Preparation And Methylene Blue Degradation Studies Of Polythiophene Based Photo-Fenton Catalyst

Due to the characteristics of high chrominance,high COD value and biological toxicity,it is difficult to treat dye wastewater effectively and harmlessly by traditional biochemical treating methods.Photocatalytic degradation technology is an effective method of wastewater degradation treatment,which can realize rapid and efficient degradation of low-concentration dye wastewater with low generation of by-products and secondary pollution.With regard to high-concentration dye wastewater,the Fenton reagent is widely used due to its satisfying decolorization rate,high COD removal performance and significant detoxification ability.Fenton-catalysis and photocatalysis technologies are often collaboratively used to improve the catalytic activity and degradation rate of organic dye wastewater,which is a hotspot in the research field of dye wastewater treatment.Recently,the catalytic degradation of organic pollutants by photo-Fenton technology focused on the screening and optimization of different functional active components.Polythiophene（PTH）,as an effective visible light responded,nonmetallic-organic stable polymer semiconductor,is widely applied to improve traditional metal oxide photocatalysts’band gap structure.However,the two-dimensional stacking structure and low valence band position of PTH materials result in many shortcomings,such as small specific surface area,low substrate adsorption capacity,high recombination rate of photoelectrons and insufficient oxidizability of photoinduced holes.Active carbon,as support of polythiophene hybrid catalyst,due to its high surface area,good electrical conductivity and easy doping properties,can effectively reduce the recombination rate of photoinduced electrons and increase the dispersion of polymers when it composited with PTH.In another aspect,active carbon can be used as a heterogeneous Fenton catalyst,which can decompose the oxidant(H₂O_2,KHSO₅,etc.)to generate strong oxidizing free radicals,thus increasing the degradation rate of the dye pollutants in wastewater.Our research group has successfully prepared GO/polythiophene photocatalyst with excellent degradation performance.However,it is difficult for industrial application due to the high cost of GO and the complex surface oxidation modification process.On the basis of polythiophene as a photocatalytic component,this paper uses cheap and facile MnO2 and activated carbon to compound with polythiophene,through the optimization of each component to improve the adsorption performance of the catalyst and photo-Fenton catalytic activity.The systematic research work is as follows:1.Through changing the oxidation polymerization method of polythiophene,a high quality polythiophene/manganese dioxide（PTH@MnO₂）absorbent material was synthesized by a simple one step oxidation-polymerization method.The absorption performance of TH@MnO₂ for methylene blue can reach 104.6 mg/g.It is found that the adsorption performance of TH@MnO₂ on the dye is primarily determined as chemical adsorption,and the adsorption sites are mainly Mn-OOH sites on the surface of the material.PTH@MnO₂ had good photocatalytic activity.The degradation rate of10 mg/L methylene blue can reach 62%.2.An oxygen-enriched activated carbon/polythiophene（KSPC/PTH）photo-Fenton composite catalyst was prepared by using a surface modification-supporting two-step method.The adsorption capacity of KSPC/PTH for methylene blue can reach480 mg _MB/g_cat.With the addition of simulated sunlight irradiation and H₂O₂（4.28 g/L）,the degradation rate of the high concentration methylene blue solution（120 mg/L）by280 mg/L KSPC/PTH can reach 86%within 40 min.At the same time,we analyzed and compared the ratio of different oxygen-containing functional groups on the KSPC surface under different heat treatment temperatures and the corresponding photocatalytic activity and Fenton-like catalytic activity of KSPC/PTH.It is inferred that the C-O groups on the surface are the Fenton-like active sites and the C=O and-COO groups on the catalyst surface enhance the photocatalytic activity of the polythiophene.The additional evidence of photoelectric characterization also proved that the C=O and-COO groups on the surface of KSPC/PTH strengthen the conduction of the photoinduced electrons,thereby improving the photocatalytic activity of the polythiophene.3.We synthesized a series of polythiophene（PTH）,poly-3-ethylthiophene（PET）,poly-3-thiophene ethanol（PTEO）,poly-3-thiophene acetic acid（PTAA）and poly-3,4-ethylenedithiophene（PEDOT）materials,and systematically studied their semiconducting properties and methylene blue degradation performance.It was confirmed that the substituents on the thiophene ring could reduce the band gap effectively and improve the catalytic activity of the thiophene polymer.At the same time,the DFT calculation of different thiophene monomers showed that oxygen group substituents on the thiophene ring can increase the dipole moment significantly（3-thiophene acetic acid,1.71 D;3,4-ethylenedithiophene,2.93 D）.Therefore,enhance the separation of polymer photogenerated electrons.Based on the different thiophene monomers,we prepared a modified oxygen-enriched activated carbon/poly-3-thiophene acetic acid（KSPC/PTAA）catalyst and its degradation rate of methylene blue could reach 0.04702 min^-1.We also adopted DFT fitting calculation and HPLC-MS analysis to deduce the possible degradation routes and intermediates in the methylene blue degradation process.4.When potassium perbisulfate（PMS）was used as an additive oxidant in the photo-Fenton reaction instead of hydrogen peroxide,we found that the modified oxygen-enriched activated carbon/poly-3-thiophene acetic acid（KSPC/PTAA）catalyst can reach a higher degradation rate of methylene blue（67.2%）within 6 min.The promotion effect of sulfate radical（SO₄^-·）on the degradation system is confirmed.SO₄^-·can significantly enhance the degradation rate and oxidation rate of methylene blue molecules,and the application range of p H of the system can be expanded.However,due to the covering effect of a large number of sulfate ions(SO₄^2-)in the system on the catalyst,the degradation performance of the catalyst was reduced in the cycle test.