A nine-fold enhancement of visible-light photocatalytic hydrogen production of g-C(3)N(4) with TCNQ by forming a conjugated structure

Photocatalytic hydrogen evolution by water splitting has become a very effective way to solve the energy crisis. For use in that process, graphitic carbon nitride (g-C(3)N(4)) has drawn much attention for its response in the visible region. However, its insufficient sunlight absorption efficiency and easy recombination of photoinduced carriers restrict its photocatalytic activity. Herein, we demonstrate a two-step liquid ultrasonic method in water to synthesize a series of tetracyanoquinodimethane (TCNQ)–C(3)N(4) photocatalysts aiming to form a conjugated structure by 7,7,8,8-TCNQ. g-C(3)N(4) was treated with APTES firstly on its surface in order to give a better interface contact with TCNQ. Benefiting from the conjugation effect between TCNQ and g-C(3)N(4), the separation and transport efficiency of photogenerated carriers were significantly improved. Besides, introducing TCNQ also broadened the absorption region. Both of these points lead to the enhancement of photocatalytic H(2) production rate, with the optimized 5% TCNQ–C(3)N(4) giving a rate nearly 9.48 times that of pure g-C(3)N(4). Also, 5% TCNQ–C(3)N(4) (U) was prepared with unmodified g-C(3)N(4), which exhibited a rate only 6.87 times that of pure g-C(3)N(4), thus validating the necessity of surface modification. Our work reveals that the rational conjugated structure could modulate the electrical and optical properties of g-C(3)N(4), yielding an improvement of photocatalytic activities.