Pd Adsorption Research Articles

Mechanism of Pd(II) adsorption by nanoscale titanium dioxide loaded bamboo shoot shell biomass.

Palladium (Pd) is widely used in catalyst, aerospace, and medical applications, but only 1% of its reserves are found in nature. So, the recovery of Pd(II) is very important. Natural fibers are a good adsorption material, and the abundant functional groups in bamboo shoot shell (BSS) fibers can form interactions with metal particles. However, few studies on Pd(II) adsorption using BSS fibers exist. In the present work, waste bamboo shoot shells were doped with titanium dioxide (TiO2) particles, and the surface activation of BSS-TiO2@CA by citric acid (CA) was carried out to prepare an efficient and recyclable adsorbent BSS-TiO2@CA for the adsorption of Pd(II). The adsorption performance, adsorption mechanism, and regeneration performance of BSS-TiO2@CA on Pd(II) were systematically analyzed by continuous adsorption experiments, characterization, and response surface method. It was found that the surface-activated waste bamboo shoot shells had an outstanding adsorption capacity of Pd(II), and the maximum adsorption rate of BSS-TiO2@CA reached 85% with a maximum adsorption capacity (Qm) of 175.74 mg/g. The functionalized use of waste bamboo shoot shells provides a new idea for the development of sustainable, cost-effective, and environmentally friendly adsorbents.

A novel hydrangea-like magnetic composite Fe3O4@MnO2@ZIF-67 for efficient selective adsorption of Pd(II) from metallurgical wastewater

The selective adsorption of palladium from wastewater is a feasible solution to solving palladium pollution and resource scarcity. Because traditional solvent extraction methods often involve the use of considerable amounts of organic solvents, research is focused on investigating adsorption techniques that can selectively remove palladium from wastewater. In this paper, the magnetic composite Fe3O4@MnO2@ZIF-67 was synthesized and its performance for the adsorption of Pd(II) in acidic water was investigated. Fe3O4@MnO2@ZIF-67 was characterized by various analytical methods such as TEM, SEM, EDS, BET, XRD, FTIR, zeta potential analysis, VSM, and TGA. The effects of palladium ion concentration, contact time, pH, and temperature on adsorption were evaluated. The kinetics were shown to follow the pseudo-second-order kinetic model and Elovich model, and the rate-limiting step was chemisorption. Thermodynamic studies showed that increasing the temperature promoted the adsorption of Pd(II), and the maximum uptake capacity of Fe3O4@MnO2@ZIF-67 for Pd(II) was 531.91 mg g−1. Interestingly, Fe3O4@MnO2@ZIF-67 exhibited superior selectivity for Pd(II) in the presence of Ir(IV), Pt(IV), and Rh(III). The adsorbent can be used repeatedly for selective adsorption of palladium. Even at the fifth cycle, the uptake rate of Pd(II) remained as high as 83.1%, and it showed a favorable adsorption capacity and selectivity for Pd(II) in real metallurgical wastewater. The adsorption mechanism was analyzed by SEM, FTIR, XRD, XPS, and DFT calculations, which indicated that electrostatic interactions and coordination with nitrogen-containing groups were involved. Fe3O4@MnO2@ZIF-67 is a promising adsorbent for the efficient adsorption and selective separation of palladium ions.

Flow cytometry-based high-throughput screening of synthetic peptides for palladium adsorption

Conventionally, the measurement of metal ion adsorption capacity in biosorbent relies on expensive and time-consuming ICP-OES technique. Herein, a semi-quantitative method to measure Pd(II) adsorption capacity of single cells has been presented by analyzing side scatter (SSC) intensity in flow cytometry. Within the sensitive range and applicable conditions, excellent linearity correlation (R2 ranges from 0.89 to 0.96) between the amount of Pd(II) absorbed on yeast and the fold increase in SSC intensity has been observed. Using this method, six strains with high Pd adsorption capacities have sorted from a yeast library with metal-binding peptides displayed (up to 107 strains) based on SSC signal intensity. The optimal peptide (EF1) displayed on yeast and E. coli surface demonstrated Pd adsorption improvements of ∼32% and ∼200%, respectively. In summary, our study proposes an alternative high-throughput method for analyzing the Pd(II) adsorption capacity of individual yeast cells, enabling the screening of specific peptides/proteins with high Pd(II) affinity from extensive libraries.

