O2 Atmosphere Research Articles

ReaxFF molecular dynamics study of co-combustion of waste tires with petroleum coke gasification residue: Combustion characteristics, gas evolution and micro mechanism

Solid wastes such as waste tires (WT) and petroleum coke gasification residue (PCGR) could be used as fuels to realize the recovery of resources. The detailed composition of WT and PCGR was determined in this study through the proximate and ultimate analyses, FTIR, XPS, and 13C NMR characterization. Based on experimental characterization results, molecular models of WT (C557H802O16S4N3) and PCGR (C156H61O5S3N) were constructed. Then, the co-combustion characteristics of WT and PCGR were in-depth investigated via the reactive force field molecular dynamics (ReaxFF MD) simulations. The migration pathways of N/S during combustion in both O2 and O2/N2 atmospheres were also elucidated. Meanwhile, the evolution of specific products with oxygen concentration and temperature was investigated. The results indicated the oxidation process began with thermal decomposition to form small fragments, which were next attacked by O radicals to generate inorganics. Additionally, the blending combustion was promoted as the molar fraction of the WT increased. The PCGR decomposed and burnt faster in fuel-lean conditions. Besides, higher temperature could accelerate the combustion process. The pyrrole/pyridine was converted to HCN and NHx in the first step and then oxidized to NOx. The production of NOx was significantly higher in the O2/N2 atmosphere than that in the O2 atmosphere. The main product was NO, with a small amount of NO2. The conversion of thiol to HS and thiophene S to COS was also observed. The COS easily reacted with H atoms to form HxS. In O2/N2 environment, CNS and elemental sulfur were formed due to the N-rich atmosphere.

Influence of oxygen partial pressure on the strain behaviour of reactively co-sputtered Ga doped ZnO thin films

Gallium doped ZnO films (GZO) were deposited by reactive co-sputtering of Zn and GaAs at different partial pressures of oxygen in Ar-O2 mixture. The GZO films were deposited at 375 °C, with GaAs area coverage of 0 - 3 % and 4 - 10 % O2 in sputtering atmosphere. The composition of GZO films was studied by X-ray photoelectron spectroscopy, which showed that the films deposited at 4 % and 5 % O2 display Ga/Zn ratio of ∼ 0.1 and contain oxygen vacancies, while those deposited at 6 % and 7 % O2 display Ga/Zn ratio of ∼ 0.01 and contain chemisorbed/interstitial oxygen. X-ray diffraction measurements supported by Raman studies revealed that undoped ZnO films are strongly c-axis oriented and display decrease of crystallite size along c-axis, along with substantial increase of hydrostatic tensile strain with increase of O2 percentage, which are attributed to the presence of interstitial oxygen. In sharp contrast, GZO films deposited at 4 % and 5 % O2 under limited oxygen availability, display smaller and mis-oriented crystallites along c-axis and large compressive strain, which is also hydrostatic, owing to the incorporation of Ga. The GZO films deposited at 6 % and 7 % O2 display improved crystallinity and decrease of compressive strain, which are attributed to reduced Ga content of the films and sufficient availability of oxygen during deposition. This study reveals the critical influence of the partial pressure of oxygen on the stoichiometry, doping concentration, crystallinity and the nature of strain in reactively sputtered GZO films.

Bismuth-Decorated Beta Zeolites Catalysts for Highly Selective Catalytic Oxidation of Cellulose to Biomass-Derived Glycolic Acid

Catalytic conversion of cellulose to liquid fuel and highly valuable platform chemicals remains a critical and challenging process. Here, bismuth-decorated β zeolite catalysts (Bi/β) were exploited for highly efficient hydrolysis and selective oxidation of cellulose to biomass-derived glycolic acid in an O2 atmosphere, which exhibited an exceptionally catalytic activity and high selectivity as well as excellent reusability. It was interestingly found that as high as 75.6% yield of glycolic acid over 2.3 wt% Bi/β was achieved from cellulose at 180 °C for 16 h, which was superior to previously reported catalysts. Experimental results combined with characterization revealed that the synergetic effect between oxidation active sites from Bi species and surface acidity on H-β together with appropriate total surface acidity significantly facilitated the chemoselectivity towards the production of glycolic acid in the direct, one-pot conversion of cellulose. This study will shed light on rationally designing Bi-based heterogeneous catalysts for sustainably generating glycolic acid from renewable biomass resources in the future.

