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2018 Volume 76 Issue 9
2018, 76(9): 659-665
doi: 10.6023/A18070273
Abstract:
Modulating the activity of radicals is of great importance for the applications in radical-based materials and radical-mediated reactions. To this end, we have proposed a new concept of "supramolecular free radicals", which refers to the free radicals stabilized or activated through supramolecular approaches. Based on the host-guest chemistry of cucurbiturils (CB), we have fabricated three kinds of supramolecular free radicals to modulate the activity and realize diverse functions. Firstly, radical anions can be stabilized by the steric effect and electrostatic effect of CB. As a result, we have constructed a highly efficient near-infrared photothermal conversion system, which displays selective antibacterial performance. Secondly, owing to the electrostatic effect of CB, radical cations can be activated to induce a significant acceleration of Fenton oxidation reaction. Thirdly, by taking advantage of the dynamic nature of host-guest interactions, we can endow the reaction intermediate with adaptive reactivity, which greatly improves the catalytic efficiency of alcohol oxidation. It is highly anticipated that this series of research opens a new horizon in supramolecular materials and supramolecular catalysis.
Modulating the activity of radicals is of great importance for the applications in radical-based materials and radical-mediated reactions. To this end, we have proposed a new concept of "supramolecular free radicals", which refers to the free radicals stabilized or activated through supramolecular approaches. Based on the host-guest chemistry of cucurbiturils (CB), we have fabricated three kinds of supramolecular free radicals to modulate the activity and realize diverse functions. Firstly, radical anions can be stabilized by the steric effect and electrostatic effect of CB. As a result, we have constructed a highly efficient near-infrared photothermal conversion system, which displays selective antibacterial performance. Secondly, owing to the electrostatic effect of CB, radical cations can be activated to induce a significant acceleration of Fenton oxidation reaction. Thirdly, by taking advantage of the dynamic nature of host-guest interactions, we can endow the reaction intermediate with adaptive reactivity, which greatly improves the catalytic efficiency of alcohol oxidation. It is highly anticipated that this series of research opens a new horizon in supramolecular materials and supramolecular catalysis.
2018, 76(9): 666-680
doi: 10.6023/A18040129
Abstract:
The scarce lithium resources would ultimately fail to satisfy the ever-growing industrial demand, especially for the large-scale stationary energy storage. Sodium-ion batteries (SIBs) are considered as promising next-generation power sources because sodium is widely available and exhibits similar chemistry to that of lithium-ion batteries (LIBs). Although sodium share similar physical and chemical properties to lithium, the lager ionic radius, heavier molar mass and less negative redox potential of Na+/Na of the sodium jointly lead to some issues beset the SIBs, such as sluggish sodiation kinetics, larger volume expansion and lower energy density, which need to be tackled to promote the practical applications of the SIBs. Therefore, developing appropriate electrode materials is crucial to achieve SIBs with long lifespan and high energy density. One-dimensional nanostructures can provide orientated electronic (ionic) transport and strong tolerance to volume change, thus enhancing the electrochemical performance of electrode materials. Electrospinning technique is a low cost and versatile method to fabricate continuous one-dimensional functional materials with various morphology and targeted components that has been widely applied in SIBs. The volume change could be buffered efficiently by facilely modifying the morphology of electrospun materials or in-situ compositing with carbon materials. Benefiting from the ultra-high aspect ratio, electrospun one-dimensional electrodes can reduce the ionic transport distance, while provide continuous transport way for electron along the longitudinal direction, which is helpful to improve the sluggish sodiation kinetics. It is also worth noting that free-standing or flexible fibers could be easily obtained via the electrospinning technique, which can be used as binder-free electrode to enhance the energy density of the batteries. The research progress on electrospun materials for sodium-ion batteries is summarized in this review, including cathode materials and anode materials. Their electrochemical performance in sodium storage is discussed in detail. The advantages and challenges of these materials were pointed out, and the future development of electrospun materials for sodium ion batteries was also prospected.
