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Unveiling the shapes of platinum nanoparticles: Why are spheres, strips, and cubes so fascinating?
Platinum nanoparticles exist in the form of suspension or colloid, usually suspended in water. This type of colloid is technically defined as a stable dispersion of particles in a fluid medium (liquid or gas). Depending on the reaction conditions, the size of the spherical platinum nanoparticles can range from about 2 to 100 nanometers (nm). These nanoparticles appear brownish-red or black in colloidal solutions and have a variety of shapes, including spheres, strips, cubes, and tetrahedrons. Platinum nanoparticles have been widely studied due to their potential applications in catalysis, medicine, and synthesis of new materials.
Synthesis method
There are two main methods for synthesizing platinum nanoparticles. One is to reduce the platinum ion precursor dispersed in the solution and use stabilizers or blocking agents to form colloidal nanoparticles; the other is to penetrate and reduce the platinum ion precursor into micropores like bauxite in the supporting materials. Some common platinum precursors include potassium hexachloroplatinic acid (K2PtCl6) or platinum chloride (PtCl2).
The shape and size of platinum nanoparticles are affected by many factors, including synthesis methods, solvents, and external conditions.
Combination of different precursors, such as ruthenium chloride (RuCl3) and chlorinated platinum acid (H2PtCl6), Also used to synthesize mixed metal nanoparticles. Common reducing agents include hydrogen (H2), sodium hydride (NaBH4) and ethylene glycol (C2H6 O2), in addition to other alcohol and plant-derived compounds. When the platinum metal precursor is reduced to neutral platinum metal (Pt0), the reaction mixture will be supersaturated and precipitate in the form of nanoscale particles. Stabilizers such as sodium polyacrylate or sodium citrate are often used to stabilize the surface of nanoparticles and prevent their aggregation.
Shape and size controls
Research shows that ligands and solvents have an important impact on the size and shape of platinum nanoparticles. Ramirez et al. reported the discovery that platinum nanoparticle seeds were prepared by decomposing Pt2(dba)3 in tetrahydrofuran (THF) under a carbon monoxide atmosphere. The particles produced under these conditions are surrounded by weakly bound THF and CO ligands and are approximately 1.2 nm in diameter. After cleaning, hexadecylamine (HDA) was added to replace THF and CO ligands. After about seven days, monodisperse spherical crystalline platinum nanoparticles with an average diameter of 2.1 nm were formed.
When stronger blocking agents such as triphenylphosphine or dedecanethiol were used, the nanoparticles retained their spherical shape, indicating the effect of HDA ligands on particle shape.
In terms of controlling shape and size, different polymer blocking agent ratios relative to changes in precursor concentration can also achieve the desired effect. Such reducing colloid synthesis can produce a variety of shapes such as tetrahedrons, cubes, irregular prisms, icosahedrons, and octahedrons, and its dispersion depends on the concentration ratio of blocking agent to precursor.
Green synthesis method
By utilizing persimmon (Diospyros kaki) leaf extract as a reducing agent, an eco-friendly synthesis from chloroplatinic acid was achieved. The synthesized nanoparticles were spherical in shape with a diameter ranging between 212 nm. Different reactions Temperature and leaf extract concentration affected the size of the synthesized particles. Through spectral analysis, it was found that the reaction was not promoted by enzymes, but was reduced by plant-derived small molecules.
Properties and applications
The chemical and physical properties of platinum nanoparticles make them suitable for a variety of research applications, including electronics, optics, catalysis, and enzyme immobilization.
Platinum nanoparticles are widely used as catalysts, including hydrogen oxidation reactions, industrial synthesis and reduction of automobile exhaust gases.
Platinum nanoparticles, under the influence of their shape, size and morphology, can exert catalytic effects in homogeneous colloidal solutions or as gas phase catalysts supported on solid materials. Their optical properties are also fascinating, as they exhibit the characteristic surface plasmon resonance (SPR) phenomenon in the ultraviolet range. This property gives them broad potential in electronics, catalysis, sensing and photovoltaic applications.
However, the biological interactions of platinum nanoparticles are still under further study, and their toxicity issues also need to be carefully considered. Although they have broad potential for medical applications, responses and effects on organisms still need to be carefully evaluated. How do platinum nanoparticles exert their effectiveness in different biological environments and what impact will they have on life? Is it worth pondering?
