Adjusted Preferential Adsorption of Intermediates via Regulation of the Electronic Structure during the Electrocatalytic CO2 Reduction Process.

The surface electronic structures of catalysts play a crucial role in CO2 adsorption and activation. Here, sulfur vacancies are introduced into CuInS2 nanosheets (Vs-CuInS2) to evaluate the effect of electronic structures at the surface-active sites on the electrochemical CO2 reduction reaction (CO2RR). Vs-CuInS2 exhibits a significant disparity in the highest FEformate/FECO (6.50) compared to that of CuInS2 (1.86). Specifically, the maximum current density (Jmax) of carbon products on Vs-CuInS2 is 78.78 mA cm-2, and a Faraday efficiency of carbon products (FEcarbon products) of ≥80% is achieved in 600 mV wide potential windows. In situ Raman measurements and density functional theory calculations elucidate the origin of the apparent alterations in the carbon product selectivity. The introduction of sulfur vacancies realizes the controllable regulation of the local electronic density around the metal active sites, inducing the transformation of *COOH and *OCHO from competitive adsorption on CuInS2 to specific adsorption on Vs-CuInS2. In addition, the regulation of electronic structures on Vs-CuInS2 inhibits *H adsorption. This work reveals the transfer of adsorption of CO2RR intermediates via regulation of the electronic structure, complementing the understanding of the mechanism for the enhanced CO2RR.

Electrochemically stable frustrated Lewis pairs on dual-metal hydroxides for electrocatalytic CO2 reduction.

The sluggish kinetics of CO2 activation and reduction severely limit the energy conversion efficiency of electrocatalytic CO2 reduction into fuels. Here, ZnSn(OH)6 with an alternating arrangement of Zn(OH)6 and Sn(OH)6 octahedral units and SrSn(OH)6 with an alternating arrangement of SrO6 and Sn(OH)6 octahedral units were adopted to check the effects of frustrated Lewis pairs (FLPs) on electrochemical CO2 reduction. The FLPs were in situ electrochemically reconstructed on ZnSn(OH)6 by reducing the electrochemically unstable Sn-OH to Sn-oxygen vacancies (Sn-OVs) as a Lewis acid site, which are able to create strong interactions with the adjacent electrochemically stable Zn-OH, a Lewis base site. Compared to SrSn(OH)6 without FLPs, the higher formate selectivity of ZnSn(OH)6 originates from the strong ability of FLPs to capture protons and activate CO2via the electrostatic field of FLPs triggering better electron transfer and strong orbital interactions under negative potentials. Our findings may guide the design of electrocatalysts for CO2 reduction with high catalytic performances.

Regulated Surface Electronic States of CuNi Nanoparticles through Metal-Support Interaction for Enhanced Electrocatalytic CO2 Reduction to Ethanol.

Developing stable catalysts with higher selectivity and activity within a wide potential range is critical for efficiently converting CO2 to ethanol. Here, the carbon-encapsulated CuNi nanoparticles anchored on nitrogen-doped nanoporous graphene (CuNi@C/N-npG) composite are designedly prepared and display the excellent CO2 reduction performance with the higher ethanol Faradaic effiency (FEethanol  ≥ 60%) in a wide potential window (600 mV). The optimal cathodic energy efficiency (47.6%), Faradaic efficiency (84%), and selectivity (96.6%) are also obtained at -0.78 V versus reversible hydrogen electrode (RHE). Combining with the density functional theory (DFT) calculations, it is demonstrated that the stronger metal-support interaction (Ni-N-C) can regulate the surface electronic structure effectively, boosting the electron transfer and stabilizing the active sites (Cu0 -Cuδ+ ) on the surface of CuNi@C/N-npG, finally realizing the controllable transition of reaction intermediates. This work may guide the designs of electrocatalysts with highly catalytic performance for CO2 reduction to C2+ products.

