Redox Behavior Research Articles

Oscillatory redox behavior of nickel catalysts observed by operando SEM

Oscillatory redox behavior of nickel catalysts observed by operando SEM

Hyphenation of lipophilic ruthenium(II)-diphosphine core with 5-fluorouracil: an effective metallodrug against glioblastoma brain cancer cells.

Glioblastoma multiforme (GBM) is the most common highly aggressive malignant brain tumor, with a very limited chance for survival post-diagnosis and post-treatment. Despite significant advancement in GBM genomics implicated in molecularly targeted chemotherapies, the prognosis remains poor and requires new drug discovery approaches. We used fluoropyrimidine 5-fluorouracil (5-FU), an antimetabolite anticancer drug conjugated or 'caged' within a lipophilic Ru(II)-diphosphine (dppe) core formulated as [RuII(dppe)2(5-FU)]PF6 (Ru-DPPE-5FU), where dppe = 1,2-bis(diphenylphosphino)ethane, and evaluated its in vitro cytotoxicity in depth with aggressive GBM cells (LN229). The hydrophilic nature of 5-FU limits its passage through the blood-brain barrier (BBB), which prevents its effective accumulation and efficacy for GBM tumors. Herein, we attempted to modulate the lipophilicity of 5-FU by inserting it within a well-designed lipophilic {Ru(dppe)2}-core with anticipated higher efficiency towards GBM. The physicochemical properties of [RuII(dppe)2(5-FU)]PF6 (Ru-DPPE-5FU) were studied using various spectroscopic and analytical techniques. The molecular structure was determined using X-ray crystallography, showing a distorted {RuP4NO} octahedral geometry with bidentate (N, O) binding of 5-FU and its aromatization in the Ru(II)-bound form. The 31P-NMR spectra of Ru-DPPE-5FU showed four closely spaced distinct 31P-signals, indicating four unique chemical environments around P, and the strong coupling constants between them make it a second-order spectrum. The RuII/RuIII redox potential in Ru-DPPE-5FU shifted by ∼0.91 V towards the anodic region as compared to its precursor complex cis-[Ru(dppe)2Cl2] (Ru-DPPE-Cl). DFT-based theoretical calculations have been performed to correlate the experimental electronic absorption spectra and redox behaviours of the complexes. The electrostatic potential (ESP) plots indicate the delocalization of the charge density on the O-/F-atom from the 5-FU ligand towards Ru(II) upon its complexation. The antioxidant properties of all the compounds were quantified by a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. The hyphenation of the 5-fluorouracil (5-FU) ligand to the lipophilic {Ru(dppe)2}-core endowed lipophilicity to Ru-DPPE-5FU with higher in vitro cytotoxicity (IC50 = 2.37 μM) against the LN229 GBM cells as compared to the hydrophilic 5-FU, suggesting efficient cellular uptake. Further biological assays indicated that the complex is highly potent in inhibiting significant proliferation and spheroid formation and restricting the migratory potentials of the GBM cells. Increased caspase 3/7 activity and the presence of apoptotic bodies at the center of 3-D GBM spheroids as revealed by AO/EB dual staining indicated a deeper penetration of the lipophilic complex. The Ru-DPPE-5FU complex displayed lower cytotoxicity in HaCaT normal cells (IC50 = 7.27 μM) in comparison to LN229 cancer cells with a selectivity index (S.I.) of ≥3. Overall, the synergism and caging of 5-FU within the hydrophobic {Ru(dppe)2}-core improves the pharmacokinetic profile of Ru-DPPE-5FU as a potent anticancer agent for glioblastoma.

An innovative transportable immune device for the recognition of α-synuclein using KCC-1-nPr-CS2 modified silver nano-ink: integration of pen-on-paper technology with biosensing toward early-stage diagnosis of Parkinson's disease.

