化学assignment:光化学反应在有机污染物环境中的研究应用

Photochemical reaction is carried out under the effect of light chemical reactions. Photochemical reaction requires molecules absorb specific wavelengths of electromagnetic radiation generated by the excited excited state, which occurs after a chemical change to a steady state, or become heat induced chemical reaction intermediate product [1]. A part of the natural environment of the near-ultraviolet light (290-400nm), are easily absorbed by organic pollutants, in the presence of the active substance strongly photochemical reaction occurs degradation of organic matter, and gradually oxidized into low molecular weight intermediate, and ultimately to carbon dioxide, water and other ions.
光化学反应，就是在光的作用下进行的化学反应。光化学反应需要分子吸收特定波长的电磁辐射，受激产生分子激发态，之后才会发生化学变化到一个稳定的状态，或者变成引发热反应的中间化学产物[1]。自然环境中有一部分的近紫外光（290-400nm），它们极易被有机污染物吸收，在有活性物质存在时就会发生强烈的光化学反应是有机物发生降解，逐步氧化成低分子中间产物，而最终生成二氧化碳、水及其他的离子。

A photochemical reaction technology

1 光化学反应技术

1.1 UV/H2O2 degradation of organic matter

Hydrogen peroxide as a strong oxidizing agent (pH 0 and 14, respectively, the corresponding redox potentials of 1.80V and 0.87V), oxidizing and strong, secure, easy to get, have been widely used for treatment of wastewater and waste gas inorganic and organic contaminants. However, for some refractory organic pollutants, only H2O2 as an oxidant, it can not be effectively degraded, while the use of UV/H2O2 combination process, UV can promote the decomposition of hydrogen peroxide, a strong oxidizing hydroxyl radical (OH) , then the radical reaction to degrade pollutants [2].  http://www.ukthesis.org/Assignment_Writing/
Chlorophenols organics because of its structural stability, poorly biodegradable, using traditional biochemical or chemical oxidation to be ineffective, in Chen Lin, etc. [3] studies were processed using UV/H2O2 system chlorophenol containing wastewater. Experimental investigation of direct sunlight (UV/N2), separate aeration (air), hydrogen peroxide plus aeration (H2O2 / air) and UV / H2O2 / air system on the total phenols and CODCr degradation effect, the results show that, UV / H2O2 / air of CODCr degradation rate has improved significantly.
Polymer flooding oil recovery technology has greatly enhanced oil recovery, but also generated a lot containing polyacrylamide (HPAM) sewage. Because the sewage high viscosity, water droplets and enhance the stability of suspended solids, so difficult to deal with the sewage [4-5]. According Cuibao Chen [6] and other studies have shown that degradation of HPAM UV/H2O2 combination than alone effect H2O2 or UV, UV effect on the degradation has significant role in promoting.#p#分页标题#e#
　1.1 UV/H2O2 降解有机物
　　过氧化氢作为一种强氧化剂（pH 值分别为0 和14 时，对应的氧化还原电位分别为1.80V和0.87V），氧化性强、安全、易得，已经被广泛用于处理废水和废气中无机和有机污染物。但是，对于一些难降解有机污染物，仅用H2O2 作为氧化剂，不能将其有效地降解，而采用UV/H2O2 联合工艺，紫外光可促使过氧化氢分解产生氧化性强的羟基自由基（OH）,进而进行自由基反应来降解污染物[2]。

1.2 UV/H2O2 degradation of organic matter
In the treatment of high concentration, biodegradable, toxic and hazardous waste aspects of UV / Fenton oxidation process technology showed more advantages than other methods, and the corresponding treatment costs with other similar methods. By Fenton strong oxidizing reagents, supplemented by ultraviolet light, can enhance the ability of Fenton reagent oxidation, reducing the amount of peroxide strong and improve processing efficiency can be effectively decomposed organic matter, and mineralization is better suitable for processing Low concentrations of organic wastewater treatment in contaminated groundwater has a unique advantage.
In the saponin production process, a large amount of industrial waste. Saponin wastewater quality with a strong acid, high concentration, and belongs biodegradable industrial waste water, the traditional treatment process is not satisfactory [7]. Hu Xiaolian [8] experimental studies, the use of home-made equipment using UV / Fenton method saponin wastewater treatment, within 2 hours of COD removal can reach 90% or more, but also has good bleaching effect.
Phenol has a strong toxicity, can lead to fainting spells, anemia and nervous system disorders and other diseases, has teratogenic, carcinogenic and mutagenic potential toxicity. It is distributed in the water, a direct threat to human health and the environment there is the important one of toxic and hazardous pollutants. Since phenol refractory, making phenol-containing wastewater by everyone's attention. Currently, the treatment of wastewater containing phenol There are many ways, but only using either method, it is difficult to achieve the intended purpose [9].
Yin Hongsheng, etc. [10] the use of UV / Fenton treatment toxicity, refractory Phenol. Experimental results show that the method has a good removal of phenol, when c (H2O2) = 12.76 mmol / L, n (Fe2 +): c (H2O2) = 1:20, pH = 3, the reaction at room temperature 30 min, COD removal rate reached 86%, phenol removal rate can reach 99%.

