Sol-gel Impregnation Research Articles

Synergistic enhancement of methane partial oxidation in heat-recirculating reactor with the composite catalytic effect of Co-based double perovskite and CeO2

The emission of low-concentration coal mine methane (LCM) resulted in serious greenhouse effect. In order to utilize the LCM efficiently, a heat-recirculating porous reactor was built to realize the catalytic partial oxidation of the methane and air mixture. The effects of composite double-perovskite catalysts on the reaction temperature and gas production were investigated at different operating parameters. The results demonstrated that the B-site of Mn obviously enhanced the low-temperature catalytic activity of Co-based double-perovskite, which improved the methane reaction rate and hydrogen yield. The highest H2 yield (YH2 = 50.3 %) was obtained by La2CoMnO6 (D-CoMn). And the A-site partial doping of Ce promoted the production of syngas (ηe−s = 50.2 %). The addition of 25 % CeO2 enhanced the methane reaction rate and syngas production efficiency of D-CoMn. However, excessive CeO2 inhibited the generation of syngas. Meanwhile, the anti-supported catalyst CoMn/25Ce-S, synthesized by the sol-gel impregnation, performed good crystal morphology and the largest concentration of oxygen vacancies ((OIII+OII)/OI = 0.9). This enhanced the partial oxidation of methane and lowered the reaction temperature. The maximum H2 selectivity (SH2 = 44.2 %) and CH4 conversion efficiency (ηCH4 = 92.7 %) were attained at T4=998 K. Moreover, the increased flow velocity and equivalency ratio led to enhanced syngas production.

One-pot conversion of non-edible oil into sustainable biodiesel using novel bifunctional heterogeneous catalyst

This study aims to produce biodiesel from indigenous non-edible feedstock of wild olive seed oil using novel bifunctional xK2O/ZrO2-Bi2O3 catalyst. The designed catalyst was prepared using sol gel-impregnation method. The textural and surface properties of the synthesized catalyst were elucidated using various analytical techniques including EDX, FTIR, XRD, SEM, BET and XPS. The catalyst provided highest biodiesel yield of 95.2 % under the optimized reaction conditions. The successful synthesis of biodiesel was confirmed by GCMS, NMR and FTIR analysis, whereas; the various physiochemical properties were investigated according to the ASTM and EN standards. The designed catalyst showed substantial reproducibility and recyclability up to four times. The mechanism for xK2O/ZrO2-Bi2O3 catalyzed transesterification reaction of WOSO was also proposed. The kinetics studies revealed that the reaction follows pseudo first order and the Ea was calculated to be 32.58 kJ mol−1.

Foamed ceramic based γ-Al₂O₃ coated catalysts with different preparation methods for ethyl nicotinate hydrogenation reaction

This study investigated the catalytic hydrogenation of ethyl nicotinate using Pd/Al2O3-SiO2 foam ceramic catalysts prepared via sol-gel impregnation (SI), sol-gel precipitation (SP), precipitation-impregnation (PI), and co-precipitation (CP). We aimed to evaluate the performance and stability of these catalysts as coatings on foam ceramic surfaces in a high-pressure hydrogen reactor at 403 K and 5 MPa. Various physicochemical characterization methods were employed to correlate catalytic performance with physicochemical properties. Results indicated that sol-gel prepared supports had higher specific surface areas, more acidic sites, and better metal-carrier interactions compared to the precipitation method. SEM analyses revealed flatter and smoother coatings from the sol-gel method, while TEM showed uniform Pd distribution with impregnation. Ultimately, the SI method provided the best catalytic performance with a conversion of 86.77 %. The conversion of the substrate remained above 80 % after five cycles.

