Br-Vacancies Induced Variable Ranging Hopping Conduction in High-Order Topological Insulator Bi4Br4.

The defects have a remarkable influence on the electronic structures and the electric transport behaviors of the matter, providing the additional means to engineering their physical properties. In this work, a comprehensive study on the effect of Br-vacancies on the electronic structures and transport behaviors in the high-order topological insulator Bi4Br4 is performed by the combined techniques of the scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES), and physical properties measurement system along with the first-principle calculations. The STM results show the defects on the cleaved surface of a single crystal and reveal that the defects are correlated to the Br-vacancies with the support of the simulated STM images. The role of the Br-vacancies in the modulation of the band structures has been identified by ARPES spectra and the calculated energy-momentum dispersion. The relationship between the Br-vacancies and the semiconducting-like transport behaviors at low temperature has been established, implying a Mott variable ranging hopping conduction in Bi4Br4. The work not only resolves the unclear transport behaviors in this matter, but also paves a way to modulate the electric conduction path by the defects engineering.

Metagenomic analysis towards understanding the effects of ammonia on chain elongation process for medium chain fatty acids production.

The production of medium chain fatty acids (MCFAs) through chain elongation (CE) from organic wastes/wastewater has attracted much attention, while the effects of a common inhibitor-ammonia has not been elucidated. The mechanism of ammonia affecting CE was studied by metagenomic. The lag phase duration of caproate production was increased, and the maximum caproate production rate was decreased by 43.4 % at 4 g-N/L, as compared to 0 g-N/L. And hydrochar (HC) alleviated the inhibition of ammonia at 4 g-N/L. Metagenomic analysis indicated that ammonia induced UBA4085 sp.FDU78 as the dominant microorganism, and metabolic reconstruction revealed its potential CE ability. Furthermore, ammonia inhibited the reverse ß oxidation pathway and Acetyl-CoA production pathway. The tolerance of UBA4085 sp.FDU78 to ammonia was associated with the uptake of inorganic ions, energy conservation, and synthesis of osmoprotectants. The present study provided a deep-insight on the ammonia tolerance mechanism on the CE process.

Syntrophic microbes involved in the oxidation of short-chain fatty acids in continuous-flow anaerobic digesters treating waste activated sludge with hydrochar.

The rapid degradation of short-chain fatty acids (SCFAs) is an essential issue of anaerobic digestion (AD), in which SCFA oxidizers could generally metabolize in syntrophy with methanogens. The dynamic responses of active metagenome-assembled genomes to low concentrations of propionate and acetate were analyzed to identify specific syntrophic SCFA oxidizers and their metabolic characteristics in continuous-flow AD systems treating waste activated sludge with and without hydrochar. In this study, hydrochar increased methane production by 19%, possibly due to hydrochar enhancing acidification and methanogenesis processes. A putative syntrophic propionate oxidizer and two acetate oxidizers contributed substantially to the syntrophic degradation of SCFAs, and hydrochar positively regulated their functional gene expressions. A significant relationship was established between the replication rate of SCFA oxidizers and their stimulation-related transcriptional activity. Acetate was degraded in the hydrochar group, which might be mainly through the syntrophic acetate oxidizer from the genus Desulfallas and methanogens from the genus Methanosarcina.IMPORTANCEShort-chain fatty acid (SCFA) degradation is an important process in the methanogenic ecosystem. However, current knowledge of this microbial mechanism is mainly based on studies on a few model organisms incubated as mono- or co-cultures or in enrichments, which cannot provide appropriate evidence in complex environments. Here, this study revealed the microbial mechanism of a hydrochar-mediated anaerobic digestion (AD) system promoting SCFA degradation at the species level and identified key SCFA oxidizing bacteria. Our analysis provided new insights into the SCFA oxidizers involved in the AD of waste activated sludge facilitated by hydrochar.

Controllable Modulation of the Electronic Properties of a Two-Dimensional Ambipolar Semiconductor by Interface Ferroelectric Polarization.

