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2018 Volume 76 Issue 6
2018, 76(6): 425-435
doi: 10.6023/A18010035
Abstract:
Recently, smart actuator materials have drawn widespread research attention due to their important applications in soft robots, artificial muscles, sensors, or micro hand device preparation. In nature, there are many examples of actuator materials. For example, sea cucumbers can alter the stiffness of their dermis within seconds to obtain survival advantages and the venus flytrap can close their leaves in a second for efficient prey capture. Pinecones and flowers respond to their environment by opening and closing with the relative humidity changes. Inspired by these natural creatures, synthetic polymer microactuators such as polymer hydrogels and polymer composites are widely developed due to their important applications based on their response to external stimuli, such as light, heat, electronic, magnetic, solvent and humidity. In this work, we review the research progress of solvent-based smart actuator materials. There are mainly two kinds of solvent-actuator based on the fabrication method and actuator mechanism:one is a two-layer structure membrane formed by active layers-support layers with different expansion coefficients. The active layer is volumetrically expanded under the action of a solvent, and the support layer is a passive holder. The other is made of rigid material skeleton with a flexible material to make a single-layer composite membrane filler. The ionic gradient or the pore structure gradient of the material itself gives rise to the directional driving behavior with a varying solvent binding gradient. Otherwise, the membrane's bending drive behavior has been achieved by inducing a single material to form an infiltration gradient by a solvent infiltration process. Solvent-based smart actuator materials are prepared by introducing moisture or solvent-responsive molecules in a polymeric material to form a bilayers or monolayer structure. The material is distorted by volume deformation due to humidity or solvent field action. At present, a great deal of research work has been devoted to converting the mechanical deformation of solvent-based smart actuator materials into electric energy and developing related intelligent application in energy transformation, liquid switching, biomimicry, transportation of liquids and smart sensing. The paper presents a pioneering outlook for the further development of the solvent actuator materials.
Recently, smart actuator materials have drawn widespread research attention due to their important applications in soft robots, artificial muscles, sensors, or micro hand device preparation. In nature, there are many examples of actuator materials. For example, sea cucumbers can alter the stiffness of their dermis within seconds to obtain survival advantages and the venus flytrap can close their leaves in a second for efficient prey capture. Pinecones and flowers respond to their environment by opening and closing with the relative humidity changes. Inspired by these natural creatures, synthetic polymer microactuators such as polymer hydrogels and polymer composites are widely developed due to their important applications based on their response to external stimuli, such as light, heat, electronic, magnetic, solvent and humidity. In this work, we review the research progress of solvent-based smart actuator materials. There are mainly two kinds of solvent-actuator based on the fabrication method and actuator mechanism:one is a two-layer structure membrane formed by active layers-support layers with different expansion coefficients. The active layer is volumetrically expanded under the action of a solvent, and the support layer is a passive holder. The other is made of rigid material skeleton with a flexible material to make a single-layer composite membrane filler. The ionic gradient or the pore structure gradient of the material itself gives rise to the directional driving behavior with a varying solvent binding gradient. Otherwise, the membrane's bending drive behavior has been achieved by inducing a single material to form an infiltration gradient by a solvent infiltration process. Solvent-based smart actuator materials are prepared by introducing moisture or solvent-responsive molecules in a polymeric material to form a bilayers or monolayer structure. The material is distorted by volume deformation due to humidity or solvent field action. At present, a great deal of research work has been devoted to converting the mechanical deformation of solvent-based smart actuator materials into electric energy and developing related intelligent application in energy transformation, liquid switching, biomimicry, transportation of liquids and smart sensing. The paper presents a pioneering outlook for the further development of the solvent actuator materials.
2018, 76(6): 436-439
doi: 10.6023/A18020080
Abstract:
Organocopper complexes play the key role in Cu-catalyzed organic reaction. This manuscript offered a method to synthesize ligand-ligated organocopper complexes. Copper acetate was used as the catalyst and 2-(aminomethyl)pyridine (2-AMP) as the ligand to react with benzoic acid to generate the organocopper complex. This complex (A1) was easily transferred from solution to gas phase via electrospray ionization mass spectrometry (ESI-MS). Firstly, the collision-induced dissociation (CID) experiment of complex ion A1 was carried out in the ion-trap analyzer to investigate the gas-phase reactivity of it (the single isotope ion with 63Cu was isolated and used in MS/MS and next ion-molecule reaction). The decarboxylation reaction was taken place upon CID to generate the fragment ion B1. Next, the ion-molecule reaction (I-MR) of B1 was introduced after ion B1 was isolated, while allyl iodide was used as the neutral reagent. The iodine group transfer product ion C1 was obtained from the ion-molecule reation. The valence state of the central metal Cu changed from +2 in B1 to +3 in C1 during this process. Then ion A3 was dissociated to form the Cu(I) complex D1 with a neutral loss of iodobenzene upon CID. During these steps, the reagent benzoic acid reacted with allyl iodide in the gas phase with Cu2+ as catalyst and 2-AMP as ligand to produce iodobenzene, thus the copper-catalyzed decarboxylative iodination reaction was created in the gas phase. From the result, the mechanism of decarboxylative iodination reaction was speculated and carefully studied. Meanwhile, this reaction was also suitable for different carboxylic acids and bidentate nitrogen ligands. The aim of this manuscript is to study the reactive copper complexes in isolated environment and solvent free-condition. The gas phase mass spectrometric results supported the proposed mechanism. This method not only detected the gas-phase reactivities of a series of organocopper complexes, but also provided significant information of the mechanism of copper-catalyzed decarboxylative iodination reaction in the condensed phase.
