Preparation Of Three-Dimensional Graphene-Based Nanozymes And Their Application In Environmental Phenolic Pollutants Detection

Considering the unavoidable drawbacks of natural enzymes,scientists have devoted to synthesizing artificial mimic enzymes in alternative ways.The boom of nanotechnology has brought new opportunities for the research of artificial mimic enzymes and nanozymes,which is emerging as a new research hotspot.Whereas,there are still some pending issues exist,such as how to adjust the size and morphology of nanozymes to feature it with multifunction nanozyme,how to prepare nanozymes with high recyclability,and how to expand the application of nanozymes in the field of environmental monitoring.By virtue of the unique properties of three-dimensional graphene foam(3DGF),this thesis presented the 3DGF-based nanozymes with excellent catalytic performance and stable reusability combining 3DGF with three typical metal oxide nanomaterials(copper oxide,ferroferric oxide,and lead dioxide)and two typical noble metal nanomaterials(gold and platinum).Using surfactants(SDS,SDBS,and CTAB)and sodium citrate(Na3Cit)as adsorbents and soft templates,the effects of additives on the size,morphology,and catalytic activity of 3DGF-based nanozymes were systematically studied.Subsequently,the effects of eight phenolic pollutants(catechol,resorcinol,hydroquinone,phenol,p-nitrophenol,m-nitrophenol,o-nitrophenol,and bisphenol A)on the catalytic activity of 3DGF-based nanozymes were investigated.Based on the various catalytic activities of 3DGF-based nanozymes,the colorimetric detection methods for hydroquinone(HQ),catechol(CC),phenol,and p-nitrophenol(PNP)with excellent performance were proposed.The proposed methods provide instructive guide for real-time,on-site application in environmental monitoring.1.Flower-like copper oxide nanoparticles(FL CuO NPs)were synthesized on 3DGF taking sodium dodecyl sulfate(SDS)as structure-directing agent and soft template.As expected,the synergistic effect between 3D GF and FL CuO NPs dramatically improved the peroxidase-like catalytic activity of 3DGF/FL CuO nanohybrid.The formation of SDS hemimicelles and the SDS/L-(-)-APP molar ratio has a significant effect on the morphology of CuO NPs and the catalytic performance of 3DGF/CuO nanohybrid.Compared with other eight phenolic pollutants,HQ could significantly inhibit the peroxidase-like catalytic activity of 3DGF/FL CuO nanohybrid.Taking the above mentioned into consideration,a colorimetric detection method for HQ was proposed.Additionally,another colorimetric approach for the quantitative determination of phenol was developed taking advantage of the fact that the peroxidase-like catalytic activity of 3DGF/FL CuO nanohybrid is effective for the coupling reaction between phenol and 4-aminoantipyrine(4-AAP).In the detection of HQ and phenol,the 3DGF/FL CuO nanohybrid exhibited high stability and excellent reusability,which could meet the requirements of low costed rapid analysis.2.The mesoporous Fe3O4 nanoparticles(m-Fe3O4 NPs)were in situ synthesized on 3D GF by solvothermal reaction in the presence of sodium citrate(Na3Cit),which was employed as electrostatic stabilizer and adsorbent.The as-prepared 3D GF/m-Fe3O4 nanohybrid possesses high peroxidase mimicking activity.By tuning the amount of Na3Cit,the size of m-Fe3O4 NPs in the nanohybrid and the related peroxidase catalytic activity of the as-prepared nanohybrid could be adjusted.The nanohybrid was successfully adopted in the sensitive and selective detection of PNP with a low detection limit of 45 nM based on the peroxidase-like activity and the PNP-mediated inhibition controllability.Moreover,the 3D GF/m-Fe3O4 nanohybrid shows to be extremely robust,as it still retains its original response to PNP after being reused for 10 times.3.Taking cetyltrimethylammonium bromide(CTAB)as an adsorbent and soft template,waxberry shape PbO2(WS PbO2)nanoparticles were synthesized on the surface of 3DGF.The 3DGF/WS PbO2 nanohybrid can directly oxidize TMB and ABTS,indicating the characteristic of both oxidase and laccase catalytic activity.The experimental results demonstrate that the CTAB hemimicelles benefits the formation of WS PbO2,thereby enhancing the oxidase-like catalytic activity of the as-prepared nanohybrid.Based on the oxidase-like catalytic activity and HQ-mediated inhibition controllability,the 3DGF/WS PbO2 nanohybrid could be used for HQ determination.The detection limit of the proposed method is reduced by one order of magnitude compared with that obtained in Chapter 2 using 3DGF/FL CuO nanohybrid as the sensing material.Utilizing the laccase-like activity of the 3DGF/WS PbO2 nanohybrid,the concentration of phenol was detected by catalyzing the coupling reaction between phenol and 4-AAP.Compared with 3DGF/FL CuO nanohybrid,3DGF/WS PbO2 nanohybrid does not need the extra addition of H2O2 or other oxidants during the detection of HQ and phenol,which is conducive to improve the accuracy of the measurement.4.Using sodium dodecylbenzene sulfonate(SDBS)as adsorbent and soft template,worm-like gold nanoparticles(WL Au NPs)were synthesized in situ on the surface of 3DGF by electrochemical reduction method.The prepared 3DGF/WL Au nanohybrid possesses peroxidase-like catalytic activity.The results show that SDBS hemimicelles promote the formation of WL Au NPs and significantly enhance the peroxidase-like catalytic activity of the 3DGF/WL Au nanohybrid.Compared with other phenolic pollutants,HQ has strong inhibiting effect on the peroxidase-like catalytic activity of the 3DGF/WL Au nanohybrid.The proposed method for HQ determination,taking the advantages of the above-mentioned fact,has the advantages of high sensitivity and good reusability.Moreover,the detection limit is lower than that obtained in Chapter 2 using the 3DGF/FL CuO nanohybrid and in Chapter 4 using the 3DGF/WS PbO2 nanohybrid.5.The Pt nanocluster(Pt NC)were grafted onto 3D GF assisted by CTAB using electro-deposition method.The 3DGF/Pt NC nanohybrid can act as an effective polyphenol oxidase(PPO)mimic apart from the intrinsic oxidase-like activity.The morphology of Pt NPs in the as-prepared 3DGF/Pt nanohybrid and its oxidase activity could be adjusted by changing the concentration of CTAB during the synthesis.The CTAB hemimicelles contributes to the formation of Pt NC on the surface of the 3DGF and in further the enhancement of the oxidase-like catalytic activity.Among the eight phenolic pollutants,HQ has a significant inhibitory effect on the oxidase-like catalytic activity of 3DGF/Pt NC nanohybrid,with the above-mentioned fact in mind,a colorimetric method was developed.The detection limit of the proposed method for HQ determination is lower than that obtained in Chapter 4 using the 3DGF/WS PbO2 nanohybrid as sensing material.In view of the as-prepared nanohybrid catechol oxidase-like activity,distinguishing colorimetric determination of CC was performed.