Fabrication Of Ag-based Composites Based On Modified G-C₃N₄ And The Mechanistic Study Of Removing Emerging Contaminants

Ag-based composites including Ag/P-g-C₃N₄,Ag₃PO₄/P-g-C₃N₄ and AgBr/P-g-C₃N₄ were synthesized using P-g-C₃N₄ materials.The Ag-based composites were used to remove emerging comtaminants under visible light irradiation.The mechanism of target compounds degradation was investigated.The effects of initial pH,dissolved organic matter?DOM?,HCO₃^-,CO₃^-and NO₃^-on target compounds degradation were studied.The intermediates of sulfamethoxazole?SMX?,ketamine?KET?and ephedrine?EPH?were identified,and the degradation pathways of those compounds were proposed as well.The major research contents and conclusions are shown as follows:?1?A series of Ag/P-g-C₃N₄ composites with different Ag amounts were synthesized by thermal polymerization combined with photo-deposition method.The composites were characterized by a series of characterization techniques and were used to degrade SMX.5%Ag/P-g-C₃N₄ composite exhibited the best performance on SMX degradation,which could degrade 100%SMX(0.1 mg·L^-1)within 20 min.The reactive species?RS?identification and scavenger experiments were carried out to find out the major RS.The result indicates that holes?h⁺?and superoxide radicals?·O₂^-?were the predominant RS involved in the system.Compared with P-g-C₃N₄,the enhanced photocatalytic activity of Ag/P-g-C₃N₄ was ascribed to the surface plasmon resonance?SPR?of metallic Ag and Schottky barrier formed on the interface of Ag and P-g-C₃N₄,which could facilitate the separation rate of e^-/h⁺pairs and lengthen the life time of photo-generated carriers.22 intermediates of SMX were identified by LC-MS/MS and the degradation pathways were proposed,which include bond break,ring open,deamination,oxidation,hydroxylation and substitution reaction.?2?Several novel Ag₃PO₄/P-g-C₃N₄ heterojunction composites were successfully constructed using an in-situ growth method,and the samples were characterized by a series of instruments.The synthesized samples were applied to remove KET,and all as-prepared samples exhibited good degradation performance on KET removal.Ag₃PO₄/P-g-C₃N₄?1:1?composite shown the best degradation performance with a pseudo-first-order rate constant?k?of 0.0326 min^-1,which was 3-and 6-folds faster than those of Ag₃PO₄ and P-g-C₃N₄.The scavenging experiments and RS identification tests revealed that holes,superoxide radicals and hydroxyl radicals?·OH?were the main reactive species in the KET removal process.The enhanced photocatalytic performance of Ag₃PO₄/P-g-C₃N₄ was attributed to the formation of metallic Ag and heterojunction structure.Low concentrations of DOM,NO₃^-or HCO₃^-accelerated the degradation rate of KET,but high levels of these constituents would inhibit the degradation.A total of 12 degradation intermediates of KET were identified,and a possible degradation pathway was proposed.Demethylation,dehydrogenation,hydroxylation deamination,ring opening,and sodium modification were the major pathways for KET degradation.Ag₃PO₄/P-g-C₃N₄ also exhibited a relatively good photocatalytic performance on KET degradation in real waters.?3?A series of AgBr/P-g-C₃N₄ composites were synthesized by precipitation-deposition and the composites were characterized by several techniques.AgBr/P-g-C₃N₄?5:1?show the best degradation performance on EPH,which could degrade 99.7%EPH(0.1 mg·L^-1)within 60 min under visible light irradiation with a rate constant of0.1022 min^-1.The RS identification and radical quenching tests indicated that holes,superoxide radicals and singlet oxygen?¹O₂?were the dominant RS involved in EPH degradation.The initial pH value influenced the EPH degradation,and the best degradation performance was found when the initial pH at 10.Low concentrations of DOM or HCO₃^-accelerated EPH degradation,but high levels of DOM or HCO₃^-inhibited EPH degradation.17 intermediates were identified and the degradation pathways of EPH by AgBr/P-g-C₃N₄ were proposed as well.The degradation pathways including hydroxylation,demethylation,deamination,oxidation,substitution,dehydration and reduction.AgBr/P-g-C₃N₄ also exhibited a relatively good photocatalytic degradation performance on EPH degradation in surface water and a secondary effluent.