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Titanium-based metal–organic framework as visible-light activated chemiresistive sensor.

A semiconducting metal–organic crystalline nanotube array (MO-CNA) was constructed by the induction of Pb⋯S secondary interactions, exhibiting highly selective and sensitive NO2 sensing with a low limit of detection.

The construction of hydrophobic nanochannel with hydrophilic sites for bionic devices to proximally mimick real bio-system is still challenging. Taking the advantages of MOF chemistry, a highly oriented CuTCPP thin film has been successfully reconstructed with ultra-thin nanosheets to produce abundant two-dimensional interstitial hydrophobic nanochannels with hydrophilic sites. Different from the classical active-layer material with proton transport in bulk, CuTCPP thin film represents a new type of active-layer with proton transport in nanochannel for bionic proton field-effect transistor (H+ -FETs). The resultant device can reversibly modulate the proton transport by varying the voltage on its gate electrode. Meanwhile, it shows the highest proton mobility of ≈9.5×10-3 cm2 V-1 s-1 and highest on-off ratio of 4.1 among all of the reported H+ -FETs. Our result demonstrates a powerful material design strategy for proximally mimicking the structure and properties of bio-systems and constructing bionic electrical devices.

The hydrolysis of earth-abundant AlIII has implications in mineral mimicry, geochemistry and environmental chemistry. Third-order nonlinear optical (NLO) materials are important in modern chemistry due to their extensive optical applications. The assembly of AlIII ions with π-conjugated carboxylate ligands is carried out and the hydrolysis and NLO properties of the resultant material are studied. A series of Al32 -oxo clusters with hydrotalcite-like cores and π-conjugated shells are isolated. X-ray diffraction revealed boundary hydrolysis occurs at the equatorially unsaturated coordination sites of AlIII ions. Charge distribution analysis and DFT calculations support the proposed boundary substitution. The Al32 -oxo clusters possess a significant reverse saturable absorption (RSA) response with a minimal normalized transmittance up to 29 %, indicating they are suitable candidates for optical limiting (OL) materials. This work elucidates the hydrolysis of AlIII and provides insight into layered materials that also have strong boundary activity at the edges or corners.

A new conductive coordination polymer (CCP), Ag(SPh–NO2)·AgNO3, with a three-dimensional (3D) non-porous structure composed of a unique 2D inorganic layered structure linked by an organic linker, was reported. The 3D CCP Ag(SPh–NO2)·AgNO3 exhibits semiconductor behavior, with electronic conductivity as high as 2.7 × 10−6 S cm−1 at 295 K, which is comparable to the vast majority of highly conductive 3D coordination polymers. The chemiresistive humidity sensing ability of Ag(SPh–NO2)·AgNO3 was studied over a wide relative humidity (RH) range (10–90% RH) at room temperature. The sensor showed exceptionally high moisture responsiveness, with a 106-fold increase in response at 90% RH and excellent sensitivity to humidity in the range of 10–80% RH. The sensing mechanism was further studied using alternating current (AC) impedance spectroscopy and direct current (DC) instantaneous reverse polarity experiments. The exceptionally high response of the Ag(SPh–NO2)·AgNO3-based sensor at high RH is attributed to the periodic arrangement of the ion species via reversible coordination bonds in the structure. H3O+ and Ag+ are easily formed on its hydrophilic surface, through which the free transport of ionic carriers dominates the conductivity change. Using density functional theory (DFT) calculations, it is further demonstrated that the reversibly coordinated AgNO3 in the structure can be easily occupied by water molecules, which is thermodynamically spontaneous in the presence of humidity. Furthermore, the functional AgNO3 groups and their reversible coordination bonds enabled Ag(SPh–NO2)·AgNO3 to show exceptionally high moisture responsiveness.

A bilayer hexagonal wheel Sn18-oxo cluster, as the largest tin-oxo wheel to date, was successfully constructed by structural directing of organic ligands. Moreover, the ligands show important effects on the electronic structure and third-order nonlinear optical properties of the Sn18-oxo wheel, which is demonstrated by detailed theoretical calculations.

