Tunable production of elemental Se vs. H 2 Se through photocatalytic reduction of selenate in synthetic mine impacted brine: engineering a recoverable Se product

• Published in: Environmental science water research & technology Vol. 9; no. 4; pp. 1069 - 1079
• Main Authors: Holmes, Andrew B., Ngan, Aldrich, Giesinger, Kayleanna, Gu, Frank
• Format: Journal Article
• Language: English
• Published: 30.03.2023
• ISSN: 2053-1400; 2053-1419
• DOI: 10.1039/D2EW00553K

In this paper, we investigate the tunability of Se reduction products (Se0(s) vs. H 2 Se (g) ) during the photocatalytic reduction of selenate over TiO 2 , using formic acid as an electron hole scavenger, in synthetic mine-impacted brines (SMIB). Photocatalytic reduction can effectively remove Se from SMIB to <2 μg L −1 from an initial Se concentration of >3300 μg L −1 in under 10 × 10 19 photons cm −2 . An increase in solution temperature led to a marked increase in selenate removal kinetics and an increase in selectivity towards H 2 Se (g) , while increasing the concentration of formic acid led to an increase in selenate removal kinetics and a decrease in the selectivity towards H 2 Se (g) . A bivariate response surface analysis was used to elucidate the mechanism behind the production of >99% gaseous H 2 Se or >85% solid Se 0 , under varying reaction conditions. Finally, a two-pronged electron transfer model is proposed to explain the selectivity towards Se0(s) vs. H 2 Se (g) under varying conditions: (i) Se0(s) is produced through direct reduction of selenate by TiO 2 conduction band electrons and (ii) H 2 Se gas is produced through electrons transferred into Se 0 , followed by an autocatalytic reduction of Se 0 to H 2 Se or through a direct reduction by CO 2 ˙ − .