Organocopper complexes play the key role in Cu-catalyzed organic reaction. This manuscript offered a method to synthesize ligand-ligated organocopper complexes. Copper acetate was used as the catalyst and 2-(aminomethyl)pyridine (2-AMP) as the ligand to react with benzoic acid to generate the organocopper complex. This complex (A1) was easily transferred from solution to gas phase via electrospray ionization mass spectrometry (ESI-MS). Firstly, the collision-induced dissociation (CID) experiment of complex ion A1 was carried out in the ion-trap analyzer to investigate the gas-phase reactivity of it (the single isotope ion with 63Cu was isolated and used in MS/MS and next ion-molecule reaction). The decarboxylation reaction was taken place upon CID to generate the fragment ion B1. Next, the ion-molecule reaction (I-MR) of B1 was introduced after ion B1 was isolated, while allyl iodide was used as the neutral reagent. The iodine group transfer product ion C1 was obtained from the ion-molecule reation. The valence state of the central metal Cu changed from +2 in B1 to +3 in C1 during this process. Then ion A3 was dissociated to form the Cu(I) complex D1 with a neutral loss of iodobenzene upon CID. During these steps, the reagent benzoic acid reacted with allyl iodide in the gas phase with Cu2+ as catalyst and 2-AMP as ligand to produce iodobenzene, thus the copper-catalyzed decarboxylative iodination reaction was created in the gas phase. From the result, the mechanism of decarboxylative iodination reaction was speculated and carefully studied. Meanwhile, this reaction was also suitable for different carboxylic acids and bidentate nitrogen ligands. The aim of this manuscript is to study the reactive copper complexes in isolated environment and solvent free-condition. The gas phase mass spectrometric results supported the proposed mechanism. This method not only detected the gas-phase reactivities of a series of organocopper complexes, but also provided significant information of the mechanism of copper-catalyzed decarboxylative iodination reaction in the condensed phase.
2018, 76(6): 440-444
doi: 10.6023/A18030083
Abstract:
C—C bond forming reactions through cross-dehydrogenative coupling (CDC) of two readily available C—H components under oxidative conditions have emerged as one of the most straightforward and economical approaches for increasing molecular complexity and functional group content with minimal waste generation. CDC reactions involving oxidative functionalization of sp3 C—H bonds of both cyclic and acyclic amines with diverse partners have been extensively explored. In sharp contrast, the CDC of corresponding ether substrates remains relatively underdeveloped. Current approaches predominantly focus on cyclic ethers as well as acyclic benzylic ethers. The CDC reaction of extensively existing unactivated acyclic ethers proved to be much more challenging, which might be ascribed to their inherent low reactivity. On the other hand, the existing protocols for unactivated ethers rely heavily on peroxide-mediated oxidation systems, which typically required high temperature and a large excess of ether substrates as the solvent. Accordingly, coupling partners that can be compatible with such harsh conditions are largely restricted to sp2 or sp3 C—H reagents with relatively low manipulation capability, such as arenes, heteroarenes, and 1, 3-dicarbonyl moieties. Alkynes represent common structural motifs spread across the fields of biology, chemistry, material science, and medicine, and act as global handles for diverse functionalities. Therefore, the development of a mild approach for CDC of unactivated acyclic ethers with terminal alkynes is highly desired. In 2014, our group developed a mild Ph3CCl/GaCl3 mediated oxidation system, allowing to achieve the oxidative C—H alkynylation of tetrahydrofuran with organoboranes. Herein, we reported the first CDC of unactivated acyclic ethers with terminal alkynes promoted by Ph3CCl/GaCl3. The reaction proceeded at room temperature in CH2Cl2, thus avoiding the employment of excess ether as the solvent. The typical procedure is as follows:a mixture of unactivated acyclic ether (2.0 mmol), terminal alkyne (0.1 mmol), Ph3CCl (0.1 mmol), and CuI (0.03 mmol) in CH2Cl2 at r.t. was added GaCl3 (0.1 mmol) in a glove box to afford the expected coupling products in moderate to good yields. The Ph3CCl/GaCl3 mediated oxidative C—H alkynylation of unactivated acyclic ethers with alkyl substituted alkynylboranes was further established to overcome the relative low efficiency for the CDC reaction involving alkyl substituted terminal alkynes.
