Mn3O4 nanoparticles decorated porous reduced graphene oxide with excellent oxidase-like activity for fast colorimetric detection of ascorbic acid.

Mn3O4 nanoparticles composed of porous reduced graphene oxide nanosheets (Mn3O4@p-rGO) with enhanced oxidase-like activity were successfully fabricated through an in-situ approach for fast colorimetric detection of ascorbic acid (AA). The residual Mn2+ in the GO suspension of Hummers method was directly reused as the manganese source, improving the atom utilization efficiency. Benefiting from the uniform distribution of Mn3O4 nanoparticles on the surface of p-rGO nanosheets, the nanocomposite exhibited larger surface area, more active sites, and accelerated electron transfer efficiency, which enhanced the oxidase-like activity. Mn3O4@p-rGO nanocomposite efficiently activate dissolved O2 to generate singlet oxygen (1O2), leading to high oxidation capacity toward the substrate 3,3',5,5'-tetramethylbenzidine (TMB) without the extra addition of H2O2. Furthermore, the prominent absorption peak of the blue ox-TMB at 652 nm gradually decreased in the presence of AA, and a facile and fast colorimetric sensor was constructed with a good linear relationship (0.5-80 µM) and low LOD (0.278 µM) toward AA. Owing to the simplicity and excellent stability of the sensing platform, its practical application for AA detection in juices has shown good feasibility and reliability compared with HPLC and the 2, 4-dinitrophenylhydrazine colorimetric method. The oxidase-like Mn3O4@p-rGO provides a versatile platform for applications in food testing and disease diagnosis.

Partially oxidized MoS2 nanosheets with high water-solubility to enhance the peroxidase-mimic activity for sensitive detection of glutathione.

Surface oxidation engineering is an effective strategy to construct nanomaterials with enhanced biocatalytic activity. In this study, a facile one-pot oxidation strategy was proposed to synthesize partially oxidized molybdenum disulfide nanosheets (ox-MoS2 NSs), which exhibit good water solubility and can be used as an excellent peroxidase substitute. Under the oxidation process, Mo-S bonds are partially broke and S atoms are replaced by excess oxygen atoms, and the released abundant heat and gases efficiently expended the interlayer distance and weaken the van der Waals forces between adjacent layers. Porous ox-MoS2 NSs can be easily exfoliated by further sonication, and the nanosheets exhibits excellent water dispersibility and no obvious sediment appear even after store for months. Benefiting from the desirable affinity property with enzyme substrates, optimized electronic structure and prominent electron transfer efficiency, the ox-MoS2 NSs exhibit enhanced peroxidase-mimic activity. Furthermore, the ox-MoS2 NSs catalyzed 3,3',5,5'-tetramethylbenzidine (TMB) oxidation reaction could be inhibited by the redox reaction that take place between glutathione (GSH) as well as the direct interaction between GSH and ox-MoS2 NSs. Thus, a colorimetric sensing platform was constructed for GSH detection with good sensitivity and stability. This work provides a facile strategy for engineering structure of nanomaterials and improving enzyme-mimic performance.

Straightforward Generation of Pillared, Microporous Graphene Frameworks for Use in Supercapacitors.

Microporous, pillared graphene-based frameworks are generated in a simple functionalization/coupling procedure starting from reduced graphene oxide. They are used for the fabrication of high-performance supercapacitor devices.