污泥基层状双氧化物/生物炭复合材料的原位制备及吸附机理

针对市政污泥中金属资源化程度低的问题，以富含铝的市政污泥为原料制备得到污泥基镁铝层状双氧化物/生物炭 (MgAl LDO@biochar) 复合材料。结合结构表征，静态吸附和动态吸附实验系统探讨LDO@biochar的吸附性能和吸附机理。结果表明，铝镁摩尔比为1∶2时，所制备LDO@biochar的比表面积和晶粒尺寸最大，其对模式污染物刚果红的吸附容量最高。在吸附过程中LDO通过“记忆效应”重构层状双氢氧化物 (LDH) 结构从而对阴离子产生吸附作用，biochar的共轭碳环和含氧官能团也可以作为污染物结合位点。污染物与吸附剂之间可通过离子交换、π-π共轭、氢键作用和静电吸引等方式结合。与阳离子型染料罗丹明B (11.30 mg·g⁻¹) 和具有单一共轭环结构的磺胺 (20.25 mg·g⁻¹) 相比，阴离子型染料酸性橙II (181.30 mg·g⁻¹) 和具有多共轭环结构的四环素 (39.49 mg·g⁻¹) 的平衡吸附容量更大，而具有多共轭环结构的阴离子型染料刚果红的平衡吸附容量高达477.46 mg·g⁻¹。本研究结果可为综合利用市政污泥制备高附加值环境功能材料提供参考。

In-situ fabrication of layered double oxides/biochar composites from municipal sludge and adsorption mechanism elucidation

Improving the metal utilization efficiency from municipal sludge is encouraged to achieve pollution mitigation and resource recovery. In this work, MgAl magnesium-aluminum layered double oxide/biochar (MgAl LDO@biochar) composite was fabricated from an Al-rich municipal sludge. The adsorption performance of LDO@biochar and the involved adsorption mechanism were investigated in terms of structural characterization, static adsorption, and dynamic adsorption experiments. The results indicated that the LDO@biochar sample obtained at an Al-Mg molar ratio of 1∶2 possessed the highest specific surface area and grain size, and as a result it exhibited the highest adsorption capacity towards the model pollutant congo red. During the adsorption process, LDO collapsed and reconstructed the layered double hydroxides (LDHs) structure due to the “memory effect”. In addition to the LDHs with specific affinity to anions, the conjugated carbon ring and oxygen-containing functional groups in biochar also served as the adsorption sites. Pollutants could be bound to the adsorbent through multiple interactions including ion exchange, π-π conjugation, hydrogen bonding and electrostatic attraction. The anionic dye Acid Orange II and tetracycline with multiple conjugated rings were adsorbed with equilibrium adsorption capacities of 181.30 and 39.49 mg·g−1, respectively, which were higher than the values for the cationic dye rhodamine B (11.30 mg·g−1) and sulfonamide with single conjugated ring (20.25 mg·g−1). The highest adsorption capacity was found on the anionic dye congo red with the largest conjugate structure, which was up to 477.46 mg·g−1. The results of this work provided a reference for the fabrication of value-added environmental functional materials from municipal sludge.