Surface microlenses for much more efficient photodegradation in water treatment

TL;DR

This study introduces polymeric microlenses on water containers to significantly boost solar-driven photodegradation efficiency, offering a portable, sustainable water purification method especially useful in remote areas.

Contribution

The paper demonstrates a novel application of surface microlenses to enhance photodegradation efficiency in water treatment, achieving 2-24 times improvement and practical implementation on water bottles.

Findings

Photodegradation efficiency increases by 2-24 times with microlenses.

Ordered microlens arrays outperform heterogeneous ones in efficiency.

Water micropollutants degrade 30-170% faster with microlens-enhanced bottles.

Abstract

The global need for clean water requires sustainable technology for purifying contaminated water. Highly efficient solar-driven photodegradation is a sustainable strategy for wastewater treatment. In this work, we demonstrate that the photodegradation efficiency of micropollutants in water can be improved by ~2-24 times by leveraging polymeric microlenses (MLs). These microlenses (MLs) are fabricated from the in-situ polymerization of surface nanodroplets. We found that photodegradation efficiency ({\eta}) in water correlates approximately linearly with the sum of the intensity from all focal points of MLs, although no difference in the photodegradation pathway is detected from the chemical analysis of the byproducts. With the same overall power over a given surface area, {\eta} is doubled by using ordered arrays, compared to heterogeneous MLs on an unpatterned substrate. Higher {\eta} from ML arrays may be attributed to a coupled effect from the focal points on the same plane that creates high local concentrations of active species to further speed up the rate of photodegradation. As a proof-of-concept for ML-enhanced water treatment, MLs were formed on the inner wall of glass bottles that were used as containers for water to be treated. Three representative micropollutants (norfloxacin, sulfadiazine, and sulfamethoxazole) in the bottles functionalized by MLs were photodegraded by 30% to 170% faster than in normal bottles. Our findings suggest that the ML-enhanced photodegradation may lead to a highly efficient solar water purification approach without a large solar collector size. Such an approach may be particularly suitable for portable transparent bottles in remote regions.