Controllable removal/release of phosphate by light-responsive layered double hydroxide composite electrode

Controllable removal/release of phosphate by light-responsive layered double hydroxide composite electrode | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Controllable removal/release of phosphate by light-responsive layered double hydroxide composite electrode Yi-Ting Lai, Da-Wei Huang, Kiruthikha Duraisathiamoorthy, Dhanaprabhu Pattappan, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8667334/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Dynamic phosphate regulation is crucial for environmental protection and sustainable phosphorus management. In this work, we developed a smart electrode by electrochemically engineering photo-responsive poly(azobenzene) into MgMn-layered double hydroxide interlayers (MgMn-LDH/Pazo) for light-switchable capacitive phosphate removal and recovery from aqueous environments. Under UV light irradiation, the trans-to-cis photoisomerization of intercalated Pazo induces the formation of multiple bonding interactions with phosphate ions, leading to an enhanced phosphate adsorption capacity from 14.08 to 55.22 mg-PO 4 /g. Upon switching to visible light, the cis-to-trans isomerization of Pazo decreases the binding affinity toward phosphate, achieving an efficient phosphate desorption with a regeneration rate of 84.6%. This optically switchable system enables selective, reversible, and tunable phosphate uptake and release, offering a sustainable solution for environmental remediation and phosphorus resource recovery. The proposed innovative strategy demonstrates excellent phosphate removal/release performance with operational controllability, positioning it as a promising candidate for next-generation smart wastewater treatment technologies. Earth and environmental sciences/Environmental sciences/Environmental chemistry/Pollution remediation Earth and environmental sciences/Environmental sciences Layered double hydroxides azobenzene photoisomerization phosphate recovery wastewater treatment Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Phosphorus is a vital element in human activities, such as agricultural productivity 1 , electronics preparation 2 , and clinical therapeutics 3 . However, the uncontrolled release of phosphate into water bodies is the major cause of eutrophication 4 , which severely disrupts aquatic ecosystems and water quality 5 , 6 . Traditional phosphate removal techniques, such as chemical precipitation and biological treatment, often suffer from inefficiencies, high operational costs, and secondary pollution concerns 7 . Therefore, the development of advanced techniques capable of controllably and selectively removing and recycling phosphate is crucial for sustainable water treatment and phosphorus resource recovery 8 . Various materials have been proposed for phosphate recovery from wastewater, including graphene 9 , activated carbon 10 , zeolites 11 , and metal-organic frameworks (MOFs) 12 , 13 . However, these materials suffer from low adsorption selectivity and high production costs, hindering their practical applications. Layered double hydroxides (LDHs) have garnered increasing attention as promising adsorbents for wastewater treatment due to their high anion exchange capacity, structural stability, cost-effectiveness, and tunable properties. LDHs consist of positively charged brucite-like layers intercalated with charge-compensating anions and water molecules, allowing for efficient phosphate uptake via electrostatic attraction, ligand exchange, and ion exchange mechanisms 14 . Extensive research has widely explored the use of LDHs for phosphate removal in environmental remediation applications 15 . For example, Nie et al. fabricated a MgAl-LDH/montmorillonite composite with a maximum phosphate adsorption capacity of 127.8 mg-P/g, which surpasses the unmodified MgAl-LDH by approximately 21% 16 . Cao et al. reported a CaLa-LDH with an impressive adsorption capacity of 194.04 mg-P/g 17 . Hatami et al. synthesized ZnAl-LDHs by a modified urea hydrolysis method, which achieved a phosphate adsorption capacity of 1.49 mmol/g, with desorption efficiencies ranging from 23.2% to 36.3%, indicating the potential applicability for slow-release phosphate fertilizers 18 . More recently, Li et al. introduced oxygen into MgLa-LDH to enhance electrostatic attraction and inner-sphere complexation, thereby improving the phosphate adsorption to 121.56 mg-PO 4 /g 19 . Despite these advancements, current LDH-based adsorbents suffer from irreversible phosphate binding, thus hampering their regeneration capability and long-term applicability. To address this challenge, several efforts have incorporated capacitive deionization (CDI) systems to achieve reversible and energy-efficient phosphate adsorption-desorption processes 20 . Herein, we demonstrated a smart electrode by in situ electrochemically engineering light-responsive poly(azobenzene) into MgMn-LDH interlayers (MgMn-LDH/Pazo) for the controllable adsorption and release of phosphate from aqueous solutions (Fig. 1 a). Azobenzene derivatives, a class of photo-switchable organic molecules with a central azo (-N = N-) linkage between two aromatic rings (Fig. 1 b), are well-known for their tunable E / Z photoisomerization upon external stimuli 21 . Upon UV light irradiation, azobenzene undergoes a transition from a thermodynamically stable trans configuration to a metastable cis configuration through π-π* and n-π* electronic transitions 22 . This photoisomerization is reversible in response to visible light or heat, enabling dynamic modulation of molecular structure and dipole moment 23 , 24 . By leveraging the light-driven photoisomerization of Pazo, the layer-by-layer electrodeposited MgMn-LDH/Pazo (Fig. 1 c) enables dynamic regulation of interlayer interactions and binding affinity toward phosphate ions under UV/visible light stimuli. The proposed controllable switching between adsorption and desorption states addresses the limitations of irreversible phosphate uptake in conventional CDI systems, paving the way for dynamic and efficient phosphate regulation and resource recovery in practical wastewater treatment applications. Results and Discussion The electrochemically layer-by-layer electrodeposition of MgMn-LDH/Pazo Films The in situ electrochemical growth of LDH nanosheets is usually carried out by applying a cathodic potential to the working electrode, which facilitates the reduction of water and nitrate ions in the precursor solution 25 , 26 . The resulting hydroxide ions subsequently react with the metal ions to form lamellar LDH structures on the electrode surface, as described in the following Eq. 2 7 : 2H 2 O + 2e − → H 2 + 2OH − (1) NO 3 − + H 2 O + 2e − → NO 2 − + 2OH − (2) (1 − x )Mg 2+ + x Mn 2+ +2OH − → Mg 1− x Mn x (OH) 2 (3) where Mn 2+ undergoes the self-oxidation to Mn 3+ upon exposure to atmospheric oxygen 26 . The intercalation of nitrate anions and water molecules into the LDH interlayer space stabilizes the layered structure. To determine the optimal electrodeposition potential, linear sweep voltammetry (LSV) was performed using precursor electrolytes containing 0.1 M Mg(NO 3 ) 2 or 0.1 M Mn(NO 3 ) 2 , as shown in Fig S1 . Onset potentials of − 1.25 V and − 1.20 V vs Ag/AgCl were identified for magnesium and manganese, respectively. Consequently, a cathodic potential of − 1.25 V was selected for the electrodeposition process. Herein, pulsed voltammetry electrodeposition was employed to grow vertically three-dimensional (3D) LDH nanosheets (Fig. 2 a) 28 . This technique enables inter-pulse re-equilibration of the electrolyte, thereby overcoming the mass transport and electric double layer limitations at the electrode/electrolyte interface 29 , allowing for the rapid formation of 3D nanostructured LDH at room temperature. In Fig. 2 b, flower-like MgMn-LDH clusters composed of hierarchically grown nanosheets can be observed, accompanied by a uniform distribution of Mg, Mn, and O elements within the clusters (Fig. 2 c). It is noted that under the same deposition time of 1000 s, the proposed pulse voltammetry method results in more 3D LDH nanosheet clusters growth compared to constant voltage deposition ( Fig S2 ), which provides more active sites and facilitates the penetration of the electrolyte for phosphate adsorption 30 . For MgMn-LDH/Pazo films, the pulsed voltage was shifted to a positive potential of 0.2 V to facilitate the intercalation of negatively charged Pazo molecules into the LDH layers, as shown in Fig. 2 d. As the bias is changed oppositely, loosely bound cations are repelled from the electrode surface under the external electric field, allowing negatively charged Pazo to migrate to the deposited LDH surface 30 , thus forming the layer-by-layer MgMn-LDH/Pazo nanostructure as the cycle repeats (Fig. 2 e). The appearance of the N element on the nanosheet cluster further confirms the incorporation of Pazo (Fig. 2 f). It is noted that the MgMn-LDH/Pazo exhibits a smaller flower-like cluster compared to pristine MgMn-LDH, suggesting that Pazo may serve as the polymer inhibitor that mitigates localized electric fields and suppresses dendritic growth 31 . In (Fig. 2 g ) , the transmission electron microscopy (TEM) image shows a 3D hierarchical flower-like morphology of MgMn-LDH nanosheets consistent with the field-emission scanning electron microscopy (FESEM) results, which is beneficial for electrolyte ions diffusion 32 . The high-resolution TEM (HRTEM) image of MgMn-LDH shows polycrystallinity with the interplanar lattice spacings of 0.249 nm (Fig. 2 h), corresponding to the (012) planes of LDHs 33 . Moreover, the selected area electron diffraction (SAED) pattern inset in (Fig. 2 h ) displays distinct diffraction rings for the (012), (015), and (018) planes 34 , indicating the successful formation of LDHs. On the other hand, nanoscale polymeric Pazo aggregation (~ 80–100 nm) can be observed in the crumpled flower-like LDH clusters (Fig. 2 i). In the HRTEM image (Fig. 2 j), a new d-spacing of 0.44 nm, which is consistent with the theoretical azobenzene interlayer length of 0.44 nm at the most probable angle of 30° between the trans-Pazo and LDH layer 35 , 36 . The SAED pattern (the inset of Fig. 2 j) shows diffused features, indicating reduced crystallinity and expansion of the interlayer spacing due to incorporation of Pazo. These findings realize the construction of MgMn-LDH/Pazo composite films within hundreds of seconds through the electrochemical layer-by-layer assembly strategy, which significantly outweighs conventional self-assembly techniques requiring tens of hours 37 , 38 . The characterization of photoisomerization of MgMn-LDH/Pazo Films. The intercalation of Pazo into the LDH layers was characterized by XRD. As shown in Fig. 3 a, the electrochemically layer-by-layer deposited films do not exhibit the characteristic diffraction peaks of typical MgMn-LDH powder at 11.2°, 22.7°, 33.8°, 38.2°, 44.6°, 59.4°, and 60.6°, corresponding to the (003), (006), (012), (015), (018), (110), and (113) planes, respectively 39 . The absence of these reflections can be attributed to the low crystallinity or unmeasurable nanocrystalline grains in the electrodeposited films 40 . The left-hand figure highlights the broadened (003) basal reflection, further confirming the low crystallinity of the electrodeposited films. XRD analysis was further conducted in the low-angle region (2θ < 10°) for the MgMn-LDH/Pazo film (Fig. 3 b). A clear downshift and broadening of the (003) reflections is observed, indicating the expansion of LDH interlayer spacing due to the successful intercalation of Pazo molecules with various orientations 36 . The photoisomerization of the MgMn-LDH/Pazo electrode was systematically