Nano Transition Metal Chalcogen Compounds For Solar Steam Generation

Solar-driven steam generation is a promising method to alleviate freshwater shortage due to its features of clean,green,and low-cost for distillation,desalination,sterilization,and water treatment.Interfacial water evaporation devices provide a practical and efficient strategy to enhance solar water evaporation performance.However,its applications are still limited by the unsatisfactory steam generation efficiency,partly caused by the poor light-to-heat conversion efficiency and inappropriate structures design of devices.To achieve high steam generation efficiency,much effort has been made by developing various broadband materials,optimizing structure designs and remain long-term stability.Transition metal chalcogen compounds,such as transition metal oxide and dichalcogenides,possess strong the full solar spectra range absorption in the visible and near infrared region,high extinction coefficient and efficient light-to-heat conversion.In this dissertation,nonstoichiometric W18O49 mesocrystal,molybdenum disulfide(MoS2)and molybdenum dioxide(MoO2)were chosen as photothermal materials.With rational structure designs,the devices provide an efficient and stable strategy for solar-driven interfacial solar steam generation.The main content can be summarized as follows:1.Hydrophobic W18O49 mesocrystal on hydrophilic PTFE membrane as efficient solar steam generation device under one sunSolar steam generation is a promising application for utilizing exhaustless solar energy to steam generation,desalination,sterilization and water treatment.Over the past decades,scientists have made many attempts that design rational structure to promote evaporation efficiency including optimizing optical absorption,photothermal conversion,heat localization,water transportation.Here,an efficient solar steam generation device was fabricated through decorating nonstoichiometric W18O49 mesocrystal,as solar light-to-heat material,onto a hydrophilic PTFE membrane.Nonstoichiometric W18O49 mesocrystals were incorporated into the membrane,confirmed by the XRD,SEM,TEM and XPS characterizations,which can transfer light to heat after absorbing sun light and lead to the water evaporation on the local area of membrane.The structure of solar steam generation device was confirmed by the results of SEM,contact angle measurements,which insured the solar steam generation device self-float on top of water and continuous water supply to the local area heated by W18O49 mesocrystals from bulk water.Under one sun illumination,the evaporated water mass loss reaches 1.13 kg m-2 for membrane thickness of M/A=9.83 g/m2 after 1 h irradiation,and membrane possesses a high efficiency of 80.7%.Limit of water evaporation rate for W18O49@PDMS mesocrystal membrane was further calculated to be 1.15 kg m-2 after 1h one-sun irradiation,with a limit of efficiency of 82.0%.The salinities of the simulated seawater reduced to the levels far below the World Health Organization(WHO)standard after desalination.The rational design enhancing evaporation perfonnance also provides enlightenment for further practical application of solar steam generation technology.2.Sponge-like MoS2 on glass fiber cloth for efficient solar-driven steam generationSolar energy-driven seawater desalination is a low-cost energy-based method to address the problem of global water shortage.Herein,a high efficiency solar-driven steam generation device is designed by in-situ hydrothermal deposition of sponge-like MoS2 on glass fiber(GF)cloth.MoS2 nanosheets are homogeneously distributed on flexible cloth and the thickness is about 1 ?m,constructing a three-dimensional(3D)rough surface.This leads to an efficient evaporation performance,attributing to the strong light absorption ability in the full solar spectrum range of MoS2,internal light scattering of the 3D nanostructure on the cloth surface,and water transportation channels of gaps between glass fibers.The evaporated water mass loss attains 1.85 kg m-2 after 1 h irradiation under one sun with an efficiency at 94%,which is much higher than that using blank membrane(28%).The potential application of as-fabricated devices for seawater desalination is demonstrated by purifying water from Yellow Sea China,and the quality of desalted water meets the standard of World Health Organization drink water requirement.The flexible and tailorable film with functional design provides a practical and efficient strategy to enhance solar water evaporation performance.3.Acid and alkali resistant MoO2 on PTFE membrane for efficient solar-driven steam generationThe development of efficient and high chemical stability photothermal materials is one of the most important issues in solar water evaporation.Herein,an acid and alkali resistant solar-driven steam generation device is designed by solvothennal method of MoO2 nanospheres on PTFE membrane.MoO2 nanospheres possess the full solar spectra range absorption,high oxidation resistance,and high acid and alkali resistance.MoO2-PTFE membrane possesses high light absorption of 92-95%over a broad solar spectrum(400-2000 nm).The MoO2 nanospheres have high oxidation resistance,withstand 80 ? of heat in air and exhibiting a strong LSPRs effect.MoO2 nanospheres keeps a stable LSPRs effect after immersing in HCl and NaOH solution with pH-3 and pH=12 for 5 h.The absorbancy at 800 nm has been significantly maintained,with 98 and 90%preserved for pH=3 and pH=12,PTFE membrane is a superior stable material,resistant to acid,alkali and high temperature.Therefore,MoO2-PTFE membrane remains stable evaporation rate in H2O,pH=3 and pH=12 solution.Acid-base situation have negligible influence on the membrane evaporation performance.Under one sun,the evaporated water mass loss attains 1.45 kg m-2 after 1 h irradiation with an efficiency at 91%.The acid and alkali resistant and oxidation resistant device provides a practical and efficient strategy for the applications of the solar steam generation,such as water treatment,desalination,and so on.