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2019 Volume 77 Issue 4
Digestive Ripening at Nanoscale and Its Application in the Preparation of Monodisperse Nanomaterials
2019, 77(4): 305-315
doi: 10.6023/A18120512
Abstract:
Recently, a digestive ripening process at nanoscale has been widely used to prepare monodisperse nanoparticles (NPs), especially for sub-10 nm small NPs, with significant advantages such as the very narrow size distribution of the obtained nanoparticles, the versatile applications for various nanoparticles and the simple operation process. However, no Chinese references are reported on digestive ripening process till now, which may limit the cognition and utility of digestive ripening method for some domestic scientists. Thus, this review starts from the discovery of the phenomenon and the proposal of mechanism for digestive ripening at nanoscale, to the analysis of influence factors including the precursor in the precipitation reaction, the digestive ripening reagent, heating treatment temperature and processing time, solvent media and so on. Then, theoretical hypothesis and the derived results are introduced based on the charged surface, the curvature effect, the interaction between NP surface and attached ligand layer, the diffusion effect and the competing reaction balance in the digestive ripening process. Subsequently, the important applications of digestive ripening method in the preparation of monodisperse nanomaterials of metal NPs, alloy NPs, quantum dots of metal oxide and metal chalcogenide, and other NPs are discussed, the obtained small metal or alloy NPs show a perfect sphere shape and a very narrow size distribution (relative standard deviation less than ±5%). Finally, the broad perspectives are proposed in the NP assembly for optical, electric and magnetic nanodevices, and the heterogeneous catalysis of monodisperse metal, alloy and semiconducotr NPs via the digestive ripening method.
Recently, a digestive ripening process at nanoscale has been widely used to prepare monodisperse nanoparticles (NPs), especially for sub-10 nm small NPs, with significant advantages such as the very narrow size distribution of the obtained nanoparticles, the versatile applications for various nanoparticles and the simple operation process. However, no Chinese references are reported on digestive ripening process till now, which may limit the cognition and utility of digestive ripening method for some domestic scientists. Thus, this review starts from the discovery of the phenomenon and the proposal of mechanism for digestive ripening at nanoscale, to the analysis of influence factors including the precursor in the precipitation reaction, the digestive ripening reagent, heating treatment temperature and processing time, solvent media and so on. Then, theoretical hypothesis and the derived results are introduced based on the charged surface, the curvature effect, the interaction between NP surface and attached ligand layer, the diffusion effect and the competing reaction balance in the digestive ripening process. Subsequently, the important applications of digestive ripening method in the preparation of monodisperse nanomaterials of metal NPs, alloy NPs, quantum dots of metal oxide and metal chalcogenide, and other NPs are discussed, the obtained small metal or alloy NPs show a perfect sphere shape and a very narrow size distribution (relative standard deviation less than ±5%). Finally, the broad perspectives are proposed in the NP assembly for optical, electric and magnetic nanodevices, and the heterogeneous catalysis of monodisperse metal, alloy and semiconducotr NPs via the digestive ripening method.
2019, 77(4): 316-322
doi: 10.6023/A18110456
Abstract:
As an ultra-wide bandgap insulating material, boron nitride has attracted intense interest due to its high thermal conductivity, high chemical and thermal stability as well as their applications in thermal interface materials, photo/electro-catalysis, and energy storage. As for the low dimensional boron nitride nanostructures, e.g., nanosheets, nanotubes, nanorods, nanowires, nanospheres, and quantum dots, the high thermal conductivity (600 W/mK) and the ultra-large bandgap (5~6 eV) make them the promising candidate for thermal conductive composites, thermoelectric materials and electronic packaging materials, which gives rise to the hot research topic on the synthesis and properties of the boron nitride nanostructures. In this review, the recent advances in the hydrothermal synthesis of boron nitride nanostructures will be fully discussed, and the remarks on the issues need to be addressed, the comprehensive understanding of the mechanism and the new approaches for the hydrothermal synthesis will be proposed in the end.
