FIELD

The present disclosure relates to metal based nanoparticles and a process for preparing the same.

BACKGROUND

Nanoparticles are defined as particulate dispersions or solid particles with a size in the range of l-1000nm. In recent years, the field of nanoparticles has grown due to their unique properties. Many industries utilize nanoparticles, for example the electronics industry, medical science, material science and environmental science.

Generally, nanoparticles are synthesized in three ways: physically by crushing larger particles, chemically by precipitation and through gas condensation. Chemical generation is highly varied and it includes laser pyrolysis, flame synthesis, combustion and sol gel approaches. Mechanical processes for producing nanoparticles include: mechanical attrition (e.g. ball milling), crushing of sponge iron powder and thermal quenching. Typically, chemical processes for producing nanoparticles include precipitation techniques, sol-gel processes and inverse-micelle methods. Other chemical or chemically-related processes include gas condensation methods, evaporation techniques, gas anti-solvent recrystallization techniques, precipitation with a compressed fluid anti-solvent and generation of particles from gas saturated solutions. The chemical methods involve hazardous reagents and/or process conditions while the physical or mechanical methods are highly energy intensive and expensive. The commercial significance of nanoparticles is limited by the nanoparticle synthesis process, which is generally energy intensive or requires toxic chemical solvents.

Biochemical synthesis of gold nanoparticles using plant material has been disclosed in various research articles and patent documents. Some representative documents which disclose biochemical synthesis of gold nanoparticles using plant material are described herein below.

Shankar et al., (Biotechnology Progress, Volume 19, Issue 6, pages 1627-1631, 2003) describes extracellular synthesis of silver nanoparticles using Geranium (Pelargonium graveolens) leaf extract. Aqueous silver nitrate solution is treated with geranium leaf extract which result in reduction of the silver ions and formation of crystalline silver nanoparticles in solution.

Shiv Shankar et al., (in Journal of Colloid and Interface Science (2004), Volume: 275, Issue: 2, Pages: 496-502) describes synthesis of Au, Ag, and bimetallic Au core-Ag shell nanoparticles using Neem (Azadirachta indica) leaf broth.

Ankamwar et al., (in Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, Volume 35, Issue 1, 2005, pages 19-26) describes synthesis of gold nanotriangles using tamarind leaf extract as the reducing agent.

Chandran et al., 2006 (Biotechnology Progress Volume 22, Issue 2, pages 577 583, 2006) describes synthesis of Gold Nanotriangles and Silver Nanoparticles using Aloe vera plant extract.

Jiale Huang et al, (Nanotechnology, Volume 18, Number 10, 2007) describes biosynthesis of silver and gold nanoparticles by using sundried Cinnamomum camphora leaf.

Narayanan et al., (Mater. Lett. 2008, 62, 4588-4591) describes synthesis of gold nanoparticles using coriander leaves.

Deshpande Raghunandan et al, (Colloids and surfaces B Biointerfaces (2010), Volume: 79, Issue: 1, Pages: 235-240) describes biosynthesis of irregular shaped gold nanoparticles from macerated aqueous extracellular dried clove (Syzygium aromaticum) buds solution.

Deshpande Raghunandan et. al., {American Journal of Analytical Chemistry, 2011, 2, 475-483) describes microwave-Assisted Rapid Extracellular Biosynthesis of Silver Nanoparticles Using Carom (Trachyspermum copticum)Seed Extract