Parkinson's disease (PD), the second most frequent neurodegenerative illness, is a neurological ailment that produces unintentional or uncontrolled body movements, which should be diagnosed in its early stages to hinder the progression. Monitoring the concentration of α-synuclein (α-Syn) in body fluids can be one of the most efficient ways for PD early detection. In this work, a paper-based electrochemical immunosensor was designed for α-Syn bio-assay in human plasma samples based on encapsulation of the biotinylated antibody on novel dendritic fibrous nanosilica ((KCC-1-nPr-CS2)-Ab). For this purpose, a three-electrode system was prepared using stabilization of silver nano-ink on photographic paper. Then, the (KCC-1-NH-CS2)-Ab was immobilized on its surface and used to detect the target antigen (α-Syn). After characterization of the prepared substrate by FE-SEM and EDS, the redox behavior of the biosensor was evaluated using chronoamperometry techniques. Under optimal experimental conditions and using a label-free strategy, the engineered immunosensor showed a linear relationship between peak current and antigen concentration in the linear range from 0.002 to 128 ng mL-1 with the lower limit of quantification of 0.002 ng mL-1. Moreover, this work involves unprecedented use of conductive nano-inks for the manufacture of α-Syn immunosensor, which is aided by the use of a mesoporous silicate dendrimer in encapsulating the α-Syn antibody, thus offering a robust and simple point-of-care device for early PD diagnosis. The ability of the proposed platform to detect small amounts of α-Syn offers a promising approach to developing low-cost, sensitive, and transportable biosensors for Parkinson's disease screening in its early stages.

A model study of ceria-Pt electrocatalysts: stability, redox properties and hydrogen intercalation.

The electrocatalytic properties of advanced metal-oxide catalysts are often related to a synergistic interplay between multiple active catalyst phases. The structure and chemical nature of these active phases are typically established under reaction conditions, i.e. upon interaction of the catalyst with the electrolyte. Here, we present a fundamental surface science (scanning tunneling microscopy, X-ray photoelectron spectroscopy, and low-energy electron diffraction) and electrochemical (cyclic voltammetry) study of CeO2(111) nanoislands on Pt(111) in blank alkaline electrolyte (0.1 M KOH) in a potential window between -0.05 and 0.9 VRHE. We observe a size- and preparation-dependent behavior. Large ceria nanoislands prepared at high temperatures exhibit stable redox behavior with Ce3+/Ce4+ electrooxidation/reduction limited to the surface only. In contrast, ceria nanoislands, smaller than ∼5 nm prepared at a lower temperature, undergo conversion into a fully hydrated phase with Ce3+/Ce4+ redox transitions, which are extended to the subsurface region. While the formation of adsorbed OH species on Pt depends strongly on the ceria coverage, the formation of adsorbed Hads on Pt is independent of the ceria coverage. We assign this observation to intercalation of Hads at the Pt/ceria interface. The intercalated Hads cannot participate in the hydrogen evolution reaction, resulting in the moderation of this reaction by ceria nanoparticles on Pt.

Mechanical insulation of aza-Pechmann dyes within [2]rotaxanes.

Aza-Pechmann derivatives have emerged as interesting building blocks for the preparation of organic electronic devices. The development of methodologies aimed to enhance their chemical stability and modulate their physical and chemical properties constitutes an interesting goal. Here we report the synthesis of mechanically interlocked aza-Pechmann dyes with benzylic amide macrocycles, along with the study of how the mechanical bond impacts their stability, photophysical and redox properties. Rotaxanes composed of Pechmann dilactams as threads exhibit one of the highest energy barriers for macrocyclic ring rotation, highlighting the strength of the attractive interactions ring-thread within the interlocked structure. Their enhanced thermal stability, compared to the non-interlocked counterparts, evidences the protective role of the macrocycle. Computational and electrochemical analyses indicate that the benzylic amide macrocycle improves the stability of the HOMO and LUMO orbitals of the interlocked dyes. Finally, spectroscopic and electrochemical data reveal that the macrocycle subtly modulates the optoelectronic and redox behaviour of the Pechmann dilactams.

Application of a distinctly bent, trinuclear, end-to-end azide bridged, mixed valence cobalt(iii/ii/iii) complex in the fabrication of photosensitive Schottky barrier diodes.

