Graphene Oxide–Reduced Graphene Oxide Janus Membrane for Efficient Solar Generation of Water Vapor

Abstract

Water purification by solar distillation technique is considered a sustainable method of producing fresh water. Thus, the development of a highly efficient solar absorber system has gained considerable attention. In this study, we report a graphene oxide (GO)− reduced graphene oxide (rGO) Janus membrane produced via laser treatment of the GO membrane under the protection of hydrogel. One side of the GO membrane is reduced to rGO using laser power, while the other side of the GO membrane is protected by hydrogel to avoid laser ablation and retain the integrity and original state of the membrane. The hydrophilicity of the GO layer and the relative hydrophobicity of the rGO layer complement each other and work synergistically. The hydrophilic GO side provides a good water transmission channel and exhibits good block salt penetration, whereas the relatively hydrophobic rGO side with a 3D rough surface increases the evaporation rate by increasing the sunlight absorption. Therefore, the resultant GO− rGO Janus membrane under 1 sun illumination exhibits a high solar-to-vapor efficiency of 91.4%, which is higher than that of most graphene-based photothermal conversion materials previously reported. Simultaneously, it is found that the GO−rGO Janus membrane is highly efficient and salt resistant and can be utilized for the purification of various types of water, including seawater and supersaturated brine. Therefore, the GO−rGO Janus membrane made may help to collect solar energy, and this research can be considered as a useful attempt to develop an efficient Janus membrane for producing fresh water.

Recent developments of hydrogel based solar water purification technology

“…Examples include using hydrophobic polydimethylsiloxane (PDMS) as the top layer, 123 adding hydrophobic Si aerogels mainly in the upper part, 34,104,164 selectively decorating the upper surface with PFOTS 162 and reducing hydrophilic GO into hydrophobic rGO at the top side via laser. 165 Furthermore, Guo et al 36 have reported a patchy surface with hydrophobic and hydrophilic parts for higher water transport speed and excellent SVG performance (4 kg m -2 h -1 with 93% energy conversion efficiency Figure 9). The hydrogel has a partial trichloro(octadecyl)silane (OTS) modified surface, with the island-shaped patches being hydrophobic and the rest being hydrophilic (Figure 9a).…”

“…43,112 Guo et al 184 recently attached catechol groups to the CTS hydrogel for hydrogen peroxide (a broad-acting antibacterial agent) generation, combining with the synergistic effect of quinone-modified AC, to enhance the anti-fouling properties and guarantee 3 months of performance maintenance. There are numerous methods to improve the anti-crystalline fouling ability, including the construction of the Janus structure 130,165 and the umbrella-shaped platform, 91 the use of ions rejection polymer, 85,152,169 the introduction of bubbles in the middle section, 140 the weight imbalance sensitive spherical platform capable of rotating and renewing the evaporation surface, 163 the millineedle array on the surface for site-specific salt crystallization without salt clogging 155 and so on. In addition, the self-floating hydrogel platform is out of the external support substrate, which is not conducive to water transport, usually by adding low-density materials ( i.e.…”

Avant‐Garde Solar–Thermal Nanostructures: Nascent Strategy into Effective Photothermal Desalination

“…Ultimately, from the present literature Janus nanoarchitectures can be established as futuristic smart material for which immense research is being carried out for photothermal desalination. Most recently, various Janus nanoarchitectures have been fabricated and investigated as an effective solar–steam generators for photothermal desalination and PMD, such as bioinspired Janus composites, [ 161 ] carbon/sponge evaporators, [ 162 ] Janus aerogel with antifouling characteristics, [ 163 ] Porphyrin–Ti 3 C 2 T x MXene Janus membrane, [ 164 ] PP nonwoven fabric incorporated with CNT/PPy fluorinated hydrophobic coated Janus structure, [ 165 ] GO/rGO Janus membrane, [ 166 ] PVDF ‐co ‐hexafluoropropylene (PVDF‐HFP) Janus nanofibrous mat, [ 167 ] Janus PP hollow fiber membrane (PP HFM), [ 168 ] and silicone/MWCNT superhydrophobic/superhydrophilic yolk/shell ( Table 4 ). [ 169 ]…”

“…membrane, [166] PVDF-co-hexafluoropropylene (PVDF-HFP) Janus nanofibrous mat, [167] Janus PP hollow fiber membrane (PP HFM), [168] and silicone/MWCNT superhydrophobic/ superhydrophilic yolk/shell (Table 4). [169]…”

Breath‐Figure Self‐Assembled Low‐Cost Janus Fabrics for Highly Efficient and Stable Solar Desalination

“…At present, solar-driven interfacial evaporation materials, including metal nanoparticles, [12,16] carbonbased materials, [17][18][19][20][21][22][23] and polymers, [24][25][26] are commonly used. Despite these designs on materials and structures that can promote the performance of solar-driven interfacial evaporation, the accumulation of salts has always hindered the practical application of this technology, especially in high salt concentration water.…”