FIELD OF INVENTION

The present invention relates generally to the field of environmental nano- technology. Specifically it pertains to an unprecedented biochemical method developed for the gainful utilization of highly invasive weeds for a novel purpose. More particularly it relates to a method for synthesizing shape and size-tunable, silver nanostructures extracellurlarly, at very benign operational conditions, in an eco-friendly, energy-saving, and cost-effective manner.

PRIOR ART

Metal nanoparticles have been the focus of a large body of scientific research due to the fact that their catalytic activity, and their antimicrobial, electronic, optical, magnetic and medical properties often vastly differ from that of the bulk materials. This large contrast in properties can be attributed to the change in surface area to volume ratio that occurs as a consequence of nano-sizing. Synthesis of metallic nanoparticles for applications in catalysis, electronics, pollution control, medicine, etc is an area of intense contemporary interest.

Prior arts for the synthesis of silver nanoparticles revealed that silver nanoparticles can be synthesized by many routes. Traditionally nanoparticles were produced only by physical and chemical methods. Some of the commonly used physical and chemical methods are ion sputtering, solvothermal synthesis, reduction and sol gel technique. But chemical synthesis methods involve hazardous reagents and/or process conditions which lead to generation of pollutants and also the presence of some toxic chemical species adsorbed on the surface may have adverse effects in medical applications. Further physical methods are highly energy- intensive and expensive.

Hence the need for biosynthesis of nanoparticles rose because of the demerits of physical and chemical processes. So in the search for alternate pathways for nanoparticle synthesis, scientists used microorganisms and then plant extracts for synthesis of metal nanoparticles. Initially bacteria were used to synthesize nanoparticles and this was later followed with the use of fungi. actinomycetes etc. But the kinetic rate for the microbiological methods for generating the metal nanoparticles is very slow.

Biochemical synthesis of silver nanoparticles has been achieved by different authors using about 70 species of botanical plants. These plants encompass fruits, vegetables, grains, cereals, spices, other foodstuff, medicinal plants, etc, for example Azadirachta indica (Shankar et al., 2004), Emblica officinalis (Ankamwar et al., 2005), Capsicum annum (Li et al., 2007), Camellia sinensis (Nestor et al., 2008), Parthenium hysterophorus (Parashar et al., 2009), Argimone maxicana (Khandelwal et al., 2010), Mimosa pudica (Marimuthu et al., 2010), Euphorbia hirta (Elumalai et al., 2010), neem (Anuradha et al., 2011) and Desmodium triflorum (Ahmad et al., 2011).

Colloids and Surfaces A: Physicochemical and Engineering Aspects 339(1-3), !
2009, 134-139 discloses green synthesis of silver nanoparticles using latex of Jatropha curves. Silver nanoparticles were successfully synthesized from AgNOs through a green route using the latex of J. curcas as reducing as well as capping agent.

The prior art Parasitology Research DOI: 10.1007/s00436-010-2212-4 discloses the evaluation of green synthesized silver nanoparticles against parasites in which AgNPs were synthesized using the leaf extract of Mimosa pudica and the fomnation of nanoparticles was observed within 6 h. The results recorded from UV- vis spectrum, Fourier transform infrared. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy support the biosynthesis and characterization of AgNPs.

Developments in Environmental Sciences,(5) , 2007, 463-485 discloses Synthesis of metal nanoparticles by inactivated plant tissues, plant extracts, and living plants. The article discusses the production of silver nano particles by bio reduction using living alfalfa plants. Further high resolution-TEM showed that the plants formed small silver nanoparticles with sizes averaging from 2 to 20 nm in diameter.

Nanoscience and Nanotechnology, 2006. ICONN '06. International Conference on Issue Date: 3-7 July 2006 discloses the synthesis of metallic nanoparticles inside live plants. The article discloses the phytosynthesis of metal nano particles using hyperaccumulator species Brassica juncea, Helianthus annus and Medicago sativa. Nanoparticles of common heavy metal ions, e.g. Ag, Cu, Co, Zn and Ni, were synthesized by exposing plants to aqueous metal salt solutions.