C—C bond forming reactions through cross-dehydrogenative coupling (CDC) of two readily available C—H components under oxidative conditions have emerged as one of the most straightforward and economical approaches for increasing molecular complexity and functional group content with minimal waste generation. CDC reactions involving oxidative functionalization of sp3 C—H bonds of both cyclic and acyclic amines with diverse partners have been extensively explored. In sharp contrast, the CDC of corresponding ether substrates remains relatively underdeveloped. Current approaches predominantly focus on cyclic ethers as well as acyclic benzylic ethers. The CDC reaction of extensively existing unactivated acyclic ethers proved to be much more challenging, which might be ascribed to their inherent low reactivity. On the other hand, the existing protocols for unactivated ethers rely heavily on peroxide-mediated oxidation systems, which typically required high temperature and a large excess of ether substrates as the solvent. Accordingly, coupling partners that can be compatible with such harsh conditions are largely restricted to sp2 or sp3 C—H reagents with relatively low manipulation capability, such as arenes, heteroarenes, and 1, 3-dicarbonyl moieties. Alkynes represent common structural motifs spread across the fields of biology, chemistry, material science, and medicine, and act as global handles for diverse functionalities. Therefore, the development of a mild approach for CDC of unactivated acyclic ethers with terminal alkynes is highly desired. In 2014, our group developed a mild Ph3CCl/GaCl3 mediated oxidation system, allowing to achieve the oxidative C—H alkynylation of tetrahydrofuran with organoboranes. Herein, we reported the first CDC of unactivated acyclic ethers with terminal alkynes promoted by Ph3CCl/GaCl3. The reaction proceeded at room temperature in CH2Cl2, thus avoiding the employment of excess ether as the solvent. The typical procedure is as follows:a mixture of unactivated acyclic ether (2.0 mmol), terminal alkyne (0.1 mmol), Ph3CCl (0.1 mmol), and CuI (0.03 mmol) in CH2Cl2 at r.t. was added GaCl3 (0.1 mmol) in a glove box to afford the expected coupling products in moderate to good yields. The Ph3CCl/GaCl3 mediated oxidative C—H alkynylation of unactivated acyclic ethers with alkyl substituted alkynylboranes was further established to overcome the relative low efficiency for the CDC reaction involving alkyl substituted terminal alkynes.
2018, 76(6): 445-452
doi: 10.6023/A18030095
Abstract:
The use of the N-adamantyl-substituted tris(NHC)borate ligand phenyltris(3-(1-adamantylimidazol-2-ylidene))borate (PhB(AdIm)3-) has enabled the preparation of the high-spin tetrahedral iron(I)-and iron(0)-N2 complexes[PhB(AdIm)3Fe(N2)] (2) and[K(18-C-6)(THF)] [PhB(AdIm)3Fe(N2)] (4), from the reduction of the ferrous precursor[PhB(AdIm)3FeCl] (1) and the iron(I) complex 2 with KC8 under N2, respectively. Single-crystal X-ray diffraction studies revealed a distorted tetrahedral coordination geometry for the iron centers in 2 and 4 with the terminally bonded N2 ligand sitting in the cavity composed by the three adamantyl groups of the borate ligand. The frequencies of the N-N stretching resonance (1928 and 1807 cm-1) of 2 and 4 are the lowest among the reported terminal N2complexes of iron(I) and iron(0), respectively. 57Fe Mössbauer spectrum (δ=0.59 mms-1; ΔEQ=1.31 mms-1) and solution magnetic susceptibility measurement (μeff=5.2(1) μB) of 2 supported its high-spin iron(I) nature. The cyclic voltammogram of 2 measured in THF shows a quasi-reversible redox waves with E1/2=-2.11 V (vs SCE), which is assignable to the corresponding redox process of[PhB(AdIm)3Fe(N2)]1-/0. In addition, the reaction of 2 with an excess amount of CO led to the formation of the bis(carbonyl)iron(I) complex, [PhB(AdIm)3Fe(CO)2] (3), that was characterized by IR spectrum, solution magnetic susceptibility measurement, 1H NMR, as well as elemental analysis. The protonation of 2 and 4 with HCl or HOTf at -78℃ only led to the formation of NH2NH2 and NH3 in low yields[less than 9(3)% and 5(3)% (per mol Fe), respectively]. However, 1, 2, and 4 proved effective catalysts for the reductive silylation of N2by KC8 and Me3SiCl to afford N(SiMe3)3 with comparable catalytic activity. The TON of these catalytic systems could reach 87 using 0.005 mmol of the catalyst, 2000 equiv. of KC8, and 2000 equiv. of Me3SiCl in 10 mL Et2O at room temperature after 24 h.
