Photocatalytic Degradation Of Organic Dyes In Dyeing Industry By Hypocrellin A

The dyeing wastewater contains many organic pollutants with good stability,high color value,poor biochemical properties and they are difficult to be degraded,which is a great danger to the environment as well as human health.Photocatalytic advanced oxidation technology is a mean to treat dyeing wastewater by generating active oxygen for the efficient oxidative degradation of persistent organic pollutants through photolysis from oxidants or photocatalysts.However,due to the short comings of commonly used inorganic photocatalysts such as inability to degrade naturally,low photocatalytic efficiency,high light requirement and complex,expensive preparation process,photocatalytic advanced oxidation technology requires greener and more efficient photocatalysts.As an ingredient in traditional Chinese medicine and a photosensitizer in photodynamic therapy,Hypocrellin A（HA）are safe,effective in photosensitizing,and has potential to be applied in advanced oxidation technology as organic photocatalysts.In this paper,a photocatalytic advanced oxidation system of HA/H₂O₂ based on the natural photosensitizer-HA was designed to cope with the limitations of photocatalysts in the photocatalytic advanced oxidation.The contents of this paper were as follows:（1）The feasibility,mechanism and kinetics of the rhodamine B’s（Rh B）degradation catalyzed by HA/H₂O₂ system were studied through the degradation experiment of Rh B in the HA micellar solution/H₂O₂ system.（2）Preparations of HA suspension and HA@MCC（Microcrystalline cellulose loaded with HA）.Degradation of Rh B catalyzed by the HA suspension/H₂O₂heterogeneous system and HA@MCC/H₂O₂ heterogeneous system were applied to study the characteristics,kinetics and reusability of organic pollutant’s degradation in the HA/H₂O₂heterogeneous system;（3）HA@Fe₃O₄ which can be recycled through magnetic force was prepared,Rh B degradation experiments,synthetic wastewater color remove experiments and degradation experiment of five different dyes catalyzed by HA@Fe₃O₄/H₂O₂heterogeneous system were applied to investigate the characteristics,kinetics,color removal of synthetic wastewater and selectivity of pigments.The main results obtained in this paper were as follows.（Ⅰ）HA can synergistically degrade Rh B as photocatalyst with H₂O₂.The degradation yield of rhodamine B(2.5×10^-5 M)by HA micellar solution/H₂O₂ homogeneous system reached 84.2%in 60 min;the degradation reaction obeyed the pseudo first reaction kinetic equation and the reaction rate constant reached 0.02797 min^-1.（Ⅱ）The synergistic degradation of Rh B by HA and H₂O₂ was mediated by hydroxyl radicals.（Ⅲ）HA can be degraded under weakly basic conditions without secondary pollution.（Ⅳ）In the heterogeneous system,the better the suspension of HA,the higher degradation yield of Rh B.60-min degradation yield of the HA suspension/H₂O₂（HA concentration of 500mg/L）system and HA@MCC/H₂O₂（HA concentration of 3.3 mg/L）system on Rh B(2.5×10^-5M)were 52.9%and 46.0%respectively（MCC achieve 34.1%degradation yield in combination with H₂O₂）.The degradation of Rh B in the heterogeneous system obeyed the pseudo first reaction kinetic equation;the reaction rate constant was 0.018 min^-1（HA concentration of 13.2mg/L）.（Ⅴ）The photocatalytic performance of HA in the heterogeneous system was reduced slightly after five cycles,the degradation yield of Rh B by the HA@MCC/H₂O₂（HA concentration of 13.2 mg/L）system decreased from 70.4%to 58.5%（Ⅵ）The degradation of Rh B by the HA@Fe₃O₄/H₂O₂ heterogeneous system obeyed the pseudo primary reaction kinetics,and the higher the encapsulation amount of HA,the better the degradation of Rh B.The reaction rate constants were 0.0064,0.0066 and 0.0104 min^-1 and the degradation rates of Rh B at 60 min were 43.3%,45.2%and 61.7%when the load capacity of HA@Fe₃O₄ was 0.30,0.42 and 0.61 g/g,respectively.（Ⅶ）The HA@Fe₃O₄/H₂O₂ heterogeneous system was able to reduce the chromaticity of synthetic wastewater,and its chromaticity removal performance showed a positive correlation with the concentration of hydrogen peroxide in the system,the concentration of HA@Fe₃O₄and the reaction time,but it was not sensitive to the p H（6-8）.（Ⅷ）The HA@Fe₃O₄/H₂O₂ heterogeneous system was more effective in removing anthraquinone dyes than azo,and also had better results for methylene blue as well as RhB.