Effect of Humic Acid on the photocatalytic degradation of oxytetracycline using Nano-Titanium Dioxide
Humic Acid is commonly found in soil and can bind to Nano-Titanium Dioxide in the environment,altering its properties and interaction mechanisms with coexisting pollutants.In this study,oxytetracycline was selected as a representative environmental contaminant.We investigated the effect of Humic Acid on the photocatalytic degradation of oxytetracycline using Nano-Titanium Dioxide under simulated solar irradiation.The results indicated that oxytetracycline readily undergoes photolysis in solution,with alkaline conditions enhancing this process.Quenching experiments revealed the involvement of hydroxyl radicals and superoxide radicals in the photolysis mechanism.Additionally,oxytetracycline demonstrated relative stability under dark reaction conditions.The degradation rate of oxytetracycline was positively correlated with both the dosage of Nano-Titanium Dioxide and the initial pH of the solution,while it was negatively correlated with the initial concentration of the solution.Additionally,the presence of Humic Acid and the formation of oxytetracycline complexes can enhance the degradation rate of oxytetracycline.As the dosage of Nano-Titanium Dioxide increased from 10 mg/L to 100 mg/L,the degradation rate of oxytetracycline rose from 39.4％to 69.9％.Conversely,when the initial concentration of oxytetracycline was elevated from 10 mg/L to 100 mg/L,the degradation rate decreased from 60.2％to 18.6％.As the pH value of the solution increased from 3 to 9,the degradation rate of oxytetracycline improved significantly,rising from 25.0％to 75.6％.Compared with the pure solution system,the degradation rate of the composite system of humic acid and oxytetracycline increased by up to 15.1 percentage points.Humic Acid exerts both promoting and inhibiting effects on the photocatalytic degradation of oxytetracycline by Nano-Titanium Dioxide.When the initial concentration of humic acid was 100 mg/L and 250 mg/L,the photocatalytic degradation of oxytetracycline was promoted,and the degradation rate was increased by 2.6 percentage points and 4.6 percentage points,respectively.Humic Acid reduces the band gap of Nano-Titanium Dioxide,which enhances its ability to utilize visible light and increases the number of active sites available for light reactions.However,at initial concentrations of Humic Acid of 500 mg/L and 1 000 mg/L,the formation of the composite inhibited the photocatalytic degradation of oxytetracycline.This inhibition occurs because Humic Acid decreases the production of superoxide radicals.
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