| In recent years,with the rapid growth of population and development of industry,the shortage of fresh water resources has become one of the main problems faced by the world.How to obtain fresh water efficiently and economically has become a research hotspot.Owing to the unparalleled advantages of solar energy in terms of sources and characteristic,solar water desalination technology has been widely concerned and rapidly developed.In order to make solar steam generation have good performance of photo-thermal conversion,thermal management,water transportation and evaporation,porous materials are often used as the base material.Among them,hydrogel material has become an important development direction of solar steam generation due to its structure and performance advantages.As a kind of three-dimensional cross-linked polymer material,which is porous and hydrous,the polymer structure and pore characteristics of hydrogel have significant influence on the transportation and vaporization of water molecules,as well as the heat loss and salt accumulation caused by the convection of water molecules.However,how to design a hydrogel-based solar steam generation with high efficiency of solar water evaporation is still a challenge.In order to solve this problem,this study used cellulose as raw material,carbon black as the light absorption agent to prepare the cellulose based solar steam generation.The distribution of photo-thermal materials in hydrogel,microstructural regulation of hydrogel and effect of functional material on the structure and properties of cellulose-based hydrogel were intensively studied;the structure-activity relationship of cellulose-based hydrogel solar steam generation was revealed;the influence of the structure design of cellulose-based hydrogel on its performance was verified.The main research contents of this paper are as follows:(1)Cellulose can be dissolved in the alkali urea system at low temperature to obtain a transparent cellulose solution,which was crosslinked with epichlorohydrin to prepared cellulose-based hydrogel.Carbon black can be effectively dispersed in cellulose solution and evenly dispersed in the system during the gelation process.When the concentration of cellulose solution was 4 wt.%,the mass ratio of cellulose solution:epichlorohydrin:carbon black was 1:0.1:0.01,the bilayer cellulose-based hydrogel solar steam generation could be formed by layered mixing of cellulose solution with and without carbon black.The upper layer was carbon black/cellulose hydrogel(CCH),and the lower layer was cellulose hydrogel(CH).The results showed that the CCH/CH bilayer solar steam generation had porous structure,good hydrophilicity and low thermal conductivity,and the light absorption of CCH layer was more than 90%in the wavelength range of 200-2500 nm.Under one sun irradiation,the water evaporation rate reached 1.58 kg·m-2·h-1 and the evaporation efficiency was 77.74%.After desalination,the concentration of ions in the purified water was reduced by 3-4 orders of magnitude,showing good desalination performance.The water evaporation rate was stable at about 1.56 kg·m-2·h-1 after 30 cycles of experiments,indicating an excellent cycling stability.The device also showed good evaporation performance in outdoor experiments,with a water yield of 10.56 L·m-2 within 12h,confirming the practical application value.(2)Study the effect of chemical and physical co-crosslinking on the structure and properties of cellulose-based hydrogel solar steam generation with double layer and double network crosslinking.The results showed that the synergistic effect of chemical crosslinking of epichlorohydrin and physical crosslinking induced by ethanol could improve the crosslinking density of the hydrogel polymer network,thus affecting the structure and performance of the device.The performance of BDCH solar steam generation,such as light absorption,heat management,water transportation and evaporation,could be affected by adjusting epichlorohydrin dosage,which had a significant impact on the operating efficiency of the device.The device showed the best performance when the mass ratio of cellulose solution to epichlorohydrin was 1:0.056 and ethanol concentration was 50 wt.%.The structure of chemical and physical crosslinking was evenly distributed in the device.The device had a hierarchical porous structure composed of micro-pores and nano-pores,improving the light absorption and water transportation performance.The light absorption reached above 94%,and the water transportation rate was increased to 0.07 g·min-1.The increase of crosslinking density of hydrogel polymer network reduced the enthalpy of evaporation to 1216 J·g-1,and increased the evaporation rate of water.Under one sun irradiation,the water evaporation rate was 2.79 kg·m-2·h-1,and the evaporation efficiency was 90.88%.The device not only had good mechanical properties,acid resistance,alkali resistance and high temperature resistance,but also showed excellent structural stability.It had self-cleaning ability for surface salt accumulation,and the water evaporation rate was stable after continuous operation for 72 h,indicating the durability of it.It exhibited good performance in seawater desalination and organic dye wastewater treatment,ion concentration reduced by 3-4 orders of magnitude after seawater desalination,and the removal rate of organic dye wastewater(30 ppm)was above 99%.(3)Using cationic guar gum(CGG)as the antibacterial agent,the effect of CGG on the structure and properties of bilayer CGG/cellulose-based hydrogel(BGCH)solar steam generation was studied.The results showed that the high hydration capacity of CGG could effectively reduce the enthalpy of evaporation of water by interaction with water and greatly improve the saturated water content and water transportation rate,but too much saturated water content would reduce the water evaporation rate of solar steam generation.By adjusting CGG dosage,the performance of BGCH solar steam generation such as light absorption,heat management,water transportation and evaporation could be changed,which had a significant impact on operation efficiency of the device.When the mass ratio of CGG to cellulose was 0.15:0.85 and ethanol concentration was 50 wt.%,the device showed the optimum performance.The uniform distribution of CGG in the device effectively reduced the enthalpy of evaporation to 1004 J·g-1 and increased the water transportation rate to 0.26 g·min-1.Under one sun irradiation,the water evaporation rate of water was up to 3.40 kg·m-2·h-1,and the evaporation efficiency was 91.92%.The device had good antibacterial performance against gram-negative bacteria(E.coli)and gram-positive bacteria(S.aureus),and the antibacterial efficiency reached 90.23%and 95.09%,respectively.It also had good water purifying capacity for bacterial suspension,and the absorbance of condensed water that was collected after purification of bacterial suspension decreased significantly,was clear and transparent.(4)Study the effect of thermosensitive material methyl cellulose(MC)on the structure and properties of MC/CGG/cellulose-based hydrogel(BMGCH)solar steam generation.The results showed that when the mass ratio of MC:CGG:cellulose was 0.10:0.09:0.81 and ethanol concentration was 50 wt.%,the BMGCH solar steam generation had good performance of light absorption,heat management,water transportation and water evaporation.The water absorption and transportation properties were affected by the hydrophobicity of methoxyl groups on MC.The saturated water content of the device was 15.61 g·g-1,and the water transportation rate was 0.24 g·min-1.Under one sun irradiation,the water evaporation rate was 3.13 kg·m-2·h-1,and the evaporation efficiency was 82.85%.MC has sol-gel properties.When MC in the device was in gel state,gel network could reduce the diffuse reflection of light and improve the light absorption rate,which was conducive to the transportation of water and the escape of steam.When MC was in sol state,the fluidity of water in hydrogel was increased,and the diffusion rate of salt ions in hydrogel was also increased.Under one sun irradiation,the water evaporation rates of the device in 0.8 wt.%,3.5 wt.%,4.0 wt.%and 10.0 wt.%NaCl solutions were 3.18,3.13,3.08 and 3.04 kg·m-2·h-1 respectively,showing good salt resistance.The device had good cyclic stability due to the fact that it could still be used for seawater desalination after the salt crystallization was removed by simple water washing.The device also showed good evaporation performance in outdoor experiments,with a water yield of 10.60 L·m-2 within 5 h,confirming the practical application value.In summary,cellulose-based hydrogel solar steam generation integrates light absorption,heat management,water transportation and water evaporation.In addition,it has the advantages of low cost,scalability and biodegradability,providing a theoretical basis for large-scale production and recyclable solar steam generation devices. |
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