Two series of new polyhedral oligomeric silsesquioxane (POSS)‐based fluorescent hybrid porous polymers, HPP‐1 and HPP‐2 , have been prepared by the Heck reaction of octavinylsilsesquioxane with 2,2′,7,7′‐tetrabromo‐9,9′‐spirobifluorene and 1,3,6,8‐tetrabromopyrene, respectively. Three sets of reaction conditions were employed to assess their effect on fluorescence. These materials exhibit tunable fluorescence from nearly no fluorescence to bright fluorescence both in the solid state and dispersed in ethanol under UV light irradiation by simply altering the reaction conditions. We speculated that the difference may be attributable to the fluorescence quenching induced by Et3N, P(o‐CH3Ph)3, and their hydrogen bromide salts employed in the reactions. This finding could give valuable suggestions for the construction of porous polymers with tunable/controllable fluorescence, especially those prepared by Heck and Sonogashira reactions in which these quenchers are used as organic bases or co‐catalysts. In addition, the porosities can also be tuned, but different trends in porosity have been found in these two series of polymers, which suggests that various factors should be carefully considered in the preparation of porous polymers with tunable/controllable porosity. Furthermore, HPP‐1 c showed moderate CO2 uptake and fluorescence that was efficiently quenched by nitroaromatic explosives, thereby indicating that these materials could be utilized as solid absorbents for the capture and storage of CO2 and as sensing agents for the detection of explosives. 相似文献
Despite being technically possible, splitting water to generate hydrogen is still practically unfeasible due mainly to the lack of sustainable and efficient catalysts for the half reactions involved. Herein we report the synthesis of cobalt‐embedded nitrogen‐rich carbon nanotubes (NRCNTs) that 1) can efficiently electrocatalyze the hydrogen evolution reaction (HER) with activities close to that of Pt and 2) function well under acidic, neutral or basic media alike, allowing them to be coupled with the best available oxygen‐evolving catalysts—which also play crucial roles in the overall water‐splitting reaction. The materials are synthesized by a simple, easily scalable synthetic route involving thermal treatment of Co2+‐embedded graphitic carbon nitride derived from inexpensive starting materials (dicyandiamide and CoCl2). The materials’ efficient catalytic activity is mainly attributed to their nitrogen dopants and concomitant structural defects. 相似文献
Single Fe atoms dispersed on hierarchically structured porous carbon (SA‐Fe‐HPC) frameworks are prepared by pyrolysis of unsubstituted phthalocyanine/iron phthalocyanine complexes confined within micropores of the porous carbon support. The single‐atom Fe catalysts have a well‐defined atomic dispersion of Fe atoms coordinated by N ligands on the 3D hierarchically porous carbon support. These SA‐Fe‐HPC catalysts are comparable to the commercial Pt/C electrode even in acidic electrolytes for oxygen reduction reaction (ORR) in terms of the ORR activity (E1/2=0.81 V), but have better long‐term electrochemical stability (7 mV negative shift after 3000 potential cycles) and fuel selectivity. In alkaline media, the SA‐Fe‐HPC catalysts outperform the commercial Pt/C electrode in ORR activity (E1/2=0.89 V), fuel selectivity, and long‐term stability (1 mV negative shift after 3000 potential cycles). Thus, these nSA‐Fe‐HPCs are promising non‐platinum‐group metal ORR catalysts for fuel‐cell technologies. 相似文献
Organically modified cage-like double four-ring spherosilicates have received considerable interest in the construction of nanosized hybrid materials, as well as building units for structural well-defined polymers. This group is extended by perfluoroalkyl ligands containing spherosilicates, synthesized by addition reaction of the octahydridodimethylsiloxyoctasilsesquioxane [H(CH3)2Si]8Si8O20 and heptadecafluorodecyl methacrylate. The resultant liquid spherosilicate substituted with eight terminal perfluoroalkyl groups was characterized by 29Si and 13C NMR spectroscopies and MALDI Time-of-Flight mass spectrometry. Partial substitution of perfluoroalkyl ligands by trimethoxysilyl containing groups provides condensable precursors for the synthesis of hydrophobic and oleophobic materials via the sol-gel process. This new spherosilicate, carrying on average four perfluoroalkyl groups and four trimethoxysilyl groups shows better hydrophobic and oleophobic properties compared with commonly used perfluoroalkyltrialkoxysilanes under identical concentration of perfluoroalkyl chains. In addition a comprehensive literature survey is given on structural well characterized, organically modified cage-like double four-ring spherosilicates. 相似文献
