Composite TiO2-based photocatalyst with enhanced performance.

TiO2 is the most studied photocatalyst because of its non-toxicity, chemical stability, and low cost. However, the problem of TiO2 is its low activity in the visible region of the spectrum. In this study, we focused on the preparation of composite photocatalytic materials with altered light absorption properties. TiO2 P25 and various metal oxides were mechanically joined by ball-milling and immobilized on glass plates. The prepared samples were evaluated based on their ability to degrade NO in gas phase. The formation of undesirable byproducts was also investigated. Four best performing composites were later chosen, characterized, and further evaluated under various conditions. According to their performance, the metal oxide additives can be divided into three groups. P25/Fe2O3 showed the most promising results-an increase in overall deNOx activity under modified ISO conditions and altered selectivity (less NO2 is formed) under both simulated outdoor and simulated indoor conditions. On the other hand, P25/V2O5 composite showed negligible photocatalytic activity. The intermediate group includes P25/WO3 and P25/ZnO photocatalysts, whose performances are similar to those of pristine P25.

Hierarchical TiO2 Layers Prepared by Plasma Jets.

Heterogeneous photocatalysis of TiO2 is one of the most efficient advanced oxidation processes for water and air purification. Here, we prepared hierarchical TiO2 layers (Spikelets) by hollow-cathode discharge sputtering and tested their photocatalytic performance in the abatement of inorganic (NO, NO2) and organic (4-chlorophenol) pollutant dispersed in air and water, respectively. The structural-textural properties of the photocatalysts were determined via variety of physico-chemical techniques (XRD, Raman spectroscopy, SEM, FE-SEM. DF-TEM, EDAX and DC measurements). The photocatalysis was carried out under conditions similar to real environment conditions. Although the abatement of NO and NO2 was comparable with that of industrial benchmark Aeroxide® TiO2 P25, the formation of harmful nitrous acid (HONO) product on the Spikelet TiO2 layers was suppressed. Similarly, in the decontamination of water by organics, the mineralization of 4-chlorophenol on Spikelet layers was interestingly the same, although their reaction rate constant was three-times lower. The possible explanation may be the more than half-magnitude order higher external quantum efficacy (EQE) compared to that of the reference TiO2 P25 layer. Therefore, such favorable kinetics and reaction selectivity, together with feasible scale-up, make the hierarchical TiO2 layers very promising photocatalyst which can be used for environmental remediation.

Removal of Ampicillin by Heterogeneous Photocatalysis: Combined Experimental and DFT Study.

A long-term exposition of antibiotics represents a serious problem for the environment, especially for human health. Heterogeneous photocatalysis opens a green way for their removal. Here, we correlated the structural-textural properties of TiO2 photocatalysts with their photocatalytic performance in ampicillin abatement. The tested nanoparticles included anatase and rutile and their defined mixtures. The nominal size range varied from 5 to 800 nm, Aeroxide P25 serving as an industrial benchmark reference. The degradation mechanism of photocatalytic ampicillin abatement was studied by employing both experimental (UPLC/MS/MS, hydroxyl radical scavenger) and theoretical (quantum calculations) approaches. Photocatalytic activity increased with the increasing particle size, generally, anatase being more active than rutile. Interestingly, in the dark, the ampicillin concentration decreased as well, especially in the presence of very small nanoparticles. Even if the photolysis of ampicillin was negligible, a very high degree of mineralization of antibiotic was achieved photocatalytically using the smallest nanoparticles of both allotropes and their mixtures. Furthermore, for anatase samples, the reaction rate constant increases with increasing crystallite size, while the degree of mineralization decreases. Importantly, the suggested degradation pathway mechanism determined by DFT modeling was in very good agreement with experimentally detected reaction products.

Ultrasonic Pretreatment as a Tool for the Preparation of Low-Defect Zeolite Mordenite.

