Rapid Quantitative Detection of Dye Concentration in Pt/TiO2 Photocatalytic System Based on RGB Sensing

This article presents an integrated strategy that couples high-efficiency photocatalytic degradation with low-cost, rapid detection to overcome the main drawbacks of conventional TiO₂-based photocatalysts, including a weak visible-light response, rapid charge-carrier recombination, and reliance on expensive instrumentation for dye concentration detection. Platinum-decorated TiO₂ (Pt/TiO₂) was prepared by photoreduction deposition, and systematic characterization confirmed the successful loading of zero-valent Pt nanoparticles onto the TiO₂ surface, significantly improving charge separation and extending absorption into the visible region. Methylene blue degradation was quantified under ultraviolet (UV) and simulated sunlight; radical-scavenging tests clarified the reaction pathway. In parallel, smartphone images of the reaction mixture were processed in ImageJto extract red-green-blue (RGB) values, which were related to dye concentration through a partial least-squares (PLS) model validated against reference UV-Vis data. Pt/TiO₂ removed 95.0% of methylene blue within 20 min of UV irradiation and 90.2% within 160 min of simulated sunlight-31.8% and 19.1% faster, respectively, than pristine TiO₂. The RGB-based PLS model achieved a coefficient of determination (R²) of 0.961 for the prediction set. By integrating photocatalysis with smartphone-based colorimetry, the proposed method enables rapid monitoring of organic dyes concentration, providing an intelligent and economical platform for industrial wastewater treatment.