Effect of Postetch Annealing Gas Composition on the Structural and Electrochemical Properties of Ti₂CT_<i>x</i> MXene Electrodes for Supercapacitor Applications

Two-dimensional Ti₂CT_<i>x</i> MXene nanosheets were prepared by the selective etching of Al layer from Ti₂AlC MAX phase using HF treatment. The MXene sheets retained the hexagonal symmetry of the parent Ti₂AlC MAX phase. Effect of the postetch annealing ambient (Ar, N₂, N₂/H₂, and air) on the structure and electrochemical properties of the MXene nanosheets was investigated in detail. After annealing in air, the MXene sheets exhibited variations in structure, morphology, and electrochemical properties as compared to HF treated MAX phase. In contrast, samples annealed in Ar, N₂, and N₂/H₂ ambient retained their original morphology. However, a significant improvement in the supercapacitor performance is observed upon heat treatment in Ar, N₂, and N₂/H₂ ambients. When used in symmetric two-electrode configuration, the MXene sample annealed in N₂/H₂ atmosphere exhibited the best capacitive performance with specific capacitance value (51 F/g at 1A/g) and high rate performance (86%). This improvement in the electrochemical performance of annealed samples is attributed to highest carbon content, and lowest fluorine content on the surface of the sample upon annealing, while retaining the original two-dimensional layered morphology and providing maximum access of aqueous electrolyte to the electrodes

Unraveling the Order and Disorder in Poly(3,4-ethylenedioxythiophene)/Poly(styrenesulfonate) Nanofilms

Conductive polymer poly­(3,4-ethylenedioxythiophene)/poly­(styrenesulfonate) (PEDOT/PSS) exhibits a tunable conductivity ranging from 0.1 to 4380 S·cm^–1 under different doping and/or dedoping strategies. However, the dependence of macroscopic electrical properties on the evolution of the microstructure is not clearly understood. This is the first study that systematically investigated the spatial arrangement of the ordered and disordered phases in PEDOT/PSS nanofilms by bright-field (BF), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) combined with electron energy loss spectroscopy (EELS) and element-thickness mapping. Our observations clarify how amorphous PSS hinders electrical transport at various length scales in the PEDOT/PSS films. Moreover, the mechanism for an enhancement in 3 orders of magnitude in electrical conductivity was proved by TEM investigation, which is mainly due to a more uniform dispersion by dedoping that opens PEDOT nanoparticle clusters in PEDOT/PSS films. Our microstructural and electrical studies show that the change in spatial arrangement and interaction of small PEDOT domains plays a considerable role in the final electron transport

Effect of Precursor Ligands and Oxidation State in the Synthesis of Bimetallic Nano-Alloys

The characteristics of bimetallic nanomaterials are dictated by their size, shape, and elemental distribution. Solution synthesis is widely utilized to form nanomaterials, such as nanoparticles, with controlled size and shape. However, the effects of variables on the characteristics of bimetallic nanomaterials are not completely understood. In this study, we used a continuous-flow synthetic strategy to explore the effects of the precursor ligands and the precursor oxidation state in the shape-controlled synthesis of platinum alloy nano-octahedra and show their effect on the nanoparticle size and the elemental distribution within the alloy nanoparticle. We demonstrate that this strategy can tune the size of monodisperse PtM (M = Ni or Cu) alloy nanocrystals ranging from 3 to 16 nm with an octahedral shape using acetylacetonate or halide precursors of Pt­(II), Pt­(IV), and Ni­(II) or Cu­(II). The nanoparticles formed from halide precursors showed an enrichment of platinum on their surfaces, and the use bromide ligands in the presence of air showed the formation of concave and uneven surface facets. The two nanocrystal precursors can be utilized independently and can control the size with a trend of Pt­(acac)₂ < PtCl₂ < PtCl₄ < PtBr₂ < PtBr₄ and M­(acac)₂ < MCl₂ < MBr₂ for the secondary metal (copper or nickel). These results open up avenues to understand the effect of the ligand shell of a precursor during the synthesis of alloy nanoparticles as well as to control, in a scalable manner, the nanomaterial size and surface chemistry

Photoresponsive Bridged Silsesquioxane Nanoparticles with Tunable Morphology for Light-Triggered Plasmid DNA Delivery