Simple Coumarin-Based Fluorescent Probe for Recognition of Pd(II) and Its Live Cell Imaging.

A simple coumarin hydrazine Schiff base bearing a thioether recognition fragment (compound CBBS) has been rationally designed and easily prepared. CBBS exhibited an excellent selectivity for Pd(II) and a low detection limit of 65 nM (S/N = 3). The fluorescence emission intensities of CBBS at 495 nm were linear to Pd(II) concentrations in a wide range from 0 to 80 μM. Moreover, CBBS has been well used in fluorescence imaging of Pd(II) in living A549 cells. CBBS as a simple coordination-based fluorescent probe will inspire the researchers to develop a polymer for selective detection and adsorption of Pd(II).

Efficient and selective recovery of gold and palladium by simple and easily synthesized polyethylenimine based polymer

Polyethylenimine (PEI) crosslinked by 5,5-dithiodisalicylic acid (TDSA) is prepared through solution polymerization and serves as an adsorbent (TDSA@PEI) for the effective adsorption of Au(III) and Pd(II). TDSA@PEI exhibits excellent adsorption performance for Au(III) in a wide pH range of 3–10. The maximum adsorption capacity of TDSA@PEI for Au(III) and Pd(II) is 2579 mg/g and 808 mg/g at 25 °C, respectively. The adsorption isotherms of the two precious metals by TDSA@PEI are more fitted well by the Langmuir model. Meanwhile, TDSA@PEI exhibits excellent selectivity and reusability for Au(III) and Pd(II) adsorption. The adsorption equilibrium was reached at 5 min for 9.8 mg/L of Pd(II), and the adsorption kinetics of both Au(III) and Pd(II) are in accordance with the pseudo-second-order kinetic model. The adsorption of Au(III) and Pd(II) by TDSA@PEI is a spontaneous, endothermic and entropy increasing process. In addition, the column separation approach proves the great applicability of TDSA@PEI in industry. The abundant amino, thioether and hydroxyl groups in TDSA@PEI are responsible for its superior performance, forming several types of interactions with Au(III) and Pd(II) ions such as electrostatic interactions, chelation and redox.

Stabilization and anchoring of palladium‐copper alloy on murexide modified carbon nanotube as a superb nanocatalyst: Excellent performance in coupling and synthetic reactions

Sketching a proper catalytic system with supplementary attributes, containing easy separation, wide surface area, supreme loading capacity, and fantastical electronic attributes, proposes an encouraging direction for efficiently using nanostructures for various applications. However, the capability to adjust the nano‐measure bimetallic particles is an adjustment for attaining superb performance in the catalytic field. Herein, an environmentally benign approach was developed for immobilizing and anchoring Pd‐Cu alloy nanoparticles on murexide (MX)‐functionalized carbon nanotubes (CNTs). Afterward, the catalytic activity of Pd2‐Cu3@MX/CNT was studied in synthesizing 2,3‐dihydro quinazoline‐4(1H)‐ones and carbon–carbon coupling reactions at sustainable reaction conditions under ultrasound irradiation. The results demonstrated that high‐affinity MX ligand and porous CNT structures than the adsorption of Pd–Cu had a unique designation in the high‐range constancy of the alloy nanoparticles and following catalytic activity. In addition, ultrasound irradiation got electrons of Pd–Cu alloy nanoparticles agitated, constructing a synergic efficacy between Cu and Pd metals for synthesis and coupling reactions. Our study represents that the designed catalyst is green, recyclable, and most suitable, providing new intuition into in high‐range constancy of bimetallic nanoparticles for broad applications.

