Aluminum nanopowder from aluminum wastes recycling: a key additive for high-performance ZnO/ZnAl₂O₄ spinels in photocatalytic wastewater treatment

This study explores the recycling of aluminum (Al) waste by synthesizing Al nanopowder, which is directly added to zinc oxide (ZnO) sol to develop zinc oxide/zinc aluminate (ZnAl₂O₄) spinels. This work investigates the impact of Al nanoparticles on the crystalline structure, physicochemical properties, and electrical characteristics of the resulting nanophotocatalyst. The hypothesis driving this research is that the addition of Al nanopowder will enhance the photocatalytic efficiency of ZnO-based photocatalysts in wastewater treatment. A series of experiments were conducted to synthesize, characterize, and test the photocatalytic performance of these materials. XRD analysis indicated an increase in crystallite size with the addition of Al nanopowder to the ZnO sol. DRS analysis showed the strong role of Al nanopowder in decreasing the bandgap so that the bandgap of the sample with 3% Al nanopowder was 2.7 eV. The PL analysis showed that direct addition of Al nanoparticles effectively reduced electron-hole recombination, leading to lower energy level reflection of absorbed light in the near-infrared range and efficient charge separation. The results revealed an increase in the surface area of the samples from 6.729 m². g⁻¹ to 11.249 m². g⁻¹ with the increase in Al content from 1% to 3% in the samples. Additionally, its photocatalytic performance was evaluated using methylene blue (MB) as the model pollutant under visible light irradiation. The Al-modified ZnO/ZnAl₂O spinels achieved a 93% degradation of MB at pH 9 within 90 min, significantly outperforming pure ZnO due to improved charge-carrier separation and a higher surface area, resulting in enhanced photocatalytic activity. The findings demonstrate a notable enhancement in the quantum yield, rising from 2.92 × 10⁻³ with ZnO to 6.95 × 10⁻³ with the 3-ZnAl₂O₄ sample. These results underscore the potential of this innovative ZnO/ZnAl₂O₄ nanocomposite for effective photocatalytic wastewater treatment, offering a sustainable approach to recycling Al waste. Graphical Abstract: (Figure presented.)