Bahareh Khezri

Noble metal (Pd, Ru, Rh, Pt, Au, Ag) doped graphene hybrids for electrocatalysis

Metal decorated graphene materials are highly important for catalysis. In this work, noble metal doped-graphene hybrids were prepared by a simple and scalable method. The thermal reductions of metal doped-graphite oxide precursors were carried out in nitrogen and hydrogen atmospheres and the effects of these atmospheres as well as the metal components on the characteristics and catalytic capabilities of the hybrid materials were studied. The hybrids exfoliated in nitrogen atmosphere contained a higher amount of oxygen-containing groups and lower density of defects on their surfaces than hybrids exfoliated in hydrogen atmosphere. The metals significantly affected the electrochemical behavior and catalysis of compounds that are important in energy production and storage and in electrochemical sensing. Research in the field of energy storage and production, electrochemical sensing and biosensing as well as biomedical devices can take advantage of the properties and catalytic capabilities of the metal doped graphene hybrids.

Chemically reduced graphene contains inherent metallic impurities present in parent natural and synthetic graphite

Graphene-related materials are in the forefront of nanomaterial research. One of the most common ways to prepare graphenes is to oxidize graphite (natural or synthetic) to graphite oxide and exfoliate it to graphene oxide with consequent chemical reduction to chemically reduced graphene. Here, we show that both natural and synthetic graphite contain a large amount of metallic impurities that persist in the samples of graphite oxide after the oxidative treatment, and chemically reduced graphene after the chemical reduction. We demonstrate that, despite a substantial elimination during the oxidative treatment of graphite samples, a significant amount of impurities associated to the chemically reduced graphene materials still remain and alter their electrochemical properties dramatically. We propose a method for the purification of graphenes based on thermal treatment at 1,000 °C in chlorine atmosphere to reduce the effect of such impurities on the electrochemical properties. Our findings have important implications on the whole field of graphene research.

Metallic Impurities in Graphenes Prepared from Graphite Can Dramatically Influence Their Properties

All at C? Graphenes prepared by the top-down exfoliation of graphite are shown to contain metallic impurities (see scheme, metal impurities shown as black dots). These impurities may dominate their properties and can have a negative influence on their potential applications.

Newly Developed Stepwise Electroless Deposition Enables a Remarkably Facile Synthesis of Highly Active and Stable Amorphous Pd Nanoparticle Electrocatalysts for Oxygen Reduction Reaction

This paper reports on highly active and stable amorphous Pd nanoparticle electrocatalysts for the oxygen reduction reaction. The amorphous catalysts were synthesized by a remarkably facile and quick electroless deposition process newly developed in this study (process time <5 min). An electrode substrate (glassy carbon, carbon cloth) was sequentially dipped for 10 s into two separate solutions of a reducing agent (sodium hypophosphite (NaH2PO2)) and Pd ions to deposit amorphous Pd nanoparticles containing phosphorus (Pd-P). By repeating the deposition cycles, the specific and mass activities of the Pd nanoparticles can be actively tuned. Owing to the nanoscale amorphous nature, the obtained Pd-P nanoparticle electrocatalysts exhibited superior specific and mass activities compared with crystalline Pd nanoparticles synthesized by another reducing agent (N2H4) and commercial Pt-loaded carbon (Pt/C) and Pd-loaded carbon (Pd/C). The specific and mass activities of the amorphous Pd-P nanoparticles were over 4.5 times and 2.6 times higher than previously reported values of Pd and Pt catalysts.

Influences of graphene oxide support on the electrochemical performances of graphene oxide-MnO2 nanocomposites

MnO2 supported on graphene oxide (GO) made from different graphite materials has been synthesized and further investigated as electrode materials for supercapacitors. The structure and morphology of MnO2-GO nanocomposites are characterized by X-ray diffraction, X-ray photoemission spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and Nitrogen adsorption-desorption. As demonstrated, the GO fabricated from commercial expanded graphite (denoted as GO(1)) possesses more functional groups and larger interplane gap compared to the GO from commercial graphite powder (denoted as GO(2)). The surface area and functionalities of GO have significant effects on the morphology and electrochemical activity of MnO2, which lead to the fact that the loading amount of MnO2 on GO(1) is much higher than that on GO(2). Elemental analysis performed via inductively coupled plasma optical emission spectroscopy confirmed higher amounts of MnO2 loading on GO(1). As the electrode of supercapacitor, MnO2-GO(1) nanocomposites show larger capacitance (307.7 F g-1) and better electrochemical activity than MnO2-GO(2) possibly due to the high loading, good uniformity, and homogeneous distribution of MnO2 on GO(1) support.

