A study published in Science Bulletin describes a solar-powered system that produces freshwater while simultaneously capturing boron from seawater and brine using a composite gel identified as (MXene-MgO)@sodium alginate (MMS). The work focuses on the interconnected pressures on water, food and energy supplies in regions such as Yemen, Pakistan and Haiti, where demand is rising and water scarcity and hunger are severe. Conventional desalination can provide drinking water, but standard processes often do not meet World Health Organization restrictions for boron in drinking water and usually discard boron rather than recovering it as a resource.
To address these limitations, the team incorporated MgO, which acts as a boron adsorbent, and MXene, which serves as both a photothermal material and an auxiliary boron adsorbent, into a sodium alginate matrix to form the MMS composite gel. Under one sun exposure, this material achieved an evaporation rate of 2.14 kilograms per square meter per hour and a boron adsorption capacity of 225.52 milligrams per square meter for nine hours. These results indicate that the MMS gel can both desalinate seawater and significantly reduce boron content in a single integrated step.
The MMS gel has a hierarchical porous structure that improves water transport and provides a large internal surface area for light absorption and ion interaction. MXene nanosheets absorb a broad spectrum of sunlight and convert it into heat at the water-air interface, while MgO nanoparticles dispersed in the matrix act as active sites for binding boron species. The design uses coupled temperature, concentration, and flow fields in the gel to accelerate boron adsorption kinetics, improving overall separation efficiency.
Outdoor trials supported the laboratory results, with MMS modules producing 5.20 kilograms per square meter of freshwater per day, while recovering 122.45 milligrams of boron per square meter. When applied in agriculture, the recovered boron increased the seed germination rate of Brassica juncea by 13 percent and approximately tripled its biomass compared to boron-deficient controls. The authors report that this desalination-coupled boron extraction provides a relatively simple and resource-efficient route for coastal areas with limited freshwater and boron-poor soils.
Research report:Solar-powered multi-field synergistic harvesting of freshwater and boron from seawater by (MXene-MgO)@sodium alginate composite gel
