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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.

Finding innovative and highly performing approaches for NOx degradation represents a key challenge to enhance the air quality of our environment. In this study, the high efficiency of PANI/TiO2 nanostructures in the NO2 abatement both in the dark and under light irradiation is demonstrated for the first time. Heterostructures were synthesized by a “green” method and their composition, structure, morphology and oxidation state were investigated by a combination of characterization techniques. The results show that the unique PANI structure promotes two mechanisms for the NO2 abatement in the dark (adsorption on the polymeric chains and chemical reduction to NO), whereas the photocatalytic behavior prevails under light irradiation, leading to the complete NOx degradation. The best-performing materials were subjected to recycling tests, thereby showing high stability without any significant activity loss. Overall, the presented material can represent an innovative and efficient night-and-day solution for NOx abatement.

The combination of TiO2 and chitosan is known to allow the achievement of implantable devices which combines the mechanical properties of TiO2, with the presence of chitosan, which ensures antibacterial properties combined with an in-situ drug-delivery of biomolecules physisorbed and/or covalently linked to chitosan. In this study, 5-aminofluorescein (5-AF), a derivative of fluorescein containing a primary amino group, has been used as model molecule to simulate a drug. This dye is characterized by low cost and low toxicity, and due to its high molar absorptivity it can easily be detected by means of absorption and emission spectroscopies. The combination of 5-AF and maleic anhydride (MA) with TiO2-chitosan materials has generated a range of novel hybrid materials tailored to applications in localized stimuli-responsive drug delivery systems. Maleic anhydride has been used as pH sensitive spacer for the covalent functionalization of the TiO2-chitosan hybrid with MA as linker molecule. This functionalization allowed to obtain a pH-sensitive hybrid material. The efficiency of the functionalization has been verified by means of different physico-chemical characterization techniques. The behaviour of the functionalized materials is related to different parameters, among which the ratio between physisorbed/coordinated and chemisorbed 5-AF and the matrix degradation. Moreover, delivery tests in simulated body solutions at different pH have been performed showing a pH-sensitive drug delivery behaviour and indicating that the release of 5-AF is favoured at basic pH.

Nanocomposites are at the heart of the present nanotechnology revolution in several strategic fields, including Green Chemistry, sensors and pollutant remediation. The promising and extensively examined nanotitania photocatalysts have performances hampered by the rapid recombination of photogenerated charge carriers. To better understand these materials, here we generalize the 2D-heterojunctions physics to 3D patchworks of intimately associated anatase and brookite mixed crystallites, i.e. multi-phase polymorphs, MPPs. The synthesized composite material is fully characterized experimentally and by simulations. We demonstrate that the anatase–brookite interphase behaves as a ground-state nano-diode containing an almost ideal nanocapacitor, associated with a net migration of electrons from anatase to brookite. Implications of the direct observation of a polarized interphase on the understanding of nanotitania photocatalysts at the atomic scale are discussed.

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.

TiO2 photocatalysts degrade pollutants in both the gas and liquid phase under UV radiation. To widen their application under solar and/or LED light, TiO2 surface decoration with noble metals offers a mean to achieve such a goal. Ag species as a decorating agent improve TiO2-based systems photoactivity and exhibit antibacterial properties under LED light and even in the dark. Ample literature is available on the synthesis of silver nanoparticles (Ag NPs) but few data are available on the interaction of such particles with micrometric samples. Indeed, micrometric samples pose less environmental and health concerns than the nano-sized powders widely adopted. The synthetic routes employed for Ag NPs decoration onto TiO2 clearly influence the photocatalytic activity, in particular referring to both NPs shape and fine structure. Thus, we report the preparation of Ag NPs by an electrochemical method followed by the subsequent decoration onto a micrometric TiO2 (Kronos 1077): different parameters, such as pH and the nature of physical nanoparticle dispersants were taken into account to evaluate their effect on the resulting Ag NPs features. We evaluated the photocatalytic activity towards the photodegradation of NOx under LED light, concluding that the best output was obtained by photocatalysts synthesised at basic pH.

