Simultaneously Utilizing Excited Holes and Electrons for Piezoelectric-Enhanced Photoproduction of H2O2 from S-Scheme 2D S-Doped VOx/g-C3N4 Nanostructures.

2D/2D step-scheme (S-scheme) piezo-photocatalysts for the production of fine chemicals, such as hydrogen peroxide (H2O2), have attracted significant attention of global scientists owing to the efficiency in utilizing surface piezoelectric effects from 2D materials to overcome rapid charge recombination in photocatalytic processes. In this research, we reported the fabrication of 2D S-doped VOx deposited on 2D g-C3N4 to produce H2O2 via the piezo-photocatalytic process with high production yields at 20.19 mmol g-1 h-1, which was 1.75 and 4.87 times higher than that from solely piezo-catalytic and photocatalytic H2O2 generation. The finding pointed out that adding sulfur (S) to VOx can help to improve the catalytic outcomes by modifying the electronic properties of pristine VOx. In addition, when coupled with g-C3N4, the presence of S limits the formation of graphene in the VOx/g-C3N4 composites, causing shielding effects and pushing the cascade reactions toward water generation in the materials. Besides, the research also sheds light on the charge transport between g-C3N4 and S-VOx under irradiation and how the composites work to trigger the formation of H2O2. The presence of S in the composite systems enhances charge transfer between two semiconductors by strengthening the internal electric fields (IEF) to drive electrons moving in one direction, as demonstrated by density functional theory (DFT) calculations. Moreover, the formation of H2O2 significantly relies on the reduction of oxygen to generate oxygenic radical species at the g-C3N4 sites. Meanwhile, S-VOx provides oxidative sites in the composites to oxidize water molecules to directly or indirectly generate H2O2 or O2, which will further participate in the reactions to produce the final products. This study confirms the validation of S-scheme piezo-photocatalysts, thus encouraging further research on developing heterojunction materials with high catalytic efficiency, which can be used in practical conditions.

Exploring the Effects of Various Two-Dimensional Supporting Materials on the Water Electrolysis of Co-Mo Sulfide/Oxide Heterostructure.

In this study, various two-dimensional (2D) materials were used as supporting materials for the bimetallic Co and Mo sulfide/oxide (CMSO) heterostructure. The water electrolysis activity of CMSO supported on reduced graphene oxide (rGO), graphite carbon nitride (gC3N4), and siloxene (SiSh) was better than that of pristine CMSO. In particular, rGO-supported CMSO (CMSO@rGO) exhibited a large surface area and a low interface charge-transfer resistance, leading to a low overpotential and a Tafel slope of 259 mV (10 mA/cm2) and 85 mV/dec, respectively, with excellent long-term stability over 40 h of continuous operation in the oxygen evolution reaction.

Nano-Dimensional Carbon Nanosphere Supported Non-Precious Metal Oxide Composite: A Cathode Material for Sea Water Reduction.

Generation of hydrogen fuel at cathode during the electrolysis of seawater can be economically beneficial considering the vast availability of the electrolyte although it faces sluggishness caused by the anode reactions. In this regard a carbon nanosphere-protected CuO/Co3O4 (CCuU) composite was synthesized through heat treatment and was used as the cathode material for electrocatalytic seawater splitting. CCuU showed a significantly low overpotential of 73 mV@10 mA cm-2, Tafel slope of 58 mV dec-1 and relatively constant activity and morphology over a long time electrocatalytic study. A synergy within metal oxide centers was observed that boosted the proton-electron transfer at the active site. Moreover, the presence of carbon support increased the electroactive surface area and stability of the composite. The activity of the CCuU was studied for HER in KOH and alkaline NaCl solution to understand the activity. This work will pave the way for designing mesoporous non-precious electrocatalysts towards seawater electrocatalysis.

ZnO/Boron Nitride Quantum Dots Nanocomposites for the Enhanced Photocatalytic Degradation of Methylene Blue and Methyl Orange.