The use of the N-adamantyl-substituted tris(NHC)borate ligand phenyltris(3-(1-adamantylimidazol-2-ylidene))borate (PhB(AdIm)3-) has enabled the preparation of the high-spin tetrahedral iron(I)-and iron(0)-N2 complexes[PhB(AdIm)3Fe(N2)] (2) and[K(18-C-6)(THF)] [PhB(AdIm)3Fe(N2)] (4), from the reduction of the ferrous precursor[PhB(AdIm)3FeCl] (1) and the iron(I) complex 2 with KC8 under N2, respectively. Single-crystal X-ray diffraction studies revealed a distorted tetrahedral coordination geometry for the iron centers in 2 and 4 with the terminally bonded N2 ligand sitting in the cavity composed by the three adamantyl groups of the borate ligand. The frequencies of the N-N stretching resonance (1928 and 1807 cm-1) of 2 and 4 are the lowest among the reported terminal N2complexes of iron(I) and iron(0), respectively. 57Fe Mössbauer spectrum (δ=0.59 mms-1; ΔEQ=1.31 mms-1) and solution magnetic susceptibility measurement (μeff=5.2(1) μB) of 2 supported its high-spin iron(I) nature. The cyclic voltammogram of 2 measured in THF shows a quasi-reversible redox waves with E1/2=-2.11 V (vs SCE), which is assignable to the corresponding redox process of[PhB(AdIm)3Fe(N2)]1-/0. In addition, the reaction of 2 with an excess amount of CO led to the formation of the bis(carbonyl)iron(I) complex, [PhB(AdIm)3Fe(CO)2] (3), that was characterized by IR spectrum, solution magnetic susceptibility measurement, 1H NMR, as well as elemental analysis. The protonation of 2 and 4 with HCl or HOTf at -78℃ only led to the formation of NH2NH2 and NH3 in low yields[less than 9(3)% and 5(3)% (per mol Fe), respectively]. However, 1, 2, and 4 proved effective catalysts for the reductive silylation of N2by KC8 and Me3SiCl to afford N(SiMe3)3 with comparable catalytic activity. The TON of these catalytic systems could reach 87 using 0.005 mmol of the catalyst, 2000 equiv. of KC8, and 2000 equiv. of Me3SiCl in 10 mL Et2O at room temperature after 24 h.
2018, 76(6): 453-459
doi: 10.6023/A18030090
Abstract:
The dispersion of single-walled carbon nanotubes (SWNTs) is a key point to develop their extensive applications. Especially, to meet the requirements of future green chemistry, the preparation of environmentally-friendly, highly stable and well-distributed SWNTs in aqueous solution becomes particularly important. Based on it, a water-soluble conjugated polyelectrolyte, namely poly[3-[6-(N-methylimidazolium)hexyl]thiophene] (P3MHT) was designed and used to disperse SWNTs through non-covalent strategy. P3MHT was synthesized by a modified Grignard metathesis (GRIM) polymerization followed by quaternization of the bromohexyl side groups of the poly[3-(6-bromohexyl)thiophene] with N-methylimidazole. The P3MHT/SWNTs nanocomposites were prepared by mixing P3MHT and SWNTs in water during ultrasonication followed by centrifugation. UV-vis absorption spectroscopy, photoluminescence (PL) spectroscopy, transmission electron microscope (TEM), Zeta-nano electric potential analyzer, thermogravimetric (TGA) analysis were applied to characterize P3MHT/SWNTs nanocomposites. Compared to the commercial sodium dodecyl sulfate (SDS) surfactant to disperse SWNTs in aqueous solution, P3MHT exhibited a much better ability to disperse SWNTs under the same condition, i.e., the concentration of SWNTs dispersed by P3MHT was about two times than that of SWNTs dispersed by SDS. In P3MHT/SWNTs nanocomposite solution, SWNTs were exfoliated to form individuals or small bundles with an average size of 298 nm. However, in SDS/SWNTs solution, SWNTs preferred to form small aggregates with an average size of more than 500 nm. The P3MHT backbones were wrapped around individual SWNTs via π-π interactions to form the charge-transfer complexes. The ionic side chains of P3MHT not only made the nanocomposites dispersed in water, but also prevented the aggregation of SWNTs by electrostatic repulsion, resulting in aqueous dispersion of P3MHT/SWNTs nanocomposites. While SDS molecules were adsorbed on the surface of SWNTs via hydrophobic alkyl chains, which was much weaker than the π-π interactions between P3MHT and SWNTs. Such P3MHT/SWNTs nanocomposite solution exhibited high stability which remained almost unchanged after 6 months while SDS/SWNTs nanocomposite had already precipitated then. Overall, it provides a promising and simple method to develop highly stable and water processed SWNTs.
