Non-Redox Removal of Indigo Carmine Using Recycled LiMn₂O₄ Cathode Materials

Non-Redox Removal of Indigo Carmine Using Recycled LiMn₂O₄ Cathode Materials | 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 Short Report Non-Redox Removal of Indigo Carmine Using Recycled LiMn₂O₄ Cathode Materials Eric M. Garcia, Talita Martins Dias, Hosane Taroco, Julio O.F Melo, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8694843/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 19 You are reading this latest preprint version Abstract Recycled LiMn₂O₄ cathode material from spent lithium-ion batteries was investigated as an adsorbent for indigo carmine under non-redox conditions. At pH 7, a Langmuir monolayer capacity of 4.95 mg·g⁻¹ was obtained, which decreased sharply to 0.13 mg·g⁻¹ at pH 11 due to electrostatic exclusion rather than loss of adsorption sites. Thermodynamic analysis revealed a low positive enthalpy (ΔH° = 1.3 ± 0.1 kJ·mol⁻¹) and a high positive entropy (ΔS° = 100 ± 2 J·mol⁻¹·K⁻¹), indicating a weakly endothermic, entropy-driven adsorption process dominated by physisorption, while the negative Gibbs free energy (ΔG°₍₂₉₈₎ = −28.5 ± 0.6 kJ·mol⁻¹) confirms spontaneity at near-neutral pH. Poisson–Boltzmann analysis showed that the increase in zeta potential magnitude from − 20 to − 60 mV at alkaline pH restricts dye accessibility, yielding an effective charge of approximately − 2.2, consistent with IC²⁻ predominance. Despite the modest capacity, the material retained > 95% efficiency over multiple adsorption–regeneration cycles, highlighting recycled LiMn₂O₄ as a stable and reusable adsorbent for non-redox dye removal. Li-ion Battery recycling Spent Cathode Indigo Carmine LiMn₂O₄ Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 30 Apr, 2026 Reviews received at journal 29 Apr, 2026 Reviewers agreed at journal 28 Apr, 2026 Reviews received at journal 27 Apr, 2026 Reviewers agreed at journal 25 Apr, 2026 Reviewers agreed at journal 24 Apr, 2026 Reviews received at journal 24 Apr, 2026 Reviewers agreed at journal 24 Apr, 2026 Reviewers agreed at journal 21 Apr, 2026 Reviewers agreed at journal 08 Mar, 2026 Reviews received at journal 04 Mar, 2026 Reviewers agreed at journal 04 Mar, 2026 Reviews received at journal 26 Feb, 2026 Reviewers agreed at journal 20 Feb, 2026 Reviewers invited by journal 12 Feb, 2026 Editor invited by journal 09 Feb, 2026 Editor assigned by journal 31 Jan, 2026 Submission checks completed at journal 31 Jan, 2026 First submitted to journal 25 Jan, 2026 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-8694843","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Short Report","associatedPublications":[],"authors":[{"id":590115633,"identity":"1fa7b8f0-64e6-4eb0-bf38-7cf92ac7c5a5","order_by":0,"name":"Eric M. Garcia","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxklEQVRIiWNgGAWjYFACxgaGDwxyIIpBgoHhAHFaGGcwGJOkhYGBmQeoBQSI08Ivfbjxs22bgT1zA/PB2zwMd/IJapHsS2yWzm0zSGxsYEu25mF4ZtlASIvBGcY25ty2PwmMDTxm0jwMhw0I2mIP0mIJdBhjA/834rQY8AC1MLYZMDY28LARp0XiDGOzZM85oF+a2Ywt5xg8I6yFv4f94YcfZQb2hu3ND2+8qbhDWAscGDaD3Um8BgYGeVIUj4JRMApGwcgCAGzvNGrD7o9pAAAAAElFTkSuQmCC","orcid":"","institution":"UFSJ","correspondingAuthor":true,"prefix":"","firstName":"Eric","middleName":"M.","lastName":"Garcia","suffix":""},{"id":590115634,"identity":"a3d17427-0b23-439d-94ca-c2181e9bffd6","order_by":1,"name":"Talita Martins Dias","email":"","orcid":"","institution":"UFSJ","correspondingAuthor":false,"prefix":"","firstName":"Talita","middleName":"Martins","lastName":"Dias","suffix":""},{"id":590115635,"identity":"6bcf8e0e-3f06-4753-941b-7791b0106aea","order_by":2,"name":"Hosane Taroco","email":"","orcid":"","institution":"UFSJ","correspondingAuthor":false,"prefix":"","firstName":"Hosane","middleName":"","lastName":"Taroco","suffix":""},{"id":590115636,"identity":"0e942f3c-8336-4263-8fe4-396bd365f832","order_by":3,"name":"Julio O.F Melo","email":"","orcid":"","institution":"UFSJ","correspondingAuthor":false,"prefix":"","firstName":"Julio","middleName":"O.F","lastName":"Melo","suffix":""},{"id":590115637,"identity":"fc91c4f3-22de-4055-bd28-21993fac5ab4","order_by":4,"name":"Cibele Silva Mariz","email":"","orcid":"","institution":"UFSJ","correspondingAuthor":false,"prefix":"","firstName":"Cibele","middleName":"Silva","lastName":"Mariz","suffix":""},{"id":590115638,"identity":"21668ac8-b5d3-4129-abee-a2834b0b003d","order_by":5,"name":"Filipe de Almeida Rocha","email":"","orcid":"","institution":"UFSJ","correspondingAuthor":false,"prefix":"","firstName":"Filipe","middleName":"de Almeida","lastName":"Rocha","suffix":""}],"badges":[],"createdAt":"2026-01-25 20:53:54","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8694843/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8694843/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":103049298,"identity":"b55a5837-2b19-48dc-9912-42f6c1cb0aed","added_by":"auto","created_at":"2026-02-20 07:39:40","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":853273,"visible":true,"origin":"","legend":"","description":"","filename":"paper3101.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8694843/v1_covered_68ff462f-6f80-4164-b78a-c9c7351183f9.