Pt nanoparticles supported on bovine-bone powder were obtained by a rather simple method consisting of immersing powder of bovine bone into a Pt+4 metal ion solution at room temperature and subsequent reduction by sodium borohydride. This method eliminates the calcination step of the usual catalyst preparation methods. The nanocomposite was characterized by transmission electron microscopy (TEM), which revealed uniformly dispersed platinum nanoparticles with average particle size of 2.2 nm ± 0.6 nm. The XPS studies exhibited the presence of 63% Pt° and 37% PtO. The catalytic activity was tested in the hydrogenation of 2-butyne-1,4-diol. The nanocomposite shows good catalytic performance with nearly 100% conversion and 83% selectivity towards 2-butene-1,4-diol.
Science and technology of nanomaterials have rapidly grown in recent years and, as a consequence, great progress in the synthesis and characterization of materials in the nanometer regime has been achieved. The applications of these nanomaterials are diverse in the chemical industry, in electronics, and even in medicine [
The conventional nanoparticle synthesis is complex and relatively expensive and is conducted at high temperatures. These undesirable features have motivated the search of a greener synthesis. To achieve so, the general approach that can be found in the literature is by modifying the reaction medium to produce the nanoparticles, mainly in the liquid phase [
Therefore, the purpose of this study was to synthesize at relatively low cost monodispersed Pt nanoparticles (NPs) onto a bovine bone, which is a renewable and novel biosupport. In addition, the catalytic activity of the as-prepared material was assessed in the hydrogenation catalytic conversion of 2-butyne-1,4-diol to 2-butene-1,4-diol.
In order to synthesize the Pt NPs, PtCl4 was used as precursor salt. For this purpose, 16.75 mg of PtCl4 was dissolved in 50 mL of deionized water, thus obtaining a final concentration of 0.001 M (solution 1). Then 7.5 mg of NaBH4 was dissolved in 50 mL of water thus obtaining a 0.01 M concentration (solution 2); pH was not adjusted. For the support bovine femur was used. This bone was washed, cleaned, and immersed in a 0.01 M HCl solution. After immersion, the bone was cut into small pieces and then powdered by a tungsten rotating piece connected to a moto-tool. The powder was then sieved with 150 mesh. An amount of 975 mg of bovine-bone powder was immersed in 50 mL of solution 1 for 30 seconds and then filtered. The reduction of Pt(IV) ions was carried out with solution 2 for 30 minutes and filtered. The resulting powder was dried overnight at room temperature. It is worth noticing that a calcination step is not necessary since Pt NPs were obtained by NaBH4 as reduction agent. It is also worth pointing out that, because of the amount of treated powder (approximately 1 g), a micellar activity might also be expected since the micelle formation of sepia cartilage collagen solutions has been previously reported [
Scanning electron microscopy (SEM) observations were carried out by JEOL JSM-6510LV equipment. The nanocomposite was attached to the sample aluminum-stub using a carbon conductive double-stick tape without coating. Elemental analysis characterization was performed using an energy-dispersive X-ray spectroscope INCA X-Sight Oxford attached to the SEM.
Transmission electronic microscopy (TEM) studies and SAED (selected area electron diffraction) technique were carried out using a JEOL JEM-2100 microscope operating at 200 kV accelerating voltage. The platinum-impregnated bovine-bone powders were suspended in 2-propanol and then ultrasonically dispersed for 5 hours at room temperature. A drop of this suspension was then placed on a Cu-grid coated with a holey carbon film. Also, the supported Pt° nanoparticles were analyzed by STEM technique.
The X-Ray Photoelectronic Spectroscopy (XPS) analysis was carried out in a JEOL JPS-9200 equipped with a Mg source (1253.5 eV), operating at 200 W and vacuum of 1 × 10−8 Torr; for all samples, the analysis area was 1 mm2. The SpecSurf™ software was used to analyze the experimental results. Charge correction was done based on the adventitious carbon signal (C1s) at 285.5 eV. Shirley method was used for background adjustment, whereas Gauss-Lorentz method was used for curve fitting.
The hydrogenation of 2-butyne-1,4-diol was carried out in a 300 mL stainless-steel Parr reactor equipped with a temperature control system, a mechanical stirrer, a pressure meter, an inner heating/cooling coil system, and sampling valve. A reservoir for H2 gas was used along with a constant pressure regulator to supply hydrogen at a constant pressure to the reactor.
In a typical hydrogenation experiment, 150 mL of 20% w/w aqueous 2-butyne-1,4-diol solution and 0.215 g of Pt-supported catalyst were loaded into the reactor. The initial concentration of the alkyne was 0.1 mol/L. The reactor was first flushed with nitrogen and then with hydrogen. After the desired temperature (328 K) was reached, the system was pressurized with hydrogen at the required pressure (6 bar) and an agitation speed of 550 rpm. Samples were obtained every 30 minutes. After the reaction was over as indicated by a constant hydrogen pressure in the reservoir, the reactor was cooled down to room temperature, the excess of hydrogen was vented out safely, and the reactor contents were removed for subsequent analysis.
