Login In
2018 Volume 39 Issue 11
2018, 39(11):
Abstract:
2018, 39(11): 1725-1729
doi: 10.1016/S1872-2067(18)63139-0
Abstract:
Organoboron compounds are widely used in synthetic chemistry, pharmaceutical chemistry and material chemistry. Among various organoboron compounds, benzylboronic esters are unique and highly reactive, making them suitable benzylation reagents. At present, the synthetic methods for the syntheses of benzylboronic esters are still insufficient to meet their demands. It is necessary to develop novel and practical methods for their preparation. In this work, a novel copper-catalyzed deoxygenative gem-hydroborylation of aromatic aldehydes and ketones has been developed. This direct and operationally simple protocol provides an effective approach for the synthesis of a variety of primary and secondary benzylboronates, in which broad functional group tolerance was presented. Widely available B2pin2 (pin=pinacol) was used as the boron source and alcoholic proton was applied as the hydride source.
Organoboron compounds are widely used in synthetic chemistry, pharmaceutical chemistry and material chemistry. Among various organoboron compounds, benzylboronic esters are unique and highly reactive, making them suitable benzylation reagents. At present, the synthetic methods for the syntheses of benzylboronic esters are still insufficient to meet their demands. It is necessary to develop novel and practical methods for their preparation. In this work, a novel copper-catalyzed deoxygenative gem-hydroborylation of aromatic aldehydes and ketones has been developed. This direct and operationally simple protocol provides an effective approach for the synthesis of a variety of primary and secondary benzylboronates, in which broad functional group tolerance was presented. Widely available B2pin2 (pin=pinacol) was used as the boron source and alcoholic proton was applied as the hydride source.
2018, 39(11): 1730-1735
doi: 10.1016/S1872-2067(18)63138-9
Abstract:
Cocatalyst plays key roles in photogenerated charge separation and surface catalytic reactions in photocatalysis. However, it is not clear if the chemical states of cocatalysts changed or remains unchanged under photocatalytic reaction conditions. Herein, taking NaTaO3 as an example, we systemically investigated the chemical states of nickel-based cocatalysts during photocatalytic water splitting reaction. It was found that photo-induced self-formation of Ni and NiO cocatalyst species take place on the surface of NaTaO3 nanocrystals. The self-formation of dual-cocatalysts not only occurs on 26-facet NaTaO3, but also takes place on a more general 6-facet NaTaO3. Our work clarified that the chemical states of cocatalysts are changing and the redox dual-cocatalysts are redistributed on the semiconductor surface owing to the reaction induced by photogenerated charges under the condition of photocatalytic reactions.
Cocatalyst plays key roles in photogenerated charge separation and surface catalytic reactions in photocatalysis. However, it is not clear if the chemical states of cocatalysts changed or remains unchanged under photocatalytic reaction conditions. Herein, taking NaTaO3 as an example, we systemically investigated the chemical states of nickel-based cocatalysts during photocatalytic water splitting reaction. It was found that photo-induced self-formation of Ni and NiO cocatalyst species take place on the surface of NaTaO3 nanocrystals. The self-formation of dual-cocatalysts not only occurs on 26-facet NaTaO3, but also takes place on a more general 6-facet NaTaO3. Our work clarified that the chemical states of cocatalysts are changing and the redox dual-cocatalysts are redistributed on the semiconductor surface owing to the reaction induced by photogenerated charges under the condition of photocatalytic reactions.
