Polymer-supported metal nanoparticles, process for production thereof and polymeric nanoreactors produced therefrom

Abstract

A process for producing polymer-supported metal nanoparticles involves confinement of metal nanoparticles in polymeric nanotubes or nanosheets in an aqueous environment using hydrophobic reactants. Metal nanoparticles supported in the polymeric nanotubes or nanosheets are substantially monodisperse and have an average particle size of 4 nm or less. The polymer-supported metal nanoparticles are useful in fuel cells, sensors, bioanalysis, biological labeling or semi-conductors, especially as catalysts.

Claims

1. A process for producing polymer-supported metal nanoparticles comprising: mixing a hydrophobic metal precursor compound in an aqueous non-reducing solvent in the presence of an organic polymer that self-organizes into nanotubes or nanosheets, the nanotubes or nanosheets confining the metal precursor compound therein; and, allowing the metal precursor compound to reduce within the nanotubes or nanosheets without addition of reducing agent to form metal nanoparticles confined in the nanotubes or nanosheets.

2. The process according to claim 1, wherein the metal nanoparticles comprise platinum.

3. The process according to claim 1, wherein the metal nanoparticles comprise gold.

4. The process according to claim 2, wherein the hydrophobic metal precursor compound comprises PtCl.sub.2.

5. The process according to claim 1, wherein the organic polymer comprises an amphiphilic alternating copolymer.

6. The process according to claim 1, wherein the organic polymer comprises poly(styrene-alt-maleic anhydride) (SMA) that self-organize into nanotubes.

7. The process according to claim 1, wherein the organic polymer comprises poly(isobutylene-alt-maleic anhydride) (IMA) that self-organize into nanosheets.

8. The process according to claim 1, wherein the organic polymer is dispersed in the aqueous non-reducing solvent, pH of the solvent is adjusted to 7, and then the hydrophobic metal precursor compound is added to the dispersion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For clearer understanding, preferred embodiments will now be described in detail by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 depicts X-ray diffraction (XRD) plots for a sample of 1 wt % SMA and PtCl.sub.2 without additional reducing agent (upper plot) and a sample of 1 wt % SMA and PtCl.sub.2 with additional reducing agent (NaBH.sub.4) (lower plot);

(3) FIG. 2A depicts a Transmission Electron Micrograph (TEM) image of platinum (Pt) nanoparticles formed by in situ reduction of PtCl.sub.2 in SMA nanotubes, alongside a graph showing the particle width distribution of the Pt nanoparticles so formed; and,

(4) FIG. 2B depicts a Transmission Electron Micrograph (TEM) image of platinum (Pt) nanoparticles formed by NaBH.sub.4 reduction of PtCl.sub.2 in SMA nanotubes, alongside a graph showing the particle width distribution of the Pt nanoparticles so formed.

(5) FIG. 3A and FIG. 3B depict ultraviolet-visible (UV-Vis) spectra tracking polymerization of pyrrole without Pt (FIG. 3A) and with Pt (FIG. 3B) in a hydrophobic cavity of SMA nanotubes.

(6) FIG. 4 depicts an ultraviolet-visible (UV-Vis) spectrum of gold (Au) nanoparticles formed by in situ reduction of AuCl in SMA nanotubes.

DETAILED DESCRIPTION

(7) Poly(styrene-alt-maleic anhydride) (SMA) is an amphiphilic alternating copolymer that forms nanotubes with a 2.8 nm interior diameter in water at pH 7. The most stable conformation obtained for the self-association at pH 7 is a tubular structure in which eight SMA molecules make one twist of a helix. The tubes can grow in length by continued regular stacking of benzene rings. The nanotubes have inner and outer diameters of about 2.8 nm and 4.1 nm, respectively. The hydrophobic groups are mainly located inside the nanotube and the hydrophilic groups are mainly on the exterior surface of the nanotube. Thus, SMA nanotubes are capable of solubilizing hydrophobic compounds inside the nanotube, while themselves being solubilizable in aqueous media due to the hydrophilic groups on the exterior surface of the nanotube.

(8) Poly(isobutylene-alt-maleic anhydride) (IMA) is an amphiphilic alternating copolymer that forms nanosheets with a sheet spacing of about 2 nm in water at pH 7. IMA copolymer at pH 7 forms double layer sheets in which the outer surfaces are hydrophilic and the center gap is hydrophobic. Thus, IMA nanosheets are capable of solubilizing hydrophobic compounds in the center gap of the nanosheet, while themselves being solubilizable in aqueous media due to the hydrophilic groups on the exterior surface of the nanosheet.

Example 1: Preparation of SMA-Based Nanoreactors with Pt

(9) 1 wt % SMA solutions were prepared by mixing poly(styrene-alt-maleic anhydride), partial methyl ester with an average Mw=350;000 (Sigma-Aldrich), with deionized water. An aqueous solution of NaOH was used to raise the pH to 7 and the mixture was sonicated until the polymer had completely dissolved. 0.1 g of platinum (II) chloride, 98% (PtCl.sub.2, Sigma-Aldrich) was weighed and mixed into 3.0 g of the 1 wt % SMA solution. The mixture was then sonicated for 90 minutes at room temperature to break up aggregated PtCl.sub.2 which would form when mixed into the solution. The sample was left to sit for 1 week until the colour of the solution start to change from a pale green to black with the formation of a precipitate. The precipitate is an excess of PtCl.sub.2 used to ensure a complete solubilisation within the polymeric nanotemplate. This colour change was equivalent to the colour change observed when an identical PtCl.sub.2/SMA solution was reduced with 1 mL of a 0.5 M NaBH.sub.4 solution, thereby confirming that reduction of the PtCl.sub.2 can occur spontaneously in the interior of the SMA nanotubes without the need for additional reducing agent.