The dispersion of single-walled carbon nanotubes (SWNTs) is a key point to develop their extensive applications. Especially, to meet the requirements of future green chemistry, the preparation of environmentally-friendly, highly stable and well-distributed SWNTs in aqueous solution becomes particularly important. Based on it, a water-soluble conjugated polyelectrolyte, namely poly[3-[6-(N-methylimidazolium)hexyl]thiophene] (P3MHT) was designed and used to disperse SWNTs through non-covalent strategy. P3MHT was synthesized by a modified Grignard metathesis (GRIM) polymerization followed by quaternization of the bromohexyl side groups of the poly[3-(6-bromohexyl)thiophene] with N-methylimidazole. The P3MHT/SWNTs nanocomposites were prepared by mixing P3MHT and SWNTs in water during ultrasonication followed by centrifugation. UV-vis absorption spectroscopy, photoluminescence (PL) spectroscopy, transmission electron microscope (TEM), Zeta-nano electric potential analyzer, thermogravimetric (TGA) analysis were applied to characterize P3MHT/SWNTs nanocomposites. Compared to the commercial sodium dodecyl sulfate (SDS) surfactant to disperse SWNTs in aqueous solution, P3MHT exhibited a much better ability to disperse SWNTs under the same condition, i.e., the concentration of SWNTs dispersed by P3MHT was about two times than that of SWNTs dispersed by SDS. In P3MHT/SWNTs nanocomposite solution, SWNTs were exfoliated to form individuals or small bundles with an average size of 298 nm. However, in SDS/SWNTs solution, SWNTs preferred to form small aggregates with an average size of more than 500 nm. The P3MHT backbones were wrapped around individual SWNTs via π-π interactions to form the charge-transfer complexes. The ionic side chains of P3MHT not only made the nanocomposites dispersed in water, but also prevented the aggregation of SWNTs by electrostatic repulsion, resulting in aqueous dispersion of P3MHT/SWNTs nanocomposites. While SDS molecules were adsorbed on the surface of SWNTs via hydrophobic alkyl chains, which was much weaker than the π-π interactions between P3MHT and SWNTs. Such P3MHT/SWNTs nanocomposite solution exhibited high stability which remained almost unchanged after 6 months while SDS/SWNTs nanocomposite had already precipitated then. Overall, it provides a promising and simple method to develop highly stable and water processed SWNTs.
2018, 76(6): 460-466
doi: 10.6023/A18020048
Abstract:
The emerging fluorescent carbon quantum dots (CQDs) have shown enormous potentials in optoelectronic applications owing to their outstanding characteristics, such as tunable stable fluorescence emission, low cost, and environment-friendliness. However, the fluorescence of most reported CQDs is dominated by surface defects, which are in general energy dissipative, hard to support lasing emission. We have previously reported the bandgap emission CQDs from blue to red with a quantum yield (QY) over 50%, which is the highest value reported for bandgap emission CQDs. The bandgap transitions in CQDs were further confirmed by size-dependent optical properties through tansmission electron microscopy (TEM), which show uniform distribution nanoparticles with averge sizes of about 1.95, 2.41, 5.0 nm for blue, green and red CQDs, and their typical high-resolution TEM (HRTEM) images further indicates that most of the CQDs exhibit uniform atomic arrangements with high degree of crystallinity. By taking advantage of the high QY of CQDs, monochrome CQDs-based random lasing with low excitation threshold have been realized by using Au-Ag bimetallic porous nanowires as scatterers for the first time. The Au-Ag bimetallic porous nanowires possess a rough surface with Au nanoparticles and abundant nanogaps, leading to the extremely broadband surface plasmonic resonance peaks over the whole visible spectral range, which is benefit for efficient random lasing. The thresholds of the monochrome CQDs-based random lasers reached about 0.27, 0.21, 0.58 MW/cm2 for blue, green and red, respectively. The full width at half maximum (FWHM) of the monochrome CQDs-based random lasers reached about 2.5, 1.9, 2.3 nm for blue, green and red, which is even comparable to the well-developed semiconductor QDs-based random lasers. The obtained random lasers show substantial stable emission color, which is of great significance for lasing display and lighting technology. Furthermore, white lasing with a CIE coordinate at (0.32, 0.33) was first demonstrated by combining red, green, blue fluorescent CQDs. This work does serve the purpose of understanding and providing significant opportunities for further improvements of CQDs-based lasers.
