Coral-like Morphology Research Articles

Polarization and biomineralization of hydroxyapatite-barium titanate composites

In the search of new materials for bone regeneration, the materials with piezoelectric properties look very promising. It has been reported that piezoelectric materials induce bone growth and enhance implant integration. Additionally, it has been found that bioactivity increases in negatively charge surfaces such as polarized BaTiO3 (BT) and polarized hydroxyapatite (HAp). Additionally, it is known that BaSO4 (BS) increases biocompatibility. Therefore, in this work, composites materials of 80BT/20BS (BTS) in different proportions with HAp (HAp/BTS: 10/90, 30/70, 50/50, 70/30 y 90/10) were prepared by a mixture of nanometric powders and then they were sintered at 1000 °C for a period of 5 h. The materials were polarized at 130, 300 and 400 °C applying a DC electric field of 1 kV/mm, during 1 h. The electric field was maintained until the material was cooled down to room temperature. The electric and piezoelectric response were measured immediately after cooling, after 1 h and after 24 h. The dielectric measurements of materials were performed at different frequencies (0.1 to 100 kHz). The polarized and unpolarized materials were immersed in simulated body fluid (1.5 SBF) for 7 and 19 days. The deposition and growth of hydroxyapatite using the biomimetic method was followed by FTIR and SEM. The polarization effect on the crystalline growth of hydroxyapatite formed from the SBF solution has been demonstrated. The process of biomineralization of HAp on HAp/BTS composites increased considerably with the addition of barium titanate, this effect greatly improved in polarized materials. The typical coral-like morphology characteristic of HAp formation from SBF deposition was observed after 7 days of SBF immersion for polarized composites. Excellent dielectric properties were determined by adding 30% Of BaTiO3, obtaining for these composites dielectric constant values of the order of 20 to 10 kHz, values similar to that of human bones. Therefore, these materials look very promising for bone regeneration.

A template-free I2-assisted pyrolysis strategy to synthesize coral-like nitrogen-doped carbon with a regulated hierarchical porous structure toward efficient oxygen reduction

Construction of hierarchical porous structures in N-doped carbon (N/C) catalysts is of great significance to promote the reaction kinetics during the electrocatalysis. However, many existing template methods used to synthesize porous carbon networks are usually complicated in operation and might undermine the catalytic active sites of N/C in the post-treatment processes (e.g., templates removal under caustic conditions). Herein, a template-free I2-assisted pyrolysis strategy is developed to regulate the morphology and porous structure of N/C thermally derived from zeolitic imidazolate frameworks. Gas-phase I2 is controllably adsorbed (by adjusting the adsorption temperature) into the porous structure of the zeolitic imidazolate frameworks and then corrodes the frameworks during the pyrolysis. The as-synthesized N/C without any post-treatment features a coral-like morphology, a large pore volume, and a meso/macropore-dominated porous structure, rendering excellent electrocatalytic performance toward oxygen reduction reaction with a half-wave potential of 0.868 V vs. RHE due to the effective exposure of active sites and enhanced mass-transfer capability. A Mg-air battery assembled with the as-synthesized coral-like N/C as the cathode catalyst exhibits an excellent peak power density of 123 mW cm−2 at 0.73 V. This I2-assisted pyrolysis strategy could be widely applicable for regulating the porous structure and morphology of carbon materials derived from different porous precursors for energy conversion and storage applications.

Coral-like potassium and phosphorous doped graphitic carbon nitride structures with enhanced charge and mass transfer dynamics toward photocatalytic hydrogen peroxide production and microbial disinfection

