Scalable Wood Hydrogel Membrane with Nanoscale Channels

Abstract

Many efforts have been dedicated to exploring nanofluidic systems for various applications including water purification and energy generation. However, creating robust nanofluidic materials with tunable channel orientations and numerous nanochannels or nanopores on a large scale remains challenging. Here, we demonstrate a scalable and cost-effective method to fabricate a robust and highly conductive nanofluidic wood hydrogel membrane in which ions can transport across the membrane. The ionically conductive balsa wood hydrogel membrane is fabricated by infiltrating poly­(vinyl alcohol) (PVA)/acrylic acid (AA) hydrogel into the inherent bimodal porous wood structure. The balsa wood hydrogel membrane demonstrates a 3 times higher strength (52.7 MPa) and 2 orders of magnitude higher ionic conductivity compared to those of natural balsa both in the radial direction (coded as R direction) and along the longitudinal direction (coded as L direction). The ionic conductivity of the balsa wood hydrogel membrane is 1.29 mS cm–1 along the L direction and nearly 1 mS cm–1 along the R direction at low salt concentrations (up to 10 mM). In addition, the surface-charge-governed ion transport also renders the balsa wood hydrogel membrane able to harvest electrical energy from salinity gradients. A current density of up to 17.65 μA m–2 and an output power density of 0.56 mW m–2 are obtained under a 1000-fold salt concentration gradient, which can be further improved to 2.7 mW m–2 by increasing the AA content from 25 wt % to 50 wt %. These findings make contributions to develop energy-harvesting systems and other nanofluidic devices from sustainable wood materials.

Multi‐Ionic Hydrogel with Outstanding Heat‐to‐Electrical Performance for Low‐Grade Heat Harvesting

“…The surface of PVA is rich in hydroxyl functional groups, which are electronegative functional groups. Therefore, it is selective for ions with different charge properties [32] . The different states of PVA play a key role in ion selectivity.…”

“…Therefore, it is selective for ions with different charge properties. [32] The different states of PVA play a key role in ion selectivity. For example, PVA/NaOH hydrogels after freeze-thaw cycles and annealing have negative ionic Seebeck coefficients, [28] while the PVA hydrogel in electrolyte state after direct thermal dissolution has a positive ionic Seebeck coefficient.…”

Construction and Ion Transport-Related Applications of the Hydrogel-Based Membrane with 3D Nanochannels

“…Natural fibers have neatly arranged nanochannels that carry a negative charge on the surface, facilitating ion transport, and the raw material is economically available. Chen et al isolated part of lignin and cellulose from a large area of balsa wood sheet and prepared the hydrogel hybrid film by in situ polymerization of polyvinyl alcohol (PVA)/acrylic acid (AA) in the channel [ 113 ]. Cellulose and hydrogels are closely bonded by hydrogen bonds, and crosslinked hydrogels in wood channels provide additional nanofluid channels and abundant charge and act as fillers to block large pore sizes.…”

Highly Flexible and Broad-Range Mechanically Tunable All-Wood Hydrogels with Nanoscale Channels via the Hofmeister Effect for Human Motion Monitoring

“…Recently, a composite hydrogel containing a natural micro-/nanofiber reinforcer was explored, which significantly improved the mechanical properties of hydrogels [21][22][23]. Typically, natural wood can be used as support material after releasing the tight connections between cellulose fibers, generating tough wood structure hydrogels for enhanced mechanical strength, super-ion transport, or pressure sensors [10,24,25].…”