Crystal Orbital Hamilton Population Research Articles

A Fundamental Perspective on the Selective Zn Substitution in Ternary Ordered Intermetallic Compound Cu6Zn2Sb2

AbstractThe unique site substitution of Zn in the structure of tetragonal and atomically ordered Cu6Zn2Sb2, followed by the formation of Cu5Zn3Sb2, has been addressed from fundamental perspectives. First principles energy calculations, and semi‐empirical electronic structure calculations using the density of states, crystal orbital Hamilton population, crystal orbital bond index and Mulliken population analysis were performed to understand the observed substitution pattern and the narrow homogeneity range of the titled compound. Mulliken and Löwdin's approach of charge analysis explain the experimentally proved ‘coloring’, based on the ‘site energy’ argument. The concept of ‘topological charge stabilization’ has been introduced in this context. Valence electron concentration and the optimization of the partially covalent Cu−Sb interactions also play pivotal role in the electronic stability of the titled phase.

Electrifying HCOOH synthesis from CO2 building blocks over Cu–Bi nanorod arrays

Precise electrochemical synthesis of commodity chemicals and fuels from CO2 building blocks provides a promising route to close the anthropogenic carbon cycle, in which renewable but intermittent electricity could be stored within the greenhouse gas molecules. Here, we report state-of-the-art CO2-to-HCOOH valorization performance over a multiscale optimized Cu-Bi cathodic architecture, delivering a formate Faradaic efficiency exceeding 95% within an aqueous electrolyzer, a C-basis HCOOH purity above 99.8% within a solid-state electrolyzer operated at 100 mA cm-2 for 200 h and an energy efficiency of 39.2%, as well as a tunable aqueous HCOOH concentration ranging from 2.7 to 92.1 wt%. Via a combined two-dimensional reaction phase diagram and finite element analysis, we highlight the role of local geometries of Cu and Bi in branching the adsorption strength for key intermediates like *COOH and *OCHO for CO2 reduction, while the crystal orbital Hamiltonian population analysis rationalizes the vital contribution from moderate binding strength of η2(O,O)-OCHO on Cu-doped Bi surface in promoting HCOOH electrosynthesis. The findings of this study not only shed light on the tuning knobs for precise CO2 valorization, but also provide a different research paradigm for advancing the activity and selectivity optimization in a broad range of electrosynthetic systems.

First-principles Study of Phase-dependent Carrier Transport Mechanism for MASnI3 Sn-based Halide Perovskite.

Organic-inorganic hybrid perovskites have attracted tremendous attentions owing to their excellent properties as next-generation photovoltaic devices. With soft covalent framework, organic-inorganic hybrid perovskites exhibit different phases at different temperatures. The band-edge features of perovskites are mainly contributed by inorganic framework, which means the structural differences between these phases would lead to complex carrier transport. We investigated the carrier transport of Sn-based organic-inorganic hybrid perovskite CH3NH3SnI3 (MASnI3), considering acoustic deformation potential scattering, ionized impurity scattering, and polar optical phonon scattering. It is found that the electron mobility of each phase of MASnI3 is strongly correlated with the Sn-I-Sn bond angle and there is in-plane/out-of-plane anisotropy. The pCOHP (projected crystal orbital Hamilton population) analysis suggested that the tilt and rotation of the [SnI6]4- octahedron influence the Sn(p)-I(p) orbital electron coupling and the electron transport, leading to different band-edge features in multiple phases. The carrier mobility with respect to temperature was further calculated for each phase of MASnI3 in respective temperature intervals, showing lower carrier mobility in high temperature. Comparing the contribution of different scattering mechanisms, it was found that the dominant scattering mechanism is polar optical phonon scattering, while multiple scattering mechanisms compete in individual cases.

Fe Crystalline Phases in Fe/C Composites Modulated the Selective Adsorption of Pb(II) from Industrial Wastewater with Cd(II): An Electronic-Scale Perspective.

