Synthesis and Applications of Nanomaterials for Photocatalysis and Electrocatalysis

This book supplies fundamental aspects regarding the use of different nanostructures as heterogeneous catalysts for energy and environmental applications. In recent decades, the attention of both scientific and industrial communities has become increasingly focused on the implementation of groundbreaking nanomaterials in all fields of human activity, especially toward improving energy efficiency and fulfilling environmental demands. Energy and environment represent a perfect blend: energy-saving environmental remediations and promising energetic devices meeting environmental concerns represent potential future challenges that humankind will face. In this context, the fine control of the nanosized species is the real tool to overcome the current issues and to improve the final performances. Herein, from an energetic point of view, oxygen evolution and reduction reactions (OER and ORR) are keys to deeply understanding the behaviour of water splitting devices and fuel cells as well as zinc/air batteries, respectively. Zinc tantalum oxynitride-based photoanodes and nitrogen-modified carbon doped with different metals will be presented and fully characterised. Concurrently, bismuth titanate nanosheets and noble metal core-shell nanoparticles can be adopted to enhance hydrogen evolution through photocatalytic water splitting, exploiting solar energy. Instead, for what concerns the environmental remediation, the use of pure (black, modified, and faceted TiO2, Ga2O3) and composite (graphene/titanate, Zn2\u2013SnO4/BiOBr, g-C3N4/Nb2O5, MnO2/TiO2 and CaIn2S4/ZnIn2S4) nanomaterials allow for air and water purification, especially under solar irradiation. Particularly, the complete photodegradation of noxious species (benzylic acid), organic dyes (rhodamine B, methylene blue and alizarin red), heavy metals (chromium), recalcitrant pharmaceutical active principles (cinnamic acid, ibuprofen and tetracycline), and VOCs (ethanol) will be thoroughly discussed. Finally, we would like to acknowledge all the authors who have contributed to this book with their scientific expertise, and we hope that the readers will find the arguments both useful and interesting

Ultrasound to improve both synthesis and pollutants degradation based on metal nanoparticles supported on TiO 2

Sonochemistry is based on acoustic cavitation, which consist in the formation, growth, and implosive collapse of bubbles within a liquid. Collapsing bubbles generate localized hot spots, characterized by temperatures up to 5000 K and pressures up to 1800 atm. These extreme conditions allow producing a variety of nanostructured and amorphous materials, as well as they are advantageous for chemical processes. Ultrasound requires inexpensive equipment and fewer steps than conventional methods. Combining ultrasound and photocatalysis enhances the performance of the processes, reduces reaction time, avoids the use of extreme physical conditions and improves the photocatalytic materials properties increasing their activity. Here, we reported the positive effect of US in synthesizing Me-modified TiO2 (Me = Ag, Cu, Mn) for pollutants degradation in gas-phase; also, we proved the advantageous application of ultrasound for the photocatalytic removal of organic compounds in water. Ultrasound produced more efficient Me-doped TiO2, which showed higher activity in visible light. When combined with photocatalytic water treatment, the organic compounds degradation and mineralization increases

Biogas upgrading by physical water washing in a micro-pilot absorption column conducted at low temperature and pressure

The European Energy Policy has currently two main goals to reach: to minimize exposure to volatility of fossil fuel prices and to reduce of greenhouse gas (GHG) emissions. To reach these targets a practical way, among the others is represented by the biogas production by anaerobic digestion (Bonoli et al., 2014) (AD) and its upgrading to biomethane. In this work the absorption of CO2is studied using a column working at atmospheric pressure and low temperature (599%) and a stream of methane (>99.9 %) in order to reproduce a typical raw biogas composition, i.e. molar fraction of methane of about 0.6. The internal temperature was monitored by a thermocouple and the inlet and outlet flow of biogas (G) was measured using a mass flowmeter while the water flow rate (L) was monitored using a magnetic induction flowmeter. The compositions were determined using a 3000A micro-Gas Chromatograph Agilent, previously calibrated. The temperature was varied between 6.5 and 20 °C and the water flow rate between about 0.5 and 5 L/h. The composition of the gas exiting the micro-pilot plant was monitored every 5 minutes until the stationary condition