This study provided insight on the design of co-doped graphitic carbon nitride (g-C3N4) structures by using potassium dihydrogen phosphate (KH2PO4) as a promising material for the supply of potassium (K) and phosphorus (P) elements. The addition of KH2PO4 to the cyanuric acid-melamine complex (CM) solution stabilized its structure by coordinating potassium ions (K+) in the hexagonal pores and dihydrogen phosphate ions (H2PO4-) in dangling bonds on the edge sites. The resultant supramolecular structure (KP-CM) with a unique skeleton governed the polycondensation process, resulting in K and P co-doped g-C3N4 structures with a distinct coral-like morphology (KP-CN). Employing the KP-CM complex as a precursor could modify the optoelectronic behaviour of the photocatalysts via the synergistic effect of the co-doping process. It could also be beneficial in terms of economic considerations by increasing the catalyst synthesis yield. The resulting g-C3N4 showed a remarkable hydrogen peroxide (H2O2) production rate of 216 µmol L−1h−1 compared to the rate of the pristine sample of 137 µmol L−1h−1. It also exhibited significant photocatalytic antibacterial activity in Escherichia coli (E. coli) disinfection.

Influence of powder properties and processing gas on the microstructural evolution of Armstrong CP-titanium and Ti6Al4V powders processed by cold spray

This paper studies the microstructural evolution of commercially pure titanium (CP-Ti) and Ti6Al4V powders manufactured by the Armstrong process deposited by cold spray with nitrogen and helium. The unique, coral-like morphology of the powders resulted in high density deposits sprayed with both nitrogen and helium carrier gasses. The plastic deformation of the CP-Ti and Ti6Al4V particles upon impact leads to refinement of the equiaxed grains present in the starting powder. CP-Ti deposits sprayed with nitrogen result in a grain size of 1 ± 0.6 μm while deposit processed with helium results in a grain size of 0.7 ± 0.2 μm with no clear difference between the grain size at particle interiors and at prior particles boundaries. The low levels of intragranular misorientation in the CP-Ti helium deposit indicated the presence of recrystallized grains. The higher grain refinement when using helium as carrier gas resulted in a weak basal plane (0001) fiber texture. Regions of ultrafine grains are also identified in the microstructure of Ti6Al4V analyzed by SEM. Microhardness values of the deposits made with these coral-like morphology powders were similar to CP-Ti and Ti6Al4V cold sprayed deposits produced with spherical powders. • The microstructure was refined in both the cold sprayed CP-Ti and Ti6Al4V deposits. • Recrystallized grains were identified in the cold sprayed CP-Ti deposit sprayed with helium gas. • EBSD of CP-Ti sprayed with helium gas revealed a weak texture in the basal <0001> direction. • The vanadium-rich regions presented in the Ti6Al4V powder are retained in the cold spray deposit.

Designing coral-like Fe2O3-regulated Se-rich CoSe2 heterostructure as a highly active and stable oxygen evolution electrocatalyst for overall water splitting

The electrocatalytic oxygen evolution reaction (OER) is the bottleneck to overall water splitting because of the slow kinetics of the four-electron transfer process. Therefore, it is of great significance to develop OER electrocatalysts with high activity, long durability, and scalability. Herein, we present a selenium-coated cobalt selenide (CoSe2@Se) catalyst that was first synthesized by in-situ growth on carbon cloth (CC) surface by hydrothermal method, followed by soaking treatment to prepare a three-dimensional coral-like Fe2O3-CoSe2@Se/CC composite. Electrochemical studies revealed that the optimized Fe2O3-CoSe2@Se/CC catalyst only requires 250 mV to reach 10 mA cm−2 current density, yields a small Tafel slope (50.2 mV dec−1), and has good stability (10 mA cm−2@70 h) in the electrocatalytic OER process. The overall water splitting using Fe2O3-CoSe2@Se/CC as anode only requires 1.58 and 1.69 V to achieve 10 and 100 mA cm−2, respectively, much better than most previously reported catalysts. Analysis showed that the three-dimensional coral-like morphology exposing more active sites and the synergy between different species (giving rise to, inter alia, a favorable electronic structure that lowers the electrode overpotential) are the key to the observed improved electrocatalytic performance. This work provides a novel strategy for the rational design of nanostructured OER hybrid catalysts in the future.

