Claims:1. A method for synthesis of metal nanoparticles comprising: reacting a solution comprising a precursor that is capable of being reduced to a metal, with tin metal in a solid-state capable of reducing the precursor to metal nanoparticles.
2. The method as claimed in claim 1, wherein the metal suitable for forming nanoparticles is transition metal selected from the group consisting of gold, silver, copper, nickel, cobalt, palladium, platinum, iridium, osmium, rhodium, ruthenium, rhenium, vanadium, chromium, manganese, niobium, molybdenum, tungsten, tantalum, iron and cadmium.
3. The method as claimed in claim 1 or 2, wherein the metal nanoparticles formed are of gold and silver metal.
4. The method as claimed in claim 1, wherein the precursor is aninorganic or organic acid or salt thereof.
5. The method as claimed in any one of the claims 1-4, wherein the precursor is selected from silver nitrate, silver acetate, silver trifluoroacetate, silver oxide, and silver chloride.
6. The method as claimed in any one of the claims 1-4, wherein the precursor is chloroauric acid or auric chloride.
7. The method as claimed in any one of the claims 1-4, wherein the method is optionally carried out for a specific duration of time for producing metal nanoparticles with controllable size.
8. The method as claimed in claim 7, wherein the time duration is varied from 10 seconds to 30 minutes.
9. The method as claimed in claim 8, wherein the time duration is 15, seconds, 30 seconds, 1 min, 2 minutes, 3 minutes, 5 minutes, 10 minutes, 20 minutes, or 30 minutes.
10. The method as claimed in claim 1, the tin metal reducing agent in solid-state is of varying surface area to obtain metal nanoparticles with different surface plasmon resonance.
11. The method as claimed in claim 1 or 7, wherein the method optionally comprises while reacting the solution comprising a precursor withtin metal reducing agent; applying one or more of a specific voltage, an alternate current waveform, or a frequency for producing metal nanoparticles with shift in surface plasmon resonance.
12. The method as claimed in claim 11, wherein the direct current with specific voltage applied is of between 50mV to 5 V.
13. The method as claimed in claim 12, wherein the specific voltage applied is selected from 50 mV, 100mV, 500 mV, 1V, 2V, 3V, 4V, and 5V.
14. The method as claimed in claim 11, wherein the specific frequency applied if from 1 kHz to 1 MHz, selected from 1kHz, 10 kHz, 100 kHz, and 1 MHz.
15. The method as claimed in claim 11, wherein the specific alternate current wave form applied is selected from a sinusoidal waveform, square waveform, triangle waveform, and trapezoidal waveform.
16. A system (100) configured to synthesize metal nanoparticles with tin metal reducing agent in solid state, the system (100) comprises a medium in the form of a solution (106) of precursor that is capable of being reduced; a pair of electrodes including a first electrode (102) and a second electrode (104) made from jumper wires with bare copper wires coated with tin metal on the fringe to act as solid-state reducing agent; each of the electrodes at least partially surrounded by or inserted into the solution of precursor; each of the electrodes connected individually to a charging circuit (108) including portable oscilloscopes and waveform generator for generating in controlled manner and monitoring various signals, their intensities and duration using waveform generator pin W1; and ground ranging from 0V to 5V for producing metal nanoparticles with desired size or surface plasmon resonance.
17. A handheld system (101) configured to synthesize metal nanoparticles with tin metal solid-state reducing agent, in which the system (101) comprises a medium in the form of a solution (106) of precursor that is capable of being reduced; a pair of electrodes including a first electrode (102) and a second electrode (104)made from jumper wires with bare copper wires coated with tin metal on the fringe acting as solid-state reducing agent; the electrodes at least partially surrounded by or inserted into the solution of precursor; a circuitry (110) captively connected to each of the electrodes by a switch for supplying pulse of direct current at a specific voltage selected from 50mV to about 5V for producing metal nanoparticles with SPR in tunable manner.
, Description:FIELD OF INVENTION
[0001] The present disclosure relates to a process for synthesis of metal nanoparticles. In particular, the present disclosure provides a method and system for synthesis of metal nanoparticles with reducing agent, which is in solid state and reusable.

BACKGROUND OF THE INVENTION
[0002] Metal nanoparticles are currently being used for multiple applications spanning around energy sector to cosmetics. Multiple products based on metal nanoparticles have come to reality which includes paint with silver nanoparticle, hand sanitizer with silver nanoparticle and ZnO nanoparticle-based sunscreens among others. The size of the metal nanoparticles plays a crucial role in all these applications due to the size-dependent behavior of the metal nanoparticles.
[0003] There has been great thrust on developing metal nanoparticles for biomedical purposes, designed to improve the pharmacokinetic profile of imaging probes or drugs and to enhance the specific targeting at the disease site. For such applications, recent works suggest that surface plasmon resonance (SPR), represents a technique of choice to characterize, screen and develop metal nanoparticles for biomedical applications.
