Acid Etching Process Research Articles

Continuously improved gas-sensing performance of Zn2SnO4 porous octahedrons by structure evolution and further ZnSnO3 nanosheets decoration

To optimize the structure and composition of the metal oxide semiconductor is one of effective approaches to improve its gas-sensing performance. In this paper, Zn2SnO4 solid octahedrons were first synthesized by a hydrothermal method, then converted to hollow structures with a shape preserved through a simple and practical acid etching process. Ultimately, the hierarchical ZnSnO3/Zn2SnO4 hollow composite with porous structure was designed and prepared by in situ growth of ZnSnO3 nanosheets on the surface of Zn2SnO4 hollow octahedrons in the seed mediated wet-chemical way. It was found that through the structure evolution from solid octahedron to hollow structure, the sensitivity of gas sensor toward triethylamine (TEA) was visibly improved. Significantly, superior TEA-sensing properties, such as lower optimal working temperature, higher sensitivity, wider linear response range, more rapid response/recovery speed and more excellent selectivity were further achieved by decorating Zn2SnO4 hollow octahedrons with ZnSnO3 nanosheets. It was remarkable that the sensor based on hierarchical ZnSnO3/Zn2SnO4 porous hollow octahedrons displayed long-term stability to TEA and anti-humidity property, suggesting its potential practical applications in detection of highly toxic TEA. The improved sensing mechanism on the strength of structure and composition evolution for the gas sensor was discussed in detail.

A Two-Step Approach to Tune the Micro and Nanoscale Morphology of Porous Niobium Oxide to Promote Osteointegration.

We present a two-step surface modification process to tailor the micro and nano morphology of niobium oxide layers. Niobium was firstly anodized in spark regime in a Ca- and P-containing solution and subsequently treated by acid etching. The effects of anodizing time and applied potential on the surface morphology is investigated with SEM and AFM, complemented by XPS compositional analysis. Anodizing with a limiting potential of 250 V results in the fast growth of oxide layers with a homogeneous distribution of micro-sized pores. Cracks are, however, observed on 250 V grown layers. Limiting the anodizing potential to 200 V slows down the oxide growth, increasing the anodizing time needed to achieve a uniform pore coverage but produces fracture-free oxide layers. The surface nano morphology is further tuned by a subsequent acid etching process that leads to the formation of nano-sized pits on the anodically grown oxide surface. In vitro tests show that the etching-induced nanostructure effectively promotes cell adhesion and spreading onto the niobium oxide surface.

Highly porous carbon nanofiber electrodes for vanadium redox flow batteries.

The electrochemical performance of carbon nanofiber (CNF) electrodes in vanadium redox flow batteries (VRFBs) is enhanced by optimizing the morphological and physical properties of low-cost electrospun CNFs. The surface area, porosity and electrical conductivity of CNFs are tailored by modifying the precursor composition, especially the sacrificing agent, Fe(acac)3, in the polymer precursor and carbonization temperature. A highly porous structure with a large surface area is generated by the catalytic growth of graphitic carbon spheres surrounding the iron nanoparticles which are removed by an acid etching process. The graphitic carbon layers formed at a high carbonization temperature improve the electrical conductivity of CNFs. The large surface area of 349 m2 g-1 together with the abundant mesopore-dominant structure leads to high wettability and high activity for redox reactions of the electrode, giving rise to enhanced electrochemical performance in VRFBs. It delivers an energy efficiency (EE) of 91.4% at a current density of 20 mA cm-2 and 79.3% at 100 mA cm-2, and maintains an average EE of 72.5% after 500 charge/discharge cycles at 100 mA cm-2.

Antibacterial toxicity of mesoporous silica nanoparticles with functional decoration of specific organic moieties

Mesoporous silica nanoparticles (MSNs) are generally considered as biocompatible nanocarriers for biomedical applications; however, no study has provided conclusive evidence regarding the antimicrobial toxicity of MSNs. Here, we systematically evaluated the toxicity of MSNs against Escherichia coli (E. coli) by investigating not only the removal rate of cetyltrimethyl ammonium bromide (CTAB) from the MSNs, but also functional decorations of specific organic moieties such as polydopamine (PDA) and graphene oxide (GO). The mortality of E coli was strongly dependent on the residual CTAB that was not completely removed from the MSNs by acid etching process. On the other hand, for the removal of CTAB from the MSNs the reduced etching time and increased H2O content in the etchant increased the survival of E. coli, probably because of the reduction of bioactive H+ ions that inhibit bacterial growth. Notably, PDA-coated and GO-wrapped MSNs demonstrated the higher toxicity than the pristine MSNs, because of the strong interplay of antibacterial activity of functional decoration (PDA and GO). This study provides a useful guideline for the design of biocompatible MSNs for biomedical applications.

