Preparation Of Polyoxometalated-based Materials For The Catalytic Oxidation Of The Phthalate Esters In Water

Phthalates（PAEs）,as important chemical synthetic substances,are widely used as plasticizers in adhesives and paints,etc.Due to the extensive use and non-chemical binding with polymers,PAEs migrated to the surrounding water through plastic aging or decomposition,which has seriously threatened the ecological environment and human health.However,there is no specific removal process for PAEs in the traditional Wastewater Treatment Plants（WWTPs）.Therefore,advanced oxidation processes（AOPs）in the conventional methods show more potential for the removal of PAEs in water compared with biodegradation and physical adsorption,which could not only achieve high degradation efficiency in a short time,but also have no secondary pollution,and would not be limited by water qualities.Polyoxometalates（POMs）are a class of mental-oxygen clusters composed of transition metals with the highest oxidation state（Mo,W and V,etc.）.Due to the structural diversity,controlled acidity and redox properties,POMs-based heterogeneous materials receive more and more attention for the removal of phenols,pesticides and dyes in water.However,it was rarely reported using POMs-based materials for the degradation of PAEs.Therefore,based on vanadomolybdophosphoric heteropoly acid(H₅PMo₁₀V₂O₄₀,H₅PMoV),four kinds of heterogeneous POMs-based materials with different active sites were constructed for the degradation of PAEs in the water of laboratory preparation and the wastewater in WWTPs.While achieving high degradation efficiency of PAEs,the possible degradation pathways and the degradation efficiency of PAEs in different water environment were also studied,which are shown as follows:（1）Amphiphilic（CTA）_n H_5-nPMoV([C₁₆H₃₃（CH₃）₃N]_nH_5-nPMoV,n=1⁵)could self-assemble into micellar nano-reactor with PMo₁₀V₂O₄₀^5-located outside of the nano-spheres and（CTA）⁺located inside of the spheres,which provided a fast concentration of diethyl phthalate（DEP）and H₂O₂ around active sites,while the presence of Br?nsted acid and PMo₁₀V₂O₄₀^5-in（CTA）_nH_5-nPMoV could effectively promote the hydrolysis of DEP and activate H₂O₂ for the generation of?OH and O₂·^-,which greatly facilitated the progress of the degradation.And（CTA）H₄PMoV exhibited the best degradation activity for the highest Br?nsted acidity among（CTA）_nH_5-nPMoV,while the degradation efficiency of DEP achieved 90.2%under the optimal conditions.In addition,the enrichment of PAEs by amphiphilic POMs-based materials,coupling with its stronger Br?nsted acidity and great redox potential allowed（CTA）H₄PMoV also beneficial for the removal of PAEs with longer alkyl（ester）chains（diallyl phthalate（DAP）and di（2-ethylhexyl）phthalate（DEHP））and trace DEP.Meanwhile,（CTA）H₄PMoV,as a heterogeneous material,exhibited high stability and great recyclability.（2）Introduction of Ag⁺could effectively improve the oxidation ability of Ag_nH_5-nPMoV and activate H₂O₂ for the generation of·OH,O₂·^-and ¹O₂,while Ag_nH_5-n-n PMoV were heterogenized.The presence of oxidation sites and acid sites in Ag_nH_5-n-n PMoV allowed DEP to be degraded through the pathways of both oxidation and hydrolysis.And higher oxidation property and certain Br?nsted acidity permitted Ag₄HPMoV show the best degradation activity among Ag_nH_5-n-n PMoV.While the degradation efficiency of DEP reached 91.0%under the optimal conditions.Besides,Ag₄HPMoV also favored for the removal of other longer ester chains of PAEs:DAP and DEHP and trace DEP,and showed long duration and stability during the degradation.（3）The existence of the lipid bilayer in H₅PMoV@lipid（n）/GO-f（n=2,4,6 and 8,which means ethylenediamine,1,4-diaminobutane,1,6-hexanediamine and 1,8-octanediamine;f=10,15,20,25 and 30 wt%,which means the loading amount of H₅PMoV）could not only provide a micro-reactive environment for the degradation,but also effectively activate H₂O₂ for the generation of·OH,O₂·^-and ¹O₂,which allowed DEP in the bilayer can be rapidly degraded by oxidation of the radicals while being adsorbed.And H₅PMoV@lipid（2）/GO-20 wt%exhibited the best degradation activity due to its lower bilayer thickness and higher electron transfer capacity,while the degradation efficiency of DEP achieved 93.0%under the optimal degradation conditions.In addition,H₅PMoV@lipid（2）/GO-20 wt%was also beneficial for the degradation of longer ester chains DAP and DEHP in water and trace DEP,which showed great heterogeneity and recyclability during the degradation.（4）It was found that the presence of macroporous structure in POMs-based biomass（Popcorn,POP）material:H₅PMoV@POP（n）（n=12,28,44,53 and 63 wt%,which means the loading amount of H₅PMoV）could not only provide a micro-reaction environment for the degradation,but also promote the activation of O₂ for the generation of·OH,O₂·^-and ¹O₂.While the couple effect of Br?nsted acidity and oxidation ability permettied DEP can be rapidly degraded through both hydrolysis and oxidation.The degradation efficiency,COD and TOC removal efficiency of DEP achieved the maximum of 80.1,72.5 and 64.4%under the optimal degradation conditions.Besides,H₅PMoV@POP（44 wt%）also showed great potential for the removal of DAP and DEHP and trace DEP in water,which showed excellent heterogeneity and stability during the degradation.（5）POMs-based materials:（CTA）H₄PMoV,Ag₄HPMoV,H₅PMoV@lipid（2）/GO-20 wt%and H₅PMoV@POP（44 wt%）,all exhibited excellent ability for the degradation of PAEs（DEP and DAP）in the different processing units of WWTPs programing with Anaerobic-Anoxic-Oxic（A²/O）process（Plant A and B）.While the existence of macroporous structure and higher adsorption ability allowed H₅PMoV@POP（44 wt%）exhibited the best degradation efficiency for PAEs in water.And the degradation efficiency for DEP（8.6μg/L）and DAP（4.5μg/L）in the secondary effluent reached 62.2%and 78.1%,respectively.The higher adsorption and oxidation ability permitted H₅PMoV@POP（44 wt%）also favor for the degradation of PAEs in the different water environment,which showed great degradation efficiency and universal applicability for the removal of PAEs in the wastewater.