Oxygen-free Conditions Research Articles

Optimisation of CFRP composite recycling process based on energy consumption, kinetic behaviour and thermal degradation mechanism of recycled carbon fibre

Abstract Pyrolysis is a thermo-chemical method to recover clean fibres from carbon fibre reinforced polymer (CFRP) composite waste under oxygen-free conditions. To ensure the recovery quality and economic efficiency of reclaimed fibres, thermal decomposition of CFRP needs to be guided by the kinetic analysis. This paper investigates the kinetic behaviour of CFRP thermal decomposition at temperatures of up to 800 °C. A thermo-gravimetric method is used to monitor the thermal decomposition of CFRP samples during the pyrolysis process. The activation energies (E) required for different conversion fractions (α) are evaluated based on five different kinetic models: four Arrhenius-type model-free methods (Friedman, OFW, KAS and Starink) and one curve fitting method (Coats-Redfern). Pyrolysis of CFRP composite wastes show that the process consists of two stages, where majority of the polymer matrix (55%) is removed in the first stage of reaction. During stage one and up to 425 °C, lower heating rates successfully lead to higher conversion fractions with lower activation energies. Moreover, by investigating physical characteristics of the recycled fibres using scanning electron microscopy (SEM) and conversion kinetics of the recycling process, it is shown that pyrolysis of the composite remains efficient until 425 °C and an oxidation process up to 550 °C is required to achieve high quality recycled carbon fibre (rCF) products. The outcomes of this research contribute to optimisation of process variables and development of highly efficient and cost effective CFRP recycling method using pyrolysis technique.

Polycyclic aromatic hydrocarbon and soot emissions in a diesel engine and from a tube reactor

An investigation into the exhaust emissions of carcinogenic polycyclic aromatic hydrocarbons (PAHs) from a diesel engine was reported. The study is reinforced by the experimental results obtained from a tube reactor aimed at examining the PAH formation processes from these fuels. The paper cantered on the 16 priority PAHs suggested by the United States Environmental Protection Agency (US-EPA). These PAHs were produced by burning conventional diesel fuel and a few binary fuels prepared by blending various proportions of toluene into heptane. Special consideration was given to the B2 subgroup of PAHs which are known human-carcinogens. Both the gas born (smaller) PAHs, as well as the larger PAHs, adsorbed onto the particulate were investigated. The engine used was a single-cylinder, light duty, high speed, diesel automotive research engine run at an Indicated Mean effective pressure (IMEP) of 7 bar. Particulate matter was also produced in a tube reactor at temperatures ranging from 1050 to 1350 °C under pyrolysis (oxygen-free) conditions to study PAH and soot formation in conditions which resemble, to an extent, those found in the core of diesel engine fuel sprays. In the diesel engine, it was found that exhaust PAHs were influenced by combustion characteristics like heat release rates and ignition delay. However, in the quiescent oxygen-free conditions of the reactor, chemical composition of the fuels and temperature dominated PAH formation.

Microfluidic synthesis of thermo-responsive block copolymer nano-objects via RAFT polymerization

Continuous flow microreactors offer advantages such as quick heat dissipation, high throughput as well as reproducible and flexible product quality. Here we present a X-ray compatible microfluidic reaction vessel suitable for studying living polymerization reactions in flow under oxygen-free conditions. Diblock copolymer nano-objects were synthesized via mixing-induced reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization in a microfluidic channel. A water-soluble macro chain transfer agent was chain-extended with N-isopropylacrylamide (NIPAm). Poly(NIPAm) is a thermo-responsive polymer with a lower critical solution temperature of 32 °C. Thus, heating the polymer solution results in the formation of micelles according to the polymerization-induced thermal self-assembly route. To implement the reaction in a microfluidic sample environment, metal-polyimide devices have been fabricated. The use of microfluidics for the synthesis of copolymers enhanced the control of reaction parameters. Moreover, the use of X-ray compatible materials paves the way for future in situ time-resolved structural studies of the flowing species.

