Metal oxide nanostructures have recently gained high attention due to advances in their synthesis, particularly hydrothermal techniques, which allow precise control over their morphology, composition, and crystallinity, as well as integration into devices. Zinc-tin oxide (ZTO) nanostructures, in particular, are notable for their sustainability and multifunctional applications, including catalysis, electronics, sensors, and energy harvesting. Their ternary oxide nature supports a broad range of functionalities. The use of seed layers during synthesis has proven to be beneficial, particularly for binary systems such as ZnO, as it not only impacts the growth of nanostructures but is also advantageous for applications requiring nanostructures supported on substrates, such as in photocatalysis and sensor technologies. This work investigates the effect of various seed layers (e.g., Cu, stainless steel, Cr, Ni) on the hydrothermal synthesis of ZTO nanostructures. Compared to seed layer free methods under similar conditions, the presence of seed layers significantly influenced the resulting structures. The study produced diverse morphologies, including ZnSnO₃ nanowires and Zn₂SnO₄ nanoparticles, octahedrons, and nanowires. Findings suggest a relationship between the seed layer’s phase and the resulting nanostructure phase. Furthermore, shorter synthesis durations favored discrete nanostructures, while longer durations facilitated the formation of thin films with nanostructured surfaces. These observations underscore the dual role of seed layers in influencing both the structural phase and growth kinetics of ZTO nanostructures.

Series on Chemistry, Energy and the EnvironmentSynthesis and Applications in Chemistry and Materials, pp. 443-482 (2024) No Access43: Sustainable Synthesis of Oxides for Electronics and PhotocatalysisR. Branquinho, E. Carlos, D. Nunes, E. Fortunato, and R. MartinsR. BranquinhoCENIMAT|i3N, Department of Materials Science, School of Science and Technology, NOVA University Lisbon and CEMOP/UNINOVA, Caparica, Portugal, E. CarlosCENIMAT|i3N, Department of Materials Science, School of Science and Technology, NOVA University Lisbon and CEMOP/UNINOVA, Caparica, Portugal, D. NunesCENIMAT|i3N, Department of Materials Science, School of Science and Technology, NOVA University Lisbon and CEMOP/UNINOVA, Caparica, Portugal, E. FortunatoCENIMAT|i3N, Department of Materials Science, School of Science and Technology, NOVA University Lisbon and CEMOP/UNINOVA, Caparica, Portugal, and R. MartinsCENIMAT|i3N, Department of Materials Science, School of Science and Technology, NOVA University Lisbon and CEMOP/UNINOVA, Caparica, Portugalhttps://doi.org/10.1142/9789811283239_0043Cited by:0 (Source: Crossref) PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: Metal oxides are an important class of materials with unique properties that are attractive for various applications, ranging from electronics to photocatalysis. Thus, the sustainable production of metal oxides is highly desirable. Solution-based synthesis methods provide a versatile and facile route to obtaining metal oxide nanomaterials with properties tailored to meet the demands of specific applications. This chapter provides an overview of wet-chemical synthesis routes to produce metal oxide nanomaterials, focusing on solution combustion synthesis and hydrothermal synthesis methods. Solution combustion synthesis is widely explored for the preparation of semiconducting (In2O3, ITO, IZO, ZTO and IGZO), insulating (Al2O3, HfO2 and ZrO2) and conductive (doped-In2O3) oxide thin films for application in printed electronic devices. Hydrothermal synthesis is preferred to prepare nanostructured powders or films (TiO2, ZnO, ZTO and WO3) with a high surface area for photocatalysis of pollutant dyes (such as methylene blue and rhodamine B) under ultraviolet (UV) radiation and/or sunlight. For each method/application, emphasis is given to processing technologies that are aligned with the Sustainable Development Goals. Keywords: Solution combustion synthesisHydrothermal synthesisoxide thin filmsNanostructuresMetal oxide devicesPhotocatalysis FiguresReferencesRelatedDetails Recommended Synthesis and Applications in Chemistry and MaterialsMetrics History KeywordsSolution combustion synthesisHydrothermal synthesisoxide thin filmsNanostructuresMetal oxide devicesPhotocatalysisPDF download

