Login In
2016 Volume 74 Issue 7
2016, 74(7): 557-564
doi: 10.6023/A16040178
Abstract:
Haloaromatics (XAr) have been widely used as pesticides, personal care agents, pharmaceuticals and flame retardants, which are now ubiquitously present in our environment. The carcinogenicity coupled with their ubiquitous occurrence have raised public concerns on the potential risks to both human health and the ecosystem posed by XAr. Advanced oxidation processes (AOPs) have been increasingly employed as an "environmentally-friendly" technology for remediating such highly toxic and recalcitrant XAr. During these AOPs systems, the most reactive radical intermediate formed at near-ambient temperature and pressure is the hydroxyl radical (·OH). Recently, we found that an intrinsic chemiluminescence can be generated during the advanced oxidation of the priority pollutant pentachlorophenol and all other XAr. Furtherly, by the complementary application of electron spin resonance (ESR) with 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin-trapping agent, fluorescence method with terephthalic acid (TPA) as the ·OH probe, chemiluminescence analysis in the presence of classic ·OH scavengers and several typical ·OH-generating systems, the chemiluminescence was confirmed to be directly dependent on the production of the extremely reactive ·OH. Further studies showed that halogenated quinoid intermediates were produced during the degradation of XAr by ·OH-generating system, which could produce weak chemiluminescence that was greatly enhanced by addition of extra ·OH. We proposed that this unusual chemiluminescence generation was due to hydroxyl radical-dependent production of halogenated quinoid intermediates and electronically excited carbonyl species. In addition, the time course of chemiluminescence emission correlated well with the degradation of XAr: when the degradation level of XAr reached the maximum, no further chemiluminescence emission could be observed. Based on these findings, we developed a rapid, sensitive, simple, and effective chemiluminescence method to not only measure trace amount of XAr, but also monitor their real-time degradation kinetics. These new findings may have broad chemical, pharmaceutical, toxicological and environmental implications for future studies on remediation of these halogenated persistent organic pollutants by AOPs.
Haloaromatics (XAr) have been widely used as pesticides, personal care agents, pharmaceuticals and flame retardants, which are now ubiquitously present in our environment. The carcinogenicity coupled with their ubiquitous occurrence have raised public concerns on the potential risks to both human health and the ecosystem posed by XAr. Advanced oxidation processes (AOPs) have been increasingly employed as an "environmentally-friendly" technology for remediating such highly toxic and recalcitrant XAr. During these AOPs systems, the most reactive radical intermediate formed at near-ambient temperature and pressure is the hydroxyl radical (·OH). Recently, we found that an intrinsic chemiluminescence can be generated during the advanced oxidation of the priority pollutant pentachlorophenol and all other XAr. Furtherly, by the complementary application of electron spin resonance (ESR) with 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin-trapping agent, fluorescence method with terephthalic acid (TPA) as the ·OH probe, chemiluminescence analysis in the presence of classic ·OH scavengers and several typical ·OH-generating systems, the chemiluminescence was confirmed to be directly dependent on the production of the extremely reactive ·OH. Further studies showed that halogenated quinoid intermediates were produced during the degradation of XAr by ·OH-generating system, which could produce weak chemiluminescence that was greatly enhanced by addition of extra ·OH. We proposed that this unusual chemiluminescence generation was due to hydroxyl radical-dependent production of halogenated quinoid intermediates and electronically excited carbonyl species. In addition, the time course of chemiluminescence emission correlated well with the degradation of XAr: when the degradation level of XAr reached the maximum, no further chemiluminescence emission could be observed. Based on these findings, we developed a rapid, sensitive, simple, and effective chemiluminescence method to not only measure trace amount of XAr, but also monitor their real-time degradation kinetics. These new findings may have broad chemical, pharmaceutical, toxicological and environmental implications for future studies on remediation of these halogenated persistent organic pollutants by AOPs.
2016, 74(7): 565-575
doi: 10.6023/A16030156
Abstract:
With the development of intelligent terminals, wearable electronic devices show a great market prospect. As one core component of the wearable electronic device, the sensor will exert a significant influence on the design and function of the wearable electronic device in the future. Compared with the traditional electrical sensors, flexible wearable sensors have the advantages of being light, thin, portable, highly integrated and electrically excellent. It has become one of the most popular electronic sensors. This review focused on recent research advances of flexible wearable sensors, including signal transduction mechanisms, general materials, manufacture processes and recent applications. Piezoresistivity, capacitance and piezoelectricity are three traditional signal transduction mechanism. For accessing the dynamic pressure in real time and developing stretchable energy harvesting devices, sensors based on the mechanoluminescent mechanism and triboelectric mechanism are promising. Common materials used in flexible wearable electronic sensors, such as flexible substrates, metals, inorganic semiconductors, organics and carbons, are also introduced. In addition to the continuously mapping function, wearable sensors also have the practical and potential applications, which focused on the temperature and pulse detection, the facial expression recognition and the motion monitoring. Finally, the challenges and future development of flexible wearable sensors are presented.