In this study, a heterostructure photocatalyst of ZnO nanoparticles decorated with boron nitride quantum dots (ZnO/BNQDs) was successfully synthesized by a simple solution procedure. The synthesized ZnO/BNQDs show that the BNQDs effectively suppress the recombination of photoinduced electrons and holes and the transfer of holes from ZnO nanoparticles by the formation of a heterojunction. The ZnO/BNQD nanocomposites thus demonstrate superior photocatalytic performances and excellent stability for the degradation of methylene blue (MB) and methyl orange (MO) under UV light irradiation. Based on the obtained results, the possible photocatalytic mechanism is proposed and discussed. Thus, the ZnO/BNQD nanocomposites demonstrate potential as an efficient low-cost photocatalyst for application in the photodegradation of organic dyes in wastewater for environmental remediation.

Enhanced Electromagnetic Interference Shielding Properties of Immiscible Polyblends with Selective Localization of Reduced Graphene Oxide Networks.

Herein, an effective technique of curing reaction-induced phase separation (CRIPS) was used to construct a reduced graphene oxide (RGO) network in the immiscible diglycidyl ether of the bisphenol A/polyetherimide (DGEBA/PEI) polyblend system. The unique chemical reduction of RGO facilitated the reduction of oxygenated groups and simultaneously appended amino groups that stimulate the curing process. The selective interfacial localization of RGO was predicted numerically by the harmonic and geometric mean technique and further confirmed by field emission transmission electron microscopy (FETEM) analysis. Due to interfacial localization, the electrical conductivity was increased to 366 S/m with 3 wt.% RGO reinforcement. The thermomechanical properties of nanocomposites were determined by dynamic mechanical analysis (DMA). The storage modulus of 3 wt.% RGO-reinforced polyblend exhibited an improvement of ~15%, and glass transition temperature (Tg) was 10.1 °C higher over neat DGEBA. Furthermore, the total shielding effectiveness (SET) was increased to 25.8 dB in the X-band region, with only 3 wt.% RGO, which represents ~99.9% shielding efficiency. These phase separation-controlled nanocomposites with selective localization of electrically conductive nanofiller at a low concentration will extend the applicability of polyblends to multifunctional structural nanocomposite applications.

Designing an intriguingly fluorescent N, B-doped carbon dots based fluorescent probe for selective detection of NO2- ions.

Low-cost nitrogen and boron-doped carbon nanodots (CPAP-CDs) with a high quantum yield (64.07%) were synthesized through a facile hydrothermal treatment. The obtained CPAP-CDs exhibited wide absorption, strong fluorescence, and pH-dependent behavior. The high fluorescence of CPAP-CDs was quenching in the presence of the nitrite ion in a concentration-dependent manner. The detection limit was as low as 6.6 nM with a wide linear detection range of 2 µM - 1 mM. Diazotization between the NO2- ion and CPAP-CDs resulted in the aggregation of CPAP-CDs and aggregation-induced emission quenching. The as-designed method was tested further with different water samples, such as tap, drinking, and seawater.

High quantum yield aminophenylboronic acid-functionalized N-doped carbon dots for highly selective hypochlorite ion detection.

High quantum yield 3-aminophenylboronic acid-functionalized nitrogen-doped carbon dots (GAAP-CDs) were fabricated using a simple hydrothermal route and used as a sensing probe for toxic hypochlorite (ClO-). The as-synthesized GAAP-CDs showed absorption peaks at 252, 297, and 370 nm and an emission peak at 375 nm with an excitation wavelength of 310 nm. The quantum yield of GAAP-CDs reached 58.28%, with no noticeable fluorescence change observed under high ionic strength conditions and a three-month long-term test. GAAP-CDs-based ClO- sensing was carried out by UV-vis absorbance and fluorescence spectroscopy; the detection limit was as low as 0.77 µM (linear range of 0-100 µM), and 0.50 µM (linear range of 0.1-100 µM), respectively. In addition, the as-synthesized GAAP-CDs showed excellent selectivity towards ClO- ions in the presence of various interfering chemicals. The satisfactory results from the proposed method of ClO- detection in tap water and drinking water samples, suggesting promising application of GAAP-CDs for ClO- detection.

Simple paper-based colorimetric and fluorescent glucose sensor using N-doped carbon dots and metal oxide hybrid structures.