The scarce lithium resources would ultimately fail to satisfy the ever-growing industrial demand, especially for the large-scale stationary energy storage. Sodium-ion batteries (SIBs) are considered as promising next-generation power sources because sodium is widely available and exhibits similar chemistry to that of lithium-ion batteries (LIBs). Although sodium share similar physical and chemical properties to lithium, the lager ionic radius, heavier molar mass and less negative redox potential of Na+/Na of the sodium jointly lead to some issues beset the SIBs, such as sluggish sodiation kinetics, larger volume expansion and lower energy density, which need to be tackled to promote the practical applications of the SIBs. Therefore, developing appropriate electrode materials is crucial to achieve SIBs with long lifespan and high energy density. One-dimensional nanostructures can provide orientated electronic (ionic) transport and strong tolerance to volume change, thus enhancing the electrochemical performance of electrode materials. Electrospinning technique is a low cost and versatile method to fabricate continuous one-dimensional functional materials with various morphology and targeted components that has been widely applied in SIBs. The volume change could be buffered efficiently by facilely modifying the morphology of electrospun materials or in-situ compositing with carbon materials. Benefiting from the ultra-high aspect ratio, electrospun one-dimensional electrodes can reduce the ionic transport distance, while provide continuous transport way for electron along the longitudinal direction, which is helpful to improve the sluggish sodiation kinetics. It is also worth noting that free-standing or flexible fibers could be easily obtained via the electrospinning technique, which can be used as binder-free electrode to enhance the energy density of the batteries. The research progress on electrospun materials for sodium-ion batteries is summarized in this review, including cathode materials and anode materials. Their electrochemical performance in sodium storage is discussed in detail. The advantages and challenges of these materials were pointed out, and the future development of electrospun materials for sodium ion batteries was also prospected.
2018, 76(9): 681-690
doi: 10.6023/A18050197
Abstract:
In recent years, solar cells (including dye-sensitized solar cells (DSSCs), quantum dots sensitized solar cells (QDSCs), and perovskite solar cells (PSCs)) have attracted wide attention due to their low cost, light weight, and high efficiency. Compared with traditional solar cells with opaque counter electrodes where the sunlight can only pass from the photoanode, bifacial solar cells, which are composed of photoanode, electrolyte, transparent counter electrode, hole transport layer can realize the purpose that sunlight can pass through the photoanode and the transparent counter electrode (CE) at the same time, which can reduce the loss of sunlight and greatly broad the light utilization of device to achieve improved opto-electronic performance. In the entire electrochemical cycle, the transparent counter electrode is regarded as reducing agent in reducing the oxidation state I3- in the electrolyte to the reduced state I- so the electrocatalytic activity, chemical stability, electrical conductivity of the transparent counter electrode directly influences the rear side photo-to-electricity efficiency of device and the preparation of transparent counter electrodes is significantly important for the device. Therefore, it is necessary to study the effect of the counter electrode on the photoelectric conversion efficiency of the bifacial solar cells. In view of the problems of low transmittance, high cost, and low light utilization of traditional CE, the transparent CE of bifacial solar cells with high power conversion efficiency and low cost are preferred. The transparent CE of bifacial DSSCs, QDSCs and PSCs are comprehensively discussed in this paper. The influence of materials choosing and interfacial modification methods of transparent counter electrode on the photovoltaic performances of bifacial devices are analyzed. The transparent counter electrodes materials mainly include metals and alloys, sulfides, selenides, conductive polymers, and so on. In conclusion, bifacial solar cells mainly have the following problems:high reflectivity of metal electrodes, corrosion of the sulfide on the electrodes and the stability of the conductive polymers. The further application prospects of these kinds of bifacial solar cells is proposed.