Bridged silsesquioxane nanocomposites with tunable morphologies incorporating <i>o</i>-nitrophenylene–ammonium bridges are described. The systematic screening of the sol–gel parameters allowed the material to reach the nanoscale with controlled dense and hollow structures of 100–200 nm. The hybrid composition of silsesquioxanes with 50% organic content homogeneously distributed in the nanomaterials endowed them with photoresponsive properties. Light irradiation was performed to reverse the surface charge of nanoparticles from +46 to −39 mV via a photoreaction of the organic fragments within the particles, as confirmed by spectroscopic monitorings. Furthermore, such nanoparticles were applied for the first time for the on-demand delivery of plasmid DNA in HeLa cancer cells via light actuation

Plasma-Assisted Synthesis of NiCoP for Efficient Overall Water Splitting

Efficient water splitting requires highly active, earth-abundant, and robust catalysts. Monometallic phosphides such as Ni₂P have been shown to be active toward water splitting. Our theoretical analysis has suggested that their performance can be further enhanced by substitution with extrinsic metals, though very little work has been conducted in this area. Here we present for the first time a novel PH₃ plasma-assisted approach to convert NiCo hydroxides into ternary NiCoP. The obtained NiCoP nanostructure supported on Ni foam shows superior catalytic activity toward the hydrogen evolution reaction (HER) with a low overpotential of 32 mV at −10 mA cm^–2 in alkaline media. Moreover, it is also capable of catalyzing the oxygen evolution reaction (OER) with high efficiency though the real active sites are surface oxides in situ formed during the catalysis. Specifically, a current density of 10 mA cm^–2 is achieved at overpotential of 280 mV. These overpotentials are among the best reported values for non-noble metal catalysts. Most importantly, when used as both the cathode and anode for overall water splitting, a current density of 10 mA cm^–2 is achieved at a cell voltage as low as 1.58 V, making NiCoP among the most efficient earth-abundant catalysts for water splitting. Moreover, our new synthetic approach can serve as a versatile route to synthesize various bimetallic or even more complex phosphides for various applications

Photoresponsive Bridged Silsesquioxane Nanoparticles with Tunable Morphology for Light-Triggered Plasmid DNA Delivery

Bridged silsesquioxane nanocomposites with tunable morphologies incorporating <i>o</i>-nitrophenylene–ammonium bridges are described. The systematic screening of the sol–gel parameters allowed the material to reach the nanoscale with controlled dense and hollow structures of 100–200 nm. The hybrid composition of silsesquioxanes with 50% organic content homogeneously distributed in the nanomaterials endowed them with photoresponsive properties. Light irradiation was performed to reverse the surface charge of nanoparticles from +46 to −39 mV via a photoreaction of the organic fragments within the particles, as confirmed by spectroscopic monitorings. Furthermore, such nanoparticles were applied for the first time for the on-demand delivery of plasmid DNA in HeLa cancer cells via light actuation

One-Pot Synthesis of Size- and Composition-Controlled Ni-Rich NiPt Alloy Nanoparticles in a Reverse Microemulsion System and Their Application

Bimetallic nanoparticles have been the subject of numerous research studies in the nanotechnology field, in particular for catalytic applications. Control of the size, morphology, and composition has become a key challenge due to the relationship between these parameters and the catalytic behavior of the particles in terms of activity, selectivity, and stability. Here, we present a one-pot air synthesis of 2 nm Ni₉Pt₁ nanoparticles with a narrow size distribution. Control of the size and composition of the alloy particles is achieved at ambient temperature, in the aqueous phase, by the simultaneous reduction of nickel and platinum precursors with hydrazine, using a reverse microemulsion system. After deposition on an alumina support, this Ni-rich nanoalloy exhibits unprecedented stability under the harsh conditions of methane dry reforming

Electrochemical Characteristics and Li⁺ Ion Intercalation Kinetics of Dual-Phase Li₄Ti₅O₁₂/Li₂TiO₃ Composite in the Voltage Range 0–3 V

