Copper atoms trapped in MXene nanochannels remove 94.9% of Bisphenol A in 5 minutes by concentrating reactants and lowering the energy needed for breakdown.
(Nanowerk Spotlight) The water flowing from your tap has likely passed through a treatment plant designed decades ago to handle threats that no longer define the problem. Bacteria, sediment, heavy metals: these the old systems manage well. But a different class of contaminant now pervades water supplies worldwide, one that slips through conventional filters and resists chemical breakdown.
Bisphenol A leaches from plastic linings. Pharmaceutical residues survive the journey from medicine cabinet to sewage plant to river. Per- and polyfluoroalkyl substances, known as PFAS or forever chemicals, accumulate in groundwater near industrial sites and military bases. These micropollutants exist at low concentrations, often parts per billion, yet their biological effects can be profound. Bisphenol A disrupts endocrine function. Certain pharmaceuticals feminize fish populations downstream of treatment plants. PFAS compounds persist in human blood for years.
The challenge is not merely detecting these chemicals but destroying them. Filtration only concentrates the problem elsewhere. Biological treatment, the workhorse of sewage processing, barely touches many synthetic molecules. What is needed is chemistry aggressive enough to rip apart stable carbon bonds and oxidize complex organic structures into harmless fragments.
Advanced oxidation processes can do this by generating reactive oxygen species, short-lived but highly aggressive molecules that attack pollutants and break them down. The trouble is efficiency. Conventional catalysts that produce these reactive species tend to waste much of their oxidizing power on side reactions or lose it entirely when the radicals self-destruct before finding a target.
Single-atom catalysts represented a conceptual leap. Instead of metal nanoparticles with most atoms buried uselessly inside, these materials disperse individual metal atoms across a support surface, making every atom available for catalysis. The approach promised maximum efficiency from minimum material. But isolated atoms carry high surface energy and tend to migrate and clump during reactions, re-forming the nanoparticles they were designed to replace.
Researchers tried anchoring single atoms within porous structures to prevent aggregation, yet most candidate materials lacked either the electrical conductivity to shuttle electrons efficiently or the structural resilience to survive harsh oxidizing conditions.
MXenes offered an intriguing alternative. First synthesized in 2011, these two-dimensional materials are built from layers of transition metal carbides or nitrides. They conduct electricity as well as metals while providing chemically active surfaces studded with oxygen-containing groups that can grip individual metal atoms. Their layered architecture creates nanoscale channels between sheets, spaces just a few atoms wide where chemistry might behave differently than on open surfaces.
The research team, comprising scientists from Nanyang Technological University and Chinese institutions, synthesized a material they call Cu-SACs/MXene. They coordinated copper ions with oxygen-functionalized MXene nanosheets, then assembled the sheets through vacuum filtration to create a layered structure with uniform channel spacing of approximately 1.37 nm.
Schematic representation of the synthesis and architecture of Cu-SACs/MXene nanochannels. (Image: Reproduced with permission from Wiley-VCH Verlag) (click on image to enlarge)
Comprehensive characterization confirms that copper exists exclusively as isolated atoms rather than nanoparticles or clusters. High-resolution electron microscopy revealed individual bright dots distributed across the MXene matrix, with measured radii of about 1.30 Å matching the theoretical atomic radius of copper. X-ray absorption spectroscopy showed no copper-copper bonding signatures, only copper-oxygen coordination with an average coordination number of 3.2.
The copper loading reached 1.8 wt.%, and the atoms maintained a mixed valence state between Cu⁺ and Cu²⁺, allowing them to cycle between oxidation states as they activate oxidant molecules.
The channeled catalyst achieved 94.9% removal of bisphenol A within 5 min, with a reaction rate 3.2 times faster than copper nanoparticles on MXene. The system demonstrated broad effectiveness against pharmaceuticals, phenolic compounds, and organic dyes, with removal efficiencies ranging from 85% for carbamazepine to 99.8% for acid orange 7.
Molecular dynamics simulations helped explain how the constrained geometry enhances performance. The narrow 1.37 nm channels concentrate oxidant molecules near the copper active sites, with mass density reaching 0.9 g cm⁻³ at the catalyst surface, approximately quadruple that observed in 10 nm channels. Analysis of molecular displacement indicated faster transport through the restricted space, meaning reactants reach active sites more quickly and interact with them more frequently.
Electron paramagnetic resonance spectroscopy identified the reactive oxygen species responsible for pollutant destruction. Singlet oxygen dominated, with additional contributions from superoxide radicals, hydroxyl radicals, and sulfate radicals. Quenching singlet oxygen reduced the degradation rate by 41.3%, the largest impact among all species tested. Singlet oxygen proves particularly valuable because of its extended lifetime and resistance to interference from other dissolved substances.
Density functional theory calculations revealed the electronic basis for these observations. The copper sites within the narrow channels exhibited the strongest oxidant adsorption energy (-5.60 eV) and the longest oxygen-oxygen bond length (1.5388 Å) among all configurations tested, indicating effective bond activation. The energy barrier for oxidant decomposition dropped to 0.074 eV compared to 0.144 eV without the channeled structure, while the final thermodynamic state became more favorable at -1.432 eV versus -1.237 eV.
The material demonstrated practical viability in continuous-flow operation with real industrial wastewater, achieving 69.5% total organic carbon reduction and over 90% reduction in aromatic compounds within 2 h. Copper leaching remained well below World Health Organization drinking water guidelines at 42.6 μg L⁻¹, indicating acceptable stability for extended operation. Toxicity analysis showed that degradation products posed substantially reduced environmental risk compared to the parent pollutants.
The work establishes a mechanistic framework connecting nanoscale confinement to enhanced single-atom catalysis through two parallel pathways. Structurally, the channels enrich reactant concentrations and shorten diffusion distances. Electronically, atomic dispersion creates flexible copper centers while the restricted environment modulates local electronic structure to strengthen oxidant binding and lower activation barriers.
This dual enhancement mechanism provides design principles that extend beyond water treatment. The researchers suggest the platform could guide development of catalysts targeting the most stubborn pollutants, including PFAS and microplastics. The self-supporting membrane architecture also integrates readily into continuous-flow systems.
If the performance demonstrated here translates to larger scales, it could help close the gap between what treatment plants were built to remove and what they now need to destroy.
For authors and communications departmentsclick to open
Lay summary
Prefilled posts
ORCID information
Jia-Cheng E. Yang (State Key Laboratory of Advanced Environmental Technology, Institute of Urban Environment, Chinese Academy of Sciences)
, 0009-0005-8690-7694 corresponding author
Darren Delai Sun (Nanyang Technological University)
, 0000-0002-1487-5671 corresponding author
Nanowerk Newsletter
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