Indian Patent No. 247068 (550/MUM/2004) discloses a process for making gold sub micron scale particles in which a gold salt solution is prepared by dissolving a salt of gold in water having conductivity less than 3 micro Siemens. Then a fresh filtered aqueous solution of plant tissue extract is prepared which is diluted with deionized water in the ratio ranging from 1:5 to 1: 25 to form an aqueous extract solution having an open circuit potential between + 0.02 and +0.2 volt and a pi I between 5.5 to 7.5 and total organic carbon content at least 7,500 ppm. The aqueous extract solution is maintained under continuous agitation at a temperature between 20 and 30 degrees Celsius. To this, a minute quantity of the gold salt is inoculated under continuous agitation such that the final concentration of the metal ion in the reaction mixture is in the range of 50 to 300 ppm. The agitation is continued for a period of 30 minutes to 5 hours to obtain a colloidal suspension of gold nano particles. Finally, the nano particles are separated from colloidal suspension by a known process such as centrifugation. The plant tissue extract used is an extract of macerated plant cells of at least one plant tissue selected from a group of tissues comprising living tissue of grasses, leaves, fruits, stems, roots and flowers and parts thereof. The invention disclosed in Indian patent No. 247068 specifically used aqueous extract of biological tissue cells that includes Aloe vera leaf extract, Neem fruit extract, Argyeria speciosa leaf extract, Bitter gourd extract, Ocimum sanctum leaf and bud extract, Calotropis procera flower extract fresh earth worm extracts, E. coli extracts, fish extracts, goat meat extracts, yeast and algae extracts.

US20090117045 discloses a method of synthesis of gold nanoparticles which involves mixing soy or lentil plant material or a reactive extract thereof with an aqueous solution containing gold salts and permitting reaction of the gold salts to form gold nanoparticles.

US20090074674 discloses a method of synthesis of gold nanoparticles by mixing an aqueous solution containing gold salts with black tea, turmeric, curcumin or cinnamon or similar naturally occurring polyphenols or flavanoids rich plant material.

US20100200501 discloses a method for making one or more metal nanoparticles which comprises: providing a solution comprising a first metal ion; providing a plant extract that comprises a reducing agent, a polyphenol, caffeine, and/or a natural solvent or surfactant; and combining the first metal ion solution and the plant extract to produce metal nanoparticles.

Various materials derived from plants or herbs such as fruits, vegetables, cereals, spices, phytochemical constituents and the like have been used for the synthesis of metal nanoparticles which have well established uses as food, medicinals or ornamentals. Also, the processes disclosed in the prior art which utilize plant based materials for the synthesis of nanoparticles are complicated and they require rigorous controls, such as maintenance of pH and temperature and agitation for achieving morphology controlled synthesis of metal nanoparticles. Furthermore, . the processes disclosed in the prior art are not economic on large scale level. Accordingly, it is desirable to develop a simple, non-hazardous, energy saving and cost effective process for synthesis of metal nanoparticles using extracts of easily available plants that have no other competing use.

OBJECTS

Some of the objects of the present disclosure are as follows:

It is an object of the present disclosure to transform the otherwise pernicious and worthless aquatic weeds into valuable feedstock for the synthesis of metal nanoparticles.

It is another object of the present disclosure to provide metal nanoparticles of desired size and shape.

It is still another object of the present disclosure to provide stabilized biocompatible metal nanoparticles.

It is another object of the present disclosure to provide a simple and cost effective method for the synthesis of stabilized metal nanoparticles using aquatic weeds.

It is yet another object of the present disclosure to provide a non-hazardous and environment friendly process for the synthesis of metal nanoparticles.

It is another object of the present disclosure to provide a process for the synthesis of metal nanoparticles which requires no elaborate separation-purification steps.

It is yet another object of the present disclosure to provide a process which is capable of producing mono and poly-dispersed metal nanoparticles.

It is a further object of the present disclosure to provide a single pot process for the synthesis of metal nanoparticles.

It is still further object of the present disclosure to provide a process for synthesis of metal nanoparticles which controls the shapes and sizes of nanoparticles.

SUMMARY

These and other objects of the present disclosure are to a great extent dealt in the disclosure.

In accordance with the present disclosure there is provided a process for manufacturing metal nanoparticles; said process comprising the following steps:

(a) preparing a solution of metal ions having concentration of 10"3 M by dissolving at least one metal salt in distilled water;

(b) preparing an aqueous solution of weeds

(c) mixing the metal ion solution and the aqueous solution of weed to obtain metal nanoparticles; and

(d) monitoring the formation of metal nanoparticles by UV-visible spectroscopy and characterization by Transmission Electron Microscopy (TEM).

Typically, the metal salt is at least one selected from the group consisting of chloroauric acid, sodium tetrachloroaurate, silver nitrate and silver acetate.

