Synthesis of TiO2/g-C3N4 nanocomposites with phosphate–oxygen functional bridges for improved photocatalytic activity

Abstract

One of the most general methods to enhance the separation of photogenerated carriers for g-C3N4 is to construct a suitable heterojunctional composite, according to the principle of matching energy levels. The interface contact in the fabricated nanocomposite greatly influences the charge transfer and separation so as to determine the final photocatalytic activities. However, the role of interface contact is often neglected, and is rarely reported to date. Hence, it is possible to further enhance the photocatalytic activity of g-C3N4-based nanocomposite by improving the interfacial connection. Herein, phosphate–oxygen (P–O) bridged TiO2/g-C3N4 nanocomposites were successfully synthesized using a simple wet chemical method, and the effects of the P–O functional bridges on the photogenerated charge separation and photocatalytic activity for pollutant degradation and CO2 reduction were investigated. The photocatalytic activity of g-C3N4 was greatly improved upon coupling with an appropriate amount of nanocrystalline TiO2, especially with P–O bridged TiO2. Atmosphere-controlled steady-state surface photovoltage spectroscopy and photoluminescence spectroscopy analyses revealed clearly the enhancement of photogenerated charge separation of g-C3N4 upon coupling with the P–O bridged TiO2, resulting from the built P–O bridges between TiO2 and g-C3N4 so as to promote effective transfer of excited electrons from g-C3N4 to TiO2. This enhancement was responsible for the improved photoactivity of the P–O bridged TiO2/g-C3N4 nanocomposite, which exhibited three-time photocatalytic activity enhancement for 2,4-dichlorophenol degradation and CO2 reduction compared with bare g-C3N4. Furthermore, radical-trapping experiments revealed that the OH species formed as hole-modulated direct intermediates dominated the photocatalytic degradation of 2,4-dichlorophenol. This work provides a feasible strategy for the design and synthesis of high-performance g-C3N4-based nanocomposite photocatalysts for pollutant degradation and CO2 reduction.