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•PEG modified TiO2 was optimized using different molecular weight by sol-gel method.•Optimized PEG modified TiO2 film showed high photocatalytic activity and stability.•Synergy of ...sonolysis and photocatalysis resulted to enhanced Rh B degradation.•Photocatalytic-Ultrasonic system exhibited high efficiency for wastewater treatment.
TiO2 photocatalyst film recently has been utilized as the potential candidate for the wastewater treatment, due to its high stability and low toxicity. In order to further increase the photocatalytic ability and stability, different molecular weight of polyethylene glycol (PEG) were used to modify TiO2 structure to synthesize porous thin film used in the developed Photocatalytic-Ultrasonic system in this work. The results showed that PEG2000 modified TiO2 calcinated under 450°C for 2h exhibited the highest photocatalytic activity, attributed to the smallest crystallite size and optimal particle size. Over 95.0% of rhodamine B (Rh B) was photocatalytically degraded by optimized PEG2000-TiO2 film after 60min of UV irradiation, while only about 50.8% of Rh B was decolored over pure TiO2 film. Furthermore, optimized PEG2000-TiO2 film was used in a circular Photocatalytic-Ultrasonic system, and the obtained synergy (0.6519) of sonophotocatalysis indicated its extremely high efficiency for Rh B degradation. In this Photocatalytic-Ultrasonic system, larger amount of PEG2000-TiO2 coated glass beads, stronger ultrasonic power and longer experimental time could result to higher degradation efficiency of Rh B. In addition, repetitive experiments showed that about 97.2% of Rh B were still degraded in the fifth experiment by sonophotocatalysis using PEG2000-TiO2 film. Therefore, PEG2000-TiO2 film used in Photocatalytic-Ultrasonic system has promising potential for wastewater treatment, due to its excellent photocatalytic activity and high stability.
In this report, we utilize the U-tube double diffusion device as a reliable, environmentally friendly method for the size-controlled synthesis of high-quality, single crystalline Pd nanowires. The ...nanowires grown in 200 and 15 nm polycarbonate template pores maintain diameters of 270 ± 45 nm and 45 ± 9 nm, respectively, and could be isolated either as individual nanowires or as ordered free-standing arrays. The growth mechanism of these nanowires has been extensively explored, and we have carried out characterization of the isolated nanowires, free-standing nanowire arrays, and cross sections of the filled template in order to determine that a unique two-step growth process predominates within the template pores. Moreover, as-prepared submicrometer and nanosized wires were studied by comparison with ultrathin 2 nm Pd nanowires in order to elucidate the size-dependent trend in oxygen reduction reaction (ORR) electrocatalysis. Subsequently, the desired platinum monolayer overcoating was reliably deposited onto the surface of the Pd nanowires by Cu underpotential deposition (UPD) followed by galvanic displacement of the Cu adatoms. The specific and platinum mass activity of the core–shell catalysts was found to increase from 0.40 mA/cm2 and 1.01 A/mg to 0.74 mA/cm2 and 1.74 A/mg as the diameter was decreased from the submicrometer size regime to the ultrathin nanometer range.
One emergent property of ferroelectric nanoparticles is the sized-induced structural distortion to a high-symmetry paraelectric phase at small particle sizes. Finite length scale effects can thus be ...advantageously employed to elucidate ferroelectric transition mechanisms. In this work, we combine infrared spectroscopy with group theory and lattice dynamics calculations to reveal the displacive nature of the ferroelectric transition in BiFeO3, a room temperature multiferroic. Systematic intensity and frequency trends in selected vibrational modes show that the paraelectric phase is Pm3̅m and the lowest frequency A1 feature is the soft mode that drives the first order transition. Finite length scale effects are also evident in the electronic structure with a red-shifted band gap in nanoscale BiFeO3 compared with that of the rhombohedral film, a result that can impact the development of ferroelectric photovoltaics and oxide-based electronics. Taken together, these findings demonstrate the foundational importance of size effects for enhancing the rich functionality and broad utility of transition metal oxides.
We have sought to improve the electrocatalytic performance of tungsten nitride through synthetic control over chemical composition and morphology. In particular, we have generated a thermodynamically ...unstable but catalytically promising nitrogen-rich phase of tungsten via a hydrothermal generation of a tungsten oxide intermediate and subsequent annealing in ammonia. The net product consisted of three-dimensional (3D) micron-scale flower-like motifs of W
2
N
3
; this architecture not only evinced high structural stability but also incorporated the favorable properties of constituent two-dimensional nanosheets. From a performance perspective, as-prepared 3D W
2
N
3
demonstrated promising hydrogen evolution reaction (HER) activities, especially in an acidic environment with a measured overpotential value of −101 mV at a current density of 10 mA/cm
2
. To further enhance the electrocatalytic activity, small amounts of precious metal nanoparticles (such as Pt and Au), consisting of variable sizes, were uniformly deposited onto the underlying 3D W
2
N
3
motifs using a facile direct deposition method; these composites were applied towards the CO
2
reduction reaction (CO
2
RR). A highlight of this series of experiments was that Au/W
2
N
3
composites were found to be a much more active HER (as opposed to either a CO
2
RR or a methanol oxidation reaction (MOR)) catalyst.
Single-crystalline perovskite nanostructures with reproducible shape have been prepared using a simple, readily scaleable solid-state reaction in the presence of NaCl and a nonionic surfactant. ...Pristine BaTiO3 nanowires have diameters ranging from 50 to 80 nm with an aspect ratio larger than 25. Single-crystalline SrTiO3 nanocubes with a mean edge length of 80 nm have been produced using a similar procedure.