Equilibrium Fractionation of Oxygen Isotopes in the U3O8-Atmospheric Oxygen System.

As a major component in the nuclear fuel cycle, octoxide uranium is subjected to intensive nuclear forensics research. Scientific efforts have been mainly dedicated to determine signatures, allowing for clear and distinct attribution. The oxygen isotopic composition of octoxide uranium, acquired during the fabrication process of the nuclear fuel, might serve as a signature. Hence, understanding the factors governing the final oxygen isotopic composition and the chemical systems in which U3O8 was produced may develop a new fingerprint concerning the history of the material and/or the process to which it was subjected. This research determines the fractionation of oxygen isotopes at different temperatures relevant to the nuclear fuel cycle in the system of U3O8 and atmospheric O2. We avoid the retrograde isotope effect at the cooling stage at the end of the fabrication process of U3O8. The system attains the isotope equilibrium at temperatures higher than 300 °C. The average δ18O values of U3O8 in equilibrium with atmospheric oxygen have been found to span over a wide range, from -9.90‰ at 300 °C up to 18.40‰ at 800 °C. The temperature dependency of the equilibrium fractionation (1000 ln αU3O8-atm.O2 ) exhibits two distinct regions, around -33‰ between 300 °C and -500 °C and -5‰ between 700 °C and -800 °C. The sharp change coincides with the transition from a pseudo-hexagonal structure to a hexagonal structure. A depletion trend in δ18O is associated with the orthorhombic structure and may result from the uranium mass effect, which might also play a role in the depletion of 5‰ versus atmospheric oxygen at high temperatures.

Ultra-Stable and Highly Efficient White Light Emitting Diodes through CsPbBr3 Perovskite Nanocrystals-Silica Composite Phosphor Functionalized with Surface Phenyl Molecules.

Poor stability of CsPbBr3 perovskite nanocrystals (NCs) to moisture/heat/light has significantly limited their application as a green phosphor, despite their outstanding luminescent properties. Here, a remarkably stable CsPbBr3 NCs-silica composite phosphor functionalized with surface phenyl molecules (CsPbBr3 -SiO2 Ph ) is synthesized by controlling low-temperature hydrolysis and condensation reaction of perhydropolysilazane in the presence of CsPbBr3 NCs followed by phenyl-functionalization. Through the process, CsPbBr3 NCs are confined in a compact silica matrix, which is impermeable to H2 O. The synthesis strategy is extended to a classical red quantum dot, CdZnSeS@ZnS NCs, to fabricate a white light emitting diode (WLED) consisting of CsPbBr3 -SiO2 Ph and CdZnSeS@ZnS-SiO2 Ph phosphor and silicone resin packaged on a commercial blue InGaN chip with luminous efficacy (LE) of 9.36 lm W-1 . The WLED undergoes enhancements in both green and red photoluminescence over time to achieve a highly efficient performance of 38.80 lm W-1 . More importantly, the WLED exhibits unprecedented operational stability of LE/LE0 = 94% after 101h-operation at 20mA (2.56V). The ultra-high operational stability and efficient performance are mainly attributed to thermal curing and aging through which grain growth occurs as well as deactivation of defect states by permeated atmospheric O2 .

Electrical energy storage properties of AgNbO3-based antiferroelectric ceramics prepared without an oxygen atmosphere by using hydrothermally synthesized powders

AgNbO3 based ceramics are commonly sintered with an O2 atmosphere. In this work, after synthesizing AgNbO3, Na-doped AgNbO3, and Ta-doped AgNbO3 powders by a hydrothermal method, the ceramics were sintered in the air atmosphere by using the synthesized powders. The novel process with the absence of an O2 atmosphere is practical and facile. The structural, dielectric, antiferroelectric, and electrical energy storage properties of fabricated ceramics were studied. Na doping has a weak influence on the structure but can significantly improve the electrical breakdown field. Ta doping induces a pure antiferroelectric phase and the electrical energy storage efficiency is improved greatly.

