Nanofibrous hydrogel-reduced graphene oxide membranes for effective solar-driven interfacial evaporation and desalination

Interfacial evaporation from light-absorbing, porous materials have offered an exciting opportunity to utilize sustainable renewable solar energy for desalination. However, the efforts to understand the fundamental mechanisms governing the interfacial evaporation have greatly lagged behind performance studies. Herein, a hybrid nanofibrous hydrogel-reduced graphene oxide (NHrG) membrane is demonstrated in this work. We experimentally characterized the state of water in the NHrG membrane and proved the presence of intermediate water in the porous membrane. By monitoring the vaporization enthalpy as a function of membrane saturation, we demonstrated that the vaporization of intermediate water dominates the interfacial evaporation process, thus playing a key role in lowering the vaporization enthalpy. The lowered enthalpy value together with other factors, such as the high light absorption efficiency enabled by reduced graphene oxide (rGO) and the porous hydrophilic network induced by electrospun hydrogel nanofibers, led to a highly efficient solar-driven interfacial evaporator. The NHrG membrane had an evaporation rate of up to 1.85 kg m−2h−1 with a high energy conversion efficiency of 95.4% under one sun irradiation. In addition, the evaporator exhibited excellent desalination performance in treating fresh seawater and achieved high removal of salt as well as heavy metal ions. Our study provides important knowledge for performance optimization and process design.