Metal Oxide Aerogels Research Articles

Reverse-engineered borohydride hydrolysis: Vacancy-rich cobalt aerogel nanowafers as high-efficiency electrode materials for supercapacitor applications

Transition metal oxide aerogels (AGLs) have garnered considerable attention over the past decade due to their unique and exceptional properties, including high porosity, extensive surface area, and ultra-low density. To meet the rising energy requirements and the need for renewable energy storage solutions, there is a growing demand for devices offering high energy and power densities. To realize such a device, a reverse borohydride hydrolysis method was employed in this study to synthesize oxygen vacancy-rich cobalt-based AGL (CoAGL) nanowafers with Co2+/Co3+ defect chemistry. Additionally, we annealed CoAGL samples at 400 °C (CoAGL@400) to successfully design and fabricate three-electrode supercapacitors. The characterization techniques encompassed X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron studies, shedding light on the X-ray properties of these AGLs. CoAGL demonstrated a specific capacitance (Csp) of 42.3 F/g in a device setup, displaying excellent cyclability and capacitance retention. Furthermore, it exhibited an energy density of 14.4 Wh/kg and a power density of 800 W/kg at a current density of 1 A/g, respectively. The practical application of the aerogel was demonstrated by fabricating a two-electrode device employing CoAGL as the key component.

Investigation of compound state of SiO2-TiO2 aerogel synthesized through controlled sol-gel reaction

In this work, a compound state of silica-titania aerogel was investigated through sol-gel reaction for hybridization of silica and titania with increasing reactivity by using high surface area and charge imbalances. By minimizing the sol-gel reaction rate difference and preparing a homogeneous and stable sol, a compound state of silica-titania aerogel could be obtained, without separation onto single metal oxide aerogel. The benefits of using the sol-gel synthesis method for synthesizing silica-titania compound aerogels are over a limit of substitution solubility and get binary metal oxide compound material. Diffraction and spectroscopic analyses showed that the heterogeneous linkage resulted from interaction among silicon, titanium, and oxygen ions. The coordination environment changes by the formation of an Si-O-Ti linkage following interaction among ions without phase separation on SiO2 and TiO2 aerogels. Thus, the atomically controlled sol-gel reaction can be used to design new metal-oxide-based compound aerogels and immiscible oxide materials.

NiO/Ni Nanowafer Aerogel Electrodes for High Performance Supercapacitors.

Transition metal oxide aerogels are a fascinating class of compounds that have received considerable attention in the last decade owing to their unique and exceptional properties, including high porosity, large surface area, and ultralow density. In this study, α-Ni(OH)2 aerogels and annealed NiO/Ni aerogels were used to design and fabricate a two-electrode supercapacitor device. The physicochemical properties of the as-synthesized aerogels were characterized through X-ray diffraction, scanning electron microscopy, transmission electron microscopy, the Brunauer-Emmett-Teller theory, and X-ray photoelectron spectroscopy studies. The annealed NiO/Ni aerogels showed a (specific capacitance of 1060 F/g) specific capacity of 422 C/g at 1 A/g current density and with good cycling stability (up to 10,000 cycles). The supercapacitor also demonstrated an energy density of 32.4 Wh/kg and power density of 1800 W/kg at a current density of 2 A/g. The specific capacitance of NiO/Ni aerogels was more than twice that of the α-Ni(OH)2 aerogels. The practical applications of the aerogel were demonstrated by fabricating a two-electrode device.

Synthesis and Photocatalysis of Metal Oxide Aerogels: A Review

Synthesis and Photocatalysis of Metal Oxide Aerogels: A Review

Metal oxide aerogels for high-temperature applications

Metal oxide aerogels for high-temperature applications

Designing Oxide Aerogels With Enhanced Sorptive and Degradative Activity for Acute Chemical Threats

Oxide aerogels are pore–solid networks notable for their low density, large pore volume, and high surface area. This three-dimensional arrangement of pore and solid provides critical properties: the high surface area required to maximize the number of active sites and a through-connected porosity that plumbs reactants to the active interior. In decontamination applications where reactivity beyond adsorption is desired to degrade deleterious molecules, oxide aerogels offer multiple avenues to add oxidative power to this unique arrangement of pore and solid. For protection against chemical warfare agents or toxic industrial chemicals, metal-oxide aerogels with their oxide/hydroxide surfaces afford stability under ambient conditions against competing sorbents such as water and oxygen. In this review, strategies to maximize sorptive capacity and degradation rate by modifying surface functionality, compositing with dissimilar oxides, or adding metallic nanoparticles and the subsequent impact on decontamination performance will be summarized and expected directions for future research will be discussed based on the observed trends.

