Reversible photochromic coatings have emerged as promising materials for optical information storage, smart packaging, and UV detection, yet commercial products often suffer from high fabrication costs, poor color-switching sensitivity, and narrow absorption ranges. In this study, a methylene blue (MB) based reversible photochromic coating was developed via systematic single-factor optimization, focusing on seven critical variables: color-changing agent type, reducing agent type, oxidizing agent dosage, catalyst type, system temperature, UV wavelength, and auxiliary material type. The optimal formulation was determined as 0.02 g MB (color-changing agent), 0.2 g SnCl2 (reducing agent), and 20 g SiO2 (auxiliary material) in 0.5 mol/L HCl medium. Under 365 nm UV irradiation, this coating exhibited rapid color switching (blue → colorless → blue) with a color-changing time of 15-19 s and recovery time of 10-13 s over 8 cycles. Spectroscopic characterization via a V-1600 spectrophotometer revealed a broad absorption range of 330-685 nm, with a maximum absorption peak at 664 nm (consistent with MB’s characteristic absorption). Cost analysis showed the optimized coating cost only 12.66 CNY/kg, which is 85.8% lower than commercial photochromic coatings (87.71 CNY/kg). Additionally, incorporating 0.5 g tris(2,2′-bipyridine)ruthenium chloride hexahydrate ([Ru(bpy)3]Cl2·6H2O) as a catalyst expanded the color transition to orange-to-black, enhancing the material’s versatility. Mechanistic studies suggested that Sn2+ mediates MB’s reduction to leucomethylene blue (colorless), while UV irradiation (365 nm) drives reoxidation to MB (blue); SiO2 acts as a dispersant to improve coating uniformity and stability. This low-cost, high-performance MB-based coating provides a scalable solution for practical photochromic applications.