Breakthroughs in the synthesis of hybrid materials have led to the development of a plethora of chemiresistors that could operate at lower and lower temperatures. Herein, we report the fabrication of novel composite materials (SnO2-GO 4:1, 8:1 and 16:1) based on graphene oxide (GO) sheets decorated with tin dioxide nanoparticles, through a controlled chemical growth. We succeeded in obtaining widely spaced isles of the metal oxide on the carbonaceous material, thus enhancing the electron transfer process (i.e. favored convergent diffusion, as investigated through cyclic voltammetric analysis), which plays a pivotal role for the final sensing behavior. Indeed, only with SnO2-GO 16:1 sample, superior responses towards gaseous ethanol were observed both at 150 °C and at RT (by exploiting the UV light), with respect to pristine SnO2 and mechanically prepared SnO2(16)@GO material. Particularly, an improvement of the sensitivity (down to 10 ppb), response and recovery times (about of 60–70 s) was assessed. Besides, all the powders were finely characterized on structural (XRPD, FTIR and Raman spectroscopies), surface (active surface area, pores volume, XPS), morphological (SEM, TEM) and electrochemical (cyclic voltammetries) points of view, confirming the effective growth of SnO2 nanoparticles on the GO sheets.

TiO2/WO3 composites are widely in the literature as engineered systems for photocatalytic and (photo)electrochemical applications, since the presence of WO3 can promote both visible light absorption and electron transfer phenomena of TiO2. The preparation of these system, depending on the preparation method, can also affect the surface feature with respect to TiO2, modifying adsorption and performance, as well as the reaction mechanisms. Here, TiO2/WO3 composites were prepared by precipitation of WO3 onto the TiO2 surface and characterized in terms of their structural, morphological, optical and surface properties. Raman and IR spectroscopy as well as a marked shift in the isoelectric point support the preferential surface location of WO3. Samples were photocatalytically tested towards the degradation of ethanol and of tetracycline and the adsorption and degradation behaviour were studied, suggesting, in both cases, significant variations of the reaction paths by the addition of WO3.

The ingredients of Pharmaceuticals and Personal Care Products (PPCPs) persist in water and conventional treatment plants are not able to remove them efficiently. Sonochemical treatment is insufficient to mineralize organics such as ibuprofen into CO2 and H2O. TiO2 degrades ibuprofen (IBP) under UV light; however, it does not reach a high grade of conversion. Here, we investigated the mineralization of ibuprofen to CO2 by TiO2 UV-C photocatalysis. We replaced nano-sized P25 (the standard catalyst) with a micro-sized commercial sample of TiO2 to preclude the use of nanoparticles which are dangerous for human health and because typical filtration systems are expensive and inefficient. We deposited micro-TiO2 on glass Raschig rings to ensure an easy recovery and reuse of the photocatalyst and we studied its performance both with a batch and a continuous reactor. Micro-TiO2 mineralized 100% of IBP in 24 h. TiO2-coated glass Raschig rings degraded 87% of IBP in 6 h of UV-C irradiation in a continuous reactor, with a mineralization of 25%. Electronspray ionization mass spectrometer (ESI-MS, positive mode) analyses identified 13 different byproducts and we hypothised a degradration pathway for IBP degradation.

Currently, photocatalytic reactions under solar illumination have attracted worldwide attention due to the tremendous set of associated environmental problems. Taking sunlight into account, it is indispensable to develop highly effective photocatalysts. Strontium titanate, SrTiO3 (STO), is a cubic perovskite-type semiconductor, an inexpensive material with high thermal stability and corrosion resistance that exhibits a similar energy bandgap to TiO2 and can represent an interesting alternative in photocatalytic applications. Particle size can significantly affect both photocatalytic and photoelectrochemical properties of a photocatalyst, thus altering the photooxidation of organic pollutants in air or water. In this context, this research aims at investigating the photocatalytic features of nano- and micro-sized commercial STO powders towards the photodegradation of diclofenac (DFC), a non-steroidal, anti-inflammatory drug, widely used as analgesic, antiarthritic, and antirheumatic. Both nano- and micro-STO photocatalysts exhibited remarkable photocatalytic efficiency towards DCF, reaching photodegradation efficiency higher than 90% within one hour. Results obtained in simulated drinking water were also compared to those obtained in ultrapure water. Both STOs showed good stability during recycling tests, maintaining high performances after three cycles. Eventually, active species were identified using various scavengers by trapping holes and radicals generated during the photocatalytic degradation process.

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.

