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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Metallic hierarchical aerogels for electrocatalytic applications

Cai, Bin 09 November 2017 (has links) (PDF)
Progress in nanotechnology has promoted an increasing interest in the rational design of the emerging hierarchical aerogels, which represents a second stage of the NC-based aerogel research. By fine-tuning the surface properties of the backbones, metallic hierarchical aerogels are able to address the growing demands of advanced electrocatalysts. In this dissertation, three types of metallic hierarchical aerogels were designed by introducing different nanostructures (i.e. hollow, porous/dendritic and core-shell) and alloy effects (with noble or transition metals) into the aerogels. Thus, as a proof-of-concept for fuel cells, advanced electrocatalytic performances have been achieved on the resulting metallic hierarchical aerogels towards both anode (oxidation of ethanol) and cathode (reduction of oxygen) reactions. First, alloyed PdxNi hollow nanospheres with controlled composition and shell thickness were utilized as building blocks for the design of hierarchical aerogels. The combination of transition-metal doping, hollow interior, as well as the 3D aerogel structure make the resulting aerogels promising electrocatalysts for ethanol oxidation with a mass activity up to 5.6-fold higher than that of the Pd/C. Second, continuously shape-engineering of the building blocks (ranging from hollow shells to dendritic shapes) was achieved by the synthesis of a series of multimetallic Ni-PdxPty hierarchical aerogels. By optimization of the nanoscale morphology and the chemical composition, the Ni-Pd60Pt40 aerogel exhibits remarkable electrocatalytic activity for oxidation of ethanol. Moreover, the particle growth mechanism underlying the galvanic replacement was revealed in terms of nanowelding of the nanoparticulate reaction intermediates based on experimental and theoretical results. Third, a universal approach was demonstrated for core-shell structuring of metallic aerogels by coating of an ultrathin Pt shell on a composition-tunable Pd-based alloyed core. Their activities for oxygen reduction exhibit a volcano-type relationship as a function of the lattice parameter of the core substrate. Largely improved Pt utilization efficiency was accomplished based on the core-shell motifs, as the mass activity reaches 5.25 A mg-1Pt which are 18.7 times higher than those of Pt/C. Different from the conventional aerogels with nanowire-like backbones, those hierarchical aerogels are generally comprised of at least two levels of architectures, i.e. an interconnected porous structure on the macroscale and a specially designed configuration at local backbones at the nanoscale. This combination “locks in” the inherent properties of the NCs, so that the beneficial genes obtained by nano-engineering are retained in the resulting monolithic hierarchical aerogels. These results expand the exploitation approach of the electrocatalytic properties of aerogels into morphology control of their NBBs and are of great importance for the future development of aerogels for many other electrochemical reactions.
12