investigated using UV-visible spectroscopy (UV-Vis). In Fig S3 , the MgMn-LDH film shows a characteristic peak at 296 nm, in agreement with previous reports 41 . For pristine Pazo, the dominant absorption band at ~ 365 nm is attributed to π → π* electronic transition, while a weaker shoulder at ~ 465 nm corresponds to n → π* transition 42 . Upon formation of the MgMn-LDH/Pazo composite, a red shift of the π → π* band to ~ 371 nm is observed, which is attributed to the ligand-metal charge transfer and electrostatic interaction between Pazo molecules and LDH nanosheets 36 , 43 . In Fig. 3 c, under UV light irradiation (λ = 365 nm), the absorbance at 371 nm reveals a pronounced decrease within the first 30 min and gradually reaches saturation after 60 min, indicating the trans-to-cis photoisomerization of Pazo moieties within the LDH structure. The kinetics of photoisomerization for the MgMn-LDH/Pazo film are shown in the inset of Fig. 3 c, which follow the double exponential decay function 36 : $$\:A\left(t\right)={A}_{1}{e}^{-t/{T}_{1}}+{A}_{2}{e}^{-t/{T}_{2}}+{A}_{3}$$ 4 where A(t) is the absorbance of 371 nm at time t ; A 1 , T 1 , A 2 , T 2 , and A 3 are fitting constants describing fast and slow isomerization processes. It is noted that the π → π* absorption band recovers again after visible light irradiation for 5 min (Fig. 3 c), demonstrating reversible cis-to-trans photoisomerization 44 . This photo-switching behavior was further confirmed by optical cycling tests in which the film was alternately irradiated with 60 min UV and 15 min visible light. The results demonstrate reversible photo-switching over multiple cycles (Fig. 3 d and S4 ) , affirming the photochemical reversibility and operational stability of the cis-trans photoisomerization for MgMn-LDH/Pazo films. The topographical changes of MgMn-LDH/Pazo films induced by light irradiation were evaluated via atomic force microscopy (AFM). In Fig. 3 e, sharp morphology can be observed on the MgMn-LDH/Pazo surface with root-mean-square (RMS) roughness (R q ) of 61.3 nm. Upon UV irradiation, the sharp peaks changed to blunt protuberances, accompanied by a significant R q decrease to 31.4 nm, suggesting a denser and more compact packing of the LDH layers 45 . Subsequent visible light exposure restored the R q to 43.7 nm, indicating the reversible switch between the light-driven trans-cis isomerization of intercalated Pazo in the composite electrode. The dynamic variation in surface morphology and molecular configuration provides a route for light-controllable phosphate adsorption/desorption behavior of the proposed MgMn-LDH/Pazo electrode in wastewater treatment applications. Electrochemical Characterizations of LDH-based Electrodes The electrochemical properties of electrodeposited LDH-based electrodes were investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a 100 ppm phosphate solution. As shown in Fig. 4 a and S5, the CV profiles of MgMn-LDH display pseudocapacitive properties with a prominent anodic peak near 0.6 V, which may result from the oxidation of Mn within the LDH structure 46 , 47 . The nearly unchanged CV curve measured under UV irradiation confirms no photo-responsivity for pristine MgMn-LDH. In contrast, the MgMn-LDH/Pazo electrode demonstrates enhanced current response, indicating improved charge transport and a higher electroactive surface area due to the incorporation of Pazo. Interestingly, under UV light irradiation, a further increase in redox peak currents is observed, suggesting that the trans-to-cis isomerization of Pazo modulates the electronic structure of the MgMn-LDH/Pazo 48,49 , leading to enhanced phosphate affinity within the electrode. The Nyquist plots (Fig. 4 b-d and Table 1 ) for all samples reveal a characteristic semicircle in the high-frequency region, followed by a quasi-linear curve in the low-frequency region, corresponding to charge-transfer and diffusion-controlled processes, respectively 50 . For the pristine MgMn-LDH electrode, the fitted equivalent circuit (inset of Fig. 4 b) comprises two charge transfer components ( R 2 and R 3 ) in parallel with constant phase elements, in series with a Warburg impedance ( W 0 ) and solution resistance ( R 1 ) 51 , reflecting a hindered interfacial kinetics and less ideal capacitive characteristics due to limited interlayer electron transport. In contrast, the MgMn-LDH/Pazo electrode (Fig. 4 c) exhibits a significantly reduced semicircle diameter, indicating a drastic decrease in charge transfer resistance ( R ct = 2.40 Ω), along with a more vertical line at low frequency for enhanced ion diffusion process 52 . These improvements can be attributed to the intercalation of the π-conjugated Pazo molecules, which bridge adjacent hydroxide layers and promote charge transport via π–π interactions 53 , 54 . In addition, intercalated Pazo enlarges the LDH interlayer spacing and provides more accessible active sites 55 , thereby enhancing both phosphate ion diffusion and charge transfer during electrochemical reaction 56 . It is noted that upon UV irradiation, the interfacial impedance increases slightly to 4.22 Ω (Fig. 4 d), which is induced by the trans-cis photoisomerization of intercalated Pazo. As illustrated in Fig. 4 e, trans-Pazo in its linear form acts as an effective interlayer bridge, facilitating the charge transfer process. However, upon photoisomerization to the cis-isomer, the bent molecular geometry creates steric hindrance in charge transfer pathway 57 , thereby impeding electron flow across the LDH interlayers. These results confirm that Pazo not only enhances charge-transfer kinetics via enhanced ion diffusion and interlayer connectivity but also provides a dynamic, light-switchable strategy for modulating electrochemical phosphate adsorption. Table 1 The comparison of the impedance form Nyquist plots for LDH-based electrodes. Materials Solution resistance Charge transfer resistance R 1 (Ω) R 2 (Ω) R 3 (Ω) MgMn-LDH 22.95 93.79 1.22 MgMn-LDH/Pazo 29.47 2.40 – MgMn-LDH/Pazo under UV 29.66 4.22 – Surface chemical states of the LDH composites X-ray photoelectron spectroscopy (XPS) was used to characterize the surface chemical states of the LDH composites and their bonding with the phosphate. In the Mg 2p spectra (Fig. 5 a), the pristine MgMn-LDH displays characteristic peaks at 49.2 eV, and 50.1 eV, corresponding to Mg-OH, and Mg-O, respectively 58 , 59 . Upon incorporation of Pazo, new signals emerge at higher binding energy at 52.2 eV for magnesium carbonates 60 , which is attributed to coordination interactions between Mg atoms and the carboxy groups of Pazo. It confirms the strong interfacial bonding and chemical interaction between the LDH layers and Pazo. In Fig. 5 b, the Mn 2p spectra exhibit identified split spin-orbit components for Mn 2p 1/2 and Mn 2p 3/2 (Δ = 11.2 eV) 20 . Upon functionalization with Pazo, the relative intensities of Mn 2+ and Mn 3+ decrease while the Mn 4+ increases, implying partial electron withdrawal from Mn sites to Pazo. This modulation of the redox state produces more phosphate-specific adsorption sites in the LDH sheets, facilitating the phosphate adsorption process 39 . The N 1s spectra further support the successful intercalation of Pazo and the mechanism of phosphate adsorption (Fig. 5 c). Before adsorption, characteristic peaks at near 407.5 eV and 400.0 eV correspond to interlayer NO 3 ⁻ and -N = N- bond in Pazo, respectively 61 . It is noted that the nitrate peak disappears after phosphate adsorption, indicating successful ion exchange with phosphate. The remaining -N = N- signal shifts and broadens, indicating potential hydrogen bonding with phosphate. To assess phosphate interaction directly, P 2p spectra were analyzed for sample electrodes after phosphate adsorption (Fig. 5 d). The splitting peaks at 132.7 eV and 133.9 eV are attributed to P 2p 3/2 for HPO 4 2– and P 2p 1/2 for H 2 PO 4 – , respectively 62 . The high proportions of HPO 4 2– confirm the dominant sorption of phosphate via both electrostatic interactions and inner-sphere coordination with metal hydroxides layers 63 . It is noted that the intensity of the H 2 PO 4 – peak increases in the MgMn-LDH/Pazo, which is attributed to the conformational hydrogen bonding of phosphate with the cis configuration of Pazo 64 . Electro-assisted phosphate adsorption/desorption performance under light stimuli Electro-assisted phosphate adsorption/desorption performance under light stimuli The electro-assisted phosphate adsorption/desorption performance of the LDH-based electrodes was evaluated under controlled light stimuli to elucidate the role of Pazo photoisomerization in regulating phosphate binding. In Fig. 6 a, the pristine MgMn-LDH electrode shows moderate phosphate uptake of 33.6 mg-PO 4 /g, with a desorption efficiency of 30.2% under visible light irradiation for 20 min. By comparison, the MgMn-LDH/Pazo electrode shows a suppressed adsorption and desorption under visible light, consistent with the trans configuration of Pazo presenting lower effective affinity toward phosphate. Upon switching the illumination to UV light, the phosphate adsorption capacity of MgMn-LDH/Pazo significantly increases by 80.7% to 39.4 mg-PO 4 /g, whereas the desorption efficiency decreases dramatically to 10.3%. This trend indicates that UV-induced trans-to-cis photoisomerization of Pazo strengthens phosphate binding due to increased steric accessibility and polarity 65 , leading to stronger interactions with phosphate. To recover phosphate efficiently, the light source was subsequently switched back to visible light during the desorption step, triggering the cis-to-trans back-isomerization and weakening the binding strength. As a result, the desorption efficiency increases by more than threefold to 37.2%, demonstrating an effective reversibility of phosphate adsorption/desorption via light and voltage stimuli. Figure 6 b presents the time-dependent phosphate adsorption of the MgMn-LDH/Pazo. The adsorption capacity reaches 55.2 mg-PO 4 /g within 60 min and then reaches a plateau, indicating fast adsorption kinetics and a high density of phosphate binding sites. Kinetic modelling reveals a better fit to the pseudo-second-order model ( R 2 = 0.9632) compared to the pseudo-first-order model ( R 2 = 0.9298), indicating the dominant phosphate chemisorption processes, contributed by a combination of ligand exchange and anion exchange within the LDH galleries 20 , as well as light-triggered conformational bonding with Pazo 39 , 64 . The reusability of the MgMn-LDH/Pazo electrode was evaluated through consecutive adsorption-desorption cycles under alternating light stimuli (Fig. 6 c). The adsorption capacity remains relatively stable (~ 40–45 mg-PO 4 /g) over four cycles, demonstrating good structural robustness and operational durability. In addition, only a gradual decline in desorption efficiency by approximately 10–20% after the fourth cycle, suggesting a tolerable reusability. The partial loss in cyclability may be attributed to photoswitching activity degradation or progressive structural densification of LDH domains 66 , 67 , thus hindering active site regeneration and ion mobility. To evaluate ion selectivity, the adsorption experiments were conducted in the presence of competing anions, including NO 3 ⁻, Cl⁻, and SO 4 2 ⁻. As shown in Fig. 6 d, MgMn-LDH/Pazo electrode exhibits substantially higher adsorption toward phosphate (47.4 mg/g) than nitrate (21.1 mg/g), chloride (18.9 mg/g), and sulfate (26.3 mg/g). This pronounced selectivity is attributed to its strong inner-sphere coordination propensity and specific binding sites within the MgMn-LDH /Pazo composite framework. These findings highlight MgMn-LDH/Pazo composite as a highly promising, photo-switchable electrode for dynamic phosphate regulation in smart