RESUMEN
Bifunctional nanocrystals which combine two kinds of materials into single nanoparticles hold great promise in photoelectrochemical (PEC) analysis, particularly for nanocrystals based on perovskite quantum dots (QDs) which generally exhibit excellent photoelectric activity yet poor stability and upconversion nanoparticles (UCNP) that normally suffer from negligible photoelectric activity. Therefore, to achieve good performance of the PEC bioassay platform, it is valuable to combine perovskite QDs with UCNP encapsulation and promote their advantages to form hybrid nanocrystals that are stable, NIR excitable, and photoelectric. Herein, the core-shell configuration of perovskite/upconversion CsPbBr2I@NaYF4:Yb,Tm (CPBI@UCNP) nanocrystals coupled with a NiMn-layered double hydroxide (NiMn-LDH)/CdS heterojunction to form a cascade sensitization structure was proposed to construct the lab-on-paper PEC device for ultrasensitive detection of malathion pesticides. Concretely, the bifunctional CPBI@UCNP nanocrystals that encapsulated CPBI QDs into UCNPs were employed as a nanoscale light source and sensitizer in the lab-on-paper system, which not only prevented the degradation of perovskite QDs but also overcame the negligible photoelectric performance of pristine UCNPs with the cooperation of photoactive CPBI QDs. The synergistic quenching effect, including fluorescence energy resonance transfer (FRET) and photoinduced electron transfer (PET), was created to realize enhanced PEC signal readout. Benefiting from the dynamic cascade sensitization structure of CPBI@UCNP/NiMn-LDH/CdS and synergistic quenching effect of FRET/PET, the ultrasensitive detection of malathion was achieved with high selectivity, reproducibility, and stability, which provided guidelines to employ perovskite/upconversion nanomaterials for lab-on-paper PEC analysis.
RESUMEN
Recovery of platinum group metals (PGMs) from secondary resources has attracted worldwide attention from environmental and economic points of view. Pyrometallurgical routes exhibit the superiority in terms of efficiency and contamination control compared to hydrometallurgical process. However, traditional pyrometallurgical processes face the challenges of excessive flux and energy consumption. In this paper, an iron capture process was proposed to recover low-grade PGMs from leaching residue of spent auto-exhaust catalysts. Slag design was explored aimed at reducing the addition amount of flux. The optimized smelting conditions were as follows: 1400 °C for 30 min, adding 40.0 wt% CaO, 22.7 wt% Na2CO3, 5.0 wt% Na2B4O7, 5.0 wt% CaF2, 15.0 wt% Fe, and 5.0 wt% C. The concentrations of Pt, Pd and Rh remaining in the smelting slag were 0.83 g/t, 4.99 g/t, and 1.47 g/t, respectively. Furthermore, the 50 kg-scale experiment implied positive economic feasibility because of saving flux dosage and smelting time. The capture mechanism was revealed by investigating the formation of the metals phase and slag phase. Matrix formed slag phase and separate with metals phase owing to differences in chemical bonding, density, viscosity, and surface tension. PGMs were proved solubilized in α-Fe as substitutional solid solutions. The formation energies for FePt, FePd, and FeRh alloys were -4.149 eV, -4.040 eV, and -4.360 eV, respectively. Finally, the obtained CaO-SiO2-Al2O3-Na2O glass slag was used for producing glass ceramics. To sum up, the iron capture process realized low energy and material consumption, high recovery efficiency of PGMs, and resource utilization of the glass slag.
Asunto(s)
Hierro , Dióxido de Silicio , Catálisis , MetalesRESUMEN
Reclamation of spent catalysts for the efficient recovery of palladium (Pd) is gaining growing attention due to its scarcity and high supply risk. Currently Pd extraction from spent catalysts through an efficient, economical, and green method has remained a challenge. In this study, Fe3+ is utilized for leaching through oxidation of Pd in a mild condition. Before leaching, distillation was proposed to remove and recover the organics from spent catalysts. The effects of HCl concentration, Fe3+ concentration, NaCl concentration, leaching time, and temperature on the leaching efficiency of Pd were investigated to determine the optimum leaching conditions. The results show that Pd extraction and dissolution of Al2O3 increase with higher HCl concentration. The effect of NaCl on Pd leaching efficiency is significant at low acid concentration (2.0 mol/L HCl). The leaching efficiency was 99.5% for Pd under the following conditions: 2.0 mol/L HCl, 4.0 mol/L NaCl, and 0.67 mol/L Fe3+ at 80 °C for 90 min. The leaching kinetics fits best to the shrinking-core model of surface chemical reaction. The activation energy for the leaching of Pd was 47.6 kJ/mol. PdCl42- was selectively adsorbed by anion exchange resin. The filtrate containing adequate H+, Cl-, and Fe3+ was reused as leaching agent. Pd leaching efficiency was over 96% after five cycle times. This study provides an efficient process for recovery of Pd from spent catalysts.