Carbocatalysis by Graphene-Based Materials

Precursor chemistry matters in boosting photoredox activity of graphene/semiconductor composites

Considerable effort has been made to fabricate graphene (GR)/semiconductor composite photocatalysts, by using graphene oxide (GO) as the most widely used precursor of GR, toward an improved efficacy of solar energy conversion. However, thus far, the role of GO in the preparation and photocatalytic activity of GR/semiconductor composites has remained rather elusive. Herein, we report a simple yet efficient approach to significantly improve the photocatalytic activity of GR/semiconductor CdS composites via the acid treatment of GO, which downsizes GO sheets into smaller ones with enhanced colloidal stability and oxygenated functional groups. The graphene/CdS composites, which are prepared using this type of downsized GO as the precursor of GR, exhibit remarkably higher visible-light photoredox activity than those prepared from the direct reduction of GO without acid treatment. Our comparative results directly highlight the important effect of physico-chemical features of GO on the preparation and thus photoactivity of GR/semiconductor composites; in particular, the rational tailoring of GO could open a new doorway to optimize the activity of GO-derived GR/semiconductor composite photocatalysts.

Magnetic graphene-carbon nanotube iron nanocomposites as adsorbents and antibacterial agents for water purification

One of the biggest challenges of the 21st century is to provide clean and affordable water through protecting source and purifying polluted waters. This review presents advances made in the synthesis of carbon- and iron-based nanomaterials, graphene-carbon nanotubes-iron oxides, which can remove pollutants and inactivate virus and bacteria efficiently in water. The three-dimensional graphene and graphene oxide based nanostructures exhibit large surface area and sorption sites that provide higher adsorption capacity to remove pollutants than two-dimensional graphene-based adsorbents and other conventional adsorbents. Examples are presented to demonstrate removal of metals (e.g., Cu, Pb, Cr(VI), and As) and organics (e.g., dyes and oil) by grapheme-based nanostructures. Inactivation of Gram-positive and Gram-negative bacterial species (e.g., Escherichia coli and Staphylococcus aureus) is also shown. A mechanism involving the interaction of adsorbents and pollutants is briefly discussed. Magnetic graphene-based nanomaterials can easily be separated from the treated water using an external magnet; however, there are challenges in implementing the graphene-based nanotechnology in treating real water.

Rationale of the effects from dopants on C-H bond activation for sp(2) hybridized nanostructured carbon catalysts

Doping has become an effective way to tune the catalytic properties of nanostructured carbon catalysts. Taking C-H activation as an example, first-principles calculations propose that the relative energy level and the BEP rule might be applicable to explain the observed doping effects. Moreover, boron doping is proposed as an effective way to enhance the catalytic performance.

Physicochemical Changes of Few-Layer Graphene in Peroxidase-Catalyzed Reactions: Characterization and Potential Ecological Effects

The environmental implications of graphene have received much attention, however, little is known about how graphene affects or may be affected by the enzymatic reactions that are critically involved in natural organic matter transformation processes. We conducted experiments to examine the role of few-layer graphene (FLG) in the reaction system of tetrabromobisphenol A (TBBPA) mediated by horseradish peroxidase (HRP). We found that TBBPA was transformed by HRP into two products that were likely formed from coupling of two TBBPA radicals via interaction of an oxygen atom on one radical and a propyl-substituted aromatic carbon atom on the other. Presence of FLG greatly increased the reaction rate by protecting HRP from inactivation. Direct reactions between TBBPA radicals and FLG were unequivocally evidenced using (14)C labeling and the characteristic photoelectron response of bromine contained in TBBPA. The thickness, size, and aggregation profile of FLG was modified by the reaction as shown by multiple characterization tools. Assessment using Daphnia magna revealed a substantial decrease in the bioaccumulation and toxicity of the FLG after being modified. The data provides the first evidence that FLG can be modified in HRP-mediated reactions and indicates that such modifications may have strong implications in its ecological effects.

Microwave Enabled One-Pot, One-Step Fabrication and Nitrogen Doping of Holey Graphene Oxide for Catalytic Applications

The unique properties of a holey graphene sheet, referred to as a graphene sheet with nanoholes in its basal plane, lead to wide range of applications that cannot be achieved by its nonporous counterpart. However, the large-scale solution-based production requires graphene oxide (GO) or reduced GO (rGO) as the starting materials, which take hours to days for fabrication. Here, an unexpected discovery that GO with or without holes can be controllably, directly, and rapidly (tens of seconds) fabricated from graphite powder via a one-step-one-pot microwave assisted reaction with a production yield of 120 wt% of graphite is reported. Furthermore, a fast and low temperature approach is developed for simultaneous nitrogen (N) doping and reduction of GO sheets. The N-doped holey rGO sheets demonstrate remarkable electrocatalytic capabilities for the electrochemical oxygen reduction reaction. The existence of the nanoholes provides a "short cut" for efficient mass transport and dramatically increases edges and surface area, therefore, creates more catalytic centers. The capability of rapid fabrication and N-doping as well as reduction of holey GO can lead to development of an efficient catalyst that can replace previous coin metals for energy generation and storage, such as fuel cells and metal-air batteries.

