Tailored dielectric, optical properties and photocatalytic performance of Mg–Zn nanoferrites by Cu 2+ substitution N. M. Basfer 1,2 , S. F. Mansour 1,3, * , and Faten Al-Hazmi 1 1 Physics Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia 2 Department of Physics, Umm Al Qura University, Mecca, Saudi Arabia 3 Physics Department, Faculty of Science, Zagazig University, Zagazig, Egypt Received: 28 March 2020 Accepted: 8 July 2020 Ó Springer Science+Business Media, LLC, part of Springer Nature 2020 ABSTRACT This research article is focused on the scrutinization of dielectric, optical and photocatalytic activity of Mg 0.8 Zn 0.2-x Cu x Fe 2 O 4 (MZC) nanoferrites upon the substitution of Cu 2? ions range (0 B x B 0.2; step 0.04). The dielectric constant and conductivity of MZC nanoferrite manifested the higher values than the pristine one. This leveraging demeanor is originated from the effective role of Fe 2? and Fe 3? in octahedral sites; as a result of occupying Cu ions in tetrahedral sites only. All MZC nanoferrites have the two types of losses; conduction and relaxation losses. The conduction process of MZC nanoferrites is attributed to three different species through different temperature ranges. Nyquist plot manifested that grain and grain boundary resistances were decreased and relaxation time enhanced from 0.79 to 7.95 ls with Cu substitution. Tauc’s plots introduced direct allowed E g for MZC nanoparticles with a red shift from (2.16 eV at x = 0.0 to 1.67 eV at x = 0.2). The degradation efficiency of RhB over MZC photocatalyst is enhanced comparing with that of pristine RhB; 92.39% for x = 0.2 in 300 min. The nanoferrite Mg 0.8 Cu 0.2 Fe 2 O 4 (x = 0.2) has the optimal merits; highest dielectric constant, conductivity, photodegradation percentage, besides lowest energy gap and moderate loss make it advisable for sundry applications as an excellent photocatalyst for wastewater treatment besides high-frequency applications and transformers cores. 1 Introduction The expeditious evolution of contemporary social civilization leads to the wastewater contamination problem by its variable industrial procedures satisfying human aspects. Particularly dyeing indus- try has long been admitted as a toxic source to environment; where dyes are predominantly used by consumers as textiles or food. More earnest, the organic dyes cause serious environmental and Address correspondence to E-mail: sfmansour@kau.edu.sa https://doi.org/10.1007/s10854-020-03972-w J Mater Sci: Mater Electron