Degradation Of Tetracycline By Peroxide Catalyzed With Layered Double Hydroxides

Antibiotics are widely used in human health and animal husbandry.However,30-90%of the antibiotics cannot be absorbed by animals,and they are discharged into the environment in the form of parent compounds or intermediates.Antibiotics pose a great threat to ecological environment.It is urgent to develop an efficient method to remove antibiotics.Advanced Oxidation Process（AOPs）becomes one of the popular technology for pollution management due to its short-period and high efficiency.Efficient degradation of pollutants depends on two key issues:the selection of oxidant and the activity of the catalyst.Persulfate and urea peroxide are commonly used oxidants in advanced oxidation process.However,the existing transition metal activators are not stable enough and prone to complexation and precipitation reactions.Hydrotalcite-like materials prepared by transition metals not only have the catalytic activity of transition metals,but also improve the stability of metals,which is an ideal catalytic material for the degradation of organic pollutants by advanced oxidation.Tetracycline is difficult to be degraded naturally due to its large amount of use.In this paper,Cu-Al LDHs and Fe-Al LDHs catalytic materials were prepared for tetracycline as the target pollutant.The degradation of tetracycline by sodium persulfate or urea hydrogen peroxide catalyzed by the prepared materials was discussed,and the related mechanism was studied.The main contents of this research including:（1）Degradation of tetracycline by sodium persulfate or urea hydrogen peroxide catalyzed with Cu-Al LDHs:Cu-Al LDHs were synthesized and characterized,and the degradation behavior of tetracycline in water by Cu-Al LDHs/SPS system was discussed.The results showed that Cu-Al LDHs were flower clusters,and the main active groups of Cu-Al LDHs/SPS system were SO₄^·-and OH^·.The optimum reaction conditions were 100 mg/L Cu-Al LDHs,1.0 mM UHP and pH=6.Tetracycline degradation rate was only 34.43%after 4 h and can be87.48%after 18 h.When urea hydrogen peroxide（UHP）was used as oxidant,the decomposition of UHP was slower than SPS,and the degradation cycle of tetracycline was longer.The optimum reaction conditions were 100 mg/L Cu-Al LDHs,1.0 mM UHP and pH=6.Tetracycline degradation rate was 34.43%after 4 h and can be 87.48%after 18 h.Free radical quenching experiment confirmed that the main active groups of the system were OH^·and O₂^·-.The results of tetracycline degradation experiments show that Cu-Al LDHs/SPS oxidation system is more suitable for the catalytic degradation of organic pollutants in water environment due to its short time and higher degradation efficiency.（2）Degradation of tetracycline by sodium persulfate or urea hydrogen peroxide catalyzed with Fe-Al LDHs:Fe-Al LDHs catalysts were synthesized by hydrothermal method and characterized.The degradation of tetracycline in water by Fe-Al LDHs/SPS system was studied.The results showed that Fe-Al LDHs had lamellar stacking structure,and the main free radicals of Fe-Al LDHs/SPS system were SO₄^·-and OH^·.The optimal removal conditions were 100mg/L Fe-Al LDHs,1.0 mM SPS and pH=6.The removal rate of tetracycline was 94.18%after24 h.The degradation of tetracycline in water by Fe-Al LDHs/UHP system was studied.The results showed that the free radicals acting on Fe-Al LDHs/UHP system were OH^·and O₂^·-.The optimal removal conditions were 100 mg/L Fe-Al LDHs,1.0 mM UHP and pH=4.The tetracycline degradation rates reached 97.01%after 24 h.The results of tetracycline degradation experiments showed that the degradation rates of tetracycline by Fe-Al LDHs/SPS and Fe-Al LDHs/UHP oxidation systems were more than 90%,which realized the efficient degradation of tetracycline in water.（3）Degradation of tetracycline in soil by urea hydrogen peroxide catalyzed with Fe-Al LDHs:In this study,the degradation of tetracycline in soil by Fe-Al LDHs/UHP oxidation system was studied and the soil safety of the system was evaluated.The results showed that the optimal removal conditions were 5.0 g/kg urea hydrogen peroxide,2.5 g/kg Fe-Al LDHs and the water-soil ratio was 2:1,the degradation rate of tetracycline reached 94.36%within 7 days.The degradation mechanism showed that Fe-Al LDHs effectively catalyzed UHP to generate OH^·and O₂^·-,and finally degraded tetracycline to carbon dioxide and water through two ways.After tetracycline degradation by Fe-Al LDHs/UHP oxidation system,the content of ammonium nitrogen and nitrate nitrogen increased,and the growth of mung bean plants was also promoted.In this study,Fe-Al LDHs and Cu-Al LDHs catalytic materials were prepared.Sodium persulfate or urea hydrogen peroxide were catalyzed to realize the efficient degradation of tetracycline in water,and urea hydrogen peroxide was catalyzed by Fe-Al LDHs to realize the degradation of tetracycline in soil.It provides a new idea about the remediation of antibiotic-contaminated in water and soil.