Search

PI fine particles encapsulating a large number of TiO2 nanoparticles (PI FPs/TiO2 NPs) were successfully fabricated rapidly and continuously by the emulsion re-precipitation method using a multistep flow synthetic system. The fabricated material, PI FPs/TiO2 NPs, was spherical in structure with a diameter of 214 nm, and the mean size of TiO2 NPs was 5.2 nm. Line scan elemental analysis with SEM-EDX showed that the TiO2 NPs were disproportionately embedded near the surface of the PI FPs. UV-vis transmission spectra revealed high UV shielding efficiency of the PI FPs/TiO2 NPs as the NPs are located near the surface.

PI fine particles encapsulating a large number of TiO

Recently, the utilization of formic acid (FA) or formate as promising hydrogen carriers through the interconversion between CO2 and HCOOH or HCO3– and HCOO–, respectively, has attracted increasing research interest. In this work, a PdAu bimetallic catalyst supported on phenylenediamine-alkalized reduced graphene oxide (Pd0.50Au0.50/PDA-rGO) was developed for catalyzing bicarbonate hydrogenation under basic conditions as well as FA/formate dehydrogenation under acidic and basic conditions. Without any additives, a very high yield (94%) of potassium formate (PF) can be achieved from the hydrogenation of potassium bicarbonate at 50 °C for 16 h. On the other hand, initial TOFs of 1.63 × 103 and 6.98 × 103 h–1 were accomplished in the dehydrogenations of 6 mol/L PF and 8 mol/L FA, respectively, at 80 °C. This work successfully demonstrates highly efficient CO2 hydrogenation and is the first report of a Pd-based heterogeneous catalyst for the additive-free dehydrogenation of concentrated (>6 mol/L) PF or FA sol...

The development of a sustainable methodology for catalytic transformation of biomass-derived compounds to value-added chemicals is highly challenging. Most of the transitions are dominated by the use of additives, complicated reaction steps and large volumes of organic solvents. Compared to traditional organic solvents, alternative reaction media, which could be an ideal candidate for a viable extension of biomass-related reactions are rarely explored. Here, we elucidate a selective and efficient transformation of a biomass-derived aldehyde (furfural) to the corresponding alcohol, promoted in compressed CO2 using a Pt/Al2O3 catalyst. Furfural contains a furan ring with CC and an aldehyde group, and is extremely reactive in a hydrogen atmosphere, resulting in several by-products and a threat to alcohol selectivity as well as catalyst life. The process described has a very high reaction rate (6000 h−1) with an excellent selectivity/yield (99%) of alcohol, without any organic solvents or metal additives. This strategy has several key features over existing methodologies, such as reduced waste, and facile product separation and purification (reduced energy consumption). Combining the throughput of experimental observation and molecular dynamics simulation, indeed the high diffusivity of compressed CO2 controls the mobility of the compound, and eventually maintains the activity of the catalyst. Results are also compared for different solvents and solvent-less conditions. In particular, combination of an effective Pt catalyst with compressed CO2 provides an encouraging alternative solution for upgradation of biomass related platform molecules.

Herein, decarbonylation of biomass-based 5-hydroxymethylfurfural (HMF) in compressed CO2 with an unexpected acceleration of the reaction rate and excellent catalytic activity is reported. Without any additive, CO surrogates, or any organic solvents, via the developed method, an excellent conversion of 99.8% and highest selectivity of furfuryl alcohol (99.6%) in 4 h at 145 °C were achieved using an alumina-supported Pd catalyst (Pd/Al2O3). The superior activity is due to the unique characteristics (miscibility of reactant gases and high diffusivity) of compressed CO2 and the synergy between CO2 and Pd/Al2O3, where CO2 plays an interesting role in accelerating the reaction by enhancing the diffusion of CO and furfuryl alcohol (both products have high solubilities in CO2), consequently shifting the equilibrium to the forward direction. Characterisation of the catalyst suggested its direct interaction with the substrate and provided an indication of the possible reaction path. Thus, a mechanism was outlined. Compared to the results obtained using organic solvents, the results obtained using compressed CO2 were superior in terms of activity, selectivity, and reaction rate. This strategy highlights easy product separation, improved catalyst life, and a simple sustainable process. The efficiency of this protocol is confirmed by its potential application to a series of aldehydes with various substituents to produce decarbonylated products in good to excellent yields.

