Organic-inorganic based nano-conjugate adsorbent for selective palladium(II) detection, separation and recovery

Abstract

The functional group containing organic ligand of N,N(octane-1,8-diylidene)di(2-hydroxy-3,5-dimethylaniline) (DHDM) was developed and then successfully anchored onto mesoporous silica for the preparation of nano-conjugate adsorbent (NCA). After fabrication, the DHDM kept open functionality for capturing palladium (Pd(II)) under optimum conditions. The NCA exhibited the distinct color formation (π–π transition) after adding the Pd(II) ions both in solid and liquid states. The solution pH played an important role in the detection and sorption of Pd(II) but the prepared NCA worked well in the acidic pH region at 1.50. The data also clarified that the NCA did not form any color and signal intensity even in the presence of diverse ions except Pd(II). The determined limit of detection to Pd(II) ions was low as 0.14 μg/L. In Pd(II) sorption, the affecting factors such as solution pH, kinetics, isotherm models, competing ions and elution/regeneration were studied in detail. The NCA confirmed the rapid sorption property and the maximum sorption capacity was 213.67 mg/g due to spherical nanosized cavities with large surface area and pore volume.The base metal of Cu(II) and Zn(II) did not hamper the Pd(II) sorption ability of NCA in the acidic pH region. Therefore, it was expected that the Pd(II) could be separated from other hard metal ions by the NCA. The data also clarified that the other competing metal ions did not decrease the Pd(II) sorption capacity and NCA had almost no sorption capacity, which suggested the high selectivity of Pd(II) ions by NCA. The adsorbed Pd(II) was eluted with 0.20 M HCl–0.20 M thiourea eluent and simultaneously regenerated into the original form. The NCA was reversible and kept remaining functionality for reuse in many cycles after an extraction/elution process without significant deterioration. Therefore the proposed NCA can be considered as a potential candidate for Pd(II) capturing from waste samples.