Comparison of digestion methods for the determination of ruthenium in catalyst materials

Drivers and Pathways for the Recovery of Critical Metals from Waste-Printed Circuit Boards

The ever-increasing importance of critical metals (CMs) in modern society underscores their resource security and circularity. Waste-printed circuit boards (WPCBs) are particularly attractive reservoirs of CMs due to their gamut CM embedding and ubiquitous presence. However, the recovery of most CMs is out of reach from current metal-centric recycling industries, resulting in a flood loss of refined CMs. Here, 41 types of such spent CMs are identified. To deliver a higher level of CM sustainability, this work provides an insightful overview of paradigm-shifting pathways for CM recovery from WPCBs that have been developed in recent years. As a crucial starting entropy-decreasing step, various strategies of metal enrichment are compared, and the deployment of artificial intelligence (AI) and hyperspectral sensing is highlighted. Then, tailored metal recycling schemes are presented for the platinum group, rare earth, and refractory metals, with emphasis on greener metallurgical methods contributing to transforming CMs into marketable products. In addition, due to the vital nexus of CMs between the environment and energy sectors, the upcycling of CMs into electro-/photo-chemical catalysts for green fuel synthesis is proposed to extend the recycling chain. Finally, the challenges and outlook on this all-round upgrading of WPCB recycling are outlined.

UiO-66 MOF-Derived Ru@ZrO2 Catalysts for Photo-Thermal CO2 Hydrogenation

The use of metal–organic frameworks (MOFs) as templates or precursors in the manufacture of heterogeneous catalysts is highly attractive due to the transfer of MOFs’ inherent porosity and homogeneous metallic distribution to the derived structure. Herein, we report on the preparation of MOF-derived Ru@ZrO2 catalysts by controlled thermal treatment of zirconium-based MOF UiO-66 with ruthenium moieties. Ru3+ (3 or 10 mol%) precursor was added to UiO-66 synthesis and, subsequently, the as-synthesized hybrid structure was calcined in flowing air at different temperatures (400–600 °C) to obtain ZrO2-derived oxides doped with highly dispersed Ru metallic clusters. The materials were tested for the catalytic photo-thermal conversion of CO2 to CH4. Methanation experiments were conducted in a continuous flow (feed flow rate of 5 sccm and 1:4 CO2 to H2 molar ratio) reactor at temperatures from 80 to 300 °C. Ru0.10@ZrO2 catalyst calcined at 600 °C was able to hydrogenate CO2 to CH4 with production rates up to 65 mmolCH4·gcat.–1·h–1, CH4 yield of 80% and nearly 100% selectivity at 300 °C. The effect of the illumination was investigated with this catalyst using a high-power visible LED. A CO2 conversion enhancement from 18% to 38% was measured when 24 sun of visible LED radiation was applied, mainly due to the increase in the temperature as a result of the efficient absorption of the radiation received. MOF-derived Ru@ZrO2 catalysts have resulted to be noticeably active materials for the photo-thermal hydrogenation of CO2 for the purpose of the production of carbon-neutral methane. A remarkable effect of the ZrO2 crystalline phase on the CH4 selectivity has been found, with monoclinic zirconia being much more selective to CH4 than its cubic allotrope.

Poly(lactic acid)/β-cyclodextrin based nanoparticles bearing ruthenium(II)-arene naproxen complex: preparation and characterisation. Analytical validation for metal determination by microwave-induced plasma optical emission spectrometry

The objectives of this work are to develop nanocarrier systems for the Ru(II)-p-cymene naproxen antitumor metallodrug, [Ru(η⁶-p-cymene)(npx)Cl] or Rupcy, based on polymeric nanoparticles (NPs) composed by the biodegradable poly(lactic acid) (PLA) and the hydrophilic polymerised β-cyclodextrin (PolyCD); to validate an analytical method for determination of Ru incorporated into the metallodrug loaded-NPs. The PolyCD was prepared by single step condensation and polymerisation reaction and incorporated as a polymer blend during the fabrication of PLA/PolyCD blends NPs and also as a core/shell structure built by adsorption of the PolyCD onto the surface of PLA NPs to give PLA(core)/PolyCD(shell) NPs. Three different loaded-systems incorporating the metallodrug (Rupcy-PLA NPs (1), Rupcy-PLA/PolyCD blends (2), and Rupcy-PLA(core)/PolyCD(shell) NPs (3)) were prepared by nanoprecipitation. The characterisation was performed by Proton Nuclear Magnetic Resonance, Matrix Assisted Laser Desorption/Ionization Time-of-Flight, Fourier-Transform Infra-red and UV-VIS Electronic Absorption Spectroscopies, Thermogravimetric Analysis, Differential Scanning Calorimetry, Dynamic Light Scattering, and Electrophoretic Light Scattering. Ru was determined by Microwave Induced Plasma Optical Emission Spectrometry (MIP-OES) with validation of the method. The metallodrug entrapment efficiency was around 90% (w/w) and drug loading was at 3-4% (w/w). The characterised metallodrug-loaded systems exhibited monomodal size distributions and appropriate hydrodynamic diameters [218.3 ± 13.5 (1), 205.4 ± 14.4 (2), 231.5 ± 22.0 (3) nm] and zeta potential values [-31.5 ± 2.2 (1), -26.1 ± 4.5 (2), -28.8 ± 6.1 (3) mV]. The validation of the MIP-OES method by evaluating selectivity, linearity, precision, accuracy, and limits of detection and quantification succeeded. The NPs parameters are compatible with colloidally stable systems. The MIP-OES method showed to be simple, reliable, and feasible to quantify indirectly the amount of the metallodrug-loaded into the PLA NPs.

