Method of making colloidal platinum nanoparticles

Abstract

Provided is a method of making colloidal platinum nanoparticles. The method includes three consecutive steps: dissolving platinum powders by a halogen-containing oxidizing agent in HCl to obtain an inorganic platinum solution containing an inorganic platinum compound; adding a reducing agent into the same reaction vessel to form a mixture solution and heating the mixture solution to undergo a reduction reaction and produce a composition containing platinum nanoparticles, residues and a gas, and guiding the gas out of the reaction vessel, wherein the amount of the residues is less than 15% by volume of the mixture solution; and adding a medium into the same reaction vessel to disperse the platinum nanoparticles to obtain colloidal platinum nanoparticles. The method is simple, safe, time-effective, cost-effective, and has the advantage of high yield.

Claims

1. A method of making colloidal platinum nanoparticles, comprising three consecutive steps: step (a): mixing and heating platinum powders and a hydrochloric acid aqueous solution containing a halogen-containing oxidizing agent in a reaction vessel to dissolve the platinum powders, so as to obtain an inorganic platinum solution, wherein the inorganic platinum solution contains an inorganic platinum compound comprising chloroplatinic acid, sodium chloroplatinate, potassium chloroplatinate, or ammonium chloroplatinate; step (b): adding a reducing agent into the inorganic platinum solution in the reaction vessel to form a mixture solution and heating the mixture solution to undergo a reduction reaction and produce a composition containing platinum nanoparticles, residues and a gas, and guiding the gas out of the reaction vessel, wherein an amount of the residues is less than 15% by volume of the mixture solution; and step (c): adding a medium into the reaction vessel to disperse the platinum nanoparticles, so as to obtain the colloidal platinum nanoparticles; wherein the consecutive steps (a) to (c) are performed in the same reaction vessel to make the colloidal platinum nanoparticles; wherein the reducing agent comprises at least one ester selected from the group consisting of carboxylate ester, cyclic ester, polymeric ester, and any combination thereof; wherein the carboxylate ester is represented by the formula (I), ##STR00004## wherein R is H or CH.sub.3, and x is an integer ranging from 1 to 16; the cyclic ester is represented by the formula (II), ##STR00005## wherein the ring contains one oxygen atom and 4 to 6 carbon atoms, and G is H, CH.sub.3 or C.sub.2H.sub.5; and the polymeric ester is represented by the formula (III), ##STR00006## wherein R is H or CH.sub.3, and n is an integer ranging from 2 to 1400.

2. The method as claimed in claim 1, wherein the halogen-containing oxidizing agent is selected from the group consisting of: HXO.sub.n, MXO.sub.n, X.sub.pO.sub.q, and any combination thereof; wherein X is Cl, Br, or I; M is K, Na or NH.sub.4; n is an integer 1, 2, 3 or 4; p is an integer 1 or 2; and q is an integer 1, 2, 3, or 5.

3. The method as claimed in claim 1, wherein the step of guiding the gas out of the reaction vessel in step (b) comprises guiding the gas produced from the reduction reaction and trapping the gas with water in a tank.

4. The method as claimed in claim 1, wherein a heating temperature in step (a) ranges from 40° C. to 100° C.

5. The method as claimed in claim 1, wherein a heating temperature in step (b) ranges from 50° C. to 150° C.

6. The method as claimed in claim 1, wherein a heating temperature in step (b) ranges from 70° C. to 130° C.

7. The method as claimed in claim 1, wherein a dispersion temperature in step (c) ranges from 20° C. to 100° C.

8. The method as claimed in claim 1, wherein a dispersion temperature in step (c) ranges from 50° C. to 80° C.

9. The method as claimed in claim 1, wherein the reducing agent further comprises citric acid, lactic acid, glycolic acid, ascorbic acid, oxalic acid, tartaric acid, 1,4-butanediol, glycerol, poly(ethylene glycol), hydroquinone, acetaldehyde, glucose, cellulose, carboxymethyl cellulose, cyclodextrin, chitin, chitosan, or any combination thereof.

10. The method as claimed in claim 1, wherein when the reducing agent is the carboxylate ester, the cyclic ester or a combination of the carboxylate ester and the cyclic ester, or when the reducing agent comprises the carboxylate ester, the cyclic ester or a combination of the carboxylate ester and the cyclic ester, and the reducing agent further comprises citric acid, lactic acid, glycolic acid, ascorbic acid, oxalic acid, tartaric acid, 1,4-butanediol, glycerol, hydroquinone, acetaldehyde, glucose, and any combination thereof, a molar ratio of the reducing agent relative to the inorganic platinum compound ranges from 1 to 40.

