An efficient removal mechanism for different hydrophilic antibiotics from aquatic environments by Cu–Al–Fe–Cr quasicrystals

The work studied the adsorption properties and mechanism of Cu–Al–Fe–Cr quasicrystals (QCs) for the adsorption of ibuprofen (IBU), tedizolid phosphate (TZD), and sulbactam sodium (SAM) for the first time. The experimental results showed that quasicrystals were good adsorbents with great potential. The structure, surface morphology, and elemental composition of QCs were investigated by XPS, XRD, SEM, EDX, particle size, DSC-TG, and FTIR. The adsorption pH, kinetics, thermodynamics, and isotherms of IBU, TZD, and SAM in QCs were systematically studied. QCs had good adsorption performance for antibiotics, and the adsorption capacities of IBU, TZD, and SAM were 46.964, 49.206, and 35.292 mg g⁻¹ at the concentration of 25 mg L⁻¹, respectively. The surface charge and hydrophobicity of QCs were affected by changing pH, thereby affecting the adsorption performance of QCs. The main driving forces of adsorption included electrostatic force and hydrophobicity.

Adsorption of three antibiotic drugs (ibuprofen, sulbactamsodium, and terdiazole phosphate) with different hydrophobicity by using Cu–Al–Fe–Cr quasicrystals with multilayer structure as the adsorbent was investigated.     

Hydrogen storage behavior of nanocrystalline and amorphous Mg–Ni–Cu–La alloys

Alloying and structural modification are two effective ways to enhance the hydrogen storage kinetics and decrease the thermal stability of Mg and Mg-based alloys. In order to enhance the characteristics of Mg₂Ni-type alloys, Cu and La were added to an Mg₂Ni-type alloy, and the sample alloys (Mg₂₄Ni₁₀Cu₂)_100−xLa_x (x = 0, 5, 10, 15, 20) were prepared by melt spinning. The influences of La content and spinning rate on the gaseous and electrochemical hydrogen storage properties of the sample alloys were explored in detail. The structural identification carried out by XRD and TEM indicates that the main phase of the alloys is Mg₂Ni and the addition of La results in the formation of the secondary phases LaMg₃ and La₂Mg₁₇. The as-spun alloys have amorphous and nanocrystalline structures, and the addition of La promotes glass formation. The electrochemical properties examined by an automatic galvanostatic system show that the samples possess a good activation capability and achieve their maximal discharge capacities within three cycles. The discharge potential characteristics were vastly ameliorated by melt spinning and La addition. The discharge capacities of the samples achieve their maximal values as the La content changes, and the discharge capacities always increase with increasing spinning rate. The addition of La leads to a decline in hydrogen absorption capacity, but it can effectively enhance the rate of hydrogen absorption. The addition of La and melt spinning significantly increase the hydrogen desorption rate due to the reduced activation energy.

In order to enhance the characteristics of Mg₂Ni-type alloys, Cu and La were added to an Mg₂Ni-type alloy, and sample alloys were prepared by melt spinning. The effects of La content and spinning rate on the hydrogen storage properties were explored.     

Insight into the electronic and thermodynamic properties of NbSi2 from first-principles calculations

The electronic and thermodynamic properties of NbSi₂ with four structures (C40, C11_b, C54 and C49) were studied in terms of first-principle calculations. The band structure and density of states of four NbSi₂ are calculated. Those disilicides show electronic properties because the band gap between the conduction band and the valence band is near the Fermi level. Their metallic character is mainly due to the strong metallic interaction between the Nb-4d state and Si-3p state. The formed Si–Si covalent bond is mainly concentrated in the valence band. The valence electron configuration of Nb–Si and Si–Si bonds is also explored. Besides, we study the thermodynamic properties of NbSi₂ as a function of temperature. The results indicate that the C54 structure has the best thermal stability in the obtained phases. In particular, the Debye temperature and heat capacity of the C54 structure are 547.8 K and 142.7 J mol⁻¹ K⁻¹, respectively. The calculated phonon DOS provides the explanation that the nature of the thermodynamic properties is mainly derived from the vibration of Si atoms.

The electronic and thermodynamic properties of NbSi₂ with four structures (C40, C11_b, C54 and C49) were studied in terms of first-principle calculations.     