Li₄Ti₅O₁₂, Li₂TiO₃, and dual-phase Li₄Ti₅O₁₂/Li₂TiO₃ composite were prepared by sol–gel method with average particle size of 1, 0.3, and 0.4 μm, respectively. Though Li₂TiO₃ is electrochemically inactive, the rate capability of Li₄Ti₅O₁₂/Li₂TiO₃ is comparable to that of Li₄Ti₅O₁₂ at different current rates. Li₄Ti₅O₁₂/Li₂TiO₃ also shows a good rate performance of 90 mA h g^–1 at a high rate of 10 C in the voltage range 1–3 V, attributable to increased interfaces in the composite. While Li₄Ti₅O₁₂ delivers a capacity retention of 88.6% at 0.2 C over 50 cycles, Li₄Ti₅O₁₂/Li₂TiO₃ exhibits no capacity fading at 0.2 C (40 cycles) and a capacity retention of 98.45% at 0.5 C (50 cycles). This highly stable cycling performance is attributed to the contribution of Li₂TiO₃ in preventing the undesirable reaction of Li₄Ti₅O₁₂ with the electrolyte during cycling. Cyclic voltammetric curves of Li₄Ti₅O₁₂/Li₂TiO₃ in the 0–3 V range exhibit two anodic peaks at 1.51 and 0.7–0.0 V, indicating two modes of lithium intercalation into the lattice sites of active material. Owing to enhanced intercalation/deintercalation kinetics in 0–3 V, the composite electrode delivers a superior rate performance of 203 mAh/g at 2.85 C and 140 mAh/g at 5.7 C with good reversible capacity retention over 100 cycles

Engineering Hydrophobic Organosilica Nanoparticle-Doped Nanofibers for Enhanced and Fouling Resistant Membrane Distillation

Engineering and scaling-up new materials for better water desalination are imperative to find alternative fresh water sources to meet future demands. Herein, the fabrication of hydrophobic poly­(ether imide) composite nanofiber membranes doped with novel ethylene-pentafluorophenylene-based periodic mesoporous organosilica nanoparticles is reported for enhanced and fouling resistant membrane distillation. Novel organosilica nanoparticles were homogeneously incorporated into electrospun nanofiber membranes depicting a proportional increase of hydrophobicity to the particle contents. Direct contact membrane distillation experiments on the organosilica-doped membrane with only 5% doping showed an increase of flux of 140% compared to commercial membranes. The high porosity of organosilica nanoparticles was further utilized to load the eugenol antimicrobial agent which produced a dramatic enhancement of the antibiofouling properties of the membrane of 70% after 24 h

Bipodal Surface Organometallic Complexes with Surface N‑Donor Ligands and Application to the Catalytic Cleavage of C–H and C–C Bonds in <i>n</i>‑Butane

We present a new generation of “true vicinal” functions well-distributed on the inner surface of SBA15: [(Si–NH₂)­(Si–OH)] (<b>1</b>) and [(Si–NH₂)₂] (<b>2</b>). From these amine-modified SBA15s, two new well-defined surface organometallic species [(Si–NH−)­(Si–O−)]­Zr­(CH₂<i>t</i>Bu)₂ (<b>3</b>) and [(Si–NH−)₂]­Zr­(CH₂<i>t</i>Bu)₂ (<b>4</b>) have been obtained by reaction with Zr­(CH₂<i>t</i>Bu)₄. The surfaces were characterized with 2D multiple-quantum ¹H–¹H NMR and infrared spectroscopies. Energy-filtered transmission electron microscopy (EFTEM), mass balance, and elemental analysis unambiguously proved that Zr­(CH₂<i>t</i>Bu)₄ reacts with these vicinal amine-modified surfaces to give mainly bipodal bis­(neopentyl)­zirconium complexes (<b>3</b>) and (<b>4</b>), uniformly distributed in the channels of SBA15. (<b>3</b>) and (<b>4</b>) react with hydrogen to give the homologous hydrides (<b>5</b>) and (<b>6</b>). Hydrogenolysis of <i>n</i>-butane catalyzed by these hydrides was carried out at low temperature (100 °C) and low pressure (1 atm). While (<b>6</b>) exhibits a bis­(silylamido)­zirconium bishydride, [(Si–NH−)₂]­Zr­(H)₂ (<b>6a</b>) (60%), and a bis­(silylamido)­silyloxozirconium monohydride, [(Si–NH−)₂(Si–O−)]­ZrH (<b>6b</b>) (40%), (<b>5</b>) displays a new surface organometallic complex characterized by an ¹H NMR signal at 14.46 ppm. The latter is assigned to a (silylimido)­(silyloxo)zirconium monohydride, [(Si–N)­(Si–O−)]­ZrH (<b>5b</b>) (30%), coexistent with a (silylamido)­(silyloxo)­zirconium bishydride, [(Si–NH−)­(Si–O−)]­Zr­(H)₂ (<b>5a</b>) (45%), and a silylamidobis­(silyloxo)­zirconium monohydride, [(Si–NH−)­(Si–O−)₂]­ZrH (<b>5c</b>) (25%). Surprisingly, nitrogen surface ligands possess catalytic properties already encountered with silicon oxide surfaces, but interestingly, catalyst (<b>5</b>) with chelating [N,O] shows better activity than (<b>6</b>) with chelating [N,N]