Environmental Chemistry•2026•DOI: 10.7524/j.issn.0254-6108.2024112101
The biological reduction of Cr(VI) to less hazardous Cr(III) is a promising strategy for remediating Cr(VI)-contaminated sites. Both biochar and riboflavin can act as electron shuttles to accelerate this bioreduction process, yet their combined effects remain poorly understood. Using Shewanella oneidensis MR-1 as a model reducing bacterium, we investigated the joint influence of biochar (average particle size 28.85 μm) and riboflavin at high (1 mmol·L−1) and low concentrations on Cr(VI) bioreduction. Individually, biochar and high-concentration riboflavin enhanced indirect electron transfer, accelerating Cr(VI) removal. However, when combined, the fast-phase reaction rate (rf0) did not significantly improve compared to single amendments. The combined action factor revealed an antagonistic inhibition between biochar and riboflavin. Mechanistically, high-concentration riboflavin saturated biochar's adsorption sites (equilibrium concentration 0.96±0.04 mmol·L−1), hindering biochar's role as an electron conduit. With a bacterial density of 3.4×10^7 cells·mL−1, the inter-bacterial distance (30.87 μm) exceeded biochar's particle size, and the per-cell riboflavin concentration (2.9×10−2 pmol·cell−1) was sufficient for riboflavin to dominate as the primary electron shuttle, while biochar's surface became coated, reducing its efficacy. These findings reveal the complex interplay between biochar and soluble organic matter in Cr(VI) bioreduction, underscoring the need to consider such antagonistic effects when designing bioremediation strategies for multi-component contaminated environments.
Environmental Chemistry•2026•DOI: 10.0000/202605-1
A method for the determination of hydrazoic acid and sodium azide in workplace air was established using ion chromatography with suppressed conductivity detection. Vapor and mist states of hydrazoic acid were collected in 40 mg·L−1 KOH absorption solution, while sol states of hydrazoic acid or sodium azide were collected on microporous membranes and eluted with 40 mg·L−1 KOH. Separation was performed on a Dionex IonPac™ AS11-HC (250 mm × 4.0 mm) anion analytical column with KOH gradient elution, followed by suppressed conductivity detection. The azide ion (N3−) exhibited good linearity in the range of 0.005–0.5 mg·L−1, with a correlation coefficient (r) of 0.9997. The limit of detection (S/N=3) was 0.002 mg·L−1, and the limit of quantification (S/N=10) was 0.005 mg·L−1. The minimum quantifiable concentrations in air were 0.00256 mg·m−3 for hydrazoic acid and 0.00387 mg·m−3 for sodium azide, based on a 10.0 mL sample solution and a 20 L air sample. Spiked recoveries ranged from 92.0% to 100.4%, with relative standard deviations (RSD, n=6) between 0.76% and 2.51%. The method is efficient, accurate, and sensitive, suitable for monitoring and safety assessment of hydrazoic acid and sodium azide in workplace air.
Environmental Chemistry•2026•DOI: 10.7524/j.issn.0254-6108.2025040705
Chromium is a common environmental metal pollutant. Shewanella oneidensis MR-1 can generate extracellular electrons, facilitating the reduction of Cr(VI) to Cr(III), thereby mitigating its toxicity. Both biochar and electroactive dissolved organic matter (e-DOM) regulate extracellular electron transfer during Cr(VI) bioreduction. In practice, surface DOM on biochar can detach and enter the environment, while the biochar matrix (BCM) remains the predominant form and coexists with e-DOM. However, the combined effects of BCM and e-DOM on microbial Cr(VI) removal are unclear. This study investigated the individual and combined impacts of biochar matrix and AQDS (a model e-DOM) on Cr(VI) reduction by S. oneidensis MR-1. Results showed that biochar matrix or AQDS alone promoted Cr(VI) removal, primarily by accelerating electron transfer during the fast reduction phase. However, when both were added, an antagonistic effect was observed, attributed to increased repulsive forces between the biochar matrix-AQDS complex and the bacterial cells, which inhibited electron transfer to Cr(VI). This research elucidates the electrochemical interactions between biochar matrix and e-DOM, providing a theoretical basis for biochar applications in environmental remediation and risk assessment.
SCIENCE CHINA Materials•2026•DOI: 10.1007/s40843-026-4103-8
The industrial production of urea through the integrated Haber–Bosch and Bosch–Meiser processes involves high energy consumption and significant CO2 emissions. Given the persistent technical challenges inherent in direct electrocatalytic methods, catalytic systems that enable the thermal coupling of N2 and CO2 under mild conditions represent a promising and sustainable approach to urea synthesis. Herein, we designed MXene-based bimetallic single-cluster catalysts, M1Ru3@Mo2CO2, in which the M1Ru3 cluster is stably anchored on the Mo2CO2 support. Using density functional theory calculations, we systematically evaluated the structural stability and adsorption capabilities of 3d transition metal variants (M = Sc to Zn) toward N2, CO2, and H2. The results demonstrate that Co1Ru3@Mo2CO2 exhibits excellent thermodynamic stability and enables the synergistic activation of N2, CO2, and H2, fulfilling the prerequisite conditions for catalyzing the direct coupling of N2 and CO2 to form urea. Further analysis reveals that Co1Ru3@Mo2CO2 efficiently promotes the direct thermal coupling of N–C into urea under mild conditions via the associative pathway, with the rate-determining step corresponding to the conversion of *NHNH2 → *NH2NH2 with the low energy barrier of 1.16 eV. Under realistic conditions of 780 K and 29 bar, the calculated turnover frequency reaches 1.01 × 10−3 s−1 site−1. The high catalytic performance arises from the ability of the Co1Ru3 bimetallic cluster to precisely modulate charge transfer between support and reaction intermediates. Moreover, the in situ generated NH2 species acts as an autocatalyst for CO2 hydrogenation, while the cluster selectively enhances the electrophilicity of the *CO intermediate, thereby facilitating the nucleophilic attack by *NH2 and ensuring efficient C–N bond formation. The finding of the outstanding performance of Co1Ru3@Mo2CO2 single cluster catalysts could bypass the energy-intensive NH3 synthesis step, reduce overall energy demand, and remain compatible with existing urea production infrastructure, thereby offering significant scientific and technological significance.