Silica-based covalent organic framework composite for efficient separation and enrichment of palladium and its heterogeneous catalysis application

Considering the necessity and challenge in palladium recovery from high-level liquid waste and hydrogen energy development, the first attempt was made to adsorb Pd(II) from simulated high-level liquid waste firstly, then to achieve in situ reduction by a simple method and followed by using it directly for efficient hydrogen production through the catalytic decomposition of formic acid. In this work, a composite of covalent organic framework and SiO2 (Tp-Azo-COF/SiO2) was prepared by wet impregnation method using SiO2 as a carrier. The characteristics of the composite were examined by SEM, EDS, BET, TG, XRD, etc. The results showed that Tp-Azo-COF/SiO2 exhibited regular silicon-based spherical shapes in microscopic form and good heat resistance. In batch experiments, Tp-Azo-COF/SiO2 was demonstrated excellent adsorption and selectivity for Pd(II) at a wide range of HNO3 acidity (1–5 M), and the separation factor was as high as 2653 at 3 M HNO3. Tp-Azo-COF/SiO2 was able to reach a maximum adsorption capacity of 85.40 mg/g at 120 min at 298 K in 3 M HNO3. FT-IR and XPS analysis show that the adsorption mechanism of Pd(II) by the composite occurs mainly on the C-NH of Tp-Azo-COF, and NO3– is also involved in the coordination. In dynamic column experiments, Tp-Azo-COF/SiO2 was demonstrated a nearly complete separation and recovery of Pd(II) with good reusability, and the enrichment coefficients all maintained at about 30. Finally, an efficient and environmentally friendly process was proposed to achieve the in situ reduction of Pd(II)-loaded Tp-Azo-COF/SiO2. Pd-loaded Tp-Azo-COF/SiO2 was demonstrated better decomposition performance than commercial Pd-based catalysts hydrogen production by the catalytic decomposition formic acid.

Synthesis of activated biochar from sustainable bamboo resources: An environment-friendly and low-cost solution for palladium (II) removal from wastewater

This article highlights the developing capabilities of low-cost activated biochar from bamboo waste used for Palladium (II) (Pd(II)) separation from man-made electroless plating solutions (ELP). From a novelty perspective, this article addresses the effect of coupled sonication and surfactant for the adsorptive elimination of Pd(II) on Bamboo stem activated carbon (BSAC) from ELP. The optimal activation procedure referred to an acid-to-bamboo ratio of 4:1 at sintering of 600–900 °C, which provided an activated carbon (AC) adsorbent with surface area analysis (BET) of 1014.36 m2/g, a value comparable to the commercially procured AC. Pd(II) adsorption characteristics in the solution of Pd with 50-500 mg/L concentration range were evaluated utilizing both agitation and sonication. Adsorption time, pH, dose, and adsorbate concentration were among the pertinent optimal batch adsorption parameters that were found. When utilizing ELP solutions without surfactant, the proposed adsorbent for agitation-assisted adsorption had a simultaneous improvement in metal intake of 6.68–43.2 mg/g and removal efficiency of 72.96–54.5% (cTAB). For cTAB-containing solutions, sonication and agitation-assisted adsorption were outperformed in terms of removal efficiency of 80.32–60.16% and metal uptake of 6.69–50.13 mg/g. Equilibrium, kinetic, and thermodynamic models with good fitting to the reported Pd(II) adsorption properties have been developed.

Guanidinium-functionalized ionic covalent organic framework for selective and efficient recovery of palladium(II) from metallurgical wastewater

Efficient and selective recovery of palladium from acidic metallurgical wastewater is of great economic and environmental importance but remains challenging. Here, two novel ionic covalent organic frameworks (iCOFs), Tp-DGCl and BT-DGCl, were synthesized by reaction of 1,3-diaminoguanidine hydrochloride with 1,3,5-triformyphloroglucinol and benzene-1,3,5-triscarbaldehyde, respectively, and then applied to the recovery of Pd(II) from metallurgical wastewater. The maximum adsorption capacities of Tp-DGCl and BT-DGCl at pH 2.0 and 298.15 K were 342.1 mg g−1 and 231.1 mg g−1, which are higher than the majority of similar reported adsorbents. The adsorption isotherms of Pd(II) on iCOFs were highly consistent with the Langmuir isotherm model. Furthermore, the kinetics of the adsorptions by Tp-DGCl and BT-DGCl conformed to the quasi-second-order kinetic model, indicating that the controlling step of adsorption is chemical adsorption. Thermodynamic studies revealed that elevated temperatures are beneficial for the recovery of Pd(II). At the same time, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, zeta potential, and density functional theory computational analysis confirmed that electrostatic attraction and coordination are the main mechanisms for Pd(II) adsorption on iCOFs. This work not only highlights that the prepared iCOFs can be used as effective reusable adsorbents to selectively adsorb Pd(II) but also opens the door for the practical application of iCOFs in recovering palladium from complex metallurgical wastewater.

