A Hollow and Compressible 3D Photothermal Evaporator for Highly Efficient Solar Steam Generation without Energy Loss

Abstract

Solar steam generation offers a sustainable strategy to mitigate global clean water scarcity. To this end, 3D photothermal evaporators have attracted increasing research interest since they can significantly improve both evaporation rate and energy efficiency. However, compared to the 2D evaporators, the 3D ones consume more raw materials and occupy more storage space, which limits their applications for practical portable solar steam generation. To address this issue, a 3D hollow and compressible photothermal evaporator is designed and fabricated which can be compressed to less than one third of its original volume, thus enabling easier transport and storage. Moreover, under 1.0 sun illumination, all evaporation surfaces of this 3D evaporator are lower in temperatures than the surrounding environment, thus providing the unique advantage of zero energy loss to the environment during solar evaporation. Due to the all‐cold evaporation surfaces, during solar evaporation, the evaporator is able to harvest massive energy from both the surrounding air and bulk water, delivering an extremely high evaporation rate of up to 7.6 kg m−2 h−1 under 1.0 sun irradiation. Furthermore, seawater desalination tests demonstrate that the device has great potential for portable solar thermal desalination by delivering clean water with a salinity well below 50 ppb.

Recent developments of hydrogel based solar water purification technology

“…33 It is noted that a solar water purification system containing reduced graphene oxide (rGO) generally exhibits a relatively high evaporation rate (2.33–2.72 kg m −2 h −1 ) and higher energy conversion efficiency (>90%) compared to the systems based on graphene and graphene oxide (GO). 59,63,74,77,102–119 This result may be attributed to the residual functional groups ( i.e. epoxy, hydroxyl) on the surface of rGO, which can be further investigated.…”

“…33 It is noted that a solar water purification system containing reduced graphene oxide (rGO) generally exhibits a relatively high evaporation rate (2.33 -2.72 kg m -2 h -1 ) and higher energy conversion efficiency ( > 90%) compared to the systems based on graphene and graphene oxide (GO). 59,63,74,77,[102][103][104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119] This result may be attributed to the residual As the youngest carbon nanomaterials, carbon dots (CDs) [132][133][134] have attracted attention due to their broad light absorption spectrum (200-800 nm) and high photothermal conversion efficiency (> 90%), so that CDs can meet the requirements of solar absorbers. 135 To further improve the performance of CDs for solar water purification, future development directions include structure adjustment and surface group modification without lowering crystallinity or wetting properties.…”

“…Carbon-based materials have been used as solar absorbers in various studies in recent years, owing to their excellent light absorption over a broad spectrum, ease of preparation, abundance and low cost. Carbon-based materials include activated carbon, 83–86 polymer 76,87–90 or biomass 82,91–95 derived carbide, carbon black 96–101 and various amorphous carbon materials and highly graphitized carbon materials, such as graphene, 56,59,63,74,77,102–122 carbon nanotubes (CNTs) 27,123–130 and their derivatives.…”

Robust 3D Graphene/Cellulose Nanocrystals Hybrid Lamella Network for Stable and Highly Efficient Solar Desalination

“…The average evaporation rates of GCLN-20 are found to be 0.97, 1.66, 2.31, 2.94, and 4.14 kg m À2 h À1 , under 0.5, 1, 1.5, 2, and 3 sun illuminations, respectively (Figure 4g,h). The solar steam evaporation efficiency (η) [25,[51][52][53][54][55] is defined as…”

Bilayer rGO‐Based Photothermal Evaporator for Efficient Solar‐Driven Water Purification[]**

“…Graphene family, as typical representatives, have been implemented in photothermal evaporation system due to their high light absorption. [6,13,14] Generally, the whole photothermal evaporation system is relatively portable, adjustable, and cost-efficient, various natural water bodies including rivers, lakes, off-shore waters, even swamps can be employed as convenient water supply scenarios for vapor generation. Of note, the discharge of industrial wastewater without proper treatment leads to the widespread existence of trace volatile organic compounds (VOCs) with complex components in natural water bodies.…”