Using Luffa Fiber to Desalinate Sea Water
Water pollution and shortage of fresh water resources are becoming global issues worthy of serious human consideration. Desalination and purification of water from seawater or wastewater are cost-effective ways to meet the growing global demand for clean water. In recent years, traditional water purification technologies, such as reverse osmosis, membrane treatment, ion exchange and some multi-effect distillation systems, have made great progress, though. However, compared with these high-cost and unsustainable technologies, solar-powered water evaporation technology has attracted the attention of researchers for its advantages such as making full use of renewable solar energy resources, causing little harm to the environment and high efficiency. The main factors affecting the high efficiency of water evaporation in solar evaporator include broadband light absorption, localization of photo thermal conversion, water conduction and water evaporation. In the past, a large number of researches, especially the synthetic carbon-based materials, plasma materials and hydrophilic foam materials, still have shortcomings such as high cost, complex preparation process, unstable evaporation efficiency and poor durability caused by salt accumulation. Nature provides abundant and inexpensive raw materials that can be transformed into sustainable high-performance multifunctional materials.
Working Principle
Recently, professor Zhu Hongli's team from Northeastern University reported a sustainable, efficient and easily prepared double layer luffa solar evaporator. The researchers first carbonized the loofah complex using a hot table, and the top carbonized layer served as an efficient solar absorber with broadband light absorption and specular light capture. In the bottom layer, due to the natural hydrophilicity of the luffa fiber and the graded structure of large pores and micro-channels, the locally heated carbonized layer is expected to supplement enough water from different sides. During seawater desalination, the salt concentration gradient of the large hole and the micro channel can realize salt exchange through the micro hole in the wall of the tube to prevent salt accumulation on the surface of the evaporator, thus ensuring long-term stability.
Loofah as an abundant renewable resources, has a good flexibility and durability, and its inherent three-dimensional porous structure, can provide internal microchannel capillary force, rich in cellulose fiber hydrophilic ensures that its excellent water absorption performance, at the same time, also have very low thermal conductivity, is an ideal interface of solar evaporation materials. After carbonization treatment, the broadband spectral absorption rate of 200 nm-2500 nm reached 95.4%, which was much higher than the light absorption capacity of untreated the fiber of loofa (48.4%).The multi-layer structure of loofah gives rise to internal light scattering and is confined to the limited space between layers. The incident light experiences multiple reflections in the rough fiber surface and the microscale macrospores formed between the fibers. The incident light experiences multiple reflections in the microchannel inside the fiber to limit the maximum extent of light within the microchannel. Due to its excellent water absorption, light absorption and heat insulation properties, the luffa- fiber solar evaporator has a high evaporation rate and an excellent evaporation efficiency of 89.9% under a simulated sunlight irradiation.
Loofah as an abundant renewable resources, has a good flexibility and durability, and its inherent three-dimensional porous structure, can provide internal microchannel capillary force, rich in cellulose fiber hydrophilic ensures that its excellent water absorption performance, at the same time, also have very low thermal conductivity, is an ideal interface of solar evaporation materials. After carbonization treatment, the broadband spectral absorption rate of 200 nm-2500 nm reached 95.4%, which was much higher than the light absorption capacity of untreated the fiber of loofa (48.4%).The multi-layer structure of loofah gives rise to internal light scattering and is confined to the limited space between layers. The incident light experiences multiple reflections in the rough fiber surface and the microscale macrospores formed between the fibers. The incident light experiences multiple reflections in the microchannel inside the fiber to limit the maximum extent of light within the microchannel. Due to its excellent water absorption, light absorption and heat insulation properties, the luffa- fiber solar evaporator has a high evaporation rate and an excellent evaporation efficiency of 89.9% under a simulated sunlight irradiation.
Broad Application Prospects
In this work, due to the nature of the hydrophilic loofah, through surface carbonization, get no complete double-layer structure of interfacial resistance, high solar spectrum absorption rate, at the same time, by the arrangement of loofah inherent good microchannel (10-20 microns) composed of micro fiber (~ 100 microns) unique hierarchical structure, can be used as a light absorber and the water pump to solar desalination. Therefore, this kind of low cost, abundant, sustainable and stable natural loofah complex efficient solar evaporator has a broad prospect of large-scale application.