[0004] Conventionally, the size of previously synthesized metal nanoparticles couldn’t be altered. For obtaining specific size metal nanoparticles, later approaches include subjecting precursors to a specific temperature and pressure during synthesis. Such approaches also require the usage of specific chemicals like reducing agents and capping agents at a particular concentration for nucleation and growth to reach desired size. Alternately, for producing metalnanoparticles with requisite surface plasmon resonance, plasma-induced non-equilibrium liquid chemistry is used to synthesize metal nanoparticles, and other physical means. Methods involving conventionally used reducing agents like sodium borohydride hinders in the application of the synthesized metal nanoparticles for specific applications like biological application unless the metal nanoparticles are purified sufficiently with additional lengthy purification steps. High voltage and subsequent generation of plasma for the synthesis of metal nanoparticles is complicated and power consuming. Thus, such current approaches fortuning metal nanoparticlesto particular size or surface plasmon resonance are complex, lengthy, energy intensive and still not very effective in providing nanoparticles with desired size and SPR. Hence, in view of rapid realization of increasing applications of metalnanoparticles with diverse sizes and SPRs, there exists an unmet need for a simple, rapid, cost-effective, method to produce metal nanoparticles with desired size and SPR in controlled manner.

OBJECTS OF THE INVENTION
[0005] An object of the present disclosure is to provide a method for synthesis of metalnanoparticles with solid state, reusable reducing agent.
[0006] One object of the present disclosure is to provide a method for synthesis of metal nanoparticles comprising reacting a precursor that is capable of being reduced to metalnanoparticles with a solid-state reducing agent.
[0007] Another object of the present disclosure is to provide a system for carrying out method for synthesis of metal nanoparticles with desired size or surface plasmon resonance in controlled manner.

SUMMARY
[0008] The present disclosure in general aspect provides a method for synthesis of metal nanoparticles with solid state reusable reducing agent.
[0009] In an aspect the present disclosure provides a method for synthesis of metal nanoparticles comprising reacting a precursor that is capable of being reduced to metal nanoparticles with a solid-state reducing agent capable of reducing the precursor and producing metal nanoparticles.
[00010] In an aspect the present disclosure provides a method for synthesis of metal nanoparticles comprising reacting a precursor that is capable of being reduced to metal nanoparticles with a solid-state reducing agent capable of reducing the precursor and producing metal nanoparticles and controlling the size or surface plasmon resonance of metal nanoparticles produced.
[00011] In one aspect the present disclosure provides a method for synthesis of metal nanoparticles comprising, reacting a solution comprising a precursor that is capable of being reduced to metal nanoparticles, with tin in a solid-state capable of reducing the precursor to metal nanoparticles.
[00012] In one aspect the present disclosure provides a method for synthesis of metal nanoparticles, in which method comprises: reacting a solution comprising a precursor that is capable of being reduced to a metal nanoparticles, with tin metal in a solid-state capable of reducing the precursor to metal nanoparticles, the reaction being carried out for a specific duration for producing metal nanoparticles with controllable size.
[00013] In one aspect the present disclosure provides a method for synthesis of metal nanoparticles, in which method comprises: reacting a solution comprising a precursor that is capable of being reduced to a metal nanoparticles, with tin metal in a solid-state capable of reducing the precursor to metal nanoparticles; and applying a voltage or alternate current waveforms or frequencies for producing metal nanoparticles with desired surface plasmon resonance.
[00014] In one aspect the present disclosure provides a method for synthesis of metal nanoparticles, in which method comprises: reacting a solution comprising a precursor that is capable of being reduced to a metalnanoparticles, with tin metal in a solid-state capable of reducing the precursor to metal nanoparticles; applying a voltage optionally with one or more of an alternate current waveforms and frequencies; and allowing the reaction to be carried out for specific duration for producing metal nanoparticles with controllable size or surface plasmon resonance or both.
[00015] In another aspect the present disclosure provides a system for carrying out method for synthesis of metal nanoparticles with desired size or surface plasmon resonance in a controlled manner.
[00016] In an aspect the present disclosure provides a system for synthesizingnano particles with tin metal solid-state reducing agent, the system (100) comprises a medium in the form of a solution (106) of precursor that is capable of being reduced to metal nanoparticles; a pair of electrodes including a first electrode (102) and a second electrode (104)made from jumper wires with bare copper wires coated with tin metal on the fringe to act as solid-state reducing agent; the electrodes at least partially surrounded by or inserted into the solution of precursor; each of the electrodes connected individually to a charging circuit (108) including portable oscilloscopes and waveform generator for generating in controlled manner and monitoring various signals, their intensities and duration using waveform generator pin W1; and ground ranging from 0V to 5Vmfor producing metal nanoparticles with desired size or SPR in controllable manner.
[00017] In one aspect the present disclosure provides a hand held prototype system (101) for synthesizing nanoparticles with tin metal solid-state reducing agent, the system (101) comprises a medium in the form of a solution (106) of precursor that is capable of being reduced; a pair of electrodes including a first electrode (102) and a second electrode (104), made from jumper wires with bare copper wires coated with tin metal on the fringe acting as solid-state reducing agent; the electrodes being at least partially surrounded by or inserted into the solution of precursor; a circuitry (110) captively connected to each of the electrodes by a switch for supplying pulse of direct current at a voltage selected from 50mV to about 5V for producing metal nanoparticles with SPR in tunable manner.