Treatment of the salicylaldimine ligands (L1H, L2H, L3H, L4H and L5H) with palladium(II) acetate in absolute ethanol gave the orthopalladation dinuclear [Pd(L1)(μ-OAc)]2, [Pd(L2)(μ-OAc)]2 and mononuclear [Pd(L3)2] with the tetradentate ligands [N, C, O] or [N, O] moiety. The ligands L1H and L2H are coordinated through the imine nitrogen and aromatic ortho carbon atoms, whereas the ligand L3H coordinated through the imine nitrogen and phenolic oxygens atoms. The Pd(II) complexes have a square-planar structure and were found to be effective catalysts for the hydrogenation of both nitrobenzene and cyclohexene. These metal complexes were also tested as catalysts in Suzuki-Miyaura coupling of aryl bromide in the presence of K2CO3. The catalytic studies showed that the introduction of different groups on the salicyl ring of the molecules effected the catalytic activity towards hydrogenation of nitrobenzene and cyclohexene in DMF at 25 and 45 °C. The Pd(II) complexes easily prepared from cheap materials could be used as versatile and efficient catalysts for different C-C coupling reactions (Suzuki-Miyaura reactions). The structure of ligands and their complexes was characterized by UV-Vis, FT-IR, 1H and 13C NMR, elemental analysis, molar conductivity, as well as by electrochemical techniques. 相似文献
Two new azo-bridged hydroxyl-rich porous organic polymers (POPs), named PPDA-P5 and TB-P5, were designed and successfully fabricated via azo-coupling reaction with per-hydroxylated pillar[5]arene macrocycle as the core and p-phenylenediamine and Troger's base (TB) diamine as the linker, respectively. Owing to the abundant nitrogen and hydroxyl groups, both polymers exhibited excellent interaction affinity toward carbon dioxide (CO2) and then were applied as efficient heterogeneous catalysts for the transformation of CO2 to cyclic carbonates with high yield, even under mild conditions. Interestingly, TB-P5 exhibited superior catalytic performance toward PPDA-P5, indicating TB's positive role as an organic base. This design strategy and results provided new insight into the development of macrocycle-based POPs in the field of heterogeneous catalysis. 相似文献
Cost‐effective carbon‐based catalysts are promising for catalyzing the electrochemical N2 reduction reaction (NRR). However, the activity origin of carbon‐based catalysts towards NRR remains unclear, and regularities and rules for the rational design of carbon‐based NRR electrocatalysts are still lacking. Based on a combination of theoretical calculations and experimental observations, chalcogen/oxygen group element (O, S, Se, Te) doped carbon materials were systematically evaluated as potential NRR catalysts. Heteroatom‐doping‐induced charge accumulation facilitates N2 adsorption on carbon atoms and spin polarization boosts the potential‐determining step of the first protonation to form *NNH. Te‐doped and Se‐doped C catalysts exhibited high intrinsic NRR activity that is superior to most metal‐based catalysts. Establishing the correlation between the electronic structure and NRR performance for carbon‐based materials paves the pathway for their NRR application. 相似文献
A new strategy for achieving stable Co single atoms (SAs) on nitrogen‐doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal–organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X‐ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as‐generated N‐doped porous carbon. Surprisingly, the obtained Co‐Nx single sites exhibit superior ORR performance with a half‐wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non‐precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials. 相似文献
Porous conjugated polymers are synthesized by metal‐catalyzed coupling reactions. The progress for porous polymers when planar or tetrahedral building blocks are connected by alkyne units into novel materials is highlighted. The most prominent reaction for the buildup of the microporous alkyne‐bridged polymers is the Sonogashira reaction, connecting alkynes to aromatic iodides or bromides. The availability of the building blocks and the potency of the Sonogashira reaction allow preparing a large variety of intrinsically porous polymeric materials, in which rigid struts connect multipronged centers. The microporous polymers are used as catalysts and as storage materials for gases and sensors. Postfunctionalization schemes, understanding of structure‐property relationships, and the quest for high porosity are pertinent.