As an ultra-wide bandgap insulating material, boron nitride has attracted intense interest due to its high thermal conductivity, high chemical and thermal stability as well as their applications in thermal interface materials, photo/electro-catalysis, and energy storage. As for the low dimensional boron nitride nanostructures, e.g., nanosheets, nanotubes, nanorods, nanowires, nanospheres, and quantum dots, the high thermal conductivity (600 W/mK) and the ultra-large bandgap (5~6 eV) make them the promising candidate for thermal conductive composites, thermoelectric materials and electronic packaging materials, which gives rise to the hot research topic on the synthesis and properties of the boron nitride nanostructures. In this review, the recent advances in the hydrothermal synthesis of boron nitride nanostructures will be fully discussed, and the remarks on the issues need to be addressed, the comprehensive understanding of the mechanism and the new approaches for the hydrothermal synthesis will be proposed in the end.
2019, 77(4): 323-339
doi: 10.6023/A18120497
Abstract:
During the past decades, extensive investigations on metal-organic frameworks (MOFs) with ultrahigh surface area for gas adsorption and separation have been reported. With the increasing number of possible MOFs, it has been a great challenge to discover high-performing MOFs of interest from numerous structures. High-throughput computational screening (HTCS) is a powerful tool to accelerate the development of MOFs for application of interest and explores the quantitative structure-property relationship (QSPR) to facilitate the rational design of top-performing MOFs. In this review, we summarize the MOF databases used for HTCS, mainly including MOFs collected from experimentally synthesized MOFs (i.e. eMOFs), and the hypothetical MOFs constructed by computer-aided tools (i.e. hMOFs). Moreover, there are currently two important screening strategies, molecular simulation and machine learning-based HTCS. A vast majority of HTCS have been performed by molecular simulations including grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations, in which the accuracy of force field parameters play a criticl role in the reliability of HTCS. GCMC is able to predict the adsorption performance of MOFs such as adsorption capacity, selectivity and heat of adsorption, whereas MD is commonly used to estimate the dynamic property of adsorbates, e.g. diffusion coefficient and permeability. Additionally, lattice GCMC and classical density functional theory (cDFT) are also highlighted for computational screening of MOFs in this review. Machine learning consisting of various algorithms is a recently developed strategy with high efficiency and low computational cost, which is a more powerful and promising technique in future. At last, the investigations on the utilization of HTCS in CH4 storage, H2 storage, CO2 capture and gas separation were outlined. By reviewing the recent research progress in HTCS, we pointed out the current challenges and opportunities for the furture development of HTCS for MOFs, which will be the major engine for the commercialization of MOFs in various applications of interests.
During the past decades, extensive investigations on metal-organic frameworks (MOFs) with ultrahigh surface area for gas adsorption and separation have been reported. With the increasing number of possible MOFs, it has been a great challenge to discover high-performing MOFs of interest from numerous structures. High-throughput computational screening (HTCS) is a powerful tool to accelerate the development of MOFs for application of interest and explores the quantitative structure-property relationship (QSPR) to facilitate the rational design of top-performing MOFs. In this review, we summarize the MOF databases used for HTCS, mainly including MOFs collected from experimentally synthesized MOFs (i.e. eMOFs), and the hypothetical MOFs constructed by computer-aided tools (i.e. hMOFs). Moreover, there are currently two important screening strategies, molecular simulation and machine learning-based HTCS. A vast majority of HTCS have been performed by molecular simulations including grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations, in which the accuracy of force field parameters play a criticl role in the reliability of HTCS. GCMC is able to predict the adsorption performance of MOFs such as adsorption capacity, selectivity and heat of adsorption, whereas MD is commonly used to estimate the dynamic property of adsorbates, e.g. diffusion coefficient and permeability. Additionally, lattice GCMC and classical density functional theory (cDFT) are also highlighted for computational screening of MOFs in this review. Machine learning consisting of various algorithms is a recently developed strategy with high efficiency and low computational cost, which is a more powerful and promising technique in future. At last, the investigations on the utilization of HTCS in CH4 storage, H2 storage, CO2 capture and gas separation were outlined. By reviewing the recent research progress in HTCS, we pointed out the current challenges and opportunities for the furture development of HTCS for MOFs, which will be the major engine for the commercialization of MOFs in various applications of interests.
