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2019 Volume 77 Issue 1
2019, 77(1): 9-23
doi: 10.6023/A18100447
Abstract:
Over the past few years, the power conversion efficiency of perovskite solar cells have shown a tremendous progress from 3.8% in 2009 to 23.3% in 2018. Perovskites have exhibited excellent advantages in photovoltaic devices and other promising optoelectronic devices owing to their exceptional material properties, including direct and tunable bandgaps, strong light absorption, high electron/hole mobilities, long charge carrier lifetimes and diffusion lengths. The outstanding performance of perovskite solar cells is closely related with the deposition techniques and material composition of perovskite films. The preparation process of perovskite film is crucial for obtaining high efficiency devices, and it usually requires to fabricate a high coverage, compact and uniform perovskite layer. At present, the preparation technology of perovskite absorption layer mainly includes one-step processing, two-step processing, dual-source thermal evaporation processing, vapor-assisted solution processing and some scalable processing methods, and there are many reports and summaries about this work. However, perovskites still have some shortcomings such as insufficient light absorption range, poor long-term stability, the lead toxicity, which need to be overcome to realize higher power conversion efficiency and further product application. Compositional control engineering of perovskite materials becomes one of the effective ways to solve the above problems, but the summary of the research in this area is still lacking. In this review, we summarize the recent progress on the perovskite materials with different component systems, including organic-inorganic lead halide perovskite, all-inorganic lead halide perovskite, low-lead perovskite and lead-free perovskite. We also discuss some representative material compositions and the research on their corresponding preparation methods, the optimization of device structure and the effects on the device performance. Moreover, we compare and summarize the advantages and disadvantages of perovskite materials with different component systems. The purpose is to provide ideas on how to improve the efficiency and stability of perovskite solar cells through compositional controlling, and finally realize commercial application.
Over the past few years, the power conversion efficiency of perovskite solar cells have shown a tremendous progress from 3.8% in 2009 to 23.3% in 2018. Perovskites have exhibited excellent advantages in photovoltaic devices and other promising optoelectronic devices owing to their exceptional material properties, including direct and tunable bandgaps, strong light absorption, high electron/hole mobilities, long charge carrier lifetimes and diffusion lengths. The outstanding performance of perovskite solar cells is closely related with the deposition techniques and material composition of perovskite films. The preparation process of perovskite film is crucial for obtaining high efficiency devices, and it usually requires to fabricate a high coverage, compact and uniform perovskite layer. At present, the preparation technology of perovskite absorption layer mainly includes one-step processing, two-step processing, dual-source thermal evaporation processing, vapor-assisted solution processing and some scalable processing methods, and there are many reports and summaries about this work. However, perovskites still have some shortcomings such as insufficient light absorption range, poor long-term stability, the lead toxicity, which need to be overcome to realize higher power conversion efficiency and further product application. Compositional control engineering of perovskite materials becomes one of the effective ways to solve the above problems, but the summary of the research in this area is still lacking. In this review, we summarize the recent progress on the perovskite materials with different component systems, including organic-inorganic lead halide perovskite, all-inorganic lead halide perovskite, low-lead perovskite and lead-free perovskite. We also discuss some representative material compositions and the research on their corresponding preparation methods, the optimization of device structure and the effects on the device performance. Moreover, we compare and summarize the advantages and disadvantages of perovskite materials with different component systems. The purpose is to provide ideas on how to improve the efficiency and stability of perovskite solar cells through compositional controlling, and finally realize commercial application.
2019, 77(1): 24-40
doi: 10.6023/A18070272
Abstract:
In the area of novel power sources, silicon anode in lithium-ion battery, with an ultrahigh theoretical specific capacity of 4200 mAh·g-1, has drawn numerous attentions and got to highlighting spot. Nevertheless, it suffers rapid capacity loss and short cyclability ascribed to the huge volume change during lithiation/delithiation process. So far, one of the most effective methods to ameliorate performances of silicon anode is to modify binders. In this way, the contact integrity among active materials, conductive additives and current collectors can be maintained, which may weaken the cracking and pulverization, keep high specific capacity as well as strengthen the cyclability of silicon anode. Considering both the advantages of silicon anode and the developments of binders, a review on silicon anode in lithium-ion battery will be demonstrated systematically. Besides, we describe the main effects of binders against battery performances. We hope that our review would provide research directions in the developments and applications of binders used in silicon anode of lithium-ion battery.
In the area of novel power sources, silicon anode in lithium-ion battery, with an ultrahigh theoretical specific capacity of 4200 mAh·g-1, has drawn numerous attentions and got to highlighting spot. Nevertheless, it suffers rapid capacity loss and short cyclability ascribed to the huge volume change during lithiation/delithiation process. So far, one of the most effective methods to ameliorate performances of silicon anode is to modify binders. In this way, the contact integrity among active materials, conductive additives and current collectors can be maintained, which may weaken the cracking and pulverization, keep high specific capacity as well as strengthen the cyclability of silicon anode. Considering both the advantages of silicon anode and the developments of binders, a review on silicon anode in lithium-ion battery will be demonstrated systematically. Besides, we describe the main effects of binders against battery performances. We hope that our review would provide research directions in the developments and applications of binders used in silicon anode of lithium-ion battery.