Microstructural evolution and mechanical properties of Al–Si–Cu–(Ge)–(Mg) alloy solidified under high pressure

The influence of high pressure on the microstructural evolution and mechanical properties of Al–Si–Cu–(Ge)–(Mg) alloys was investigated. With the increased solidification pressure, the secondary dendrite arm spacing (SDAS) of Al decreases, and the eutectic Si undergoes a transformation from the coarse acicular morphology to the coral-like morphology. The well-refined microstructure is attributed to the accelerated nucleation rate and the restrained crystal growth rate under high pressure. The morphological transformation of eutectic Si is ascribed to the synergetic effect of the high undercooling and Cu segregation at the outer surfaces of Si. Besides, the study shows that multiple nano-sized particles emerge in the alloys solidified under high pressure due to the high solid solubility of elements and increased nuclei. These nano-sized particles act as dominating strengthening phases leading to enhanced hardness and compressive strength compared with alloys solidified under atmospheric pressure. The as-cast alloy MG solidified under 4 GPa has the highest mechanical properties with a hardness of 135.2 HV and compressive stress of 721 MPa. The strengthening contribution of variable nano-sized particles was discussed. These results indicate that high pressure can be used as an effective method to introduce structural refinement and nano-sized strengthening phases, thus providing a potential way to improve mechanical properties of Al–Si–Cu-based alloys.

Bimetallic MOFs-derived coral-like Ag-Mo2C/C interwoven nanorods for amperometric detection of hydrogen peroxide.

Coral-like Ag-Mo2C/C-I and blocky Ag-Mo2C/C-II composites were obtained from one-step in situ calcination of [Ag(HL)3(Mo8O26)]n·nH2O [L: N-(pyridin-3-ylmethyl) pyridine-2-amine] under N2/H2 and N2 atmospheres, respectively. The coral-like morphology of Ag-Mo2C/C-I is composed of interwoven nanorods embedded with small particles, and the nano-aggregate of Ag-Mo2C/C-II is formed by cross-linkage of irregular nanoparticles. The above composites are decorated on glassy carbon electrode (GCE) drop by drop to generate two enzyme-free electrochemical sensors (Ag-Mo2C/C/GCE) for amperometric detection of H2O2. In particular, the coral-like Ag-Mo2C/C-I/GCE sensor possesses rapid response (1.2 s), high sensitivity (466.2 μA·mM-1·cm-2), and low detection limit (25 nM) towards trace H2O2 and has wide linear range (0.08 μM~4.67 mM) and good stability. All these sensing performances are superior to Ag-Mo2C/C-II/GCE, indicating that the calcining atmosphere has an important influence on microstructure and electrochemical properties. Theexcellent electrochemical H2O2 sensing performance of Ag-Mo2C/C-I/GCE sensor is mainly attributed to the synergism of unique microstructure, platinum-like electron structure of Mo2C, strong interaction between Mo and Ag, as well as the increased active sites and conductivity caused by co-doped Ag and carbon. Furthermore, this sensor has been successfully applied tothe detection of H2O2 in human serum sample, contact lens solution, and commercial disinfector, demonstrating the potential in related fields of environment and biology. Graphical abstract.

Ammonia gas sensing properties and density functional theory investigation of coral-like Au-SnSe2 Schottky junction

This paper introduces a coral-like Au-modified SnSe2 nanocomposite prepared by a simple hydrothermal method. The pure- and Au-modified SnSe2 film sensors were prepared on the substrate with interdigitated electrodes by drop coating. The compositions, morphologies and microstructures of the as-synthesized nanomaterials were observed using transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The Au-modified SnSe2 nanocomposite has a coral-like morphology assembled from many irregular and very thin nanosheets. The gas performances of the film sensors at room temperature were tested through a series of experiments. The experimental results demonstrated that the Au-modified SnSe2 nanocomposite film sensor had excellent response characteristics, extremely short response/recovery time, outstanding gas selectivity and stability towards ammonia gas compared with the pure one. In addition, the first-principle density functional theory (DFT) was employed to simulate the effect of Au modification on gas adsorption behavior, clarifying the internal mechanism of gas sensing by combining with Au-SnSe2 Schottky junction. These results verified that the Au-modified SnSe2 film sensor is a high-performance candidate for enhanced ammonia gas sensing properties at room temperature.