The emerging fluorescent carbon quantum dots (CQDs) have shown enormous potentials in optoelectronic applications owing to their outstanding characteristics, such as tunable stable fluorescence emission, low cost, and environment-friendliness. However, the fluorescence of most reported CQDs is dominated by surface defects, which are in general energy dissipative, hard to support lasing emission. We have previously reported the bandgap emission CQDs from blue to red with a quantum yield (QY) over 50%, which is the highest value reported for bandgap emission CQDs. The bandgap transitions in CQDs were further confirmed by size-dependent optical properties through tansmission electron microscopy (TEM), which show uniform distribution nanoparticles with averge sizes of about 1.95, 2.41, 5.0 nm for blue, green and red CQDs, and their typical high-resolution TEM (HRTEM) images further indicates that most of the CQDs exhibit uniform atomic arrangements with high degree of crystallinity. By taking advantage of the high QY of CQDs, monochrome CQDs-based random lasing with low excitation threshold have been realized by using Au-Ag bimetallic porous nanowires as scatterers for the first time. The Au-Ag bimetallic porous nanowires possess a rough surface with Au nanoparticles and abundant nanogaps, leading to the extremely broadband surface plasmonic resonance peaks over the whole visible spectral range, which is benefit for efficient random lasing. The thresholds of the monochrome CQDs-based random lasers reached about 0.27, 0.21, 0.58 MW/cm2 for blue, green and red, respectively. The full width at half maximum (FWHM) of the monochrome CQDs-based random lasers reached about 2.5, 1.9, 2.3 nm for blue, green and red, which is even comparable to the well-developed semiconductor QDs-based random lasers. The obtained random lasers show substantial stable emission color, which is of great significance for lasing display and lighting technology. Furthermore, white lasing with a CIE coordinate at (0.32, 0.33) was first demonstrated by combining red, green, blue fluorescent CQDs. This work does serve the purpose of understanding and providing significant opportunities for further improvements of CQDs-based lasers.
2018, 76(6): 467-474
doi: 10.6023/A18020069
Abstract:
We synthesized three kinds of MnO2 powder with different crystalline phases including α-MnO2 nanoflowers, β-MnO2 nanorods and δ-MnO2 micro-particles. The structure and morphology of prepared MnO2 were studied by XRD (X-ray diffraction), SEM (Scanning Electron Microscope), TEM (Transmission Electron Microscope) and XPS (X-ray photoelectron spectroscopy), systematically. Adsorption process was conducted in NH4Cl solution (40 mg·L-1 NH3-N) and actual water samples containing NH4+, Ca2+, Mg2+, K+ and Na+, respectively. The results demonstrate that δ-MnO2 with 7.2 Å interlayer spacing which is a little larger than the diameter of hydrated ammonium (6.62 Å) has high adsorption capacity; α-MnO2 with[2×2] tunnel of 4.6 Å has less adsorption capacity than that of δ-MnO2, and β-MnO2 whose[1×1] tunnel is just 1.89 Å, barely has adsorption capacity. Then MnO2NPs/GF (MnO2 nanoplates decorated graphite felt) was prepared via a facile in-situ redox process. Graphite felt (GF) was immersed in KMnO4 solution (4 g·L-1, pH=2) at 65℃ for 5 h to get MnO2NPs/GF. GF not only reacted as the reductant of KMnO4, but also acted as 3D framework to support the in-situ deposited MnO2NPs. MnO2NPs/GF shows high adsorption capacity (15 mg·g-1) and good selectivity (86.7%). In repetitive adsorption-desorption experiments, MnO2NPs/GF not only exhibits good stability after 20 cycles, but also decreases the concentration of NH3-N to as low as 1 mg·L-1. The thermodynamics experiment demonstrates that the adsorption isotherm fit well with Langmuir isotherm, and the adsorption process corresponds to the pseudo-second-order model. The excellent performance of MnO2NPs/GF is attributed to the following three aspects. Firstly, the 7.2 Å interlayer spacing of δ-MnO2 is suitable for the exchange-adsorption of NH4+. Secondly, the ultra-thin MnO2 nanoplate arrays, which vertically grow on the graphite felt substrate, provide fast path and convenient interface for ion exchange. Finally, the interlaced nanoplates with self-supported structure ensure its high stability. In a conclusion, MnO2NPs/GF has a bright future in the field of ammonium removal.
