Photochemical Generation Mechanisms And Quantum Yield Quantitative Structure-activity Relationship Models Of Reactive Species From Dissolved Organic Matter

Photochemical degradation is the main way to eliminate organic pollutants in surface water,and dissolved organic matter?DOM?plays an important role in the photodegradation of organic pollutants in water.DOM absorbs solar energy to produce various photoactive intermediate species?PPRIs?,such as: excited triplet DOM?³DOM*?,singlet oxygen?1O2?,hydroxyl radical?·OH?,etc.These PPRIs can react with natural substances in water or pollutants from man-made sources and participate in the geochemical cycle of carbon.The structural components and physical and chemical properties of DOM from different sources are obviously different,which in turn makes their ability to generate PPRIs different.However,the microscopic mechanism of DOM photosensitization to produce PPRIs is unclear.The contribution of different groups to their photochemical activity and the quantitative prediction of their ability to generate different PPRIs remain to be studied.This study focuses on the microscopic mechanism of DOM photosensitization to generate ³DOM*,1O2 and ·OH.The quantum yield and steady-state concentration of three PPRIs generated by measuring small molecule analogs with different structures are based on OECD guidelines.The actual DOM generates QSAR models of ³DOM*,1O2 and ·OH quantum yields,and the mechanism is explained to clarify the microscopic mechanism of DOM photosensitization to generate three kinds of PPRIs.The main conclusions are as follows:?1?The range of ?³DOM* of DOM analogues is?0.05 ± 0.01?× 10^-2 to?13.52 ± 1.23?× 10^-2,and the ?³DOM* of ketones is generally higher.From the perspective of the structure of DOM analogs,complex functional groups such as carboxyl groups and hydroxyl groups increase the compound's light absorption capacity,thereby promoting the conversion of DOM to ³DOM*,and the subsequent formation of ¹O₂ and other active products.In addition,the composition of DOM contains many aromatic ketones and aldehydes,which have a strong absorption effect on ultraviolet light.The outer valence electrons can easily absorb the energy of the photon transition from the ground state to the excited state,generating an excited triplet state with a large energy.?2?The range of ?_1O2 for DOM analogues is?0.54 ± 0.23?× 10^-2 to?62.03 ± 2.97?× 10^-2,and aromatic ketones ?_1O2 are higher.From the point of view of the structure of DOM analogs,the presence of carbonyl groups plays a positive role in the generation of ¹O₂ from DOM small molecule analogs.The generation of ¹O₂ is also related to the hydrophobicity of DOM molecules.The quantum yield of ketones to generate active species is generally high for quinones,and ³DOM* with a higher quantum yield,the quantum yield of ¹O₂ is also higher.?3?The ?·OH range of DOM analogs is?1.01 ± 0.33?× 10-5 to?59.02 ± 1.43?× 10-5.From the perspective of the structure of DOM analogs,the electronegativity of molecules has a positive effect on the generation of DOM small molecule analogs ·OH analogs are generated if the reaction of gaining and losing electrons is stronger in the competitive reaction of gaining and losing electrons The value of the ·OH quantum yield is usually small.When the electron loss reaction predominates,DOM analogs are generated.The ·OH quantum yield is large.Although ·OH is also derived from ³DOM*,the generation is more complicated.The correlation between excited triplet and singlet oxygen quantum yields is poor.?4?Based on the quantum yield results measured experimentally,a QSAR model that predicts the quantum yields of three active species,³DOM*,1O2 and ·OH,was constructed by multiple linear regression?MLR?.All models have good fitting goodness and excellent.The robustness and prediction ability of the system can accurately predict the quantum yield of ³DOM*,1O2 and ·OH generated by photo-generation of SRFA and riboflavin.