-
摘要: 石墨烯量子点作为纳米炭家族中独特的一员,由于其高比表面、丰富的表面化学反应位点和高电荷转移性能,已成为全解水和金属-空气电池等领域中的重要催化剂。了解石墨烯量子点在多相催化中的催化机理有助于合理设计高性能石墨烯量子点基催化剂。本文综述了近年来石墨烯量子点基多相催化剂的合成、改性及在全解水、金属-空气电池等领域应用的研究进展。讨论了目前石墨烯量子点基催化剂研究中存在的问题,并对设计高性能石墨烯量子点基催化剂的前景进行了展望。Abstract: Graphene quantum dots (GQDs), as a unique member of the nanocarbon family, have become important catalysts for overall water splitting and metal-air batteries because of their high specific surface area, abundant surface chemical reaction sites and high electron mobility. Understanding the fundamental catalytic mechanism of GQDs in heterogeneous catalysis is conducive to the rational design of high performance GQD-based catalysts. This article summarizes current research progress in the synthesis, modification and applications of GQD-based heterogeneous catalysts in overall water splitting, metal-air batteries and other fields. The issues related to the use of GQD-based catalysts in these fields are discussed together with their future development.
-
Key words:
- Graphene quantum dots /
- Catalysts /
- Overall water splitting /
- Metal-air batteries
-
Figure 2. Synthesis of GQDs: (a-e) the top-down methods, (a) solvothermal of dimethylformamide (Reproduced with permission[34], Copyright 2013, American Chemical Society), (b) acid oxidation of carbon fibers (Reproduced with permission[30], Copyright 2012, American Chemical Society), (c) electrochemical oxidation of graphite (Reproduced with permission[36], Copyright 2009, American Chemical Society), (d) microwave-assisted oxidation cutting of graphene oxide (Reproduced with permission[38], Copyright 2012, Royal Society of Chemistry), (e) physical grinding of graphite with tartrate tetrahydrate (Reproduced with permission[39], Copyright 2016, Wiley-VCH), f-h) the bottom-up methods, (f) carbonization of rice powder (Reproduced with permission[41], Copyright 2016, Royal Society of Chemistry), (g) hydrothermal treatment of citric acid (Reproduced with permission[44], Copyright 2012, Elsevier) and (h) microwave-assisted hydrothermal treatment of catecholamines (Reproduced with permission[45], Copyright 2016, Wiley-VCH).
Figure 3. (a) Schematic diagram of NGQD catalyst for CO2 hydrogenation at moderate reaction temperatures, (b) X-ray absorption near edge spectrum of N K-edge for NGQDs (the inset is a scheme of different N−C bonds (pyridinic (black), pyrrolic (blue), and graphitic N (pink))), (c) dependence of CO2 conversion on temperature over NGQDs/Al2O3 with three different loadings (0.8 wt %, 1 wt % and 3 wt %) and (d) dependence of CO and CH4 selectivity on temperature over NGQDs/Al2O3 with three different loadings (Reproduced with permission[65], Copyright 2012, American Chemical Society).
Figure 4. (a) Schematic of the synthesis of hydrophilic and hydrophobic GQDs (C12-GQDs) from commercially available graphite nanopowder, (b) stacked photoluminescence emission spectra of GQDs, C12-GQDsHexane and C12-GQDsToluene (at an excitation wavelength of 360 nm) and (c) proposed photoluminescence mechanism of the GQDs and functionalized GQDs (C12-GQDs) (Reproduced with permission[77], Copyright 2018, Royal Society of Chemistry).
Figure 5. (a) Energy profile diagram of dye-sensitized Rho-GQDs system for H2 evolution under visible light irradiation, (b) comparison of H2 evolution efficiency between covalent-bonded dye-sensitized Rho-GQDs system and Rho/GQDs system attached via electrostatic interactions along with virgin GQDs and Rhodamine 123 dye, (c) photocatalytic HER efficiency of covalent-bonded Rho-GQDs with different weight percentages of Rho after 4 h of visible light (λ>400 nm) irradiation and (d) photocatalytic HER performance with Rho-GQDs in presence of 2 wt%-Pt as a co-catalyst during photocatalytic water splitting under visible light irradiation using 10 vol% triethanolamine as a sacrificial electron donor (Reproduced with permission[82], Copyright 2020, Elsevier).
Figure 6. (a) Schematic illustration of the preparation of Ni3S2-NGQDs/NF electrodes, and its utilization as OER and HER electrocatalysts for alkaline water splitting, (b) polarization curves of Ni3S2-NGQDs/NF, Ni3S2/NF, RuO2-Pt-C/NF and NF and (c) chronoamperometric curves obtained in a constant current (J = 10 mA·cm−2) bulk water electrolysis with Ni3S2-NGQDs/NF, Ni3S2/NF, and RuO2-Pt-C/NF electrodes (Reproduced with permission[95], Copyright 2017, Wiley-VCH).