Fe oxide or Fe0-based materials display weak removal capacity for Pb(II), especially in the presence of Cd(II), and the electronic-scale mechanisms are not reported. In this study, Fe3C(220) modified black carbon (BC) [Fe3C(220)@BC] with high adsorption and selectivity for Pb(II) from industrial wastewater with Cd(II) was developed. The quantitative experiment suggested that Fe species accounted for 80.5-100 and 18.4-33.8% of Pb(II) and Cd(II) removal, respectively. Based on X-ray absorption near-edge structure analysis, 57.3% of adsorbed Pb2+ was reduced to Pb0; however, 61.6% of Cd2+ existed on Fe3C@BC. Density functional theory simulation unraveled that Cd(II) adsorption was attributed to the cation-π interaction with BC, whereas that of Pb(II) was ascribed to the stronger interactions with different Fe phases following the order: Fe3C(220) > Fe0(110) > Fe3O4(311). Crystal orbital bond index and Hamilton population analyses were innovatively applied in the adsorption system and displayed a unique discovery: the stronger Pb(II) adsorption on Fe phases was mediated by a combination of covalent and ionic bonding, whereas ionic bonding was mainly accounted for Cd(II) adsorption. These findings open a new chapter in understanding the functions of different Fe phases in mediating the fate and transport of heavy metals in both natural and engineered systems.

Deformability, inherent mechanical properties and chemical bonding of Al11Nd3 in Al-Nd target material

Microstructure uniformity of the Al-Nd target materials with Al11Nd3 significantly affects the performance of the fabricated Al-Nd film, which is widely used as wiring material in large-size thin-film transistor liquid crystal display (TFT-LCD) panels. Understanding the inherent mechanical properties and chemical bonds of Al11Nd3 is crucial for homogenizing the Al-Nd target. Here, by a combined experimental and ab-initio theoretical study, the microstructure and deformability of the Al-3wt%Nd alloy and the inherent mechanical properties and chemical bonds of Al11Nd3 were investigated comprehensively. The Al-3 wt%Nd alloy is composed of the pre-eutectic α-Al matrix and the eutectic α-Al and a high stable α-Al11Nd3 phase. During the plastic deformation, the eutectic microstructure transforms from a cellular to a lamellar shape, while the morphology and dimension of α-Al11Nd3 are not changed significantly. By examining ideal tensile strength, elastic moduli, hardness and brittleness-ductility, the hardness-brittleness of α-Al11Nd3 is quantitatively evaluated, accounting for its difficulties of plastic deformation and fragmentation. Combining band structure, population analysis, topological analysis and crystal orbital Hamilton population, we found that α-Al11Nd3 possesses two types of chemical bonds: the Nd-Al and Al-Al bonds. The former is a typical ionic bond with electron transfer from Nd to Al, while the latter, dominated by both 3s-3p and 3p-3p interactions, is a weak covalent bond. The mixed chemical bond is responsible for the high hardness-brittleness of α-Al11Nd3. This work is expected to lay a foundation for Al-Nd alloy and catalyze the fabrication of high-quality Al-Nd target materials.

Theoretical regulating the T-site composition of Janus MXenes achieving efficient bifunctional ORR/OER catalysts

The development of metal-air batteries relies heavily on efficient bifunctional catalysts for oxygen reduction/evolution reactions (ORR/OER). Herein, we employ first-principles calculations to investigate the structure-activity relationship between the composition of terminal atoms and the catalytic activity of Pt-doped VCl-Ti2CO2-xClx single-atom catalysts (SACs). Firstly, the results demonstrate clear linear correlations between the composition and the work function, interlayer average transfer charges (Δq), and the integrated crystal orbital Hamilton population (ICOHP) of the Pt-O bond that adsorbs OH. Besides, the difference in the average transferred charge between the Ti and the C layers (Δq5-3) and the ICOHP of Pt-O bond adsorbing OH can be used as effective descriptors of bifunctional performance of Pt-doped VCl-Ti2CO2-xClx. Furthermore, the bonding and charge transfer between the active site Pt and adsorbed intermediate OH are elucidated, revealing the bridging role of dxz and dz2 orbitals of Pt during the activation process. Based on the above understanding, we reported a catalyst of Pt-VCl-Ti2CO0.22Cl1.78 with a low bifunctional overpotential (ηBi = 1.00 V), effectively reducing the overpotential of Pt-doped Ti2CO2. This study extensively investigates the impact of terminal composition control on the ORR/OER activity, providing robust support for the design of highly active Janus MXene-based SACs.