11. The method as claimed in claim 1, wherein the medium in step (c) comprises an aqueous solution including a dispersing agent; wherein the dispersing agent comprises citric acid, lactic acid, poly(lactic acid), sodium hydroxide, hexadecylamine, oleylamine, tetraoctylammonium bromide, dodecanethiol, poly(ethylene glycol), polyvinylpyrrolidone, or any combination thereof.

12. The method as claimed in claim 11, wherein a molar concentration of the dispersing agent ranges from 0.001 M to 0.1 M.

13. The method as claimed in claim 11, wherein a molar ratio of the dispersing agent relative to the platinum nanoparticles ranges from 1 to 100.

14. The method as claimed in claim 11, wherein a molar ratio of the dispersing agent relative to the platinum nanoparticles ranges from 3 to 30.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic flow diagram illustrating a method for making colloidal platinum nanoparticles in accordance with the instant disclosure;

(2) FIG. 2 is a schematic flow diagram illustrating a method of making colloidal platinum nanoparticles in accordance with the prior art;

(3) FIG. 3 is a FT-IR spectrum of the colloidal platinum nanoparticles obtained in Example 1 of the instant disclosure;

(4) FIG. 4 is a UV-Vis spectrum of the colloidal platinum nanoparticles obtained in Example 1 of the instant disclosure;

(5) FIG. 5 is a UV-Vis spectrum of the colloidal platinum nanoparticles obtained in Example 2 of the instant disclosure;

(6) FIG. 6 is a UV-Vis spectrum of the colloidal platinum nanoparticles obtained in Example 3 of the instant disclosure;

(7) FIG. 7 is a UV-Vis spectrum of the colloidal platinum nanoparticles obtained in Example 4 of the instant disclosure;

(8) FIG. 8 is a UV-Vis spectrum of the colloidal platinum nanoparticles obtained in Example 5 of the instant disclosure;

(9) FIG. 9 is a FT-IR spectrum of the colloidal platinum nanoparticles obtained in Example 5 of the instant disclosure;

(10) FIG. 10 is a UV-Vis spectrum of the colloidal platinum nanoparticles obtained in Example 6 of the instant disclosure;

(11) FIGS. 11A-1 to 11A-3 are TEM images of the colloidal platinum nanoparticles obtained in Example 1 of the instant disclosure;

(12) FIGS. 11B-1 to 11B-3 are TEM images of the colloidal platinum nanoparticles obtained in Example 5 of the instant disclosure;

(13) FIG. 12 is a DLS size distribution profile of the colloidal platinum nanoparticles obtained in Example 2 of the instant disclosure; and

(14) FIG. 13 is a zeta potential diagram of the colloidal platinum nanoparticles obtained in Practical Example 1 of the instant disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(15) Hereinafter, one skilled in the arts can easily realize the advantages and effects of the instant disclosure from the following examples. Therefore, it should be understood that the descriptions proposed herein are just preferable examples for the purpose of illustrations only, not intended to limit the scope of the disclosure. Various modifications and variations could be made in order to practice or apply the instant disclosure without departing from the spirit and scope of the disclosure.

(16) Process of Making Colloidal Platinum Nanoparticles

(17) In the following examples, infrared (IR) spectra were recorded on Agilent Technologies Cary630 Fourier transform (FT)-IR spectrometer. Inductively coupled plasma-optical emission spectra (ICP-OES) were measured on Perkin Elmer optima 8X00 spectrometer. Ultraviolet-visible (UV-Vis) spectra were measured on Agilent Technologies Cary60 UV-Vis spectrophotometer. Transmission electron microscopy (TEM) images were recorded on Hitachi H-7100 microscope. Size and zeta potential analyses were measured on Otsuka ELSZ-2000ZS DLS. All the reagents were reagent grade and used as purchased without further purification. All the reagents were reagent grade and were used without further purification. Platinum powders were purchased from Acros Organics. Ultra-pure water was purchased from Hao Feng Biotech Co.

Comparative Example 1

Using Aqua Regia to Dissolve Platinum in HCl and Synthesis of Colloidal Platinum Nanoparticles by Using Citric Acid as the Reducing Agent

(18) First, in step (a′), platinum powders (19.5 mg, 0.10 mmol) and aqua regia (1 mL of aqueous solution containing 36 wt % hydrochloric acid and 68 wt % nitric acid) were placed in a 10 mL flat-bottomed flask to form a reaction mixture. The reaction mixture was stirred at 60° C. for 10 minutes until all the platinum powders were consumed to give a solution containing chloroplatinic acid. After completion of the reaction, concentrated hydrochloric acid was added into the solution containing chloroplatinic acid for several times and heated at 100° C. for evaporation until no brown gas of nitrogen oxides evolved. Therefore, an aqueous solution containing chloroplatinic acid hexahydrate [H.sub.2PtCl.sub.6(H.sub.2O).sub.6] was obtained.

