Bond Charge Research Articles

Heteroatom-Doped Nickel Sulfide for Efficient Electrochemical Oxygen Evolution Reaction

Heteroatom doping is an effective strategy to regulate electrocatalysts for the oxygen evolution reaction (OER). Nonmetal heteroatoms can effectively engineer geometric and electronic structures and activating surface sites of catalysts due to their unique radius and the electronegativity of nonmetal atoms. Hence, the surface geometric and electronic structure and activity of nonmetal atoms (X, X = B, C, N, O, P)-doped Ni3S2 (X-Ni3S2) were studied to screen high-performance Ni3S2-based OER electrocatalysts through density functional theory calculation. Theoretical results demonstrated that dopants in X-Ni3S2 can alter bond length and charge of surface, modify active sites for intermediates adsorption, and adjust the theoretical overpotential. Among all dopants, C can effectively modulate surface structure, activate surface sites, weaken the adsorption of key intermediates, decrease theoretical overpotential, and enable C-Ni3S2 with the best theoretical OER activity among all X-Ni3S2 with the lowest theoretical overpotential (0.46 eV). Further experimental results verified that the synthesized C-Ni3S2 performed an improved OER activity in the alkaline condition with a considerably enhanced overpotential of 261 mV at 10 mA cm−2 as well as a Tafel slope of 95 mV dec−1 compared to pristine Ni3S2.

Tourmaline guiding the electric field and dechlorination pathway of 2,3-dichlorophenol by Desulfitobacterium hafniense

The dehalogenation of organohalides has been a research hotspot in bioremediation field; however, the influence of tourmaline, a natural ore that can generate spontaneous electric field, on organohalide-respiring bacteria (OHRB) and their dechlorination process is not well known. In this study, the effect and mechanism of tourmaline on the reductive dechlorination of 2,3-dichlorophenol (2,3-DCP) by Desulfitobacterium hafniense DCB-2T were explored. The characterization results confirmed that tourmaline had good stability and the optimal dosage of tourmaline was 2.5 g/L, which shortened the total time required for dechlorination reaction to 72 hr. Besides, tourmaline amendment also increased the proportion of 2-chlorophenol (2-CP) from 18% to 30% of end products, while that of 3-CP decreased correspondingly. The theoretical calculations showed that the bond charge of the ortho-substituted chlorine declined from -0.179 to -0.067, and that of meta-substituted chlorine increased from -0.111 to -0.129, which indicated that the spontaneous electric field of tourmaline affected the charge distribution of 2,3-DCP and was more conducive to the generation of 2-CP. Overall, tourmaline with the spontaneous electric field affected the reductive dechlorination pathway of Desulfitobacterium,and the tourmaline-OHRB combining system might serve as a novel strategy for the bioremediation of environments polluted with chlorinated phenols.

Experimental and theoretical calculation of pKa values of substituted-2,4,6-trinitrodiphenylamines

The pKa values of eighteen 2,4,6-trinitrodiphenylamine derivatives were determined experimentally from their UV–vis spectra and their values were also calculated using quantum chemical methods. The accuracy of the various levels of theory and basis sets were assessed using the solvation model based on density and conductor-like screening model. Linear correlation coefficients of the calculated pKa values are in the range 0.44 – 0.89, 0.11 – 0.90 and 0.43 – 0.90, when compared with those obtained experimentally, for the 6-311++G(d,p), 6-31+G(d,p) and 6-31G(d) basis sets respectively. Increasing the size of the basis set by adding polarization and diffuse functions increase the average errors in the calculations, for ωB97XD functional in acetonitrile. Such variation was not observed in other functionals. Furthermore, the mean signed errors (MSE) for calculations with semiempirical methods are highly comparable but with very poor linear correlation coefficients. The M06-2X functional, in combination with the 6-31+G(d,p), 6-311++G(d,p) and 6-31G(d) basis sets, gave a much better performance than the other functionals used in the present study. The effect of empirical dispersion in the PM6-DH + method was not significant, as the results are similar to those obtained with AM1 and PM7. A strong correlation was observed for the pKa values obtained experimentally with Hammett σ constants, CN bond lengths and charges.

