Unraveling Differences in the Effects of Ammonium/Amine-Based Additives on the Performance and Stability of Inverted Perovskite Solar Cells.

Additive engineering, with its excellent ability to passivate bulk or surface perovskite defects, has become a common strategy to improve the performance and stability of perovskite solar cells (PVSCs). Among the various additives reported so far, ammonium salts are considered an important branch. It is worth noting that although both ammonium-based additives (R-NH3 +) and amine-based additives (R-NH2) are derivatives of ammonia (NH3), the functions of the two can be easily confused due to their structural similarities. Moreover, there is no comprehensive comparative analysis of them in the literature. Here, the differences between phenethylammonium iodide (PEA+) and phenethylamine (PEA) additives are revealed experimentally and theoretically. The results clearly show that PEA outperforms PEA+ in terms of device performance and stability based on the following three factors: i) PEA's defect passivation capability is superior to that of PEA+; ii) PEA has better hydrophobicity to hinder water ingress; and iii) PEA completely improves the stability of PVSCs by enhancing thermal stability and inhibiting iodide migration in perovskite more effectively than PEA+. As a result, the power conversion efficiency (PCE) of the inverted methylammonium triiodide (MAPbI3) device using PEA increases by ≈15% to over 21%. More importantly, this device exhibits greater ability to prevent water invasion, thermal-induce degradation, and inhibit iodide ion migration, resulting in better long-term stability.

Observation of Antiferroelectric Domain Walls in a Uniaxial Hyperferroelectric.

Ferroelectric domain walls are a rich source of emergent electronic properties and unusual polar order. Recent studies show that the configuration of ferroelectric walls can go well beyond the conventional Ising-type structure. Néel-, Bloch-, and vortex-like polar patterns have been observed, displaying strong similarities with the spin textures at magnetic domain walls. Here, the discovery of antiferroelectric domain walls in the uniaxial ferroelectric Pb5Ge3O11 is reported. Highly mobile domain walls with an alternating displacement of Pb atoms are resolved, resulting in a cyclic 180° flip of dipole direction within the wall. Density functional theory calculations show that Pb5Ge3O11 is hyperferroelectric, allowing the system to overcome the depolarization fields that usually suppress the antiparallel ordering of dipoles along the longitudinal direction. Interestingly, the antiferroelectric walls observed under the electron beam are energetically more costly than basic head-to-head or tail-to-tail walls. The results suggest a new type of excited domain-wall state, expanding previous studies on ferroelectric domain walls into the realm of antiferroic phenomena.

PdMoPtCoNi High Entropy Nanoalloy with d Electron Self-Complementation-Induced Multisite Synergistic Effect for Efficient Nanozyme Catalysis.

Engineering multimetallic nanocatalysts with the entropy-mediated strategy to reduce reaction activation energy is regarded as an innovative and effective approach to facilitate efficient heterogeneous catalysis. Accordingly, conformational entropy-driven high-entropy alloys (HEAs) are emerging as a promising candidate to settle the catalytic efficiency limitations of nanozymes, attributed to their versatile active site compositions and synergistic effects. As proof of the high-entropy nanozymes (HEzymes) concept, elaborate PdMoPtCoNi HEA nanowires (NWs) with abundant active sites and tuned electronic structures, exhibiting peroxidase-mimicking activity comparable to that of natural horseradish peroxidase are reported. Density functional theory calculations demonstrate that the enhanced electron abundance of HEA NWs near the Fermi level (EF) is facilitated via the self-complementation effect among the diverse transition metal sites, thereby boosting the electron transfer efficiency at the catalytic interface through the cocktail effect. Subsequently, the HEzymes are integrated with a portable electronic device that utilizes Internet of Things-driven signal conversion and wireless transmission functions for point-of-care diagnosis to validate their applicability in digital biosensing of urinary biomarkers. The proposed HEzymes underscore significant potential in enhancing nanozymes catalysis through tunable electronic structures and synergistic effects, paving the way for reformative advancements in nano-bio analysis.

Electrothermally-Driven Ultrafast Chemical Modulation of Multifunctional Nanocarbon Aerogels.