(19) Subsequently, in step (b), citric acid (200 mg, 1.04 mmol) was added into the flat-bottomed flask to form a mixture solution. Then, the flat-bottomed flask was placed on a hot plate and heated at 130° C. for 10 minutes to perform a reduction reaction. The reduction reaction produced a composition containing platinum nanoparticles, residues and HCl gas; the amount of the residues was almost 3% by volume of the mixture solution. During the reduction reaction, HCl gas produced therefrom was guided out through the recovery port attached to the flat-bottomed flask and was trapped with 40 mL water in an Erlenmeyer flask for collection.

(20) Finally, in step (c), 200 mL of water as the medium was added into the flat-bottomed flask to disperse the platinum nanoparticles in the flat-bottomed flask, and said solution was heated at 70° C. for 10 minutes to obtain colloidal platinum nanoparticles, which were measured by ICP-OES to analyze the amounts of the heavy metal impurities, and the results were shown in Table 1.

(21) TABLE-US-00001 TABLE 1 the analytical result of ICP-OES of Comparative Example 1 Heavy metal impurities Al Cr Cu Fe Mg Mn Ni Zn Concentration 1.45 0.07 0.02 2.67 1.1 0.09 0.32 0.41 (ppm)

(22) Hereinafter, the procedures of making colloidal platinum nanoparticles illustrated below were conducted by using the method as shown in FIG. 1.

Example 1

Synthesis of Colloidal Platinum Nanoparticles Using Citric Acid as the Reducing Agent

(23) First, in step (a), platinum powders (19.2 mg, 0.10 mmol) and 1 mL of concentrated hydrochloric acid aqueous solution containing 36 wt % of HCl were placed in a 10 mL flat-bottomed flask. Then, 1 mL of aqueous solution containing NaClO.sub.2 (20 mg, 0.22 mmol) and NaClO.sub.3 (60 mg, 0.57 mmol) was added into the flat-bottomed flask to obtain a reaction mixture. The reaction mixture was stirred and heated at 60° C. for 10 minutes until all platinum powders were consumed to obtain an inorganic platinum solution containing sodium chloroplatinate (Na.sub.2PtCl.sub.6).

(24) Subsequently, in step (b), citric acid (200 mg, 1.04 mmol) was added into the flat-bottomed flask and mixed with the solution containing Na.sub.2PtCl.sub.6 to form a mixture solution. Then, the flat-bottomed flask was placed on a hot plate and heated at 130° C. for 10 minutes to perform a reduction reaction. The reduction reaction produced a composition containing platinum nanoparticles, residues and HCl gas; the amount of the residues was almost 3% by volume of the mixture solution. During the reduction reaction, HCl gas produced therefrom was guided out through the recovery port attached to the flat-bottomed flask, and was trapped with 40 mL water in an Erlenmeyer flask for collection.

(25) Finally, in step (c), 200 mL of water as the medium was added into the flat-bottomed flask to disperse the platinum nanoparticles in the flat-bottomed flask, and said solution was heated at 70° C. for 10 minutes to obtain colloidal platinum nanoparticles whose UV-Vis absorption spectrum was shown in FIG. 4. In addition, the resulting colloidal platinum nanoparticles were confirmed by the FT-IR spectrum as shown in FIG. 3. TEM images of the product of Example 1 were shown in FIGS. 11A-1 to 11A-3. Moreover, the product of Example 1 was measured by ICP-OES to analyze its amounts of heavy metal impurities, and the results were shown in Table 2.

(26) TABLE-US-00002 TABLE 2 the analytical result of ICP-OES of Example 1 Heavy metal impurities Al Cr Cu Fg Mg Mn Ni Zn Concentration 0.04 0.02 0.01 0.03 0.06 ND 0.01 0.03 (ppm)

Example 2

Synthesis of Colloidal Platinum Nanoparticles Using Citric Acid as the Reducing Agent and Glycerol as the Dispersing Agent

(27) First, in step (a), platinum powders (19.8 mg, 0.10 mmol) and 1 mL of concentrated hydrochloric acid aqueous solution containing 36 wt % of HCl were placed in a 10 mL flat-bottomed flask. Then, 1 mL of aqueous solution containing HIO.sub.3 (60 mg, 0.31 mmol) and HClO.sub.4 (50 μL of 70 wt % HClO.sub.4(aq), 0.58 mmol) was added into the flat-bottomed flask to obtain a reaction mixture. The reaction mixture was stirred and heated at 60° C. for 10 minutes until all platinum powders were consumed to obtain an inorganic platinum solution containing chloroplatinic acid (H.sub.2PtCl.sub.6).