Even though printed metal oxide thin film transistors (TFTs) have been a central topic of research in the past decade, the most notable results still require scarce elements such as gallium and indium, or high annealing temperatures (>= 400 degrees C) when using sustainable raw materials such as zinc and tin. In this work, safe, abundant and inexpensive materials such as zinc, tin and aluminum are explored to reach low-cost thin films and devices with both the semiconductor and dielectric layers deposited by inkjet printing and annealed at lower temperatures (300 degrees C). Alumina (AlOx) and zinc tin oxide (ZTO) inks containing a theoretical optimal V% of ethylene glycol were optimized for production of uniform and reproducible AlOx/ZTO thin film layers. Common ink parameters (such as the reverse Ohnesorge, capillary, Webber and Reynolds numbers) were evaluated and compared with relevant literature on inkjet drop formation mechanisms. Inks within theoretical optimal parameter values were printing optimized in terms of drops per inch, number of layers, UV substrate surface activation, print speed, and post- annealing. A high-quality dielectric of two alumina layers was printed, having a breakdown field above 2.93 +/- 0.33 MV cm(-1), and a dielectric constant of 7.74 +/- 0.73 at 1 kHz. TFTs of inkjet printed (IJP) ZTO/AlOx layers were produced with a maximum I-On/I-Off ratio of 10(3) and a saturation mobility of 2.2 cm(2) V-1 s(-1). This approach not only advances the field of printed electronics but also addresses concerns related to material scarcity, thermal budget, and production costs.

Printed metal oxide devices have been widely desired in flexible electronic applications to allow direct integration on foils and to reduce electronic waste and associated costs. Especially, semiconductor devices made from non-critical raw materials, such as Zn, Sn (and not, for example, In), have gained significant interest. Despite considerable progress in the field, the upscale requirements from lab to fab scale to produce these materials and devices remain a challenge. In this work, we report the importance of solution combustion synthesis (SCS) when compared with sol–gel in the production of zinc tin oxide (ZTO) thin films using a solvent (1-methoxypropanol) that has lower environmental impact than the widely used and toxic 2-methoxyethanol. To assure the compatibility with low-cost flexible substrates in high-throughput printing techniques, a low annealing temperature of 140 °C was achieved for these thin films by combining SCS and infrared annealing in a short processing time. These conditions allowed the transition from spin-coating (lab scale) to flexographic printing (fab scale) at a printing speed of 10 m min−1 in a roll-to-roll pilot line. The ZTO (1:1 Zn:Sn-ratio) diodes show a rectification ratio of 103, a low operation voltage (⩽3 V), promising reproducibility and low variability. The results provide the basis for further optimisation (device size, encapsulation) to meet the requirements of diodes in flexible electronics applications such as passive-matrix addressing, energy harvesting and rectification.

Smart textiles consist of discrete devices fabricated from-or incorporated onto-fibres. Despite the tremendous progress in smart textiles for lighting/display applications, a large scale approach for a smart display system with integrated multifunctional devices in traditional textile platforms has yet to be demonstrated. Here we report the realisation of a fully operational 46-inch smart textile lighting/display system consisting of RGB fibrous LEDs coupled with multifunctional fibre devices that are capable of wireless power transmission, touch sensing, photodetection, environmental/biosignal monitoring, and energy storage. The smart textile display system exhibits full freedom of form factors, including flexibility, bendability, and rollability as a vivid RGB lighting/grey-level-controlled full colour display apparatus with embedded fibre devices that are configured to provide external stimuli detection. Our systematic design and integration strategies are transformational and provide the foundation for realising highly functional smart lighting/display textiles over large area for revolutionary applications on smart homes and internet of things (IoT).

Incrustations are a common conservation problem, particularly in artworks exposed to water. Calcium-rich layers tend to build over their surface making cleaning interventions necessary to improve the chemical stability and restore readability. Harmfulness tests are crucial for selecting cleaning methodologies for glazed surfaces due to their mechanical and chemical susceptibility. This study selected a combination of cleaning methods to test their adequacy to remove a Ca incrustations from a modern glazed artwork. The tested methods were mechanical (dry-blasting with sand, alumina and peach) and chemical (HNO3, Na(3)EDTA, Ionex H and Kalkrent (R) an "environmental friendly" commercial detergent). To assess the effect of the cleaning methods replica substrates of the glazed ceramic were subjected to the different methodologies. Harmfulness was assessed by: (i) mass variation measurements to evaluate the material loss; (ii) microscopy techniques (optical, scanning electron and confocal laser microscopy) to evaluate morphological and surface topography alterations and (iii) mu-Raman to detect changes in the glass structure. Results indicated that the glassy phase was the most affected, and Ionex H was the less harmful of the tested cleaning products. The first in situ testing revealed that a combined approach will be most effective using microblasting for reducing the thickness of the incrustation, followed by the selected chemical method Ionex H. (C) 2022 Elsevier Masson SAS. All rights reserved.

