Synthesis and characterization of samarium and nitrogen doped TiO2 photocatalysts for photo-degradation of 4-acetamidophenol in combination with hydrodynamic and acoustic cavitation

In the present work, samarium (Sm) and nitrogen (N) doped TiO2 photocatalysts have been synthesized using conventional sol-gel process (CSP) and ultrasound assisted sol-gel process (USP). Detailed characterizations of catalysts have been performed using PL, UV-DRS, XPS, XRD, FTIR, FESEM, and EDX analysis. Photocatalytic activity of the catalysts has also been evaluated for the degradation of 4-Acetamidophenol (4-AMP) using different combinations of ultraviolet (UV) irradiation, hydrodynamic cavitation (HC) and ultrasound (US). Initially, the effects of operating parameters i.e. catalyst dosage, solution pH, and 4-AMP initial concentration on the extent of degradation have been investigated. It was observed that degradation of 4-AMP followed first order reaction kinetics and almost 50% degradation with a degradation rate constant of 4.4 x 10(-3)(min(-1)) was achieved using only photocatalytic oxidation at an optimum TiO2 catalyst loading of 2 g/L and natural pH (6.8). Nearly 60% and 63% degradation were obtained using Sm and N doped TiO2 at the optimized molar ratio of Sm to TiO2 (1.5:1) and N to TiO2 (1:1) respectively. It was also established that combination of photocatalytic oxidation with US and HC yielded synergistic results with extent of degradation as 87% and 91% respectively under optimized conditions in 180 min treatment. Energy efficiency (mg/J) was estimated on the basis of the amount of pollutant degraded per unit energy delivered. The hybrid method of HC and photocatalytic oxidation exhibited higher energy efficiency (9.0 x 10 -6 mg/J) which was almost 9 folds higher than the energy efficiency of the sonophotocatalytic process. The degradation by-products formed during the combined treatment of HC and photocatalytic oxidation were identified by LC-MS.