The present paper presents anthracite – a low cost and naturally abundant coal – as a potential adsorbent of the azo dye Acid Yellow 42, evaluating parameters such as dye concentration, temperature and ionic strength. A thermodynamic and kinetic approach was also described. Interactions between the adsorbate and anthracite were described by isothermal titration as well. Anthracite was characterized by TGA/DTA, FT-IR, X-ray, TEM/EDS. The adsorption system anthracite-dye reached equilibrium in less than 10 min at room temperature, with a maximum adsorption capacity as high as 47 mg g. A multi-layer pattern is observed according to the Freundlich adsorption model and the adsorption kinetics is best explained by the pseudo-second-order model. A chemisorption phenomenon drives the initial process, followed by a multi-layer physisorption phenomenon between dye molecules, with a prevalence of electrostatic interactions. The adsorption of acid yellow 42 onto anthracite is a spontaneous (ΔG° = −11.68 kJ mol) and endothermic (ΔH° = 58.59 kJ mol) process, suggesting that the driving force to promote adsorption is the increase of the degree of freedom in the interface anthracite/solution (ΔS° = 70.26 kJ mol). The amount of AY immobilized at the surface of anthracite increased with the temperature rising, evidencing an endothermic process. Cations and anions influence the adsorption process, not obeying and following Hofmeister series, respectively. Ionic charge lead to increase Zeta potential. Therefore, anthracite highlights as a potential adsorbent material for azo dyes compared with other natural materials and some activated carbons.

中文翻译：

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无烟煤上的偶氮染料吸附：热力学、动力学和向升效应的观点

本文提出无烟煤（一种低成本且天然丰富的煤炭）作为偶氮染料酸性黄 42 的潜在吸附剂，评估染料浓度、温度和离子强度等参数。还描述了热力学和动力学方法。吸附质和无烟煤之间的相互作用也通过等温滴定来描述。通过TGA/DTA、FT-IR、X射线、TEM/EDS对无烟煤进行了表征。吸附体系无烟煤-染料在室温下不到10 min就达到平衡，最大吸附量高达47 mg·g。根据 Freundlich 吸附模型观察到多层模式，并且吸附动力学最好由伪二阶模型解释。化学吸附现象驱动初始过程，随后是染料分子之间的多层物理吸附现象，并普遍存在静电相互作用。酸性黄42在无烟煤上的吸附是自发（ΔG° = -11.68 kJ mol）和吸热（ΔH° = 58.59 kJ mol）过程，表明促进吸附的驱动力是吸附自由度的增加。无烟煤/溶液界面（ΔS° = 70.26 kJ mol）。随着温度的升高，固定在无烟煤表面的AY量增加，这证明了吸热过程。阳离子和阴离子影响吸附过程，分别不服从和遵循霍夫迈斯特级数。离子电荷导致 Zeta 电位增加。因此，与其他天然材料和一些活性炭相比，无烟煤突出作为偶氮染料的潜在吸附材料。