Ultrahigh-temperature Joule-heating of carbon nanostructures opens up unique opportunities for property enhancements and expanded applications. This study employs rapid electrical Joule-heating at ultrahigh temperatures (up to 3000 K within 60 s) to induce a transformation in nanocarbon aerogels, resulting in highly graphitic structures. These aerogels function as versatile platforms for synthesizing customizable metal oxide nanoparticles while significantly reducing carbon emissions compared to conventional furnace heating methods. The thermal conductivity of the aerogel, characterized by Umklapp scattering, can be precisely adjusted by tuning the heating temperature. Utilizing the aerogel's superhydrophobic properties enables its practical application in filtration systems for efficiently separating toxic halogenated solvents from water. The hierarchically porous aerogel, featuring a high surface area of 607 m2 g-1, ensures the uniform distribution and spacing of embedded metal oxide nanoparticles, offering considerable advantages for catalytic applications. These findings demonstrate exceptional catalytic performance in oxidative desulfurization, achieving a 98.9% conversion of dibenzothiophene in the model fuel. These results are corroborated by theoretical calculations, surpassing many high-performance catalysts. This work highlights the pragmatic and highly efficient use of nanocarbon structures in nanoparticle synthesis under ultrahigh temperatures, with short heating durations. Its broad implications extend to the fields of electrochemistry, energy storage, and high-temperature sensing.

Cationic or Neutral: Dependence of Photophysical Properties of Bis-alkynylphosphonium Pt(II) Complexes on Ancillary Ligand.

A series of D-π-A alkynylphosphonium salts with different linker between donor and acceptor groups was used to synthesize two series of trans-bis-alkynylphosphonium Pt(II) complexes with different ancillary ligands (triphenylphosphine, P series, and cyanide, CN series). The nature of the ancillary ligand manages the overall charge and emission properties of the complexes obtained. In addition, the variation of the linker in alkynylphosphonium ligands allows fine-tuning the luminescence wavelength. Dicationic series P is unstable in solution under UV excitation, whereas in the solid state, these complexes are the first example of phosphorescent trans-phosphine-bis-alkynyl Pt(II) compounds. Neutral series CN demonstrates bright emission in solution, including dual emission for 2CN complex with biphenyl linker in alkynylphosphonium ligands. However, in the solid state for the CN series drastic decrease in the emission quantum yield compared to the P series was observed. DFT calculations reveal the complicated emission nature for the both P and CN series with various contributions of 3ILCT, 3LLCT and 3MLCT states. However, in the naphthyl-containing derivatives 3P and 3CN, the dominating 3LC character with some admixture of CT states is postulated.

Synergistic effects of sulfur vacancies and internal electric fields in FeS/MoS2 heterojunctions: A new approach to photocatalytic chromium removal.

Molybdenum disulfide (MoS2) is heralded as an exemplary two-dimensional (2D) functional material, largely attributed to its distinctive layered structure. Upon forming heterojunctions with reducing species, MoS2 displays remarkable photocatalytic properties. In this research, we fabricated a novel heterojunction photocatalyst, FeS/MoS2-0.05, through the integration of FeS with hollow MoS2. This composite aims at the efficient photocatalytic reduction of hexavalent chromium (Cr(VI)). A comprehensive array of characterization techniques unveiled that MoS2 flakes, dispersed on FeS, provide numerous active sites for photocatalysis at the heterojunction interface. The inclusion of FeS seemingly promotes the formation of sulfur vacancies on MoS2. Consequently, this heterojunction catalyst exhibits photocatalytic activity surpassing pristine MoS2 by a factor of 3.77. The augmented activity of the FeS/MoS2-0.05 catalyst is attributed chiefly to an internal electric field at the interface. This field enhances the facilitation of charge transfer and separation significantly. Density functional theory (DFT) calculations, coupled with experimental analyses, corroborate this observation. Additionally, DFT calculations indicate that sulfur vacancies act as pivotal sites for Cr(VI) adsorption. Significantly, the adsorption energy of Cr(VI) species shows enhanced favorability under acidic conditions. Our results suggest that the FeS/MoS2-0.05 heterojunction photocatalyst presents substantial potential for the remediation of Cr(VI)-contaminated wastewater.

