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In this work, it is proposed an environmental friendly sonophotocatalytic approach to efficiently treat polluted waters from industrial dyes exploiting ZnO micro- and nano-materials. For the first time, we deeply investigated the generation of reactive oxygen species (ROS) under ultrasound stimulation of different ZnO structures by Electron Paramagnetic Resonance Spectroscopy (EPR). Indeed, five zinc oxide (ZnO) micro- and nano-structures, i.e. Desert Roses (DRs), Multipods (MPs), Microwires (MWs), Nanoparticles (NPs) and Nanowires (NWs), were studied for the Rhodamine B (RhB) sonodegradation under ultrasonic irradiation. The DRs microparticles demonstrated the best sonocatalytic performance (100% degradation of RhB in 180 min) and the highest OH· radicals generation under ultrasonic irradiation. Strikingly, the coupling of ultrasound and sun-light irradiation in a sonophotodegradation approach led to 100% degradation efficiency, i.e. color reduction, of RhB in just 10 min, revealing a great positive synergy between the photocatalytic and sonocatalytic mechanisms. The RhB sonophotocatalytic degradation was also evaluated at different initial dye concentrations and with the presence of anions in solution. It was demonstrated a good stability over repeated cycles of dye treatment, which probe the applicability of this technique with industrial effluents. In conclusion, sonophotocatalytic degradation synergizing sunlight and ultrasound in the presence of DRs microparticles shows a great potential and a starting point to investigate further the efficient treatment of organic dyes in wastewater.

The need to reduce the costs of renewable energy sources such as (bio)electrochemical systems, has pushed the research towards alternative materials, especially for cathodes performing the oxygen reduction reaction, trying to maintain a catalytic efficiency close to that of platinum or platinum-based catalysts. In this work, at first, we present a manganese oxide-based catalyst in the form of xerogel, providing a complete description of the material. Later on, we present the comparison of two nanostructured manganese oxide-based catalysts, prepared from the same precursor, manganese acetate, but with different templating agents and with two different nanostructures: the xerogel previously discussed, and the nanofibers. With these two nanostructures, we prepared carbon-based electrodes, obtaining cathodes to be tested in microbial fuel cells. One of these cathodes performed very well and its performance was comparable to that of the reference which used Pt/C as catalyst.

In this work we present a green approach to the synthesis of nitrogen-doped carbon-based aerogels with good conductivity and catalytic properties. With the aim to design an easily sustainable process, the starting precursors were selected among abundant waste-related organic materials. The naturally-derived polysaccharide agar worked as the carbon source in a water solution, while an amino acid, glycine or lysine has been used as the nitrogen source. By this synthesis approach, nitrogen defects were created into a 3D porous aerogel: they successfully acted as active catalytic sites for the reaction of oxygen reduction to water as demonstrated by electrochemical measurements. The best performing materials have been tested as cathodes in microbial fuel cells for 50 days, in conditions close to those the device could face in a real environment. The glycine derived carbon aerogels with the higher content of pyridinic nitrogen, as confirmed by several morphological characterizations, showed the best performance.

In this work we investigated the behavior of TiO2 nanotube (NT) arrays, grown by anodic oxidation of Ti foil, as catalysts for the oxygen reduction reaction (ORR) in alkaline water solution. In particular, as-grown amorphous NTs were compared to crystalline anatase nanostructures, obtained following two different procedures, namely thermal and vapor-induced crystallizations. The catalytic activity of these materials toward the ORR was evaluated by cyclic voltammetry measurements. ORR polarization curves, combined with the rotating disk technique, indicated a predominant four-electrons reduction path, especially for crystalline samples. The effect of the structural characteristics of the investigated materials on the catalytic activity was analyzed in details by electrochemical impedance spectroscopy. The catalytic performance of the crystalline NTs is only slightly lower with respect to the reference material for fuel cell applications, namely platinum, but is in line with other cost-effective catalysts recently proposed in the literature. However, if compared to the larger part of these low-cost catalysts, anodically-grown TiO2 NTs are characterized by a synthesis route which is highly reproducible and easily up-scalable.

