| As freshwater shortage becoming more and more serious,the development of efficient and sustainable green desalination technology is still a hot research topic at present.Conventional desalination technologies（such as reverse osmosis（RO）,etc.）are so sensitive to salinity that cannot be applied to the treatment of high salinity seawater or wastewater.In addition,the high energy consumption in the treatment process is also a crucial challenge to be resolved.Thermal desalination technology can not only break through the limit of high salinity,but also coupled with renewable energy（such as solar energy,etc.）to accomplish desalination and sewage reuse.Therefore,based on thermal desalination technology,a series of efficient distillation membranes and evaporators were developed for water purification.The main research results are as follows:（1）A novel superhydrophobic distillation membrane with rough surface structure and low surface energy was prepared by surface modification method based on one-step impregnation and fluorination.The desalination performance,membrane wetting and fouling features of the superhydrophobic distillation membrane in the process of treating surfactant,organic pollutant and practical reverse osmosis wastewater were studied.The results revealed that the water contact angle of prepared membrane was up to 159°.During direct contact membrane distillation（DCMD）,it maintained excellent wetting resistance and fouling resistance even in the presence of sodium dodecyl sulfate（SDS）and humic acid（HA）of the feed solutions containing 3.5 wt%Na Cl.Meanwhile,during handling practical RO wastewater for 24 h,the superhydrophobic distillation membrane maintained stable permeation flux(23.70 L m-2 h-1),excellent salt rejection（>99%）and chemical oxygen demand（COD）removal effect（100%）.（2）In order to solve the scaling and wetting problems of superhydrophobic MD membrane in the treatment of complex salt wastewaters,an omniphobic MD membrane with re-entrant rough structure,secondary rough structure and extremely low surface energy was successfully prepared by a three-step method of electrospinning,in-situ growth and fluorination modification.The wetting resistance,scaling resistance and MD performance of omniphobic MD membrane in treating of challenging wastewater were investigated by adding surfactants,mineralized pollutants and mineral oil to feed solutions containing 3.5 wt%Na Cl.The results revealed that the omniphobic MD membrane revealed prominent omniphobicity with high contact angle values of 151.49°,140.64°,119.59°,and 107.5°to water,mineral oil,4 m M SDS and ethanol,respectively.In the DCMD process with a temperature difference of 40℃for continuous 72 h,the omniphobic membrane maintained stable and efficient desalination performances(the permeate fluxs were 17.78 L m-2 h-1,18.56 L m-2 h-1 and 16.03 L m-2 h-1,respectively,and the salt rejection were nearly 100%)when treating the feed solution containing SDS,Ca SO4 and mineral oil(The initial fluxes were 17.45 L m-2 h-1,18.56 L m-2 h-1and 18.78 L m-2 h-1,respectively).Meanwhile,after strong physical action and long time mineralized pollution experiment,the omniphobic MD membrane still remained stable re-entrant and secondary rough structure,proving that it had excellent long-term structural stability.（3）In order to address the high energy consumption of traditional membrane distillation,the renewable energy solar energy was used to couple with membrane distillation technology.A polyacrylonitrile/carbon nanotube/starch（PAN/CNT/starch）hydrogel-based self-thermal MD membrane with hydrophilic and waterproof properties was prepared by two steps of electrospinning and in situ gelation.The self-thermal MD membrane located the evaporation surface directly on the membrane surface by photothermal transformation.It breaked the conventional mode that the evaporation surface of the traditional hydrophobic self-thermal membrane located on the feed water side,and thus solving the heat loss caused by the transmembrane resistance and temperature polarization.The effects of the gel layer thickness,airflow rate and sunlight intensity on evaporation performance of starch hydrogel-based self-thermal MD membrane were systematically studied.Meanwhile,the contribution of solar radiation energy and environmental energy in promoting evaporation were discussed.During solar membrane distillation,the results revealed that the evaporation performance could be efficiently managed by regulating the airflow rate and sunlight intensity under the combination of solar radiation energy and environmental energy.Under 1.0 sun illumination and the airflow rate of 0.8 m s-1,the evaporation rate of self-thermal MD membrane was 1.63 kg m-2h-1,and the corresponding solar energy efficiency was up to 85%.Its water production rate was 2.95times that of the hydrophobic self-thermal membrane.In addition,the starch hydrogel-based self-thermal MD membrane maintained stable evaporation performance during treating real seawater for 5 days,showing good durability.（4）In this study,seawater desalination and wastewater treatment were studied by using solar interface evaporation with simple equipment in order to address the disadvantages that membrane distillation which needs centralized and complex equipment.Meanwhile,the gel layer material of starch hydrogel-based self-thermal MD membrane prepared above was extended and applied to the development of solar evaporator.A hydrophilic CNT/starch hybrid biohydrogel evaporator with light absorption,thermal insulation,transport and evaporation functions were prepared by a simple gelatination/freeze-thaw process.The results showed that the coordination of superhydrophilicity and porous water transport channel generated by freeze-thaw ensured excellent water supply capacity of evaporator.And it contained a large amount of intermediate water with low enthalpy of evaporation which could be vaporized with low energy consumption.Therefore,the composite evaporator presented an evaporation rate as high as 2.77 kg m-2 h-1 with an evaporation efficiency of～88%under 1.0 sun.The CNT/starch hybrid biohydrogel evaporator was endowed with self-cleaning and salt resistance ability through an equilibrium established by water transport-induced salt ion absorption and diffusion-enabled salt ion discharge.Hence,the evaporator presented remarkable long-term salt durability and high desalination performance during real seawater treatment for 5 days and outdoor evaporation desalination.In addition,during the treatment of various kinds of wastewaters（the different p H range of acid and alkali wastewater:0–14,dye wastewater and heavy metal wastewater）and actual reverse osmosis wastewater,the CNT/starch hybrid biohydrogel evaporator displayed steady and efficient purification performance.（5）In order to solve the environment and cost problems caused by the use of carbon based photothermal materials,a hydrophilic all biomass-based hydrogel solar evaporator was prepared by using cheap and safe squid ink as photothermal material and starch as hydrogel matrix material through simple gelation,retrogradation and freeze-thaw.The effects of the ratio of squid ink to starch,porous structure and thickness of evaporator on photothermal evaporation performance were studied.The results showed that the evaporation rate of the evaporator was up to 2.07 kg m-2 h-1 under 1.0 sun illumination maintaining an energy efficiency of 93.7%as the mass ratio of squid ink to starch was 1:20,the freeze-thaw number was 7 and the thickness of evaporator was 5 mm.Meanwhile,the evaporation rate of the evaporator was proportional to the evaporation height in the process of solar evaporation.The results revealed that the evaporation rate was 1.27 times that of the evaporator with 5 mm thickness by capturing environmental energy while harnessing the solar energy through increasing the evaporator height from 5 to 50 mm.In seawater desalination,the prepared evaporator had high salt resistance（it could treatment simulated seawater with salinity up to 15.0 wt%）and good self-regeneration ability,showing a long-term practical application prospect. |
PDF Full Text Request