Study On Adsorption Of Environmental Organic Pollutants By Admicelles

Organic pollutants such as polycyclic aromatic hydrocarbons,phenolic compounds,dyes and pesticides get into the water and the soil,which seriously threatens human health.The removal of organic pollutants has attracted extensive attentions of the researchers.Adsorption has become an important method to deal with environmental organic pollutants due to its simple operation,a great diversity of adsorbent materials and cost effectiveness.Though non-polar adsorbents have a good adsorption efficiency for the hydrophobic organic pollutants,it is difficult to disperse hydrophobic adsorbents in water.The surfactants could form the aggregates at the solid-aqueous interface based on the molecular interaction between the surfactant molecules and the solid materials.The surface aggregates self-assembled by the surfactant at a certain concentration,are termed admicelles.Similar to the micelles,the admicelles can also solubilize sparingly soluble and insoluble compounds in aqueous solutions,and the process called adsolubilization.Owing to favorable wettability,the admicelles is a potential absorbent for adsorption of the hydrophobic substances in aqueous medium.In the present work,the solid materials with conjugated?bonds were modified by the cationic surfactant based on the strong molecular interaction of cation-?electrons,and the admicelles with a hydrophobic inner core and a hydrophilic surface were formed on the surface of the hydrophobic solid materials.Therefore,the adsorbents could be dispersed well in aqueous solution and organic pollutants in the water could be adsolubilized by the admicelles.In the dissertation,a series of new admicelles adsorbents were developed to adsorb hydrophobic organic pollutants.The systematic investigations were carried out in the aspects of the solid substrate,the optimization of the admicelles formation conditions,the characterization of the admicelles,organic pollutant adsorption performance,and the admicelle formation mechanism.The main research work and the results in the dissertation are summarized as follows:1.The adsorption behavior of bisphenol A?BPA?on hexadecyl trimethyl ammonium bromide?CTAB?modified graphite was investigated thoroughly to develop a novel absorbent material.Atomic force microscopy?AFM?revealed that conical admicelles formed on the surface of graphite.Once modification of the cationic surfactant CTAB,the specific surface area of graphite decreased significantly from 1.46 m²/g to 0.95 m²/g,which confirmed the formation of the larger size admicelles on the surface of graphite.In the FT-IR spectrum,new peaks of 2917 and 2849 cm^-1 from the stretching vibration of C-H of methyl and methylene appeared after CTAB-modified on graphite.After adsorption of BPA,the peaks of benzene ring vibration appeared from 1632 to 1457 cm^-1,and the stretching vibration of O-H in BPA showed in the peak of 3425 cm^-1.FT-IR experimental results further verified that graphite was modified with CTAB and BPA was adsorbed by the CTAB-modified graphite.CTAB concentration and incubation time affected the formation of the admicelle on the surface of graphite,9.5 mmol/L CTAB and 24 h incubation were chosen in process of CTAB modification of graphite.There is strong interaction between BPA and CTAB,which was characterized by UV spectra of BPA mixed with various concentrations of CTAB.pH of BPA solution influences significantly on BPA adsorption by CTAB-modified graphite.As pH<pKa,the adsorption amount is much more than that as pH?pKa.BPA with a molecular form was easily adsolubilized by the admicelles because a neutral molecule has greater hydrophobicity than BPA with ionic form and easily be solubilized in the admicelles.As pH?pKa,BPA existed in anionic form.Although the electrostatic interaction between BPA and CTAB enhances,the adsorption amount decreases.It indicats that the adsolubilization is primary and the electrostatic mechanism is secondary during BPA adsorption by CTAB-modified graphite.Owing to cation-?electrons and hydrophobic interaction between CTAB and BPA,CTAB-modified graphite exhibited superior adsorption capacity for BPA,with a maximum adsorption capacity of 125.01 mg/g,3.7 times as that of original graphite.The adsorption kinetic curves of BPA on modified graphite were shown to follow a pseudosecond-order rate.The adsorption process was observed to be both spontaneous and exothermic complied with the Freundlich model.2.In above-mentioned work,CTAB-modified graphite was found to have good adsorption properties for environmental pollutants BPA.Therefore,salicylic acid,phenanthrene and aniline was selected as the representative of negatively charged,neutral molecules and positively charged organic pollutants,respectively,to investigate the adsorption performance by CTAB-modified graphite.The effect of pH on the adsorption of salicylic acid,phenanthrene and aniline by CTAB-modified graphite was studied.To explore the applicability of CTAB-modified graphite for the adsorption of organic pollutants,70semi-volatile organic compounds were tested.The result