# Green Approaches to Carbon Nanostructure-Based Biomaterials
## 2 Green Routes to Prepare Carbon Nanomaterials for Biomedical Applications
### Fullerenes  
Fullerenes are spheroidal molecules composed solely of carbon, of which the most widely known is C\({}_{60}\), composed of 60 carbon atoms. Their nanosize and peculiar electronic properties rendered them the subject of many investigations for potential uses in nanomedicine [81], including drug delivery [82], photodynamic [83], antioxidant [84; 85], and even antiviral [86] therapy. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Carbon Nanostructure** & **Green Route** & **Carbon Source** & **Solvent** & **Application** & **Reference** \\ \hline Fullerenes 1  & Catalytic thermal decomposition & Plastic waste & n.a. & n.a. & [51] \\ \hline Nano-onions & Carbonization & Tomatoes & Water & Theranostics & [52] \\  & Hydrothermal & Citric acid & Water & n.a. & [53] \\ \hline  & Calcination & Gynostemma plant & Water & Bioimaging & [54] \\  & Electrochemistry & Graphite & Water/ethanol & Radioimaging & [55] \\  & Gamma irradiation & Graphite & Water/ethanol & Photodynamic & [56] \\  & Hydrothermal & Chitosan & Water & pH sensing & [57] \\  & Hydrothermal & Cyanobacteria & Water & Composites & [58] \\  & Hydrothermal & Fruit flesh & Water & Ag\({}^{+}\) sensing & [59] \\  & Hydrothermal & Fruit juice & Water & Bioimaging & [60] \\  & Hydrothermal & Fruit peel & Water & Hg\({}^{++}\) sensing & [61] \\  & Hydrothermal & Fruit waste & Water/ethanol & Bioimaging & [62] \\ CQDs & Hydrothermal & Green tea & Water & Photodynamic & [63] \\  & Hydrothermal & Red cabbage & Water & Fluorescent ink & [64] \\  & & & & Antioxidant & [65] \\  & Hydrothermal & Sugarcane bagasse & Water & Antibacterial & [65] \\  & & & & & \\  & Hydrothermal & Wheat straw & Water & Bioimaging & [66] \\  & Microwave & Cellulose & Water & Biomaterials & [67] \\  & Microwave & Roasted chickpeas & Water & Bioimaging & [68] \\  & Pyrolysis & Citric acid & Water & Hg\({}^{++}\) sensing & [69] \\  & Pyrolysis & Zingiberis rhizoma & Water & Analgesic & [70] \\  & Sand bath & Fruit peel & Water & Bioimaging & [71] \\  & Sonochemical & Gelatin & Water & Bioimaging & [72] \\ \hline NDs & Laser ablation & Coal & Ethanol & n.a. & [73] \\ \hline oxidized NDs 2  & Microplasma jet & NDs & Water & n.a. & [74] \\ \hline oxidized CNHs 2  & UV/H\({}_{2}\)O\({}_{2}\) oxidation & CNHs & Water & Drug delivery & [75] \\ \hline oxidized CNTs 2  & UV-ozone & CNT fibers & n.a. & Electronics & \\ \hline GO 2, 3 & Electrochemical & Graphite & Acid water & (Bio)materials & [76] \\  & Photoelectrochemical & Graphite & Water & (Bio)materials & [77] \\ \hline  & Mushroom-extracted & GO 3  & Water & n.a. & [78] \\ rGO 2, 3 & Cysteine reductant & GO 3  & Water/ethanol & Drug delivery & [79] \\  & Ascorbic acid reductant & GO 3  & Water & Neuroscience & [80] \\ \hline \hline \end{tabular}  
* 1 magnetic derivative composite. 2 the green route refers solely to the functionalization of the nanocarbon and not the preparation of the carbon nanostructure scaffold used as starting material. 3 (r)GO = (reduced) graphene oxide.  
\end{table} 
Table 1: Recent examples of green methods to produce carbon nanostructures, their oxidized and reduced forms, suitable for biomedical applications. Fullerenes can be synthesized by many methods, which mainly involve the vaporization of graphite or similar carbon sources, and that include arc-evaporation, pyrolysis, radio-frequency plasma, or laser ablation. Moreover, fullerenes purification requires large volumes of organic solvents due to their generally low solubility [81]. Therefore, the development of green procedures for their preparation is not at all trivial. However, the use of microwaves [87] can be beneficial in reducing reaction times and temperatures, although even this convenient development has not solved the many challenges faced by the industry to produce fullerenes at a low cost [88].