https://www.lehigh.edu/operando/Publications/1999%20Titania-silica%20molec%20struc%20physico-chemical.pdf

Titania-silica as catalysts : molecular structural characteristics and physico-chemical properties

Fundamentals and applications of pervaporation through zeolite membranes

Photocatalytic water treatment using nanocrystalline titanium dioxide (NTO) is a well-known advanced oxidation process (AOP) for environmental remediation. With the in situ generation of electron-hole pairs upon irradiation with light, NTO can mineralize a wide range of organic compounds into harmless end products such as carbon dioxide, water, and inorganic ions. Photocatalytic degradation kinetics of pollutants by NTO is a topic of debate and the mostly reporting Langmuir-Hinshelwood kinetics must accompanied with proper experimental evidences. Different NTO morphologies or surface treatments on NTO can increase the photocatalytic efficiency in degradation reactions. Wisely designed photocatalytic reactors can decrease energy consumption or can avoid post-separation stages in photocatalytic water treatment processes. Doping NTO with metals or non-metals can reduce the band gap of the doped catalyst, enabling light absorption in the visible region. Coupling NTO photocatalysis with other water-treatment technologies can be more beneficial, especially in large-scale treatments. This review describes recent developments in the field of photocatalytic water treatment using NTO.

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Photocatalytic Water Treatment by Titanium Dioxide: Recent Updates

Alternative energy technologies are greatly hindered by significant limitations in materials science. From low activity to poor stability, and from mineral scarcity to high cost, the current materials are not able to cope with the significant challenges of clean energy technologies. However, recent advances in the preparation of nanomaterials, porous solids, and nanostructured solids are providing hope in the race for a better, cleaner energy production. The present contribution critically reviews the development and role of mesoporosity in a wide range of technologies, as this provides for critical improvements in accessibility, the dispersion of the active phase and a higher surface area. Relevant examples of the development of mesoporosity by a wide range of techniques are provided, including the preparation of hierarchical structures with pore systems in different scale ranges. Mesoporosity plays a significant role in catalysis, especially in the most challenging processes where bulky molecules, like those obtained from biomass or highly unreactive species, such as CO2 should be transformed into most valuable products. Furthermore, mesoporous materials also play a significant role as electrodes in fuel and solar cells and in thermoelectric devices, technologies which are benefiting from improved accessibility and a better dispersion of materials with controlled porosity.

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Mesoporous materials for clean energy technologies

Crystalline microporous solids are an important class of inorganic materials with uses in different areas impacting our everyday lives, namely as catalysts, adsorbents, and ion exchangers. Advancements in synthesis have been invaluable in expanding the classical aluminosilicate zeolites to new unique framework types and compositions, motivating innovative developments. However, the inexhaustible post-synthetic options to tailor zeolite properties have been and will continue to be indispensable to realize emerging and to improve conventional applications. Starting from the routine drying and template removal processes that every zeolite must experience prior to use, a wide spectrum of treatments exists to alter individual or collective characteristics of these materials for optimal performance. This review documents the toolbox of post-synthetic strategies available to tune the properties of zeolitic materials for specific functions. The categorisation is based on the scale at which the alteration is aimed at, including the atomic structure (e.g. the introduction, dislodgment, or replacement of framework atoms), the micropore level (e.g. template removal and functionalisation by inorganic and organic species), and the crystal and particle levels (e.g. the introduction of auxiliary porosity). Through examples in the recent literature, it is shown that the combination of post-synthetic methods enables rational zeolite design, extending the characteristics of these materials way beyond those imposed by the synthesis conditions.

Tailored crystalline microporous materials by post-synthesis modification

Ge-ZSM-5 zeolites have been synthesized and characterized by SEM, n-hexane adsorption, XRD, MAS NMR, IR, and Raman spectroscopy. Despite the large size of the germanium atoms, up to 12.8 Ge/unit cell could be incorporated into the MFI framework. In order to rationalize this, a site preference of the germanium atoms in the lattice is proposod. Although a large amount of germanium is incorporated, only small changes in the unit cell parameters and lattice vibration frequencies are observed, suggesting that the T-T and T-O distances in the framework are nearly unchanged. However, the T-O-T deformation band is significantly broadened and shifted to higher wavenumber. From these findings it is deduced that the incorporation of germanium leads mainly to a decrease in the T-O-T angle