Synthesis, spectral characterization, and theoretical investigation of the photovoltaic properties of (E)-6-(4-(dimethylamino)phenyl)diazenyl)-2-octyl-benzoisoquinoline-1, 3-dione

This research work focuses on the synthesis, characterization through spectra (FT-IR, UV–vis, and 1H-NMR) investigations, and the use of density functional theory (DFT) along with time-dependent density functional theory (TD-DFT) to investigate the electronic, structural, reactivity, photophysical properties, and the photovoltaic properties of a novel (E)-6-(4-(dimethylamino)phenyl)diazenyl)-2-octyl-benzoisoquinoline-1,3-dione. The structure of the synthesized compound was modeled using the Gaussian09W and GaussView6.0.16 softwares employing B3LYP and 6–31 + G(d) basis set. The DFT studies was performed in order to investigate the Frontier Molecular Orbital (FMO), Natural Bond Orbital (NBO), charge distribution, Nonlinear Optics (NLO), and stability of the titled molecule. The HOMO–LUMO energy gap which corresponds to the difference between HOMO and LUMO energies of the studied compound was found to be 2.806 eV indicating stiff and smooth nature of the titled molecule. This accounts for the less stability and high chemical reactivity of the compound. The photovoltaic properties were conducted to evaluate the light harvesting efficiency (LHE), short circuit current density (JSC), Gibbs free energy of injection (Delta {G}_{inj}), open cycled voltage (VOC) and Gibbs free energy regeneration (Delta {G}_{reg}) and solar cell conversion efficiency. Interestingly, the results obtained were found to be in good agreement with other experimental and computational findings.

First-principles study of the effect of N on the ∑5 (210) [001] grain boundary of γ-Fe

High-nitrogen austenitic steels possess excellent properties owing to the solid solution strengthening of nitrogen, which is widely used in many fields. So it’s significant to investigate the effect of nitrogen on the properties of high austenitic nitrogen steels. In order to get atomic scale understanding of the influence of nitrogen, the first principles method was used to investigate the energetics, site preference, and segregation of nitrogen at γ-Fe ∑5 (210) [001] grain boundary (GB) and different atomic layers near GB plane. It is found that the nitrogen atom prefers to occupy the octahedral site. As nitrogen locates at different atomic layers away from the GB plane, the segregation energy presents increase first and then decrease. The mechanical properties were analyzed by Rice-Wang theory and theoretical tensile stress test, which shows that nitrogen at ∑5 (210) [001] GB has an embrittling effect on GB cohesion, while nitrogen located away from the GB plane presents a strengthening effect. The underlying mechanism was analyzed by bond length, charge density, and density of states (DOS). The segregation of nitrogen at ∑5(210) [001] grain boundary has negative effect on grain boundary cohesion, while nitrogen locating away from grain boundary plane presents strengthening effect on grain boundary.

DFT study about capturing of toxic sulfur gases over cyclic tetrapyrrole

The development of sensors that can detect hazardous analytes selectively and accurately, particularly sulfur based irritants, is quite essential. The infinite-conjugation in cyclic conducting polymers make them highly sensitive to toxic analytes. We implemented B3LYP-D3/6–311 + G (d, p) level to explore the sensing mechanism of cyclic tetrapyrrole (CTPy) for reliable detection of carbonyl sulfide, carbon disulfide, hydrogen sulfide sulfur monoxide, sulfur dioxide and sulfur trioxide using the DFT practice. The interaction energies, Eint ranges from –25.6 to –89.2 kJ mol−1 for sulfur gases over CTPy. Charge transfer interactions in complexes are predicted using natural bond orbital (NBO) and charge decomposition (CDA) analysis. The reduced density gradient (RDG) method supports hydrogen bonding and dispersion interactions in the complexes. The decrease in HOMO-LUMO energy gaps, as well as the red shifting of λmax in UV–Visible spectra, demonstrate sensitivity of CTPy towards sulfur gases. The improved conductivity of complexes is owing to production of numerous energy levels inoccupied and virtual orbitals closer to the Fermi level in DOS spectra. Furthermore, PDOS spectra reveal that CTPy is chiefly contribute to energy of HOMO. The recent findings show CTPy has a significant sensitivity to sulfurirritants. We hope that the above findings and their implications will give valuable suggestions for an experimentalist in designing extremely sensitive hazardous analyte sensors employing CTPy.

