Pd Adsorption Research Articles

A novel defect-rich Prussian blue analogue based on controlled doping strategy: Exceptional adsorption performance of platinum group metals and enhanced stability

The efficient separation of platinum group metals (PGMs, mainly Pd, Ru, and Rh) from high level liquid waste (HLLW) is of growing significance for resolving challenges in radioactive waste treatment and achieving sustainable development. Based on Prussian blue analogues (PBAs) with tunable compositions and morphologies, a defect-rich but also excellently stable cobalt-doped aluminum hexacyanoferrate (Co/KAlFC) was successfully synthesized for the separation of PGMs using defect engineering. Interestingly, the defects in Co/KAlFC induced an increase in active sites and vacancies, leading to a remarkable enhancement of PGM adsorption capacity compared to the undoped KAlFC. While maintaining the same excellent Pd(II) adsorption capacity, the convenient access provided by the defects led to a reduction of the Pd(II) adsorption equilibrium time to 30 min, as well as a 3-fold and 7-fold increase in the adsorption capacity for Ru(III) and Rh(III), respectively. The experimental and characterization results revealed that the adsorption mechanism of defect-rich Co/KAlFC on PGM was mainly a synergistic effect of ion-exchange and chemical complexation, and the enhanced electrostatic interaction promoted the adsorption process. The valence state of Fe shifted from divalent to trivalent during the adsorption process, which affected the strength of coordination interaction between PGMs and Fe-CN- at N-atom. Overall, this study not only demonstrated that Co/KAlFC is an excellent candidate for the removal of PGM from HLLW but also provided a new idea for the rational design and development of inorganic materials with exceptional properties and stability.

Selective Sorption of Noble Metals on Polymer Gel Modified with Ionic Liquid.

The solid phase extraction of Au, Ir, Pd, Pt, and Rh on a polymer gel modified with ionic liquid containing methylimidazolium groups (MIA-PG) has been investigated. The positively charged surface of the sorbent is highly suitable for the sorption of stable chlorido complexes of the studied analytes, while the retention of base metals Cu, Fe, Ni, Zn, and Mn is negligible. Optimization experiments performed showed that, at 0.05 M HCl, the degree of sorption of Au, Ir, Pd, and Pt is above 95%, and only for Rh, the maximum degree is 65%; complete elution is achieved in the mixture of thiourea in HCl. The results obtained from the equilibrium adsorption studies are fitted in various adsorption models, such as Langmuir and Freundlich, and the model parameters have been evaluated. The kinetics analysis indicated that the adsorption of Au, Ir, Pd, Pt, and Rh onto the sorbent follows the pseudo-second-order model. Intraparticle diffusion and ion exchange reactions were the rate-limiting steps. Analytical procedures were developed for Pd, Pt, and Rh determination in road dust and soil and for Au determination in copper ore and copper concentrate. The procedures are validated by the analysis of certified reference materials. Analytical figures of merit confirmed their applicability in routine laboratory practice.

Pd-Adsorbing CrS2 monolayer as sensing material for detecting CO, C2H2, and C2H4 in dissolved gases: A first-principles study

This study employs density functional theory to initially examine the adsorption characteristics of Pd atom on CrS2 monolayer (termed Pd@CrS2). Subsequently, the adsorption capabilities of Pd@CrS2 monolayer for CO, C2H2, and C2H4 are simulated to assess its prospects for dissolved gas detection. Stable adsorption of Pd atoms onto the CrS2 monolayer atop Cr atoms is observed with a binding energy of −2.69 eV. Pd@CrS2 exhibits chemisorption towards CO, C2H2, and C2H4 with respective adsorption energies of −1.49, −1.13, and −1.22 eV. The band structure and density of states analysis indicate significant alterations in the electronic properties of CrS2 upon Pd adsorption and upon exposure to the gases. The bandgap of Pd@CrS2 is modified by −29.6 %, −24.7 %, and −27.1 % after CO, C2H2, and C2H4 adsorption, corresponding to highly sensitive detection responses of −99.6 %, −98.9 %, and −99.3 %. The research highlights the gas sensing capabilities of Pd@CrS2 monolayers for monitoring the operational status in dissolved gas analysis, showcasing the promising application potential of CrS2.

