Mesoporous aluminosilica sensors for the visual removal and detection of Pd(II) and Cu(II) ions

Abstract

A general design for optical chemical nanosensors is necessary for the development of efficient sensing systems with high flexibility and low capital cost for the controlled recognition of heavy and toxic metals. In the present work, we designed optical chemical nanosensors for the colorimetric recognition and simultaneous removal of Cu(II) and Pd(II) ions. The optical nanosensors were designed by direct immobilization of a synthesized N,N′-disalicylidene-4,5-diamino-6-hydroxy-2-mercaptopyrimidine (DSAHMP) chelate onto hexagonal mesoporous aluminosilica carriers. The natural surfaces and active acid sites of the aluminosilicas strongly induced H-bonding and dispersive interactions with the DSAHMP chelate, leading to the formation of stable sensors without leaching of the chelate during sensing assays of metal ions. No elution of the probe molecules was evident with the addition of Cu(II) and Pd(II) analyte ions during the sensing process. In addition, the structural features of the open-pore, hexagonal mesostructures led to high rates of accessibility and adsorption capacity of the DSAHMP chelate. Within such a tailored nanosensor design, the ability to achieve flexibility in the specific activity of the electron acceptor/donor strength of the chemically responsive DSAHMP molecular probe enabled easy generation and transduction of optical color signals as a response to DSAHMP-Cu(II) or DSAHMP-Pd(II) binding events, even at ultra-trace concentrations (10−9mol/dm3) of heavy metals. The functional and solid design of the nanosensors offered a simple, one-step sensing procedure for both the quantitate and visual detection of such elements from their sources without the need for sophisticated instruments. Controlled sensing and removal assays significantly enhanced nanosensor functionality in terms of long-term stability, reversibility, and selectivity. The key result in our study is that the design-made nanosensors exhibited significant ion-selectivity toward the target ions in environmental and waste disposal samples.