In recent years, solar cells (including dye-sensitized solar cells (DSSCs), quantum dots sensitized solar cells (QDSCs), and perovskite solar cells (PSCs)) have attracted wide attention due to their low cost, light weight, and high efficiency. Compared with traditional solar cells with opaque counter electrodes where the sunlight can only pass from the photoanode, bifacial solar cells, which are composed of photoanode, electrolyte, transparent counter electrode, hole transport layer can realize the purpose that sunlight can pass through the photoanode and the transparent counter electrode (CE) at the same time, which can reduce the loss of sunlight and greatly broad the light utilization of device to achieve improved opto-electronic performance. In the entire electrochemical cycle, the transparent counter electrode is regarded as reducing agent in reducing the oxidation state I3- in the electrolyte to the reduced state I- so the electrocatalytic activity, chemical stability, electrical conductivity of the transparent counter electrode directly influences the rear side photo-to-electricity efficiency of device and the preparation of transparent counter electrodes is significantly important for the device. Therefore, it is necessary to study the effect of the counter electrode on the photoelectric conversion efficiency of the bifacial solar cells. In view of the problems of low transmittance, high cost, and low light utilization of traditional CE, the transparent CE of bifacial solar cells with high power conversion efficiency and low cost are preferred. The transparent CE of bifacial DSSCs, QDSCs and PSCs are comprehensively discussed in this paper. The influence of materials choosing and interfacial modification methods of transparent counter electrode on the photovoltaic performances of bifacial devices are analyzed. The transparent counter electrodes materials mainly include metals and alloys, sulfides, selenides, conductive polymers, and so on. In conclusion, bifacial solar cells mainly have the following problems:high reflectivity of metal electrodes, corrosion of the sulfide on the electrodes and the stability of the conductive polymers. The further application prospects of these kinds of bifacial solar cells is proposed.
2018, 76(9): 691-700
doi: 10.6023/A18040178
Abstract:
All-conjugated rod-rod block copolymers (BCPs) have gained immense interest over the past few years because they combine fascinating self-assembly properties of BCPs with the optical and electronic properties of conjugated polymers. Based on it, an all-conjugated rod-rod BCPs, poly(3-hexylselenophene)-b-poly[3-(6-hydroxyl)hexylthiophene] (P3HS-b-P3HHT) with hydroxyl groups as side substitution groups was synthesized via the Grignard metathesis (GRIM) method. The introduction of side hydroxyl groups was designed to endow different polarity between P3HS and P3HHT blocks and enrich the solution structures of P3HS-b-P3HHT. During thermal annealing, the cross-linking of hydroxyl groups was also utilized to improve the thermal stability of poly(3-hexylthiophene) (P3HT)-based organic field-effect transistors (OFETs) when blended with a certain amount of P3HS-b-P3HHT. On one hand, the use of mixed solvents provided an effective way to control the self-assembly behavior of P3HS-b-P3HHT. Depending on the mixed solvent ratio (i.e., chloroform/pyridine or methanol/pyridine), the rod-rod interaction of the copolymer chains was controlled, yielding a series of nanostructures such as nanoribbons, nanofibers, and nanospheres. Detailed morphologies and the corresponding photophysical behavior of different nanostructures were characterized by transmission electron microscope and UV-vis absorption spectra. The conformations of the P3HS and P3HHT chains in the solutions influenced their photophysical properties greatly. On the other hand, based on the thermal cross-linkable properties of hydroxyl groups, a certain amount of P3HS-b-P3HHT was mixed with P3HT homopolymer to fabricate P3HS-b-P3HHT/P3HT OFETs. For control samples, the charge carrier mobility of pure P3HT-based OFETs was improved with the increased annealed temperatures up to 170℃, then decreased significantly when the temperature further increased to 200℃. While overall, the charge carrier mobilities of P3HS-b-P3HHT/P3HT OFETs were lower than those of pure P3HT-based OFETs, they were improved with the increased temperature to 200℃. It was found the P3HS-b-P3HHT(10%)/P3HT OFETs exhibited the charge carrier mobility of 0.040 cm2·V-1·s-1 after annealing at 200℃ for 1 h, which was higher than P3HT OFETs (0.025 cm2·V-1·s-1) under the same experimental condition. It was due to the cross-linking of hydroxyl groups in P3HS-b-P3HHT retain the crystallization structures of P3HT, thus improved the thermal stability of OFETs. Overall, this work demonstrates a new polythiophene-polyselenophene BCP with controlled nanostructures by solvent blending and promising application in OFETs to improve their thermal stability.
