Persulfate And Dissolved Oxygen Activation By Single-atom Zinc Catalysts For The Removal Of Aqueous Organic Contaminants

With the development of social and economy,various emerging contaminants have emerged,which brings new challenges to water quality safety and security.Therefore,efficient water treatment technology is the key to water pollution prevention and control.Dpersulphate advance oxidation technology has a promising application in the field of new pollutant removal from water environment,as the reaction process can generate strong oxidative reactive oxygen species.Currently,the construction of new and efficient heterogeneous catalytic systems is the main research direction for persulphate oxidation technology,the core of which lies in the de-sign and synthesis of highly active and stable catalysts.Compared with conventional persulfate activation catalysts,single-atom catalysts with high metal atom efficiency,unique ligand envi-ronment and strong metal carrier interaction have shown excellent catalytic performance in the activation of persulfate,and rapidly becoming a research hotspot in the field of water treatment.However,currently reported single-atom catalysts central metal for persulfate activation mainly based on conventional transition metals with completely occupied 3d electron orbitals,such as iron（Fe）,cobalt（Co）,manganese（Mn）and copper（Cu）elements,whose leaching during the catalytic reaction may be potentially harmful to the environment.Meanwhile,persulphate acti-vation reactions usually require the addition of high concentrations of persulphate,which not only increases resource consumption but also results in large amounts of sulphate ions(SO₄^2-)remaining in the solution after the reaction.In addition,dissolved oxygen（DO）,a natural green oxidant commonly found in water,has been shown to be involved in the formation of reactive oxygen species during persulphate activation,but its contribution to pollutant removal is rela-tively limited.To address those issues,in this thesis,two single-atom zinc catalysts were syn-thesised using an intrinsically inert zinc element with fully occupied 3d electron orbitals as the metal centre,to investigate their efficacy and mechanism of activating persulfate and DO for the removal of organic pollutants from water,and to investigate their potential for practical wastewater treatment applications.The main studies include:A high-loading and low-valence zinc single-atom catalyst efficiently activate peroxodisul-phate（PDS）and dissolved oxygen（DO）to degrade the organic pollutants in water.The mono-atomic zinc catalyst(Zn_SA-N-C)was prepared by secondary calcination.A series of characteri-sation results confirmed the successful synthesis of monoatomic Zn catalysts with both Zn-N₄and Zn-N₃ coordination structures.The formation of the Zn-N₃ coordination configuration gives the zinc atom more free delocalized electrons around the catalyst,enhancing the interaction with the PDS and the contaminant.As a result,the Zn_SA-N-C catalyst exhibits limited activation of dissolved oxygen,requiring the addition of PDS to enhance contaminant removal,with an activation PDS ratio activation of 0.11 L min^-1 m^-2,much higher than the currently reported activated PDS or PMS single-atom.The experimental results showed that the strong adsorption of PDS on the Zn_SA-N-C surface formed Zn_SA-N-C-PDS*complexes,which promoted the elec-tron-rich pollutant electron flow to the Zn_SA-N-C-PDS*complexes to achieve rapid oxidative degradation of the pollutant,while the reduction of PDS occurred to form SO₄^2-.Due to the electron transfer mechanism,the Zn_SA-N-C/PDS system exhibits good environmental tolerance and long-term efficacy in the treatment of organic pollutants,which has some practical appli-cations.Activation of dissolved oxygen by porous single-atom Zn catalysts for the oxidation of organic pollutants in water.Based on the study in the previous chapter that single-atom zinc catalysts can activate DO,a single-atom zinc catalyst with more well-developed pores（Zn-N-C）was produced by high-temperature carbonization.It has a Zn-N₄ coordination structure with a high specific surface area of 1061.35 m² g^-1,enhancing the electron transfer between the catalyst and the pollutant and DO.Without the addition of PDS,the Zn-N-C catalyst is able to directly activate DO for the oxidation of organic pollutants.Experimental results confirm that the activation of DO by the Zn-N-C catalyst alone produces superoxide anion radicals(O₂^●-),while at the same time the Zn-N-C catalyst receives electron-rich pollutant electrons and trans-fers them to the DO to strengthen its reduction on the Zn-N-C surface to produce additional O₂^●-,accelerating the degradation of the pollutant to achieve self-purification of the water en-vironment.The catalyst is used for the purpose of self-purification of water environment.In addition to exhibiting good performance in molecular oxygen activation,Zn-N-C also exhibits good stability and is effective in the treatment of actual dyeing wastewater.The successful syn-thesis and application of Zn-N-C catalysts with molecular oxygen activation capacity under atmospheric air conditions provides a new approach for the development of low-consumption and high-efficiency water self-purification industries.