Preparation of a covalent organic framework-modified silica-gel composite for the effective adsorption of Pd(II), Zr(IV) and Mo(VI) from nitric acid solution

Preparation of a covalent organic framework-modified silica-gel composite for the effective adsorption of Pd(II), Zr(IV) and Mo(VI) from nitric acid solution

Nitrogen-rich sulfur-containing heterocyclic adsorbents for effective selective adsorption of Au(III)/Pd(II)/Pt(IV)

Recovering precious metals from secondary resources has elicited considerable attention, and exploring an efficient adsorbent is a challenge. In this work, we have specifically tailored three highly effective adsorbents (THDA@PEI, DCTA@PEI and DCTD@PEI) by crosslinking PEI with sulfur-containing heterocyclic cross-linking agents (2,5-thiophenedicarboxaldehyde, 2,4-dichlorothiazole and 3,4-dichloro-1,2,5-thiadiazole) for recovery of Au(III), Pd(II), and Pt(IV). These agents are distinguished by a range of nitrogen atom counts that extend from zero to two, offering a foundation for exploring the correlation between their molecular structure and adsorption performance. THDA@PEI, DCTA@PEI, and DCTD@PEI exhibit remarkable adsorption capacities for Au(III), Pd(II), and Pt(IV), with values reaching up to 2169, 2240, and 2536 mg/g for Au(III), 771, 886, and 846 mg/g for Pd(II), and 832, 1021, and 887 mg/g for Pt(IV), respectively. Among the three materials, DCTD@PEI stands out with a broader pH applicability range for both gold (pH 2 to 9) and platinum (pH 1 to 11) adsorption and exhibits a more rapid adsorption rate for Au and Pd. The adsorption processes of the three adsorbents on precious metals are spontaneous and entropy-increasing processes. Increasing the adsorption temperature could improve the adsorption performance of the three adsorbents, except for Pd adsorption by DCTD@PEI. All of the three adsorbents exhibit good selectivity and reusability for Au, Pd, and Pt, with DCTA@PEI being the most outstanding. It is observed that an increase in nitrogen content in the adsorbents correlates positively with the improvement of key performance indicators, including a wider pH range, higher adsorption capacity, faster kinetics, better selectivity, and enhanced reusability, while the substituent positions of crosslinking agents also have a strong impact on the adsorption performance, especially for Pd and Pt.

Efficient palladium ion adsorption and catalyst preparation from pharmaceutical wastewater using amino-functionalized Ti3C2

This paper reports the recovery and reuse of Pd ions from pharmaceutical wastewater using amino-modified Ti3C2. Ti3C2–NH2 was synthesized by modifying (3-aminopropyl)triethoxysilane and the successful substitution of some surface functional groups of Ti3C2; the decrease in material thickness was verified by characterization. This study revealed that the presence of amino groups significantly enhanced the Pd(II) adsorption capacity of Ti3C2. The effects of the adsorbent material, adsorbent dosage, pH, initial concentration of Pd ions, presence of competing cations, and contact time on the adsorption performance were investigated. The maximum adsorption capacity of 20 mg of Ti3C2–NH2 was 986.65 mg/g in 100 ml of a Pd-ion solution with an initial concentration of 200 mg/l at pH 3. A pseudo-second-order kinetic model fitted well with the experimentally obtained rate data, indicating that the main mode of Pd-ion removal by Ti3C2–NH2 was via chemical reduction. Finally, the catalyst exhibited excellent performances during the photocatalytic and Suzuki coupling reactions with yields of 81 % and 95 %, respectively. The results demonstrated that Ti3C2–NH2 is an excellent material for adsorbing Pd ions and can effectively recycle these ions from pharmaceutical wastewater.

