Study On Performance Of G-C₃N₄（Metal）/Gr/TiO₂ Z-scheme Photocatalysts For Degradation Of Inorganic Nitrogen In Water

Study and development of green and mild photocatalysis technology show great potential in solving nitrogen pollution.Z-Scheme heterojunction composites show great potential in photocatalytic removal of inorganic nitrogen.However,the selectivity of Z-Scheme photocatalysts for oxidizing ammonia nitrogen and reducing nitrate nitrogen still needs to be improved,and the reaction mechanism is still unclear.For the above problems,this thesis deposited the metals of Ag or Pd/Cu on the g-C₃N₄/Gr/Ti O₂Z-scheme photocatalytic system by photo-reduction method to achieve efficient removal of ammonia nitrogen and nitrate nitrogenin water.The structures and denitrification mechanisms of g-C₃N₄（Metal）/Gr/Ti O₂Z system materials were discussed.The research conclusions were as follows:1.The g-C₃N₄（Ag）/Gr/Ti O₂material was successfully prepared by sequential photo-reduction,electrostatic adsorption and hydrothermal synthesis processes.The optimal composition of the composite catalyst was determined by the photocatalytic degradation and mineralization of Rhodamine B（Rh B）,and the morphological structure,optical property,and photo-generated charge carrier separation performance of the material were characterized and analyzed.The results showed that the g-C₃N₄（5%Ag）/Gr/300%Ti O₂composite exhibited good photocatalytic performance for the degradation and mineralization of Rh B,the degradation efficiency reached 99.7%,and the removal efficiency of total organic carbon（TOC）was74.5%.This is because the silver nanoclusters deposited on g-C₃N₄accelerated the O₂reduction process,resulting in the efficient charge carrier separation efficiency of the Z-scheme photocatalyst.2.The g-C₃N₄（Ag）/Gr/Ti O₂Z-scheme photocatalytic material with optimal composition was used for the oxidation of ammonia nitrogen and the reduction of nitrate nitrogen under visible light irradiation.The performance of the g-C₃N₄（Ag）/Gr/Ti O₂composite on oxidizing ammonia nitrogen and reducing nitrate nitrogen were investigated.The effects of active species such as free radicals on the reaction process were analyzed,and the specific pathways and reaction mechanisms of photocatalytic oxidation of ammonia nitrogen and reduction of nitrate nitrogen were described.It was concluded that the catalyst deposited by single metal Ag can effectively inhibit the recombination of charge carriers,and then generate more·O₂^–to oxidize ammonia nitrogen,and the efficiency of catalytic oxidation of ammonia nitrogen reached 87.75%;And the strong built-in electric field generated by Ag promoted the reduction of nitrate nitrogen by photo-generated electrons,and the reduction efficiency was50.46%.3.Compared with g-C₃N₄（Ag）/Gr/Ti O₂material,the g-C₃N₄（Pd-Cu）/Gr/Ti O₂Z-scheme photocatalytic material was prepared for the oxidation of ammonia nitrogen and the reduction of nitrate nitrogen.And results showed that the degradability and selectivity of the material for ammonia nitrogen oxidation and nitrate nitrogen reduction were improved under the bimetal deposition system.The prepared materials were characterized and analyzed,and the reaction products were studied.The experimental results proved that,compared with single-metal materials,there was an electronic interaction between the bimetals,and the combined effect strengthened the selectivity of the degraded products.The g-C₃N₄（Pd-Cu）/Gr/Ti O₂Z-scheme heterojunction with bimetal deposition produced more active species to oxidize ammonia nitrogen and reduce nitrate nitrogen,The degradation efficiencies of ammonia nitrogen and nitrate nitrogen reached 95%and 57.78%within 4 h,respectively.Compared with g-C₃N₄（Ag）/Gr/Ti O₂,the bimetallic composite g-C₃N₄（Pd-Cu）/Gr/Ti O₂improved the removal efficiency of total nitrogen in ammonia nitrogen from 39.89%to 64.26%,the removal effeciency of total nitrogen in nitrate nitrogen increased from 11.7%to 20.1%.