2019, 77(4): 340-350
doi: 10.6023/A18100414
Abstract:
Oral cancer is head and neck cancer, and cancer tissue is located in the oral cavity. The non-invasive early diagnosis is an effective method to reduce the death of the disease. The oral cancer-related substances are first released into the saliva, which is convenient, safe and non-invasive, and is the first choice for screening and early diagnosis of oral cancer. In this paper, the specific types and the commonly used detection methods of the salivary tumor biomarkers at home and abroad were summarized and compared. Specifically, the latest application of new electrochemical biosensor in the detection of the salivary tumor biomarkers associated with oral cancer was mainly described. Futhermore, the summary of its future directions and the potential applications was proposed, which provided reference for the further research and application of the salivary tumor biomarkers in oral cancer.
Oral cancer is head and neck cancer, and cancer tissue is located in the oral cavity. The non-invasive early diagnosis is an effective method to reduce the death of the disease. The oral cancer-related substances are first released into the saliva, which is convenient, safe and non-invasive, and is the first choice for screening and early diagnosis of oral cancer. In this paper, the specific types and the commonly used detection methods of the salivary tumor biomarkers at home and abroad were summarized and compared. Specifically, the latest application of new electrochemical biosensor in the detection of the salivary tumor biomarkers associated with oral cancer was mainly described. Futhermore, the summary of its future directions and the potential applications was proposed, which provided reference for the further research and application of the salivary tumor biomarkers in oral cancer.
2019, 77(4): 351-357
doi: 10.6023/A19010009
Abstract:
It is known that fluoride and phosphate in aqueous solution can accelerate the photocatalytic degradation of phenol over anatase or P25 TiO2. But the mechanism still remains under debate. In this work, an anion-free anatase TiO2 is prepared, followed by deposition with 0.52 wt% Pt (Pt/TiO2). Reaction was performed in aqueous solution at initial pH 5.2, where 99% of anions were in the form of F- or H2PO4-. On the addition of 0.1~30 mmol/L anions, the rate constants of phenol degradation (kobs) were all increased, confirming the positive effect of fluoride and phosphate, respectively. Interestingly, there was a linear relationship between the increase of kobs and the amounts of anion adsorption, the slope of which became larger in the order of fluoride>phosphate, and Pt/TiO2>TiO2. These observations indicate that the positive effect of anions originates from the adsorbed anions on solid, and that fluoride was more active than phosphate. A (photo)electrochemical measurement showed that fluoride and phosphate were negative and positive, respectively, to O2 reduction, but they were all beneficial to phenol oxidation. Furthermore, in the presence of fluoride and phosphate, the flat band potentials of TiO2 were shifted by -159 and 89 mV, respectively. The former favors orbital overlapping of phenol with TiO2 valence band, and the latter favors orbital overlapping of O2 with TiO2 conduction band, all of which promotes the interfacial charge transfers. Since inorganic anions are widely present, this result would benefit the mechanism study of a semiconductor photocatalyis and its application. As a reference, pure anatase was prepared from the hydrolysis of tetrabutyl titanate, followed by calcination in air at 400℃ for 2 h. The solid was then deposited with Pt, produced in situ from the photocatalytic reduction of H2PtCl6 in the presence of methanol. Solid was characterized with X-ray diffraction, N2 adsorption, Raman, and X-ray photoelectron spectroscopy. After Pt deposition, anatase phase remained unchanged, but the solid pores were blocked by a mixture of Pt and PtO2. Photoreactions were performed at room temperature under UV light at wavelengths equal to and longer than 320 nm. Organic compounds and inorganic anions were quantitatively analyzed with a high performance liquid and ionic chromatography, respectively. (Photo)electrochemical measurement was performed in a three-electrode compartment, where a Pt gauze was used as counter electrode, and a AgCl/Ag as reference electrode.