In accordance with one of the embodiments of the present disclosure the method of preparing an aqueous solution of weed comprises the following steps:

a. obtaining plant material from aquatic weed;

b. treating the plant material by at least one operation selected from the group consisting of sorting, cleaning and sizing;

c. obtaining an aqueous solution of weed by boiling the plant material in distilled water at a temperature of about 95 °C to 100 °C for a period below 30 minutes followed by cooling and filtration.

Typically, the plant material is at least one selected from the group consisting of leaves, stems/ petioles and roots of aquatic weed.

Typically, the aquatic weed is at least one selected from the group consisting of Salvinia molesta, Pistia stratiotes and Eichhornia crassipes.

Typically, the proportion of metal ion solution to aqueous solution of weed ranges between 1:1 and 1:9.

Typically, the proportion of metal ion solution to aqueous solution of weed to water ranges between 1: 0.1: 0.1 and 1: 9:9.

In one of the embodiments of the present disclosure the metal nanoparticles are mono-dispersed.

In accordance with another embodiment of the present disclosure the metal nanoparticles are poly-dispersed.

In accordance with another embodiment of the present disclosure the method step of mixing the metal ion solution and the aqueous solution of weed further comprises addition of water.

In accordance with another aspect of the present disclosure there is provided colloidal metal nanoparticles prepared by a process of the present disclosure. The size of the nanoparticles ranges prepared by the process disclosed in the present disclosure ranges between 1 nm to 100 nm depending on the formulation used.

Typically, the colloidal metal nanoparticles are selected from the group comprising of gold nanoparticles and silver nanoparticles

Typically, the nanoparticles are in a form selected from the group consisting of mono-dispersed and poly-dispersed.

Typically, the shape of the nanoparticles is selected from the group consisting of spherical, triangle, pentagonal, polygonal, rod, flower like and hexagonal morphology.

BRIEF DESCRIPTION OF THE DRAWINGS

Morphology of the synthesized gold nanoparticles using plant extracts (Salvinia molesta, Pistia stratiotes and Eichhornia crassipes) were determined using transmission electron microscopic (TEM) studies.

The TEM micrographs (figure 1 - 3) of different formulations revealed the presence of gold nanoparticles of spherical/ triangular/ pentagonal/ polygonal/ rod/ flower like/ hexagonal shapes with sizes ranging between 1-100 nm.

A) Fig. 1 illustrates composite visuals of transmission electron microscope (TEM) micrographs and selected area (electron) diffraction (SAED) patterns of gold nanoparticles synthesized using Salvinia molesta extracts.

1) Fig. la illustrates monodispersed gold nanoparticles synthesized using leaves of Salvinia molesta

2) Fig. lb illustrates polydispersed gold nanoparticles synthesized using leaves of Salvinia molesta

3) Fig. lc illustrates monodispersed gold nanoparticles synthesized using roots of Salvinia molesta

4) Fig. Id illustrates polydispersed gold nanoparticles synthesized using roots of Salvinia molesta

B) Fig. 2 illustrates composite visuals of transmission electron microscope (TEM) micrographs and selected area (electron) diffraction (SAED) patterns of gold nanoparticles synthesized using Pistia stratiotes extracts.

1) Fig. 2a illustrates monodispersed gold nanoparticles synthesized using leaves of Pistia stratiotes

2) Fig. 2b illustrates polydispersed gold nanoparticles synthesized using leaves of Pistia stratiotes

3) Fig. 2c illustrates monodispersed gold nanoparticles synthesized using roots of Pistia stratiotes

4) Fig. 2d illustrates polydispersed gold nanoparticles synthesized using roots of Pistia stratiotes

C) Fig. 3 illustrates composite visuals of transmission electron microscope (TEM) micrographs and selected area (electron) diffraction (SAED) patterns of gold nanoparticles synthesized using Eichhornia crassipes extracts.