2018, 39(11): 1736-1745
doi: 10.1016/S1872-2067(18)63150-X
Abstract:
Efficient, stable, and noble-metal-free electrocatalysts for both the oxygen evolution reaction and the hydrogen evolution reaction are highly imperative for the realization of low-cost commercial water-splitting electrolyzers. Herein, a cost-effective and ecofriendly strategy is reported to fabricate coral-like FeNi(OH)x/Ni as a bifunctional electrocatalyst for overall water splitting in alkaline media. With the assistance of mild corrosion of Ni by Fe(NO3)3, in situ generated FeNi(OH)x nanosheets are intimately attached on metallic coral-like Ni. Integration of these nanosheets with the electrodeposited coral-like Ni skeleton and the supermacroporous Ni foam substrate forms a binder-free hierarchical electrode, which is beneficial for exposing catalytic active sites, accelerating mass transport, and facilitating the release of gaseous species. In 1.0 mol L-1 KOH solution, a symmetric electrolyzer constructed with FeNi(OH)x/Ni as both the anode and the cathode exhibits an excellent activity with an applied potential difference of 1.52 V at 10 mA cm-2, which is superior to that of an asymmetric electrolyzer constructed with the state-of-the-art RuO2-PtC couple (applied potential difference of 1.55 V at 10 mA cm-2). This work contributes a facile and reliable strategy for manufacturing affordable, practical, and promising water-splitting devices.
Efficient, stable, and noble-metal-free electrocatalysts for both the oxygen evolution reaction and the hydrogen evolution reaction are highly imperative for the realization of low-cost commercial water-splitting electrolyzers. Herein, a cost-effective and ecofriendly strategy is reported to fabricate coral-like FeNi(OH)x/Ni as a bifunctional electrocatalyst for overall water splitting in alkaline media. With the assistance of mild corrosion of Ni by Fe(NO3)3, in situ generated FeNi(OH)x nanosheets are intimately attached on metallic coral-like Ni. Integration of these nanosheets with the electrodeposited coral-like Ni skeleton and the supermacroporous Ni foam substrate forms a binder-free hierarchical electrode, which is beneficial for exposing catalytic active sites, accelerating mass transport, and facilitating the release of gaseous species. In 1.0 mol L-1 KOH solution, a symmetric electrolyzer constructed with FeNi(OH)x/Ni as both the anode and the cathode exhibits an excellent activity with an applied potential difference of 1.52 V at 10 mA cm-2, which is superior to that of an asymmetric electrolyzer constructed with the state-of-the-art RuO2-PtC couple (applied potential difference of 1.55 V at 10 mA cm-2). This work contributes a facile and reliable strategy for manufacturing affordable, practical, and promising water-splitting devices.
2018, 39(11): 1746-1752
doi: 10.1016/S1872-2067(18)63151-1
Abstract:
An efficient and highly chemoselective heterogeneous catalyst system for quinoline hydrogenation was developed using unsupported nanoporous palladium (PdNPore). The PdNPore-catalyzed chemoselective hydrogenation of quinoline proceeded smoothly under mild reaction conditions (low H2 pressure and temperature) to yield 1,2,3,4-tetrahydroquinolines (py-THQs) in satisfactory to excellent yields. Various synthetically useful functional groups, such as halogen, hydroxyl, formyl, ethoxycarbonyl, and aminocarbonyl groups, remained intact during the quinoline hydrogenation. No palladium was leached from PdNPore during the hydrogenation reaction. Moreover, the catalyst was easily recovered and reused without any loss of catalytic activity. The results of kinetic, deuterium-hydrogen exchange, and deuterium-labeling experiments indicated that the present hydrogenation involves heterolytic H2 splitting on the surface of the catalyst.
An efficient and highly chemoselective heterogeneous catalyst system for quinoline hydrogenation was developed using unsupported nanoporous palladium (PdNPore). The PdNPore-catalyzed chemoselective hydrogenation of quinoline proceeded smoothly under mild reaction conditions (low H2 pressure and temperature) to yield 1,2,3,4-tetrahydroquinolines (py-THQs) in satisfactory to excellent yields. Various synthetically useful functional groups, such as halogen, hydroxyl, formyl, ethoxycarbonyl, and aminocarbonyl groups, remained intact during the quinoline hydrogenation. No palladium was leached from PdNPore during the hydrogenation reaction. Moreover, the catalyst was easily recovered and reused without any loss of catalytic activity. The results of kinetic, deuterium-hydrogen exchange, and deuterium-labeling experiments indicated that the present hydrogenation involves heterolytic H2 splitting on the surface of the catalyst.