Indium oxide (In2O3)-based transparent conducting oxides (TCOs) have been widely used and studied for a variety of applications, such as optoelectronic devices. However, some of the more promising dopants (zirconium, hafnium, and tantalum) for this oxide have not received much attention, as studies have mainly focused on tin and zinc, and even fewer have been explored by solution processes. This work focuses on developing solution-combustion-processed hafnium (Hf)-doped In2O3 thin films and evaluating different annealing parameters on TCO’s properties using a low environmental impact solvent. Optimized TCOs were achieved for 0.5 M% Hf-doped In2O3 when produced at 400 °C, showing high transparency in the visible range of the spectrum, a bulk resistivity of 5.73 × 10−2 Ω.cm, a mobility of 6.65 cm2/V.s, and a carrier concentration of 1.72 × 1019 cm−3. Then, these results were improved by using rapid thermal annealing (RTA) for 10 min at 600 °C, reaching a bulk resistivity of 3.95 × 10 −3 Ω.cm, a mobility of 21 cm2/V.s, and a carrier concentration of 7.98 × 1019 cm−3, in air. The present work brings solution-based TCOs a step closer to low-cost optoelectronic applications.

The present study is focused on the synthesis of zirconium dioxide (ZrO2) nanomaterials using the hydrothermal method assisted by microwave irradiation and solution combustion synthesis. Both synthesis techniques resulted in ZrO2 powders with a mixture of tetragonal and monoclinic phases. For microwave synthesis, a further calcination treatment at 800 °C for 15 min was carried out to produce nanopowders with a dominant monoclinic ZrO2 phase, as attested by X-ray diffraction (XRD) and Raman spectroscopy. The thermal behavior of the ZrO2 nanopowder was investigated by in situ XRD measurements. From the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images, the presence of near spherical nanoparticles was clear, and TEM confirmed the ZrO2 phases that comprised the calcinated nanopowders, which include a residual tetragonal phase. The optical properties of these ZrO2 nanopowders were assessed through photoluminescence (PL) and PL excitation (PLE) at room temperature (RT), revealing the presence of a broad emission band peaked in the visible spectral region, which suffers a redshift in its peak position, as well as intensity enhancement, after the calcination treatment. The powder resultant from the solution combustion synthesis was composed of plate-like structures with a micrometer size; however, ZrO2 nanoparticles with different shapes were also observed. Thin films were also produced by solution combustion synthesis and deposited on silicon substrates to produce energy storage devices, i.e., ZrO2 capacitors. The capacitors that were prepared from a 0.2 M zirconium nitrate-based precursor solution in 2-methoxyethanol and annealed at 350 °C exhibited an average dielectric constant (κ) of 11 ± 0.5 and low leakage current density of 3.9 ± 1.1 × 10−7 A/cm2 at 1 MV/cm. This study demonstrates the simple and cost-effective aspects of both synthesis routes to produce ZrO2 nanomaterials that can be applied to energy storage devices, such as capacitors.

The contamination of water resources by pollutants resulting from human activities represents a major concern nowadays. One promising alternative to solve this problem is the photocatalytic process, which has demonstrated very promising and efficient results. Oxide nanostructures are interesting alternatives for these applications since they present wide band gaps and high surface areas. Among the photocatalytic oxide nanostructures, zinc tin oxide (ZTO) presents itself as an eco-friendly alternative since its composition includes abundant and non-toxic zinc and tin, instead of critical elements. Moreover, ZTO nanostructures have a multiplicity of structures and morphologies possible to be obtained through low-cost solution-based syntheses. In this context, the current work presents an optimization of ZTO nanostructures (polyhedrons, nanoplates, and nanoparticles) obtained by microwave irradiation-assisted hydrothermal synthesis, toward photocatalytic applications. The nanostructures’ photocatalytic activity in the degradation of rhodamine B under both ultraviolet (UV) irradiation and natural sunlight was evaluated. Among the various morphologies, ZTO nanoparticles revealed the best performance, with degradation > 90% being achieved in 60 min under UV irradiation and in 90 min under natural sunlight. The eco-friendly production process and the demonstrated ability of these nanostructures to be used in various water decontamination processes reinforces their sustainability and the role they can play in a circular economy.