1) Fig. 3a illustrates monodispersed gold nanoparticles synthesized using leaves of Eichhornia crassipes

2) Fig. 3b illustrates polydispersed gold nanoparticles synthesized using leaves of Eichhornia crassipes

3) Fig. 3c illustrates monodispersed gold nanoparticles synthesized using petiole of Eichhornia crassipes

4) Fig. 3d illustrates polydispersed gold nanoparticles synthesized using petiole of Eichhornia crassipes

5) Fig. 3e illustrates monodispersed gold nanoparticles synthesized using roots of Eichhornia crassipes

6) Fig. 3f illustrates polydispersed gold nanoparticles synthesized using roots of Eichhornia crassipes

DETAILED DESCRIPTION

The processes for the synthesis of metal nanoparticles using plant derived materials disclosed in the prior art documents suffer with various drawbacks such as these processes are complicated and require rigorous controls, such as maintenance of pH and temperature under agitation for achieving morphology controlled synthesis of metal nanoparticles. In view of this, the inventors of the present disclosure envisaged a simple process for the synthesis of stabilized colloidal metal nanoparticles using aquatic weeds which operate at ambient temperature, pressure and humidity. The inventors of the present disclosure found that the process enables easy control of the shapes and sizes of nanoparticles.

Furthermore, it is found that the process of the present disclosure requires no elaborate separation - purification steps and is capable of producing mono and poly-dispersed nanoparticles.

Aquatic weeds are those unwanted plants which grow and complete their life cycle in water and cause harm to aquatic environment and to related eco-environment. Aquatic weeds can be classified according to their habitat and morphological characteristics. The major weeds can be categorized as submerged weeds, emerged weeds, and dispersed weeds, shoreline and ditch weeds, bank weeds, marshland and swamp weeds and phreatophytes. Out of 140 aquatic weeds, the following arc of primary concern to India: Eichhornia crassipes; 2. Salvinia molesta; 3. Pistia stratiotes; 4. Ipomoea spp.; 5. Hydrilla verticillata; 6. Nymphaea stellata; 7. Chara spp.; 8. Typha angustata; 9. Vallisneria spiralis; 10. Nelumbo nucifera: 11. Nitella spp.

Eichhornia crassipes, commonly known as Water Hyacinth, is an aquatic plant native to the Amazon basin. It is often considered a highly problematic invasive species outside its native range. It has become an ecological plague, suffocating the lake, diminishing the fish reservoir and the local economies. There are economic impacts when the weed blocks boat access. The effects on transportation and fishing are immediately felt. Where the weed is prolific, there is a general increase in several diseases, as the weed creates excellent breeding areas for mosquitoes and other insects. There are increased incidents of skin rash, cough, malaria, encephalitis, bilharzias, gastro intestinal disorders and schistosomiasis. Water hyacinth also interferes with water treatment, irrigation and water supply. It can smother aquatic life by deoxygenating the water and it reduces nutrients for young fish in sheltered bays. It has blocked supply intakes for the hydroelectric plant, interrupting electrical power for entire cities. The weed also interrupts local subsistence fishing, blocking access to the beaches. Several biological control agents have been released to control it.

Salvinia molesta, commonly known as giant Salvinia, is an aquatic fern, native to south-eastern Brazil. It is a free floating plant that does not attach to the soil, but instead remains buoyant on the surface of a body of water. The fronds are 0.5 4 cm long and broad, with a bristly surface caused by the hair-like strands that join at the end to form eggbeater shapes. The plant's growth clogs waterways and blocks sunlight needed by other aquatic plants and especially algae to carry out photosynthesis thereby oxygenating the water. As it dies and decays, decomposers use up the oxygen in the water. It also prevents the natural exchange of gases between the air & the body of water the plant has invaded causing the waterway to stagnate. This can kill any plants, insects or fish trapped underneath its growth. Its ability to grow and cover a vast area makes it a threat to biodiversity. The growth habit of Salvinia also is problematic to human activities including flood mitigation, conservation of endangered species & threatened environments, boating and irrigation.

Pistia stratiotes is often called water cabbage, water lettuce or Nile cabbage. It is a perennial monocotyledon with thick, soft leaves that form a rosette. It floats on the surface of the water with its roots hanging submersed beneath floating leaves. It is a common aquatic weed in the United States. Mats of Pistia block gas exchange at the air-water interface, reducing the oxygen in the water and killing fish. They also block light, killing native submerged plants and alter immersed plant communities by crushing them. Mosquitoes of the genus Mansonioides that carry disease complete their life cycle only in the presence of aquatic plants such as Pistia, laying their eggs under the leaves.

