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Sol-Gel Preparation of Nanomaterials

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A special issue of Nanomaterials (ISSN 2079-4991).

Deadline for manuscript submissions: closed (15 December 2018) | Viewed by 61003

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Prof. Dr. Erhard Kemnitz

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Full University Professor, Chemistry Department, Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, D-12489 Berlin, Germany
Interests: mechanistic aspects of heterogeneously catalysed fluorination reactions, non-aqueous fluorolytic sol–gel synthesis of nanoscopic metal fluorides; nano metal fluorides as solid Lewis acids; nano metal hydroxide fluorides as biacidic Brønsted/Lewis acids and bases; metal fluoride sols for antireflective coating; inorganic–organic hybrid materials based on nano metal fluorides
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Dear Colleagues,

Nanomaterial chemistry has become an extremely important area of research over the past 20 years. Although many different nanomaterials have already found industrial applications we are still just at the beginning of a new scientific and industrial revolution driven by the advances in nanomaterials science.

Over the past decades, many new synthesis techniques have been developed that give access to the fascinating world of nanomaterials with different chemical and physical properties. The sol-gel synthesis certainly is one of the most powerful synthesis routes in terms of the wide variety of synthesis approaches and technical applications. Especially the classical (aqueous) sol-gel synthesis route, mainly forced by the development of silica, was but still is in the focus of thousands of chemists and materials scientists worldwide.

However, motivated by new developments like atomic layer deposition, ALD, and others, non-aqueous sol-gel synthesis approaches have been developed recently, thus extending the synthesis access toward nanoscopic new materials.

Therefore, it is the intention of the Special Issue of Nanomaterials to present the current state-of-the-art in the sol-gel-based synthesis approaches towards nanomaterials. Characteristic properties and fields of applications of those materials may highlight the potential of these synthesis approaches. On a first glance, there is no restriction on classes of sol-gel formed nanomaterials as well as field of application. Therefore, in the present Special Issue, contributions from leading groups in the field with the aim of giving a balanced view of the current state-of-the-art in the sol-gel-synthesis field are invited.

Prof. Dr. Erhard Kemnitz
Guest Editor

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Keywords

Sol-Gel Synthesis
Nanomaterials
Nanotechnology
Mechanistic Synthesis Aspects
Properties
Applications

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Published Papers (10 papers)

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16 pages, 2336 KiB

Open AccessArticle

Controlled Synthesis and Microstructural Properties of Sol-Gel TiO₂ Nanoparticles for Photocatalytic Cement Composites

by Elena Cerro-Prada, Sara García-Salgado, M. Ángeles Quijano and Fernando Varela

Nanomaterials 2019, 9(1), 26; https://doi.org/10.3390/nano9010026 - 25 Dec 2018

Cited by 53 | Viewed by 5471

Abstract

Titania nanoparticles are intensely studied for photodegradation applications. Control of nanoscale morphology and microstructural properties of these materials is critical for photocatalytic performance. Uniform anatase-type TiO₂ nanoparticles were prepared by the sol-gel process using titanium isopropoxide as precursor. Controlled annealing up to 400 °C established crystallization and particle size ranging between 20 and 30 nm. Detailed thermal examination reveals that anatase phase transformation into rutile is affected by the annealing temperature and by the initial particle size. The anatase to rutile phase transformation occurs in the nanoparticles at 550 °C. The Total Reflection X-ray Fluorescence (TXRF) study of the anatase nanoparticles shows a shift towards higher energy in the Ka Ti line of 10 eV, related to structural defects. These features were discussed in the photocatalytic behavior of several cement-based materials modified with the so-prepared anatase nanoparticles. The photocatalytic activity of the anatase-type TiO₂/cement mortar system is evaluated from the degradation of Methylene Blue (MB) under UV irradiation, monitored through the absorbance at 665 nm. The results show that the photocatalytic composites exhibit up to 76.6% degradation efficiency. Mechanical testing of the nano-TiO₂ modified cementitious composites evinces a moderate reinforcement of the strength properties at long ages. Full article

(This article belongs to the Special Issue Sol-Gel Preparation of Nanomaterials)

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13 pages, 7610 KiB

Open AccessArticle

Influence of Synthesis Conditions on Microstructure and NO₂ Sensing Properties of WO₃ Porous Films Synthesized by Non-Hydrolytic Sol–Gel Method

by Sikai Zhao, Yanbai Shen, Pengfei Zhou, Guodong Li, Cong Han, Dezhou Wei, Xiangxi Zhong, Yunhai Zhang and Yuxin Ao

