Highly ordered mesoporous TiO_2 nanomeshes with tunable pore periodicity via self-limiting modular monolayer assembly of monomicelles

Domain: biology
Published: 2026-03-11
Editorial outcome: minor_revision

Abstract
Precisely controlling the two-dimensional (2-D) modular assembly of monolayer micelle building blocks into free-standing highly-ordered mesoporous crystalline nanomeshes with adjustable pore periodicity and configuration remains a significant challenge. Here, highly-uniform free-standing ultrathin mesoporous TiO nanomeshes with periodically arranged pore arrays have been synthesized via a self-limiting modular monolayer assembly of monomicelles. The resultant free-standing mesoporous TiO nanomeshes are perforated by monolayer long-range ordered hexagonal pore arrays with through mesopores (~ 25 nm in diameter), forming highly periodic 2-D mesostructures with a thickness of ~ 17 nm and a specific surface area of ~ 97 m2 g−1. The pore periodicity can accurately be controlled from ~ 30 to 51 nm by varying the precursor-to-template ratio. As a proof of concept, the TiO nanomeshes are deployed as anode protectors in Sn aqueous batteries, with a prolonged cycle life of over 1400 h at 1.0 mA cm–2.

Introduction
The isolation of graphene and the demonstration of its unique dimension-related properties have sparked enormous interest in two-dimensional (2-D) materials.1-3 Recently, 2-D porous crystalline materials (PCMs) have emerged as a major topic in materials science and nanotechnology due to their size-selective molecular transport channels, tunable electronic bandgap, and boosted edge active sites.4-6 The integration of these features into an ultrathin monolayer platform makes 2-D PCMs ideal candidates for high-flux semiconducting nanosieves, suitable for applications in separation, sensing, catalysis, energy storage and conversion.7-9 The practical utility of these materials, however, critically depends on the ability to induce periodically highly-ordered nanopores to precisely tailor their surface architectures and electronic properties.10-12 In this context, significant advancements have been accomplished in synthesizing ultrathin nanomeshes with inherently periodic micropore arrays, such as porous graphene,13,14 zeolite15,16 and metal/covalent-organic framework (MOF/COF)17,18 monolayers. Nonetheless, these nanomeshes face considerable limitations regarding their compositions and electronic structures, particularly in terms of developing desirable pores with large sizes and tunable configurations. Such issues substantially hinder the modulation of mass and charge transport.19 Therefore, the development of 2-D ultrathin mesoporous semiconductor nanomeshes with periodically arranged mesopore arrays could offer compelling properties, potentially enabling new opportunities for applications.

The soft micelle-directed assembly approaches have been holding great promise for synthesizing 2-D mesoporous semiconductor nanomeshes, offering an exceptional capability for creating customizable mesopores within 2-D lattices from the bottom level. Numerous efforts to develop the block copolymer lithography have been very successful in fabricating high-quality semiconductor nanomeshes featuring ultrathin thickness and highly ordered mesopore arrays.20-22 However, achieving such precise structural control of nanomeshes typically requires the complex multi-step processing with high costs and inefficient throughput.23 More critically, these microfabrication strategies remain constrained to successive iterations of 2-D material configurations, which intrinsically restricts the compositional diversity and structural programmability achievable through the nanocrystal-based modular assembly in 2-D superlattice engineering.24

Recent developments have demonstrated a 2-D interface-directed assembly paradigm utilizing surfactant-oligomer composite micelles as modular building blocks. These micellar units can self-assemble in a monolayer manner at two-phase interfaces, facilitating the synthesis of diverse 2-D mesoporous architectures with tunable compositions.25,26 Nevertheless, current implementations face two critical challenges. First, the inherent thermodynamic instability of oligomer/micelle assembly units promotes the excessive intermicellar cross-linking, even under dilute conditions, resulting in multilayered micelle structures rather than ideal monolayers.27,28 While a set of approaches involving the spatial confinement and interfacial constraint have been implemented to enforce monolayer formation for nanomeshes, realizing the highly structural uniformity across macroscopic dimensions remains elusive so far.29 The second challenge originates from compromised mesopore ordering mechanisms. The formation of highly ordered mesoporous nanomeshes requires the regular arrangement of composite micelle units within a monolayer at the interface, which relies on the continuous defect correction through the micellar exchange between interfacial arrays and bulk solution during the assembly process.30 However, this self-repair mechanism is severely restricted by the confinement-induced suppression of molecular mobility, resulting in irregular mesopore configurations.31 Meanwhile, strong interfacial interactions also hinder the lateral rearrangement and cooperative alignment of micellar building blocks at interfaces, disrupting the long-range ordering in micellar monolayers for highly ordered mesopore arrays.32,33 The contradictory requirements of confined growth and ordered organization in nanomesh synthesis cannot be reconciled by conventional synthetic methodologies. Therefore, the modular fabrication of ultrathin mesoporous monolayer nanomeshes with periodically arranged mesopore arrays remains a grand challenge.

Here, 2-D ultrathin mesoporous monolayer TiO nanomeshes with periodically arranged mesopore arrays have successfully been synthesized by a self-limiting modular monolayer assembly method of monomicelles. The principal features of this method include the formation of unique charged titania cluster-copolymer composite monomicelle modules with electrostatic stabilization by using acetic acid (HAc) to mediate the hydrolysis of the titania precursors, and the subsequent manipulation of the monomicelle assembly in a monolayer manner on crystalline NaCl salt substrate by centrifugation. They direct the growth of the 2-D ultrathin mesoporous TiO nanomeshes with highly ordered pore arrays. The free-standing mesoporous monolayer TiO nanomeshes, obtained after the removal of the copolymer template and NaCl substrate, exhibit a highly-uniform ultrathin nanoperforated 2-D morphology (~ 17 nm in thickness) with a large lateral dimension of several microns and monolayered through mesopores (~ 25 nm in diameter). The in-plane mesopores are arranged hexagonally with a long-range order, forming highly periodic mesopore arrays. The periodicity of the arrays (defined as the center-to-center distance between two neighbouring mesopores) can be accurately adjusted from ~ 30 to 51 nm by varying the precursor-to-template ratio. The resultant mesoporous TiO nanomeshes possess a large specific surface area of ~ 97 m2 g-1 and highly crystalline ultrathin perforated frameworks, and are proved to be a good Sn anode protector in Sn aqueous batteries. The modified Sn anode with TiO nanomeshes shows an enhanced anti-corrosion ability, accelerated surface charge transfer and rapid ion transport, enabling uniform Sn metal plating/stripping and significantly extending lifespan to over 1400 h (only 48 h for the bare Sn anode).