Molecular dynamics simulations of the initial oxidation process on ferritic Fe–Cr alloy surfaces

Oxidation processes of metallic interconnects are crucial to the operation of solid oxide fuel cells (SOFCs), and ferritic Fe–Cr alloy is one of the most important metallic interconnect materials. Based on the ReaxFF reactive potential, the interaction of O₂ molecules with three types of surfaces (100, 110, 111) of ferritic Fe–Cr alloy has been studied by classical molecular dynamics at constant O₂ concentrations and temperatures. The initial oxidation process is systematically studied according to the analysis of O₂ absorption rate, charge variations, charge distributions, mean squared distributions, and oxidation rate. The results reveal that it is easier and faster for the Cr atoms to lose electrons than for the Fe atoms during the oxidation process. The obtained oxidation rate of Cr atoms is larger and the formation of Cr₂O₃ takes precedence over that of FeO. And the thickness of oxidation layers of different surfaces could be determined quantitatively. We also find that the high O₂ concentration accelerates the oxidation process and obviously increases the thickness of oxidation layers, while the temperature has a weaker effect on the oxidation process than the O₂ concentration. Moreover, the (110) surface presents the best oxidation resistance compared to the other two surfaces. And the (110) surface is efficient in preventing Fe atoms from being oxidized. Here we explore the initial oxidation process of Fe–Cr alloy and the corresponding results could provide theoretical guides to the related experiments and applications as metallic interconnects.

Based on the ReaxFF reactive potential, the interaction of O₂ molecules with three types of surfaces (100, 110, 111) of ferritic Fe–Cr alloy has been studied by classical molecular dynamics at constant O₂ concentrations and temperatures.     

Insight into the enhanced photocatalytic activity of Mo and P codoped SrTiO3 from first-principles prediction

In this study, the synergistic effect of cation codoping (Mo and the cation P) on the band structure of SrTiO₃ is demonstrated to enhance its photocatalytic activity. The electronic structure and optical properties of (Mo + P) codoped SrTiO₃ are examined by performing GGA + U calculations. The results show that the strong hybridization between the Mo 4d states and the O 2p states assisted by the non-metal P leads to the formation of fully occupied and delocalized intermediate states (IBs) near the valence band of SrTiO₃. The proximity of IBs to the valence band resulted in the ability to separate photo-excited electrons from reaction holes, which helps to ensure efficient electron replenishment reducing the probability of trapping electrons from the CB. This kind of metal Mo and non-metal P-compensated codoping can efficiently narrow the band gap and enhance the visible-light absorption. Moreover, the positions of the band edges after codoping (Mo + P) are found to be thermodynamically favorable for water splitting.

In this study, the synergistic effect of cation codoping (Mo and the cation P) on the band structure of SrTiO₃ is demonstrated to enhance its photocatalytic activity.     

Nucleation and growth for magnesia inclusion in Fe–O–Mg melt

The crystallization process of magnesia in iron melt begins with nucleation, which determines the structure and size of magnesia inclusions. Thus, it is necessary to have a deep insight into the crystallization of magnesia by two-step nucleation mechanisms. In this work, the two-step nucleation method was used to investigate the behavior during the early stages of magnesia inclusions crystallization. A first principles method was applied to calculate the thermodynamic properties of magnesia crystal from various cluster structures for the formation of magnesia inclusions. Based on the numerical results, the nucleation mechanism of magnesia in liquid iron has been discussed. The magnesia clusters appear as the structural units for Mg-deoxidation reaction in the liquid iron, and the residual magnesia clusters are the reason for the supersaturation ratio or the excess oxygen for MgO formation in the liquid iron. Based on the comparison between Mg-deoxidation equilibrium experiments and numerical results, the previous experiments may be in a different thermodynamic state. The equilibrium reaction product should be not only magnesia clusters but also bulk-magnesia in those equilibrium experiments.

The crystallization process of magnesia involves two steps.     

Electronic structure of strain-tunable Janus WSSe–ZnO heterostructures from first-principles

The electronic structure of semiconducting 2D materials such as monolayer transition metal dichalcogenides (TMDs) are known to be tunable via environment and external fields, and van der Waals (vdW) heterostructures consisting of stacks of distinct types of 2D materials offer the possibility to further tune and optimize the electronic properties of 2D materials. In this work, we use density functional theory (DFT) calculations to calculate the structure and electronic properties of a vdW heterostructure of Janus monolayer WSSe with monolayer ZnO, both of which possess out of plane dipole moments. The effects of alignment, biaxial and uniaxial strain, orientation, and electric field on dipole moments and band edge energies of this heterostructure are calculated and examined. We find that the out of plane dipole moment of the ZnO monolayer is highly sensitive to strain, leading to the broad tunability of the heterostructure band edge energies over a range of experimentally-relevant strains. The use of strain-tunable 2D materials to control band offsets and alignment is a general strategy applicable to other vdW heterostructures, one that may be advantageous in the context of clean energy applications, including photocatalytic applications, and beyond.

