Concave microlens arrays with tunable curvature for enhanced photodegradation of organic pollutants in water: A non-contact approach

Solar-driven photodegradation for water treatment faces challenges such as low energy conversion rates, high maintenance costs, and over-sensitivity to the environment. In this study, we develop reusable concave microlens arrays (MLAs) for more efficient solar photodegradation by optimizing light distribution. Concave MLAs with the base radius of $\sim 5$ μm are fabricated by imprinting convex MLAs to polydimethylsiloxane elastomers. Concave MLAs possess a non-contact reactor configuration, preventing MLAs from detaching or being contaminated. By precisely controlling the solvent exchange, concave MLAs are fabricated with well-defined curvature and adjustable volume on femtoliter scale. The focusing effects of MLAs are examined, and good agreement is presented between experiments and simulations. The photodegradation efficiency of organic pollutants in water is significantly enhanced by 5.1-fold, attributed to higher intensity at focal points of concave MLAs. Furthermore, enhanced photodegradation by concave MLAs is demonstrated under low light irradiation, applicable to real river water and highly turbid water.