Effect of the Synthetic Parameters over ZnO in the CO2 Photoreduction

Zinc oxide (ZnO) is an attractive semiconductor material for photocatalytic applications, owing to its opto-electronic properties. Its performances are, however, strongly affected by the surface and opto-electronic properties (i.e., surface composition, facets and defects), in turn related to the synthesis conditions. The knowledge on how these properties can be tuned and how they are reflected on the photocatalytic performances (activity and stability) is thus essential to achieve an active and stable material. In this work, we studied how the annealing temperature (400 °C vs. 600 °C) and the addition of a promoter (titanium dioxide, TiO₂) can affect the physico-chemical properties of ZnO materials, in particular surface and opto-electronic ones, prepared through a wet-chemistry method. Then, we explored the application of ZnO as a photocatalyst in CO₂ photoreduction, an appealing light-to-fuel conversion process, with the aim to understand how the above-mentioned properties can affect the photocatalytic activity and selectivity. We eventually assessed the capability of ZnO to act as both photocatalyst and CO₂ adsorber, thus allowing the exploitation of diluted CO₂ sources as a carbon source.

Terahertz Time-Domain Spectroscopy in Reflection Configuration for Inorganic and Mineral Pigment Identification

This work demonstrates terahertz time-domain spectroscopy (THz-TDS) in reflection configuration on a class of inorganic and mineral pigments. The technique is validated for pictorial materials against the limitations imposed by the back-reflection of the THz signal, such as weak signal intensity, multiple signal losses and distortion, as well as the current scarce databases. This work provides a detailed description of the experimental procedure and method used for the determination of material absorption coefficient of a group of 10 pigments known to be used in ancient frescoes, that are, Cu-based (azurite, malachite, and Egyptian blue), Pb-based (minium and massicot), Fe-based (iron oxide yellow, dark ochre, hematite, and Pompeii red) pigments and mercury sulfide (cinnabar), and classified the vibrational modes of the molecular oxides and sulfides for material identification. The results of this work showed that the mild signal in reflection configuration does not limit the application of THz-TDS on inorganic and mineral pigments as long as (i) the THz signal is normalized with a highly reflective reference sample, (ii) the secondary reflected signals from inner interfaces are removed with a filtering procedure, and (iii) the limitations at high frequencies imposed by the dynamic range of the instrument are considered. Under these assumptions, we were able to differentiate molecular phases of the same metal and identify azurite, Egyptian blue, minium, and cinnabar, isolating the molecular vibrations up to 125 cm^-1. The established approach demonstrated to be reliable, and it can be extended for the study of other materials, well beyond the reach of the heritage domain.

One-Pot Transformation of Citronellal to Menthol Over H-Beta Zeolite Supported Ni Catalyst: Effect of Catalyst Support Acidity and Ni Loading

Citronellal was converted to menthol in a one-pot approach using H-Beta zeolite-based Ni catalyst in a batch reactor at 80 °C, under 20 bar of total pressure. The effects of H-Beta acidity (H-Beta-25 with the molar ratio SiO2/Al2O3 = 25 and H-Beta-300 with SiO2/Al2O3 = 300) and Ni loading (5, 10 and 15 wt %) on the catalytic performance were investigated. Ni was impregnated on H-Beta support using the evaporation-impregnation method. The physico-chemical properties of the catalysts were characterized by XRD, SEM, TEM, ICP-OES, N2 physisorption, TPR, and pyridine adsorption–desorption FTIR techniques. Activity and selectivity of catalysts were strongly affected by the Brønsted and Lewis acid sites concentration and strength, Ni loading, its particle size and dispersion. A synergetic effect of appropriate acidity and suitable Ni loading in 15 wt.% Ni/H-Beta-25 catalyst led to the best performance giving 36% yield of menthols and 77% stereoselectivity to ( ±)-menthol isomer at 93% citronellal conversion. Moreover, the catalyst was successfully regenerated and reused giving similar activity, selectivity and stereoselectivity to the desired ( ±)-menthol isomer as the fresh one.

Graphical Abstract

Selective Hydrogenation of 5-Hydroxymethylfurfural to 1-Hydroxy-2,5-hexanedione by Biochar-Supported Ru Catalysts

The development of sustainable and efficient catalysts -namely Ru supported on activated biochars- is carried out for the selective hydrogenation of 5-hydroxymethylfurfural (HMF) to 1-hydroxy-2,5-hexanedione (HHD). Activated biochars obtained from pyrolysis and steam-based physical activation of two different biomasses from animal (leather tannery waste; A_Lw ) and vegetal (hazelnut shells; A_HSw ) origins show completely different chemical, textural, and morphological properties. Compared to A_Lw , after impregnation with 0.5 wt % Ru, A_HSw , with inner micro-mesochannels and cavities and higher layer stacking disorder, leads to better trapping and anchoring of Ru nanoparticles on the catalyst and a suitable Ru single crystal dispersion. This leads to a highly active Ru/A_HSw catalyst in the proposed reaction, giving more than 80 % selectivity to HHD and full HMF conversion at 100 °C with 30 bar H₂ for 3 h. Ru/A_HSw also shows promising performance compared to a commercial Ru/C catalyst.