Catalytic hydrogenolysis of the C O bond of diphenyl ether (a lignin model compound) was investigated as a function of hydrogen pressure in scCO2 medium in the presence of water. Using commercially available Rh/C catalyst, the C O bond cleavage of diphenyl ether mainly results phenolic monomer at 80 °C. Hydrogen pressure is one of the key parameters because (i) C O bond cleavage and the hydrogenation of aromatic rings are two competitive reactions; very sensitive to hydrogen pressure and (ii) hydrogen has complete solubility in scCO2. Therefore, a critical control of hydrogen pressure was essential to reach the targeted cleavage of the C O bond when the reaction was conducted in scCO2 medium under pressurized condition. Depending on the hydrogen pressure, a significant change in the ratio of monocyclic:bicyclic products from 91:9 (0.2 MPa) to 58:42 (2 MPa) was revealed in the shortest reaction time of 5 min. Thus, low hydrogen pressure was the effective choice for the scission of the C O bond, whereas higher hydrogen pressure hydrogenate the aromatic ring due to the higher coverage of hydrogen on the catalytic surface. Amount of the catalyst (catalyst:substrate ratio) displayed a subtle effect on the breakage of the C O bond. A threshold ratio of 1:5 was preferred under the present reaction condition as the increased amount hampered the substrate:water ratio and hydrogenation of the aromatic ring occurred. In addition, as the change in temperature is associated with the change in the physical properties of scCO2, hence, the effect on the transformation of DPE was complicated and difficult to explain. Furthermore, different organic solvents as neat, along with CO2 and with water also has substantial impact on the rapture of C O bond. The obtained results from the solvent studies again proved that scCO2 along with water was the best choice for C O bond breakage and water is the driving force to mediate the reaction. In addition, a combination catalyst (Ni+Rh) was also tested for the same reaction under the similar working condition. Preliminary results suggested a synergistic effect in terms of the selectivity of monocyclic compounds.

The dehydrogenation of biomass-based 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) was achieved utilizing an activated carbon supported rhodium (Rh/C) catalyst under mild reaction conditions. The developed method successfully afforded complete conversion and the highest selectivity of DFF (>99%) without any additive, conventional hydrogen acceptor and oxidant. The efficiency of the method is achieved by the addition of compressed carbon dioxide (scCO2) and the synergistic effect of scCO2 and Rh/C, where scCO2 plays a pivotal role in accelerating the reaction by removing hydrogen, and consequently shifting the equilibrium to the forward direction. Optimization of different reaction parameters ensures the achievement of high conversion and selectivity. Characterization of the catalyst using different spectroscopic techniques suggests an interaction between the substrate and the catalyst and provides an indication of the possible reaction pathway, thus a mechanism would be outlined. The rate determining step of the reaction was calculated through mechanistic investigations involving theoretical calculations together with experimental analysis. One of the most attractive features of the method developed in this study is the reverse reaction of DFF, which can be achieved in one-pot without the addition of any external hydrogen. This process has successful application to the dehydrogenation of a variety of alcohols with different substituents.

High-pressure hydrogen is of great interest in the industrial utilization of hydrogen energy, especially for hydrogen fuel cell vehicles. In this work, a method of automatic high-pressure H2 generation by the decomposition of formic acid, a recently renowned hydrogen storage material, in the presence of a heterogeneous catalyst (palladium nano-particles on a graphene oxide catalyst (Pd/PDA–rGO)) was proposed. This catalyst can effectively catalyze the decomposition of formic acid to produce high-pressure H2 and CO2 over 35 MPa without any detectable formation of CO or other by-products. For example, a 36.3 MPa total gas pressure was successfully achieved using an aqueous solution of 6.7 mol L−1 formic acid and 6.7 mol L−1 sodium formate at 80 °C. This research provided a preliminary study on the automatic high-pressure hydrogen gas generation by the decomposition of formic acid without any compression facilities in the presence of a heterogeneous catalyst, which can be easily separated from the reaction process, for hydrogen energy utilization.

The development of a sustainable methodology for catalytic transformation of biomass-derived compounds to value-added chemicals is highly challenging. Most of the transitions are dominated by the use of additives, complicated reaction steps and large volumes of organic solvents. Compared to traditional organic solvents, alternative reaction media, which could be an ideal candidate for a viable extension of biomass-related reactions are rarely explored. Here, we elucidate a selective and efficient transformation of a biomass-derived aldehyde (furfural) to the corresponding alcohol, promoted in compressed CO

A high-pressure and high-temperature (HPHT) water microflow chemical process was utilized for the synthesis of benzazole derivatives. The current approach enables the extremely rapid production of various 2-arylbenzazoles including benzimidazoles, benzoxazoles, and benzthiazole in excellent yields.