All-conjugated rod-rod block copolymers (BCPs) have gained immense interest over the past few years because they combine fascinating self-assembly properties of BCPs with the optical and electronic properties of conjugated polymers. Based on it, an all-conjugated rod-rod BCPs, poly(3-hexylselenophene)-b-poly[3-(6-hydroxyl)hexylthiophene] (P3HS-b-P3HHT) with hydroxyl groups as side substitution groups was synthesized via the Grignard metathesis (GRIM) method. The introduction of side hydroxyl groups was designed to endow different polarity between P3HS and P3HHT blocks and enrich the solution structures of P3HS-b-P3HHT. During thermal annealing, the cross-linking of hydroxyl groups was also utilized to improve the thermal stability of poly(3-hexylthiophene) (P3HT)-based organic field-effect transistors (OFETs) when blended with a certain amount of P3HS-b-P3HHT. On one hand, the use of mixed solvents provided an effective way to control the self-assembly behavior of P3HS-b-P3HHT. Depending on the mixed solvent ratio (i.e., chloroform/pyridine or methanol/pyridine), the rod-rod interaction of the copolymer chains was controlled, yielding a series of nanostructures such as nanoribbons, nanofibers, and nanospheres. Detailed morphologies and the corresponding photophysical behavior of different nanostructures were characterized by transmission electron microscope and UV-vis absorption spectra. The conformations of the P3HS and P3HHT chains in the solutions influenced their photophysical properties greatly. On the other hand, based on the thermal cross-linkable properties of hydroxyl groups, a certain amount of P3HS-b-P3HHT was mixed with P3HT homopolymer to fabricate P3HS-b-P3HHT/P3HT OFETs. For control samples, the charge carrier mobility of pure P3HT-based OFETs was improved with the increased annealed temperatures up to 170℃, then decreased significantly when the temperature further increased to 200℃. While overall, the charge carrier mobilities of P3HS-b-P3HHT/P3HT OFETs were lower than those of pure P3HT-based OFETs, they were improved with the increased temperature to 200℃. It was found the P3HS-b-P3HHT(10%)/P3HT OFETs exhibited the charge carrier mobility of 0.040 cm2·V-1·s-1 after annealing at 200℃ for 1 h, which was higher than P3HT OFETs (0.025 cm2·V-1·s-1) under the same experimental condition. It was due to the cross-linking of hydroxyl groups in P3HS-b-P3HHT retain the crystallization structures of P3HT, thus improved the thermal stability of OFETs. Overall, this work demonstrates a new polythiophene-polyselenophene BCP with controlled nanostructures by solvent blending and promising application in OFETs to improve their thermal stability.
