Biomass-Derived 3D Photothermal Composite Carbon-Based Aerogel For Solar Desalination

Recently,the shortage of freshwater and the energy crisis caused by the rapid economic development have become increasingly serious.Desalination of sea water to produce fresh water is expected to solve the problem of fresh water shortage because sea water is the most abundant water resource on the earth.However,the high energy consumption,large equipment footprint and high cost of traditional seawater desalination technology are not conducive to the requirements of sustainable development.Solar energy as a resource rich,clean and sustainable energy,so combining solar energy with seawater desalination to develop solar-driven seawater desalination technology is expected to become one of the important ways to alleviate the shortage of freshwater and energy crisis.The most important part of a solar-driven desalination system is the solar absorber,which converts sunlight into heat energy to evaporate water.Therefore,it is of great significance to develop the photothermal conversion materials with excellent performance.Carbon-based materials have been gradually applied in the field of solar-driven seawater desalination due to high absorption of sunlight in a wide spectrum and excellent photothermal conversion efficiency.In addition,among the various forms of solar evaporation,interface evaporation largely avoids heat loss to the water body and has more efficient water evaporation performance because of the separation of photothermal conversion materials from bulk water.Based on this,this paper selected bacterial cellulose,a low-cost and eco-friendly biomass material,as the precursor to design and construct a series of three-dimensional carbon-based photothermal aerogels applied in solar interfacial evaporation,and studied the characteristics of their morphology and structural stability,and investigated the evaporation performance in different water environments such as seawater.The main research contents are described as follows:Here,using bacterial cellulose nanofibers（BCNFs）as precursor,three-dimensional photothermal carbon aerogel（Cu/PDA/BCCA）loaded with copper nanoparticles（Cu NPs）was prepared by dopamine deposition modification,freeze-drying and high temperature pyrolysis.Cu/PDA/BCCA was characterized by SEM,XRD,XPS,etc.At the same time,its structural stability,water evaporation performance and evaporation performance in different water environments were investigated.Studies had shown that the deposition of dopamine made BCNFs stronger,thus improving the overall structural stability of carbon aerogel.At the same time,its functional groups also played the role of chelating metal ions.And PDA endowed Cu/PDA/BCCA excellent hydrophilicity,which ensured the transport of water during evaporation.It can be found that Cu/PDA/BCCA exhibited high photoabsorption and rapid photothermal conversion due to the carbon-based materials and the localized surface plasmon resonance（LSPR）effect of Cu NPs.The side of the three-dimensional carbon aerogel could absorb energy from the environment through thermal radiation and convection because the side temperature was lower than the ambient temperature,making Cu/PDA/BCCA-3 with high energy conversion efficiency in the solar interfacial evaporation.Under 1.0 sun,Cu/PDA/BCCA-3achieved 2.07 kg·m^-2·h^-1water evaporation rate and 115.36%photothermal conversion efficiency.For seawater desalination,Cu/PDA/BCCA showed excellent desalination effect and durability during long-term evaporation.In addition,it also exhibited efficient water evaporation and purification effect for different solution evaporation.Further,a more stable photothermal conversion semiconductor material was selected to overcome the problem that metal nanoparticles were easy to fall off in strong acid and base solution.The MoS₂nanoflowers with photothermal conversion performance was prepared by hydrothermal synthesis and combined with PDA modified BCNFs.Then,the 3D MoS₂-carbon-based photothermal composite aerogel（MPCA）was constructed after freeze-drying and high temperature pyrolysis.The MPCA was characterized by SEM,TEM and XRD,and the structural stability and evaporation performance of the prepared MPCA in the process of solar interfacial evaporation were investigated.The results showed that the MPCA maintained a stable structure even when it was wet.Due to the excellent synergistic photothermal effect of MoS₂and carbon-based materials,the absorbance of 98.53%was achieved in a wide spectrum range.At the same time,the water evaporation rate and photothermal conversion efficiency of MPCA reached 2.34 kg·m^-2·h^-1and 132.55%under 1.0 sun because of the advantages of three-dimensional porous structure and side cold evaporation effect.In practical application,MPCA showed efficient evaporation performance and purification effect in seawater,strong acid and alkali and dye solution,and exhibited the structural stability of strong acid and alkali resistance.Moreover,the solar interface evaporation device was simplified by constructing an integrated water-storage and photothermal conversion evaporator,which could realize the water evaporation mode without external water supply and circulating water evaporation,indicating the practical application in portable freshwater production system.