Enhancing saline water evaporation rates via floatable, conductive nanoparticles embedded in superhydrophobic cotton gauze at air-water interface

Abstract

A significant portion of the earth's surface is composed of water, and all breathing organisms require freshwater to survive. Unfortunately, most of the water on earth's surface is saltwater, not freshwater, and very soon, freshwater will become short in supply in many locations. The principles of water evaporation for saltwater desalination play a crucial role in solving this crisis using renewable resources. Even though the implementation of this solution is hindered by several challenges, such as the delicate nature of solar thermal devices, intricate fabrication methods, and the high cost associated with these devices. This study demonstrates a model for enhancing saline water evaporation rates with an affordable and energy-efficient approach using floatable superhydrophobic cotton gauze with conductive nanoparticle inclusions. The fabrication process of the floatable superhydrophobic cotton gauze involves a multi-step process that begins with the application of spray coating a double layer of base coat homogenized with conductive nanoparticles—carbon black, pristine graphene, and carbon nanotubes (CNTs) and a subsequent layer with hydrophobic silica nanoparticles on cotton gauze, making the conductive nanoparticle-embedded superhydrophobic cotton gauze. This results in the cotton gauze floating on the air-water interface. The next step involves exposing the air-water interface to simulated solar infrared (IR) light, which has a power of 125 W and a light density of approximately 440 W/m2. In this study, the base coat layer adhesives were homogenized with 0.05 %, 0.1 %, and 0.5 % of conductive nanoparticles. As a result of this process, the whole incident light is converted into heat at the air-water interface of different types of base fluid, including saltwater, tap water, and deionized (DI) water. The water evaporation tests were carried out to assess the effectiveness of the air-water interface heating and evaluate its ability to transform light into heat under ambient pressure. Test results indicated that 0.1 % of carbon black, graphene, and CNT nanoparticle-embedded superhydrophobic cotton gauze offered superior water evaporation results than 0.05 % and 0.5 % of the same nanoparticles. The evaporation rate of saltwater is significantly improved by over 7.73 % when using 0.1 % of carbon black nanoparticles embedded in superhydrophobic cotton gauze. The temperature of the superhydrophobic cotton gauze, which contains 0.1 % of carbon black nanoparticles, increased from 18.5 °C to 72.8 °C during the evaporation process. This results in an evaporation rate of 4.4 mg/h.cm2, demonstrating the effectiveness of 0.1 % of carbon black nanoparticle-embedded superhydrophobic cotton gauze in enhancing the water evaporation rate. The higher temperature at the air-water interface, instead of heating the bulk quantity of the saltwater was exhibited in the floatable conductive nanoparticle-embedded superhydrophobic cotton gauze, providing a possible explanation for the enhanced evaporation and freshwater productions.