Ligand-functionalized Anderson-type Polyoxometalate for Efficient Selective Cationic Dye Adsorption

Ligand-functionalized Anderson-type Polyoxometalate for Efficient Selective Cationic Dye Adsorption | 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 Research Article Ligand-functionalized Anderson-type Polyoxometalate for Efficient Selective Cationic Dye Adsorption Hongji Kang, Lili Yang, Yuqi Liu, Ke Su, Hao Zhang, Xiaoxue Huang, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3849763/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract The issue of treating organic dyes in industrial wastewater has long been a subject of grave concern in the fields of environmental protection and public health. In an attempt to explore efficient solutions to this problem, this work focuses on the selective adsorption approach towards dyes molecules based on a Anderson-type polyoxometalate (POM, noted as POM-1 ) as potential adsorbent, which has been functionalized with organic groups. Adsorption experiments revealed that POM-1 displayed efficient adsorption capabilities towards the cationic dye methyl blue (MB) with almost complete adsorption within 25 min, and the adsorption rate was calculated as 98%. A rapid and consecutive filtering experiments have also been performed and further proved the excellent adsorption behavior of POM-1 towards MB. We envision that the functionalization of carboxylic ligands increased the negative charges of anionic POM, greatly promotes the interactions between adsorbent and cationic MB via electrostatic effect. Polyoxometalates Anderson-type Cationic dyes Selective adsorption Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction The excess emission of the organic dyes in wastewater have potential toxicity caused serious pollution to the environment, which has been aroused more and more attentions. Organic dyes could be categorized based on their chemical composition, usage, and ability to dissolve in water-based solutions, and also hardly degrade under the natural conditions, due to their structure stabilities and high solubility [ 1 – 5 ] . Therefore, the search for an appropriate method to remove these organic dyes is not only of great significance but also an urgent necessity. Comparatively, physical adsorption has been acknowledged as a more straightforward, uncomplicated, and energy-efficient approach, which does not involve any harmful byproducts and allows for the easy separation of the solid adsorbents that bind the dyes to their surface, leaving no trace behind. Despite the numerous porous adsorbents have been reported and garnered attention in the scientific community [ 6 – 14 ] , there is still a dire need for more adsorbents that possess efficient, rapid, and selective adsorption capabilities. These new adsorbents should be designed specifically for the adsorption of specific dyes, taking into account their structural features, charges, or sizes. This would not only enhance the overall adsorption process but would also contribute to the development of more sustainable and environmentally-friendly solutions for the removal of dyes from wastewater. Polyoxometalates (POMs) represent a category of polynuclear oxygen-bridged clusters consisting of early transition metals in their high oxidation state, which exhibit diverse topological structures [ 15 – 20 ] . Especially, the functionalization of organic ligand into POMs units endow these materials a wide range of potential properties that extensively applied in various fields, including catalysis, medicine, ion exchange, molecular materials, photochemistry, electrochemistry, and magnetism [ 21 – 26 ] . In terms of the structural feature, the planar Anderson-type POMs consisting of a central XO 6 octahedron unit and six edge-sharing MO 6 octahedron units, could be easily functionalized by grafting triol-based ligands on each side of units, which provides the potential functional sites to modify them through hydroxyl substitution reaction, generating a large range of organic functionalized Anderson-type POMs under well design with unique physical and chemical properties. Therefore, considering these remarkable structure and property performance of organic functionalized Anderson-type POMs [ 27 – 31 ] , these materials could be selected as one kinds of promising organic dyes adsorbents, contributing to the development of more sustainable and environmentally-friendly solutions for the removal of dyes from wastewater [ 32 – 34 ] . Herein, in order to take full advantage of these clusters with negative charge, an Anderson-type POM ( POM-1) with carboxylic-based ligands were selected to study its adsorption ability for organic dyes. The incorporation of carboxylic groups with high deprotonation could increase the negative-charged in POM-1 . The adsorption experiments revealed that POM-1 displayed efficient adsorption capabilities towards the cationic dye MB in a high rate with almost complete adsorption within 25 min. The competitive and consecutive filtering experiments have also been performed and further proved the excellent efficient and selective adsorption behavior of POM-1 towards cationic MB via electrostatic effect. Experimental General methods details All chemicals and solvents are purchased from commercial sources without further purification. The collection of Powder X-ray diffraction (PXRD) patterns was performed using a Bruker AXS D8 Advance X-ray diffractometer. The infrared spectrum (IR) was collected by NEXUS instrument using KBr particles. The UV-visible spectrum of the liquid was analyzed using a TU-1901 UV-visible spectrometer, which had a scanning range of 200–800 nm. The 1 H NMR spectra were acquired using a Bruker Avance 400 spectrometer. X-ray photoelectron spectroscopy (XPS) characterization was carried out by using a Thermo Scientific K-Alpha + spectrometer with Al Kα X-ray (1486.6 eV) as the light source. Preparation of 4-HOOC(C 6 H 4 )CH 2 NHC(CH 2 OH) 3 (H 4 L) The ligand H 4 L was synthesized according to the method reported in the literature [ 35 ] . P-bromomethylbenzoic acid (3.78g) was added to a 300 mL tris (hydroxymethyl) aminomethane (10.18g) aqueous solution in 2 min. After stirring the reactant at room temperature for 20 hours, the solid 4-bromomethylbenzoic acid was completely dissolved after 30 min and white precipitate appeared after 7 hours. The white precipitate was separated by filtration, subjected to two washes with 20 mL of water each, followed by two washes with 15 mL of acetone each. Subsequently, the precipitate was dried under vacuum