2019, 77(1): 41-46
doi: 10.6023/A18090374
Abstract:
Photon upconversion based on triplet-triplet annihilation (TTA) composed of organic photosensitizer and emitter, has attracted widespread attention due to its unique photophysical properties and enormous applications in photovoltaic cells, photocatalysis, bio-imaging, and photodynamic therapy. Particularly, in biological systems, long-wavelength excitation light can efficiently reduce the interference of background fluorescence and increase the penetration depth of biological tissue, thereby avoiding the use of high-energy excitation light and reducing the damage to biological samples. However, most of the upconversion dyes based on TTA mechanism are water-insoluble organic compounds, which greatly limits their application in the biological field. Herein we synthesized a TTA upconversion system based on silica nanoparticles, which can achieve upconversion emission in water. Specifically, the photosensitizer (fluorinated tetraphenylporphyrin platinum) and the emitter (siloxane derivatized 9, 10-diphenylanthracene) for photon upconversion were designed and synthesized, whose upconversion performance in dichloromethane solution was firstly studied by UV-Vis spectrophotometer and fluorescence spectrometer. Clear blue upconversion emission from emitter could be observed when the photosensitizer was excited by 532 nm laser. The triplet energy transfer efficiency between photosensitizer and emitter is 60%. The optimal ratio of photosensitizer to emitter was 1:40. Based on this ratio, the stable upconversion silica nanoparticles with uniform size in water were constructed by micellar template method. The average diameter characterized by transmission electron microscopy (TEM) is 15.5 nm and the hydration diameter characterized by dynamic light scattering (DLS) is 22.5 nm. When the 532 nm laser is used as the excitation source, the upconversion emission in water was achieved. Their upconversion luminescence lifetime and quantum yield are 12 μs and 0.8%, respectively. Finally, the upconversion mechanism in silica nanoparticles was studied. The upconversion intensities in silica nanoparticles show quadratic and first-order dependences on the incident intensity in the low and high excitation intensity ranges respectively, proving a triplet-triplet annihilation mechanism.
Photon upconversion based on triplet-triplet annihilation (TTA) composed of organic photosensitizer and emitter, has attracted widespread attention due to its unique photophysical properties and enormous applications in photovoltaic cells, photocatalysis, bio-imaging, and photodynamic therapy. Particularly, in biological systems, long-wavelength excitation light can efficiently reduce the interference of background fluorescence and increase the penetration depth of biological tissue, thereby avoiding the use of high-energy excitation light and reducing the damage to biological samples. However, most of the upconversion dyes based on TTA mechanism are water-insoluble organic compounds, which greatly limits their application in the biological field. Herein we synthesized a TTA upconversion system based on silica nanoparticles, which can achieve upconversion emission in water. Specifically, the photosensitizer (fluorinated tetraphenylporphyrin platinum) and the emitter (siloxane derivatized 9, 10-diphenylanthracene) for photon upconversion were designed and synthesized, whose upconversion performance in dichloromethane solution was firstly studied by UV-Vis spectrophotometer and fluorescence spectrometer. Clear blue upconversion emission from emitter could be observed when the photosensitizer was excited by 532 nm laser. The triplet energy transfer efficiency between photosensitizer and emitter is 60%. The optimal ratio of photosensitizer to emitter was 1:40. Based on this ratio, the stable upconversion silica nanoparticles with uniform size in water were constructed by micellar template method. The average diameter characterized by transmission electron microscopy (TEM) is 15.5 nm and the hydration diameter characterized by dynamic light scattering (DLS) is 22.5 nm. When the 532 nm laser is used as the excitation source, the upconversion emission in water was achieved. Their upconversion luminescence lifetime and quantum yield are 12 μs and 0.8%, respectively. Finally, the upconversion mechanism in silica nanoparticles was studied. The upconversion intensities in silica nanoparticles show quadratic and first-order dependences on the incident intensity in the low and high excitation intensity ranges respectively, proving a triplet-triplet annihilation mechanism.
2019, 77(1): 47-53
doi: 10.6023/A18080344
Abstract:
The cell performance and Pt utilization of low-Pt proton exchange membrane fuel cells (PEMFCs) have been significantly improved through incorporating carbon materials into the conventional Pt/C catalytic layer of the membrane electrode assembly (MEA). However, the introduction methods for the carbon materials have not been investigated. In this work, carbon nanotube (CNT) as an additive was added to the low-Pt loading catalytic layer (0.1 mgPt·cm-2) by two methods:a separated CNT layer deposited on the top of the conventional Pt/C layer (CCM-1) and a mixture layer by blending CNT and Pt/C catalyst (CCM-2). The conventional low-Pt loading catalytic layer was employed as control group (CCM-0). The microstructure of the catalytic layers was characterized by scanning electron microscopy, transmission electron microscopy and nitrogen sorption isotherms method. The electrochemical properties of the catalytic layer and membrane electrode were evaluated by cyclic voltammetry (CV), electrochemical impedance (EIS) and linear scanning voltammetry. The results indicated that the cell performance of the conventional low-Pt loading catalyst coated membrane was improved by the introduction of CNTs in both CCM-1 and CCM-2. Compared to the conventional CCM (CCM-0) with a peak power density of 0.522 W·cm-2 at 70℃ and 100% relative humidity (RH) without backpressure, the maximum power densities of CCM-1 and CCM-2 have been improved by 22.4% and 60.0% under the same test conditions, respectively. The increased performance of CCM-1 is believed to result from the enhancement of contact interface between the catalytic layer and the gas diffusion layer in CCM-1 and consequent decrease of the contact resistance. Furthermore, the outstanding power density of CCM-2 is not only owing to the decreased interface contact resistance between the CCM and the gas diffusion layer, but also due to the significant improvement of gas transmission in the catalytic layer, which leads to the decrease of electrochemical reactant resistance and then improvement of the Pt utilization. That has been confirmed by the Pt utilization of 34.4%, 35.6% and 44.7% for CCM-0, CCM-1 and CCM-2. In addition, it also was confirmed by the extremely low power output (2.9 mW·cm-2) of a CCM with only CNT in the catalytic layer when the fuel cell was tested at 70℃ and 100% RH without back pressure. In addition, the optimum loading of CNT in the mixed catalytic layer is 37.5 μg·cm-2 with the peak power density of 0.91 W·cm-2. This work shows that mixing of CNT and Pt/C catalyst into a catalytic layer is an effective method for improving the Pt utilization and reducing the loading of Pt catalyst.