Aquatic weeds are more abundant than plants used in the prior art and have no competing use. The control of these invasive aquatic weeds is becoming a problem as it requires high cost. There remains a need for finding methods for their utilization so that the cost of harvesting them can be recovered as their presence in water bodies causes serious harm. Thus there is a need for the utilization of these aquatic weeds in an efficient manner that will lead to both economical and ecological benefit.

The inventors of the present disclosure utilized these weeds for the synthesis of stabilized metal nanoparticles. Thus utilization of these weeds for nanoparticlc synthesis in the present disclosure not only provides stabilized metal nanoparticles but also help to clear the weeds from the environment.

The process for the preparation of colloidal metal nanoparticles such as gold nanoparticles and silver nanoparticles in accordance with the present disclosure is described herein below.

Initially, a solution of metal ions having concentration of 10~3 M is prepared by dissolving at least one metal salt in distilled water.

The metal salt used for the preparation of a solution of metal ion includes but is not limited to chloroauric acid, sodium tetrachloroaurate, silver nitrate and silver acetate. Depending upon the types of nanoparticles to be prepared, the metal salt is selected.

Separately, an aqueous solution of weed is prepared. The process of the preparation of aqueous solution of weed involves the following steps: In the first step, plant material from an aquatic weed is obtained. The aquatic weed is at least one selected from the group consisting of Salvinia molesta, Pistia stratiotes and Eichhornia crassipes. The plant material used is at least one selected from the group consisting of leaves, stems/petioles and roots of aquatic weed. The selected plant material is then subjected to sorting, cleaning and sizing. The plant material is then boiled in distilled water at a temperature of about 95 °C to 100 °C for a period below 30 minutes followed by cooling and filtration.

In the next step, the metal ion solution and the aqueous solution of weed is mixed in appropriate stoichiometric proportions to obtain metal nanoparticles. The proportion of metal ion solution to aqueous solution of weed is maintained in range between 1:1 and about 1:9. The formation of metal nanoparticles is monitored by UV-visible spectroscopy. The metal nanoparticles formed are mono-dispersed and /or poly-dispersed.

The process of the present disclosure is one pot synthesis process which includes simultaneous addition of the weed extract and the metal ion solution in stoichiometric ratios in glass/fiber glass reactors.

The inventors of the present disclosure also tried addition of water during mixing the metal ion solution and the aqueous solution of weed. The proportion of metal ion solution to aqueous solution of weed to water is maintained in the range of about 1:0.1:0.1 and 1:9:9.

The present disclosure also provides metal nanoparticles prepared by a process of the present disclosure. The size of the nanoparticles ranges between 1 nm to 100 nm. The colloidal metal nanoparticles in accordance with the present disclosure include but are not limited to gold nanoparticles and silver nanopartilces. Preferably, in accordance with the present disclosure colloidal gold nanoparticles are provided. The nanoparticles of the present disclosure are in a form selected from the group consisting of mono-dispersed and poly-dispersed.

The shape of the nanoparticles prepared in accordance with the present disclosure is selected from the group consisting of spherical, triangle, pentagonal, polygonal, rod, flower like and hexagonal shapes.

The size and shape of the metal nanoparticles is determined by using Transmission electron microscopy.

The principle underlying the synthesis of stabilized colloidal metal nanoparticles using extracts of weed is as follows:-

The reduction process is mediated by the presence of secondary metabolites present in the extracts. Macromolecules such as polymers and oligomers adsorb on the surface of the metal nanoparticles and form a protective layer, which sterically stabilizes the nanoparticles.

The active and major biochemical ingredients present in the weed plants which are involved in the synthesis of the metal nanoparticles are as follows:

(i) Salvinia molesta: Amides and polyols.

(ii) Pistia stratiotes: Amides

(iii) Eichhornia crassipes: Amides, terpenoids, flavonoids and polysaccharides.