Precise control of charge carrier type and density of two-dimensional (2D) ambipolar semiconductors is the prerequisite for their applications in next-generation integrated circuits and electronic devices. Here, by fabricating a heterointerface between a 2D ambipolar semiconductor (hydrogenated germanene, GeH) and a ferroelectric substrate (PbMg1/3Nb2/3O3-PbTiO3, PMN-PT), fine-tuning of charge carrier type and density of GeH is achieved. Due to ambipolar properties, proper band gap, and high carrier mobility of GeH, by applying the opposite local bias (±8 V), a lateral polarization in GeH is constructed with a change of work function by 0.6 eV. Besides, the built-in polarization in GeH nanoflake could promote the separation of photoexcited electron-hole pairs, which lead to 4 times enhancement of the photoconductivity after poling by 200 V. In addition, a gradient regulation of the work function of GeH from 4.94 to 5.21 eV by adjusting the local substrate polarization is demonstrated, which could be used for data storage at the micrometer size by forming p-n homojunctions. This work of constructing such heterointerfaces provides a pathway for applying 2D ambipolar semiconductors in nonvolatile memory devices, photoelectronic devices, and next-generation integrated circuit.

Recovery capability of anaerobic digestion from ammonia stress: Metabolic activity, energy generation, and genome-centric metagenomics.

Excessive ammonia stresses anaerobic digestion (AD) significantly. Although there has been progress in understanding AD under ammonia exposure, investigations on AD liberated from ammonia exposure are limited. Here, the recovery capability of AD from ammonia stress was evaluated, by examining specific methanogenic activity, energy-conserving capability, microbial community succession, and metabolic pathway reconstruction. The findings demonstrated that ammonia stress relief resulted in < 50% methane recovery, with propionate conversion identified as the critical impediment to AD reactivation. Energy generation could not recovered either. Efforts to mitigate ammonia stress failed to restore acetoclastic methanogens, e.g., Methanothrix soehngenii, and proved futile in awakening propionate oxidizers, e.g., Desulfobulbus. Interestingly, a symbiotic metabolism emerged, prevailing in stress-relieved AD due to its energy-conserving advantage. This study underscores the importance of targeted interventions, including stimulating acetoclastic methanogenesis, propionate oxidation, and energy generation, as priorities for AD recovery following ammonia stress, rather than focusing solely on ammonia level management.

Recent Progresses of Polarons: Fundamentals and Roles in Photocatalysis and Photoelectrocatalysis.

Photocatalysis and photoelectrocatalysis are promising ways in the utilization of solar energy. To address the low efficiency of photocatalysts and photoelectrodes, in-depth understanding of their catalytic mechanism is in urgent need. Recently, polaron is considered as an influential factor in catalysis, which brings researchers a new approach to modify photocatalysts and photoelectrodes. In this review, brief introduction of polaron is given first, followed by which models and recent experimentally observations of polarons are reviewed. Studies about roles of polarons in photocatalysis and photoelectrocatalysis are listed in order to provide some inspiration in exploring the mechanism and improving the efficiency of photocatalysis and photoelectrocatalysis.

Towards layer-selective quantum spin hall channels in weak topological insulator Bi4Br2I2.

Weak topological insulators, constructed by stacking quantum spin Hall insulators with weak interlayer coupling, offer promising quantum electronic applications through topologically non-trivial edge channels. However, the currently available weak topological insulators are stacks of the same quantum spin Hall layer with translational symmetry in the out-of-plane direction-leading to the absence of the channel degree of freedom for edge states. Here, we study a candidate weak topological insulator, Bi4Br2I2, which is alternately stacked by three different quantum spin Hall insulators, each with tunable topologically non-trivial edge states. Our angle-resolved photoemission spectroscopy and first-principles calculations show that an energy gap opens at the crossing points of different Dirac cones correlated with different layers due to the interlayer interaction. This is essential to achieve the tunability of topological edge states as controlled by varying the chemical potential. Our work offers a perspective for the construction of tunable quantized conductance devices for future spintronic applications.

Rapid self-heating synthesis of Fe-based nanomaterial catalyst for advanced oxidation.

