Ultrasound-assisted synthesis of ZnO photocatalysts for gas phase pollutant remediation: Role of the synthetic parameters and of promotion with WO3.

The synthesis of ZnO photocatalysts by ultrasound-assisted technique was here investigated. Several experimental parameters including the zinc precursor (acetate, chloride, nitrate), sonication conditions (amplitude, pulse) and post-synthetic thermal treatment (up to 500 °C) were studied. Crystalline ZnO samples were obtained without thermal treatments due to the adopted reactant ratios and synthesis temperature. Sonication plays a major role on the morphological oxide features in terms of particle size and surface area, the latter showing a 20-fold increase with respect to conventional synthesis. Interestingly, 1 and 3 s sonication pulses led to morphological properties similar to continuous sonication. A thermal treatment at moderate temperatures (400-450 °C) promoted the loss of surface hydroxylation and the formation of lattice defects, while higher temperatures were detrimental for the sample morphology. The prepared ZnO was decorated with WO3 particles comparing an ultrasound-assisted technique using 1 s pulses with a conventional approach, giving rise to composites with promoted visible light absorption. Samples were tested towards the photocatalytic degradation of nitrogen oxides (500-1000 ppb) in humidified air under both UV and visible light. By carefully controlling the synthetic procedure, better performance were observed with respect to the commercial benchmark. Samples from ultrasound-assisted syntheses, also in the case of pulsed sonication, showed consistently better results than conventional references, in particular for ZnO-WO3 composites. The composite by ultrasound-assisted synthesis showed > 95% degradation in 180 min and doubled NOx degradation under visible light with respect to the conventional composite.

Photocatalytic and Oxidative Synthetic Pathways for Highly Efficient PANI-TiO2 Nanocomposites as Organic and Inorganic Pollutant Sorbents.

Polyaniline (PANI)-materials have recently been proposed for environmental remediation applications thanks to PANI stability and sorption properties. As an alternative to conventional PANI oxidative syntheses, which involve toxic carcinogenic compounds, an eco-friendly procedure was here adopted starting from benign reactants (aniline-dimer and H2O2) and initiated by ultraviolet (UV)-irradiated TiO2. To unlock the full potential of this procedure, we investigated the roles of TiO2 and H2O2 in the nanocomposites synthesis, with the aim of tailoring the properties of the final material to the desired application. The nanocomposites prepared by varying the TiO2:H2O2:aniline-dimer molar ratios were characterized for their thermal, optical, morphological, structural and surface properties. The reaction mechanism was investigated via mass analyses and X-ray photoelectron spectroscopy. The nanocomposites were tested on both methyl orange and hexavalent chromium removal. A fast dye-sorption was achieved also in the presence of interferents and the recovery of the dye was obtained upon eco-friendly conditions. An efficient Cr(VI) abatement was obtained also after consecutive tests and without any regeneration treatment. The fine understanding of the reaction mechanism allowed us to interpret the pollutant-removal performances of the different materials, leading to tailored nanocomposites in terms of maximum sorption and reduction capability upon consecutive tests even in simulated drinking water.

PA6 and Halloysite Nanotubes Composites with Improved Hydrothermal Ageing Resistance: Role of Filler Physicochemical Properties, Functionalization and Dispersion Technique.

Polyamide 6 (PA6) suffers from fast degradation in humid conditions due to hydrolysis of amide bonds, which limits its durability. The addition of nanotubular fillers represents a viable strategy for overcoming this issue, although the additive/polymer interface at high filler content can become privileged site for moisture accumulation. As a cost-effective and versatile material, halloysite nanotubes (HNT) were investigated to prepare PA6 nanocomposites with very low loadings (1-45% w/w). The roles of the physicochemical properties of two differently sourced HNT, of filler functionalization with (3-aminopropyl)triethoxysilane and of dispersion techniques (in situ polymerization vs. melt blending) were investigated. The aspect ratio (5 vs. 15) and surface charge (-31 vs. -59 mV) of the two HNT proved crucial in determining their distribution within the polymer matrix. In situ polymerization of functionalized HNT leads to enclosed and well-penetrated filler within the polymer matrix. PA6 nanocomposites crystal growth and nucleation type were studied according to Avrami theory, as well as the formation of different crystalline structures (α and γ forms). After 1680 h of ageing, functionalized HNT reduced the diffusion of water into polymer, lowering water uptake after 600 h up to 90%, increasing the materials durability also regarding molecular weights and rheological behavior.

