Iridium Oxide Nanoparticles and Iridium/Iridium Oxide Nanocomposites: Photochemical Fabrication and Application in Catalytic Reduction of 4-Nitrophenol

Abstract

Hydrous iridium oxide (IrOx) nanoparticles (NPs) with an average diameter of 1.7 ± 0.3 nm were prepared via photochemical hydrolysis of iridium chloride in alkaline medium at room temperature. The photoinduced hydrolysis was monitored by time-dependent ultraviolet-visible (UV-vis) spectroscopy, and the effects of the incident wavelength and irradiation time on the production of IrOx NPs were systematically investigated. It was found that UV-vis irradiation is crucial for the generation of IrOx NPs during the hydrolysis of IrCl3, and once the irradiation was turned off, the hydrolysis reaction stopped immediately. The production rate of IrOx NPs greatly depended on the incident wavelength. There is a critical wavelength of 500 nm for the hydrolysis reaction, and IrOx NPs can only be produced under the illumination with an incident wavelength shorter than 500 nm. Moreover, the shorter the incident wavelength, the faster the growth rate of IrOx NPs. The obtained IrOx NPs were highly stable during two months of storage at 4 °C. The Ir/IrOx nanocomposites were prepared by surface reduction of IrOx NPs with NaBH4. The microstructure of the Ir/IrOx composite was characterized by transmission electron microscopy (TEM), and the presence of zero-valence Ir was confirmed by the X-ray diffraction (XRD) result. The Ir/IrOx nanocomposite exhibited good catalytic activity and high recycling stability toward the reduction of 4-nitrophenol. The catalytic activity per unit surface area of the Ir/IrOx composite catalyst was increased by a factor of 15 compared to that of pure Ir catalyst. The presence of the Ir/IrOx interfaces in the composite catalyst is believed to be responsible for the high activity.

Hierarchical Cu@MnO2 Core–shell Nanowires: A Nonprecious‐Metal Catalyst with an Excellent Catalytic Activity Toward the Reduction of 4‐Nitrophenol

“…As the amount of NaBH 4 substantially exceeds that of 4‐NP in the system, the reaction can be treated as a pseudo‐first‐order reaction with respect to the concentration of 4‐NP . Thus the kinetics information can be obtained according to Equations (1)–(3): …”

“…As a result of their high specific surface area and strong adsorption ability, numerous nanomaterials have been used to catalyze the reduction of 4‐NP. These can be classified into three main categories, namely, noble metals (Ag, Au, Pt, Pd, Ir, etc. ), non‐noble metals (Cu, Mn, etc.…”

Spontaneous Deposition of Iridium onto Nickel Substrates for the Oxygen Evolution Reaction

“…For solution C (prepared from IrCl 3 ), clear peaks at 327 and 390 nm and a small peak at 550 nm were observed, and as expected the overall absorbance of this solution was much lower than the solutions prepared from H 2 IrCl 6 [22,23]. In this case, the peak at 390 nm is assigned to Ir(H 2 O) 3 Cl 3 [18], and the peak at 327 nm is assigned to the hydrolysis product [Ir(OH) 6 ] 3- [24]. Interestingly, others have suggested that ageing the precursor solution prior to use can greatly improve the deposition process [7,10,16], so it is worthwhile to note that the aged IrCl 3 solution reported elsewhere [10] 2-peaks and the development of a spectra similar to the initial IrCl 3 solution ( Figure 1b).…”

“…that between 550 and 800 nm) increased considerably during the deposition process, most likely due to the formation of IrO x nanoparticles within the solution (which exhibit a broad absorption peak around 570-580 nm [21,24,26]). In some cases, a faint blue precipitate was observed in solution B after deposition which is likely to be IrO x .…”

“…As solution B did not contain HCl like solutions A and C, this proton consumption would increase the pH near the Ni surface, which would hydrolyse [21,24,26] and possibly IrO x deposition directly onto the Ni substrate through a surface assisted nucleation process. This mechanism of oxide layer formation is very similar to cathodic deposition of oxides such as CoO x [27], which uses cathodic hydrogen evolution to increase the surface pH thereby initiating localised oxide nucleation.…”