Layered double hydroxides (LDHs) or hydrotalcite-like materials of the type Mg1 -xAlx(OH) 2 (Xn- ) x/n ·zH2O are most readily prepared when Xn- is the carbonate ion. Although many other LDHs undergo facile ion-ex...Layered double hydroxides (LDHs) or hydrotalcite-like materials of the type Mg1 -xAlx(OH) 2 (Xn- ) x/n ·zH2O are most readily prepared when Xn- is the carbonate ion. Although many other LDHs undergo facile ion-exchange reactions, the carbonate ion in LDHs is known to be very difficult to replace by conventional ion-exchange. We have developed a simple synthesis of adipate-pillared LDHs of the type Mg4A12 (OH) 12 [O2C (CH2)4CO2]· 4H2O by direct reaction of free adipic acid with an LDH carbonate precursor. The materials obtained have been characterized by XRD, FT-IR and DTA. It is shown that by appropriate choice of reaction conditions, the carbonate ions in the precursor can be completely replaced by adipate ions. The adipate-pillared LDHs retain a layered structure with an interlayer distance of 1. 40urn. The interlayer adipate ions are lost on heating the material to 39℃.展开更多
A hydrotalcite-like Mg 2+ /Al 3+ layered double hydroxide(LDH) material was prepared by means of a modified coprecipitation method involving a rapid mixing step followed by a separate aging process. LDH calci...A hydrotalcite-like Mg 2+ /Al 3+ layered double hydroxide(LDH) material was prepared by means of a modified coprecipitation method involving a rapid mixing step followed by a separate aging process. LDH calcined at 500 ℃, denoted as CLDH, was characterized by XRD, IR and BET surface area measurements. CLDH has a poor crystalline MgO-like structure with a high surface area and porosity. CLDH was used as a support for the immobilization of penicillin G acylase(PGA). The effect of varying the immobilization conditions, such as pH, contact time and the ratio of enzyme to support, on the activity of the immobilized enzyme in the hydrolysis of penicillin G has been studied. It was found that the activity of the immobilized enzyme decreased slightly with decreasing pH and reached a maximum after a contact time of 24 h. The activity of the immobilized enzyme increased with increasing the ratio of enzyme to support. It was found that the adsorption of PGA inhibited the expected reaction of CLDH with an aqueous medium to regenerate a LDH phase. Its original activity(36%) after 15 cycles of reuse of the immobilized enzyme was retained, but no further loss in the activity was observed.展开更多
文摘Layered double hydroxides (LDHs) or hydrotalcite-like materials of the type Mg1 -xAlx(OH) 2 (Xn- ) x/n ·zH2O are most readily prepared when Xn- is the carbonate ion. Although many other LDHs undergo facile ion-exchange reactions, the carbonate ion in LDHs is known to be very difficult to replace by conventional ion-exchange. We have developed a simple synthesis of adipate-pillared LDHs of the type Mg4A12 (OH) 12 [O2C (CH2)4CO2]· 4H2O by direct reaction of free adipic acid with an LDH carbonate precursor. The materials obtained have been characterized by XRD, FT-IR and DTA. It is shown that by appropriate choice of reaction conditions, the carbonate ions in the precursor can be completely replaced by adipate ions. The adipate-pillared LDHs retain a layered structure with an interlayer distance of 1. 40urn. The interlayer adipate ions are lost on heating the material to 39℃.
基金Supported by the National Natural Science Foundation of China( No.2 99730 0 4 )
文摘A hydrotalcite-like Mg 2+ /Al 3+ layered double hydroxide(LDH) material was prepared by means of a modified coprecipitation method involving a rapid mixing step followed by a separate aging process. LDH calcined at 500 ℃, denoted as CLDH, was characterized by XRD, IR and BET surface area measurements. CLDH has a poor crystalline MgO-like structure with a high surface area and porosity. CLDH was used as a support for the immobilization of penicillin G acylase(PGA). The effect of varying the immobilization conditions, such as pH, contact time and the ratio of enzyme to support, on the activity of the immobilized enzyme in the hydrolysis of penicillin G has been studied. It was found that the activity of the immobilized enzyme decreased slightly with decreasing pH and reached a maximum after a contact time of 24 h. The activity of the immobilized enzyme increased with increasing the ratio of enzyme to support. It was found that the adsorption of PGA inhibited the expected reaction of CLDH with an aqueous medium to regenerate a LDH phase. Its original activity(36%) after 15 cycles of reuse of the immobilized enzyme was retained, but no further loss in the activity was observed.
