Photocatalytic performances of cobalt sulfides prepared by solution combustion synthesis using mixed fuels

Abstract

Cobalt sulfide powders (CoS, Co9S8 and CoS1.97) were synthesized by solution combustion method using conventional and microwave heating routes. The powders were obtained using cobalt nitrate as both cobalt source and oxidizer together with proper amounts of thiourea as sulfidizing agent and glycine as an auxiliary reductant. Effects of thiourea and glycine amounts in conjunction with the type of combustion route, on the phase constituents, microstructure and optical properties were studied using infrared spectroscopy, thermal analysis, X-ray diffractometry, electron microscopy and diffuse reflectance spectrometry techniques. The results revealed that single phase cobalt sulfides can be delivered by precise adjustment of thiourea and glycine amounts and a proper heating (conventional or microwave) route. Co9S8 single phase was obtained using equal amounts of thiourea and glycine by both microwave and conventional heating modes. Using thiourea/glycine ratio of 1.5, leads to the formation of CoS1.97 single phase by conventional heating, while CoS was obtained when microwave heating was applied. Increasing the amount of thiourea caused particle size increment. Maximum photocatalytic degradation efficiency (89 and 89.5%) of methylene blue was obtained at pH = 9 for microwave combusted samples. Quenching tests in the presence of •OH− radical scavenger (isopropyl alcohol) showed that the major oxidizing species were • OH− radicals.