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Hydrogen, as the smallest atom and a key component of water, can penetrate into materials in various forms (e.g., atoms, molecules), which has significant effects on their properties; hence, the diffusion behavior of hydrogen has aroused widespread attention. One of the major compositions in the Earth's interior is MgO. Thus, the diffusion behavior of hydrogen in MgO under high pressure is vital for understanding the water cycle in the Earth's interior. However, the hydrogen diffusion behavior in MgO under high pressure is still poorly understood. Herein, the hydrogen diffusion behaviors in MgO with increasing pressure are systematically investigated in the framework of first-principles methods. Our results show that separated H atoms tend to converge to form H2 molecules, and H2 molecules tend to gather together. The energy barriers of both H and H2 diffusion in MgO increase with pressure. Notably, our results illustrate that hydrogen prefers to diffuse in solid MgO in its molecular state even under high pressure. Furthermore, the attempt frequency of hydrogen in MgO increases with temperature, while it decreases with pressure. This study will deepen our understanding of hydrogen diffusion behavior in MgO under high pressure and provide guidance for studies on particle diffusion in solid materials under extreme conditions. [ABSTRACT FROM AUTHOR]

As an efficient electron and proton donor, reduced nicotinamide adenine dinucleotide (NADH) coenzyme holds great promise in the enzymatic industry; however, the high cost of NADH regeneration and its stoichiometric consumption in the catalytic process hinders its widespread application. Inspired by the process of natural photosynthesis, we report a green photoelectrochemical (PEC) strategy to realize NADH regeneration on a polyterthiophene (pTTh) semiconductor by using water and solar energy as reaction sources. The pTTh shows an unprecedentedly positive onset potential of 0.6 V vs. RHE for achieving an enzymatically active product of 1,4-NADH under simulated sunlight illumination. When operating the reaction at 0.1 V vs. RHE for 3 h, 2.8 mM 1,4-NADH can be generated, and the turnover frequency (TOF) is determined to be 3.73 h−1. Besides, the produced 1,4-NADH can be in situ employed to assist glutamate dehydrogenase in catalyzing α-ketoglutarate to produce L -glutamate. This study demonstrates a sustainable pathway to produce high value-added NADH on a polymer semiconductor by converting solar energy. [ABSTRACT FROM AUTHOR]

Defect engineering, used to scatter phonons, is a widely used methodology to suppress the lattice thermal conductivity and improve the thermoelectric performance. Thus, understanding the effects of defects on the lattice thermal conductivity is an essential issue. However, the current thermal conductivity calculation methods are limited by either efficiency or accuracy in dealing with the defects: achieving the high order force constants for solving the phonon Boltzmann transport equations is time consuming; the traditional Debye–Callaway (DC) model ignores the local geometry relaxations around defects. The potentials used in molecular dynamics simulations are usually the empirical potentials. Utilizing the machine learning methodology, we train the deep neural network potential (NNP) for the defected PbTe compound, a remarkable thermoelectric material with large potential applications. The NNP is validated using the static energy, mechanical properties, kinetic properties, and phonon dispersions of PbTe systems. With the accurate NNP, the corresponding lattice thermal conductivity is then calculated using the molecular simulations (MD) under the Green–Kubo (GK) approximations, which balances the computational cost and accuracy. For the pristine PbTe compound, the simulated lattice thermal conductivities are in good agreement with experimental measurements. For the intrinsic point defected PbTe system, our NNP + MD + GK produces reasonable lattice thermal conductivities compared to those from the DC model. By comparing the simulated results with those using the DC model, we provide a strain correction factor f0 in the DC model of defect strain effects on the lattice thermal conductivity. From our simulations, the grain boundaries in PbTe scatter the medium wavelength phonons and significantly suppress the lattice thermal conductivity. In addition, the synergistic effect of twin boundaries and point defects could further reduce the lattice thermal conductivity. Our work provides a theoretical methodology not only to simulate heat transport in the defected material but also understand the phonon scattering behaviors of different defects. [ABSTRACT FROM AUTHOR]