Nanomaterials 2019, 9(1), 8; https://doi.org/10.3390/nano9010008 - 21 Dec 2018

Cited by 14 | Viewed by 4389

Abstract

Nanostructured tungsten trioxide porous films were prepared by a non-hydrolytic sol–gel method following the inorganic route in which ethanol and PEG were used as the oxygen-donor and structure-directing reagent, respectively. The effects of aging time of the precursor solution, PEG content, and calcination temperature on the structure, morphology, and NO₂ sensing properties of WO₃ films were systematically investigated by using the techniques of X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and gas sensing measurements. The results demonstrated that a series of WO₃ films with different microstructures could be obtained by manipulating the synthesis parameters. Furthermore, a suitable synthesis condition of WO₃ films for NO₂ sensing application was determined. Full article

(This article belongs to the Special Issue Sol-Gel Preparation of Nanomaterials)

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12 pages, 24150 KiB

Open AccessArticle

Design and Evaluation of Europium Containing Mesoporous Bioactive Glass Nanospheres: Doxorubicin Release Kinetics and Inhibitory Effect on Osteosarcoma MG 63 Cells

by Ying Zhang, Meng Hu, Xiang Wang, Zhufa Zhou and Yu Liu

Nanomaterials 2018, 8(11), 961; https://doi.org/10.3390/nano8110961 - 21 Nov 2018

Cited by 33 | Viewed by 4126

Abstract

Functional ions and drug factors play a vital role in stimulating bone tissue regeneration as we understand it. In this work, europium-containing mesoporous bioactive glass nanospheres (Eu/MBGs), composed of 60% SiO₂—(36–x)%CaO—x%Eu₂O₃—4%P₂O₅ (x = 0, 0.5, 1, 2 mol%), were prepared by a facile sol-gel process. The results indicate that Eu ions play an important role to influence the microstructure of MBGs, in which a suitable concentration of Eu (1 mol%) increases their surface area (502 m²/g) as well as their pore volume (0.34 cm³/g). Proper doping of Eu ions in MBGs can observably induce apatite mineralization and improve the doxorubicin (DOX) release behavior. Furthermore, DOX-loaded Eu/MBGs could maintain a long-term inhibitory effect on the viability of osteosarcoma MG 63 cells. This work has demonstrated that it is possible to develop functional Eu/MBGs by combining excellent apatite-mineralization ability, controllable drug (DOX) release and antitumor functions for the therapy of bone tissue regeneration. Full article

(This article belongs to the Special Issue Sol-Gel Preparation of Nanomaterials)

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16 pages, 27889 KiB

Open AccessArticle

Non-Aqueous Sol-Gel Synthesis of FePt Nanoparticles in the Absence of In Situ Stabilizers

by Tobias Preller, Dirk Menzel, Saskia Knickmeier, Julian Cedric Porsiel, Bilal Temel and Georg Garnweitner

Nanomaterials 2018, 8(5), 297; https://doi.org/10.3390/nano8050297 - 3 May 2018

Cited by 14 | Viewed by 5179

Abstract

The synthesis of FePt nanocrystals is typically performed in an organic solvent at rather high temperatures, demanding the addition of the in situ stabilizers oleic acid and oleylamine to produce monomodal particles with well-defined morphologies. Replacing frequently-used solvents with organic media bearing functional moieties, the use of the stabilizers can be completely circumvented. In addition, various morphologies and sizes of the nanocrystals can be achieved by the choice of organic solvent. The kinetics of particle growth and the change in the magnetic behavior of the superparamagnetic FePt nanocrystals during the synthesis with a set of different solvents, as well as the resulting morphologies and stoichiometries of the nanoparticles were determined by powder X-ray diffraction (PXRD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES)/mass spectrometry (ICP-MS), and superconducting quantum interference device (SQUID) measurements. Furthermore, annealing of the as-prepared FePt nanoparticles led to the ordered L1₀ phase and, thus, to hard magnetic materials with varying saturation magnetizations and magnetic coercivities. Full article

(This article belongs to the Special Issue Sol-Gel Preparation of Nanomaterials)

