Preparation Of Carbon Nanotubes For Highly Efficient Solar Steam Generation

As water shortage has become a prevalent and serious problem in the world,purification of water from sea water and waste water has attracted much attention.As water evaporation driven by solar energy can provide 90%of the humidity content in the atmosphere to maintain the global water cycle,solar steam generation for production of clean water from seawater and waste water,which is renewability and free of pollution,is regarded as a promising route to solve water shortage problem.However,the purification of water through the direct exposure of sea water or waste water under natural solar is too inefficient to widely apply due to the sluggish water evaporation.Recently,incorporating sunlight absorbers into rational structure that confining heat only within thin evaporation surface for highly efficient solar steam generation via photo-thermal convention has raised much attention.Various sunlight absorbers such as gold nanoparticles,aluminum nanoparticles,polypyrrole,MXene and kinds of carbonaceous materials(carbon dots,carbon black,carbon nanotubes(CNTs),graphene,graphite)have been widely studied and they are integrated into solar steam generation device in the form of porous membrane or three dimensional(3D)porous network.However,wide application is still a challenge because of the relatively low conversion efficiency,high cost,performance degradation and even inability to scale up.Among various photothermal materials,carbon nanotubes have attracted much attention due to its superior absorbance in the solar spectrum wavelength range.Carbon nanotubes(CNTs)have been known as the best candidate for the realizations of ideal black-body,which can absorb all incident electromagnetic radiation,regardless of frequency or angle of incidence and efficiently converts light to heat.In addition,CNTs have extraordinary mechanical and stability,which are promising for large-scale practical photothermal application.Though many methods have been devoted to the synthesis of CNTs,including arc-discharge,chemical vapor deposition,laser ablation,flame synthesis and so on,they are usually time-consuming with complicate precedure and equipment,and typically limited to relatively small-scale production and batchwise operation.In our work,we use carbon nanotubes as a sunlight absorber with good solar light-harvesting efficiency and stability.The main work of this thesis includes:1.Here,we present a simple,effective,and scalable strategy to design and prepare carbon nanotubes "forest" just by burning the ferric acetylacetonate(Fe(acac)3)ethanol solution on the three dimensional(3D)Ni foam under ambient condition.Morover,this universal method is versatile and generally applicable,which can be extended to a broad variety of substrates regardless of their composition and dimension,including Fe/Ni foam,copper foam,aluminum and titanium foil,glass fiber paper and carbon fiber cloth,showing high adaptability for different requirement.And,this way of preparing carbon nanotubes can realize macroscopic production.2.The obtained carbon nanotube/Ni foam(CNT/NF)composites can be directly used for light-to-heat conversion,without any post treatment,exhibiting an outstanding photothermal performance,where the porous CNTs networks work as the highly efficient absorber of the incident solar light irradiation and provide a large amount of water transport channels,the simultaneously formed Fe2O3 nanoparticles anchoring on the CNTs increase the hydrophilicity of the porous network and ensure adequate water transportion.The as-produced CNT/NF composite achieved 81.3%and 93.7%light-to-heat conversion efficiency under the illumination intensity of 1 sun(1 kW/m2)and 3 sun respectively.The CNT/NF composites can not only realize the desalination of seawater but also generate clean water from waste water,considered as a promising solar photothermal material and promoting research on the application of carbon nanotubes for practical solar energy utilization.3.The CNT/NF-SHS composite is synthesized by a simple self-propagating method without the assistance of the solvents and acetylacetone iron is as precursor,similarly.Meanwhile,by adding polyvinyl alcohol(PVA),the PVA can greatly facilitate the water evaporation and enhance the evaporation rate owing to the reduced water evaporation enthalpy in the hydrogel network.Here we report a hydrogel-based solar vapor generator with a water evaporation rate of 2.0 kg/m2/h under one sun(1 kW/m2),additionally,the as-synthsized samples hold promise for practical applications of seawater desalination and wastewater treatment.