A mixed-valence trinuclear cobalt(iii)-cobalt(ii)-cobalt(iii) complex, [(μ-1,3-N3)Co3L(N3)3]·MeOH has been synthesized using a tetradentate N2O2 donor 'reduced Schiff base' ligand, H2L {1,3-bis(2-hydroxybenzylamino)2,2-dimethylpropane} and azide as anionic co-ligand. The complex has been characterised by elemental analysis, IR, UV-vis spectroscopy and single-crystal X-ray diffraction studies etc. The cobalt(iii)-cobalt(ii)-cobalt(iii) skeleton in the complex is non-linear and non-centrosymmetric. The redox behavior of the complex was studied by using Cyclic Voltammetry (CV). The complex is found to be a semiconductor material as confirmed by determining the band gap of this complex by experimental as well as theoretical studies. The band gap in the solid state has been determined experimentally. The conductivity of the synthesized complex based device improves considerably in illumination conditions from the non-illuminated conditions. The complex has also been used to fabricate Schottky barrier diodes.

Oscillatory phase transition induced structural extension during iron oxide reduction

Probing the molecular-level redox behavior and mechanism of oxides is essential to developing innovative applications in different fields such as catalysis, but remains a challenge for the scientific community. Using in-situ transmission electron microscopy, here we provide an overall reduction view of single-crystalline α-Fe2O3 with different characteristics from the conventional wisdom of oxide reduction. Specifically, the formation of epitaxial nanoislands with concomitant oscillatory phase transitions (α-Fe2O3→defective γ-Fe2O3→α-Fe2O3) at the subsurface is observed during reduction. The dynamic equilibrium of lattice oxygen at the surface and the limited oxygen replenishment from the deep layer drive the α-Fe2O3→defective γ-Fe2O3 transformation in the subsurface, while the polymorphic transition (defective γ-Fe2O3→α-Fe2O3) spontaneously occurs under heating conditions. Such oscillatory phase transition is accompanied by the release of asymmetric stress, inducing the extension of epitaxial nanoislands. Our work highlights the complexity of reduction by providing an integral picture of oxide reduction, which contributes to the understanding of the site evolution of oxide-based catalysts in their working state.

Low-temperature redox activity and alcohol ammoxidation performance on Cu- and Ru-incorporated ceria catalysts.

Transition-metal-incorporated cerium oxides with Cu and a small amount of Ru (Cu0.18Ru0.05CeOz) were prepared, and their low-temperature redox performance (<423 K) and catalytic alcohol ammoxidation performance were investigated. Temperature-programmed reduction/oxidation under H2/O2 and in situ X-ray absorption fine structure revealed the reversible redox behavior of the three metals, Cu, Ru, and Ce, in the low-temperature redox processes. The initially reduced Ru species decreased the reduction temperature of Cu oxides and promoted the activation of Ce species. Cu0.18Ru0.05CeOz selectively catalyzed the production of benzonitrile in the ammoxidation of benzyl alcohol. H2-treated Cu0.18Ru0.05CeOz showed a slightly larger initial conversion of benzyl alcohol than O2-treated Cu0.18Ru0.05CeOz, suggesting that the reduced structure of Cu0.18Ru0.05CeOz was active for the ammoxidation. The integration of both Cu and Ru resulted in the efficient promotion of ammoxidation, in which the Ru species were involved in the conversion of benzyl alcohol and Cu species were required for selective production of benzonitrile.

Chemical and redox non-innocence in low-valent molybdenum β diketonate complexes: novel pathways for CO2 and CS2 activation.

The investigation of fundamental properties of low-valent molybdenum complexes bearing anionic ligands is crucial for elucidating the molybdenum's role in critical enzymatic systems involved in the transformation of small molecules, including the nitrogenase's iron molybdenum cofactor, FeMoco. The β-diketonate ligands in [Mo(acac)3] (acac = acetylacetonate), one of the earliest low-valent Mo complexes reported, provide a robust anionic platform to stabilize Mo in its +III oxidation state. This complex played a key role in demonstrating the potential of low-valent molybdenum for small molecule activation, serving as the starting material for the preparation of the first reported molybdenum dinitrogen complex. Surprisingly however, given this fact and the widespread use of β-diketonate ligands in coordination chemistry, only a very limited number of low-valent Mo β-diketonate complexes have been reported. To address this gap, we explored the redox behavior of homoleptic molybdenum tris-β-diketonate complexes, employing a tertiary butyl substituted diketonate ligand (dipivaloylmethanate, tBudiket) to isolate and fully characterize the corresponding Mo complexes across three consecutive oxidation states (+IV, +III, +II). We observed marked reactivity of the most reduced congener with heterocumulenes CE2 (E = O, S), yet with very distinct outcomes. Specifically, CO2 stoichiometrically carboxylates one of the β-diketonate ligands, while in the presence of excess CS2, catalytic reductive dimerization to tetrathiooxalate occurs. Through the isolation and characterization of reaction products and intermediates, we demonstrate that the observed reactivity results from the chemical non-innocence of the β-diketonate ligands, which facilitates the formation of a common ligand-bound intermediate, [Mo( tBudiket)2( tBudiket·CE2)]1- (E = O, S). The stability of this proposed intermediate dictates the specific reduction products observed, highlighting the relevance of the chemically non-innocent nature of β-diketonate ligands.