conditions, resulting in a yield of 3.2 g. The 1 H NMR spectrum is consistent with the literature. Preparation of [N(n-C 4 H 9 ) 4 ] 4 [(MnMo 6 O 18 )(HL)(L)]·3DMF (POM-1) The mixture containing [N(n-C 4 H 9 ) 4 ] 4 [α-Mo 8 O 26 ] (1.100 g, 0.50 mmol), Mn(OAc) 3 ·2H 2 O (0.201 g, 0.67 mmol), H 4 L (0.438 g), tetrabutylammonium bromide (0.215 g, 0.67 mmol), and 20 mL DMF was subjected to stirring at 85°C for 22 hours. The suspension was centrifuged, and the orange supernatant was placed in an ether atmosphere. After 2 days, orange crystals were formed. In order to enhance the yield, the crystal underwent additional diffusion in an ether atmosphere for a duration of 7 days, followed by drying, resulting in the acquisition of 0.982 g. The synthetic route is presented in Scheme 1 . Adsorption experiments The adsorption experiment was conducted using the following method: POM-1 (3×12 mg) was prepared and added to 3×5 mL solutions of MB, rhodamine 6G (Rh6G) and methyl orange (MO), each with a concentration of 1×10 − 3 mol·L − 1 . The solutions were then placed in a dark environment. Subsequently, 75 µL of the supernatant was extracted and combined with 2925 µL of deionized water to prepare a 3 mL solution. The concentration of the organic dye solution was determined using ultraviolet/visible spectrophotometry at regular intervals. Results and Discussion POM-1 possesses a symmetric configuration with two H L 4− ligands grafted on both sides of [MnMo 6 O 18 ] cluster, and exhibits a relatively high level of stability. Infrared spectrum of POM-1 revealed the medium intensity absorption peaks near 2960 and 2873 cm − 1 correspond to the C-H stretching vibration of the ν (−CH2) group. The weak absorption peak near 1381 cm − 1 corresponds to the C-N stretching vibration of ν C−N . It can be observed that the moderate absorption peak near 1649 to 1482 cm − 1 corresponds to the ν C=C stretching vibration peak, which is indicative of the benzene ring structure in the organic ligand. Additionally, the weak absorption peak near 1152 to 1037 cm − 1 corresponds to the δ C−H in-plane bending vibration, also associated with the benzene ring structure in the organic ligand. The strong absorption peaks near 939 to 665 cm − 1 correspond to the out-of-plane bending vibrations of γ C−H , which are indicative of the benzene ring structure in the organic ligand. The IR spectrum of POM-1 was consistent with the reported Anderson-type POM cluster. The valence states of POM-1 were characterized by X-ray photoelectron spectroscopy (XPS) test. The XPS diagram of POM-1 is shown in the Fig. 1 . Two peaks at 235.1 eV and 232 eV, corresponding to Mo 6+ 3d 3/2 and Mo 6+ 3d 5/2 , respectively, while the peaks at 653.8eV and 641.9eV could be attributed to Mn 3+ 2p 1/2 and Mn 3+ 2p 3/2 , respectively. In addition, 657.6eV is the satellite peak of Mn 3+ 2p 1/2 and 646.2eV is the satellite peak of Mn 3+ 2p 3/2 . These results indicated that valence states of Mo and Mn in POM-1 are + 6 and + 3, respectively, which are consistent with those of the raw materials. In order to explore and verify the adsorption performance of POM-1 , we selected cationic organic dye MB and Rh6G for the selective adsorption experiments, and analyzed the adsorption performance of POM-1 for different organic dyes by ultraviolet-visible spectrophotometer. The structural formulas of used organic dyes are presented in Table S1 . Firstly, the adsorption properties of POM-1 towards MB were investigated. The prepared POM-1 , weighing 12 mg, was introduced into a 5 mL solution of MB with a concentration of 1 × 10 − 3 mol·L -1 . The mixture was then kept in a dark environment and monitored the layer pellucid liquid by UV-Vis. As depicted in Fig. 2 (a), UV-Vis adsorption spectrum of MB aqueous solution exhibits a strong adsorption at λ max = 664 nm, and the peak were decreased sharply with the extension of adsorption time. The adsorption process could complete within 25 min with the color of MB solution changed from blue to transparent, and the adsorption rate was calculated as 97.4%, according to the function of 1- A / A 0 × 100%, where A 0 is the absorbance of the original MB solution, and A is the absorbance of MB solution at different time intervals using POM-1 as absorbent. These results indicated that POM-1 has significant adsorption ability for MB. The MB concentration changes as a function of time are plotted in Fig. 2 b, and the adsorption process of POM-1 showed a pseudo-second-order kinetic behaviors. In terms of the adsorption mechanism, we speculate that the positive-charged MB and the negative-charged POM-1 are greatly beneficial for the electrostatic interaction between them. In addition, when changing MB into other cationic dye, Rh6G, with larger size than MB, the adsorption behavior of POM-1 shows quite different under the same conditions. UV-Vis adsorption spectra of Rh6G aqueous solution using POM-1 as absorbent reveal that only 60.5% decrease of absorbance after 6 h, and the color of the solution remains its original color (Fig. 2 c). Extending the detection time could not enhance the adsorption rate. Within 6 h, the adsorption process of POM-1 also showed a pseudo-second-order kinetic behaviors towards Rh6G (Fig. 2 d). These result suggest that the matching charges and suitable sizes are both play the significant roles in the adsorption capacities of POM-1 towards organic dyes. In order to verify these speculation, control experiments have been further carried out by selecting an anionic organic dye, methyl orange (MO) with similar size with MB, to study the adsorption ability of POM-1 under the same conditions that introducing 12 mg of POM-1 into a 5 mL solution of MO with a concentration of 2×10 − 3 mol·L -1 . As shown in Fig. 3 a, MO solution exhibits a characteristic absorption peak at 465 nm, and almost no reduction of the absorbance occurs after 100 min or even longer detection time. These results indicated the weak adsorption capacity of POM-1 towards the anionic MO, due to the negative-negative charge repulsive effect, and also could give a fully proof for the adsorption mechanism that the electrostatic interaction is the main factor affecting this adsorption process. Competitive adsorption experiments were also conducted with the mixture solutions of MB with MO under the same concentration in the presence of POM-1 . After 15 min, the absorbance of the characteristic peak of MB at 664 nm were sharply decreased, while the characteristic peak of MB at 465 nm were still remained unchanged (Fig. 3 b). The adsorption rate