Fluorine-mediated porosity and crystal-phase tailoring of meso-macroporous F[sbnd]TiO2 nanofibers and their enhanced photocatalytic performance

Abstract

We present the synthesis of surface-fluorinated, rutile-rich, meso-macroporous TiO2 nanofibers via simple post-treatment in a 5% hydrogen fluoride solution at room temperature and atmospheric pressure. Using various characterization methods, we demonstrate that the anatase phase of the nanofiber can be used as a sacrificial template to ensure appropriate porosity characteristics in the TiO2 nanofibers. From scanning electron microscopy results, it was confirmed that the dimensions of the nanofibers do not change after the hydrogen fluoride post-treatment. However, x-ray diffraction and transmission electron microscopy results confirm that the proportion of the rutile phase increases after hydrogen fluoride post-treatment. After hydrogen fluoride treatment, small pores with diameter below 10 nm almost disappear, and the pore size distribution ranges from mesopore (<50 nm) to macropore (~100 nm). The x-ray photoelectron spectroscopy results show the disappearance of the Si peak and surface fluorination after the treatment. Further, tests showed that nanofibers treated for 10 h and 20 h have excellent photocatalytic activity compared with pristine nanofibers. We expect hydrogen fluoride treated nanofibers to exhibit superior performance in certain applications where the rutile phase and meso- to macro-sized pores are desirable, such as heterogeneous catalysis and oxygen evolution.