Elastic Aerogels of Cellulose Nanofibers@Metal–Organic Frameworks for Thermal Insulation and Fire Retardancy

Abstract

HIGHLIGHTS • The study reveals the great potential of metal-organic framework (MOF)-based nanocomposites in thermal insulation and fire retardancy applications. • A nanoengineering approach was developed to process MOFs into freestanding, mechanically strong, and elastic aerogels, which may boost the fundamental research and practical applications of MOFs in these areas. ABSTRACT Metal-organic frameworks (MOFs) with high microporosity and relatively high thermal stability are potential thermal insulation and flame-retardant materials. However, the difficulties in processing and shaping MOFs have largely hampered their applications in these areas. This study outlines the fabrication of hybrid CNF@MOF aerogels by a stepwise assembly approach involving the coating and cross-linking of cellulose nanofibers (CNFs) with continuous nanolayers of MOFs. The cross-linking gives the aerogels high mechanical strength but superelasticity (80% maximum recoverable strain, high specific compression modulus of ~ 200 MPa cm 3 g −1 , and specific stress of ~ 100 MPa cm 3 g −1).

Thermally induced fire early warning aerogel with efficient thermal isolation and flame‐retardant properties

“…With a density of 4.3 mg/cm 3 , pure CNF aerogel possesses a thermal conductivity of 40.43 mW/mK, which is similar with those of the currently used commercial TIMs, such as polystyrene foams (30–40 mW/mK) and polyurethane foams (20–50 mW/mK) 49 . The thermal conductivities of CNF/APP‐15 and CNF‐GO/APP composite aerogel are as low as 43.32 and 43.38 mW/mK, respectively, which are similar with those of the previously reported CNF‐based aerogels 50,51 . Furthermore, the incorporation of APP and GO exerts negligible influence on the thermal conductivity of CNF aerogel.…”

Highly Crystalline PEDOT Nanofiber Templated by Highly Crystalline Nanocellulose

“…The thermal conductivity of PEDOT nanofibrillar aerogels can be as low as 0.05 W m −1 K −1 as a result of the abundant micropores in the stacked nanofibers ( Figure S15, Supporting Information), which reduce the free movement of gas to a few nanometers, smaller than in free space (around 75 nm). [31,32] This results in applied heat being retained at the surface of the aerogel which, when combined with the photothermal conversion ability and porosity of PEDOT aerogels, makes them ideal candidates for solar thermal steam applications (Figure 4h and Figure S16, Supporting Information). When floating on water under 1 sun illumination, the surface temperature of the aerogel increases to ≈50 °C rapidly (in 100 s), generating a stable gradient of ≈30 °C between the upper and lower sides of the aerogel; this can induce fast water evaporation at a rate of ≈1.2 kg h −1 m −2 .…”

Effect of metal‐oxide nanoparticle presence and alginate cross‐linking on cellulose nanocrystal‐based aerogels

“…The stress–strain curves of CNC‐ALG aerogels showed two distinct deformation stages, during the first stage (ε < 20%) strain increases linearly and very fast practically without pressure reflecting porous deformation. Meanwhile at second stage (20% < ε < 80%) curves showed an exponential growth due to the suffered densification 72 . In this stage, the achieved densification is maximum at the end of the curve (80% < ε < 90%) where for small strain percentages the required pressure increases markedly.…”