Large-scale production of high-quality elastic structural color films based on hydrogen bond and colloidal charge co-driven silica microsphere self-assembly

Photonic crystals (PCs) could revolutionize the modern engineering field. However, the commonly used large-scale roll-to-roll fabrication techniques are limited by the utilization of complex materials and devices. In this work, a method combining evaporative self-assembly and roll-to-roll precision printing was used for the ultrafast fabrication of large-area colloidal crystals. In this process, hydrogen bonding and colloidal charge cooperate to promote the formation of highly ordered colloidal crystals from SiO2 particles with virtually crack-free textures. The as-fabricated PCs films exhibits excellent optical and mechanical properties, including uniform and saturated colors (1 > ΔE·ab for 27 orthogonal points), long service life (>12 months), a wide operating temperature range (25–90 °C), superior bending resistance (>190,000 cycles), good folding resistance (>320 cycles), and excellent reversibility (>27,000 cycles). This work provides new insights into the self-assembly of colloidal SiO2 particles that will enable the application of PCs films in the back covers of mobile phones and multicolor displays.

Theoretical study on thermally activated delayed fluorescent molecules based on space charge transfer

Thermally Activated Delayed Fluorescent (TADF) molecules with through-space charge transfer (TSCT) have broad application potential in organic light-emitting diodes. In this paper, five TPA-ace based molecules with different electron-withdrawing groups and TSCT property are investigated using polarizable continuum model (PCM) combined with density functional theory (DFT) and time-dependent functional theory (TD-DFT) in Methylcyclohexane, Toluene and Dichloromethane. It is found that stronger electron-withdrawing ability of acceptors could induce redshift of emission and smaller energy gap between the first singlet excited state (S1) and the first triplet excited state (ΔEST). The ratio of TSCT to through bond charge transfer (TBCT) for S1 of TPA-ace-TRZ is calculated quantitatively, which further confirmed the TSCT character of TPA-ace-TRZ. The TADF property is also analyzed based on the calculation of spin–orbit coupling and the (reverse) intersystem crossing rates between S1 and T1. Our calculation results would favor the understanding of TSCT-TADF.

Metallization of hydrogen by intercalating ammonium ions in metal fcc lattices at lower pressure

Metallic hydrogen is capable of showing room temperature superconductivity, but its experimental syntheses are extremely hard. Therefore, it is desirable to reduce the synthesis pressure of metallic hydrogen by adding other chemical elements. However, for most hydrides, the metallization of hydrogen by “chemical precompression” to achieve high-temperature superconductivity still requires relatively high pressure, making experimental synthesis difficult. How to achieve high-temperature superconductivity in the lower-pressure range (≤50 GPa) is a key issue for realizing practical applications of superconducting materials. Toward this end, this work proposes a strategy for inserting ammonium ions in the fcc crystal of metals. High-throughput calculations of the periodic table reveal 12 elements that can form kinetically stable and superconducting hydrides at lower pressures, where the highest superconducting transition temperatures of AlN2H8, MgN2H8, and GaN2H8 can reach up to 118, 105, and 104 K. Pressure-induced bond length changes and charge transfer reveal the physical mechanism of high-temperature superconductivity, where the H atom continuously gains electrons leading to the transition of H+ ions to atomic H, facilitating metallization of hydrogen under less extreme high pressure. Our results also reveal two strong linear scalar relationships: one is the H-atom charge vs superconducting transition temperature, and the other is the first ionization energy vs the highest superconducting transition temperature. In addition, ZnN2H8, CdN2H8, and HgN2H8 were found to be superconductors at ambient pressure, and the presence of interstitial electrons suggests that they are also electrides, whose relatively low work functions (3.03, 2.78, and 3.05 eV) imply that they can be used as catalysts for nitrogen reduction reactions as well.

