Layered double hydroxides are one class or kind of 2 D layered materials that are considered promising for use in the supercapacitor.Although there have been many studies on the structure,composition,properties,and el...Layered double hydroxides are one class or kind of 2 D layered materials that are considered promising for use in the supercapacitor.Although there have been many studies on the structure,composition,properties,and electrode fabrication of layered double hydroxides,none summarize the effects of various modification methods on the structure and performance of layered double hydroxides in the supercapacitor.In a bid to fill this gap,in this review,we summarize the progress of modification methods such as exfoliation,intercalation,vacancy,doping,phase transformation,and composition regulation of layered double hydroxides in the field of the supercapacitor and put forward some opinions regarding the progress of research on the methods used in modifying the layered double hydroxides.展开更多
Ni/Mg/Al layered double hydroxides(LDHs) with different n(Ni)∶n(Mg)∶n(Al) ratio values were prepared via a coprecipitation reaction. Then Ni/Mg/Al mixed oxides were obtained by calcination of these LDHs precursors. ...Ni/Mg/Al layered double hydroxides(LDHs) with different n(Ni)∶n(Mg)∶n(Al) ratio values were prepared via a coprecipitation reaction. Then Ni/Mg/Al mixed oxides were obtained by calcination of these LDHs precursors. Carbon nanotubes were produced in the catalytic decomposition of propane over the Ni/Mg/Al mixed oxide catalysts. The quality of as-made nanotubes was investigated by SEM and TEM. The nanotubes were multiwall with a high length-diameter ratio and appeared to be flexible. The catalytic activities of these mixed oxides increased with increasing the Ni content. The Ni/Mg/Al mixed oxide with the highest Ni content [n(Ni)/n(Mg)/n(Al)=1/1/1] showed the highest activity and the carbon nanotubes grown on its surface had the best quality.展开更多
Layered double hydroxides consisting of layers with cationic charges may be potential candidates of cationic microparticles forming synergetic retention effect with anionic polyacrylamide. In this work, the layered do...Layered double hydroxides consisting of layers with cationic charges may be potential candidates of cationic microparticles forming synergetic retention effect with anionic polyacrylamide. In this work, the layered double hydroxides with various molar ratios of Mg/Al were synthesized by co-precipitation of magnesium chloride and aluminum chloride and peptized by intense washing with water. The chemical formula, particle size, Zeta potential of the layered double hydroxide were analyzed. It was found that positively charged magnesium aluminum hydroxide with particle diameter in nanoparticle size could be prepared. The Zeta potential and particle size vary with the feed molar ratio of Mg/Al and the peptizing process, respectively. The Zeta potential is also pH dependent. The retention experiments carried out on DDJ show that when used together with anionic polyacrylamide, the positively charged colloidal double hydroxide greatly improves the retention of reed pulps. The chemical formula, particle size and Zeta potential of the colloidal double hydroxide all affect its retention behavior.展开更多
Although hydrotalcite, or layered double hydroxides (LDHs), is not a common mineral, it is an important material that can be easily synthesized in laboratory. In this study, structural evolvement and BET surface area ...Although hydrotalcite, or layered double hydroxides (LDHs), is not a common mineral, it is an important material that can be easily synthesized in laboratory. In this study, structural evolvement and BET surface area changes of heat treated Mg/Al-LDH is evaluated by XRD, TEM and N2-BET analyses. The results indicate that the magnesium-aluminum LDH with carbonate as interlayer anion, periclase-like oxides was formed at temperatures of 400-800℃. Meanwhile, 2-3 nanometer mesoporous were formed during decomposition of LDH. However, the heat treated samples still preserve the morphology of the original LDH plates. Periclase-like formed from LDH heat treatment may re-hydrolyze and recover the structure of LDH. However, crystallinity of the recovered LDH is lower than that of the original LDH. This heat treatment will result in formation of (Mg, Al)-oxide nano-crystals and nanopores among the nano-crystals. When heating temperature exceeds 1000, the periclase-like (Mg, Al)-oxide is transformed into a composite with periclase (MgO) and spinel phases. The periclase can be re-hydrolyzed and dissolved in HCl solution. After acid treatment, the sample with a high surface area is composed of spinel nano-crystals and nanopores among them. Our results will provide a new and economic way to synthesize mesoporous materials through pathways of phase transformation of precursor materials with different composition.展开更多