The cell performance and Pt utilization of low-Pt proton exchange membrane fuel cells (PEMFCs) have been significantly improved through incorporating carbon materials into the conventional Pt/C catalytic layer of the membrane electrode assembly (MEA). However, the introduction methods for the carbon materials have not been investigated. In this work, carbon nanotube (CNT) as an additive was added to the low-Pt loading catalytic layer (0.1 mgPt·cm-2) by two methods:a separated CNT layer deposited on the top of the conventional Pt/C layer (CCM-1) and a mixture layer by blending CNT and Pt/C catalyst (CCM-2). The conventional low-Pt loading catalytic layer was employed as control group (CCM-0). The microstructure of the catalytic layers was characterized by scanning electron microscopy, transmission electron microscopy and nitrogen sorption isotherms method. The electrochemical properties of the catalytic layer and membrane electrode were evaluated by cyclic voltammetry (CV), electrochemical impedance (EIS) and linear scanning voltammetry. The results indicated that the cell performance of the conventional low-Pt loading catalyst coated membrane was improved by the introduction of CNTs in both CCM-1 and CCM-2. Compared to the conventional CCM (CCM-0) with a peak power density of 0.522 W·cm-2 at 70℃ and 100% relative humidity (RH) without backpressure, the maximum power densities of CCM-1 and CCM-2 have been improved by 22.4% and 60.0% under the same test conditions, respectively. The increased performance of CCM-1 is believed to result from the enhancement of contact interface between the catalytic layer and the gas diffusion layer in CCM-1 and consequent decrease of the contact resistance. Furthermore, the outstanding power density of CCM-2 is not only owing to the decreased interface contact resistance between the CCM and the gas diffusion layer, but also due to the significant improvement of gas transmission in the catalytic layer, which leads to the decrease of electrochemical reactant resistance and then improvement of the Pt utilization. That has been confirmed by the Pt utilization of 34.4%, 35.6% and 44.7% for CCM-0, CCM-1 and CCM-2. In addition, it also was confirmed by the extremely low power output (2.9 mW·cm-2) of a CCM with only CNT in the catalytic layer when the fuel cell was tested at 70℃ and 100% RH without back pressure. In addition, the optimum loading of CNT in the mixed catalytic layer is 37.5 μg·cm-2 with the peak power density of 0.91 W·cm-2. This work shows that mixing of CNT and Pt/C catalyst into a catalytic layer is an effective method for improving the Pt utilization and reducing the loading of Pt catalyst.
2019, 77(1): 54-59
doi: 10.6023/A18080335
Abstract:
Sulfonated porous polystyrene microspheres as heterogeneous catalyst for preparation of biodiesel were prepared by a facile two-step synthesis process in this work. Firstly, monodisperse porous cross-linked polystyrene microspheres were prepared by reflux-precipitation polymerization, in which different ratio of styrene (St) and divinylbenzene (DVB) were used as monomer and cross-linker, respectively. Then the obtained polystyrene microspheres were sulfonated by chlorosulfonic acid. The structure and composition of the related polystyrene microspheres were characterized by FT-IR, X-ray photoelectron spectroscopy, elemental analysis, thermogravimetric analysis, Brunauer-Emmett-Teller (BET) surface area analysis, transmission electron microscope, particle size and zeta potential analysis. In order to adjust the sulfonated degree and acid density, the reaction parameters such as solvent dosage, swelling time, amount of chlorinated sulfonic acid, sulfonated temperature and sulfonated time were investigated carefully. The optimum conditions for the sulfonated reaction are as follows:0.5 g of cross-linked polystyrene microspheres was swollen with 5 mL of CCl4, and then sulfonated with 0.3 mL of chlorosulfonic acid at 50℃ for 75 min. In addition, the effect of crosslinking degree on the specific surface area and acid density of the sulfonated polystyrene microspheres were also studied. The as-prepared sulfonated polystyrene microspheres exhibited high acid density (2.611 mmol·g-1), good thermal stability (up to about 200℃) and appropriate specific surface area. The sulfonated porous polystyrene microspheres as catalyst were applied in the esterification reaction of oleic acid and methanol. Our experimental results showed that the functional particles possessed very high catalytic activity, which was much higher than polystyrene ion exchange resin (Ameberlyst-15) and close to concentrated sulfuric acid. The catalytic activity still maintained 92% of the initial activity after 3 runs of recycling use, and the shedding of sulfonic acid groups was almost negligible. This paper demonstrates a simple, green and controllable strategy to develop sulfonated porous polystyrene microspheres with high catalytic activity and good durability for preparation of biodiesel.