Thermal processing under oxygen–free condition of blueberry puree: Effect on anthocyanin, ascorbic acid, antioxidant activity, and enzyme activities

The effect of thermal treatment of blueberry was investigated using a designed grinding and continuous packaging system under oxygen–free conditions. The grinding, packaging, and heating at 90 °C for 30 min under anaerobic condition were compared to heating under aerobic conditions, showing complete inactivation of oxidative enzymes. Heating without oxygen retained anthocyanins and ascorbic acid whereas heating in atmospheric air does not. Delphinidin glycoside was mostly influenced by oxygen deficiency during heating, followed by petunidin and malvidin glycosides. The differences in oxygen sensitivity may be closely associated with the number of hydroxylation in the B ring. The result of anthocyanin led to higher antioxidant activity and redness values of purees heated without oxygen than purees heated with oxygen. Consequently, thermal processing under oxygen–free condition can prevent oxidation of anthocyanin, resulting in higher retention of color and nutritional values of blueberry products.

Impacts of cryogenic sampling processes on iron mineral coatings in contaminated sediment

This study focused on comparing iron mineral coatings found in contaminated sediments from a cryogenic (Cryo Core) core versus an Anaerobic Core (collected under oxygen-free and ambient conditions). After thawing the Cryo Core in an oxygen-free glovebox, a suite of analyses was applied on sediments from both cores: pH, redox potential, X-ray fluorescence (XRF), X-ray diffraction (XRD), and field-emission scanning electron microscopy (FESEM) with energy dispersive X-ray analyzer (EDX). Among the iron minerals identified, crystalline pyrite was found throughout the Cyro Core sediment samples, which is in contrast to that observed for the Anaerobic Core. Moreover, mackinawite and greigite that were ubiquitous in the Anaerobic Core were not observed in Cryo Core samples. To better understand why the metastable minerals were not present, a freeze/thaw process was simulated on Anaerobic Core samples using a liquid‑nitrogen quench with surface coatings characterized by FESEM/EDX. In these quenched samples, mackinawite was no longer observed, and in its place was pyrite. In addition, both greigite and pyrite were found to be unique morphologically after quenching. Dissolution and re-precipitation of iron sulfide coatings during the freeze/thaw process appears to affect the geochemistry of the pore water through two main mechanisms of freeze-concentration and freezing potential.

Sulfate as a terminal electron acceptor in toluene oxidation in anaerobic conditions

In aerobic conditions, many of microorganisms cause decomposition of saturated hydrocarbons. Little publications are available relative to anaerobic transformation of these compounds, which provides substantial сapiltal saving for waste water treatment. At the same time, cultures found among aerobic decomposers of petroleum products are characterized by the ability to use elements with variable valence as terminal electron acceptors in oxidation of organic substances. Their ability to decompose aliphatic hydrocarbons helps to identify some of them.Purpose: studying the ability of a selected association of immobilized bacteria on a fibrous carrier to utilize sulfate as a terminal electron acceptor for toluene oxidation.Methodology/approach: Analytical summarizing of results, literature review, laboratory research based on standard and modern up-to-date methodologies with the use of modern analytical equipment.Findings: The availability of using microorganism selection is shown for expanding the range of polluting strippants in biological purification; the main directions are determined for the process intensification by immobilization of active sludge on a fibrous carrier. The ability of microorganisms to oxidize toluene under oxygen-free (anaerobic) conditions is studied in the laboratory conditions.Research implications: monoaromatic hydrocarbons, toluene, in particular, can be changed by selected associations of decomposers using terminal electron acceptors in oxidation of nitrates and sulfates.

The development of a fully integrated 3D printed electrochemical platform and its application to investigate the chemical reaction between carbon dioxide and hydrazine

The combination of computer assisted design and 3D printing has recently enabled fast and inexpensive manufacture of customized ‘reactionware’ for broad range of electrochemical applications. In this work bi-material fused deposition modeling 3D printing is utilized to construct an integrated platform based on a polyamide electrochemical cell and electrodes manufactured from a polylactic acid-carbon nanotube conductive composite. The cell contains separated compartments for the reference and counter electrode and enables reactants to be introduced and inspected under oxygen-free conditions. The developed platform was employed in a study investigating the electrochemical oxidation of aqueous hydrazine coupled to its bulk reaction with carbon dioxide. The analysis of cyclic voltammograms obtained in reaction mixtures with systematically varied composition confirmed that the reaction between hydrazine and carbon dioxide follows 1/1 stoichiometry and the corresponding equilibrium constant amounts to (2.8 ± 0.6) × 103. Experimental characteristics were verified by results of numerical simulations based on the finite-element-method.

