Ultrasonic Spray Pyrolysis-derived Fe-doped MgO Thin Films
Ultrasonic spray pyrolysis-derived Fe-doped MgO thin films for enhanced photocatalytic performance
In order to optimize the photocatalytic performance of magnesium oxide (MgO) thin films with wide band gap, this paper uses the large-scale ultrasonic spray pyrolysis (USP) process to prepare MgO thin films with different iron doping ratios on glass substrates. The regulation mechanism of doping concentration on the microstructure, optical properties and photocatalytic performance of the films is systematically explored, and the optimal process parameters of doping modification are determined to provide technical support for the development and application of environmental photocatalytic materials.
The study used magnesium acetate tetrahydrate and ferric chloride hexahydrate as precursors, and adjusted the molar ratio of iron salts to prepare pure MgO and five groups of iron doped MgO films at 0.5at.%, 1at.%, 2at.%, 4at.%, and 8at.%. The samples were characterized comprehensively by XRD, SEM, UV visible spectroscopy, and photoluminescence (PL) spectroscopy, and the photocatalytic performance of the thin film was evaluated by degradation experiments of methylene blue (MB) dye under ultraviolet light.
The XRD test results indicate that all samples maintain a pure cubic MgO crystal structure without the formation of impurities. Iron doping can effectively regulate the crystallinity and grain size of thin films. As the doping concentration changes, the diffraction peak intensity and full width at half maximum of the thin film undergo regular changes. SEM morphology observation shows that the pure MgO film has a dense grain structure and uniform surface. With the increase of iron doping, the phenomenon of grain agglomeration and cluster stacking intensifies, and the surface roughness of the film significantly increases.
Optical performance tests have shown that iron doping has a non monotonic control effect on the optical bandgap of thin films: when the doping ratio is increased to 4%, the bandgap of the film continues to widen, and when the doping concentration continues to increase, the bandgap slightly narrows. This rule is determined by the competition between grain size effects and lattice defect electronic states. The PL spectrum shows obvious fluorescence quenching phenomenon, confirming that iron doping can introduce non radiative recombination channels, effectively suppress the rapid recombination of photo generated electron hole pairs, and provide more active carriers for photocatalytic reactions.
The photocatalytic degradation experiment showed that iron doping modification can significantly improve the pollutant degradation ability of MgO thin films, among which the 0.5at.% low doping amount sample has the best performance, with a methylene blue degradation efficiency of 87.19% and a reaction rate constant of 0.0114 min ⁻¹. When the doping concentration is too high, severe crystal cluster aggregation significantly reduces the catalytic active sites on the film surface, induces lattice distortion defects, and leads to continuous degradation of photocatalytic performance.
In summary, precise control of iron doping concentration is the key to optimizing the photocatalytic performance of MgO thin films. Low concentration iron doping can improve catalytic efficiency by constructing intermediate energy levels, capturing photogenerated carriers, and increasing surface active sites, while high doping can cause structural defects to degrade performance. This study clarifies the internal relationship of “doping concentration – microstructure – photocatalytic performance”, verifies the application value of ultrasonic spray pyrolysis process in the modified wide band gap oxide photocatalytic materials, and provides a reference for the industrial preparation of photocatalytic films for water pollution treatment.
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