2018, 39(11): 1753-1761
doi: 10.1016/S1872-2067(18)63135-3
Abstract:
Photocatalytic hydrogen (H2) evolution is a promising approach for future sustainable energy utilization. However, it is still a great challenge to develop efficient and stable metal-free photocatalysts with broadband solar absorption in the visible region for H2 production. Metal-free graphene quantum dot (GQD) is an emerging candidate for this purpose because of its good water-solubility and tunable band gap. On the other hand, metal phosphides (Ni2P, Co2P, etc) have been demonstrated as novel noble-metal-free cocatalysts for water splitting, which can efficiently separate electron-hole pairs and enhance the photocatalytic activities. Herein, we report for the first time on the use of OH-functionalized GQDs (OH-GQDs) photosensitizer coupled with Ni2P nanoparticles for photocatalytic H2 production with λ > 420 nm light. The H2 production rate is~94 times higher than that of bare OH-GQDs, which is even comparable to that of OH-GQDs with 1.0 wt% Pt cocatalyst. This enhancement is probably due to the semiconductor-cocatalyst interface interaction between Ni2P and OH-GQDs to facilitate efficient charge transfer process.
Photocatalytic hydrogen (H2) evolution is a promising approach for future sustainable energy utilization. However, it is still a great challenge to develop efficient and stable metal-free photocatalysts with broadband solar absorption in the visible region for H2 production. Metal-free graphene quantum dot (GQD) is an emerging candidate for this purpose because of its good water-solubility and tunable band gap. On the other hand, metal phosphides (Ni2P, Co2P, etc) have been demonstrated as novel noble-metal-free cocatalysts for water splitting, which can efficiently separate electron-hole pairs and enhance the photocatalytic activities. Herein, we report for the first time on the use of OH-functionalized GQDs (OH-GQDs) photosensitizer coupled with Ni2P nanoparticles for photocatalytic H2 production with λ > 420 nm light. The H2 production rate is~94 times higher than that of bare OH-GQDs, which is even comparable to that of OH-GQDs with 1.0 wt% Pt cocatalyst. This enhancement is probably due to the semiconductor-cocatalyst interface interaction between Ni2P and OH-GQDs to facilitate efficient charge transfer process.
2018, 39(11): 1762-1769
doi: 10.1016/S1872-2067(18)63145-6
Abstract:
Acrylic acid (AA) and its ester, methyl acrylate (MA), were produced by a green one-step aldol condensation reaction of dimethoxymethane and methyl acetate. The reaction was conducted over ZSM-35 zeolites with different concentrations of Brönsted acid, which were prepared by the sodium ion-exchange process with H-form zeolite. The acidic property of HZSM-35 was studied in detail through infrared experiments. About 51% of all bridging OH groups were distributed in cages, while 23% and 26%, respectively, were distributed in 10-and 8-ring channels. The catalytic performance was enhanced by a high concentration of Brönsted acid, indicating that Brönsted acid is an active site for the aldol condensation reaction. The ZSM-35 zeolite possessing a concentration of Brönsted acid as high as 0.049 mmol/g demonstrated excellent performance with a MA+AA selectivity of up to 73%.
Acrylic acid (AA) and its ester, methyl acrylate (MA), were produced by a green one-step aldol condensation reaction of dimethoxymethane and methyl acetate. The reaction was conducted over ZSM-35 zeolites with different concentrations of Brönsted acid, which were prepared by the sodium ion-exchange process with H-form zeolite. The acidic property of HZSM-35 was studied in detail through infrared experiments. About 51% of all bridging OH groups were distributed in cages, while 23% and 26%, respectively, were distributed in 10-and 8-ring channels. The catalytic performance was enhanced by a high concentration of Brönsted acid, indicating that Brönsted acid is an active site for the aldol condensation reaction. The ZSM-35 zeolite possessing a concentration of Brönsted acid as high as 0.049 mmol/g demonstrated excellent performance with a MA+AA selectivity of up to 73%.