In this article, we address two key challenges in the development of electrocatalysts for direct methanol fuel cells by rationally tailoring the morphology and chemical composition of Pd-based ...nanowires (NWs) for enhanced performance. First, we have examined the morphology and composition-dependent performance of Pt1–x Pd x NWs toward the methanol oxidation reaction (MOR). Elemental Pt NWs were found to possess a significant morphology-dependent enhancement of nearly 3-fold in terms of peak MOR-specific activity over that of commercial Pt NP/C. In addition, tailoring the chemical composition in Pt1–x Pd x NWs can lead to measurable increases in MOR kinetics, which can be attributed to improved oxidation of formic acid and, potentially, increased selectivity for a direct, CO-free pathway. Second, we have explored the stability of ORR performance in the presence of measurable concentrations of methanol as a function of chemical composition in Pt1–x Pd x NWs and Pt-free Pd9Au NWs. In the context of the Pt1–x Pd x NWs, a distinctive volcano-type dependence has been noted with respect to chemical composition, and on the basis of the MOR activities and methanol tolerant ORR behavior, Pt7Pd3 NWs have been highlighted as an optimal catalyst architecture. We have also analyzed the methanol tolerance in Pd9Au NWs, which represents a highly active, durable Pt-free alternative to traditional Pt-based nanostructured catalysts. Herein, we have demonstrated that Pd9Au NWs (0.42 mA/cm2) with no effective Pt content can outperform Pt-based nanostructures, such as Pt NWs (0.32 mA/cm2) and nanoparticulate Pt NP/C (0.24 mA/cm2) in the presence of 4 mM methanol/0.1 M HClO4.
“Flower‐like” motifs of Li4Ti5O12 were synthesized by using a facile and large‐scale hydrothermal process involving unique Ti foil precursors followed by a short, relatively low‐temperature ...calcination in air. Moreover, a detailed time‐dependent growth mechanism and a reasonable reaction scheme were proposed to clearly illustrate and highlight the structural evolution and subsequent formation of this material. Specifically, the resulting “flower‐like” Li4Ti5O12 microspheres consisting of thin nanosheets provide for an enhanced surface area and a reduced lithium‐ion diffusion distance. The high surface areas of the exposed roughened, thin petal‐like component nanosheets are beneficial for the interaction of the electrolyte with Li4Ti5O12, which thereby ultimately provides for improved high‐rate performance and favorable charge/discharge dynamics. Electrochemical studies of the as‐prepared nanostructured Li4Ti5O12 clearly revealed their promising potential as an enhanced anode material for lithium‐ion batteries, as they present both excellent rate capabilities (delivering 148, 141, 137, 123, and 60 mAh g−1 under discharge rates of 0.2, 10, 20, 50, and 100 C, at cycles of 50, 55, 60, 65, and 70, respectively) and stable cycling performance (exhibiting a capacity retention of ≈97 % from cycles 10–100, under a discharge rate of 0.2 C, and an impressive capacity retention of ≈87 % by using a more rigorous discharge rate of 20 C from cycles 101–300).
Stop and smell the flowers: 3 D hierarchical flower‐shape Li4Ti5O12 motifs are synthesized by using a facile and rapid hydrothermal process involving short reaction times, relatively low reaction temperatures, and reusable and recyclable Ti precursors. The resulting Li4Ti5O12 electrodes exhibit remarkably high rate capability and cycling stability as compared with analogous, previously reported motifs.
To create truly effective electrocatalysts for the cathodic reaction governing proton exchange membrane fuel cells (PEMFC), namely the oxygen reduction reaction (ORR), necessitates an accurate and ...detailed structural understanding of these electrocatalysts, especially at the nanoscale, and to precisely correlate that structure with demonstrable performance enhancement. To address this key issue, we have combined and interwoven theoretical calculations with experimental, spectroscopic observations in order to acquire useful structural insights into the active site geometry with implications for designing optimized nanoscale electrocatalysts with rationally predicted properties. Specifically, we have probed ultrathin (∼2 nm) core–shell Pt∼Pd9Au nanowires, which have been previously shown to be excellent candidates for ORR in terms of both activity and long-term stability, from the complementary perspectives of both DFT calculations and X-ray absorption spectroscopy (XAS). The combination and correlation of data from both experimental and theoretical studies has revealed for the first time that the catalytically active structure of our ternary nanowires can actually be ascribed to a PtAu∼Pd configuration, comprising a PtAu binary shell and a pure inner Pd core. Moreover, we have plausibly attributed the resulting structure to a specific synthesis step, namely the Cu underpotential deposition (UPD) followed by galvanic replacement with Pt. Hence, the fundamental insights gained into the performance of our ultrathin nanowires from our demonstrated approach will likely guide future directed efforts aimed at broadly improving upon the durability and stability of nanoscale electrocatalysts in general.
Perovskite oxides with a chemical formula of ABO3 (in which A=either alkaline, alkaline‐earth, or rare‐earth metal ions and B=d‐block transition metals) have been widely investigated because of their ...inherently unusual and simultaneously desirable electronic and magnetic properties. These materials may act as cost‐effective, more earth‐abundant, and high‐performance alternatives to commercial Pt/Pd‐based catalysts for electrocatalysis. In their Review article on page 7779 ff., S. S. Wong et al. highlight advances in the use of perovskite metal oxides as both catalysts and catalyst supports towards the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) within a direct methanol fuel cell (DMFC) configuration.
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