Deposition and assembly of magnesium hydroxide nanostructures on zeolite 4a surfaces

A method was developed to precipitate and assemble magnesium hydroxide nanostructures on zeolite 4A surfaces at mild conditions. The effects of process variables such as precursor concentration, type of base added, and synthesis time on the composition, size, and morphology of the resulting Mg(OH) 2 / zeolite 4A nanocomposites were investigated. It was determined that the presence of a weak base such as ammonium hydroxide is essential to the control of the morphology of the magnesium hydroxide (Mg(OH)2) nanostructures.;Properties of the Mg(OH)2 / zeolite 4A nanocomposites such as surface area, pore volume and composition were characterized via BET and TGA. Mg(OH)2 / zeolite 4A nanocomposites and bare zeolite 4A were dispersed in UltemRTM polymer to form a mixed matrix films and their thermal and mechanical properties were investigated. It was found that the addition of bare zeolites to the polymer led to a decrease in the mechanical properties of the polymer composite. However, some of the adverse effects could be mitigated if the polymer is loaded with Mg(OH)2 / zeolite 4A nanocomposites.;Isotherms for the adsorption of Mg(OH)2 petals on zeolite 4A were measured in order to determine optimum conditions for the formation of nanocomposites at ambient conditions. The loading of the Mg(OH)2 was determined from the adsorption isotherms. It was also found that the adsorption of Mg(OH)2 on zeolite A yields H-type isotherms and involves 3 mechanisms: ion exchange, surface adsorption of Mg2+ ions, and surface precipitation of Mg(OH)2. H-type isotherms indicate that there may be very strong specific interactions between Mg(OH)2 and zeolite 4A. In the absence of a base such as ammonium hydroxide, the predominant processes are ion exchange and surface adsorption of Mg2+ ions. In the presence of ammonium hydroxide, Mg(OH)2 crystals are precipitated on the surface of zeolite 4A at moderate Mg2+ ions concentration. The loading of Mg(OH)2 increases with increasing Mg2+ ions concentration.;A detailed examination of the interactions between Mg(OH)2 and functional groups on the zeolite surface was conducted. Solid-state 29Si, 27Al, and 1H NMR spectra were coupled with FTIR measurements, pH and adsorption studies, and thermogravimetric analyses to determine the interactions of Mg(OH)2 with surface functional groups and to characterize structural changes in the resulting zeolite after Mg(OH)2 deposition. It was discovered that acid-base interactions between the weakly basic Mg(OH)2 and the acidic bridging hydroxyl protons on zeolite surface represent the dominant mechanism for the growth of Mg(OH)2 nanostructures on the zeolite surface. This suggests that precipitation combined with self-assembly on specific sites of zeolite may be used to make functional hydroxide / zeolite or oxide / zeolite composites for applications in catalysis, gas sensing, and membranes.