Properties and applications of Zeolites

Abstract

Zeolites are aluminosilicate solids bearing a negatively charged honeycomb framework of micropores into which molecules may be adsorbed for environmental decontamination, and to catalyse chemical reactions. They are central to green-chemistry since the necessity for organic solvents is minimised. Proton-exchanged (H) zeolites are extensively employed in the petrochemical industry for cracking crude oil fractions into fuels and chemical feedstocks for other industrial processes. Due to their ability to perform cation-exchange, in which the cations that are originally present to counterbalance the framework negative charge may be exchanged out of the zeolite by cations present in aqueous solution, zeolites are useful as industrial water-softeners, in the removal of radioactive Cs+ and Sr2+ cations from liquid nuclear waste and in the removal of toxic heavy metal cations from groundwaters and run-off waters. Surfactant-modified zeolites (SMZ) find particular application in the co-removal of both toxic anions and organic pollutants. Toxic anions such as arsenite, arsenate, chromate, cyanide and radioactive iodide can also be removed by adsorption into zeolites that have been previously loaded with co-precipitating metal cations such as Ag+ and Pb2+ which form practically insoluble complexes that are contained within the zeolite matrix.

Exploiting Large‐Pore Metal–Organic Frameworks for Separations through Entropic Molecular Mechanisms

“…[91] These authors showedt hat the withdrawal of electronic chargef rom the linker leads to enhanced acidity for the hydrogena toms on the linker,w hich can form weakh ydrogen-bond interactions with the oxygen atoms of CO 2 .T hey also found that the binding capacity of the linker with an itro functional group for CO 2 is much higher,o wing to the strong effect of the nitro group on polarizing the CO 2 molecule. To rrisi et al [92] studied the effect of introducingp olar groups (NO 2 , NH 2 ,O H, SO 3 H, and COOH)i nto benzene linkers. They showed that the strongest interaction is with the lone-pair-donation atoms (N, O) of the side groups.…”

“…[22] There is ac onceptual differenceb etween adsorption of small versus large molecules. In contrastt ol arger molecules, small gas molecules such as CO 2 ,O 2 ,N 2 ,a nd CH 4 have little or no shape/size differences relative to the framework. They behavem ore like af luid inside large pores of nanoporous materials.…”

“…Nanoporous materialssuch as zeolites, [1,2] metal-organic frameworks (MOFs), [3][4][5][6][7] andz eolitic imidazolate frameworks (ZIFs) [8] offer great potential as energy-efficient alternatives to conventional separation processes like distillation, absorption, and extraction.B esides being industrially relevant, they are scientifically interesting and allow us to gain an understanding of the fundamentals of the separation mechanisms governing adsorbed molecules in confinement. Separation in nanoporous materials relies on adsorption [9] and diffusion, [10] and can be achievedt hrough size/shapee xclusion (steric separation), differences in adsorbate-adsorbent interactions and adsorbate packing (thermodynamic equilibrium effects), as well as differences in the diffusion rate of adsorbatesw ithin the adsorbent channels.…”

Stability Improvement of Immobilized a-amylase using Nano Pore Zeolite

“…applications such as water purification and softening, separation of gases, nuclear industry, and sensors (6)(7)(8)(9)(10)(11)(12)(13)(14). They can also act as suitable supports for immobilization of enzymes (15)(16)(17)(18).…”

Ash management at Canfor Pulp - turning a waste product into a profit stream

“…Zeolites are naturally occurring crystalline aluminum-silicates that are used for lon exchange, gas adsorption and water adsorption, with the unique property that they can remove contaminants using anion exchange and then be recharged and reused (Rhodes, 2010). Fly ash can be converted into low grade zeolites, which are particularly well suited for the removal of phosphates and heavy metals from wastewater.…”