Photodegraduation Of Methyl Orange By Cu(â…¡) And Tartaric Acid/Oxalic Acid

Azo dyes are widely used in various fields such as foodstuffs, textiles, leather, clothing and printing. A large amount of industrial wastewater is discharged into the environment during the dyeing process, which leads to an increasingly serious environmental problem due to the complicated structure, poor biodegradability and high toxicity of azo dyes. Therefore, it is of great significance to explore an effective method to remove these toxic pollutants. In recent years, researchers have paid close attention to photocatalytic technology which can effectively destroy a variety of stable organic pollutants. In this paper, we mainly studied the influencing factors, optimum condition and the possible mechanism of photocatalytic degradation of methyl orange by Cu(Ⅱ) assisted with tartaric acid/oxalate acid.In chapter I:The catalysis of Cu(Ⅱ) in the photodegradation of methyl orange (MO) assisted with tartaric acid (TA) was studied through batch experiments. The results show that the photodegradation of MO is slow when Cu(Ⅱ) or organic acid exists alone. However, the decoloration of MO can be markedly enhanced in the presence of both Cu(Ⅱ) and organic acid when Cu(Ⅱ) and TA forms complexes which can produce hydroxyl free radical (·OH) and other free radicals of high chemical activity under the irradiation of ultraviolet light. And the experiment demonstrates that hydroxyl radical (·OH) which has a property of strong oxidizing plays the leading role in this reaction. The initial concentration pH, temperature, and illumination intensity play important roles in this process. Results show that MO is almost completely removed by 10 mmol/L tartaric acid solution and 1 mmol/L Cu(Ⅱ) at pH 4 in 120 min. The degradation reaction occurs in two phases. At the initial initiation stage, degradation rate is relatively slow, and significantly increases at a later acceleration stage.In chapter Ⅱ:Photodegradation of methyl orange by Cu(Ⅱ) assisted with oxalic acid and its possible reaction mechanism were studied through batch experiments in a pH range of 2.0 to 8.0 at 25℃. The results show that the photodegradation of MO can be markedly accelerated by oxalic acid together with Cu(Ⅱ) under ultraviolet light irradiation than that in the single system. Cu(Ⅱ)-oxalic acid complexes produce hydroxyl free radical (·OH) and other free radicals of chemical activity under the irradiation of ultraviolet light. And ·OH which has a property of strong oxidizing that can remove almost all kinds of organic pollutants efficiently plays a leading role in this reaction. Ultraviolet light can accelerate the degradation of MO due to its high energy. Initial concentrations of methyl orange, oxalic acid and Cu(Ⅱ), and acidity have significant impact on the reaction. The results show that the photodegradation rate in Cu(Ⅱ)-oxalic acid system under different acidity is pH4> pH6 >pH8>pH2.