With the development of intelligent terminals, wearable electronic devices show a great market prospect. As one core component of the wearable electronic device, the sensor will exert a significant influence on the design and function of the wearable electronic device in the future. Compared with the traditional electrical sensors, flexible wearable sensors have the advantages of being light, thin, portable, highly integrated and electrically excellent. It has become one of the most popular electronic sensors. This review focused on recent research advances of flexible wearable sensors, including signal transduction mechanisms, general materials, manufacture processes and recent applications. Piezoresistivity, capacitance and piezoelectricity are three traditional signal transduction mechanism. For accessing the dynamic pressure in real time and developing stretchable energy harvesting devices, sensors based on the mechanoluminescent mechanism and triboelectric mechanism are promising. Common materials used in flexible wearable electronic sensors, such as flexible substrates, metals, inorganic semiconductors, organics and carbons, are also introduced. In addition to the continuously mapping function, wearable sensors also have the practical and potential applications, which focused on the temperature and pulse detection, the facial expression recognition and the motion monitoring. Finally, the challenges and future development of flexible wearable sensors are presented.
2016, 74(7): 576-581
doi: 10.6023/A16020080
Abstract:
A chiral phosphoric acid-catalyzed asymmetric[4+2] cycloaddition of o-hydroxyl styrenes with o-quinone methides (o-QMs) generated in situ from o-hydroxybenzyl alcohols has been established. O-Hydroxybenzyl alcohols could transform into o-QM intermediates under the catalysis of chiral phosphoric acid (CPA), which are easily activated by CPA via hydrogen-bonding interaction. On the other hand, o-hydroxyl styrenes could also be activated by CPA via forming a hydrogen bond between the hydroxyl group of styrenes and the phosphoryl oxygen of CPA. So, by selecting o-hydroxybenzyl alcohols as precursors of dienes and o-hydroxyl styrenes as dienophiles under the catalysis of CPA, this catalytic asymmetric[4+2] cycloaddition provided an efficient strategy for constructing enantioenriched chroman framework with two stereogenic centers. A variety of substituted o-hydroxybenzyl alcohols and o-hydroxyl styrenes bearing either electron-donating or electron-withdrawing groups could be applicable to the reaction, delivering chiral chroman derivatives in high yields, considerable enantioselectivities and excellent diastereoselectivities (up to 78% yield, 72% ee, most of examples > 95:5 dr). The electronic nature of the substituents has some effect on the reaction. Namely, the electron-donating groups were beneficial to both the reactivity and the enantioselectivity. Based on the control experiments, it is suggested that the o-hydroxyl styrenes and the o-QM intermediates generated from o-hydroxybenzyl alcohols were simultaneously activated by CPA via forming double hydrogen bonds, thus facilitating the reaction in an enantioselective way. A representative procedure for the enantioselective[4+2] cycloaddition reaction is as following: 1, 2-dichloroethane (1 mL) was added to the mixture of o-hydroxybenzyl alcohols (0.1 mmol), o-hydroxyl styrenes (0.12 mmol), the chiral phosphoric acid (0.005 mmol), and 3 Å molecular sieves (100 mg). After being stirred at 50 ℃ for 12 h, the reaction mixture was filtered to remove the molecular sieves, and the solid powder was washed with ethyl acetate. The resultant solution was concentrated under the reduced pressure to give the residue, which was purified through flash column chromatography on silica gel to afford the pure chiral chroman derivatives.
A chiral phosphoric acid-catalyzed asymmetric[4+2] cycloaddition of o-hydroxyl styrenes with o-quinone methides (o-QMs) generated in situ from o-hydroxybenzyl alcohols has been established. O-Hydroxybenzyl alcohols could transform into o-QM intermediates under the catalysis of chiral phosphoric acid (CPA), which are easily activated by CPA via hydrogen-bonding interaction. On the other hand, o-hydroxyl styrenes could also be activated by CPA via forming a hydrogen bond between the hydroxyl group of styrenes and the phosphoryl oxygen of CPA. So, by selecting o-hydroxybenzyl alcohols as precursors of dienes and o-hydroxyl styrenes as dienophiles under the catalysis of CPA, this catalytic asymmetric[4+2] cycloaddition provided an efficient strategy for constructing enantioenriched chroman framework with two stereogenic centers. A variety of substituted o-hydroxybenzyl alcohols and o-hydroxyl styrenes bearing either electron-donating or electron-withdrawing groups could be applicable to the reaction, delivering chiral chroman derivatives in high yields, considerable enantioselectivities and excellent diastereoselectivities (up to 78% yield, 72% ee, most of examples > 95:5 dr). The electronic nature of the substituents has some effect on the reaction. Namely, the electron-donating groups were beneficial to both the reactivity and the enantioselectivity. Based on the control experiments, it is suggested that the o-hydroxyl styrenes and the o-QM intermediates generated from o-hydroxybenzyl alcohols were simultaneously activated by CPA via forming double hydrogen bonds, thus facilitating the reaction in an enantioselective way. A representative procedure for the enantioselective[4+2] cycloaddition reaction is as following: 1, 2-dichloroethane (1 mL) was added to the mixture of o-hydroxybenzyl alcohols (0.1 mmol), o-hydroxyl styrenes (0.12 mmol), the chiral phosphoric acid (0.005 mmol), and 3 Å molecular sieves (100 mg). After being stirred at 50 ℃ for 12 h, the reaction mixture was filtered to remove the molecular sieves, and the solid powder was washed with ethyl acetate. The resultant solution was concentrated under the reduced pressure to give the residue, which was purified through flash column chromatography on silica gel to afford the pure chiral chroman derivatives.
