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Electron microscopy investigation of spark plasma sintered ZrO2 added ZrB2–SiC composite

The impact of introducing nano-sized ZrO2 additive on the sinterability and microstructure development of ZrB2–SiC composite was studied. The spark plasma sintering (SPS) technique was selected as the manufacturing method, and the as-sintered sample reached a relative density value slightly higher than 98.5%. Advanced electron microscopy techniques along with X-ray diffraction (XRD) were used to characterize the final composite. The XRD assessment revealed the formation of two in-situ phases, namely ZrC and ZrSiO4, along with the initial phases. Thermodynamic evaluations suggested the possible formation of a liquid phase due to an interaction among the available oxides (e.g., ZrO2, SiO2, and B2O3). This assumption was fortified by the presence of an amorphous phase in the scanning electron microscopy (SEM) analysis. Finally, transmission electron microscopy (TEM) verified the formation of such …

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Hierarchical molybdenum disulfide on carbon nanotube–reduced graphene oxide composite paper as efficient catalysts for hydrogen evolution reaction

Herein, we report a composite structure composed of vertically grown molybdenum disulfide (MoSx) nanosheets supported by conductive carbon nanotube–reduced graphene oxide (CNT–rGO) on Vietnamese traditional paper (MoSx/CNT–rGO/VTP) for a high-performance electrochemical hydrogen evolution reaction (HER). In the fabrication, CNT–rGO is first prepared on VTP by roll coating, following which the vertically aligned MoS2 nanosheets are synthesized on the surface of CNT–rGO/VTP through a simple hydrothermal reaction. The catalyst exhibits excellent HER electrocatalytic activity including a low onset potential of 190 mV, Tafel slope of 59 mV dec−1, and excellent stability in an acidic electrolyte solution. The excellent catalytic performance can be attributed to the abundant active edges provided by the vertically aligned MoSx nanosheets, as well as the effective electron transport provided by the CNT …

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Valorization of biomass waste to engineered activated biochar by microwave pyrolysis: Progress, challenges, and future directions

Biomass waste represents the promising surrogate of fossil fuels for energy recovery and valorization into value-added products. Among thermochemical conversion techniques of biomass, pyrolysis appears to be most alluring owing to its low pollutant emission and diverse products formation. The current pyrolysis applications for valorization of biomass waste is reviewed, covering the key concepts, pyrolysis mode, operating parameters and products. To date, existing types of pyrolysis include conventional pyrolysis (poor heat transfer due to non-selective heating), vacuum pyrolysis (lower process temperature because of vacuum), solar pyrolysis (entirely “green” with solar-powered), and a newly touted microwave pyrolysis. In microwave pyrolysis of biomass, the heat transfer is more efficient as the heat is generated within the core of material by the interaction of microwave with biomass. The plausible mechanisms …

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Recent progress in TiO2-based photocatalysts for hydrogen evolution reaction: A review

TiO2 has gained tremendous attention as a cutting-edge material for application in photocatalysis. The performance of TiO2 as a photocatalyst depends on various parameters including morphology, surface area, and crystallinity. Although TiO2 has shown good catalytic activity in various catalysis systems, the performance of TiO2 as a photocatalyst is generally limited due to its low conductivity and a wide optical bandgap. Numerous different studies have been devoted to overcome these problems, showing significant improvement in photocatalytic performance. In this study, we summarize the recent progress in the utilization of TiO2 for the photocatalytic hydrogen evolution reaction (HER). Strategies for modulating the properties toward the high photocatalytic activity of TiO2 for HER including structural engineering, compositional engineering, and doping are highlighted and discussed. The advantages and limitations of each modification approach are reviewed. Finally, the remaining obstacles and perspective for the development of TiO2 as photocatalysts toward high efficient HER in the near future are also provided.

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Combined biochar vertical flow and free-water surface constructed wetland system for dormitory sewage treatment and reuse

A two-stage treatment system that included vertical flow (VF) and free-water surface (FWS) constructed wetlands was investigated for the dual purposes of sewage treatment and reuse. The VF included four layers (biochar, sand, gravel, and sandy soil), and the FWS was installed after the VF and used as a polishing tank. Two types of local plants, namely Colocasia esculenta and Canna indica, were planted in the VF and FWS, respectively. The system operated for approximately six months, and the experimental period was categorized into four stages that corresponded to changes in the hydraulic loading rate (HLR) (0.02–0.12 m/d). The removal efficiencies for total suspended solids (TSS), chemical oxygen demand (COD), biological oxygen demand (BOD5), ammonia (NH4-N), and total coliform (Tcol) were 71 ± 11%, 73 ± 13%, 79 ± 11%, 91 ± 3%, and 70 ± 20%, respectively. At HLRs of 0.04–0.06 m/d, the COD and BOD5 levels satisfied Vietnam's irrigation standards, with removable rates of 64% and 88%, respectively, and the TSS and Tcol levels satisfied Vietnam's standards for potable water. Furthermore, the NO3-N levels satisfied the reuse limits, whereas the NH4-N levels exceeded the reuse standards. At high HLRs (e.g., 0.12 m/d), all the effluent parameters, except Tcol and NO3-N, exceeded the standards.

