Development of the PANI/MWCNT Nanocomposite-Based Fluorescent Sensor for Selective Detection of Aqueous Ammonia

Abstract

The present work reported the polyaniline (PANI) and multiwalled carbon nanotube (MWCNT)-based nanocomposite as a sensing material for the determination of aqueous ammonia by the enhanced fluorescence method. The excitation wavelength-dependent photoluminescence (PL) intensity has shown dual emission peaks at 340 and 380 nm that correspond to two different excitation energy states. The pH-based PL intensity and zeta potential variation were analyzed to optimize the suitable medium for aqueous ammonia sensing. Zeta potential was found to shift from 4 to −21 mV upon changing the pH of the the solution from acidic to alkaline medium. The fluorescence intensity of PANI/MWCNTs was found to increase upon increasing the pH from 3.0 to 6.0 (acidic region) and exhibits a plateau upon further increasing the pH from 7.0 to 12 (basic region). The PANI/MWCNT composite has shown a linear response to aqueous ammonia concentration varying from 25 to 200 μM with a correlation coefficient (R 2) of 0.99 and a limit of detection of 15.19 μM. The presence of relevant interference molecules and physiological ions had no influence on the detection of aqueous ammonia. Field-level study demonstrated that the level of aqueous ammonia can be determined selectively by using the PANI/MWCNT composite for various applications. The mechanism for the selective detection of aqueous ammonia is deliberated in detail.

Optimization and Analytical Behavior of Electrochemical Sensors Based on the Modification of Indium Tin Oxide (ITO) Using PANI/MWCNTs/AuNPs for Mercury Detection

“…The carbon nanotubes are properly embedded in the PANI matrix due to interfacial bonding between MWCNTs and the PANI matrix. The greater amount of PANI covers MWCNTs and forms the PANI/MWCNT composite [ 11 ]. Such a structure could afford a high effective surface area for the adsorption and diffusion of mercury, thus improving the sensitivity of electrochemical sensors [ 18 ].…”

“…The interactions between PANI and carboxyl functional MWCNTs take place due to electrostatic interactions between –COO − groups of MWCNTs and the –NH + of the aniline monomer, the hydrogen bonding between –OH groups on MWCNTs and the –NH group of the aniline monomer, and also a small amount of –π staking between the π-bonds of the MWCNTs and the quinoid ring of the aniline monomer [ 11 ]. Such a strong interaction ensures that the aniline monomer is absorbed on the surface of the MWCNTs which serve as the core and the self-assembly template (deposition) during the formation of tubular nanocomposites.…”

“…PANI templating by MWCNTs provided a head-to-tail structure under the optimized condition. When AuNPs are added, the intermolecular hydrogen bonds are weak and new hydrogen bonds are formed between PANI and MWCNTs, which facilitate the rotation and movement of the molecular chain [ 11 , 20 ].…”

“…For PANI-MWCNTs, the main peaks at 1455, 1137 and 658 cm −1 belong to the C=C stretching of the benzenoid ring and quinoid ring, C–N stretching of the secondary aromatic amine and C–S–C symmetric, respectively [ 22 ]. The absorption band at 2330 cm −1 and 2114 cm −1 is attributed to the stretching vibration of C=N, meanwhile, bands at 1498.83 cm −1 and 1455.96 cm −1 are assigned to –C–N stretching of 2° amines of quinoid and benzenoid structures of PANI due to polymerization of aniline to form a PANI chain linked through –NH– bonds of Au with two free –NH 2 group at its ends [ 11 ]. The peak of the C–O bond of the free –COOH group is present at 1029 cm −1 .…”

“…Composites made from a conductive polymer, such as polyaniline (PANI), and nanoparticles, such as multiwalled carbon nanotubes (MWCNTs) and gold nanoparticles (AuNPs), have been widely used in electrochemical sensors. The synergistic action between the high conductivity and stability of PANI [ 10 ], the high aspect ratio and exceptional mechanical strength of MWCNTs [ 11 ] and favorable electrocatalytic behavior of AuNPs could greatly enhance the sensor sensitivity and electroanalytical signals [ 12 , 13 ]. In this perspective, herein, for the first time, a PANI/MWCNT/AuNP-modified ITO electrode was developed by the direct electrodeposition of PANI, MWCNTs and AuNPs on a film-coated ITO electrode.…”