High Defect Concentration Research Articles

Correlation between femoral and tibial footprint of the anterior cruciate ligament using specific (CLASS) MRI novel sequences

Breaking the capacity barrier in intercalation-type anode materials for lithium-ion batteries while preserving other essential electrochemical properties remains a significant challenge. Here, using perovskite SrVO3 as a model, we demonstrate the feasibility of employing defect engineering to provide extra active sites for electrochemical reactions. Defective SrxVO3-δ samples with a unique amorphous-crystalline dual-phase structure are successfully prepared by regulating the nonstoichiometric Sr/V ratio and using a non-equilibrium solution combustion strategy to alleviate nucleation. The dual-phase SrxVO3-δ electrodes, which take advantage of both the high defect concentration advantage of amorphous and the high electrical/ionic conductivity of crystalline, give a high specific capacity of 508 mAh/g at a safe potential of 1.0 V vs. Li/Li+, showing a 40% increase over SrVO3 electrodes and outperforming most state-of-the-art intercalation-based anodes. In addition, when coupling with LiFePO4 cathode, the SrxVO3-δ electrodes can operate over 10,000 cycles with 91% capacity retention, overcoming the limited structural stability exhibited in typical defective electrodes. The study demonstrates the viability of modulating the crystallinity in intercalation-based anodes to enhance electrochemical performance and paves the way for the advancement of Li-ion battery technology.

CuCeOx/CuO Catalyst Derived from the Layered Double Hydroxide Precursor: Catalytic Performance in NO Reduction with CO in the Presence of Water and Oxygen.

Valencies of metal species and lattice defects, such as oxygen vacancies, play a pivotal role in metal oxide-catalyzed reactions. Herein, we report a promising synthetic strategy for preparing CuO-supported CuCeOx catalysts (CuCeOx/CuO) by calcination of a hydrotalcite precursor [Cu6Ce2(OH)16]CO3·nH2O. The structural and chemical properties of catalysts were characterized by XRD, ICP-AES, TEM, TPR, NH3-TPD, XPS, Raman spectroscopy, and N2 adsorption, which revealed that the thermal pretreatment in an oxidative atmosphere caused segregation and reconstitution processes of the precursor, resulting in a mesoporous catalyst consisting of well-dispersed CuO-supported CuCeOx clusters of 1.8-3.2 nm in size with a high population of oxygen vacancies. The as-prepared catalyst shows excellent catalytic performance in the reduction of NO by CO in the absence as well as in the presence of water and oxygen. This behavior is attributed to its high oxygen defect concentration facilitating the interplay of the redox equilibria between Cu2+ and reduced copper species (Cu+/Cu0) and (Ce4+/Ce3+). The high surface population of oxygen vacancies and in situ-generated metallic copper species have been evidenced by Raman spectroscopy and X-ray photoelectron spectroscopy. The layered double hydroxide-derived CuCeOx/CuO also showed good water tolerance and long-term stability. In situ infrared spectroscopy investigations indicated that adsorbed hyponitrite species are the main reaction intermediates of the NO conversion as also corroborated by theoretical simulations.

Automated classification of pediatric age from 12-lead ECG using deep residual convolutional neural networks

