Surface Structural Defects Research Articles

Experimental investigation and molecular dynamics simulations of plasma treatment on the interface properties of carbon fiber-reinforced PI resin composites

ABSTRACT This paper examines surface modification of carbon fibers using low-temperature plasma and investigates the temperature-dependent interfacial properties of high-performance polyimide-based composites. Additionally, the mechanisms by which air and argon plasma treatments enhance the high-temperature interfacial properties of carbon fiber-reinforced polymers (CFRP) are examined. First, the changes in physical morphology and surface structural defects of carbon fibers under different plasma atmospheres are discussed: carbon fibers develop surface protrusions after various plasma treatments, and a grooved morphology forms after argon plasma treatment. The ID/IG ratio (R value) of the carbon fiber surface increased from 1.25 in untreated fibers to 1.37 after air plasma treatment, and further to 1.60 after argon plasma treatment. The short-beam shear strength test results show that at 300°C, the ILSS (interlaminar shear strength) of argon plasma-treated laminates increased from 67.70 MPa to 87.69 MPa, a 29.53% improvement. The ILSS of air plasma-treated laminates reached 81.46 MPa, a 20.33% improvement. Argon plasma-treated laminates showed more stable interlaminar shear performance at high temperatures, maintaining an interfacial retention rate of 85.11% at 300°C. Secondly, the mechanisms by which air and argon plasma modification enhance the high-temperature interface performance of CFRP are as follows: Air treatment, due to the dual effects of chemical bonding and physical etching, allows the laminated plates to exhibit excellent performance at room temperature. However, in high-temperature environments, the chemical bonding effect is easily affected and damaged, significantly reducing the interface retention rate of the laminated plates. The etching effect of argon treatment is quite significant, which means that the improvement effect of argon mainly manifests in the mechanical interlocking action, with the chemical bonding effect being relatively small. The physical effect of mechanical interlocking is less influenced by temperature, thus the high-temperature retention rate of the laminate is relatively high. Furthermore, molecular dynamics models of the interface were built using atomic simulation to explore how plasma modification introduces active groups that enhance the interface at the molecular level. The impact of these modifications on interfacial structure and energy was analyzed using molecular dynamics metrics. Both experimental and molecular dynamics simulation results confirm that plasma treatment has a positive regulatory effect on the interface.

Impact of -OH surface defects on the electronic and structural properties of nickel oxide thin films.

Nickel oxide-based thin films and nanomaterials are a current focus of intense research efforts due to the broad range of end uses in a variety of applications. While the chemico-physical properties of bulk NiO crystals, characterized by a wide band gap (4.0-4.3 eV), antiferromagnetic ordering and p-type character, have been extensively studied, for NiO films/nanomaterials the microscopic-level relationships between the surface defect structure and electronic properties are far from being completely elucidated. In the present work, we show that, by using density functional theory with the Hubbard correction (DFT+U), -OH surface defects, almost ubiquitous on oxide surfaces, can directly influence the electronic structure of NiO(100) model slabs. Depending on the exact defect chemical structure and surface defect density, the energy gap of the -OH bearing NiO(100) system can be engineered, and its behaviour can be modulated from p-type to n-type. The insights provided herein may be of importance for the modulation of NiO nanosystem properties as a function of specific applications, an important issue for their eventual real-world utilization.

Surface Ionic Conduction of Ce0.8Gd0.2O2-Δ Multilayer Thin Films with Large Amount of Oxygen Vacancies

