Abstract
The infamous ‘structure–property relationship’ is a long-standing problem for the design, study and development of novel functional materials. Most conventional characterization methods, including diffraction and crystallography, give us a good description of long-range order within crystalline materials. In recent decades, methods such as Solid State NMR (SS NMR) are more widely used for characterization of crystalline solids, in order to reveal local structure, which could be different from long-range order and sometimes hidden from long-range order probes. In particular for zeolites, this opens a great avenue for characterization through studies of the local environments around Si and Al units within their crystalline frameworks. In this paper, we show that some structural modifications occur after partially exchanging the extraframework Na + ions with monovalent, Li + , K + , Rb + and NH 4 + and divalent, Ca 2 + cations. Solid state NMR is deployed to study the local structure of exchanged materials, while average stricture changes can be observed by powder diffraction (PXRD). To corroborate our findings, we also employ Fourier Transform Infrared spectroscopy (FT-IR), and further characterization of some samples was done using Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray spectroscopy (EDX).
Highlights
IntroductionWe can make more than 200 synthetic zeolites in the laboratory [1,2]
Most zeolite syntheses employ Organic Structure Directing Agents (OSDAs), such as TMA-OH (Tetramethylammonium Hydroxide) or crown-ether, which act as templates to guide the formation of particular types of zeolite pores and channels [3,4,5,6]
Due to the high manufacturing costs of producing these organic materials, which cannot be recovered after calcination, current research is becoming more concerned with optimising synthesis conditions in order to produce pure zeolites in the absence of OSDAs [3,7]
Summary
We can make more than 200 synthetic zeolites in the laboratory [1,2] They are classed as porous materials as they possess cages, channels and open void spaces within their highly crystalline frameworks. Most zeolite syntheses employ Organic Structure Directing Agents (OSDAs), such as TMA-OH (Tetramethylammonium Hydroxide) or crown-ether, which act as templates to guide the formation of particular types of zeolite pores and channels [3,4,5,6]. This reduces the chance of producing competing zeolite phases.
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