(28) Subsequently, in step (b), citric acid (160 mg, 0.8 mmol) was added into the flat-bottomed flask and mixed with the solution containing H.sub.2PtCl.sub.6 to form a mixture solution. Then, the flat-bottomed flask was placed on a hot plate and heated at 130° C. for 10 minutes to perform a reduction reaction. The reduction reaction produced a composition containing platinum nanoparticles, residues and HCl gas; the amount of the residues was almost 3% by volume of the mixture solution. During the reduction reaction, HCl gas produced therefrom was guided out through the recovery port attached to the flat-bottomed flask and was trapped with 40 mL water in an Erlenmeyer flask for collection.

(29) Finally, in step (c), 200 mL of an aqueous solution containing glycerol (800 mg, 8.7 mmol) as the medium was added into the flat-bottomed flask to disperse the platinum nanoparticles in the flat-bottomed flask, and said solution was heated at 70° C. for 10 minutes to obtain colloidal platinum nanoparticles whose UV-Vis absorption spectrum was shown in FIG. 5. In addition, the size distribution profile of the colloidal platinum nanoparticles analyzed by the DLS was shown in FIG. 12.

Example 3

Synthesis of Colloidal Platinum Nanoparticles Using Citric Acid as the Reducing Agent and Lactic Acid as the Dispersing Agent

(30) First, in step (a), platinum powders (19.0 mg, 0.10 mmol) and 1 mL of concentrated hydrochloric acid aqueous solution containing 36 wt % of HCl were placed in a 10 mL flat-bottomed flask. Then, 1 mL of aqueous solution containing KIO.sub.3 (70 mg, 0.33 mmol) and KClO.sub.4 (30 mg, 0.22 mmol) was added into the flat-bottomed flask to obtain a reaction mixture. The reaction mixture was stirred and heated at 60° C. for 10 minutes until all platinum powders were consumed to obtain an inorganic platinum solution containing potassium chloroplatinate (K.sub.2PtCl.sub.6).

(31) Subsequently, in step (b), citric acid (80 mg, 0.42 mmol) was added into the flat-bottomed flask and mixed with the solution containing K.sub.2PtCl.sub.6 to form a mixture solution. Then, the flat-bottomed flask was placed on a hot plate and heated at 130° C. for 10 minutes to perform a reduction reaction. The reduction reaction produced a composition containing platinum nanoparticles, residues and HCl gas; the amount of the residues was almost 3% by volume of the mixture solution. During the reduction reaction, HCl gas produced therefrom was guided out through the recovery port attached to the flat-bottomed flask and was trapped with 40 mL water in an Erlenmeyer flask for collection.

(32) Finally, in step (c), 200 mL of an aqueous solution containing lactic acid (800 mg, 8.9 mmol) as the medium was added into the flat-bottomed flask to disperse the platinum nanoparticles in the flat-bottomed flask, and said solution was heated at 70° C. for 10 minutes to obtain colloidal platinum nanoparticles whose UV-Vis absorption spectrum was shown in FIG. 6.

Example 4

Synthesis of Colloidal Platinum Nanoparticles Using Citric Acid as the Reducing Agent and Poly(Ethylene Glycol) as the Dispersing Agent

(33) First, in step (a), platinum powders (19.7 mg, 0.10 mmol) and 1 mL of concentrated hydrochloric acid aqueous solution containing 36 wt % of HCl were placed in a 10 mL flat-bottomed flask. Then, 1 mL of aqueous solution containing KClO.sub.3 (70 mg, 0.57 mmol) and KClO.sub.4 (20 mg, 0.14 mmol) was added into the flat-bottomed flask to obtain a reaction mixture. The reaction mixture was stirred and heated at 60° C. for 10 minutes until all platinum powders were consumed to obtain an inorganic platinum solution containing potassium chloroplatinate.

(34) Subsequently, in step (b), citric acid (100 mg, 0.52 mmol) was added into the flat-bottomed flask and mixed with the solution containing potassium chloroplatinate to form a mixture solution. Then, the flat-bottomed flask was placed on a hot plate and heated at 130° C. for 10 minutes to perform a reduction reaction. The reduction reaction produced a composition containing platinum nanoparticles, residues and HCl gas; the amount of the residues was almost 3% by volume of the mixture solution. During the reduction reaction, HCl gas produced therefrom was guided out through the recovery port attached to the flat-bottomed flask and was trapped with 40 mL water in an Erlenmeyer flask for collection.