The size of TiO2 can significantly affect both its photocatalytic and photo-electrochemical properties, thus altering the photooxidation of organic pollutants in air or water. In this work, we give an account of the photo-electrochemical and photocatalytic features of some nanosized TiO2 commercial powders towards a model reaction, the photooxidation of acetone. Cyclic voltammograms (CV) of TiO2 particulate electrodes under UV illumination experiments were carried out in either saturated O2 or N2 solutions for a direct correlation with the photocatalytic process. In addition, the effect of different reaction conditions on the photocatalytic efficiency under UV light in both aqueous and gaseous phases was also investigated. CV curves with the addition of acetone under UV light showed a negative shift of the photocurrent onset, confirming the efficient transfer of photoproduced reactive oxygen species (ROSs), e.g., hydroxyl radicals or holes to acetone molecules. The photocatalytic experiments showed that the two nano-sized samples exhibit the best photocatalytic performance. The different photoactivity of the larger-sized samples is probably attributed to their morphological differences, affecting both the amount and distribution of free ROSs involved in the photooxidation reaction. Finally, a direct correlation between the photocatalytic measurements in gas phase and the photo-electrochemical measurements in aqueous phase is given, thus evincing the important role of the substrate-surface interaction with similar acetone concentrations. This work has been developed in part in the context of project RTI2018–102061–B–I00 financed by FEDER/Ministerio de Ciencia e Innovación-Agencia Estatal de Investigación.

Highlights • US-assisted photocatalysis by ZnO leads to efficient mineralization of diclofenac. • Synergistic effects are observed only when ZnO nanorods are used. • Tests in simulated water matrix show enhanced performance with respect to TiO2. • Reaction intermediates of photo- and sonophotocatalysis are identified., The degradation of diclofenac has been realized for the first time by a piezo-enhanced sonophotocatalytic approach based on ZnO. The sonophotocatalytic degradation showed a slight enhancement in the degradation of the parent compound, whereas strong synergistic effects were observed for the mineralization process when suitable ZnO morphologies are used, reaching 70% of complete degradation of 25 ppm diclofenac using 0.1 g/L ZnO in 360 min. Tests in a complex water matrix show enhanced diclofenac removal, outperforming a TiO2 benchmark photocatalyst. These promising experimental results promote this process as a good alternative to traditional degradation approaches for remediation of real water matrices.

Fungi, molds, and algae are abundant in the environment, leading in many cases to different types of infections and diseases, such as immune suppression/reduced immune function, respiratory diseases, allergies, asthma, and superficial and subcutaneous infections (skin, keratinous tissues, and mucous membranes), among others. These organisms infect billions of people and cause millions of deaths worldwide, putting a massive and costly strain on healthcare systems. As such, there is an urgent need to develop safe and cost-effective continuous self-sterilizing systems to prevent bacterial and viral infections. Apart from polymeric or metallic systems, photocatalytic systems are currently being investigated, in particular photo-self-cleaning materials made of silver nanoparticle (AgNP)-doped titanium dioxide (TiO2). This chapter evaluates the photoactivity of commercial AgNP-doped TiO2 Porcelain Gres Tiles for preventing growth of fungi (molds) and algae on surfaces.

Photocatalysis is a green technology for tackling water and air contamination. A valid alternative to the most exploited photocatalytic material, TiO2, is bismuth oxyhalides, which feature a wider bandgap energy range and use visible radiation to attain photoexcitation. Moreover, their layered structure favors the separation of photogenerated electron&ndash, hole pairs, with an enhancement in photocatalytic activity. Controlled doping of bismuth oxyhalides with metallic bismuth nanoparticles allows for further boosting of the performance of the material. In the present work, we synthesized Y%Bi-doped BiO(Cl0.875Br0.125) (Y = 0.85, 1, 2, 10) photocatalysts, using cetyltrimethylammonium bromide as the bromide source and varying the chloride source to assess the impact that both length and branching of the hydrocarbon chain might have on the framing and layering of the material. A change in the amount of the reducing agent NaBH4 allowed tuning of the percentage of metallic bismuth. After a thorough characterization (XRPD, SEM, TEM, UV-DRS, XPS), the photocatalytic activity of the catalysts was tested in the degradation of NOx under visible light, reaching a remarkable 53% conversion after 3 h of illumination for the material prepared using cetylpyridinium chloride.

