Treasuring industrial sulfur by-products: A review on add-value to reductive sulfide and sulfite for contaminant removal and hydrogen production

Reductive sulfur-containing by-products (S-BPs) released from industrial process mainly exist in the simple form of sulfide and sulfite. In this study, recent advances to remove and make full use of reductive S-BPs to achieve efficient contaminant removal and hydrogen production are critically reviewed. Sulfide, serves as both reductant and nucleophile, can form intermediates with the catalyst surface functional group through chemical interaction, efficiently promoting the catalytic reduction process to remove contaminants. Sulfite assisted catalytic process could be classified to the advanced reduction processes (ARPs) and advanced oxidation processes (AOPs), mainly depending on the presence of dissolved oxygen (DO) in the solution. During ARPs, sulfite could generate reductive active species including hydrated electron (e(aq)(-)), hydrogen radical (Hmiddot), and sulfite radical (SO3 center dot-) under the irradiation of UV light, leading to the efficient reduction removal of a variety of contaminants. During AOPs, sulfite could first produce SO3 center dot- under the action of the catalyst or energy, initiating a series of reactions to produce oxysulfur radicals. Various contaminants could be effectively removed under the role of these oxidizing active species. Sulfides and sulfites could also be removed along with promoting hydrogen production via photocatalytic and electrocatalytic processes. Besides, the present limitations and the prospects for future practical applications of the process with these S-BPs are proposed. Overall, this review gives a comprehensive summary and aims to provide new insights and thoughts in promoting contaminant removal and hydrogen production through taking full advantage of reductive S-BPs.

Automated summary

This study critically reviews recent advances in the removal and utilization of reductive sulfur-containing by-products (S-BPs) from industrial processes for efficient contaminant removal and hydrogen production. Sulfide acts as both reductant and nucleophile, promoting the catalytic reduction process for contaminant removal. Sulfite-assisted catalytic processes can generate reductive active species, leading to efficient reduction removal of contaminants. Sulfides and sulfites can also be removed and hydrogen can be produced through photocatalytic and electrocatalytic processes.