Flexible Fire‐Resistant Photothermal Paper Comprising Ultralong Hydroxyapatite Nanowires and Carbon Nanotubes for Solar Energy‐Driven Water Purification

Abstract

harvested and converted into heat for steam generation. [3] Because the existing ions, organics, and bacteria can be separated in the cost-effective and environmentally friendly process, solar energy-driven water evaporation is considered as a highly promising technology to purify water. [3b,4] Conventional water steam generation systems require many optical concentrators to achieve sufficiently high temperatures for heating water, low efficiency and high investment are the shortcomings. [3b] In this regard, recent studies focused on the localized heating of interfacial water based on photothermal materials with effective light absorption and light-to-heat conversion capabilities. [5] Nanoparticles such as gold, [6] titanium sesquioxide, [7] and alumina [8] were proposed for steam generation and water purification, but the low chemical stability, high cost, and low yield limit their large-scale applications. Carbon-based materials including graphene, carbon black, and carbon nanotubes have promising applications owing to their broadband light absorption, high stability, and low cost, [9] which are the most important prerequisites to ensure high solar energy conversion and practical application in water purification.Rational structural design for solar energy-driven water steam generation devices is significant to achieve high water evaporation efficiency and potential large-scale application. In the concept of heat localization, [10] the light-absorbing materials are integrated into the floating and thermally insulating substrates, which can effectively reduce the heat loss to the bulk water and enhance the water evaporation efficiency. Chen and co-workers developed a floating double-layer structure composed of exfoliated graphite and porous carbon foam with a water steam generation efficiency as high as 85% under 10 kW m −2 irradiation. [10a] A variety of solar energy-driven water evaporation devices with a bilayer structure, such as carbonized mushroom/polystyrene foam, [11] reduced graphene oxide/ bacterial nanocellulose biofoam, [12] graphene aerogel/polystyrene foam, [13] and carbon nanotube-coated wood, [14] were reported for high-efficiency water steam generation. However, these designed devices require precise and complicated fabrication processes, which limit their practicability and large-scale applications.Efficient utilization of abundant solar energy for clean water generation is considered a sustainable and environment friendly approach to mitigate the global water crisis. For this purpose, this study reports a flexible fire-resistant photothermal paper by combining carbon nanotubes (CNTs) and fire-resistant inorganic paper based on ultralong hydroxyapatite nanowires (HNs) for efficient solar energy-driven water steam generation and water purification. Benefiting from the structural characteristics of the HN/CNT photothermal paper, the black CNT surface layer exhibits a high light absorbability and photothermal conversion capability, the HN-based inorganic paper acts as a thermal insulator wit...

Cellular Structured CNTs@SiO2 Nanofibrous Aerogels with Vertically Aligned Vessels for Salt‐Resistant Solar Desalination

“…The IR pictures of temperature distribution during solar desalination were recorded by an IR thermal imager (TiS75, Fluke Ltd., USA). The corresponding photothermal conversion efficiency was calculated using the following formula: η = mh v /C opt P 0 , where η is the photothermal conversion efficiency, [23,55] m is the evaporation rate caused by light irradiation, in which the evaporation rate in dark has already subtracted out, h v is the total enthalpy of water, which is composed of the phase change enthalpy and sensible heat, C opt is the light concentration factor of the solar simulator, and P 0 is the standard solar irradiation power (1 kW m −2 ).…”

Designing a bioinspired synthetic tree by unidirectional freezing for simultaneous solar steam generation and salt collection

“…The dry PVA matrix had a low thermal conductivity of 0.16 W m −1 K −1 because of its porous structure. When the PVA matrix was filled with water, the thermal conductivity obviously increased to 0.57 W m −1 K −1 , indicating that thermal convection was inhibited in the water channels and favorable for heat localization 12 …”

“…When the PVA matrix was filled with water, the thermal conductivity obviously increased to 0.57 W m −1 K −1 , indicating that thermal convection was inhibited in the water channels and favorable for heat localization. 12 Because of the asymmetric T-shaped structure of the bionic synthetic tree, the salt concentration distribution is uneven due to water evaporation. We used the COM-SOL Multiphysics software to perform simulations to F I G U R E 2 Fabrication scheme and characterization of bioinspired polymeric wood.…”

“…Attention has mainly focused on high absorption in the solar spectrum, low thermal loss from the evaporation surface and sufficient water supply for evaporation 6,9–11 . Various absorbers, such as carbon‐based materials, conjugated polymers, semiconductors, and plasmonic nanomaterials, have been designed to float on the surface of water 2,12–15 . However, to reduce heat loss in the form of heat conduction to bulk water, water is usually transported to the evaporation surface via capillary channels, where salt accumulation easily occurs 16–20 .…”

“…6,[9][10][11] Various absorbers, such as carbon-based materials, conjugated polymers, semiconductors, and plasmonic nanomaterials, have been designed to float on the surface of water. 2,[12][13][14][15] However, to reduce heat loss in the form of heat conduction to bulk water, water is usually transported to the evaporation surface via capillary channels, where salt accumulation easily occurs. [16][17][18][19][20] The accumulated salt can severely reduce the adsorption efficiency, clog the water path, and decrease the evaporation area.…”