Introducing Porosity into Refractory Molybdenum Boride through Controlled Decomposition of a Metastable Mo-Al-B Precursor.

The high temperatures typically required to synthesize refractory compounds preclude the formation of high-energy morphological features, including nanoscopic pores that are beneficial for applications, such as catalysis, that require higher surface areas. Here, we demonstrate a low-temperature multistep pathway to engineer mesoporosity into a catalytic refractory material. Mesoporous molybdenum boride, α-MoB, forms through the controlled thermal decomposition of nanolaminate-containing sheets of the metastable MAB (metal-aluminum-boron) phase Mo2AlB2 and amorphous alumina. Upon heating, the Mo2AlB2 layers of the Mo2AlB2-AlOx nanolaminate, which is derived from MoAlB, begin to bridge and decompose, forming inclusions of alumina in a framework of α-MoB. The alumina can be dissolved in aqueous sodium hydroxide in an autoclave, forming α-MoB with empty and accessible pores. Statistical analysis of the morphologies and dimensions of the pores reveals a correlation with grain size, which relates to the pathway by which the alumina inclusions form. The transformation of Mo2AlB2 to α-MoB is topotactic due to crystal structure relationships, resulting in a high density of stacking faults that can be modeled to account for the observed experimental diffraction data. Porosity was validated by comparing surface areas and demonstrating catalytic viability for the hydrogen evolution reaction.

Incorporation of Metal Phosphide Domains into Colloidal Hybrid Nanoparticles.

Colloidal hybrid nanoparticles have generated considerable attention in the inorganic nanomaterials community. The combination of different materials within a single nanoparticle can lead to synergistic properties that can enable new properties, new applications, and the discovery of new phenomena. As such, methodologies for the synthesis of hybrid nanoparticles that integrate metal-metal, metal chalcogenide, metal oxide, and oxide-chalcogenide domains have been extensively reported in the literature. However, colloidal hybrid nanoparticles containing metal phosphide domains are rare, despite being attractive systems for their potentially unique catalytic, photocatalytic, and optoelectronic properties. In this Forum Article, we report a study of the synthesis of colloidal hybrid nanoparticles that couple the metal phosphides Ni2P and CoxPy with Au, Ag, PbS, and CdS using heterogeneous seeded-growth reactions. We also investigate the transformation of Au-Ni heterodimers to Au-Ni2P, where phosphidation of preformed metal-metal hybrid nanoparticles offers an alternative route to metal phosphide systems. We also study sequential cation-exchange reactions to target specific metal phosphide hybrids, i.e., the transformation of Ni2P-PbS into Ni2P-Ag2S and then Ni2P-CdS. Throughout all of these pathways, the accompanying discussion emphasizes the synthetic rationale, as well as the challenges in synthesis and characterization that are unique to these systems. In particular, the observation of oxide shells that surround the phosphide domains has implications for the potential photocatalytic applications of these hybrid nanoparticles.

Phosphine-Induced Phase Transition in Copper Sulfide Nanoparticles Prior to Initiation of a Cation Exchange Reaction.

Cation exchange reactions of colloidal copper sulfide nanoparticles are widely used to produce derivative nanoparticles having unique compositions, metastable crystal structures, and complex heterostructures. The copper sulfide crystal structure plays a key role in the mechanism by which cation exchange occurs and the product that forms. Here, we show that digenite copper sulfide nanoparticles undergo a spontaneous phase transition to tetragonal chalcocite in situ, prior to the onset of cation exchange. Room-temperature sonication of digenite (Cu1.8S) in trioctylphosphine, a Lewis base that drives cation exchange, extracts sulfur to produce tetragonal chalcocite (Cu2S). The subtle structural differences between digenite and tetragonal chalcocite are believed to influence the accessibility of cation diffusion channels and concomitantly the mechanism of cation exchange. Structural relationships in nanocrystal cation exchange are therefore dynamic, and intermediates generated in situ must be considered.

Multi-Step Topochemical Pathway to Metastable Mo2AlB2 and Related Two-Dimensional Nanosheet Heterostructures.