Highly Effective Photocatalytic Radical Reactions Triggered by a Photoactive Metal-Organic Framework.

On account of their inherent reactive properties, radical reactions play an important role in organic syntheses. The booming photochemistry provides a feasible approach to trigger the generation of radical intermediates in organic reaction processes. Thus, developing effective photocatalysts becomes the key step in radical reactions. In this work, the triphenylamine moiety with photoactivity is successfully embedded in a highly porous and stable metal-organic framework (MOF), and the obtained MOF, namely, Zr-TCA, naturally displays a photoactive property derived from the triphenylamine-based ligand. In photocatalytic studies, the triphenylamine-based Zr-TCA not only exhibits a high catalytic activity on the aerobic oxidation of sulfides via the generation of the superoxide radical anion (O2•-) under light irradiation but also shows good efficiency in the trifluoromethylation of arenes and heteroarenes by the formation of the trifluoromethyl radical (CF3•) as an intermediate. Moreover, the high performance of Zr-TCA can be well maintained over a wide range of substrates in these radical reactions, and the recycled Zr-TCA still retains its excellent photocatalytic activity. The high recyclability and catalytic efficiency to various substrates make the constructed triphenylamine-based Zr-TCA a promising photocatalyst in diverse radical reactions.

Oxygen vacancy and nitrogen doping collaboratively boost performance and stability of TiO2-supported Pd catalysts for CO2 photoreduction: a DFT study.

The regulation of interfacial charge transfer, optimization of active sites, and maintenance of stability are effective strategies for improving catalytic performance. The effect of the oxygen vacancy (VO) and nitrogen doping on these parameters for CO2 photoreduction on Pd10/TiO2(101) was studied using density functional theory calculations. The results demonstrate that introduction of the VO could trigger reversed electron transfer, making the VO and Pd atoms the active center for CO2 reduction. However, the VO is repaired by the dissociated O atom. The combined effect of the VO and N is related to the position of N. Although the substitutional N (NS) can delocalize electrons at the VO, it cannot improve the activity and stability. The interstitial N (Ni) located below the VO forms Ni-Ti bonds with two Ti atoms adjacent to the VO. This can delocalize the electrons near the VO, and the five-fold-coordinated titanium (Ti5C) replaces the VO as the active center, thus enhancing the reactivity and protecting the VO. Further research indicates that the co-modification of the VO and Ni improves photoexcited electron transfer and distribution, which would in turn promote CO2 reduction. The results of this study propose that surface defect engineering holds great promise for boosting CO2 photoreduction by integrating functions of electron density modulation and catalysis.

Amorphous TiO2 as a multifunctional interlayer for boosting the efficiency and stability of the CdS/cobaloxime hybrid system for photocatalytic hydrogen production.

The construction of both highly efficient and stable hybrid artificial photosynthetic systems comprising semiconductors as photosensitizers and abundant metal-based molecular complexes as cocatalysts for photocatalytic H2 generation remains challenging. Herein, we report an effective and stable CdS/cobaloxime hybrid system prepared by inserting an amorphous TiO2 (a-TiO2) interlayer with adjustable thickness and by covalently-surface-attaching molecular cobaloxime catalysts. This hybrid system displayed outstanding photocatalytic H2 production and reached a maximum rate of ∼25 mmol g-1 h-1, which was ∼20.8 times that of pure CdS and 1.7 times that of the CdS/cobaloxime system without an a-TiO2 interlayer (CdS/Co). More importantly, 6 nm a-TiO2 uniformly coated CdS nanorods (CdS NRs) exhibited exceptional 200 h long-term catalytic behaviour under ≥420 nm visible light irradiation. However, the H2 production performance of the CdS/Co hybrid system decreased significantly over 10 h. Density functional theory (DFT) calculations indicated that the a-TiO2 surface can provide abundant bonding sites for the effective immobilization of molecular catalysts. Moreover, Mott-Schottky electrochemical measurements and femtosecond transient absorption spectroscopy revealed that the a-TiO2 interlayer had favourable band levels that could fasten the photoexcited electron transfer from CdS to molecular cobaloxime and could extract holes with intraband electronic states generated by defects, thus prohibiting CdS photocorrosion and improving the stability of the hybrid system. This study proposes a strategy for designing multifunctional interlayers for the effective immobilization of molecular catalysts, beneficial regulation of photoinduced charge carriers, and improvement of the stability as well as facilitation of the construction of artificial photosynthetic hybrid systems with high efficiency and durability.

