Study On Preparation Of Polypyrrole Modified TiO₂ Visible-light Photocatalyst Supported On Activated Carbon And Its Application

TiO₂ has widely been used in various fields of wastewater treatment,air purification,disinfection and clean energy production because of its non-toxicity,chemical stability,high efficiency,easy synthesis and low cost.However,the two drawbacks of wide-band gap TiO₂?Eg=3.0-3.2 eV?which severely blocking up its practical application.One is that TiO₂ is confined to absorb the ultraviolet?UV?light of overall solar spectrum?only 3-5%in total solar energy?;the other is that the photo-generated electrons and holes are prone to recombination and thus resulting in low utilization of light quantum.In addition,the problems of easy agglomeration,difficult separation and recovery also exist in the nano-TiO₂ based materials.The gallic acid wastewater is an important pollution source in our country,which is complex components,difficult to degrade organic matter,high COD concentration,high toxicity,low biodegradability and difficult to deal with.It is of great practical significance and has wide application values to study on the application of TiO₂ photocatalytic technology in the treatment of the gallic acid wastewater.In this paper,the easily separated and recycled PPy-TiO₂/CSC composite photocatalysts was prepared by adhesive method using the modified TiO₂ as photocatalyst and the biomass material of activated carbon as its carrier for the visible light type.The photocatalytic degradation was studied by using the supported photocatalyst under the illumination of xenon lamp?simulated solar light?in the light of the wastewater from the production of gallic acid in the forest industry.The main contents and conclusions of this paper are as follows:?1?Visible-light photocatalyst,polypyrrole?PPy?modified TiO₂?PPy-TiO₂?was prepared by chemical oxidation and in situ polymerization using the pyrrole?Py?photosensitizer as the polymer monomer and industrial grade nano-TiO₂?Degussa P25 Ti02?as raw material.The effects of the addition of pyrrole,the amount of oxidant,the time of ultrasonic mixing,the reaction time and other factors on the photocatalytic activity of PPy-TiO₂,were investigated by using 400 W metal halide lamp?simulated visible light?as light source and methyl orange as the target pollutants and was optimized using the L9?34?orthogonal experimental design.The prepared samples were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,Fourier transform infrared spectroscopy?FT-IR?and UV-Vis diffuse reflectance spectra?UV-Vis DRS?,Laser Raman spectroscopy?LRS?,and so on.The results showed that the optimum reaction conditions were ammonium persulfate?APS?oxidant,n?TiO₂?:n?ammonium persulfate?:n?ammonium persulfate?was 1:0.0345:0.069?mole ratio?,the ultrasonic time was 30 min and the reaction time was 5h.PPy-TiO₂ photocatalyst has a higher photocatalytic activity compared with pure TiO₂ under visible light.Photocatalytic degradation rate of methyl orange solution?30 mg/L?reached 68.41%for 30 min,and the various factors affect the trend of the order of the reaction time and the dosage of Py,APS and ultrasonic time.The absorption of PPy-TiO₂ is enhanced than that of nano-sized TiO₂ in the visible region,and the red shift occurs.PPy modified TiO₂ nanoparticles crystal which is still a mixture of anatase and rutile crystal and has not changed,oxidative polymerization of pyrrole polypyrrole after successfully coated onto the surface of Ti02 nanoparticles on the strong interaction.The oxidative polymerization of pyrrole was successfully coated onto the surface of TiO₂ nano particles.?2?The PPy-TiO₂/CSC photocatalyst was prepared by adhesive method using coconut shell activated carbon as carrier and PPy-TiO₂ as photocatalytic active ingredient in the optimal process preparing conditions.The effects were investigated for the factors of the loading ratio of PPy-TiO₂ and activated carbon,the amount of inorganic sodium silicate,the amount of photocatalyst and the initial concentration of target pollutant solution,and the kinetic studies were also carried out for the photocatalytic degradation of stationary phases with different initial concentrations.The prepared PPy-TiO₂/CSC samples were also characterized by FT-IR and SEM-EDS.When the dosage of PPy-TiO₂,sodium silicate and coconut shell was 3:3:10?mass ratio?,the photocatalytic activity of PPy-TiO₂/CSC was the best.For 40 mg/L 200 mL methyl orange solution,the decolorization rate was higher than that of 200 g PPy-TiO₂/CSC,which was up to 90.96%with a 400 W gold halide light illumination for 30 min,and the results of kinetic analysis showed that the photocatalytic degradation of PPy-TiO₂/CSC was consistent with first-order kinetics for methyl orange solution with different concentrations.Moreover,the results of FT-IR and SEM-EDS show that PPy-TiO₂ has been successfully loaded onto coconut shell activated carbon and most of the pores and surface of activated carbon are filled and coated with PPy-TiO₂ photocatalyst.?3?Under the illumination of 500 W xenon lamp,the results showed the photocatalytic degradation of the PPy-TiO₂/CSC was affected by pH value,H2O2 amount,light time and catalyst dosage for wastewater of gallic acid production through the single factor experiment and orthogonal test.The optimum conditions were as follows:pH=7,the dosage of PPy-TiO₂/CSC catalyst was 0.5 g,the adding amount of 3%H2O2 was about 0.3 mL,and the illumination time was 2.5 h for 100 mL gallic acid wastewater diluted 10 times.Under the above conditions,the removal rate of CODcr can reach 88.52%,which has reached the national wastewater discharge standard,and the effect of various factors on photocatalytic efficiency are in turn:catalyst amount,H2O2 amount pH value and illumination time.At the same time,the prepared PPy-TiO₂/CSC photocatalyst has good stability and photocatalytic activity in the degradation of gallic acid wastewater,and can be reused after separation and recovery.Therefore,it is feasible to treat the actual wastewater using the prepared PPy-TiO₂/CSC photocatalysts using solar light.