Gd-doped CeO2 (GDC) with high chemical stability is a good electrolyte material with high oxygen ion conduction above 600°C and surface proton conduction below 100°C in thin film form [1]. In particular, Ni-GDC cermet material is well known as anode electrode of solid oxide fuel cell (SOFC) operating at medium temperature region. Ni is suitable for the anode as it has the characteristics of being inexpensive and having high catalytic activity, which enhances the hydrogen oxidation reaction. Ni is characterized by its low cost, high catalytic activity, and enhanced hydrogen oxidation reaction. Mixtures of electronic conductors such as Ni and ionic conductors such as Yttria-stabilized zirconia (YSZ) and GDC are often used as anode materials because they expand the three-phase interface [2].Based on these backgrounds, we have attempted to realize high conductivity in GDC (Ce0.90Gd0.10O2-δ) thin films, which contain a large amount of oxygen vacancies and lattice distortion. if the GDC films show high ionic conductivity above σ T~10-1Scm-1K, the performance of SOFCs and EDLTs will be dramatically improved. performance of SOFC and EDLT will be dramatically improved. To realize this goal, thin films were prepared by sputtering method, the relationship between surface defect structure and ionic conductivity was investigated in detail, and electrodes were fabricated on the thin films with Pt and Ni thin films.Based on these backgrounds, in this study, we tried to realize high conductivity by fabricating electrodes with Ni thin films on GDC (Ce0.90Gd0.10O2- δ) with large amount of oxygen vacancies and lattice distortion. If the GDC thin films show high ionic conductivity above σ T~10-1Scm-1K, the performance of SOFCs and EDLTs will improve dramatically. In order to realize this purpose, we fabricated thin films by the sputtering method and studied in detail the relationship between the surface defect structure and ionic conductivity.The GDC thin films were prepared on Al2O3 (0001) substrates by RF magnetron sputtering using ceramic targets. The target size had a diameter of 47 mm and thickness of 3 mm. The RF power of the ceramic target was fixed at 30 W. The flow rate of Ar gas controlled by a mass-flow controller was kept at approximately 2.81 ccm. The pressure of Ar gas was fixed at 3.5 × 10−3 Torr during the deposition. The film thicknesses ~30 and ~110 nm to probe the changes in the lattice constant and the conductivity. The electrode film was fabricated on the GDC thin film using a similar method with Pt and Ni metal targets. Electrical conductivity was measured by the AC impedance method. The measurement range was 600 °C to 20 °C. The result when only Ar was filled at the time of measurement is called As-deposited, and the result when a 4:1 mixture of Ar and gases was filled at the time of measurement is called -annealed.Arrhenius plots at low temperatures below 100 °C are shown in Fig. The thin films with Pt electrode are designated as Pt-GDC and those with Ni electrode as Ni-GDC. The PES spectra show that the OH- peak appears after Wet annealing. Therefore, it can be said that surface proton conduction by the Grotthuss mechanism is taking place [3]. In comparison for Pt-GDC, the O2 annealed condition resulted in higher conductivity than the As-deposited condition. This is thought to be due to the reduction of oxygen defects in the thin film by O2 annealing and the dominance of proton conduction. Ni-GDC resulted in lower conductivity than Pt-GDC under the two conditions. For Ni-GDC, there are reports that the peak power density varied with the voltage at the time of deposition [4], that ohmic resistance decreased by moderately thickening the anode and that the power density was highest at 800 nm thickness [4], and that the oxygen reduction reaction at the cathode was promoted by the grain boundaries and lattice defects report [5] that grain boundaries and lattice defects promote the oxygen reduction reaction at the cathode.Reference[1] M, Shirpor et al. Phys. Chem. Chem. Phys., 13 (2011) 937-940.[2] I.D. Unachukwu et al. Journal of Power Sources 556 (2023) 232436[3] D. Nishioka et al, Nanoscale Res. Lett. 15 (2020) 42-49[4] S, Ryu et al. ACS Appl. Mater. Interfaces 2023, 15, 11845−11852[5] Y, Li et, al, Scientific Reports 6, 22369 (2016) Figure 1

Excellent antibiotic degradation through PMS activation via bio derived Fe-Mn oxides with tunable defect concentration: Synergy between singlet oxygen oxidation and electron transfer