Results
Synthesis and characterization. The highly ordered mesoporous monolayer TiO nanomeshes were successfully prepared by a self-limiting modular monolayer assembly of monomicelles on NaCl salt surfaces with the aid of centrifugation (Figure 1). Initially, the polyethylene oxide-block-polystyrene (PEO-b-PS, Figure S1)/titania spherical composite monomicelles could be formed in a mixed acidic solvent containing tetrabutyl titanate (TBOT) as the Ti precursor after stirring at room temperature (Figure S2). Subsequently, a monolayer of periodically arranged composite monomicelles could be formed on the NaCl salts (Figure S3) immersed in the composite monomicelle-containing solution, by centrifuging at 2150 × g for 3 minutes using a plastic centrifuge tube, followed by an aging process. Ultimately, the highly crystalline, free-standing, periodically mesoporous monolayer TiO nanomeshes were obtained after removing surfactant templates and NaCl substrate in turn by the calcination at 400 °C for 3 h and a subsequent washing step with water.

The scanning electron microscopy (SEM) images (Figure 2a, b) reveal that the resultant annealed free-standing TiO nanomeshes display a highly-uniform 2-D morphology with a mean size of ~ 1.1 μm (Figure S4). The in-plane through-mesopores can be clearly observed in the TiO nanomeshes, which are hexagonally arranged over the whole 2-D architecture to form periodically ordered arrays. The transmission electron microscopy (TEM) image (Figure 2c) shows the 2-D highly-uniform ultrathin structure of the TiO nanomeshes with monolayered mesopore arrays arranged in a long-range order manner. The high-magnification TEM image (Figure 2d) further confirms the periodic monolayer mesopore arrays with a pore size of ~ 25 nm and a periodicity (the centre-to-centre distance between two neighbouring pores) of ~ 40 nm. High-resolution TEM (HRTEM) images (Figure 2e) show that the mesopore walls are crystalline TiO and the lattice spacing of d = 0.35 nm matches the (101) plane of anatase. The selected area electronic diffraction (SAED) pattern (Inset of Figure 2e) displays well-resolved diffraction rings and numerous spots, further indicating a crystallized anatase nanomeshes. The high-angle annular dark-field scanning TEM (HAADF-STEM) and energy dispersive X-ray spectroscopy (EDS) mapping images (Figure 2f) demonstrate that Ti and O elements are uniformly distributed within the whole nanomesh. The thermogravimetry (TG) curve (Figure S5) of TiO nanomeshes shows only a minor, nearly linear mass decrease up to 800 °C without the obvious combustion step, consistent with the removal of the PEO-b-PS template during calcination. The atomic force microscopy (AFM) tomography (Figure 2g) and multimode (Figure S6) images reveal that the mesoporous TiO nanomeshes have rough surfaces with a thickness of ~ 17 nm (Figure 2h), which is smaller than the mesopore size (~ 25 nm). It suggests that only one layer of mesopores is close packed in 2-D plane.

The powder X-ray diffraction (PXRD) pattern (Figure 3a) shows well-defined diffraction peaks at 25.3, 37.7, 48.0, 53.8, 55.1, 62.0, 62.6, 68.6, 70.2, 73.9, 74.9 and 76.0°, which can be indexed to the 101, 004, 200, 105, 211, 213, 204, 116, 220, 107, 215 and 301 reflections of anatase, demonstrating the crystalline anatase phase (space group I4 /amd, JCPDS card no. 01-071-1167) of the 2D mesoporous TiO nanosheets. The TiO grain size is calculated from Scherrer equation to be 2.6 nm, consistent with that (2.8 nm) observed from HRTEM result (Figure 2e). The Raman spectrum of the TiO nanomeshes (Figure 3b) exhibits a strong band at around ∼144 cm–1, which is attributed to the Eg mode of anatase. The 2-D grazing-incidence small-angle X-ray scattering (GISAXS) pattern (Figure S7) shows two prominent spots extended along q on the right of the X-ray beam, indicating the in-plane ordered through-pores. The corresponding 1-D intensity profile (Figure 3c) further displays three peaks at q-values of ~ 0.156, 0.274 and 0.317 nm-1 (d /d ratios: 1.00 : 0.571 : 0.493), indexable as 100, 110 and 200 reflections associated with p6mm hexagonal symmetry. The intense 100 peak reflects a d spacing of ~ 40.3 nm, corresponding to a pore-to-pore distance of ~ 46.5 nm. Nitrogen adsorption-desorption isotherms (Figure 3d) reveal type IV curves with a small hysteresis at high relative pressure (P/P ≈ 0.9-1.0). The Brunauer-Emmett-Teller (BET) specific surface area is calculated to be about 92 m2 g−1. The corresponding pore size distribution curves (inset) derived from the adsorption branches of the isotherms by using the Barrett-Joyner-Halenda (BJH) method clearly show a centered pore size at 25 nm, in agreement with the TEM results. These results could be attributed to stacking-induced effective channels and inter-sheet slits. The BJH-derived feature size serves as a semi-quantitative reference to the dimension of through-pores, consistent with TEM observations. The X-ray photoelectron spectroscopy (XPS) spectrum for Ti 2p (Figure 3e) shows two bands at 465.2 (Ti 2p ) and 459.5 eV (Ti 2p ), assigned to Ti4+ oxidation states. For the XPS spectrum of O 1s (Figure 3f), the two peaks at binding energies of 530.8 and 532.2 eV can be detected, which is attributed to lattice oxygen atoms in a fully coordinated environment and Ti−OH species, respectively.

