Vol.: (0123456789) 1 3 J Nanopart Res (2023) 25:142 https://doi.org/10.1007/s11051-023-05801-7 RESEARCH PAPER Na doped CuO as a new Day‑ Night (Photo) Catalyst Mittal Bathwar · Vijayaraghavan R Received: 30 January 2023 / Accepted: 28 June 2023 © The Author(s), under exclusive licence to Springer Nature B.V. 2023 Abstract Oxide semi-conductors such as TiO 2 , ZnO, CuO have been extensively studied for long time for its photocatalytic activity and its applica- tion in waste water treatment. These semiconductors on excitation with UV or visible light generate e − -h + pairs that react with O 2 / H 2 O respectively to pro- duce Reactive Oxygen Species (ROS) such as O 2 −• , • OH radicals. These ROS degrade the contaminants in water. There is a need for catalysts that produce these ROS even in absence of light (dark) and such Day-Night catalysts are signifcant from the point of view of 24 × 7 operation. Towards this objective, Na doped CuO, Cu 1−x Na x O (x = 0 to 0.1) has been syn- thesized, characterized by X-ray difraction (XRD), Transmission electron microscopy (TEM), X-Ray photoelectron spectroscopy (XPS) and Ultra violet visible-difuse refectance spectroscopy (UV-DRS). The particle size of Cu 1−x Na x O is in the range of 25 to 75 nm. Its photocatalytic activity has been reported for the frst time. These compositions exhibit Photo- catalytic activity in dark (in absence of light) too and is attributed to super oxide species generated due to vacancies created esp in Na doped compositions. Hence, the Na doped CuO acts as Day-Night catalysts and the rates of degradation are higher than those reported earlier for CuO. Reactive Oxygen Species (ROS) liberated from its aqueous suspensions have been estimated and correlated to its activity. Keywords Metal oxides · Hydrogen peroxide · Methylene blue · Photocatalyst · Reactive oxygen species · Hydroxyl radicals · Nanostructures · Colloids Introduction Oxides of transition metals are an important class of semiconductor materials fnding many diferent appli- cations [1–5]. Among these CuO is an important p type semiconductor with a narrow band gap. It fnds applications in high Tc superconductors, catalysis, gas sensor, pigments, solar cells and cathode mate- rial [6–9]. Transition metal oxides are potential can- didates for environmental applications too due to its photocatalytic activity, low cost and stability [10–12]. The dyes in waste water from dye industries, textile industries which are the common sources of pol- lutants can be photo catalytically degraded into non–toxic components by the semiconductor transi- tion metal oxides so that the efuents are safe. Among the oxides, TiO 2 , ZnO have been extensively studied for this purpose [13]. In search of better photocata- lysts, CuO has also been explored owing to its band Supplementary Information The online version contains supplementary material available at https://doi. org/10.1007/s11051-023-05801-7. M. Bathwar · V. R (*)  Department of Chemistry, School of Advanced Sciences, Vellore Institute of Technology, Vellore 632 014, India e-mail: rvijayaraghavan@vit.ac.in