Highly Selective Reduction of Nitrate by Zero-Valent Aluminum (ZVAI) Ball-Milled Materials at Circumneutral pH: Important Role of Microgalvanic Cells for Depassivation of ZVAl and N₂-Selectivity

Abstract

The passivation of zero-valent aluminum (ZVAl) limits its application in environmental remediation. Herein, a ternary composite material Al–Fe–AC is synthesized via a ball-milling treatment on a mixture of Al0, Fe0, and activated carbon (AC) powders. The results show that the as-prepared micronsized Al–Fe–AC powder could achieve highly efficient nitrate removal and a nitrogen (N2)-selectivity of >75%. The mechanism study reveals that, in the initial stage, numerous Al//AC and Fe//AC microgalvanic cells in the Al–Fe–AC material could lead to a local alkaline environment in the vicinity of the AC cathodes. The local alkalinity depassivated the Al0 component and enabled its continuous dissolution in the subsequent second stage of reaction. The functioning of the AC cathode of the Al//AC microgalvanic cell is revealed as the primary reason accounting for the highly selective reduction of nitrate. The investigation on the mass ratio of raw materials manifested that an Al/Fe/AC mass ratio of 1:1:5 or 1:3:5 was preferable. The test in simulated groundwater suggested that the as-prepared Al–Fe–AC powder could be injected into aquifers to achieve a highly selective reduction of nitrate to nitrogen. This study provides a feasible method to develop high-performance ZVAl-based remedial materials that could work in a wider pH range.

Rapid Oxidation of Ammonia Nitrogen to Nitrogen Gas by UV-Activated Persulfate with Calcium Oxide

“…The concentrations of NO 2 – and NO 3 – were determined by using ion chromatography (ICS-1100, DIONEX, USA). The removal rate of TN ( R (TN)) and N 2 selectivity ( S (N 2 )) can be calculated using eqs and : italicR ( TN ) = normalΔ italicC ( TN ) italicC 0 ( TN ) × 100 % italicS ( N 2 ) = normalΔ italicC ( TN ) − normalΔ italicC ( N 2 O ) − normalΔ italicC ( NO x ) normalΔ italicC ( NH 4 + ‐ N ) × 100 % where C 0 (TN) presents the initial concentration of TN (mg N/L) and Δ C (TN), Δ C (NH 4 + -N), Δ C (N 2 O), and Δ C (NO x ) are the changed concentrations of TN, NH 4 + -N, N 2 O, and NO x after reaction, respectively . Total organic carbon (TOC) was measured with a TOC analyzer (TOC, Analytik Multi NC 3100).…”

Electrochemical Nitrate Reduction: Ammonia Synthesis and the Beyond

“…[236] Other materials, such as pure metals, alloys, metal oxides, metal hydroxides, spinel oxides, perovskites, and polymers, were also reported as the electrochemical NO 3 RR catalysts, while their performances and mechanisms still need to be further optimized and clarified. [134,[237][238][239][240][241][242][243][244][245][246][247][248][249][250][251][252][253][254] Diverse advanced electrocatalysts development can meet the demand for nitrate removal and conversion under different application scenarios, such as drinking water treatment and ammonia production at regions with a lack of electricity or remote areas. Besides, vast materials exploration can avoid the problems that exist with current Cu-based catalysts, such as strong adsorption toward nitrite and unsatisfactory ammonia FE at high current densities.…”

Joule Heating Induced Reductive Iron–Magnesium Bimetallic Nanocomposite for Eminent Heavy Metal Removal

“…The unregulated discharge of heavy metal-containing wastewater (such as Cr­(VI), Sb­(V), Ni­(II), and Cu­(II)) from mining, printing and dyeing, and other human activities, poses a severe threat to the self-operation of the ecosystem. , Fe 0 -based materials are recognized as excellent electron donors and reductants for environmental remediation due to their strong reactivity. − Notwithstanding these merits, their efficiency in heavy metal removal remains unsatisfactory due to passivation and aggregation issues encountered in practical applications. , To address this limitation, an effective strategy involves incorporating a secondary metal to form Fe-based bimetallic nanoparticles, thereby enhancing their pollutant removal activity via the formed galvanic effect or hydrogen atom generation. − However, most metals with positive redox potential or catalytic properties, such as Pd, Pt, Ag, Cu, Ni, and Pb, are often limited by cost or toxicity. − Therefore, it is imperative to select cost-effective and environmentally friendly metals for bimetallic modification.…”