Portable electrochemical sensing platform based on amidated GO-MOF and PEDOT:PSS for high-efficient detection of ponceau 4R

A promising electrochemical sensing platform for the detection of ponceau 4R in food has been fabricated based on the carboxylated graphene oxide (GO-COOH), metal-organic framework (MOF) UIO-66-NH2, and poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). To this end GO-COOH was covalently coupled with UIO-66-NH2 through amide reaction, endowing the material (GO-CONH-UIO-66) unique hierarchical pores and high chemical stability and as a result improving the conductivity of MOF and the dispersion of GO. After the addition of PEDOT:PSS into GO-CONH-UIO-66, the continuity and conductivity of the composite (PEDOT:PSS/GO-CONH-UIO-66) have been further enhanced, due to the high conductivity, favorable film-forming, and hydrophilic properties of PEDOT:PSS. Systematic electrochemical experiments confirm that the PEDOT:PSS/GO-CONH-UIO-66/GCE shows satisfactory electrochemical sensing properties towards the detection of ponceau 4R, with a wide linear detection range of 0.01-30 μM, a low limit of detection of 3.33 nM, and a high sensitivity of 0.606 μA μM-1 cm-2. The PEDOT:PSS/GO-CONH-UIO-66 sensing platform was successfully used to detect ponceau 4R in beverage, and the detection results were compared with  high-performance liquid chromatography. As a result, the PEDOT:PSS/GO-CONH-UIO-66 composite shows a promising application prospect for rapid detection of ponceau 4R in food and will play significant role in food safety detection and supervision.

Highly Efficient Capture of Volatile Iodine by Conjugated Microporous Polymers Constructed Using Planar 3- and 4-Connected Organic Monomers

The effective capture and recovery of radioiodine species associated with nuclear fuel reprocessing is of significant importance in nuclear power plants. Porous materials have been proven to be one of the most effective adsorbents for the capture of radioiodine. In this work, we design and synthesize a series of conjugated microporous polymers (CMPs), namely, TPDA-TFPB CMP, TPDA-TATBA CMP, and TPDA-TECHO CMP, which are constructed based on a planar rectangular 4-connected organic monomer and three triangular 3-connected organic monomers, respectively. The resultant CMPs are characterized using various characterization techniques and used as effective adsorbents for iodine capture. Our experiments indicated that the CMPs exhibit excellent iodine adsorption capacities as high as 6.48, 6.25, and 6.37 g g-1 at 348 K and ambient pressure. The adsorption mechanism was further investigated and the strong chemical adsorption between the iodine and the imine/tertiary ammonia of the CMPs, 3D network structure with accessible hierarchical pores, uniform micromorphology, wide π-conjugated structure, and high-density Lewis-base sites synergistically contribute to their excellent iodine adsorption performance. Moreover, the CMPs demonstrated good recyclability. This work provides guidance for the construction of novel iodine adsorbent materials with high efficiency in the nuclear power field.

Barbituric and thiobarbituric acid-based UiO-66-NH2 adsorbents for iodine gas capture: Characterization, efficiency and mechanisms

Efficient iodine gas capture is necessitated in many industries like spent nuclear fuel off-gas treatment in view of environmental protection and resource recycling. However, the adsorption efficiency and stability of the current adsorbents are limited. In the present work, efficient and stable barbituric and thiobarbituric acid-based UiO-66-NH₂ adsorbents (i.e., UiO-66-NH-B.D and UiO-66-NH-T.D, respectively) have been synthesized by post-synthetic covalent modification. Characterization approaches, including SEM-EDS, TEM, XRD, FTIR, XPS, ¹H NMR, TGA and BET, are used to obtain information on the properties and adsorption mechanisms of these metal-organic framework (MOF) adsorbents. The kinetics and mechanisms involved are studied in detail. The treatment efficiency and recyclability of the adsorbents are checked and compared with the adsorbents reported in previous works. The results show that the current adsorbents are potentially suitable for efficient iodine gas capture. High maximum iodine adsorption amount by UiO-66-NH-B.D and UiO-66-NH-T.D (1.17 and 1.33 g/g) was achieved under 75 °C. These new adsorbents are thermally stable for iodine adsorption and regenerated and reused with good performance. The adsorption mechanisms were revealed based on experimental results, indicating that iodine is adsorbed by both physisorption and chemisorption.