Valley-Dependent Electronic Properties of Metal Monochalcogenides GaX and Janus Ga2XY (X, Y = S, Se, and Te).

Two-dimensional (2D) materials have shown outstanding potential for new devices based on their interesting electrical properties beyond conventional 3D materials. In recent years, new concepts such as the valley degree of freedom have been studied to develop valleytronics in hexagonal lattice 2D materials. We investigated the valley degree of freedom of GaX and Janus GaXY (X, Y = S, Se, Te). By considering the spin-orbit coupling (SOC) effect in the band structure calculations, we identified the Rashba-type spin splitting in band structures of Janus Ga2SSe and Ga2STe. Further, we confirmed that the Zeeman-type spin splitting at the K and K' valleys of GaX and Janus Ga2XY show opposite spin contributions. We also calculated the Berry curvatures of GaX and Janus GaXY. In this study, we find that GaX and Janus Ga2XY have a similar magnitude of Berry curvatures, while having opposite signs at the K and K' points. In particular, GaTe and Ga2SeTe have relatively larger Berry curvatures of about 3.98 Å2 and 3.41 Å2, respectively, than other GaX and Janus Ga2XY.

Modulation of Properties in [1]Benzothieno[3,2-b][1]benzothiophene Derivatives through Sulfur Oxidation.

This study explores the impact of sulfur oxidation on the structural, optical, and electronic properties of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives, specifically focusing on 2,7-dibromo BTBT (2,7-diBr-BTBT) and its oxidized forms, 5,5-dioxide (2,7-diBr-BTBTDO) and 5,5,10,10-tetraoxide (2,7-diBr-BTBTTO). The bromination of BTBT followed by sequential oxidation with m-chloroperoxybenzoic acid yielded the target compounds in good yields. They were characterized using a wide array of analytical techniques including different spectroscopic methods, X-ray analysis, thermal analysis, and quantum chemical calculations. The results revealed that sulfur oxidation significantly alters the crystal packing, thermal stability, and optoelectronic properties of BTBT derivatives. Notably, the oxidized forms exhibited increased thermal stability and enhanced emission properties, with quantum yields exceeding 99%. These findings provide valuable insights for designing advanced organic semiconductors and fluorescent materials with tunable properties, based on the BTBT core.

Product Selectivity Control in the Brønsted Acid-Mediated Reactions with 2-Alkynylanilines.

Brønsted acid-catalysed/mediated reactions of the 2-alkynylanilines are reported. While metal-catalysed reactions of these valuable building blocks have led to the establishment of robust protocols for the selective, diverse-oriented syntheses of significant heterocyclic derivatives, we here demonstrate the practical advantages of an alternative methodology under metal-free conditions. Our investigation into the key factors influencing the product selectivity in Brønsted acid-catalysed/mediated reactions of 2-alkynylanilines reveals that different reaction pathways can be directed towards the formation of diverse valuable products by simply choosing appropriate reaction conditions. The origins of chemo- and regioselectivity switching have been explored through Density Functional Theory (DFT) calculations.

A New BODIPY-Based Receptor for the Fluorescent Sensing of Catecholamines.

The human body synthesizes catecholamine neurotransmitters, such as dopamine and noradrenaline. Monitoring the levels of these molecules is crucial for the prevention of important diseases, such as Alzheimer's, schizophrenia, Parkinson's, Huntington's, attention-deficit hyperactivity disorder, and paragangliomas. Here, we have synthesized, characterized, and functionalized the BODIPY core with picolylamine (BDPy-pico) in order to create a sensor capable of detecting these biomarkers. The sensing properties of the BDPy-pico probe in solution were studied using fluorescence titrations and supported by DFT studies. Catecholamine sensing was also performed in the solid state by a simple strip test, using an optical fiber as the detector of emissions. In addition, the selectivity and recovery of the sensor were assessed, suggesting the possibility of using this receptor to detect dopamine and norepinephrine in human saliva.

Direct Visualization of Defect-Controlled Diffusion in van der Waals Gaps.

