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 ([C₁₆mim]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.