Graphene's unique thermal, electric and mechanical properties originate from its structure, including being single-atom thick, two-dimensional and extensively conjugated. These structural elements endow graphene with advantageous thermal, electric and mechanical properties. However, the application of graphene is challenged by issues of production, storage and processing. Therefore, the stabilization and modification of graphene have attracted extensive interest. In this review we summarize the strategies for chemical modification of graphene, the influence of modification and the applications in various areas. Generally speaking, chemical modification can be achieved via either covalent or non-covalent interactions. Covalent modifications often destroy some of the graphene conjugation system, resulting in compromising some of its properties. Therefore, in this review we focus mainly on the non-covalent modification methodologies, e.g. π–π stacking interactions and van der Waals force, because the non-covalent modifications are believed to preserve the natural structure and properties. We also discuss the challenges associated with the production, processing and performance enhancement. Future perspectives for production of graphene in large size with fewer defects and under milder conditions are discussed along with the manipulation of graphene's electric, mechanical and other properties.

Carbon quantum dots (CQDs) are attracting tremendous interest owing to their low toxicity, water dispersibility, biocompatibility, optical properties and wide applicability. Herein, CQDs with an average diameter of (4.0 ± 0.2) nm and high crystallinity were produced simply from the electrochemical oxidation of a graphite electrode in alkaline alcohols. The as-formed CQDs dispersion was colourless but the dispersion gradually changed to bright yellow when stored in ambient conditions. Based on UV-Vis absorption, fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM), this colour change appeared to be due to oxygenation of surface species over time. Furthermore, the CQDs were used in specific and sensitive detection of ferric ion (Fe³⁺) with broad linear ranges of 10–200 μM with a low limit of detection of 1.8 μM (S/N = 3). The application of the CQDs for Fe³⁺ detection in tap water was demonstrated and the possible mechanism was also discussed. Finally, based on their good characteristics of low cytotoxicity and excellent biocompatibility, the CQDs were successfully applied to cell imaging.