The Sonophotocatalytic Degradation of Pharmaceuticals in Water by MnOx-TiO2 Systems with Tuned Band-Gaps

Advanced oxidation processes (AOPs) are technologies to degrade organic pollutants to carbon dioxide and water with an eco-friendly approach to form reactive hydroxyl radicals.Photocatalysis is an AOP whereby TiO2 is the most adopted photocatalyst. However, TiO2 features a wide (3.2 eV) and fast electron-hole recombination. When Mn is embedded in TiO2, it shifts the absorption wavelength towards the visible region of light, making it active for natural light applications. We present a systematic study of how the textural and optical properties of Mn-doped TiO2 vary with ultrasound applied during synthesis. We varied ultrasound power, pulse length, and power density (by changing the amount of solvent). Ultrasound produced mesoporous MnOx-TiO2 powders with a higher surface area (101\u2013158 m2 g 121), pore volume (0-13\u20130.29 cc g 121), and smaller particle size (4\u201310 \ub5m) than those obtained with a conventional sol-gel method (48\u2013129 m2 g 121, 0.14\u20130.21 cc g 121 , 181 \ub5m, respectively). Surprisingly, the catalysts obtained with ultrasound had a content of brookite that was at least 28%, while the traditional sol-gel samples only had 7%. The samples synthesized with ultrasound had a wider distribution of the band-gaps, in the 1.6\u20131.91 eV range, while traditional ones ranged from 1.72 eV to 1.8 eV. We tested activity in the sonophotocatalytic degradation of two model pollutants (amoxicillin and acetaminophen). The catalysts synthesized with ultrasound were up to 50% more active than the traditional samples

Use of a sol-gel hybrid coating composed by a fluoropolymer and silica for the mitigation of mineral fouling in heat exchangers

The technology of the organic/inorganic hybrid coating was employed in the preparation of a hydrophobic coating (contact angle higher than 140\ub0) for fouling mitigation on stainless steel heat transfer surfaces. A commercial triethoxysilane perfluoropolyethers was combined with a sol-gel silica network with the aim to increase the mechanical and thermal resistance of the films when exposed to aggressive liquid environments as the heat exchanging fluids. The experimentation on a shell and tube heat exchanger pilot plant confirmed the ability of the hybrid coating to prolong the crystallization fouling induction period of 200 h in respect to an uncoated heat exchanger, operating in the same conditions. Moreover, the fouling particles deposited on the coated heat transfer surfaces had only slight adhesion strength toward the coated surfaces and were easily removed by inducing higher wall shear stresses inside the tubes of the plant

Perfluoropolyethers coatings design for fouling reduction on heat transfer stainless steel surfaces

The scope of this research is to obtain a film coating on stainless steel surfaces in order to reduce the interaction between the metal surface and the precipitates, so to mitigate fouling in heat exchangers. Perfuoropolyethers were used to obtain nano-range fluorinated layers in order to make hydrophobic the stainless steel surfaces. A pilot plant with two identical heat exchangers was built to investigate the ability of the hydrophobic coating of preventing fouling. The heat exchangers, installed in parallel, operated at the same temperature and pressure conditions, i.e. laminar flow regime and inlet flow temperatures of 291\u2013293 K for cold streams and 313\u2013333 K for hot streams. We compared the heat transfer performance of the two heat exchangers. After a five months operation the decrease in the heat transferred was 56% for the coated heat exchanger and 62% for the uncoated heat exchanger. Moreover, the increase of heat transfer resistance due to scale on the uncoated heat exchanger, with respect to the coated one, was three times higher

Photocatalytic porcelain grés large slabs digitally coated with AgNPs-TiO2

TiO2 is employed as both photocatalytic and structural materials, leading to its applications in external coatings or in interior furnishing devices, including cement mortar, tiles, floorings, and glass supports. The authors have already demonstrated the efficiency of photoactive micro-sized TiO2 and here its industrial use is reported using the digital printing to coat porcelain gr\ue9s slabs. Many advantages are immediately evident, namely rapid and precise deposition, no waste of raw materials, thus positively affecting the economy of the process. Data for the thin films deposited by digital printing were compared with those obtained for the conventional spray method. The use of metal-doped TiO2 is also reported so that the photoactivity of these materials can be exploited even under LED light. The digital inkjet printed coatings exhibited superior photocatalytic performance owing to both higher exposed surface area and greater volume of deposited anatase, as well as the greater areal distribution density of thinly and thickly coated regions. Moreover, the presence of TiO2 doped silver increased the efficiency of the materials in NOx degradation both under UVA and LED lights

