Enhancement Effects of Cobalt Phosphate Modification on Activity for Photoelectrochemical Water Oxidation of TiO₂ and Mechanism Insights

Cobalt phosphate-modified nanocrystalline TiO₂ (nc-TiO₂) films were prepared by a doctor blade method using homemade nc-TiO₂ paste, followed by the post-treatments first with monometallic sodium orthophosphate solution and then with cobalt nitrate solution. The modification with an appropriate amount of cobalt phosphate could greatly enhance the activity for photoelectrochemical (PEC) water oxidation of nc-TiO₂, superior to the modification only with the phosphate anions. It is clearly demonstrated that the enhanced activity after cobalt phosphate modification is attributed to the roles of cobalt­(II) ions linked by phosphate groups with the surfaces of nc-TiO₂ mainly by means of the surface photovoltage responses in N₂ atmosphere. It is suggested that the linked cobalt­(II) ions could capture photogenerated holes effectively to produce high-valence cobalt ions, further inducing oxidation reactions with water molecules to rereturn to cobalt­(II) ions. This work is useful to explore feasible routes to improve the performance of oxide-based semiconductors for PEC water splitting to produce clean H₂ energy

Facile Synthesis of Surface-Modified Nanosized α‑Fe₂O₃ as Efficient Visible Photocatalysts and Mechanism Insight

In this study, α-Fe₂O₃ nanoparticles with high visible photocatalytic activity for degrading liquid-phase phenol and gas-phase acetaldehyde have been controllably synthesized by a simple one-pot water-organic two-phase separated hydrolysis-solvothermal (HST) method. Further, the visible photocatalytic activity is enhanced greatly after modification with a proper amount of phosphate. The enhanced activity is attributed to the increased charge separation by promoting photogenerated electrons captured by the adsorbed O₂ by means of the atmosphere-controlled surface photovoltage spectra, along with the photoelectrochemical I–V curves. On the basis of the O₂ temperature-programmed desorption measurements, it is suggested for the first time that the promotion effect results from the increase in the amount of O₂ adsorbed on the surfaces of Fe₂O₃ by the partial substitution of −Fe–OH with −Fe–O–P–OH surface ends. Expectedly, the positive strategy would be also applicable to other visible-response nanosized oxides as efficient photocatalysts. This work will provide us with a feasible route to synthesize oxide-based nanomaterials with good photocatalytic performance