Effect of Nitrogen Doping on the Optical Bandgap and Electrical Conductivity of Nitrogen-Doped Reduced Graphene Oxide

Sensitive sensing of GLA and ISL based on highly conductivity nitrogen-doped carbon synergistic dual-template molecularly imprinted ratiometric electrochemical sensor

A novel ratiometric Molecularly Imprinted Electrochemical sensor for the specific marker of Glycyrrhiza glabra L. was developed in this work. To achieve simultaneous detection of two analytes on one sensor, we constructed a double template molecular imprinted electrochemical sensor with glabridin (GLA) and isoliquiritin (ISL) as templates. Further, Ferrocene/ZIF-8 (Fc/ZIF-8) composites were prepared via a one-pot solvothermal reaction and coated on the surface of a glassy carbon electrode (GCE), and the oxidation of Fc was presented as the internal reference signal. Nitrogen-doped carbon (NOC) with high conductivity was further loaded on the modified GCE. Based on theoretical exploration and computer directional simulation of density functional theory (DFT), the optimal functional monomer and the best ratio of double template molecules to functional monomer were screened. Under optimal conditions, the sensor produced electrochemical curves when exposed to a solution containing GLA and ISL. As the concentration of GLA and ISL increased, the peak current intensity of GLA and ISL (IGLA and IISL) also increased, while the peak current intensity of Fc (as a reference signal) remained relatively constant. The values of IGLA/IFc and IISL/IFc showed excellent linear relationships with GLA and ISL concentrations in the range of 0.1-160 μM and 0.5-150 μM, respectively. The detection limits were 0.052 μM and 0.27 μM (S/N = 3), respectively. Due to the imprinting effect of MIP and the existence of a reference signal, the sensor exhibited excellent selectivity and anti-interference ability and was successfully applied to the quality evaluation of Glycyrrhiza glabra L.

Nitrogen-doped carbon nano-onions/polypyrrole nanocomposite based low-cost flexible sensor for room temperature ammonia detection

One of the frontier research areas in the field of gas sensing is high-performance room temperature-based novel sensing materials, and new family of low-cost and eco-friendly carbon nanomaterials with a unique structure has attracted significant attention. In this work, we propose a novel low-cost flexible room temperature ammonia gas sensor based on nitrogen-doped carbon nano-onions/polypyrrole (NCNO-PPy) composite material mounted low-cost membrane substrate was synthesized by combining hydrothermal and in-situ chemical polymerization methods. The proposed flexible sensor revealed high sensing performance when employed as the sensing material for ammonia detection at room temperature. The NCNO-PPy ammonia sensor exhibited 17.32% response for 100 ppm ammonia concentration with a low response time of 26 s. The NCNO-PPy based flexible sensor displays high selectivity, good repeatability, and long-term durability with 1 ppm as the lower detection limit. The proposed flexible sensor also demonstrated remarkable mechanical robustness under extreme bending conditions, i.e., up to 90° bending angle and 500 bending cycles. This enhanced sensing performance can be related to the potential bonding and synergistic interaction between nitrogen-doped CNOs and PPy, the formation of defects from nitrogen doping, and the presence of high reactive sites on the surface of NCNO-PPy composites. Additionally, the computational study was performed on optimized NCNO-PPy nanocomposite for both with and without NH3 interaction. A deeper understanding of the sensing phenomena was proposed by the computation of several electronic characteristics, such as band gap, electron affinity, and ionization potential, for the optimized composite.

A review of piezoelectric MEMS sensors and actuators for gas detection application

Piezoelectric microelectromechanical system (piezo-MEMS)-based mass sensors including the piezoelectric microcantilevers, surface acoustic waves (SAW), quartz crystal microbalance (QCM), piezoelectric micromachined ultrasonic transducer (PMUT), and film bulk acoustic wave resonators (FBAR) are highlighted as suitable candidates for highly sensitive gas detection application. This paper presents the piezo-MEMS gas sensors' characteristics such as their miniaturized structure, the capability of integration with readout circuit, and fabrication feasibility using multiuser technologies. The development of the piezoelectric MEMS gas sensors is investigated for the application of low-level concentration gas molecules detection. In this work, the various types of gas sensors based on piezoelectricity are investigated extensively including their operating principle, besides their material parameters as well as the critical design parameters, the device structures, and their sensing materials including the polymers, carbon, metal-organic framework, and graphene.

