Development of a Low-Cost Microphotoreactor from Recycled Materials: Application to Nb ₂ O ₅ @H ₂ TPP-Catalyzed Methylene Blue Degradation

A low-cost, robust, and easy-to-operate photoreactor with automatic temperature control, achieved through heat sinks, cooling fans, a temperature sensor, and a microcontroller (Arduino Nano), was manually constructed using predominantly discarded materials, without the need for sophisticated instrumentation. The light source employed was a 3 W RGB LED lamp with infrared (IR) remote control. The electromagnetic radiation spectra (white, blue, green, and red) were determined by UV-vis spectroscopy; additionally, the irradiance and luminous flux of these radiations were evaluated. For luminous flux determination, a lux meter was developed based on a BH1750-FVI sensor coupled to the Arduino Nano. The characterizations indicated that red radiation exhibits the highest irradiance and luminous flux values when compared to blue and green radiations. The estimated cost for constructing the photoreactor was US$ 41.50, which is significantly lower than that of commercially available photoreactors, whose prices typically exceed US$ 3000.00. To validate the performance of the photoreactor, the photocatalytic degradation of methylene blue (MB) was carried out using a novel Nb₂O₅@H₂TPP material as the photocatalyst. This material was synthesized by physical mixing of niobium pentoxide (Nb₂O₅) and 5,10,15,20-tetraphenylporphyrin (H₂TPP). The resulting photocatalyst was comprehensively characterized by X-ray diffraction, UV-vis diffuse reflectance spectroscopy (UV-vis/DRS), scanning electron microscopy, zeta potential measurements, infrared spectroscopy, and thermogravimetric analysis. The MB degradation reactions were initially conducted following a factorial experimental design. This analysis identified MB concentration as a negative factor in the degradation percentage, catalyst mass as a positive factor, and reaction time as a nonsignificant variable within the time range explored. Based on these findings, MB degradation reactions were performed under different ranges of incident light wavelengths (white, blue, green, and red). The MB degradation percentages observed were 32% under white light, 34% under blue light, 42% under green light, and 44% under red light exposure.