Improved photocatalytic activities of g-C3N4 nanosheets by effectively trapping holes with halogen-induced surface polarization and 2,4-dichlorophenol decomposition mechanism

It is highly desired for g-C3N4 nanosheets as efficient photocatalysts to greatly enhance the photogenerated charge separation by trapping holes. Herein, it is clearly demonstrated mainly by means of the steady-state surface photovoltage spectra, the time-resolved surface photovoltage responses in N2 and the fluorescence spectra related to the produced [rad]OH amount that the modified chloride with a proper amount could effectively trap the photogenerated holes so as to greatly enhance the charge separation of g-C3N4, leading to the obviously-improved photocatalytic activities for degrading 2,4-dichlorophenol (2,4-DCP) and converting CO2 to CH4. Interestingly, similar positive effects on g-C3N4 are also confirmed after modification with other halogen anions, like Br− and F−, whereas the Cl− modifier is the best one. Although the used Cl− and Br− have different mechanism for capturing holes from the modified F−, it is concluded that it is feasible to greatly enhance the charge separation by the halogen-induced surface polarization. As excepted, the formed [rad]OH as the hole-modulated direct products could dominate the photocatalytic degradation of 2,4-DCP. Moreover, the possible decomposition mechanism closely related to [rad]OH attack is proposed through the detected main intermediates. This work will help us to well understand the importance to trap the photogenerated holes for efficient photocatalysis on g-C3N4, and also provide a feasible strategy to improve the photocatalytic activities of g-C3N4 for environmental remediation and energy production.