基于异构联苯二酐的热塑性聚酰亚胺性能研究

制备了一系列基于异构联苯二酐[2,2’,3,3’-联苯四甲酸二酐(3,3’-BPDA)、2,3’,3,4’-联苯四甲酸二酐(3,4’-BPDA)和3,3’,4,4’-联苯四甲酸二酐(4,4’-BPDA)]的聚酰亚胺(PI)均聚物和共聚物,比较研究了这些聚合物的热学和力学性能。结果表明,当二胺结构相同时,基于3,3’-BPDA和3,4’-BPDA的PI均聚物或共聚物较基于4,4’-BPDA的均聚物有更高的玻璃化转变温度(Tg)和更好的热加工性;当二酐结构相同时,基于对苯二胺(PDA)的PI的Tg高于基于4,4’-二氨基二苯醚(ODA)的PI。基于3,4’-BPDA/PDA的PI具有最高的Tg,其值为382℃,由其制备的薄膜的拉伸强度为100 MPa,拉伸弹性模量为1.8 GPa,断裂伸长率为12%。基于4,4’-BPDA/PDA的PI薄膜具有最高的拉伸性能,其拉伸强度为307 MPa,拉伸弹性模量为4.1 GPa,断裂伸长率为23%。基于3,4’-BPDA/ODA和3,3’-BPDA/4,4’-BPDA(1/1)/ODA的PI模塑料均具有高于300℃的Tg和较好的力学性能,其冲击强度分别达到82.3 kJ/m2和94 kJ/m2。

High-performance ZIF-8 membranes:preparation and their uranium adsorption performance

In this study,the ZIF-8 membrane(ZIF-8/PP-g-MAH)is prepared by in situ synthesis of ZIF-8 on irradiation-pretreated polymer substrates to improve the uranium adsorption performance and address the recycling problems of ZIF-8 powder.The effects of pH,contact time,and uranium concentration on the adsorption of ZIF-8/PP-g-MAH were investigated.Adsorption isotherm and kinetics analysis show that ZIF-8/PP-g-MAH has a high adsorption capacity of 478.5 mg/g,which is 1.26 times higher than that of ZIF-8,and a rapid adsorption equilibrium of 120 min,which is shortened to one-third of that required for ZIF-8(360 min).The adsorption process of ZIF-8/PP-g-MAH is consistent with that of the Langmuir isotherm and pseudo-second-order dynamic model.ZIF-8/PP-g-MAH also exhibits good selectivity for uranium in simulated seawater.The high adsorption performance of ZIF-8/PP-g-MAH is attributed to its membrane structure,which improves the utilization of coordination sites,including Zn-OH,C-N,and C=N.This study provides an efficient adsorption material for rapid uranium extraction,thus promoting the development of uranium extraction technologies.

本体共聚合制备丙烯／1-丁烯合金及表征

以球形高效负载的TiCl4/MgCl2/邻苯二甲酸二异丁酯(DIBP)为催化剂,采用本体聚合方法进行丙烯与1-丁烯共聚合研究.考察了共单体效应对共聚活性及聚合物立构规整性的影响;表征了共聚物的结构.结果表明,随着1-丁烯/丙烯投料比的增加,聚合活性呈先升高后降低的趋势,在1-丁烯/丙烯摩尔投料比为0.26条件下聚合活性达到最高,并随着共聚物中1-丁烯含量的增加,共聚物的熔点明显下降,分子量降低,分子量分布变窄,同时共聚物力学性能有明显提高,透明度逐渐增加.

