Wastewater Treatment Using High-Performance In Situ Formed Double-Heterojunction Janus Photocatalyst Microparticles Shaped via a Microfluidic Device

In this work, a heterogeneous photocatalysis system is fabricated for treating wastewater containing organic dyes and pharmaceutical substances. Double-heterojunction Janus photocatalysts are formed on the surface of size-tunable polydimethylsiloxane (PDMS) microparticles shaped via simple and low-cost coflow microfluidic devices. Ag⁰/Ag⁰-TiO₂/TiO₂ Janus-like photocatalysts are synthesized on the surface of porous PDMS microparticles as the support in which the metal-semiconductor heterojunction of Ag⁰/Ag⁰-TiO₂ and the second heterojunction of Ag⁰-TiO₂/TiO₂ are created in situ, leading to the formation of Ag⁰/Ag⁰-TiO₂/TiO₂@PDMS photocatalysis systems. To form the heterojunctions on the PDMS surface, the polymer chain etching method is employed as a desired strategy to have half of the TiO₂ nanoparticles on the surface of microparticles, which are treated by a Ag source. Using salt additives and the etching method, PDMS microparticles are made porous, providing more surface area for photoreactions. Surprisingly, the highest decomposition efficiencies of 94.4 and 91.1% are achieved for rhodamine B(RhB) and tetracycline (TC), respectively, under visible light for 60 min pH 11, a light source at a distance of 2 cm, 5 mM AgNO₃, 10 wt % TiO₂, 7 wt % NaCl, and 20 gm/L photocatalyst, which are conditions that result in the best performance for RhB degradation. Regarding the stability of the photocatalysts, no significant change is observed in the performance after five cycles.