Metal-organic frameworks (MOFs) combined with ZnO quantum dots as a fluorescent sensing platform for phosphate

In this work, we demonstrated that metal-organic frameworks (MOFs) and ZnO quantum dots (QDs) were successfully employed to design an effective fluorescent sensing platform for phosphate (Pi), thanks to the interactions among the ZnO QDs, MOFs and phosphate ions. The amine-Zn interaction and electrostatic interaction between negatively charged MOFs and positively charged ZnO QDs resulted in the quenching of ZnO QDs fluorescence due to electron-transfer processes, along with the formation of flower-like complex. After introducing Pi ions into the QDs-MOFs system, the burst of Pi ions could inhibit the quenching effect, and recover the fluorescence of ZnO QDs. Furthermore, the fluorescence intensities were dependent on the concentrations of Pi ions and scarcely affected by other possible interfering species. The present fluorescent sensing platform had good sensitivity (the slope of the calibration curve), with a linear range of 0.5-12 mu M and detection limit of 53 nM (S/N= 3). The sensing mechanism of Pi was also investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD), and the results indicated that the Pi ions inhibited the quenching effect via breaking the interactions between MOFs and ZnO QDs, and caused the collapsing of MOFs. Finally, the proposed methodology was used satisfactorily for the assessment of Pi in environmental aqueous samples, which opened a new avenue for Pi determination. (C) 2014 Elsevier B.V. All rights reserved.