Synthesis of enhanced corrosion resistant Fe-B-C-Ti amorphous ribbons and evaluation of their photodegradation efficiency under light irradiation.

Fe-based amorphous alloys have been found to be very efficient in the degradation of water pollutants due to their unique atomic arrangements with long-range disordered structure. In this work, Fe-B-C-Ti amorphous ribbons were successfully synthesized and showed high catalytic efficiency in the degradation of methylene blue (MB) under simulated sunlight and across a wide pH range. The catalytic efficiency was evaluated under different conditions to optimize the degradation performance. The amorphous ribbon Fe75B10C10Ti5 was found to exhibit the highest photocatalytic activity as explained by its optical and photoelectrochemical properties. It can degrade MB completely with low Fe-leaching and significant recyclability at pH close to a neutral range (pH 5). The degradation mechanisms can be explained in terms of photocatalytic activity along with the galvanic cell effect which contributed to the efficient MB degradation. This work provides a comprehensive idea for the synthesis of amorphous alloys by optimizing their elemental composition and also explains the catalytic activity of partially crystallized regions on the ribbon surface. The significant corrosion resistance and the quick degradation of MB in a wide pH range in a recyclable manner by these easily separable and highly efficient catalysts indicate great potential for their practical application.

MXene-coated biochar as potential biocathode for improved microbial electrosynthesis system.

Microbial electrosynthesis (MES) holds tremendous large scale energy storage potential. By promoting the bioconversion of carbon dioxide (bicarbonate) into useful chemical commodities, this technique utilizes renewable energy and reduces carbon footprint. However, expensive electrode materials, low current densities, and multiple electrosynthesis products are major challenges to this field. To this end, this study examines a multilayered and conductive MXene structure that was coated on a cost-effective biochar substrate and tested as a MES cathode. These results show this coating yielded improved electrical conductivity, increased charge transfer efficiency, and selective microbial enrichment characteristics, resulting in a 2.3-fold increase in cathodic current production in comparison to the uncoated biochar. Moreover, an increase in active sites improved mass transfer and microbial growth, producing 1.7-fold increase in butyrate in comparison to the uncoated control. Considering that electrode attached microbial communities play a major role in final products, microbial community analyses was completed, suggesting that selective microbial enrichment was promoted as Firmicutes (66%), Proteobacteria (13%), and Bacteroidetes (12%) (i.e., exoelectrogenic and butyrate producing phyla) which were dominant in the MXene-coated biochar biofilm. These results show that biochar modification is an effective technique for achieving selective products through MES.

MnCo2O4 coated carbon felt anode for enhanced microbial fuel cell performance.

A highly efficient anode is very crucial for an improved microbial fuel cell (MFC) performance. In this study, a binder-free manganese cobalt oxide (MnCo2O4@CF) anode was synthesized using a conventional carbon felt (CF) by a facile hydrothermal method. A large electrochemically active and rough electrode surface area of MnCo2O4@CF anode improved the substrate fluxes and microbial adhesion/growth. Furthermore, the electrochemical tests on the synthesized anode confirmed the superior bioelectrochemical activity, reduced ion transfer resistance, and excellent capacitance. This resulted in an improved power density (945 mW/m2), which was 3.8 times higher than that of CF anode. The variable valence state, high stability and biocompatibility of MnCo2O4@CF resulted in continuous current density performance for five MFC cycles. High-throughput biofilm analysis revealed the enrichment of electricity producing phylum of Proteobacteria and Bacteroidetes (∼90.0%), which signified that the modified MnCo2O4 anode accelerated the enrichment of electro-active microbes.

Nickel ferrite/MXene-coated carbon felt anodes for enhanced microbial fuel cell performance.

