Opportunities for in situ electro-regeneration of organic contaminant-laden carbonaceous adsorbents.

Adsorptive separation technologies have proven to be effective on organic contaminant removal in aqueous water. However, the breakthrough of contaminants is inevitable and can be at relatively low bed volumes, which makes the regeneration of spent adsorbents an urgent need. Electrochemically induced regeneration processes are given special attention and may provide ease of operation through in situ regeneration avoiding (i) removal and transport adsorbents, and (ii) avoiding use of hazardous chemicals (i.e., organic solvents, acids, or bases). Therefore, this review article critically evaluates the fundamental aspects of in situ electro-regeneration for spent carbons, and later discusses specific examples related to the treatment of emerging contaminants (such as per- and polyfluoroalkyl substances or PFAS). The fundamental concepts of electrochemically driven processes are comprehensively defined and addressed in terms of (i) adsorbent characteristics, (ii) contaminant properties, (iii) adsorption/regeneration driving operational parameters and conditions, and (iv) the competitive effects of water matrices. Additionally, future research needs and challenges to enhance understanding of in situ electro-regeneration applications for organic contaminants (specifically PFAS)-laden adsorbents are identified and outlined as a future key perspective.

Enabling circular economy by N-recovery: Electrocatalytic reduction of nitrate with cobalt hydroxide nanocomposites on copper foam treating low conductivity groundwater effluents.

Fertilizers play a vital role in the food-energy-water nexus. The traditional method of artificial nitrogen fixation to produce ammonia is a high-energy intensive centralized process that has caused an imbalance of the N-cycle due to the release of N-species to water. Electrocatalytic nitrate reduction (ENR) to ammonia is a promising N-resource recovery alternative that can enable the circular reuse of ammonia in decentralized settings. However, the primary challenge is identifying selective and affordable electrocatalysts. Identifying electrodes that rely on something other than platinum-group metals is required to surpass barriers associated with using expensive and endangered elements. In this study, an earth-abundant bimetallic catalyst, Cu/Co(OH)x, prepared and optimized by electrodeposition, demonstrates superior ammonia production. Under environmentally relevant conditions of 30 mg NO3--N L-1, Cu/Co(OH)x showed higher ammonia production than pristine Cu foam with 0.7 and 0.3 mmol NH3 gcat-1 h-1, respectively. The experimental evaluation demonstrated direct reduction and catalytic hydrogenation mechanisms in Cu/Co(OH)x sites. Leaching analyses suggest that Cu/Co(OH)x has outstanding stability with negligible metal concentration below the maximum contaminant level for both Cu and Co. These results provide a framework for using earth-abundant materials in ENR with comparable efficiency and energy consumption to platinum-group materials.

Photoelectrocatalytic decolorization of azo dyes with nano-composite oxide layers of ZnO nanorods decorated with Ag nanoparticles.

Photoelectrocatalysis provides an excellent frame for the application of photocatalytic nanostructured materials on easy recoverable supports. This study reports the two-step synthesis of hierarchically nanostructured ZnO/Ag composite photoelectrodes. Wurtzite ZnO was selectively electronucleated as spheroidal seeds on fluor doped tin oxide substrates and nanodecorated with Ag nanoclusters under electrochemical control. Hierarchically organized nanorods were selectively chemically grown on the plane (002) perpendicular to the substrate from ZnO/Ag seeds. Solutions emulating dye effluents with the usual contents of 0.1 M of NaCl and a model azo dye (Methyl Orange) were decolorized using ZnO/Ag nanorods in different treatments. Photocatalysis attained discrete decolorizations of 8% whereas photoelectrocatalysis completely decolorized solutions after 60 min. The influence of the metal/semiconductor interface (ZnO/Ag) as introduced Schottky barrier is studied demonstrating a four-fold enhancement on decolorization kinetics respect bare ZnO nanorods. The influence of the seed growth control on the final photoelectrocatalytic response is reported to control the hierarchical organization of nanorods. This resulted in different decolorization kinetics as result of the differences on the efficient use of the delivered photons conditioned by the photoelectrode structure.