Inorganic aerogels have been attracting great interest owing to their distinctive structures and properties. However, the practical applications of inorganic aerogels are greatly restricted by their high brittleness and high fabrication cost. Herein, inspired by the cancellous bone, we have developed a novel kind of hydroxyapatite (HAP) nanowire-based inorganic aerogel with excellent elasticity, which is highly porous (porosity ≈ 99.7%), ultralight (density 8.54 mg/cm, which is about 0.854% of water density), and highly adiabatic (thermal conductivity 0.0387 W/m·K). Significantly, the as-prepared HAP nanowire aerogel can be used as the highly efficient air filter with high PM filtration efficiency. In addition, the HAP nanowire aerogel is also an ideal candidate for continuous oil-water separation, which can be used as a smart switch to separate oil from water continuously. Compared with organic aerogels, the as-prepared HAP nanowire aerogel is biocompatible, environmentally friendly, and low-cost. Moreover, the synthetic method reported in this work can be scaled up for large-scale production of HAP nanowires, free from the use of organic solvents. Therefore, the as-prepared new kind of HAP nanowire aerogel is promising for the applications in various fields.

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...

Traditional paper made from plant cellulose fibers is easily destroyed by either liquid or fire. In addition, the paper making industry consumes a large amount of natural trees and thus causes serious environmental problems including excessive deforestation and pollution. In consideration of the intrinsic flammability of organics and minimizing the effects on the environment and creatures, biocompatible ultralong hydroxyapatite nanowires are an ideal building material for inorganic fire-resistant paper. Herein, a new kind of free-standing, highly flexible, superhydrophobic, and fire-resistant layered inorganic paper has been successfully prepared using ultralong hydroxyapatite nanowires as building blocks after the surface modification with sodium oleate. During the vacuum filtration, ultralong hydroxyapatite nanowires assemble into self-roughened setalike microfibers, avoiding the tedious fabrication process to construct the hierarchical structure; the self-roughened microfibers further form the inorganic paper with a nacrelike layered structure. We have demonstrated that the layered structure can significantly improve the resistance to mechanical destruction of the as-prepared superhydrophobic paper. The as-prepared superhydrophobic and fire-resistant inorganic paper shows excellent nonflammability, liquid repellency to various commercial drinks, high thermal stability, and self-cleaning property. Moreover, we have explored the potential applications of the superhydrophobic and fire-resistant inorganic paper as a highly effective adsorbent for oil/water separation, fire-shielding protector, and writing paper.