Crystalline porous ionic salts (CPISs) represent a new type of porous materials constructed by electrostatic interaction, however, synthesis of CPISs bearing pre-designed functionality while exhibiting permanent porosity is still challenging. Herein we report the facile synthesis of a series of CPISs 1-3 built from photocatalytic-active polyoxometalate (POM) clusters and cationic Zr-based capsules, which showed open porous frameworks with BET surface area up to 33 m2/g and high activity and selectivity for photo-driven aerobic oxidation of alcohols to aldehydes. Compared with the pristine POM cluster {W10}, 1 can promote the reaction in much higher efficiency due to the concerted catalysis of preinstalled {W10} and Zr-based capsule together with open channels. This work highlights the advantage of CPISs as porous heterogeneous catalysts in organic transformation, and may shed light on the rational design of more delicate CPISs-derived functional materials. 相似文献
Basic ionic liquids as environmental-friendly solvents and catalysts with high activity and selectivity and easily recovered materials were used to replace traditional bases such as KOH, NaOH, K2CO3, NaHCO3, NaOAc, triethylamine, or tetrabutylammonium acetate. Using the traditional bases generally suffered from disadvantages such as waste production, corrosion and environmental problems. Basic ionic liquids offering a new possibility for developing environmentally friendly basic catalysts due to the combination of the advantages of inorganic bases and ionic liquids. They are flexible, nonvolatile,noncorrosive, and immiscible with many organic solvents. Basic ionic liquids (BILs) have been used in base-catalyzed processes such as Michael addition, Markovnikov addition, Knoevenagel condensation, Henry reaction, Mannich reaction, oximation, Feist-Benary reaction and etc. In this short review, we wish to present an overview of the types, properties, synthesis and applications of basic ionic liquids. 相似文献
Borocarbonitride (BCN) materials are newly developed oxidative dehydrogenation catalysts that can efficiently convert alkanes to alkenes. However, BCN materials tend to form bulky B2O3 due to over-oxidation at the high reaction temperature, resulting in significant deactivation. Here, we report a series of super stable BCN nanosheets for the oxidative dehydrogenation of propane (ODHP) reaction. The catalytic performance of the BCN nanosheets can be easily regulated by changing the guanine dosage. The control experiment and structural characterization indicate that the introduction of a suitable amount of carbon could prevent the formation of excessive B2O3 from BCN materials and maintain the 2D skeleton at a high temperature of 520 °C. The best-performing catalyst BCN exhibits 81.9 % selectivity towards olefins with a stable propane conversion of 35.8 %, and the propene productivity reaches 16.2 mmol h−1 g−1, which is much better than hexagonal BN (h-BN) catalysts. Density functional theory calculation results show that the presence of dispersed rather than aggregated carbon atoms can significantly affect the electronic microenvironment of h-BN, thereby boosting the catalytic activity of BCN. 相似文献
The development of low-cost, efficient, and stable electrocatalysts for the oxygen reduction reaction (ORR) is desirable but remains a great challenge. Herein, we made a highly reactive and stable isolated single-atom Fe/N-doped porous carbon (ISA Fe/CN) catalyst with Fe loading up to 2.16 wt %. The catalyst showed excellent ORR performance with a half-wave potential (E1/2) of 0.900 V, which outperformed commercial Pt/C and most non-precious-metal catalysts reported to date. Besides exceptionally high kinetic current density (Jk) of 37.83 mV cm−2 at 0.85 V, it also had a good methanol tolerance and outstanding stability. Experiments demonstrated that maintaining the Fe as isolated atoms and incorporating nitrogen was essential to deliver the high performance. First principle calculations further attributed the high reactivity to the high efficiency of the single Fe atoms in transporting electrons to the adsorbed OH species. 相似文献
Two novel tetra‐armed microporous organic polymers have been designed and synthesized via a nickel‐catalyzed Yamamoto‐type Ullmann cross‐coupling reaction or Suzuki cross‐coupling polycondensation. These polymers are stable in various solvents, including concentrated hydrochloric acid, and are thermally stable. The homocoupled polymer YPTPA shows much higher Brunauer–Emmet–Teller‐specific surface area up to 1557 m2 g−1 than the copolymer SPTPA (544 m2 g−1), and a high CO2 uptake ability of 3.03 mmol g−1 (1.13 bar/273 K) with a CO2/N2 sorption selectivity of 17.3:1. Both polymers show high isosteric heats of CO2 adsorption (22.7–26.5 kJ mol−1) because the incorporation of nitrogen atoms into the skeleton of microporous organic polymers enhances the interaction between the pore wall and the CO2 molecules. The values are higher than those of the porous aromatic frameworks, which contain neither additional polar functional groups nor nitrogen atoms, and are rather close to those of previously reported microporous organic polymers containing the nitrogen atoms on the pore wall. These data show that these materials would be potential candidates for applications in post‐combustion CO2 capture and sequestration technology.
