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2022 Volume 38 Issue 4
2022, 38(4): 569-577
doi: 10.11862/CJIC.2022.055
Abstract:
Single - crystal LiNi0.6Co0.2Mn0.2O2 (NCM622) was prepared by a facile solid - state calcination method at 910 ℃ using Ni0.6Co0.2Mn0.2(OH)2 and LiOH·H2O as the precursors with no excess of LiOH·H2O. As-obtained material can be used to make electrode slurry directly with no need to wash, dry, and anneal. Electrochemical tests showed that the single-crystal NCM622 has a high specific capacity and a long cycle life. The first discharge capacity of the sample was 181.2 mAh·g-1 at 0.1C and 174.4 mAh·g-1 at 0.3C. Under a current density of 0.3C, the sample delivered a discharge capacity of 150.7 mAh·g-1 after 300 cycles with a capacity retention of 86.4%. After 500 cycles at 0.3C, a relatively high discharge capacity of 141.2 mAh·g-1 was still maintained with a capacity retention of 81.0%. The electrochemical performance of single-crystal NCM622 prepared at 910 ℃ was better than that of polycrystalline NCM622 prepared at 850 ℃ and large-size single-crystal NCM622 prepared at 940 and 960 ℃, indicating that the reasonable calcination temperature for single crystal NCM622 was 910 ℃. The results show that the structural stability of single-crystal NCM622 can be maintained during repeated cycling.
Single - crystal LiNi0.6Co0.2Mn0.2O2 (NCM622) was prepared by a facile solid - state calcination method at 910 ℃ using Ni0.6Co0.2Mn0.2(OH)2 and LiOH·H2O as the precursors with no excess of LiOH·H2O. As-obtained material can be used to make electrode slurry directly with no need to wash, dry, and anneal. Electrochemical tests showed that the single-crystal NCM622 has a high specific capacity and a long cycle life. The first discharge capacity of the sample was 181.2 mAh·g-1 at 0.1C and 174.4 mAh·g-1 at 0.3C. Under a current density of 0.3C, the sample delivered a discharge capacity of 150.7 mAh·g-1 after 300 cycles with a capacity retention of 86.4%. After 500 cycles at 0.3C, a relatively high discharge capacity of 141.2 mAh·g-1 was still maintained with a capacity retention of 81.0%. The electrochemical performance of single-crystal NCM622 prepared at 910 ℃ was better than that of polycrystalline NCM622 prepared at 850 ℃ and large-size single-crystal NCM622 prepared at 940 and 960 ℃, indicating that the reasonable calcination temperature for single crystal NCM622 was 910 ℃. The results show that the structural stability of single-crystal NCM622 can be maintained during repeated cycling.
2022, 38(4): 578-588
doi: 10.11862/CJIC.2022.075
Abstract:
Owing to the advantages of large specific capacity, high work potential, rich reserves, and low price, manganese dioxide (MnO2) material has become the most potential material for the cathode in aqueous zinc batteries (AZBs). However, it still has problems with poor structural stability and complex electrochemical storage mechanism. Herein, a kind of Ti3C2Tx/MnO2 composite material based on bract - liked structural of MnO2 deposited on Ti3C2Tx was prepared by a two-step method, and the structure, composition, and morphology of the composite were characterized by X - ray powder diffraction (XRD), X - ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The zinc storage performance of Ti3C2Tx/MnO2 cathode were evaluated in different aqueous electrolyte (2 mol·L-1 ZnSO4, 2 mol·L-1 ZnSO4+0.1 mol·L-1 MnSO4, 30 mol·L-1 tetraethylammonium triflate (TEAOTf)+1 mol·L-1 ZnCF3SO3 (ZnOTf), 3 mol·L-1 ZnOTf), respectively. As a result, Ti3C2Tx/MnO2 cathode displayed two obvious discharge platforms in 2 mol·L-1 ZnSO4 and 2 mol·L-1 ZnSO4+0.1 mol·L-1 MnSO4 solution, which is attributed to the co-insertion of H+ and Zn2+ due to the weak acidic electrolyte. The initial platform region at 1.0 V occurred in the first step is the insertion of H+, and the subsequent reaction is the insertion of Zn2+ into Ti3C2Tx/MnO2 electrode. However, in the neutral of 3 mol·L-1 ZnOTf and 30 mol·L-1 TEAOTf+1 mol·L-1 ZnOTf electrolyte, the insertion of H+ into the Ti3C2Tx/MnO2 cathode hardly appears, and the obtained discharge capacity may mainly come from the intercalation of Zn2+. Moreover, the utilization of ultra -high concentration electrolyte could not only improve the reversibility of Ti3C2Tx/MnO2 electrode material but also effectively inhibit the dissolution of electrode material in the cycling process (78.2% capacity retention after 100 cycles at 0.2 A·g-1).
Owing to the advantages of large specific capacity, high work potential, rich reserves, and low price, manganese dioxide (MnO2) material has become the most potential material for the cathode in aqueous zinc batteries (AZBs). However, it still has problems with poor structural stability and complex electrochemical storage mechanism. Herein, a kind of Ti3C2Tx/MnO2 composite material based on bract - liked structural of MnO2 deposited on Ti3C2Tx was prepared by a two-step method, and the structure, composition, and morphology of the composite were characterized by X - ray powder diffraction (XRD), X - ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The zinc storage performance of Ti3C2Tx/MnO2 cathode were evaluated in different aqueous electrolyte (2 mol·L-1 ZnSO4, 2 mol·L-1 ZnSO4+0.1 mol·L-1 MnSO4, 30 mol·L-1 tetraethylammonium triflate (TEAOTf)+1 mol·L-1 ZnCF3SO3 (ZnOTf), 3 mol·L-1 ZnOTf), respectively. As a result, Ti3C2Tx/MnO2 cathode displayed two obvious discharge platforms in 2 mol·L-1 ZnSO4 and 2 mol·L-1 ZnSO4+0.1 mol·L-1 MnSO4 solution, which is attributed to the co-insertion of H+ and Zn2+ due to the weak acidic electrolyte. The initial platform region at 1.0 V occurred in the first step is the insertion of H+, and the subsequent reaction is the insertion of Zn2+ into Ti3C2Tx/MnO2 electrode. However, in the neutral of 3 mol·L-1 ZnOTf and 30 mol·L-1 TEAOTf+1 mol·L-1 ZnOTf electrolyte, the insertion of H+ into the Ti3C2Tx/MnO2 cathode hardly appears, and the obtained discharge capacity may mainly come from the intercalation of Zn2+. Moreover, the utilization of ultra -high concentration electrolyte could not only improve the reversibility of Ti3C2Tx/MnO2 electrode material but also effectively inhibit the dissolution of electrode material in the cycling process (78.2% capacity retention after 100 cycles at 0.2 A·g-1).
