Ti foil

Ammonium heptamolybdate tetrahydrate (NH₄)₆Mo₇O₂₄ 4H₂O (99.5%) was obtained from Reachem (Bratislava, Slovakia), whereas thiourea, (NH₂)₂CS (99%), and L-cysteine were purchased from Sigma-Aldrich (St. Louis, MO, USA) and used as received. The Ti specimens with the working surface of 1.0 cm² (7 × 7 mm²) and a tag (1 × 30 mm²) were cut from Ti foil (99.7 at%, 0.127 mm thick, Aldrich). For Ti surface anodizing, NH₄F and H₃PO₄ were purchased from Reachem, Bratislava, Svovakia. Aqueous solution for hydrogen evolution was prepared from deionized water (18.4 MΩ) and analytically grade sulfuric acid.

The Ti foil was purchased from Sigma-Aldrich (99.7%, 0.127 mm). Ethylene glycol (EG), sodium borohydride (NaBH₄), copper chloride (CuCl₂), chloroauric acid (HAuCl₄), and palladium chloride (PdCl₂) were from Sinopharm Chemical Reagent Co., Ltd, China. Ammonia fluoride (NH₄F), 4-NP, MB, RhB, MO, silver nitrate (AgNO₃) and ethanol were obtained from Beijing Regent Co. China. Deionized (DI) water was used throughout the experiments with a resistivity of 18.2 MΩ cm.

TNAs were prepared by an optimized three-step anodization process. A Ti foil (0.25 mm thick, 99.7% purity, Sigma-Aldrich, St. Louis, MO) with an area of 2 × 3 cm was degreased by ultrasonic agitation for 30 min each in acetone, isopropanol, and deionized water and then dried with N₂ gas. The ethylene glycol electrolyte contained 0.25 wt.% NH₄F (98% purity, Sigma-Aldrich, St. Louis, MO) and 2 vol.% deionized water. Anodization was performed in a two-electrode system in which the Ti foil served as the working electrode and a Pt plate (2 × 3 cm) served as the counter electrode. Anodization was conducted at room temperature at a constant voltage of 60 V for 20 min (Figure 2). Afterward, the as-prepared TNAs were removed by sonication for 5 min in methanol. The second-step anodization was done for 50 min under the same conditions. The as-prepared amorphous TNAs were crystallized into an anatase phase at 450°C for 2 h in air at a heating rate of 1°C/min. After another round of anodization for 10 min under the same conditions, followed by immersion in 30% H₂O₂ solution for 10 min, the anatase TNAs were detached from the Ti substrate. After rinsing and drying, the self-standing TNAs were cut into 5 × 5 mm squares for transfer onto the photoelectrode.

Ti foil (thickness: 0.10 mm, Advent, 99.6+%), ethanol (96% and absolute, Sigma Aldrich, St. Louis, MO, USA), Ti titanium(IV) isopropoxide, potassium hydroxide (reagent grade, 90%, flakes, Sigma Aldrich, St. Louis, MO, USA), phosphate-buffered saline PBS (tablets, Sigma Aldrich, St. Louis, MO, USA), ultra-pure deionized water (miliQ, Merck KGaA, Darmstadt, Germany), glutaraldehyde—GA (25% in H₂O, Sigma Aldrich, St. Louis, MO, USA), fluorescein phalloidin (Molecular Probes, Thermo Fisher Scientific, Waltham, MA, USA), Triton X-100 (Sigma Aldrich, St. Louis, MO, USA), 4′,6-diamidino-2-phenylindole—DAPI (Sigma Aldrich, St. Louis, MO, USA), SlowFade reagent (Thermo Fisher Scientific, Waltham, MA, USA).