It is known that fluoride and phosphate in aqueous solution can accelerate the photocatalytic degradation of phenol over anatase or P25 TiO2. But the mechanism still remains under debate. In this work, an anion-free anatase TiO2 is prepared, followed by deposition with 0.52 wt% Pt (Pt/TiO2). Reaction was performed in aqueous solution at initial pH 5.2, where 99% of anions were in the form of F- or H2PO4-. On the addition of 0.1~30 mmol/L anions, the rate constants of phenol degradation (kobs) were all increased, confirming the positive effect of fluoride and phosphate, respectively. Interestingly, there was a linear relationship between the increase of kobs and the amounts of anion adsorption, the slope of which became larger in the order of fluoride>phosphate, and Pt/TiO2>TiO2. These observations indicate that the positive effect of anions originates from the adsorbed anions on solid, and that fluoride was more active than phosphate. A (photo)electrochemical measurement showed that fluoride and phosphate were negative and positive, respectively, to O2 reduction, but they were all beneficial to phenol oxidation. Furthermore, in the presence of fluoride and phosphate, the flat band potentials of TiO2 were shifted by -159 and 89 mV, respectively. The former favors orbital overlapping of phenol with TiO2 valence band, and the latter favors orbital overlapping of O2 with TiO2 conduction band, all of which promotes the interfacial charge transfers. Since inorganic anions are widely present, this result would benefit the mechanism study of a semiconductor photocatalyis and its application. As a reference, pure anatase was prepared from the hydrolysis of tetrabutyl titanate, followed by calcination in air at 400℃ for 2 h. The solid was then deposited with Pt, produced in situ from the photocatalytic reduction of H2PtCl6 in the presence of methanol. Solid was characterized with X-ray diffraction, N2 adsorption, Raman, and X-ray photoelectron spectroscopy. After Pt deposition, anatase phase remained unchanged, but the solid pores were blocked by a mixture of Pt and PtO2. Photoreactions were performed at room temperature under UV light at wavelengths equal to and longer than 320 nm. Organic compounds and inorganic anions were quantitatively analyzed with a high performance liquid and ionic chromatography, respectively. (Photo)electrochemical measurement was performed in a three-electrode compartment, where a Pt gauze was used as counter electrode, and a AgCl/Ag as reference electrode.
2019, 77(4): 358-364
doi: 10.6023/A18120505
Abstract:
Methyl transfer reactions are of great significance in the field of synthetic chemistry and life sciences. So far, most of the reported methyl migration reactions have occurred between different types of molecules. Therefore, it is of certain value to search for new methyl transfer reactions. In this study, fenthion, a most common insecticide in the environment, was selected as the studied object, and electrospray ionization mass spectrometry (ESI-MS) was used as the analytical tool to conduct highly sensitive analysis of the reaction system, so as to explore the possibility of methyl transfer reaction in fenthion molecules under the condition of trifluoroacetic acid and nanometer titanium dioxide. Other than m/z 279 (protonated fenthion), some new product ions (m/z 293 and m/z 265) could be observed in the fingerprint MS of fenthion reaction solution. Tandem MS experiments showed that the intensity of product ion m/z 231 (elimination of CH3SH) in the dissociation of m/z 279 from fenthion reaction solution were different from that from protonated fenthion standard. This indicated that the methyl in the fenthion could transfer from oxygen atom to unsaturated sulfur atom via 1, 3-methyl transfer, forming isomer a2, which led to the high intensity of product ion m/z 231 in the dissociation of m/z 279 from fenthion reaction solution. Under the assistance of acid, the methyl cation continued to transfer from sulfur atom in a2 to the unsaturated sulfur atom in another fenthion molecule, forming a3 (m/z 293) and a4 via intermolecular methyl transfer reaction, which was verified by tandem MS experiments of ions at m/z 293 and m/z 265. In addition, density functional theory (DFT) calculations were carried out to confirm the mechanism of intramolecular and intermolecular methyl transfer reactions of fenthion. In order to observe the phenomenon of methyl transfer more intuitively, the effects of different acids, metal oxides, reaction time and reaction temperature on the signal intensities of ions at m/z 265 and m/z 293 of intermolecular methyl transfer reactions of fenthion were investigated. It could be concluded that under the conditions of trifluoroacetic acid and nanometer titanium dioxide, and 60℃ ultrasound reaction for 6 h, the proportion of intermolecular methyl transfer reactions of fenthion was the highest. In this study, intramolecular and intermolecular methyl transfer reactions were both discovered and investigated in fenthion, which can not only provide a method to study methyl transfer reactions, but also propose a new idea for the study of degradation of fenthion.
