Water scarcity is a significant challenge faced by people worldwide, and desalination technologies have gained importance as a means to provide clean water. Desalination is the process of eliminating salt and other impurities from seawater or brackish water in order to make it appropriate for human consumption or industrial use. Desalination can be an effective solution, but it is not without its limitations. The current desalination technologies are high initial costs and energy-intensive, requiring a significant amount of energy to operate. This energy demand can strain existing power grids and exacerbate environmental issues, particularly if the energy is derived from fossil fuels. Solar vapor generator systems based on hydrogels are a promising alternative to today’s energy-intensive desalination technologies. Thermal and water management govern the performance of solar vapor generator systems; however, considerable effort has been devoted to improving thermal management to obtain high evaporation rates, while research on the water management of hydrogels remains limited. One of the primary challenges associated with hydrogel-based solar vapor generator systems is their limited capacity for water replenishment, which can result in decreased evaporation rates and decreased efficiency. In addition, conventional hydrogels utilized in solar vapor generator systems frequently suffer from low durability and contamination issues, which can diminish their performance over time.
In a new study published in the peer-reviewed Journal of Materials Chemistry A. PhD candidates Shudi Mao, Casey Onggowarsito, An Feng and Stella Zhang, Prof. Long D. Nghiem and Dr. Qiang Fu from University of Technology Sydney presented the approach of development and performance evaluation of a novel cryogel-based solar vapor generator system for seawater desalination. The cryogel-based solar vapor generator developed using a facile freeze-thaw method. The polymer constituents were combined with deionized water to form a homogenous solution, which was then frozen for 24 hours at -20 degrees Celsius. The frozen solution was thawed at ambient temperature to form a cryogel. The cryogel was subsequently rinsed with deionized water to eliminate any unreacted monomers or impurities. The authors used various advanced techniques, such as scanning electron microscopy, fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and contact angle measurements, to evaluate the properties and efficacy of the cryogel-based solar vapor generator materials. Experiments were also conducted to determine the evaporation rate, salt rejection rate, durability, and contamination resistance of the cryogel-based solar vapor generator materials.
The research team compared their new cryogel-based solar vapor generator system to conventional hydrogel-based solar vapor generator systems and discovered that their system had several advantages. They observed that newly developed cryogels evaporated faster than hydrogels. This was due to the cryogels’ interconnected pores, which enabled rapid water replenishment and efficient transport of water molecules to the surface for evaporation. Additionally, cryogels were more durable and resistant to contamination than hydrogels. Using both types of gels, multiple cycles of desalination were conducted and it was discovered that cryogels retained 90% of their initial performance after 10 cycles, whereas hydrogels retained only 60% of their initial performance after 5 cycles. This was most likely because cryogels have a more open structure than hydrogels, making them less susceptible to obstruction or fouling. In addition, the authors assessed the impact of incorporating graphene oxide as a photothermal material into their cryogel-based solar vapor generator system. They reported that graphene oxide could absorb light over a broad spectrum of wavelengths, making it a useful photothermal material for solar-powered desalination applications. The addition of trace quantities of graphene oxide increased evaporation rates and enhanced the performance of cryogels in comparison to those without graphene oxide.
In conclusion, the findings suggested that this novel approach had great potential as an alternative to current energy-intensive desalination technologies, due to its high evaporation rates, good durability, resistance to fouling, and ability to incorporate photothermal materials such as graphene oxide. In a statement to Advances in Engineering, Dr. Qiang Fu explained this new innovative desalination system offers a promising approach to address water scarcity by leveraging the power of solar energy and the unique properties of cryogel materials.
Shudi Mao, Casey Onggowarsito, An Feng, Stella Zhang, Qiang Fu, Long D. Nghiem. A cryogel solar vapor generator with rapid water replenishment and high intermediate water content for seawater desalination. Journal of Materials Chemistry A, Issue 2, 2023, Pages 858–867.