Nanopump for Low-temperature and Efficient Solar Water Evaporation

Water evaporation is a ubiquitous phenomenon in nature and the essential component of the water cycle on the earth. A high evaporation rate is required for application in desalination and sterilization, but remains a great challenge at a relatively low temperature under solar irradiation. In this study, free-standing membranes of highly ordered nanotube arrays are synthesized by anodizing the Zr-30Ti alloy. The vertical tubular structure provides three-dimensional channels for water transportation, and the superhydrophilic nature provides capillary force for continuous water pumping. This forms a three-dimensional and vertical alignment of ultrathin water films at the nanoscale (an inverse structure of nanotube arrays); in this scenario, the large interfacial contact between tube walls and the water film results in efficient heat transfer and mass transport, thus facilitating water evaporation. The use of the Zr-30Ti alloy produces ZrO2 nanotubes where some of the Zr ions are substituted by Ti counterparts. This incorporates a large number of oxygen vacancies by lowering its formation energy and extends light absorption up to 1600 nm. The Zr(Ti)O-2 nanotube membranes with superhydrophilic vertical channels and strong light absorption function as a nanopump for solar water evaporation, with an evaporation rate of 1.64 kg m(-2) h(-1) under 1 sun irradiation at 20.5 degrees C, which is much higher than the state-of-the-art reports employing metal compounds.