2016, 74(7): 582-586
doi: 10.6023/A16030114
Abstract:
As cathode materials in lithium-ion batteries, layered vanadium oxides have been extensively studied and used in many aspects varying from industrial production to our daily life, due to their excellent physical property and gorgeous lithium storage performance. During lithiation/delithiation, layered vanadium oxides such as V2O5 xerogel (with a bilayer structure), undergoes "lattice breathing" which leads to the deactivation of electrode materials and fast capacity fading, which limits its large-scale application. In this work, VOx is used as the cathode material of lithium-ion batteries to study the "lattice breathing" phenomenon. The phase evolution has been observed and studied via in situ method. The X-ray diffraction (XRD) patterns show typical (001) diffraction peaks characteristic of vanadium oxide xerogel structure and also confirm the good crystallinity. This compound with crystal parameters of a＝4.56 Å, b＝14.87 Å, c＝12.38 Å, α＝117.26°, β＝96.02°, γ＝81.86°, forms a triclinic structure. Results of scanning electron microscope (SEM) and transmission electron microscope (TEM) further verify the layered structure of VOx. The thermo gravimetric analysis (TGA) at air and nitrogen atmosphere shows that the carbon content of the sample is about 2.4 wt% and the water content is about 2.1%. As lithium-ion battery cathode the initial discharge capacity of the compound is about 136 mA·h/g at a current density of 100 mA/g, with a capacity retention of 92.6% after 50 cycles. To study the lithium storage mechanism of VOx, electrochemical discharge/charge processes are further investigated by in situ XRD. It is found that the lattice plane diffraction displays three different stages linked during the insertion and deinsertion of lithium ions, indicating three solid solution reactions. During discharge process, the three diffraction changes show continuous shifts to higher diffraction angles, demonstrating three different continuous contraction processes with the insertion of lithium ions. Nevertheless, the evolution of the (001) peak is swift during the beginning and the end of discharge, in contrast to the slow deviation of the intermediate process. In the whole process, the diffraction pattern displays periodic changes, confirming the reversibility of the reaction process. The corresponding calculations of d001 during the discharge/charge process prove the notable discontinuity between these three stages. In addition, cycling experiments conducted at the higher and the lower temperature indicate that the electrochemical performance of this compound is highly sensitive to temperature.
As cathode materials in lithium-ion batteries, layered vanadium oxides have been extensively studied and used in many aspects varying from industrial production to our daily life, due to their excellent physical property and gorgeous lithium storage performance. During lithiation/delithiation, layered vanadium oxides such as V2O5 xerogel (with a bilayer structure), undergoes "lattice breathing" which leads to the deactivation of electrode materials and fast capacity fading, which limits its large-scale application. In this work, VOx is used as the cathode material of lithium-ion batteries to study the "lattice breathing" phenomenon. The phase evolution has been observed and studied via in situ method. The X-ray diffraction (XRD) patterns show typical (001) diffraction peaks characteristic of vanadium oxide xerogel structure and also confirm the good crystallinity. This compound with crystal parameters of a＝4.56 Å, b＝14.87 Å, c＝12.38 Å, α＝117.26°, β＝96.02°, γ＝81.86°, forms a triclinic structure. Results of scanning electron microscope (SEM) and transmission electron microscope (TEM) further verify the layered structure of VOx. The thermo gravimetric analysis (TGA) at air and nitrogen atmosphere shows that the carbon content of the sample is about 2.4 wt% and the water content is about 2.1%. As lithium-ion battery cathode the initial discharge capacity of the compound is about 136 mA·h/g at a current density of 100 mA/g, with a capacity retention of 92.6% after 50 cycles. To study the lithium storage mechanism of VOx, electrochemical discharge/charge processes are further investigated by in situ XRD. It is found that the lattice plane diffraction displays three different stages linked during the insertion and deinsertion of lithium ions, indicating three solid solution reactions. During discharge process, the three diffraction changes show continuous shifts to higher diffraction angles, demonstrating three different continuous contraction processes with the insertion of lithium ions. Nevertheless, the evolution of the (001) peak is swift during the beginning and the end of discharge, in contrast to the slow deviation of the intermediate process. In the whole process, the diffraction pattern displays periodic changes, confirming the reversibility of the reaction process. The corresponding calculations of d001 during the discharge/charge process prove the notable discontinuity between these three stages. In addition, cycling experiments conducted at the higher and the lower temperature indicate that the electrochemical performance of this compound is highly sensitive to temperature.