[00018] These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[00019] The following drawings form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[00020] Figure 1: A) shows change in colour of reaction solution before and after performing the method of synthesis as per Example 1confirming the formation of silver nanoparticles and gold nanoparticlesafter exposing corresponding salt solutions to reducing agent tin metal in solid state; B) is UV-VISabsorbance graph exhibiting SPR peaks at 412 nm and 536 nm respectively of silver and gold nanoparticles synthesized as per Example 1.
[00021] Figure 2: A) shows colour of reaction solution before and after performing the method of synthesis as per Example 1A, change in colour of reaction solution confirms formation of silvernanoparticles with tin metal as reducing agent in solid state, as against no change in colourdue to no formation of nanoparticles of control and reaction solutions exposed to comparative copper and leadmetal granules respectively; B) is UV-VISabsorbance graph exhibiting SPR peaks at 416 nm and 412 nm respectively of silver nanoparticles synthesized as per Example1A and Example 2 by subjecting salt solution to tin metal reducing agent in solid state and additionally applying voltage of 100 mv.
[00022] Figure 3: Represents an X-Ray Diffraction (XRD) graph exhibiting peaks corresponding to (111), (200), (220) and (311) phase of gold and silver nanoparticles synthesized as per Example 1.
[00023] Figure 4: Shows high-resolution transmission electron microscopy (HRTEM), transmission electron microscopy (TEM), high-angle annular dark-field (HAADF), and selected area (electron) diffraction (SAED)images of silver nanoparticles synthesized as per Example 1. Figs. A) shows HRTEM image taken at 5 nm scale, B) shows TEM image at 50 nm scale exhibiting spherical silver nanoparticles, C) shows HAADF image taken at 50 nm scale and D) SAED pattern of the silver nanoparticles.
[00024] Figure 5: Shows HRTEM, TEM, HAADF, and SAED images of gold nanoparticles synthesized as per Example 1. Figs. A) shows HRTEM image taken at 2 nm scale, B) shows HRTEM image at 5 nm scale exhibiting spherical silver nanoparticles, C) shows TEM image taken at 50 nm scale exhibiting gold spherical nanoparticles and D) SAED pattern of the gold nanoparticles.
[00025] Figure 6: Shows a UV-VIS absorbance graph exhibiting varying SPR peaks of silver nanoparticles synthesized as per Example 2 with different areas of tin metal granule acting as reducing agent in solid state.
[00026] Figure 7: Shows a UV-VIS absorbance graph exhibiting different SPR peaks of silver nanoparticles synthesized at varying duration of reaction time as per Example 3.
[00027] Figure 8: Show TEM images of silver nanoparticles synthesized as per Example 3. A) shows bigger dendrite like nanoparticles produced in 20-30 seconds, B) showing spherical nanoparticles produced in 2 minutes and C) smaller nanoparticles produced in 5 minutes.
[00028] Figure 9: Shows an X-ray photoelectron spectroscopy (XPS) spectra of tin metal surface showing binding energy peak indicated as 3d. Figs A) shows before, B) shows after exposure to silver nitrate and C) shows after exposure to auric chloride while carrying out reaction as per Example 1.
[00029] Figure 10: Shows an XPS spectra of tin metal surface showing binding energy peaks: A) 3d corresponding to Ag after exposure to silver nitrate, C) 4f corresponding to Au after exposure to auric chloride, and B) – C) no binding energy peaks corresponding to N and Cl, signifying their absence while carrying out reation as per Example 1.
[00030] Figure 11: A) Shows a representative portable oscilloscope-based system for carrying out metal nanoparticle synthesis in accordance with one of the exemplary embodiments of the present disclosure. B) It is a line diagram of the representative portable oscilloscope-based system for carrying out metal nanoparticle synthesis with reference numerals.
[00031] Figure 12: Shows a UV-VISabsorbance graph exhibiting shift in SPR peaks of silver nanoparticles synthesized as per Example 4 after exposing precursor silver nitrate solution (5 ml) to tin metal granule acting as reducing agent (area 670 mm2) for different time durations with and without voltage discharge. A steady increase in the absorbance of the SPR is observed for synthesis with voltage of 1V, which is not seen in synthesis without voltage.
[00032] Figure 13: A) Shows change in colour of reaction solutions after performing the method of synthesis of gold nanoparticles as per Example 5 by subjecting chloroauric acid dissolved in water to different direct current (DC) voltage for 20 min through tin metal electrode acting as reducing agent in solid state; B) is UV-VISabsorbance graph exhibiting SPR peaks at about 540 nm of the synthesized gold nanoparticles.
[00033] Figure 14: A) Shows change in colour of reaction solutions after performing the method of synthesis of gold nanoparticles as per Example 6 by subjecting chloroauric acid dissolved in water to direct current (DC) voltage of 1V for 20 min through tin metal electrode acting as reducing agent in solid state, and different frequencies for 20 min through tin metal as electrode; B) is UV-VISabsorbance graph exhibiting SPR peaks at about 534 nm of the synthesized gold nanoparticles.
