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Pyrogenic biomass carbon has been deemed a promising alternative to Pt/C for the oxygen reduction reaction (ORR) owing to its low cost, excellent activity, and eco-friendly properties. Herein, a porous carbon tube material derived from kapok fibres was prepared by combining activation with pyrolysis. Electrochemical measurements demonstrated that the kapok fibre-derived material prepared at 900°C had excellent ORR performance with a half-wave potential −0.14 V (vs. Ag/AgCl) close to that of commercial Pt/C (−0.13 V vs. Ag/AgCl) in 0.1 mol L−1KOH. The prepared material also displayed remarkable methanol tolerance and durability. Furthermore, the maximum power density output of the microbial fuel cell using the prepared material was (801±40) mW m−2, comparable to that of the Pt/C cathode ((778±31) mW m−2). The present work provides a facile way of using economical and renewable biomass to develop a porous structure and high-activity cathode ORR catalyst for fuel cell applications.

Sustainable textile wastewater treatment strongly demands an indispensable paradigm shift from removal of contaminants to effective recovery of resources. In this work, a hybrid tight ultrafiltration (TUF) and bipolar-membrane electrodialysis (BMED) process was explored to recover resources (i.e., dye extraction, acid/base conversion, and pure water regeneration) from highly saline textile wastewater. Using a TUF membrane with 5000 Da molecular weight cutoff (MWCO) can obtain a sufficient rejection (>99.6%) of both reactive and direct dyes, due to the dye aggregation. Additionally, the considerably large pore size of the TUF membrane endowed the process with free transport of NaCl and Na2SO4(i.e., >99.42%), exhibiting promise as an alternative means of separation of dyes and Na2SO4. Additionally, an integrated TUF-based diafiltration was designed to separate the model dye (i.e., reactive blue 194) and Na2SO4. Particularly, reactive blue 194 was remarkably concentrated from 997.9 to 7952.8 mg·L–1by the TUF membrane with 99.5% dye recovery and 99.95% desalination efficiency after 8.0 diavolumes. Furthermore, a trace amount (i.e., 2.7 mg·L–1) of reactive blue 194 was observed in Na2SO4-containing TUF permeate, enabling a subsequent BMED operation. With the implementation of BMED, the Na2SO4-containing TUF permeate was sufficiently desalinated for acid/base conversion and pure water regeneration with no obvious fouling on the ion exchange membranes. These results demonstrate a potential applicability of the hybrid TUF/BMED process for sustainable management of textile wastewater, providing a strategy for practical applications in treatment of other high-salinity wastewaters.

Surface modification with advanced nanomaterials (i.e., 2D nanosheets) can be used to strategically tailor membrane properties, providing improved solute permselectivity to targeted molecules. In particular, 2D graphite-like carbon nitride (g-C3N4) nanosheets are a promising alternative for membrane modification, due to their exceptional physicochemical properties and facile synthesis. Herein, high-flux nanofiltration (NF) membranes were designed using bio-inspired co-deposition of hydrophilic g-C3N4nanosheets with a polydopamine (PDA)/polyethylenimine (PEI) layer onto porous ultrafiltration (UF) substrates. The g-C3N4nanosheets created additional nanochannels in the PDA/PEI layer to facilitate water molecule transport, resulting in high permeability (28.4 ± 1.2 L m−2h−1bar−1). Particularly, the bio-inspired layer structure was tailored from the UF to the NF (592 Da) scale by incorporating g-C3N4nanosheets, thereby breaking through the permeability–selectivity trade-off effect. The tailored NF membrane enabled ultrahigh retention of three reactive dyes (610–630 Da, >99.3%) and low salt rejection (2.9% for NaCl; 7.6% for Na2SO4), significantly promoting the fractionation of dyes and salts for dye desalination. Additionally, the hydrophilic g-C3N4nanosheets with oxygen plasma treatment further enhanced the wettability of the membrane surfaces, resulting in a superior antifouling performance. This study indicates the promise of g-C3N4nanosheets to engineer high-flux NF membranes with desirable fractionation performance for sustainable treatment of highly saline wastewater.

Use of tight ultrafiltration (UF) membranes has created a new pathway in fractionation of dye/salt mixtures from textile wastewater for sustainable resource recovery. Unexpectedly, a consistently high rejection for the dyes with smaller sizes related to the pore sizes of tight UF membranes is yielded. The potential mechanism involved in this puzzle remains unclear. In this study, seven tailored UF membranes with molecular weight cut-offs (MWCOs) from 6050 to 17530 Da were applied to separate dye/salt mixtures. These UF membranes allowed a complete transfer for NaCl and Na2SO4, due to large pore sizes. Additionally, these UF membranes had acceptably high rejections for direct and reactive dyes, due to the aggregation of dyes as clusters for enhanced sizes and low diffusivity. Specifically, the membrane with an MWCO of 7310 Da showed a complete rejection for reactive blue 2 and direct dyes. An integrated UF-diafiltration process was subsequently designed for fractionation of reactive blue 2/Na2SO4mixture, achieving 99.84% desalination efficiency and 97.47% dye recovery. Furthermore, reactive blue 2 can be concentrated from 2.01 to 31.80 g·L–1. These results indicate that UF membranes even with porous structures are promising for effective fractionation of dyes and salts in sustainable textile wastewater treatment.

The interaction of As(V) with zerovalent iron (ZVI) and H2O system was studied under oxic and anoxic conditions. XRD and XPS analysis of the ZVI confirmed the core–shell Fe0structure with an outer coating of iron oxide/hydroxide. Batch experiments showed that the rate of removal of As(V) was very fast for oxic compared to anoxic condition. Under open atmospheric environment, the analysis revealed that ZVI spontaneously reacts with water and oxygen to form a number of iron oxide/hydroxides and the As(V) is removed from the solution by sorption/coprecipitation onto these corrosion products. However, reduction of As(V) did not take place in such experimental conditions. On the other hand, in anoxic conditions, reduction of As(V) to As(III) and As(0) was demonstrated via XPS analysis. Electrons, Fe2+(s), and H(s)formed from Fe0oxidation were thought to be the reducing agents for such reduction process. Therefore, the inherent oxide/hydroxide layer on the ZVI surface plays an important role and helps in the indirect reduction of As(V). Thus, the present study delineates the possible mechanism of As(V) reduction with ZVI-H2O system where the formation of As(0) is important in view of arsenic immobilization.