GREEN CHEMISTRY

Green chemistry, also called sustainable chemistry, focuses on the design and processes that minimize or eliminate hazardous chemicals. Chemicals should be designed such that, at the end of their function, they break down into innocuous degradation products and do not harm the environment. It is based on 12 principles that provide a framework for learning about designing processes and products to minimize hazards. These 12 principles are as follws:

• 1. Prevent waste—It is better to prevent waste than to treat or clean up after it has been created.
• 2. Atom economy—To maximize the incorporation of all materials used in the process into the final product.
• 3. Less hazardous chemical syntheses—To design such synthetic methods to use and generate substances that possess little or no toxicity to human health and environment.
• 4. Designing safer chemicals—Chemicals should be designed to prevent the efficacy of function while reducing toxicity.
• 5. Safer solvents and auxiliaries—The use of auxiliary substances such as solvents, separation agents should be made unnecessary wherever possible.

• 6. Design for energy efficacy—Energy requirements should be recognized for their environmental and economic impacts. Synthetic methods should be conducted at ambient temperature and pressure.
• 7. Use of renewable feedstocks—A raw material or feedstock should be renewable rather than depleting wherever possible.
• 8. Reduce derivatives—Unnecessary derivatization of chemical processes should be minimized or avoided.
• 9. Catalysis—Catalytic reagents used should be as selective as possible.
• 10. Design for degradation—Chemicals should be so designed that they break down into iimocuous products at the end of their function and do not persist.
• 11. Real-time analysis for pollution prevention—Analytical methodologies should be further developed to allow real-time in-process monitoring and control prior to the formation of hazardous substances.
• 12. Inherently safer chemistry for accident prevention—Substances used in the chemical processes should be such chosen to minimize the potential for chemical accidents, explosions, fire, etc.

APPROACH OF NANOTECHNOLOGY IN NANOTECHNOLOGY

Green and biogenic bottom-up synthesis attracting many researchers due to the feasibility and less toxic nature of processes. These processes are cost-effective and environmentally friendly, where the synthesis of NPs is accomplished via biological systems such as using plant extracts. Bacteria, yeast, fungi, aloe vera, tamarind, and even human cells are used for the synthesis of NPs. Au NPs have been synthesis from the biomass of wheat and oat (Parveen et al., 2016) and using microorganism and plant extracts as a reducing agent (Ahmed et ah, 2016). NPs have been prepared by several physical and chemical approaches depending on the accessibility and viability of procedures to attain the essential applications (Mohanpuria et al., 2008; Sun and Zeng, 2002). The wet chemistry method is one among the methods for the preparation of nanomaterials, where the metal reduction is carried out in solution using several chemical reductants, such as hydrazine hydrate, sodium borohydride, and trisodium citrate (Wu and Chen, 2003; Qi et al., 1997). All of these chemicals are toxic. They are stabilized by applications, frequently hazardous stabilizers, to avoid aggregation. These approaches have been widely applied, but the stabilizers, reactants, reductants and several organic solvents employed in these approaches are toxic and hazardous to the environment (Tolaymat et al., 2010; Thomas et al., 2011). Various physical and chemical processes have been exploited in the synthesis of several NPs. However, these methodologies involve the use of toxic, hazardous chemicals that may pose potential environmental and biological risks. The process of agglomeration and sintering involves many toxic hydrocarbons and solvents.

Capping agents are widely used in the stabilization and controlling the shape morphology of NPs. Most of the stabilizers, usually adsorbing on the surface of the NPs, may significantly alter the surface properties of the nanomaterials, and increasing severe toxicity concerns strictly hinder the biological applications of such nanomaterials (De Jong and Bonn, 2008). The synthesis of NPs by physical approaches involving laser ablation, arc discharge, ball milling regularly needs high-temperature and -pressure conditions, demanding a tremendous amount of energy (Thakkar et al., 2010). The concept of green chemistiy becomes more significant in these circumstances (Sheldon, 2012). Heteroatom functionalized long-chain hydrocarbons, such as oleic acid, oelylamine, and trioctylphosphine, control the size and dispersability of NPs by binding strongly through heteroatoms (Park et al., 2007). Biochemical NP synthesis, beyond being environmentally friendly, is simple, cost-effective, more reproducible, and have defined physicochemical properties.