Plastic bags, primarily composed of carbon-carbon backbone polymers, are one of many manmade materials that persist in the environment due to their resistance to degradation and low recycling rates.
Scientists hope to reduce pollution by converting these high-carbon-content materials (up to 84.74 % carbon) into a feedstock for carbon quantum dots (CQDs).
CQDs are particularly effective for Fe3+ sensing because they have tunable fluorescent emissions, high stability, low toxicity, and can easily be surface modified. Fluorescence quenching through photoinduced electron transfer allows for high selectivity in detecting Fe3+ ions in water samples.
Conventional recycling processes to yield such feedstocks involve pyrolysis and hydrothermal techniques, which, although able to reduce synthesis times, typically require high temperatures and additives to enhance quantum yield. These conditions limit scalability and cost-efficiency.
To move toward sustainable, large-scale production, researchers sought to develop a method that minimizes chemical input and energy consumption without compromising performance.
Study: Optimized Pyrolysis-Hydrothermal Synthesis
The study, published in Carbon Research, introduces a modified synthesis process using pyrolysis followed by hydrothermal treatment with low concentrations of hydrogen peroxide (<7 wt %) as an oxidizing agent.
However, to reduce the energy cost of this method, the team systematically optimized three parameters: hydrogen peroxide concentration, hydrothermal duration, and the mass of pyrolysis product.
After shredding, one gram of plastic bag waste was pyrolyzed at 300 °C for four hours to produce crude carbon. This material was then mixed with hydrogen peroxide and processed in a Teflon-lined autoclave at 180 °C for varying times. The final CQD-containing solution was isolated via centrifugation at 4000 rpm in two 15-minute cycles.
Performance and Stability Testing
To assess optical stability, CQDs were exposed to ultraviolet light (0-120 min), and their fluorescence spectra were recorded. Long-term stability was evaluated by monitoring fluorescence intensity at ambient conditions over 35 days.
The CQDs were also assessed for stability across a wide pH range (pH 2-13) and in NaCl solutions of varying ionic strength (0.5 to 2.0 M).
The team tested the sensitivity and selectivity of the synthesized CQDs for Fe3+ detection using both drinking and river water samples spiked with Fe3+ at 0, 40, and 80 µM concentrations.
Fluorescence was measured at 320 nm and the CQDs showed a strong linear response to Fe3+, with a high correlation coefficient (R2 = 0.9983) and a low detection limit of 9.50 µM.
Recovery rates ranged from 94 % to 102 %, and relative standard deviations were consistently low (0.06 % to 0.44 %), indicating the method's reliability for practical sensing applications.
Structural and Optical Characteristics
Under the optimized synthesis conditions of six hours of hydrothermal conversion, 0.25 g of pyrolysis product, and five wt % hydrogen peroxide, CQDs were synthesized that displayed bright blue fluorescence under UV light and appeared yellow under visible light, with a quantum yield of 10.04 %.
Microscopic and spectroscopic analyses revealed a graphite-like carbon framework with oxygen-containing surface defects. The conversion mechanism involved polymer bond cleavage during pyrolysis, followed by oxidation, carbonization, and passivation during hydrothermal treatment.
Download your PDF now!
Industrial and Environmental Relevance
The study's proposed method offers a simplified, scalable route for CQD production using plastic bag waste.
With its low temperature requirements, reduced chemical usage, short synthesis time, and minimal operational costs, it is positioned as a viable strategy for industrial nanomaterials production and environmental monitoring.
Journal Reference
Lestari, R., Kamiya, Y., Wahyuningsih, T. D., Kartini, I. (2025). Recycling of plastic bag waste into carbon quantum dots using optimized pyrolysis-hydrothermal methods for selective Fe (III) sensing. Carbon Research, 4(1), 51. DOI: 10.1007/s44246-025-00221-9, https://link.springer.com/article/10.1007/s44246-025-00221-9
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.