Figure 7. (a) The synthesis processes of Mo-Ni3S2/NF and G-Mo-Ni3S2-2/NF, (b, c) HRTEM images of G-Mo-Ni3S2, (d) polarization curves and (e) the long-term durability test at 1.65 V of GQDs-Mo-Ni3S2 for overall water splitting, the inset shows the photograph of generated gas bubbles on both electrodes (Reproduced with permission[96], Copyright 2019, Elsevier).
Figure 8. (a) Schematic illustration of the synthesis procedure for GH-BGQD; (b) SEM (Inset of (b) is the photograph image of GH-BGQD), (c, d) TEM images of the GH-BGQD composite, (e) polarization curves of GH-BGQD//GH-BGQD and Pt/C//Ir/C for overall water splitting in 0.1 mol L−1 KOH, (f) chronopotentiometric curves of the GH-BGQD electrode for 70 h at 10 mA·cm−2 and 1.61 V (The inset shows the photograph of generated gas bubbles on both electrodes) (Reproduced with permission[97], Copyright 2019, Wiley-VCH).
Figure 9. (a) Schematic configuration of the solid-state Zn-air battery, (b) discharge curves of Zn-air battery with GH-BGQD as the air electrode at various current densities, (c) polarization curves and corresponding power density plots, (d) specific capacity of the GH-BGQD based Zn-air battery at a current density of 10 mA·cm−2, (e) discharge/charge cycling curves for the GH-BGQD based Zn-air battery at a current density of 5 mA·cm−2 (20 min per cycle) and (f) discharge/charge cycling curves for the GH-BGQD based Zn-air battery at a current density of 10 mA·cm−2 under different bending states (Reproduced with permission[97], Copyright 2019, Wiley-VCH).
Figure 10. (a) Discharge polarization curves of the Zn-air batteries based on NiCo2S4/CC, N-GQDs/NiCo2S4/CC, and Pt/C+Ir/C/CC catalysts and the corresponding power densities, (b) charge/discharge polarization curves of the Zn-air battery based on NiCo2S4/CC, N-GQDs/NiCo2S4/CC, and Pt/C+Ir/C/CC and (c) galvanostatic charge/discharge curve of the Zn-air battery based on the N-GQDs/NiCo2S4/CC catalyst at a current density of 20 mA·cm−2 (Reproduced with permission[112], Copyright 2019, Wiley-VCH).
Figure 11. (a) Illustration of standard redox potentials and the energy-level of GQD, (b) time courses of H2 evolution and (c) CO2 reduction of all GQD types under visible light (420-800 nm) and (d) schematic illustration of GQD-BNPTL Z-scheme photocatalysis of CO2 reduction ( Reproduced with permission[81], Copyright 2018, American Chemical Society).
Table 1. The comparison of different GQDs-based electrocatalysts for overall water splitting.
Electrocatalysts Overall water splitting Current density
J (mA·cm−2)Overpotential at the
corresponding J (mV)Cell voltage at
10 mA·cm−2 (V)Electrolyte Ref. Ni3S2-GQDs OER 10 300 / 1 mol L−1 KOH [95] HER 10 274 Ni3S2-NGQDs OER 10 216 1.58 1 mol L−1 KOH [95] HER 10 218 NiCo2P2/GQDs OER 10 340 1.61 1 mol L−1 KOH [90] HER 10 52 GQDs-Mo-Ni3S2 OER 20 326 1.58 1 mol L−1 KOH [96] HER 10 68 GH-BGQD OER 10 1600 (Potential) 1.61 0.1 mol L−1 KOH [97] HER 10 300 (Potential) Table 2. The comparison of different GQDs-based electrocatalysts for metal-air batteries.
Catalyst material Open circuit potential (V) Power density (mW·cm−2) Electrolyte Ref. GH-GQD / ~74 6 mol L−1 KOH aqueous [89] Pt/C / ~72 6 mol L−1 KOH aqueous [89] GH-BGQD 1.40 112 Polyvinylalcohol hydrogel film containing
2.0 mol L−1 KOH and 0.2 mol L−1 ZnCl2[97] Pt/C+Ir/C 1.36 95 Polyvinylalcohol hydrogel film containing
2.0 mol L−1 KOH and 0.2 mol L−1 ZnCl2[97] N-GQDs/NiCo2S4/CC ~1.5 75.2 6 mol L−1 KOH containing 0.2 mol L−1 zinc acetate [112] Pt/C+Ir/C ~1.54 ~68 6 mol L−1 KOH containing 0.2 mol L−1 zinc acetate [112] N-GQDs/NiCo2S4/CC 1.41 26.2 2 mol L−1 KOH/PVA gel electrolyte with 0.2 mol L−1 zinc acetate [112] N-GH-GQD / ~90 6 mol L−1 KOH aqueous [113] Pt/C / ~72 6 mol L−1 KOH aqueous [113] -