2018, 39(11): 1770-1781
doi: 10.1016/S1872-2067(18)63121-3
Abstract:
Herein, we report an excellent, supported Ru(Ⅲ)-ChCl/AC catalyst with lower Ru content, where the ionic complex ChRuCl4 serves as the active component for acetylene hydrochlorination. The prepared heterogeneous Ru-10%ChCl/AC catalyst shows excellent activity and long-term stability. In this system, ChCl provides an environment for the ChRuCl4 to be stabilized as Ru(Ⅲ), thus suppressing the reduction of the active species and the aggregation of ruthenium species during the reaction. The interaction between reactants and catalyst species was investigated by catalyst characterizations in combination with DFT calculations to disclose the effect of the ChRuCl4 complex and ChCl on the catalytic performance. This inexpensive, efficient, and long-term catalyst is a competitive candidate for application in the hydrochlorination industry.
Herein, we report an excellent, supported Ru(Ⅲ)-ChCl/AC catalyst with lower Ru content, where the ionic complex ChRuCl4 serves as the active component for acetylene hydrochlorination. The prepared heterogeneous Ru-10%ChCl/AC catalyst shows excellent activity and long-term stability. In this system, ChCl provides an environment for the ChRuCl4 to be stabilized as Ru(Ⅲ), thus suppressing the reduction of the active species and the aggregation of ruthenium species during the reaction. The interaction between reactants and catalyst species was investigated by catalyst characterizations in combination with DFT calculations to disclose the effect of the ChRuCl4 complex and ChCl on the catalytic performance. This inexpensive, efficient, and long-term catalyst is a competitive candidate for application in the hydrochlorination industry.
2018, 39(11): 1782-1791
doi: 10.1016/S1872-2067(18)63134-1
Abstract:
Rh(Ⅲ)-catalyzed C-H activation of N-protected anilines and chemo-divergent couplings with acroleins/enones have been realized for synthesis of three classes of heterocycles. The oxidative coupling of N-pyridylaniline afforded dihydroquinolones with the acrolein being a major hydrogen acceptor. When the directing group was replaced by pyrimidyl in the same system, redox-neutral coupling occurred to afford hemiaminal ethers. Oxidative annulation of N-pyridylanilines with enones using AgBF4 oxidant afforded atropisomeric quinolinium salts.
Rh(Ⅲ)-catalyzed C-H activation of N-protected anilines and chemo-divergent couplings with acroleins/enones have been realized for synthesis of three classes of heterocycles. The oxidative coupling of N-pyridylaniline afforded dihydroquinolones with the acrolein being a major hydrogen acceptor. When the directing group was replaced by pyrimidyl in the same system, redox-neutral coupling occurred to afford hemiaminal ethers. Oxidative annulation of N-pyridylanilines with enones using AgBF4 oxidant afforded atropisomeric quinolinium salts.
2018, 39(11): 1792-1803
doi: 10.1016/S1872-2067(18)63142-0
Abstract:
A novel p-n heterostructure photocatalyst m-Bi2O4/BiOCl was successfully synthetized through a facile ion-etching method. Via adjusting the added volume of HCl solution, a series of different ratios of composite photocatalysts were obtained. The as-prepared samples of physical, chemical and optical characteristics were examined by X-ray diffraction, scanning electron microscope, transmission electron microscope, energy dispersive X-ray spectroscopy, selected-area electron diffraction, Fourier transform infrared absorption, Raman microscope, N2 adsorption-desorption, X-ray photoelectron spectroscopy and UV-vis spectrum technologies. The photocatalysts showed high degradation rate and complete mineralization ability for methyl orange and tetracycline solution under visible light. The reaction rate constant of m-Bi2O4/BiOCl for methyl orange was 52.28 times higher than that of BiOCl. The characterization presented a good stability of materials. Furthermore, the photocurrent response test certified that the heterostructure effectively accelerated the separation and migration of photo-generated carries. The scavenger experiments evidenced that hole (h+) and superoxide radical (·O2-) were the primary active radicals. A possible photocatalytic mechanism was proposed. This work provided an alternative photocatalyst applied to water environmental remediation.
