Photocatalytic degradation mechanism of pharmaceutical agent salbutamol using Mn-doped TiO 2 nanoparticle under visible light irradiation

Abstract

Abstract In this present work, the photocatalytic degradation of salbutamol [2-(tert-butylamino)-1-(4-hydroxyl-3-hydroxymethylphenyl)ethanol] under visible irradiation using Mn-doped TiO2. The Mn-doped TiO2 nanoparticles were synthesized by sol-gel method with the ratio of 0.1%, 0.2% and 0.3%. The significant characteristics including rutile/anatase phase ratio, specific surface area and band gap energy was due to the amount of Mn doping; the narrowest band gap energy of 2.80 eV was observed in the 0.2% Mn-doped TiO2 with the specific surface area of 89.36 m2/g and 10.87/ 89.13 of rutile/anatase phase. The investigation involved salbutamol photocatalytic degradation, kinetic study and identification of intermediate compounds. The results indicated that the 0.2% Mn-doped TiO2 obtained the best salbutamol removal of 95% under irradiation time of 180 min. The salbutamol was slowly degraded to the intermediate compounds in the first 60 min (k = 0.0088 1/min) and they was dramatically mineralized to small hydrocarbon fragments and carbon dioxide in the later irradiation times (k = 0.0179 1/min). According to the HPLC-MS results, the possible degradation pathways of salbutamol were proposed; 2-(tert-butylamino)-1-(3,4-dihydroxyphenyl)ethanone, 2-(tert-butylamino)-ethanol and 2-(tert-butylamino)-1-(4-hydroxyl-3-hydroxymethylphenyl)ethanone were initially formed and then transformed to 2-(methylamino)-1-(3,4-dihydroxyphenyl)ethanone, 2-(tert-butylamino)-acetic acid, hydroqunone and 1-(4-hydroxylphenyl)ethanol. The mineralization of all intermediate compounds was verified by 90% of COD reduction and the effluent contained relatively low COD concentration of 7.8 mg/L.