Preparation Of Carbon-coated Silicon Oxide Composites And Study Of Their Photothermal Water Evaporation And Electrical Conductivit

The shortage of fresh water resources has become one of the main challenges to human survival and development.About 97.5%of the water resources on Earth are seawater,which cannot be directly drinkable,and solar energy is a green energy given by nature.Therefore,seawater desalination technology using abundant solar energy resources has become a research hotspot.In the solar desalination technology,the development of efficient and stable,corrosion resistant,pollution resistant photothermal conversion materials are the key to generating fresh water driven by solar energy.The reported photothermal conversion materials include plasma metal nanoparticles,semiconductors,organic polymer materials,carbon-based materials,etc.Among them,carbon material has a wide light absorption spectrum,excellent photothermal conversion performance,chemical stability and other characteristics,has been widely concerned.However,the mechanical strength of carbon-based materials ispoor and the high cost of graphene carbon materials with good photothermal conversion efficiency restricts the application of carbon-based materials.In this paper,the chemically stable silicon oxide was used as the carrier and the waste recycled polystyrene foam（white pollution）was used as the carbon source.Various carbon composites of different silicon oxide（powder,fiber）materials were prepared through the polymer pyrolysis carbon deposition method,and the photothermal conversion and electrical conductivity of these carbon composites were investigated.In Chapter 2,a series of carbon-coated silica materials were prepared by using waste polystyrene foam as carbon source and sand,white carbon black,NaY molecular sieve and other materials as carriers.Then,carbon coated silicon oxide/polyvinyl alcohol porous hydrogel composites were prepared by combining carbon coated silicon oxide with polyvinyl alcohol hydrogel by freezing-polymerization-thawing method.Transmission electron microscopy（TEM）,X-ray diffraction（XRD）,specific surface area and pore size analysis（BET）,X-ray photoelectron spectroscopy（XPS）and other characterization methods were used to characterize the carbon coated on silicon oxide matrix particles.The results showed that the graphene carbon was successfully coated on the surface of silicon oxide matrix particles by polystyrene pyrolysis method.Subsequently,the carbon coated silicon oxide/polyvinyl alcohol porous hydrogel series samples were further characterized by scanning electron microscopy（SEM）.The results showed that the composite was porous three-dimensional network structure,which laid a foundation for good water transport performance.Xenon lamp was used as the light source to simulate sunlight to test the simulated seawater evaporation performance of the material.The results showed that the water evaporation rate of the composite（CYPG-4）prepared by NaY molecular sieve with more porous structure and better graphitization effect was the highest.The surface temperature of CYPG-4 can reach59.3℃after 60 min with a water evaporation rate of 1.34 kg m^-2h^-1with an efficiency of 95.6%under 0.8 sunlight intensity.In Chapter 3,in order to explore the effect of water transport performance on the photothermal simulated seawater evaporation,the performance of different hydrogels in simulated seawater desalination experiment was investigated.Carbon coated NaY molecular sieve/polyacrylamide porous hydrogel（CYAG）was prepared by one step photoinitiated polymerization of NaY molecular sieve and polyacrylamide hydrogel.The simulated seawater evaporation test showed that under 0.8 sunlight intensity,the water evaporation rate(0.71 kg m^-2h^-1)of CYAG sample was only half of that of CYPG-4(1.34 kg m^-2h^-1),and its evaporation efficiency was 43.6%.This is because the distribution of carbon-coated NaY molecular sieve in CYAG is not uniform,resulting in the pore channel at the top of CYAG being filled with molecular sieve,and the water cannot be transported to the evaporation surface in time.The overall water transport rate of CYAG cannot meet the water evaporation rate of the surface,so the water evaporation efficiency is low.In Chapter 4,carbon coated glass fiber（CGF）was prepared by using glass fiber cloth with high mechanical strength as the carrier.Carbon coated glass fiber cloth（CGFAG）with hydrophilic properties was prepared by placing acrylamide soaked CGF under ultraviolet lamp.The samples were characterized by SEM,Raman spectroscopy,TEM and XPS.The results showed that the glass fiber was covered with a graphene-like carbon layer about 200 nm thick.The CGF was characterised using SEM,which revealed spiral,uniform and neat cracks on the surface of the CGF.Water contact angle tests showed that the composite of hydrogels successfully transformed the hydrophobic CGF into a material with excellent hydrophilicity（CGFAG）.Subsequently,the water evaporation capacity of CGFAG was tested,and the results showed that the water evaporation rate of the sample increased with the increase of the concentration of acrylamide,but when the concentration of acrylamide was too large,the water evaporation rate of the surface would be affected.Under the irradiation of 0.8 sunlight intensity,the water evaporation rate of CGFAG-3 is 1.24 kg m^-2h^-1,and the efficiency is 86.9%.In Chapter 5,the electrical conductivity and electromagnetic shielding performance of CGF samples were studied and analyzed.A series of CGF samples were prepared by changing the deposition time and deposition temperature of carbon,and the electrical conductivity of CGF series samples was tested.The results show that the high the deposition temperature give the better conductivity of carbon layer.However,the longer deposition time resulued the worse the conductivity with the same deposition temperature.When the deposition temperature was 1000℃and deposition time was 2 h,the conductivity of CGF-1000-2 carbon layer was the highest,which was 5.5×10⁴S m^-1.The electromagnetic shielding efficiency of CGF-1000-2without epoxy resin composite was 37-39 d B.Then the composite material can be prepared by mixing CGF with epoxy resin.The electromagnetic shielding performance of the composite material is analyzed,and it is found that the electromagnetic shielding performance is the best when CGF is four layers,and the shielding efficiency is up to 32 d B.