Facile Preparation of MnO₂-Deposited Wood for High-Efficiency Solar Steam Generation

Abstract

Wood, a natural renewable material, has drawn great attention in solar steam generation in recent years due to its intrinsic properties such as high hydrophilicity and low thermal conductivity. Until now, great achievements have been made in increasing the light absorption of wood-based solar evaporators, mainly through surface carbonization and coating. However, the complicated and cost-intensive preparation process of the light absorption layer prevents its large-scale application. In particular, the carbonized and coated surface could be importantly influenced by the scouring effect of waves and the corrosion of salt water. Herein, a facile, low-cost, and scalable in situ reduction method has been developed to prepared KMnO4 oxidized wood (K-wood) for solar steam generation, which not only shows high evaporation performance but also has high structural stability. In the preparation process, the reaction-product black MnO2 particles will be uniformly distributed on the surface of wood, making the K-wood exhibit a high solar absorbance of about 94%. Moreover, the K-wood could still maintain the inherent high hydrophilicity and excellent thermal insulation performance. Benefitting from all of these advantages, the K-wood achieved a high evaporation rate (1.22 kg m–2 h–1) and a high evaporation efficiency (81.4%) under 1 sun illumination (1 kW m–2). Importantly, the K-wood also exhibits excellent structural stability, such as having good acid–base resistance and also washing resistance, and could even withstand an ultrasound treatment for even 2 h. The reusability of the K-wood was also tested, and the evaporation rate remains nearly unchanged after 20 cycles in seawater evaporation. Moreover, the condensate water obtained by the homemade collection device shows low ion concentrations, demonstrating that the K-wood possesses an excellent ability in seawater desalination treatment. This study provides a simple method to manufacture a high-strength wood-based solar steam evaporation device, which has potential for future large-scale applications.

Co‐Hydrothermal Carbonization of Cotton Stalks and MnO2 for Direct Solar Steam Generation with High Efficiency

“…This corresponds to the binding energies of Mn 2p3/2 and Mn 2p1/2 with a spin energy separation of 11.7. [37] These spectral features further confirm the presence of MnO 2 particles on the H-CS/MnO 2 surface. These results provide strong evidence that the co-hydrothermal carbonization of CS and MnO 2 can lead to a stable combination of MnO 2 with CS and the structure of CS has changed.…”

“…This phenomenon further indicates that the successful loading of MnO 2 greatly improves the light absorption performance of the material, and it is mainly due to the irregular loading of MnO 2 , which extends the optical path of multiple scattering (Figure 3g), reduces the reflectivity and increases the absorption. [ 37 ]…”

“…The reasons lie in two aspects. On the one hand, MnO 2 , as a black stable material, has excellent photothermal conversion properties [ 37 ] with low cost. On the other hand, HTC ensures the hydrophilicity of the material and the stable loading of MnO 2 .…”

Recent Progress on the Solar‐Driven Interfacial Evaporation Based on Natural Products and Synthetic Polymers

“…Inspired by the high transpiration of rice, Liu and coworkers [ 79 ] developed a general device to generate steam from rice straw, which has the evaporation rate of 1.20 kg m −2 h −1 , and the conversion efficiency is 75.8%, and the daily net water consumption of the device is 6.40–7.90 kg m −2 and 4.60–5.60 kg m −2 on sunny and cloudy days, respectively (Figure 3d). Zhao and coworkers [ 80 ] also built a 3D foam absorber with carbonized rice husk as raw material.…”

Natural Porous Materials for Interfacial Solar Steam Generation toward Clean Water Production

“…The NP-based solar absorber has by far demonstrated the highest efficiencies because of its superior electronic, optical, and thermal properties. [20][21][22][23][24][25][26][27] Among them, gold NPs, [28,29] aluminum NPs, [20,30] MXene, [31,32] carbon nanotubes (CNTs), [33,34] graphene, [35,36] carbon dots, [37,38] carbon black, [39,40] polymers, [41,42] plasmonic NPs, and [41,43] black oxide NPs [44,45] have been widely investigated in recent years. However, none of them hit extreme popularity because of the higher cost and poor extensibility.…”