Insights into the first multi-transition-metal containing Ruddlesden–Popper-type cathode for all-solid-state fluoride ion batteries

The first multi-transition metal cathode was examined for fluoride ion batteries, showing different redox behaviour of cobalt and nickel on charging and discharging.

Binuclear cyclometalated Ir(III) complexes with bis-bidentate butterfly-shaped ligands: synthesis, characterization, and application in efficient yellow-orange light-emitting electrochemical cells.

Two yellow-to-orange-emitting binuclear iridium complexes of the form [Ir2(ppy)4(N^N)](ClO4)2 (namely IrL1 and IrL2) were designed and synthesized, using phenylpyridine (ppy) as a cyclometalating ligand (C^N) and phenanthroimidazole-based bridging compounds as ancillary ligands (N^N), to explore the effect of sterically hindered bulky bridging ligands and their substituents on the electronic and emission properties of the related ionic transition metal complexes (iTMCs) and the performance of iTMC-based light-emitting electrochemical cells (iTMC-LECs). In CH2Cl2 solution, complexes IrL1 and IrL2 afford yellow-to-orange emission centered at 570 and 582 nm with PLQYs of 27% and 36%, respectively. The reversible and quasi-reversible redox behaviors of both complexes are shown to reveal the excellent stability of the emitters in solution. The electrochemical and photophysical data indicate that the substitution at the C2 position of the imidazole moiety does not significantly affect the electronic properties of the complexes. IrL1 and IrL2-based LECs show yellow-to-orange electroluminescence centered at 586 and 598 nm, with a maximum luminance (Lmax) of 430 and 570 cd m-2 and current efficiencies of 3.45 and 4.50 cd A-1, respectively. However, compared with their corresponding archetypecomplex, IrL1, and IrL2-based LECs exhibit several fold higher Lmax, which highlights the role of these ligands in the design of emitters.

Flow electrosynthesis of phosphinamides and phosphoramidates through P–N coupling

A robust flow electrochemical method for P–N and P–O oxidative coupling under mild conditions has been developed. Cyclic voltammetry (CV) was employed to investigate the redox behaviour of reactants.

Ferrocenyl-triazole complexes and their use in heavy metal cation sensing.

Complexes tris((1-ferrocenyl-1H-1,2,3-triazol-4-yl)methyl)amine (3), bis((1-ferrocenyl-1H-1,2,3-triazol-4-yl)methyl)amine (6), bis((1-ferrocenyl-1H-1,2,3-triazol-4-yl)methyl)ether (7), and 1-ferrocenyl-1H-1,2,3-triazol-4-yl)methanamine (9) were synthesized using the copper-catalyzed click reaction. Complexes 3, 6, 7, and 9 were characterized using NMR (1H and 13{1H}) and IR spectroscopy, elemental analysis, and mass spectrometry. Structures of 3, 7, and 9 in the solid state were determined using single-crystal X-ray diffraction. It was found that the triazole rings were planar and slightly twisted with respect to the cyclopentadienyl groups attached to them. Chains and 3D network structures were observed due to the presence of π⋯π and C-H⋯N interactions between the cyclopentadienyl and triazole ligands. A reversible redox behavior of the Fc groups between 239 and 257 mV with multicycle stability was characteristic for all the compounds, revealing that the electrochemically generated species Fc+ remained soluble in dichloromethane. Electrochemical sensor tests demonstrated the applicability of all the complexes to enhance the quantification sensing behavior of the screen-printed carbon electrode (SPCE) toward Cd2+, Pb2+, and Cu2+ ions.