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Chitosan-mediated facile green synthesis of size-controllable gold nanostars for effective photothermal therapy and photoacoustic imaging

With the large near-infrared (NIR) absorption and the high NIR photothermal effect, gold nanostar (AuNS) has potential application in the biomedical field. However, the complicated synthesis process with toxic precursors is a serious issue for its practice. Herein, we reported a novel green synthesis procedure using chitosan polymer from marine and vitamin C for the preparation of AuNS. For the first time, chitosan was used as a stabilizer, shape-directing, and size-controllable agents for the preparation of AuNS. The size of the obtained AuNS ranged from 111 to 225 nm with different λmax. The AuNS exhibited near-infrared absorption with the excellent biocompatibility toward non-cancerous cell line (MG63) and cancerous cell line (MDA-MB-231). The in vitro photothermal therapy and photoacoustic imaging with assisting of obtained AuNS were also proved the high efficiency of these nanoparticles.

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Photothermal Responsive Porous Membrane for Treatment of Infected Wound

Wound infection is a big issue of modern medicine because of multi-drug resistance bacteria; thus, developing an advanced therapy is curial. Photothermal therapy (PTT) is a newly noninvasive strategy that employs PTT agents to transfer near-infrared (NIR) light energy into heat to kill bacterial pathogens. In this work, the PTT agent-containing dressing was developed for the first time to treat the wound infection. Palladium nanoparticles (PdNPs) were chosen as PTT agents because of their high stability, good biocompatibility, excellent photothermal property, and simple-green preparation. With the flexibility and wettability, highly porous membrane chitosan/polyvinyl alcohol (CS/PVA) membrane was chosen as the dressing. The prepared wound dressings exhibited excellent biocompatibility, high porosity, a high degree of swelling, high moisture retention, and high photothermal performance. The treatment of PdNPs loading CS/PVA dressing (CS/PVA/Pd) and laser irradiation killed most of the bacteria in vitro. The proposed PTT agent containing wound dressing introduces a novel strategy for the treatment of wound infection.

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Silk Fibroin-Based Biomaterials for Biomedical Applications: A Review

Since it was first discovered, thousands of years ago, silkworm silk has been known to be an abundant biopolymer with a vast range of attractive properties. The utilization of silk fibroin (SF), the main protein of silkworm silk, has not been limited to the textile industry but has been further extended to various high-tech application areas, including biomaterials for drug delivery systems and tissue engineering. The outstanding mechanical properties of SF, including its facile processability, superior biocompatibility, controllable biodegradation, and versatile functionalization have allowed its use for innovative applications. In this review, we describe the structure, composition, general properties, and structure-properties relationship of SF. In addition, the methods used for the fabrication and modification of various materials are briefly addressed. Lastly, recent applications of SF-based materials for small molecule drug delivery, biological drug delivery, gene therapy, wound healing, and bone regeneration are reviewed and our perspectives on future development of these favorable materials are also shared. View Full-Text

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SnO2@WS2 /p-Si Heterostructure Photocathode for Photoelectrochemical Hydrogen Production

This study reports an effective method to enhance the performance of photoelectrochemical (PEC) solar water reduction. We design and prepare SnO2@WS2 NF heterostructure on p-Si, that has better visible light-absorption, as well as low recombination of electron–hole pairs. Consequently, a -3.5mA cm−2 photocurrent density at 0 V vs. a reversible hydrogen electrode is obtained using SnO2@WS2, and bare SnO2 and WS2 photocathodes exhibit values of -0.6 and -0.36 mA cm−2, respectively, showing the combined effects of these two materials for excellent hydrogen evolution reaction performance. Additionally, the photocurrent stability of the sample reveals the improved efficiency for the separation of generated charge carriers. Our study provides experimental and theoretical evidence that SnO2 doping improves the properties of WS2 for efficient PEC solar water reduction.

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Facile synthesis of W2C@ WS2 alloy nanoflowers and their hydrogen generation performance

Two–dimensional transition metal dichalcogenides such as MoS2 and WS2 nanosheets, nanoflowers, and nanoparticles have been investigated as potential materials for the hydrogen evolution reaction (HER). Besides 2D–TMDs, MXene materials, which are transition metal carbides/nitrides, are promising candidates for energy storage and conversion applications. In this work, alloys of tungsten carbides and tungsten disulfides have been fabricated through a facile hydrothermal method without using any complex structure of carbon or polymer source for carbonization. The fabricated alloys were characterized by X-ray diffraction analysis, field emission scanning microscopy, atomic force microscopy, Raman spectra, and X-ray photoelectron spectroscopy. The results indicated both W2C and WS2 have hexagonal structure in the alloy compound. W2C@WS2 nanomaterials exhibit abundant flower-shaped active …