[1] Gu S Y, Hsieh C T, Mallick B C, et al. Infrared-assisted synthesis of highly amidized graphene quantum dots as metal-free electrochemical catalysts[J]. Electrochimica Acta,2020,360:137009. doi: 10.1016/j.electacta.2020.137009 [2] Kundu S, Bramhaiah K, Bhattacharyya S. Carbon-based nanomaterials: In the quest of alternative metal-free photocatalysts for solar water splitting[J]. Nanoscale Advances,2020,2(11):5130-5151. doi: 10.1039/D0NA00569J [3] Li J P, Yang S W, Deng Y, et al. Emancipating target-functionalized carbon dots from autophagy vesicles for a novel visualized tumor therapy[J]. Advanced Functional Materials,2018,28(30):1800881. doi: 10.1002/adfm.201800881 [4] Huang H, Yang S W, Liu Y, et al. Photocatalytic polymerization from amino acid to protein by carbon dots at room temperature[J]. ACS Applied Bio Materials,2019,2(11):5144-5153. doi: 10.1021/acsabm.9b00805 [5] Xu A L, Wang G, Li Y Q, et al. Carbon-based quantum dots with solid-state photoluminescent: Mechanism, implementation and application[J]. Small,2020,16:2004621. doi: 10.1002/smll.202004621 [6] Liu W W, Li M, Jiang G P, et al. Graphene quantum dots-based advanced electrode materials: Design, synthesis and their applications in electrochemical energy storage and electrocatalysis[J]. Advanced Energy Materials,2020,10(29):2001275. doi: 10.1002/aenm.202001275 [7] Zhang Z P, Zhang J, Chen N, et al. Graphene quantum dots: An emerging material for energy-related applications and beyond[J]. Energy & Environmental Science,2012,5(10):8869-8890. [8] Bak S, Kim D and Lee H. Graphene quantum dots and their possible energy applications: A review[J]. Current Applied Physics,2016,16(9):1192-1201. doi: 10.1016/j.cap.2016.03.026 [9] Tetsuka H. 2D/0D graphene hybrids for visible-blind flexible UV photodetectors[J]. Scientific Reports,2017,7(1):5544. doi: 10.1038/s41598-017-05981-y [10] Nguyen D A, Oh H M, Duong N T, et al. Highly enhanced photoresponsivity of a monolayer WSe2 photodetector with nitrogen-doped graphene quantum dots[J]. ACS Applied Materials & Interfaces,2018,10(12):10322-10329. [11] Tajik S, Dourandish Z, Zhang K Q, et al. Carbon and graphene quantum dots: A review on syntheses, characterization, biological and sensing applications for neurotransmitter determination[J]. RSC Advances,2020,10(26):15406-15429. doi: 10.1039/D0RA00799D [12] Younis M R, He G, Lin J, et al. Recent advances on graphene quantum dots for bioimaging applications[J]. Frontiers in Chemistry,2020,8:424. doi: 10.3389/fchem.2020.00424 [13] Liu W, Zhang R, Kang Y, et al. Preparation of nitrogen-doped carbon dots with a high fluorescence quantum yield for the highly sensitive detection of Cu2+ ions, drawing anti-counterfeit patterns and imaging live cells[J]. New Carbon Materials,2019,34(4):390-402. doi: 10.1016/S1872-5805(19)30024-1 [14] Wang G, He P, Xu A L, et al. Promising fast energy transfer system between graphene quantum dots and the application in fluorescent bioimaging[J]. Langmuir,2019,35(3):760-766. doi: 10.1021/acs.langmuir.8b03739 [15] Xu A L, He P, Ye C C, et al. Polarizing graphene quantum dots toward long-acting intracellular reactive oxygen species evaluation and tumor detection[J]. ACS Applied Materials & Interfaces,2020,12(9):10781-10790. [16] Tong X, Wei Q L, Zhan X X, et al. The new graphene family materials: Synthesis and applications in oxygen reduction reaction[J]. Catalysts,2016,7(12):1-26. doi: 10.3390/catal7010001 [17] Li M M, Ni W, Kan B, et al. Graphene quantum dots as the hole transport layer material for high-performance organic solar cells[J]. Physical Chemistry Chemical Physics,2013,15(43):18973-18978. doi: 10.1039/c3cp53283f [18] Kim J K, Kim S J, Park M J, et al. Surface-engineered graphene quantum dots incorporated into polymer layers for high performance organic photovoltaics[J]. Scientific Reports,2015,5:14276. doi: 10.1038/srep14276 [19] Luo Z M, Qi G Q, Chen K Y, et al. Microwave-assisted preparation of white fluorescent graphene quantum dots as a novel phosphor for enhanced white-light-emitting diodes[J]. Advanced Functional Materials,2016,26(16):2739-2744. doi: 10.1002/adfm.201505044 [20] Li Y Q, Dong H, Tao Q, et al. Enhancing the magnetic relaxivity of MRI contrast agents via the localized superacid microenvironment of graphene quantum dots[J]. Biomaterials,2020,250:120056. doi: 10.1016/j.biomaterials.2020.120056 [21] Ponomarenko L A, Schedin F, Katsnelson M I, et al. Chaotic dirac billiard in graphene quantum dots[J]. Science,2008,320:356-358. doi: 10.1126/science.1154663 [22] Zhang Z Z, Chang K. Tuning of energy levels and optical properties of graphene quantum dots[J]. Physical Review B,2008,77(23):235411. doi: 10.1103/PhysRevB.77.235411 [23] Li