A novel Zr-MOF and its In2S3/Zr-MOF heterojunction materials for decontamination of Cr(vi) and reactive blue 13 via fluorescence sensing detection and photochemical redox†

Zr-MOFs play pivotal roles in water environmental chemistry, owing to their exceptional resistance against hydrolysis. But most Zr-MOFs mainly absorb ultraviolet light, which limits their widespread applications. Here, an entirely novel Zr-MOF was elaborately designed and fabricated. This Zr-MOF exhibits excellent photoluminescence and highly selective fluorescence quenching sensing abilities towards Cr₂O₇²⁻ and CrO₄²⁻ ions, even in the presence of other single or mixed anions/cations. Notably, its fairly low detection limits (DL) were determined to be 3.98 and 5.82 ppb, providing rather high fluorescence quenching constant (K_sv) values of 4.32 × 10⁴ and 2.23 × 10⁴ M⁻¹, and quantitative detection capability, respectively. Competitively absorbing excitation light energy and coordinating with the Zr-MOF by Cr(VI) were rigorously validated as the potential fluorescence quenching mechanisms. Moreover, the inherent optical-electronic properties endow it with considerable photochemical decolorization potential for reactive dye RB13 under UV light. To further polish its band state, novel heterojunction materials In₂S₃/Zr-MOF (labeled as M3, M5 and M7) were then fabricated. Under low-energy xenon lamp irradiation, M3 can reduce Cr(VI) by 98.4% within 60 min, affording a pretty high reaction rate constant of 0.069 min⁻¹, which was confirmed to be 2.3 and 12.7 times that of bare In₂S₃ and the Zr-MOF, respectively. And the decontamination efficiency of M5 for RB13 was calculated to be 97.42%, with reaction rate constants of 15.6 and 36.8 times that of pristine In₂S₃ and the Zr-MOF. By virtue of free radical trapping experiments and EPR tests, combined with the electron flow direction analyzed by XPS, the In₂S₃/Zr-MOF was confirmed to be a typical type-II heterojunction. This study provides a feasible way to overcome the limitations of Zr-MOF platforms and offers an innovative concept for designing novel bi-functional water environment monitoring and remediation materials.