Organic–inorganic hybrid mesoporous monoliths for selective discrimination and sensitive removal of toxic mercury ions

The selective optical sensing is attracting strong interest due to the use of “low-tech” spectroscopic instrumentation to detect relevant chemical species in biological and environmental processes. Our development has focused on tailoring specific solid mesoporous monoliths to be used as highly sensitive solid sensors for simple and simultaneous naked-eye detection and removal processes of extremely toxic heavy metal ions such as mercury ions in aquatic samples. The methods are emerging to design optical disc-like sensors by the immobilisation two different organic groups; however, the first organic moiety can enhance the polarity of the inorganic mesoporous disc-like monoliths “additional agents” and the second one can act as a recognition center “probe”. The latter one such as tetraphenylporphine tetrasulfonic acid (TPPS) probe led to facile handling of signal read-out with visual detection of ultra-trace concentrations of mercury ions at the same frequency as the human eye. The facile signaling was quantitatively evident using simple spectrophotometric techniques to indicate the TPPS–Hg(II) ion binding events. Control sensing assays of Hg(II) ions such as contact-time “signal response time”, thickness of support-based sensor, reaction temperature, and pH were established for achieving enhanced signal response and color intensities. Based on our results, these new classes of optical cage sensors exhibited long-term stability of recognition and signaling functionalities of Hg(II) ions that in general provided extraordinary sensitivity, selectivity, reusability, and fast kinetic detection and quantification of Hg(II) ions in our environment.

A successful design of organic–inorganic disc-like sensor monoliths show advanced features of a further control of the sensing assay that can be governed by facile handling of signal read-out optical measurements at trace levels (~10⁻⁹ mol/dm³) of Hg(II) ions in fast response time (1 min).