Pd-Ru pair on Pt surface for promoting hydrogen oxidation and evolution in alkaline media

Hydrogen oxidation reaction in alkaline media is critical for alkaline fuel cells and electrochemical ammonia compressors. The slow hydrogen oxidation reaction in alkaline electrolytes requires large amounts of scarce and expensive platinum catalysts. While transition metal decoration can enhance Pt catalysts’ activity, it often reduces the electrochemical active surface area, limiting the improvement in Pt mass activity. Here, we enhance Pt catalysts’ activity without losing surface-active sites by using a Pd-Ru pair. Utilizing a mildly catalytic thermal pyrolysis approach, Pd-Ru pairs are decorated on Pt, confirmed by extended X-ray absorption fine structure and high-angle annular dark-field scanning transmission electron microscopy. Density functional theory and ab-initio molecular dynamics simulations indicate preferred Pd and Ru dopant adsorption. The Pd-Ru decorated Pt catalyst exhibits a mass-based exchange current density of 1557 ± 85 A g−1metal for hydrogen oxidation reaction, demonstrating superior performance in an ammonia compressor.

Hierarchical V2O3 spiny hollow nanosphere for efficient adsorption of precious metal ions in complicated matrices

Treatment of precious metals in electronic waste has attracted tremendous attention and is essential for both environmental protection and resource sustainable development. In this study, a novel adsorbent for precious metal ions, V2O3 spiny hollow nanospheres (p-V2O3 SHN), was synthesized through a one-step hydrothermal-assisted methodology for the adsorption of Au(III), Ag(I), Pd(II), and Pt(IV) from the leaching solution of electronic waste. The results reveal that the p-V2O3 SHN hierarchy was successfully constructed with a hollow structure and dense spiny morphology. The prepared p-V2O3 SHN can effectively remove precious metal ions such as Au(III), Ag(I), Pd(II), and Pt(IV), with the selective capture order being Au(III) > Ag(I) > Pt(IV) > Pd(II) > other metal ions. This superior adsorption capability can be attributed to the multi-diffusible, intermingled composition, and numerous active sites decorating the p-V2O3 SHN hierarchy, facilitating the uptake of Au(III), Ag(I), Pd(II), and Pt(IV) ions from electronic waste. The Langmuir model provided a better fit for the uptake process, revealing maximum uptake capacities of 833.33 mg/g for Au(III), 370.37 mg/g for Ag(I), 77.51 mg/g for Pd(II), and 42.01 mg/g for Pt(IV) on p-V2O3 SHN. Remarkably, p-V2O3 SHN exhibited a robust affinity for the adsorbate due to the presence of surface defects and reduction. The new p-V2O3 SHN also demonstrated good reusability for three sorption cycles, highlighting its potential for electronic waste treatment. Due to its facile synthesis and excellent efficiency, hierarchical p-V2O3 SHN presents itself as a promising candidate for the selective uptake of Au(III), Ag(I), Pt(IV), and Pd(II) from electronic waste.

Electron Bridge Effect Induced by Oxygen‐Bridged Ga on PdMo Bimetallene Nanoribbons for Boosting Electrocatalytic Alkynol Semihydrogenation

AbstractThe utilization of green hydrogen sources in H2O for alkynols electrocatalytic semihydrogenation reaction (ESHR) at ambient temperature provides a promising pathway toward the sustainable conversion of alkynols. However, it is still a great challenge to construct specific interfacial structure to adjust the electronic structure of Pd for the purpose of altering the strong adsorption of Pd with active hydrogen to enhance the production of alkenols. Here, the atomically dispersed GaOx‐PdMo bimetallene nanoribbons (GaOx‐PdMo BNRs) via oxygen bridging Ga atoms is designed to the surface of PdMo BNRs for 2‐methyl‐3‐butyn‐2‐ol (MBY) ESHR to the synthesis of 2‐methyl‐3‐buten‐2‐ol (MBE). The GaOx‐PdMo BNRs achieve the excellent MBE selectivity (≈97.4%), Faraday efficiency (≈96.1%), and maintain long‐term stability. Density functional theory demonstrates that the top electron‐enriched Ga atoms and the bottom electron‐deficient Pd atoms construct a “pyramidal” interface via the oxygen bridge. The unique surface can effectively activate H2O and weaken interaction between catalyst and MBE, thus promoting MBE generation. Moreover, the electron bridge effect between Ga‐O‐PdMo can induce p‐d orbital hybridization to achieve lower the d‐band center of surface Pd thus modulating the reactants adsorption. This work provides a strategy to improve ESHR performance by electron bridge effect to modulate interfacial electron distribution.