Methyl transfer reactions are of great significance in the field of synthetic chemistry and life sciences. So far, most of the reported methyl migration reactions have occurred between different types of molecules. Therefore, it is of certain value to search for new methyl transfer reactions. In this study, fenthion, a most common insecticide in the environment, was selected as the studied object, and electrospray ionization mass spectrometry (ESI-MS) was used as the analytical tool to conduct highly sensitive analysis of the reaction system, so as to explore the possibility of methyl transfer reaction in fenthion molecules under the condition of trifluoroacetic acid and nanometer titanium dioxide. Other than m/z 279 (protonated fenthion), some new product ions (m/z 293 and m/z 265) could be observed in the fingerprint MS of fenthion reaction solution. Tandem MS experiments showed that the intensity of product ion m/z 231 (elimination of CH3SH) in the dissociation of m/z 279 from fenthion reaction solution were different from that from protonated fenthion standard. This indicated that the methyl in the fenthion could transfer from oxygen atom to unsaturated sulfur atom via 1, 3-methyl transfer, forming isomer a2, which led to the high intensity of product ion m/z 231 in the dissociation of m/z 279 from fenthion reaction solution. Under the assistance of acid, the methyl cation continued to transfer from sulfur atom in a2 to the unsaturated sulfur atom in another fenthion molecule, forming a3 (m/z 293) and a4 via intermolecular methyl transfer reaction, which was verified by tandem MS experiments of ions at m/z 293 and m/z 265. In addition, density functional theory (DFT) calculations were carried out to confirm the mechanism of intramolecular and intermolecular methyl transfer reactions of fenthion. In order to observe the phenomenon of methyl transfer more intuitively, the effects of different acids, metal oxides, reaction time and reaction temperature on the signal intensities of ions at m/z 265 and m/z 293 of intermolecular methyl transfer reactions of fenthion were investigated. It could be concluded that under the conditions of trifluoroacetic acid and nanometer titanium dioxide, and 60℃ ultrasound reaction for 6 h, the proportion of intermolecular methyl transfer reactions of fenthion was the highest. In this study, intramolecular and intermolecular methyl transfer reactions were both discovered and investigated in fenthion, which can not only provide a method to study methyl transfer reactions, but also propose a new idea for the study of degradation of fenthion.
