Membrane-Based Osmotic Heat Engine with Organic Solvent for Enhanced Power Generation from Low-Grade Heat

We present a hybrid osmotic heat engine (OHE) system that uses draw solutions with an organic solvent for enhanced thermal separation efficiency. The hybrid OHE system produces sustainable energy by combining pressure-retarded osmosis (PRO) as a power generation stage and membrane distillation (MD) utilizing low-grade heat as a separation stage. While previous OHE systems employed aqueous electrolyte draw solutions, using methanol as a solvent is advantageous because methanol is highly volatile and has a lower heat capacity and enthalpy of vaporization than water. Hence, the thermal separation efficiency of a draw solution with methanol would be higher than that of an aqueous draw solution. In this study, we evaluated the performance of LiCl–methanol as a potential draw solution for a PRO–MD hybrid OHE system. The membrane transport properties as well as performance with LiCl–methanol draw solution were evaluated using thin-film composite (TFC) PRO membranes and compared to the results obtained with a LiCl–water draw solution. Experimental PRO methanol flux and maximum projected power density of 47.1 L m^–2 h^–1 and 72.1 W m^–2, respectively, were achieved with a 3 M LiCl–methanol draw solution. The overall efficiency of the hybrid OHE system was modeled by coupling the mass and energy flows between the thermal separation (MD) and power generation (PRO) stages under conditions with and without heat recovery. The modeling results demonstrate higher OHE energy efficiency with the LiCl–methanol draw solution compared to that with the LiCl–water draw solution under practical operating conditions (i.e., heat recovery <90%). We discuss the implications of the results for converting low-grade heat to power

Low-Temperature Carbon Capture Using Aqueous Ammonia and Organic Solvents

Current postcombustion CO₂ capture technologies are energy intensive, require high-temperature heat sources, and dramatically increase the cost of power generation. In this work, we introduce a new carbon capture process requiring significantly lower temperatures and less energy, creating further impetus to reduce CO₂ emissions from power generation. In this process, high-purity CO₂ is generated through the addition of an organic solvent (acetone, dimethoxymethane, or acetaldehyde) to a CO₂ rich, aqueous ammonia/carbon dioxide solution under room-temperature and -pressure conditions. The organic solvent and CO₂-absorbing solution are then regenerated using low-temperature heat. When acetone, dimethoxymethane, or acetaldehyde was added at a concentration of 16.7% (v/v) to 2 M aqueous ammonium bicarbonate, 39.8, 48.6, or 86.5%, respectively, of the aqueous CO₂ species transformed into high-purity CO₂ gas over 3 h. Thermal energy and temperature requirements for recovering acetaldehyde, the best-performing organic solvent investigated, and the CO₂-absorbing solution were 1.39 MJ/kg of CO₂ generated and 68 °C, respectively, 75% less energy than the amount used in a pilot chilled ammonia process and a temperature 53 °C lower. Our findings exhibit the promise of economically viable carbon capture powered entirely by abundant low-temperature waste heat

Antimicrobial Electrospun Biopolymer Nanofiber Mats Functionalized with Graphene Oxide–Silver Nanocomposites

Functionalization of electrospun mats with antimicrobial nanomaterials is an attractive strategy to develop polymer coating materials to prevent bacterial colonization on surfaces. In this study we demonstrated a feasible approach to produce antimicrobial electrospun mats through a postfabrication binding of graphene-based nanocomposites to the nanofibers’ surface. A mixture of poly­(lactide-<i>co</i>-glycolide) (PLGA) and chitosan was electrospun to yield cylindrical and narrow-diameter (356 nm) polymeric fibers. To achieve a robust antimicrobial property, the PLGA–chitosan mats were functionalized with graphene oxide decorated with silver nanoparticles (GO–Ag) via a chemical reaction between the carboxyl groups of graphene and the primary amine functional groups on the PLGA–chitosan fibers using 3-(dimethylamino)­propyl-<i>N</i>′-ethylcarbodiimide hydrochloride and <i>N</i>-hydroxysuccinimide as cross-linking agents. The attachment of GO–Ag sheets to the surface of PLGA–chitosan fibers was successfully revealed by scanning and transmission electron images. Upon direct contact with bacterial cells, the PLGA–chitosan mats functionalized with GO–Ag nanocomposites were able to effectively inactivate both Gram-negative (<i>Escherichia coli</i> and <i>Pseudomonas aeruginosa</i>) and Gram-positive (<i>Staphylococcus aureus</i>) bacteria. Our results suggest that covalent binding of GO–Ag nanocomposites to the surface of PLGA–chitosan mats opens up new opportunities for the production of cost-effective, scalable, and biodegradable coating materials with the ability to hinder microbial proliferation on solid surfaces

Heterogeneous WS_<i>x</i>/WO₃ Thorn-Bush Nanofiber Electrodes for Sodium-Ion Batteries

Heterogeneous electrode materials with hierarchical architectures promise to enable considerable improvement in future energy storage devices. In this study, we report on a tailored synthetic strategy used to create heterogeneous tungsten sulfide/oxide core–shell nanofiber materials with vertically and randomly aligned thorn-bush features, and we evaluate them as potential anode materials for high-performance Na-ion batteries. The WS_<i>x</i> (2 ≤ <i>x</i> ≤ 3, amorphous WS₃ and crystalline WS₂) nanofiber is successfully prepared by electrospinning and subsequent calcination in a reducing atmosphere. To prevent capacity degradation of the WS_<i>x</i> anodes originating from sulfur dissolution, a facile post-thermal treatment in air is applied to form an oxide passivation surface. Interestingly, WO₃ thorn bundles are randomly grown on the nanofiber stem, resulting from the surface conversion. We elucidate the evolving morphological and structural features of the nanofibers during post-thermal treatment. The heterogeneous thorn-bush nanofiber electrodes deliver a high second discharge capacity of 791 mAh g^–1 and improved cycle performance for 100 cycles compared to the pristine WS_<i>x</i> nanofiber. We show that this hierarchical design is effective in reducing sulfur dissolution, as shown by cycling analysis with counter Na electrodes