Introduction

Hydrogen peroxide (H2O2), regarded as a versatile and valuable chemical, presents widespread applications across environmental purification, paper bleaching, biomedical and pharmaceutical applications, industrial chemical synthesis, and clean fuel evolution1,2,3,4. Currently, the primary industrial method for H2O2 production is through the anthraquinone process (AO), which involves several challenges, including substantial energy consumption and risks associated with storage and transportation5,6. These limitations drive the search for alternative routes that are energy-efficient, environmentally benign, and suitable for on-demand, decentralized generation. Piezocatalysis has recently attracted growing attention as such an approach, offering inherently green operation and high reaction efficiency7,8. Similar to artificial photosynthesis—where photoexcitation generates electron–hole pairs that are separated by internal electric fields and directed to distinct catalytic sites—mechanically activated piezoelectric materials produce polarization fields and built-in piezoelectric potentials that drive the spatial separation of mechanically induced charge carriers. In this process, electrons migrate to reduction-favored sites to perform the oxygen reduction reaction (ORR), while holes migrate to oxidation-favored sites to carry out the water oxidation reaction (WOR), collectively enabling H2O2 formation9,10.

Bi4Ti3O12 (BTO), a widely studied piezoelectric material, consists of regularly stacked [Bi2O2]2+ layers alternating with perovskite‑like [Bi2Ti3O10]2−units11,12,13,14,15. Its favorable band structure, high piezoelectric response, and intrinsic ferroelectric polarization make it a promising candidate for piezocatalytic H2O2 generation16,17. However, large‑scale application is hindered by intrinsic limitations, including rapid recombination of piezo‑generated electron–hole pairs, a low density of catalytically active sites, and inefficient transport of piezo‑induced carriers18. Various modification strategies—including heterostructure construction, noble‑metal loading, and the use of sacrificial agents—have been investigated to promote carrier transport and reduce recombination losses19,20,21,22. While heterostructures with staggered energy levels can facilitate interfacial charge separation, and noble metals or sacrificial agents can act as efficient electron or hole acceptors, these approaches do not adequately address bulk recombination, which occurs on ultrafast timescales (picoseconds to nanoseconds). This fundamental limitation severely restricts carrier utilization for O2 activation and suppresses overall H2O2 productivity. Overcoming these constraints requires strategies that concurrently strengthen bulk polarization fields and improve interfacial charge extraction, enabling precise spatial control of carrier pathways to prolong lifetimes, optimize energy-level alignment, and enhance O2 activation kinetics.

Iodine (I), a non‑metallic halogen dopant, offers abundant valence electrons, environmental benignity, and the ability to modulate the electronic structure of catalysts, making it an attractive candidate for bulk modification and as a mild Lewis acid23,24. With a higher electronegativity (2.66) than B (2.04), S (2.58), and P (2.19), iodine can enhance electrical conductivity by forming charge-transfer complexes with the host lattice25,26. Iodine doping has been shown to narrow the bandgap of functional materials, suppress bulk carrier recombination, and improve polarization strength27,28. In addition, its multiple accessible redox states enable valence‑state transformations during operation, while its relatively large atomic radius favors substitution or adsorption at lattice edges and defect sites, potentially increasing surface area and exposing more active sites29. However, excessive doping can distort the crystal lattice and introduce recombination centers, diminishing piezocatalytic efficiency. To complement bulk charge separation, surface modification with an electron‑accepting cocatalyst, such as MXene can increase surface electron density and accelerate reduction‑reaction kinetics30,31. The integration of iodine‑induced bulk polarization enhancement with MXene‑based interfacial electron sinks thus offers a dual‑field approach—combining built‑in and external electric fields—to simultaneously mitigate bulk recombination and overcome surface kinetic limitations.

Given the persistent challenges of ultrafast bulk recombination and the scarcity of surface-active sites in single-phase BTO, we designed a catalyst architecture that integrates halogen heteroatom doping with cocatalyst surface engineering to target both bulk and interfacial limitations. Specifically, iodine doping strengthens the internal polarization field within the BTO lattice, enhancing hole localization, suppressing bulk electron–hole recombination, and accelerating water oxidation kinetics. In parallel, coupling MXene nanosheets onto the surface creates an efficient interfacial electron sink, increasing surface electron density, facilitating carrier transport, and boosting ORR activity. This dual-modification strategy—combining bulk polarization enhancement with interfacial charge-extraction capability—optimizes both charge separation and utilization, thereby enabling high-rate, selective piezocatalytic H2O2 generation. Such a design provides a robust framework for overcoming intrinsic performance bottlenecks in piezoelectric catalysts.

