{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,24]],"date-time":"2026-09-24T17:06:46Z","timestamp":1790269606982,"version":"4.1.0"},"reference-count":81,"publisher":"MDPI AG","issue":"19","license":[{"start":{"date-parts":[[2026,9,24]],"date-time":"2026-09-24T00:00:00Z","timestamp":1790208000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>Waste-derived natural polymers offer a route to low-cost sorbents for toxic metal ions, but reported performance is difficult to compare because precursor composition, polymer processing, modification, and experimental conditions vary widely. This critical review examines silk fibroin, banana peel, orange peel, and pectin as structurally distinct platforms and evaluates how macromolecular chemistry, esterification, ionic crosslinking, morphology, and regeneration influence metal uptake. Particular attention is given to the distinction between untreated biomass, isolated biopolymers, and chemically engineered materials; to mechanistic evidence from spectroscopy, elemental analysis, ion exchange, and controlled structural modification; and to the limitations of interpreting Langmuir or pseudo-second order fitting as direct proof of adsorption mechanism. The literature supports strong roles for pectic carboxyl groups and Ca2+-mediated exchange in several cation-binding systems, while silk fibroin provides a reusable protein-based matrix with different donor-site chemistry. Across the four platforms, high qmax values are not transferable material constants and do not by themselves establish selectivity, practical treatment performance, or analytical sensitivity. Major gaps include precursor standardization, matched comparison of raw and modified sorbents, multicomponent and real-water testing, nonlinear model evaluation, continuous-flow studies, regeneration stability, metal recovery, and end-of-life management. Diffuse-reflectance sensing is considered as a downstream value-added function once a reproducible biosorbent has been established. An evidence-based roadmap is proposed for converting polymer-rich wastes into controlled, regenerable, and application-oriented biosorbents.<\/jats:p>","DOI":"10.3390\/polym18192336","type":"journal-article","created":{"date-parts":[[2026,9,24]],"date-time":"2026-09-24T16:29:53Z","timestamp":1790267393000},"page":"2336","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Waste-Derived Natural Polymer Biosorbents for Toxic Metal Ions: Structure\u2013Sorption Relationships, Modification Strategies, and Prospects for Solid-Phase Sensing"],"prefix":"10.3390","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9904-9979","authenticated-orcid":false,"given":"Aisha","family":"Nurlybayeva","sequence":"first","affiliation":[{"name":"Department of Chemistry and Chemical Technology, M.Kh. Dulaty Taraz University, Taraz 080000, Kazakhstan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3116-3518","authenticated-orcid":false,"given":"Zulaykho","family":"Smanova","sequence":"additional","affiliation":[{"name":"Department of Analytical Chemistry, Faculty of Chemistry, National University of Uzbekistan, Tashkent 100174, Uzbekistan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zhanna","family":"Tazhiyeva","sequence":"additional","affiliation":[{"name":"Department of Chemistry and Chemical Technology, M.Kh. Dulaty Taraz University, Taraz 080000, Kazakhstan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zulfiya","family":"Unerbayeva","sequence":"additional","affiliation":[{"name":"Department of Chemistry, Kazakh National Pedagogical University named after Abai, Almaty 050010, Kazakhstan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1002-2046","authenticated-orcid":false,"given":"Raikhan","family":"Rakhmetullayeva","sequence":"additional","affiliation":[{"name":"Department of Chemistry and Technology of Organic Substances, Natural Compounds and Polymers, Faculty of Chemistry and Chemical Technology, Al-Farabi Kazakh National University, Almaty 050040, Kazakhstan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6820-5219","authenticated-orcid":false,"given":"Gulsim","family":"Matniyazova","sequence":"additional","affiliation":[{"name":"Higher School of Natural Sciences, Astana International University, Astana 010000, Kazakhstan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ainur","family":"Seitkhan","sequence":"additional","affiliation":[{"name":"Department of Environmental Management and Engineering, L.N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Raushan","family":"Taubayeva","sequence":"additional","affiliation":[{"name":"Department of Chemistry and Chemical Technology, M.Kh. Dulaty Taraz University, Taraz 080000, Kazakhstan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0002-5022-4814","authenticated-orcid":false,"given":"Bekzat","family":"Saurbayeva","sequence":"additional","affiliation":[{"name":"School of International Engineering, D. Serikbayev East Kazakhstan Technical University, Ust-Kamenogorsk 070004, Kazakhstan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Aitkul","family":"Aidarova","sequence":"additional","affiliation":[{"name":"Department of Chemistry and Chemical Technology, M.Kh. Dulaty Taraz University, Taraz 080000, Kazakhstan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1237-9711","authenticated-orcid":false,"given":"Ergali","family":"Rustem","sequence":"additional","affiliation":[{"name":"Faculty of Architecture, Construction and Transport, Mukhtar Auezov South Kazakhstan University, Shymkent 160012, Kazakhstan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,24]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Sheraz, M., Sun, X.-F., Siddiqui, A., Hu, S., and Song, Z. (2025). Research Advances in Natural Polymers for Environmental Remediation. 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