Adsorption of Pd(II) ions by electrospun fibers with effective adsorption sites constructed by N, O atoms with a particular spatial configuration: Mechanism and practical applications

The separation and recovery of palladium from electronic waste (e-waste) are of great significance as they can alleviate environmental pollution and avoid resource loss. Herein, a novel nanofiber modified by 8-hydroxyquinoline (8-HQ-Nanofiber) with adsorption sites co-constructed by N and O atoms of hard bases was fabricated, which has good affinity properties for the Pd(II) ions belonging to soft acid in the leachate of e-waste. The adsorption mechanism of 8-HQ-Nanofiber for Pd(II) ions was revealed from the perspective of molecular level relied on a series of characterizations, such as FT-IR, ss-NMR, Zeta potential, XPS, BET, SEM and DFT. The adsorption of Pd(II) ions on 8-HQ-Nanofiber reached equilibrium within 30 min and the maximum uptake capacity was 281 mg/g at 318.15 K. The adsorption behavior of Pd(II) ions by 8-HQ-Nanofiber was described by the pseudo-second-order and Langmuir isotherm models. The 8-HQ-Nanofiber exhibited relatively good adsorption performance after 15 times of column adsorption. Finally, based on hard and soft acids and bases (HSAB) theory, a strategy to regulate the Lewis alkalinity of adsorption sites by specific spatial structures is proposed, which provides a new direction for the design of adsorption sites.

Thermodynamic and kinetic isotope effects on hydrogen absorption by Pd–Al2O3 pellets

Palladium has been widely served as the separation material in the hydrogen isotope separation process on account of its unique hydrogenation characteristics. To reduce Pd pulverization effect and improve the gas flow rate, Pd–Al2O3 (Pd deposited on Al2O3) is commonly used as the separation material. It is crucial to grasp the hydrogen absorption and desorption thermodynamics and kinetic isotope effect of Pd–Al2O3 material, which favours raising the separation efficiency. In this work, the effect of PdO existing in the fresh Pd–Al2O3 on the thermodynamic character of Pd–Al2O3–H(D) system and the porous substrate effect on the hydrogen absorption kinetics of Pd–Al2O3 were investigated. It shows that PdO could totally reduce to Pd after primary hydrogen adsorption-desorption, leading to decreased hydrogen absorption capacity. However, it has no effect on the enthalpy and entropy values of Pd–Al2O3–H (D) system. The kinetic analysis of hydrogen adsorption of Pd–Al2O3 shows that the hydrogen absorption of Pd–Al2O3 could be fitted by Mample model, a special case of the JMAK model, and the interface-controlled model can be deduced. The porous substrate influences the rate of hydrogen adsorption of Pd–Al2O3. The SEM and XRD results show that after 60 hydrogen absorption-desorption cycles, the surface of Pd–Al2O3 pellet has a slight change with a pulverization rate of 3.3 wt%, although the high-strength alumina support can withstand the stress caused by Pd expansion during hydrogen absorption.

Synthesis of carbon disulfide modified chitosan resin and its adsorption properties for palladium(Ⅱ) in wastewater

A novel chitosan resin microsphere (CDCR) adsorbent, which was synthesized by secondary crosslinking and carbon disulfide modification, and was evaluated for its efficacy in recovering palladium from wastewater. The physicochemical properties and adsorption mechanism of CDCR were determined using scanning electron microscope energy dispersive system (SEM-EDS), fourier-transform infrared spectroscopy (FTIR), simultaneous thermal analyzer (TG-DSC), X-ray photoelectron spectroscopy (XPS), etc. The experimental results showed that its saturated adsorption capacity was about 204.34 mg/g. And the adsorption process of Pd(Ⅱ) was found to be in accordance with the pseudo-second-order kinetic model and the Freundlich model. Thermodynamic analysis indicated that the reaction between CDCR and Pd(Ⅱ) was a spontaneous endothermic process. CDCR showed good reusability, maintaining a Pd(Ⅱ) removal efficiency of 99.99% after eight adsorption–desorption cycles. In the multi-ion coexistence solution, CDCR also exhibited excellent selectivity towards Pd(Ⅱ) adsorption. Furthermore, the adsorption of Pd(Ⅱ) by CDCR was primarily attributed to electrostatic interaction with protonated amine groups and complexation with sulfur groups.

