| In view of the fact that people have realized the importance of protecting the environment and saving resources,especially the search for fresh water resources and the development and utilization of solar energy,it has aroused widespread concern.Therefore,people are committed to the development of new photothermal materials,using the solar energy for desalination to obtain fresh water and achieve the purpose of protecting the environment and saving resources.However,there are many problems,such as low performance of solar evaporated water,high cost of solar evaporator preparation,complex preparation process and difficult to achieve large-scale application,which seriously limit the large-scale application of seawater desalination.Therefore,in this paper,we are committed to explore a simple and low-cost method to prepare efficient solar evaporator for desalination.Graphene aerogels have attracted wide attention due to their efficient broadband absorption.Graphene aerogels can not only efficiently absorb sunlight,but also heat up the interface to accelerate the overflow of water vapor,and the porous network structure exists in aerogels,which provides water and steam escape channels for aerogels.In addition,graphene aerogel has excellent mechanical properties and resilience,and can maintain stable structure and performance in harsh conditions and long-term use.However,as graphene aerogels have strong hydrophobicity,they lead to low evaporative performance as solar evaporators.In order to improve the performance of solar evaporators and solve the problem of strong hydrophobicity of graphene,we prepared graphene/clay composite aerogels with excellent mechanical properties through pre-reduction,frozen and complete reduction process.The hydrophilic and hydrophobic of complex aerogels can be adjusted by changing the type and content of clay.Among them,attapulgite has obvious improvement on the hydrophobicity of aerogels,so that the contact angle of aerogels can be adjusted from 134°to 79°.Under the intensity of 1kW m-2,the evaporation rate of graphene/attapulgite composite aerogel reaches 1.41 kg m-2 h-1,and the efficiency of solar evaporated water reached 92.5%.Moreover,graphene/attapulgite composite aerogels have excellent mechanical properties and resilience characteristics.They maintain stable structure and performance in long-term cycling tests,and can remove salt impurities by repeated immersion and washing.Although graphene/clay composite aerogels have excellent mechanical properties and efficient evaporation properties,the sample preparation process is complex and difficult to prepare large-scale and specific-shape samples,which limiting their use in large-scale seawater desalination.In order to solve the problem of preparing large-scale solar evaporators difficultly,we developed a simple and low-cost method to fabricate three-dimensional elastic graphene/cellulose nanocrystal(CNCs)lamella network(GCLN)for high-efficiency solar evaporated water,which based on commercial foam as substrate and used simple impregnation,reduction,and atmospheric drying.The average evaporation rate of GCLN-20 will be up to 1.66 kg m-2 h-1 and the efficiency of solar evaporated water reach 91.2%under 1.0 kW m-2 solar radiation due to the excellent photothermal conversion properties of graphene and the excellent hydrophilic properties of CNCs.GCLN also shows excellent durability and stability under a series of harsh conditions.Due to the strong network structure,GCLN showed stable evaporation performance and structural stability in durability test(more than 20 days,120 minutes per day).In addition,thanks to the processability of melamine foam,3D shaped GCLN can be easily prepared.3D GCLN shows evaporation rates of 1.59 kg m-2 h-1(under solar radiation of 0.5 kW m-2),which is better than the theoretical limit of evaporation rates(0.74 kg m-2 h-1).Therefore,GCLN with low-cost and high performance can be used for large-scale seawater desalination under natural light conditions. |
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