In this paper we describe a simple colorimetric method for the sensitive and selective detection of Ba ²⁺ ions, using 11-mercaptoundecylphosphonic acid functionalized gold nanoparticles (AuNPs–MPA) in aqueous solution.

3- and 4-pyridineboronic acids have been combined with trimesic and pyromellitic acids to give three molecular complexes of compositions [(3PBAH⁺)(H₂TMA⁻)] (1), [(3PBAH⁺)₂(H₂PMA²⁻)] (2), and [(4PBAH⁺)₂(H₂PMA²⁻)]·2H₂O (3) (3PBA = 3-pyridineboronic acid, 4PBA = 4-pyridineboronic acid, H₃TMA = trimesic acid, H₄PMA = pyromellitic acid). The products have been characterized by elemental analysis, infrared spectroscopy, single-crystal X-ray diffraction analysis and luminescence spectroscopy. The structural analysis revealed that the hydrogen bonding interactions of the resulting 2D and 3D assemblies involve at least one of the following charge-assisted synthons: –B(OH)₂⋯⁻OOCR, RCOOH⋯⁻OOCR or PyN⁺–H⋯⁻OOCR. The dimensions are enhanced by additional hydrogen bonds as well as π–π stacking interactions, which include B⋯π interactions in two crystal structures. Intermolecular close contacts have also been examined by Hirshfeld surface analysis, which by means of the associated 2D fingerprint plots enabled similarities and differences in the crystal structures to be revealed. Solid-state photoluminescence spectroscopy of compounds 1–3 revealed that variations of the π–π stacking in the molecular aggregates induced changes in the emission behavior.

A new, sustainable polypropylene terephthalate (PPT) coating was synthesized from recycled polyethylene terephthalate (PET) and applied onto a hydraulic concrete substrate to improve its durability. For the first step, PET bottle wastes were ground and depolymerized by glycolysis using propylene glycol (PG) in a vessel-type reactor (20–180 °C) to synthesize bis(2-hydroxypropyl)-terephthalate (BHPT), which was applied as a coating to one to three layers of hydraulic concrete substrate using the brushing technique and polymerized (150 °C for 15 h) to obtain PPT. PET, BHPT, and PPT were characterized by FT-IR, PET, and PPT using TGA, and the PPT coatings by SEM (thickness), ASTM-D3359-17 (adhesion), and water contact angle (wettability). The durability of hydraulic concrete coated with PPT was studied using resist chloride ion penetration (ASTM-C1202-17), carbonation depth at 28 days (RILEM-CPC-18), and the absorption water ratio (ASTM-C1585-20). The results demonstrated that the BHPT and PPT were synthetized (FT-IR), and PPT had a similar thermal behavior to PET (TGA); the PPT coatings had good adhesion to the substrate, with thicknesses of micrometric units. PPT coatings presented hydrophilic hydrophilic behavior like PET coatings, and the durability of hydraulic concrete coated with PPT (2–3 layers) improved (migration of chloride ions decreased, carbonation depth was negligible, and the absorption water ratio decreased).

A facile colorimetric method for rapid determination of Cr(III) ions was developed using 11-mercaptoundecylphosphonic acid modified gold nanoparticles (AuNPs-MPA) in aqueous medium. The reaction of AuNPs-MPA + Cr(III) ions were were characterized by FTIR and Uv-Vis spectroscopy. The presence of Cr(III) easily induced aggregation of AuNPs-MPA, resulting in the color change from pink to blue. This method exhibited excellent selectivity toward Cr(III) compared to other metal cations. Optimal detection of Cr(III) was found in a pH range from 4 to 9, the detection time within 8 min. In addition, the developed effective probe has been successfully applied to detect Cr(III) water samples.