As a new carbon material in the twenty-first century, carbon nanotubes (CNTs) have excellent optical, electrical, magnetic, thermal, chemical, and mechanical properties. There are many synthesis methods to produce CNTs. Compared with other methods, chemical vapor deposition (CVD) is the most effective method that has broad prospects for large-scale control of CNTs in recent years due to its simple equipment, simple operation, and lower cost. In order to gain a comprehensive understanding of the controlling parameters about the formation of CNTs, this chapter reviews the latest progress in the preparation of CNTs by CVD from three of the most important influencing factors: carbon sources, catalysts, and substrates. Among them, the catalyst is the most influential factor for the morphology, structure, and properties of CNTs. It should be pointed out that many growth factors can control the particle size distribution, composition, and structure of the catalysts, such as catalyst substrate, metal transition components added, calcination temperature, etc.

Graphene quantum dots (GQDs) are promising for bioimaging applications due to their unique optical properties and good biocompatibility. However, the facile synthesis of GQDs with long-wavelength emission and high quantum yield (QY) under long-wavelength excitation is still a challenge. Herein, dual-emissive GQDs were synthesized via a facile one-pot solvothermal method using 2,7-dihydroxynaphthalene (2,7-DHN) and piperazine anhydrous (PA) as the raw materials. The obtained GQDs exhibited a green-emission band (core state emission) and a red-emission band (surface state emission), which originated from the inner π-conjugated structure and various surface functional groups, respectively. The π-conjugated structure mainly comes from the aromatic rings in 2,7-DHN, and the N–H of PA acts as the main nitrogen source, which is beneficial for the QY. The obtained GQDs showed obvious concentration-dependent optical properties. Importantly, they are able to generate red emission with a high absolute QY of 54.9% in ethanol and 24.9% in water, among the best values of reported GQDs. In addition, the prepared GQDs have good water-solubility, low cytotoxicity, and superior stability against photobleaching. Based on the above advantages, the as-prepared GQDs were successfully applied for labeling HeLa cells in vitro. Therefore, our prepared GQDs demonstrated that they can be an efficient biomarker for fluorescent bioimaging.