High-photoluminescence (PL) graphene quantum dots (GQDs) were synthesized by a simple one-pot hydrothermal process, then separated by dialysis bags of different molecular weights. Four separated GQDs of varying sizes were obtained and displayed different PL intensities. With the decreasing size of separated GQDs, the intensity of the emission peak becomes much stronger. Finally, the GQDs of the smallest size revealed the most energetic PL intensity in four separated GQDs. The PL energy of all the separated GQDs shifted slightly, supported by density functional theory calculations.

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With the development of the times, more and more pollutants such as dyes produced by industry have inevitably caused harm to human health. Dyes are complex and stable in structure, and traditional methods of physically and chemically processing dyes have been proven to be inefficient. The heterogeneous photocatalytic technology has been widely regarded as one of the most promising processes for the treatment of harmful organic wastewater. In this paper, copper oxide (CuO) nanomaterials were synthesized via a hydrothermal method and it was found that the stirring temperature can regulate its morphology and structure, which in turn affects the optical, electrical and catalytic properties of the final product. By controlling the stirring temperature, CuO nanomaterials in the range of ~30-500 nm were obtained. The as-prepared composites were characterized using X-ray diffraction, transmission electron microscope, scanning electron microscopy, and ultraviolet-visible spectroscopy techniques, among others. After a possible mechanism was proposed according to the above data, the photocatalytic performance of the CuO nanomaterials was evaluated by measuring the decomposition rate of rhodamine B (RhB) solutions. The results indicated that the CuO obtained at 100 oC exhibited excellent photocatalytic activity in comparison to other samples, with around 93% degradation of the RhB solution after 80 min. Finally, the recycling performance of the CuO nanomaterials was also tested and found to be extremely stable, with a high degradation level of 78% maintained after five cycles. In conclusion, the CuO nanomaterials are efficient catalysts for the complete degradation of RhB.