Eco friendly synthesis of the LiY(MoO4)2 coral-like quantum dots in biotemplate MOF (QD/BioMOF) for in vivo imaging and ibuprofen removal from an aqueous media study

Here as the first new research study on the bio quantum dots on metal–organic frameworks (BQDMOFs), we synthesized coral-like LiY(MoO4)2 BQDMOFs with hydrothermal method as an eco-friendly and cost effective approach. The lecithin as complex mixtures of lipids such as phospholipids which was extracted from egg yolk was applied not only as emulsifier for the formation of LiY(MoO4)2 quantum dots, but also acts as organic ligand and auxiliary linker agent on the base structure of the organic frameworks. The effect of such factors as pH (3–11), show with increasing pH from 3 up to 11 solubility increases and as a result the ibuprofen removal increases.The BQDMOFs structures were synthesized on the base of an organic frameworks with coral-like morphology with diameter in a range about 8–20 nm. The physicochemical properties, Ibuprofen removal from an aqueous media and in vivo imaging studies were investigated on the LiY(MoO4)2 BQDMOFs structures. Final products were characterization with analyze nanoparticle size using the well-known technique of dynamic light scattering (DLS), High-performance thin-layer chromatography (HPTLC), Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Infrared spectroscopy (IR) and the UV–Visible spectrum. From the sum of the results it can be established that LiY(MoO4)2 BQDMOFs structures acts not only as a super-radiant photoluminescence (SRP) substance for use in in vivo imaging in small animal researches but also as a surface-specific material which can be use in removal of ibuprofen drug from an aqueous media. The photocatalyst results of the LiY(MoO4)2 BQDMOFs shows high removal efficiency of ibuprofen (more than 99%) after 60 min under the UV light.

Investigation of the influences of ternary Mg addition on the solidification microstructure and mechanical properties of as-cast Al–10Si alloys

A hypoeutectic Al–10Si-2.0 Mg ternary alloy with high strength and high ductility was developed for as-cast service conditions. The effects of eutectic-forming element Mg on the primary α-Al dendrites, eutectic Si structure, Mg2Si intermetallic compound, mechanical properties and fracture behavior were systematically investigated via multiscale characterization methods. Interestingly, the results demonstrated that with the increasing Mg content, the secondary dendrite arm spacings of the primary α-Al dendrites were significantly reduced, and the grain size was refined, while the flaky eutectic Si structure was fully modified into a coral-like morphology. Additionally, the size of the Mg2Si intermetallic phase sharply decreased, and it was distributed much more uniformly in the interdendritic/intergranular eutectic regions. In contrast with the binary Al–10Si alloy, the yield strength, the ultimate tensile strength and the fracture strain were substantially enhanced to 159.4 MPa, 275.3 MPa and 14.1%, respectively, which correspond to improvements of 131.0%, 70.4% and 27.0%, respectively. The underlying mechanisms that were responsible for the evolution of the microstructure and mechanical properties are explicitly discussed.

A coral-like hematite photoanode on a macroporous SnO2: Sb substrate for enhanced photoelectrochemical water oxidation

Oxygen evolution over semiconductor photoanodes plays a decisive role in water splitting via photoelectrochemical (PEC) process. While the hematite photoanode with a photocurrent threshold of 600 nm is promising for practical PEC water oxidation, it still suffers from the small minority carrier diffusion length, which makes it difficult to realize adequate light absorption and efficient charge separation concurrently. To address this issue, hematite nanorods were grown on macroporous SnO2:Sb substrates, forming a coral-like hematite (ATO-Fe2O3) photoanode. The ATO-Fe2O3 photoanode exhibited a 150 mV cathodic shift of onset relative to Fe2O3 nanorods directly on planar SnO2:F (FTO-Fe2O3). The photocurrent density reached 1.32 mA cm−2 at 1.23 V vs. RHE, approximately 8.8 times higher than FTO-Fe2O3, and it was further increased to 1.81 mA cm−2 after passivation with a thin TiO2 overlayer. The improved photocurrent was attributed to the increased light harvesting, reduced charge transfer resistance (Rct), and smaller contact area of oxygen bubble to hematite photoanode. Our research confirmed the effectiveness of macroporous ATO templated coral-like morphology on balancing the adequate light absorption and efficient charge separation issues of hematite photoanodes. This research may also be applicable to other semiconductor photoanodes for high-efficiency PEC water splitting.

