| Nowadays,the shortage and pollution of water resources have become a strategic issue restricting the development of countries in the world.Thus,it is imperative to explore green and efficient water purification technologies.In such a case,solar-driven photothermal evaporation has attracted much attention due to its low energy consumption and environmental burden.Among various evaporation systems,hydrogel-based interfacial evaporators confine the evaporation region to the air-water interface.Meanwhile,their inherent three-dimensional network structure and lower evaporation enthalpy could significantly improve the photothermal conversion efficiency.Although the related research of such evaporators has made certain progress,their practical application is still hindered by the high cost of raw materials and cumbersome preparation processes.Besides,the current evaporators mainly adopt single-layer structure,often leading to unnecessary heat loss.In view of the existing key problems,based on commercial polyvinyl alcohol(PVA)and viscose nonwovens(NF),a fabric/hydrogel bilayer evaporator combining good photothermal conversion performance and 3D water paths was constructed.Moreover,its application potential in the fields of seawater desalination and wastewater treatment was studied.The main research contents and conclusions are as follows:Firstly,the hydrogel substrate with high mechanical strength,excellent water-absorbing ability and dimensional stability is crucial for evaporation systems.Herein,physically crosslinked PVA/Starch composite hydrogels were obtained through the blend of PVA and starch in different ratios and followed by freezing/thawing cycles.The structural changes of these composite hydrogels were analyzed using SEM,FTIR and XRD,so that the interactions between PVA and starch were understood.Upon such a background,the effects of polymer ratio on swelling behavior and mechanical properties of hydrogels and the underlying mechanism were further studied.The results indicated that the crystallinity and crosslinking density of composite hydrogels decreased with the addition of starch,resulting in a relatively porous structure.With the change of internal structure,the intermediate water binding capacity of such hydrogels significantly improved,but was accompanied by the decrease in mechanical properties.Taking various factors into account,the optimal ratio was initially selected.Finally,the fatigue resistance and vaporization enthalpy of the selected hydrogel were investigated,validating its feasibility as the substrate of evaporator.Secondly,during the fabrication of photothermal conversion layer,carboxylated cellulose nanofibers(CNF)were introduced to improve the dispersion of carbon black(CB)and obtain uniform and stable CB dispersion.Then,carbon black deposited fabric(CB@NF)was prepared by vacuum filtration with NF as carrier.Owing to the existence of CB,CB@NF exhibited broadband absorption in the range of 320-2500 nm with the absorbance of 77.9%-94.4%,which guaranteed its superb photothermal conversion properties.Finally,CB@NF/PVA/Starch bilayer composite and evaporator were constructed,in which CB@NF served as photothermal layer and PVA/Starch hydrogel as substrate.The interfacial toughness of this composite was up to?200 J m-2 due to the fiber reinforcement effect and multiple hydrogen bonds among polymers,which could meet the requirements of practical application.Additionally,the evaporation rate of corresponding evaporator reached 1.08 kg m-2 h-1 under 1 sun,and maintained the stability after long-time irradiation.Furthermore,its inherent self-cleaning effect can effectively prevent the performance degradation caused by salt deposition.With the abovementioned advantages,this evaporator could be used for direct purification of seawater,inorganic or organic sewage,providing a novel research approach for the recycling of water resources in less developed countries and regions. |
PDF Full Text Request