Metal hydroxide-based hydrogels for the thermal preparation of Mg–Zn–O particles

Abstract

The thermal treatment of magnesium and zinc hydroxy hydrogels prepared at different ratios leads to three distinct particle systems: (i) Mg-rich systems form spherical-shaped heterogeneous nanoparticles with size in the range of 11–32 nm, while (ii) increasing the amount of Zn leads to the formation of elongated nanorods and further (iii) to the formation of unprecedented sandwiched rod-like MgO–ZnO heterostructures with evidence of layered growth. Structural analysis confirms segregated cubic MgO and wurtzite ZnO domains rather than solid solutions, with Mg-domains promoting isotropic growth and Zn-based ones favoring anisotropic extension along the c-axis. The photoluminescence spectra for Zn-rich systems is dominated by excitonic emission (λ = 380 nm) along with low defect emission (λ = 440–450 nm), while Mg-rich ones exhibit surface-state transitions (400–430 nm) from MgO electronic decay, showing an intensity dependence on particle size distribution. Notably, the 1 : 1 combination gives rise to a distinct spectral pattern, most likely due to the lower particle size, which may enhance interfacial electronic coupling. The particles are formed at 400 °C, which is remarkably energy-efficient compared to the 500–700 °C range in the conventional methods. This hydrogel-blending approach provides a versatile platform for designing oxide nanomaterials with tailored architecture and properties.