of POM-1 towards MB is about 87.2% at 15 min, consistent with the adsorption rate (85.67%, 15 min) in the single MB solution, suggesting that the presence of other dyes could not affect the adsorption capacity of POM-1 . We could conclude that compound 1 exhibits an efficient and selective adsorption capacity for the size-suitable cationic dye MB and an obvious excluding behavior towards another anionic dyes, acting as a promising adsorbent used for the separation of different charged organic dyes. Considering the remarkable adsorption capacity of POM-1 towards MB, a set of rapid filter devices was established. A plastic dropper without top was chosen as the basic module, and the cotton was compacted to the bottom of the device, and 24 mg of POM-1 was compressed in the upper layer. A solution of MB with a concentration of 1×10 − 3 mol·L -1 was introduced into the upper part of the apparatus, and the solution underwent gradual compression through POM-1 layer due to the force of gravity. In this case, the color of the added MB solution was changed from blue to colorless after filtration, and the UV-vis absorbance of the filtered MB solution was almost eliminated after a single cycle (Fig. 4 a), indicating rapid adsorption rate of POM-1 towards MB. This rapid adsorption could be consecutive used for at least 30 rounds (1 mL MB solution for each addition). Furthermore, a mixture solution consisting of MB and MO under the same concentration was added into the upper of the filtering set, and only yellow solution could be observed after filtration (Fig. 4 b). These results revealed that only MB has been adsorbed with MO remaining in the solution, suggesting that the presence of other competitive dyes could not affect the rapid and selective adsorption behavior of POM-1 . This observation could also examined by the UV-vis spectra analysis. Reusability and stability are the crucial factors for the practical application of adsorbents. After the adsorption, POM-1 could be obtained through either filtration or centrifugal separation and the color of the sample were changed from yellow to dark blue (Fig. 5 a). The isolated sample were further analyzed by IR spectra. Compared with spectra of free POM-1 and MB, it can be seen that the IR spectrum of POM-1 adsorbed MB consists of the characteristic peaks of free POM-1 and MB, indicating the stable skeleton of POM-1 during the adsorption process (Fig. 5 b). The peak at 648 cm -1 is the typical characteristic peak of POM-1 [ 36 ] . The infrared spectrum of MB adsorbed by POM also contains the characteristic peak of POM-1. The 2800–3100 cm -1 range represents the C-H stretching vibration peak of -CH 2 . Although organic dye MB does not contain -CH 2 , the IR spectrum of MB adsorbed by POM shows the stretching vibration peak in this range, indicating the presence of POM-1 . The stretching vibration peak of the C-S bond in MB is at 1324 cm -1 . However, in the infrared spectrum of MB adsorbed by POM, the stretching vibration peak of the C-S bond is observed at 1228 cm -1 . This shift may be attributed to the interaction between POM-1 and MB through electrostatic effects [ 13 , 37 ] . At the same time, the infrared spectrum of MB adsorbed by POM shows a decrease to a certain extent in the peak range of 1200–1350 cm -1 , which is also attributed to the electrostatic effect. Subsequently, desorption experiments of MB were conducted by a continuous oscillation of the isolated sample added in other 20 mL deionized water. After 2h oscillation, the colour of the solution could be recover to blue, suggesting that the adsorbed MB could be desorbed from the adsorbent POM-1 . However, the desorbed MB could be further adsorbed in this system within 20 min, without any decreased of efficiency (Fig. 5 c). These results demonstrated the favorable cyclic adsorption capabilities of POM-1 towards MB. Conclusion In conclusion, this work reported a carboxylic-functionalized Anderson-type POM cluster as an excellent selective adsorbent for dyes. The enhanced negative-charged POM-1 could greatly promote the efficient adsorption towards the cationic dye MB within 25 min. Additionally, the electrostatic interaction is also influenced by the appropriate size, resulting in only 60.4% adsorption rate of POM-1 towards Rh6G with a larger molecular size. A rapid and consecutive filtering device has been established to demonstrate the remarkable adsorption behavior of POM-1 towards MB, indicating its promising potential for industrial wastewater treatment. Declarations Ethical Approval Not applicable Funding This work was co-financed by National Natural Science Foundation of China (21901147) and Natural Science Foundation of Shandong Province (ZR2018BB002). Availability of data and materials The crystal data (CCDC 2008219 in this paper) can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected] , or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. References X. Bai, J. Shi, Z. Y. Zhang, M. Hu, J. Chai, L. Xu, X. Jin, X. Shi, P. K. Jin, J. Clean. Prod. 138375, 421 (2023). F. X. Deng, E. Brillas, Sep. Purif. Technol. 123764, 316 (2023). H. Wu, Z. Z. Liu, A. Li, H. Yang, Chemosphere. 207, 174 (2017). M. Ismail, K. Akhtar, M. 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Sara Dawood, Tushar Kanti Sen, Water Res. 1946, 46 (2012). Scheme Scheme 1 is available in Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files KangSI.docx TOC.png Graphical Abstract floatimage1.png Scheme 1.Schematic of synthetic route of POM-1. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 01 Feb, 2024 Reviews received at journal 24 Jan, 2024 Reviewers agreed at journal 22 Jan, 2024 Reviewers agreed at journal 22 Jan, 2024 Reviewers agreed at journal 22 Jan, 2024 Reviewers invited by journal 22 Jan, 2024 Editor assigned by journal 12 Jan, 2024 Submission checks completed at journal 12 Jan, 2024 First submitted to journal 10 Jan, 2024 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. 