Iron-based catalysts are promising candidates for advanced oxidation process-based wastewater remediation. However, the preparation of these materials often involves complex and energy intensive syntheses. Further, due to the inherent limitations of the preparation conditions, it is challenging to realise the full potential of the catalyst. Herein, we develop an iron-based nanomaterial catalyst via soft carbon assisted flash joule heating (FJH). FJH involves rapid temperature increase, electric shock, and cooling, the process simultaneously transforms a low-grade iron mineral (FeS) and soft carbon into an electron rich nano Fe0/FeS heterostructure embedded in thin-bedded graphene. The process is energy efficient and consumes 34 times less energy than conventional pyrolysis. Density functional theory calculations indicate that the electron delocalization of the FJH-derived heterostructure improves its binding ability with peroxydisulfate via bidentate binuclear model, thereby enhancing ·OH yield for organics mineralization. The Fe-based nanomaterial catalyst exhibits strong catalytic performance over a wide pH range. Similar catalysts can be prepared using other commonly available iron precursors. Finally, we also present a strategy for continuous and automated production of the iron-based nanomaterial catalysts.

Topological Flat Bands in 2D Breathing-Kagome Lattice Nb3 TeCl7.

Flat bands (FBs) can appear in two-dimensional (2D) geometrically frustrated systems caused by quantum destructive interference (QDI). However, the scarcity of pure 2D frustrated crystal structures in natural materials makes FBs hard to be identified, let alone modulate FBs relating to electronic properties. Here, the experimental evidence of the complete electronic QDI induced FB contributed by the 2D breathing-kagome layers of Nb atoms in Nb3 TeCl7 (NTC) is reported. An identical chemical state and 2D localization characteristics of the Nb breathing-kagome layers are experimentally confirmed, based on which NTC is demonstrated to be a superior concrete candidate for the breathing-kagome tight-binding model. Furthermore, it theoretically establishes the tunable roles of the on-site energy over Nb sites on bandwidth, energy position, and topology of FBs in NTC. This work opens an aveanue to manipulate FB characteristics in these 4d transition-metal-based breathing-kagome materials.

Biochar promoted microbial iron reduction in competition with methanogenesis in anaerobic digestion.

Microbial Fe (III) reduction generally could outcompete methanogenesis due to its thermodynamic advantage, while the low bioavailability of Fe (III) compounds limits this process in the anaerobic digestion system, which could result in the low recovery of vivianite. Therefore, this study investigated the competition between Fe (III) reduction and methanogenesis in the presence of different biochar (pyrochar and hydrochar). The results showed that pyrochar obtained at 500 °C (P5) resulted in the highest Fe (III) reduction (80.3%) compared to the control experiment (29.1%). P5 also decreased methane production by 9.4%. Both conductivity and surface oxygen-containing functional groups contributed to the promotion of direct electron transfer for Fe (III) reduction. Genomic-centric metatranscriptomics analysis showed that P5 led to the highest enrichment of Geobacter soli A19 and induced the significant expression of out membrane cytochrome c and pilA in Geobacter soli A19, which was related to higher Fe (III) reduction.

Microbial insights towards understanding the role of hydrochar in enhancing phenol degradation in anaerobic digestion.

Anaerobic digestion (AD) of wastewater is the most promising bioprocess for organic conversion, however, phenol is toxic and resistant to anaerobic degradation. The current study compared the effect of hydrochar and granular activated carbon (GAC) on AD of phenol at four concentrations (100 mg/L, 250 mg/L, 500 mg/L and 1000 mg/L). Results demonstrated that hydrochar significantly improved the methane production rate and reduced the lag phase at all concentrations of phenol. The methane production rate was improved by about 50% at both 100 mg/L and 250 mg/L phenol, while it was raised by >160% at 500 mg/L and 1000 mg/L phenol by hydrochar. The GAC only increased the methane production rate at 500 mg/L and 1000 mg/L due to high adsorption capacity. Further, the adsorption of phenol by hydrochar had no apparent impact on the methane production rate, even though certain amounts of phenol were adsorbed. At 500 mg/L, the amount of methane produced significantly increased, so 16S rRNA transcripts sequencing and metabolomic analysis were conducted. 16S rRNA transcripts sequencing analysis indicated that hydrochar resulted in the enrichment of syntrophic bacteria (e.g., Syntrophorhabdus & Syntrophobacter) and Methanosaeta, which might be related with direct interspecies electron transfer. Further, it was noticed that the growth of Methanobacterium was repressed at 500 mg/L phenol, while hydrochar promoted its growth. Phenol was degraded into L-tyrosine and then followed the benzoate degradation pathway for methane production as revealed by metabolomic analysis. In addition, metabolomic analysis also revealed that hydrochar promoted the degradation of all metabolites and enhanced the phenol degradation into methane.

