Subscriber access provided by UNIV OF SOUTHERN INDIANA Review sp2/sp3 framework from diamond nanocrystals: A key bridge of carbonaceous structure to carbocatalysis Xiaoguang Duan, Wenjie Tian, Huayang Zhang, Hongqi Sun, Zhimin Ao, Zongping Shao, and Shaobin Wang ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.9b01565 • Publication Date (Web): 12 Jul 2019 Downloaded from pubs.acs.org on July 16, 2019 Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. 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Page 1 of 58 ACS Catalysis 1 2 3 4 5 6 2 3 7 sp /sp framework from diamond nanocrystals: A key bridge of 8 9 carbonaceous structure to carbocatalysis 10 11 12 13 14 Xiaoguang Duana, Wenjie Tian a, Huayang Zhang a, Hongqi Sun b, Zhimin Aoc, Zongping Shaod,e, 15 16 Shaobin Wang a,e* 17 18 19 20 21 22 23 a School of Chemical Engineering, The University of Adelaide, Adelaide, SA 5005, Australia 24 b 25 School of Engineering, Edith Cowan University, Joondalup, WA 6027, Australia 26 c School of Environmental Science and Engineering, Institute of Environmental Health and Pollution 27 28 Control, Guangdong University of Technology, Guangzhou 510006, China 29 d 30 State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry & 31 Chemical Engineering, Nanjing University of Technology, Nanjing 210009, Jiangsu, China 32 33 e Department of Chemical Engineering, Curtin University, Perth, WA 6102, Australia 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 1 ACS Paragon Plus Environment ACS Catalysis Page 2 of 58 1 2 3 Abstract 4 5 3 6 Diamond nanocrystals in robust sp hybridization are appealing carbonaceous materials in the material 7 community, whose structure can be transformed into unique sp2/sp3 nanohybrids as bulky 8 9 nanodiamonds (NDs) and sp2 concentric onion-like carbons (OLC). Functionalized NDs have been 10 11 used as carbocatalysts to drive a diversity of heterogeneous reactions, presenting promising catalytic 12 13 performances, great stability/durability, and low toxicity compared with other carbonaceous and metal 14 materials. More importantly, the tuneable configurations of NDs-related materials from sp3 to sp2/sp3 15 16 and sp2 carbons endow them as ideal chemical probes to elucidate the intrinsic nature toward metal- 17 18 free catalysis. Herein, a comprehensive overview is presented in the synthesis, properties, 19 functionalization and characterization of NDs-based materials as well as their recent applications in 20 21 fuel cell reactions, carbon dioxide reduction, photocatalysis, organic synthesis, oxidative 22 23 dehydrogenation reactions, and advanced oxidation processes. More importantly, we provide an 24 25 insightful discussion on unveiling the intrinsic catalytic centers and structure-reactivity chemistry of 26 NDs in redox reactions from an atomic level. Advanced protocols were proposed for regulating the 27 28 electronic structures of NDs by surface and structural engineering toward better carbocatalysis, which 29 30 assists to provide valuable guidance for the rational design of ND-based materials toward target 31 32 catalytic processes. Finally, future research opportunities were proposed to address the current 33 dilemmas in materials synthesis to facilitate mechanistic studies by theoretical computations, to enable 34 35 structural/surface functionalization of NDs for advanced catalysis, and to expand the NDs-based 36 37 materials toward other promising chemical reactions. 38 39 Keywords: nanodiamond, sp2/sp3 hybrids, carbocatalysis, structure-performance regime, redox 40 41 reaction 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 ACS Paragon Plus Environment Page 3 of 58 ACS Catalysis 1 2 3 1. Introduction 4 5 6 Recently, nanoscaled carbonaceous materials, namely nanocarbons, have thrust into the limelight as 7 rising stars in material communities and significantly renovated the catalytic processes in a green and 8 9 sustainable manner, attributing to earth abundance of carbon, tunable structure, high robustness, rich 10 11 functionality, and featured electronic configurations. Of particular interest, nanocarbon allotropes such 12 2 13 as fullerene, carbon nanotubes, and graphene are hybridized with sp configuration and perfectly 14 packed in the honeycomb lattice with a conjugated π system to be constructed into different dimensions. 