Microporous Hyper-Cross-Linked Polymers with High and Tuneable Content of Pyridine Units: Synthesis and Application for Reversible Sorption of Water and Carbon Dioxide

New hyper-cross-linked porous organic polymers (POPs) with a high content of pyridine segments (7.86 mmol pyridine g^-1 ), and a micro/mesoporous texture are reported. The networks are achieved by the chain-growth homopolymerization of 2,6- and 3,5-diethynylpyridines. The pyridine segments form links interconnecting the polyacetylene main chains in these networks. The content of pyridine segments in the networks can be tuned by copolymerizing diethynylpyridines with 1,3-diethynylbenzene. The pyridine rings in the networks serve as base and hydrophilic centers for the sorption of CO₂ and water. The homopolymer pyridine networks are highly efficient in the low-pressure adsorption/desorption of CO₂ . This sorption mode is promising for the postcombustion removal of CO₂ from the fuel gas. The poly(3,5-diethynylpyridine) network exhibits high efficiency in capturing and releasing water vapor (determined capacity 376 mg g^-1 at 298 K and relative humidity (RH) = 90% is one of the highest values reported for POPs) and is a promising material for the cyclic water harvesting from air. The reported networks are characterized by ¹³ C cross-polarization magic angle spinning NMR, thermogravimetric analysis, and N₂ adsorption/desorption and their efficiency in CO₂ and H₂ O capturing is discussed in relation to the content and type of incorporated pyridine segments.

The Effects of Oxygen Functional Groups on Graphene Oxide on the Efficient Adsorption of Radioactive Iodine

Oxygen-containing functional groups tend to induce a strong interaction between solid adsorbents and iodine molecules, yet have not been systematically investigated. Herein, on the basis of a series of nitric acid-treated graphene oxide (GO) with different contents of oxygen functional groups for iodine adsorption, it was found that the iodine uptake capacity is proportionate to the oxygen content and the diversities of oxygen-containing groups. The density functional theory (DFT) calculation results also suggest that oxygen-containing groups result in strong interactions between iodine molecules and the adsorbents through a covalent bond-forming process, among which -OH groups possess a higher adsorption energy averagely. Such theoretical and experimental work deepens our understanding of the effects of oxygen functional groups on iodine adsorption and provides novel ideas for future design and synthesis of high-performance solid adsorbents for radioactive iodine.

Tunable Strategies Involving Flexibility and Angularity of Dual Linkers for a 3D Metal-Organic Framework Capable of Multimedia Iodine Capture

