Engineering surface polarization on bismuth titanate for efficient piezo-catalytic water purification

Engineering surface polarization on bismuth titanate for efficient piezo-catalytic water purification | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 30 January 2026 V1 Latest version Share on Engineering surface polarization on bismuth titanate for efficient piezo-catalytic water purification Authors : Zhou Zhong , Li Ma , Ya-Ying Yang , Yu-Xin Yuan , Yi-Hao Guo , Yi-Dong Hou , Jian Lu , and jian Lü 0000-0002-0015-8380 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.176973856.66314369/v1 111 views 60 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract The utilization of mechanical energy to drive piezo-catalytic water purification holds significant promise for practical applications. However, severe charge recombination and sluggish reaction kinetics on catalyst surface limit the catalytic activity. In this study, we report a strategy for boosting charge separation and surface reactions by modulating the surface polarization of bismuth titanate (Bi4Ti3O12; BTO) via iodine grafting. Kelvin probe force microscopy (KPFM), theoretical calculations and piezoresponse force microscopy (PFM) indicate that iodine grafting significantly enhances surface polarization via enlarging interlayer potential difference and expanding the ferroelectric domain on BTO surface. The enhanced surface polarization not only improves the piezoelectric coefficients (d33) and piezoelectric current of BTO by factors of 1.8 and 4, respectively, but also promotes oxygen adsorption and the formation of the key intermediate *OOH, which accelerates singlet oxygen generation. As a result, the iodine-grafted BTO (BTO-I) exhibits an efficient piezo-catalytic tetracycline degradation of 96.6% within 60 minutes, which is 3.5 times faster than that of pristine BTO. Meanwhile, the degradation system also shows excellent stability, broad applicability, and ecological friendliness. This study provides new insights into the design of piezo-catalytic materials through surface polarization engineering and highlights their potential for environmental remediation. Full Paper Piezoelectricity Engineering surface polarization on bismuth titanate for efficient piezo-catalytic water Zhou Zhong, Li Ma, Ya-Ying Yang, Yu-Xin Yuan, Yi-Hao Guo, Yi -Dong Hou, Jian Lu, and Jian Lü * Zhou Zhong, Li Ma, Ya-Ying Yang, Yu-Xin Yuan, Yi-Hao Guo, Jian Lü Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China E-mail: [email protected] Zhou Zhong, Yi -Dong Hou State Key Laboratory of Photocatalysis on Energy and Environment, Fuzhou University, Fuzhou 350116, China. Jian Lu CNNP Nuclear Power Operations Management Co., Ltd., Jiaxing, Zhejiang 314300, China Jian Lü FAFU−DAL Joint College (International College), Fujian Agriculture and Forestry University, Fuzhou 350108, China Keywords: surface polarization, piezo-catalysis, water purification, bismuth titanate, singlet oxygen Abstract : The utilization of mechanical energy to drive piezo-catalytic water purification holds significant promise for practical applications. However, severe charge recombination and sluggish reaction kinetics on catalyst surface limit the catalytic activity. In this study, we report a strategy for boosting charge separation and surface reactions by modulating the surface polarization of bismuth titanate (Bi 4 Ti 3 O 12 ; BTO) via iodine grafting. Kelvin probe force microscopy (KPFM), theoretical calculations and piezoresponse force microscopy (PFM) indicate that iodine grafting significantly enhances surface polarization via enlarging interlayer potential difference and expanding the ferroelectric domain on BTO surface. The enhanced surface polarization not only improves the piezoelectric coefficients (d 33 ) and piezoelectric current of BTO by factors of 1.8 and 4, respectively, but also promotes oxygen adsorption and the formation of the key intermediate *OOH, which accelerates singlet oxygen generation. As a result, the iodine-grafted BTO (BTO-I) exhibits an efficient piezo-catalytic tetracycline degradation of 96.6% within 60 minutes, which is 3.5 times faster than that of pristine BTO. Meanwhile, the degradation system also shows excellent stability, broad applicability, and ecological friendliness. This study provides new insights into the design of piezo-catalytic materials through surface polarization engineering and highlights their potential for environmental remediation. 1. Introduction Organic pollutants in the water body pose significant and widespread risks to human health and ecosystems. [1-3] Photodegradation and microbial degradation represent the primary natural pathways for organic pollutants breakdown. [4-6] Piezoelectric catalysis is an emerging technology that harnesses mechanical energy (ultrasound, vibration, or vortex etc.) to initiate redox reactions via inducing charge separation within piezoelectric materials. [7] This approach has demonstrated significant potential in diverse fields, including environmental remediation, energy conversion, and biomedical applications. [8,9] In particular, the application of piezoelectric catalysis for water purification has attracted increasing scientific and technological interest. [10-12] An external mechanical force applied to a piezoelectric material can induce relative displacement between positive and negative ions within the crystal lattice, resulting in the formation of electric dipole moments and piezoelectric polarization. [13] Consequently, a piezoelectric potential is generated across the material with positive and negative charges accumulating at opposite ends, thereby triggering redox reactions on the surface. [14] Based on the principles of piezoelectric catalysis, enhancing the piezoelectric response fundamentally relies on increasing the polarization degree while reducing the probability of charge recombination. [15,16] Ferroelectric materials are ideal piezoelectric catalysts, which exhibit spontaneous polarization that can be reversed in direction or altered in magnitude by an external electric field. [17] Nevertheless, severe surface charge recombination substantially diminishes