Lightweight and robust electrospun zirconia fiber reinforced carbon aerogel composites for efficient microwave absorption and heat insulation

Carbon aerogel (CA) is recognized as a promising microwave absorption (MA) material, but it remains greatly challenging to integrate the multiple functions of MA, mechanical strength, and heat insulation. In this work, a novel zirconia fiber reinforced CA (ZF/CA) composite is successfully fabricated via electrospinning technology coupled with a sol-gel impregnation process for the first time. The density (0.132–0.206 g/cm3) of the obtained ZF/CA composites can be regulated by simply varying the initial sol concentration, thus effectively tuning their performance. Notably, the ZF/CA composites display excellent MA properties, with a strong absorption of −80.30 dB at the thickness of merely 1.71 mm and the optimal effective absorption bandwidth reaches 5.16 GHz, which is a significant improvement compared to CA (−11.70 dB, 0.58 GHz). Simultaneously, the brittleness and cracking problems of CA are effectively addressed by the soft reinforcement strategy of electrospun zirconia fibers, and superior mechanical strength is obtained. Furthermore, the nanopore structure and hierarchical design endow the ZF/CA composites with low thermal conductivity (0.029–0.038 W m−1 K−1) and favorable heat insulation performance. Outstanding MA capacity and excellent heat insulation properties along with lightweight construction and high strength make ZF/CA composites a great candidate for efficient MA and heat insulation.

Tailoring microstructure and properties of porous mullite-based ceramics via sol-gel impregnation

Nanotechnology has been introduced into the refractory industry decades ago. However, there are still some peculiarities that hinder its routine application. Poor mechanical strength is one of them. Here we present the fabrication technique for mullite porous ceramics using a calcium-free colloidal binder system followed by secondary sol-gel impregnation intended for fabrication of large up-scaled monoliths. The primary foam was prepared via direct foaming of slurry containing colloidal silica, gelling agents, surfactant, silica fume, and different types of alumina. The foam mixture was cast, de-molded and dried using a cascade drying procedure. The investigation of mullitization that occurred during the high-temperature treatment was studied by XRD and TG-DTA analysis. The optimized sintering curve was then applied to obtain the highest mechanical properties. The resulting foam (with open porosity, volume density about 900 kg/m3 and mechanical strength about 10 MPa) was further processed by the impregnation step. The applied silica or combined silica/aluminum sol and unreacted alumina underwent secondary mullitization during following high-temperature treatment, which significantly enhanced the mechanical strength (up to 18 MPa). The secondary mullitization process was also investigated by HT-XRD and TG-DTA analysis. Foam microstructure was observed by an electron scanning microscope. Thermal conductivity of as-prepared ceramics foams varied from 0.3 to 0.4 W/m·K. The foam wall porosity evolution was studied by mercury intrusion porosimeter and estimated from image analysis.

Efficiency and mechanism of enhanced norfloxacin removal using amorphous TiO2-modified biochar

Inadequate treatment of antibiotic-contaminated wastewater, including compounds such as norfloxacin (NOR), poses a substantial treat to both ecological safety and human well-being. An innovative approach was devised to address NOR pollution using amorphous TiO2 modified biochar (A-TiO2/BC) prepared via sol-gel impregnation. The resultant had a commendably specific surface area of 131.8 m2/g−1, which was 1.91 times more than the original surface area of unmodified BC. A-TiO2/BC also exhibited abundant hydroxyl and oxygen-containing functional groups, thereby provided adequately active sites for NOR adsorption. R2 values obtained from NOR isotherm adsorption models descended in order of Freundlich < Temkin < Sips < Langmuir, which indicated that the NOR removal by A-TiO2/BC mainly complied with monolayer adsorption accompanied by heterogeneous surface adsorption. Under weakly acidic conditions, NOR adsorption benefits from the synergistic physicochemical interactions of A-TiO2 and BC. Notably, A-TiO2/BC demonstrated an impressive NOR adsorption capacity of up to 78.14 mg g−1, with a dosage of 20 mg L−1 at 25 °C under pH 6. Such A-TiO2 modified biochar thus presents a promising alternative for NOR removal.

