Degradation Of Marine Diesel Pollution By Lanthanide Oxide/Zinc Oxide Composite Nano Photocatalyst Under Visible Light

With the continuous development of science and technology,the demand of mankind for the exploitation,transportation and utilization of offshore oil is increasing day by day,which will inevitably bring about a large amount of marine oil pollution.Among many marine oil treatment technologies,photocatalytic technology is favored by more researchers for its advantages of stability,high efficiency and no secondary pollution.Zinc oxide semiconductor?ZnO?has become a promising photocatalyst due to its wide band gap,non-toxicity and harmlessness.The electron spin angle momentum,orbital angular momentum interaction and coupling of the lanthanide oxides produce a very large energy level sublayer,leading to the electronic transition of f-f,resulting in a linear absorption spectrum.This transition allows the lanthanide oxide to selectively absorb visible light,which is used to upconvert luminescence due to the large number of metastable levels.In this paper,nanometer scale ZnO photocatalysts were successfully prepared by chemical precipitation method and were coprecipitated with lanthanide oxides to prepare nano-scale Yb₂O₃/ZnO,Er₂O₃/ZnO and Pr₆O₁₁/ZnO upconversion materials composite photocatalysts.The photocatalyst and polypropylene spheres were coupled to prepare supported composite photocatalysts.The photocatalytic performance and photocatalytic kinetics of four kinds of photocatalysts were studied with diesel in seawater as the target pollutant and with visible light as light source.In the visible light conditions,the supported photocatalyst treatment of marine diesel oil pollution,crude oil pollution achieved good results,and laid the foundation for the treatment of marine oil pollution.The results are as follows:?1?The ZnO nanoparticles were prepared by precipitation method.The samples were characterized by X-ray diffraction?XRD?and scanning electron microscope?SEM?.Under the condition of UV light and visible light,the single factors such as the dosage of ZnO,the initial concentration of diesel,the pH value of seawater,the concentration of hydrogen peroxide and illumination time factors were changed.The degradation efficiency of diesel pollution in seawater was explored under different single-factor conditions and different lighting conditions.The results show that self-made nano-ZnO exhibits ellipsoidal shape.ZnO particles are evenly distributed with high crystallinity and high purity.Under the same conditions,the removal efficiency of nano-ZnO photocatalyst under UV light was higher than that under visible light.Under UV light irradiation,the removal rate of diesel showed‘inverted U-shape'under different dosage,initial diesel concentration,hydrogen peroxide concentration and pH value conditions,and had an excellent removal rate.The growth trend under the illumination time showed that the increase of illumination time was beneficial to the increase of diesel removal rate in a short period of time.The highest removal rates of diesel by ZnO in seawater under visible light are all low,with an average removal rate of about 30%-40%.Most of the removal rate is due to the evaporation of diesel oil.?2?The Yb₂O₃/ZnO,Er₂O₃/ZnO and Pr₆O₁₁/ZnO nanocomposites were prepared by coprecipitation method,and marine diesel oil was taken as the target pollutant.The effects of pH value,initial concentration of diesel,dosage of catalyst,doping ratio of catalyst,concentration of hydrogen peroxide and illumination time on photocatalytic activity were studied.The photocatalytic conditions were optimized and the following conclusions were drawn.The Yb₂O₃/ZnO,Er₂O₃/ZnO and Pr₆O₁₁/ZnO composite nano-photocatalysts'particle dispersion is good,and the average particle size is 40.97,40.94 and 51.18 nm,respectively.The optimized conditions of photocatalytic diesel contaminated by Yb₂O₃/ZnO,Er₂O₃/ZnO and Pr₆O₁₁/ZnO in seawater are:when the initial diesel concentration was 0.05,0.10 and 0.20 g/L,the dosage of catalyst was 0.4,0.6 and 0.4 g/L,the doping ratio of catalyst was 40%,40%and 30%,the pH was7.0,10.0 and 6.0,the concentration of hydrogen peroxide was 4.0,4.0 and 6.0 mg/L and the irradiation time was 1.5,1.5 and 2.5 h,the diesel removal rate was 95.48%,98.60%and 90.81%through the verification experiment.The order of influence of various factors on the diesel removal rate is as follows:illuminationt time>concentration of hydrogen peroxide>pH value>doping ratio of catalyst>dosage of catalyst>initial concentration of diesel?Yb₂O₃/ZnO?;doping ratio>dosage>H₂O₂concentration>initial concentration of diesel>illumination time>pH value?Er2O3/ZnO?;illumination time>initial concentration of diesel>dosage of catalyst>concentration of hydrogen peroxide>doping ratio of catalyst>pH value of seawater(Pr₆O₁₁/ZnO).?3?By comparing the effects of Yb₂O₃/ZnO,Er₂O₃/ZnO and Pr₆O₁₁/ZnO composite