carrier utilization, thereby limiting the overall catalytic performance. Specifically, ferroelectric materials typically possess surfaces composed of numerous nanoscale regions with distinct polarization orientations, known as ferroelectric or piezoelectric domains. [18] These small and dispersive domains tend to induce pronounced electron–hole recombination between the adjacent domains due to the opposite polarization direction. [8] Moreover, enhancing the surface polarization intensity remains necessary to further improve charge separation efficiency. Surface ion modification offers a promising strategy to tailor the electronic structure of semiconductors, generating surface states distinct from the bulk phase. [19,20] This process can induce electric dipole moments to enhance surface polarization, thereby suppressing surface charge recombination through the polarized electric field. [21,22] Additionally, modifications in the surface electronic structure may influence the size and distribution of ferroelectric domains, offering another way to prevent charge recombination by spatial isolation. [23,24] Recently, halogen ion anchoring has emerged as an effective method for regulating surface electronic structures of non-ferroelectric materials, showing great promise in both photocatalytic and piezoelectric catalytic applications. For instance, Liu et al. incorporated Cl − into BiVO 4 piezoelectric materials, inducing distortion of BiO 8 polar groups and significantly improving piezo-photoelectrochemical water oxidation performance. [25] Similarly, Wang et al. achieved the localized electric fields in CdBiO 2 I and CdBiO 2 Br by surface iodide-grafting, which led to the enhanced photocatalytic activity. [26,27] Inspired by these studies, the introduction of halogen ions onto ferroelectric material appears both rational and feasible, offering a viable route to regulate the surface polarization. Bismuth titanate (Bi 4 Ti 3 O 12 ; BTO), an Aurivillius-structured ferroelectric material, has garnered considerable attention due to its spontaneous polarization, layered crystal architecture, and anisotropic physical characteristics. [28-30] In this work, iodine-grafted BTO was synthesized via a straightforward impregnation method. The incorporation of iodide ions markedly enhanced the piezoelectric catalytic performance of BTO, with the rate constant for tetracycline (TC) degradation by BTO-I being 3.5 times higher than that of BTO. This improvement stemmed from the enhanced surface polarization induced by I-grafting, which resulted in a stronger piezoelectric response and more efficient 1 O 2 generation pathway. This study provides novel insights into enhancing piezoelectric catalytic activity and demonstrates its potential application for water environmental remediation. 2. Methods 2.1 Synthesis of Bi 4 Ti 3 O 12 A total of 0.84 g of [CH 3 (CH 2 ) 3 O] 4 Ti (titanium tetrabutoxide), 6.0 g of NaOH, and 1.6 g of Bi(NO 3 ) 3 •5H 2 O were dissolved in 30 mL of deionized water under continuous stirring. The resultant mixture was subjected to ultrasonic treatment for 15 min, followed by magnetic stirring at 600 rpm for 1 h. Subsequently, the solution was transferred into a 50 mL Teflon-lined autoclave and heated at 180 °C for 20 h in an oven. After cooling to room temperature, the obtained precipitate was collected via centrifugation and alternately washed six times with deionized water and anhydrous ethanol to remove residual impurities. Finally, the product was dried in a vacuum oven at 60 °C for 12 h and labeled as BTO. 2.2 Synthesis of Iodine-grafted Bi 4 Ti 3 O 12 In a typical procedure, 0.5 g of as-prepared BTO powder was dispersed into 80 mL of KI solutions with varying concentrations (C KI = 0.001, 0.01, 0.1 and 0.2 M). The suspensions were ultrasonicated for 30 min and then continuously stirred at room temperature for 15 h to ensure sufficient surface I-grafting. After reaction completion, the solid products were separated by centrifugation, thoroughly washed with deionized water to remove unbound iodide ions, and subsequently dried at 60 °C for 12 h in a vacuum oven. The resulting samples were denoted as BTO-I x , where x corresponds to the KI concentration used during modification (x = 0.001, 0.01, 0.1, 0.2). 2.3 Piezoelectric catalytic degradation of Tetracycline The piezoelectric catalytic degradation of tetracycline was conducted using a high-power digital ultrasonic cleaner (Kunshan Shumei Co., Ltd., KQ-400KDE). In a standard experiment, 15 mg of catalyst was introduced into 50 mL of 5 ppm TC aqueous solution. Prior to ultrasonic irradiation, the suspension was magnetically stirred for 30 min to achieve adsorption-desorption equilibrium. The mixture was then placed in a reaction vessel and subjected to ultrasonic treatment. During the process, 2.0 mL aliquots were periodically withdrawn at 15-min intervals, filtered through a 0.22 μm syringe filter, and analyzed using a UV–vis spectrophotometer (Shimadzu UV−2600, Japan) to determine the residual TC concentration. The ultrasonic system operated at a frequency of 40 kHz and a power output of 320 W. To maintain a stable reaction temperature, the reactor was immersed in a water bath maintained at approximately 25 °C via a circulating cooling system. 3. Results and discussion 3.1 Characterization of iodine grafted Bi 4 Ti 3 O 12 A series of BTO-I x samples were synthesized via a simple impregnation method by dispersing BTO in KI aqueous solutions with concentrations ranging from 0.001 to 0.2 mol/L, resulting in BTO-I 0.001 , BTO-I 0.01 , BTO-I 0.1 , and BTO-I 0.2 , respectively. The iodine content was quantified to be 0.06 wt.%, 0.23 wt.%, 0.22 wt.% and 0.26 wt.