Advanced Self-Cleaning Surfaces.

Hydrophobicity, olephobicity, hemophobicity, amphiphobicity, omniphobicity, icephobicity [...].

Recent Advances in the Use of Green Corrosion Inhibitors to Prevent Chloride-Induced Corrosion in Reinforced Concrete.

Inhibitors for the prevention of corrosion in reinforced concrete are chemical substances able to reduce carbon steel reinforcements corrosion without altering the overall properties of concrete. Today, many commercially available substances have a negative impact on human safety during either the inhibitor synthesis, their handling or application in field. Green corrosion inhibitors are nontoxic, biodegradable and environmentally biocompatible substances. They are generally made of extracts from natural plants or waste, which are abundantly available in several countries. The majority of green inhibitor molecules usually contain multiple bonds, aromatic rings, polar functional groups and electronegative atoms as P, N, S or O; the latter are able to coordinate with metal cations to form protective layers on the metallic surface of the reinforcements, so as to inhibit the development (initiation and/or propagation) of the corrosion process. In this review, the most recent achievements on the study and investigation of green corrosion inhibitors for concrete structures are presented and discussed. Inhibitors are classified based on their nature and inhibition mechanism. The inhibition effectiveness of the substances is compared with the well-established effective nitrite-based inhibitor, distinguishing between accelerated and long-term tests. Based on the available data, a summary of corrosion inhibitors efficiency is reported.

The Improvement of Durability of Reinforced Concretes for Sustainable Structures: A Review on Different Approaches.

The topic of sustainability of reinforced concrete structures is strictly related with their durability in aggressive environments. In particular, at equal environmental impact, the higher the durability of construction materials, the higher the sustainability. The present review deals with the possible strategies aimed at producing sustainable and durable reinforced concrete structures in different environments. It focuses on the design methodologies as well as the use of unconventional corrosion-resistant reinforcements, alternative binders to Portland cement, and innovative or traditional solutions for reinforced concrete protection and prevention against rebars corrosion such as corrosion inhibitors, coatings, self-healing techniques, and waterproofing aggregates. Analysis of the scientific literature highlights that there is no preferential way for the production of "green" concrete but that the sustainability of the building materials can only be achieved by implementing simultaneous multiple strategies aimed at reducing environmental impact and improving both durability and performances.

Suspended Multifunctional Nanocellulose as Additive for Mortars.

Cellulose derivatives have found significant applications in composite materials, mainly because of the increased mechanical performance they ensure. When added to cement-based materials, either in the form of nanocrystals, nanofibrils or micro/nanofibers, cellulose acts on the mixture with fresh and hardened properties, affecting rheology, shrinkage, hydration, and the resulting mechanical properties, microstructure, and durability. Commercial cotton wool was selected as starting material to produce multifunctional nanocelluloses to test as additives for mortars. Cotton wool was oxidized to oxidized nanocellulose (ONC), a charged nanocellulose capable of electrostatic interaction, merging cellulose and nanoparticles properties. Oxidized nanocellulose (ONC) was further functionalized by a radical-based mechanism with glycidyl methacrylate (GMA) and with a mixture of GMA and the crosslinking agent ethylene glycol dimethacrylate (EGDMA) affording ONC-GMA and ONC-GMA-EGDMA, both multifunctional-charged nanocellulose merging cellulose and bound acrylates properties. In this work, only ONC was found to be properly suitable for suspension and addition to a commercial mortar to assess the variation in mechanical properties and water-mortar interactions as a consequence of the modified microstructure obtained. The addition of oxidized nanocellulose caused an alteration of mortar porosity, with a decreased percentage of porosity and pore size distribution shifted towards smaller pores, with a consequent increase in compressive resistance, decrease in water absorption coefficient, and increased percentage of micropores present in the material, indicating a potential improvement in mortar durability.

Magnetically Recoverable TiO2/SiO2/γ-Fe2O3/rGO Composite with Significantly Enhanced UV-Visible Light Photocatalytic Activity.

In this paper, we report the preparation of a new composite (TiO2/SiO2/γ-Fe2O3/rGO) with a high photocatalytic efficiency. The properties of the composite were examined by different analyses, including X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), photoluminescence (PL), UV-Visible light diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy (FTIR), Raman, vibrating-sample magnetometer (VSM), and nitrogen gas physisorption (BET) studies. The photocatalytic efficiency of the proposed composite was evaluated by the degradation of methylene blue under UV and visible light, and the results were compared with titanium dioxide (TiO2), where degradation increased from 30% to 84% and 4% to 66% under UV and visible light, respectively. The significant increase in photocatalytic activity may be explained by the higher adsorption of dye on the surface of the composite and the higher separation and transfer of charge carriers, which in turn promote active sites and photocatalytic efficiency.

Heterostructured TiO2/SiO2/γ-Fe2O3/rGO Coating with Highly Efficient Visible-Light-Induced Self-Cleaning Properties for Metallic Artifacts.