The vital role of the spin polarization in the electrocatalytic N2 reduction reaction (eNRR) stimulates us to explore the potential of the newly discovered two-dimensional (2D) vdW ferromagnetic materials as NRR electrocatalysts. Here, using density functional theory (DFT) computations, we report the first theoretical prediction that the single-layer defective Fe3GeTe2 acts as a 2D ferromagnetic material toward the NRR with outstanding electrocatalytic activity and high selectivity. Notably, all six hydrogenation steps are exothermic and spontaneous. The highly centralized spin-polarization on the exposed Fe4 center in defective Fe3GeTe2 leads to strong backdonation and substantial activation of the NN triple bond. Moreover, the metallic character of the defective Fe3GeTe2 ensures high-speed transport of carriers. This work not only provides a quite promising electrocatalyst for the NRR but also promotes the application of emerging 2D ferromagnets in the field of energy conversion.

Present herein is the first example of aluminium nanoring assembly by fatty acids. And the auxiliary alcohol sites can be modified either by monohydric alcohols (AlOC-33 to AlOC-35) or diols (AlOC-36 to AlOC-38). The monohydric alcohol modified ten-membered aluminium (Al10) rings are coplanar, while the diol modified ones possess a saddle-shaped configuration. Interestingly, the diol modified Al10 ring (AlOC-36) can convert into a coplanar ring (AlOC-33-B). AlOC-33-B possesses a similar molecular structure but a different supramolecular structure with AlOC-33. The structural transformation is confirmed to be a thermodynamically spontaneous process through density-functional theory (DFT) calculations.

Many metal-organic cages (MOCs) and a few hydrogen-bonded organic cages (HOCs) have been investigated, but little is reported about cooperative self-assembly of MOCs and HOCs. Herein, we describe an unprecedented MOC&HOC co-crystal composed of tetrahedral Ti4 L6 (L=embonate) cages and in-situ-generated [(NH3 )4 (TIPA)4 ] (TIPA=tris(4-(1H-1,2,4-triazol-1-yl)phenyl)amine) cages. Chiral transfer is observed from the enantiopure Ti4 L6 cage to enantiopure [(NH3 )4 (TIPA)4 ] cage. Two homochiral supramolecular frameworks with opposite handedness (PTC-235(Δ) and PTC-235(Λ)) are formed. Such MOC&HOC co-crystal features high stability in water and other solvents, affording single-crystal-to-single-crystal transformation to trap CH3 CN molecules and identify disordered NH4 + cations. A tablet pressing method is developed to test the third-order nonlinear optical property of KBr-based PTC-235 thin film. Such a thin film exhibits an excellent optical limiting effect.

We report the first example of carbon nanotube (CNT)-like assembly of the titanium (Ti) framework, Ti oxo inorganic cluster (Ti6O6) hexagonal rings into a titanium oxide (Ti–O) nanotube, prepared b...

The development of metal-organic frameworks (MOFs) with nonlinear optical (NLO) properties is of pronounced significance for optical devices. Herein, a series of 2D MOFs ZnTPyP(M) (TPyP = 5,10,15,20-tetrakis(4-pyridyl)porphyrin, M = Cu, Ni, Mn, H2) films with [010]-orientation growth composed of ultrathin nanosheets from a pyridylporphyrinic ligand are first obtained by using a liquid-phase epitaxial (LPE) layer-by-layer (lbl) growth approach. ZnTPyP(M) films show a giant nonlinear optical limiting (OL) response and can be modulated by tuning the type of metalloporphyrinic ligands. As a result, ZnTPyP(Cu) film exhibits the highest nonlinear absorption coefficient of 5.7 × 10-6 m/W compared to other reported NLO materials. Density functional theory calculations were consistent with the experimental results, revealing that the tunable π-π* local excitation and the increased delocalization of the metalloporphyrinic group regulate the NLO performance of ZnTPyP(M) films. These findings provide new insight into the effect of 2D porphyrinic MOFs toward the NLO response and offer new film candidates for nonlinear OL application.

Recently, carbon dioxide capture and conversion, along with hydrogen from renewable resources, provide an alternative approach to synthesis of useful fuels and chemicals. People are increasingly interested in developing innovative carbon dioxide hydrogenation catalysts, and the pace of progress in this area is accelerating. Accordingly, this perspective presents current state of the art and outlook in synthesis of light olefins, dimethyl ether, liquid fuels, and alcohols through two leading hydrogenation mechanisms: methanol reaction and Fischer-Tropsch based carbon dioxide hydrogenation. The future research directions for developing new heterogeneous catalysts with transformational technologies, including 3D printing and artificial intelligence, are provided. Carbon dioxide (CO2) capture and conversion provide an alternative approach to synthesis of useful fuels and chemicals. Here, Ye et al. give a comprehensive perspective on the current state of the art and outlook of CO2 catalytic hydrogenation to the synthesis of light olefins, dimethyl ether, liquid fuels, and alcohols.

