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Surface modified silica nanoparticles are well-established composite materials. To improve their embedding and application behavior, surface energy analysis has been performed before and after silanization with mercaptopropyltrimethoxysilane (MPTMS) using inverse gas chromatography technique (IGC). Experiments with two silica materials have been conducted at infinite dilution to determine the dispersive component of the surface energy (γsd) as well as the specific component (γssp) using the van Oss theory and a least-squares procedure evaluating the IGC data of 8 polar probe molecules collectively (instead of evaluating only the data of a pair of monopolar probes as is often the case in IGC studies). After surface silylation, the total surface energy (γst) of pyrogenic silica nanoparticles decreased from 225 mJ/m2 to 149 mJ/m2 referring to both a reduced wettability and an increased hydrophobicity of the MPTMS-modified sample. Moreover, the acidity/basicity parameters according to the van Oss and the Gutmann approach indicated that the acidity of the silica surface decreases by MPTMS grafting. In addition, IGC at finite concentration (using isopropanol as probe molecule) was applied to obtain the energetic heterogeneity of the silica surface. The results showed a bimodal energy distribution with maxima at about 18 and 25 kJ/mol and a reduction of the higher energetic sites from 65% to only 35% after MPTMS treatment. Overall, it can be seen that the dominance of specific interactions on silica surfaces is maintained even after extensive silanization. These findings are in agreement with the results of 29Si CP MAS NMR measurements which confirm the assignment of higher energetic sites to silanol groups. For the interpretation of the IGC results, quantum chemical calculations proved the preferred interaction of isopropanol onto silica surfaces via hydrogen bridging.
Frank Bauer; Ralf Meyer; Marko Bertmer; Sergej Naumov; Majd Al-Naji; Julia Wissel; Martin Steinhart; Dirk Enke. Silanization of siliceous materials, part 3: Modification of surface energy and acid-base properties of silica nanoparticles determined by inverse gas chromatography (IGC). Colloids and Surfaces A: Physicochemical and Engineering Aspects 2021, 618, 126472 .
AMA StyleFrank Bauer, Ralf Meyer, Marko Bertmer, Sergej Naumov, Majd Al-Naji, Julia Wissel, Martin Steinhart, Dirk Enke. Silanization of siliceous materials, part 3: Modification of surface energy and acid-base properties of silica nanoparticles determined by inverse gas chromatography (IGC). Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2021; 618 ():126472.
Chicago/Turabian StyleFrank Bauer; Ralf Meyer; Marko Bertmer; Sergej Naumov; Majd Al-Naji; Julia Wissel; Martin Steinhart; Dirk Enke. 2021. "Silanization of siliceous materials, part 3: Modification of surface energy and acid-base properties of silica nanoparticles determined by inverse gas chromatography (IGC)." Colloids and Surfaces A: Physicochemical and Engineering Aspects 618, no. : 126472.
A new preparation concept of a partially porous solid-state bilayer electrolyte (BE) for high-temperature sodium-ion batteries has been developed. The porous layer provides mechanical strength and is infiltrated with liquid and highly conductive NaAlCl4 salt, while the dense layer prevents short circuits. Both layers consist, at least partially, of Na-β-alumina. The BEs are synthesized by a three-step procedure, including a sol-gel synthesis, the preparation of porous, calcined bulk material, and spin coating to deposit a dense layer. A detailed study is carried out to investigate the effect of polyethylene oxide (PEO) concentration on pore size and crystallization of the bulk material. The microstructure and crystallographic composition are verified for all steps via mercury intrusion, X-ray diffraction, and scanning electron microscopy. The porous bulk material exhibits an unprecedented open porosity for a NaxAlOy bilayer-system of ≤57% with a pore size of ≈200–300 nm and pore volume of ≤0.3 cm3∙g−1. It contains high shares of crystalline α-Al2O3 and Na-β-alumina. The BEs are characterized by impedance spectroscopy, which proved an increase of ionic conductivity with increasing porosity and increasing Na-β-alumina phase content in the bulk material. Ion conductivity of up to 0.10 S∙cm−1 at 300 °C is achieved.
Antonia Hoppe; Cornelius Dirksen; Karl Skadell; Michael Stelter; Matthias Schulz; Simon Carstens; Dirk Enke; Sharon Koppka. Sodium Solid Electrolytes: NaxAlOy Bilayer-System Based on Macroporous Bulk Material and Dense Thin-Film. Materials 2021, 14, 854 .
AMA StyleAntonia Hoppe, Cornelius Dirksen, Karl Skadell, Michael Stelter, Matthias Schulz, Simon Carstens, Dirk Enke, Sharon Koppka. Sodium Solid Electrolytes: NaxAlOy Bilayer-System Based on Macroporous Bulk Material and Dense Thin-Film. Materials. 2021; 14 (4):854.
Chicago/Turabian StyleAntonia Hoppe; Cornelius Dirksen; Karl Skadell; Michael Stelter; Matthias Schulz; Simon Carstens; Dirk Enke; Sharon Koppka. 2021. "Sodium Solid Electrolytes: NaxAlOy Bilayer-System Based on Macroporous Bulk Material and Dense Thin-Film." Materials 14, no. 4: 854.