To realize this design strategy, we designed an iodine-doped Bi4Ti3O12 catalyst coupled with surface-anchored MXene nanosheets (denoted as MBTO-I). The optimized MBTO-I achieved a piezocatalytic H2O2 production rate of 98.17 μmol g−1 min−1 under ambient conditions without sacrificial agents, surpassing the performance of most reported piezoelectric materials. Combined analyses from theoretical calculations, piezoelectric electrochemical impedance spectroscopy, and current–voltage measurements via conductive atomic force microscopy (CAFM) reveal that iodine doping strengthens the bulk polarization field and suppresses carrier recombination, while MXene coupling functions as an interfacial electron sink, increasing surface electron density and enhancing O2 adsorption and activation. This configuration preserves a larger fraction of piezo-generated electrons for reaction, accelerates water oxidation kinetics, and improves ORR activity. The catalyst exhibits excellent stability and reusability, with the generated H2O2 effectively applied to bacterial sterilization and degradation of representative organic pollutants. Furthermore, chemical analyses and biological assays confirmed substantial reductions in the toxicity of sulfamethoxazole (SMX) degradation products. These findings demonstrate that integrating bulk polarization enhancement with interfacial charge-extraction provides an effective route to overcome the intrinsic limitations of single-phase piezocatalysts.

Results

Catalyst design rationale

Figure 1a displays a schematic illustration of the MBTO-I system. Pristine BTO faces the challenges of weak intrinsic piezoelectric response, insufficient number of piezo-generated electrons and low carrier transportation, which collectively constrain its piezocatalytic efficiency. Our work addresses these limitations through the combined strategy of nonmetal elemental doping and cocatalyst loading. Specifically, iodine was chosen as a dopant to substitute oxygen in BTO, while MXene nanosheets were loaded onto the catalyst surface to form the MBTO-I system. This catalyst architecture design achieves enhanced polarization field, bulk/surface separation and transportation of carriers, as well as the superior redox ability (MBTO was shown in Supplementary Fig. 1). As shown in Fig. 1b, iodine element introduction and MXene loading can effectively enhance activation of O2. The ICOHP results further show that iodine introduction can reduce the interaction between BTO and *OOH intermediates, thereby stabilizing the O–OH bond and facilitating the generation of H2O2 (Fig. 1c). This conclusion is also confirmed in the electron localization function analysis, in which gradual shortening of the O–OH bond length in *OOH is observed in the designed samples (Fig. 1d). Meanwhile, introducing iodine and MXene cocatalyst can move the d-band center of Ti 3d orbital of pristine BTO downward, which will be beneficial for the water oxidation reaction (Fig. 1e). Specifically, the interaction between BTO and *OH intermediates in MBTO-I sample can be effectively reduced according to the ICOHP results, which can stabilize the O–H bond and inhibit the four-electron water oxidation process (Fig. 1f). The gradual shortening of the O–H bond in the electron localization function analysis further supports the above conclusion (Fig. 1g). These combined features are highly advantageous for boosting the piezocatalytic production of H2O2 under ambient conditions (Fig. 1h). As we hypothesized, the designed MBTO-I catalyst exhibits a superior piezocatalytic H2O2 evolution performance. It is noteworthy that substituting BTO with BiVO4, ZnO, or BaTiO3 to form MBiVO4-I, MZnO-I, and MBaTiO3-I also enables highly enhanced H2O2 evolution performance (Fig. 1i and Supplementary Figs. 2–5), indicating the general applicability of the design of I doping and MXene coupling.

Fig. 1: Catalyst design and modeling.
Fig. 1: Catalyst design and modeling.The alternative text for this image may have been generated using AI.
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a Schematic representation of the material design for MBTO-I. b–d Orbital and electron localization analysis of the oxygen reduction and e–g water oxidation processes of pristine BTO, BTO-I, and MBTO-I, respectively. h Schematic diagram of piezocatalytic H2O2 production towards as-prepared MBTO-I under ambient conditions. i Universal experiments of other piezoelectric materials in producing H2O2. Source data are provided as a Source data file.

Catalyst synthesis and characterization

The designed MBTO-I was prepared by high-temperature calcination and a two-step room-temperature stirring method (Fig. 2a). Specifically, pristine BTO was obtained through the calcination of a mixture including Bi2O3, P25, NaCl, and KCl. The modified BTO-I sample was achieved through the dipping method, while the ultrathin MXene nanosheet was synthesized by a stripping strategy. The optimized MBTO-I sample can be obtained through the room-temperature self-assembly approach. The morphology and structure of as-prepared catalysts are firstly characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Pristine BTO exhibits an irregular nanosheet morphology, and the structure remains unchanged after iodine doping in BTO (Fig. 2b, c, and Supplementary Figs. 6–8). Raman spectra are tested to confirm the successful iodine doping in BTO. The result shows that the vibration modes at 117 and 272 cm−1 are weakened with iodine element grafting (Fig. 2d)32. Pristine MXene displays a mono-layer nanosheet structure while our optimized MBTO-I catalyst exhibits a sheet stacking structure (Fig. 2e, f, and Supplementary Fig. 9). The crystal facet with spacings of 0.27 and 0.23 nm is ascribed to the crystal face of the BTO (020) and Ti3C2 (103), respectively (Fig. 2g)15,33. The elemental mapping images reveal the titanium (Ti), oxygen (O), bismuth (Bi), iodine (I), and carbon (C) are evenly distributed throughout the MBTO-I catalyst, confirming the homogeneous distribution (Fig. 2h). The composition and chemical states of the prepared catalysts are further investigated through X-ray diffraction spectroscopy (XPS). The peaks detected at 159.5 and 164.8 eV in the Bi 4f spectra are ascribed to Bi 4f7/2 and Bi 4f5/2, respectively (Fig. 2i). The peak detected at 458 eV is ascribed to Ti 2p3/2 and the binding energy of Ti 2p for MBTO-I displays a remarkable shift to high energy compared with that of pristine BTO and BTO-I, indicating the change in the chemical states of Ti atoms (Fig. 2j). For O 1s spectra, no significant change is detected in BTO sample while the binding energy of O 1s shifts towards higher energy in MBTO-I sample, indicating strong electronic interaction exists between BTO-I and MXene (Supplementary Fig. 10). The I 3d peaks for BTO-I and MBTO-I exhibit characteristic peaks at 619.1 and 630.6 eV, corresponding to the orbitals of I 3d5/2 and I 3d3/2 of I− (Fig. 2k)34. Notably, compared with pristine BTO, the binding energies of Bi 4f, Ti 2p and O 1s in MBTO-I are shifted to higher values, suggesting that MXene accepts negative charges and that a strong interaction exists between BTO and MXene. XRD patterns exhibit that the structure of BTO is retained after MXene coupling and iodine doping, suggesting that elemental doping and cocatalyst loading will not destroy the basic structure of BTO (Supplementary Fig. 11). The optimized MBTO-I catalyst exhibits an outstanding piezocatalytic H2O2 evolution performance, as discussed below.

