Electrochemical-based approaches for the treatment of forever chemicals: Removal of perfluoroalkyl and polyfluoroalkyl substances (PFAS) from wastewater

Electrochemical based approaches for the treatment of recalcitrant water borne pollutants are known to exhibit superior function in terms of efficiency and rate of treatment. Considering the stability of Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are designated as forever chemicals, which generating from various industrial activities. PFAS are contaminating the environment in small concentrations, yet exhibit severe environmental and health impacts. Electro-oxidation (EO) is a recent development that treats PFAS, in which different reactive species generates at anode due to oxidative reaction and reductive reactions at the cathode. Compared to water and wastewater treatment methods those being implemented, electrochemical approaches demonstrate superior function against PFAS. EO completely mineralizes (almost 100 %) non-biodegradable organic matter and eliminate some of the inorganic species, which proven as a robust and versatile technology. Electrode materials, electrolyte concentration pH and the current density applying for electrochemical processes determine the treatment efficiency. EO along with electrocoagulation (EC) treats PFAS along with other pollutants from variety of industries showed highest degradation of 7.69 mmol/g of PFAS. Integrated approach with other processes was found to exhibit improved efficiency in treating PFAS using several electrodes boron-doped diamond (BDD), zinc, titanium and lead based with efficiency the range of 64 to 97 %.

Synthesis and Characterization of Silver and Graphene Nanocomposites and Their Antimicrobial and Photocatalytic Potentials

Microbial pathogens and bulk amounts of industrial toxic wastes in water are an alarming situation to humans and a continuous threat to aquatic life. In this study, multifunctional silver and graphene nanocomposites (Ag)_1−x(GNPs)_x [25% (x = 0.25), 50% (x = 0.50) and 75% (x = 0.75) of GNPs] were synthesized via ex situ approach. Further, the synthesized nanocomposites were explored for their physicochemical characteristics, such as vibrational modes (Raman spectroscopic analysis), optical properties (UV visible spectroscopic analysis), antibacterial and photocatalytic applications. We investigated the antimicrobial activity of silver and graphene nanocomposites (Ag-GNPs), and the results showed that Ag-GNPs nanocomposites exhibit remarkably improved antimicrobial activity (28.78% (E. coli), 31.34% (S. aureus) and 30.31% (P. aeruginosa) growth inhibition, which might be due to increase in surface area of silver nanoparticles (AgNPs)). Furthermore, we investigated the photocatalytic activity of silver (AgNPs) and graphene (GNPs) nanocomposites in varying ratios. Interestingly, the Ag-GNPs nanocomposites show improved photocatalytic activity (78.55% degradation) as compared to AgNPs (54.35%), which can be an effective candidate for removing the toxicity of dyes. Hence, it is emphatically concluded that Ag-GNPs hold very active behavior towards the decolorization of dyes and could be a potential candidate for the treatment of wastewater and possible pathogenic control over microbes. In the future, we also recommend different other in vitro biological and environmental applications of silver and graphene nanocomposites.

Visible light photodegradation of 2,4-dichlorophenol using nanostructured NaBiS2: Kinetics, cytotoxicity, antimicrobial and electrochemical studies of the photocatalyst

Removal of the hazardous and endocrine-disrupting 2,4-dichlorophenol (2,4-DCP) from water bodies is crucial to maintain the sanctity of the ecosystem. As a low bandgap material (1.37 eV), NaBiS₂ was hydrothermally prepared and used as a potential photocatalyst to degrade 2,4-DCP under visible light irradiation. NaBiS₂ appeared to be highly stable and remained structurally undeterred despite thermal variations. With a surface area of 6.69 m²/g, NaBiS₂ has enough surface-active sites to adsorb the reactive molecules and exhibit a significant photocatalytic activity. In alkaline pH, the adsorption of 2,4-DCP on NaBiS₂ appeared to decrease whereas, the acidic and neutral environments favoured the degradation. An increase in the photocatalyst dosage enhanced the degradation efficiency from 81 to 86 %, because of higher vacant adsorbent sites and the electrostatic attraction between NaBiS₂ and 2,4-DCP. The dominant scavengers degraded 2,4-DCP by forming a coordination bond between chlorine's lone pair of electrons and the vacant orbitals of bismuth, following the order hole> OH > singlet oxygen. Being non-toxic to both natural and aquatic systems, NaBiS₂ exhibits antifungal properties at higher concentrations. Finally, the electron-rich NaBiS₂ is an excellent electrocatalyst that effectively degrades organic pollutants and is a promising material for industrial and environmental applications.

Configuring Optimal FeS2@Carbon Nanoreactor Anodes: Toward Insights into Pyrite Phase Change/Failure Mechanism in Rechargeable Ni-Fe Cells

Pyrite FeS₂ has long been a research focus as the alternative anode of rechargeable Ni-Fe cells owing to its eye-catching merits of great earth-abundance, attractive electrical conductivity, and output capacity. However, its further progress is impeded by unsatisfactory cyclic behaviors due to still "ill-defined" phase changes. To gain insights into the pyrite working principles/failure factors, we herein design a core-shell hybrid of a FeS₂@carbon nanoreactor, an optimal anode configuration approaching the practical usage state. The resultant electrodes exhibit a Max. specific capacity of ∼272.89 mAh g^-1 (at ∼0.81 A g^-1), remarkably improved cyclic longevity/stability (beyond ∼80% capacity retention after 10³ cycles) and superior rate capability (∼146.18 mAh g^-1 is remained at ∼20.01 A g^-1) in contrast to bare FeS₂ counterparts. The as-built Ni-Fe full cells can also output impressive specific energy/power densities of ∼87.38 Wh kg^-1/ ∼ 11.54 kW kg^-1. Moreover, a refreshed redox reaction working mechanism of "FeS₂OH ↔FeS₂↔Fe⁰_{(in pyrite domains)}" is redefined based on real-time electrode characterizations at distinct operation stages. In a total cyclic period, the configured pyrite-based anodes would stepwise undergo three critical stages nominally named "retention", "phase transition/coexistence", and "degradation", each of which is closely related to variations on anodic compositions/structures. Combined with optimal electrode configurations and in-depth clarifications on inherent phase conversions, this focus study may guide us to maximize the utilization efficiency of pyrite for all other aqueous electrochemical devices.