Tailoring phosphine ligands for improved C-H activation: insights from Δ-machine learning. - In: Digital discovery, ISSN 2635-098X, Bd. 0 (2024), 0, insges. 15 S.
Transition metal complexes have played crucial roles in various homogeneous catalytic processes due to their exceptional versatility. This adaptability stems not only from the central metal ions but also from the vast array of choices of the ligand spheres, which form an enormously large chemical space. For example, Rh complexes, with a well-designed ligand sphere, are known to be efficient in catalyzing the C-H activation process in alkanes. To investigate the structure-property relation of the Rh complex and identify the optimal ligand that minimizes the calculated reaction energy ΔE of an alkane C-H activation, we have applied a Δ-machine learning method trained on various features to study 1743 pairs of reactants (Rh(PLP)(Cl)(CO)) and intermediates (Rh(PLP)(Cl)(CO)(H)(propyl)). Our findings demonstrate that the models exhibit robust predictive performance when trained on features derived from electron density (R2 = 0.816), and SOAPs (R2 = 0.819), a set of position-based descriptors. Leveraging the model trained on xTB-SOAPs that only depend on the xTB-equilibrium structures, we propose an efficient and accurate screening procedure to explore the extensive chemical space of bisphosphine ligands. By applying this screening procedure, we identify ten newly selected reactant-intermediate pairs with an average ΔE of 33.2 kJ mol−1, remarkably lower than the average ΔE of the original data set of 68.0 kJ mol−1. This underscores the efficacy of our screening procedure in pinpointing structures with significantly lower energy levels.
https://doi.org/10.1039/D4DD00037D
FCF-LDH/BiVO4 with synergistic effect of physical enrichment and chemical adsorption for efficient reduction of nitrate. - In: Green energy & environment, ISSN 2468-0257, Bd. 9 (2024), 7, S. 1112-1121
Photoelectrochemical NO3− reduction (PEC NITRR) not only provides a promising solution for promoting the global nitrogen cycle, but also converts NO3− to the important chemicals (NH3). However, it is still a great challenge to prepare catalysts with excellent NO3− adsorption/activation capacity to achieve high NITRR. Herein, we designed a novel Fe2+Cu2+Fe3+LDH/BiVO4 (FCF-LDH/BVO) catalyst with synergistic effect of chemical adsorption and physical enrichment. Fe2+ in FCF-LDH/BVO provides the rich Lewis acid sites for the adsorption of NO3−, and the appropriate layer spacing of FCF-LDH further promotes the physical enrichment of NO3− in its interior, thus realizing the effective contact between NO3− and active sites (Fe2+). FCF-LDH/BVO showed excellent NH3 production performance (FENH3 = 66.1%, rNH3 = 13.8 μg h−1 cm−2) and selectivity (FENO2- = 2.5%, rNO2- = 4.9 μg h−1 cm−2) in 0.5 mol L−1 Na2SO4 electrolyte. In addition, FCF-LDH/BVO maintains the desirable PEC stability for six cycle experiments, showing great potential for practical application. The 14NO3− and 15NO3− isotope test provides strong evidence for further verification of the origin of N in the generated NH3. This LDH catalyst has a great potential in PEC removal of NO3− from groundwater.
https://doi.org/10.1016/j.gee.2023.05.011
Effect of orbital symmetry on probing the single-molecule Kondo effect. - In: Physical review, ISSN 2469-9969, Bd. 109 (2024), 24, L241401, S. L241401-1-L241401-6
The low-energy excitation spectrum of a metal-free phthalocyanine molecule on Ag(111) is probed in scanning tunneling spectroscopy experiments. The use of functionalized p-orbital and s-orbital tips leads to markedly different results. While CO-terminated p-wave tips probe the zero-energy Abrikosov-Suhl resonance induced by the molecular Kondo effect, Ag-coated s-wave tips - in strong contrast - feign the absence of the Kondo effect due to a missing Abrikosov-Suhl resonance. Reducing the vertical distance between the s-orbital tip and the molecule progressively unveils the resonance, compatible with findings for the p-orbital tip in the far tunneling range. A mechanism based on orbital overlap is suggested as the tentative origin of the observations. The CO-functionalized tip is then used to explore the altered Kondo effect of the tautomerized phthalocyanine.