Based on the hybrid functional, we find that at 0 GPa, pristine CsV3Sb5 has a magnetic moment of 0.28 μB per vanadium atom, which is suppressed at a pressure of 2.5 GPa resulting in a spin-crossover. Since the ground state of CsV3Sb5 with charge density wave (CDW) distortion is a non-magnetic state, the magnetic moment of V atoms in pristine CsV3Sb5 will be suppressed by the temperature-induced CDW transition at 94 K. The schematic evolution of magnetic moments as functions of pressure and temperature is presented. At low temperature, CsV3Sb5 is a rare example of materials hosting a pressure-induced magnetic moment, and we suggest that the effects of magnetic moments of V atoms should be considered for understanding its properties. [ABSTRACT FROM AUTHOR]

Correction for 'Photoelectrochemical NADH regeneration on a polymer semiconductor-based photocathode' by Nanxin Li et al., Green Chem., 2023, 25, 5247–5256, https://doi.org/10.1039/D3GC00559C. [ABSTRACT FROM AUTHOR]

Spin-crossover combined with metal–insulator transition and superconductivity has been found in 2D transition-metal phosphorous trichalcogenides when tuning them by high pressure. Simulation of such intriguing spin-crossover behaviors is crucial to understanding the mechanism. The Hubbard U correction is widely used to describe the strong on-site Coulomb interaction in the d electrons of transition-metal compounds, while the U values are sensitive to the crystal field and spin state varying greatly with pressure. In this work, we show that taking MnPS3 as an example and based on a uniform parameter set, the hybrid functional calculations give a spin-crossover pressure of 35 GPa consistent with experimental observation (30 GPa), which is less than half of the existing reported value (63 GPa) using the Hubbard U correction. Notably, we find a spin-crossover induced transition from an antiferromagnetic semiconductor with monoclinic stacking-order to a ferromagnetic semiconductor with rhombohedral stacking-order, and the ferromagnetism originates from the partially occupied t2g orbitals. Different from previous understanding, the Mott metal–insulator transition of MnPS3 does not occur simultaneously with the spin-crossover but in a pressurized low-spin phase. [ABSTRACT FROM AUTHOR]

Over the past few decades, the concept of hydrogen bonds, in which hydrogen is electrophilic, has been extended to halogen bonds, chalcogen bonds and pnicogen bonds. Herein, we show that such a non-covalent bonding also exists in noble gas compounds. Using first principles calculations, we illustrate the O…Xe–O bond in molecular crystal XeO3 and its effect on the behavior of this compound under pressure. Our calculations show that the covalent Xe–O bond lengths were elongated with increasing pressure and correspondingly the Xe–O stretching vibration frequencies were red shifted, which is similar to the change of H-bonds under pressure. The O…Xe–O bond and related hopping of O between neighboring Xe sites also correspond to the structural changes in the XeO3 compounds at about 2 GPa. Our study extends the concept of hydrogen bonding to include all p-block elements and show a new bonding type for Noble gas elements in which it acts as an electrophilic species. [ABSTRACT FROM AUTHOR]

The pressure-induced evolution of AgO crystal structures and the oxygen environment of Ag atoms were investigated by means of density functional theory with a hybrid functional and a structure prediction method. Under ambient conditions, AgO has two nonequivalent Ag1 and Ag2 sites that adopt linear and square planar oxygen environment configuration, respectively, corresponding to Ag mixed-valence states. The results show that both the coordination environment and the valence state of the Ag1 site are sensitive to pressure and will gradually approach those of the Ag2 site as it increases. The band gap also decreases significantly and at 75 GPa AgO experiences a pressure-induced semiconductor-to-metal transition. At ∼77 GPa, there is a structural transition from monoclinic (P21/c) to trigonal (R3̅m), accompanied by a valence state transition from the mixed-valence state to a single-valence state. [ABSTRACT FROM AUTHOR]