% respectively using inductively coupled plasma mass spectrometry (ICP-MS). The results revealed that the iodine content did not increase linearly with the KI concentration, which may be attributed to the strong chemical adsorption of I − ions on the BTO surface. Once the surface adsorption sites were saturated, further increases in KI concentration could not lead to higher iodine loading. The crystal structure of the samples was analyzed by powder X-ray diffraction (PXRD), as shown in Figure 1a. All characteristic diffraction peaks of BTO and BTO-I x matched well with the standard BTO reference pattern (PDF #72-1019), [31,32] indicating that I-grafting did not alter the intrinsic crystalline framework of BTO. No additional diffraction peaks were observed for BTO-I x , which confirmed that iodine was incorporated onto the surface without forming secondary phases. BTO is a typical Bi-based layered material composed of alternating fluorite-type [Bi 2 O 2 ] layers and perovskite-type [Bi 2 Ti 3 O 10 ] layers, as schematically illustrated in Figure 1b. Scanning electron microscopy (SEM) image revealed that BTO consisted of spherical aggregates formed by the self-assembly of square nanoplates of approximately 200 nm (Figure 1c), which are interlocked in a vertically cross-linked manner. I-grafting did not affect the morphology or size of BTO, as evidenced by the SEM image of BTO-I 0.1 (Figure 1d). Transmission electron microscopy (TEM) further confirmed the hierarchical nanostructure of BTO aggregates. High-resolution TEM analysis revealed two sets of perpendicular lattice fringes with an interplanar spacing of 0.27 nm, corresponding to the (200) and (020) crystal planes (Figure 1e). [33] Elemental mapping in Figure 1f via TEM energy dispersive spectroscopy (EDS) demonstrated uniform distributions of Bi, Ti, O and I across the sample surface, providing direct evidence for successful I-grafting onto BTO. X-ray photoelectron spectroscopy (XPS) was employed to investigate the chemical composition and valence states of elements at the surface of BTO and BTO-I 0.1 . As shown in Figure 1g, the surface of pristine BTO contained only Bi, Ti, O, and trace amounts of adventitious carbon, whereas the spectrum of BTO-I exhibited a distinct signal corresponding to I. In the high-resolution XPS spectra (Figure S1), the binding energies of Bi 4f and O 1s remained unchanged between BTO and BTO-I 0.1 , while the Ti 2p peak shifted by 0.1 eV toward higher binding energy after I-grafting. This shift suggested that I − ions were chemically bonded to Ti atoms rather than physically adsorbed on the surface. [21] Raman spectroscopy, known for its high sensitivity to lattice disorder, was used to probe structural changes and surface defects. As shown in Figure 1h, Raman bands below 200 cm −1 were associated with vibrations of heavier atoms, whereas those between 250–300 cm −1 corresponded to the stretching modes of [TiO 6 ] octahedra. [34] Upon I-grafting, the Raman peaks at 116 cm −1 and 269 cm −1 shifted to higher wavenumbers (120 cm −1 and 275 cm −1 ), indicating that I induced changes in the vibrational behavior of the BTO lattice through strong chemical bonding interactions. Moreover, zeta potential measurements were conducted to assess surface charge properties. As depicted in Figure 1i, the zeta potential of pristine BTO was negative, whereas I-grafting resulted in a positive surface charge. This reversal strongly indicated that I-grafting significantly alters the physicochemical characteristics of BTO surface. [35] Figure 1 . (a) PXRD patterns of BTO and BTO-I x . (b) Schematic diagram of crystal structure of BTO. SEM image of (c) BTO and (d) BTO-I 0.1 . (e) TEM image and (f) element mapping of BTO-I 0.1 . (g) XPS of survey, (h) Raman spectra, and (i) zeta potential of BTO and BTO-I 0.1 . Scale bars are 200 nm (c, d, e, f). 3.2 Piezo-catalytic tetracycline degradation The piezo-catalytic degradation performance was systematically evaluated under ultrasound (US) using tetracycline as a model pollutant. As shown in Figure 2a, ultrasound alone (without catalyst) was unable to induce TC decomposition while the pristine BTO achieved a TC removal rate of 64.6% in 60 min. By contrast, the TC degradation efficiency of I-grafted BTO-I 0.001 , BTO-I 0.01 , BTO-I 0.1 , and BTO-I 0.2 was significantly improved to 79.6%, 90.1%, 96.6%, and 93.3%, respectively. The rate constant for TC degradation by BTO-I 0.1 was 3.5 times higher than that of pure BTO (Figure S2). Mineralization rate as an essential indicator for the complete degradation of organics was assessed via the total organic carbon (TOC) analysis. Unlike the pristine BTO (4.2% mineralization), BTO-I x showed mineralization rates above 20% (Figure 2b), which was consistent with their respective removal efficiencies. The TC removal shown by BTO-I x and BTO remained below 24% in the absence of ultrasonic irradiation (Figure S3), confirming that the TC degradation was primarily due to piezoelectric catalytic reactions rather than simple adsorption processes. To exclude the influence of K + ions, control experiments were performed using KBr in replacement of KI under identical conditions. As shown in Figure 2c, the BTO sample impregnated with KBr solution (BTO-KBr) exhibited minimal enhancement in TC degradation compared to the pristine BTO, confirming that the improved performance was primarily attributed to the I − ions rather than K + ions. The zeta potential of BTO-KBr displayed negative characteristics (Figure S4), which was opposite to those of BTO-KI (Figure 1i). This observation suggested that either Br − ions were unsuccessfully grafted onto the BTO surface, or, if grafted, they failed to effectively alter the surface electronic structure of BTO. Consequently, the piezoelectric catalytic degradation efficiency of BTO-KBr toward TC showed no enhancement. Moreover, BTO-NaI displayed similar degradation activity to that of the BTO-KI when I − ions were introduced via NaI solution. These observations confirm that minimal I-grafting is able to significantly enhance the piezoelectric catalytic activity. Given that BTO-I 0.1 exhibited the highest catalytic activity and served as a representative of the series, it was selected as the model catalyst (denoted as BTO-I hereafter) for further study. The degradation performance of BTO-I towards varying TC concentrations was evaluated (Figure S5), demonstrated higher removal efficiency at lower TC concentrations (e.g. 3.0 to 5.0 ppm), notwithstanding a degradation rate of 85% at a concentration of 10 ppm. The effects of catalyst dosage, solution pH, and ultrasonic power were also investigated (Figure S6, S7). The