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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.

Increasing the photocatalytic efficiency of earth-abundant wide-bandgap semiconductors is of high interest for the development of cheap but effective light-driven chemical conversion processes. In this study, the coupling of ZnO and TiO2 with low contents of the rare-earth Ce species aimed to assess the photo-catalytic performance of the two semiconductors (SC). Structural and optical characterizations were performed to estimate the effect of the different interactions between Zn2+, Ti4+ and Ce4+ ions, and how the photo-responsive behaviour of Ce-Ti and Ce-Zn composites was affected. Therefore, photo-catalytic tests were performed for all Ce-modified SC to assess both their photo-oxidative and photo-reductive properties. Amongst all the tested materials, only Zn-based samples resulted in being suitable for the photo-oxidation of the methylene blue (MB) organic pollutant in a synthetic-dependent fashion.

A two component three degree simplex lattice experimental design was employed to evaluate the impact of different mixing fractions of TiO2 and ZnO on an ordered mesoporous SBA-15 support for CO2 photoreduction. It was anticipated that the combined advantages of TiO2 and ZnO: low cost, non-toxicity and combined electronic properties would facilitate CO2 photoreduction. The fraction of ZnO had a statistically dominant impact on maximum CO2 adsorption (β2 = 22.65, p-value = 1.39 × 10-4). The fraction of TiO2 used had a statistically significant positive impact on CO (β1 = 9.71, p-value = 2.93 × 10-4) and CH4 (β1 = 1.43, p-value = 1.35 × 10-3) cumulative production. A negative impact, from the interaction term between the fractions of TiO2 and ZnO, was found for CH4 cumulative production (β3 = -2.64, p-value = 2.30 × 10-2). The systematic study provided evidence for the possible loss in CO2 photoreduction activity from sulphate groups introduced during the synthesis of ZnO. The decrease in activity is attributed to the presence of sulphate species in the ZnO prepared, which may possibly act as charge carrier and/or radical intermediate scavengers.

The Venetian marmorino is a traditional material used for wall coating in Venice city, composed of hydrated lime and marble powders, and is part of the cultural heritage of the city. Several surface damage processes can negatively affect its aesthetic properties, such as the formation of stain deposits of different origin (i.e. pollution, bio-deterioration, vandalism) which eventually change the colour of this material. An appealing way to avoid these deposits rely on inducing self-bleaching features by introducing a photocatalyts on this material. In the present work, TiO2-based and ZnO-based photocatalysts were introduced within the marmorino, then evaluating how the addition of these materials influenced the compositional, structural and morphological properties though X-ray diffraction (XRD), N2 physisorption and electron microscopy (SEM). ZnO-modified samples, which exhibited comparable morphological and structural properties, were further analyzed to get information concerning the surface compostion and the opto-electronic properties, through attenuated total reflectance (ATR) spectroscopy and photoluminescence (PL), respectively, in turn related to the presence of defects and heterojunctions. The self-bleaching activity was evaluated by irradiation in mild condition (room temperature) in air using a dye as model stain compound. Finally, the morphological, surface and opto-electronic properties of the photocatalyst-modified marmorino were correlated to the activity results, aiming to understand how they can influence the material performances, and thus how to design an active self-bleaching Venetian marmorino.

CO2 photoreduction has claimed as appealing process to upgrade a waste gas into valuable fuels or chemicals. Titanium dioxide (TiO2) is one of the most popular material used as catalyst for this reaction, having however a poor activity. The utilization of transparent, insulating and highly porous scaffolds to support a photoactive phase has been reported as one of the possible strategies to improve the performances of this material. In this work, two silica-based materials with different porosity type and level, were involved as support for the TiO2 and assessed in the gas-phase CO2 photoreduction with H2O. The morphological, structural and surface properties were then evaluated by means of different characterization techniques, aiming to correlate them with the catalytic activity and selectivity. The TiO2-SiO2 composites revealed a comparable activity compared to pure TiO2, despite the low fraction of photoactive phase due to improved light harvesting and reagents adsorption on the composites. The CO2 capture/photoconverting ability was evaluated, to explore the potentiality as multifunctional material.

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. Considering various transmission routes of coronavirus, one approach to fight against the virus is preventing its propagation by means of disinfecting air, skin or surfaces. A thorough and rational application of an EPA (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 surfaces 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.

Hydrogen production has been investigated through the photoreforming of glucose, as model molecule representative for biomass hydrolysis. Different copper- or nickel-loaded titania photocatalysts have been compared. The samples were prepared starting from three titania samples, prepared by precipitation and characterized by pure Anatase with high surface area, or prepared through flame synthesis, i.e., flame pyrolysis and the commercial P25, leading to mixed Rutile and Anatase phases with lower surface area. The metal was added in different loading up to 1 wt % following three procedures that induced different dispersion and reducibility to the catalyst. The highest activity among the bare semiconductors was exhibited by the commercial P25 titania, while the addition of 1 wt % CuO through precipitation with complexes led to the best hydrogen productivity, i.e., 9.7 mol H2/h kgcat. Finally, a basic economic analysis considering only the costs of the catalyst and testing was performed, suggesting CuO promoted samples as promising and almost feasible for this application.

Nickel-based catalysts were investigated for hydrogen production by ethanol steam reforming. A suitable support was assessed among the metal oxides TiO2, ZrO2 and CeO2. Alongside catalytic testing with ethanol-water mixture, a series of characterization measurements were carried out: N2-physisorption, XRD, TPR, TPO, CO2-TPD, SEM, AAS and IC. Zirconium and cerium oxides proved to be suitable supports, even if both still suffer from coking phenomena. The effects of doping both by calcium oxide and gold nanoparticles were checked. Doping by calcium oxide prevented deactivation and highly increased the hydrogen yield. Moreover, the addition of gold nanoparticles greatly improved the hydrogen yield. The combination of the two dopants resulted in the best performing catalyst: the basic doping by CaO and the promotion of the water gas shift reaction by gold nanoparticles contributed to the highest hydrogen production.

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.

The development of sustainable yet efficient technologies to store solar light into high energy molecules, such as hydrocarbons and hydrogen, is a pivotal challenge in 21st century society. In the field of photocatalysis, a wide variety of chemical routes can be pursued to obtain solar fuels but the two most promising are carbon dioxide photoreduction and photoreforming of biomass-derived substrates. Despite their great potentialities, these technologies still need to be improved to represent a reliable alternative to traditional fuels, in terms of both catalyst design and photoreactor engineering. This review highlights the chemical fundamentals of different photocatalytic reactions for solar fuels production and provides a mechanistic insight on proposed reaction pathways. Also, possible cutting-edge strategies to obtain solar fuels are reported, focusing on how the chemical bases of the investigated reaction affect experimental choices.