Patent Description:
Several methods for producing silver nanowires have been proposed previously.

Document <CIT>discloses a process for producing silver nanoparticles consisting of a silver nitrate reaction with polyvinylpyrrolidone (PVP) in the presence of ethylene glycol. Depending on the reaction conditions different morphology and dimensions, namely silver nanowires, can be obtained.

Document <CIT> discloses the synthesis of silver nanowires using polyquaterniums and silver salts.

Document <CIT> discloses silver nanowires produced by mixing and heating (polyol method) a silver salt precursor, a reducing solvent (a reduction agent), and capping agent such as vinylpyrrolidone-co-vinylimidazole copolymers (PIC) instead of PVP.

Document <CIT> discloses a method for producing silver nanowires, in an alcohol solvent having dissolved therein a silver compound, a chloride, a bromide, an alkali metal hydroxide, an aluminium salt and an organic protective agent.

Document <CIT> discloses a metal aerogel includes a plurality of metal nanowires formed into a porous three-dimensional structure where pores in the structure are anisotropic, however there is no mention of using perylene bisimide in the synthesis, using PVP instead.

Document <CIT> discloses a method of forming monodispersed metal nanowires from silver nitrate, no mention is made to using perylene bisimide in the method.

Document <CIT> discloses a method for manufacturing a functional polymer nanofiber composite and a method for manufacturing a functional substrate using the same. No mention is made to using perylene bisimide in the method.

The present invention relates to a method for producing silver nanowires according to claim <NUM>.

In one embodiment the silver metal salt is selected from silver nitrate or silver acetate.

In one embodiment a carbon-based material is added to the mixture in a ratio of perylene bisimide of formula (<NUM>), silver metal salt and carbon-based material in a <NUM>:<NUM>:<NUM> to <NUM>:<NUM>:<NUM> mass ratio.

In one embodiment the carbon-based material is selected from carbon nanotubes, multi-walled carbon nanotubes, single wall carbon nanotube, carbon nanofibers and graphene nanoplatelets.

In one embodiment the solvent is selected from ethylene glycol, or a mixture of dimethylformamide and water.

In one embodiment ethylene glycol is added in a variable amount maintaining the concentration of silver metal salt between <NUM>/ml to <NUM>/ml.

In one embodiment a mixture of dimethylformamide and water in a ratio of <NUM>:<NUM> to <NUM>:<NUM> is added in a variable amount, maintaining the concentration of silver metal salt between <NUM>/ml to <NUM>/ml.

In one embodiment the resulting precipitate is washed with ethanol and dried at a temperature between <NUM> and <NUM> to obtain dried silver nanowires.

In one embodiment the mixture is sonicated before heating when ethylene glycol is used as solvent.

In one embodiment, when a mixture of dimethylformamide and water is used as solvent, two additional aliquots of the initial amount of water are added every two hours to the mixture under heat.

The present invention relates to a method for producing silver nanowires, through reduction and silver precipitation in the form of wire in a solvent having dissolved therein a silver compound and a perylene bisimide (PBI) of formula (<NUM>).

Depending on the solvent and reducing agent used, silver nanowires with different shapes are obtained. Furthermore, this invention also relates to the synthesis of silver nanowires in situ on carbon-based materials, such as carbon nanotubes (CNT).

The present invention proposes to solve the problems in the field and provide a simple method for the production of silver nanowires with industrial potential to be used as conductive filler in fields of application, such as conductive adhesives and conductive inks for electronic applications.

According to the invention, short and long silver nanowires can be stably produced with high yields. Silver nanowires can be advantageous for different applications, such as production of conductive adhesives or conductive inks. The simplicity of the production methods herein presented may allow industrialization at very competitive costs.

Furthermore, the use of perylene bisimides of formula (<NUM>) coordinated with silver salts enables the synthesis of silver nanowires with high yields using dimethylformamide/water (DMF/H<NUM>O) or ethylene glycol (EG) as solvent and reducing agent, with no need to use high molecular weight protective agents, such as PVP.

For easier understanding of this application, figures are attached in the annex that represent the preferred forms of implementation which nevertheless are not intended to limit the technique disclosed herein.

Now, preferred embodiments of the present application will be described in detail with reference to the annexed drawings. However, they are not intended to limit the scope of this application.

The method for producing silver nanowires comprises the following steps:.

The silver nanowires of the present invention can also be produced in the presence of cabon-based materials, following the same method.

The method for producing silver nanowires on carbon-based materials comprises the following steps:.

In one embodiment, the silver metal salt is selected from silver nitrate or silver acetate.

