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Keywords = microwave sol-gel synthesis

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14 pages, 1039 KiB  
Article
Enhanced Magnetic and Dielectric Performance in Fe3O4@Li0.5Cr0.5Fe2O4 Core/Shell Nanoparticles
by Mohammed K. Al Turkestani
Nanomaterials 2025, 15(14), 1123; https://doi.org/10.3390/nano15141123 - 19 Jul 2025
Viewed by 324
Abstract
This study presents the first successful integration of Fe3O4 and Li0.5Cr0.5Fe2O4 into a well-defined core/shell nanostructure through a two-step synthesis that combines co-precipitation and sol–gel auto-combustion methods. Unlike conventional composites, the core/shell design [...] Read more.
This study presents the first successful integration of Fe3O4 and Li0.5Cr0.5Fe2O4 into a well-defined core/shell nanostructure through a two-step synthesis that combines co-precipitation and sol–gel auto-combustion methods. Unlike conventional composites, the core/shell design effectively suppresses the magnetic dead layer and promotes exchange coupling at the interface, leading to enhanced saturation magnetization, superior magnetic heating (specific absorption rate; SAR), and improved dielectric properties. Our research introduces a novel interfacial engineering strategy that simultaneously optimizes both magnetic and dielectric performance, offering a multifunctional platform for applications in magnetic hyperthermia, electromagnetic interference (EMI) shielding, and microwave devices. Full article
(This article belongs to the Section Nanoelectronics, Nanosensors and Devices)
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17 pages, 1570 KiB  
Article
Overcoming Scaling Challenges in Sol–Gel Synthesis: A Microwave-Assisted Approach for Iron-Based Energy Materials
by Judith González-Lavín, Ana Arenillas and Natalia Rey-Raap
Microwave 2025, 1(2), 6; https://doi.org/10.3390/microwave1020006 - 30 Jun 2025
Viewed by 315
Abstract
There is currently an effort to scale up sol–gel nanomaterials without compromising quality, and microwave heating can pave the way for this due to its heating efficiency, resulting in a fast and homogeneous process. In this work, the sol–gel synthesis of transition metal [...] Read more.
There is currently an effort to scale up sol–gel nanomaterials without compromising quality, and microwave heating can pave the way for this due to its heating efficiency, resulting in a fast and homogeneous process. In this work, the sol–gel synthesis of transition metal aerogels, specifically iron-based aerogels, is studied using a microwave-assisted sol–gel methodology in an open-system multimode device as a potential route to scale-up production. Different approaches were tested to evaluate the best way to increase yield per batch, with different vessel shapes and volumes. It is shown that the shape and size of the vessel can be determinant in the interaction with microwaves and, thus, in the heating process, influencing the sol–gel reactions and the characteristics and homogeneity of the obtained nanomaterials. It has been found that a wide vessel is preferable to a tall and narrow one since the heating process is more homogeneous in the former and the sol–gel and cross-linking reactions take place earlier, which improves the mechanical properties of the final nanomaterial. For mass production of nanomaterials, the interaction of the reagents with the microwave field must be considered, and this depends not only on their nature but also on their volume, shape, and arrangement inside the cavity. Full article
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33 pages, 1666 KiB  
Review
Synthesis, Characterization, and Application of Magnetic Zeolite Nanocomposites: A Review of Current Research and Future Applications
by Sabina Vohl, Irena Ban, Janja Stergar and Mojca Slemnik
Nanomaterials 2025, 15(12), 921; https://doi.org/10.3390/nano15120921 - 13 Jun 2025
Viewed by 1070
Abstract
Magnetic zeolite nanocomposites (NCs) have emerged as a promising class of hybrid materials that combine the high surface area, porosity, and ion exchange capacity of zeolites with the magnetic properties of nanoparticles (NPs), particularly iron oxide-based nanomaterials. This review provides a comprehensive overview [...] Read more.
