Silver nano particle using tea

Aim: Preparation and characterization of nano particles of silver using tea leaves.

Theory:

Nanotechnology is defined as the study and use of particle structures between 1 nanometer and 100 nanometers in size.

Nanoparticles (NPs) have wide range of applications in areas such as health care, cosmetics, food and feed, environmental health, mechanics, optics, biomedical sciences, chemical industries, electronics, space industries, drug-gene delivery, energy science, optoelectronics, catalysis, single electron transistors, light emitters, nonlinear optical devices, and photo-electrochemical applications.

Silver NPs are of interest because of the unique properties which can be incorporated into antimicrobial applications, biosensor materials, composite fibers, cryogenic super-conducting materials, cosmetic products, and electronic components.

Silver nanoparticles are also extensively studied because of their unique properties such as excellent electrical and thermal conductivity, chemical stability, catalytic activity, non-linear optical behavior and antimicrobial effects.

Synthesis of Ag NPs

Several physical and chemical methods have been used for synthesizing and stabilizing silver NPs.

Chemical method for Synthesis of Ag NPs

The most common approach for synthesis of silver NPs is chemical reduction by organic and inorganic reducing agents.

In general, different reducing agents such as sodium citrate, ascorbate, sodium borohydride (NaBH₄), hydrazine, elemental hydrogen, Tollen’s reagent, N,N-dimethylformamide (DMF), and poly (ethylene glycol) block copolymers are used for reduction of silver ions (Ag⁺) in aqueous or non-aqueous solutions.

These reducing agents reduce Ag⁺ and lead to the formation of metallic silver (Ag⁰), which is followed by agglomeration into oligomeric clusters.

These clusters eventually lead to the formation of metallic colloidal silver particles.

All these substances are considered to be noxious and environmentally unfriendly.

Moreover, most of these methods require intricate controls or nonstandard conditions making them quite expensive.

Green Method for Synthesis of Ag NPs

Green chemistry is the design, development, and implementation of chemical products and processes to reduce or eliminate the use and generation of substances that are hazardous to human health and to the environment.

Green synthesis methods employing either biological microorganisms or plant extracts have emerged as a simple and alternative to chemical synthesis.

Green synthesis provides advancements over chemical methods as it is environment friendly, cost effective, and easily scaled up for large scale synthesis.

The synthesis of nanoparticles by using plant extracts can be advantageous over other biological processes because it eliminates the elaborate process of maintaining cell cultures and can be suitably scaled up for large scale production under non-aseptic environments.

Tea leaf extract (Camellia sinensis) has been used to synthesize silver nanoparticles.

Tea leaf contains polyphenols and terpenoids, such as β-cariophyllene, linalool, cis-jasmone, α-terpineol, δ-cadiene, indole, geraniol, caffeine and theophylline among the major bio-components, which assist in the synthesis of nanoparticle.

Procedure:

Tea Extract

2 g of tea leaves were taken in 500 mL distilled water and heated at about 60 ⁰C for 10-15 min in boiling water bath. The extract was cooled at room temperature and then filtered by using Whattman filter paper.

Silver nitrate solution

Silver nitrate aqueous solution of 1 mM was prepared by dissolving 0.017 g of silver nitrate salt in 100 mL of distilled water.

Synthesis of silver nanoparticles

Add 1 mL of tea extract to the 20 ml of the AgNO₃ solution in a 100 mL beaker and the content was allowed to stand for about 20-30 minutes.

Colour of Ag nanoparticles

After the addition of the tea extract to the aqueous AgNO₃ solution, the color of the mixture changed from colorless to light brown after 5-10 minutes and eventually to dark brown. This color change indicates the formation of Ag nanoparticles in the solution. Tea extract without AgNO₃ did not show any color changes.

In the silver nanoparticles, electrons oscillate collectively. These oscillations affect how light interacts with the nanoparticles.

The specific oscillations depend on the particles’ size and shape, so particles of different sizes have different colors. Thus, solution color gives an approximate idea of the particle size.

Nanoparticle size can be monitored more accurately by taking UV-Vis absorption spectra.

Characterization of Ag-NPs:

UV-Visible spectroscopy: The reduction of silver ions in the colloidal solution (formation of Ag nanoparticles) was confirmed by UV-Visible spectroscopy.

A small aliquot from Ag NPs was taken in a quartz cuvette and observed for wavelength scanning between 300 to 700 nm with distilled water as a reference.

Absorption peaks of silver nanoparticles synthesized using tea extract solutions were obtained at wavelength of 420 nm.

A broad absorption peak was observed at 432 nm, which is a characteristic band for the Ag nanoparticles.

Silver nanoparticles have free electrons, which give surface Plasmon resonance (SPR) absorption band, due to the combined vibration of electrons of silver nanoparticles in resonance with light wave.

Result: The Ag nanoparticles were synthesized by green approach using tea leaves extract and characterized by UV-Vis spectroscopy.

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