Towards bio-safe and easily redispersible bare ZnO quantum dots engineered via organometallic wet-chemical processing

Colloidal quantum dots (QDs) are of widespread importance for their unique combination of physicochemical properties and a number of prospective applications, and the search for efficient synthetic methods to produce readily dispersible, functionally stable and ligand-free quantum dot-based inks is a vital and timely area of research. We describe a convenient room-temperature and non-external-surfactant-assisted organometallic synthetic strategy for the reproducible preparation of solution-processable organic ligand-free zinc oxide (ZnO) QDs. The process involves the controlled transformation of a DMSO solution of commercially available diethylzinc upon exposition towards atmospheric air, where H2O and O2 act simultaneously as oxygen sources, and DMSO acts both as a solvent and a low-molecular-weight l-type surface protector. The resulting QDs with a narrow size distribution (4.7 ± 0.8 nm) were comprehensively characterized with a combination of various analytical techniques, which nicely documented their unique stabilities when dried, precipitated, re-dissolved or exposed to air. Moreover, to substantiate idealized surface passivation of the resulting QDs, we investigated their stability in the biological environment and nano-specific activity toward selected normal and cancer cell lines, and no significant toxic effect was revealed. Undoubtedly, the reported one-step-one-pot organometallic approach paves the way to high-quality and bio-stable ZnO QDs coated by an easily and reversibly removable organic shell, auguring applications in a vast array of devices and nanomedicine.

Alkali-induced metal-based coconut shell biochar for efficient catalytic removal of H2S at a medium–high temperature in blast furnace gas with significantly enhanced S selectivity

The low S selectivity of catalysts for H2S removal significantly hinders its application in blast furnace gas desulfurization. In this study, Cu-based coconut shell biochar was modified with different types and contents of alkali species. The results showed that the S selectivity close to 100% was prolonged from 0 to 750 min. At the same time, the sulfur capacity was increased from 242.1 mg/g (before the modification) to 373.4 mg/g by using K2CO3-induced Cu-based biochar at 120 °C. In CO, H2O, and O2 atmosphere, H2S was dissociated and oxidized to elemental S. Additionally, K2CO3 exhibited an elemental S anchoring effect, making the S more stable at medium–high temperatures and weakening the reactivity of S with CO and ·O2–. Thus, less COS and SO2 were generated. Moreover, the basic sites enhanced by K2CO3 promoted the hydrolysis of COS to generate H2S, which entered the desulfurization cycle. K2CO3 also showed a synergistic effect with the active components, generating more ·O2– to promote the oxygenation of H2S. The regeneration efficiency of the catalyst could be stabilized above 90%. These findings could provide guidance and reference for designing and applying desulfurization catalysts with high S selectivity and activity.

Comparative investigation on combustion characteristics of ADN-based liquid propellants in inert gas and oxidizing gas atmospheres with resistive ignition method

An experimental investigation was performed to study combustion characteristics of ADN based liquid propellant droplet with resistive ignition method. The experiment was conducted in Ar atmosphere and different oxidizing gas atmospheres under an on-load voltage range of 190–230 V; the oxidizing gases included N2O, NO and O2. The influence of the atmosphere, on-load voltage, droplet volume on the ignition energy, ignition delay time, burning duration, and droplet equivalent diameter development during ignition and combustion was studied. ADN based liquid propellant showed feasibility to combustion by the resistive ignition method in the inert gas atmosphere. The ignition energy accounted for more than 80 % of the total energy during the ignition and combustion process. With the increase of the droplet volume, the value of the ignition delay time and burning duration increased. The atmosphere had a significant influence on the burning duration and droplet diameter, but had little influence on the ignition delay time. Under our experiment conditions, the N2O and O2 atmospheres improved the combustion process, while, the NO atmosphere inhibited the oxidation of methanol.

Synthesis, processing and metal ion detection capability of a fluorescent polymer based on pyrene group

A pyrene-containing polyimide (p-PI) was synthesized from a diamine monomer and 4,4′-(Hexafluoroisopropylidene)diphthalic anhydride via one step polycondensation procedure. The polymer possessed good solubility due to the large rigid non-planar conjugated side groups. Therefore, the fluorescence test paper could be produced by a convenient method. The "turn-on" fluorescent response of the test paper to Fe3+ and Pb2+ was observed. In addition, this polymer possessed excellent thermal and thermooxidative stability. The onset decomposition temperatures (Td) of p-PI in O2 and N2 atmosphere were 431 and 442°C, respectively. There was a good linear relationship (R2 = 0.9943) of the p-PI film between fluorescence intensity and temperature from 298 to 408K. This polymer could be considered as fluorescence chemosensor for detecting metal ions and a temperature sensor for monitoring environment in the future.