Highly Sensitive Lactic Acid Biosensors Based on Photoresist Derived Carbon

In this study, a highly sensitive electrochemical capacitive lactic acid enzymatic sensor based on a carbon-microelectromechanical system (C-MEMS) is developed. The sensing platform of the biosensor, which is photoresist-derived carbon (PDC) microelectrode, was synthesized by pyrolysis of photo-patterned photoresist polymer in oxygen-free and high-temperature conditions. The surfaces of the microelectrodes were functionalized by the oxygen-plasma pretreatment technique to form –COOH functional groups. The lactate oxidase enzyme was immobilized on the carboxylic group covered surfaces of the microelectrodes. The sensor demonstrated the detection of lactic acid over a wide dynamic range of 0.1- $5000~\mu \text{M}$ with a low detection limit of $1.45~\mu \text{M}$ (S/N=3). The sensitivity found to be 33.48 mF.cm−2. (Log (M))−1. This mediator-free lactic acid sensor exhibited 80.07% accuracy in the presence of uric and ascorbic acid and only a 2.35% decrease of measured capacitance in 20 days, which implies good selectivity and high stability. The presented results show that the C-MEMS based lactic acid biosensor is a promising contender for the highly demanding point of care health monitoring applications.

Catalytic transformation of the marine polysaccharide ulvan into rare sugars, tartaric and succinic acids

The green macroalga Ulva rigida represents a promising feedstock for biorefinary due to its fast growth and cosmopolitan distribution. The main component of the cell walls of U. rigida is a sulfated glucuronorhamnan polysaccharide known as ulvan. Herein it was found that due to the high (hydrogen)sulfate group content of ulvan, hydrothermal autohydrolysis at 130 °C renders a high percentage of rhamnose (78–79 % recovery from the initial content in the raw material), a rare sugar of high added value. In addition, acid catalysis by a triflate-based graphene oxide under oxygen-free conditions at 180 °C affords moderate amounts of tartaric acid (24–26 %). The same triflate-based graphene oxide catalyst under oxygen pressure yields remarkably high percentages of succinic acid (65 %). The catalyst preserves its activity for at least five consecutive reuses.

Oxygen Gradients and Structure of the Ciliate Assemblages in Floodplain Lake

This paper presents the results of studies on the structure of the ciliate population in a freshwater lake. The classification of the ciliated communities based on the analysis of the distribution of ciliate population density in the lake along the oxygen gradients, taking into account their oxygen preferences, was proposed. It was shown that the distribution of ciliated protozoa in the space of a reservoir is determined not by such spatial units as the water column, bottom, and periphytal, but by the oxygen gradients. Four types of habitats with different oxygen regimes were distinguished: With stably high oxygen concentration, stably low oxygen concentration, stably oxygen-free conditions, and conditions with a high amplitude of diurnal oxygen variations. The location of these habitats in the space of the lake and their seasonal changes were determined. On the basis of the quantitative development of ciliate populations, zones of optima and tolerance ranges of some ciliate species in the oxygen gradient were established. The oxygen preferences were established for the species from four distinguished assemblages: Microoxyphilic, oxyphilic, euryoxyphilic, and anoxyphilic (anaerobic). The presence or the absence of a certain type of assemblage in the reservoirs depends solely on the parameters of the oxygen gradients. The diversity of the ciliated protozoa in water bodies also depends on the stability and diversity of the oxygen gradients.

Investigating the Effect of Processing Parameters on the Products of Hydrothermal Carbonization of Corn Stover

Corn stover is an abundant and underused source of lignocellulose waste biomass that can be transformed into a high-quality energy resource using hydrothermal carbonization (HTC). This investigation has focused on the effect of processing parameters on the products of HTC—namely solid fuel or hydrochar and liquid and gas fractions. HTC was conducted in a temperature-controlled small batch reactor with corn stover and deionized water under oxygen-free conditions obtained by pressurizing the reactor headspace with nitrogen gas. The properties of the hydrochar and liquid and gas fractions were evaluated as a function of the process temperature (250–350 °C), residence time (30–60 min) and biomass/water ratio (0.09–0.14). Central composite design modules in a response surface methodology were used to optimize processing parameters. The maximum mass yield, energy yield and high heating value (HHV) of the hydrochar produced were 29.91% dry weight (dw), 42.38% dw and 26.03 MJ/kg, respectively. Concentrations of acetic acid and hydrogen gas were 6.93 g/L and 0.25 v/v%, respectively. Experimental results after process optimization were in satisfactory agreement with the predicted HHV. The optimal HTC process parameters were determined to be 305 °C with a 60 min residence time and a biomass/water ratio of 0.114, yielding hydrochar with a HHV of 25.42 MJ/kg. The results confirm the feasibility of an alternative corn stover management system.