Magnetic zeolite nanocomposites (NCs) have emerged as a promising class of hybrid materials that combine the high surface area, porosity, and ion exchange capacity of zeolites with the magnetic properties of nanoparticles (NPs), particularly iron oxide-based nanomaterials. This review provides a comprehensive overview of the synthesis, characterization, and diverse applications of magnetic zeolite NCs. We begin by introducing the fundamental properties of zeolites and magnetic nanoparticles (MNPs), highlighting their synergistic integration into multifunctional composites. The structural features of various zeolite frameworks and their influence on composite performance are discussed, along with different interaction modes between MNPs and zeolite matrices. The evolution of research on magnetic zeolite NCs is traced chronologically from its early stages in the 1990s to current advancements. Synthesis methods such as co-precipitation, sol–gel, hydrothermal, microwave-assisted, and sonochemical approaches are systematically compared, emphasizing their advantages and limitations. Key characterization techniques—including X-Ray Powder Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning and Transmission Electron Microscopy (SEM, TEM), Thermogravimetric Analysis (TGA), Nitrogen Adsorption/Desorption (BET analysis), Vibrating Sample Magnetometry (VSM), Zeta potential analysis, Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), and X-Ray Photoelectron Spectroscopy (XPS)—are described, with attention to the specific insights they provide into the physicochemical, magnetic, and structural properties of the NCs. Finally, the review explores current and potential applications of these materials in environmental and biomedical fields, focusing on adsorption, catalysis, magnetic resonance imaging (MRI), drug delivery, ion exchange, and polymer modification. This article aims to provide a foundation for future research directions and inspire innovative applications of magnetic zeolite NCs. Full article
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24 pages, 3339 KiB  
Article
Mesostructured Silica–Zirconia–Tungstophosphoric Acid Composites as Catalyst in Calcium Channel Blocker Nifedipine Synthesis
by Edna X. Aguilera, Ángel G. Sathicq, Alexis Sosa, Marcelo C. Murguía, José J. Martínez, Luis R. Pizzio and Gustavo P. Romanelli
Catalysts 2025, 15(6), 537; https://doi.org/10.3390/catal15060537 - 28 May 2025
Viewed by 608
Abstract
This work studies the effect of mesostructured silica–zirconia–tungstophosphoric acid (SiO2-ZrO2-TPA) composites used as catalysts in the synthesis of nifedipine by the Hantzsch methodology. The selectivity for nifedipine is determined, along with that of secondary products that may form depending [...] Read more.
This work studies the effect of mesostructured silica–zirconia–tungstophosphoric acid (SiO2-ZrO2-TPA) composites used as catalysts in the synthesis of nifedipine by the Hantzsch methodology. The selectivity for nifedipine is determined, along with that of secondary products that may form depending on the reaction conditions. The materials were synthesized via the sol–gel method and characterized by N2 adsorption–desorption isotherms, infrared spectroscopy (FT-IR), 31P solid-state nuclear magnetic resonance (NMR-MAS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectra (XPS), and potentiometric titration. The characterization results from the XPS spectra showed that as the Si/Zr ratio drops, the Si-O-Si signal size decreases, while the Zr-O signal size increases. Characterization by titration indicated that an increase in the total acidity of the material, resulting from support modification with tungstophosphoric acid (H3PW12O40, TPA), enhances the reaction yield. The catalytic activity in the solvent-free Hantzsch reaction was evaluated under thermal heating and microwave irradiation. The experiments conducted at 80 °C achieved a maximum yield of 57% after 4 h of reaction using the Si20Zr80TPA30 catalyst (50 mg), while by microwave heating, the yield significantly improved, reaching 77% in only 1 h of reaction. This catalyst exhibited stability and reusability without significant loss of activity up to the third cycle. Depending on the type of material and the reaction conditions, it is possible to modify the selectivity of the reaction, obtaining a 1,2-dihydropyridine isomeric to nifedipine. Reaction intermediates and other minor secondary products that may be formed in the process were also evaluated. Full article
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24 pages, 5572 KiB  
Review
Research Progress on Microwave Synthesis of 3d Transition Metal (Mn, Fe, Co, and Ni) Oxide Nanomaterials for Supercapacitors
by Chengqi Sun, Maosheng Ge, Shuhuang Tan, Yichen Liu, Haowei Wang, Wenhao Jiang, Shoujun Zhang and Yin Sun
Molecules 2025, 30(8), 1843; https://doi.org/10.3390/molecules30081843 - 19 Apr 2025
Cited by 1 | Viewed by 759
Abstract
3d transition metal oxides composed of Mn, Fe, Co, and Ni have emerged as promising candidates for supercapacitor electrode materials due to their high theoretical specific capacitance, abundant redox-active sites, variable oxidation states, environmental friendliness, and low cost. Various synthesis strategies have been [...] Read more.
