静电纺丝法制备纳米磷酸铋及其光催化降解亚甲基蓝的研究

发布时间：2018-04-13 11:44

本文选题：磷酸铋 + 光催化　；参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：光催化氧化技术在处理难降解有机废水领域以高效低耗、无二次污染等优点受到广泛关注,而该技术对有机污染物去除率很大程度上取决于光催化材料的结构、物化特性,因此选择合适的光催化材料极其重要。磷酸铋因其本身具有的特殊结构和半导体特性而具有非常优异的紫外光光催化活性,光催化活性约为传统紫外光催化剂二氧化钛粉末催化剂的3.2倍。本文以静电纺丝技术为制备方法,结合溶胶凝胶法制备了磷酸铋纳米纤维催化剂,以这两种催化剂为基础,以亚甲基蓝为降解底物,考察了在紫外光下对亚甲基蓝的降解率和矿化率。相对于水热法制备的磷酸铋颗粒拥有很高的对亚甲基蓝溶液的降解效率。静电纺丝制备的磷酸铋纳米纤维,相对于水热法制备的磷酸铋颗粒,光电化学性质有着明显的差异,在光照或者暗态条件下,磷酸铋纳米纤维的交流阻抗半径明显的比纳米颗粒的阻抗半径小,磷酸铋纳米纤维会更容易发生光化学反应,从而导致光催化速率的变化,是影响其活性的主要因素。而且无论是磷酸铋颗粒或者是磷酸铋纤维,相对于TiO2都有着很高的活性,这是因为磷酸根的诱导效应有利于电子空穴的分离和传导。这种磷酸根在光催化反应中的优势和对活性的制约因素可能对其它非金属含氧酸盐光催化剂具有一定的普适性。结合第一性原理DFT(Density Functional Theory)计算,磷酸铋的能带结构、态密度和电子云密度进行了计算和分析,磷酸铋的能带主要为O的2p和Bi的6p轨道杂化生成,结合紫外可见吸光度测试,利用经典的Schoonen公式,计算磷酸铋的价带位置约为3.67 V vs.标准氢电极(SHE),这预示着磷酸铋的光生空穴具有很强的氧化性,从而有利于空穴直接氧化有机污染物和羟基自由基的生成,从而有利于光催化反应的进行。在电子云密度计算中可知,磷酸铋结构中磷酸根具有很强的吸电子作用,从而使得电子云密度集中于磷酸根附近,形成了一个内建电场,从而可以吸引大量的光生电子,从而变相的促进了光生电子的分离,这可能是磷酸铋具有较强光催化活性的一个原因。此外,论文对于磷酸铋光催化降解MB的实验进行了变量探究,譬如pH值和染料初始浓度对光催化活性的影响进行了研究和讨论。发现处理时间在100min时,制备的磷酸铋纤维和商业TiO2对亚甲基蓝的降解率分别为87%和63%,反应均为表一级反应动力学,动力学常数分别为0.0206和0.0073min-1。此外,还对纳米磷酸铋纤维降解亚甲基蓝的实验进行了过程优化,最优参数确定为pH值为3和亚甲基蓝初始浓度为50mg/L。最后本实验对纳米磷酸铋纤维对亚甲基蓝的降解机理进行了浅析,并在空穴捕获剂和自由基捕获剂的投加实验中确认反应以自由基降解过程为主。
[Abstract]:Photocatalytic oxidation technology is widely concerned in the field of treatment of refractory organic wastewater, such as high efficiency and low consumption, no secondary pollution and so on. However, the removal rate of organic pollutants by this technology depends to a great extent on the structure, physicochemical properties of photocatalytic materials.Therefore, the selection of appropriate photocatalytic materials is extremely important.Bismuth phosphate has excellent UV photocatalytic activity due to its special structure and semiconductor properties. The photocatalytic activity of bismuth phosphate is about 3.2 times that of traditional TiO2 powder catalyst.In this paper, bismuth phosphate nanofiber catalysts were prepared by electrospinning and sol-gel method. Based on these two catalysts, methylene blue was used as the substrate for the degradation of bismuth phosphate nanofibers.The degradation rate and mineralization rate of methylene blue under ultraviolet light were investigated.Bismuth phosphate particles prepared by hydrothermal method have high degradation efficiency of methylene blue solution.The photochemical properties of bismuth phosphate nanofibers prepared by electrostatic spinning are obviously different from those prepared by hydrothermal method.The AC impedance radius of bismuth phosphate nanofibers is obviously smaller than that of nanoparticles. The photochemical reaction of bismuth phosphate nanofibers is more likely to occur, which leads to the change of photocatalytic rate, which is the main factor affecting the activity of bismuth phosphate nanofibers.Moreover, both bismuth phosphate particles and bismuth phosphate fibers have high activity compared with TiO2, which is due to the fact that the induced effect of phosphate is conducive to the separation and conduction of electron holes.The advantages of this kind of phosphate in photocatalytic reaction and the restriction factors on its activity may have a certain universality for other non-metal oxygenated photocatalysts.The energy band structure, density of states and electron cloud density of bismuth phosphate are calculated and analyzed in combination with first-principles DFT(Density Functional Theory calculations. The energy bands of bismuth phosphate are mainly generated by O 2p and Bi 6p orbital hybrids.Using the classical Schoonen formula, the valence band position of bismuth phosphate is calculated to be about 3.67 V vs.This indicates that the photogenerated holes of bismuth phosphate are highly oxidized, which is conducive to the direct oxidation of organic pollutants and hydroxyl radicals in the holes, thus facilitating the photocatalytic reaction.In the calculation of electron cloud density, it can be seen that the phosphate in bismuth phosphate structure has very strong electron absorption effect, which makes the electron cloud density concentrate near phosphate radical, forming a built-in electric field, which can attract a large number of photogenerated electrons.As a result, the photocatalytic activity of bismuth phosphate may be one of the reasons for the photocatalytic activity of bismuth phosphate.In addition, the experiments of bismuth phosphate photocatalytic degradation of MB were investigated, such as the effects of pH value and dye initial concentration on the photocatalytic activity.It was found that the degradation rates of methylene blue by bismuth phosphate fiber and commercial TiO2 were 87% and 63% respectively when the treatment time was in 100min. The kinetics constants were 0.0206 and 0.0073 min-1, respectively.In addition, the process of degradation of methylene blue by nano-bismuth phosphate fiber was optimized. The optimum parameters were determined as pH 3 and initial concentration of methylene blue 50 mg / L.Finally, the degradation mechanism of methylene blue by nano-bismuth phosphate fiber was analyzed, and it was confirmed that the reaction was dominated by free radical degradation in the experiment of hole trapping agent and free radical trapping agent.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X703

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