HF Etching Research Articles

Functional Tailoring of Multi-Dimensional Pure MXene Nanostructures for Significantly Accelerated Electromagnetic Wave Absorption.

Transition metal carbide (Ti3 C2 Tx MXene), with a large specific surface area and abundant surface functional groups, is a promising candidate in the family of electromagnetic wave (EMW) absorption. However, the high conductivity of MXene limits its EMW absorption ability, so it remains a challenge to obtain outstanding EMW attenuation ability in pure MXene. Herein, by integrating HF etching, KOH shearing, and high-temperature molten salt strategies, layered MXene (L-MXene), network-like MXene nanoribbons (N-MXene NRs), porous MXene monolayer (P-MXene ML), and porous MXene layer (P-MXene L) are rationally constructed with favorable microstructures and surface states for EMW absorption. HF, KOH, and KCl/LiCl are used to functionalize MXene to tune its microstructure and surface state (F- , OH- , and Cl- terminals), thereby improving the EMW absorption capacity of MXene-based nanostructures. Impressively, with the unique structure, proper electrical conductivity, large specific surface area, and abundant porous defects, MXene-based nanostructures achieve good impedance matching, dipole polarization, and conduction loss, thus inheriting excellent EMW absorption performance. Consequently, L-MXene, N-MXene NRs, P-MXene ML, and P-MXene L enable a reflection loss (RL ) value of -43.14, -63.01, -60.45, and -56.50dB with a matching thickness of 0.95, 1.51, 3.83, and 4.65mm, respectively.

Gas sensing performance of Nb2CTx synthesized by hydrothermal assisted in-situ HF generation etching method

The Nb2CTx prepared by hydrothermal-assisted in-situ HF generation etching was investigated in terms of its gas sensor performance. The Nb2CTx was obtained by mixing Nb2AlC with pure water, hydrochloric acid, and fluoride (LiF or NH4F) and then hydrothermally treated at 180 °C for 24 h. This in-situ HF generation etching by hydrothermal treatment was more efficient and safer in the synthesis of the Nb2CTx than the direct HF etching. The Nb2CTx etched with LiF had relatively wide interlayer spacing because the hydration radius of Li+ was larger than that of NH4+. The results also suggest that Nb2O5 is formed during the synthesis process. These results suggest that interlayer spacing, surface termination, and secondary phases formation can be controlled by the etchant, and that hydrothermal treatment extended the applicability of insoluble etchants. The Nb2CTx synthesized with LiF was evaluated as a gas sensor at room temperature in air in the presence of designated concentrations of 6 different gases, which exhibited good sensitivity and repeatability and fast recovery time, except for NH3. Hydrothermal-assisted etching contributed to providing sufficient interlayer spacing for the gas response without an exfoliation process.

Effect of Surface Modifications on Surface Roughness of Ti6Al4V Alloy Manufactured by 3D Printing, Casting, and Wrought.

This work aimed to comprehensively evaluate the influence of different surface modifications on the surface roughness of Ti6Al4V alloys produced by selective laser melting (SLM), casting and wrought. The Ti6Al4V surface was treated using blasting with Al2O3 (70-100 µm) and ZrO2 (50-130 µm) particles, acid etching with 0.017 mol/dm3 hydrofluoric acids (HF) for 120 s, and a combination of blasting and acid etching (SLA). It was found that the optimization of the surface roughness of Ti6Al4V parts produced by SLM differs significantly from those produced by casting or wrought processes. Experimental results showed that Ti6Al4V alloys produced by SLM and blasting with Al2O3 followed by HF etching had a higher surface roughness (Ra = 2.043 µm, Rz = 11.742 µm), whereas cast and wrought Ti6Al4V components had surface roughness values of (Ra = 1.466, Rz = 9.428 m) and (Ra = 0.940, Rz = 7.963 m), respectively. For Ti6Al4V parts blasted with ZrO2 and then etched by HF, the wrought Ti6Al4V parts exhibited higher surface roughness (Ra = 1.631 µm, Rz = 10.953 µm) than the SLM Ti6Al4V parts (Ra = 1.336 µm, Rz = 10.353 µm) and the cast Ti6Al4V parts (Ra = 1.075 µm, Rz = 8.904 µm).

