Bioinspired Ultrastable MXene/PEDOT:PSS Layered Membrane for Effective Salinity Gradient Energy Harvesting from Organic Solvents

Abstract

The waste organic solvents containing inorganic salts have been considered sustainable resources, which can effectively capture salinity gradient energy using ion-selective membranes. However, it still remains a great challenge to fabricate the ion-selective membranes with high conversion efficiency and stability in an organic system. Here, the bioinspired nacre-like layered MXene/poly­(3,4-ethylenedioxythiophene)–poly­(styrenesulfonate) (PEDOT:PSS) (MP) composite membranes for capturing salinity gradient energy from an organic solvent are fabricated via filtration method, in which PEDOT:PSS molecules are introduced into MXene interlayers. Accordingly, the MP membrane exhibits high mechanical property and wonderful stability in common organic solvents. As expected, the power generation of the MP membrane reaches up to 3216 ± 603 nW in a 2/0.001 M methanol (Met)–LiCl solution and a record high power generation of 6926 ± 959 nW after adding NaOH into the Met–LiCl solution, which is superior to the previous report. Both experimental and theoretical studies confirm that the MP membrane has excellent cation selectivity and fast ion transport performance. The results are attributable to an increased interlayer spacing between MXene layers and an improved cation selectivity due to the insertion of PEDOT:PSS chains and the enhanced dissociation of negative charges by NaOH. The ultrastable two-dimensional (2D) nanochannel membrane provides practical application for harvesting energy from waste organic solvents.

Enhanced Osmotic Energy Conversion with Ultrahigh Ionic Conductivity in Sodium Polystyrenesulfonate/Cellulose Nanofiber Composite Membranes

“…Additionally, the EDS analysis of the S-element highlighted the uniform distribution of PSS within the PSS/CNF composite membrane (Figure e). Figure f displays the obtained PSS/CNF composite membrane, characterized by its colorless and transparent nature, flexibility, and foldability, rendering it suitable for capturing osmotic energy . The inset, as shown in Figure f, exhibits the water contact angle of the PSS/CNF composite membrane, which measures approximately 47°, differing from both pure PSS and pure CNF membranes (Figure S3).…”

“…Figure 1f displays the obtained PSS/CNF composite membrane, characterized by its colorless and transparent nature, flexibility, and foldability, rendering it suitable for capturing osmotic energy. 32 The inset, as shown in Figure 1f, exhibits the water contact angle of the PSS/CNF composite membrane, which measures approximately 47°, differing from both pure PSS and pure CNF membranes (Figure S3). This lower contact angle indicates higher hydrophilicity in the composite membranes due to the presence of abundant hydroxyl groups and carboxyl groups in CNFs and a significant number of sulfonate groups in PSS.…”

“…Notably, the ionic conductivity of the PSS/CNF composite membrane, especially in the low concentration region, reaches 0.12 S cm −1 , which is significantly higher than that of pure CNF membranes. Comparing the PSS/CNF composite membrane to other nanofluidic membranes reported in the relevant literature studies (Figure 2e and Table S1), it becomes evident that the PSS/CNF composite membrane demonstrates exceptional high ionic conductivity, surpassing most cellulosebased nanofluidic membranes (ionized wood, 41 ionized loofah, 50 NBCM, 51 RCNF, 52 BC-CMC, 34 N-ABC and P-ABC, 53 PNIPAM-g-sCC, 12 NBC/NGO, 54 GO/CNF, 46 g-C 3 N 4 /CNF, 40 WS 2 /CNF, 55 and MXene/CNF 18 ) and several polymeric membranes (SPEEK, 56 BCP, 57 SPAEK/IPAES-ICM, 13 MXene/PSS, 33 MXene/PEDOT:PSS, 32 GO-MAP, 58 GO/PDA, 59 and PAA/MMT 60 ). This enhancement is attributed to the synergy between PSS and CNFs, which not only provides sufficient nanochannels but also addresses the charge density deficiency observed in pure CNF membranes, thereby facilitating faster cation transport within the nanochannels of the composite membranes.…”

“…Among them, polystyrenesulfonate (PSS) stands out as a conductive polymer rich in sulfonic acid groups­(−SO 3 – ), , making it highly hydrophilic and water-soluble. In recent years, many attempts to incorporate PSS into two-dimensional lamellar materials to improve the ion selectivity of nanofluidic devices have confirmed the great significance of PSS in fine-tuning the surface charge density of nanochannels as a nanofluidic component for regulating the ion-selective transport. − However, polymer membranes, including PSS, generally characterized by a dense structure and poor mechanical properties, severely limit practical applications.…”

Photo-controllable Ion-Gated Metal–Organic Framework MIL-53 Sub-nanochannels for Efficient Osmotic Energy Generation

“…Once the SP-MIL-53 sub-nanochannels had UV illumination, however, a larger amount of the K + ions were transported along the side of the sub-nanochannel (Figure S23b). , The fast transfer of K + ions in the sub-nanochannels was mainly attributed to the following reasons. Under UV illumination, the quasi-planar MC molecules close to one side of the sub-nanochannel could provide enough space for cation transport (Figure S23c).…”