Shielding of surface photogenerated charges by SiO2 coating for the photocatalytic degradation of air pollutants

• Novel SiO2-coated TiO2 nanocrystals was prepared.
• SiO2 coating controlled the crystallinity and crystal size of inner TiO2.
• SiO2 coating efficiently shielded the photo-induced charges on the TiO2 surface.
• SiO2 coating did not inhibit the transfer of toluene.

TiO2 has promising applications in air purification and self-cleaning but is usually inactivated by floating particulate matters. The inactivation is due to the accumulation of photogenerated charges on TiO2 surface. The surface charges significantly enhance the adsorption of particulate matters and thus block incident light. To shield photogenerated charges on TiO2 surface, a series of nanocomposites composed of inner TiO2 nanocrystals and SiO2 coating was synthesized using ethylenediamine as SiO2 coating assistant. XRD, N2 adsorption/desorption, TEM, surface photovoltage, UV–vis, and GC-FID were used to study the effect of SiO2 coating on the structure of inner TiO2 nanocrystals, the ability of shielding surface charges, the adsorption of airborne particles, and the removal efficiency of toluene. The results showed that SiO2 coating efficiently shielded the photogenerated charges on the TiO2–SiO2 interface and reduced the adsorption of airborne particles but did not diminish the transfer of toluene from air to photocatalytic sites on the TiO2 surface. The crystallinity and crystal size of inner TiO2 gradually decreased with increased amount of SiO2 coating. TiO2@SiO2-50 with a small crystal size of 9.2 nm and relatively high crystallinity showed the best photoactivity. This work may provide a new strategy to overcome the problem of TiO2 inactivation by haze pollution.

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