Role of the growth step on the structural, optical and surface features of TiO2/SnO2 composites.

TiO2/SnO2 composites have attracted considerable attention for their application in photocatalysis, fuel cells and sensors. Structural, morphological, optical and surface features play a pivotal role in photoelectrochemical applications and are critically related to the synthetic route. Most of the reported synthetic procedures require high-temperature treatments in order to tailor the sample crystallinity, usually at the expense of surface hydroxylation and morphology. In this work, we investigate the role of a treatment in an autoclave at a low temperature (100°C) on the sample properties and photocatalytic performance. With respect to samples calcined at 400°C, the milder crystallization treatment promotes anatase phase, mesoporosity and water chemi/physisorption, while reducing the incorporation of heteroatoms within the TiO2 lattice. The role of Sn content was also investigated, showing a marked influence, especially on the structural properties. Notably, at a high content, Sn favours the formation of rutile TiO2 at very low reaction temperatures (100°C), thanks to the structural compatibility with cassiterite SnO2. Selected samples were tested towards the photocatalytic degradation of tetracycline in water under UV light. Overall, the low-temperature treatment enables to tune the TiO2 phase composition while maintaining its surface hydrophilicity and gives rise to well-dispersed SnO2 at the TiO2 surface.

Preparation and Application of Hybrid Nanomaterials.

The growing demand of new materials with tailored physicochemical properties has propelled hybrid materials to a position of prominence in materials science by virtue of their remarkable new properties and multifunctional nature. [...].

Triply green polyaniline: UV irradiation-induced synthesis of a highly porous PANI/TiO2 composite and its application in dye removal.

An environmentally benign procedure for the preparation of polyaniline/TiO2 composites is presented. The UV irradiation-induced synthesis leads to materials with good crystallinity and tailored morphology, showing promising sorption and recycle properties in dye removal tests. A reaction mechanism is proposed on the basis of LC-MS and FT-IR investigations.

Sculpturing patterns of plasmonic silver nanoprisms by means of photocatalytic lithography.

The controlled shaping of nanoparticles' morphology is one of the pillars of nanotechnology. Here, we demonstrate that photocatalytic lithography, a technique already proved to be useful in materials science, can act as a dry etching technique for noble metal nanoparticles. Triangular silver nanoprisms are self-assembled on titanium dioxide films and photocatalytically shaped into discoidal particles upon irradiation with near-UV light. The obtained patterned surfaces show a dramatically different surface-enhanced Raman scattering response, suggesting the utility of our approach for the development of sensors. The photocatalytic nature of the particle shaping is demonstrated and a plausible mechanism drawn by performing photocatalysis in different configurations (direct and remote) and by irradiating in different solvents.

A Close Look at the Structure of the TiO2-APTES Interface in Hybrid Nanomaterials and Its Degradation Pathway: An Experimental and Theoretical Study.

The surface functionalization of TiO2-based materials with alkylsilanes is attractive in several cutting-edge applications, such as photovoltaics, sensors, and nanocarriers for the controlled release of bioactive molecules. (3-Aminopropyl)triethoxysilane (APTES) is able to self-assemble to form monolayers on TiO2 surfaces, but its adsorption geometry and solar-induced photodegradation pathways are not well understood. We here employ advanced experimental (XPS, NEXAFS, AFM, HR-TEM, and FT-IR) and theoretical (plane-wave DFT) tools to investigate the preferential interaction mode of APTES on anatase TiO2. We demonstrate that monomeric APTES chemisorption should proceed through covalent Si-O-Ti bonds. Although dimerization of the silane through Si-O-Si bonds is possible, further polymerization on the surface is scarcely probable. Terminal amino groups are expected to be partially involved in strong charge-assisted hydrogen bonds with surface hydroxyl groups of TiO2, resulting in a reduced propensity to react with other species. Solar-induced mineralization proceeds through preferential cleavage of the alkyl groups, leading to the rapid loss of the terminal NH2 moieties, whereas the Si-bearing head of APTES undergoes slower oxidation and remains bound to the surface. The suitability of employing the silane as a linker with other chemical species is discussed in the context of controlled degradation of APTES monolayers for drug release and surface patterning.

