Hydrothermal Treatment for Constructing K Doping and Surface Defects in g-C3N4 Nanosheets Promote Photocatalytic Hydrogen Production
Benefit from its exceptional visible light absorption,cost-effectiveness,outstanding stability,and non-toxic,gra-phitic carbon nitride(GCN)has emerged as an up-and-coming candidate for visible light photocatalysis.Despite these re-markable properties,the practical utilization of these materials as photocatalysts has been hindered by challenges,such as the high recombination rate of photogenerated charge carriers and limited active reaction sites owing to its inherently low surface area.Among the various strategies aimed at overcoming these limitations,controlled manipulation of morphology is recog-nized as an effective approach for enhancing the photocatalytic performance of carbon nitride.In this investigation,we em-ployed a hydrothermal treatment method involving potassium cyanate to modify pristine GCN,resulting in the production of carbon nitride nanosheets featuring surface defects,which we designate as CCN-m(with'm'representing the mass of potas-sium cyanate,while maintaining a constant usage of 2 g of GCN).Specifically,the GCN precursor,synthesized via the mel-amine condensation process at 550 ℃ for 3 h,was dispersed in a potassium cyanate solution using ultrasonication and stir-ring.The suspension was then placed in a Teflon-lined autoclave and maintained at 160 ℃ for 8 h.For the photocatalytic assessment,we utilized a Labsolar-6A test system from Perfeclight,employing a 300 W xenon lamp as the incident light source(with a cut-off filter at λ＞420 nm).Triethanolamine served as the sacrificial hole agent,and Pt was employed as the co-catalyst.This evaluation revealed that the post-modulation strategy substantially enhanced the photocatalytic capacity of GCN for H2 evolution.Notably,CCN-4 exhibited an impressive H2 evolution rate of 319.5 μmol·g-1·h-1,representing a sub-stantial 6.2 times increase compared to pristine GCN.Further characterization through scanning electron microscopy,trans-mission electron microscopy,and N2 adsorption-desorption isotherms indicated a reduction in the thickness of carbon nitride and the formation of mesopores,resulting in an increased number of surface reaction sites.X-ray diffraction patterns illus-trated a gradual decrease in the layer spacing of carbon nitride with an increasing amount of added potassium cyanate.Pho-tocurrent response,electrochemical impedance spectroscopy,room-temperature solid-state electron paramagnetic resonance(EPR)spectroscopy,and contact angle measurements collectively demonstrated that surface modification reduced interfacial charge transfer resistance and improved charge carrier separation efficiency.This study not only extends the research avenues for hydrothermal intercalation-exfoliation of graphitic carbon nitride but also offers valuable insights into the efficient syn-thesis of g-C3N4 nanosheets with surface defects.
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