| With the rapid development of the world economy,a series of severe environmental pollution and energy shortage problems emerge.For example,heavy metal and organic pollutants in water pose serious threats to the human health and ecological systems.Therefore,people are committed to seeking high efficiency and energy-saving material fabrication technologies,developing novel and environmentally friendly functional materials,which can provide new technical support for environmental governance and energy use.Nano titanium dioxide has been widely used in adsorption,photocatalysis,solar cells and so on,due to its unique physicochemical properties such as non-toxicity,low cost and chemical stability.However,the wide band gap of nano-titanium dioxide,low quantum efficiency,tendency of agglomeration and material loss during the preparation and application processes,limit its practical applications.Therefore,reducing material loss in use,mitigating particle agglomeration,increasing adsorption capacity and improving photocatalytic activity of nano-titanium dioxide,have become the major focuses of many research works.In this thesis,we first aim to solve the problems of easy particle agglomeration,high temperature and high pressure,long time and complicated procedures needed in the preparation process of nano-titanium dioxide.Microwave assisted strengthening technology was applied to prepare a series of titanium dioxide nanoparticles,where the inorganic reagent-titanyl sulfate was used as the precursor.The effects of crystal structure and morphology on adsorption and photocatalytic activity were investigated.Next,in order to reduce the loss of nanoparticles during application and minimize nanoparticle agglomeration,we used cellulose fibers as the template/substrate to grow and immobilize in situ the nano-titanium dioxide and obtain titanium dioxide-cellulose composite fibers.The composite was then explored for Pb2+removal from water and the adsorption mechanism was studied.Subsequently,to improve the adsorption capacity and efficiency to achieve a continuous adsorption process,the titanium dioxide-cellulose composite filter media/membrane was prepared using wet-laid technology and then its use in flow-through adsorption of low-concentration Pb2+ was investigated.Furthermore,a titanium dioxide-porous carbon fiber material with specific structural properties was obtained by high-temperature carbonization and activation of the composite fibers for enhanced photocatalytic activity.The adsorption and photocatalytic property for hexavalent chromium,organic pollutants-phenol and methylene blue dyes were studied in detail.The main results achieved in this thesis are as follows:(1)Assisted by microwave irradiation,high surface area and mesoporous nano TiO2 photocatalysts were synthesized via fast hydrolysis(within 30 min)of inorganic titanyl sulfate.Followed by a post-annealing treatment at 700 ?,the nano TiO2 with mixed rutile and anatase crystallines were obtained.The morphology and structure of the TiO2 nanoparticles were controlled by the TiOSO4:H2SO4 volume ratio(pH)and reaction temperature.The H2SO4 added in the reaction system not only affected the hydrolysis kinetics,but also controlled the nucleation and crystallization processes.When the volume ratio of TiOSO4:H2SO4 was 5:3 and the reaction temperature was at 90 ?,mesoporous TiO2 nanoparticles with rough surface were obtained,and their photocatalytic degradation of methylene blue was evaluated under visible light.The results showed that the self-made TiO2 had a 6-fold enhancement in photocatalytic activity compared to commercial P25.(2)The cellulose fibers were used as templet to immobilize nano-TiO2 via in situ hydrolysis of titanium oxysulfate under microwave irradiation,and as a result,a hierarchically structured TiO2-cellulose composite was obtained.It was found that under the same experimental conditions,when cellulose was added to the reaction system,the reaction became faster and the size of the TiO2 nanoparticles became smaller,indicating that the hydroxyl groups on the surface of the cellulose served as the nucleation sites and regulated the crystallization of nano TiO2.As a result,TiO2 with a size of 100 nm was immobilized on cellulose surface by hydrogen bonds,which still retained the hierarchical structure of cellulose even after loaded with TiO2.The composite was characterred with mesoporous structure and high specific surface area,which led to rapid adsorption of Pb2+ from water with a maximum capacity of 42.5 mg/g.The adsorption fitted Freundlich isotherms and was pseudo-second order in kinetics.By XPS analysis,it was found that chemical interaction between Pb2+ and TiO2 occurred to form the Pb-O bond and an inner sphere complex that helped accelerate the adsorption.In addition,the adsorbent was easily regenerated for a number of times without significant reduction in its adsorption performances.(3)To improve the utilization efficiency and adsorption capacity of TiO2-cellulose composite,the material was wet-laid into a filter membrane with relatively uniform pore size districution for the removal of low-concentration Pb2+ in water through adsorptive filtration.The influences of initial concentration,flow rate and membrane thickness on breakthrough curves were studied.The adsorption behavior was found to be independent of the initial Pb2+ concentration and flow rate,but related to the thickess of the membrane.According to the Bed Depth Service Time(BDST)model,a filter membrane with a thickness of less than 0.01 cm would be sufficient to effectively prevent solute penetration.With a volume of merely 2.07 cm3,the membrane could treat 150.0 liters of water containing 50 ?g/L of Pb2+ to the drinking water standard,indicating the high utilization and removal efficiency of the membrane.In addition,the membrane was also Pb2+ selective over co-existing cations,and could be easily regenerated and reused without obvious reduction in performance.(4)To improve the photocatalytic performance of TiO2-cellulose,where cellulose was used both as a template and a carbon source,hierarchically structured and porous N-doped TiO2-porous carbon fibers were synthesized by carbonizing the material at 800 ? and activating at 850 ?.In this case,cellulose not only acted as a substrate to bond TiO2 nanoparticles,but also functioned as a carbon source that was converted into carbon with a porous structure during carbonization and activation.More interestingly,it was discovered that without using an additional organic nitrogen source and a reducing agent,Ti4+ was reduced to Ti3+ and N was doped into TiO2 lattice to form N doped TiO2.This happened because the automatic generation of H2 and carbon that acted as reducing agents in the process of cellulose carbonization pyrolysis in the nitrogen atomsphere.The obtained carbon fibers with high specific surface area and large pore volume displayed rapid adsorption rate and high adsorption capacity of methylene blue,phenol and Cr(?).In addition,due to the formation of a new energy level structure by N and Ti3+ doping,Uhe composite material was endowed with a narrow band gap and effectively photo-catalyzed the oxidation of phenol and the reduction of Cr(?)under UV-vis or visible light irradiation.The removal of phenol and Cr(?)were 9.2 and 8.8 times than commercial P25 under UV-visible light,respectively,indicating the material's great potential in environmental remediation. |
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