Water hyacinth powder -assisted preparation of defects-rich and flower-like BiOI/Bi5O7I heterojunctions with excellent visible light photocatalytic activity

Abstract

Flower-like BiOI/Bi5O7I type-II heterojunctions with oxygen vacancies (OVs) have been in-situ constructed by calcining flower-like BiOI obtained by a hydrothermal tactic with the assistance of water hyacinth powder (WHP). The photocatalysts were characterized by specific surface area, X-ray diffraction pattern (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron spin resonance spectroscopy (ESR). The efficient photogenerated carriers separation of the photocatalysts was demonstrated by surface photovoltage spectrum (SPS) and photocurrent experiments. The trapping experiments determine that h+ and •O2− are the main active free radicals in the visible light driven (VLD) photocatalytic system. Low-temperature ESR proves the existence of OVs, which greatly promotes the photocatalytic activity. When the mass ratio of WHP/Bi(NO3)3•5H2O is 8%, the prepared BiOI/Bi5O7I photocatalyst represents the best photocatalytic performance under visible light irradiation. The removal rate constant of Rhodamine B (RhB) and phenol over the 8% samples is 0.022 min−1 and 0.24 h−1, which is 27 and 3-fold of that over the 0% sample, respectively. The effective transfer and efficient utilization of photogenerated e−/h+ and the presence of OVs jointly improve the activity of the BiOI/Bi5O7I composite photocatalyst. This work develops an effective strategy for synthesis of visible light driven photocatalytic materials by taking advantage of biomass.