Solution Combustion Synthesis, Characterization, and Photoelectrochemistry of CuNb2O6 and ZnNb2O6 Nanoparticles

This study reports on the solution combustion synthesis of two different ternary niobium oxides, namely, p-CuNb2O6 and n-ZnNb2O6. Such ternary oxides are attractive candidates in the Holy Grail search for efficient and stable semiconductors for solar energy conversion and environmental remediation. We demonstrate how this time- and energy-efficient method is capable of synthesizing high surface area and crystalline nanoparticles of the above compounds with enhanced optoelectronic properties. The synthesized crystalline samples were characterized by powder X-ray diffraction (with Rietveld refinement for phase purity), diffuse reflectance UV-visible and Raman spectroscopy, electron microscopy, and photoelectrochemical (PEC) techniques. The band structure of these oxides was probed by linear sweep voltammetry and by measuring their photoaction spectra (internal photon to electron conversion efficiency vs wavelength). The obtained bandgap energy values (1.9 and 3.2 eV for the Cu- and Zn-containing compounds, respectively) were in reasonable agreement with those obtained via electronic structure calculations (2.07 and 3.53 eV). Finally, p-CuNb2O6 showed promising activity for the PEC reduction of CO2, while n-ZnNb2O6 was active for sulfite and water photooxidation.