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• A wood coated with MWCNT@GNP is used in double-layer photoabsorber for interfacial mathod. • Evaporated mass of GNP@MWCNT in interfacial and volumetric methods was investigated. • Effect of paraffin wax as PCM in solar steam generation was evaluated. • Performance of PCMs in interfacial and volumetric methods was compared. The rate of evaporation in direct solar steam generation can be increased by employing several techniques. One of the passive techniques that can be used for the improvement of system performance is the use of phase change materials (PCMs). An experimental study was carried out to explore the role of PCMs in energy storage and continuous evaporation in a direct solar steam generation (SSG) system. For this purpose, volumetric and surface methods have been employed and compared in the absence and presence of PCMs. A nanofluid composed of MWCNT@GNP (a nanocomposite of graphene and multiwall carbon nanotubes) and water was used as a photoabsorber in the volumetric method, whereas poplar wood coated with MWCNT@GNP was chosen for the surface method. The results indicated that paraffin wax PCMs around the bulk fluid with benefiting from excellent capability of energy storage gave a superb performance for continuance of vapor production in both methods. The PCMs have a significant impact on maintaining the evaporation rate at night. However, in the presence of PCMs, the photoabsorber in the volumetric method represented much better performance compared to the surface method. [Display omitted] [ABSTRACT FROM AUTHOR]

Water vapor is vital both as an energy carrier and as an intermediary state for removing impurities from water. In nature, transpiration occurs when water is transported (against gravity) from the roots to the underside of leaves where it evaporates. Using this process, one large tree can pump and purify 400 L of water each day. Based on trunk cross-sectional area, this corresponds to a water flux range of ∼100–1000 kg/m2day, but based on evaporation area it only corresponds to a rate of ∼0.1 kg/m2day. Compared to industrial mechanisms of producing water vapor (i.e. typical thermal-driven systems have a flux of ∼4000 kg/m2day), natural wood has a relatively low flux. In an effort to boost the flux of sustainable, natural wood, we investigated wood surface modifications, laser carbonization and deposition of gold nanolayers, which achieved an instantaneous evaporation rate of ∼4 kg/m2h—under 3 kW/m2 light intensity, exceeding all previous studies of synthetic materials (including 3.8 kg/m2h reported by Zhou et al. in a 2016 Nature Photonics article) for solar steam generation applications. The cost analysis of different natural and synthetic material-based techniques for solar steam generation indicated that the carbonization and laser treatments are very cost-effective and even the gold coating was comparable to previously reported synthetic materials. Based on these results, we suggest that natural, surface-modified poplar wood could represent a viable alternative to synthetic materials for liquid/vapor separation. • Treated wood samples as evaporators were tested with a solar simulator (1–3 Suns). • Poplar wood sample of 5 mm length had the best capillary action. • Laser treatment was reported as a fast and accurate way of carbonizing wood surface. • Gold nanolayer coating and carbonized wood surfaces showed high solar absorption. • Combination method led to a record of 4.02 kg/m2 h evaporation rate at 3 Suns. [ABSTRACT FROM AUTHOR]

Interfacial solar steam generation (SSG) has emerged as a promising solution to address the global challenges of water scarcity. Herein, for the first time, by pressing micro-scale sawdust into a polystyrene mold using a manual hydraulic press and enclosing it in an aluminum grid (S/Al), a substrate for SSG was made. Adjusting the porosity of the SSG device has a significant effect on the evaporation performance due to its potential in regulating the transfer of bulk water to the evaporation surface and controlling the thermal conductivity of substrate. The optimal sawdust-based photoabsorber with a 62% porosity represented 59% evaporation efficiency under 2.2 kW m−2. In addition, to improve the photothermal performance for the first time, vanadium dioxide nanoparticles doped by tungsten (W3-VO 2) as a photothermal layer on the sawdust-based substrate were used. The results were compared with those of carbonized sawdust-based substrate supported by black aluminum grid (S/C/Al–B). The excellent performance belonged to S/Al/W3-VO 2 device with 90% evaporation efficiency under 2.2 kW m−2 which was 3.3 and 1.2 times greater than pure water and S/C/Al–B, respectively. The concentration of four ions of Na+, Mg2+, K+, and Ca2+, which are responsible for the salinity of water, in the collected seawater after condensation of vapor decreased by about three orders of magnitude. Due to high performance, environmentally friendly, cost-effectiveness, and availability of the proposed device, the S/Al/W3-VO 2 photoabsorber can be used in remote areas for large-scale applications. Herein, the double-layer SSG device consisting of sawdust as a substrate and tungsten-doped vanadium dioxide NPs as photothermal material is designed. The advantages of sawdust including low cost, accessibility, ability to regulate porosity leads to control of water transfer and TC of the substrate. Although the performance of the double-layer SSG device is optimized by adjusting the permeability of substrates, heat loss, long-term stability, and cost-effectiveness of the devices are still challenging and require further research. In this work, sawdust is molded into polystyrene to minimize the manipulation of the chemical structure and then it is pressed under various pressures. Finally, it is enclosed in an aluminum grid to prevent the photoabsorber device from being damaged after the expansion due to water absorption. The aluminum grid in addition to keep sawdust in the mold, thanks to its plasmonic properties which increases the light absorption of the SSG device. To enhance the aluminum light absorption, the color was changed to black by coating W3-VO 2 NPs on the substrate. • A cost effective approach is suggested to harvesting solar energy. • A sawdust coated with W doped VO 2 is used in interfacial solar steam generation. • Performance of the carbonized sawdust with W -VO 2 was compared. • Sawdust-based photoabsorber with the porosity of 62% showed high solar absorption. • S/Al/W3-VO 2 photoabsorber can be used as low-cost for a large-scale application. [ABSTRACT FROM AUTHOR]

• The solar evaporation efficiency of 93.45% was achieved by wood covered by VO 2 -Ba. • The ratio of preparation cost to evaporation flux is 1.16 USD kg−1 m−2 h−1. • The concentration of Na+ of Caspian seawater reduced from 3138.19 to 2.63 ppm. Interfacial solar steam generation (SSG) as a green desalination technique offers significant potential to obtain freshwater. For the first time, the performance of alkaline earth metals doped VO 2 nanoparticles (VO 2 @alkaline earth metals) as highly efficient photothermal materials coated on poplar wood as a sustainable substrate in SSG of seawater is investigated. Among the fabricated photoabsorbers, the wood coated with VO 2 doped with Ba, W/VO 2 -Ba, had the highest solar evaporation efficiency of 93.45% under 1 sun (1 sun = 1 kW m−2). For this photoabsorber, the concentration of Na+ of seawater (3138.19 ppm) reduced to 2.63 ppm after desalination. The ratio of preparation cost to evaporation flux was calculated as 1.16 USD kg−1 m−2 h−1. The efficiency of W/VO 2 -Ba did not change significantly after 20 cycles. [Display omitted] [ABSTRACT FROM AUTHOR]