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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-3849763","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":266702918,"identity":"7d8c71d1-20fc-416d-a1e6-428220955dbc","order_by":0,"name":"Hongji Kang","email":"","orcid":"","institution":"Shandong University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Hongji","middleName":"","lastName":"Kang","suffix":""},{"id":266702919,"identity":"fb8059ad-b031-47e1-94c7-5cbdc56a3c53","order_by":1,"name":"Lili Yang","email":"","orcid":"","institution":"Shangqiu Product Quality Inspection and Research Center","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Lili","middleName":"","lastName":"Yang","suffix":""},{"id":266702920,"identity":"5980fd9f-1e2e-456b-bd4c-c6427382a84b","order_by":2,"name":"Yuqi Liu","email":"","orcid":"","institution":"Shandong University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yuqi","middleName":"","lastName":"Liu","suffix":""},{"id":266702921,"identity":"9e41f2a4-b364-42ca-9b01-0121c12e4bba","order_by":3,"name":"Ke Su","email":"","orcid":"","institution":"Shangqiu Product Quality Inspection and Research Center","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ke","middleName":"","lastName":"Su","suffix":""},{"id":266702922,"identity":"3f0794f7-0b9b-4065-a708-d2700cd95438","order_by":4,"name":"Hao Zhang","email":"","orcid":"","institution":"Shandong University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Hao","middleName":"","lastName":"Zhang","suffix":""},{"id":266702923,"identity":"1b5a4ff9-618c-40b4-9fca-bede03ff2472","order_by":5,"name":"Xiaoxue Huang","email":"","orcid":"","institution":"Shandong University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xiaoxue","middleName":"","lastName":"Huang","suffix":""},{"id":266702924,"identity":"09b4b6bf-a746-49f3-af12-113f3a17e271","order_by":6,"name":"Lu Yang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0klEQVRIie3LMQuCQBTA8SeCk+lqS/URDgQJivwqHoItUpuzk1MfQOlL9BEubnAxXQ9qMFoaHBxbgs6gtdMt6P7w4D14PwCZ7FerYQlAuk3rSzwIOFGHETqAoPxE7zipXINtCbQRBXMfC0ixCeY4OeOM+aCkJQXrQgSEhA7ixEOcqKOEArI8AamajpTumzx7ERbaNU6IcuiI0oeMWeOAV/o4K27ouCvXusUExKhCu22jlWvk+Fo/osXETAVkRkCzPgfho3//501jUFvhl0wmk/13L0HsSdLU4RM2AAAAAElFTkSuQmCC","orcid":"","institution":"Shandong University of Technology","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Lu","middleName":"","lastName":"Yang","suffix":""}],"badges":[],"createdAt":"2024-01-10 08:52:43","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3849763/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3849763/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":49625211,"identity":"2fc4e276-428f-478d-87a3-cb16568b1ff5","added_by":"auto","created_at":"2024-01-15 13:58:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":465754,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Mn 2p XPS spectrum of \u003cstrong\u003ePOM-1\u003c/strong\u003e; (b) Mo 3d XPS spectrum of \u003cstrong\u003ePOM-1\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-3849763/v1/c7d4f87e8cc3de78b9b50dc4.png"},{"id":49625215,"identity":"a9edb0b2-1dcc-483f-a2fe-0e9bc3711e02","added_by":"auto","created_at":"2024-01-15 13:58:56","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":546522,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(\u003c/strong\u003ea) UV-Vis adsorption spectra of MB aqueous solution using \u003cstrong\u003ePOM-1\u003c/strong\u003e as absorbent at different adsorption times; (b) Corresponding plots of C\u003csub\u003et\u003c/sub\u003e/C\u003csub\u003e0\u003c/sub\u003e of MB versus time during the adsorption; (c) UV-Vis adsorption spectra of Rh6G aqueous solution using \u003cstrong\u003ePOM-1\u003c/strong\u003e as absorbent at different adsorption times; (d) Corresponding plots of C\u003csub\u003et\u003c/sub\u003e/C\u003csub\u003e0\u003c/sub\u003e of Rh6G versus time during the adsorption.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-3849763/v1/f217e126c2bd3e2c17a9aaa9.png"},{"id":49625210,"identity":"0b1c1934-ef40-49f8-92b1-5fe43bc70353","added_by":"auto","created_at":"2024-01-15 13:58:56","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":339821,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(\u003c/strong\u003ea) UV-Vis adsorption spectra of MO aqueous solution in the presence of \u003cstrong\u003ePOM-1\u003c/strong\u003e at different adsorption times; (b) Competitive adsorption curves of MB and MO in the presence of \u003cstrong\u003ePOM-1\u003c/strong\u003e at different adsorption times.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-3849763/v1/82b7a18e80d2f6fbb9e34c4d.png"},{"id":49625212,"identity":"448167c8-50b4-4a0f-ba32-015d1ac74e93","added_by":"auto","created_at":"2024-01-15 13:58:56","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":314560,"visible":true,"origin":"","legend":"\u003cp\u003e(a) UV-Vis adsorption spectra of MB solution before and after passed through the \u003cstrong\u003ePOM-1 \u003c/strong\u003epacked filtering apparatus; (b) UV-Vis adsorption spectra of MB and MO solution before and after passed through the \u003cstrong\u003ePOM-1\u003c/strong\u003e-packed filtering apparatus. Inset: picture of the filtering process.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-3849763/v1/bf2204f9b6a124f2389f6a38.png"},{"id":49625702,"identity":"4b816394-a8cf-4b73-9790-3dcb50675b0a","added_by":"auto","created_at":"2024-01-15 14:06:56","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":976665,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Pictures of \u003cstrong\u003ePOM-1\u003c/strong\u003e before and after MB adsorption; (b) IR spectra of \u003cstrong\u003ePOM-1\u003c/strong\u003e, MB and \u003cstrong\u003ePOM-1\u003c/strong\u003e after adsorption of MB; (c) Pictures of desorption, and re-adsorption process of MB solution.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-3849763/v1/3ad4f5396c8b479f3c37ae09.png"},{"id":49626019,"identity":"c634c51c-2879-489f-a14d-b062a0e8e013","added_by":"auto","created_at":"2024-01-15 14:14:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1162291,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3849763/v1/1f20333b-e4a4-4e64-be47-03d6fd08d39a.pdf"},{"id":49625209,"identity":"418d12ab-d30b-4b84-ad80-989dee459e68","added_by":"auto","created_at":"2024-01-15 13:58:56","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1190500,"visible":true,"origin":"","legend":"","description":"","filename":"KangSI.docx","url":"https://assets-eu.researchsquare.com/files/rs-3849763/v1/06c7b0c9d0a165b012dc0e0e.docx"},{"id":49625701,"identity":"551f4c2b-2ae0-4da8-89ff-2be2599bb67b","added_by":"auto","created_at":"2024-01-15 14:06:56","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":2620904,"visible":true,"origin":"","legend":"\u003cp\u003eGraphical Abstract\u003c/p\u003e","description":"","filename":"TOC.png","url":"https://assets-eu.researchsquare.com/files/rs-3849763/v1/79e2d24dd3737d3e31b67454.png"},{"id":49625213,"identity":"bdb7b461-e373-4ce9-81f3-5d68fc4eded3","added_by":"auto","created_at":"2024-01-15 13:58:56","extension":"png","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":159320,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1.