Читать книгу Carbon Nanofibers - Группа авторов - Страница 41

With the advent of nanotechnology, the first question that arose was how to synthesize the desired nanoparticles, resulting in the evolution of many physical and chemical methods [1] to synthesize various nanomaterials. The curious nature of human beings has always directed them to look to nature for solutions to many questions. Primitive man exploited his gray matter to unlock the mystery of plants and the possibilities stored in them, be it for food, shelter, weapons, medicine, source of energy (fire), clothes, etc. With the increase in their intellectual capacities they used plants for developing vehicles, furniture, pulleys and the list goes on. The scenario is no different today; nanotechnologists have turned their attention to plants for solving puzzles to synthesize nanoparticles. Scientists have realized the perfection of nanosized particles (DNA) apparent in their mega impact. Biological materials are highly organized from the molecular to the nanoscale, microscale and macroscale, often in a hierarchical manner with intricate nano-architecture that ultimately makes up a myriad of different functional elements. Nature uses commonly found materials. Properties of the materials surfaces result from a complex interplay between the surface structure and the morphology and physical and chemical properties. Many materials, surfaces and devices provide materials and fibers with high mechanical strength, biological self-assembly, antireflection properties, structural coloration, thermal insulation, self-healing and sensory aid mechanisms, which are just some of the examples found in nature that are of interest in fabricating nanoparticles. Carbon nanomaterials (CNMs) are on the verge of becoming an important material for various industrial applications. One of the hurdles in the production of CNMs is the cost of the raw material. There are two components in producing the CNM, the precursors and the technique of the synthesis. It is almost certain that chemical vapor deposition (CVD) technique would be most suitable for the production of large quantities of CNM. As a result, the CVD technique is being explored by many research groups for the synthesis of CNM. This book encompasses the various aspects of carbon nanofibers (CNF), one of them being their synthesis, and plants have provided a unique platform that offers their metabolites as well as organs as a base or precursor to fabricate CNF.

No doubt there are many chemical precursors, mostly hydrocarbons, that have been used for synthesis of CNF [2]; but most of them are chemicals derived from fossil fuels. Fossil fuels are destined for depletion in the very near future. Hence, as an alternative to fossil fuel-derived materials Sharon’s group started looking at plant-derived materials as a precursor of carbon nanomaterials including CNF, because carbon is known to be a vital constituent of all living organisms.

Sharon’s group was the first to begin developing carbon nanomaterials from both plant parts and plant metabolites over more than the last two decades from many plants [1–5]. The advantages of using plant materials are that they can be cultivated when desired, hence are regenerative material, and are low-cost material. Moreover, plant tissues are composed of oils, lipids, carbohydrates, proteins, cellulose, lignin, etc., which are a rich source of carbon.

Both CNTs and CNFs appear almost the same under SEM analysis. Both are like a hollow cylinder. The outer layer of CNT is made of unbroken graphene sheet whereas CNFs are made of broken graphene sheet. Biogenic CNF has been mostly synthesized by high temperature pyrolysis (Figure 2.13). The parameters that affect the synthesis process are the same as for the standard CVD process of CNM synthesis, i.e., temperature, duration of pyrolysis, carrier gas, catalyst and precursor (plant part or plant metabolite).