Phosphorus-doped cobalt oxide/cobalt sulfide heterostructure for enhanced oxygen evolution

Regulating the distribution of valence charges near the Fermi level and d-band center of metal atom active sites is crucial for developing highly efficient and stable catalysts for oxygen evolution reaction (OER), yet it remains a significant challenge. In this study, we prepared phosphorus-doped Co3O4/Co9S8 catalysts with a mesoporous nanorod morphology and Mott-Schottky heterojunction. Compared to Co3O4, Co9S8 and Co3O4/Co9S8, this catalyst exhibits enhanced OER properties with an overpotential of 156 mV at 10 mA cm−2, 380 mV at 50 mA cm−2, and 450 mV at 100 mA cm−2. Moreover, when a voltage of 2.0 V vs. RHE is applied, the current density reaches 350 mA cm−2. Density functional theory (DFT) calculations reveal that the coupling of Co3O4 and Co9S8 interfaces and phosphorus doping lead to the rearrangement of d-orbital electrons of Co atoms on the crystal plane, optimizing the d-band center. Crystal orbital Hamilton population (COHP) analysis shows that the partial anti-bonding state transitions into the unoccupied region, reducing the anti-bonding state and enhancing the bonding state, thus significantly improving the adsorption for the target intermediate (*OOH), resulting in higher intrinsic activity. This study demonstrates that the pathway of doping this heterojunction with P synergistically enhances the catalytic activity of this composite for OER in water splitting electrocatalysis.

Tunable Multicolor Emission and High Thermal Stability in Single‐Matrix Luminescent Crystals Based on Calcium Perovskites for Advanced Solid‐State Lighting Applications

AbstractThe development of environmentally friendly full‐inorganic luminescent materials with tunable emission properties and exceptional thermal stability is of paramount importance for applications in optoelectronic devices, solid‐state lighting, and anti‐counterfeiting technologies. In this study, a novel luminescent crystal based on calcium perovskites Cs2CaCl4·2H2O (CCCH) are explored using a hydrothermal method. Simultaneous co‐doping of CCCH with Sn2+ and Mn2+ yields the s‐p transition‐induced cyan light from Sn2+ and d‐d transition‐induced yellow light from Mn2+. It demonstrates effective energy transfer from self‐trapped exciton (STE) of matrix CCCH and s‐p transition of Sn2+ to Mn2+, synergizing composite white lights with tunable colors. Furthermore, the incorporation of Sn2+ into CCCH introduces a red shift from blue to cyan emission with a remarkable enhancement in luminescent intensity by a factor of 12 times. The crystal orbital Hamiltonian populations (─COHP) calculations revealed the crucial role of Mn2+ in lattice stability, as evidenced by the decomposition temperature exceeding 305 °C for CCCH:Sn2+,Mn2+ whereas 210 °C for undoped CCCH matrix. This research provides a comprehensive investigation of the luminescent properties of CCCH:Sn2+,Mn2+ crystal, holding significant promise for practical technological advancements in lighting and anti‐counterfeiting technologies.

Structural and electronic properties of AlGaN nanowires modulated by Al component and sectional size: A first principles study with DFT+U method

AlGaN nanowires have plenty of applications in optoelectronic functional devices. However, the electronic characteristics and stability of AlGaN nanowires are rarely explored, especially for an actual prediction of bandgaps with varying Al components. In this work, we utilize first principles calculation with DFT + U method to study the stability, charge redistribution, band structures, density of states of AlxGa1-xN alloy nanowires with x spanning from 0 to 1. The results indicate that the stability of the nanowire is enhanced with increasing nanowire diameter and Al component. The bond length in the outermost layer, vertical to the specified direction, is stretched as the Al component increases. The bandgap of nanowire is larger than that of bulk phase and the bowing parameter of nanowire is relatively low. According to the analysis of density of states (DOS), the migration of band structures is attributed to N-p states at VBM and Ga-s and Al-p states at CBM. The calculation of Crystal Orbital Hamilton Population (COHP) reveals the variation of bandgap with changing Al component and diameter. According to the analysis of electron density difference and charge transfer, Al atom has a stronger electron negativity and the electron density surrounding Ga is more delocalized compared Al atom. The results obtained in this study is expected to give some guidance for the preparation of optoelectronic devices based on AlGaN nanowires.