Development and characterization of MAO/PLA-nHA nanocomposite coatings on pure zinc for orthopedic applications

Zinc (Zn)-based medical alloys are considered to be a biodegradable material with great potential. Hydroxyapatite (HA) can improve the osteogenic properties of Zn alloys, but its adhesion strength needs improvement. In this study, a micro-arc oxidation (MAO) interlayer and polylactic acid (PLA) composite layers containing different contents of nano-HA (nHA) were successively prepared on the pure Zn surface by MAO and sol–gel impregnation methods. The adhesion results showed that PLA could enhance the adhesion of HA on the Zn surface, where the adhesion of the Zn/MAO/PLA-nHA (7:3) composite coating was close to that of the pure PLA layer. In addition, the degradation rate of the implant could be controlled by varying the content of nHA in the composite coating while significantly improving its bioactivity. Finally, the addition of nHA increased the roughness of the surface of the composite coating, which was favorable for cell adhesion and proliferation. The highest adhesion density of MC3T3-E1 osteoblasts was exhibited on the Zn/MAO/PLA-nHA (7:3) composite coating. The Zn/MAO/PLA-nHA (7:3) composite coatings showed good adhesion, wettability, corrosion resistance, and excellent cytocompatibility. Thus, this study provides a reasonable design guide for the modification of degradable Zn alloy surfaces in bone tissue engineering biomaterials.

Multifunctional Carbon Fiber Reinforced C/SiOC Aerogel Composites for Efficient Electromagnetic Wave Absorption, Thermal Insulation, and Flame Retardancy.

Carbon fiber composites have great application prospects as a potential electromagnetic (EM) wave-absorbing material, yet it remains extremely challenging to integrate multiple functions of EM wave absorption, mechanical strength, thermal insulation, and flame retardancy. Herein, a novel carbon fiber reinforced C/SiOC aerogel (CF/CS) composite is successfully prepared by sol-gel impregnation combined with an ambient drying process for the first time. The density of the obtained CF/CS composites can be controlled just by changing sol-gel impregnation cycles (original carbon fiber felt (S0), and samples with one (S1) and two (S2) impregnation cycles are 0.249, 0.324, and 0.402 g cm-3, respectively), allowing for efficient tuning of their properties. Remarkably, S2 displays excellent microwave absorption properties, with an optimal reflection loss of -65.45dB, which is significantly improved than S0 (-10.90dB). Simultaneously, compared with S0 (0.75 and 0.30MPa in the x/y and z directions), the mechanical performance of S2 is dramatically improved with a maximum compressive strength of 10.37 and 4.93MPa in the x/y and z directions, respectively. Moreover, CF/CS composites show superior thermal insulation capability than S0 and obtain good flame-retardant properties. This work provides valuable guidance and inspiration for the development of multifunctional EM wave absorbers.

A novel combustion drying technology for in-situ preparation of glass fiber composite SiO2 aerogel thin felt with excellent thermal insulation performance

Glass fiber reinforced composite aerogel felt is an important thermal insulation material, but its thermal insulation performance is often compromised due to the limitation of preparation methods. In this study, the high performance glass fiber composite silica aerogel insulation thin felt was successfully prepared by in-situ sol-gel impregnation and combustion drying process for the first time. Especially, the drying time for the whole procedure is extremely quick, only taking a few minutes. The composite felt shows the characteristics of light weight, porous, hydrophobic, and has good mechanical properties. More importantly, due to the unique composite structure of the prepared felt, it has extremely low thermal conductivity (0.016 W/(m·K)) and thermal stability. The infrared thermal imager further confirmed that glass fiber composite silica aerogel thin felt has excellent thermal insulation ability, and has promising application potential in the thermal management system of power battery. Finally, the preparation process and drying mechanism based on sol-gel impregnation combined with combustion drying technology were discussed. Compared with the common technology, the preparation method has significant advantages of high efficiency and low cost, which offer an innovative technical approach for producing composite aerogel felt.

Novel fibrous/nano-Al2O3 insulation composites produced using sol-gel impregnation for energy-saving

The sol-gel method is a technique used to create a controlled porous structure by building up colloidal particles during the gelation process. In this study, a sol-gel method was utilized to prepare fibrous/nano-Al2O3 insulation composites using glass fiber, nano-Al2O3, and silica sol as primary materials for performance characterization. The samples exhibited high porosities (78.35–81.30%) and low thermal conductivities (0.084–0.159 W m−1 k−1 at 200–600 °C). The introduction of nano-Al2O3 resulted in a well-distributed aperture hierarchy and promoted multidirectional heat transfer paths. The fibers were arranged in a three-dimensional structure, overlapping each other, while the nano-powders were dispersed in a liquid phase and cross-linked to form a spatial mesh structure. The findings of this research have potential applications in heat preservation and energy-saving.

