Organic-inorganic hybrid nanocomposite-based gas sensors for environmental monitoring

Abstract

Figure 1.

Schematic of gas sensor fabrication techniques.

Figure 2.

Yearly publications and patents in the field of organic–inorganic hybrid nanocomposites. (Source: web of science and world intellectual property organization.)

Figure 3.

Various strategies adopted for the synthesis of organic−inorganic hybrid nanocomposites along with schematic representation.

Figure 4.

Types of chemical/physical interactions during the fabrication of organic−inorganic hybrid nanocomposites.

Figure 5.

Appropriate approaches for the processing of organic–inorganic hybrid nanocomposites for various applications.

Figure 6.

Electrical polymerization and electrophoretic deposition of organic−inorganic hybrid nanocomposites.

Figure 7.

Organic−inorganic hybrid nanocomposites used for gas sensing applications.

Figure 8.

Energy band gap diagram of organic−inorganic hybrid nanocomposites on gas exposure.

Figure 9.

Pictorial representation of Ni-poly(EDT-co-TAA) before and after exposure to toluene (A and B); variation of the response of Ni-poly(EDT-co-TAA) hybrid toluene concentration (C); and (D) variation of the response of Pd-poly(EDT-co-TAA) hybrids to acetone concentration. Reprinted with permission from ref 126. Copyright 2010 Institute of Physics.

Figure 10.

Inset in (A), the sensor array in the measuring cell and the oscillator circuits, (A) sensing responses at 200 ppm of octane and toluene at room temperature. (B) Testing of repeatability of the S4 sensors exposed to different concentrations of toluene over 5 months at room temperature. Reprinted with permission from ref 127. Copyright 2012 Elsevier.

Figure 11.

Inset in (A) SEM image of typical electrospun SWCNT-PMMA composite nanofibers. (A) Comparison of the sensor response profile of a flow-through sensing material with a printed electrode and a nonflow-through sensing mat on commercial IME electrodes, and (B) comparison of the sensitivities. Reprinted with permission from ref 143. Copyright 2013 Elsevier.

Figure 12.

Inset (A) SEM image of MCNT-PMMA hybrid (a), schematic presentation of bridging of PMMA and (b) in a MWCNT random network. (A) Selectivity of a MWCNT-PMMA and CNT random network when exposed to methanol, water, toluene, and chloroform vapors. (B) Effect of analyte concentration on MWCNT-PMMA response amplitude Ar for methanol, water, toluene, and chloroform vapors. Reprinted with permission from ref 144. Copyright 2011 Royal Society of Chemistry.

Figure 13.

(A and B) Chemical structure of TPP and Pr monomers 1 and 2, schematic representation of QMB coatings, where R in PPy backbone corresponds to H or monomer 2 substituents, and the relative sensitivity to 1-butanol for QMBs modified with SWCNT−Pr electro-polymers. (C) Relative response study of all 5 QCM gas sensors as a function of gas concentration. Reprinted with permission from ref 145. Copyright 2012 Elsevier.

Figure 14.

Effect of HCl gas on a organic−inorganic hybrid nanocomposite, schematic of gas sensor fabrication, and gas sensing response of a nanocomposite as a function of HCl concentration. Reprinted with permission from ref 82. Copyright 2004 Elsevier.

Figure 15.

Microelectrodes before (A) and after (B) the deposition of the AC-DEP-assembled PEDOT/PSS-SWCNTs composite film, (C) FE-SEM images of the PEDOT/PSS-SWCNTs composite films doped with SWCNTs (5 mg/mL), (D) selective responses of the drop-coated and AC-DEP-assembled PEDOT/PSSSWCNTs composite films to various vapors at 10 ppm, and (E) the calibration of the sensor response to NH₃ gas at 2–300 ppm and the linear response range (insert). Reprinted with permission from ref 160. Copyright 2013 Elsevier.

Figure 16.

(A) Optical microscope image of the sensor and (B) TiO₂ microfibers encased with PANI nanograins. (C) Current responses of a sensor made of TiO₂ microfibers encased with PANI nanograins to different concentrations of NH₃ gas as a function of time (left) and reproducibility of the sensor exposed to 10 ppb NH₃ gas (right). Reprinted with permission from ref 164. Copyright 2010 American Chemical Society.

Figure 17.

(A) SEM image of a PANI nanowire network grown on Au IDE at the end of second step. (B) SEM image of a gold nanoparticle-functionalized PANI nanowire network across gold microelectrodes. (C) Response and recovery behavior of sensor as a function of 0.1 ppb, 1 ppb, 10 ppb, 100 ppb, 500 ppb, and 1 ppm of H₂S gas. (D) Response R/R₀% of a gold-nanoparticle-functionalized PANI nanowire-network-based chemiresistive sensor as a function of H₂S concentration. Reprinted with permission from ref 168. Copyright 2009 American Institute of Physics.