2019, 77(4): 365-370
doi: 10.6023/A18120484
Abstract:
Isocyanates is a widely-used chemical in many manufacturing industries, such as polymer industry, pharmaceutical production and production of a variety of agricultural chemicals. However, it is harmful to human health due to the volatility. Therefore, it is necessary to develop methods to detect isocyanates quickly and conveniently, especially to gaseous isocyanates. In this work, a novel fluorescent probe, N-buty-4-hydroxy-1, 8naphthalimide, was developed for detection of isocyanates. This fluorescence probe can be synthesized by a simple three-steps synthetic route, and the overall yield of the whole synthesizing process reached 75%. In the absence of isocyanate, the probe solution displays an emission centering at 596 nm when excited at 370 nm, which is yellow to the naked eye. Once isocyanate is added, the fluorescence of solution changes from yellow to blue, and the process finishes in 4 min. The detecting limit of this probe to isocyanates is calculated to be 112 nmol·L-1. It is also proved that this probe possesses excellent selectivity for isocyanate and distinct anti-interference to common organic volatilized compounds. In addition, the reaction mechanism between the probe and isocyanate were proved by HPLC, NMR and ESI-MASS. Results show that the hydroxy group on the 4th position of naphthalene ring of probe reacts with isocyanate group (-NCO) of isocyanate, and resulting in carbamates, which alter 4th substituent group of probe molecule and lead to change of fluorescence. In order to detect the gaseous isocyanates directly, test paper are developed based on N-buty-4-hydroxy-1, 8naphthalimide. When the test paper exposed to isocyanates vapor, the yellow fluorescence fade away gradually and a blue fluorescence appear in 6 min. And the test paper possesses excellent selectivity for gaseous isocyanate and distinct anti-interference to common VOCs. In conclusion, this strategy is an efficient way to detect gaseous isocyanates, and it may provide a referable approach for directly monitoring the volatile organic compounds in air.
Isocyanates is a widely-used chemical in many manufacturing industries, such as polymer industry, pharmaceutical production and production of a variety of agricultural chemicals. However, it is harmful to human health due to the volatility. Therefore, it is necessary to develop methods to detect isocyanates quickly and conveniently, especially to gaseous isocyanates. In this work, a novel fluorescent probe, N-buty-4-hydroxy-1, 8naphthalimide, was developed for detection of isocyanates. This fluorescence probe can be synthesized by a simple three-steps synthetic route, and the overall yield of the whole synthesizing process reached 75%. In the absence of isocyanate, the probe solution displays an emission centering at 596 nm when excited at 370 nm, which is yellow to the naked eye. Once isocyanate is added, the fluorescence of solution changes from yellow to blue, and the process finishes in 4 min. The detecting limit of this probe to isocyanates is calculated to be 112 nmol·L-1. It is also proved that this probe possesses excellent selectivity for isocyanate and distinct anti-interference to common organic volatilized compounds. In addition, the reaction mechanism between the probe and isocyanate were proved by HPLC, NMR and ESI-MASS. Results show that the hydroxy group on the 4th position of naphthalene ring of probe reacts with isocyanate group (-NCO) of isocyanate, and resulting in carbamates, which alter 4th substituent group of probe molecule and lead to change of fluorescence. In order to detect the gaseous isocyanates directly, test paper are developed based on N-buty-4-hydroxy-1, 8naphthalimide. When the test paper exposed to isocyanates vapor, the yellow fluorescence fade away gradually and a blue fluorescence appear in 6 min. And the test paper possesses excellent selectivity for gaseous isocyanate and distinct anti-interference to common VOCs. In conclusion, this strategy is an efficient way to detect gaseous isocyanates, and it may provide a referable approach for directly monitoring the volatile organic compounds in air.