The effects of the ultrasonic (US) pretreatment of synthesis gel for the preparation of mordenite zeolite were studied in comparison with the classical stirring method. Even though the US pretreatment was performed before the hydrothermal crystallization, it significantly affected the properties of the obtained mordenite crystals. The US-assisted procedure resulted in a material with improved textural characteristics, in particular, the micropore volume accessible for nitrogen molecules in the as-made form. On the other hand, mordenite prepared with the classical stirring method demonstrated comparable sorption properties only after a postsynthetic treatment. Moreover, in the case of US-pretreated mordenite, altered crystal shape and more homogeneous morphology were observed. 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) demonstrated that the US pretreatment introduced structural changes on the atomic level, resulting in fewer defects (reflected in the number of silanol groups) and less pore blockage (affected by Na+ cations) for the as-made sample.

The development of a fully integrated 3D printed electrochemical platform and its application to investigate the chemical reaction between carbon dioxide and hydrazine.

The combination of computer assisted design and 3D printing has recently enabled fast and inexpensive manufacture of customized 'reactionware' for broad range of electrochemical applications. In this work bi-material fused deposition modeling 3D printing is utilized to construct an integrated platform based on a polyamide electrochemical cell and electrodes manufactured from a polylactic acid-carbon nanotube conductive composite. The cell contains separated compartments for the reference and counter electrode and enables reactants to be introduced and inspected under oxygen-free conditions. The developed platform was employed in a study investigating the electrochemical oxidation of aqueous hydrazine coupled to its bulk reaction with carbon dioxide. The analysis of cyclic voltammograms obtained in reaction mixtures with systematically varied composition confirmed that the reaction between hydrazine and carbon dioxide follows 1/1 stoichiometry and the corresponding equilibrium constant amounts to (2.8 ± 0.6) × 103. Experimental characteristics were verified by results of numerical simulations based on the finite-element-method.

Mechanochemical Pretreatment for Efficient Solvent-Free Synthesis of SSZ-13 Zeolite.

The economical and environmentally benign synthesis of SSZ-13 zeolite was possible due to the mechanochemical activation of dry reagents by planetary mill. Contrary to manual grinding in a mortar, the proposed automatized approach is scalable and reproducible. This solvent-free process provided a huge gain in product/gel ratios, significantly minimized reaction space and organic structure-directing agent use, and allowed for the elimination of agitation. Obtained materials were comparable to the product of "classical" syntheses. The use of different silica sources resulted in SSZ-13 zeolites with various characteristics: different Si/Al ratio and crystal size.

Toxicity of TiO2, ZnO, and SiO2 Nanoparticles in Human Lung Cells: Safe-by-Design Development of Construction Materials.

Rapid progress in the development of highly efficient nanoparticle-based construction technologies has not always been accompanied by a corresponding understanding of their effects on human health and ecosystems. In this study, we compare the toxicological effects of pristine TiO2, ZnO, SiO2, and coated SiO2 nanoparticles, and evaluate their suitability as additives to consolidants of weathered construction materials. First, water soluble tetrazolium 1 (WST-1) and lactate dehydrogenase (LDH) assays were used to determine the viability of human alveolar A549 cells at various nanoparticle concentrations (0-250 µg mL-1). While the pristine TiO2 and coated SiO2 nanoparticles did not exhibit any cytotoxic effects up to the highest tested concentration, the pristine SiO2 and ZnO nanoparticles significantly reduced cell viability. Second, as all developed nanoparticle-modified consolidants increased the mechanical strength of weathered sandstone, the decisive criterion for the selection of the most suitable nanoparticle additive was as low toxicity as possible. We believe that this approach would be of high importance in the industry, to identify materials representing top functional properties and low toxicity, at an early stage of the product development.

Designing Porphyrinic Covalent Organic Frameworks for the Photodynamic Inactivation of Bacteria.

Microbial colonization of biomedical devices is a recognized complication contributing to healthcare-associated infections. One of the possible approaches to prevent surfaces from the biofilm formation is antimicrobial photodynamic inactivation based on the cytotoxic effect of singlet oxygen, O2(1Δg), a short-lived, highly oxidative species, produced by energy transfer between excited photosensitizers and molecular oxygen. We synthesized porphyrin-based covalent organic frameworks (COFs) by Schiff-base chemistry. These novel COFs have a three-dimensional, diamond-like structure. The detailed analysis of their photophysical and photochemical properties shows that the COFs effectively produce O2(1Δg) under visible light irradiation, and especially three-dimensional structures have strong antibacterial effects toward Pseudomonas aeruginosa and Enterococcus faecalis biofilms. The COFs exhibit high photostability and broad spectral efficiency. Hence, the porphyrinic COFs are suitable candidates for the design of antibacterial coating for indoor applications.