Delamination of multilayer Ti3C2Tx MXene alters its adsorpiton and reduction of heavy metals in water

MXenes are considered as an emerging class of two-dimensional (2D) adsorbent for various environmental applications. In this work, two different morphologies of Ti3C2Tx MXene (multilayer (ML-Ti3C2Tx) and delaminated titanium carbide (DL-Ti3C2Tx)) were prepared through mild in situ HF etching and further delamination. The structural differences between the two were explored with a focus on their effects on the performance and mechanism of removing heavy metals from water. In comparison to ML-Ti3C2Tx, DL-Ti3C2Tx had more oxygen-containing functional groups, higher specific surface area (19.713 vs. 8.243 m2/g), larger pore volume (0.135 vs. 0.040 cm3/g), higher maximum Pb(II) adsorption capacity (77.0 vs. 56.68 mg/g), but lower maximum Cu(II) adsorption capacity (23.08 vs. 55.46 mg/g). Further investigation revealed that the removal of Pb(II) by the MXenes was mainly controlled through electrostatic attraction and surface complexation mechanisms, while Cu(II) was removed mainly through surface reduction by Ti-related groups. Because delamination of ML-Ti3C2Tx increased the surface area and surface functional groups, DL-Ti3C2Tx became a better sorbent for Pb(II) in water. During sonication, however, delamination inevitably led to partial oxidation of Ti3C2Tx nanosheets and thus weakened the reducing ability of DL-Ti3C2Tx for Cu(II) in water. Nevertheless, both ML- and DL-Ti3C2Tx not only exhibited excellent heavy metal adsorption capacity under different solution conditions, but also showed good reusability. Findings of this study indicate that Ti3C2Tx MXenes are promising adsorbents for treating heavy metal pollutants in water.

Cation Vacancy Clusters in Ti3C2Tx MXene Induce Ultra‐Strong Interaction with Noble Metal Clusters for Efficient Electrocatalytic Hydrogen Evolution

AbstractMXenes are promising substrates for supported noble metal electrocatalysts. Yet, it is a significant challenge to modulate the metal–support interaction (MSI) for enhancing catalytic performance. Herein, employing a facile HF etching method, the cation vacancy structures in Ti3C2Tx MXenes are controllably tuned, producing nearly vacancy‐free (Ti3C2Tx‐V0), single Ti atom vacancy (Ti3C2Tx‐VS), or Ti vacancy cluster (Ti3C2Tx‐VC) engineered MXenes. Ruthenium atomic clusters, as a model catalyst, successfully anchor on all MXene substrates. Different from the terminal O/F coordination groups on routine Ti3C2Tx MXene surfaces, the Ti vacancy clusters in Ti3C2Tx‐VC create unique lattice carbon ligand environment toward Ru species, which induces ultra‐strong MSI. As a result, compared to Ti3C2Tx‐V0 and Ti3C2Tx‐VS, the Ti3C2Tx‐VC modulated Ru clusters (Ru@Ti3C2Tx‐VC) exhibit the optimized balance of H2O adsorption/dissociation and OH/H desorption, thereby delivering superior electrocatalytic performance in the alkaline hydrogen evolution reaction (HER). Within the wide range from laboratory‐level (90 mA cm−2) to industrial‐level (1.5 A cm−2) current density, Ru@Ti3C2Tx‐VC outperforms commercial Pt/C in terms of overpotential and mass activity. Moreover, as a universal substrate for noble metal catalysts, Ti3C2Tx‐VC can also anchor Ir/Pt/Rh atomic clusters and enable excellent HER catalytic activity. This work expands the scope of the MSI between MXene and noble metal catalysts.

