Electro-Driven in Situ Construction of Functional Layer Using Amphoteric Molecule: The Role of Tryptophan in Ion Sieving

Anion-controlled Zn(II) coordination polymers with 1-(tetrazo-5-yl)-3-(triazo-1-yl) benzene as an assembling ligand: synthesis, characterization, and efficient detection of tryptophan in water

Tryptophan regulates and participates in various physiological systems in the human body, and its excessive intake has harmful effects. Therefore, detecting and monitoring tryptophan in water and distinguishing it from other amino acids are necessary. In addition to their excellent luminescence, coordination polymer-based sensors have good stability and high sensitivity and selectivity for sensing applications. In this work, two luminescent coordination polymers (CPs), [Zn(ttb)Cl]_n (1) and [Zn₂(ttb)₂(OH)(NO₃)]_n (2), were obtained through the solvothermal reaction of different Zn(II) salts with a rarely studied multidentate N-donor ligand, 1-(tetrazo-5-yl)-3-(triazo-1-yl) benzene (Httb). Crystallographic investigations revealed that the structure of 1 exhibits a 2D fes net with Cl^- anions acting as terminal charge balancers, and that of 2 features a 3D ant net with NO₃^- anions in a rare monodentate bridging (μ₂-O-η¹:η¹) mode. In terms of stability tests, 2 has better thermal and water stability than 1. Although both show good fluorescence performance, specific tryptophan detection, and excellent anti-interference ability, 2 has higher K_SV (111 852.6 M^-1), a lower limit of detection (LOD = 23.6 nM), and a better recovery rate than 1. Cytotoxicity experiments proved that 2 has extremely low toxicity and thus has great potential for in vivo detection. Therefore, CP 2 is a suitable candidate for advanced practical applications for the efficient sensing of tryptophan in water. The luminescence of the ligands was also calculated using DFT theory and further discussed through experiments. The quenching mechanism that occurs after tryptophan addition was explored through Hirshfeld surface analysis.

A comprehensive review on the synthesis and applications of ion exchange membranes

Ion exchange membranes (IEMs) are undergoing prosperous development in recent years. More than 30,000 papers which are indexed by Science Citation Index Expanded (SCIE) have been published on IEMs during the past twenty years (2001-2020). Especially, more than 3000 papers are published in the year of 2020, revealing researchers' great interest in this area. This paper firstly reviews the different types (e.g., cation exchange membrane, anion exchange membrane, proton exchange membrane, bipolar membrane) and electrochemical properties (e.g., permselectivity, electrical resistance/ionic conductivity) of IEMs and the corresponding working principles, followed by membrane synthesis methods, including the common solution casting method. Especially, as a promising future direction, green synthesis is critically discussed. IEMs are extensively applied in various applications, which can be generalized into two big categories, where the water-based category mainly includes electrodialysis, diffusion dialysis and membrane capacitive deionization, while the energy-based category mainly includes reverse electrodialysis, fuel cells, redox flow battery and electrolysis for hydrogen production. These applications are comprehensively discussed in this paper. This review may open new possibilities for the future development of IEMs.

Electrodialytic Desalination of Tobacco Sheet Extract: Membrane Fouling Mechanism and Mitigation Strategies

In the papermaking industry (reconstituted tobacco), a large number of tobacco stems, dust, and fines are discharged in the wastewater. This high salinity wastewater rich in ionic constituents and nicotine is difficult to be degraded by conventional biological treatment and is a serious threat that needs to be overcome. Electrodialysis (ED) has proved a feasible technique to remove the inorganic components in the papermaking wastewater. However, the fouling in ion exchange membranes causes deterioration of membranes, which causes a decrease in the flux and an increase in the electrical resistance of the membranes. In this study, the fouling potential of the membranes was analyzed by comparing the properties of the pristine and fouled ion exchange membranes. The physical and chemical properties of the ion exchange membranes were investigated in terms of electrical resistance, water content, and ion exchange capacity, as well as studied by infrared spectroscopy (IR) spectra, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analyses. The results indicated that the membrane fouling is caused by two different mechanisms. For the anion exchange membranes, the fouling is mainly caused by the charged organic anions. For the cation exchange membrane, the fouling is caused by minerals such as Ca²⁺ and Mg²⁺. These metal ions reacted with OH⁻ ions generated by water dissociation and precipitated on the membrane surface. The chemical cleaning with alkaline and acid could mitigate the fouling potential of the ion exchange membranes.