Three-dimensional Direct Writing Of Photocatalytic Systems And Property Study

The efficient utilization of solar energy for efficient solar conversion（e.g.artificial photosynthesis,photocatalytic degradation etc）is a hot research area,and is of high significance for the energy crisis and environmental problems.Three dimensional direct writing can realize controlled construction of three dimensional complicated architectures of various materials such as metals,ceramics,polymers and hydrogels,which can provide new pathways for the construction of three-dimensional efficient photocatalytic systems.The research utilize three-dimensional direct writing technique for the contruction of titanates artificial photosynthetic systems and flexible C₃N₄ based aerogel,respectively.Microstructure characterization,rheology property,porosity characterization are used to investigate the influences of different inks on the rheology property,print style,print dimensions,porosity and so on.The research also investigate the influences of different print mediums on the print style and structure formation effects.We use simulation method and experimental results to reveal the relationships between three-dimensional architectures and photocatalytic property/gas diffusion property.The first part we fabricated well-patterned periodic hierachical Titanates APS for CO₂ photo-reduction via three-dimensional direct writing technique.We first characterized rheology properties of TiO₂ based ink,followed by adding surfactants to increase the specific surface area.The ink exhibited highly shear thinning behavior with plateau modulus about 10⁴ Pa is suitable for direct writing,by which,3Dperiodic structures with 10μm filaments are accessible.Through introducing surfactant DBSA,the specific area of APS reached 64.17m²/g,which is an order of magnitude larger than the sample without surfactant.SiO₂ nanoparticles with diameters of 15 nm and 30 nm were further added to obtain much larger mesopores in order to create hierarchical mesoporous structure which can promote gas diffusion.Direct writing process of TiO₂ APS can be extended to other Titanate materials such as SrTiO₃.CO₂ photo-reduction tests were carried out under UV and visible light irradiation in the absence of any sacrificial agents,CO and CH₄ yield rates of 3D APS sample were 0.152 and 0.134μmol·g^-1·h^-1respectively,which was 25%higher than powder sample.The promotion of reduction efficiency can be attributed to the 3D periodic structure,which can facilitate the gas diffusion during the reduction process.To further illustrate the effect of 3D hierarchical structure on mass transport,the gas diffusion process was simulated through COMSOL.It was found that the gas diffusion process in the printed structure was faster than slab structure.All the experiment and simulation results show that the 3D directed structure is able to facilitate the CO₂ reduction process.Aim at the challenge of recycling the powder photocatalysts,we fabricated well-patterned periodic flexible free-standing carbon nitride based hybrid aerogel membrane via 3D direct writing and supercritical drying techniques.We first characterized rheology properties of C₃N₄ based ink.C₃N₄ nanosheets with high surface area（331.5 m²/g）were not suitable for direct writing because of the low yield stress.We used C₃N₄nanosheets/sodium alginate hybrid ink to direct write in different reservoirs.Three dimensional structure was well hold in F127 and CaCl₂/glycerol reservoir.However the reservoir can dissolved into ink if direct writing in F127 gel and was difficult to be washed off.Direct writing in air without reservoirs was also carried out,but the structure obtained deformed easily.we found that the CaCl₂/glycerol reservoir is the best for direct writing.Supercritical drying technique was further employed to remove liquid residue in the structures.The direct written C₃N₄ based aerogel has application in wastewater treatment.The study provides new pathways for the design and construction of three-dimensional photocatalytic systems.It also provides experimental fundamental and technique supports for the design of multi-dimensional architectures,which is of high significance for the scientific research.