\u003c/strong\u003eSchematic of synthetic route of \u003cstrong\u003ePOM-1\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-3849763/v1/0e2a9f3bec644d53a39503f3.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"Ligand-functionalized Anderson-type Polyoxometalate for Efficient Selective Cationic Dye Adsorption","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe excess emission of the organic dyes in wastewater have potential toxicity caused serious pollution to the environment, which has been aroused more and more attentions. Organic dyes could be categorized based on their chemical composition, usage, and ability to dissolve in water-based solutions, and also hardly degrade under the natural conditions, due to their structure stabilities and high solubility \u003csup\u003e[\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e. Therefore, the search for an appropriate method to remove these organic dyes is not only of great significance but also an urgent necessity. Comparatively, physical adsorption has been acknowledged as a more straightforward, uncomplicated, and energy-efficient approach, which does not involve any harmful byproducts and allows for the easy separation of the solid adsorbents that bind the dyes to their surface, leaving no trace behind. Despite the numerous porous adsorbents have been reported and garnered attention in the scientific community \u003csup\u003e[\u003cspan additionalcitationids=\"CR7 CR8 CR9 CR10 CR11 CR12 CR13\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e, there is still a dire need for more adsorbents that possess efficient, rapid, and selective adsorption capabilities. These new adsorbents should be designed specifically for the adsorption of specific dyes, taking into account their structural features, charges, or sizes. This would not only enhance the overall adsorption process but would also contribute to the development of more sustainable and environmentally-friendly solutions for the removal of dyes from wastewater.\u003c/p\u003e \u003cp\u003ePolyoxometalates (POMs) represent a category of polynuclear oxygen-bridged clusters consisting of early transition metals in their high oxidation state, which exhibit diverse topological structures \u003csup\u003e[\u003cspan additionalcitationids=\"CR16 CR17 CR18 CR19\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. Especially, the functionalization of organic ligand into POMs units endow these materials a wide range of potential properties that extensively applied in various fields, including catalysis, medicine, ion exchange, molecular materials, photochemistry, electrochemistry, and magnetism \u003csup\u003e[\u003cspan additionalcitationids=\"CR22 CR23 CR24 CR25\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e. In terms of the structural feature, the planar Anderson-type POMs consisting of a central XO\u003csub\u003e6\u003c/sub\u003e octahedron unit and six edge-sharing MO\u003csub\u003e6\u003c/sub\u003e octahedron units, could be easily functionalized by grafting triol-based ligands on each side of units, which provides the potential functional sites to modify them through hydroxyl substitution reaction, generating a large range of organic functionalized Anderson-type POMs under well design with unique physical and chemical properties. Therefore, considering these remarkable structure and property performance of organic functionalized Anderson-type POMs \u003csup\u003e[\u003cspan additionalcitationids=\"CR28 CR29 CR30\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u003c/sup\u003e, these materials could be selected as one kinds of promising organic dyes adsorbents, contributing to the development of more sustainable and environmentally-friendly solutions for the removal of dyes from wastewater \u003csup\u003e[\u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eHerein, in order to take full advantage of these clusters with negative charge, an Anderson-type POM (\u003cb\u003ePOM-1)\u003c/b\u003e with carboxylic-based ligands were selected to study its adsorption ability for organic dyes. The incorporation of carboxylic groups with high deprotonation could increase the negative-charged in \u003cb\u003ePOM-1\u003c/b\u003e. The adsorption experiments revealed that \u003cb\u003ePOM-1\u003c/b\u003e displayed efficient adsorption capabilities towards the cationic dye MB in a high rate with almost complete adsorption within 25 min. The competitive and consecutive filtering experiments have also been performed and further proved the excellent efficient and selective adsorption behavior of \u003cb\u003ePOM-1\u003c/b\u003e towards cationic MB \u003cem\u003evia\u003c/em\u003e electrostatic effect.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eGeneral methods details\u003c/h2\u003e \u003cp\u003eAll chemicals and solvents are purchased from commercial sources without further purification. The collection of Powder X-ray diffraction (PXRD) patterns was performed using a Bruker AXS D8 Advance X-ray diffractometer. The infrared spectrum (IR) was collected by NEXUS instrument using KBr particles. The UV-visible spectrum of the liquid was analyzed using a TU-1901 UV-visible spectrometer, which had a scanning range of 200\u0026ndash;800 nm. The \u003csup\u003e1\u003c/sup\u003eH NMR spectra were acquired using a Bruker Avance 400 spectrometer. X-ray photoelectron spectroscopy (XPS) characterization was carried out by using a Thermo Scientific K-Alpha\u0026thinsp;+\u0026thinsp;spectrometer with Al Kα X-ray (1486.6 eV) as the light source.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of 4-HOOC(C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003e)CH\u003csub\u003e2\u003c/sub\u003eNHC(CH\u003csub\u003e2\u003c/sub\u003eOH)\u003csub\u003e3\u003c/sub\u003e (H\u003csub\u003e4\u003c/sub\u003eL)\u003c/h2\u003e \u003cp\u003eThe ligand H\u003csub\u003e4\u003c/sub\u003eL was synthesized according to the method reported in the literature \u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e. P-bromomethylbenzoic acid (3.78g) was added to a 300 mL tris (hydroxymethyl) aminomethane (10.18g) aqueous solution in 2 min. After stirring the reactant at room temperature for 20 hours, the solid 4-bromomethylbenzoic acid was completely dissolved after 30 min and white precipitate appeared after 7 hours. The white precipitate was separated by filtration, subjected to two washes with 20 mL of water each, followed by two washes with 15 mL of acetone each. Subsequently, the precipitate was dried under vacuum conditions, resulting in a yield of 3.2 g. The \u003csup\u003e1\u003c/sup\u003eH NMR spectrum is consistent with the literature.