A comparative study on the photo-removal of a few selected priority organic pollutants in aqueous suspension using vanadium-doped-ZnO/MWCNT

Highly efficient vanadium doped ZnO nano-rods supported with MWCNTs (V@ZnO/MWCNT) have been fabricated using a convenient sol–gel impregnation method.

Composite Nanoarchitectonics of LaNi0.95Fe0.05O3/Muscovite for Enhanced Photocatalytic Activity

AbstractPowder-type semiconductor photocatalysts are widely applicable but their defects (e.g. easy agglomeration during preparation and recyclability in the suspension system) limit their practical application. In the current study, perovskite oxide photocatalytic material was loaded onto a muscovite substrate to overcome the problems of low stability, easy agglomeration, and difficult recovery. A photocatalytically active LaNi0.95Fe0.05O3/muscovite composite material was synthesized by a sol-gel impregnation method. Phase composition, morphology, and interfacial interaction of the composites, denoted as LNFBY-x (x: mass ratio of LNF to muscovite), were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and other analytical methods. According to the results, the particle size of LNF nanoparticles was regulated effectively by compounding with muscovite, and the agglomeration of LNF decreased. LNF nanoparticles were distributed evenly and attached in dense fashion to the surface of muscovite, thereby increasing the contact area with the reaction medium. The nanoparticles were connected to the silicon-oxygen tetrahedral sheet of the muscovite via Si–O–La, Si–O–Ni, and Si–O–Fe bonds, which increased the bonding strength between the composite components and expedited the transfer of photogenerated charge. More highly active oxygen species were produced, and a growing number of chemically active moieties (٠O2- and ٠OH) was generated in the photocatalytic reaction. LNFBY-1.00 demonstrated the best photocatalytic activity. A degradation rate of methyl orange of 99.03% was achieved after visible-light irradiation for 120 min, which decreased to 75.75% after five repeated uses, thereby indicating high stability and recycling ability. The photocatalytic LaNi0.95Fe0.05O3/muscovite composite material exhibited potential for application in environmental remediation practices.

Effect of preparation method on the performance of Fe-Ag/Al2O3 catalyst in the selective catalytic reduction of NO with propene

Previous works demonstrated that the Fe-Ag/Al2O3 catalyst could efficiently reduce NO into N2 by propene with a good resistance towards H2O and SO2. In this work, the effect of preparation method on the performance of Fe-Ag/Al2O3 catalyst in the selective catalytic reduction (SCR) of NO with propene was investigated. Three typical methods, viz., physical grinding (PG), direct impregnation (DI) and sol-gel-impregnation (SGI), were comparatively used to load the active components onto the supports. The results indicate that all the catalysts prepared by these three methods display good tolerance towards water vapor and SO2. However, they are rather different in the denitration efficiency; the maximum NO removal efficiency of the catalysts prepared by three methods follows the order of SGI (100%) > PG (62%) > DI (58%). Various characterization results reveal that the catalytic performance of Fe-Ag/Al2O3/CM was mainly related to the porous surface and Fe-Ag interaction. By using the SGI approach, the primary support of cordierite and the secondary support of Al2O3 work together to achieve a large surface area and an intense interaction between Fe and Ag on the resultant DP-Fe/Ag/Al2O3/CM catalyst, forming the bimetal AgFeO2 oxide and displaying the best reducibility. In terms of the PG method, the prepared GR-Fe/Ag/Al2O3 catalyst is powdery and shows the largest surface area; however, without cordierite serving as the monolithic support, Ag2O and Fe3O4 exist as separate oxides together with a hint of elemental Ag. As a result, the GR-Fe/Ag/Al2O3 catalyst shows poor reducibility due to the lack of porous surface to facilitate the Fe-Ag interaction. In contrast, the DP-Fe/Ag/CM catalyst prepared using the DI method shows rather poor dispersion of Fe and Ag due to the absence of the secondary support of Al2O3; in fact, individual Ag2O and Fe3O4 agglomerate on the catalyst surface and no AgFeO2 species is detected. Therefore, the DP-Fe/Ag/CM catalyst, with the surface area of only 1/4 of that for Fe-Ag/Al2O3/CM-SGI, exhibits the poorest activity in the SCR of NO by propene.