A thermo-chemical treatment method was used to produce biogenic amorphous silica from South African sugarcane and maize residues. Different fractions of South African sugarcane (leaves, pith, and fiber) were processed for silica production. The biomass samples were leached with either 7 wt% citric acid or 7 wt% sulfuric acid at 353 K for 2 h prior to being rinsed, dried and combusted using a four-step program ranging from room temperature to 873 K in a furnace. The characterization of the pre-treated biomass samples was conducted using thermogravimetric analysis (TG/DTA), X-ray fluorescence analysis (XRF) and elemental analysis (CHN), while the final products were characterized by XRF, X-ray diffraction (XRD), elemental analysis, nitrogen physisorption and scanning electron microscopy (SEM). Citric acid pre-treatment proved to be an attractive alternative to mineral acids. Amorphous biogenic silica was produced from sugarcane leaves in good quality (0.1 wt% residual carbon and up to 99.3 wt% silica content). The produced biogenic silica also had great textural properties such as a surface area of up to 323 m2 g−1, average pore diameter of 5.0 nm, and a pore volume of 0.41 cm3 g−1.
Ncamisile Nondumiso Maseko; Denise Schneider; Susan Wassersleben; Dirk Enke; Samuel Ayodele Iwarere; Jonathan Pocock; Annegret Stark. The Production of Biogenic Silica from Different South African Agricultural Residues through a Thermo-Chemical Treatment Method. Sustainability 2021, 13, 577 .
AMA StyleNcamisile Nondumiso Maseko, Denise Schneider, Susan Wassersleben, Dirk Enke, Samuel Ayodele Iwarere, Jonathan Pocock, Annegret Stark. The Production of Biogenic Silica from Different South African Agricultural Residues through a Thermo-Chemical Treatment Method. Sustainability. 2021; 13 (2):577.
Chicago/Turabian StyleNcamisile Nondumiso Maseko; Denise Schneider; Susan Wassersleben; Dirk Enke; Samuel Ayodele Iwarere; Jonathan Pocock; Annegret Stark. 2021. "The Production of Biogenic Silica from Different South African Agricultural Residues through a Thermo-Chemical Treatment Method." Sustainability 13, no. 2: 577.
In this study, a suitable route for the selective functionalization of the outer surface of MCM-48-type mesoporous silica nanoparticles (MSNs) and its impact on the physicochemical properties were investigated. The synthesis of MCM-48 nanoparticles with intact cubic ordered mesopore structure and functionalized outer particle surface was managed by postsynthetic and co-condensation modification routes with 3-methacryloxypropyltrimethoxy-silane (MPS). The results of FTIR, 29Si and 13C NMR, thermogravimetric, and elemental analysis confirmed the successful silane surface grafting by both methods. The nitrogen sorption analysis showed the selective outer surface functionalization by the postsynthetic route for the synthesized MCM-48 nanoparticles containing the template still inside the pore channels and in the case of the co-condensation route via late addition of the silane precursors into the synthesis batch containing a fully grown silica. The solvent type in the former approach and silane addition time during the particle growth in the later route showed a significant impact on the silane content and site selective binding. The amount of grafted silane was determined by thermogravimetric and elemental analysis. It was found to increase using toluene in the postsynthetic modification route. The average particle size measured from SEM/TEM analysis ranges from 290 to 350 nm. The cubic ordered pore structure of the final silane grafted MSNs was fully preserved in both functionalization routes as corroborated from XRD analysis. In conclusion, MCM-48 nanoparticles selectively functionalized on the outer particle surface are favorable candidates for the subsequent site selective grafting reactions.
Shewaye Yismaw; Stefan G. Ebbinghaus; Marianne Wenzel; David Poppitz; Roger Gläser; Jörg Matysik; Frank Bauer; Dirk Enke. Selective functionalization of the outer surface of MCM-48-type mesoporous silica nanoparticles at room temperature. Journal of Nanoparticle Research 2020, 22, 1 -15.
AMA StyleShewaye Yismaw, Stefan G. Ebbinghaus, Marianne Wenzel, David Poppitz, Roger Gläser, Jörg Matysik, Frank Bauer, Dirk Enke. Selective functionalization of the outer surface of MCM-48-type mesoporous silica nanoparticles at room temperature. Journal of Nanoparticle Research. 2020; 22 (9):1-15.
Chicago/Turabian StyleShewaye Yismaw; Stefan G. Ebbinghaus; Marianne Wenzel; David Poppitz; Roger Gläser; Jörg Matysik; Frank Bauer; Dirk Enke. 2020. "Selective functionalization of the outer surface of MCM-48-type mesoporous silica nanoparticles at room temperature." Journal of Nanoparticle Research 22, no. 9: 1-15.
This work addresses the advanced textural characterization of biogenic silica obtained from different Si-accumulating biomasses and agricultural waste products like rice, oat and spelt husk as well as horsetail. These materials exhibit a non-uniform, disordered pore structure in a broad size range deviating from well-ordered “artificial” species of porous materials. For the first time in literature, this contribution determines and validates mainly the mesoporosity by means of nitrogen physisorption, positron annihilation lifetime spectroscopy (PALS) and hyperpolarized 129Xenon NMR (HP-129Xe NMR). Nitrogen physisorption and HP 129Xe NMR both were able to describe the pore structure in the mesopore range. In addition, the specific surface area and the mesopore volume were determined by nitrogen physisorption. PALS complemented the results by an assessment of microporosity in biogenic silica. It was shown that biogenic silica contains micropores (1.5 nm–1.9 nm), mesopores in a broad range and indications of macroporosity. In addition, the results led to the assumption that different plant origins and plant species evoke different textural properties and inter-connections between the pores in biogenic silica. This contribution demonstrates that only a combination of all techniques is viable to characterize the non-uniform and complex pore structure of biogenic silica of different origin.
