Template-free precursor-surface-etching route to porous, thin g-C3N4 nanosheets for enhancing photocatalytic reduction and oxidation activity

Metal-free graphitic carbon nitride (g-C3N4) has sparked considerable interest due to its efficient photocatalytic activity in many fields. Development of new tactics toward improving the photocatalytic performance of g-C3N4 remains active and challenging. In this study, we uncover an unprecedented template-free precursor (melamine) pre-treatment protocol to achieve porous g-C3N4 nanosheets for efficient photocatalytic reduction and oxidation reaction. The introduction of thiourea solution in the hydrothermal pre-treatment process etches the surface of melamine, thus yielding the porous, thin g-C3N4 nanosheets. The microstructure and porosity of g-C3N4 can be adjusted only by controlling the thiourea amount. The as-obtained porous g-C3N4 nanosheets are found to be endowed with not only increased specific surface area, but also enhanced photoabsorption in the visible light region. Systematic characterizations of the charge movement behavior (transient photocurrent, linear sweep voltammetry, electrochemical impedance spectra, photoluminescence and surface photovoltage spectroscopy) disclose that the separation of photogenerated charge carriers is remarkably boosted by fabricating such a porous nanosheet structure. Benefiting from these advantages, porous g-C3N4 nanosheets present profoundly enhanced visible-light photocatalytic performance for H-2 evolution (3.3-fold increase) and NO removal from the gaseous phase (5.5 times increase) in contrast to the pristine bulk g-C3N4. Our current study may offer an alternative approach to designing high-performance g-C3N4 nanomaterials for energy and environmental applications.