2022, 38(4): 589-598
doi: 10.11862/CJIC.2022.058
Abstract:
The plastic melamine-formaldehyde, which was synthesized from melamine, formaldehyde, and urea, was used as the precursor for the formation of the melamine-formaldehyde scaffold by the microwave foaming method. Then, Au was deposited on the melamine-formaldehyde scaffold by the magnetron sputtering. Finally, Au deposited graphite carbon nitride (Au@g-C3N4) scaffold with a specific surface area of 1 480 m2·g-1 was successfully prepared by the thermal polymerization at 550 ℃. After deposited 6% Au, the UV - Vis spectrum of Au@g - C3N4 scaffold showed a new absorption peak at 550 nm, its absorption band edge was shifted to 507 nm, and its bandgap was reduced to 2.45 eV. Moreover, the fluorescence intensity and the electrochemical impedance decreased significantly, and the photocurrent increased from 0.28 to 0.62 μA·cm-2. The deposition of Au not only widens the UV - Vis absorption performance of Au@g-C3N4 scaffold but also inhibits the recombination of the electron -hole pairs. The photocatalytic performance of Au@g-C3N4 scaffold was stable, and its photocatalytic degradation rate for rhodamine B was about one time higher than that of g - C3N4 scaffold. Additionally, the Au@g - C3N4 scaffold would be easy to recycle and be reused in the applications, because the Au@g-C3N4 scaffold has suitable tensile strength and toughness.
The plastic melamine-formaldehyde, which was synthesized from melamine, formaldehyde, and urea, was used as the precursor for the formation of the melamine-formaldehyde scaffold by the microwave foaming method. Then, Au was deposited on the melamine-formaldehyde scaffold by the magnetron sputtering. Finally, Au deposited graphite carbon nitride (Au@g-C3N4) scaffold with a specific surface area of 1 480 m2·g-1 was successfully prepared by the thermal polymerization at 550 ℃. After deposited 6% Au, the UV - Vis spectrum of Au@g - C3N4 scaffold showed a new absorption peak at 550 nm, its absorption band edge was shifted to 507 nm, and its bandgap was reduced to 2.45 eV. Moreover, the fluorescence intensity and the electrochemical impedance decreased significantly, and the photocurrent increased from 0.28 to 0.62 μA·cm-2. The deposition of Au not only widens the UV - Vis absorption performance of Au@g-C3N4 scaffold but also inhibits the recombination of the electron -hole pairs. The photocatalytic performance of Au@g-C3N4 scaffold was stable, and its photocatalytic degradation rate for rhodamine B was about one time higher than that of g - C3N4 scaffold. Additionally, the Au@g - C3N4 scaffold would be easy to recycle and be reused in the applications, because the Au@g-C3N4 scaffold has suitable tensile strength and toughness.
2022, 38(4): 599-610
doi: 10.11862/CJIC.2022.066
Abstract:
Mg1 -xCux TiO3 (0.00 ≤ x ≤ 0.20) microwave ceramics were prepared by the solid - state reaction method. The effects of CuO sintering aids on the microstructure and microwave dielectric properties of MgTiO3 ceramics were investigated. It was shown that the Cu2+ ions could enter the MgTiO3 lattice and substitute Mg2+ ions forming Mg1 -xCuxTiO3 solid solution. A moderate amount of CuO can promote the densification sintering of MgTiO3 ceramics and reduce the sintering temperature due to the liquid phase. The A-site substitution of Cu2+ ions alters the distortion of the TiO6 octahedra. With the increase of Cu2+ ions content in MgTiO3 ceramics, the structural stability was weakened. With the addition of CuO content, the quality factor (Qf) of the sample decreased owing to inhomogeneous grain growth and the appearance of the liquid phase. Meanwhile, the reduction of relative density, structural stability, and average covalency of Mg1-xCu xTiO3 ceramics would deteriorate the Qf value of the sample. The dielectric constants (εr) of samples were related to the ionic polarizability, impurity phase, and TiO6 octahedra distortion. The temperature coefficients of resonant frequency (τf) decreased with the increase of TiO6 octahedra distortion. When x= 0.08, the sample could achieve densification sintering at 1 150 ℃ and the τf value was improved to -3.4×10-5 ℃-1.
Mg1 -xCux TiO3 (0.00 ≤ x ≤ 0.20) microwave ceramics were prepared by the solid - state reaction method. The effects of CuO sintering aids on the microstructure and microwave dielectric properties of MgTiO3 ceramics were investigated. It was shown that the Cu2+ ions could enter the MgTiO3 lattice and substitute Mg2+ ions forming Mg1 -xCuxTiO3 solid solution. A moderate amount of CuO can promote the densification sintering of MgTiO3 ceramics and reduce the sintering temperature due to the liquid phase. The A-site substitution of Cu2+ ions alters the distortion of the TiO6 octahedra. With the increase of Cu2+ ions content in MgTiO3 ceramics, the structural stability was weakened. With the addition of CuO content, the quality factor (Qf) of the sample decreased owing to inhomogeneous grain growth and the appearance of the liquid phase. Meanwhile, the reduction of relative density, structural stability, and average covalency of Mg1-xCu xTiO3 ceramics would deteriorate the Qf value of the sample. The dielectric constants (εr) of samples were related to the ionic polarizability, impurity phase, and TiO6 octahedra distortion. The temperature coefficients of resonant frequency (τf) decreased with the increase of TiO6 octahedra distortion. When x= 0.08, the sample could achieve densification sintering at 1 150 ℃ and the τf value was improved to -3.4×10-5 ℃-1.