Regulating the defect sites and structural composition of metal-based metal catalysts is an effective strategy to improve the activity of activating PMS to degrade pollutants. Herein, bio derived Fe/Mn composite oxides (BFMO) rich in oxygen vacancy composed of crystalline manganese oxide coated with amorphous iron oxide was prepared through microbial mediation, and used for PMS activation in the degradation of tetracycline (TC). After 60 minutes reaction, the removal rate of TC achieved 92.4 %−98.8 % within wide pH range of 3–12. Besides, this system has outstanding anti-interference ability to common ions and humic acid (HA). The outstanding catalytic performance stemmed from the non-radical pathway for producing singlet oxygen (1O2) and electron transfer, facilitated by defect-rich polyvalent Mn and amorphous Fe species. Polyvalent Mn species accelerate the electron transfer process, and its surface defect structure further promotes the adsorption of pollutants on the surface of the materials. The redox cycle of Fe3+/Fe2+ was accelerate via electron-rich groups. This study explored the synergy triggered by microbe-mediated defect sites and structure-dependent, providing a design strategy for environmental remediation of PMS activated by Fe/Mn based bimetallic catalysts with strong resistance to environmental interference.

Surface nitrogen defect modified crystalline carbon nitride spheres with boosted carrier dynamics for efficient solar hydrogen production

Engineering of the defective structure and crystallinity of semiconductor photocatalysts to promote carrier dynamics has attracted considerable attention. This study presents the design of surface nitrogen defect modified crystalline carbon nitride spheres (QCN) with synergistically boosted surface and bulk carrier separation through a rapid thermal treatment coupled with a flux assisted strategy. Using supramolecular self-assembled polymer as the precursor, spherical crystalline CN heterojunctions are firstly prepared by a molten salt method to improve the separation of bulk carriers. Abundant nitrogen defects are then introduced onto the surface of crystalline CN through the following quick thermal treatment in air, which can generate a higher exciton density and drive rapid migration of surface carriers by acting as effective electron sinks. Furthermore, the defect level also improves the visible light utilization and provides more active centers for reactant adsorption and activation. As a result, QCN samples exhibit excellent performance in photocatalytic hydrogen evolution, with an optimal hydrogen production rate 4.3 times higher than that of pristine bulk CN under visible light irradiation. Moreover, the photocatalytic activities of QCN are dependent on the concentration of nitrogen defects, which can be flexibly adjusted via thermal treatment temperature. Such a two-step regulation strategy combining the distinctive advantages of surface defect structure and high crystallinity is beneficial for synergistic enhancement of photocatalytic performance, and provides new insights for sustainable energy production in the future.

Dual-element substitution induced integrated defect structure to suppress voltage decay and capacity fading of Li-rich Mn-based cathode

Li-rich manganese-based oxide (LRMO) is considered one of the most promising cathode materials for next-generation lithium-ion batteries due to its high energy density. However, many issues need to be addressed before its large-scale commercialization, including significant voltage decay and capacity fading. Herein, a Sn4+/Na+ co-doping induced integrated defect structure (oxygen vacancies, stacking faults, and surface spinel phase) strategy is proposed to suppress the voltage decay and enhance the cycling performance of LRMO. The integrated surface defect structures have significantly favorable effects on the LRMO, where the oxygen vacancies remove surface labile oxygen and suppress surface oxygen release, the induced stacking faults alleviate the stress accumulation during cycling, the surface spinel phase promotes the Li+ diffusion and prevents the outward migration of cations, and the co-doped Sn4+/Na+ stabilize the layered structure. As a result, the modified sample Na2SnO3-1 % (NSO-1) achieves excellent cycling performance (capacity of 207 mAh/g and capacity retention of 96.71 % after 100 cycles at 0.5C) and a smaller voltage decay (less than 1.5 mV per cycle) compared with the unmodified LRMO. This work provides a new valuable strategy to suppress capacity fading and voltage decay of LRMO through dual-element substitution induced surface defect engineering.