https://doi.org/10.1103/PhysRevB.109.L241401
The effect of zinc substitution on the optical properties of Sm3+ doped zinc borate glasses. - In: Optical materials, ISSN 1873-1252, Bd. 154 (2024), 115606, S. 1-19
Zinc borate glasses are a relatively well known glass type that can be produced at comparably low temperatures. Variations in both the type and concentration of network modifier atoms induce structural alterations within the glass matrix. If doped with optically active dopants, e.g. rare earth ions, compositional changes also affect the local surrounding of the dopants and consequently their optical properties such as emission peak shape and peak ratio. To investigate the effect of different low field strength network modifier ions in zinc borate glasses two glass series were prepared using the melt quench technique; Sm3+ was used as dopant ion: 50B2O3, xK2O, (49-x)ZnO, 1Sm2O3 (x = 5,10,15, …, 30 mol%) and 50B2O3, 30MO, 19ZnO, 1Sm2O3 (M = Ca, Sr and Ba). It is found that the substitution of ZnO for K2O notably enhances the intensity of the red Sm3+emission. Based on the literature this effect is attributed to a change in symmetry at the rare earth position. Additionally, the effect of network modifier concentrations and the different network modifier types on the Sm3+ absorption spectra is examined, discussed and compared to literature data. Furthermore, the glasses are characterized according to their density, refractive index, molar volume, and oxygen packing density.
https://doi.org/10.1016/j.optmat.2024.115606
A remaining useful life prediction algorithm incorporating real-time and integrated model for hidden actuator degradation. - In: ISA transactions, ISSN 1879-2022, Bd. 0 (2024), 0, S. 1-15
This paper proposed a prediction algorithm for the degraded actuator taking into account the impact of estimation error of hidden index in the closed-loop system. To this end, a unified prediction framework is established to evaluate the hidden degradation information and recursively update the degradation model parameters simultaneously. The advantage is that the prediction framework can comprehensively compensate the estimation error of hidden degradation index caused by system uncertainty. To jointly estimate the degradation information in avoidance of the impact of system uncertainty, a modified adaptive Kalman filter is designed, and the proof of stability is provided. With the priori estimate from the filter, the degradation model parameters are updated by the inverse filtering probability based on Bayes’ theorem. It is followed by the computation of the remaining useful life (RUL) prediction utilizing aforementioned hidden degradation information and the latest degradation model. The effectiveness of the proposed RUL prediction algorithm is demonstrated by the degraded actuator in the continuous casting process.
https://doi.org/10.1016/j.isatra.2024.05.033
On the static performance of aerostatic elements. - In: Precision engineering, Bd. 89 (2024), S. 1-10
Porous aerostatic bearings and seals offer several advantages in precision engineering applications. The static performance of aerostatic elements, i.e., bearings and seals, is investigated both experimentally and numerically. This study presents a method, a test setup, and a measurement of the air gap pressure distribution with high spatial and temporal resolution. This study presents experimental and numerical results of the load capacity, air gap height, static stiffness, air consumption, and air gap pressure distribution. The experimental results are compared to a numerical model based on the modified Reynolds equation. Furthermore, boundaries for the operating parameter space of the investigated seal are determined by stiffness and leakage. The experimental results and the numerical model showed good correlation, providing corroborative evidence for the accuracy of the measurement setup and the feasibility of the pressure measurement method.
https://doi.org/10.1016/j.precisioneng.2024.05.017
Effects of N2 plasma modification on the surface properties and electrochemical performance of Ni foam electrodes for double-chamber microbial fuel cells. - In: Materials advances, ISSN 2633-5409, Bd. 0 (2024), 0, insges. 7 S.