In one embodiment the solvent is selected from ethylene glycol in a variable amount maintaining the concentration of silver metal salt between <NUM>/ml to <NUM>/ml, or a mixture of dimethylformamide and water in a ratio of <NUM>:<NUM> to <NUM>:<NUM>, in a variable amount, maintaining the concentration of silver metal salt between <NUM>/ml to <NUM>/ml.

In the present method the solvent acts as a reducing agent.

The synthesis of silver nanowires was carried out in the presence of PBI of formula (<NUM>) coordinated with the silver ion that is reduced in the presence of ethylene glycol or dimethylformamide/water.

In one embodiment the mixture is preferably heated at <NUM>.

In one embodiment the resulting precipitate obtained is washed with ethanol and dried at a temperature between <NUM> and <NUM>, preferably <NUM>, to obtain dried silver nanowires.

In one embodiment the cabon-based materials are selected from, but not limited to, carbon nanotubes (CNT), multi-walled carbon nanotubes (MWCNTs), single wall carbon nanotube (SWCNTs), carbon nanofibers and graphene nanoplatelets.

The synthesis of PBI (<NUM>) resulted from the combination of the commercially available perylenetetracarboxilic dianhydride with <NUM>,<NUM>-diaminopentane (<FIG>) at <NUM>.

The possibility to prepare silver nanowires in the presence of carbon-based material, such as CNT was also demonstrated in Examples <NUM> and <NUM>; <FIG> and <FIG>.

Once again, the concentration of PBI showed to be determinant for the synthesis of silver nanowires. For reactions carried out in ethylene glycol the range of PBI concentration varied from <NUM>/mL to <NUM>/mL, the best results were obtained with <NUM>/mL (example <NUM>). In DMF/water the range of PBI concentration varied from <NUM>/mL to <NUM>/mL and the best results were obtained with <NUM>/mL (example <NUM>).

Parameters such as temperature and reaction time can influence the shape and growth of the silver nanoparticles. The synthesis of silver nanowires was performed in a temperature range from <NUM> to <NUM> and reaction time from <NUM> to <NUM>. The best results were obtained at <NUM> for <NUM>.

The morphology of the silver nanowires depends on the concentration of PBI (<NUM>). The studies showed that, depending on the solvent, different shapes of silver nanowires can be obtained.

In one embodiment, short silver nanowires can be obtained when DMF/H<NUM>O is used as solvent (Example <NUM>; <FIG>).

In another embodiment, long silver nanowires with a length up to <NUM> can be obtained when ethylene glycol is used as solvent (Example <NUM>; <FIG>).

Herein below, specific examples of the present invention will be presented. The examples described below are intended to facilitate the understanding of the present disclosure, however the present disclosure is not limited to these examples.

Approximately <NUM> equiv. (<NUM>) of <NUM>,<NUM>-diaminopentane (<NUM>) were added to <NUM> mmol (<NUM>) of perylenetetracarboxilic dianhydride (<NUM>) (as shown in scheme of <FIG>). The mixture was heated at <NUM> under magnetic stirring for approximately <NUM>. Distilled water was added to the mixture and the suspension was filtered and washed with additional water, ethanol and diethyl ether. The product (PBI) was finally dried under vacuum at <NUM> for <NUM> (reaction yield: <NUM> %).

In a <NUM> flask, <NUM> mmol (<NUM>) of AgNO<NUM>, <NUM> of dimethylformamide (DMF) and <NUM>µL of water were added to <NUM> mmol (<NUM>) of PBI (<NUM>), prepared according to the procedure described in comparative example <NUM>, and the mixture was maintained under magnetic stirring (<NUM> rpm) at a temperature between <NUM> and <NUM> for <NUM>. The reaction proceeded at <NUM> for <NUM> under magnetic stirring (<NUM> rpm) and two additional aliquots of water were added during the reaction time, one after <NUM> and the other after <NUM> of reaction. The solution was cooled to <NUM> during <NUM> and the precipitated solid was collected by filtration, washed with ethanol and dried at <NUM> under vacuum for <NUM>. Final weight: <NUM>; reaction yield <NUM> %. The material obtained was finally observed by scanning electron microscopy (<FIG>).

In a <NUM> flask, <NUM> mmol (<NUM>) of PBI (<NUM>) prepared according to the procedure described in comparative example <NUM> and <NUM> mmol (<NUM>) of AgNO3 were dissolved in <NUM> of EG under sonication in an ultra-sound bath at a temperature between <NUM> and <NUM> for <NUM>. After sonication, the reaction was carried out at <NUM> for <NUM> under magnetic stirring (<NUM> rpm). The solution was cooled to <NUM> during <NUM> and the precipitated solid was collected by filtration, washed with ethanol and dried at <NUM> under vacuum for <NUM>. Final weight: <NUM>; reaction yield: <NUM> %. The material obtained was finally observed by scanning electron microscopy (<FIG>).

