounts of nitrite and nitrate were formed by having more than 99% of nitrogen gas selectivity.

Photocatalytical reduciton of nitrate ions using Pd embedded core-shell TiO2/SiO2 composite catalyst

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