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Sunlight-driven photocatalytic degradation is an effective and eco-friendly technology for the removal of organic pollutants from contaminated water. Herein, we describe the one-step synthesis of Cu-Cu 2 O-Cu 3 N nanoparticle mixtures using a novel non-aqueous, sol-gel route and their application in the solar-driven photocatalytic degradation of methylene blue. The crystalline structure and morphology were investigated with XRD, SEM and TEM. The optical properties of the as-prepared photocatalysts were investigated with Raman, FTIR, UV-Vis and photoluminescence spectroscopies. The influence of the phase proportions of Cu, Cu 2 O and Cu 3 N in the nanoparticle mixtures on the photocatalytic activity was also investigated. Overall, the sample containing the highest quantity of Cu 3 N exhibits the highest photocatalytic degradation efficiency (95%). This enhancement is attributed to factors such as absorption range broadening, increased specific surface of the photocatalysts and the downward band bending in the p-type semiconductors, i.e., Cu 3 N and Cu 2 O. Two different catalytic dosages were studied, i.e., 5 mg and 10 mg. The higher catalytic dosage exhibited lower photocatalytic degradation efficiency owing to the increase in the turbidity of the solution.

This review addresses the most recent advances in the synthesis approaches, fundamental properties and photocatalytic activity of Cu 3 N nanostructures. Herein, the effect of synthesis conditions, such as solvent, temperature, time and precursor on the precipitation of Cu 3 N and the formation of secondary phases of Cu and Cu 2 O are surveyed, with emphasis on shape and size control. Furthermore, Cu 3 N nanostructures possess excellent optical properties, including a narrow bandgap in the range of 0.2 eV-2 eV for visible light absorption. In that regard, understanding the effect of the electronic structure on the bandgap and on the optical properties of Cu 3 N is therefore of interest. In fact, the density of states in the d-band of Cu has an influence on the band gap of Cu 3 N. Moreover, the potential of Cu 3 N nanomaterials for photocatalytic dye-degradation originates from the presence of active sites, i.e., Cu and N vacancies on the surface of the nanoparticles. Plasmonic nanoparticles tend to enhance the efficiency of photocatalytic dye degradation of Cu 3 N. Nevertheless, combining them with other potent photocatalysts, such as TiO 2 and MoS 2, augments the efficiency to 99%. Finally, the review concludes with perspectives and future research opportunities for Cu 3 N-based nanostructures.