In situ epitaxial growth of Ag3PO4 quantum dots on hematite nanotubes for high photocatalytic activities

Abstract

Effective construction of semiconductor hetero-nanostructures (HNSs) with a well-defined hetero-interface is of great importance. So far, highly developed liquid-phase chemical routes are often restricted by their heavy use of surfactants and/or organic solvents, which inevitably introduce passivated surfaces and interfacial defects in the resultant HNSs. Here, we have developed a novel and efficient in situ epitaxial growth strategy to fabricate HNSs of Ag₃PO₄ quantum dots (QDs) on the external surface of hematite (Fe₂O₃) nanotubes (NTs) (Ag₃PO₄/Fe₂O₃ NT-HNSs), by intentionally employing chemically adsorbed phosphate anions on the surface of Fe₂O₃ NTs to control the reaction kinetics of phosphate anions and Ag⁺ ions in aqueous solution. In this synthetic strategy, the chemically adsorbed phosphate anions on the surface of the Fe₂O₃ NTs play the dual functions of heterogeneous nucleation and in situ epitaxial growth of Ag₃PO₄ QDs along the direction of (311) on the (113) crystal plane of Fe₂O₃ NTs. That is, they precipitate Ag⁺ ions via gradual dissociation of free phosphate anions and so generate Ag₃PO₄ QDs, and they serve as a bridge and bond for in situ epitaxial growth of Ag₃PO₄ QDs on Fe₂O₃NTs. Due to the unique coupling of the hetero-interfaces and internal electric field, the as-obtained Ag₃PO₄/Fe₂O₃ NT-HNSs show efficient separation of photogenerated charge carriers and remarkable enhancement of their reduction and oxidation abilities by a Z-scheme photocatalytic form, significantly improving visible-light photocatalytic activity for decolorization of the organic pollutant rhodamine B. They exhibit a photocatalytic rate constant as large as 3.6 × 10⁻² min⁻¹, which is two orders of magnitude greater than that of single Fe₂O₃ NTs (9.1 × 10⁻⁴ min⁻¹), single Ag₃PO₄ QDs (1.6 × 10⁻⁴ min⁻¹) as well as the mixture of the two (7.1 × 10⁻⁴ min⁻¹), suggesting a highly efficient photocatalyst. The in situ epitaxial growth strategy proposed here constitutes a novel example for fine construction of hetero-nanostructures for solar utilization.