A synergistic adsorption and on-mode fluorescent detection based on directly grown Co₃O₄@ZIF-8 nanocomposites for...

Here in, a fluorescent Co₃O₄@ZIF-8 nanocomposite was synthesized by embedding Co₃O₄ nanoparticles within Zeolitic Imidazolate Framework-8 (ZIF-8) during room-temperature growth. Formaldehyde sensing arises from a synergistic adsorption-photoluminescence coupling: initial rapid physical adsorption of formaldehyde within ZIF-8 micropores, followed by chemisorption on embedded Co₃O₄ surfaces. The ZIF-8 framework provides high surface area and accessible pore walls, enabling diffusion and weak interactions (viz., van der Waals forces and hydrogen bonding with imidazolate N atoms) that modulate the local environment around fluorophores. Co₃O₄ a p-type semiconductor with Co²⁺/Co³⁺, offers Lewis acid sites that form strong interactions with the formaldehyde carbonyl, enabling partial charge transfer and surface binding that further influence the photoluminescent state. Collectively, these coupled adsorption events alter the local electronic environment and enhance fluorescence, with a measurable emission increase at 417 nm upon 350 nm excitation. The composite's properties were examined using various techniques such as Powder X-ray diffraction (PXRD), Field-emission scanning electron microscopy (FE-SEM), Energy dispersive X-ray analysis mapping (EDX), and transmission electron microscopy (TEM). The composite showed increased fluorescence intensity (On-mode) in the presence of formaldehyde, with a detection range from 0.1 to 11 μg mL^-1. The detection limit was obtained 0.051 μg mL-1. This fluorescence-based detection method was successfully used to measure formaldehyde levels in industrial wastewater, hospital and medical center, research laboratory, Bahmanshir water, Abadan industrial town, and municipal water sources.