Denise Schneider; Ahmed G. Attallah; Susan Wassersleben; Marianne Wenzel; Jörg Matysik; Reinhard Krause-Rehberg; Dirk Enke. Advanced textural characterization of biogenic silica by nitrogen physisorption, positron annihilation lifetime spectroscopy and hyperpolarized 129Xe NMR spectroscopy. Microporous and Mesoporous Materials 2020, 307, 110515 .
AMA StyleDenise Schneider, Ahmed G. Attallah, Susan Wassersleben, Marianne Wenzel, Jörg Matysik, Reinhard Krause-Rehberg, Dirk Enke. Advanced textural characterization of biogenic silica by nitrogen physisorption, positron annihilation lifetime spectroscopy and hyperpolarized 129Xe NMR spectroscopy. Microporous and Mesoporous Materials. 2020; 307 ():110515.
Chicago/Turabian StyleDenise Schneider; Ahmed G. Attallah; Susan Wassersleben; Marianne Wenzel; Jörg Matysik; Reinhard Krause-Rehberg; Dirk Enke. 2020. "Advanced textural characterization of biogenic silica by nitrogen physisorption, positron annihilation lifetime spectroscopy and hyperpolarized 129Xe NMR spectroscopy." Microporous and Mesoporous Materials 307, no. : 110515.
The influence of a hierarchically structured pore system of a silica sol–gel support for application as a functional component in an acetylcholinesterase‐based enzyme array, with respect to its efficiency (response time, in particular) is investigated. Careful adjustment of synthesis parameters and a novel drying method allow to prepare monolithic silica sol–gel membranes with monomodal or hierarchical pore structures. These supports enable direct comparison regarding the influence of morphological properties on maximum acetylcholinesterase (AChE) loading by a membrane and on the apparent reaction rate of the AChE‐catalyzed degradation of acetylcholine at identical enzyme loading. It is shown for the first time that the hierarchical, meso‐macroporous material is superior over the monomodal structures (of either mesopores or macropores) regarding combined functionality and transport efficiency, as reflected in the apparent reaction rates. The advantage of the mesopores in a hierarchical system is manifested in higher maximum enzyme loading than for purely macroporous material, while the presence of macropores results in less obstructed transport that for a purely mesoporous material, which in turn reduces the response time.
Richard Kohns; Nicole Anders; Dirk Enke; Ulrich Tallarek. Influence of Pore Space Hierarchy on the Efficiency of an Acetylcholinesterase‐Based Support for Biosensorics. Advanced Materials Interfaces 2020, 8, 1 .
AMA StyleRichard Kohns, Nicole Anders, Dirk Enke, Ulrich Tallarek. Influence of Pore Space Hierarchy on the Efficiency of an Acetylcholinesterase‐Based Support for Biosensorics. Advanced Materials Interfaces. 2020; 8 (4):1.
Chicago/Turabian StyleRichard Kohns; Nicole Anders; Dirk Enke; Ulrich Tallarek. 2020. "Influence of Pore Space Hierarchy on the Efficiency of an Acetylcholinesterase‐Based Support for Biosensorics." Advanced Materials Interfaces 8, no. 4: 1.
This article combines a systematic literature review on the fabrication of macroporous α-Al2O3 with increased specific surface area with recent results from our group. Publications claiming the fabrication of α-Al2O3 with high specific surface areas (HSSA) are comprehensively assessed and critically reviewed. An account of all major routes towards HSSA α-Al2O3 is given, including hydrothermal methods, pore protection approaches, dopants, anodically oxidized alumina membranes, and sol-gel syntheses. Furthermore, limitations of these routes are disclosed, as thermodynamic calculations suggest that γ-Al2O3 may be the more stable alumina modification for ABET > 175 m2/g. In fact, the highest specific surface area unobjectionably reported to date for α-Al2O3 amounts to 16–24 m2/g and was attained via a sol-gel process. In a second part, we report on some of our own results, including a novel sol-gel synthesis, designated as mutual cross-hydrolysis. Besides, the Mn-assisted α-transition appears to be a promising approach for some alumina materials, whereas pore protection by carbon filling kinetically inhibits the formation of α-Al2O3 seeds. These experimental results are substantiated by attempts to theoretically calculate and predict the specific surface areas of both porous materials and nanopowders.
Simon Carstens; Ralf Meyer; Dirk Enke. Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations. Materials 2020, 13, 1787 .
AMA StyleSimon Carstens, Ralf Meyer, Dirk Enke. Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations. Materials. 2020; 13 (7):1787.
Chicago/Turabian StyleSimon Carstens; Ralf Meyer; Dirk Enke. 2020. "Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations." Materials 13, no. 7: 1787.
