改性被广泛用于提高原始水炭(HBC)和焦炭(BC)的吸附性能。然而,很少报道改良HBC和BC对污染物去除的比较。在这项研究中,最初生产了来自稻草的原始HBC和BC,然后使用柠檬酸(CA)作为改性剂合成CA修饰的HBC(CAHBC)和CA修饰的BC(CABC)。此外,研究了生物炭对亚甲基蓝(MB)的吸附性能。结果表明,BC表现出相对粗糙的表面,含有更多的矿物质(灰),而HBC具有丰富的含O官能团和较少的矿物质。CA改性部分去除BC表面的矿物质,削弱了离子交换,表面络合,和n-π相互作用,导致对MB的吸附能力较低。相比之下,CA在HBC表面产生更多的含O官能团,这加强了氢键和静电相互作用,从而增加对MB的吸附能力。二室模型与CAHBC对MB的吸附过程有较好的拟合,HBC和CAHBC吸附MB的等温线数据适用于Freundlich模型。CAHBC对MB的最高吸附量为80.13mg·g-1,比CABC高27.66%。傅里叶变换红外光谱和X射线光电子能谱分析表明,CAHBC表面官能团中的羧基在MB吸附过程中起着至关重要的作用。此外,CAHBC在宽范围的pH值(4.0-10.0)和共存离子的干扰下表现出良好的性能,还具有回收能力。此外,CAHBC生物炭对MB的吸附是自发的,放热,随机性程度增加过程。因此,HBC的CA修饰是一种有前途的策略,可用于从水生环境中去除MB。
Modification is widely used to enhance the adsorption performance of pristine hydrochar (HBC) and pyrochar (BC). However, comparisons between modified HBC and BC toward pollutant removal have rarely been reported. In this study, pristine HBC and BC derived from rice straw were first produced, and then citric acid (CA) was used as a modifier to synthesize CA-modified HBC (CAHBC) and CA-modified BC (CABC). Furthermore, the adsorption performance of biochars toward methylene blue (MB) was investigated. The results showed that BC exhibits relatively rough surfaces and contains more minerals (ash), whereas HBC has plentiful O-containing functional groups and fewer minerals. CA modification partially removed minerals from the surface of BC, which weakened the ion exchange, surface complexation, and n-π interaction, resulting in a lower adsorption ability toward MB. By contrast, CA produced more O-containing functional groups on the surface of HBC, which strengthened the hydrogen bonding and electrostatic interaction, thus increasing the adsorption capacity toward MB. The two-compartment model showed a good fit to the adsorption process of MB on CAHBC, and the isotherm data for MB adsorption by HBC and CAHBC are suitable for the Freundlich model. The highest adsorption amount of MB using CAHBC was 80.13 mg·g-1, which was 27.66% higher than that for CABC. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis indicated that the carboxyl groups in the surface functional groups of CAHBC played a crucial role in the MB adsorption process. In addition, CAHBC showed a good performance for a wide range of pH values (4.0-10.0) and under the interference of coexisting ions, and also presented a recycling ability. Furthermore, the adsorption of MB on CAHBC biochar was a spontaneous, exothermic, degree-of-randomness-increasing process. Consequently, CA modification of HBC is a promising strategy and could be used for MB removal from aquatic environments.