Synthesis and characterization of Ge-ZSM-5 zeolites

Highly dealuminated faujasite-type zeolites with different dealumination histories, different pore structures, and Si:Al ratios ranging from 40:1 to 300:1 have been investigated by temperature-programmed desorption of ammonia (NH 3 -TPD) and by FTIR spectroscopy: ultrastable zeolite Y (US-Ex), dealuminated by hydrothermal treatment and a subsequent extraction of the extraframework aluminum; DAY, dealuminated by exchange with SiCl 4 ; and the recently synthesized ZSM-20, dealuminated hydrothermally. A correlation could be established between the amount of adsorbed NH 3 determined by TPD and the integrated absorbances of N-H bending bands in the FTIR spectra

Characterization of highly dealuminated faujasite-type zeolites: ultrastable zeolite Y and ZSM-20

The chemical bonding of titanium in MFI-type zeolites (Ti-silicalite) has been investigated using x-ray photoelectron spectroscopy (XPS). Different titanium silicalites as well as pure titania (anatase) have been analysed. We have found a distinctively higher binding energy of the Ti 2p photoelectrons in Ti-silicalite than in titania- or anatase-containing silicalite. Ti has the same oxidation state in all solids under study. We attribute the difference in binding energy to different oxygen coordinations of the titanium in the framework of Ti-silicalite (tetrahedral) and anatase (octahedral). This suggestion is supported by XPS-studies of TiO2SiO2 glasses and TiO2SiO2 mixed oxides where a similar shift was found. Additional Raman-spectroscopy investigations of the samples indicate the existence of tetrahedrally coordinated titanium by the appearance of a characteristic band at ∼ 965 cm−1. Non-framework TiO2 species containing octahedrally coordinated titanium could also be distinguished by XPS. Further Ti incorporation is indicated by the expansion of the unit cell which is related to the Ti 2p intensity for the framework titanium.

XPS‐investigation of titanium modified MFI‐type zeolites

Zr-doped titania of anatase structure type has been prepared by a combined sol–gel and chemical vapour deposition (CVD) process. The material has been characterized by XRD, TEM and chemical analysis. The photocatalytic performance has been investigated in the oxidative decomposition of the pharmaceutical ibuprofen (IBP) down to low ppm concentrations. The change of the composition of the reaction solution after photocatalytic treatment was followed by UV–Vis spectroscopy and GC/MS. Formation of reaction intermediates was studied by HPLC coupled electrospray ionization time-of-flight mass spectrometry ESI-TOF-MS. The catalytic performance has been studied by varying the catalyst and substrate concentration as well as changing the catalyst-to-substrate ratio. The influence of pH, adsorption and re-use of the catalyst has been tested. The results confirm the high catalytic activity of Zr-doped titania compared to pure titania at low catalyst loading. The material shows the improved textural mesoporosity. However, more reaction intermediates were formed, leading to faster deactivation of the photocatalyst. ESI-TOF-MS measurements point to the formation of a couple of reaction intermediates, which poison the catalyst.

Photocatalytic properties of Zr-doped titania in the degradation of the pharmaceutical ibuprofen

In the present article, the synthesis of TiO2/diazonium/graphene oxide and its photocatalytic activity for methylene blue (MB) degradation have been demonstrated. The functionalization of graphene oxide (GO) with diazonium salt (diazonium-GO) was conducted for enhancing the dispersibility of GO in distilled water. TiO2 was highly dispersed in diazonium-GO to form TiO2/diazonium/graphene. The obtained specimens were characterized by X-ray diffraction, FT-IR spectroscopy, Raman spectroscopy, UV-Vis spectroscopy, scanning electron microscope, transmission electron microscopy, and X-ray photoelectron spectroscopy. It was found that the TiO2 phase in TiO2/diazonium/GO composites can be controlled by adjusting the amount of ethanol or titanium oxide in the reactant mixture. The obtained composites exhibited photocatalytic activities for methylene blue degradation (MB). The composite with ac. 70% anatase can provide the highest MB degradation efficiency. The studying of some intermediates for MB photocatalytic degradation using LC-MS showed that structure of MB by the cleavage and oxidation of one or more of the methyl group substituent on the amine groups lead to form compounds with low molecular masses. Total organic carbon studies confirmed a complete mineralization of MB. The present catalyst was stable and recyclable after three times with a negligible loss of catalytic activity. In addition, the TiO2/diazonium/GO can also photocatalyze for the degradation of some other dyes (phenol, methyl red, and Congo red).

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Vu Anh Tuan

Papers

Synthesis and characterization of Ge-ZSM-5 zeolites

Characterization of highly dealuminated faujasite-type zeolites: ultrastable zeolite Y and ZSM-20

XPS‐investigation of titanium modified MFI‐type zeolites

Photocatalytic properties of Zr-doped titania in the degradation of the pharmaceutical ibuprofen

TiO2/Diazonium/Graphene Oxide Composites: Synthesis and Visible-Light-Driven Photocatalytic Degradation of Methylene Blue