B-doped graphene quantum dots implanted into bimetallic organic framework as a highly active and robust cathodic catalyst in the microbial fuel cell.

Developing efficient and durable oxygen reduction reaction (ORR) cathodic catalysts plays an essential role in application of microbial fuel cells (MFCs). Herein, the B-doped graphene quantum dots implanted into bimetallic organic framework (BGQDs/MOF-t) are fabricated by a facile electro-deposition. Results show that, the in-situ growth of FeCoMOF on nickel foam can effectively assist construction of nanoflowers with compact connections, thus improves the conductivity. More importantly, this nano-network can serve as the template for the implantation of BGQDs through powerful interface of M-O-C bonding, avoiding π-π rearrangement and providing efficient charge transfer and abundant edge active sites. Benefitting from the enhanced electrode/electrolyte transport interface, abundant catalytic sites and low charge transfer resistance, the BGQDs/MOF-15 exhibits excellent ORR activity, superior to commercial Pt/C catalyst. In the MFC with the BGQDs/MOF-15 cathode, the maximum power density of 703.55 mW m-2 is achieved, which is 1.53 times of that of the Pt/C cathode. In addition, the BGQDs/MOF-15 cathode maintains great stability over 800 h, while that of Pt/C reduces to 61% of the initial voltage. This work opens new opportunities for developing efficient and durable MOF-derived ORR catalyst.

Visible-light-driven Z-scheme Zn3In2S6/AgBr photocatalyst for boosting simultaneous Cr (VI) reduction and metronidazole oxidation: Kinetics, degradation pathways and mechanism.

It is urgently needed to develop high-performance materials that can synchronously remove heavy metals and organic pollutants. Herein, the visible-light responsive Zn3In2S6/AgBr composites were prepared for concurrent removals of metronidazole (MNZ) and Cr (VI). In the Cr (VI)-MNZ coexisting system, the removals of MNZ and Cr (VI) using the optimized Zn3In2S6/AgBr-15 photocatalyst reached 98.2% and 94.8% within 2 h, respectively; higher than those using counterparts. The radical species trapping and electron spin resonance (ESR) results demonstrated that ·OH was the most dominated species for MNZ oxidation, and photo-generated electrons were responsible for Cr (VI) reduction. Besides, slight competition for ·O2- during the simultaneous MNZ degradation and Cr (VI) reduction occurred. Energy band structure analysis, ESR and the outstanding photocatalytic performance for MNZ and Cr (VI) removals demonstrated that the Zn3In2S6/AgBr-15 was a Z-scheme photocatalyst, which promoted photo-induced carrier's separation. Possible MNZ degradation pathways and mechanism over the Z-scheme Zn3In2S6/AgBr were also proposed based on the identified intermediates. This study could inspire new ideas for design of efficient Z-scheme photocatalysts for wastewater treatment.

Research on the Fracture Behavior of Steel-Fiber-Reinforced High-Strength Concrete.

The behavior of steel fiber concrete, which is the most widely used building material, has been widely examined. However, methods for calculating Fracture parameters differ by fracture behavior of SFHSC with different strengths. In this study, the fracture behavior of steel-fiber-reinforced high-strength concrete (SFHSC) was -investigated using three-point bending tests. A total of 144 notched concrete beams with a size of 100 mm × 100 mm × 515 mm were tested for three-point bending in 26 groups. The effects of the steel fiber volume ratio, steel fiber type, and relative notch depth on the fracture toughness (KIC) and fracture energy (GF) of SFHSC specimens were studied. The results show that an increase in the volume fraction of steel fiber (ρf) added to high-strength concrete (HSC) significantly improves the fracture behavior of HSC. As compared to milled and sheared corrugated steel fibers, cut bow steel fibers significantly improve the fracture behavior of SFHSC. The effect of incision depth changes on the KIC and GF of SFHSC and HSC for the comparison group has no common characteristics. With an increase in incision depth, the values of KIC of the SFHSC specimens decrease slightly. The GF0.5/GF0.4 of the SFHSC specimens show a decreasing trend with an increase in ρf. According to the test results, we propose calculation models for the fracture behavior of SFHSC with different strengths. Thus, we present a convenient and accurate method to calculate fracture parameters, which lays a foundation for subsequent research.

Different refractory organic substances degradation and microbial community shift in the single-chamber bio-photoelectrochemical system.