Understanding sulfur poisoning of bimetallic Pd-Pt methane oxidation catalysts and their regeneration

Pd-Pt/Al2O3 and Pd-Pt/CeO2-ZrO2-Y2O3-La2O3 methane oxidation catalysts were investigated under typical lean-burn gas engine conditions with respect to sulfur poisoning and during reactivation, particularly under the most efficient rich conditions. Sulfation of the noble metal and the support material led to pronounced catalyst deactivation. A pronounced transfer of sulfates to the support, particularly alumina, only partially protects the noble metal. In situ X-ray absorption spectroscopy gave insight into the nature and evolution of Pd species during regenerative treatment. Although palladium sulfate that formed during poisoning is decomposed at approximately 200 °C in oxygen-free conditions, support regeneration requires higher temperatures, which result in PdS formation above 400 °C. Despite its high stability under rich conditions, PdS decomposition by oxidation in lean atmosphere leads to the recovery of the activity. In addition, water vapor that is present during the rich regeneration exhibited a beneficial effect on the regeneration with higher catalytic activity after regeneration.

Oxygen-generating smart hydrogels supporting chondrocytes survival in oxygen-free environments

Cartilage is one of our body’s tissues which are not repaired automatically by itself. Problems associated with cartilage are very common worldwide and are considered the leading cause of pain and disability. Smart biomaterial or “Four dimensional” (4D) biomaterials has started emerging as a suitable candidate, which are principally three dimensional (3D) materials that change their morphology or generate a response measured at space and time to physiologic stimuli. In this context, the release of oxygen through hydrogels in contact with water is considered as 4D biomaterials. The objective of this study is to develop strategies to release oxygen in a sustainable and prolonged manner through hydrogels systems to promote chondrocytes survival in oxygen-free environment. The 4D biomaterials are engineered from gelatin methacryloyl (GelMA) loaded with calcium peroxide (CPO), which have the ability to generate oxygen in a controlled and sustained manner for up to 6 days. The incorporation of CPO into the hydrogel system provided materials with enhanced mechanical and porosity properties. Furthermore, the hydrogels promoted chondrocyte survival and reduced cell death under oxygen-free conditions.

Stability and Behavior in Carbonate Cores for New Enhanced-Oil-Recovery Polymers at Elevated Temperatures in Hard Saline Brines

SummaryThe goal of this work was to identify viable polymers for use in the polymer flooding of high-temperature carbonate reservoirs with hard, saline brines. This study extensively examined recent enhanced-oil-recovery (EOR) polymers for stability, including new 2-acrylamido-tertbutylsulfonic acid (ATBS) polymers with a high degree of polymerization, scleroglucan, n-vinylpyrrolidone (NVP)-based polymers, and hydrophobic associative polymers. For each polymer, stability experiments were performed over a 2-year period under oxygen-free conditions (less than 1 ppb) at various temperatures up to 180°C in brines with total dissolved solids (TDS) ranging from 0.69 to 24.4%, including divalent cations from 0.034 to 2.16%. Use of the Arrhenius analysis was a novel feature of this work. This rarely used method allows a relatively rapid assessment of the long-term stability of EOR polymers. Rather than wait years or decades for results from conventional stability studies at the reservoir temperature, reliable estimates of the time-temperature stability relations were obtained within 2 years. Arrhenius analysis was used to project polymer-viscosity half-lives at the target reservoir temperature of 99°C. The analysis suggests that a set of ATBS polymers will exhibit a viscosity half-life over 5 years at 120°C and over 50 years at 99°C, representing a novel finding of this work and a major advance for extending polymer flooding to higher temperatures.For five polymers that showed potential for application at higher temperatures, corefloods were performed under anaerobic conditions. Another novel feature of this work was that anaerobic floods were performed without using chemical oxygen scavengers, chemical stabilizing packages, or chelating agents (that are feared to alter rock properties). Using carbonate cores and representative conditions, corefloods were performed to evaluate polymer retention, rheology in porous media, susceptibility to mechanical degradation, and the residual resistance factor for each of the polymers at 99°C.

