Ch3coona

The BiVO₄ electrodes were prepared as previously reported procedure [19 (link)]. Solutions for electrodeposition were prepared by dissolving 10 mM Bi(NO₃)₃ (98 %, Alfa Aesar) in a solution of 35 mM VOSO₄ (97 %, Sigma Aldrich) at pH < 0.5 with HNO₃ (65 %, Acros Organics). Then 2 M CH₃COONa (≥99.0 %, Alfa Aesar) was added, raising the pH to ∼5.1, which was then adjusted to pH 4.7 with a few drops of HNO₃. Acetate serves to stabilize other insoluble Bi (III) ions at pH 4.7. This mildly acidic pH condition must be used because at pH lower than 2 where Bi(III) is soluble, no film can be formed while at pH higher than 5, V (IV) precipitates from solution. A three-electrode cell was used for electrodeposition, with an fluorine-doped tin oxide (FTO, 8 Ω/□, Hartford Glass Co.) coated glass substrate as working electrode, a Ag/AgCl (4 M KCl) as reference electrode and a platinum foil as counter electrode. A potentiostat (Sloartron SI 1287) was used for electrodeposition. Deposition of amorphous Bi–V–O films was carried out potentiostatically at 1.9 V vs Ag/AgCl (4 M KCl) for 5 min at 70 °C (ca. 2 mA cm⁻²). The as-deposited films were converted to crystalline BiVO₄ and amorphous V₂O₅ by annealing at 500 °C for 1 h in air, and pure BiVO₄ was achieved by dissolving the V₂O₅ in 1 M KOH under stirring for 20 min.

As-synthesized NMCP/rGO was prepared using a sol-gel method and a high temperature sintering method (Figure 1). At the beginning, the sieved 5 wt.% GO powder was put into DI-water, and the GO dispersion was formed by shaking it for 1 h in an input shaker. After the temperature of the GO dispersion reached 80 °C, 1 mmol chromium nitrate nonahydrate (Cr(NO₃)₃·9H₂O, 98.5%, Alfa-Aesar, Ward Hill, MA, USA) completely dissolved in 100 mL DI water was added, and the temperature was maintained at 80 °C with continuous stirring. Then, 1 mmol citric acid (C₆H₈O₇·H₂O, 95%, Sigma-Aldrich, Burlington, MA, USA), 1 mmol manganese acetic acid tetrahydrate ((CH₃COO)₂Mn·4H₂O, ≥99%, Acros-Organi, Janssen-Pharmaceuticalaan, Geel, Belgium), 4 mmol anhydrous sodium acetate (CH₃COONa, 98%, Alfa-Aesar, Ward Hill, MA, USA), 1.25 g ascorbic acid (C₆H₈O₆, 99%, Acros-Organi, Janssen-Pharmaceuticalaan, Geel, Belgium), and 1.025 mL phosphoric acid (H₃PO₄, 86%, Echo Chemical Co., Ltd., Miaoli, Taiwan.) were added, and stirred at 80 °C for 1 h, dried in a circulating oven at 120 °C, and finally sintered at 750 °C under argon atmosphere for 9 h. To prepare pristine NMCP, the same procedure described in the previous part was used, only without the step of adding GO in the preparation process of NMCP/rGO.

The ɛ-caprolactam (ECL) monomer with reduced moisture content for anionic polymerization (AP-Nylon^®) was purchased from Brüggemann Chemical (Heilbronn, Germany). Before use, it was kept under vacuum for 1 h at 23 °C. As a polymerization activator, Brüggolen C20^® (C20) from the same company was used. The initiator sodium dicaprolactamato-bis-(2-methoxy-ethoxo)-aluminate (Dilactamate^®, DL, 85% solution in Toluene) was purchased from Katchem (Prague, Czech Republic) and applied without further treatment. Toluene, xylene, methanol and other solvents were all of analytic grade, purchased from Merck (Lisbon, Portugal) and used as received. GOx from Aspergillus Niger type VIII, D–(+) glucose (purum p.a.), NaH₂PO₄·2H₂O, 99% (purum p.a.), Na₂HPO₄·2H₂O, (98%), NaCl (99%) and CH₃COOH (99%) were purchased from Merck/Sigma Aldrich, Lisbon, Portugal. HRP from Amoracia rusticana and CH₃COONa (99%) were purchased from Alfa Aesar (Lancashire, UK). 3,3′,5,5′-Tetramethylbenzidine (TMB, 99%) was purchased from Acros Organic (Porto Salvo, Portugal). Pebax MH 1657 resin (block copolymer with 60% soft polyethylene oxide segments and 40% PA6 hard segments) was kindly donated by Arkema (Serquigny, France), and poly(ethylene terephthalate) film (Melinex^®) was supplied by Addev Materials (Lyon, France).