Atomization of noble metals enable their electrocatalysis applications with low cost, whereas the isolated mononuclear site after atomization might lead leads to limited performance. Herein, we present a general strategy of atomically confined alloying (ACA) to synthesize an electrocatalyst of single atom iridium-trapping cobalt nanosheets with dual-reactive Ir–Co sites. The atomic Ir@Co nanosheets (1.7 wt% Ir) exhibit excellent oxygen evolution reaction (OER) performance with a small overpotential (273 mV at 10 mA cm−2) and high stability, higher than that of the Ir/C catalyst (290 mV at 10 mA cm−2). More importantly, density functional theory (DFT) calculations combined with experiments demonstrated that water oxidation proceeded on atomic Ir@Co nanosheets via a dinuclear tandem mechanism, in which Ir–Co dual sites cooperatively worked in favour of the sequential transfer from Co–OH* to Ir–O* via a Co–O–Ir intermediate, and stabilization of OOH* species by hydrogen bonding interaction. The cooperative mechanism based on a dinuclear electrocatalyst by ACA is hoped to open up more possibilities of single atom noble metal electrocatalysts for various applications.

Hybrid organic–inorganic halide perovskite solar cells have recently attracted much attention because of their highly efficient photovoltaic performance. However, perovskite solar cells suffer from intrinsic instabilities, which limit their commercial applications. In this study, we partially substituted the methyl-ammonium (MA) cation in MA lead iodide perovskite (MAPbI3) and investigated the geometric structures and electronic and optical properties by first-principles calculations to determine their thermodynamic stabilities and optical band gaps. The results suggest that substitution of the Az cation in the A-site can enhance the stability of the MA1−xAzxPbI3 system. However, the formation energies indicate that the MA1−xCyxPbI3 series is less stable. The estimated power conversion efficiency of MA0.50Az0.50PbI3 is 23.06%, which is higher than that of MAPbI3. Notably, MA1−xAzxPbI3 (0.50 < x < 0.75) is predicted to be a promising candidate for photovoltaic applications because it has the highest theoretical power conversion efficiency, which is attributed to its optimal band gap. These results suggest that an organic cation mixing strategy can be used to tune the stability, band gap, and photovoltaic performance of hybrid perovskites, which will be particularly useful for designing light-harvesting materials for perovskite solar cells.

Mixed-cation lead halide perovskites have emerged as a new class of promising photovoltaic materials for perovskite solar cells. Formamidinium (FA), methylammonium (MA), and Cs cations are widely studied in the field of mixed-cation hybrid halide perovskites. In this work, we have investigated ethylammonium (CH3CH2NH3, EA) as an alternative cation to explore the stabilities and electronic properties of mixed MA1−xEAxPbI3 perovskites. The results indicate that replacing MA with EA is a more effective way to improve the stabilities of the mixed MA1−xEAxPbI3 perovskites except for MA0.75EA0.25PbI3. The band gap of MA1-xEAxPbI3 slightly increases with x from 0.25 to 1.00, which is quite different from the MA–FA mixed-cation perovskites. The results indicate that the c axis distortion of the Pb–I–Pb bond angles can play a greater role in tuning the band gap. Moreover, the mixed MA1−xEAxPbI3 perovskites show comparable absorption abilities in the visible light region to the pure MAPbI3 structure. We hope that our study will be greatly helpful for further experiments to find more efficient perovskite materials in the future.

Developing efficient and inexpensive oxygen evolution reaction (OER) catalysts is one of the critical issues in energy storage and conversion technology. Herein, an oriented thin film of 3-D MOF Co/Ni(BDC)2TED (BDC = 1,4-benzenedicarboxylate; TED = triethylenediamine) nanosheet arrays is first obtained on Cu foam by a liquid-phase epitaxial layer-by-layer growth approach. The obtained thin film of bimetallic MOF nanosheet arrays has preferred growth with [001]-orientation and strong adhesion on the substrates without the use of binder materials, which provides more accessible active sites for electrocatalytic performance. The OER activity of such surface-mounted MOF nanosheet arrays can be optimized effectively via tuning the thicknesses and Co/Ni ratios. The Co/Ni(BDC)2TED grown on Cu foam with 40 cycles at a Co/Ni ratio of 1/1 shows superior OER activity with required overpotentials of 260 and 287 mV to achieve current densities of 10 and 50 mA cm−2 and excellent stability. The experiments and theoretical calculations reveal that the synergistic effect of Co/Ni and rich metal sites dominated by nanosheet interfaces improve the electrocatalytic activity. This work provides more insight into the OER activity of the MOF thin film as an electrode material and presents a new strategy for developing promising highly efficient electrocatalysts in practical applications.

