Design And Preparation Of Multifunctional Composite Materials And Their Application Research In Solar Steam And Energy Conversion

With the growth of the global population and the intensification of environmental pollution,energy shortages and clean water scarcity have become important threats hindering the sustainable development of human society and the economy.High-efficiency solar-driven water evaporation technology using solar energy converts water evaporation through solar heat and produces clean water and energy at the same time,providing great prospects for human water shortage and energy crisis solutions.Compared to traditional seawater desalination techniques,solar-driven interface evaporation（SDIE）is considered an efficient technology because it enables higher photothermal conversion and evaporation efficiency on the evaporation surface.However,integrating all functions into a single SDIE system remains a major challenge for its large-scale applications,such as salt accumulation,evaporation rate and stability of solar evaporators,thermal management,intermittent sunlight,volatile organic compounds,and water production efficiency.This dissertation report nanocomposites of Mn O₂ nanowires（NWs）,carbon dots（CDs）,polypyrrole（PPy）,and magnetite（Fe₃O₄）.Based on the design and synthesis of a series of multi-functional nanocomposites used as solar thermal conversion materials,the construction of multi-functional solar evaporation devices,around the key scientific and technical issues such as efficient photothermal conversion,optimized thermal management,suitable water transport,high-throughput water collection,and excellent salt resistance through experiments and computational simulations.To achieve stable and efficient solar thermal conversion and clean water production and explore its desalination capability,wastewater treatment,antibacterial disinfection,solar thermal power generation,and solar thermal/application prospects in areas such as piezoelectric energy conversion.The main research contents and innovative results are as follows:1.Chemically advection-driven salt-resistant solar steam generator（SSG）.SSGs are constructed on polyurethane（PU）substrates by carbon-dots modified manganese dioxide nanowires（Mn O₂ NWs）and polypyrrole（PPy）in situ polymerization（Mn CDs@PPy）.The evaporator structure is further insulated by non-woven fabrics,and the study found that the flow driving force of the hot brine in the desalination experiment（2 g/100 min）is derived from the salinity gradient,and the ultra-flexible and self-cleaning Mn CDs@PPy SSG can achieve 1.68 kg m^-2 h^-1.The evaporation rate and the photothermal conversion efficiency（～96.4%,solar to steam）using brine（10 wt%）and wastewater containing heavy metal ions（30 wt%）are also effectively improved.This work provides detailed theoretical calculations of salt accumulation in SSG waterways and proposes a solution to this problem.Small application practices have found that the yield of clean water obtained in Shahu lake water including volatile organic compounds,microorganisms,and oil emulsions can reach 13.60 kg m^-2 day^-1.2.MnO₂@PPy/Chitosan（SPM-CH）Hydrogel Solar Steam Generator.Using the synergy of Mn O₂ NWs and PPy composites with chitosan,a flexible semiconductor hydrogel was constructed for desalination and wastewater treatment.In situ polymerization of Mn O₂nanowires/SPM-CH hydrogels enhance solar absorption（94%）,its crosslinked vertically aligned macroporous structure（～0.5μm）promote salt-resistant channels,compression strain up to 42%,excellent hydration properties are conducive to the formation of intermediate water cluster molecules and enhance the water yield(1.78 kg m^-2h^-1).The SPM-CH hydrogel enables solitary heat accumulation on the evaporative surface（40.8℃）and it is optimized through heat transfer strategies via COMSOL Multiphysics simulation software to achieve effective thermal management.Outdoor experiments in natural sunlight have shown that clean water can be generated from Shahu lake wastewater at a rate of 17.02 kg m^-2/day.3.MnO₂@PPy-based dual-function device for water production/power generation.One deed for two needs inspired bi-functional Mn O₂@PPy nanocomposites（NCs）were synthesized for convective solar evaporation and enhanced thermoelectricity.The convective evaporation structure was developed using Mn O₂@PPy NCs photothermal layer anchored on the combination of super hydrophilic polyurethane wicks localized by polyethylene terephthalate thermal barrier.This work report real-time experimental evidence of salinity gradient potential through these localized convective wicks and computational fluid dynamics（CFD）simulation