Yao Tang,Xiaoyu Zhou,Ming Lei,Huimin Wang,Anqi Lu,Guihua Zhang,Lihua Zhu,Kangle Lv,Heqing Tang
It is still urgently needed to clarify how the reductive dehalogenation is accelerated by the interaction between the catalyst and the reducing agent. In the present work, both Pd and Cu were observed to induce the debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) with hydrazine hydrate (N 2 H 4 ·H 2 O) as reducing agent. In the case of Pd system, all the added BDE47 was debrominated to bromine-free products within 20 min. However, much different debromination behaviors of BDE47 were observed when Cu was used as the catalyst: in the initial stage the debromination efficiency of BDE47 could reach up to 55.3% within 0.5 min; nevertheless the complete debromination could not be achieved by prolonging reaction time. With the aid of DFT calculations, the above-mentioned great differences were attributed to the affinity of Pd to both H and N atoms, and strong Cu–N coordination existed between Cu and the adsorbed hydrazine molecules. The dissociation energy for the cleavage of N–H and N-N bonds of N 2 H 4 ·H 2 O adsorbed on Cu was very low, and hence the debromination of BDE47 was ultra-fast due to the spontaneously cleavage of N–H bond but it was inhibited at the later stage by the generated ammonium species (poisoning effect to the Cu catalyst) due to N-N bond cleavage. In contrast, the dissociation energy for the cleavage of N–H bond on the surface of Pd was higher and no ammonium was detected. These guarantee the continuously fast and complete debromination of BDE47 and its intermediates. These new insights to the catalytic mechanism through the interaction between the catalyst and the reducing agent will help to construct an efficient system to remove halogenated organic pollutants .
Kai-Yao Wang,Yang Liu,Jia-Ying Zhu,Lin Cheng,Cheng Wang
Deep investigations on the synthetic and structural chemistry of heterometallic chalcogenidostannates bear fundamental significance for the establishment of the structure–property relationship that would offer guidance on the functional material innovation. Presented here are four ammonium- and/or alkylammonium-directed M–Sn–Q (M = Zn, Cd; Q = S, Se) compounds, namely, [NH4]7[H3O]3Zn4Sn4S17 (1), [NH4]5[(CH3)2NH2]Zn4Sn5S17 (2), [CH3CH2NH3]22Zn16Sn12Se51(H2O)4·16H2O (3), and [NH4]2CdSnSe4 (4). All four compounds were synthesized in deep eutectic solvents (DESs) or ethylamine aqueous solution, both of which function simultaneously as reaction media and structure-directing agents. Compound 1 consists of discrete P1-[Zn4Sn4S17]10– clusters templated by mixed [NH4]+/[H3O]+ cations. In compound 2, such P1 clusters are bridged by Sn4+ ions in a 4,4-connection mode to form a [Zn4Sn5S17]n6n– framework with three types of cavities (I–III) varying in size. The two smaller cavities (I and II) accommodate NH4+ while the larger one(III) is occupied by [(CH3)2NH2]+, reflecting the rational size-dependence of cations on cavities. Compound 3 features an [Zn16Sn12Se51(H2O)4]n22n– open framework constructed from the 4,3-connection of P1-[Zn4Sn4Se17]10– clusters and {Zn(H2O)}2+ bridges. This linkage mode contributes to a large cage-like subunit (inner dimension: 21.99 × 9.06 Å2) and therefore an ultrahigh porosity that are occupied by [CH3CH2NH3]+ cations and water molecules (volume fraction: 57.7%). Compound 4 exists as a stacking of [CdSnSe4]n2n– chains, which are composed of alternatively arranged {CdSe4} and {SnSe4} tetrahedra, in combination with [NH4]+ cations as both charge-compensating and space-filling agents. Detailed synthetic, structural, and topological analyses were performed on these solid materials, coupled with extensive investigations on their optical and thermal properties. Compound 3 exhibits an efficient Sr2+ adsorption performance, featuring ultrafast kinetics (94.69% in 5 min), high removal rate (98.57% in 20 min) at equilibrium, and high capacity (104.17 ± 23.53 mg g–1).
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