Sulfonated porous polystyrene microspheres as heterogeneous catalyst for preparation of biodiesel were prepared by a facile two-step synthesis process in this work. Firstly, monodisperse porous cross-linked polystyrene microspheres were prepared by reflux-precipitation polymerization, in which different ratio of styrene (St) and divinylbenzene (DVB) were used as monomer and cross-linker, respectively. Then the obtained polystyrene microspheres were sulfonated by chlorosulfonic acid. The structure and composition of the related polystyrene microspheres were characterized by FT-IR, X-ray photoelectron spectroscopy, elemental analysis, thermogravimetric analysis, Brunauer-Emmett-Teller (BET) surface area analysis, transmission electron microscope, particle size and zeta potential analysis. In order to adjust the sulfonated degree and acid density, the reaction parameters such as solvent dosage, swelling time, amount of chlorinated sulfonic acid, sulfonated temperature and sulfonated time were investigated carefully. The optimum conditions for the sulfonated reaction are as follows:0.5 g of cross-linked polystyrene microspheres was swollen with 5 mL of CCl4, and then sulfonated with 0.3 mL of chlorosulfonic acid at 50℃ for 75 min. In addition, the effect of crosslinking degree on the specific surface area and acid density of the sulfonated polystyrene microspheres were also studied. The as-prepared sulfonated polystyrene microspheres exhibited high acid density (2.611 mmol·g-1), good thermal stability (up to about 200℃) and appropriate specific surface area. The sulfonated porous polystyrene microspheres as catalyst were applied in the esterification reaction of oleic acid and methanol. Our experimental results showed that the functional particles possessed very high catalytic activity, which was much higher than polystyrene ion exchange resin (Ameberlyst-15) and close to concentrated sulfuric acid. The catalytic activity still maintained 92% of the initial activity after 3 runs of recycling use, and the shedding of sulfonic acid groups was almost negligible. This paper demonstrates a simple, green and controllable strategy to develop sulfonated porous polystyrene microspheres with high catalytic activity and good durability for preparation of biodiesel.
2019, 77(1): 60-65
doi: 10.6023/A18080323
Abstract:
The ever-growing crises of fossil fuel shortage and environmental pollution urgently call for the exploration of clean and renewable energies. Fuel cells present high power efficiency and emit zero pollutants, showing great potential in the future energy system. The main bottleneck of fuel cell commercialization is the sluggish oxygen reduction reaction (ORR) at the cathode. To date, the most active electrocatalysts for ORR are platinum and its alloys. However, the scarcity, high cost and susceptibility to methanol crossover of precious metals hinder the large-scale application of fuel cells. The development of highly efficient and stable non-precious metal ORR electrocatalysts with high resistance to methanol crossover is of great significance. M/N/C (M=Fe, Co, etc.) catalysts are attractive non-precious metal based ORR electrocatalysts and their performance depends on the density of active sites on the catalyst surface. The common synthesis of M/N/C catalysts is to pyrolyze the mixture of metal salt, nitrogen-containing precursor and carbon support. However, so-synthesized catalysts usually contain large metal-based particles, leading to the shortcomings of low density and partial embedding of active sites. Graphitic carbon nitride (g-C3N4) with high concentration of pyridine-like nitrogen in heptazine heterorings can provide abundant and uniform nitrogen coordination sites, which can capture metal ions by the interaction between metal ions and N sites. In addition, g-C3N4 would be decomposed largely during pyrolysis, which is beneficial to form highly exposed M/N/C active sites by pyrolyzing the g-C3N4 with adsorbed metal ions. Herein, we reported the construction of Co/N/C electrocatalysts with highly exposed active sites. Specifically, the g-C3N4 was uniformly supported on the surface of high-conductive hierarchical carbon nanocages (hCNC) by the impregnation and pyrolysis process, leading to the formation of g-C3N4/hCNC composite. Co2+ ions were then captured by the g-C3N4 species on the surface owing to the interaction between the lone pair electrons of nitrogen and the Co2+ ions, and the subsequent pyrolysis led to the Co/N/C catalysts with highly exposed active sites, high conductivity and multiscale pore structure. The optimized catalyst obtained at 800℃ exhibits excellent ORR performance in alkaline medium, with a high onset potential (0.97 V) comparable to commercial Pt/C catalyst, while much better stability and high immunity to methanol crossover. This study demonstrates an effective strategy for the construction of high-efficient M/N/C catalysts with highly exposed active sites.
