Potential of magnetic silver-coupled zinc and copper ferrite nanoparticles as visible-light photocatalysts towards the degradation of dyes

Abstract

Increased environmental concerns about water pollution and scarcity have driven the development of innovative processes and technologies to address these issues. Photocatalysis using nanomaterials is auspicious, with proven efficiency in degrading different pollutants. Ferrite nanoparticles (MFe₂O₄) stand out for their dual functionality, photocatalytic activity and potential superparamagnetic behavior, that make them highly appealing for environmental applications, as they facilitate both pollutant degradation and safe recollection, contributing to nanosafety. This work compared two synthesis methods, sol–gel and solvothermal, for synthesizing mixed zinc and copper ferrites (Zn_0.5Cu_0.5Fe₂O₄). Characterization results revealed a bandgap suitable for visible light absorption and superparamagnetic properties reaching 37 emu g⁻¹ of saturation magnetization. However, the photocatalytic efficiency of ferrites was minimal due to the recombination of electron–hole pairs (e⁻/h⁺). Despite that, the ferrites exhibited a high adsorption capacity for the cationic dye Malachite Green (MG), but photocatalytic degradation was low. To suppress the high e⁻/h⁺ recombination, a novel, fast method, was used to incorporate silver onto the ferrite surface. This modification significantly improved the activity of the ferrites, especially in the nanoparticles synthesized by sol–gel, achieving 90% removal. In contrast, ferrites synthesized by the solvothermal method, beside exhibiting a strong capacity to adsorb MG (55.99%), proved to be photocatalytically inefficient. This highlights the distinct functional strengths of the two synthesis methods, with sol–gel favoring photocatalytic activity and solvothermal favoring adsorption. Relevant parameters, including the amount of silver and nanomaterial concentration, were optimized during the study, resulting in a degradation of 61.89%, at a rate of 0.0381 h⁻¹ under visible light. Toxicity tests were also conducted. After irradiation MG samples still exhibited high toxicity towards the bacteria Vibrio fisheri, demonstrating that despite color removal, degradation by-products may still be present causing the toxic effect.