Manganese oxides (MnxOy) are considered as a promising catalyst alternative to platinum in fuel cell applications. In fact, a proper catalyst is needed in order to facilitate the oxygen reduction reaction (ORR) at the cathode, and platinum is considered the best material due to its low overpotential for this reaction. Contrary to platinum, MnxOy is inexpensive, environmentally friendly and can be shaped into several nanostructures; furthermore, most of them show significant electro-catalytic performance. Several strategies have been carried out in order to increase their efficiency, by preparing light and high-surface area materials. In this framework, nanofibres are among the most promising nanostructures that can be used for this purpose. In this work, a study of the thermal, morphological and catalytic behavior of MnxOy nanofibres obtained through the electrospinning technique is proposed. Emphasis is given to the thermal evolution of the precursors, proposing a possible crystallization mechanism of the different manganese oxides obtained. It turns out that manganese oxide nanofibres exhibit good catalytic performance for the ORR, comparable to those obtained by using Pt-based catalysts.

The use of nanomaterials in the field of bone tissue engineering implants is continuously dealing with the development of innovative solutions to common problems, as infection by colonization with common microbial agents, antibiotic bacterial resistance, and the formation of new bone tissue. Among them, ZnO nanostructures are promising candidates thanks to their intrinsic antimicrobial activity and high biocompatibility. In this paper we aim to analyse the behaviour of ZnO nanocrystals (ZnO NCs), prepared with a new synthetic approach and not embedded in any composite matrix, for bone implants applications in-vitro. In particular, we have developed a novel, fast and reproducible microwave-assisted synthesis, obtaining highly-crystalline, round-shaped ZnO NCs of 20 nm in diameter as an extremely-stable colloidal solution in ethanol. Part of them were also chemically functionalized by anchoring amino-propyl groups to the ZnO surface (ZnO-NH2 NCs). Thus, the role of both ZnO NCs concentration and surface chemistry are tested in terms of biocompatibility towards pre-osteoblasts cells, promotion of cell proliferation and differentiation, and also in terms of antimicrobial activity against Gram positive and negative bacteria, such as Escherichia coli and Staphylococcus aureus, respectively. The results propose the ZnO-NH2 NCs as the most promising candidate to solve infections disease in bone implants and promote bone tissue proliferation at the same time, even at high concentrations. Whereas further investigations are needed for example to clarify the mechanism inhibiting biofilm formation and to investigate their role in in-vivo assays, we demonstrated that a fine and reproducible control over the chemical and structural parameters in ZnO nanomaterials can open new horizons in the use of functionalized ZnO NCs as a highly biocompatible and osteoinductive nanoantibiotic agent for bone tissue engineering.

The lack of low-cost, durable and highly efficient electrocatalysts to perform oxygen reduction reaction (ORR) still represents a significant challenge for the development of fuel cells cathodes. Recently, Pt-free metalloporphyrins supported on N-doped reduced graphene oxide (N-rGO) have been proposed as innovative ORR catalysts characterized by notable stability and superior performance. In this paper, we propose a fast and green microwave-assisted method to synthetize manganese-nitrogen co-doped rGO, characterized by catalytic activity comparable to Pt-containing materials and improved long-term stability. Theoretical calculations and experimental results showed that our synthetic method produces N-rGO matrices which coordinate Mn2+ ions in porphyrin-like structures. These Mn/N-rGO complexes are responsible for the outstanding performance of the proposed catalyst, being able to weaken O–O molecular bond, thus effectively reducing the activation energy towards oxygen catalytic reaction. Our findings open the path to a green co-doping process of graphene for the production of low-cost and efficient alternatives to noble metals-based ORR catalysts.

Nitrogen-doped reduced graphene oxide is successfully synthesized and functionalized with hydroxylated copper ions via one-pot microwave-assisted route. The presence of cationic Cu coordinated to the graphene layer is fully elucidated through a set of experimental characterizations and theoretical calculations. Thanks to the presence of these hydroxyl-coordinated Cu2+ active sites, the proposed material shows good electrocatalytic performance for the oxygen reduction reaction, as evidenced by an electron transfer number of almost 4 and by high onset and half-wave potentials of 0.91 V and 0.78 V vs. the reversible hydrogen electrode, respectively. In addition, the N-doped Cu-functionalized graphene displays a superior current retention with respect to a commercial Pt/C catalyst during the stability test, implying its potential implementation in high-performance fuel cells and metal-air batteries.

