Facile synthesis of highly efficient nano-structured gallium zinc oxynitride solid solution photocatalyst for visible-light overall water splitting

• GaZnON solid solution was synthesized through a facile technique. Due to nanoporosity distributed within the bulk and over the surface of the synthesized photocatalyst, the surface area of the synthesized photocatalyst is increased significantly, as compared to a solid solution prepared through the traditional method.
• Due to low synthesis time, Zn evaporation at a high temperature was avoided, and a Zn-rich solid solution (up to x = 0.66) was synthesized.
• A hydrogen evolution rate of 84 μmol h−1 (AQY = 2.5%) was achieved; this is among the highest rates reported in open literature for visible light water-splitting.
• The effectiveness of Zn2+ and Ga3+ layered double hydroxides (LDHs) precursors for a GaZnON solid solution preparation was confirmed experimentally through measuring the H2 and O2 gas evolutions.

Gallium-zinc oxynitride (GaZnON) solid solution is a photocatalyst capable of effective overall water splitting under visible light. In order to address the inefficiencies of the synthesis of GaZnON solid solution (e.g., 10+ h at 850 °C under 250 ml min−1 NH3 flow), a facile technique is proposed. The technique utilizes crystalline Ga3+ and Zn2+ layered double hydroxides (LDHs) material as an atomic-level uniform precursor, and urea as the nanotemplated source of nitrogen. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis confirm the formation of wurtzite GaZnON in a 12 min process through distribution of the uniform Ga3+ and Zn2+ LDHs precursor within the nanotemplate formed through urea pyrolysis. The structural, optical, and electrochemical properties of the prepared samples were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, and photoluminescence (PL) analysis. The newly synthesized photocatalyst consists of nanopores distributed uniformly through the surface and bulk of the solid solution particles; the presence of these nanopores improves the active surface area of the photocatalyst up to seven times, as compared to the one for traditionally prepared solid solution photocatalyst. The proposed technique is capable of controlling the composition of the final photocatalyst in a wide range of ZnO content ([Zn]/[Zn + Ga] up to 0.66). Apparent quantum yield (AQY) up to 2.5% at 420–440 was achieved by the photocatalyst with bulk [Zn]/[Zn + Ga] = 0.32, loaded with 1 wt% Rh nanoparticles. The effect of crystal defects and Zn content of the solid solution on the PL emission of the samples revealed that the GaZnON samples prepared with the LDHs precursor contain fewer crystal imperfections, which aids their water-splitting performance. The performance of the newly synthesized photocatalyst is among the highest reported in the open literature for photocatalysts loaded with a single co-catalyst. This photocatalyst has potential for future improvement through enhancement of the crystalline structure and improvement of the charge separation.

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