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• WO 3 /MoO 3 /g-C 3 N 4 and Serratia marcescens catalyze the production of acetate in photo-assisted MES. • Appreciable high production of acetate and coulombic efficiency are achieved. • WO 3 /MoO 3 and g-C 3 N 4 interact in a Z-scheme mechanism to enhanced electrons-holes separation. • Photo-induced electrons on the conduction band of semiconductor enhance H 2 production. • Photo-generated holes favor higher current and thus higher acetate production. The efficient production of acetate from HCO 3 − is demonstrated in a photo-assisted microbial electrosynthesis system (MES) incorporating a WO 3 /MoO 3 /g-C 3 N 4 heterojunction photo-assisted biocathode supporting Serratia marcescens Q1 electrotroph. The WO 3 /MoO 3 /g-C 3 N 4 structured electrode consisting of a layer of g-C 3 N 4 coated on graphite felt decorated with W/Mo oxides nanoparticles exhibited stable photocurrents, 4.8 times higher than the g-C 3 N 4 electrode and acetate production of 3.12 ± 0.20 mM/d with a CE acetate of 73 ± 4 % and current of 2.5 ± 0.3 A/m2. Photo-induced electrons on the conduction bands of WO 3 /MoO 3 /g-C 3 N 4 favoured hydrogen evolution, which was metabolized by S. marcescens with HCO 3 − to acetate, while the holes were refilled by the electrons travelling from the anode. Such mechanism reduced the interfacial resistances creating a supplementary driving force leading to higher acetate production. The biocompatible components of WO 3 /MoO 3 /g-C 3 N 4 synergistically couple light-harvesting and further catalyze S. marcescens to acetate from HCO 3 −, providing a feasible strategy for achieving sustainable high rates of acetate production. [ABSTRACT FROM AUTHOR]

• WO 3 /MoO 3 /g-C 3 N 4 and Serratia marcescens catalyze Cr(VI) removal and acetate production. • Photo-generated electrons increase the rates of HCO 3 − and Cr(VI) reductions. • Photo-generated holes increase the circuital current. • Higher circuital currents improve Cr(VI) removal and acetate production. The removal of the hazardous heavy metal Cr(VI) in water and the simultaneous production of acetate from the reduction of inorganic carbon (HCO 3 −) is demonstrated in a photo-assisted microbial electrosynthesis (MES) system incorporating WO 3 /MoO 3 /g-C 3 N 4 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/m2 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 WO 3 /MoO 3 /g-C 3 N 4 , and 1.6-fold (acetate production) and 1.8-time (circuital current) of those in the absence of both Cr(VI) and WO 3 /MoO 3 /g-C 3 N 4. Photogenerated WO 3 /MoO 3 /g-C 3 N 4 conduction bands electrons favored both direct or indirect (via S. marcescens) reductions of Cr(VI) and H+, with the latter producing H 2 which was further metabolized by S. marcescens with HCO 3 − to 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. [ABSTRACT FROM AUTHOR]