Using strain engineering to optimize novel heterostructure materials to produce hydrogen from water.     

Insight into trifluoromethylation – experimental electron density for Togni reagent I

3,3-Dimethyl-1-(trifluoromethyl)-1,3-dihydro-1-λ3,2-benziodoxole represents a popular reagent for trifluoromethylation. The σ hole on the hypervalent iodine atom in this “Togni reagent” is crucial for adduct formation between the reagent and a nucleophilic substrate. The electronic situation may be probed by high resolution X-ray diffraction: the experimental charge density thus derived shows that the short intermolecular contact of 3.0 Å between the iodine and a neighbouring oxygen atom is associated with a local charge depletion on the heavy halogen in the direction of the nucleophile and visible polarization of the O valence shell towards the iodine atom. In agreement with the expectation for λ3-iodanes, the intermolecular O⋯I–C_aryl halogen bond deviates significantly from linearity.

The experimentally observed electron density for the “Togni reagent” explains the interaction of the hypervalent iodine atom with a nucleophile.

A “halogen bond” denotes a short contact between a nucleophile acting as electron density donor and a (mostly heavy) halogen atom as electrophile;^1,2 halogen bonds are a special of σ hole interactions.^3–5 Such interactions do not only play an important role in crystal engineering;^6–11 rather, the concept of a nucleophile approaching the σ hole of a neighbouring atom may also prove helpful for understanding chemical reactivity.The title compound provides an example for such a σ hole based reactivity: 3,3-dimethyl-1-(trifluoromethyl)-1,3-dihydro-1-λ3,2-benziodoxole, 1, (Scheme 1) commonly known as “Togni reagent I”, is used for the electrophilic transfer of a trifluoromethyl group by reductive elimination. The original articles in which the application of 1¹² and other closely related “Togni reagents”¹³ were communicated have been and still are highly cited. Trifluoromethylation is not the only application for hypervalent iodine compounds; they have also been used as alkynylating¹⁴ or azide transfer reagents.^15,16 The syntheses of hypervalent iodanes and their application in organofluorine chemistry have been reviewed,¹⁷ and a special issues of the Journal of Organic Chemistry has been dedicated to Hypervalent Iodine Catalysis and Reagents.¹⁸ Recently, Pietrasiak and Togni have expanded the concept of hypervalent reagents to tellurium.¹⁹Open in a separate windowScheme 1Lewis structure of the Togni reagent, 1.Results from theory link σ hole interactions and chemical properties and indicate that the electron density distribution associated with the hypervalent iodine atom in 1 is essential for the reactivity of the molecule in trifluoromethylation.²⁰ Lüthi and coworkers have studied solvent effects and shown that activation entropy and volume play relevant roles for assigning the correct reaction mechanism to trifluoromethylation via1. These authors have confirmed the dominant role of reductive elimination and hence the relevance of the σ hole interaction for the reactivity of 1 in solution by ab initio molecular dynamics (AIMD) simulations.^21,22 An experimental approach to the electron density may complement theoretical calculations: low temperature X-ray diffraction data of sufficient resolution allow to obtain the experimental charge density and associate it with intra- and inter-molecular interactions.^23–25 Such advanced structure models based on aspherical scattering factors have also been applied in the study of halogen bonds.^26–30 In this contribution, we provide direct experimental information for the electronic situation in Togni reagent I, 1; in particular, we analyze the charge distribution around the hypervalent iodine atom.Excellent single crystals of the title compound were grown by sublimation.^§ The so-called independent atom model (IAM), i.e. the structure model based on conventional spherical scattering factors for neutral atoms, confirms the solid state structure reported by the original authors,¹² albeit with increased accuracy. As depicted in Fig. 1, two molecules of 1 interact via a crystallographic center of inversion. The pair of short intermolecular O⋯I contacts thus generated can be perceived as red areas on the interaction-sensitive Hirshfeld surface.³¹Open in a separate windowFig. 1Two neighbouring molecules of 1, related by a crystallographic center of inversion. The short intermolecular I⋯O contacts show up in red on the Hirshfeld surface³² enclosing the left molecule. (90% probability ellipsoids, H atoms omitted, symmetry operator 1 − x, 1 − y, 1 − z).The high resolution of our diffraction data ^¶ for 1 allowed an atom-centered multipole refinement^33,34 and thus an improved model for the experimental electron density which takes features of chemical bonding and lone pairs into account. Fig. 2 shows the deformation density, i.e. the difference electron density between this advanced multipole model and the IAM in the same orientation as Fig. 1.