[00034] Figure 15: A) Shows change in colour of reaction solutions after performing the method of synthesis of gold nanoparticles as per Example 7 by subjecting chloroauric acid dissolved water to direct current (DC) voltage of 1V for 20 min through tin metal electrode acting as reducing agent in solid state and different waveforms; B) is UV-VISabsorbance graph exhibiting SPR peaks at about 546 nm of the synthesized gold nanoparticles.
[00035] Figure 16: A) Shows change in colour of reaction solutions after performing the method of synthesis of silver nanoparticles as per Example 8 by subjecting silver nitrate dissolved in water to different DC voltage for 30 min through tin metal electrode acting as reducing agent in solid state; B) is UV-VISabsorbance graph exhibiting SPR peaks at about 412 nm of the synthesized silver nanoparticles.
[00036] Figure 17: A) It represents an illustrative handheld prototype of system for synthesizing metal nanoparticles comprising a tin metal electrode as a solid-state reducing agent removably connected to a power source for applying DC voltage. B) It is a line diagram of the illustrative handheld prototype of systemfor synthesizing metal nanoparticles with reference numerals.
[00037] Figure 18: Shows a is UV-VISabsorbance graph exhibiting SPR peak of almost the same wavelength of silver nanoparticles produced separately at constant reaction time of 2 and 10 minutes with the tin metal reducing agent in solid state confirming reusability of tin metal reducing agent.
[00038] Figure 19: It is a schematic representation of the plausible reducing reaction involved in the synthesis of metal nanoparticles carried out in accordance with the present disclosure by reacting corresponding precursor salt solution with tin metal solid-state reducing agent.
DETAILED DESCRIPTION OF THE INVENTION
[00039] Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and modifications. The disclosure also includes all such steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any or more of such steps or features.
[00040] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[00041] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[00042] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[00043] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[00044] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.
[00045] All methods described herein can be performed in suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[00046] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[00047] Various terms are used herein. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[00048] The present disclosure relates to a method for synthesis of metal nanoparticles with desired size or surface plasmon resonance in controlled manner.
[00049] In one embodiment the present disclosure provides a method for synthesis of metal nanoparticles comprising: reacting a precursor that is capable of being reduced to metal nanoparticles, with a solid-state reducing agent which also controls the size or surface plasmon resonance of metal nanoparticles produced. It has been unexpectedly found that the tin in a solid-state is capable of reducing the precursor and exposure of the precursor to a tin plate or an electrode comprising tin in solid-state, reduces the precursor producing metal nanoparticles. However, other metals like copper, aluminum and lead failed to act as reducing agent to form nanoparticles of metals like silver and gold. The tin metal being in the solid-sate can be reused repeatedly for reducing precursor and forming nanoparticles. Unlike using tin salt in a liquid form as a reducing agent for non-aqueous synthesis of metal nanoparticles where the reducing agent is lost during synthesis reaction. However, in accordance with the present disclosure, the tin metal in solid-state as a reducing agent can be reused for aqueous controlled synthesis of metal nanoparticles.
[00050] In one embodiment the present disclosure provides a method for synthesis of metal nanoparticles comprising reacting a solution comprising a precursor that is capable of being reduced to metalnanoparticles with tin metal in a solid-state capable of reducing the precursor to metal nanoparticles.
[00051] The nanoparticles can be of a metal preferably a transition metal for example selected from the group consisting of a gold, silver, copper, nickel, cobalt, palladium, platinum, iridium, osmium, rhodium, ruthenium, rhenium, vanadium, chromium, manganese, niobium, molybdenum, tungsten, tantalum, iron and cadmium.
[00052] In one embodiment, the metal suitable for forming nanoparticles are preferably gold and silver.
[00053] In one embodiment the precursor can be an inorganic or organic acid or a salt thereof.
[00054] In preferred embodiment the precursor is an inorganic acid or salt thereof.
[00055] In one embodiment the precursor for forming nanoparticles of silver comprises at least one selected from but not limiting to silver nitrate, silver acetate, silver trifluoroacetate, silver oxide, silver chloride or the like.
[00056] In one embodiment the precursor for forming nanoparticles of gold comprises chloroauric acid or auric chloride or the like.
[00057] In one embodiment the present disclosure provides a method for synthesis of metal nanoparticles, in which method comprises: reacting a solution comprising a precursor that is capable of being reduced to a metalnanoparticles, with tin metal in a solid-state capable of reducing the precursor to metal nanoparticles, the reaction being carried out for a specific duration for producing metal nanoparticles with controllable size. This has been again a surprising finding that that reduction or increase in the size of metal nanoparticles can be tuned by changing the synthesis reaction time without changing any other parameters.
[00058] In an embodiment the method for synthesis of metal nanoparticles comprises reacting a solution comprising a precursor with the tin metal can be carried out for about 10 seconds to about 30 minutes, preferably from 30 seconds to 10 minutes.
