Synthesis, characterization and photocatalytic properties of novel zinc germanate nano-materials

We report the first instance of a hydrothermal synthesis of zinc germanate (Zn2GeO4) nano-materials having a variety of morphologies and photochemical properties in surfactant, template and catalyst-free conditions. A systematic variation of synthesis conditions and detailed characterization using X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, Raman spectroscopy, electron microscopy, X-ray photoelectron spectroscopy and small angle X-ray scattering led to a better understanding of the growth of these particles from solution. At 140 oC, the zinc germanate particle morphology changes with pH from flower-shaped at pH 6.0, to poly-disperse nano-rods at pH 10 when the Zn to Ge ratio in the synthesis solution is 2. When the Zn to Ge ratio is reduced to 1.25, mono-disperse nano-rods could be prepared at pH 7.5. Nanorod formation is also independent of the addition of cetyltrimethylammonium bromide (CTAB), in contrast to previous reports. Photocatalytic tests show that Zn2GeO4 nano-rods (by weight) and flower shaped (by surface area) are the most active for methylene blue dye degradation among the synthesized zinc germanate materials. -- Graphical abstract: Zinc germanate materials were synthesized possessing unique morphologies dependent on the hydrothermal synthesis conditions in the absence of surfactant, catalyst or template. These novel materials are characterized and evaluated for their photocatalytic activities. Display Omitted Highlights: → Zinc germanate synthesized hydrothermally (surfactant free) with unique morphologies. → Flower-shaped, nano-rods, globular particles obtained dependent on synthesis pH. → At 140 oC, they possess the rhombohedral crystal irrespective of synthesis conditions. → They are photocatalytically active for the degradation of methylene blue. → Potential applications could be photocatalytic water splitting and CO2 reduction.