Monodispersed spherical silica nanoparticles with a cubic mesostructure were synthesized in a fast and innovative way using triethanolamine (TEA) and the triblock copolymer Pluronic® F127 as particle growth inhibitors to control the particle size in a range from 420 to 62 nm. In this study, we described a synthesis of mesoporous silica nanoparticles (MSNs) with MCM-48 structure at room temperature with adequate control of particle monodispersity, shape, and size using TEA. Based on particle characterization, TEA can efficiently act as catalyst and at the same time as particle growth controlling additive. A mixture of TEA and Pluronic® F127 additives was used to obtain very small MSNs (62 nm), whereby the quality of MCM-48 silica is associated with the composition of the additives used and thus also with the final particle size. A finely dispersed and high-quality MCM-48 material with ~ 100% yield, excellent textural properties, and a particle size of 295 nm was synthesized within only 35 min using excess TEA as particle size controlling and dispersion agent together with ammonia as additional catalyst. Solvent extraction combined with ion exchange removed the surfactant efficiently. All prepared MSNs showed good textural properties, tunable particle sizes with narrow size distributions, and good dispersity in water, which make them highly promising as carriers for biomolecules in biomedical applications.
Shewaye Yismaw; Richard Kohns; Denise Schneider; David Poppitz; Stefan G. Ebbinghaus; Roger Gläser; Ulrich Tallarek; Dirk Enke. Particle size control of monodispersed spherical nanoparticles with MCM-48-type mesostructure via novel rapid synthesis procedure. Journal of Nanoparticle Research 2019, 21, 258 .
AMA StyleShewaye Yismaw, Richard Kohns, Denise Schneider, David Poppitz, Stefan G. Ebbinghaus, Roger Gläser, Ulrich Tallarek, Dirk Enke. Particle size control of monodispersed spherical nanoparticles with MCM-48-type mesostructure via novel rapid synthesis procedure. Journal of Nanoparticle Research. 2019; 21 (12):258.
Chicago/Turabian StyleShewaye Yismaw; Richard Kohns; Denise Schneider; David Poppitz; Stefan G. Ebbinghaus; Roger Gläser; Ulrich Tallarek; Dirk Enke. 2019. "Particle size control of monodispersed spherical nanoparticles with MCM-48-type mesostructure via novel rapid synthesis procedure." Journal of Nanoparticle Research 21, no. 12: 258.
This work introduces a cost and time efficient procedure to specifically increase mesopore volume and specific surface area of biogenic silica (specific surface area: 147 m2 g−1 and mesopore volume: 0.23 cm3 g−1) to make it suitable for applications in adsorption or as catalyst support. The target values were a specific surface area of ~500 m2 g−1 and a mesopore volume of ~0.40–0.50 cm3 g−1 as these values are industrially relevant and are reached by potential concurring products such as precipitated silica, silica gel, and fumed silica. The applied process of partial pseudomorphic transformation was carried out as a single reaction step in a microwave reactor instead of commonly used convective heating. In addition, the conventionally used surfactant cetyltrimethylammonium bromide (CTABr) was substituted by the low-cost surfactant (Arquad® 16-29, cetyltrimethylammonium chloride (CTACl) aqueous solution). The influence of microwave heating, type of surfactant as well as the concentration of NaOH and CTACl on the textural and structural properties of the modified biogenic silica was investigated using nitrogen adsorption as well as scanning and transmission electron microscopy. The results show that the textural parameters of the modified biogenic silica can be exactly controlled by the amount of NaOH in the reaction solution. By variation of the NaOH concentration, specific surface areas in the range of 215–1,001 m2 g−1 and mesopore volumes of 0.25–0.56 cm3 g−1 were achieved after reaction at 393 K for 10 min. The presented microwave route using the low-cost surfactant solution decreases the reaction time by 99% and as shown in an example for German prices, lowers the costs for the surfactant by 76–99%.
Denise Schneider; Ralf Kircheis; Susan Wassersleben; Wolf-Dietrich Einicke; Roger Gläser; Dirk Enke. Low-Cost Microwave-Assisted Partial Pseudomorphic Transformation of Biogenic Silica. Frontiers in Chemistry 2019, 7, 575 .
AMA StyleDenise Schneider, Ralf Kircheis, Susan Wassersleben, Wolf-Dietrich Einicke, Roger Gläser, Dirk Enke. Low-Cost Microwave-Assisted Partial Pseudomorphic Transformation of Biogenic Silica. Frontiers in Chemistry. 2019; 7 ():575.
Chicago/Turabian StyleDenise Schneider; Ralf Kircheis; Susan Wassersleben; Wolf-Dietrich Einicke; Roger Gläser; Dirk Enke. 2019. "Low-Cost Microwave-Assisted Partial Pseudomorphic Transformation of Biogenic Silica." Frontiers in Chemistry 7, no. : 575.