Fig. 2: Surface morphology and chemical composition.
Fig. 2: Surface morphology and chemical composition.The alternative text for this image may have been generated using AI.
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a Schematic diagram for sample preparation. TEM images of b pristine BTO, c BTO-I, d Raman spectra of pristine BTO and BTO-I. TEM images of e MXene and f MBTO-I. g HRTEM image of MBTO-I. h EDS-mapping of MBTO-I. XPS spectra of i Bi 4f, j Ti 2p and k I 3d. Source data are provided as a Source data file.

Piezocatalytic H2O2 production performance

The piezocatalytic performance of the samples for H2O2 production was assessed without any sacrificial agents under pure water and air conditions (Fig. 3a). The optimized MBTO-I catalyst achieves a superior H2O2 yield (327.25 μM), far exceeding than that of pristine BTO (30.43 μM), BTO-I (216.59 μM), MBTO (252.69 μM) and MXene (32.31 μM), respectively. Control experiments including different loadings of MXene, iodine element doping and pH of reaction solution are further investigated (Supplementary Figs. 12–15). The results exhibit that the H2O2 yield can achieve the highest in the optimized MBTO-I catalyst with 50 μM KI solution and 1 mL MXene solution under air condition and solution pH of 5. Meanwhile, the optimized MBTO-I exhibits a similar H2O2 yield under different water quality, suggesting that our designed piezocatalyst has the potential to apply in the real water (Fig. 3b). Cycling experiments and catalyst characterizations before and after piezocatalytic reaction are tested to confirm the superior stability of the as-prepared catalyst (Fig. 3c and Supplementary Figs. 16, 17). The piezocatalytic H2O2 performance obtained in this work exceeds most of the previously published research works (Fig. 3d and Supplementary Table 1)7,9,21,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50.

Fig. 3: Piezocatalytic performance of catalyst.
Fig. 3: Piezocatalytic performance of catalyst.The alternative text for this image may have been generated using AI.
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a Piezocatalytic H2O2 evolution of as-prepared samples. b Piezocatalytic H2O2 evolution of optimized MBTO-I under different water quality. c Cycling tests of piezocatalytic H2O2 evolution over MBTO-I. d Performance comparison of the piezocatalytic H2O2 evolution rates of previous works. e Quenching experiments of piezocatalytic H2O2 evolution on MBTO-I. DMPO spin-trapping ESR spectra for f •O2− in methanol and g •OH in water of BTO and MBTO-I, respectively. h H2O2 selectivity at different potentials of BTO and MBTO-I. i The energy band structure of BTO and BTO-I. j, k Schematic diagram of MBTO-I towards H2O2 production through the ORR and WOR pathways using piezoelectric catalysis. The error bars were obtained based on three independent piezocatalytic experiments. Source data are provided as a Source data file.

Quenching experiments and the electron spin resonance (ESR) technique are measured to investigate the mechanism of H2O2 generation. A substantial decrease of H2O2 yield is observed when adding p-benzoquinone (P-BQ) as the trapping agent of •O2− (Fig. 3e). This suggests that •O2− is the main active specie in the piezocatalytic generation of H2O2 by MBTO-I. When Mn(AC)3 is used as an electron scavenger, the yield of H₂O₂ is decreased significantly, indicating that the piezoelectric catalytic production of H₂O₂ by MBTO-I is a dual-channel process dominated by oxygen reduction and assisted by water oxidation51. In general, there are two ways to produce H₂O₂ through water oxidation: the direct route (2H2O + 2 h+→ H2O2 + 2H+) and the indirect route (H2O + h+→ OH + H+, 2•OH → H2O2). When introducing tert-butanol (TBA) as the •OH trapping agent, a decrease of H2O2 yield is detected and it suggests that the WOR process can generate H2O2 through the indirect route38. Further combination of TBA and Mn(AC)3 observe that a small amount of H2O2 is still generated, indicating that the water oxidation pathway involves both direct and indirect pathways. The higher ESR signals of both •O2− and •OH in MBTO-I catalyst indicate that iodine doping and cocatalyst loading can effectively improve the piezoelectric carrier transportation and enhance the ORR and WOR reaction (Fig. 3f, g). Additionally, considering H₂O₂ can also be generated via a non-radical pathway (1O2 + 2 h+ + 2H+ → H2O2), we further detected the presence of 1O2 through ESR analysis (Supplementary Fig. 18a). However, quenching experiments using L-tryptophan revealed that 1O2 contributes minimally to H2O2 production (Supplementary Fig. 18b). The yield of H2O2 (5.23 µM) is almost negligible without the addition of a catalyst, indicating that H2O2 is produced by the piezocatalyst under piezoelectric driving force (Supplementary Fig. 19). The electron transfer numbers and H2O2 selectivity are determined by rotating ring-disk electrode (RRDE) polarization curves (Fig. 3h and Supplementary Fig. 20). The electron transfer number of MBTO-I is close to 2 and the H2O2 selectivity value of MBTO-I is up to 95%, suggesting its 2e− oxygen reduction reaction.

