Visible-light-activated photocatalysis of malodorous dimethyl disulphide using nitrogen-enhanced TiO2

This study evaluated the feasibility of applying a visible-light-activated photocatalytic technique to cleanse air dimethyl disulphide (DMDS) at low concentration conditions (0.027-5.4 ppm), by using nitrogen-enhanced TiO2. In addition, the applicability of a backup adsorption unit for the secondary control of DMDS exiting from the photocatalytic oxidation (PCO) unit was investigated. The PCO unit functioned effectively for the control of DMDS at low concentration levels ( < or = 0.027 ppm) for long-time periods (at least 603 h). However, rapid photocatalyst deactivation levels were observed during photocatalytic processes with a higher DMDS input concentration (IC) (2.7 ppm). The photocatalyst reactivated with humidified or dried air, under visible-light irradiation, did not regain all its initial activities. The photocatalytic degradation efficiencies (PDEs) for DMDS were close to 100% for the relative humidity (RH) range of 45-55%, whereas they were between 86% and 91% and between 78% and 82% regarding the RH ranges of 10-20% and 80-90%, respectively. The PDEs via the PCO alone were close to 100% during this time period for the lowest IC conditions (0.027 ppm), whereas they decreased gradually for the other ICs. The FTIR spectra of the photocatalysts, as well as a solid-liquid extraction method, suggested the formation of sulphate groups on the catalyst surface during a photocatalytic process. Methanol was identified as a gaseous by-product. In addition, the backup adsorption unit could be effectively utilized to remove methanol, under a broad indoor pollution level (0.027-5.4 ppm), as well as DMDS exiting from the PCO units.