(35) Finally, in step (c), 200 mL of an aqueous solution containing poly(ethylene glycol) (800 mg, 1.0 mmol) as the medium was added into the flat-bottomed flask to disperse the platinum nanoparticles in the flat-bottomed flask, and said solution was heated at 70° C. for 10 minutes to obtain colloidal platinum nanoparticles whose UV-Vis absorption spectrum was shown in FIG. 7.

Example 5

Synthesis of Colloidal Platinum Nanoparticles Using Methyl Lactate as Both the Reducing Agent and the Dispersing Agent

(36) First, in step (a), platinum powders (18.8 mg, 0.10 mmol) and 1 mL of concentrated hydrochloric acid aqueous solution containing 36 wt % of HCl were placed in a 10 mL flat-bottomed flask. Then, 1 mL of aqueous solution containing NaClO.sub.2 (20 mg, 0.22 mmol) and NaClO.sub.3 (60 mg, 0.57 mmol) was added into the flat-bottomed flask to obtain a reaction mixture. The reaction mixture was stirred and heated at 60° C. for 10 minutes until all platinum powders were consumed to obtain an inorganic platinum solution containing sodium chloroplatinate.

(37) Subsequently, in step (b), methyl lactate (64 mg, 0.62 mmol) was added into the flat-bottomed flask and mixed with the solution containing sodium chloroplatinate to form a mixture solution. Then, the flat-bottomed flask was placed on a hot plate and heated at 130° C. for 20 minutes to perform a reduction reaction. The reduction reaction produced a composition containing platinum nanoparticles, residues and HCl gas; the amount of the residues was almost 3% by volume of the mixture solution. During the reduction reaction, HCl gas produced therefrom was guided out through the recovery port attached to the flat-bottomed flask and was trapped with 40 mL water in an Erlenmeyer flask for collection.

(38) Finally, in step (c), 200 mL of an aqueous solution containing methyl lactate (800 mg, 7.7 mmol) as the medium was added into the flat-bottomed flask to disperse the platinum nanoparticles in the flat-bottomed flask, and said solution was heated at 70° C. for 10 minutes to obtain colloidal platinum nanoparticles whose UV-Vis absorption spectrum was shown in FIG. 8. In addition, the resulting colloidal platinum nanoparticles were confirmed by the FT-IR spectrum as shown in FIG. 9. TEM images of the product of Example 5 were shown in FIGS. 11B-1 to 11B-3.

Example 6

Synthesis of Colloidal Platinum Nanoparticles Using Methyl Lactate and Citric Acid as the Combined Reducing Agent

(39) First, in step (a), platinum powders (19.5 mg, 0.10 mmol) and 1 mL of concentrated hydrochloric acid aqueous solution containing 36 wt % of HCl were placed in a 10 mL flat-bottomed flask. Then, 1 mL of aqueous solution containing KClO.sub.3 (70 mg, 0.57 mmol) and KClO.sub.4 (20 mg, 0.14 mmol) was added into the flat-bottomed flask to obtain a reaction mixture. The reaction mixture was stirred and heated at 60° C. for 10 minutes until all platinum powders were consumed to obtain an inorganic platinum solution containing potassium chloroplatinate.

(40) Subsequently, in step (b), citric acid (60 mg, 0.31 mmol) and methyl lactate (31 mg, 0.3 mmol) were added into the flat-bottomed flask and mixed with the solution containing potassium chloroplatinate to form a mixture solution. Then, the flat-bottomed flask was placed on a hot plate and heated at 130° C. for 10 minutes to perform a reduction reaction. The reduction reaction produced a composition containing platinum nanoparticles, residues and HCl gas; the amount of the residues was almost 3% by volume of the mixture solution. During the reduction reaction, HCl gas produced therefrom was guided out through the recovery port attached to the flat-bottomed flask and was trapped with 40 mL water in an Erlenmeyer flask for collection.

(41) Finally, in step (c), 200 mL of water as the medium was added into the flat-bottomed flask to disperse the platinum nanoparticles in the flat-bottomed flask, and said solution was heated at 70° C. for 10 minutes to obtain colloidal platinum nanoparticles whose UV-Vis absorption spectrum was shown in FIG. 10.