Zn2GeO4-x/ZnS heterojunctions fabricated via in situ etching sulfurization for Pt-free photocatalytic hydrogen evolution: interface roughness and defect engineering.

Interface engineering has been regarded as a promising strategy for enhancing the catalytic activities of heterojunction photocatalysts. Herein, we have adopted an in situ etching sulfurization method to construct a Zn2GeO4-x/ZnS intimate heterojunction, which exhibited excellent photocatalytic H2 production in the absence of a Pt co-catalyst. Distinctively, TEM and HRTEM measurements showed that the interface of the Zn2GeO4-x/ZnS heterojunction became rough (topologically) due to in situ etching sulfurization, and etching was found to be strongly dependent on the crystal orientation. Moreover, the surface of the Zn2GeO4 nanorods from flat (100) planes evolved into an irregular coastline-like structure topologized with (110) and (113) high-index planes. ICP and elemental distribution measurements indicated that during the precipitation of ZnS via in situ etching sulfurization, the migration and dissolution of Zn and Ge ions on the Zn2GeO4(100) plane led to the roughening of the interface and the evolution of crystal planes. XPS and EPR analyses showed that Zn2GeO4-x/ZnS contained more oxygen vacancies with structural evolution. The theoretical calculations demonstrated that oxygen defects were prone to be generated on the Zn2GeO4(113) plane and formed the Ge3c3+-VO complexes. Compared to the inactive (100) plane, etching caused the Zn2GeO4(110) planes to have a higher number of threefold coordinated germanium (Ge3c4+) and (113) high-index planes that possessed abundant active sites (Ge3c3+-VO complexes), which dramatically decreased the barrier and reaction energy of H2O dissociation. This work not only provides fundamental insights into the topological interface evolution and facet-dependent defect distribution but also offers a strategy for the design of efficient photocatalysts for H2 production without the use of Pt as a co-catalyst based on a multifunctional interface.

Synergistic engineering of architecture and composition in NixCo1-xMoO4@CoMoO4 nanobrush arrays towards efficient overall water splitting electrocatalysis.

Implementing the hierarchical structures of non-noble-metal-based electrocatalysts and modulating their composition can help accelerate surface reactions and fulfill the promise of renewable energy devices via water splitting. Herein, molybdenum-based compounds are constructed on activated nickel foam (act-NF) by a one-step hydrothermal growth. The product generated on the act-NF is NixCo1-xMoO4@CoMoO4, with a novel 3D hierarchical heterostructure, wherein the one-dimensional CoMoO4 nanorods are hierarchically integrated with the two-dimensional NixCo1-xMoO4 nanosheets (NCMO@CMO/act-NF). The formation of NixCo1-xMoO4@CoMoO4 attributes to the release and diffusion of Ni2+ from act-NF. Heterogeneous NixCo1-xMoO4@CoMoO4 has compositional differences, and synergistic interaction between cobalt and nickel results in the modulated electronic states. Meanwhile, the hierarchical structure facilitates the exposure of active sites. Combining these two advantages, NCMO@CMO/act-NF presents a low η10 value of 61 and 180 mV in 1.0 M KOH for the HER and OER, respectively, and it shows a low cell voltage of 1.46 V for overall water splitting with robust stability. DFT calculations reveal that Ni doping leads to the charge depletion of Co, which further optimizes the d-band center of metal sites and tunes the adsorption of adsorbates to facilitate the water splitting reaction. Thus, a promising strategy of incorporating the nanostructure design with compositional modulation is presented to develop functional materials for energy conversion.

