Optimization of electrochemical regeneration of intercalated MXene for the adsorptive removal of ciprofloxacin: Prospective mechanism.

2D-Ti3C2Tx MXene nanosheets intercalated with sodium ions (SI-Ti3C2Tx) were synthesized and utilized in simultaneous adsorption and electrochemical regeneration with ciprofloxacin (CPX). The primary focus of this study is to investigate the long-term stability of SI-Ti3C2Tx MXene and to propose the underlying regeneration mechanisms. The successful synthesis of Ti3AlC2, Ti3C2Tx MXene, and SI-Ti3C2Tx MXene was confirmed using X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. Electrochemical regeneration parameters such as charge passed, regeneration time, current density, and electrolyte composition were optimized with values of 787.5 C g-1, 7.5 min, 10 mA cm-2, and 2.5w/v% sodium chloride, respectively, enabling the complete regeneration of the SI-Ti3C2Tx MXene. In addition, the electrochemical regeneration significantly enhanced CPX removal from the SI-Ti3C2Tx MXene owing to partial amorphization, disorderliness, increased functional groups, delamination, and defect creation in the structure. Thus, the synthesized nano-adsorbent has proven helpful in practical water treatment with optimized electrochemical regeneration processes.

Sodium-alginate-laden MXene and MOF systems and their composite hydrogel beads for batch and fixed-bed adsorption of naproxen with electrochemical regeneration.

Sodium alginate (SA)-laden two-dimensional (2D) Ti3C2Tx MXene (MX) and MIL-101(Fe) (a type of metal-organic framework (MOF)) composites were prepared and used for the removal of naproxen (NPX), following the adsorption and electrochemical regeneration processes. The fixed-bed adsorption column studies were also conducted to study the process of removal of NPX by hydrogels. The number of interactions via which the MX-embedded SA (MX@SA) could adsorb NPX was higher than the number of pathways associated with NPX adsorption on the MIL-101(Fe)-embedded SA (MIL-101(Fe)@SA), and the MX and MIL-101(Fe) composite embedded SA (MX/MIL-101(Fe)@SA). The optimum parameters for the electrochemical regeneration process were determined: charge passed and current density values were 169.3 C g-1 and 10 mA cm-2, respectively, for MX@SA, and the charge passed and current density values were 16.7 C g-1 and 5 mA cm-2, respectively, for both MIL-101(Fe)@SA and MX/MIL-101(Fe)@SA. These parameters enabled excellent regeneration, consistent over multiple adsorption and electrochemical regeneration cycles. The mechanism for the regeneration of the materials was proposed that the regeneration of MX@SA and MIL-101(Fe)@SA involved the indirect electrooxidation process in the presence of OH radicals, and the regeneration of MX/MIL-101(Fe)@SA involved the indirect oxidation process in the presence of active chlorine species.

Enhanced bio-electrochemical performance of microbially catalysed anode and cathode in a microbial electrosynthesis system.

Most bio-electrochemical systems (BESs) use biotic/abiotic electrode combinations, with platinum-based abiotic electrodes being the most common. However, the non-renewability, cost, and poisonous nature of such electrode systems based on noble metals are major bottlenecks in BES commercialisation. Microbial electrosynthesis (MES), which is a sustainable energy platform that simultaneously treats wastewater and produces chemical commodities, also faces the same problem. In this study, a dual bio-catalysed MES system with a biotic anode and cathode (MES-D) was tested and compared with a biotic cathode/abiotic anode system (MES-S). Different bio-electrochemical tests revealed improved BES performance in MES-D, with a 3.9-fold improvement in current density compared to that of MES-S. Volatile fatty acid (VFA) generation also increased 3.2-, 4.1-, and 1.8-fold in MES-D compared with that in MES-S for acetate, propionate, and butyrate, respectively. The improved performance of MES-D could be attributed to the microbial metabolism at the bioanode, which generated additional electrons, as well as accumulative VFA production by both the bioanode and biocathode chambers. Microbial community analysis revealed the enrichment of electroactive bacteria such as Proteobacteria (60%), Bacteroidetes (67%), and Firmicutes + Proteobacteria + Bacteroidetes (75%) on the MES-S cathode and MES-D cathode and anode, respectively. These results signify the potential of combined bioanode/biocathode BESs such as MES for application in improving energy and chemical commodity production.

Electrocatalytic oxidation of antidiabetic drug metformin adsorbed on intercalated MXene.

Two-dimensional (2D) Ti3C2Tx transition metal carbide (MXene) nanosheets intercalated with sodium ions (SI-Ti3C2Tx MXene) were used in the adsorption and electrochemical regeneration process for removal of the antidiabetic drug metformin (MF) as a model emerging pollutant. After MF adsorption, SI-Ti3C2Tx MXene oxidized the MF on its surface through its electrocatalytic activity at very low current density and cell potential. For complete oxidation the optimum parameters were 0.525 C g-1, 0.005 mA cm-2, and pH 6 in absence of NaCl or 26.25 C g-1 and 0.5 mA cm-2 in the presence of 2.5 w/v% NaCl. The overall regeneration of SI-Ti3C2Tx is governed by a combined mechanism, i.e., desorption followed by degradation. The degradation mechanism, such as direct electron transfer or indirect oxidation, depends on the applied operating conditions. Thus, the investigation suggests that these 2D sheets are good nanoadsorbents as well as good electrocatalysts and proves their usefulness in practical water-treatment applications.

Development of a three-dimensional macroporous sponge biocathode coated with carbon nanotube-MXene composite for high-performance microbial electrosynthesis systems.

Microbial electrosynthesis (MES) is a renewable energy platform capable of reducing the carbon footprint by converting carbon dioxide/bicarbonate to useful chemical commodities. However, the development of feasible electrode structures, inefficient current densities, and the production of unfavorable electrosynthesis products remain a major challenge. To this end, a three-dimensional (3D) macroporous sponge coated with a carbon nanotube/MXene composite (CNT-MXene@Sponge) was evaluated as an MES cathode. The macroporous scaffold, together with intrinsic electrical conductivity, enhanced the charge transfer efficiency and selective microbial enrichment characteristics of the CNT-MXene@Sponge cathode resulted in an average current density of -324 mA m-2, which was substantially higher than that of the uncoated (-100 mA m-2), CNT (-141 mA m-2), and MXene (-214 mA m-2) coated sponge electrode. The uniform 3D structure and abundant active sites of the coated material facilitated mass diffusion and microbial growth, which produced 1.5 orders of magnitude higher butyrate than the uncoated sponge. The high-throughput sequencing results showed the selective enrichment of electrogenic and butyrate-producing phylum, Firmicutes. These results suggest that the MES performance could be enhanced using the collective features of large-pore network structure, such as better conductivity, improved capacitance, and selective microbial enrichment.

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.