Surface modification of porous glass beads by ethanol-based 3-mercaptopropyltrimethoxysilane (MPTMS) grafting solutions is directly evidenced by nitrogen adsorption, elemental analysis, thermogravimetry, infrared and 29Si CP MAS NMR spectroscopy. Furthermore, the energetic characterization of the surface is essential to understand comprehensively the physico-chemical interactions between the pristine and MPTMS-modified surface and its gas/liquid-phase environment. In this study, inverse gas chromatography (IGC) is used to characterize the surface properties of porous glass (PG). By means of IGC at infinite dilution (IGC-ID), the dispersive component of the surface energy (γsd), the enthalpy and entropy of adsorption of C6-C10 hydrocarbon probes were determined at temperatures between 30 and 120 °C. The specific component of the surface energy (γssp) at the temperature of 120 °C has been obtained via the Van Oss theory and a least-squares procedure evaluating the IGC data of 8 polar probe molecules collectively. After surface silylation, the total surface energy (γst) decreased from 402 to 255 mJ/m² indicating both a reduced wettability and an increased hydrophobicity of the MPTMS-modified PG. Moreover, the acidity/basicity parameters according to the Van Oss and the Gutmann approach indicated that the acidity of the PG surface decreases by MPTMS grafting. Using n-octane and isopropanol probes, IGC at finite concentration (IGC-FC) was applied to obtain their adsorption isotherms and subsequently the BET specific surface areas. In addition, the surface heterogeneity of the studied PGs was also computed. The energy distribution functions of adsorption sites were monomodal (peak maximum at about 22 kJ/mol) for the n-octane probe, while isopropanol revealed a bimodal distribution function (maxima at about 18 and 25 kJ/mol) on both pristine and MPTMS-modified PG. Furthermore, the proportion of high energy sites (apparently assigned to Si‒OH groups) has been reduced by surface modification from 65 % to only 35 % despite a high surface coverage of ˜10 MPTMS species/nm2. These findings are in agreement with the results of 29Si CP MAS NMR measurements and are supported by DFT calculations on the adsorption of isopropanol and n-octane on the surface of a silica cluster model.
Frank Bauer; Ralf Meyer; Saskia Czihal; Marko Bertmer; Ulrich Decker; Sergej Naumov; Hans Uhlig; Martin Steinhart; Dirk Enke. Functionalization of porous siliceous materials, Part 2: Surface characterization by inverse gas chromatography. Journal of Chromatography A 2019, 1603, 297 -310.
AMA StyleFrank Bauer, Ralf Meyer, Saskia Czihal, Marko Bertmer, Ulrich Decker, Sergej Naumov, Hans Uhlig, Martin Steinhart, Dirk Enke. Functionalization of porous siliceous materials, Part 2: Surface characterization by inverse gas chromatography. Journal of Chromatography A. 2019; 1603 ():297-310.
Chicago/Turabian StyleFrank Bauer; Ralf Meyer; Saskia Czihal; Marko Bertmer; Ulrich Decker; Sergej Naumov; Hans Uhlig; Martin Steinhart; Dirk Enke. 2019. "Functionalization of porous siliceous materials, Part 2: Surface characterization by inverse gas chromatography." Journal of Chromatography A 1603, no. : 297-310.
Utilization of biomass either as a renewable energy source or for the generation of biogenic materials has received considerable interest during the past years. In the case of rice husk (RH) and rice straw (RS) with high silica contents in the fuel ash, these approaches can be combined to produce high-grade biogenic silica with purities >98 wt % from combustion residues. The overall process can be considered nearly neutral in terms of CO2 emission and global warming, but it can also address disposal challenges of rice husk and rice straw. For the resulting biogenic silica, several advanced application opportunities exist, e.g., as adsorbents, catalysts, drug delivery systems, etc. This article provides a comprehensive literature review on rice husk and rice straw combustion as well as applied strategies for raw material pre-treatment and/or post-treatment of resulting ashes to obtain high quality biogenic silica. Purity of up to 97.2 wt % SiO2 can be reached by combustion of untreated material. With appropriate fuel pre-treatment and ash post-treatment, biogenic silica with purity up to 99.7 wt % can be achieved. Studies were performed almost exclusively at a laboratory scale.
Hossein Beidaghy Dizaji; Thomas Zeng; Ingo Hartmann; Dirk Enke; Thomas Schliermann; Volker Lenz; Mehdi Bidabadi. Generation of High Quality Biogenic Silica by Combustion of Rice Husk and Rice Straw Combined with Pre- and Post-Treatment Strategies—A Review. Applied Sciences 2019, 9, 1083 .
AMA StyleHossein Beidaghy Dizaji, Thomas Zeng, Ingo Hartmann, Dirk Enke, Thomas Schliermann, Volker Lenz, Mehdi Bidabadi. Generation of High Quality Biogenic Silica by Combustion of Rice Husk and Rice Straw Combined with Pre- and Post-Treatment Strategies—A Review. Applied Sciences. 2019; 9 (6):1083.
Chicago/Turabian StyleHossein Beidaghy Dizaji; Thomas Zeng; Ingo Hartmann; Dirk Enke; Thomas Schliermann; Volker Lenz; Mehdi Bidabadi. 2019. "Generation of High Quality Biogenic Silica by Combustion of Rice Husk and Rice Straw Combined with Pre- and Post-Treatment Strategies—A Review." Applied Sciences 9, no. 6: 1083.
