Synthesizing Bi 1-x Co x Fe 1-y Zn y O 3 Nanoparticles and Investigating Their Structural, Optical and Photocatalytic Properties Seyed Ebrahim Musavi Ghahfarokhi 1 & Leila Ghanbari 1 & Iraj Kazeminezhad 1,2 # Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract In this study, Bi 1-x Co x Fe 1-y Zn y O 3 nanoparticles with values of (x, y (= 0.0, 0.2; 0.05, 0.15; 0.1, 0.1; 0.15, 0.05; and 0.2, 0.0 were prepared at 650 °C and annealed for 1 h by the sol-gel method. The optical and photocatalytic properties of bismuth ferrite were studied by the substitution of cobalt and zinc elements for bismuth and iron under various percentages. X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM), and UV-visible spectrophotometer were used to characterize the prepared samples. The results of the structural analyses showed that by increasing the amount of Co and Zn doped, the structure of the samples changed from rhombohedral to rectangular phase. Moreover, the ferromagnetic properties of the samples were improved with variation in the amount of Co and Zn doped. Also, the results of optical experiments revealed that the bandgap and photocatalytic properties of the samples were decreased by changing the amount of Co and Zn doped. Keywords Bi 1-x Co x Fe 1-y Zn y O 3 nanoparticles . Structural properties . Magnetic properties . Photocatalytic properties . Optical properties 1 Introduction An investigation of the magnetic and electrical properties of bismuth ferrite (BiFeO3) was carried out for the first time in 1960 by Smolenskii et al. [1, 2]. In 2003, the observations of unexpected electrical and magnetic properties in BiFeO3 (BFO) thin films triggered theoretical and experimental stud- ies that have been done on this material [2, 3]. Up until now, many studies have been done on the nanoparticles and bulk properties of this material [4, 5]. Recently, a few researchers have investigated the effect of particle size on the properties of BiFeO 3 . They have shown that particle size is an important factor in controlling the properties of these materials [6, 7]. Bismuth ferrite (BiFeO 3 ) has a distorted structure of perov- skite (ABO 3 ) and rhombohedral with the R3c space group. Studies have shown that ferroelectric properties in the BiFeO 3 are related to the coupling of 6s orbital discontinuous electrons to the cation Bi 3+ and that the magnetic property can be attributed to the exchange of Fe 3+ spin interactions in the orbital’s semi-filled. The antiparasitic torque of the iron cat- ions in the G-type arrangement results in a weak local mag- netic moment in the bismuth ferrite structure due to the diver- sified exchange interaction. The magnetization in the BiFeO 3 can be controlled by the chemical substitution of rare earth elements for Bi [8]. Bismuth ferrite (BiFeO 3 ) is one of the most important multiferroic materials. In the above- mentioned room temperature, this material has a simulta- neously ferroelectric phase with Curie temperature (T c = 1103 K) and G-type antiferromagnetic phase with Neel tem- perature (T N = 643 K). The term “multiferroics” is first used in 1994 and refers to materials that are simultaneously ferromag- netic, ferroelectric, or ferroelastic. Today, multiferroics are often referred to as the materials that exhibit the two properties of ferroelectricity and ferromagnetism (antiferromagnetism). These two phenomena arise from the fact that those electrons have charge and spin. Recently, due to the toxicity of lead and the need for an international community to find a suitable alternative to lead-based compounds such as lead zirconate Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10948-020-05661-5) contains supplementary material, which is available to authorized users. * Seyed Ebrahim Musavi Ghahfarokhi musavi_ebrahim@yahoo.co.uk; Mousavi355@scu.ac.ir 1 Department of Physics, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran 2 Center for Research on Laser and Plasma, Shahid Chamran University of Ahvaz, Ahvaz, Iran Journal of Superconductivity and Novel Magnetism https://doi.org/10.1007/s10948-020-05661-5