Fabrication Of Carbon Nanotube Composite Membranes And Its Solar Evaporation Characteristics

As an inexhaustible natural and non-polluting renewable energy source,solar energy has broad application prospects in alleviating the current energy and water shortage challenges faced by human beings at present.By converting solar energy into heat and further acting on many practical freshwater production engineering applications such as solar desalination,human demand for freshwater resources can be met to some extent.Some photothermal materials with good absorption properties in the entire solar spectrum,such as metal nanoparticles,carbon-based nanoparticles,etc.,have excellent photothermal conversion capabilities.By combining these photothermal materials with a support substrate,a photothermal composite me mbrane having excellent light absorption and heat conversion properties can be obtained.Due to the inexhaustible characteristics of solar energy,the application of these photothermal composite membranes in the field of solar desalination can theoretically obtain an unlimited amount of fresh water resources.Therefore,in the future,such photothermal composite membranes are expected to be more widely used in fields such as solar desalination.In this paper,two composite membranes with carbon nanotubes as photothermal materials were developed,including carbon nanotube-polyvinylidene fluoride composite membrane and carbon nanotube-filter paper composite membrane.According to the concept of interfacial solar vapor conversion,a membrane distillation device and an integrated evaporation device was designed.The structure characterization and its application in the mechanism of photothermal evaporation have been studied in detail and deeply.The first one is the photothermal evaporation characteristic of a carbon nanotube-polyvinylidene fluoride composite membrane.The composite membrane was prepared by a phase inversion method to realize immobilization of the carbon nanotube photothermal material.The composite membrane has high light absorption performance in the entire solar spectrum,and its own microporous structure gives it good hydrophilicity,ensuring that the membrane remains wet during evaporation.In order to reduce the additional heat loss from the membrane to the bulk water during solar evaporation,a membrane distillation device was designed and assembled.Its main components include a carbon nanotube-polyvinylidene fluoride membrane as a solar absorption and photothermal conversion layer,a qualitative filter paper disc as a water supplier and four strip filter paper strips connected to the disc,and an aerogel blanket as an thermal insulator.The effects of carbon nanotube concentration and light intensity on the solar evaporation performance of the carbon nanotube-polyvinylidene fluoride composite membrane and corresponding membrane distillation device were systematically studied and the cycle stability was tested.An solar conversion efficiency of 84.6%and a corresponding evaporation rate of 1.31 kg m^-22 h^-1 were achieved at a simulated solar light intensity of 1 kW m^-2.The second is the photothermal evaporation characteristics of carbon nanotube-filter paper composite membrane.The carbon nanotube-polyvinylidene fluoride particles in the casting solution are uniformly supported on the hydrophilic filter paper by the spin coating method,thereby imparting excellent light absorption performance;the heat loss of the membrane is remarkably lowered by the load of the polyurethane foam.An integrated evaporation device that achieves perfect coupling of light absorption,water transport and thermal management was constructed.The prepared composite membrane exhibited a high solar absorption rate of more than95%,and a high solar conversion efficiency of about 88%was obtained under the il umination of 1 kW m^-2.