^|| The orientation of an oxygen lone pair (blue arrow) pointing towards the σ hole of the heavy halogen in the inversion-related molecule and the region of positive charge at this iodine atom (red arrow) are clearly visible. Single-bonded terminal halides are associated with one σ hole opposite to the only σ bond, thus resulting in a linear arrangement about the halogen atom. Different geometries and potentially more than a single σ hole are to be expected for λ3-iodanes such as our target molecule, and as a tendency, the resulting halogen bonds are expected to be weaker than those subtended by single-bonded iodine atoms.³⁵ In agreement with these theoretical considerations, the closest I⋯O contacts in 1 amount to 2.9822(9) Å. This distance is significantly shorter than the sum of the van-der-Waals radii (I, 1.98 Å; O, 1.52 Å (ref. 36)) but cannot compete with the shortest halogen bonds between iodine and oxygen^37,38 or iodine and nitrogen.^39–41Fig. 1 and ​and22 show that the C_aryl–I⋯O contacts are not linear; they subtend an angle C10–I1⋯O1′ of 141.23(3)° at the iodine atom. On the basis of theoretical calculations, Kirshenboim and Kozuch³⁵ have suggested that the split σ holes should be situated in the plane of the three substituents of the hypervalent atom and that halogen and covalent bonds should be coplanar. Fig. 3 shows that the C_aryl–I⋯O interaction in 1 closely matches this expectation, with the next oxygen neighbour O1′ only 0.47 Å out of the least-squares plane through the heavy halogen I1 and its three covalently bonded partners C1, O1 and C10.Open in a separate windowFig. 2Deformation density for the pair of neighbouring molecules in 1; the dashed blue and red arrows indicate regions of opposite charge. (Contour interval 0.10e Å⁻³; blue lines positive, red lines negative, green lines zero contours, symmetry operator 1 − x, 1 − y, 1 − z).Open in a separate windowFig. 3A molecule of 1, shown [platon] along O1⋯C1, and its halogen-bonded neighbour O1ⁱ. Symmetry operator 1 − x, 1 − y, 1 − z.The Laplacian, the scalar derivative of the gradient vector field of the electron density, emphasizes local charge accumulations and depletions and it allows to assess the character of intra- and inter-molecular interactions. A detailed analysis of all bonds in 1 according to Bader''s Atoms In Molecules theory⁴² is provided in the ESI.^‡ We here only mention that the electron density in the bond critical point (bcp) of the short intermolecular I⋯O contact amounts to 0.102(5)e Å⁻³; we are not aware of charge density studies on λ3-iodanes, but both the electron density and its small positive Laplacian match values experimentally observed for halogen bonds involving O and terminal I in the same distance range.⁴³The crystal structure of 1 necessarily implies additional contacts beyond the short halogen bond shown in Fig. 1 and ​and2.2. The shortest among these secondary interactions is depicted in Fig. 4: it involved a non-classical C–H⋯F contact with a H⋯F distance of 2.55 Å.Open in a separate windowFig. 4C–H⋯F contact in 1; additional information has been compiled in the ESI.^‡ Symmetry operators i = 1 − x, 1 − y, 1 − z; ii = 1 − x, 1 − y, −z.The topological analysis of the experimental charge density reveals that this non-classical C–H⋯F hydrogen bond and all other secondary contacts are only associated with very small electron densities in the bcps. Table S8 in the ESI^‡ provides a summary of this analysis and confirms that the I⋯O halogen bond discussed in Fig. 1 and ​and22 represents by far the most relevant intermolecular interaction.The relevance of this halogen bond extends beyond the crystal structure of 1: Insight into the spatial disposition of electrophilic and nucleophilic regions and hence into the expected reactivity of a molecule may be gained from another electron-density derived property, the electrostatic potential (ESP). The ESP for the pair of interacting molecules in 1 is depicted in Fig. 5.Open in a separate windowFig. 5Electrostatic potential for a pair of molecules in 1 mapped on an electron density isosurface (ρ = 0.5e Å⁻³; program MoleCoolQt^44,45). Fig. 5 underlines the complementary electrostatic interactions between the positively charged iodine and the negatively charged oxygen atoms. One can easily imagine to “replace” the inversion-related partner molecule in crystalline 1 by an incoming nucleophile.The ESP tentatively obtained for a single molecule in the structure of 1 did not differ significantly from that derived for the inversion-related pair (Fig. 5), and even the results from theoretical calculations in the gas phase for an isolated molecule²⁰ are in good qualitative agreement with our ESP derived from the crystal structure. In the absence of very short contacts, polarization by neighbouring molecules only has a minor influence on the ESP. The experimentally observed electron density matches the proven reactivity for the title compound, and we consider it rewarding to extend our charge density studies on related hypervalent reagents.     

