| The energy and substances needed for the growth of all living things on earth is provided by photosynthesis.In the conversion process between inorganic matter and organic matter,the oxygen needed for human survival was released.Chlorophyll molecules absorb light energy when exposed to sunlight,then water were break down into oxygen and hydrogen ions by the calcium-manganese cluster under the electron transfer process.In order to make use of solar energy effectively,researchers have designed countless new materials to construct artificial photosynthetic system,in which the light harvesting pigment/inorganic semiconductor photosynthetic system has become one of the widely concerned artificial photosynthesis systems due to its advantages of cheap,easily availabel and green,as well as environmental protection.As the most commonly used inorganic semiconductor photocatalyst at present,titanium dioxide material has the advantages of light stability,non-toxicity and harmlessness,yet there are also many shortcomings that limit the development of the material,such as it just can be stimulated by UV light and have high recombination efficiency of photogenerated electrons.Generally speaking,the material structure determines its performance.In order to enhance their properties in field of photocatalysis,scientists have prepared a variety of new titanium dioxide nanomaterials with different structure,such as nanotubes,nanspheres,nanowires,nanoflowers and nanosheets.Among these materials,the titanium dioxide hollow material can increase the photosynthetic efficiency obviously,due to its larger specific surface area,abundant active sites and more photosensitizer adsorption sites.Based on a large number of domestic and foreign literature reports and the research foundation of the group,the first work of this paper takes phospholipid vesicles as the template,introducing tetrabutyl titanate into hydrophobic area of the phospholipid bilayer by the means of internal interface limited domain method.Thus the hydrolytic condensation reaction was confined in hydrophobic area to form an ultra-thin titanium dioxide shell.Through high-temperature calcination the phospholipid vesicle template were removed and a kind of titanium dioxide vesicle material with an ultra-thin shell structure were obtained eventually.In the second work,titanium dioxide vesicle material was sensitized by the natural dye chlorophyll to simulate PSII system of thylakoid membrane.The performance of capturing light and releasing oxygen in visible light and mechanism of photocatalytic water oxidation of the composite was investigated by molecular simulation and other characterization methods.In particular,we carried out the research as below:(1)This paper taking phospholipid vesicles as the template,introducing tetrabutyl titanate into hydrophobic area of the phospholipid bilayer by the means of internal interface limited domain method.Thus the hydrolytic condensation reaction was confined in hydrophobic area to form an ultra-thin titanium dioxide shell.Through freeze-drying method and high-temperature calcination,the phospholipid vesicle template was removed and titanium dioxide vesicle material with an ultra-thin shell structure was obtained eventually.By means of SEM,TEM,EDS and laser particle size analyzer,it was proved that the prepared TiO2 vesicle material has a complete morphology,without collapse and damage phenomenon,and the mainly chemical composition is TiO2.Spectroscopic Ellipsometry speculated that the thickness of the shell layer of TiO2 vesicle material was about 3 nm.Next,Infrared spectrum shown that TiO2 vesicle material mainly contains Ti-O-Ti characteristic peaks,and X-ray photoelectron spectroscopy analysis were used to further prove that TiO2 vesicle material mainly contains Ti and O elements.Using XRD and HRTEM,it was found that TiO2 vesicle material contain both anatase and rutile phases,of which anatase phase occupies a dominant position after high temperature calcination at 800?.The ultraviolet-visible diffuse reflectance spectroscopy was used to detect the light absorption properties of ultra-thin TiO2 vesicle material and commercially TiO2 nanoparticle(P25),the energy band gaps were calculated to be 3.16 eV and 3.20 eV respectively.It was found that the surface of TiO2 vesicle material has more negative charge by using Zeta potentiometer.Finally,methyl violet and methylene blue degradation experiments are used to compare the photocatalytic performance of the two kinds of titanium dioxide materials,it shown that ultra-thin TiO2 vesicle material has a faster conversion efficiency of photogenerated electrons.After 30 minutes of ultraviolet light irradiation,the degradation rate of TiO2 vesicle material can reach about 81%and 95.33%for methyl violet and methylene blue respectively.(2)In order to construct artificial thylakoid bionic material and simulate the photoreaction stage of PSII system,organic dye chlorophyll molecules were loaded on the surface of TiO2 vesicle material to prepare TiO2 vesicle/chlorophyll composite material.By means of SEM and TEM,it was proved that the TiO2 vesicle/chlorophyll composite material has a complete structure and good dispersion.The Mg element was evenly distributed on the surface of TiO2 vesicle by EDS analysis.The use of UV-Vis spectrophotometer showed that the chlorophyll dye extended the light absorption range of the composite from ultraviolet to visible region.In addition,the electrochemical workstation was used to detect its transient photocurrent response and electrochemical impedance,it was speculated that the composite material had faster and more excellent photoelectric conversion efficiency.Finally,test results of the Clark oxygen electrode showed that the ultra-thin TiO2 vesicle/chlorophyll composite material has certain properties of light-harvesting and oxygen evolution.The mechanism of interfacial photoelectron transfer studied by molecular simulation and other characterization methods. |
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