Preparation of chitosan resin by two-step crosslinking method and its adsorption for palladium in wastewater

To preserve the activity of amine groups on chitosan, chitosan resin (CR) was synthesized using the reversed-phase suspension two-step crosslinking method for the adsorption of palladium from wastewater. The effects of varying the amounts of chitosan, liquid paraffin, ethyl acetate, formaldehyde solution, and epichlorohydrin on the adsorption capacity of CR were investigated using both single-factor experiments and response surface methodology. The preparation conditions for the chitosan resin were optimized, and its adsorption properties were systematically evaluated. The results indicated that CR exhibited a high saturated adsorption capacity for palladium, reaching 195.22 mg·g-1. The adsorption kinetics followed the pseudo-second-order model, while the adsorption isotherms were well described by the Sips model. Thermodynamic analysis demonstrated that the adsorption process was spontaneous and endothermic. Furthermore, CR maintained exceptional stability, with a palladium removal efficiency exceeding 99.8 % even after eight adsorption-desorption cycles. The primary adsorption mechanism is attributed to the interaction between palladium ions and the protonated amino groups of the chitosan resin.

Hydrazone-Linked Covalent Organic Framework Catalyst via Efficient Pd Recovery from Wastewater

Global consumption and discharge of palladium (Pd) have raised environmental concerns but also present an opportunity for the sustainable recovery and reuse of this precious metal. Adsorption has proven to be an efficient method for the selective recovery of Pd from industrial wastewater. This study investigated a hydrazone-linked covalent organic framework (Tfpa-Od COF) as a potential material for the high-affinity adsorption of Pd2+ ions from wastewater, achieving a Kd value of 3.62 × 106 mL g-1. The electron-rich backbone of the COF contributes to its excellent selective removal efficiency (up to 100%) and adsorption capacity of 372.59 mg g-1. Furthermore, the Pd-adsorbed COF was evaluated as a sustainable catalyst for the Suzuki-Miyaura coupling reaction, demonstrating good catalytic conversion and recyclability. This work attempts to showcase a protocol for reusing waste palladium generated in water to fabricate heterogeneous catalysts and, thereby, promote the circular economy concept.

Waste Polyethylene-Derived Carbon Dots: Administration of Metal-Free Oxidizing Agents for Tunable Properties and Photocatalytic Hyperactivity

The possibility of converting waste plastics into carbon dots (CDs) with 100% efficiencies using KMnO4 has emerged as a significant discovery in mitigating plastic pollution and upcycling. However, the lack of tunability of their properties, viz. aerial O2 harvesting, light-induced autophagy, and photoactivity using air as a free oxidant, has remained a bottleneck. Besides, the toxicity of KMnO4 makes the process less sustainable. Attempting to bridge these gaps, herein, we demonstrate the preparation of CDs using polyethylene with enormous controllability of their properties by utilizing less-toxic and metal-residue-free oxidizers, e.g., H2O2, HNO3, HClO4, and NaClO. We obtain structurally diverse CDs with controllable luminescent quantum yields (∼0.5-8%), excitonic lifetimes (1.3-2.3 ns), and binding energies (147-290 meV). These CDs exhibit a hugely extended range of molecular O2 harvesting (∼405-650 μM) with different amounts of strongly and weakly surface-bound O2 molecules within an estimated ratio of ∼0.77-2.51. Autophagy varied from 14 days to a nearly "no-autophagy" show. We efficiently utilized their oxygen harvesting and photocatalytic abilities to synthesize imine compounds from the corresponding amines in the open air (rate constant of ∼0.055 min-1), surpassing the literature efficiencies achieved using an O2 flow and noble metals. Notably, due to oxygen harvesting by CDs, no additional rate enhancement was observed after O2 purging, establishing the role of CDs in making free air an excellent oxidizing agent.