wastewater treatment applications. These results underscore the potential of MgMn-LDH/Pazo for sustainable phosphate management in wastewater through photo-switchable ion affinity. As illustrated in Fig. 7 , phosphate uptake during electro-assisted adsorption is governed not only by the intrinsic capture pathways of MgMn-LDH 68 : (i) electrostatic attraction between phosphate anions and the positively charged LDH layers, (ii) inner-sphere complexation/ligand coordination with surface metal hydroxyl sites, and (iii) anion exchange with interlayer nitrate ions, but also by the light-responsive interaction with Pazo. Under UV irradiation, the photoisomerization of Pazo modulates its molecular polarity and configuration, leading to enhanced phosphate adsorption. In the desorption step, with reversing the applied potential and switching the illumination to visible light, the generated electrostatic repulsion force drives desorption, while exchangeable Cl – and OH – in the regeneration solution competitively displace the bound phosphate 20 . In addition, the visible-light-induced back-isomerization to trans-Pazo decreases the effective binding strength toward phosphate, thereby accelerating desorption and improving regeneration efficiency. Table 2 summarizes the phosphate regulation performance of proposed MgMn-LDH/Pazo electrode with previously reported benchmarking studies 69 – 74 . The results show that these coupled electrochemical and photochemical mechanisms enable the MgMn-LDH/Pazo electrode to exhibit high adsorption capacity and reversibility for efficiently phosphate management. By integrating photo-switchable Pazo with the tunable interlayer chemistry of LDHs, this developed capacitive system demonstrates rapid kinetics, high adsorption capacity, encouraging cyclability, and strong phosphate selectivity, paving a novel avenue for controllable phosphate regulation in smart wastewater treatment and nutrient recovery applications. Table 2 Comparisons of phosphate adsorption/desorption performance of MgMn-LDH/Pazo with other reported capacitive systems. Electrode materials Phosphate concentration (ppm) Solution volume (mL) Adsorption/desorption time (min) Adsorption capacity (mg/g) Desorption efficiency (%) Ref. ZnZr-COOH/CNT 10 N.A. a 360/90 20.26 ~ 50 2022 69 ZnFe-PANI/CNT 10 70 120/90 28.56 87.5 2024 70 Gu-PAH/CNT Composite 0.5 mM 50 15/15 24.2 ~ 100 2022 71 AC/Ca-La LDH 60 40 360/N.A. 34.8 78 2025 72 FeN-co-doped carbon 15 100 480/240 12.84 84 2024 73 NiFe-LDH/ACF N.A. 100 180/N.A. 33.48 N.A. 2022 74 MgMn-LDH/Pazo 100 20 60/60 55.2 84.6 This work a N.A.: Not Applicable. Conclusion In this work, a photo-responsive MgMn-LDH/Pazo composite electrode was developed to enable controllable phosphate adsorption and release under coupled electrical bias and light stimulation. Structural characterizations confirmed successful incorporation of photoisomeriable Pazo within the LDH framework, which not only reduces interfacial impedance for efficient charge-transfer and ion diffusion within LDH electrodes, but also enables dynamical regulation of phosphate adsorption/desorption behaviors. Under UV irradiation, the trans-to-cis isomerization of Pazo provides conformational hydrogen bonding sites for phosphate, facilitating the electro-assisted adsorption process, whereas visible light induces back-isomerization of Pazo, thereby weakening the binding strength toward phosphate and accelerating desorption processes. The superior phosphate adsorption capacity of 55.2 mg-PO 4 /g and desorption efficiency of 84.6% highlight the MgMn-LDH/Pazo as a photo-switchable electrode for controllable phosphate management. These coupled electrochemical and photochemical strategy enables high operational reusability and selectivity for phosphate capture/release, offering a promising pathway toward smart wastewater treatment systems and nutrient recovery applications. Experimental methods Materials MnCl 2 (≥ 97%) from Thermo scientific USA, MgCl 2 (98%) from Showa Chemicals Co. Ltd, NaNO 3 (99%), Poly[1-4-(3carboxy-4-hydroxyphenyl-azo) benzenesulfonamido)-1,2-ethanediyl, sodium salt (Pazo) were purchased from Avantor Performance Materials, Inc. ITO glass (UR-ITO007, thickness of 0.7 mm), carbon felt (thickness of 2 mm) were purchased from Grand Chemical Co. LTD, and Na 2 HPO 4 .2H 2 O (99%) was purchased from Inter Country Corporation. In situ electrochemical growth of MgMn-LDH and MgMn-LDH/Pazo film The MgMn-LDH film was synthesized via a square-wave pulsed electrodeposition technique using a three-electrode system, where the ITO glass with a working area of 1×1 cm 2 (defined by insulating tape) served as the working electrode, a Pt sheet was used as the counter electrode, and Ag/AgCl functioned as the reference electrode. The working and counter electrodes were placed 1 cm apart. The precursor solution containing 0.03 M MgCl 2 , 0.01 M MnCl 2 , and 0.15 M Na 2 NO 3 in 200 mL deionized (DI) water was used as the electrolyte. Chronoamperometry was carried out using a workstation (Metrohm Autolab, AUT302N) by applying a pulsed voltage of − 1.25 V for 50 s, followed by a rest at 0 V for 5 s. This cycle was repeated 20 cycles to form the MgMn-LDH thin film. For the preparation of the MgMn-LDH/Pazo composite film, 0.025 wt% of Pazo was slowly added to the above-mentioned precursor solution. The deposition was carried out using alternating pulsed voltages of − 1.25 V and 0.2 V for 50 s and 5 s, respectively, with repetition of 20 cycles to layer-by-layer electrodeposition of MgMn-LDH/Pazo film. Characterizations The structural characterization of the LDH-based materials was carried out by the X-ray diffractometer (Rigaku, Ultima IV), where the angle 2 theta below 10° was characterized using BRUKER, D8 DISCOVER. Surface morphological analysis was examined using the FESEM (Hitachi, S-5200) and high-resolution transmission electron microscopy (HRTEM, JEOL 2100F). The Optical properties of the prepared films were investigated using UV-visible spectroscopy (UV-Vis, Jasco, V-770). The atomic force microscopy (AFM) analysis was employed to assess the surface topography. The chemical bonding states and elemental composition were investigated by X-ray photoelectron spectroscopy (XPS, ULVAC-PHI Inc, PHI 5000 VersaProbe III). The electrochemical measurements were conducted using a potentiostat/galvanostat workstation (Metrohm, Autolab AUT302N) with a three-electrode system, as described previously. Linear sweep voltammetry (LSV) was employed to determine the onset potential for electrodeposition, which was defined as the intersection point between the tangential lines of the horizontal background current and the initial rise in current response. Cyclic voltammetry (CV) was measured using Metrohm Autolab NOVA 2 (AUT302N). Electrochemical impedance spectroscopy (EIS) measurements were performed at open circuit potential over a frequency range of 0.1–10,000 Hz with an amplitude of 10 mV. A 20 ml of 100 ppm Na 2 HPO 4 solution was used as the electrolyte. The Nyquist diagrams were analysed using Z-view software to simulate equivalent circuit models. The phosphate concentration was determined using LaMotte Smart 3 Colorimeter, USA. Photoresponsivity tests The photoisomerization process of the electrodeposited MgMn-LDH/Pazo film was investigated to evaluate the light-induced molecular trans-to-cis switching of the Pazo. Here, a 300 W xenon lamp equipped with an optical filter (PLS-SXE300+-230501014) was used to provide monochromatic UV light (λ = 365 nm). The UV-Vis absorption spectroscopy was used to monitor the photoisomerization process. To reverse the isomerization, the UV light-irradiated samples were subsequently exposed to visible light (λ > 400 nm). Adsorption and desorption tests of phosphate in water The capacitive phosphate adsorption/desorption experiments were carried out in a 20 mL of 100 ppm of Na 2 HPO 4 solution using a three-electrode system, where the electrodeposited LDH-based films on carbon felt are the working electrode (working area of 1×1 cm 2 ), and a Pt sheet was used as the counter electrode. Phosphate adsorption was performed by applying a constant potential of 1.0 V for 60 min, accompanied by UV irradiation throughout the adsorption process. The phosphate adsorption capacity is calculated through the Eq. 2 0 : $$\:\text{A}\text{d}\text{s}\text{o}\text{r}\text{p}\text{t}\text{i}\text{o}\text{n}\:\text{c}\text{a}\text{p}\text{a}\text{c}\text{i}\text{t}\text{y}\:\left({q}_{e}\right)=\:\frac{\left({C}_{i}-\:{C}_{f}\right)\:\times\:\:V}{\text{M}}$$ 5 where C i and C f are the initial and final concentrations of phosphate in the solution (ppm), V is the volume of the solution in (L), and M is the mass of the adsorbent materials (g). For desorption, a square-wave alternating voltage ranging from − 2.0 to 0 V was applied using a waveform generator (DG800 PRO, RIGOL) for 60 min in a 20 mL regeneration solution containing 0.5 M NaOH + 0.5 M NaCl, while the illumination source was switched to visible light to induce cis-to-trans photoisomerization of Pazo. The phosphate desorption efficiency was calculated through the following equation: Desorption efficiency (%) \(\:\:=\:\frac{The\:amount\:of\:phosphate\:release\:\left(mg\right)}{Adsorption\:capacity}\times\:100\%\) (6) It enables the investigation of the dynamic, photoresponsive capability of the MgMn-LDH/Pazo electrode for smart phosphate regulation. Declarations Supplementary data Supplementary data to this article can be found online at Linear sweep voltammograms, SEM images of the electrochemical in situ growth of MgMn-LDH, UV-Vis absorption spectra of MgMn-LDH, Pazo, and MgMn-LDH/Pazo films, UV-visible absorption spectra of multilayer films of MgMn-LDH/Pazo under alternating UV (365 nm) and visible light exposure. The CV cycles of electrodeposited films with/without UV irradiation. Acknowledgement This work was financially supported by the National Science and Technology Council (NSTC) numbers NSTC 113-2222-E-131-004 and NSTC 114-2221-E-131-025, Ming Chi University of Technology (MCUT), and the MCUT Formosa Center. The authors would like to thank the Low-angle XRD Inspection and Testing at Formosa Center, Yunlin, Taiwan. The authors also thank the Ming Chi University of Technology for funding and facilities. Author contributions Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The authors are listed as inventors on a provisional of T.W. patent (I895191) and US patent (under review) from the Ming Chi University of Technology, which describes the material design and photo-switchable working mechanism. The remaining authors declare no competing interests. Data availability Data will be made available on request. 