We devised an alternative, faster and simple method to prepare hierarchically nanoporous ZnO powders (NZnO) via a quick interfacial reaction (double emulsion) from the mixtures of zinc nitrate hexahydrate (solution, Zn(NO₃)₂·6H₂O), n-hexane (C₆H₁₄), ammonium bicarbonate (NH₄HCO₃), Tween 80 (C₆₄H₁₂₄O₂₆) and Span 80 (C₂₄H₄₄O₆), which was calcined at 450 °C. Due to the micro/nanopore structures, the obtained NZnO powders had a larger surface area (∼69.7 m² g⁻¹) than the commercial ZnO powders. For the thermoelectric evaluation, the textured NZnO pellets (T-NZnOP) were prepared by low pressure spark plasma sintering (SPS) using the newly synthesized NZnO powders (NZnO). In this study, the synthesized NZnO powders that were made into T-NZnOP (sample pellets) showed a significantly lower thermal conductivity with distinctive electrical properties when compared to the bulk commercial ZnO powders. The thermoelectric enhancement can be attributed to the nanopore distribution found in the porous T-NZnOP material which demonstrates the potential usefulness of this method for other porous oxide thermoelectric (TE) materials.

We show an eco-friendly non-toxic approach to the synthesis of nano-size hollow silicate particles (NSHSPs) templated using hydroxyapatite (1.75 Ca/P) nanoparticles.