results indicated that optimal degradation was achieved with a catalyst dosage above 0.3 g/L, under neutral to weakly acidic conditions, and at an ultrasonic power of 320 W. Moreover, common cations (Mg 2+ , Cu 2+ , Ca 2+ ) and anions (Cl − , NO 3 − , SO 4 2− ) exhibited minimal interference to the degradation process as shown in Figure S8. In tap water and river water systems, the TC degradation achieved over 90% within 60 min, whereas the TC degradation rate in seawater still exceeded 80%, demonstrating considerable robustness for practical applications (Figure 2d). In addition to TC, the BTO-I also exhibited high degradation efficiency towards a wide range of organic pollutants including ciprofloxacin (CIP; 95.8%), methylene blue (MB; 97.7%), rhodamine B (RhB; 99.2%), dichlorophenol (DCP; 96.1%), and phenol (PE; 92.6%), demonstrating its broad applicability and universality (Figure 2e). Stability tests through five consecutive cycles revealed that the BTO-I/US system retained 86.2% degradation efficiency (Figure 2f). The slight decline in performance likely resulted from the inevitable loss of surface-grafted iodine under prolonged ultrasonic exposure, as the iodine content declined from 0.22% to 0.18 wt.% detected by ICP-MS. Recycled samples were characterized by SEM and XRD, in which nearly identical characteristics were sustained due to unchanged morphology and crystal structure of the catalyst (Figure S9, S10). Potentially harmful intermediates generated during the degradation of tetracycline are likely posing additional environmental risks. Therefore, high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS) was utilized to identify intermediate products formed during the piezoelectric catalytic degradation process mediated by BTO-I, and two plausible degradation pathways were proposed in Figure 2g (see Figure S11 for details). The toxicities of TC degradation products were predicted using the Toxicity Estimation Software Tool (T.E.S.T.) based on the quantitative structure-activity relationship (QSAR) approach (Table S1). [36,37] The results indicated a marked reduction in the acute toxicity, mutagenicity, bioconcentration factor and developmental toxicity of the intermediates (Figure S12). Furthermore, the accuracy of toxicity prediction was validated using Shewanella oneidensis , a bacterium ubiquitous in aquatic and sedimentary systems. As shown in the Figure 2h, few Shewanella oneidensis colonies were able to grow on the solid medium containing TC, whereas distinct bacterial colonies were observed on the medium with degraded TC, indicating that the degradation products of TC exhibit extremely low toxicity. These findings confirm that the intermediates produced during the TC degradation process pose significantly reduced ecological and environmental risks. Figure 2. (a) TC degradation curves and (b) TOC removal rate of various catalysts. TC degradation curves of BTO-I (c) with different treatment and (d) in various water matrices. (e) Removal rate towards various organic contaminants. (f) cycle degradation experiment of BTO-I. (g) TC degradation pathways. (h) Photograph of colony on agar plates with TC and degraded TC. 3.3 I-grafting-induced surface polarization Kelvin probe force microscopy (KPFM) was employed to measure the polarization by the surface potentials. As shown in Figure 3a and 3b, the surface potentials of BTO and BTO-I relative to the substrate were 26 mV and 51 mV, respectively. This result confirmed that I-grafting enhances the surface polarization. [38] To further validate this, the polarization electric field (PEF) strength was evaluated using the model proposed by Kanata,[39] with the calculation methodology detailed in the Supporting Information. The charge density (ρ) and surface potential (V s ) were determined through transient photocurrent and open-circuit voltage respectively (Figure S13, S14). The resulting calculations displayed in Figure 3c indicate that the relative PEF strength of BTO-I is 2.1 times greater than that of BTO, thereby confirming that I-grafting effectively enhances the surface polarization of BTO. The fluorescence intensity of BTO-I is markedly lower than that of pristine BTO under 340-nm light excitation (Figure S15), suggesting a stronger driving force for charge separation, that is, an intensified PEF. Besides, BTO-I exhibits a smaller semicircle radius in the Nyquist plot compared to BTO (Figure S16), demonstrating a reduced charge transfer resistance which may derived from the enhanced polarization. Figure 3 . KPFM images and corresponding line-scanning surface potential profile of (a) BTO and (b) BTO-I. (c) relative PFE intensity of BTO and BTO-I. (d) Differential charge density of BTO-I. (e) BTO crystal structure along the x-axis. (f) Slices of charge density across planes 1–4 of BTO (upper row) and BTO-I (lower row). (g) Electrostatic potential distribution of BTO (left) and BTO-I (right) (isosurface value: 0.01 e/Bohr 3 ). (h) Electrostatic potential along z-axis. To directly elucidate the influence of I-grafting on the surface polarization of BTO, density functional theory (DFT) calculations were performed to analyze the electronic and electrostatic properties of BTO and BTO-I. Based on XPS analysis and previous studies, a structural model of BTO-I was proposed (Figure S17), which demonstrated that iodine was chemically bonded to the BTO surface through interactions with Ti atoms. [21] Differential charge density demonstrates that the Ti–I bond resides in a charge-enriched region, while most areas surrounding the I and Ti atom exhibit charge depletion (Figure 3d). The charge enrichment zone between Ti and I atoms indicates the presence of a shared electron cloud which is a characteristic feature of chemical bonding. The reduced charge density around Ti atoms aligns with the increased binding energy of Ti 2p observed in XPS, validating the rationality of this structural model. Figure 3e shows a schematic representation of the BTO crystal structure along the x-axis. Charge density slices across planes 1–4 of BTO are displayed in the upper row of Figure 3f, while corresponding slices of BTO-I are shown in the lower row. A clear