Example 7

Synthesis of Colloidal Platinum Nanoparticles Using Iodic Acid and Ammonium Perchlorate as the Combined Halogen-Containing Oxidizing Agent and Citric Acid as the Reducing Agent

(42) First, in step (a), platinum powders (19.2 mg, 0.10 mmol) and 1 mL of concentrated hydrochloric acid aqueous solution containing 36 wt % of HCl were placed in a 10 mL flat-bottomed flask. Then, 1 mL of aqueous solution containing HIO.sub.3 (20 mg, 0.11 mmol) and NH.sub.4ClO.sub.4 (52 mg, 0.44 mmol) was added into the flat-bottomed flask to obtain a reaction mixture. The reaction mixture was stirred and heated at 60° C. for 10 minutes until all platinum powders were consumed to obtain an inorganic platinum solution containing ammonium chloroplatinate [(NH.sub.4).sub.2PtCl.sub.6].

(43) Subsequently, in step (b), citric acid (120 mg, 0.63 mmol) was added into the flat-bottomed flask and mixed with the solution containing (NH.sub.4).sub.2PtCl.sub.6 to form a mixture solution. Then, the flat-bottomed flask was placed on a hot plate and heated at 130° C. for 10 minutes to perform a reduction reaction. The reduction reaction produced a composition containing platinum nanoparticles, residues and HCl gas and NH.sub.3 gas; the amount of the residues was almost 3% by volume of the mixture solution.

(44) Finally, in step (c), 200 mL of water as the medium was added into the flat-bottomed flask to disperse the platinum nanoparticles in the flat-bottomed flask, and said solution was heated at 70° C. for 10 minutes to obtain colloidal platinum nanoparticles.

Example 8

Synthesis of Colloidal Platinum Nanoparticles Using Citric Acid as the Reducing Agent

(45) First, in step (a), platinum powders (19.2 mg, 0.10 mmol) and 1 mL of concentrated hydrochloric acid aqueous solution containing 36 wt % of HCl were placed in a 10 mL flat-bottomed flask. Then, 1 mL of aqueous solution containing NaClO.sub.2 (70 mg, 0.77 mmol) was added into the flat-bottomed flask to obtain a reaction mixture. The reaction mixture was stirred and heated at 60° C. for 10 minutes until all platinum powders were consumed to obtain an inorganic platinum solution containing sodium chloroplatinate.

(46) Subsequently, in step (b), citric acid (120 mg, 0.63 mmol) was added into the flat-bottomed flask and mixed with the solution containing sodium chloroplatinate to form a mixture solution. Then, the flat-bottomed flask was placed on a hot plate and heated at 130° C. for 10 minutes to perform a reduction reaction. The reduction reaction produced a composition containing platinum nanoparticles, residues and HCl gas; the amount of the residues was almost 3% by volume of the mixture solution. During the reduction reaction, HCl gas produced therefrom was guided out through the recovery port attached to the flat-bottomed flask and was trapped with 40 mL water in an Erlenmeyer flask for collection.

(47) Finally, in step (c), 200 mL of water as the medium was added into the flat-bottomed flask to disperse the platinum nanoparticles in the flat-bottomed flask, and said solution was heated at 70° C. for 10 minutes to obtain colloidal platinum nanoparticles.

Example 9

Synthesis of Colloidal Platinum Nanoparticles Using γ-Butyrolactone as the Reducing Agent and Citric Acid as the Dispersing Agent

(48) First, in step (a), platinum powders (19.2 mg, 0.10 mmol) and 1 mL of concentrated hydrochloric acid aqueous solution containing 36 wt % of HCl were placed in a 10 mL flat-bottomed flask. Then, 1 mL of aqueous solution containing NaClO.sub.2 (20 mg, 0.22 mmol) and NaClO.sub.3 (60 mg, 0.57 mmol) was added into the flat-bottomed flask to obtain a reaction mixture. The reaction mixture was stirred and heated at 60° C. for 10 minutes until all platinum powders were consumed to obtain an inorganic platinum solution containing sodium chloroplatinate.

(49) Subsequently, in step (b), γ-butyrolactone (70 mg, 0.81 mmol) was added into the flat-bottomed flask and mixed with the solution containing sodium chloroplatinate to form a mixture solution. Then, the flat-bottomed flask was placed on a hot plate and heated at 130° C. for 10 minutes to perform a reduction reaction. The reduction reaction produced a composition containing platinum nanoparticles, residues and HCl gas; the amount of the residues was almost 3% by volume of the mixture solution. During the reduction reaction, HCl gas produced therefrom was guided out through the recovery port attached to the flat-bottomed flask and was trapped with 40 mL water in an Erlenmeyer flask for collection.

