Semiconductor Photocatalysts For The Photocatalytic Oxidation Of Phenol And Its Derivatives Based On The Principle Of Energy Level Matching

Considering phenolic wastewater is difficult to be degraded under normal circumstances,it is a good way to select efficient semiconductor photocatalysts to degrade phenolics based on photocatalysis oxidation technology,and phenolics will be broken down into carbon dioxide?CO₂?and water?H₂O?.Studying the performance that different energy level of energy band of semiconductor photocatalysts on a series of phenolics' photocatalysis oxidation according to the energy level matching relationship between semiconductor photocatalysts and organic pollutants,it will lay the foundation for the industrial application of phenolic wastewater's photocatalytic oxidation.The main idea of this paper is: using quantum chemistry calculation,UV-Vis diffuse reflectance spectroscopy,Mott-Schottky experiment and cyclic voltammetry etc.to obtain the energy level of semiconductor photocatalysts' energy band,and the energy level of phenol and its derivatives' HOMO and LUMO molecular orbital.Based on energy level matching,the difference among the performance of photocatalysts on phenol and its derivatives' photocatalytic oxidation has been analyzed and discussed.The difference among the holes,photo-generated charges and hydroxyl radicals' performance on phenol and its derivatives' photocatalytic oxidation has been explored,and phenol and its derivatives' photocatalytic oxidation mechanism has been proposed and discussed briefly.The contents mainly contain as following:1.Adopt dissolution with heating,impregnation,precipitation,grinding and calcination these methods to prepare TiO₂,WO₃,V₂O₅ and CdS,and WO₃-ITO,V₂O₅-ITO,CdS-ITO and TiO₂-ITO conductive glass films have been synthesized.The glassy carbon electrode modified with GO/SWCNT-Nafion polymer composites is also prepared.2.Through quantum chemistry calculation and related formulas,we obtain the virtual energy level of semiconductor photocatalysts' energy band,phenol and its derivatives' HOMO and LUMO molecular orbital.The actual valence band and conduction band energy level of photocatalysts are obtained with Motto-scottky test,UV-vis DRS and the energy level relationship diagram of n-type semiconductors' energy band,and the actual HOMO and LUMO molecular orbital energy level of phenol and its derivatives are obtained by Cyclic Voltammetry test,.3.Using the prepared photocatalysts for the degradation experiments of phenol and its derivatives: using CdS,TiO₂?P25?,WO₃ and V₂O₅ for phenol's photocatalysis oxidation experiments,and using TiO₂ for phenol and its derivatives' photocatalysis oxidation experiments.The experimental results show that: the activity order of the photocatalysts is: P25 > WO₃ > V₂O₅ > CdS,and the degradation effect order of phenol and its derivatives is: hydroquinone > phenol > p-nitrophenol > p-chlorophenol.According to the thermodynamics and electrochemistry,it could be known that the lower the valence band energy level potentials of the photocatalysts own,the higher photocatalysis performance they own,and the higher of the HOMO energy level potentials of phenolics own,the easier they could be photodegraded.4.By adding sacrificial agents of three active substances,we find that the contribution ratio of active substances to the photocatalysis oxidation of phenol and its derivatives is that h⁺: e^-: HO· = 1: 4: 4.Thus,it could be concluded that phenol and its derivatives are photodegraded mainly through indirect interaction of photo-generated electrons or direct interaction of hydroxyl radicals.The photocatalysis oxidation mechanism of phenol and its derivatives follows the following procedure: First,they are oxidized into hydroquinone and derivatives of hydroquinone.Then they are oxidized into quinone and derivatives of quinone.Then the structure of phenyl ring is destroyed,and form maleic acid and formic acid.Finally,they are completely decomposed into carbon dioxide and water.