Construction of SiO2-TiO2/g-C3N4 composite photocatalyst for hydrogen production and pollutant degradation: Insight into the effect of SiO2

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Using low-cost precipitated silica (SiO2) as the carrier, a ternary SiO2-TiO2/g-C3N4 composite photocatalyst was prepared via the sol-gel method associated with a wet-grinding process. The as-prepared composite exhibits photocatalytic hydrogen production and pollutant degradation performance under solar-like irradiation. The effect of SiO2 carrier on the properties of the heterostructure between TiO2 and g-C3N4 (CN) was systematically studied. It is found that SiO2 has important effects on promoting the interaction between TiO2 and CN. The particle size of TiO2 and CN was obviously reduced during the calcination process due to the effects of SiO2. Especially, the TiO2 particles exhibit monodispersed state with particle size below 10 nm (quantum dots), resulting in the improvement of the contact area and the interaction between TiO2 and CN, and leading to the formation of efficient TiO2/CN Z-scheme heterostructure in SiO2-TiO2/CN. Besides, the introduction of SiO2 can increase the specific surface area and light absorption of SiO2-TiO2/CN, further promoting the photocatalytic reaction. As expected, the optimum SiO2-TiO2/CN composite exhibits 12.3, 3.1 and 2.9 times higher photocatalytic hydrogen production rate than that of SiO2-TiO2, CN and TiO2/CN under solar-like irradiation, while the photocatalytic active component in SiO2-TiO2/CN is only about 60 wt%. Moreover, the rhodamine B degradation rate of SiO2-TiO2/CN is also higher than that of SiO2-TiO2, CN and TiO2/CN.