An intelligent cooling material modified with carbon dots for evaporative cooling and UV absorption.

The emergence of cooling technology has brought about huge social benefits to society, but it is also accompanied by the serious problem of energy consumption. In countries close to the equator, intense solar radiation is accompanied by unbearable high temperatures and strong ultraviolet radiation. Therefore, we prepared a simple hydrogel with good evaporative cooling, which can work continuously and has good UV absorption, to solve the indoor cooling and UV radiation problems. Polyacrylamide (PAM) in the hydrogel provides a mechanically strong backbone, and polyethylene glycol (PEG) slows water loss and provides the hydrogel with the ability to reflect infrared light. Lithium bromide (LiBr) is a highly efficient water vapor absorbent, which can provide the hydrogel with water regeneration capability. Carbon dots (CDs) can provide excellent UV absorption for hydrogels, and CDs (4.28 kJ kg-1 K-1) have a higher specific heat capacity than water (4.20 kJ kg-1 K-1), which can store more heat for a better indoor cooling effect. The composite hydrogel has a good prospect of application in the windows of residential and high-rise buildings.

The use of nanofibrillated cellulose to fabricate a homogeneous and flexible graphene-based electric heating membrane.

Nanofibrillated cellulose (NFC) as a natural macromolecule, binder, dispersant, enhancer, was utilized to facilitate the assembly of graphene sheets, imparting a steady stacked structure by the sheets to the electric heating membrane with flexibility and uniform heating performance. Strong interface bonding formed in the membrane, which combined graphene sheets to be a steady conductive network structure for electric heating. The membrane attained an equilibrium temperature rise to 60°C in 3min under 2000Wm-2, which increased linearly with increasing power density and graphene content. Decreased resistance between two electrodes was caused by electric-heat coupling effect which led to a decrease in the membrane's oxygen-containing groups as conducting electrification. The temperature distributing on membrane surface, and that as bent and distorted to different angles even simultaneously at the electric heating status, were all characterized by infrared thermal imaging to indicate the uniform distribution and well bonding performance between NFC and graphene, as well as the great flexibility in the biomass membrane. This study would further broaden the utilization of the natural nanocellulose-graphene biomass composites.

Thin Electric Heating Membrane Constructed with a Three-Dimensional Nanofibrillated Cellulose⁻Graphene⁻Graphene Oxide System.

Nanofibrillated cellulose (NFC) and graphene oxide (GO) with reinforcing and film-forming properties were employed with graphene to develop a novel and thin electric heating membrane with heat dissipation controllability. A negative charge was found on the surface of GO and NFC in aqueous dispersions, which contributed to the homogeneous distribution of the graphene sheets. The membrane had a good laminated structure with three-dimensional interaction between GO and NFC, with embedded graphene sheets. Conductivity was characterized as a function of the amount of graphene, thus giving control over to the heating power by adjusting the ratio of graphene. Subsequent electric heating tests can remove irregularities on the GO and graphene sheet, improving the laminated structure further. The temperature on the surface of the membrane presented an exponential increasing regularity with time. Under the same power density and time, the stabilized temperature rise of membranes was higher when grammage was higher, which was characterized by the linear function of the power density. Low-grammage membranes (1 and 4 g·m-2) also exhibited regular and even stabilized temperature rises. The indicated structure and heating performance of the membrane, as well as the variation induced by Joule heating, would drive its applications.