In this paper, nitrogen-doped (ND) and nitrogen-magnesium co-doped (NMD) chars were synthesized by different combinations of pyrolysis-activation steps of anaerobically digested fiber (ADF), wheat straw (WS), and Douglas fir wood (DFW) to adsorb phosphate from aqueous solutions. Five different series of char were produced through different methods: (1) biomass pyrolyzed under N₂, (2) biomass pyrolyzed under N₂ followed by activation with ammonia, (3) biomass pyrolyzed and char activated both in the presence of NH₃, (4) biomass impregnated with MgCl₂ pyrolyzed under N₂, and (5) biomass impregnated with MgCl₂ pyrolyzed under NH₃. Proximate analysis, elemental composition, gas physisorption, inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) techniques were used to characterize the resulting chars. All the chars derived from ADF (independent of the procedure used) showed the best phosphate adsorption capacity, likely due to their higher ash content. Pyrolysis of ADF under NH₃ resulted in char with phosphate adsorption capacity of 95 mg/g (254% higher than char produced under N₂). Results from kinetic study show almost all phosphate adsorption by ND-ADF (one step) char occurred within 2 h. Richie nth-order model fits well the sorption process indicating that phosphate adsorption on the surface of the ND-ADF (one step) char was mediated by multiple mechanisms. Equilibrium data were fitted to different adsorption isotherms and the Langmuir-Freundlich and Redlich Peterson adsorption models provided the best fit. We hypothesized that the presence of Ca and Mg in the ADF enhanced N fixation and leads to higher phosphate adsorption. Therefore, we studied the effect of MgCl₂ impregnation on DFW and WS pyrolyzed and activated under NH₃. Our hypothesis was confirmed, and DFW and WS chars doped with Mg and N showed phosphate adsorption of 216 and 122 mg/g, respectively (37- and 24-fold increase compared with chars produced only under N₂).

Graphical abstract

中文翻译：

---

氮镁共掺杂生物炭对磷酸盐的吸附

本文通过厌氧消化纤维（ADF），小麦秸秆（WS）和花旗松（Douglas fir wood）的不同热解活化步骤的组合，合成了氮掺杂（ND）和氮镁共掺杂（NMD）炭（ DFW）从水溶液中吸附磷酸盐。通过不同的方法生产了五个不同系列的炭：（1）在N ₂下热解的生物质，（2）在N ₂下热解的生物质，然后用氨水活化，（3）在NH ₃存在下热解和炭化的生物质， （4）在N ₂下热解的MgCl ₂浸渍的生物质，（5）在NH ₃下热解的MgCl ₂浸渍的生物质。近程分析，元素组成，气体物理吸附，电感耦合等离子体质谱（ICP-MS），X射线光电子能谱（XPS），X射线粉末衍射（XRD），傅里叶变换红外光谱（FTIR），扫描电子显微镜（SEM）和能量色散X射线光谱（EDS）技术用于表征生成的炭。源自ADF的所有炭（独立于所使用的程序）均显示出最佳的磷酸盐吸附能力，这可能是由于其较高的灰分含量。在NH ₃下热解ADF生成的焦炭具有95 mg / g的磷酸盐吸附容量（比在N ₂下生成的焦炭高254％）。动力学研究的结果表明，ND-ADF（一步法）炭几乎所有的磷酸盐吸附均在2小时内发生。Richie n阶模型很好地拟合了吸附过程，表明ND-ADF（一步法）炭表面上的磷酸盐吸附是由多种机制介导的。平衡数据适用于不同的吸附等温线，Langmuir-Freundlich和Redlich Peterson吸附模型提供了最佳拟合。我们假设ADF中Ca和Mg的存在会增强N固定，并导致更高的磷酸盐吸附。因此，我们研究了MgCl ₂浸渍对在NH ₃下热解和活化的DFW和WS的影响。。我们的假设得到了证实，掺有Mg和N的DFW和WS煤焦分别显示了216和122 mg / g的磷酸盐吸附（与仅在N ₂下生产的煤焦相比增加了37倍和24倍）。

图形概要