Hydrazide-functionalized covalent organic frameworks exhibit ultra-high palladium adsorption capacity and excellent selectivity

Palladium is a rare resource and is found in extremely low concentration in the earth’s crust. Therefore, the efficient recovery of palladium from wastewater is significant but remains challenging. Herein, two acyl hydrazone-functionalized covalent organic frameworks (DMTH-FTD and DHTH-FTD) were synthesized and their adsorption properties for Pd(II) in water were investigated. The DHTH-FTD has an exceptional adsorption capacity of 714.1 mg‧g−1 for Pd(II) at pH 1.0, which is the highest value among all the crystalline porous adsorbents that have been reported so far. At a concentration of 50 mg‧L−1, 96.3 % of Pd(II) can be removed in a short period of time, which still maintains up to 92.2 % after five cycles. Both DMTH-FTD and DHTH-FTD both demonstrate excellent Pd(II) selectivity, with removal rates of 93.4 % and 99.6 % of Pd(II) from 17 coexisting competing ions. The FT-IR spectroscopy, point zero charge (PZC), XPS and DFT calculations reveal that the mechanisms behind the efficient adsorption of Pd(II) by DHTH-FTD is attributed to the chelation between O and N atoms and Pd(II). This work not only provides a new research idea for the efficient adsorption and recovery of Pd(II), but also contributes to the development of covalent organic materials.

Efficient capture of palladium from nuclear wastewater by the sulfide and thiol modified covalent organic framework

The effective separation of palladium isotopes from high-level radioactive waste offers significant advantages, not only in ensuring the safe management and disposal of radioactive materials but also in addressing the scarcity of noble metals. In this study, a covalent organic framework (COF-SSH) modified with thiol and thioether groups is synthesized for the purpose of palladium separation. The experimental results demonstrate that the adsorption of Pd(II) occurs rapidly, reaching equilibrium within just 10 min. The adsorption isotherm for Pd(II) aligns well with the Langmuir model, revealing a maximum adsorption capacity of 420.2 mg/g at 3 M HNO3. Through Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS), and Density Functional Theory (DFT) analyses, the interaction between Pd and S atoms as being crucial for the adsorption process is identified. Moreover, COF-SSH exhibits exceptional selectivity for Pd(II) in simulated nuclear wastewater and maintains its performance throughout six consecutive adsorption and regeneration cycles. These results suggest that COF-SSH is a promising adsorbent for palladium separation, offering both acid resistance and high selectivity, making it a valuable candidate to the field of radioactive waste management and noble metal recovery.

Amine-rich cyclotriphosphazene (P3N3) nano-cages for enhanced and selective Au(III) and Pd(II) recovery and hydrogen generation: Waste-to-resource tactics

Designing a new material for precious metals (PMs) recovery is of ultimate significance in the quest to explore highly efficient, selective, and stable adsorbents for a sustainable economy and green environment. Herein, novel amine-rich cyclotriphosphazene poly(tetrakis(4-aminophenyl)methane-co-cylotriphosphazene)- porous nano-cages (PTC-PNC) and microspheres (PTC-MS) were synthesized for adsorption and selective recovery of Au(III) and Pd(II) in aqueous solution. A combination of the abundant amine groups and the cage-like porous morphology of PTC-PNC makes it an ideal absorbent for recovery of the Au(III) (1592 mg g−1, pH 1.0, 60 oC) and Pd(II) (1372 mg g−1, pH 1.0, 60 oC) with high selectivity which was slightly decreased up to 8-11% even in the presence of 13 co-existing metals ions while an ultra-high recovery of 99% was obtained. The unique cage-like morphology of the PTC-PNC guarantees a fast adsorption equilibrium while the adsorption isotherm specifies a pseudo-second-order kinetic behavior and Langmuir isotherm. Amine groups were the most energetically favorable sites for the capturing and chelating of Au(III) and Pd(II) ions followed by their partial reduction to Au0 and Pd0. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron spectroscopy (HRTEM) analysis were employed to explore interactions and reduction mechanisms during the adsorption process. Adopting the waste-to-resource approach, after Au(III) and Pd(II) recovery, these adsorbents were applied for catalytic hydrogen generation from ammonia borane (AB) hydrolysis. Due to its favorable electronic structure, the PTC-PNC@Pd exhibited a higher hydrogen generation than PTC-PNC@Au. The as-synthesized PTC-PNC could be employed as a promising material for other MPs' selective recovery and green energy generation applications.

