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

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334.58μm和20.30 nm减小到233.81μm和16.95 nm,比表面积从0.70 m^(2)/g增加到0.96 m^(2)/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。

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 differentpH, 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 atpH=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.