3d transition metal oxides composed of Mn, Fe, Co, and Ni have emerged as promising candidates for supercapacitor electrode materials due to their high theoretical specific capacitance, abundant redox-active sites, variable oxidation states, environmental friendliness, and low cost. Various synthesis strategies have been developed to fabricate these nanostructures, including hydrothermal/solvothermal methods, sol–gel processing, and microwave-assisted synthesis. Among them, microwave irradiation technology, with its rapid heating characteristics and unique thermal/non-thermal effects, offers significant advantages in controlling crystallinity and particle size distribution, suppressing particle agglomeration, and enhancing material purity. Furthermore, microwave effects facilitate the self-assembly and morphological evolution of transition metal oxides, promote the formation of crystal defects, and strengthen interfacial interactions. These effects enable precise microstructural tuning, leading to an increased specific surface area and a higher density of active sites, ultimately enhancing specific capacitance, rate capability, and cycling stability. In recent years, microwave-assisted synthesis has made significant progress in constructing 3d transition metal oxides and their composites, particularly in the development of single-metal and binary-metal oxides, as well as their hybrids with carbon-based materials (e.g., graphene and carbon nanotubes) and other metal oxides. This review systematically summarizes the research progress on microwave-assisted techniques for 3d transition metal oxide-based nanomaterials, with a particular focus on the role of microwave effects in morphology control, interfacial optimization, and electrochemical performance enhancement. Additionally, key challenges in current research are critically analyzed, and potential optimization strategies are proposed. This review aims to provide new insights and perspectives for advancing microwave-assisted synthesis of 3d transition metal oxides in energy storage applications. Full article
(This article belongs to the Section Materials Chemistry)
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19 pages, 14656 KiB  
Article
Research Progress on Development of PVP-Ag-Doped LaMnO3 Composites for Methyl Orange Degradation
by Adina Căta, Madalina-Gabriela Ivanovici, Paula Svera, Ioana Maria Carmen Ienașcu and Paula Sfirloaga
Metals 2025, 15(2), 151; https://doi.org/10.3390/met15020151 - 1 Feb 2025
Viewed by 1196
Abstract
Water pollution caused by emerging contaminants is increasing due to rising urbanization, industrialization, and agriculture production; therefore, new materials with high efficiency for wastewater decontamination are needed. A perovskite material based on 1% Ag-doped LaMnO3 synthesized through a sol–gel technique was combined [...] Read more.