The optical band gaps of BTO and BTO-I are calculated to be 3.28 and 3.22 eV, respectively, while XPS valence band spectra of BTO and BTO-I were conducted as well (Supplementary Figs. 21–23). According to the equation Evb = Φ + Evb-xps−4.44 eV (where Φ is the work function of the XPS instrument, 4.40 eV), the positions of the valence bands (VBs) of BTO and BTO-I are determined to be 2.04 and 1.88 V (with respect to the NHE), respectively52. Based on the above, the energy band structures of as-prepared samples are obtained, and it can be noted that all prepared samples can meet the theoretical potential requirements for H2O2 production by ORR and WOR (Fig. 3i). In our designed MBTO-I catalyst system, MXene cocatalyst is considered as a main reduction site with accumulated piezo-generated electrons, while iodine element doping into BTO can enhance the water oxidation reaction kinetics and suppress the bulk recombination of piezogenerated carriers, thus spontaneously contributing to improving the ORR and WOR. The detailed dual-channel piezocatalytic H2O2 process is illustrated in Fig. 3j, k. The properties of prepared samples and enhanced mechanism of H2O2 production are described as follows.

Piezoelectric properties

The piezoelectric effect caused by the piezoelectric crystal under the action of mechanical forces is investigated through the first-principles calculations based on density functional theory (DFT). Structural models of pristine BTO, BTO-I and MBTO-I under 0 and 5% strain conditions are displayed in Fig. 4a. The dipole moments of pristine BTO, BTO-I and MBTO-I unit cells under 5% strain are provided to investigate the effect of iodine element doping and MXene cocatalyst loading on polarization enhancement (Fig. 4b). The results show that the unit dipole moment of MBTO-I increases to 0.512 eÅ, which is 2.28 and 1.90 times as that of pristine BTO (0.225 eÅ) and BTO-I (0.269 eÅ), confirming the improvement of polarization by iodine doping and MXene loading. Additionally, the total charge transfer and Bader charge of the detailed atomic layers for pristine BTO, BTO-I, and MBTO-I are provided, and the results further confirm that iodine element doping and MXene cocatalyst can be beneficial for enhancing the polarization effect (Fig. 4c–g).

Fig. 4: Piezoelectric properties of catalysts.
Fig. 4: Piezoelectric properties of catalysts.The alternative text for this image may have been generated using AI.
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a Structural models of BTO, BTO-I and MBTO-I under 5% strain condition. b The dipole moments and c the total charge transfer of BTO, BTO-I, and MBTO-I with 0 and 5% strain condition. d The models of BTO and BTO-I divided into several strips under 5% strain condition. e–g The charge transfer and Bader charge of detailed atomic layers for BTO, BTO-I and MBTO-I. Source data are provided as a Source data file.

To clarify the intrinsic roles of iodine doping and MXene loading on promoting H2O2 evolution, electrochemical tests are further measured. As-prepared MBTO-I displays the lowest semicircular Nyquist plot radius in comparison to pristine BTO and BTO-I, respectively, suggesting that a lower electron transfer resistance existing in MBTO-I catalyst (Fig. 5a). Compared with pristine BTO and BTO-I, MBTO-I exhibits a higher current intensity both in the negative/positive sweep LSV current curves, indicating that iodine element doping and MXene cocatalyst loading can enhance the ORR and WOR kinetics of BTO (Fig. 5b, c). Piezoresponse force microscopy exhibits that all the prepared catalysts display well-formed amplitude–voltage butterfly curves under tip bias (Fig. 5d–f and Supplementary Figs. 24–26). Meanwhile, the absolute value of piezoelectric slope derived from amplitude curves for MBTO-I (179.0 pm/V) further confirms a higher piezoresponse compared to pristine BTO (128.4 pm/V) and BTO-I (167.1 pm/V), respectively, indicating a robust driving force and strong piezoelectricity in MBTO-I for the piezocatalytic reaction53. The local currents of the prepared BTO and MBTO-I catalysts are investigated using conductive atomic force microscopy (CAFM) in contact mode by controlling the mechanical force (Fig. 5g, h). The current of MBTO-I is significantly changed with increasing force in comparison to pristine BTO, indicating that MBTO-I has a more pronounced mechanical force response and generates sufficient charges when a force is applied (Fig. 5i–k). COMSOL Multiphysics of pristine BTO, BTO-I, and MBTO-I are further used to simulate the correlation between mechanical forces and piezoelectric responses. The results show that MBTO-I exhibits a higher piezoelectric potential generated by iodine element doping and MXene loading under the action of lateral force (Supplementary Fig. 27). These findings imply that the interaction between MXene and BTO-I improves the piezoelectric output of the catalyst.