In recent years, the modification of electrode materials for enhancing the power generation of microbial fuel cells (MFCs) has attracted considerable attention. In this study, a conventional carbon felt (CF) electrode was modified by NiFe2O4 (NiFe2O4@CF), MXene (MXene@CF), and NiFe2O4-MXene (NiFe2O4-MXene@CF) using facile dip-and-dry and hydrothermal methods. In these modified CF electrodes, the electrochemical performance considerably improved, while the highest power density (1385 mW/m2), which was 5.6, 2.8, and 1.4 times higher than those of CF, NiFe2O4@CF, and MXene@CF anodes, respectively, was achieved using NiFe2O4-MXene@CF. Furthermore, electrochemical impedance spectroscopy and cyclic voltammetry results confirmed the superior bioelectrochemical activity of a NiFe2O4-MXene@CF anode in a MFC. The improved performance could be attributed to the low charge transfer resistance, high conductivity and number of catalytically active sites of the NiFe2O4-MXene@CF anode. Microbial community analysis demonstrated the relative abundance of electroactive bacteria on a NiFe2O4-MXene@CF anodic biofilm rather than CF, MXene@CF, and NiFe2O4@CF anodes. Therefore, these results suggest that combining the favorable properties of composite materials such as NiFe2O4-MXene@CF anodes can open up new directions for fabricating novel electrodes for renewable energy-related applications.

Photocatalytic degradation of methylene blue with P25/graphene/polyacrylamide hydrogels: Optimization using response surface methodology.

An environment-friendly hydrogel was synthesized by entrapping Degussa P25 on the surface of a reduced graphene oxide (rGO)-polyacrylamide (PAM) matrix.The PAM content of the P25-rGO-PAM (PGP) hydrogel considerably influenced the adsorption and photocatalytic degradation of methylene blue (MB), and the optimal PAM content was 10% (w/v). Furthermore, rGO not only enhanced the adsorption capacity of the hydrogel by increasing the surface area but also increased the photodegradation efficiency synergistically by separating electron-hole pairs. The reaction kinetic constant for MB degradation by the hydrogel was 0.0276 min-1, which was three and five times the reaction kinetic constants of P25-PAM and rGO-PAM hydrogels, respectively. The synthesized PGP showed high stability and its MB degradation efficiency was considerably high up to five consecutive cycles under UV-irradiation. The eco-friendly nature of the hydrogel was evaluated on the basis of bacterial inactivation, and the treated water was found to be safe for use. Three key operating parameters (initial MB concentration, temperature, and pH) were optimized for maximizing MB removal using a response surface methodology. The complete MB removal efficiency was obtained for the optimal conditions of pH 9.4, a temperature of 31.2 °C, and an initial MB concentration of 5.2 mg/L.

Investigating the role of anodic potential in the biodegradation of carbamazepine in bioelectrochemical systems.

Anode potential is a critical factor in the biodegradation of organics in bioelectrochemical systems (BESs), but research on these systems with complex recalcitrant co-substrates at set anode potentials is scarce. In this study, carbamazepine (CBZ) biodegradation in a BES was examined over a wide range of set anode potentials (-200 to +600 mV vs Ag/AgCl). Current generation and current densities were improved with the increase in positive anode potentials. However, at a negative potential (-200 mV), current generation was higher as compared to that for +000 and +200 mV. The highest CBZ degradation (84%) and TOC removal efficiency (70%) were achieved at +400 mV. At +600 mV, a decrease in CBZ degradation was observed, which can be attributed to a low number of active bacteria and a poor ability to adapt to high voltage. This study signified that BESs operated at optimum anode potentials could be used for enhancing the biodegradation of complex and recalcitrant contaminants in the environment.

Exfoliation of Titanium Aluminum Carbide (211 MAX Phase) to Form Nanofibers and Two-Dimensional Nanosheets and Their Application in Aqueous-Phase Cadmium Sequestration.