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9 pages, 2809 KiB

Open AccessArticle

Cobalt-Assisted Morphology and Assembly Control of Co-Doped ZnO Nanoparticles

by Xianying Han, Sebastian Wahl, Patrícia A. Russo and Nicola Pinna

Nanomaterials 2018, 8(4), 249; https://doi.org/10.3390/nano8040249 - 17 Apr 2018

Cited by 32 | Viewed by 6396

Abstract

The morphology of metal oxide nanostructures influences the response of the materials in a given application. In addition to changing the composition, doping can also modify the morphology of a host nanomaterial. Herein, we determine the effect of dopant concentration, reaction temperature, and reaction time on the morphology and assembly of Co_xZn_1−xO nanoparticles synthesized through non-aqueous sol-gel in benzyl alcohol. With the increase of the atom % of cobalt incorporated from 0 to 15, the shape of the nanoparticles changes from near spherical, to irregular, and finally to triangular. The tendency of the particles to assemble increases in the same direction, with Co_0.05Zn_0.95O consisting of non-assembled particles, whereas Co_0.15Zn_0.85O consists of triangular nanoparticles forming spherical structures. The morphology and assembly process are also sensitive to the reaction temperature. The assembly process is found to occur during the nucleation or the early stages of particle growth. The cobalt ions promote the change in the shape during the growth stage of the nanoparticles. Full article

(This article belongs to the Special Issue Sol-Gel Preparation of Nanomaterials)

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13 pages, 4003 KiB

Open AccessArticle

The Effect of Different Coupling Agents on Nano-ZnO Materials Obtained via the Sol–Gel Process

by Violeta Purcar, Raluca Şomoghi, Sabina Georgiana Niţu, Cristian-Andi Nicolae, Elvira Alexandrescu, Ioana Cătălina Gîfu, Augusta Raluca Gabor, Hermine Stroescu, Raluca Ianchiş, Simona Căprărescu and Ludmila Otilia Cinteză

Nanomaterials 2017, 7(12), 439; https://doi.org/10.3390/nano7120439 - 12 Dec 2017

Cited by 67 | Viewed by 8793

Abstract

Hybrid nanomaterials based on zinc oxide were synthesized via the sol–gel method, using different silane coupling agents: (3-glycidyloxypropyl)trimethoxysilane (GPTMS), phenyltriethoxysilane (PhTES), octyltriethoxysilane (OTES), and octadecyltriethoxysilane (ODTES). Morphological properties and the silane precursor type effect on the particle size were investigated using dynamic light scattering (DLS), environmental scanning electron microscopy (ESEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray diffraction (XRD). The bonding characteristics of modified ZnO materials were investigated using Fourier transform infrared spectroscopy (FTIR). The final solutions were deposited on metallic substrate (aluminum) in order to realize coatings with various wettability and roughness. The morphological studies, obtained by ESEM and TEM analysis, showed that the sizes of the ZnO nanoparticles are changed as function of silane precursor used in synthesis. The thermal stability of modified ZnO materials showed that the degradation of the alkyl groups takes place in the 300–500 °C range. Water wettability study revealed a contact angle of 142 ± 5° for the surface covered with ZnO material modified with ODTES and showed that the water contact angle increases as the alkyl chain from the silica precursor increases. These modified ZnO materials, therefore, can be easily incorporated in coatings for various applications such as anti-corrosion and anti-icing. Full article

(This article belongs to the Special Issue Sol-Gel Preparation of Nanomaterials)

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13 pages, 5136 KiB

Open AccessFeature PaperArticle

Sol-Gel-Synthesis of Nanoscopic Complex Metal Fluorides

by Alexander Rehmer, Kerstin Scheurell, Gudrun Scholz and Erhard Kemnitz

Nanomaterials 2017, 7(11), 362; https://doi.org/10.3390/nano7110362 - 2 Nov 2017

Cited by 9 | Viewed by 5578

Abstract

The fluorolytic sol-gel synthesis for binary metal fluorides (AlF₃, CaF₂, MgF₂) has been extended to ternary and quaternary alkaline earth metal fluorides (CaAlF₅, Ca₂AlF₇, LiMgAlF₆). The formation and crystallization of nanoscopic ternary CaAlF₅ and Ca₂AlF₇ sols in ethanol were studied by ¹⁹F liquid and solid state NMR (nuclear magnetic resonance) spectroscopy, as well as transmission electron microscopy (TEM). The crystalline phases of the annealed CaAlF₅, Ca₂AlF₇, and LiMgAlF₆ xerogels between 500 and 700 °C could be determined by X-ray powder diffraction (XRD) and ¹⁹F solid state NMR spectroscopy. The thermal behavior of un-annealed nanoscopic ternary and quaternary metal fluoride xerogels was ascertained by thermal analysis (TG/DTA). The obtained crystalline phases of CaAlF₅ and Ca₂AlF₇ derived from non-aqueous sol-gel process were compared to crystalline phases from the literature. The corresponding nanoscopic complex metal fluoride could provide a new approach in ceramic and luminescence applications. Full article

