Activated carbons have been prepared from rice husk (RH) and coffee husk (CH) using ZnCl₂ as activating agent. These materials were characterized by thermogravimetric and elemental analysis, infrared spectroscopy (FTIR), the point of zero charge (PZC), scanning electron microscopy (SEM), and nitrogen adsorption. The removal efficiency of the obtained adsorbents was tested using indigo carmine (IC) at different pH, as a model dye, in both distilled water and textile wastewater. The results showed that the dye adsorption on the natural adsorbents and the activated carbons was favorable at acidic pH (3.0). Moreover, the best IC removal in both matrices was reached by the material prepared from CH and activated with ZnCl₂ (CH-ZnCl₂). This result correlated well with the higher value PZC (7.1), large specific surface area and porosity characteristics. Additionally, the dye adsorption on the CH-ZnCl₂ surface was improved using the smaller particle size and the optime dose of adsorbent; also, the adsorptions obtained were much better than those of a commercial activated carbon. Furthermore, the isotherms study showed the adsorption to be monolayer type according to Langmuir and Redlich-Peterson equations. The adsorption kinetics followed a pseudo-second-order kinetic model, and intra-particle diffusion showed that IC adsorption on the surface is faster than inside CH-ZnCl₂. The thermodynamic suggest that the IC adsorption is a typical physical process, which is spontaneous and endothermic. According to density functional theory calculations and experimental FTIR analysis, oxygenated groups and aromatic rings are the most relevant during the IC adsorption through hydrogen bonds and π-π interactions.

已使用ZnCl ₂作为活化剂从稻壳（RH）和咖啡壳（CH）制备了活性炭。这些材料的特征在于热重和元素分析，红外光谱（FTIR），零电荷点（PZC），扫描电子显微镜（SEM）和氮吸附。使用靛蓝胭脂红（IC）在不同pH下作为模型染料，在蒸馏水和纺织废水中测试了获得的吸附剂的去除效率。结果表明，在酸性pH（3.0）下，染料对天然吸附剂和活性炭的吸附效果良好。此外，由CH制备并用ZnCl ₂（CH-ZnCl ₂）。该结果与较高的PZC（7.1），较大的比表面积和孔隙率特性密切相关。另外，使用较小的粒径和适时的吸附剂剂量可以改善染料在CH-ZnCl ₂表面的吸附。同样，获得的吸附也比市售活性炭好得多。此外，等温线研究表明，根据Langmuir和Redlich-Peterson方程，吸附为单层型。吸附动力学遵循伪二级动力学模型，颗粒内扩散表明表面上的IC吸附比CH-ZnCl ₂内部快。。热力学表明，IC吸附是一个典型的物理过程，是自发的并且是吸热的。根据密度泛函理论计算和实验FTIR分析，在通过氢键和π-π相互作用进行IC吸附期间，氧化基团和芳环最为相关。