The size of TiO2 (either nanometric or micrometric) can significantly affect both its photocatalytic and photoelectrochemical properties, thus altering the photooxidation of organic pollutants in air or water. The purpose of this work is to give an account of the photoelectrochemical and photocatalytic features of some nano- and micro-sized TiO2 commercial powders towards a model reaction, the photooxidation of acetone. Cyclic voltammograms (CV) of TiO2 particulated electrodes under UV illumination experiments were carried out in either saturated O2 or N2 solutions for a direct correlation with the photocatalytic process. In addition, the effect of different reaction conditions on the photocatalytic efficiency under UV light in both aqueous and gaseous phases was also investigated. CV curves with the addition of acetone under UV light showed a negative shift of the photocurrent onset, confirming the efficient transfer of photoproduced reactive oxygen species (ROSs), e.g., hydroxyl radicals, or holes to acetone molecules. The photocatalytic experiments showed that the two nano-sized samples exhibit the best photocatalytic performance. The different photoactivity of the micro-sized samples is probably attributed to their morphological differences, affecting both the amount and distribution of free ROSs involved in the photooxidation reaction.

Sn-modification of TiO2 photocatalysts has been recently proposed as a suitable strategy to improve pollutant degradation as well as hydrogen production. In particular, visible light activity could be promoted by doping with Sn2+ species, which are, however, thermally unstable. Co-promotion with N and Sn has been shown to lead to synergistic effects in terms of visible light activity, but the underlying mechanism has, so far, been poorly understood due to the system complexity. Here, the structural, optical, and electronic properties of N,Sn-copromoted, nanostructured TiO2 from sol-gel synthesis were investigated: the Sn/Ti molar content was varied in the 0&ndash, 20% range and different post-treatments (calcination and low temperature hydrothermal treatment) were adopted in order to promote the sample crystallinity. Depending on the adopted post-treatment, the optical properties present notable differences, which supports a combined role of Sn dopants and N-induced defects in visible light absorption. X-ray absorption spectroscopy at the Ti K-edge and Sn L2,3-edges shed light onto the electronic properties and structure of both Ti and Sn species, evidencing a marked difference at the Sn L2,3-edges between the samples with 20% and 5% Sn/Ti ratio, showing, in the latter case, the presence of tin in a partially reduced state.

The major drawback of oxide-based sensors is the lack of selectivity. In this context, SnxTi1&minus, xO2/graphene oxide (GO)-based materials were synthesized via a simple hydrothermal route, varying the titanium content in the tin dioxide matrix. Then, toluene and acetone gas sensing performances of the as-prepared sensors were systematically investigated. Specifically, by using 32:1 SnO2/GO and 32:1 TiO2/GO, a greater selectivity towards acetone analyte, also at room temperature, was obtained even at ppb level. However, solid solutions possessing a higher content of tin relative to titanium (as 32:1 Sn0.55Ti0.45O2/GO) exhibited higher selectivity towards bigger and non-polar molecules (such as toluene) at 350 &deg, C, rather than acetone. A deep experimental investigation of structural (XRPD and Raman), morphological (SEM, TEM, BET surface area and pores volume) and surface (XPS analyses) properties allowed us to give a feasible explanation of the different selectivity. Moreover, by exploiting the UV light, the lowest operating temperature to obtain a significant and reliable signal was 250 &deg, C, keeping the greater selectivity to the toluene analyte. Hence, the feasibility of tuning the chemical selectivity by engineering the relative amount of SnO2 and TiO2 is a promising feature that may guide the future development of miniaturized chemoresistors.

The major drawback of oxide-based sensors is the lack of selectivity. In this context, SnxTi1−xO2/graphene oxide (GO)-based materials were synthesized via a simple hydrothermal route, varying the titanium content in the tin dioxide matrix. Then, toluene and acetone gas sensing performances of the as-prepared sensors were systematically investigated. Specifically, by using 32:1 SnO2/GO and 32:1 TiO2/GO, a greater selectivity towards acetone analyte, also at room temperature, was obtained even at ppb level. However, solid solutions possessing a higher content of tin relative to titanium (as 32:1 Sn0.55Ti0.45O2/GO) exhibited higher selectivity towards bigger and non-polar molecules (such as toluene) at 350 °C, rather than acetone. A deep experimental investigation of structural (XRPD and Raman), morphological (SEM, TEM, BET surface area and pores volume) and surface (XPS analyses) properties allowed us to give a feasible explanation of the different selectivity. Moreover, by exploiting the UV light, the lowest operating temperature to obtain a significant and reliable signal was 250 °C, keeping the greater selectivity to the toluene analyte. Hence, the feasibility of tuning the chemical selectivity by engineering the relative amount of SnO2 and TiO2 is a promising feature that may guide the future development of miniaturized chemoresistors.