With increased interest in screening of young people for potential causes of sudden death, accurate automated detection of ventricular pre-excitation (VPE) or Wolff–Parkinson–White syndrome (WPW) in the pediatric resting ECG is important. Several recent studies have shown interobserver variability when reading screening ECGs and thus an accurate automated reading for this potential cause of sudden death is critical. We designed and tested an automated algorithm to detect pediatric VPE optimized for low prevalence.Digital ECGs with 12 leads or 15 leads (12-lead plus V3R, V4R and V7) were selected from multiple hospitals and separated into a testing and training database. Inclusion criterion was age less than 16 years. The reference for algorithm detection of VPE was cardiologist annotation of VPE for each ECG. The training database (n = 772) consisted of VPE ECGs (n = 37), normal ECGs (n = 492) and a high concentration of conduction defects, RBBB (n = 232) and LBBB (n = 11). The testing database was a random sample (n = 763). All ECGs were analyzed with the Philips DXL ECG Analysis algorithm for basic waveform measurements. Additional ECG features specific to VPE, mainly delta wave scoring, were calculated from the basic measurements and the average beat. A classifier based on decision tree bootstrap aggregation (tree bagger) was trained in multiple steps to select the number of decision trees and the 10 best features. The classifier accuracy was measured on the test database.The new algorithm detected pediatric VPE with a sensitivity of 78%, a specificity of 99.9%, a positive predictive value of 88% and negative predictive value of 99.7%.This new algorithm for detection of pediatric VPE performs well with a reasonable positive and negative predictive value despite the low prevalence in the general population.

Large-strain functional fatigue properties of superelastic metastable β titanium and NiTi alloys: A comparative study

This paper investigates the fatigue behavior of superelastic NiTi and two metastable β titanium alloys - commercial Beta III (Ti-11.5Mo-6Zr-4.5Sn wt%) and Ti2448 (Ti–24Nb–4Zr–8Sn wt%) alloys. In situ cyclic tensile tests performed under synchrotron X-ray radiation were used to precisely characterize the stress induced martensitic (SIM) transformation occurring in these alloys. For the NiTi alloy, an intermediate B2-R SIM transformation was detected before the B2-B19′ SIM transformation and no plastic deformation occurred until failure. All metastable β titanium alloys that were solution-treated before testing underwent a reversible β-α" SIM transformation and plastic deformation prior to failure. Low-cycle strain-controlled fatigue tests were performed in tension-tension strain-controlled mode at 37 °C to evaluate large-strain functional fatigue properties. The fatigue life of metastable β titanium alloys was found to be much better than that of NiTi alloy at large applied strains. After a rapid evolution during the first cycles, the mechanical response was found to be constant for NiTi alloy while it evolved continuously for metastable β titanium alloys. In addition, failure occurred suddenly in NiTi, whereas cyclic softening was observed before failure in metastable β titanium alloys. Fatigue properties at higher applied strains are mainly hindered by SIM transformation and defects generated at austenite/martensite interfaces during cycling. This explains why the studied NiTi alloy showed lower fatigue properties than metastable β titanium alloys. In fact, while SIM transformation is homogeneously nucleated in metastable β titanium alloys, SIM transformation is highly localized in NiTi, resulting in higher concentration of defects that promote crack nucleation and, in turn, degrade the functional fatigue properties.

Myth behind Metastable and Stable n-Hexylammonium Bromide-Based Low-Dimensional Perovskites

In perovskite solar cells, passivating the surface or interface that contains a high concentration of defects, specifically deep-level defects, is one of the most important topics to substantially enhance the power conversion efficiency and stability of the devices. Long-chain alkylammonium bromides have been widely and commonly adapted for passivation treatment. However, the mechanism behind is still not well explored as the formation route and the exact structure of these alkylammonium bromide-based low-dimensional perovskites are unclear. Herein, we investigate the physical and chemical properties of an n-hexylammonium bromide (HABr)-based low-dimensional perovskite including both thin films and single crystals. First of all, the HA2PbBr4 perovskite film and aged single crystal demonstrate different X-ray diffraction patterns from those of the fresh as-prepared single crystal. We found that the fresh HA2PbBr4 single crystal exhibits a metastable phase as its structure changes with aging due to the relaxation of crystal lattice strains, whereas the HA2PbBr4 perovskite film is pretty stable as the aged single crystal. Upon reacting with FAPbI3, HABr can be intercalated into the FAPbI3 lattice to form a mixed-cation perovskite of HAFAPbI3Br, which is in a dynamic equilibrium of decomposition and formation. In contrast, the reaction of HABr with excess PbI2 forms a stable HA2PbI2Br2 perovskite. Based on such findings, we rationally develop a HA2PbI2Br2-passivated FACs-based perovskite by reacting HABr with excess PbI2, the photovoltaics based on which are more stable and efficient than those passivated by the HAFAPbI3Br perovskite. Our discovery paves way for a more in-depth study of bromide-containing low-dimensional perovskites and their optoelectronic applications.

