*2.1. Wastewater*

Levafix Dark Blue dye, which is a kind of reactive azo dye, is commonly applied in the textile dyeing industry due to its high fastness profile, and it meets most requirements set by textile manufacturers. In this regard, commercial Levafix Dark Blue dye was used in the current study as a model synthetic pollutant. Thus, Levafix Dark Blue dye was used to prepare synthetic wastewater effluent. Levafix Dark Blue was supplied by DyStar Management Co., Ltd., Shanghai, China. The dye was used as received without further purification or treatment. The dye is dark blue and regarded as a bi-functional, combined anchor. The dye powder was used with no purification or further treatment. Initially, to attain the synthetic dye effluent, a stock solution of 1000 ppm of Levafix Dark Blue dye was prepared, which was then diluted, as required, for successive dilutions to obtain different concentrations according to the experimental conditions.

#### *2.2. Preparation of Fuller's Earth-Based Fenton Catalyst*

Naturally occurring Fuller's earth clay was collected from a deposit located in the southeastern desert in Egypt. After collection, the Fuller's earth clay was subjected to electric oven drying (105 ◦C) to remove any moisture content. Generally, the characteristics of clay, including its chemical and physical features, might be modified and enhanced through various treatments in order to improve its natural capacity to achieve better treatment results [14]. Such modifications could improve the physicochemical and mineralogical characteristics of the substance. Acid and thermal treatments of Fuller's earth are techniques widely applied to attain clay modification. Such techniques modify the mineralogical composition and chemical structure of Fuller's earth substance, as well as leading to surface activation according to the authors' preliminary work. Thus, next, the Fuller's earth was ball-milled to attain a fine powder. Afterward, the material was sieved (200 mesh) and cooked with hydrochloric acid. Then, 15 gm of the material was cooked

with 200 mL HCl acid (10 M) through heating (70 ◦C) and stirring for 1.5 h. Subsequently, the resultant aqueous media were successively washed with distilled water to reach a neutral pH. Subsequently, the solution was filtered, and the resultant solid powder was subjected to calcination (600 ◦C) for thermal activation purposes.