Hydrotalcite-type anionic clays are a group of important materials used in adsorption processes, mainly for organic pollutants removal due the layered double hydroxide structure. The layer-interlayer interactions prov...Hydrotalcite-type anionic clays are a group of important materials used in adsorption processes, mainly for organic pollutants removal due the layered double hydroxide structure. The layer-interlayer interactions provide a structural memory even after dehydration and dehydroxylation process, since a very stable interlayer anions are part of material composition, like the carbonate one. A limited numbers of trivalent modifier cations can replace the aluminium cation due the ionic radii mismatch or oxidation state restrictions. Transition metal cations can replace the aluminium one in octahedral site of hydroxide lamellas in order to improve the adsorptive behaviors. In this work, we have investigate three compositions of carbonated magnesium-aluminium hydrotalcite with dif-ferent iron (III) contents through the co-precipitation method at pH 11 and aging step at 60°C for 6 hours. Thermal analysis was performed aiming the determination of the hydration water and hydroxyl amounts in dried precipitate samples, taking in account the results obtained for X-ray diffractometry, infrared spectroscopy, and nitrogen adsorption-desorption characterization for several thermally treated samples. All of synthesized samples showed high surface areas, even for high temperature of thermal treatment. The co-substitution with iron (III) reduced the temperature of dehydration and dehydroxylation process, but the co-substitution at 5 mol% provides other desirables characteristics, like a more amount of rhombohedral HDL phase and higher porosity, even after the thermal treatment at 500°C for 4 hours. This result makes that composition very applicable as a reusable adsorbent material in order to removal several types of micro-pollutant compounds in aqueous media.展开更多
The preparation of ZnAlLa-hydrotalcite-like compounds [ZnAlLa-HTLcs] was studied.ZnAlLa-HTLcs were synthesized by a method of variable pH with the raw materials of Zn(NO3)2,Al(NO3)3, La(NO3)3, and NaOH. The effects of...The preparation of ZnAlLa-hydrotalcite-like compounds [ZnAlLa-HTLcs] was studied.ZnAlLa-HTLcs were synthesized by a method of variable pH with the raw materials of Zn(NO3)2,Al(NO3)3, La(NO3)3, and NaOH. The effects of some factors (i.e. pH values, the mole ratio of Al3+ to La3+,temperature and the period of hydrothermal treatment) on the preparation of HTLcs were discussed systematically. XRD, TG-DTA, FT-IR spectroscopy, and ICP were performed to characterize ZnAlLa-HTLcs samples, and the thermal stability of HTLcs was also discussed. It was shown that unique ZnAlLa-HTLcs with high crystallinity can be prepared, under the conditions of pH=5.5-6.5, n(Zn2+)/n(Al3++La3+)=2and the atomic ratio of La3+ to Al3+ ranging from 0.07 to 2, hydrothermal treatment at 120 ℃ for 5h. When the calcination of the HTLcs is performed at temperatures above 200 ℃, ZnO phase is detected with Al2O3 and La2O3 spreading on its top. The complex metal oxides derived from ZnAlLa-HTLcs at 500 ℃ have higher catalytic activity and selectivity than those from ZnAl-HTLcs for the esterification of acetic acid with n-butanol under the same reaction conditions.展开更多
Salt freezing damage has severe impacts on durability of cement-based materials(CBMs).Calcined layered double hydroxide(CLDH),as an efficient environmental-friendly adsorption material,can impart excellent salt freezi...Salt freezing damage has severe impacts on durability of cement-based materials(CBMs).Calcined layered double hydroxide(CLDH),as an efficient environmental-friendly adsorption material,can impart excellent salt freezing resistance to CBMs.In this work,salt freezing resistance improvement of CBMs incorporated with CLDH was experimentally evaluated by chloride binding capacity,mass loss rate,relative dynamic elastic modulus,setting time,compressive strength,and micro structure tests.Beside these,the salt freezing damage model was established to effectively express the quantitative relationship between influencing factors and evaluation indexes of the salt freezing resistance of CBMs.Results show that CLDH can reconstruct its original layered structure to form reconstructed layered double hydroxide(RLDH).RLDH combines with chloride ions to form RLDH-Cl recrystallization,which can improve chloride binding capacity and pore structures of CBMs to relieve the salt freezing damage.The salt freezing damage model indicates that the suitable CLDH content can evidently alleviate the salt freezing damage,which facilitates the quantitative analysis of the effect of CLDH on the salt freezing resistance of CBMs.展开更多
基金The authors gratefully acknowledge the financial support provided by the project of Technological Innovation and Application Development in Chongqing(cstc2019jscxmsxm0378)the National Natural Science Foundation of China(Grant No.21576034 and 51908092)+1 种基金the State Education Ministry and Fundamental Research Funds for the Central Universities(2019CDQYCL042,2019CDXYCL0031,106112017CDJXSYY0001,2018CDYJSY0055,106112017CDJQJ138802,106112017CDJSK04XK11,and 2018CDQYCL0027)the Joint Funds of the National Natural Science Foundation of China-Guangdong(Grant No.U1801254).
