Cationic imprinting of Pb(II) within composite networks based on bovine or fish chondroitin sulfate

Molecularly Imprinted Methyl-Modified Hollow TiO2 Microspheres

The possibility of generating organically modified hollow TiO₂ microspheres via a simple sol-gel synthesis was demonstrated for the first time in this work. A mixture of titania precursors, including an organically modified precursor, was used to obtain methyl-modified hollow TiO₂ microspheres selective for bilirubin by the molecular imprinting technique (Methyl-HTM-MIM). Methyl-HTM-MIM were prepared by a sol-gel method using titanium (IV) isopropoxide (TTIP), and methyltitanium triisopropoxide (MTTIP) as precursors. Two ratios of titania precursors were tested (1/6 and 1/30 mol_MTTIP/mol_TTIP). With the characterization results obtained by the SEM and ATR-FTIR techniques, it was possible to establish that only the 1/30 mol_MTTIP/mol_TTIP ratio allowed for the preparation of hollow spheres with a reasonably homogeneous methylated-TiO₂ shell. It was possible to obtain a certain degree of organization of the hybrid network, which increased with calcination temperatures. By adjusting isothermal adsorption models, imprinting parameters were determined, indicating that the new methylated microspheres presented greater selectivity for bilirubin than the totally inorganic hollow TiO₂ microspheres. The effectiveness of the molecular imprinting technique was proven for the first time in an organically modified titania material, with imprinting factor values greater than 1.4, corresponding to a significant increase in the maximum adsorption capacity of the template represented by the molecularly imprinted microspheres. In summary, the results obtained with the new methyl-HTM-MIM open the possibility of exploring the application of these microspheres for selective sorption (separation or sensing, for example) or perhaps even for selective photocatalysis, particularly for the degradation of organic compounds.

Improved Metal Cation Optosensing Membranes through the Incorporation of Sulphated Polysaccharides

Optosensing chitosan-based membranes have been applied for the detection of heavy metals, especially in drinking water. The novelty of this study is based on the use of sulphated polysaccharides, in such optosensing membranes, aiming at an improved analytical performance. The sulphated polysaccharides, such as ulvan, fucoidan and chondroitin sulfate, were extracted from by-products and wastes of marine-related activities. The membranes were developed for the analysis of aluminum. The variation in the visible absorbance of the sensor membranes after the contact between the chromophore and the aluminum cation was studied. The membranes containing sulphated polysaccharides showed improved signals when compared to the chitosan-only membrane. As for the detection limits for the membranes containing ulvan, fucoidan and chondroitin sulfate, 0.17 mg L⁻¹, 0.21 mg L⁻¹ and 0.36 mg L⁻¹ were obtained, respectively. The values were much lower than that obtained for the chitosan-only membrane, 0.52 mg L⁻¹, which shows the improvement obtained from the sulphated polysaccharides. The results were obtained with the presence of CTAB in analysis solution, which forms a ternary complex with the aluminum cation and the chromophore. This resulted in an hyperchromic and batochromic shift in the absorption band. When in the presence of this surfactant, the membranes showed lower detection limits and higher selectivity.