Diffusion processes govern fundamental phenomena such as phase transformations, doping, and intercalation in van der Waals (vdW) bonded materials. Here, the diffusion dynamics of W atoms by visualizing the motion of individual atoms at three different vdW interfaces: hexagonal boron nitride (BN)/vacuum, BN/BN, and BN/WSe2, by recording scanning transmission electron microscopy movies is quantified. Supported by density functional theory (DFT) calculations, it is inferred that in all cases diffusion is governed by intermittent trapping at electron beam-generated defect sites. This leads to diffusion properties that depend strongly on the number of defects. These results suggest that diffusion and intercalation processes in vdW materials are highly tunable and sensitive to crystal quality. The demonstration of imaging, with high spatial and temporal resolution, of layers and individual atoms inside vdW heterostructures offers possibilities for direct visualization of diffusion and atomic interactions, as well as for experiments exploring atomic structures, their in situ modification, and electrical property measurements of active devices combined with atomic resolution imaging.

Boosting the Efficiency of Red Thermally Activated Delayed Fluorescence via Conjugation Enhancement in Push-Pull Naphthalimide Derivatives.

In this work, we synthesize a series of push-pull compounds bearing naphthalimide as the electron acceptor and tetraphenylethylene (TPE)/triphenylamine (TPA)/phenothiazine (PTZ) as the electron rich/electron donor units. These moieties are arranged in highly conjugated quadrupolar structures. The structure-property relationships are investigated through a joint experimental time-resolved spectroscopic and computational TD-DFT study. The femtosecond transient absorption and fluorescence up-conversion experiments reveal ultrafast photoinduced intramolecular charge transfer. This is likely the key factor leading to efficient spin-orbit CT-induced intersystem crossing for the TPA- and PTZ-derivatives as well as to small singlet-to-triplet energy gap. Consequently, evidence for a delayed fluorescence component is found together with the main prompt emission in the fluorescence kinetics both in solution and in thin film. The weight of the Thermally Activated Delayed Fluorescence (TADF) is greatly enhanced when these fluorophores are used as guests in solid-state host matrices. TADF is interestingly revealed in the orange-red region of the visible. Such long wavelength emission is here observed with surprisingly large fluorescence quantum yields, thanks to the conjugation enhancement achieved in these newly synthesized structures relative to previous studies. Our findings may be thus promising for the future development of efficient third generation TADF-based OLEDs.

Lifshitz Transition in a Single-Atom-Thick GdxYb1-xPb3 Kagome Compound on Si(111).

Lanthanide (Ln) elements Gd and Yb alloyed with a Pb monolayer on the Si(111) substrate form LnPb3 compounds having the same crystal structure. They comprise a single-atom-thick Pb layer arranged in a slightly distorted kagome lattice with Ln atoms filling the hexagonal voids. They have similar electronic band structures except for the Fermi level position, which varies between the divalent Yb- and trivalent Gd-containing compounds by ∼0.47 eV. The ability to create a 2D solid solution with the unified continuous Pb layer and hexagonal voids randomly filled with either Gd or Yb atoms allows precise control of the Fermi level position. Small alteration of the Fermi level triggers drastic changes in the Fermi surface topology due to the Lifshitz transition, hence in the physical properties. In particular, the sheet resistance of the GdxYb1-xPb3/Si(111) system can be controllably varied over an order of magnitude range.

Unraveling the Role of Li and Mg Substitution in Layered Sodium Oxide Cathodes for Sodium-Ion Batteries.

Substituting electrochemically active elements such as Li and Mg in P2-type layered sodium oxide is an effective strategy for developing competitive cathode materials for sodium-ion batteries. However, the lack of atomic-level understanding regarding the distribution of substitution positions complicates the comprehension of the roles of substituting atoms and the mechanism of sodium-ion intercalation. In this study, we identified the stable configurations of Na in Na0.75Ni0.3Mn0.7O2 and Na0.75Li0.15Mg0.05Ni0.1Mn0.7O2 materials using the site exclusion method. Through simulating the complete charging process for both materials, the structure evolution of the cathodes during the cycling and the impact of the partial substitution of Ni elements by Li and Mg atoms were comprehensively elucidated. Our findings revealed that Mg atoms effectively regulate the distribution of forces within the materials, essentially serving as supportive pillars within the cathode. Meanwhile, Li atoms efficiently mitigated electron localization, consequently diminishing volume fluctuations during the charging process. More importantly, the substitution with Li and Mg atoms could synergistically reduce the interaction between transition metals and sodium ions, thereby reducing the diffusion energy barrier of Na ions. This study not only enhances the comprehension of substituted metal atoms in P2 layered oxides but also offers new insights for the development of sodium-ion cathode materials.