How to Realize Ultrahigh Photochromic Performance for Real-Time Optical Recording in Transparent Ceramics.

A combination of transparency and photochromic (PC) properties in ferroelectrics has promising application potential in smart windows and optical storage/imaging. Nonetheless, limited by understanding the underlying PC mechanism, a splendid PC performance is rarely achieved in transparent ferroelectrics. Here, a strategy to construct deep-lying traps by ion-doping induced defect engineering in (K0.5Na0.5)NbO3-based ferroelectric ceramics is proposed. Based on the improved density functional theory simulations, a high concentration of vacancy defects can be realized by codoping 1 mol % Pr and 4 mol % Ba in (K0.5Na0.5)NbO3, which helps achieving deep-lying traps and then superior PC performance. Through traditional pressureless sintering, highly transparent ceramics with designed optimal composition have been fabricated in a wide sintering temperature range (1170-1210 °C), exhibiting an ultrafast PC feature, i.e., 0.1 s response time (by illumination of 400 nm light), along with high PC efficiency (5.8 cm2·W-1) and PC rate (7.1 s-1), preeminent among reported inorganic PC transparent materials. Additionally, the ceramics have been utilized for real-time optical recording, displaying unambiguous patterning with long-time preservation (21 days). This research supplies a paradigm for designing high-performance PC transparent materials in optical applications and helps deepen the comprehensive understanding of the PC mechanism.

Lattice softness regulates recombination and lifetime of carrier in Germanium doped CsPbI2Br perovskite: First principles DFT and NAMD simulations

Perovskite materials are characterized by high concentration of intrinsic defects. These defects lead to non-radiative recombination of electron and hole pairs, which is one of the major factors leading to the poor performance of the optoelectronic devices fabricated from these materials. Using the first-principles method, we have demonstrated that energy loss due to non-radiative recombination is suppressed in defective CsPbI2Br (D-CsPbI2Br) with the doping of Germanium (Ge) in CsGexPb1-xI2Br (x ​= ​0.15). Bromine vacancy (VBr) in CsPbI2Br introduces localized states as seen in the PDOS, however, doping of Ge eliminates these states. Using nonadiabatic molecular dynamics (NA-MD) and time-domain density functional theory, we show that the lifetime of the charge carriers is extended in Ge-doped CsPbI2Br (D-GeCsPbI2Br) by a factor of 3 and the dephasing time shortens to 6.2 ns. The electron localization function (ELF) plots of bulk CsPbI2Br (B–CsPbI2Br) show that charge localization increases around the Ge atom and it decreases the interaction between Pb atoms. In D-CsPbI2Br, phonons from a wide range of frequencies participate in scattering, and weak non-adiabatic (NA) coupling between electron and phonon in association with phonon modes in the low-frequency spectrum is responsible for extending the lifetime of charge carriers. Strong dynamic disorder in molecular dynamics (MD) simulations points to softening of lattice in D-GeCsPbI2Br. The increase in lattice softness of the Ge-doped is confirmed by the reduced value of bulk modulus (13.2 ​GPa) in D-GeCsPbI2Br as compared to the value in D-CsPbI2Br (13.6 ​GPa). Computing inverse participation ratio (IPR) gives the degree of localization of charge in the valence-band maximum (VBM) and conduction-band minimum (CBM). We have investigated the behavior of IPR and carrier lifetime with temperature, and based on these results, we found that lattice softness and a lifetime of charge carriers increase in D-GeCsPbI2Br.