The separation of Pd and CeO2 on the inner surface of controlled porous glass (CPG, obtained from phase-separated borosilicate glass after extraction) yields long-term stable and highly active methane combustion catalysts. However, the limited availability of the CPG makes such catalysts highly expensive and limits their applicability. In this work, porous silica obtained from acid leached rice husks after calcination (RHS) was used as a sustainable, cheap and broadly available substitute for the above mentioned CPG. RHS-supported Pd-CeO2 with separated CeO2 clusters and Pd nanoparticles was fabricated via subsequent impregnation/calcination of molten cerium nitrate and different amounts of palladium nitrate solution. The Pd/CeO2/RHS catalysts were employed for the catalytic methane combustion in the temperature range of 150–500 °C under methane lean conditions (1000 ppm) in a simulated off-gas consisting of 9.0 vol% O2, and 5.5 vol% CO2 balanced with N2. Additionally, tests with 10.5 vol% H2O as co-feed were carried out. The results revealed that the RHS-supported catalysts reached the performance of the cost intensive benchmark catalyst based on CPG. The incorporation of Pd-CeO2 into RHS additionally improved water-resistance compared to solely Pd/CeO2 lowering the required temperature for methane combustion in presence of 10.5 vol% H2O to values significantly below 500 °C (T90 = 425 °C).
Dongjing Liu; Dominik Seeburg; Stefanie Kreft; René Bindig; Ingo Hartmann; Denise Schneider; Dirk Enke; Sebastian Wohlrab. Rice Husk Derived Porous Silica as Support for Pd and CeO2 for Low Temperature Catalytic Methane Combustion. Catalysts 2019, 9, 26 .
AMA StyleDongjing Liu, Dominik Seeburg, Stefanie Kreft, René Bindig, Ingo Hartmann, Denise Schneider, Dirk Enke, Sebastian Wohlrab. Rice Husk Derived Porous Silica as Support for Pd and CeO2 for Low Temperature Catalytic Methane Combustion. Catalysts. 2019; 9 (1):26.
Chicago/Turabian StyleDongjing Liu; Dominik Seeburg; Stefanie Kreft; René Bindig; Ingo Hartmann; Denise Schneider; Dirk Enke; Sebastian Wohlrab. 2019. "Rice Husk Derived Porous Silica as Support for Pd and CeO2 for Low Temperature Catalytic Methane Combustion." Catalysts 9, no. 1: 26.
The front cover artwork for issue 24/2018 is provided by scientists at the Universität Leipzig, Max Planck Institute of Colloids and Interfaces, and Institute for Non‐Classical Chemistry e. V. (Germany). The image illustrates the use of IR microimaging for monitoring the mean concentration of both reactant and product molecules within a catalyst particle during a chemical reaction, allowing the one‐shot determination of its effectiveness factor. The front cover idea and design by Alaa Al‐Naji is greatly acknowledged. See the Full Paper itself at https://doi.org/10.1002/cctc.201801530.
Christian Chmelik; Michael Liebau; Majd Al-Naji; Jens Möllmer; Dirk Enke; Roger Gläser; Jörg Kärger. One-Shot Measurement of Effectiveness Factors of Chemical Conversion in Porous Catalysts. ChemCatChem 2018, 10, 5553 -5553.
AMA StyleChristian Chmelik, Michael Liebau, Majd Al-Naji, Jens Möllmer, Dirk Enke, Roger Gläser, Jörg Kärger. One-Shot Measurement of Effectiveness Factors of Chemical Conversion in Porous Catalysts. ChemCatChem. 2018; 10 (24):5553-5553.
Chicago/Turabian StyleChristian Chmelik; Michael Liebau; Majd Al-Naji; Jens Möllmer; Dirk Enke; Roger Gläser; Jörg Kärger. 2018. "One-Shot Measurement of Effectiveness Factors of Chemical Conversion in Porous Catalysts." ChemCatChem 10, no. 24: 5553-5553.
The proposed scheme enables academic laboratories to prepare hierarchical silica monoliths as continuous-flow microreactors for kinetic studies in heterogeneous catalysis.
Richard Kohns; Christian P. Haas; Alexandra Höltzel; Christian Splith; Dirk Enke; Ulrich Tallarek. Hierarchical silica monoliths with submicron macropores as continuous-flow microreactors for reaction kinetic and mechanistic studies in heterogeneous catalysis. Reaction Chemistry & Engineering 2018, 3, 353 -364.
AMA StyleRichard Kohns, Christian P. Haas, Alexandra Höltzel, Christian Splith, Dirk Enke, Ulrich Tallarek. Hierarchical silica monoliths with submicron macropores as continuous-flow microreactors for reaction kinetic and mechanistic studies in heterogeneous catalysis. Reaction Chemistry & Engineering. 2018; 3 (3):353-364.
Chicago/Turabian StyleRichard Kohns; Christian P. Haas; Alexandra Höltzel; Christian Splith; Dirk Enke; Ulrich Tallarek. 2018. "Hierarchical silica monoliths with submicron macropores as continuous-flow microreactors for reaction kinetic and mechanistic studies in heterogeneous catalysis." Reaction Chemistry & Engineering 3, no. 3: 353-364.
Enhancing the activity and stability of catalysts is a major challenge in scientific research nowadays. Previous studies showed that the generation of an additional pore system can influence the catalytic performance of porous catalysts regarding activity, selectivity, and stability. This study focuses on the epoxide-mediated sol-gel synthesis of mixed metal oxides, NiAl2O4 and CoAl2O4, with a spinel phase structure, a hierarchical pore structure, and Ni and Co contents of 3 to 33 mol % with respect to the total metal content. The sol-gel process is accompanied by a polymerization-induced phase separation to introduce an additional pore system. The obtained mixed metal oxides were characterized with regard to pore morphology, surface area, and formation of the spinel phase. The Brunauer-Emmett-Teller surface area ranges from 74 to 138 m2·g-1 and 25 to 94 m2·g-1 for Ni and Co, respectively. Diameters of the phase separation-based macropores were between 500 and 2000 nm, and the mesopore diameters were 10 nm for the Ni-based system and between 20 and 25 nm for the cobalt spinels. Furthermore, Ni-Al spinels with 4, 5, and 6 mol % Ni were investigated in the dry reforming of CH4 (DRM) with CO2 to produce H2 and CO. CH4 conversions near the thermodynamic equilibrium were observed depending on the Ni content and reaction temperature. The Ni catalysts were further compared to a noble metal-containing catalyst based on a spinel system showing comparable CH4 conversion and carbon selectivity in the DRM.
