Table 5 Comparative performance between representative bio-based cation-binding membranes/filters for Li⁺ and Fe³⁺

Membrane/Filter Material	Active Sites	Target cations	Operating Mode	Flux (L·m^-2 ·h^-1)^a	pH	IEC_max (mmol·g^-1)	q_,max^b (mg·g⁻¹)	Regenerability (cycles)	Ref.
MA- and SA-treated wood (MSp/SSp)	-COO^-	Li⁺ Fe³⁺	Gravity-driven, dead-end filtration	MSp: 264 ± 125 SSp: 215 ± 63 MSp: 173 ± 69 SSp: 230 ± 69	5–6.5	MSp:2.69 SSp: 2.04	MSp: 14 (Li⁺) SSp: 19 (Li⁺) MSp: 32 (Fe³⁺) SSp: 50 (Fe³⁺)	MSp: Stable (3) SSp: Varies (3)	This work
HMO/cellulose	HMO	Li⁺	Diffusion cell (no external force)	––	6–7	3.1	21.6	Stable (8)	58
Cross-linked phosphorylated cellulose	PO₄^3-	Li⁺	Batch, dynamic packed-bed column	390–1559	––	3.6 – 4.9	~25–34	––	33
Sulfonated cellulose microspheres	–SO₃^⁻	Li⁺	Batch/column adsorption	5400	4–10	2.35	16	Stable ( < 5)	59
Amine-modified chitosan resins	DETA and TEPA polyamines	Fe³⁺	Column adsorption	764	2.5	DETA: 1.4 TEPA: 3.2	DETA: 78 TEPA: 179	––	60
Chitosan derivatives	ECH, GLA, EGDE	Fe³⁺	Batch adsorption	––	3	Unmod: 1.67 ECH: 1.29 GLA: 0.92 EGDE: 0.82	Unmod: 91 ECH: 73 GLA: 52 EGDE: 46.	––	9
Nafion™ 117	PFSA (fixed –SO₃^-)	Na⁺	Electro-chemical/ electro-dialytic processes	––	0-14	0.95–1.01^[c]	6 (Li⁺) 17 (Fe³⁺)	Stable (high)	61
DOWEX™ 50WX8	Sty–DVB gel resin (fixed –SO₃^-)	Na⁺	Packed-bed ion exchange	––	0–14	4.24-5.05^[d]	30–35 (Li⁺) 79–94 (Fe³⁺)	Stable (high)	62

HMO hydrogen manganese oxide, DETA diethylenetriamine, TEPA triethylenepentamine, GLA glutaraldehyde, ECH epichlorohydrin, EGDE ethylene glycol diglycidyl ether, PFSA perfluorosulfonic acid, Sty–DVB styrene-divinylbenzene copolymer.
^aFlux values for packed-bed column studies are not directly comparable to membrane permeance without accounting for bed porosity and pressure drop.
^bMaximum adsorption capacity, also by definition IEC_max = q_max × |z | /M_ion, where M_ion is the ionic weight having equivalent charge ‘z’.
^cProvided by technical supplier as total acid capacity (meq/g).
^dEstimated as: \({\mathrm{IEC}}_{\mathrm{dry}}\left(\frac{\mathrm{mmol}}{g}\right)=\frac{{q}_{\mathrm{wet}}\left|z\right|}{{w}_{\mathrm{ship}}\left(1-{x}_{w}\right)}\,\)

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