Thalappil Pradeep

In this work, we investigate the effect of electrolyte composition on mineral fragmentation in electrosprayed aqueous microdroplets. Quartz (SiO2) and corundum (α-Al2O3) suspensions containing transition-metal ions in different oxidation states (Fe2+/Fe3+, Cu+/Cu2+, and Cr2+/Cr3+), as well as representative monovalent (Na+, K+) and divalent (Mg2+, Ca2+) cations, were electrosprayed under identical conditions. Among the tested transition-metal salt formulations, the lower-oxidation-state systems were associated with fragmentation at lower applied voltages and smaller nanoparticles, whereas the higher-oxidation-state systems required higher applied voltages for comparable fragmentation. Similar trends were observed across all transition-metal cations (Fe2+/Fe3+, Cu+/Cu2+, Cr2+/Cr3+) on both mineral systems. The generality of this approach, where a foreign ion enhances disintegration efficiency, was further supported by the efficient formation of silica nanoparticles in the presence of the imidazolium-based ionic liquid, BMIM-Cl. Finite-element simulations coupling electrostatics with two-phase flow reveal that moderate volume charge densities (∼10 C·m–3) sustain asymmetric “rough” Coulombic fission with prolonged droplet–mineral contact, whereas high charge densities (50–100 C·m–3) trigger rapid “fine” fission into progeny droplets, dissipating electrostatic energy before effective mineral breakage. These results demonstrate that electrolyte composition is an experimental variable for tuning microdroplet-mediated mineral disintegration and motivate further investigation of the physicochemical factors underlying the observed trends.

Microplastics (MPs) and per‐ and polyfluoroalkyl substances (PFAS) co‐occur in natural and drinking waters, where they persist, accumulate, and pose risks to ecological and human health. Their mitigation demands integrated detection and remediation beyond single‐function platforms. Here, we report Ag@TiO ₂ nanobrushes (NBs), fabricated entirely by ambient charged microdroplet deposition, as a unified substrate for MP capture, SERS‐based sensing, and photocatalytic PFAS degradation. In a two‐step electrospray process, 1D Ag nanowire arrays (Ag NBs) were grown over large areas and overcoated with TiO ₂ . During overcoating, a Marangoni‐type capillary rearrangement drives Ag nanoparticles to the wire periphery, yielding an Ag@TiO ₂ architecture with a percolated plasmonic network in a photoactive TiO ₂ scaffold. The 3D NB network traps MP beads, while dense electromagnetic 3D hotspots enable SERS detection of Rhodamine 6G (LOD ∼38 fM; EF ∼6 × 10 ⁷ ) and 1 µm polystyrene beads (LOD ∼31.6 ng mL ⁻¹ ; EF ∼ 10 ⁵ ) across DI, tap, and simulated seawater. The unmodified substrate drives photocatalytic degradation of perfluorooctanoic acid under ambient sunlight, confirmed by mass spectrometry. This is the first fully electrosprayed platform, integrating MP trapping, femtomolar‐level SERS detection, and PFAS photoremediation, thereby demonstrating ambient charged microdroplets as a scalable route to multifunctional nanostructures for water monitoring and remediation.

Thalappil Pradeep, Kaoru Tamada, Haiwon Lee and Dong-Hwan Kim introduce the Nanoscale themed collection on the changing canvas of nano.

We unravel the complete structural architecture of the polymorphic Na ₃ [Ag ₂₉ (BDT) ₁₂ (TPP) ₄ ] nanocluster (NC) using three‐dimensional electron diffraction (3D ED) of microscopic crystals. By drop‐casting nanocluster solution directly onto microscopy grids, we achieve in situ crystallization of nanometer‐sized polymorphs and independently resolve co‐existing cubic and trigonal phases crystal‐by‐crystal from a single grid square. Using difference electrostatic potential (DESP) maps derived from empirical 3D ED data, we pinpoint the specific lattice locations of the elusive Na ⁺ counterions and observe distinct coordination environments across the two polymorphs. In the densely packed, solvent‐free cubic phase, Na ⁺ binds exclusively to thermodynamically favored pockets formed by one core‐anchored and two staple sulfur atoms. Conversely, within the open, solvated trigonal lattice, Na ⁺ occupies both these core‐anchored sites and alternative positions coordinated entirely by three sulfur atoms of an outer Ag ₃ S ₃ staple motif. These findings establish 3D ED as a powerful tool for resolving nanoscale polymorphic mixtures and demonstrate how macroscopic crystal packing influences local ionic interactions, providing key structural insights for the design of cluster‐based assemblies.

We unravel the complete structural architecture of the polymorphic Na ₃ [Ag ₂₉ (BDT) ₁₂ (TPP) ₄ ] nanocluster (NC) using three‐dimensional electron diffraction (3D ED) of microscopic crystals. By drop‐casting nanocluster solution directly onto microscopy grids, we achieve in situ crystallization of nanometer‐sized polymorphs and independently resolve co‐existing cubic and trigonal phases crystal‐by‐crystal from a single grid square. Using difference electrostatic potential (DESP) maps derived from empirical 3D ED data, we pinpoint the specific lattice locations of the elusive Na ⁺ counterions and observe distinct coordination environments across the two polymorphs. In the densely packed, solvent‐free cubic phase, Na ⁺ binds exclusively to thermodynamically favored pockets formed by one core‐anchored and two staple sulfur atoms. Conversely, within the open, solvated trigonal lattice, Na ⁺ occupies both these core‐anchored sites and alternative positions coordinated entirely by three sulfur atoms of an outer Ag ₃ S ₃ staple motif. These findings establish 3D ED as a powerful tool for resolving nanoscale polymorphic mixtures and demonstrate how macroscopic crystal packing influences local ionic interactions, providing key structural insights for the design of cluster‐based assemblies.

