Fabrication of calix[4]arene-attached mesoporous ammonium molybdophosphate-silica hybrid and its application as an adsorbent for cesium ions

The cesium cation is a common contaminant in medical and industrial products as well as in nuclear wastes, and it can present a serious risk to human health. Thus, the development of novel and facile methods for detection and elimination of cesium ions is important for environmental and biological systems. Mesoporous ammonium molybdophosphate-silica hybrid particles (AMP/Al-SiO2) were prepared, and the particles were immobilized on the calix[4]arene-based receptor 1 by a covalent bond between the carboxylic acid and amine, yielding the hybrid product AMP/Al-SiO2-1. In an evaluation of Cs+ adsorption on both particles, 57.8 mg g(-1) of Cs+ was adsorbed by AMP/Al-SiO2 while 72.2 mg g(-1) was adsorbed by AMP/Al-SiO2-1. The increased adsorption capacity of AMP/Al-SiO2-1 was due to a synergistic effect of the complex formation between 1 and Cs+ by a coordination bond. Additionally, the fluorescence intensity of AMP/Al-SiO2-1 was enhanced upon addition of Cs+. No significant fluorescence changes were observed in the parallel experiments with other metal ions such as Na+, K+, Mg2+, Rb+, Ca2+, Ba2+, Ag+, Ni2+, Zn2+ and Sr2+ ions. These findings confirmed that the AMP/Al-SiO2-1 can be useful as a chemoprobe for selective detection of Cs+ ions over a range of other metal ions in aqueous solution. We also determined that the fluorescence changes of AMP/Al-SiO2-1 were almost constant between pH 3 and 12. These results imply that the AMP/Al-SiO2-1 is applicable as a portable fluorogenic sensor for detection of Cs+ ions in environmental field studies.