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21 Nanoscale Nanoscale Cite this: DOI: 10.1039/c0xx00000x www.rsc.org/xxxxxx Dynamic Article Links ? Review This journal is ? The Royal Society of Chemistry [year] [journal], [year], [vol], 00C00 |

2 1. Introduction Over the past decades, the growing awareness of environmental protection and energy conservation has stimulated intensive research on solar energy utilization.1 In the domain of pollutants elimination and solar energy conversion, semiconductor

5 photocatalysis has emerged as one of the most fascinating technologies2-5 . Nevertheless, the wide band gap and low solar- energy utilization efficiency remain the bottleneck of the photocatalysts to satisfy the requirement of applications in a practical way. For instance, the traditional TiO2 is limited for its

10 poor performances associated with visible light application. As a result, it is urgent to seek for efficient visible-light-driven (VLD) photocatalysts. For this objective, various modified TiO2 and TiO2-alternative photocatalysts have been fabricated.6-17 Currently, it is still a challenge to design new photocatalysts that

15 are abundant, stable and facile in fabrication besides high visible- light performance. In the search for robust and stable VLD semiconductor photocatalysts, a polymeric semiconductor, graphitic carbon nitride (g-C3N4), has recently attracted tremendous attention. The

20 heptazine ring structure and high condensation degree enable metal-free g-C3N4 to possess many advantages such as good physicochemical stability, as well as an appealing electronic structure combined with a medium-band gap (2.7 eV).18 These unique properties make g-C3N4 a promising candidate for visible

25 light photocatalytic applications utilizing solar energy. In addition, g-C3N4 is abundant and easily-prepared via one-step polymerization of cheap feedstocks like cyanamide,18,19 urea,20-22 thiourea,23,24 melamine 25-27 and dicyandiamide.28,29 Nevertheless, pure g-C3N4 suffers from shortcomings such as rapid

30 recombination of photo-generated electron-hole pairs, small specific surface area and low visible light utilization efficiency.21-

29 Consequently, the exploration of facile and dependable strategies to synthesize the modified g-C3N4-based photocatalysts with improved physicochemical properties and high

35 photocatalytic activities is of increasing requirement. The g-C3N4 has a unique two-dimensional layered structure, which is favorable for hybridizing with other components. Very recently, several approaches have been employed to enhance the visible light photocatalytic performance of g-C3N4, such as formation of

40 surface coupling hybridization utilizing TaON,30 Bi2WO6,31 graphene,32 construction of mesoporous structure,33 doping with metal or nonmetal species Fe,34 Ag,35 Au,36 Pd,37 S,38 B39 and P40 and sensitizing by organic dyes.41 Among these approaches, formation of heterostructures demonstrates a great potential to

45 promote the photocatalytic performance of g-C3N4 because the electronChole pairs can be efficiently separated, and charge carriers could transfer across the interface of the heterostructure to restrain the recombination. In a coupling process, g-C3N4 based heterostructures not only

50 can be formed by combining with visible light excited photocatalytic semiconductor materials with a narrow band gap such as CdS,42 Bi2WO3,43 BiOI44 ), but also can combine with UV excited photocatalysts with large band gap (such as as TiO2,45 ZnO,46 ZnWO4

47 ), which can largely broaden the application of