Carbon quantum dots for photocatalytic wastewater treatment: Mechanistic insights and economic feasibility

Carbon quantum dots (CQDs) have emerged as versatile photocatalytic agents owing to their tunable band structures, abundant surface functionalities, and excellent electron–hole separation capacity. Despite numerous reports of high pollutant degradation efficiencies, progress toward real-world implementation remains fragmented. This systematic review, conducted under Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines which synthesizes 105 high-quality studies published between 2020 and 2025. Distinct from prior narrative reviews, this study focuses on linking synthesis strategies including hydrothermal, microwave-assisted, solvothermal, and biomass-derived routes with application outcomes across antibiotics, dyes, and phenolic pollutants. The analysis highlights the growing role of biomass precursors as sustainable alternatives to chemical feedstocks, while also identifying trade-offs in yield, doping control, and scalability. A techno-economic lens is introduced, comparing precursor costs and estimating treatment costs per cubic meter of wastewater. While 90% degradation efficiencies are frequently achieved, challenges remain in energy demand, long-term stability, and performance under complex wastewater matrices. This review consolidates the evidence base and proposes a roadmap for scalable and cost-effective CQDs-based photocatalysis, offering practical insights to bridge laboratory innovation with industrial application. © 2026 Elsevier Ltd