A new strategy for the fluorescent and colorimetric sensing of hydrogen peroxide (H2O2) and glucose based on the metal oxide - carbon-dot hybrid structure was investigated. The sensing system is related to the catalytic oxidation reaction of glucose-by-glucose oxidase (GOx) to H2O2. In this study, a metal oxide hybrid with nitrogen-doped carbon dots (MFNCDs) that showed intrinsic peroxidase-like activity was synthesized and used as a catalyst instead of GOx to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to blue-emitting oxidized TMB (oxTMB) in the presence of hydrogen peroxide (H2O2). The fluorescence of MFNCDs/TMB at 405 nm was quenched in the presence of H2O2 through the inner filter effect (IFE) and electron transfer within MFNCDs, oxTMB, and glucose system. Therefore, the fluorescence and absorbance intensity can be applied to the quantitative determination of the concentration of H2O2 and glucose with a wide linear range. The detection limit for H2O2 and glucose based on the colorimetric method were as low as 84 nM and 0.41 µM, respectively. In contrast, the detection limit for H2O2 and glucose based on the fluorescent method were as low as 97 nM and 0.85 µM, respectively. Furthermore, the colorimetric readout on the paper device based on the changing color of the solution could also be integrated with a smartphone platform to conduct the on-site analysis of glucose without the use of the spectrometer. In addition, this dual sensor can be applied to detect glucose in real serum with highly accurate results, making it a good candidate for biosensor applications.

Construction and Mechanism Analysis of a Self-Assembled Conductive Network in DGEBA/PEI/HRGO Nanocomposites by Controlling Filler Selective Localization.

Herein, a feasible and effective approach is developed to build an electrically conductive and double percolation network-like structure via the incorporation of highly reduced graphene oxide (HRGO) into a polymer blend of diglycidyl ether of bisphenol A/polyetherimide (DGEBA/PEI). With the assistance of the curing reaction-induced phase separation (CRIPS) technique, an interconnected network of HRGO is formed in the phase-separated structure of the DGEBA/PEI polymer blend due to selective localization behavior. In this study, HRGO was prepared from a unique chemical reduction technique. The DGEBA/PEI/HRGO nanocomposite was analyzed in terms of phase structure by content of PEI and low weight fractions of HRGO (0.5 wt.%). The HRGO delivered a high electrical conductivity in DGEBA/PEI polyblends, wherein the value increased from 5.03 × 10-16 S/m to 5.88 S/m at a low content of HRGO (0.5 wt.%). Furthermore, the HRGO accelerated the curing reaction process of CRIPS due to its amino group. Finally, dynamic mechanical analyses (DMA) were performed to understand the CRIPS phenomenon and selective localization of HRGO reinforcement. The storage modulus increased monotonically from 1536 MPa to 1660 MPa for the 25 phr (parts per hundred in the DGEBA) PEI polyblend and reached 1915 MPa with 0.5 wt.% HRGO reinforcement. These simultaneous improvements in electrical conductivity and dynamic mechanical properties clearly demonstrate the potential of this conductive polyblend for various engineering applications.

Multicolor Emitting N-Doped Carbon Dots Derived from Ascorbic Acid and Phenylenediamine Precursors.

In this research, we report the green, blue, and orange color emitting N-doped carbon dots (CDs), which are being synthesized from ascorbic acid and o-/m-/p-phenylenediamine (o-PDA, m-PDA, and p-PDA, respectively). The effects of the solvent polarity and solution pH on the PL emission properties of the as-synthesized CDs have been systematically investigated. It has been observed that the PL emission of the as-synthesized CDs decreases with the increase in solvent polarity due to the greater agglomeration. The surface charge of CDs also shows prominent effects on the pH-dependent PL emission properties.

Uncovering the actual inner-filter effect between highly efficient carbon dots and nitroaromatics.

High performance sensors can be produced by adequately designing the chemical structure and uncovering the actual detection mechanism. In this study, a fluorescent probe was synthesized for various nitroaromatic molecules, including stereochemically varied nitrophenols and nitroaniline. A systematic investigation of the influence of various analytes on the luminescence behavior of the as-synthesized carbon dot (CDs) revealed the inner-filter effect to be the major detection mechanism. The extinction coefficient and spectral overlap were found to be the critical parameters for high sensitivity and good selectivity rather than the functional groups of the CDs and analytes.

ZnO-Associated Carbon Dot-Based Fluorescent Assay for Sensitive and Selective Dopamine Detection.

