The Research On Photocatalytic Performance And Mechanism Of Modified Graphite Phase Carbon Nitride And Its Composites

With the rapid development of population and industrialization,the rapid consumption of fossil energy and serious environmental pollution limit the survival and development of human beings.In order to solve environmental problems and energy crisis,it is urgent to develop green and sustainable energy.As a kind of clean energy,solar energy has attracted much attention.How to use solar energy efficiently has become a big problem.Photocatalysis technology can reach the conversion of solar energy to chemical energy,it can be used to degrade organic pollutants to deal with environmental pollution.It can also be used in energy development to alleviate the energy crisis.As a potential photocatalyst,graphitic carbon nitride（g-C₃N₄）has attracted much attention due to its advantages such as good stability,suitable band gap,adjustable electronic structure,and band structure.However,g-C₃N₄also has some obvious shortcomings,such as a small specific surface area,high photogenic electron and hole recombination rate,and small visible light absorption range.Therefore,how to improve the photocatalytic activity of g-C₃N₄is the focus of current research.In this paper,a novel photocatalyst-modified g-C₃N₄was prepared by morphological regulation,heterojunction construction,and defect engineering,and its photocatalytic activity was evaluated by applying it to the photocatalytic degradation of antibiotics and the production of hydrogen peroxide（H₂O₂）.In addition,the microstructure,morphological characteristics,and photochemical properties of the synthesized samples were systematically investigated,and the mechanism of the photocatalytic reaction was described.The main research content of this paper is as follows:1.Well-designed MXene-derived Carbon-doped TiO₂coupled porous g-C₃N₄to enhance the degradation of ciprofloxacin hydrochloride under visible light irradiationIn this study,a novel S-scheme heterojunction composite g-C₃N₄/C-TiO₂was prepared by one-step calcination using melamine and MXene powder as precursors and NH₄Cl as templates..The gas generated during the calcination process not only strips the massive g-C₃N₄into a porous structure with a larger surface area but also strips the aggregated MXene-derived carbon-doped titanium dioxide（C-TiO₂）into smaller particles,making the two materials bond more closely.In addition,due to the increase of the specific surface area of the sample and the formation of S-scheme heterojunction,the reactive sites on the surface of the photocatalyst were increased,and the separation efficiency of photogenerated electrons and holes was also improved,thus increasing the photocatalytic activity of the sample.Within 50 minutes,the degradation rate of ciprofloxacin hydrochloride（CIP·HCl）by g-C₃N₄/C-TiO₂reached 88.14%under the visible light（λ≥420 nm）,which is 8.9 times higher than that of pure g-C₃N₄.Finally,the properties of the photocatalysts and the mechanism of photocatalytic reaction were investigated through a series of characterizations,and the possible degradation path of ciprofloxacin was deduced.2.Synthesis of double defects in g-C₃N₄to enhance the H₂O₂production by dual-electronO₂reductionIn this work,g-C₃N₄nanosheets（N₂-SCN-4）with-C≡N defects and S-defects are constructed by calcination using guanidine carbonate and trithiocyanic acid as precursors.Under the visible light（λ≥420 nm）,the N₂-SCN-4 production efficiency of hydrogen peroxide reached 1423.3μmol·g^-1·h^-1,which is 15.4 times higher than the original g-C₃N₄.The introduced-C≡N defects can promote the adsorption of H⁺,and the S-defects provide the active center for the adsorption and activation ofO₂.In addition,the morphology,structure,and photochemical properties of the samples were investigated through a series of characterizations,and the mechanism and selectivity of photocatalytic hydrogen peroxide production were discussed in detail.The photogenic charge separation efficiency and the selectivity of double electron oxygen reduction（ORR）are improved by the introduction of double defects.This work provides a way to improve the activity of photocatalysts.