EK. Elumalal at ai, IJ. Phann. Sci. & Res. Vol.2 (9), 2010, 549-554 discloses the extracellular synthesis of silver nanoparticles using leaves of Euphorbia hirta and their antibacterial activities. Aqueous extract of shade dried leaves of Euphorbia hirta was used for the synthesis of silver (Ag) nanoparticles. SEM image divulges that silver nanoparticles are quite polydispersed and the size ranges from 40 nm to 50 nm.

International Journal of Nanotechnology and Applications 4(2), 2010, 95-101 disclose green synthesis of silver nanoparticles from the unexploited weed resources. The bioreduction property of three aquatic weed leaves extracts Ipomoea aquatica (Convolvuaceae), Enhydra fluctuans (Asteraceae) and Ludwigia adscendens (Onagraceae) in the synthesis of silver nanoparticles was investigated by UV -Vis spectrophotometry, Scanning Electron Microscopy (SEM) and Thennal Gravimetric Analysis (TGA).

US patent 2010/0200501 AI discloses methods of making and using the compositions of metal nanoparticles formed by green chemistry synthetic techniques. The cited patent explains a method for making one or more metal nanoparticles, comprising combining the metal ion solution (AgNOs) and the plant extract to produce metal nanoparticles. The plant extract used in the invention are tea, coffee, parsley, sorghum, mmioram. and/or lemon balm.

US patent 2005/0009170 AI discloses the use of plants for the production of metal nanoparticles. In particular, precious metals such as gold, silver and platinum can be produced using alfalfa. The cited prior art discloses a method of producing a precious metal nanoparticle in a plant comprising: (a) selecting a plant growth environment comprising a precious metal source; (b) growing a plant in said plant growth environment; and (c) isolating said precious metal nanoparticle.

The advantage of using plants, as reveled in above mentioned prior arts and many other known prior arts, for the synthesis of nanoparticles is that they are easily available, safe to handle and possess a broad variability of metabolites that may aid in reduction.
Preparation of nanoparticles using plants may involve either the use of live plants (phytosynthesis) or just the plants extracts.

Preparation of nanoparticles using live plants involves exposing plants to aqueous metal salt solutions. The plant absorb/accumulate the metals which is then extracted/isolated to obtain the metal nanoparticles from the plant biomass, which further involves complicated techniques. All these parameters make the procedure too complicated and tedious.

Synthesis of nanoparticles using plant extract of the prior art involves species which are useful to mankind in varied number of ways. The plants discussed in the prior arts also finds potential application in the field of medicine, agriculture etc. Hence their employment in nanoparticles synthesis, when done on a large-scale, will not only clash with their already well-established uses but would also, consequently, entail substantial costs of production.

Hence, plants which are useless or weeds which are otherwise not only worthless but also harmful to the environment need to be gainfully utilized for the synthesis of metal nanoparticles. The gainful utilization of whole plants or weeds for a process of synthesizing nanoparticles under simplified conditions, devoid of complicated techniques and special isolation/extraction procedures is needed in the state of art.

OBJECT OF THE INVENTION

The main object of the present invention is to synthesize silver nanoparticles utilizing the otherwise worthless weeds by a clean-green, environment-friendly, and inexpensive process.

Another object of the present invention is to utilize atleast one of weeds selected from the group comprising of lantana, ipomoea, mimosa, and coral vine for the synthesis of silver nanoparticles.

Another object of the present invention is to utilize a combination of weeds selected from the group comprising of lantana, ipomoea, mimosa, and coral vine for the synthesis of silver nanoparticles.

Another object of the present invention is to utilize a combination of four weeds, lantana, ipomoea, mimosa, and coral vine for the synthesis of silver nanoparticles.

Another objective is to utilize the otherwise worthless weeds (lantana, ipomoea, mimosa, and coral vine) in a gainful manner by the generation and stabilization of silver nanoparticles, thereby making mechanical removal of these weeds remunerative.

Yet another object of the present is to utilize the whole plant extract of the weeds instead of just leaves or any specific part of the plant and there by ensuring full utilization of the harmful weeds in the synthesis of silver nanoparticles, thus leaving no waste.

Yet another object of the present invention is to is to optimize a process for the synthesis of both mono and polydispersed silver nanoparticle.

Yet another object of the present invention is to develop a simplified process for the synthesis of silver nanoparticles under conditions like ambient temperature, pressure with out toxic reactants and products.

