Design And Performance Of Solar Evaporator Based On Cellulose Nanofiber Gels

Solar steam generator is a technology that uses abundant solar energy to obtain clean water.Cellulose-based hydrogels have a network of 3D cross-linked polymer gels swollen by water molecules.Hydrogel-based solar evaporators can be prepared by carboxylated cellulose（CNF-COOH）which interacts with other polymer materials.This paper designs and demonstrates two hydrogels for solar evaporation:1)Carboxylated cellulose nanofibers（CNF-COOH）and polyethylenimine（PEI）are cross-linked through electrostatic interaction and hydrogen bonding,and different gels are prepared by adjusting the type of photothermal materials and the ratio of CNF-COOH and PEI.At the same time,the effect of height on the evaporation properties of the gel is explored in this article.Among them,CPGs prepared by r GO as photothermal materials showed low apparent density and low thermal conductivity(0.035 W m^-1 K^-1),super hydrophilic（the water contact angle≈0°）and high light absorption ability（90%）.As a result,it exhibits excellent performance as a solar evaporator.Under one sun,the evaporation efficiency of CPG with a height of 3 cm can reach 2.6 kg m^-2 h^-1,and the evaporation efficiency can reach 93.5%.2)CPG-Ag was designed and synthesized on the basis of CPG.The properties of CPG-Ag have been investigated for different heights and silver loading.The introduction of Ag NPs enhanced the mechanical strength,compression properties and light absorption of CPG（93%）,reduced the evaporation enthalpy of water in the gel(1768J g^-1),and increased the thermal conductivity(0.045 W m^-1 K^-1).The evaporation rate of CPG-Ag reached 3.6 kg m^-2 h^-1 with the efficiency of 96.25%due to the synergistic effect of water transport,light absorption,thermal management and enthalpy of evaporation.In addition,it is of some generality that this method can also improve the evaporation rate of other hydrogel materials.