validates its optimization for synchronous hot brine flow（10 g Na Cl/180 min）and vapor generation.The self-regenerating design promotes solitary interfacial heat accumulation（42.8℃）to generate freshwater yield at the rate of 12.31 kg m^-2/day under natural sunlight from seawater（3.5 wt%）.The photo-thermoelectric generator achieved enhanced output power density(Pout～12.3 Wm^-2),and open circuit current（Iout～61.3 m A）under 1 k W m^-2 solar irradiations.This work will also insight the waste heat recovery into useful purpose,salt rejection strategies towards zero liquid discharge phenomena.4.Polypyrrole-Nickel Foam（IPNF）Solar Steam Generator.Polypyrrole（PPy）polymer gained tremendous research attention as a photothermal material owing to its facile and low-cost ultra-black coating through various polymerization techniques.A bilayer solar evaporation structure was designed by in-situ polymerization of nickel foam（IPNF）as a photothermal layer which is assembled with polyurethane foam for intensifying solar heat accumulation,and seawater desalination.The IPNF surface achieved intensified solitary heat（49.5℃）at the liquid-air interface due to its Omnidirectional solar absorption offering an efficient evaporation rate(1.74 kg m^-2 h^-1)and solar to-vapor conversion efficiency（90%）under 1 k W m^-2 solar irradiation.This work also investigated the different behaviors of water clusters under intensified solar heat accumulation of polymeric network of polypyrrole.The stability of the IPNF solar evaporator and its evaporative performances during long-term operations(13.27 kg m^-2/8 h under 1 k W m^-2)under seawater conditions（3.5 wt%,Na Cl）engrained its potential as a salt-resistant evaporator（3.2 g Na Cl/240 min）.COMSOL heat transfer simulations were also performed to substantiate the intensified solitary heat at the evaporation surface for effective desalination excluding primary and heavy metal ions.5.Manganese dioxide nanosheets/polyvinylidene fluoride（MnO₂/PVDF）tri-generation system.Multi-functional Mn O₂ nanosheets/polyvinylidene fluoride（PVDF）solar evaporator membranes fabricated for simultaneous freshwater production,power generation,and wearable tactile sensing applications.The incorporation of hierarchical Mn O₂ nanosheets transformed the dielectric and ferroelectric properties compared with the pure PVDF-HFP membrane.The so-fabricated Mn O₂/PVDF composite membrane successfully achieved an open-circuit voltage of 20V and a short-circuit current of 0.10μA under the repeated mechanical force of 10 N at the frequency of 2 Hz.Wearable membrane demonstrated the ability to harvest the biomechanical energy of human movements,such as finger and joint tapping,and wearable shoe sole to harvest energy from walking and running.More importantly,the impregnation of polypyrrole over Mn O₂/PVDF composite membrane（Mn PVDF@PPy）was carried out for the fabrication of efficient solar evaporation,achieving an enhanced evaporation rate of 1.85 kg m^-2 h^-1 under one sun irradiation.However,waste heat could also be recovered through Mn PVDF@PPy membrane-inspired photo-thermoelectric generator,that achieved an open-circuit voltage of 135 m V and a short-circuit current of 33 m A under one sun.Thus,this piezo-photo-thermo hybrid system serves as a power generation in all weather conditions and continuously provides safe drinking water.6.Iron tetroxide@polypyrrole（Fe₃O₄@PPy）water production/power generation dual-function device.Donnan exclusion inspired in-situ polymerized magnetite（Fe₃O₄@PPy）nanospheres were anchored on a cellulose evaporator for efficient rejection of volatile ammonia（NH₄⁺）or cationic methylene blue（MB）dyes in agricultural wastewater slurry.The synergic resistance of NH₄⁺compounds and cationic MB dyes was achieved without sacrificing the evaporation rate through optimization of the positively charged R-NH⁺groups present on the surface of Fe₃O₄@PPy nanospheres.Highly charged solar evaporator engrained with excellent solar adsorption（95%）,oil-repellent cellulosic water channels,flexibility（75%）for synchronous vapor generation,and enhanced Donnan exclusion towards NH₄⁺compounds from oil emulsified NH₄Cl.H₂O slurry（25 wt%）.Furthermore,highly charged nanospheres photo-thermoelectric nanogenerator achieved power density(P_out～45.4 Wm^-2,I_out～101 m A)along with solar to electric conversion efficiency（γ=2.27%）under 2k W m^-2 solar irradiations,possesses a significant potential towards waste heat recovery of solar-driven devices.This work will insight into the advanced avenues for multifunctional integration of clean energy utilization toward water-energy nexus and agricultural wastewater remediation.