Yet another object of the present is to develop a process for the synthesis of mono and poly dispersed silver nanoparticles under benign, non hazardous, process conditions.

Yet another object of the present invention is to produce silver nano particles of desired size and shape by a clean-green, environment-friendly, and inexpensive process.

Yet another object of the present invention is to utilize the harmful and undesirable weeds as they have to be otherwise controlled by using herbicides, and other control methods which toxify the environment.

SUMMARY OF THE INVENTION

The present invention relates to an eco-friendly and green, one pot synthesis route for the production of silver nanoparticles. The silver nanoparticles of the present invention is synthesized by the utilization of any one of the weeds extracts selected from the group comprising of lantana, ipomoea, mimosa, and coral vine or combinations thereof. The process achieves successfully the gainful utilization of four harmful weeds which are not only worthless but are harmful to environment. With this process it is possible to obtain mono and poly dispersed silver nanoparticles of desired size and shape.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention relates to an eco-friendly and green, one pot extracellular synthesis route for the production of silver nanoparticles.

In one of the preferred embodiment the present invention shall discloses a process of synthesizing the silver nanoparticles utilizing atleast one of the weeds/plants extracts selected from the group comprising of lantana, ipomoea, mimosa, and coral vine.

In another preferred embodiment the present invention shall disclose a process of synthesizing the silver nanoparticles utilizing combination of weeds/plants extracts selected from the group comprising of lantana, ipomoea, mimosa, and coral vine.

In another preferred embodiment the present invention shall disclose a process of synthesizing the silver nanoparticles utilizing combination of the four weeds extracts lantana, ipomoea, mimosa, and coral vine.

In most preferred embodiment the present invention shall disclose a process for biosynthesis of plant-metal based nano particles by reacting a silver metal salt solution and a weed extract. The biosynthesis of silver nano particles is done in aqueous solution such that the aqueous metal ions when exposed to the weed extract reduces to nano particles. The weed extract is a whole weed extract of lantana, ipomoea, mimosa, coral vine or combination. The weed extract acts as a reducing-cum-stabilizing agent and converts the metal salt which is silver nitrate into metal nano particles, having generally an uniform size. The uniform particle size of the metal nano particles is between 7nm and 100nm. The nano particles may be recovered by using known conventional recovery method selected from the group consisting of density gradient centrifugation.

As per the invention the size of the nanoparticles is determined by the concentration and proportion of the metal salt solution and weed extract. By manipulating the stoichiometry and the proportions of silver salt solution and plant extracts, yields of AgNPs of varying size are achieved. This is determined by the characterization studies using UV-Vis spectral patterns, Hr-SEM, TEM.

Further more the size of the nanoparticles depend on the reducing property of the weed extract. For Example : A particular proportion (Metal salt solution and weed extract) exhibits varying spectral pattern when studied among the species. The variation is due to the difference in size and shape of the particles synthesized. Thus size of the particles formation is determined by the reducing-cum-capping property of the weeds.

Also "time" is a factor influencing the size of the nanoparticles for example: particular reaction mixture is continuously monitored under UV-Vis spectral recording. The size of the particle synthesized is determined by its peak wavelength, shift in wavelength and broadness of the peak formed.

The present invention utilizes terrestrial weeds lantana (Lantana camara), Ipomoea (Ipomoea carnea), mimosa (Mimosa pudica) and coral vine (Antigonon leptopus) which are freely available in several parts of the world in very huge quantities for the synthesis and stabilization of silver nanoparticles. These weeds are not merely worthless but are regarded as a nuisance. In fact expenditure equivalent to billions of rupees is routinely incurred across the world in attempts to eradicate these weeds, or control them with herbicides. This is because these weeds play havoc with the economic productivity and ecological integrity of land and water; and cause very seriously adverse impacts on human and livestock health.

Among the four terrestrial weeds used in this invention, lantana (Lantana camara), Ipomoea (Ipomoea carnea) and coral vine (Antigonon leptopus) have not been used for nanoparticle synthesis ever before.The prior arts disclose the utilization of mimosa (Mimosa pudica) for the synthesis of silver nanoparticles but the prior art disclose a process solely based on the use of leaves of Mimosa species. In contrast the present invention is based on the use of the whole plant of M. pudica, as also of the other three weeds. This is a very significant improvement because on one hand it enhances the utility value of each plant manifold (by enabling the use of the whole plant instead of just leaves) and on the other hand it makes the utilization of the invasives so potentially gainful that it may become remunerative to control the invasives through their harvesting and use. Hence the invention has far-reaching beneficial portent for the protection of large tracts of terrestrial ecosystems.