This paper presents a simple and highly efficient method for dopamine detection using water-soluble carbon dot nanoparticles. The ZnO-associated carbon dots (CDZs) were synthesized using a green chemical strategy. An examination of the effects of biomolecules on the fluorescence of CDZs revealed selective dopamine-induced quenching. In a phosphate buffer (pH = 7.4) medium, a detection limit of 1.06 nM was obtained. This "turn off" phenomenon was attributed to the electronic interaction between CDZs and dopamine, during the oxidation of dopamine. At lower pH, however, the effects of dopamine on the fluorescence of CDZs were insignificant as the oxidation of dopamine was hindered when the proton concentration was increased. This method was found to be free from the interference of coexisting molecules, that is, ascorbic acid and uric acid. This sensing platform was applied successfully in biological fluids to confirm the practical significance of the as-designed sensor.

Effect of GO Additive in ZnO/rGO Nanocomposites with Enhanced Photosensitivity and Photocatalytic Activity.

Zinc oxide/reduced graphene oxide nanocomposites (ZnO/rGO) are synthesized via a simple one-pot solvothermal technique. The nanoparticle-nanorod turnability was achieved with the increase in GO additive, which was necessary to control the defect formation. The optimal defect in ZnO/rGO not only increased ZnO/rGO surface and carrier concentration, but also provided the alternative carrier pathway assisted with rGO sheet for electron-hole separation and prolonging carrier recombination. These properties are ideal for photodetection and photocatalytic applications. For photosensing properties, ZnO/rGO shows the improvement of photosensitivity compared with pristine ZnO from 1.51 (ZnO) to 3.94 (ZnO/rGO (20%)). Additionally, applying bending strain on ZnO/rGO enhances its photosensitivity even further, as high as 124% at r = 12.5 mm, due to improved surface area and induced negative piezoelectric charge from piezoelectric effect. Moreover, the photocatalytic activity with methylene blue (MB) was studied. It was observed that the rate of MB degradation was higher in presence of ZnO/rGO than pristine ZnO. Therefore, ZnO/rGO became a promising materials for different applications.

Blue emitting nitrogen-doped carbon dots as a fluorescent probe for nitrite ion sensing and cell-imaging.

This study examined the efficiency of pH-dependent, fluorescent carbon dots for the sensing of hazardous anions in aqueous media and cell imaging. The nitrite anion, an important water-soluble element for environmental and biological systems, requires continuous monitoring because a high concentration can affect the systems severely. The as-synthesized carbon dots efficiently detected the nitrite anion in aqueous solution through a fluorescent 'Turn Off' phenomenon. The quenching mechanism was investigated through proper microscopic and spectroscopic studies. The limit of detection and linear detection range were 7.9 nM and 2.3µM-7.7 mM, respectively. The sensitivity was tested with different water samples. In a parallel experiment, the as-synthesized carbon dots were used as a cell-imaging probe for HeLa cells, highlighting their potential in different biological studies.

Reshaping of triangular silver nanoplates by a non-halide etchant and its application in melamine sensing.

Although triangular silver (Ag) nanoplates are intrinsically unstable, this characteristic has been taken advantage of in the development of a novel sensing platform. However, most of these applications have relied on halide ions as etchants. In the current work, we used sodium 4-vinylbenzenesulfonate (Na-VBS) as a new powerful etchant of triangular silver (Ag) nanoplates. When aged with Na-VBS at room temperature, Na-VBS etched Ag nanoplates nearly as powerfully as halides did, and these nanoplates rapidly transformed into oblate nanospheroids. This shape evolution permitted tuning of the corresponding localized surface plasmon resonance (LSPR) features of the Ag nanostructures. Interestingly, passivation of the Ag nanoplate surface with melamine was shown to protect the nanoplates from Na-VBS-induced etching. The rate of change of the color and spectral features of the Ag nanoplate solution exposed to Na-VBS was found to be strongly correlated with the concentration of melamine in the solution. This association allowed us to apply this system to the development of a novel platform for sensing melamine.

NiMn2O4 spinel binary nanostructure decorated on three-dimensional reduced graphene oxide hydrogel for bifunctional materials in non-enzymatic glucose sensor.