Fig. 5: Piezoelectrochemistry and piezoelectric properties.
Fig. 5: Piezoelectrochemistry and piezoelectric properties.The alternative text for this image may have been generated using AI.
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a Piezoelectric electrochemical impedance spectroscopy of BTO, BTO-I, and MBTO-I under ultrasonic condition. Negative sweep LSV current curves (b) and positive sweep LSV current curves (c) of BTO, BTO-I, and MBTO-I under ultrasonic condition. Butterfly amplitude loop and phase curves of d BTO, e BTO-I, and f MBTO-I. Mapping images of piezoelectric current response of g BTO and h MBTO-I. Current–voltage (I–V) measured i BTO and j MBTO-I by CAFM. k Corresponding peak fitting from CAFM. Source data are provided as a Source data file.

Density functional theory calculations

Density functional theory calculations are provided to investigate the piezocatalytic mechanism of H2O2 evolution. Through PDOS analysis of the electronic structure of BTO, its valence band is mainly contributed by the orbitals of O, while the conduction band is contributed by the orbitals of Ti. The introduction of I does not significantly change the bandgap of BTO, which is consistent with the results of the ultraviolet-visible absorption spectrum. However, for MBTO-I, the excellent conductivity of MXene endows BTO with metallic properties, enabling the generation of more piezoelectric carriers and free electrons, thereby enhancing catalytic activity. (Supplementary Figs. 28–30). The energy difference between the vacuum and Fermi levels can be estimated based on the electrostatic potential. We calculated the theoretical work functions of pristine BTO, BTO-I and MBTO-I to be 6.3, 6.5, and 4.9 eV, respectively (Fig. 6a–c). This means that iodine element doping can make the Fermi level of BTO move downward, and the work function difference becomes obvious, which can create a stronger internal electric field between BTO-I and MXene. The charge density distribution between BTO-I and MXene exhibits that the electron accumulation area is in BTO and the consumption area is in MXene, indicating that iodine element doping contributes to the WOR while MXene introduction is beneficial for the ORR (Fig. 6d). Subsequent theoretical calculations of adsorption energies for H₂O and O₂ revealed that the active sites for WOR are located at the Ti sites of BTO, while those for ORR are at the Ti sites of MXene (Supplementary Figs. 31 and 32). The O2 adsorption energy on MBTO-I (−2.74 eV) is larger than that on BTO (−1.69 eV) and BTO-I (−1.96 eV), at the same time, MBTO-I and O2 have the highest number of electron transfers, which suggests that MXene loading and iodine element doping can effectively enhance O2 and H2O adsorption (Fig. 6e). The Gibbs free energies of ORR on BTO, BTO-I, and MBTO-I are further calculated and the results show that: compared with pristine BTO (−0.34 eV) and BTO-I (−0.52 eV), MBTO-I (−0.91 eV) catalyst exhibits the strongest thermodynamically favorable reaction in the O2 → *OOH process while also possessing the lowest H₂O₂ desorption energy (0.12 eV) (Fig. 6f). For the WOR reaction, the Gibbs free energy for the adsorption of two water molecules on the catalyst surface to form one H2O2 molecule was calculated. The results indicate that compared with pristine BTO, BTO-I exhibits lower energy for the formation of *OH and H2O2. (Fig. 6g). This suggests that iodine element doping improves the water oxidation kinetics of pristine BTO, theoretical calculations of electron transfer numbers and piezoelectric catalytic experiments further confirm the above conclusions (Supplementary Figs. 33 and 34). To investigate the fundamental reason for WOR enhancement, PDOS calculations are further performed for Ti (in BTO) and O (in *OH) (Fig. 6h–j). The results indicate that the introduction of I and MXene can gradually reduce the d-band center of Ti, thereby increasing the electron occupancy of antibonding states after Ti site and O site of *OH intermediate interaction (Fig. 6k–m). This ultimately weakens the interaction of *OH on Ti, which is beneficial for stabilizing the bond of *O–H intermediate and promoting the H2O2 formation According to the results of the Gibbs free energy diagram, compared with pristine BTO and BTO-I, the optimized MBTO-I has the most favorable ORR production activity. Based on the above, iodine element doping and MXene loading can effectively activate O2 and form H2O2, accelerate the water oxidation kinetics, thus achieving high H2O2 evolution performance.

