From Naturally Occurring to Engineered Nano-Biochar: Properties, Feasibility, and Challenges for Sustainable Environmental Remediation.

Nano-biochar, present both as naturally occurring pyrogenic carbon and as an engineered product of controlled pyrolysis, with particle sizes typically ranging from a few to several hundred nanometers, exhibits up to 97-fold greater specific surface area, 20-fold higher maximum adsorption capacity for methylene blue, and enriched oxygen-containing surface functional groups (e.g., ─OH, ─COOH, ─C═O) relative to bulk biochar, emerging as a promising nanomaterial for environmental remediation. Despite growing research interest, existing reviews have focused predominantly on its beneficial properties, leaving toxicity, recoverability, and scalability insufficiently addressed, which limits the translation of nanoscale properties into engineering practice. To bridge this gap, this review critically synthesizes current knowledge on nano-biochar from an engineering application perspective, covering its properties, remediation benefits, technical feasibility, and integration with advanced technologies including artificial intelligence, membrane reactors, advanced oxidation processes, and 3D printing. Application risks and safeguard strategies are critically assessed, alongside a conceptual sustainable paradigm to connect nanoscale material performance with real-world deployment. Future studies are suggested to prioritize reliable detection techniques, improved recovery or detoxification strategies, and low-input, high-efficiency technologies within a One Health framework to ensure safe deployment.