Effective Adsorption of Precious Metal Palladium over Polyethyleneimine-Functionalized Alumina Nanopowder and Its Reusability as a Catalyst for Energy and Environmental Applications

Pd "Kills Two Birds with One Stone" for the Synthesis of Catalyst: Dual Active Sites of Pd Triggers the Kinetics of O2 Electrocatalysis

Noble metal-based catalyst, despite their exorbitant cost, are the only successful catalyst for bifunctional oxygen electrocatalysis owing to their capability to drive forward the reaction rate kinetically. Therefore, it is desirable to diminish the noble metal loading without any compromise in the catalyst performance. In this study, the aim to achieve two goals with one action via a single-step route to have ultra-low loading of Pd in the catalyst. The Pd is used as a catalyst for C─C bond formation followed by complexation reactions or vice versa, in conventional Suzuki-Miyaura cross-coupling (SMCC) reaction, which yields a Pd-based porous organic polymer. Interestingly, it is found that dispersed Pd nanocluster (PdNC ) is present together with Pd single atom doped into nanocarbon (Pd-NC) matrix in the catalyst (PdNC /Pd-NC800 ) that obtained after pyrolysis of the porous polymer. The catalyst exhibits remarkable bifunctional activity and durability towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Further, it is studied that the in situ attenuated total reflection infrared (ATR-IR) spectroscopy at different electrochemical potentials during ORR and OER to observe the reaction intermediates. The homemade zinc-air battery with the catalyst displayed great performance, establishing the significance of PdNC /Pd-NC800 as a bifunctional oxygen electrocatalyst.

Adsorption of palladium from chloride aqueous solution using silica alginate nanomaterial

The adsorption characteristics of palladium from chloride aqueous solution onto the silica alginate (SA-Si) nanomaterial have been investigated. The prepared nanomaterial (SA-Si) was characterized by various advanced techniques that ensured a successful preparation process. Different adsorption parameters including the solution pH, shaking time, palladium ion concentration, adsorbent dosage, and temperature were investigated. The experimental results showed that the pseudo-first-order model provided the best fitting for the palladium ions adsorption, and the time required to reach equilibrium was 90.0 min. The adsorption isotherm result from palladium was well described by the Langmuir isotherm model and the maximum adsorption capacity of (SA-Si) nanomaterial was estimated as 12.50 mg/g for Pd(II). Moreover, the thermodynamic results demonstrated that Pd(II) sorption onto (SA-Si) nanomaterial was endothermic and spontaneous. Additionally, the SA-Si nanomaterial can be used as an effective adsorbent for the sorption of Pd(II) from various metal ions present in fission products.

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), PtCl₆^2-) and palladium (Pd(II), PdCl₄^2-), 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.

Mechanically Robust Hybrid Gel Beads Loaded with "Naked" Palladium Nanoparticles as Efficient, Reusable, and Sustainable Catalysts for the Suzuki-Miyaura Reaction

The increase in demand for Pd and its low abundance pose a significant threat to its future availability, rendering research into more sustainable Pd-based technologies essential. Herein, we report Pd scavenging mechanically robust hybrid gel beads composed of agarose, a polymer gelator (PG), and an active low-molecular-weight gelator (LMWG) based on 1,3:2,4-dibenzylidenesorbitol (DBS), DBS-CONHNH ₂ . The robustness of the PG and the ability of the LMWG to reduce Pd(II) in situ to generate naked Pd(0) nanoparticles (PdNPs) combine within these gel beads to give them potential as practical catalysts for Suzuki-Miyaura cross-coupling reactions. The optimized gel beads demonstrate good reusability, green metrics, and most importantly the ability to sustain stirring, improving reaction times and energy consumption compared to previous examples. In contrast to previous reports, the leaching of palladium from these next-generation beads is almost completely eliminated. Additionally, for the first time, a detailed investigation of these Pd-loaded gel beads explains precisely how the nanoparticles are formed in situ without a stabilizing ligand. Further, detailed catalytic investigations demonstrate that catalysis occurs within the gel beads. Hence, these beads can essentially be considered as robust "nonligated" heterogeneous PdNP catalysts. Given the challenges in developing ligand-free, naked Pd nanoparticles as stable catalysts, these gel beads may have future potential for the development of easily used systems to perform chemical reactions in "kit" form.