discrepancy in charge density at positions 1–4 between BTO and BTO-I was observed, indicating that I-grafting significantly alters the electronic structure of at least four atomic layers within the BTO lattice. [40] Further analysis of the electrostatic potential distributions revealed distinct differences between the two models, in which a larger isosurface range corresponds to lower electrostatic potential values. It is evident that the iodine modifies the electrostatic potential landscape of BTO, particularly near the iodine atom, where a notable decrease in potential is observed (Figure 3g). In contrast, the electrostatic potential of atomic layers distant from iodine remains largely unaffected. Quantitative analysis of the electrostatic potential along the z-axis confirms this trend: the [Bi 2 Ti 3 O 10 ] layer adjacent to iodine exhibits a reduced electrostatic potential, whereas the [Bi 2 O 2 ] layer remains unchanged (Figure 3h). This variation increases the potential difference between [Bi 2 Ti 3 O 10 ] and [Bi 2 O 2 ] layers, thus enhancing the polarization of BTO surface. [41] Moreover, the work function, defined as the minimum energy required to transfer an electron from the Fermi level to the vacuum level, can be affected by surface polarization. The work functions (Φ) for BTO and BTO-I are 9.18 eV and 8.77 eV, respectively, which also reflect the change in surface polarization. 3.4 Piezoelectric properties of bismuth titanate To investigate the differences in piezoelectric behavior between BTO and BTO-I, piezoresponse force microscopy (PFM) was employed to analyze phase and amplitude characteristics. Figure 4a and 4d display the height images of BTO and BTO-I, respectively, while Figure 4b and 4e show the corresponding phase angle distributions, which reflect the polarization direction. Hence, regions with different color represent the ferroelectric domains with distinct orientation. [37,42] Compared to the small and dispersive ferroelectric domains of BTO, those of BTO-I became larger and more concentrated, which is conducive to an overall improvement in surface polarization and restrain the charge combination. The amplitude reflects the deformation of the materials under applied voltage.[43] As shown in Figure 4c and 4f, the increased color intensity in each region of BTO-I indicated a greater deformation under a given voltage, demonstrating a stronger inverse piezoelectric effect. Upon reversing the voltage from −10 V to +10 V, both samples displayed typical butterfly-shaped hysteresis loops and a 180° phase shift, as an indicative of ferroelectric domain reversal (Figure 4g and 4h). [44] The amplitude of BTO-I was approximately 2.5 times that of BTO at −10 V (2.0 nm vs. 0.8 nm), confirming its superior piezoelectric response. The piezoelectric coefficients (d 33 ) were 40 pm/V for BTO and 73 pm/V for BTO-I (Figure S18). The 1.8-fold increase in d 33 validated that I-grafting significantly enhanced the piezoelectric effect for BTO. In addition, transient piezoelectric current shown in Figure 4i indicated that BTO-I coated on ITO glass generated a current density approximately 4 times higher than that of BTO subjected to ultrasound, verifying that enhanced surface polarization substantially improves the piezoelectric response of BTO. Figure 4 . (a) Height, (b) phase angle and (c) amplitude image of BTO. (d) Height, (e) phase angle and (f) amplitude image of BTO-I. Butterfly-shaped amplitude curve and phase hysteresis loop of (g) BTO and (h) BTO-I. (i) Transient piezoelectric current of BTO and BTO-I. Scale bars are 200 nm (a, b, c, d, e, f). 3.5 Surface reactions on bismuth titanate Surface polarization not only enhances the piezoelectric response but may also affect the surface reactions. To reveal the crucial reactive oxygen species (ROS) and the generation pathways in the piezo-catalytic degradation process, radical quenching experiments were first conducted using AgNO 3 , tryptophan (Trp), p-benzoquinone (p-BQ), and tert-butanol (TBA) to selectively trap electrons, 1 O 2 , O 2 •− , and •OH, respectively. [45] As shown in Figure 5a and 5b, The contribution of electrons, holes and •OH to TC degradation was limited, as indicated by the minor effect of AgNO 3 and TBA in both systems. In comparison, adding the scavenger of 1 O 2 and O 2 •− caused a significantly greater suppression of the degradation rate, implying that 1 O 2 and O 2 •− were the primary ROS in the degradation process. It is worth noting that O 2 •− was not capable of oxidizing organic substances due to its low redox potential (E(O 2 /O 2 •− ) = −0.33 V vs. RHE, pH=7). [46] Given an extended lifetime of 1 O 2 in D 2 O over H 2 O, the solvent isotope effect was employed to probe the involvement of 1 O 2 . The accelerated degradation of TC in D₂O/Air relative to the H₂O/Air system, as depicted in Figure 5c, unambiguously identified 1 O 2 as the pivotal ROS. Further confirmation of the ROS was obtained via electron paramagnetic resonance (EPR) spectroscopy. The sextet peak in Figure 5d, triplet peak in Figure 5e, and quadruplet peak in Figure 5f correspond to O 2 •− , 1 O 2 and •OH signals, respectively. In both systems, the distinct signals of O 2 •− and 1 O 2 confirm their significant contributions. In contrast, the relatively weak signal of •OH indicates its limited role, which was in accordance with the quenching experiments. Importantly, all EPR signals of ROS were more intensive in the BTO-I/US system compared to the BTO/US system. Additionally, the BTO-I/US system also exhibited stronger scavenging effects in radical quenching experiments. These findings collectively confirm that 1 O 2 was the primary ROS during piezoelectric catalysis and I-grafting significantly promote the generation of 1 O 2 . Since AgNO 3 , an electron sacrificial agent for promoting photogenerated holes, did not enhance 1 O 2 formation, the energy transfer pathway (O 2 •− + h + → 1 O 2 ) can be excluded. [47] On the contrary, the electron transfer pathway (O 2 → O 2 •− → 1 O 2 ) is thus considered the more plausible route. Argon-, air-, and oxygen-saturated TC solutions were first applied to trace the origin of 1 O 2 . [48] The degradation