Synthesis and characterization of various zeolites and study of dynamic adsorption of dimethyl methyl phosphate over them
Graphical abstract
Thermal desorption pattern of DMMP over various zeolites (a) 1st desorption and (b) 2nd desorption.
Introduction
Zeolites are aluminosilicates with small practical size used to remove organic matter, drug residues, trace metal ions and lots of pollutant from the wastewaters due to their adsorption and ion exchange capacity. Because of these potential applications several groups have developed synthetic methods for preparing nanocrystalline zeolites [1], [2]. Zeolites exhibit good properties of adsorption and have been used for the minimization of toxicological effects of toxic metal ions and other pollutants. In our previous work we studied sorption of trace metal ions from wastewater on clintonite [3]. Wagner and Bartram examined zeolite adsorbency with potential chemical reactivity in a study of NaY (and AgY) zeolite activity against VX and one of its simulants, O, S- diethyl phenylphosphonothiolate (DEPPT) [4].
Dimethyl methylphosphonate [DMMP, CH3PO(OCH3)2] due to its organophosphorus compound elemental composition that mimics nerve agents, is commonly considered as a simulant for CWAs and insecticides, such as the G-series nerve agents tabun (GA), sarin (GB), soman (GD) and paraoxon [5]. DMMP has also become a significant environmental and food chain pollutant due to its large consumption as a common additive for anti-foaming agents, plasticizers, stabilizers, textile conditioners and antistatic agents [6]. Consequently, DMMP sensors and adsorbents with high sensitivity, rapid response, low energy consumption and good reversibility at room temperature are highly desirable, not only for neurotoxin detection for counter-terrorism purposes, but also for environmental protection and medical diagnoses for risk management [7], [8], [9].
Templeton and Weinberg [10] described the adsorption and decomposition of DMMP on aluminum oxide surface at temperature ranged from 200 to 673 K. Ekerdt et al. [11] discussed the decomposition chemistry of organophosphorus compounds interacting with metal and metal oxide surfaces. He has also highlighted on significant research directions for surface chemical sciences, surface reaction chemistry, solid-state synthesis and organometallic cluster chemistry. Work has also been carried out for the infrared study of adsorbed organophosphorus on silica [12]. Attempts were also made by Cao et al. to study the higher temperature thermo catalytic decomposition of dimethyl methylphosphonate on activated carbon to carbon dioxide, methanol and phosphorus pentaoxide [13]. Yang et al. studied sorption and decomposition of dimethyl DMMP to methylphosphonate on Sodium X-type faujasite zeolite [14].
DMMP a low molecular weight and highly volatile toxic chemical needs to be removed from the environment. Zeolites used in present study will perform the physical adsorption of DMMP and also hydrolysis of some amount of physisorbed vapors by the water content present on the surface of zeolites.
Section snippets
Reagents and chemicals
Sodium hydroxide from Aldrich, sodium aluminate from Riedel-deHaën, sodium metasilicate from Aldrich, alumina trihydrate from Aldrich, sodium silicate from Merck, hexanimine from Aldrich, silica (Aerosil 200) from Degussa, potassium hydroxide from Merck, tetramethylamonium chloride (TMA)Cl from Aldrich, dimethyl methyl phosphate (DMMP) from Merck and deionized water.
Instrumentation
Teflon lined autoclave for zeolite synthesis, Shimadzu XRD 6000 equipment for X-ray diffraction (XRD), Shimadzu FT-IR
Characterization of zeolites
The above obtained synthesized zeolite samples were characterized by XRD, FTIR, N2 BET surface area, NH3-TPD, SEM and EDS techniques.
Conclusion
Synthesized zeolites were characterized with various techniques and dynamic adsorption of dimethyl methyl phosphate over these zeolites was carried out successfully. Zeolite-X was found to have highest adsorption capacity because of its high surface area. For all zeolites adsorption was found to be high initially and it then decreases with increase in injected volume. Further desorption experiments were also carried out successfully and desorption pattern revealed that desorption has occurred
Acknowledgments
Authors are highly thankful to DRDO, New Delhi for financial assistance, and DDRE, Gwalior for characterization of the synthesized materials and providing necessary laboratory facilities.
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