In Situ Investigation of Defect Site Formation in Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (SWCNTs) exhibit a photostable excitonic fluorescence in the short wave near-infrared (SWIR). Recently, the covalent functionalization of nanotubes opened new avenues to manipulate their excitonic fluorescence [1]. These “organic color centers (OCCs)” act as localized potential wells on the nanotube surface, trapping locally otherwise diffusing excitons. This effectively results in an increase in the SWCNT emission, the trapped excitons avoiding possible quenching sites along the nanotube surface (structural defects, nanotube ends) [2]. This new radiative pathway results in a shifting of the SWCNT emission towards longer wavelengths and allows SWCNT excitation on their first-order excitonic transition (ca. SWIR) [3]. Altogether, these properties make OCC-functionalized SWCNTs particularly attractive for various applications ranging from biological imaging to quantum information. Yet, the functionalization reaction of SWCNTs with OCC is still poorly understood, stochastic and, as a result, poorly controlled. To gain knowledge and control over these reactions, we developed a two-color imaging platform to image simultaneously both the SWCNT and OCC emissions in situ during the functionalization reaction [4]. We will present how this platform allows to monitor the kinetics of the functionalization reaction and further discuss our findings which provide insights on the interactions existing between OCCs and the SWCNT surface.[1] A. H. Brozena et al., Nat. Rev. Chem., vol. 3, no. 6, pp. 375–392, 2019[2] N. Danné et al., ACS Nano, vol. 12, no. 6, pp. 6059–6065, 2018[3] A. K. Mandal et al., Sci. Rep., vol. 10, no. 1, pp. 1–9, 2020[4] B.P. Lambert et al., in preparation

Enhanced Dynamic Operational Stability of Ni-Based Electrodes for Alkaline Water Electrolysis

Due to the accelerating paradigm shift toward renewable energy, water electrolysis systems have been evaluated for their ability to act as long-term renewable energy stores, wherein the energy is stored in the form of hydrogen gas. However, when renewable energy sources are employed, the power provided is intermittent, so developing highly active and durable electrode materials that function under these conditions is necessary. In particular, the irregular power supply accelerates severe degradation of the Ni-based electrodes due to irreversible surface oxidation, structural defects or collapse of the layered structure. Herein, we designed and fabricated Ni-based binary electrodes for alkaline water electrolyzers (Ni-Al & Ni-P electrodes for HER, Ni-Fe LDH electrodes for OER), and evaluated their electrochemical performance under dynamic operating conditions. Importantly, no significant OER & HER performance degradation was observed after the lab-scale dynamic operation tests, and no structural deformation or metal ion dissolution was found to occur. We further demonstrated the stability under the dynamic using advanced analysis and simulation techniques (XAS, in-situ ICP-MS, DFT calculations)

In situ DRIFTs-based comprehensive reaction mechanism of photo-thermal synergetic catalysis for dry reforming of methane over Ru-CeO2 catalyst

Solar-driven photo-thermal dry reforming of methane (DRM) is an environmentally friendly production route for high-value-added chemicals. However, the lack of thorough understanding of the mechanism for photo-thermal reaction has limited its further development. Here, we systematically investigated the mechanism of photo-thermal DRM reaction with the representative of Ru/CeO2 catalyst. Through in situ DRIFTs and transient experiments, comprehensive investigation into the reaction steps and their reactive sites in the process of DRM reaction were conducted. Besides, the excitation and migration direction of photo-electron was determined by ISI-XPS experiments, and the change of surface defect structure induced by light was characterized by ISI-EPR experiments. Based on the above results, the photo-enhancement effect on each micro-reaction step was determined. This study provides a theoretical basis for the industrialization of photo-thermal DRM reaction and its development of catalysts.

High-Entropy Engineering Reinforced Surface Electronic States and Structural Defects of Hierarchical Metal Oxides@Graphene Fibers toward High-Performance Wearable Supercapacitors.

Construction advanced fibers with high Faradic activity and conductivity are effective to realize high energy density with sufficient redox reactions for fiber-based electrochemical supercapacitors (FESCs), yet it is generally at the sacrifice of kinetics and structural stability. Here, a high-entropy doping strategy is proposed to develop high-energy-density FESCs based on high-entropy doped metal oxide@graphene fiber composite (HE-MO@GF). Due to the synergistic participation of multi-metal elements via high-entropy doping, the HE-MO@GF features abundant oxygen vacancies from introducing various low-valence metal ions, lattice distortions, and optimized electronic structure. Consequently, the HE-MO@GF maintains sufficient active sites, a low diffusion barrier, fast adsorption kinetics, improved electronic conductivity, enhanced structural stability, and Faradaic reversibility. Thereinto, HE-MO@GF presents ultra-large areal capacitance (3673.74mFcm-2) and excellent rate performance (1446.78mFcm-2 at 30mAcm-2) in 6M KOH electrolyte. The HE-MO@GF-based solid-state FESCs also deliver high energy density (132.85µWhcm-2), good cycle performance (81.05% of capacity retention after 10,000 cycles), and robust tolerance to sweat erosion and multiple washing, which is woven into the textile to power various wearable devices (e.g., watch, badge and luminous glasses). This high-entropy strategy provides significant guidance for designing innovative fiber materials and highlights the development of next-generation wearable energy devices.

