Non-Standard Characterisation Techniques for Zeolites: from formation to application

At present, more than 230 different zeolite topologies have been characterised, each exhibiting different properties which lead to very specific applications. Due to the limited understanding of zeolite crystallisation, zeolite synthesis is arguably still more of an art than a science, with trial and error being one of the main strategies for discovery of new zeolites. A thorough understanding of zeolite formation is essential for unlocking their full potential: rational zeolite design. Since the early stages of zeolite formation strongly depend on convection and thus on gravity, dedicated hardware has been developed for microgravity experiments on board the International Space Station in order to shed more light on the underlying formation mechanism and the governing kinetics. Given the limited number of experimental techniques available for in situ investigation of zeolite formation, the potential of electrochemical impedance spectroscopy (EIS) to complement commonly used diagnostics has been explored. EIS allows to access multiple aspects of the precursor solution simultaneously by a relatively quick and simple in situ impedance measurement. Moreover, EIS firstly managed to observe the chemical exchange between oligomers and nano-aggregates during zeolite synthesis. This increased understanding of zeolite formation can be exploited in diverse industrial applications. Regioselectively breaking the interlayer bonds in a three-dimensional UTL crystal yields ultrathin zeolite nanosheets that overcome the typical diffusion limitations encountered in many industrial applications. An improved three-step process has been designed for the production of mixed-matrix membranes in which UTL layers are delaminated by extrusion in a polyethylene matrix and subsequently aligned by biaxial squeeze deformation. The mild processing conditions and the variation of the strain during the squeeze deformation additionally allow a precise control over the size and alignment of the zeolite layers. The result is a porous matrix containing well-aligned UTL sheets with aspect ratios exceeding the state of the art by an order of magnitude. This makes the UTL membranes, in combination with EIS or ellipsometry, a very interesting candidate for e.g. the development of more sensitive and faster-responding gas sensors.nrpages: 178status: publishe

Invited Lecture - Material formation through self-organisation: understand to innovate synthesis

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Multidiagnostic analysis of silicate speciation in clear solutions/sols for zeolite synthesis

The formation of zeolites in presence of tetraalkylammonium cations from so-called clear solutions using silicon alkoxides is a highly complex process which challenges experimental chemistry. Most clear solutions are better described as clear sols as they contain nanosized silicate particles, which are formed during hydrolysis of the Si source before self-assembly into the zeolite framework. This process spans multiple time- and length-scales and only a combination of different analysis methods allows revelation of molecular level zeolite formation mechanisms. On the example of the early stages of the formation of zeolite beta from clear solutions/sols the different windows of observation of liquid-state 29Si and 27Al nuclear magnetic resonance (NMR) spectroscopy, small angle X-ray scattering (SAXS), dynamic light scattering (DLS) and mass spectrometry (MS) are demonstrated. Each diagnostic means by itself needs to be carefully assessed for its window of temporal and spatial resolution which can be achieved by exploiting the overlapping information available from their combination. © 2013 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: Multidiagnostic analysis of silicate speciation in clear solutions/sols for zeolite synthesis journaltitle: Microporous and Mesoporous Materials articlelink: http://dx.doi.org/10.1016/j.micromeso.2013.08.027 content_type: article copyright: Copyright © 2013 Elsevier Inc. All rights reserved.status: publishe

Toxicity of nanoparticles embedded in paints compared to pristine nanoparticles, in vitro study

The unique physicochemical properties of nanomaterials has led to an increased use in the paint and coating industry. In this study, the in vitro toxicity of three pristine ENPs (TiO2, Ag and SiO2), three aged paints containing ENPs (TiO2, Ag and SiO2) and control paints without ENPs were compared. In a first experiment, cytotoxicity was assessed using a biculture consisting of human bronchial epithelial (16HBE14o-) cells and human monocytic cells (THP-1) to determine subtoxic concentrations. In a second experiment, a new coculture model of the lung-blood barrier consisting of 16HBE14o- cells, THP-1 and human lung microvascular endothelial cells (HLMVEC) was used to study pulmonary and extrapulmonary toxicity. The results show that the pristine TiO2 and Ag ENPs have some cytotoxic effects at relative high dose, while pristine SiO2 ENPs and all aged paints with ENPs and control paints do not. In the complex triculture model of the lung-blood barrier, no considerable changes were observed after exposure to subtoxic concentration of the different pristine ENPs and paint particles. In conclusion, we demonstrated that although pristine ENPs show some toxic effects, no significant toxicological effects were observed when they were embedded in a complex paint matrix.publisher: Elsevier articletitle: Toxicity of nanoparticles embedded in paints compared to pristine nanoparticles, in vitro study journaltitle: Toxicology Letters articlelink: http://dx.doi.org/10.1016/j.toxlet.2014.11.030 content_type: article copyright: Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.status: publishe

Key Molecular Mechanisms for Zeolite Formation - Moving Towards Rational Zeolite Design

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Multidiagnostic Analysis to Track Zeolite Formation

