Bifunctional sensor of pentachlorophenol and copper ions based on nanostructured hybrid films of humic acid and exfoliated layered double hydroxide via a facile layer-by-layer assembly

Abstract

A new, highly sensitive bifunctional electrochemical sensor for the simultaneous determination of pentachlorophenol (PCP) and copper ions (Cu2+) has been developed, where organic–inorganic hybrid ultrathin films were fabricated by alternate assembly of humic acid (HA) and exfoliated Mg–Al-layered double hydroxide (LDH) nanosheets onto ITO substrates via a layer-by-layer (LBL) approach. The multilayer films were then characterized by means of UV–vis spectrometry, scanning electron microscopy (SEM), and atomic force microscope (AFM). These films were found to have a relatively smooth surface with almost equal amounts of HA incorporated in each cycle. Its electrochemical performance was systematically investigated. Our results demonstrate that such a newly designed (LDH/HA)n multilayer films, combining the individual properties of HA (dual recognition ability for organic herbicides and metal ions) together with LDH nanosheets (a rigid inorganic matrix), can be applied to the simultaneous analysis of PCP and Cu(II) without interference from each other. The LBL assembled nanoarchitectures were further investigated by X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR), which provides insight for bifunctional sensing behavior. Under the optimized conditions, the detection limit was found to be as low as 0.4nM PCP, well below the guideline value of PCP in drinking water (3.7nM) set by the United States Environmental Protection Agency (U.S. EPA), and 2.0nM Cu2+, much below the guideline value (2.0mgL−1, ~31.2nM) from the World Health Organization (WHO), respectively. Toward the goal for practical applications, this simple and cost-effective probe was further evaluated by monitoring PCP and Cu(II) in water samples.