Investigation on surface strength of acid fracture from scratch test

Acid fracture surface strength plays an important role in acid fracture conductivity. Previous experimental studies have proven mechanical deterioration of carbonate after acid etching. However, such conclusion drawn from cylindrical samples could not be applied into conductivity evaluation as such samples represent the rock mechanical properties of the carbonate mass rather than the fracture surface. As another representative of fracture surface strength, embedment strength has not met an agreement on the evolution pattern during acid etching. So the absence of fracture surface strength measurement data during acid etching causes a challenge to conductivity evaluation and acid fracturing optimization. In an effort to overcome this challenge, scratch test was adopted for the measurement of the fracture surface strength before and after acid etching, as scratch test could acquire the uniaxial compressive strength of asperities on the fracture surface. In an aim to study the influence of mineral composition, acid contact time and acid injection rate, acid etching experiments under different etching conditions were carried out. The scratch test results uncovered the strong heterogeneity on the limestone samples, and strength of limestone fracture surface would experience both rising and declining trend during acid etching process. Dolomite in limestone samples was responsible for the strength increase while Calcite contributed to the decrease of strength according to the X-ray diffraction experimental results. What is more, the rising Dolomite strength and the decreasing Calcite strength affected the average strength of acidized fracture inherently. As acid contact time increased, the firstly strengthened then weakened Dolomite strength and constantly decreasing Calcite strength gave rise to an average surface strength change tendency that rises in the beginning and later declines. The change tendency of surface strength clearly indicated an optimal acid contact time in acid fracturing operation. Calcite strength showed the decreasing trend and Dolomite exhibited both the rising and decreasing trend as injection rate increased, resulting in an indefinite evolution trend of average strength of acid fracture surface.

Achieving fully reversible conversion in Si anode for lithium-ion batteries by design of pomegranate-like Si@C structure

Si/C materials are considered as the most promising anodes for the next generation lithium ion batteries. However, the Si/C anodes with high Coulombic efficiency are still a challenge. Here, pomegranate-like Si@C microspheres are successfully prepared with inexpensive AlSi alloy by surface modification, coating with resin, carbonization and acid etching processes. As high as 84.98% initial Coulombic efficiency (ICE) and 100% Coulombic efficiency are obtained for the sample (Si40@C3), and the specific capacity still maintained over 620 mAh g−1 with capacity retention of 70.4% over 250 cycles. The excellent electrochemical performance could be attributed to the distinctive pomegranate-like Si@C structure, which either stabilizes the porous structure of Si particle by inhibiting the volume expansion and pulverization or improves the electrochemical property by the appropriate carbon coating layer. This would provide a helpful guide to synthesize the Si/C anode with high ICE and Coulombic efficiency and stable cycling.

Establishing Structure-Function Relationship of Iridium-Cobalt Oxide As Oxygen Evolution Reaction (OER) Catalyst in Acidic and Alkaline Media