2016, 74(7): 587-592
doi: 10.6023/A16040196
Abstract:
Direct methanol fuel cells (DMFC) have attracted extensive attention as ideal candidates for automotive and portable applications owing to the fascinating advantages such as high conversion efficiency, environmental friendliness, safety, wide sources of methanol, and simple cell structure. Electrocatalysts are one of crucial factors limiting the performance of DMFC. Nowadays, precious Pt-based catalyst, in spite of costliness and scarcity, is the most popular catalyst for methanol oxidation reaction (MOR) at anode due to the much better performances than those of the non-Pt catalysts. But there exists some shortcomings such as poor CO-tolerance and durability. Pt alloying with other metals, e.g. Ru, is an effective strategy to improve the catalytic performance. In addition, the support with a large specific surface area (SSA), high conductivity and suitable porous structure, such as sp2 carbon, could lead to high dispersion, high utilization and stability of Pt-based nanoparticles, also favorable for MOR. Recently, by in situ MgO template method, we reported the unique 3D hierarchical carbon-based nanocages featured with ultrahigh SSA, micro-meso-macro-pore coexistence, good conductivity and easy doping, which exhibited excellent electrochemical performances. Herein, taking the advantages of nitrogen-dopant anchoring function and unique mesostructures of hierarchical N-doped carbon nanocages (hNCNC), we report the Pt-Ru electrocatalysts immobilized on hNCNC (Pt-Ru/hNCNC) prepared via modified microwave-assisted ethylene glycol (EG) reduction method. The so-constructed Pt-Ru/hNCNC catalysts with ca. 30 wt% loading and tunable atomic ratio of Pt to Ru have a highly homogeneous dispersion of metal nanoparticles with the average size of ca. 3 nm. The alloying Pt-Ru/hNCNC catalysts demonstrate good CO-tolerance, high MOR activity and durability, superior to those of the counterparts of Pt/hNCNC and commercial PtRu/C. The good electrochemical performance can be ascribed to the synergistic effects of the bifunctional effect due to introduction of Ru, small size and high dispersion of metal nanoparticles induced by the large SSA and nitrogen participation of hNCNC, and multi-scaled hierarchical pore structures beneficial to the mass transportation. These results proposed a potential strategy to develop the high-performance Pt-based MOR catalysts based on the novel mesostructured hNCNC.
Direct methanol fuel cells (DMFC) have attracted extensive attention as ideal candidates for automotive and portable applications owing to the fascinating advantages such as high conversion efficiency, environmental friendliness, safety, wide sources of methanol, and simple cell structure. Electrocatalysts are one of crucial factors limiting the performance of DMFC. Nowadays, precious Pt-based catalyst, in spite of costliness and scarcity, is the most popular catalyst for methanol oxidation reaction (MOR) at anode due to the much better performances than those of the non-Pt catalysts. But there exists some shortcomings such as poor CO-tolerance and durability. Pt alloying with other metals, e.g. Ru, is an effective strategy to improve the catalytic performance. In addition, the support with a large specific surface area (SSA), high conductivity and suitable porous structure, such as sp2 carbon, could lead to high dispersion, high utilization and stability of Pt-based nanoparticles, also favorable for MOR. Recently, by in situ MgO template method, we reported the unique 3D hierarchical carbon-based nanocages featured with ultrahigh SSA, micro-meso-macro-pore coexistence, good conductivity and easy doping, which exhibited excellent electrochemical performances. Herein, taking the advantages of nitrogen-dopant anchoring function and unique mesostructures of hierarchical N-doped carbon nanocages (hNCNC), we report the Pt-Ru electrocatalysts immobilized on hNCNC (Pt-Ru/hNCNC) prepared via modified microwave-assisted ethylene glycol (EG) reduction method. The so-constructed Pt-Ru/hNCNC catalysts with ca. 30 wt% loading and tunable atomic ratio of Pt to Ru have a highly homogeneous dispersion of metal nanoparticles with the average size of ca. 3 nm. The alloying Pt-Ru/hNCNC catalysts demonstrate good CO-tolerance, high MOR activity and durability, superior to those of the counterparts of Pt/hNCNC and commercial PtRu/C. The good electrochemical performance can be ascribed to the synergistic effects of the bifunctional effect due to introduction of Ru, small size and high dispersion of metal nanoparticles induced by the large SSA and nitrogen participation of hNCNC, and multi-scaled hierarchical pore structures beneficial to the mass transportation. These results proposed a potential strategy to develop the high-performance Pt-based MOR catalysts based on the novel mesostructured hNCNC.
