Ultra-Small Platinum Nanoparticles with High Catalytic Selectivity Synthesized by an Eco-friendly Method Supported on Natural Hydroxyapatite

Article abstract of DOI:10.1007/s10562-019-02919-z

Abstract: The biosynthesis of Pt-nanoparticles (Pt NPs) supported on bovine bone powder was conducted by an environmentally friendly method that consists on immersing bovine bone powder into a Pt⁴⁺ metal ion solution at room temperature, atmospheric pressure and subsequent reduction by Heterotheca inuloides. It is worth pointing out that a calcination process is not required for the synthesis of this catalyst by the method reported herein. The nanocomposite was characterized by transmission electron microscopy (TEM), which revealed uniformly dispersed platinum nanoparticles with quasi-spherical form and average particle size of 7.1?nm. The XPS studies exhibited the presence of 47.62% Pt° and 51.84% PtO. The catalyst activity was tested in the selective hydrogenation of 2-butyne-1,4-diol towards 2-butene-1,4-diol. The nanocomposite exhibits a reasonable catalytic performance with nearly 100% conversion of the alkyne and 96% selectivity towards 2-butene-1,4-diol. Graphic Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02919-z

Catalysis Letters
https://doi.org/10.1007/s10562-019-02919-z
Ultra‑Small Platinum Nanoparticles with High Catalytic Selectivity
Synthesized by an Eco‑friendly Method Supported on Natural
Hydroxyapatite
S. A. Gama‑Lara2 · R. Natividad1 · A. R. Vilchis‑Nestor1 · Rafael López‑Castañares3 · I. García‑Orozco3 ·
María G. Gonzalez‑Pedroza4 · Raúl A. Morales‑Luckie1
Received: 8 May 2019 / Accepted: 19 July 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
The biosynthesis of Pt-nanoparticles (Pt NPs) supported on bovine bone powder was conducted by an environmentally
friendly method that consists on immersing bovine bone powder into a Pt4+ metal ion solution at room temperature, atmos-
pheric pressure and subsequent reduction by Heterotheca inuloides. It is worth pointing out that a calcination process is not
required for the synthesis of this catalyst by the method reported herein. The nanocomposite was characterized by transmis-
sion electron microscopy (TEM), which revealed uniformly dispersed platinum nanoparticles with quasi-spherical form and
average particle size of 7.1 nm. The XPS studies exhibited the presence of 47.62% Pt° and 51.84% PtO. The catalyst activity
was tested in the selective hydrogenation of 2-butyne-1,4-diol towards 2-butene-1,4-diol. The nanocomposite exhibits a
reasonable catalytic performance with nearly 100% conversion of the alkyne and 96% selectivity towards 2-butene-1,4-diol.
Graphic Abstract
Keywords Platinum nanoparticles · Green nanosynthesis · Bionanotechnology · Heterotheca inuloides · Selective catalyst
3
* R. Natividad
reynanr@gmail.com
Laboratorio de Investigación y Desarrollo de Materiales
Avanzados Facultad de Química, Universidad Autónoma del
Estado de México, A.P. A-20, 50120 Toluca, Mexico
* Raúl A. Morales-Luckie
4
ramluckie@gmail.com
Doctorado en Ciencia de Materiales de la Facultad
de Química, Universidad Autónoma del Estado de
México, Paseo Colón Esquina Paseo Tollocan S/N,
C.P. 50000 Toluca, Estado de México, Mexico
1
Centro Conjunto de Investigación en Química Sustentable
UAEM-UNAM, Universidad Autónoma del Estado de
México, Carretera Toluca-Atlacomulco Km 14.5, San
Cayetano, 50200 Toluca, Estado de México, Mexico
2
Universidad del Valle de México, De Las Palmas 439, San
Jorge Pueblo Nuevo, 52164 Metepec, Estado de México,
Mexico
Vol.:(0123456789)
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S. A. Gama-Lara et al.
are economic viability, environmentally friendly, easily
scalable, and that can be performed at room temperature
and atmospheric pressure. In this research, Heterotheca
inuloides (Mexican arnica) was assessed as reducing agent
to synthesize platinum nanoparticles on bovine bone in
order to prove that this biosynthesis is low-cost, sim-
ple, friendly to the environment (the only used solvent
is water and strong reducing agents are not required). In
addition, the catalytic activity of the as-prepared material
was assessed in the hydrogenation of 2-butyne-1,4-diol
towards 2-butene-1,4-diol.
1 Introduction
In the last decades, the study of nanostructured systems
has been conducted by diferent research groups. This is
because such systems exhibit unique properties that allow
them to be applied in diferent areas like catalysis, health
care and others [1–4].