Emerging pollutant mixture mineralization by TiO2 photocatalysts. The role of the water medium.

Pharmaceutics and personal care products (PPCPs) are raising growing concern due to their widespread usage and resistance to conventional remediation techniques. Several of them raise significant health and environmental concerns, especially when present in complex mixtures. Due to their chemical resistance, Advanced Oxidation Processes (AOPs) are needed for their complete removal from surface and wastewaters. In the present work, photocatalysis by titanium dioxide (TiO2) under UV and simulated solar irradiation was adopted to degrade tetracycline hydrochloride, paracetamol, caffeine and atenolol, both as single pollutants and in mixtures. All molecules showed high removal and mineralization degrees. Moreover, no interference effects decreased the efficiency of the processes in the case of pollutant mixtures, achieving 60% of mineralization after 6 h. An immobilized TiO2 system was also developed by depositing titania on titanium meshes. A 50% mineralization degree of the pollutant mixture was obtained after 6 h, revealing a suitable efficiency for field applications. Eventually, the impact of the matrix composition on the photocatalytic efficiency was investigated by studying the reaction both in simulated drinking water and in commercial bottled mineral water. The scavenger role played by HCO3- species appears to be dominant in inhibiting the mineralization.

Trace detection of tetrahydrocannabinol (THC) with a SERS-based capillary platform prepared by the in situ microwave synthesis of AgNPs.

In the present study, an ultra-sensitive and highly reproducible novel SERS-based capillary platform was developed and utilized for the trace detection of tetrahydrocannabinol (THC). The approach combines the advantages of microwave-assisted nanoparticle synthesis, plasmonics and capillary forces. By employing a microwave-assisted preparation method, glass capillaries were reproducibly coated with silver nanoparticles in a batch fabrication process that required a processing time of 3 min without needing to use any pre-surface modifications or add surfactants. The coated capillaries exhibited an excellent SERS activity with a high reproducibility and enabled the detection of low concentrations of target molecules. At the same time, only a small amount of analyte and a short and simple incubation process was required. The developed platform was applied to the spectroscopic characterization of tetrahydrocannabinol (THC) and its identification at concentration levels down to 1 nM. Thus, a highly efficient detection system for practical applications, e.g., in drug monitoring/detection, is introduced, which can be fabricated at low cost by using microwave-assisted batch synthesis techniques.

Self-cleaning properties in engineered sensors for dopamine electroanalytical detection.

Fouling and passivation are the major drawbacks for a wide applicability of electroanalytical sensors based on nanomaterials, especially in biomedical and environmental fields. The production of highly engineered devices, designed ad hoc for specific applications, is the key factor in the direction of overcoming the problem and accessing effective sensors. Here, the fine-tuning of the system, composed of a highly ordered distribution of silver nanoparticles between a bottom silica and a top titania layer, confers multifunctional properties to the device for a biomedical complex challenge: dopamine detection. The crucial importance of each component towards a robust and efficient electroanalytical system is studied. The total recovery of the electrode performance after a simple UV-A cleaning step (self-cleaning), due to the photoactive interface and the aging resistance, is deeply investigated.

Nanocrystalline W3O3 polymorphs. Surfactant assisted growth steps to tailor microstructure and NO2 response.

