Preparation Of Photocatalytic Materials And Their High Efficiency For Catalytic Reactions

In recent years,the development of green,environmental-friendly,sustainable energy sources such as wind energy,water energy,wave energy,biomass energy,solar energy have attracted world attention Solar energy is undoubtedly the most ideal renewable energy due to its large storage and wide distribution.Solar energy's radiation into the earth just accounts for only one 2.2 billionth of the sun total radiation,but it is enough for human's consumption for more than 3000 years.Now,photothermal conversion,photoelectric conversion,photochemical and photobio logical conversion are belong to solar energy appication.Photocatalysis,as a clean,mild and environmentally friendly technology,has attracted wide attention in industry and academia.Biomass is not only rich in reserves,but also widely distributed as solar energy.The annual world biomass production is 170 billion tons,however,only about 3.5%is used by human beings.Cellulose,hemicellulose and lignocellulose are the most abundant biomass.High temperature thermal,chemical,physical,biological treatment are the main ways for the biomass conversion.The transformation of biomass into fuel by the utilization of solar energy has attracted much attention in recent years,which is one of the most effective ways to solve the energy crisis and environmental problems.Therefore,this thesis focuses on the photocatalytic conversion of biomass through catalytic reaction.The main innovations of this work include:(1)For the first time,cellulose was reformed in NaOH/urea water system for the highly efficient hydrogen production through the photocatalytic method;(2)The cellobiose was hydrolyzed under visible light and mild conditions by using non-plasma transition metal iridium nanoparticles as photothermal catalyst;(3)The anatase TMS were prepared from different titanium precursors by one-step gel method which could realize a high a efficient degradation of RhB under light;(4)Anatase TMS with large specific surface area and controllable size were prepared by one-step gel method through using titanium sulfate as the precursor,which could be used for the efficient reduction of hexavalent chromium in water;(5)AgNPs were successfully loaded on NCM for the first time and the resulted NCM-Ag could efficiently catalyze the epoxidation of olefins.The main contents and conclusions of this thesis include the following five parts.Cellulose solution was prepared by dissolving cellulose in NaOH/urea solution.The results of XRD and NMR showed that cellulose molecules have been dispersed in NaOH/urea aqueous solution and forms homogeneous system.The direct photocatalytic reforming of cellulose for hydrogen production was studied.The results showed that the hydrogen production efficiency of cellulose in NaOH/urea solution was nearly five times higher than that of suspended cellulose in aqueous solution with Pt-TiO2 as catalyst.At the same time,the effects of photocatalyst,crystal phase,metal cocatalyst,Pt loading and temperature on photocatalytic reaction were studied.The optimum activity of photocatalytic reforming of cellulose for hydrogen production was 2870 ?mol/h/g.In this study,NaOH/urea aqueous solution has the following important role in the production of H2(2870 ?mol/h/g)by photocatalytic reforming of cellulose.(1)Cellulose molecules dissolved in NaOH/urea aqueous solution are easier to contact with photocatalyst,(2)the C-C bonds of Cellulose in aqueous solution of NaOH/urea is more likely to break down than that of insoluble cellulose molecules which has a large amount of intramolecular and intermolecular hydrogen bonds,(3)the CO2 produced by the photocatalytic reaction further promotes the photocatalytic reaction by reacting with NaOH.This work provides the possibility of hydrogen production from biomass under mild photocatalytic conditions,and opens up a new way of renewable energy utilization.Iridium-magnesium oxide(Ir/MgO)catalyst was prepared by impregnation method.The results by TEM and UV-Vis spectra show that Ir nanoparticles have been successfully introduced onto MgO surface.The hydrolysis of cellobiose to glucose can be realized under mild conditions and visible light irradiation by using the photothermal effect of Ir/MgO.Importantly,the photothermal effect of Ir/MgO greatly reduces the reaction temperature.At the same time,the kind of catalyst support,loading amount of noble metal,calcination temperature and light intensity all have important influence on the hydrolysis of cellobiose.The results show that Ir nanoparticles could efficiently perform the conversion from light to heat,which is beneficial to the conversion of cellobiose.This work provides the possibility for the efficient cleavage of 1,4-glucosidic bond of cellulose.Anatase TMS were prepared from different titanium precursors by sol-gel method.The results show that different titanium precursor solutions can be used to prepare TMS with good dispersion and uniform particle size.SEM and TEM were used to study the morphology and microstructure of TMS.The specific surface area was determined by BET.The specific area of TMS were 200 m2/g by the BET method.XRD,Raman and XPS were used to study the phase composition and the existence status of TMS.The formation mechanism of TMS is mainly based on the spontaneous aggregation of TiO2 nanoparticles and mesoporous microspheres due to the combination of particles promoted by temperature.Its catalytic activity was studied by photocatalytic degradation of RhB.The results showed that the photocatalytic degradation of RhB by microspheres was favorable,and the photocatalytic degradation rate remained almost unchanged in five successive cycles,indicating that TMS were stable and suitable for removing pollutants in water.This work provides a new method for gabricating TiO2 with flexible morphology.Anatase TMS were prepared by one step gel method with titanium sulfate as precursor.The experimental results show that the size of TMS can be adjusted in the range of 0.6-4 ?m by adjusting the oil-water ratio.The morphology and microstructure of TMS were studied by SEM and TEM.The specific surface area of TMS wasdetermined to be 200-260 m2/g by N2 adsorption.The phase composition and existence status were studied by XRD,Raman and XPS.The microspheres formation is mainly based on the spontaneous aggregation of TiO2 nanoparticles and mesoporous microspheres due to the combination of particles promoted by temperature.The catalytic activity was studied by photocatalytic reduction of Cr(?)in water.The results show that the photocatalytic reduction of Cr(?)by TMS is perfect,and the photocatalytic degradation rate is almost unchanged in five continuous cycles,indicating that TMS are stable and suitable for the treatment of Cr(?).NCM composed of nanofibers were prepared by sol-gel transformation from chitin solution dissolved in NaOH/urea solution at low temperature.AgNPs were prepared by in-situ reduction of silver nitrate with trisodium citrate and immobilized on chitin nanofibers.NCM-Ag were made of chitin and AgNPs.SEM and TEM,and XRD proved that AgNPs was loaded on the nanofibers.The size of AgNPs can be controlled at 10-70 nm.The results of XPS and FT-IR show that the interaction between chitin and AgNPs is mainly through the binding of chitin nanofibers and AgNPs to form coordination bonds.NCM-Ag has nano-porous structure,high surface area and high stability in organic solvents.At the same time,the selectivity of NCM-Ag is as high as 90%in the catalytic reaction of olefins to epoxides(especially styrene to styrene epoxides).This work opens up a green way for the fabrication of noble metal nanoparticles with NCM as the carrier,and shows a potential application prospect.In this thesis,photocatalytic technology is used for effectively converting biomass into energy and chemicals,as well as removing pollutants from wastewater.This provides new ideas and methods for the rational utilization of solar energy and biomass.These basic research results not only show academic value and innovation,but also meet the requirements of sustainable development strategy.Therefore,this paper has scientific significance and application prospect.