Nickel-manganese spinel oxide (NiMn2O4) was hybridized with reduced graphene oxide hydrogel (rGOH) via a facile solvothermal process and a highly porous three-dimensional (3D) structure was constructed. NiMn2O4/rGOH exhibited excellent electrochemical performance due to the high specific surface area, excellent electrocatalytic activity, and enhanced electrical conductivity due to the synergetic effects between the two components. The NiMn2O4/rGOH exhibited excellent glucose sensing performance with high sensitivity (1310.8 µA mM-1 cm-2), a wide linear range (2 µM-20 mM), rapid response time (<3.5 s), and anti-interference properties. Furthermore, it also showed excellent supercapacitor performance with a high capacitance (396.85 F g-1) and excellent energy and power density on account of the large surface area and pseudo-capacitor behavior of NiMn2O4. A self-powered glucose sensor can be fabricated with NiMn2O4/rGOH as both supercapacitor and glucose sensing electrodes.

Highly enhanced visible light water splitting of CdS by green to blue upconversion.

This paper reports a new class of visible light water splitting photocatalysts based on a triplet-triplet annihilation (TTA) upconversion (UC) process. The TTA-UC core composed of platinum-octaethyl-porphyrin (Pt(OEP)) and 9,10-diphenylanthracene (DPA) can upconvert low energy green light to high energy blue light with a high quantum yield. Using a silica nanocapsule (SNC), the quenching caused by oxygen can be avoided, even in aqueous solutions. The enhancement factor of the photocatalytic activity induced by the UC was estimated to be approximately 3, which indicates that the green to blue UC by the encapsulated Pt(OEP)/DPA can enhance the water splitting activity of CdS significantly. The reduced graphene oxide (rGO) attached to the CdS photocatalyst further enhances the water splitting activity via effective charge separation and suppressed recombination.

Three-Dimensional Porous Nitrogen-Doped NiO Nanostructures as Highly Sensitive NO2 Sensors.

Nickel oxide has been widely used in chemical sensing applications, because it has an excellent p-type semiconducting property with high chemical stability. Here, we present a novel technique of fabricating three-dimensional porous nitrogen-doped nickel oxide nanosheets as a highly sensitive NO2 sensor. The elaborate nanostructure was prepared by a simple and effective hydrothermal synthesis method. Subsequently, nitrogen doping was achieved by thermal treatment with ammonia gas. When the p-type dopant, i.e., nitrogen atoms, was introduced in the three-dimensional nanostructures, the nickel-oxide-nanosheet-based sensor showed considerable NO2 sensing ability with two-fold higher responsivity and sensitivity compared to non-doped nickel-oxide-based sensors.

Durability Improvement of Pt/RGO Catalysts for PEMFC by Low-Temperature Self-Catalyzed Reduction.

Pt/C catalyst used for polymer electrolyte membrane fuel cells (PEMFCs) displays excellent initial performance, but it does not last long because of the lack of durability. In this study, a Pt/reduced graphene oxide (RGO) catalyst was synthesized by the polyol method using ethylene glycol (EG) as the reducing agent, and then low-temperature hydrogen bubbling (LTHB) treatment was introduced to enhance the durability of the Pt/RGO catalyst. The cyclic voltammetry (CV), oxygen reduction reaction (ORR) analysis, and transmittance electron microscopy (TEM) results suggested that the loss of the oxygen functional groups, because of the hydrogen spillover and self-catalyzed dehydration reaction during LTHB, reduced the carbon corrosion and Pt agglomeration and thus enhanced the durability of the electrocatalyst.

Surfactant-treated graphene covered polyaniline nanowires for supercapacitor electrode.

Surfactant-treated graphene/polyaniline (G/PANI) nanocomposites were prepared by the MnO2 template-aided oxidative polymerization of aniline (ANI) on the surfactant-treated graphene sheets. The electrochemical performances of the G/PANI nanocomposites in a three-electrode system using an aqueous sulfuric acid as an electrolyte exhibited a specific capacitance of 436 F g(-1) at 1 A g(-1), which is much higher than the specific capacitance of pure PANI (367 F g(-1)). Such a higher specific capacitance of the G/PANI nanocomposite inferred an excellent synergistic effect of respective pseudocapacitance and electrical double-layer capacitance of PANI and graphene.