L L, Wu G H, Yang G H, et al. Focusing on luminescent graphene quantum dots: Current status and future perspectives[J]. Nanoscale,2013,5(10):4015-4039. doi: 10.1039/c3nr33849e [24] Yan Y B, Gong J, Chen J, et al. Recent advances on graphene quantum dots: From chemistry and physics to applications[J]. Advanced Materials,2019,31:1808283. doi: 10.1002/adma.201808283 [25] Farshbaf M, Davaran S, Rahimi F, et al. Carbon quantum dots: Recent progresses on synthesis, surface modification and applications[J]. Artificial Cells Nanomedicine and Biotechnology,2018,46(7):1331-1348. doi: 10.1080/21691401.2017.1377725 [26] Zhao C H, Song X B, Liu Y, et al. Synthesis of graphene quantum dots and their applications in drug delivery[J]. Journal of Nanobiotechnology,2020,18(1):142. doi: 10.1186/s12951-020-00698-z [27] Bera D, Qian L, Tseng T K, et al. Quantum dots and their multimodal applications: A review[J]. Materials,2010,3(4):2260-2345. doi: 10.3390/ma3042260 [28] Pan D Y, Zhang J C, Li Z, et al. Hydrothermal route for cutting graphene sheets into blue-luminescent graphene quantum dots[J]. Advanced Materials,2010,22(6):734-738. doi: 10.1002/adma.200902825 [29] El-Hnayn R, Canabady-Rochelle L, Desmarets C, et al. One-step synthesis of diamine-functionalized graphene quantum dots from graphene oxide and their chelating and antioxidant activities[J]. Nanomaterials,2020,10(1):104. doi: 10.3390/nano10010104 [30] Peng J, Gao W, Gupta B K, et al. Graphene quantum dots derived from carbon fibers[J]. Nano Letters,2012,12(2):844-849. doi: 10.1021/nl2038979 [31] Kundu S, Yadav R M, Narayanan T N, et al. Synthesis of N, F and S co-doped graphene quantum dots[J]. Nanoscale,2015,7(27):11515-11519. doi: 10.1039/C5NR02427G [32] Chen G X, Zhuo Z W, Ni K, et al. Rupturing C60 molecules into graphene-oxide-like quantum dots: Structure, photoluminescence, and catalytic application[J]. Small,2015,11(39):5296-5304. doi: 10.1002/smll.201501611 [33] Zhang C G, Li J J, Zeng X S, et al. Graphene quantum dots derived from hollow carbon nano-onions[J]. Nano Research,2017,11(1):174-184. [34] Liu Q, Guo B D, Rao Z Y, et al. Strong two-photon-induced fluorescence from photostable, biocompatible nitrogen-doped graphene quantum dots for cellular and deep-tissue imaging[J]. Nano Letters,2013,13(6):2436-2441. doi: 10.1021/nl400368v [35] Tian R B, Zhong S T, Wu J, et al. Solvothermal method to prepare graphene quantum dots by hydrogen peroxide[J]. Optical Materials,2016,60:204-208. doi: 10.1016/j.optmat.2016.07.032 [36] Lu J, Yang J X, Wang J Z, et al. One-pot synthesis of fluorescent carbon nanoribbons, nanoparticles, and graphene by the exfoliation of graphite in ionic liquids[J]. ACS Nano,2009,3(8):2367-2375. doi: 10.1021/nn900546b [37] Li Y, Hu Y, Zhao Y, et al. An electrochemical avenue to green-luminescent graphene quantum dots as potential electron-acceptors for photovoltaics[J]. Advanced Materials,2011,23(6):776-780. doi: 10.1002/adma.201003819 [38] Chen S, Liu J W, Chen M L, et al. Unusual emission transformation of graphene quantum dots induced by self-assembled aggregation[J]. Chemical Communications,2012,48(61):7637-7639. doi: 10.1039/c2cc32984k [39] Yoon H, Chang Y H, Song S H, et al. Intrinsic photoluminescence emission from subdomained graphene quantum dots[J]. Advanced Materials,2016,28(26):5255-5261. doi: 10.1002/adma.201600616 [40] Ali J, Siddiqui G U D, Yang Y J, et al. Direct synthesis of graphene quantum dots from multilayer graphene flakes through grinding assisted co-solvent ultrasonication for all-printed resistive switching array[J]. RSC Advances,2016,6:5068-5078. doi: 10.1039/C5RA21699K [41] Kalita H, Mohapatra J, Pradhan L, et al. Efficient synthesis of rice based graphene quantum dots and their fluorescent properties[J]. RSC Advances,2016,6(28):23518-23524. doi: 10.1039/C5RA25706A [42] Bian S Y, Shen C, Qian Y T, et al. Facile synthesis of sulfur-doped graphene quantum dots as fluorescent sensing probes for Ag+ ions detection[J]. Sensors and Actuators B: Chemical,2017,242:231-237. doi: 10.1016/j.snb.2016.11.044 [43] Wang L, Wang Y L, Xu T, et al. Gram-scale synthesis of single-crystalline graphene quantum dots with superior optical properties[J]. Nature Communications,2014,5:5357. doi: 