Layered double hydroxide-like Mg_3Al_(1–x)Fe_x materials as supports for Ir catalysts: Promotional effects of Fe doping in selective hydrogenation of cinnamaldehyde

Supported Ir catalysts were prepared using layered double hydrotalcite‐like materials,such as Mg3Al1-xFex,containing Fe and Al species in varying amounts as supports.These Ir catalysts were applied for the selective hydrogenation of cinnamaldehyde(CAL).When x was changed from 0(Ir/Mg3Al)to 1(Ir/Mg3Fe),the rate of CAL hydrogenation reached a maximum at approximately x=0.25,while the selectivity to unsaturated alcohol,i.e.,cinnamyl alcohol,monotonously increased from 44.9%to 80.3%.Meanwhile,the size of the supported Ir particles did not change significantly with x,remaining at 1.7-0.2 nm,as determined by transmission electron microscopy.The chemical state of Ir and Fe species in the Ir/Mg3Al1-xFex catalysts was examined by temperature programmed reduction by H2 and X‐ray photoelectron spectroscopy.The surface of the supported Ir particles was also examined through the in‐situ diffuse reflectance infrared Fourier‐transform of a probe molecule of CO.On the basis of these characterization results,the effects of Fe doping to Mg3Al on the structural and catalytic properties of Ir particles in selective CAL hydrogenation were discussed.The significant factors are the electron transfer from Fe2+in the Mg3Al1–xFex support to the dispersed Ir particles and the surface geometry.

Advanced Pt‐based intermetallic nanocrystals for the oxygen reduction reaction

Proton exchange membrane fuel cells(PEMFCs)are considered ideal energy‐conversion devices because of their environmentally friendly nature and high theoretical energy efficiency.However,cathodic polarization,which is a result of the sluggish oxygen reduction reaction(ORR)kinetics,is a significant source of energy loss and reduces fuel cell efficiency.Further,the need to use Pt in commercial Pt/C cathodes has restricted their large‐scale application in fuel cells because of its high cost and poor durability.Thus,improvements in the activity and durability of Pt‐based catalyst are required to reduce the amount of Pt required and,thus,costs,while increasing the ORR rate and fuel cell power density and promoting widespread PEMFC commercialization.In recent years,atomically ordered Pt‐based intermetallic nanocrystals have received tremendous attention owing to their excellent activity and stability for the ORR.Therefore,in this review,we first introduce the formation of intermetallic compounds from the perspective of thermodynamics and kinetics to lay a theoretical foundation for the design of these compounds.In addition,optimization strategies for Pt‐based ordered intermetallic catalysts are summarized in terms of the catalyst composition,size,and morphology.Finally,we conclude with a discussion of the current challenges and future prospects of Pt‐based ordered alloys.This review is designed to help readers gain insights into the recent developments in and rational design of Pt‐based intermetallic nanocrystals for the ORR and encourage research that will enable the commercialization of PEMFCs.

Surface density of synthetically tuned spinel oxides of Co^(3+) and Ni^(3+) with enhanced catalytic activity for methane oxidation

Spinel oxides containing Co and Ni are a promising substitute as a noble metal catalyst for methane combustion.Achieving a complete oxidation of methane under 400°C remains challenging,andhydrothermal 60 h NiClittle impact on activity,especially at high space velocities due to the long hydrothermal time with less absorbed oxygen species and crystal defects.Overall,these results help clarify methane activa-tion mechanisms and aid the development of more efficient low-cost catalysts.

Recent advances in one-dimensional nanostructures for energy electrocatalysis

Catalysts play decisive roles in determining the energy conversion efficiencies of energy devices.Up to now,various types of nanostructured materials have been studied as advanced electrocatalysts.This review highlights the application of one‐dimensional(1D)metal electrocatalysts in energy conversion,focusing on two important reaction systems-direct methanol fuel cells and water splitting.In this review,we first give a broad introduction of electrochemical energy conversion.In the second section,we summarize the recent significant advances in the area of 1D metal nanostructured electrocatalysts for the electrochemical reactions involved in fuel cells and water splitting systems,including the oxygen reduction reaction,methanol oxidation reaction,hydrogen evolution reaction,and oxygen evolution reaction.Finally,based on the current studies on 1D nanostructures for energy electrocatalysis,we present a brief outlook on the research trend in 1D nanoelectrocatalysts for the two clean electrochemical energy conversion systems mentioned above.