Fig. 6: Theoretical calculation analysis.
Fig. 6: Theoretical calculation analysis.The alternative text for this image may have been generated using AI.
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Electrostatic potentials of a BTO, b BTO-I, and c MXene. d Electronic distribution at the interface of MBTO-I. e Oxygen adsorption energy. f Gibbs free energy of H2O2 production of BTO, BTO-I and MBTO-I and g Gibbs free energy of H2O2 production by WOR in BTO and BTO-I. h–j PDOS of Ti (in BTO) and O (in *OH) in BTO, BTO-I, and MBTO-I, respectively. k–m Diagram illustrating d-band to increase the antibonding occupancy to weaken Ti–Oads bonds. Source data are provided as a Source data file.

Demonstration of downstream applications of generated H₂O₂

To evaluate the potential real applications of produced H2O2 through the piezocatalytic process, we conducted antimicrobial properties and different pollutants degradation tests. The results show that the H2O2 collected from experiments of MBTO-I exhibits direct inactivation of bacteria with 100 % efficiency and superior degradation rate constants towards various classical pollutants (Fig. 7a, b). It also eliminates the antibacterial effect of the catalyst itself (Supplementary Fig. 35). The degradation products of SMX were characterized by LC-MS, and the chromatographic fragments of the products were identified through peak analysis. Based on the variations in m/z and the previous literatures, possible degradation pathways of SMX are provided in Fig. 7c. Firstly, cleavage of the HN–SO2 bond produces P1 (m/z = 98) and P2 (m/z = 157). Subsequently, P1 undergoes hydroxyl radical attack to generate P3 (m/z = 114). On this pathway, the amino-group of P3 was attacked to form P5 (m/z = 112), which is further oxidized to nitro-containing P7 (m/z = 128). Ultimately, P7 loses the nitro group to form P8 (m/z = 83). In parallel, the amino group on the benzene ring of P2 may be removed to yield P4 (m/z = 142), or its sulfone group can be replaced by a hydroxyl group to form P6 (m/z = 109). P6 then undergoes ring opening to generate P9. In addition, SMX’s isoxazole ring opens to produce P10 (m/z = 215), while C–S bond cleavage on its benzene ring generates P11 (m/z = 178) and P12 (m/z = 162). Ultimately, all byproducts are degraded through hydroxylation, aromatic ring epoxidation, and complete mineralization. Considering the intermediate degradation cannot be precisely quantified, and interactions may occur, model biotoxicity experiments are provided to investigate the toxicity changes. Specifically, we used zebrafish as a model organism to re-evaluate the toxicity of degradation solutions54. Zebrafish embryos (24 h post-fertilization, hpf) were exposed to degradation solutions, and their malformations were monitored (Fig. 7d). Zebrafish cultured in SMX solution exhibited severe growth abnormalities and mortality, whereas those in SMX-D solution showed growth patterns nearly identical to the control group. Survival and hatching rates were further quantified (Fig. 7e). Compared to the control group, no significant differences were observed in survival or hatching rates among zebrafish exposed to SMX-D solution. Additionally, the movement trajectories of 120 hpf zebrafish were monitored using a zebrafish behavior monitoring system (Fig. 7f–h). Under alternating light-dark cycles (switching every 10 min), the movement trajectories and locomotion rates of zebrafish were continuously monitored for 20 min. Zebrafish cultured in SMX solution exhibited sparse movement trajectories, indicating that the toxic changes impaired locomotor function. In contrast, the behavior of zebrafish cultured in SMX-D solution was consistent with the blank group, demonstrating that the toxicity of SMX-D degradation products is negligible. Furthermore, we investigated the condition of mung bean sprouts cultured by the degraded tetracycline hydrochloride (TC) solution and piezocatalytic degradation of TC solution  through optimized MBTO-I encapsulated in hydrogel (Supplementary Figs. 36–39). The results indicate that the MBTO-I piezocatalytic system shows effective sterilization property and has the potential to large-scale degradation.

Fig. 7: Application potential analysis.
Fig. 7: Application potential analysis.The alternative text for this image may have been generated using AI.
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a Antimicrobial properties of H2O2 production via MBTO-I. b Degradation efficiency of different pollutants and c the possible degradation pathways of SMX towards MBTO-I. d Growth of zebrafish cultured in the different solution. e The zebrafish hatching. f Zebrafish swimming trajectory g distance and h speed in 20 min light from the darkness alternating. SMX Sulfamethoxazole solution, SMX-D Sulfamethoxazole solution after degradation. The error bars were obtained based on three independent piezocatalytic experiments. Source data are provided as a Source data file.

Discussion

To sum up, the integration of MXene nanosheets with iodine atom-doped Bi4Ti3O12 (MBTO-I) successfully achieves synchronous separation and transfer of carriers, resulting in enhanced piezocatalytic performance. The optimized MBTO-I catalyst displays a superior H2O2 production rate of 5890 µmol g−1 h−1 in pure water without any sacrificial agents, outperforming most reported piezocatalysts. Piezoelectric electrochemical impedance spectroscopy and conductive atomic force microscopy reveal that the enhanced piezocatalytic performance stems from efficient bulk carrier separation and transportation of abundant piezo-generated electrons induced by enhanced internal polarization field and external electric field. Additionally, theoretical calculations confirm the pivotal roles of iodine element and MXene in facilitating the H2O2 production through the oxygen reduction and water oxidation reaction in BTO. This work establishes a robust approach for overcoming intrinsic bulk and surface limitations in piezoelectric catalysts, offering design principles for next-generation piezocatalytic systems for sustainable H2O2 production and environmental remediation.