2018, 76(9): 701-708
doi: 10.6023/A18060245
Abstract:
Remediation of nuclear wastewater containing U(Ⅵ) is very important to human health and environmental ecosystems. Recently, numerous kinds of adsorbents such as clay minerals, carbon-based material and layered double hydroxides etc. have been extensively investigated for effective containing U(Ⅵ) wastewater treatment. A representative class of two-dimensional material, "Mxene" has received multidisciplinary interests due to their widespread application in the fields of batteries, supercapacitors and wastewater treatment. Unfortunately, the adsorption capacity of pristine Mxene is frequently limited due to the low quantity of surface functional groups. It was obviously that synthesizing functionalized Mxene materials with plenty functional groups is of great importance for wastewater remediation. In this manuscript, polyaniline modified Mxene composites (PANI/Ti3C2Tx) were successfully synthesized by a in situ polymerization method and were characterized by a series of methods including SEM, FT-IR, XRD and XPS techniques. The adsorption behavior of U(Ⅵ) on PANI/Ti3C2Tx was systematically explored by batch experiment. The experiment results showed that the removal process was obviously affected by the ion strength, indicating the formation of outer-sphere surface complexes. Meanwhile, the thermodynamic results manifested that the adsorption process was spontaneous and endothermic reaction. Based on Langmuir model fit, the maximum adsorption capacity of U(Ⅵ) on polyaniline modified Mxene composites was calculated to be 102.8 mg/g at pH=5.0 and 298 K, which was superior than that of U(Ⅵ) on pristine Ti3C2Tx (36.6 mg/g). In addition, spectroscopy characterizations including Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy were applied to study the underlying interaction mechanism, which was mainly attributed to the strong surface complexion between surface functional groups (oxygen-containing groups and amino groups) and U(Ⅵ). This work herein pointed out that PANI/Ti3C2Tx materials were promising adsorbent for the efficient removal of U(Ⅵ) in the environmental pollution remediation.
Remediation of nuclear wastewater containing U(Ⅵ) is very important to human health and environmental ecosystems. Recently, numerous kinds of adsorbents such as clay minerals, carbon-based material and layered double hydroxides etc. have been extensively investigated for effective containing U(Ⅵ) wastewater treatment. A representative class of two-dimensional material, "Mxene" has received multidisciplinary interests due to their widespread application in the fields of batteries, supercapacitors and wastewater treatment. Unfortunately, the adsorption capacity of pristine Mxene is frequently limited due to the low quantity of surface functional groups. It was obviously that synthesizing functionalized Mxene materials with plenty functional groups is of great importance for wastewater remediation. In this manuscript, polyaniline modified Mxene composites (PANI/Ti3C2Tx) were successfully synthesized by a in situ polymerization method and were characterized by a series of methods including SEM, FT-IR, XRD and XPS techniques. The adsorption behavior of U(Ⅵ) on PANI/Ti3C2Tx was systematically explored by batch experiment. The experiment results showed that the removal process was obviously affected by the ion strength, indicating the formation of outer-sphere surface complexes. Meanwhile, the thermodynamic results manifested that the adsorption process was spontaneous and endothermic reaction. Based on Langmuir model fit, the maximum adsorption capacity of U(Ⅵ) on polyaniline modified Mxene composites was calculated to be 102.8 mg/g at pH=5.0 and 298 K, which was superior than that of U(Ⅵ) on pristine Ti3C2Tx (36.6 mg/g). In addition, spectroscopy characterizations including Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy were applied to study the underlying interaction mechanism, which was mainly attributed to the strong surface complexion between surface functional groups (oxygen-containing groups and amino groups) and U(Ⅵ). This work herein pointed out that PANI/Ti3C2Tx materials were promising adsorbent for the efficient removal of U(Ⅵ) in the environmental pollution remediation.
2018, 76(9): 709-714
doi: 10.6023/A18060225
Abstract:
Multimodality imaging can integrate structural/functional information from different imaging tools, thus provide more accurate diagnosis than each single imaging modality. Au nanoclusters (AuNCs) are unique and have rich X-ray attenuation and fluorescent properties based on strong quantum confinement effect (SQCE); however, there is a huge challenge to simultaneously improve both X-ray imaging ability and fluorescent properties by adjusting sizes under the requirements of in vivo biological application. In this study, using rGSH as reductant and stabilizer, we developed a sub-nanometer ultrasmall AuNCs (Us-Au15NCs) as an optimized multimodal imaging probe with enhanced imaging ability by accurately adjusting pH to 8. For the first time, the in vitro both enhanced fluorescent and X-ray computed tomography (CT) bimodal imaging ability of AuNCs were investigated. By adjusting the pH and the proportion of Au3+ ions to GSH, the fluorescence intensity of the Us-AuNCs was strengthened and the emission peak showed red-shifts from 510 nm to 683 nm. While promising and exciting, the attenuation coefficient verified by the HU (hounsfield unit) values was increased almost linearly with the ratio increasing, which preserved the excellent X-ray imaging ability of Us-AuNCs. In addition, With a demonstrated better X-ray attenuation property than that of clinically used iodinated small molecular contrast agent (e.g., Iohexol), the developed Us-Au15NCs enabled efficient and enhanced CT imaging. Thus, the synthesized Us-Au15NCs characterised by UV-vis spectra and fluorescence spectra could simultaneously possess superior CT contrast ability and significant photoluminescence properties. Transmission electron microscopy (TEM) results revealed that the morphology was uniform spherical shape. Moreover, the Us-Au15NCs shows excellent stability, low cytotoxicity and good biocompatibility. Furthermore, the prepared Us-Au15NCs was confirmed to be effective and applicable for fluorescent imaging of 4T1 tumor cells, which determining that the Us-Au15NCs was more effectively involved with the cancer cells. The significance of this study is that rather than the synthesis of Us-AuNCs only, the prepared Us-Au15NCs may serve as multimodality imaging contrast agent with fluorescence and CT imaging for clinical diagnosis application.
