A dual-emission Eu(Ⅲ) functionalized multi-ligand MOFs for wide range pH sensing

Reliable sensing of pH is very important in daily life. Herein, we construct a luminescent material Eu(BTA)@CPP3 for wide range pH sensing (1.19–13.90) with blue (∼430 nm) and red (∼613 nm) luminescent centers. First, amino-terephthalic acid (BDC-NH2) is partially replaced by 1,2,4-Benzenetricarboxylic acid (BTC) to construct multi-ligand UiO-66-NH2. Second, using the coordinating post-synthetic method, we successfully incorporate a red emission center (Eu-BTA, benzoyltrifluoroacetone) into the frameworks of multi-ligand UiO-66-NH2. To obtain the best luminescent material, all the parameters during the synthesis process are adjusted. Interestingly, Eu(BTA)@CPP3 shows three types of luminescent response modes in the process of pH sensing, including red emission quenching (1.19 < pH < 7.56), red emission quenching while blue emission enhancing (8.36 < pH < 12.04), and blue emission quenching (12.20 < pH < 13.98). The response mechanisms of each mode are discussed carefully. The luminescent color changes from red (natural and acidic solution) to blue (base solution), which can be identified by the naked eye. Furthermore, a luminescent pH test paper based on Eu(BTA)@CPP3 is prepared and is used to determine the pH practically.