2022, 38(4): 611-619
doi: 10.11862/CJIC.2022.081
Abstract:
High-voltage LiNi0.5Mn1.5O4 materials with controllable morphology were prepared by an improved coprecipitation - high - temperature solid - phase method. A low - temperature and high - pressure reaction environment was designed based on the characteristics that lithium salt - containing crystal water was easy to dehydrate. The prereaction process introduced before high-temperature calcination, can effectively improve the mixing uniformity and reactivity of lithium salt and oxide precursor, inhibiting the formation of impurity phase and reducing the mixing degree of metal ions. By adjusting the pre-reaction temperature, the morphology and particle size of LiNi0.5Mn1.5O4 materials were controllable. The results showed that the samples synthesized by the pre - reaction temperature of 180 ℃ had a regular octahedral single crystal morphology and relatively uniform size distribution, which effectively inhibit the electrode/electrolyte interface reaction so that the synthesized materials showed excellent cycle stability and rate performance. Its capacity retention rate reached 95.3% after 400 cycles at 1C and room temperature, and the specific capacity of 120.9 mAh·g-1 could still be released at 20C.
High-voltage LiNi0.5Mn1.5O4 materials with controllable morphology were prepared by an improved coprecipitation - high - temperature solid - phase method. A low - temperature and high - pressure reaction environment was designed based on the characteristics that lithium salt - containing crystal water was easy to dehydrate. The prereaction process introduced before high-temperature calcination, can effectively improve the mixing uniformity and reactivity of lithium salt and oxide precursor, inhibiting the formation of impurity phase and reducing the mixing degree of metal ions. By adjusting the pre-reaction temperature, the morphology and particle size of LiNi0.5Mn1.5O4 materials were controllable. The results showed that the samples synthesized by the pre - reaction temperature of 180 ℃ had a regular octahedral single crystal morphology and relatively uniform size distribution, which effectively inhibit the electrode/electrolyte interface reaction so that the synthesized materials showed excellent cycle stability and rate performance. Its capacity retention rate reached 95.3% after 400 cycles at 1C and room temperature, and the specific capacity of 120.9 mAh·g-1 could still be released at 20C.
2022, 38(4): 620-628
doi: 10.11862/CJIC.2022.074
Abstract:
The nucleation and crystal growth of hydroxyapatite (HA) crystals are closely related to surfactants and the initial calcium - phosphorus molar ratio (nCa, 0/nP, 0). In this work, HA nanofibers with high flexibility and aspect ratio have been synthesized by using oleic acid as the surfactant. The effect of nCa, 0/nP, 0 on the microstructures of the as - prepared products was investigated by X - ray diffraction (XRD), FTIR, field emission scanning electron microscope (FESEM), and energy-dispersive X-ray spectra (EDS). The formation mechanisms of HA nanofibers were proposed to better explain the effect of oleic and nCa, 0/nP, 0 based on the microstructure evolution. Ultralong HA nanofibers with high crystallinity and flexibility were synthesized with nCa, 0/nP, 0=0.8 -1.2, but too high and too low nCa, 0/nP, 0 will weaken the effect of oleic acid in inducing the preferential growth of HA along the c axis, which lead to the formation of amorphous knotted or low crystalline nanoneedle bundle-like products, respectively. The preferred growth direction of HA changes from a-axis to c-axis with the decrease of nCa, 0/nP, 0, but too low nCa, 0/nP, 0 causes HA to tend to grow along the a-axis and c-axis at the same time.
The nucleation and crystal growth of hydroxyapatite (HA) crystals are closely related to surfactants and the initial calcium - phosphorus molar ratio (nCa, 0/nP, 0). In this work, HA nanofibers with high flexibility and aspect ratio have been synthesized by using oleic acid as the surfactant. The effect of nCa, 0/nP, 0 on the microstructures of the as - prepared products was investigated by X - ray diffraction (XRD), FTIR, field emission scanning electron microscope (FESEM), and energy-dispersive X-ray spectra (EDS). The formation mechanisms of HA nanofibers were proposed to better explain the effect of oleic and nCa, 0/nP, 0 based on the microstructure evolution. Ultralong HA nanofibers with high crystallinity and flexibility were synthesized with nCa, 0/nP, 0=0.8 -1.2, but too high and too low nCa, 0/nP, 0 will weaken the effect of oleic acid in inducing the preferential growth of HA along the c axis, which lead to the formation of amorphous knotted or low crystalline nanoneedle bundle-like products, respectively. The preferred growth direction of HA changes from a-axis to c-axis with the decrease of nCa, 0/nP, 0, but too low nCa, 0/nP, 0 causes HA to tend to grow along the a-axis and c-axis at the same time.
2022, 38(4): 629-636
doi: 10.11862/CJIC.2022.073
Abstract:
The binding of melittin (Mel) to Calf Thymus DNA (CT-DNA) and conformation change were described by circular dichroism (CD) spectra, UV-Vis spectra, fluorescence spectra, and isothermal titration calorimetry (ITC) in 10 mmol·L-1 HEPES buffer (pH=7.4). The results showed that Mel could form a complex with CT-DNA. The for- mation of the complex changed the conformation of Mel from random coil to α-helix as shown by CD spectra. The red edge excitation shift (REES) studies of tryptophan (Trp) residue in Mel indicated that Trp residue is located in the more hydrophobic environment in the complex with DNA, exactly as demonstrated by fluorescence lifetime and acrylamide experiments. Additionally, the double helix structure of CT-DNA changed and the CT-DNA melting tem- perature (Tm) increased from 64.3 to 66.2 ℃ once a complex was formed with Mel. Finally, the ITC experiment dem- onstrated that the binding of Mel to CT-DNA is an endothermic process. The interaction between Mel and CT-DNA was further characterized by an equilibrium association constant (Ka) of about 105 L·mol-1. The enthalpy contribu- tion to the free energy of binding was little, and nearly three times less than the entropic term TΔS calculated from measured values of Ka and ΔH. Thus, the binding of CT -DNA to Mel is primarily driven by entropy, demonstrating electrostatic and hydrophobic interactions playing roles in the formation of the complex. The ionic strength effect and single - stranded DNA (ssDNA) quenching effect further verified that electrostatic interaction and hydrophobic interactions coexist between them and electrostatic interaction is the predominant one.
