The Research And Application Of Smart Polymer-based And Heteroatom Doped Graphene

The structure and properties of graphene and graphene derivatives have brought about widely academic research and broad application in various fields. The polymer-modification and other means could effectively adjust their morphology and electronic structure, and make them endowed with novel functional application. To achieve excellently smart graphene and heteroatoms-doping porous graphene and their derivatives have become the research focus from chemical, biology and other fields. This paper introduces a simple and convenient preparation method of temperature-sensitive graphene composite through the use of temperature-sensitive hyperbranched polymers. Secondly, poly(ionic liquid) microgel was utilized as templates to have successfully prepared porous phosphorus and nitrogen co-doped graphene and its electrochemical properties were studied. Thirdly, a simple and convenient preparation method of a low concentration of ammonia etching graphene quantum dots was employed to obtain a multidimensional hybrid structure. Finally, a double labeled functional microsphere was synthesized for the DNA testing of genetically modified foods. The specific research works are included in the following parts:1 Thermosensitive Hyperbranched Polyethylenimine Partially Substituted with N-isopropylacrylamide Monomer:Thermodynamics and for Graphene Oxide FishingA thermosensitive hyperbranched polyethylenimine partially substituted with N-isopropylacrylamide (NIPAM) monomer (HPEI-pNIPAM) was obtained and its thermodynamics was compared with the previously reported fully substituted hyperbranched HPEI-NIPAM polymer by calorimetric and turbidity measurements, one-dimensional and two-dimensional correlation infrared spectroscopy technologies. With less NIPAM units embedded into the interior of HPEI backbone, more hydrogen bonds between C=O and D2O for HPEI-pNIPAM could be transformed into C=O/D-N ones and less C=O related intermediates were formed in the heating process. Moreover, in both the heating and cooling process of HPEI-pNIPAM, collapse and restoration of the branched backbone will proceed firstly and then was followed by the formation and debonding of self-associated C=O/D-N hydrogen bonds respectively in the same process, all of which might be due to the fact that the less conformational confinement effect in the interior backbone lead to the formation of a weaker hydrophobic-hydrophobic interaction. The residual NH groups in the hyperbranched thermosensitive HPEI-pNIPAM polymer could be used as a "fishing hook" to grasp the graphene oxide by nucleophilic addition reaction, meanwhile, it could also be served as a blocking agent to prevent the aggregation of graphene during its preparation process; Finally, a thermosensitive graphene was obtained. The new composite has a good potential for various biomedical or biosensor applications and provides opportunities for other similar hyperbranched polymer to realize multistimuli-responsive effect.2 Poly(ionic liquid) microgel-template directed to porous N and P co-doped graphene and the electrochemical applications.Cross-linked polyphosphorous ionic liquid (PPIL) were prepared via a one-step dispersion polymerization process of ionic liquid monomer and ethylene dimethacrylate (EDMA). The hydrophobic inner core of PPIL was swollen with methanol molecules, during the hydrothermal treatment, methanol molecules entrapped in the swollen inner core was squeezed out and the hydrophobic inner core became more compact. Therefore, the size of the PPIL nanoparticles was decreased. When the PPIL was mixed homogeneously with a low-concentration ammonia solution of graphite oxide, during the hydrothermal step, thin sheet wrap more tightly onto the microgel spheres, meanwhile, the microgels became more compact and positive as the solvent molecules would be expelled from the inner swollen core. After calcinations, the results show that the porous graphene have large surface area and pore volume, pore walls were very thin and are composed of several layers of graphene sheet. Because the phosphorus and nitrogen atoms existed in the PPIL microgel and ammonia respectively, both of them are doped into the surface of graphene. The porous N-P co-doped graphene can be used as an effective electrode material for supercapacitor, they have good cycle stability and high specific capacitance of 199 F/g, in addition, they show efficient catalysis ability for oxygen reduction reaction with better selectivity and long-term stability than commercial Pt/C catalyst.3 Graphene quantum dots hybrids as efficient metal-free electrocatalyst for the oxygen reduction reactionNitric acid was used to prepare one-dimensional graphene quantum dots of 35 nm in size and 0.7 nm in thickness by oxidizing carbon fiber. Low-concentration ammonia solution was utilized as an etching agent in the hydrothermal process to prepare smaller size of zero-dimensional graphene quantum dots on the surface of the one-dimensional graphene quantum dots, and meanwhile dope it with the N atom. By adjusting the experimental temperature and reaction time, a range of fluorescent graphene quantum dots were obtained from emitting yellow to blue under irradiation by UV lamp. As the etching proceeding, a large number of defects and holes were produced, then the hybrid graphene quantum dots having a large number of active sites, and when used as an oxygen reduction reaction catalyst, the catalytic performance are better than commercially available Pt/C catalyst.4 Meditating metal co-enhanced fluorescence and SERS in core-shell nanosphere as bifunctional biosensor for multiple DNA targetsA new design of simultaneously realizing metal enhanced fluorescence and coenhanced surface enhanced Raman scattering was prepared by embedding Ag nanoparticle into fluorophore and SERS active metal concentric hybrid microsphere (Ag@first SiO2 spacer@FiTC+SiO2@second SiO2 spacer@Au nanoaggregate). This architecture has three distinct characteristics, which make it more favorable to be applied in an efficient assay in practice than a sole fluorescence-, SERS-or their conventional combination-based assay protocol. Among them, one is to employ Ag nanoparticle as an efficient fluorescence enhancer to overcome the common fluorescence quenching around Au nanoaggregates. Secondly, Ag nanoparticle behaves like a mirror, thus incident light that passes through the SERS-active Au nanoaggregate and the intervening dielectric layer of SiO2 could be reflected multiply from the surface of Ag nanoparticle and coupled with the light at the nanogap between the Au nanoaggregate to further amplify Raman intensity, resulting in enhancement factor for fluorescence and SERS ～1.6-fold and ～300-fold higher than those obtained in the absence of silver core under identical experimental conditions, respectively. The last is to assemble fluorophore and SERS reporters onto different layers of the concentric hybrid microsphere, resulting in a feasible fabrication protocol when a large number of agents need to be involved into the dual-mode encoding carriers. A proof-of-concept chip-based DNA sandwich hybridization assay using genetically modified organisms as a model system has been investigated based on the concentric hybrid microsphere. The high specificity and sensitivity of the assays suggest that the new architecture has a very good potential for various bioanalytical applications and provides opportunities for other similar metal nanoparticles to realize co-enhancement effect.