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Non-Redox Removal of Indigo Carmine Using Recycled LiMn₂O₄ Cathode Materials","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-industrial-chemistry-and-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Industrial Chemistry and Materials](https://link.springer.com/journal/44508)","snPcode":"44508","submissionUrl":"https://submission.nature.com/new-submission/44508/3?","title":"Discover Industrial Chemistry and Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Li-ion Battery, recycling, Spent Cathode, Indigo Carmine, LiMn₂O₄","lastPublishedDoi":"10.21203/rs.3.rs-8694843/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8694843/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRecycled LiMn₂O₄ cathode material from spent lithium-ion batteries was investigated as an adsorbent for indigo carmine under non-redox conditions. At pH 7, a Langmuir monolayer capacity of 4.95 mg\u0026middot;g⁻\u0026sup1; was obtained, which decreased sharply to 0.13 mg\u0026middot;g⁻\u0026sup1; at pH 11 due to electrostatic exclusion rather than loss of adsorption sites. Thermodynamic analysis revealed a low positive enthalpy (ΔH\u0026deg; = 1.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 kJ\u0026middot;mol⁻\u0026sup1;) and a high positive entropy (ΔS\u0026deg; = 100\u0026thinsp;\u0026plusmn;\u0026thinsp;2 J\u0026middot;mol⁻\u0026sup1;\u0026middot;K⁻\u0026sup1;), indicating a weakly endothermic, entropy-driven adsorption process dominated by physisorption, while the negative Gibbs free energy (ΔG\u0026deg;₍₂₉₈₎ = \u0026minus;28.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6 kJ\u0026middot;mol⁻\u0026sup1;) confirms spontaneity at near-neutral pH. Poisson\u0026ndash;Boltzmann analysis showed that the increase in zeta potential magnitude from \u0026minus;\u0026thinsp;20 to \u0026minus;\u0026thinsp;60 mV at alkaline pH restricts dye accessibility, yielding an effective charge of approximately\u0026thinsp;\u0026minus;\u0026thinsp;2.2, consistent with IC\u0026sup2;⁻ predominance. Despite the modest capacity, the material retained\u0026thinsp;\u0026gt;\u0026thinsp;95% efficiency over multiple adsorption\u0026ndash;regeneration cycles, highlighting recycled LiMn₂O₄ as a stable and reusable adsorbent for non-redox dye removal.\u003c/p\u003e","manuscriptTitle":"Non-Redox Removal of Indigo Carmine Using Recycled LiMn₂O₄ Cathode Materials","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-17 06:50:34","doi":"10.21203/rs.3.rs-8694843/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-30T21:26:10+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-29T08:01:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"192244834176641236627440441514408677825","date":"2026-04-28T10:56:27+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-27T05:15:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"325866179886389412632542397358105786934","date":"2026-04-25T12:13:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"202152471796018594907277036197988440739","date":"2026-04-24T07:51:38+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-24T07:06:55+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"17851387398898143721325507319738098132","date":"2026-04-24T05:31:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"195561721029052097737602762537612667148","date":"2026-04-21T11:01:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"327339027895713487180612037266670296255","date":"2026-03-08T21:02:46+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-04T21:26:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"75198102937968713099829092895701636107","date":"2026-03-04T20:35:27+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-26T12:49:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"332752817315968231534715589504640221410","date":"2026-02-20T14:02:08+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-12T08:28:48+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-02-09T11:01:04+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-31T16:03:38+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-01-31T16:01:29+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Industrial Chemistry and Materials","date":"2026-01-25T20:42:28+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-industrial-chemistry-and-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Industrial Chemistry and Materials](https://link.springer.com/journal/44508)","snPcode":"44508","submissionUrl":"https://submission.nature.com/new-submission/44508/3?","title":"Discover Industrial Chemistry and Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"31f8a775-2d55-47f2-a956-bd1d83d9593e","owner":[],"postedDate":"February 17th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Revision requested","date":"2026-04-30T21:26:10+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-29T08:01:54+00:00","index":60,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-05T11:08:13+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-17 06:50:34","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8694843","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8694843","identity":"rs-8694843","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}