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Supplementary Files SupportingInformation.docx Controllable removal/release of phosphate by light-responsive layered double hydroxide composite electrode SupportingInformationclean.docx Controllable removal/release of phosphate by light-responsive layered double hydroxide composite electrode Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8667334","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":579409864,"identity":"210ef414-c814-491e-b510-83332076adbf","order_by":0,"name":"Yi-Ting Lai","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABEklEQVRIiWNgGAWjYBACPgbGBiAlwcDADqQTCmDibLi1sIG1JAC18BwA0gYgMWaIFh6cWkAgAWQRiCBKC/vhxgc/f1jkyUe+TvzwwIAhmn9G/gGGD2WHGezBhmDRwpPYbNiTIFFseDt3swTQYbkzbiQzMM44d5iBB5cWhsQ2CZ4EicSNs3M3gLVskEhmYOZtA2qRxqGF/2H7zz8gLTPPbv4B1/IXnxaJxDZmkC3zJXi3IWxhxKvlYbO0TJpE4gae3G0WCQYSuTPOPDY42HMunYfn/gOsWvj50x9+fGNTlzi//ezmmz8qbHL72xMfPvhRZi3H3nMAqxY4MIDIS4BJEBtXtCCAfANBJaNgFIyCUTBSAQC0J1nXJqkVugAAAABJRU5ErkJggg==","orcid":"","institution":"Ming Chi University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Yi-Ting","middleName":"","lastName":"Lai","suffix":""},{"id":579409865,"identity":"1e3c4519-5c0a-4775-9705-b6332561145b","order_by":1,"name":"Da-Wei Huang","email":"","orcid":"","institution":"Ming Chi University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Da-Wei","middleName":"","lastName":"Huang","suffix":""},{"id":579409866,"identity":"153244a1-35ed-4bcb-8021-6d89d06f398f","order_by":2,"name":"Kiruthikha Duraisathiamoorthy","email":"","orcid":"","institution":"MING CHI UNIVERSITY OF TECHNOLOGY and NATIONAL TAIWAN UNIVERSITY OF SCIENCE AND TECHNOLOGY","correspondingAuthor":false,"prefix":"","firstName":"Kiruthikha","middleName":"","lastName":"Duraisathiamoorthy","suffix":""},{"id":579409869,"identity":"4ae929c8-6da9-43a3-b72b-81487a2fb7e2","order_by":3,"name":"Dhanaprabhu Pattappan","email":"","orcid":"","institution":"MING CHI UNIVERSITY OF TECHNOLOGY","correspondingAuthor":false,"prefix":"","firstName":"Dhanaprabhu","middleName":"","lastName":"Pattappan","suffix":""},{"id":579409873,"identity":"d7d96a6c-b68b-4552-8a34-e3c17113f628","order_by":4,"name":"Chen-Jie Liao","email":"","orcid":"","institution":"MING CHI UNIVERSITY OF TECHNOLOGY","correspondingAuthor":false,"prefix":"","firstName":"Chen-Jie","middleName":"","lastName":"Liao","suffix":""},{"id":579409874,"identity":"221bf67c-0559-4345-be51-92ca696e6a70","order_by":5,"name":"Yu-Jr Chang","email":"","orcid":"","institution":"MING CHI UNIVERSITY OF TECHNOLOGY","correspondingAuthor":false,"prefix":"","firstName":"Yu-Jr","middleName":"","lastName":"Ch","suffix":"Jr"}],"badges":[],"createdAt":"2026-01-22 08:42:33","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8667334/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8667334/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":101635950,"identity":"d6160b3d-85fb-4736-b639-24f7e7c66b2e","added_by":"auto","created_at":"2026-02-02 06:28:51","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":531720,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eIn situ\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e electrodeposition of MgMn-LDH/Pazo for controllable phosphate adsorption/release.\u003c/strong\u003e(a) Schematic representation of photoresponsive MgMn-LDH/Pazo for phosphate adsorption and desorption under UV and visible light stimuli, respectively. (b) The structure of Pazo. (c) Schematic of LDH nanosheets \u003cem\u003ein situ\u003c/em\u003e growth on an Indium tin oxide (ITO) substrate.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8667334/v1/a0a31a2d99d4c4c76c33009d.png"},{"id":101635952,"identity":"9accf32d-2228-46a5-ad73-53d54da75024","added_by":"auto","created_at":"2026-02-02 06:28:51","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1517679,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMorphological and structural characterization of electrochemically layer-by-layer electrodeposited LDH-based films.\u003c/strong\u003e (a) Schematic illustration of pulse voltammetry electrodeposition of MgMn-LDH, with corresponding (b) SEM image and (c) EDS mapping. The scale bars represent 5 μm in all images. (d) Schematic illustration of pulse voltammetry electrodeposition of MgMn-LDH/Pazo, and its (e) SEM image and (f) EDS mapping. The scale bars are 5 μm in all images. TEM images of electrodeposited (g) MgMn-LDH and (i) MgMn-LDH/Pazo. The inset in (i) shows a magnified image. HRTEM images of (h) MgMn-LDH and (j) MgMn-LDH/Pazo. Both insets are their SAED patterns, confirming the polycrystalline LDH structure.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8667334/v1/7576c5a3c314401bbd757073.png"},{"id":101635947,"identity":"b19e3df0-d592-43a3-9d7f-e3c0e172a496","added_by":"auto","created_at":"2026-02-02 06:28:50","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":641093,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStructural and photoresponsive characteristics of MgMn-LDH/Pazo films.\u003c/strong\u003e (a) XRD patterns of electrodeposited MgMn-LDH-based films compared with MgMn-LDH powder. The inset is enlarged view of the broadened (003) peak in the film samples. (b) XRD pattern for MgMn-LDH/Pazo in the low-angle region (2θ \u0026lt; 10°) shows a down-shifted and broadening (003) peak, suggesting increased interlayer spacing due to Pazo intercalation. (c) UV-Vis spectra of MgMn-LDH/Pazo under UV exposure of 120 min, followed by visible light irradiation for 15 min. The inset is kinetic analysis of the trans-to-cis photoisomerization process fitted to a double-exponential decay model. (d) Reversible optical switching behavior of MgMn-LDH/Pazo films under alternating UV (365 nm) and visible light exposure, monitored at 371 nm. (e) Reversible surface roughness change upon alternating light irradiation.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8667334/v1/3415522ee21af393d6947e39.png"},{"id":101635949,"identity":"8de3749d-b88c-4068-adcb-5ab44e6e400e","added_by":"auto","created_at":"2026-02-02 06:28:50","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":417345,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical characterizations of LDH-based electrode under UV irradiation.\u003c/strong\u003e (a) CV curves of MgMn-LDH and MgMn-LDH/Pazo films with/without UV irradiation in 100 ppm phosphate solution at a scan rate of 50 mV/s. EIS analysis of (b) MgMn-LDH, (c) MgMn-LDH/Pazo and (d) MgMn-LDH/Pazo under UV irradiation. Corresponding equivalent circuit models are shown as insets. (e) Schematic diagrams illustrating the proposed charge transport pathways within the interlayer of MgMn-LDH-based materials. Upon UV exposure, the bent structure of cis-Pazo creates a barrier for charge transfer compared with linear trans-isomer.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8667334/v1/37511d0a584ed9347d46b708.png"},{"id":101635953,"identity":"72fb7ac7-a843-47fd-8bb0-bc22e8e73213","added_by":"auto","created_at":"2026-02-02 06:28:51","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":235591,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterizations of the bonding of the LDH composites.\u003c/strong\u003e XPS spectra of high-resolution (a) Mg 2p and (b) Mn 2p for both MgMn-LDH and MgMn-LDH/Pazo electrodes. (c) The XPS high-resolution N 1s for MgMn-LDH/Pazo electrode before and after phosphate adsorption. (d) The high-resolution P 2p spectra for MgMn-LDH and MgMn-LDH/Pazo electrodes after phosphate adsorption. The inset schematic structure represents the conformational hydrogen bonding of phosphate with the cis-Pazo.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8667334/v1/4bf1c178ed94487b16bd016d.png"},{"id":101635955,"identity":"c2e62759-207a-4b7e-a691-7dc2d19d66e1","added_by":"auto","created_at":"2026-02-02 06:28:58","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":159629,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe investigations of phosphate adsorption/desorption performance of LDH-based electrodes.\u003c/strong\u003e(a) The electro-assisted adsorption/desorption under light stimuli. The adsorption was performed under a constant potential of 1.0 V for 30 min, while the desorption tests were conducted using the regeneration solution of 0.5 M NaOH + 0.5 M NaCl, with a square-wave alternating voltage ranging from −2.0 to 0 V for 30 min. The purple background color represents the experiments conducted under UV light irradiation. (b) The time-dependent adsorption analysis for MgMn-LDH/Pazo under UV light. (c) Phosphate recovery cycle tests by MgMn-LDH/Pazo under alternating light stimuli. Both the adsorption and desorption times are 60 min. (d) The selectivity of MgMn-LDH/Pazo toward different ions.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8667334/v1/db34c531614ad66cabedb506.png"},{"id":101635954,"identity":"1ec07f0f-8eb0-42a2-9c4a-f38e67d0828d","added_by":"auto","created_at":"2026-02-02 06:28:52","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":606393,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMechanisms of the photo-switchable phosphate adsorption/desorption for MgMn-LDH/Pazo electrodes.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8667334/v1/94e37b1a950b2dc586626699.png"},{"id":105034823,"identity":"b5cd1c9a-09ae-4d39-904e-ab9a2f0e70fb","added_by":"auto","created_at":"2026-03-20 07:24:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5165728,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8667334/v1/6d648179-bf9a-4df5-b4d6-b26806b199f5.pdf"},{"id":101635951,"identity":"cf8a659f-f4b7-493c-99fb-79daac2a032b","added_by":"auto","created_at":"2026-02-02 06:28:51","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":965774,"visible":true,"origin":"","legend":"Controllable removal/release of phosphate by light-responsive layered double hydroxide composite electrode","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-8667334/v1/9d0693db20ee04ede6f039a5.docx"},{"id":101753449,"identity":"00d2af22-33b1-44b4-aec9-97a72ce89746","added_by":"auto","created_at":"2026-02-03 10:40:05","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":962706,"visible":true,"origin":"","legend":"Controllable removal/release of phosphate by light-responsive layered double hydroxide composite electrode","description":"","filename":"SupportingInformationclean.docx","url":"https://assets-eu.researchsquare.com/files/rs-8667334/v1/c43960f8d5f7a31869c6bb71.docx"}],"financialInterests":"\u003cb\u003eYes\u003c/b\u003e there is potential Competing Interest.\nThe authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Yi-Ting Lai, and Da-Wei Huang are listed as inventors on a provisional of T.W. patent (I895191) and US patent (under review) from the Ming Chi University of Technology, which describes the material design and photo-switchable working mechanism. The remaining authors declare no competing interests.","formattedTitle":"Controllable removal/release of phosphate by light-responsive layered double hydroxide composite electrode","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePhosphorus is a vital element in human activities, such as agricultural productivity\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, electronics preparation\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, and clinical therapeutics\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. However, the uncontrolled release of phosphate into water bodies is the major cause of eutrophication\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e, which severely disrupts aquatic ecosystems and water quality\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Traditional phosphate removal techniques, such as chemical precipitation and biological treatment, often suffer from inefficiencies, high operational costs, and secondary pollution concerns\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Therefore, the development of advanced techniques capable of controllably and selectively removing and recycling phosphate is crucial for sustainable water treatment and phosphorus resource recovery\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Various materials have been proposed for phosphate recovery from wastewater, including graphene\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e, activated carbon\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e, zeolites\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, and metal-organic frameworks (MOFs)\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. However, these materials suffer from low adsorption selectivity and high production costs, hindering their practical applications.