Selection Rules of Transition Metal Dopants for Prussian Blue Analogs Enabling Highly Reversible Sodium Storage

AbstractRational element doping is demonstrated as an effective strategy to optimize crystal stability and enhance the electronic conductivity of Prussian blue analogs (PBAs) to achieve a satisfactory sodium storage performance. However, unraveling the dopant selection principles is still a big challenge. Herein, the integrated crystal orbital Hamilton population (ICOHP) function is adopted to evaluate the strength of chemical bonds of N‐transition metals (N‐TM) and guide the dopant selection. Among the series of ICOHP values for N‐TM (TM = Mn, Fe, Co, Ni, Cu, Zn), the Cu─N bond exhibits the lowest ICOHP value, which indicates that Cu doping can improve the stability of PBAs compared to other dopants. Experimentally, among TM‐substituted Fe‐based PBAs (TMFeHCFs), the as‐prepared sample with 20 at.% Cu doping (CuFeHCF‐2) exhibits the best cycling performance, with a capacity retention of 83.5% after 400 cycles at 1 C, which is consistent with the theoretical calculation results. In addition, in situ XRD and in situ, Raman reveal a highly reversible monoclinic‐cubic two‐phase conversion and redox‐active pairs, respectively. This study provides valuable guidelines for dopant selection to enhance the performance of PBAs cathodes.

Exploration of sodium thiosulfate for leaching of cobalt-containing pyrite: A DFT study

The paper presents the theoretical calculation results of exploratory research relating to the leaching of cobalt-containing pyrite using sodium thiosulfate as a lixiviant. It is well known that density functional theory (DFT) calculations can qualitatively evaluate the exchange of matter and energy between the mineral system and the surroundings, which greatly expands the breadth and depth of leaching process. Thus, DFT method was used to determine the effectiveness of sodium thiosulfate (Na2S2O3) as a lixiviant for the leaching of cobalt-containing pyrite in this study. The analyses of DFT calculations illustrated that thiosulfate can be well adsorbed on the surface of cobalt-containing pyrite due to the formation of S-Fe and O-Co bonds between the S 3p orbital and O 2p orbital in sodium thiosulfate and the Fe 3d orbital and Co 3d orbital in cobalt-containing pyrite. Analysis of crystal orbital Hamilton population (COHP) indicated that Fe-S and S-Co bonds became longer when the thiosulfate adsorbed on the surface of the cobalt-containing pyrite, resulting in the weakening of interactions between S and Fe or Co atoms. Overall, the findings suggested that sodium thiosulfate was a promising lixiviant，favored the dissolution of Fe and Co.

Addressing the Activity and Selectivity Challenges for CO2 Reduction via Transition‐Metal‐Free Homo‐ and Hetero‐Biatomic Catalysts Embedded in Two‐Dimensional Networks

