A Series of Rare Earth Phenolates Substituted by Alkyl Groups for D,L-Lactide Ring-Opening Polymerization

Single component rare earth phenolates substituted by various alkyl groups have been prepared and the correlation between the aryloxides＇ structure and catalytic activity in the ring-opening polymerization of D,L-lactide has also been investigated.The catalytic activity of all rare earth aryloxides,characteristics of the ring-opening polymerization as well as polymerization kinetics and mechanism were investigated.The results showed that both phenolates＇ catalytic activities and polymerization characteristics changed regularly,keeping in good concordance with variations in substitutents＇ number on phenol and structure of aryloxide ligands.The stronger ability of electron-donation of alkyl groups,the higher catalytic activity.Moreover,the more numbers of substituted alkyl on phenyl ring,the higher catalytic activity.The analyses of polymer ends revealed that the polymerization proceeded via a coordination-acyl-oxygen bond cleavage-insertion mechanism.

Theoretical Investigation on the Geometries and Properties of Guanine-BX_3 (X = F, Cl) Complex

Geometries and binding energies were predicted at the B3LYP/6-311＋G＊ level for the guanine-BX3 （X = F, Cl） systems and four isomers with no imaginary frequencies have been obtained for both guanine-BF3 and guanine-BCl3, respectively. Single energy calculations using much larger basis sets （6-311＋G（2df, p） and aug-cc-pVDZ were carded out as well. It was found that the most stable isomer of guanine-BF3 is BF3 connected to N3 of guanine with the stabilization energy of-19.93 kcal/mol （BSSE corrected）, while that of guanine-BC13 is BC13 connected to O10 of guanine having stabilization energy of -15.02 kcal/mol at the same level. The analyses for the combining interaction between BX3 and guanine with the atom-in-molecules theory （AIM） and natural bond orbital （NBO） methods have been performed. The results indicated that all the isomers are formed with σ-p type interactions between guanine and BX3, in which pyridine-type nitrogen or carbonyl oxygen or nitrogen atom of amino group offers its lone pair electrons to the empty p orbital of boron atom and the concomitance of charge transfer from guanine to BX3 has occurred. Still, one or two hydrogen bonds exist in some isomers of guanine-BX3 system and contribute to the stability of complex systems. Frequency analysis suggested that the stretching vibration of BX3 undergoes a red shift in complexes. Guanine-BF3 complex is more stable than guanine-BC13 although the B-Y （Y=N, O） bond distance in the latter is shorter.

Formation of Two F_(2)^(+)-Like Centers Coexisting in KCl:Li^(+),Na^(+),OH^(-)Crystal

To enlargen tuning range in a single host material,we have simultaneously created(F_(2)^(+))Li^(+),H^(-)(F_(2)^(+))Na^(+),H color centers in KCl:Li^(+),Na^(+),OH^(-)crystal,whose emission wavelength covers from 1.45 to 2.45μm.The experiments prove that two coexisting F_(2)^(+)-like centers in KCl have high concentration and good stability.

Optimizing Electrocatalytic Hydrogen Evolution Stability via Minimal Bubble Adhesion at Electrodeposited Crack-Structured NiP_(x)Catalysts

In response to the ongoing energy crisis,advancing the field of electrocatalytic water splitting is of utmost significance,necessitating the urgent development of high-performance,cost-effective,and durable hydrogen evolution reaction catalysts.But the generated gas bubble adherence to the electrode surface and sluggish separation contribute to significant energy loss,primarily due to the insufficient exposure of active sites,thus substantially hindering electrochemical performance.Here,we successfully developed a superaerophobic catalytic electrode by loading phosphorus-doped nickel metal(NiP_(x))onto various conductive substrates via an electrodeposition method.The electrode exhibits a unique surface structure,characterized by prominent surface fissures,which not only exposes additional active sites but also endows the electrode with superaerophobic properties.The NiP_(x)/Ti electrode demonstrates superior electrocatalytic activity for hydrogen evolution reaction,significantly outperforming a platinum plate,displaying an overpotential of mere 216 mV to achieve a current density of-500 mA cm^(-2) in 1 M KOH.Furthermore,the NiP_(x)/Ti electrode manifests outstanding durability and robustness during continuous electrolysis,maintaining stability at a current density of-10 mA cm^(-2) over a duration of 2000 h.Owing to the straightforward and scalable preparation methods,this highly efficient and stable NiP_(x)/Ti electrocatalyst offers a novel strategy for the development of industrial water electrolysis.

Preparation of Gd_2O_3:Eu^(3+) downconversion luminescent material and its application in dye-sensitized solar cells

Gd_2O_3 :Eu^(3+) downconversion luminescent powder was prepared using the homogeneous precipitation method. Its optical properties were analyzed and it was introduced into a dye-sensitized solar cell (DSSC). As a luminescence medium, Gd_2O_3 :Eu^(3+) improved light harvesting via conversion luminescence and increased the photocurrent of the DSSC. As a p-type dopant insulating rare earth oxides form an energy barrier, and the Gd_2O_3 :Eu^(3+) elevated the energy level of the oxide film and increased the photovoltage. The photoelectric conversion efficiency for a DSSC with Gd_2O_3 :Eu^(3+) doping (6 : 100) reached 7.01%, which was 17.4% higher than the photoelectrical conversion efficiency of a DSSC without Gd 2 O 3 :Eu 3+ doping.