Bimetallic NiMoN Nanowires with a Preferential Reactive Facet: An Ultraefficient Bifunctional Electrocatalyst for Overall Water Splitting.

Faceted nanomaterials with highly reactive exposed facets have been the target of intense researches owing to their significantly enhanced catalytic performance. NiMoN nanowires with the (100) facet preferentially exposed were prepared by an in situ N/O exchange and the morphology tuned by using a rationally designed NiMoO4 precursor. The facet-tuned NiMoN nanowires exhibited excellent electrocatalytic activity for the hydrogen evolution reaction (HER) under both alkaline and acidic conditions that was comparable to that of noble metal platinum. DFT calculations further revealed that the catalytic activity of NiMoN nanowires towards HER on the (100) reactive facet is significantly greater than that on the (001) or (101) facets, owing to the low adsorption free energy of H* (ΔGH* ) on the (100) facet. The NiMoN nanowires also demonstrated outstanding activity towards the alkaline oxygen evolution reaction and an excellent durable activity for overall water splitting, with a cell potential as low as 1.498 V at 20 mA cm-2 . This work provides insights into improving electrocatalytic activity and developing advanced non-noble metal bifunctional electrocatalysts.

Solid-Solution Anion-Enhanced Electrochemical Performances of Metal Sulfides/Selenides for Sodium-Ion Capacitors: The Case of FeS2- xSe x.

Transition-metal sulfides/selenides are explored as advanced electrode materials for nonaqueous sodium-ion capacitors, using FeS2- xSe x as an example. A solid solution of S/Se in FeS2- xSe x allows it to combine the high capacity of FeS2 and the good diffusion kinetics of FeSe2 together, thereby exhibiting excellent cycle stability (∼220 mA h g-1 after 6000 cycles at 2 A g-1) and superior rate capability (∼210 mA h g-1 at 40 A g-1) within 0.8-3.0 V. These results are much better than those of FeS2 and FeSe2, confirming the advantages of S/Se solid solution, as supported by EIS spectra, DFT calculations, and electronic conductivity. As FeS2- xSe x is paired with the activated carbon (AC) as Na-ion capacitors, this device is also better than sodium-ion batteries of FeS2- xSe x//Na3V2(PO4)3 and sodium-ion capacitors of metal oxides//AC, particularly at high rates. These results open a new door for the applications of sulfides/selenides in another device of electrochemical energy storage.

Critical Role of Water and Oxygen Defects in C-O Scission during CO2 Reduction on Zn2GeO4(010).

Exploration of catalyst structure and environmental sensitivity for C-O bond scission is essential for improving the conversion efficiency because of the inertness of CO2. We performed density functional theory calculations to understand the influence of the properties of adsorbed water and the reciprocal action with oxygen vacancy on the CO2 dissociation mechanism on Zn2GeO4(010). When a perfect surface was hydrated, the introduction of H2O was predicted to promote the scission step by two modes based on its appearance, with the greatest enhancement from dissociative adsorbed H2O. The dissociative H2O lowers the barrier and reaction energy of CO2 dissociation through hydrogen bonding to preactivate the C-O bond and assisted scission via a COOH intermediate. The perfect surface with bidentate-binding H2O was energetically more favorable for CO2 dissociation than the surface with monodentate-binding H2O. Direct dissociation was energetically favored by the former, whereas monodentate H2O facilitated the H-assisted pathway. The defective surface exhibited a higher reactivity for CO2 decomposition than the perfect surface because the generation of oxygen vacancies could disperse the product location. When the defective surface was hydrated, the reciprocal action for vacancy and surface H2O on CO2 dissociation was related to the vacancy type. The presence of H2O substantially decreased the reaction energy for the direct dissociation of CO2 on O2c1- and O3c2-defect surfaces, which converts the endoergic reaction to an exoergic reaction. However, the increased decomposition barrier made the step kinetically unfavorable and reduced the reaction rate. When H2O was present on the O2c2-defect surface, both the barrier and reaction energy for direct dissociation were invariable. This result indicated that the introduction of H2O had little effect on the kinetics and thermodynamics. Moreover, the H-assisted pathway was suppressed on all hydrated defect surfaces. These results provide a theoretical perspective for the design of highly efficient catalysts.