[00059] The metal nanoparticles produced in accordance with the present disclosure can be of size ranging from about 50 nm to about 5 nm, preferably from 20 nm to about 7 nm.
[00060] In one embodiment the precursor is exposed to the tin metal reducing agent in solid-state of varying surface area to obtain metal nanoparticles with different surface plasmon resonance. For enhanced formation of metal nanoparticles with blue shift in SPR peak, the precursor solution is exposed to tin metal reducing agent with increased surface area.
[00061] In another embodiment the present disclosure provides a method for synthesis of metal nanoparticles with varying surface plasmon resonance, in which method comprises: reacting a solution comprising a precursor that is capable of being reduced to metalnanoparticles, with tin metal in a solid-state capable of reducing theprecursor to metal nanoparticles; and applying a specific voltage or alternate current waveform or frequency for producing metal nanoparticles with varyingsurface plasmon resonance.
[00062] In an embodiment the metal nanoparticles with shift in surface plasmon resonance can be obtained by applying direct current with specific voltage while contacting the precursor to the tin metal solid-state reducing agent. The direct current with 50mV to 5 V voltage may be applied for obtaining metal nanoparticles with desired shift in surface plasmon resonance. In an embodiment, the direct current with voltage to be applied can be selected from 50 mV, 100mV, 500 mV, 1V, 2V, 3V, 4V, 5V or more.
[00063] In an embodiment the metal nanoparticles with shift in surface plasmon resonance can be obtained by applying a specific frequency while contacting the precursor with the tin metal solid-state reducing agent. The frequencies thatmay be applied for obtaining metal nanoparticles with desired shift in surface plasmon resonance may range from about 1 kHz to about 1 MHz. In an embodiment, the frequency to be applied can be selected from 1kHz, 10 kHz, 100 kHz, 1 MHz, or more.
[00064] In an embodiment the metal nanoparticles with shift in surface plasmon resonance can be obtained by applying specific alternate current wave form while contacting the precursor to the tin metal solid-state reducing agent. The alternate current with waveform that may be applied for obtaining metal nanoparticles with desired shift in surface plasmon resonance may be selected from a sinusoidal waveform, square waveform, triangle waveform, or trapezoidal waveform.
[00065] In one embodiment the present disclosure provides a method for synthesis of metal nanoparticles, in which method comprises: reacting a solution comprising a precursor that is capable of being reduced to metalnanoparticles, with tin metal in a solid-state capable of reducing the precursor to metal nanoparticles; applying a voltage in combination with one or more of an alternate current waveform or frequency; and allowing the reaction to be carried out for specific duration for producing metal nanoparticles with varying surface plasmon resonance.
[00066] In another embodiment the present disclosure provides one or more system(s)configured for carrying out method for synthesis of metal nanoparticles with desired size or surface plasmon resonance in a controlled manner.
[00067] Referring to Figure 11, Fig. 11A) is a representative portable oscilloscope-based system for carrying out metal nanoparticle synthesis in accordance with one of the exemplary embodiments of the present disclosure and Fig. 11B) is a line diagram of the representative portable oscilloscope-based system for carrying out metal nanoparticle synthesis with reference numerals. Referring to the same, the system (100) is configured to synthesize nanoparticles with tin metal solid-state reducing agent, the system (100) comprises a medium in the form of a solution (106) of precursor that is capable of being reduced; a pair of electrodes including a first electrode (102) and a second electrode (104) made from jumper wires with bare copper wires coated with tin metal on the fringe to act as solid-state reducing agent; each of the electrodes at least partially surrounded by or inserted into the solution of precursor; each of the electrodes connected individually to a charging circuit (108) including portable oscilloscopes and waveform generator for generating in controlled manner and monitoring various signals, their intensities and duration using waveform generator pin W1; and ground ranging from 0V to 5Vfor producing metal nanoparticles with desired size or SPR in controllable manner.
[00068] Referring to Figure 17, Fig. 17A) represents an illustrative handheld prototype of system for synthesizing metal nanoparticles comprising a tin metal electrode as a solid-state reducing agent removably connected to a power source for applying DC voltage and Fig. 17B) is a line diagram of the illustrative handheld prototype of system for synthesizing metal nanoparticles with reference numerals. Referring to the same, a held system (101) is configured to synthesize nanoparticles with tin metal solid-state reducing agent, the system (101) comprises a medium in the form of a solution (106) of precursor that is capable of being reduced; a pair of electrodes including a first electrode (102) and a second electrode (104), made from jumper wires with bare copper wires coated with tin metal on the fringe acting as solid-state reducing agent; the electrodes at least partially surrounded by or inserted into the solution of precursor; a circuitry (110) captively connected to each of the electrodes by a switch for supplying pulse of direct current at a specific voltage selected from 50mV to about 5V for producing metal nanoparticles with SPR in tunable manner.
