Effect of Oxyfluorination of PFA-Coated Metal Mesh with Superhydrophobic Properties on the Filtration Performance of SiO2 Microparticles.

Recently, semiconductor wastewater treatment has received much attention due to the emergence of environmental issues. Acid-resistant coatings are essential for metal prefilters used in semiconductor wastewater treatment. Perfluoroalkoxy alkane is mainly used as an acid-resistant coating agent, since PFA has inherent superhydrophobicity, water permeability is lowered. To solve this problem, the surface of the PFA-coated metal mesh was treated via an oxyfluorination method in which an injected mixed gas of fluorine and oxygen reacted with the surface functional groups. Surface analysis, water contact angle measurement, and water permeability tests were performed on the surface-treated PFA-coated mesh. Consequently, the superhydrophobic surface was effectively converted to a hydrophobic surface as the PFA coating layer was surface-modified with C-O-OH functional groups via the oxyfluorination reaction. As a result of using simulation solutions that float silica particles of various sizes, the permeability and particle removal rate of the surface-modified PFA-coated stainless-steel mesh were improved compared to those before surface modification. Therefore, the oxyfluorination treatment used in this study was suitable for improving the filtration performance of SiO2 microparticles in the PFA-coated stainless-steel mesh.

Correlation of EDLC Capacitance with Physical Properties of Polyethylene Terephthalate Added Pitch-Based Activated Carbon.

The electric double-layer capacitor (EDLC) has attracted attention by using activated carbon (AC) as an active electrode material with a high power density and high cost-efficiency in industrial applications. The EDLC has been actively developed over the past decade to improve the power density and capacitance. Extensive studies on EDLCs have been conducted to investigate the relation of EDLC capacitance to the physical properties of AC, such as the specific surface area, pore type and size, and electrical conductivity. In this study, EDLC was fabricated with AC, and its capacitance was evaluated with the physical properties of AC. The AC was prepared using petroleum-based pitch synthesized using pyrolysis fuel oil (PFO) with polyethylene terephthalate (PET). The AC based on PFO and PET (PPAC) exhibited high specific surface area and low micropore fraction compared to the PFO-based AC without PET addition (PAC). Furthermore, the reduction of the EDLC capacitance of PPAC was smaller than that of PAC, as the scan rate was increased from 5 to 100 mV s-1. It was determined that the minor reduction of capacitance with an increase in the scan rate resulted from the development of 4 nm-sized mesopores in PPAC. In addition, a comprehensive correlation of EDLC capacitance with various physical properties of ACs, such as specific surface area, pore characteristics, and electrical conductivity, was established. Finally, the optimal properties of AC were thereupon derived to improve the EDLC capacitance.

Ultrathin rGO-wrapped free-standing bimetallic CoNi2S4-carbon nanofibers: an efficient and robust bifunctional electrocatalyst for water splitting.

Electrochemical water splitting represents an ideal strategy for producing clean hydrogen as an energy carrier that serves as an alternative to fossil fuels. As an effective method for hydrogen production, an efficient inexpensive multifunctional electrocatalyst with high durability is designed. Herein, we describe the heterostructural design of a three-dimensional catalytic network with self-embedded CoNi2S4 nanograins grown on electrospun carbon nanofibers (CoNi2S4-CNFs) with anchored thin-layer reduced graphene oxide. This is achieved via facile electrospinning followed by carbonization, low-temperature sulfidation, and surface functionalization. As a bifunctional catalyst, CoNi2S4-CNFs exhibited robust high activity toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline medium. The anchored ultrathin graphene oxide layer promoted the stability and durability of the catalytic network with an efficient path for the transportation of electrons. The rGO-anchored CoNi2S4-CNFs yielded overpotential values of 228 mV and 205 mV for the HER and OER, respectively, that drives a current density of 20 mA cm-2 in an alkaline medium. Notably, the excellent electrochemical properties are attributed to the functional effect of the CoNi2S4 on the CNF network. The ultrathin feature of rGO improved the durability of the catalytic network. Moreover, using the rGO-anchored CoNi2S4-CNFs as a cathode and anode in a two-electrode water splitting system required a cell voltage of only 1.55 V to reach a current density of 10 mA cm-2. These CNFs exhibited outstanding durability for 48 h. The present work offers new insight for the design of a catalytic network with a non-noble metal catalyst that exhibits excellent electrocatalytic activity and durability on the metal sulfides in overall water splitting.

Droplet-Based Microfluidic Reactor for Synthesis of Size-Controlled CdSe Quantum Dots.