Surface potential variation across (hk1) and non-(hk1) grain boundaries of antimony triselenide

Electronic materials that can tolerate defects or create self-passivated interfaces expand the horizons to more sustainable electronic devices. Two heuristic models suggest that (i) antimony triselenide is a defect tolerant semiconductor (to certain point defects) and that (ii) the boundaries of grains with a specific orientation are self-passivated. Yet, experimental support or scrutiny of these models is lacking. Partly because measuring a passive quality of a material is perplexing. A possible way forward is to measure defect activity in correlation with other experimental evidence for defect presence, for example, by relating the grain boundaries’ (GBs) nanostructure and electronic quality. One measure of the electronic quality is the magnitude of the surface potential variation across grain boundaries—a high (charged) defect concentration and low defect tolerance typically leads to a significant surface potential variation. On the other hand, direct observation of defects (e.g., by electron microscopy) and a small surface potential variation indicates that the material is defect tolerant. In parallel, a comparison of the surface potential variation across grain boundaries in films with grains of different orientations provides a qualitative measure of the self-passivation of material because only certain crystallographic surfaces are expected to be self-passivated. Herein we report that regardless of the grains’ mutual respective orientation, the grain boundaries of antimony triselenide have a relatively benign electronic quality. This is evident in a shallow surface potential variation across grain boundaries (10–50 mV; 195 GBs were investigated). Yet, a high-resolution TEM investigation reveals that a variety of defects is prevalent at and near the GBs. Additionally, we found that GBs in films with distinct (hk1) orientation indeed have a lower surface potential variation than grains with (hk0) orientation. These findings support both heuristic models and provide a practical way to scrutinize defect tolerance in other polycrystalline semiconductors.

Wearable perovskite solar cells by aligned liquid crystal elastomers

In a flexible perovskite solar cell, the bottom interface between perovskite and the electron-transporting layer is critical in determining its efficiency and reliability. High defect concentrations and crystalline film fracturing at the bottom interface substantially reduce the efficiency and operational stability. In this work, a liquid crystal elastomer interlayer is intercalated into a flexible device with the charge transfer channel toughened by the aligned mesogenic assembly. The molecular ordering is instantly locked upon photopolymerization of liquid crystalline diacrylate monomers and dithiol-terminated oligomers. The optimized charge collection and the minimized charge recombination at the interface boost the efficiency up to 23.26% and 22.10% for rigid and flexible devices, respectively. The liquid crystal elastomer-induced suppression of phase segregation endows the unencapsulated device maintaining >80% of the initial efficiency for 1570 h. Moreover, the aligned elastomer interlayer preserves the configuration integrity with remarkable repeatability and mechanical robustness, which enables the flexible device to retain 86% of its original efficiency after 5000 bending cycles. The flexible solar cell chips are further integrated into a wearable haptic device with microneedle-based arrays of sensors to demonstrate a pain sensation system in virtual reality.

Environmentally Friendly Improvement of Plasmonic Nanostructure Functionality towards Magnetic Resonance Applications

Plasmonic nanostructures have attracted a broad research interest due to their application perspectives in various fields such as biosensing, catalysis, photovoltaics, and biomedicine. Their synthesis by pulsed laser ablation in pure water enables eliminating various side effects originating from chemical contamination. Another advantage of pulsed laser ablation in liquids (PLAL) is the possibility to controllably produce plasmonic nanoparticles (NPs) in combination with other plasmonic or magnetic materials, thus enhancing their functionality. However, the PLAL technique is still challenging in respect of merging metallic and semiconductor specific features in nanosized objects that could significantly broaden application areas of plasmonic nanostructures. In this work, we performed synthesis of hybrid AuSi NPs with novel modalities by ultrashort laser ablation of bulk gold in water containing silicon NPs. The Au/Si atomic ratio in the nanohybrids was finely varied from 0.5 to 3.5 when changing the initial Si NPs concentration in water from 70 µg/mL to 10 µg/mL, respectively, without requiring any complex chemical procedures. It has been found that the laser-fluence-insensitive silicon content depends on the mass of nanohybrids. A high concentration of paramagnetic defects (2.2·× 1018 spin/g) in polycrystalline plasmonic NPs has been achieved. Our findings can open further prospects for plasmonic nanostructures as contrast agents in optical and magnetic resonance imaging techniques, biosensing, and cancer theranostics.