The binding of melittin (Mel) to Calf Thymus DNA (CT-DNA) and conformation change were described by circular dichroism (CD) spectra, UV-Vis spectra, fluorescence spectra, and isothermal titration calorimetry (ITC) in 10 mmol·L-1 HEPES buffer (pH=7.4). The results showed that Mel could form a complex with CT-DNA. The for- mation of the complex changed the conformation of Mel from random coil to α-helix as shown by CD spectra. The red edge excitation shift (REES) studies of tryptophan (Trp) residue in Mel indicated that Trp residue is located in the more hydrophobic environment in the complex with DNA, exactly as demonstrated by fluorescence lifetime and acrylamide experiments. Additionally, the double helix structure of CT-DNA changed and the CT-DNA melting tem- perature (Tm) increased from 64.3 to 66.2 ℃ once a complex was formed with Mel. Finally, the ITC experiment dem- onstrated that the binding of Mel to CT-DNA is an endothermic process. The interaction between Mel and CT-DNA was further characterized by an equilibrium association constant (Ka) of about 105 L·mol-1. The enthalpy contribu- tion to the free energy of binding was little, and nearly three times less than the entropic term TΔS calculated from measured values of Ka and ΔH. Thus, the binding of CT -DNA to Mel is primarily driven by entropy, demonstrating electrostatic and hydrophobic interactions playing roles in the formation of the complex. The ionic strength effect and single - stranded DNA (ssDNA) quenching effect further verified that electrostatic interaction and hydrophobic interactions coexist between them and electrostatic interaction is the predominant one.
2022, 38(4): 637-644
doi: 10.11862/CJIC.2022.069
Abstract:
In this study, the electronic structures and magnetic and optical properties of Mg2Ge doping with transition metal elements X (X=Sc, Cr, and Mn) were investigated by density functional theory (DFT). The lattice constants, band structures, density of states, and optical parameters were calculated for all compounds. The results show that the Fermi level of Mg2Ge can enter into the conduction band after doping with Sc, and Mg2 Ge turns into an n-type degenerate semiconductor. It can lead to spin splitting of the band structure and density of states of Mg2Ge near Fermi level after doping with Cr and Mn, resulting in a net magnetic moment, which is shown as a semi-metallic magnet and dilute magnetic semiconductor. The net magnetic moment of the system is derived from the 3d orbital electrons of impurity atoms and their induced polarization of Ge4p state and Mg2p state spintronics. Compared with the intrinsic Mg2Ge, the doping systems have an improvement in the static permittivity, which indicates that the photocatalytic activity of Mg2Ge is enhanced. In terms of the absorption coefficient, the compounds with impurity atoms extend the absorption range, and the best enhancement appears near-infrared band.
In this study, the electronic structures and magnetic and optical properties of Mg2Ge doping with transition metal elements X (X=Sc, Cr, and Mn) were investigated by density functional theory (DFT). The lattice constants, band structures, density of states, and optical parameters were calculated for all compounds. The results show that the Fermi level of Mg2Ge can enter into the conduction band after doping with Sc, and Mg2 Ge turns into an n-type degenerate semiconductor. It can lead to spin splitting of the band structure and density of states of Mg2Ge near Fermi level after doping with Cr and Mn, resulting in a net magnetic moment, which is shown as a semi-metallic magnet and dilute magnetic semiconductor. The net magnetic moment of the system is derived from the 3d orbital electrons of impurity atoms and their induced polarization of Ge4p state and Mg2p state spintronics. Compared with the intrinsic Mg2Ge, the doping systems have an improvement in the static permittivity, which indicates that the photocatalytic activity of Mg2Ge is enhanced. In terms of the absorption coefficient, the compounds with impurity atoms extend the absorption range, and the best enhancement appears near-infrared band.
2022, 38(4): 645-653
doi: 10.11862/CJIC.2022.078
Abstract:
Chain-like small SemSn (2≤m +n≤4) molecules were successfully constructed in the ultra-microporous car- bons (UMC) by the incorporation of Se into the chain - like small S2-4 molecules and space - confining of UMC, and then used as cathode materials for lithium-sulfur (Li-S) batteries. Compared with the chain-like small S2-4 molecules, the chain - like small SemSn (2≤m+n≤4) molecules have higher electronic conductivity, lower lithiation energy, and higher electrochemical activity. Moreover, the obtained UMC/SemSn (2≤m+n≤4) composites exhibited a one -step sol- id conversion behavior during the discharge process, which could effectively prohibit the shuttle and loss of active materials in Li - S batteries. Compared with UMC/S2-4 composites, UMC/SemSn (2≤m+n≤4) composites deliver lower charge-transfer resistance and higher discharge specific capacity. Therefore, UMC/SemSn-40 (2≤m+n≤4, wSeS2∶wUMC=4∶6) composites maintained a high reversible specific capacity of 844 mAh·g-1 at the current rate of 0.1C after 100 cycles and long-term cycling stability over 500 cycles with the capacity decay rate of about 0.07% per cycle at the current rate of 0.5C.
Chain-like small SemSn (2≤m +n≤4) molecules were successfully constructed in the ultra-microporous car- bons (UMC) by the incorporation of Se into the chain - like small S2-4 molecules and space - confining of UMC, and then used as cathode materials for lithium-sulfur (Li-S) batteries. Compared with the chain-like small S2-4 molecules, the chain - like small SemSn (2≤m+n≤4) molecules have higher electronic conductivity, lower lithiation energy, and higher electrochemical activity. Moreover, the obtained UMC/SemSn (2≤m+n≤4) composites exhibited a one -step sol- id conversion behavior during the discharge process, which could effectively prohibit the shuttle and loss of active materials in Li - S batteries. Compared with UMC/S2-4 composites, UMC/SemSn (2≤m+n≤4) composites deliver lower charge-transfer resistance and higher discharge specific capacity. Therefore, UMC/SemSn-40 (2≤m+n≤4, wSeS2∶wUMC=4∶6) composites maintained a high reversible specific capacity of 844 mAh·g-1 at the current rate of 0.1C after 100 cycles and long-term cycling stability over 500 cycles with the capacity decay rate of about 0.07% per cycle at the current rate of 0.5C.