2016, 74(7): 593-596
doi: 10.6023/A16030160
Abstract:
Dopamine (DA) is one of neurotransmitters in the human central nervous system and plays a very important role on human behavior and brain function. It is necessary to detect dopamine and determine its concentration in organism. Of all the dopamine detection methods reported, fluorescence probes exhibit high efficiency, considerate specifity and potential for real-time detection. Considering the high quantum field and strong trend to form an excimer of pyrene fluorophore, a fluorescent probe hydroxy(mesityl)(pyren-1-yl)borane (HMPB) based on pyrenyl boron compound was designed, synthesized and utilized in dopamine detection. In the phosphate buffer solution (PBS) with the aid of surfactant decyltrimethylammonium bromide, the water-insoluble HMPB could show two fluorescent bands: a monomer band of peaked at 388 nm and an excimer band peaked at 484 nm. The solubility of HMPB improved after addition of DA because it could react with HMPB to form a new compound HMPB-DA and it is better to dissolve in water. The excimer pyrenyl, therefore, gradually dissociated to generate monomer pyrenyl. Accordingly, as the addition of DA, fluorescent intensity at 484 nm (I484 nm) decreased, while intensity at 388 nm (I388 nm) increased. Within 10 min, the fluorescence intensity reached saturation and the ratio of I388 nm to I484 nm have great changed after adding dopamine. HMPB exhibited significant fluorescent response when the concentration range of DA is 10 nmol/L to 600 nmol/L in 10 min, which matched the physiologic concentration of DA. The ratio of I388 nm to I484 nm could be utilized to determine the concentration of dopamine. The detection limit of HMPB was as low as 14.6 nmol/L. HMPB showed no response to common amino acids, saccharides, proteins, ions, catecholamin and other bioactive molecules, even if the interference molecules were at high concentrations. Meanwhile, HMPB can be used to detect dopamine in urine of organisms. With fast response, high sensitivity and accuracy, HMPB represented considerable potential to act as a DA detector in physiological environment, which could become a promising tool in biochemistry, molecular biology and diagnostics investigation.
Dopamine (DA) is one of neurotransmitters in the human central nervous system and plays a very important role on human behavior and brain function. It is necessary to detect dopamine and determine its concentration in organism. Of all the dopamine detection methods reported, fluorescence probes exhibit high efficiency, considerate specifity and potential for real-time detection. Considering the high quantum field and strong trend to form an excimer of pyrene fluorophore, a fluorescent probe hydroxy(mesityl)(pyren-1-yl)borane (HMPB) based on pyrenyl boron compound was designed, synthesized and utilized in dopamine detection. In the phosphate buffer solution (PBS) with the aid of surfactant decyltrimethylammonium bromide, the water-insoluble HMPB could show two fluorescent bands: a monomer band of peaked at 388 nm and an excimer band peaked at 484 nm. The solubility of HMPB improved after addition of DA because it could react with HMPB to form a new compound HMPB-DA and it is better to dissolve in water. The excimer pyrenyl, therefore, gradually dissociated to generate monomer pyrenyl. Accordingly, as the addition of DA, fluorescent intensity at 484 nm (I484 nm) decreased, while intensity at 388 nm (I388 nm) increased. Within 10 min, the fluorescence intensity reached saturation and the ratio of I388 nm to I484 nm have great changed after adding dopamine. HMPB exhibited significant fluorescent response when the concentration range of DA is 10 nmol/L to 600 nmol/L in 10 min, which matched the physiologic concentration of DA. The ratio of I388 nm to I484 nm could be utilized to determine the concentration of dopamine. The detection limit of HMPB was as low as 14.6 nmol/L. HMPB showed no response to common amino acids, saccharides, proteins, ions, catecholamin and other bioactive molecules, even if the interference molecules were at high concentrations. Meanwhile, HMPB can be used to detect dopamine in urine of organisms. With fast response, high sensitivity and accuracy, HMPB represented considerable potential to act as a DA detector in physiological environment, which could become a promising tool in biochemistry, molecular biology and diagnostics investigation.