Effects of Sm on Fe–Mn catalysts for Fischer–Tropsch synthesis

Sm-promoted FeMn catalysts were prepared by the co-precipitation method and characterized by N₂ adsorption, XRD, CO-TPD, H₂-TPD, CO₂-TPD, H₂-TPR, XPS and MES. It was found that compared with the un-promoted catalyst, when Sm was added at a proper content, the catalyst showed a larger BET surface area and promoted the formation of iron particles with a smaller size. The presence of Sm could increase the surface charge density of iron, which enhanced the Fe–C bond and promoted the stability and amount of CO dissociated adsorption, as confirmed by XPS and CO-TPD. Furthermore, according to MES, Sm could promote the formation of Fe₅C₂, which was the active phase of FTS. In addition, Sm could also enhance the basicity of the catalysts and suppress the H₂ adsorption capacity, which inhibited the hydrogenation reaction and the conversion of olefins to paraffins, as verified by the results of CO₂-TPD and H₂-TPD. According to the FTS performance results, compared with the observations for the un-promoted catalysts, when the molar ratio of Sm to Fe was 1%, the CO conversion increased from 63.4% to 70.4%, the sum of light olefins in the product distribution increased from 26.6% to 32.6, and the ratio of olefins to paraffins increased to 4.18 from 4.09.

The effect of samarium on iron-based catalysts for Fischer–Tropsch synthesis was investigated.     

Thermodynamic insight into the growth of calcia inclusions at the nanoscale: the case of Fe–O–Ca melt

A thermodynamic model was developed to investigate the relationship between the thermodynamics of nano-CaO as a deoxidation reaction product and their size in an Fe–O–Ca melt. The results of thermodynamic model coupling with DFT (density functional theory) calculation prediction showed that the solubility product of calcium and oxygen for nanoscale CaO decreased with the increase of calcia product size in an Fe–O–Ca melt. The existing experimental data about the Ca-deoxidation equilibrium in liquid iron are covered by the region between the bulk-calcia equilibrium curve and the nano-CaO of 2 nm size curve. This result indicates that the partial product in most of the Ca-deoxidation experiments could be nanoscale CaO particles. Most of the Ca-deoxidation experimental equilibrium states are not reaching the equilibrium state between bulk calcia and liquid iron but a multi-equilibria between bulk- and nano-CaO and liquid iron.

Thermodynamics of the formation of nano-CaO in liquid iron is important to explore the relationship between deoxidation reaction and size of inclusions, and is very useful in the size controlling of inclusions.     

Insight into carbon quantum dot–vesicles interactions: role of functional groups

Understanding carbon quantum dot–cell membrane interaction is essential for designing an effective nanoparticle-based drug delivery system. In this study, an attempt has been made to study the interaction involving phosphatidylcholine vesicles (PHOS VES, as model cell membrane) and four different carbon quantum dots bearing different functional groups (–COOH, –NH₂, –OH, and protein bovine serum albumin coated) using various tools such as PL behavior, surface charge on vesicles, QCM, ITC, TEM, LSV, and FTIR. From the above studies, it was observed that the –NH₂ terminating carbon dots were capable of binding strongly with the vesicles whereas other functional groups bearing carbon dots were not significantly interacting. This observation was also supported by direct visual evidence as shown by transmission electron microscopy, which shows that the polyethyleneimine carbon dot (PEICD) bearing –NH₂ functionality has greater affinity towards PHOS VES. The mechanistic insight presented in the paper indicates greater possibility of higher H-bonding, signifying better interaction between –NH₂ functionalized carbon dots and PHOS VES supported by FTIR, QCM, ITC and TEM. Moreover, the transport of neurotransmitters (which are generally amine compound) in neurons for cellular communication through synapse is only possible through vesicular platforms, showing that in our body, such interactions are already present. Such studies on the nano–bio interface will help biomedical researchers design efficient carbon-based nanomaterial as drug/gene delivery vehicles.

An interaction study at the nano–bio interface involving phosphatidylcholine vesicles (as a model cell membrane) and four different carbon dots bearing different functional groups (–COOH, –NH₂, –OH, and BSA-coated).     

