Numerical Investigation of Graphene as a Back Surface Field Layer on the Performance of Cadmium Telluride Solar Cell

This paper numerically explores the possibility of ultrathin layering and high efficiency of graphene as a back surface field (BSF) based on a CdTe solar cell by Personal computer one-dimensional (PC1D) simulation. CdTe solar cells have been characterized and studied by varying the carrier lifetime, doping concentration, thickness, and bandgap of the graphene layer. With simulation results, the highest short-circuit current (I_sc = 2.09 A), power conversion efficiency (η = 15%), and quantum efficiency (QE~85%) were achieved at a carrier lifetime of 1 × 10³ μs and a doping concentration of 1 × 10¹⁷ cm⁻³ of graphene as a BSF layer-based CdTe solar cell. The thickness of the graphene BSF layer (1 μm) was proven the ultrathin, optimal, and obtainable for the fabrication of high-performance CdTe solar cells, confirming the suitability of graphene material as a BSF. This simulation confirmed that a CdTe solar cell with the proposed graphene as the BSF layer might be highly efficient with optimized parameters for fabrication.     

Computational Screening of 3 d Transition Metal Atoms Anchored on Defective Graphene for Efficient Electrocatalytic N2 Fixation

The synthesis of ammonia (NH₃) through the electrochemical reduction of molecular nitrogen (N₂) is a promising strategy for significantly reducing energy consumption compared to traditional industrial processes. Herein, we report the design of a series of monovacancy and divacancy defective graphenes decorated with single 3d transition metal atoms (TM@MVG and TM@DVG; TM=Sc−Zn) as electrocatalysts for the nitrogen-reduction reaction (NRR) aided by density functional theory (DFT) calculations. By comparing energies for N₂ adsorption as well as the free energies associated with *N₂ activation and *N₂H formation, we successfully identified V@MVG, with the lowest potential of −0.63 V, to be an effective catalytic substrate for the NRR in an enzymatic mechanism. Electronic properties, including Bader charges, charge density differences, partial densities of states, and crystal orbital Hamilton populations, are further analyzed in detail. We believe that these results help to explain recent observations in this field and provide guidance for the exploration of efficient electrocatalysts for the NRR.     

Disposable Electrochemical Sensor for Food Colorants Detection by Reduced Graphene Oxide and Methionine Film Modified Screen Printed Carbon Electrode

A facile synthesis of reduced graphene oxide (rGO) and methionine film modified screen printed carbon electrode (rGO-methionine/SPCE) was proposed as a disposable sensor for determination of food colorants including amaranth, tartrazine, sunset yellow, and carminic acid. The fabrication process can be achieved in only 2 steps including drop-casting of rGO and electropolymerization of poly(L-methionine) film on SPCE. Surface morphology of modified electrode was studied by scanning electron microscopy (SEM). This work showed a successfully developed novel disposable sensor for detection of all 4 dyes as food colorants. The electrochemical behavior of all 4 food colorants were investigated on modified electrodes. The rGO-methionine/SPCE significantly enhanced catalytic activity of all 4 dyes. The pH value and accumulation time were optimized to obtain optimal condition of each colorant. Differential pulse voltammetry (DPV) was used for determination, and two linear detection ranges were observed for each dye. Linear detection ranges were found from 1 to 10 and 10 to 100 µM for amaranth, 1 to 10 and 10 to 85 µM for tartrazine, 1 to 10 and 10 to 50 µM for sunset yellow, and 1 to 20 and 20 to 60 µM for carminic acid. The limit of detection (LOD) was calculated at 57, 41, 48, and 36 nM for amaranth, tartrazine, sunset yellow, and carminic acid, respectively. In addition, the modified sensor also demonstrated high tolerance to interference substances, good repeatability, and high performance for real sample analysis.     

The Effects of Hydrophobicity and Textural Properties on Hexamethyldisiloxane Adsorption in Reduced Graphene Oxide Aerogels

To expand the applications of graphene-based materials to biogas purification, a series of reduced graphene oxide aerogels (rGOAs) were prepared from industrial grade graphene oxide using a simple hydrothermal method. The influences of the hydrothermal preparation temperature on the textural properties, hydrophobicity and physisorption behavior of the rGOAs were investigated using a range of physical and spectroscopic techniques. The results showed that the rGOAs had a macro-porous three-dimensional network structure. Raising the hydrothermal treatment temperature reduced the number of oxygen-containing groups, whereas the specific surface area (S_BET), micropore volume (V_micro) and water contact angle values of the rGOAs all increased. The dynamic adsorption properties of the rGOAs towards hexamethyldisiloxane (L2) increased with increasing hydrothermal treatment temperature and the breakthrough adsorption capacity showed a significant linear association with S_BET, V_micro and contact angle. There was a significant negative association between the breakthrough time and inlet concentration of L2, and the relationship could be reliably predicted with a simple empirical formula. L2 adsorption also increased with decreasing bed temperature. Saturated rGOAs were readily regenerated by a brief heat-treatment at 100 °C. This study has demonstrated the potential of novel rGOA for applications using adsorbents to remove siloxanes from biogas.     

