Defective Black TiO2: Effects of Annealing Atmospheres and Urea Addition on the Properties and Photocatalytic Activities

A series of black TiO2 with and without the addition of urea were successfully prepared using a simple one-step synthetic method by calcination under different atmospheres (vacuum, He, or N2). The physicochemical, optical, and light-induced charge transfer properties of the as-prepared samples were characterized by various techniques. It was found that a vacuum atmosphere was more beneficial for the formation of oxygen vacancies (OVs) than the inert gases (He and N2) and the addition of urea-inhibited OVs formation. The samples annealed in the vacuum condition exhibited better visible-light adsorption abilities, narrower bandgaps, higher photo-induced charge separation efficiency, and lower recombination rates. Hydroxyl radicals (·OH) were the dominant oxidative species in the samples annealed under a vacuum. Finally, the samples annealed under vacuum conditions displayed higher photocatalytic activity for methylene blue (MB) degradation than the samples annealed under He or N2. Based on the above, this study provides new insights into the effects of annealing atmospheres and urea addition on the properties of black TiO2.

Effect of urea on gas and effluent losses, microbial populations, aerobic stability and chemical compositivo of corn (Zea mays L.) silage

We evaluated the effects of urea addition on gas and effluent losses, fermentation profile, microbial populations, aerobic stability and chemical composition of corn silages. A completely randomised design with five levels of urea (0, 0.5, 1.0, 1.5, and 2.0% based on dry matter) and five replicates was used. A decreasing linear effect of urea levels on effluent losses in corn silages was observed. In parallel, an increasing linear effect of urea levels on pH, increasing from 3.49 to 4.12 in silages without urea in relation to silages with the maximum urea level, was also observed. Urea addition improved the aerobic stability of the silages, with 62 h for the silages without urea and from 90 to >96 h for the silages with urea. Based on the results of the principal components, two groups (I and II) could be distinguished. The most discriminating variables in group I were dry matter (-0.9), pH (-1.2) and lactic acid bacteria (-0.9), while in group II, effluent losses (1.0), ethanol (1.0), acetic acid (0.8) and gas losses (0.8) were most important. The use of urea at inclusion levels of around 2% in corn silage reduced gas losses, improved the nutritive value and promote the aerobic stability of silages. Highlights: The addition of urea in the corn silages increased the pH values from 3.49 (control) to 4.12 (2% of urea DM). The use of urea improved chemical composition of corn silages. The addition of urea reduced the moulds and yeast populations in the corn silages after exposure to air. Urea addition improved the aerobic stability of the corn silages.

Biomethane Yield, Physicochemical Structures, and Microbial Community Characteristics of Corn Stover Pretreated by Urea Combined with Mild Temperature Hydrotherm

The corn stover (CS)’s compact structure makes it challenging for microorganisms to use in anaerobic digestion (AD). Therefore, improving CS biodegradability has become a key focus in AD studies. Methods are being targeted at the pretreatment of CS, combining advanced urea with mild temperature hydrotherm pretreatment to study its effect on promoting the AD process of CS. The biomethane yield, physicochemical structure, and microbial community characteristics were investigated. CS samples were assigned into groups differed by a range of pretreatment times (from 24 to 96 h) and set at a temperature of 50 °C with a 2% urea addition. Results revealed that the 72-h group obtained the highest biomethane yield of 205 mL/g VS−1, volatile solid (VS) and total solid (TS) removal rates of 69.3% and 47.7%, which were 36.7%, 25.3% and 27.5% higher than those of untreated one, respectively. After conducting several analyses, results confirmed the pretreatment as a method for altering CS microstructures benefits biomethane production. The most resounding differences between pretreated and untreated groups were observed within a microbial community, an integral factor for improved AD performance. This study serves to confirm that this specific pretreatment is an effective method for enhancing biomethane production in CS.

