Photodegradation Of Tetracycline By Fe(Ⅲ)–carboxylate Complex In Aqueous Solutions

Pharmaceuticals and personal care products (PPCPs) are now recognized as a new class of emerging pollutants and have been the subject of increasing concern and scientific interest in recent decade. Antibiotics have been used extensively in PPCPs. Tetracyclines constitute one of the most important antibiotic families and rank second in production and usage worldwide. They are frequently used as human and animal treatment against infectious diseases and growth promoter in livestock and aquiculture.In this study, the photochemical removal of tetracycline (TC) and the reaction mechanism in the Fe(Ⅲ)-oxalate and Fe(Ⅲ)-citrate system under simulated sunlight was investigated.The Design Expert software (version 7.1.3 Stat-Ease, Inc.) was used for the experimental design and data analysis. The results of analysis of response surface and variance (ANOVA) showed the factors contributions. The software also showed the optimizing photochemical treatment condition.The photochemical removal of tetracycline (TC) in the Fe(Ⅲ)-oxalate system under simulated sunlight was investigated. Four factors as initial concentration of TC (0-90μM), pH (3.0-7.0), Fe(Ⅲ) (0-40μM), oxalate (0-400μM) were selected in the experiment to explore the effects of on the photodegradation of TC in aqueous solutions. Fⅳe levels of each factor was designed with six replicates of the center point condition (50.0μM TC, pH 7.0, 20μM Fe(Ⅲ), 200μM citrate). A total of 30 experiments were explored and the rate constants were input into Design-Expert as the response factor of the design. The analysis indicated that the initial concentrations of TC, pH, Fe(Ⅲ) had remarkable effect on the photodegradation of TC. It can be concluded that (ⅰ) the rate constants of photodegradation decreased markedly with increasing initial concentration of TC, (ⅱ) the pH of the solution decided the Fe(Ⅲ)-oxalate species which are the function of the formation of·OH. Thus the higher pH will lead to formation of Fe2O3; (ⅲ) the degradation effective of Fe(Ⅲ)-oxalate species were higher than Fe(Ⅲ) and this indicated the photoreactive of Fe(Ⅲ)-oxalate complexes is higher than Fe(Ⅲ)-OH.The photochemical removal of tetracycline (TC) in the Fe(Ⅲ)-citate system under simulated sunlight was investigated. Four factors as initial concentration of TC (0-90μM), pH (5.0-9.0), Fe(Ⅲ) (0-40μM), citrate (0-400μM) were selected in the experiment to explore the effects of on the photodegradation of TC in aqueous solutions. Fⅳe levels of each factor was designed with six replicates of the center point condition (50.0μM TC, pH 7.0, 20μM Fe(Ⅲ), 200μM citrate). The rate constants were input into Design-Expert as the response factor of the design. The optimizing photochemical treatment condition was as follows: [TC]₀ = 10.5μM, pH = 6.9, [Fe(Ⅲ)]₀ = 33.8μM, and [citrate]₀ = 324μM with corresponding pseudo-first-order rate constant 0.0323 min^-1. It can be concluded that (ⅰ) lower initial concentration of TC was more favorable for the removal of the antibiotic in the Fe(Ⅲ)-citrate system; (ⅱ) an increase of Fe(Ⅲ) or citrate concentration facilitated the degradation of TC under otherwise identical conditions; (ⅲ) The quenching experiments verified the degradation of TC was attributed to attack of·OH formed in the Fe(Ⅲ)-citrate system under simulated sunlight; (ⅳ) Fe(Ⅲ)-citrate complexes were highly effective catalyst for the degradation of TC at near-neutral pH in aqueous solution.This results suggested that Fe(Ⅲ)-citrate was highly effective catalyst for the removal of TC and available in near-natural waters. And it was significant for the antibiotic wastewater treatment.