2022, 38(4): 654-664
doi: 10.11862/CJIC.2022.077
Abstract:
Secondary thermal exfoliation is an effective method to synthesize 2D carbon nitride nanosheets (CNN). Further broadening the visible light response and optimizing the photoelectric conversion efficiency are effective strategies to improve the photocatalytic performance of CNN materials. In this work, we report thiophene-ring doped carbon nitride nanosheet photocatalysts (CNN-Thx) prepared from in situ polymerization doping and secondary thermal exfoliation using 2-aminothiophene-3 -carbonitride as the molecular doping source. Thiophene-ring with excellent chemical properties was stably doped into conjugated CNN nanosheets. After secondary thermal exfoliation, the products maintained 2D hybrid conjugated polymer structures, and the thiophene-ring was still stably doped in the CNN conjugated heterocyclic skeleton. Thiophene-ring doping causes the further expansion of the π-conjugated system, reduces the bandgap, broadens the visible light absorption range, and accelerates the photoelectric conversion efficiency of the catalysts. At the same time, thermal exfoliation cooperated with thiophene doping leads to a more significant n-π* transition, which greatly improves the photocatalytic activity of the catalysts. The results showed that CNN-Thx had significantly enhanced photocatalytic reduction performance, in which the H2 evolution activity of CNN-Th10 reached 322.8 μmol·h-1, and the generated H2O2 concentration reached 223.1 μmol·L-1 after 4 h, which were 3.6 and 22.3 times that of CNN, respectively.
Secondary thermal exfoliation is an effective method to synthesize 2D carbon nitride nanosheets (CNN). Further broadening the visible light response and optimizing the photoelectric conversion efficiency are effective strategies to improve the photocatalytic performance of CNN materials. In this work, we report thiophene-ring doped carbon nitride nanosheet photocatalysts (CNN-Thx) prepared from in situ polymerization doping and secondary thermal exfoliation using 2-aminothiophene-3 -carbonitride as the molecular doping source. Thiophene-ring with excellent chemical properties was stably doped into conjugated CNN nanosheets. After secondary thermal exfoliation, the products maintained 2D hybrid conjugated polymer structures, and the thiophene-ring was still stably doped in the CNN conjugated heterocyclic skeleton. Thiophene-ring doping causes the further expansion of the π-conjugated system, reduces the bandgap, broadens the visible light absorption range, and accelerates the photoelectric conversion efficiency of the catalysts. At the same time, thermal exfoliation cooperated with thiophene doping leads to a more significant n-π* transition, which greatly improves the photocatalytic activity of the catalysts. The results showed that CNN-Thx had significantly enhanced photocatalytic reduction performance, in which the H2 evolution activity of CNN-Th10 reached 322.8 μmol·h-1, and the generated H2O2 concentration reached 223.1 μmol·L-1 after 4 h, which were 3.6 and 22.3 times that of CNN, respectively.
2022, 38(4): 665-674
doi: 10.11862/CJIC.2022.079
Abstract:
The theoretical study of reaction mechanism and relationship between chiral configuration and property of chiral ruthenium complexes is an important topic. In this work, the chiroptical properties of the mixed-ligand ruthenabenzene complex [RuBen(PPh3)2(Phen) (L-Cys)]2+ (Phen=phenanthroline, L-Cys=L-cysteine) have been explored using the hybrid density functional theory (DFT). The geometrical and electronic structures and subsequent frequency verifications were calculated using the B3LYP method with the mixed basis set: the ECP28MWB pseudopotential with its (8s 7p6d2f)/[6s5p3d2f] valence basis set for ruthenium, and 6-311G(d) for other atoms. Based on these, the excited energies, rotational and oscillator strengths, as well as the electronic circular dichroism (ECD) spectra, were then calculated employing the time-dependent DFT method with the same functional and basis set. In all cases, solvent (water) effects were included using the polarized continuum model (PCM). Additionally, the intricate exciton-splitting pattern in the short wavelength region was analyzed using the exciton chirality method (ECM). The calculated ECD spectra were in good agreement with the observed ones as far as their band shape, signs, and relative intensities were concerned. The Λ/Δ configurations at the octahedral core dominate the distribution of the ECD curves, and the λ/δ twists of the L-Cys rings only affect the relative intensities of the absorption bands, while the contributions of the R/S chiral carbon atoms are negligible. The absorption bands above 340 nm are characterized by the π → π * transitions mixed with some metal-centered d → d transitions. The two pairs of ECD bands below 340 nm with clearly different intensities could be assigned to the classical (the strong one) and nonclassical (the weak one) exciton coupling, respectively. Both show a positive exciton-splitting pattern for the Λ-configuration, which could be used as a criterion to determine the absolute configurations of similar complexes. Additionally, comparing with mixed-ligand inorganic ruthenium complexes reveals the similarities and differences in their chiroptical properties.
The theoretical study of reaction mechanism and relationship between chiral configuration and property of chiral ruthenium complexes is an important topic. In this work, the chiroptical properties of the mixed-ligand ruthenabenzene complex [RuBen(PPh3)2(Phen) (L-Cys)]2+ (Phen=phenanthroline, L-Cys=L-cysteine) have been explored using the hybrid density functional theory (DFT). The geometrical and electronic structures and subsequent frequency verifications were calculated using the B3LYP method with the mixed basis set: the ECP28MWB pseudopotential with its (8s 7p6d2f)/[6s5p3d2f] valence basis set for ruthenium, and 6-311G(d) for other atoms. Based on these, the excited energies, rotational and oscillator strengths, as well as the electronic circular dichroism (ECD) spectra, were then calculated employing the time-dependent DFT method with the same functional and basis set. In all cases, solvent (water) effects were included using the polarized continuum model (PCM). Additionally, the intricate exciton-splitting pattern in the short wavelength region was analyzed using the exciton chirality method (ECM). The calculated ECD spectra were in good agreement with the observed ones as far as their band shape, signs, and relative intensities were concerned. The Λ/Δ configurations at the octahedral core dominate the distribution of the ECD curves, and the λ/δ twists of the L-Cys rings only affect the relative intensities of the absorption bands, while the contributions of the R/S chiral carbon atoms are negligible. The absorption bands above 340 nm are characterized by the π → π * transitions mixed with some metal-centered d → d transitions. The two pairs of ECD bands below 340 nm with clearly different intensities could be assigned to the classical (the strong one) and nonclassical (the weak one) exciton coupling, respectively. Both show a positive exciton-splitting pattern for the Λ-configuration, which could be used as a criterion to determine the absolute configurations of similar complexes. Additionally, comparing with mixed-ligand inorganic ruthenium complexes reveals the similarities and differences in their chiroptical properties.
