Study on indole adsorption of Zr-and Hf-based metal-organic frameworks for fluoride ion detection

Abstract

Zr- and Hf-based metal-organic frameworks (MOFs) have recently garnered much attention especially for water purification such as removal of toxic organic compounds in fertilizers, pesticides, and metal ions. Moreover, these MOFs are candidates for biosensor materials due to their low toxicity, diverse properties, high surface area, active sites, and stability. In this research, Zr- and Hf-BDC materials were prepared by a solvothermal method and characterized by advanced techniques, including X-ray diffraction, scaning electron microscope (SEM), thermogravimetric analysis (TGA), and nitrogen adsorption. The structural and property analysis results showed that Zr-BDC and Hf-BDC have high crystallinity, thermal stability over 500oC, and surface area according to the B.E.T equation from 950 to 1450 m2 g-1. These MOFs exhibited indole adsorption with capacities of over 150 mg g-1 and loading efficiency above 80%. The ability of the Zr-BDC and Hf-BDC to capture fluoride ions after indole encapsulation was demonstrated based on the fluorescence on and off mechanism of the indole signal compound. The indole carrier system showed an effective capture of fluoride ions at a concentration of 1000 ppm after 120 min. This study demonstrated the potential of porous materials carrying indole signaling compounds in the fabrication of sensors that capture fluoride ions in water and in biological environments.