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Transition metal oxides are widely pursued as potent electrocatalysts for the oxygen evolution reaction (OER). However, single-metal chromium catalysts remain underexplored due to their intrinsic activity limitations. Herein, we successfully synthesize mixed-valence, nitrogen-doped Cr2O3/CrO3/CrN@NC nanoelectrocatalysts via one-step targeted pyrolysis techniques from a binuclear Cr-based complex (Cr2(Salophen)2(CH3OH)2), which is strategically designed as a precursor. Comprehensive pyrolysis mechanisms were thoroughly delineated by using coupled thermogravimetric analysis and mass spectrometry (TG-MS) alongside X-ray diffraction. Below 800 °C, the generation of a reducing atmosphere was noted, while continuous pyrolysis at temperatures exceeding 800 °C promoted highly oxidized CrO3 species with an elevated +6 oxidation state. The optimized catalyst pyrolyzed at 1000 °C (Cr2O3/CrO3/CrN@NCs-1000) demonstrated remarkable OER activity with a low overpotential of 290 mV in 1 M KOH and excellent stability. Further density functional theory (DFT) calculations revealed a much smaller reaction energy barrier of CrO3 than the low oxidation state species for OER reactivity. This work reveals fresh strategies for rationally engineering chromium-based electrocatalysts and overcoming intrinsic roadblocks to enable efficient OER catalysis through a deliberate oxidation state and compositional tuning.

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Intercropping legume with grass has potential to increase biomass and protein yield via biological N2-fixation (BNF) benefits, whereas the joint effects of biochar (BC) coupled with deficit irrigation on intercropping systems remain elusive. A 15N isotope-labelled experiment was implemented to investigate morpho-physiological responses of faba bean-ryegrass intercrops on low- (550 °C, LTBC) or high-temperature BC (800 °C, HTBC) amended sandy-loam soil under full (FI), deficit (DI) and partial root-zone drying irrigation (PRD). LTBC and HTBC significantly reduced intrinsic water-use efficiency (WUE) by 12 and 14 %, and instantaneous WUE by 8 and 16 %, respectively, in faba bean leaves, despite improved photosynthetic (An) and transpiration rate (Tr), and stomatal conductance (gs). Compared to FI, DI and PRD lowered faba bean An, gs and Tr, but enhanced leaf-scale and time-integrated WUE as proxied by the diminished shoots Δ13C. PRD enhanced WUE as lower gs, Tr and guard cell length than DI-plants. Despite higher carbon ([C]) and N concentration ([N]) in faba bean shoots amended by BC, the aboveground C- and N-pool of faba bean were reduced, while these pools increased for ryegrass. The N-use efficiency (NUE) in faba bean shoots was reduced by 9 and 14 % for LTBC and HTBC, respectively, but not for ryegrass. Interestingly, ryegrass shoots had 52 % higher NUE than faba bean shoots. The N derived from atmosphere (% Ndfa) was increased by 2 and 9 % under LTBC and HTBC, respectively, while it decreased slightly by reduced irrigation. Quantity of BNF in faba bean aboveground biomass decreased with HTBC coupled with reduced irrigation, mainly towards decreased biomass and soil N uptake by faba bean. Therefore, HTBC might not be a feasible option to improve WUE and BNF in faba bean-ryegrass intercropping, but PRD is permissible as the clear trade-off between BC and PRD.

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Volatile organic compounds (VOCs) emitted from biomass burning impact air quality and climate. Laboratory studies have shown that the variability in VOC speciation is largely driven by changes in combustion conditions and is only modestly impacted by fuel type. Here, we report that emissions of VOCs measured in ambient smoke emitted from western US wildfires can be parameterized by high- and low-temperature pyrolysis VOC profiles and are consistent with previous observations from laboratory simulated fires. This is demonstrated using positive matrix factorization (PMF) constrained by high- and low-temperature factors using VOC measurements obtained with a proton-transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) on board the NASA DC-8 during the FIREX-AQ (Fire Influence on Regional and Global Environments and Air Quality) project in 2019. A linear combination of high- and low-temperature factors described more than 70% of the variability of VOC emissions of long-lived VOCs in all sampled wildfire plumes. An additional factor attributable to atmospheric aging was required to parameterize short-lived and secondarily produced VOCs. The relative contribution of the PMF-derived high-temperature factor for a given fire plume was strongly correlated with the fire radiative power (FRP) at the estimated time of emission detected by satellite measurements. By combining the FRP with the fraction of the high-temperature PMF factor, the emission ratios (ERs) of VOCs to carbon monoxide (CO) in fresh wildfires were estimated and agree well with measured ERs (r2 = 0.80-0.93).