[00069] Referring to Figure 19 there is provided a plausible reducing reaction involved in the synthesis of metal nanoparticles carried out in accordance with the present disclosure by reacting corresponding precursor salt solution with tin metal solid-state reducing agent. The Figure 19 depicts that when the solution of precursor is exposed to a tin metal in a solid-state, the tin metal reacts vigorously with precursor solution with high reducing potential and thereby acts as a solid-state reducing agent causing formation of respective metal nanoparticles. The tin metal being in a solid-state can be used several times as a reducing agent without any significant loss of the metal during each synthesis reaction thereby rendering the method economical.
[00070] Although the subject matter has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible.
ADVANTAGES OF THE PRESENT INVENTION
[00071] The present disclosure provides a simple and rapid method for synthesis of metalnano particles with desired size or surface plasmon resonance in a controlled manner.
[00072] The method of the present disclosure for aqueous controlled synthesis of metal nanoparticles is economical since the reducing agent tin metal being in a solid-state can be reused several times without any significant loss of the metal during each synthesis reaction.
[00073] The present disclosure provides a method for synthesizing metal nanoparticles with desired size in controlled manner, wherein the reduction or increase in the size of metal nanoparticles can be achieved by changing the synthesis reaction time without changing any other parameters.
[00074] The present disclosure provides a tunable method for synthesizing metal nanoparticles with desired size and surface plasmon resonance by simply applying specific voltage, frequency, AC waveform signal or combination thereof while carrying out the reaction of the precursor and tin metal in solid-state.
[00075] The method of the present disclosure as such avoids reaction to be carried out at a very high temperatures, for very lengthy period, or hazardous chemicals, thus rendering the method efficient as well as environment friendly.
[00076] The present disclosure provides a system with much simpler configuration for synthesizing metal nanoparticles with desired size in a controlled manner, wherein the system is configured to expose the solution of precursor to the electrode devise comprising tin metal as a solid-state reducing agent along with the usage of voltage or frequency.
[00077] The present disclosure satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.
[00078] The disclosure will now be illustrated with working examples, which is intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices and materials are described herein. It is to be understood that this disclosure is not limited to particular methods, and experimental conditions described, as such methods and conditions may vary.
Example 1
Synthesis of silver nanoparticles and gold nanoparticles with tin metal reducing agent
[00079] Tin metal granule(0.4 g with surface area of 670 mm2) was dipped into aqueous precursor solutions of silver nitrate and auric chloride of 5 mM concentration. Silver and gold nanoparticles formation was observed by the color change from transparent to a yellowish color indicating the formation of silver nanoparticles and also color change from transparent to red wine color or purplish color indicating the formation of gold nanoparticles respectively as can be seen from (Figure 1A). Further, a UV Vis absorbance spectroscopy scan was taken using a 96 well plate from 300 nm to 800 nm using TECAN 200 Infinity Plate reader. As can be seen from the UV-VISabsorbance graph (Figure 1B) the narrow peak of Surface Plasmon Resonance (SPR) at 412 nm and 536 nm confirms formation of silver and gold nanoparticles respectively.
[00080] Formation of silver and gold nanoparticles were further confirmed by X-Ray Diffraction. An X-Ray Diffraction (XRD) graph exhibiting peaks corresponding to (111), (200), (220) and (311) phase of gold and silver confirms formation of respective nanoparticles (Figure 3).
[00081] Additionally, Transmission Electron Microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field (HAADF), and selected area (electron) diffraction (SAED) analysis/imaging were carried out of silver and gold nanoparticles. Figures 4- A) shows HRTEM image taken at 5 nm scale, B) shows TEM image at 50 nm scale exhibiting spherical silver nanoparticles, C) shows HAADF image taken at 50 nm scale, and D) SAED pattern of the silver nanoparticles.Figures5 - A) shows HRTEM image taken at 2 nm scale, B) shows HRTEM image at 5 nm scale exhibiting spherical silver nanoparticles, C) shows TEM image taken at 50 nm scale exhibiting gold spherical nanoparticles, and D) SAED pattern of the gold nanoparticles.
[00082] X-Ray Photoelectron Spectroscopy studies (XPS) was also done on the surface of the tin metal solid-state reducing agent beforeand after synthesis. Peaks at 493.4 eV and 485 eV corresponding to SnO before the synthesis of silver and gold nanoparticles respectively (Figure 9A), and no such peaks after exposure to silver nitrate (Figures 9B) and after exposure to auric chloride (Figure 9C) confirms absence of SnO after synthesis of silver and gold nanoparticles. Similarly, peak 3dcorresponding to Ag after exposure to silver nitrate(Figure 9A) (Figures 9B-9C) presence of tin in the same state confirms that tin metal can be used again for such synthesis.
[00083] Also, XPS spectra of Ag 3d, Au 4f, N and Cl were carried out. Figure 10 is an XPS spectra of tin metal surface showingbinding energy peaks: A) 3d corresponding to Ag after exposure to silver nitrate, C) 4f corresponding to Au after exposure to auric chloride, and B) – C) no binding energy peaks corresponding to N and Cl, signifying their absence after carrying out the synthesis.