(50) Finally, in step (c), 200 mL of an aqueous solution containing citric acid (240 mg, 1.25 mmol) as the medium was added into the flat-bottomed flask to disperse the platinum nanoparticles in the flat-bottomed flask, and said solution was heated at 70° C. for 10 minutes to obtain colloidal platinum nanoparticles.

Example 10

Synthesis of Colloidal Platinum Nanoparticles Using Poly(Lactic Acid) (PLA) as the Reducing Agent and Citric Acid as the Dispersing Agent

(51) First, in step (a), platinum powders (19.2 mg, 0.10 mmol) and 1 mL of concentrated hydrochloric acid aqueous solution containing 36 wt % of HCl were placed in a 10 mL flat-bottomed flask. Then, 1 mL of aqueous solution containing NaClO.sub.2 (72 mg, 0.80 mmol) was added into the flat-bottomed flask to obtain a reaction mixture. The reaction mixture was stirred and heated at 60° C. for 10 minutes until all platinum powders were consumed to obtain an inorganic platinum solution containing sodium chloroplatinate.

(52) Subsequently, in step (b), PLA (360 mg) was added into the flat-bottomed flask and mixed with the solution containing sodium chloroplatinate to form a mixture solution. Then, the flat-bottomed flask was placed on a hot plate and heated at 130° C. for 12 minutes to perform a reduction reaction. The reduction reaction produced a composition containing platinum nanoparticles, residues and HCl gas; the amount of the residues was almost 3% by volume of the mixture solution. During the reduction reaction, HCl gas produced therefrom was guided out through the recovery port attached to the flat-bottomed flask and was trapped with 40 mL water in an Erlenmeyer flask for collection.

(53) Finally, in step (c), 200 mL of an aqueous solution containing citric acid (800 mg, 4.2 mmol) as the medium was added into the flat-bottomed flask to disperse the platinum nanoparticles in the flat-bottomed flask, and said solution was heated at 70° C. for 10 minutes to obtain colloidal platinum nanoparticles.

Practical Example 1 of Hyaluronic Acid-Colloidal Platinum Nanoparticles

Synthesis of Colloidal Platinum Nanoparticles Using Citric Acid as the Reducing Agent

(54) First, in step (a), platinum powders (19.2 mg, 0.10 mmol) and 1 mL of concentrated hydrochloric acid aqueous solution containing 36 wt % of HCl were placed in a 10 mL flat-bottomed flask. Then, 1 mL of aqueous solution containing NaClO.sub.2 (20 mg, 0.22 mmol) and NaClO.sub.3 (60 mg, 0.57 mmol) was added into the flat-bottomed flask to obtain a reaction mixture. The reaction mixture was stirred and heated at 60° C. for 10 minutes until all platinum powders were consumed to obtain an inorganic platinum solution containing sodium chloroplatinate.

(55) Subsequently, in step (b), citric acid (200 mg, 1.04 mmol) was added into the flat-bottomed flask and mixed with the solution containing sodium chloroplatinate to form a mixture solution. Then, the flat-bottomed flask was placed on a hot plate and heated at 130° C. for 10 minutes to perform a reduction reaction. The reduction reaction produced a composition containing platinum nanoparticles, residues and HCl gas; the amount of the residues was almost 3% by volume of the mixture solution. During the reduction reaction, HCl gas produced therefrom was guided out through the recovery port attached to the flat-bottomed flask and was trapped with 40 mL water in an Erlenmeyer flask for collection.

(56) Finally, in step (c), 200 mL of water as the medium was added into the flat-bottomed flask to disperse the platinum nanoparticles in the flat-bottomed flask, and said solution was heated at 70° C. for 10 minutes to obtain colloidal platinum nanoparticles whose zeta potential was −38.03 mV as shown in FIG. 13.

(57) After the colloidal platinum nanoparticles was cooled to room temperature (25° C.), 0.8 mL of said colloidal platinum nanoparticles was taken and mixed with 12 mL of an aqueous solution containing 2.3 wt % of hyaluronic acid, so as to obtain a clear light brown solution containing hyaluronic acid-colloidal platinum nanoparticles whose zeta potential was −32.86 mV.

(58) Discussion of the Results

(59) Based on the results of Examples 1 to 10, the instant disclosure directly employs platinum metal powders as the metal source. In the same reaction vessel, the platinum metal powders were dissolved by the halogen-containing oxidizing agent first, and next different kinds of reducing agents were used to form platinum nanoparticles, and then diverse kinds of mediums were added to disperse said platinum nanoparticles to obtain colloidal platinum nanoparticles. Compared with the conventional methods, the method of the instant disclosure does not have to produce and purify chloroplatinic acid or chloroplatinate salts. The instant disclosure can make the platinum powders as the starting material converted to colloidal platinum nanoparticles through consecutive steps in a same reaction vessel without transferring containers in the middle. Hence, the instant disclosure does not include complicated procedures, so it has advantages of simplicity, low loss, and high yield.

