Surface-effect on detection ability of fluorescent Eu(btc) metal-organic frameworks to metal ions

Eu(btc) metal organic frameworks (MOFs) were prepared by co-precipitation method via 1,2,4-benzenetricarboxylic acids (H3btc) connecting with Eu3+ ions, and the morphology was controlled from compact spherical to irregular honeycomb by adjusting the pH of reaction solutions. The luminescence properties of Eu(btc) MOFs are found to be related to the surface morphology of products, and the compact spherical one performs stronger emission intensity. The sensing ability of Eu(btc) MOFs to 11 kinds of metal ions was investigated and a prominent quenching effect occurrs in Fe3+, Cr3+ or Ni2+ solutions. Based on UV–vis absorption analysis, an “ion-fence” model presents the competition to absorb exciting light between Eu(btc) MOFs and adsorbed metal ions. Based on Stern-Volmer equation, the Eu(btc) detection is found with higher Ksv value and a lower detection limit. Meanwhile, a higher sensing efficiency is confirmed in the Eu(btc) MOFs with loose honeycomb due to aggravating porous surface offering much more sites for metal ions.