The rational synthesis of metastable inorganic solids, which is a grand challenge in solid-state chemistry, requires the development of kinetically controlled reaction pathways. Topotactic strategies can achieve this goal by chemically modifying reactive components of a parent structure under mild conditions to produce a closely related analogue that has otherwise inaccessible structures and/or compositions. Refractory materials, such as transition metal borides, are difficult to structurally manipulate at low temperatures because they generally are chemically inert and held together by strong covalent bonds. Here, we report a multistep low-temperature topotactic pathway to bulk-scale Mo2AlB2, which is a metastable phase that has been predicted to be the precursor needed to access a synthetically elusive family of 2-D metal boride (MBene) nanosheets. Room-temperature chemical deintercalation of Al from the stable compound MoAlB (synthesized as a bulk powder at 1400 °C) formed highly strained and destabilized MoAl1-xB, which was size-selectively precipitated to isolate the most reactive submicron grains and then annealed at 600 °C to deintercalate additional Al and crystallize Mo2AlB2. Further heating resulted in topotactic decomposition into bulk-scale Mo2AlB2-AlOx nanolaminates that contain Mo2AlB2 nanosheets with thickness of 1-3 nm interleaved by 1-3 nm of amorphous aluminum oxide. The combination of chemical destabilization, size-selective precipitation, and low-temperature annealing provides a potentially generalizable kinetic pathway to metastable variants of refractory compounds, including bulk Mo2AlB2 and Mo2AlB2-AlOx nanosheet heterostructures, and opens the door to other previously elusive 2-D materials such as 2-D MoB (MBene).

Pneumothorax in cystic fibrosis: beyond the guidelines.

Pneumothorax is a serious but common complication in patients with cystic fibrosis (CF). It has adverse prognostic implications as well as associations with subsequent reduction in lung function and significant risk of recurrence. Management dilemmas frequently occur that are beyond current guidelines. We review the evidence and highlight management difficulties in pneumothoraces in CF.

Vanadium and Niobium MXenes-Bilayered V2 O5 Asymmetric Supercapacitors.

MXenes offer high metallic conductivity and redox capacitance that are attractive for high-power, high-energy storage devices. However, they operate limitedly under high anodic potentials due to irreversible oxidation. Pairing them with oxides to design asymmetric supercapacitors may expand the voltage window and increase the energy storage capabilities. Hydrated lithium preintercalated bilayered V2 O5 ( δ-Lix V2 O5 ·nH2 O) is attractive for aqueous energy storage due to its high Li capacity at high potentials; however, its poor cyclability remains a challenge. To overcome its limitations and achieve a wide voltage window and excellent cyclability, it is combined with V2 C and Nb4 C3 MXenes. Asymmetric supercapacitors employing lithium intercalated V2 C (Li-V2 C) or tetramethylammonium intercalated Nb4 C3 (TMA-Nb4 C3 ) MXenes as the negative electrode, and a δ-Lix V2 O5 ·nH2 O composite with carbon nanotubes as the positive electrode in 5 m LiCl electrolyte operate over wide voltage windows of 2 and 1.6 V, respectively. The latter shows remarkably high cyclability-capacitance retention of ≈95% after 10 000 cycles. This work highlights the importance of selecting appropriate MXenes to achieve a wide voltage window and a long cycle life in combination with oxide anodes to demonstrate the potential of MXenes beyond Ti3 C2 in energy storage.

M5X4: A Family of MXenes.

MXenes are two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides typically synthesized from layered MAX-phase precursors. With over 50 experimentally reported MXenes and a near-infinite number of possible chemistries, MXenes make up the fastest-growing family of 2D materials. They offer a wide range of properties, which can be altered by their chemistry (M, X) and the number of metal layers in the structure, ranging from two in M2XTx to five in M5X4Tx. Only one M5X4 MXene, Mo4VC4, has been reported. Herein, we report the synthesis and characterization of two M5AX4 mixed transition metal MAX phases, Ti2.5Ta2.5AlC4 and Ti2.675Nb2.325AlC4, and their successful topochemical transformation into Ti2.5Ta2.5C4Tx and Ti2.675Nb2.325C4Tx MXenes. The resulting MXenes were delaminated into single-layer flakes, analyzed structurally, and characterized for their thermal and optical properties. This establishes a family of M5AX4 MAX phases and their corresponding MXenes. These materials were experimentally produced based on guidance from theoretical predictions, leading to more exciting applications for MXenes.

Influence of highly effective modulator therapy on the sputum proteome in cystic fibrosis.

