Synthesis, properties, and applications of carbyne nanocrystals

Since the first observation of fullerene nearly three decades ago, allotropes of carbon, including carbon nanotube and graphene, have been the focus of considerable research because of their remarkable physical and chemical properties that suggest the potential for a wide variety of practical applications. Well known, in terms of carbon-atom hybridization, well-established forms of carbon are diamond with the three-dimensional sp 3 -hybridized carbon atoms and graphite with the two-dimensional sp 2 -hybridized carbon atoms which have been known and utilized for millennia. Additionally, more carbon allotropes, such as fullerenes, nanotubes and graphene composed of sp 2 -hybridized carbon, and Lonsdaleite and C 8 composed of sp 3 -hybridized carbon each show unique properties, usually different from those of either diamond or graphite, offering technological breakthroughs. Sequentially, there is the third carbon, i.e., carbyne with the one-dimensional sp -hybridization, which would result in an allotrope of carbon, whereas diamond and graphite feature three- and two-dimensional ones, respectively. Recently, carbyne nanocrystals (CNCs), the condensed phase of carbyne with the finite chain length and the one-dimensional sp -hybridized carbon atoms with the alternating carbon–carbon single and triple bonds, the dubbed the third carbon, have been synthesized in the laboratory ( Science Advances 2015; 1 (9): e1500857), and these CNCs are white powders, so they are called white carbon . Interestingly, there have been many works showing that CNCs possess potential applications in luminescence, nonlinear optics, optoelectronic sensing and biomedicine probes. Therefore, these findings above imply that we have being on the threshold of a new era of carbyne science and technology. This review aims to be a comprehensive, authoritative, critical, and accessible review of general interest to the material community. Therefore, the review will survey the latest progresses of CNCs, provide a comprehensive understanding of synthesis, structure, property, and applications of CNCs, and put forward the perspective for the further development of CNCs. Firstly, we will present the basic understanding of classification and definition of carbyne. The history of carbyne research will be introduced and different definitions of carbyne in different periods are summarized. Next, a reasonable classification of carbyne research is proposed. Secondly, we will briefly introduce various approaches for the synthesis of carbyne and focus on describing LAL technique which is more suitable to produce CNCs compared with other methods. Thirdly, we will summarize structure, properties, and related applications of CNCs, including electronics, optics and magnetism, and optoelectronic and biomedical applications. Finally, we will summarize the development and unresolved issues so far, and suggest the future direction in this emerging and promising research field.