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Photochromic inks have shown disadvantages, such as poor durability and high cost. Self-healable hydrogels have shown photostability and durability. Herein, a viologen-based covalent polymer was printed onto a paper surface toward the development of a multi-stimuli responsive chromogenic sheet with thermochromic, photochromic, and vapochromic properties. Viologen polymer was created by polymerizing a dialdehyde-based viologen with a hydroxyl-bearing dihydrazide in an acidic aqueous medium. The viologen polymer was well immobilized as a colorimetric agent into a polyvinyl alcohol (PVA)/tricarboxy cellulose (TCC)-based self-healable hydrogel. The viologen/hydrogel nanocomposite films were applied onto a paper surface. The coloration measurements showed that when exposed to ultraviolet light, the orange layer printed on the paper surface switched to green. The photochromic film was used to develop anti-counterfeiting prints using the organic hydrogel composed of a PVA/TCC composite and a viologen polymer. Reversible photochromism with strong photostability was observed when the printed papers were exposed to UV irradiation. A detection limit was monitored in the range of 0.5–300 ppm for NH3(aq). The exposure to heat (70 °C) was found to reversibly initiate a colorimetric change. [ABSTRACT FROM AUTHOR]

The elimination of metal ions from industrial waste water is one of the most significant environmental needs. For the first time, two chitosan hydrogels that we had previously synthesized, cross-linked with varying concentrations of trimellitic anhydride isothiocyanate (represented by H1 and H2), were utilized in this investigation to adsorb Cu(II) ions. We found that pH 6, 25 °C, 200 mg L−1 of Cu(II) ions concentration, and 15 mg of hydrogel dosage were the ideal parameters for Cu(II) ion elimination. The kinetics of their adsorption fitted to the pseudo-second-order model with the highest correlation coefficient (R2) values equal to 0.999 and 1.00 for H1 and H2, respectively. The experimental qe values were found when H1 was equal to 97.59 mg g−1 (theoretical value is equal to 98.04 mg g−1) and H2 was equal to 96.20 mg g−1 (theoretical value is equal 99.01 mg g−1). The hydrogels achieved a removal effectiveness of 97.59% and their adsorption isotherms matched the Freundlich model, indicating the multi-layered and homogeneous adsorption nature. The removal of copper ions is significantly driven by the physisorption phenomenon. The hydrogels have a great possibility to be utilized as promising, efficacious, reusable adsorbents for industrial wastewater remediation. Thus, incorporation of a cross-linker, containing binding centers for Cu(II) ions, between chitosan chains is a good way to obtain suitable efficient adsorbents which are good choices for application in the field of metal elimination. [ABSTRACT FROM AUTHOR]

Pd(II) with the Schiff base ligand 2-Hydroxy-3-Methoxy Benzaldehyde-Thiosemicarbazone (HMBATSC) (L2) and 2-aminobenzothiazole (2-ABZ) (L1) was synthesized. The Schiff base ligand and the Palladium(II) complex were characterized by C.H.N.S, FT-IR, conductance studies, magnetic susceptibility, XRD, and TGA. From the elemental analysis and spectral data, the complex was proposed to have the formula [Pd(HMBATSC)(2-ABZ)H2O]. The interaction between the Pd(II) complex and DNA was examined through various methods, including UV–Vis spectroscopy, fluorescence techniques, and DNA viscosity titrations. The findings provided strong evidence that the interaction between the Pd(II) complex and DNA occurs through the intercalation mode. The analysis yielded the following values: a Stern–Volmer quenching constant (ksv) of 1.67 × 104 M−1, a quenching rate constant (kq) of 8.35 × 1011 M−1 s−1, a binding constant (kb) of 5.20 × 105 M−1, and a number of binding the sites (n) of 1.392. DFT studies suggest that the azole derivative may act as an electron donor through pyridine nitrogen, while the Schiff base ligand may act as an electron donor via oxygen and sulfur atoms. TDDFT calculations indicate that the intramolecular charge transfer from the Schiff base to Pd(II) is responsible for the complex's fluorescence quenching. The powder X-ray diffraction data revealed that the complex is arranged in a monoclinic system. The resulting Pd(II) complex was investigated for its antimicrobial activity and demonstrated antibacterial efficiency. Interestingly, it showed potent activity against E. coli and E. niger that was found to be more powerful than that recorded for Neomycin. [ABSTRACT FROM AUTHOR]