*2.1. Materials Synthesis*

TiO2 nanosheets were synthesized through a solvothermal method [48]. In a typical synthesis, 4 mL of deionized water and 20% aqueous TiCl3 (99.99%, Acros Organics) each were added dropwise in 50 mL of ethylene glycol (99.99%, Fisher Scientific) under continuous stirring. The dark brown solution was then heated to 150 ◦C for 6 h in a PTFE-lined stainless steel autoclave. The subsequent slurry was washed several times with

deionized water and ethanol, and dried at 80 ◦C for 24 h to obtain bronze TiO2 (TiO2-B) nanosheets. Hierarchical anatase-bronze hybrid TiO2 nanosheets were obtained by heattreating TiO2-B nanosheets at 400 ◦C for 2 h under air flow (heating and cooling rates of 10 ◦C/min).
