Carbon-based Nanomaterials For High-performance Solar-vapor Generation

Solar-vapor generation utilized abundant solar energy to evaporate water with the potential use of the fresh-water condensate to meet the grand challengenes confronting the sustainable growth of our society.A host of materials and systems have been developed to achieve highly efficient light-to-vapor conversion.However,design of the light-to-heat conversion materials were mainly focus on the solar absorption performance,which was proven limited for vapor generation.Meanwhile,the latent heat during vapor condensation was lost in the traditional solar-vapor generation device.In addition,the condensation process was rarely considered in previous studieds.As a result,the evaporation rate was unsatisfactory,the light-vapor conversion efficiency and the clean water production was limited.Herein,we proposed hollow carbonized cotton microfibers(HCMFs)as efficient solar evaporator,octadecylamine-carbon quantum dots(C₁₈-CQDs)functionlized membrane as vapor passing material,and carbon-based polyacrylamide-calcium chloride(HCMFs-PAM-Ca Cl₂)hybrid hydrogel as vapor collector.Combine with novel system design,the device achevied highly efficient solar-vapor generation,effective latent heat recovery,and clean water production.The details are as follows:(1)Hollow carbonized cotton microfibers for high-performance solar-vapor generation.Developing low-cost,high-performance solar-thermal conversion materials is one key factor for solar-vapor generation in practical applications.In this chapter,we proposed a highly-efficient solar-vapor generation material with hollow frameworks design.The structural material was achived through carbonization and freezing-hollowing of natural cotton microfibers.The as-prepared material absorbed broad range of solar spectrum.Moreover,hierarchical water pathways were constructed in the HCMFs,which significantly increased water transport rate and enhanced water evaporation process by equivalent vaporization enthalpy reduction via meniscus-thin film evaporation in the capillary-structured hollow fibers.Combined with heat management design,the solar evaporator achived a record high evaporation rate of 3.2kg m^-2 h^-1 and an extremely high light to vapor conversion efficiency of 92%.The outstanding perforamcne of the evaporator demonstrated a promising way for solar-vapor generation technology in practical applications.(2)C₁₈-CQDs functionlized membrane for heat recovery in multiple-stage solar-vapor generation system.Latent heat recovery was proven to be an effective method for further increase the vapor generation performance of the solar-vapor generation technology.Membrane with unique permselectivity and high vapor flux plays an important role in heat recovery system.In this chaper,we explored a vapor-passing membrane via cross-linking reaction between C₁₈-CQDs and cotton fibers.The as-prepared C₁₈-CQDs membrane exhibited unique permselectivity and a high vapor flux above 145 kg m^-2 h^-1.With the novel system design,the multiple-stage solar evaporator successfully gained latent heat from the vapor with a heat recovery rate of 32%.Meanwhile,a cold source was also conducted on the last stage of the system,which increased fresh water production rate by enhancement of the condensation process.In addition,the C₁₈-CQDs membrane exhibited good oil-water separation performance and outstanding stability in abnormal conditions,which provided a prototype in water-related applications.(3)HCMFs-PAM-Ca Cl₂ hydrogel for vapor harvesting and clean water production in solar-vapor generation system.Clean water production during solar-vapor generation process was important for water-related practical applications.In this chapter,we proposed that water production of solar-vapor generation can be enhanced by atmospheric water havesting(AWH)technology.As proof of concenpt,a hygroscopic hydrogel was fabricated via polymerization of acrylamide on HCMFs skeletons and followed by loading of Ca Cl₂.Combined with vapor chamber design,the HCMFs-PAM-Ca Cl₂ hybrid hydrogel effectively collected vapor during solar-vapor generation process,and the clean water production rate was 5%higher than the traditional solar-vapor generation device.This novel design provided a new method for further improving the solar-vapor generation performace in water-related applications.