The widespread use of nuclear power poses severe health and environmental risks owing to the nonregulated release and disposal of radioactive wastes in the environment. Among these wastes, the capture and removal of radioactive iodine poses a big challenge. To develop a novel material for capturing molecular iodine, we have strategically synthesized a nitrogen-rich three-dimensional (3D) metal-organic framework (MOF), {[Mn₂(oxdz)₂(tpbn)(H₂O)₂]·2C₂H₅OH}_n (1), utilizing a bent heterocyclic dicarboxylate linker (H₂oxdz: (4,4'-(1,3,4-oxadiazole-2,5-diyl)dibenzoic acid)) and a flexible bis(tridentate) ligand (tpbn: N, N', N″, N‴-tetrakis(2-pyridylmethyl)-1,4-diaminobutane). Based on its single-crystal structure, 1 is an eightfold interpenetrated 3D framework, consisting of a unique 4-connected {Mn₂(tpbn)} subunit, in which the pores line up with the nitrogen atoms of the oxadiazole moiety. This can be considered as a big leap for the development of 3D MOFs using flexible bis(tridentate) ligands. To emphasize the role of the flexible methylene chain length in such ligand in the dimensionality of the resultant framework, the tphn (N, N', N″, N‴-tetrakis(2-pyridylmethyl)-1,6-diaminohexane) ligand with two additional methylene groups provides a one-dimensional (1D) CP {[Mn₂(oxdz)₂(tphn)(H₂O)]·CH₃OH}_n (2). This spacer chain lengthening has a profound effect on the coordination of such ligand with Mn(II), further affecting the binding of oxdz. The inherent polarizable nature of the oxadiazole moiety and the presence of permanent pore of dimensions (19.122 × 19.253 Ų) in 1 have been exploited for the capture/removal of iodine not only from vapor and an organic solution but also from an aqueous media. It exhibits competent 100% reversible sorption of iodine with an uptake capacity of (1.1 ± 0.05) g/g of 1. The uptake value has been corroborated by both gravimetric and titrimetric analyses. The interaction of iodine with 1 has been notably studied with molecular simulations, kinetic models of sorption, field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDX) analysis. Moreover, 1 is highly stable and is recyclable without much loss of sorption capability up to five cycles.

Fluorescent conjugated microporous polymers containing pyrazine moieties for adsorbing and fluorescent sensing of iodine

Two kinds of fluorescent conjugated microporous polymers containing pyrazine moieties were prepared by the polymerization reaction of 2,5-di-triphenylamine-yl-pyrazine (DTPAPz) and N,N,N',N'-tetrapheny-2,5-(diazyl) pyrazine (TDPz) with 2,4,6-trichloro-1,3,5-triazine (TCT) through Friedel-Crafts reaction using the methanesulfonic acid as a catalysts. Both CMPs have high thermal stability and decomposition temperature reaches above 596 and 248 °C under nitrogen atmosphere, respectively. By right of porous morphology and electron-donating nitrogen, as well as electron-rich π-conjugated structures, the adsorption performance for iodine vapor on the CMPs is very excellent, which can reach 441% and 312%. In addition, fluorescence studies showed that the two CMPs exhibited high fluorescence sensitivity to electron-deficient iodine, o-nitrophenol (o-NP), and picric acid (PA) via fluorescence quenching.

Augmented polyhydrazone formation in water by template-assisted polymerization using dual-purpose supramolecular templates

Template-assisted polymerization using donor–acceptor supramolecular templates results in higher M_w and M_n values, decreased critical hydrogelation concentrations, and increased gel recovery velocity following shear-induced breakdown.

Amorphous Porous Organic Polymers Based on Schiff-Base Chemistry for Highly Efficient Iodine Capture

Porous organic polymers (POPs) have been considered as prominent adsorbents for volatile iodine. So far, both crystalline and amorphous POPs have accomplished excellent iodine capture capability. Considering the difficulty and challenges in preparing perfect crystalline POPs, more explorations into developing versatile amorphous POPs are needed. Herein, amorphous POPs based on the Schiff-base reaction were designed and synthesized for volatile iodine removal. Four amorphous POPs products named as NDB-H, NDB-S, ADB-HS, and ADB-S obtained under different solvothermal conditions were investigated in terms of their morphologies, porosity, and their iodine enrichment performance in detail. It is noteworthy that excellent efficiency for removing iodine vapor was acquired for NDB-S (≈425 wt %), ADB-HS (≈345 wt %), and ADB-S (≈342 wt %). Remarkably, NDB-H exhibited an iodine capture capacity up to ≈443 wt %. Excellent reusability was obtained as well. Amorphous NDB-H has accomplished an extremely high iodine capture performance, illustrating the great chance to exploit versatile amorphous POPs for iodine enrichment and removal based on Schiff-base chemistry.