Multimodality imaging can integrate structural/functional information from different imaging tools, thus provide more accurate diagnosis than each single imaging modality. Au nanoclusters (AuNCs) are unique and have rich X-ray attenuation and fluorescent properties based on strong quantum confinement effect (SQCE); however, there is a huge challenge to simultaneously improve both X-ray imaging ability and fluorescent properties by adjusting sizes under the requirements of in vivo biological application. In this study, using rGSH as reductant and stabilizer, we developed a sub-nanometer ultrasmall AuNCs (Us-Au15NCs) as an optimized multimodal imaging probe with enhanced imaging ability by accurately adjusting pH to 8. For the first time, the in vitro both enhanced fluorescent and X-ray computed tomography (CT) bimodal imaging ability of AuNCs were investigated. By adjusting the pH and the proportion of Au3+ ions to GSH, the fluorescence intensity of the Us-AuNCs was strengthened and the emission peak showed red-shifts from 510 nm to 683 nm. While promising and exciting, the attenuation coefficient verified by the HU (hounsfield unit) values was increased almost linearly with the ratio increasing, which preserved the excellent X-ray imaging ability of Us-AuNCs. In addition, With a demonstrated better X-ray attenuation property than that of clinically used iodinated small molecular contrast agent (e.g., Iohexol), the developed Us-Au15NCs enabled efficient and enhanced CT imaging. Thus, the synthesized Us-Au15NCs characterised by UV-vis spectra and fluorescence spectra could simultaneously possess superior CT contrast ability and significant photoluminescence properties. Transmission electron microscopy (TEM) results revealed that the morphology was uniform spherical shape. Moreover, the Us-Au15NCs shows excellent stability, low cytotoxicity and good biocompatibility. Furthermore, the prepared Us-Au15NCs was confirmed to be effective and applicable for fluorescent imaging of 4T1 tumor cells, which determining that the Us-Au15NCs was more effectively involved with the cancer cells. The significance of this study is that rather than the synthesis of Us-AuNCs only, the prepared Us-Au15NCs may serve as multimodality imaging contrast agent with fluorescence and CT imaging for clinical diagnosis application.