A novel nanohybrid composite of TiO2, SiO2, γ-Fe2O3, and reduced graphene oxide (TiO2@Si:Fe:rGO) is fabricated by the sol-gel method. The properties of the coated film were examined by structural and self-cleaning analyses using simulated discoloration/soiling and roofing tests. The fabricated transparent TiO2@Si:Fe:rGO composite showed excellent photoactivity and wettability, behaving well in self-cleaning applications. The addition of SiO2 improved the crystalline structure and surface hydroxylation of TiO2 nanoparticles. γ-Fe2O3 decreased the recombination rate of e-/h+ pairs, and significantly improved photocatalytic activity under visible light. Moreover, rGO sheets as excellent electron acceptors and transporters also reduced recombination, as well as affected wettability, achieving superhydrophilicity under irradiation. The coated substrate showed excellent resistance to simulated acid rain and significantly preserved the substrate from soiling in roofing tests.

Special Issue: Novel Photoactive Materials.

Photoactivity represents the ability of a material to activate when interacting with light. It can be declined in many ways, and several functionalities arising from this behavior of materials can be exploited, all leading to positive repercussions on our environment. There are several classes of effects of photoactivity, all of which have been deeply investigated in the last few decades, allowing researchers to develop more and more efficient materials and devices. The special issue "Novel Photoactive Materials" has been proposed as a means to present recent developments in the field; for this reason the articles included touch different aspects of photoactivity, from photocatalysis to photovoltaics to light emitting materials, as highlighted in this editorial.

Binders alternative to Portland cement and waste management for sustainable construction-part 1.

This review presents "a state of the art" report on sustainability in construction materials. The authors propose different solutions to make the concrete industry more environmentally friendly in order to reduce greenhouse gases emissions and consumption of non-renewable resources. Part 1-the present paper-focuses on the use of binders alternative to Portland cement, including sulfoaluminate cements, alkali-activated materials, and geopolymers. Part 2 will be dedicated to traditional Portland-free binders and waste management and recycling in mortar and concrete production.

Photocatalytic Activity of Nanotubular TiO2 Films Obtained by Anodic Oxidation: A Comparison in Gas and Liquid Phase.

The availability of immobilized nanostructured photocatalysts is of great importance in the purification of both polluted air and liquids (e.g., industrial wastewaters). Metal-supported titanium dioxide films with nanotubular morphology and good photocatalytic efficiency in both environments can be produced by anodic oxidation, which avoids release of nanoscale materials in the environment. Here we evaluate the effect of different anodizing procedures on the photocatalytic activity of TiO2 nanostructures in gas and liquid phases, in order to identify the most efficient and robust technique for the production of TiO2 layers with different morphologies and high photocatalytic activity in both phases. Rhodamine B and toluene were used as model pollutants in the two media, respectively. It was found that the role of the anodizing electrolyte is particularly crucial, as it provides substantial differences in the oxide specific surface area: nanotubular structures show remarkably different activities, especially in gas phase degradation reactions, and within nanotubular structures, those produced by organic electrolytes lead to better photocatalytic activity in both conditions tested.

Corrosion of titanium: Part 2: Effects of surface treatments.

Titanium is well known as one of the most corrosion-resistant metals. However, it can suffer corrosion attacks in some specific aggressive conditions. To further increase its corrosion resistance, it is possible either to modify its surface, tuning either thickness, composition, morphology or structure of the oxide that spontaneously forms on the metal, or to modify its bulk composition. Part 2 of this review is dedicated to the corrosion of titanium and focuses on possible titanium treatments that can increase corrosion resistance. Both surface treatments, such as anodization or thermal or chemical oxidation, and bulk treatments, such as alloying, are considered, highlighting the advantages of each technique.

Corrosion of titanium: Part 1: aggressive environments and main forms of degradation.

Titanium has outstanding corrosion resistance due to the external natural oxide protective layer formed when it is exposed to an aerated environment. Despite this, titanium may suffer different forms of corrosion in severe environments: uniform corrosion, pitting and crevice corrosion, hydrogen embrittlement, stress-corrosion cracking, fretting corrosion and erosion. In this first review, forms of corrosion affecting titanium are analyzed based on a wide literature review. For each form of corrosion, the mechanism and most severe environment are reported according to the current understanding.In the second part, this review will address the possible surface treatments that can increase corrosion resistance on commercially pure titanium: Electrochemical anodizing, thermal oxidation, chemical oxidation and bulk treatments such as alloying will be considered, highlighting the advantages of each technique.

TiO2 Nanotubes Arrays Loaded with Ligand-Free Au Nanoparticles: Enhancement in Photocatalytic Activity.

