Synthesis and characterization of mordenite zeolite from metakaolin and rice husk ash as a source of aluminium and silicon

Experimental and Computational Approaches for the Structural Study of Novel Ca-Rich Zeolites from Incense Stick Ash and Their Application for Wastewater Treatment

At present, chemical Si/Al sources are mainly used as precursor materials for the manufacturing of zeolites. Such precursor materials are quite expensive for commercial synthesis. Here, we have reported the synthesis of Ca-based zeolite from incense stick ash waste by the alkali-treatment method for the first time. Incense stick ash (ISA) was used as a precursor material for the synthesis of low Si zeolites by the alkali-treatment method. The as-synthesized zeolites were characterized by various instruments like particle size analyzer (PSA), Fourier transform infrared (FTIR), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), electron diffraction spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray fluorescence (XRF). FTIR and XRD helped in the identification of the microstructure and crystalline nature of the zeolites and also confirmed the synthesis of Ca-based zeolite with two thetas at 25.7°. The microscopic analysis by FESEM and TEM exhibited that the size of synthesized Ca-rich zeolites varies from 200 to 700 nm and they are aggregated and cuboidal in shape. Additionally, structural, electronic, and density of states’ characteristics of gismondine (Ca2Al4Si4O16·9H2O) structures were evaluated by computational simulations (first principle, density functional theorem). The structural optimization of structures was carried out in the first stage under the lowest condition of total energy and forces acting on atoms for the lattice constant, as well as the available experimental and theoretical findings. The present research approach predicted the transformation of ISA waste into a value-added mineral, i.e., zeolite, which was further used for the removal of both heavy metals and alkali metals from fly ash-based wastewater using inductively coupled plasma-optical emission spectroscopy (ICP-OES).

Synthesis of Hierarchical MOR-Type Zeolites with Improved Catalytic Properties

Hierarchical MOR-type zeolites were synthesized in the presence of hexadecyltrimethylammonium bromide (CTAB) as a porogen agent. XRD proved that the concentration of CTAB in the synthesis medium plays an essential role in forming pure hierarchical MOR-type material. Above a CTAB concentration of 0.04 mol·L-1, amorphous materials are observed. These hierarchical mordenite possess a higher porous volume compared to its counterpart conventional micrometer crystals. Nitrogen sorption showed the presence of mesoporosity for all mordenite samples synthesized in the presence of CTAB. The creation of mesopores due to the presence of CTAB in the synthesis medium does not occur at the expense of zeolite micropores. In addition, mesoporous volume and BET surface seem to increase upon the increase of CTAB concentration in the synthesis medium. The Si/Al ratio of the zeolite framework can be increased from 5.5 to 9.1 by halving the aluminum content present in the synthesis gel. These synthesized hierarchical MOR-type zeolites possess an improved catalytic activity for n-hexane cracking compared to large zeolite crystals obtained in the absence of CTAB.

Study involving removal of azo dye Direct Orange 34 by adsorption in zeolite–clay system

Recently, dyes have procured a wide range of application in the textile industry. These organic compounds possess toxic agents and act as water pollutants. Such dyes can be extracted by adsorption to prevent water pollution. The present work proposes removal of azo dye Direct Orange 34 from the aqueous solution using mixtures of sodalite zeolite (Si/Al ratio 2.5) and clay (vermiculite in 1.0, 2.5, 5.0 g). The methodology involves a system with different stages of separation, considering specified retention time (72, 48, 24, 12, 6 h) of adsorbate and dye concentrations (100, 50, 25, 10, 5 mg/L). The zeolite–vermiculite mixture has a high potential of dye removal due to extensive surface area and porosity with excellent cation exchange capacity conferring its adsorbent property. High concentrations (50 and 100 mg/L) and longer retention times than 48 h results in 50% removal of dyes, whereas a low concentration level (25, 10, 5 mg/L) increases the removal efficiency (74%). Henceforth, the experiment concluded that the zeolite–clay mixtures are capable of azo dye extraction.