IL-Functionalized Mg3Al-LDH as New Efficient Adsorbent for Pd Recovery from Aqueous Solutions

Palladium is a noble metal of the platinum group metals (PGMs) with a high value and major industrial applications. Due to the scarce palladium resources, researchers' attention is currently focused on Pd ions recovery from secondary sources. Regarding the recovery process from aqueous solutions, many methods were studied, amongst which adsorption process gained a special attention due to its clear advantages. Moreover, the efficiency and the selectivity of an adsorbent material can be further improved by functionalization of various solid supports. In this context, the present work aims at the synthesis and characterization of Mg₃Al-LDH and its functionalization with ionic liquid (IL) (Methyltrialkylammonium chloride) to obtain adsorbent materials with high efficiency in Pd removal from aqueous solutions. The maximum adsorption capacity developed by Mg₃Al-LDH is 142.9 mg Pd., and depending on the functionalization method used (sonication and co-synthesis, respectively) the maximum adsorption capacity increases considerably, q_max-Mg₃Al IL-US = 227.3 mg/g and q_max-Mg₃Al IL-COS = 277.8 mg/g.

Methacrylate-Based Polymeric Sorbents for Recovery of Metals from Aqueous Solutions

The industrialization and urbanization expansion have increased the demand for precious and rare earth elements (REEs). In addition, environmental concerns regarding the toxic effects of heavy metals on living organisms imposed an urgent need for efficient methods for their removal from wastewaters and aqueous solutions. The most efficient technique for metal ions removal from wastewaters is adsorption due to its reversibility and high efficiency. Numerous adsorbents were mentioned as possible metal ions adsorbents in the literature. Chelating polymer ligands (CPLs) with adaptable surface chemistry, high affinity towards targeted metal ions, high capacity, fast kinetics, chemically stable, and reusable are especially attractive. This review is focused on methacrylate-based magnetic and non-magnetic porous sorbents. Special attention was devoted to amino-modified glycidyl methacrylate (GMA) copolymers. Main adsorption parameters, kinetic models, adsorption isotherms, thermodynamics of the adsorption process, as well as regeneration of the polymeric sorbents were discussed.

Fast and efficient adsorption of palladium from aqueous solution by magnetic metal-organic framework nanocomposite modified with poly(propylene imine) dendrimer

In this study, a magnetic metal-organic framework (MMOF) was synthesized and post-modified with poly(propyleneimine) dendrimer to fabricate a novel functional porous nanocomposite for adsorption and recovery of palladium (Pd(II)) from aqueous solution. The morphological and structural characteristics of the prepared material were identified by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmet-Teller (BET) isotherm, and vibrating sample magnetometer (VSM). The results confirmed the successful synthesis and post-modification of MMOF. Semispherical shape particles (20-50 nm) with appropriate magnetic properties and a high specific surface area of 120 m²/g were obtained. An experimental design approach was performed to show the effect of adsorption conditions on Pd(II) uptake efficiency of the dendrimer-modified magnetic adsorbent. The study showed that the Pd(II) uptake on dendrimer-modified MMOF was well described by the Langmuir isotherm model with the highest uptake capacity of 291 mg/g under optimal condition (adsorbent content of 12.5 mg, Pd ion concentration of 80 ppm, pH = 4, and contact time of 40 min). The adsorption kinetics of Pd(II) ions was suggested to be a pseudo-first-order model. The results revealed a faster adsorption rate and higher adsorption capacity (about 43%) for dendrimer-modified MMOF. Finally, the reusability of the provided adsorbent was evaluated. This work provides a valuable strategy for designing and developing efficient magnetic adsorbents based on MOFs for the adsorption and recovery of precious metals.

Chemically modified rice husk as an effective adsorbent for removal of palladium ions

Bio-matrix of rice husk and Mobil Composition of Matter No. 41 (MCM-41) was modified with alizarin red S for preconcentration of Pd²⁺ prior flame atomic absorption spectrometric determination. The prepared bio-matrix (RH@MCM-41@ARS) was characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope, energy dispersive X-ray spectrometer (SEM/EDX) and surface area studies. The impact of different parameters (solution pH, amount of sorbent, contact time, sample volume, initial Pd²⁺ concentration and diverse ions) on the uptake of Pd²⁺ were evaluated. The maximum adsorption capacity of Pd²⁺ onto RH@MCM-41@ARS was 198.2 mg g^-1 at optimum conditions. Applying the optimized procedure as a preconcentration step led to limit of detection of 0.13 μg L^-1 and dynamic analytical range up to 500 μg L^-1. The sorbent was regenerated by 0.5 mol L^-1 thiourea for at least 10 cycles without significant reduction of adsorption capacity. The method was applied for preconcentration of Pd²⁺ from real samples.

