Surface Microlenses for Much More Efficient Photodegradation in Water Treatment

The global need for clean water requires sustainabletechnology for purifying contaminated water. Highly efficient solar-drivenphotodegradation is a sustainable strategy for wastewater treatment. In thiswork, we demonstrate that the photodegradation efficiency of micro-pollutants in water can be improved by similar to 2-24 times by leveragingpolymeric microlenses (MLs). These microlenses (MLs) are fabricated fromthe in situ polymerization of surface nanodroplets. We found thatphotodegradation efficiency (eta) in water correlates approximately linearlywith the sum of the intensity from all focal points of MLs, although nodifference in the photodegradation pathway is detected from the chemicalanalysis of the byproducts. With the same overall power over a given surfacearea, eta is doubled by using ordered ML arrays, compared to heterogeneousMLs on an unpatterned substrate. A higher eta from ML arrays may beattributed to a coupled effect from the focal points on the same plane thatcreates high local concentrations of active species to further speed up the rate of photodegradation. As a proof-of-concept for MLs-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 werephotodegraded by 30%-170% faster than in normal bottles. Ourfindings suggest that the MLs-enhanced photodegradation maylead to a highly efficient solar water purification approach without a large-sized solar collector. Such an approach may be particularlysuitable for portable transparent bottles in remote regions.