ZnO nanostructures are grown by a simple chemical vapour deposition method directly on a stainless steel disc current collector and successfully tested in lithium cells. The structural/morphological characterization points out the presence of well-defined polycrystalline nanostructures having different shapes and a preferential orientation along the c -axis direction. In addition, the high active surface of the ZnO nanostructures, which accounts for a large electrode/electrolyte contact area, and the complete wetting with the electrolyte solution are considered to be responsible for the good electrical transport properties and the adequate electrochemical behaviour, as confirmed by cyclic voltammetry and galvanostatic charge/discharge cycling. Indeed, despite no binder or conducting additives are used, when galvanostatically tested in lithium cells, after an initial decay, the ZnO nanostructures can provide a rather stable specific capacity approaching 70 μA h cm −2 (i.e., around 400 mA h g −1 ) after prolonged cycling at 1 C, with very high Coulombic efficiency and an overall capacity retention exceeding 62%.

Vertically oriented arrays of high surface area TiO2 nanotubes (NTs) are fabricated by the fast and facile anodic oxidation of a titanium foil. The formation of well-defined one-dimensional nanotubular carpets is assessed by means of morphological Field Emission Scanning Electron Microscopy characterisation, while X-ray diffraction analysis and Transmission Electron Microscopy imaging confirm the amorphous nature of the samples. The electrochemical response evaluated in lab-scale lithium cells is highly satisfying with near-theoretical initial specific capacity and remarkable rate capability, noteworthy in the absence of binders and conductive agents, which would affect the overall energy density. A specific capacity exceeding 200 mAh g−1 is observed at very high 24 C and approx. 80 mAh g−1 are retained even at very high 96 C rate, thus accounting for the promising prospects in storage devices conceived for high power applications. Moreover, the NTs can perform with good cycling stability and capacity retention approaching 50% of the initial value after very long-term operation along with improved durability (> 2000 cycles).

Lithiated vanadium oxides with polyelectrochromic behaviour are reported here for the first time. Electrochrome was obtained by means of a simple and solvent-free solid state reaction. Clear XPS evidence indicates that the electro-generation of the red color is due to the dismutation of surface-adsorbed O2− species with subsequent formation of red colored V5+–O22− complexes. The reaction is switched electrochemically by oxidation of the surface V4+ centers.

Herein we report a novel, easy, fast and reliable microwave-assisted synthesis procedure for the preparation of colloidal zinc oxide nanocrystals (ZnO NCs) optimized for biological applications. ZnO NCs are also prepared by a conventional solvo-thermal approach and the properties of the two families of NCs are compared and discussed. All of the NCs are fully characterized in terms of morphological analysis, crystalline structure, chemical composition and optical properties, both as pristine nanomaterials or after amino-propyl group functionalization. Compared to the conventional approach, the novel microwave-derived ZnO NCs demonstrate outstanding colloidal stability in ethanol and water with long shelf-life. Furthermore, together with their more uniform size, shape and chemical surface properties, this long-term colloidal stability also contributes to the highly reproducible data in terms of biocompatibility. Actually, a significantly different biological behavior of the microwave-synthesized ZnO NCs is reported with respect to NCs prepared by the conventional synthesis procedure. In particular, consistent cytotoxicity and highly reproducible cell uptake toward KB cancer cells are measured with the use of microwave-synthesized ZnO NCs, in contrast to the non-reproducible and scattered data obtained with the conventionally-synthesized ones. Thus, we demonstrate how the synthetic route and, as a consequence, the control over all the nanomaterial properties are prominent points to be considered when dealing with the biological world for the achievement of reproducible and reliable results, and how the use of commercially-available and under-characterized nanomaterials should be discouraged in this view.

