摘要
光催化技术是一项新型废水处理及净化技术,与其他传统的水处理技术相比具有降解完全、高效、价廉、稳定和可以利用太阳光等优点,因而具有良好的应用前景。利用太阳光处理污水而最常用的是TiO2,然而该种物质需要紫外活化,有诸多弊端,因而用可见光作为光能源处理污水一直是科学家所追求的目标。1998年,Ikeda等人首次宣布用Cu2O作光催化剂可在阳光-下将水分解成氢气和氧气,预示着Cu2O在可见光下具有很好的光催化性能。块体Cu2O量子效率较低,产生的光生电子一空穴对容易复合。当粒度从微米级变为纳米级时,复合率降低,可提高量子效率。本实验的目的是要用简单的方法制备出粒径较小,且形貌均一的纳米级氧化亚铜,并探讨纳米级氧化亚铜的光催化活性。
实验选择亚硫酸钠还原硫酸铜的方法来制备Cu2O,操作方便,产物纯净。本文首次在溶液中加入缓冲溶液,调解溶液的pH值。通过多次的试验发现溶液的合适pH值为5.0左右,所以选用HAc-NaAc缓冲体系。采用化学分析、扫描电子显微镜、X-射线衍射等测试手段对样品进行了表征,确定了在水热条件下制备氧化亚铜的最佳反应条件。
通过水热法制备的Cu2O单因素实验和正交实验结果发现影响制备氧化亚铜的主要因素有反应时间、反应温度、缓冲剂的用量和反应物的配比,得出水热制备氧化亚铜的最佳实验条件为:反应温度353K、反应时间4h、缓冲剂的用量为反应溶液的2倍、填充度为8.0。得到产品的颜色为紫红色,产物较纯净,颗粒在200nm左右,近似为球形。氧化亚铜的产率为92%,用氧化还原法滴定测得氧化亚铜的含量为98.67%。
而后,我们利用制得的Cu2O粉末进行光催化性能研究,并将降解得主要对象定为甲基橙作为有机指示剂,自制纳米Cu2O粉末在可见光照射下能够对甲基橙溶液起到很好的降解作用。通过实验得到Cu2O降解甲基橙溶液的适宜运行参数为:催化剂质量浓度为1.3 g/L～1.7g/L,pH值为8～12,甲基橙溶液初始浓度为20mg/L～60 mg/L,反应时间70min,温度0℃～35℃。对于初始浓度为40mg/L的甲基橙溶液,在日光灯的照射下,(溶液pH值为8,催化剂含量为1.5g/L)反应70 min脱色率可达92.1%,避光暗处则脱色率可达69.1%。
实验表明H2O2的加入能够对甲基橙溶液的降解起到很好的促进作用,但H2O2的浓度不宜过高,适当的浓度范围应控制在1%以内。使用超声搅拌可以在反应初期提高甲基橙溶液的降解效率,但由于温度升高的缘故,使得最终的降解率下降。将自制纳米Cu2O回收再利用,其对甲基橙溶液的脱色效果随回收次数的增加呈下降趋势,但回收后的纳米Cu2O对甲基橙仍然有较好的脱色效果,回收7次后,对40 mg/L的甲基橙溶液脱色率可达50 %。
最后,本文对甲基橙的光催化降解机理和动力学进行研究,经计算多数条件下甲基橙的降解反应属于二级反应,但随着条件的变化,反应级数及动力学方程都会发生变化。
Photocatalysis is emerging as a promising technology for wastewater treatment and water purification. The advantages of this technique over the traditional waste water treatment include complete mineralizaion, high degradation efficiency, low cost, good stability, and the potential to utilize sunlight as UV source. TiO2, as a kind of photocatalyst, can be used to degrade organic contamination with dramatic effects. However, there is also some shortcoming, this kind of matter needs the ultraviolet activation, thus using the visible light as the light energy to processing sewage always is a goal which the scientist pursues. In 1998, Ikeda et al firstly showed that Cu2O could decompose H2O to H2 and O2 in the sunlight. It predicts that Cu2O may be employed as a promising catalyst under visible light. As we know, the quantum efficiency of bulk Cu2O is quite low while increase as thescale of Cu2O transform from micrometer to nanoscale.The aim we pray is to synthesize small-scale nano Cu2O with uniform morphologies by simple method, and then discuss the activities of photocatalysis of nanoCu2O.
Cuprous oxide can be prepared from cupric sulfate and sodium sulfite solution.The raw material, such as cupric sulfate and sodium sulfite, is easy to obtain. In this paper, the buffer solution of acetic acid and sodium acetate (HAc-NaAc) is first used to adjust the valve of pH. The sample was analyzedand characterized by using Chemistry Analysis, SEM,XRD, and DTA-TG. The optimal reaction condition of preparing cuprous oxide is confirmed in hydrothermal synthesis.
The results of single-factor experiment and orthogonal test experiment of hydrot -hermal synthesis method showed that the main factors which influenced the prepa -ration were reaction time, reaction temperature, the dosage of reactant, and the filling factor. The optimal experiment conditions of the hydrothermal synthesis method were four hours of reaction time and 353K of reaction temperature, the dosage of the buffer reagent was two times as much as the dosage of reactive solution, and the best filling ratio was 0.80. The yield was 92%, the content was98.67%.
the Cu2O powder was used to research on the photocalcatalysis performance, and will degrade the main object to decide as the methyl orange to take the organic indica -tor, the self-made nanometer Cu2O powder will be able to playthe very good degeneration role under the visible light illuminationto the methyl orange solution. The results of optimum parameters were as following: the mass concentration of nano-Cu2O 1.3g/L ~1.5g/L ; the initial concentration of methyl orange 20mg/L ~60 mg/L ; the reaction time 70 min; the reaction temperature 0℃～35℃. Regarding the initial density is the 40mg/L methyl orange solution,under the daylight lampilluminati -on, (the solution pH value is 8,catalyst content is 1.5g/L) responded 70 min decoloriz -ation rate mayreach 92.1%, evades the light hidden place decolorization rate to be possible to reach 69.1%.
The experiment indicated that H2O2 can accelerate the methyl orange solution’s degeneration, but the H2O2 density scope should be controled in 1%. The supersonic stirs may enhance the methyl orange solution degeneration in the initial period , because the temperature increment, the final degeneration rate drop . Useing the self- made nanometer Cu2O recycling, it assumes the drop tendency to the methyl orange solution decolorization effect along with the recycling number of times increase. But recycled nanometer Cu2O still have the better decolorization effect to the methyl orange, after being recycled 7 times, 40 mg/L methyl orange solution decolorization rate might reach to 50%.
Finally, the kinetics of the photocatalytic reaction of the of Methly was research -ed . According to the computation , the methyl orange degradation reaction belongs to two levels under most conditions. Under different conditions, the kinetic equati on is different.
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