Sira Srinives

Hexavalent chromium removal mechanism using conducting polymers

We report detoxification of Cr(VI) into Cr(III) using electrochemically synthesized polyaniline (PANI), polypyrrole (PPY), PANI nanowires (PANI-NW) and palladium-decorated PANI (PANI-Pd) thin films. Percent Cr(VI) reduction was found to be decreased with an increase in pH from 1.8 to 6.8 and with initial Cr(VI) concentration ranging from 2.5 to 10mg/L. Efficacy of PANI increased at higher temp of 37 °C as compared to 30 °C. PANI-Pd was found to be most effective for all three initial Cr(VI) concentrations at pH 1.8. However, efficacy of PANI-Pd was significantly reduced at higher pHs of 5 and 6.8. Efficacy of PANI and PANI-NW was found to nearly the same. However, there was a significant reduction in effectiveness of PANI-NW at 10mg/L of Cr(VI) at all the three pHs studied, which could be attributed to degradation of PANI-NW by higher initial Cr(VI) concentration. PPY and PANI-NW were found to be highly sensitive with respect to pH and Cr(VI) initial concentration. Chromium speciation on PANI film was carried out by total chromium analysis and XPS, which revealed Cr(III) formation and its subsequent adsorption on the polymer. PANI-Pd and PANI are recommended for future sensor applications for chromium detection at low pH.

ZnS nanocrystals decorated single-walled carbon nanotube based chemiresistive label-free DNA sensor

We fabricated ZnS nanocrystals decorated single-walled carbon nanotube (SWNT) based chemiresistive sensor for DNA. Since the charge transfer in the hybrid nanostructures is considered to be responsible for many of their unique properties, the role of ZnS nanocrystals toward its performance in DNA sensor was delineated. It was found that the free carboxyl groups surrounding the ZnS nanocrystals allowed large loading of single strand DNA (ssDNA) probe that provided an ease of hybridization with target complementary c-ssDNA resulting in large electron transfer to SWNT. Thus it provided a significant improvement in sensitivity toward c-ssDNA as compared to bare SWNT based DNA sensor.

A miniature chemiresistor sensor for carbon dioxide.

A carpet-like nanostructure of polyaniline (PANI) nanothin film functionalized with poly(ethyleneimine), PEI, was used as a miniature chemiresistor sensor for detection of CO2 at room temperature. Good sensing performance was observed upon exposing the PEI-PANI device to 50-5000 ppm CO2 in presence of humidity with negligible interference from ammonia, carbon monoxide, methane and nitrogen dioxide. The sensing mechanism relied on acid-base reaction, CO2 dissolution and amine-catalyzed hydration that yielded carbamates and carbonic acid for a subsequent pH detection. The sensing device showed reliable results in detecting an unknown concentration of CO2 in air.

Potassium Iodide-Functionalized Polyaniline Nanothin Film Chemiresistor for Ultrasensitive Ozone Gas Sensing

Polyaniline (PANI) nanostructures have been widely studied for their sensitivity to atmospheric pollutants at ambient conditions. We recently showed an effective way to electropolymerize a PANI nanothin film on prefabricated microelectrodes, and demonstrated its remarkable sensing performance to be comparable to that of a one-dimensional nanostructure, such as PANI nanowires. In this work, we report further progress in the application of the PANI nanothin film chemiresistive sensor for the detection of ozone (O3) by modifying the film with potassium iodide (KI). The KI-PANI sensor exhibited an excellent sensitivity to O3 (8–180 ppb O3 concentration rage) with a limit of detection of 230 ppt O3, and exquisite selectivity against active chemicals such as nitrogen dioxide (NO2) and sulfur dioxide (SO2). The sensing mechanism of the sensor relied on iodometric chemistry of KI and O3, producing triiodide (I3−) that partially doped and increased electrical conductivity of the PANI film. The sensitivity and selectivity of the KI-functionalized PANI film demonstrates the potential use for KI-PANI-based O3 sensing devices in environmental monitoring and occupational safety.