2022, 38(4): 675-684
doi: 10.11862/CJIC.2022.080
Abstract:
To explore a high-performance anode for lithium-ion batteries, 2D-layered Ti3C2Tx with high conductivity and stability was prepared by acid etching, and petal-shaped VS2 nanosheets with high theoretical specific capacity were prepared by solvothermal method. Then the 2D-layered Ti3C2Tx-MXene@VS2 hybrid was obtained by a simple liquid-phase mixing method. The morphology and structure of this hybrid were systematically characterized by scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy, X-ray diffraction, and energy-dispersive X-ray diffraction, while the electrochemical properties were studied by cyclic voltammetry, galvanostatic charge/discharge, long cycle life, and AC impedance spectroscopy. The results indicate that VS2 nanosheets are uniformly distributed between the layers and on the surface of Ti3C2Tx. The hybrid had a high reversible capacity (610.5 mAh·g-1 at 0.1 A·g-1), good rate performance (197.1 mAh·g-1 at 2 A·g-1), and good cycle stability (874.9 mAh·g-1 at 0.2 A·g-1 after 600 cycles; 115.9 mAh·g-1 at 2 A·g-1 after 1 500 cycles).
To explore a high-performance anode for lithium-ion batteries, 2D-layered Ti3C2Tx with high conductivity and stability was prepared by acid etching, and petal-shaped VS2 nanosheets with high theoretical specific capacity were prepared by solvothermal method. Then the 2D-layered Ti3C2Tx-MXene@VS2 hybrid was obtained by a simple liquid-phase mixing method. The morphology and structure of this hybrid were systematically characterized by scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy, X-ray diffraction, and energy-dispersive X-ray diffraction, while the electrochemical properties were studied by cyclic voltammetry, galvanostatic charge/discharge, long cycle life, and AC impedance spectroscopy. The results indicate that VS2 nanosheets are uniformly distributed between the layers and on the surface of Ti3C2Tx. The hybrid had a high reversible capacity (610.5 mAh·g-1 at 0.1 A·g-1), good rate performance (197.1 mAh·g-1 at 2 A·g-1), and good cycle stability (874.9 mAh·g-1 at 0.2 A·g-1 after 600 cycles; 115.9 mAh·g-1 at 2 A·g-1 after 1 500 cycles).
2022, 38(4): 685-694
doi: 10.11862/CJIC.2022.070
Abstract:
In this work, nickel phosphide (Ni2P) nanosheets were dispersed uniformly on graphene (G) to fabricate the Ni2P/G composite. Furthermore, the S/Ni2P/G sulfur-based composite was prepared further for lithium-sulfur batteries. Due to the strong chemical absorbability and high electrocatalytic activity of Ni2P nanosheets towards soluble polysulfides, S/Ni2P/G composite showed superior electrochemical performance. In particular, under the condition of high sulfur content (80.3%) and low electrolyte usage (15 μL·mg-1), S/Ni2P/G composite delivered a high initial specific discharge capacity of 1 164.7 mAh·g-1 and good cycling stability. In addition, due to the high tap density of 1.02 g·cm-3, S/Ni2P/G composite showed a high volumetric capacity of 954.0 mAh·cm-3, almost 1.6 times of that for S/G composite.
In this work, nickel phosphide (Ni2P) nanosheets were dispersed uniformly on graphene (G) to fabricate the Ni2P/G composite. Furthermore, the S/Ni2P/G sulfur-based composite was prepared further for lithium-sulfur batteries. Due to the strong chemical absorbability and high electrocatalytic activity of Ni2P nanosheets towards soluble polysulfides, S/Ni2P/G composite showed superior electrochemical performance. In particular, under the condition of high sulfur content (80.3%) and low electrolyte usage (15 μL·mg-1), S/Ni2P/G composite delivered a high initial specific discharge capacity of 1 164.7 mAh·g-1 and good cycling stability. In addition, due to the high tap density of 1.02 g·cm-3, S/Ni2P/G composite showed a high volumetric capacity of 954.0 mAh·cm-3, almost 1.6 times of that for S/G composite.
2022, 38(4): 695-704
doi: 10.11862/CJIC.2022.076
Abstract:
Hollow tubular g-C3N4/Ag3PO4 composite catalyst was prepared by chemical precipitation method. The structure, morphology, and optical properties of the composite catalyst were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), and fluores- cence emission spectroscopy. The results showed that Ag3PO4 nanoparticles can be uniformly dispersed on the surface of hollow tubular g-C3N4, and closely combined to form a heterojunction. The photocatalytic activity of the composite catalyst under visible light irradiation was studied by the degradation of tetracycline hydrochloride (TC). The results showed that the degradation rate of TC over the hollow tubular g-C3N4/Ag3PO4 composite catalyst was 98% within 80 min, and its degradation reaction rate constant was three times that of pure Ag3PO4. After five cycles, the degradation rate of TC by the composite catalyst maintained 87%, indicating excellent stability. The capture experiment showed that hole (h+) and superoxide anion (·O2-) were the main active species in the photocatalytic reaction. Based on the energy band theory, the Z-scheme photocatalytic mechanism of g-C3N4/Ag3PO4 composite catalyst heterojunction was proposed.
Hollow tubular g-C3N4/Ag3PO4 composite catalyst was prepared by chemical precipitation method. The structure, morphology, and optical properties of the composite catalyst were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), and fluores- cence emission spectroscopy. The results showed that Ag3PO4 nanoparticles can be uniformly dispersed on the surface of hollow tubular g-C3N4, and closely combined to form a heterojunction. The photocatalytic activity of the composite catalyst under visible light irradiation was studied by the degradation of tetracycline hydrochloride (TC). The results showed that the degradation rate of TC over the hollow tubular g-C3N4/Ag3PO4 composite catalyst was 98% within 80 min, and its degradation reaction rate constant was three times that of pure Ag3PO4. After five cycles, the degradation rate of TC by the composite catalyst maintained 87%, indicating excellent stability. The capture experiment showed that hole (h+) and superoxide anion (·O2-) were the main active species in the photocatalytic reaction. Based on the energy band theory, the Z-scheme photocatalytic mechanism of g-C3N4/Ag3PO4 composite catalyst heterojunction was proposed.