Insight into anionic and cationic flotation discrepancy of quartz with altered surface roughness by acid etching

Surface roughness has a significant effect on mineral flotation. In this study, the surface roughness of quartz was altered using HF etching and their values before and after acid etching were quantified using AFM. Anionic flotation experiments with CaCl2 as activator and sodium oleate (NaOL) as collector, and cationic flotation experiments with dodecyl trimethyl ammonium chloride (DTAC) as collector were carried out for both the raw and acid-etched samples. The results showed that acid etching is beneficial to increase the surface roughness of quartz. The rougher quartz particle has higher recovery and quicker flotation rate during anionic flotation, while lower recovery and slower flotation rate during cationic flotation. The role of surface roughness in the discrepancy of these two flotations was investigated in terms of surface chemistry by X-ray photoelectron spectroscopy, UV spectrophotometer, surface force tensiometer, and zeta potential analyzer. The rougher sample was confirmed to have more unsaturated interfacial active sites, adsorbed more Ca2+ and NaOL, and exhibited higher hydrophobicity in anionic flotation. Differently, the rougher sample was verified to have less interfacial negative charge, adsorbed less DTAC, and exhibited weaker hydrophobicity in cationic flotation. Taken together, the surface roughness altered by acid etching has different effects on the adsorption capacity of NaOL and DTAC, thus affecting the wettability and floatability of quartz particles inconsistently in anionic and cationic flotation.

Synthesis of 2D/2D structural Ti3C2 MXene/g-C3N4 via the Schottky junction with metal oxides: Photocatalytic CO2 reduction with a cationic scavenger

A series of Ti3C2/CN/Cu2O and Ti3C2/CN/ZnO ternary nanocomposites were successfully fabricated by the integration of 2D Ti3C2 MXene and 2D polymeric carbon nitride (CN) with ZnO and Cu2O. The HF etching on Ti3C2 MXene offered significant improvement for the photocatalyst fabrication, while the close 2D/2D junction of Ti3C2/CN created the Schottky junction to enable proficient electron transfer in the ternary nanocomposite. Next, the junction of 2D MXene and 2D CN with the metal oxides (Cu2O and ZnO) prevented the quick recombination of photoexcited electrons and holes and contributed multiple electron pathways for the CO2/CH3OH process. At the same time, the formation of analogue Z-scheme heterojunctions through the synergistic effect of 2D Ti3C2 MXene and 2D metal-free CN with ZnO contributed to the rapid separation and transfer of photogenerated charge carriers. As a result, the photocatalytic CO2 reduction activity of Ti3C2/CN/Cu2O and Ti3C2/CN/ZnO ternary nanocomposites was significantly enhanced. Meanwhile, adding a Na2SO3 sacrificial electron donor with pure water and NaHCO3 solvent system supply in CO2 photoreduction experiments contributed to the formation of CH3OH. In particular, the yield of CH3OH was up to 18.72% and 19.98%, 5times and 6-times fold than the pure Cu2O and ZnO, while 3-times fold than the TCCN in a water system. In a NaHCO3 solvent with the sacrificial electron donor, the CH3OH rates over Ti3C2/CN/ZnO and Ti3C2/CN/Cu2O were 22.41% and 20.12%. Taking into account the chemical and structural tunability of ternary nanocomposites, the excellent photocatalytic ability of Ti3C2/CN/ZnO and Ti3C2/CN/Cu2O could be used in the future production of hydrocarbon fuels, as well as increasing the possibility of using 2D MXene in photocatalyst fabrication.

Effect of Ceramic Conditioners on Surface Morphology, Roughness, Contact Angle, Adhesion, Microstructure, and Composition of CAD/CAM Ceramics.