Precious Metal Recovery from Wastewater Using Bio-Based Techniques

The recovery of metals from waste material has been on the increase in the past few years due to a number of reasons such as supporting the diversification of metal supply resources. In addition, the alternative use of the waste material for metal recovery can add to the main production line, boosting production throughput and profitability thus, allowing companies to sustain their activities during times of low commodity prices. While there has been a lot of research and interest in the recovery of precious metals such as platinum group metals (PGMs), Au, and Ag from solid waste material, there has been limited focus on the recovery of these value metals from wastewater. This is mostly related to challenges associated with finding cost-effective technologies that can recover these metals from solutions of low metal concentrations. In recent years, bio-based technologies have, however, become established as potential alternatives to traditional techniques in the treatment of wastewater due to their ability to recover metals from solutions of low concentrations. While wastewater might be characterized by some significant value metal content, it also contains other components that have potential economic value if recovered or converted to by-products. Such an approach may not only provide an opportunity for extraction of metal resources from wastewater but also contributes toward the circular economy. This chapter presents insights into precious metal recovery from wastewater using bio-based technologies, compares such an approach to the traditional techniques, explores the recovery of other value-added products and finally considers some of the challenges associated with the large-scale application of the bio-based technologies.

Efficient treatment of palladium from wastewater by acrolein cross-linked chitosan hydrogels: Adsorption, kinetics, and mechanisms

Herein we present a study on the preparation and properties of a hydrogel adsorbent for treatment of wasted palladium souring from actial petrochemical industrial wastewater. Chitosan was used as the raw material and acrolein as the cross-linking agent for the hydrogel (A/CS). The adsorption behaviors of the hydrogel for Pd(II) ions were characterized and analyzed. The effect of pH, temperature, adsorption kinetics, and thermodynamics were investigated. Langmuir models were employed to describe the adsorption isotherms, while the pseudo-second-order equation was applied to describe the adsorption kinetics. The experimental results demonstrated that the adsorption was a monolayer chemical adsorption, and the adsorption capacity was found to reach 505.05 mg/g under optimal conditions. In addition, FT-IR and XPS analyses, combined with MS calculations confirmed that chelation and electrostatic attraction were dominated in the adsorption process. Overall, the development of this hydrogel adsorbent will provide a practical approach to the treatment of industrial wastewater containing palladium and have great potential for practical applications.

Recovery of Homogeneous Platinoid Catalysts from Pharmaceutical Media: Review on the Existing Treatments and the Perspectives of Membrane Processes

Catalyst recovery is a major challenge for reaching the objectives of green chemistry for industry. Indeed, catalysts enable quick and selective syntheses with high reaction yields. This is especially the case for homogeneous platinoid catalysts which are almost indispensable for cross-coupling reactions often used by the pharmaceutical industry. However, they are based on scarce, expensive, and toxic resources. In addition, they are quite sensitive and degrade over time at the end of the reaction. Once degraded, their regeneration is complex and hazardous to implement. Working on their recovery could lead to highly effective catalytic chemistries while limiting the environmental and economic impacts of their one-time uses. This review aims to describe and compare conventional processes for metal removal while discussing their advantages and drawbacks considering the objective of homogeneous catalyst recovery. Most of them lead to difficulty recycling active catalysts due to their ability to only treat metal ions or to chelate catalysts without the possibility to reverse the mechanism. However, membrane processes seem to offer some perspectives with limiting degradations. While membranes are not systematically the best option for recycling homogeneous catalysts, current development might help improve the separation between pharmaceutical active ingredients and catalysts and enable their recycling.

A model for the adsorption process of water dissolved elements flowing into reactive porous media: Characterization and sizing of water mining/filtering systems

This study presents a mathematical model describing the adsorption-desorption process of water dissolved elements onto reactive porous materials during filtering operations performed under dynamic flow conditions. The developed model is based on a reversible second order adsorption kinetic featuring the progressive reduction of the purifying capacity of the filtering material due to the gradual exhaustion of the active sites available for solute retention. It enables the simulation of the performances of water filtering systems through the use of parameters having a clear chemical-physical significance or it can be used for the estimation of these parameters to characterize the adsorption properties of the reactive material. Starting from the same adsorptive conceptual model used for the filtering system marked by ongoing flowing conditions, an adaptation for static systems was performed on the mathematical framework in order to process the same chemical physical parameters in both schemes. Adsorption laboratory tests were carried out to validate the developed model. Results show that the kinetic constants and adsorption capacities (a maximum of about 45 mg g^-1 was obtained for the tested material) are highly comparable, both within the same experimental system, and between different experimental setup. This confirms the validity of the developed model which is able to perfectly fit the observed concentration data in all tested configurations.