The effect of TBOT content on the structural parameters of the mesoporous TiO nanomeshes was investigated. By such a simply regulating synthetic procedure, the monolayer pore periodicity can be well controlled. TEM images (Figure 4a-d) show that the monolayer TiO nanomeshes with different pore periodicities are all highly uniform, indicating the high control of this self-limiting monomicelle assembly. High-magnification TEM images (Figure 4e-h) further show that all the mesoporous TiO nanomeshes possess hexagonally-arranged well-ordered mesopores with a similar diameter (~ 25 nm). While the pore wall thickness increases with the uniform neck width (the smallest edge-to-edge distance between two neighbouring pores) ranging from ~ 5.2 (Figure 4e), 13.0 (Figure 4f), 18.2 (Figure 4g) to 26.4 nm (Figure 4h) as the amounts of TBOT increase (0.2, 0.3, 0.4 and 0.5 mL), respectively. With the precisely tunable pore walls, the pore periodicity of arrays (the centre-to-centre distance between two neighbouring pores) can be adjusted from ~ 30.2, 38.0, 43.2 to 51.4 nm. When the amounts of TBOT reach to 0.6 mL, the pore periodicity of the mesoporous TiO nanomeshes is about 50 nm, without obvious change compared to that of the nanomeshes prepared by using 0.5 mL of TBOT (~ 5 in precursor-to-template ratio) (Figure S8). It suggests that excess precursor TBOT in the solution could not be assembled with the surfactant molecules into the mesostructures, removed from the NaCl substrates during the centrifugation process. The thickness of pore walls can be controlled by changing the polymer-to-precursor ratio with the constant mesostructure, which is attributed to the preformed stable monomicelles prior to the assembly process.

Moreover, the centrifugation speed, substrate, solvent and relative humidity effects were also investigated on the assembly process of the mesoporous TiO nanomeshes. At a low centrifugation speed of 424 × g, the obtained nanomeshes obviously show the hexagonal monolayer mesopore arrays but multilayered mesoporous structures at the edge (Figure S9). When increasing the centrifugation speed, the highly-ordered mesoporous monolayer TiO nanomeshes with homogeneously hexagonal mesopore arrays can be obtained at the centrifugation speed of 955, 1699, 2654 and 3823 × g (Figure S10). These results clearly indicate that the centrifugal force plays an important role in controlling the formation of the monolayered mesostructures but does not influence their mesophases. In addition, except for NaCl powders, silicon wafers with hydrophilic surface (Figure S11) and those coated by carbon with hydrophobic surface (Figure S12) were used as the assembly substrates. On these substrates, hexagonally ordered mesoporous monolayer TiO nanomeshes can be formed by the spin-coating method, similar to those synthesized on the NaCl substrate by the centrifugation process (Figure S13 and S14). It suggests that the substrate property is not the major factor governing the formation of the monolayer TiO nanomeshes. Furthermore, when the HAc is not added, many thick mesoporous layers can be observed (Figure S15). Upon increasing the relative humidity during aging to 60 %, the nanomeshes show elongate channels and larger ring-like pores, indicating the micelle coalescence induced by the strong condensation of TiO frameworks (Figure S16).

The assembly process was studied by terminating reaction at different intervals. The clear orange solution was first generated after being stirred at the room temperature (Figure S2a), indicating that the precursor TBOT has been hydrolyzed under the chelation of acetic acid assembled with surfactants. In this solution, PEO-b-PS/titania spherical composite monomicelles were formed with PS segments as a core and titania-associated PEO segments as a shell (Figure S2b-d). The ζ potential of such composite monomicelles was measured to be about +15.7 mV in ethanol, implying the electrostatic repulsive interaction between the monomicelles (Figure S17). After the centrifugation process at 2150 × g, the composite monomicelles were deposited in a discontinuous distribution on the NaCl substrate, resulting in an irregular micellar monolayer (Figure S18). In the subsequent solvent-evaporation during drying at 40 C, the monomicelles consisting of the monolayer were arranged with an almost identical intermicellar distance, forming a very regular hexagonal non-close-packed pattern (Figure S19). With further drying at 100 C, the patterned micelle protrusions were turned into a continuous film with hexagonally-arranged monolayer mesopores (Figure S20 and S21). During calcination at 400 °C, the bottom of pores begins to opens gradually (Figure S22), forming ring-like through pores in the end (Figure S23). The nanomeshes on the NaCl substrates after the calcination show an average size of ~ 1.4 μm, slightly larger than the free-standing nanomeshes, which implys some sample fragmentation during the NaCl crystal removal (Figure S24).

