Single-site tin-grafted anatase TiO2 for photocatalytic hydrogen production: Toward understanding the nature of interfacial molecular junctions formed in semiconducting composite photocatalysts

Interfacial Ti–O–Sn linkages are proposed as the key bridge to accelerate electron transfer from TiO2 to the mononuclear Sn moiety, where H2 is released. The enhanced H2 production of photocatalytic methanol reforming on tin-modified anatase originates from efficient charge separation at the molecular junction. [Display omitted] ► Preparation of single-site tin-grafted anatase TiO2 photocatalysts by a SOMC route. ► A nuclearity-depended enhancement of H2 production over Sn/TiO2 photocatalysts. ► The molecular junction consists of the interfacial TiIV–O–SnIV linkages. ► The molecular junction controls the enhancement amplitude of H2 production. ► H2 release appears at the Sn moieties trapping photogenerated electrons of TiO2. This work focuses on the nature of enhanced H2 production over SnO2/TiO2 composite photocatalysts. Three kinds of Sn-modified TiO2 materials were prepared by different methods. Photocatalytic H2 production from methanol/water solution as a model reaction was used to evaluate the photocatalytic properties of the materials. The chemical states of Sn were characterized in detail by transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption fine structure spectroscopy. The results reveal a Sn nuclearity-dependent enhancement of H2 production over Sn/TiO2 photocatalysts. According to the characterization results, it was well established that the number of TiIV–O–SnIV linkages formed at the TiO2–SnO2 interface determines the enhancement amplitude of H2 production. The photogenerated electrons of TiO2 across the interfacial linkages are transferred into the mononuclear Sn moieties grafted on the (101) and (001) planes, where H2 is presumably released. An interatomic electron transfer pathway for accelerating photocatalytic H2 production over Sn/TiO2 catalysts was proposed based on this work.