Water pollution caused by emerging contaminants is increasing due to rising urbanization, industrialization, and agriculture production; therefore, new materials with high efficiency for wastewater decontamination are needed. A perovskite material based on 1% Ag-doped LaMnO3 synthesized through a sol–gel technique was combined with PVP in a 1:10 (w/w) ratio and subjected to different temperature and microwave conditions at various time intervals. The composite materials were obtained as thin films (S1, S2) or powders (S3) and were analyzed by modern techniques. The SEM analysis showed strongly agglomerated, asymmetric formations for the S1, S2 materials; as for the S3 composite, irregularly shaped grains of perovskite were deposited on the polymer surface. Small, round formations across the surface, mainly organized as clusters with conic/square-shaped particles and observed asperity on top, were highlighted by AFM images. The XRD spectra confirmed the presence of both the perovskite and PVP phases, and the crystallite size of the materials was determined to be in the range of 33–43 nm. The structural analyses, FT-IR, and Raman spectroscopy proved the interactions between the perovskite and the polymer, which led to novel composite materials. The different methods used for the synthesis of the new materials influenced their features and behavior. Moreover, the composites were successfully tested for methyl orange (MO) elimination from an acidic aqueous solution in dark conditions, with fast and complete (>95%) MO degradation at pH = 2. Full article
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14 pages, 5507 KiB  
Article
Designing and Optimizing Electrode Materials for Energy Harvesting in CAPMIX Cells
by Belén Lobato, Samantha L. Flores, Lucía dos Santos-Gómez, Ana B. García, Alberto M. Pernía, Miguel J. Prieto, María G. Busto and Ana Arenillas
Nanomaterials 2024, 14(24), 2031; https://doi.org/10.3390/nano14242031 - 18 Dec 2024
Viewed by 1234
Abstract
The growing demand for clean, decentralized energy has increased interest in blue energy, which generates power from water with different salt concentrations. Despite its potential as a renewable, low-cost energy source, optimizing electrode materials remains a challenge. This work presents a nanomaterial developed [...] Read more.
The growing demand for clean, decentralized energy has increased interest in blue energy, which generates power from water with different salt concentrations. Despite its potential as a renewable, low-cost energy source, optimizing electrode materials remains a challenge. This work presents a nanomaterial developed via microwave-assisted sol-gel methodology for blue energy applications, where ion diffusion and charge storage are critical. AX-7 carbon, designed for this study, features wide pores, enhancing ion diffusion. Compared to commercial NORIT carbon, AX-7 has a higher mesopore volume and external surface area, improving its overall performance. The synthesis process has been optimized and scaled up for evaluation in CAPMIX electrochemical cell stacks. Moreover, the lower series resistance (Rs) significantly boosts energy recovery, with AX-7 demonstrating superior performance. This advantage is especially evident during fresh-water cycles, where this material achieves significantly lower Rs compared to the commercial one. Full article
(This article belongs to the Section Energy and Catalysis)
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22 pages, 2578 KiB  
Review
Recent Advancements in Catalysts for Petroleum Refining
by Muhammad Saeed Akhtar, Sajid Ali and Wajid Zaman
Catalysts 2024, 14(12), 841; https://doi.org/10.3390/catal14120841 - 21 Nov 2024
Cited by 16 | Viewed by 8613
Abstract
In petroleum refining, catalysts are used to efficiently convert crude oil into valuable products such as fuels and petrochemicals. These catalysts are employed in a range of processes, including catalytic cracking, hydrotreating, and reforming to meet stringent fuel quality standards. This review explores [...] Read more.