Electrochemical performances. The mesoporous TiO nanomeshes were dispersed in ethanol, forming a film on the surface of a Sn foil (Sn@meso-TiO ), acting as the anode protector for Sn aqueous batteries (Figure 5a). The SEM images (Figure S25a, b) show that staggered nanomeshes uniformly covered the Sn foil surface, forming a protective layer with a thickness of ∼ 3 μm. The contact angle of the Sn@meso-TiO anode is measured to be about 55.3°, obviously smaller than that of the bare Sn anode (~ 81.5°) (Figure 5b). It clearly indicates that the Sn@meso-TiO anode exhibits a significantly improved electrolyte affinity compared with the bare Sn anode, which would facilitate the uniform Sn plating/stripping. The cyclic voltammetry (CV) tests at various scan rates were employed to investigate the diffusion kinetics for the Sn-ion diffusion (Figure S26a, b). The Sn@meso-TiO anode shows a higher Sn2+ diffusion coefficient (D 2+) of than the bare Sn electrode (Figure S26c). The ionic transference number of the Sn@meso-TiO anode is 0.74, higher than that (0.43) of the bare Sn anode (Figure S27). The Tafel curves measured in acidic electrolyte (Figure 5c) show that the Sn@meso-TiO anode yields a corrosion current (I ) of 9.5 mA cm−2, which is only about a half of that for the bare Sn foil (18.4 mA cm−2). The markedly decreased corrosion current suggests the enhanced anti-corrosion after coating mesoporous TiO nanomeshes on Sn foils for anode protectors. Electrochemical impedance spectroscopy (EIS) analyses at various temperatures (Figure 5d, Figure S28 and Figure S29) reveal that the Sn@meso-TiO anode exhibits a much smaller charge transfer resistance (R ) value than that of the bare Sn anode (0.5 Ω for Sn@meso-TiO vs. 5.2 Ω for bare Sn). The activation energy (E ) of Sn@meso-TiO anode is calculated to be 48.2 kJ mol−1, smaller than that of the bare Sn anode (51.5 kJ mol−1), implying that the meso-TiO protector promotes an increased surface electron mobility and enhanced electrochemical activity by improved electrolyte affinity. Also, the ordered mesoporous structures of the TiO protectors induce a uniform ion accessibility, inhibiting the uneven Sn deposition and high activation barriers at nucleation sites. The diffusion current for the Sn@meso-TiO electrode is much higher than that for bare Sn (Figure 5e), which further confirms the accelerated ion diffusion behavior benefited from the mesoporous structure and improved electrolyte wettability of the mesoporous TiO nanomesh protector. The symmetric cell tests (Figure 5f) show a prolonged cycle life for the Sn@meso-TiO anode of over 1400 h at 1.0 mA cm–2 and a very short one for the bare Sn anode of only 48 h, demonstrating a significantly improved cycling stability. The Sn@meso-TiO anode achieves a Coulombic efficiency of 99.8% over 700 cycles at 1 mA cm-2, while the bare Sn anode shows a low Coulombic efficiency of 97% and fails in fewer than 100 cycles due to a short circuit (Figure S30). Under high areal capacity of 5 mA cm-2, the Sn@meso-TiO anode still shows a prolonged cycle life of the Sn@meso-TiO anode for over 370 h at 5.0 mA cm–2 (Figure S31). Moreover, Sn@meso-TiO anode exhibits lower electrode polarization (within 4.0 mV for Sn@meso-TiO vs. over 10 mV for bare Sn), indicating an accelerated surface charge transfer process and ion diffusion. In-situ side-view optical images upon the plating process (Figure 5g) show that the Sn nucleation on the Sn@meso-TiO anode is homogeneous, and a dense and smooth surface is observed. In contrast, for the bare Sn anode, the initial Sn nucleation is inhomogeneous, leading to apparent dendrites growth after 20 min due to the inhomogeneous concentration field caused by a low diffusion. Laser confocal scanning microscopy (LCSM) tests (Figure 5h and Figure S32) show a uniform Sn plating for the Sn@meso-TiO anode with an altitude intercept of 5.7 µm and a surface roughness (S , arithmetic mean height) within 0.6 µm. Whereas the bare Sn anode exhibits large Sn humps with an altitude intercept of 67.4 µm and a S of 4.2 μm.

The Sn anodes with a similarly thick layer of TiO nanoparticles (Sn@NP-TiO ) were also prepared (Figure S25c, d). The Sn@NP-TiO anode show a much shorter cycle life (90 h at 1.0 mA cm–2) than the Sn@meso-TiO anode (Figure S33a). The EIS analyses (Figure S33b) reveal that the Sn@NP-TiO anode exhibits a higher R value than the Sn@meso-TiO anode (2.2 Ω for Sn@NP-TiO vs. 0.5 Ω for Sn@meso-TiO ). It indicates that the hexagonally ordered through-pores act as ion channels, enabling a high ionic conductivity and homogeneous ion flux, which cannot achieve by the tortuous ion pathways in the non-uniform porous nanoparticle aggregates.

Methods
Chemicals
Monomethyl poly(ethylene oxide) (M : 50 00 g·mol−1) was purchased from Aldrich. Copper (I) bromide (CuBr), styrene, pyridine, and Al O were purchased from Shanghai Chemical Reagent Co., Ltd. N,N,N′,N″,N″-pentamethyl diethylenetriamine (PMDETA) was purchased from Acros. Acetylacetone, tetrahydrofuran (THF), anhydrous ethyl ether, petroleum ether, tetrabutyl titanate (TBOT), zirconium acetylacetonate (Zr(acac) ), aluminum acetylacetonate (Al(acac) ), hafnium chloride (HfCl ), cerium chloride (CeCl ), hydrochloric acid (HCl, 36-38 wt%), and acitic acid (HAC) were purchased from Sino-Pharm Chemical Reagent Co., Ltd. All chemicals were used as received without further purification.

Preparation of polyethylene oxide-block-polystyrene (PEO-b-PS) diblock copolymer
The amphiphilic diblock copolymer templates were prepared by a well-established atom transfer radical polymerization (ATRP) method involving two steps. The first step was the synthesis of macroiniator PEO-Br. 20.0 g of monomethoxy PEO5000 was dissolved in 60 mL of THF. Then, 40 mL of pyridine was added to obtain a homogeneous solution. The solution was cooled in an ice-water bath. To it, 3.00 g of 2-bromoisobutyryl bromide (13 mmol) was added dropwise under stirring for 30 min. The resultant solution was further stirred at 30 C overnight. After cooling to room temperature, 200 mL of cold ether was added to the solution. The white product of PEO-Br was precipitated from the reaction solution. It was washed with cold ether and further dried in vacuum.

In the second step, 3.00 g of PEO-Br (0.53 mmol), 0.08 g of CuBr (0.57 mmol), 0.10 g of PMDETA (0.57 mmol), and 15.0 g of styrene (144 mmol) were added to an ampoules bottle. The bottle, containing reactants, was fully degassed with three freeze-pump-thaw cycles and sealed under vacuum. It was subsequently immersed in a thermostated oil bath at 110 C under stirring to allow polymerization of styrene. The reaction continued for 3 h, after which the system was cooled down to room temperature. The gel-like product was dissolved in 50 mL of THF and filtered through Al O column to remove Cu complex. Petroleum ether (200 mL) was poured into the solution to precipitate PEO-b-PS block copolymer. The copolymer was then dried in vacuum without the further purification step. The yield was 70 wt% on the basis of initial styrene amount.

