Vibrational and Resistance Responses for Ether-Amine Solutions of the Buckypaper-Based Chemiresistor Sensor

Abstract

The development of miniaturized sensors has become relevant for the detection of chemical/biological substances, since they use and detect low concentrations, such as flocculants based on amines for the mining industry. In this study, buckypaper (BP) films based on carboxylic acid functionalized multi-walled carbon nanotubes (f-MWCNTs) were produced through vacuum filtration on cellulose filter paper to carry out sensory function in samples containing ether-amine (volumes: 1%, 5%, 10% and 100%). The morphological characterization of the BPs by scanning electron microscopy showed f-MWCNT aggregates randomly distributed on the cellulose fibers. Vibrational analysis by Raman spectroscopy indicated bands and sub-bands referring to f-MWCNTs and vibrational modes corresponding to chemical bonds present in the ether-amine (EA). The electrical responses of the BP to the variation in analyte concentration showed that the sensor differentiates deionized water from ether-amine, as well as the various concentrations present in the different analytes, exhibiting response time of 3.62 ± 0.99 min for the analyte containing 5 vol.% EA and recovery time of 21.16 ± 2.35 min for the analyte containing 10 vol.% EA, revealing its potential as a real-time response chemiresistive sensor.

Keywords: buckypaper; ether-amine; selectivity; sensor.

Figure 1

Schematic representation of the buckypaper production stages.

Figure 2

Schematic illustration showing (a) sensor element made with the dimensions of the BP and the coverslip and (b) setup for chemiresistive characterization of the sensor element.

Figure 3

SEM micrograph of the BP in (a) cross and (b) superior view, at 894× and 17,700× magnifications, respectively.

Figure 4

Comparative Response (%) as a function of time for 5 µL of (a) deionized water (DW), (b) ether-amine 100 vol.% (EA100), and at concentrations of (c) 1 vol.% (EA1), (d) 5 vol.% (EA5), and (e) 10 vol.% (EA10). In On, the analyte is dripped, and in Off, it starts sensor recovery.

Figure 5

PCA Biplot generated with two PCs (PC1: 71.43% and PC2: 20.40%) for 3 cycles of samples EA1, EA5, and EA10.

Figure 6

Raman spectra showing the bands and sub-bands obtained by Lorentzian deconvolutions (a) f-CNTs (as received), (b) BP without analyte (as produced), (c) BP + DW, (d) BP + EA1, (e) BP + EA5, (f) BP + EA5 and (g) BP + EA100.

Figure 7

Intensity ratios of the sub-bands related to defects and graphitization of the outermost tubes (blue circles), degree of amorphous carbon (red squares), and normalized relative areas corresponding to the amorphous and crystallinity of the sample.