Ambient-pressure operando soft X-ray absorption spectroscopy (soft-XAS) was applied to study the reactivity of hydroxylated SnO2 nanoparticles toward reducing gases. H2 was first used as a test case, showing that the gas phase and surface states can be simultaneously probed: Soft-XAS at the O K-edge gains sensitivity toward the gas phase, while at the Sn M4,5-edges, tin surface states are explicitly probed. Results obtained by flowing hydrocarbons (CH4 and CH3CHCH2) unequivocally show that these gases react with surface hydroxyl groups to produce water without producing carbon oxides and release electrons that localize on Sn to eventually form SnO. The partially reduced SnO2 – x layer at the surface of SnO2 is readily reoxidized to SnO2 by treating the sample with O2 at mild temperatures (>200 °C), revealing the nature of “electron sponge” of tin oxide. The experiments, combined with DFT calculations, allowed devising of a mechanism for dissociative hydrocarbon adsorption on SnO2, involving direct reduction of Sn sites at the surface via cleavage of C–H bonds and the formation of methoxy- and/or methyl-tin species at the surface.

Valorisation of lignocellulosic biomass for chemical production is one of the main challenges of the 21st century. Levulinic acid (LA) has been chosen as the target product due to its potential as an intermediate to produce a wide variety of other chemicals. The attention has been focused on the formulation of an active solid acid catalyst for the hydrolysis of glucose to LA. Therefore, a deep modification of SBA-15 with sulfonic groups was performed using post-synthesis grafting method. In particular, this work focuses on the role of different grafting solvents. Since the traditional solvents such as toluene or hexane, are flammable and toxic, a safer and more environmentally friendly solvent, a mixture of water and NaCl has been investigated. It was found that the nature of the solvent highly affects the morphological and chemical features of the materials. Thus, the best catalytic results were obtained with the catalyst prepared in water and NaCl; indeed 30 % and 16 % of LA yield were obtained from fructose and glucose hydrolysis at 180 °C respectively. Water and NaCl mixture guarantees the best distribution of sulfonic groups over the surface, leading to the most balanced acid catalyst.

Recently, TiO2–Montmorillonite-based composites have attracted a great deal of attention as efficient photocatalysts for the degradation/reduction of organic contaminants and heavy metals in waters and wastewaters. It can be claimed that the most popular benefits of using TiO2–Montmorillonite photocatalysts are an enhancement in the photocatalytic removal of contaminants due to their high adsorption capacity, high photocatalytic activity of nanoscaled TiO2 deposited on Montmorillonite surface and low costs. Otherwise, the use of naked nanoscaled TiO2 is not recommended because of its low adsorption ability, fast agglomeration in water and due to the issue of recovery of such small particles from water. Differently from naked TiO2, the photocatalytic removal of contaminants by TiO2–Montmorillonite is enhanced through the mechanism so-called Adsorb & Shuttle (A&S) which is based on the use of highly adsorbing domains to increase the quantity of contaminants near TiO2 photocatalytic sites. Adsorb & Shuttle process can be affected by TiO2–Montmorillonite characteristics (i.e. TiO2 loading, surface area, pore size and degree of TiO2 crystallinity) as well as the type of contaminant. In this chapter, the following points will be highlighted: (i) mechanisms of TiO2 photocatalysis for the removal of organic contaminants and heavy metals, (ii) recent progress on synthesis of TiO2–Montmorillonite photocatalysts via different methods and (iii) recent discussions regarding the photocatalytic removal of contaminants by TiO2–Montmorillonite composites.

