| The shortage of fresh water as one of the global crises has driven countries to announce strategic plans for sustainable water resources development.Among the technologies for obtaining fresh water,solar-driven water evaporation with advantages of low energy consumption,environmental friendliness and high efficiency,is considered to be one of the most promising and sustainable technologies to extract fresh water.Exploring high-efficiency solar evaporators is critical to realize highly efficient energy conversion efficiency.Although a variety of evaporators have been developed,there are still great challenges for the evaporators including their preparation cost,stability,energy conversion efficiency,salt resistance and pollution resistance.In this work,starch was selected as raw material to form the porous framework of the evaporator due to its easy availability,eco-friendliness and low cost.The structure and composition of the evaporator was modulated by introducing carbon dots（CDs）with intriguing properties（e.g.,rich oxygenated groups,ability to intimately integrate with other materials）and adopting low temperature carbonization in order to enhancing light absorption,reducing thermal loss,facilitating water/vapor transportation and reducing water evaporation enthalpy so as to improve solar energy conversion efficiency and durability of the evaporator.（1）The introduced CDs enhanced polymerization and carbonization of starch chains by virtue of the interaction with starch chains,and effectively tailored the structure and composition of the obtained C-CDSA.CDs were first prepared using coal pitch as raw material via oxidation etching by formic acid and hydrogen peroxide,and then mixed with starch.After gelatinization,retrogradation,freeze-thaw and freeze-drying,the carbon dots modified starch aerogel（CDSA）was fabricated.Carbonized carbon dots-modified starch aerogel C-CDSA was finally obtained after carbonization treatment of CDSA at 270℃.C-CDSA displayed a three-dimensional（3D）interconnected porous structure with larger pore size and thinner pore wall as well as higher porosity compared to carbonized starch aerogel（C-SA）.Meanwhile,due to the low carbonization temperature and the feature of CDs with rich oxygenated groups,a higher content of oxygenated groups were preserved in C-CDSA.By virtue of the structural and compositional advantages,C-CDSA showed enhanced light harvesting,desired thermal insulation,fast water transportation and superiority in reducing water evaporation enthalpy.（2）The obtained C-CDSA showed high conversion efficiency and excellent physicochemical stability as well as durability.C-CDSA showed a high water evaporation rate of 2.29 kg m-2 h-1 with energy conversion efficiency of 93.5%.And C-CDSA not only presented stable evaporation rate over 10 cycles test,but also showed no obvious decrease of water evaporation ability in acidic and alkaline solution.Moreover,benefiting from the favorable porous structure with larger pore size and higher porosity which ensured rapid water replenishment,C-CDSA exhibited the same evaporation rate in 10 wt%NaCl solution as that in pure water under natural sunlight with an average intensity of 0.8 k W m-2 from 9:00 to 17:00,exhibiting excellent salt rejecting capacity.No accumulated salts were observed on surface of C-CDSA.Furthermore,C-CDSA also showed similar evaporation rate in organic pollutant methylene blue（MB）solution(15 mg L-1)with that in pure water.The work developed a low-cost and eco-friendly C-CDSA with high conversion efficiency,excellent physicochemical stability and durability,which holds great promise for practical solar water evaporation applications. |
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