A simple and highly efficient method was developed for the transformation of furfural (a biomass derived aldehyde) to furfurylamine by reductive amination using an aqueous solution of ammonia and molecular hydrogen as an amine source and a reducing agent, respectively. By choosing a suitable catalyst, such as Rh/Al2O3, and reaction conditions, a very high selectivity of furfurylamine (∼92%) can be achieved within the reaction time of 2 h at 80 °C. A detailed analysis of the reaction system sheds some light on the reaction pathway and provides an understanding about each elementary step. The reaction was believed to proceed via an imine pathway although no such intermediate was detected because of the highly reactive nature. Optimization of different reaction parameters such as hydrogen pressure, temperature and substrate/ammonia mole ratio is shown to be critical to achieve high selectivity of furfurylamine. Time-dependent reaction profiles suggested that a Schiff base type intermediate was in the detectable range, which offers indirect evidence of the formation of imine. Competitive hydrogenation and amination of an aldehyde group were strongly dictated by the nature of the metal used. The studied protocol represents an environmentally benign process for amine synthesis, which can be effectively extended to the other aldehydes also. The studied catalyst could be recycled successfully without any significant loss of catalytic activity.

The use of supercritical carbon dioxide (scCO2)/water for the conversion of diphenyl ether was investigated over Rh/C catalysts to achieve the cleavage of C–O bond under mild reaction conditions. In the studied reaction system, ethereal C–O bond was cleaved by hydrogenolysis and hydrolysis, which was strongly hampered if the reaction was conducted individually in CO2 or in water. A combined effect was desirable to achieve targeted cleavage because of the beneficial effect of a mild acidic environment generated through the dissolution of CO2 in water. Optimization of hydrogen pressure suggested a competition between diphenyl ether and hydrogen as the reaction rate (TOF) was significantly decreased with increased hydrogen pressure. In addition, the role of water was also evaluated and prompted the requirement of a suitable amount of water for cleavage. Mechanistic investigations through theoretical calculations together with experimental analysis illustrated that hydrogenolysis and hydrolysis were two reaction paths responsible for the rapture of the C–O bond.

The reverse water gas shift (rWGS) reaction using a supported zeolite catalyst containing molybdenum (Mo) was investigated. The Mo-based catalyst is expected to be effective for selective conversion of CO2 into CO. The focus of this work was on the performance of the Mo-based catalyst and the effect of adding copper (Cu) to the catalyst. The Mo catalyst exhibited high CO selectivity (99 %) with CO2 conversion of 14.3 % at 773 K. The activity of the catalyst containing Cu as an additive depended on the Mo/Cu ratio. For a series of Mo(x)Cu(1-x)/Faujasite (FAU) catalysts (x: metal content, mmol/g), the Mo(0.8)Cu(0.2)/FAU catalyst exhibited the best performance. X-ray diffraction, X-ray photoelectron spectroscopy and temperature-programmed reduction with hydrogen analysis of the Mo(x)Cu(1-x)/FAU catalysts revealed that the presence of Cu as an additive influenced the reduction step of MoO3 to MoO2, with MoO3 being the active species. Transmission electron microscopy verified morphology of MoO3 and Cu particles on the support. The excellent performance of the prepared Mo(0.8)Cu(0.2)/FAU catalyst was due to facilitation of the reduction process involving the Mo species.

The hydrogenation of HMF has been conducted in a neutral aqueous medium. Without any additive, HMF was hydrogenated to 2,5-bis-(hydroxymethyl)furan (BHMF) with complete conversion and selectivity (98.9%) using Pt/MCM-41 as catalyst. A very low temperature of 35 °C and 0.8 MPa of hydrogen pressure was used to accomplish the highest selectivity of BHMF within a reaction time of 2 h. Different reaction parameters such as reaction time, hydrogen pressure and the amount of water was optimized to achieve the highest catalytic activity. In particular, the presence or absence of water and the amount of water played an important role to determine the conversion and product distribution of the reaction. For instance, in the absence of water or a large excess of water, the selectivity of BHMF was decreased. In addition, instead of water the influence of three different groups of organic solvent were also explored to obtain BHMF under the studied reaction conditions. It has been observed that the studied organic solvents strongly influenced the catalytic performance, such as solvents with a negative δ value, which followed a clear trend with the substrate conversion, whereas no impact was observed for solvents with a positive δ value. Catalyst recycling experiments revealed that the catalyst could be recycled several times without any significant loss of catalytic activity.