Lead-free hybrid perovskites have attracted great attention as environmentally friendly light absorber layers. In this work, we report on Te-based double perovskites A2TeI6 (A = Tl, K, NH4, Rb, Cs, CH3NH3, and CH(NH2)2) as potential candidates for optoelectronic applications. The structural stability and electronic and optical properties of these Te-based double perovskite materials are investigated by using first-principles calculations. These Te-based double perovskites exhibit good structural stability, tunable band gap, and strong optical absorption. These Te-based double perovskites show promising optoelectronic properties, and may be potential candidates for photovoltaic applications. Our calculated results can provide a deep insight into developing lead-free perovskite solar cells.

The design and construction of efficient electrode materials are significant for electrochemical energy conversion and storage technologies. The oxygen evolution reaction (OER) is a key process in water splitting devices and metal–air batteries. Herein, we report conductive metal–organic framework (C-MOF) nanowire arrays on carbon cloth as a promising electrocatalyst for OER. The pyrolysis-free C-MOF electrocatalyst can maintain intrinsic molecular active sites in the MOFs. The as-prepared electrode possesses overpotentials of ∼213 and 300 mV at 10 and 150 mA cm−2 and long-term stability in 1 M KOH, respectively. Control experiments and Fourier-transform extended X-ray absorption fine structure (EXAFS) and Mossbauer spectra indicate that the Fe doped in the Ni-based MOFs may serve as highly effective OER active sites. Density functional theory (DFT) calculations reveal an unusual self-adaptable property of the Fe active sites, which enables the OER intermediates to generate additional hydrogen bonds with the neighboring layer, thus lowering the free energy in the OER process. Our findings may provide an alternative method for developing MOF electrocatalysts in frontier potential applications.

Perovskite photovoltaic materials are gaining significant attention due to their excellent photovoltaic properties. In this study, density functional theory calculations were performed to investigate the structure and electronic and optical properties of CsGeI3 under hydrostatic strain. The results show that the band gap of CsGeI3 can be tuned from 0.73 eV to 2.30 eV under different strain conditions. The results indicate that the change in the band gap under strain is likely to be determined by the Ge–I–Ge bond angle. Interestingly, the length of the short Ge–I bond remains unchanged, whereas that of the long Ge–I bond exhibits an evident increment with strain ranging from −4% to 4%. A suitable band gap (1.36 eV) of CsGeI3 can be obtained under a strain of −1%. Both the calculated elastic constants and the phonon spectrum imply that this structure is stable under the abovementioned condition. Bandgap narrowing induces a red shift of the light absorption spectrum of CsGeI3 by extending the onset light absorption edge. These results are important for understanding the effects of strain on the halide perovskites and guiding the experiments to improve the photovoltaic performance of the perovskite solar cells.

In recent years, all-inorganic lead-free CsGe0.5Sn0.5I3 has been proposed as a promising candidate for perovskite solar cells. In the present study, the stability and optoelectronic properties of the CsGeX3 and Cs2GeX6 (X = Cl, Br, I) compounds and mixed CsGe1-xSnxI3 perovskites have been explored using first-principles calculations. The results indicate that the CsGeX3 compounds and Cs2GeCl6 are stable at room temperature, while Cs2GeBr6 and Cs2GeI6 are unstable. A phase transition is revealed for the CsGe1-xSnxI3 systems when the ratio of Sn doping is over 0.53. In addition, both CsGe2/3Sn1/3I3 and CsGe0.25Sn0.75I3 show the potential tendency for phase segregation. CsGe2/3Sn1/3I3 and CsGe0.25Sn0.75I3 have suitable band gaps and exhibit strong absorption coefficients, which are the promising candidates for solar cells. Our work demonstrates the favorable optoelectronic properties of novel lead-free mixed Ge–Sn perovskites for single-junction solar cells.

