Fabrication of nanostructured materials for environmental remediation and sensing

Detection and remediation of environmental contaminants is an area of concern and growing research. Cr(VI) is acutely toxic, a proven mutagen and a carcinogen whereas Cr(III) is believed to be an essential element. Furthermore, the development of probes for the detection of biologically significant contaminants using conducting polymers has been of considerable interest. Consequently, the major objective of this research is to develop new class of nanostructured materials based on Polyamic acid for the reduction of Cr(VI) to Cr(III).;We hereby make the first report on colloidal palladium nanoparticles (Pd-NPs) catalyzed reduction of Cr(VI) to Cr(III) using either formic acid (FA) or polyamic acid (PAA) as reducing agents. The reduction concept exploits our recent discovery that FA and/or PAA either as solution, amorphous powders or as continuous film on electrode can act as reducing agents to significantly reduce the toxic Cr(VI) to benign Cr(III) without generating significant wastes. Practical applications of Pd-NPs/FA mixture in removing Cr(VI) in different kinds of soil has been demonstrated with a 99.9% conversion rate. The reversibility of PAA in the reduction of Cr (VI) provides a reusable source of PAA. Consequently, a nanoreactor has been fabricated and tested for the reduction of Cr(VI) to Cr(III).;In the remediation process, PAA is first used as a reducing agent to prepare different sizes of palladium nanoparticles which are subsequently used to catalyze the reduction of Cr(VI). The electrochemical reduction of Cr(VI) as investigated on a PAA modified Au-electrode shows that Cr(VI) can undergo a chemically reversible reduction in acidic media. High electrochemical reduction efficiency is achieved in the presence of PAA. This is a significant discovery as most methods of Cr (VI) remediation such as bacterial degradation take weeks and sometimes months for complete reduction. The reversibility of PAA in the reduction of Cr (VI) provides a reusable source of PAA, hence a possible source of green remediation.;Based on the successful use of FA and PAA in Cr(VI) reduction, a nanoreactor has been fabricated and tested for the reduction of Cr(VI) to Cr(III) using three sets of reducing agents namely; formic acid, polyamic acid and hydrogen sulfide generated from elemental sulfur at an elevated temperature. All the reactions were catalyzed by palladium nanoparticles generated within the nanoreactor.;The second part of this study is dedicated to the design and fabrication of a generic and versatile bimolecular immobilization platform using PAA modified Au-electrode. PAA modified gold electrode surface functionalized with biological moieties has proved desirable in enhancing biomolecular recognition at the interface and promotes signal amplifications in the biosensor response. PAA acts as the immobilization matrix as well as the physicochemical transducer by converting a chemical signal into an electrical signal. PAA modified Au-electrode template is easy and inexpensive and applicable to various biomolecules. Its application to piezoelectric and amperometric immunosensing provides simpler, more specific, and less expensive sensing system compared to ordinal immunosensors.;Finally the development of the first electrochemical characterization of pain biomarkers particularly the Arachidonic acid (AA), cyclooxygenase-2 enzyme (COX-2) and the prostaglandin PGG2 is reported. The development of an electrochemical immunosensor for monitoring these pain biomarkers through direct electron transfer between arachidonic acid metabolites and the electrode is discussed. An enzyme modified electrode that dramatically enhanced bio-electrocatalytic activity towards AA is subsequently reported.