showed that,similar to BPA the CTAB-modified graphite has a larger adsorption capacity for salicylic acid as pH<pKa.As pH?pKa,the salicylic acid ionized,and the adsorption capacity decreased.It indicated that the smaller the molecular polarity,the easier the adsolubilization by the admicelles.pH did not affect the adsorption of the neutral phenanthrene by the CTAB-modified graphite.In the range of pH 2.0-12.0,aniline would not adsorbed by the CTAB-modified graphite.The results showed that the adsorption capacity of the modified graphite to salicylic acid was the largest,the equilibrium adsorption capacity reached 9.28 mg/g.It had a good adsorption performance for neutral molecule phenanthrene,the equilibrium adsorption capacity was 3.62 mg/g.CTAB-modified graphite had hardly adsorption capacity for positively charged aniline.The adsorption kinetic curves of salicylic acid on CTAB-modified graphite were shown to follow a pseudosecond-order rate.The adsorption process was observed to be complied with the Freundlich model.70 kinds of semi-volatile organic compound were adsorbed by CTAB-modified graphite.25 kinds of organic pollutants could be removed with the rate more than 70%.Among them,polycyclic aromatic hydrocarbons?PAHs?accounted for 44%,phenols accounted for 36%,and cycloolefins,ethers,phthalic acid esters?PAES?and benzene accounted for 20%.It can be seen that the CTAB-modified graphite has the best adsorption effeciency on PAHs with large?bonds.The cation-?electron interaction between CTAB and the pollutants with the large?bond,the hydrophobicity of the pollutants,and the electrostatic interaction between the pollutants and CTAB determine the adsorption capacity of CTAB-modified graphite for semi-volatile organic compounds.3.Adsorption behavior of phenanthrene on CTAB-modified polystyrene?PS?microspheres was investigated thoroughly to develop a novel adsorbent material.PS microspheres was synthesized by dispersion polymerization,in which the dispersant was polyvinylpyrrolidone?PVP?and styrene as the monomer.The morphologies of PS microspheres were characterized through scanning electron microscopy?SEM?.They were uniform in size with an average diameter of 1.3?m?RSD=5.6%,n=100?.AFM images showed that conical admicelles made of CTAB replaced polyvinylpyrrolidone?PVP?macromolecules on the surface of the PS microspheres.The stronger cation-?electron interaction between CTAB and PS microspheres than between PVP and PS microspheres caused PVP to be easily replaced by CTAB molecules during modification.After CTAB modification,the specific surface area of the PS microspheres increased noticeably from 0.56to 2.08 m²/g,which confirmed that the formation of discrete CTAB admicelles replaced PVP macromolecules coated on the surface of the PS microspheres,consistent with AFM conclusion.The conductivity of the PS dispersion was measured,there were two inflection points in the conductivity-CTAB concentration curve:0.78 and 1.72 mmol/L.The first was the CMC of CTAB admicelles on the PS microspheres,and the second was the CMC of CTAB micelles in the solution,which further confirmed the formation of the admicelles on PS microspheres.The CMC of CTAB admicelle is 2/3 of CMC in the aqueous solution.The result verified that CTAB formed admicelles on the surface of the PS microspheres.Cation-?electron interaction between CTAB and phenanthrene helped adsolubilize phenanthrene in the admicelles on the CTAB-modified PS microspheres.CTAB concentration and incubation time affected the formation of the admicelle on the surface of PS microspheres.1.72 mmol/L was proposed as the CTAB concentration and the optimal incubation time for the PS microspheres modification was 18 h.The equilibrium adsorption capacity of the CTAB-modified PS microspheres for phenanthrene was 11.67 mg/g,nearly three times of the untreated PS microspheres.The adsorption kinetic curves of phenanthrene on CTAB-modified PS microspheres followed a pseudo-second-order model.The adsorption process closely fit the Freundlich model,which indicated a multilayer adsorption process,rather than monolayer behavior.4.CTAB admicelles modified on magnetic PS nanocomposites were exploited as a novel adsorbent material to facilitate magnetic separation.Magnetic PS?MPS?nanoparticles?NPs?were synthesized by miniemulsion polymerization,where PVP as an emulsifier,styrene and oleate modified Fe₃O₄ NPs dispersed in octane as an oil phase.MPS NPs and CTAB-modified MPS NPs were characterized with transmission electron microscopy?TEM?,vibrating sample magnetometer?VSM?,AFM,BET,Zeta potential and conductivity analysis.TEM showed that MPS NPs were regularly spherical and the average size was 140 nm?n=100,RSD=12.6%?.The results revealed that Fe₃O₄ NPs were dispersed in PS matrix rather than the core-shell structure.Notably,Fe₃O₄ NPs were prone to moving on the surface of the nanosphere.One reason for this movement might be the incompatibility between Fe₃O₄ NPs and PS.Another reason was due to the coordination effect between Fe₃O₄ and PVP.Fe₃O₄NPs were pulled by PVP into the surface and pushed by PS in the inner portion of the spheres.Both