2018, 76(9): 715-722
doi: 10.6023/A18050192
Abstract:
Dendrimers are a class of novel polymer materials, which have received a lot of attention in past decades. The property of a dendrimer material strongly depends on the conformational details of the molecules, including the monomer density distribution, the functional end-group distribution, and the molecular size. In this paper, we consider a dendrimer composed of flexible and long spacers, immersed in the athermal or good solvent. A self-consistent field theory (SCFT) with a pre-averaged excluded volume potential is employed to calculate the density profiles of the segments and the radius of gyration R of the dendrimers. The stretched conformation of the spacers, and the scaling laws between the dendrimer size and its topologic parameters are analyzed. Our main results are:(1) The segment density of the dendrimers obeys the "dense-core" model, and decreases smoothly along the radial direction. (2) Due to the folding-back conformation, the local density of the end-segments is proportional to the local segment density. The density profile of the end-segments does not have a lifted peak at the outer layer of the spherical molecule. (3) The conformation of the spacers with lower generation numbers is strongly stretched in the central region where the segments are crowded. The first-generation spacers are mostly stretched. However, the spacers with higher generation numbers are much weakly stretched in the outer region. (4) Our self-consistent field theory calculations give the scaling law of the dendrimer size R~(GP)1/5N2/5, where G is the generation number of the dendrimer, P is the spacer segment number, and N is the total segment number. This agrees with the Flory mean field calculation for dendrimer based on full segment number. But it disagrees with the pioneer theories based on a linear side chains and the results from Monte Carlo simulations, which gave R~(GP)2/5N1/5. This disagreement is attributed to the limited bond length in simulations and the unlimited stretchable spacers in SCFT. (5) If G is fixed, the scaling law is simplified to R~P3/5 in good solvent, which agrees with the pioneer theories.
Dendrimers are a class of novel polymer materials, which have received a lot of attention in past decades. The property of a dendrimer material strongly depends on the conformational details of the molecules, including the monomer density distribution, the functional end-group distribution, and the molecular size. In this paper, we consider a dendrimer composed of flexible and long spacers, immersed in the athermal or good solvent. A self-consistent field theory (SCFT) with a pre-averaged excluded volume potential is employed to calculate the density profiles of the segments and the radius of gyration R of the dendrimers. The stretched conformation of the spacers, and the scaling laws between the dendrimer size and its topologic parameters are analyzed. Our main results are:(1) The segment density of the dendrimers obeys the "dense-core" model, and decreases smoothly along the radial direction. (2) Due to the folding-back conformation, the local density of the end-segments is proportional to the local segment density. The density profile of the end-segments does not have a lifted peak at the outer layer of the spherical molecule. (3) The conformation of the spacers with lower generation numbers is strongly stretched in the central region where the segments are crowded. The first-generation spacers are mostly stretched. However, the spacers with higher generation numbers are much weakly stretched in the outer region. (4) Our self-consistent field theory calculations give the scaling law of the dendrimer size R~(GP)1/5N2/5, where G is the generation number of the dendrimer, P is the spacer segment number, and N is the total segment number. This agrees with the Flory mean field calculation for dendrimer based on full segment number. But it disagrees with the pioneer theories based on a linear side chains and the results from Monte Carlo simulations, which gave R~(GP)2/5N1/5. This disagreement is attributed to the limited bond length in simulations and the unlimited stretchable spacers in SCFT. (5) If G is fixed, the scaling law is simplified to R~P3/5 in good solvent, which agrees with the pioneer theories.
