High-Efficiency Recovery of Acetic Acid from Water Using Electroactive Gas-Stripping Membranes.

Recovery of carbon-based resources from waste is a critical need for achieving carbon neutrality and reducing fossil carbon extraction. We demonstrate a new approach for extracting volatile fatty acids (VFAs) using a multifunctional direct heated and pH swing membrane contactor. The membrane is a multilayer laminate composed of a carbon fiber (CF) bound to a hydrophobic membrane and sealed with a layer of polydimethylsiloxane (PDMS); this CF is used as a resistive heater to provide a thermal driving force for PDMS that, while a highly hydrophobic material, is known for its ability to rapidly pass gases, including water vapor. The transport mechanism for gas transport involves the diffusion of molecules through the free volume of the polymer matrix. CF coated with polyaniline (PANI) is used as an anode to induce an acidic pH swing at the interface between the membrane and water, which can protonate the VFA molecule. The innovative multilayer membrane used in this study has successfully demonstrated a highly efficient recovery of VFAs by simultaneously combining pH swing and joule heating. This novel technique has revealed a new concept in the field of VFA recovery, offering promising prospects for further advancements in this area. The energy consumption was 3.37 kWh/kg for acetic acid (AA), and an excellent separation factor of AA/water of 51.55 ± 2.11 was obtained with high AA fluxes of 51.00 ± 0.82 g.m-2hr-1. The interfacial electrochemical reactions enable the extraction of VFAs without the need for bulk temperature and pH modification.

Photochemical and electrochemical reduction of graphene oxide thin films: tuning the nature of surface defects.

Individual and combined photo(electro)chemical reduction treatments of graphene oxide thin films have been performed to modulate the type of defects introduced into the graphene sheets during the reduction. These were characterized by X-ray photoelectron and Raman spectroscopies, nuclear reaction analysis and electrochemical methods. Illumination of the graphene oxide thin film electrodes with low irradiance simulated solar light provoked the photoassisted reduction of the material with negligible photothermal effects. The photoreduced graphene oxide displayed a fragmented sp2 network due to the formation of a high density of defects (carbon vacancies) and the selective removal of epoxides and hydroxyl groups. In contrast, the electrochemical reduction under mild polarization conditions favored the formation of sp3 defects over vacancies, with a preferential removal of carbonyl and carboxyl groups over hydroxyl/epoxides. Used in conjunction, mild photochemical and electrochemical treatments allowed the obtainment of reduced graphene oxides with varied reduction degrees (ca. C/O ratio ranging from 4.9 to 2.2), and surface defects. Furthermore, the electrochemical reduction prevented the formation of vacancies during the subsequent illumination step. In contrast, both types of defects were accumulated when the GO electrode was first exposed to illumination and then polarized.