Controllable Preparation And Application Of Functionalized Polysulfone Hollow Microspheres

Polymer hollow microsphere is a kind of polymer sphere which possesses micron/submicron size with hollow structure.The unique size and structure characteristics endow the polymer hollow microspheres with many advantages,such as excellent mass transfer kinetics,various surface/internal structures,large specific surface area,high storage space,settlement resistance and easy recycling,which have been widely used in many fields.However,there are still many fundamental challenges in using polymer hollow microspheres in practical applications,such as poor cycling stability and selective adsorption,complex procedures,easy decomposition under harsh environments(e.g.,high temperature,acid/alkali conditions,light irradiation,etc.),which have restricted the application prospects of polymer hollow microspheres.Therefore,it's urgent to develope a hollow microsphere which can satisfy the requirements of harsh environment and functionalized applications.In this regard,polysulfone(PSF)is a kind of thermoplastic polymer with prominent performance,which occupies many merits such as excellent irradiation stability,acid/alkali resistant,outstanding mechanical strength and thermal stability,accessible molding and preparation.Hence,this thesis used the PSF material to prepare microspheres,and structure engineering was conducted with different modification methods to adjust its morphology structure and functionalized application ability.The obtained PSF hollow microspheres exhibit diverse structure and morphology,high removal rate for organic pollutants,and high reusability,and are capable to withstand harsh environment,the main results are as follows:1.The polysulfone hollow microspheres(HPSF-MCs)were prepared via non-solvent exchange-evaporation induced phase separation(NE-EIPS)with hollow structure and thin shell.The hydrophilic cosolvent was introduced into the hydrophobic solution system and bidirectional diffusion with water was occurred in continuous phase.The type and ratio of hydrophilic(high boiling point)/hydrophobic(low boiling point)solvents were adjusted to study the influence of solvent volatilization and diffusion rate on the morphology and structure of HPSF-MCs.The results show that good solubility(low solubility parameter difference)between the mixed solvent and PSF is the key to obtain narrow distribution and complete spherical structure of HPSF-MCs.As the ratio of 1/5 for hydrophilic/hydrophobic solvent,the diffusion removal of hydrophilic cosolvent has little effect on the stability of the emulsion system,and the uniform size of the prepared HPSF-MCs is obtained.In addition,the influence of molecular weight of PSF on the size and structure of HPSF-MCs was systematically studied.As a result,a positive linear correlation is found between the relative viscosity of the solvent with the particle size of microspheres,and the particle size of HPSF-MCs increases with the the molecular weight of PSF increasing.Surfactants with different hydrophilic/oleophilic values were added to prepare HPSF-MCs.O/W type of surfactants is favorable to form stable emulsions,and HPSF-MCs with uniform morphology and narrow size distribution could be obtained.2.In order to effectively remove organic pollutants from aqueous solution,HPSF-MCs with hollow structure and high porosity were served as the substrates,and nano titanium dioxide(TiNPs)with UV photocatalytic activity was used as Pickering emulsifier and functional catalyst.A series of Ti O₂ nanoparticles/polysulfone composite hollow microspheres(TiNPs/HPSF-CMCs)loaded with different amounts of TiNPs were prepared and applied for photocatalytic degradation of organic pollutants.The results show that the specific surface area and density of nanoparticles on TiNPs/HPSF-CMCs surface increases as the TiNPs loading increasing on the composite microspheres.Meanwhile,the viscosity increase and phase separation delay in prepared solutions,resulting in the internal porosity decreasing and the density of TiNPs/HPSF-CMCs increasing.The density increase is not conducive to the stable suspension of TiNPs/HPSF-CMCs in organic pollutants solution,and the photocatalytic efficiency of composite microspheres is reduced.In addition,the prepared TiNPs/HPSF-CMCs delivers the ability of adsorption and photocatalytic degradation for organic pollutants.TiNPs/HPSF-CMCs-0.40 with a density close to that of solution,can completely degrade methylene blue(MB)dye within 120 min in both dynamic and static photocatalytic experiments.TiNPs/HPSF-CMCs also exhibits excellent recycling and stable degradation ability under acidic conditions.The removal efficiency of MB for the TiNPs/HPSF-CMCs retained 96.5%,even after 20 