Activation of Titanium for Synthesis of Supported and Unsupported Metallic Nanoparticles

Abstract

Titanium (Ti) resists corrosion due to spontaneous passivation and subsequent formation of a stable, substantially inert oxide film. This passive film limits the reducing ability of Ti in wet chemical synthesis. Aggressive anions are applied here to destabilize Ti passivity, with the objective of activating Ti as a reducing agent for wet-chemical synthesis, through the formation of unsupported and supported metallic nanoparticles (MNPs). For instance, within the first minute of Ti immersion in a standard gold solution (SGS), 1000 ± 3 μg Au/mL in 2% HCl, gold nanoparticles (AuNPs) in solution (unsupported) and a considerable population of highly dispersed AuNPs on Ti (Ti-supported AuNPs) are obtained. This occurs at room temperature, without using reducing agents, stabilizers, or any chemical pre-treatments. Electrochemical measurements revealed that the passivity of Ti was destabilized (oxide thinning/dissolution) in the SGS. The addition of F − to the SGS promoted destabilization of the passive film, and hence activated the reducing ability of Ti. This in turn resulted in significant increase in the population of AuNPs on Ti. Reduction of cations in solution by the active nascent (atomic) hydrogen (H) generated by substrate (Ti) dissolution, promoted by the addition of F − , in acidic medium is confirmed here and discussed vs. conductivity of the oxide (passive) film and solution pH. Experimental findings reveal that the relevance of H as the actual reducing agent is limited to instantaneous and non-conductive passive films. Solution pH studies on such passive films show that the Nernst equation (dE H/H + /d(pH) = −0.059 V) controls the wet chemical synthesis of MNPs rather than E o reduction of the base metal (the substrate). Based on polarization measurements, the prepared Ti-supported AuNPs are demonstrated here as highly active electrocatalysts (better than Pt) for the hydrogen evolution reaction (HER) in 0.1 M HCl solution.Nanoparticles constitute a key area of research and development in the burgeoning field of nanotechnology. The attraction of nanoparticles lies in the myriad of attractive characteristics which can be achieved by reducing suitable materials from the bulk to the nanometer size, these characteristics ranging from increased surface/volume ratio to novel quantum confinement effects. 1 Examples of property enhancements include magnetic, optical, biosensing, thermoelectric, semiconducting, catalytic, energy storage and thermal properties. 2-7 An interesting aspect of nanoparticles is the wide range of material classes in which nanoparticles are useful, including semiconductor, dielectric, metallic, ceramic, composite and polymer nanoparticles. For these reasons, metal nanoparticles have attracted a high interest in scientific research and industrial applications. [8][9][10] Metal nanoparticles (MNPs) can be produced by reducing metal salts with reducing agents and stabilizing them with capping ligands, 11 and they can be subsequently attached to another metal. However, it is more desirable to d...

The Influence of Microstructure on the Passive Layer Chemistry and Corrosion Resistance for Some Titanium-Based Alloys

“…Further, Figure 9a demonstrates that the rate of j a decay, and consequently the rate of passive layer growth, diminished upon alloying Ti with V and Nb. These results further confirm the influence of the alloying elements V and Nb, with V being more active than Nb, which, when added to Ti, weakened its passivity viadepassivation (destabilizing the passive oxide film through oxide film thinning/dissolution [56]). This in turn madethe passive film more susceptible to pitting.…”

Exploring the Influence of the Microstructure on the Passive Layer Chemistry and Breakdown for Some Titanium-Based Alloys in Normal Saline Solution

“…10 (a) demonstrates that the rate of ja decay, and consequently the rate of passive layer growth, diminishes upon alloying Ti with V and Nb. These results further confirm the acceleration influence of the alloying elements V and Nb, with V being more active than Nb, which when added to Ti weakened its passivity via depassivation (destabilizing the passive oxide film through oxide film thinning/dissolution [43]). This in turn makes the passive film more susceptible to pitting.…”

Room-Temperature Wet Chemical Synthesis of Au NPs/TiH2/Nanocarved Ti Self-Supported Electrocatalysts for Highly Efficient H2 Generation

“…The morphologies of such catalysts are displayed in Figure . Our previous study revealed that the formation of metallic Au on Ti surface was not due to a simple galvanic displacement between metallic Ti and Au 3+ in the precursor solution. The actual reducing agent by which Au 3+ ions are reduced to the corresponding metallic form proved to be the atomic hydrogen (H) produced as a result of the interaction between water molecules and the base metal (Ti).…”

“…Catalysts 1 and 2 (Self-Supported TiH 2 /Nanostructured Ti). Ti foils (99.7% metal basis and 0.25 mm thick) were first cut into small sheets (1.0 cm × 1.0 cm) and polished as described elsewhere, 25,26 then dipped into 10 mL of two etching baths, namely, 98% H 2 SO 4 solution without (bath 1, for the preparation of catalyst 1) and 0.1 M NH 4 F (bath 2, for catalyst 2 synthesis) at room temperature. After 15 min of soaking, the etched Ti sheets (i.e., catalysts 1 and 2) were taken out of the etching bath and washed several times with water and ethanol before drying their surfaces with the N 2 gas to be ready for surface analysis and electrochemical characterization.…”

“…Lu et al 23 combined Ti with copper (Cu) to produce a hierarchical nanoporous highly efficient copper−titanium bimetallic electrocatalyst for the HER in alkaline solutions. In our lab, the surface of Ti was decorated with highly dispersed Ag 24 or Au 25 nanoparticles for enhanced electrochemical generation of H 2 .…”