In the field of fuel cells, oxygen plays a key role as the final electron acceptor. To facilitate its reduction (Oxygen Reduction Reaction—ORR), a proper catalyst is needed and platinum is considered the best one due to its low overpotential for this reaction. By considering the high price of platinum, alternative catalysts are needed and manganese oxides (Mn x O y ) can be considered promising substitutes. They are inexpensive, environmental friendly and can be obtained into several forms; most of them show significant electro-catalytic performance, even if strategies are needed to increase their efficiency. In particular, by developing light and high-surface area materials and by optimizing the presence of catalytic sites, we can obtain a cathode with improved electro-catalytic performance. In this case, nanofibers and xerogels are two of the most promising nanostructures that can be used in the field of catalysis. In this work, a study of the morphological and catalytic behavior of Mn x O y nanofibers and xerogels is proposed. Nanofibers were obtained by electrospinning, while xerogels were prepared by sol-gel and freeze drying techniques. Despite of the different preparation approaches, the obtained nanostructured manganese oxides exhibited similar catalytic performance for the ORR, comparable to those obtained from Pt catalysts.

In the present paper, we use zinc oxide nanoparticles under the excitation of ultraviolet (UV) light for the generation of Reactive Oxygen Species (ROS), with the aim of further using these species for fighting cancer cells in vitro. Owing to the difficulties in obtaining highly dispersed nanoparticles (NPs) in biological media, we propose their coating with a double-lipidic layer and we evaluate their colloidal stability in comparison to the pristine zinc oxide NPs. Then, using Electron Paramagnetic Resonance (EPR) coupled with the spin-trapping technique, we demonstrate and characterize the ability of bare and lipid-coated ZnO NPs to generate ROS in water only when remotely actuated via UV light irradiation. Interestingly, our results reveal that the surface chemistry of the NPs greatly influences the type of photo-generated ROS. Finally, we show that lipid-coated ZnO NPs are effectively internalized inside human epithelial carcinoma cells (HeLa) via a lysosomal pathway and that they can generate ROS inside cancer cells, leading to enhanced cell death. The results are promising for the development of ZnO-based therapeutic systems.

Silicon is a very attractive Li-ion battery anode material due to its high theoretical capacity, but proper nanostructuring is needed to accommodate the large volume expansion/shrinkage upon reversible cycling. Hereby, novel mesoporous Si nanostructures are grown at room temperature by simple and rapid Pulsed Laser Deposition (PLD) directly on top of the Cu current collector surface. The samples are characterized from the structural/morphological viewpoint and their promising electrochemical behavior demonstrated in lab-scale lithium cells. Depending on the porosity, easily tuneable by PLD, specific capacities approaching 250 μAh cm−2 are obtained. Successively, newly elaborated bi-component silicon/carbon nanostructures are fabricated in one step by alternating PLD deposition of Si and C, thus resulting in novel multi-layered composite mesoporous films exhibiting profoundly improved performance. Alternated deposition of Si/C layers by PLD is proven to be a straightforward method to produce multi-layered anodes in one processing step. The addition of carbon and mild annealing at 400°C stabilize the electrochemical performance of the Si-based nanostructures in lab-scale lithium cells, allowing to reach very stable prolonged reversible cycling at improved specific capacity values. This opens the way to further reducing processing steps and processing time, which are key aspects when upscaling is sought

Thermoset initiator-free membranes are prepared by the UV-induced photopolymerization of thiol and (meth)acrylic monomers having polyethylene oxide chains, being known that the use of such monomers can lead to the formation of readily degradable membranes. The photopolymerization of different formulations is studied and the influence of the addition of a monofunctional methacrylate is investigated. By incorporation of lithium bis(oxalate)borate salt, solid polymer electrolytes are prepared and used as electrolyte membranes in Li-ion batteries. The ionic conductivity of the samples is measured and correlated to their thermal characteristics. The best performing sample shows encouraging cycling behaviour when tested in a truly-solid state lab-scale lithium test cell, thus enlightening the promising prospects of the newly designed polymer electrolytes. Furthermore, a preliminary degradation study is performed demonstrating the possibility to hydrolytically degrade the proposed UV cured networks making them extremely appealing for the development of sustainable and easily recyclable, thus greener, energy power sources.

Single phase wurtzitic porous ZnO thin films are obtained by a simple two-step method, involving the sputtering deposition of a sponge-like metallic Zn layer, followed by a moderately low temperature treatment for the complete zinc oxidation. Thanks to its 3D nanostructuration, the superimposition of small branches able to grow in length almost isotropically and forming a complex topography, sponge-like ZnO can combine the fast transport properties of one dimensional material and the high surface area usually provided by nanocrystalline electrodes. When galvanostatically tested in lithium cell, after the initial decay, it can provide an almost stable specific capacity higher than 50 μAh cm −2 after prolonged cycling at estimated 0.7 C, with very high Coulombic efficiency.