In petroleum refining, catalysts are used to efficiently convert crude oil into valuable products such as fuels and petrochemicals. These catalysts are employed in a range of processes, including catalytic cracking, hydrotreating, and reforming to meet stringent fuel quality standards. This review explores recent advancements in refining catalysts, focusing on novel materials, enhanced synthesis methods, and their industrial applications. The development of nano-, hierarchically structured, and supported metal catalysts has led to significant improvements in catalyst selectivity, yield, and longevity. These innovations are particularly important for processes such as hydrocracking, fluid catalytic cracking, and catalytic reforming, where catalysts improve conversion rates, product quality, and environmental sustainability. Advances in synthesis techniques such as sol-gel processes, microwave-assisted synthesis, and atomic layer deposition have further optimized catalyst performance. Environmental considerations have also driven the development of catalysts that reduce harmful emissions, particularly sulfur oxides and nitrogen oxides while promoting green catalysis through the use of bio-based materials and recyclable catalysts. Despite these advancements, challenges remain, particularly in scaling novel materials for industrial use and integrating them with existing technologies. Future research should focus on the exploration of new catalytic materials, such as metal-organic frameworks and multi-functional catalysts, which promise to further revolutionize the refining industry. This review thus demonstrates the transformative potential of advanced catalysts in enhancing the efficiency and environmental sustainability of petroleum refining. Full article
(This article belongs to the Special Issue Feature Papers in "Industrial Catalysis" Section)
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45 pages, 14895 KiB  
Review
Advances and Challenges in WO3 Nanostructures’ Synthesis
by Odeilson Morais Pinto, Rosimara Passos Toledo, Herick Ematne da Silva Barros, Rosana Alves Gonçalves, Ronaldo Spezia Nunes, Nirav Joshi and Olivia Maria Berengue
Processes 2024, 12(11), 2605; https://doi.org/10.3390/pr12112605 - 20 Nov 2024
Cited by 6 | Viewed by 3278
Abstract
In recent decades, nanoscience has experienced rapid global advancements due to its focus on materials and compounds at the nanoscale with high efficiency across diverse applications. WO3 nanostructures have proven to be a unique material in the development of new technologies due [...] Read more.
In recent decades, nanoscience has experienced rapid global advancements due to its focus on materials and compounds at the nanoscale with high efficiency across diverse applications. WO3 nanostructures have proven to be a unique material in the development of new technologies due to their electrical, optical, and catalytic properties. They have been used as raw materials for the fabrication of electrochromic devices, optoelectronic devices, hydrogenation catalysts, gas sensors, adsorbents, lithium-ion batteries, solar driven-catalysts, and phototherapy. One of the most striking characteristics of WO3 is its morphological diversity, spanning from 0D to 2D, encompassing nanoparticles, nanowires, nanofibers, nanorods, nanosheets, and nanoplates. This review discusses common synthesis methods for WO3 nanostructures, including hydrothermal and solvothermal methods, microwave-assisted synthesis, sol-gel, electrospinning, co-precipitation, and solution combustion, with emphasis on the advantages and challenges of each of them. The processes involved, the obtained morphologies, and the resulting applications are also presented. As evidenced here, the fine control of the synthesis parameters allows the production of nanostructures with controlled phase, morphology, and size, essential aspects for the production of high-performance WO3-based devices. Full article
(This article belongs to the Section Materials Processes)
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14 pages, 8192 KiB  
Article
Effects of TiO2 Nanoparticles Synthesized via Microwave Assistance on Adsorption and Photocatalytic Degradation of Ciprofloxacin
by Debora Briševac, Ivana Gabelica, Davor Ljubas, Arijeta Bafti, Gordana Matijašić and Lidija Ćurković
Molecules 2024, 29(12), 2935; https://doi.org/10.3390/molecules29122935 - 20 Jun 2024
Cited by 7 | Viewed by 1912
Abstract
In this study, the optimal microwave-assisted sol-gel synthesis parameters for achieving TiO2 nanoparticles with the highest specific surface area and photocatalytic activity were determined. Titanium isopropoxide was used as a precursor to prepare the sol (colloidal solution) of TiO2. Isopropanol [...] Read more.
