Preliminary study of the use of β-SiC foam as a photocatalytic support for water treatment

Simulation of solar photocatalytic reactor with immobilized photocatalyst for degradation of pharmaceutical pollutants

This study focuses on the simulation of a solar photocatalytic reactor with linear parabolic reflectors and continuous fluid flow. The simulation approach was initially validated against experimental data reported by Miranda-Garcia et al. Catal Today 151:107-113 (2010), yielding a high degree of accuracy of approximately 0.99%. In this article, the effect of light intensity, Reynolds number, and fluid residence time on the performance of a photoreactor system using titanium dioxide catalyst and ibuprofen pollutant has been investigated. The results show that the intensity of light intensity has an effect of up to 29% on the decomposition of pollutant. With the increase of radiation intensity, the removal of pollutants reached from 85.5% to 99.46%. It has been demonstrated that higher flow turbulence significantly impacts removal efficiency, achieving rates of up to 71%. Moreover, enhancing the fluid's residence time through implementing a recirculating flow within the photoreactor has resulted in a 13% enhancement in removal efficiency. These results can be an important guide for optimizing the design of photocatalytic reactors. By adjusting the examined parameters, it is possible to obtain a higher efficiency in the removal of pollutants, which will be very effective in the scaling and industrial design of solar reactors.

SiC Foams for the Photocatalytic Degradation of Methylene Blue under Visible Light Irradiation

SiC foams were synthesized by impregnating preceramic polymer into polyurethane foam templates, resulting in a photo-catalytically active material for the degradation of methylene blue. The crystalline structure, electronic properties, and photocatalytic performance of the SiC foams were characterized using a series of experimental techniques, including X-ray diffraction, electron microscopy, energy dispersive X-ray spectroscopy, N2 physisorption measurements, UV-visible spectroscopy, and methylene blue photodegradation tests. The original polyurethane template's microporous structure was maintained during the formation of the SiC foam, while additional mesopores were introduced by the porogen moieties added to the preceramic polymers. The prepared SiC-based photocatalyst showed attractive photocatalytic activity under visible light irradiation. This structured and reactive material offers good potential for application as a catalytic contactor or membrane reactor for the semi-continuous treatment of contaminated waste waters in ambient conditions.

Porous Silicon Carbide (SiC): A Chance for Improving Catalysts or Just Another Active-Phase Carrier?

There is an obvious gap between efforts dedicated to the control of chemicophysical and morphological properties of catalyst active phases and the attention paid to the search of new materials to be employed as functional carriers in the upgrading of heterogeneous catalysts. Economic constraints and common habits in preparing heterogeneous catalysts have narrowed the selection of active-phase carriers to a handful of materials: oxide-based ceramics (e.g. Al₂O₃, SiO₂, TiO₂, and aluminosilicates-zeolites) and carbon. However, these carriers occasionally face chemicophysical constraints that limit their application in catalysis. For instance, oxides are easily corroded by acids or bases, and carbon is not resistant to oxidation. Therefore, these carriers cannot be recycled. Moreover, the poor thermal conductivity of metal oxide carriers often translates into permanent alterations of the catalyst active sites (i.e. metal active-phase sintering) that compromise the catalyst performance and its lifetime on run. Therefore, the development of new carriers for the design and synthesis of advanced functional catalytic materials and processes is an urgent priority for the heterogeneous catalysis of the future. Silicon carbide (SiC) is a non-oxide semiconductor with unique chemicophysical properties that make it highly attractive in several branches of catalysis. Accordingly, the past decade has witnessed a large increase of reports dedicated to the design of SiC-based catalysts, also in light of a steadily growing portfolio of porous SiC materials covering a wide range of well-controlled pore structure and surface properties. This review article provides a comprehensive overview on the synthesis and use of macro/mesoporous SiC materials in catalysis, stressing their unique features for the design of efficient, cost-effective, and easy to scale-up heterogeneous catalysts, outlining their success where other and more classical oxide-based supports failed. All applications of SiC in catalysis will be reviewed from the perspective of a given chemical reaction, highlighting all improvements rising from the use of SiC in terms of activity, selectivity, and process sustainability. We feel that the experienced viewpoint of SiC-based catalyst producers and end users (these authors) and their critical presentation of a comprehensive overview on the applications of SiC in catalysis will help the readership to create its own opinion on the central role of SiC for the future of heterogeneous catalysis.