Silicon is very attractive as active material for Li-ion battery anodes due to its high theoretical capacity, but proper nanostructuring is needed to accommodate the large volume expansion/shrinkage upon reversible cycling. This would overcome the destructuration induced by the lithiation/delithiation processes, often resulting in poor long-term performance. Hereby, novel mesoporous silicon nanostructures are grown at room temperature by Pulsed Laser Deposition (PLD) directly on top of the Cu current collector surface, and their promising electrochemical behaviour demonstrated in lab-scale lithium cells. Depending on the porosity, easily tunable by PLD, initial specific capacities approaching 300 µAh cm- 2 are obtained with a quasi-stable reversible cycling. Engineering voids at the nanoscale, by direct introduction of specific porosity during growth, opens up the route for the effective use of silicon as lithium battery anode without the need for any binder or conductive additive which would lower the overall energy density.

Vertically oriented arrays of TiO2 nanotubes (NTs) are fabricated by fast and facile, thus easily up-scalable, anodic oxidation of a titanium foil followed by rapid thermal annealing. The structural/morphological characterization shows the formation of well defined one-dimensional nanotube carpets, while the X-ray diffraction analysis reveals the pure anatase crystalline structure of the thermal treated samples. The electrochemical response in laboratory-scale lithium cells is highly satisfying: at a very high discharge/charge rate of 12C, the NTs can perform with good stability and capacity retention after long-term cycling along with improved durability (>1100 cycles). High surface area, self-induced doping, short diffusion path and fast kinetics of the unidirectionally aligned TiO2 nanotube arrays are intriguing prospects which can be considered responsible for the noticeable electrochemical performance obtained in the absence of foreign ingredients such as binders and conductive agents, which would affect the overall energy density.

In this chapter, we give an overview about the use of zinc oxide (ZnO) nanomaterials in the biomedical field, looking at the ongoing research and identifying the needs and improvements for future perspectives. We start describing the properties of ZnO at the nanoscale and considering the requirements to have a nanomaterial interfacing with different biological environments. We then report how synthetic approaches allow the obtainment of biocompatible ZnO nanostructures detailing the strategies to pursue their biostability and dispersibility in biological fluids. In a further step, we consider the requirements and tests used to evaluate nanomaterial hemocompatibility, focusing on the strategies for obtaining hemocompatible, yet injectable, ZnO nanoparticles. An evaluation on the mechanisms underlying the intrinsic cytotoxicity of ZnO nanomaterials is also presented taking chance of these features for the engineerization of efficient therapeutics against cancer, of antibacterial agents, and for tissue engineering solutions.

Zinc oxide nanocrystals (ZnO-NCs) doped with transition metal elements or rare earth elements can be probed for magnetic resonance imaging to be used as a molecular imaging technique for accurate diagnosis of various diseases. Herein, we use Mn as a candidate of transition metal elements and Gd as a presenter of rare earth elements. We report an easy and fast coprecipitation method exploiting oleic acid to synthesize spherical-shaped, small-sized doped ZnO-NCs. We show the improved colloidal stability of oleate-stabilized doped ZnO-NCs compared to the doped ZnO-NCs synthesized by conventional sol&ndash, gel synthesis method, i.e., without a stabilizing agent, especially for the Mn dopant. We also analyze their structural, morphological, optical, and magnetic properties. We are able to characterize the persistence of the crystalline properties (wurtzite structure) of ZnO in the doped structure and exclude the formation of undesired oxides by doping elements. Importantly, we determine the room-temperature ferromagnetism of the doped ZnO-NCs. This oleate-stabilized coprecipitation method can be subjected as a standard procedure to synthesize doped and also co-doped ZnO-NCs with any transition metal elements or rare earth elements. In the future, oleate-stabilized Gd/Mn-doped ZnO-NCs can be exploited as magnetic resonance imaging (MRI) contrast agents and possibly increase the signal intensity on T1-weighted images or reduce the signal intensity on T2-weighted images.