Chromophore appended DPA-based copper(II) complexes with a diimine motif towards DNA binding and fragmentation studies.

Mixed ligand copper(II) complexes [Cu(L1)(bpy)](ClO4)21 and [Cu(L2)(bpy)](ClO4)22 (where L1 = 1-(anthracen-9-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine, L2 = 1-(pyren-1-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine and bpy = 2,2'-bipyridine) were synthesised and characterised thoroughly via different analytical and spectroscopic techniques i.e., UV-vis spectroscopy, fluorescence spectroscopy, FT-IR spectroscopy, HRMS and EPR spectroscopy. The molecular structures of the synthesised complexes were obtained using the single-crystal X-ray diffraction technique. Both complexes exhibited penta-coordinated and acquired distorted square pyramidal geometry. The redox behaviour of complexes 1 and 2 was investigated by employing cyclic voltammetry. The DNA binding study was carried out by UV-vis spectrophotometry using double-stranded salmon sperm DNA (ds-ss-DNA). The binding constant (Kb) values of 1 and 2 were 0.11 × 104 M-1 and 1.05 × 104 M-1, respectively, which indicates that 2 has better binding ability than 1. This might be due to the higher conjugative abilities with the extended surface area of the aromatic pyrene ring compared to the anthracene moiety. The fluorescence quenching experiments were also performed with EB bound DNA (EB-DNA) and Stern-Volmer constant (KSV) values were calculated as 1.23 × 105 M-1 and 1.39 × 105 M-1 for 1 and 2, respectively, suggesting that 2 showed stronger interaction with ss-DNA than 1. The molecular docking data support the DNA-binding studies, with the sites and mode of interactions against B-DNA varying with 1 and 2. Evaluation of the DNA binding properties of the complexes to linearized plasmid DNA indicated that 2 had modest DNA binding properties, which is a pre-requisite for a genotoxic agent. The effect of 1 and 2 on cell survival was analysed using HeLa cells by MTT assay and it was observed that the IC50 values of 1 and 2 were 43.7 μM and 18.6 μM, respectively. Our study paves the way for the designing of bio-inspired novel mixed metal complexes, which shows promising results for further exploration of molecular and mechanistic studies towards the development of non-platinum based economical metallodrugs.

Multielectron transfer and field-induced slow magnetic relaxation in opto-electroactive spin crossover cobalt(ii) complexes: structure–function correlations

A unique series of spin-crossover cobalt(ii)-pyridine-2,6-dimine molecular nanomagnets as prototypes of molecular spin quantum transitors and capacitors exhibiting a dual metal- and ligand-centred multielectron redox behaviour is reported.

Mixed-ligand copper(ii)-diimine complexes of 3-formylchromone-N 4-phenyl thiosemicarbazone: 5,6-dmp co-ligand confers enhanced cytotoxicity.

The promising biological applications of thiosemicarbazone derivatives have inspired the design, synthesis, and study of their Cu(ii) complexes for anticancer therapeutic applications. Herein, we have evaluated the DNA/protein binding, DNA cleaving, and cytotoxic properties of four mixed-ligand Cu(ii) complexes of the type [Cu(L)(diimine)](NO3) 1-4, where HL is 4-oxo-4H-chromene-3-carbaldehyde-4(N)-phenylthiosemicarbazone and diimine is 2,2'-bipyridine (bpy, 1) 1,10-phenanthroline (phen, 2), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp, 3), or dipyrido-[3,2-f:2',3'-h]-quinoxaline (dpq, 4). Interestingly, complex 3 with higher lipophilicity shows stronger DNA binding and oxidative DNA cleavage, higher ROS production, and more reversible redox behaviour, resulting in its remarkable cytotoxicity (IC50, 1.26 μM) against HeLa cervical cancer cells, and rendering it 5 times more potent than the widely used drug cisplatin. The same complex induces enhanced apoptotic cell death on HeLa cells but lower toxicity towards the non-cancerous PBMC cells. Molecular docking studies suggest that all the complexes bind in the minor groove of DNA and subdomain II of HSA, which is in close agreement with the experimental results. Also, 3 shows cytotoxicity higher than the analogous mixed ligand Cu(ii) complexes, reported already, emphasizing the importance of co-ligand in tuning the anticancer activity.

