1：Experimental Design and Method Selection:

A hydrothermal method was used to prepare Pt–C-mesoporous TiO2 catalysts with varying Pt loadings (0.5–1.5 wt%). The photocatalytic activity was tested in a gaseous phase CO2 photoreduction system using H2O as an electron donor and a Hg lamp as the UV light source.

2：5–5 wt%). The photocatalytic activity was tested in a gaseous phase CO2 photoreduction system using H2O as an electron donor and a Hg lamp as the UV light source. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: Samples were prepared with different Pt loadings and hydrothermal reaction times to optimize the photocatalytic activity.

3：List of Experimental Equipment and Materials:

Tetrabutyl titanate, ethanol, hexachloroplatinum (IV) acid hydrate, tetraethyl orthosilicate, acetic acid, pure TiO2, Milli-Q water puri?cation system, Shimadzu XRD-6000 X-ray diffractometer, UV-vis spectrometer (UV-2550, Shimadzu, Japan), transmission electron microscopy (JEM2100F), scanning electron microscopy (Nova NanoSEM 230), BET Sorptometer (BET201-A, Porous Materials Inc.), Pyrex glass reactor, 400 W Hg lamp, Gas Chromatography Personal GC

4：Experimental Procedures and Operational Workflow:

10 The catalysts were prepared, characterized, and tested for CO2 photoreduction. The system was degassed, CO2 was introduced, and the reactor was irradiated with UV light. The effluent gases were analyzed using gas chromatography.

5：Data Analysis Methods:

The photocatalytic activity was evaluated based on the CH4 production rate. The materials were characterized using XRD, UV-vis absorption spectra, TEM, SEM, and BET surface area analysis.