Construction of MIL-125 derived 2D TiO2@C nanocake/Au/3D peony-like BiOI Z-scheme heterojunction for sensitive and facile photoelectrochemical sensing assay of Cr (VI) based on competitive consumption of surface sacrificial agent

Herein, an advanced 2D TiO2@C nanocake/Au/3D peony-like BiOI Z-scheme heterojunction was first designed as matrix for photoelectrochemical (PEC) assay by using heavy metal ion hexavalent chromium (Cr (VI)) as a model. First, via calcination of titanium-based MOF (MIL-125), the p-type 2D TiO2@C nanocake with carboxyl was obtained. Second, Au NPs was generated in situ on the 2D TiO2@C nanocake surface. Third, amino functionalized 3D peony-like BiOI was combined with 2D TiO2@C/Au nanocake by electrostatic interaction to form the 2D TiO2@C/Au/3D BiOI Z-scheme heterostructure. Due to large surface area, multidimensional charge transfer paths and matched energy levels, this heterostructure produced a large photocurrent. Besides, Au NPs acted as electron shuttle mediator to engineer a Z-scheme charge transfer pathway. Simultaneously, ascorbic acid (AA) acted as surface sacrificial agent to eliminate photogenerated holes, enhancing the photocurrent. Cr (VI) could compete with the matrix for AA consumption by reduction reaction, leading to the decline in photocurrent. Based on the excellent 2D TiO2@C/Au/3D BiOI Z-scheme heterostructure and target-induced competitive consumption of surface sacrificial agent strategy, Cr (VI) was sensitively and accurately assayed (linear range, 10 nM to 200 μM; detection limit, 6 nM). The developed PEC sensing platform may have great prospect in environment monitoring.