The photocatalytic reduction of CO 2 to CO in single-phase, high-pressure mixtures of supercritical CO 2 and N , N -dimethylformamide (DMF), using fac -ReCl(bpy)(CO) 3 as a catalyst in the presence of triethanolamine as a sacrificial electron donor has been investigated. The catalytic efficiency was found to be strongly influenced by both the CO 2 and DMF concentrations. For example, the turnover number (TON) for CO formation increases linearly with CO 2 pressure up to 60 at 17.8 MPa/60 °C. It also increases dramatically as the [DMF] is increased from 3.8 to 6.3 M, and then remains almost constant with further increases in [DMF]. This resulted in an optimized TON of 62 at 17.8 MPa CO 2 /60 °C and [DMF] = 6.3 M, and an initial turnover frequency (TOF) of ∼56 h −1 at 17.8 MPa CO 2 /60 °C and [DMF] = 11.4 M. These values are 5× and 2.3× higher, respectively than those obtained under biphasic low-pressure conditions (0.1 MPa CO 2 ), demonstrating that significant improvements in catalytic performance are possible through the use of high concentrations of CO 2 . Manipulation of the incident light intensity led to further improvements in both TON (up to 72 under low light levels) and TOF (up to 117 h −1 under the highest light level investigated).

Potential-dependent transformations of surface structures, Pt oxidation states, and Pt–O bondings in Pt/C, Au(core)-Pt(shell)/C (denoted as Au@Pt/C), and Pd(core)-Pt(shell)/C (denoted as Pd@Pt/C) cathode catalysts in polymer electrolyte fuel cells (PEFCs) during the voltage-stepping processes were characterized by in situ (operando) X-ray absorption fine structure (XAFS). The active surface phase of the Au@Pt/C for oxygen reduction reaction (ORR) was suggested to be the Pt3Au alloy layer on Au core nanoparticles, while that of the Pd@Pt/C was the Pt atomic layer on Pd core nanoparticles. The surfaces of the Pt, Au@Pt and Pd@Pt nanoparticles were restructured and disordered at high potentials, which were induced by strong Pt–O bonds, resulting in hysteresis in the structural and electronic transformations in increasing and decreasing voltage operations. The potential-dependent restructuring, disordering, and hysteresis may be relevant to hindered Pt performance, Pt dissolution to the electrolyte, and degra...

In this work, supercritical carbon dioxide (scCO2), and scCO2/H2O were investigated for the processing of biomass-derived compounds such as 5-hydroxymethylfurfural (5-HMF), furfural and tetrahydrofurfuryl alcohol (THFA) into a vast array of fuel and non-fuel related chemicals. Higher solubility of reactant gasses in scCO2 results in an acceleration of the reaction rate and enhancement of the product selectivity. As a reaction medium, scCO2 offers promise to play a role in the conversion of 5-HMF to linear alkane, which relies heavily on hydrogen concentration. Furthermore, 5-HMF can be successfully converted to 2,5-dimethylfuran (a fuel additive) with the highest selectivity (100%) in ascCO2/H2O mixture. In the presence of H2O, scCO2 creates an acidic environment and contributes to improving the selectivity of 2,5-dimethylfuran. Similarly, furfural also produces 2-methylfuran through the hydrogenation/hydrogenolysis of the C–O bond. 1,5-pentanediol, which is used as a monomer in the polyester industry, could be conveniently obtained with 91% selectivity from THFA in scCO2 under the homogeneous conditions of a CO2–H2-substrate. Hence, the remarkable advantage of the present catalytic system has confirmed the potential utilisation of alternative “green” solvents in the conversion of different biomass based compounds.

A high-pressure and high-temperature (HPHT) water microflow chemical process was utilized for the synthesis of benzazole derivatives. The current approach enables the extremely rapid production of various 2-arylbenzazoles including benzimidazoles, benzoxazoles, and benzthiazole in excellent yields.

An exceptionally rapid hydrogenation of nitrobenzene to aniline [TOF=252,000 h−1] over palladium containing MCM-41 (Pd/MCM-41) with excellent yield of >99% can be achieved in supercritical carbon dioxide at 50 °C and a hydrogen pressure of 2.5 MPa. It has been observed that this promising method preferred a single phase between liquid substrate and carbon dioxide-hydrogen system. The ascendancy of the supercritical carbon dioxide medium is established in comparison with the conventional organic solvent and solvent-less conditions. Changes in the reaction parameters such as carbon dioxide and hydrogen pressure, temperature and the reaction time do not affect the selectivity. A combined experimental and theoretical study has elucidated the mechanism under the studied reaction condition because experimental observations revealed a direct conversion of nitrobenzene to aniline. However, density functional theory (DFT) calculation shows that the direct conversion is energetically unfavourable; hence, a stepwise mechanism has been proposed. Theoretical predictions and experimental observations suggested that the rate-limiting step of nitrobenzene conversion is different from that of the liquid phase hydrogenation. This catalytic process can also be successfully extended to the hydrogenation of other aromatic nitro compounds with different substituents. Easy separation of the liquid product from catalyst and the use of an environmentally friendly solvent make this procedure a viable and an attractive green chemical process.