Metallic hierarchical aerogels for electrocatalytic applications

Cai, Bin 25 September 2017 (has links)
Progress in nanotechnology has promoted an increasing interest in the rational design of the emerging hierarchical aerogels, which represents a second stage of the NC-based aerogel research. By fine-tuning the surface properties of the backbones, metallic hierarchical aerogels are able to address the growing demands of advanced electrocatalysts. In this dissertation, three types of metallic hierarchical aerogels were designed by introducing different nanostructures (i.e. hollow, porous/dendritic and core-shell) and alloy effects (with noble or transition metals) into the aerogels. Thus, as a proof-of-concept for fuel cells, advanced electrocatalytic performances have been achieved on the resulting metallic hierarchical aerogels towards both anode (oxidation of ethanol) and cathode (reduction of oxygen) reactions. First, alloyed PdxNi hollow nanospheres with controlled composition and shell thickness were utilized as building blocks for the design of hierarchical aerogels. The combination of transition-metal doping, hollow interior, as well as the 3D aerogel structure make the resulting aerogels promising electrocatalysts for ethanol oxidation with a mass activity up to 5.6-fold higher than that of the Pd/C. Second, continuously shape-engineering of the building blocks (ranging from hollow shells to dendritic shapes) was achieved by the synthesis of a series of multimetallic Ni-PdxPty hierarchical aerogels. By optimization of the nanoscale morphology and the chemical composition, the Ni-Pd60Pt40 aerogel exhibits remarkable electrocatalytic activity for oxidation of ethanol. Moreover, the particle growth mechanism underlying the galvanic replacement was revealed in terms of nanowelding of the nanoparticulate reaction intermediates based on experimental and theoretical results. Third, a universal approach was demonstrated for core-shell structuring of metallic aerogels by coating of an ultrathin Pt shell on a composition-tunable Pd-based alloyed core. Their activities for oxygen reduction exhibit a volcano-type relationship as a function of the lattice parameter of the core substrate. Largely improved Pt utilization efficiency was accomplished based on the core-shell motifs, as the mass activity reaches 5.25 A mg-1Pt which are 18.7 times higher than those of Pt/C. Different from the conventional aerogels with nanowire-like backbones, those hierarchical aerogels are generally comprised of at least two levels of architectures, i.e. an interconnected porous structure on the macroscale and a specially designed configuration at local backbones at the nanoscale. This combination “locks in” the inherent properties of the NCs, so that the beneficial genes obtained by nano-engineering are retained in the resulting monolithic hierarchical aerogels. These results expand the exploitation approach of the electrocatalytic properties of aerogels into morphology control of their NBBs and are of great importance for the future development of aerogels for many other electrochemical reactions.
13

Self – supporting Hierarchical Porous PtAg Alloy Nanotubular Aerogels as Highly Active and Durable Electrocatalysts

Eychmüller, Alexander, Liu, Wei, Haubold, Danny, Rutkowski, Bogdan, Oschatz, Martin, Hübner, Rene, Werheid, Matthias, Ziegler, Christoph, Sonntag, Luisa, Lin, Shaohua, Herrmann, Anne-Kristin, Geiger, Dorin, Terlan, Bürgehan, Gemming, Thomas, Borchardt, Lars, Kaskel, Stefan, Czyrska-Filemonowicz, Alexandra 28 September 2018 (has links)
Developing electrocatalysts with low cost, high activity, and good durability is urgently demanded for the wide commercialization of fuel cells. By taking advantage of nanostructure engineering, we fabricated PtAg nanotubular aerogels (NTAGs) with high electrocatalytic activity and good durability via a simple galvanic replacement reaction between the in situ spontaneous gelated Ag hydrogel and the Pt precursor. The PtAg NTAGs have hierarchical porous network features with primary networks and pores from the interconnected nanotubes of the aerogel and secondary networks and pores from the inter-connected thin nanowires on the nanotube surface, and show very high porosities and large specific surface areas. Due to the unique structure, the PtAg NTAGs exhibit greatly enhanced electrocatalytic activity towards formic acid oxidation, reaching 19 times higher metal based mass current density as compared to the commercial Pt black. Furthermore, the PtAg NTAGs show outstanding structural stability and electrochemical durability during the electrocatalysis. Noble metal based NTAGs are promising candidates for applications in electrocatalysis not only for fuel cells, but also for other energy related systems.
14

Characterization of Methyltrimethoxysilane Sol-Gel Polymerization and the Resulting Aerogels.

