ABSTRACT
Nanomaterials (NMs) are finding applications in diverse disciplines and industries. The two fundamental approaches of NM synthesis are the top-down and bottom-up procedures involving physical, chemical and biological methods. As the nanomaterials exhibit peculiar and strict size-dependent properties, the uniformity or homogeneity of the size dimensions is a pre-requisite attribute. The other important characteristics are the process condition requirements i.e. precursor concentration, reducing agent type and concentration, pH, temperature, ease of production of high volumes and economic feasibility. At present, these chemical and biological techniques have emerged as well-adapted and utilized for even scaled up or commercial synthesis of nanomaterials. These two techniques exhibit unique advantages, besides a few inherent drawbacks which affect the monodisperse nature of the generated nanomaterials. The critical factors such as the generation of environment polluting reaction wastes, energy-intensiveness for the chemical and inconsistency/variation or complexity of the components of the living cells or their extracts, time-limitation, poor yield and low purity of the biological techniques are the major limitations. Furthermore, both techniques are affected by reaction optimization parameters such as temperature, pH and concentration of reactants/extracts/reducing agents. This manuscript presents critical variations among these two viable NM synthesis techniques and the possible agricultural applications of the generated nanomaterials.
