Crystal phase-controlled synthesis of BiPO4 and the effect of phase structure on the photocatalytic degradation of gaseous benzene

Abstract

As a typical wide-band-gap semiconductor, BiPO4 (BPO) has a great potential for photocatalytical degradation of highly stable benzene (C6H6) that has been regarded as a priority hazardous VOC substance in the indoor atmosphere. Hexagonal (H-BPO), monoclinic (M-BPO), and their mixture phase BiPO4 (M/H-BPO) were selectively synthesized to study the effect of BPO phase structure on the degradation of C6H6. The samples were characterized by several techniques, including X-ray diffraction, FTIR spectroscopy, UV–vis diffuse reflection spectroscopy, N2 absorption-desorption measurements, scanning/transmission electron microscopy, and X-ray photoelectron spectroscopy. The results indicated that the monoclinic phase was a thermodynamically stable phase. The band gap energy of H-BPO, M-BPO, and M/H-BPO was 3.74, 3.93 and 3.86eV, respectively. A transformation from rice-like hexagonal BPO to monoclinic phase nanorods was realized through varying the hydrothermal temperature and the composition of the solvent. The degradation of C6H6 was closely associated with the crystalline phase of BPO and the mineralization rates decreased in order of M– (7.3)>M/H– (1.51)>H-BPO (0.51μmol·h−1·m−2). The rates were higher than that of well-known P25 (0.34μmol·h−1·m−2). The highest activity of M-BPO could be ascribed to its intrinsic distortion of PO4 tetrahedron and the largest band gap structure. OH, O2−, and photoinduced holes were the major oxidation species accounting for the destruction of C6H6.