Morphology study of metal oxide nanoparticles and aerogels produced via thermal decomposition of metal carbonyls in supercritical carbon dioxide

In this work, a process of thermal decomposition of metal carbonyls in oxygen-enriched supercritical carbon dioxide was studied. Manganese, iron, cobalt, and tungsten carbonyls were found to be soluble in supercritical CO2 at relatively mild conditions. For each metal carbonyl studied in this work, the thermal decomposition led to the formation of branched agglomerated structures throughout the high-pressure vessel. More specifically, for manganese and iron carbonyls, the procedure yielded partially monolithic aerogel-like structures, while for cobalt and tungsten carbonyls, the formation of branched aggregates was observed. The morphology of all the obtained metal oxides was studied by means of TEM. The study revealed that all materials consisted of individual nanoparticles with sizes between 2 and 40 nm. Pore structure was investigated by analyzing N2 adsorption/desorption curves. The specific surface area varied greatly depending on the type of oxide from 10 m2/g for CoOx to 130 m2/g for MnOx.

Curcumin-loaded metal oxide aerogels: supercritical drying and stability.

Curcumin, known as a potential antioxidant and anti-inflammatory agent, has major limitations for its therapeutic use because of its lack of water solubility and relatively low bioavailability. We report for the first time the loading of different metal oxide aerogels with curcumin. The aerogels were prepared via the sol–gel process and dried under supercritical conditions. Mixing curcumin with the metal precursors prior to the formation of the solid network ensures maximum entrapment. The curcumin–network interactions stabilize the organic moiety and create hybrid aerogels as potential vehicles for curcumin in various media. The aerogels were characterized by FTIR spectroscopy, thermogravimetric analysis, electron microscopy, and fluorescence spectroscopy to confirm their hybrid nature. The stability study by fluorescence spectroscopy revealed three distinct behaviors depending on the nature of the metal oxide: (i) a minor interaction between curcumin and the solid network slightly affecting the microenvironment; (ii) a quenching phenomenon when iron is present explained by a coordination between the iron ions and curcumin; and (iii) a strong complexation of the metal ions with curcumin after gelation.

Metal oxide aerogels: Preparation and application for the uranium removal from aqueous solution

The low density CeO2, Pr2O3 and Nd2O3 aerogels were synthesized by a novel solution-freeze-drying-calcination route. The bulk densities of the CeO2, Pr2O3 and Nd2O3 aerogels were calculated to be 8.10, 10.67 and 9.80 mg/cm3, respectively. Moreover, the structure of metal oxide aerogels was similar due to the same template materials, which made them possible to be appealing materials for adsorption. The maximum adsorption capacity for U(VI) of the CeO2, Pr2O3 and Nd2O3 aerogels reached 481.5, 840.6 and 587.3 mg/g (pH = 7, T = 25 °C), respectively, which were much higher than most of other modified metal oxides. Moreover, at low concentration of U(VI) (5 mg/L), it was completely dislodged by CeO2 aerogel and the remaining U(VI) was below 0.006 mg/L, which was lower than the effluent standards of United States Environmental Protection Agency and World Health Organization. Besides, after five cycles, the adsorption efficiency of metal oxide aerogels almost remained at a high level. Due to the excellent adsorption performance and high reusability, the three metal oxide aerogels would be promising adsorbents for the removal of U(VI).

