Study Of Solar Spectrally Selective Absorption Performance Of The Porous C/TiO₂ Nanocomposite Films Prepared By PIPS Method

With the aggravation of energy and environmental issues, the development of new energy technologies become a major breakthrough in solving the world’s energy problems, and the preparation and study of solar selective absorption films of solar thermal technology has become the focus of attention. Based on the overall investigating of the research status of selective absorption film at home and abroad,for the first time using one step polymerization induced phase separation process within the framework of wet chemistry to prepare porous C/TiO2 nanocomposite films on copper substrate with high solar absorptance (a>0.95) and low thermal emittance (e<0.1) in this thesis. On this basis, not only the influence of concentration of nitric acid, povidone k30 (PVP) and photopolymerizable monomer PETA in the precursor on surface morphology and optical properties of C/TiO2 nanocomposite films, but also the role in the film preparation process have been studied,in order to determine the optimal process parameters.The results can be shown as follows:(1) Nitric acid can be used to regulate the surface morphology of film by its impact on the polycondensation rate and photopolymerization, and ultimately influences the optical properties of the films. With the decrease of nitric acid, the average pore size, carbon content and the thickness of the porous composite film decrease. The solar absorptance (a) and thermalemittance (e) of the optimized single layer film with a thickness of about 300 nm were about 0.948 and 0.12, respectively, yielding an optimized photothermal conversion efficiency n=0.828 corresponding to the HNO3 concentration 0.4(molar ratio). The films also show good stability under the high temperature (-500℃).(2) PVP works as a sol modifier advantaging the mean size of the interconnected macropores, residual carbon content, and films thickness, but suppresses the order degree of the carbon remained in the films. The high-resolution transmission electron microscopy demonstrated that a small amount of graphite particles with size of around 1.1 nm embedded in the cavity of the porous while the wall of the porous consists of amorphous carbon and titania composites. With the decrease of PVP, both the average pore size and the thickness of the porous composite film decrease. The single layer of as-prepared porous C/TiO2 nanocomposite films exhibits high solar absorptance (a=0.928-0.959) with low thermal emittance (ε=0.074-0.105), yielding an optimized photothermal conversion efficiency η=0.864 corresponding to the PVP concentration 4 wt.%.(3) PETA works as photomonomer in the photopolymerization, directly affecting the relative molecular weight of polymer formed by photopolymerization to regulate the morphology and residual carbon of nanocomposite films, and ultimately affect the film selective absorption properties. The high-resolution transmission electron microscopy demonstrated that the residual carbon is uniformly distributed in the porous C/TiO2 nanocomposite films.With the increase of PETA, both the average pore size and the thickness of the porous composite film increase. The single layer of as-prepared porous C/TiO2 nanocomposite films exhibits high solar absorptance (a=0.954-0.965) with low thermal emittance (ε=0.06-0.12), yielding an optimized photothermal conversion efficiency (η=0.845-0.894) corresponding to the PETA concentration 0.3-0.9(molar ratio).The excellent solar selective absorption properties and good environmental resistance performance of the porous C/TiO2 nanocomposite films prepared with the optimal distribution ratio almost meet industry needs and has good application prospects.