Fiber-Based Gas Filter Assembled via In Situ Synthesis of ZIF-8 Metal Organic Frameworks for an Optimal Adsorption of SO2: Experimental and Theoretical Approaches.

For environmental protection from exposure to airborne toxic gases, metal organic frameworks (MOFs) have drawn great attention as gas adsorbent options, with their advantages in chemical tailorability and large porosity. To develop a fiber-based gas filter that is effective against SO2 gas, zeolite imidazole framework-8 (ZIF-8) was applied to polypropylene nonwoven by various methods. Among the tested methods, the sol-gel impregnation method showed the highest ZIF-8 loading efficiency. There existed an optimal loading of ZIF-8 for the maximum adsorption efficiency, and it was associated with the accessibility of gas molecules to the ZIF-8 pores and active sites. Dominant adsorption processes and mechanisms were investigated by fitting the theoretical sorption models to experimental data. The results demonstrate that the increased ZIF-8 loading to fibers, beyond a certain level, may hinder the diffusivity and increase the barrier effect, eventually decreasing the adsorption efficiency. This study is novel and significant in that a multifaceted approach, including experimental analysis, theoretical investigation, and computational modeling, was made for scrutinizing the intricate phenomena occurring in the gas sorption process. The results of this study provide the fundamental yet practical information on the manufacturing considerations for the optimal design of MOF-loaded fibrous adsorbents.

The importance of physical parameters for the penetration depth of impregnation products into cementitious materials: Modelling and experimental study

The performance of impregnation treatments used for protection and remediation of porous building materials relies on sufficient penetration depth. The penetration of sol–gel impregnation products into partially saturated porous material is driven by capillary suction and depends on material properties, such as pore size distribution on one hand, and on the other hand on sol physical properties, viscosity, density, surface tension and contact angle, along with the time in which the sol gels. In this work we analyse, by the way of modelling and experiments, the penetration depth of a sol–gel impregnation product as the function of pore size distribution and sol properties. The main goal is to determine the importance of sol’s physical properties for the penetration depth for a specific pore size, which will serve as a basis of the optimization of impregnation products to maximize their penetration depth. The model is first calibrated in terms of penetration depth and sol uptake by the experimental data obtained from mortar samples each with a specific pore-size distribution. The correlation between penetration depth and physical parameters is then established by the use of Monte-Carlo method. The results show that the most important parameters for the optimization are surface tension, whose influence increases for larger pores, and gelation time, which with decreasing importance for larger pores.

Construction of CeO2/TiO2 heterojunctions immobilized on activated carbon fiber and its synergetic effect between adsorption and photodegradation for toluene removal

Toluene, as one of the most representative volatile organic compounds (VOCs), poses a serious threat to the atmospheric environment and human health. Herein, cerium dioxide (CeO2)/TiO2 immobilized on activated carbon fiber (ACF) is fabricated by ultrasonic-assisted sol-gel impregnation method for toluene removal. Characterizations of CeO2/TiO2/ACF composites reveal that CeO2 disperses or covers the surface of TiO2/ACF, and Ce4+ does not enter the lattice of TiO2 to replace Ti4+. The TEM and UV-vis analysis indicate the formation of heterojunction between TiO2 and CeO2. The Ce4+/Ce3+ redox centers significantly boost the separation efficiency of electron-hole pairs. The maximum removal efficiency of 1.5% CeO2/TiO2/ACF can reach up to 90%, much higher than 54% over TiO2/ACF. The CeO2/TiO2/ACF composites exhibit high removal efficiency of toluene due to the synergetic effects between adsorption and photodegradation. The gas-phase photodegradations are benzene, benzaldehyde, hexane, phenol, O-xylene, and phenylethyl acetate.

Improvement of White Spruce Wood Dimensional Stability by Organosilanes Sol-Gel Impregnation and Heat Treatment.