The ever-growing crises of fossil fuel shortage and environmental pollution urgently call for the exploration of clean and renewable energies. Fuel cells present high power efficiency and emit zero pollutants, showing great potential in the future energy system. The main bottleneck of fuel cell commercialization is the sluggish oxygen reduction reaction (ORR) at the cathode. To date, the most active electrocatalysts for ORR are platinum and its alloys. However, the scarcity, high cost and susceptibility to methanol crossover of precious metals hinder the large-scale application of fuel cells. The development of highly efficient and stable non-precious metal ORR electrocatalysts with high resistance to methanol crossover is of great significance. M/N/C (M=Fe, Co, etc.) catalysts are attractive non-precious metal based ORR electrocatalysts and their performance depends on the density of active sites on the catalyst surface. The common synthesis of M/N/C catalysts is to pyrolyze the mixture of metal salt, nitrogen-containing precursor and carbon support. However, so-synthesized catalysts usually contain large metal-based particles, leading to the shortcomings of low density and partial embedding of active sites. Graphitic carbon nitride (g-C3N4) with high concentration of pyridine-like nitrogen in heptazine heterorings can provide abundant and uniform nitrogen coordination sites, which can capture metal ions by the interaction between metal ions and N sites. In addition, g-C3N4 would be decomposed largely during pyrolysis, which is beneficial to form highly exposed M/N/C active sites by pyrolyzing the g-C3N4 with adsorbed metal ions. Herein, we reported the construction of Co/N/C electrocatalysts with highly exposed active sites. Specifically, the g-C3N4 was uniformly supported on the surface of high-conductive hierarchical carbon nanocages (hCNC) by the impregnation and pyrolysis process, leading to the formation of g-C3N4/hCNC composite. Co2+ ions were then captured by the g-C3N4 species on the surface owing to the interaction between the lone pair electrons of nitrogen and the Co2+ ions, and the subsequent pyrolysis led to the Co/N/C catalysts with highly exposed active sites, high conductivity and multiscale pore structure. The optimized catalyst obtained at 800℃ exhibits excellent ORR performance in alkaline medium, with a high onset potential (0.97 V) comparable to commercial Pt/C catalyst, while much better stability and high immunity to methanol crossover. This study demonstrates an effective strategy for the construction of high-efficient M/N/C catalysts with highly exposed active sites.
2019, 77(1): 66-71
doi: 10.6023/A18070301
Abstract:
Imines and their derivatives are versatile chemical intermediates for the synthesis of pharmaceuticals, polymer materials, biologicals and so on. The oxidative coupling of amines was demonstrated to be a promising one pot synthetic procedure for imines, and considerable efforts have been devoted to it. A new type of catalyst based on Mo2C was successfully prepared by roasting the mixture synthesized by using the interaction between ionic bonds with dopamine (DA) and phosphomolybdate (PMo). In a typical procedure, solid product was pyrolyzed in a tube furnace at 800℃ for 3 h in N2 with heating rate of 5℃/min, and the sample PDA-PMo-800 was achieved. The catalyst was characterized and analyzed by Fourier transform infrared (FT-IR), N2 adsorption desorption (BET), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), and Raman spectrometer (Raman), thermo gravimetric analyzer (TG), energy dispersive spectrometer (EDS). It was found that the catalyst had morphologies of flower shaped spheres and certain specific surface area (102 m2·g-1). As a catalyst, it can be used in the oxidation coupling reaction of benzyl amine to synthesize the imine under the condition of no solvent and oxygen as oxidant. Typically, amine (5 mmol) and catalyst (0.03 g) was added into a 25 mL sealed round-bottomed flask and kept vigorously stirring at 100℃ under O2 balloon for 10 h. After completion, the catalyst was separated by centrifugation with N, N-dimethylformamide, washed with ethanol, dried in a vacuum, and reused for the next time. The filtrate was identified by GC-MS, and the conversion and yield were analyzed by GC (SP-6890A) equipped with a FID detector. The results showed that a high conversion rate and selection rate can be achieved. And the catalyst can be used repeatedly and maintained a high conversion rate under the same conditions. The successful design of this catalyst not only combines metal materials with organic materials, but also makes a preparation for transition metals to replace noble metals. In addition, carbonized metal was used as a catalyst for coupling reaction, which provided a new idea for the application of carbonized metals to organic reactions.
Imines and their derivatives are versatile chemical intermediates for the synthesis of pharmaceuticals, polymer materials, biologicals and so on. The oxidative coupling of amines was demonstrated to be a promising one pot synthetic procedure for imines, and considerable efforts have been devoted to it. A new type of catalyst based on Mo2C was successfully prepared by roasting the mixture synthesized by using the interaction between ionic bonds with dopamine (DA) and phosphomolybdate (PMo). In a typical procedure, solid product was pyrolyzed in a tube furnace at 800℃ for 3 h in N2 with heating rate of 5℃/min, and the sample PDA-PMo-800 was achieved. The catalyst was characterized and analyzed by Fourier transform infrared (FT-IR), N2 adsorption desorption (BET), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), and Raman spectrometer (Raman), thermo gravimetric analyzer (TG), energy dispersive spectrometer (EDS). It was found that the catalyst had morphologies of flower shaped spheres and certain specific surface area (102 m2·g-1). As a catalyst, it can be used in the oxidation coupling reaction of benzyl amine to synthesize the imine under the condition of no solvent and oxygen as oxidant. Typically, amine (5 mmol) and catalyst (0.03 g) was added into a 25 mL sealed round-bottomed flask and kept vigorously stirring at 100℃ under O2 balloon for 10 h. After completion, the catalyst was separated by centrifugation with N, N-dimethylformamide, washed with ethanol, dried in a vacuum, and reused for the next time. The filtrate was identified by GC-MS, and the conversion and yield were analyzed by GC (SP-6890A) equipped with a FID detector. The results showed that a high conversion rate and selection rate can be achieved. And the catalyst can be used repeatedly and maintained a high conversion rate under the same conditions. The successful design of this catalyst not only combines metal materials with organic materials, but also makes a preparation for transition metals to replace noble metals. In addition, carbonized metal was used as a catalyst for coupling reaction, which provided a new idea for the application of carbonized metals to organic reactions.