Improved catalytic activity on the thermal decomposition of ammonium perchlorate and efficient adsorption of uranium using a novel ultra-low density Al2O3-based aerogels

The ultra-low density AlCl3-chitosan composite aerogel was prepared via a novel solution-freeze-drying technology. Then, the AlCl3-chitosan aerogel was carbonized or calcined to remove the chitosan template, yielding ultra-low density Al2O3-based aerogels with good formation ability. The density of Al2O3-based aerogels were about 9 mg/cm3 via this method. Moreover, the Al2O3-based aerogel obtained from the calcination of AlCl3-chitosan aerogel copied the open networks of thin flakes layered structure of chitosan template. The as-prepared Al2O3 aerogel had a low thermal conductivity of about 0.039 W/m K after high temperature treatment at 1000 °C, demonstrating its good thermal insulation property. The results of TG/DSC showed that the Al2O3-(0.2 wt% Pt) catalysts could decrease decomposition temperature of ammonium perchlorate (AP) by 51.1 °C and the exothermic heat was increased from 133.2 J/g to 1552.7 J/g. The maximum adsorption amounts for U(VI) of Al2O3 aerogel reached 769.9 mg/g, which was about 2 times higher than that of Al2O3 with other forms. Accordingly, the Al2O3 aerogel with thin flakes layered structure and ultra-low density possessed great potential application in thermal insulation, adsorption and catalyst supports. Meanwhile, the solution-freeze-drying technology is simple and easy to control, providing a new strategy for the preparation of ultra-low density metal oxide aerogels.

Thermal decomposition of manganese carbonyl in supercritical CO2 as a simple and effective approach to obtain manganese oxide aerogels

A novel approach to synthesize metal oxide aerogels is presented. The monolith aerogel structure is formed using dimanganese decacarbonyl as a precursor at elevated temperatures directly in supercritical CO2. Unlike previously described and developed sol–gel approaches, the proposed synthetic route requires only several hours without any necessity either to add any additional reaction-promoting liquid agents or to perform prolonged gel aging, solvent exchange, or supercritical drying steps. The morphology of the obtained aerogels was studied by means of scanning and transmission electron microscopy. Using low-temperature nitrogen adsorption technique, it was demonstrated, that achievable surface area of the aerogels could be tailored by varying the precursor concentration. Eventually, aerogels with a specific surface area of up to 170 m2/g were obtained.

Facile synthesis of a novel ultra-low density praseodymium oxide aerogel for catalyst and adsorbent

The pure praseodymium oxide aerogel with ultra-low density (about 10.7 mg/cm3) was prepared by using solution-freeze-drying-calcination method for the first time. The results of BET, SEM and TEM indicated that the pure praseodymium oxide aerogel belonged to the mesoporous material, which showed a typical three-dimensional porous structure. The results of TG/DSC showed that the praseodymium oxide aerogel could decrease the ammonium perchlorate decomposition temperature by 54.7 °C and enhance the heat production from 121.3 J/g to 838.5 J/g. The maximum adsorption amounts of praseodymium oxide aerogel reached 251.1 mg/g for uranium. This method provides a new strategy for preparation of low density metal oxide aerogels.

Metal Oxide Aerogels with Controlled Crystallinity and Faceting from the Epoxide-Driven Cross-Linking of Colloidal Nanocrystals

Metal Oxide Aerogels with Controlled Crystallinity and Faceting from the Epoxide-Driven Cross-Linking of Colloidal Nanocrystals

Metal Oxide Aerogels with Controlled Crystallinity and Faceting from the Epoxide-Driven Cross-Linking of Colloidal Nanocrystals

Metal Oxide Aerogels with Controlled Crystallinity and Faceting from the Epoxide-Driven Cross-Linking of Colloidal Nanocrystals

Synthesis and Properties of Metal Oxide Aerogels via Ambient Pressure Drying.

Metal oxide aerogels such as zirconia (ZrO₂), titania (TiO₂), and alumina (Al₂O₃) aerogels are very interesting nanoporous materials applicable as thermal insulators, catalysts, sensors, and so on. To obtain the aerogels, the first key step is a sol-gel process to prepare the gel followed by either supercritical drying, ambient pressure drying, or freeze-drying. Although the expensive and energy-intensive supercritical drying method restricts the commercialization of the aerogels, ambient pressure drying has shown great potential as an alternative and very simple method for aerogel synthesis. The sol-gel method and preparation parameters such as hydrolysis water, the silylating agent concentration, and the thermal treatment temperature have a profound impact on the textural and structural properties of the aerogels. Therefore, in this review, we study the synthesis and the influence of these parameters on the properties of metal oxide aerogels via ambient pressure drying.