The present disclosure will now be described with the help of following non-limiting examples.

EXAMPLES

Example 1) Preparation of weed solution

The plant material was obtained from aquatic weed (Salvinia molesta , Pistia stratiotes and Eichhornia crassipe) parts e.g. leaves, stems, petiole, flowers and roots and was sorted, cleaned and cut to. 10 g dry weight equivalent of the aquatic weed part was added to one litre of distilled water and boiled in a waterbath at a temperature of about 95°C at ambient pressure for 3 minutes followed by cooling and filtration. The weed extract obtained was in the form of an aqueous solution.

The fresh plant portions were used for the extract preparation. The prepared extracts were stored at 4°C under refrigeration and used within 3 days of preparation for nanoparticle production. When extracts were used after storing them for longer than 3 days, a slow diminishing of their activity was witnessed in terms of slower rate of nanoparticle formation and also diminishing extent of nanoparticle formation. Hence freshly prepared extracts or the ones stored at 4°C for upto 3 days are recommended for best results.

Example 2) Preparation of Gold nanoparticles using Salvinia molesta

a) Preparation of mono-dispersed gold nanoparticles using leaves of Salvinia molesta:-

Aqueous solution of the Salvinia molesta leaves was prepared by the process as described in example 1. A gold ion solution was prepared by dissolving chloroauric acid in distilled water to obtain a final solution with concentration of 10"3 M. 1.0 ml of the solution of the Salvinia molesta and 1.0 ml of the gold ion solution were mixed. To this, 8.0 ml of distilled water was added with continuous gentle mixing. The formation of gold nanoparticles was monitored using UV-visible spectroscopy. The size and shape of the gold nanoparticles was detected by Transmission Electron Microscopy. The gold nanoparticles formed were monodispersed. The shape of the nanoparticles was found to be spherical and the average diameter of the nanoparticles was found to be 12.5nm.

b) Preparation of polydispersed gold nanoparticles using leaves of Salvinia molesta:-

The process as described in example 2 (a) was repeated with the difference that 3.0 ml of solution of Salvinia molesta leaves and 7.0 ml of gold ion solution were used. The gold nanoparticles formed were polydispersed with various shapes and sizes as follows:

1) Shape: Polygonal; Avg. Size: 20 nm;
2) Shape: Triangular; Avg. Size: 50 nm;
3) Shape: Rod; Avg. Size: 40 nm; and
4) Shape: Spherical; Avg. Size: 10 nm
c) Preparation of monodispersed gold nanoparticles using roots of Salvinia molesta:-

The process as described in example 2 (a) was repeated with the difference that 1.0 ml of solution of Salvinia molesta roots, 1.0 ml of gold ion solution and 8 ml of water were used. The gold nanoparticles formed were found to be mono-dispersed. The shape of the nanoparticles was found to be spherical and the diameter of the nanoparticles was found to be 20nm.

d) Preparation of polydispersed gold nanoparticles using roots of Salvinia molesta: -

The process as described in example 2 (a) was repeated with the following difference. The gold nanoparticles were prepared using 0.5 ml of solution of Salvinia molesta roots, 1.0 ml of gold ion solution and 8.5 ml of water. The gold nanoparticles formed were found to be poly-dispersed. The gold nanoparticles formed were polydispersed with various shapes and sizes as follows:

i) Shape: flower like; Avg. Size: 125 nm; and ii) Shape: Spherical; Avg. Size: 25 nm

Example 3 Preparation of Gold nanoparticles using Pistia stratiotes:-

a) Preparation of monodispersed gold nanoparticles using leaves of Pistia stratiotes'.-

The process as described in example 2 (a) was repeated with the following difference. The gold nanoparticles were prepared using 1 ml of solution of Pistia stratiotes leaves, 4.0 ml of gold ion solution and 5 ml of water. The gold nanoparticles formed were found to be mono-dispersed. The shape of the nanoparticles was found to be spherical and the diameter of the nanoparticles was found to be 11.5nm.

b) Preparation of polydispersed gold nanoparticles using leaves of Pistia stratiotes:-

