Mechanochemical fabrication of ZnO nanoparticle inks for eco-friendly low-cost thin film environmental sensors
Date
2026
Authors
Boakye, Gibson Asumani
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Abstract
The increasing demand for low-cost, scalable, and energy-efficient sensing technologies has driven significant interest in nanomaterial-based thin film sensors. This thesis presents the fabrication and characterization of zinc oxide (ZnO) nanoinks via a low processing temperature mechanochemical planetary ball milling (PBM) approach for the fabrication of eco-friendly, flexible, and low-cost gas sensors. The study focuses on establishing a low input energy, simple and scalable solution-based process that enables the direct conversion of bulk ZnO powder into functional nanoinks suitable for thin film deposition. ZnO nanoinks were prepared through wet ball milling under varying conditions, including milling speed 200 rpm to 1000 rpm, time 10 minutes to 120 minutes, and solvent type (DI water, ethylene glycol and Isopropyl alcohol), to investigate their influence on nanoparticle size, morphology, and dispersion. Thin films were subsequently fabricated by deposited the nanoinks onto a wide range of low-cost substrates including glass slide, filter, plain and lined paper, plastic polymer, foil, ceramic and flexible materials using an adjustable blade applicator technique to form films with controlled thickness (15 μm to 50 μm) and uniformity. The versatility of substrate selection highlights the potential for low-cost and flexible sensor fabrication. Material characterization was conducted using techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy, and energy dispersive X-ray spectroscopy (EDX), confirming the formation of nanoscale ZnO. Variations in milling conditions were observed to affect particle size, dispersion, and film morphology. Initial gas sensing measurements of the fabricated ZnO thin films on different substrates was evaluated under various conditions, including different gas species (Hydrogen, dry air and argon), gas concentrations (low and high), and different flow systems (static and continuous flow) at room temperature. The sensors demonstrated measurable and reproducible responses across both low and high gas concentrations, with response magnitude increasing as gas concentration increased. These results represent a proof-of-concept for room-temperature sensing using solution-processed ZnO films. The data indicated that sensors milled at 200 rpm had response times of 610–750 seconds under static flow, and 750 rpm sample reaches about 2100 seconds under continuous flow. Recovery times were generally faster with less variations, 560–660 seconds for most samples. Glass-based films generally exhibited quicker response and recovery kinetics than paper-based substrates. The sensing mechanism may be attributed to surface adsorption and desorption processes involving oxygen species, which modulate charge carrier concentration and electrical conductivity upon exposure to target gases. This work demonstrates that PBM-fabricated ZnO nanoinks enable low-cost, scalable fabrication of flexible thin film gas sensors. The preliminary gas sensing results provide insight into how processing conditions influence material properties and sensing behavior, highlighting potential for environmental, industrial, and wearable sensing applications.
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Keywords
zinc oxide nanoinks, mechanochemical planetary ball milling (PBM), flexible thin film gas sensors, room-temperature sensing, printed eco-friendly electronics