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Lookup NU author(s): Professor Lidija Siller
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
In the present study, we report a surfactant free ammonia and carbamide precursor-modulated engineering of self-assembled flower-like 3D NiO nanostructures based on ordered β-Ni(OH)2 and turbostratic Ni3(OH)4(NO3)2 nanoplate structured intermediates. By employing a variety of complementary structural and spectroscopic techniques, fundamental insight into the structural and chemical transformation from intermediates to NiO nanoparticles (NPs) is provided. FTIR, Raman and DSC show that the transformation of intermediates to NiO NPs goes through subsequent loss of NO3− and OH− species, through double step phase transformation at 306 °C and 326 °C, corresponding to free interlayers ions and H2O species loss, followed by loss of chemically bonded OH− and NO3− ions. In contrast, transformation to NiO NPs via ammonia route proceeds as a single phase-transition, accompanied with loss of OH− species at 298 °C.The full transformation to NiO nanoparticles (NPs) of both intermediates is achieved at 350 °C by annealing in the air atmosphere. Ammonia derived NPs keep the nanoflower morphology by self-assembly into nanoplates, enabled by H2O mediated adhesion on the NiO NPs {100} type neutral surfaces. In contrast, structural transformations of turbostratic Ni3(OH)4(NO3)2 nanoplates result in formation of NiO NPs dominantly shaped by inert polar OH terminated (111) atomic planes, which leads to loss of initial self-assembled 3D structure. DFT calculations support these observations, confirming that H2O adsorbs dissociatively on polar {111} surfaces, while only physisorption is energetically feasible on {100} surfaces. Besides different surface morphology that drives NPs water interaction, the NiO NPs obtained by two different routes have overall different properties, such ascarbamide derived NiO NPs are almost 3 times larger (15.5 nm vs 5.4 nm), possess larger band gap (3.6 eV vs 3.2 eV), and are more Ni deficient. The intensity ratio of the surface optical (SO) modes to the transversal and longitudinal optical modes (TO and LO) is ~ 40 times higher in the NiO NPs obtained from β-Ni(OH)2 as compared to those obtained from Ni3(OH)4(NO3)2. While the LO and TO phonon lifetimes are similar in both NiO products, the SO phonon lifetime is an order of magnitude shorted in NiO obtained from β-Ni(OH)2, reflecting the much smaller NP size.This work elucidates the formation of NiO NPs and their self-assembly via ammonia and carbamide hydroxide precursors. The choice of the precursor defines the size, morphology, crystallographic surface orientations and band gap of the NiO NPs, with Ni deficiency providing pathways of utilizing their application as a p-type material. Moreover, precursor choice allows precise nanoengineering of both polar and neutral surfaces dominated NiO NPs, which are of exceptional importance to the use of NiO in catalysis.
Author(s): Pejova B, Eid A, Lari L, Althumali A, Kerrigan A, Šiller L, Pejov Lj, Lazarov VK
Publication type: Article
Publication status: Published
Journal: Nanoscale
Year: 2024
Pages: epub ahead of print
Online publication date: 20/09/2024
Acceptance date: 19/09/2024
Date deposited: 07/10/2024
ISSN (print): 2040-3364
ISSN (electronic): 2040-3372
Publisher: Royal Society of Chemistry
URL: https://doi.org/10.1039/D4NR03255A
DOI: 10.1039/D4NR03255A
Data Access Statement: The datasets generated and analysed during the current study are available from the authors on reasonable request.
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