Photochemical Generation and Characterization of C-Aminophenyl-Nitrilimines: Insights on Their Bond-Shift Isomers by Matrix-Isolation IR Spectroscopy and Density Functional Theory Calculations.

The intriguing ability of C-phenyl-nitrilimine to co-exist as allenic and propargylic bond-shift isomers motivated us to investigate how substituents in the phenyl ring influence this behavior. Building on our previous work on the meta- and para-OH substitution, here we extended this investigation to explore the effect of the NH2 substitution. For this purpose, C-(4-aminophenyl)- and C-(3-aminophenyl)-nitrilimines were photogenerated in an argon matrix at 15 K by narrowband UV-light irradiation (λ = 230 nm) of 5-(4-aminophenyl)- and 5-(3-aminophenyl)-tetrazole, respectively. The produced nitrilimines were further photoisomerized to carbodiimides via 1H-diazirines by irradiations at longer wavelengths (λ = 380 or 330 nm). Combining IR spectroscopic measurements and DFT calculations, it was found that the para-NH2-substituted nitrilimine exists as a single isomeric structure with a predominant allenic character. In contrast, the meta-NH2-substituted nitrilimine co-exists as two bond-shift isomers characterized by propargylic and allenic structures. To gain further understanding of the effects of phenyl substitution on the bond-shift isomerism of the nitrilimine fragment, we compared geometric and charge distribution data derived from theoretical calculations performed for C-phenyl-nitrilimine with those performed for the derivatives resulting from NH2 (electron-donating group) and NO2 (electron-withdrawing group) phenyl substitutions.

Restructuring and Hydrogen Evolution on Sub-Nanosized PdxBy Clusters.

As a Pt-group element, Pd has been regarded as one of the alternatives to Pt-based catalysts for the hydrogen evolution reaction (HER). Herein, we performed density functional theory (DFT) computations to explore the most stable structures of PdxBy (x = 6, 19, 44), revealed the in situ structural reconstruction of these clusters under acidic conditions, and evaluated their HER activity. We found that the presence of B can prevent underpotential hydrogen adsorption and activate the H atoms on the cluster surface for the HER. The theoretical calculations show that the reaction barrier for the HER on ~1 nm sized Pd44B4 can be as low as 0.36 eV, which is even lower than for the same-sized Pt and Pd2B nanoparticles. The ultra-high HER activity of sub-nanosized PdxBy clusters makes them a potential new and efficient HER electro-catalyst. This study provides new ideas for evaluating and designing novel nanocatalysts based on the structural reconstruction of small-sized nanoparticles in the future.

Elucidating Mechanism and Selectivity in Pyridine Functionalization through Silylium Catalysis.

The functionalization of aromatic N-heterocycles through silylium activation demonstrates exceptional selectivity and efficiency. Density functional theory (DFT) calculations unveil the detailed silylium catalysis mechanism and elucidate the origins of selectivity in this reaction. The phosphoramidimidate sulfonamide (PADI) precatalyst orchestrates of the catalytic cycle via three elementary steps. The Brønsted acidity of precatalyst significantly influences both the formation of silylium-based Lewis acid active species and the silylium activation of pyridine. Unlike disulfonimide (DSI)-type precatalysts, both Tf2NH and PADI precatalysts with strong acidities can easily promote the generation of activated silylium pyridine species. A semi-enclosed 'rigid' electronegative cavity in PADI-type anions constructs a well-defined recognition site, facilitating engagement with the positively charged silylium pyridine species. Due to the high electrophilicity and less steric demand at the C4-position of the pyridine substrate, the product with C4-regioselectivity was predominantly generated.