A comprehensive DFT evaluation of catalytic and optoelectronic properties of BaTiO3 polymorphs

BaTiO3 exhibits promising photocatalytic characteristics and has the potential to be employed in photocatalytic water splitting and pollutant degradation. Herein, we have investigated the structural, electronic, and optical properties of BaTiO3 in the framework of density functional theory (DFT). The obtained results are found to be consistent with theoretical results. However, using hybrid HSE06 functional, the calculated bandgap values are 3.254, 3.894, 3.694, 3.519, and 3.388 eV corresponding to cubic, rhombohedral, orthorhombic, tetragonal, and hexagonal phase of BaTiO3 polymorphs. This is the first time a DFT calculation touched over the experimental bandgap values of BaTiO3 polymorphs.Electronic band structure analysis revealed that all the BaTiO3 polymorphs exhibit semiconducting character with indirect bandgap except hexagonal structure which possesses direct bandgap. The density of states (DOS), Mulliken bond analysis and charge density distribution indicates considerable hybridization between O-2p and Ti-3d states caused to the formation of upper valence band (VB) and lower conduction band (CB). The wide bandgap and suitable redox potential of BaTiO3 polymorphs will be effective for water splitting as well as breakdown organic contaminants under UV–vis irradiation. The lower electron effective mass of the polymorphs indicates higher electrical conductivity. The energy dependent optical parameters show close agreement with the underlying electronic band structure. The high absorptivity, lower reflectivity and optical anisotropy (orthorhombic and tetragonal) of the polymorphs suggested that these could be a potential candidate for UV based optical device applications as well as to design wave guides, dielectric condensers and optical display devices.

Vacancy diffusion on a brominated Si(100) surface: Critical effect of the dangling bond charge state.

Silicon dangling bonds (DBs) on an adsorbate-covered Si(100) surface can be created in a scanning tunneling microscope (STM) with high precision required for a number of applications. However, vacancies containing DBs can diffuse, disrupting precisely created structures. In this work, we study the diffusion of Br vacancies on a Si(100)-2 × 1-Br surface in an STM under typical imaging conditions. In agreement with previous work, Br vacancies diffuse at a positive sample bias voltage. Here, we demonstrated that only vacancies containing a positively charged DB hop across the two atoms of a single Si dimer, while vacancies containing neutral and negatively charged DBs do not. Calculations based on density functional theory confirmed that positively charged Br (and Cl) vacancies have a minimum activation barrier. We propose that diffusion operates by both one-electron and two-electron mechanisms depending on the applied voltage. Our results show that the DB charge has a critical effect on the vacancy diffusion. This effect should be taken into account when imaging surface structures with charged DBs as well as when studying the diffusion of other atoms and molecules on the Si(100) surface with vacancies in an adsorbate layer.

Elucidating the facet-dependent reactivity of Cr[sbnd]Mn catalyst for selective catalytic reduction of NOx with NH3

The facet-dependent reactivity of CrMn catalysts was still unclear, hindering the further enhancement of their low-temperature SCR performance. Herein, the facet-dependent reactivity of CrMn1.5O4 catalyst for NH3-SCR of NOx was innovatively illustrated by numerous characterizations and density functional theory (DFT) calculations. Exposed (100) facet of CrMn1.5O4 catalyst exhibited best low-temperature SCR activity with ≥90 % NO conversion within 148–296 °C and 2.86 × 10−3 mol/(g·s) reaction rate within 160–240 °C. The characterizations revealed that (100) facet could induce the increase of BET specific area, electron transfer, concentration of Mn4+ and Oα, surface acidity, redox ability, NH3 and NOx adsorption/activation capacity. Subsequently, DFT calculations demonstrated that (100) facet exhibited the strongest affinity for NH3 and NO due to its unique 3O3c-Mn5c-2O4c bond and abundant charges transfer near the active adsorption sites, and Brønsted acid and oxygen vacancies were most easily formed on (100) facet. Furthermore, H2O formation as the rate determining step easily occurred on (100) facet. Eventually, we successfully improved the low-temperature SCR activity of CrMn1.5O4 catalyst by further tailoring highly active (100) facet from 0.754 to 0.865. This work provides the deeper understanding of facet-dependent reactivity and a good strategy to improve the catalytic activity of the catalysts.

Is an Inductive Effect Explicit Account Required for Atomic Charges Aimed at Use within the Force Fields?

