Study On Preparation And Properties Of Hydrophilic Graphene And Its Composites

Graphene was a kind of two-dimensional materials with the thickness of a single layer carbon atoms.It had been applied in many fields such as capacitors,sewage treatment,construction and solar cell because of excellent electron transfer rate,mechanical strength and adsorption capacity.But its insolubility limited its applications.Thus,how to prepare homogeneous composite materials by improving the dispersion of graphene had become current research focus.Phenylhydrazine-4-sulfonic acid?PHS?simultaneously possesses hydrazine and sulfonic groups in its molecule.So it was designed as the modifier and reductant of graphene oxide?GO?to synthesize novel hydrophilic graphene?HG?in this paper.Then its composites and homogeneous functional materials were prepared by HG as the raw materials reacting with Fe₃O₄,polymer and/or Ti O₂ in aqueous solutions.The structures and morphologies of the corresponding products were characterized and analyzed.And the properties of the products and their synthesis and effect mechanisms were also investigated.These results laid the foundation of the development and application of the novel hydrophilic graphene and its composite materials.GO was prepared by using the improved Hummers' methods from graphite as raw materials reacting with oxygenant potassium permanganate for 12 h at 50 ? in the presence of the mixed acid?concentrated sulfuric and phosphoric acid?.GO demonstrated the transparent and thin layered structure under TEM and a better crystal structure with its diffraction peaks at 2? = 9.0°.Hydrophilic graphene?HG?was synthesized from PHS?called HGa?or PHS with caustic soda?called HGb?by the reduction of GO at 85? for12 h under nitrogen environment through a facile one-pot method.The reaction processes were mainly summarized as below: the absorbed PHS were inserted into the layers of GO sheets and reacted with the oxygen-containing groups especially carbonyl groups on the surface of GO sheets.The PHS residue containing highly polar water-soluble sulfonic acidgroup increased steric hindrance and electron repelling effects among the layers,reducedthe surface energy of HG,and prevented HG sheets from aggregating.Besides,the residual groups of PHS gave HG good water solubility.The solubility of HGa and HGb in water could be up to 12.66 mg·m L-1 and 9.27 mg·m L-1,respectively.And the solutions could be kept for months without any precipitation.Besides,HG solutions possessed good compatibility and stability in the p H range of 2-12.They were also able to homogeneously disperse in polar organic solvents,such as DMF,DMSO,and the aqueous solutions of ethanol,polyvinyl alcohol and cyclodextrin.The UV absorption wavelength of HG solutions was between 260 and 283 nm due to the presence of unsaturated carbon skeleton and aromatic groups;HG sheets showed thin,transparent and less folded morphology,indicating the less degree of aggregation;HG exhibited a weaker crystallized structure because of the presence of the organic group.As seen from the result of TGA and DTA,the percent of weight loss for HGa and HGb at 350-670 ? was 62.2% and 54.3%,respectively,The results indicated when the sulfonic acid groups were converted into their sodium salts,the thermal stability of HG increased.Fe₃O₄/HG composites were prepared in alkaline aqueous solution from HG and an iron precursor of Fe Cl3·6H₂O and?NH4?2Fe?SO4?2·6H₂O at 85 ? for 1 h by one-step chemical co-precipitation method.The characterization results demonstrated that Fe₃O₄ particles with average size of 9.15-21.80 nm were uniformly dispersed on the HG sheet,and with the increase of HG content,the size of Fe₃O₄ particles in Fe₃O₄/HG gradually decreased.Fe₃O₄/HG composites exhibited ferrimagnetic,higher coercivity,lower specific saturation magnetization and better adsorption for Rhodamine B and Cr3+ ions.Their adsorption kinetics followed the pseudo second-order kinetic model,the adsorption process was controlled jointly by the intraparticle diffusion and chemical adsorption of adsorbent surface.Photo-Fenton reaction results demonstrated that Fe₃O₄/HG composites had better photocatalytic effect in a short time.When the loading capacity of HG in Fe₃O₄/HG composites was 53.81 wt%,the catalytic efficiency could reach be 87.68% and the catalytic rate could be 0.055 mg·min-1.The main reason might be contributed to thehigher electronic conductivity of HG,which speeded up the conversion efficiency of Fe3+/Fe2+.Test results showed that Zeta potential of Fe₃O₄/HG could be up to 38.1 mv.Meanwhile,the higher HG content was,the greater Zeta potential values showed.Thus,the dispersion and stability of Fe₃O₄/HG composites in water could be regulated by the content of HG.Two kinds of film material of Fe₃O₄ /PVA?FP?and Fe₃O₄/HG/PVA?GFP?were prepared at 85 ? for 1 h with Fe Cl3·6H₂O,?NH4?2Fe?SO4?2·6H₂O and PVA as raw material in the absence or presence of HG by one-step chemical co-precipitation method.The characterization results demonstrated that Fe₃O₄ particles with average particle diameter of 8.19-17.58 nm in FP were spherical and were uniformly distributed in the PVA;Fe₃O₄ particles in GFP had many forms such as spherical,net and rod.FP and GFP showed ferrimagnetic characteristic.Compared with FP,GFP had higher thermal stability and flame retardancy.When the content of HG reached to 1.2 wt%,GFP exhibited the highest tensile strength?198.13 MPa?,maximum absorption energy?0.58 J?,higher maximum strain?629.57%?and young's modulus?0.31 GPa?.GFP had excellent mechanical properties because of their synergetic effect by crosslinking among the Fe₃O₄ particles,HG and PVA.TiO₂/HG composites were prepared from HG and titanium tetrachloride in acidic conditions by low temperature hydrolysis method and ultrasonic method,respectively.The results showed that with the effect of ultrasonic,Ti O₂ particles with the size of 0.21-0.38?m were dispersed uniformly in Ti O₂/HG composites,and the crystal formation belonged to stabile rutile phase;Ti O₂ particles prepared by low temperature hydrolysis methods were 0.23-0.38 ?m,slightly aggregating and being a mixture of rutile and anatase phase.And with the increase of HG content,rutile phase gradually decreased.Thus,the crystal formation of Ti O₂ was regulated by the amount of HG.The results of methyl orange photodegradation reaction demonstrated that Ti O₂/HG composites had higher photodegradative efficiency.Then with the increase of HG content,photoreaction efficiency and degradation rate gradually increased.The reason was that the presence of HG increased carrier mobility and inhibited the recombination between photo-generated electron and hole pair in Ti O₂.Compared with the products prepared by low temperaturehydrolysis method,the products obtained by ultrasonic method showed better photocatalytic efficiency.HG and Ti O₂/HG composites inhibited the growth of Escherichia coli and their antibacterial rates were 82.61% and 89.85%,respectively.The results indicated that TiO₂/HG was conducive to the production of active free radicals,thus it played an obvious bacteriostasis effect on Escherichia coli.