Fibrillar networks of glycyrrhizic acid for hybrid nanomaterials with catalytic features

Self-assembly of the naturally occurring sweetening agent, glycyrrhizic acid (GA) in water is studied by small-angle X-ray scattering and microscopic techniques. Statistical analysis on atomic force microscopy images reveals the formation of ultralong GA fibrils with uniform thickness of 2.5 nm and right-handed twist with a pitch of 9 nm, independently of GA concentration. Transparent nematic GA hydrogels are exploited to create functional hybrid materials. Two-fold and three-fold hybrids are developed by introducing graphene oxide (GO) and in situ-synthesized gold nanoparticles (Au NPs) in the hydrogel matrix for catalysis applications. In the presence of GO, the catalytic efficiency of Au NPs in the reduction of p-nitrophenol to p-aminophenol is enhanced by 2.5 times. Gold microplate single crystals are further synthesized in the GA hydrogel, expanding the scope of these hybrids and demonstrating their versatility in materials design.

Organoamine-functionalized graphene oxide as a bifunctional carbocatalyst with remarkable acceleration in a one-pot multistep reaction

In this work, we reported the synthesis of bifunctional carbocatalyst with acid-base dual-activation mechanism by introducing organoamines on the basal planes of graphene oxide (GO). Interestingly, GO-supported primary amine (AP-GO) exclusively promoted one-pot Henry-Michael reactions with excellent activity to give synthetically valuable multifunctionalized nitroalkanes. Notably, it also exhibited significantly higher activity than those using propylamine, activated carbon-supported primary amine, and mesoporous silica-supported primary amine as the catalysts. This superior catalytic performance originated from the unique properties of AP-GO, which provided the acid-base cooperative effect by the appropriate positioning of primary amines on their basal planes and carboxyl acids along their edges and the decreased diffusion resistance of the reactants and the intermediates during the multistep catalytic cycles because of its open two-dimensional sheet-like structure. Moreover, it could be readily recycled by simple filtration and subsequently reused without significant loss of its catalytic activity in a six times run test.

Increased active sites and their accessibility of a N-doped carbon nanotube carbocatalyst with remarkably enhanced catalytic performance in direct dehydrogenation of ethylbenzene

This work presents a facile, low-cost, but efficient strategy for synthesizing HN-CNTs with enlarged active sites and their accessibility to reactants for the direct dehydrogenation of ethylbenzene.

Graphene-supported metal/metal oxide nanohybrids: synthesis and applications in heterogeneous catalysis

This minireview outlines recent advances in the design and catalytic applications of graphene-supported metal/metal oxide nanohybrids.

A pH-mediated enhancement of the graphene carbocatalyst activity for the reduction of 4-nitrophenol

A significant protruding graphene edge effect on the carbocatalytic activity of a graphene film for efficient conversion of 4-nitrophenol to 4-aminophenol.

Covalent functionalization of N-doped graphene by N-alkylation

N-Functionalization of N-graphene is described by the first time. It can be efficiently achieved combining phase transfer catalysis and microwave irradiation. The influence of functionalization on the optical band gap is studied.

Wool-anchored Pd(OAc)2 complex: a highly active and reusable catalyst for desulfurative coupling reactions

A biomacromolecule-anchored palladium complex, wool-Pd(OAc)₂, was used as a catalyst for the Liebeskind–Srogl desulfurative coupling reactions of pyrimidin-yl thioether derivatives with terminal alkynes and arylboronic acids.

Porous graphene-based material as an efficient metal free catalyst for the oxidative dehydrogenation of ethylbenzene to styrene

Reduced porous graphene oxide as a metal free catalyst was selected for the oxidative dehydrogenation of ethylbenzene to styrene and it exhibited high activity and stability.

A novel magnetic palladium catalyst for the mild aerobic oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid in water

Magnetically separable, graphene oxide-supported palladium nanoparticles showed high catalytic activity for the aerobic oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid.

Graphene oxide (GO)-catalyzed multi-component reactions: green synthesis of library of pharmacophore 3-sulfenylimidazo[1,2-a]pyridines

Graphene oxide (GO)-catalyzed multi-component reactions: green synthesis of library of pharmacophore 3-sulfenylimidazo[1,2-a]pyridines

Graphene oxide nanosheets: a highly efficient and reusable carbocatalyst catalyzes the Michael-cyclization reactions of 4-hydroxycoumarins, 4-hydroxypyrone and 4-hydroxy-1-methylquinolinone with chalcone derivatives in aqueous media

Graphene oxide nanosheets: a highly efficient and reusable carbocatalyst catalyzes the Michael-cyclization reactions of 4-hydroxycoumarins, 4-hydroxypyrone and 4-hydroxy-1-methylquinolinone with chalcone derivatives in aqueous media.

The preparation and catalytic performance of graphene-reinforced ion-exchange resins

The structural and thermal stability of graphene-based polymer nanocomposites were improved with chemical bonded interaction of graphene within the polymer networks.

Multiple roles of graphene in heterogeneous catalysis

This review provides a brief but comprehensive understanding of the different roles of graphene in heterogeneous catalysis, i.e., its use as a catalyst support and its intrinsic catalytic properties originating from the defects and heteroatom-containing functionalities.

Graphene-based catalysis for biomass conversion

This perspective summarizes the advances and challenges of graphene-based materials in the conversion of biomass into chemicals and biofuels.

The graphene/nucleic acid nanobiointerface

In this critical review, we present the recent advances in the design and fabrication of graphene/nucleic acid nanobiointerfaces, as well as the fundamental understanding of their interfacial properties and various nanobiotechnological applications.