Owing to its unique electrochemical properties and high energy density, hydrogen is one of the leading alternative energy carriers towards a growing share of decarbonized society. However, current hydrogen production is still heavily relies on fossil fuels, with natural gas reforming as the primary source. Electrochemical water splitting process is an environmentally friendly approach when coupled with renewable energy technologies, such as solar or wind. Despite its high cost, iridium oxide (IrO2) is the most commonly used catalyst for the sluggish oxygen evolution reaction (OER). To further enhance the performance and reduce the cost, it is essential to establish a fundamental understanding of OER mechanism. Combining Ir with other non-noble metals is one strategy to improve Ir utilization that would exhibit the advantageous properties of both materials. Cobalt is one of the metals considered in the literature that can be combined with Ir to enhance its activity. Previous literature reported that incorporating Co into the IrO2 structure can modify the conductivity and the electrochemical properties of the catalyst. In this work, we synthesized binary Ir-Co metal oxide in a 1:1 molar ratio via surfactant-assisted Adam’s fusion method to control its structure. The electrochemical OER performance was evaluated using half-cell tests in acidic and alkaline media. Preliminary results show that incorporating Co with Ir improved the catalytic activity compared to homemade IrO2 and commercially available catalysts of Ir black and IrOx. By employing acid etching process, the performance of homemade Ir-Co oxide was further improved in both acid and alkaline media. In terms of durability, despite the enhanced beginning of life performance, the acid-etched Ir-Co sample show significant activity loss (~ 34%) in alkaline media. In contrast, for acid media, both the non-etched and the etched Ir-Co samples show similar and minor degradation (~8-9%). In our results, catalysts without Co content (homemade and commercial) did not show any degradation in acid media and lower degradation rate than Co-containing catalysts in alkaline media. Full-cell electrolyzer stability tests were done, and the results show similar degradation behavior compared to half-cell experiments. To establish a better understanding of the mechanism, several physicochemical characterizations were performed to establish potential structure-function relationships. The X-ray diffraction results indicate that the non-etched sample formed a biphasic oxide dominated by rutile IrO2 (101) and Co3O4 (311). Meanwhile, the acid-etched sample only shows the IrO2 (101) peak, suggesting that Co atoms are either removed or doped in the IrO2 matrix. Energy dispersive x-ray spectroscopy performed in scanning transmission electron microscope and x-ray photoelectron spectroscopy both confirmed the elemental composition and agreed well with the XRD results. The initial findings from this work propose a scalable synthesis method for Ir-Co oxide electrocatalyst, achieving higher performance with a reduced Ir loading.

Study on a novel fixed and free abrasive combined wire sawing multi-crystalline silicon wafers for wet acid texturization

In preparation of solar cells, the multi-crystalline silicon (mc-Si) wafers cut by diamond wire sawing can't obtain the ideal texturization effect when using the wet acid etching process. In this paper, a novel fixed and free abrasive combined wire saw technology for slicing mc-Si wafers is proposed. Diamond saw wire is used as the main processing tool, and free SiC abrasive particles are added into the lubricating coolant to lap the surface of mc-Si wafers. The results show that there are no significant saw marks and ductile smooth area on the surface of mc-Si wafer processed by the combined wire sawing when the SiC abrasive mass fraction is appropriate. The surface roughness and fracture strength of mc-Si wafers in parallel and perpendicular the saw wire motion directions tend to be the same. And the anisotropy of mechanical properties of mc-Si wafers in different directions is significantly reduced, which is conducive to reducing the wafers breakage. Compared with the diamond wire sawn wafer, the reflectivity of the mc-Si wafer cut by the combined wire sawing is greatly reduced after wet acid etching, which can meet the needs of solar cell preparation. The research results provide references for the development of PV mc-Si slicing technology.

Activated carbon fiber yarns with birnessite-type MnO2 and oxygen-functional groups for high-performance flexible asymmetric supercapacitors

Carbon fiber yarn (CFY) is deemed to be an ideal fiber flexible substrate because of its excellent mechanical flexibility, conductivity, and low-cost. In this study, positive electrode was prepared by hydrothermal process to form a birnessite-type MnO2 interconnected 3D nanostructure loading on the carbon fiber yarn (MnO2@CFY). Using an acid-etching process, the oxygen-containing functional groups successfully introduce to the surface of carbon fiber yarn (OCFY) as the negative electrode. The asymmetric all-solid-state flexible fiber-shaped supercapacitor (AFFSC) based on as-prepared MnO2@CFY and OCFY delivers an excellent volumetric energy density of 11.05 mWh cm−3 at a volumetric power density of 100.32 mW cm−3, maintaining 95.33% capacitance retention after 5000 bending cycles.