Sustainable and Selective Modern Methods of Noble Metal Recycling

Noble metals exhibit broad arrange of applications in industry and several aspects of human life which are becoming more and more prevalent in modern times. Due to their limited sources and constantly and consistently expanding demand, recycling of secondary and waste materials must accompany the traditional mineral extractions. This Minireview covers the most recent solvometallurgical developments in regeneration of Pd, Pt, Rh, Ru, Ir, Os, Ag and Au with emphasis on sustainability and selectivity. Processing-by selective oxidative dissolution, reductive precipitation, solvent extraction, co-precipitation, membrane transfer and trapping to solid media-of eligible multi-metal substrates for recycling from waste printed circuit boards to end-of-life automotive catalysts are discussed. Outlook for possible future direction for noble metal recycling is proposed with emphasis on sustainable approaches.

Amino-Alkylphosphonate-Grafted TiO2: How the Alkyl Chain Length Impacts the Surface Properties and the Adsorption Efficiency for Pd

Amino-alkylphosphonic acid-grafted TiO₂ materials are of increasing interest in a variety of applications such as metal sorption, heterogeneous catalysis, CO₂ capture, and enzyme immobilization. To date, systematic insights into the synthesis-properties-performance correlation are missing for such materials, albeit giving important know-how towards their applicability and limitations. In this work, the impact of the chain length and modification conditions (concentration and temperature) of amino-alkylphosphonic acid-grafted TiO₂ on the surface properties and adsorption performance of palladium is studied. Via grafting with aminomethyl-, 3-aminopropyl-, and 6-aminohexylphosphonic acid, combined with the spectroscopic techniques (DRIFT, ³¹P NMR, XPS) and zeta potential measurements, differences in surface properties between the C1, C3, and C6 chains are revealed. The modification degree decreases with increasing chain length under the same synthesis conditions, indicative of folded grafted groups that sterically shield an increasing area of binding sites with increasing chain length. Next, all techniques confirm the different surface interactions of a C1 chain compared to a C3 or C6 chain. This is in line with palladium adsorption experiments, where only for a C1 chain, the adsorption efficiency is affected by the precursor concentration used for modification. The absence of a straightforward correlation between the number of free NH₂ groups and the adsorption capacity for the different chain lengths indicates that other chain-length-specific surface interactions are controlling the adsorption performance. The increasing pH stability in the order of C1 < C3 < C6 can possibly be associated to a higher fraction of inaccessible hydrophilic sites due to the presence of folded structures. Lastly, the comparison of adsorption performance and pH stability with 3-aminopropyl(triethoxysilane)-grafted TiO₂ reveals the applicability of both grafting methods depending on the envisaged pH during sorption.

Selective Pd recovery from acidic leachates by 3-mercaptopropylphosphonic acid grafted TiO2: does surface coverage correlate to performance?

Modification of metal oxides with organophosphonic acids (PAs) provides the ability to control and tailor the surface properties. The metal oxide phosphonic acid bond (M-O-P) is known to be stable under harsh conditions, making PAs a promising candidate for the recovery of metals from complex acidic leachates. The thiol functional group is an excellent regenerable scavenging group for these applications. However, the research on organophosphonic acid grafting with thiol groups is very limited. In this study, four different metal sorbent materials were designed with different thiol surface coverages. An aqueous-based grafting of 3-mercaptopropylphosphonic acid (3MPPA) on mesoporous TiO₂ was employed. Surface grafted thiol groups could be obtained in the range from 0.9 to 1.9 groups per nm². The different obtained surface properties were studied and correlated to the Pd adsorption performance. High Pd/S adsorption efficiencies were achieved, indicating the presence of readily available sorption sites. A large difference in their selectivity towards Pd removal from a spend automotive catalyst leachate was observed due to the co-adsorption of Fe on the titania support. The highest surface coverage showed the highest selectivity (K _d: 530 mL g^-1) and adsorption capacity (Q _max: 0.32 mmol g^-1) towards Pd, while strongly reducing the co-adsorption of Fe on remaining TiO₂ sites.

