本文要点：
基于膜的渗透发电技术既可以提供可持续能源，又可以利用生态友好的能量转换机制解决环境污染问题。共价有机框架(COF)膜由于其多孔性、轮廓分明的孔和可调的表面化学性质而成为这种应用的有吸引力的选择。然而，用于快速离子传输的多孔结构的精确设计仍然是一个挑战。
在这里，作者将最初随机取向的COF纳米通道设计成高度轴向排列的构型，通过界面聚合，然后与不同的离子，包括Ca2+、Mg2+、Al3+、Fe3+、Zn2+、Co2+和Cu2+配位，提供金属离子配位的COF框架。
值得注意的是，代表性的Ca-COF表现出0.93的优异阳离子选择性和0.06 S·m-1的离子电导率。当应用于渗透能量收集时，Ca-COF膜在天然海水和河水的混合物中提供了320.8 W m-2的创纪录输出功率密度。
通过强调排列金属离子配位的COF纳米通道在提高离子选择性和渗透性方面的重要性，我们的策略提出了释放渗透能量收集技术潜力的途径。
Fig. 1 | Synthesis and characterization of Ca-COF membranes. a, The synthesis process and the chemical structure of both the COF and Ca-COF membranes, highlighting the Ca-COF coordination structure, indicated by a black dotted circle. b, HR-TEM image of the Ca-COF membrane with a hexagonal lattice structure; scale bar: 2 nm. Each experiment was repeated three times independently with similar results. c, Grazing incidence wide-angle X-ray scattering pattern of the Ca-COF membrane. d, Zeta potentials of the COF and Ca-COF membranes in a KCl electrolyte, along with the molecular electrostatic potentials depicted for the COF and Ca-COF membranes in the top and bottom right images, respectively: Ca (green), N (blue), C (grey), O (pink) and H (white). e, Normalized X-ray absorption near edge structure spectra at the Ca K-edge for the Ca-COF and CaCO3 references. a.u., arbitrary units. f, Fourier-transformed k3-weighted EXAFS spectra at the Ca K-edge for Ca-COF, along with the fitting curve of Ca-COF at the Ca K-edge in R space. g. Wavelet transform EXAFS plot of the Ca-COF membrane. h, Optimized DFT model of Ca-COF with the computed bond lengths.
Fig. 2 | The ion permeability/selectivity and osmotic energy conversion of the membranes. a, Ion conductivities of COF and Ca-COF membranes in a KCl electrolyte with concentrations ranging from 10−6 M to 1 M. Experimental data are represented by dots, while the dashed line depicts the fitting results of the bulk solution. Insets are the schematic diagrams of Ca-COF channels (top left) and COF channels (lower left). b, I–V curves of COF and Ca-COF membranes in 0.001 M KCl. c, Ion selectivity defined as the ion transference number (t+) across COF and Ca-COF membranes in various NaCl gradients, including 0.05 M/0.01 M NaCl, 0.5 M/0.01 M NaCl, 1 M/0.01 M NaCl and 5 M/0.01 M. The error bars and the centre for the error bars are the standard deviation and the average of three independent measurements, respectively. d, Schematic representation of experimental set-up used for harvesting osmotic energy. e, Output power densities and current densities of COF and Ca-COF membranes in a 0.5 M/0.01 M NaCl gradient. f, Energy conversion efficiencies (ŋ) of COF and Ca-COF membranes in different NaCl gradients, including 0.05 M/0.01 M NaCl, 0.5 M/0.01 M NaCl, 1 M/0.01 M NaCl and 5 M/0.01 M. The error bars and the centre for the error bars are the standard deviation and the average of three independent measurements, respectively. g, Current densities and output power densities depending on the external load resistances for the Ca-COF membrane using natural seawater/river water. h, The long-term stability plots of energy conversion for the Ca-COF membrane in natural seawater/river water, showing variations in potential, output power density and current density over time.
Fig. 3 | Numerical simulations. a, Numerical simulation results for total ion concentrations (Ccation + Canion) within both Ca-COF and COF nanochannels. b,c, MD simulation snapshots of the COF membrane at 0 ns and at 4 ns. d,e, MD simulation snapshots of the Ca-COF membrane at 0 ns and at 4 ns. f, Transfer quantities of K+ or Cl– ions versus time under the COF channels with a fixed interlayer distance of 0.32 nm. g, Transfer quantities of K+ or Cl– ions versus time under Ca-COF nanochannels with a fixed interlayer distance of 0.34 nm.
Fig. 4 | Wider applicability of axially aligned M-COF membranes. a–f, Metal 2p XPS spectra of M-COF; insets show digital photographs of the respective M-COF membranes. g, The surface-charge densities on the M-COF surface. h, Ion permeabilities of M-COFs in a 0.5 M/0.01 M NaCl salinity gradient. i, The output power densities of M-COF membranes in a 0.5 M/0.01 M NaCl salinity gradient.
https://doi.org/10.1038/s41893-024-01493-6
