Study Of The Surface Modification Of Fe₃O₄ Nanoparticles And The Preparation & Application Of Their Composites Films

Magnetic nanomaterials possess not only the general chemical and physical properties of nanomaterials but also special magnetic properties.They can be controlled and separated under a magnetic field,which provides them potential applications in the fields of environmental engineering and catalysis.Fe₃O₄ nanomaterials attacted plenty of attentions because of their special properties such as superparamagnetism and high surface activity.However,agglomeration easily appeared because of the interaction among particles,which hindered their applications in the fields of physics,chemistry,and biology.Therefore,surface modification or hybridization of Fe₃O₄ nanomaterials with other nanomaterials were often performed.Multiple functions were also endowed on Fe₃O₄ nanoparticles during that process.In this thesis,surface-modification of Fe₃O₄ nanomaterials and their hybridization with carbon nanotubes and graphene were studied using scanning electron microscopy?SEM?,transmission electron microscope?XPS?,Xray diffraction?XRD?,light microscope and so on.A detailed investigation was then carried out on the catalysis function of the Pickering emulsion stabilized by these materials,as well as their demulsification properties.We have developed a universal method for the surface-modification of Fe₃O₄ nanomaterials.Octadecyltrimethoxysilane?ODTS?was used to cap the surfaces of the water soluable magnetic nanoparticles,thereby allowing their transfer into nonpolar solution.The resulting hydrophobic magnetic nanoparticles could be transferred back into aqueous solution by subsequently cove ring them with lipid monolayer.Modification of the nanomatials with hybrid membrane was realized.The demonstrated universal reversible phase-transfer protocol was also successfully applicable to other kinds of nanoparticles such as TiO₂,CeO₂,Ag and CNTs.Fe₃O₄/CNTs hybrid film stabilized Pickering emulsions were obtained under a synergic effect of covalent bond,molecular polymerization,and electrostatic adsorption by the reaction of Fe₃O₄ and CNTs with excess ODTS dispersed in hexane,and subsequent addition of poly?diallyldimethylammonium chloride??PDDA?aqueous solution.The hybrid film ruptured into small hybrid patches after addition of ethanol,and could also regenerate to stabilize PEs again.Under the “rupture and regeneration” mechanism,Pd nanoparticles were embedded into the hybrid film to form Fe₃O₄/CNTs-Pd.The catalytic ability of emulsions stabilized by Pd functionalized hybrid patches was investigated,as well as the influence of the amount of Pd functionalized hybrid membranes on catalytic performance for the hydrogenation of acetone.The emulsion system could finish the hydrogenation of acetone to isopropanol in 20 minutes with a yield of 99.5 ± 0.4% with no byproducts.The same batch of Pd functionalized patches was recycled 10 times without loss of the yield of isopropanol.The hybrid-patch formed PEs showed a great potential for the application in catalytic field.MRGO was fabricated by simultaneously forming Fe₃O₄ nanoparticles and reducing graphene oxide?GO?.The MRGO modified with ODTS were used as effective particulate emulsifiers to produce stable W/O Pickering emulsions containing PDDA in water phase.ODTS and PDDA modified MRGO was obtained by the evaporation of the W/O Pickering emulsions.The palladium nanoparticles were embedded into the surface of the MRGO using an in situ reduction method.The catalytic performance of Pd functionalized MRGO?MRGO-Pd?formed Pickering emulsion for the oxidative degradation of Sudan ? and the hydrogenation of p-nitrotoluene was investigated.We studied the influence of different quantity of catalysts,concentrations of oxidant or reductant and substrate concentration on the catalytic ability.In the oxidative degradation of Sudan? by the emulsion system,the obtained optimal conditions were: initial Sudan ? concentration of 0.79 m M,H2O2 concentration of 1.9 g/L,the catalyst dosage of 1.2 g/L,reaction time of 100 min,with the highest Sudan? removal efficiency of 99.6%.In the hydrogenation of p-nitrotoluene by the emulsion system,the obtained optimal conditions were: initial concentration p-nitrotoluene of 10 m M,NaBH₄ concentration of 20 g/L,the catalyst dosage of 2 g/L,reaction time of 40 min,with the hydrogenation yield of 99.8%.The same batch of MRGO-Pd was recycled 6 times without loss of the catalytic activity.The MRGO stabilized Pickering emulsion has a great potential in the catalytic field.At last,the demulsification ability of ODTS modified MRGO magnetic demulsifiers was studied.The prepared novel magnetic demulsifier can be applied to O/W?and O/W?systems to remove oil?and water?with remarkable separation efficiency.The demulsification efficiency can reach 96.8±2.9% for W/O emulsion and 97.9±2.1% for O/W emulsion with 25 g/L and 75 g/L demulsifier,respectively.The demusification ability of MRGO@ODTS is more effective for W/O emulsions than that for O/W emulsions.Moreover,they could be rapidly collected in the presence of an external magnetic field for recyc ling,which means that the dosage of demulsifier used to treat the oil field wastewater could be drastically reduced.The recyclability tests of MRGO@ODTS showed there was no obvious decline of demulsification efficiency within ten cycles.The bifunctional demulsifier may find great potential in oil-water separation in industry.