Photo/electrochemical CO2 splitting is impeded by the low cost-effective catalysts for key reactions: CO2 reduction (CDRR) and water oxidation. A porous silicon and nitrogen co-doped carbon (SiNC) nanomaterial by a facile pyrolyzation was developed as a metal-free bifunctional electrocatalyst. CO2 -to-CO and oxygen evolution (OER) partial current density under neutral conditions were enhanced by two orders of magnitude in the Tafel regime on SiNC relative to single-doped comparisons beyond their specific area gap. The photovoltaic-driven CO2 splitting device with SiNC electrodes imitating photosynthesis yielded an overall solar-to-chemical efficiency of advanced 12.5 % (by multiplying energy efficiency of CO2 splitting cell and photovoltaic device) at only 650 mV overpotential. Mechanism studies suggested the elastic electron structure of -Si(O)-C-N- unit in SiNC as the highly active site for CDRR and OER simultaneously by lowering the free energy of CDRR and OER intermediates adsorption.

In order to probe into the roles of the promoters Pt, Ru and B in inhibiting the deactivation of Co catalysts in FTS reactions, the adsorption ability of neighboring surface C and subsurface C atom around the promoters (Pt, Ru and B), and the mechanisms of surface C diffusion, accumulation, hydrogenation and penetration are examined by density functional theory calculations over the promoters Pt, Ru and B-modified Co catalysts, as well as the pure Co catalysts. Our results clearly show that compared to Co catalysts, both PtCo and RuCo bimetallic catalysts promote surface C hydrogenation, and inhibit surface C diffusion, accumulation and penetration, and therefore the ability of resistance toward deactivation and the stability of Co-based catalysts are enhanced; the promoter B cannot effectively improve the ability of resistance toward deactivation. Thus, the sequence for resistance toward deactivation of Co-based catalyst is BCo

The electrochemical CO2 reduction (ECDRR), as a key reaction in artificial photosynthesis to implement renewable energy conversion/storage, has been inhibited by the low efficiency and high costs of the electrocatalysts. Herein, we synthesize a fluorine-doped carbon (FC) catalyst by pyrolyzing commercial BP 2000 with a fluorine source, enabling a highly selective CO2 -to-CO conversion with a maximum Faradaic efficiency of 90 % at a low overpotential of 510 mV and a small Tafel slope of 81 mV dec-1 , outcompeting current metal-free catalysts. Moreover, the higher partial current density of CO and lower partial current density of H2 on FC relative to pristine carbon suggest an enhanced inherent activity towards ECDRR as well as a suppressed hydrogen evolution by fluorine doping. Fluorine doping activates the neighbor carbon atoms and facilitates the stabilization of the key intermediate COOH* on the fluorine-doped carbon material, which are also blocked for competing hydrogen evolution, resulting in superior CO2 -to-CO conversion.

Two-dimensional (2D) hydrogen evolution reaction (HER) electrocatalysts have attracted great attention due to their unique electronic properties and high activities. Recently, a new 2D monolayer material of MoSi2N4 has been successfully synthesized and its semiconducting property and excellent ambient stability have also been demonstrated (Science 2020, 369, 670). Here, a systematic screening of catalysts for HER among N- and Si-defective MoSi2N4-supported single non-precious transition metal (TM) and non-metal (NM) atom catalysts is performed by means of density functional theory (DFT) calculations. Interestingly, the single O/P/Fe/Nb atom doped N-(Si-) defective MoSi2N4 monolayer were found to possess excellent HER performance presenting a near-zero ΔGH, which is comparable to or even better than the state-of-the-art Pt-based materials. Moreover, the novel HER activities of some TM doped structures were explained by the “states filling” model. The energy level of the first available unoccupied states for accommodating hydrogen drops after the introduction of TM atom, which modulates the hydrogen binding strength. This work opens the door for the application of MoSi2N4 monolayer and other related 2D materials in the field of energy conversion.

MoS2, as a low-cost catalyst for hydrogen evolution reaction (HER), suffers from poor catalytic performance on the basal plane. Herein, by doping 19 main-group elements on the S-defective MoS2 nanosheet, the most promising MoS2-based catalysts for the HER are screened with high-throughput density functional theory (DFT) calculations. Remarkably, the doping of main-group elements except chalcogens can improve the activity of the MoS2 basal plane to a certain extent. The S-defective MoS2 monolayer doped with In/Ge atom (In3@MoS2 and Ge3@MoS2) show excellent HER performance, and their reaction barrier is even lower than that of commercial Pt/C catalyst. In In3@MoS2 and Ge3@MoS2, the In/Ge atoms act as electron donors to increase the unoccupied anti-bonding orbital, which enhances the interaction of In/Ge-H bonding. On the other hand, the unique co-existence of electron-depletion and electron-accumulation regions near In/Ge atoms enables the adsorption of free radical H to be moderate. Moreover, the In/Ge atoms also increase the conductivity of MoS2, especially the In atom brings a new impurity state near the Fermi level. This work presents a promising strategy for exploiting high-performance MoS2-based catalysts for HER, and would stimulate more researchers to optimize other two-dimensional materials by doping main-group elements for HER.

