In this study, Fe3O4 nanoparticle-loaded biochar derived from the pomelo peel (FO-PPB) was synthesized and applied as an affordable material for the adsorption of Reactive Red 21 (RR21) in an aqueous solution. The characteristics of FO-PPB were evaluated by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), Raman spectra, Fourier transform infrared spectra (FTIR), and Brunauer–Emmett–Teller (BET) surface area. The adsorption process of FO-PPB with RR21 was evaluated through batch experiments to examine various parameters including solution pH, contact time, adsorbent dose, initial RR21 concentration, and solution temperature. Results show that FO-PPB produced by the impregnation ratio between iron (Fe) and pomelo peel biochar (PPB) of 5 : 1 (w/w) had the best adsorption performance. The adsorption capacities of PPB and FO-PPB at optimum experimental conditions (solution pH 3, contact time of 60 min, solution temperature of 40°C, initial RR21 concentration of 300 mg/L, and adsorbent dose of 2 g/L) were 18.59 and 26.25 mg/g, respectively. The adsorption isotherms of RR21 on PPB and FO5-PPB were described well by Langmuir and Sips models with high R2 values of 0.9826 and 0.9854 for FO5-PPB and 0.9701 and 0.9903 for PPB, respectively. The obtained data also well matched the pseudo-first-order and pseudo-second-order models with R2 values ≥ 0.96. Chemisorption through sharing or electronic exchange was determined as the main adsorption mechanism.

中文翻译：

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来自柚皮的磁性 Fe3O4 纳米颗粒生物炭用于从水溶液中吸附反应性红 21

在这项研究中，合成了来自柚皮 (FO-PPB) 的负载 Fe3O4 纳米颗粒的生物炭，并将其用作一种经济实惠的材料，用于在水溶液中吸附活性红 21 (RR21)。通过扫描电子显微镜 (SEM)、能量色散 X 射线光谱法 (EDX)、X 射线衍射 (XRD)、拉曼光谱、傅里叶变换红外光谱 (FTIR) 和 Brunauer-Emmett-出纳员 (BET) 表面积。通过批量实验评估 FO-PPB 与 RR21 的吸附过程，以检查各种参数，包括溶液 pH 值、接触时间、吸附剂剂量、初始 RR21 浓度和溶液温度。结果表明，铁(Fe)与柚皮生物炭(PPB)的浸渍比为5:1(w/​​w)制备的FO-PPB吸附性能最好。PPB 和 FO-PPB 在最佳实验条件下（溶液 pH 3，接触时间 60 min，溶液温度 40°C，初始 RR21 浓度 300 mg/L，吸附剂剂量 2 g/L）的吸附容量为分别为 18.59 和 26.25 毫克/克。Langmuir 和 Sips 模型很好地描述了 RR21 在 PPB 和 FO5-PPB 上的吸附等温线，FO5-PPB 的 R2 值分别为 0.9826 和 0.9854，PPB 的 R2 值分别为 0.9701 和 0.9903。获得的数据也很好地匹配了伪一阶和伪二阶模型，R2 值≥0.96。通过共享或电子交换的化学吸附被确定为主要的吸附机制。和吸附剂剂量 2 g/L) 分别为 18.59 和 26.25 mg/g。Langmuir 和 Sips 模型很好地描述了 RR21 在 PPB 和 FO5-PPB 上的吸附等温线，FO5-PPB 的 R2 值分别为 0.9826 和 0.9854，PPB 的 R2 值分别为 0.9701 和 0.9903。获得的数据也很好地匹配了伪一阶和伪二阶模型，R2 值≥0.96。通过共享或电子交换的化学吸附被确定为主要的吸附机制。和吸附剂剂量 2 g/L) 分别为 18.59 和 26.25 mg/g。Langmuir 和 Sips 模型很好地描述了 RR21 在 PPB 和 FO5-PPB 上的吸附等温线，FO5-PPB 的 R2 值分别为 0.9826 和 0.9854，PPB 的 R2 值分别为 0.9701 和 0.9903。获得的数据也很好地匹配了伪一阶和伪二阶模型，R2 值≥0.96。通过共享或电子交换的化学吸附被确定为主要的吸附机制。