Novel Long-Chain Fatty Acid (LCFA)-Degrading Bacteria and Pathways in Anaerobic Digestion Promoted by Hydrochar as Revealed by Genome-Centric Metatranscriptomics Analysis.

A large amount of long-chain fatty acids (LCFA) are generated after lipids hydrolysis in anaerobic digestion (AD), and LCFA are difficult to be biodegraded. This study showed that hydrochar (HC), which was produced during the hydrothermal liquefaction of organic wastes, significantly increased the methane production rate (by 56.9%) of oleate, a typical refractory model LCFA. Genomic-centric metatranscriptomics analysis revealed that three novel microbes (Bin138 Spirochaetota sp., Bin35 Smithellaceae sp., and Bin54 Desulfomonilia sp.) that were capable of degrading LCFA were enriched by HC, which played an important role in the degradation of oleate. LCFA was degraded to acetate through the well-known LCFA ß-oxidation pathway and the combined ß-oxidation and butyrate oxidation pathway. In addition, it was found that HC promoted the direct interspecies electron transfer (DIET) between Methanothrix sp. and Bin54 Desulfomonilia sp. The enriched new types of LCFA-degrading bacteria and the promotion of DIET contributed to the improved methane production rate of oleate by HC. IMPORTANCE Long-chain fatty acids (LCFA) are difficult to be degraded in anaerobic digestion (AD), and the known LCFA degrading bacteria are only limited to the families Syntrophomonadaceae and Syntrophaceae. Here, we found that hydrochar effectively promoted AD of LCFA, and the new LCFA-degrading bacteria and a new metabolic pathway were also revealed based on genomic-centric metatranscriptomic analysis. This study provided a new method for enhancing the AD of organic wastes with high content of LCFA and increased the understanding of the microbes and their metabolic pathways involved in AD of LCFA.

Microbial shifts in anaerobic digestion towards phenol inhibition with and without hydrochar as revealed by metagenomic binning.

The inhibition of anaerobic digestion (AD) by phenolic compounds is an obstacle to the efficient treatment of organic wastes. Besides, hydrochar produced from hydrothermal liquefaction of biomass has been previously reported to enhance AD. The present study aimed to provide deep insights into the microbial shifts at the species level to phenol (0-1.5 g/L) inhibition in AD of glucose with and without hydrochar by metagenomic analysis. Phenol higher than 1 g/L had severe inhibition on both the amount and rate of methane production in control experiments, while hydrochar significantly enhanced methane production, especially at phenol 1 g/L and 1.5 g/L. From metagenomic analysis, 78 High-quality metagenome-assembled genomes (MAGs) were obtained. Principal components analysis showed that the microbial communities were shifted when phenol concentration was increased to 0.25 g/L in control experiments and 1 g/L in hydrochar experiments. In control experiments, no MAGs involved in acetogenesis were found at phenol 1.5 g/L and Methanothrix sp.FDU243 was also inhibited. However, hydrochar resulted in the maintenance of several MAGs involved in acetogenesis and Methanothrix sp.FDU243 even at phenol 1.5 g/L, ensuring a persistent methane production. Furthermore, 6 phenol-degrading MAGs were identified, shifting dependent on the concentrations of phenol and the presence of hydrochar.

Linking Genome-Centric Metagenomics to Kinetic Analysis Reveals the Regulation Mechanism of Hydroxylamine in Nitrite Accumulation of Biological Denitrification.