15 16 These nanocarbons demonstrate as promising metal-free catalysts to drive various chemical reactions 17 1-3 18 with outstanding catalytic efficiency, desirable selectivity, high durability and stability. The catalytic 19 sites of the nanocarbons have been unveiled to be the heteroatom dopants, oxygen functionalities, edge 20 21 geometry and structural defects, making it a complicated system to identify the intrinsic role of carbon 22 23 in catalysis. 4-7 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 Figure 1. (a) A schematic model illustrating the structure of detonation nanodiamond. (b) Closer view 53 2 54 of surface region of nanodiamond covered with surface functional groups and sp carbon and (c) 55 illustration of the sp3 carbon framework in the core. Reproduced with permission from ref 23. 56 57 Copyright 2012 Springer Nature. 58 59 60 3 ACS Paragon Plus Environment ACS Catalysis Page 4 of 58 1 2 3 On the other hand, diamond nanocrystals stand out among the carbon community due to the unique 4 5 sp3 hybridization in tetrahedral bonding units, which can be expanded from a zero-dimensional cluster 6 7 to a three-dimensional framework with versatile face-centered terminations. Bulk diamond can be 8 downsized from microscope to nanoscale and engaged in a diversity of applications due to their 9 10 exceptional physical features. For instance, diamonds are the hardest materials in nature and their 11 12 extreme mechanical robustness has been commercially applied for cutting, drilling, and polishing 13 8-11 14 materials. Benefited from the excellent thermal conductivity (22 W/(cm·K)) and stability, diamond 15 can be utilized in semiconductor manufacturing to prevent the substrate from overheating. Compared 16 17 with other nanocarbon allotropes, nanodiamonds (NDs) have manifested superior chemical stability, 18 19 ultralow toxicity and great biocompatibility, which can be leveraged in bioimaging and biosensing 20 12-14 21 techniques as well as drug delivery to grift large synthetic molecules in targeting therapy. 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 Figure 2. Transformation from nanodiamonds (sp3) to hybrids (sp2/sp3) and carbon onions (sp2) by 50 51 thermal annealing and summary of their physical properties. Reproduced with permissions from ref 52 53 17. Copyright 2016 The Royal Society of Chemistry and ref 152. Copyright 2014 Wiley. 54 55 56 57 Distinct from the bulk scale, diamond nanocrystals typically present as spherical nanoparticles with a 58 59 large surface-to-volume ratio. The unique morphology enables the exposure of high fraction of 60 4 ACS Paragon Plus Environment Page 5 of 58 ACS Catalysis 1 2 3 diamond carbon atoms at the surface and subsurface regions. As shown in Figure 1, the dangling bonds 4 5 of unsaturated carbons at the grain boundary of nanodiamond would typically undergo significant 6 2 7 surface relaxation to be fabricated into partially sp hybridized carbon domains or be stabilized with 8 hydrogen and oxygen atoms to reduce the surface energy.15-16 More intriguingly, thermal treatment 9 10 can decompose the surface functionalities and facilitate the phase transition from diamond 11 12 terminations into fullerene-like graphitic shells. This feature affords the conversion of sp3-hybridized 13 3 2 2 14 NDs into either a uniform core/shell (sp /sp ) hybrid or concentric graphitic carbon onion (sp carbons) 15 regulated by the annealing ambience (Figure 2).17-18 Therefore, engineered NDs can provide a 16 17 promising platform for investigating the intrinsic nature of sp2, sp3 carbons and their hybrid in metal- 18 19 free catalysis. More importantly, the relative proportions of the sp2 shell and sp3 core can be 20 21 deliberately governed in the self-assembled nanohybrids. Similar to graphene-based materials, the 22 graphitic shell can inherit all the fascinating properties of sp2 carbons with a conjugated π electron 23 24 system, which can be further engineered with a diversity of defects, heteroatom dopants, and 25 19-21 26 functionalities.