cycles.Moreover,TiNPs/HPSF-CMCs also showed high MB removal ability(93.8%)at acidic condition(p H=1).In general,the high catalysis efficiency,excellent reusability and good stability make this kind of TiNPs/HPSF-CMCs a promising photocatalyst for the water organic pollution treatment.This work affords a guidance to the development of functional polysulfone hollow microspheres.3.In the previous study,TiNPs/HPSF-CMCs with stable adsorption and catalytic degradation ability was successfully prepared.However,the process of adsorption and removal of organic pollutants only exists on the outer surface of the microsphere,and the abundant pore structure of the microspheres inner cavity and shell is not fully utilized.In order to sufficiently use the internal and external structure of microspheres,polysulfone hollow microspheres(PHPSF-MCs)with particle size is 77.9-105.9?m and submicron pore size(0.3-3.7?m)were prepared by adding polyethylene glycol(PEG)as porogen.By virtue of the excellent pore-forming properties of PEG,the inner and outer surfaces of the porous materials are connected,leading to the inner cavities and porous shells of hollow microspheres fully utilized in pollutant removal process.The effects of PEG molecular weight and dosage on particle size distribution,surface porosity and shell thickness of PHPSF-MCs were investigated.The results show that viscosity of the system increase as the molecular weight of PEG increasing,and the phase separation of polymer solution is delayed,along with large size PHPSF-MCs obtained.Meanwhile,the shell thickness of microspheres increased to 14.0?m,with the porosity of microspheres decreasing.PEG bonding to water in solution to form aqueous phase,which is removed during phase separation,resulting in pore structure.Early phase separation occurs during phase transformation of PEG with low molecular weight,resulting in larger surface pores.When the Mw of PEG range from 2000 to 4000,the low solubility parameter difference between PEG and solvent is conducive to the formation of microporous structure with narrow pore distribution.PEG with high molecular weight is agglomerated to form macro-aqueous phase under the influence of interfacial tension between two phases,and macro-porous structure is forming after phase transformation.Whereas,the amount of PEG has no effect on the pore size of PHPSF-MCs surface,but the pore number and size of PHPSF-MCs are changed.In addition,the adsorption results show that the adsorption of MB dye molecules on PHPSF-MCs conforms to the pseudo-second-order kinetics and Langmuir isothermal model,with the monolayer adsorption state.The as-prepared PHPSF-MCs exhibit a separation efficiency of 6 and 12.9 times for MB dyes and oilthan that of the original HPSF-MCs,respectively.Therefore,this kind of HPSF-MCs holds a promising for the water organic pollution treatment.4.In order to further improve the removal rate of organic pollutants by PHPSF-MCs and endow it selective adsorption ability,chloromethyl was introduced into the polysulfone molecule to prepare chloromethyl polysulfone,and then chloromethyl polysulfone hollow microspheres were obtained by NE-EIPS method.Subsequently,the chloromethyl of polysulfone hollow microspheres were substituted by azide functional group and Huisgen cycloaddition reaction of azide alkynyl group.Wherein,the porous hollow carboxylated polysulfone microspheres with carboxyl group(PH-CPSF-MCs)and the porous hollow sulphonated polysulfone microspheres with sulfonic group(PH-SPSF-MCs)were obtained,as an efficient adsorbent for removing cationic dyes from sewage.The resulting PH-CPSF-MCs and PH-SPSF-MCs possess a hollow core sponge-like shell structure,high surface area,good chemical inertness and structural stability.The results show that the surface electronegativity of the functionalized microspheres is enhanced after modification,and PH-CPSF-MCs has the lowest surface negative potential(-41.9 m V).In addition,alkaline conditions are favorable for the ionization of functionalized groups on the surface of PH-CPSF-MCs and PH-SPSF-MCs,thus promoting the electrostatic adsorption capacity of cationic dyes on the surface of functionalized microspheres.Meanwhile,the maximum adsorption capacity of PH-CPSF-MCs for MB dye reaches 154.5 mg g^–1 owing to the interaction of?-?and hydrogen bond.Benefiting from the electrostatic repulsion of identical charges,the negatively charged PH-CPSF-MCs and PH-SPSF-MCs show excellent selective adsorption properties for cationic dyes(100%for cationic dyes and less than 10%for anionic dyes)in the mixed dyes.These results manifest that PH-CPSF-MCs and PH-SPSF-MCs are a potential adsorbent with long-term purification capabilities,which are expected to be used in small and large-scale sewage treatment.