Polarization and inductive effects are the concepts that have been widely used in qualitative and even quantitative descriptions of experimentally observed properties in chemistry. The polarization effect has proven to be important in cases of biomolecular modeling though still the vast majority of molecular simulations use the classical non-polarizable force fields. In the last few decades, a lot of effort has been put into promoting the polarization effect and incorporating it into modern force fields and charge calculation methods. In contrast, the inductive effect has not attracted such attention and is effectively absent in both classic and modern force fields. Thus, a question is whether this difference corresponds to the difference in the physical significance of the effects and their explicit account, or is an artifact that should be corrected in the next generation of force fields. The significance of the electronic effects is studied in this paper through the prism of performance of specific models for atomic charge calculation that take into explicit account a nested set of effects: the formal charge, the nearest neighbors, the inductive effect, and finally the model, which takes into account all effects, which are possible to account for using atomic charges. The specific choice for the methods is the following: formal charges, MMFF94 bond charge increments, Dynamic Electronegativity Relaxation (DENR), and RESP. We propose a special scheme for the separate estimation of each particular effect contribution. By pairwise comparing the residual molecular electrostatic potential (MEP) errors of those charge models (aimed at best reproducing the quantum chemical reference MEP), we sequentially revealed how the account of each effect contributes to the better-quality MEP reproduction. The following relative importance of effects was estimated; thus, the natural hierarchy of the effects was established. First, the account of formal charges is of primordial importance. Second, the nearest neighbors account is the next in significance. Third, the explicit account of inductive effect in empirical charge calculation schemes was shown to significantly─both qualitatively and quantitatively─improve the quality of MEP reproduction. Fourth, the contribution of polarization is indirectly assessed. Surprisingly, it is of the order of magnitude of the inductive effect even for the molecular systems, for which it is anticipated to be more significant. Finally, the relative importance of anisotropic effects in neutral molecules was additionally reviewed.

Sulfate radicals induced from peroxymonosulfate on electrochemically synthesized TiO2-MoO3 heterostructure with Ti-O-Mo bond charge transfer pathway for potential organic pollutant removal under solar light irradiation.

Here, a novel method for synthesis of heterostructured TiO2-MoO3 (MT) nanosheets photocatalyst by utilizing a facile electrochemical method and examined it's photocatalytic activity by the degradation of tetracycline hydrochloride (TCH), a model of organic pollutants, in the presence of peroxymonosulfate (PMS) under solar light irradiation (SL) was reported for the first time. The influence of several factors on the degradation efficiency including the initial concentration of TCH, solution pH, catalyst dosage, PMS concentration, and the existence of inorganic anions was explored. The MT-15/PMS system displayed a promising photocatalytic performance and up to 97% of TCH was degraded in 90min the rate of the degradation reaction of MT-15/PMS was the highest (0.05299 min-1) compared to 0.00251, 0.00337, 0.00546, 0.00735, 0.01337min-1of TiO2-P25, TiO2-P25/PMS, MoO3, MoO3/PMS, and MT-15 respectively. The enhancement can be attributed to several reasons. First, the 2D morphology of the optimized heterostructure photocatalyst plays a significant role in providing much more active sites on its surface. Next, the boosted light absorption efficiency and higher photoproduced electron-hole pair separation ability, induced by the unique direct transformation of photogenerated electrons from the valance band of TiO2 to the conduction band of MoO3 via the Ti-O-Mo bond formed at the interface of MT heterostructure. Finally, the appropriate accessible reactive sites for the activation of PMS together with the synergistic effect between activation of PMS and photocatalytic processes eased the production of active species for the degradation of pollutants. Based on the scavenger experiments and EPR analysis, hydroxide and sulfate radicals were found to be the dominant free radical active species in the degradation process. Furthermore, the synergistic degradation reaction mechanism was proposed.

DFT insight into Cd2+, Hg2+, Pb2+, Sn2+, As3+, Sb3+, and Cr3+ heavy metal ions adsorption onto surface of bowl-like B30 nanosheet