TiO2 and TiO2-Carbon Hybrid Photocatalysts for Diuron Removal from Water

TiO2 and TiO2-activated carbon (AC) photocatalysts have been prepared (by sol-gel synthesis), characterized, and tested in the removal of diuron from water under simulated solar light. The preparation variables of the two series of catalysts are: (i) heat-treatment temperature of bare TiO2 (350, 400, 450 and 500 °C) and (ii) activated carbon content (0.5, 1, 5, and 10 wt.%) in TiO2-AC samples heat-treated at 350 °C. The activated carbon was previously prepared by hydrothermal carbonization of saccharose and has spherical shape. The heat-treatment temperature does not determine the efficiency of TiO2 for diuron photocatalytic degradation, but clearly influences the diuron adsorption capacity. The capacity of TiO2-AC samples for diuron removal increases with the carbon content and it is the result of combined diuron adsorption and photodegradation. Thus, the sample with highest carbon content (10 wt.% nominal) leads to the highest diuron removal. The TiO2-AC photocatalysts have proved to be capable of degrading diuron previously adsorbed in dark conditions, which allows their regeneration.

Ti-Modified LaFeO3/β-SiC Alveolar Foams as Immobilized Dual Catalysts with Combined Photo-Fenton and Photocatalytic Activity

Ti-modified LaFeO₃/β-SiC alveolar foams were used as immobilized, highly robust dual catalysts with combined photocatalytic wet peroxide oxidation and photocatalytic activity under UV-A light. They were prepared by incipient wetness impregnation of a β-SiC foam support, by implementing a sol-gel Pechini synthesis at the foam surface in the presence of dried amorphous sol-gel titania as a titanium source. The physicochemical and catalytic features suggest the stabilization at the foam surface of a substituted La_1-xTi_xFeO₃ catalyst analogous to its powdery counterpart. Taking 4-chlorophenol removal in water as a model reaction, its dual nature enables both high reaction rates and full total organic carbon (TOC) conversion because of a synergy effect, while its macroscopic structure overcomes the drawback of working with powdery catalysts. Further, it yields photonic efficiencies for degradation and mineralization of ca. 9.4 and 38%, respectively, that strongly outperform those obtained with a reference TiO₂ P25/β-SiC foam photocatalyst. The enhancement of the catalyst robustness upon Ti modification prevents any Fe leaching to the solution, and therefore, the optimized macroscopic foam catalyst with 10 wt % catalyst loading operates through pure heterogeneous surface reactions, without any activity loss during reusability test cycles.

Novel Precursor-Derived Meso-/Macroporous TiO₂/SiOC Nanocomposites with Highly Stable Anatase Nanophase Providing Visible Light Photocatalytic Activity and Superior Adsorption of Organic Dyes

Titania (TiO₂) is considered to have immense potential as a photocatalyst, the anatase phase in particular. There have been numerous attempts to push the limits of its catalytic activity to higher wavelengths to harness the visible electromagnetic radiation. Most of the investigations till date have been restricted to fine-tuning the bandgap by doping, control of defect chemistry at the surface and several to first principle simulations either with limited success or success at the cost of complexities in processing. Here, we report a simple and elegant way of preparing ceramics through precursor chemistry which involves synthesis of macroporous and mesoporous nanocomposites with in situ formation of TiO₂ nanocrystals into a robust and protecting SiOC matrix. The in situ nanoscaled TiO₂ is anatase of size 9–10 nm, which is uniformly distributed in an amorphous SiOC matrix forming a new generation of nanocomposites that combine the robustness, structural stability and durability of the SiOC matrix while achieving nanoscaled TiO₂ functionalities. The stabilization of the anatase phase even at temperature as high as 1200 °C was evident. With an average pore size of 6.8 nm, surface area of 129 m²/g (BET) and pore volume of 0.22 cm³/g (BET), mesoporosity was achieved in the nanocomposites. The composites exhibited visible light photocatalytic activity, which is attributed to the Ti–O–C/TiC bonds resulting in the reduction of band gap by 0.2 to 0.9 eV. Furthermore, the heterojunction formed between the amorphous SiOC and crystalline TiO₂ is also expected to minimize the recombination rate of electron-hole pair, making these novel nanocomposites based on TiO₂ extremely active in visible wavelength regime.