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The use of UV/ozone-treated MoS 2 nanosheets for extended air stability in organic photovoltaic cells

MoS2 nanosheets obtained through a simple sonication exfoliation method are employed as a hole-extraction layer (HEL) to improve the efficiency and air stability of organic photovoltaic cells (OPVs). The reduction in the wavenumber difference, appearance of a UV-vis peak, and atomic force microscopy images indicate that MoS2 nanosheets are formed through the sonication method. The OPVs with MoS2 layers show a degraded performance with a power conversion efficiency (PCE) of 1.08%, which is lower than that of OPVs without HEL (1.84%). After performing the UV/ozone (UVO) treatment of the MoS2 surface for 15 min, the PCE value increases to 2.44%. Synchrotron radiation photoelectron spectroscopy data show that the work function of MoS2 increases from 4.6 to 4.9 eV upon UVO treatment, suggesting that the increase in the PCE value is caused by the bandgap alignment. Upon inserting poly(3,4 …

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Dual use of tantalum disulfides as hole and electron extraction layers in organic photovoltaic cells

UV/ozone treated (UVO-treated) TaS2 and non-treated TaS2 nanosheets are introduced into organic photovoltaic cells (OPVs) as hole extraction layers (HEL) and electron extraction layers (EEL). TaS2 nanosheets are obtained via ultrasonic vibration and size-controlled by centrifugation. Atomic force microscopy (AFM) images reveal that the thickness and lateral size of TaS2 nanosheets are approximately 1 and 70 nm, indicating that uniform and ultrathin TaS2 nanosheets are obtained. The work function of TaS2 increases from 4.4 eV to 4.9–5.1 eV after applying UVO treatment by forming Ta2O5. In addition, the power conversion efficiencies of normal OPV with UVO-treated TaS2 and inverted OPV with TaS2 are 3.06 and 2.73%, which are higher than those of OPV without TaS2 (1.56% for normal OPV and 0.22% for inverted OPV). These results indicate that TaS2 is a promising material for HEL and EEL layers in …

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UV/ozone‐treated WS2 hole‐extraction layer in organic photovoltaic cells

WS2 nanosheets obtained through a simple sonication exfoliation method are employed as a hole‐extraction layer to improve the efficiency of organic photovoltaic cells (OPVs). A reduction in the wavenumber difference in the Raman spectra, the appearance of a UV absorption peak, and atomic force microscopy images indicate that WS2 nanosheets are formed through the sonication method. The power conversion efficiency (PCE) values of OPVs with and without untreated WS2 layers are both 1.84%. After performing a UV‐ozone (UVO) treatment on the WS2 surface for 15 min, the PCE increases to 2.4%. Synchrotron radiation photoelectron spectroscopy data show that the work function of WS2 increases from 4.9 eV to 5.1 eV upon UVO treat‐ ment, suggesting that the increase in the PCE value is caused by the band alignment. Upon inserting poly(3,4‐ethylenedioxythiophene):poly(styrene‐sulfonate) (PEDOT …

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Use of silane-functionalized graphene oxide in organic photovoltaic cells and organic light-emitting diodes

Graphene oxide (GO) and silane-functionalized GO (sGO) sheets obtained through a simple sonication exfoliation method are employed as hole transport layers to improve the efficiency of organic photovoltaic (OPV) cells and organic light-emitting diodes (OLED). GO was functionalized using (3-glycidyl oxypropyl)trimethoxysilane (GPTMS) and triethoxymethylsilane (MTES). The appearance of new peaks in the Fourier-transform infrared spectra of the sGOs indicates the formation of Si–O–C, Si–O–Si, Si–H, and Si–O–C moieties, which provide evidence of the addition of silane to the GO surface. Furthermore, the appearance of Si–O–Si bonds in the synchrotron radiation photoelectron spectra (SRPES) of the MTES-sGO and GPTMS-sGO samples suggests that silane groups were effectively functionalized onto the GO sheets. An OPV cell with GO layers showed a lower performance with a power conversion …

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Chemical Compositions and Mosquito Larvicidal Activities of Essential Oils from Piper Species Growing Wild in Central Vietnam

Mosquitoes are the deadliest animals on earth and are the vectors of several neglected tropical diseases. Recently, essential oils have emerged as potential renewable, cost-effective, and environmentally benign alternatives to synthetic pesticides for control of mosquitoes. In this work, thirteen species of Piper were collected from different areas of central Vietnam. The essential oils were obtained by hydrodistillation and analyzed by gas chromatography–mass spectrometry. The essential oils were screened for mosquito larvicidal activity against Aedes aegypti. Four of the Piper essential oils showed outstanding larvicidal activity against Ae. aegypti, namely P. caninum, P. longum, P. montium, and P. mutabile, with LC 50 and LC 90 values less than 10 µg/mL. Multivariate analysis has correlated concentrations of β-caryophyllene, β-bisabolene, α-pinene, and β-pinene with mosquito larvicidal activity. View Full-Text

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