The single-chamber bio-photoelectrochemical system (BPES) with a BiOBr photocathode was developed for acid orange 7 (AO7), 2,4 dichlorophenol (2,4-DCP) and chloramphenicol (CAP) degradation under solar irradiation. Photoelectrochemical characterizations showed that the optimized BiOBr-photocathode exhibited great light-response property and excellent electrochemcial performance. Moreover, desired TOC removals were achieved for various organic pollutants, with the values of 90.97% (AO7), 81.41% (2,4-DCP) and 78.47% (CAP). Besides, the lower cathode potentials in the illuminated BPESs were favorable to efficient pollutants degradation. Significant microbial community shifts were observed among the inoculation and anodic biofilms from the BPES, and the most dominated species in anodic biofilms acclimated to various pollutants were Geobacter and Pseudomonas, which have the abilities of extracellular electrons transfer and organics degradation. Some other species that different from the inoculation were also identified from the BPES biofilms. This study suggested that BPES had great potential for refractory organics degradation.

Photocathode optimization and microbial community in the solar-illuminated bio-photoelectrochemical system for nitrofurazone degradation.

To further enhance the bio-photoelectrochemical system (BPES) performance for nitrofurazone (NFZ) degradation and current output, the g-C3N4/CdS photocathode was optimized, and microbial community shift from inoculation to the BPES was analyzed. Results showed that photocathode with g-C3N4/CdS (mass ratio of 1:9) loading of 7.5 mg/cm2 exhibited the best performance, with NFZ removal of 83.14% (within 4 h) and current of ~9 mA in the BPES. Proteobacteria accounted for the largest proportion: 66.53% (inoculation), 71.89% (microbial electrolysis cell (MEC) anode), 74.67% (BPES anode) and 57.31% (BPES cathode), respectively. In addition, Geobacter was the most dominant genus in MEC and BPES anode and cathode, which occupied 31.64%, 67.73% and 41.34%, respectively. The microbial compositions of BPES anode and cathode were similar, but different from that of MEC anode. Notably, Rhodopseudomonas, a photosynthetic species, was detected in the BPES. Cognition of microbial community in the BPES is important for advancing its development.

Nitrofurazone degradation in the self-biased bio-photoelectrochemical system: g-C3N4/CdS photocathode characterization, degradation performance, mechanism and pathways.

In this study, a self-biased bio-photoelectrochemical system (SB-BPES) was constructed using a bioanode and the g-C3N4/CdS heterojunction photocathode for nitrofurazone (NFZ) degradation under solar irradiation. The physio-chemical properties and optical performance of photocatalysts were characterized, and photo-electrochemical properties of various photocathodes were analyzed. Results showed that g-C3N4/CdS exhibited the broadest visible light absorption range (to 594 nm) and the most efficient e--h+ separation; and its corresponding photocathode showed the highest photocurrent (9.8 µA), and the lowest charge transfer resistance (5.43 ☓ 103 Ω). In the solar-illuminated SB-BPES with g-C3N4/CdS photocathode, about 80% of NFZ removal rate was achieved within 10 h. More importantly, TOC removal of 62.6% was achieved in 24 h, which was 1.8 times of that from the open circuit SB-BPES, and 4.3 folds of that from microbial degradation; also, about 1.5 times of those from SB-BPES with g-C3N4 and CdS photocathodes. Besides, reproducible current generations (∼1.0 mA) were produced. These verified that it was a self-sustained system for spontaneously pollutants degradation and electricity generation. Moreover, possible degradation mechanism and pathways were proposed according to the identified intermediates. This study provides inspiration for synchronic improving refractory organics degradation and net energy recovery.

Bio-photoelectrochemcial system constructed with BiVO4/RGO photocathode for 2,4-dichlorophenol degradation: BiVO4/RGO optimization, degradation performance and mechanism.

A single-chamber bio-photoelectrochemical system (BPES) constructed with BiVO4/reduced graphene oxide (RGO) photocathode was proposed for 2,4-dichlorophenol (2,4-DCP) degradation under simulated solar irradiation. The BiVO4/RGO (B/G) composites were synthesized, optimized and characterized by various techniques to analyze their physico-chemical and photocatalytic properties. Results showed that B/G (5 wt% - 9 h - 150 °C) exhibited the best photocatalytic activity for 2,4-DCP degradation, which was 1.5 times of that of BiVO4, due to its better light absorption, faster electrons transfer, and more efficient photo-generated e- - h+ separation. Reactive species trapping experiments revealed that ·OH was the main radical leading to 2,4-DCP degradation, and h+ also influenced 2,4-DCP removal. The 2,4-DCP (20 mg/L) removal rate and current output from the illuminated BPES were much higher than those of the unilluminated reactor (68.5 % vs. 41.8 %, 60.31 A/m3 vs. 40.07 A/m3) in 24 h, and the cathode potential was more negative, indicating that photocathode catalytic process was favorable to pollutants degradation and energy generation. Intermediates of 2,4-DCP degradation in the BPES were identified, and accordingly, possible degradation pathway and mechanism were proposed. This research advanced the development of efficient photocathode and mechanism of recalcitrant wastewater treatment in the BPES.