Controlled Synthesis And Photodynamic Application Of Porous Fiber Surface Heterostructures

Sunlight and water are available and renewable resources in nature,but the rapid development of industry and agriculture leads to the lack of water resources.The effective utilization of solar energy to obtain and use natural water through photoelectric and photothermal conversion is considered to be a promising method to produce renewable energy.In this application field,the construction of various heterojunction materials can effectively enhance the light absorption properties,and thus become a research hotspot.However,the surface morphology regulation and interface engineering of heterojunction materials still need to be further investigated to improve the light collection efficiency.In the meanwhile,the growth and construction mechanism need to be further explored to be applied to solar driven water splitting and collection.In this work,a series of fiber heterojunction materials Al OOH/Al₂O₃@TiO₂,RGO/Al OOH/Al₂O₃,Fe₂O₃@TiO₂,Co-carbon are designed,and their growth mechanism and application in photoelectric and photothermal conversion were explored.The specific research is as follows:（1）Ultra-thin and microporous Al OOH/Al₂O₃nanosheets were topologically grown on the surface of TiO₂nanofibers by hydrothermal synthesis using only water as solvent.The experimental results indicated that TiO₂nanofibers could reduce the surface energy of the released Al species in the hydrothermal process,thus the layered Al OOH was synthetized in situ.Metastable Al OOH tends to dehydrate to Al₂O₃,featured with a well maintained 2D structure with sharp corners,steps,and enriched micropores.These structures provide sufficient active sites for the reaction.Based on these characteristics,the nanosheets on the nanofibers exhibited an adsorption capacity of 2856-3370 mg/g for RHB.The promoted light capture efficiency by vertically connected nanosheets further achieved the effective photodegradation of RHB within 1 hour.（2）By introducing graphene oxide（GO）into the hydrothermal process and using GO sheets as reliable catalysts to adjust the growth kinetics of Al OOH/Al₂O₃nanosheets.By adjusting GO contents,the oxygen-containing functional groups of GO provided the nucleation sites of Al₂O₃species and hindered their growth in a limited space.The experimental results showed that the morphology of Al₂O₃heterojunction evolved from nanoflakes to nanospikes outside TiO₂nanofibers.Due to the unique morphology and effective electron transfer pathway,the photocurrent density of RGO/Al OOH/Al₂O₃@TiO₂nanofibers is 3.5 times higher than that of pure Al OOH/Al₂O₃@TiO₂nanofibers under visible-light irradiation.（3）Inspired by the nature behaviors that the leaves on ivy prefer to be shielded from each other to ensure the maximum surface areas exposed to the sun,a biomimetic heterostructure was constructed by combining hydrothermal method with electrospinning.The experiment and finite element simulation indicated that the two-dimensional Fe₂O₃nanosheets could improve the light-harvesting effiency via multiple refraction.The enhanced light absorption performance also benefits from the abundant oxygen vacancies in the heterojunctions.The oxygen vacancy could acted as active sites and hinder the recombination of electron-hole pairs.When used as photoanode,the heterostructure surface exhibited a small contact angle（22.4^°）and the oxygen bubbles generated rapidly escaped from the surface after only 60 ms,indicating its excellent hydrophilicity and hydrophobicity.The tests of contact angles and the dynamic simulation of the release of bubbles confirmed that the functionalized surface could quickly release bubbles and adjust the surface/interface active sites.Based on these characteristics,the heterostructure achieved the excellent photoelectric performance,superior to other photoelectric materials.（4）Using low-cost and renewable waste cotton fabric as raw materials,a carbon based nanofiber heterojunctions was designed by combining carbonization oxidation and impregnation method.The experimental results showed that the nanofiber possessed a unique"slit hole structure"to ensure that the light could be refracted multiple-times between the holes.The unique branched structure of heterostructures could enhance the light-trapping effect by multiple-light scattering,achieving in a photothermal conversion efficiency of up to90%and the evaporation rate of 1.44 kg/（m²·h）under 0.5 solar radiation.On the other hand,the pleats on the surface of hydrophilic carbon fiber membrane provided sufficient capillary force and rich mass transfer channels for hygroscopic small molecules to capture water.Under the synergistic effect,Co-Carbon nanofiber exhibited excellent moisture absorption of capacity 5.19 g g^-1in 97%RH.The excellent moisture absorption and heat-collection performance ensured the Co-Carbon nanofiber membrane further applied to wearable sweat collection equipment.The daily water production could reach 9 L/m²（the illumination time of12 h）and the conversion rate of sweat to water is 21.8%.