Tuning sulfur vacancies in CoS2 via a molten salt approach for promoted mercury vapor adsorption

Metal sulfides are emerging and efficient adsorbents for mercury removal. However, the major active sites responsible for their superior Hg0 adsorption ability are still disputable. Here, we proposed that sulfur vacancies play an important role in Hg0 removal over metal sulfides. Moreover, tuning the sulfur vacancies in CoS2 appears to be a feasible route to strengthen its mercury adsorption ability. Since traditional methods for adjusting the sulfur vacancies in metal sulfides are very complicated and hard to scale up, a simple, and cost-effective molten salt approach is employed to tune the concentrations of the sulfur vacancies in CoS2. The Hg0 removal efficiency of CoS2 is positively correlation with the density of sulfur vacancies, which can be facilely tuned by altering the cobalt precursors and annealing temperatures. The CoS2 derived from cobalt chloride and cobalt sulfate with higher concentrations of sulfur vacancies distinctly outperforms the ones derived from cobalt nitrate and cobalt acetate. Higher annealing temperature can generate higher concentration of sulfur vacancies, leading to a better mercury capture performance. CoS2-500-CA attained by annealing treatment of KSCN and cobalt acetate at 500 °C displays excellent mercury capture ability with Hg0 removal efficiency of 100% at reaction temperatures of 80–100 °C plausibly due to its high density of sulfur vacancies and big pore diameter. CoS2-500-CA is insusceptible to 100–200 ppm NO or 150–300 ppm SO2.