Bio-inspired Synthesis And Application Of Porous TiO₂and ZrO₂in Agarose Gels

As important inorganic semiconductor materials, porous TiO2and ZrO2havebeen intensively investigated in materials science because of their high specificsurface area, ordered pore channel, good optical and chemical property, stability,non-toxicity and low cost. Previous studies have shown that the gel can not only beused as a limited diffusion reaction medium for crystal growth, but also beincorporated in the crystal as the template for synthesizing porous materials. In viewof this, this study has been focused on the biomimetic synthesis of porous TiO2andZrO2in the agarose gel medium. The morphology, structure and chemical propertiesof the mineralized samples were investigated by SEM, TEM, XRD, TGA, BET, FTIRand UV-Vis spectra. The effects of different conditions on the properties of porousTiO2and ZrO2were also studied.The photocatalytic properties of porous TiO2andfluoride adsorption ability of porous ZrO2were evaluated.(1) Porous TiO2materials were successfully prepared in the agarose gel by usingthe cheap and readily available (NH4)2TiF6and NaOH as precursors. The obtainedporous TiO2materials are composed of anatase TiO2grains with size about13.2nm,and possess hollow cube structure with a side length about500-700nm. Mesoporesaround3.8nm are found, which proves that the agarose gel fibers have incorporatedinto the TiO2materials and acted as a template for the mesopore. After calcinated at300-600°C, the porous and hollow structure are still preserved, which testifies thehigher thermal stability of porous TiO2materials. The reaction and the nucleation ratecan be regulated by changing the reaction time, the ratio of reactants, and the gelconcentration, so as to control the size and morphology of the porous TiO2materials.A mechanism is postulated to tentatively elucidate the formation of porous TiO2mineralized in agarose gel medium. First, the hollow quasi-cubic NH4TiOF3intermediate was formed in gel, and can be convert to anatase due to the role ofagarose gel. When the composites are immersed into hot water, the originalquasi-cubic structure is retained and porous structure is formed after removal of thegel fibe. Moreover, during the degradation of methylene blue and oil refiningwastewater, porous TiO2exhibited better photocatalytic activity than DegussaP25. (2) Porous ZrO2materials were successfully prepared in the agarose gel by usingZrOCl2and NH3·H2O as precursors. The prepared porous ZrO2materials aretetragonal phase which comprise of grains about11.8nm in size. Bimodal mesoporesabout3.8and5.5nm in size are found, which may be formed through removing theagarose gel fbers embedded in ZrO2materials. The pore structure and specific surfacearea of porous ZrO2materials can be adjusted by changing the reaction conditions, forexample, increasing the concentration of the agarose gel or decrease the concentrationof ZrOCl2can increase the pore size and specific surface area. The porous ZrO2materials exhibit excellent adsorption capacity for fluoride ions. It is found that theacidic environment can promote the adsorption capacity, while the existence ofco-existing ions with higher charge reduce the adsorption capacity.