Transient crystallisation of rare earth carbonates during the hydrothermal oxidation of siderite.

The researchers investigated the interaction between multi-component rare earth element-bearing aqueous solutions and siderite grains under hydrothermal conditions. Our study investigates the interaction between multi-component rare earth element (REE; La, Ce, Pr, Nd, Dy)-bearing aqueous solutions and siderite (FeCO3) grains under hydrothermal conditions (50-205 °C). The results revealed a solution-mediated mineral replacement reaction that occurs via a multi-step crystallisation pathway involving the formation of iron oxides (goethite, α-FeO(OH), and hematite, Fe2O3), metastable REE-bearing minerals (kozoite, REE(CO3)(OH), and bastnasite, REE(CO3)(OH,F)), and cerianite (CeO2). Siderite stability, dissolution, and subsequent mineral formation are temperature and pH-dependent. At low temperatures, REE carbonate formation is inhibited by a goethite coating, creating a partial equilibrium situation. Higher temperatures increase dissolution rates and enable kozoite and bastnasite formation. The redox behaviour of Fe and Ce combined with the temperature, and the availability of CO3 2- govern this crystallisation sequence. Continued oxidation promotes decarbonation processes by acidifying the aqueous solution, dissolving all carbonates, and resulting in hematite and cerianite crystallisation as thermodynamically stable phases. Understanding iron carbonate, oxide and REE interactions can inform new resource targets and improve recovery and separation techniques.

Structure and redox behaviour of a paramagnetic Rh-Pt-Cu-Pt-Rh heterometallic-extended metal-atom chain.

A paramagnetic, pentanuclear, metal-metal bonded complex comprising three metals is isolated. The Cu dx2-y2 orbital of the Rh-Pt-Cu-Pt-Rh chain contains an unpaired electron. The close energetic levels and symmetric overlap of the Cu dx2-y2 and Rh-Pt δ* induces a charge-transfer reaction to achieve the diamagnetic Rh-Pt-Cu-Pt-Rh complex.

Redox Behavior of Arsenic (III) and Copper (II) Mixtures on Ultraflat Au (111) Thin Film Electrodes

The electrochemical behavior of arsenic on gold (Au) electrodes surfaces is of great interest as As is well-recognized as a highly toxic and relatively ubiquitous ground water species. The United States Environmental Protection Agency (USEPA) and World Health Organization (WHO) drinking water standards for arsenic are 10 PPB, or 𝜇g L-1 [1]. These minute ion concentrations necessitate the use of analytical methods with high sensitivity and a low susceptibility to cross interferences. Electrochemical stripping voltammetry is a well-established electroanalytical method for arsenic ions [2]. Polycrystalline gold electrodes are often used due to their high redox stability and relatively low overpotential for hydrogen evolution. We recently explored the use of ultra-flat, thin film, Au(111) electrodes to replace polycrystalline Au for As stripping voltammetry. Previous studies on oriented single crystals showed relatively narrow stripping peaks with greatly improved peak to background ratios on the (111) surfaces [3]. We observed comparatively similar or better stripping behavior on the Au(111) thin film electrodes with correspondingly far less gold usage per electrode. Unfortunately, copper is a known interference for arsenic stripping electroanalysis, with a strong affinity for UPD deposition on gold. We therefore studied the deposition behavior of Cu on Au(111) thin film electrodes and the co- deposition of Cu and As on the Au(111) thin film electrodes to evaluate cross interference effects. Copper redox behavior in 0.5M H2SO4 was characterized by cyclic voltammetry, electro- deposition and linear stripping voltammetry (LSV) measurements. Strong Cu UPD behavior was observed on Au(111) thin films with sharper, better defined redox peaks than polycrystalline electrodes. Arsenic and Cu ions were also co-deposited over a wide range of Cu (II) and As (III) concentrations. Complex redox behavior was observed with strong indications of Cu-As alloy formation. This was confirmed via angle resolved, X-ray Photoemission Spectroscopy (XPS) measurements. Our results also indicate that the electrodeposition efficiency during LSV of As is increased by the co-deposition of Cu. The results of this study have important implications for understanding the nature of Cu (II) interference with electrochemical detection of trace As (III) in water.[1] USEPA. National Secondary Drinking Water Regulations. 2009. https://www.epa.gov/sdwa/drinking-water- regulations-and-contaminants (accessed.[2] USEPA. METHOD 7063: ARSENIC IN AQUEOUS SAMPLES AND EXTRACTSBY ANODIC STRIPPING VOLTAMMETRY (ASV). 1996.[3] Casuse-Driovínto, T. Q.; Rizo, R.; Benavidez, A.; Brearley, A. J.; Cerrato, J. M.; Garzon, F. H.; Herrero, E.; Feliu, J. M. Increased Sensitivity and Selectivity for As(III) Detection at the Au(111) Surface: Single Crystals and Ultraflat Thin Films Comparison. The Journal of Physical Chemistry C 2022, 126 (48), 20343-20353. DOI: 10.1021/acs.jpcc.2c05541.