We synthesized three kinds of MnO2 powder with different crystalline phases including α-MnO2 nanoflowers, β-MnO2 nanorods and δ-MnO2 micro-particles. The structure and morphology of prepared MnO2 were studied by XRD (X-ray diffraction), SEM (Scanning Electron Microscope), TEM (Transmission Electron Microscope) and XPS (X-ray photoelectron spectroscopy), systematically. Adsorption process was conducted in NH4Cl solution (40 mg·L-1 NH3-N) and actual water samples containing NH4+, Ca2+, Mg2+, K+ and Na+, respectively. The results demonstrate that δ-MnO2 with 7.2 Å interlayer spacing which is a little larger than the diameter of hydrated ammonium (6.62 Å) has high adsorption capacity; α-MnO2 with[2×2] tunnel of 4.6 Å has less adsorption capacity than that of δ-MnO2, and β-MnO2 whose[1×1] tunnel is just 1.89 Å, barely has adsorption capacity. Then MnO2NPs/GF (MnO2 nanoplates decorated graphite felt) was prepared via a facile in-situ redox process. Graphite felt (GF) was immersed in KMnO4 solution (4 g·L-1, pH=2) at 65℃ for 5 h to get MnO2NPs/GF. GF not only reacted as the reductant of KMnO4, but also acted as 3D framework to support the in-situ deposited MnO2NPs. MnO2NPs/GF shows high adsorption capacity (15 mg·g-1) and good selectivity (86.7%). In repetitive adsorption-desorption experiments, MnO2NPs/GF not only exhibits good stability after 20 cycles, but also decreases the concentration of NH3-N to as low as 1 mg·L-1. The thermodynamics experiment demonstrates that the adsorption isotherm fit well with Langmuir isotherm, and the adsorption process corresponds to the pseudo-second-order model. The excellent performance of MnO2NPs/GF is attributed to the following three aspects. Firstly, the 7.2 Å interlayer spacing of δ-MnO2 is suitable for the exchange-adsorption of NH4+. Secondly, the ultra-thin MnO2 nanoplate arrays, which vertically grow on the graphite felt substrate, provide fast path and convenient interface for ion exchange. Finally, the interlaced nanoplates with self-supported structure ensure its high stability. In a conclusion, MnO2NPs/GF has a bright future in the field of ammonium removal.
2018, 76(6): 475-482
doi: 10.6023/A17120557
Abstract:
G-Quadruplex can be a promising candidate as molecular electronic device due to the ability of transferring hole. Extensive studies have reported that fast deprotonation of guanine radical cation (G·+) to form a neutral radical G(-H)· is the most important reaction in competition with hole transfer in DNA, hindering potential applications of DNA in molecular electronics. We thus carry out joint experimental and theoretical studies on deprotonation of G·+ in human telomere G-quadruplex AG3(T2AG3)3by using nanosecond laser flash photolysis and quantum chemical calculations. Upon 355 nm laser photolysis of Na2S2O8, instantaneously generated SO4·- radical oxidizes G base in the G-quadruplex to G·+. In the time-resolved absorption spectra that record the reaction of G-quadruplex with SO4·- at different temperatures, the transient absorptions of G(N(2)-H)· featured by absorption band at 640 nm are observed. It turns out that the G-quadruplex deprotonation product is G(N(2)-H)· and the deprotonation site is thereby validated to be amino proton. To obtain the activation energy of the G·+ deprotonation in G-quadruplex, the N(2)-H deprotonation rate constants at different temperatures varying from 280 to 300 K in steps 5 K are measured at a high G-quadruplex concentration, where the deprotonation has been proved to be the rate-limiting step in our previous work. Based upon Arrhenius equation, the deprotonation activation energy of G·+ in G-quadruplex is determined to be 20.0±1.0 kJ/mol. Further, the potential energy profile for the G·+ deprotonation in G-quadruplex is calculated at M062X/6-31G(d) level by carefully taking into account hydration environment of G·+ in G-quadruplex. The calculated energy barrier of 26.4 kJ/mol matches with the measured activation energy value, indicating the calculated potential energy profile can describe the deprotonation process of G·+ in the G-quadruplex. These theoretical and experimental results provide valuable dynamics information and mechanistic insights for potential applications of DNA structures in electronic device.