Introduction The formation of zeolites in presence of tetraalkylammonium cations from so-called clear solutions using silicon alkoxides is a highly complex process. Our research aims to identify the key mechanisms on a molecular scale with the goal of understanding the factors that drive the formation of zeolites [1]. For this purpose we have used electrospray ionization mass spectrometry (ESI-MS), 29Si and 27Al liquid-NMR spectrometry, DOSY NMR (diffusion experiments) and small angle X-ray scattering (SAXS). Results and Discussion Here, we report the molecular mechanisms involved in the formation of microporous zeolite beta from liquid phase (Fig.1). The connectivity of both, oligomers and nanoparticles (NPs), has been quantitatively analysed, as well as the incorporation of Al in NPs and the specific interaction of silica-template within NPs. These data are compared with previous results on zeolites ZSM-5 (MFI), ZSM-11 (MEL) and SSZ-13 (CHA) from which general processes are concluded independently of the zeolite and/or template investigated [2]. Figure1. Zeolite beta crystallization from clear solution monitored by 29Si NMR. [1] Castro et al (2013) Micropor. Mesopor. Mat. (in press). [2] Eilesrten et al (2012) Chem. Mater. 24, 571-578status: publishe

Monitoring Early Zeolite Formation via in situ Electrochemical Impedance Spectroscopy

Hitherto zeolite formation is not fully understood. Although electrochemical impedance spectroscopy has proven to be a versatile tool for characterizing ionic solutions, it was never used for monitoring zeolite growth. We show here that EIS can quantitatively monitor zeolite formation, especially during crucial early steps where other methods fall short.crosscheck: This document is CrossCheck deposited related_data: Supplementary Information identifier: E. Breynaert (ORCID) copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: This article is freely available. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (CC BY 3.0) history: Received 3 February 2016; Accepted 19 March 2016; Accepted Manuscript published 21 March 2016; Advance Article published 29 March 2016; Version of Record published 7 April 2016status: publishe

Revisiting Silicalite-1 Nucleation in Clear Solution by Electrochemical Impedance Spectroscopy

EIS was used to detect and investigate nucleation in silicalite-1 clear solutions. Whereas zeolite nucleation was previously assumed to be a step event, inducing a sharp discontinuity around a Si/OH ratio of 1, complex bulk conductivity measurements at elevated temperatures reveal a gradual decay of the conductivity with increased silicon concentrations. Inverse Laplace transformation of the complex conductivity allows to observe the chemical exchange phenomena governing nano-aggregate formation. At low temperatures, the fast exchange between dissociated ions and ion pairs leads to a gradual decay of the conductivity with increasing silicon content. Upon heating, the exchange rate is slower and the residence time of ion pairs inside the nano-aggregates is increasing, facilitating the crystallization process. This results in a bilinear chemical exchange and gives rise to the discontinuity at the Si/OH ratio of 1, as observed by Fedeyko et al. EIS allows to observe slow chemical exchange processes occurring in zeolite precursors. Up to now, such processes could only be observed using techniques such as nuclear magnetic or electron paramagnetic resonance spectroscopy. In addition, EIS enables the quantification of interfacial processes via the double-layer capacitance. The electrical double layer thickness, derived from the double-layer capacitance, shows a similar gradual decay and confirms that the onset of nano-aggregate formation is indeed not narrowly defined.status: publishe

Toxicity of Nanoparticles Embedded in Paints Compared with Pristine Nanoparticles in Mice

The unique physical and chemical properties of nanomaterials have led to their increased use in many industrial applications, including as a paint additive. For example, titanium dioxide (TiO2) engineered nanoparticles (ENPs) have well-established anti-UV, self-cleaning, and air purification effects. Silver (Ag) ENPs are renowned for their anti-microbial capabilities and silicon dioxide (SiO2) ENPs are used as fire retardants and anti-scratch coatings. In this study, the toxic effects and biodistribution of three pristine ENPs (TiO2, Ag, and SiO2), three aged paints containing ENPs (TiO2, Ag, and SiO2) along with control paints without ENPs were compared. BALB/c mice were oropharyngeally aspirated with ENPs or paint particles (20 μg/aspiration) once a week for 5 weeks and sacrificed either 2 or 28 days post final aspiration treatment. A bronchoalveolar lavage was performed and systemic blood toxicity was evaluated to ascertain cell counts, induction of inflammatory cytokines, and key blood parameters. In addition, the lung, liver, kidney, spleen, and heart were harvested and metal concentrations were determined. Exposure to pristine ENPs caused subtle effects in the lungs and negligible alterations in the blood. The most pronounced toxic effects were observed after Ag ENPs exposure; an increased neutrophil count and a twofold increase in pro-inflammatory cytokine secretion (keratinocyte chemoattractant (KC) and interleukin-1ß (IL-1ß)) were identified. The paint containing TiO2 ENPs did not modify macrophage and neutrophil counts, but mildly induced KC and IL-1ß. The paints containing Ag or SiO2 did not show significant toxicity. Biodistribution experiments showed distribution of Ag and Si outside the lung after aspiration to respectively pristine Ag or SiO2 ENPs. In conclusion, we demonstrated that even though direct exposure to ENPs induced some toxic effects, once they were embedded in a complex paint matrix little to no adverse toxicological effects were identified.status: publishe