| Energy consumption and environment pollution are two major problems for the world today.Vigorously developing clean energy technology is an important way to determine the sustainable development.Due to its abundant natural resources,outstanding physical and chemical properties,low-dimensional carbon-based composite materials can provide a good development platform for environmental monitoring,clean energy conversion and utilization.Compared with the bulk materials,low-dimensional carbon matrix composites based on carbon quantum dots?CQDs?can demonstrate more excellent photochemical and electrochemical properties,and are widely applied in the field of electrochemical sensors,photocatalysis and electrochemical energy storage.Moreover,they are of great significant meaning in shape-controlled,the realization of functional assembly and improvement of catalytic performance.The present dissertation has focused on the design,preparation and application of low-dimensional carbon matrix composites based on CQDs.A series of high-quality and high-performance low-dimensional carbon-based composite materials were synthesized and the properties of electrochemical sensors,photocatalysis and supercapacitors were researched,including graphene quantum dots?GQDs?modified electrode,CQDs/Proton-functionalized graphitic carbon nitride?HpCN?,CQDs/Polypyrrole nanowire?PPy-NW?and CQDs/PPy composite.They have shown the unique advantages and wide applicability of electrostatic self-assembly and electrochemical polymerization,and also demonstrated the good application prospects of low-dimensional carbon-based composites in the field of photoelectrochemistry.The main results can be summarized as follows:1.An electrostatic self-assembly strategy to prepare GQDs attached onto surface of glassy carbon electrode?GCE?was proposed.The electrochemical behavior of hydroquinone?HQ?and catechol?CC?on the resulting modified electrodes were carefully investigated.Under the optimum conditions,the thus-prepared GQDs modified electrode exhibited higher electrocatalytic oxidation capacity and better selectivity for HQ and CC than GCE and OH–/GCE.The linear range of HQ was 4.0 600.0 ?M and 6.0 400.0 ?M for CC,the detection limit was 0.40 ?M and 0.75 ?M,respectively.The modified electrode was also applied to detect the real samples with satisfactory results.Above all,the GQDs/GCE has a good reproducibility,stability and practical application ability.2.A novel approach to obtain CQDs/HpCN composite via the electrostatic self-assembly strategy was proposed.Compared with bulk g-C3N4 and HpCN,the CQDs/HpCN composite exhibited excellent electron transfer properties through ultraviolet-visible diffuse reflectance spectroscopy?DRS?,electrochemical impedance spectroscopy?EIS?.The CQDs/HpCN composite also significantly enhanced photoactivity in the photoelectrochemical i-t curve test and degradation of methylene blue?MB?solution under visible light irradiation.The results showed that the degradation efficiency of MB could be reached 90 % under visible light irradiation for 1.5 h over CQDs/HpCN composite,and the CQDs/HpCN composite had the highest photocurrent density of 1.89 ?A·cm-2.Furthermore,CQDs/HpCN composite also could be used as an effective photocatalyst for MB degradation with good stability.3.A new dotted line structure of CQDs/PPy-NW with superior electrochemical properties was designed and constructed via electrostatic self-assembly strategy.In a three-electrode cell,the CQDs/PPy-NW composite electrode displayed a specific capacitance of 306 F·g-1 at a current density of 0.5 A·g-1 and retained 66.8 % capacitance when the current density increased by 80 times(from 0.5 to 40 A·g-1).In addition,the as-fabricated symmetric supercapacitor was able to offer a large areal capacitance(248.5 mF·cm-2 at 0.2 mA·cm-2),higher energy density(26.5 ?Wh·cm-2)and good rate capability,the supercapacitor still retained good cycling stability even at a high current density of 5 mA·cm-2?85.2 % capacitance retention after 5 000 cycles?.In conclusion,the good electrochemical properties suggest a great potential of the CQDs/PPy-NW in the development of high-performance supercapacitor electrode materials.4.A flexible electrode,using stainless steel wire meshes coated with CQDs/PPy composite as electrode,is prepared by an efficient and controllable potentiostatic electropolymerization method?without added electrolyte?.Due to the advantages of both graphite and quantum dots,the CQDs can play a supporting electrolyte role during the electropolymerization process.The pyrrole monomeric radical cations?Py·+?would gradually polymerized on surface of the CQDs to form the porous “nano-islands” structure of CQDs/PPy composite.Compared with the dense pure PPy membrane,such “nano-islands” structure not only greatly increase an effective interface area to improve the charge transfer,but also facilitate the fast transfer of charge carriers during the charge-discharge process.Furthermore,benefiting from superior electrochemical properties of CQDs and PPy,the as-prepared CQDs/PPy composite flexible all-solid-state supercapacitors exhibited outstanding electrochemical performance with the areal capacitance 315 mF·cm-2(corresponding to specific capacitance of 308 F·g-1)at a current density of 0.2 mA·cm-2 and long cycle life with 85.7 % capacitance retention after 2 000 cycles at a current density of 2 mA·cm-2.Furthermore,the flexible energy storage devices showed a stable electrochemical performance under different bending conditions,and the devices could connected in series powered a red LED.These impressive results fully demonstrated that CQDs/PPy was a kind of electrochemical energy storage materials with excellent performance.5.To improve the energy density of electrochemical capacitor,a novel asymmetric supercapacitor using CQDs/GR as the negative electrode and the CQDs/PPy composite as the positive electrode in the polymer gel electrolyte was constructed.The TEM images showed that the formation of low-dimensional carbon-based composites through the ?-? interactions and the van der Waals attraction between graphene oxides and CQDs.The as-fabricated asymmetric supercapacitor device possessed a stable potential of 1.6 V and exhibited a high energy density of 44.4 Wh·kg-1.The excellent cycling stability after 2000 cycles is competitive to other asymmetric supercapacitor devices reported previously.These impressive results suggested that feasibility of CQDs/GR low-dimensional carbon-based composite materials as the negative electrode of the asymmetric supercapacitor device,which further promoted the development of high performance asymmetric supercapacitors. |
PDF Full Text Request