Electron reduction for the preparation of rGO with high electrochemical activity

Molecularly imprinted electrochemical sensor based on CoNi-MOF/RGO nanocomposites for sensitive detection of the hippuric acid

Toluene, a volatile organic compound, may have adverse effects on the nervous and digestive system when inhaled over an extended period. The assessment of environmental toluene exposure can be effectively conducted by detecting hippuric acid (HA), a toluene metabolite. In this investigation, a molecularly imprinted electrochemical sensor was developed for HA detection, utilizing the synergistic effects of reduced graphene oxide (RGO) and a bimetallic organic skeleton known as CoNi-MOF. Initially, graphene oxide (GO) was synthesized using a modified Hummers' method, and RGO with better conductivity was achieved through reduction with ascorbic acid (AA). Subsequently, CoNi-MOF was introduced to enhance the material's electron transport capabilities further. The molecularly imprinted membrane was then prepared via electropolymerization to enable selective HA recognition. Under optimal conditions, the synthesized sensor exhibited accurate HA detection within a concentration range of 2-800 nM, with a detection limit of 0.97 nM. The sensor's selectivity was assessed using a selectivity coefficient, yielding an imprinting factor of 6.53. The method was successfully applied to the quantification of HA in urine, demonstrating a favorable recovery rate of 93.4%-103.9%. In conclusion, this study presents a practical platform for the detection of human metabolite detection.

Realizing Highly-Ordered Laser-Reduced Graphene for High-Performance Flexible Microsupercapacitor

Laser reduction of graphene oxide (GO) with direct-write technology is promising to develop miniaturized energy storage devices because of highly flexible, mask-free, and chemical-free merits. However, laser reduction of GO is often accompanied with deflagration (spectacular and violent deoxygenating reaction), leading reduced graphene oxide (rGO) films into brittle and irregular internal structure which is harmful to the applications. Here, a pre-reduction strategy is demonstrated to avoid this deflagration and realize a uniform laser-reduced GO (LrGO) matrix for the application of flexible micro-supercapacitors (MSCs).The pre-reduction process with ascorbic acid decreases the content of oxygen-containing functional groups on GO in advance, and thus relieves gases emission and avoids unconstrained expansion during the laser reduction process. In addition, a self-assembled skeleton with pre-reduced GO (PGO) nanosheets could be constructed which is a more appropriate aforehand framework for laser reduction to establish controllable rGO films with the homogenous porosity. The quasi-solid-state MSCs assembled with laser-reduced PGO exhibit the maximum areal capacitance of 88.32 mF cm-2 , good cycling performance (capacitance retention of 82% after 2000 cycles), and outstanding flexibility (no capacitance degradation after bending for 5000 times). This finding provides opportunities to enhance quality of LrGO which is promising for micro-power devices and beyond.

Flower-like WSe2 used as bio-matrix in ultrasensitive label-free electrochemical immunosensor for human immunoglobulin G determination

The abnormal concentrations of human immunoglobulin G (hIgG) refers to many kinds of diseases. Analytical methods with the characteristics of rapid response, easy operation and high sensitivity should be designed to accurately determinate the hIgG levels in human serum. In this work, a label-free electrochemical immunosensor based on WSe₂/rGO was developed to sensitively detect human immunoglobulin G. First, the flower-like transition metal dichalcogenides (TMDCs) Tungsten Diselenide (WSe₂) with large effective specific surface area and porous structure was synthesized by hydrothermal synthesis. As a bio-matrix, the flower-like WSe₂ efficiently increased the active sites for loading antibodies. Meanwhile, reduced graphene oxide (rGO) obtained by tannic acid reduction was used to improve the current response of the sensing interface. WSe₂ was combined with rGO and the electrochemical active surface area (ECSA) of the sensing interface was enlarged to 2.1 times that of GCE. Finally, the combination of flower-like WSe₂ and rGO broadened the detection range and reduced the detection limit of the sensing platform. The immunosensor exhibited a high sensitivity with a wide linear range of 0.01-1000 ng/mL and low detection limit of 4.72 pg/mL. The real sample analysis of hIgG were conducted under optimal conditions, and the spiked recovery rates were between 95.5 and 104.1%. Moreover, satisfactory results were obtained by testing the stability, specificity and reproducibility of the immunosensor. Therefore, it can be concluded that the as-proposed immunosensor has the application potential of clinical analyze of hIgG in human serum.

Electrosynthesis of electrochemically reduced graphene oxide/polyaniline nanowire/silver nanoflower nanocomposite for development of a highly sensitive electrochemical DNA sensor

A novel nanostructured electrode material based on electrochemically reduced graphene oxide/polyaniline nanowires/silver nanoflowers (ERGO/PANi NWs/AgNFs) was fabricated site-specifically onto a Pt microelectrode (0.80 mm² area) using a three-step electrochemical procedure: electrosynthesis of ERGO, electropolymerization of PANi NWs, and electrodeposition of AgNFs. Synergistic and complementary properties of ERGO, PANi NWs and AgNFs, including high electrochemical activity, large surface area, and high biocompatibility, were obtained. Besides, the electrosynthesis method allowed the direct formation of the desired nanomaterial onto the Pt microelectrode, so the adhesion between the sandwich-structured nanocomposite and the electrode surface was also improved. The optimized ERGO/PANi NWs/AgNFs nanocomposite was used for the first time to develop an electrochemical DNA sensor. As a result, the DNA probe immobilization was facilitated and the electrochemical signals of the DNA sensor were enhanced. The detection limit of the DNA sensor was 2.70 × 10⁻¹⁵ M. Moreover, potential miniaturization for fabrication of a lab-on-a-chip system, direct detection, high sensitivity, and good specificity are the advantages of the fabricated DNA sensor.

