| The environmental pollution caused by population growth and climate change,as well as the shortage of water resources and energy have put enormous pressure on the development of society and the progress of human beings.The technologies that tackle water scarcity issues at the expense of aggravating energy and environmental problems cannot relieve the existing pressure at the root and cannot be implemented in the long term.Therefore,it is urgent to develop sustainable,energy-saving,simple and green water purification technologies to generate clean water.As a kind of renewable energy,solar energy has shown obvious advantages in abundance and sustainability.Solar-thermal conversion is a direct way to harvest solar energy for heating and energy storage applications,and environmentally friendly water treatment technologies based on solar-thermal conversion can provide effective solutions to the clean water shortage issues.Therefore,it is of great significance to prepare and study solar-thermal conversion composite materials for seawater desalination and wastewaters purification.In this paper,we designed and prepared an all-weather porous carbon-based evaporator with solar-thermal and electrothermal effects.At the same time,the salt resistance and water evaporation performances of the evaporator in the process of seawater desalination can be improved by coating hydrophobic candle soot on the grooved surfaces of the hydrophilic and porous carbon.Although most evaporators can remove inorganic salts and pollutants from water through water evaporation process,few people pay attention to the removal of organic pollutants in bulk water.Therefore,3D pinecone evaporators modified with molybdenum disulfide(MoS2)with solar-thermal and photocatalytic functions were prepared to degrade organic pollutants in the bulk water during the solar steam generation process.In addition,to better integrate solar-thermal water evaporation with photocatalytic degradation and realize the continuity of the two processes,a flow bed system was introduced in the study.The constructed flow bed system can achieve solar-thermal water evaporation and photocatalytic degradation of wastewater during the inflow and outflow processes simultaneously and continuously.The main research contents and results are given as follows:1.Preparation of solar-thermal and electrothermal all-weather porous carbon evaporators and studies on their water evaporation performances:Most of the solar evaporators cannot work normally in the situations with low light or no light,in which their working time and output of purified water would be greatly limited.In this study,woods were carbonized and then activated by potassium hydroxide(KOH)to prepare hydrophilic porous carbon materials(ACWs)with excellent conductivity.In order to further increase the surface areas of ACWs and enhance their salt resistance,hydrophobic candle soot was coating on the grooved surfaces of ACWs.Thus,all-weather porous carbon evaporation devices with solar-thermal and electrothermal effects were obtained.The porous channels of ACWs are responsible for the rapid upward transport of water to the evaporation surfaces,and their high conductivity ensures enough heat generation with low voltage for water evaporation.In addition,the hydrophobic candle ash layer benefits efficient evaporation of water and prevents the salt accumulation on the surfaces of evaporators.Benefiting from the unique structural designs,the environmentally friendly wood-based evaporator is capable of harvesting solar energy for thermally evaporating water on the basis of the solar-thermal energy conversion with a pure water evaporation rate of 1.49 kg m-2 h-1 and an evaporation efficiency of 77.2%under one-sun irradiation.Even in the absence of solar light,the evaporator can still achieve an efficient water evaporation rate of 6.86 kg m-2 h-1 with an applied voltage of 6 V through its electrothermal effect.By integrating the solar-thermal and electrothermal energy conversion mechanisms,an ultrahigh water evaporation rate of 11.73 kg m-2 h-1 is readily achieved under one-sun irradiation and with an applied voltage of 6 V.2.Preparation of molybdenum disulfide modified 3D pine cone evaporators and studies on their solar-thermal evaporation and photocatalytic degradation performances:Most of the current researches mainly focus on improving the water evaporation rate and the solar-thermal conversion efficiency,but little attention is paid to the removal of organic pollutants accumulated in bulk water.In order to achieve solar-thermal water evaporation and photocatalytic degradation of organic pollutants at the same time,a 3D pine cone solar evaporator modified with MoS2(HPM)was prepared through a one-step hydrothermal method by taking full advantages of the hydrophilicity and 3D structures of natural pine cones and the solar-thermal conversion effect of MoS2.The vertically arranged central axis and spirally arranged scales of natural pine cones can not only transfer bulk water upward to the evaporation surfaces,but also absorb more solar light from different incident angles for solar-thermal evaporation and photodegradation of wastewaters under omnidirectional irradiations.The uniformly loaded MoS2 nanoflowers can not only further enhance the solar-thermal energy conversion efficiency,but also decompose organic pollutants in the bulk water by their photocatalytic degradation effects.The results show that HPM evaporator reveals a highly efficient water evaporation rate of 1.85 kg m-2 h-1 and a high solar-thermal conversion efficiency of 96%under 1 kW m-2 irradiation.The powdery HPM can also photodegrade organic pollutants of methylene blue(MB)and rhodamine B(RhB)with high removal efficiencies of 96%and 95%,respectively.In the solar-thermal water purification process,by floating in simulated wastewaters containing MB,the 3D HPM evaporator can generate clean water by simultaneous solar-thermal evaporation and photocatalytic degradation.Under 1 kW m-2 irradiation,the MB degradation efficiency and water evaporation rate of 3D HPM evaporator can reach 87%and 1.43 kg m-2 h-1,respectively.The integration of solar-thermal steam generation and photocatalytic degradation functions make HPM evaporators have broad application prospect in high-yield wastewaters purification process.3.Regulating photogenerated carriers for enhanced solar-driven water evaporation and photocatalytic degradation in a flow-state water treatment process:In order to settle the problems of low mass and heat transfer efficiencies,insufficient illumination of catalysts and pollutants,inability to operate continuously and low production efficiency of static solar-thermal evaporation and photocatalyst degradation process,a bacterial cellulose/ferric oxide/carbon nanotubes composite(BFC)membrane was obtained for continuous and simultaneous solar-thermal evaporation and photocatalytic degradation in flow bed system under solar irradiation.In this study,bacterial cellulose(BC)with excellent hydrophilicity and film forming properties is used as the matrix material,and the ferric oxide(α-Fe2O3)acts as both the solar-thermal conversion material for solar-driven water evaporation and the catalyst for pollutants removal in photocatalytic degradation process by absorbing short-wave photons.While the solar-thermal component carbon nanotube(CNT)can convert long-wave photons into heat to evaporate water and accelerate the catalytic process by facilitating the separation of photogenerated charges and holes.It was also found that the photothermal conversion and photocatalytic effects of BFC can be mutually reinforcing.The introduction of flow bed system not only realizes continuous photocatalytic degradation and solar-thermal water evaporation,but also increases the luminous areas of pollutants and catalysts,as well as improves the heat and mass transfer.The results show that the evaporation rate of simulated wastewater containing methyl orange(MO)or ofloxacin(OFL)can reach 1.45 kg m-2 h-1 at optimal flow rate of 4 mL h-1 under 1 kW m-2 irradiation.In addition,at the flow rate of 4 mL h-1 and 3 kW m-2,the removal efficiency of OFL can reach 98%.In this study,a solar water purification system based on the flow bed was constructed.When it is applied to treat simulated wastewaters containing herbicide 2,4-dichlorophenoxyacetic acid(2,4-D),the yield of purified water which can be applied for agricultural irrigation is about 12.17 kg m-2 h-1,including the water from solar steam generation with an evaporation rate of 1.43 kg m-2 h-1 and the water from photocatalytic degradation with a purified rate of 10.74 kg m-2 h-1.The purified water can realize real-time and on-demand crop growth through the solar water purification cultivation platform,which promotes the practical application of the flow bed system. |
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