(This article belongs to the Special Issue Sol-Gel Preparation of Nanomaterials)

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17 pages, 7300 KiB

Open AccessFeature PaperArticle

Sol-Gel Derived Adsorbents with Enzymatic and Complexonate Functions for Complex Water Remediation

by Roman P. Pogorilyi, Ievgen Pylypchuk, Inna V. Melnyk, Yurii L. Zub, Gulaim A. Seisenbaeva and Vadim G. Kessler

Nanomaterials 2017, 7(10), 298; https://doi.org/10.3390/nano7100298 - 28 Sep 2017

Cited by 27 | Viewed by 6182

Abstract

Sol-gel technology is a versatile tool for preparation of complex silica-based materials with targeting functions for use as adsorbents in water purification. Most efficient removal of organic pollutants is achieved by using enzymatic reagents grafted on nano-carriers. However, enzymes are easily deactivated in the presence of heavy metal cations. In this work, we avoided inactivation of immobilized urease by Cu (II) and Cd (II) ions using magnetic nanoparticles provided with additional complexonate (diethylene triamine pentaacetic acid or DTPA) functions. Obtained nanomaterials were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). According to TGA, the obtained Fe₃O₄/SiO₂-NH₂-DTPA nanoadsorbents contained up to 0.401 mmol/g of DTPA groups. In the concentration range C_eq = 0–50 mmol/L, maximum adsorption capacities towards Cu (II) and Cd (II) ions were 1.1 mmol/g and 1.7 mmol/g, respectively. Langmuir adsorption model fits experimental data in concentration range C_eq = 0–10 mmol/L. The adsorption mechanisms have been evaluated for both of cations. Crosslinking of 5 wt % of immobilized urease with glutaraldehyde prevented the loss of the enzyme in repeated use of the adsorbent and improved the stability of the enzymatic function leading to unchanged activity in at least 18 cycles. Crosslinking of 10 wt % urease on the surface of the particles allowed a decrease in urea concentration in 20 mmol/L model solutions to 2 mmol/L in up to 10 consequent decomposition cycles. Due to the presence of DTPA groups, Cu²⁺ ions in concentration 1 µmol/L did not significantly affect the urease activity. Obtained magnetic Fe₃O₄/SiO₂-NH₂-DTPA-Urease nanocomposite sorbents revealed a high potential for urease decomposition, even in presence of heavy metal ions. Full article

(This article belongs to the Special Issue Sol-Gel Preparation of Nanomaterials)

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10 pages, 2288 KiB

Open AccessArticle

Thermal Conductivity of a Nanoscale Yttrium Iron Garnet Thin-Film Prepared by the Sol-Gel Process

by Yun Young Kim

Nanomaterials 2017, 7(9), 247; https://doi.org/10.3390/nano7090247 - 31 Aug 2017

Cited by 9 | Viewed by 5568

Abstract

The thermal conductivity of a nanoscale yttrium iron garnet (Y₃Fe₅O₁₂, YIG) thin-film prepared by a sol-gel method was evaluated using the ultrafast pump-probe technique in the present study. The thermoreflectance change on the surface of a 250 nm thick YIG film, induced by the irradiation of femtosecond laser pulses, was measured, and curve fitting of a numerical solution for the transient heat conduction equation to the experimental data was performed using the finite difference method in order to extract the thermal property. Results show that the film’s thermal conductivity is 22–83% higher than the properties of bulk YIG materials prepared by different fabrication techniques, reflecting the microstructural characteristics and quality of the film. Full article

(This article belongs to the Special Issue Sol-Gel Preparation of Nanomaterials)

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Review

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19 pages, 24587 KiB

Open AccessFeature PaperReview

Sol-Gel Processing of MgF₂ Antireflective Coatings

by Peer Löbmann

Nanomaterials 2018, 8(5), 295; https://doi.org/10.3390/nano8050295 - 2 May 2018

Cited by 24 | Viewed by 7015

Abstract

There are different approaches for the preparation of porous antireflective λ/4 MgF₂ films from liquid precursors. Among these, the non-aqueous fluorolytic synthesis of precursor solutions offers many advantages in terms of processing simplicity and scalability. In this paper, the structural features and optical performance of the resulting films are highlighted, and their specific interactions with different inorganic substrates are discussed. Due to their excellent abrasion resistance, coatings have a high potential for applications on glass. Using solvothermal treatment of precursor solutions, also the processing of thermally sensitive polymer substrates becomes feasible. Full article

(This article belongs to the Special Issue Sol-Gel Preparation of Nanomaterials)

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