Example 1A
Comparative Example with exposure of silver precursor to tin, copper and lead plates
[00084] Tin, copper, aluminum and lead metal granules (individually 0.4 g with surface area of 670 mm2) were dipped separately into aqueous precursor solutions of silver nitrate of 5 mM concentration. Similarly, copper, aluminum and lead metal granules metal (0.4 g with surface area of 670 mm2) were dipped into aqueous precursor solutions of silver nitrate of 5 mM concentration. In control sample no plate was inserted. Change in colour of reaction solutions before and after performing the method of synthesis was observed. As can be seen from Figure 2A, change in colour of reaction solution exposed to tin metal granuleconfirms formation of silver nanoparticles and that the tin metal in sold-state is capable of acting as reducing agent, whereas, no change in colour of control and reaction solutions exposed to copper and lead metal granules respectively confirm that no nanoparticles were formed as such metals do not act as reducing agent. The same is also confirmed from UV-VIS absorbance graph showing peak at 416 confirming formation of nanoparticles as against no peak formation with control and use of copper and lead metal granules (Figure 2B).
Example 2
Synthesis of silver nanoparticles with tin metal reducing agent and application of voltage
[00085] In set-I, tin metal granule(0.4 g with surface area of 670 mm2) was dipped into aqueous precursor solution of silver nitrate of 5 mM concentration. In set-II, tin metal (0.4 g with surface area of 670 mm2) was dipped into aqueous precursor solution of silver nitrate of 5 mM concentration and direct current of 100 mV voltage was applied. UV Vis absorbance spectroscopy scan was taken using a 96 well plate from 300 nm to 800 nm using TECAN 200 Infinity Plate reader. As can be seen from the UV-VISabsorbance graph (Figure 2B) a Surface Plasmon Resonance (SPR) peak at 412 nm was observed for nanoparticles synthesized as per set-I without applying the voltage as against SPR peak at 416 for nanoparticles synthesized as per set-II carried out with application of 100 mV voltage, thus confirming that by applying specific voltage it is possible to synthesize metal nanoparticles with desired SPR.
Example 3
Synthesis of silver nanoparticles with tin metal reducing agent with different surface areas
[00086] Tin metal granules of different surface areas 17.5 mm2, 42.5 mm2, 167.9 mm2, 418.7 mm2, were dipped separately into aqueous precursor solution of silver nitrate of 5 mM concentration. In control sample no plate was inserted. UV Vis absorbance spectroscopy scan was taken using a 96 well plate from 300 nm to 800 nm using TECAN 200 Infinity Plate reader. As can be seen from the UV-VISabsorbance graph (Figure 6) in absence of SPR peak for samples with 17.5 mm2, 42.5 mm2 tin metal granules, such lower surface area is not desirable for producing silver nanoparticles, whereas SPR peaksat 412 nm and 416 nm respectively for tin metal granules with surface areas of 167.9 mm2, 418.7 mm2,it can be inferred that tin metal with surface area higher than 165 mm2 is effective in synthesizing metal nanoparticles with desired SPR.
Example 4
Synthesis of silver nanoparticles with tin metal reducing agent and varying time of exposure
[00087] Tin metal granule (0.4 g with surface area of 670 mm2) was dipped into aqueous precursor solution of silver nitrate of 5 mM concentration(500 µl) for different duration of time at 15 seconds, 30 seconds, 60 seconds, 120 seconds, 180 seconds, 300 seconds, and 600 seconds. AUV Vis absorbance spectroscopy scan was taken using a 96 well plate from 300 nm to 800 nm using TECAN 200 Infinity Plate reader. As can be seen from the UV-VISabsorbance graph (Figure 7) a blue shift is observed from 420 nm to 410 nm with increasing time exposure of the precursor to tin metal.
[00088] Additionally, a Transmission Electron Microscopy (TEM) was carried out of the nanoparticles synthesized with each of the time period of exposure of tin metal to silver nitrate. As can be seen from Figure 8, size variation was observed of silver nanoparticles synthesized after exposing tin metal to silver nitrate in different timescale. A) Bigger dendrite like structures was observed at 20-30 seconds, B) spherical nanoparticles of about 15 nm to 20 nm were observed at 120 seconds and C) smaller nanoparticles of about 7 nm to about 9 nm size were observed at 300 seconds. This confirms that desired size metal nanoparticles can be synthesized by exposing the precursor to tin metal reducing agent at specific time duration.
Example 5
Synthesis of silver nanoparticles with tin metal reducing agent while varying time of exposure with and without applying voltage
[00089] In one set, synthesis of silver nanoparticles was carried out by dipping tin metal granule(0.4 g with surface area of 670 mm2) separately into aqueous precursor solution of silver nitrate of 5 mM concentration(5 ml) for different duration of time at 1 min, 3 mins, 5 mins, 10 mins, and 20 mins. In another set, the same was repeated except that during the synthesis direct current with voltage of 1V was applied to each of the reaction samples. AUV-VIS absorbance spectroscopy scan was taken using a 96 well plate from 300 nm to 800 nm using TECAN 200 Infinity Plate reader. As can be seen from the UV-VISabsorbance graph (Figure 12) a steady increase in the absorbance of the SPR is observed for synthesis with application of voltage which is not observed in synthesis without application of voltage. This proves that it is possible to synthesize metal particles with varying SPR by varying time of exposure of precursor to tin metal reducing agent, and significant shift in SPR at the same time can be obtained by applying direct current of specific voltage.