Preparation of highly ordered mesoporous monolayer TiO nanomeshes
In a typical synthesis, 0.4 g of TBOT was added to 10 mL of THF solution of the block copolymer (1.0 wt%, containing 0.1 g of PEO-b-PS) with HCl (1.5 mL, 37 %) and acetic acid (0.5 mL, 98 %), the solution was stirred for ~ 2 h at room temperature. The obtained TiO sol was poured into a plastic centrifuge tube (100 mL) filled with NaCl crystals (30 g), and the centrifuge tube was shaken so that the TiO sol completely soaked the surface of the NaCl particles. The mixture was then centrifuged at room temperature at a rotational speed (2150 × g for 3 minutes). Then they were transferred to a Petri dish and aged at 30 °C (humidity ~ 30%), 40 and 100 °C for 24 h, respectively. The mixture was calcined at 400 °C for 3 h in air, with a heating rate of 1 °C min−1. Finally, the free-standing highly-ordered mesoporous monolayer TiO nanomeshes were obtained after washing by 100 mL of water to remove the NaCl substrate.

Preparation of the mesoporous TiO nanomeshes with various mass ratio of TBOT to PS-b-PEO
In a typical synthesis, 0.2 g (0.3, 0.4, 0.5, or 0.6 g) of TBOT was added to 10 mL of THF solution of block co-polymer (1.0 wt%, containing 0.10 g of PEO-b-PS) with HCl (1.5 mL, 37 %) and acetic acid (0.5 mL, 98 %), the solution was stirred for ~ 2 h at room temperature. The obtained TiO sols were poured into a plastic centrifuge tube filled with NaCl crystals, and the centrifuge tube was shaken so that the TiO sols were completely soaked the surface of the NaCl particles. The mixture was then centrifuged at room temperature at a rotational speed of 2150 × g for 3 min. Then they were transferred to a Petri dish and aged at 30 °C (humidity ~ 30%), 40 and 100 °C for 24 h, respectively. The mixture was calcined at 400 °C for 3 h in air with a heating rate of 1 °C min−1. Finally, the monolayer ordered mesoporous TiO nanomeshes were obtained after the water washing.

Preparation of mesoporous TiO nanomeshes at various centrifugation speeds
The obtained TiO sol was poured into a plastic centrifuge tube filled with NaCl crystals, and the centrifuge tube was shaken so that the TiO sol completely soaked the surface of the NaCl particles. The mixture was then centrifuged at room temperature at different centrifugation speeds of 424, 955, 1699, 2654 and 3823 × g for 3 min, respectively. The obtained complex was kept at room temperature for 12 h to evaporate THF, followed by further heating in an oven at 40 °C for 24 h and at 100 °C for 24 h. They were calcined at 400 °C for 3 h in air with a heating rate of 1 °C min−1, followed by the subsequent washing.

Preparation of mesoporous monolayer ZrO nanomeshes
0.40 g of Zr(acac) was added to 10 mL of THF solution of the block copolymer (1.0 wt%, containing 0.10 g of PEO-b-PS) with HNO (0.5 mL, 37 %) and acetic acid (0.3 mL, 98 %), the solution was stirred for ~ 4 h at room temperature. The following procedures were the same with that for the synthesis of TiO nanomeshes.

Preparation of mesoporous monolayer Al O nanomeshes
0.40 g of Al(acac) was added to 10 mL of THF solution of the block copolymer (1.0 wt%, containing 0.10 g of PEO-b-PS) with HNO (0.5 mL, 37 %) and acetic acid (0.3 mL, 98 %), the solution was stirred for ~ 12 h at room temperature. The following procedures were the same with that for the synthesis of TiO nanomeshes.

Preparation of mesoporous monolayer HfO nanomeshes
0.40 g of HfCl was added to 10 mL of THF solution of the block copolymer (1.0 wt%, containing 0.10 g of PEO-b-PS) with HNO (0.5 mL, 37 %) and acetic acid (0.3 mL, 98 %), the solution was stirred for ~ 2 h at room temperature. The following procedures were the same with that for the synthesis of TiO nanomeshes.

Preparation of mesoporous monolayer Zr Ce O nanomeshes
0.40 g of Zr(acac) and 0.04 g of CeCl was added to 10 mL of THF solution of the block copolymer (1.0 wt%, containing 0.10 g of PEO-b-PS) with HNO (0.5 mL, 37 %) and acetic acid (0.3 mL, 98 %), the solution was stirred for ~ 2 h at room temperature. The following procedures were the same with that for the synthesis of TiO nanomeshes.

Characterization
Transmission electron microscopy (TEM) measurements were conducted on a JEM-2100 F microscope (JEOL, Japan) operated at 200 kV. Field-emission scanning electron microscopy (FESEM) images were taken on a Hitachi Model S-4800 microscope. Samples used for TEM and FESEM analyses were prepared by dropping of the TiO dispersion in ethanol on amorphous carbon-coated copper grids and silicon substrates, respectively. Atomic force microscopy (AFM) measurements were performed in tapping mode (Multimode IV, Veeco) after depositing the samples on a mica. A silicon cantilever (TESP-SS, Veeco) with a normal tip radius of < 5 nm was used after cleaning in UV/ozone for 15 min. Synchrotron radiation small-angle X-ray scattering (SAXS) measurements were performed at Beamline BL16B of Shanghai Synchrotron Radiation Facility (SSRF). The d-spacing values were calculated from the formula d = 2π/q. SAXS measurements were taken on a Nanostar U small-angle X-ray scattering system (Bruker, Germany) using Cu Kα radiation (40 kV, 35 mA). Wide-angle X-ray diffraction (WAXRD) patterns were recorded with a Bruker D8 powder X-ray diffractometer (Germany) using Cu Kα radiation (40 kV, 40 mA). Nitrogen sorption isotherms were measured at 77 K with a Micromeritics Tristar 3020 analyzer (USA). Before measurements, the samples were degassed in a vacuum at 180 °C for at least 12 h. The Brunauer−Emmett−Teller (BET) method was utilized to calculate the specific surface areas. The pore size distributions were derived from the adsorption branches of isotherms using the Barrett−Joyner−Halenda (BJH) model.

