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Abstract
Zinc oxide (ZnO) nanostructures were synthesized on carbon nanotubes cotton (CNTC) network as flexible substrate. The impact of synthesis temperature on structural and morphology of zinc oxide nanostructures via chemical bath deposition method was investigated. The CNTC was derived from environmentally friendly hydrocarbon source of waste cooking palm oil. The nanostructures were grown with prior deposition of ZnO buffer layer for growth patterning localization. It was observed that high temperature influenced the morphology of zinc nanorod (ZNR) grown on CNTC and its aspect ratio. In addition, the electrical conductivity of the ZNR/CNTC hybrid was found to be higher than that of the CNTC alone indicates that the hybridized material provides seamless passage that efficiently allow more electron movement passing through it. This hybrid offers promising future as CNTC substate is flexible, readily available hydrocarbon source, and low cost. It also could be a useful material in the applications of solar energy and sensors.
Introduction
The development of hybrid nanomaterials combining metal oxides with carbon-based substrates has garnered significant interest due to their potential in flexible electronics, energy harvesting, and sensing applications. Zinc oxide (ZnO) is a versatile semiconductor with a wide bandgap (3.37 eV) and high exciton binding energy (60 meV), making it suitable for optoelectronic and piezoelectric applications. Carbon nanotubes cotton (CNTC), derived from waste cooking palm oil, offers a flexible, lightweight, and sustainable substrate. This study evaluates the growth of ZnO nanostructures (ZNR) on CNTC using chemical bath deposition (CBD) and examines the effects of synthesis temperature on their structural, morphological, and electrical properties.
Carbon nanotube cotton (CNTC) is a flexible material that can be integrated with commercial substrates such as polyethylene terephthalate (PET) and polyethersulfone (PES), making it suitable for practical applications in filtration, water treatment, and as an adsorbent for oil spill cleanup. Carbon nanotubes (CNTs) exhibit remarkable versatility, existing in various forms such as powder, sheets, and highly detailed nanostructures, each with distinct structural and morphological characteristics. The CNT powder, as seen in the Fig. 1 (i), appears as a fine, black granular material, typically derived from carbon-rich precursors, offering a high surface area suitable for numerous applications. Fig. 2 (ii) shows CNT sheet, a flexible and cohesive structure formed by assembling CNT networks, which demonstrates the material's potential for scalable and adaptable uses. Under magnification, as revealed in Fig 1 (iii) and (iv), CNTs display intricate fibrous networks with a highly porous and interconnected morphology, highlighting their nanoscale tubular structure and uniformity. These microscopic views, captured via scanning electron microscopy, emphasize the material's exceptional structural integrity and surface texture, which are critical for advanced technological applications.
Fig. 1: The CNTs in various forms, (i) powder, (ii) in bulk, (iii) sheet, (iv) network of nanotubes under high maginfication
The motivation of this study is on enhancing the electrical and optical properties of nano-scaled zinc oxide (ZnO), a material widely recognized for its semiconductor characteristics and potential applications in optoelectronics, sensors, and energy devices. The key challenge lies in optimizing these properties, which are significantly influenced by the physical dimensions of ZnO nanorods, specifically their length and diameter. Variations in these dimensions can alter the material's bandgap, charge carrier mobility, and light absorption or emission capabilities, thereby affecting its performance in practical applications. To address this, the proposed solution involves systematically varying the synthesis temperature during the growth process of ZnO nanorods. This approach allows for a detailed examination of how temperature impacts the growth kinetics, crystal structure, and morphology of the nanorods. By adjusting the synthesis temperature, it is possible to control the aspect ratio and alignment of the nanorods, which in turn can enhance their electrical conductivity and optical responsiveness. This method provides a pathway to tailor the material properties for specific needs, such as improving efficiency in solar cells or sensitivity in gas sensors, leveraging the direct correlation between synthesis conditions and the resulting nanorod characteristics.
Results and Discussion
Morphology and Structural Analysis
Fig 2: (i) ZnO buffer layer on CNTC and ZnO nanostructures growth at temperatures of (ii) 60 ℃, (iii) 90 ℃ and (iv) 120 ℃
FESEM images in Fig. 2 revealed that the morphology of ZnO nanostructures was significantly influenced by synthesis temperature. At 60°C, the nanostructures exhibited short, irregularly shaped nanorods with low aspect ratios. At 90°C, well-define ZNR with improved alignment and higher aspect ratios (length-to-diameter ratio ~10) were observed. At 120°C, the nanorods became longer and denser, with aspect ratios reaching ~12, indicating enhanced growth kinetics at higher temperatures. The ZnO buffer layer ensured uniform nucleation and localization of ZNR on the CNTC surface. XRD analysis confirmed the formation of wurtzite-phase ZnO with a preferential (002) orientation, indicating vertical growth of nanorods along the c-axis. The crystallinity improved with increasing temperature, as evidenced by sharper and more intense diffraction peaks at 120°C.
Electrical Conductivity
The electrical conductivity of the ZNR/CNTC hybrid was significantly higher than that of bare CNTC. At room temperature, the CNTC exhibited a conductivity of approximately 3 S/cm, while the ZNR/CNTC hybrid synthesized at 120°C showed a conductivity of 8 S/cm. The enhanced conductivity is attributed to the seamless integration of ZnO nanorods with the CNTC network, which facilitates efficient electron transport through the hybrid structure. The ZNR provide additional conductive pathways, reducing the contact resistance within the CNTC matrix.
Conclusion
This study highlights the significant influence of synthesis temperature on the material's morphology, crystallinity, and electrical performance. The findings demonstrate that higher temperatures enhance the growth of well-aligned, high-aspect-ratio nanorods and improve crystallinity, leading to a hybrid material with superior electrical conductivity compared to bare CNTC. The use of an environmentally friendly CNTC substrate derived from waste cooking palm oil further emphasizes the potential for sustainable and cost-effective production. These results suggest that the ZNR/CNTC hybrid holds great promise for practical applications in flexible electronics, solar energy, and sensing technologies, offering a versatile and efficient material platform for future innovations.
References
Written by:
Juraina Md Yusof
Functional Nanomaterials Devices Laboratory
Institute of Nanoscience and Nanotechnology
Date of Input: 28/08/2025 | Updated: 28/08/2025 | roslina_ar
Institute of Nanoscience and Nanotechnology,
Universiti Putra Malaysia,
43400 Serdang,
Selangor Darul Ehsan, Malaysia