In the context of nanoparticles synthesis, special atten-
tion has been given to the use of environmentally friendly
reagents and materials in order to increase the sustainabil-
ity of the synthesis process [4]. Actually, it can be said that
green chemistry is the goal of many researchers around the
globe [1, 3–10]. It is of special interest the supports where
nanoparticles are dispersed [5, 11–17]. Support materials
such as silica [14], amorphous titania, cellulose [2], nylon,
hexylamine and calcite (CaCO3), among others, have been
used [2, 11, 13]. The use of bio-supports such as cork [15],
cotton [11, 16], bone [12] and shells, results in a rela-
tively low-cost, renewable and environmentally friendly
way of supporting metal nanoparticles [12–16]. For exam-
ple, the one-step synthesis of platinum nanoparticles sup-
ported on wood has been reported. This was conducted
by using hydroxyl groups (OH−) as reducing agent. The
synthesized nanomaterial exhibited a high and relatively
stable activity in the catalytic reduction of p-nitrophenol
[17]. In the present investigation, bovine bone powder was
used as support. This material is constituted by 60–70%
hydroxyapatite [Ca10(PO4)6(OH)2]. This is advantageous
since the OH− and PO43− groups work as binding sites for
the metal nanoparticles. In addition, bovine bone powder
is a low-cost, easy-to-treat, biodegradable and renewable
material. Furthermore, hydroxyapatite importantly con-
tributes to the mechanical strength, chemical stability at
extreme pH and thermal stability of the synthesized com-
posite. At the same time, hydroxyapatite works as a nano-
reactor and provides of stability to nanoparticles, improv-
ing the catalytic efect.
2 Materials and Methods
2.1 Pt/Bovine Bone Biosynthesis
The precursor compound of platinum nanoparticles was
PtCl4. A 1 mM solution was prepared with 50 mL of deion-
ized water (solution 1). Solution 2 was prepared by boiling
during 5 min in an Erlenmeyer fask, 1 g of dried H. inu-
loides with 100 mL of distilled water. In order to prepare the
support, a bovine femur was washed, cleaned and immersed
in a 0.01 M HCl solution. Later, the support was dried in an
oven at 40 °C for 24 h, then it was crushed and sieved by
using a 170 mesh. 975 mg of the so obtained powder was
added to solution 1 and after 30 s, the powder was fltered.
The reduction of Pt(IV) ions was carried out with solution
2 during 1 h and then fltered. The resulting material was
dried at room temperature overnight. Calcination is a com-
mon practice in the synthesis of heterogeneous catalysts, in
this case, however, it is worth noticing that the synthesized
composite was not calcined at any time. A micellar activity
might also be expected since the micelle formation of sepia
cartilage collagen solutions has been previously reported
[29].
2.2 Characterization
Diferent methods (laser ablation or chemical meth-
ods) have been used to obtain metal nanoparticles. In
this sense, several investigations have reported biological
methods to reduce metal nanoparticles using bioreducers
such as honey [18], safron [19], tannins [20], nopal [21],
caliandra [21], Camellia sinenses [22], fruits [23], chili,
bacteria, alfalfa, among many others [4, 18, 19, 22–24].
In this sense, plant extracts containing bioactive particles
such as alkaloids, phenolic acids, polyphenols, benzoic
acid, cofeic acid and proteins, have been reported [11,
20, 21, 25–27] to play an important role in reducing and
stabilizing metallic ions. It is also well known that the use
of typical chemical methods leads to toxic products for
both, environment and humans [4, 28]. On the other hand,
the known advantages of biosynthesis or green synthesis
Transmission electronic microscopy (TEM) and selected
area electron difraction (SAED) studies were carried out
using a JEOL JEM-2100 microscope operating at 200 kV
accelerating voltage. The platinum-impregnated bovine bone
powder was suspended in 2-propanol and then ultrasonically
dispersed for 5 h at room temperature. A drop of this suspen-
sion was then placed on a Cu-grid coated with a holey car-
bon flm. Also, the supported platinum nanoparticles were
analyzed by SEM technique.
The X-ray photoelectronic spectroscopy (XPS) analy-
sis 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 results.
1 3

Ultra-Small Platinum Nanoparticles with High Catalytic Selectivity Synthesized by an…
Charge correction was done based on the adventitious car-
bon signal (C 1s) at 284.5 eV. Shirley method was used for
background adjustment, whereas Gauss-Lorentz method was
used for curve ftting.
Samples were analyzed by gas chromatography with
a fame ionization detector using a 456 SCION GC (DB-
WAX 52 column, length 32 m, inner diameter= 0.3 mm)
and helium (30 mL/min) as a carrier gas, according to previ-
ously reported analysis methods [30–33]. Reaction samples
were injected into the GC and analyzed under the following
conditions: temperature detector was set at 518 K, injector
temperature at 513 K, the initial oven temperature was 353 K
and this was raised up to 493 K at a rate of 10 K/min. This
fnal oven temperature was kept constant for 3 min.
