Nitro-electron trapping engineering for enhanced BPA degradation by metal free nitro-COFs

Metal-free covalent organic frameworks (COFs) often face a critical trade-off wherein high photocatalytic activity relies on complex, expensive designs while cost-effective alternatives lack efficiency and stability. To address these issues, a nitro-functionalized COF (COF-NO₂) was developed via a one-step condensation method for bisphenol A (BPA) degradation. The –NO₂ groups act as intramolecular electron traps, narrowing the bandgap and boosting charge separation. COF-NO₂ achieved 97.3% BPA degradation within 120 min ( k  = 0.031 min −1 ) with over 85% efficiency across five consecutive cycles. Moreover, it exhibited high efficiency across a broad pH range (3−11) and showed broad-spectrum activity toward various bisphenols, including bisphenol S, bisphenol F, bisphenol C, and 4-chlorophenol. Quantitative structure–activity relationship analysis identified HOMO energy as the key descriptor governing degradation kinetics for bisphenols. In pretreated petrochemical wastewater, COF-NO₂ also attained over 75% BPA removal, demonstrating practical potential. This molecular design promoted ·O₂ − generation and selective bond cleavage in BPA, thereby enabling efficient mineralization and a 44% reduction in toxicity. A continuous-flow fluidized bed reactor was designed and achieved 97.4% BPA removal in 180 min through optimized light-flow coupling. Furthermore, low-cost g-C₃N 4 was introduced to integrate with highly active COF-NO₂, forming a composite that reduced material costs by 20% while maintaining over 80% degradation efficiency. This work presents a synergistic strategy combining molecular orbital engineering with heterojunction design, offering a feasible route to cost-effective and scalable metal-free COFs.