The present invention is non-hazardous and inexpensive. It is also novel in many other ways. Synthesis of silver nanoparticles was achieved in one step process. Biochemicals responsible for the reduction and stabilization are found in the plant extracts. Once aqueous metal salt solution is added, nucleation starts without any intermediary products such as AgO, AgCI. This is confirmed by the EDAX spectrum, where only clear peak of Ag is found at 3 keV along with least peaks of other elements C, N and O.

Further the attempts were made to optimize the process for both mono and polydisperssed silver nanoparticles synthesis. This is achieved by balancing the concentration and proportions of aqueous extract and source metal solution.

The optimization has been based on manipulating the stoichiometry and finding proportions of silver and plant extracts, which maximize nanoparticle recovery. Preliminary studies were performed by recording the UV-Vis pattern of reaction mixture (aqueous silver salt solution and plant extracts) in different stoichiometric proportions. Based on the resultant peak wavelength and absorbance, optimization of the stoichiometry was done for the process of nanoparticles synthesis in the system.

Characterisation of the synthesized Nanoparticles, were determined by SEM, Hr- SEM, and TEM analysis, the average particle size was 53.5 nm.

In the process of Invention besides aqueous solution of metal ion, the process employs only extract of the weeds and no hazardous chemical. It enables easy control of the shapes and sizes of nanoparticles. The diagnostic tool for controlling the nanoparticle formation and consistency of its shape/size is spectrophotometry which is a relatively inexpensive and half standard tool. By varying concentration and relative proportions of metal ion and weed extracts, the control was achieved as primarily diagnosed by spectrophotometry and confirmed by XRD, Hr-SEM and TEM.

It is based on a process which operates at ambient temperature, humidity, and pressure and which is totally non-hazardous. It is performed at room temperature and pressure without the need of control of temperature, pressure, rigorous humidity, etc.

The process is such that no toxic pollutant is generated. No special culture- preparation and isolation procedures, which are common in bioprocesses-are required for the process. The process is easily scalable.

WE CLAIM:

1. A process for extracellular biosynthesis of silver nano particles by using whole plant of terrestrial weeds, the said process consisting of:-

- Reacting a metal salt and a weed extract as a reducing-cum-stabilizing agent thereby converting the metal salt into metal nano particles, having generally an uniform size wherein the uniform particle size of the said metal nano particles is between 7nm and 100nm and recovering the metal nano particles so produced therein,

- Characterized in the weed extract as whole weed extract of lantana, ipomoea, mimosa, coral vine or combination there of, and in the metal salt which is silver nitrate, and wherein the said biosynthesis of metal nano particles is done in aqueous solution such that the aqueous metal ions when exposed to the weed extract generates nano particles

2. The process as claimed in claim 1 wherein the reaction of metal salt with the weed extract initiates nucleation but without forming any intermediates such as AgO , AgCl and others.

3. A process as claimed in claim 1, wherein the size of the nano particles is determined by the reducing property of the weed extract.

4. A process as claimed in claim 1, wherein the size of the nano particles is determined by the concentration of the weed extract and the metal salt.

5. A process as claimed in claim 1, wherein the size of the nano particles is determined by the proportion and concentration of the silver ion and the weed extract.

6. A process as claimed in claim 1, wherein the size of the nano particles is determined by the quantity of the weed extract and the metal salt.

7. A process as claimed in claim 1, wherein the shape of the nano particles is determined by the proportion and concentration of the silver ion and the weed extract.

8. A process as claimed in claim 1, wherein the size of the nano particles is determined by the time of the synthesis process.

9. A process as claimed in claim 1, wherein the nano particles so obtained is mono dispersed.

10. A process as claimed in claim 1, wherein the nano particles so obtained is poly dispersed.

11. A process as claimed in claim 1, wherein the nano particles may be recovered by using known conventional recovery method selected from the group consisting of density gradient centrifugation.