Photonic Microfluidic Technologies for Phytoplankton Research.

Phytoplankton is a crucial component for the correct functioning of different ecosystems, climate regulation and carbon reduction. Being at least a quarter of the biomass of the world's vegetation, they produce approximately 50% of atmospheric O2 and remove nearly a third of the anthropogenic carbon released into the atmosphere through photosynthesis. In addition, they support directly or indirectly all the animals of the ocean and freshwater ecosystems, being the base of the food web. The importance of their measurement and identification has increased in the last years, becoming an essential consideration for marine management. The gold standard process used to identify and quantify phytoplankton is manual sample collection and microscopy-based identification, which is a tedious and time-consuming task and requires highly trained professionals. Microfluidic Lab-on-a-Chip technology represents a potential technical solution for environmental monitoring, for example, in situ quantifying toxic phytoplankton. Its main advantages are miniaturisation, portability, reduced reagent/sample consumption and cost reduction. In particular, photonic microfluidic chips that rely on optical sensing have emerged as powerful tools that can be used to identify and analyse phytoplankton with high specificity, sensitivity and throughput. In this review, we focus on recent advances in photonic microfluidic technologies for phytoplankton research. Different optical properties of phytoplankton, fabrication and sensing technologies will be reviewed. To conclude, current challenges and possible future directions will be discussed.

Cathodoluminescent Imaging of ZnO:N Films: Study of Annealing Processes Leading to Enhanced Acceptor Luminescence

A worldwide effort is under way to understand the activation of acceptor states in ZnO with the motivation to achieve persistent p‐type conductivity. In this study, cathodoluminescent (CL) imaging, electron microscopy (SEM), secondary‐ions mass spectrometry (SIMS), and X‐ray diffraction (XRD) are used to compare ZnO:N films subjected to a rapid thermal annealing process (RTP) in N2 and O2 atmosphere at 400–900 °C. The study, performed for ZnO:N films with nitrogen concentration of 2 × 1018 at cm−3 grown under O‐rich conditions is directed to establish the optimal atmosphere and temperature at which acceptor‐related CL is enhanced and correlated with structural properties. XRD shows that crystallite size increases from ≈100 to ≈250 nm with increasing annealing temperature up to 800 °C. The low‐temperature (LT) CL maps reveal that the acceptor‐ and donor‐related CL mostly derives from different crystallites. Both annealing medium and temperature influence acceptor‐related CL intensity, which is higher under oxygen annealing. It is observed that the intensity of acceptor‐related CL increases with annealing temperature up to 800 °C and then decreases. Noticeable donor‐related emission appears only after RTP at 700 °C and becomes prominent for RTP at 900 °C

Serial Gene Expression Profiling of Neural Stem Cells Shows Transcriptome Switch by Long-Term Physioxia from Metabolic Adaption to Cell Signaling Profile.

Oxygen is an essential factor in the cellular microenvironment with pivotal effects on neural development with a particular sensitivity of midbrain neural stem cells (NSCs) to high atmospheric oxygen tension. However, most experiments are still performed at atmospheric O2 levels (21%, normoxia), whereas mammalian brain tissue is physiologically exposed to substantially lower O2 tensions around 3% (physioxia). We here performed serial Affymetrix gene array analyses to detect expression changes in mouse fetal NSCs from both midbrain and cortical tissues when kept at physioxia compared to normoxia. We identified more than 400 O2-regulated genes involved in cellular metabolism, cell proliferation/differentiation, and various signaling pathways. NSCs from both regions showed a low number but high conformity of regulated genes (9 genes in midbrain vs. 34 in cortical NSCs; 8 concordant expression changes) after short-term physioxia (2 days) with metabolic processes and cellular processes being the most prominent GO categories pointing to cellular adaption to lower oxygen levels. Gene expression profiles changed dramatically after long-term physioxia (13 days) with a higher number of regulated genes and more diverse expression patterns when comparing the two NSC types (338 genes in midbrain vs. 121 in cortical NSCs; 75 concordant changes). Most prominently, we observed a reduction of hits in metabolic processes but an increase in biological regulation and signaling pointing to a switch towards signaling processes and stem cell maintenance. Our data may serve as a basis for identifying potential signaling pathways that maintain stem cell characteristics in cortical versus midbrain physioxic stem cell niches.

