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Magnetic rice-straw-derived biochar (MRBC) composites were synthesized by binding magnetite to the surface of the biochar for the highly efficient removal of Hg(II) from an aqueous solution. The maximum adsorption capacity of the adsorbent was 85.8 mg/g, which is much higher than those of other previously reported adsorbents for Hg(II) removal. The experimental data exhibited a good fit with a pseudo-second-order kinetic model, and the adsorption behavior followed the Langmuir isotherm. A thermodynamic study indicated that Hg(II) adsorption was spontaneous and endothermic. The individual effects and interactions of three key parameters such as initial Hg(II) concentration, adsorbent dosage, and pH were investigated by the Box–Behnken design of response surface methodology. The maximum removal efficiency of Hg(II) was 94.91% under an optimal condition of pH 3.9, an initial Hg(II) concentration of 14.3 mg/L, and an adsorbent dosage of 4.5 g/L. In the adsorption–desorption investigation, the MRBC was reusable for five adsorption–desorption cycles. The synthesized MRBC is a simple and inexpensive absorbent that can be readily isolated from a solution using a magnet after Hg(II) remediation. [Display omitted] • Magnetic rice-straw-derived biochar (MRBC) was synthesized and characterized. • The MRBC composites showed very high Hg(II) adsorption capacity. • The Langmuir isotherm gave the best fit to experimental adsorption data. • RSM was employed to determine the optimal conditions for enhanced Hg(II) removal. [ABSTRACT FROM AUTHOR]

Self-assembled composite porous structures comprising CuCo 2 O 4 microflowers and NiO hexagonal nanosheets were synthesized on a conducting 3D Ni foam surface [CCO/NO] using a simple hydrothermal method. This unique composite assembly was further characterized and electrochemically evaluated as a binder-free positive electrode for hybrid supercapacitor application. The study showed that the CCO/NO exhibited a maximum areal capacitance of 1444 mF cm−2, significantly higher than the parent CuCo 2 O 4 and NiO electrodes, with remarkable stability of 88.5% for 10,000 galvanostatic charge-discharge cycles. Key features for the enhanced electrochemical performance of CCO/NO can be related to a lowered diffusion resistance because the hybrid nanocomposite porous assembly generates short diffusion paths for electrolyte ions and more active sites for reversible faradaic transition for charge storage. The hybrid supercapacitor was assembled using activated carbon as a negative electrode and CCO/NO as a positive electrode in alkaline electrolyte, performed at an improved potential of 1.6 V. Device showed a maximum areal capacitance of 122 mF cm−2, a maximum areal energy density of 43 μWh cm−2, and a maximum areal power density of 5.1 mW cm−2. This hybrid supercapacitor showed remarkable cyclic stability up to 98% for 10,000 cycles. This study encourages the development of low-cost, high-performance, durable electrode designs using hybrid composite for next-generation energy storage systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dual biocatalyzed anode and cathode MES successfully degraded 91% MTF. • Dual biocatalyzed MES showed 10.3-times higher current density than control. • Bioanode exhibited excellent acetic and propionic acid electrosynthesis performance. • Proteobacteria & Bacteroidetes (acetate/propionate-producing phyla) dominated bioanode. The removal of different pharmaceuticals and personal care products from surface water is crucial. This study focused on the removal and transformation of metformin (MTF), an emerging contaminant in aqueous solutions using a dual biocatalyzed microbial electrosynthesis system (MES). Successful biodegradation of MTF (91 %) was achieved within 120 h with improved bioelectrochemical performance. The current density (−849 mA/m2) with drug loading at 0.5 ppm was 10.3, 7.6, and 2.4 times higher than that of the control, 0.1 ppm, and 0.3, ppm, respectively. Volatile fatty acids (VFAs) production also improved with excellent acetate, propionate, and butyrate production at dual biocatalyzed MES. Liquid chromatography mass spectrometry studies indicated improved mineralization with more MTF bioproducts. MTF regulated the microbial flora through enrichment of the electroactive phyla Proteobacteria and Bacteroidetes. This study provides a new perspective for the use of dual biocatalyzed microbial electrosynthesis systems in bioremediation research. [ABSTRACT FROM AUTHOR]