Biphase-Interface Enhanced Sodium Storage and Accelerated Charge Transfer: Flower-Like Anatase/Bronze TiO2/C as an Advanced Anode Material for Na-Ion Batteries.

Flower-like assembly of ultrathin nanosheets composed of anatase and bronze TiO2 embedded in carbon is successfully synthesized by a simple solvothermal reaction, followed with a high-temperature annealing. As an anode material in sodium-ion batteries, this composite exhibits outstanding electrochemical performances. It delivers a reversible capacity of 120 mA h g-1 over 6000 cycles at 10 C. Even at 100 C, there is still a capacity of 104 mA h g-1. Besides carbon matrix and hierarchical structure, abundant interfaces between anatase and bronze greatly enhance the performance by offering additional sites for reversible Na+ storage and improving the charge-transfer kinetics. The interface enhancements are confirmed by discharge/charge profiles, rate performances, electrochemical impedance spectra, and first-principle calculations. These results offer a new pathway to upgrade the performances of anode materials in sodium-ion batteries.

Conductive Polymer-Coated VS4 Submicrospheres As Advanced Electrode Materials in Lithium-Ion Batteries.

VS4 as an electrode material in lithium-ion batteries holds intriguing features like high content of sulfur and one-dimensional structure, inspiring the exploration in this field. Herein, VS4 submicrospheres have been synthesized via a simple solvothermal reaction. However, they quickly degrade upon cycling as an anode material in lithium-ion batteries. So, three conductive polymers, polythiophene (PEDOT), polypyrrole (PPY), and polyaniline (PANI), are coated on the surface to improve the electron conductivity, suppress the diffusion of polysulfides, and modify the interface between electrode/electrolyte. PANI is the best in the polymers. It improves the Coulombic efficiency to 86% for the first cycle and keeps the specific capacity at 755 mAh g(-1) after 50 cycles, higher than the cases of naked VS4 (100 mAh g(-1)), VS4@PEDOT (318 mAh g(-1)), and VS4@PPY (448 mAh g(-1)). The good performances could be attributed to the improved charge-transfer kinetics and the strong interaction between PANI and VS4 supported by theoretical simulation. The discharge voltage ∼2.0 V makes them promising cathode materials.

A theoretical study of O2 activation by the Au7-cluster on Mg(OH)2: roles of surface hydroxyls and hydroxyl defects.

Using density functional theory (DFT) calculations, we investigated O2 activation by the Au7-cluster supported on the perfect and hydroxyl defective Mg(OH)2(0001) surface. It is revealed that hydroxyl groups on the perfect Mg(OH)2(0001) surface can not only enhance the stability of the Au7-cluster, but also help the adsorption of the O2 molecule through hydrogen-bonding interactions with the 2nd-layered interfacial Au sites. Density of states (DOS) analysis shows that the d-band centers of the 2nd-layered interfacial Au atoms are very close to the Fermi level, which thereby reduce the Pauli repulsion and promote the O2 adsorption. These two responses make the 2nd-layered interfacial Au atoms favor O2 activation. Interestingly, the surface hydrogen atoms activated by the 1st-layered Au atoms can facilitate the O2 dissociation process as well. Such a process is dynamically favorable and more inclined to occur at low temperatures compared to the direct dissociation process. Meanwhile, the hydroxyl defects of Mg(OH)2(0001) located right under the Au7-cluster can also up-shift the d-band centers of the surrounding Au atoms toward the Fermi level, enhancing its catalytic activity for O2 dissociation. In contrast, the d-band center of Au atoms surrounding the hydroxyl defect near the Au7-cluster exhibits an effective down-shift to lower energies, and therefore holds low activity. These results unveiled the roles of surface hydroxyls and hydroxyl defects on the Au/Mg(OH)2 catalyst in O2 activation and could provide a theoretical guidance for chemists to efficiently synthesize Au/hydroxide catalysts.

