Anomalous Thermo-osmotic Conversion Performance of Ionic Covalent-Organic-Framework Membranes in Response to Charge Variations

The development of efficient thermo-osmotic energy conversion devices has fascinated scientists and engineers for several decades in terms of satisfying the growing energy demand. The fabrication of ionic membranes with a high charge population is known to be a critical factor in the design of high-performance power generators for achieving high permselectivity and, consequently, high power extraction efficiency. Herein, we experimentally demonstrated that the thermo-osmotic energy conversion efficiency was improved by increasing the membrane charge density; however, this enhancement occurred only within a narrow window and subsequently exhibited a plateau over a threshold density. The complex interplay between pore−pore interactions and fluid structuration for ion transport across the upscaled nanoporous membranes helped explain the obtained results with the aid of numerical simulations. Consequently, the power generation efficiency of the multipore membrane deteriorated, deviating considerably from the case of simple linear extrapolation of the behavior of the single-pore counterparts. A plateau in the output electric power was observed at a moderate charge density, affording a value of 210 W m−2 at a 50-fold salinity difference with a temperature gradient of 40 K. This study has far-reaching implications for discerning an optimal range of membrane charge populations for augmenting the energy extraction, rather than intuitively focusing on achieving high densities.

Computer simulation to predict size distribution of track-etched nanopores

Track-etched nanoporous membranes prepared by swift heavy ion irradiation are promising for separation processes such as water purification. However, one drawback is that multiple pores are undesirably formed by pore overlapping to reduce separation performance. The techniques for predicting the size and amount of multiple pores in detail are still underdeveloped, which hinders the precise membrane design. In this study, a computer simulation program was developed to predict the size distribution of the track-etched pores. The program generates a number of single pores on the virtual grid plane to simulate random ion bombardment, finds multiple pores containing several single pores, and determines the multiple pore size by counting the inside grid points. All the multiple pores are categorized into different size classes, and the areal percentage occupied by the pores belonging to each size class is estimated. The simulation algorithm and the results of a model case simulation were described.

Спектральные оптические свойства керамических нанопористых мембран на основе анодного оксида алюминия и покрытия из серебра в парах аммиака

Spectral optical properties of synthesized ceramic nanoporous membranes based on anodic aluminum oxide coated silver in saturated ammonia gas flow have been experimentally investigated. Based on the measured transmission spectra and detected interference part of the spectra in wavelength range from 550 to 900 nm, temporal and spectral dependencies of the effective optical thickness and its changes in non-equilibrium conditions were obtained due to adsorption of ammonia molecules on silver film surface. According to detected and measured interference maximum shifts up to 14 nm in transmission spectra of Al2O3 + Ag membranes in ammonia gas flow, the possibility of constructing a selective interferometric optical sensors with 10 − 15 min response time is shown.

A Novel Numerical Procedure to Estimate the Electric Charge in the Pore from Filtration of Single-Salt Solutions

The assessment of physicochemical parameters governing the transport of ions through nanoporous membranes is a major challenge due to the difficulty in experimental estimation of the dielectric constant of the solution confined in nanopores and the volumetric membrane charge. Numerical identification by adjusting their values to fit experimental data is a potential solution, but this method is complicated for single-salt solutions due to the infinite number of couples that can describe a rejection curve. In this study, a novel procedure based on physical simplifications which allows the estimation of a range of values for these two parameters is proposed. It is shown here that the evolution of the interval of membrane charge with salt concentration can be described in all the experimental conditions by the Langmuir–Freundlich hybrid adsorption isotherm. Finally, it is highlighted that considering the mean dielectric constant and the adsorption isotherms assessed from a range of concentrations allowed a good prediction of rejection curves, irrespective of the salt and membrane considered.