Selective capture of Pd(II) from aqueous media by ion-imprinted dendritic mesoporous silica nanoparticles and re-utilization of the spent adsorbent for Suzuki reaction in water

The development of highly efficient adsorptive material for the selective capture of Pd(II), and re-utilization of spent Pd(II)-loaded adsorbent as an efficient catalyst for organic synthesis are of great significance, but challenging. Particularly, the heterogeneous palladium-catalyzed Suzuki reaction in aqueous media is much more challenging than that of homogeneous. Herein, several novel Pd(II) ion-imprinted polymers (PIIPs) based on dendritic fibrous silica particles are constructed by surface ion imprinting technology (SIIT), using Schiff base and pyridine groups functionalized organosilicon as functional monomer. The PIIP-3 prepared by 3 g of functional monomer exhibits the best adsorption performance, and shows ultrafast (10 min) and selective capture of Pd(II) with high uptake capacity (382.5 mg/g). Moreover, the waste Pd(II) loaded PIIP-3 (PIIP-3-Pd) can serve as a catalyst towards the Suzuki reaction in water, affording 94.2 % yield of the desired product. Interestingly, the PIIP-3-Pd can be reused 12 times without an appreciable decrease in catalytic activity, which is probably due to the imprinted cavity and specific recognition site of PIIP-3 can match and recapture Pd active species in a complex catalytic environment. Thus, this work demonstrates huge potentials of SIIT to enhance the selectivity of adsorption process and increase the lifetime of catalysts.

CO2-assisted 'Weathering' of Steel Slag-Derived Calcium Silicate Hydrate: A Generalized Strategy for Recycling Noble Metals and Constructing SiO2-Based Nanocomposites

The spent adsorbent loaded by toxic metals is a solid hazardous waste which could cause significant secondary pollution due to potential possible additional release of metal ions. Therefore, the main subject is direct reutilization of spent adsorbents which can further economically and realistically offer new features, like recycling metal adsorbed, or formation of functional SiO₂-based nanocomposites. The nanoporous structure and negative surface charges enable steel slag-derived amorphous calcium silicate hydrate (CSH) to retain effectively the incoming metal ions (e. g. Au³⁺, Ag⁺, Pd²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ce³⁺, Y³⁺, and Gd³⁺) by chemisorption. Sparked by natural carbonation 'weathering', which ultimately sequestrates atmospheric CO₂ by alkaline silicate minerals to leach calcium from mineral matrix, the decalcification reactions of metal-bearing CSH results in successful recovery of noble metals (Ag, Au, Pd) upon NaOH etching the resultant SiO₂ support. Further, SiO₂-based heterostructures, containing nanocrystalline metals (e. g. Au⁰, Ag⁰, Pd⁰, Fe⁰, Co⁰, Ni⁰, Cu⁰, and Zn⁰) or rare-earth oxides (e. g. CeO₂, Y₂O₃, and Gd₂O₃), are formed after reduction in H₂/Ar (5 vol% H₂) flow, which is also very important for the multipurpose immobilization of diverse hybrid materials on SiO₂ surface (e. g. Cu⁰-Ag⁰@SiO₂, Cu⁰-CeO₂@SiO₂, and Cu⁰-Ag⁰-CeO₂@SiO₂).

Synthesis of a Highly Selective Scavenger of Precious Metals from a Printed Circuit Board Based on Cellulose Filter Paper Functionalized with a Grafted Polymer Chain Bearing N-Methyl-2-hydroxyethylcarbamothioate Moieties