Interfacial self-assembled of covalent organic framework onto MXenes for efficient enrichment and recovery of Au(III) and Pd(II) from aqueous solution

Recovery of precious metal ions in wastewater could not only improve resource utilization, but also could reduce environmental pollution. Herein, a composite of TpPa@Nb2C was constructed by an interfacial self-assembled method and explored the synergistic adsorption effects for precious metals. The structure and morphology of the composites were analyzed by advanced characterization techniques, followed by parametric analysis of Au(III)/Pd(II) adsorption from the simulated wastewater. The results showed that the grafting of COFs with abundant reducing active sites on the MXenes could significantly improve the selectivity and adsorption capacity. Meanwhile, the interaction was found as monolayer way and controlled by chemistry process, and the maximum equilibrium Au(III) and Pd(II) uptake reached up to 910.1 and 386.2 mg/g, respectively. The competitive adsorption study showed that the co-existence of impurities had little effect on the removal rate. The mechanism analysis demonstrated that the precious metal ions were reduced to elemental gold/palladium on the network of TpPa@Nb2C, and they got three electrons or two electrons from the hydroxyl groups through redox reaction, respectively. Thus, this study provided an excellent material for enrichment and recovery of precious metals in waste liquid and the treatment of e-waste.

Core–shell MOF@COF composites for ultra-efficient selective recovery of Pd(II)

Developing efficient and selective recovery of Pd(II) adsorbents is crucial for addressing environmental pollution issues. Among them, covalent organic framework (COF) and metal organic framework (MOF) composites due to the multi-site functional groups are expected to exhibit excellent Pd(II) adsorption. However, the design and preparation of COF and MOF composite adsorbents for highly efficient adsorption of heavy metal Pd(II) still face many challenges. Herein, we constructed a series of novel core–shell structure UiO-66-NH2@TAP-COF (denoted as M@C) adsorbents (M@C-X, X = 1–5, representing different MOF doses) by Schiff base reaction and applied in the adsorption of Pd(II). The findings indicated that the M@C-3 exhibited ultra-high adsorption performance, reaching a capacity of 2134.1 mg/g, and displayed excellent selectivity, making it the best among similar materials. Experimental data and density functional theory (DFT) calculations revealed that the efficient and selective adsorption of Pd(II) is attributed to coordination interaction and strong electrostatic between Pd(II) and the abundant N and O groups in M@C. This work demonstrates the significant potential of the constructed core–shell M@C composites for the efficient and selective recovery of precious metal Pd(II).

Selective recovery of palladium from wastewater by modified PVC waste pipe

Green, efficient, and cost effective methods of recycling palladium (Pd) from wastewater have attracted increasing attention. In the present study, polyvinyl chloride (PVC) was utilized as a backbone for N-(3-aminopropyl)-imidazole to graft onto and yield an adsorbent suited for selective Pd recovery from wastewater by chlorine coordination. Batch experiments showed that the self-synthesized adsorbent had a Pd(II) adsorption rate of >99% at pH 1.0–3.0 and >93% in 4 min. The selectivity of the adsorbent in a complex mixed system containing high concentrations of typical base metals (CCu(II):CZn(II):CPd(II) = 66:33:1) was investigated, and the adsorbent demonstrated much higher selectivity for Pd (97.59%) than for Cu (0.52%) and Zn (2.96%). The adsorbent can also be reused as the adsorption rate remained above 99% after five cycles. Furthermore, waste PVC pipes also could be used as the synthetic raw material. The adsorbent demonstrated a high adsorption rate even when synthesized from discarded PVC pipes and the adsorption rate reached over 93% in 2 h and reached 95.15% at equilibrium in 4 h. Scanning electron microscopy and energy-dispersive spectrometry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to analyze the adsorption mechanism, which was attributed to electrostatic interaction and intermolecular interaction. The self-synthesized adsorbent is potentially applicable to the green recovery of Pd from wastewater owing to its high adsorption rate and selectivity.