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of [N(n-C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e9\u003c/sub\u003e)\u003csub\u003e4\u003c/sub\u003e]\u003csub\u003e4\u003c/sub\u003e[(MnMo\u003csub\u003e6\u003c/sub\u003eO\u003csub\u003e18\u003c/sub\u003e)(HL)(L)]\u0026middot;3DMF (POM-1)\u003c/h2\u003e \u003cp\u003eThe mixture containing [N(n-C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e9\u003c/sub\u003e)\u003csub\u003e4\u003c/sub\u003e]\u003csub\u003e4\u003c/sub\u003e[α-Mo\u003csub\u003e8\u003c/sub\u003eO\u003csub\u003e26\u003c/sub\u003e] (1.100 g, 0.50 mmol), Mn(OAc)\u003csub\u003e3\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO (0.201 g, 0.67 mmol), H\u003csub\u003e4\u003c/sub\u003eL (0.438 g), tetrabutylammonium bromide (0.215 g, 0.67 mmol), and 20 mL DMF was subjected to stirring at 85\u0026deg;C for 22 hours. The suspension was centrifuged, and the orange supernatant was placed in an ether atmosphere. After 2 days, orange crystals were formed. In order to enhance the yield, the crystal underwent additional diffusion in an ether atmosphere for a duration of 7 days, followed by drying, resulting in the acquisition of 0.982 g. The synthetic route is presented in Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eAdsorption experiments\u003c/h2\u003e \u003cp\u003eThe adsorption experiment was conducted using the following method: \u003cb\u003ePOM-1\u003c/b\u003e (3\u0026times;12 mg) was prepared and added to 3\u0026times;5 mL solutions of MB, rhodamine 6G (Rh6G) and methyl orange (MO), each with a concentration of 1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e mol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The solutions were then placed in a dark environment. Subsequently, 75 \u0026micro;L of the supernatant was extracted and combined with 2925 \u0026micro;L of deionized water to prepare a 3 mL solution. The concentration of the organic dye solution was determined using ultraviolet/visible spectrophotometry at regular intervals.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003e \u003cb\u003ePOM-1\u003c/b\u003e possesses a symmetric configuration with two H\u003cb\u003eL\u003c/b\u003e\u003csup\u003e4\u0026minus;\u003c/sup\u003e ligands grafted on both sides of [MnMo\u003csub\u003e6\u003c/sub\u003eO\u003csub\u003e18\u003c/sub\u003e] cluster, and exhibits a relatively high level of stability. Infrared spectrum of \u003cb\u003ePOM-1\u003c/b\u003e revealed the medium intensity absorption peaks near 2960 and 2873 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to the C-H stretching vibration of the ν\u003csub\u003e(\u0026minus;CH2)\u003c/sub\u003e group. The weak absorption peak near 1381 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to the C-N stretching vibration of ν\u003csub\u003eC\u0026minus;N\u003c/sub\u003e. It can be observed that the moderate absorption peak near 1649 to 1482 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to the ν\u003csub\u003eC=C\u003c/sub\u003e stretching vibration peak, which is indicative of the benzene ring structure in the organic ligand. Additionally, the weak absorption peak near 1152 to 1037 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to the δ\u003csub\u003eC\u0026minus;H\u003c/sub\u003e in-plane bending vibration, also associated with the benzene ring structure in the organic ligand. The strong absorption peaks near 939 to 665 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to the out-of-plane bending vibrations of γ\u003csub\u003eC\u0026minus;H\u003c/sub\u003e, which are indicative of the benzene ring structure in the organic ligand. The IR spectrum of \u003cb\u003ePOM-1\u003c/b\u003e was consistent with the reported Anderson-type POM cluster.\u003c/p\u003e \u003cp\u003eThe valence states of \u003cb\u003ePOM-1\u003c/b\u003e were characterized by X-ray photoelectron spectroscopy (XPS) test. The XPS diagram of \u003cb\u003ePOM-1\u003c/b\u003e is shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Two peaks at 235.1 eV and 232 eV, corresponding to Mo\u003csup\u003e6+\u003c/sup\u003e3d\u003csub\u003e3/2\u003c/sub\u003e and Mo\u003csup\u003e6+\u003c/sup\u003e3d\u003csub\u003e5/2\u003c/sub\u003e, respectively, while the peaks at 653.8eV and 641.9eV could be attributed to Mn\u003csup\u003e3+\u003c/sup\u003e2p\u003csub\u003e1/2\u003c/sub\u003e and Mn\u003csup\u003e3+\u003c/sup\u003e2p\u003csub\u003e3/2\u003c/sub\u003e, respectively. In addition, 657.6eV is the satellite peak of Mn\u003csup\u003e3+\u003c/sup\u003e2p\u003csub\u003e1/2\u003c/sub\u003e and 646.2eV is the satellite peak of Mn\u003csup\u003e3+\u003c/sup\u003e2p\u003csub\u003e3/2\u003c/sub\u003e. These results indicated that valence states of Mo and Mn in \u003cb\u003ePOM-1\u003c/b\u003e are +\u0026thinsp;6 and +\u0026thinsp;3, respectively, which are consistent with those of the raw materials.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn order to explore and verify the adsorption performance of \u003cb\u003ePOM-1\u003c/b\u003e, we selected cationic organic dye MB and Rh6G for the selective adsorption experiments, and analyzed the adsorption performance of \u003cb\u003ePOM-1\u003c/b\u003e for different organic dyes by ultraviolet-visible spectrophotometer. The structural formulas of used organic dyes are presented in Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e. Firstly, the adsorption properties of \u003cb\u003ePOM-1\u003c/b\u003e towards MB were investigated. The prepared \u003cb\u003ePOM-1\u003c/b\u003e, weighing 12 mg, was introduced into a 5 mL solution of MB with a concentration of 1 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e mol\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e. The mixture was then kept in a dark environment and monitored the layer pellucid liquid by UV-Vis. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a), UV-Vis adsorption spectrum of MB aqueous solution exhibits a strong adsorption at λ\u003csub\u003emax\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;664 nm, and the peak were decreased sharply with the extension of adsorption time. The adsorption process could complete within 25 min with the color of MB solution changed from blue to transparent, and the adsorption rate was calculated as 97.4%, according to the function of 1-\u003cem\u003eA\u003c/em\u003e/\u003cem\u003eA\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e \u0026times; 100%, where \u003cem\u003eA\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e is the absorbance of the original MB solution, and \u003cem\u003eA\u003c/em\u003e is the absorbance of MB solution at different time intervals using \u003cb\u003ePOM-1\u003c/b\u003e as absorbent. These results indicated that \u003cb\u003ePOM-1\u003c/b\u003e has significant adsorption ability for MB. The MB concentration changes as a function of time are plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, and the adsorption process of \u003cb\u003ePOM-1\u003c/b\u003e showed a pseudo-second-order kinetic behaviors. In terms of the adsorption mechanism, we speculate that the positive-charged MB and the negative-charged \u003cb\u003ePOM-1\u003c/b\u003e are greatly beneficial for the electrostatic interaction between them. In addition, when changing MB into other cationic dye, Rh6G, with larger size than MB, the adsorption behavior of \u003cb\u003ePOM-1\u003c/b\u003e shows quite different under the same conditions. UV-Vis adsorption spectra of Rh6G aqueous solution using \u003cb\u003ePOM-1\u003c/b\u003e as absorbent reveal that only 60.5% decrease of absorbance after 6 h, and the color of the solution remains its original color (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). Extending the detection time could not enhance the adsorption rate. Within 6 h, the adsorption process of \u003cb\u003ePOM-1\u003c/b\u003e also showed a pseudo-second-order kinetic behaviors towards Rh6G (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). These result suggest that the matching charges and suitable sizes are both play the significant roles in the adsorption capacities of \u003cb\u003ePOM-1\u003c/b\u003e towards organic dyes.\u003c/p\u003e \u003cp\u003eIn order to verify these speculation, control experiments have been further carried out by selecting an anionic organic dye, methyl orange (MO) with similar size with MB, to study the adsorption ability of \u003cb\u003ePOM-1\u003c/b\u003e under the same conditions that introducing 12 mg of \u003cb\u003ePOM-1\u003c/b\u003e into a 5 mL solution of MO with a concentration of 2\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e mol\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, MO solution exhibits a characteristic absorption peak at 465 nm, and almost no reduction of the absorbance occurs after 100 min or even longer detection time. These results indicated the weak adsorption capacity of \u003cb\u003ePOM-1\u003c/b\u003e towards the anionic MO, due to the negative-negative charge repulsive effect, and also could give a fully proof for the adsorption mechanism that the electrostatic interaction is the main factor affecting this adsorption process. Competitive adsorption experiments were also conducted with the mixture solutions of MB with MO under the same concentration in the presence of \u003cb\u003ePOM-1\u003c/b\u003e. After 15 min, the absorbance of the characteristic peak of MB at 664 nm were sharply decreased, while the characteristic peak of MB at 465 nm were still remained unchanged (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). The adsorption rate of \u003cb\u003ePOM-1\u003c/b\u003e towards MB is about 87.2% at 15 min, consistent with the adsorption rate (85.67%, 15 min) in the single MB solution, suggesting that the presence of other dyes could not affect the adsorption capacity of \u003cb\u003ePOM-1\u003c/b\u003e. We could conclude that compound \u003cb\u003e1\u003c/b\u003e exhibits an efficient and selective adsorption capacity for the size-suitable cationic dye MB and an obvious excluding behavior towards another anionic dyes, acting as a promising adsorbent used for the separation of different charged organic dyes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eConsidering the remarkable adsorption capacity of \u003cb\u003ePOM-1\u003c/b\u003e towards MB, a set of rapid filter devices was established. A plastic dropper without top was chosen as the basic module, and the cotton was compacted to the bottom of the device, and 24 mg of \u003cb\u003ePOM-1\u003c/b\u003e was compressed in the upper layer. A solution of MB with a concentration of 1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e mol\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e was introduced into the upper part of the apparatus, and the solution underwent gradual compression through \u003cb\u003ePOM-1\u003c/b\u003e layer due to the force of gravity. In this case, the color of the added MB solution was changed from blue to colorless after filtration, and the UV-vis absorbance of the filtered MB solution was almost eliminated after a single cycle (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea), indicating rapid adsorption rate of \u003cb\u003ePOM-1\u003c/b\u003e towards MB. This rapid adsorption could be consecutive used for at least 30 rounds (1 mL MB solution for each addition). Furthermore, a mixture solution consisting of MB and MO under the same concentration was added into the upper of the filtering set, and only yellow solution could be observed after filtration (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). These results revealed that only MB has been adsorbed with MO remaining in the solution, suggesting that the presence of other competitive dyes could not affect the rapid and selective adsorption behavior of \u003cb\u003ePOM-1\u003c/b\u003e. This observation could also examined by the UV-vis spectra analysis.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eReusability and stability are the crucial factors for the practical application of adsorbents. After the adsorption, \u003cb\u003ePOM-1\u003c/b\u003e could be obtained through either filtration or centrifugal separation and the color of the sample were changed from yellow to dark blue (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). The isolated sample were further analyzed by IR spectra. Compared with spectra of free \u003cb\u003ePOM-1\u003c/b\u003e and MB, it can be seen that the IR spectrum of \u003cb\u003ePOM-1\u003c/b\u003e adsorbed MB consists of the characteristic peaks of free \u003cb\u003ePOM-1\u003c/b\u003e and MB, indicating the stable skeleton of \u003cb\u003ePOM-1\u003c/b\u003e during the adsorption process (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). The peak at 648 cm\u003csup\u003e-1\u003c/sup\u003e is the typical characteristic peak of POM-1 \u003csup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/sup\u003e. The infrared spectrum of MB adsorbed by POM also contains the characteristic peak of POM-1. The 2800\u0026ndash;3100 cm\u003csup\u003e-1\u003c/sup\u003e range represents the C-H