Solution-based synthesis of metal oxides has been attracting a lot of attention due to the low-cost, high-throughput, and efficient control over chemical composition. These materials also have outstanding properties such as high optical transparency, chemical and thermal stability, and mechanical toughness. In addition, facile tailoring of physical and chemical attributes of these materials leads to multifunctionality that allows their applications in different areas, like sensing, energy, and flexible displays. Particularly for large-area electronics, the exploration of crucial components, the thin film transistor (TFT) and their key material constituents, e.g., the semiconductor, the dielectric, the conductor as well as substrates opens up enormous opportunity to bring forth next generation devices. This chapter focuses on recent low-temperature approaches, such as combustion synthesis and (UV, NIR) irradiation treatments which allow realization of printable flexible TFTs. Moreover, special attention is given to solution-based preparation of high-к oxide dielectrics that play a critical role to achieve efficient TFTs. Finally, a detailed discussion on emerging printing techniques and current challenges is undertaken.

Zinc-tin oxide (ZTO) nanostructures appear as one of the most promising material systems for a new generation of nanodevices. In this work, a microwave-assisted hydrothermal synthesis to produce different shapes of Zn2SnO4 nanostructures (nanoparticles, octahedrons and nanoplates) is presented. Reproducible and homogeneous results were obtained with the advantage of reducing up to 20 h the synthesis time when compared to using a conventional oven. Furthermore, the photocatalytic activity of the Zn2SnO4 nanostructures in the degradation of rhodamine B under UV light was studied. Zn2SnO4 nanoparticles demonstrated better performance with >90% of degradation being achieved in 2.5 h.

The massification of Internet of Things (IoT) and Smart Surfaces has increased the demand for nanomaterials excelling at specific properties required for their target application, but also offering multifunctionality, conformal integration in multiple surfaces and sustainability, in line with the European Green Deal goals. Metal oxides have been key materials for this end, finding applications from flexible electronics to photocatalysis and energy harvesting, with multicomponent materials as zinc tin oxide (ZTO) emerging as some of the most promising possibilities. This chapter is dedicated to the hydrothermal synthesis of ZTO nanostructures, expanding the already wide potential of ZnO. A literature review on the latest progress on the synthesis of a multitude of ZTO nanostructures is provided (e.g., nanowires, nanoparticles, nanosheets), emphasizing the relevance of advanced nanoscale techniques for proper characterization of such materials. The multifunctionality of ZTO will also be covered, with special attention being given to their potential for photocatalysis, electronic devices and energy harvesters.

High-permittivity (k) oxide dielectrics have been widely demanded concerning the Internet of Things (IoT) requirements, such as flexible large-area manufacturing, energy efficiency, low-cost processes, and sustainable electronics, especially in thin-film transistors (TFTs). From there emerged the necessity of printing energyefficient (vacuum-free) eco-devices using low-temperature methods (e.g., combustion synthesis, posttreatments) in the production and processing of nanomaterials, thus reducing the human carbon footprint. However, currently the main deposition method used is typically spin-coating which requires higher temperatures and long annealing times, not compatible with the printing industry. Besides the concerns with process integration, the market highly demands high-k dielectrics with great stability and high yield. To surpass these challenges, some crucial parameters in the ink design need to be considered to guarantee successful upscale for large-area electronics manufacturing.

Printed combustion-based aluminium oxide (AlOx) resistive switching devices produced at low temperature show a high reproducibility (95%) and multilevel cell operation with potential for hardware security applications.

Solution-based metal oxide thin films allow the achievement of ultralow-power and high-density resistive-switching (RS) devices by using low-cost and simple processes being compatible with large-area manufacturing. By controlling key parameters of the metal oxide synthesis categorized in article number 2004328 by Emanuel Carlos, Asal Kiazadeh, Elvira Fortunato, and co-workers, the performance of solution-based RS devices is enhanced to be implemented for neuromorphic and memory applications.

