Peroxymonosulfate Activated By Metal Oxides For Catalytic Degradation Of Water Pollutants

With the development of industrialization,the living standards of people have been continuously improving,but the problem of water contamination has become more and more serious.Researchers have adopted methods such as adsorption,filtration or co-precipiation to cope with the water pollutant in various countries.In recent years,advanced oxidation processes of peroxymonosulfate(the main active material is HSO5-,PMS)activated by heat,ultraviolet light and transition metal oxides have gradually achieved wide attention in the environmental field.Among numerous activation approaches,transition metal oxides have attracted much attention due to their high catalytic activity and energy saving.However,there are still some problems in the process of PMS activation.For example,powder catalysts need the post-treatment after catalysis and are difficult to reuse,which is easy to cause secondary environmental pollution;the catalytic efficiency needs to be further improved,and it is necessary to prepare new catalytic materials.Therefore,two different systems are constructed to solve the above problems and detailed research contents are as follows:(1)Preparation of high performance ?-Fe2O3 nanodisk/bacterial cellulose membranes and their photocatalytic propertiesIn order to solve the problems of separation and reuse of the catalyst,a-Fe2O3 nanodisk/bacterial cellulose membranes as high-performance sulfate-radical-based visible light photocatalysts are synthesized for the first time.The bacterial cellulose with excellent mechanical stability and film-forming feature not only benefits the formation of a stable membrane to solve the separation and recycling problems but also helps disperse and accommodate a-Fe2O3 nanodisks.Thus,the visible light absorption performance can be enhanced,which is beneficial to improve the visible light degradation efficiency of PMS systems for dyes under both stirring and flowing states.Particularly,the optimized composite membrane photocatalyzes organic dyes under a flowing bed state for 84 h with the catalytic efficiency up to 100%and can be easily separated after the reaction,confirming its excellent catalytic performance and long-term stability.Even under varied flow rates(3-16 mL h-1),it can efficiently degrade rhodamine B and orange II.When the flow rate goes back from high to low,it can quickly recover the original performance,demonstrating the high activity and stability of a-Fe2O3/bacterial cellulose membrane.This part of the work shows that the construction of a-Fe2O3/bacterial cellulose membrane can effectively promote the catalytic efficiency of the whole system and solve the separation and recycling problem.(2)Preparation of high performance flower-like cobalt silicates and their catalytic mechanismFlower-like cobalt silicates(CoSiOx)are synthesized by controlling the adding amount of NH4Cl and the hydrothermal time in this part because there are a large quantity of hydroxyl groups on the surface of CoSiOx,which can act as active sites of the catalytic reaction to accelerate the degradation process.After controlling the morphology,CoSiOx has a flower-like structure clustered by small nanosheets with a high specific surface area(665.2 m2 g-1),which can fully expose the surface active sites during PMS activation,thus reduce the time of rate-limiting step in the process of PMS activation and activate PMS to generate active free radicals.50 ppm of methylene blue can be completely degraded within 9 min at room temperature using CoSiOx-10 as the catalyst with 0.2 g L-1 of PMS and the degradation rate can be up to 0.387 min-1.In addition,this catalyst exhibits excellent catalytic degradation performance under different conditions,suggesting the excellent universality.This is because there is a large amount of active singlet oxygen,which is not easily interfered by the background inorganic and organic substances in the water,in addition to the common effective sulfate radicals and hydroxyl radicals in the CoSiOx/PMS system.The work in this part proves that the controllable regulation of the catalyst morphology and the structural design can effectively improve the catalytic effect of the whole PMS system.