A super-hydrophilic surface enhanced by the hierarchical reticular porous structure on a low-modulus Ti–24Nb–4Zr–8Sn alloy

ABSTRACT In this study, we fabricated a super-hydrophilic (θ < 5°) hierarchical reticular porous structure on the surface of Ti–24Nb–4Zr–8Sn (Ti2448) by combining sandblasting, dual acid-etching, and alkali thermal treatment. The super-hydrophilic hierarchical structure on the surface contained fine well-distributed nanopores with random microscale structures, leading to extremely high surface hydrophilicity. The sand blasting and dual acid-etching processes (SLA) and alkaline treatment (AT) resulted in the formation of microscale structures and nanopores, respectively. The formation mechanism of the hierarchical reticular porous structures was also examined. The average size of the nanopores on the surface of the SLA + AT Ti2448 sample was 86.3 nm, and the hierarchical structure contained several biocompatible components, including TiO2, Ti2ZrO, ZrTiO4, Nb2O5, Ti2O3, and ZrO2. Because of their super-hydrophilic and chemically biocompatible characteristics, hierarchical Ti2448 structural candidates are expected to be more suitable as implants for successful osseointegration.

Double transition metal MXene (TixTa4\u2212xC3) 2D materials as anodes\xa0for Li-ion\xa0batteries

A bi-metallic titanium–tantalum carbide MXene, TixTa(4−x)C3 is successfully prepared via etching of Al atoms from parent TixTa(4−x)AlC3 MAX phase for the first time. X-ray diffractometer and Raman spectroscopic analysis proved the crystalline phase evolution from the MAX phase to the lamellar MXene arrangements. Also, the X-ray photoelectron spectroscopy (XPS) study confirmed that the synthesized MXene is free from Al after hydro fluoric acid (HF) etching process as well as partial oxidation of Ti and Ta. Moreover, the FE-SEM and TEM characterizations demonstrate the exfoliation process tailored by the TixTa(4−x)C3 MXene after the Al atoms from its corresponding MAX TixTa(4−x)AlC3 phase, promoting its structural delamination with an expanded interlayer d-spacing, which can allow an effective reversible Li-ion storage. The lamellar TixTa(4−x)C3 MXene demonstrated a reversible specific discharge capacity of 459 mAhg−1 at an applied C-rate of 0.5 °C with a capacity retention of 97% over 200 cycles. An excellent electrochemical redox performance is attributed to the formation of a stable, promising bi-metallic MXene material, which stores Li-ions on the surface of its layers. Furthermore, the TixTa(4−x)C3 MXene anode demonstrate a high rate capability as a result of its good electron and Li-ion transport, suggesting that it is a promising candidate as Li-ion anode material.

Synthesis and characterization of boron‐acrylate/Santa Barbara Amorphous‐15 polymer composite

AbstractIn the present work, boron‐acrylate/Santa Barbara Amorphous (SBA)‐15 polymer composite was synthesized using free radical polymerization method. Firstly, SBA‐15 was functionalized with 3‐(trimethoxysilyl)propyl methacrylate to obtain chemically bonded boron acrylate (BAc) polymer on the SBA‐15 surface. The structural analysis was evaluated via Fourier‐transform infrared spectroscopy and solid‐state nuclear magnetic resonance 13C. Samples were also characterized by using scanning electron microscopy, X‐ray powder diffraction, N2 adsorption/desorption and thermogravimetric analysis. In order to examine the BAc polymers in the mesopores, the silica framework was removed via hydrofluoric acid etching process. The results indicated that the synthesis of boron‐acrylate/SBA‐15 polymer composite was performed successfully. Thermal stabilities of the composites were higher with greater amounts of BAc polymer in mesopores under oxidative conditions.

Metal alkoxide-derived Co@NC/NCNS as a highly efficient bifunctional oxygen electrocatalyst.

A promising bifunctional catalyst integrating Co@NC units and porous structure carbon nanosheets (Co@NC/NCNS) is in situ prepared by the calcination and subsequent acid etching of a mixture containing metal alkoxide and melamine. Benefiting from the synergism among the active sites and porous structure, the optimal Co@NC/NCNS-800 exhibits superior activity for the ORR/OER.