2016, 74(7): 597-602
doi: 10.6023/A16020098
Abstract:
Ion channels that exist in the living systems play important roles in maintaining normal physiological processes, and they have attracted great attentions of scientists because of their unique property in many biological activities. Learning from nature become an important source of new materials development. Inspired by natural biological ion channels, artificial polyethylene terephthalate (PET) nanochannel was built by track-etched method and served as one kind of the biomimetic ion channels in this paper. By introducing the idea of asymmetric modification in the PET cylindrical nanochannels, we designed and fabricated an artificial nanochannel system with high and controllable rectification, which ion transport properties can be regulated by Au nanoparticles. PET cylindrical nanochannels are modified with 2-undecyl-1-disulfide ureidoethyl quaternary imidazolinium salt (SUDEI) by electrostatic adsorption, resulting in positively charged on one side of PET cylindrical nanochannels. Since the other side of nanochannels are negatively charged, this membrane exhibits rectified properties with asymmetric charge distribution and geometric structure. The movement of cation presents a priority direction, which is from SUDEI side to the other side, and the opposite direction is suppressed. The ion transportation properties of the nanochannels can be investigated by measuring the current-voltage characteristics, and the diode-like behavior is quantified by the current rectification ratios. By introducing the SUDEI, PET nanochannels have a non-linear ion transport properties, showing better gating performance. In addition, the rectification ratios of this system can be regulated by SUDEI modification time and Au nanoparticles. SUDEI contains active sulfur element, resulting in Au nanoparticles stably bounding to SUDEI with Au—S bond. Therefore, the addition of Au nanoparticles can further increase the nanogating ratio because it can reduce the effective diameter of the cylindrical nanochannels, making the system more asymmetrical. And the ion transport in this system exhibits excellent stability. This system provides a new design idea for further research on more complicated functionalization and smart nanochannel systems.
Ion channels that exist in the living systems play important roles in maintaining normal physiological processes, and they have attracted great attentions of scientists because of their unique property in many biological activities. Learning from nature become an important source of new materials development. Inspired by natural biological ion channels, artificial polyethylene terephthalate (PET) nanochannel was built by track-etched method and served as one kind of the biomimetic ion channels in this paper. By introducing the idea of asymmetric modification in the PET cylindrical nanochannels, we designed and fabricated an artificial nanochannel system with high and controllable rectification, which ion transport properties can be regulated by Au nanoparticles. PET cylindrical nanochannels are modified with 2-undecyl-1-disulfide ureidoethyl quaternary imidazolinium salt (SUDEI) by electrostatic adsorption, resulting in positively charged on one side of PET cylindrical nanochannels. Since the other side of nanochannels are negatively charged, this membrane exhibits rectified properties with asymmetric charge distribution and geometric structure. The movement of cation presents a priority direction, which is from SUDEI side to the other side, and the opposite direction is suppressed. The ion transportation properties of the nanochannels can be investigated by measuring the current-voltage characteristics, and the diode-like behavior is quantified by the current rectification ratios. By introducing the SUDEI, PET nanochannels have a non-linear ion transport properties, showing better gating performance. In addition, the rectification ratios of this system can be regulated by SUDEI modification time and Au nanoparticles. SUDEI contains active sulfur element, resulting in Au nanoparticles stably bounding to SUDEI with Au—S bond. Therefore, the addition of Au nanoparticles can further increase the nanogating ratio because it can reduce the effective diameter of the cylindrical nanochannels, making the system more asymmetrical. And the ion transport in this system exhibits excellent stability. This system provides a new design idea for further research on more complicated functionalization and smart nanochannel systems.
Adsorption and Reaction Kinetic Studies of the Heterogeneous Catalytic Hydrogenation for Polystyrene
2016, 74(7): 603-611
doi: 10.6023/A16030117
Abstract:
We applied silica hollow microspheres with through holes in the shell as supports to prepare Pd-based supported catalyst (Pd/SHMs) for heterogeneous catalytic hydrogenation of polystyrene (PS) and also systematically studied the adsorption and reaction behavior of PS molecules over Pd/SHMs. The dynamic adsorption and reaction models of PS molecules under different temperatures have been established and the partially hydrogenated products were also comprehensively analyzed. The result shows that both the adsorption capacity and saturation time are increased as the temperature increasing and this hydrogenation reaction is confirmed to be a first-order reaction and the activation energy is calculated to be 58.3 kJ·mol-1. After separating and purifying three samples with different hydrogenation degrees, we further analyzed the partially hydrogenated products and the results show that they are all actually comprised of two kinds of substances with different properties, one with high hydrogenation conversion rate (ca. 85%) and the other with low hydrogenation ratio (ca. 25%). It is proved that PS heterogeneous hydrogenation process exists secondary adsorption and competitive adsorption phenomenon, and obeys the Blocky mechanism. This work lays the foundation for PS adsorption and hydrogenation reaction and is also favorable for the understanding of the adsorption and catalytic process for other unsaturated polymers over heterogeneous catalysts.
