1. IntroductionIntensive research o

1. Introduction
Intensive research on carbon nitride materials has been arisen since the prediction drawn by Liu and Cohen that carbon nitrides have potential to be the ultrahard materials [1]. With a wealth of attractive properties such as reliable chemical and thermal endurance, super hardness, low density, wear resistance, water resistivity and biocompatibility, carbon nitrides become one of the most promising materials for surface modification, light emitting device, photocatalysis, etc. [2], [3] and [4]. Among various analogs, graphitic carbon nitride (g-C3N4) constructed via tri-s-triazine units is considered as the most stable allotrope in ambient environment.

To date, search suitable new energy resources as well as pollution-degradation strategies become significant important to solve the energy crisis and environmental problems. With outstanding merits including pollution-free and inexhaustible supply, solar light is believed as the most ideal routines to resolve the energy crisis and pollution-disposing power. However, low energy conversion efficiency still restricts its further development. Therefore, carbon nitrides, an analog of graphite with special electronic properties, have been a candidate of new photocatalyst in recent years. Large number of studies has been carried out on the synthesis and application of g-C3N4 as metal-free catalyst due to its medium band gap structure [5]. Inspiring works have been reported to successfully achieve g-C3N4 as photocatalyst for water-splitting, opening up a new gate of research on its photocatalytic performance [2].

The lone pair of nitrogen endows the tri-s-triazine tectonic units with special electronic structure [6], so does the 2-D π layer structure of g-C3N4 constructed by tri-s-triazine. As an n-type semiconductor, the tunable band gap of g-C3N4 provides a flexible channel not only to achieve both controllable lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO), which significantly affects the photoelectronic performance of g-C3N4 as a functional layer, but also to simplify the modification process mainly by elemental doping or heterojunctions structure construction coupling with other semiconductor, further broadening its application range.

Generally, various morphologies can be obtained flexibly by template modeling. Among them, mesoporous graphite carbon nitride (mpg-C3N4) with large internal surface area and intrinsic properties is a suitable host material for semiconductor, a representative application with immobile metal nanoparticles to constructed heterojunctions semiconductor was summarized recently [7]. In addition, basing on the optical modification along with binding with specific guest via functional group (single bondNHsingle bond, double bond; length as m-dashNsingle bond, single bondNH2) exist on the surface of g-C3N4, high optical sensitivity can be obtained benefit from numerous functional group bringing by large internal surface, which can be applied as optical sensors [8], [9] and [10].

In this review, we firstly discuss the electronic structure of g-C3N4. Secondly, we aim to summarize the application of g-C3N4 ranging from photocatalytic to photoelectronic base on its unique electronic properties. Finally, relationship between photocatalytic and photoelectronic properties is tried to construct with providing the pathway to modified electronic structure of g-C3N4 for enhancing the performance on its photoelectronic properties.

Kết quả (Việt) 1:

1. giới thiệuCác nghiên cứu chuyên sâu về cacbon nitrua tài liệu đã được phát sinh từ dự báo rút ra bởi lưu và Cohen cacbon nitrit có tiềm năng để là các tài liệu ultrahard [1]. Với một sự giàu có của các tài sản hấp dẫn như hóa chất đáng tin cậy và độ bền nhiệt, siêu độ cứng, mật độ thấp, mặc sức đề kháng, điện trở suất nước và biocompatibility, cacbon nitrit trở thành một trong các tài liệu hứa hẹn nhất để sửa đổi bề mặt, ánh sáng phát ra thiết bị, photocatalysis, vv [2], [3] và [4]. Trong số các chất thay bữa nhất, graphitic cacbon nitrua (g-C3N4) xây dựng thông qua đơn vị tri-s-triazine được coi là ôzon ổn định nhất trong môi trường xung quanh.To date, search suitable new energy resources as well as pollution-degradation strategies become significant important to solve the energy crisis and environmental problems. With outstanding merits including pollution-free and inexhaustible supply, solar light is believed as the most ideal routines to resolve the energy crisis and pollution-disposing power. However, low energy conversion efficiency still restricts its further development. Therefore, carbon nitrides, an analog of graphite with special electronic properties, have been a candidate of new photocatalyst in recent years. Large number of studies has been carried out on the synthesis and application of g-C3N4 as metal-free catalyst due to its medium band gap structure [5]. Inspiring works have been reported to successfully achieve g-C3N4 as photocatalyst for water-splitting, opening up a new gate of research on its photocatalytic performance [2].The lone pair of nitrogen endows the tri-s-triazine tectonic units with special electronic structure [6], so does the 2-D π layer structure of g-C3N4 constructed by tri-s-triazine. As an n-type semiconductor, the tunable band gap of g-C3N4 provides a flexible channel not only to achieve both controllable lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO), which significantly affects the photoelectronic performance of g-C3N4 as a functional layer, but also to simplify the modification process mainly by elemental doping or heterojunctions structure construction coupling with other semiconductor, further broadening its application range.
Generally, various morphologies can be obtained flexibly by template modeling. Among them, mesoporous graphite carbon nitride (mpg-C3N4) with large internal surface area and intrinsic properties is a suitable host material for semiconductor, a representative application with immobile metal nanoparticles to constructed heterojunctions semiconductor was summarized recently [7]. In addition, basing on the optical modification along with binding with specific guest via functional group (single bondNHsingle bond, double bond; length as m-dashNsingle bond, single bondNH2) exist on the surface of g-C3N4, high optical sensitivity can be obtained benefit from numerous functional group bringing by large internal surface, which can be applied as optical sensors [8], [9] and [10].

In this review, we firstly discuss the electronic structure of g-C3N4. Secondly, we aim to summarize the application of g-C3N4 ranging from photocatalytic to photoelectronic base on its unique electronic properties. Finally, relationship between photocatalytic and photoelectronic properties is tried to construct with providing the pathway to modified electronic structure of g-C3N4 for enhancing the performance on its photoelectronic properties.