Given hydroxylamine accumulation in various nitrification systems and its potential mechanism in regulating the subsequent denitrification process were unraveled in this study. Hydroxylamine (>0.5 mgN/L) immediately induced nitrite accumulation of activated sludge by inhibiting the activities of nitrite reductases and their electron transport modules (Complex III and cytochrome c). Moreover, long-term exposure to 0.5-2.5 mgN/L hydroxylamine accelerated the functional transformation from denitrification to denitratation under low C/N conditions. However, genome-centric metagenomics indicated that a genotypic complete rather than truncated denitrifier Thauera aminoaromatica TJ127 was enriched and mainly responsible for acetate storage and nitrate reduction of the denitratation community. Interestingly, its enrichment resulted in nitrite production and reduction sequentially but reduced nitrate only to nitrite under carbon-limited conditions (C/N ≤ 3.0). Thus, it showed higher tolerance to hydroxylamine than the concurrent phenotype denitrifiers in activated sludge. Moreover, due to its higher anoxic storage capability in the feast phase, this enrichment became highly specialized by decreasing the feast/famine ratio, and thus a satisfactory denitratation performance was still maintained without hydroxylamine. These results suggested that the transient release of hydroxylamine from nitrification may interfere with subsequent denitrification metabolism, but its continuous accumulation is beneficial for achieving denitratation, which could steadily provide nitrite for mainstream anammox.

Current challenges of hydrothermal treated wastewater (HTWW) for environmental applications and their perspectives: A review.

Hydrothermal treatment (HT) is an emerged thermochemical approach for the utilization of biomass. In the last decade, intense research has been conducted on bio-oil and hydrochar, during which extensive amount of hydrothermal treated wastewater (HTWW) is produced, containing large amount of organic compounds along with several toxic chemicals. The composition of HTWW is highly dependent on the process conditions and organic composition of biomass, which determines its further utilization. The current study provides a comprehensive overview of recent advancements in HTWW utilization and its properties which can be changed by varying different parameters like temperature, residence time, solid concentration, mass ratio and catalyst including types of biomasses. HTWW characterization, parameters, reaction mechanism and its application were also summarized. By considering the challenges of HTWW, some suggestions and proposed methodology to overcome the bottleneck are provided.

Combined microbial transcript and metabolic analysis reveals the different roles of hydrochar and biochar in promoting anaerobic digestion of waste activated sludge.

Hydrothermal pretreatment of waste activated sludge (WAS) could eliminate the rate limiting step of anaerobic digestion (AD) -hydrolysis. However, the high organic loading rate may cause acid accumulation, thus leading to an unstable system. This study compared the effect of different hydrochar (HC2-260°C and HC3-320°C) and biochar (BC5-500°C and BC7-700°C) on AD of hydrothermal pretreated WAS (HPS). Results demonstrated that hydrochar was superior to biochar in the methane yield and production rate, especially HC2. HC2 had the highest surface oxygen-containing functional groups that could facilitate direct interspecies electron transfer (DIET). The enhanced methane yield was related with the increased protein utilization, and hydrochar and biochar enriched different microbes related to protein degradation. Metabolomic analysis showed the significantly changed metabolites induced by hydrochar and biochar were involved in fatty acids and amino acids-related metabolism, indicating the rapid conversion of intermediated products, which was consistent with the microbial community structure results. Hydrochar and biochar also induced upregulation of metabolites related to microbial metabolic activity and extracellular electron transfer. Although biochar induced the same metabolic changes, the alterations of these metabolites were weaker than those of hydrochar. The results of this study offered new insights into the molecular mechanisms of enhanced AD of HPS by hydrochar and biochar.

Phenol promoted caproate production via two-stage batch anaerobic fermentation of organic substance with ethanol as electron donor for chain elongation.