A novel p-n heterostructure photocatalyst m-Bi2O4/BiOCl was successfully synthetized through a facile ion-etching method. Via adjusting the added volume of HCl solution, a series of different ratios of composite photocatalysts were obtained. The as-prepared samples of physical, chemical and optical characteristics were examined by X-ray diffraction, scanning electron microscope, transmission electron microscope, energy dispersive X-ray spectroscopy, selected-area electron diffraction, Fourier transform infrared absorption, Raman microscope, N2 adsorption-desorption, X-ray photoelectron spectroscopy and UV-vis spectrum technologies. The photocatalysts showed high degradation rate and complete mineralization ability for methyl orange and tetracycline solution under visible light. The reaction rate constant of m-Bi2O4/BiOCl for methyl orange was 52.28 times higher than that of BiOCl. The characterization presented a good stability of materials. Furthermore, the photocurrent response test certified that the heterostructure effectively accelerated the separation and migration of photo-generated carries. The scavenger experiments evidenced that hole (h+) and superoxide radical (·O2-) were the primary active radicals. A possible photocatalytic mechanism was proposed. This work provided an alternative photocatalyst applied to water environmental remediation.
2018, 39(11): 1804-1813
doi: 10.1016/S1872-2067(18)63129-8
Abstract:
The CeO2-TiO2 (CeTi) and CeO2/WO3-TiO2 (CeWTi) catalysts were prepared by a sol-gel precipitation method and their NH3-NO/NO2 selective catalytic reduction (SCR) performance was studied. N2O formation and effect of oxygen concentration on SCR performance over CeWTi catalyst were also investigated while varying the NO2/NOx ratio. Results indicate that fast SCR behavior of CeWTi catalyst has the best NH3-NO/NO2 SCR performance due to the catalyst reoxidation rate by NO2 higher than by O2. Compared with CeTi catalyst, CeWTi catalyst exhibits higher de-NOx performance under NH3-NO/NO2 SCR conditions. As the CeTi and CeWTi catalysts exhibit similar redox property, addition of WO3 provides more acid sites which accelerate the reaction between NH4NO3 and NO to get a superior low-temperature activity. Amount of N2O formation shows a peak at 250℃ mainly derived from NH4NO3 decomposition.
The CeO2-TiO2 (CeTi) and CeO2/WO3-TiO2 (CeWTi) catalysts were prepared by a sol-gel precipitation method and their NH3-NO/NO2 selective catalytic reduction (SCR) performance was studied. N2O formation and effect of oxygen concentration on SCR performance over CeWTi catalyst were also investigated while varying the NO2/NOx ratio. Results indicate that fast SCR behavior of CeWTi catalyst has the best NH3-NO/NO2 SCR performance due to the catalyst reoxidation rate by NO2 higher than by O2. Compared with CeTi catalyst, CeWTi catalyst exhibits higher de-NOx performance under NH3-NO/NO2 SCR conditions. As the CeTi and CeWTi catalysts exhibit similar redox property, addition of WO3 provides more acid sites which accelerate the reaction between NH4NO3 and NO to get a superior low-temperature activity. Amount of N2O formation shows a peak at 250℃ mainly derived from NH4NO3 decomposition.