Electrochemical measurements
In-situ optical observation of Sn plating was conducted on an optical microscope (AW33T-4k, Hangzhou Aoweisi Technology Co., Ltd.) equipped with a homemade transparent symmetric cell. The Tafel curves of Sn electrodes were tested on an electrochemical workstation (DH7000, Jiangsu Donghua Analytical Instrument Co., Ltd) at the scan rate of 5 mV s–1. Chronoamperogram (CA) characterization was conducted at the potential of –0.50 V vs. Ag/AgCl in a home-made three-electrode test cell. Electrochemical impedance spectra (EIS) were obtained in a frequency range of 100 kHz to 100 mHz at open-circuit voltage with an AC voltage of 5 mV. Confocal laser scanning microscopy (CLSM) images of Sn plating in different electrodes were obtained via the confocal laser scanning microscope (CHOTEST, VT6000). Before image acquisition, the electrodes were plated at 5 mA cm–2 with 1 mAh cm–2. The electrolyte wettability was measured by a contact angle measuring instrument (SDC-100), with an electrolyte of 2 M H SO +0.2 M SnSO . Sn symmetric cells were assembled in CR2032 coin cells using bare Sn and/or Sn@meso-TiO electrodes (diameter of 12 mm) with glass fiber (GFD, diameter of 16 mm) separator. The cycling performance of symmetric cells was tested by the Neware BTS-4000 batteries test system.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The authors present a method that utilizes the self-assembly of block copolymers to form an array of spherical micelles as a template for fabricating a TiO₂ nanomesh. By leveraging electrostatic repulsion and steric hindrance, the approach demonstrates more precise structural control compared to previously reported micelle-based methods. However, the significance of the study is questionable for the following reasons, and the reviewer would recommend considering a transfer to a more suitable journal.\n1) Specialty and Generality of the Process\n1-1) As the authors mentioned in the Introduction, 2D nanomesh structures with controlled thickness have already been widely reported through other methods such as block copolymer lithography. It is difficult to identify the unique specialty of the presented methodology in this context.\n1-2) It is unclear whether this approach can be considered a general method for fabricating various types of nanomeshes beyond TiO₂. If the method is limited to specific elements or cluster oligomers, broader applicability and novelty of the proposed procedure may be significantly reduced.\n1-3) The reviewer would also like to inquire whether this method allows for the fabrication of nanomesh layers on a large scale, beyond flake-sized samples. This aspect is closely related to the concern raised in 1-1) regarding the novelty and practical significance of the approach.\n2) Minor Comments\n2-1) The authors provide a rationale for the formation of the monolayer structure in the Discussion section. While the description appears reasonable, supporting experimental data are recommended to strengthen the claim.\n2-2) Additional explanation regarding the removal process of the polymer (carbon) within the film is recommended. The calcination temperature applied does not appear to be sufficient for complete polymer decomposition, and the carbon profile in the EDS mapping image (Figure 2f) is difficult to interpret definitively.\n2-3) It is recommended that the AFM images shown in Figures 2g–h be re-measured, as the current data appear unclear and may not adequately support the claims.\n2-4) In the electrochemical tests, a more appropriate control group is suggested. Rather than using Sn foil without a protective layer, data comparing with a non-uniform porous TiO₂ structure could better highlight the advantages and specificity of the proposed method, thereby reinforcing the impact of the manuscript.", "reviewer_2": "The manuscript by Zhang et al. proposes an interesting self-limiting modular monolayer assembly of monomicelles strategy for the synthesis of ordered 2D mesoporous TiO2 nanomeshes. The synthesis provides a new opportunity to simultaneously realize periodically arranged mesopore arrays and uniform crystalline monolayer architecture control. The quality of data in this manuscript is at a high level, and the materials were well characterized with the sophisticated facilities. The superior electrochemical performances of TiO2 nanomeshes as Sn anode protectors in Sn aqueous batteries are also demonstrated, involving the enhanced anti-corrosion ability, charge/ion transfer, and lifespan. Such materials are promising in aqueous batteries. Overall, the manuscript is well-organized with high novelty, which may attract broad interest from multidisciplinary research communities. Hence, I recommend accepting this manuscript after the following comments are addressed.\n1. In terms of the pore periodicity tuning section (Figure 4), what causes the tunability of the wall thickness for hexagonal mesopores? Why does the mesophase of the nanomeshes not change after altering the precursor-to-template ratio?\n2. The structural evolution to nanomeshes during the calcination process remains unclear. The authors claimed that “under the subsequent calcination, the matter of the bottom pore walls migrates to surrounding regions to form the through-mesopore arrays, which is driven by the minimization of the surface energy” (line 328). More data and explanations need to be provided.\n3. Why can the mesoporous TiO2 nanomeshes reduce the activation energy of the Sn electrode (Figure 5d)?\n4. Is the mesoporous TiO2 nanomeshes protective layer beneficial for improving the Coulombic efficiency of Sn plating/stripping? Please supplement the relevant experiments.\n5. In the article, only the CA test was used to investigate the diffusion behavior. More testing methods need to be employed for verification. For example, CV curves under different scanning rates should be provided. The influence of mesoporous TiO2 nanomeshes protective layer on the ionic transference number needs to be further revealed.\n6. The charge/discharge curves of Sn@meso-TiO2 under high current need to be supplemented. Does the mesoporous TiO2 nanomeshes protective layer still function under high areal capacity?", "reviewer_3": "Review Zhao et al Nat Comm 2025\nIn this work, Zhang et al. present the creation of mesoporous titania thin free-standing nanomeshes with controllable pore diameter and interpore distance. The procedure uses pre-formed Ti-oxo-micelle hybrid building blocks that self-assemble onto surfaces, assisted by centrifugation, followed by an Evaporation-Induced Self-Assembly (EISA) process.\nThis methodology leads to practically monomicellar thin films or self-supported 2D sheets (thickness below 20 nm) with controlled perforations when the substrate is NaCl, which can be removed through washing.\nInterestingly, this method is an advance on previous work that resorted to interface-directed assembly, which is more experimentally costly, and in principle is valuable to attaining higher quantities of materials in a reproducible fashion. I find that this manuscript dwells in the limit of incremental work (the group has world-leading experience in mesoporous materials ans lately has demonstrated the potential of these hybris block-copolymer-metal-oxo nanobuilding block assemblies) and an original way to create anisotropic ultrathin mesoporous meshes through controlled processing.