Increased N2O Production from Soil Organic Matter Following a Simulated Fall-Freeze-Thaw Cycle: Effects of Fall Urea Addition, Soil Moisture, and History of Manure Applications

Adding nitrogen substrates to soils can induce short-term changes in soil organic matter (SOM) transformations – a response termed the ‘priming effect’. However, it is unknown how priming effects on nitrous oxide (N2O) emissions can be altered following a strong freeze-thaw cycle. A mesocosm experiment evaluated two soil managements: with and without history of manure applications. These soils were subjected to three moisture regimes: Low, Medium and High. Apart from the controls, which received no N, we banded 15N-labelled urea into these soils representing a typical fall fertilization, and subsequently simulated a wide fall-freeze-thaw cycle, with temperatures from + 2, to -18, and finally + 23°C, respectively. The overall highest N2O production was observed 1 day after thawing. At that time, measurements of N2O site preference indicated that denitrification produced 83% of the N2O flux. Relative to the unamended controls (baseline), adding urea consistently triggered a 24% greater cumulative N2O production specifically originated from SOM following thawing (245 vs. 305 µg N2O-N kg− 1 soil, P = 0.022). This substantiates a positive priming of SOM that manifested shortly after the rapid, wet thawing of the soils. Soils having a manure history or higher moisture also exhibited an augmented production of N2O from SOM (Ps < 0.01). Although the overall priming of SOM was positive, two weeks after thawing, negative priming of daily N2O fluxes also occurred, but only in soils under High moisture. Besides urea additions, the propensity for primed N2O emissions from SOM after thawing was influenced by increasing moisture and earlier manure applications.

Microplastic fibers affect dynamics and intensity of CO2 and N2O fluxes from soil differently

Microplastics may affect soil ecosystem functioning in critical ways, with previously documented effects including changes in soil structure and water dynamics; this suggests that microbial populations and the processes they mediate could also be affected. Given the importance for global carbon and nitrogen cycle and greenhouse warming potential, we here experimentally examined potential effects of plastic microfiber additions on CO2 and N2O greenhouse gas fluxes. We carried out a fully factorial laboratory experiment with the factors presence of microplastic fibers (0.4% w/w) and addition of urea fertilizer (100 mg N kg− 1) using one target soil. The conditions in an intensively N-fertilized arable soil were simulated by adding biogas digestate at the beginning of the incubation to all samples. We continuously monitored CO2 and N2O emissions from soil before and after urea application using a custom-built flow-through steady-state system, and we assessed soil properties, including soil structure. Microplastics affected soil properties, notably increasing soil aggregate water-stability and pneumatic conductivity, and caused changes in the dynamics and overall level of emission of both gases, but in opposite directions: overall fluxes of CO2 were increased by microplastic presence, whereas N2O emission were decreased, a pattern that was intensified following urea addition. This divergent response is explained by effects of microplastic on soil structure, with the increased air permeability likely improving O2 supply: this will have stimulated CO2 production, since mineralization benefits from better aeration. Increased O2 would at the same time have inhibited denitrification, a process contributing to N2O emissions, thus likely explaining the decrease in the latter. Our results clearly suggest that microplastic consequences for greenhouse gas emissions should become an integral part of future impact assessments, and that to understand such responses, soil structure should be assessed.

Microplastic fibers affect dynamics and intensity of CO2 and N2O fluxes from soil differently

Microplastics may affect soil ecosystem functioning in critical ways, with previously documented effects including changes in soil structure and water dynamics; this suggests that microbial populations and the processes they mediate could also be affected. Given the importance for global carbon and nitrogen cycle and greenhouse warming potential, we here experimentally examined potential effects of plastic microfiber additions on CO2 and N2O greenhouse gas fluxes. We carried out a fully factorial laboratory experiment with the factors presence of microplastic fibers (0.4% w/w) and addition of urea fertilizer (100 mg N kg−1). The conditions in an intensively N-fertilized arable soil were simulated by adding biogas digestate at the beginning of the incubation to all samples. We continuously monitored CO2 and N2O emissions from soil before and after urea application using a custom-built flow-through steady-state system, and we assessed soil properties, including soil structure. Microplastics affected soil properties, notably increasing soil aggregate water-stability and pneumatic conductivity, and caused changes in the dynamics and overall level of emission of both gases, but in opposite directions: overall fluxes of CO2 were increased by microplastic presence, whereas N2O emission were decreased, a pattern that was intensified following urea addition. This divergent response is explained by effects of microplastic on soil structure, with the increased air permeability likely improving O2 supply: this will have stimulated CO2 production, since mineralization benefits from better aeration. Increased O2 would at the same time have inhibited denitrification, a process contributing to N2O emissions, thus likely explaining the decrease in the latter. Our results clearly suggest that microplastic consequences for greenhouse gas emissions should become an integral part of future impact assessments, and that to understand such responses, soil structure should be assessed.