胡椒梗生物炭PB-200对亚甲基蓝的吸附特性及机理

Characteristic and Mechanism of Methylene Blue Adsorption by Pepper Stem Biochar

摘要:

以胡椒梗为原料，在200 ℃氮气条件下热解，制备胡椒梗生物炭PB-200。在不同pH、吸附时间、温度和初始浓度的条件下对亚甲基蓝（MB）进行批量吸附实验；用扫描电镜（SEM），利用表面积和孔隙度分析仪、粒度分析仪、Zeta电位分析仪、傅立叶变换红外光谱仪（FT-IR）、元素分析仪等对其进行表征，探究其吸附机理。实验结果表明，PB-200在pH=3~11间均有较好的吸附性能（72.34~144.91 mg/g）且吸附量随着pH的升高而增加；吸附过程符合准二级动力学模型（R2≥0.99）；等温吸附模型拟合发现，Langmiur模型能很好地描述PB-200对MB的吸附行为（R2≥0.99）；在pH=7，25 ℃条件下，初始MB的质量浓度为100 mg/L，将20 mg PB-200投入40 mL MB溶液时，吸附量可达到115.08 mg/g。表征结果表明，PB-200与胡椒梗相比，平均粒径和孔径分别从334.58 μm和20.30 nm减小到233.81 μm和16.95 nm，比表面积从0.70 m2/g增加到0.96 m2/g；PB-200的氧元素含量达到39.59%，具有大量的含氧官能团和丰富的孔道结构；PB-200的理化性质较胡椒梗有明显的提升，其吸附以化学吸附为主，是单层吸附和静电吸附。PB-200是一种去除废水中MB的高效吸附剂。

Abstract:

In this study, pepper stem, one of wastes from preliminary processing of pepper, was used as raw material to produce pepper stem biochar (PB-200) by pyrolysis in a nitrogen atmosphere under 200 ℃. Adsorption characteristics of PB-200 on methylene blue (MB) was researched by batch adsorption experiment under different pH, adsorption time, temperature and initial concentration conditions; and it was characterized by scanning electron microscopy (SEM), surface area and porosity analyzer, particle size analyzer, zeta potential analyzer, Fourier-transform infrared (FT-IR) spectrometer, elemental analyzer, etc to investigate the mechanism of the biochar adsorption. The results showed that PB-200 resulted in good adsorption performance at pH=3~11, and as the pH increased from 3 to 11, the adsorption of PB-200 increased from 72.34 to 144.91 mg/g. The kinetic studies showed that the experimental data was fitted by the pseudo second-order model well (R2≥0.99); and the isothermal adsorption process of MB can be better described by the Langmuir adsorption isotherms model than the Freundlich model (R2≥0.99). The adsorption capacity of MB was up to 115.08 mg/g under the condition of an initial MB concentration of 100 mg/L when the biochar (20 mg) was mixed with MB solution (40 mL, pH 7.0) for 24 h at 25 ℃. It can be seen that PB-200 is an efficient adsorbent for removing MB in wastewater. Compared with pepper stems, the average particle size and pore size of PB-200 were reduced from 334.58 μm and 20.30 nm to 233.81 μm and 16.95 nm, respectively, and the specific surface area was increased from 0.70 m2/g to 0.96 m2/g; rich pore structure and oxygen-containing functional groups were demonstrated by the SEM, FT-IR and elemental analysis. The physical properties of PB-200 were significantly improved compared with Pepper stem; the adsorption of MB was chemisorption (electrostatic adsorption and and monalayer adsorption). PB-200 is an efficient adsorbent for removing methylene blue.