A novel nanostructured material based on ERGO/PANi NWs/AgNFs was electrosynthesized on a Pt microelectrode and was used for the first time to develop an electrochemical DNA sensor.

Applications of Plasma-Assisted Systems for Advanced Electrode Material Synthesis and Modification

Research on advanced electrode materials (AEMs) has been explosive for the past decades and constantly promotes the development of batteries, supercapacitors, electrocatalysis, and photovoltaic applications. However, traditional preparation and modification methods can no longer meet the increasing requirements of some AEMs because some of the special reactions are thermodynamically and/or kinetically unfavorable and thus need harsh conditions. Among various recently developed advanced materials synthesis and modification routes, the plasma-assisted (PA) method has received increasing attention because of its unique and different "species reactivity" nature, as well as its wider and adjustable operating conditions. In this Spotlight on Applications, we highlight some recent developments and describe our recent progress by applying PA systems in the synthesis and modification of AEMs, including direct processing, PA deposition, and plasma milling (P-milling). The mechanisms of how plasma works for specific reactions are reviewed and discussed. It is shown that the PA technique has become a powerful and efficient tool in the following areas, including but not limited to materials synthesis, doping, surface modification, and functionalization. Finally, the prospect and challenges are also proposed for AEM preparation and modification using PA systems. This article aims to provide up-to-date information about the progress of PA technology in the fields of chemistry and materials science.

Electron-assisted synthesis of g-C3N4/MoS2 composite with dual defects for enhanced visible-light-driven photocatalysis

g-C3N4/MoS2 composites were successfully prepared by an electron-assisted strategy in one step. Dielectric barrier discharge (DBD) plasma as an electron source, which has low bulk temperature and high electron energy, can etch and modify the surface of g-C3N4/MoS2. The abundant N and S vacancies were introduced in the composites by plasma. The dual defects promoted the recombination and formation of heterojunctions of the g-C3N4/MoS2 composite. It exhibited stronger light harvesting ability and higher charge separation efficiency than that of pure g-C3N4 and MoS2. Compared with the sample by traditional calcination method, the plasma-sample showed better performance for degrading rhodamine B (RhB) and methyl orange. RhB is completely degraded within 2 hours on g-C3N4/MoS2 by plasma. A mechanism for the photocatalytic degradation of organic pollutants via the composites was proposed. An electron-assisted strategy provides a green and effective platform to achieve catalysts with improved performance.

Noble Metal-Free TiO2-Coated Carbon Nitride Layers for Enhanced Visible Light-Driven Photocatalysis

Composites of g-C3N4/TiO2 were one-step prepared using electron impact with dielectric barrier discharge (DBD) plasma as the electron source. Due to the low operation temperature, TiO2 by the plasma method shows higher specific surface area and smaller particle size than that prepared via conventional calcination. Most interestingly, electron impact produces more oxygen vacancy on TiO2, which facilitates the recombination and formation of heterostructure of g-C3N4/TiO2. The composites have higher light absorption capacity and lower charge recombination efficiency. g-C3N4/TiO2 by plasma can produce hydrogen at a rate of 219.9 μmol·g-1·h-1 and completely degrade Rhodamine B (20mg·L-1) in two hours. Its hydrogen production rates were 3 and 1.5 times higher than that by calcination and pure g-C3N4, respectively. Electron impact, ozone and oxygen radical also play key roles in plasma preparation. Plasma has unique advantages in metal oxides defect engineering and the preparation of heterostructured composites with prospective applications as photocatalysts for pollutant degradation and water splitting.

A Novel Route to Manufacture 2D Layer MoS2 and g-C3N4 by Atmospheric Plasma with Enhanced Visible-Light-Driven Photocatalysis

An atmospheric plasma treatment strategy was developed to prepare two-dimensional (2D) molybdenum disulfide (MoS₂) and graphitic carbon nitride (g-C₃N₄) nanosheets from (NH₄)₂MoS₄ and bulk g-C₃N₄, respectively. The moderate temperature of plasma is beneficial for exfoliating bulk materials to thinner nanosheets. The thicknesses of as-prepared MoS₂ and g-C₃N₄ nanosheets are 2-3 nm and 1.2 nm, respectively. They exhibited excellent photocatalytic activity on account of the nanosheet structure, larger surface area, more flexible photophysical properties, and longer charge carrier average lifetime. Under visible light irradiation, the hydrogen production rates of MoS₂ and g-C₃N₄ by plasma were 3.3 and 1.5 times higher than the corresponding bulk materials, respectively. And g-C₃N₄ by plasma exhibited 2.5 and 1.3 times degradation rates on bulk that for methyl orange and rhodamine B, respectively. The mechanism of plasma preparation was proposed on account of microstructure characterization and online mass spectroscopy, which indicated that gas etching, gas expansion, and the repulsive force of electron play the key roles in the plasma exfoliation. Plasma as an environmentally benign approach provides a general platform for fabricating ultrathin nanosheet materials with prospective applications as photocatalysts for pollutant degradation and water splitting.