Jan Herwig; Juliane Titus; Jens Kullmann; Nicole Wilde; Thomas Hahn; Roger Gläser; Dirk Enke. Hierarchically Structured Porous Spinels via an Epoxide-Mediated Sol–Gel Process Accompanied by Polymerization-Induced Phase Separation. ACS Omega 2018, 3, 1201 -1212.
AMA StyleJan Herwig, Juliane Titus, Jens Kullmann, Nicole Wilde, Thomas Hahn, Roger Gläser, Dirk Enke. Hierarchically Structured Porous Spinels via an Epoxide-Mediated Sol–Gel Process Accompanied by Polymerization-Induced Phase Separation. ACS Omega. 2018; 3 (1):1201-1212.
Chicago/Turabian StyleJan Herwig; Juliane Titus; Jens Kullmann; Nicole Wilde; Thomas Hahn; Roger Gläser; Dirk Enke. 2018. "Hierarchically Structured Porous Spinels via an Epoxide-Mediated Sol–Gel Process Accompanied by Polymerization-Induced Phase Separation." ACS Omega 3, no. 1: 1201-1212.
Pre-shaped mesoporous amorphous rice husk ash (RHA) and MCM-41 derived from RHA as a silica source were transformed into MFI-type zeolites using two different structure-directing agents. Tetrapropylammonium hydroxide (TPAOH) was utilized as an alkali source for silica dissolution and structure control during the direct transformation of RHA into zeolite. A monopropylamine (PA)-containing alkaline solution (NaOH) was used for the pseudomorphic transformation of RHA or MCM-41 into zeolite. The hydrothermal conversion of RHA or MCM-41 into MFI-type zeolites was investigated as a function of reaction time at 175 °C. With PA as template, the crystallization took place inside and on the outer surface of RHA or MCM-41 without losing the original shape of the initial silica sources, while TPAOH led to the formation of conventional MFI-type zeolite crystals due to the complete dissolution of RHA. The final products were characterized by X-ray diffraction, nitrogen adsorption, scanning electron microscopy, and optical emission spectroscopy.
Hallah Ahmad Alyosef; Hans Roggendorf; Denise Schneider; Alexandra Inayat; Julia Welscher; Wilhelm Schwieger; Tom Münster; Gert Kloess; Suzan Ibrahim; Dirk Enke. Comparative Study between Direct and Pseudomorphic Transformation of Rice Husk Ash into MFI-Type Zeolite. Molecules 2017, 23, 1 .
AMA StyleHallah Ahmad Alyosef, Hans Roggendorf, Denise Schneider, Alexandra Inayat, Julia Welscher, Wilhelm Schwieger, Tom Münster, Gert Kloess, Suzan Ibrahim, Dirk Enke. Comparative Study between Direct and Pseudomorphic Transformation of Rice Husk Ash into MFI-Type Zeolite. Molecules. 2017; 23 (1):1.
Chicago/Turabian StyleHallah Ahmad Alyosef; Hans Roggendorf; Denise Schneider; Alexandra Inayat; Julia Welscher; Wilhelm Schwieger; Tom Münster; Gert Kloess; Suzan Ibrahim; Dirk Enke. 2017. "Comparative Study between Direct and Pseudomorphic Transformation of Rice Husk Ash into MFI-Type Zeolite." Molecules 23, no. 1: 1.
Characterization of mesoporous materials today is routinely performed recording the adsorption isotherm of nitrogen at 77 K. The pore size distribution (PSD) can subsequently be determined using either thermodynamics or statistical mechanics based approaches. While nitrogen has evolved as the reference adsorptive, other gases are often used to extract more information from the isotherm. This contribution is focused on the calculation of a PSD from the water vapor isotherm. It is demonstrated that water adsorption provides accurate results comparable to the standard nitrogen adsorption.
Nikolaj Georgi; Andrei Kolesnikov; Hans Uhlig; Jens Möllmer; Michael Rückriem; Andreas Schreiber; Jürgen Adolphs; Dirk Enke; Roger Gläser. Characterization of Porous Silica Materials with Water at Ambient Conditions. Calculating the Pore Size Distribution from the Excess Surface Work Disjoining Pressure Model. Chemie Ingenieur Technik 2017, 89, 1679 -1685.
AMA StyleNikolaj Georgi, Andrei Kolesnikov, Hans Uhlig, Jens Möllmer, Michael Rückriem, Andreas Schreiber, Jürgen Adolphs, Dirk Enke, Roger Gläser. Characterization of Porous Silica Materials with Water at Ambient Conditions. Calculating the Pore Size Distribution from the Excess Surface Work Disjoining Pressure Model. Chemie Ingenieur Technik. 2017; 89 (12):1679-1685.