10.1038/ncomms6357 [44] Dong Y Q, Shao J W, Chen C Q, et al. Blue luminescent graphene quantum dots and graphene oxide prepared by tuning the carbonization degree of citric acid[J]. Carbon,2012,50(12):4738-4743. doi: 10.1016/j.carbon.2012.06.002 [45] Jeon S J, Kang T W, Ju J M, et al. Modulating the photocatalytic activity of graphene quantum dots via atomic tailoring for highly enhanced photocatalysis under visible light[J]. Advanced Functional Materials,2016,26(45):8211. doi: 10.1002/adfm.201603803 [46] Shen S L, Wang J J, Wu Z J, et al. Graphene quantum dots with high yield and high quality synthesized from low cost precursor of aphanitic graphite[J]. Nanomaterials,2020,10(2):375. doi: 10.3390/nano10020375 [47] Lee N E, Jeong J M, Lim H S, et al. Ultraviolet/blue light emitting high-quality graphene quantum dots and their biocompatibility[J]. Carbon,2020,170:213-219. doi: 10.1016/j.carbon.2020.08.015 [48] Wang Y, Shao Y Y, Matson D W, et al. Nitrogen-doped graphene and its application in electrochemical biosensing[J]. ACS Nano,2010,4(4):1790-1798. doi: 10.1021/nn100315s [49] Gopalakrishnan K, Govindaraj A, Rao C N R. Extraordinary supercapacitor performance of heavily nitrogenated graphene oxide obtained by microwave synthesis[J]. Journal of Materials Chemistry A,2013,1(26):7563-7565. doi: 10.1039/c3ta11385j [50] Gong K P, Du F, Xia Z H, et al. Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction[J]. Science,2009,323(5915):760-764. doi: 10.1126/science.1168049 [51] Wang Z J, Jia R R, Zheng J F, et al. Nitrogen-promoted self-assembly of N-doped carbon nanotubes and their intrinsic catalysis for oxygen reduction in fuel cells[J]. ACS Nano,2011,5(3):1677-1684. doi: 10.1021/nn1030127 [52] Panchakarla L S, Govindaraj A, Rao C N R. Boron- and nitrogen-doped carbon nanotubes and graphene[J]. Inorganica Chimica Acta,2010,363(15):4163-4174. doi: 10.1016/j.ica.2010.07.057 [53] Dong Y Q, Pang H C, Yang H B, et al. Carbon-based dots co-doped with nitrogen and sulfur for high quantum yield and excitation-independent emission[J]. Angewandte Chemie,2013,52(30):7800-7804. doi: 10.1002/anie.201301114 [54] Benítez-Martínez S, Valcárcel M. Graphene quantum dots in analytical science[J]. Trends in Analytical Chemistry,2015,72:93-113. doi: 10.1016/j.trac.2015.03.020 [55] Tam T V, Trung N B, Kim H R, et al. One-pot synthesis of N-doped graphene quantum dots as a fluorescent sensing platform for Fe3+ ions detection[J]. Sensors and Actuators B: Chemical,2014,202:568-573. doi: 10.1016/j.snb.2014.05.045 [56] Ju J, Chen W. Synthesis of highly fluorescent nitrogen-doped graphene quantum dots for sensitive, label-free detection of Fe (III) in aqueous media[J]. Biosens Bioelectron,2014,58:219-225. doi: 10.1016/j.bios.2014.02.061 [57] Du Y, Guo S J. Chemically doped fluorescent carbon and graphene quantum dots for bioimaging, sensor, catalytic and photoelectronic applications[J]. Nanoscale,2016,8(5):2532-2543. doi: 10.1039/C5NR07579C [58] Kuo N J, Chen Y S, Wu C W, et al. One-pot synthesis of hydrophilic and hydrophobic N-doped graphene quantum dots via exfoliating and disintegrating graphite flakes[J]. Scientific Reports,2016,6:30426. doi: 10.1038/srep30426 [59] Majumder T, Mondal S P. Advantages of nitrogen-doped graphene quantum dots as a green sensitizer with ZnO nanorod based photoanodes for solar energy conversion[J]. Journal of Electroanalytical Chemistry,2016,769:48-52. doi: 10.1016/j.jelechem.2016.03.018 [60] Sun L, Luo Y, Li M, et al. Role of pyridinic-N for Nitrogen-doped graphene quantum dots in oxygen reaction reduction[J]. Journal of Colloid and Interface Science,2017,508:154-158. doi: 10.1016/j.jcis.2017.08.047 [61] Fu Y, Gao G Y, Zhi J F. Electrochemical synthesis of multicolor fluorescent N-doped graphene quantum dots as a ferric ion sensor and their application in bioimaging[J]. Journal of Materials Chemistry B,2019,7(9):1494-1502. doi: 10.1039/C8TB03103G [62] Li Y, Zhao Y, Cheng H H, et al. Nitrogen-doped graphene quantum dots with oxygen-rich functional groups[J]. Journal of American Chemical Society,2012,134(1):15-18. doi: 10.1021/ja206030c [63] Li Q Q, Zhang S, Dai L M, et al. Nitrogen-doped colloidal graphene quantum dots and their size-dependent