Research On The Photocatalytic Performance Of G-C₃N₄/BiOX（X=Cl,Br,I） Nanocomposite

Environmental pollution and energy shortages have caused widespread concern.Graphite-like carbon nitride（g-C₃N₄）has attracted attention as a new organic photocatalyst.However,pure g-C₃N₄ has low specific surface area and high electron-hole recombination rate,which restricts its performance improvement.Bismuth oxyhalide（Bi OX）shows excellent adaptability.After discussing the basic theory of g-C₃N₄/Bi OX,cetyltrimethylammonium bromide（CTAB）was used to modify g-C₃N₄ to prepare modified BCN.After that,BCN and oxygen vacancy BiOI were combined to construct BCN/BiOI heterojunction materials.XRD,SEM,TEM,EPR,PL and other methods were used to study the composition,morphology,energy band structure,and performance of photocatalytic hydrogen production and pollutant degradation of the samples,to reveal the internal mechanism of the improvement of its photocatalytic performance.The research status of g-C₃N₄/Bi OX was systematically discussed in detail from the aspects of preparation method,structure mechanism and application field.It reveals the structural characteristics of g-C₃N₄/Bi OX and its shortcomings in hydrogen production and pollutant degradation.The advantages and disadvantages of preparation methods such as hydrothermal method,hydrolysis method,electrospinning method and self-assembly method were compared.The mechanism characteristics of photoelectric charge transport in Type II,direct Z-type heterojunction and indirect Z-type heterojunction were analyzed.The application prospects and shortcomings of the g-C₃N₄/Bi OX composite photocatalytic material in the fields of pollutant degradation,CO₂ reduction,hydrogen production and so on were discussed.The modified g-C₃N₄（BCN）was prepared by hydrothermal method.The modified BCN showed a higher hydrogen production rate than pure g-C₃N₄,and the hydrogen production rate of BCN-3 could reach 690.2μmol h^-1g^-1,which was 3.2 times that of pure g-C₃N₄,greatly improved the photocatalytic efficiency of g-C₃N₄.The results of its morphology,band structure and photocurrent response show that the light absorption range of BCN was slightly reduced due to the size effect.However,the increase of conduction band position is conducive to the capture of photogenerated electrons by surface water molecules.The enhancement of photocurrent response indicated that the charge transfer efficiency of BCN is improved.It is found that the fundamental reason for the improvement of photocatalytic efficiency is that the enhancement of light absorption ability due to the improvement of band gap.BCN/V_o-BiOI composite photocatalytic materials were prepared by hydrolysis method.In the experiment of degrading tetracycline hydrochloride（TC）,the degradation effect of a series of BCN/V_o-BiOI composite catalysts were significantly improved.BCN/V_o-BiOI-20 showed the best performance with the degradation rate up to 0.01896 min^-1,which was 2.3 and 1.9 times that of pure g-C₃N₄ and pure BiOI,respectively.It can be observed by SEM that the V_o-BiOI in the BCN/V_o-BiOI-20 heterojunction is uniformly loaded on the BCN,which is conducive to the transfer of interface charges.The existence of oxygen vacancies（OVs）were detected in ESR.The weak photoluminescence intensity indicated that the carrier recombination rate was low.The detection of hydroxyl radicals（·OH）and superoxide radicals（·O₂^-）proved that the synthesized material had a Z-type heterojunction structure,which was beneficial to the separation and transport of photogenerated charges in the interface.Based on this,the catalytic reaction mechanism of BCN/V_o-BiOI-20 composites in the degradation process of TC was proposed.