The process as described in example 2 (a) was repeated with the following difference. The gold nanoparticles were prepared using 1 ml of solution of Pistia stratiotes leaves, 5.0 ml of gold ion solution and 4 ml of water. The gold nanoparticles formed were found to be poly-dispersed with various shapes and sizes as follows:

i) Shape: Triangular ; Avg. Size: 40 nm;
ii) Shape: Pentagonal; Avg. Size: 25 nm; and
iii) Shape: Hexagonal; Avg. Size: 55 nm
c) Preparation of monodispersed gold nanoparticles using roots of Pistia
stratiotes'.-

The process as described in example 2 (a) was repeated with the following difference. The gold nanoparticles were prepared using 2 ml of solution of Pistia stratiotes roots and 4.0 ml of gold ion solution. The gold nanoparticles formed were found to be mono-dispersed. The shape of the nanoparticles was found to be spherical and the diameter of the nanoparticles was found to be 13.5nm.

d) Preparation of polydispersed gold nanoparticles using roots of Pistia stratiotes'.-

The process as described in example 2 (a) was repeated with the following difference. The gold nanoparticles were prepared using 2 ml of solution of Pistia stratiotes roots and 8.0 ml of gold ion solution. The gold nanoparticles formed were found to be poly-dispersed with various shapes and sizes as follows:

i) Shape: Triangular; Avg. Size: 95 nm; and

ii) Shape: Pentagonal; Avg. Size: 27.5 nm

Example 4: Preparation of Gold nanoparticles using Eichhornia crassipes:-

a) Preparation of monodispersed gold nanoparticles using leaves of
Eichhornia crassipes:-

The process as described in example 2 (a) was repeated with the following difference. The gold nanoparticles were prepared using 1.5 ml of solution of Eichhornia crassipes leaves, 3.0 ml of gold ion solution and 5.5 ml of water. The gold nanoparticles formed were found to be mono-dispersed. The shape of the nanoparticles was found to be spherical and the diameter of the nanoparticles was found to be 17.5nm.

b) Preparation of polydispersed gold nanoparticles using leaves of Eichhornia crassipes:-

The process as described in example 2 (a) was repeated with the following difference. The gold nanoparticles were prepared using 3 ml of solution of Eichhornia crassipes leaves and 7.0 ml of gold ion solution.

The gold nanoparticles formed were found to be poly-dispersed, with various shapes and sizes as follows:

i) Shape: Triangular; Avg. Size: 40 nm; and

iii) Shape: Pentagonal; Avg. Size: 30 nm

c) Preparation of monodispersed gold nanoparticles using petioles of Eichhornia crassipes:-

The process as described in example 2 (a) was repeated with the following difference. The gold nanoparticles were prepared using 5 ml of solution of Eichhornia crassipes petioles, 1.0 ml of gold ion solution and 4 ml of water. The gold nanoparticles formed were found to be mono-dispersed. The shape of the nanoparticles was found to be spherical and the diameter of the nanoparticles was found to be 12.5nm.

d) Preparation of polydispersed gold nanoparticles using petioles of
Eichhornia crassipes:-

The process as described in example 2 (a) was repeated with the following difference. The gold nanoparticles were prepared using 5 ml of solution of Eichhornia crassipes petioles and 5.0 ml of gold ion solution. The gold nanoparticles formed were found to be poly-dispersed, with various shapes and sizes as follows:

i) Shape: Triangular; Avg. Size: 22.5 nm; ii) Shape: Pentagonal; Avg. Size: 100 nm; and iii) Shape: Truncated triangle; Avg. Size: 150nm

e) Preparation of monodispersed gold nanoparticles using roots of Eichhornia crassipes:-

The process as described in example 2 (a) was repeated with the following difference. The gold nanoparticles were prepared using 1 ml of solution of Eichhornia crassipes roots, 3.0 ml of gold ion solution and 6 ml of water. The gold nanoparticles formed were found to be mono-dispersed. The shape of the nanoparticles was found to be spherical and the diameter of the nanoparticles was found to be 25nm.

f) Preparation of polydispersed gold nanoparticles using roots of Eichhornia crassipes:-