3D coral-like gold/carbon paper electrode modified with covalent and cross-linked enzyme aggregates for electrochemical sensing of glucose

The three-dimensional (3D) coral-like gold/carbon paper (Au/CP) electrode was prepared by a simple one-step electrodeposition procedure assisted by hydrogen evolution without any additive, and used as a support of glucose oxidase (GOx). GOx was immobilized onto the 3D porous electrode Au/CP in a process combining covalent attachment and cross-linking enzyme aggregates to fabricate the biosensor GOxEA-Au/CP. The structure and electrochemical properties of prepared electrodes were tested and characterized by scanning electron microscopy (SEM), chronocoulometry, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The gold coating with coral-like morphology can be found on the Au/CP surface, and the biosensor we fabricated exhibits high sensitivity (96.27 μA mM−1 cm−2) to glucose with a considerably wide linear response range (0.002–21.97 mM) as well as a low detection limit (0.6 μM) for glucose detection. In human serum samples, the detection of glucose based on this sensor has high detection stability and recovery, which means the as-prepared electrode is expected to be served as a competitive candidate for developing enzymatic glucose biosensors.

Effect of microwave time on the structural and luminescence properties of YAG:Ce prepared by microwave solution combustion (MSC) synthesis

Microwave solution combustion (MSC) synthesis is an attractive synthesis method to produce luminescent phosphor materials. The combustion reaction triggered by the interaction between microwave radiation and reducing agents (fuels) can produce high quality nano-sized materials. In this work, yttrium aluminium garnet (YAG) doped with 0.3 mol % cerium (Ce3+) was synthesized with MSC method and later fabricated with a blue LEDs to generate white light. The effect of different microwave time on structural, morphological and optical properties of the resulting phosphor materials were investigated. Results showed that the crystallinity of the YAG:Ce crystallinity was improved when the microwave time was increased. The phosphor powders have exhibited porous and coral-like morphology, which signified that precursors materials have successfully undergone crystal grain growth from the combustion process. Luminescence properties of YAG:Ce was due to the occurrence of an electronic transition from 4f ground state to the 5d excited state. The fabricated white LEDs (w-LEDs) have shown a higher emission intensity around yellow region was achieved when the microwave time was increased.

Enhanced electro-catalytic activity of palladium nanocoral structures with platinum incorporation

One of the most vital problems in fuel cell research is the synthesis of low cost, active and stable electro-catalyst for anodic and cathodic reactions. In this work, palladium nanostructures with a coral-like morphology (PdNC) is deposited on reduced graphene oxide (rGO) by electrochemical method. The nanocoral exhibits superior activity towards methanol oxidation (MOR) and oxygen reduction reactions (ORR) in alkaline media. To improve the efficiency, Pt is deposited on the surface by galvanic replacement. Presence of Pt on palladium nanocoral (PdNC-Pt) leads to an enhanced catalytic activity for both the electrode reactions. A mass activity of 1700 mA mg−1 at 1.04 V for MOR and a current density of −5.72 mA cm−2 and an onset potential of 0.86 V vs RHE is observed for ORR. Both the electrode reactions result in higher current than the commercial Pd/C and Pt/C catalysts. A remarkable improvement in durability is seen for ORR after depositing Pt.