Complex Formation and Hydrolytic Processes of Protected Peptides Containing the -SXH- Motif in the Presence of Nickel(II) Ion.

Interactions between metal ions and proteins are considered reversible, such as the coordination of a metal ion to a protein or enzyme, but irreversible processes like the oxidative reactions, aggregation or hydrolytic processes may occur. In the presence of Ni(II)-ions selective hydrolysis of the peptides containing the -SXH- or -TXH- motif was observed. Since the side chain of histidine serves as the metal ion binding site for many native proteins, and very often histidine is present in a -SXH- or -TXH- sequence, to study the complex formation and hydrolytic processes in presence of nickel(II) ion four peptides were synthesised: Ac-SKHM-NH2, A3SSH-NH2, A4SSH-NH2, AAAeKSH-NH2. The Ni(II)-induced hydrolysis of Ac-SKHM-NH2 peptide occurs rapidly in alkaline medium already at room temperature. In two peptides containing -SSH- sequence on the C-termini, the N-terminal part is the major binding site for the nickel(II) ion, but the formation of dinuclear complexes was also observed. In the [Ni2LH-6]2- complex of hexapeptide, the coordination sphere of the metal ions is saturated with deprotonated Ser-O-, which does not result in hydrolysis of the peptide. For A4SSH-NH2, both Ni(II) ions fulfill the conditions for hydrolysis, which was confirmed by HPLC analyses at pH ~ 8.2 and 25 °C.

Interfacial interaction mechanism between Mn doped highly conjugated biochar and berberine hydrochloride.

MnSO4-modified biochar (Mn-BC) was synthesized to remove berberine hydrochloride (BH) from wastewater by utilizing tea waste as raw material and MnSO4 as modifier. Brunel Emmett Taylor (BET) analysis reveals that the specific surface area (SSA) and average pore size (Dave) of Mn-BC are 1.4 and 7 times higher than those of pristine biochar apart, attributing to the dissociation effect can promote the dispersion of MnSO4 in the pores of the biochar. Meanwhile, the doping of Mn not only introduces additional oxygen-containing functional groups (OCFGs), but also modulates the π electron density. Furthermore, Response surface method (RSM) analysis reveals that Mn-BC dosage has the most significant effect on BH removal, followed by BH concentration and pH value. Kinetic and isothermal studies reveal that the BH adsorption process of Mn-BC was mainly dominated by chemical and monolayer adsorption. Meanwhile, density functional theory (DFT) calculations confirm the contribution of Mn doping to the conjugation effect in the adsorption system. Originally proposed Mn-BC is one potentially propitious material to eliminate BH from wastewater, meanwhile this also provides a newfangled conception over the sustainable utilization of tea waste resources.

Enhancing visible light photocatalytic activity of holmium doped g-C3N4 and DFT theoretical insights.

In the search of novel photocatalysts to increase the effect of visible light in photocatalysis, g-C3N4 (CN) has become a shining star. Rare earth metals have been used as dopant material to reinforce the photocatalytic activity of CN due to their unique electron configuration recently. In this present study, the pure and different amounts of Ho-doped g-C3N4 (HoCN) photocatalysts were successfully synthesized using urea as a precursor by the one-pot method. Morphological, structural, optical, and vibrational properties of the synthesized photocatalysts were characterized by SEM, EDX, XRD, TGA, XPS, FTIR, PL, TRPL, Raman, DRS, and BET analyses. In addition, theoretical calculations using density functional theory (DFT) were meticulously carried out to delve the changes in the structural and electronic structure of CN with holmium doping. According to calculations, the chemical potential, electrophilicity, and chemical softness are higher for HoCN, while HOMO-LUMO gap, dipole moment, and the chemical hardness are lower for the pure one. Thus, holmium doping becomes desirable with low chemical hardness which indicates more effectivity and smaller HOMO-LUMO gap designate high chemical reactivity. To determine the photocatalytic efficiency of the pure and doped CN photocatalysts, the degradation of methylene blue (MB) was monitored under visible light. The results indicate that holmium doping has improved the photocatalytic activities of CN samples. Most strikingly, this improvement is noticeable for the 0.2 mmol doped CN sample that showed two times better photocatalytic activity than the pure one.