Spatial pattern of orbital-to millennial-scale East Asian stalagmite δ18O variations during MIS 3

The Asian hydroclimate variability during the early and middle Marine Isotope Stage (MIS) 3 was reconstructed from a high-resolution stalagmite δ18O record from Qixing Cave in southern China, which exhibited an extraordinarily strong precessional cycle. When compared with other cave records (mostly) from East Asia, covering a latitudinal transect from 23° to 38°N, it can be found that the magnitude of precessional-scale stalagmite δ18O variations decreases when the latitude increases, approximately from 3‰ to 1‰. In contrast, the amplitude of Heinrich stadials (HSs) in these stalagmite δ18O records enhances with increasing latitudes, from 1‰ to 2‰, reflecting an alleviated effect of high-latitude climate changes on the low-latitude hydroclimate, or a relative contribution from Westerlies-borne and near-sourced 18O-enriched moisture at northern China. In southern China, orbital-scale changes in stalagmite δ18O closely match variations of the atmospheric CH4 concentration and δ18O of the atmospheric O2, suggesting a coherent response of low-latitude ecological and hydrological processes. In addition, a weaker precessional cycle in northern China is possibly related to the relative supply of near-sourced moisture source, where the Westerly wind can exert a substantial role. Therefore, precessional to millennial-scale changes in East Asian stalagmite δ18O records could be further modulated by local processes, rendering them a spatially contrasting trait. A pervasive imprint of muted precessional rainfall changes in loess records from northern China suggests a regionally distinct rhythm of moisture availability, in agreement with the stalagmite records from higher latitudes.

Use of δ18Oatm in dating a Tibetan ice core record of Holocene/Late Glacial climate

Ice cores from the northwestern Tibetan Plateau (NWTP) contain long records of regional climate variability, but refrozen meltwater and dust in these cores has hampered development of robust timescales. Here, we introduce an approach to dating the ice via the isotopic composition of atmospheric O2 in air bubbles (δ18Oatm), along with annual layer counting and radiocarbon dating. We provide a robust chronology for water isotope records (δ18Oice and d-excess) from three ice cores from the Guliya ice cap in the NWTP. The measurement of δ18Oatm, although common in polar ice core timescales, has rarely been used on ice cores from low-latitude, high-altitude glaciers due to (1) low air pressure, (2) the common presence of refrozen melt that adds dissolved gases and reduces the amount of air available for analysis, and (3) the respiratory consumption of molecular oxygen (O2) by micro-organisms in the ice, which fractionates the δ18O of O2 from the atmospheric value. Here, we make corrections for melt and respiration to address these complications. The resulting records of water isotopes from the Guliya ice cores reveal climatic variations over the last 15,000 y, the timings of which correspond to those observed in independently dated lake and speleothem records and confirm that the Guliya ice cap existed before the Holocene. The millennial-scale drivers of δ18Oice are complex and temporally variable; however, Guliya δ18Oice values since the mid-20th century are the highest since the beginning of the Holocene and have increased with regional air temperature.

Modified Poly(Heptazine Imides): Minimizing H2O2 Decomposition to Maximize Oxygen Reduction.

Photocatalysis provides a sustainable pathway to produce the consumer chemical H2O2 from atmospheric O2 via an oxygen reduction reaction (ORR). Such an alternative is attractive to replace the cumbersome traditional anthraquinone method for H2O2 synthesis on a large scale. Carbon nitrides have shown very interesting results as heterogeneous photocatalysts in ORR because their covalent two-dimensional (2D) structure is believed to increase selectivity toward the two-electron process. However, an efficient and scalable application of carbon nitrides for this reaction is far from being achieved. Poly(heptazine imides) (PHIs) are a more powerful subgroup of carbon nitrides whose structure provides high crystallinity and a scaffold to host transition-metal single atoms. Herein, we show that PHIs functionalized with sodium and the recently reported fully protonated PHI exhibit high activity in two-electron ORR under visible light. The latter converted O2 to up to 1556 mmol L-1 h-1 g-1 H2O2 under 410 nm irradiation using inexpensive but otherwise chemically demanding glycerin as a sacrificial electron donor. We also prove that functionalization with transition metals is not beneficial for H2O2 synthesis, as the metal also catalyzes its decomposition. Transient photoluminescence spectroscopy suggests that H-PHIs exhibit higher activity due to their longer excited-state lifetime. Overall, this work highlights the high photocatalytic activity of the rarely examined fully protonated PHI and represents a step forward in the application of inexpensive covalent materials for photocatalytic H2O2 synthesis.

