Synthesis of PAM/TiO2 composite microspheres with hierarchical surface morphologies

PAM/TiO2 composite microspheres with hierarchical surface structures were synthesized by the reaction between tetrabutyl titanate (TBOT) located within porous polyacrylamide (PAM) microgels and water in a moist atmosphere. The morphology and composition of the composite microspheres were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FI-IR), X-ray diffraction (XRD), N-2 absorption analysis, and mercury porosimetry, respectively. The results indicated that the composite microspheres, with different hierarchical surface morphologies, could be obtained by controlling the cross-linking degree of the porous PAM microgels, the relative humidity of the gas phase, the amount of residual impregnation liquid, and the TBOT concentration in the porous PAM microgels. Although the surface morphologies of the composite microspheres are varied, the morphologies are typically divided into three categories: (1) wrinkled surfaces covered with large dense TiO2 particles; (2) porous structures sparsely suffused with large TiO2 particles along the fringes and inner walls of the porous channels; and (3) macroporous surfaces with small TiO2 particles distributed ubiquitously. The incorporation of TiO2 particles into PAM microgels resulted in an obvious increase in specific surface area, and the pore size distribution of the microspheres depended strongly on the size of TiO2 particles. The method described herein provides a potential way for fine-tuning the morphology and surface property of composite microspheres. Additionally, this method can be used to fabricate various composite materials through altering the precursor and/or polymeric microgel template.