Layer-By-Layer Assembly of π-Conjugated Amine and ZnO Nanohybrids for Room Temperature CO2 Detection
Authors: Mandal Biswajit , Biswas Ankan , Shree Aarya , Das Apurba K. , Mukherjee Shaibal 
Published: May 2020

I. Abstract
Present study explores on the development of low molecular weight π-conjugated organic amine and metal oxide based nanohybrids for room temperature carbon dioxide (CO2) sensing application rather than using conventional polymer of organo-amines [1-4]. In this study, in-situ growth of naphthalene based π-conjugated amine (NBA) and zinc oxide (ZnO) nanohybrids thin-film were grown and their room temperature CO2 sensing performance is investigated.
II. Experimental
In a typical experimental procedure, equimolar Zn(NO3)2∙6H2O and hexamethylenetetramine (HMTA) were added in a 20 mL of deionized water under constant stirring for 15 min at 65 °C, then NBA (10 mg) was added slowly in the solution under vigorous stirring until the solution becomes uniform reddish color. After that, the solution was transferred into a Teflon lined autoclave where the flexible substrate was placed vertically in the solution and kept at 95 °C for 3 h reaction time.
III. Results and discussion
Figure 1(a) shows FESEM image of hexagonal NBA-ZnO nanohybrids. EDX pattern of the NBA-ZnO nanohybrids reveals the presence of elemental C, N, Zn, and O. The sensor response to 500 ppm, 1000 ppm, 2000 ppm, 5000, and 10000 ppm CO2 were 9.1, 14.2, 21.4, 30.3, and 36.6, respectively (Figure 1(b)). The sensor response to 23%, 43%, 62%, and 85% RH was 29.9%, 29.2%, 29.4%, and 29.2%, respectively. The response changes were negligible with the increase in the relative humidity, which can be attributed to the hydrophobic nature of NBA (due to the presence of hydrophobic phenyl and naphthalene rings). During hydrothermal synthesis of NBA-ZnO nanohybrids, in the beginning, hexagonal zinc hydroxide nuclei forms from the reaction of reagents (Zn(NO3)2∙6H2O and HMTA) in the solution with the help of temperature treatment at 65 °C and constant stirring. After adding NBA in the solution, the carboxylic groups of NBA create covalent bonds with zinc hydroxide to give structural stability to the nanohybrid architecture. At the same time, the hexagonal zinc hydroxide nuclei get transformed into the nuclei of inorganic-hydroxide phases in the lamellar NBA-ZnO hybrid (Figure 1(c)).

Acknowledgment

Biswajit Mandal grateful to MeitY for providing fellowship under Visvesvaraya PhD scheme for Electronics and IT. Prof. Shaibal Mukherjee is thankful to MeitY for Young Faculty Research Fellowship (YFRF) under Visvesvaraya PhD scheme for Electronics and IT. This publication is an outcome of the R&D work undertaken in the project under the Visvesvaraya PhD scheme of Ministry of Electronics & Information Technology, being implemented by Digital India Corporation. Authors are thankful to FESEM and EDX facilities, which are integral parts of Sophisticated Instrument Centre (SIC) of IIT Indore.

References

[1] R. Zhou, D. Schmeisser, and W. Göpel, “Mass sensitive detection of carbon dioxide by amino group-functionalized polymers,” Sensors Actuators B Chem., vol. 33, no. 1–3, pp. 188–193, Jul. 1996.
[2] M. S. Nieuwenhuizen and A. J. Nederlof, “A SAW gas sensor for carbon dioxide and water. Preliminary experiments,” Sensors Actuators B Chem., vol. 2, no. 2, pp. 97–101, May 1990.
[3] B. Sun, G. Xie, Y. Jiang, and X. Li, “Comparative CO2-Sensing Characteristic Studies of PEI and PEI/Starch Thin Film Sensors,” Energy Procedia, vol. 12, pp. 726–732, Jan. 2011.
[4] R. Zhou, S. Vaihinger, K. E. Geckeler, and W. Göpel, “Reliable CO2 sensors with silicon-based polymers on quartz microbalance transducers,” Sensors Actuators B Chem., vol. 19, no. 1–3, pp. 415–420, Apr. 1994.

Figure 1