A group of researchers led by Dr. Marta Prześniak-Welenc from the Institute of Nanotechnology and Materials Engineering, Gdańsk University of Technology has conducted research on effective water purification through solar energy. They investigated the role of NH₄V₄O₁₀ and its rGO composite in combating organic and inorganic pollutants. The results were published in the journal “Scientific Reports". Their research was conducted on a commercial access mode at the SOLARIS Centre on the ASTRA beamline.

The photocatalytic activity of NH₄V₄O₁₀ (NVO) and its composite with rGO (NVO/rGO) were investigated. Samples were synthesized via a facile one-pot hydrothermal method and successfully characterized using XRD, FTIR, Raman, XPS, XAS, TG-MS, SEM, TEM, N2 adsorption, PL and UV‒vis DRS. The results indicate that the obtained NVO and NVO/rGO photocatalysts exhibited efficient absorption in the visible wavelength region, a high content of V⁴⁺ surface species and a well-developed surface area. Such features resulted in excellent performance in methylene blue photodegradation under simulated solar light illumination. In addition, the composite of NH₄V₄O₁₀ with rGO accelerates the photooxidation of the dye and is beneficial for photocatalyst reusability. Moreover, it was shown that the NVO/rGO composite can be successfully used not only for the photooxidation of organic pollution but also for the photoreduction of inorganic pollutants such as Cr(VI). Finally, an active species trapping experiment was conducted, and the photodegradation mechanism was discussed.
The photocatalytic activity of synthesized NVO and NVO/rGO was evaluated towards methylene blue (MB) degradation and Cr(VI) to Cr(III) reduction under simulated solar light illumination. The XANES and XPS analysis confirmed a significant presence of V⁴⁺ ions on the photocatalytic materials' surface, distinguishing them from the bulk. This surface enrichment of V⁴⁺ ions played a pivotal role in the excellent MB photodegradation performance of both materials, along with their well-developed surface area. The positive impact of rGO in terms of the activity and stability of the photocatalyst was especially pronounced. Reactions carried out in the presence of specific scavengers revealed differences in the mechanism of photocatalyst action. In the case of NVO, ·OH and h + play a critical role in MB photodegradation, while for NVO/rGO, ·O2- radicals are the dominant active species responsible for dye degradation. Moreover, the proposed composite showed activity in the photoreduction of highly toxic Cr(VI) ions in an acidic environment.

Figure 1. Schematic diagram of the band-energy levels of NVO/rGO with the possible photocatalytic mechanism.

Figure 2. a) V 2p XPS spectra of NVO/rGO b) V K-edge XANES spectra (the inset shows the relation between the vanadium oxidation state and the edge position).

Written by: Marta Prześniak-Welenc

Link to the publication: M. Nadolska, M. Szkoda, K. Trzciński, J. Ryl, A. Lewkowicz, K. Sadowska, J. Smalc-Koziorowska, and M. Prześniak-Welenc, New Light on the Photocatalytic Performance of NH4V4O10 and Its Composite with RGO, Sci Rep 13, 3946 (2023). doi: 10.1038/s41598-023-31130-9