Study On Removal Of Pollutants In Water By Photocatalytic Composites System

In recent years,water pollution has become serious gradually,and it has begun to seriously threaten human living environment.At present,there are many methods for treating sewage,like physical method,biological treatment method,and chemical method.Among many water treatment technologies,photocatalytic technology is a novel treatment technology which attracts wide attention.Photocatalysts rely on the sunlight absorbed from nature to excite active species such as electrons and holes,and then degrades pollutants in water.However,with the low concentration of pollutants in water,the concentration of photocatalytic degradation will become lower during the degradation process,so the photocatalytic degradation rate will slow down,and the pollutants cannot be completely removed.Therefore,this article attempts to combinate photocatalysis with other technologies to promote the removal of pollutants and focuses on the photocatalysis-adsorption and photocatalysis-photothermal synergetic effect.This article will solve the problems in photocatalysis from the following two aspects:?1?Design a photocatalytic-adsorption composite system,and fix C₃N₄ on a commercial melamine resin foam with rich pore structure to improve the utilization of sunlight,which is beneficial for the material transport in the reaction process,and apply the material to the removal of organic pollutants in flowing water.?2?Build a photocatalytic-photothermal synergetic system,using a large number of reducing groups and reaction sites on the surface of the two-dimensional photothermal material Ti₃C₂T_x and photon electron to remove heavy organic ions in water.And hole and reactive oxygen species produced in photocatalysis reaction are used to degrade organics in the water phase.In addition,photothermal can effectively condense reactants and promote the chemical reactions.The main research contents of this article are:?1?Photocatalytic-adsorption composite system for organic pollutants in waterUrea and graphene oxide?GO?are used as raw materials,and the C₃N₄/GO composite is grown in situ on a melamine resin foam with rich porous structure during heat treatment.This material can effectively reduce the accumulation of C₃N₄ powder,whose specific surface area is 111.1 m²/g,and the pore volume is 0.44 cm³/g,which is conducive to mass transfer,enhances the contact between the catalytic active center and the pollutant,and promotes photocatalysis.In addition,GO can be used as a bridge to increase the loading area of C₃N₄,which can facilitate the separation of photo-generated carriers and promote the progress of photocatalysis.The bond between C₃N₄ and GO,GO and MF makes it difficult for photocatalyst and GO fall off from MF skeleton,which is beneficial to the reuse of catalyst.The material still exerts good photocatalytic-adsorption activity fot removing pollutant effect after 6 cycles.The two effects show a good synergic function,which is mainly reflected in the following:photocatalysis can continuously degrade the pollutants adsorbed on the surface of the material,causing the adsorption to regenerate,leding to the adsorption process to continue.While adsorption facilitates the migration of pollutants to the catalyst,making organic matter is rapidly degraded,thereby promoting the progress of photocatalysis.In addition,the intermediates generated during the photocatalytic process will be completely degraded by photocatalysis due to the adsorption effect in reaction,so as to avoid secondary pollution.?2?Synergistic effect of photocatalytic-photothermal system for silver ion recovery and degradation of organic pollutants in water.Two-dimensional layered material Ti₃C₂T_x is prepared by solvent intercalation method.The material has excellent photothermal properties,which can efficiently condense pollutants,and photothermal causes the system temperature to rise.Besides,the chemical reactions rate increase as well.In addition,silver ions in the solution are gradually reduced to the surface of the material during the reaction.Due to the reduce of silver,the light absorption of the material is enhanced and the capture of light energy is improved.Silver has good electrical conductivity and is conducive to the carriers transfer during the reaction.And the material's hydrophilicity is constantly enhanced,the surface energy is also improved.In order to reduce the surface energy to a stable state,the material is more likely to adsorb pollutants from surrounding solution,which is beneficial to the contact of the photocatalytic reaction sites with the pollutants.The reduction of silver can effectively enhance the light-to-heat conversion capacity of the material.Under the same lighting conditions,the material after recovering silver has a higher surface temperature.Infrared thermal imaging results show that the material after reducing silver?55.8 ^oC?is 2.9 ^oC higher than TCM within 300 s.In addition,the light-vapor conversion efficiency of Ag/TCM-5 is 80.98%,which is higher than TCM?77.21%?.It indicates that the reduction of silver can effectively promote the photo-thermal conversion.Compared with pure photocatalysis,the system shows significant photocatalytic-photothermal synergistic performance in removing pollutants.In the Ag/TCM-5 system,the 100%silver is recoveryed in 150 minutes.Without photocatalysis and photothermal effects,it is difficult to remove all metal ions only by the reducing groups on the TCM surface.In addition,the pseudo-first-order kinetic constant(0.0333 min^-1)of the degradation of RhB by the Ag/TCM-5 is 9.25 times that of the pure photocatalytic system which is TCM?25 ^oC?(0.0036 min^-1)and 4.56 times of TCM without silver(0.0073 min^-1).It shows that the recovery of silver effectively promotes photocatalytic degradation of organics.In this reaction system,on the one hand,photothermal effect accelerates the rate of silver reduction and the degradation of organics,and promotes the generation and migration of photo-generated carriers.On the other hand,the electrons generated by photocatalysis accelerate the reduction of silver ions to substance,thereby improving the capture of light energy by the material and indirectly promoting the progress of photothermal reaction.