Hydrogenation of aniline to cyclohexylamine was carried out in supercritical carbon dioxide using a variety of noble metal (Pt, Pd and Rh) catalysts. At 80 °C and 8 MPa of CO2 pressure, >95% of aniline conversion with 93% selectivity to cyclohexylamine was achieved on 5% Rh/Al2O3. A strong influence of phase behaviour related to the CO2 pressure was found on the conversion and selectivity. Optimization of reaction parameters resulted in a higher overall activity in the biphase (liquid substrate + gaseous H2 and CO2) than in the single phase (liquid substrate–CO2–H2) condition. It has been found that the interaction of CO2 with amine leads to the formation of solid carbamic acid, which enhanced the selectivity of cyclohexylamine, but reduced the conversion significantly. Furthermore, reaction temperature played a crucial role in preventing the formation of carbamic acid and also maintained a reasonably high reaction performance in terms of conversion and selectivity.

A new reaction setup equipped with micro tubular reactor with thin catalytic metal inner surface (Pd or Pd–Cu alloy) was developed for the reactions in high-pressure and high-temperature water (HPHT-H2O) flow. To evaluate the catalytic performance of this micro tubular reactor, Sonogashira C–C coupling of iodobenzene and ethynylbenzene was investigated by using this system under alkaline aqueous medium. Under the optimized reaction conditions of 250 °C and 16 MPa of pressure, diphenylethyne was obtained with good yield and 100% selectivity within a very short residence time of ∼1.6 s. The reaction proceeds without any additional promoters, additives or organic solvents. Leaching of catalytic metal from the reactor tube was not found under the studied reaction conditions. Alloying of Pd with Cu remarkably improved the efficiency of the reaction due to co-catalytic effect that is related to the easy electron transfer between two metals.

High-pressure and high-temperature water (HPHT-H2O) microreaction system was proven to be an efficient method to carry out the non-catalytic Claisen rearrangement. Allyl phenyl ether undergoes Claisen rearrangement to obtain o-allylphenol with a very high yield and selectivity of 98% within a short reaction time of 13.4 s at 265 °C and 5 MPa pressure. Compare to the solvent-free microreaction, HPHT-H2O plays an important role to accelerate the reaction as a catalyst by transferring a proton along locally formed hydrogen bond with the substrate. Finally, the obtained product can be separated completely from the aqueous suspension within the time range of 40 min to 24 h after the reaction. Even though the reaction has occurred in aqueous conditions, little side reactions, such as hydrolysis, hydration, or pyrolysis, was found.

The highly selective hydrogenation of adiponitrile proceeds effectively in supercritical carbon dioxide (scCO2) to produce 6-aminocapronitrile with excellent selectivity of 100% over rhodium/alumina (Rh/Al2O3) and without any additive, which is impossible in classical organic solvents. The presence of CO2 can be beneficial or mandatory for the exclusive formation of the aminonitrile as it can act as a solvent to enhance the activity and also as temporary protecting agent to increase the selectivity. These results successfully show the general concept of using scCO2 as a protective medium for the selectivity control of dinitrile to aminonitrile reactions. Recycling of the catalyst and further extension of this method to other dinitriles were also investigated.

Silica sphere with porous structure has been synthesized in supercritical carbon dioxide. The structure originates from a delicate CO(2) trapping phenomenon intended for void formation in the inorganic framework. Silicate polymerization and subsequent removal of CO(2) by depressurization leaves the porous architecture. The key factor to obtain stable porous spherical structure was CO(2) pressure. Different characterization techniques such as X-ray diffraction, scanning and transmission electron microscopy and N(2) adsorption-desorption isotherm were used to determine the framework structure, morphology and porosity of the material. Microscopic visualization of calcined material suggested that the spherical structure was consisted of macroporous windows of diameter approximately 100 nm and the space between macropores presents a wormhole like mesoporous/microporous structure. The pore diameter of the mesoporous structure has been calculated as approximately 3 nm. X-ray diffraction and N(2) adsorption isotherm analysis confirmed the presence of micropores and also the macropores. In addition, the resulting material possess high thermal and hydrothermal stability associated with fully SiO(4) cross-linking. The spherical structure with different types of porosity was successfully obtained without using any molding agent.

