New bidental sulfur-doped graphene quantum dots modified with gold as a catalyst for hydrogen generation

Graphene quantum dots for biosensing and bioimaging

Graphene Quantum Dots (GQDs) are low dimensional carbon based materials with interesting physical, chemical and biological properties that enable their applications in numerous fields. GQDs possess unique electronic structures that impart special functional attributes such as tunable optical/electrical properties in addition to heteroatom-doping and more importantly a propensity for surface functionalization for applications in biosensing and bioimaging. Herein, we review the recent advancements in the top-down and bottom-up approaches for the synthesis of GQDs. Following this, we present a detailed review of the various surface properties of GQDs and their applications in bioimaging and biosensing. GQDs have been used for fluorescence imaging for visualizing tumours and monitoring the therapeutic responses in addition to magnetic resonance imaging applications. Similarly, the photoluminescence based biosensing applications of GQDs for the detection of hydrogen peroxide, micro RNA, DNA, horse radish peroxidase, heavy metal ions, negatively charged ions, cardiac troponin, etc. are discussed in this review. Finally, we conclude the review with a discussion on future prospects.

Improving the Performance of Pd for Formic Acid Dehydrogenation by Introducing Barium Titanate

Formic acid, a safe and widely available organic compound, produces hydrogen under mild conditions, with the existence of Pd-based catalysts. Efficiently generating hydrogen via formic acid decomposition (FAD) is restricted by the cleavage of the C-H bond in adsorbed HCOO* and strong adsorption of hydrogen on the Pd surface. Herein, tetragonal-phase barium titanate (TBT) was in situ grown on reduced graphene oxide (rGO) to support Pd (Pd/TBT/rGO) for FAD. The internal electric field exists around TBT owing to its spontaneous polarization capacity. The physical characterizations illustrate that the introduction of barium titanate affects the catalytic performance of the catalyst by decreasing the particle size of Pd nanoparticles (NPs) and forming electron-rich Pd. The as-synthesized Pd/TBT/rGO exhibited excellent catalytic activity and hydrogen selectivity for FAD with a high initial turnover frequency up to 3019.72 h-1 at 333 K. The reason for this enhancement is not only the small-size Pd NPs but also the internal electric field from TBT, which promotes the desorption of adsorbed hydrogen on the Pd surface. Additionally, the electron-rich Pd is favorable to the cleavage of the C-H bond in HCOO*. This work will improve the understanding of the characterization of barium titanate and provide a new design strategy for the FAD catalyst.

Chitosan-Derived Nitrogen-Doped Carbon as a Support of Cobalt(II)-Phthalocyanine/Gold Nanoparticles for Photocatalytic Water Splitting

Water splitting is considered one of the worthy approaches to generate hydrogen as a green fuel with diverse applications. Promoting this reaction with the photocatalytic strategy enjoys a free source of solar energy, without the use of expensive instruments. In this research, gold nanoparticles and cobalt(II)-phthalocyanine were deposited on nitrogen-doped carbon, obtained from chitosan, to afford a photocatalytic water splitting at the rate of 792 mol molAu-1 h-1. Gold as the catalyst in contact with cobalt(II)-phthalocyanine as the sensitizer and nitrogen-doped carbon as the support/semiconductor provided a desired heterojunction for the photocatalytic purpose. The nanocomposite showed remarkable light harvesting in the region of visible light with a band gap of 2.01 eV. While a facile protocol to the synthesis of the mentioned photocatalyst by a simple thermal treatment of cobalt(II)-phthalocyanine and chitosan could be invaluable, this research pointed out the significance of cobalt(II)-phthalocyanine as the sensitizer in the gold photocatalytic transformations.