In recent years, all-inorganic lead-free double perovskites as promising photovoltaic materials have received great attention. In this study, we have investigated the stability, electronic and optical properties of the pure and mixed halide Ti-based double perovskites. The calculated lattice parameters of the pure Ti-based double perovskites agree well with the available experimental values. These Ti-based double perovskites show good stability based on the calculations of their formation energies. The predicted band gaps of Cs2TiX6 (X = Cl, Br, I) within the GGA + U framework are in good agreement with their experimental values. Moreover, we find that the band gap increases slightly when inorganic cation changes from K to Rb and Cs in A2TiCl6. The electronic and optical properties can be tuned by changing the concentration of doping Cl. Cs2TiI2Cl4 has a suitable direct band gap with 1.60 eV, which is considered as an ideal candidate material for single-junction solar cells. Our study shows that the mixed halide Ti-based double perovskites can become nontoxic and environmentally stable materials with excellent optoelectronic properties for applications in perovskite solar cells.

Although numerous superior nonlinear optical (NLO) crystals for the UV-vis to the near-infrared (IR) region have been established, the development of an efficient NLO material capable of broadband second harmonic generation (SHG) in the mid-IR region is still a big challenge. In this work, we performed hybrid functional calculations to accurately assess the mid-IR NLO capabilities of a group of I3–V–VI4 compounds (with I = Ag or Cu, V = P or As, and VI = S or Se). The linear and nonlinear optical properties of these crystals were predicted and analyzed. This group of compounds display moderate optical anisotropy of refraction (0.1 > Δn > 0.03) to fulfill the phase-matching conditions. In particular, the static SHG coefficients of Cu3AsS4, Ag3PSe4 and Cu3PSe4 are predicted to be about twice that of the benchmark AgGaSe2. A detailed analysis of their precise electronic structures and local dipole moments suggests that it is the coupling of the large dipole moment vector of the constituent asymmetry [I–VI4] tetrahedron and the strong covalent character between V and VI ions that contributes to the large SHG response. These candidates would promote the development of the mid-IR NLO functional materials.

The oxygen evolution reaction (OER) is known to be the bottleneck of water-splitting. Ag3PO4 is a highly efficient visible light photocatalyst for dye degradation and water oxidation to O2, with a higher OER rate than BiVO4 and WO3. Despite extensive studies on Ag3PO4, the surface properties including surface electronic states, reaction sites and mechanisms of OER on Ag3PO4 surfaces are not clear at present. Herein, we reported a comparative first-principles density functional theory study of the bulk, surface properties and the mechanism of OER on the three primary low index facets of Ag3PO4: (100), (110) and (111). We revealed for the first time that the rate-limiting step of the OER on Ag3PO4 (100), (110) and (111) surfaces is the dehydrogenation of HO* (HO* → O* + H+ + e−), which is different from most reported metal oxides and nitrides like TiO2 and g-C3N4. The OER process on the (100) surface tends to proceed by following a different mechanism as that on the (110) and (111) surfaces. The illumination of the Ag3PO4 (100), (110), and (111) surfaces with solar light provides enough overpotential for the OER to proceed spontaneously. In particular, the free energy change of removal of the first proton from water on the Ag3PO4 (111) surface is much lower than that on (100) and (110) surfaces, giving an explanation for the experimentally observed higher catalytic activity of the (111) surface. The exposed phosphorus atoms on the Ag3PO4 (111) surface promote the dehydrogenation of H2O and suppress the formation of mid-gap states. Our results are profound for understanding the underlying mechanism of the photocatalytic water oxidation process occurring on Ag3PO4 surfaces, and serve as a foundation for developing new high-performance Ag3PO4 based photocatalysts for water splitting and organic contaminant decomposition.