Wood is a living material with a dimensional stability problem. White spruce wood is a Canadian non-permeable wood that is used for siding applications. To improve this property, white spruce wood was treated with organosilanes sol-gel treatment with different moisture content (oven dried, air dried, and green wood). No major morphological changes were observed after treatment. However, organosilanes were impregnated into the cell wall without densifying the wood and without modifying the wood structure. Si-O-C chemical bonds between organosilanes and wood and Si-O-Si bonds were confirmed by FTIR and NMR, showing the condensation of organosilanes. The green wood (41% moisture content) showed only 26% dimensional stability due to the presence of too much water for organosilanes treatment. With a moisture content of 14%–18% (oven dried or air dried wood), the treatment was adapted to obtain the best improvement in dimensional stability of 35% and a 25% reduction of water vapor sorption. Finally, impregnation with organosilanes combined with the appropriate heat treatment improved the dimensional stability of white spruce wood by up to 35%. This treated Canadian wood could be an interesting option to validate for siding application in Canada.

Synergetic effect between adsorption and photodegradation on rGO/TiO2/ACF composites for dynamic toluene gaseous removal.

The toluene poses a serious threat to the atmospheric environment and human health. Herein, the reduced graphene oxide (rGO)/TiO2 immobilized on the activated carbon fiber (ACF) are fabricated by ultrasonic assisted sol-gel impregnation method to photodegrade dynamic toluene. Characterizations of rGO/TiO2/ACF composites reveal that the majority of graphene oxide (GO) is reduced to rGO and rGO/TiO2 is evenly loaded onto the ACF surface in the form of a smooth film. Furthermore, the photoelectrochemical experiments demonstrate both rGO and ACF can enhance significantly the separation efficiency of electron-hole pairs. The maximum removal efficiency of rGO/TiO2/ACF-0.75% can be up to 85% under ultraviolet irradiation. The rGO/TiO2/ACF exhibits more excellent adsorption and photodegradation activity for dynamic toluene than both rGO/TiO2 and ACF due to the synergetic effect rather than a simple linear combination of the rGO/TiO2 and ACF for toluene conversion. The possible photodegradation pathway is proposed according to intermediates measured by GC-MS, and adsorption coupling photocatalytic mechanisms are discussed.

Preparation of Biomorphic Porous SiC Ceramics from Bamboo by Combining Sol-Gel Impregnation and Carbothermal Reduction.

This study investigated the feasibility of using bamboo to prepare biomorphic porous silicon carbide (bio-SiC) ceramics through a combination of sol–gel impregnation and carbothermal reduction. The effects of sintering temperature, sintering duration, and sol–gel impregnation cycles on the crystalline phases and microstructure of bio-SiC were investigated. X-ray diffraction patterns revealed that when bamboo charcoal–SiO2 composites (BcSiCs) were sintered at 1700 °C for more than 2 h, the resulting bio-SiC ceramics exhibited significant β-SiC diffraction peaks. In addition, when the composites were sintered at 1700 °C for 2 h, scanning electron microscopy micrographs of the resulting bio-SiC ceramic prepared using a single impregnation cycle showed the presence of SiC crystalline particles and nanowires in the cell wall and cell lumen of the carbon template, respectively. However, bio-SiC prepared using three and five repeated cycles of sol–gel impregnation exhibited a foam-like microstructure compared with that prepared using a single impregnation cycle. Moreover, high-resolution transmission electron microscopy and selected area electron diffraction revealed that the atomic plane of the nanowire of bio-SiC prepared from BcSiCs had a planar distance of 0.25 nm and was perpendicular to the (111) growth direction. Similar results were observed for the bio-SiC ceramics prepared from bamboo–SiO2 composites (BSiCs). Accordingly, bio-SiC ceramics can be directly and successfully prepared from BSiCs, simplifying the manufacturing process of SiC ceramics.

Influence of temperature and oxygen on the growth of large-scale SiC nanowires

This paper examines the influence of temperature and oxygen on the growth of large-scale silicon carbide nanowires by using a combination of sol–gel impregnation and carbothermal reduction methods.