\nAuthors employ a wealth of characterization techniques to determine structural features of the synthesized materials, and they also demonstrate that wall thickness, a very relevant aspect, can be tailored in a straightforward way. The microscopy evidence is compelling regarding the pore structure and pore diameter; the XRD and Raman spectroscopy clearly show that the materials are mainly composed of nanocrystalline anatase, which is expectable for the heat budget allocated (400°C, 3h). However, some characterization aspects might need improvement (see below). Authors also show that these nanomeshes contribute to improve durability of Sn electrodes. In the last part, authors propose\nIn general, this contribution is valuable and original, showing an interesting platform for further development.\nHowever, some aspects regarding system tunability and the proposed mechanism of formation require further improvement. I recommend authors to work out the comments below and submit a revised version to be reviewed before publication. Please find specific comments below.\nMajor Comments:\n1. Although the group has high expertise in this kind of synthesis and S1b shows SEM images of “frozen micelles”, the compositional information of such building blocks is not totally clear in this autonomous work. It might be useful to add EDS information to determine the Ti and O distribution of a sample similar to the one shown in the S1b figure, or else provide a lower-angle SAXS pattern to obtain the gyration radius and the hybrid micelle shape; this information should be included in the ESI.\n2. Authors claim that they obtain “a highly-uniform 2-D morphology with a large lateral size in the range of several microns” (p. 7). SEM pictures show that, but can authors make an estimation of the distribution of sizes of the ordered 2D morphologies? Are the circular patterns observed in Figure 2c. regular patterns? The origin of those circular patterns could be dewetting of the substrate, did authors explore further?\n3. The SAXS pattern provided in Figure 3c is not completely clear. Authors assign peak positions as if it were traditional mesoporous materials; the peak positions obtained from the maxima look reasonable for a hexagonal structure, and so are reported (authors, please provide the dhkl/d100 ratios for structural check). However, here we have very anisotropic 2D materials that can present orientation. Authors should clearly show how did they treated the SAXS data of Figure 3c. There are two issues that require attention. First, authors should clarify which kind of measurement and sample conditioning (i.e., transmission, grazing, oriented sample, powder, etc) and how they integrated the scattering/diffraction. It is important that authors present the SAXS 2D detector readout to verify the samples orientation and better appraise the meso-distances. A 2D mesh with vertical pores aligned parallel to the beam would present no off-plane signals, for example. Also, there is a peak smearing towards higher q values. Does this signal derive from a radial integration of the detector plate? Authors should improve this characterization section, because it is important towards the claim of controlled 2D meshes.\n4. The discussion section (Page 13 and following) is interesting, and it is clear that this case is an exreme case of EISA. I would suggest improving certain points to unify these interesting results in the framework of previous literature. Please see my specific comments to paper claims:\na. “the realization of the self-limiting, long-range ordered 276 monolayer assembly is predominantly determined by the electrostatic interactions 277 among the composite monomicelle building modules.” The formation of the organized structure can be interpreted in terms of an interaction potential that reflects the adequate balance of the attraction between the building blocks (i.e., the hybrid micelles) and the repulsion due to electrostatics (i.e., here the surface charges Ti-oxo-acetate species). An interesting and accurate analysis, of the general EISA approach and the forces at play can be found in the theory developed by Tang et al (https://doi.org/10.1039/C7CP05304E). I suggest authors work in order to discuss their results in this framework, as this can open new paths.\nb. “The PEO shell can interact with titania oligomers formed by the hydrolysis of TBOT through hydrogen bonding and electrostatic attraction”. These aspects have been well discussed for titania systems by the Sanchez group (https://doi.org/10.1039/B002518F and https://doi.org/10.1039/B006139P), which then has been reinforced by the Tang paper cited above. A more recent discussion was provided in https://doi.org/10.1039/C2NR11817C. I suggest also including some brief discussion into this relevant previous work, because the results presented and discussed here are fully coherent with those previous works. I believe that discussing in this broader scenario will give more weight and a unifying framework of understanding.\nc. “Notably, the hydrolysis of TBOT is controlled by chelation with HCl and acetic acid (HAc)”. This phrase is not clear. I would suggest rephrasing as”the hydrolysis of TBOT is controlled by a balance between chelation by acetic acid (HAc) and HCl as a hydrolysis catalyst”.\nd. “In this case, titanium alkoxides readily react with carboxylic acids via a non-hydrolytic condensation pathway to form Ti-O-Ti bonds”. I have estimated that the water content in the solution (issued from the HCl 37%) is ca. 1.1g in the starting solutions, this is approximately 0,062 mole. Considering that in the typical case, TBOT contents is roughly 0.0012 mole, tha water:Ti ratio is ca. 50. Therefore, there is no possibility of a non-hydrolytic condensation, which requires higher temperatures and absence of water. I find that there is no need to refer to non-hydrolytic condensation, when a hydrolysis-condensation path controlled by HCl (HCl:Ti=15) and acetate (AcO:Ti=6) is perfectly suitable and explains adequately the findings (see Sanchez papers cited above). Therefore, authors should reconsider their arguments and reframe their approach, as the conditions explored here rule out a non-hydrolytic condensation mechanism.\ne. Authors ascribe the formation of a monomicellar film mainly to the strong repulsions between positively charged Ti-oxo-acetato/polymer hybrid micelles. This is a plausible explanation. However, we can also see that the initial sol is relatively dilute, and this might lead to very thin coatings after deposition (for example, dilution has been exploited in the so-called nanocrater thin mesoporous films, reposrted here DOI: 10.1002/smll.200500333).\nMinor remarks:\nPage 6: “the dissociative polyethylene…”. A dissociative polymer characteristically presents dynamic covalent bonds that can be broken and reformed under specific solicitations (e.g., light, temperature or chemical stimuli). The BC templated used does not have the characteristics of a dissociative polymer. However, it could be argued that the hybrid micelles can be considered as such. Also, I could not find the polymer MW (authors claim although in p9 It is stated (~ 5 in precursor-to-template ratio)”, can authors provide MW?