A Pyridyltriazol Functionalized Zirconium Metal-Organic Framework for Selective and Highly Efficient Adsorption of Palladium

This work reports the synthesis of pyridyltriazol-functionalized UiO-66 (UiO stands for University of Oslo), namely, UiO-66-Pyta, from UiO-66-NH₂ through three postsynthetic modification (PSM) steps. The good performance of the material derives from the observation that partial formylation (∼21% of -NHCHO groups) of H₂BDC-NH₂ by DMF, as persistent impurity, takes place during the synthesis of the UiO-66-NH₂. Thus, to enhance material performance, first, the as-synthesized UiO-66-NH₂ was deformylated to give pure UiO-66-NH₂. Subsequently, the pure UiO-66-NH₂ was converted to UiO-66-N₃ with a nearly complete conversion (∼95%). Finally, the azide-alkyne[3+2]-cycloaddition reaction of 2-ethynylpyridine with the UiO-66-N₃ gave the UiO-66-Pyta. The porous MOF was then applied for the solid-phase extraction of palladium ions from an aqueous medium. Affecting parameters on extraction efficiency of Pd(II) ions were also investigated and optimized. Interestingly, UiO-66-Pyta exhibited selective and superior adsorption capacity for Pd(II) with a maximum sorption capacity of 294.1 mg g^-1 at acidic pH (4.5). The limit of detection (LOD) was found to be 1.9 μg L^-1. The estimated intra- and interday precisions are 3.6 and 1.7%, respectively. Moreover, the adsorbent was regenerated and reused for five cycles without any significant change in the capacity and repeatability. The adsorption mechanism was described based on various techniques such as FT-IR, PXRD, SEM/EDS, ICP-AES, and XPS analyses as well as density functional theory (DFT) calculations. Notably, as a case study, the obtained UiO-66-Pyta after palladium adsorption, UiO-66-Pyta-Pd, was used as an efficient catalyst for the Suzuki-Miyaura cross-coupling reaction.

A cationic porous organic polymer for high-capacity, fast, and selective capture of anionic pollutants

The emerging ionic porous organic materials have achieved various applications in different fields, however, there is limited study on using them to capture ionic pollutants from water. Here we demonstrate a facile method to prepare a cationic porous organic polymer via catalyst-free Schiff base reaction. The imidazolium-based polymer (ImPOP-1) was constructed through copolymerizing cationic molecules with low-cost benzidine. The as-prepared ImPOP-1 exhibits high capacity (e.g., 476.2 mg g^-1 for Pd (II) and 578.5 mg g^-1 for AO7^-), excellent selectivity (e.g., more than 99% removal efficiency for Pd (II) in the presence of 100 times excess of SO₄^2-), and fast kinetics (e.g., 98.6% removal efficiency within 5 min for Pd (II) ions) to the anionic pollutants including organic dyes and heavy metal ions. The excellent performance on scavenging anionic pollutants from water suggests that ImPOP-1 holds promising potential as an ion exchange material for water remediation.

Wastes generated by automotive industry – Spent automotive catalysts

Rhodium, ruthenium, palladium, and platinum are classified as platinum group metals (PGM). A demand for PGM has increased in recent years. Their natural sources are limited, therefore it is important, and both from economical and environmental point of view, to develop effective process to recover PGM from waste/secondary sources, such as spent automotive catalysts. Pyrometallurgical methods have always been used for separation of PGM from various materials. However, recently, an increasing interest in hydrometallurgical techniques for the removal of precious metals from secondary sources has been noted. Among them, liquid-liquid extraction by contacting two liquid phases: aqueous solution of metal ions and organic solution of extractant is considered an efficient technique to separate valuable metal ions from solutions after leaching from spent catalysts.

A perspective on diverse adsorbent materials to recover precious palladium and the way forward

A perspective on diverse adsorbent materials for the recovery of palladium.