Phase Behaviors,Physicochemical Properties Of Surfactant-free Microemulsions And Their Applications In Nanomaterials Synthesis

Surfactant-free microemulsion?SFME?systems have similar microstructures and physicochemical properties to surfactant-based microemulsion?SBME?systems,but they contain no surfactants and cosurfactants that are harmful to the environment.They have wide application prospects in enzymatic reactions,chemical reactions and nanomaterials syntheses,etc.SFMEs have attracted more and more attention in recent years.Constructing new type of SFME systems and studying their microstructures and properties are of important practical significance for expanding the application scope of the SFME systems.In this thesis,halogenated hydrocarbons and esters were selected as the oil phase and propan-2-ol was used as the?amphi-solvent?to construct SFME systems.The phase behaviors,physicochemical properties of each system were examined.The applications of the SFME systems in the synthesis of nanomaterials such as SiO₂,BaCrO₄,TiO₂ were also investigated.The thesis consists of four parts.The first part is the introduction.The second part is the construction of water/propan-2-ol/trichloroethylene SFME system and its application in the synthesis of silica nanomaterials.The third part is the phase behavior,solubilization property of water/propan-2-ol/tetrachloroethylene SFME system and its application in BaCrO₄ synthesis.The fourth part is the synthesis of nano-TiO₂ using the SFME as template and its photocatalytic property.? IntroductionThe definition and development process of microemulsions were briefly introduced in this chapter.The definition and characterization methods of SFMEs were discussed.The applications of SFMEs in enzymatic reactions,chemical reactions and nanomaterials synthesis were summarized.The research progress of SFMEs was reviewed.? The construction of water/propan-2-ol/trichloroethylene SFME system and its application in the synthesis of silica nanomaterialsA novel type of SFME system containing water/propan-2-ol/trichloroethylene was constructed.1.The ternary phase diagram of the SFME system at 25°C was drawn by visual titration.The microstructures and physicochemical properties were investigated by conductance,UV-vis absorption spectroscopy,surface tension,dynamic light scattering and electron microscopy.2.Solid silica nanoparticles?SSNs?,hollow silica nanoparticles?HSNs?and silica-based yolk-shell nanoparticles?SYSNs?were synthesized by using the O/W SFME as a template.The effects of both the concentrations of the precursor tetraethoxysilane?TEOS?and the catalyst ammonia,and the composition of the microemulsion template on the morphology and size of the SYSNs were investigated.It was found that the size of the synthesized SYSNs increases with the size of the O/W droplets and the concentrations of TEOS and ammonia.Thus,the size of SYSNs can be adjusted.3.The adsorption properties and adsorption kinetics of methylene blue?MB?on the synthesized SSNs,HSNs and SYSNs were evaluated respectively.The results showed that the larger the S_BET values,the stronger the adsorption capacity of the nanomaterials for MB.The adsorption capacity of the SYSNs reaches 33.14 mg g^-1.The adsorption kinetics of SYSNs,HSNs,and SSNs for MB were all well fitted to the pseudo-second-order kinetic model.?Thephasebehavior,solubilizationof water/propan-2-ol/tetrachloroethylene SFME system and its application in BaCrO₄ synthesisAnothernoveltypeofSFMEsystemcontaining water/propan-2-ol/tetrachloroethylene was constructed.1.The single-phase region of the SFME system was divided into oil-in-water?O/W?,bicontinuous?B.C.?,and water-in-oil?W/O?types by electrical conductivity method.UV-vis absorption spectroscopy and surface tension were also used to examine the microstructures of the SFME system,and the results were consistent with the conductivity method.2.The solubilization performances of some metal salts?K₃Fe?CN?₆?CoCl₂?CuCl₂?and biomolecule?riboflavin?in the SFME system were investigated by UV-vis absorption spectroscopy.It can be concluded that the system has strong solubilization ability for above inorganic salts and riboflavin.The solubilization of CoCl₂ and riboflavin revealed the formation of the W/O SFME droplets.3.BaCrO₄ nanomaterials were synthesized using W/O SFME as a template.The size of BaCrO₄ nanomaterials was adjusted by changing the reaction time.? The synthesis of nano-TiO₂ using SFME system as template and its photocatalytic propertyA third novel SFME system containing water/propan-2-ol/vinyl acetate was constructed.1.The ternary phase diagram of the SFME system at 25°C was also drawn.The single-phase region of the system was divided into oil-in-water?O/W?,bicontinuous?B.C.?,and water-in-oil?W/O?types of microemulsions.Using methyl orange as a probe,the polarity of the microenvironment of the SFME was studied by UV-vis spectroscopy.2.TiO₂ nanoparticles?Nano-TiO₂?were synthesized by the microemulsion-hydrothermal method.The effects of hydrothermal temperature,titanium source?TBT?and ammonia on the morphology,size and crystallinity of Nano-TiO₂ were studied.The results showed that with the increases in the hydrothermal temperature,the crystallinity of the TiO₂ synthesized gradually increases.The concentrations of TBT and ammonia have important effects on the synthesis of Nano-TiO₂.3.Nano-TiO₂ with relatively large size was synthesized at high temperature,and the effect of calcination temperature on its morphology and crystal phase was investigated.4.The photocatalytic activity of the synthesized Nano-TiO₂ samples on methylene blue?MB?was investigated.The results showed that the photocatalytic activity of the sample is related to the crystallinity and crystal phase of the nano-TiO₂.The TiO₂ nanomaterials synthesized at higher hydrothermal temperature have better photocatalytic performance.