Hydrogenation of Carbon Monoxide in the Liquid Phase: Influence of the Synthetic Methods on Characteristics and Activity of Hydrogenation Catalysts

Oxygenate fuels are a promising solution to urban air pollution, reducing soot emissions by big margins. Formaldehyde is a major building block for the synthesis of oxygen-rich fuels. Herein we report the synthesis, characterisation and testing of ruthenium on alumina catalysts for the methanol-mediated CO hydrogenation towards oxygenates with the formaldehyde oxidation state. We varied the synthesis parameters and could see interesting correlation between synthesis parameters, final metal loading, crystallite sizes and catalyst activity. The catalysts were tested in a high-pressure three-folded reactor plant in the CO hydrogenation in methanolic media. Interesting relationships between catalyst synthesis, structure and activity could be gained from these experiments.

[Ru(tmphen)3]2[Fe(CN)6] and [Ru(phen)3][Fe(CN)5(NO)] complexes and formation of a heterostructured RuO2-Fe2O3 nanocomposite as an efficient alkaline HER and OER electrocatalyst

Water electrolysis is one of the most capable processes for supplying clean fuel. Herein, two novel ionic Ru(II)-Fe(II) complexes, [Ru(tmphen)₃]₂[Fe(CN)₆] and [Ru(phen)₃][Fe(CN)₅(NO)], where tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline and phen = 1,10-phenanthroline, were synthesized and characterized by UV-Vis spectroscopy, elemental analysis, FT-IR, and single-crystal X-ray structural analysis. By thermally decomposing the [Ru(tmphen)₃]₂[Fe(CN)₆] complex at 600 °C for 4 h, a heterostructured RuO₂-Fe₂O₃ nanocomposite was fabricated through a facile one-pot treatment and then characterized by FT-IR, XRD, FT-Raman, UV-Vis (DRS), ICP-OES, FE-SEM, TEM, TGA/DTG, BET, and XPS analyses, which revealed the formation of highly crystalline RuO₂-Fe₂O₃ nanoparticles with an average size of 8-12 nm. The prepared nanocomposite was an efficient heterostructured electrocatalyst for performing water-splitting redox reaction processes, including hydrogen and oxygen evolution reactions (HER and OER) in alkaline solutions. In this regard, RuO₂ and Fe₂O₃ samples were also prepared through thermal decomposition of [Ru(tmphen)₃](NO₃)₂ and K₄[Fe(CN)₆] precursors, respectively, as control experiments to compare their HER and OER electrocatalytic activity with that of the RuO₂-Fe₂O₃ nanocomposite. Specifically, the RuO₂-Fe₂O₃ nanocomposite exhibited significant electrocatalytic performance, generating 10 mA cm^-2 current density at -148 and 292 mV overpotentials, and the Tafel slope results from fitting the LSV curves to the Tafel equation were -43 and 56.08 mV dec^-1 for the HER and OER, respectively. Therefore, the heterostructured RuO₂-Fe₂O₃ nanocomposite can be viewed as a bi-functional electrocatalyst for HER and OER because it exploits the synergistic effects of heterostructures and active sites at its interface.

Ru nanoparticles supported on alginate-derived graphene as hybrid electrodes for the hydrogen evolution reaction

Ultra-small Ru NPs grown on biomass-derived bare/P-doped graphene supports yield efficient and durable electrocatalytic H2 production from water.

On the support dependency of the CO2 methanation – decoupling size and support effects

The influence of the support basicity, according to the Lewis and Brønsted definition, was investigated for the CO₂ methanation over isostructural Ru catalysts.

Controlling the selectivity of bimetallic platinum–ruthenium nanoparticles supported on N-doped graphene by adjusting their metal composition

Bimetallic platinum–ruthenium nanoparticles supported on N-doped graphene as chemoselective hydrogenation catalysts.

Multielemental composition of suet oil based on quantification by ultrawave/ICP-MS coupled with chemometric analysis

Suet oil (SO) has been used commonly for food and medicine preparation. The determination of its elemental composition has became an important challenge for human safety and health owing to its possible contents of heavy metals or other elements. In this study, ultrawave single reaction chamber microwave digestion (Ultrawave) and inductively coupled plasma-mass spectrometry (ICP-MS) analysis was performed to determine 14 elements (Pb, As, Hg, Cd, Fe, Cu, Mn, Ti, Ni, V, Sr, Na, Ka and Ca) in SO samples. Furthermore, the multielemental content of 18 SO samples, which represented three different sources in China: Qinghai, Anhui and Jiangsu, were evaluated and compared. The optimal ultrawave digestion conditions, namely, the optimal time (35 min), temperature (210 °C) and pressure (90 bar), were screened by Box-Behnken design (BBD). Eighteen samples were successfully classified into three groups by principal component analysis (PCA) according to the contents of 14 elements. The results showed that all SO samples were rich in elements, but with significant differences corresponding to different origins. The outliers and majority of SO could be discriminated by PCA according to the multielemental content profile. The results highlighted that the element distribution was associated with the origins of SO samples. The proposed ultrawave digestion system was quite efficient and convenient, which could be mainly attributed to its high pressure and special high-throughput for the sample digestion procedure. Our established method could be useful for the quality control and standardization of elements in SO samples and products.