The process as described in example 2 (a) was repeated with the following difference. The gold nanoparticles were prepared using 3 ml of solution of Eichhornia crassipes roots and 9.0 ml of gold ion solution. The gold nanoparticles formed were found to be poly-dispersed with various shapes and sizes as follows:

i) Shape: Triangular; Avg. Size: 37.5 nm; and
ii) Shape: Hexagonal; Avg. Size: 70 nm

TECHNICAL ADVANCEMENT AND ECONOMIC SIGNIFICANCE:

- The present disclosure provides a simple, cost effective and non-hazardous method for the synthesis of stabilized metal nanoparticles using aquatic weeds that have no other competing use.

- The present disclosure provides stabilized biocompatible metal nanoparticles of desired size and shape.

- The present disclosure provides a process for the synthesis of metal nanoparticles which requires no elaborate separation-purification steps.

- The present disclosure provides a single pot process which controls the shapes and sizes of nanaoparticles and is capable of producing mono and poly-dispersed metal nanoparticles.

- The present disclosure provides a process for the synthesis of metal nanoparticles which operates at ambient temperature, humidity and pressure and therefore can easily be scaled up to higher levels.

- The metal nanoparticles synthesized by the process of the present disclosure have wide applications in various fields including but not limited to catalysis, medical applications and the like.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a statement in the specification specific to the contrary.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

We claim:

1. A process for manufacturing colloidal metal nanoparticles; said process comprising the following steps:

(a) preparing a solution of metal ions having concentration of 10"3 M by dissolving at least one metal salt in distilled water;

(b) preparing an aqueous solution of weed;

(c) mixing the metal ion solution and the aqueous solution of weed to obtain metal nanoparticles; and

(d) monitoring the formation of metal nanoparticles by UV-visible spectroscopy and characterization by Transmission Electron Microscopy (TEM).

2. The process as claimed in claim 1 wherein the metal is selected from the group comprising of gold and silver.

3. The process as claimed in claim 1 wherein the metal salt is at least one selected from the group consisting of chloroauric acid, sodium tetrachloroaurate, silver nitrate and silver acetate

4. The process as claimed in claim 1 wherein the method of preparing an aqueous solution of weed comprises the following steps:

- obtaining plant material from aquatic weed;

- treating the plant material by at least one operation selected from the group consisting of sorting, cleaning and sizing;

- obtaining an aqueous solution of weed by boiling the plant material in distilled water at a temperature of about 95 °C to 100 °C for a period below 30 minutes followed by cooling and filtration.

5. The process as claimed in claim 1, wherein the plant material is at least one selected from the group consisting of leaves, stems/ petioles and roots of aquatic weed.

6. The process as claimed in claim 1, wherein the aquatic weed is at least one selected from the group consisting of Salvinia molesta, Pistia stratiotes and Eichhornia crassipes.

7. The process as claimed in claim 1, wherein the proportion of metal ion solution to aqueous solution of weed ranges between 1:1 and 1:9.

8. The process as claimed in claim 1, wherein the proportion of metal ion solution to aqueous solution of weed to water ranges between 1: 0.1: 0.1 and 1: 9:9.

9. The process as claimed in claim 1, wherein the metal nanoparticles are mono-dispersed.

10. The process as claimed in claim 1, wherein method step of mixing further comprises addition of water.

11. The process as claimed in claim 1, wherein the metal nanoparticles are poly- dispersed.

12. Colloidal metal nanoparticles prepared by a process as claimed in claim 1, wherein the size of the nanoparticles ranges between 1 nm to 100 nm.

13. The colloidal metal nanoparticles as claimed in claim 12, wherein the metal nanoparticles are selected from gold nanoparticles and silver nanoparticles.

14. The colloidal metal nanoparticles as claimed in claim 12, wherein the nanoparticles are in a form selected from the group consisting of mono-dispersed and poly-dispersed.

15. The colloidal metal nanoparticles as claimed in claim 12, wherein the shape of the nanoparticles is selected from the group consisting of spherical, triangle, pentagonal, polygonal, rod, flower like and hexagonal morphology.