Theoretical Study On Removal Mechanism Of Methoxyphenol Pollutants From Atmosphere And Papermaking Wastewater

The use of biomass fuel brings opportunities to the development of new energy in the world,but also causes environmental problems that can not be ignored.A large number of methoxyphenols produced during the combustion and pyrolysis of biomass contain unsaturated carbon-carbon double bonds,which promote the oxidation reaction between them and oxidizing agents(such as OH radical,NO3 radical,Cl atom and O3)widely existing in the atmosphere to achieve degradation.Through the complex atmospheric chemical process,these compounds will lead to the formation of secondary organic aerosol(SOA),which will affect the entire atmospheric environment and then be harmful for human health.Methoxyphenols in the atmosphere enter the water through the process of drying and wetting sedimentation and water circulation,which may cause harm to aquatic organisms to a certain extent.Biomass is an important raw material in pulp and paper industry.A large amount of chloromethoxyphenol pollutants are produced in pulp bleaching process.Due to the serious environmental pollution caused by pulp bleaching wastewater,the removal of chloromethoxyphenols have become a research hotspot in recent years.In the nighttime atmosphere,NO3· is the main oxidant,and the reactivity of NO3·with methoxyphenol pollutants is similar to that of ·OH in the daytime.At present,studies on methoxyphenol pollutants with NO3·,an important nocturnal oxidant,are mainly focused on the kinetic level,with few explanations on the reaction mechanism.For the removal of chloromethoxyphenol pollutants in papermaking wastewater,the traditional physical,chemical methods and biochemical methods are common methods at present.Using new two-dimensional nanomaterials as photocatalysts for the removal of refractory organic pollutants has become a hot research topic in recent years.In this paper,the gas reaction of three methoxyphenol pollutants(guaiacol(GUA),4-methylguaiacol(4-MG)and 4-ethylguaiacol(4-EG))with NO3· were studied by density functional method,to reveal the oxidation degradation mechanism of these pollutants,and explore the effect of substituents on reaction activity.In addition,three novel two-dimensional nonmetallic nanomaterials were designed to study their photocatalytic mechanisms for the removal of chloromethoxyphenol pollutants from papermaking wastewater.The research results of this paper are as follows:(1)Oxidation and degradation of atmospheric methoxyphenols and its derivatives with NO3·NO3· addition and H abstraction are two major reaction channels for the initial reaction of three methoxyphenol pollutants with NO3·.The atmospheric life was 64 s?0.82 h and 0.19 h at 298 K,1 atm and typical tropospheric NO3· concentrations.Three methoxyphenols have a high reactive activity with NO3· at night,which should be considered in pollution source analysis and air pollution model research.The aquatic toxicity of methoxyphenol pollutants increases with the alkyl chain length,associated with the hydrophobicity of the compounds.The toxicity of degradation products is generally reduced,but nitrosubstituted products are still harmful and slightly toxic,so future experimental research and evaluation should be emphasized.(2)Effect of substituents on the reaction activity of aromatic compounds with NO3·The reactivity of NO3· with aromatic compounds(ACs)depends on the electronic properties of the substituents.The electron donating group promotes the reaction,and the electron withdrawing group inhibit the reaction.Oxidation reaction of NO3· and ACs is more likely in atmospheric water phase than in gas phase.Most of the ACs and their transformed products are harmful or even toxic to all three aquatic organisms(fish,green algae,and water fleas).Because NO3· are large amounts of oxidants in the nighttime atmosphere,they are essential in the chemical reactions of the atmosphere.(3)Photocatalytic degradation of chloromethoxyphenol pollutants in paper wastewaterWith the model compound of the main toxic substance in paper bleaching wastewater,the photocatalytic degradation mechanism of chloromethoxyphenols from paper wastewater with three new two dimensional nano materials(BCN?g-C3N4 and g-C2N)was studied.The results show that carbon doped BN nanosheets have excellent adsorption and catalytic properties,narrow band gap and are a promising photocatalyst for removing chloromethoxyphenols.The introduction of nonmetal atoms(B?P and S)reduces the band gap of g-C3N4 and g-C2N,leads to the delocalization of HOMO and LUMO and presents partial separation,thus increasing the mobility of the carrier.The nonmtal doped g-C3N4 and g-C2N showed significantly enhanced visible light absorption,absorption of methoxyphenol pollutants,and photocatalytic activity.