The finding that transition metals on Mo2C-supported nanocatalysts are promising for water-gas shift (WGS) reactions at room temperature has generated much excitement. However, the progress achieved with computational chemistry in this area is far behind that of experimental studies. Accordingly, density functional theory (DFT) calculations have been used to design the catalytic activity center structure and study the stabilities and catalytic performances of transition metals doped on β-Mo2C(001) surfaces. A new catalyst that comprises atomically dispersed Pt over Mo2C was designed using DFT. The bimetallic Mo2C surfaces doped with single metal Pt exhibit catalytic activities similar to those of the Pt systems for WGS, while demonstrating the advantages of lower costs and higher thermal stabilities. Importantly, the Pt@Mo2C catalyst is more efficient than the pure Pt catalyst for H2 production under the same reaction conditions. Meanwhile, the density of active sites of Pt@Mo2C(001) for H2 production is considerably increased due to its highly dispersed Pt structure. Therefore, Mo and Pt can synergistically increase H2 production. These findings are significantly beneficial for establishing the relationship between the structure and characteristics of the catalyst, understanding the catalytic activities of single-atom catalysts, and gaining insight into the feasibility of developing substitutes for expensive noble metal catalysts.

Development of nonprecious metal-based electrocatalysts with highly efficient oxygen reduction reaction (ORR) has increasingly attracted wide attention in energy conversion and storage systems. In this work, we stepwise grow cobalt chelated COF TpBpy (Co-TpBpy) on silica nanospheres to form core–shell SiO2@Co-TpBpy nanospheres. After calcination high temperatures and removing silica template, cobalt subnanoclusters dispersed in N-doped carbon (N/C) nanocages are obtained for ORR. As a result, the Co-TpBpy-800 nanocages exhibit highly efficient activity on electrocatalytic ORR with 0.831 V of half-wave potential and high stability. Moreover, DFT calculation verifies the resulting unique nanocages reveal an unconventional five-step ORR process in which it skips the intermediate OOH* because the oxygen dissociation and adsorption directly occur on the catalyst surface. The present work will help the development of highly-efficient nonprecious metal-based catalysts for various energy applications.

Recently, 2D ferromagnets have emerged as a hot research topic, especially after the exfoliation of monolayer ferromagnetic Fe3GeTe2 from its bulk structure (Nature 2018, 563, 94; Nat. Mater. 2018, 17, 778). In this work, we systematically report the adsorption behavior of CO, CO2, H2, H2O, NO, and O2 on the pristine and Te-deficient Fe3GeTe2 (FGT and d-FGT) monolayer using hybrid density functional theory. We find that the toxic gas molecules (CO and NO) and O2 molecular are chemically anchored at the surface of the pristine FGT, while the H2O, CO2, and H2 are physically associated with FGT. Interestingly, the introduction of Te deficiency would significantly enhance the covalent interactions between the substrate and the gas molecules, especially for CO2 and H2O, whose adsorption type has evolved from physisorption to chemisorption. Furthermore, the adsorption capacity of (d-)FGT to gas molecules is found to be stronger than that of the two well-studied 2D materials: MoS2 and MXenes. Meanwhile, the adsorption changes the electronic structure of (d-)FGT but does not change the metallicity of FGT. This work provides a valuable reference for the application of 2D metallic ferromagnetic materials in the field of catalysis, sensors, gas storage, and environmental remediation.

LiB3O5 (LBO), although with high nonlinearity, is angular non-phase matched in deep ultraviolet second harmonic generation (SHG) processes due to its small birefringence. The structural configuration distortion is a promising way to improve the birefringence. By means of first principles computations, the effect of strain along the a, b and c-axes on the birefringence of LBO is systematically predicted in this work. We find that the birefringence can be effectively and considerably enhanced (to 0.075 at 266 nm) by applying a rather weak strain (0.42 GPa) along the c-axis. Such a strain-induced increase in the birefringence of LBO is favourable for extending the shortest wavelength that can be produced by means of the SHG process. The results indicate that strain-engineering is an effective strategy for enhancing birefringence, which behaves like a switch to control the generation of deeper coherent light output for some nonlinear optical crystals.

A first-principles study of the structure, elastic and piezoelectric properties of A3BO7 (A = Ga, Al; B = P, As) using the density functional perturbation theory (DFPT) has been performed. The structure-properties relation was established. We found that the piezoelectric constant is highly sensitive to the distortion of crystal structures. The larger A–O–B bridging angle θ is, the smaller piezoelectric stress coefficient e15 will be. The obtained piezoelectric tensor d15 of Ga3AsO7 is −23.9 pC/N, which is more than ten times larger than the d11 of SiO2. The new finding will be useful in the applications of Ga3AsO7 in the piezoelectric devices with high Curie temperature.