2.3 Hydrogenation of 2‑Butyne‑1,4‑diol
The hydrogenation of 2-butyne-1,4-diol was carried out in a
300 mL stainless-steel Parr reactor equipped with a tempera-
ture control system, a mechanical stirrer, pressure indicator,
an inner heating/cooling coil system and sampling valve. A
reservoir for H2 gas was used along with a constant pres-
sure regulator to supply hydrogen at a constant pressure to
the reactor.
3 Results and Discussion
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
frst fushed 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 a 550 rpm stirring speed was set at all experiments.
Samples were obtained every 30 min.
3.1 Characterization
3.1.1 Transmission Electron Microscopy (TEM) Analysis
Figure 1a–c shows BF-STEM images where the platinum
nanoparticles supported on bovine bone dust are clearly
observed. The diference in electronic density allows to
diferentiate the platinum from the support that is consti-
tuted by hydroxyapatite (carbon, calcium, phosphorus and
Fig. 1 a–c BF-STEM images of
Pt nanoparticles on bovine bone
powder, at diferent magnifca-
tions, d size distribution of
platinum nanoparticles
1 3

S. A. Gama-Lara et al.
oxygen), BFSTEM shows metallic particles in a darker color.
The particle size is in the range of 3 to 40 nm, with few
exemptions that are out of the particle size distribution. The
images reveal that quasi-spherical Pt NPs with low size and
low polydispersity are obtained into the bovine bone sur-
face. These images correspond to a randomly chosen part
of the substrate and can be considered as representative of
the overall size and shapes of the particles.
In addition, XPS was used to determine the oxidation
state of the platinum nanoparticles. The narrow spectra in
the Pt 4f region and its curve ftting, show two oxidation
states for platinum (Fig. 3). The components at 70.9 eV
(4f7/2) and 74.4 eV (4f5/2) can be attributed to metallic
platinum in around 47.62% of the total platinum, the energy
separation of 4f7/2 and 4f5/2 is 3.5 eV corresponding to
that reported for platinum, the ratio proportion intensity of
the orbitals 4f7/2 with respect to 4f5/2 is 4:3 as it could be
corroborated. The signals at 72.5 eV (4f7/2) and 76.7 eV
(4f5/2) correspond to 51.84% of the total platinum and can
be ascribed to platinum oxide. The energy separation of
4f7/2 and 4f5/2 is 3.1 eV corresponding to that reported
for platinum, the ratio proportion intensity of the orbitals
4f7/2 with respect to 4f5/2 is 4:3 as it could be corroborated.
These images correspond to Pt nanoparticles on the
bovine bone powder after 5 h of ultrasonication. The aver-
age diameter of synthesized nanoparticles was found to be
7.1 nm, taking into account 600 nanoparticles approximately
(Fig. 1).
The use of bovine bone as catalytic support and H. inu-
loides as reducer is rather novel. This synthesis method is
relatively low-cost and environmentally friendly since the
reducer and the support are easily biodegradable, the solvent
is water and the calcination step followed by reduction with
hydrogen is eliminated. Moreover, the chemical structure
of hydroxyapatite can form stable compounds and anchor
the metal ions.
Figure 2 shows two images of HRTEM where two parti-
cles of platinum supported on bovine bone powder can be
observed, one of the platinum particles has an interplanar
distance of 2.25 Å which corresponds to the plane (111)
for metallic platinum FCC. In the other micrograph, two
interplanar distances are identifed, one with 2.25 Å that
corresponds to the plane (111) of FCC metallic platinum
(JCPDS card 00-004-0802) and the other with 2.66 Å that
corresponds to the plane (101) of tetragonal platinum oxide
(JCPDS card 00-043-1100). Therefore, it can be concluded
that the platinum nanoparticles are polycrystalline.
By observing the shape and chemical composition of nan-
oparticles, a fast reduction appears to rule the synthesis of
platinum nanoparticles with H. inuloides as reducing agent
since polycrystalline isotropic particles are obtained [34].
Fig. 3 XPS spectra corresponding to the 4f5/2 (pink line) and Pt
4f7/2 (dark green line) regions of the platinum nanoparticles sup-
ported on bovine bone dust
Fig. 2 HRTEM micrograph Pt-
nanobiocomposite
1 3

Ultra-Small Platinum Nanoparticles with High Catalytic Selectivity Synthesized by an…
These results indicate that the reduction of Pt(IV) to Pt°
indeed took place and that Pt nanoparticles were supported
onto the bovine bond powder in controlled size and shape.