electrocatalytic activity for the oxygen reduction reaction[J]. Journal of American Chemical Society,2012,134(46):18932-18935. doi: 10.1021/ja309270h [64] Saidi W A. Oxygen reduction electrocatalysis using N-doped graphene quantum-dots[J]. The Journal of Physical Chemistry Letters,2013,4(23):4160-4165. doi: 10.1021/jz402090d [65] Wu J J, Wen C, Zou X L, et al. Carbon dioxide hydrogenation over a metal-free carbon-based catalyst[J]. ACS Catalysis,2017,7(7):4497-4503. doi: 10.1021/acscatal.7b00729 [66] Li X M, Lau S P, Tang L B, et al. Sulphur doping: A facile approach to tune the electronic structure and optical properties of graphene quantum dots[J]. Nanoscale,2014,6(10):5323-5328. doi: 10.1039/C4NR00693C [67] Qu D, Zheng M, Du P, et al. Highly luminescent S, N co-doped graphene quantum dots with broad visible absorption bands for visible light photocatalysts[J]. Nanoscale,2013,5(24):12272-12277. doi: 10.1039/c3nr04402e [68] Fan T J, Zhang G X, Jian L F, et al. Facile synthesis of defect-rich nitrogen and sulfur co-doped graphene quantum dots as metal-free electrocatalyst for the oxygen reduction reaction[J]. Journal of Alloys and Compounds,2019,792:844-850. doi: 10.1016/j.jallcom.2019.04.097 [69] Wei J M, Liu B T, Zhang X, et al. One-pot synthesis of N, S co-doped photoluminescent carbon quantum dots for Hg2+ ion detection[J]. New Carbon Materials,2018,33(4):333-340. doi: 10.1016/S1872-5805(18)60343-9 [70] Dey S, Govindaraj A, Biswas K, et al. Luminescence properties of boron and nitrogen doped graphene quantum dots prepared from arc-discharge-generated doped graphene samples[J]. Chemical Physics Letters,2014,595-596:203-208. doi: 10.1016/j.cplett.2014.02.012 [71] Favaro M, Ferrighi L, Fazio G, et al. Single and multiple doping in graphene quantum dots: Unraveling the origin of selectivity in the oxygen reduction reaction[J]. ACS Catalysis,2014,5(1):129-144. [72] Fei H L, Ye R Q, Ye G L, et al. Boron- and nitrogen-doped graphene quantum dots-graphene hybrid nanoplatelets as efficient electrocatalysts for oxygen reduction[J]. ACS Nano,2014,8(10):10837-10843. doi: 10.1021/nn504637y [73] Sun Y P, Zhou B, Lin Y, et al. Quantum-sized carbon dots for bright and colorful photoluminescence[J]. Journal of American Chemical Society,2006,128(24):7756-7757. doi: 10.1021/ja062677d [74] Tachi S, Morita H, Takahashi M, et al. Quantum yield enhancement in graphene quantum dots via esterification with benzyl alcohol[J]. Scientific Reports,2019,9(1):14115. doi: 10.1038/s41598-019-50666-3 [75] Zhu S J, Zhang J H, Tang S J, et al. Surface chemistry routes to modulate the photoluminescence of graphene quantum dots: From fluorescence mechanism to up-conversion bioimaging applications[J]. Advanced Functional Materials,2012,22:4732-4740. doi: 10.1002/adfm.201201499 [76] Zheng X T, Ananthanarayanan A, Luo K Q, et al. Glowing graphene quantum dots and carbon dots: Properties, syntheses and biological applications[J]. Small,2015,11(14):1620-1636. doi: 10.1002/smll.201402648 [77] Deka M J, Dutta A, Chowdhury D. Tuning the wettability and photoluminescence of graphene quantum dots via covalent modification[J]. New Journal of Chemistry,2018,42(1):355-362. doi: 10.1039/C7NJ03280C [78] Arunragsa S, Seekaew Y, Pon-On W, et al. Hydroxyl edge-functionalized graphene quantum dots for gas-sensing applications[J]. Diamond and Related Materials,2020,105:107790. doi: 10.1016/j.diamond.2020.107790 [79] Gao T, Wang X, Zhao J, et al. Bridge between temperature and light: bottom-up synthetic route to structure-defined graphene quantum dots as a temperature probe in vitro and in cells[J]. ACS Applied Materials & Interfaces,2020,12(19):22002-22011. [80] Kwon W, Kim Y H, Kim J H, et al. High color-purity green, orange, and red light-emitting diodes based on chemically functionalized graphene quantum dots[J]. Scientific Reports,2016,6:24205. doi: 10.1038/srep24205 [81] Yan Y B, Chen J, Li N, et al. Systematic bandgap engineering of graphene quantum dots and applications for photocatalytic water splitting and CO2 reduction[J]. ACS Nano,2018,12(4):3523-3532. doi: 10.1021/acsnano.8b00498 [82] Dinda D, Park H, Lee H J, et al. Graphene quantum dot with covalently linked Rhodamine dye: A high efficiency photocatalyst