Na2moo4

The BiVO₄ precursor solution was prepared from a mixture of bismuth nitrate hexahydrate (BiN₃O₉·5H₂O, 99.99% Aldrich), vanadyl acetylacetonate (C₁₀H₁₄O₅V, 98% Aldrich) and sodium molybdate (Na₂MoO₄, Aldrich) at a mole ratio of 100:96:4 that was added to a solution of 1:0.12 acetylacetone (C₅H₈O₂, Fluka) and acetic acid (CH₃COOH, 99.70%, DAE). After sonication for 10 min, a dark green solution was obtained. Care was taken such that visible floating matter was not present, and the solution was used within 1 day after preparation to avoid sedimentation and prevent void filling of the mesoporous WO₃ bottom layer. The final mole concentration of Bi was 0.09 M. A total of 100 μl of the BiVO₄ precursor solution was dropped on the as-prepared mesoporous WO₃ bottom layer and kept for 1 min for solution penetration with the following spin coating process (5 s, 500 r.p.m. plus 30 s, 1,500 r.p.m.). The samples were then dried at 100 °C for 10 min, and then annealing at 300, 400, 500 °C for 5 min, respectively. During the annealing processes, W could be naturally doped into the BiVO₄ because of the intimate contact of the two components in the embedded structure. This process was conducted in a dry and well-ventilated environment and repeated five times. Finally, the samples were annealed in a box furnace at 500 °C for 2 h.

With the exception of hygromycin B (Panreac Applichem), all chemicals were from Sigma-Aldrich: paromomycin, streptomycin, Na₂CrO₄, Na₂MoO₄, Na₃VO₄, 4,4′-diisothio-cyanatostilbene-2,2′-disulphonate (DIDS), sodium malonate, sodium oxalate, NaHCO₃, Na₂SeO₄, Na₂S₂O₃, Na₂WO₄, Na₂S₄O₆. With the exception of DIDS (in 0.1 M potassium bicarbonate), stock solutions of all chemicals used to inhibit growth were prepared in distilled water and added to growth media at the specified final concentrations. All stock solutions were filter-sterilized before additions to media.