Defect Engineering in Carbon-Based Metal-FreeCatalysts: Active Sites, Reduction Mechanisms, and 3D Architectures forSustainable 4-Nitrophenol Reduction

Abstract

Nitrophenols (NPs), classified as priority pollutantsdue to their significant toxicity, persistence, and bioaccumulation potential,pose severe threats to ecosystems and human health. Catalytic reduction,particularly the conversion of NPs like 4-nitrophenol (4-NP) to less toxicaminophenols using sodium borohydride (NaBH₄), represents apromising remediation strategy. While conventional metal-based catalysts facelimitations including high cost, poor durability, and potential metal leaching,carbon-based metal-free catalysts (C-MFCs) have emerged as highly efficient,sustainable, and cost-effective alternatives. However, the precise reactionmechanisms governing NP reduction over C-MFCs remain ambiguous, and significantdebate surrounds the nature of the active sites and the structure-activityrelationships dictating performance. This review systematically elucidates thecatalytic sites and associated reduction mechanisms in C-MFCs. Wecomprehensively summarize design principles centered on defect engineeringstrategies, encompassing single-atom (N, S, B, P, O), dual-atom (B,N; N,S;N,P), and tri-atom (B,N,F; N,P,F) doping, alongside non-doping defects such asedge and pore defects. The critical structure-performance relationships linkingthese engineered active sites to catalytic activity (e.g., turnover frequency,TOF) are analyzed, integrating experimental evidence and theoretical insights.Furthermore, strategies for constructing three-dimensional architectures toenhance active site accessibility and catalyst stability are highlighted. Thiswork provides fundamental insights to guide the rational design ofnext-generation high-performance C-MFCs for sustainable nitrophenol pollutioncontrol.

Keywords

Carbon-based metal-free catalysts / Nitrophenols / Catalytic reduction / Catalytic hydrogenation mechanisms / Environmentalremediation

Acknowledgments

The work was financially supported by the Fund of National Natural Science Foundation of China (No. 52063016, No. 52372048, No. 52202336), the Fund of Key Laboratory of Advanced Materials of Ministry of Education (No. Advmat-2421).

Author Contributions

Investigation, Software, Writing—Original Draft Preparation, X.Y.; Resources, Q.L.; Validation, Conceptualization, Funding, L.W.; Investigation, Funding, Formal analysis, B.Z.; Funding, Formal analysis, Z.W. Supervision, Project administration, Funding, Z.H.; Writing—review & editing, Project administration, Conceptualization, M.W.

Ethics Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Relevant information and dates can be made available upon request.

Funding

We express our thanks for funding support from the National Natural Science Foundation of China (No. 52063016, No. 52372048, No. 52202336), the Key Laboratory of Advanced Materials of Ministry of Education (No. Advmat-2421).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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