Chitosan (CS) with good hydrophilicity and charged property was used to modify graphene oxide (GO), the obtained GO-CS was used as a novel modifier to fabricate thin film composite forward osmosis (FO) membranes. The results revealed that the amino groups on CS reacted with carboxyl groups on GO, and the lamellar structure of the GO nanosheets was peeled off by CS, resulting in the reducing of their thicknesses. The GO-CS improved the hydrophilicity of polyethersulfone (PES) substrate, and their contact angles decreased to 64° with the addition of GO-CS in the substrate. GO-CS also increased the porosity of the substrate and surface roughness of FO membrane, thereby optimizing the water flux and reverse salt flux of FO membrane. The average water flux of the FO membrane reached the optimal flux of 21.34 L/(m 2 h) when GO-CS addition was 0.5 wt%, and further addition of GO-CS to the substrate would decrease the water flux of FO membrane, and the reverse salt flux also decreased to the lowest value of 2.26 g/(m 2 h). However, the salt rejection of the membrane increased from 91.4% to 95.1% when GO-CS addition increased from 0.5 to 1.0 wt% under FO mode using 1 mol/L sodium chloride (NaCl) solution as draw solution (DS). In addition, high osmotic pressure favored water permeation, and at the same concentration of DS, magnesium chloride (MgCl 2 ) exhibited better properties than NaCl. These results all suggested that GO-CS was a good modifier to fabricate FO membrane, and MgCl 2 was a good DS candidate.
Nan Li,Yu Han,Feiyue Yu,Wei Wang,Qin Liu,Xiaoming Qian,Zhiwei Xu,Hui Deng,Mingjing Shan
Graphical A novel composite forward osmosis (FO) membrane was fabricated by introducing a chitosan (CS) sublayer between nanofibers and polyamide (PA) layer, which was beneficial to forming thin and defect-free PA layer and improved binding strength between substrate and selective layer. A novel composite forward osmosis (FO) membrane was fabricated by introducing a chitosan (CS) sublayer between nanofibers and polyamide (PA) layer, which was beneficial to forming thin and defect-free PA layer and improved binding strength between substrate and the selective layer. Results exhibited low reverse salt flux (0.73 gMH) while maintained high water flux (85.4 LMH), which were better than that in other reports. In order to further improve permeability of membranes, oxidized multiwall carbon nanotubes (OMWNTs) were added into PA layer based on the optimized sublayer. The crosslinking degree of PA layer was reduced, leading to loose PA layers, which promoted the increase of water flux. After modifying, water flux reached 96.9 LMH without sacrificing salt rejection. It was worth mentioning that PAN/CS composite FO membrane, which could adjust microstructure of support layer and selective layer respectively, may provide a promising way for preparing membranes with anticipated separation performance.
Cellulose aerogel evaporators provide a sustainable strategy to balance energy consumption and freshwater production due to their biocompatibility, renewability, high specific surface area, and large porosity. Inspired by the abundant hierarchal, interconnected water transport channels in luffa vine (LV) that favor efficient evaporation, this study designed an aerogel with vertical channels having micropores on their walls. Fibrillated luffa vine cellulose fibers (LVFB) prepared via mechanochemical methods, retained their original pore structures, and then they were combined with sodium alginate (SA). The aerogel with hierarchical pore structure (LSA-D) was fabricated through directional freeze-drying and calcium ion cross-linking. The natural pore structures of LVFB and the vertical channels in the aerogel led to effective reduction in thermal conductivity (0.055 W⋅m −1 ⋅K −1 ) and enhancement in water absorption rate (17.3 g⋅g −1 ). Moreover, fiber micropores facilitated intercommunication of water and salts among different channels to achieve efficient salt reflux. Next, graphene oxide coating and thermal reduction further improved the light absorption and photothermal conversion efficiency. The final aerogel evaporator exhibited an evaporation rate of up to 2.70 kg⋅m −2 ⋅h −1 under 1-sun illumination, and no salt accumulation was observed during continuous evaporation in brine for 36 h. The aerogel demonstrated significant purification capabilities toward wastewater containing organic dye, heavy metal solutions, and acidic solutions in simulated real-world environments. This study not only enhances the efficient utilization and added value of LV, but also provides innovative design ideas for the structural design of solar evaporator materials, offering significant practical application prospects in addressing the global freshwater crisis.
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