Ultrasound-enhanced photodegradation of Diclofenac Na

Diclofenac sodium, a non-steroidal anti-inflammatory drug, is an emerging water pollutant that cannot be removed by conventional wastewater treatment plants. Combined processes based on hydrodynamic cavitation (sonolysis) and heterogeneous photocatalysis are highly promising for the degradation and mineralization of refractory drugs [1,2]. Nevertheless, the use of nanoparticles as photocatalyst is not suitable in real applications for environmental and health hazard [3] as well as for the complex photocatalyst retrieval at the end of the process. For this reasons, we studied the photocatalyzed degradation of Diclofenac Na using micrometric titanium dioxide photocatalyst (Kronos 1077, 0.1 g/L), both bare and decorated with silver. Moreover, the synergic effect of pulsed ultrasound was tested. Initial concentrations of diclofenac sodium in the 25-50 ppm range were tested. Tests were performed in a batch jacketed reactor. A UVA lamp set sideway irradiated the solution with a power of 30 W/m2 and an ultrasonic horn (20 kHz) sonicated the solution. HPLC-UV and HPLC-MS determined Diclofenac degradation and the main byproducts. A total organic carbon analyzer (TOC, Shimadzu) calculated the fraction of Diclofenac mineralized. An example of photodegradation run is reported in figure. A positive synergy coupling ultrasounds with photocatalysis is confirmed, mainly with the use of Ag nanoparticles-TiO2. We observed both a faster molecule degradation and its complete mineralization

Ultrasound-assisted synthesis of WOx-decorated ZnO photocatalysts for NOx abatement

Heterojunctions based on ZnO have numerous applications, such as water splitting, sensing and energy storage [1]. Recently, ZnO/WO3 composites have shown promising results in the sonocatalytic and photocatalytic degradation of aqueous and gas pollutants [2]. Several synthetic approaches have been reported, including chemical vapor deposition, magnetron sputtering, hydrothermal methods and high temperature annealing. Ultrasound-assisted synthesis can provide a scalable and cost-effective strategy to tailor the catalyst structural and morphological properties [3]. In the present work, pristine ZnO and ZnO/WOx composites were synthesized via a sonochemical method, studying the role of the ultrasound amplitude and mode (continuous/pulsed), metal precursor, WOx content and post-synthetic annealing. The resulting materials were extensively characterized, investigating their structural, morphological, optical, and surface properties. Samples were tested towards the photocatalytic removal of NOx under both UV and visible light irradiation in a batch reactor. A good degree of crystallinity is appreciable even before calcination and better morphological features are observed with respect to reference samples prepared without ultrasounds. The morphological properties can be further tuned by changing the metal precursor and adding a post-synthetic annealing step. Photocatalytic activity is promoted with respect to both benchmark samples (Figure 1)

An ultrasound-assisted photocatalytic treatment to remove an herbicidal pollutant from wastewaters

Pollutants of emerging concern contaminate surface and ground water. Advanced oxidation processes treat these molecules and degrade them into smaller compounds or mineralization products. However, little information on coupled advanced oxidation techniques and on the degradation pathways of these pollutants is available to identify possible ecotoxic subproducts. In the present work, we investigate the ultrasound assisted photocatalytic degradation pathway of the herbicide Isoproturon. We worked in batch mode in a thermostatic glass reactor. We compared the activity of nanometric TiO2 P25 with that of Kronos 1077, a micrometric TiO2. We discuss the individual, additive and synergistic degradation action of photolysis, sonolysis, sonophotolysis, and sonophotocatalysis by varying catalyst loading and/or ultrasound power for the last three techniques. With 0.1 g L 121 catalyst, photocatalysis and sonophotopcatalysis completely degrade Isoproturon within 240 min and 60 min, respectively (>99% conversion). Sonophotocatalysis breaks Isoproturon down into smaller molecules than photocatalysis alone