Nanocrystalline WO3 samples are synthesized by different procedures. The first series of samples are obtained by sol-gel reaction, starting from WCI6, followed by thermal treatments in the range 300-750 degrees C. To improve the oxide microstructure, a second series of samples is obtained by submitting the xerogels, obtained from the sol-gel reaction, to prolonged (170 h) hydrothermal (HT) growth steps in the presence of a surfactant, either non-ionic (Lutensol ON70) or ionic (cetylpyridinium chloride), and to a final firing. The HT treatment, in the presence of cetylpyridinium chloride is also combined with Ag promotion (1% Ag). The phase composition of all samples is characterized jointly by XRD Rietveld refinement and Raman spectroscopy. The observed different temperature domains of the nanocrystalline WO3 polymorphs with respect to bulk systems are attributed to the occurrence of surface relaxation phenomena. TEM and SEM images show that the samples submitted to the surfactant HT treatment present a generally improved microstructure while the presence of Ag induces crystallite growth and sintering between the particles. The NO2 sensing measurements show for all samples that the film response decreases with the operating temperatures and is promoted by the presence of humidity. The samples obtained by the surfactant HT treatment show a much better sensor performance with respect to the other samples, the more so in the case of the cationic molecules. The role played by the HT treatment in promoting the features of the WO3 samples is discussed also on grounds of Raman analyses in the water-OH stretching region.

Photodegradation of Pollutants in Air: Enhanced Properties of Nano-TiO(2) Prepared by Ultrasound.

Nanocrystalline TiO(2) samples were prepared by promoting the growth of a sol-gel precursor, in the presence of water, under continuous (CW), or pulsed (PW) ultrasound. All the samples turned out to be made of both anatase and brookite polymorphs. Pulsed US treatments determine an increase in the sample surface area and a decrease of the crystallite size, that is also accompanied by a more ordered crystalline structure and the samples appear to be more regular and can be considered to contain a relatively low concentration of lattice defects. These features result in a lower recombination rate between electrons and holes and, therefore, in a good photocatalytic performance toward the degradation of NO(x) in air. The continuous mode induces, instead, the formation of surface defects (two components are present in XPS Ti 2p(3/2) region) and consequently yields the best photocatalyst. The analysis of all the characterization data seems to suggest that the relevant parameter imposing the final features of the oxides is the ultrasound total energy per volume (E(tot)/V) and not the acoustic intensity or the pulsed/continuous mode.

Aged titania nanoparticles: the simultaneous control of local and long-range properties.

TiO(2) nanoparticles are obtained by combining a sol-gel preparative route with hydrothermal aging steps, performed in mild conditions, of varying time lengths. Both aged and un-aged samples are thermally treated at 300 and 600 degrees C, for the same length of time. The crystal structures, the phase composition, and crystallite sizes are analyzed by powder X-ray diffraction. Raman spectra of anatase nanocrystals with average sizes of 7-10 nm are reported and the correlation between the Raman band shape of the main feature at 144 cm(-1) and the crystallite size is discussed. Nitrogen physisorption by Brunauer-Emmett-Teller (BET) method is adopted to evaluate the particles surface area and mesopore size and size distribution. The role played by the hydrothermal step in affecting the physicochemical properties of the powders is discussed also with respect to the H(2)O/TiO(2) interactions as apparent from Raman spectroscopy investigations of the O-H stretching range (3000-3800 cm(-1)).

Structural and spectroscopic investigations of blue, vanadium-doped ZrSiO4 pigments prepared by a sol-gel route.

A sol-gel reaction starting from silicon and zirconium alkoxides, in water-ethanol mixtures, was employed to obtain vanadium-doped zirconium silicate powders (zircon). The reactions were performed by modulating both (a) the amount of the vanadium salt in the starting mixture and also (b) the amount of mineralizer (NaF). The products of the sol-gel reaction were calcined at 600, 800, 1000, and 1200 degrees C. The samples were characterized by X-ray powder diffraction (XRPD), electron paramagnetic resonance spectroscopy (EPR), scanning electron microscopy (SEM), X-ray absorption near-edge spectroscopy (XANES), and diffuse UV-vis-near-IR reflectance spectroscopy. Results from the structural, morphological, and optical characterization are examined and cross-compared to produce a consistent picture of the key factors leading to the formation, growth, and optical properties of the reaction products.