Tailored graphene quantum dots improve heavy-metal immobilization in municipal solid waste incineration fly ash under low-cement conditions

Cement solidification/stabilization is widely used to immobilize heavy metals in municipal solid waste incineration fly ash (IFA), but the need for relatively high cement dosages increases the volume of solidified products, treatment cost, and landfill pressure. This study hypothesizes that highly dispersed, oxygen-functionalized graphene quantum dots (GQDs) can enhance heavy metal immobilization under low-cement conditions by promoting hydration-product formation and providing additional metal-binding sites. To test this hypothesis, tailored GQDs were synthesized and incorporated into cement-IFA matrices with a cement-to-IFA mass ratio of 1:5. The immobilization performance and mechanism were evaluated using combined leaching, speciation, microstructural, solution removal, and molecular dynamics analyses. The optimized GQD-modified matrix reduced Pb, Cd, and Zn leaching by 61.7–85.6% and promoted their transformation into more stable chemical fractions. Multiscale analyses indicate that GQDs promote the formation and polymerization of calcium (alumino) silicate hydrate gels, thereby strengthening the physical encapsulation of heavy metals. Meanwhile, oxygen-containing surface groups on GQDs interact with heavy metal ions and suppress their mobility. These synergistic effects improve heavy metal immobilization in the low-cement IFA treatment system. This study provides a feasible strategy for enhancing hazardous IFA treatment under low-cement conditions and suggests a potential engineering application for GQDs. © 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.