2022, 38(4): 705-715
doi: 10.11862/CJIC.2022.065
Abstract:
Ten ferrocenyl Schiff bases 1-10 were synthesized and characterized using UV-Vis spectroscopy, FT-IR, elemental analysis, 1H and 13C NMR spectroscopy. The synthesized compounds were evaluated against 11 bacteria strains (Bacillus subtilis ATCC19659, Klebsiella aerogenes ATCC13882, Enterococcus faecalis ATCC13047, Myco- bacterium smegmatis MC2155, Staphylococcus epidermidis ATCC14990, Staphylococcus aureus ATCC25923, Esche-richia coli ATCC25922, Enterobacter cloacae ATCC13047, Klebsiella oxytoca ATCC8724, Proteus mirabilis ATCC7002, Proteus vulgaris ATCC6380). The results obtained from antibacterial assay indicated that the synthe- sized Schiff bases 1-10 inhibited potential growth of Klebsiella aerogenes with the minimum inhibitory concentration (MIC) ranging from 15.6 to 31.25 μg·mL-1 and Enterococcus faecalis with MIC the range between 31.25 and 125 μg· mL-1 in comparison with the standard nalidixic acid and streptomycin sulfate.
Ten ferrocenyl Schiff bases 1-10 were synthesized and characterized using UV-Vis spectroscopy, FT-IR, elemental analysis, 1H and 13C NMR spectroscopy. The synthesized compounds were evaluated against 11 bacteria strains (Bacillus subtilis ATCC19659, Klebsiella aerogenes ATCC13882, Enterococcus faecalis ATCC13047, Myco- bacterium smegmatis MC2155, Staphylococcus epidermidis ATCC14990, Staphylococcus aureus ATCC25923, Esche-richia coli ATCC25922, Enterobacter cloacae ATCC13047, Klebsiella oxytoca ATCC8724, Proteus mirabilis ATCC7002, Proteus vulgaris ATCC6380). The results obtained from antibacterial assay indicated that the synthe- sized Schiff bases 1-10 inhibited potential growth of Klebsiella aerogenes with the minimum inhibitory concentration (MIC) ranging from 15.6 to 31.25 μg·mL-1 and Enterococcus faecalis with MIC the range between 31.25 and 125 μg· mL-1 in comparison with the standard nalidixic acid and streptomycin sulfate.
2022, 38(4): 716-724
doi: 10.11862/CJIC.2022.067
Abstract:
Three new 2D lanthanide complexes with the formula [Ln2(dmpa)4]Cl2, where Ln=Eu (1), Tb (2), Dy (3), have been prepared based on the ligand 2, 2-bis(hydroxymethyl)propionic acid (Hdmpa) under solvothermal conditions and characterized by IR spectrum, elemental analysis, powder X-ray diffraction, thermogravimetric analysis, and single-crystal X-ray diffraction. These complexes are isostructural in which individual Ln(Ⅲ) ions are linked by carboxyl groups into 2D layers which are further assembled into 3D supramolecular structures by intermolecular interactions. Magnetic investigations on Dy complex indicate the presence of weak ferromagnetic interactions transmitted by carboxyl groups. And photoluminescence studies reveal that the Eu(Ⅲ) and Tb(Ⅲ) complexes exhibit charac- teristic red-light and green-light emissions, respectively.
Three new 2D lanthanide complexes with the formula [Ln2(dmpa)4]Cl2, where Ln=Eu (1), Tb (2), Dy (3), have been prepared based on the ligand 2, 2-bis(hydroxymethyl)propionic acid (Hdmpa) under solvothermal conditions and characterized by IR spectrum, elemental analysis, powder X-ray diffraction, thermogravimetric analysis, and single-crystal X-ray diffraction. These complexes are isostructural in which individual Ln(Ⅲ) ions are linked by carboxyl groups into 2D layers which are further assembled into 3D supramolecular structures by intermolecular interactions. Magnetic investigations on Dy complex indicate the presence of weak ferromagnetic interactions transmitted by carboxyl groups. And photoluminescence studies reveal that the Eu(Ⅲ) and Tb(Ⅲ) complexes exhibit charac- teristic red-light and green-light emissions, respectively.
Two 3D Microporous Zn-MOF for Fluorescence Sensing of Fe3+, Cr2O72-, and Acetone in Aqueous Solution
2022, 38(4): 725-734
doi: 10.11862/CJIC.2022.068
Abstract:
Two 3D microporous zinc metal-organic frameworks, formulated as [Zn3(DBA)(OH)(1, 10-phen)2]n (1) and {[Zn2(HDBA)(4, 4′-bipy)1.5]·H2O}n (2) (H5DBA=(3, 5-di(2′, 4′-dicarboxylphenyl)benzoic acid; 1, 10- phen=1, 10-phenan- throline; 4, 4′-bipy=4, 4′ -bipyridine), were synthesized under solvothermal conditions. Structural analysis shows that 1 could be described as a 3D microporous framework based on the trinuclear metal units, while 2 exhibits the micro- porous structure from the binuclear zinc groups. Compared with 2, 1 demonstrated a strong luminescence in the water, so it could be used as luminescent sensors for detection of Fe3+, Cr2O72-, and acetone molecules with high selectivity and sensitivity.
Two 3D microporous zinc metal-organic frameworks, formulated as [Zn3(DBA)(OH)(1, 10-phen)2]n (1) and {[Zn2(HDBA)(4, 4′-bipy)1.5]·H2O}n (2) (H5DBA=(3, 5-di(2′, 4′-dicarboxylphenyl)benzoic acid; 1, 10- phen=1, 10-phenan- throline; 4, 4′-bipy=4, 4′ -bipyridine), were synthesized under solvothermal conditions. Structural analysis shows that 1 could be described as a 3D microporous framework based on the trinuclear metal units, while 2 exhibits the micro- porous structure from the binuclear zinc groups. Compared with 2, 1 demonstrated a strong luminescence in the water, so it could be used as luminescent sensors for detection of Fe3+, Cr2O72-, and acetone molecules with high selectivity and sensitivity.