New luminescent Ln-MOFs, [Ln2(D-cam)(Himdc)2(H2O)2] (Ln = Eu 1, Tb 2, D-H2cam = D-camphoric acid, H3imdc = 4,5-imidazole dicarboxylic acid) have been synthesized via hydro(solvo)thermal reactions. X-ray single crystal structure analysis reveals that they are isomorphic and both crystallize in the orthorhombic space group Pna21. Compound 1 shows good chemical resistance to both acidity and alkalinity solutions with pH ranging from 2 to 13 and is highly stable in several boiling solvents, which make it potentially useful for wide-range pH sensors, especially in the physiological environment with pH = 6.8–8.0. Careful adjusting of the codoping ratio of Eu3+/Tb3+ into the same framework of 1 affords a mixed Ln-MOF, formulated as [Eu0.7Tb0.3(D-cam)(Himdc)2(H2O)2]3, which has demonstrated to be a viable probe for sensing temperature in a wide temperature range from 100 to 450 K.

A facile electrochemical plating method by means of applying voltage onto zinc electrodes in a 1,3,5-benzenetricarboxylic acid (H3BTC) electrolyte has been developed to prepare fluorescent MOF films (Zn3(BTC)2). The composition of as-prepared MOF films is confirmed by powder X-ray diffraction (PXRD) and the surface morphology is examined by scanning electron microscopy (SEM). Voltage and fabrication time are found to be the key parameters for the formation and morphology control of MOF films. Additionally, the as-prepared MOF films, due to their evident fluorescence, are explored for potential applications in detecting nitro explosives with a detection limit as low as 0.5 ppm. The fluorescent MOF films can be further applied to distinguish nitro explosives by varying the solution concentration. Moreover, the MOF films exhibit excellent reusability in consecutive nitro explosive detection reactions. It has been demonstrated that the electrochemical plating method reported here offers a reliable and efficient way to prepare MOF films with controllable morphology for nitro explosive detection.

We present the first-principle calculations on the electronic excitations and second-order properties in solution phase of two typical inorganic trinuclear anionic clusters, [MoCu2S4(SPh)2]2− and [Mo2CuS4]1−(edt)2(PPh3) (edt=1,2-ethanedithiolato) in the framework of density functional theory (DFT). The computed excitation energies are in good agreement with the outcome of the measurements. The predicted values of the molecular quadratic hyperpolarizabilities are of the comparable order of those of the typical organometallic chromophores. We demonstrate the significant contributions to the second-order responses from the charge transfers between the metal centers (MMCT) which are ascribed to the direct metal–metal bonding interactions in these two charged clusters. This meaningful ligand-independent mechanism for the second-order response largely relates to metal–metal bonding strength, and the understanding will benefit to the future design of the new-generation molecular based nonlinear optical materials and optoelectronic devices by means of the conscious tuning of metal–metal interactions and metal-core structures of inorganic polynuclear clusters.

The intrinsic white-light-emitting properties of a lanthanide metal-organic framework that approach requirements for solid-state lighting are easily improved by incorporating minute quantities of red-emitting Eu(3+) into the host framework by virtue of the isostructural character of the La(3+) and Eu(3+) compounds and efficient sensitization of ligands toward Eu(3+) ions.

Two novel cobalt(II) coordination polymers [Co2(H2O)4(Hbidc)2]n (1) and [Co(Hbidc)]n (2), (Hbidc = 1H-benzimidazole-5,6-dicarboxylate) were synthesized hydrothermally by treating CoSO4 and H3bidc at 160 or 220 °C, respectively. X-Ray diffraction analyses showed that compound 1 is a 1-D chain polymer with dimer units [Co2(H2O)4(Hbidc)2] and the infinite chains of compound 1 array uniformly towards the crystallographic a-axis in a 3-D supramolecular framework which possesses abundant hydrogen-bonding interactions between uncoordinated carboxylo-oxygen atoms and coordinated water molecules or N–H groups in imidazole rings. Compound 2 is a novel five-coordinated cobalt(II) chain compound exhibiting a 2-D polymeric network with parallel zip-like cobalt–carboxylate chains along the crystallographic b-axis and the 2-D polymeric networks of compound 2 exhibit a layered arrangement, in which the strong hydrogen-bonding interaction between uncoordinated carboxylo-oxygen atoms and N–H groups in the imidazole rings play a key role in the final 3-D supramolecular architectures. Magnetic studies revealed that compound 1 shows a ferromagnetic coupling between two CoII ions in the dimer unit and compound 2 exhibits an antiferromagnetic property.