Photocatalytic activity of porous multiwalled carbon nanotube-TiO2 composite layers for pollutant degradation.

TiO2 nanoparticles are suitable building blocks nanostructures for the synthesis of porous functional thin films. Here we report the preparation of films using brookite, P25 titania and anatase pristine nanoparticles and of nanocomposite layers combining anatase nanoparticles and multi-walled carbon nanotube (MWCNT) at various concentrations. The structure and phase composition of the layers were characterized by X-ray diffraction and Raman spectroscopy. Their morphology and texture properties were determined by scanning electron microscopy and krypton adsorption experiments, respectively. Additionally to a strong absorption in the UV range, the composites exhibited light absorption in the visible range as well. The photocatalytic performance of the layers was tested in the degradation of aqueous solutions of 4-chlorophenol serving as a model of an eco-persistent pollutant. Besides the determination of the decrease in the concentration of 4-chlorophenol, also the formation of intermediate degradation products, namely hydroquinone and benzoquinone, was followed. The presence of MWCNTs had a beneficial effect on the photocatalytic performance, a marked increase in the photocatalytic degradation rate constant being observed even at very low concentrations of MWCNTs. Compared to a P25 reference layer, the first order rate reaction constant increased by about 100% for the composite films containing MWCNTs at concentrations above 0.6 wt%. The key parameters for the enhancement of the photocatalytic performance are discussed. The presence of carbon nanotubes influences beneficially the degradation of 4-chlorophenol by an attack of the primarily photoproduced hydroxyl radicals onto the 4-chlorophenol molecules. The degradation due to the direct charge transfer is practically not influenced at all.

Combined biocidal action of silver nanoparticles and ions against Chlorococcales (Scenedesmus quadricauda, Chlorella vulgaris) and filamentous algae (Klebsormidium sp.).

Despite the extensive research, the mechanism of the antimicrobial and biocidal performance of silver nanoparticles has not been unequivocally elucidated yet. Our study was aimed at the investigation of the ability of silver nanoparticles to suppress the growth of three types of algae colonizing the wetted surfaces or submerged objects and the mechanism of their action. Silver nanoparticles exhibited a substantial toxicity towards Chlorococcales Scenedesmus quadricauda, Chlorella vulgaris, and filamentous algae Klebsormidium sp., which correlated with their particle size. The particles had very good stability against agglomeration even in the presence of multivalent cations. The concentration of silver ions in equilibrium with nanoparticles markedly depended on the particle size, achieving about 6 % and as low as about 0.1 % or even less for the particles 5 nm in size and for larger ones (40-70 nm), respectively. Even very limited proportion of small particles together with larger ones could substantially increase concentration of Ag ions in solution. The highest toxicity was found for the 5-nm-sized particles, being the smallest ones in this study. Their toxicity was even higher than that of silver ions at the same silver concentration. When compared as a function of the Ag(+) concentration in equilibrium with 5-nm particles, the toxicity of ions was at least 17 times higher than that obtained by dissolving silver nitrite (if not taking into account the effect of nanoparticles themselves). The mechanism of the toxicity of silver nanoparticles was found complex with an important role played by the adsorption of silver nanoparticles and the ions released from the particles on the cell surface. This mechanism could be described as some sort of synergy between nanoparticles and ions. While our study clearly showed the presence of this synergy, its detailed explanation is experimentally highly demanding, requiring a close cooperation between materials scientists, physical chemists, and biologists.

Tailoring the morphology of mesoporous titania thin films through biotemplating with nanocrystalline cellulose.

