Development of Functionalized Zeolite Hybrids as Potential Adsorbents

Abstract

The industrial revolution has led to an unequal and uncontrolled distribution of the toxic substances in different compartments of the environment. A large number of researchers have offered specific solution to combat the hazardous and toxic substances. The real challenge faced today is the complex interaction of the pollutants in each compartment compelling the scientists to develop materials offering one spot solution applicable to a wide range of toxicants. The present investigation is an effort to synthesize a range of different materials having multi-dimensional potential for removing diverse pollutants with general efficacy and limited specificity. Though a number of materials fall under the same category, the Zeolites and their tailored forms offer advantages such as thermal stability, low-cost, ease of availability, and high sorption affinity. Zeolites and their functionalized hybrids have attracted interest from academic and industrial laboratories due to high catalytic and exchange properties. In the present research, Zeolite as base material is synthesized from economical precursors using hydrothermal method. Post modification for synthesis of functionalized hybrids is attempted with doping of metals (Cu, Zn, and Cu/Zn), organic moieties ((Thiophene, Dibenzothiophene, and Thiophene/ Dibenzothiophene), and combination of both into the Zeolite framework. On the basis of induced functionality the eleven hybrids of Zeolite are grouped into three categories. The purpose of preparation of hybrids is to have diverse functional groups on the surface of a single Zeolite to adsorb a variety of pollutants from environmental media. The synthesized materials are subjected to a series of characterization techniques to determine surface and bulk properties for effective adsorption. The successful incorporation of the functional groups (Thiol, CH3, and Metal-Oxygen) is indicated by FTIR, BET surface area and SEM analysis proposes that crevices and channels serve as pores for uptake of incoming pollutants. Further, EDX shows silica and alumina percentage which is involved in developing zeolite framework (internal and external linkages) for binding. The thermal stability of Zeolite (360-570°C) is assessed from TGA studies. XRD demonstrates the amorphous nature of Zeolite framework that generally decreases on functionalization. Zeolite and the functionalized hybrids are applied for the removal of Metals (Hg, As), Dyes (Methylene Blue, Methyl Orange), Polyaromatic Hydrocarbons (Benzene, Naphthalene, Phenanthrene, and Pyrene), Sulfur (Model Fuel, Commercial fuel) and Insecticide (Imidacloprid). For each application, closed batch adsorption protocol is followed. The results of adsorption experiments confirm the efficiency of synthesized hybrids as adsorbents for the removal of a number of pollutants. Generally, mercury showed better removal than arsenic on the adsorbents. Moreover all Zeolite based hybrids testifies the fitness of pseudo-second order kinetics & Langmuir and Freundlich isotherms for the removal of mercury and arsenic. The hybrids depict higher removal capacity for methylene blue in comparison to methyl orange. Moreover Zeolites shows good removal potential for sulphur, Imidacloprid and polyaromatic as well.