2018, 39(11): 1814-1820
doi: 10.1016/S1872-2067(18)63119-5
Abstract:
Vanadium-chromium oxides (VCrO) were usually prepared by high-temperature solid-state reactions; however, mixed phases were frequently produced and the morphology of the products was not well controlled. In this work, we prepared amorphous VCrO precursors by using V2O5 and CrO3 and alcohols or mixtures of alcohol and water via solvothermal reaction at 180℃. The precursors were then calcined under nitrogen at various temperatures. The products were characterized by powder X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. It was revealed that pure-phase nanocrystalline orthorhombic CrVO4 was obtained when methanol or methanol/water was used as the solvothermal medium and the precursor was calcined at 700℃. The size of the CrVO4 crystals was around 500 nm when methanol was used, whereas it reduced significantly to less than 50 nm when a mixture of methanol and water was used. The sizes could be effectively tuned from 10 to 50 nm by varying the methanol/water volume ratio. To the best of our knowledge, this is the first report on the synthesis of pure-phase CrVO4 nanocrystals. The nano-CrVO4 showed almost the highest catalytic activity for the ammoxidation of 2,6-dichlorotoluene to 2,6-dichlorobenzonitrile among the reported bi-component composite oxides, owing to its smaller particle size, larger specific surface area, and more exposed active centers.
Vanadium-chromium oxides (VCrO) were usually prepared by high-temperature solid-state reactions; however, mixed phases were frequently produced and the morphology of the products was not well controlled. In this work, we prepared amorphous VCrO precursors by using V2O5 and CrO3 and alcohols or mixtures of alcohol and water via solvothermal reaction at 180℃. The precursors were then calcined under nitrogen at various temperatures. The products were characterized by powder X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. It was revealed that pure-phase nanocrystalline orthorhombic CrVO4 was obtained when methanol or methanol/water was used as the solvothermal medium and the precursor was calcined at 700℃. The size of the CrVO4 crystals was around 500 nm when methanol was used, whereas it reduced significantly to less than 50 nm when a mixture of methanol and water was used. The sizes could be effectively tuned from 10 to 50 nm by varying the methanol/water volume ratio. To the best of our knowledge, this is the first report on the synthesis of pure-phase CrVO4 nanocrystals. The nano-CrVO4 showed almost the highest catalytic activity for the ammoxidation of 2,6-dichlorotoluene to 2,6-dichlorobenzonitrile among the reported bi-component composite oxides, owing to its smaller particle size, larger specific surface area, and more exposed active centers.
2018, 39(11): 1821-1831
doi: 10.1016/S1872-2067(18)63141-9
Abstract:
The SAPO-34 catalysts were modified with metal cations by different processes (conventional ion exchange (CIE), template-assisted ion incorporation (TⅡ) and alcoholic ion exchange (AIE)), systematically characterized by XRD, XRF, N2 adsorption-desorption, UV-VIS, H2-TPR, EPR, SEM, EDX, XPS, NH3-TPD, 1H NMR and IGA, and applied in MTO reaction. The metal cations incorporation introduces extra diffusion hindrance by metallic species located in the cavity of SAPO-34. In particular, the Zn cations-modified SAPO-34 catalysts exhibit core-shell like structure, with Si-rich and Zn-rich sublayer near the external surface, which favors the coke deposition at the beginning of MTO reaction, exerts marked impact on the diffusion of the generated products with relatively large molecular size (e.g. propylene), and significantly increases the selectivity to ethylene and the ratio of ethylene to propene in the MTO reaction.
The SAPO-34 catalysts were modified with metal cations by different processes (conventional ion exchange (CIE), template-assisted ion incorporation (TⅡ) and alcoholic ion exchange (AIE)), systematically characterized by XRD, XRF, N2 adsorption-desorption, UV-VIS, H2-TPR, EPR, SEM, EDX, XPS, NH3-TPD, 1H NMR and IGA, and applied in MTO reaction. The metal cations incorporation introduces extra diffusion hindrance by metallic species located in the cavity of SAPO-34. In particular, the Zn cations-modified SAPO-34 catalysts exhibit core-shell like structure, with Si-rich and Zn-rich sublayer near the external surface, which favors the coke deposition at the beginning of MTO reaction, exerts marked impact on the diffusion of the generated products with relatively large molecular size (e.g. propylene), and significantly increases the selectivity to ethylene and the ratio of ethylene to propene in the MTO reaction.
