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The development of a strategy to stabilise the cubic phase of HfO2 at lower temperatures is necessary for the emergence of unique properties that are not realised in the thermodynamically stable monoclinic phase. A very high temperature (>2600 °C) is required to produce the cubic phase of HfO2, whereas the monoclinic phase is stable at low temperature. Here, a novel rapid synthesis strategy was designed to develop highly crystalline, pure cubic-phase HfO2 nanoparticles (size <10 nm) using microwave irradiation. Furthermore, the as-prepared nanoparticles were converted to different morphologies (spherical nanoparticles and nanoplates) without compromising the cubic phase by employing a post-hydrothermal treatment in the presence of surface modifiers. The cytotoxicities and proliferative profiles of the synthesised cubic HfO2 nanostructures were investigated over the MCF-7 breast cancer cell line, along with caspase-3/7 activities. The low-temperature phase stabilisation was significantly attributed to surface imperfections (defects and deformations) induced in the crystal lattice by the desirable presence of Na2S·xH2O and NaOH. Our work provides unprecedented insight into the stabilisation of nanoscale cubic-phase HfO2 in ambient environments; the method could be extended to other challenging phases of nanomaterials.

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In the search for non-traditional seed oils, physicochemical parameters, fatty acid (FA) and triacylglycerol (TAG) profiles for five Botswana seed oils, obtained by Soxhlet extraction, were determined. GC-MS and 1 H-NMR analyses showed the FA profiles for mkukubuyo, Sterculia africana, and manketti, Ricinodendron rautanenii, seed oils dominated by linoleic and oleic acids, 26.1, 16.7 and 51.9, 24.4%, respectively, with S. africana containing significant amounts of cyclic FAs (19.9%). Mokolwane, Hyphaene petersiana, seed oil was typically lauric; 12:0 and 14:0 acids were 25.9 and 13.4%, respectively. Morama, Tylosema esculentum, seed oil resembled olive oil; 18:1 (47.3%) and 18:2 (23.4%) acids dominated. Moretologa-kgomo, Ximenia caffra, seed oil had 45.8% of 18:1 FA, plus significant amounts of very long chain FAs: 26:1 (5.8%), 28:1 (13.9%), 30:1 (3.9%), and acetylenic acids, 9a-18:1 (1.5%) and 9a, 11t-18:2 (16.0%). TAG classes and regiochemistry were determined with ESI-FTICR-MS, and 13 C-NMR spectra, respectively. Morama showed seven major TAG classes with C54:4 and C54:3 dominating; mokolwane had 16 major classes with C32:0, C38:0 and C42:2 dominating; manketti had 11 major classes with C54:7, C54:6 and C54:4 dominating; mkukubuyo had 12 major classes with C52:4, C52:3 and C54:4 dominating; moretologa-kgomo had 30 major TAG classes with C64:5, C64:3 and C62:3 dominating. Saturated FAs were generally distributed over the sn-1(3) position for morama, manketti, and moretologa-kgomo but at the sn-2 position for mokolwane and mkukubuyo. These findings indicate that morama and manketti seed oils can be developed for food uses, whilst moretologa-kgomo and mkukubuyo seed oils only for nonfood uses.

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