Dynamic restructuring induced Cu nanoparticles with ideal nanostructure for selective multi-carbon compounds production via carbon dioxide electroreduction

Production of multi-carbon (C2+) products via electrochemical CO2 reduction reaction (CO2RR) has aroused intensive interest in this decade. However, it is still a great challenge in large-scale synthesis of electrocatalysts for C2+ compounds production with high selectivity and rate in neutral electrolyte. In this study, a robust and scalable aqueous synthesis method was proposed to prepare CuO nanosheets, which was directly used as CO2RR electrocatalyst. The catalyst underwent dynamic restructuring during the pre-reduction stage, which significantly changed the morphology, crystalline structure and electrochemical properties of the catalyst. As a result, the pristine CuO nanosheets gradually evolved to coral-like Cu nanoparticle ensembles (CL-Cu NEs). In 0.1 M KHCO3 at −1.1 V vs. RHE, the CL-Cu NEs exhibited a faradaic efficiency and partial current density of C2+ products of 72.1% and 25.2 mA cm−2 respectively and no degradation was observed in 15 h running. In contrast to many Cu-based catalysts showing considerable C2+ products selectivity, the (sub)surface oxygen and Cu+ species were unlikely to play a significant role in this study. The strong performance of CL-Cu NEs was ascribed to the synergism between the coral-like morphology and abundant Cu(1 0 0)/Cu(1 1 1) interfaces. This methodology may provide a cost-effective approach for large-scale preparation of CO2RR electrocatalysts with ideal nanostructure.

Failure dynamics of spherical and irregular shaped Ti splats deposited on sapphire by cold spray

Single splats of commercially pure Ti are deposited onto sapphire by cold spray under two spray conditions to achieve different in-flight powder velocities. The powders used have two morphologies: spherical powder (SP), manufactured by plasma gas atomization, and irregular powder (IP), manufactured by the Armstrong process, with a coral-like morphology. The adhesion strength of the single splats is measured by splat adhesion testing. By use of a specialized in situ scratch tester, interface failure during splat adhesion testing is observed through the sapphire substrate. Particle velocity does not significantly influence the adhesion strength and failure mechanism of SP splats. After deposition, the SP splat has an interface pore in its center which acts as an initiation site for crack propagation during splat adhesion testing. After failure, a well bonded portion of Ti remains on the substrate in the shape of a ring. IP splats deposited at low velocity show similar, well adhering, rings on the surface in localized locations scattered throughout the interface. An increase in velocity for IP splats led to an increase in adhesion strength and a nearly continuous well adhering interface. The behaviour of IP splats is understood by electron channelling contrast images of cross-sections where low velocities resulted in little change in microstructure while high velocities led to a highly deformed microstructure at the interface.

Synergistic effect of poly(3,4-ethylenedioxythiophene), reduced graphene oxide and aluminium oxide) as counter electrode in dye-sensitized solar cell

Abstract A new counter electrode which makes use of reduced graphene oxide (rGO), poly (3,4-ethylenedioxythiophene) (PEDOT) and aluminium oxide (Al2O3) was developed to enhance the performance of dye-sensitized solar cell (DSSC) device in replacing platinum as a counter electrode. PEDOT/rGO-Al2O3 was fabricated through the deposition of rGO/Al2O3 on indium tin oxide (ITO) glass by cyclic voltammetry followed by the deposition of PEDOT via chronoamperometry. The morphology of PEDOT/rGO-Al2O3 showed the combination of the wrinkled paper-like structure of rGO and coral-like morphology of PEDOT with nanoparticles of alumina, which gave the positive synergistic effects of the counter electrode to increase the performance of the DSSC. The electrochemical analyses indicated that PEDOT/rGO-Al2O3 exhibited a good electrocatalytic activity to act as a counter electrode in DSSC compared to PEDOT-rGO, PEDOT and rGO. The PEDOT/rGO-Al2O3 achieved power conversion efficiency (PCE) of 2.15%, which is higher compared to PEDOT-rGO (1.00%), PEDOT (0.69%) and rGO (0.09%).

