Mechanism of biochar on photochemical processes and imidacloprid transformation
To explore the effect mechanism of biochar application on reactive intermediates(RIs)in paddy water,a field experiment was conducted from June to September 2022,and three treatments were set up:chemical fertilizer(CK),rice husk biochar(25%RH)and corn stalk biochar(25%CS).The content and properties of photosensitizer,the concentration of RIs and the photolysis rate of imidacloprid(IMD)were measured in paddy water.The results showed that compared with chemical fertilizer,the application of rice husk biochar and corn straw biochar significantly increased the steady-state concentrations of reactive intermediates(RIs),·OH,3DOM*and 1O2 by 0.92%-71.97%,21.29%-137.00%and 10.42%-370.24%,respectively.The promoting effect of biochar on RIs at seedling stage was more significant than that at tillering stage.The mechanism of biochar promoting the production of RIs was further analyzed.Compared with fertilizer treatment,the application of biochar significantly increased the content of fulvic acid and tryptophan in paddy water,which was the main reason that biochar promoted the production of photoactive components in paddy water.In addition,compared with fertilizer treatment,the biochar treatment also significantly promoted the degradation rate of IMD,which was increased from 1.72×10-2 h-1 to 3.76×10-2 h-1.The quenching reaction proved that the contribution of·OH,3DOM*and 1O2 to the degradation of IMD was 41.78%,62.70%and 9.76%,respectively.The application of biochar was conducive to the accumulation of chromophores and fluorescent substances in paddy water,thus promoting the photochemical process and increasing the RIs concentration.Therefore,biochar application accelerated IMD degradation in paddy water.The corn straw biochar from herbal materials had a stronger effect on increasing the steady-state concentration of RIs and the degradation rate of IMD in paddy water than rice husk biochar.
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