Hollow Zinc Oxide Microsphere–Multiwalled Carbon Nanotube Composites for Selective Detection of Sulfur Dioxide

Abstract

This work reports the first utilization of anthocyanin extracted from black rice (Oryza sativa L.) grains as a structure-directing agent for the synthesis of hollow zinc oxide (ZnO) spheres via a simple solvothermal reaction and their subsequent modifications with various amounts of multiwalled carbon nanotubes (MWCNTs). Following hybridization with MWCNTs, some MWCNTs are observed to penetrate into the inner cavities of the spheres, while ZnO nanoparticles are formed on the surface of some MWCNTs. When employed as a sulfur dioxide (SO 2 ) sensor, the ZnO−MWCNT (15:1) composite displays a high response of 156 to 70 ppm of SO 2 at an optimum temperature of 300 °C as well as good selectivity to SO 2 with the response to 50 ppm of SO 2 gas being 3 times higher than those to other gases, such as CO, CO 2 , methanol, toluene, hexane, and xylene. Interestingly, the sensing behavior of this composite is strongly influenced by the proportion of MWCNTs. Specifically, n-type sensing behavior is observed for both ZnO−MWCNT (10:1) and (15:1) composites, while p-type behavior is observed for the ZnO−MWCNT (5:1) composite. The switch in sensing behavior suggests the major contribution of p-type MWCNTs to the electronic and sensing properties of the ZnO/MWCNT composites. The density functional theory (DFT) simulations on the adsorption of SO 2 on the ZnO/CNT system reveal that the SO 2 molecule only chemically interacts with the O adatom of ZnO (i.e., oxygen atom adsorbed on the surface of ZnO) to form sulfur trioxide (SO 3 ), and charge transfer is observed from ZnO to CNT, which enhances the change in resistance of the composite sensor upon exposure to SO 2 gas.

Mechanical Performance and Applications of CNTs Reinforced Polymer Composites—A Review

“…Variations in the barrier potential of CNTs-metal contact or CNTs-CNTs junctions cause changes in CNT resistance in defect free CNTs. The gases released during the combustion of fossil fuels, such as CO 2 [ 131 , 132 , 133 ], CO [ 134 , 135 , 136 , 137 ], SO 2 [ 138 , 139 , 140 , 141 , 142 , 143 , 144 , 145 , 146 , 147 ], NO 2 [ 136 , 148 , 149 , 150 , 151 , 152 , 153 , 154 , 155 ], and NO [ 156 , 157 ], adsorb on the CNT surface either physically or chemically. Figure 6 shows the bonding behaviour and charge transfer between CNTs and the molecules of C–O.…”

An Electrospun Nanofibrous Sensor Based on a Porous (Cr/Zn) Slats Oxide for Voltammetric Detection of Ezetimibe Drug in Real Samples

“…The SW-AdsASV crests of 1.0 nmol L À 1 EZT in pH 6 (B-R buffer), and at E acc = 0.0 V for 40 s were recorded using different quantities [0.5 %-2.0 %] of [CrZn 3 ] BSO nano- In general, the pH of the analyte has a significant effect on the I c of modulated sensors because of the ion substitution reaction between the sample and the surface of the constructed sensor. Therefore, the effect of the various B-R buffers (2)(3)(4)(5)(6)(7)(8)(9)(10)(11) on the magnitude of I c in 1.0 nmol L À 1 EZT was evaluated at E acc = 0.0 V for 40 s using the 1.0 % [CrZn 3 ] MCPS, as shown in Figure S9. The magnitude of the ox.…”

“…In particular, the fabrication of sensor materials with novel nanostructures is essential to achieve superior electrochemical sensing performance [1]. Zinc oxide (ZnO) is an excellent n-type semiconductor with several advantages [2][3][4]. The minuscule size of the ZnO nanostructure could enhance the kinetic transfer rate of the analyte upon the surface of the material leading to reductions in the time required for the attendant analysis.…”

Oxygen sensing with individual ZnO:Sb micro-wires: effects of temperature and light exposure on the sensitivity and stability

“…When a ZnO wire is exposed to oxygen, some oxygen atoms get adsorbed to the wire's conducting layer, thus either compensating the vacancies or interacting with H impurities and in either case significantly reducing the conductance of the wire [1,[13][14][15][16][17]. Multiple sensing schemes and materials combinations have been proposed that revolve around the ZnO surface sensitivity to ambient gases [18][19][20][21][22]. Yet, light exposure and temperature increase also affect surface oxygen atoms and cause a large increase in conductance [23][24][25].…”