Tuning strategies and structure effects of electrocatalysts for carbon dioxide reduction reaction

Carbon dioxide emissions have increased due to the consumption of fossil fuels,making the neutralization and utilization of CO_(2) a pressing issue.As a clean and efficient energy conversion process,electrocatalytic reduction can reduce carbon dioxide into a series of alcohols and acidic organic molecules,which can effectively realize the utilization and transformation of carbon dioxide.This review focuses on the tuning strategies and structure effects of catalysts for the electrocatalytic CO_(2) reduction reaction(CO_(2)RR).The tuning strategies for the active sites of catalysts have been reviewed from intrinsic and external perspectives.The structure effects for the CO_(2)RR catalysts have also been discussed,such as tandem catalysis,synergistic effects and confinement catalysis.We expect that this review about tuning strategies and structure effects can provide guidance for designing highly efficient CO_(2)RR electrocatalysts.

Preparation of graphene/MgCl_2-supported Ti-based Ziegler-Natta catalysts by the coagglomeration method and their application in ethylene polymerization

We report a facile coagglomeration method for preparing graphene (G)/MgCl2‐supported Ti‐based Ziegler‐Natta catalysts. The effects of graphene feed ratio on catalyst morphology and ethylene polymerization behavior were examined. The synthesized catalyst exhibited very high activity for ethylene polymerization. The resultant polyethylene (PE)/G nanocomposites showed a layered morphology, and the graphene fillers were well dispersed in the PE matrix. In addition, the thermal stability and mechanical properties of PE were significantly enhanced with the introduction of a very small amount of G fillers (0.05 wt%). This work provides a facile approach to the production o fhigh‐performance PE.

Meta-analysis of commercial Pt/C measurements for oxygen reduction reactions via data mining

The rotating disk electrode technique is commonly used for screening and characterizing the performance of electrocatalysts for the oxygen reduction reaction(ORR).However,a reliable performance comparison of different electrocatalysts from different labs remains a challenge because of the inconsistency in the measurement of commercial Pt/C.Commercial Pt/C has been adopted extensively as a reference for evaluating the ORR performance of a new electrocatalyst.However,the reported ORR performances of commercial Pt/C from different labs could be significantly different because of multiple factors.Herein,we conducted a meta‐analysis of the ORR performance of commercial Pt/C via data mining of the literature.This revealed the optimal testing conditions for the most repeatable ORR performance,with commercial Pt/C in both acid and alkaline electrolytes;the optimal Pt loading was 20μg/cm^(2) on a 4 mm glassy carbon working electrode.The value of 0.84±0.03 V was suggested as the“Golden reference”of the commercial Pt/C(with Pt 20 wt%)ORR half‐wave potential for the performance evaluation of other ORR catalysts in both acid and alkaline electrolytes.The conclusion obtained through the meta‐analysis was confirmed by experiments.This study provides general guidance for a reliable measurement of the ORR performance of commercial Pt/C as a reference.

Synthesis of CO_(2)-Based Re-processable Slight Cross-Linked Polyurea Thermosets

The use of CO_(2) as monomer to synthesize polymer materials is an important and potential applications topic from the viewpoint of green and sustainable chemistry.A new kind of CO_(2)-based polyurea(PUa)was synthesized by polycondensation of CO_(2) with 4,7,10-trioxa-1,13-tridecanediamine and tris(2-aminoethyl)amine(TAEA).TAEA was used as cross-link reagent.The mechanical properties of PUa were significantly improved by inserted the crosslink agent of TAEA.The formed slight cross-linked PUa exhibited excellent mechanical properties with tensile strength of 26.8 MPa,elongation at break of 34%and Young’s modulus of 351 MPa.Moreover,it could be remolded for 3 times without obvious change in the mechanical properties,which are ascribed to the hydrogen bonding interaction among the main chains and the slight cross-linked structure.In addition,the synthesized CO_(2)-based PUa is of outstanding thermal performance with an initial decomposition temperature above 300℃,besides it is tolerance for a variety of organic solvents.