Based on the hybrid functional, we find that at 0 GPa, pristine CsV 3 Sb 5 has a magnetic moment of 0.28 μ B per vanadium atom, which is suppressed at a pressure of 2.5 GPa resulting in a spin-crossover. Since the ground state of CsV 3 Sb 5 with charge density wave (CDW) distortion is a non-magnetic state, the magnetic moment of V atoms in pristine CsV 3 Sb 5 will be suppressed by the temperature-induced CDW transition at 94 K. The schematic evolution of magnetic moments as functions of pressure and temperature is presented. At low temperature, CsV 3 Sb 5 is a rare example of materials hosting a pressure-induced magnetic moment, and we suggest that the effects of magnetic moments of V atoms should be considered for understanding its properties.

Spin-crossover combined with metal-insulator transition and superconductivity has been found in 2D transition-metal phosphorous trichalcogenides when tuning them by high pressure. Simulation of such intriguing spin-crossover behaviors is crucial to understanding the mechanism. The Hubbard U correction is widely used to describe the strong on-site Coulomb interaction in the d electrons of transition-metal compounds, while the U values are sensitive to the crystal field and spin state varying greatly with pressure. In this work, we show that taking MnPS3 as an example and based on a uniform parameter set, the hybrid functional calculations give a spin-crossover pressure of 35 GPa consistent with experimental observation (30 GPa), which is less than half of the existing reported value (63 GPa) using the Hubbard U correction. Notably, we find a spin-crossover induced transition from an antiferromagnetic semiconductor with monoclinic stacking-order to a ferromagnetic semiconductor with rhombohedral stacking-order, and the ferromagnetism originates from the partially occupied t2g orbitals. Different from previous understanding, the Mott metal-insulator transition of MnPS3 does not occur simultaneously with the spin-crossover but in a pressurized low-spin phase.

Over the past few decades, the concept of hydrogen bonds, in which hydrogen is electrophilic, has been extended to halogen bonds, chalcogen bonds and pnicogen bonds. Herein, we show that such a non-covalent bonding also exists in noble gas compounds. Using first principles calculations, we illustrate the OXe-O bond in molecular crystal XeO 3 and its effect on the behavior of this compound under pressure. Our calculations show that the covalent Xe-O bond lengths were elongated with increasing pressure and correspondingly the Xe-O stretching vibration frequencies were red shifted, which is similar to the change of H-bonds under pressure. The OXe-O bond and related hopping of O between neighboring Xe sites also correspond to the structural changes in the XeO 3 compounds at about 2 GPa. Our study extends the concept of hydrogen bonding to include all p-block elements and show a new bonding type for Noble gas elements in which it acts as an electrophilic species.

The biological effects of aluminium have received much attention in recent years. Speciation of Al is of basic relevance as it concerns its reactivity and bioavailability. A differential pulse voltammetry (DPV) procedure is proposed for speciation analysis of Al(III) in natural waters and biological fluids using six catechols (L-dopa, dopamine, epinephrine, norepinephrine, caffeic acid and o-benzenediol) as electroactive ligands. The decrease of the DPV anodic peak current for each catechol ligand is linear with the increase of Al concentration. This speciation analysis idea is based on the measurement of the complexation capacity, namely, different affinities of Al(III) for catechols and organic ligands under two pH conditions. The labile monomeric Al fraction (mainly inorganic aluminium) is determined at pH 4.6, while the total monomeric Al fraction is determined at pH 8.5. The principle for Al(III) speciation analysis by an electrochemical method is discussed. This sensitive and simple fractionation method is successfully applied to the speciation analysis of Al in natural waters and the results agree well with those of Driscoll's method. The speciation analysis of Al in biological fluids is also explored and the results are compared with those obtained by ultrafiltration and dialysis. Compared with other speciation protocols the electrochemical method possesses some remarkable advantages: rapidity, high sensitivity, cheap instrumentation and a simple operation procedure.