Dong, Hanjiang 08 1900 (has links)
Methyl-functionalized porous silica is of considerable interest as a low dielectric constant film for semiconductor devices. The structural development of these materials appears to affect their gelation behaviors and impact their mechanical properties and shrinkage during processing. 29Si solution NMR was used to follow the structural evolution of MTMS (methyltrimethoxysilane) polymerization to gelation or precipitation, and thus to better understand the species that affect these properties and gelation behaviors. The effects of pH, water concentration, type of solvents, and synthesis procedures (single step acid catalysis and two-step acid/base catalysis) on MTMS polymerization were discussed. The reactivity of silicon species with different connectivity and the extent of cyclization were found to depend appreciably on the pH value of the sol. A kinetic model is presented to treat the reactivity of both silicon species involved in condensations separately based on the inductive and steric effects of these silicon species. Extensive cyclization in the presence of acid, which was attributed to the steric effects among numerous reaction pathways for the first time, prevents MTMS gelation, whereas gels were obtained from the two-step method with nearly random condensations. The experimental degree of condensation (DC) at the gel point using the two-step procedure was determined to be 0.86, which is considerably higher than that predicted by the current accepted theories. Both chemical and physical origins of this high value were suggested. Aerogels dried by supercritical CO2 extraction were characterized by FTIR, 13C and 29Si solid-state NMR and nitrogen sorption. The existence of three residual groups (Si-OH, Si-OCH3, and Si-OC2H5) was confirmed, but their concentrations are very low compared to silica aerogels. The low concentrations of the residual groups, along with the presence of Si-CH3, make MTMS aerogels permanently hydrophobic. To enhance applicability, MTMS aerogels were successfully prepared that demonstrated shrinkage less than 10% after supercritical drying; proving that the rigidity of the gel network is not the sole factor, suggesting in the literature, to cause the huge shrinkage in many hybrid aerogels reported. An important finding of this work is that MTMS aerogels can be prepared without tedious solvent exchange and surface modification if the molar ratio of water/MTMS increases to 8, substantially reducing the cost of aerogel production. This result was attributed to MTMS's fully condensation and low concentrations of ring species.
15

SILICA AEROGEL-POLYMER NANOCOMPOSITES AND NEW NANOPARTICLE SYNTHESES

Boday, Dylan Joseph January 2009 (has links)
Aerogels are extremely high surface area, low density materials with applications including thermal and acoustic insulators, radiation detectors and cometary dust particle traps. However, their low density and aggregate structure makes them extremely fragile and practically impossible to machine or handle without breaking. This has led to the development of aerogel composites with enhanced mechanical properties through the addition of polymers or surface modifiers. To date, attempts to strengthen aerogels have come with significant increases in density and processing time. Here I will describe our search for a solution to these problems with our invention using methyl cyanoacrylate chemical vapor deposition (CVD) to strengthen silica, aminated silica and bridged polysilsesquioxane aerogels. This approach led to a strength improvement of the composites within hours and the strongest composite prepared had a 100x strength improvement over the precursor aerogel. We also developed the first approach to control the molecular weight of the polymers that reinforce silica aerogels using surface-initiated atom transfer radical polymerization (SI-ATRP). Although PMMA reinforcement of silica aerogels improved the mechanical properties, further strength improvements were achieved by cross-linking the grafted PMMA. Additionally, we developed the first silica aerogels reinforced with polyaniline nanofibers that were strong and electrically conductive. Reinforcing silica aerogels with polyaniline allowed them to be used as a sensor for the detection of protonating and deprotonating gaseous species. Finally we developed a new approach for the synthesis of silica and bridged polysilsesquioxane spheres using a surfactant free synthesis. This approach allowed for the first in-situ incorporation of base sensitive functionalities during the sol-gel polymerization.
16

Produção de aerogel a partir de nanofibras de celulose obtidas de resíduos da indústria moveleira (Pinus elliottii var. elliottii) para sorção de óleos