The conversion of organic wastes/wastewater into medium chain fatty acids (MCFAs) such as caproate has attracted much attention, while the effects of toxic compounds on the process have rarely been studied. The present study investigated the effects of phenol (0-1.5 g/L), which is a toxicant and present in various organic wastes, on the caproate production in the chain elongation (CE) process with ethanol as electron donor via two-stage batch anaerobic fermentation of glucose. The results showed phenol ≤ 1 g/L did not affect short chain fatty acids (SCFAs) production, while 1 g/L phenol increased caproate production by 59.9% in the following CE process. The higher selectivity of caproate and higher consumption of ethanol contributed to the higher caproate production at 1 g/L phenol. It was also shown 1 g/L phenol had more positive effect on CE of butyrate than acetate. 1.5 g/L phenol inhibited both SCFAs production and CE processes. 16S rRNA genes analysis showed phenol had slight effect on the microbial communities for SCFAs production, while it obviously changed the dominant microbes in CE process. For CE process, metagenomic analysis was further conducted and phenol mainly affected fatty acid biosynthesis (FAB) pathway, but not reverse ß-oxidization (RBO) pathway. 1 g/L phenol increased the abundances of genes in FAB pathway, which could be related with the higher caproate production. Genome reconstruction identified the dominant microbial species in CE process, which were changed with different concentrations of phenol. Most of the dominant species were new microbial species potentially involved in CE. The syntrophic cooperation between Petrimonas mucosa FDU058 and Methanofollis sp. FDU007 might play important role in increased caproate production at 1 g/L phenol, and their adaption to phenol could be due to the presence of genes relating with active efflux system and refolding of proteins.

Genome-Centric Metatranscriptomics Analysis Reveals the Role of Hydrochar in Anaerobic Digestion of Waste Activated Sludge.

Anaerobic digestion (AD) of waste activated sludge (WAS) has been widely used, while it poses problems including low methane yield and production rate. Hydrochar is produced by hydrothermal liquefaction of biomass; however, little is known about the role of hydrochar in promoting AD of WAS. The present study showed that hydrochar increased the methane production rate by 30.8% and yield by 31.4% of hydrothermal pretreated dewatered WAS. Hydrochar increased the methane production rate and yield by enhancing the acidification and methanogenesis processes. Genomic-centric metatranscriptomics were used to identify the metabolic activities and transcriptomic response of individual metagenome-assembled genomes that were enriched by hydrochar. Although Methanosarcina sp. FDU0106 had been shown unable to used H2, it had the complete pathway for the reduction of CO2 to methane. Syntrophomonas sp. FDU0164 expressed genes for extracellular electron transfer via electrically pili, suggesting that Syntrophomonas sp. FDU0164 and Methanosarcina sp. FDU0106 were exchanging electrons via direct interspecies electron transfer. The expression of pili was decreased, indicating that hydrochar could replace its roles. Additionally, Firmicutes sp. FDU0048, Proteiniphilum sp. FDU0082, and Aminobacterium mobile FDU0089 were related to the degradation of organics, which could be related to the enhanced methane yield.

Metagenomic analysis reveals the fate of antibiotic resistance genes in two-stage and one-stage anaerobic digestion of waste activated sludge.

Waste activated sludge (WAS) from wastewater treatment plants is an important reservoir of antibiotic resistance genes (ARGs). The fate of ARGs in this process was not revealed previously. The present study applied metagenomic approach to examine the occurrence and fate of ARGs in thermophilic alkaline fermentation followed by mesophilic anaerobic digestion (TM), by comparison with mesophilic alkaline fermentation followed by mesophilic anaerobic digestion (MM) and one-stage mesophilic anaerobic digestion (M) process. The removal efficiency of two-stage anaerobic digestion (AD) to total ARGs is higher than that of one-stage AD. The hydrogen and methane production stages of two-stage AD processes have dissimilar impact on the fate of ARGs. Macrolide, lincosamide, and streptogramin (MLS) resistance genes were enriched, especially in the hydrogen production reactors of TM and MM processes. Statistical analysis of metagenomic profiles analysis suggested that bacA may be the differential ARG subtype of two-stage AD process. ARG-like sequences encoding antibiotic efflux pump, antibiotic inactivation and antibiotic target alteration mechanisms were identified as the dominant ARGs resistance mechanisms in all samples. Procrustes analysis showed that microbial community composition structured the resistome. Co-occurrence patterns between ARGs and microbial phylogeny revealed that 26 bacterial species might be potential hosts of 94 ARG subtypes.