The objective of this study was to investigate the effect of surface treatments in maximum profile valley depth (Rv), surface roughness (Sa), contact angle (Ca), shear bond strength (SBS) of a light-cured resin cement, microstructure, and composition of two CAD/CAM ceramics: Cerec Blocs/Dentsply Sirona (feldspathic - FEL) and Empress CAD/Ivoclar Vivadent (leucite-reinforced - LEU). The ceramic specimens were submitted to six surface treatments: (1) 5% hydrofluoric acid (HF) - 20 seconds; (2) 5% HF - 60 seconds; (3) 10% HF - 20 seconds; (4) 10% HF - 60 seconds; (5) self-etching ceramic primer (MEP) - 20 seconds; and (6) MEP - 60 seconds. Specimens treated with HF received silane application for 1 minute. Rv and Sa were evaluated in a confocal laser microscope (n=10) and the Ca in a goniometer (n=6). For the SBS test, two resin cement cylinders were bonded to each specimen, one tested after 24 hours in distilled water storage (37°C) and the other after one year (n=10). The microstructures and compositions were analyzed by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) (n=4). Rv, Sa, and Ca data were analyzed by two-way ANOVA, and the SBS data by three-way ANOVA, all followed by post-hoc Tukey's test (α=0.05). Results: Surface treatments with HF always produced higher Rv and Sa, and lower Ca than MEP 60s for both ceramics. After 1-year water storage, FEL ceramic treated with MEP for 60 seconds produced higher SBS values than HF treatments, whereas for LEU ceramic there were no differences among treatments. Application of MEP for 20 or 60 seconds produced no difference in Rv, Sa, Ca, and SBS for both ceramics. Surface treatments produced considerable differences in ceramic topography, but subtle ones in composition, for both ceramics. Conclusions: The results indicated that for FEL ceramic, MEP application for 60 seconds yielded higher SBS compared with HF etching, while for LEU ceramic the surface treatments did not influence the SBS results.

Amphiphilic Bowl-Shaped Janus Particles Prepared via Thiol-Ene Click Reaction for Effective Oil-Water Separation.

Janus particles for oil-water separation have attracted widespread attention in recent years. Herein, we prepared a bowl-shaped Janus particle that could rapidly separate oil and water through a thiol-ene click reaction and selective etching. Firstly, snowman-like composite microspheres based on silica and mercaptopropyl polysilsesquioxane (SiO2@MPSQ) were prepared by a hydrolytic condensation reaction and phase separation, and the effects of the rotational speed and molar ratios on their microscopic morphologies were investigated. Subsequently, bowl-shaped Janus particles with convex hydrophilic and concave oleophilic surfaces were prepared via a thiol-ene click reaction followed by HF etching. Our amphiphilic bowl-shaped Janus particles could remarkably separate micro-sized oil droplets from an n-heptane-water emulsion with a separation efficiency of >98% within 300 s. Based on the experimental and theoretical results, we proposed the underlying mechanism for the coalescence of oil droplets upon the addition of the amphiphilic bowl-shaped Janus particles.

Fabrication of Substrate-Integrated Waveguide Using Micromachining of Photoetchable Glass Substrate for 5G Millimeter-Wave Applications

A millimeter-wave substrate-integrated waveguide (SIW) was firstly demonstrated using the micromachining of photoetchable glass (PEG) for 5G applications. A PEG substrate was used as a dielectric material of the SIW, and its photoetchable properties were used to fabricate through glass via (TGV) holes. Instead of the conventional metallic through glass via (TGV) array structures that are typically used for the SIW, two continuous empty TGV holes with metallized sidewalls connecting the top metal layer to the bottom ground plane were used as waveguide walls. The proposed TGV walls were fabricated by using optical exposure, heat development and anisotropic HF (hydrofluoric acid) etching of the PEG substrate, followed by a metal sputtering technique. The SIW was fed by microstrip lines connected to the waveguide through tapered microstrip-to-waveguide transitions. The top metal layer, including these feedlines and transitions, was fabricated by selective metal sputtering through a silicon shadow mask, which was prefabricated by a silicon deep-reactive ion-etching (DRIE) technique. The developed PEG-based process provides a relatively simple, wafer-level manufacturing method to fabricate the SIW in a low-cost glass dielectric substrate, without the formation of individual of TGV holes, complex time-consuming TGV filling processes and repeated photolithographic steps. The fabricated SIW had a dimension of 6 × 10 × 0.42 mm3 and showed an average insertion loss of 2.53 ± 0.55 dB in the Ka-band frequency range from 26.5 GHz to 40 GHz, with a return loss better than 13.86 dB. The proposed process could be used not only for SIW-based devices, but also for various millimeter-wave applications where a glass substrate with TGV structures is required.

