Metal-organic framework-derived trimetallic oxides with dual sensing functions for ethanol.

Metal-organic framework (MOF)-derived metal oxide semiconductors have recently received extensive attention in gas sensing applications due to their high porosity and three-dimensional architecture. Still, challenges remain for MOF-derived materials, including low-cost and facile synthetic methods, rational nanostructure design, and superior gas-sensing performances. Herein, a series of Fe-MIL-88B-derived trimetallic FeCoNi oxides (FCN-MOS) with a mesoporous structure were synthesized by a one-step hydrothermal reaction followed by calcination. The FCN-MOS system consists of three main phases: α-Fe2O3 (n-type), CoFe2O4, and NiFe2O4 (p-type), and the nanostructure and pore size can be controlled by altering the content of α-Fe2O3, CoFe2O4, and NiFe2O4. The sensors based on FCN-MOS exhibit a high response of 71.9, a good selectivity towards 100 ppm ethanol at 250 °C, and long-term stability up to 60 days. Additionally, the FCN-MOS-based sensors show a p-n transition gas sensing behavior with the alteration of the Fe/Co/Ni ratio.

Additional ratios of hydrolysates from lignocellulosic digestate at different hydrothermal temperatures influencing anaerobic digestion performance.

Hydrothermal treatment (HT) is envisaged as a promising technology to treat the lignocellulosic biomass. HT temperature is an important parameter influencing the hydrolysate compositions such as organic compounds and potential inhibitors, and therefore affect the subsequential anaerobic digestion (AD) process. Herein, HT-AD was employed to treat the wheat straw-derived digestate. The HT temperature of 190 °C was proved to be the best performance with a higehst reducing sugar yield (45.05 mg g-1) in the hydrolysate and a highest methane yield (120.8 mL gTS-1) from the AD of the hydrolysate, which was 42.5% higher than the methane yield in the control without the hydrolysate addition (84.8 mL gTS-1). 3-Furaldehyde was the dominant organic in the hydrolysates. The HT temperature of 210 °C led to the presence of AD inhibitory moieties (e.g., phenols and furans) in the hydrolysate, resulting in a low methane yield. Although the treatments with the addition of 100% hydrolysate outperformed those of 50% hydrolysate in the methane yields in the late stage, the latter had higher methane yields in the first stage, suggesting that the additional ratios of hydrolysates should be carefully considered in AD, especially the detrimental effects of inhibitors and adaptability issues of AD consortia. The MiSeq sequencing showed that the hydrolysis/acidogenesis was dominant in the first stage, while methanogenesis became dominant in the late stage with the acetoclastic/hydrogenotrophic methanogens (Methanosarcina and Methanobacterium) enriched in the hydrolysate-feeding reactors. These findings demonstrated that a integration of HT-AD was a promising approach for the digestate valorization and to reduce the potential carbon emission from waste treatments.

Effects of different pretreatment methods on biogas production and microbial community in anaerobic digestion of wheat straw.

The pretreatment of wheat straw has been recognized to be an essential step prior to anaerobic digestion, owing to the high abundance of lignocellulosic materials. In order to choose economical and effective techniques for the disposal of wheat straw, effects of five pretreatment methods including acid, alkali, co-pretreatment of acid and alkali, CaO2, and liquid digestate of municipal sewage sludge on anaerobic digestion of wheat straw were investigated by analyzing biogas production and organic matter degradation in the study. The results showed that among these pretreatment methods, the methane yield was highest in the liquid digestate pretreated-wheat straw with 112.6 mL gTS-1, followed by the acid, alkali, and CaO2 pretreatments, and the lowest was observed in the co-pretreatment of acid and alkali. Illumina MiSeq sequencing of the microbial communities in the anaerobic digesters revealed that the genera Ruminiclostridium including Ruminiclostridium and Ruminiclostridium 1, Hydrogenispora, and Capriciproducens were the main hydrolytic bacteria, acidogenic bacteria, and acetogenic bacteria, respectively, in the anaerobic digesters. Capriciproducens and Hydrogenispora dominated in the first and the later stages, respectively, in the anaerobic digesters, which could work as indicators of the anaerobic co-digestion stage of sludge and wheat straw. The total solid and SO42--S contents of the solid digestate and the NH4+-N concentration of the liquid digestate had a significant influence on the microbial community in the digesters. These findings indicated that liquid digestate pretreatment was a potential option to improve the anaerobic digestion of wheat straw, due to the low cost without additional chemical agents.

Effects of oxygen tension on the microbial community and functional gene expression of aerobic methane oxidation coupled to denitrification systems.

Aerobic CH4 oxidation coupled to denitrification (AME-D) can not only mitigate the emission of greenhouse gas (e.g., CH4) to the atmosphere, but also reduce NO3- and/or NO2- and alleviate nitrogen pollution. The effects of O2 tension on the community and functional gene expression of methanotrophs and denitrifiers were investigated in this study. Although higher CH4 oxidation occurred in the AME-D system with an initial O2 concentration of 21% (i.e., the O2-sufficient condition), more NO3--N was removed at the initial O2 concentration of 10% (i.e., the O2-limited environment). Type I methanotrophs, including Methylocaldum, Methylobacter, Methylococcus, Methylomonas, and Methylomicrobium, and type II methanotrophs, including Methylocystis and Methylosinus, dominated in the AME-D systems. Compared with type II methanotrophs, type I methanotrophs were more abundant in the AME-D systems. Proteobacteria and Actinobacteria were the main denitrifiers in the AME-D systems, and their compositions varied with the O2 tension. Quantitative PCR of the pmoA, nirS, and 16S rRNA genes showed that methanotrophs and denitrifiers were the main microorganisms in the AME-D systems, accounting for 46.4% and 24.1% in the O2-limited environment, respectively. However, the relative transcripts of the functional genes including pmoA, mmoX, nirK, nirS, and norZ were all less than 1%, especially the functional genes involved in denitrification under the O2-sufficient condition, likely due to the majority of the denitrifiers being dormant or even nonviable. These findings indicated that an optimal O2 concentration should be used to optimize the activity and functional gene expression of aerobic methanotrophs and denitrifiers in AME-D systems.