We report the synthesis and practical application of a novel scavenger for precious metals. The scavenger was prepared from cellulose filter paper with grafted chains of poly(glycidyl methacrylate) modified with a novel ligand group of N-methyl-2-hydroxyethylcarbamothioate moieties, introduced by the reaction with O-1-mercapto-3-phenoxypropan-2-yl N-methyl-2-hydroxyethylcarbamothioate. Batch experiments were performed to evaluate the capability of the scavenger in ranges of pH and acid concentration as well as to determine the kinetics and isotherm models. The scavenger was found to adsorb only Ag(I), Pd(II), and Au(III) from an aqueous media in the presence of coexisting ions of different bases and precious metals at wide ranges of pH and acid concentration. The adsorption rates fit a pseudo-second-order kinetic equation, and the adsorption reached equilibrium within 60 min. The isotherm studies indicated that the obtained data were a good fit with the Langmuir model. The maximum adsorption capacities of Ag(I), Pd(II), and Au(III) were 126.95, 124.67, and 230.67 mg g-1, respectively. Regeneration experiments indicated that the adsorbent maintained 97% of its initial efficiency even after five adsorption/desorption cycles. The scavenger was effectively utilized to recover Ag(I), Pd(II), and Au(III) from an aqua regia solution of waste printed circuit boards.

Synthesis, Characterization and Application of Polypyrrole Functionalized Nanocellulose for the Removal of Cr(VI) from Aqueous Solution

Heavy metals are toxic substances that pose a real danger to humans and organisms, even at low concentration. Therefore, there is an urgent need to remove heavy metals. Herein, the nanocellulose (NC) was synthesized by the hydrolysis of cellulose using sulfuric acid, and then functionalized using polypyrrole (ppy) through a polymerization reaction to produce polypyrrole/nanocellulose (ppy/NC) nanocomposite. The synthesized nanocomposite was characterized using familiar techniques including XRD, FT-IR, SEM, TEM, and TGA. The obtained results showed a well-constructed nanocomposite with excellent thermal stability in the nano-sized scale. The adsorption experiments showed that the ppy/NC nanocomposite was able to adsorb hexavalent chromium (Cr(VI)). The optimum pH for the removal of the heavy metal was pH 2. The interfering ions showed minor effect on the adsorption of Cr(VI) resulted from the competition between ions for the adsorption sites. The adsorption kinetics were studied using pseudo 1st order and pseudo 2nd order models indicating that the pseudo second order model showed the best fit to the experimental data, signifying that the adsorption process is controlled by the chemisorption mechanism. Additionally, the nanocomposite showed a maximum adsorption capacity of 560 mg/g according to Langmuir isotherm. The study of the removal mechanism showed that Cr(VI) ions were removed via the reduction of high toxic Cr(VI) to lower toxic Cr(III) and the electrostatic attraction between protonated ppy and Cr(VI). Interestingly, the ppy/NC nanocomposite was reused for Cr(VI) uptake up to six cycles showing excellent regeneration results. Subsequently, Cr(VI) ions can be effectively removed from aqueous solution using the synthesized nanocomposite as reusable and cost-effective adsorbent.

A New Perspective on Adsorbent Materials Based Impregnated MgSiO3 with Crown Ethers for Palladium Recovery

The study of new useful, efficient and selective structures for the palladium ions’ recovery has led to the development of a new series of macromolecules. Thus, this study presents a comparative behavior of two crown benzene ethers that modify the magnesium silicate surface used as adsorbent for palladium. These crown ethers are dibenzo18-crown-6 (DB18C6) and dibenzo 30-crown-10 (DB30C10). The obtained materials were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared spectroscopy (FT-IR). The specific surface area (BET) and point of zero charge (PZC) of the two materials were determined. The palladium ions’ recovery from synthetic aqueous solutions studies aimed to establish the adsorption mechanism. For this desideratum, the kinetic, equilibrium and thermodynamic studies show that MgSiO₃-DB30C10 have a higher adsorption capacity (35.68 mg g⁻¹) compared to MgSiO₃-DB18C6 (21.65 mg g⁻¹). Thermodynamic studies highlight that the adsorption of Pd(II) on the two studied materials are spontaneous and endothermic processes. The positive values of the entropy (ΔS⁰) suggest that the studied adsorption processes show a higher disorder at the liquid/solid interface. Desorption studies were also performed, and it was found that the degree of desorption was 98.3%.