Actinide and lanthanide dioxide lattice dilatation mechanisms with defect ingrowths

AbstractThe effects of irradiation‐induced defects on the fluorite‐structured dioxide materials were investigated in the literature and explained with complex physical phenomena. An interpretation that can simply explain their effects on the structure has not been put forward so far. However, in a recent atomistic simulation study, a specific defect was found to be directly responsible for the α‐particle irradiated UO2 lattice dilatation, and there was a linear relationship between them. It was also determined that this linear equation has two different slopes at low and high defect concentrations. In this paper, it was found that these phenomenon were not specific to UO2 and applicable to all fluorite‐structured actinide and lanthanide dioxides studied here (CmO2, AmO2, CeO2, UO2, NpO2, PuO2, ThO2). The findings provide clues to the existence of more general law. The results have the potential to lead to significant improvements, such as why different radiation types (α‐particle, α‐decay, fission) swell the lattice at different saturation levels.

Size-matched dicarboxylic acid for buried interfacial engineering in high-performance perovskite solar cells

Tin dioxide (SnO2) is considered to be one of the most promising electron transport layers (ETLs) in perovskite solar cells (PSCs). Considering high concentrations of defects and energy level mismatch at the ETL/perovskite interface, buried interfacial engineering aids in boosting the efficiency and stability of PSCs. Herein, three dicarboxylic acids (DAs) including oxalic acid (OA), propanedioic acid (PA) and succinic acid (SA) are selected to modify the interface between perovskite layers and ETLs. It is demonstrated that DAs can enhance interfacial interaction between SnO2 and perovskite by esterification reaction and hydrogen bonding. In particular, OA with appropriate size can passivate two hydroxyl groups on SnO2 surfaces simultaneously, resulting in more favorable energy level alignment and better defect passivation ability amongst the three dicarboxylic buffer layers. Correspondingly, the power conversion efficiency of the OA-modified PSC increases substantially from 21.20% (reference device) to 22.91%, with a fill factor up to 83.1%. This work verifies that the buried interfacial engineering can effectively improve PSC performance, and also suggests the possibility of using size-matched symmetric molecules to modify ETLs for performance enhancement.

Porous Organic Cage Induced Spontaneous Restructuring of Buried Interface Toward High‐Performance Perovskite Photovoltaic

AbstractIn perovskite solar cells (PSCs), the buried interface containing high concentrations of defects is critical for efficient charge extraction toward high‐performance device. Herein, porous organic cage (POC) is introduced between tin dioxide and perovskite to spontaneously reconstitute the buried interface. Through the chemical linkage formed by polydentate chelation of POC with SnO2 and perovskite, the buried interface achieves greatly reduced defect density and enhanced carrier extraction. More importantly, it is found that iodide ions in aged devices to migrate down to the electron transport layer and even invade the ITO electrode, changing the work function of ITO. This detrimental effect can be well resolved by POC since the host‐guest interaction of POC can effectively suppress the iodide ions trying to migrate downward. As a result, the PSC fabricated by POC‐restructured strategy yields a superior PCE of 24.13%. Moreover, the unencapsulated PSCs exhibit conspicuous improved long‐term stability and retain 93% of its initial efficiency after 5000 h in ambient condition.