CdSe quantum dots (QDs) with a uniform size distribution were synthesized using a droplet-based microfluidic reactor. The droplet-based microfluidic reactor enabled continuous production of CdSe QDs at a temperature of less than 250 °C in an extremely shorter reaction time (less than 30 s) when compared with the batch reactor. The photoluminescence (PL) and ultraviolet (UV) absorption spectra of the CdSe QDs were recorded at different reaction times and the size and optical properties of the QDs were discussed. The structure morphology and elemental composition of the CdSe QDs were determined using a transmission electron microscopy (TEM) and electrondispersive spectroscopy (EDS). The size of CdSe QDs prepared using the microfluidic reactor was estimated to be from 1.6 to 2.6 nm with an average size of 2.2 nm. This droplet-based microfluidic reactor has the potential to be automated system continuous synthesis of CdSe QDs.

Variation in the c-axis conductivity of multi-layer graphene due to H2 exposure.

The variation of the c-axis conductivity of a multilayer graphene (MLG) as a function of H2 pressure from vacuum to 20 bar has been investigated. MLG was connected to the electrodes vertically using a wet transfer process. After exposure to H2 gas pressure up to 20 bar, the chemisorption of dissociated atomic hydrogen on MLG affects its electrical and structural properties. The formation of C-H bonds causes a decoupling of graphene layers, and then interferes with charge transfer through the out of plane. As a result, the c-axis conductivity decreases. Furthermore, the electron doping effect and the decoupling of the layers were confirmed using Raman spectroscopy. Hydrogenated carbons induce a defect structure of MLG which results in the expansion of layers. We observed a 43.54% increase in the thickness of the MLG after H2 exposure using atomic force microscopy.

Bioreceptor-free, sensitive and rapid electrochemical detection of patulin fungal toxin, using a reduced graphene oxide@SnO2 nanocomposite.

In this research, we successfully synthesized a reduced graphene oxide/tin oxide (rGO/SnO2) composite for the electrochemical detection of fungal contaminant, patulin (PAT) that does not require a biological or chemical receptor or specific antibodies. The resulting rGO/SnO2 composite exhibited promising electrochemical properties and demonstrated outstanding performance in the direct measurement of PAT levels in contaminated apple juice samples. The differential pulse voltammetric response of the rGO/SnO2 composite electrode exhibited a linear relationship with PAT concentration in the 50-600 nM range and had a lower detection limit of 0.6635 nM. The sensor electrode exhibited high sensitivity, reliable reproducibility, and good selectivity. The designed electrochemical sensor was also tested against the time-consuming and conventional high-performance liquid chromatography (HPLC) approach for the detection of PAT in spiked apple juice samples. We found that the electrochemical sensor had ability to rapidly detect PAT in apple juice samples without the need of extraction or clean-up steps and achieved a higher recovery rate (74.33 ± 0.70 to 99.26 ± 0.70%) within a short-time analysis than did by the HPLC (61.97 ± 1.78 to 84.31 ± 1.96%), thus illustrating its feasibility for use in agricultural and food safety industries.

Electroactive Ultra-Thin rGO-Enriched FeMoO4 Nanotubes and MnO2 Nanorods as Electrodes for High-Performance All-Solid-State Asymmetric Supercapacitors.

A flexible asymmetric supercapacitor (ASC) with high electrochemical performance was constructed using reduced graphene oxide (rGO)-wrapped redox-active metal oxide-based negative and positive electrodes. Thin layered rGO functionality on the positive and the negative electrode surfaces has promoted the feasible surface-active sites and enhances the electrochemical response with a wide operating voltage window. Herein we report the controlled growth of rGO-wrapped tubular FeMoO4 nanofibers (NFs) via electrospinning followed by surface functionalization as a negative electrode. The tubular structure offers the ultrathin-layer decoration of rGO inside and outside of the tubular walls with uniform wrapping. The rGO-wrapped tubular FeMoO4 NF electrode exhibited a high specific capacitance of 135.2 F g-1 in Na2SO4 neutral electrolyte with an excellent rate capability and cycling stability (96.45% in 5000 cycles) at high current density. Meanwhile, the hydrothermally synthesized binder-free rGO/MnO2 nanorods on carbon cloth (rGO-MnO2@CC) were selected as cathode materials due to their high capacitance and high conductivity. Moreover, the ASC device was fabricated using rGO-wrapped FeMoO4 on carbon cloth (rGO-FeMoO4@CC) as the negative electrode and rGO-MnO2@CC as the positive electrode (rGO-FeMoO4@CC/rGO-MnO2@CC). The rationally designed ASC device delivered an excellent energy density of 38.8 W h kg-1 with a wide operating voltage window of 0.0-1.8 V. The hybrid ASC showed excellent cycling stability of 93.37% capacitance retention for 5000 cycles. Thus, the developed rGO-wrapped FeMoO4 nanotubes and MnO2 nanorods are promising hybrid electrode materials for the development of wide-potential ASCs with high energy and power density.