In this study, the optimal microwave-assisted sol-gel synthesis parameters for achieving TiO2 nanoparticles with the highest specific surface area and photocatalytic activity were determined. Titanium isopropoxide was used as a precursor to prepare the sol (colloidal solution) of TiO2. Isopropanol was used as a solvent; acetylacetone was used as a complexation moderator; and nitric acid was used as a catalyst. Four samples of titanium dioxide were synthesized from the prepared colloidal solution in a microwave reactor at a temperature of 150 °C for 30 min and at a temperature of 200 °C for 10, 20, and 30 min. The phase composition of the TiO2 samples was determined by X-ray diffraction analysis (XRD) and Fourier-transform infrared spectroscopy (FTIR). Nitrogen adsorption/desorption isotherms were used to determine the specific surface area and pore size distributions using the Brunauer–Emmett–Teller (BET) method. The band-gap energy values of the TiO2 samples were determined by diffuse reflectance spectroscopy (DRS). The distribution of Ti and O in the TiO2 samples was determined by SEM-EDS analysis. The effects of adsorption and photocatalytic activity of the prepared TiO2 samples were evaluated by the degradation of ciprofloxacin (CIP) as an emerging organic pollutant (EOP) under UV-A light (365 nm). The results of the photocatalytic activity of the synthesized TiO2 nanoparticles were compared to the benchmark Degussa P25 TiO2. Kinetic parameters of adsorption and photocatalysis were determined and analyzed. It was found that crystalline TiO2 nanoparticles with the highest specific surface area, the lowest energy band gap, and the highest photocatalytic degradation were the samples synthesized at 200 °C for 10 min. The results indicate that CIP degradation by all TiO2 samples prepared at 200 °C show a synergistic effect of adsorption and photocatalytic degradation in the removal process. Full article
(This article belongs to the Special Issue The Application of Microwave-Assisted Technology in Chemical Reaction)
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12 pages, 3695 KiB  
Article
One-Step Microwave Synthesis of New Hybrid Phosphor (CSSC) for White Light-Emitting Diodes
by Maxim Sychov, Mariia Keskinova, Andrey Dolgin, Igor Turkin, Kazuhiko Hara and Hiroko Kominami
Ceramics 2023, 6(4), 2086-2097; https://doi.org/10.3390/ceramics6040128 - 19 Oct 2023
Cited by 2 | Viewed by 1874
Abstract
The possibility of synthesizing a new hybrid phosphor CSSC (mixture of 0.5 CaSrSiO4:Eu2+: 0.29 Ca6Sr4Si6O21Cl2:Eu2+: 0.21 Ca10Si6O21Cl2:Eu2+) [...] Read more.
The possibility of synthesizing a new hybrid phosphor CSSC (mixture of 0.5 CaSrSiO4:Eu2+: 0.29 Ca6Sr4Si6O21Cl2:Eu2+: 0.21 Ca10Si6O21Cl2:Eu2+) using a one-step microwave synthesis method is demonstrated. The concentrations of europium and calcium in the synthesized phosphors were optimized at 1 and 10 mol. %, respectively, to achieve maximum brightness and color rendering index. The optimal conditions for the synthesis of phosphors in a microwave furnace were determined as 750 °C for 10 min. The resulting phosphor exhibited a wide luminescence spectrum that covered the entire visible region, resulting in a high color rendering index and a warm white luminescence when used as a light source. It is shown that the sol–gel method for preparing the charge mixture for the new phosphor allows for a 35% higher luminescence brightness compared to the solid-phase method, due to a more uniform distribution of the activator. Full article
(This article belongs to the Special Issue Composite Nanopowders: Synthesis and Applications)
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20 pages, 3794 KiB  
Article
Circular Design and Functionalized Upcycling of Waste Commodity Polystyrene via C-H Activation Using Microwave-Assisted Multicomponent Synthesis
by Shegufta Shetranjiwalla, Claire Cislak and Kevin M. Scotland
Polymers 2023, 15(14), 3108; https://doi.org/10.3390/polym15143108 - 21 Jul 2023
Cited by 4 | Viewed by 2354
Abstract
The inefficient reuse and recycling of plastics—and the current surge of medical and take-out food packaging use during the pandemic—have exacerbated the environmental burden. This impels the development of alternative recycling/upcycling methods to pivot toward circularity. We report the use of the Mannich [...] Read more.