Contamination of water resources by heavymetal ions, is a drastic environmental concern. In this study, the interaction of Cd2+, Hg2+, Pb2+, Sn2+, As3+, Sb3+, and Cr3+ metal ions onto surface of the bowl-like B30 nanosheet was scrutinized based on density functional theory (DFT) calculations. Adsorption energy (Eads) values revealed that the As3+ interacted better with bowl-like B30 nanosheet in comparison to other metal ions, having adsorption energy values of −299.57 and −628.56 kcal mol−1in the gas phase and aqueous media, respectively. However, Hg2+, Pb2+, and Sn2+ metal ions physically adsorbed onto bowl-like B30 nanosheet in the gas phase because of their much less value of adsorption energy. The sign of adsorptionGibbs free energy change(ΔGads) and adsorption enthalpy change (ΔHads) values for all complexes was found to be negative in the gas phase and aqueous media, which indicated that the adsorption process is spontaneous and exothermic. Frontier molecular orbital (FMO) analysis exhibited a decrease in the HOMO-LUMO energy gap of studied complexes, boosting the electrical conductivity of these complexes. Natural bond orbital (NBO) analysis and charge decomposition analysis (CDA) revealed donor–acceptor charge transfer interactions in the complexes. The UV–vis results depicted that λmax was red-shifted during interactions of meal ions with bowl-like B30 nanosheet. Finally,quantum theoryof atoms in molecules (QTAIM) exhibited that the interaction between As3+ metal ion and the nanosheet is covalent in nature, while the other metal ions have predominantly electrostatic with partially covalent and non-covalent characters. The theoretical results of the study represented the feasibility of applying bowl-like B30 nanosheet to remove heavy metal ions, especially As3+ and providing information for experimental researchers to treat wastewaters.

TMP/Pd complex immobilized on graphene oxide for efficient pseudocapacitive energy storage with combined experimental and DFT study

Designing sophisticated energy sources that can offer a large amount of electricity for various energy storage uses is a pressing need. In this study, Trimethoprim (TMP) was functionalized as a rich supply of nitrogen and oxygen on graphene oxide (FGO-TMP), using graphene oxide layers adorned with trimethoprim functional groups. Then, using a simple approach to synthesize FGO-TMP/Pd complex for supercapacitor applications, palladium ions were reacted and fixed on the FGO-TMP composite surface. The FGO-TMP/Pd composite produced was characterized as a symmetric capacitor with a capacitance of 330F/g at 5 mV s−1 and high energy and power densities of 60.3 W h Kg−1 and 1200 W kg−1, respectively. After 10,000 cycles at 8 A/g, this symmetric device retained 93.7 percent of its original capacitance, proving the remarkable capacitive performance of the developed platform as well as ultra-stability for such sophisticated energy storage devices. Topological analysis of the electron density distribution and its Laplacian at the bonding critical points and Bader atomic charges of the GO layer in both FGO-TMP and FGO-TMP/Pd composites confirms more concentrated bond charges in FGO-TMP/Pd, indicating effective improvement in electrode material behavior in a supercapacitor.

Ab initio study of the optoelectronic properties of α-Ba2SnS4

The electronic structure and optical properties of a ternary thiostannate compound (α-Ba2SnS4) have been successfully predicted via ab initio calculations. Optimized structure was confirmed by both Bond Valence Sum (BVS) and charge distribution (CHARDI) validation models, which showed a reduction in the coordination number of the barium atom after structure optimization. The band structure confirmed that the α-Ba2SnS4 is a semiconductor material with a direct band gap, and the calculated band gap energy was 2.469 eV which was in good agreement with other literature reports. Calculated optical spectra (dielectric function, refractive index, reflectivity, absorption, energy loss function) of the compound exhibited a significant optical anisotropy. A plot of the dielectric function showed four transition frequencies, while the determinate frequencies values were consistent with the density of states. A high absorptivity of the electromagnetic waves in both visible and near UV regions was observed in the absorption spectra, which indicated the possible application of this compound in optoelectronic field as photocatalysts. The mechanical stability of this compound has been verified by the phonon calculation.

Single-atom transition metals supported on defective graphene for electrochemical reduction of acetonitrile to ethylamine

The electrochemical acetonitrile (CH3CN) reduction reaction provides an alternative to produce ethylamine (CH3CH2NH2) under ambient conditions but remains challenging. Using density functional theory (DFT) calculations, we explored the catalytic performance of four types of graphene-based single-atom catalysts (SACs) total of 32 materials toward the CH3CN reduction reaction. We identified that two highly stable SACs, namely Cr@N4 and Mn@N4, can greatly accelerate both reaction thermodynamics and kinetics with small energy barriers. In particular, these two SACs can effectively suppress the competitive hydrogen evolution reaction (HER) by selective adsorption of key intermediate of *CH3CN rather than *H, which feature superior catalytic selectivity. More impressively, the activity trends of various candidates can be directly correlated to the adsorption energy of *CH3CHN (ΔE(*CH3CHN)), and the underlying activity origin is ascribed by the enhancement of the adsorption for the *CH3CHN. Furthermore, detailed electronic property analyses indicate that the bonding/anti-bonding interactions of different active metal centers with *CH3CHN are the key factor determining the adsorption strength. The more bonding contributions below the Fermi level (Ef) lead to the stronger *CH3CHN combination on active metal centers, while the anti-bonding state is opposite. As a result, Cr@N4 stands out among these candidates, which can tune the performance of acetonitrile reduction reaction by balancing the reactivity of CH3CN and the desorption of CH3CH2NH2. Our results unveil that the excellent catalytic activity of Cr@N4 for CH3CN reduction reaction can be further confirmed by calculating the bond lengths and charge variations. With the elongation of CN bond in the adsorbed CH3CHxNHy, CH3CN molecule can be effectively activated on Cr@N4. Overall, this work addresses a promising active catalyst and will be of a guidance of great theoretical significance to construct carbon-based materials supported transition metal single-atom electrocatalysts for the CH3CN reduction reaction.