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High-temperature pyrolysis of waste tires is a promising method to produce high-quality carbon black. In this study, carbon black formation characteristics were investigated during tire pyrolysis at 1000-1300 °C with residence times of < 1 s, 1-2 s, and 2-4 s. It is shown that with temperature increasing from 1000 °C to 1300 °C carbon black yield was increased from 10% to 27% with residence times of 2-4 s. Carbon black exhibited a core-shell nanostructure over 1100 °C and the graphitization degree was promoted with the temperature and residence time. While the mean particle diameter decreased with the temperature to 69 nm at 1300 °C and further increased by residence time. The molecular-level evolution from tire to initial carbon black was further revealed by reactive force field molecular dynamics simulations. Light oil, gas, and radicals were transformed to initial cyclic molecules and long carbon chains via carbon-addition-hydrogen-migration, H-abstraction-C2H2-addition, and radical-chain reactions, subsequently forming PAHs. The coupling of PAHs aliphatic side chains formed large graphene layers that gradually bent to fullerene-like cores and generated incipient carbon black. The process mechanism from volatiles evolution to carbon black was proposed, which may be helpful for obtaining high-quality carbon black from high-temperature pyrolysis of waste tires.

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Introducing oxygen-vacancy into the surface of the non-enzymatic sensor is supposed to be an effective way to improve inherently low catalytic activity and specificity of non-enzymatic sensors. In this work, CuO/C was synthesized at different temperatures using metal-organic frameworks as sacrificial templates to receive additional content of oxygen-vacancy. The product with the highest oxygen vacancy was found at 400 °C (named CuO/C-400 °C), which increased catalytically active sites and enhanced the charge-transfer efficiency. The sensing performance was afterward explored by amperometry under an optimal applied potential at 0.5 V (vs. SCE), presenting a broad detection range from 5.0 µM to 25.325 mM (R2 = 0.9998) with a sensitivity of 244.71 µA mM- 1 cm- 2, and a detection limit of 1 µM. Furthermore, the reliability and selectivity of CuO/C-400 °C sensors were extensively explored in the presence of artificial serum/saliva samples with gradient glucose concentrations. The human blood samples were also detected with high recoveries compared with the clinical Hexokinase method. Hence, the prepared CuO/C-400 °C sensor with a broad detection range and high selectivity can be applied for the diabetes diagnosis ex vivo without further dilution for real-time analysis in practical applications.

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Recently, magnetic particle imaging (MPI) has shown diverse biomedical applications such as cell tracking, lung perfusion, image-guided hyperthermia, and so forth. However, the currently reported MPI agents cannot achieve the possible theoretical detection limit of MPI (20 nM). A previous theoretical study has shown that the MPI performance of superparamagnetic iron oxide nanoparticles (SPIONs) can be enhanced by carbon supporting and metal doping. In the current study, a series of mixed metal metal-organic framework-derived carbon supporting SPIONs were synthesized by pyrolysis. Among the synthesized SPIONs, the MPI signal intensity of ZnFe2O4/C@PDA was found to be 4.7 times higher than the commercial MPI contrast (Vivotrax) having the same Fe concentration. ZnFe2O4/C@PDA also showed the highest MPI intensity in tumor-bearing-mice among all tested samples. Furthermore, they were found highly biocompatible and showed linear cell quantification. This work can open new avenues for the design and development of novel and high-performance MPI agents.

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The catalytic/electrocatalytic performance of platinum (Pt) nanostructures highly relates to their morphology. Herein, we propose a facile self-template pyrolysis strategy at high temperature to synthesize one-dimensionally holey Pt nanotubes (Pt-hNTs) using PtII-dimethylglyoxime complex (PtII-DMG) nanorods as the reaction precursor. The coordination capability of DMG results in the generation of PtII-DMG nanorods, whereas the reducibility of DMG at high temperature leads to the reduction of PtII species in PtII-DMG nanorods. During the reaction process, the inside-out Ostwald ripening phenomenon leads to the hollow morphology of Pt-hNTs. Benefiting from the physical characteristics of hollow and holey structure, Pt-hNTs with clean surface show superior electroactivity and durability for catalyzing ethanol electrooxidation as well as hydrogen evolution reaction in alkaline media. Under optimized experimental conditions, the constructed symmetric Pt-hNTs||Pt-hNTs ethanol electrolyzer only requires an electrolysis voltage of 0.40 V to achieve the electrochemical hydrogen production, demonstrating a highly energy saving strategy relative to traditional water electrolysis.

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The effect of heating rates ranging from 5 °C min-1 to 350 °C min-1 on the yields of pyrolysis products of wood and its main pseudo-components (cellulose, hemicellulose and lignin) have been investigated at a temperature of 800 °C in a horizontal fixed bed reactor. Results showed a successive dramatic increase and decrease in gas and liquid yields, respectively, while the yields of solid products showed a gradual decrease as heating rates increased. Increased gas formation and an increasingly aromatic oil/tar support the theory of rapid devolatilization of degradation products with increasing heating rate, leading to extensive cracking of primary pyrolysis vapours. Solid products with coal-like calorific value and large surface areas were obtained. CO became the dominant gas both on a mass and volume basis, at the heating rate of 350 °C min-1 for all samples except xylan, which also produced a significant yield of CO2 (20.3 wt% and 25.4 vol%) compared to the other samples. Cellulose produced a gas product with highest calorific value of 35 MJ kg-1 at the highest heating rate. Results also indicate that the three main pseudo-components of biomass each exert a different influence on the products of high temperature pyrolysis of woody biomass.

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