Evolution of Morphology and Distribution of Salt Crystals on a Photothermal Layer during Solar Interfacial Evaporation

Abstract

Solar interfacial evaporation (SIE) by leveraging photothermal conversion could be a clean and sustainable solution to the scarcity of fresh water, decontamination of wastewater, and steam sterilization. However, the process of salt crystallization on photothermal materials used in SIE, especially from saltwater evaporation, has not been completely understood. We report the temporal and spatial evolution of salt crystals on the photothermal layer during SIE. By using a typical oil lamp evaporator, we found that salt crystallization always initiates from the edge of the evaporation surface of the photothermal layer due to the local fast flux of the vapor to the surroundings. Interestingly, the salt crystals exhibit either compact or loose morphology, depending on the location and evaporation duration. By employing a suite of complementary analytical techniques of Raman and infrared spectroscopy and temperature mapping, we followed the evolution and spatial distribution of salt crystals, interfacial water, and surface temperature during evaporation. Our results suggested that the compact crystal structure may emerge from the recrystallization of salt in an initially porous structure, driven by continuous water evaporation from the porous and loose crystals. The holistic view provided in this study may lay the foundation for effective strategies for mitigation of the negative impact of salt crystallization in solar evaporation.

Photothermal Properties and Solar Water Evaporation Performance of Lignin-Based Polyurethane Foam Composites

“…The average evaporation rate of LPUF–PANI during the 10 cycles was 3.11 kg m –2 h –1 , indicating its excellent stability during use. Most water evaporation materials suffer from the problem of salt accumulation, i.e., with the continuous evaporation of water, salt deposition occurs in the internal pores and on the material surface, which results in a gradual decrease in water evaporation performance . LPUF was prepared with 5% lignin doping, and the effect of salt concentration on the solar water evaporation performance of LPUF–PANI was investigated by loading PANI onto the surface of LPUF through an optimized process with salt concentrations of 3.5, 5, 10, and 15 wt %.…”

Versatile GO/ANFs Aerogel for Highly Efficient Solar-Powered Water Purification in Wide Environments

“…Until now, various modern desalination strategies have been used for producing fresh water, including ultraviolet (UV) filtration, reverse osmosis (RO), and chemical filtration. − For example, RO is currently the most widely used desalination technology, but it has the disadvantage of high construction and maintenance costs . Solar steam generation is an emerging solar-assisted desalination technology that holds great promise for addressing water and energy shortages because of its high photothermal conversion efficiency, cost effectiveness, and sustainability. − Specifically, interfacial solar evaporation is attracting increasing interest due to its ability to realize local, efficient heating of a small amount of water at the evaporation interface to fully utilize solar energy. − In recent years, there have been extensive attempts to develop interfacial solar evaporators for the production of clean water. − Despite the considerable evaluation of the purification of pure NaCl brine, little research has been done on the actual desalination of seawater. This challenge arises because actual seawater is much more complex than sodium chloride brine .…”

Green Synthesis of Polyurethane Sponge-Grafted Calcium Alginate with Carbon Ink Aerogel with High Water Vapor Harvesting Capacity for Solar-Driven All-Weather Atmospheric Water Harvesting

“…This AWH method is less energy-consuming, green, and easily manipulative. , It is thus crucial to find appropriate materials that can achieve high photothermal conversion efficiencies. Currently, photothermal conversion materials are mainly categorized into carbon, polymer, semiconductor, and metal nanoparticle materials. − In particular, carbon-based materials have the advantages of spectral solar absorptive capacity and high-temperature stability, which make them important candidates for high photothermal conversion efficiency. However, graphene and carbon nanotubes are expensive, and high-temperature carbonized biochar materials are energy-consuming and environmentally unfriendly. , While, commercially available carbon inks are much cheaper, easier to use on a large scale, and environmentally friendly by comparison.…”