Bulk substitution of F-terminations from Ti3C2Tx MXene by cation pillaring and gas hydrolysation

Applications of 2D MXenes are limited by the difficulty of controlling bulk termination groups after the initial HF etching step without forming surface oxides. Here, we report on gas hydrolysation using a continuous flow of Ar (g) with a controlled partial pressure of H2O (g) as a new method to change the terminations of multilayered Ti3C2Tx MXene particles (T = O, OH and F), and demonstrate pre-intercalation of cations as a necessity for successful hydrolysation as it enables water molecules to enter the Ti3C2Tx MXene structure. Hydrolysation of pristine HF-etched Ti3C2Tx shows no compositional change before oxidation into a TiO2/C composite starts at T > 300 ˚C. However, by pre-intercalating various cations into the MXene, a pillaring of the structure is achieved, which for certain cations (K+ and Na+) remains even after hydrolysation at 300 ˚C. By hydrolysing K-intercalated Ti3C2Tx at 300 ˚C, a significant bulk F reduction of 78 % was achieved, accompanied by a comparable increase in O content and insignificant surface oxidation of the particles. For other cations (Mg2+, Li+ and TBA+) the expanded interlayer spacing collapsed upon hydrolysation, resulting in no significant compositional changes. Moreover, hydrolysation is shown to give higher selectivity towards F removal compared to air annealing, which instead resulted in the oxidation of C to CO2 and the formation of TiOF2. In Li-ion battery half cells, the intercalation of K-ions reduces both the capacity and energy efficiency compared to pristine Ti3C2Tx. Nevertheless, hydrolysation increases the capacity and intercalation voltage, and is thus a feasible method to control the electrochemical performance of Ti3C2Tx MXene. In summary, gas hydrolysation is demonstrated as a selective and efficient method to substitute F terminations with O-related terminations in multilayered MXene particles and pave the way for utilisation on other MXene compositions.

Constructing Exfoliated, Ti3C2Tx MXene-Dispersed, LaCoO3 and pC3N4-Based Nanocomposites with In Situ Grown Titania through Etching/Oxidation for Stimulating Solar H2 Production

The use of a well-designed Ti3C2 MXene with in situ embedded titania nanoparticles to construct a porous carbon nitride (pCN)/LaCoO3 Z-scheme and S-scheme heterojunction for stimulating solar hydrogen production has been explored. A novel oxidized/etched approach was employed to produce MXene to maximize charge separation in LaCoO3 perovskite-dispersed pCN. On increasing the HF etching time from 24 to 48 h, the amount of titania embedded over the MXene was increased, enabling 1.71 times more H2 evolution. More importantly, integrated etched/oxidized Ti3C2 nanoflowers showed more reaction area with enhanced light absorption, which was more prominent with increased temperature. The H2 evolution was significantly increased due to in situ embedded TiO2. Comparatively, optimized 15Ti3C2Tx/pCN was found to be more efficient at lower temperatures, which was further increased 7-fold with a 10Ti3C2Tx/pCN-coupled LaCoO3 Z-scheme heterojunction. This obvious enhancement was evidently due to utilizing the maximum redox potential with good interface interaction among the components to promote charge carrier separation. Among the sacrificial agents, TEOA was found to be more promising, with 9.1 times more H2 production due to its strong bond with amine-based pCN, which was further confirmed by quantum analysis. In conclusion, the Z-scheme photosystem is promising for efficient mobility and separation of charges and would also be beneficial for other solar energy applications.

Auger electron spectroscopy mapping of lithium niobate ferroelectric domains with nano-scale resolution

The +/−Z ferroelectric domains in periodically poled lithium niobate are characterized with Auger electron spectroscopy. The -Z domains have a higher Auger O-KLL transition amplitude than the +Z domains. Based on this, Auger electron spectroscopy mapping can be used on the O-KLL peak to image the +/-Z domain structure. This new characterization technique is confirmed with HF etching, and compared to SEM imaging. Spatial resolution down to 68 nm is demonstrated.

