BiPO4 nanocrystal/BiOCl nanosheet heterojunction as the basis for a photoelectrochemical 4-chlorophenol sensor

4-Chlorophenol (4-CP) is a toxic chlorinated organic pollutant that can result in many harmful effects, such as carcinogenesis, teratogenesis, and mutagenesis, and that has recently attracted increasingly widespread attention. Therefore, it is necessary to develop a highly sensitive and selective method for the detection of 4-CP in water. A sensitive photoelectrochemical sensor based on the heterojunction between a BiPO4 nanocrystal and a BiOCl nanosheet (BiPO4/BiOCl) was designed for detecting 4-CP. The BiPO4/BiOCl heterojunction was synthesized via an in situ hydrothermal method with the assistance of ionic liquids (ILs) 1-hex-adecyl-3-methylimidazolium chloride ([C(16)mim] Cl) and 1-octyl-3-methylimidazolium dihydrogen phosphate ([Omim] H2PO4). Compared to pure BiOCl and pure BiPO4, the BiPO4/BiOCl heterojunction possessed effective separation of photoinduced electron-hole pairs, resulting in enhanced photoelectrochemical performance. When considering this enhanced photoelectrochemical response in terms of 4-CP, the photoelectrochemical sensor that was designed based on the BiPO4/BiOCl heterojunction presented a strong linear relationship, a wide range, a low detection limit, and high repeatability, specificity and stability. Therefore, the photoelectrochemical sensor presented here can be considered an effective analytical method for monitoring 4-CP. This work not only provides a simple synthetic method for the production of BiPO4 nanocrystals, but also broadens the application of BiPO4-based heterojunction materials in photoelectrochemical sensors.