Effect of solution concentration on the physicochemical and electrostatic air-cleaning properties of electrodeposited Zn thin films

Abstract

In this study, zinc (Zn) thin films were electrodeposited on steel substrates using final deposition-bath ZnSO₄·7H₂O electrolyte concentrations of 40, 60, 80, and 100 mM to investigate their physicochemical properties and electrostatic air-cleaning (EAC) performance. The structural, morphological, and surface characteristics of the films were systematically correlated with particulate removal performance. X-ray diffraction (XRD) confirmed the formation of polycrystalline hexagonal close-packed (HCP) crystal structure of Zn, with the crystallite size increasing from 43.4 nm to 62.1 nm as the electrolyte concentration increased to 80 mM and subsequently decreasing to 53.7 nm at 100 mM. Atomic force microscopy (AFM) revealed an increase in average particle size from 205.58 nm to 370.45 nm and root mean square (RMS) surface roughness from 53.39 nm to 95.2 nm up to 80 mM, followed by a decrease to 219.1 nm and 54.89 nm, respectively, at 100 mM. The optimized ZM₃ electrode, deposited from a final bath concentration of 80 mM exhibited a thickness of 678 ± 2 nm and porous nanoflake morphology with nanoflake thickness of approximately 50–62 nm. Under an applied voltage of ± 8.5 kV, ZM₃ generated the highest negative-ion concentration of approximately 3.60 × 10⁵ ions cm^− 3. Consequently, it achieved the maximum particle removal efficiency (PRE) of 80.30 ± 1.10% within 120 s and an air-cleaning factor (ACF) of 11.39 ± 0.37 after 405 s, compared with 7.15 ± 0.25 for the uncoated steel electrode. Furthermore, the time required for the measured concentrations in the experimental chamber for ZM₃ EAC are found to be 135 s for PM_2.5 and 75 s for PM₁₀, respectively, while maintaining a low ozone concentration of 0.030 ppm after 405 s. The results demonstrate that electrolyte concentration strongly influences Zn-film crystallinity, particle size, surface roughness, morphology, ion generation, and EAC performance, with 80 mM providing the optimum balance for rapid particulate removal and enhanced indoor air-cleaning performance under controlled laboratory conditions.