Magnetic-field-assisted spark discharge synthesis of ZnO–SnO2 composite thin films: Enhanced photocatalytic and humidity-sensing performance via lorentz force-guided nanoparticle formation

This work employs magnetic-field-assisted spark discharge to fabricate ZnO–SnO₂ nanocomposite thin films with enhanced photocatalytic and humidity-sensing performance under ambient conditions. The application of a 450 mT magnetic field during sparking effectively confined plasma species and steered charged molten droplets via the Lorentz force. This resulted in thicker, denser, and more uniform films compared with those prepared without magnetic assistance. Comprehensive structural characterization using SEM, TEM, XRD, Raman, and XPS confirmed the formation of a ZnO–SnO₂ heterostructure with improved crystallinity, reduced lattice disorder, and modified defect states induced by magnetic confinement. Functionally, the magnetically assisted films exhibited significantly enhanced photocatalytic activity toward methylene blue under visible-light irradiation, achieving rapid photodecolorization with a substantially faster degradation rate than non-magnetic films. In addition, the films demonstrated high humidity sensitivity with fast response and recovery, minimal hysteresis, and stable operation over a wide relative humidity range. These improvements are attributed to the combined effects of enhanced crystallinity, intimate interfacial contact, and defect-engineered nanostructured surfaces. Overall, this work demonstrates, for the first time, that magnetic-field-assisted spark discharge is a rapid, scalable, and vacuum-free approach for engineering multifunctional ZnO–SnO₂ thin films, offering strong potential for environmental remediation and sensing applications.