Solutions-Class-12-Chemistry-Chapter-16-Green Chemistry and Nano chemistry-Maharashtra Board

(b) Sustainable development

(b) lindane

(b) Greek word meaning dwarf

(a) Absorption of functional groups

(d) Paul T. Anastas

The atom economy of a process can be calculated using the following formula.

Lindane

Scanning electron microscopy (SEM)

Carbon black

Gerd Binning and Heinrich Rohrer. (Nobel prize 1986)

1 nm = 10⁹ m

• The concept of green chemistry was coined by Paul T. Anastas.
• Green Chemistry is the application of chemistry to decrease or eliminate the usage or creation of hazardous compounds by environmentally conscious design of chemical products and processes.

• Sustainable development is the development that meets the needs of the present, without compromising the ability of future generations to meet their own needs.
• We can attain sustainable development by using the twelve green chemistry principles.

• The green chemistry approach acknowledges Earth's natural capacity to handle waste and pollution.
• It plays a crucial role when society's waste exceeds its natural capacity.
• Green chemistry reduces hazardous compound use in chemical production by supporting new technologies.
• It reduces capital investment for pollution protection and promotes pollution avoidance in chemical production.
• Green chemistry also protects the ozone layer, crucial for life on Earth.
• It controls global warming and is the beginning of the green revolution.
• This exciting time presents new challenges for chemists involved in chemical discovery, manufacturing, and use.
• Green chemistry helps save the environment and earth, crucial for our future.

(a) XRD - X-ray diffraction

(b) TEM - Tunneling Electron Microscope

(c) STM - Scanning Tunneling Microscope

(d) FTIR - Fourier Transform Infrared Spectroscope

(e) SEM - Scanning Electron Microscope

(a) Nanoscience : The study of phenomena and manipulation of materials at atomic, molecular and macromolecular scales where properties differ significantly from those at a larger scale is called nanoscience.

(b) Nanotechnology : The design, characterization, production and application of structures, device and system by controlling shape and size at nanometer scale is called nanotechnology.

(c) Nanomaterial : A material having structural components with at least one dimension in the nanometer scale that is 1 - 100 nm is called the nanomaterial. Nanomaterials are larger than single atoms but smaller than bacteria and cells.

(d) Nanochemistry : It is the combination of chemistry and nanoscience. It deals with designing and synthesis of materials of nanoscale with different size and shape, structure and composition and their organization into functional architectures.

• Nanotechnology plays an important role in water purification techniques. Silver nanoparticles act as highly effective bacterial disinfectant, remove E.Coli from water. Silver nanoparticles (AgNps) is a cost effective alternative technology they are used in water purification system to get safe drinking water.
• Nanostructures on lotus leaves repel water which carries dirt as it rolls off. Lotus effect is the basis of self cleaning windows.

• Zinc oxide (ZnO) and Titanium dioxide (TiO2) nanoparticles are used sunscreen lotions.
• The chemicals protect the skin against harmful u.v (ultraviolet) rays by absorbing or reflecting the light and prevent the skin from damage.

• The principle aims to use green solvents, such as water and supercritical CO, instead of volatile halogenated organic solvents like CH₂Cl₂, CHCl₂, and CCl₄, for chemical synthesis and other purposes.
• Water is a safer, benign solvent, while hazardous solvents like dichloromethane and chloroform are hazardous and cause significant waste.
• Toxic solvents affect millions of workers, consumers, and the environment, causing significant environmental and health impacts.
• Finding safer solvents or designing solvent-free processes is crucial for improving processes and products.
• It is essential to choose the safest solvent for each reaction step and minimize the use of solvents and auxilary substances, as they contribute to waste.

A substance which speeds up the rate of a reaction without itself being changed chemically in the reaction is called a catalyst. It helps to increase selectivity, minimise waste and reduce reaction time and energy demands.

Examples : Hydrogenation of oil the catalyst used are platinum or palladium,

Raney nickel.

Principles of green chemistry :

(1) Prevention of waste or by products :

• To prevent generating waste, there is the need to develop the zero waste technology (ZWT).
• ZWT in a chemical synthesis should result in waste product being zero or minimum.
• To use the waste product of one system as the raw material for other system is also the aim of ZWT.

Example :

• Cement and brick industry can use the bottom ash of thermal power station as the raw material.
• Effluent coming out from cleansing of machinery parts may be used as coolant water in thermal power station.

(2) Less hazardous chemical synthesis :

• The safest possible design for chemical reactions and synthesis processes is necessary to prevent the production of hazardous waste during chemical operations.
• It was discovered that the pesticide DDT (diphenyltrichloroethane), which was once in use, was hazardous to humans. As a result, benzene hexachloride (BHC) has taken the position of DDT as an insecticide, one of the γ-isomer (gamma) of BHC is called gammexane or lindane.

(3) Designing Safer Chemicals :

This principle is quite similar to the previous one.

• There is a need to develop safer chemicals to protect chemical workers from exposure to harmful environments.
• Adipic acid is extensively used in polymer industry. In synthesis of adipic acid, benzene is used as the starting material, but benzene is carcinogenic and being volatile organic compound (VOC) it pollutes the air and environment.
• To overcome this health hazard Green technology developed by Drath and Frost, adipic acid is enzymatically synthesised from glucose.

Atom economy is a measure of the amount of atoms from the starting material that are present in the final product at the end of a chemical process.

Good atom economy means most of the atoms of the reactants are incorporated in the desired products. Only small amount of waste is produced, hence lesser problem of waste disposal.

The atom economy of a process can be calculated using the following formula.

Example :

Atom economy of fermentation of sugar (glucose) to ethanol. (2 marks)

C₆H₁₂O₆(aq) → 2C₂H₅OH(aq)  +2CO₂(g)

Atomic masses of C = 12, H = 1, O = 16

Formula wt of glucose = 180

Formula wt of ethanol = 46

Relative mass/wt of desired useful product in the equation = 2 x 46 = 92

% Atom economy = 92/180 x 100 = 51.1%

• A commonly used technique in organic synthesis is the use of protecting or blocking group.
• Finally, on completion of reaction deprotection of the group is required. This leads to unnecessary increase in the number of steps and decreased atom economy.
• The green chemistry principle aims to develop processes to avoid necessary steps i.e. (minimization of steps).
• When biocatalyst is used very often there is no need for protection of selective group.

Example : Conversion of m-hydroxyl benzaldehyde to m-hydroxybenzoic acid.

• Sol : Sols are dispersions of colloidal particles in a liquid. Colloids are solid particles with diameter of 1-100 nm.
• Gel : A gel is interconnected rigid network with pores of submicrometer dimensions and polymeric chains whose average length is greater than a micrometer.

Sol-gel Process : A sol-gel process is an inorganic polymerisation reaction. It is generally carried out at room temperature. It includes four steps : Hydrolysis, polycondensation, drying and thermal decomposition. This method is widely used to prepare oxide materials.

The reactions involved in the sol-gel process can be described as follows :

MOR + H₂O → MOH + ROH  ..(hydrolysis)

metal alkoxide

MOH + ROM → M-O-M + ROH  ..(condensation)

• Formation of different stable solution of the alkoxide or solvated metal precursor
• Gelation resulting from the formation of an oxide or alcohol-bridged network. (gel) by a polycondensation reaction.
• Aging of the gel means during that period gel transforms into a solid mass.
• Drying of the gel : In this step, water and other volatile liquids are removed from the gel network.
• Dehydration : The material is heated at temperatures upto 800 ⁰

Lotus is an example of self cleansing. Nanostructures on lotus leaves repel water which carries dirt as it rolls off. Lotus effect is the basis of self cleaning windows.