Bamboo-like nitrogen-doped carbon nanotubes on iron mesh for electrochemically-assisted catalytic oxidation

In this study, bamboo-like nitrogen-doped carbon nanotubes (BN-CNTs) are successfully deposited on etched iron mesh (d-Fe) using chemical vapor deposition (CVD) method with acetonitrile as precursor. The acidic etching process is necessary for the special BN-CNTs structure formation by exposing more Fe0 sites. The BN-CNTs/d-Fe is then evaluated for the electrochemically-assisted PMS activation to degrade phenol. Under cyclic voltammetry (CV, 0–1 V vs. RHE) assistant, 20 ppm phenol can be degraded in 30 min with a rate constant of 0.2837 min−1, ~78 times more than that without CV. Some Fe3+ species in the catalyst will be reduced at the initial stage, a two-step pseudo-first-order kinetic is thus used for the degradation curves fitting. Both the structure defects and doped nitrogen atoms are responsible for the high catalytic activity of BN-CNTs. According to the quenching tests, both radical and non-radical processes are present for PMS activation, thus obtaining enhanced organics removal efficiency. The electrochemically assistant could enhance the PMS adsorption on the electrode as well as electrons transfer between Fen+ and PMS, thus increasing the PMS activation efficiency. The utilization of earth-abundant Fe mesh for the fabricating free-standing electrodes provide a potential low-cost and effective strategy of waste water remediation.

Synthesis of α–MnO2–like rod catalyst using YMn2O5 A–site sacrificial strategy for efficient benzene oxidation

The elimination of benzene, a typical volatile organic pollutant, is one of the most challenging topics for environmental scientists. Catalytic oxidation technology is considered the most efficient approach for its elimination. Herein, we report the successful preparation of a novel α–MnO2–like rod catalyst via an acid etching route and propose YMn2O5 mullite as a novel precursor. The optimized α–MnO2–like rod catalyst showed significantly improved benzene oxidation activity compared to the raw YMn2O5 and commercial MnO2 catalysts, resulting in 100 % benzene conversion at 200 °C at a GHSV of 60,000 mL g–1 h–1. Notably, the α–MnO2–like rod catalyst performance at lower temperatures (100–175 ℃) exceeded that of a commercial Pt/Al2O3 catalyst. The excellent catalytic performance of the α–MnO2–like rod catalyst is associated with its low–temperature reducibility and abundant surface–active oxygen species. During the acid etching process, more Mn3+ is oxidized to Mn4+, and more surface oxygen vacancies are generated on the α–MnO2–like rod catalyst, which provides more adsorption sites for oxygen molecules to promote the benzene oxidation reaction. The α–MnO2–like rod catalyst should be a great alternative to commercial noble metal catalysts for the elimination of volatile organic pollutants, especially at lower temperatures.

Separation and Identification of Minerals Composing the Silica Sands (Southwestern Tunisia)

Separation and identification of minerals composing the Tunisian silica sands have been conducted by acid etching and hot filtration/sedimentation (HFS) without affecting the quartz component. It was found that the hot acid etching process is an effective method to separate quartz and clay minerals in the silica sand. The SEM micrographs of the silica sand show rough surface and some cracks with irregular shapes. The surface becomes clean and smooth after acid etching process. After chemical dissolution, the clay minerals were recovered by hot filtration following by sedimentation at low temperature. FT-IR, EDS maps, and secondary electron (SE) analyses of separated clay minerals reveal the presence of Fe2O3, montmorillonite, and kaolinite minerals. The LIBS analysis of clay minerals shows the presence of Al, Fe, Ca, Al, and Mg. The sequential etching process can be introduced in the purification methods as an effective way to separate quartz from clay minerals.

Metal Atom-Doped Co3 O4 Hierarchical Nanoplates for Electrocatalytic Oxygen Evolution.

Electrocatalysts based on hierarchically structured and heteroatom-doped non-noble metal oxide materials are of great importance for efficient and low-cost electrochemical water splitting systems. Herein, the synthesis of a series of hierarchical hollow nanoplates (NPs) composed of ultrathin Co3 O4 nanosheets doped with 13 different metal atoms is reported. The synthesis involves a cooperative etching-coordination-reorganization approach starting from zeolitic imidazolate framework-67 (ZIF-67) NPs. First, metal atom decorated ZIF-67 NPs with unique cross-channels are formed through a Lewis acid etching and metal species coordination process. Afterward, the composite NPs are converted to hollow Co3 O4 hierarchical NPs composed of ultrathin nanosheets through a solvothermal reaction, during which the guest metal species is doped into the octahedral sites of Co3 O4 . Density functional theory calculations suggest that doping of small amount of Fe atoms near the surface of Co3 O4 can greatly enhance the electrocatalytic activity toward the oxygen evolution reaction (OER). Benefiting from the structural and compositional advantages, the obtained Fe-doped Co3 O4 hierarchical NPs manifest superior electrocatalytic performance for OER with an overpotential of 262 mV at 10 mA cm-2 , a Tafel slope of 43 mV dec-1 , and excellent stability even at a high current density of 100 mA cm-2 for 50 h.