2018, 39(11): 1832-1841
doi: 10.1016/S1872-2067(18)63120-1
Abstract:
Sepiolite@LDH (Sep@LDH) composites were designed and prepared based on the assembly of layered double hydroxides (LDH) on acidified sepiolites (Sep) for the simultaneous photocatalytic degradation of methyl orange (MO) and methylene blue (MB). The structure, morphology, texture, optical properties, and photocatalytic performance of the prepared Sep@LDH were studied in detail. Among the Sep@LDH composites, Sep4@LDH (4.0 g Sep) exhibited the highest photocatalytic activity under visible-light irradiation, which could be attributed to its large surface area, high crystallinity, and plentiful active sites on its surface. The photodegradation of the dyes followed a pseudo first-order kinetic model (Langmuir-Hinshelwood model), indicating that the copious and homogeneous active sites on the surface of the composites contributed to the high photocatalytic activity. The photodegradation mechanism was studied by examining the active species (·OH, h+, and·O2- anions) using appropriate scavengers. It was found that·OH radicals played a critical role in the photocatalytic process of MO and MB, where the generation of·OH radicals occurred on the electron/hole (e-/h+) pairs on the surface of the Sep@LDH composites.
Sepiolite@LDH (Sep@LDH) composites were designed and prepared based on the assembly of layered double hydroxides (LDH) on acidified sepiolites (Sep) for the simultaneous photocatalytic degradation of methyl orange (MO) and methylene blue (MB). The structure, morphology, texture, optical properties, and photocatalytic performance of the prepared Sep@LDH were studied in detail. Among the Sep@LDH composites, Sep4@LDH (4.0 g Sep) exhibited the highest photocatalytic activity under visible-light irradiation, which could be attributed to its large surface area, high crystallinity, and plentiful active sites on its surface. The photodegradation of the dyes followed a pseudo first-order kinetic model (Langmuir-Hinshelwood model), indicating that the copious and homogeneous active sites on the surface of the composites contributed to the high photocatalytic activity. The photodegradation mechanism was studied by examining the active species (·OH, h+, and·O2- anions) using appropriate scavengers. It was found that·OH radicals played a critical role in the photocatalytic process of MO and MB, where the generation of·OH radicals occurred on the electron/hole (e-/h+) pairs on the surface of the Sep@LDH composites.
2018, 39(11): 1842-1853
doi: 10.1016/S1872-2067(18)63114-6
Abstract:
Persulfate decontamination technologies utilizing radical-driven processes are powerful tools for the treatment of a broad range of impurities. However, the design of high-performance catalytic activators with multi-functionality remains a great challenge. Therefore, in this study, three-dimensional multifunctional FexOy/N-GN/CNTs (N-GN:nitrogen-doped graphene, CNTs:carbon nanotubes) heterojunctions, which can be employed as microwave absorbers and catalysts, were synthesized via a solvothermal method and applied to activate peroxymonosulfate for the degradation of methylene blue (MB). X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), scanning electron microscope (SEM), and X-ray photoelectron microscopy (XPS) analyses revealed that the FexOy were anchored in-situ onto the N-GN network. Using MB as the model organic dye, various factors, such as degradation systems, PMS loading, initial organic pollutant concentration, and catalyst dosage were optimized. The results revealed that the remarkable efficiency was attributable to the synergistic effects of carbon, nitrogen, and iron-based species. The oxidation system corresponded to the pseudo-first-order kinetic with a k value of~0.33 min-1. It was demonstrated that both SO4·- and OH· were the predominant reactive species through quenching experiments. Because these heterojunctions were employed as microwave absorbers and have a semiconductor-like texture, the Fe/N co-rich hierarchical porous carbon skeleton favored electron transport and storage. These heterojunctions increase the options for transitional metal catalysts and highlights the importance of designing other heterojunctions for specific applications, such as supercapacitors, energy storage, CO2 capture, and oxygen reduction electrocatalysts.