N,P-Doped Carbon Nanodots for Food-Matrix Decontamination, Anticancer Potential, and Cellular Bio-Imaging Applications.

We report a facile one-step thermal treatment method for the synthesis of biocompatible, fluorescent nitrogen-phosphorus-doped carbon nanodots (NPCDs) as multifunctional agents for the food matrix decontamination, cancer targeting, and cellular bio-imaging. NPCDs exhibit high toxicity towards L. monocytogenes, as illustrated by fluorescent live-dead cell counting, disruption of membrane permeability/potential, changes in the levels of cellular ions, genetic materials, and proteins, as well as intracellular production of reactive oxygen species. The tryptophan and protein peaks released in NPCDs treated cells contributed to indole ring breathing and correlated with induced cell death. NPCDs significantly inhibited bacterial biofilm formation on a solid substrate. NPCDs-coated low-density polyethylene (LDPE) film crosslinked with 1% aminopropyltriethoxy silane (APTES) via silane-hydroxyl linking as a food-grade wrap significantly reduced bacterial counts in a raw chicken food model. Furthermore, NPCDs induced apoptosis in HeLa cervical cancer cells, as confirmed by the distorted cell morphology, fluorescence microscopic analysis, presence of fragmented nuclei and the qPCR results of mRNA expression levels of apoptotic markers. Moreover, NPCDs were also applicable in utilized for the cellular bio-imaging of KM12-C colon cancer cells under confocal microscopy owing to their excellent luminescence properties. Overall, NPCDs represent a promising platform to reduce the environmental health risks associated with hazardous pathogens, anticancer targeting, and their application in cellular bio-imaging as multifunctional targets/nanocarriers.

The facile and simple synthesis of poly(3,4ethylenedioxythiophene) anchored reduced graphene oxide nanocomposite for biochemical analysis.

In this article, we demonstrate the potentiostatic electrodeposition of poly(3,4-ethylenedioxythiophene) (PEDOT) on reduced graphene oxide (RGO) to develop a nanocomposite-modified electrode that separates three coexisting biofluids - ascorbic acid (AA), dopamine (DA), and uric acid (UA) - in a 0.1 M Phosphate buffer solution at a physiological pH (7.4). The texture, physicochemical properties, and electrochemical behavior of the PEDOT-RGO were explored using UV-visible spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, electron microscopic techniques, and electrochemical impedance spectroscopy (EIS). A PEDOT-RGO/GCE was evaluated with respect to a bare GCE, RGO/GCE, and PEDOT/GCE for the simultaneous sensing of AA, DA, and UA. The difference in voltammetric peak potentials was about 180 mV between AA and DA and 120 mV between DA and UA. The differential pulse voltammetric sensor provided a linear calibration for a wide concentration range (0.1-907 µM for AA, 0.1-901 µM for DA, and 0.1-701 µM for UA) with detection limits of 1.5 µM, 0.6 µM, and 0.2 µM for AA, DA, and UA, respectively. The developed sensor was validated by the detection of AA, DA, and UA in a vitamin C tablet, a dopamine hydrochloride injection, and human serum samples.

On-site detection of sub-mg/kg melamine mixed in powdered infant formula and chocolate using sharp-edged gold nanostar substrates.

We report a facile method for sample preparation and sensitive on-site detection of melamine in powdered infant formula and chocolate using Raman spectroscopy on sharp-edged gold nanostars (AuNSs). The aggregation of AuNSs by sodium chloride (1.2 M) facilitates the more sensitive detection of melamine in comparison with spherical gold nanoparticles (AuNPs). Density functional theory quantum mechanical calculations were performed to determine the energetic stability on gold cluster atoms. Our spectroscopic data indicated that AuNSs are an efficient platform for detecting melamine in food mixtures. The detection limits of melamine in powdered infant formula and chocolate were found to be ~0.1 mg/kg and ~1 mg/kg, respectively, on AuNPs, whereas they were observed to be ~0.01 mg/kg and ~0.1 mg/kg, respectively, on AuNSs. Using a handheld Raman spectrometer, a sub-mg/kg detection of melamine in both powdered infant formula and chocolate could be achieved within a few minutes.

Fabrication of Palladium Nanoparticles on Porous Aromatic Frameworks as a Sensing Platform to Detect Vanillin.

