The Center for Nanochemistry (CNC) at Peking University is one of the pioneering institutions promoting the emerging field of nanochemistry, a frontier of chemistry aimed at discovering materials and structures at the nanometer scale and exploring dimensionality effects on chemical systems. Since its antecedent, the nanochemistry laboratory, was initiated in early June of 1993, the CNC has passed a 20 year innovative journey with numerous exciting achievements: the CNC has been the incubator of the nanochemistry curricula for graduate students at Peking University since 2002, has held the Nanochemistry Symposia in the Annual Meeting of the Chinese Chemical Society (CCS) since 2004, and the Chinese Nanochemistry Society was founded in 2013 as a new branch of the CCS. The broad research activities at the CNC cover self-assembly systems, surface-enhanced Raman spectroscopy (SERS), tip chemistry, nanoelectronics and molecular electronics, as well as low-dimensional carbon materials such as carbon nanotubes, graphene, and graphyne, which has been one of the CNC's particular favorites over the last one and a half decades. This special issue was organized to focus on these nanocarbons as a commemorative gift for the CNC's 20th birthday.
The first pioneering contribution of the CNC to nanocarbon society was the chemical self-assembly of carbon nanotubes on solid surfaces. Inspired by the self-assembly of small organic molecules, the CNC reported the first self-assembly of “giant” one-dimensional, single-walled carbon nanotubes (SWNTs) on gold in 2000. The CNC methodology developed for self-assembly on various solid substrates has since been widely used in carbon nanotube-based nanoelectrochemistry, chemical sensors, and functional devices.
The CNC has been one of the representative institutions working on the controlled growth of single-walled carbon nanotubes. Using the chemical vapor deposition (CVD) furnace, CNC chemists have made fantastic progress toward the structural control of SWNTs. Well-known achievements include chirality-cloning growth and diameter-designed growth using sp2 carbon catalysts, based on a novel “VS” growth model. Using chemically tailored smart tapes, the pristine surface-grown SWNTs can be perfectly separated into “metallic” and “semiconducting” arrays, opening a practical pathway for carbon nanotube electronics.
In early 2008, the CNC barged into the graphene world. Profiting from its strong CVD experience, the CNC team quickly demonstrated its abilities on the controlled growth of two-dimensional graphene and its hybrid materials, as evidenced by a number of innovative growth methods such as strict monolayer growth via synergistic bimetal alloys, bilayer growth via van der Waals epitaxy, mosaic graphene via two-step grafting growth, segregation-only growth, wrinkle engineering, etc. Another of the CNC's adventures and a contribution to this stimulating area is the photochemical engineering of graphene. Using photogenerated free radicals, the CNC has achieved the high-efficiency chemical modification of inert graphene. Examples include photochlorination, photomethylation, photocatalytic oxidation, and Janus graphene.
Raman spectroscopy of low-dimensional carbon materials is another research focus of the CNC team. Using resonant Raman spectroscopy, the CNC team has demonstrated that resonant Raman spectra of SWNTs depend on the strain type and that the strain can affect/modulate the geometric structure of SWNTs, indicating Raman spectroscopy is a powerful and useful tool for the study and characterization of strain in SWNTs. The CNC team also used graphene to open up a unique platform for SERS studies, in which graphene can be used as a flat substrate for SERS and can improve the SERS performance. Combining graphene and SERS-active metal substrates, SERS spectra are cleaner and more reproducible with fewer fluctuations. This flexible graphene-based substrate can be used for the direct and in-situ measurement of samples with any morphology.
In addition to this fundamental interest in nanocarbons, the CNC has also devoted itself to molecular/nanoelectronic devices and biosensors. Supported by this strong carbon materials research, the CNC team has developed universal methodologies to create reliable molecular devices based on point contacts formed from carbon nanotubes or graphene through covalent amide linkages. A unique feature of these devices is that they consist of only one or two molecules as conductive elements. This implies a great potential for future applications in ultrasensitive biosensors and accurate molecular diagnostics.
This special issue contains 26 papers with one concept article, nine review articles, nine communications, and seven full papers, all contributed by CNC members, alumni, and collaborators. The content of these papers cover a broad range of low-dimensional carbon materials research, including the controlled synthesis of low-dimensional carbon materials, photochemical engineering and Raman spectroscopy of sp2 nanocarbons, and applications of carbon nanomaterials for energy storage and conversion, sensors, and field-effect transistors. As related current fascinating topics, h-BN, h-BN/graphene hybrids, and MoS2 are also included in this special issue.
We have received great support and cooperation from Dr. Jose Oliveira, Editor-in-Chief of Small, and Dr. Guangchen Xu of Small for organizing this special issue. Our gratitude goes to the whole editorial office of Small. Without their professional and enthusiastic work, this special issue could not possibly have become a reality on time. Last but not least, we are greatly indebted to all the contributing authors of this special issue. The cover page was carefully designed by Teng Gao, a PhD student of the CNC family. We sincerely hope that the readers of Small will enjoy this special issue.