Promoted Activity of Surface Hydroxyls on γ-Al2O3 Mineral Dust with the Coexistence of SO2 and NH3.

Sulfate and ammonium formed on mineral dust can be mutually accelerated through the heterogeneous reactions of coexisting SO2 and NH3. However, little is known about the underlying mechanism, especially the pivotal reactive sites. Using combined Born-Oppenheimer molecular dynamics simulations and density functional theory calculations, the results show that, compared to that of SO2 or NH3 alone on the γ-Al2O3 surface, the increased level of formation of sulfate and ammonium can be attributed to the promoted activity of the surface-bridged hydroxyl with the coexistence of SO2 and NH3. In the specific mechanism, the O and H of the surface-bridged hydroxyl group are attacked by the adjacent SO2 and NH3, respectively, which directly enhances the formation of absorbed sulfite and ammonium, and indirectly facilitates the production of sulfate by oxidation of atmospheric O2. The proposed mechanisms can be broadly applied to other aluminum-based suspended dust particles, such as kaolinite, montmorillonite, and clay dust.

δ18O of O2 in a Tibetan Ice Core Constrains Its Chronology to the Holocene

AbstractDating of the Tibetan ice cores is often challenging with great uncertainties. The significant age difference between the Guliya ice core (∼760 ka [thousand years]) and other Tibetan ice cores (Holocene origin) necessitates new approaches to resolve the inconsistency. Here, we present the atmospheric O2 δ18O (δ18Oatm) profile of the 216.6 m Chongce ice core. Our data suggest that post depositional alterations significantly changed δ18Oatm. We reject samples with melt layers, and reconstruct the δ18Oatm values with two extreme correction approaches: a minimum isotopic correction based on gas loss fractionation, and a maximum isotopic correction based on respiration fractionation. We consequently estimate the age range of the Chongce ice core to be 2.763–7.192 ka at the depth of 215.14 m, and ∼3–9.799 ka at the depth of 215.61 m. Our work provides an independent line of evidence for the Holocene origin of the Chongce ice core.

Glycerol Valorization Towards Glycolic Acid Production Over Cu-Based Biochar Catalyst.

Glycerol valorization towards high-value chemicals is of particular importance to increase the value chain of biodiesel production. In this study, the catalytic activity of a series of cheap Cu-based catalysts for glycerol conversion is investigated. Cu supported on activated carbon (AC, obtained through carbonization of coconut shell) exhibits outstanding catalytic activity for the selective conversion of glycerol into glycolic acid (GcA) in O2 atmosphere, affording up to 68.3 % GcA yield. The combination of experimental results with theoretical calculations reveals that glyceraldehyde is the key reaction intermediate. The high specific surface area and surface oxygenated groups of AC enable the formation of CuO nanoparticles with small size and uniform dispersion. In addition, the surface oxygen vacancy on Cu/AC might help to activate reaction intermediates, and the electron transfer from Cu to AC facilitates the oxidation of glycerol to GcA. Cu loaded onto AC also significantly inhibits C-C breakage to generate formic acid as a byproduct. This work might aid the development of approaches for glycerol application and afford profitable possibilities for sustainable biodiesel.

A Double‐Edged Sword: The Role of Sulfate in Anoxic Marine Phosphorus Cycling Through Earth History

AbstractModern anoxic marine sediments release phosphorus (P) to seawater, driving feedbacks at multiple timescales. On sub‐Myr timescales, anoxic P regeneration amplifies ocean deoxygenation; on multi‐Myr timescales, it stabilizes atmospheric O2. Some authors have extended this thinking to the Precambrian: by analogy, widespread ocean anoxia would imply extensive P regeneration from sediments. However, this neglects the role of sulfate in P regeneration. While abundant in seawater today, sulfate was scarce in the Precambrian. Here a simple model is used to isolate the role of sulfate in anoxic P cycling. The model reproduces known feedbacks driven by anoxic P regeneration in a high‐sulfate world, but shows muted P regeneration in low‐sulfate, anoxic sediments. The transition between “limited” and “enhanced” P regeneration is thus controlled by sulfate. As a result, sulfate is a double‐edged sword wielded by the anoxic P cycle: it can amplify oxygenation or deoxygenation depending on environmental context.