The effects of Sn content on the corrosion behavior and mechanical properties of Mg–5Gd–3Y–xSn–0.5Zr alloys

The effects of Sn content on the corrosion behavior and mechanical properties of Mg–5Gd–3Y–0.5Zr alloy were studied by SEM, EDS, XRD and electrochemical testing. Results show that Sn can refine the grain size and promote the precipitation of Mg₅(Gd,Y) phase. When the Sn content is 1.5–2 wt%, a needle-like Mg₂Sn phase will be precipitated in the alloy. Mg–5Gd–3Y–1Sn–0.5Zr alloy had the lowest corrosion rate, which is attributed to the barrier effect of the grain boundary and dispersed Mg₅(Gd,Y) phase on corrosion. However, the Mg₂Sn phase formed by excessive Sn addition will accelerate galvanic corrosion. At the same time, Mg–5Gd–3Y–1Sn–0.5Zr alloy had best mechanical properties. In 1.5Sn and 2Sn alloys, the cleavage effect of the needle-like Mg₂Sn phase on the matrix reduced mechanical properties.

The effects of Sn content on the corrosion behavior and mechanical properties of Mg–5Gd–3Y–0.5Zr alloy were studied by SEM, EDS, XRD and electrochemical testing. Results show that Sn can refine the grain size and promote the precipitation.     

A first-principles calculation of structural,mechanical, thermodynamic and electronic properties of binary Ni–Y compounds

The intermetallic compounds between rare earth (RE) elements and transition metal elements have been comprehensively researched due to their appealing magnetic, electronic, optical and thermal properties, in which Ni–Y alloys are one kind of important system. In this work, a systematic investigation concerned with structures, elastic, and thermodynamic properties of Ni₁₇Y₂, Ni₅Y, Ni₇Y₂, Ni₃Y, Ni₂Y, NiY, Ni₂Y₃ and NiY₃ in Ni–Y systems is implemented by means of first-principles calculations. NiY has the lowest formation enthalpy within −0.49 kJ per mol per atom. Ni₅Y has the largest bulk modulus, shear modulus and Young''s modulus of 181.71 GPa, 79.75 GPa and 208.70 GPa, respectively. Furthermore, the effects of different concentrations of yttrium on the mechanical and thermal properties of Ni–Y compounds are estimated by using the Voigt–Reuss method. The electronic density of states and chemical bonding between Ni and Y are key factors that determine mechanical and thermodynamic properties of these compounds. What''s more, results indicate that all compounds are dynamically stable as shown by the calculated phonon dispersions.

A systematic investigation concerned with structures, elastic, and thermodynamic properties of Ni₁₇Y₂, Ni₅Y, Ni₇Y₂, Ni₃Y, Ni₂Y, NiY, Ni₂Y₃ and NiY₃ in Ni–Y system.     

Mn promotes the rate of nucleation and growth of precipitates by increasing Frenkel pairs in Fe–Cu based alloys

Fe–1.0Cu (at%) and Fe–1.2Cu–2.2Mn alloys aged at 450 °C for 0.25 h, 1 h, 2 h, and 16 h after solution treatment at 900 °C for 2 h are investigated to reveal the role of the addition of Mn on the Cu precipitates in Fe–Cu based alloys. Density functional theory (DFT) total energy calculations on point defects and their influence on Cu precipitates are also performed to understand the nucleation and growth of Cu precipitates. Experiments show that addition of Mn can slightly increase the aging peak hardness by 10 HV; by using atom probe tomography (APT) and optical microscopy, we identify that the increase in hardness derives from both grain refinement and the increase of number density of precipitates. DFT calculations show that Mn increases the formation possibility of Frenkel pairs, i.e., atomic vacancy and self-interstitial atoms, and these two types of defects both serve as nucleation sites of Cu precipitates, resulting in the increase of the nucleation centers number density, which is consistent with our APT experiments on the very initial stage of aging. Moreover, calculated results show that Mn increases the density of atomic vacancies and promotes the evolution rate of Cu precipitates, which accounts for our APT experiments where precipitates in Fe–Cu–Mn grow more quickly than in Fe–Cu. Finally, we also discuss the relationship between Mn content in reactor pressure vessel steels and its irradiation damage effects.

Fe–1.0Cu (at%) and Fe–1.2Cu–2.2Mn alloys aged at 450 °C for 0.25 h, 1 h, 2 h, and 16 h after solution treatment at 900 °C for 2 h are investigated to reveal the role of the addition of Mn on the Cu precipitates in Fe–Cu based alloys.     

