A 2D porous Fe2O3/graphitic-C3N4/graphene ternary nanocomposite with multifunctions of catalytic hydrogenation, chromium(vi) adsorption and detoxification is reported.

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In view of the high toxicity of Cr(VI), simple and rapid on-site analytical approaches are in high demand for environment monitoring. Herein, an innovative chemosensor is developed for on-site sensitive detection of Cr(VI) in minutes by the naked eye. The chemosensor consists of gallic acid-capped gold nanoparticles (GA-Au NPs), methylene blue (MB), and NaBH 4 . In the presence of Cr(VI) ions, the reduction of MB by NaBH 4 is able to greatly accelerate due to the Cr(VI)-stimulated catalytic activity of GA-Au NPs, resulting in a color switching of MB from blue to colorless for the quantitative detection of Cr(VI). The chemosensor in solution exhibits excellent selectivity and ultrahigh sensitivity to Cr(VI), with the detection limits of 0.05 nM by UV−vis spectroscopy and 0.1 nM by the naked eye. Similarly, a paper-based chemosensor is obtained by immobilization of GA-Au NPs and MB onto a piece of filter paper, offering a more convenient approach for rapid on-site detection of Cr(VI). In addition, H 2 O 2 as an oxidizing agent is employed to convert Cr(III) into Cr(VI), thus achieving speciation analysis of Cr. The applicability of a chemosensor is also validated by the detection of Cr speciation in water samples with satisfactory recoveries.

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In this study, a crystal porous organic framework (POF) belonging to ctn topology (POFct-1) is synthesized to selectively scavenge Hg(II) and Cu(II) ions. The maximum adsorption capacities of 167.19 mg g −1 and 135.60 mg g −1 are achieved toward Hg(II) and Cu(II) ions, respectively. In addition, the Langmuir isotherm model plus pseudosecond-order kinetic model for Hg(II) and Cu(II) ions can well describe the adsorption process of POFct-1. After five repeated uses, POFct-1 still exhibits high adsorption capacities. Conversely, a POF in amorphous form (POFct-2) is synthesized by changing the pressure and atmospheric conditions. The distribution coefficients of Cu (II) ions for the crystal (POFct-1) and amorphous (POFct-2) forms are 1.01 × 10 5 and 5.93 × 10 2 mL g −1 in a single ion solution, respectively. These results indicate that the POF in crystal form exhibits increased adsorption selectivity toward Cu(II) ions. The diverse structures and performances of POFs present them as promising candidates in selective adsorption of heavy metal ions.