文摘Layered double hydroxides are one class or kind of 2 D layered materials that are considered promising for use in the supercapacitor.Although there have been many studies on the structure,composition,properties,and electrode fabrication of layered double hydroxides,none summarize the effects of various modification methods on the structure and performance of layered double hydroxides in the supercapacitor.In a bid to fill this gap,in this review,we summarize the progress of modification methods such as exfoliation,intercalation,vacancy,doping,phase transformation,and composition regulation of layered double hydroxides in the field of the supercapacitor and put forward some opinions regarding the progress of research on the methods used in modifying the layered double hydroxides.
文摘Ni/Mg/Al layered double hydroxides(LDHs) with different n(Ni)∶n(Mg)∶n(Al) ratio values were prepared via a coprecipitation reaction. Then Ni/Mg/Al mixed oxides were obtained by calcination of these LDHs precursors. Carbon nanotubes were produced in the catalytic decomposition of propane over the Ni/Mg/Al mixed oxide catalysts. The quality of as-made nanotubes was investigated by SEM and TEM. The nanotubes were multiwall with a high length-diameter ratio and appeared to be flexible. The catalytic activities of these mixed oxides increased with increasing the Ni content. The Ni/Mg/Al mixed oxide with the highest Ni content [n(Ni)/n(Mg)/n(Al)=1/1/1] showed the highest activity and the carbon nanotubes grown on its surface had the best quality.
文摘Layered double hydroxides consisting of layers with cationic charges may be potential candidates of cationic microparticles forming synergetic retention effect with anionic polyacrylamide. In this work, the layered double hydroxides with various molar ratios of Mg/Al were synthesized by co-precipitation of magnesium chloride and aluminum chloride and peptized by intense washing with water. The chemical formula, particle size, Zeta potential of the layered double hydroxide were analyzed. It was found that positively charged magnesium aluminum hydroxide with particle diameter in nanoparticle size could be prepared. The Zeta potential and particle size vary with the feed molar ratio of Mg/Al and the peptizing process, respectively. The Zeta potential is also pH dependent. The retention experiments carried out on DDJ show that when used together with anionic polyacrylamide, the positively charged colloidal double hydroxide greatly improves the retention of reed pulps. The chemical formula, particle size and Zeta potential of the colloidal double hydroxide all affect its retention behavior.
基金the National Natural Science Foundation of China (No. 40472026) the 0utstanding 0verseas Chinese Scholars Fund of Chinese Academy of Sciences (2003-1-7).
文摘Although hydrotalcite, or layered double hydroxides (LDHs), is not a common mineral, it is an important material that can be easily synthesized in laboratory. In this study, structural evolvement and BET surface area changes of heat treated Mg/Al-LDH is evaluated by XRD, TEM and N2-BET analyses. The results indicate that the magnesium-aluminum LDH with carbonate as interlayer anion, periclase-like oxides was formed at temperatures of 400-800℃. Meanwhile, 2-3 nanometer mesoporous were formed during decomposition of LDH. However, the heat treated samples still preserve the morphology of the original LDH plates. Periclase-like formed from LDH heat treatment may re-hydrolyze and recover the structure of LDH. However, crystallinity of the recovered LDH is lower than that of the original LDH. This heat treatment will result in formation of (Mg, Al)-oxide nano-crystals and nanopores among the nano-crystals. When heating temperature exceeds 1000, the periclase-like (Mg, Al)-oxide is transformed into a composite with periclase (MgO) and spinel phases. The periclase can be re-hydrolyzed and dissolved in HCl solution. After acid treatment, the sample with a high surface area is composed of spinel nano-crystals and nanopores among them. Our results will provide a new and economic way to synthesize mesoporous materials through pathways of phase transformation of precursor materials with different composition.