Novel micro tubular reactors composed of Inconel 625 support, TiO 2 /Ti intermediate layer and thin catalytic metal film (Pd, Pd−Cu alloy, Pt, Rh, and Au) were fabricated by continuous electroless plating technique. The reactors withstood high temperature (400 °C) and high pressure (30 MPa) water flow without loss of catalytic metals. The high catalytic efficiency of the reactors was demonstrated by the rapid and complete decomposition of organic dye in the flow system.

The use of supercritical carbon dioxide (scCO2) on the hydrogenation of benzonitrile was investigated over Pd and other metal catalysts. Without any additive, benzonitrile was hydrogenated to benzylamine with high conversion (90.2%) and selectivity (90.9%) using the Pd/MCM-41 catalyst. A strong influence of CO2 pressure on the conversion and selectivity were observed. As the CO2 pressure increases, the conversion was increased, and after reaching the maximum at around 8–10 MPa, it decreased. Moreover, simply by tuning the CO2 pressure, it is possible to obtain benzylamine or dibenzylamine. For instance, at lower pressure CO2 acts as a protecting agent, leading to the formation of the primary amine, but at higher pressure, the yield of primary amine as well as the solubility of the imine intermediate in CO2 increases, which results high selectivity for dibenzylamine. A plausible mechanism has been proposed to show the role of CO2 on the selectivity toward primary and secondary amines. The results confirm that the presence of CO2 is mandatory for the formation of benzylamine with high selectivity. Furthermore, the other reaction parameters, such as reaction time, H2 pressure, temperature etc., also affect the conversion as well as selectivity of benzylamine. This process has been extended to the hydrogenation of a series of different nitrile compounds.

Anomalous polyimide (PI) nanoparticles with controllable morphology, i.e., porous hollow structures, hollow structures, or bowl-like structures, were fabricated by blending a second polymer with poly(amic acid) (PAA, the precursor of PI) through the reprecipitation method and subsequent imidization. The phase separation between PAA and the porogen induced the formation of various hollow PI nanoparticles. The hollow morphology was mainly affected by the compatibility/interaction between PAA and the porogen. Hollow PI nanoparticles with superficial pores (ca. 30 nm), smooth surface, or holes in their surfaces can be obtained by selecting a suitable porogen, respectively.

Nanoparticles composed of Eu-complex and polyimide were successfully fabricated through an improved reprecipitation method, followed by a chemical imidization. In this process, the excess addition of triethylamine, which inhibits acid decomposition of Eu-complex, provided intense luminescent nanoparticles. These nanoparticles showed intense red luminescence assigned to Eu3+, which showed broader peaks compared with an Eu-complex powder and peak shifts. These results imply that Eu-complex molecules were dispersed in the PI matrix homogeneously and strongly affected by the matrix. Moreover, composition with polyimide improved UV resistance of Eu-complex.

Polyimide (PI) is a candidate material that is showing promise for use in a wide range of applications in several advanced technologies. In this study, we employed the reprecipitation method and subsequent imidization to prepare unique hollow PI nanoparticles (NPs) by blending a suitable polymer porogen with the PI precursor in the form of individual NPs. The hollow structures were induced through phase separation between the PI and the porogen, a process that was influenced by the compatibility between the two polymers. We then assembled multilayered films by depositing the hollow PI NPs electrophoretically onto a substrate. After spin-coating a solution of the PI precursor and then subjecting the system to thermal treatment, the individual PI NPs were bound to their adjacent neighbors, thereby improving the film strength to some extent. We obtained dense, uniformly packed films having controlled thicknesses in the range from 500 nm to 10 μm. This strategy provided films in which air voids existed betwee...

We have used the reprecipitation method and subsequent two-step imidization to fabricate highly porous polyimide (PI) nanoparticles possessing crater-like surface pores (depths, diameters: tens of nanometers) from poly(amic acid) (PAA) derivatives in the presence of poly(sodium-4-styrenesulfonate) (PSS) as a polyelectrolytic porogen. The porous structures arose presumably through segregative microphase separation of PAA and PSS (i.e. repulsion between PAA and PSS in the presence of a common solvent) and subsequent removal of PSS. The addition of this strong polyelectrolyte improved the degree of porosity of the resulting PI nanoparticles and allowed controllable release of the porogen. The resulting porous PI nanoparticles exhibited a high thermal stability (5% weight loss at temperature 450°C). This technique is suitable for the preparation of novel low-k materials and their surface-related applications. Copyright © 2008 John Wiley & Sons, Ltd.