Methods

Chemicals and materials

Bismuth oxide (Bi2O3·, 99%), P25 (99%), Sodium Chloride (NaCl, 99%), Potassium Chloride (KCl, 99%) para-benzoquinone (p-BQ, 99.5%), potassium hydrogen phthalate (99.8%) and absolute ethanol were purchased from Macklin Biochemical Technology Co., Ltd. phosphate buffer (pH = 7.0), tert-butyl alcohol (TBA, 99.5%), manganese acetate dihydrate (MnAC3. 2H2O, 97%), potassium iodide (KI, 99%), methanol (MeOH) and lithium fluoride (LiF) were purchased from Aladdin Biochemical Technology Co., Ltd. All purchased chemicals were used directly without any purification.

The synthesis of Bi4Ti3O12 (BTO)

Typically, 5 mmol Bi2O3, 7.5 mmol P25, 0.1 mol NaCl and 0.4 mol KCl are mixed evenly and ground thoroughly. The thoroughly ground sample was then placed in a muffle furnace and heated at a rate of 5 °C/min to 750 °C, where it was maintained for 6 h. After cooling naturally, it was removed and centrifuged multiple times with deionized water to thoroughly remove inorganic salts.

The synthesis of iodine-doped Bi4Ti3O12 (BTO-I)

A series of BTO-I samples were synthesized by treating BTO in the KI solutions with different concentrations. 0.2 g BTO and KI solution (30 mL) were stirred at room temperature for 24 h and then washed with deionized water repeatedly, and finally dried at 60 °C for 12 h. The concentrations of KI were set to 0.025, 0.05, 0.1, and 0.2 M in the reaction solution.

The synthesis of iodine and MXene-doped Bi4Ti3O12 (MBTO-I)

One hundred milligrams of BTO-I (0.05 M KI) were added in 30 ml of anhydrous alcohol, dispersed well in a beaker and then X ml (X = 0.5, 1, 2) of MXene solution was added in it. The preparation method of MXene is based on previous work33. The mixed solution is stirred for 24 h at room temperature. The product is also collected by centrifugation, washed three times with DI water and anhydrous ethanol, and then dried under vacuum at 30 °C overnight.

Characterization

The crystal structure is revealed by the powder X-ray diffraction (XRD) on a Bragg-Brentano diffractometer (D8-tools, Germany) equipped with a Cu Kα source, and the scanning region was from 10° to 80°. The morphology of the samples was from a field emission scanning electron microscope (FESEM) (Hitachi, SU8010, Japan). The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) images were acquired by a JEOLJEM-2100F (UHR) field emission transmission electron microscope. X-ray photoelectron spectroscopy (XPS) was performed on a Thermo ESCALAB 250Xi instrument with Al KαX-ray radiation. For XPS data fitting: spectra were recorded and analyzed using Thermo Avantage software, which were calibrated according to the binding energy of C 1s (284.8 eV) of adventitious carbon. A Shirley-type background subtraction was performed prior to peak fitting. Nonmetallic peaks (oxides, hydroxides) were modeled with a fixed 30/70% Lorentzian/Gaussian peak shape. Peaks corresponding to the metallic state have been modeled with an asymmetric peak mimicking the shape of the Doniach-Sunjic line. During the fitting process, the full width at half-maximum of all peaks were constrained to vary within a small range (±0.05 eV) of the reference spectra values. FTIR data were recorded by a PerkinElmer Frontier Transform spectrometer. The UV–visible absorption spectra of the samples were obtained by UV–vis spectrophotometer (Shimadzu, UV-2550, and Japan). Electron spin resonance (ESR) analysis was performed using electron spin resonance spectrometer (Jeol/JES-FA200). The piezoelectric force microscopy (PFM) and conductive atomic force microscopy (CAFM) of as-prepared samples were analyzed by atomic force microscope (AFM) equipped with relevant modules.

Piezocatalytic H2O2 production

Piezocatalytic H2O2 production was carried out under pure water and air conditions without any sacrificial agents: a conventional ultrasonicator is used for piezoelectric catalytic production of H2O2. The reactor is a 50 ml Schlenk tube, located in the center of vibration of the ultrasonic machine (6 cm from the edge and 2 cm from the bottom, the depth of the water level is 10 cm, and the temperature of the water bath is 15 °C unless otherwise indicated, controlled by circulating water cooling. Unless otherwise specified, the reaction time for all piezoelectric catalytic H2O2 production is 20 min. Specifically, 5 mg of catalyst was dispersed in 30 mL of pure water and placed in an ultrasonic cleaner (40 kHz, 100 W, LICHEN, China). The generation of H2O2 was investigated by iodometry, specifically, 1 mL of the solution removed from the reactor was added to 1 mL of 0.4 M aqueous potassium iodide (KI) and 1 mL of 0.1 M aqueous potassium hydrogen phthalate, the solution was then analyzed using a UV–visible spectrophotometer at 350 nm. The pH of the solution is adjusted using 0.1 M HCl or NaOH. For the cycling test: MBTO-I inevitably undergoes mass loss during piezoelectric catalytic experiments and collection processes. To ensure the use of the same amount of catalyst (5 mg) in each cycle, the following method was employed for the cycling test. MBTO-I samples (approximately 200 mg) were suspended in 50 mL of pure water, and sonicated for 20 min. The solid was collected by filtration and thoroughly washed with ultrapure water. The resulting solid powder was dried under vacuum at 60 °C for 12 h. Subsequently, 10 mg of MBTO-I was used for the second cycle test. This process was repeated for the third, fourth, and so on, up to the sixth cycle.