Persulfate decontamination technologies utilizing radical-driven processes are powerful tools for the treatment of a broad range of impurities. However, the design of high-performance catalytic activators with multi-functionality remains a great challenge. Therefore, in this study, three-dimensional multifunctional FexOy/N-GN/CNTs (N-GN:nitrogen-doped graphene, CNTs:carbon nanotubes) heterojunctions, which can be employed as microwave absorbers and catalysts, were synthesized via a solvothermal method and applied to activate peroxymonosulfate for the degradation of methylene blue (MB). X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), scanning electron microscope (SEM), and X-ray photoelectron microscopy (XPS) analyses revealed that the FexOy were anchored in-situ onto the N-GN network. Using MB as the model organic dye, various factors, such as degradation systems, PMS loading, initial organic pollutant concentration, and catalyst dosage were optimized. The results revealed that the remarkable efficiency was attributable to the synergistic effects of carbon, nitrogen, and iron-based species. The oxidation system corresponded to the pseudo-first-order kinetic with a k value of~0.33 min-1. It was demonstrated that both SO4·- and OH· were the predominant reactive species through quenching experiments. Because these heterojunctions were employed as microwave absorbers and have a semiconductor-like texture, the Fe/N co-rich hierarchical porous carbon skeleton favored electron transport and storage. These heterojunctions increase the options for transitional metal catalysts and highlights the importance of designing other heterojunctions for specific applications, such as supercapacitors, energy storage, CO2 capture, and oxygen reduction electrocatalysts.
2018, 39(11): 1854-1860
doi: 10.1016/S1872-2067(18)63101-8
Abstract:
A series of zwitterionic-type quaternary ammoniums (ZTQAs) with varying lengths of alkyl chains combined with KI were synthesized and considered as catalysts for the coupling reaction of CO2 and various terminal epoxides. The prolonged alkyl chain of ZTQAs exhibited temperature-responsive self-separation in propylene carbonate (PC). The interaction between ZTQAs and KI was confirmed by X-ray photoelectron spectroscopy and quantum chemical calculations. This interaction strengthened the nucleophilicity of the I- ion, favoring the catalytic reaction. The 3-(dimethyltetradecylammonium) propane sulfonate (DTPS)/KI showed an excellent yield of PC (95.1%) at 125℃, 1.5 MPa, and 1 mol% loading of catalyst. The precipitate formed spontaneously from the catalytic system, providing high catalytic activity of the homogeneous catalyst, as well as easy recovery of the heterogeneous catalyst.
A series of zwitterionic-type quaternary ammoniums (ZTQAs) with varying lengths of alkyl chains combined with KI were synthesized and considered as catalysts for the coupling reaction of CO2 and various terminal epoxides. The prolonged alkyl chain of ZTQAs exhibited temperature-responsive self-separation in propylene carbonate (PC). The interaction between ZTQAs and KI was confirmed by X-ray photoelectron spectroscopy and quantum chemical calculations. This interaction strengthened the nucleophilicity of the I- ion, favoring the catalytic reaction. The 3-(dimethyltetradecylammonium) propane sulfonate (DTPS)/KI showed an excellent yield of PC (95.1%) at 125℃, 1.5 MPa, and 1 mol% loading of catalyst. The precipitate formed spontaneously from the catalytic system, providing high catalytic activity of the homogeneous catalyst, as well as easy recovery of the heterogeneous catalyst.