Tunable and convenient synthesis of highly dispersed Fe–Nx catalysts from graphene-supported Zn–Fe-ZIF for efficient oxygen reduction in acidic media

The development of low-cost, efficient and stable electrocatalysts for the oxygen reduction reaction (ORR) is desirable but remains a great challenge. We report a convenient and efficient synthesis approach of highly dispersed Fe–N_x catalysts for ORR. Typically, Fe–Zn-ZIF (zeolitic imidazolate frameworks) nanocrystals cast as precursor and graphene as supports, highly dispersed Fe–N_x species were fabricated with PVP (polyvinyl pyrrolidone) as surfactant via pyrolysis. With the help of graphene and surfactant, the agglomeration of iron particles has been avoided during pyrolysis, and the size and morphology of ZIF particles intercalating into the graphene layers can be regulated precisely as well. The amount of Fe–N_x active sites in C-rGO-ZIF catalyst arrived 4.29%, which is obviously higher than most monodispersed non-precious metal catalysts reported. The obtained C-rGO-ZIF catalyst exhibits a high onset potential of 0.89 V and a half-wave potential of 0.77 V, which is only 30 mV away from Pt/C in acidic media. The active sites of the catalyst was characterized and found to be the highly dispersed Fe–N_x species, large and accessible specific surface area of graphene and abundant active nitrogen atoms. When the C-rGO-ZIF catalyst was applied in the cathode of fuel cell, the power density can reach up to 301 mW cm⁻², which highlights a practical application potential on small power supplies.

A tunable and convenient synthesis approach of highly dispersed Fe–N_x catalysts for ORR in acidic media was reported.     

Promoted dispersion and uniformity of active species on Fe–Ce–Al catalysts for efficient NO abatement

Fe–Ce–Al catalysts were synthesized by the co-precipitation method (labeled as Fe–Ce–Al–P), co-impregnation method (Fe–Ce–Al–I), and direct mixing method (Fe–Ce–Al–M), respectively, and used for effective removal of NO. The synthesized catalysts were characterized by many methods including N₂ physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), NH₃-temperature programmed desorption (NH₃-TPD), H₂-temperature programmed reduction (H₂-TPR), high-resolution transmission electron microscopy (HR-TEM), and energy dispersive spectroscopy (EDS) mapping. The results show that the synthesis methods greatly influence the catalytic performance of catalysts. The Fe–Ce–Al–P catalyst prepared by the co-precipitation method yields the highest catalytic performance, while the Fe–Ce–Al–I and Fe–Ce–Al–M catalysts exhibit relatively low catalytic activity. The co-precipitation method can promote the accumulation and dispersion of more surface active species on the catalyst surface, and provide smaller particle size of active species and generate more uniform particle size distribution, while these characteristics can''t be obtained by the co-impregnation method and direct mixing method. Moreover, the co-precipitation method could produce the highest surface area and enhanced redox ability and surface acidity of the catalyst, which resulted from the high dispersion and uniform distribution of surface active species. These may be the key factors to the superior catalytic performance of the Fe–Ce–Al–P catalyst.

Fe–Ce–Al catalysts were synthesized by the co-precipitation method (labeled as Fe–Ce–Al–P), co-impregnation method (Fe–Ce–Al–I), and direct mixing method (Fe–Ce–Al–M), respectively, and used for effective removal of NO.     

Facile synthesis of a hollow Ni–Fe–B nanochain and its enhanced catalytic activity for hydrogen generation from NaBH4 hydrolysis

A hollow Ni–Fe–B nanochain is successfully synthesized by a galvanic replacement method using a Fe–B nanocomposite and a NiCl₂ solution as the template and additional reagent, respectively. Both the concentration of Ni and the morphology of the resulting Ni–Fe–B alloy are controlled by varying the duration of the replacement process during the synthesis. The Ni–Fe–B sample synthesized for 60 min (Ni–Fe–B-60) shows the best catalytic activity at 313 K, with a hydrogen production rate of 4320 mL min⁻¹ g_cat⁻¹ and an activation energy for the NaBH₄ hydrolysis reaction of 33.7 kJ mol⁻¹. The good performance of Ni–Fe–B-60 towards the hydrolysis of NaBH₄ can be ascribed to both hollow nanochain structural and electronic effects. Furthermore, the effects of temperature, catalyst amount, and concentration of NaOH and NaBH₄ on the hydrolysis process are systematically studied, and an overall kinetic rate equation is obtained. The hollow Ni–Fe–B nanochain catalyst also shows good reusability characteristics and maintained its initial activity after 5 consecutive cycles.

A hollow Ni–Fe–B nanochain is successfully synthesized by a galvanic replacement method using a Fe–B nanocomposite and a NiCl₂ solution as the template and additional reagent, respectively.     