In addition, antimicrobial experiments were applied, Rhodospirillum, Alcaligenes and Escherichia coli as model organisms and cultured on nutrient agar plates using sterile petri dishes. Subsequently, the bacterial concentration was controlled at 103 CFU mL−1 with PBS, and then 2 mL H2O2 from piezocatalytic experiments was added to 1 mL of bacteria suspension and mixed thoroughly. Finally, the solution (3 mL) was added to the nutrient agar and incubated at 37 °C for 24 h. For degradation tests, 20 mg of catalyst was added to 30 ml of pollutant solution (10 mg L−1). The absorbance spectra of the supernatant obtained after centrifugation were characterized using UV–vis spectrophotometer to determine the concentration of the target pollutant. For the preparation of hydrogels, 1.2 g of acrylamide powder (AM), 4 mg of ammonium persulfate, and 8 mg of N,N-methylenebis(acrylamide) and 10 μL of N,N,N’,N’-tetramethylethylenediamine (TEMED) were dissolved in 4 mL of deionized water. Then, 4 mg of catalyst was added to the solution and vigorously stirred until uniformly dispersed. Subsequently, the mixed dispersion was poured into an acrylic mold and polymerized under 365 nm UV irradiation for 5 min. Finally, the mold was removed to obtain the catalyst-embedded PAM hydrogel. The final dimensions: 1.1 cm (diameter) × 2 cm (Height).

Toxicity assessment experiment

Zebrafish embryos from Nanjing EzeRinka Biotechnology Co., Ltd. were used to investigate the toxicity of the degraded sulfamethoxazole (SMX). Randomly selected 24 h post fertilization (hpf) zebrafish embryos were divided into three groups, including ultrapure water (blank), SMX (10 mg/L), and SMX degraded for 180 min. All groups consisted of three parallel replicates conducted simultaneously. Each treatment group contained 15 embryos and 10 mL of exposure solution. The exposure solutions were renewed daily and maintained at pH 7.6 ± 0.1, and dead embryos were removed in time during the exposure experiment. The exposure was completed in an illumination incubator at a temperature of 28 ± 1 °C with a 14:10 h light:dark photoperiod. The hatching and mortality rates were recorded at 48, 72, and 120 hpf, respectively. After the exposure experiment, all zebrafish were transferred to clean water for recovery. Four zebrafish (120 hpf) were randomly selected from each treatment, and their movement trajectories under alternating 20-min light and dark conditions were recorded by a ZebraBox zebrafish behavioral system (ViewPoint Behaviour Technology, Lyon, FR).

The rotating ring disk electrode (RRDE) measurement

RRDE test was used to evaluate the number of transferred electrons (n) and H2O2 selectivity in the ORR reaction. The RRDE tests were conducted in an O2-saturated phosphate buffer (pH = 7.0) solution with a rotating speed of 1600 rpm. The number of transferred electrons (n) is calculated according to the following formula:

$$n=4\times \frac{{I}_{d}}{{I}_{d}+\frac{{I}_{r}}{N}}$$
(1)

The selectivity of H2O2 is calculated by the following formula:

$${H}_{2}{O}_{2}\%= 2\times \frac{\frac{{I}_{r}}{N}}{{I}_{d}+\frac{{I}_{r}}{N}}\times 100\%$$
(2)

where Ir is the ring current, Id is the disk current, and N is the collection efficiency (N = 0.256).

Computational methods

All spin-polarized density functional theory (DFT) calculations were performed with the plane−wave basis set as implemented in the Vienna ab initio simulation package (VASP, version number: 5.4.4)55,56, and the electrons and ions interactions were described by the projector augmented wave (PAW) potential57,58. The exchange–correlation interactions were determined by the Perdew–Burke–Ernzerhof (PBE) functional within the generalized gradient approximation (GGA)59. The plane wave energy cutoff of 500 eV, and the convergence criterion for the residual force and energy was set to 0.01 eV Å−1 and 10-6eV, respectively. The empirical correction in Grimme’s method (DFT + D3) was used to describe the van der Waals (vdW) interactions60. The Brillouin region was sampled by the Monkhorst-Pack method with a 6 × 6 × 1 k-point mesh. The change in the Gibbs free energy (ΔG) for each possible step during the piezocatalytic synthesis of hydrogen peroxide was obtained using the computational hydrogen electrode (CHE) model61,62. According to this model, the changes in Gibbs free energy (∆G) for all chemical steps were defined as: ΔG = ΔE + ΔEZPE−TΔS, where the reaction energy (ΔE) can be directly obtained by analyzing the DFT total energies. The zero-point energy difference (ΔEZPE) between the products and the reactants can be computed from the vibrational frequencies. ΔS is the change in entropy between the products and the reactants at room temperature (T = 298.15 K).