Efficient utilization of photoelectron-hole at semiconductor-microbe interface for pyridine degradation with assistance of external electric field.

In this study, enhanced pyridine bio-photodegradation with assistance of electricity was achieved. Meanwhile, photoelectron-hole played a vital role in accelerating pyridine biomineralization. The significant separation of photoelectron-hole was achieved with an external electric field, which provided sufficient electron donors and acceptors for pyridine biodegradation. The enhanced electron transport system activity also revealed the full utilization of photoelectron-hole by microbes at semiconductor-microbe interface with assistance of electricity. Microbial community analysis confirmed the enrichment of functional species related to pyridine biodegradation and electron transfer. Microbial function analysis and microbial co-occurrence networks analysis indicated that upregulated functional genes and positive interactions of different species were the important reasons for enhanced pyridine bio-photodegradation with external electric field. A possible mechanism of enhanced pyridine biodegradation was proposed, i.e., more photoelectrons and holes of semiconductors were utilized by microbes to accelerate reduction and oxidation of pyridine with the assistance of electrical stimulation. The excellent performance of the photoelectrical biodegradation system showed a potential alternative for recalcitrant organic wastewater treatment.

Enhanced bio-photodegradation of p-chlorophenol by CdS/g-C3N4 3D semiconductor-microbe interfaces.

p-chlorophenol (p-CP), one of the highly toxic chlorinated organic compounds, is recalcitrant in conventional biodegradation process. This study reported a synergistic degradation protocol of 3D semiconductor-microbe interfaces, in which graphite felts (GF) and CdS/g-C3N4 nanocomposites were chosen as the carrier and semiconductor for enhanced p-CP degradation. Based on microstructure, photoelectrochemical and degradation performance analysis, the optimal CdS content in CdS/g-C3N4 nanocomposites was 10 wt%. The efficiencies of p-CP and TOC removal in bio-photodegradation system were as high as 95% and 77% without extra electron acceptors/donors, which were far better than those in traditional photodegradation and biodegradation system. High-throughput sequencing analysis suggested that p-CP degradation related species (Chryseobacterium, Stenotrophomonas and Rhodopseudomonas), electroactive species (Chryseobacterium, Stenotrophomonas, Hydrogenophaga and Cupriavidus) and hydrogen-utilizing species (Hydrogenophaga and Cupriavidus) were enriched at 3D semiconductor-microbe interfaces. The enrichment of functional species played a crucial role for p-CP removal and mineralization at 3D semiconductor-microbe interfaces. Moreover, the mechanism of enhanced p-CP bio-photodegradation at 3D semiconductor-microbe interfaces was investigated by utilizing Phylogenetic Investigation of Communities by Reconstruction of Unobserved States 2 (PICRUSt2). The results showed that the genes involved in p-CP biodegradation, hydrogen metabolism and extracellular electron transfer were remarkably enriched. Possible mechanism for enhancement of p-CP degradation in bio-photodegradation system was proposed, in which photocatalytic H2 and photoelectron transfer played an important role for enhancing p-CP mineralization by microbes. 3D semiconductor-microbe interfaces could maintain excellent performance for p-CP degradation after long-term operation, which provide a potential alternative for the enhanced treatment of wastewater containing p-CP.

BiVO4/FeOOH semiconductor-microbe interface for enhanced visible-light-driven biodegradation of pyridine.

Pyridine, a highly toxic nitrogen-containing heterocyclic compound, is recalcitrant in the conventional biodegradation process. In this study, BiVO4/FeOOH semiconductor-microbe interface was developed for enhanced visible-light-driven biodegradation of pyridine, where the efficiencies of pyridine removal (100%), total organic carbon (TOC) removal (88.06±3.76%) and NH4+-N formation (84.51±8.95%) were remarkably improved, compared to the biodegradation system and photodegradation system. The electron transport system activity and photoelectrochemical analysis implied the significant improvement of photogenerated carriers transfer between microbes and semiconductors. High-throughput sequencing analysis suggested functional species related to pyridine biodegradation (Shewanella, Bacillus and Lysinibacillus) and electron transfer (Shewanella and Tissierella) were enriched at the semiconductor-microbe interface. The light-excited holes played a crucial role in promoting pyridine mineralization. This study demonstrated that this bio-photodegradation system would be a potential alternative for the efficient treatment of wastewater containing recalcitrant pollutant such as pyridine.

Substantially enhanced anaerobic reduction of nitrobenzene by biochar stabilized sulfide-modified nanoscale zero-valent iron: Process and mechanisms.

Nanoscale zero-valent iron (nZVI), although being increasingly used in anaerobic systems for strengthening the removal of various refractory pollutants, is limited by various inherent drawbacks, such as easy precipitation, passivation, poor mass and electron transfer. To address the above issues, biochar stabilized sulfide-modified nZVI (S-nZVI@BC) was added into an up-flow anaerobic sludge blanket (UASB) to investigate the enhancement of anaerobic biodegradation of nitrobenzene (NB) and its impacts on microbial community structure. The results demonstrated that both NB reduction and aniline formation could be substantially facilitated in S-nZVI@BC coupled system compared to other anaerobic ones coupled with nZVI or S-nZVI. The dosage of S-nZVI@BC resulted in the formation of densely packed aggregates, evidently increased the extracellular polymeric substances content, promoted the volatile fatty acids transformation and stimulated the methane yield. Furthermore, species related to fermentation (Bacteroides and Longilinea), methanogenesis (Methanosarcina and Methanomethylovorans), electroactivity (Pelobacter, Thiobacillus and Phaselicystis) as well as reduction (Desulfovibrio) were considerably enriched in S-nZVI@BC coupled system. The activities of electron transport, total adenosine triphosphate, nitroreductase and NAD(P)H, which were closely related to microbial activity and NB transformation, were increased noticeably in S-nZVI@BC coupled anaerobic system. This study demonstrated the promising potential for long-term operation and full-scale application of S-nZVI@BC coupled system for the treatment of NB containing wastewater.

Controlled self-assembly of triphenylene-based molecular nanostructures.

Molecular nanostructures of the disc-shaped molecule hexapentyloxytriphenylene have been fabricated on length scales ranging from 30 nm to 1.5 mum following self-assembly arising from pi-pi interactions in organic solvents. The size and density of the molecular nanostructures deposited onto glass and indium tin oxide-coated glass substrates were characterized by atomic force microscopy. Dynamic light scattering and spectroscopic evidence of predeposition aggregation in solution are presented, suggesting that the nanostructures are organized in solution and then deposited onto the substrate. Correlations between the relative solvent polarity and the size of molecular nanostructures as well as between the solute concentration in dilute solutions and their density on the substrate are discussed.