The inefficient reuse and recycling of plastics—and the current surge of medical and take-out food packaging use during the pandemic—have exacerbated the environmental burden. This impels the development of alternative recycling/upcycling methods to pivot toward circularity. We report the use of the Mannich three-component coupling reaction for the modification of polystyrene (PS) recovered with a 99.1% yield from waste food containers to form functionalized nitrogen and oxygen-rich PS derivatives. A series of functionalized PS with increasing moles of formaldehyde (F) and morpholine (M) (0.5 × 10−2, 1.0 × 10−2, and 2.0 × 10−2 mol) was achieved using a sol–gel-derived Fe-TiO2 catalyst in a solvent-free, microwave-assisted synthesis. Modified polymers were characterized with viscometry, 1H NMR, 13CNMR (DEPT) FTIR, XPS, UV, and TGA. Functionalization scaled with an increasing ratio, validating the 3CR approach. Further functionalization was constrained by a competing oxidative degradation; however, the varying hydrogen bond density due to nitrogen and oxygen-rich species at higher ratios was shown to compensate for molecular weight loss. The integration of the N-cyclic quaternary ammonium cations exhibited the potential of functionalized polymers for ion-exchange membrane applications. Full article
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16 pages, 3971 KiB  
Article
Innovative Synthetic Approaches for Sulphate-Promoted Catalysts for Biomass Valorisation
by Alessia Giordana, Cristina Pizzolitto, Elena Ghedini, Michela Signoretto, Lorenza Operti and Giuseppina Cerrato
Catalysts 2023, 13(7), 1094; https://doi.org/10.3390/catal13071094 - 12 Jul 2023
Cited by 1 | Viewed by 1724
Abstract
In the present research, we report on an innovative and quick procedure for the synthesis of metal oxides: a sol-gel procedure which is followed by two steps that are assisted by microwaves (MW) heating. First, MW heating promotes gel drying and successively permits [...] Read more.
In the present research, we report on an innovative and quick procedure for the synthesis of metal oxides: a sol-gel procedure which is followed by two steps that are assisted by microwaves (MW) heating. First, MW heating promotes gel drying and successively permits the calcination of the xerogel in a few minutes, using a susceptor that rapidly reaches high temperatures. The procedure was employed for the synthesis of zirconium dioxide (ZrO2), and MW-assisted calcination enables the collection of tetragonal ZrO2, as confirmed by different experimental techniques (PXRD, HR-TEM and Raman spectroscopy). Using this MW-assisted sol-gel procedure, a promoted sulphated zirconia (SZ) has been obtained. Both the nature and strength of SZ surface acidity have been investigated with FTIR spectroscopy using CO and 2,6-dimethylpyridine (2,6-DMP) as probe molecules. The obtained materials were tested as catalysts in acid hydrolysis of glucose to give 5-(hydroxymethyl)furfural (5-HMF). One of the obtained catalysts exhibited a better selectivity towards 5-HMF with respect to SZ material prepared by a classical precipitation route, suggesting that this procedure could be employed to obtain a well-known catalyst with a less energy-consuming procedure. Catalytic results also suggest that good selectivity to 5-HMF can be achieved in aqueous media in the presence of weak Lewis and Brønsted sites. Full article
(This article belongs to the Special Issue Advanced Materials for Application in Catalysis)
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23 pages, 23264 KiB  
Article
Photocatalytic Performance of Sn–Doped TiO2 Nanopowders for Photocatalytic Degradation of Methyl Orange Dye
by Luminița Predoană, Elena Mădălina Ciobanu, Gabriela Petcu, Silviu Preda, Jeanina Pandele-Cușu, Elena Maria Anghel, Simona Viorica Petrescu, Daniela Cristina Culiță, Adriana Băran, Vasile-Adrian Surdu, Bogdan Ștefan Vasile and Adelina C. Ianculescu
Catalysts 2023, 13(3), 534; https://doi.org/10.3390/catal13030534 - 6 Mar 2023
Cited by 19 | Viewed by 2905
Abstract
The tin-doped TiO2 powders obtained by sol-gel and microwave-assisted sol-gel methods were investigated. The synthesis took place in a basic medium (pH 10, ammonium hydroxide, 25%) starting from tetrabutyl orthotitanate in its parental alcohol. In the case of the dopant, Tin(II) 2-ethylhexanoate [...] Read more.