This study assessed the feasibility of using a plasma-modified Ni foam as an anode to improve the electrochemical performance of double-chamber microbial fuel cells (MFCs). Scanning electron microscopy results showed that Ni foam exhibited an open cellular structure and rough surface morphology, providing a large contact area between bacteria and anodes in the MFCs. N2 plasma modification did not influence the surface morphology of the Ni foam, whereas the hydrophobic surfaces of the Ni foam became highly hydrophilic. X-ray photoelectron spectrometer results revealed that Ni-N and NH3 functional groups, formed on the surface of the Ni foam during the N2 plasma modification, were responsible for its highly hydrophilic surface. Electrochemical measurements demonstrated that the highest power density of the MFC configured with an unmodified Ni foam anode electrode (166.9 mW m−2) was much higher than those of the MFCs configured with dense Ni rod (5.1 mW m−2) or graphite rod (29.5 mW m−2) anodes because Ni foam combined the advantages of an open cellular structure and good electrical conductivity. The highest power density of MFC configured with Ni foam was further improved to 247.1 mW m−2 after 60 min N2 plasma treatment owing to the high hydrophilicity of the N2 plasma-modified Ni foam electrodes, which facilitated bacteria adhesion and biofilm formation.
https://doi.org/10.1039/D4MA00153B
A novel digitalization approach for smart materials - ontology-based access to data and models. - In: Advanced engineering materials, ISSN 1527-2648, Bd. n/a$v2024 (2024), n/a, 2302208, S. 1-12
Smart materials react to physical fields (e.g., electric, magnetic, and thermal fields) and can be used as sensors, actuators, and generators due to their bidirectional behavior. Easy and multiscale access to material data and models enables efficient research and development with regard to the selection of appropriate materials and their optimization towards specific applications. However, different working principles, measurement and analysis methods, as well as data storage approaches lead to heterogeneous and partly inconsistent datasets. The ontology-based data access (OBDA) is a suitable method to access such heterogeneous datasets easily and quickly, while material models can transform material data across certain scales for different applications. In order to connect both capabilities, an extended approach enabling an ontology-based data and model access (OBDMA) is presented, also supporting findable, accessible, interoperable, and re-usable (FAIR). The OBDMA system comprises four main levels, the query, the ontology, the mapping, and the database. Storing knowledge at these different levels increases the interchangeability and enables variable datasets, which is essential, especially for dynamic research fields such as smart materials. In this article, the principles and advantages of the OBDMA approach are demonstrated for different subclasses of smart materials, but can be transferred to other materials, too.
https://doi.org/10.1002/adem.202302208
Morphologies of reactive nanolayer stacks sputtered on ceramic low-temperature cofired ceramic substrates having a micrometer-scale surface roughness. - In: Advanced engineering materials, ISSN 1527-2648, Bd. n/a (2024), n/a, 2302284, S. 1-8
The deposition of reactive multilayer systems (RMSs) is investigated on low-temperature cofired ceramic (LTCC) substrates having different surface morphologies. In this study, the morphologies of RMS layers that are deposited on glass-ceramic LTCC substrates are analyzed. Different surface morphologies are prepared through pretreatments of the LTCC surface. The considered surfaces encompass an untreated natural LTCC surface, a modified sintered LTCC surface by laser ablation, a surface with a deposited metallization layer, and finally, a surface with an additional solder layer put on the deposited metallization layer. The different pretreatments lead to significant differences in the roughness of the LTCC substrates, resulting in different reaction velocities and peak temperatures on the various surface morphologies after the RMS's reaction. As a result, different grades of structural integrity (liftoff, crack formation) between the reacted RMS layer and the LTCC are observed.
https://doi.org/10.1002/adem.202302284
In situ observation and reduction of hot-cracks in laser additive manufacturing. - In: Communications materials, ISSN 2662-4443, Bd. 5 (2024), 84, S. 1-10
Cracking during Laser Additive Manufacturing is a problem for many higher-strength aluminium alloys, including AA6061. Here, we used a pulsed laser with ramp-down power modulation to improve the cracking resistance by about 50% compared to the use of a rectangular pulsed laser. Using synchrotron in situ X-ray imaging at 100,000 images s−1, ground truth data was obtained about changes in melt pool geometry, solidification rate, and thermal gradients were calculated. An analytical hot cracking model was developed to show that these changes lead to a decreased hot tear susceptibility. Therefore, laser pulse modulation can be an effective tool to reduce crack susceptibility of alloys. More fundamentally, the results demonstrate that modifying thermal conditions provides a pathway to crack elimination in LAM and the model established in our study sets the foundation for further complex laser manipulation in modifying the printability and resulting mechanical properties of hard-to-process alloys in Laser Additive Manufacturing.
https://doi.org/10.1038/s43246-024-00522-3