The electrochemical nitrate reduction reaction (NitRR) to ammonia (NH₃) offers a sustainable route for simultaneous wastewater treatment and green NH₃ synthesis, yet it demands highly active and selective catalysts. Single-atom Fe-N-C catalysts show promise but often suffer from aggregation and limited mass transport. Herein, we constructed a composite electrocatalyst by confining Fe single atoms within an alkali-modified biochar support (Fe-N-C + OHBC). The OHBC framework features a hierarchical porous structure that enhances the mass transfer, increases the electrochemically active surface area, and creates a confined microenvironment around the Fe–N_x sites. This synergistic integration significantly boosts the NitRR performance. The Fe-N-C + OHBC catalyst achieves a remarkable NH₃ yield rate of 11.46 mg·h⁻¹·cm^–2 at −0.71 V vs. reversible hydrogen electrode (RHE) and a high Faradaic efficiency of 93.03% at −0.45 V vs. RHE, substantially outperforming its individual components. Mechanistic studies reveal that the Fe single atoms are the primary active centers, while OHBC facilitates proton-coupled electron transfer and enriches local reactant concentration. Furthermore, the catalyst demonstrates excellent stability over 80 h and maintains high performance under various pH levels and in the presence of common interfering ions, showcasing its potential for practical nitrate remediation and decentralized NH₃ production.

Traditional lanthanum-based powdered adsorbents for phosphate recovery often face challenges such as powder loss, low stability, and high material costs, while lacking agricultural applicability. To address these limitations and bridge water treatment with agricultural reuse, we developed a novel composite adsorbent, PFS-PVA-La, by incorporating La(OH)₃ nanoparticles onto a polyvinyl alcohol (PVA)-coated polyurethane foam sponge (PFS) matrix. The designed material serves dual functions: efficient phosphorus capture from water and subsequent utilization as a hydroponic growth substrate. The results demonstrate that the PFS-PVA-La configuration effectively mitigates the issue of powder loss typically associated with traditional lanthanum-based adsorbents, retaining 94% of the original adsorption capacity of La(OH)₃ nanoparticles. Moreover, the PFS-PVA-La exhibits a high phosphorus adsorption capacity of 39.66 mg_P/g, surpassing the performance of most existing composite adsorbents. La(OH)₃ nanoparticles are physically encapsulated within cross-linked PVA layers on the hydrophilic, three-dimensional pore structure of the PFS. The mechanism for phosphate recovery by PFS-PVA-La is attributed to inner-sphere complexation, pore filling, and electrostatic interactions, all of which are significantly enhanced by the incorporation of PVA and La(OH)₃ nanoparticles. Importantly, hydroponic experiments demonstrate the prepared adsorbent’s agricultural value: When used as growth substrate for lettuce, PFS-PVA-La increases fresh weight by 23% compared to control groups while maintaining optimal leaf chlorophyll and vitamin C levels. This work offers a stable, cost-effective material for phosphorus management while creating new value in hydroponic food production.

Developing electrocatalysts that exhibit both high activity and ammonia selectivity for nitrate reduction is a significant and demanding challenge, primarily due to the complex nature of the multiple-electron reduction process involved. An encouraging approach involves coupling highly active precious metals with transition metals to enhance catalytic performance through synergy. Here, we report a ruthenium-nickel alloy catalyst with nanosheets (Ru-Ni NSs) structure that achieves a remarkable ammonia Faradaic efficiency of approximately 95.93%, alongside a yield rate of up to 6.11 g·h⁻¹·cm⁻². Moreover, the prepared Ru-Ni NSs exhibit exceptional stability during continuous nitrate reduction in a flow reactor for 100 h, maintaining a Faradaic efficiency of approximately 90% and an ammonia yield of 37.4 mg·L⁻¹·h⁻¹ using 0.05 M nitrate alkaline electrolyte. Mechanistic studies reveal that the catalytic process follows a two-step pathway, in which HONO serves as a migration intermediate. The presence of a partially oxidized Ru (002) surface enhances the adsorption of nitrate and facilitates the release of the migration intermediate by adjusting the strength of the electrostatic and covalent interactions between the adsorbate and the surface, respectively. On the other hand, the Ni (111) surface promotes the utilization of the migration intermediate and requires less energy for NH₃ desorption. This tandem process contributes to a high catalytic activity of Ru-Ni NSs towards nitrate reduction.

Biochar-based transition metal catalysts have been identified as excellent peroxymonosulfate (PMS) activators for producing radicals used to degrade organic pollutants. However, the radical-dominated pathways for PMS activation severely limit their practical applications in the degradation of organic pollutants from wastewater due to side reactions between radicals and the coexisting anions. Herein, bimetallic Fe/Mn-loaded hydroxyl-rich biochar (FeMn-OH-BC) is synthesized to activate PMS through nonradical-dominated pathways. The as-prepared FeMn-OH-BC exhibits excellent catalytic activity for degrading tetracycline at broad pH conditions ranging from 5 to 9, and about 85.0% of tetracycline is removed in 40 min. Experiments on studying the influences of various anions (HCO₃⁻, NO₃⁻, and H₂PO₄⁻) show that the inhibiting effect is negligible, suggesting that the FeMn-OH-BC based PMS activation is dominated by nonradical pathways. Electron paramagnetic resonance measurements and quenching tests provide direct evidence to confirm that ¹O₂ is the major reactive oxygen species generated from FeMn-OH-BC based PMS activation. Theoretical calculations further reveal that the FeMn-OH sites in FeMn-OH-BC are dominant active sites for PMS activation, which have higher adsorption energy and stronger oxidative activity towards PMS than OH-BC sites. This work provides a new route for driving PMS activation by biochar-based transition metal catalysts through nonradical pathways.