Exploring the effects of nanocrystal facet orientations in g-C3N4/BiOCl heterostructures on photocatalytic performance.

Effective separation and migration of photogenerated electron-hole pairs are two key factors to determine the performance of photocatalysts. It has been widely accepted that photocatalysts with heterojunctions usually exhibit excellent charge separation. However, the migration process of separated charges in the heterojunction structures has not been fully investigated. Herein, photocatalysts with heterojunctions are constructed by loading g-C3N4 nanoparticles onto BiOCl nanosheets with different exposed facets (BOC-001 and BOC-010). The g-C3N4 nanoparticles with decreasing size and increasing zeta potential could induce stronger coupling and scattering in the heterojunction. The relationship between the crystal facet orientation in the BiOCl nanosheets and charge separation/effective migration behaviours of the materials is investigated. The visible light photocatalytic activity of the composites is evaluated by methyl orange (MO) and phenol degradation experiments, and the results show that ng-CN/BOC-010 composites exhibit higher photocatalytic performance than that of ng-CN/BOC-001 composites. Both photoelectrochemical and fluorescence emission measurements indicate that the different exposed facets in ng-CN/BiOCl composites could induce the migration of the photogenerated electrons in different ways, but do not significantly alter the separation efficiencies. The separated electrons in ng-CN/BOC-010 undergo a shorter transport distance than that of ng-CN/BOC-001 to reach the surface reactive sites. The study may suggest that the crystal facet orientation in polar semiconductors is a critical factor for designing highly efficient heterojunction photocatalysts.

Structural diversities and related properties of four coordination polymers synthesized from original ligand of 3,3',5,5'-azobenzenetetracarboxylic acid.

Four new coordination polymers, namely [Co(H2O2abtc)(bibp)]n (), {[Mn1.5(Oabtc)(H2O)2]·(H2bmib)0.5·H2O}n (), {[Cd1.5(O2abtc)]·(H2bmib)0.5·2H2O}n (), and {[Cd(nip)(bibp)]·0.5H2O}n (),were constructed under solvothermal conditions in the presence of two bis(imidazole) bridging linkers (bimb = 1,4-bis(2-methylimidazol-1-ylmethyl)benzene, bibp = 4,4'-bis(imidazol-1-yl)biphenyl). The unstable azo ligand of 3,3',5,5'-azobenzenetetracarboxylic acid (H4abtc) could be oxidized and resulted in three oxidized derivatives of H4Oabtc (one N atom was oxidized), H4O2abtc (two N atoms were oxidized), and H2nip (one H4abtc was oxidized to two 5-nitroisophthalic acids). Their structures were determined by single-crystal X-ray diffraction and further characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analysis. Complex exhibited an interestingly 2D + 2D → 3D parallel entangled network based on 4-connected (4(4)·6(2))-sql sheets. Complex was found to be a {Mn3(COO)6} trinuclear SBU based 2D (3,6)-connected (4(3))2(4(6)·6(6)·8(3))-kgd sheet. While complex displays a {Cd3(COO)8} trinuclear SBUs based 3D (4,8)-connected (4(6))2(4(12)·6(12)·8(4))-flu network. Complex can be regard as a {Cd2(COO)2} binuclear SBUs based 6-connected (4(4)·6(11))-6T8 framework. In addition, the magnetic property of complexes , and the luminescence properties of complexes , were investigated.