Study on in-situ Mg_2Si/Al-Si composites with different compositions

Effects of chemical composition and heat treatment on microstructures and mechanical properties of in-situ Mg2Si/Al-Si composites were investigated. It was found that, in the microstructure of an Al-5.7wt% Mg2Si composite with 8.2wt% extra Si, the binary eutectic Mg2Si locates at the grain boundaries with an undeveloped Chinese script-like morphology, and the primary reAl is formed into a cell structure due to the selective modification effect of the modifiers of mischmetal and Strontium salt; whereas in the composite with a near Al-Mg2Si eutectic composition and little extra Si content, the intercrescence eutectic Mg2Si formed with the binary eutectic a-Al grows into integrated Chinese script- like shape. As Si content increases, the eutectic Mg2Si dendrite becomes coarser in morphology but less in volume fraction. Hardness and tensile strength of the cast Mg2Si/Al-Si composites do not increase with increasing of Mg content, but they are related to the size and morphology of the eutectic and primary Mg2Si phases. Heat treatment with optimal parameters is an effective way to improve the properties of the in-situ composites.

Synergistic extraction and separation of thorium from rare earths in chloride media using mixture of Cextrant 230 and Cyanex 923

In order to lower the usage of expensive Cyanex 923 and increase the extraction capacity of the system of Cextrant 230,the synergistic extraction of thorium from chloride media by a mixture of Cextrant 230 and Cyanex 923 was investigated.The maximum synergistic enhancement coefficient(R)of 1.53 is obtained at 1:1 molar ratio of Cextrant 230/Cyanex 923.The syne rgistic extracted species of Th^(4+)is determined as ThCl_(4)·2Cextrant 230·Cyanex 923.The synergistic extraction of Th^(4+)is an entropy-driven exothermic process.The loading capacity of 0.60 mol/L mixed extractant for thorium is about 17.10 g/L(calculated as ThO_(2)),and the loaded thorium in the organic phase can be effectively stripped by distilled water.For comparison,rare earth cations are barely extracted under the similar conditions,suggesting that the mixtures can be applied to separate thorium from rare earths.A cascade extraction process was developed based on the synergistic extraction system to separate thorium from the hydrochloric acid leaching of bastnaesite.The content of thorium in the leaching solution decreases obviously from 19.90 mg/L to1.4μg/L by 3 stages of extraction,which is superior to sole Cextrant 230 or Cyanex 923.The introduction of Cextrant 230 into the extraction system not only lowers the usage of Cyanex 923 but also enhances the selective extraction of thorium at low acidity,implying that the synergistic extraction system can selectively extract thorium more efficiently and economically than the sole systems.

Application of upconversion luminescence in dye-sensitized solar cells

An upconversion luminescence powder TiO2:(Er3+,Yb3+) is prepared by a hydrothermal method and used to fabricate dye-sensitized solar cell (DSSC).The TiO2:(Er3+,Yb3+) powder undergoes upconversion luminescence,converting infrared light which the dye can not absorb into visible light with wavelengths of 510-700 nm which the dye can absorb,increasing the photocurrent of the DSSC.TiO2:(Er3+,Yb3+) also acts as a p-type dopant,heightening the Fermi level of the oxide film,which increases the photovoltage of the DSSC.The best performance of the DSSC is found when the ratio of TiO2/luminescence powder is 1/3 in the luminescence layer.Under simulated solar irradiation of 100 mW cm-2 (AM 1.5),the DSSC containing TiO2:(Er3+,Yb3+) doping achieves a light-to-electricity energy conversion efficiency of 7.28% compared with 6.41% for the undoped DSSC.

Ring-opening polymerization of 2,2-dimethyltrimethylene carbonate using rare earth aryl oxides substituted by alkyl groups

Single component rare earth aryl oxides substituted by various alkyl groups [Ln(OAr)3] such as methyl,isopropyl,and tertbutyl have been developed to initiate the ring-opening polymerization of 2,2-dimethyltrimethylene carbonate(DTC).The catalytic activity of rare earth aryl oxides,characteristics of the ring-opening polymerization as well as the polymerization kinetics and mechanism were intensively examined.The experimental results turn out that the catalytic activity of Ln(OAr)3 changes in good concordance with variation of ligands' structure and number of alkyl groups on benzene ring.The greater the ability of electron-donation of alkyl groups,the greater the catalytic activity.Moreover,the greater the number of substituted alkyls on benzene ring,the greater the catalytic activity.The results show that rare earth tris(2,4,6-tri-tert-butylphenolate)s [Ln(OTTBP)3](Catalyst 1) exhibit rather great activity in all lanthanide aryl oxides.Investigations of the polymerization mechanism by 1H NMR spectroscopy revealed that the DTC monomer inserted into the growing chains with acyloxygen bond cleavage.

RING-OPENING POLYMERIZATION OF L-LACTIDE WITH RARE EARTH ARYLOXIDES SUBSTITUTED BY VARIOUS ALKYL GROUPS

Rare earth aryloxides substituted by various alkyl groups [Ln（OAr）3] such as methyl, isopropyl and tertbutyl, were used as single component catalysts to affect ring-opening polymerization of L-lactide （LLA）. The catalytic activity, polymerization characteristics, polymerization kinetics and the mechanism were studied. It was found that the catalytic activity of rare earth aryloxides is influenced by both the structure and the number of alkyl groups on the phenyl ring. The stronger the electron-donation ability of the alkyl group, the higher the catalytic activity will be. An increase in the number of the substitute group will result in a higher catalytic activity. Lanthanum tris（2,4,6-tri-tert-butylphenolate） [La（OTTBP）3] exhibits the highest activity among all lanthanum aryloxides. According to the ^1H-NMR data, it was proposed that the LLA polymerization proceeded via a coordination-insertion mechanism involving cleavage of acyl-oxygen bond of the laetide.