Experimental and theoretical unraveling of the electrocatalytic hydrodechlorination of chlorinated phenol using Pd promoted by oxygen vacancies in TiO2 array

The electrocatalytic dichlorination (EHDC) shows a promising potential to degrade chlorinated phenols (CPs). It is also a green technology in reducing the corresponding hazardous impact on the environment. In this study, we constructed a catalytic structure which was Pd on a TiO2 array with oxygen vacancies on carbon fibre paper substrate (Pd/TiO2/CFP) by a relatively mild route. Due to the presence of the oxygen vacancies, the resulting strong metal-support interaction (SMSI) effect has been identified which featured a redistribution of spatial charge in Pd/TiO2. The electron flow from the oxygen vacancies in the TiO2 to Pd facilitated the adsorption of Pd with 4-chlorophenol (4-CP) and endowed the Pd metal with an improved chemical reaction kinetics even at a low Pd loading. Experimentally, we studied the dependence of pH, concentration of 4-CP, and working potential on the reaction conditions of EHDC. The results showed that the conversion of 4-CP reached 100 % within 180 min with an apparent rate constant of 2.9 × 10-2 min−1 and the dominant product was phenol (P). The multi-cycle test illustrated that the Pd/TiO2/CFP electrode showed superior stability. The results also revealed that the comprehensive catalytic behavior was much better than those of the Pd/CFP and the TiO2/CFP electrodes. The density function theory (DFT) calculations indicated that 4-CP was more preferably absorbed on Pd/TiO2/CFP than Pd/CFP due to the SMSI assistance. This study provides a valuable guide in the preparation of precious metal-based electrodes for EHDC with a reduced loading and cost but without performance compromise.

Efficient and Selective Removal of Palladium from Simulated High-Level Liquid Waste Using a Silica-Based Adsorbent NTAamide(C8)/SiO2-P.

In order to realize the effective separation of palladium from high-level liquid waste (HLLW), a ligand-supported adsorbent (NTAamide(C8)/SiO2-P) was prepared by the impregnation method in a vacuum. The SiO2-P carrier was synthesized by in situ polymerization of divinylbenzene and styrene monomers on a macroporous silica skeleton. The NTAamide(C8)/SiO2-P adsorbent was fabricated by impregnating an NTAamide(C8) ligand into the pore of a SiO2-P carrier under a vacuum condition. The adsorption performance of NTAamide(C8)/SiO2-P in nitric acid medium has been systematically studied. In a solution of 0.2 M HNO3, the distribution coefficient of Pd on NTAamide(C8)/SiO2-P was 1848 mL/g with an adsorption percentage of 90.24%. With the concentration of nitric acid increasing, the adsorption capacity of NTAamide(C8)/SiO2-P decreases. Compared to the other 10 potential interfering ions in fission products, NTAamide(C8)/SiO2-P exhibited excellent adsorption selectivity for Pd(II). The separation factor (SFPd/other metals > 77.8) is significantly higher than that of similar materials. The interference of NaNO3 had a negligible effect on the adsorption performance of NTAamide(C8)/SiO2-P, which maintained above 90%. The adsorption kinetics of Pd(II) adsorption on NTAamide(C8)/SiO2-P fits well with the pseudo-second order model. The Sips model is more suitable than the Langmuir and Freundlich model for describing the adsorption behavior. Thermodynamic analysis showed that the adsorption of Pd(II) on NTAamide(C8)/SiO2-P was a spontaneous, endothermic, and rapid process. NTAamide(C8)/SiO2-P also demonstrated good reusability and economic feasibility.

Advancements in sustainable platinum and palladium recovery: unveiling superior adsorption efficiency and selectivity with a novel silica-anchored acylthiourea adsorbent.