GO-HFIPPH covered a-IGZO thin film transistor for gate tunable DMMP detection

Field-effect transistor (FET) type gas sensors are showing their great attractions to researchers due to their miniature size, gate tunable sensitivity and compatibility with CMOS technology. Amorphous indium gallium zinc oxide (a-IGZO) thin film transistors have the advantage of simple preparation method, high mobility and potential for large-scale integration, which has been widely investigated in recent years. The traditional method of obtaining selectivity of semiconductor sensing materials is to make chemical decorations directly to the semiconductor active layer, which may damage the material’s properties. In this paper, we decorate graphene oxide (GO) with p-hexafluoroisopropanol phenyl (HFIPPH) to form GO-HFIPPH, and then use GO-HFIPPH to physically modify a-IGZO TFT through self-assembly to prepare a FET-type dimethyl methylphosphonate (DMMP) sensor. The proposed sensor shows good sensitivity and selectivity to DMMP, and has a 61.1 nA response to 200 ppb DMMP with 42 s and 26 s response/recovery time. In addition, the sensing mechanism is explained based on hydrogen bond theory, heterojunction and charge transportation of the a-IGZO transistor. We believe our GO-HFIPPH/a-IGZO TFT DMMP sensor will show a significant value for FET-type gas sensor design.

Germanium-doped hydroxyapatite: Synthesis and characterization of a new substituted apatite

Hydroxyapatite (HAp) is the major component of all boney tissues in mammals. Because of this omnipresence in the living world, HAp possesses an exceptional biocompatibility. The downside of this omnipresence, however, comes in the form of its mild to moderate biological activities. One means of augmenting these activities involves the doping of HAp with foreign ions. Here, the first synthesis and characterization of HAp doped with germanium ions is being reported. Germanium was deliberately integrated into the crystal lattice of HAp in the form of germanate anions. Approximately two thirds of the germanate ions introduced into the hydrothermal solution got incorporated into the HAp lattice, yielding the approximate stoichiometry of Ca10-x(PO4)5.62+y(GeO3)0.38(OH)2-z. Germanates replaced the phosphates of stoichiometric HAp and induced the expansion of the HAp lattice both along the screw axis of the calcium ion hexagons and in the direction parallel to the basal plane. Simultaneously, the larger size and the triple valency of the germanate ion as compared to the smaller and trivalent phosphates prompted the bond distortion and charge compensation through defect formation, which reduced the crystallinity and increased the microstrain of the HAp lattice. Vibrational spectroscopic analyses corroborated these crystallographic effects by demonstrating the enhanced heterogeneity of the environments surrounding the active modes after germanate ions were incorporated into HAp. Conforming to La Châtelier's principle, this reduction of the crystallographic order increased the capacity of the material for integration of adventitious carbonates. However, the inclusion of germanate ions induced a partial shift of these carbonates to the hydroxyl channel sites, thus decreasing the ratio of the B-type carbonation to the A-type carbonation. Introduced into HAp, germanium acted as a superb regulator of the particle size and morphology, enhancing their fineness and uniformity. Inclusion of germanate ions also increased the electrophoretic mobility and hydrodynamic surface charge density of the particles by reducing their size and by inducing a more stochastic distribution of terminal ionic groups due to the bending of the crystal facets. Overall, the doping of HAp with germanate ions facilitated the production of narrowly dispersed nanorods with a moderately enhanced structural disorder and with a pronounced potential for the biomedical niche.