Surface Microlenses for Much More Efficient Photodegradation in Water Treatment

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 (η) 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, η is doubled by using ordered ML arrays, compared to heterogeneous MLs on an unpatterned substrate. A higher η 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 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 were photodegraded by 30%–170% faster than in normal bottles. Our findings suggest that the MLs-enhanced photodegradation may lead to a highly efficient solar water purification approach without a large-sized solar collector. Such an approach may be particularly suitable for portable transparent bottles in remote regions.

Enhanced photocatalytic degradation of organic contaminants in water by highly tunable surface microlenses

“…A higher concentration of active species in the MLs-induced system is confirmed by ESR characterization in our previous work. 57 Similar to the photolysis system without catalysis, the ESR spectra in Figure 5 suggested that the photodegradation with ZnO as the catalyst could also be accelerated, due to the larger amount of free radicals from the focusing effect of surface MLs.…”

“…61 The condition used to fabricate the random surface MLs was the optimized one in our previous work. 57 After the standard solvent exchange process, the chamber filled with liquid was sealed and horizontally set under UV light (365 nm, Analytik Jena UV lamp) for 15 min. Surface ML arrays (MLAs) in the photodegradation processes were fabricated with lauryl methacrylate (LMA, Acros Organics) as the monomer in solution A.…”

“…On a smaller scale, the acceleration of the photoreactions by surface MLs was validated through the in-situ photoreduction of silver nitrate 42 and the direct photolysis of micropollutants. 57 Therefore, such surface MLs are also expected to be effective in enhancing the solar-driven photocatalytic degradation of contaminants in water. Implementing surface MLs based on the solvent exchange process as a candidate strategy for enhancing photodegradation efficiency under insufficient irradiation is worthy of investigation.…”

Degradation of Model Compounds by 1O2-Generating Photosensitizer–Doped Membranes

“…There is considerable interest in sustainable new technologies that avoid disinfection byproducts. − Two conventional alternatives, ozonation and UV radiation, have their own limitations. − While little to no harm to humans and aquatic life is caused by UV-radiation-based processes, they are less cost-effective than chlorination . Alternatively, bacteria and viruses are more effectively destroyed by ozone.…”

“…24−26 While little to no harm to humans and aquatic life is caused by UV-radiation-based processes, they are less cost-effective than chlorination. 27 Alternatively, bacteria and viruses are more effectively destroyed by ozone. Still, ozonation is not cost-effective for the treatment of water with substantial amounts of particulate matter or total organic carbon, as well as high biochemical or chemical oxygen demand.…”