Simultaneous desulfurization and denitrification by electrodialysis

In recent years, simultaneous desulfurization and denitrification technology has gradually become a research hotspot at home and abroad. The purpose of this paper is to study simultaneous desulfurization and denitrification of electrodialysis/Fe(II) system. In order to study the electrochemical effect on simultaneous desulfurization and denitrification by electrodialysis, simultaneous purification experiments on SO2, NO2 and NO were carried out under the conditions of electrification and non-electrification respectively. The purification effects of electrodialysis/Fe(II) system on SO2, NO2 and NO were investigated. The results show that the simultaneous purification of SO2 and NOx is inhibited by each other when no power is applied, mainly because of the competition between Fe (II) and O2. The synergistic effect between SO2 and NOx occurs after charging. The desulfurization product SO32− is reduced to S and S2− in the cathode. The system enhances the purification effect of SO2 and NOx through the oxidation-reduction cycle of S2− in the cathode. After that, the effects of oxygen content, current and Fe (II) content on desulfurization and denitrification efficiency were further investigated. The effect of current on SO2 purification rate was first increased and then decreased, while the purification rate of NOx increased with the increase of current; The removal efficiency of SO2 and NOx is better under oxygen-free and hypoxia conditions; The effect of Fe(II) content on SO2 purification rate was not significant, but on NOx purification was significant. The purification rate of NOx increased significantly after adding 0.1 mol/L Fe(II) into the system, but decreased continuously afterwards with the increase of Fe(II) content. Finally, the reaction mechanism of simultaneous desulfurization and denitrification was analyzed, and the transformation process of sulfur and nitrate in the system was discussed.

Acridine radical acts as photoreductant

Reduction, the process of pushing electrons into molecules, is an important transformation for chemical synthesis. But it often requires harsh reagents, like alkali metals, or transformations that can be difficult to scale up, such as reactions that require dissolving metals. Chemists led by the University of North Carolina at Chapel Hill’s David A. Nicewicz have now identified a gentler reagent—an acridine radical (shown), catalytically generated in situ—that can do many of the same reactions when used with ultraviolet light. Nicewicz’s team discovered the photoreductant while working with acridinium salts as photooxidation catalysts. During that work, they found that the acridine radical was indefinitely stable under oxygen-free conditions and had a reduction potential on par with that of elemental lithium. This, the chemists note, makes the acridine radical “one of the most potent chemical reductants reported” (Nature 2020, DOI: 10.1038/s41586-020-2131-1). Nicewicz and colleagues used the acridine radical to reduce N-tosyl species,

Effect of Electron Acceptor on Hydrocarbon Pollution Degradation Rate Caused by Bacteria of the Genus Rhodococcus under Anaerobic Conditions

The effect of the concentration of an oxygen acceptor in the form of a nitrate-containing salt on the rate and mechanism of hydrocarbon degradation (HC) in actual soil samples extracted from wells of 1 to 5 m in depth from areas allocated for future urban development under the influence of bacterial strains belonging to the genus Rhodococcus (R. ruber Ac-1513 D and R. erythropolis Ac-1514 D) is studied. Initial soil samples containing up to 9.8% HC were capable of producing biogas for 59 years under anaerobic conditions, in the absence of an oxygen acceptor, under the influence of methane-forming indigenous microorganisms. At the same time, the content of fire-dangerous methane in gas products ranged from 8 to 36%, which makes housing development in such areas unacceptable without preliminary treatment. To accelerate hydrocarbon degradation by oil-oxidizing bacteria under non-specific oxygen-free conditions, it was proposed to use an electron acceptor, calcium nitrate. The mechanism of hydrocarbon degradation in the presence of Ca(NO3)2 through denitrification has been established. It is shown that effect of calcium nitrate studied in the presence of three concentrations (1.25, 2.5, and 5.0%) on denitrification and anaerobic HC degradation was reversely proportional, which may be associated with the inhibition of the denitrification process by high concentrations of Ca(NO3)2. In the presence of a minimum concentration of calcium nitrate (1.25%), maximum rates of anaerobic HC degradation in the soil are of k = 1.27 and 0.32 year–1 during warm and cold seasons, respectively. The content of the main non-flammable reaction product, carbon dioxide in the gas mixture was 99% by volume. Thus, the complete decomposition of the hydrocarbon and the gas generation phase may be completed within 1 year, which is 59 times faster than processes occurring in the absence of an oxygen acceptor.

