Enhanced photocatalytic activity of ZnS/TiO2 nanocomposite by nitrogen and tetrafluoromethane plasma treatments

Abstract

In the present study, the photocatalytic performance of ZnS/TiO 2 nanocomposite was investigated through the photodegradation of Acid Blue 113 (AB113) dye under ultraviolet light exposure. TiO 2 and ZnS-based nanocomposites suffer from relatively wide bandgap energy and low adsorption capacity which limit their photocatalytic applications. These problems can be suppressed by modifying the surface of nanocomposite particles by the non-thermal plasma. Herein, surface modification of the ZnS/TiO 2 nanocomposite was performed using a dielectric-barrier discharge plasma under nitrogen (N 2 ) and tetrafluoromethane (CF 4 ) gases. The characteristics of the plasma-treated nanocomposites were evaluated by XRD, FTIR, Raman, FESEM, EDS, BET, BJH, and DRS analyses. According to the results, by applying plasma treatment, cation and anion vacancies are produced that reduces the band gap energy of the photocatalyst hence improves its performance. The results indicate that the photocatalytic efficiency of the N 2 -plasma-treated nanocatalyst has been almost two times higher than that of the untreated ZnS/TiO 2 . It was found that after 25 min of UV irradiation, the AB113 was almost completely degraded in the presence of N 2 -plasma-treated ZnS/TiO 2 nanocomposite (about 95%), whereas, it was degraded by 64% and 46% in the presence of CF 4 -plasma-treated ZnS/TiO 2 and untreated ZnS/TiO 2 , respectively. This study presents a new approach to designing cost-effective plasma-treated photocatalysts to degrade organic contaminants in wastewater.Keywords ZnS/TiO 2 composite particles, Plasma catalysis, N 2 and CF 4 plasmas, DBD plasma reactor, Photocatalytic activityThe wastes from industrial and agricultural wastewater are very hazardous to human beings and can seriously damage different ecosystems 1-3 . To solve this problem, photocatalysts could provide a promising approach to degrade organic pollutants due to their low cost, biostability, nontoxic, and harmless properties 4,5 . Photocatalysis can be defined as the chemical reaction process involving light and a catalyst [6][7][8] . Over the last few years, significant progress has been made in the advancement of heterojunction photocatalysts aimed at enhancing their catalytic effectiveness. This has been achieved by generating intermediate states between the valence and conduction bands using external impurities 9 . Creating a heterojunction structure between two semiconductors, like ZnS and TiO 2 , can enhance the separation and movement of electron-hole pairs generated by light 10,11 . In this regard, various UV-responsive TiO 2 -based catalysts such as ZnO/TiO 2 12 , CdS/TiO 2 13 , WO 3 /TiO 2 14 , and ZnS/TiO 2 15,16 have been fabricated and used as photocatalysts. The ZnS/TiO 2 photocatalyst demonstrates improved photostability and enhanced performance compared to its individual components [17][18][19] . However, TiO 2 -based composites suffer from relatively wide bandgap energy and low adsorption capacity which limits their photocatalytic applications [20][21][22][23] . Num...