Single-atom catalysts (SACs) have
emerged as efficient materials
in the elimination of aqueous organic contaminants; however, the origin
of high activity of SACs still remains elusive. Herein, we identify
an 8.1-fold catalytic specific activity (reaction rate constant normalized
to catalyst’s specific surface area and dosage) enhancement
that can be fulfilled with a single-atom iron catalyst (SA-Fe-NC)
prepared via a cascade anchoring method compared to the iron nanoparticle-loaded
catalyst, resulting in one of the most active currently known catalysts
in peroxymonosulfate (PMS) conversion for organic pollutant oxidation.
Experimental data and theoretical results unraveled that the high-activity
origin of the SA-Fe-NC stems from the Fe–pyridinic N4 moiety, which dramatically increases active sites by not only creating
the electron-rich Fe single atom as the catalytic site but also producing
electron-poor carbon atoms neighboring pyridinic N as binding sites
for PMS activation including synchronous PMS reduction and oxidation
together with dissolved oxygen reduction. Moreover, the SA-Fe-NC exhibits
excellent stability and applicability to realistic industrial wastewater
remediation. This work offers a novel yet reasonable interpretation
for why a small amount of iron in the SA-Fe-NC can deliver extremely
superior specific activity in PMS activation and develops a promising
catalytic oxidation system toward actual environmental cleanup.
Single‐atom catalysts (SACs) are widely investigated in Fenton‐like reactions for environmental remediation, wherein their catalytic performance can be further improved by coordination structure modulation, but the relevant report is rare. Herein, a series of atomically dispersed cobalt catalysts with diverse coordination numbers (denoted as CoNx, x represents nitrogen coordination number) are synthesized and their peroxymonosulfate (PMS) conversion performance is explored. The catalytic specific activity of CoNx is found to be dependent on coordination number of single atomic Co sites, where the lowest‐coordinated CoN2 catalyst exhibits the highest specific activity in PMS activation, followed by under‐coordinated CoN3 and normal CoN4. Experimental and theoretical results reveal that reducing coordination number can increase the electron density of single Co atom in CoNx, which governs the Fenton‐like performance of CoNx catalysts. Specifically, the entire Co–pyridinic NC motif serves as active centers for PMS conversion, where the single Co atom, and pyridinic N‐bonded C atoms along with nitrogen vacancy neighboring the unsaturated Co–pyridinic N2 moiety account for PMS reduction and oxidation toward radical and singlet oxygen (1O2) generation, respectively. These findings provide a useful avenue to coordination number regulation of SACs for environmental applications.
Nanoscale materials modified by crystal defects exhibit significantly different behaviours upon chemical reactions such as oxidation, catalysis, lithiation and epitaxial growth. However, unveiling the exact defect-controlled reaction dynamics (e.g. oxidation) at atomic scale remains a challenge for applications. Here, using in situ high-resolution transmission electron microscopy and first-principles calculations, we reveal the dynamics of a general site-selective oxidation behaviour in nanotwinned silver and palladium driven by individual stacking-faults and twin boundaries. The coherent planar defects crossing the surface exhibit the highest oxygen binding energies, leading to preferential nucleation of oxides at these intersections. Planar-fault mediated diffusion of oxygen atoms is shown to catalyse subsequent layer-by-layer inward oxide growth via atomic steps migrating on the oxide-metal interface. These findings provide an atomistic visualization of the complex reaction dynamics controlled by planar defects in metallic nanostructures, which could enable the modification of physiochemical performances in nanomaterials through defect engineering.
Quantum tunnelling offers a unique opportunity to study nanoscale objects with atomic resolution using electrical readout. However, practical implementation is impeded by the lack of simple, stable probes, that are required for successful operation. Existing platforms offer low throughput and operate in a limited range of analyte concentrations, as there is no active control to transport molecules to the sensor. We report on a standalone tunnelling probe based on double-barrelled capillary nanoelectrodes that do not require a conductive substrate to operate unlike other techniques, such as scanning tunnelling microscopy. These probes can be used to efficiently operate in solution environments and detect single molecules, including mononucleotides, oligonucleotides, and proteins. The probes are simple to fabricate, exhibit remarkable stability, and can be combined with dielectrophoretic trapping, enabling active analyte transport to the tunnelling sensor. The latter allows for up to 5-orders of magnitude increase in event detection rates and sub-femtomolar sensitivity.
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