Synthesis of poly(N1,N1,N6,N6-tetraallylhexane-1,6-diammonium dichloride) microparticles for removing Mo(VI) in aqueous solution

A novel poly(N1,N1,N6,N6-tetraallylhexane-1,6-diammonium dichloride) (PTAHDADC) microparticle was prepared via inverse emulsion polymerization. The adsorption characteristics and mechanism for Mo(VI) in an aqueous solution were investigated systemically. Results showed that PTAHDADC had a high positively charge density with a positive charge at every six CH2 (or CH) units and presented a coral-like morphology, with macropores distributed in 30–130 μm, and a porosity of up to 46.52%. The Mo(VI) removal efficiency was >99% at pH = 3.0–4.0. The adsorption data could be effectively described using the Langmuir and pseudo-second-order kinetic models. The maximum adsorption capacity was up to 394.11 mg·g−1 at 293 K. The adsorption process was rapid, and reached equilibrium within 120 min with an adsorption activation energy Ea of 41.15 kJ·mol−1. The adsorption process of Mo(VI) by PTAHDADC was accompanied by the partial ion exchange of counterion Cl−, the partial deprotonation of functional groups (CH2)3N+H on PTAHDADC, and the new interaction and bond formation between Mo(VI) and PTAHDADC. Mo(VI) removal by PTAHDADC was a process of spontaneously endothermic entropy increment, which involves physisorption, electrostatic attraction, ion exchange, and chemisorption. PTAHDADC offers a simple synthesis and excellent adsorption performance and recyclability. Therefore, PTAHDADC is a highly potential adsorbent for removing Mo(VI) ions from wastewater and has a broad application prospect.

Synthesis, Characterization, Directional Crystal Growth Mechanism and Photocatalytic Activity of Three-Dimensional Hierarchical Fern-Like Nanostructures of BaTiO3

BaTiO3 with fern-like nano-structural morphology has been successfully synthesized via a simple sol-gel method followed by ageing process and was characterized by X-ray powder diffraction (PXRD) and Raman spectroscopy. The composition and the morphology was confirmed by scanning electron microscopy (SEM) with Energy dispersive X-ray spectroscopy and (high-resolution) transmission electron microscopy (TEM/HRTEM). The bonding linkage between Ba, Ti and O in the BaTiO3 sample was obtained by FTIR study. The band gap was calculated by using Kubelka-Munk function based on UV-absorption spectroscopic studies. The binding state of the elements present in BaTiO3 were obtained from XPS analysis. The details pertaining to thermal decomposition process of the uncalcined barium titanyl oxalate to barium titanate was obtained from TGA analysis. The surface area was determined by BET adsorption-desorption isotherms. The plausible directional growth mechanism of different BaTiO3 facets forming fern-like clusters is discussed in detail. The fern-like BaTiO3 exhibited only Ì´ 10% higher photocatalytic activity compared to the BaTiO3 with coral-like morphology for the degradation of methyl orange (MO) dye under UV irradiation.The photocatalytic degradation was also explored by the addition of H2O2 as electron scavenger, KI as surface hydroxyl radical scavenger and TBA as bulk hydroxyl radical scavenger.

A Stable and Electrocatalytic Iron Electrode for Oxygen Evolution in Alkaline Water Electrolysis

Iron electrodes disintegrate in alkali at the anodic potentials needed for oxygen evolution. Hence, relatively expensive nickel-based electrodes and substrates have been the workhorse of materials for industrial water electrolysis. We report here a novel surface-modification method that transforms iron into an electrocatalytically-active and robust oxygen evolution electrode for alkaline water electrolysis. This surface modification consists of an electrochemical oxidation step followed by a thermal decomposition step. The electrochemical oxidation of the iron substrate in alkali transformed the surface to high surface area iron(II) hydroxide with a coral-like morphology that converted to magnetite upon heat treatment. On this high-surface area substrate an electrocatalytic layer of amorphous nickel hydroxide was produced by the thermal decomposition step. Such a surface-modified iron electrode exhibited an extremely low overpotential of 195 mV at 10 mA/cm2 and a low Tafel slope of 43 mV/decade. The electrochemical oxidation step during preparation results in doubling of the electrochemically active area. Even after 1500 h of oxygen evolution at 10 mA/cm2, there was no noticeable change in the electrode potential, morphology, or surface composition of these iron electrodes. This durability was attributed to the conductive oxide layer of magnetite that protects iron surface at the anodic potentials of oxygen evolution. The remarkable electrocatalytic activity was attributed to the amorphous layer of nickel hydroxide. Development of such a robust and electrochemically-active iron electrode presents a unique opportunity for the advancement of alkaline water electrolysis.