The tunable porosity of titania thin films is a key factor for successful applications in photovoltaics, sensing, and photocatalysis. Here, we report on nanocrystalline cellulose (NCC) as a novel shape-persistent templating agent enabling the straightforward synthesis of mesoporous titania thin films. The obtained structures are highly porous anatase morphologies having well-defined, narrow pore size distributions. By varying the titania-to-template ratio, it is possible to tune the surface area, pore size, pore anisotropy, and dimensions of titania crystallites in the films. Moreover, a post-treatment at high humidity and subsequent slow template removal can be used to achieve pore widening; this treatment is also beneficial for the multilayer deposition of thick films. The resulting homogeneous transparent films can be directly spin- or dip- coated on glass, silicon, and transparent conducting oxide (TCO) substrates. The mesoporous titania films show very high activity in the photocatalytic NO conversion and in the degradation of 4-chlorophenol. Furthermore, the films can be successfully applied as anodes in dye-sensitized solar cells.

High photocatalytic activity of transparent films composed of ZnO nanosheets.

Nanometric thin films were prepared by dip-coating and inkjet printing ZnO nanosheets on glass plates. The side-by-side alignment of the ZnO nanosheets on the substrate resulted in thin, transparent, oriented ZnO surfaces with the high-energy {001} facets exposed. The method of nanosheet deposition affected the film morphology; the dip-coated films were very smooth and nonporous, while the inkjet-printed films were rough and porous with the estimated void volume approximately 60-70% of the total film volume. The first-order rate constants for the photocatalytic degradation of 4-chlorophenol on the nanosheet-based films were approximately 2 times larger than those on nanocolumnar ZnO films or ZnO films prepared by the sol-gel technique. We attribute the high photocatalytic activity of the ZnO nanosheets to the fact that their {001} facets were predominantly exposed to the oxidized substrate. This surface arrangement and the simplicity of fabricating the ZnO nanosheet-based films make them promising for the construction of optical devices and dye-sensitized solar cells.

Adsorption and photocatalytic and photosensitised bleaching of acid orange 7 on multilayer mesoporous films of TiO2.

A series of mesoporous films of titania of different thicknesses are prepared and their surface areas and porosities determined by physical adsorption using Kr as the adsorbate. The amounts of acid orange 7 (AO7) adsorbed by these films are found to be proportional to their measured surface areas and so the possibility of using this as a method of determining the surface area of thin titania films is discussed. The initial rates of UV-driven photocatalytic- and visible-driven photosensitised-bleaching of AO7 in solution, upon UVA and visible light irradiation, respectively, are also directly dependent upon the measured surface areas of the titania films. The quantum efficiencies for the UV photocatalytic- and visible photosensitised-bleaching of AO7 by the thickest of the AO7 films were estimated to be 0.08 and 0.01%, respectively.

A facile synthesis of mesoporous crystalline tin oxide films involving a base-triggered formation of sol-gel building blocks.

We have developed a new facile procedure for manufacturing crystalline thin films of SnO2 with a uniform mesoporous architecture and full crystallinity of the walls. The procedure is based on the evaporation-induced self-assembly (EISA) of prehydrolyzed tin oxide precursor directed by a commercially available Pluronic polymer. The formation of the tin oxide precursor, which can be self-assembled into a mesoporous structure, is achieved by an addition of ammonium hydroxide to a tin tetrachloride solution. The relative concentration of ammonium hydroxide as well as the duration and temperature of the hydrolysis reaction influence significantly the properties of hydrolyzed tin oxide species and the mesostructure assembled from them. The films coated from these precursor solutions and calcined at 300 °C to 400 °C exhibit a well-developed worm-like porosity with a wall to wall distance of ca. 18 nm, a surface area of up to 50 cm2 cm(-2) (corresponding to 55±5 m2 g(-1)), and high crystallinity.

Mesoporous films of TiO(2) as efficient photocatalysts for the purification of water.

Variably thick mesoporous TiO(2) films were prepared by alternately dip- and spray-coating using sol containing titanium(IV) alkoxide, concentrated HCl and suitable block-copolymer as a structure directing agent. The film thickness was controlled by varying the number of deposited layers. Their porosity was homogeneous: surface area and pore volume increased linearly with increasing number of deposited layers. Photoactivity of the films was tested employing photocatalytic degradation of 10(-4) M 4-chlorophenol in a 60 mL photoreactor under UV irradiation at 365 nm. The incident light intensity was 1 mW cm(-2). The degradation rate constants increased with increasing number of layers, proportional to their absorbances. However, the progressive improvement of the photocatalytic performance slightly decreased with the increasing number of layers. The spray-coating layers exhibited lower photocatalytic performance due to their smaller thicknesses.