Role of cationic surfactants in palladium adsorption of commercial ion exchange resins using electroless plating solutions

AbstractThis work investigates the role of cationic surfactants in the adsorption of palladium ions from synthetic electroless plating solutions using a commercial resin, Lewatit TP-214. This would also help us in determining the batch adsorption experiments elaborated on the optimal parameters such as surfactant concentration, pH, dosage, initial metal ion concentration for the development of an ion-exchange resin with high metal removal efficiency. Critical micelle concentration (CMC) appears to be an important parameter in determining the adsorption behavior of ion-exchange resins with palladium ions. Equilibrium models were measured for their fitness with the obtained Pd (II) batch adsorption characteristics and Freundlich isotherm confirms the heterogeneous Pd (II) adsorption on Lewatit TP-214. FTIR analysis confirmed that the Pd (II) metal uptake of Lewatit TP-214 resin largely depends on amine groups (-NH2+ and -NH+) and the donor atoms attached to cationic surfactant. The optimized choice of adsorption parameters (pH of 8, dosage of 1 g/L, and contact time of 300 min) of Lewatit TP-214 adsorbent provided the highest metal uptake and removal efficiency as 201.7 mg/g and 90.16%, respectively, for the lowest Pd concentration of 300 mg/L.

Ethylenediamine functionalized waste polyethylene terephthalate-derived metal-organic framework for adsorption of palladium ions from aqueous solutions

The recovery of palladium metal is essential in order to meet its growing global demand and also to address water pollution crisis. Herein, MIL-101(Cr)/ED was fabricated from waste polyethylene terephthalate (PET) bottles and modified using ethylenediamine (ED) to retrieve divalent palladium (Pd(II)) metal ions from aqueous environment. The successful grafting of ED moieties onto MIL-101(Cr) was established by the appearance of broad bands at around 2800–3300 cm−1 on the Fourier transform infrared spectrum which was supported by the increase in binding energy using density functional theory. The adsorption experiments revealed that higher Pd(II) ion intake occurred using 30 mg of MIL-101(Cr)/ED in acidic media of pH = 3.0. The data fit better on the Langmuir isotherm with the correlation coefficient (R2) 0.9089. At 25 °C, the MIL-101(Cr)/ED achieved a substantial enhancement in the intake capacities of 454.2 mg.g−1. Kinetics data demonstrated to comply with pseudo-second order, achieving a rapid rate of Pd(II) adsorption by the MIL-101(Cr)/ED in less than 3 min given by the rate constant k2 = 0.02065 g.mg−1.min−1. The MIL-101(Cr)/ED has high affinity for Pd(II) ions as more than 80% removal was achieved even in presence of other ions. These observations revealed the potential utilization of MIL-101(Cr)/ED as an adsorbent to efficiently extract Pd(II) ions from wastewater.

Impact of pretreatment and thiol modifiers on the partial oxidation of glutaraldehyde using Pd/Al2O3

