Superfast structural transformation as a naked-eye detector: conversion of quasi-HKUST to Fe(BTC) for the detection of Fe(iii)

Abstract

Structural transformation is always attractive and valuable, but in most cases are time-consuming and incomplete. The use of quasi metal–organic frameworks (Q-MOFs), a new class of large-scale structurally deficient MOFs with high concentrations of unsaturated metal centers, could revolutionize the field of MOFs. In this study, quasi-HKUST-1 (Hong Kong University of Science and Technology) is transformed into Fe(BTC) (BTC: 1,3,5-benzenetricarboxylate) MOF in a very short time in the presence of aqueous Fe³⁺ (ferric cation) solution with a simultaneous significant color change from blue to orange. Therefore, this super-fast structural transformation can be used as a naked-eye indicator of Fe³⁺. With lower amounts of Fe³⁺, where the created structure is negligible, Q-HKUST acts as a fluorescence sensor of Fe³⁺. It should be noted that this structural transformation of the intact HKUST occurred very slowly and is carried out with much higher concentrations of Fe³⁺. This study is of interest owing to the importance of quasi MOFs as intermediate materials, a method for very quickly preparing Fe(BTC) at ambient temperature, and also from the practical point of view of naked-eye detection of Fe³⁺.