Ir Nanoparticle Morphology Control And Its Catalytic Performance

Due to their some special physical and chemical properties, Ir nanoparticles with different shape, including Ir nano-needles, Ir nano-spheres, Ir nano-wires, and Ir nano-rods, can be used in electronic technology, biomedical science, petrochemical, aviation, environmental protection. However, there is less literatures about the synthesis of shape-selective Ir nanoparticles. In this paper, Ir nanoparticles with different morphologies and particle size were synthesized using photochemical synthesis. Catalytic properties of Ir nanoparticles for C18H37SiH3were investigated. The formation mechanism of Ir nanoparticles and the catalytic mechanism of Ir nanoparticles with different morphologies and particle size for C18H37SiH3were studied. Here, Ir nanoparticles were synthesized by photochemical synthesis in alkaline PEG-400aqueous solution using Chlorine iridium acid as a precursor, PEG-400as dispersing agent,2,7-DHN as a reducing agent. The as-prepared catalysts were characterized by UV spectrophotometer, the zeta potential instrument, TEM, EDS, XPS, and Fourier transform infrared spectroscopy (FT-IR). The results showed as follows:(1) The UV absorption spectra of iridium colloid occurs regular variation with the synthesis time. The UV absorption spectra varied slightly when the reaction time were6hours, indicating that reaction completely. However, the UV absorption spectra changed if the ultraviolet irradiation time was extended to16hours;(2) The test results of the zeta potential indicate the stability of the colloid is good. The stability of the colloids decreased with increasing of the pH value. The higher concentration of reducing agent, the more stable colloid would be obtained. The stability of Iridium colloids synthesized under4h of UV-irradiation is the best.(3) TEM images revealed that Ir nanoparticles synthesized in this paper have different morphologies, including needle-shaped, nano-wires, nano-spheres and nano-rods. The morphology and size of the iridium nanoparticles were seriously affected by the reaction time. TEM images showed that there are so many activities dispersed on the surface of Ir nanoparticles and the average size of these activities was 3±0.5nm.(4) TEM images of Ir nanoparticles synthesized in PEG-400-free aqueous solution showed that the nature of Ir element contributed to the formation of the iridium nano-particles with different morphology. In the absence of2,7-DHN, Ir nanoparticles were not synthesized. This indicates that PEG-400just act as dispersing agent and not reducing agent.(5)The XPS results showed that the surface chemical state of iridium nanoparticles were metal state (Ir0) and uncompletly reducing state (Irδ+).(6) The catalytic activity of iridium nanoparticles with different morphologies were tested by the infrared spectrometer. Ir nano-wires and Ir nano-spheres show higher catalytic activity for C18H37SiH3. The electrochemical test results suggest that the iridium nanoparticles show no electrocatalytic activity for methanol oxidation. Ir nanoparticles showed high catalytic activity for C18H37SiH3, and the catalytic properties of Ir nano-spheres was the best.The formation mechanism of Ir nanoparticles was investigated. We think the concentration of reducing agent and the Ir(Ⅳ) precursor plays a important role in the formation of Ir nanoparticles, including nano-needles, nano-spheres, and nano-rods. The formation of Ir nano-needle is the result of its nature and having nothing to do with the template or dispersing agent. The formation of Ir nano-spheres and Ir nano-rods has to do with saturation of Ir(Ⅳ) complexes. The formation mechanism of Ir nano-wires and Ir nano-dendritics is not clear, needing to further study.