Fabrication And Performance Of Direct Ink Writing Adsorbents And Photocatalysts

Geopolymers and TiO₂photocatalytic materials are widely used in the field of wastewater treatment because of their excellent adsorption and photocatalytic properties.The geopolymer’s three-dimensional framework formed by the reaction of aluminosilicate mineral materials with alkali activators such as Na₂SiO₃and composed of aluminum-oxygen tetrahedron[AlO₄],silicon-oxygen tetrahedron[SiO₄]and equilibrium structure negative alkali metal ions（Li⁺,Na⁺,K⁺,etc.）has outstanding cationic（group）pollutant removal ability because alkali metal ions can be exchanged with cations in liquid.TiO₂has the advantages of simple preparation process,low cost and strong redox ability,and it can take advantage of solar photocatalysis to degrade organic pollutants in wastewater.However,there are still difficulties in recovery in the practical application of powder adsorption and photocatalytic materials with outstanding properties,affecting the timeliness of reuse and renewal.Therefore,it is of great practical value and significance to design and realize the controllable transformation of powder adsorption and photocatalyst to macro-structure easy to recover and with outstanding performance.Traditional molding methods such as gel casting and tape casting cannot effectively make the design of complex interconnected pores come true,and it is difficult to meet the forming of monolithic adsorption/photocatalyst with well-developed micro-macro pore structure.Direct Ink Writing（DIW）achieves rapid forming of complex 3D components by formulating printing slurry with powder and precursor solutes to reduce cost and processing difficulty.In this paper,geopolymer adsorption sieve（GAS）and TiO₂photocatalytic degradation sieve（TPDS）are prepared based on a sieve model with well-developed pores,and their DIW molding process and performance are investigated.The main research contents of this paper are as follows:The rheological properties,physical phase composition,microstructure and adsorption mechanism of the GAS slurry for direct-ink-writing 3D printing were researched.The results showed that the storage modulus（G’）and yield stress（τ₀）of the slurry increased significantly with the increase of kaolin content during the preparation of the printing slurry;the 5×5 model structure had the best pore distribution according to the results of analyzing the pore structure conditions of finished products using different models after drying;when methylene blue（MB）was used as the target contaminant,it took 200 min for GAS to reach adsorption equilibrium,and the removal rate reached 83.6%.The pseudo-first-order,pseudo-second-order and Weber-Morris kinetics adsorption curves fitting of adsorption curves proved that the adsorption of GAS to MB is influenced by electrostatic effects and the adsorption rate was limited by the boundary liquid layer diffusion and intraparticle diffusion;the combination of characterization and density functional theory（DFT）calculations confirmed that the adsorption of GAS to MB was influenced by a combination of electrostatic interaction,hydrogen bond and electron transfer.The preparation,physical phase composition,microstructure morphology and photocatalytic degradation mechanism of the TPDS for direct-ink-writing 3D printing were researched.The results showed that in the process of preparing the printing slurry from TiO₂and tetrabutyl titanate,the addition of citric acid can make the hydroxyl groups on the surface of TiO₂particles interact with the hydroxyl or carboxyl on the citric acid molecule to produce steric hindrance,thus making the particles in the slurry uniformly dispersed;when tetracycline hydrochloride（TCCH）was used as the target contaminant,it took 210 min for TPDS to reach adsorption equilibrium,and the removal rate reached 94.27%;The pseudo-first-order,pseudo-second-order and Weber-Morris kinetic fitting of the degradation curves confirmed that the photocatalytic degradation affected the diffusion of boundary layer and weakened the diffusion of pollutant particles to the interior;after four cycling experiment,the efficiency of TiO₂photocatalytic degradation sieve still reached 91%for TCCH degradation,which proved that TPDS has good chemical stability.