This study addresses the pressing issue of depleting natural resources of platinum group metals (PGMs), driven by their widespread use in modern applications and increasing demand for renewable energy technologies. With conventional sources dwindling, the search for economically viable recovery methods from alternative sources has become crucial. Our focus was on innovating efficient recovery strategies, leading to the development of two novel silica-anchored adsorbents: DTMSP-BT-SG, a highly efficient acylthiourea adsorbent, and BTMSPA-SG, a silica-anchored amine adsorbent. We conducted comprehensive experiments under PGM mining wastewater conditions, varying parameters such as adsorbent mass, pH, concentration, contact time, competing ions, and volume. DTMSP-BT-SG demonstrated exceptional performance, achieving maximum adsorption efficiencies of >98% for Pt and >99% for Pd at pH 2, 0.5 g L-1 dosage, and 5 mg L-1 concentration. In contrast, under the same conditions, BTMSPA-SG recovered <56% and <89% of Pt and Pd, respectively. The experimental data for both adsorbents were analysed using Langmuir and Freundlich isotherm models for concentration and pseudo-first and second-order models for contact time. The Langmuir model best described the adsorption data, indicating homogenous monolayer adsorption of Pt and Pd. The kinetic models suggested a pseudo-second-order process, implying chemisorption. Furthermore, in the presence of competing ions and other PGMs, DTMSP-BT-SG exhibited significantly higher recovery rates for Pt and Pd compared to BTMSPA-SG. Overall, DTMSP-BT-SG emerged as a more selective and efficient adsorbent across varied parameters. Its exceptional adsorption efficiency, coupled with cost-effectiveness, positions it as a promising and competitive recovery agent for extracting PGMs from mining wastewaters.

Pd-functionalized Ti3C2Tx MXenes for realization of flexible, selective, self-heated H2 sensing

We introduce a simple approach to realize selective H2 gas sensing using Pd-decoration on Ti3C2Tx MXene. Ti3C2Tx MXene was initially prepared using Ti3AlC2 MAX phase by etching in HF solution and then different amounts of Pd-decoration (1.1, 1.4, 2.3 and 2.6 at%) on Ti3C2Tx MXene were performed using simple reduction of PdCl2 salt. Various characterizations showed that Pd was uniformly dispersed on Ti3C2Tx MXene nanosheets. The sensors were operated at 25 °C under a self-heating operation. The sensor with an optimal amount of Pd-decoration (2.3 at%) under an applied voltage of 2 V showed a greater response to H2 gas, with excellent selectivity. Additionally, the optimal sensor retained its performance even after 1000 times tilting and 5000 times bending, demonstrating its high resistance to flexibility. Enhanced selectivity to H2 gas was ascribed to the catalytic activity of Pd (adsorption of hydrogen by Pd) and formation of Pd-Ti3C2Tx MXene heterojunctions. This research highlights the possibility of realization of a selective H2 sensor with good flexibility and workability at 25 °C with low power consumption.

Bio-based nitrogen doped carbon-silica composites from low value sugarcane by-products for the selective adsorption of Au(III) from aqueous systems

This study investigates the development of carbon-silica composite (CSC) adsorbents with tuneable surface properties for gold adsorption from silica and molasses. Nitrogen modification of the CSC adsorbents was achieved through a facile urea impregnation onto the CSC, followed by pyrolysis at 400 °C (400C-5A). Exceptional Au(III) adsorption was demonstrated from acidic solutions, with a maximum adsorption capacity of 416.9 mg g−1. While CSC with no nitrogen modification (400C) only exhibits an adsorption capacity of 337.9 mg g−1. Langmuir isotherm model and pseudo-second order kinetic model were found to best describe the adsorption behaviour for Au(III) sorption on both nitrogen-modified and non-modified CSC. Urea modification led to nitrogen containing graphitic, pyridinic and pyrrolic functionalities, of which pyridinic groups were active sites for metal coordination, leading to enhanced adsorption and high selectivity towards Au and Pd. Au adsorptions of greater than 99.8% were revealed using both modified and unmodified CSC, even at low concentrations of gold (5 or 10 ppm). X-ray Photoelectron spectroscopy (XPS) analysis of 400C-5A following adsorption indicated the presence of both Au(0) and Au(III), demonstrating that adsorption took place through both chelation and an adsorption-reduction mechanism. These effective adsorbents derived from abundantly available, low cost, bio-based chemicals or low value by-products could create new opportunities for Au and/or Pd adsorption from acidic solutions.