Nonblinking Core–Multishell InP/ZnSe/ZnS Quantum Dot Bioconjugates for Super-resolution Imaging

Colloidal quantum dots (QDs) are vital fluorescent probes with several optical features superior to those found in organic dyes for microscopy imaging. However, the emission blinking behavior of a single QD is an intrinsic drawback for stimulated emission depletion microscopy (STED) or structured illumination microscopy techniques. Herein, we present a rational strategy for the synthesis of a type of deterministic, environmentally friendly, small nonblinking core–multishell InP/ZnSe/ZnS QD using a hydrofluoric acid (HF) etching passivation. The strategy includes four steps: synthesis of the InP core, synthesis of oil-phase core–multishell InP/ZnSe/ZnS QDs using hydrogen fluoride and trioctylphosphine etching passivation, promotion of the water solubility of QDs modified by 3-mercaptopropionic acid (MPA), and enhanced biotargeting of core–multishell InP/ZnSe/ZnS QDs by surface coupling technology. The suppressed blinking mechanism was primarily attributed to surface wrapping shells and HF etching passivation of surface dangling bonds, which reduced surface nonradiative recombination. Nonblinking QDs exhibit high fluorescence efficiency (∼90%), good photostability (>20 min), a large Stokes shift (>135 nm), biocompatibility of the cell viability (>90%), and high targeting. Furthermore, super-resolution multifocal structured illumination microscopy imaging of subcellular structures labeled using these QDs confirmed a resolution improvement of greater than 2.6-fold compared to wide-field microscopy. The results indicate that the nonblinking QDs can function as excellent probes for use in the long-term super-resolution visualization of subcellular dynamics.

Improved U(VI) electrosorption performance of hierarchical porous heteroatom-doped electrode based on double-template method

As an indispensable element in the field of nuclear energy, uranium (U(VI)) is widely concerned because it is abundant and easy to obtain from seawater. Herein, we report a promising dual-template strategy to prepare heteroatom-doped carbon materials with hierarchical micro−/meso−/macroporous from low-cost biomass precursors. The carbon materials with hierarchical porosity nitrogen/oxygen are synthesized through freeze-drying, high-temperature thermal treatment and subsequent HF etching treatment by in-situ growth of SiO2 on the precursor with ethyl silicate as silicon source and introduction of ZnCl2 as hard template and starch/ammonia as carbon and nitrogen source. Based on the advantages of three-dimensional interconnected hierarchical porous heteroatom doping, the electrosorption capacity reaches 67.25 mg/g, and the removal efficiency is as high as 98.45%, when the initial UO2(NO3)2 concentration is 80 mg/L in capacitive deionization. The isothermal adsorption of nitrogen doped hierarchical porous carbon (NHPC) is consistent with the Langmuir model, with a maximum electrosorption capacity of 152.43 mg/g, good cycle stability and high charge efficiency (energy consumption is only 0.77 kg-U kWh−1). Fascinatingly, the initial UO2(NO3)2 concentration is 80 mg/L and it also has a high adsorption capacity in 3.5 wt% NaCl solution, and the U(VI) removal efficiency could reach 42.5% after 8 h of continuous adsorption, with high selectivity. The prepared adsorbent NHPC shows good selectivity for U(VI) in the solution of 11 metal ions co-existing, and the effective selectivity Kd value of U(VI) is 1620.84 mL/g. Finally, X-ray photoelectron spectroscopy analysis reveals that in addition to Coulomb interaction and chelation during the adsorption process, there is also a synergistic effect of the conversion of U(VI) to UO2 under electric drive to improve the adsorption capacity of U(VI).

Constructing Active Sites on Self-Supporting Ti3C2Tx (T = OH) Nanosheets for Enhanced Photocatalytic CO2 Reduction into Alcohols

Ti3C2Tx (T = OH) was first prepared from Ti3AlC2 by HF etching and applied into a photocatalytic CO2 reduction. Then, the Ti3C2Tx nanosheets present interbedded a self-supporting structure and extended interlayer spacing. Meanwhile, the Ti3C2Tx nanosheets are decorated with abundant oxygen-containing functional groups in the process of etching, which not only serve as active sites but also show efficient charge migration and separation. Among Ti3C2Tx materials prepared by etching for different times, Ti3C2Tx-36 (Etching time: 36 h) showed the best performance for photoreduction of CO2 into alcohols (methanol and ethanol), giving total yield of 61 μmol g catal.−1, which is 2.8 times than that of Ti3AlC2. Moreover, excellent cycling stability for CO2 reduction is beneficial from the stable morphology and crystalline structure. This work provided novel sights into constructing surface active sites controllably.

