Fabrication Of Multi-functional Carbon-based Photothermal Materials For Interfacial Solar Vapor Generation

As a new generation of desalination and wastewater treatment technology,interfacial solar vapor generation（ISVG）technology has a promising application prospect due to its high photothermal conversion efficiency,fast water evaporation rate,low cost,and environmental friendliness,etc.Meanwhile,carbon-based materials have become a kind of competitive candidate for photothermal conversion materials in ISVG application systems due to their excellent wide spectrum absorption performance,efficient photothermal conversion capability,stable physical and chemical properties,as well as good scalability.However,there exists a series of urgent problems to be solved in carbon-based ISVG systems,such as larger conductive heat loss,severe salt deposition on the evaporation surface,and low photothermal utilization efficiency at low light intensities and simplex function,etc.In the present work,a series of carbon-based ISVG systems are designed and constructed based on the strategies of material surface morphology modification for improving light absorption,the environmental energy input for enhancing water evaporation rate,solar-concentrated effect for improving photothermal conversion property,and one-way flow effect for the removal of salt deposition,which optimizes solar energy conversion,energy transfer,mass transfer and vapor diffusion at interfaces and enable efficient and stable seawater desalination,sewage treatment and green power conversion driven by solar irradiation.The main results are summarized as followings:（1）Construction of interfacial solar-driven water-electricity cogeneration system based on graphene oxide nanoribbons paper intercalated with alkaline earth metal ions.Using graphene oxide nanoribbons（GONRs）as substrate,self-supported GONRs paper with alkaline earth metal ions intercalation for photothermal conversion was prepared by the ring-opening and coordination reaction between alkaline earth metal ions and oxygen-containing functional groups.Combined with the thermoelectric module,a multi-functional ISVG system was constructed.Based on the ring-opening and coordination interactions between alkaline earth metal ions and graphene oxide nanoribbons,the surface morphology and structural composition of the thin film material are regulated to optimize the solar energy conversion at the evaporation interface,thus improving the broad-spectrum absorption performance and mechanical properties of the photothermal conversion material,which enables the cogeneration system to exhibit efficient photothermal conversion performance,good thermoelectric performance and long-time cycle stability.Under 100 m W cm^-2 intensity irradiation,the ISVG system based on GONRs paper with barium ion intercalation achieves a photothermal conversion efficiency of 91.5%and an output power density of 0.11 Wm^-2.The performance of the system is stable during 21 days of the outdoor natural light experiment.The highest fresh water collection rate and the highest output voltage can reach 7.0 kg m^-2 day^-1 and 0.47 V,respectively,during the outdoor test.（2）Construction of interfacial solar vapor generation enhanced by environmental energy input based on biomass carbon material.A photothermal carbon material with a natural three-dimensional structure was fabricated by low-temperature carbonization using natural corncob as raw material.The corncob-derived monolithic carbon possesses well-interconnected hierarchical micro/nano pore structures,which provide numerous pathways for the transportation of raw water.It is revealed that the unique structure of the corncob-based carbon enables the reduction of water evaporation enthalpy,which enhances the water evaporation rate.More importantly,the unique pore structure on the side around the monolith carbon allows the occurrence of side evaporation and the input of environmental energy.By optimizing the experimental conditions such as carbonization temperature and bare leakage height,the optimal design of energy transfer and gas diffusion of the system is achieved,as a result,the corncob-derived carbon-based interface solar water evaporation system exhibits an ultrahigh evaporation rate of 4.16 kg m^-2 h^-1 under 100 m W cm^-2 intensity irradiation.The ISVG system of corncob-derived carbon material also shows excellent long-time cyclic stability and salt deposition resistance.A demonstration experiment for real seawater desalination is carried out outdoor under natural light for 20 days,the system works steadily and achieves the highest fresh water collection rate up to 12.32 kg m^-2 day^-1.（3）Water-electricity cogeneration based on solar concentration effect and water flow effect.An ISVG system with a solar-concentrated effect and one-way water flow effect was fabricated by hot pouring and drying at room temperature based on the reversible sol-gel property of agarose gel,which was mainly consisted of aluminum foil as light-condenser and thermally-reduced graphene oxide nanoribbons as photothermal conversion material.The concentrated solar effect optimizes solar energy conversion and energy transfer at the evaporation interface through continuous and precise autonomous collection of incident solar energy,enabling the system to achieve an ultra-high water evaporation rate of 3.45 kg m^-2 h^-1 at a light intensity of 100 m W cm^-2 and up to 1.62 kg m^-2 h^-1 at a low light intensity of 50 m W cm^-2.Moreover,the one-way flow effect in the system optimizes the mass transfer during desalination through the continuous diffusion and convection of water,thus effectively avoiding salt accumulation at the evaporation interface.At the same time,the combination of unidirectional flow and the structural properties of the composite material enables sustainable and stable flow potential generation by harvesting water flow energy,and voltage output of 0.47V and maximum output power of 0.63μW are achieved during the experiment lasting for 160h.Therefore,the combination of carbon material with solar-concentrated effect and one-way water flow effect can promote the coupling enhancement of water evaporation performance and power generation performance of the system,which may provide a new pathway for making the most utilization of energy.