Nitrogen-containing organic compounds: Origins, toxicity and conditions of their photocatalytic mineralization over TiO2

Sustainable water management remains a global concern to meet the food needs of industrial and agricultural activities. Therefore, pollution abatement techniques, cheap and environmentally, are highly desired and recommended. The present review is devoted to the origin and the toxicity of nitrogen-containing organic compounds in water. The progress made in removing these pollutants, in recent years, is addressed. However, a prominent place is given to the photocatalytic degradation process using the TiO₂ as a semiconductor, the conditions for good mineralization and especially the factors influencing it. The parameters that impact the performance of this method are the pH, the temperature, the reactor used, the light, the concentration of the pollutant, the amount of catalyst, etc. Up to now, the importance of one parameter relative to another has not been established because in the context of the photocatalytic degradation, certain parameters are often tightly coupled. Consequently, the mineralization is dependent on the initial degree of oxidation of nitrogen atom contained in the pollutant to be degraded. The hydroxyl nitrogen is primarily converted into nitrate ions (NO₃^-), while the amides and the primary amines are converted into ammonium ions (NH₄⁺).

Silicon carbide foam as a porous support platform for catalytic applications

This review provides an overview of the use of foam-structured SiC as a porous support platform in some typical catalytic processes both for gas-phase and liquid-phase reactions, such as H₂S selective oxidation, Friedel–Crafts benzoylation and Fischer–Tropsch synthesis.

TiO2/β-SiC foam-structured photoreactor for continuous wastewater treatment

INTRODUCTION

This study of photocatalytic degradation of wastewater was carried out in alveolar cell β-SiC foam-structured photocatalytic reactors working in a recirculation mode. The immobilization of TiO2 on β-SiC foams was efficiently obtained through a sol-gel technique in acidic conditions.

DISCUSSION

In order to optimize degradation yields obtained by the foam-structured prototype reactor for the photocatalytic water treatment, the operating conditions of the photoreactor have been investigated and the efficiency of the process was evaluated by measuring the photocatalytic degradation of Diuron (3-(3,4-dichlorophenyl)-1,1-dimethyl-urea)) under UV irradiation. Kinetic studies were carried out by investigating the influence of different parameters controlling the reaction (TiO2 loading and β-SiC foam cell size). The ageing of TiO2/β-SiC foam photocatalytic materials and the mineralization (TOC, Cl-, NO3- and NH4+) of Diuron were investigated.

Photodegradation of indigo carmine and methylene blue dyes in aqueous solution by SiC-TiO2 catalysts prepared by sol-gel

Indigo carmine and methylene blue dyes in aqueous solution were photodegraded using SiC-TiO(2) catalysts prepared by sol-gel method. After thermal treatment at 450°C, SiC-TiO(2) catalysts prepared in this work showed the presence of SiC and TiO(2) anatase phase. Those compounds showed specific surface area values around 22-25 m(2)g(-1), and energy band gap values close to 3.05 eV. In comparison with TiO(2) (P25), SiC-TiO(2) catalysts showed the highest activity for indigo carmine and methylene blue degradation, but this activity cannot be attributed to the properties above mentioned. Therefore, photocatalytic performance is due to the synergy effect between SiC and TiO(2) particles caused by the sol-gel method used to prepare the SiC-TiO(2) catalysts. TiO(2) nanoparticles are well dispersed onto SiC surface allowing the transfer of electronic charges between SiC and TiO(2) semiconductors, which avoid the fast recombination of the electron-hole pair during the photocatalytic process.