Chicago/Turabian StyleNikolaj Georgi; Andrei Kolesnikov; Hans Uhlig; Jens Möllmer; Michael Rückriem; Andreas Schreiber; Jürgen Adolphs; Dirk Enke; Roger Gläser. 2017. "Characterization of Porous Silica Materials with Water at Ambient Conditions. Calculating the Pore Size Distribution from the Excess Surface Work Disjoining Pressure Model." Chemie Ingenieur Technik 89, no. 12: 1679-1685.
Surface modification of mesoporous biogenic silica (rice husk ash) by aqueous and ethanol-based 3-aminopropyltriethoxysilane (APTES) grafting solutions has been investigated using 29Si NMR, ESI-MS, TGA, surface-sensitive NH2 titration, and DFT method. Prior to grafting, a rapid formation of ladder-like aminosilane oligomers has been observed in both solvents limiting the grafting time for the mostly desired formation of a monomolecular organosilane layer to few minutes. An excess of water yielded a long-term stable equilibrium between the oligomerized APTES species within the grafting solution promising a reproducible surface modification. After curing at 120 °C, washing studies showed that these oligomeric aminosilane clusters have been successfully grafted but yielding a heterogeneous surface morphology with even pore blocking rather than a dense, uniform aminosilane monolayer. In addition, the optimized structures of three different grafting modes between APTES and a silica cluster model were obtained by DFT calculations. The results indicated that bond lengths and angles of the different grafting modes reveal no substantial structural distortions. Nevertheless, the ladder-like grafting mode is given preferential consideration because the DFT results are in accordance with the ESI-MS and 29Si NMR findings.
Frank Bauer; Saskia Czihal; Marko Bertmer; Ulrich Decker; Sergej Naumov; Susan Wassersleben; Dirk Enke. Water-based functionalization of mesoporous siliceous materials, Part 1: Morphology and stability of grafted 3-aminopropyltriethoxysilane. Microporous and Mesoporous Materials 2017, 250, 221 -231.
AMA StyleFrank Bauer, Saskia Czihal, Marko Bertmer, Ulrich Decker, Sergej Naumov, Susan Wassersleben, Dirk Enke. Water-based functionalization of mesoporous siliceous materials, Part 1: Morphology and stability of grafted 3-aminopropyltriethoxysilane. Microporous and Mesoporous Materials. 2017; 250 ():221-231.
Chicago/Turabian StyleFrank Bauer; Saskia Czihal; Marko Bertmer; Ulrich Decker; Sergej Naumov; Susan Wassersleben; Dirk Enke. 2017. "Water-based functionalization of mesoporous siliceous materials, Part 1: Morphology and stability of grafted 3-aminopropyltriethoxysilane." Microporous and Mesoporous Materials 250, no. : 221-231.
Micelle-templated silica (MTS)-composites with flexible macroscopic shape, monomodal or bimodal (hierarchical) pore structure, and high mechanical stability can be prepared by partial or complete pseudomorphic transformation of porous glasses (PG). The state of research concerning synthesis, transformation mechanism, characterization, and application of MTS/PG-composites is reviewed and the investigation of the transformation products by 129Xe NMR spectroscopy and the direct synthesis of Al-MCM-41/PG-composites are introduced. Finally, several approaches like a double-templating strategy for pore protection is shown.
Hans Uhlig; Julia Hollenbach; Matthias Rogaczewski; Jörg Matysik; Felix J. Brieler; Michael Fröba; Dirk Enke. Pseudomorphic Transformation of Porous Glasses into Micelle-Templated Silica. Chemie Ingenieur Technik 2017, 89, 863 -875.
AMA StyleHans Uhlig, Julia Hollenbach, Matthias Rogaczewski, Jörg Matysik, Felix J. Brieler, Michael Fröba, Dirk Enke. Pseudomorphic Transformation of Porous Glasses into Micelle-Templated Silica. Chemie Ingenieur Technik. 2017; 89 (7):863-875.
Chicago/Turabian StyleHans Uhlig; Julia Hollenbach; Matthias Rogaczewski; Jörg Matysik; Felix J. Brieler; Michael Fröba; Dirk Enke. 2017. "Pseudomorphic Transformation of Porous Glasses into Micelle-Templated Silica." Chemie Ingenieur Technik 89, no. 7: 863-875.
On-line control and monitoring in heterogeneous catalysis utilizing high-performance supports allows rapid screening of intrinsic reaction parameters in continuous-flow mode.
Christian P. Haas; Tibor Müllner; Richard Kohns; Dirk Enke; Ulrich Tallarek. High-performance monoliths in heterogeneous catalysis with single-phase liquid flow. Reaction Chemistry & Engineering 2017, 2, 498 -511.
AMA StyleChristian P. Haas, Tibor Müllner, Richard Kohns, Dirk Enke, Ulrich Tallarek. High-performance monoliths in heterogeneous catalysis with single-phase liquid flow. Reaction Chemistry & Engineering. 2017; 2 (4):498-511.
Chicago/Turabian StyleChristian P. Haas; Tibor Müllner; Richard Kohns; Dirk Enke; Ulrich Tallarek. 2017. "High-performance monoliths in heterogeneous catalysis with single-phase liquid flow." Reaction Chemistry & Engineering 2, no. 4: 498-511.