\nPage 8: “The powder X‐ray diffraction (PXRD) pattern (Figure 3a) further confirms the good 162 crystallinity of the mesoporous monolayer TiO2 nanomeshes”. “Good” is not a technical term. Authors should be more specific, and comment on the matching of the sample to pure anatase reference structure, elaborate about the absence or presence of minor crystalline phases and report a crystallite size, and if there is an orientation.\nPage 8. Authors state that they derive the PSD from the adsorption branches. The sorption curves in Fig. 3c show a loop that could be classified as H1. In mesoporous systems that present H1 loops, the desorption curve reflects better equilibrium and thus is preferable to calculate pore diameter (see, e.g., DOI: 10.1002/cite.201000064), which is the basis of BJH analysis (i.e., Kelvin equation under equilibrium). Please authors, improve this analysis.\nESI:\nPage 4: “The copolymer was then dried in vacuum. The 58 yield was 70 wt% on the basis of initial styrene amount.”. I assume there is no further purification step. Authors might be interested in providing an estimation of the polymer MW.\nPage 4, “were obtained after 70 washing to remove the NaCl substrate.”, please specify solvent and volume, as this is essential for reproducibility.\nTypos and Expressions:\nPage 9, substitute “nanmeshes” with “nanomeshes”\nPage 10, substitute “miltilayer” with \"multilayer”\nDr. Galo J. A. A. Soler-Illia", "reviewer_4": "This is a generally interesting study on periodically ordered nanostructures of free-standing TiO2 flakes by a template-directed synthesis. The authors present comprehensive characterization of their materials, including electrochemical properties. However, I see a couple of open questions, which is why I cannot recommend publication of the work in present state:\nAuthors characterize their materials as \"mesoporous\". Technically, the term \"pore\" is not adequate, since, by definition (IUPAC), a \"pore\" is deeper than wide, which is not the case here (width: 25 nm, depth: 17 nm). Admittedly, this reference to mere terminology may be unimportant. However, the characterization of the \"porosity\" by N2 physisorption analysis is flawed due to misinterpretation of the data. The isotherms are clearly not \"characteristic type IV curves with distinguishable capillary condensation step\". Such capillary condensation cannot be expected for \"mesopores\" that are only 17 nm long (compared to 25 nm width) in the first place. Consistently, no capillary condensation step can be recognized in the isotherm (figure 3d), and it is entirely unclear how the BJH \"pore\" size distribution shown in the inset is derived from the isotherm.\nAuthors fail to provide conclusive information about the lateral size of the TiO2 flakes. To start with, the shape and size (size distribution, actually) of the NaCl crystals need to be characterized. Next, the dimensions of the TiO2 layers at the NaCl surfaces should be analyzed. Finally, and most importantly, it is essential that the size of the free-standing flakes after removal of the NaCl substrate be thoroughly investigated, including a comprehensive statistical analysis of size distribution. This is most critical for the electrochemical studies (see below).\nAuthors claim that the TiO2 flakes can be applied as a corrosion protecting layer at a Sn anode. To this end, they explain that the flakes form \"a film on the surface of a Sn foil\" but fail to prove this. Do single flakes cover the Sn surface homogeneously and continuously? How large are the flakes, to start with (see above)? How thick is the protective layer (is it a single layer of flakes)? Is the impact of the TiO2 layer on the electrochemical performance indeed related to the periodic nanostructure (\"porosity\") of the flakes? A similarly thick layer of TiO2 (nano)particles might have the same impact; such control experiments are not undertaken by the authors. Besides, how was the \"charge transfer resistance (Rct)\" calculated from the impedance spectra? Authors need to show the entire analytical procedure (circuit equivalent, fits to data, etc.)."}, "author_response": "We appreciate the reviewer for the valuable comments. All issues the reviewer mentioned below, especially some concerning the significance of this work, have been carefully considered and accordingly addressed in current manuscript. The specialty, versatility and scalability of this study have been further demonstrated and understood by the more detailed data and in-depth discussion.\nWe thank the reviewer for acknowledging the novelty of our method for its improved structural control. More importantly, we believe that our work represents a substantial advance in the field of the 2-D nanomesh fabrication for the following key reasons:\n1. It demonstrates a novel self-limiting assembly mechanism, driven by the electrostatic repulsion, which is fundamentally different from the conventional confinement-based micelle-directed methods. This mechanism intrinsically ensures the large-area, highly-ordered mesoporous monolayer formation, which is a significant challenge that existing methods struggle to overcome.\n2. It provides the accurate and continuous tunability of the mesopore periodicity (from ~ 30 to 50 nm) through simply adjusting precursor-to-template ratio, moving beyond the limitations fixed by block copolymer molecular weights in the block copolymer lithography.\n3. The substrate-agnostic and centrifugation-based process offers a more simplified, versatile, scalable route to free-standing nanomeshes or large-scale periodic patterns compared to the block copolymer lithography approach, enhancing their potential for practical application.\nWe have seriously revised the manuscript to better highlight these significant advances in response to the comments provided. We are confident that the mechanistic insights, the level of control achieved, and the enhanced performance in battery applications can be of broad interest to the readership of this journal."}, {"round": 2, "reviewer_comments": {"reviewer_1": "I appreciate the authors' thorough responses to all review comments. Overall, considering the revisions and response for other reviewers’ comment, I am optimistic about the manuscript’s suitability for publication in Nature Communications, with only a few remaining minor points.\n1. The authors present a tunable pore size range of approximately 30–50 nm. I recommend adding a brief discussion on potential strategies or material design considerations that could enable further pore size reduction, particularly regarding the feasibility and prospects of achieving finer membrane structures.\n2. To further emphasize the versatility and significance of block copolymer–based fabrication strategies, the authors may consider citing the following recent review, which provides a comprehensive overview of advanced block copolymer lithography and related patterning techniques:\nYang, G. G. et al. Nat. Rev. Electr. Eng. 2024, 1, 124–138.", "reviewer_2": "The authors have addressed my comments, and the paper can be published in its current form.", "reviewer_3": "The authors have made an effort to solve the requests, and this reviewer agrees with all the corrections and the point-by-point discussions. The paper has improved, and the advice is publish without further modifications.", "reviewer_4": "The authors have improved their manuscript, and my previous concerns have now been solved. I recommend publication."}, "author_response": "We appreciate the reviewer for the positive comments. We have accepted them and seriously revised the manuscript."}]

Decision letter