efficiency was significantly reduced under argon atmosphere while increased under oxygen-saturated conditions compared to air (Figure 5c), which indicated sufficient oxygen concentration could promote 1 O 2 generation. [49] Furthermore, O 2 •− and 1 O 2 were semi-quantitatively analyzed using Nitroblue tetrazolium (NBT) and 1,3-diphenylisobenzofuran (DPBF) as probes, respectively. The concentrations of O 2 •− and 1 O 2 gradually increased within 5 min of reaction; however, the concentrations of both species decreased to a negligible level upon the addition of p-BQ (O 2 •− scavenger) (Figure S19). These observations indicated a strong correlation between O 2 •− and 1 O 2 . Numerous studies reveal that 1 O 2 is mainly produced from O 2 •− via the •OOH intermediate, positioning •OOH as a potential key species in the O 2 •− to 1 O 2 transition. [50,51] This hypothesis was tested using superoxide dismutase (SOD), a specific •OOH quencher, with the reaction monitored by EPR. As expected, SOD addition entirely eliminated the 1 O 2 signal (Figure S20), implicating •OOH as an indispensable intermediate. The role of •OOH was further investigated using potassium dichromate (K 2 Cr 2 O 7 ), an electron scavenger that targets •OOH. Consistent with the SOD experiment, K 2 Cr 2 O 7 also quenched the 1 O 2 EPR signal completely (Figure S20). These findings provide compelling evidence that •OOH is a crucial intermediate, leading to the proposed 1 O 2 generation pathway: O 2 → *O 2 → *OOH → 1 O 2 . Figure 5 . Quenching experiments of ROS in (a) BTO/US and (b) BTO-I/US system. (c) TC degradation curves of BTO-I in different solution. EPR spectra of (d) O 2 •− , (e) 1 O 2 , and (f) •OH. (g) O 2 -TPD on catalysts. (h) Free energy of intermediates. O 2 -temperature-programmed desorption (O 2 -TPD) was employed to investigate the oxygen adsorption sites and their interactions on BTO and BTO-I. As shown in Figure 5g, the desorption peak for BTO, originally at 439 °C, shifted to a higher temperature of 462 °C after iodine grafting. This positive shift and enhanced intensity of desorption peaks indicate that BTO-I possesses a stronger chemical adsorption affinity for oxygen, which is in agreement with the enhanced degradation rate in oxygen-saturated TC solution in Figure 5c. Moreover, DFT calculations were performed to determine the free energies of the critical *O 2 and *OOH intermediates on the (001) facet, with their optimized configurations shown in the Figure S21. Iodine grafting markedly reduced the free energy of *OOH on the BTO surface from –0.29 eV to –1.34 eV (Figure 5h). This substantial decrease indicates a stabilized *OOH intermediate on the BTO-I surface. Consequently, the formation reaction of OOH (*O 2 •− + H⁺ → *OOH) transitions from slightly endothermic (ΔG = +0.28 eV) to highly exothermic (ΔG = –1.03 eV). This energetic favorability facilitates the rapid conversion of *O 2 to *OOH on BTO-I, thus promoting the surface reactions of 1 O 2 generation along the O 2 → *O 2 → *OOH → 1 O 2 pathway. In brief, iodine grafting induced surface polarization not only facilitate the piezoelectric conversion via reduce the charge recombination, but also promote the surface reaction of 1 O 2 generation, which is illustrated in Figure 6. Figure 6. Schematic diagram of I-grafting-induced surface polarization boosts charge separation and surface reactions. 4. Conclusion In summary, this study demonstrates that iodine-grafting-induced surface polarization engineering effectively enhances the piezo-catalytic performance of bismuth titanate for water purification. The optimized BTO-I achieves 96.6% tetracycline degradation within 60 min with a rate constant 3.5 times greater than pristine BTO, while maintaining excellent stability, broad applicability to various organic pollutants, robust performance in complex water matrices, and ecological friendliness. Theoretical and experimental results demonstrate that I-grafting not only creates a greater electrostatic potential difference between [Bi 2 O 2 ] and [Bi 2 Ti 2 O 10 ] layers, but also induced larger ferroelectric domains on BTO surface, collectively leading to a strengthened polarization electric field. This enhanced polarization serves as a more powerful driving force for the efficient separation of piezo-induced electron-hole pairs under ultrasonic excitation. Meanwhile, the polarized surface enhances oxygen adsorption and, more importantly, thermodynamically stabilizes the critical *OOH intermediate. This alteration lowers the energy barrier for the conversion of O 2 to 1 O 2 , thereby accelerating the reaction kinetics. This work provides a feasible surface polarization strategy for designing high-performance piezo-catalytic materials and offers fundamental insights into the synergy between charge separation and surface catalytic reactions for advanced environmental remediation technologies. Supporting Information Supporting Information is available from the Wiley Online Library or from the author. Conflict of Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements Z. Z. acknowledges the financial support by the Open Project Program of the State Key Laboratory of Photocatalysis on Energy and Environment (Grant No. SKLPEE-KF202403), Fuzhou University, and the Natural Science Foundation of Fujian Province (Grant No. 2021J05029). J. L. is grateful for the financial support from National Natural Science Foundation of China (NSFC, Grant No. 22371042). We would also like to acknowledge the technical support from Instrumental Analysis Center of Fujian Agriculture and Forestry University. Received: (will be filled in by the editorial staff) Revised: (will be filled in by the editorial staff) Published online: (will be filled in by the editorial staff) References [1] J. Xu, K. Gu, P. Wang, P. Cheng, H. Che, C. Tang, K. Zhang, Y. Ao, Nat. Commun. , 2025 , 16 , 7908 . [2] K.F. Kayani, Sep. Purif. Technol. , 2025 , 364 , 132418. [3] J.-T. Wang, Y.-L. Cai, X.-J. Liu, X.-D. Zhang, F.-Y. Cai, H.-L. Cao, Z. Zhong, Y.-F. Li, J. Lü, J. Hazard. Mater. , 2022 , 424 , 127596. [4] F. Li, J. Wei, D. Wang, Y. Han, D. Han, J. Gong, Chem. Eng. J. , 2024 , 481 148633. [5] Z. Ling, Y. Gu, B. He, Z. Chen, H. Hu, H. Liu, W. Ding, S. Zhang, Sep. Purif. Technol. , 2024 , 349 , 127841. [6] Y. Ma, J. Wang, S. Leng, Int. 