Study On Solar-Driven Interfacial Evaporation Of Array-Based Nanomaterials And Applications For Solar Energy Conversion

Energy and water are fundamental resources for human existence,development of society and economy.Nowadays,energy and water shortage has become the most urgent global issues.Solar energy is abundant,clean,and sustainable.Utilization of solar energy is an approach to address the global issue of energy shortage.Solar distillation can generate clean water from unpurified water sources,which is a promising and environmentally friendly avenue to water shortage.However,poor light absorption and large heat losses result in low evaporation efficiency,hindering practical applications of this technology.Solar-driven interfacial evaporation has drawn great attention.Only water on air-liquid interface is heated,avoiding unnecessarily heating bulk water,leading to significantly improved evaporation efficiency.Recent researches point key elements to achieve high-performance solar evaporation:efficient light absorption,effective heat localization,and efficient water transport.Various advanced synthetic materials have been developed and demonstrated high solar evaporation efficiency.However,they often suffer from high manufacturing costs or complex fabrication processes.Recently,natural materials have been developed due to low cost,natural abundance,and easy availability.Compared with the advanced synthetic materials,their performance for solar evaporation is worse.Furthermore,solar distillation will be ineffective when water sources are polluted by volatile organic compounds（VOCs）.They also evaporate and concentrate in collected water.In this dissertation,we study array-based nanomaterials.The performance of our natural material-based system on solar-driven evaporation is competitive with that of advanced synthetic materials.Through one-step plasma treatment,graphene arrays（this is,vertically-oriented graphenes）are grown on the lotus（denoted as lotus/VG）without any external carbon source.Graphene arrays serve as light-trapping structures to enhance light absorption,leading to high light absorption of 99.2%,which is twice higher than that of pristine lotus.After plasma treatment,T-shaped geometry and channels are preserved well.One-dimensional（1D）water pathway enabled by T-shaped geometry facilitates minimizing thermal loss to bulk water,leading to efficient heat localization.Due to capillary forces caused by channels,the lotus/VG stem exhibits high flow rate of 75 mm s^-1,which is 5 times as rapid as the natural lotus.Oxygen-containing functional groups are bonded on VGs,leading to the super-hydrophilicity.Due to the above merits,our lotus/VG nanostructures demonstrate the highest solar evaporation efficiency of～90%under one sun(1 k W m^-2)among natural material-based systems.The lotus/VG demonstrates great potential for applications such as sludge drying and wastewater treatment.For the practical application,we explore the array-based photothermal materials with photocatalytic function in this dissertation.We achieve simultaneous evaporation and VOC removal using Ti O₂-loaded Cu O nanowire-covered Cu foam(Ti O₂-Cu O-Cu_foam).Due to light-trapping structure enabled by Cu O nanowire arrays,Ti O₂-Cu O-Cu_foam exhibits high light absorption of 91%.Growth of Cu O nanowires changes smooth surface of Cu foam into rough surface,resulting in super-hydrophilicity.Open nanowire channels induce capillary forces.Cu O array-based nanomaterials exhibit ultrafast water transport(5 mm s^-1).1D water pathway enabled by narrow Cu O“leg”avoids direct contact of light absorber and bulk water,with extremely low conductive heat loss（0.3%）.Schottky junction between Ti O₂ and Cu O is constructed to improve photocatalytic activity.Taking advantage of these merits,Ti O₂-Cu O-Cu_foamdemonstrated high evaporation efficiency（86.6%）and VOC removal efficiency（80%）under one sun.Decreasing dimension of water pathway results in reduced heat loss to bulk water,leading to improved solar evaporation performance.Ti O₂-Cu O-Cu_foamdemonstrate high evaporation efficiency（>84%）under a wide range of solar intensities.Meanwhile,it can work well under real sunlight.Ti O₂-Cu O-Cu_foam demonstrates great potential in seawater desalination and VOC removal,and could provide inspiration for development of solar energy conversion devices for clean water generation.