Chong Liu, a,b Chengming Li,a Xuedong Fu,aFazal Raziq,a Yang Qu, a and Liqiang Jing, a *

In this paper, the silicate-capped ZnO/g-C3N4 nanocomposites have been successfully fabricated by a simple wet chemical process. The photocatalytic activities of g-C3N4 for degradation of phenol and production of H2 are greatly enhanced after coupling with a proper amount of nanocrystalline ZnO. This is attributed to the prolonged lifetime and increased separation of photogenerated charges mainly based 10 on the atmosphere-controlled steady-state surface photovoltage spectra and the time-resolved surface photovoltage responses. Interestingly, the lifetime and separation of photogenerated charges are further improved after introducing silicate groups as linkers between ZnO and g-C3N4 , consequently leading to the enhanced photocatalytic activities, even 4 times high compared to g-C3N4 . Obviously, the built silicate linkers as bridges are much favorable for charge transfer and separation in the fabricated heterojunctional 15 nanocomposites and then for efficient photocatalysis. The present work provides with a simple and feasible idea to enhance the photogenerated charge separation so as to improve the photoactivities of nanocomposites.

Experimental Section

Photocatalytic activity measurements The photocatalytic activities of the samples were examined by 5 photocatalytic degradation of phenol and water splitting to produce H2 . In a typical liquid-phase photocatalytic experiment, a 150 W Xenon lamp was chosen as a light source, 0.1 g of photocatalyst and 20 mL of 10 mg/L phenol aqueous solution were mixed by stirring for 1h in an open glass reactor under light 10 irradiation. The distance between the light source and the reactor was 10 cm. After centrifugation, the phenol concentrations were analyzed by the 4-aminoantipyrine spectrophotometric method at the characteristic optical absorption (510 nm) of phenol with a Shimadzu UV-2550 spectrophotometer. 15 The photocatalytic experiment for hydrogen production was conducted in an inline hydrogen production system (AuLight, Beijing, CEL-SPH2N). Powder photocatalyst (0.1g) was suspended in a mixture of distilled water (80 mL), methanol (20 mL) and 1.0 wt % Pt from Pt(cod)2 in the reaction cell by using a 20 magnetic stirrer. Prior to the reaction, the mixture was deaerated by evacuation to remove O2 and CO2 dissolved in water. The reaction was carried out by irradiating the mixture with light from a xenon lamp (300 W). Gas evolution was observed under photoradiation, being analyzed by an inline gas chromatograph 25 .

Conclusions 

In this work, it is demonstrated that the separation of photogenerated charges of g-C3N4 is enhanced by coupling with a proper amount of nanocrystalline ZnO, leading to the enhanced photocatalytic activities for degrading phenol and producing H2 . 85 Interestingly, it is concluded for the first time that the introduction of silicate bridge in the fabricated ZnO/g-C3N4 nanocomposite is much favourable for charge transfer and separation, well responsible for the higher photocatalytic activity of silicate-bridged ZnO/g-C3N4 nanocomposite than that of ZnO/g-C3N4 one, even 4 times high compared with g-C3N4 90 . Therefore, it is suggested that the built bridges with silicate groups are beneficial to improve the heterojunctional connection situation between different constituents so as to enhance the photocatalytic performance. This would provide with a feasible 95 strategy to design and synthesize high-performance nanocomposite photocatalysts for degrading pollutants and water splitting. 

Acknowledgements 

This work was supported by the NSFC (U1401245), the National 100 Key Basic Research Program of China (2014CB660814), the Program for Innovative Research Team in Chinese Universities (IRT1237), the Research Project of Chinese Ministry of Education (213011A), the Specialized Research Fund for the Doctoral Program of Higher Education (20122301110002), the 105 Natural Science Fundation of Heilongjiang Province for Youths (QC2012C077), and the Science Foundation for Excellent Youth of Harbin City of China (2014RFYXJ002).