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Mollenhauer, J. Janek, D. Schröder, Chem. Rev ., 2021 , 121 , 12445. Iodine-grafting induces an enhanced surface polarization on bismuth titanate via enlarging interlayer potential difference and expanding the ferroelectric domain, which not only improves the piezoelectric response but also promotes the generation of singlet oxygen. As a result, the BTO-I exhibits a more efficient piezo-catalytic degradation efficiency, which is 3.5 times faster than that of pristine BTO. Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2018. Supporting Information Engineering surface polarization on bismuth titanate for efficient piezo-catalytic water purification Zhou Zhong a,b , Li Ma a , Ya-Ying Yang a , Yu-Xin Yuan a , Yi-Hao Guo a , Yi -Dong Hou b , Jian Lu c , and Jian Lü a,d* a Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China b State Key Laboratory of Photocatalysis on Energy and Environment, Fuzhou University, Fuzhou 350116, China. c CNNP Nuclear Power Operations Management Co., Ltd., Jiaxing, Zhejiang 314300, China d FAFU−DAL Joint College (International College), Fujian Agriculture and Forestry University, Fuzhou 350108, China. * Corresponding authors. E-mail: [email protected] (J.L.) Materials (Bi(NO 3 ) 3 ·5H 2 O), tetracycline, ciprofloxacin, rhodamine B, dichlorophenol, phenol, Nitroblue tetrazolium, 1,3-diphenylisobenzofuran, deuterium oxide (D 2 O) were purchased from Aladdin Co. Ltd. (Shanghai, China). C 16 H 36 O 4 Ti, NaOH, KI, KBr, NaI, tert-butanol, AgNO 3 and tryptophan were obtained from China National Pharmaceutical Chemical Reagent Co. Ltd. P-benzoquinone, methylene blue were purchased from Shanghai Maclean Biochemical Technology Co., Ltd. All the above reagents are of analytical grade and have not been further purified before use. Deionized water was prepared using a UPT-I-5 T ultrapure water system (resistance ≥ 18.25 MΩ cm). Toxicity assays on Shewanella oneidensis The experiments were conducted under sterile condition and all utensils were sterilized at 120 ºC for 20 min. Each culture medium consists of Luria–Bertani (LB) plates, 1.0 mL of TC solution and 200 µL of activated Shewanella oneidensis solution, respectively. The cultures were grown in an incubator at 37 ºC. The bacterial growth status was recorded by photograph. Electrochemical measurements The electrochemical measurements were performed using a CHI700F electrochemical workstation (Shanghai Chenhua). The catalyst ink was prepared by dispersing 5 mg of the catalyst in a mixture of 450 μL anhydrous ethanol and 50 μL of 5% Nafion solution, followed by ultrasonication for 30 min. Subsequently, 100 μL of the homogeneous suspension was drop-cast onto a conductive glass substrate (1 cm × 1 cm) and dried at room temperature. A conventional three-electrode system was employed, consisting of the catalyst-coated conductive glass as the working electrode, a platinum mesh as the counter electrode, and an Ag/AgCl electrode as the reference electrode, with freshly prepared 0.1 M Na 2 SO 4 solution as the electrolyte. The piezoelectric transient current response was recorded under intermittent ultrasound irradiation (10 s on / 20 s off) for three consecutive cycles. For electrochemical impedance spectroscopy (EIS), the frequency range was set between 100 kHz and 0.01 Hz, with a modulation amplitude of 5.0 mV. Quantitative analysis of ROS The concentration of 1 O 2 was identified by degradating 1,3-dephenylisobenzofuran (DPBF) due to the molar ratio was 1:1, the concentration of DPBF was determined by UV-vis spectrum at 410 nm. Typically, 13.5 mg DBPF was dissolved in 0.5 mL toluene and then the mixture was added into 50 mL ethanol for further tests. The concentration of •O 2 – was identified by react with nitro-blue tetrazolium (NBT, 1 mM). Given the fact that 1 mol Nitroblue tetrazolium (NBT) can react with 4 mol •O 2 – . We quantified the concentration of generated •O 2 – by recording the residual concentration of NBT on a UV-vis spectrophotometer (maximum absorbance at 260 nm). Density functional theory (DFT) calculations Our spin-polarized DFT calculations were carried out in the Vienna ab initio simulation package (VASP) based on the plane-wave basis sets with the projector augmented-wave method. The exchange-correlation potential was treated by using a generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) parametrization. The van der Waals correction of Grimme’s DFT-D3 model was also adopted. Lattice parameters of structure were a = 10.82 Å, b = 10.90 Å, and c = 30.44 Å. 2 × 2 × 1 Gamma k-point sampling is used for the Brillouin zone integration. The structures were fully relaxed until the maximum force on each atom was less than 0.02 eV/Å, and the energy convergent standard was 10 -5 eV. The energy cutoff was set to be 450 eV. Calculation of intensity of internal electric field In the case that the photocatalyst is a single component, the intensity of the IEF can be measured using the model developed by Kanata. The model proves that the IEF strength is determined by surface potential and surface charge density Where V s is the surface potential, V; ρ is the surface charge density, C/m 2 ; ε is low frequency dielectric constant; ε 0 is the vacuum dielectric constant, 8.854 × 10 −12 F/m. When the crystals are similar, the difference in ε is negligible. Surface potential V s can be detected using the KPFM mode of atomic force microscopy (AFM). The surface charge density ρ is obtained by equation 2 Where k is the Boltzmann constant, J K −1 ; T is the absolute temperature, K −1 ; ε is the relative dielectric constant; e 0 is the electron charge, C; n is the number of electrolytes per unit volume, m −3 ; z is the valence state of the electrolyte, ψ 0 is the surface potential which can be measured by zeta potential. According to the above formula, the charge density (ρ) and surface potential (V s ) were determined through transient photocurrent and open-circuit voltage, respectively. Figure S1 . XPS spectra of (a) Bi 4f, (b) Ti 2p, (c) O1s