Design and engineering heterojunctions for the photoelectrochemical monitoring of environmental pollutants: A review

Highly toxic pollutants, e.g. heavy metal ions, phenolics, toxins and pesticides, have posed major threats to ecosystem security and public health. It is imperative to develop simple, low cost, sensitive and reliable techniques for detecting these contaminants in the environment. Compared with traditional analytic techniques, photoelectrochemical (PEC) sensing as a newly emerged approach possesses a low background noise and high sensitivity, opening a new platform for rapid and accurate monitoring of the concerned pollutants. The performance of advanced PEC sensors is fundamentally related to the microstructures and configurations of semiconductor-based photoactive nanomaterials. Therefore, a multidisciplinary research effort focusing on the rational design and synthesis of innovative photoactive nanomaterials has recently emerged. This paper provides a comprehensive review on the engineered semiconductors (i.e. doped-semiconductors) and their heterojunctions (e.g. semiconductor-semiconductor, semiconductor-carbon, semiconductor-metal and multicomponent heterojunction) as well as their emerging applications in PEC sensing and monitoring. Particular attention has been paid to various morphologies, e.g. 0D quantum dots (QDs) and nanoparticles (NPs), 1D nanowires (NWs), nanotubes (NTs) and nanorods (NRs), 2D nanosheets (NSs) and 3D aligned arrays, and their effects on the sensing performances. Moreover, the signal response mechanisms and performance evaluations (e.g. sensitivity, linear range, limit of detection, selectivity and stability) of the constructed PEC sensors are discussed. At last, critical challenges and future research perspectives in the fields are proposed.