Enhancing the evaporation rate of 3D solar evaporators by coating their surface with N-doped graphene and MnCoGe alloy compounds

The utilization of solar evaporators to produce fresh water from seawater and from polluted water sources is a promising approach to palliate the global water shortage crisis. In this research, coconut/agave-fibers based 3D-sponges were used as biodegradable support to make solar evaporators. A graphene coating was deposited on the biodegradable sponges (FG evaporator) and was evaluated to desalinate seawater (from Puerto-Vallarta Beach, Mexico) under natural sunlight. This evaporator produced an evaporation-rate/evaporation-efficiency of 1.55 kg m^-2·h^-1/77.3 %. Next, a second evaporator was fabricated by depositing an extra layer of N-doped graphene (NG) on the graphene layer and this evaporator reached an evaporation-rate/evaporation-efficiency of 2.05 kg m^-2·h^-1/81.6 %. The evaporation-rate/evaporation-efficiency of the evaporators were enhanced even more (up to 2.32 kg m^-2·h^-1/89.4 %) after depositing MnCoGe (MCG) alloy particles instead of NG on the evaporators. Thus, the evaporation rate of the evaporator made with MCG was enhanced 32 % with respect to the evaporator made only with the graphene coating. All the evaporators were subjected to 10 consecutive cycles of use and the maximum reduction in the evaporation rate was 6 %. Later, tap water was contaminated with 2,4-dichlorophenoxyacetic acid (2,4-DCP) herbicide (20 ppm). Next, this contaminated water was put in contact with the solar evaporator made with MCG alloy and it was completely decontaminated as confirmed by the UV-Vis spectra for the clean water. In general, adding the MCG alloy on the evaporators (previously coated with graphene), reduced the heat losses and the water enthalpy, which increased the evaporation rate of the water. The results of this investigation indicate that 3D graphene evaporators can be constructed on biodegradable fibers, which diminished the environmental impact of expired evaporators.