Photocatalytic degradation of octadecylamine and 4-dodecylmorpholine over titanium based photocatalyst: Activity and mechanism insights

More than 70% of the potash fertilizer globally is produced by the froth flotation process, in which octadecylamine (ODA) and 4-dodecylmorpholine (DMP) are predominantly used as flotation agents. As the potash fertilizer production rapidly rises, the increased ODA and DMP levels found in aquatic environments jeopardize the stability of ecosystems and the production of high-value chemicals. Herein, photocatalytic ODA and DMP degradation in aqueous medium over titanium based photocatalyst was carried out. The degradation rates of ODA and DMP all reached up to 100% at 6 h and 3 h, respectively, over the anatase TiO2 (TiO2-A), much higher than those of 40% and 25% over the rutile TiO2 (TiO2-R). TOC removal rates of ODA and DMP over the TiO2-A can reach up to 100% within 45 h and 25 h, respectively. Excellent stability and recyclability of TiO2-A were also observed in five test cycles of complete ODA and DMP degradation. Photoelectrochemical characterizations reveal more efficient carrier transfer and hole-electron pair separation in TiO2-A. Total organic carbon (TOC) and total nitrogen (TN) results indicate that the photocatalytic degradation initiates with the deterioration of the N element in DMP and ODA molecules, followed by the C elements. In particular, the involved N species are finally transformed into NO3-. Furthermore, hydroxyl radical is the dominant reactive species responsible for ODA and DMP degradation, as demonstrated by scavenger quenching tests and electron spin resonance. The possible degradation pathways and mechanisms of DMP and ODA are proposed following TOC, TN, FTIR, and GC–MS analyses. This work sheds light on the rational design and fabrication of highly efficient photocatalysts for the degradation of flotation agents in potash fertilizer production.