1.3 UV/O3 degradation of organic matter
UV/O3 is ozone and UV radiation combined with the reaction is complete, fast, no secondary pollution. UV/O3 method synergistic advantages: (1) organic materials are activated under UV radiation, thereby easily oxidized and decomposed by ozone; (2) dissolved in water in the UV irradiation of ozone generated hydroxyl radicals (HO ·) [11], thereby accelerating the rate of removal of organic matter in water. Currently, UV/O3 technology has been widely used biodegradable organics processing of hexachlorobenzene (HCB) is mainly used for prevention and treatment of fungal membrane cereal crop seeds hazards organochlorine fungicides, but also the production of other chlorinated intermediates . HCB structural stability, poorly biodegradable, bioaccumulative, on human health and the environment have a serious hazard. Wei Japan, etc. [12] using the UV/O3 method for degradation of HCB in water. His study compared the individual UV, ozone and UV/O3 alone for HCB removal, where UV <O3 <UV/O3.#p#分页标题#e#

Nitrosodimethylamine (NDMA) as a typical representative of nitrosamines, a potent carcinogenic organic compounds due to disinfect drinking water and wastewater treatment process can produce NDMA [13], therefore NDMA in water pollution caused by foreign attention of scholars, NDMA rather special physical and chemical properties, is a semi-volatile substances, but also has a high solubility in water, so the conventional water treatment processes can not be effectively removed. Xu Bing Bing, etc. [14] for the study of human and UV/H2O2 2 UV/O3 oxidation degradation of the Advanced level of water in Central Asia nitrosodimethylamine (NDMA) and control dimethylamine (DMA) the ability to generate a comparative study . The results show that, UV/H2O2 can effectively degrade NDMA, but can not control the formation of NDMA degradation products DMA; UV/O3 advanced oxidation technology not only can effectively remove NDMA, while the formation of DMA also has good control effect.

1.4 US / UV degradation of organic compounds
US / UV system catalytic oxidation technology is in the ultrasonic oxidation technology developed, the basic principle of including the role of ultrasound in air and free radical reaction principle. Ultrasonic cavitation generated during the local high temperature and pressure to cause pyrolysis of organic material [15], and a water molecule cleavage free radicals react with the bulk solution, to form the final product. Combination of chemistry and photochemistry of the sound, can the two complement each other, play advantage, and enhance the yield of hydroxyl radicals, promote degradation of organic matter, increasing the reaction rate.
Naomi, etc. [16] In naphthol blue black (NBB) as an example of the US / UV water purification treatment of textile dyes kind of research work. The results show that the combined action of ultrasound and UV and water can greatly facilitate the reactants and products photocatalytic oxidation catalyst in the conversion of the surface, thus greatly accelerating the reaction. Ultrasonic conjunction with UV, the reaction between the reaction rate faster than the increase and is also high, while there are many large salinity extent.
FWA-CBW, can absorb ultraviolet light and a blue or blue-violet excitation of fluorescent organic compounds, soluble in water, but CBW complex structure, is a typical refractory compounds. Therefore, the choice of the appropriate method of its treatment worthy of study [17]. Chen Qingyun, etc. [18] studied the US / UV degradation even usage of such substances. The results showed that the initial concentration of 40mg / L, ultrasonic power is 500W, p H 9, H2O2 addition amount of 30 m L / L, the reaction conditions, for 120 min, the degradation rate of the fluorescent whitening agent up to 95%.

1.5 TiO2 photocatalytic degradation of organic compounds
Photocatalytic oxidation in the water by adding a certain amount of photosensitive semiconductor material, with a certain energy of light irradiation, the light of the semiconductor material is excited electron - hole pairs, the adsorption of dissolved oxygen of the photosensitive semiconductor surface, molecules of water and contaminants to accept electronic or a hole, and thus a series of redox reactions, degradation of toxic pollutants to non-toxic or less toxic substances a method can greatly improve the treatment effect [1].#p#分页标题#e#
Semiconductor catalysts include TiO2, ZnO, CdS, WO3 and Fe2O3, etc. [19]. Bahnemann, etc. [20] on the photocatalytic oxidation of various catalysts pentachlorophenol study concluded: TiO2 and ZnO best catalytic activity, CdS also has good activity, but in light of ZnO and CdS unstable, that photo-oxidation by light corrosion competition. Chemical properties of TiO2, photochemical properties are very stable and non-toxic cheap, ample supply, Gu used as photocatalyst.
Philippines is a U.S. EPA developed 16 kinds of PAHs priority control a face carcinogenic to humans. Philippine water-soluble small and difficult to completely mineralized, degradation problems. In the text Sheng [21] The study used the Philippine pre-adsorbed onto the catalyst surface approach to overcome its water solubility characteristics. Study compared different media surface (SiO2, Al2O3, TiO2) phenanthrene degradation rate, results showed that TiO2 in the degradation rate much faster.
Pesticides are generally divided into herbicides and pesticides, the harm a wide range, in the atmosphere, soil and water stay a long time, so its decomposition to remove much attention. Fei Ge, etc. [22] fixed film of TiO2 photocatalytic degradation of methamidophos, and achieved good results, organic phosphorus removal efficiency of 100%, COD removal rate reached 85.64%, emissions of COD reduced to 5. 93 mg / L, up to the national level of industrial wastewater discharge standards.
Bisphenol A (BPA) is an epoxy resin and a polycarbonate resin used in the manufacture of intermediate raw materials, are widely used in industrial production. Since BPA widely distributed in the environment, at high concentrations, with endocrine disrupting properties, so its environmental behavior under scrutiny. Gu Chenzhong etc. [23] using the UV-TiO2 photocatalytic oxidation degradation of BPA, under certain conditions, BPA can basically Photocatalytic Degradation completely.