Surface modification of Co3O4 nanostructures using wide range of natural compounds from rotten apple juice for the efficient oxygen evolution reaction

In this study, a new strategy has been produced to use a rotten apple juice as a source for the surface modification of Co3O4 nanostructures, giving rise to efficient electro-catalysts for driving oxygen evolution reaction (OER) at relatively low over potential. We have studied the morphology, chemical composition, and crystalline aspects of Co3O4 nanostructures using different analytical techniques. The Co3O4 nanostructures grown with rotten apple juice were observed with low impurity of Fe and P, surface modification, reduced particle size, high concentration of oxygen vacancies, defects and cubic phase of Co3O4. Furthermore, we have used the surface modified Co3O4 nanostructures for water electrolysis and noticed the significant performance towards OER in alkaline conditions. The electrochemical characterization revealed that the Co3O4 nanostructure prepared with 20 mL of rotten apple juice exhibits an overpotential value of 269 mV at 20 mA/cm2 current density. The charge transport resistance (Rct) at the interface was estimated around 118.9 Ω, confirming an excellent reaction kinetics on the Co3O4 nanostructures and highly supported efficient performance towards OER. The Co3O4 nanostructures prepared with 20 mL of rotten apple juice has shown an acceptable durability for 40 h, verifying the long-term use. The performance of Co3O4 nanostructures with apple juice could be attributed to high oxygen vacancies due to high density of Co2+ ions on the surface, impurities of Fe and P, reduced nanoparticle size, defects in the structures, and favorable chemical composition. At the end, surface modified Co3O4 nanostructures was observed as an outperformed electrocatalyst when prepared with rotten apple juice. Therefore, this can be used in diverse purposes including energy conversion and storage applications.

The effect of the surface patterning by ion beam irradiation on the Ag directional outflow in Ag/AlN nano-multilayers

Surface templating of nano-multilayers is a promising step for the advanced industrial application of these nanomaterials. In the present work, the effect of focused ion beam modification of Ag/AlN nano-multilayer near-surface region on the Ag surface outflow is revealed. Surface patterning by ion beam irradiation leads to the formation of a higher amount of Ag crystals in relation to the intact surface region. Heat treatment initiates grooving of Ag grain boundaries, resulting in the formation of channels in the nano-multilayer volume. These channels act as pathways for mass transport of Ag to the film surface. Ion bombardment creates regions of high concentration of non-equilibrium defects, which locally increase the driving force for grooving and channeling, thereby promoting creation of more pathways for Ag surface migration. The obtained experimental results indicate that surface modification by focused ion beam can be used for production of nano-multilayers with designed templates of surface outflow.

Oxygen Vacancy-Rich Amorphous BiVO4 Nanoparticles for Colorimetric Sensing

Defects in crystalline nanozymes play a critical role in enhancing their performances and related catalytic events. However, creating a high concentration of active and robust defects in well-explored crystalline metal oxides to achieve high-performance single-enzymatic activity is challenging. Herein, amorphous BiVO4 beyond traditional crystalline nanozymes is prepared via a facile solution-processed coprecipitation method favorable to large-scale manufacturing to mimic enzymatic properties. As expected, the specially designed amorphous material without any post-treatments has sufficient and robust oxygen vacancies, which are highly active in converting oxygen to reactive radicals (O2–•). Simultaneously, the negatively charged surface has a high affinity for the substrate, facilitating charge transfer between materials and substrates and, in turn, providing higher catalytic efficiency compared to the crystalline counterparts. Most importantly, the sample can only mimic oxidase-like activity rather than the multienzyme-like activity generally observed in most reported crystalline metal oxides, which is a step forward in the development of nanozymes. This amorphous BiVO4-based system is also evaluated for the sensitive and selective detection of l-cysteine. The study provides insight into nanozyme development and highlights the great potential of amorphous materials in addition to amorphous BiVO4.

Transforming NiCo2O4 nanorods into nanoparticles using citrus lemon juice enhancing electrochemical properties for asymmetric supercapacitor and water oxidation.