\u003c/p\u003e \u003cp\u003eLayered double hydroxides (LDHs) have garnered increasing attention as promising adsorbents for wastewater treatment due to their high anion exchange capacity, structural stability, cost-effectiveness, and tunable properties. LDHs consist of positively charged brucite-like layers intercalated with charge-compensating anions and water molecules, allowing for efficient phosphate uptake \u003cem\u003evia\u003c/em\u003e electrostatic attraction, ligand exchange, and ion exchange mechanisms\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Extensive research has widely explored the use of LDHs for phosphate removal in environmental remediation applications\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. For example, Nie et al. fabricated a MgAl-LDH/montmorillonite composite with a maximum phosphate adsorption capacity of 127.8 mg-P/g, which surpasses the unmodified MgAl-LDH by approximately 21%\u003csup\u003e16\u003c/sup\u003e. Cao et al. reported a CaLa-LDH with an impressive adsorption capacity of 194.04 mg-P/g \u003csup\u003e17\u003c/sup\u003e. Hatami et al. synthesized ZnAl-LDHs by a modified urea hydrolysis method, which achieved a phosphate adsorption capacity of 1.49 mmol/g, with desorption efficiencies ranging from 23.2% to 36.3%, indicating the potential applicability for slow-release phosphate fertilizers\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. More recently, Li et al. introduced oxygen into MgLa-LDH to enhance electrostatic attraction and inner-sphere complexation, thereby improving the phosphate adsorption to 121.56 mg-PO\u003csub\u003e4\u003c/sub\u003e/g \u003csup\u003e19\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eDespite these advancements, current LDH-based adsorbents suffer from irreversible phosphate binding, thus hampering their regeneration capability and long-term applicability. To address this challenge, several efforts have incorporated capacitive deionization (CDI) systems to achieve reversible and energy-efficient phosphate adsorption-desorption processes\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. Herein, we demonstrated a smart electrode by \u003cem\u003ein situ\u003c/em\u003e electrochemically engineering light-responsive poly(azobenzene) into MgMn-LDH interlayers (MgMn-LDH/Pazo) for the controllable adsorption and release of phosphate from aqueous solutions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). Azobenzene derivatives, a class of photo-switchable organic molecules with a central azo (-N\u0026thinsp;=\u0026thinsp;N-) linkage between two aromatic rings (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), are well-known for their tunable \u003cem\u003eE\u003c/em\u003e/\u003cem\u003eZ\u003c/em\u003e photoisomerization upon external stimuli\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. Upon UV light irradiation, azobenzene undergoes a transition from a thermodynamically stable trans configuration to a metastable cis configuration through π-π* and n-π* electronic transitions\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. This photoisomerization is reversible in response to visible light or heat, enabling dynamic modulation of molecular structure and dipole moment\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. By leveraging the light-driven photoisomerization of Pazo, the layer-by-layer electrodeposited MgMn-LDH/Pazo (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) enables dynamic regulation of interlayer interactions and binding affinity toward phosphate ions under UV/visible light stimuli. The proposed controllable switching between adsorption and desorption states addresses the limitations of irreversible phosphate uptake in conventional CDI systems, paving the way for dynamic and efficient phosphate regulation and resource recovery in practical wastewater treatment applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eThe electrochemically layer-by-layer electrodeposition of MgMn-LDH/Pazo Films\u003c/h2\u003e \u003cp\u003eThe \u003cem\u003ein situ\u003c/em\u003e electrochemical growth of LDH nanosheets is usually carried out by applying a cathodic potential to the working electrode, which facilitates the reduction of water and nitrate ions in the precursor solution\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. The resulting hydroxide ions subsequently react with the metal ions to form lamellar LDH structures on the electrode surface, as described in the following Eq.\u0026nbsp;2\u003csup\u003e7\u003c/sup\u003e:\u003c/p\u003e \u003cp\u003e2H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;2e\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026rarr; H\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;2OH\u003csup\u003e\u0026minus;\u003c/sup\u003e (1)\u003c/p\u003e \u003cp\u003eNO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e + H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;2e\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026rarr; NO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e + 2OH\u003csup\u003e\u0026minus;\u003c/sup\u003e (2)\u003c/p\u003e \u003cp\u003e(1\u0026thinsp;\u0026minus;\u0026thinsp;\u003cem\u003ex\u003c/em\u003e)Mg\u003csup\u003e2+\u003c/sup\u003e + \u003cem\u003ex\u003c/em\u003eMn\u003csup\u003e2+\u003c/sup\u003e +2OH\u003csup\u003e\u0026minus;\u003c/sup\u003e\u0026rarr; Mg\u003csub\u003e1\u0026minus;\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e (3)\u003c/p\u003e \u003cp\u003ewhere Mn\u003csup\u003e2+\u003c/sup\u003e undergoes the self-oxidation to Mn\u003csup\u003e3+\u003c/sup\u003e upon exposure to atmospheric oxygen\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. The intercalation of nitrate anions and water molecules into the LDH interlayer space stabilizes the layered structure.\u003c/p\u003e \u003cp\u003eTo determine the optimal electrodeposition potential, linear sweep voltammetry (LSV) was performed using precursor electrolytes containing 0.1 M Mg(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e or 0.1 M Mn(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e, as shown in \u003cb\u003eFig \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e. Onset potentials of \u0026minus;\u0026thinsp;1.25 V and \u0026minus;\u0026thinsp;1.20 V vs Ag/AgCl were identified for magnesium and manganese, respectively. Consequently, a cathodic potential of \u0026minus;\u0026thinsp;1.25 V was selected for the electrodeposition process. Herein, pulsed voltammetry electrodeposition was employed to grow vertically three-dimensional (3D) LDH nanosheets (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. This technique enables inter-pulse re-equilibration of the electrolyte, thereby overcoming the mass transport and electric double layer limitations at the electrode/electrolyte interface\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e, allowing for the rapid formation of 3D nanostructured LDH at room temperature. In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, flower-like MgMn-LDH clusters composed of hierarchically grown nanosheets can be observed, accompanied by a uniform distribution of Mg, Mn, and O elements within the clusters (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). It is noted that under the same deposition time of 1000 s, the proposed pulse voltammetry method results in more 3D LDH nanosheet clusters growth compared to constant voltage deposition (\u003cb\u003eFig S2\u003c/b\u003e), which provides more active sites and facilitates the penetration of the electrolyte for phosphate adsorption\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor MgMn-LDH/Pazo films, the pulsed voltage was shifted to a positive potential of 0.2 V to facilitate the intercalation of negatively charged Pazo molecules into the LDH layers, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed. As the bias is changed oppositely, loosely bound cations are repelled from the electrode surface under the external electric field, allowing negatively charged Pazo to migrate to the deposited LDH surface\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e, thus forming the layer-by-layer MgMn-LDH/Pazo nanostructure as the cycle repeats (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). The appearance of the N element on the nanosheet cluster further confirms the incorporation of Pazo (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). It is noted that the MgMn-LDH/Pazo exhibits a smaller flower-like cluster compared to pristine MgMn-LDH, suggesting that Pazo may serve as the polymer inhibitor that mitigates localized electric fields and suppresses dendritic growth\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg\u003cb\u003e)\u003c/b\u003e, the transmission electron microscopy (TEM) image shows a 3D hierarchical flower-like morphology of MgMn-LDH nanosheets consistent with the field-emission scanning electron microscopy (FESEM) results, which is beneficial for electrolyte ions diffusion\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. The high-resolution TEM (HRTEM) image of MgMn-LDH shows polycrystallinity with the interplanar lattice spacings of 0.249 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh), corresponding to the (012) planes of LDHs\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. Moreover, the selected area electron diffraction (SAED) pattern inset in (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh\u003cb\u003e)\u003c/b\u003e displays distinct diffraction rings for the (012), (015), and (018) planes \u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e, indicating the successful formation of LDHs. On the other hand, nanoscale polymeric Pazo aggregation (~\u0026thinsp;80\u0026ndash;100 nm) can be observed in the crumpled flower-like LDH clusters (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei). In the HRTEM image (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ej), a new d-spacing of 0.44 nm, which is consistent with the theoretical azobenzene interlayer length of 0.44 nm at the most probable angle of 30\u0026deg; between the trans-Pazo and LDH layer\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. The SAED pattern (the inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ej) shows diffused features, indicating reduced crystallinity and expansion of the interlayer spacing due to incorporation of Pazo. These findings realize the construction of MgMn-LDH/Pazo composite films within hundreds of seconds through the electrochemical layer-by-layer assembly strategy, which significantly outweighs conventional self-assembly techniques requiring tens of hours\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003cb\u003eThe characterization of photoisomerization of MgMn-LDH/Pazo Films.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe intercalation of Pazo into the LDH layers was characterized by XRD. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, the electrochemically layer-by-layer deposited films do not exhibit the characteristic diffraction peaks of typical MgMn-LDH powder at 11.2\u0026deg;, 22.7\u0026deg;, 33.8\u0026deg;, 38.2\u0026deg;, 44.6\u0026deg;, 59.4\u0026deg;, and 60.6\u0026deg;, corresponding to the (003), (006), (012), (015), (018), (110), and (113) planes, respectively \u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. The absence of these reflections can be attributed to the low crystallinity or unmeasurable nanocrystalline grains in the electrodeposited films \u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. The left-hand figure highlights the broadened (003) basal reflection, further confirming the low crystallinity of the electrodeposited films. XRD analysis was further conducted in the low-angle region (2θ\u0026thinsp;\u0026lt;\u0026thinsp;10\u0026deg;) for the MgMn-LDH/Pazo film (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). A clear downshift and broadening of the (003) reflections is observed, indicating the expansion of LDH interlayer spacing due to the successful intercalation of Pazo molecules with various orientations \u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe photoisomerization of the MgMn-LDH/Pazo electrode was systematically investigated using UV-visible spectroscopy (UV-Vis). In \u003cb\u003eFig S3\u003c/b\u003e, the MgMn-LDH film shows a characteristic peak at 296 nm, in agreement with previous reports \u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. For pristine Pazo, the dominant absorption band at ~\u0026thinsp;365 nm is attributed to π \u0026rarr; π* electronic transition, while a weaker shoulder at ~\u0026thinsp;465 nm corresponds to n \u0026rarr; π* transition \u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. Upon formation of the MgMn-LDH/Pazo composite, a red shift of the π \u0026rarr; π* band to ~\u0026thinsp;371 nm is observed, which is attributed to the ligand-metal charge transfer and electrostatic interaction between Pazo molecules and LDH nanosheets\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e. In Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, under UV light irradiation (λ\u0026thinsp;=\u0026thinsp;365 nm), the absorbance at 371 nm reveals a pronounced decrease within the first 30 min and gradually reaches saturation after 60 min, indicating the trans-to-cis photoisomerization of Pazo moieties within the LDH structure. The kinetics of photoisomerization for the MgMn-LDH/Pazo film are shown in the inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, which follow the double exponential decay function \u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:A\\left(t\\right)={A}_{1}{e}^{-t/{T}_{1}}+{A}_{2}{e}^{-t/{T}_{2}}+{A}_{3}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eA(t)\u003c/em\u003e is the absorbance of 371 nm at time \u003cem\u003et\u003c/em\u003e; \u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, and \u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sub\u003e are fitting constants describing fast and slow isomerization processes. It is noted that the π \u0026rarr; π* absorption band recovers again after visible light irradiation for 5 min (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec), demonstrating reversible cis-to-trans photoisomerization \u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e. This photo-switching behavior was further confirmed by optical cycling tests in which the film was alternately irradiated with 60 min UV and 15 min visible light. The results demonstrate reversible photo-switching over multiple cycles (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed and S4\u003cb\u003e)\u003c/b\u003e, affirming the photochemical reversibility and operational stability of the cis-trans photoisomerization for MgMn-LDH/Pazo films.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe topographical changes of MgMn-LDH/Pazo films induced by light irradiation were evaluated \u003cem\u003evia\u003c/em\u003e atomic force microscopy (AFM). In Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, sharp morphology can be observed on the MgMn-LDH/Pazo surface with root-mean-square (RMS) roughness (R\u003csub\u003eq\u003c/sub\u003e) of 61.3 nm. Upon UV irradiation, the sharp peaks changed to blunt protuberances, accompanied by a significant R\u003csub\u003eq\u003c/sub\u003e decrease to 31.4 nm, suggesting a denser and more compact packing of the LDH layers\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e. Subsequent visible light exposure restored the R\u003csub\u003eq\u003c/sub\u003e to 43.7 nm, indicating the reversible switch between the light-driven trans-cis isomerization of intercalated Pazo in the composite electrode. The dynamic variation in surface morphology and molecular configuration provides a route for light-controllable phosphate adsorption/desorption behavior of the proposed MgMn-LDH/Pazo electrode in wastewater treatment applications.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eElectrochemical Characterizations of LDH-based Electrodes\u003c/h3\u003e\n\u003cp\u003eThe electrochemical properties of electrodeposited LDH-based electrodes were investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a 100 ppm phosphate solution. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and S5, the CV profiles of MgMn-LDH display pseudocapacitive properties with a prominent anodic peak near 0.6 V, which may result from the oxidation of Mn within the LDH structure\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e,\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e. The nearly unchanged CV curve measured under UV irradiation confirms no photo-responsivity for pristine MgMn-LDH. In contrast, the MgMn-LDH/Pazo electrode demonstrates enhanced current response, indicating improved charge transport and a higher electroactive surface area due to the incorporation of Pazo. Interestingly, under UV light irradiation, a further increase in redox peak currents is observed, suggesting that the trans-to-cis isomerization of Pazo modulates the electronic structure of the MgMn-LDH/Pazo\u003csup\u003e48,49\u003c/sup\u003e, leading to enhanced phosphate affinity within the electrode.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Nyquist plots (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb-d and Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) for all samples reveal a characteristic semicircle in the high-frequency region, followed by a quasi-linear curve in the low-frequency region, corresponding to charge-transfer and diffusion-controlled processes, respectively\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e. For the pristine MgMn-LDH electrode, the fitted equivalent circuit (inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb) comprises two charge transfer components (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sub\u003e) in parallel with constant phase elements, in series with a Warburg impedance (\u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e) and solution resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e)\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e, reflecting a hindered interfacial kinetics and less ideal capacitive characteristics due to limited interlayer electron transport. In contrast, the MgMn-LDH/Pazo electrode (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec) exhibits a significantly reduced semicircle diameter, indicating a drastic decrease in charge transfer resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ect\u003c/em\u003e\u003c/sub\u003e = 2.40 Ω), along with a more vertical line at low frequency for enhanced ion diffusion process \u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e. These improvements can be attributed to the intercalation of the π-conjugated Pazo molecules, which bridge adjacent hydroxide layers and promote charge transport \u003cem\u003evia\u003c/em\u003e π\u0026ndash;π interactions \u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e,\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e. In addition, intercalated Pazo enlarges the LDH interlayer spacing and provides more accessible active sites \u003csup\u003e\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e, thereby enhancing both phosphate ion diffusion and charge transfer during electrochemical reaction\u003csup\u003e\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e. It is noted that upon UV irradiation, the interfacial impedance increases slightly to 4.22 Ω (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed), which is induced by the trans-cis photoisomerization of intercalated Pazo. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee, trans-Pazo in its linear form acts as an effective interlayer bridge, facilitating the charge transfer process. However, upon photoisomerization to the cis-isomer, the bent molecular geometry creates steric hindrance in charge transfer pathway \u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e, thereby impeding electron flow across the LDH interlayers. These results confirm that Pazo not only enhances charge-transfer kinetics \u003cem\u003evia\u003c/em\u003e enhanced ion diffusion and interlayer connectivity but also provides a dynamic, light-switchable strategy for modulating electrochemical phosphate adsorption.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe comparison of the impedance form Nyquist plots for LDH-based electrodes.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eMaterials\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSolution resistance\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eCharge transfer resistance\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e (Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e (Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sub\u003e (Ω)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMgMn-LDH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e22.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e93.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.22\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMgMn-LDH/Pazo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e29.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMgMn-LDH/Pazo under UV\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e29.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eSurface chemical states of the LDH composites\u003c/h3\u003e\n\u003cp\u003eX-ray photoelectron spectroscopy (XPS) was used to characterize the surface chemical states of the LDH composites and their bonding with the phosphate. In the Mg 2p spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), the pristine MgMn-LDH displays characteristic peaks at 49.2 eV, and 50.1 eV, corresponding to Mg-OH, and Mg-O, respectively \u003csup\u003e\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e,\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e. Upon incorporation of Pazo, new signals emerge at higher binding energy at 52.2 eV for magnesium carbonates \u003csup\u003e\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e, which is attributed to coordination interactions between Mg atoms and the carboxy groups of Pazo. It confirms the strong interfacial bonding and chemical interaction between the LDH layers and Pazo. In Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, the Mn 2p spectra exhibit identified split spin-orbit components for Mn 2p\u003csub\u003e1/2\u003c/sub\u003e and Mn 2p\u003csub\u003e3/2\u003c/sub\u003e (Δ\u0026thinsp;=\u0026thinsp;11.2 eV) \u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. Upon functionalization with Pazo, the relative intensities of Mn\u003csup\u003e2+\u003c/sup\u003e and Mn\u003csup\u003e3+\u003c/sup\u003e decrease while the Mn\u003csup\u003e4+\u003c/sup\u003e increases, implying partial electron withdrawal from Mn sites to Pazo. This modulation of the redox state produces more phosphate-specific adsorption sites in the LDH sheets, facilitating the phosphate adsorption process \u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe N 1s spectra further support the successful intercalation of Pazo and the mechanism of phosphate adsorption (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). Before adsorption, characteristic peaks at near 407.5 eV and 400.0 eV correspond to interlayer NO\u003csub\u003e3\u003c/sub\u003e⁻ and -N\u0026thinsp;=\u0026thinsp;N- bond in Pazo, respectively \u003csup\u003e\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e. It is noted that the nitrate peak disappears after phosphate adsorption, indicating successful ion exchange with phosphate. The remaining -N\u0026thinsp;=\u0026thinsp;N- signal shifts and broadens, indicating potential hydrogen bonding with phosphate. To assess phosphate interaction directly, P 2p spectra were analyzed for sample electrodes after phosphate adsorption (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). The splitting peaks at 132.7 eV and 133.9 eV are