A metal-free additive texturization method used for diamond-wire-sawn multi-crystalline silicon wafers

Diamond-wire-sawn (DWS) technique has been widely applied in PV industry. However, this technique still has a big challenge when it is used for multi-crystalline silicon (mc-Si) because its reflectivity of DWS mc-Si etched by the conventional acid etching solution (HF/HNO3/H2O system) is quite higher. This paper proposes a metal-free additive texturization method, in which polyethylene glycol (PEG) is added to the HF/HNO3/H2O system to reduce the reaction rate of silicon wafers and improve the wettability of the etching liquid and the surface of mc-Si wafers. The etching points will gradually turn into nanopores instead of worm-like structures due to low reaction rates. Those nanopores form a gradually changed refractive index between silicon and air, which immensely reduces the surface reflectivity of mc-Si wafers. The mc-Si wafers processed in the experiment have an average surface reflectivity of about 16.9% in the wavelength range of 300–1100 nm, which is generally lower than the mc-Si wafers etched by the conventional acid etching process. This technical route has been applied to fabricate the 156 mm × 156 mm DWS mc-Si solar cells, and finally, the conversion efficiency of 19.39% has been obtained. Moreover, this approach matches well with the current PV industrial processes, showing a promising prospect.

Stress and Deformation of Optimally Shaped Silicon Microneedles for Transdermal Drug Delivery

In this study, we demonstrated the fabrication of the concave conic shape microneedle with the aid of COMSOL Multiphysics simulation. The stress and buckling of the microneedle structure were simulated by applying various loads ranging from 50 to 800 g perpendiculars to the tip in order to predict the occurrence of microneedles structure deformation. The simulation study indicated that the surface buckling deformation does not occur to the microneedle structure with the increment of the load. The microneedles with dimensions of height and diameter tip ranging from 60 to 100 μm and 1 to 4 μm, respectively had been fabricated via an etching process in a mixture of hydrofluoric acid, nitric acid, and acetic acid. Three optimized microneedles but different in the structures were fabricated via the acidic etching process. The reproducibility of 3 different microneedle structures was 15, 20, and 60%, respectively. Stress and buckling analyses of the fabricated microneedles were further carried out on the rat skin. The obtained experimental results show promising applications for the deep dermis, stratum corneum to epidermis layer penetration.

Hierarchical porous ε-MnO2 from perovskite precursor: Application to the formaldehyde total oxidation

A simple template-free method, based on a mineral acid etching process using manganite perovskite (LaMnO3) as precursor, was successfully developed to obtain a series of 3D meso/macro-porous materials. The LaMnO3 transformation was fully investigated using ICP, XRD, N2 physisorption, TPR, TPD, SEM, TEM/EDS and XPS. This transformation proceeds through a soft-chemical process involving the dissolution of trivalent lanthanum and manganese from the perovskite structure and the dismutation of Mn3+ cations into MnO2 and Mn2+ species. Strength and oxidizing properties of the acid used as modifying agent strongly impact textural and redox surface properties of the resulting materials. Specifically, extending the acid etching duration promotes the surface area and pore volume of the materials while developing interconnected macro-mesoporous networks. In our case, this soft process allowed us to obtain the ε-MnO2 phase with hierarchical porosity without any template. Superior catalytic properties of ε-MnO2 were observed toward HCHO oxidation as well as a good catalytic stability with respect to other macro-mesoporous counterparts. In the light of the experimental results, such performances can be related to the formation of a meso/macro-porous structure conferring high surface area and good accessibility of the active surface sites. The latter exhibit greater redox ability of the manganese species and a higher density of active surface oxygen species with respect to the perovskite precursor.