A green approach was adopted to exfoliate a Ti2AlC MAX phase. The exfoliated nanostructures (Alk-Ti2Cfibr and Alk-Ti2Csheet) with exceptional mechanical, thermal, and water stabilites, as well as abundant oxygenated active binding sites, were synthesized via a controlled hydrothermal treatment in an alkaline environment. The successful synthesis of nanofibers and sheetlike nanostructures was inferred with scanning electron microscopy and X-ray diffraction analyses. Field emission scanning electron microscopy, field-emission transmission electron microscopy, Raman spectroscopy, Brunauer-Emmett-Teller surface area, ζ-potential analyses, and X-ray photoelectron spectroscopy were utilized to investigate the material's characteristics and its structural changes after metal ion adsorption. Heavy metal ion adsorption of the synthesized nanostructures was assessed in batch tests based on Cd2+ ion sequestration; the maximum adsorption capacity for Cd2+ was 325.89 mg/g, which is among the highest values reported for similar materials such as graphene oxide and its derivatives. The detailed quantitative investigation confirmed the interaction of hydroxyl groups with Cd2+ ions by electrostatic interactions, adsorption-coupled oxidation, and complex formation. Owing to their unique structure, high porosity, large specific surface area, and oxygenated functional groups, Alk-Ti2Csheet nanosheets were highly time-efficient for Cd2+ removal. Moreover, Alk-Ti2Cfibr and Alk-Ti2Csheet nanostructures were tested for simulated groundwater, showing that synthesized nanostructures were capable for removing Cd2+ ions at the ppb level. The results obtained from this study suggested that nanostructures synthesized using this route could provide a new approach to prepare and exfoliate additional MAX phases for the removal of heavy metal ions and other pollutants in the environment.

Effect of rGO loading on Fe3O4: A visible light assisted catalyst material for carbamazepine degradation.

Carbamazepine (CBZ), an anticonvulsant drug, is one of the most recalcitrant pharmaceuticals detected in wastewater. For the photocatalytic degradation of CBZ, visible light assisted heterogeneous Fenton-like hybrid composites were synthesized via a co-precipitation method by anchoring magnetite (Fe3O4) with reduced graphene oxide (rGO). The rGO loading not only reduced the aggregation of Fe3O4 nanoparticles, but also increased the adsorption capacity of the hybrid composites. The mass ratio of rGO in the composites substantially affected CBZ photocatalytic degradation and a 10 wt% rGO loading (rGF10) provided nearly complete CBZ degradation within 3 h. Moreover, the addition of rGO reduced the charge recombination of the bare Fe3O4 nanoparticles and provided more accessible reactive sites, enhancing the degradation capacity. The visible light excited Fe3O4 nanoparticles yielded reactive species such as hydroxyl radicals (·OH), holes (h+), and superoxide radicals (O2·-) during the photodegradation process that were evaluated by using specific scavengers during the degradation experiment. The hybrid catalyst was effective under wide pH ranges (from 3 to 9) and showed faster degradation rates in the acidic condition. The composites were magnetically separable, easily regenerated, and exhibited considerably high photocatalytic activity up to five cycles.

Photodegradation of microcystin-LR using graphene-TiO2/sodium alginate aerogels.

In this study, sustainable graphene oxide-TiO2/sodium alginate and reduced graphene oxide-TiO2/sodium alginate aerogels were synthesized and the potential of these aerogels was investigated for microcystin-LR degradation in aqueous solution. Along with the role of alginate in the synthesis of aerogels, effects of different concentrations of photocatalyst, photolysis, pH, and combination of TiO2 (anatase)/Degussa P25 with graphene were investigated in lieu of microcystin-LR photodegradation.The complete degradation of microcystin-LR was attained in case of reduced graphene oxide-TiO2/sodium alginate aerogel-not in graphene oxide-TiO2/sodium alginate aerogel case-by the synergistic effect of adsorption and photodegradation. The recyclability study of reduced graphene oxide-TiO2/sodium alginate aerogel demonstrated high stability and photoactivity and the degradation efficiency was not much hampered during six consecutive cycles of degradation reaction. The possible fragmentation pathways were also proposed based on identified intermediate products. High adsorption and degradation synergy and ease of separation/recycling of reduced graphene oxide-TiO2/sodium alginate aerogel can make it a suitable option for removing microcystin-LR from water systems.