Example 6
Synthesis of gold nanoparticles with tin metal reducing agent while applying varied voltage
[00090] Gold nanoparticles were synthesized by separately dipping tin metal granule(0.4 g with surface area of 670 mm2) into separate aqueous precursor solution of auric chloride of 5 mM concentration(500 µl) and to each of the solutions, direct current with specific voltage at 50 mV, 100 mV, 500 V, 1V, 2V, 3V, 4V, and 5Vwas applied. In control sample no voltage was applied. As can be seen from Figure 13A, application of voltage increased the formation of gold nanoparticles. AUV-VIS absorbance spectroscopy scan was taken using a 96 well plate from 300 nm to 800 nm using TECAN 200 Infinity Plate reader. As can be seen from the UV-VISabsorbance graph (Figure 13B) shift in SPR was observed for different voltage applied as compared to 540 nm at 1V voltage. This proves that gold nanoparticles with desired SPR can be synthesized by applying different voltage.
Example 7
Synthesis of gold nanoparticles with tin metal reducing agent while applying varying frequency
[00091] Gold nanoparticles were synthesized by separately dipping tin metal granule(0.4 g with surface area of 670 mm2) into separate aqueous precursor solution of auric chloride of 5 mM concentration(500 µl) and each of the solutions was subjected to specific frequency of 1kHz, 10 kHz, 100 kHz, and 1 MHz. As can be seen from Figure 14A, application of frequency increased the formation of gold nanoparticles. AUV-VIS absorbance spectroscopy scan was taken using a 96 well plate from 300 nm to 800 nm using TECAN 200 Infinity Plate reader. As can be seen from the UV-VISabsorbance graph (Figure 14B) shift in SPR was observed for different frequency applied as compared to 534 nm at frequency of 10 kHz. This proves that gold nanoparticles with desired SPR can be synthesized by applying different frequency.
Example 8
Synthesis of gold nanoparticles with tin metal reducing agent while applying different waveforms
[00092] Gold nanoparticles were synthesized by separately dipping tin metal granule(0.4 g with surface area of 670 mm2) into separate aqueous precursor solution of auric chloride of 5 mM concentration(500 µl) and to each of the solutions,different waveform was applied such as sinusoidal, square, triangle, and trapezoidal. As can be seen from Figure 15A, application of specific waveform increased the formation of gold nanoparticles. AUV-VIS absorbance spectroscopy scan was taken using a 96 well plate from 300 nm to 800 nm using TECAN 200 Infinity Plate reader. As can be seen from the UV-VISabsorbance graph (Figure 15B) shift in SPR was observed for different waveforms applied as compared to 546 nm at sinusoidal waveform. This proves that gold nanoparticles with desired SPR can be synthesized by applying different waveforms.
Example 9
Synthesis of silver nanoparticles with tin metal reducing agent while applying varied voltage
[00093] Silver nanoparticles were synthesized by separately dipping tin metal granule(0.4 g with surface area of 670 mm2) into separate aqueous precursor solution of silver nitrate of 5 mM concentration(500 µl) and to each of the solutions direct current with specific voltage at 50 mV, 100 mV, 500 V, and 1V was applied. In control sample no voltage was applied. As can be seen from Figure 16A, application of voltage increased the formation of silver nanoparticles. AUV-VIS absorbance spectroscopy scan was taken using a 96 well plate from 300 nm to 800 nm using TECAN 200 Infinity Plate reader. As can be seen from the UV-VISabsorbance graph (Figure 16B) shift in SPR was observed for different voltage applied as compared to 412 nm at 50 mV voltage. This proves that silver nanoparticles with desired SPR can be synthesized by applying different voltage.
Example 10
Reusability studies of tin metal as solid state reducing agent for producing silver nanoparticles
[00094] In one set, synthesis of silver nanoparticles was carried out by dipping tin metal granule(0.4 g with surface area of 670 mm2)into aqueous precursor solution of silver nitrate of 5 mM concentration(5 ml) for duration of 2 minutes. In another set the same process was repeated using the same tin metal granule for duration of 10 minutes. AUV-VIS absorbance spectroscopy scan was taken using a 96 well plate from 300 nm to 800 nm using TECAN 200 Infinity Plate reader. As can be seen from the UV-VISabsorbance graph (Figure 18) silver nanoparticles produced exhibitSPR peak of similar wavelengths in reaction time of 2 and 10 min using the same tin metal granule in two separate sets. This proves reusability of the tin metal to reduce the precursor and produce respective metal nanoparticles when used repeatedly.
[00095] From the foregoing, it will be appreciated that, although specific embodiments of the invention have been described herein merely for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention and should not be construed so as to limit the scope of the invention or the appended claims in any way.