本文選題：磷酸鉍 + 光催化　； 參考：《哈爾濱工業(yè)大學》2017年碩士論文

【摘要】：光催化氧化技術(shù)在處理難降解有機廢水領(lǐng)域以高效低耗、無二次污染等優(yōu)點受到廣泛關(guān)注,而該技術(shù)對有機污染物去除率很大程度上取決于光催化材料的結(jié)構(gòu)、物化特性,因此選擇合適的光催化材料極其重要。磷酸鉍因其本身具有的特殊結(jié)構(gòu)和半導體特性而具有非常優(yōu)異的紫外光光催化活性,光催化活性約為傳統(tǒng)紫外光催化劑二氧化鈦粉末催化劑的3.2倍。本文以靜電紡絲技術(shù)為制備方法,結(jié)合溶膠凝膠法制備了磷酸鉍納米纖維催化劑,以這兩種催化劑為基礎(chǔ),以亞甲基藍為降解底物,考察了在紫外光下對亞甲基藍的降解率和礦化率。相對于水熱法制備的磷酸鉍顆粒擁有很高的對亞甲基藍溶液的降解效率。靜電紡絲制備的磷酸鉍納米纖維,相對于水熱法制備的磷酸鉍顆粒,光電化學性質(zhì)有著明顯的差異,在光照或者暗態(tài)條件下,磷酸鉍納米纖維的交流阻抗半徑明顯的比納米顆粒的阻抗半徑小,磷酸鉍納米纖維會更容易發(fā)生光化學反應,從而導致光催化速率的變化,是影響其活性的主要因素。而且無論是磷酸鉍顆粒或者是磷酸鉍纖維,相對于TiO2都有著很高的活性,這是因為磷酸根的誘導效應有利于電子空穴的分離和傳導。這種磷酸根在光催化反應中的優(yōu)勢和對活性的制約因素可能對其它非金屬含氧酸鹽光催化劑具有一定的普適性。結(jié)合第一性原理DFT(Density Functional Theory)計算,磷酸鉍的能帶結(jié)構(gòu)、態(tài)密度和電子云密度進行了計算和分析,磷酸鉍的能帶主要為O的2p和Bi的6p軌道雜化生成,結(jié)合紫外可見吸光度測試,利用經(jīng)典的Schoonen公式,計算磷酸鉍的價帶位置約為3.67 V vs.標準氫電極(SHE),這預示著磷酸鉍的光生空穴具有很強的氧化性,從而有利于空穴直接氧化有機污染物和羥基自由基的生成,從而有利于光催化反應的進行。在電子云密度計算中可知,磷酸鉍結(jié)構(gòu)中磷酸根具有很強的吸電子作用,從而使得電子云密度集中于磷酸根附近,形成了一個內(nèi)建電場,從而可以吸引大量的光生電子,從而變相的促進了光生電子的分離,這可能是磷酸鉍具有較強光催化活性的一個原因。此外,論文對于磷酸鉍光催化降解MB的實驗進行了變量探究,譬如pH值和染料初始濃度對光催化活性的影響進行了研究和討論。發(fā)現(xiàn)處理時間在100min時,制備的磷酸鉍纖維和商業(yè)TiO2對亞甲基藍的降解率分別為87%和63%,反應均為表一級反應動力學,動力學常數(shù)分別為0.0206和0.0073min-1。此外,還對納米磷酸鉍纖維降解亞甲基藍的實驗進行了過程優(yōu)化,最優(yōu)參數(shù)確定為pH值為3和亞甲基藍初始濃度為50mg/L。最后本實驗對納米磷酸鉍纖維對亞甲基藍的降解機理進行了淺析,并在空穴捕獲劑和自由基捕獲劑的投加實驗中確認反應以自由基降解過程為主。
[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.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：X703

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