Flexible Disk Ultramicroelectrode for High-Resolution and Substrate-Tolerable Scanning Electrochemical Microscopy Imaging.

A simple and universal strategy for fabricating flexible 25 μm platinum (Pt) disk ultramicroelectrodes (UMEs) was proposed, where a pulled borosilicate glass micropipette acted as a mold for shaping the flexible tip with flexible epoxy resin. The whole preparation procedure was highly efficient, enabling 10 or more probes to be manually fabricated within 10 h. Intriguingly, this technique permits an adjustable RG ratio, tip length, and stiffness, which could be tuned according to varying experimental demands. Besides, the electroactive area of the probe could be exposed and made renewable with a thin blade, allowing its reuse in multiple experiments. The flexibility characterization was then employed to optimize the resin/hardener mass ratio of epoxy resin and the tip position during HF etching in the fabrication process, suggesting that more hardener, a larger RG value, or a longer tip length obtained stronger deformation resistance. Subsequently, the as-prepared probe was examined by optical microscopy, cyclic voltammetry, and SECM approach curves. The results demonstrated the probe possessed good geometry with a small RG ratio of less than 3 and exceptional electrochemical properties, and its insulating sheath remained undeformed after blade cutting. Owing to the tip's flexibility, it could be operated in contactless mode with an extremely low working distance and even in contact mode scanning to achieve high spatial resolution and high sensitivity while guaranteeing that the tip and samples would suffer minimal damage if the tip crashed. Finally, the flexible probe was successfully employed in three scanning scenarios where tilted and 3D structured PDMS microchips, a latent fingerprint deposited on the stiff copper sheet, and soft egg white were included. In all, the flexible probe encompasses the advantages of traditional disk UMEs and circumvents their principal drawbacks of tip crash and causing sample scratches, which is thus more compatible with large specimens of 3D structured, stiff, or even soft topography.

High-Temperature Magnesiothermic Reduction Enables HF-Free Synthesis of Porous Silicon with Enhanced Performance as Lithium-Ion Battery Anode.

Porous silicon-based anode materials have gained much interest because the porous structure can effectively accommodate volume changes and release mechanical stress, leading to improved cycling performance. Magnesiothermic reduction has emerged as an effective way to convert silica into porous silicon with a good electrochemical performance. However, corrosive HF etching is normally a mandatory step to improve the electrochemical performance of the as-synthesized silicon, which significantly increases the safety risk. This has become one of the major issues that impedes practical application of the magnesiothermic reduction synthesis of the porous silicon anode. Here, a facile HF-free method is reported to synthesize macro-/mesoporous silicon with good cyclic and rate performance by simply increasing the reduction temperature from 700 °C to 800 °C and 900 °C. The mechanism for the structure change resulting from the increased temperature is elaborated. A finite element simulation indicated that the 3D continuous structure formed by the magnesiothermic reduction at 800 °C and 900 °C could undertake the mechanical stress effectively and was responsible for an improved cyclic stability compared to the silicon synthesized at 700 °C.

Acid dissolution of ultrathin glass-ceramic and its correlation with flexural strength

