Recognizing that evaporation and condensation (distillation) to produce purified water is typically a slow and extremely inefficient process that needs significant industrial infrastructure and system costs, researchers at the University of Texas at Austin have developed a solar vapor generator from a novel hydrogel material that uses natural sunlight to efficiently produce purified and desalinated water.
The hierarchically nanostructured gel (HNG), or hydrogel skeleton, is fabricated from a hybrid of polyvinyl alcohol (PVA) and polypyrrole (PPy), creating a molecular mesh that facilitates water evaporation when exposed to natural sunlight. A patent has been filed for the process, which not only removes impurities, but also naturally removes salt and could be engineered to remove other targeted pollutants.
In one experiment, a solar-powered HNG sample floating on a large volume of brine water was able to evaporate water at a record-high rate of 3.2 kg/m2 per hour using 94% solar energy from 1 sun irradiation, producing 18–23 liters of water per square meter of the HNG material. The PVA hydrogel (water-soluble polymer) acts as a skeleton that has good mechanical properties to support the whole structure, while the PPy serves as an effective light absorber to convert solar energy to heat. The as-obtained gel is black in color, flexible, and elastic. Reference: F. Zhao et al., Nature Nanotechnol. online, doi:10.1038/s41565-018-0097-z (Apr. 2, 2018).