2019, 77(4): 371-378
doi: 10.6023/A19010012
Abstract:
Recently, it has been widely reported that CO2 was utilized to produce valuable chemical feedstock with copper/zinc and metal oxide based catalysts, yet harsh conditions (high pressure and high temperature, etc.) are still essential for the activity and selectivity. Compared with the harsh conditions required in the direct conversion of CO2 to achieve high selectivity and activity, mild conditions in the indirect conversion of CO2 through the carbonate intermediate provides an alternative. Since CO2 can be easily transferred to carbonate under mild and even atmospheric pressure of CO2 in many reports, hydrogenation of carbonates to methanol at ambient condition presents an attractive strategy for the indirect conversion of CO2 with higher catalytic activity. In our previous work, we have reported that Cu/SiO2 catalyst achieved satisfying performance for the hydrogenation of diethyl carbonate with poor stability at long term running due to the agglomeration of active metal. Herein, we present that the catalytic activity and stability of the catalysts in the hydrogenation of carbonates could be efficiently improved by the addition of Cr. In this research, various Cr-promoted Crx-Cu/SiO2 catalysts were synthesized through an ammonia evaporation method. The effect of added Cr on the catalytic performance was investigated by the hydrogenation of diethyl carbonate (DEC) as a probe reaction system. The results showed that the Crx-Cu/SiO2 catalyst with 3 wt% Cr performed the preferable activity. Under the reaction conditions of temperature of 503 K, hydrogen pressure of 2.5 MPa and liquid hourly space velocity (LHSV) of 1.0 h-1, the conversion of DEC could be 99%, while the selectivity of product methanol (86.2%) and space-time yields (STY) of methanol (5.6 mmolMeOH·gcat-1·h-1) were enhanced significantly. The physicochemical properties of Crx-Cu/SiO2 catalysts were characterized by X-ray diffraction (XRD), N2 physical adsorption and desorption, transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR) and in-situ diffuse reflection infrared Fourier transform spectroscopy (In-situ DRIFTS). The results revealed that the dispersion of active copper species was significantly improved. The copper chromite species formed by the interaction of copper and chromium could optimize the distribution of Cu(0) and Cu(Ⅰ) and regulate adsorption construction of reactant, efficiently improving the catalytic performance and stability for the hydrogenation of diethyl carbonate to methanol.
Recently, it has been widely reported that CO2 was utilized to produce valuable chemical feedstock with copper/zinc and metal oxide based catalysts, yet harsh conditions (high pressure and high temperature, etc.) are still essential for the activity and selectivity. Compared with the harsh conditions required in the direct conversion of CO2 to achieve high selectivity and activity, mild conditions in the indirect conversion of CO2 through the carbonate intermediate provides an alternative. Since CO2 can be easily transferred to carbonate under mild and even atmospheric pressure of CO2 in many reports, hydrogenation of carbonates to methanol at ambient condition presents an attractive strategy for the indirect conversion of CO2 with higher catalytic activity. In our previous work, we have reported that Cu/SiO2 catalyst achieved satisfying performance for the hydrogenation of diethyl carbonate with poor stability at long term running due to the agglomeration of active metal. Herein, we present that the catalytic activity and stability of the catalysts in the hydrogenation of carbonates could be efficiently improved by the addition of Cr. In this research, various Cr-promoted Crx-Cu/SiO2 catalysts were synthesized through an ammonia evaporation method. The effect of added Cr on the catalytic performance was investigated by the hydrogenation of diethyl carbonate (DEC) as a probe reaction system. The results showed that the Crx-Cu/SiO2 catalyst with 3 wt% Cr performed the preferable activity. Under the reaction conditions of temperature of 503 K, hydrogen pressure of 2.5 MPa and liquid hourly space velocity (LHSV) of 1.0 h-1, the conversion of DEC could be 99%, while the selectivity of product methanol (86.2%) and space-time yields (STY) of methanol (5.6 mmolMeOH·gcat-1·h-1) were enhanced significantly. The physicochemical properties of Crx-Cu/SiO2 catalysts were characterized by X-ray diffraction (XRD), N2 physical adsorption and desorption, transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR) and in-situ diffuse reflection infrared Fourier transform spectroscopy (In-situ DRIFTS). The results revealed that the dispersion of active copper species was significantly improved. The copper chromite species formed by the interaction of copper and chromium could optimize the distribution of Cu(0) and Cu(Ⅰ) and regulate adsorption construction of reactant, efficiently improving the catalytic performance and stability for the hydrogenation of diethyl carbonate to methanol.
