Journal: Nature Communications
Article Title: Protonation and deprotonation of edges in graphene oxide and MXenes as a driving force for actuation in responsive 2D membranes
doi: 10.1038/s41467-025-63800-9
Figure Lengend Snippet: a Surface charge density of GO and MXene flakes at different pH, calculated using potentiometric titration. b Schematic diagram of the pH-programmed self-assembly process, where uncharged protonated flakes (gray) deposit first, followed by charged deprotonated flakes (brown). c Thermal actuation performance of GO and MXene at 100 °C. The actuators prepared at different pH. d X-ray photoelectron spectroscopy (XPS) of O1s analysis of GO membranes. The O1s spectrum further supports these observations. At pH2, the relative atomic concentrations of the functional groups are as follows: -OH (2.37 at%), C-O (55.18 at%), C=O (42.45 at%). At pH6, the concentrations are -OH (16.45 at%), C-O (66.55 at%), 531.03 eV C = O (16.99 at%). At pH10, the concentrations are C=O (44.28 at%), C-O (53.47 at%) and -OH (2.25 at%). e XPS of O1s analysis of MXene membranes. At pH2, the relative atomic concentrations of the functional groups are as follows: C-Ti-OH (38.45 at%), C-Ti-O (39.65 at.%), Ti-O (21.90 at%). At pH 6, the concentrations are C-Ti-OH (35.85 at%), C-Ti-O (39.92 at%), Ti-O (24.23 at%). At pH 10, the concentrations are Ti-H 2 O (2.57 at%), C-Ti-OH (32.10 at%), C-Ti-O (41.18 at%), Ti-O (24.15 at%). f Differential FTIR spectra of GO and MXene membranes at various pH, highlighting the C=O band at 1600–1700 cm −1 . The set-up for in-situ FTIR experiments before and after infrared irradiation is shown in Supplementary Fig. . The spectra were obtained by subtracting the room-temperature data from those after 3 min of infrared light irradiation. After infrared irradiation, a decrease in C=O band intensity is observed. Additionally, pH-dependent peak shifts are evident: under acidic conditions (pH 2), the C=O peak exhibits a red shift compared to alkaline conditions (pH 10), indicating protonation of carbonyl groups. g Thermal actuating performance of pH-programmed GO and MXene multilayers with different pH. The pH 2 GO membrane remains thermally unresponsive, while the pH 6 membrane exhibits the largest curvature. The pH 10 membrane bends under heating, but with a smaller curvature compared to pH 6, reflecting reduced thermal asymmetry. Actuator dimensions: 4 ×20 mm. Source data are provided as a file.
Article Snippet: The XRD patterns were obtained by a thin-film X-ray diffractometer (TF-XRD, Bruker D8 Advance).
Techniques: Titration, Spectroscopy, Functional Assay, In Situ, Irradiation, Membrane
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