High‐Entropy Engineering Reinforced Surface Electronic States and Structural Defects of Hierarchical Metal Oxides@Graphene Fibers toward High‐Performance Wearable Supercapacitors (Adv. Mater. 35/2024)

High‐Entropy Engineering Reinforced Surface Electronic States and Structural Defects of Hierarchical Metal Oxides@Graphene Fibers toward High‐Performance Wearable Supercapacitors (Adv. Mater. 35/2024)

Wood Fiber-Based Triboelectric Material with High Filtration Efficiency and Antibacterial Properties and Its Respiratory Monitoring in Mask.

Self-powered wearable electronic products have rapidly advanced in the fields of sensing and health monitoring, presenting greater challenges for triboelectric materials. The limited surface polarity and structural defects in wood fibers restrict their potential as substitutes for petroleum-based materials. This study used bagasse fiber as the raw material and explored various methods, including functionalizing cellulose nanofibrils (CNFs) with polydopamine (PDA), in situ embedding of silver particles, filtration, and freeze-drying. These methods aimed to enhance the triboelectric output, antibacterial properties, and filtration properties of lignocellulosic materials. The Ag/PDA/CNF-based triboelectric nanogenerator (TENG) demonstrated an open-circuit voltage of 211 V and a short-circuit current of 18.1 μA. An aerogel prepared by freeze-drying the Ag/PDA/CNF material, combined with a polyvinylidene fluoride nanofiber structure fabricated by electrospinning, constitutes the TENG unit. A self-powered respiratory detection mask was created using this combination, achieving a filtration efficiency of 94.23% for 0.3 μm particles and an antibacterial rate exceeding 99%. In addition, it effectively responded to respiratory frequency signals of slow breathing, normal breathing, and shortness of breath, with the output electrical signal correlating with the respiratory frequency. This study considerably contributes to advancing wood fiber-based triboelectric materials as alternatives to petroleum-derived materials in self-powered wearable electronic products for medical applications.

Surface quality and microstructure evolution in fused silica under SF6/Ar reactive ion beam etching

The SF6/Ar reactive ion beam etching (RIBE) was proposed to explore the evolution of surface quality, subsurface defects, surface molecular structure, and chemical composition of fused silica. Also, the mechanism of reactive ion beam etching of fused silica surfaces was discussed. The results show that RIBE can maintain the original surface roughness by choosing suitable process parameters. this etching process can suppress the replication and expansion of subsurface defects and the deposition of reactants without bringing obvious contamination. The concentration of structural defects reaches a minimum at an etching depth of about 2 μm. However, further etching may lead to an increase in the chemical structure defects on the surface. The evolution of the intrinsic ring structure demonstrates that most intrinsic defects tend to reorganize into short (Si-O) ring structures. The etching mechanisms of Ar ions were discussed by simulating the stopping power and energy deposition. Phonon dissipation through atomic displacements and atomic vibrations is an important way of energy loss. Phonon vibrations and atomic dislocations induced by nuclear collisions are not only important factors causing the enhancement of electron-phonon coupling but also important causes of surface structural defects. The researches provide a theoretical basis for in-depth understanding of fused silica surface defect repair.