We applied silica hollow microspheres with through holes in the shell as supports to prepare Pd-based supported catalyst (Pd/SHMs) for heterogeneous catalytic hydrogenation of polystyrene (PS) and also systematically studied the adsorption and reaction behavior of PS molecules over Pd/SHMs. The dynamic adsorption and reaction models of PS molecules under different temperatures have been established and the partially hydrogenated products were also comprehensively analyzed. The result shows that both the adsorption capacity and saturation time are increased as the temperature increasing and this hydrogenation reaction is confirmed to be a first-order reaction and the activation energy is calculated to be 58.3 kJ·mol-1. After separating and purifying three samples with different hydrogenation degrees, we further analyzed the partially hydrogenated products and the results show that they are all actually comprised of two kinds of substances with different properties, one with high hydrogenation conversion rate (ca. 85%) and the other with low hydrogenation ratio (ca. 25%). It is proved that PS heterogeneous hydrogenation process exists secondary adsorption and competitive adsorption phenomenon, and obeys the Blocky mechanism. This work lays the foundation for PS adsorption and hydrogenation reaction and is also favorable for the understanding of the adsorption and catalytic process for other unsaturated polymers over heterogeneous catalysts.
2016, 74(7): 612-619
doi: 10.6023/A16030141
Abstract:
Co-crystal technology has effectively improved the safety of 2, 4, 6, 8, 10, 12-hexanitro-2, 4, 6, 8, 10, 12-hexaazaisowurtzitane (CL20) and retained high detonation velocity, detonation pressure and other properties of CL20. To study why thermal sensitivity of CL20/1, 3-dinitrobenzene (DNB) co-crystal can be effectively reduced, simulations of the pyrolysis process of CL20/DNB co-crystal, CL20/TNT co-crystal, CL20 crystal and DNB crystal system were made with ReaxFF/lg force field reactive molecular dynamics in this paper. This paper provides from atomic level detailed information on thermal decomposition processes of CL20, DNB, CL20/DNB co-crystal and CL20/TNT co-crystal such as reaction pathway, contributing to a better understanding of differences between co-crystal and pure crystal. The results show that CL20/DNB co-crystal has lower thermal sensitivity than CL20 and CL20/TNT co-crystal, but has higher thermal sensitivity than DNB, which is consistent with experimental data. Besides, the initial reaction pathways of CL20 and CL20/DNB were found, which reveals the reasons why co-crystal can effectively reduce CL20 thermal sensitivity. CL20 and CL20/DNB have similar initial reaction pathways: N—NO2 bond of CL20 molecules breaks, working as a dominant role in the initial stage of thermal decomposition under the condition of different temperatures, followed by cage skeleton structure breaking reaction. We found two reasons for the decrease rate of CL20 in CL20/DNB co-crystal decomposition: (A) The huge number of DNB molecules in the initial reaction stage prevents effective collision between CL20 and the intermediate reactants, thus lowering the speed of CL20 thermal decomposition. (B) Part of DNB molecules react with CL20 molecules and the intermediate products, producing C6H4N3O6, C6H4N4O8 and C10H10N14O16 etc., which decrease concentration of CL20. Both are explanations from microscopic mechanism on why the thermal sensitivity of CL20/DNB co-crystal is lower than that of CL20 crystal. In addition, CL20/DNB co-crystal and CL20 have similar main reactants, such as NO2, NO3, N2, N2O2, HNO, H2O, CO2, and HONO etc. Through the analysis of the reaction kinetics, we obtain activation barrier of CL20 system and CL20/DNB system. This study confirms the fact that co-crystallization is an effective way to decrease the thermal sensitivity for CL20 while retaining high detonation performance.