AbstractDesigning low‐cost and stable electrocatalysts with enhanced activity and selectivity for CO2 valorization to useful chemicals and fuels faces enormous challenges to address the pressing climate change concerns. Synergistic interactions between the atoms in double atom catalysts has emerged as a promising tool to tune and boost CO2 activation and reduction. In this work, we systematically designed highly stable transition‐metal‐free homo‐ and hetero‐biatomic catalysts based on Al, Be, B and Si supported on TCNQ monolayer for CO2 reduction to C1 products using dispersion corrected periodic density functional theory calculations. Our findings reveal that transition‐metal‐free homo‐and hetero‐biatomic TCNQ catalysts can effectively capture and activate the CO2 molecule with binding energies ranging from 0.09 to 2.35 eV. Extensive free energy calculations to screen the favourable reaction pathways to different C1 products (CO, HCOOH, CH3OH and CH4) demonstrate that Al2‐TCNQ, AlBe‐TCNQ and BeSi‐TCNQ stand out as potential candidates for catalyzing CO2RR to methanol in a selective manner, suppressing the competitive HER simultaneously. Remarkably, BeSi‐TCNQ shows the best catalytic activity towards CO2 reduction to methanol at record low limiting potential of −0.29 V with spontaneous desorption of the final product. From the in‐depth examination of the electronic structure details, integrated projected density of states and crystal orbital Hamilton populations are used to understand and rationalize the binding interactions between the adsorbed CO2 molecule and the homo‐ or hetero‐biatomic TCNQ catalysts. Moreover, the ΔG*COOH‐ΔG*CO2 and ΔG*HCOOH‐ΔG* OCHO/*COOH values are found to provide reasonable guidance to evaluate the overall CO2RR performance of homo‐ and hetero‐biatomic TCNQ catalysts, respectively. Therefore, our findings provide significant insights for designing transition metal‐free homo‐ and hetero‐biatomic catalysts with intriguing properties for improving CO2 utilization and conversion.

Theoretically exploring bioinspired enzyme-like [formula omitted] with organic ion axial ligand for electrocatalytic nitrate reduction to ammonia

Electrocatalytically driven reduction of nitrate (NO3−) from NO3−-laden wastewater to ammonia (NH3) has emerged as a promising complementary strategy to the energy-intensive Haber-Bosch process. Herein, based on density functional theory (DFT) calculations, 14 organic ionic groups are found to significantly improve the electrocatalytic reduction of NO3− to NH3 (eNO3RR-to-NH3) activity of typical M−N4−C (M = Fe, Co, and Ni) catalysts by axially ligating metal center, among which Ethyl thiolate axially ligated Co−N4−C exhibits the highest eNO3RR-to-NH3 activity with the limiting potential (UL) of -0.11 V. 4-Mercaptobenzoic acid and Thiophenolate axially ligated Fe−N4−C can inhibit the NN coupling reaction while having high eNO3RR-to-NH3 activity (UL = -0.16, -0.31 V, respectively) and thus have better NH3 selectivity. Furthermore, ΔGH*NO and ICOHP (integrated crystal orbital hamilton populations) between the 3d orbital of M and 2p orbital of N (*NO) atoms show remarkable volcano relationship for L−Fe−N4−C systems and linear relationship with R-Square of 0.83 occurs for L−Co−N4−C systems. There is an excellent linear relationship (R-Square is 0.88) between ICOHP and UL for the L−Co−N4−C systems. Hence, the ICOHP can work as an excellent thermodynamic activity descriptor for eNO3RR-to-NH3 over L−Co−N4−C catalysts. The three catalysts are concluded to be promising electrocatalysts for eNO3RR-to-NH3.

Parameter modulation on p-type doping of AlGaN nanowires

The p-type doping process during the growth of AlGaN nanowires directly influences the optoelectronic properties of the related devices. However, research on the p-type ionization mechanism in AlxGa1-xN nanowires remains limited. In this work, we utilize first principles calculations to investigate p-type doping in AlxGa1-xN nanowires under different structural variables (Al component, doping element, doping site, and doping concentration). Our results demonstrate that p-type doping in AlxGa1-xN nanowires is an endothermic process, and increased dopant concentration leads to a decrease in system stability. Moreover, we found that dopant atoms are easier to substitute for Ga atoms than Al atoms. Among the three doping elements (Zn, Be and Mg), Zn exhibits the most challenging doping difficulty, while Be shows the easiest doping process, with Mg falling in between. Crystal Orbital Hamilton Population (COHP) and bond population calculations reveal the mechanism for the variation in doping structure stability. Doping induces a rearrangement of energy level orbitals, resulting in changes in the band gap. Specifically, the valence band exhibits an overall upward trend crossing the Fermi level, showing the p-type conductive properties. Notably, a significant decrease in electron density near Mg and Be leads to the formation of p-type conductive properties. The changes in hole density and effective mass further confirm the formation of p-type conductivity after doping. Additionally, structures with lower Al composition exhibit higher doping ionization degrees. This study is expected to provide a theoretical basis for the growth, preparation, and application of optoelectronic devices based on p-type AlGaN nanowires.