Highly-efficient peroxymonosulfate activation by porous nano-MgO for tetracycline degradation: Surface hydroxyl groups and oxygen vacancies synergetic mediated nonradical process

Heterogeneous transition metal activation of peroxymonosulfate (PMS)-based advanced oxidation processes is limited by low cycling efficiency, secondary contamination, and high toxicity. In this study, a non-transition metal porous nano-MgO catalyst from natural dolomite was synthesized and PMS activation was performed to degrade tetracycline (TC). The nano-MgO/PMS system could achieve TC degradation of 88.09 % within 20 min under the optimum parameters (nano-MgO dosage of 0.2 g·L−1, PMS concentration of 0.3 mM), exceeding the efficiency of the PMS-alone system (11.66 %) by 7-fold, which was related to large specific surface area (41.19 m2·g−1) and defect structure of porous nano-MgO catalysts. As revealed by the quenching tests and electron paramagnetic resonance (EPR) analysis, different from transition metal activation PMS where radicals are generated, singlet oxygen (1O2) was essential in the nano-MgO/PMS oxidation process. Notably, the density functional theory (DFT) calculations demonstrated that nano-MgO with surface hydroxyl groups and oxygen vacancies exhibited the longer O-O bond length (1.47 Å), stronger adsorption energy of PMS (-4.07 eV), and faster electron transfer (0.91 e) than the only nano-MgO with surface hydroxyl groups, proving the surface hydroxyl groups and oxygen vacancies active sites in nano-MgO could synergistically mediate the PMS activation process. Furthermore, the proposed three TC degradation pathways and the toxicity evaluation of intermediates suggested that nano-MgO/PMS system have good ecological safety. This work offers an innovative approach for the cost-effective preparation of porous magnesium oxide with highly efficiency, offering a new perspective for understanding the PMS activation mechanism induced by non-transition metal.

Boosting mechanical properties of carbon fibers by gas-liquid dual-effect approach

The tensile strength and tensile modulus of existing carbon fibers (CFs) are 3 %–5 % of the theoretical values, which greatly limits the performance of CFs when used alone or as a reinforcing material. To increase the chemical reaction activity and roughness of the surface of CFs based on the enhancement of their mechanical properties, a comprehensive treatment of CFs was carried out by the gas-liquid dual-effect method. CFs were oxidized at high temperatures after immersion treatment using cobalt nitrate solution, and the effects of cobalt nitrate solution concentration, oxidation time, and calcination temperature on the surface morphology, functional groups, structural defects, and mechanical properties of CFs were investigated by the controlled-variable method. The results showed that when the concentration of cobalt nitrate solution was 0.2 molL-1, the calcination temperature was 200 °C, and the oxidation time was 4 h, the modification effect was the best. At this time, the tensile strength of CF is 6104.50 MPa, which is 40.35 % higher than that of the pure CF, and the tensile modulus is 378.56 GPa, which is 13.27 % higher than that of the pure CF, with a significant enhancement effect. It can offer feasible ideas for further research and development of CF composites, and provide an effective way to promote the industrialization of modified CFs for application.

Revealing La doping activation or inhibition of crystal facet effects in Co3O4 for catalytic combustion and water resistance improvement

It was challenging to enhance the catalytic activity and water resistance of transition metal oxides in the CH4 treatment process. Here, La with large atomic radii was doped onto Co3O4 on the (110), (111) and (100) crystal facets, respectively, and successfully doped into the (110) and (100) lattices, but accumulation occurs on the (111) crystal surface. Doping La into the Co3O4 lattice achieved a dual excitation effect for surface optimization and structural defects, causing lattice expansion, enhancing the electrophilicity of the O atoms in the vicinity of La, and significantly stimulating the Co-O bond. This significantly improved reactive oxygen species content, CH4 adsorption capacity, and gaseous oxygen activation and replenishment capability for higher catalytic activity. Conversely, the (111) facet with accumulated La showed an opposite trend. Meanwhile, La doping effectively improved the stability of Co3O4 and weakened its hydrophilicity, which effectively enhanced its water resistance. This research provided a viable strategy for designing high-performance and water-resistant Co3O4-based catalysts.

