Selective fluorescent and colorimetric staining of polyurethane microplastics by using a solvatochromic-based dye applicable to environmental samples: Experimental and theoretical implication to adsorption mechanism

This study introduced a fluorescent and colorimetric dye, PPEO ((E)-1-phenyl-3-(pyrene-1-yl)prop-2-en-1one), optimized for the specific detection of polyurethane (PU) microplastics. The unique photophysical properties of PPEO, including solvatochromism, were comprehensively analyzed using UV–vis and fluorescence spectroscopy, along with theoretical calculations. The optimal staining condition for PU with PPEO was meticulously determined, focusing on solvent composition, staining time, and dye concentration. The optimal condition consisted of a 20% water/ethanol solution with a 10-min staining duration, which facilitated the differentiation of PU from other microplastics and non-plastic particles through distinctive green fluorescence and yellow coloration. Under the optimized conditions, the ability of PPEO to detect PU was consistent regardless of the size and color of PU, the degree of PU degradation, and pH variation of the solvent. Practically, PPEO could selectively detect PU over other microplastics in diverse environmental matrices, including water samples (from river and sea) and soil samples. The staining mechanism of PPEO to PU was proposed to be the adsorption process, based on various surface analyses like thermogravimetric analysis (TGA), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray photoelectron spectroscopy (XPS). Through extensive theoretical calculations, it was suggested that hydrogen bonding and Van der Waals (VdW) interaction would play a crucial role in the selective detection of PU by PPEO. These findings demonstrated that PPEO might prove to be an efficient and cost-effective agent for the identification and differentiation of PU, marking a significant advancement in the field of microplastics research.