Silica-derived nanostructured catalysts (SDNCs) are a class of materials synthesized using nanocasting and templating techniques, which involve the sacrificial removal of a silica template to generate highly porous nanostructured materials. The surface of these nanostructures is functionalized with a variety of electrocatalytically active metal and non-metal atoms. SDNCs have attracted considerable attention due to their unique physicochemical properties, tunable electronic configuration, and microstructure. These properties make them highly efficient catalysts and promising electrode materials for next generation electrocatalysis, energy conversion, and energy storage technologies. The continued development of SDNCs is likely to lead to new and improved electrocatalysts and electrode materials. This review article provides a comprehensive overview of the recent advances in the development of SDNCs for electrocatalysis and energy storage applications. It analyzes 337,061 research articles published in the Web of Science (WoS) database up to December 2022 using the keywords “silica”, “electrocatalysts”, “ORR”, “OER”, “HER”, “HOR”, “CO2RR”, “batteries”, and “supercapacitors”. The review discusses the application of SDNCs for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2RR), supercapacitors, lithium-ion batteries, and thermal energy storage applications. It concludes by discussing the advantages and limitations of SDNCs for energy applications. 相似文献
Nonprecious metal catalysts for the oxygen reduction reaction are the ultimate materials and the foremost subject for low‐temperature fuel cells. A novel type of catalysts prepared by high‐pressure pyrolysis is reported. The catalyst is featured by hollow spherical morphologies consisting of uniform iron carbide (Fe3C) nanoparticles encased by graphitic layers, with little surface nitrogen or metallic functionalities. In acidic media the outer graphitic layers stabilize the carbide nanoparticles without depriving them of their catalytic activity towards the oxygen reduction reaction (ORR). As a result the catalyst is highly active and stable in both acid and alkaline electrolytes. The synthetic approach, the carbide‐based catalyst, the structure of the catalysts, and the proposed mechanism open new avenues for the development of ORR catalysts. 相似文献
Two types of organic–inorganic hybrid base catalysts are prepared. Organic-functionalized molecular sieves (OFMSs); in particular,
“amine-immobilized porous silicates” are designed based on common idea to immobilize catalytic active sites on silicate surface.
Silicate–organic composite materials (SOCMs), such as “ordered porous silicate–quaternary ammonium composite materials”, are
the precursors of ordered porous silicates obtained during the synthesis. Both the OFMS and the SOCM are used as the catalysts
for Knoevenagel condensation and Michael addition reactions. Among the OFMSs, there is clear tendency that the use of molecular
sieve with larger pore volume and/or surface area gives the product in higher yield. Aminopropylsilyl (AP)-tethered mesoporous
silicate such as AP-MCM-41 gives the Knoevenagel condensation product in high yield under mild conditions. No loss of activity
is observed after repeated use for three times. The SOCMs are also active for the same reaction. The OFMSs are effective when
the supports have large pore volume and/or surface area and the reaction is carried out in polar solvents ethanol and DMF.
However, the activity of the OFMSs is considerably low in a non-polar solvent such as benzene. In contrast, the SOCMs are
remarkably active in benzene. The organic cation–MCM-41 composite is more active than the composite of an organic cation and
a microporous silicate such as zeolite beta and ZSM-12. In the SOCM catalysts, (SiO)3SiO−(+NR4) moieties located at the accessible sites are considered to play some important roles. The active species are absent in the
liquid phase after the reaction. The recycle of the catalyst was possible without significant loss of activity when the substrates
are enough reactive. The mechanism of the reaction over SOCM catalyst is discussed. 相似文献