(60) From the comparison of ICP-OES results of Comparative Example 1 and Example 1, the colloidal platinum nanoparticles made from Example 1 have higher purity than the colloidal platinum nanoparticles made from Comparative Example 1. That is because Comparative Example 1 adopts crude chloroplatinic acid as the raw material which is obtained from using aqua regia to dissolve the platinum powders without undergoing further refining steps such as concentration and recrystallization. As a result, the colloidal platinum nanoparticles made from Comparative Example 1 contain higher concentration of metal impurities. By contrast, the method of Example 1 of the instant disclosure adopts the halogen-containing oxidizing agent to dissolve the platinum powders, and directly gets highly pure chloroplatinic acid which does not need to undergo a cumbersome refining step. The technical means of the instant disclosure can simplify the process and ensure that the obtained colloidal platinum nanoparticles have a high purity. Accordingly, it demonstrates that the instant disclosure, by using the halogen-containing oxidizing agent to dissolve the platinum powders, has the advantages of time-effectiveness, cost-effectiveness and high quality of the product compared to the conventional method of dissolving platinum by aqua regia.

(61) Further, the method of Examples 1 to 10 uses non-toxic and biocompatible reducing agents of citric acid, glycerol, lactic acid, poly(ethylene glycol), and esters including methyl lactate, γ-butyrolactone or poly(lactic acid). It is more eco-friendly and suitable to be applied in the present society.

(62) From the comparison of FIG. 5 of Example 2 and FIG. 6 of Example 3, said all-wavelength UV-Vis absorption spectra in FIGS. 5 and 6 are obviously different, so it demonstrates that selection of different dispersing media for the platinum nanoparticles makes colloidal platinum nanoparticles have different characteristics. As nanonization and colloidalization of the platinum nanoparticles are processed by two steps, wider ranges of both reducing agents and dispersing medium are applicable to the method of the instant disclosure. Accordingly, it is more convenient to apply in various industrial and medical applications.

(63) Compared with the conventional process, the concentration of platinum ions derived from the inorganic platinum compound is relatively high in Examples 1 to 10 because of the low solution volume in the reaction vessel by heating and evaporating the mixture solution during the reduction reaction. That is conducive to enhance the collision probability of reactant molecules and thereby accelerate the reaction rate. Further, by means of guiding the gas such produced from the reduction reaction out of the reaction vessel at the same time, it facilitates proceeding of the forward reaction, and therefore the reaction time for making metal nanoparticles can be shortened to within 20 minutes, even merely 10 minutes. This is a cost-effective process, and faster reaction rate of reduction yields a narrower size distribution of metal nanoparticles. Accordingly, said platinum nanoparticles in homogeneous size distribution do not require further filtration, so the yield can improve.

(64) Unlike the conventional method that involves a hazardous process in adding a solution containing platinum ions rapidly to a boiling solution of reducing agent, the instant disclosure by heating a pre-mixed solution of the solution containing the inorganic platinum compound and reducing agents even in a large scale is a much safer manner. Moreover, the instant disclosure proceeds in an easy and efficient manner by just using simple setup without complicated apparatus of reactor or stirring equipment apparatus.

(65) Further, using organic reducing and dispersing agents in water makes colloidal platinum nanoparticles have good quality and stability.

(66) Besides, the anions (e.g. Cl.sup.−) can be guided out of the reaction vessel in a form of gas (e.g. HCl) by heating in step (b) of the instant disclosure. Subsequently, said gas can be trapped by water for reuse. As most anions can be removed from the colloidal platinum nanoparticles, said colloidal platinum nanoparticles have high stability and zeta potential without appreciable interference of anions.

(67) Based on the result of Practical Example 1, the product containing hyaluronic acid-colloidal platinum nanoparticles made by the method of the instant disclosure has a −32.86 mV of zeta potential, which is near the zeta potential (−32.03 mV) of the colloidal platinum nanoparticles as the raw material. It demonstrates that the colloidal platinum nanoparticles made by the instant disclosure have good quality and stability without the interference of anions. As a result, the colloidal platinum nanoparticles can be applied to derive other colloidal platinum products through a quite easy and fast process.

(68) Even though numerous characteristics and advantages of the instant disclosure have been set forth in the foregoing description, together with details of the structure and features of the disclosure, the disclosure is illustrative only. Changes may be made in the details, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.