and (d) I 3d of BTO and BTO-I 0.1 . Figure S2 . Rate constants of TC degradation on various catalysts. Figure S3 . TC removal curve in the absence of ultrasonic irradiation Figure S4 . Zeta potential of BTO and BTO-Br (0.1 M KBr). Figure S5 . The degradation performance of BTO-I against varying TC concentrations Figure S6 . The degradation performance of BTO-I with various (a) dosage and (b) pH. Figure S7 . TC degradation curves under different power. Figure S8 . TC degradation curve on BTO-I with common (a) cations and (b) anions. Figure S9 . SEM images of BTO-I before and after the TC degradation reaction. Figure S10. PXRD patterns of BTO-I before and after the TC degradation reaction. Figure S11 . TC degradation pathway. Figure S12 . (a) Acute toxicity, (b) mutagenicity, (c) bioconcentration factor, (d) and developmental toxicity of the intermediates Toxicity was assessed based on the 96-h median lethal concentration (LC 50 ), defined as the concentration required to cause mortality in 50% of fathead minnow. As illustrated in Figure S12a, the acute toxicity of pristine TC is below 1 mg/L, classifying as highly toxic, whereas the toxicity of intermediate compounds gradually decreases with the progressive degradation process. Among these, P4, P7 and P8 are categorized as toxic P6, P3, P5, P9, P11 and P2 as harmful in a decreasing order, and the intermediate P10 particularly exhibits low toxicity. These observations indicate a substantial reduction in the toxicity of most degradation products compared to the parent compound TC. Mutagenicity refers to the capacity of chemical substances to induce genetic mutations or DNA damage, potentially leading to carcinogenesis, hereditary disorders, or cellular dysfunction. In this context, the mutagenicity of intermediates P4, P6, P9, P10 and P11 transitions from positive to negative as degradation proceeds (Figure S12b). The bioconcentration factor (BCF) serves as a key parameter for evaluating the potential of a chemical to accumulate within organisms. As depicted in Figure S12c, all intermediates exhibit relatively low BCF values except P10 that demonstrates low toxicity and non-mutagenic characteristics notwithstanding showing a higher BCF. Developmental toxicity describes the adverse effects of chemical exposure during embryonic, fetal or juvenile developmental stages, including structural malformations, functional impairments or growth inhibition. As shown in Figure S12d, all intermediates except P4 exhibit lower developmental toxicity than the original TC molecule. Figure S13. Surface charge density of (a) BTO and (b) BTO-I. According to the previous report, by integrating the measured transient photocurrent density minus the steady-state values of photocurrent with respect to time, the value is proportional to the number of negative charges accumulated at the surface [1-3]. As shown in Figure S12, the integral areas (filled areas) are calculated to be 0.61 and 1.03 for BTO and BTO-I, that is, the values of surface charge density are 0.61 and 1.03 μC/cm 2 , respectively. Figure S14. Open-circuit voltage of BTO and BTO-I. Figure S15. Solid PL spectra of BTO and BTO-I Figure S16. Electrochemical impedance spectra of BTO and BTO-I. Figure S17 . Optimized structural models of BTO and BTO-I. Figure S18 . Piezoelectric coefficients of BTO and BTO-I. Figure S19. Relative concentration of (a) •O 2 – and (b) 1 O 2 determined by NTB and DBPF as chromogenic agent. Figure S20. EPR of singlet oxygen with SOD and K 2 Cr 2 O 7 . Figure S21. Configuration of (a) BTO + O 2 , (b) BTO + OOH, (c) BTO-I + O 2 , and (d) BTO-I + OOH. Table S1 . Detailed parameters of various indicators of the degradation intermediates. TCH 0.90 0.60 Positive 0.71 0.86 P1 6.62 0.66 Positive 0.36 0.85 P2 64.04 0.61 Positive 0.09 0.72 P3 17.87 0.65 Positive 0.32 0.88 P4 3.90 0.15 Negative 1.83 0.98 P5 26.74 0.51 Positive 2.02 0.48 P6 13.23 0.05 Negative 3.32 0.17 P7 0.93 0.67 Positive 0.66 0.81 P8 4.44 0.94 Positive 4.20 0.75 P9 43.86 0.44 Negative 3.94 0.69 P10 227.57 -0.05 Negative 13.68 0.66 P11 60.32 0.06 Negative 3.30 0.59 References [1] Y. Liu, Y. Shi, X. Xin, Z. Zhao, J. Tan, D. Yang, Z. Jiang, Boosting electron transfer of Ti-MOFs via electron-deficient boron doping for high-efficiency photocatalytic nitrogen fixation, Applied Catalysis B: Environment and Energy, 363 (2025) 124815. [2] H. Li, R. Chen, L. Sun, Y. Wang, Q. Liu, Q. Zhang, C. Xiao, Y. Xie, Hole Polaron-Mediated Suppression of Electron–Hole Recombination Triggers Efficient Photocatalytic Nitrogen Fixation, Adv. Mater., 36 (2024) 2408778. [3] X. Wu, F. Zhang, L. Niu, J. Liu, J. Li, D. Wang, J. Fan, X. Li, C. Shao, X. Li, Y. Liu, Promoting photocatalytic nitrogen reduction for aqueous nitrogenous fertilizer from organic wastewater over p-BiOBr/n-Bi 2 MoO 6 hetero-nanofibers, Chem. Eng. J., 470 (2023) 144108. 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Keywords bismuth titanate piezo-catalysis singlet oxygen surface polarization water purification Authors Affiliations Zhou Zhong Fujian Agriculture and Forestry University View all articles by this author Li Ma Fujian Agriculture and Forestry University View all articles by this author Ya-Ying Yang Fujian Agriculture and Forestry University View all articles by this author Yu-Xin Yuan Fujian Agriculture and Forestry University View all articles by this author Yi-Hao Guo Fujian Agriculture and Forestry University View all articles by this author Yi-Dong Hou Fuzhou University View all articles by this author Jian Lu CNNP Nuclear Power CNNP Nuclear Power Operations Management Co., Ltd. View all articles by this author jian Lü 0000-0002-0015-8380 [email protected] Fujian Agriculture and Forestry University View all articles by this author Metrics & Citations Metrics Article Usage 111 views 60 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Zhou Zhong, Li Ma, Ya-Ying Yang, et al. Engineering surface polarization on bismuth titanate for efficient piezo-catalytic water purification. Authorea . 30 January 2026. DOI: https://doi.org/10.22541/au.176973856.66314369/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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