Oliveira, Pablo Beluck de 01 November 2017 (has links)
O petróleo é uma matéria-prima de grande valor econômico. Buscando a substituição de matérias-primas não-renováveis, óleos vegetais vêm sendo usados cada vez mais como matéria-prima para combustíveis e polímeros. Derramamentos durante o manuseio de óleos são graves problemas ambientais. Fibras vegetais são usadas há muito tempo para a sorção de óleos em derramamentos. Resíduos de madeira na forma de serragem já são usados como sorventes de óleos, sendo um recurso barato e disponível. Entretanto, as características hidrofílicas das fibras vegetais reduzem sua capacidade de sorção de óleos. Os aerogéis de celulose tornaram-se um produto de grande interesse nessa área devido à sua alta porosidade (95 a 99%), baixa massa específica (0,004 to 0,15 g.cm-3) e alta área superficial (>60,m².g-1), além da abundância e sustentabilidade da celulose. O objetivo deste trabalho foi desenvolver um aerogel hidrofóbico de nanofibras de celulose a partir de resíduos da indústria moveleira (Pinus elliottii var. elliottii) processados por hidrólise ácida com explosão a vapor para a sorção de petróleo e óleos vegetais. No processo de explosão a vapor a melhor condição experimental foi observada para uma razão volumétrica de ácido acético e ácido nítrico 15:2:1 a 120°C e 30 minutos com rendimento superior a 90% em celulose e a remoção completa da hemicelulose e da lignina. Após a liofilização foi obtido um aerogel com massa específica 0,046 0,0013 g.cm-3 e porosidade 97,08 0,08%. A hidrofobização do aerogel gerou um ângulo de contato de 138,78º 0,78º. O aerogel mostrou capacidade de sorção máxima experimental (CSME) de 19,55 0,10 góleo.gaerogel-1 para petróleo e 13,73 0,62 góleo.gaerogel-1 para o óleo vegetal. A produção de nanofibras de celulose deu-se através de meios físicos (moagem) e a hidrofobização foi efetuada por modificação superficial das fibras com organosilanos (MTMS) por deposição a vapor. Na hidrólise do resíduo da indústria moveleira dois reagentes ácidos (ácido acético e ácido nítrico) foram testados individual e simultaneamente, com variações de temperatura, tempos e quantidade de reagente. A fração sólida rica em celulose obtida foi cominuída em moinho de pedras por 5 horas a 2500 rpm em uma suspensão com 1,5% m/m. O gel obtido foi congelado por 48 horas a -20ºC para posterior liofilização a -40ºC por 50 horas. Os aerogéis obtidos na liofilização foram tratados com o organosilano via deposição em fase vapor por 5 horas a 70ºC. O resíduo da indústria moveleira foi caracterizado quanto ao teor de celulose, hemicelulose, lignina, cinzas, extrativos e umidade. O processo de explosão a vapor foi caracterizado através do rendimento individual dos seus componentes (celulose e hemicelulose). Ensaios de massa específica aparente, ângulo de contato, porosidade, caracterização morfológica por microscopia eletrônica de varredura de emissão de campo, ensaios de sorção de óleos e cinética de sorção em meio homogêneo e heterogêneo de sorção de petróleo e óleo de soja foram realizados para caracterizar o aerogel. Modelos cinéticos de pseudoprimeira, pseudossegunda e pseudoenésima ordem foram ajustados aos dados experimentais em suas formas lineares e não-lineares. A sorção em meio homogêneo de petróleo foi bem ajustada com o modelo linear de pseudoprimeira ordem. A sorção de óleo vegetal foi bem ajustada tanto pelo modelo de pseudoprimeira ordem quanto pelo modelo de pseudossegunda ordem. Os modelos na forma não-linear indicaram um melhor ajuste dos dados experimentais pelo modelo de pseudoenésima ordem (n=0,95) para o petróleo e pelo modelo de pseudoprimeira ordem para o óleo vegetal. Os ajustes cinéticos mostraram que em meio heterogêneo a CSME se mantém constante em relação ao meio homogêneo, mas foi observada uma menor taxa de sorção. / Submitted by cmquadros@ucs.br (cmquadros@ucs.br) on 2018-02-01T18:30:09Z No. of bitstreams: 1 Dissertacao Pablo Beluck de Oliveira.pdf: 3113740 bytes, checksum: c1c0b51adf3c34f0f55f7579081223d8 (MD5) / Made available in DSpace on 2018-02-01T18:30:10Z (GMT). No. of bitstreams: 1 Dissertacao Pablo Beluck de Oliveira.pdf: 3113740 bytes, checksum: c1c0b51adf3c34f0f55f7579081223d8 (MD5) Previous issue date: 2018-02-01 / Ministério do Trabalho e Emprego, MTE. / Petroleum is a feedstock of great economic value. Due to the aim for non-renewable feedstocks substitution, vegetable oils have been used ever more as a feedstock for fuels and polymers. Spills during oil handling are serious environmental problems. Vegetable fibers have been used for a long time now as oil sorbents during spills. Wood residues as sawdust are currently used as oil sorbents, being a cheap and available resource. However, the hydrophilic profile of vegetable fibers reduce their capacity of oil sorption. Cellulose aerogels have become a product of great interest in the oil spill remediation field due to their high porosity (95 to 99%), low specific mass (0,004 to 0,15 g.cm-3) and high surface area (>60,m².g-1), besides cellulose abundance and sustainability. The objective of this work was to develop a hydrophobic aerogel from nanocellulose nanofibers obtained from furniture industry residues (Pinus elliottii var. elliottii) processed via steam explosion acid hydrolysis for petroleum and vegetable oil sorption. In the steam explosion process the best experimental condition was observed for a volumetric acetic acid and nitric acid ratio of 15:2:1 at 120ºC and 30 minutes with a cellulose yield higher than 90% and complete removal of hemicellulose and ligning. After lyophilization an aerogel of specific mass 0,046 0,0013 g.cm-3 and porosity 97,08 0,08% was obtained. Aerogel hydrophobization yielded a contact angle of 138,78º 0,78º. The aerogel exhibited a top experimental sorption capacity (CSME) of 19,55 0,10 goil.gaerogel-1 for petroleum and 13,73 0,62 goil.gaerogel-1 for vegetable oil. Cellulose nanofibers were produced by physical means (grinding) and hydrophobization was accomplished via vapor-phase deposition of organosilane (MTMS). In wood residue hydrolysis two acids were tested (nitric acid and acetic acid) simultaneously and individually, with variations of temperature, time and reagent amount. The solid fraction rich in cellulose was grinded in a rock mill for 5 hours at 2500 rpm in a 1,5% m/m suspension in water. The obtained gel was frozen for 48 hours at -20ºC for lyophilization at -40ºC for 50 hours. The aerogels obtained by lyophilization were treated with organosilane via vapor-phase deposition for 5 hours at 70ºC. The furniture industry residue was characterized as for its amounts of cellulose, hemicellulose, lignin, ashes, extractives and humidity. The process of steam explosion was characterized through the yields of individual components (cellulose and hemicellulose). Procedures like specific mass, contact angle, porosity, morphological characterization by scanning electron microscope with field emission gun, oil absorption tests and absorption kinetic in homogeneous and heterogeneous medium of petroleum and soy oil absorption were performed to characterize the aerogel. Kinetic models of pseudo-first, pseudo-second and pseudo-nth order were fitted to experimental data in their linear and non-linear forms. The absorption in homogeneous medium of petroleum was well fitted by pseudo-first linear kinetic model. Absorption of vegetable oil was well fitted by both pseudo-first and pseudo-second models. Models in non-linear form indicated a better fit for experimental data by the pseudo-nth order model (n=0,95) for petroleum and by pseudo-first order for vegetable oil. Kinetic adjusts showed that in heterogeneous medium CSME is maintained, but sorption rate is smaller.
17