Novel porous polyimides (PIs) having diameters of several hundred nanometers have been fabricated successfully from precursor poly(amic acid) (PAA) derivatives with poly(acrylic acid) (PAS) as the porogen, using a reprecipitation method and subsequent imidization. The superficial high porosity with deep pores was introduced when using a more compatible combination of PAA and the porogen, i.e., PI (BPDA-PDA) and PAS rather than PI (10FEDA-4FMPD and PAS); the pore sizes ranged from 20 to 100 nm. The resulting porous PI nanoparticles had thermally stabilities (determined from their 5% weight loss temperatures at 400 °C) similar to those of corresponding PI nanoparticles lacking porous structures. Microphase separation within the PAA nanoparticles after reprecipitation induced the porous surface structure, the properties of which were influenced by the molecular weight of PAS and the chemical structure of PAA. These unique porous PI nanoparticles have great potential for application as low-k materials in next-generation technologies.

Porous polyimide (PI) nanoparticles were fabricated using the reprecipitation method, with a second polymer as a porogen, and subsequent imidization. Poly(acrylic acid) was a suitable porogen for generating unprecedented PI nanoparticles having superficial nanopores, the sizes of which were in the range 20−70 nm. The porous morphology of the PI nanoparticles was affected mainly by the molecular weight and content of poly(acrylic acid). After thermal imidization, almost no poly(acrylic acid) remained inside the porous PI nanoparticles. Infrared spectroscopy and thermogravimetric analysis indicated that the porous nanoparticles consisted purely of PI and exhibited high thermal stability (5% weight loss temperature: 400 °C). The porous structure probably resulted from microphase separation of poly(amic acid) and poly(acrylic acid) during the reprecipitation process. This strategy provides a new means for improving the degree of porosity of PI nanoparticles, which have the potential for application as altern...

Luminescence properties of Eu 3+ -doped 6FDA-6F polyamic acid (PAA) and polyimide (PI) films were investigated. Eu 3+ -doped PAA films showed a luminescence assigned to Eu 3+ just after preparation. However, the luminescence intensity decreased with increases in UV-irradiation treatment time. On the other hand, Eu 3+ -doped PI films showed unique luminescence properties. The films showed no luminescence just after preparation. However, the luminescence intensity ascribed to Eu 3+ increased with increases in the UV-irradiation treatment time. In contrast, the luminescence intensity decreased with elevation of the heat-treatment temperature and disappeared at 220 °C. After the luminescence vanished, the luminescence intensity again increased with increases in the UV-irradiation treatment time. The luminescence of the matrix similarly changed upon UV-irradiation and thermal treatment. It is proposed that luminescence properties of Eu 3+ doped PI films is based on a reversible changes in the luminescence of the matrix caused by UV-irradiation and thermal treatment, resulting in changes in the luminescence of Eu 3+ due to the energy transfer from the matrix to Eu 3+ .

We have studied the defect structures and mechanism for the luminescence of non-doped, Tb 3+ -doped and Tb 3+ –Zn 2+ codoped alumina films treated at various temperatures from 300 to 800 °C. The electron paramagnetic resonance (EPR) spectra observed before UV-irradiation are attributable to the non-bridging oxygen radicals; Al–O–O at treatment temperatures of 300–500 °C and Al–O at 800 °C. The UV-light irradiation of the non-doped alumina films gives the EPR spectra with the 27 Al hyperfine splitting. There exists a good correlation between the treatment temperature dependence on the light-induced EPR signal intensity of the trapped electron and the NMR peak intensity due to the five-coordinated aluminum ion. We concluded that the electron is captured at the oxygen vacancy connected with the five-coordinated aluminum. The broad EPR spectra due to the ground state of the Tb 3+ ion were observed in the Tb 3+ -doped and Tb 3+ –Zn 2+ codoped alumina films. The Tb 3+ concentration dependence of the EPR signal intensity due to the non-bridging oxygens suggests that Tb 3+ prefers to form Al–O–Tb bonds and prevent to form a cluster of rare earth ions itself. The light-induced EPR signal of the electron trapped at oxygen vacancy next the five-coordinated aluminum was also observed for the Tb 3+ –Zn 2+ codoped alumina film, which produced a long-lasting luminescence. The photogenerated trapped electron remained for several minutes under the room temperature. These experimental facts indicate that the five-coordinated aluminum ions act as the trapping sites to produce the long-lasting luminescence.

The thick alumina films (0.2–0.5 μm) were prepared on quartz glass and nickel substrates by a dipping method using an alumina sol derived from an aqueous AlCl3 solution. The hardness of this coating was compared to those of similarly coated substrates that had been heat-treated at various temperatures. The hardness of the alumina coating increased with increasing heat-treatment temperature. This sol gave crack-free and well-coated substrates that could be heat-treated to temperatures up to 800°C. This may have been due to the formation of an amorphous mixed oxide interface layer between the alumina films and the substrates. At temperatures higher than 900°C, problems with the coating started to appear because the oxide layer formed into α-alumina accompanying evolution of stress in the interface.