2018, 76(9): 723-728
doi: 10.6023/A18060231
Abstract:
An ultrasonic method and a tetrahydrofuran-mixed dispersion method were used to synthesize two heat-treated cobalt phthalocyanine catalysts supported on carbon nanotubes, CoPc-CNT-S and CoPc-CNT-R, respectively. The ultrasonic process was that mixing cobalt phthalocyanine and carbon nanotubes in isopropanol under ultrasound condition within 30 min, while the tetrahydrofuran-mixed dispersion method was that mixing cobalt phthalocyanine and carbon nanotubes in tetrahydrofuran at 80℃ lasting 4 h. Then the pyrolysis process was carried out in a tube furnace under Argon (Ar) atmosphere with a heating rate of 5℃/min to 800℃ and lasting 2 h. Thermogravimetric Analysis (TGA) results showed that cobalt content of CoPc-CNT-S was 8.1 wt% while CoPc-CNT-R was 7.0 wt%. Moreover, X-ray photoelectron spectroscopy (XPS) results gave a conclusion that nitrogen content of CoPc-CNT-R (5.22%) is twice more than CoPc-CNT-S (2.08%). In comparsion with CoPc-CNT-R, CoPc-CNT-S has more pyrrole nitrogen on the surface. The fuel cell tests in a PEM/AEM hybrid fuel cell showed that the activity and stability of CoPc-CNT-S performed better than CoPc-CNT-R. Power density of CoPc-CNT-S hold at 18.6 mW/cm2 in H2/O2 hybrid AEM/PEM fuel cell for 15 h and CoPc-CNT-R can only hold at 9 mW/cm2. The current density of CoPc-CNT-S maintain at 68 mA/cm2 after stability test in H2/O2 hybrid AEM/PEM fuel cell for 20 h under 50 mV, but the stablity of CoPc-CNT-S fluctuate between 20 mA/cm2 to 40 mA/cm2. The reason can be concluded that ultrasonic method and tetrahydrofuran-mixed dispersion method can cause different kind of nitrogen doped on catalyst to influence electrocatalytic properties. The phenomenon that the electron transfer resistance of CoPc-CNT-S was lower than CoPc-CNT-R after working in PEM/AEM fuel cells for 5 h and 15 h can prove indirectly that the activity of CoPc-CNT-R using for the cathode catalyst H2/O2 hybrid AEM/PEM fuel cell is obviously less than CoPc-CNT-S. These observations may result from the cooperative effect from the similar ratio of pyridinic and pyrrolic nitrogen which may accelerate the catalytic activity of CoPc-CNT-S toward oxygen reduction reaction.
An ultrasonic method and a tetrahydrofuran-mixed dispersion method were used to synthesize two heat-treated cobalt phthalocyanine catalysts supported on carbon nanotubes, CoPc-CNT-S and CoPc-CNT-R, respectively. The ultrasonic process was that mixing cobalt phthalocyanine and carbon nanotubes in isopropanol under ultrasound condition within 30 min, while the tetrahydrofuran-mixed dispersion method was that mixing cobalt phthalocyanine and carbon nanotubes in tetrahydrofuran at 80℃ lasting 4 h. Then the pyrolysis process was carried out in a tube furnace under Argon (Ar) atmosphere with a heating rate of 5℃/min to 800℃ and lasting 2 h. Thermogravimetric Analysis (TGA) results showed that cobalt content of CoPc-CNT-S was 8.1 wt% while CoPc-CNT-R was 7.0 wt%. Moreover, X-ray photoelectron spectroscopy (XPS) results gave a conclusion that nitrogen content of CoPc-CNT-R (5.22%) is twice more than CoPc-CNT-S (2.08%). In comparsion with CoPc-CNT-R, CoPc-CNT-S has more pyrrole nitrogen on the surface. The fuel cell tests in a PEM/AEM hybrid fuel cell showed that the activity and stability of CoPc-CNT-S performed better than CoPc-CNT-R. Power density of CoPc-CNT-S hold at 18.6 mW/cm2 in H2/O2 hybrid AEM/PEM fuel cell for 15 h and CoPc-CNT-R can only hold at 9 mW/cm2. The current density of CoPc-CNT-S maintain at 68 mA/cm2 after stability test in H2/O2 hybrid AEM/PEM fuel cell for 20 h under 50 mV, but the stablity of CoPc-CNT-S fluctuate between 20 mA/cm2 to 40 mA/cm2. The reason can be concluded that ultrasonic method and tetrahydrofuran-mixed dispersion method can cause different kind of nitrogen doped on catalyst to influence electrocatalytic properties. The phenomenon that the electron transfer resistance of CoPc-CNT-S was lower than CoPc-CNT-R after working in PEM/AEM fuel cells for 5 h and 15 h can prove indirectly that the activity of CoPc-CNT-R using for the cathode catalyst H2/O2 hybrid AEM/PEM fuel cell is obviously less than CoPc-CNT-S. These observations may result from the cooperative effect from the similar ratio of pyridinic and pyrrolic nitrogen which may accelerate the catalytic activity of CoPc-CNT-S toward oxygen reduction reaction.
