Research On The Oxidization Of Organic Pollutants From Water By Co/BiVO₄-SO₄^-· Photo-Fenton-Like Method

Nowadays,with the continuous improvement of China's economy,the waste water produced in the production and life has the characteristics of large quantity,complex water quality,high poisonousness,etc.,which makes it difficult for the traditional methods to meet the requirements of water quality,and high cost of sewage treatment has become a bottleneck in the field of sewage treatment of our country.A advanced oxidation technology that cobalt ions activate persulfacte to produce sulfate radical?SO₄^-·?can effectively decompose the refractory organic pollutant in the waste water into some non-toxic small molecular substances.This technology not only overcomes the dependence of the traditional Fenton technology on pH,but also does not produce a large amount of iron mud due to the precipitation of ferric ions.However,the superfluous Co²⁺itself has some toxicity to the environment in the actual production,so the development of heterogeneous catalysts has become a hot research topic.The photocatalytic technology that takes semiconductor as a representative is a new clean energy technology,especially the photocatalytic technology based on BiVO₄,which can produce living free radicals in the visible light to remove the organic pollutants.Redox heterojunction structure is formed by loading the transition metal Co on the surface of the carrier BiVO₄,can this composite material not only improve the photocatalytic activity of the material,but also can activate persulfate to turn Fenton-like reaction,besides,the two reaction can produce synergistic effect through mutual promotion.?1?BiVO₄/Bi₂VO₅ heterojunction photocatalytic material can be synthesized by adopting one-step hydrothermal method and using DMF?N,N-dimethylformamide?as adjuvant.The structural characterization was analyzed by means of XRD,SEM,HRTEM,XPS,UV-Vischaracterization to demonstrate the relationship between the structure and properties of the material.The band gaps of different catalysts were confirmed by Ultraviolet-visible spectroscopy?DRS?.The photocatalytic activity of BiVO₄/Bi₂VO₅ heterojunction material under different hydrothermal temperatures was investigated under the visible light irradiation,taking Methylene blue as a model pollutant,the results showed that the catalyst produced at220?had the highest catalytic activity.Based on the Fermi level definition,the transport and separation mechanism of photo-generated carriers in heterojunction materials were discussed in detail.Besides,it was indirectly proved that the existence of Bi₂VO₅ was helpful to the separation of photo-generated electrons and electron holes through the quenching experiment of free radicals and photoluminescence fluorescence spectrum.?2?Co-BiVO₄ redox heterojunction material with different Co loadings were synthesized by one-step hydrothermal method,taking Co?NO₃?₂·6H₂O as the Co source.The morphology characterization and photoelectric properties of the prepared nanometer photocatalytic material were analyzed by means of XRD,SEM,HRTEM,XPS,UV-Vis characterization.The photocatalytic properties of different materials were investigated by using Methylene blue as the target pollutant and visible light as the light source.The results showed that the photocatalytic activity of Co-BiVO₄ composite photocatalyst was higher than that of pure BiVO₄.When the ratio of Bi and Co was 2:1,the photocatalytic activity of Co-Bi VO₄ was the highest,and the photocatalytic reaction rate was 4 times higher than that of pure BiVO₄.Besides,it was further proved through the constant voltage photocurrent response test that the formed Co-BiVO₄ redox heterojunction could contribute to the separation of electrons and holes,at the same time,the related mechanism of the redox heterojunction to improve the photocatalytic activity were analyzed in detail.?3?Based on the previous experiments,a composite system of taking SO₄^-·as the main part and co-existing with·OH was constructed by using Co-BiVO₄ composite catalyst synergizing with sodium persulfate under visible light.The catalytic activity of different systems was evaluated by the degradation rate of Paracetamol,which showed that the“Vis/PS/Co-BiVO₄”system had the highest catalytic activity.Through the experiments of exploring the effect of different pH on the activity of“Vis/PS/Co-BiVO₄”system,it was found that the system had higher catalytic activity in the range of 3-9,and the highest catalytic activity appeared under neutral and alkaline conditions.The recovery experiment of the catalyst showed that the catalyst used in this system could be recycled.Through the comparison of different experiments,it was proved that the“Vis/PS/Co-BiVO₄”system had several advantages,such as saving the persulfate dosage,shortening the reaction time,reducing the experiment cost,getting rid of the dependence of traditional Fenton on pH,avoiding secondary pollution and so on.Besides,the related mechanism of the synergistic effect that was put forward by the research institute was also analyzed in detail.