2022, 38(4): 735-744
doi: 10.11862/CJIC.2022.063
Abstract:
A Zinc metal-organic framework (Zn-MOF) based on H4bta (1, 2, 3, 5-benzene tetracarboxylic acid) and bpy (4, 4′- dipyridine) ligands, namely {[Zn2(bta) (bpy) (H2O)2]·H2O}n (1), have been hydrothermally synthesized and structurally characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction analysis. MOF 1 shows a 3D network structure. The completely deprotonated (bta)4- ligand adopts a μ6 -η1 -η2 -η2 -η1 chelating and bridging coordination mode. Interestingly, 1 is a high sensitivity, good selectivity, and multi-response fluorescence sensor, which can be used for detection of Fe3+, 2, 4, 6-trinitrophenol, and ornidazole. In addition, the thermal stability of 1 was also studied.
A Zinc metal-organic framework (Zn-MOF) based on H4bta (1, 2, 3, 5-benzene tetracarboxylic acid) and bpy (4, 4′- dipyridine) ligands, namely {[Zn2(bta) (bpy) (H2O)2]·H2O}n (1), have been hydrothermally synthesized and structurally characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction analysis. MOF 1 shows a 3D network structure. The completely deprotonated (bta)4- ligand adopts a μ6 -η1 -η2 -η2 -η1 chelating and bridging coordination mode. Interestingly, 1 is a high sensitivity, good selectivity, and multi-response fluorescence sensor, which can be used for detection of Fe3+, 2, 4, 6-trinitrophenol, and ornidazole. In addition, the thermal stability of 1 was also studied.
2022, 38(4): 745-751
doi: 10.11862/CJIC.2022.071
Abstract:
This is the first time that coordination polymers (CPs) with the ligand 2, 6-bis(3′-pyridyl)-tetrathiafulva- lene(3′-py-TTF-3-py) has been reported. These two CPs are isostructural with formulated as [Zn(3′-py-TTF-3-py)2 (TPA)] n (1) and [Co(3′-py-TTF-3-py)2(TPA)]n (2), (H2TPA=terephthalic acid). The X -ray single- crystal diffraction shows that 1 and 2 are 2D coordination polymers. The photoelectric experiment results show that the S…S interac- tions and the center metal in the CPs have an important impact on their photocurrent responses.
This is the first time that coordination polymers (CPs) with the ligand 2, 6-bis(3′-pyridyl)-tetrathiafulva- lene(3′-py-TTF-3-py) has been reported. These two CPs are isostructural with formulated as [Zn(3′-py-TTF-3-py)2 (TPA)] n (1) and [Co(3′-py-TTF-3-py)2(TPA)]n (2), (H2TPA=terephthalic acid). The X -ray single- crystal diffraction shows that 1 and 2 are 2D coordination polymers. The photoelectric experiment results show that the S…S interac- tions and the center metal in the CPs have an important impact on their photocurrent responses.
2022, 38(4): 752-764
doi: 10.11862/CJIC.2022.064
Abstract:
Herein, we fabricated silver nanoparticle - doped activated microporous carbon spheres (Ag/AMCSs) through a combining method of spray drying, carbonization, and KOH activation by using chitosan as a precursor. Based on a series of characterization and performance studies, Ag/AMCSs are confirmed to be able to function as both an adsorbent and a catalyst for the reduction of Congo red (CR) in the presence of NaBH4 due to the high porosity and high dispersion of silver nanoparticles. Adsorption studies were performed by varying pH, contact time, and initial concentration, and it was found that the adsorption process could be well estimated by the pseudo-second-order kinetic plot and Langmuir models, and the maximum adsorption capacity of Ag/AMCSs was estimated as 445 mg·g-1. For the reduction of CR, the rate constant k was calculated up to 0.311 min-1, and the conversion efficiency of CR remained at 95% after 5 successive cycles.
Herein, we fabricated silver nanoparticle - doped activated microporous carbon spheres (Ag/AMCSs) through a combining method of spray drying, carbonization, and KOH activation by using chitosan as a precursor. Based on a series of characterization and performance studies, Ag/AMCSs are confirmed to be able to function as both an adsorbent and a catalyst for the reduction of Congo red (CR) in the presence of NaBH4 due to the high porosity and high dispersion of silver nanoparticles. Adsorption studies were performed by varying pH, contact time, and initial concentration, and it was found that the adsorption process could be well estimated by the pseudo-second-order kinetic plot and Langmuir models, and the maximum adsorption capacity of Ag/AMCSs was estimated as 445 mg·g-1. For the reduction of CR, the rate constant k was calculated up to 0.311 min-1, and the conversion efficiency of CR remained at 95% after 5 successive cycles.
2022, 38(4): 765-773
doi: 10.11862/CJIC.2022.072
Abstract:
A Ni(Ⅱ) complex, [Ni(C40H44N4O8)]Cl2·4CH3OH, with a 28-membered macrocyclic Schiff base ligand of an N4O2 donor set has been prepared by the [2+2] reaction of 1, 2-bis(2-methoxy -6-formylphenoxy)ethane with ethylenediamine in a 1∶1 stoichiometric ratio in the presence of Ni(Ⅱ) ion employing the template strategy. The complex was characterized by elemental analysis, infrared spectroscopy, powder X -ray diffraction, single-crystal X - ray diffraction, and density functional theory quantification calculations. The structural analysis demonstrates that Ni(Ⅱ) ion is six -coordinate by four N atoms from C=N groups, two O atoms from ether groups, forming a distorted octahedral geometry. Urease inhibitory activity and molecular docking simulation studies show that the Ni(Ⅱ) complex proved to be a good candidate for the inhibition of jack bean urease.
A Ni(Ⅱ) complex, [Ni(C40H44N4O8)]Cl2·4CH3OH, with a 28-membered macrocyclic Schiff base ligand of an N4O2 donor set has been prepared by the [2+2] reaction of 1, 2-bis(2-methoxy -6-formylphenoxy)ethane with ethylenediamine in a 1∶1 stoichiometric ratio in the presence of Ni(Ⅱ) ion employing the template strategy. The complex was characterized by elemental analysis, infrared spectroscopy, powder X -ray diffraction, single-crystal X - ray diffraction, and density functional theory quantification calculations. The structural analysis demonstrates that Ni(Ⅱ) ion is six -coordinate by four N atoms from C=N groups, two O atoms from ether groups, forming a distorted octahedral geometry. Urease inhibitory activity and molecular docking simulation studies show that the Ni(Ⅱ) complex proved to be a good candidate for the inhibition of jack bean urease.