Strategy for Nano‐Catalysis in a Fixed‐Bed System

For industry applications of nano-catalysts, the main bottlenecks are the low loading per unit support area and the slow flow rate through the support particles. By growing a dense Au nanowire forest on a loose network of glass fibers, continuous-flow catalysis can be achieved with a processing rate about 100 times that of the best literature rate.

Influence of real-world environments on the motion of catalytic bubble-propelled micromotors

Self-propelled autonomous micromachines have recently been tasked to carry out various roles in real environments. In this study, we expose the microjets to various types of water that are present in the real world, examples include tap water, rain water, lake water and sea water, and we sought to investigate their behaviors under real world conditions. We observed that the viability and mobility of the catalytic bubble jet engines are strongly influenced by the type of environmental water sample. Amongst the four water samples tested, the seawater sample exhibits the strongest influence, completely disabling any motions arising from the microjets. The motion of the microjets is also reduced in tap water, which contains large quantities of inorganic ions that have been purposely introduced into tap water via processing in water treatment plants. Lake water and rain water samples exhibited the least influence on the microjets motion. All of the four water samples were also characterized by determining their ion compositions and conductivities, and we will show that there is a distinct correlation between the reduced mobility of the microjets with the ion content of the water found in real environments.

CO2 reduction: the quest for electrocatalytic materials

Rising levels of carbon dioxide (CO2) are of significant concern in modern society, as they lead to global warming and consequential environmental and societal changes. It is of importance to develop industries with a zero or negative CO2 footprint. Electrochemistry, where one of the reagents is electrons, is an environmentally clean technology that is capable of addressing the conversion of CO2 to value-added products. The key factor in the process is the use of catalytic electrode materials that lead to the desired reaction and product. Significant progress in this field has been achieved in the past two years. This review discusses the progress in the development of electrocatalysts for CO2 reduction achieved during this time period.

Human Transport Protein Carrier for Controlled Photoactivation of Antitumor Prodrug and Real-Time Intracellular Tumor Imaging

Current anticancer chemotherapy often suffers from poor tumor selectivity and serious drug resistance. Proper vectors for targeted delivery and controlled drug release play crucial roles in improving the therapeutic selectivity to tumor areas and also overcoming the resistance of cancer cells. In this work, we developed a novel human serum albumin (HSA) protein-based nanocarrier system, which combines the photoactivatable Pt(IV) antitumor prodrug for realizing the controlled release and fluorescent light-up probe for evaluations of drug action and efficacy. The constructed Pt(IV)-probe@HSA platform can be locally activated by light irradiation to release the active Pt species, which results in enhanced cell death at both drug-sensitive A2780 and cisplatin-resistant A2780cis cell lines when compared to the free prodrug molecules. Simultaneously, the cytotoxicity caused by light controlled drug release would further lead to the cellular apoptosis and trigger the activation of caspases 3, one crucial protease enzyme in apoptotic process, which could cleave the recognition peptide moiety (DEVD) with a flanking fluorescent resonance energy transfer (FRET) pair containing near-infrared (NIR) fluorophore Cy5 and quencher Qsy21 on the HSA nanocarrier surface. The turn-on fluorescence in response to caspase-3 could be assessed by fluorescence microscopy and flow cytometry analysis. Our results supported the hypothesis that such a unique design may present a successful platform for multiple roles: (i) a biocompatible protein-based nanocarrier for drug delivery, (ii) the controlled drug release with strengthened therapeutic effects, (iii) real-time monitoring of antitumor drug efficacy at the earlier stage.

Corrosion of self-propelled catalytic microengines

Here we show that rolled-up and electroplated catalytic microjet engines undergo dramatic corrosion in fuel solution.