Novel Mesoporous Zeolites from Industrial Solid Wastes for Remediation of Textile Wastewater

Abstract

Ever-increasing population and industrialization directly influence air, soil, and water. Coal fly ash (CFA) and Red mud (RM) are significant inorganic wastes that take a large area of land for their disposal. Since water pollution and waste disposal play a vital role in affecting human beings and the environmental system, the merits of this waste are that it contains silicon and aluminum element, which is suitable for synthesizing versatile nano zeolite. This study mainly focuses on fabricating ETL structure type novel EU-12 nanosized mesoporous zeolite from CFA by sonication-assisted hydrothermal treatment method (SAH). CFA and the produced EU-12 nano zeolite were characterized by XRD, FESEM, EDS, XRF, TEM, RAMAN, DSC-TGA, BET surface area measurements, XPS, and zeta potential analysis for the first time. Sonication-assisted hydrothermal treatment method produced EU-12 nano zeolite in less crystallization time than the hydrothermal treatment method. TEM was used to identify the particle size of EU-12 nano zeolite in the range of 5 to 200 nm. Crystallinity % of EU-12 was obtained by analyzing XRD peaks as 76.39%. The optimized condition for EU-12 nano zeolite synthesis was: calcination temperature 850 °C, FA/NaOH 1:8, sonication time 30 min, hydrothermal treatment time 8 hours at 100 °C. The discharge of wastewater, mainly dyes, from various industries is a major problem of the present period because of its carcinogenic and other chronic effects. Therefore, transition metal sulfide loaded EU-12 coal fly ash-based nano zeolite photocatalysts were synthesized by the sono-hydrothermal method followed by ion exchange with seven different transition metal sulfides. The band gap of all synthesized photocatalysts was found to be ≤ 3.44 eV. Furthermore, the efficiency of synthesized zeolite and photocatalysts were determined in terms of adsorption efficiency towards cationic dyes such as Crystal violet (CV), Rhodamine B (RhB), and Methylene Blue (MB). Due to high adsorption efficiency and morphological properties, we propose that the synthesized nano zeolite can play a significant role as a low cost adsorbent in the remediation of toxic industrial dyes. The photoactivity of the photocatalysts was examined by degrading rhodamine b. The results indicated that transition metal sulfide/EU-12 photocatalysts had strong photoactivity under visible light compared to a dark environment. Furthermore, the efficiency of photocatalysts was determined in terms of degradation efficiency towards RhB, which was found to be a maximum of 98.62% for 0.2M CdS/EU-12 at 2 gL-1 of catalyst dose and 10 mg/l of dye concentration in 3 hours under a visible light source of 200 W. Magnetic Zeolite 4A was synthesized by the co-precipitation method and was used for cationic dye adsorption (RhB, MB, CV). The results indicated that magnetic zeolite had strong adsorption ability, easy to separate magnetic zeolite catalyst from the aqueous medium, and is reusable. The kinetics, adsorption isotherm, and thermodynamics were also studied for CdS/EU-12 photocatalyst. The study opens the possibility of scaling up the methodology for simultaneous recycling, recusing solid waste, and treating toxic dye.