SAIP2026

CH 4 detection capabilities of Co 3 O 4 - ZnO nanofibers: synergistic effects of p-n junction

8 Jul 2026, 15:50

20m

Lecture Hall GH1 (University of the Western Cape)

Oral Presentation Track A - Physics of Condensed Matter and Materials Physics of Condensed Matter and Materials

Speaker

Ms Khanyisile Nkuna (Materials Physics Research Institute (MPRI), School of Physics, University of the Witwatersrand, Johannesburg 2000, South Africa)

Description

Khanyisile Nkuna1*, Rudolph Erasmus1, Teboho Mokhena2 and Katekani Shingange1
1Materials Physics Research Institute (MPRI), School of Physics, University of the Witwatersrand, Johannesburg 2000, South Africa
2Mintek Nanotechnology Innovation Centre, Randburg 2194, South Africa
Correspondence: 2318077@students.wits.ac.za

Abstract :
Chemiresistive gas sensors are widely used for gas detection due to their low cost, simple fabrication, and rapid response. These sensors operate by changing electrical resistance when exposed to target gases, making them suitable for environmental monitoring, industrial safety, and healthcare applications. However, their performance is often limited by poor selectivity, low sensitivity in complex environments, and instability under varying operating conditions. The combination of p-type and n-type semiconductor materials to form a heterojunction is an effective strategy to overcome these limitations. In this study, one-dimensional (1D) cobalt oxide (Co3O4) and zinc oxide (ZnO) nanofibers were combined to form a p-n heterojunction (Co3O4-ZnO) using the electrospinning technique. Co3O4 exhibits excellent catalytic activity and p-type conductivity, while ZnO is a stable n-type semiconductor with high electron mobility. The heterojunction enhances charge separation and transfer, thereby improving gas response and sensitivity. ZnO, Co3O4, and Co3O4-ZnO were successfully synthesized via electrospinning. X-ray diffraction (XRD) confirmed that ZnO has a hexagonal wurtzite structure, Co₃O₄ has a spinel cubic structure, and both phases co-exist in the composite. Scanning electron microscopy (SEM) showed smooth nanofibers before annealing and coarser structures after annealing. The band gaps of ZnO, Co3O4, and Co3O4-ZnO were determined to be 3.39 eV, 2.55 eV, and 3.61 eV, respectively, using diffuse reflectance spectroscopy (DRS). Photoluminescence (PL) analysis revealed defect-related emission bands centred at 488 nm and 688 nm.The materials demonstrated selective detection of methane (CH4) at an operating temperature of 300 °C. The gas sensing mechanism and contributing factors will be further discussed.

Keywords : Gas sensor , 1D , ZnO, Co3O4, p-n heterojunction.