Comparative evaluation of dithiocarbamate-modified cellulose and commercial resins for recovery of precious metals from aqueous matrices

Economic and ecological issues motivate the recovery of precious metals (PMs: Ag, Au, Pd, and Pt) from secondary sources. From the viewpoint of eco-friendliness and cost-effectiveness, biomass-based resins are superior to synthetic polymer-based resins for PM recovery. Herein, a detailed comparative study of bio-sorbent dithiocarbamate-modified cellulose (DMC) and synthetic polymer-based commercial resins (Q-10R, Lewatit MonoPlus TP 214, Diaion WA30, and Dowex 1X8) for PM recovery from waste resources was conducted. The performances and applicability of the selected resins were investigated in terms of sorption selectivity, effect of competing anions, sorption isotherms, impact of temperature, and PM extractability from industrial wastes. Although the sorption selectivity toward PMs in acidic solutions by DMC and other resins was comparable, the sorption efficiency of commercial resins was adversely affected by competing anions. The sorption of PMs fitted the Langmuir model for all the studied resins, except Q-10R, which followed the Freundlich model. The maximum sorption capacity of DMC was 2.2-42 times higher than those of the resins. Furthermore, the PM extraction performance of DMC from industrial wastes exceeded that of the commercial resins, with a sorption efficiency ≥99% and a DMC dosage of 5-40 times lower.

From Waste to Green Applications: The Use of Recovered Gold and Palladium in Catalysis

The direct use in catalysis of precious metal recovery products from industrial and consumer waste is a very promising recent area of investigation. It represents a more sustainable, environmentally benign, and profitable way of managing the low abundance of precious metals, as well as encouraging new ways of exploiting their catalytic properties. This review demonstrates the feasibility and sustainability of this innovative approach, inspired by circular economy models, and aims to stimulate further research and industrial processes based on the valorisation of secondary resources of these raw materials. The overview of the use of recovered gold and palladium in catalytic processes will be complemented by critical appraisal of the recovery and reuse approaches that have been proposed.

Dispersive micro-solid phase extraction with a magnetic nanocomposite followed by electrothermal atomic absorption measurement for the speciation of thallium

A magnetic dispersive micro-solid phase extraction procedure for the determination of the thallium content in waters is presented. The incorporation in the sample (10 mL) of a small amount of graphene-Fe₃O₄ composite (3.6 mg) in the presence of 10^-4 mol L^-1 Aliquat 336 at pH 2 results in the complete retention of both thallium(I) and thallium(III). After separation with a magnet, the micro-solid phase recovered is treated with 0.05 mL of a 0.1 mol L^-1 sodium ethylenediaminetetracetate solution at pH 9, and the supernatant obtained after application of the magnet is introduced in the electrothermal atomizer of an atomic absorption spectrometer to obtain the signal corresponding to the total thallium content. For speciation, the trivalent form in a second sample aliquot is separated by means of a liquid-liquid extraction stage with chloroform and methyl trioctyl ammonium in the presence of bromide, and the signal corresponding to the monovalent form is obtained, the concentration of thallium(III) being obtained by difference. The enrichment factor is 185, which permits a detection limit as low as 0.01 μg L^-1 of the analyte to be achieved. The relative standard deviation for five measurements at the 0.1 μg L^-1 thallium level is below 5%. The reliability of the procedure is verified by analysing five certified reference samples for which speciation data are also given.

Zero-valent palladium dissolution using NaCl/CuCl2 solutions

Pd, Rh, Pt are employed in a wide range of applications, such as catalytic converters, fuel cells and electronic devices. In the last years, an increasing pressure on their market was recorded due to a growing demand and limited resources. Therefore, the recovery of these materials from wastes represents an interesting goal to be achieved. The most widely proposed techniques for recovering the palladium from wastes are leaching and ion exchange. Strong oxidizers, acids and high temperature (343-363 K) are used for leaching, leading problems for the environment and the safety. In this work the attention was focused on a system containing zero-valent palladium nanoparticles in which the leaching is performed in mild acidic conditions, by using chloride solutions containing cupric ions (NaCl/CuCl₂). The process was studied at varying temperature, pH, chloride and cupric ion concentrations. Good results were obtained at pH 5.0 and temperatures between 288 K and 333 K. The process is more acceptable than the traditional ones from a safety point of view being characterized by less severe conditions (pH and temperatures). A shrinking spherical particles model was adopted to analyse the experimental data from which a development under a kinetic control was demonstrated.