Cryogenic, noncontact temperature sensing is essential for emerging technologies. Here, ligand isomerism modulates photophysical properties of atomically precise nanoclusters, enabling cryogenic optical thermometry. We synthesized emissive [Ag17(m1-CBT)12]3– (Ag17m1-CBT; m1-CBT = meta-carborane-1-thiol) and compared it with structurally analogous but nonemissive [Ag17(o1-CBT)12]3– (Ag17o1-CBT). Despite nearly identical structures and steric environments, the weaker electron-accepting meta-carborane ligand enhances radiative decay, increasing the solid-state quantum yield from 0.97% K–1, respectively. The resulting films exhibit red-emission quantum yields of 59% at 300 K and 99% at 77 K, with negligible spectral shifts, establishing ligand isomerism as a powerful strategy for nanocluster-based cryogenic thermometry.

We report the hydrolytic cleavage of C–O bonds in aliphatic ethers at cryogenic water ice surfaces under ultrahigh vacuum conditions. Ethers are conventionally resistant to hydrolysis, requiring strong Brønsted acids and elevated temperatures for C–O bond activation; their reactivity toward neutral water ice at temperatures as low as 10–50 K is therefore unexpected. Using Cs+ reactive ion scattering and low-energy sputtering in combination with isotopic labeling (H2O vs D2O), we demonstrate that dimethyl ether (DME), tert-butyl methyl ether (tBuOMe), and diethyl ether (DEE) undergo hydrolysis to form the corresponding deuterated alcohols upon contact with amorphous and crystalline D2O ice between 10 and 150 K. Isotopic incorporation establishes D2O ice as the source of the incorporated hydrogen. CH3OD was formed even at 10 K in codeposited DME-D2O films and it persisted on crystalline ice, while tBuOMe exhibited distinct product selectivity through the appearance of a tert-butyl carbocationic fragment in low-energy sputtering. These observations reveal an unexpected chemical reactivity of cryogenic water ice toward aliphatic ethers and establish ether hydrolysis as a previously unexplored low-temperature surface reaction.

Electrochemical CO2 reduction (eCO2R) to energy-dense hydrocarbons is central to sustainable carbon recycling, although achieving selective conversion at high current density and lower overpotential remains challenging. Here, we explore three molecularly precise nanomaterials, comprising nearly square planar Cu4 kernel protected by isomeric carborane-thiolate (CBT) cages, viz., Cu4-oCBT (ortho-carborane), Cu4-mCBT (meta-carborane), and Cu4-ICBT (iodinated-ortho-carborane), for eCO2R. Among them, Cu4-mCBT shows the most favorable performance, achieving ∼74% overall eCO2R selectivity and a CH4 Faradaic efficiency (FE) of ∼45% at high current densities of 500 mA cm–2 (−0.87 V vs RHE) while maintaining promising production of C2+ products. Furthermore, Cu4-mCBT and Cu4-ICBT catalysts deliver industrially relevant CH4 partial current densities (JCH4 ∼ 323 mA cm–2 at −0.99 V) at low overpotential, representing competitive performance compared to Cu nanoclusters (NCs) stabilized by conventional ligands. First-principles calculations reveal that Cu4-mCBT lowers the free energy barrier for *CHO to *CHOH hydrogenation, the rate-limiting step for methane formation, due to better orbital interactions with the intermediates. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) confirms the transient intermediate species formed in the predicted eCO2R-to-CH4 pathway. Charge density difference, projected density of states, and in situ X-ray absorption studies demonstrate the primary catalytic role of the Cu-core, while three-dimensional cage-like ligand shells modulate the electronic structure of exposed metal atoms, thereby optimizing the intermediate binding. This study investigates the catalytic performance of carborane-appended tetranuclear copper clusters toward CO2 reduction pathways and elucidates their structure–activity relationships.

Despite the significant advancements in noble metal-based nanocluster research, challenges remain in making specific metal kernel geometries, especially protected by bulky ligand shells. Here, we synthesized and structurally characterized a neutral silver cluster, [Ag14(TRZ)12(TPP)3], where TRZ and TPP refer to 6-(dibutylamino)–1,3,5-triazine-2,4-dithiolate and triphenylphosphine, respectively. The cluster was synthesized under ambient conditions using a TPP-assisted, solvent-mediated structural transformation from the [Ag31(TRZ)10]2– precursor cluster. This non-face-centered cubic (non-fcc) cluster features a central Ag5 trigonal bipyramidal core surrounded by a distinct Ag(6+3) tricapped trigonal prismatic (TTP) shell. This type of unconventional metal skeleton differs significantly from the well-known fcc-type Ag14 cluster, which typically has an octahedral Ag6 core and a cubic Ag8 shell. It is also the first metal cluster to be structurally resolved with TRZ ligands. Quantum chemical calculations indicate that although the non-fcc Ag14 skeleton has a lower cohesive energy than the fcc Ag14 analogues, bulky TRZ ligands featuring multiple sulfide linkages and n-butyl chains stabilize it. The as-synthesized Ag14 cluster is non-emissive, but exposure to oxygen converts it into an orange-emitting species. Density functional theory calculations indicate that the TTP Ag(6+3) shell prefers binding with oxygen. Emissive lifetime and femtosecond transient absorption showed that oxygenation provided greater stabilization of excited states than the parent Ag14 cluster. This study presents a new approach for designing metal clusters with unique structural frameworks with unconventional ligand environments and allows for harvesting surface-sensitive electronic properties.