Oxidative conversion of biomass-derived compounds to value-added chemicals is challenging due to the tendency of multi-functional reactants to overoxidize. Catalyst performance can be sensitive to both synthesis and pretreatment conditions. Additionally, coating the catalyst with self-assembled monolayers (SAMs) has shown promise in modulating activity and selectivity. Here, the liquid-phase partial oxidation of glutaraldehyde (GA) to glutaric semialdehyde (GSA) was investigated as a model reaction using a Pd/Al2O3 catalyst, with and without various thiolate SAM modifiers. Reductive pretreatment of the catalyst showed enhancement in the activity and a shortening of an apparent induction period relative to the untreated catalyst. The selectivity for GSA was further found to be sensitive to the identity of the SAM layers, with hydrophilic thioglycerol (TG) and thiolactic acid (TLA) coatings showing an enhancement in selectivity to GSA; the TG coating raised selectivity from ∼ 60 % (on uncoated catalyst and catalysts coated with hydrophobic thiols) to ∼ 80 % at identical conversion (∼ 30 %). However, the TG coating exhibited lower catalytic rates compared to UC and hydrophobically coated materials. Morphological and electronic causes were ruled out with various materials characterization techniques. Density functional theory (DFT) calculations suggested that hydrogen bonding stabilizes adsorption of GSA compared to the uncoated Pd surface. However, a large stabilization of glutaric acid (GAC) adsorption for TG-coated Pd was also predicted, likely leading to accumulation of this overoxidation product and lower overall rates. Inhibition of the rate of GA partial oxidation by GAC adsorption was then corroborated experimentally. Finding ways to stabilize the less-oxidized intermediates with more specificity is thus suggested as a strategy to improve rate and selectivity.

Adsorptive of vanadium and palladium ions using chitin-extracted from shrimp shell wastes: genetic programming modeling

In this study, chitin was extracted from shrimp shells (SS) and characterized by scanning electron microscopy, X-ray diffraction, and Fourier transforms infrared spectroscopy. And investigate the adsorption of vanadium (V) and palladium (Pd) toxic metals onto the chitin. The effect of parameters such as the concentration of V and Pd, contact time, solution pH, adsorbent dose, cations, and anions were studied on the adsorption process. Kinetic, isotherm, and thermodynamic models were investigated. Genetic programming (GP) is used to obtain an appropriate equation showing the relationship between the variables. Experimental optimum conditions were found in the V and Pd concentrations of 25 mg/L, pH of 9, an adsorbent dose of 0.8 g/L and a contact time of 15 minutes. The maximum adsorption capacities (q m) of 13.15 and 12.65 mg/g were obtained for V and Pd, respectively. Among the anions and cations examined in this study, Ca2+ and SO4 2- had the greatest effect on the absorption of V and Pd on chitin. The adsorption kinetics followed a pseudo-second-order kinetic model and the equilibrium data showed a good fit of the Langmuir model and demonstrated a monolayer and favorable physisorption process. The thermodynamic analysis depicted that the process of adsorbing V and Pd using chitin was endothermic and spontaneous. Findings also presented GP as a potential tool for identifying the behavior of V and Pd adsorption. It can be concluded that chitin extracted from SS wastes, as a nontoxic and cheap adsorbent, could efficiently remove V and Pd from aqueous solutions.

Efficient separation of palladium from high-level liquid waste with novel adsorbents prepared by sulfhydryl organic ligands containing imidazole, thiazole and oxazole composited with XAD7HP

Separation of palladium from high level liquid waste (HLLW) not only manages the dispose of HLLW, but could also aid in overcoming the shortage of palladium resources. Herein, three novel adsorbents, namely, 2-mercaptobenzimidazole (MBI)/XAD7HP, 2-mercaptobenzothiazole (MBT)/XAD7HP, 2-mercaptobenzoxazole (MBO)/XAD7HP were prepared by vacuum impregnation method using Amberlite XAD7HP resin (XAD7HP) as the carrier for the selective separation of Pd(II) from simulated HLLW. SEM-EDS (Scanning Electron Microscopy), BET (Brunauer-Emmett-Teller) and PXRD (Powder X-ray diffraction) analysis showed that the ligands were successfully impregnated into the carrier. The saturated adsorption capacities of MBI/XAD7HP, MBT/XAD7HP, MBO/XAD7HP in 0.5 M HNO3 were 126.2 mg Pd/g, 137.6 mg Pd/g, 98.4 mg Pd/g, respectively, and excellent adsorption and separation performance towards Pd(II) (SFPd/other metals > 500 and Kd > 104 mL/g from 0.1 to 4 M HNO3) were also achieved. The adsorption kinetics and adsorption isotherms for Pd(II) matched well with pseudo-second-order kinetic model and Langmuir model, indicating that the adsorption for Pd(II) by three adsorbents were monolayer chemical adsorption. The adsorption mechanism was analyzed by FT-IR, XPS combined with DFT calculation. The extremely high selectivity of three adsorbents towards Pd(II) among 15 metal ions is due to the soft N and S donor atoms at ligands which have good affinity for Pd(II) in HNO3 solution. As MBT/XAD7HP exhibited the best adsorption and separation properties, it is supposed to have more application potential for the separation of Pd(II) from HLLW.