attributed to P 2p\u003csub\u003e3/2\u003c/sub\u003e for HPO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e and P 2p\u003csub\u003e1/2\u003c/sub\u003e for H\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e, respectively\u003csup\u003e\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e. The high proportions of HPO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e confirm the dominant sorption of phosphate via both electrostatic interactions and inner-sphere coordination with metal hydroxides layers \u003csup\u003e\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e. It is noted that the intensity of the H\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e peak increases in the MgMn-LDH/Pazo, which is attributed to the conformational hydrogen bonding of phosphate with the cis configuration of Pazo \u003csup\u003e\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eElectro-assisted phosphate adsorption/desorption performance under light stimuli\u003c/h3\u003e\n\u003cdiv class=\"Heading\"\u003eElectro-assisted phosphate adsorption/desorption performance under light stimuli\u003c/div\u003e \u003cp\u003eThe electro-assisted phosphate adsorption/desorption performance of the LDH-based electrodes was evaluated under controlled light stimuli to elucidate the role of Pazo photoisomerization in regulating phosphate binding. In Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, the pristine MgMn-LDH electrode shows moderate phosphate uptake of 33.6 mg-PO\u003csub\u003e4\u003c/sub\u003e/g, with a desorption efficiency of 30.2% under visible light irradiation for 20 min. By comparison, the MgMn-LDH/Pazo electrode shows a suppressed adsorption and desorption under visible light, consistent with the trans configuration of Pazo presenting lower effective affinity toward phosphate. Upon switching the illumination to UV light, the phosphate adsorption capacity of MgMn-LDH/Pazo significantly increases by 80.7% to 39.4 mg-PO\u003csub\u003e4\u003c/sub\u003e/g, whereas the desorption efficiency decreases dramatically to 10.3%. This trend indicates that UV-induced trans-to-cis photoisomerization of Pazo strengthens phosphate binding due to increased steric accessibility and polarity \u003csup\u003e\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e\u003c/sup\u003e, leading to stronger interactions with phosphate. To recover phosphate efficiently, the light source was subsequently switched back to visible light during the desorption step, triggering the cis-to-trans back-isomerization and weakening the binding strength. As a result, the desorption efficiency increases by more than threefold to 37.2%, demonstrating an effective reversibility of phosphate adsorption/desorption \u003cem\u003evia\u003c/em\u003e light and voltage stimuli.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb presents the time-dependent phosphate adsorption of the MgMn-LDH/Pazo. The adsorption capacity reaches 55.2 mg-PO\u003csub\u003e4\u003c/sub\u003e/g within 60 min and then reaches a plateau, indicating fast adsorption kinetics and a high density of phosphate binding sites. Kinetic modelling reveals a better fit to the pseudo-second-order model (\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.9632) compared to the pseudo-first-order model (\u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.9298), indicating the dominant phosphate chemisorption processes, contributed by a combination of ligand exchange and anion exchange within the LDH galleries \u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, as well as light-triggered conformational bonding with Pazo \u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e,\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e\u003c/sup\u003e. The reusability of the MgMn-LDH/Pazo electrode was evaluated through consecutive adsorption-desorption cycles under alternating light stimuli (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). The adsorption capacity remains relatively stable (~\u0026thinsp;40\u0026ndash;45 mg-PO\u003csub\u003e4\u003c/sub\u003e/g) over four cycles, demonstrating good structural robustness and operational durability. In addition, only a gradual decline in desorption efficiency by approximately 10\u0026ndash;20% after the fourth cycle, suggesting a tolerable reusability. The partial loss in cyclability may be attributed to photoswitching activity degradation or progressive structural densification of LDH domains \u003csup\u003e\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e,\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e\u003c/sup\u003e, thus hindering active site regeneration and ion mobility.\u003c/p\u003e \u003cp\u003eTo evaluate ion selectivity, the adsorption experiments were conducted in the presence of competing anions, including NO\u003csub\u003e3\u003c/sub\u003e⁻, Cl⁻, and SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003e⁻. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed, MgMn-LDH/Pazo electrode exhibits substantially higher adsorption toward phosphate (47.4 mg/g) than nitrate (21.1 mg/g), chloride (18.9 mg/g), and sulfate (26.3 mg/g). This pronounced selectivity is attributed to its strong inner-sphere coordination propensity and specific binding sites within the MgMn-LDH /Pazo composite framework. These findings highlight MgMn-LDH/Pazo composite as a highly promising, photo-switchable electrode for dynamic phosphate regulation in smart wastewater treatment applications.\u003c/p\u003e \u003cp\u003eThese results underscore the potential of MgMn-LDH/Pazo for sustainable phosphate management in wastewater through photo-switchable ion affinity. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, phosphate uptake during electro-assisted adsorption is governed not only by the intrinsic capture pathways of MgMn-LDH \u003csup\u003e\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u003c/sup\u003e: (i) electrostatic attraction between phosphate anions and the positively charged LDH layers, (ii) inner-sphere complexation/ligand coordination with surface metal hydroxyl sites, and (iii) anion exchange with interlayer nitrate ions, but also by the light-responsive interaction with Pazo. Under UV irradiation, the photoisomerization of Pazo modulates its molecular polarity and configuration, leading to enhanced phosphate adsorption.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the desorption step, with reversing the applied potential and switching the illumination to visible light, the generated electrostatic repulsion force drives desorption, while exchangeable Cl\u003csup\u003e\u0026ndash;\u003c/sup\u003e and OH\u003csup\u003e\u0026ndash;\u003c/sup\u003e in the regeneration solution competitively displace the bound phosphate \u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. In addition, the visible-light-induced back-isomerization to trans-Pazo decreases the effective binding strength toward phosphate, thereby accelerating desorption and improving regeneration efficiency. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e summarizes the phosphate regulation performance of proposed MgMn-LDH/Pazo electrode with previously reported benchmarking studies \u003csup\u003e\u003cspan additionalcitationids=\"CR70 CR71 CR72 CR73\" citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e\u003c/sup\u003e. The results show that these coupled electrochemical and photochemical mechanisms enable the MgMn-LDH/Pazo electrode to exhibit high adsorption capacity and reversibility for efficiently phosphate management. By integrating photo-switchable Pazo with the tunable interlayer chemistry of LDHs, this developed capacitive system demonstrates rapid kinetics, high adsorption capacity, encouraging cyclability, and strong phosphate selectivity, paving a novel avenue for controllable phosphate regulation in smart wastewater treatment and nutrient recovery applications.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparisons of phosphate adsorption/desorption performance of MgMn-LDH/Pazo with other reported capacitive systems.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElectrode materials\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePhosphate concentration (ppm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSolution volume (mL)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAdsorption/desorption time (min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAdsorption capacity (mg/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDesorption efficiency (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eRef.\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZnZr-COOH/CNT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eN.A.\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e360/90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e20.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e~\u0026thinsp;50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2022\u003csup\u003e69\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZnFe-PANI/CNT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e120/90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e28.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e87.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2024\u003csup\u003e70\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGu-PAH/CNT Composite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.5 mM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15/15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e24.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e~\u0026thinsp;100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2022\u003csup\u003e71\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAC/Ca-La LDH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e360/N.A.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e34.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2025\u003csup\u003e72\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFeN-co-doped carbon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e480/240\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2024\u003csup\u003e73\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNiFe-LDH/ACF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN.A.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e180/N.A.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e33.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eN.A.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2022\u003csup\u003e74\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMgMn-LDH/Pazo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e60/60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e55.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e84.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eThis\u003c/p\u003e \u003cp\u003ework\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003csup\u003ea\u003c/sup\u003eN.A.: Not Applicable.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this work, a photo-responsive MgMn-LDH/Pazo composite electrode was developed to enable controllable phosphate adsorption and release under coupled electrical bias and light stimulation. Structural characterizations confirmed successful incorporation of photoisomeriable Pazo within the LDH framework, which not only reduces interfacial impedance for efficient charge-transfer and ion diffusion within LDH electrodes, but also enables dynamical regulation of phosphate adsorption/desorption behaviors. Under UV irradiation, the trans-to-cis isomerization of Pazo provides conformational hydrogen bonding sites for phosphate, facilitating the electro-assisted adsorption process, whereas visible light induces back-isomerization of Pazo, thereby weakening the binding strength toward phosphate and accelerating desorption processes. The superior phosphate adsorption capacity of 55.2 mg-PO\u003csub\u003e4\u003c/sub\u003e/g and desorption efficiency of 84.6% highlight the MgMn-LDH/Pazo as a photo-switchable electrode for controllable phosphate management. These coupled electrochemical and photochemical strategy enables high operational reusability and selectivity for phosphate capture/release, offering a promising pathway toward smart wastewater treatment systems and nutrient recovery applications.