Design and preparation of highly active TiO₂ photocatalysts by modulating their band structure

Titanium dioxide photocatalysts with high reduction potential and visible light response hold great promise in photochemical conversion. Here, we used a simple glycine doping method to synthesize novel N-TiO₂@C photocatalysts with upward shifted conduction bands and narrowed band gaps as well as inhibited recombination of photoinduced electron-hole pairs. The N-TiO₂@C photocatalysts exhibited higher visible light response and remarkably enhanced photocatalytic activity in the production of nicotinamide adenine dinucleotide (NADH) by photomediated reduction of NAD⁺ without any electron mediator. The yield of NADH was up to 70.3 % far greater than that of the undoped TiO₂ (11.3 %), and it stabilized at ca. 60 % after 10 cycles. The viability of coupling NADH regeneration with enzymatic reaction (alcohol dehydrogenase) was established in aldehyde reduction where formaldehyde was specifically reduced to methanol. These findings shed new light on the modulation of the band structure of semiconductors and develop an electron mediator free strategy for NADH-dependent artificial photosynthesis through coupled photocatalytic and enzymatic approaches.