Activation of Peroxymonosulfate by P-Doped Cow Manure Biochar for Enhancing Degradation of 17β-Estradiol

Sulfate radical-based advanced oxidation processes exhibit great potential for the degradation of organic pollutants. In this study, P-doped biochar (PBC500) was successfully synthesized by the pyrolysis of H3PO4-impregnated cow manure waste and was employed to activate peroxymonosulfate (PMS) for the elimination of 17β-estradiol (E2). The characterization results showed that the surface area, defective structure, and functional groups (C=O and phosphorus-containing groups) of biochar increased after H3PO4 modification. PBC500 exhibited high PMS activation activity and excellent E2 degradation capacity; 97.91% of 3 mg/L E2 can be removed within 90 min using 0.2 g/L PBC500 and 1 mM PMS. Based on the quenching experiments and X-ray photoelectron spectroscopy (XPS) analysis, defective structures, C=O, and P-C groups on biochar act as active sites to promote the catalytic oxidation of E2 by generating O2− and 1O2. In addition, PBC500 displayed excellent reusability, achieving 65.15% E2 degradation after three reuse cycles. Overall, this study presented a new technique that supports a high efficiency, environmentally friendly, and low cost treatment method for E2 wastewater and simultaneously provided a new option for the resource utilization of livestock waste.

Theoretical limits of magnetic detection of structural surface defects at the nanometre scale

ABSTRACT We present a theoretical study on the magnetic signals of structural surface defects like cracks or indents combined with inhomogeneities on the surface or subsurface inclusions of soft ferromagnetic metals like body-centred cubic Fe or amorphous CoFeB. We discuss limits of early detection of small surface defects on the basis of calculated magnetic stray fields few tens of nm above the surface. The considered surface imperfections have extensions of a few nm which correspond to low multiples of the magnetic exchange lengths of Fe or CoFeB. The detection of such small inhomogeneities requires that the sensor is about as close to the surface as the size of the inhomogeneity is. Furthermore, the step width of a scanning sensor must be of the same size as well. Both these requirements may be fulfilled for instance by scanning microscopy with diamond nitrogen-vacancy-centre quantum sensors.

In Situ Creation of Surface Defects on Pd@NiPd with Core-shell Hierarchical Structure Toward Boosting Electrocatalytic Activity.

A deep insight into surface structural evolution of the catalyst is a challenging issue to reveal the structure-activity relationship. In this contribution, based on a surface alloying strategy, the dual-functional Pd@NiPd catalyst with a unique core-shell hierarchical structure is developed through selective crystal growth, surface cocrystallization, directional self-assembly, and reduction process. The surface defects are created in situ on the outer NiPd alloy layer in the electrochemical redox processes, which endow the Pd@NiPd catalyst with excellent electrocatalytic activity of hydrogen generation reaction (HER) and oxygen generation reaction (OER) in alkaline media. The optimal Pd@NiPd-2 catalyst requires an overpotential of only 18 mV that is far lower than Pt/C benchmark (43 mV) at the current density of 10 mA cm-2 for the HER, and 210 mV that is far lower than RuO2 benchmark (430 mV) at 50 mA cm-2 for the OER. Density functional theory (DFT) calculations reveal that the outstanding electrocatalytic activity is originated from the creation of surface defect structure that induces a significant reduction in the adsorption and dissociation energy barriers of H2O molecules in the HER and a decrease in the conversion energy from O* to OOH* that resulted from the synergy of two adjacent Pd sites by forming O-bridge. This work affords a typical paradigm for exploiting efficient catalysts and investigating the dependence of electrocatalytic activity on the surface structural evolution.

Recovery of rhenium, a strategic metal, from copper smelting effluent

Rhenium is a key metal in high technology. It is important how to effectively and selectively recover perrhenate from copper smelting acidic effluent. A CH3COOK activated hierarchical biochar from bamboo shoot shell was prepared to efficiently and selectively adsorb perrhenate in the acidic solution. Some adsorption experiment factors such as initial pH, adsorbent dose, contact time, and temperature have been comprehensively tested. The maximum adsorption capacity of the adsorbent for perrhenate reached up to 84.63 mg/g. Spontaneous physical adsorption was possible adsorption mechanism according to thermodynamic analysis. The intensified hydrophobic surface and graphitic defect structure of the adsorbent accounted for its excellent selectivity to hydrophobic perrhenate. Regeneration experiments showed that the CH3COOK activated hierarchical biochar was reusable. The CH3COOK activated hierarchical biochar has the high potency for highly efficient and selective recovery of perrhenate from the acidic solution generated by the copper smelting process.