Co-crystal technology has effectively improved the safety of 2, 4, 6, 8, 10, 12-hexanitro-2, 4, 6, 8, 10, 12-hexaazaisowurtzitane (CL20) and retained high detonation velocity, detonation pressure and other properties of CL20. To study why thermal sensitivity of CL20/1, 3-dinitrobenzene (DNB) co-crystal can be effectively reduced, simulations of the pyrolysis process of CL20/DNB co-crystal, CL20/TNT co-crystal, CL20 crystal and DNB crystal system were made with ReaxFF/lg force field reactive molecular dynamics in this paper. This paper provides from atomic level detailed information on thermal decomposition processes of CL20, DNB, CL20/DNB co-crystal and CL20/TNT co-crystal such as reaction pathway, contributing to a better understanding of differences between co-crystal and pure crystal. The results show that CL20/DNB co-crystal has lower thermal sensitivity than CL20 and CL20/TNT co-crystal, but has higher thermal sensitivity than DNB, which is consistent with experimental data. Besides, the initial reaction pathways of CL20 and CL20/DNB were found, which reveals the reasons why co-crystal can effectively reduce CL20 thermal sensitivity. CL20 and CL20/DNB have similar initial reaction pathways: N—NO2 bond of CL20 molecules breaks, working as a dominant role in the initial stage of thermal decomposition under the condition of different temperatures, followed by cage skeleton structure breaking reaction. We found two reasons for the decrease rate of CL20 in CL20/DNB co-crystal decomposition: (A) The huge number of DNB molecules in the initial reaction stage prevents effective collision between CL20 and the intermediate reactants, thus lowering the speed of CL20 thermal decomposition. (B) Part of DNB molecules react with CL20 molecules and the intermediate products, producing C6H4N3O6, C6H4N4O8 and C10H10N14O16 etc., which decrease concentration of CL20. Both are explanations from microscopic mechanism on why the thermal sensitivity of CL20/DNB co-crystal is lower than that of CL20 crystal. In addition, CL20/DNB co-crystal and CL20 have similar main reactants, such as NO2, NO3, N2, N2O2, HNO, H2O, CO2, and HONO etc. Through the analysis of the reaction kinetics, we obtain activation barrier of CL20 system and CL20/DNB system. This study confirms the fact that co-crystallization is an effective way to decrease the thermal sensitivity for CL20 while retaining high detonation performance.
2016, 74(7): 620-628
doi: 10.6023/A16010060
Abstract:
The mixture of citric acid and histidine was used as the carbon source for the preparation of histidine-functionalized graphene quantum dots via a high temperature pyrolysis (CH-GQD). The as-prepared CH-GQD is composed of graphene sheets with an average size of 3.5 nm. The edge of graphene sheets contains the rich of hydrophilic groups. The product is very soluble in water and displays strong and stable fluorescence emission. CH-GQD was coated on the surface of silica nanoparticles to obtain graphene quantum dots-silicon composite. Then, the lithium ion battery was assembled and its electrochemical performance was investigated, in which the composite electrode and metal lithium plate were used as the anode and the cathode, respectively. The results show that the introduction of CH-GQD leads to decrease of the electron transfer impedance of the silicon cathode by more than 14.7 times, increase of the lithium ion diffusion coefficient between the electrode and the electrolyte by 310 times, and reduce of storage lithium capacity fading caused by the side reactions of the silicon atoms with the electrolyte molecules. The first discharge capacity of CH-GQD@Si cell reaches 3325 mAh·g-1 at the current density of 50 mA·g-1 and 1119 mAh·g-1 at the current density of 1000 mA·g-1. The discharge capacity can remain 1454.4 mAh·g-1 at least after 100 cycles at the current density of 100 mA·g-1. The battery performance of CH-GQD@Si composite electrode is obviously better than that of pristine silicon anode and the modified silicon anode with the graphene quantum dots (CA-GQD), which was produced by the pyrolysis of citric acid and alanine. Because the difference in the structure between CH-GQD and CA-GQD only is the imidazole groups on the edge of their graphene sheets, the above result also proves that the imidazole group plays important roles to improve the electrochemical performance of the composite electrode.
The mixture of citric acid and histidine was used as the carbon source for the preparation of histidine-functionalized graphene quantum dots via a high temperature pyrolysis (CH-GQD). The as-prepared CH-GQD is composed of graphene sheets with an average size of 3.5 nm. The edge of graphene sheets contains the rich of hydrophilic groups. The product is very soluble in water and displays strong and stable fluorescence emission. CH-GQD was coated on the surface of silica nanoparticles to obtain graphene quantum dots-silicon composite. Then, the lithium ion battery was assembled and its electrochemical performance was investigated, in which the composite electrode and metal lithium plate were used as the anode and the cathode, respectively. The results show that the introduction of CH-GQD leads to decrease of the electron transfer impedance of the silicon cathode by more than 14.7 times, increase of the lithium ion diffusion coefficient between the electrode and the electrolyte by 310 times, and reduce of storage lithium capacity fading caused by the side reactions of the silicon atoms with the electrolyte molecules. The first discharge capacity of CH-GQD@Si cell reaches 3325 mAh·g-1 at the current density of 50 mA·g-1 and 1119 mAh·g-1 at the current density of 1000 mA·g-1. The discharge capacity can remain 1454.4 mAh·g-1 at least after 100 cycles at the current density of 100 mA·g-1. The battery performance of CH-GQD@Si composite electrode is obviously better than that of pristine silicon anode and the modified silicon anode with the graphene quantum dots (CA-GQD), which was produced by the pyrolysis of citric acid and alanine. Because the difference in the structure between CH-GQD and CA-GQD only is the imidazole groups on the edge of their graphene sheets, the above result also proves that the imidazole group plays important roles to improve the electrochemical performance of the composite electrode.
