Kaolin-supported nanoscale zero-valent iron (K-NZVI) was synthesized via a green synthesis method, in which leaf extract of Ruellia tuberosa was used as a reducing agent. The synthesized K-NZVI was used for decolorization of Reactive Black 5 (RB5), an azo dye widely used in textile industry. The XRD patterns of the K-NZVI particles show the characteristic peaks of Fe⁰, indicating that Fe⁰ nanoparticles (NZVI) were successfully synthesized on the kaolin surface. The SEM, TEM images and EDS elemental mapping show that the NZVI particles are well dispersed on the kaolin surface, thus, reducing the extent of NZVI aggregation. Batch experiments for decolorization of RB5 were carried out to investigate the effects of process parameters including solution pH, initial dye concentration and contact time. The results show that high decolorization efficiencies are obtained in acidic pH. Increasing initial dye concentration causes the decolorization efficiency to decrease, whereas increasing contact time results in higher efficiency. Furthermore, after five cycles of reuse of K-NZVI, the decolorization efficiency slightly decreases, indicating high reusability and stability of K-NZVI. The disappearance of the characteristic peaks of RB5 solution recorded by a UV–Vis spectrophotometer indicates cleavage of the azo bonds and, thus, the decomposition of RB5 in the solution. From a kinetic analysis performed at various RB5 concentrations, the decolorization process of RB5 by K-NZVI is well fit by the pseudo-first-order kinetic model.

高岭土支持的纳米尺度零价铁（K-NZVI）中的溶液经由绿色合成方法，其中的叶提取物合成的块根芦莉草用作还原剂。合成的K-NZVI用于活性黑5（RB5）的脱色，活性黑5是在纺织工业中广泛使用的一种偶氮染料。K-NZVI颗粒的XRD图谱显示Fe ⁰的特征峰，表明Fe ⁰在高岭土表面成功合成了纳米粒子（NZVI）。SEM，TEM图像和EDS元素图谱表明NZVI颗粒很好地分散在高岭土表面上，从而降低了NZVI聚集的程度。进行了RB5脱色的分批实验，以研究工艺参数（包括溶液的pH值，初始染料浓度和接触时间）的影响。结果表明，在酸性pH值下可获得较高的脱色效率。初始染料浓度的增加会导致脱色效率降低，而接触时间的增加会导致更高的效率。此外，在重复使用K-NZVI五个循环之后，脱色效率会略有下降，这表明K-NZVI具有很高的可重复使用性和稳定性。紫外可见分光光度计记录的RB5溶液特征峰的消失表明偶氮键断裂，因此RB5在溶液中分解。通过在各种RB5浓度下进行的动力学分析，通过拟一级动力学模型可以很好地拟合K-NZVI对RB5的脱色过程。