Porous Organic Polymers for Selective Palladium Recovery and Heterogeneous Catalysis.

Palladium (Pd) recycling from waste materials is an important approach in order to meet the growing demand for Pd originating from its broad range of applications including automotive industry, electronics and catalysis. In this article, we discuss the design principles of solid-sorbents for efficient recovery of Pd from waste sources with a particular emphasis on porous organic polymers (POPs), which emerged as promising porous materials for Pd recovery due to their tunable chemical functionality, stability and porosity. We discuss the critical role of binding sites and porosity in the Pd uptake capacity, adsorption kinetics and selectivity. We also highlight the use of captured Pd within the polymer networks as heterogeneous catalysts for cross-coupling reactions.

Adsorption of Pd(II) from wastewater by a functionalized metal-organic framework with aminopyridine structure: Performance and mechanism

Metal-organic frameworks are recognized as a new kind of potential adsorbent for wastewater treatment because of their tunable pore size, high surface area and modifiable functionality. In this work, 2,6-diaminopyridine functionalized UiO-66-NH2 (UiO-66-DAP) was synthesized by a post-modification strategy and was applied to the adsorption of Pd(Ⅱ) from aqueous solution. The aminopyridine structure on UiO-66-DAP greatly improved the adsorption performance for Pd(II), with an adsorption capacity of 190.95 mg/g. The adsorption process of Pd(Ⅱ) on UiO-66-DAP was consistent with the pseudo-second-order kinetic model and the Langmuir adsorption isotherm. Thermodynamic studies confirmed that the adsorption process was endothermic and spontaneous. Regeneration studies showed that UiO-66-DAP was stable and recyclable. Moreover, UiO-66-DAP could maintain high selectivity to Pd(Ⅱ) even in a wastewater containing multiple interfering metal ions. According to the results of Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), zeta potential, comparative experiments and DFT calculations, the chelation and electrostatic attraction between Pd(Ⅱ) and the aminopyridine structural unit are the dominant mechanisms. Using UiO-66-DAP as an adsorbent, this study provides a promising way for the separation of palladium form wastewater.

Sedimentable polyethyleneimine-modified yeast residue enhances the selective adsorption of Pd(II) by altering isoelectric point

Modifying the surface of microorganisms is a common method for increasing microbial adsorption capacity although further treatment of the microorganisms is required to facilitate the use. However, only a few studies have explored how to simultaneously achieve selective adsorption ability and convenient separation. In this paper, the maximum Pd(II) adsorption capacity on polyethyleneimine (PEI)-modified Pichia pastoris residue (PEI-PR) was achieved at a PEI:glutaraldehyde (GA) ratio of 4:1. An adsorption kinetics study showed that PEI-modified biomass (PEI-PR) reached adsorption equilibrium within 180 min, and the adsorption conformed to the pseudo-second-order model. Using the Langmuir adsorption isotherm, the maximum adsorption capacity for Pd(II) at pH 3 was found to be 587.67 mg∙g−1 of dry weight. After five adsorption–desorption cycles, PEI-PR could maintain 90.35% of its initial adsorption capacity. Moreover, PEI-PR showed satisfactory selectivity to Pd(II) in simulated multi-metal solution. The selective adsorption efficiency of PEI-PR was mainly due to the introduction of a large number of amino and imino groups onto the surface of the biomass through PEI modification, which caused the increase of the isoelectric point from 4.64 to 9.46. At a pH value lower than its isoelectric point, PEI-PR became protonated and thus was positively charged. As a result, it could only undergo electrostatic adsorption with negatively charged Pd(II) chloride complex ions, rather than with other positively charged metal ions. The adsorption complex could be separated from the solution via sedimentation. This research presents a new approach for preparation of microbial adsorbent with selective adsorption capacity and can conveniently be separated from a solid–liquid mixture. It is a green approach for efficient microbial adsorption and recovery of Pd(II).