Figure 18.

(A) Schematic of the NO₂ reaction with PHTh conducting polymer, (B) energy band of hetero p−n junction with and without NO₂ exposure, (C) resistance change of a RRPHTh−SnO₂ nanocomposite vs NO₂ gas concentration, and (D) resistance change vs time by CO + NO₂ gas concentration in RRPHTh−TiO₂ films. Reprinted with permission from ref 110. Copyright 2005 Elsevier.

Figure 19.

(A) SEM image of electrode and stepwise fabrication of fluidic-based gas sensor, (B) NO sensor response curves exhibiting selectivity over nitrite and ammonia, both species added three times separately; 1, 2, and 3 mM concentrations were obtained after each injection; (inset) NO calibration plots in two different media, and (C) amperometric response of the microfluidic NO detector with flowing test solutions containing different levels of NO; flow rate 50 μL/min, (a) 350 nM, (b) 100 nM, (c) 200 nM, and (d) 40 nM. Reprinted with permission from ref 109. Copyright 2010 American Chemical Society.

Figure 20.

(A) Structure of the IDE electrode, (B) SEM images: MWCNT (a), poly(1,5-DAN) (b), surface of the film IDE/MWCNT/poly(1,5-DAN), and (c) surface morphologies of MWCNT/poly(1,5-DAN) at 10 cycles (d) and at 25 cycles (e). (C) Response of the IDE/MWCNT/poly(1,5-DAN) film formed with 10 polymerization cycles to different concentrations of NO₂. (D) Response−recovery cycles of the IDE/MWCNT/poly(1,5-DAN) film formed with 10 polymerization cycles to 5 ppm of NO₂ and pure air; the inset depicts the last cycles. Reprinted with permission from ref 178. Copyright 2013 Elsevier.

Figure 21.

(A) 3D crystalline structure of CuBDC MOF. (B) Spatial arrangement of different liquid layers during the synthesis of CuBDC MOF nanosheets, (i) corresponds to a benzene 1,4-dicarboxylic acid (BDCA) solution, (ii) the solvent spacer layer, and (iii) solution of Cu₂C ions, respectively. (C) 3D-reconstructed FIB−SEM tomogram of a MOF−polymer composite. (D) CO₂ separation performance of a MOF membrane with reference to a standard membrane of polyamide (PI). Reprinted with permission from ref 183. Copyright 2014 Nature Publishing Group.

Figure 22.

(A) CVs of CO (0.01, 0.03, 0.05, 0.07, 0.09, 0.3, 0.5, and 0.7 mM) at Pt/PAN/MWCNTs/WGE; the upper inset depicts the dependence of reduction peak currents of CO on the concentration. The lower inset shows the accumulation effect of 0.1 mM CO at Pt/PAN/MWCNTs/WGE. (B) CVs of CO (1.0, 3.0, 5.0, 7.0, 9.0, 30.0, and 50.0 μm) at Pt−Ni/PAN/MWCNTs/WGE made in solution concentration ratio of Pt−Ni of 1:1 using constant potential and CV step; the upper inset shows the dependence of oxidation peak currents of CO on the concentration. The lower inset shows the accumulation effect of 0.1 mM CO at Pt−Ni/PAN/MWCNTs/WGE. Buffer: 0.5 M HClO₄. Scan: 50 mV s⁻¹. Reprinted with permission from ref 189. Copyright 2009 Elsevier.

Figure 23.

Effect of CO gas on an organic−inorganic hybrid nanocomposite surface. Reprinted with permission from ref 81. Copyright 2004 Elsevier.

Figure 24.

(A) Schematic structures of the Co(III)VXG and Co(IV)VXG host−guest materials. (B) Wireframe structural representation of the cationic Co(IV)TRPyP and Co(III)TRPyP species. The respective chloride salts were used for the preparation of the host−guest nanocomposites with VXG. (C) AFM images of Co(III)VXG (a) and Co(IV)VXG (b) films on mica substrates in a more densely packed region and at the Co(III)VXG film edge. (D) Plot of R/R₀ as a function of the percentage of water (v/v) in ethanol/water mixtures, for IDE Co(III)VXG and Co(IV)VXG sensors. Inset: plot of ln(1 – R/R₀) vs (% water). Reprinted with permission from ref 207. Copyright 2010 Elsevier.