| With the development of industry,water pollution and water scarcity have become serious global problems.Due to the abundant seawater storage on Earth,efficient solar evaporation is a promising way to alleviate freshwater shortages.Solar-driven interface evaporation(SDIE)is attracting attention for its potential applications in desalination and wastewater treatment.At present,many two-dimensional fabric evaporators have been developed for SDIE.However,the weak adhesion between fabric and light-absorbing materials,low evaporation rate-efficiency,and salt crystallization hinder their application in SDIE.Hydrogel materials have become a new platform for solar interface evaporation due to their excellent biocompatibility and significant reduction of latent heat of evaporation.Though many high-performance hydrogel-based SDIE devices have been developed,there are still some challenges.For example,how to improve the mechanical properties of hydrogel-based evaporators to ensure evaporation stability and durability and how to further reduce the latent heat of evaporation of water to obtain more efficient SDIE for purification of seawater as well as other wastewater.Therefore,a series of composite hydrogel materials with multi-level network structure were prepared by designing and regulating the chemical composition and interface of polymers and nanofillers,optimizing the water transport path.By exploring the influence of material microstructure and water transport path on the evaporation performance of solar interface,efficient desalination of seawater,corrosive wastewater and dyes is realized.The research content of this thesis is mainly divided into the following three parts:1.Preparation of fabric intercalated polyvinyl alcohol(PVA)/acidified carbon nanotubes(ACNTs)hydrogels(FICH)and its application in solar-driven desalinationA fabric intercalated composite hydrogel(FICH)for SDIE was prepared by a simple ice template method.ACNTs are homogeneously distributed in the hydrogel and form hydrogen bonds with macromolecular chains.Water can be indirectly transported to the composite hydrogel through the two-dimensional waterway formed by the superhydrophilic fabric,and this indirect contact water transport mode makes FICH have good thermal management and can effectively reduce heat loss;At the same time,the hydrogel network reduces the enthalpy of evaporation of the composite fabric to water,so the thin FICH evaporator with excellent photothermal conversion performance has a high evaporation rate(up to 2.47 kg·m-2·h-1),good salt resistance,and long-term evaporation stability and durability.In addition,FICH can work normally for the evaporation of certain corrosive and emulsion solutions,showing broad application prospects in solar desalination.2.Preparation of PVA@ACNTs composite hydrogel(PACH)and its application in solardriven desalinationIn the previous chapter,although the prepared fabric intercalated composite hydrogel membrane has good solar interface evaporation performance and salt rejection,the interface adhesion between hydrogel and fabric is weak,and the salt discharge to high salinity seawater needs to be improved.To this end,in this chapter,we prepared a PVA@ACNTs composite hydrogel for solar-powered desalination.Water is transported directly to the evaporation surface via a three-dimensional gel network for evaporation,significantly increasing the rate of water transport compared to indirectly touching two-dimensional waterways.At the same time ACNTs are uniformly dispersed in the hydrogel and forms hydrogel bonding with PVA macromolecules,greatly improving the mechanical properties of the polymer hydrogel.With excellent light absorption,heat localization and water transport capabilities,the composite hydrogel evaporator possesses a high evaporation rate(up to 3.85 kg·m-2·-1)and a photothermal conversion efficiency of 87.6%.This hydrogel evaporator can work in a high concentration brine or during cyclic evaporation,exhibiting outstanding salt rejection performance and long-term durability.The high performance ACNTs filled hydrogel shows promising applications in solar desalination.3.Preparation of polydopamine(PDA)/PVA@ACNTs composite hydrogel(PPCH)and its application in desalination and dye adsorptionIn the previous chapter,the prepared composite hydrogel has good mechanical properties and salt rejection,but due to the isotropic structure that prolongs the water transport path to a certain extent,the salt resistance and photothermal conversion efficiency of the composite hydrogel still need to be improved,and its mechanical properties still need to be further improved.Considering the increasing pollution of seawater,how to remove organic dyes in seawater and realize the multi-function of solar interface evaporators is also crucial.In this chapter,PDA/PVA@ACNTs complex hydrogels were prepared by directed cryotherapy.The intermolecular interaction of superhydrophilic PDAs and oxygen-enriched ACNTs with macromolecules and the vertically oriented water transport channels inside the gel synergistically improve the hydrophilic effect of the composite hydrogel,resulting in better salt resistance and energy conversion efficiency(91.6%),and the evaporation rate up to 3.43 kg·m-2·h-1.At the same time,the mechanical properties of the composite hydrogel are further improved.In addition,due to the electrostatic interaction between electron-rich PDAs and ACNTs and positrified dyes and the accumulation of π-π,the prepared composite hydrogels can effectively adsorb methylene blue(MB)in dye wastewater,showing broad application prospects in the field of solar desalination and dye adsorption. |
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