[论文解读] Decoupling Precipitation and Surface Complexation during Mn(II) Removal by Biochar via Experiments and Atomistic Simulations

Audrey Ngambia, Anastasiia Gavrilova+5 more|arXiv (Cornell University)|Mar 23, 2026

Adsorption and biosorption for pollutant removal被引用 0

一句话总结

本研究结合实验与原子级模拟，将生物炭对 Mn(II) 的去除解耦为沉淀驱动路径和表面络合驱动路径，揭示进料原料、热解温度及表面去质子化如何控制机制。

ABSTRACT

Manganese(II) mobilised by mining activity poses a persistent water-quality challenge, yet the mechanisms by which low-cost sorbents, such as biochar, sequester Mn(II) remain poorly resolved. This study identifies the specific chemical drivers of Mn(II) sequestration by combining fixed-bed column and batch experiments with atomistic molecular dynamics simulations. Oilseed rape straw biochars, produced at 350 extdegree C, 550 extdegree C, and 700 extdegree C, removed 20-50% of dissolved Mn from acidic influent (pH 4, 5 ppm). High-temperature biochar achieved the greatest removal ($\sim$50%) and rapidly increased effluent pH to 9, triggering alkaline precipitation. Conversely, lower-temperature biochars removed 20-30% of Mn while maintaining a near-neutral pH (7-7.5). Enhanced \ce{K+} release in these systems indicates significant cation exchange and non-precipitative pathways. Molecular simulations confirmed that while neutral surfaces show weak Mn(II) association, deprotonated sites drive strong adsorption through inner-sphere complexation ($\sim$50% removal) and outer-sphere association ($\sim$10%). These results establish a mechanistic framework to distinguish between precipitation-led and surface-complexation-led removal. By providing specific chemical criteria for Mn-targeted sequestration, this work enables the rational design of engineered biochars for sustainable water remediation.

研究动机与目标

• Identify how biochar pyrolysis temperature and feedstock influence Mn(II) sequestration mechanisms.
• Decouple Mn removal into precipitation, cation exchange, and surface complexation pathways.
• Use atomistic simulations to resolve surface interactions without ash contributions.
• Link experimental observations with molecular-level adsorption motifs to guide biochar design.

提出的方法

• 将固定床柱和批量实验与在350°C、550°C和700°C制备的油菜籽壳生物炭结合。
• 对四种无灰生物炭模型（W400、W800、S400、S800）及去质子化变体进行原子级分子动力学模拟，研究 Mn 吸附机制。
• 将内配位定义为 Mn–O/N ≤ 0.30 nm，外配位定义为 Mn 与表面杂原子在 0.60 nm 内的结合。
• 量化 Mn 吸收及在模型中的内层-外层贡献的分配。
• 分析 FTIR 以推断 Mn 暴露后表面功能团的变化。

Figure 1 : Manganese uptake over time from 5 ppm solution by OSR350 (purple), OSR550 (cyan) and OSR700 (yellow), and the changes in pH of the solution.

实验结果

研究问题

• RQ1 在不同热解温度和原料条件下，生物炭对 Mn(II) 去除的主导机制是什么？
• RQ2 阳离子交换、表面络合和沉淀分别对 Mn 去除有多大贡献，如何在实验和计算上区分？
• RQ3 表面去质子化如何影响生物炭上的 Mn 吸附图式？
• RQ4 原子级模拟是否能解析无灰、表面特异的 Mn 交互，而 Bulk 实验无法揭示？
• RQ5 为实现针对性 Mn 捕获而设计生物炭的规则是什么？

主要发现

• 高温生物炭（OSR700）实现约 50% 的 Mn 去除，pH 快速上升至约 9，表明在这些条件下沉淀路径占主导。
• 低温生物炭（OSR350/OSR550）去除了 20–30% 的 Mn，pH 接近中性，指示更显著的非沉淀路径包括阳离子交换和表面络合。
• 阳离子交换对 Mn 吸收有贡献，尤以 OSR350/OSR550 为显著，表现为 K+ 及其他阳离子的释放，尽管在高温炭中并未按化学计量解释所有 Mn 吸收。
• 分子动力学显示 Mn 与去质子化的表面基团形成内层配位络合（在 W400-DP 中约占 Mn 吸收的 47.7–57.3%），并在所有模型中存在外层配位；质子化的低温模型则表现出较少的 Mn-表面结合。
• 无灰、去质子化的生物炭表面通过与苯酚/茚醌氧的内层配位实现强力 Mn 吸附，而高孔隙度的高温模型更多依赖孔扩散实现外层 Mn 吸收。
• FTIR 指示 OSR350/OSR550 表面的 Mn–O 相互作用；而 OSR700 的光谱演变有限，与矿物控制的 Mn 保留（沉淀）一致。

Figure 2 : Representative Mn adsorption motifs on biochar, illustrated for S400-DP and S800. In the deprotonated systems, the dominant motif is an inner-sphere complex (ISC) formed by monodentate coordination to ${-}\text{O}{\vphantom{\text{X}}}^{\vphantom{\smash[t]{\text{2}}}\hphantom{\text{}}\text