At the beginning of the industrial productions, porcelain gres tiles were considered as just a technical material, esthetically not very beautiful. Today thanks to new industrial production methods, both properties and beauty of these materials completely fit the market requests. Besides these noteworthy architectural features, new surface properties have been introduced in the last generation of these materials. In particular, deposition of TiO2 transforms the traditional ceramic into a photocatalytic eco-active material able to reduce polluting molecules present in air and water, to eliminate bacteria, and to reduce the surface dirt thanks to the self-cleaning property. The problem of photocatalytic materials resides in the fact that it is necessary an ultraviolet (UV) light source to activate the oxidation processes on the surface of the material, processes that are turned off inexorably when the material is illuminated by LED lights and, even more so, when we are in darkness. The commercial TiO2, which is used for the traditional photocatalytic coating, has been doped with metals in order to activate it even in the visible region and thus in the presence of sunlight or LED. The presence of dopant metals (patent WO2016157155), specifically Ag, also allows the material to work as well as antibacterial in the dark, by eliminating one of the negative features of photocatalytic building materials. This chapter will report all the material characterization and photocatalytic tests including antibacterial tests (under UV, LED, and in the dark as well), from the most common such as Escherichia coli to the most dangerous such as methicillin-resistant Staphylococcus aureus.

TiO2 modification by both non-metal and metal species is a popular strategy to promote the semiconductor visible light absorption and photocatalytic performance. In this work, tin and zinc are compared as metal promoters to enhance the photocatalytic activity of N-doped TiO2 under solar light. The synthesized samples were tested under both UV and simulated solar irradiation toward the photocatalytic degradation of tetracycline, an emerging water pollutant. All copromoted samples (N + Sn and N + Zn) revealed higher efficiency under solar light in the mineralization of the pollutant with respect to both the pristine and N-doped ones. The enhanced photocatalytic efficiency of these samples was traced back to the modifications introduced by the different guest species to the structural (X-ray Powder Diffraction, XRPD), morphological (High-Resolution Transmission Electron Microscopy, HR-TEM and Brunauer-Emmett-Teller analysis, BET), spectroscopic (X-ray Photoelectron Spectroscopy, XPS, Energy Dispersive X-ray Spectroscopy, EDX and Diffuse Reflectance Spectroscopy, DRS) and surface features (ζ-potential). In this regard, the increased surface area, the modifications of the phase composition and the enhanced visible light harvesting seem to play a pivotal role in affecting the photocatalytic performance. Mass spectrometry analyses allowed us to identify several reaction intermediates and propose different degradation mechanisms depending on the type of metal promoter.

Titanium dioxide is the most popular photocatalyst to degrade organic pollutants in air, as well as in water. The principal drawback preventing its commercial application lies in its limited absorption of the visible light (400-700nm), while it is active under UV irradiation (≤387nm). Supporting noble metals in the form of nanoparticles on TiO2 increases its activity in the visible range. However, both the synthesis of noble metal nanoparticles and their deposition on TiO2 are multi-step processes that often require organic solvents. Here, we deposit Ag nanoparticles from AgNO3 on the surface of micrometric TiO2 with H2O as a solvent and under ultrasound irradiation at 30Wcm-2. Ultrasound increases the surface amount of Ag on TiO2 with heterogeneous size distribution of Ag nanoparticles, which are bigger and overlaid (1-20nm vs. 0.5-3nm) compared to the sample obtained in traditional conditions (TEM images). While this change in morphology had no effect on acetone photodegradation under UV light, the 5%, 10%, and 20% Ag-TiO2 degraded 17%, 20% and 24% acetone under visible light, respectively. The 10% by weight Ag-TiO2 sample obtained in absence of ultrasound only degraded 14% acetone in 6h, while the bare TiO2 was not active.

We synthesized Ce doped TiO2 (Cex-T) and tested it in the photocatalytic degradation of NOx and ethanol under visible light. Pristine TiO2 (T) and different dopant ratios of Ce-TiO2 (Cex-T; x=0 to 1.0 wt%) were prepared by a water-based sol-gel method followed by spray drying. The successful doping of Ce in the lattice structure of TiO2 was confirmed by several characterizations such as X-ray diffraction (XRD), energy dispersive X-ray (EDX), Fourier transform infrared (FTIR), and Raman spectroscopy. All the prepared catalysts grew as spherical grains with a polycrystalline anatase phase. Ce0.8T revealed the lowest bandgap among all the prepared catalysts (2.8 eV) compared to 3.2 eV for T. The highest degradation of NOx and ethanol was attained by Ce0.8T (26±1% and 23±1%), which was 2.8 and 1.5 times the degradation by T, Furthermore, we proposed the photocatalytic degradation mechanism by the reactive oxidant species (ROS).