Perovskite-type lanthanum nickel oxide (lanthanum nickelate, LaNiO3) nanoparticles with high photocatalytic activity were synthesized via a mechanochemical route. A high-energy planetary ball mill was employed for mechanochemical preparation of an activated precursor of LaNiO3 via a solid-state reaction of LaCl3, NiCl2, and NaOH. The mechanochemical treatment was performed for 1 h at a revolution speed of the milling pot of 600 rpm. In comparison to an un-milled precursor, a simple mixture of La(OH)3, Ni(OH)2, and NaCl, the activated precursor demonstrated that the mechanochemical treatment contributes to the formation of LaNiO3 at low temperatures. This effect, in turn, leads to reduction of the optical band gap, i.e., enhancement of the visible light photocatalytic activity. Standard characterization techniques confirmed that crystalline round LaNiO3 nanoparticles with a median diameter of 46 nm, a surface area of 23 m 2 /g, and an optical band gap of 1.09 eV were obtained after calcination of the mechanochemically treated precursor at 873 K for 1 h. The visible-light-driven 2 photocatalytic activity was evaluated based on the photodegradation of methyl orange in an aqueous solution. The LaNiO3 catalyst nanoparticles efficiently decomposed methyl orange more than 99% of methyl orange was removed from the solution in 2 h, indicating that the LaNiO3 nanoparticles possess good photocatalytic properties.
To synthesize nitrogen-doped carbon nanofibers (N-CNFs) at high growth rates and low temperatures less than 673 K, nickel species (metallic nickel and nickel oxide) supported on alumina particles were used as the catalysts for an acetonitrile catalytic chemical vapor deposition (CVD) process. The nickel:alumina mass ratio in the catalysts was fixed at 0.05:1. The catalyst precursors were prepared from various nickel salts (nitrate, chloride, sulfate, acetate, and lactate) and then calcined at 1073 K for 1 h in oxidative (air), reductive (hydrogen-containing argon), or inert (pure argon) atmospheres to activate the nickel-based catalysts. The effects of precursors and calcination atmosphere on the catalyst activity at low temperatures were studied. We found that the catalysts derived from nickel nitrate had relatively small crystallite sizes of nickel species and provided N-CNFs at high growth rates of 57 ± 4 g-CNF/g-Ni/h at 673 K in the CVD process using 10 vol% hydrogen-containing argon as the carrier gas of acetonitrile vapor, which were approximately 4 times larger than that of a conventional CVD process. The obtained results reveal that nitrate ions in the catalyst precursor and hydrogen in the carrier gas can contribute effectively to the activation of catalysts in low-temperature CVD. The fiber diameter and nitrogen content of N-CNFs synthesized at high growth rates were several tens of nanometers and 3.5 ± 0.3 at.%, respectively. Our catalysts and CVD process may lead to cost reductions in the production of N-CNFs.
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