Polystyrene and Poly(ethylene glycol)-b-Poly(ε-caprolactone) Nanoparticles with Porphyrins: Structure, Size, and Photooxidation Properties.

The transport of a photosensitizer to target biological structures followed by the release of singlet oxygen is a critical step in photodynamic therapy. We compared the (photo)physical properties of polystyrene nanoparticles (TPP@PS) of different sizes and self-assembled poly(ethylene glycol)-b-poly(ε-caprolactone) core/shell nanoparticles (TPP@PEG-PCL) with different lengths of copolymer blocks, both suitable for the transport of the tetraphenylporphyrin (TPP) photosensitizer. The singlet oxygen was formed inside both nanoparticles after irradiation with visible light. Its kinetics was controlled by the size of TPP@PS; its lifetime (τΔ) increased with increasing nanoparticle size (from 6.5 to 16 μs) because of hindered diffusion into the external aqueous environment, where it was quickly deactivated. Accordingly, the prolongation of the singlet oxygen-sensitized delayed fluorescence kinetics was found for TPP@PS of high size. The TPP@PEG-PCL self-assemblies allowed for enhanced oxygen diffusion, and the estimated low values of τΔ ≈ 3.7 μs were independent of the size of building blocks. The delayed fluorescence in oxygen-free conditions originating from triplet-triplet annihilation indicated a high mobility of TPP in the PCL core in comparison with fixed molecules in the PS matrix. Photooxidation of uric acid revealed the highest efficacy for TPP@PS of small sizes, whereas the largest TPP@PS exhibited the lowest activity, and the efficacy of TPP@PEG-PCL remained independent of the sizes of the building blocks.

Low concentration of Fe(II) to enhance the precipitation of U(VI) under neutral oxygen-rich conditions

Immobilization of U(VI) by naturally ubiquitous ferrous ions (Fe(II)) has been considered as an efficient and ecofriendly method to retard the migration of aqueous U(VI) at many nuclear sites and surface environments. In this study, we conducted Fe-U coprecipitation experiments to investigate the mechanism and stability of uranium (U) precipitation induced by a small quantity of Fe(II) under oxygen-rich conditions. The experimental results suggest that the sedimentation rates of U(VI) by Fe(II) under neutral oxygen-rich conditions are more than 96%, which are about 36% higher than those without Fe(II) and 16% higher than those under oxygen-free conditions. The Fe-U coprecipitates were observed to remain stable under slightly acidic to neutral and oxygen-rich conditions. Fe(II) primarily settles down as low-crystalline iron oxide hydroxide. U(VI) mainly precipitates as three forms: 16–20% of U forms uranyl hydroxide and metaschoepite, which is absorbed on the surface of the solids; 52–56% of U is absorbed as discrete uranyl phases at the internal pores of iron oxide hydroxide; and 27–29% of U is probably incorporated into the FeO(OH) structure as U(V) and U(VI). The U(V) generated via one-electron reduction is somewhat resistant to the oxidation of O2 and the acid dissolution. In addition, nearly 70% of U and only about 15% of Fe could be extracted in 24 h by a hydrochloric acid solution with the H+ concentration ([H+]) of 0.01 M, revealing that U(VI) immobilization by low concentration of Fe(II) combined with O2 has potential applications in the separation and recycling of aqueous uranium.

Exploring the Phototoxicity of Hypoxic Active Iridium(III)-Based Sensitizers in 3D Tumor Spheroids.

Among all molecules developed for anticancer therapies, photodynamic therapeutic agents have a unique profile. Their maximal activity is specifically triggered in tumors by light, and toxicity of even systemically delivered drug is prevented in nonilluminated parts of the body. Photosensitizers exert their therapeutic effect by producing reactive oxygen species via a light-activated reaction with molecular oxygen. Consequently, the lowering of pO2 deep in solid tumors limits their treatment and makes essential the design of oxygen-independent sensitizers. In this perspective, we have recently developed Ir(III)-based molecules able to oxidize biomolecules by type I processes under oxygen-free conditions. We examine here their phototoxicity in relevant biological models. We show that drugs, which are mitochondria-accumulated, induce upon light irradiation a dramatic decrease of the cell viability, even under low oxygen conditions. Finally, assays on 3D tumor spheroids highlight the importance of the light-activation step and the oxygen consumption rate on the drug activity.