Understanding the active sites of Fe–N–C materials and their properties in the ORR catalysis system

Metal–N–C-based catalysts prepared by pyrolysis are frequently used in the oxygen reduction reaction (ORR). Zeolitic imidazolate frameworks (ZIFs), a type of metal organic framework (MOF), are selected as precursors due to their special structure and proper pore sizes. A series of Fe–N–C catalysts with different concentrations of 2-methylimidazole were prepared with a simple solvothermal-pyrolysis method, and the transformation productivity, morphology and ORR activity were investigated. It was found that the Fe–N–C catalyst with a 2-methylimidazole concentration of 0.53 mol L⁻¹ had the best performance. In 0.1 M KOH solution, the half-wave potential was 0.852 V (vs. RHE), with the highest electrochemically active surface area (ECSA) of 94.1 cm², and the ORR reaction was dominated by a 4-electron process. The current only decreased by 10.5% after 50 000 s of chronoamperometry (CA), while the half-wave potential only decreased 20 mV in 3 M methanol. Additionally, this catalyst cannot be poisoned by Cl⁻ and SO₃²⁻ ions in the ORR process. Finally, some typical ions including SCN⁻, Fe(CN)₆³⁻ and Fe(CN)₆⁴⁻ were used to inhibit the active sites, and it was determined that Fe(ii) is the real active species. The series of synthesis and testing experiments has significance in guiding optimization of the synthesis conditions and analysis of the mechanism of active sites in Fe–N–C materials.

Metal–N–C-based catalysts prepared by pyrolysis are frequently used in the oxygen reduction reaction (ORR).     

Effect of unmelted lime on the element distribution behavior on a CaO–SiO2–MgO–Al2O3–FeO–CaF2(–Cr2O3) slag

In this study, a CaO–SiO₂–Al₂O₃–MgO–FeO–CaF₂(–Cr₂O₃) slag was chosen according to the compositions of the stainless steel slag for industrial production, and a CaO block was added to the molten slag after the synthetic slag was fully melted. The influences of unmelted lime on the distribution of elements and the structure of product layers at the lime/slag boundary, particularly the existing state of chromium oxide in the chromium-bearing stainless steel slag, were deeply discussed by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and FactSage 7.1. The experiment results indicated that when the unmelted lime existed in the CaO–SiO₂–Al₂O₃–MgO–FeO–CaF₂ slag system, two product layers of periclase (MgO) and dicalcium silicate (Ca₂SiO₄) at the boundary of the CaO block were formed. However, when the CaO block was added in the CaO–SiO₂–Al₂O₃–MgO–FeO–CaF₂–Cr₂O₃ stainless steel slag, besides MgO and Ca₂SiO₄ product layers, needle-shaped calcium chromite (CaCr₂O₄) was also precipitated around the CaO block. Moreover, a small amount of Cr dissolved in the periclase phase. Eh–pH diagrams showed that the CaCr₂O₄ and MgO phase unstably existed in a weak acid aqueous solution. Therefore, the existence of unmelted lime in the stainless steel slag could enhance the leachability of chromium.

The effect of unmelted lime on the distribution of elements and structure of product layers in CaO–SiO₂–MgO–Al₂O₃–FeO–CaF₂(–Cr₂O₂) stainless steel slag and the action of unmelted lime phase mechanism in experimental slags was conducted.     

High-yield synthesis of Ce modified Fe–Mn composite oxides benefitting from catalytic destruction of chlorobenzene

Ce–Fe–Mn catalysts were prepared by an oxalic acid assisted co-precipitation method. The influence of Ce doping and calcination temperature on the catalytic oxidation of chlorobenzene (as a model VOC molecule) was investigated in a fixed bed reactor. The Mn₃O₄ phase was formed in Ce–Fe–Mn catalysts at low calcination temperatures (<400 °C), which introduced more chemisorbed oxygen, and enhanced the mobility of O atoms, resulting in an improvement of the reduction active of Mn₃O₄ and Fe₂O₃. Additionally, CeO₂ has strong redox properties, and Ce⁴⁺ would oxidize Mn^x+ and Fe^x+. Therefore, the interaction of Ce, Fe and Mn can improve the content of surface chemisorbed oxygen. As compared with Fe–Mn catalysts, the catalytic conversion of chlorobenzene over Ce(5%)–Fe–Mn-400 was about 99% at 250 °C, owing to high specific surface area, Mn₃O₄ phase, and Ce doping. However, with the increase in roasting temperature, the performance of the catalysts for the catalytic combustion of chlorobenzene was decreased, which probably accounts for the formation of the Mn₂O₃ phase in Ce–Fe–Mn-500 catalysts, leading to a decrease in the specific surface area and concentration of chemically adsorbed oxygen. As a result, it can be expected that the Ce–Fe–Mn catalysts are effective and promising catalysts for chlorobenzene destruction.

Ce–Fe–Mn catalysts were prepared by an oxalic acid assisted co-precipitation method.