Dual-emissive Ru@UiO-66-NH₂ composite for selective visual detection of phosphate and arsenate

The existence of excess phosphate (Pi) and arsenate ions [As(V)] in environment water poses significant risks to ecosystem as well as public health and often interfere each other during detection process. Although some ratiometric sensors exhibited high sensitivity towards individual Pi and As(V), few of them were applied for visual detection and portable sensing. Therefore, we need to design a convenient strategy for selective visual detection of Pi and As(V).

Dual-emissive zirconium-based metal-organic frameworks (UiO-66-NH₂) encapsulated tris(2,2-bipyridyl)ruthenium (II) chloride hexahydrate [Ru(bpy)₃²⁺] composite, denoted as Ru@UiO-66-NH₂, has been synthesized by one-pot approach and used for ratiometric fluorescence detection of Pi and As(V). Under single excitation of 295 nm, the composite exhibited two emissions at 435 and 618 nm, originating from UiO-66-NH₂ and Ru(bpy)₃²⁺, respectively. Upon the addition of Pi (or As(V)), the ligand-to-metal charge transfer (LMCT) process was weakened owing to their strong affinities with Zr-O node, inducing the enhanced blue fluorescence and unchangeable red one. In addition, they triggered clear fluorescence changes from red to pink and finally to blue. With the assistance of smartphone, visual detection of Pi and As(V) can be achieved with a limit of detection (LOD) of 0.8 μM and 1.5 μM, respectively. Furthermore, Pi and As(V) could be separately detected via the introduction of proper masking agents.

The detection method developed in this work has successfully been applied to detect Pi and As(V) in actual water samples. For the first time, Ru@UiO-66-NH₂ was used for the visual detection of Pi and As(V). This work broadens the latent applications of MOF composites for on-site monitoring in environment safety assessment.