High-capacity/high-rate hybrid column for high-performance ion exchange.

Herein, a fixed-bed high-capacity/high-rate (HC/HR) hybrid column was developed using commercial ion-exchange beads (IEBs) and ion-exchange fibers (IEFs). The as-fabricated HC/HR hybrid column exhibited excellent breakthrough bed volume (BV) and utilization efficiency of capacity (UEC) at a high service flow rate (SFR) for the adsorption of Cd(II). The IEBs displayed a high adsorption capacity of 235.2 ± 9.8 mg g-1 and slow adsorption kinetics (k2 = 0.0001 g mg-1 min-1) for the sorption of Cd(II); meanwhile, the IEFs showed a maximum adsorption capacity of only 146.3 ± 7.5 mg g-1, which is lower than that of the IEBs, but fast kinetics (k2 = 0.0130 g mg-1 min-1). At an SFR of 104.23 BV h-1, the HC/HR hybrid column showed excellent performance for the sorption of Cd(II), having a high breakthrough BV of 1009.11 and a UEC of 92.86%; these values are much higher than those of the IEB-packed column. Furthermore, at an increased SFR (318.47 BV h-1), the HC/HR hybrid column maintained its high performance, demonstrating a breakthrough BV of 568.80 and UEC of 83.90%. The regeneration experiment indicates that 97% of the initial capacity was retained. Thus, the HC/HR hybrid column could easily be applied to existing column systems and shows promising performance in ion-exchange processes.

Surface Modified Nano Fly Ash as an Activator in the Reduction of Ketones.

Surface modified nano fly ash has been used as an activator, in the reduction of a few cyclic and acyclic ketones with NaBH4 as reducing agent. Exclusive formation of trans-4--butyl cyclohexanol was observed in such case. Reduction of 3-methylcyclohexanone yielded only cis-3-methylcyclohexanol (equatorial -OH). In case of reduction of other substituted cyclohexanones, propensity to form more of equatorial alcohol was observed. The chemical yields of various alcohols were high (∼95-99%). The rates of reductions of the ketones were also appreciably high. It appears that the silanol groups present in the surface modified fly ash cause nucleophilic activation of the carbonyl groups leading to faster reaction rate. Exclusive formation of the epimer with equatorially disposed -OH group is most likely due to the same reason. Finally, the advantage of the activator lies in its low cost.

Chitosan-thioglycolic acid composite cross-linked with glutaraldehyde for selective recovery of Au(III) ions from e-waste leachate via reduction-coupled adsorption and incineration.

The recovery of gold (Au) from electronic waste (e-waste) has gained significant attention due to its high Au content and economic feasibility compared to natural ores. This study presents a facile, single-step approach to prepare the chitosan-thioglycolic acid composite crosslinked with glutaraldehyde (CS-TGA-GA) and demonstrates its unique capability for precious metal management, which is a less investigated application area for thiolated chitosan materials. The novel cost-effective biosorbent CS-TGA-GA demonstrated a very high adsorption capacity of 1351.9 ± 96 mg/g and selectivity for Au(III) from an acidic e-waste solution at pH 1 and 298 K. The high adsorption capacity and selectivity of the sorbent can be attributed to the abundance of -NH2, -OH, and -SH groups present on its surface. Various characterizations, such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffractometry, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy, as well as sorption experiments, including pH, kinetic, and isotherm studies, were performed. The kinetic data align with a pseudo-second-order model and the isotherm data can be well expressed by the Freundlich model. The CS-TGA-GA composite effectively facilitated the conversion of Au(III) to Au(0), leading to the formation of Au nanoparticles that aggregated in the reaction vessel over time. Subsequently, the Au-loaded CS-TGA-GA underwent an incineration procedure, yielding recovered Au with a purity of 99.6%, as measured by X-ray fluorescence. In addition to its large uptake capacity, acid stability, and recyclability, the prepared sorbent showed a highly selective uptake of Au(III) ions in a solution containing various metal ions leached from waste printed circuit boards. These results highlight the potential of CS-TGA-GA as an adsorbent for the recovery of Au from e-waste leachate, thereby contributing to sustainable resource management.

Graphene oxide-based dendritic adsorbent for the excellent capturing of platinum group elements.

Herein, we report amino functionalized thermally stable graphene oxide-based dendritic adsorbent (GODA) with the highest sorption capacity ever recorded for platinum group elements (PGEs), including platinum (Pt(IV), PtCl62-) and palladium (Pd(II), PdCl42-), from highly acidic aqueous solutions. The GODA was designed and synthesized to have fully ionized amine binding sites and was characterized in detail. The detail batch adsorption experiment along with kinetic, isotherm, and thermodynamic studies were carried out to investigate the adsorption efficacy of GODA. For both Pt(IV) and Pd(II), the experimental data are more accurately fitted with the pseudo-second-order and the intraparticle diffusion kinetic models and Langmuir isotherm model as compared to the pseudo-first-order kinetic model and Freundlich and Temkin isotherm models, respectively. The material showed the highest ever adsorption capacities of 827.8 ± 27.7 mg/g (4.24 ± 0.00 mmol/g) and 890.7 ± 29.1 mg/g (8.37 ± 0.00 mmol/g) for Pt(IV) and Pd(II), respectively, at pH 1. The adsorption equilibriums were achieved within 70 min and 65 min for Pt(IV) and Pd(II), respectively. The thermodynamic parameters indicate that the adsorptions of both metals are spontaneous. The binding mechanisms are considered to be electrostatic interactions, hydrogen bonding, cationic-π bonding, and surface complexation between the sorbent and the sorbates. Furthermore, the as-prepared GODA exhibited high thermal stability and significant acid-resistance at pH 1. The GODA demonstrated excellent regeneration and reusability for Pt(IV) and Pd(II) over five adsorption/desorption cycles, indicating its excellence in practical applications.