High efficiency photocatalytic degradation of Ambroxol over Mn doped TiO2: Experimental designs, identification of transformation products, mineralization and mechanism

Ambroxol (AMB) is a drug commonly used for chronic bronchitis prevention. Once released in surface water, this recalcitrant chemical becomes a hazardous pollutant. Here, we investigated the ability of 1% Mn-doped TiO2 (Mn-TiO2) to mineralize AMB by photocatalysis. We studied the morphology, and the physical and electrochemical properties of Mn-TiO2 using X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, X-ray fluorescence, BET method, UV–visible, and electrochemical study and optimized the AMB degrading experimental conditions through response surface methodology (RSM). Mn-TiO2 at the dose of 0.625 g·L−1 allowed the complete photodegradation of AMB (30 ppm) at pH 7 under UVA light irradiation for 30 min while total mineralization in CO2 (>96%) was achieved after 24 h of irradiation. Mn-TiO2 was 1.6-time more efficient than TiO2 Degussa P25. Product studies were also carried out by liquid chromatography coupled to electrospray high resolution mass spectrometry. Twenty-one photodegradation products were detected and identified. In addition, ionic chromatography analyses revealed the release of Br−, NH4+, and NO3− at respectively 97, 63 and 35% of the total Br, and N initially present in AMB. Finally, the reusability of the photocatalyst was also tested. After four cycles, the almost complete photodegradation of AMB was achieved showing that Mn-TiO2 was highly stable. This work brings new physical characteristics on Mn-TiO2 photocatalyst. Moreover, it is the first study investigating the photocatalytic degradation of recalcitrant AMB drug.