Ultrasmall titania nanocrystals and their direct assembly into mesoporous structures showing fast lithium insertion.

Ultrasmall and highly soluble anatase nanoparticles were synthesized from TiCl(4) using tert-butyl alcohol as a new reaction medium. This synthetic protocol widens the scope of nonaqueous sol-gel methods to TiO(2) nanoparticles of around 3 nm with excellent dispersibility in ethanol and tert-butanol. Microwave heating was found to enhance the crystallinity of the nanoparticles and to drastically shorten the reaction time to less than 1 h at temperatures as low as 50 degrees C. The extremely small size of the nanoparticles and their dispersibility make it possible to use commercial Pluronic surfactants for evaporation-induced self-assembly of the nanoparticulate building blocks into periodic mesoporous structures. A solution of particles after synthesis can be directly used for preparation of mesoporous films without the need for particle separation. The mesoporous titania coatings fabricated using this one-pot procedure are crystalline and exhibit high surface areas of up to 300 m(2)/g. The advantages of the retention of the mesoporous order with extremely thin nanocrystalline walls were shown by electrochemical lithium insertion. The films made using microwave-treated nanoparticles showed supercapacitive behavior with high maximum capacitance due to quantitative lithiation with a 10-fold increase of charging rates compared to a standard reference electrode made from 20 nm anatase particles.

Niobium-doped titania nanoparticles: synthesis and assembly into mesoporous films and electrical conductivity.

Crystalline niobium-doped titania nanoparticles were synthesized via solvothermal procedures using tert-butyl alcohol as a novel reaction medium, and their assembly into mesoporous films was investigated. The solvothermal procedure enables the preparation of crystalline doped and undoped nonagglomerated titania nanoparticles, whose size can be controlled from 4 to 15 nm by changing the reaction temperature and time. The anatase lattice of these particles can incorporate more than 20 mol % of Nb ions. The nanoparticles can be easily dispersed at high concentrations in THF to form stable colloidal suspensions and can be assembled into uniform porous mesostructures directed by the commercial Pluronic block copolymer F127. The resulting mesoporous films show a regular mesostructure with a d spacing of about 17 nm, a uniform pore size of about 10 nm with crystalline walls, a high porosity of 43%, and a large surface area of 190 m(2) cm(-3). Substitutional doping with niobium ions drastically increases the electrical conductivity of the titania particles. The electrical conductivity of as-prepared nanoparticles containing 20 mol % of Nb is 2 x 10(-5) S cm(-1); it increases to 0.25 S cm(-1) after treatment at 600 °C in nitrogen.

Functionalized mesoporous silica films as a matrix for anchoring electrochemically active guests.

Mesoporous silica thin films were shown to be an appropriate matrix for immobilization of discrete electroactive moieties, yielding uniform transparent thin film electrodes with defined texture and enhanced electrochemical activity. The mesoporous silica films prepared on conducting FTO-coated glass substrate were postsynthetically functionalized. Alkoxysilanes were used as precursors for subsequent grafting via ionic or covalent bonds of representative electroactive species, such as polyoxometalate PMo12O(40)3-, hexacyanoferrate(III), and ferrocene. The electrochemically active concentration within the silica-based composite electrodes achieves 90, 260, and 60 micromol cm(-3) for polyoxometalate, hexacyanoferrate(III), and ferrocene, respectively. The amount of molecules involved in the charge-transfer sequence is proportional to the film thickness and comparable to the total amount of embedded guests. Thus, eventually the whole bulk volume of the modified silica films is electrochemically accessible. Immobilization in the chemically modified silica matrix alters the redox potential of the electroactive molecules. Electron exchange between the adjacent redox centers (electron hopping) is proposed as a possible charge propagation pathway through the insulating silica matrix, which is supported by the fact that the high charge uptake is observed also for the hybrid electrodes with the covalently anchored redox guests.