| As a clean and inexhaustible energy resource,solar energy has been an eternal pursuit of development of human energy.Compared with the complex and costly and inefficient system of photoelectric transformation,it is no doubt that solar photothermal can be one of the most straightforward and efficient ways to use solar energy.How to convert the low grade and discontinuous solar energy into high grade heat energy,so as to maximize the use of solar energy,has become the key to break through the bottleneck of solar thermal applications of photothermal conversion material.The key to this solar thermal application is to develop efficient and stable photothermal materials.In this thesis,an efficient,new and totally different way of solar energy photothermal conversion is studied--solar steam generation,which is preparation of nanomaterial with high and stable performance of the photothermal conversion,fully absorbing the heat generated by the solar energy and evaporating water immediately.Based on preparation of three-dimension porous and robust floating materials,we investigate on the photothermal properties of graphene oxide-based nanocomposites and three-dimension reduced graphene oxide aerogel.Those major works are as follows:1.Investigation on photothermal effects of nanocomposite of graphene oxide and Au nanoparticles:we used nanocomposites of graphene oxide?GO?and gold?Au?nanoparticles to generate solar vapor under natural sunlight.In order to qualify the enhance effect of Au nanoparticles on GO nanofluids,the changes on steam pressure,mass loss and temperature of water were utilized to study the solar photothermal properties of GO-Au nanocomposites in water.We have studied the effect on photothermal performance by different additions of Au nanoparticles to GO nanofluids,which demonstrated that the addition of trace Au nanoparticles in GO nanofluids could enhance both the generation rate of solar vapor and the absorption capacity of solar energy.When the addition of Au nanoparticles is 15.6 wt‰,the water vaporization efficiency could be up to 59.2%.The solar steam generation method can produce pure water,which enable potential applications in sterilization of waste,seawater desalination,as well as solar steam drive and disinfection.2.Preparation and photothermal properties of graphene aerogel:GO dispersion was prepared by GO power,and then graphene oxide aerogel?GOM?was obtained through freeze-drying method.The reduced graphene oxide aerogel was prepared by photo-reduction,which was rolled to get graphene aerogel?GA?,and GA is for the first time used to harvest solar energy.Compared with GO dispersion,reduced GO dispersion and pure water,GA can not only convert almost the entire incident solar light to heat,but self-float on the surface of water and pump the interface water to form a constant water steam.Infrared images were used to demonstrate that the heat location effect exists in the surface of GA.Thus,GA could absorb sunlight and convert the light to heat,which could not only accelerate the evaporation of water,but also prevent the heat from transferring into bulk water,reducing the heat loss.Heat flow meter method was used to measure the thermal conductivity of GA in air,which is0.1868 W m-1 K-1.The solar steam generation efficiencies of 53.6%and 82.7%are achieved at light intensity of 1 kW m-2and 10 kW m-2,respectively.Furthermore,this efficiency is still kept at a high value and the morphology of GA is hardly broken after ten cycles of testing.Steam generation through efficiently harvesting solar energy is a highly promising technology for sterilization of waste,seawater desalination. |
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