Polyethylene Glycol Functionalized Graphene Oxide Nanoparticles Loaded with Nigella sativa Extract: A Smart Antibacterial Therapeutic Drug Delivery System

Flaky graphene oxide (GO) nanoparticles (NPs) were synthesized using Hummer’s method and then capped with polyethylene glycol (PEG) by an esterification reaction, then loaded with Nigella sativa (N. sativa) seed extract. Aiming to investigate their potential use as a smart drug delivery system against Staphylococcus aureus and Escherichia coli, the spectral and structural characteristics of GO-PEG NPs were comprehensively analyzed by XRD, AFM, TEM, FTIR, and UV- Vis. XRD patterns revealed that GO-PEG had different crystalline structures and defects, as well as a higher interlayer spacing. AFM results showed GONPs with the main grain size of 24.41 nm, while GONPs–PEG revealed graphene oxide aggregation with the main grain size of 287.04 nm after loading N. sativa seed extract, which was verified by TEM examination. A strong OH bond appeared in FTIR spectra. Furthermore, UV- Vis absorbance peaks at (275, 284, 324, and 327) nm seemed to be correlated with GONPs, GO–PEG, N. sativa seed extract, and GO –PEG- N. sativa extract. The drug delivery system was observed to destroy the bacteria by permeating the bacterial nucleic acid and cytoplasmic membrane, resulting in the loss of cell wall integrity, nucleic acid damage, and increased cell-wall permeability.     

Binary Metal Oxide Adsorbed Graphene Modified Glassy Carbon Electrode for Detection of Riboflavin

Tungsten oxide (W) decorated titanium oxide (T) adsorbed onto a graphene (Gr) and modified the glassy carbon electrode for the electrochemical quantification of riboflavin (RF) in edible food and pharmaceuticals. For comparison, nanocomposites are formed using graphene oxide (GO), reduced graphene oxide (rGO) and pure graphite (G) sheets to study the electrochemical activities towards riboflavin. The ternary WTGr modified GCE shows the highest electrocatalytic activity due to synergetic interactions between the metal oxide and graphene. The electrochemical observations are supported by the SEM, HRTEM, XRD, UV-Vis, Zeta potential (ζ) and size data. The sensor shows a wide linear range 20 nM–2.5 μM with a detection limit 25.24 nM and sensitivity (4.249×10⁻⁸ A/nM). The fabricated sensor is validated in real samples.     

A New Nanocomposite Based on Pt-rGO Embedded Polymelamine Formaldehyde Nanocomposite for Reduction of Carbon Dioxide

Here, polymelamine formaldehyde was decorated on the surface of reduced graphene oxide whose surface was then electrodeposited with a sub-monolayer of platinum nanoparticles. The nanocomposite thus prepared was characterized using several spectroscopic methods. Using the nanocomposite as a potential electrocatalyst for carbon dioxide reduction, the products were detected by Raman spectroscopy, gas chromatography, ¹³C-NMR spectroscopy, and gas chromatography-mass spectrometry. The analytical results identified methanol as the main product of CO₂ reduction. Moreover, analysis of the liquid products confirmed methanol as the predominant product with a current density of 0.4 mA/cm and a Faradaic efficiency of 93 %.     

Stages of melting of graphene model in two-dimensional space

Spontaneous melting of a perfect crystalline graphene model in 2D space is studied via molecular dynamics simulation. Model containing 10⁴ atoms interacted via long-range bond-order potential (LCBOP) is heated up from 50 to 8,450 K in order to see evolution of various thermodynamic quantities, structural characteristics and occurrence of various structural defects. We find that spontaneous melting of our graphene model in 2D space exhibits a first-order behaviour of the transition from solid 2D graphene sheet into a ring-like structure 2D liquid. Occurrence and clustering of Stone–Wales defects are the first step of melting process followed by breaking of C–C bonds, occurrence/growth of various types of vacancies and multi-membered rings. Unlike that found for melting of a 2D crystal with an isotropic bonding, these defects do not occur homogeneously throughout the system, they have a tendency to aggregate into a region and liquid phase initiates/grows from this region via tearing-like or crack-propagation-like mechanism. Spontaneous melting point of our graphene model occurs at T_m = 7,750 K. The validity of classical nucleation theory and Berezinsky–Kosterlitz–Thouless–Nelson–Halperin–Young (BKTNHY) one for the spontaneous melting of our graphene model in strictly 2D space is discussed.     

Electro‐optic switching with liquid crystal graphene

Graphene oxide (GO) particles in aqueous dispersions can form liquid crystal (LC) phases at extremely low concentrations due to the extremely high aspect ratio of the flakes and noticeably, they possess an extremely large Kerr coefficient attractive for low power consumption electro‐optic devices. Reduced graphene does not easily form LC phases in water due to its hydrophobic nature but here we show that stable dispersions of reduced graphene oxide can be realized with surfactants and that they exhibit birefringence upon shearing as well as under application of electric fields. The performance of the system is largely superior to GO LC possessing longer time stability and drastically improved electro‐optic properties with an induced birefringence twice as large at the same field strength thanks to the almost recovery of graphene properties upon reduction. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Graphene screen‐printed radio‐frequency identification devices on flexible substrates

Despite the great promise of printed flexible electronics from 2D crystals, and especially graphene, few scalable applications have been reported so far that can be termed roll‐to‐roll compatible. Here we combine screen printed graphene with photonic annealing to realize radio‐frequency identification devices with a reading range of up to 4 meters. Most notably our approach leads to fatigue resistant devices showing less than 1% deterioration of electrical properties after 1000 bending cycles. The bending fatigue resistance demonstrated on a variety of technologically relevant plastic and paper substrates renders the material highly suitable for various printable wearable devices, where repeatable dynamic bending stress is expected during usage. All applied printing and post‐processing methods are compatible with roll‐to‐roll manufacturing and temperature sensitive flexible substrates providing a platform for the scalable manufacturing of mechanically stable and environmentally friendly graphene printed electronics.