Lignin-Based Carbon Nanomaterials-The Future Scope

Carbon, a versatile material available in nature, can assume various allotropic forms, which improves its chances of useful exploitation in various applications. The application scope increases for carbon when it is brought to nanosize structures, like fullerenes and related materials, carbon nanotubes, carbon nanofibers, graphene, and carbon nanocomposites with better mechanical, thermal, electronic, and electrical properties, coupled with chemical robustness. Various precursor materials used for carbon nanostructures include hydrocarbons, carbonaceous industrial wastes, carbon blacks, carbon nano-onions etc. The high cost of precursors in particular is caused by petro-based sources, and manufacturing costs are narrowing the applications of carbon materials in high-performance structural materials. One alternative is biobased precursor materials like lignin, a polymeric aromatic compound with various side chain substituents found in plant cell walls. Lignin consists of more than 60 % carbon on a theoretical basis and can be a green carbon source for the production of carbon-based nanomaterials. Worldwide data show that the paper and pulp industry alone produces similar to 50 x 10(9) kg of lignin per annum. The E20 or E30 norms of biofuel blending shows that each ton of biomass produces similar to 15-25 % (w/w) of lignin as a by-product. Therefore, precursor material limitation can be avoided if lignin-based sources are used for nanomaterial production. In addition to these, animal manure from herbivores can also be considered for the same beause the manure contains significant amounts of microbial, processed lignin in the rumen with decreased degree of polymerization, making it suitable to play with the structure for various applications, particularly with nanocomposites. Some of the applications based on lignin might require preliminary functionalizations to the source material. Lignin-based nanomaterials have various applications in many biocompatible-based applications, such as for cancer diagnosis, drug delivery, optical sensors, tissue engineering, energy storage devices, air filtration, oil-water separation, electronics, and catalysis, etc.