Fabrication,Characterization And Photocatalytic Properties Of Graphene Quantum Dots/Polyaniline

As a new type of nanometer material,graphene quantum dots(GQDs)are a quasi zero dimensional graphene material with special edge effect and surface structure,being usually used as a visible light-induced nanocatalyst and assisting semiconductor photocatalytic materials with photocatalytic degradation of organic pollutants due to their small band gaps.Further more,GQDs are expected to be widely used in the field of photocatalytic degradation as a good electron acceptor and visible absorption capacity.Polyaniline(PANI)as a conducting polymer has the advantages of high chemical stability,corrosion protection,non-toxic and low cost synthesis.Because of its higher absorption coefficient in the visible light,it is often used as a good electron donor to suppress the recombination of electron-hole pairs and improve the separation efficiency of charges.The defective structure of GQDs can graft with PANI well in the process of surface doping so as to achieve good solubility in water system and increase the effective utilization of photocatalyst.The modification of graphene quantum dots by polyaniline was used to treat the wastewater effectively.A simple in-situ polymerization method was employed to prepare GQDs-PANI on the basis of hydrothermal synthesis of GQDs with citric acid as the carbon source.The obtained GQDs,GQDs-PANI were characterized and their structural information was determined through transmission electron microscopy(TEM),X-ray diffraction meter(XRD),X-ray photoelectron spectroscopy(XPS),Fourier transform infrared spectroscopy(FTIR),UV-Vis absorption spectroscopy(UV),photoluminescence spectroscopy(PL),and electron spin resonance spectra(ESR).The photocatalytic performance was demonstrated on the degradation of methylene blue(MB).Results revealed that The polymer formed separate island-like matrices with embedded GQDs.The GQDs exhibited bright blue luminescence under UV light irradiation and excitation-independent photoluminescent behavior under excitation wavelengths of 300~420 nm.FTIR studies indicated that both GQDs and GQDs-PANI were rich in oxygen-containing functional groups(OCFGs).Compared with pure GQDs and PANI,the photocatalytic degradation rate of GQDs-PANI was dramatically improved by 30% within 90 min.This improvement was attributed to the enhanced interconnection of GQDs with island-like polymer matrices,which facilitated carrier transport within the polymer matrices.And the GQDs played important roles in absorbing solar light as a photocenter and suppressing charge recombination as a charge separation center.The excited electrons stored in GQDs are trapped by O2 molecules to produce the superoxide radicals(-?2O).In addition,abundant holes(h+)are left on the valence band of PANI,which can be trapped by surface hydroxyl groups or adsorbed water to produce hydroxyl free radicals(?OH).Both-?2O and ?OH are active species which effectively decompose the organic pollutant for example MB.At the same time,we carried out the cyclic degradation experiment of GQDs-PANI.The photocatalytic degradation rate of MB with GQDs-PANI at 180 min still maintains at about 86% after three recycles.The results show that GQDs-PANI has excellent chemical stability.The recycling of photocatalyst has been essential in practical application.The reusable photocatalytic degradation materials can effectively degrade organic pollutants and maintain the advantages of low cost,low pollution and renewability in the degradation process.Sustainable governance of environmental issues will be of great significance.Therefore,GQDs-PANI can be used as a kind of recyclable photocatalyst in the field of wastewater treatment.