G-Quadruplex can be a promising candidate as molecular electronic device due to the ability of transferring hole. Extensive studies have reported that fast deprotonation of guanine radical cation (G·+) to form a neutral radical G(-H)· is the most important reaction in competition with hole transfer in DNA, hindering potential applications of DNA in molecular electronics. We thus carry out joint experimental and theoretical studies on deprotonation of G·+ in human telomere G-quadruplex AG3(T2AG3)3by using nanosecond laser flash photolysis and quantum chemical calculations. Upon 355 nm laser photolysis of Na2S2O8, instantaneously generated SO4·- radical oxidizes G base in the G-quadruplex to G·+. In the time-resolved absorption spectra that record the reaction of G-quadruplex with SO4·- at different temperatures, the transient absorptions of G(N(2)-H)· featured by absorption band at 640 nm are observed. It turns out that the G-quadruplex deprotonation product is G(N(2)-H)· and the deprotonation site is thereby validated to be amino proton. To obtain the activation energy of the G·+ deprotonation in G-quadruplex, the N(2)-H deprotonation rate constants at different temperatures varying from 280 to 300 K in steps 5 K are measured at a high G-quadruplex concentration, where the deprotonation has been proved to be the rate-limiting step in our previous work. Based upon Arrhenius equation, the deprotonation activation energy of G·+ in G-quadruplex is determined to be 20.0±1.0 kJ/mol. Further, the potential energy profile for the G·+ deprotonation in G-quadruplex is calculated at M062X/6-31G(d) level by carefully taking into account hydration environment of G·+ in G-quadruplex. The calculated energy barrier of 26.4 kJ/mol matches with the measured activation energy value, indicating the calculated potential energy profile can describe the deprotonation process of G·+ in the G-quadruplex. These theoretical and experimental results provide valuable dynamics information and mechanistic insights for potential applications of DNA structures in electronic device.
2018, 76(6): 483-490
doi: 10.6023/A18040128
Abstract:
Confined water became a recent hot topic in water science due to its extremely abundant structural phase behavior. However, there exist few studies focused on the coexistence of two or more confined water phases and their related properties. We present a methodology for studying the coexistences of two confined phases of water, based on a series equilibrium molecular-dynamics (MD) simulations using isobaric-isoenthalpic ensembles to iteratively predict the melting temperatures of the low dimensional confined crystal phase of water. The methodology is applied to the coexistence of the monolayer ice and water (described with a simple water model, i.e. SPC/E model) confined in the 0.65 nm size pore, yielding a direct determination of the melting point and extensive atomic-scale characterization for the mono-molecular layer containing the confined ice-water coexistence line. A finite value of lateral pressure (5000 bar) is adopted in the simulation, to mimic the high-pressure environment of the water molecules confined in the bi-graphene pocket in a recent experiment by Algara-Siller et al.[Nature, 519, 443 (2015)]. The rough structural type and the capillary fluctuation of the line, the microscopic mechanism of the solid-liquid structural transition along the line, as well as the transport of the point defect in the solid side of the coexistence line are identified directly from the MD trajectories. Various profiles of different thermodynamic properties across the coexistence line illustrate the unique features for the in-plane coexistence of the monolayer confined ice-water system, e.g., the unexpected large width of the crystal-melt transition region, and the compression state along the solid-liquid phase coexistence line. The methodology presented in the current study can be easily applied to the coexistence of multilayer confined ice and water phases, as well as the many other types of water models beyond the SPC/E used in current work. The achievement of the low dimensional confined ice-water phase coexistence could potentially facilitate the fundamental advancements in thermodynamics and kinetic theories of the low dimensional water science.
Confined water became a recent hot topic in water science due to its extremely abundant structural phase behavior. However, there exist few studies focused on the coexistence of two or more confined water phases and their related properties. We present a methodology for studying the coexistences of two confined phases of water, based on a series equilibrium molecular-dynamics (MD) simulations using isobaric-isoenthalpic ensembles to iteratively predict the melting temperatures of the low dimensional confined crystal phase of water. The methodology is applied to the coexistence of the monolayer ice and water (described with a simple water model, i.e. SPC/E model) confined in the 0.65 nm size pore, yielding a direct determination of the melting point and extensive atomic-scale characterization for the mono-molecular layer containing the confined ice-water coexistence line. A finite value of lateral pressure (5000 bar) is adopted in the simulation, to mimic the high-pressure environment of the water molecules confined in the bi-graphene pocket in a recent experiment by Algara-Siller et al.[Nature, 519, 443 (2015)]. The rough structural type and the capillary fluctuation of the line, the microscopic mechanism of the solid-liquid structural transition along the line, as well as the transport of the point defect in the solid side of the coexistence line are identified directly from the MD trajectories. Various profiles of different thermodynamic properties across the coexistence line illustrate the unique features for the in-plane coexistence of the monolayer confined ice-water system, e.g., the unexpected large width of the crystal-melt transition region, and the compression state along the solid-liquid phase coexistence line. The methodology presented in the current study can be easily applied to the coexistence of multilayer confined ice and water phases, as well as the many other types of water models beyond the SPC/E used in current work. The achievement of the low dimensional confined ice-water phase coexistence could potentially facilitate the fundamental advancements in thermodynamics and kinetic theories of the low dimensional water science.