A comparative study of structural, mechanical, electronic and optical properties of InTe monolayer & homo-bilayer

We have done a comparative study between InTe monolayer and van der Waals homo-bilayer. Four different stacking AA, AAʹ, AB, ABʹ are taken into consideration in which possible three stackings AAʹ, AB, ABʹ are considered for the calculations. The homo-bilayer is simulated for the 10ps via ab-intio molecular dynamics to ensure kinetic stability. The mechanical properties show that the InTe homo-bilayer is more elastic than its monolayer. The indirect to direct bandgap modulations are seen from the electronic properties. The Telluride atom has a major role in the electron transfer between the layer of the homo-bilayer. The Crystal Orbital Hamilton Populations calculation is done to observe the bonding nature. Enhancement is seen in the absorption coefficient of order 105 cm−1. The highest refractive index of 3.88 is observed in the visible region. Reflectivity increases in the visible and ultraviolet regions whereas the transmittivity decreases in homo-bilayer than monolayer.

Mn-assisted Fe-electrocoagulation strategy for enhanced efficient arsenic removal and its mechanism

Electrocoagulation (EC) is a facile technique for removing arsenic (As) pollutants from different water matrices with high efficiency. In this work, a novel strategy of Mn-assisted Fe EC was developed to further enhance the removal efficiency of arsenite [As(III)] from wastewater. When 1 mM of MnCl2 was added to an Fe-EC system, the As removal efficiency reached 99.99%, and the residual concentration was only 9 μg/L, which is lower than the World Health Organization’s limit for drinking water. The characteristics of the generated flocs by four different EC processes in Fe, Fe-Mn, Fe-As, and Fe-Mn-As systems were investigated. The results showed that Mn2+ promoted the formation of FeOOH, FeOx, MnOx, FeHAsO4, and MnHAsO4 through low crystallinity and a high surface area. Density functional theory simulation and crystal orbital hamiltonian population confirmed that the generated Fe-Mn flocs had a greater adsorption affinity for As(III) and arsenate [As(V)]. The possible reactions in the EC processes and reaction mechanisms were also hypothesised. The current work provides meaningful insights into understanding the mechanisms of Mn-assisted Fe-EC systems, and further confirms its potential for practical applications in As pollution treatment.

Unleashing the impact of Nb-doped, single crystal, cobalt-free P2-type Na0.67Ni0.33Mn0.67O2 on elevating the cycle life of sodium-ion batteries

A synergistic stabilization effect in a Nb-doped P2-type single crystal cobalt-free layered oxide cathode material, offering remarkable cycling stability and high-power performance for Na-ion batteries have unveiled in this study. The introduction of Nb in the transition metal layer not only reduces the electronic band gap but also enhances electronic conductivity and mitigates ionic diffusion energy barriers. The induction of a robust Nb-O bond expedites electron and Na+ transfer, contributing to the stabilization of the host structure is further confirmed through the density functional theory calculations, including electron localization function (ELF) and crystal orbital Hamiltonian population (COHP). To the best of our knowledge, this study is the first to demonstrate a homogeneous distribution of niobium throughout the single crystal, specifically doped at the nickel site within the bulk, without inducing atomic-scale surface reorganization. The presence of single crystals improves various kinetic factors, demonstrating the profound correlation between structural defects and chemical proliferation, thereby reducing the evolution of oxygen gas. The P2-type Nb-doped single crystal cathode (Na0.67Ni0.31Mn0.67Nb0.02O2) exhibits remarkable capacity retention, >95 % after 100 cycles at 0.1 C and >90 % after an extended cycling of 2000 cycles at 1 C. Practical assessments in complete cell setups with a pre-sodiated hard carbon anode further validate the material's viability, showcasing capacity retention of over 93 % after 100 cycles in a coin cell and approximately 89 % in a pouch cell format. This comprehensive study establishes the transformative potential of Nb-doped single crystal cobalt-free P2-type layered oxide cathode materials, marking a significant advancement in sodium-ion battery technology.