Statement of problemWhen glass-ceramics are treated with hydrofluoric acid (HF), not only the area of application is affected but also other surfaces. Information regarding the correlation of the dissolution caused by HF and the flexural strength of the ceramic is lacking. PurposeThe purpose of this in vitro study was to investigate the effect of HF etching protocols on the flexural strength of 2 glass-ceramics, the correlation of their flexural strength with the internal and lateral dissolution, and the differences in Weibull characteristics concerning the etching protocols. Material and methodsSpecimens (4×12×0.3mm) of leucite-reinforced glass-ceramic—LEU (IPS Empress) and of lithium disilicate-reinforced glass-ceramic—LD (IPS e.max) were prepared. The specimens were divided into 5 groups (n=12) according to etching protocol: control—untreated; hydrofluoric acid (HF) 5% for 20 seconds (HF5%20s); HF5%60s; HF10%20s; and HF10%60s. Flexural strength was evaluated through 3-point bend testing. The fractured specimens were submitted to a morphological and metrical analysis of each pattern (LEU I–IV, LD I–III) on the lateral surface (LS) and of the dissolution areas (μm2) on the internal surface (IS) using a scanning electron microscopy (SEM) and a software program (FIJI). Flexural strength (MPa) values were analyzed by 1-way ANOVA, Bonferroni test, and Weibull and the correlation between flexural strength and dissolution by Pearson correlation coefficient (α=.05). ResultsANOVA revealed that the HF etching protocol was significant (P<.001) for LEU ceramic. When HF10%60s was applied, LEU showed Weibull characteristic strength (σθ) values lower than those of the other protocols. LD showed no difference in σθ and reliability (m) among the groups. The internal dissolution areas concerning LEU had a significant high negative correlation with the flexural strength (r=-0.6; P<.001). LEU-IV on the LS was the only pattern to show a significant decrease in flexural strength (r=-0.3, P<.05). ConclusionsSpecial care should be taken when applying hydrofluoric acid on glass-ceramic restorations. Protocols with higher hydrofluoric acid concentrations and longer application times were more related to greater internal areas of dissolution which reduced the flexural strength of leucite ceramics.

Effect of surface treatments on bond durability of zirconia-reinforced lithium silicate ceramics: An in vitro study

Statement of problemThe influence of surface treatments on the bond durability of zirconia-reinforced lithium silicate ceramics (ZLS) is unclear. PurposeThe purpose of this in vitro study was to evaluate the effect of different surface treatments on the bond durability of zirconia-reinforced lithium silicate ceramic after long-term thermocycling. Material and methodsFive computer-aided design and computer-aided manufacturing (CAD-CAM) dental ceramic blocks, including 2 zirconia-reinforced lithium silicate ceramic materials (Vita Suprinity/VS and Cetra Duo/CD), 2 commonly used glass-ceramic materials (e.max CAD/EM and Empress CAD/EP), and 1 yttria-stabilized zirconia (Y-TZP, Zenostar/ZS) were tested. Rectangular ceramic blocks were divided into 6 groups and subjected to different surface treatments: group Control (no treatment), group Uni (universal adhesive), group HF (hydrofluoric acid), group CoJet, group HF+Uni (HF and universal adhesive), and group CoJet+Uni (CoJet and universal adhesive). Subsequently, the specimens were cemented to composite resin blocks, sectioned into rectangular microbars of approximately 2×2×12 mm in size, and assigned to 2 groups with and without 100 000 thermal cycles (n=15 per group). The microtensile bond strength (μTBS) test was performed using a universal testing machine. Failure modes were observed with a stereomicroscope and scanning electron microscope (SEM). Three-way analysis of variance (ANOVA) followed by post hoc pairwise comparisons was performed to evaluate the effects of surface treatments, ceramics, and thermocycling on μTBS (α=.05). ResultsThe μTBS (MPa) was affected by the surface treatment (P<.001), ceramic type (P<.001), and thermocycling (P<.001). The bond strength after HF etching and universal adhesive treatment was highest in glass-ceramic groups (VS, CD, EP, and EM), while CoJet combined with universal adhesive indicated the highest bond strength in the ZS group before (34.3 ±4.2 MPa) and after thermocycling (16.0 ±2.9 MPa). No significant differences for μTBS were found among ZLS (VS and CD), lithium disilicate ceramic group (EM), and leucite-based ceramic group (EP, P>.05), but they demonstrated better bond strength than zirconia (ZS group, P<.01) after thermocycling. Adhesive failure increased in all groups, and the cohesive failure of glass-ceramic decreased after thermocycling. ConclusionsZLS showed similar μTBS with traditional glass-ceramics, including lithium disilicate ceramic and leucite-based ceramic, and more durable bonding than zirconia to resist thermocycling. Moreover, the combination of HF and universal adhesive treatments was the most effective method for ZLS among all the different surface treatments in this study.