2019, 77(1): 72-83
doi: 10.6023/A18090365
Abstract:
Stock solutions of organic micro-pollutants with low water solubility are commonly prepared using organic solvents in laboratory studies on degradation of these organic compounds. Dilution of the stock solution unavoidably introduces a small amount of organic solvent into the experimental working solutions. This could possibly affect the estimation of the degradation rate constants (kobs) of these organic micro-pollutants by UV-based oxidation processes. To demonstrate this problem, the effect of organic solvents on the degradation rate of atrazine (ATZ) has been investigated in the sole-UV, UV/H2O2 and UV/TiO2 process at the concentration levels that would likely be derived from stock solutions. Organic solvent methanol (MeOH) commonly used for stock-solution preparation was selected. The degradation of ATZ was investigated under ultraviolet irradiation (253.7 nm). The reaction was conducted in an annular photochemical reactor, in the axis of which a low-pressure mercury lamp (LPUV) was installed. The photon flux into the solution from the LPUV was determined to be at 1.18×10-7 Einstein/s. A magnetic stirrer was located at the bottom of the reactor to maintain homogeneity of the reacting solution. A thermostatic water recirculation system was used to control the solution temperature at 20±0.5℃. Prior to irradiation, the mercury lamp was ignited for 30 min for a stable output. UV photo-oxidation was performed with ultrapure water containing an initial 0.1 or 5 mg/L ATZ and different volume ratio of methanol. Solution pH value of 4.0, 7.0 and 10.0 was buffered using phosphate or borate. Determination of ATZ using ultra-performance liquid chromatography-electrospray-triple quadrupole mass spectrometry coupled with an ACQUITYTM UPLC BEH C8 separation column. The results show that the reaction rate of ATZ in UV/TiO2 process could be affected significantly by the presence of MeOH, even at a concentration well below that possibly introduced during the preparation of working solutions from the organic solvent stock solutions (e.g. 0.01%, V/V). With the increase of MeOH concentration, the kobs of ATZ in UV/TiO2 process gradually decreases. The organic solvents having a stronger reaction activity with·OH tend to impose a greater effect on the kobs of ATZ. However, MeOH does not affect kobs of photolysis of ATZ in sole-UV process, and a small effect for the kobs of ATZ in UV/H2O2 process. In addition, MeOH in the reaction system does not affect the speciation and degradation pathway of ATZ under different UV-based oxidation processes. The findings here provide a plausible explanation for the discrepancies in the reaction rate constants reported in the literature for some organic micro-pollutants during the UV-based oxidation processes.
Stock solutions of organic micro-pollutants with low water solubility are commonly prepared using organic solvents in laboratory studies on degradation of these organic compounds. Dilution of the stock solution unavoidably introduces a small amount of organic solvent into the experimental working solutions. This could possibly affect the estimation of the degradation rate constants (kobs) of these organic micro-pollutants by UV-based oxidation processes. To demonstrate this problem, the effect of organic solvents on the degradation rate of atrazine (ATZ) has been investigated in the sole-UV, UV/H2O2 and UV/TiO2 process at the concentration levels that would likely be derived from stock solutions. Organic solvent methanol (MeOH) commonly used for stock-solution preparation was selected. The degradation of ATZ was investigated under ultraviolet irradiation (253.7 nm). The reaction was conducted in an annular photochemical reactor, in the axis of which a low-pressure mercury lamp (LPUV) was installed. The photon flux into the solution from the LPUV was determined to be at 1.18×10-7 Einstein/s. A magnetic stirrer was located at the bottom of the reactor to maintain homogeneity of the reacting solution. A thermostatic water recirculation system was used to control the solution temperature at 20±0.5℃. Prior to irradiation, the mercury lamp was ignited for 30 min for a stable output. UV photo-oxidation was performed with ultrapure water containing an initial 0.1 or 5 mg/L ATZ and different volume ratio of methanol. Solution pH value of 4.0, 7.0 and 10.0 was buffered using phosphate or borate. Determination of ATZ using ultra-performance liquid chromatography-electrospray-triple quadrupole mass spectrometry coupled with an ACQUITYTM UPLC BEH C8 separation column. The results show that the reaction rate of ATZ in UV/TiO2 process could be affected significantly by the presence of MeOH, even at a concentration well below that possibly introduced during the preparation of working solutions from the organic solvent stock solutions (e.g. 0.01%, V/V). With the increase of MeOH concentration, the kobs of ATZ in UV/TiO2 process gradually decreases. The organic solvents having a stronger reaction activity with·OH tend to impose a greater effect on the kobs of ATZ. However, MeOH does not affect kobs of photolysis of ATZ in sole-UV process, and a small effect for the kobs of ATZ in UV/H2O2 process. In addition, MeOH in the reaction system does not affect the speciation and degradation pathway of ATZ under different UV-based oxidation processes. The findings here provide a plausible explanation for the discrepancies in the reaction rate constants reported in the literature for some organic micro-pollutants during the UV-based oxidation processes.