The interest in advanced photocatalytic technologies with metal oxide-based nanomaterials has been growing exponentially over the years due to their green and sustainable characteristics. Photocatalysis has been employed in several applications ranging from the degradation of pollutants to water splitting, CO2 and N-2 reductions, and microorganism inactivation. However, to maintain its eco-friendly aspect, new solutions must be identified to ensure sustainability. One alternative is creating an enhanced photocatalytic paper by introducing cellulose-based materials to the process. Paper can participate as a substrate for the metal oxides, but it can also form composites or membranes, and it adds a valuable contribution as it is environmentally friendly, low-cost, flexible, recyclable, lightweight, and earth abundant. In term of photocatalysts, the use of metal oxides is widely spread, mostly since these materials display enhanced photocatalytic activities, allied to their chemical stability, non-toxicity, and earth abundance, despite being inexpensive and compatible with low-cost wet-chemical synthesis routes. This manuscript extensively reviews the recent developments of using photocatalytic papers with nanostructured metal oxides for environmental remediation. It focuses on titanium dioxide (TiO2) and zinc oxide (ZnO) in the form of nanostructures or thin films. It discusses the main characteristics of metal oxides and correlates them to their photocatalytic activity. The role of cellulose-based materials on the systems' photocatalytic performance is extensively discussed, and the future perspective for photocatalytic papers is highlighted.

Water pollutants are currently a major concern, demanding for simple processes for water treatment, photocatalysis being one of the most efficient and promising processes. Metal oxide materials are being widely studied for this application, due to their wide band gaps, with nanostructures being particularly interesting because of their high surface-to-volume ratio. In this context, zinc-tin oxide (ZTO) nanostructures are quite appealing owing to the multiplicity of structures and morphologies possible to achieve with low-cost solution-based synthesis and to the lack of critical elements in favor of abundant and nontoxic ones. In this work, three different ZTO nanostructures, namely, ZnSnO3 nanowires, Zn2SnO4 nanoparticles, and Zn2SnO4 polyhedrons, were studied for the photodegradation of methylene blue and rhodamine B under both UV and visible light irradiation. The nanostructures were synthesized by a low-cost seed-layer-free hydrothermal method at only 200 degrees C, compatible with direct growth on flexible substrates. ZnSnO3 nanowires in the powder form, reported as photocatalytic agents for the first time, showed enhanced photocatalytic activity, especially under UV light, degrading both dyes in only 90 min and outperforming Zn2SnO4 nanoparticles and polyhedrons. Photocatalysis under visible light is also demonstrated, with a degradation of >40% of rhodamine B in 12 h. This work shows the feasibility of a simple, low-cost fabrication method and sustainable, nontoxic materials to achieve structures with efficient photocatalytic activity.

Excimer laser annealing (ELA) combined with combustion synthesis leads to high quality metal oxide TFTs in a short processing time.

Lately, printed oxide electronics have advanced in the performance and low-temperature solution processability that are required for the dawn of low-cost flexible applications. However, some of the remaining limitations need to be surpassed without compromising the device electronic performance and operational stability. The printing of a highly stable ultra-thin high-kappa aluminum-oxide dielectric with a high-throughput (50 m min(-1)) flexographic printing is accomplished while simultaneously demonstrating low-temperature processing (<= 200 degrees C). Thermal annealing is combined with low-wavelength far-ultraviolet exposure and the electrical, chemical, and morphological properties of the printed dielectric films are studied. The high-kappa dielectric exhibits a very low leakage-current density (10(-10) A cm(-2)) at 1 MV cm(-1), a breakdown field higher than 1.75 MV cm(-1), and a dielectric constant of 8.2 (at 1 Hz frequency). Printed indium oxide transistors are fabricated using the optimized dielectric and they achieve a mobility up to 2.83 +/- 0.59 cm(2) V-1 s(-1), a subthreshold slope <80 mV dec(-1), and a current ON/OFF ratio >10(6). The flexible devices reveal enhanced operational stability with a negligible shift in the electrical parameters after ageing, bias, and bending stresses. The present work lifts printed oxide thin film transistors a step closer to the flexible applications of future electronics.