for hydrogen evolution[J]. Carbon,2020,167:760-769. doi: 10.1016/j.carbon.2020.06.041 [83] Yang H B, DongY Q, Wang X Z, et al. Graphene quantum dots-incorporated cathode buffer for improvement of inverted polymer solar cells[J]. Solar Energy Materials & Solar Cells,2013,117:214-218. [84] Pan D Y, Jiao J K, Li Z, et al. Efficient separation of electron-hole pairs in graphene quantum dots by TiO2 heterojunctions for dye degradation[J]. ACS Sustainable Chemistry & Engineering,2015,3(10):2405-2413. [85] Dutta M, Sarkar S, Ghosh T, et al. ZnO/graphene quantum dot solid-state solar cell[J]. The Journal of Physical Chemistry C,2012,116(38):20127-20131. doi: 10.1021/jp302992k [86] Rajender G, Kumar J, Giri P K. Interfacial charge transfer in oxygen deficient TiO2-graphene quantum dot hybrid and its influence on the enhanced visible light photocatalysis[J]. Applied Catalysis B: Environmental,2018,224:960-972. doi: 10.1016/j.apcatb.2017.11.042 [87] Gao Y T, Hou F, Hu S, et al. Graphene quantum-dot-modified hexagonal tubular carbon nitride for visible-light photocatalytic hydrogen evolution[J]. ChemCatChem,2018,10(6):1330-1335. doi: 10.1002/cctc.201701823 [88] Zhou X M, Tian Z M, Li J, et al. Synergistically enhanced activity of graphene quantum dot/multi-walled carbon nanotube composites as metal-free catalysts for oxygen reduction reaction[J]. Nanoscale,2014,6(5):2603-2607. doi: 10.1039/c3nr05578g [89] Wang M R, Fang Z, Zhang K, et al. Synergistically enhanced activity of graphene quantum dots/graphene hydrogel composites: A novel all-carbon hybrid electrocatalyst for metal/air batteries[J]. Nanoscale,2016,8(22):11398-11402. doi: 10.1039/C6NR02622B [90] Tian J Q, Chen J, Liu J Y, et al. Graphene quantum dot engineered nickel-cobalt phosphide as highly efficient bifunctional catalyst for overall water splitting[J]. Nano Energy,2018,48:284-291. doi: 10.1016/j.nanoen.2018.03.063 [91] Luo P H, Jiang L Q, Zhang W L, et al. Graphene quantum dots/Au hybrid nanoparticles as electrocatalyst for hydrogen evolution reaction[J]. Chemical Physics Letters,2015,641:29-32. doi: 10.1016/j.cplett.2015.10.042 [92] Wu X C, Guo S W, Zhang J Y. Selective oxidation of veratryl alcohol with composites of Au nanoparticles and graphene quantum dots as catalysts[J]. Chemical Communications,2015,51(29):6318-6321. doi: 10.1039/C5CC00061K [93] Morales-Guio C G, Stern L A, Hu X. Nanostructured hydrotreating catalysts for electrochemical hydrogen evolution[J]. Chemical Society Reviews,2014,43(18):6555-6569. doi: 10.1039/C3CS60468C [94] Guo B, Yu K, Li H, et al. Coral-shaped MoS2 decorated with graphene quantum dots performing as a highly active electrocatalyst for hydrogen evolution reaction[J]. ACS Applied Materials & Interfaces,2017,9(4):3653-3660. [95] Lv J J, Zhao J, Fang H, et al. Incorporating nitrogen-doped graphene quantum dots and Ni3S2 nanosheets: A synergistic electrocatalyst with highly enhanced activity for overall water splitting[J]. Small,2017,13(24):1700264. doi: 10.1002/smll.201700264 [96] Li J F, Zhang X Q, Zhang Z H, et al. Graphene-quantum-dots-induced facile growth of porous molybdenum doped Ni3S2 nanoflakes as efficient bifunctional electrocatalyst for overall water splitting[J]. Electrochimica Acta,2019,304:487-494. doi: 10.1016/j.electacta.2019.03.023 [97] Tam T V, Kang S G, Kim M H, et al. Novel graphene hydrogel/B‐doped graphene quantum dots composites as trifunctional electrocatalysts for Zn-Air batteries and overall water splitting[J]. Advanced Energy Materials,2019:1900945. doi: 10.1002/aenm.201900945 [98] Li Q Q, Chen B L, Xing B S. Aggregation kinetics and self-assembly mechanisms of graphene quantum dots in aqueous solutions: cooperative effects of pH and electrolytes[J]. Environmental Science & Technology,2017,51(3):1364-1376. [99] Rahman M A, Wang X J, Wen C. High energy density metal-air batteries: A review[J]. Journal of The Electrochemical Society,2013,160(10):A1759-A1771. doi: 10.1149/2.062310jes [100] Yang D J, Zhang L J, Yan X C, et al. Recent progress in oxygen electrocatalysts for zinc-air batteries[J]. Small Methods,2017,1(12):1700209. doi: 10.1002/smtd.201700209 [101] Peng Z Q, Freunberger S A, Chen Y H, et al. A reversible and higher-rate Li-O2 