2019, 77(1): 84-89
doi: 10.6023/A18080357
Abstract:
Hydrogen, a clean, efficient and sustainable energy, can be produced via electrochemical water splitting, during which two key processes, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), occur simultaneously at the two electrodes of an electrolytic cell. Nevertheless compared to the two-electron process of HER, OER, a four-electron process, is of the inherently kinetic hysteresis step, which can dramatically diminish the overall energy conversion efficiency. The highly active noble-metal-based catalyst RuO2 is considered to be one of the most efficient state-of-the-art OER catalysts. However the high cost and element scarcity significantly hinder their practical applications. Thus it is particularly urgent to develop highly-active but low-cost non-noble-metal alternatives. Iron/nickel alloy based catalysts have been widely studied owing to their promising performances. In this work, we prepared iron/nickel alloy nanoparticles embedded in N-doped hierarchically porous carbon (Fe0.64Ni0.36@NC), by simultaneously adsorbing metal precursors and dopamine on surface of SiO2 macroporous hard templates, and then annealing the system and etching the templates. In electrochemical measurements, Fe0.64Ni0.36@NC shows a superior OER activity in alkaline solution, which only needs an overpotential as low as 286 mV to deliver a current density of 10 mA·cm-2, being significantly lower than the value of 380 mV for RuO2. Besides, the catalyst displays no obvious activity decrease after 2000 cycles of continuous CV scanning, corresponding to an excellent durability. The observed nice performances of the alloy catalyst in alkaline solution can be ascribed to two critical structural features:(1) the macroporous structures made by stacking of SiO2 microspheres own relatively thin layer of carbon framework, thus the embedded iron/nickel alloy particles can well activate the surrounding carbon layer to expose copious active sites; (2) the graphitized N-doped carbon layers well protect the alloy nanoparticles from corrosion, thus improving the durability of the catalysts. This work gave a nice design for the highly efficient non-noble-metal OER catalysts.
Hydrogen, a clean, efficient and sustainable energy, can be produced via electrochemical water splitting, during which two key processes, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), occur simultaneously at the two electrodes of an electrolytic cell. Nevertheless compared to the two-electron process of HER, OER, a four-electron process, is of the inherently kinetic hysteresis step, which can dramatically diminish the overall energy conversion efficiency. The highly active noble-metal-based catalyst RuO2 is considered to be one of the most efficient state-of-the-art OER catalysts. However the high cost and element scarcity significantly hinder their practical applications. Thus it is particularly urgent to develop highly-active but low-cost non-noble-metal alternatives. Iron/nickel alloy based catalysts have been widely studied owing to their promising performances. In this work, we prepared iron/nickel alloy nanoparticles embedded in N-doped hierarchically porous carbon (Fe0.64Ni0.36@NC), by simultaneously adsorbing metal precursors and dopamine on surface of SiO2 macroporous hard templates, and then annealing the system and etching the templates. In electrochemical measurements, Fe0.64Ni0.36@NC shows a superior OER activity in alkaline solution, which only needs an overpotential as low as 286 mV to deliver a current density of 10 mA·cm-2, being significantly lower than the value of 380 mV for RuO2. Besides, the catalyst displays no obvious activity decrease after 2000 cycles of continuous CV scanning, corresponding to an excellent durability. The observed nice performances of the alloy catalyst in alkaline solution can be ascribed to two critical structural features:(1) the macroporous structures made by stacking of SiO2 microspheres own relatively thin layer of carbon framework, thus the embedded iron/nickel alloy particles can well activate the surrounding carbon layer to expose copious active sites; (2) the graphitized N-doped carbon layers well protect the alloy nanoparticles from corrosion, thus improving the durability of the catalysts. This work gave a nice design for the highly efficient non-noble-metal OER catalysts.
2019, 77(1): 90-94
doi: 10.6023/A18080318
Abstract:
Photochromic materials of oxygen-containing yttrium hydride exhibit reversible switching properties that can find applications in the energy saving windows, optical switching devices. However, the photochromic mechanisms of the oxygen-containing yttrium hydride has been not clarified yet. The optical modulation and durability of the films need to be improved. In this paper, oxygen-containing yttrium hydride films covered with hydrogen catalytic-palladium layers were prepared on a glass substrate by a direct-current (DC) magnetron sputtering methods. Firstly, oxygen-containing yttrium hydride thin films were deposited by DC magnetron sputtering of the Y targets in a 0.4 Pa with argon (purity 6N) and hydrogen (5N) mixed gas. Secondly, a thin film of Pd was deposited on the surface of YHx:O layer. Moreover, the effects of the Pd layer in the optical regulation state, crystal structure, surface microstructure and the content of each element of the oxygen-containing yttrium hydride films were investigated by means of SEM, XRD, and XPS methods. In the initial state, the films showed a transparent state with high transmittance in the visible and near-IR range same with single layer of the YHx:O. After exposure to xenon or visible light, the solar transmittance (Tsol) of the films sharply decreased by 37.39%. The result can be found that the coloring process (illumination process) of YHx:O thin films can be promoted and the optical regulation range can be increased after covered with a Pd layer. Investigation of the crystal structure by XRD demonstrates YHx:O covered with Pd, the same crystalline state with the YHx:O thin films has been found. After illumination, all reflection peaks of the YHx:O films slightly moving towards the larger angles with smaller lattice parameter (~5.30 Å) due to the deoxidation of YHx:O films. It can be seen from the EDS data that the oxygen contents in the YHx:O film decreases, while the yttrium contents increases, which is consistent with that of the single layer films. The XPS survey scans analysis of the YHx:O and Pd/YHx:O was also studied. After illumination, all peaks of the single layer slightly moving towards the larger angles. But the double layer have reverse result with above.