BACKGROUND: There have been dramatic clinical improvements in people with cystic fibrosis (PwCF) commenced on the cystic fibrosis conductance regulator (CFTR) modulator elexacaftor/tezacaftor/ivacaftor (ETI). Sputum proteomics is a powerful research technique capable of identifying important airway disease mechanisms. Using this technique, we evaluated how ETI changes the sputum proteome in PwCF. METHODS: Sputum samples from 21 CF subjects pre- and post- ETI, 6 CF controls ineligible for ETI, and 15 healthy controls were analysed by liquid chromatography mass spectrometry. RESULTS: Post-ETI, mean FEV1 % increased by 13.7 % (SD 7.9). Principal component and hierarchical clustering analysis revealed that the post-ETI proteome shifted to an intermediate state that was distinct from pre-ETI and healthy controls, even for those achieving normal lung function. Functional analysis showed incomplete resolution of neutrophilic inflammation. The CF control sputum proteome did not alter. At the protein-level many more proteins increased in abundance than decreased following ETI therapy (80 vs 30; adjusted p value <0.05), including many that have anti-inflammatory properties. Of those proteins that reduced in abundance many were pro-inflammatory neutrophil-derived proteins. Several important respiratory proteases were unchanged. CONCLUSIONS: Sputum proteomics can provide insights into CF lung disease mechanisms and how they are modified by therapeutic intervention, in this case ETI. This study identifies imbalances in pro- and anti- inflammatory proteins in sputum that partially resolve with ETI even in those achieving normal spirometry values. This post-ETI intermediate state could contribute to ongoing airway damage and therefore its relevance to clinical outcomes needs to be established.

The relationship between lung disease severity and the sputum proteome in cystic fibrosis.

BACKGROUND: Proteomics can reveal molecular pathways of disease and provide translational perspectives to inform clinical decision making. Although several studies have previously reported the cystic fibrosis airway proteome, the relationship with severity of lung disease has not been characterised. The objectives of this observational study were to investigate differences in the CF sputum proteome associated with disease severity and identify potential markers of disease with translational potential. METHODS: Sputum samples from healthy volunteers and cystic fibrosis subjects (some prescribed modulator therapies) were analysed using liquid-chromatography tandem mass spectrometry. Severity of lung disease was based on baseline spirometry (percentage predicted forced expiratory volume in 1 s, FEV1%). RESULTS: Multiple sputum proteins (108 increased; 202 decreased) were differentially expressed in CF (n = 38) and healthy volunteers (n = 32). Using principal component analysis and hierarchical clustering, differences in sputum proteome were observed associated with progressive lung function impairment. In CF subjects, baseline FEV1% correlated with 87 proteins (positive correlation n = 20, negative n = 67); most were either neutrophil derived, or opposed neutrophil-driven oxidant and protease activity. CONCLUSION: Predictable and quantifiable changes in the CF sputum proteome occurred associated with progressive lung function impairment, some of which might have value as markers of disease severity in CF sputum. Further work validating these markers in other patient cohorts and exploring their clinical utility is needed.

Plasmon-Mediated Chiroptical Second Harmonic Generation from Seemingly Achiral Gold Nanorods.

Throughout nature, simple rules explain complex phenomena, such as the selective interaction of chiral objects with circularly polarized light. Here, we demonstrate chiroptical signals from gold nanorods, which are seemingly achiral structures. Shape anisotropy due to atomic-level faceting and rounding at the tips of nanorods, which are free of chiral surface ligands, induces linear-to-circular polarization modulation during second harmonic generation. The intrinsic nanorod chiroptical response is increased by plasmon-resonant excitation, which preferentially amplifies circularly polarized harmonic signals. This structure-plasmon interplay is uniquely resolved by polarization-resolved second harmonic generation measurements. The material's second-order polarizability is the product of the structure-dependent lattice-normal susceptibility and local surface plasmon field vectors. Synthetically scalable plasmon-supporting nanorods that amplify small circular dichroism signals provide a simple, assembly-free platform for chiroptical transduction.

Management of non-cystic fibrosis bronchiectasis.

Bronchiectasis is a common respiratory condition, characterised by abnormal bronchial dilatation, that often leads to recurrent airway infection and inflammation. It is an increasingly recognised respiratory condition, both as a primary lung disease but also co-existing with other respiratory diseases, such as chronic obstructive pulmonary disease and asthma. Diagnosis can have important treatment implications. There are shared systematic approaches to treatment, such as sputum clearance techniques, prompt treatment of exacerbations and, in certain circumstances, regular antibiotic therapy. It is vital to target antibiotic therapy appropriately, and knowledge of the patient's airway microbiology can assist with this. Certain infective and colonising organisms, such as Pseudomonas aeruginosa, cause worse patient outcomes and so need prompt treatment with appropriate antibiotics. In addition to this general management approach, there are many different underlying causes of bronchiectasis that should be identified wherever possible, to support more targeted therapy and prevent disease progression. This article provides a guide to the key principles of diagnosing and managing bronchiectasis, and outlines situations where more specialist respiratory support is required.