In
the present work, the photocatalytic degradation of
salbutamol
[2-(tert-butylamino)-1-(4-hydroxyl-3-hydroxymethylphenyl)ethanol]
under visible irradiation using Mn-doped TiO2 is investigated.
The Mn-doped TiO2 nanoparticles were synthesized by the
sol–gel method with ratios of 0.1, 0.2, and 0.3%. Significant
characteristics, including the rutile/anatase phases ratio, specific
surface area, and band gap energy, were due to the amount of Mn doping;
the narrowest band gap energy of 2.80 eV was observed in 0.2% Mn-doped
TiO2 with specific surface areas of 89.36 m2/g and 10.87/89.13 of rutile/anatase phases. The investigation involved
salbutamol photocatalytic degradation, a kinetic study, and the identification
of intermediate compounds. The results indicated that 0.2% Mn-doped
TiO2 obtained the best salbutamol removal of 95% under
an irradiation time of 180 min. Salbutamol slowly degraded to the
intermediate compounds in the first 60 min (k = 0.0088
1/min), and these intermediate compounds were dramatically mineralized
to small hydrocarbon fragments and carbon dioxide in the later irradiation
times (k = 0.0179 1/min). According to the high-performance
liquid chromatography–mass spectrometry (HPLC-MS) results,
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, hydroquinone, and
1-(4-hydroxylphenyl)ethanol, respectively. The mineralization of all
intermediate compounds was verified by 90% chemical oxygen demand
(COD) reduction, and the effluent contained a relatively low COD concentration
of 7.8 mg/L.