the two interaction caused the movement of Fe₃O₄ NPs to the edge of the MPS NPs.The saturation magnetization?Ms?of MPS NPs and CTAB-modified MPS NPs were 49.04 emu/g and 32.52 emu/g,respectively.The high Ms value of MPS NPs was obtained because the magnetic Fe₃O₄ NPs remained on the superficial layer of the nanospheres.In comparison with Ms of Fe₃O₄@PS NPs prepared with SDS as an emulsifier,Ms of MPS NPs with PVP as an emulsifier doubled.After modification of CTAB,the Ms value decreased sharply.The CTAB modification layer might shield the magnetism.Unexpectedly,AFM images showed that the large admicelles were formed on MPS NPs as a result of PVP,the height of the aggregates was 64 nm,5.3 times as much as on PS microsphere.In addition to the weak molecular interaction between PVP and PS,a coordination interaction between Fe₃O₄ and PVP caused the PVP anchored on MPS NPs.Once CTAB-modified MPS NPs,the height of the aggregates increased to 99.9 nm.It was speculated that based on the soft templates of PVP aggregates,CTAB molecules might self-assemble further owing to a hydrophobic interaction and cation-?electron interaction between CTAB and PS on the surface of MPS NPs.After CTAB modification,the specific surface area of the MPS NPs declined noticeably from 2.36 to 1.06m²/g,which verified indirectly that the bigger CTAB admicelles were formed.After modification,Zeta potential values shifted from-25.96 to 22.49 mV,which implied that CTAB modified on the surface of the MPS NPs.Two inflection points appeared at the curve of MPS NPs,which implied there were two CMC values of MPS NPs aqueous dispersion at0.78 and 1.72 mmol/L,respectively.The result was the same as that of PS microspheres.The first CMC was attributed to CTAB conical admicelles on the surface of MPS NPs,and the second inflexion point indicated CTAB micelles formed in the aqueous solution.Cation-?electron interaction helped phenanthrene to be adsolubilized in CTAB admicelles on MPS NPs.The equilibrium adsorption capacity of the CTAB-modified MPS NPs for phenanthrene was 24.3 mg/g,increased by 1.7,2.1,and 6 times as that of the MPS NPs,CTAB-modified PS microspheres and PS microspheres,respectively.5.The previous work showed that the PVP aggregates on the surface of MPS NPs have an adsorption to phenanthrene.In this work,Fe₃O₄@SiO₂ NPs were synthesized by miniemulsion polymerization,polyvinylpyrrolidone?PVP?modified Fe₃O₄@SiO₂ NPs as a new adsorbent material was studied.Phenanthrene was selected as the representative of the hydrophobic pollutant to evaluate its adsorption performance.The NPs had core-shell structures with magnetic Fe₃O₄ as the core and SiO₂ as the shell.The magnetic core was firstly prepared with miniemulsion self-assembly,then SiO₂ shell was synthesized by St?ber method where PVP as nanoclusters stabilizer.The original and PVP modified Fe₃O₄@SiO₂NPs were characterized with transmission electron microscopy?TEM?,VSM,X-ray photoelectron spectroscopy?XPS?,FT-IR,AFM,FT-IR,X-ray diffraction?XRD?,as well as BET.It could be seen that the original and PVP modified Fe₃O₄@SiO₂ NPs had uniform size and core-shell structure.Both of them had an average diameter of 128 nm?n=100,RSD=9.2%?.XRD analysis showed that after coating the particles with silica,all of the diffraction peaks of Fe₃O₄@SiO₂ NPs were indicative of a magnetite phase.It suggested that the cubic structure of Fe₃O₄ was preserved.The Ms of the original and modified Fe₃O₄@SiO₂NPs were 30.78 emu/g and 30.89 emu/g,respectively.Compared with the SiO₂ shell,the effect of PVP admicelles on magnetic shielding was negligible.It was shown that the characteristic peaks of original and PVP modified Fe₃O₄@SiO₂ NPs in FT-IR spectra were the same but the characteristic peaks of PVP molecules increased after modification.XPS certified that PVP molecules were embedded in the shell of Fe₃O₄@SiO₂ NPs,since PVP was used in preparation of Fe₃O₄ nanocluster as a protective agent.After modified,besides in SiO₂shell,PVP was also found on the surface of Fe₃O₄@SiO₂ NPs.AFM images showed that column-shaped admicelles formed upon the surface of Fe₃O₄@SiO₂ NPs,the aggregates height elevated from 0.8 to 12.6 nm.The specific surface area of Fe₃O₄@SiO₂ NPs reduced considerably from 88.74 to 60.82 m²/g,which verified large aggregations formed on the surface of Fe₃O₄@SiO₂ NPs.Hydrophobic interaction helped phenanthrene to be adsolubilized in PVP admicelles.The equilibrium adsorption capacity of PVP modified Fe₃O₄@SiO₂ NPs for phenanthrene was 18.84 mg/g,2.01 times as that of Fe₃O₄@SiO₂ NPs.Based on the fact that admicelles are easily destroyed by organic solvents,the pollutants absorbed by CTAB or PVP modified magnetic nanomaterial are removed conveniently by washing with ethanol to strip the admicelles,as well as the pollutants.After magnetic separation,the magnetic nanomaterials are collected,and followed by a simple surfactant adsorption process.The magnetic nanomaterial admicelle adsorbent can be regenerated and used repeatedly.The regeneration process is simple and fast.Therefore,the magnetic nanomaterial admicelle adsorbent has a large application prospects.