# Hydrophobic Modification of Alginate Nanofibrous Membrane by Group IV Elements Ion Crosslinking

## TL;DR

Researchers made hydrophobic membranes from alginate using metal ions, which can separate oil and water and also adsorb dyes.

## Contribution

A new method for modifying alginate membranes with group IV metal ions to enhance oil-water separation and dye adsorption.

## Key findings

- Zirconium- and titanium-crosslinked membranes effectively blocked water while allowing oil to pass.
- Titanium-crosslinked membranes showed UV-assisted dye removal due to photoactive properties.
- Membranes retained some polar sites for methylene blue adsorption despite hydrophobic modification.

## Abstract

Hydrophobic nanofiber membranes derived from the biopolymer alginate were fabricated by electrospinning followed by metal ion crosslinking, and their potential as oil-water separation membranes was primarily investigated. Sodium alginate (SA) was co-electrospun with polyethylene glycol and subsequently crosslinked using calcium chloride and group IV metal ions (zirconium or titanium). Metal ion crosslinking changed the surface wettability of the nanofiber membranes, as confirmed by water contact angle measurements. Both zirconium- and titanium-crosslinked SA nanofiber membranes exhibited effective gravity-driven oil–water separation with complete water blocking. Although hydrophobic modification reduced direct water affinity, the resulting membranes retained residual adsorption capability toward methylene blue, indicating the presence of accessible internal polar sites. The adsorption behavior varied depending on the crosslinking ion. In addition, titanium-crosslinked membranes showed an auxiliary UV-assisted dye removal contribution under irradiation, arising from photoactive Ti species. These findings demonstrate that metal ion crosslinking provides a practical route for tuning the functional properties of alginate nanofiber membranes, with oil-water separation as the primary application and dye adsorption/photocatalysis as secondary functionalities.