The tin-doped TiO2 powders obtained by sol-gel and microwave-assisted sol-gel methods were investigated. The synthesis took place in a basic medium (pH 10, ammonium hydroxide, 25%) starting from tetrabutyl orthotitanate in its parental alcohol. In the case of the dopant, Tin(II) 2-ethylhexanoate as SnO2 precursor was used in the amount of 1, 2, or 4 mol % SnO2. Based on thermal analysis data, the powders were thermally treated in air, at 500 °C. The comparative investigation of the structure and morphology of the nanopowders annealed at 500 °C was performed by scanning electron microscopy (SEM), high-resolution transmission electron microscopy with selected area electron diffraction (HRTEM/SAED), scanning transmission electron microscopy (STEM) coupled with EDX mapping, Fourier transmission infrared (FTIR), UV–Vis, Raman and photoluminescence (PL) spectroscopy, X-ray diffraction (XRD), and X-ray florescence spectroscopy (XRF). The obtained materials were tested for the photocatalytic removal of methyl orange dye from aqueous solutions. High degradation efficiencies (around 90%) were obtained by Sn doping after 3 h of UV light irradiation. Full article
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15 pages, 4658 KiB  
Article
Structural and Spectroscopic Effects of Li+ Substitution for Na+ in LixNa1−xCaLa0.5Er0.05Yb0.45(MoO4)3 Upconversion Scheelite-Type Phosphors
by Chang Sung Lim, Aleksandr Aleksandrovsky, Maxim Molokeev, Aleksandr Oreshonkov and Victor Atuchin
Crystals 2023, 13(2), 362; https://doi.org/10.3390/cryst13020362 - 20 Feb 2023
Cited by 14 | Viewed by 2263
Abstract
New triple molybdates LixNa1−xCaLa0.5(MoO4)3:Er3+0.05/Yb3+0.45 (x = 0, 0.05, 0.1, 0.2, 0.3) were manufactured successfully using the microwave-assisted sol-gel-based technique (MAS). Their room-temperature crystal structures were determined in space group [...] Read more.
New triple molybdates LixNa1−xCaLa0.5(MoO4)3:Er3+0.05/Yb3+0.45 (x = 0, 0.05, 0.1, 0.2, 0.3) were manufactured successfully using the microwave-assisted sol-gel-based technique (MAS). Their room-temperature crystal structures were determined in space group I41/a by Rietveld analysis. The compounds were found to have a scheelite-type structure. In Li-substituted samples, the sites of big cations were occupied by a mixture of (Li, Na, La, Er, Yb) ions, which provided a linear cell volume decrease with the Li content increase. The increased upconversion (UC) efficiency and Raman spectroscopic properties of the phosphors were discussed in detail. The mechanism of optimization of upconversion luminescence upon Li content variation was shown to be due to the control of excitation/energy transfer channel, while the control of luminescence channels played a minor role. The UC luminescence maximized at lithium content x = 0.05. The mechanism of UC optimization was shown to be due to the control of excitation/energy transfer channel, while the control of luminescence channels played a minor role. Over the whole spectral range, the Raman spectra of LixNa1−xCaLa0.5(MoO4)3 doped with Er3+ and Yb3+ ions were totally superimposed with the luminescence signal of Er3+ ions, and increasing the Li+ content resulted in the difference of Er3+ multiple intensity. The density functional theory calculations with the account for the structural disorder in the system of Li, Na, Ca, La, Er and Yb ions revealed the bandgap variation from 3.99 to 4.137 eV due to the changing of Li content. It was found that the direct electronic transition energy was close to the indirect one for all compounds. The determined chromaticity points (ICP) of the LiNaCaLa(MoO4)3:Er3+,Yb3+ phosphors were in good relation to the equal-energy point in the standard CIE (Commission Internationale de L’Eclairage) coordinates. Full article
(This article belongs to the Special Issue Rare Earths-Doped Materials (Volume II))
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