One-Step Solvothermal Synthesis by Ethylene Glycol to Produce N-rGO for Supercapacitor Applications

Graphene and its derivatives have emerged as peerless electrode materials for energy storage applications due to their exclusive electroactive properties such as high chemical stability, wettability, high electrical conductivity, and high specific surface area. However, electrodes from graphene-based composites are still facing some substantial challenges to meet current energy demands. Here, we applied one-pot facile solvothermal synthesis to produce nitrogen-doped reduced graphene oxide (N-rGO) nanoparticles using an organic solvent, ethylene glycol (EG), and introduced its application in supercapacitors. Electrochemical analysis was conducted to assess the performance using a multi-channel electrochemical workstation. The N-rGO-based electrode demonstrates the highest specific capacitance of 420 F g^-1 at 1 A g^-1 current density in 3 M KOH electrolyte with the value of energy (28.60 Whkg^-1) and power (460 Wkg^-1) densities. Furthermore, a high capacitance retention of 98.5% after 3000 charge/discharge cycles was recorded at 10 A g^-1. This one-pot facile solvothermal synthetic process is expected to be an efficient technique to design electrodes rationally for next-generation supercapacitors.

Broad-Spectrum Antibacterial Activity of Synthesized Carbon Nanodots from d-Glucose

Carbon nanodots, a class of carbon nano-allotropes, have been synthesized through different routes and methods from a wide range of precursors. The selected precursor, synthetic method, and conditions can strongly alter the physicochemical properties of the resulting material and their intended applications. Herein, carbon nanodots (CNDs) have been synthesized from d-glucose by combining pyrolysis and chemical oxidation methods. The effect of the pyrolysis temperature, equivalents of oxidizing agent, and refluxing time were studied on the product and quantum yield. In the optimum conditions (pyrolysis temperature of 300 °C, 4.41 equiv of H2O2, 90 min of reflux) CNDs were obtained with 40% and 3.6% of product and quantum yields, respectively. The obtained CNDs are negatively charged (ζ-potential = -32 mV), excellently dispersed in water, with average diameter of 2.2 nm. Furthermore, ammonium hydroxide (NH4OH) was introduced as dehydrating and/or passivation agent during CNDs synthesis resulting in significant improvement of both product and quantum yields of about 1.5 and 3.76-fold, respectively. The synthesized CNDs showed a broad spectrum of antibacterial activities toward different Gram-positive and Gram-negative bacteria strains. Both synthesized CNDs caused highly colony forming unit reduction (CFU), ranging from 98% to 99.99% for most of the tested bacterial strains. However, CNDs synthesized in the absence of NH4OH, due to a negatively charged surface enriched in oxygenated groups, performed better in zone inhibition and minimum inhibitory concentration. The elevated antibacterial activity of high-oxygen-containing carbon nanodots is directly correlated to their ROS formation ability.

One Pot Synthesis of Graphene through Microwave Assisted Liquid Exfoliation of Graphite in Different Solvents

This study presents an easy and quick method for the synthesis of graphene from graphite in a set of solvents, including n-Hexadecane (n-Hexa), dimethylsulfoxide (DMSO), sodium hydroxide (NaOH), 1-octanol (OCTA), perchloric acid (PA), N,N-Dimethylformamide (DMF), ethylene glycol (EG), and ethylene diamine (ED), via microwave (MW) energy. The properties of final products were determined by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-Vis) spectroscopy, and the four-point probe technique. The XRD spectra of most of the MW-assisted graphene products showed peaks at 2θ = 26.5° and 54°. Layer numbers extend from 2 and 25, and the leading comes about were gotten by having two-layered products, named as graphene synthesized in dimethylsulfoxide (G-DMSO), graphene synthesized in ethylene glycol (G-EG), and graphene synthesized in 1-octanol (G-OCTA). G-DMF has the highest electrical conductivity with 22 S/m. The electrical conductivity is higher when the dipole moment of the used solvent is between 2 and 4 Debye (D). The FTIR spectra of most of the MW-assisted graphene products are in line with commercial graphene (CG). The UV-Vis spectra of all MW-assisted graphene products showed a peak at 223 nm referring to characteristic sp2 C=C bonds and 273 nm relating to the n → π * transition of C-O bonds.

A novel facile one-pot synthesis of photothermally responsive carbon polymer dots as promising drug nanocarriers

Luminescent and photothermic carbon polymer dots (CPDs-PNM), composed of a carbonized core and cross-linked chains of poly(N-isopropylacrylamide), were synthetized by a novel, simple, solvent- and reagent-free method. The formation of CPDs-PNM was controlled by both temperature and heating time. The CPDs-PNM exhibited LCST behaviour, high photothermal conversion efficiency, curcumin loading capacity and no toxicity to eukaryotic cells. Proof of concept experiments confirmed an excellent thermally induced drug release activity to be used for photothermally controlled drug release.