2019, 77(4): 379-386
doi: 10.6023/A18110475
Abstract:
Mercury is an important pollutant, which has attracted wide attention in recent years. Up to now, based on surface enhanced raman spectroscopy (SERS) strategy for detection of Hg2+ is very attractive due to its high sensitivity among various detection methods. Based on the "turn-off" mechanism, we synthesized a magnetic Fe3O4@Ag nanomaterial for SERS detection of Hg2+. The magnetic-plasma resonance nanoparticles, which combine magnetic and plasma resonance properties, can be used for SERS detection of mercury ions with high sensitivity and selectivity. Firstly, the magnetic nanoparticles were prepared by solvothermal reaction, and silver nanoparticles were coated on the surface of magnetic nanoparticles after modification of amino groups. By modifying the positively charged PDADMAC, polyDADMAC (PDDA) layer, the negatively charged methyl orange probe molecule is adsorbed on the surface of Fe3O4@Ag, and in the presence of Hg2+, a significant decrease in SERS signal can be observed. Due to the short-time reaction of Hg2+ and Ag nanoparticles, an amalgam is formed on the surface of the Ag particles, which affects the surface plasmon resonance (SPR) characteristics of the Ag nanoparticles, resulting in enhanced attenuation of the electromagnetic field. And the short-time reaction of Hg2+ and Ag nanoparticles also leads to a decrease in the surface zeta potential of the Ag nanoparticles and affects the adsorption of the Raman probe molecules on the surface, resulting in a decrease in the SERS signal. Therefore, the decrease of SERS intensity in the presence of Hg2+ is mainly attributed to the interaction between Hg2+ and Ag nanoparticles. Through our experiments, it can be proved that the detection limit of the method based on "turn-off" mechanism for detecting Hg2+ ions can be as low as 10-10 mol/L. In addition, this method also shows high selectivity for divalent mercury ions. The SERS nanosensor designed in this experiment can be used to detect the specificity and ultra-sensitivity of Hg2+ in the environment, and it also provides great potential for the construction of SERS nanosensor for heavy metal ions.
Mercury is an important pollutant, which has attracted wide attention in recent years. Up to now, based on surface enhanced raman spectroscopy (SERS) strategy for detection of Hg2+ is very attractive due to its high sensitivity among various detection methods. Based on the "turn-off" mechanism, we synthesized a magnetic Fe3O4@Ag nanomaterial for SERS detection of Hg2+. The magnetic-plasma resonance nanoparticles, which combine magnetic and plasma resonance properties, can be used for SERS detection of mercury ions with high sensitivity and selectivity. Firstly, the magnetic nanoparticles were prepared by solvothermal reaction, and silver nanoparticles were coated on the surface of magnetic nanoparticles after modification of amino groups. By modifying the positively charged PDADMAC, polyDADMAC (PDDA) layer, the negatively charged methyl orange probe molecule is adsorbed on the surface of Fe3O4@Ag, and in the presence of Hg2+, a significant decrease in SERS signal can be observed. Due to the short-time reaction of Hg2+ and Ag nanoparticles, an amalgam is formed on the surface of the Ag particles, which affects the surface plasmon resonance (SPR) characteristics of the Ag nanoparticles, resulting in enhanced attenuation of the electromagnetic field. And the short-time reaction of Hg2+ and Ag nanoparticles also leads to a decrease in the surface zeta potential of the Ag nanoparticles and affects the adsorption of the Raman probe molecules on the surface, resulting in a decrease in the SERS signal. Therefore, the decrease of SERS intensity in the presence of Hg2+ is mainly attributed to the interaction between Hg2+ and Ag nanoparticles. Through our experiments, it can be proved that the detection limit of the method based on "turn-off" mechanism for detecting Hg2+ ions can be as low as 10-10 mol/L. In addition, this method also shows high selectivity for divalent mercury ions. The SERS nanosensor designed in this experiment can be used to detect the specificity and ultra-sensitivity of Hg2+ in the environment, and it also provides great potential for the construction of SERS nanosensor for heavy metal ions.