文摘Hydrotalcite-type anionic clays are a group of important materials used in adsorption processes, mainly for organic pollutants removal due the layered double hydroxide structure. The layer-interlayer interactions provide a structural memory even after dehydration and dehydroxylation process, since a very stable interlayer anions are part of material composition, like the carbonate one. A limited numbers of trivalent modifier cations can replace the aluminium cation due the ionic radii mismatch or oxidation state restrictions. Transition metal cations can replace the aluminium one in octahedral site of hydroxide lamellas in order to improve the adsorptive behaviors. In this work, we have investigate three compositions of carbonated magnesium-aluminium hydrotalcite with dif-ferent iron (III) contents through the co-precipitation method at pH 11 and aging step at 60°C for 6 hours. Thermal analysis was performed aiming the determination of the hydration water and hydroxyl amounts in dried precipitate samples, taking in account the results obtained for X-ray diffractometry, infrared spectroscopy, and nitrogen adsorption-desorption characterization for several thermally treated samples. All of synthesized samples showed high surface areas, even for high temperature of thermal treatment. The co-substitution with iron (III) reduced the temperature of dehydration and dehydroxylation process, but the co-substitution at 5 mol% provides other desirables characteristics, like a more amount of rhombohedral HDL phase and higher porosity, even after the thermal treatment at 500°C for 4 hours. This result makes that composition very applicable as a reusable adsorbent material in order to removal several types of micro-pollutant compounds in aqueous media.
基金Supported by Shanxi Province Natural Science Funds.(20001015)
文摘The preparation of ZnAlLa-hydrotalcite-like compounds [ZnAlLa-HTLcs] was studied.ZnAlLa-HTLcs were synthesized by a method of variable pH with the raw materials of Zn(NO3)2,Al(NO3)3, La(NO3)3, and NaOH. The effects of some factors (i.e. pH values, the mole ratio of Al3+ to La3+,temperature and the period of hydrothermal treatment) on the preparation of HTLcs were discussed systematically. XRD, TG-DTA, FT-IR spectroscopy, and ICP were performed to characterize ZnAlLa-HTLcs samples, and the thermal stability of HTLcs was also discussed. It was shown that unique ZnAlLa-HTLcs with high crystallinity can be prepared, under the conditions of pH=5.5-6.5, n(Zn2+)/n(Al3++La3+)=2and the atomic ratio of La3+ to Al3+ ranging from 0.07 to 2, hydrothermal treatment at 120 ℃ for 5h. When the calcination of the HTLcs is performed at temperatures above 200 ℃, ZnO phase is detected with Al2O3 and La2O3 spreading on its top. The complex metal oxides derived from ZnAlLa-HTLcs at 500 ℃ have higher catalytic activity and selectivity than those from ZnAl-HTLcs for the esterification of acetic acid with n-butanol under the same reaction conditions.
基金supported by the National Natural Science Foundation of China(No.20573065)the Natural Science Foundation of Shandong Province of China(Nos.Z2005B02 and Z2006B06).
基金This work is supported by Science and Technology Development Project of Xinjiang Production and Construction Corps (No. 2021DB005)Project of Department of Transport of Shaanxi Province (21-53K)+1 种基金the Central Plains Thousand People Plan of Henan Province (204200510004)the Fundamental Research Funds for the Central Universities, CHD (300102312724, 300102312402). The authors also thank to the reviewers for their valuable comments and suggestions concerning our manuscript.
文摘Salt freezing damage has severe impacts on durability of cement-based materials(CBMs).Calcined layered double hydroxide(CLDH),as an efficient environmental-friendly adsorption material,can impart excellent salt freezing resistance to CBMs.In this work,salt freezing resistance improvement of CBMs incorporated with CLDH was experimentally evaluated by chloride binding capacity,mass loss rate,relative dynamic elastic modulus,setting time,compressive strength,and micro structure tests.Beside these,the salt freezing damage model was established to effectively express the quantitative relationship between influencing factors and evaluation indexes of the salt freezing resistance of CBMs.Results show that CLDH can reconstruct its original layered structure to form reconstructed layered double hydroxide(RLDH).RLDH combines with chloride ions to form RLDH-Cl recrystallization,which can improve chloride binding capacity and pore structures of CBMs to relieve the salt freezing damage.The salt freezing damage model indicates that the suitable CLDH content can evidently alleviate the salt freezing damage,which facilitates the quantitative analysis of the effect of CLDH on the salt freezing resistance of CBMs.