Recently, the nanostructured nickel-cobalt bimetallic oxide (NiCo2O4) material with high electrochemical activity has received intensive attention. Beside this, the biomass assisted synthesis of NiCo2O4 is gaining popularity due to its advantageous features such as being low cost, simplicity, minimal use of toxic chemicals, and environment-friendly and ecofriendly nature. The electrochemical activity of spinel NiCo2O4 is associated with its mixed metal oxidation states. Therefore, much attention has been paid to the crystal quality, morphology and tunable surface chemistry of NiCo2O4 nanostructures. In this study, we have used citrus lemon juice consisting of a variety of chemical compounds having the properties of a stabilizing agent, capping agent and chelating agent. Moreover, the presence of several acidic chemical compounds in citrus lemon juice changed the pH of the growth solution and consequently we observed surface modified and structural changes that were found to be very effective for the development of energy conversion and energy storage systems. These naturally occurring compounds in citrus lemon juice played a dynamic role in transforming the nanorod morphology of NiCo2O4 into small and well-packed nanoparticles. Hence, the prepared NiCo2O4 nanostructures exhibited a new surface-oriented nanoparticle morphology, high concentration of defects on the surface (especially oxygen vacancies), sufficient ionic diffusion and reaction of electrolytic ions, enhanced electrical conductivity, and favorable reaction kinetics at the interface. The electrocatalytic properties of the NiCo2O4 nanostructures were studied in oxygen evolution reaction (OER) at a low overpotential of 250 mV for 10 mA cm-2, Tafel slope of 98 mV dec-1, and durability of 40 h. Moreover, an asymmetric supercapacitor was produced and the obtained results indicated a high specific capacitance of (Cs) of 1519.19 F g-1, and energy density of 33.08 W h kg-1 at 0.8 A g-1. The enhanced electrochemical performance could be attributed to the favorable structural changes, surface modification, and surface crystal facet exposure due to the use of citrus lemon juice. The proposed method of transformation of nanorod to nanoparticles could be used for the design of a new generation of efficient electrocatalyst materials for energy storage and conversion uses.

Green, Water-Based Synthesis of ZnO Nanostructures

We report on the synthesis of zinc oxide (ZnO) nanostructures using a simple, green, waterbased process, without the aid of any chemical precursor or external energy source. Zinc plates were immersed in deionized water and kept at ambient conditions in a dark cabinet for up to 21 days. After immersion, the reaction products were analyzed using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence spectroscopy and Raman spectroscopy. After short immersion times (1-3 days), ZnO agglomerates with a high concentration of oxygen defects were formed, which overlapped along the c axis to form ZnO nanoflowers. After long immersion times (21 days), ZnO microswords with smooth surfaces, well-defined tips, and less oxygen defects were formed. This low-cost, low-energy synthesis process is an attractive alternative to produce ZnO nanostructures with low impact on the environment.

Cooperativity of silanol defect chemistry in zeolites.

Deboronation treatment of zeolite B-SSZ-55 can generate vacancy defects consisting of four silanol groups (silanol nests). However, 1H solid-state NMR spectroscopy indicates the prevalence of two silanol groups (silanol dyads) instead of four silanol groups. Such silanol dyads must be formed by the silanol condensation of two silanol groups at the silanol nests. Yet, the exact mechanism of this condensation and detailed structure of the silanol defect are not known. Here, the structure and formation mechanism of silanol dyads in the SSZ-55 zeolite have been investigated by both cluster and periodic density functional theory calculations. The calculated 1H NMR chemical shifts agree with the experimental values, showing that the silanol dyads are indeed commonly present at the vacancies and the vacancy density plays a role in the relaxation of the zeolite framework. The nature (size) of the silanol clusters influences their acidity.

Photocatalytic water oxidation over LaWO0.6N2.4 mesoporous single crystals under visible and near-infrared light illumination

Narrow-bandgap perovskite oxynitrides emerge as a promising class of inorganic photocatalysts to store solar energy into chemical fuels. However, conventional synthetic routes generally introduce a high defect concentration to these...