(Invited) Sustainable Recycling of Metals from Solar Cells

The share of solar energy is increasing worldwide, leading to a widespread use of solar panels. Knowing that the 80 Mt of waste solar panels will be produced by 2050, sustainable processes must be designed in order to deal with the inevitable increase of waste solar cells in the coming years.The main advantage associated with recycling is to avoid the inevitable dispersion of hazardous materials in the environment occurring when the solar cells are landfilled. It also reduces the need for primary mineral resources and may reduce the supply risk for important components like silicon wafers, for which the production is concentrated in a few countries. The recycling process applied plays a major role to allow reducing the carbon footprint of solar cells, advocating in favour of sustainable practices for solar cells recycling.Mono-crystalline solar cells representing 90% of the market, it is therefore this kind of solar cells that are more likely to reach their end-of-life soon. Mono-crystalline solar cells are made of an aluminium frame surrounding the solar module. Underneath a glass layer, layers of ethylene vinyl acetate (EVA) encapsulate the solar cell. The solar cell in itself is made of a silicon wafer with aluminium and silver electrode as well as a silicon nitride anti-reflective coating. Recycling of the metals, particularly silver, is the main economic driver for solar cells recycling.Recycling mono-crystalline solar cells involves a mechanical removal of the aluminium frame and the junction box prior to removal of the glass and EVA layers. Different process were evaluated to get rid of EVA. Solvent-assisted dissolution allowed EVA dissolution but it requires the use of harmful solvents and often leads to breakage of the solar cell. Pyrolysis allows to recover the wafer intact while removing the glass and polymers layers. Provided that the thermal treatment is applied under an inert atmosphere, EVA decomposition leads to relatively non-toxic chemicals such as acetic acid. Recent developments include laser assisted would lead to efficient and straightforward removal of EVA.The removal of metals from the solar cells involves the use of harsh chemicals such as hydrofluoric acid for the removal of silicon nitride, nitric acid to solubilise silver and sodium hydroxide for the dissolution of aluminium. Recently, the use of aqueous brines was introduced to recover silver and aluminium from solar cells. A green and re-usable oxidising agent such as iron(III) chloride can be used to oxidise and dissolve silver, as evidenced in Figure 1, which shows a solar cells before (up) and after (down) etching, revealing the removal of the white silver lines.Using water as a solvent, silver dissolution is impossible due to the low chloride content. By increasing the chloride content, oxidation of silver and its dissolution becomes possible due to the formation of iron-chloride and silver-chloride complexes which have a different redox behaviour and a higher solubility. Overall, silver is completely dissolved in about 10 minutes without using any acids or harmful chemical. Silver can be easily recovered by precipitation or cementation, while the oxidising agent can be regenerated using oxygen from air or via electrolytic means. The objective of this presentation is to give an overview of the current recycling options and provide some guidance on the best and more sustainable practices for the complete recycling of solar cells. The choice is guided by techno-economic analysis and life cycle assessment as well as experimental demonstration of the recycling on real waste solar cells. Figure 1