Artificial membranes are widely used to mimic the selective transport behavior of biological ion channels and pumps, particularly their stimulus-responsive regulation capabilities. Herein, solid-state nanochannels are chemically functionalized with glycine (Gly) and pentylamine to precisely tune interfacial chemistry and surface charge states. Owing to distinct pore sizes and geometric confinement, cylindrical and conical nanochannels exhibit markedly different pH-responsive ion transport mechanisms. In cylindrical nanochannels with relatively large diameters, ion transport is dominated by bulk ionic conduction, and the pH dependence mainly arises from the different mobilities of H+ and OH- ions. In contrast, conical nanochannels with narrow tips display surface-charge-governed transport, where pH and salt concentration jointly modulate electric double layer overlap and ion current rectification. Under acidic conditions, the functionalized nanochannels show suppressed ionic conduction associated with a hydrophobic interfacial state, while alkaline environments induce enhanced conduction due to increased surface charge density and wettability. These results establish a geometry-dependent pH-gating mechanism, providing a rational design strategy for responsive ion-transport membranes in sensing and separation applications.
Nuclear energy plays a crucial role as a clean energy source in modern society. The use of nuclear energy will result in the generation of a large amount of radioactive nuclear wastewater. Separation of nuclides from radioactive wastewater is crucial for the safe disposal of nuclear wastes and the sustainable development of resources. However, it remains a great challenge to achieve precise separation between different radionuclide ions due to their similar properties. Herein, we constructed a radiation-resistant graphene-based membrane via ethylenediaminetetraacetic acid (EDTA) functionalization with highly stable and aligned two-dimensional subnanochannels, which exhibits adjustable ion diffusion energy barrier and ultrahigh radionuclide ion selectivity. The functional groups within the GO-EDTA channel exhibit strong affinitive binding interactions with Sr2+ and La3+. The mono/multivalent metal-ion selectivity up to 485 and 1300 for Cs+/Sr2+ and Cs+/La3+, respectively, outperforms other reported membranes. Besides, the channel can still maintain stable separation performance under irradiation conditions. Furthermore, using quartz crystal microbalance, we break down the contributions of partitioning at the pore mouth and intrapore diffusion to the overall energy barrier for salt transport, indicating that the precise separation of ions is achieved by regulating the diffusion energy barrier. This work provides a mechanism for the design of membranes with high ionion selectivity and demonstrates the application potential of nuclear resource recycling.
Dynamic constitutional frameworks (DCFs), connecting monomers via reversible covalent bonds, can initiate the assembly of gold nanoparticles (AuNps) with distinctive optoelectronic and surface chemical properties. A previous study indicated that these nanomaterials are particularly valuable for carbonic anhydrase immobilization and stabilization, with potential applications in biocatalysis and biosensing. However, further studies with different enzymes are needed to prove their universality. Therefore, this research focuses on immobilizing phosphotriesterase (PTE), an effective degrader of toxic organophosphates, on AuNp‐DCF conjugates. PTE is integrated with citrate‐ and PEG‐stabilized AuNps or imine‐based DCFs resulting in stable, homogeneous PTE‐AuNp‐DCF assemblies. The conjugates exhibit high bonding affinity and changes in the PTE's secondary structure, which did not deactivate the enzyme. The catalytic performance of immobilized PTE is evaluated by measuring the p‐nitrophenol (p‐NP) production in a similar way is sense the paraoxon during its enzymatic hydrolysis, used as a model organophosphate. PTE immobilized to PEG 2000 ‐AuNps assembled with DCF‐PEG1500 shows the highest reaction rate (13.7 × 10 −6 ± 0.82 M min −1 ), outperforming that immobilized to citrate‐stabilized AuNps (3.71 × 10 −6 ± 0.21 M min −1 ). Furthermore, these PTE‐PEG‐AuNp‐DCF conjugates at a 1/25 molar ratio display a residual reaction rate, 3.6 times higher than that of all other conjugates. Free amino groups exposed on the surface of AuNps facilitate optimal assembly with DCF‐PEG through aldehyde/amino exchange reactions, preserving PTE activity. These results highlight the potential of PTE‐DCF‐AuNp conjugates to intercept and transform small molecules like paraoxon.
Neutron scattering and molecular dynamics are used to unravel the microscopic mechanisms that govern methane diffusion in MFI zeolite (silicalite-1). First, using neutron scattering for silicalite-1 loaded with different methane amounts, we analyze the experimental dynamic structure factor S(q, ( q, !) ) in terms of molecular rotations and translations. While the rotational diffusion is found to be nearly independent of the zeolite loading, the translational diffusivity drastically decreases with the adsorbed amount. To gain insights into the diffusion mechanisms, trajectories obtained using molecular dynamics simulations are analyzed by determining mean square displacements < dr2(t)> 2 ( t ) > and incoherent scattering functions F(q, t). ( q, t ) . We also determine how anisotropy affects diffusion by considering independently the x , y and z directions. While the activation energy for diffusion is found to be weakly dependent on methane loading, the self-diffusivity decreases as the loading increases. Both the experimental and molecular simulation results suggest that steric repulsion between confined molecules - which increases as the loading increases - drastically affects diffusion. Using a free volume theory, we provide a simple formalism to predict consistently diffusion in the internal porous network of MFI zeolite. To demonstrate the applicability of this simple yet robust framework, we show that the free volume theory accurately captures diffusion in each direction of space but also when the size of the adsorbate molecule is arbitrarily increased.