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eExperimental methods\u003c/h2\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eMnCl\u003csub\u003e2\u003c/sub\u003e (\u0026ge;\u0026thinsp;97%) from Thermo scientific USA, MgCl\u003csub\u003e2\u003c/sub\u003e (98%) from Showa Chemicals Co. Ltd, NaNO\u003csub\u003e3\u003c/sub\u003e (99%), Poly[1-4-(3carboxy-4-hydroxyphenyl-azo) benzenesulfonamido)-1,2-ethanediyl, sodium salt (Pazo) were purchased from Avantor Performance Materials, Inc. ITO glass (UR-ITO007, thickness of 0.7 mm), carbon felt (thickness of 2 mm) were purchased from Grand Chemical Co. LTD, and Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e.2H\u003csub\u003e2\u003c/sub\u003eO (99%) was purchased from Inter Country Corporation.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eIn situ\u003c/b\u003e \u003cb\u003eelectrochemical growth of MgMn-LDH and MgMn-LDH/Pazo film\u003c/b\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe MgMn-LDH film was synthesized \u003cem\u003evia\u003c/em\u003e a square-wave pulsed electrodeposition technique using a three-electrode system, where the ITO glass with a working area of 1\u0026times;1 cm\u003csup\u003e2\u003c/sup\u003e (defined by insulating tape) served as the working electrode, a Pt sheet was used as the counter electrode, and Ag/AgCl functioned as the reference electrode. The working and counter electrodes were placed 1 cm apart. The precursor solution containing 0.03 M MgCl\u003csub\u003e2\u003c/sub\u003e, 0.01 M MnCl\u003csub\u003e2\u003c/sub\u003e, and 0.15 M Na\u003csub\u003e2\u003c/sub\u003eNO\u003csub\u003e3\u003c/sub\u003e in 200 mL deionized (DI) water was used as the electrolyte. Chronoamperometry was carried out using a workstation (Metrohm Autolab, AUT302N) by applying a pulsed voltage of \u0026minus;\u0026thinsp;1.25 V for 50 s, followed by a rest at 0 V for 5 s. This cycle was repeated 20 cycles to form the MgMn-LDH thin film.\u003c/p\u003e\u003cp\u003eFor the preparation of the MgMn-LDH/Pazo composite film, 0.025 wt% of Pazo was slowly added to the above-mentioned precursor solution. The deposition was carried out using alternating pulsed voltages of \u0026minus;\u0026thinsp;1.25 V and 0.2 V for 50 s and 5 s, respectively, with repetition of 20 cycles to layer-by-layer electrodeposition of MgMn-LDH/Pazo film.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e\n\u003ch3\u003eCharacterizations\u003c/h3\u003e\n\u003cp\u003eThe structural characterization of the LDH-based materials was carried out by the X-ray diffractometer (Rigaku, Ultima IV), where the angle 2 theta below 10\u0026deg; was characterized using BRUKER, D8 DISCOVER. Surface morphological analysis was examined using the FESEM (Hitachi, S-5200) and high-resolution transmission electron microscopy (HRTEM, JEOL 2100F). The Optical properties of the prepared films were investigated using UV-visible spectroscopy (UV-Vis, Jasco, V-770). The atomic force microscopy (AFM) analysis was employed to assess the surface topography. The chemical bonding states and elemental composition were investigated by X-ray photoelectron spectroscopy (XPS, ULVAC-PHI Inc, PHI 5000 VersaProbe III). The electrochemical measurements were conducted using a potentiostat/galvanostat workstation (Metrohm, Autolab AUT302N) with a three-electrode system, as described previously. Linear sweep voltammetry (LSV) was employed to determine the onset potential for electrodeposition, which was defined as the intersection point between the tangential lines of the horizontal background current and the initial rise in current response. Cyclic voltammetry (CV) was measured using Metrohm Autolab NOVA 2 (AUT302N). Electrochemical impedance spectroscopy (EIS) measurements were performed at open circuit potential over a frequency range of 0.1\u0026ndash;10,000 Hz with an amplitude of 10 mV. A 20 ml of 100 ppm Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e solution was used as the electrolyte. The Nyquist diagrams were analysed using Z-view software to simulate equivalent circuit models. The phosphate concentration was determined using LaMotte Smart 3 Colorimeter, USA.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003ePhotoresponsivity tests\u003c/h2\u003e \u003cp\u003eThe photoisomerization process of the electrodeposited MgMn-LDH/Pazo film was investigated to evaluate the light-induced molecular trans-to-cis switching of the Pazo. Here, a 300 W xenon lamp equipped with an optical filter (PLS-SXE300+-230501014) was used to provide monochromatic UV light (λ\u0026thinsp;=\u0026thinsp;365 nm). The UV-Vis absorption spectroscopy was used to monitor the photoisomerization process. To reverse the isomerization, the UV light-irradiated samples were subsequently exposed to visible light (λ\u0026thinsp;\u0026gt;\u0026thinsp;400 nm).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eAdsorption and desorption tests of phosphate in water\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe capacitive phosphate adsorption/desorption experiments were carried out in a 20 mL of 100 ppm of Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e solution using a three-electrode system, where the electrodeposited LDH-based films on carbon felt are the working electrode (working area of 1\u0026times;1 cm\u003csup\u003e2\u003c/sup\u003e), and a Pt sheet was used as the counter electrode. Phosphate adsorption was performed by applying a constant potential of 1.0 V for 60 min, accompanied by UV irradiation throughout the adsorption process. The phosphate adsorption capacity is calculated through the Eq.\u0026nbsp;2\u003csup\u003e0\u003c/sup\u003e:\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Equ2\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:\\text{A}\\text{d}\\text{s}\\text{o}\\text{r}\\text{p}\\text{t}\\text{i}\\text{o}\\text{n}\\:\\text{c}\\text{a}\\text{p}\\text{a}\\text{c}\\text{i}\\text{t}\\text{y}\\:\\left({q}_{e}\\right)=\\:\\frac{\\left({C}_{i}-\\:{C}_{f}\\right)\\:\\times\\:\\:V}{\\text{M}}$$\u003c/div\u003e \u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003ewhere \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sub\u003e are the initial and final concentrations of phosphate in the solution (ppm), V is the volume of the solution in (L), and M is the mass of the adsorbent materials (g). For desorption, a square-wave alternating voltage ranging from \u0026minus;\u0026thinsp;2.0 to 0 V was applied using a waveform generator (DG800 PRO, RIGOL) for 60 min in a 20 mL regeneration solution containing 0.5 M NaOH\u0026thinsp;+\u0026thinsp;0.5 M NaCl, while the illumination source was switched to visible light to induce cis-to-trans photoisomerization of Pazo. The phosphate desorption efficiency was calculated through the following equation:\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003eDesorption efficiency (%)\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\:=\\:\\frac{The\\:amount\\:of\\:phosphate\\:release\\:\\left(mg\\right)}{Adsorption\\:capacity}\\times\\:100\\%\\)\u003c/span\u003e\u003c/span\u003e (6)\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eIt enables the investigation of the dynamic, photoresponsive capability of the MgMn-LDH/Pazo electrode for smart phosphate regulation.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eSupplementary data\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSupplementary data to this article can be found online at\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eLinear sweep voltammograms, SEM images of the electrochemical \u003cem\u003ein situ\u003c/em\u003e growth of MgMn-LDH, UV-Vis absorption spectra of MgMn-LDH, Pazo, and MgMn-LDH/Pazo films, UV-visible absorption spectra of multilayer films of MgMn-LDH/Pazo under alternating UV (365 nm) and visible light exposure. The CV cycles of electrodeposited films with/without UV irradiation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was financially supported by the National Science and Technology Council (NSTC) numbers NSTC 113-2222-E-131-004 and NSTC 114-2221-E-131-025, Ming Chi University of Technology (MCUT), and the MCUT Formosa Center. The authors would like to thank the Low-angle XRD Inspection and Testing at Formosa Center, Yunlin, Taiwan. The authors also thank the Ming Chi University of Technology for funding and facilities.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The authors are listed as inventors on a provisional of T.W. patent (I895191) and US patent (under review) from the Ming Chi University of Technology, which describes the material design and photo-switchable working mechanism. 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Water Sci Technol 86:3014\u0026ndash;3027. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2166/wst.2022.383\u003c/span\u003e\u003cspan address=\"10.2166/wst.2022.383\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Layered double hydroxides, azobenzene, photoisomerization, phosphate recovery, wastewater treatment","lastPublishedDoi":"10.21203/rs.3.rs-8667334/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8667334/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDynamic phosphate regulation is crucial for environmental protection and sustainable phosphorus management. In this work, we developed a smart electrode by electrochemically engineering photo-responsive poly(azobenzene) into MgMn-layered double hydroxide interlayers (MgMn-LDH/Pazo) for light-switchable capacitive phosphate removal and recovery from aqueous environments. Under UV light irradiation, the trans-to-cis photoisomerization of intercalated Pazo induces the formation of multiple bonding interactions with phosphate ions, leading to an enhanced phosphate adsorption capacity from 14.08 to 55.22 mg-PO\u003csub\u003e4\u003c/sub\u003e/g. Upon switching to visible light, the cis-to-trans isomerization of Pazo decreases the binding affinity toward phosphate, achieving an efficient phosphate desorption with a regeneration rate of 84.6%. This optically switchable system enables selective, reversible, and tunable phosphate uptake and release, offering a sustainable solution for environmental remediation and phosphorus resource recovery. The proposed innovative strategy demonstrates excellent phosphate removal/release performance with operational controllability, positioning it as a promising candidate for next-generation smart wastewater treatment technologies.\u003c/p\u003e","manuscriptTitle":"Controllable removal/release of phosphate by light-responsive layered double hydroxide composite electrode","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-02 06:28:29","doi":"10.21203/rs.3.rs-8667334/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"3f6057da-ad98-4b4b-b21f-03a55faff364","owner":[],"postedDate":"February 2nd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":61650213,"name":"Earth and environmental sciences/Environmental sciences/Environmental chemistry/Pollution remediation"},{"id":61650214,"name":"Earth and environmental sciences/Environmental sciences"}],"tags":[],"updatedAt":"2026-03-18T20:25:36+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-02 06:28:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8667334","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8667334","identity":"rs-8667334","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}