Effect of phase transition on the piezoelectric properties of scandium-alloyed gallium nitride

In this study, the piezoelectric properties of scandium-alloyed gallium nitride (ScGaN), which is expected to be applied to microelectromechanical systems devices, are evaluated by first-principles calculations. The piezoelectric constant (d33) of GaN is found to increase by up to approximately 30 times upon the addition of 62.5 mol. % of Sc. The piezoelectric stress constant (e33) increases and the elastic constant (C33) decreases with increasing Sc content of ScGaN, driving the rise of d33. The improved piezoelectric properties of ScGaN compared with those of GaN are largely attributed to elastic softening, which is thought to be related to the transition from a wurtzite to hexagonal boron nitride (h-BN) structure driven by the change in bonding states between atoms caused by the addition of Sc to GaN. The crystal orbital Hamilton population analysis suggests that addition of Sc to GaN results in the combination of weaker Sc–N and Ga–N bonding, which makes the crystal structure unstable. This weakened bonding is thought to be the main cause of the destabilization of the wurtzite structure and transition to the h-BN structure of ScGaN. The elastic softening associated with this structural transition leads to the dramatic improvement in piezoelectric properties.

Embedded metal inducing electron accumulation of multi-mesoporous pyridinic-N doped carbon for enhancing *COOH adsorption in electrochemical CO2 reduction

Nitrogen-doped carbon (NC) for carbon dioxide reduction reaction (CO2RR) are promising candidates. However, its selectivity and activity are limited by the undeveloped pore and limited electronic effect. Herein, we propose a strategy of three birds with one stone to utilize the embedded nickel for inducing electron-rich pyridinic-NC with multimodal porous structure based on the hard template assisted sacrificial template method. Nickel acts as sacrificial agent and inducer to facilitate the formation of mesoporous and reactive nitrogen species for capturing and activating reactants, respectively. Besides, we find that nickel as electron donor endows the NC with electron accumulation for participating actively in PCET reaction. The resultant Ni0.87-NC-1-AE exhibits an eminent FECO of 97.6 % with excellent activity and stability. In-situ Raman spectroscopy and the projected crystal orbital Hamilton populations (pCOHP) confirm the accumulation of *COOH and the stable adsorption of *COOH on the surface. What’s more, the well-designed experiments and DFT calculations accurately locate pyridinic-N as the active site, where the aggregated electrons donated by nickel significantly reduce the energy barrier of rate-determining step and promote the desorption of CO. This work provides an instructive perspective to construct advanced NC electrocatalysts with high mass transfer efficiency and high catalytic activity.

Hardness of surface hydroxyls and its pivotal role in the flotation of cassiterite from quartz via lead ions activation

Current research has trouble explaining the selective flotation mechanism realized by metal ions, which hinders the advancement of effective flotation techniques. In this work, the selective activation flotation of cassiterite from quartz with Pb2+ is taken as an example to illustrate the pivotal roles of surface hydroxyls in selective flotation. Accordingly, flotation, adsorption amount, and X-ray photoelectron spectroscopy (XPS) measurements and systematic first-principles calculations have been used to investigate the roles of hydroxyl groups on the selective adsorption of Pb2+. The obtained flotation, adsorption amount, and XPS test results consistently show that the Pb2+ can more strongly interplay with cassiterite than quartz resulting in selective flotation of cassiterite from quartz. The electron localization functional results illustrate that the electron localization of oxygen of Si-O bonds is stronger than the Sn-O bond resulting in the weaker electron migration ability (high hardness) of oxygen atoms of quartz than oxygen atoms of cassiterite. This makes the cassiterite surface hydroxyl groups less hard than quartz. Further crystal orbital Hamilton population and partial density of states show that the Pb2+ interacts with the oxygen atoms on cassiterite forming chemical bonds before and after the adsorption of benzohydroxamic acid (BHA). On the other hand, the interaction of Pb2+ with quartz is physical in the presence of BHA. The strong adsorption of Pb2+ on cassiterite makes it easier for BHA adsorption which accounts for the selective flotation of cassiterite from quartz. This work sheds new light on establishing a consistent and dependable theory that the hardness of surface hydroxyls is the original factor affecting the selective adsorption of metal ions on oxide mineral surfaces.