Produção de aerogel a partir de nanofibras de celulose obtidas de resíduos da indústria moveleira (Pinus elliottii var. elliottii) para sorção de óleos

Oliveira, Pablo Beluck de 01 November 2017 (has links)
O petróleo é uma matéria-prima de grande valor econômico. Buscando a substituição de matérias-primas não-renováveis, óleos vegetais vêm sendo usados cada vez mais como matéria-prima para combustíveis e polímeros. Derramamentos durante o manuseio de óleos são graves problemas ambientais. Fibras vegetais são usadas há muito tempo para a sorção de óleos em derramamentos. Resíduos de madeira na forma de serragem já são usados como sorventes de óleos, sendo um recurso barato e disponível. Entretanto, as características hidrofílicas das fibras vegetais reduzem sua capacidade de sorção de óleos. Os aerogéis de celulose tornaram-se um produto de grande interesse nessa área devido à sua alta porosidade (95 a 99%), baixa massa específica (0,004 to 0,15 g.cm-3) e alta área superficial (>60,m².g-1), além da abundância e sustentabilidade da celulose. O objetivo deste trabalho foi desenvolver um aerogel hidrofóbico de nanofibras de celulose a partir de resíduos da indústria moveleira (Pinus elliottii var. elliottii) processados por hidrólise ácida com explosão a vapor para a sorção de petróleo e óleos vegetais. No processo de explosão a vapor a melhor condição experimental foi observada para uma razão volumétrica de ácido acético e ácido nítrico 15:2:1 a 120°C e 30 minutos com rendimento superior a 90% em celulose e a remoção completa da hemicelulose e da lignina. Após a liofilização foi obtido um aerogel com massa específica 0,046 0,0013 g.cm-3 e porosidade 97,08 0,08%. A hidrofobização do aerogel gerou um ângulo de contato de 138,78º 0,78º. O aerogel mostrou capacidade de sorção máxima experimental (CSME) de 19,55 0,10 góleo.gaerogel-1 para petróleo e 13,73 0,62 góleo.gaerogel-1 para o óleo vegetal. A produção de nanofibras de celulose deu-se através de meios físicos (moagem) e a hidrofobização foi efetuada por modificação superficial das fibras com organosilanos (MTMS) por deposição a vapor. Na hidrólise do resíduo da indústria moveleira dois reagentes ácidos (ácido acético e ácido nítrico) foram testados individual e simultaneamente, com variações de temperatura, tempos e quantidade de reagente. A fração sólida rica em celulose obtida foi cominuída em moinho de pedras por 5 horas a 2500 rpm em uma suspensão com 1,5% m/m. O gel obtido foi congelado por 48 horas a -20ºC para posterior liofilização a -40ºC por 50 horas. Os aerogéis obtidos na liofilização foram tratados com o organosilano via deposição em fase vapor por 5 horas a 70ºC. O resíduo da indústria moveleira foi caracterizado quanto ao teor de celulose, hemicelulose, lignina, cinzas, extrativos e umidade. O processo de explosão a vapor foi caracterizado através do rendimento individual dos seus componentes (celulose e hemicelulose). Ensaios de massa específica aparente, ângulo de contato, porosidade, caracterização morfológica por microscopia eletrônica de varredura de emissão de campo, ensaios de sorção de óleos e cinética de sorção em meio homogêneo e heterogêneo de sorção de petróleo e óleo de soja foram realizados para caracterizar o aerogel. Modelos cinéticos de pseudoprimeira, pseudossegunda e pseudoenésima ordem foram ajustados aos dados experimentais em suas formas lineares e não-lineares. A sorção em meio homogêneo de petróleo foi bem ajustada com o modelo linear de pseudoprimeira ordem. A sorção de óleo vegetal foi bem ajustada tanto pelo modelo de pseudoprimeira ordem quanto pelo modelo de pseudossegunda ordem. Os modelos na forma não-linear indicaram um melhor ajuste dos dados experimentais pelo modelo de pseudoenésima ordem (n=0,95) para o petróleo e pelo modelo de pseudoprimeira ordem para o óleo vegetal. Os ajustes cinéticos mostraram que em meio heterogêneo a CSME se mantém constante em relação ao meio homogêneo, mas foi observada uma menor taxa de sorção. / Ministério do Trabalho e Emprego, MTE. / Petroleum is a feedstock of great economic value. Due to the aim for non-renewable feedstocks substitution, vegetable oils have been used ever more as a feedstock for fuels and polymers. Spills during oil handling are serious environmental problems. Vegetable fibers have been used for a long time now as oil sorbents during spills. Wood residues as sawdust are currently used as oil sorbents, being a cheap and available resource. However, the hydrophilic profile of vegetable fibers reduce their capacity of oil sorption. Cellulose aerogels have become a product of great interest in the oil spill remediation field due to their high porosity (95 to 99%), low specific mass (0,004 to 0,15 g.cm-3) and high surface area (>60,m².g-1), besides cellulose abundance and sustainability. The objective of this work was to develop a hydrophobic aerogel from nanocellulose nanofibers obtained from furniture industry residues (Pinus elliottii var. elliottii) processed via steam explosion acid hydrolysis for petroleum and vegetable oil sorption. In the steam explosion process the best experimental condition was observed for a volumetric acetic acid and nitric acid ratio of 15:2:1 at 120ºC and 30 minutes with a cellulose yield higher than 90% and complete removal of hemicellulose and ligning. After lyophilization an aerogel of specific mass 0,046 0,0013 g.cm-3 and porosity 97,08 0,08% was obtained. Aerogel hydrophobization yielded a contact angle of 138,78º 0,78º. The aerogel exhibited a top experimental sorption capacity (CSME) of 19,55 0,10 goil.gaerogel-1 for petroleum and 13,73 0,62 goil.gaerogel-1 for vegetable oil. Cellulose nanofibers were produced by physical means (grinding) and hydrophobization was accomplished via vapor-phase deposition of organosilane (MTMS). In wood residue hydrolysis two acids were tested (nitric acid and acetic acid) simultaneously and individually, with variations of temperature, time and reagent amount. The solid fraction rich in cellulose was grinded in a rock mill for 5 hours at 2500 rpm in a 1,5% m/m suspension in water. The obtained gel was frozen for 48 hours at -20ºC for lyophilization at -40ºC for 50 hours. The aerogels obtained by lyophilization were treated with organosilane via vapor-phase deposition for 5 hours at 70ºC. The furniture industry residue was characterized as for its amounts of cellulose, hemicellulose, lignin, ashes, extractives and humidity. The process of steam explosion was characterized through the yields of individual components (cellulose and hemicellulose). Procedures like specific mass, contact angle, porosity, morphological characterization by scanning electron microscope with field emission gun, oil absorption tests and absorption kinetic in homogeneous and heterogeneous medium of petroleum and soy oil absorption were performed to characterize the aerogel. Kinetic models of pseudo-first, pseudo-second and pseudo-nth order were fitted to experimental data in their linear and non-linear forms. The absorption in homogeneous medium of petroleum was well fitted by pseudo-first linear kinetic model. Absorption of vegetable oil was well fitted by both pseudo-first and pseudo-second models. Models in non-linear form indicated a better fit for experimental data by the pseudo-nth order model (n=0,95) for petroleum and by pseudo-first order for vegetable oil. Kinetic adjusts showed that in heterogeneous medium CSME is maintained, but sorption rate is smaller.
18