Which Are the Main Surface Disinfection Approaches at the Time of SARS-CoV-2?

Among many guidelines issued by the World Health Organization to prevent contagion from novel coronavirus (SARS-CoV-2), disinfection of animate and inanimate surfaces has emerged as a key issue. One effective approach to prevent its propagation can be achieved by disinfecting air, skin, or surfaces. A thorough and rational application of an Environmental Protection Agent for disinfection of surfaces, as well as a good personal hygiene, including cleaning hands with appropriate products (e.g., 60–90% alcohol-based product) should minimize transmission of viral respiratory pathogens such as SARS-CoV-2. Critical issues, associated with the potential health hazard of chemical disinfectants and the ineffective duration of most of the treatments, have fostered the introduction of innovative and alternative disinfection approaches. The present review aims to provide an outline of methods currently used for inanimate surface disinfection with a look to the future and a focus on the development of innovative and effective disinfection approaches (e.g., metal nanoparticles, photocatalysis, self-cleaning, and self-disinfection) with particular focus on SARS-CoV-2. The research reviews are, usually, focused on a specific category of disinfection methods, and therefore they are limited. On the contrary, a panoramic review with a wider focus, as the one here proposed, can be an added value for operators in the sector and generally for the scientific community.

Multifunctional and Environmentally Friendly TiO2-SiO2 Mesoporous Materials for Sustainable Green Buildings

This work deals with the formulation of environmentally friendly, cheap, and readily-available materials for green building applications, providing the function of air purificator by improving the safety and the comfort of an indoor environment. High surface area TiO₂–SiO₂ samples, prepared by a simple, cost effective, and scalable synthetic approach, proved to be effective in maximizing the properties of each component, i.e., the photocatalytic properties of titania and the high surface area of silica. TiO₂ was introduced onto an ordered mesoporous silica Santa Barbara Amorphous-15 (SBA-15), that is featured by interesting insulating features, by using an incipient wetness impregnation method. The photocatalytic activity was evaluated in gas phase oxidation of ethylbenzene, which was selected as model volatile organic compound (VOC) molecule. The morphological, textural and structural features along with the electronic properties, the hydrophilicity and heat capacity of the materials were investigated in depth by scanning electron microscopy, powder X-ray diffraction, N2 physisorption, diffuse reflectance UV-Vis, FT-IR spectroscopies, and modulated DSC (MDSC) dynamic scan. Outstanding performances in the ethylbenzene abatement results are promising for further application in the green building sector.

Titanium Dioxide-Based Nanocomposites for Enhanced Gas-Phase Photodehydrogenation

Light-driven processes can be regarded as a promising technology for chemical production within the bio-refinery concept, due to the very mild operative conditions and high selectivity of some reactions. In this work, we report copper oxide (CuO)-titanium dioxide (TiO₂) nanocomposites to be efficient and selective photocatalysts for ethanol photodehydrogenation under gas phase conditions, affording 12-fold activity improvement compared to bare TiO₂. In particular, the insertion method of the CuO co-catalyst in different TiO₂ materials and its effects on the photocatalytic activity were studied. The most active CuO co-catalyst was observed to be highly dispersed on titania surface, and highly reducible. Moreover, such high dispersion was observed to passivate some surface sites where ethanol is strongly adsorbed, thus improving the activity. This kind of material can be obtained by the proper selection of loading technique for both co-catalysts, allowing a higher coverage of photocatalyst surface (complex-precipitation in the present work), and the choice of titania material itself. Loading copper on a high surface area titania was observed to afford a limited ethanol conversion, due to its intrinsically higher reactivity affording to a strong interaction with the co-catalyst.

Systematic study of TiO2/ZnO mixed metal oxides for CO2 photoreduction

A novel example using a systematic design of experiments mixture design for developing mixed metal oxide photocatalysts for CO₂ photoreduction.

TiO2 nanoparticles vs. TiO2 nanowires as support in hydrogen peroxide direct synthesis: the influence of N and Au doping

Nitrogen doping is a new strategy to improve catalysts for H₂O₂ direct synthesis.

Highly dispersed gold on zirconia: characterization and activity in low-temperature water gas shift tests

Gold-loaded zirconia and sulfated zirconia catalysts were tested in the low-temperature water gas shift reaction. The samples were characterized by N2 adsorption analysis, temperature-programmed reduction, X-ray diffraction, pulse-flow CO chemisorption, FTIR spectroscopy, and high-resolution transmission electron microscopy. A reference catalyst, Au/TiO2, provided by the World Gold Council was investigated for comparison. CO chemisorption and FTIR data indicate the presence of only highly dispersed gold clusters on the sulfated sample and both small clusters and small particles on the non-sulfated sample. Both gold-zirconia catalysts are much more active than the Au/TiO2 reference sample over all the temperature range investigated. The sample prepared on sulfated zirconia exhibits higher stability than the catalyst on unmodified zirconia. The prominent role in the water gas shift reaction of gold clusters in close contact with the support was deduced.