Photochromic materials of oxygen-containing yttrium hydride exhibit reversible switching properties that can find applications in the energy saving windows, optical switching devices. However, the photochromic mechanisms of the oxygen-containing yttrium hydride has been not clarified yet. The optical modulation and durability of the films need to be improved. In this paper, oxygen-containing yttrium hydride films covered with hydrogen catalytic-palladium layers were prepared on a glass substrate by a direct-current (DC) magnetron sputtering methods. Firstly, oxygen-containing yttrium hydride thin films were deposited by DC magnetron sputtering of the Y targets in a 0.4 Pa with argon (purity 6N) and hydrogen (5N) mixed gas. Secondly, a thin film of Pd was deposited on the surface of YHx:O layer. Moreover, the effects of the Pd layer in the optical regulation state, crystal structure, surface microstructure and the content of each element of the oxygen-containing yttrium hydride films were investigated by means of SEM, XRD, and XPS methods. In the initial state, the films showed a transparent state with high transmittance in the visible and near-IR range same with single layer of the YHx:O. After exposure to xenon or visible light, the solar transmittance (Tsol) of the films sharply decreased by 37.39%. The result can be found that the coloring process (illumination process) of YHx:O thin films can be promoted and the optical regulation range can be increased after covered with a Pd layer. Investigation of the crystal structure by XRD demonstrates YHx:O covered with Pd, the same crystalline state with the YHx:O thin films has been found. After illumination, all reflection peaks of the YHx:O films slightly moving towards the larger angles with smaller lattice parameter (~5.30 Å) due to the deoxidation of YHx:O films. It can be seen from the EDS data that the oxygen contents in the YHx:O film decreases, while the yttrium contents increases, which is consistent with that of the single layer films. The XPS survey scans analysis of the YHx:O and Pd/YHx:O was also studied. After illumination, all peaks of the single layer slightly moving towards the larger angles. But the double layer have reverse result with above.
2019, 77(1): 95-102
doi: 10.6023/A18080351
Abstract:
The dendrimers are a unique class of branched macromolecules with defined architectures synthesized by iterative reaction steps. Because of their highly branched structures, the dendrimers have a wide potential application in many fields, including sensing, drug delivery, catalysis, etc. In order to understand the thermal equilibrium behavior of the dendritic homopolymers in solution, we derived the self-consistent field theory (SCFT) for the dilute dendrimer solutions. The center segment is anchored on the origin of the space, and the shape of the dendrimer is assumed to be spherically symmetric. The pre-averaged interaction parameter u is employed to represent the volume exclusion interaction between the segments. We only focus on the dendrimer immersed in the θ solvent, where the volume exclusion interaction between the segments is negligible (u=0). The number density of the segments, φ(r), is calculated via systematically changing the topological parameters of the molecule, including the functionality f0 of the central segment, the functionality f of the branching points, the degree of polymerization of the spacers P, and the total generation number G. With all parameter combinations, φ(r) was found always maximized at the center and monotonically decreasing along the radial direction. Thus, the dendrimers in θ solvent obeys the "dense-core" model instead of the "dense-shell" model. Increasing f0, f and G results in the increase of φ(r) with any radius r. However, increasing P causes the decrease of φ(r) near the center region and the increase of φ(r) with larger r. The size of the dendrimer, analyzed by calculating the radius of gyration R, increases with f0, f, G and P. R calculated by our SCFT agrees well with the results obtained by the Rouse dynamics. With large f0, f and G, both SCFT and the Rouse dynamics predict the scaling law <R2>≈GPa2.
The dendrimers are a unique class of branched macromolecules with defined architectures synthesized by iterative reaction steps. Because of their highly branched structures, the dendrimers have a wide potential application in many fields, including sensing, drug delivery, catalysis, etc. In order to understand the thermal equilibrium behavior of the dendritic homopolymers in solution, we derived the self-consistent field theory (SCFT) for the dilute dendrimer solutions. The center segment is anchored on the origin of the space, and the shape of the dendrimer is assumed to be spherically symmetric. The pre-averaged interaction parameter u is employed to represent the volume exclusion interaction between the segments. We only focus on the dendrimer immersed in the θ solvent, where the volume exclusion interaction between the segments is negligible (u=0). The number density of the segments, φ(r), is calculated via systematically changing the topological parameters of the molecule, including the functionality f0 of the central segment, the functionality f of the branching points, the degree of polymerization of the spacers P, and the total generation number G. With all parameter combinations, φ(r) was found always maximized at the center and monotonically decreasing along the radial direction. Thus, the dendrimers in θ solvent obeys the "dense-core" model instead of the "dense-shell" model. Increasing f0, f and G results in the increase of φ(r) with any radius r. However, increasing P causes the decrease of φ(r) near the center region and the increase of φ(r) with larger r. The size of the dendrimer, analyzed by calculating the radius of gyration R, increases with f0, f, G and P. R calculated by our SCFT agrees well with the results obtained by the Rouse dynamics. With large f0, f and G, both SCFT and the Rouse dynamics predict the scaling law <R2>≈GPa2.