(10) Further confirmation that the platinum precursor compound PtCl.sub.2 is reduced in situ in the SMA nanotubes without the addition of additional reducing agent is evident from X-ray diffraction (XRD) (FIG. 1). The XRD spectra were obtained at a wavelength of 0.6888 Å. Peaks corresponding to the Pt (111) crystal face at 17.49° and the (200) crystal face at 20.22° (JCPDS 04-0802) are evident in both the plot for the in situ reduction (upper plot) and the NaBH.sub.4 reduction (lower plot). This shows that Pt nanoparticles are present in the sample where no NaBH.sub.4 reduction occurred, which can only be a result of spontaneous reduction of PtCl.sub.2 in the SMA nanotubes.

(11) Particle size of the Pt nanoparticles may be determined from Transmission Electron Microscopy (TEM). TEM was performed at the Canadian Centre for Electron Microscopy on both the sample of Pt-SMA obtained from spontaneous in situ reduction (FIG. 2A) and the sample obtained from NaBH.sub.4 reduction (FIG. 2B). The dominant crystal face was determined from the TEM images and the d-spacing determined. The average d-spacing for the Pt nanoparticles in the NaBH.sub.4 reduced sample was 0.198±0.007 nm, while the average d-spacing for the Pt nanoparticles in the spontaneously reduced sample was 0.197±0.007 nm. There is no significant difference between the two samples and they correspond to the (200) miller index. From the graphs in FIG. 2A and FIG. 2B showing the particle width distribution of the Pt nanoparticles, it is evident that all of the particles have a width less than about 3 nm and that the average particle width is less than about 2 nm. Both samples comprise nanoparticles having an average particle size of 1.89±0.09 nm at the 95% confidence level.

Example 2: Use of Pt-SMA Nanoreactors in Catalysis

(12) With reference to FIG. 3A and FIG. 3B, enhanced catalytic activity of the Pt-SMA nanoreactor of Example 1 was demonstrated by using UV-Vis spectroscopy to monitor the polymerization of pyrrole within the polymeric nanotemplate. FIGS. 3A and 3B demonstrate the efficiency of the Pt catalyst inside the SMA nanotemplate in aqueous solution at neutral pH. SMA alone has previously been reported to spontaneously trigger the polymerization of pyrrole due to the confinement effect, but the reaction requires about 1 month to show any measureable change. The high surface-to-volume Pt nanoparticles in the SMA polymer nanotemplate were used to help catalyze the pyrrole polymerization under the confinement effect. It was found that with the presence of Pt nanoparticles in the SMA nanotubes, the polymerization of pyrrole requires only a third of the time to start to show a measurable change according to UV-Vis spectroscopy. Thus, the start of the characteristic polypyrrole peak occurs after only 8 days with the presence of the Pt nanoparticles in 1 wt % SMA. This peak does not appear for the 1 wt % SMA sample without Pt nanoparticles until 24 days after the start of the reaction. This demonstrates the additional catalytic activity of the SMA nanoreactor with the inclusion of Pt nanoparticles.

Example 3: Preparation of SMA-based Nanoreactors with Au

(13) The procedure described in Example 1 was adapted to prepare Au-SMA nanoreactors, except that gold (I) chloride (AuCl) replaced PtCl.sub.2 as the precursor compound. FIG. 4 is a UV-Vis spectrum of gold nanoparticles prepared in this example, where the peak at 550 nm in the spectrum is characteristic of Au nanoparticles.

REFERENCES

(14) The contents of the entirety of each of which are incorporated by this reference. Chan A S W, Groves M, Malardier-Jugroot. (2009) Conformational Analysis of Alternating Copolymers and their Association into Nanoarchitectures. NSTI-Nanotech 2009, Vol. 2, 2009. Chan A S W, Groves M, Malardier-Jugroot. (2009) Synthesis and Characterization of Polypyrrole Nanowires Using Alternating Amphiphilic Copolymer Nanotubes as Templates. Nanotech Conference & Expo 2009. Houston, Tex., May 3-7, 2009. Chan A S W, Groves M, Malardier-Jugroot. (2010) Environmentally Friendly Synthesis of Polypyrrole within Polymeric Nanotemplates—Mechanism of Polypyrrole Synthesis. Nanotech Conference & Expo 2010. Anaheim, Calif., Jul. 21-24, 2010. Malardier-Jugroot C, van de Ven T G M, Whitehead M A. (2005) Characterisation of a novel self-association of an alternating copolymer into nanotubes in solution. NSTI-Nanotech 2004, ISBN 0-9728422-9-2 Vol. 3, 2004. Mayer A, Antonietti M. (1998) Investigation of polymer-protected noble metal nanoparticles by transmission electron microscopy: control of particle morphology and shape. Colloid Polym Sci. 276, 769-779. Lazzara T D, Whitehead M A, van de Ven T G M. (2009) Linear nano-templates of styrene and maleic anhydride alternating copolymers. European Polymer Journal. 45, 1883-1890. Li X, Malardier-Jugroot C. (2013) Confinement Effect in the Synthesis of Polypyrrole within Polymeric Templates in Aqueous Environments. Macromolecules. 46, 2258-2266. Whitehead M A, Malardier-Jugroot C, Van De Ven T G M, Lazzara T D. (2008) Method for Fabricating Intrinsically Conducting Polymer Nanorods. US 2008/0265219 published Oct. 30, 2008.

(15) The novel features will become apparent to those of skill in the art upon examination of the description. It should be understood, however, that the scope of the claims should not be limited by the embodiments, but should be given the broadest interpretation consistent with the wording of the claims and the specification as a whole.