Here, we report the fabrication of palladium nanoparticles on porous aromatic frameworks (Pd/PAF-6) using a facile chemical approach, which was characterized by various spectro- and electrochemical techniques. The differential pulse voltammetry (DPV) response of Pd/PAF-6 toward the vanillin (VA) sensor shows a linear relationship over concentrations (10-820 pM) and a low detection limit (2 pM). Pd/PAF-6 also exhibited good anti-interference performance toward 2-fold excess of ascorbic acid, nitrophenol, glutathione, glucose, uric acid, dopamine, ascorbic acid, 4-nitrophenol, glutathione, glucose, uric acid, dopamine, and 100-fold excess of Na(+), Mg(2+), and K(+) during the detection of VA. The developed electrochemical sensor based on Pd/PAF-6 had good reproducibility, as well as high selectivity and stability. The established sensor revealed that Pd/PAF-6 could be used to detect VA in biscuit and ice cream samples with satisfactory results.

Fabrication of 3D honeycomb-like porous polyurethane-functionalized reduced graphene oxide for detection of dopamine.

A three dimensional reduced graphene oxide/polyurethane (RGO-PU) porous material with connected pores was prepared by physical adsorption of RGO onto the surface of porous PU. The porous PU was prepared by directional melt crystallization of a solvent, which produced high pores with controlled orientation. The prepared RGO-PU was characterized by scanning electron microscopy, spectroscopy and electro-chemical methods. The RGO-PU porous material revealed better electrochemical performance, which might be attributed to the robust structure, superior conductivity, large surface area, and good flexibility. Differential pulse voltammetry (DPV) analysis of DA using the RGO-PU exhibited a linear response range over a wide DA concentration of 100-1150pM, with the detection limit of 1pM. This sensor exhibited outstanding anti-interference ability towards co-existing molecules with good stability, sensitivity, and reproducibility. Furthermore, the fabricated sensor was successfully applied for the quantitative analysis of DA in human serum and urine samples with acceptable recovery, which indicates its feasibility for practical application.

Electrodeposition of flower-like nickel oxide on CVD-grown graphene to develop an electrochemical non-enzymatic biosensor.

We demonstrated a non-enzymatic cholesterol sensor based on a nickel oxide (NiO) and high quality graphene composite for the first time. Graphene was grown by a chemical vapor deposition technique (CVD). The nanocomposite was fabricated through the electrodeposition of nickel hydroxide onto the surface of the CVD-grown graphene, which was followed by thermal annealing. The successful formation of the NiO/graphene composite was confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The deposition of flower-like NiO onto the graphene surface was confirmed by scanning electron microscopy. Electrochemical analyses were conducted to investigate the characteristics of the sensor during the detection of cholesterol. The sensor showed a high sensitivity of 40.6 mA µM-1 cm-2, a rapid response time of 5 s, and a low detection of limit of 0.13 µM. We also investigated the effects of common interfering substances on the ability of the sensor to detect cholesterol. Furthermore, we successfully determined the cholesterol in a milk sample using the developed sensor. The composite electrode exhibited excellent detection of cholesterol with good reproducibility and long-term stability owing to the combined effects of NiO and graphene.

Immobilization of myoglobin on Au nanoparticle-decorated carbon nanotube/polytyramine composite as a mediator-free H2O2 and nitrite biosensor.

A novel composite film was designed for use as a highly selective mediator-free amperometric biosensor, and a method was created for accomplishing direct electrochemistry of myoglobin on a multi-walled carbon nanotube and tyramine-modified composite decorated with Au nanoparticles on a glassy carbon electrode. The ultraviolet-visible and electrochemical impedance spectroscopy results showed that myoglobin retained its native conformation in the interaction with Au-PTy-f-MWCNT. The surface coverage of Mb-heme-Fe((II)/(III)) immobilized on Au-PTy-f-MWCNT and the heterogeneous electron-transfer rate constant were 2.12 × 10(-9) mol cm(-2) and 4.86 s(-1), respectively, indicating a higher loading capacity of the nanocomposite for direct electron transfer of Mb onto the electrode surface. The proposed Mb/Au-PTy-f-MWCNT biofilm exhibited excellent electrocatalytic behavior toward the reduction of H2O2 and the oxidation of nitrite with linear ranges of 2 to 5000 µM and 1 to 8000 µM and lower detection limits of 0.01 µM and 0.002 µM, respectively. An apparent Michaelis-Menten constant of 0.12 mM indicated that the Mb immobilized on the Au-PTy-f-MWCNT film retained its native activity. This biosensor can be successfully applied to detect H2O2 and nitrite in disinfectant cream, eye drops, pickle juice, and milk samples.