photocatalysts on photocatalytic activity under different conditions,the photocatalytic UV-Vis diffuse reflectance spectra and their forbidden band widths was studied.Each factor on the photocatalytic degradation effect contrast was also studied.The photocatalytic activity mechanism was analyzed and the economic cost of the composite photocatalyst was estimated.Based on the results of the study,it was concluded that the UV-visible diffuse reflectance spectra shifted red-shifted when the doping ratio of lanthanides was increased,and the bandgaps of Y20,E20 and P20were 3.0,3.1 and 2.4 eV,respectively.It is known that the photocatalytic activity of the three composite photocatalysts is much higher under the same conditions than relying solely on diesel vaporization?no photocatalyst?.When the doping ratio of the three composite photocatalysts is 20%,the best degradation rates of diesel pollutants exist.Under the same reaction conditions,Yb₂O₃/ZnO,Er₂O₃/ZnO and Pr₆O₁₁/ZnO are suitable for treating wastewater with low concentration.Under the same conditions,the photocatalytic activity of Pr₆O₁₁/ZnO is better when the solution is acidic,and the photocatalytic activity of Er2O3/ZnO is better when the solution is alkaline.The most economical composite photocatalyst is Er2O3/ZnO.When the composite photocatalyst is illuminated,the photocatalyst electrons are excited by the valence band to the conduction band.The f-layer orbit in the lanthanide oxide can capture the excitation electron to the conduction band to prevent recombination of electron-hole pairs and generate a large amount of hydroxyl radicals,which is favorable for the photocatalytic reaction.Under the condition that the photocatalytic effects of the three photocatalysts are all good,it is most economical to choose the Er₂O₃/ZnO photocatalyst.?4?The influence of catalyst dosage,doping ratio,initial concentration of diesel,pH value of seawater and concentration of hydrogen peroxide on the reaction kinetics of Er₂O₃/ZnO were investigated.The data were processed by the first-order reaction rate equation and the second-order reaction rate equation.The first-order reaction rate equation was found to be more suitable for the kinetics of diesel oxidation in Er2O3/ZnO photocatalytic oxidation of seawater.Finally,based on the L-H model,the kinetic equation of total photocatalytic oxidation under the experimental conditions was calculated and the following conclusions were drawn:within a certain range,the pH value of seawater has a significant effect on the photocatalytic reaction rate.The influences of various factors on the diesel pollution in seawater degraded by Er₂O₃/ZnO were ranked as follows:pH of seawater>doping ratio of catalyst?initial concentration of diesel?concentration of hydrogen peroxide>dosage of catalyst.The pH value of seawater,doping ratio,concentration of hydrogen peroxide,dosage of catalyst and reaction rate have a positive correlation,and the initial concentration of diesel has a negative correlation,that is,the former four are favorable for the photocatalytic oxidation reaction within a certain range,and the latter has an inhibitory effect on photocatalytic oxidation within a certain range.The dosage of catalyst has little influence on the photocatalytic oxidation reaction rate.From the point of view of raw material saving,a higher reaction rate can be obtained even with a small amount of catalyst.?5?The supported photocatalyst prepared by using polypropylene polyhedral spheres as the carrier was prepared by the coupling agent method.The effects of three lanthanide doped photocatalysts on the degradation of diesel fuel were studied to investigate the photocatalytic activity of the three supported photocatalysts.The supported and non-supported photocatalysts for diesel degradation were compared.The three types of supported photocatalysts were recovered to compare the degradation effect of diesel oil and the degradation effect of the supported photocatalyst on crude oil was studied.The following conclusions were obtained:the distribution of supported photocatalyst particles is good and the coverage is good,and the film will not fall off in seawater.Three kinds of lanthanide doping photocatalysts have strong photocatalytic activity and photocatalytic efficiency,and the treatment of diesel pollution is short time,high speed and high rate of degradation.The supported photocatalyst prepared by the coupling agent method not only has strong adsorption,but also has good photocatalytic properties.The recovered supported photocatalyst has less loss of catalyst and can be recycled at least three times.The photocatalytic activity and the adsorption performance of the recovered supported photocatalyst are also good.The supported photocatalyst has a high removal rate of crude oil.When the illumination time is 8.0 hours,the removal rate of crude oil with different initial concentrations can reach 90%.