stretching vibration peak of -CH\u003csub\u003e2\u003c/sub\u003e. Although organic dye MB does not contain -CH\u003csub\u003e2\u003c/sub\u003e, the IR spectrum of MB adsorbed by POM shows the stretching vibration peak in this range, indicating the presence of \u003cb\u003ePOM-1\u003c/b\u003e. The stretching vibration peak of the C-S bond in MB is at 1324 cm\u003csup\u003e-1\u003c/sup\u003e. However, in the infrared spectrum of MB adsorbed by POM, the stretching vibration peak of the C-S bond is observed at 1228 cm\u003csup\u003e-1\u003c/sup\u003e. This shift may be attributed to the interaction between \u003cb\u003ePOM-1\u003c/b\u003e and MB through electrostatic effects \u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e. At the same time, the infrared spectrum of MB adsorbed by POM shows a decrease to a certain extent in the peak range of 1200\u0026ndash;1350 cm\u003csup\u003e-1\u003c/sup\u003e, which is also attributed to the electrostatic effect. Subsequently, desorption experiments of MB were conducted by a continuous oscillation of the isolated sample added in other 20 mL deionized water. After 2h oscillation, the colour of the solution could be recover to blue, suggesting that the adsorbed MB could be desorbed from the adsorbent \u003cb\u003ePOM-1\u003c/b\u003e. However, the desorbed MB could be further adsorbed in this system within 20 min, without any decreased of efficiency (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). These results demonstrated the favorable cyclic adsorption capabilities of \u003cb\u003ePOM-1\u003c/b\u003e towards MB.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn conclusion, this work reported a carboxylic-functionalized Anderson-type POM cluster as an excellent selective adsorbent for dyes. The enhanced negative-charged \u003cb\u003ePOM-1\u003c/b\u003e could greatly promote the efficient adsorption towards the cationic dye MB within 25 min. Additionally, the electrostatic interaction is also influenced by the appropriate size, resulting in only 60.4% adsorption rate of \u003cb\u003ePOM-1\u003c/b\u003e towards Rh6G with a larger molecular size. A rapid and consecutive filtering device has been established to demonstrate the remarkable adsorption behavior of POM-1 towards MB, indicating its promising potential for industrial wastewater treatment.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical Approval\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was co-financed by National Natural Science Foundation of China (21901147) and Natural Science Foundation of Shandong Province (ZR2018BB002).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe crystal data (CCDC 2008219 in this paper) can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eX. 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Soc. 15095, 129 (2007).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSara Dawood, Tushar Kanti Sen, Water Res. 1946, 46 (2012).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Scheme","content":"\u003cp\u003eScheme 1 is available in Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-cluster-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Journal of Cluster Science](https://www.springer.com/journal/10876) ","snPcode":"10876","submissionUrl":"https://mc.manuscriptcentral.com/jocl","title":"Journal of Cluster Science","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Polyoxometalates, Anderson-type, Cationic dyes, Selective adsorption","lastPublishedDoi":"10.21203/rs.3.rs-3849763/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3849763/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe issue of treating organic dyes in industrial wastewater has long been a subject of grave concern in the fields of environmental protection and public health. In an attempt to explore efficient solutions to this problem, this work focuses on the selective adsorption approach towards dyes molecules based on a Anderson-type polyoxometalate (POM, noted as \u003cb\u003ePOM-1\u003c/b\u003e) as potential adsorbent, which has been functionalized with organic groups. Adsorption experiments revealed that \u003cb\u003ePOM-1\u003c/b\u003e displayed efficient adsorption capabilities towards the cationic dye methyl blue (MB) with almost complete adsorption within 25 min, and the adsorption rate was calculated as 98%. A rapid and consecutive filtering experiments have also been performed and further proved the excellent adsorption behavior of \u003cb\u003ePOM-1\u003c/b\u003e towards MB. We envision that the functionalization of carboxylic ligands increased the negative charges of anionic POM, greatly promotes the interactions between adsorbent and cationic MB \u003cem\u003evia\u003c/em\u003e electrostatic effect.\u003c/p\u003e","manuscriptTitle":"Ligand-functionalized Anderson-type Polyoxometalate for Efficient Selective Cationic Dye Adsorption","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-15 13:58:51","doi":"10.21203/rs.3.rs-3849763/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-02-01T16:58:12+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-01-25T00:06:01+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"bdb4a23f-44fe-462d-989d-543239b80392","date":"2024-01-22T19:56:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"b142f367-9278-42f0-8884-6aa1d4e73d0e","date":"2024-01-22T19:45:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"659e0031-f2f4-4363-8b19-14bbb5ad84c4","date":"2024-01-22T19:45:18+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-01-22T19:21:53+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-01-12T13:59:58+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-01-12T12:02:03+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Cluster Science","date":"2024-01-10T08:51:37+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-cluster-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Journal of Cluster Science](https://www.springer.com/journal/10876) ","snPcode":"10876","submissionUrl":"https://mc.manuscriptcentral.com/jocl","title":"Journal of Cluster Science","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"efedc822-da7d-4c42-91ef-ef5f671abe79","owner":[],"postedDate":"January 15th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-03-06T15:06:19+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-15 13:58:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3849763","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3849763","identity":"rs-3849763","version":["v1"]},"buildId":"cBFmMYwuxLRRLfASyISRj","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}