A new protocol to synthesize size-controlled Au nanoparticles (NPs) loaded onto vertically aligned anatase TiO2 nanotubes arrays (TNTAs) prepared by electrochemical anodization is reported. Ligand-free Au NPs (<10 nm) were deposited onto anatase TNTAs supports, finely tuning the Au loading by controlling the immersion time of the support into metal vapor synthesis (MVS)-derived Au-acetone solutions. The Au/TNTAs composites were characterized by electron microscopies (SEM, (S)TEM), X-ray diffraction, X-ray photoelectron spectroscopy, and UV-vis spectroscopy. Their photocatalytic efficiency was evaluated in toluene degradation in air under ambient conditions without thermal or chemical postsynthetic treatments. The role of Au loadings was pointed out, obtaining a three times enhancement of the pristine anatase TNTAs activity with the best sample containing 3.3 µg Au cm-2.

Anodic oxidation as a means to produce memristive films.

PURPOSE: In the past few years there has been growing interest in memristive devices. These devices rely on thin metal oxide films with a peculiar structure and composition, making precise control of oxide features vital. To this end, anodic oxidation allows a very large range of oxides to be formed on the surface of valve metals, whose thickness, structure and functional properties depend on the process parameters introduced. This work reports how memristive anodic oxides were obtained on titanium and other valve metals, such as niobium and tantalum. METHODS: Anodic oxidation was performed on valve metals by immersion in H2SO4 or H3PO4 electrolytes and application of voltages ranging from 10 to 90 V. The memristive behavior was evaluated by cyclic voltammetry. RESULTS: The behavior of differently grown oxides was compared to identify the best conditions to achieve good memristive performances. High voltages were identified as not suitable due to the excessive oxide thickness, while below 20 V the film was not thick and uniform enough to give a good response. Surface preparation also played a major role in the observation of memristive properties. CONCLUSIONS: Optimal surface preparation and anodizing conditions were seen to give high memristive perfomances on both titanium and niobium oxides, while on tantalum oxides no reproducibility was achieved.

Effects of photoactivated titanium dioxide nanopowders and coating on planktonic and biofilm growth of Pseudomonas aeruginosa.

We exploited the ability of photocatalytic titanium dioxide (TiO(2)) as an agent for the biofilm control. Two photocatalytic systems were investigated: a 3 g L(-1) suspension of TiO(2) nanopowder in demineralized water and glass slides coated with a TiO(2) thin film, achieved by sol-gel deposition. A running protocol for the photoactivation of TiO(2) was set up using the dye rhodamine B. The microorganisms studied were Pseudomonas stutzeri, Pseudomonas aeruginosa and a Bacillus cereus-group as planktonic cells. P. aeruginosa biofilms were also studied at both the solid-liquid and the solid-air interface. The TiO(2) nanopowder produced 1-log reduction of Bacillus sp. planktonic cells in 24 h, 2-log reduction of P. stutzeri planktonic cells in 30 min and 1-log reduction of P. aeruginosa planktonic cells in 2 h compared with non-photo-activated TiO(2). TiO(2) thin film produced almost a complete eradication of P. aeruginosa planktonic cells (initial concentration 10(8) cells mL(-1)) in 24 h compared to a 3-log reduction caused by UV-A light alone. In contrast, neither the photocatalytic treatment with TiO(2) film nor that with TiO(2) nanopowder had any effect on P. aeruginosa biofilms at all the interfaces investigated. Possible explanations for these findings, and for the discrepancy between this work and literature data, are discussed.

Anodic oxidation of titanium: from technical aspects to biomedical applications.

Titanium biomaterials are widely employed to produce medical components, such as hip and knee-joint prostheses, bone plates and screws, dental implants, pacemaker cases, surgical equipment, etc. Their diffusion is ascribed to the broad spectrum of optimal mechanical and surface properties, such as the corrosion resistance and correlated low ionic release, the biocompatibility, and especially, the enhanced osseointegration that can be achieved by surface modifications, particularly by suitable anodizing treatments. This review is intended to provide a survey of the wide class of anodic oxidation treatments on titanium, focusing on the oxide structures, morphologies, and compositions that best apply to the variegated fields of titanium applications.

Mechanical characterization of an innovative dental implant system.

PURPOSE: The research presented is aimed at the characterization of the mechanical resistance of an innovative system of an abutment-fixture connection in dental implants. This innovative connection system is composed of a triangular prismatic connection designed to improve the anti-rotational properties of the implant, and to seal any gap between the abutment and the fixture. METHODS: The mechanical performances of the dental implant system were investigated by means of static mechanical strength tests, which allowed the identification of the bending, torque and compression resistance of the system, and fatigue testing, according to the practice standard - ISO 14801. Surface finishing was also analyzed by scanning electron microscopy (SEM) observations and laser profilometry tests. RESULTS: The analyzed implant exhibited good mechanical characteristics, both in static and in fatigue tests. Moreover, the gap between the fixture and the abutment detected by SEM analyses was restricted, both before and after fatigue tests, being approximately 4 mum in the worst case observed: this is representative of optimal sealing against fluid infiltration. CONCLUSIONS: The modification of traditional dental implants with the introduction of a triangular prismatic connection system not only allowed the implant rotational stability and sealing performances to increase, but also conferred optimal mechanical resistance to the implant.