Structural diversity and magnetic properties of six metal-organic polymers based on semirigid tricarboxylate ligand of 3,5-bi(4-carboxyphenoxy)benzoic acid.

Solvothermal reactions of the semirigid 3,5-bi(4-carboxyphenoxy)benzoic acid (H3BCP) and transitional metal cations with the help of three ancillary bridging imidazole linkers afforded six coordination polymers, namely, [Co(HBCP)(1,4-bib)0.5]n (), {[Mn1.5(BCP)(1,4-bib)0.5(µ2-H2O)(H2O)2]·(1,4-bib)0.5}n (), {[Mn0.5(1,4-bib)(H2O)]·(H2BCP)}n (), {[Fe(BCP)0.5(HCOO)0.5(4,4'-bibp)0.5]·2H2O}n (), [Ni2.5(HBCP)(BCP)(4,4'-bibp)2(µ2-H2O)(H2O)2]n (), and [Ni(HBCP)(1,4-bidb)1.5(H2O)2]n (), (1,4-bib = 1,4-bis(1H-imidazol-4-yl)benzene, 1,4-bidb = 1,4-bis(1-imidazol-yl)-2,5-dimethyl benzene, 4,4'-bibp = 4,4'-bis(imidazol-1-yl)biphenyl). Their structures and properties were determined by single-crystal and powder X-ray diffraction analyses, IR spectra, elemental analyses, thermogravimetric analyses (TGA), and X-ray photoelectron spectroscopy (XPS). Complex displays unusual 2D + 2D→2D parallel entangled networks consisting of (3,4)-connected 3,4L83 sheets. Complex exhibits an interesting 2-fold interpenetrated framework with a trinodal (4,4,6)-connected (3·4·5·6(2)·7)2(3·6·7(4))2(3(2)·4(2)·5(2)·6(2)·7(6)·9) topology. The host network of complex is a 2D 4-connected (4(4)·6(2))-sql sheet. Complex affords unprecedented 3D (4,6,6)-coordinated framework with point symbol of (4(5)·6)(4(8)·6(7))(4(9)·6(3)·8(3))2, in which the 1D helix water chains occupy the void channels. Complex can be regarded as a novel self-penetrating (4,4,4,5)-coordinated framework with point symbol of (4·5(4)·6)2(4·6(5)·7·8(3))2(5·6·7·8(3))2(5(2)·8(3)·9(2)), which contains two interpenetrated (3,4,4,5)-coordinated (4·5(4)·6)2(4·6(5)·7·8(3))2(5·6·7)2(5(2)·8(3)·9(2)) subnets linked by µ2-H2O. Complex shows a 1D ladder chain, which are further assembled into a 3D supramolecular structure via O-HO and ππ interactions. Moreover, magnetic studies indicate that both complex and show antiferromagnetic properties.

Pressure-induced ferroelastic phase transition in SnO2 from density functional theory.

High-pressure ferroelastic transition of rutile- to CaCl2-type SnO2 is investigated within density functional theory and Landau free energy theory. The calculated Landau energy map around the ground state is successfully used to clarify the softening mechanism of B1g mode (order parameter Q) and the coupling mechanism between the soft B1g mode and the soft transverse acoustic (TA) mode (strain ɛ). It is found that the Sn-O-Sn bending induced soft B1g mode effectively slows the excess energy increase caused by bond stretching, while the coupling between the soft B1g mode and the soft TA mode further decreases the energy since the lattice distortion strain ɛ minimizes the SnO6 octahedral distortion. Q induced Landau Gibbs free energy is interpreted as the sum of the bond stretching energy, bending energy, and octahedral distortion energy, while that induced by ɛ is interpreted as the lattice distortion energy.

Syntheses, crystal structures and UV-visible absorption properties of five metal-organic frameworks constructed from terphenyl-2,5,2',5'-tetracarboxylic acid and bis(imidazole) bridging ligands.

