Journal of Hazardous Materials 244–245 (2013) 209–216 Contents lists available at SciVerse ScienceDirect Journal of Hazardous Materials jou rn al h om epage: www.elsevier.com/loc ate/jhazmat Comparative study on CO 2 and CO sensing performance of LaOCl-coated ZnO nanowires Nguyen Van Hieu ∗ , Nguyen Duc Khoang, Do Dang Trung, Le Duc Toan, Nguyen Van Duy, Nguyen Duc Hoa International Training Institute for Materials Science (ITIMS), Hanoi University of Science and Technology (HUST), No. 1 Dai Co Viet, Hanoi, Viet Nam h i g h l i g h t s ◮ High performance CO 2 and CO gas sensors were prepared via a simple route. ◮ CO 2 and CO gas-sensing performance of LaOCl-coated ZnO nanowires were compared. ◮ The coating LaOCl enhanced response to both CO 2 as well as CO gases. ◮ The LaOCl-coating sensors had short response–recovery time to CO 2 , but not to CO. a r t i c l e i n f o Article history: Received 17 May 2012 Received in revised form 8 November 2012 Accepted 10 November 2012 Available online xxx Keywords: ZnO nanowires LaOCl Functionalization Gas sensor a b s t r a c t Carbon dioxide (CO 2 ) and carbon monoxide (CO) emissions from industries and combustion fuels such as coal, oil, hydrocarbon, and natural gases are increasing, thus causing environmental pollution and climate change. The selective detection of CO 2 and CO gases is important for environmental monitoring and industrial safety applications. In this work, LaOCl-coated ZnO nanowires (NWs) sensors are fabricated and characterized for the detection of CO 2 (250–4000 ppm) and CO (10–200 ppm) gases at different operating temperatures. The effects of the LaCl 3 coating concentration and calcination temperature of the sensors are studied. They are found to have a strong influence on the sensing performance to CO 2 gas, but a relatively slight influence on that to CO. The LaOCl coating enhances the response and shortens the response and recovery times to CO 2 compared with those to CO. The enhanced response of the LaOCl- coated ZnO NW sensors is attributed to the extension of the electron depletion layer due to the formation of p-LaOCl/n-ZnO junctions on the surfaces of the ZnO NWs. © 2012 Elsevier B.V. All rights reserved. 1. Introduction In the past few years, great efforts have been made to reduce and prevent global warming and climate change. Among them, the monitoring and control of CO and CO 2 gas emissions from motor vehicles, industries, and other sources of pollutants are of great important. Thus, the new generation of gas sensors that are cost- effective, highly sensitive, highly selective, and stable has been extensively studied [1]. In practical, the selective detection of CO 2 and CO based on semiconductor gas sensors is still facing great chal- lenges for developing the sensing systems used in environmental monitoring as well as industrial safety applications [2]. ∗ Corresponding author at: International Training Institute for Materials Science (ITIMS), Hanoi University of Science and Technology (HUST), No.1, Dai Co Viet Road, Hanoi, Viet Nam. Tel.: +84 4 38680787; fax: +84 4 38692963. E-mail address: hieu@itims.edu.vn (N. Van Hieu). The functionalizing semiconductor metal oxides nanowires (NWs) with catalytic nanoparticles (NPs) are not only cost-effective but also is very powerful pathway for dramatically improving the sensitivity and selectivity of the NWs [3]. The enhancement of the gas-sensing properties of surface-functionalized NWs can be understood from different aspects, including the (i) manipulation of the acid-based properties of the NW surface, (ii) catalytic promotion, (iii) change in donor density, and (iv) extension of the electron depletion layer by establishing p–n junctions [6]. So far, various catalytic NPs such as Au, Pd, Pt, CuO, NiO, Co 3 O 4 , and La 2 O 3 have been employed to functionalize the surface of SnO 2 , ZnO, and In 2 O 3 NWs for enhancing selective detection of the NWs to various gases, including C 2 H 5 OH, H 2 S, NO 2 , CO, and H 2 [6–16]. Among these works, much attention has been devoted to the system of n-type semiconducting NWs functionalized with p-type catalytic NPs because they significantly improve the selectivity and sensitivity of the NWs-based sensors. For example, p-type CuO-functionalized SnO 2 NWs sensors increase the response to 20 ppm H 2 S up to 74-fold compared with pristine SnO 2 NWs sensor 0304-3894/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhazmat.2012.11.023