In a <NUM> flask, <NUM> mmol of AgNO3 and <NUM> of CNTs (MWCNTs or SWCNTs) were combined with <NUM> mmol of PBI (<NUM>) prepared according to the procedure described in comparative example <NUM> and added to <NUM> of dimethylformamide with <NUM>µl of water. The mixture was maintained under magnetic stirring (<NUM> rpm) at a temperature between <NUM> and <NUM> for <NUM>. The reaction proceeded at <NUM> for <NUM> under magnetic stirring (<NUM> rpm). The solution was cooled to a temperature between <NUM> and <NUM> for <NUM> and the precipitated solid was collected by filtration, washed with ethanol, dried at <NUM> under vacuum for <NUM>. Final weight: <NUM> - <NUM>; reaction yield: <NUM> - <NUM> %. The material obtained was finally observed by scanning electron microscopy (<FIG>).

In a <NUM> flask, <NUM> mmol of PBI (<NUM>) prepared according to the procedure described in comparative example <NUM>, <NUM> mmol of AgNO<NUM> and <NUM> of CNTs (MWCNTs or SWCNTs) were dissolved/dispersed in <NUM> of EG under sonication in an ultra-sound bath at a temperature between <NUM> and <NUM> for <NUM>. After sonication, the reaction was carried out at <NUM> for <NUM> under magnetic stirring (<NUM> rpm). The solution was cooled to <NUM> during <NUM> and the precipitated solid was collected by filtration, washed with ethanol, dried at <NUM> under vacuum for <NUM>. Final weight: <NUM> - <NUM>; reaction yield: <NUM> - <NUM> %. The material obtained was finally observed by scanning electron microscopy (<FIG>).

The production of silver nanowires in the presence of carbon nanotubes was conducted in three main steps:.

A solution <NUM> of synthesized PBI (<NUM>; <NUM> mmol), in DMF (<NUM>) and another solution <NUM> of AgNO3, (<NUM>; <NUM> mmol; <NUM> equiv. ) in ethanol (<NUM>), were stirred for <NUM> at room temperature. Solution <NUM> was added to solution <NUM> and the resulting mixture was stirred at room temperature for <NUM> days. At the end of the reaction, diethyl ether and n-hexane (<NUM>:<NUM>) were added and the solid was filtered, washed with diethyl ether and n-hexane and dried for <NUM> at <NUM> under vacuum. Final weight of PBI-Ag: <NUM>.

A suspension <NUM> of functionalized SWCNTs (<NUM>) in <NUM> of DMF and a solution <NUM> with the PBI-Ag (<NUM>), in <NUM> of ethanol, were stirred for <NUM> between <NUM> and <NUM>. Solution <NUM> was added to suspension <NUM> and the resulting mixture was stirred at <NUM> to <NUM> for <NUM> day. At the end of the reaction diethyl ether and n-hexane (<NUM>:<NUM>), were added and the solid was filtered, washed with diethyl ether and n-hexane and dried, for <NUM> at <NUM> under vacuum. Final weight of PBI-Ag-SWCNTs: <NUM>.

To <NUM> of the solid collected from step <NUM> (PBI-Ag-SWCNTs) was added <NUM> of EG and <NUM> of AgNO3. The mixture was sonicated in an ultra-sound bath at a temperature between <NUM> and <NUM> for <NUM>. After sonication, the reaction was carried out at <NUM> for <NUM> under magnetic stirring (<NUM> rpm). The solution was cooled to <NUM> during <NUM> and the precipitated solid was collected by filtration, washed with ethanol and dried at <NUM> under vacuum. Final weight: <NUM>. The material obtained was finally observed by scanning electron microscopy (<FIG>).

Claim 1:
A method for producing silver nanowires comprising the following steps:
Heating and stirring a mixture of perylene bisimide of formula (<NUM>) and a silver metal salt in a <NUM>:<NUM> to <NUM>:<NUM> mass ratio, at a temperature between <NUM> and <NUM>, during <NUM> to <NUM>, in the presence of a solvent;
Cooling the solution between <NUM> and <NUM> for <NUM> to <NUM>;
Collecting and filtering the resulting precipitate to isolate the silver nanowires;
wherein formula (<NUM>) is
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