Study On Preparation Of Organic Conjugated Photocatalyst And Its Removal Of Pollutants In Water

The excessive use of coal,oil,and natural gas has caused serious consequences such as environmental pollution and resource depletion that humans cannot ignore.Traditional solutions to environmental pollution problems have limited their applications because of high energy consumption and secondary pollution.Therefore,it is imperative to find new technologies or materials to solve this problem.The rise of photocatalytic technology has met people’s needs to a certain extent,but many photocatalysts have inefficient absorption and utilization of visible light and insufficient light response capabilities.Therefore,it is of great significance to find materials with high catalytic efficiency.Organic conjugate materials have attracted researchers in photocatalytic degradation,hydrogen production,and adsorption due to their excellent light response capabilities,suitable forbidden band width,excellent physical and chemical stability,and precise adjustment of the skeleton structure.However,the effect of some polymer materials after synthesis is not satisfactory,which requires us to find ways to introduce characteristic groups to modify and improve their performance.In this dissertation,the degradation of tetracycline and norfloxacin in aqueous solution based on the Schiff base reaction based on the condensation of different aldol monomer materials as a photocatalyst was studied in three aspects.(1)Two new polymers,BTTh-1 and BTTh-2,were designed and synthesized.They are made by reacting two aldehyde units with melamine.Both aldehyde units are based on o-phenylenediamine.The difference between the final aldehyde units is that thiophene groups are introduced into the aldehyde monomer units of BTTh-2.Through the introduction of thiophene units,the differences between the two materials in the photocatalytic degradation of tetracycline were explored,and characterization experiments proved that the materials were successfully prepared,and the degradation mechanism was studied.It was found that the degradation efficiency of BTTh-2 for tetracycline(90.9%)was much higher than that of BTTh-1(40.7%).Through characterization results,we found that BTTh-2 has stronger charge separation ability and faster transmission rate.In addition,after photoexcitation,the recombination ability of photo-generated holes and electrons is weak,and it has a stronger ability to absorb and use visible light,a narrower forbidden band width,and better thermal stability.(2)Six polymers such as ThTA-1,ThTA-2,ThTA-3 and BATA-1,BATA-2,BATA-3 are prepared with 4,4 ’,4’ ’-(1,3,5-triazine-2,4,6-triyl)triphenylamine as an amine unit,2,5-thiophenedicarboxaldehyde,thieno[3,2-b]thiophene-2,5-dicarbaldehyde,dithieno[3,2-b:2’,3’-d]thiophene-2,6-dicarbaldehyde and terephthalaldehyde,4,4’-biphenyldialdehyde,1,4-bis(4-aldehyde phenyl)benzene,etc.For materials of ThTAs series,in the degradation experiment of tetracycline aqueous solution,increasing the number of thiophene in the polymerized monomer can effectively improve the degradation of the polymer under visible light,and can obtain a better morphology,specifically,the degradation efficiency of ThTA-1,ThTA-2,and ThTA-3 is 50.1%,68.8%,and 91.6%,respectively;and the degradation tendency of norfloxacin in this series of materials is similar,57.9,75.1 and 86.8%,respectively.For BATA series materials,increasing the number of biphenyl rings in the polymerized monomer will decrease the catalytic efficiency,specifically,from BATA-1,BATA-2 to BATA-3,the degradation efficiency of the tetracycline aqueous solution was reduced from 74.2% to49.7%,until 29.6%;and this series of materials have no degradation effect on norfloxacin solution.The effects of increasing the number of thiophene and biphenyl ring groups on the photocatalytic performance of polymers were investigated by testing diffuse light absorption,photocurrent response,AC impedance,specific surface area,fluorescence,and thermal stability.Specifically,ThTA-3 containing three thiothiophene group monomers or BATA-1 with a benzene ring unit monomer has relatively strong photo-charged charge carrier separation and transmission capabilities under light stimulation.And the ability to absorb and use visible light is higher,the morphology is better,and the thermal stability is better.(3)Three polymers such as ThME-1,ThME-2,ThME-3 are prepared with melamine as an amine unit,2,5-thiophenedicarboxaldehyde,thieno[3,2-b]thiophene-2,5-dicarbaldehyde,dithieno[3,2-b:2’,3’-d]thiophene-2,6-dicarbaldehyde.The experimental results of degradation of tetracycline and norfloxacin aqueous solution show that the polymer ThME-3 containing three thiothiophene units in the polymerization monomer has the best photocatalytic efficiency for the target pollutant under visible light.For tetracycline,the degradation rates under the action of ThME-1,ThME-2,and ThME-3 were 20.4%,58.1%,and 73.7%,respectively.Moreover,the degradation trend of norfloxacin is also the same,which can reach 32.2%,46.4% and 56.9% under the action of the three catalysts,respectively.A series of tests explored the effect of an increase in the number of thiophene groups on the photocatalytic performance of its polymers.This result trend is consistent with the degradation trend of ThTAs series polymers.Specifically,ThME-3containing three thiothiophene monomers has a relatively strong photo-charged charge carrier separation and transmission ability under the stimulation of light.In addition,the absorption and utilization of visible light is higher,and the forbidden band width is also narrower.