Fluorescent Polyethylene by In Situ Facile Synthesis of Carbon Quantum Dots Facilitated by Silica Nanoparticle Agglomerates

Abstract

We describe an in situ facile synthetic approach to prepare carbon quantum dot (CQD) fluorescent markers (FMs) for polyethylene (PE) in the presence of agglomerated silica nanoparticles (SiO2 NPs) under mild reaction conditions. First SiO2 NPs, prepared by the Stöber method, were dispersed in toluene. This dispersion was added to a PE solution in toluene. After heating (either in air or under Ar) a fluorescent mixture was obtained. After drying, PE films were obtained by compression molding, which showed strong blue fluorescence, attributed to CQDs. SiO2 NPs loading values varied between 0.5 and 4 wt %. Subsequent to isolation, the fluorescent CQDs were characterized by TEM, UV–vis, and fluorescence spectroscopy. TEM imaging unveiled a lattice spacing value of 0.21 nm of the isolated fluorescent particles which is typical for (100) graphite plane lattice spacing in CQDs. UV spectroscopy and fluorescence measurements show characteristic absorption and excitation spectra for the aromatic core and oxidized surface defects typically observed for CQDs. The emission maximum for PE/CQD samples increased from 394 to 408 nm when the reaction temperature was decreased from 110 to 90 °C, which is attributed to increasing oxygen content in the reaction mixture upon decreasing the reaction temperature. When the reaction was performed under Ar, the PE/CQD samples emitted in the ultraviolet region (286 nm). Finally, we demonstrated that PE samples marked with CQDs can be easily visually identified upon irradiating with 367 nm light. Thus, the marked PE can be used, for example, as a labeling ingredient in master batches for component identification and in recycling.

Photoluminescence Performance and Photocatalytic Activity of Modified Carbon Quantum Dots Derived from Pluronic F127

“…The UV-Vis absorption spectra of the samples are displayed in Figure 4 a. To our knowledge, the absorption peaks caused by the π-π* transition (C=C) and the n-π* transition (C=O) were located in the range of 200–300 nm for all samples [ 26 , 38 , 39 , 40 ]. Figure 4 b shows the PL emission peaks for samples of O-CQDs, N-CQDs, and Cl-CQDs at different excitation wavelengths (280 nm, 280 nm, and 380 nm, respectively).…”

Enabling the Polymer Circular Economy: Innovations in Photoluminescent Labeling of Plastic Waste for Enhanced Sorting

“…The synthesized CQDs could be extracted from the residual materials and reinserted into virgin PE to label them, or alternately, the crude reaction material could be mixed directly with virgin PE at a 10 wt % loading. 36 Both forms of CQDlabeled PE were visibly distinct from unlabeled PE when viewed under UV (367 nm) light (Figure 7). However, it is not yet clear whether the additional incorporation of the degraded PE and SiO 2 nanoparticles has an appreciable effect on the mechanical properties of the labeled PE.…”

“…The synthesized CQDs could be extracted from the residual materials and reinserted into virgin PE to label them, or alternately, the crude reaction material could be mixed directly with virgin PE at a 10 wt % loading . Both forms of CQD-labeled PE were visibly distinct from unlabeled PE when viewed under UV (367 nm) light (Figure ).…”

“…In one of the most recent publications on the use of photoluminescent markers in commodity plastics, Yin et al took a slightly different approach by incorporating SiO 2 nanoparticles into a PE solution. 36 The SiO 2 nanoparticles in this study were not designed to be emissive and are instead used in the method as an active site to partially degrade PE under moderate heating into photoluminescent carbon quantum dots (CQDs). CQDs are a small particulate (<10 nm) allotrope of carbon, often with some type of surface passivation.…”

“…The sample shapes relate to pure PE (rectangles), the crude PE material containing CQDs and SiO 2 (circles), and PE containing only the isolated CQDs (triangles). Reproduced from ref . Copyright 2021 American Chemical Society.…”