The solvothermal reactions of terphenyl-2,5,2',5'-tetracarboxylic acid (H4tptc) and transition metal cations (Ni(II), Mn(II)) afford five novel coordination polymers (CPs) in the presence of four bis(imidazole) bridging ligands (1,3-bimb = 1,3-bis(imidazol-1-ylmethyl)benzene, 1,4-bmib = 1,4-bis(2-methylimidazol-1-ylmethyl)benzene, 4,4'-bibp = 4,4'-bis(imidazol-1-yl)biphenyl, 4,4'-bimbp = 4,4'-bis(imidazol-1-ylmethyl)biphenyl), namely, [M(tptc)(0.5)(1,3-bimb)(H2O)]n (M = Ni for 1, Mn for 2), {[Ni(tptc)(0.5)(1,4-bmib)]·0.25H2O}n (3), {[Ni(tptc)(0.5)(4,4'-bibp)2(H2O)]·2H2O}n (4) and {[Ni(tptc)(0.5)(4,4'-bimbp)(1.5)(H2O)]·H2O}n (5). Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Complexes 1 and 2 are isomorphous and exhibit a 3D (3,4)-connected tfi framework with the point Schläfli symbol of (4·6(2))(4·6(6)·8(3)). Complex 3 shows an unprecedented 3D (4,4)-connected framework with the point Schläfli symbol of (4·6(4)·8(2))2(4(2)·8(4)). Complex 4 displays a novel 2D self-catenating 5-connected network with the Schläfli symbol of (4(6)·6(4)) based on three interpenetrating 4(4)-sql subnets. Complex 5 features a 2D 3-connected 6(3)-hcb network built from interesting chains with loops. To the best of our knowledge, the 3D (4,4)-connected (4·6(4)·8(2))2(4(2)·8(4)) host-framework of 3 and 2D self-catenating 5-connected (4(6)·6(4)) network of 4 have never been documented to date. Moreover, the UV-Visible absorption spectra of complexes 1-5 have been investigated.

The roles of surface structure, oxygen defects, and hydration in the adsorption of CO(2) on low-index ZnGa(2)O(4) surfaces: a first-principles investigation.

The effects of the surface atomic and electronic structures, oxygen defects, and hydration on CO2 adsorption on ZnGa2O4(100), (110), and (111) surfaces were studied using density functional theory (DFT) slab calculations. For the perfect (100) surface, the most stable adsorption state involved the Zn-O-Ga bridge site, with an adsorption energy of 0.16 eV. In the case of the (110) and (111) surfaces, the strongest binding occurred on the Zn-O bridge sites, with much lower adsorption energies of -0.22 eV and -0.35 eV, respectively. In addition, the perfect surfaces showed CO2 activation ability, but dissociation adsorption could not proceed. The oxygen vacancies on these three surfaces (1) made the metal sites beside them carry less positive charge and further reduced the adsorption energies on these metal sites, and (2) created efficient adsorption sites that allowed even dissociative adsorption. The most favorable molecular and dissociative adsorption states both involved the O3c vacancy site of the (100) surface, and these two processes were spontaneous with adsorption energies of 0.74 eV and 0.80 eV, respectively. When H2O molecules are present on the perfect and defective surfaces, the generation of hydrogen bonds between H2O and CO2 would slightly enhance the stability of adsorption (except for that on the surface), making them energetically favorable. However, the co-adsorption of H2O could also increase the energy barriers for the decomposition reactions on the defective surfaces, making them kinetically unfavorable. Furthermore, the oxygen vacancy defects showed good activity for H2O adsorption and decomposition, as well. Thus, when both H2O and CO2 were present in the adsorption system, H2O would compete with CO2 for the oxygen vacancy sites and further decrease the amount of CO2 adsorption and decomposition. These findings have important implications for the decomposition of CO2 on the ZnGa2O4 surfaces and can provide theoretical guidance for chemists to efficiently synthesize ZnGa2O4 catalysts.