Biomass chitosan/sodium alginate colorimetric imprinting hydrogels with integrated capture and visualization detection for cadmium(II)

Due to Cd(II) with highly toxic, persistent and bioaccumulative, the discharge of it into the environment brings serious pollution. Developing strategies that are efficient, low-cost, pollution-free and specific to removing Cd(II) from wastewater is therefore of great urgency and prime importance. A novel chitosan/sodium alginate ionic imprinting(IICA) hydrogels with specific adsorption capacity for Cd(II) was prepared through freeze-thaw and ion imprinting, and finally the colorimetric sensor (IICAS) was prepared via introducing Rhodamine B(RhB) and Victoria blue(VBB) by immersion to achieve visual detection of Cd(II). The IICA hydrogels with imprinted hole structure had higher adsorption capacity and better specific selectivity for Cd(II). As well as internal diffusion, coordination, ion exchange, and hydrogen bonding influenced the adsorption rate. Moreover, the IICAS exhibited good selective detection ability and linearity for Cd(II) with the fitted correlation coefficient (R2) = 0.98, limit of detection (LOD) = 35 nmol/L. Combined with the smartphone platform, portable and quantitative detection of Cd(II) can be achieved, Within the 0-100 mg/L range, R2 remained 0.94, and LOD was 75 nmol/L. This strategy of preparing a novel whole biomass IICAS integrating capture and visual detection provides a new insight into the construction of a promising candidate sensor for the removal and detection of Cd(II).

Torsional flexibility in zinc-benzenedicarboxylate metal-organic frameworks

We explore the role and nature of torsional flexibility of carboxylate-benzene links in the structural chemistry of metal-organic frameworks (MOFs) based on Zn and benzenedicarboxlyate (bdc) linkers. A particular motivation is to understand the extent to which such flexibility is important in stabilising the unusual topologically aperiodic phase known as TRUMOF-1. We compare the torsion angle distributions of TRUMOF-1 models with those for crystalline Zn/1,3-bdc MOFs, including a number of new materials whose structures we report here. We find that both periodic and aperiodic Zn/1,3-bdc MOFs sample a similar range of torsion angles, and hence the formation of TRUMOF-1 does not require any additional flexibility beyond that already evident in chemically-related crystalline phases. Comparison with Zn/1,4-bdc MOFs does show, however, that the lower symmetry of the 1,3-bdc linker allows access to a broader range of torsion angles, reflecting a greater flexibility of this linker.

Spectrophotometric Determination of Trace Amount of Total FeII/FeIII and Live Cell Imaging of a Carboxylato Zn(II) Coordination Polymer

The coordination polymer, (Zn(II)-CP, 1), {[Zn(2,6-NDC)(4-Cltpy)](H₂O)₄} (1) (2,6-H₂NDC = 2,6-naphthalene dicarboxylic acid and 4-Cltpy = 4'-chloro-[2,2';6',2″]terpyridine) is structurally characterized by single crystal X-ray diffraction measurement and other physicochemical studies (PXRD, FTIR, thermal analysis, microanalytical data). 4-Cltpy acts as end-capping ligand, and NDC^2- is a carboxylato bridging motif to constitute ZnN₃O₂ distorted trigonal bipyramid core that propagates to construct 1D chain. The coordination polymer, 1, detects total iron (Fe³⁺ and Fe²⁺) in aqueous solution by visual color change, colorless to pink. Absorption spectrophotometric technique in aqueous medium measures the limit of detection (LOD) 0.11 μM (Fe²⁺) and 0.15 μM (Fe³⁺), and binding constants (K_d) are 6.7 × 10⁴ M^-1 (Fe³⁺) and 3.33 × 10⁴ M^-1 (Fe²⁺). Biocompatibility of 1 is examined in live cells, and intracellular Fe²⁺ and Fe³⁺ are detected in MDA-MB 231 cells. Zn(II) substitution is assumed upon addition of Fe^III/Fe^II solution to the suspension of the coordination polymer, 1, in water-acetonitrile (41:1) (LZn^II + Fe^III/II → LFe^III + Zn^II, where L is defined as coordinated ligands), which is accompanied by changing from colorless to pink at room temperature. The color of the mixture may be assumed to the charge transfer transition from carboxylate-O to Cltpy via Fe(II/III) bridging center (carboxylate-O-Fe-CltPy). The product isolated from the reaction is finally characterized as Fe(III)@1-CP. It is presumed that product Fe(II)@1-CP may undergo fast aerial oxidation to transform Fe(III)@1-CP. The Fe^III exchanged framework (Fe(III)@1-CP) has been characterized by PXRD, IR, TGA and energy dispersive X-ray analysis (EDX)-SEM. The MTT assay calculates the cell viability (%), and the tolerance limit is 100 μM to total Fe²⁺ and Fe³⁺.