Efficient conversion of bicarbonate (HCO3−) to acetate and simultaneous heavy metal Cr(VI) removal in photo-assisted microbial electrosynthesis systems combining WO3/MoO3/g-C3N4 heterojunctions and Serratia marcescens electrotroph

Abstract

The removal of the hazardous heavy metal Cr(VI) in water and the simultaneous production of acetate from the reduction of inorganic carbon (HCO3 -) is demonstrated in a photo-assisted microbial electrosynthesis (MES) system incorporating WO3/MoO3/g-C3N4 Z-scheme heterojunctions and Serratia marcescens Q1 electrotroph cathode. The rates of acetate production (6.1 ± 0.3 mg/L/h) and Cr(VI) removal (4.5 ± 0.1 mg/L/h) recorded at a circuital current of 2.8 ± 0.1 A/m 2 were 2.4-fold (acetate production), 1.7-time (Cr(VI) removal) and 1.6-fold (circuital current) of those in the controls recorded in the absence of WO3/MoO3/g-C3N4, and 1.6-fold (acetate production) and 1.8-time (circuital current) of those in the absence of both Cr(VI) and WO3/MoO3/g-C3N4. Photogenerated WO3/MoO3/g-C3N4 conduction bands electrons favored both direct or indirect (via S. marcescens) reductions of Cr(VI) and H + , with the latter producing H2 which was further metabolized by S. marcescens with HCO3to yield acetate. The higher circuital current drawn under photoirradiation conditions refilled the photo-generated valence band holes in the semiconductor and provided the driving force for the reduction reactions. This study provides an alternative and feasible approach for achieving complete removal of toxic heavy metal from water and industrial waters with simultaneous conversion of inorganic carbon to key block chemicals.

Biophotoelectrochemistry for renewable energy and environmental applications

“…Bittencourt et al (2020) integrated brown algae Laminaria hyperborean with TiO 2 to achieve the reduction of Cr 6+ to Cr 3+ , although its performance was lower than that of the L. hyperborean coated with FeCl 3 . A biocathode was prepared with Serratia marcescens and WO 3 /MoO 3 / g-C 3 N 4 heterojunctions in a BPEC system, which allowed the simultaneous reduction of Cr 6+ and H + , and the produced H 2 was further used for acetate production (Huang et al, 2021). Those results provide a potential strategy for efficient removal of toxic heavy metal from wastewater, along with the simultaneous conversion of inorganic carbon to key block chemicals.…”

Fabrication of an S-Scheme AgBr–PI Heterojunction for Biphenyl A Degradation and Its Degradation Pathways and Mechanism

“…The photocurrent density follows the sequence of PI < AgBr < 0.5-AP. These results indicated that 0.5-AP exhibited evidently high carrier separation efficiency compared with PI and AgBr. − Simultaneously, 0.5-AP expresses the minimum Nyquist cycle (Figure b), indicating that the charge transfer resistance of 0.5-AP is the least among the prepared samples. − At the same time, Figure c illustrates that when the excitation wavelength is 380 nm, all samples have a strong absorption peak around 480 nm, which is due to the photoinduced electrons and holes recombining. Nevertheless, the PL emission intensity was decreased after AgBr combination with PI, implying enhanced charge separation efficiency. − To obtain further evidence for the photoinduced carriers separation rates of the three abovementioned samples, time-resolved photoluminescence was conducted.…”

Toward Excellence in Photocathode Engineering for Photoelectrochemical CO2 Reduction: Design Rationales and Current Progress

“…[174] Electrotrophs, which contain electroactive membrane proteins, redox mediators, or appendages can also be selected or genetically engineered to better mediate electron transfer from semiconductor to microbes. [168,175] The use of diffusible redox mediators is also typical to facilitate the interelectron transfer. In particular, NAD(P) + , [176] bipyridinium salts [165b,177] (e.g., methyl viologen), rhodium complexes [178] are commonly used as redox mediators in enzymatic PEC systems (Figure 10B).…”