Upconversion metal (Zr, Hf, and Ta) oxide aerogels.

A major obstacle in developing upconversion aerogels is the incompatibility of the highly-developed porosity and the crystal structure required for converting light to a shorter wavelength. We propose a novel method for creating a sol-gel procedure for synthesizing metal (Zr, Hf, and Ta) oxide upconverison aerogels uniformly doped with Er3+ and Yb3+ by precisely adjusting the calcination conditions.

Conformal carbon coated TiO2 aerogel as superior anode for lithium-ion batteries

A kind of carbon coated TiO2 (TiO2@C) aerogels were synthesized by a designed organic epoxide cross-linking process upon the titania alcogel followed with CO2 supercritical drying and direct carbonization of the organic coatings under argon atmosphere. The achieved composite aerogels were composed of small anatase TiO2 nanocrystals (∼5 nm) coated by conformal ultrathin carbon coatings and showed high specific surface area ∼235.7 m2 g−1 and average pore size ∼11 nm. As anode material for lithium-ion batteries (LIBs), the TiO2@C aerogels exhibited a superior high rate performance and deliver a capacity of 133 mAh g−1 after 3000 cycles at 10 C. This study supplied a rational and controllable method for the preparation of carbon coated TiO2 aerogel materials and other metal oxide aerogel with conformal carbon coatings which are expected as a promising high-performance anode material for LIBs.

Metal Oxide Aerogels with Controlled Crystallinity and Faceting from the Epoxide-Driven Cross-Linking of Colloidal Nanocrystals.

We present a novel method to produce crystalline oxide aerogels which is based on the cross-linking of preformed colloidal nanocrystals (NCs) triggered by propylene oxide (PO). Ceria and titania were used to illustrate this new approach. Ceria and titania colloidal NCs with tuned geometry and crystal facets were produced in solution from the decomposition of a suitable salt in the presence of oleylamine (OAm). The native surface ligands were replaced by amino acids, rendering the NCs colloidally stable in polar solvents. The NC colloidal solution was then gelled by adding PO, which gradually stripped the ligands from the NC surface, triggering a slow NC aggregation. NC-based metal oxide aerogels displayed both high surface areas and excellent crystallinity associated with the crystalline nature of the constituent building blocks, even without any annealing step. Such NC-based metal oxide aerogels showed higher thermal stability compared with aerogels directly produced from ionic precursors using conventional sol-gel chemistry strategies.

The investigation of an organic acid assisted sol-gel method for preparing monolithic zirconia aerogels.

In our previous work, a citric acid assisted sol–gel method was developed for preparing monolithic metal oxide aerogels. Such method adopted citric acid as the gelator, which replaced the well-studied proton scavenger propylene oxide. In this work, we have further extended this “organic acid assisted” sol–gel method and investigated the gelation mechanism. Four different organic acids (butanedioic acid, l-malic acid, l-aspartic acid and mercaptosuccinic acid) with an identical main chain but different side groups were used as the gelators for preparing monolithic zirconia aerogels. It was found that complex interactions including covalent bond and coordination bond interactions between organic acids and zirconium ions were vital to give a rigid gel network. After supercritical drying, crystalline zirconia aerogels can be obtained with high surface areas over 330 m2 g−1 and large pore volumes over 3.574 cm3 g−1.

Effect of differentiated textural properties of tin oxide aerogels on anode performance in lithium-ion batteries

Tin oxide aerogels with different textural structures were obtained using epoxide-initiated gelation of a tin precursor and two different gel drying methods, i.e., ambient pressure drying (APD) and supercritical extraction (SCE) processes. The pore diameters of the tin oxide aerogels synthesized by the APD and SCE methods were 11.3 and 25.3 nm, respectively. Tin oxide aerogels with smaller pore sizes and larger specific surface areas as well as slightly smaller pore volumes and porosities were obtained by the APD process. Different retention properties were observed for the anode materials prepared by APD and SCE, (71.8% and 10.9% after 80 cycles, respectively). This study revealed a relationship between the pore structure of the metal oxide anode material and its cyclability in Li-ion batteries, with metal oxide aerogels with small pore sizes and large specific surface areas showing greatly improved cycling stability in Li-ion battery applications owing to enhanced stability of the pore structure.