Modern Inorganic Aerogels

Ziegler, Christoph, Wolf, André, Liu, Wei, Herrmann, Anne-Kristin, Gaponik, Nikolai, Eychmüller, Alexander 15 May 2018 (has links) (PDF)
Essentially, the term aerogel describes a special geometric structure of matter. It is neither limited to any material nor to any synthesis procedure. Hence, the possible variety of materials and therefore the multitude of their applications are almost unbounded. Here we present a comprehensive picture of the most promising developments in the field during the last decades.
19

Function-led Design of Aerogels: Self-assembly of Alloyed PdNi Hollow Nanospheres for Efficient Electrocatalysis

Cai, Bin, Wen, Dan, Liu, Wei, Herrmann, Anne-Kristin, Benad, Albrecht, Eychmüller, Alexander January 2015 (has links)
Amelioration of the building blocks is a plausible approach to graft aerogels with distinguished properties while preserving the aerogel superiority. However, the incorporation of designated properties into metallic aerogels, especially catalytically beneficial morphologies and transition metal doping, still remains a challenge. Here, we report on the first case of an aerogel electrocatalyst composed entirely of alloyed PdNi hollow nanospheres (HNSs) with controllable chemical composition and shell thickness. The synergy of the transition metal doping, combined with the hollow building blocks and the three dimensional network structure make the PdNi HNS aerogels promising electrocatalysts towards ethanol oxidation, among which the Pd83Ni17 HNS aerogel shows a 5.6-fold enhanced mass activity compared to commercial Pd/C. This work expands the exploitation approach of electrocatalytic properties of aerogels into morphology and composition control of its building blocks.
20

Studies on Transparent, Highly Porous Materials Based on Organopolysiloxanes / 有機ポリシロキサン系透明高気孔率材料に関する研究

Shimizu, Taiyo 23 March 2017 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20198号 / 理博第4283号 / 新制||理||1615(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)准教授 中西 和樹, 教授 北川 宏, 教授 島川 祐一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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