Latest ArticlesIn this paper, CuO/TiO2 p-n heterojunction was developed as a new surface enhanced Raman scattering (SERS) substrate to magnify Raman signal of 4-mercaptobenzoic acid (4-MBA) molecule. In the heterojunction-molecule system, CuO as an "electron capsule" can not only offer more electrons to inject into the surface state energy level of TiO2 and consequently bring additional charge transfer, but also improve photogenerated carrier separation efficiency itself due to strong interfacial coupling in the interface of heterojunction, which together boost SERS performance of the heterojunction substrate. As expected, owing to the enhanced charge collection capacity and the improvement of photogenerated carrier separation efficiency derived from internal electric field and strong interface coupling provided in the interface of heterojunction, this substrate exhibits excellent SERS detection sensitivity towards 4-MBA, with a detection limit as low as 1 × 10−10 mol/L and an enhancement factor of 8.87 × 106.
Comprehensive fundamental understanding of CO hydrogenation reactions over Cu and ZnCu alloy surfaces is of great importance. Herein, we report a comparative DFT calculation study of elementary surface reaction network of CO hydrogenation reactions on stepped Cu(211), Cu(611), ZnCu(211) and ZnCu(611) surfaces. On ZnCu(211) and ZnCu(611) surfaces, the energetic favorable reaction path of CO hydrogenation reaction follows CO* → HCO* → H2CO* → H3CO* → CH3OH* → CH3OH with H3CO* hydrogenation as the rate-limiting step and proceeds more facilely on ZnCu(611) surface than on ZnCu(211) surface. On Cu(211) and Cu(611) surfaces, the energetic favorable reaction path of CO hydrogenation reaction follows CO* → HCO* → HCOH* → H2COH* → H3COH* → CH3* → CH4* → CH4 with H2COH* hydrogenation as the rate-limiting step and proceeds more facilely on Cu(611) than on Cu(211). The key difference of CO hydrogenation reaction on ZnCu alloy surface and Cu is that the resulting CH3OH* species desorbs to produce CH3OH on ZnCu alloy but undergoes H*-assisted decomposition to CH3* and eventually to CH4 on Cu surface. These results successfully unveil elementary surface reaction networks and structure sensitivity of Cu and ZnCu alloy-catalyzed CO hydrogenation reactions.
Co3O4 has been widely explored in electrocatalytic 5-hydroxymethyl-furfural (HMF) oxidation. However, the poor intrinsic ability has seriously limited its electrochemical ability. Heteroatom-doping is an efficient method to enhance the electrocatalytic ability of catalyst by regulating electronic structure. Herein, we have modulated the electronic structure of Co3O4 by high valance Mo6+-doping. With the introduction of Mo6+, the content of Co2+ was increased and metal-oxygen bond was strength. Electrochemical results suggested that the electrocatalytic ability of Co3O4 towards HMF oxidation has been dramatically improved and reaction kinetics has been fasten. Theoretical calculations demonstrated that the surrounding cobalt sites after Mo6+-doping with assembled electron has a strong adsorption ability towards HMF molecule leading to more favourable oxidation of HMF. Post characterizations demonstrated pristine Co3O4 structure was kept after electrolysis cycles and CoOOH active species were formed. This work provides a valuable reference for developing efficient heteroatom-doped electrocatalysts for HMF oxidation.
Developing sustainable and powerful heterogeneous catalytic systems to convert sulfides into high-value sulfoxide products has become a particularly appealing field and an arduous challenge. In this work, two porous polyoxometalate-pillared metal-organic frameworks, formulated as H3n[Cu3(pidc)2(H2O)2.5]2[PW12O40]n·xH2O (n = 1.5, x = 6 for 1, n = 1, x = 12 for 2; and H3pidc = 2-(3-pyridinyl)-1H-imidazole-4,5-dicarboxylic acid), were consciously manufacture and employed for heterogeneously catalyzed sulfide-sulfoxide transformation. Structural analysis shows that 1 and 2 exhibit similar porous frameworks with nearly identical two-dimensional metal-organic layers further pillared by tetradentate POM ligands with different coordination modes, which also result in the porosity of 1 being almost twice that of 2. In catalyzing the conversion of methyl phenyl sulfide (MPS) to methyl phenyl sulfoxide (MPSO), 1 can convert nearly 100% of MPS into MPSO within 30 min, while 2 achieved the similar results requires 50 min. The higher activity of 1 may be attributed to its larger channel that can provide more active sites and more efficient mass transfer process. Systematic structure-activity analyses and mechanistic studies revealed dual-reaction pathways driven by POM sites and metal sites assisted by the structural microenvironment.
Although bone morphogenetic protein (BMP) and WNT signaling play pivotal roles in bone development, homeostasis, and regeneration, the applications of proteins to stimulate corresponding signaling pathways showed limited outcomes in the repair and regeneration of bone defects that might be attributed to the reciprocal interventions of these pathways. In order to satisfy the combinational and sequential activation of BMP and WNT pathways, inspired by the heterogeneous hydrogel-liked structures of Brasenia, heterogeneous alginate/chitosan hydrogels were fabricated and spatially loaded with FK506 and BIO to achieve sustained and sequential release of the activators. Alkaline phosphatase staining, alizarin red staining and qRT-PCR results suggested that FK506 and BIO enhanced osteoblastic differentiation in vitro when used separately. Besides, by mixing and matching the activators and the hydrogel layers, a superior releasing mode that a combination of early FK506 release and following BIO release was identified via both in vitro and in vivo explorations for most efficient bone regeneration. These results suggested that drug-loaded heterogeneous hydrogels possess great potentials in treating bone loss defects for future clinical practice.