2D-Ti 3 C 2 T x MXene nanosheets intercalated with sodium ions (SI–Ti 3 C 2 T x) 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 Ti 3 AlC 2 , Ti 3 C 2 T x MXene, and SI–Ti 3 C 2 T x 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–Ti 3 C 2 T x MXene. In addition, the electrochemical regeneration significantly enhanced CPX removal from the SI–Ti 3 C 2 T x 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. [Display omitted] • SI–Ti 3 C 2 T x MXene serves as a promising candidate for the adsorption and electrochemical regeneration process. • The optimum conditions enable 100% regeneration of SI–Ti 3 C 2 T x. • Electrochemical treatment regenerates the adsorbent and improves the adsorption tendency. • SI–Ti 3 C 2 T x exhibited stability over ten regeneration cycles. • Regeneration occurs by a combined mechanism i.e. desorption followed by degradation. [ABSTRACT FROM AUTHOR]

Sodium alginate (SA)-laden two-dimensional (2D) Ti 3 C 2 T x 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. [Display omitted] [ABSTRACT FROM AUTHOR]

The toxic perfluorooctanoic acid (PFOA) is widely spread in terrestrial and aquatic habitats owing to its resistance to conventional degradation processes. Advanced techniques to degrade PFOA requires drastic conditions with high energy cost. In this study, we investigated PFOA biodegradation in a simple dual biocatalyzed microbial electrosynthesis system (MES). Different PFOA loadings (1, 5, and 10 ppm) were tested and a biodegradation of 91% was observed within 120 h. Propionate production improved and short-carbon-chain PFOA intermediates were detected, which confirmed PFOA biodegradation. However, the current density decreased, indicating an inhibitory effect of PFOA. High-throughput biofilm analysis revealed that PFOA regulated the microbial flora. Microbial community analysis showed enrichment of the more resilient and PFOA adaptive microbes, including Methanosarcina and Petrimonas. Our study promotes the potential use of dual biocatalyzed MES system as an environment-friendly and inexpensive method to remediate PFOA and provides a new direction for bioremediation research. [Display omitted] • 91% PFOA biodegradation via dual biocatalyzed microbial electrosynthesis in 120nullh. • PFOA inhibited microbial growth and current density. • PFOA regulated microbial flora and enriched PFOA-resistant microbes. • Propionic acid production improved and short carbon chain intermediates detected. • Methanosarcina and Petrimonas growth highest in PFOA-exposed biofilm. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Dual biocatalyzed MES-D showed improved bioelectrochemical performance than single MES-S. • MES-D exhibited 3.9 times higher current density than MES-S. • Acetate, propionate, butyrate production improved 3.2, 4.1, and 1.8 times in MES-D. • Proteobacteria dominated cathode in MES-S. • Firmicutes , Proteobacteria and Bacteroidetes dominated in MES-D. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) Ti 3 C 2 T x transition metal carbide (MXene) nanosheets intercalated with sodium ions (SI–Ti 3 C 2 T x 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–Ti 3 C 2 T x 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–Ti 3 C 2 T x 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. [Display omitted] • SI–Ti 3 C 2 T x MXene was successfully synthesized for metformin adsorption and electrocatalytic degradation. • SI–Ti 3 C 2 T x MXene showed 100% adsorptive capacity for multiple adsorption and regeneration cycles. • The physicochemical characteristics of MXene were retained after multiple cycles of adsorption and regeneration. • SI–Ti 3 C 2 T x MXene showed excellent electrocatalytic properties, which enabled oxidation at low cell potentials. • The proposed system should be useful for practical wastewater treatment applications. [ABSTRACT FROM AUTHOR]