Efficient recovery of palladium nanoparticles from industrial wastewater and their catalytic activity toward reduction of 4-nitrophenol

Discharge of heavy metals from various sources of industrial wastewater poses significant environmental and health concerns. Thus, efficient recovery of precious metals from wastewater employing sustainable, rapid, and cost-effective treatment methods is highly desirable. In this work, palladium nanoparticles (Pd NPs) were successfully recovered from industrial wastewater using a pulsed laser process in the absence of additives or reducing agents. Notably, the developed approach is faster and more environmentally friendly than other conventional recovery methods. The recovered Pd NPs were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and inductively coupled plasma optical emission spectroscopy (ICP-OES). Various pulsed laser parameters (i.e., laser wavelength, power, and irradiation time) were optimized to obtain ideal conditions for the pulsed laser ablation process. Effective recovery of the Pd metal from industrial wastewater was achieved at a laser wavelength of 355 nm, power of 40 mJ/pulse, and irradiation time of 30 min. The Pd NPs exhibited excellent catalytic activity toward the reduction of 4-nitrophenol. Thus, the recovered materials showed remarkable potential for application in degradation of toxic aromatic nitro compounds in the environment.

Chelating polymers with valuable sorption potential for development of precious metal recycling technologies

A special attention is currently focused on the recovery of Au, Ag, Pt, Pd and Rh from both primary and secondary sources. From the wide range of sorbents that have been used in this respect, the required selectivity is proved only by the chelating polymers containing donor N, O and S atoms in their functional groups. This work presents the recent published researches on this topic, pointing out the capabilities of chelating sorbents based on organic synthetic polymers for a sustainable development. The chelating sorbents are differentiated and reviewed according to their synthesis strategy and compatibility with synthetic and real matrices. First, an overview on the novel functionalized polymers and impregnated resins with good selectivity for the recovery of most valuable precious metals from synthetic leach solutions is given. Subsequently, the performances of these materials in the selective and preconcentrative recovery of Au, Ag, Pt, Pd and Rh from simulated and real leachates are discussed. The viability of an integrated approach for the determination of precious metals from simulated solutions by solid phase spectrometry is highlighted. The transposition of chelating polymers’ potential in challenging technologies for precious metal recovery-reuse-recycling needs further research on directions that are proposed.

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.

Synthesis of macrocyclic polyphenol resin by methylene crosslinked calix[4]arene (MC-[4]H) for the adsorption of palladium and platinum ions

A novel macrocyclic polyphenol resin, a calix[4]arene derivative, namely, a methylene crosslinked calix[4]arene (MC-[4]H), was successfully synthesised by demethylation of MC-[4]CH₃.

Use of poly(vinylidene fluoride-co-vinyl dimethylphosphonate) copolymers for efficient extraction of valuable metals

The radical copolymerisation of vinylidene fluoride (VDF) with vinyl dimethyl phosphonate (VDMP) initiated by various kinds of initiators is presented.

New sulfur-containing polymeric sorbents based on 2,2′-thiobisethanol dimethacrylate

The first step in obtaining of a specific polymer sorbent containing sulfur atoms was the synthesis of a functional monomer – 2,2′-thiobisethanol dimethacrylate (TEDM). Synthesis consists of the reaction of 2,2′-thiobisethanol with methacryloyl chloride in the presence of triethylamine in methylene chloride. The new poly(dimethacrylate)s materials containing sulfur atoms were synthesized in radical suspension polymerization. Homopolymerization of 2,2′-thiobisethanol dimethacrylate and its copolymerization with ethylene glycol dimethacrylate or pentaerythritol tetraacrylate were carried out. The selection of synthesis conditions determines the parameters of the polymer structure and its properties. The presence of sulfur atoms in polymer chains resulted in specific donor-acceptor interactions, which can intensify sorption ability towards metal ions belonging to the group of soft acids. Therefore, the sorption properties of the obtained materials have been determined based on the recovery of precious metal ions, such as gold(III) and silver(I).