| In the context of the green strategy of"carbon peaking and carbon neutral",cooling/heating energy consumption,which already accounts for more than 40%of global energy consumption,has become the main driving force of total energy consumption growth,aggravating energy scarcity and environmental degradation,and how to effectively reduce cooling/heating energy consumption is an urgent issue in the energy field.Many solutions such as structural optimization of buildings,addition of insulated walls,and installation of geothermal air conditioners have been applied to some extent,but these approaches can be limited by many factors,such as high cost of installation and maintenance,poor environmental adaptability,and poor ubiquity.Therefore,it is important to conduct research on radiation heat transfer of green energy-saving materials and its process enhancement to promote sustainable development and build a conservation-oriented society.In this paper,we will start from the interface problem of fibrous laminated membrane,make full use of the advantages of cellulose and functional nanomaterials for intensive emission in the mid-infrared band and strong reflection in the sunlight band,explore the radiation heat transfer law of fibrous membrane and its application in building thermal management and human thermal management,and establish the key ways to strengthen the radiation heat transfer process of flexible fibrous membrane.The main contents are as follows:(1)Preparation of flexible Zn O@cellulose membrane and its applications in building passive coolingStarting from the most widely used cellulose,with its excellent porous structure and rough surface,flexible Zn O@cellulose membranes were prepared by growing Zn O nanorods in situ on the cellulose surface by sol-gel and hydrothermal methods,followed by soaking them with sodium laurate solution to complete the hydrophobic modification.The prepared flexible cellulose membranes show excellent solar reflectance(84%)and infrared emissivity(0.78),which can effectively reduce heat input and enhance thermal radiation output,and achieve a temperature drop of 5°C in the simulation experiments,showing excellent radiation cooling performance.The static water contact angle of the membrane after hydrophobic modification reaches 150°and the rolling angle is 7°,showing super hydrophobicity.This excellent property can effectively avoid the weakening of radiation performance due to the contamination of the surface by sewage,and the floating dust and impurities adhering to the surface can be removed by simple rinsing with water,which significantly improves the durability of the flexible membrane and can solve the problems of unstable radiation performance in practical applications.(2)Preparation of bilayer gel cellulose membrane with bionic structure and its application in passive cooling of buildingsInspired by the natural way of biological response to the hot environment,a bilayer gel cellulose membrane with a bionic structure,combining radiative cooling and evaporative heat dissipation,was designed and prepared to address the shortcomings of the above-mentioned flexible membrane with a single cooling method and significant heat convection/heat conduction(thermal parasitism)effect.The purified bacterial cellulose was first freeze-dried to obtain a bacterial cellulose aerogel membrane;then the resulting aerogel membrane was hydrophobically modified by chemical vapor deposition using methyltrimethoxysilane(MTMS);finally,a PVA hydrogel solution was drop-cast on one side of the modified aerogel membrane,and when the hydrogel gelation was completed,a bilayer gel membrane with a bionanogel structure was obtained.The covalent bond vibration contained in cellulose itself makes it have good absorption in infrared band,in addition,the bacterial fibers are entangled with each other and the pores formed are conducive to scattering sunlight;moreover,bacterial cellulose can show super high visible reflectivity(98.8%)and high infrared emissivity(0.86).The excellent adiabatic properties of aerogel film significantly reduce the thermal parasitic effect and maintain the cooling efficiency of the material.In addition,the MTMS modification makes the inherent hydrophilicity of bacterial cellulose change to hydrophobicity,avoiding the collapse of aerogel structure and surface fouling,which improves the durability of the material and the longevity of the cooling performance.As an excellent water storage material,the hydrogel can efficiently remove its own heat by evaporating water to achieve efficient cooling.The bilayer gel cellulose film with bionic structure prepared in this work realizes the coupling of radiative cooling and evaporative heat dissipation functions,and completes the functional enhancement of passive cooling.The final bilayer gel achieves a stable temperature drop of nearly 16°C under direct sunlight,which provides a feasible solution for the application of bionanostructures in the field of passive cooling and indicates that bionanostructures have great potential for application in passive cooling.(3)Preparation of of Zn O@Cellulose/MXene flexible Janus membrane and its application in personal thermal managementBoth of the above-mentioned flexible fibrous membranes are designed for passive radiative cooling in hot environments,which only consider the thermal comfort needs of people in hot environments,without considering the problem of overcooling caused by radiative cooling in cold regions or in cold times,which leads to additional energy consumption and reduced thermal comfort.Based on this,a layer of MXene nanosheets was deposited on one side of the flexible Zn O@Cellulose membrane to make a Zn O@Cellulose/MXene flexible Janus membrane with integrated radiative cooling and radiative heating.The Zn O side still maintains good radiative cooling performance,while the extremely low visible reflectance(9%)and low infrared emissivity(0.283)of the MXene side enable it to efficiently absorb sunlight and prevent heat from dissipating outward.Experimental results show that the Zn O side can provide a temperature drop of 5°C and the MXene side can provide a temperature rise of 7°C under direct sunlight,and the cooling and heating functions of this Janus film can be switched by a simple flip,indicating that this flexible Janus film successfully integrates radiative cooling and heating into a single membrane,giving the membrane the ability to cope with people’s thermal comfort requirements in various scenarios.It solves the shortcomings of general radiant heat management materials with a single function,and demonstrates considerable radiant heat management performance and potential for a wide range of applications.(4)Preparation of dual-mode flexible multifunctional fibrous laminated membrane and its application in personal thermal managementMXene not only possesses excellent radiative heating performance,but also has many other unique properties,such as ultra-high electrical conductivity and good electromagnetic shielding performance.Based on the above flexible Janus cellulose membrane,the MXene layer was foamed to enhance its electromagnetic shielding performance.The specific process is as follows:high-purity aluminum is first deposited on one side of the cellulose film by magnetron sputtering,followed by in situ growth of zinc-aluminum bimetallic hydroxide(Zn-Al LDH)on the surface of cellulose fibers using hydrothermal method,followed by deposition of MXene layer on the other side by vacuum filtration,and finally MXene is foamed with hydrazine hydrate to obtain a bimodal flexible fiber laminated membrane.Under the strong direct sunlight(>1000 W/m~2)in summer,the Zn-Al LDHs side showed an exceptionally significant temperature drop(about 18°C);while the temperature of MXene side was much higher than that of LDH side(up to 85°C).In addition to passive radiative thermal management,the introduction of MXene also provides an active Joule thermal function to cope with the scenario when the radiative performance is hindered.The membrane has been experimentally tested to warm up to 71.6°C in one minute when a low voltage of 1.5 V is applied,providing a large amount of heat quickly and providing a variety of thermal management means for the wearer.While providing excellent thermal management performance,the film also shows good electromagnetic shielding performance(43.9 d B),far exceeding that of common commercial electromagnetic shielding materials,which not only provides thermal comfort on demand in different scenarios,but also effectively resists the intrusion of electromagnetic interference. |
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