3.2 Catalytic Activity
The catalytic activity of the synthesized powder was estab-
lished in the hydrogenation of 2-butyne-1,4-diol. This reac-
tion has been reported to be catalyzed by metallic Pt or Pd
[32, 33, 35]. Therefore, the exhibited catalytic activity can
be taken as an additional proof of the presence of metal-
lic nanoparticles obtained by employing the bio-reducer H.
inuloides. Nevertheless, the XPS results shows the presence
of oxidized Pt and the catalytic contribution of this specie
should not be discarded [36]. The referenced reaction has
Fig. 4 Concentration and selectivity profles for the hydrogenation of
been reported to proceed as depicted in Scheme 1. Accord-
ing to this scheme, the consumption of the frst hydrogen
mole leads to the production of the usually desired inter-
mediary, 2-butene-1,4-diol. The further consumption of H2
produces the saturated diol (butanediol) and by-products like
crotyl alcohol and/or butanol. Thus, in the context of this
reaction, achieving a high selectivity towards 2-butene-1,4-
diol, represents a challenge that has been usually addressed
by adding chemical bases or by modifying the reactor hydro-
dynamics [32]. Figure 4 is the evidence that the synthesized
material not only exhibits catalytic activity but also a high
selectivity (0.96) towards the alkene.
2-butyne-1,4-diol. Reaction conditions: temperature, 328 K; pressure,
6 bar; initial concentration, 20% aqueous solution of 2-butyne-1,4-
diol; active concentration of the catalyst, 0.215 mg; stirring speed,
550 rpm; total volume, 1.5×10−4 m3
when the surface coverage by the alkyne is relatively high.
This results in the zero-order kinetic equation regarding
2-butyne-1,4-diol [37].
Finally, it is worth noticing that the synthesized catalyst
consisting on platinum nanoparticles supported on bovine
bone powder, eliminates the use of base addition to obtain a
selectivity above 90% in the hydrogenation of 2-butyne-1,4-
diol. For the same reaction, Telkar et al. indicate that with
1% Pt/CaCO3 they obtained a selectivity of 83% and when
adding ammonia in the hydrogenation reaction, 100% selec-
tivity is obtained [35]. This suggests that the attained high
selectivity in this work might be ascribed to an enhanced
basicity of the biosynthesized catalyst. A heterogeneous
catalyst selectivity, however, might be infuenced by other
factors like particle size and shape [38]. In this case, as
we are dealing with nanoparticles, it is very likely that the
observed high selectivity might also be related to the aver-
age nanoparticle size (7.1 nm). In this regard, it has been
demonstrated [38] that nanoparticle size might change the
activation energy of a specifc reaction and thus selectivity.
In the same work [38], it was shown that platinum nano-
particles shape (cubes or cuboctahedra) leads to complete
diferent products distribution in the hydrogenation of ben-
zene. Therefore, the fact of having obtained semi-spherical
The kinetics of the 2-butyne-1,4-diol hydrogenation
was established by the integral method. A linear relation-
ship between 2-butyne-1,4-diol concentration and reac-
tion time was found when plotting the former versus the
latter. By doing this, the specifc rate constant was found
to be ko = 0.001 mol/dm3 min. Thus, it can be concluded
that under the studied conditions, the hydrogenation rate is
independent of the alkyne concentration (zero order reac-
tion regarding 2-butyne-1,4-diol). This reaction has been
reported to follow a Langmuir–Hinshelwood mechanism
when using Pd as active phase [32, 33, 37].
This mechanism suggests that both H2 and the alkyne, are
chemisorbed and compete for the same type of sites. It has
been demonstrated [32] though, that the alkyne chemisorbs
stronger than hydrogen and that olefns. This implies that
the adsorption equilibrium constant for the alkyne is much
higher than that of the other compounds. Therefore, the
adsorption of hydrogen and the products can be neglected
Scheme 1 2-butyne-1,4-diol
hydrogenation scheme [33]. A:
2-butyne-1,4-diol, B: 2-butene-
1,4-diol, C: butane-1,4-diol, D:
crotyl alcohol, E: n-butanol
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S. A. Gama-Lara et al.
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Metallic platinum nanoparticles supported on bovine bone
powder were synthesized by using as reducing agent H.
inuloides (Mexican arnica). The average diameter of syn-
thesized nanoparticles was found to be 7.1 nm. The result-
ing bio-nanocomposite exhibits catalytic activity to con-
duct hydrogenation reactions with high selectivity (96.5%)
towards the intermediary in a consecutive hydrogenation
reaction.
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Acknowledgements We thank Dr. Gustavo López-Téllez (CCIQS,
Universidad Autónoma del Estado de México) for assistance in XPS
studies and Citlalit Martínez for technical support. S.A. Gama-Lara
acknowledges CONACYT fnancial support to conduct postgraduate
studies. CONACYT Project 269093 is also acknowledged.
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RWD, Mendis de Silva R, Udagama PV (2017) Honey mediated
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Compliance with Ethical Standards
Conflict of interest The authors declare no confict of interest.
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