The withdrawn liquid samples were analyzed by gas chromatography with a flame ionization detector using a VARIAN CP3800 GC (DB-WAX 52 column, length 32 m, inner diameter = 0.3 mm) and helium (30 ml/min) as carrier gas, according to previous reported analysis methods [
In this work, in order to prevent sintering and to control nanoparticles size and morphology, the use of a bovine bone was assessed as novel support for Pt nanoparticles (NPs) synthesis. The formation of the metallic platinum phase in solution in the investigated system is the direct result of the transfer of electrons from the reducing agent, NaBH4, to Pt(IV) ions according to reaction [
When bone in bulk was used, micrometric rather than nanometric size Pt particles were obtained. This fact could be explained by the ability of bone powder to avoid the platinum ions agglomeration, since there is a large distance between metal ions. Bovine-bone powder is an ideal substrate for the formation of nanoparticles due to its high porosity (200–900
In Table
Elemental weight% for EDS elemental analysis of Figures
Element | Elemental weight% of bone | Elemental weight% of bone/Pt NPs |
---|---|---|
C K | 15.78 | 15.18 |
O K | 42.98 | 41.15 |
P K | 13.08 | 12.41 |
Ca K | 28.16 | 27.56 |
Pt M | | 3.71 |
(a) SEM image of bovine-bone powder, 20 kV. (b) SEM image of bovine-bone powder after the synthesis of nanoparticles of platinum, 20 kV. (c) EDS spectrum: the analyzed area is indicated by the pink square. ((a) and (d)) EDS spectrum: the analyzed area is indicated by the pink square in (b).
The supported Pt NPs were further identified by STEM. Figure
((a), (b), (c), and (g)) BF-STEM images of Pt nanoparticles in bovine-bone powder, in different magnifications 200 kV. ((d), (e), and (f)) HAADF-STEM images of supported Pt nanoparticles on bovine-bone powder.
Mei et al. [
Figure
Size distribution of platinum nanoparticles.
Figure
HRTEM micrograph Pt-nanobiocomposite.
XPS was used to determine the oxidation state of the elements in the bovine-bone powder and the platinum nanoparticles. The narrow spectra in the Pt 4f region and its curve fitting show two oxidation states for platinum (Figure
XPS spectra corresponding to the Pt 4f5/2 and 4f7/2 regions of the platinum nanoparticles supported over bovine-bone dust.
The catalytic activity of the system Pt/bovine-bone was tested in the 2-butyne-1,4-diol hydrogenation reaction in a continuously stirred slurry reactor. Figure
Concentration-time profile for 2-butyne-1,4-diol hydrogenation. Reaction conditions: temperature, 328 K; pressure, 6 bar; initial concentration = 0.1 mol/L; active concentration of catalyst, 0.215 mg; stirring speed, 550 rpm; total volume, 1.5 × 10−4 m3.
Darder et al. [
Reaction Scheme
2-Butyne-1,4-diol hydrogenation scheme [
Bovine-bone powder is an efficient, low-cost support of platinum nanoparticles. The synthesis of this novel bionanocomposite is plausible by the direct reduction of the metallic salt and this method leads to obtaining 2.2 ± 0.6 nm metallic platinum nanoparticles. This synthesis method is of relatively low cost and environmentally friendly since the support is a waste material, the solvent is water, and the calcination step is eliminated. The platinum nanoparticles have electrostatic interactions with the hydroxyl group of the hydroxyapatite on the surface of the bovine-bone powder.
Finally, the system of bovine-bone powder with 1% platinum NPs possesses a high catalytic activity and selectivity for hydrogenation reactions. A nearly 100% conversion of 2-butyne-1,4-diol was achieved. The maximum attained selectivity towards 2-butene-1,4-diol was 83% at high conversions. This selectivity is mainly affected by the alkane presence.
The authors declare that they do not have conflicts of interest.
This project was supported by a grant from the National Institute on Minority Health and Health Disparities (G12MD007591) from the National Institutes of Health. Dr. Alfredo Rafael Vilchis-Nestor TEM imaging acquisition data at the Kleberg Advanced Microscopy Center of UTSA is acknowledged. The authors thank Dr. Gustavo López-Téllez (CCIQS, Universidad Autónoma del Estado de México) for assistance in XPS studies. S. A. Gama-Lara acknowledges CONACYT financial support to conduct postgraduate studies. CONACYT Project no. 269093 is also acknowledged.