Research On The Removal Of Organic Pollutants In Water By Modified Perovskite Photocatalyst

With the continuous development of economy and industrialization,more and more pollutants are discharged into water,causing harm to water environment and aquatic life.Organic dyes are one of the most pollutants in water during textile dyeing,agriculture,and pharmaceutical industrial processes etc.Therefore,dyes and antibiotics are regarded as the important organic pollutant in water due to their difficulty in processing and high residue levels.These toxic organic pollutants could not be removed efficiently by traditional water treatment technologies,so more effective treatment technology is needed to completely remove these refractory pollutants.Advanced oxidation technology with high oxidation efficiency and non-selectivity for pollutants,is widely studied in recent years.Photocatalysis is one kind of new environmentally friendly wastewater treatment technology among them,which main principle is using semiconductor irradiated by solar light for purification of water.Therefore,photocatalytic technology has attracted more and more attention due to its advantages of high treatment efficiency and no secondary pollution,and has been developing vigorously in the field of environmental science.Perovskite ABO3 powder is a research hotspot in the field of photocatalysis due to its multi-variable gap width and potential for efficient use of sunlight.The main problems addressed in this paper are the low separation efficiency,poor degradation effect and lack of efficient visible light response of the photogenic electrons in the single phase ABO3 powder.First,LaNiO3 composite oxide with relatively high photocatalytic activity was selected to improve its quantum efficiency and expand the visible light response range by means of semiconductor composite and element substitution.Then,the photocatalytic activity of the modified catalysts was studied and the photocatalytic mechanism under different conditions was investigated.The main conclusions of the study are as follows:1.Among perovskite LaBO3(B=Fe,Co,Ni)which were synthesized by sol-gel method,LaNiO3 has stronger visible light absorption and methyl orange degradation rate,which proves that the photocatalytic activity of ABO3 to degrade organic pollutants has positive correlation with both its absorption efficiency of visible light and electronegative size of metal ions at B position.During the preparation of ANiO3(A=La,Ce,Pr,Gd)with a rare earth element at the A site,experimental results show that the tolerance factor ??[0.75,1]cannot be used as a necessary and sufficient condition for the synthesis of cubic ABO3.Non-lanthanum rare earth elements are more inclined to generate high-valent oxides under atmospheric air calcination,which may be related to the number of electrons in the outer layer.The 4f electron layers of the+3 valence ions of Ce and Pr both have unpaired electrons and cannot form a single phase stable structure.At the same time,the influence of the amount of n(La3+)/n(Ni3+)on the structure and photocatalytic performance of LaNiO3 was explored.Experiments show that the excess Ni has no effect on the main structure of LaNiO3,but will reduce its photocatalytic capacity.The reason is that Ni2+ ions cannot serve as active sites for photocatalytic reactions,but can increase the probability of reaction between organic pollutants and the active center of the catalyst through adsorption.2.The calcination temperature in the one-step synthesis of LaNiO3/TiO2 plays a key role in the formation of the catalyst structure and catalytic performance.The sample at 700? has the smallest particle size and highest photocatalytic activity.With the decrease of the calcination temperature,LaNiO3 cannot be formed,the main component of the catalyst is NiO,the particle size is large,and the photocatalytic performance is poor.When the calcination temperature is higher than 700?,the particle size of the LaNiO3/TiO2 composite increases,and the the photocatalytic capacity of orange again decreased.Using active species quenching experiments to determine that OH and ·O2-are the main active species produced in the photocatalytic system,and proposed the mechanism of the LaNiO3/TiO2 heterojunction interface.The formation of step-scheme heterojunction structure will not only improve the efficiency of photogenic electron hole separation,but also hinder the growth and agglomeration of grains,leading to the reduction of particle size,thus shortening the transfer path of photogenic electrons from the semiconductor interior to the surface.The photocatalytic activity was still higher after the catalyst was loaded onto the surface of different supports,and the degradation efficiency was positively correlated with the surface area of supports.3.After the A-site element is partially substituted in LaNiO3,the Ce-substituted catalyst has the highest photocatalytic activity.With the increase of the substitution ratio,the photocatalytic degradation efficiency of the catalyst does not promote significantly,but the content of CeO2-x increases accordingly.The adsorption amount of the catalyst to norfloxacin was positively correlated with the amount of CeO2-x.Compared with pure LaNiO3,Ce substituted samples have smaller grain size and higher photocatalytic activity.The structure of LaNiO3 with single substitution of element B is more stable,and the catalyst with the substitution of Cu element has the highest photocatalytic activity.With the increase of substitution ratio,the impurity phase appears,and the photocatalytic activity of the catalyst decreases.By co-doping Ce/Cu into LaNiO3,the activity of the prepared catalyst was stronger than that of the single substitute catalyst.The degradation rates of Lao.9Ce0.1Ni0.9Cu0.1O3 were 2 times,1.52 times and 1.36 times that of LaNiO3,La0.9Ce0.1NiO3 and LaNio.9Cu0.1O3,respectively,which proved that double substitution had superposition effect on the enhancement of LaNiO3 photocatalytic activity.