Preparation And Solar Evaporation Of Bio-based Polysaccharide/Polyacrylamide Composite Hydrogel

Direct solar photothermal evaporation water purification is a promising technology to solve the shortage of fresh water resources.The basic principle is that solar evaporator absorbs solar energy and converts it into heat energy to drive liquid water evaporation for water purification and collection.Hydrogel has a unique three-dimensional network structure and strong hydrophilicity,and has been developed and applied in solar photothermal water evaporation technology.However,the current problems of hydrogel evaporators such as high energy demand during use,low fresh water yield,insufficient stability,and secondary pollution after scrapping limit their large-scale development.Meanwhile,the influence of the interaction between polymer chains and water molecules in hydrogels on the water evaporation energy demand and water evaporation rate has not been fully studied.Therefore,this research topic uses polyacrylamide as the hydrogel matrix,uses ferric oxide,biomass carbon black and carbon nanotubes as solar photothermal materials,and introduces natural polysaccharides containing different hydroxyl functional groups into the polyacrylamide network to synthesize green,stable and efficient hydrogels.And in-depth exploration of the effect of the number of hydroxyl functional groups on the regularity of the water state,water evaporation enthalpy and water evaporation rate in the hydrogel.The main research contents are as follows:Using cheap ferric oxide,natural pectin and acrylamide as raw materials,a composite hydrogel solar evaporator of ferric oxide/pectin/polyacrylamide was prepared by solution polymerization.The absorption rate was 94.72%with the addition of ferric oxide.The introduction of pectin can improve the hydrophilicity and regulate the water state in the composite hydrogel.The test results of Raman spectroscopy and dark evaporation show that the ratio of intermediate water to free water is 1.41,and the equivalent evaporation enthalpy is about 1468 J g^-1,obviously lower than pure water(2450 J g^-1).The test shows that under the light intensity of 1 k W m^-2,the photothermal steam generation rate is 2.7 kg m^-2 h^-1,and it has a strong ability to purify the dye solution.Watermelon peel was used as biomass carbon source,and cellulose macromolecules were cross-linked and polymerized with polyacrylamide network to form a biomass carbon black/cellulose/polyacrylamide composite hydrogel with good mechanical properties and low cost.Compared with ferric oxide,biomass carbon black can be completely dispersed and less likely to form precipitation,and the light absorption rate is up to 95.85%.Compared with pectin,cellulose contains more hydroxyl functional groups in its molecular structure,which helps to increase the intermediate water content in the composite hydrogel.The results showed that the ratio of intermediate water to free water inside the composite hydrogel increased to 1.62,and the calculated equivalent enthalpy of evaporation decreased to 1215 J g^-1.The tests show that the evaporation rate of the composite hydrogel can reach up to 3.02kg m^-2 h^-1,and it has great desalination performance.A solution polymerization reaction was carried out by thermal initiation,and a super-hydrophilic,low evaporation enthalpy,and degradable carbon nanotube/starch/polyacrylamide composite hydrogel was obtained.Compared with other photothermal materials,carbon nanotubes can be dispersed evenly and have excellent light absorption performance,and the light absorption rate has increased to 97.2%.Compared with cellulose and pectin,the molecular structure of starch contains more hydrophilic hydroxyl functional groups,which can further regulate the water state of the composite hydrogel and reduce the energy demand for water evaporation.The water state tests of composite hydrogels with different mass ratios of starch and acrylamide showed that the ratio of intermediate water to free water was as high as 1.86,and the corresponding equivalent enthalpy of evaporation was as low as 960 J g^-1.Under one sunlight intensity,the evaporation rate of the composite hydrogel is as high as 3.38 kg m^-2 h^-1.At the same time,the composite hydrogel has a strong cycle test ability,and can be degraded by natural mildew.By introducing solar photothermal materials and natural polyhydroxy polysaccharides into the hydrogel network structure,the light absorption rate is improved,the hydrophilicity is enhanced,the interaction between the polymer chain and water molecules is adjusted,the content of intermediate water inside hydrogel is increased,and the energy required for hydrogel to evaporate is reduced.A new design strategy for green,efficient and stable hydrogel solar evaporators is provided.