Titanium dioxide (TiO₂) has been widely used as a potential candidate for the production of green hydrogen using the artificial photosynthesis approach. However, the wide bandgap (∼3.3 eV) of anatase TiO₂ makes it difficult to absorb a large fraction of the solar radiation reaching the Earth, thus providing a low photocatalytic activity. Anatase TiO₂ absorbs only 4% of solar radiation, which can be improved by engineering its bandgap to enhance absorption in the visible region. In the literature, many strategies have been adopted to improve the photocatalytic activity of TiO₂, such as metal and non-metal doping and heterojunctions. These techniques have shown incredible enhancement in visible light absorption and improved photocatalytic activity due to their ability to lower the bandgap of pure TiO₂ semiconductors. This review highlights different techniques like doping, heterojunctions, acidic modification, creating oxygen vacancies, and temperature- and pressure-dependence, which have improved the photochemical response of TiO₂ by improving charge-transfer efficiencies. Additionally, the charge-transfer mechanism and enhancement in the photochemical response of TiO₂ is discussed in each portion separately.

Carbon dioxide conversion into value‐added products offers a promising strategy to mitigate greenhouse gas emissions while enabling sustainable fuel production. Among the available approaches, photocatalytic CO ₂ reduction has attracted significant attention, particularly when combined with advanced catalyst design and reaction engineering. In this work, Cu‐doped SrTiO ₃ is employed as a model photocatalyst to systematically investigate the influence of reaction phase on CO ₂ reduction performance across three distinct reaction configurations: solid–liquid (SL), solid–gas (SG), and pressurized solid–gas (PSG). The results demonstrate that the reaction phase strongly affects both activity and product selectivity. The SG configuration exhibits the highest performance, reaching accumulated yields of 11.13 µmol g ⁻¹ of CH ₄ and 2.32 µmol g ⁻¹ of CO after 4 h of reaction, owing to enhanced reactant accessibility and reduced mass‐transfer limitations. In contrast, the SL configuration shows the lowest gaseous‐product activity due to limited CO ₂ solubility and accumulation of dissolved intermediates, while favoring the formation of oxygenated liquid products such as methanol and ethanol. The PSG system displays intermediate performance, where increased CO ₂ availability is partially offset by hindered product desorption. These findings highlight reaction‐phase engineering as a key factor governing photocatalytic CO ₂ conversion efficiency and selectivity.