Abstract
In previous work we have developed a dicarboxylate functionalized polymer that demonstrated chemical sensing. It showed good response to pH changes as well as to varying concentrations of copper and calcium ions. Our recent in-vest- tigations showed interesting results upon testing the functionalized sensing polymer on heavy metals. This sensor is composed of microspheres of polyvinyl benzyl malonate lightly-cross-linked with divinyl benzene dispersed in a hydrogel membrane. The response of the optical sensor is based on the interaction between the metal cations with the deprotonated functional group. The polymer, thus, undergoes shrinking as a result of neutralization of adjacent negative charges on the back-bone of the polymer. This causes significant changes in the optical properties of the sensing element. The optical changes were measured as absorbance vs. wavelength as the sensing membrane is exposed to solutions of varying concentrations of heavy metal ions. The sensor showed significant increase in absorbance up to a concentration of 5 × 10-3 M to the following metal ions: Ni2+, Zn2+, and Cd2+. Furthermore, the studied capacity of the derivatized microspheres showed close values to Ni2+, Zn2+, Cd2+ (1.20, 1.09, 1.08 mmol/g respectively). These kinds of properly functionalized polymers appear to be suitable, versatile sensing elements for the detection of low concentrations of heavy metal ions. In addition, all of the tested heavy metals showed a similar value of the equilibrium formation constant, (log Kf1 is 2.63). In contrast, the sensor showed no significant response to varying concentrations of K+ and Mg2+ metal ions.
Highlights
Chemical sensors based on swellable suitably functionalized polymer microspheres with dimensions of the order of a few micrometers suspended and entrapped in a hydrogel membrane have become of great interest in analytical studies [1,2,3]
Our recent investigations showed interesting results upon testing the functionalized sensing polymer on heavy metals. This sensor is composed of microspheres of polyvinyl benzyl malonate lightly-cross-linked with divinyl benzene dispersed in a hydrogel membrane
The optical changes were measured as absorbance vs. wavelength as the sensing membrane is exposed to solutions of varying concentrations of heavy metal ions
Summary
Chemical sensors based on swellable suitably functionalized polymer microspheres with dimensions of the order of a few micrometers suspended and entrapped in a hydrogel membrane have become of great interest in analytical studies [1,2,3]. There is a great need to develop chemical sensors for the detection of heavy metal ions [4]. Such sensors exhibit superior properties over other optical and electrical sensors due to their excellent resistance to photodegradation and electrical interference [5,6,7]. This leads to a lower percentage of water and an increase in the refractive index of the polymer. This changes the optical properties of the polymer which can be detected by measuring either light transmission or reflection. The tested heavy metal ions were Ni2+, Zn2+ and Cd2+
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