Novel polyimide nanoparticles confining maximum 12.5 wt % of highly dispersed Au nanoparticles (size: 5.6 nm) were continuously fabricated by using a multistep microfluidic reaction system; the par...

A facile and continuous synthesis method of polyimide hollow nanoparticles has been developed by microemulsion reprecipitation method using a microfluidic system within a short reaction time (10 s)...

Rare earth ion (Tb 3+ and Eu 3+ )-doped alumina films were prepared by the aqueous sol-gel method under various conditions. The influences of the OH groups (phonon relaxation) and rare earth ion concentration (cross-relaxation) on luminescence were examined. In regard to the former relaxation, at treatment temperature above 600°C, reciprocal lifetime decreased with OH concentration, and below 500°C, decreased markedly and nonlinearly. On the other hand, in regard to the latter relaxation, there was negligible effect on luminescence for these doped films. The quantitative treatment was tried to lifetime considering these influences. Tb 3+ and Eu 3+ co-doped alumina films showed enhanced Eu 3+ luminescence by the energy transfer from Tb 3+ to Eu 3+ . Eu 3+ luminescence intensity increased with a greater Tb 3+ concentration.

チタンアルコキシドとセルロースのゲル形成を利用して, 固定化菌体酵母 (S. cerevisiae) を調製した. その特性をエタノール発酵とβ-ケトエステルの還元で調べ, ネイティブ菌体の場合と比較した. アルギン酸を用いる従来の包括方法では使用できないリン酸緩衝液でも使用できた. しかし, 反応時間が長くなると菌体が増殖し, 繊維表面からの逸脱が認められた.

Rare earth ion (Er 3+ , Eu 3+ and Sm 3+ )-doped alumina films have been prepared by the sol–gel method, using AlCl 3 -derived alumina sol. The effects of dopant concentration and treatment temperatures on the photo-properties of absorption and emission have been examined for the doped films. These sol–gel-derived alumina matrices gave a high-dopant concentration (∼15 mol% per alumina).

Palladium oxide (PdO) nanoparticles supported on B, Al and Ga modified mesoporous MCM-41with different Si/M ratios (where, M = B, Al or Ga) varied from 100 to 5 was synthesized in one-pot. Developed materials were characterized by several techniques such as XRD, TEM, UV–Vis, XPS and TG-DTA. A highly ordered structure was revealed by XRD for all the support materials depending on Si/M ratio. TEM analysis evidenced the presence of spherical PdO particles. Interestingly, the particle sizes correlated well with Si/M ratio as well as the nature of M. Spectroscopic characterization of calcined materials suggested the presence of Pd 2+ , whereas XPS confirmed the existence of Pd 2+ in PdO form. The catalytic activity of resultant materials was investigated by the chemoselective hydrogenation of chloronitrobenzene in supercritical carbon dioxide. All the materials exhibit excellent conversion of chloronitrobenzene and selectivity to chloroaniline within the reaction time of 50 min. at 35 °C. Substitution of Si by trivalent metal cation improved the catalytic performance of B and Ga containing catalysts. Among the three catalysts, superior catalytic activity was observed for Pd/B-MCM-41 with highest conversion (100%) and selectivity to chloroaniline (100%) and thus, followed the reactivity order of PdO/B > PdO/Ga > PdO/Al. Considering o- , m- and p -chloronitrobenzene, for all the materials conversion followed the order of p- > m- > o- , whereas selectivity to chloroaniline for all three isomers were strongly influenced by the trivalent metal ion in the support material.

A simple and highly efficient Rh/C catalyzed route for the cleavage of the C–O bond of aromatic ether at 80 °C in the presence of 0.5 MPa of H2 in the scCO2–water medium is reported; CO2 pressure and water play a key role under the tested conditions.

A simple and highly efficient Rh/C catalyzed route for the cleavage of the C–O bond of aromatic ether at 80 °C in the presence of 0.5 MPa of H2 in the scCO2–water medium is reported; CO2 pressure and water play a key role under the tested conditions.

In the reaction of the substituted aromatic nitro-compounds the order of reactivity is ortho < meta < para.

Continuous flow synthesis of gold nanoparticles was demonstrated using a microchannel reactor with glucose reduction in aqueous alkaline medium. Particle size, morphology, and visual/optical properties of the dispersion liquid were controlled dynamically by tuning of the rate of NaOH addition. Characteristic star-like nanoparticles formed spontaneously as a quasi-stable state, but they changed the morphology to round shape and showed spectral change over time.