Rapid Crystallization and Fluorescence of Poly(ethylene terephthalate) Using Graphene Quantum Dots as Nucleating Agents

In this study, graphene quantum dots (GQDs) with a diameter of ~3 nm were successfully synthesized and incorporated into a poly(ethylene terephthalate) (PET) matrix to fabricate PET/GQDs nanocomposites. The impact of GQDs on the crystallization and thermal stability of the PET/GQDs nanocomposites was investigated. It was observed that the addition of only 0.5 wt% GQDs into the nanocomposites resulted in a significant increase in the crystallization temperature (peak temperature) of PET, from 194.3 °C to 206.0 °C during the cooling scan process. This suggested that an optimal concentration of GQDs could function as a nucleating agent and effectively enhance the crystallization temperature of PET. The isothermal crystallization method was employed to analyze the crystallization kinetics of the PET/GQDs nanocomposites, and the data showed that 0.5 wt% GQDs significantly accelerated the crystallization rate. Furthermore, the incorporation of GQDs into the PET matrix imparted photoluminescent properties to the resulting PET/GQDs nanocomposites. The PET crystals with GQDs as crystal nuclei and the crazes caused by defects played a vital role in isolating and suppressing the concentration quenching of GQDs. This effect facilitated the detection of defects in PET.

ZnO NRs/rGO Photocatalyst in a Polymer-Based Microfluidic Platform

This paper reports the development of ZnO NRs/rGO-based photocatalysts integrated into a tree-branched polymer-based microfluidic reactor for efficient photodegradation of water contaminants. The reactor system includes a photocatalytic reactor, tree-branched microfluidic channels, and ZnO nanorods (NRs) coated with reduced graphene oxide (rGO) on a glass substrate within an area of 0.6 × 0.6 cm2. The ZnO NRs/rGO acts as a photocatalyst layer grown hydrothermally and then spray-coated with rGO. The microfluidic system is made of PDMS and fabricated using soft lithography (micro molding using SU-8 master mold patterned on a silicon wafer). The device geometry is designed using AutoCAD software and the flow properties of the microfluidics are simulated using COMSOL Multiphysics. The microfluidic platform’s photocatalytic process aims to bring the nanostructured photocatalyst into very close proximity to the water flow channel, reducing the interaction time and providing effective purification performance. Our functionality test showed that a degradation efficiency of 23.12 %, within the effective residence time of less than 3 s was obtained.

Reduced Graphene Oxide as a Platform for the Immobilization of Amino-Cyclodextrins

In the present work, we reported on a method to combine amino β-cyclodextrins (CD1) with reduced graphene oxide (obtained by the electrochemical reduction of graphene oxide, erGO) to produce a glassy carbon electrode (GCE) modified with both CD1 and erGO (CD1-erGO/GCE). This procedure avoids the use of organic solvents such as hydrazine or long reaction times and high temperatures. The material combining both CD1 and erGO (CD1-erGO/GCE) was characterized by SEM, ATR-FTIR, Raman, XPS, and electrochemical techniques. As proof-of-concept, the determination of the pesticide carbendazim was carried out. The spectroscopic measurements, especially XPS, proved that CD1 was covalently attached to the surface of the erGO/GCE electrode. The attachment of cyclodextrin at the reduced graphene oxide produced an increase in the electrochemical behavior of the electrode. The cyclodextrin-functionalized reduced graphene oxide, CD1-erGO/GCE, showed a larger sensitivity (1.01 μA/μM) and a lower limit of detection for carbendazim (LOD = 0.50 μM) compared with the non-functionalized material, erGO/GCE, (sensitivity = 0.63 μA/μM and LOD = 4.32 μM, respectively). Overall, the results of the present work show that this simple method is suitable to attach cyclodextrins to graphene oxide, maintaining their inclusion abilities.

Seawater Splitting for Hydrogen Generation Using Zirconium and Its Niobium Alloy under Gamma Radiation

Hydrogen production is produced for future green energy. The radiation–chemical yield for seawater without a catalyst, with Zr, and with Zr1%Nb (Zr = 99% Nb = 1%) were (G(H₂) = 0.81, 307.1, and 437.4 molecules/100 eV, respectively. The radiation–thermal water decomposition increased in γ-radiation of the Zr1%Nb + SW system with increasing temperature. At T = 1273 K, it prevails over radiation processes. During the radiation and heat radiation heterogeneous procedures in the Zr1% Nb + SW system, the production of surface energetic sites and secondary electrons accelerated the accumulation of molecular hydrogen and Zr1%Nb oxidation. Thermal radiation and thermal processes caused the metal phase to collect thermal surface energetic sites for water breakdown and Zr 1%Nb oxidation starting at T = 573 K.