| With the rapid development of industrialization,urbanization and agricultural modernization in modern society,more and more nitrogen-containing wastewater is discharged by human activities.Nitrate in water will lead to water eutrophication and pose a serious threat to human health.The treatment of nitrogen-containing wastewater has become a problem of concern all over the world.At present,the methods to remove nitrate in water mainly include biological denitrification,reverse osmosis,ion exchange,electrodialysis and photocatalysis.Biological denitrification,reverse osmosis,ion exchange,electrodialysis and other methods have been used to remove nitrate in water.However,these technologies are expensive,usually need to carry out follow-up treatment of the generated wastewater,and the nitrogen conversion rate is low,Photocatalytic treatment of nitrogenous wastewater is a chemical reaction that converts nitrate into intermediate product nitrite,by-product ammonia nitrogen and nitrogen under the action of photocatalysis.Compared with traditional nitrogenous wastewater treatment technology,photocatalytic reduction of nitrate nitrogen technology is more environmentally friendly,and can completely degrade pollutants without secondary pollution.Photocatalysis is an environmentally friendly and promising denitrification technology for the treatment of nitrogenous wastewater,And has received extensive attention at present.g-C3N4/Ag(1 wt%,2 wt%,5 wt%,10 wt%)photocatalyst was prepared by calcination and photodeposition.The catalyst was characterized by XRD,SEM,XPS,UV-Vis diffuse reflectance spectrum and Fourier infrared spectrum.The photocatalytic reduction of nitrate nitrogen in water was studied by photocatalyst.The characterization results showed that gC3N4/Ag(1 wt%,2 wt%,5 wt%,10 wt%)photocatalyst was successfully synthesized.The local structure of g-C3N4 material is composed of heptazine units,and the silver in g-C3N4/Ag has metallic properties.g-C3N4 still maintains a structural integrity after the deposition of Ag particles,and the absorption of photocatalyst in the range of visible light spectrum gradually increases with the increase of the proportion of doped silver.The experimental results show that g-C3N4/Ag(5 wt%)is treated with 50 mM formic acid as hole scavenger,When the catalyst dosage is 0.4 g and the initial solution pH is 2,the nitrogen-containing wastewater with nitrate nitrogen concentration of 50 mg/L can be treated.The nitrate nitrogen conversion rate can reach 88%and the nitrogen selectivity is 83%.Compared with g-C3N4/Ag(5 wt%),g-C3N4/Ag(1 wt%),g-C3N4/Ag(2 wt%)and g-C3N4/Ag((10 wt%),the denitrification performance of gC3N4/Ag is significantly better,which shows that increasing the proportion of silver doped catalyst to a certain extent can improve the nitrate nitrogen conversion rate,but the nitrate nitrogen removal rate decreases with the increase of silver loading proportion.Excessive silver loading will increase the size of silver particles and reduce the ability of catalyst to store electrons,As a result,the removal rate of nitrate nitrogen decreased.From the analysis of reaction mechanism,when g-C3N4 is irradiated by visible light with photon energy equal to or higher than g-C3N4 band gap(2.7eV),g-C3N4/Ag is excited to form electron hole pair,NO3converted to NO2-、NH4+、N2 under the action of electrons.BiOBr/Ag(1 wt%,2 wt%,5 wt%,10 wt%)photocatalysts were prepared by hydrothermal synthesis and photodeposition.The catalysts were characterized by XRD,SEM,XPS,UV-Vis diffuse reflectance spectroscopy and Fourier infrared spectroscopy.The photocatalytic reduction of nitrate nitrogen in water was studied by photocatalyst.The characterization results showed that BiOBr/Ag(1 wt%,2 wt%,5 wt%,10 wt%)photocatalyst was successfully prepared,and the catalyst was not disturbed by other substances.At the same time,the silver in BiOBr/Ag has metallic properties,and BiOBr still maintains a structural integrity after the deposition of Ag particles.With the increase of the proportion of doped silver,the catalyst shows continuous strong absorption in the range of 200-800 nm,and the absorption of visible light tends to be stable,which shows that the introduction of Ag into BiOBr can improve the light absorption of the catalyst in the visible region.Experimental results show that BiOBr/Ag(2 wt%)was used to treat nitrogen-containing wastewater with nitrate nitrogen concentration of 50 mg/L under the conditions of 50 mM formic acid as hole scavenger,catalyst dosage of 0.4 g and initial solution pH of 4.The nitrate nitrogen conversion rate could reach 90%and nitrogen selectivity was 88%.Compared with BiOBr/Ag(1 wt%),BiOBr/Ag(5 wt%)and BiOBr/Ag(10 wt%),BiOBr/Ag(2 wt%)has the best nitrate nitrogen removal effect,and with the increase of silver loading ratio,nitrate nitrogen removal first increases and then decreases,indicating that an appropriate amount of silver particles can effectively prolong the separation time of photogenerated electrons and holes and improve the photocatalytic reduction effect of nitrate nitrogen.From the analysis of reaction mechanism,under visible light irradiation,the photogenerated electrons produced by BiOBr and Ag will be excited from the valence band to the conduction band,NO3-converted to NO2-、NH4+、N2 under the action of electrons.Due to the close interface contact between Ag and BiOBr,some electrons in BiOBr will be transferred to the Ag conduction band,which can promote the separation of electrons and holes to a certain extent,so as to improve the nitrate nitrogen reduction efficiency.The Ag loaded on BiOBr/Ag can enhance the absorption of visible light and promote the separation of photogenerated carriers.g-C3N4/BiOBr/Ag(1 wt%,2 wt%,5 wt%,10 wt%)photocatalyst was prepared by hydrothermal synthesis and photodeposition.The catalyst was characterized by XRD,SEM,XPS,UV-Vis diffuse reflectance spectroscopy and Fourier infrared spectroscopy.The photocatalytic reduction of nitrate nitrogen in water was studied by photocatalyst.The characterization results showed that g-C3N4/BiOBr/Ag(1 wt%,2 wt%,5 wt%,10 wt%)photocatalysts were successfully prepared and were not disturbed by other substances.However,XRD shows that the diffraction peak intensity of Ag particles is weak,which may be due to the relatively small amount of Ag deposited on the surface of photocatalyst.The Tensile vibration of C-N and C=N,the symmetric Tensile vibration of Bi-O and the antisymmetric Tensile vibration of Bi-Bi appear in the FT-IR diagram.These peaks appear in the sample,which can well explain the synthesis of g-C3N4/BiOBr,and the introduction of Ag particles does not change the chemical structure of the sample.At the same time,silver in g-C3N4/BiOBr/Ag has metallic properties.g-C3N4/BiOBr/Ag(2 wt%)was used as hole scavenger with 50 mM formic acid,the dosage of catalyst was 0.2 g and the initial solution pH was 4 to treat nitrogencontaining wastewater with nitrate nitrogen concentration of 50 mg/L.The nitrate nitrogen conversion rate was 88%and the nitrogen selectivity was 87%.Compared with gC3N4/BiOBr/Ag(1 wt%),g-C3N4/BiOBr/Ag(5 wt%),and g-C3N4/BiOBr/Ag(10 wt%),gC3N4/BiOBr/Ag(2 wt%)showed the best nitrate nitrogen removal effect.From the analysis of reaction mechanism,under visible light irradiation,g-C3N4 and BiOBr will be excited by light to produce electrons and holes,which are located in the valence band and conduction band respectively,NO3-is converted to NO2-、NH4+、N2 under the action of electrons.Ag can cause plasma resonance(SPR)on the surface of g-C3N4/BiOBr,which can improve the activity of photocatalyst. |
PDF Full Text Request