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Freshwater production from seawater and atmospheric moisture enabled by a solar-driven water generator

Periodic Reporting for period 1 - SWaG (Freshwater production from seawater and atmospheric moisture enabled by a solar-driven water generator)

Reporting period: 2020-07-01 to 2022-06-30

This project intends to develop a small device for solar-induced desalination and atmospheric-water harvesting. Specifically, it will develop the photothermal cryogels that can generate potable water in two ways. The first way is with the solar desalination achieved through solar-induced evaporation of seawater followed by condensation of the vapour generated. The second is through atmospheric-water harvesting through the absorption of water vapour followed by water recovery via solar-induced evaporation. The project could serve as a solution for decentralised water production in remote communities and disaster relief applications.
1. Explanation of the work carried per WP
1. 1 Work Package 1 (WP1)
WP1 - Comparison of PSA/PPy cryogels (PPCs) with different structures
The main task in WP1 was to synthesise, characterize and evaluate the performance of PPC with different structures. Furthermore, the structure-property-performance relationship of the PPCs for solar desalination and moisture capture was also established.
Work conducted:
i. Conducted a thorough literature review on polymeric hydrogels applied for water treatment – wrote and published a review paper based on this.
ii. Experimented on using two different approaches for fabrication of PPC samples via (a) in situ polymerization of PPy on the surface of pre-formed PSA cryogels and (b) formation of PSA cryogel in the presence of pre-polymerized PPy chains forming a semi-interpenetrating network (semi-IPN). However, we found that the method (b) was unsuccessful because of severe PPy aggregation prior to gelation resulting in non-uniform dispersion of PPy. It also affected the cryogelation rate – thus preventing the formation of macropores in the resultant PPC. As such, we focused on method (a) for further development of PPC.
iii. Using method (a), PPC samples with significantly different morphologies (i.e. honeycomb versus lamellarized structures) were fabricated by tuning the concentration of precursor pyrrole.
iv. The following materials properties of the resultant PPC samples were characterized in detailed:
a. Morphology and pore structures
b. Distribution of PPy in the PSA
c. Chemical interactions between PPy and PSA
d. Thermal behavior
e. Water wetting and transport properties of PPCs
f. Photoabsorption and photothermal properties of PPCs
v. The PPy formation mechanism was also investigated and explored to better understand how to control the synthesis process in order to form materials with specific structures and properties.
vi. Correlation between the structure-property-performance relationship for the PPC as a solar evaporator has been studied. This can be a useful guideline for the rational design and synthesis of efficient solar evaporators in the future.
This WP has been fully completed. In line with planned Deliverable, we have successfully developed a PSA/PPy cryogel. Furthermore, the following Milestones have also been achieved:
i. Completed the data acquisition on the characteristics and performance of the PPC samples with different structures.
ii. Developed deeper insights into the materials design for improved solar desalination and moisture capture.
1.2 Work Package 2 (WP2)
WP2 - Fabrication of high-performance SWaG
In the original DoA, it was planned that the high-performance SWaG will be prepared by coupling the best PPC from WP1 to the best thermal management strategy identified in this WP.
Work conducted:
i. Using the best PPC sample from WP1, two different modes of operation, namely floating and standing were compared. The standing mode can provide a better heat management strategy because the PPC sample is not in constant contact with a large amount of bulk water, thus heat loss is minimized.
ii. The solar evaporation efficiencies of the sample when operated in the two different modes were compared.
iii. Investigated the reason why the standing mode resulted in higher solar evaporation rate.
iv. An alternative thermal management strategy is proposed that employs a bilayered structure consisting of (i) a PPy-coated paper as the top photothermal layer and (ii) a bottom layer of a PSA cryogel which functions as not only the moisture sorber, but also as a thermal barrier and water transporter.
v. The PPy-coated paper and PSA cryogels used in the bilayer configuration were fabricated using the gained know-how from WP1.

1.4 Work Package 4 (WP4)
WP4 – Management and training
In the original DoA, this WP groups tasks related to progress review and management of the project and the Fellow’s career development throughout the course of the Action.
Work conducted:
i. In accordance with Section 1.2 in the DoA, the Fellow and the Supervisor have also planned and carried out training activities outlined in a Personalized Development Plan.
ii. The Fellow, under the advisement of the Supervisor along with IIT Projects Office, has been learning how to deal with contingency and unexpected results, mitigate risks, and adopt alternatives for unforeseen circumstances.
In line with the Milestones delineated in the DoA, the Supervisor and the Fellow have agreed on the work plan, milestones and deliverables for the project as well as the personalized career development plan (PCDP) during the course of the implementation of the Action. Briefly, the following summarizes the training activities that have been completed.
It can be expected that, at the end of the project, the successful demonstration of the application of a SWaG in solar desalination and atmospheric-water harvesting could not only lead to advancement in scientific knowledge and materials innovation, but it could also have impactful societal and humanitarian implications because it addresses a global challenge – water security. Significantly, due to the infrastructure-independence of its operation, SWaG can complement mainstream water technologies in bridging the water supply gap by providing a viable decentralized solution to the populations most afflicted by water scarcity, i.e. the poor displaced in remote communities or those residing in disaster-prone regions.
3 D Photothermal Cryogels