battery[J]. Science,2012,337:563-566. doi: 10.1126/science.1223985 [102] Lu Y C, Xu Z C, Gasteiger H A, et al. Platinum-gold nanoparticles: A highly active bifunctional electrocatalyst for rechargeable lithium-air batteries[J]. Journal of American Chemical Society,2010,132(35):12170-12171. doi: 10.1021/ja1036572 [103] Yan W N, Cao X C, Ke K, et al. One-pot synthesis of monodispersed porous CoFe2O4 nanospheres on graphene as an efficient electrocatalyst for oxygen reduction and evolution reactions[J]. RSC Advances,2016,6(1):307-313. doi: 10.1039/C5RA23306B [104] Zhu J B, Xiao M L, Zhang Y L, et al. Metal-organic framework-induced synthesis of ultrasmall encased NiFe nanoparticles coupling with graphene as an efficient oxygen electrode for a rechargeable Zn-air battery[J]. ACS Catalysis,2016,6(10):6335-6342. doi: 10.1021/acscatal.6b01503 [105] Wei L, Karahan H E, Zhai S L, et al. Amorphous bimetallic oxide-graphene hybrids as bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries[J]. Advanced Materials,2017,29(38):1701410. doi: 10.1002/adma.201701410 [106] Wang Q, Lei Y, Chen Z, et al. Fe/Fe3C@C nanoparticles encapsulated in N-doped graphene-CNTs framework as an efficient bifunctional oxygen electrocatalyst for robust rechargeable Zn-air batteries[J]. Journal of Materials Chemistry A,2018,6(2):516-526. doi: 10.1039/C7TA08423D [107] Liu W W, Zhang J, Bai Z Y, et al. Controllable urchin-like NiCo2S4 microsphere synergized with sulfur-doped graphene as bifunctional catalyst for superior rechargeable Zn-air battery[J]. Advanced Functional Materials,2018,28(11):1706675. doi: 10.1002/adfm.201706675 [108] Song J H, Zhu C Z, Fu S F, et al. Optimization of cobalt/nitrogen embedded carbon nanotubes as an efficient bifunctional oxygen electrode for rechargeable zinc-air batteries[J]. Journal of Materials Chemistry A,2016,4(13):4864-4870. doi: 10.1039/C6TA00615A [109] Han X P, Wu X Y, Zhong C, et al. NiCo2S4 nanocrystals anchored on nitrogen-doped carbon nanotubes as a highly efficient bifunctional electrocatalyst for rechargeable zinc-air batteries[J]. Nano Energy,2017,31:541-550. doi: 10.1016/j.nanoen.2016.12.008 [110] Cheng H, Li M L, Su C Y, et al. Cu-Co bimetallic oxide quantum dot decorated nitrogen-doped carbon nanotubes: a high-efficiency bifunctional oxygen electrode for Zn-air batteries[J]. Advanced Functional Materials,2017,27(30):1701833. doi: 10.1002/adfm.201701833 [111] Li Z H, Shao M F, Yang Q H, et al. Directed synthesis of carbon nanotube arrays based on layered double hydroxides toward highly-efficient bifunctional oxygen electrocatalysis[J]. Nano Energy,2017,37:98-107. doi: 10.1016/j.nanoen.2017.05.016 [112] Liu W W, Ren B H, Zhang W Y, et al. Defect-enriched nitrogen doped-graphene quantum dots engineered NiCo2S4 nanoarray as high-efficiency bifunctional catalyst for flexible Zn-air battery[J]. Small,2019,15(44):1903610. doi: 10.1002/smll.201903610 [113] Wang M G, Fang J, Hu L T, et al. Defects-rich graphene/carbon quantum dot composites as highly efficient electrocatalysts for aqueous zinc/air batteries[J]. International Journal of Hydrogen Energy,2017,42:21305-21310. doi: 10.1016/j.ijhydene.2017.07.045 [114] Tu X J, Wang Q, Zhang F, et al. CO2-triggered reversible phase transfer of graphene quantum dots for visible light-promoted amine oxidation[J]. Nanoscale,2020,12:4410-4417. doi: 10.1039/C9NR10195K [115] Rojas-Andrade M D, Nguyen T A, Mistler W P, et al. Antimicrobial activity of graphene oxide quantum dots: impacts of chemical reduction[J]. Nanoscale Advances,2020,2:1074-1083. doi: 10.1039/C9NA00698B [116] Kuo W S, Chen H H, Chen S Y, et al. Graphene quantum dots with nitrogen-doped content dependence for highly efficient dual-modality photodynamic antimicrobial therapy and bioimaging[J]. Biomaterials,2017,120:185-194. doi: 10.1016/j.biomaterials.2016.12.022 [117] Ding Y, Cheng H H, Zhou C, et al. Functional microspheres of graphene quantum dots[J]. Nanotechnology,2012,23:255605. doi: 10.1088/0957-4484/23/25/255605 [118] Wu M H, Chen H Q, Lv L P, et al. Graphene quantum dots modification of yolk-shell Co3O4@CuO microspheres for boosted lithium storage performance[J]. Chemical Engineering Journal,2019,373:985-994. doi: 10.1016/j.cej.2019.05.100