Long afterglow organic-inorganic hybrid materials have attracted much attention in recent years and are widely used in information security, biological imaging and many other fields. Since up-conversion long-persistence materials are promising for bio-optical imaging due to their high penetration depth and elimination of autofluorescence background, it is highly desirable to combine down-conversion and up-conversion pathways to obtain smart materials with excitation-dependent tunable room-temperature phosphorescence properties. In this work, a metal-organic framework (Zn-DCPS-BIMB), consisting of divalent zinc ions, o-bis(imidazol-1-ylmethyl)benzene and 4,4′-dicarboxydiphenylsulfone, is designed to stabilize triplet excitons, coordinate the emission of different ligands, and endow materials with tunable emission color and up-conversion properties via heavy atoms effects promoting single-triplet orbital coupling and intersystem crossing.
CO oxidation is a benchmark in heterogeneous catalysis for evaluation of redox catalysts due to its practical relevance in many applications and the fundamental problems associated with its very high activity at low temperatures. Among which, Co3O4 is one of the most active non-precious metal catalysts. Exposed crystal planes and cobalt sites are considered to be important for its high catalytic activity. Herein, we demonstrate an enhanced CO oxidation activity by a defect-rich mesoporous Co3O4 that prepared by a designed dual-template method. Two different kinds of silicas are used as hard-templates at the same time, resulting in a defect-rich mesoporous Co3O4 with a surface area as high as 169 m2/g. This catalyst exhibited a very high catalytic activity for low temperature CO oxidation with a light-off temperature at −73 ℃ under the space velocity of 80,000 mL h-1 gcat-1. Further studies reveal that the high surface area promotes the lattice oxygen mobility, surface rich of Co2+ species and active oxygen species are crucial for the high catalytic activity. Moreover, the dual-template approach paves a way towards the design and construction of high-surface-area mesoporous metal oxides for various applications.
We report that the photoinduced dynamics of the phytochrome chromophore is strongly dependent on the protonation/deprotonation states of the pyrrole ring. The on-the-fly surface hopping dynamics simulations were performed to study the photoisomerization of different protonation/deprotonation phytochrome chromophore models. The simulation results indicate that the deprotonations at the pyrrole rings significantly modify the photoinduced nonadiabatic dynamics, leading to distinctive population decay dynamics and different reaction channels. Such feature can be well explained by the formation of the different hydrogen bond network patterns. Therefore, the proper understanding of the photoisomerization mechanism of phytochrome chromophore must take the hydrogen bond network into account. This work provides the new insights into the photobiological functions of phytochrome chromophore and suggests the possible ideas to control of its photoconversion processes for further rational engineering in optical applications.
Two triphenylamine-based star-type push-pull chromophores (T1, T2) were designed and synthesized. Triphenylamine serves as the central core and acts as an electron-donating group surrounded by electron-withdrawing pentafluorobenzene or N, N-dimethyl substituted tetrafluorobenzene, which are connected by ethylene bridges. Single-crystal X-ray diffraction confirmed the structures and molecular arrangement of two chromophores. The systematic photophysical research of T1 and T2 absorption characteristics was carried out to gain a better understanding of how structure-property relationships affect the observed nonlinear optical absorption phenomenon. Complementary calculations based on density functional theory (DFT) further confirmed the experimental results. Both chromophores exhibited excellent two-photon absorption (TPA) properties in CH2Cl2. Notably, T2 has more remarkable nonlinear optical absorption effects with the TPA cross-section up to 4.24 × 107 GM. By adjusting the electronic structures of the chromophores through introducing pentafluorobenzene or N, N-dimethyl as functional groups with different electron-donating or withdrawing behaviors, the TPA performance of the small organic molecule could be greatly enhanced. These molecular structures with push-pull systems were excellent candidates for different two-photon applications.
Lithium-sulfur (Li-S) batteries have been regarded as the candidate for the next-generation energy storage system due to the high theoretical specific capacity (1675 mAh/g), energy density (2600 Wh/kg) and the abundance of elemental sulfur, but the application of Li-S batteries is impeded by a series of problems. Recently, all-solid-state Li-S batteries (ASSLSBs) have drawn great attention because many drawbacks such as safety issues caused by metallic lithium anodes and organic liquid electrolytes can be overcome through the use of solid-state electrolytes (SEs). However, not only the problems brought by sulfur cathodes still exist, but more trouble arouses from the interfaces between SEs and cathodes, hampering the practical application of ASSLSBs. Therefore, in order to deal with the problems, enormous endeavors have been done on ASSLSB cathodes during the past few decades, including engineering of cathode active materials, cathode host materials, cathode binder materials and cathode structures. In this review, the electrochemical mechanism and existing problems of ASSLSBs are briefly introduced. Subsequently, the strategies for developing cathode materials and designing cathode structures are presented. Then there follows a brief discussion of SE problems and expectations, and finally, the challenges and perspectives of ASSLSBs are summarized.
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