Graphene and Rice-Straw-Fiber-Based 3D Photothermal Aerogels for Highly Efficient Solar Evaporation

Abstract

Solar-steam generation is one of the most promising technologies to mitigate the issue of clean water shortage using sustainable solar energy. Photothermal aerogels, especially the three-dimensional (3D) graphene-based aerogels, have shown unique merits for solar-steam generation, such as lightweight, high flexibility, and superior evaporation rate and energy efficiency. However, 3D aerogels require much more raw materials of graphene, which limits their large-scale applications. In this study, 3D photothermal aerogels composed of reduced graphene oxide (RGO) nanosheets, rice-straw-derived cellulose fibers, and sodium alginate (SA) are prepared for solar-steam generation. The use of rice straw fibers as skeletal support significantly reduces the need for the more expensive RGO by 43.5%, turning the rice straw biomass waste into value-added materials. The integration of rice straw fibers and RGO significantly enhances the flexibility and mechanical stability of the obtained photothermal RGO−SA−cellulose aerogel. The photothermal aerogel shows a strong broad-band light absorption of 96−97%. During solar-steam generation, the 3D photothermal aerogel effectively decreases the radiation and convection energy loss while enhancing energy harvesting from the environment, leading to an extremely high evaporation rate of 2.25 kg m −2 h −1 , corresponding to an energy conversion efficiency of 88.9% under 1.0 sun irradiation. The salinity of clean water collected during the evaporation of real seawater is only 0.37 ppm. The materials are environmentally friendly and cost-effective, showing great potential for real-world desalination applications.

Boosting solar steam generation by structure enhanced energy management

“…One promising path to achieve an energy efficiency beyond the theoretical limit (i.e., >100%) under 1.0 sun is to increase the net energy gain from environment during solar-steam generation [33,[37][38][39][40]. To achieve this, in the past a couple of years, 3D photothermal structures were designed and investigated [41].…”

“…To achieve this, in the past a couple of years, 3D photothermal structures were designed and investigated [41]. For example, when a 3D cylinder instead of a 2D photothermal surface is presented under vertical light irradiation, the photothermal effect of the top surface drives the interfacial solar-steam generation [37,39,40]. The temperature at the top surface is normally higher than the surrounding environmental temperature, which inevitably leads to energy loss to the environment via convection and radiation.…”

Nanoenabled Photothermal Materials for Clean Water Production

“…Besides, the rGO‐silk fabric demonstrated excellent washing ability, flexibility, and remarkable electrical strength for cheap, durable, and portable applications of solar steam generation. [ 86 ] In 2019, reduced graphene oxide (RGO)/cotton fabric‐based unique solar evaporative system was fabricated with porous polyacrylonitrile foam (VOPPF). The reported system was vertically aligned enabling its self‐desalination as illustrated in Figure 6c.…”

Ultra‐Black Pinecone for Efficient Solar Steam Generation under Omnidirectional Illumination

“…), semiconductors (Cu x S, [ 20,21 ] MoS 2 , [ 22,23 ] TiO x , [ 24,25 ] etc. ), polymers, [ 26–31 ] MXene, [ 11,32 ] carbon materials, [ 2,7,8,33–44 ] and composite materials [ 45–48 ] have been developed. However, there are still many challenges, including material cost, industrial scale‐up, and outdoor performance degradation, that need to be overcome.…”