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This article deals with the Raman spectroscopic research of aluminum–graphene (Al–Gr) composites obtained by aqueous suspension-based mixing to improve dispersion of graphene sheets in composite powders. Raman spectra of composite powders reflect encapsulated nanostructure of Al–Gr composite powders and chemical interaction of oxygen groups on graphene oxide (GO) with magnesium ions (Mg2+), depending on the added Mg2+ content. First, the enhanced Raman signal for our composite powders is an apparent evidence of that graphene sheets with uniform dispersion on Al matrix are in close contact with the spherical surface of Al powders. The polarization dependence of the Raman spectra, which are dependent on the incident laser spot, also confirms that the graphene sheets surrounded the spherical powder. SEM image, XPS and FT-IR spectra for the composite powders provide additional data to decipher the Raman analysis results. [ABSTRACT FROM AUTHOR]

In this work, a new route for preparation of graphene reinforced aluminum (Al) matrix composites with enhanced dispersion and strength has been discussed based on aqueous suspension mixing procedure. Mg 2+ ions added into mixture were used as binding bridge that anchored graphene sheets to the surface of Al powder, improving affinity and binding capacity of graphene sheets with Al matrix. Graphene nanosheets have double dispersion behaviors on Al matrix with increasing of Mg 2+ concentration following colloidal theory (DLVO theory and Schulze-Hardy rule). Although composite billet consolidated through spark plasma sintering (SPS) has only 3 wt% content of graphene, but it was significantly reinforced in strength affected by the dispersion degree of graphene on composite matrix. [ABSTRACT FROM AUTHOR]

Precise control over doping of photocatalysts is required to modulate their photocatalytic activity in visible light-driven reactions. Here, a single precursor-employing bottom-up approach is developed to produce different heteroatom-doped graphene quantum dots (GQDs) with unique photocatalytic activities. The solvothermal reaction of a norepinephrine precursor with redox active and condensable moieties effectively produces both nitrogen/sulfur codoped GQDs (NS-GQDs) and nitrogen-doped GQDs (N-GQDs) by simply varying solvents (from dimethyl sulfoxide to water) under microwave irradiation. As-prepared NS-GQDs and N-GQDs show similar lateral sizes (3-4 nm) and heights (1-2 nm), but they include different dopant types and doping constitution and content, which lead to changes in photocatalytic activity in aerobic oxidative coupling reactions of various amines. NS-GQDs exhibit much higher photocatalytic activity in reactions under visible light than N-GQDs and oxygen-doped GQDs (O-GQDs). The mechanism responsible for the outstanding photocatalytic activity of NS-GQDs in visible light-driven oxidative coupling reactions of amines is also fully investigated. [ABSTRACT FROM AUTHOR]