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Hydrothermal carbonization (HTC) converts wet biomass into hydrochar and a process liquid, but aromatic compounds in the products have been reported as a roadblock for soil applications as they can inhibit germination, plant growth, and soil microbial activity. Here, we compared HTC and hydrothermal humification (HTH) of cow manure digestate while varying the initial alkaline content by adding KOH. HTH converted 37.5 wt% of the feedstock to artificial humic acids (A-HAs) found in both solid and liquid, twice that of HTC. HTH reduced phenolic and furanic aromatic compounds by over 70% in solids and 90% in liquids. The A-HAs in HTH resemble natural humic acids (N-HA), based on FTIR, UV–vis spectra, and CHN and XRD analysis. The HTH liquid possesses 60% higher total organic carbon (TOC) than HTC. Although one-third of TOC can be precipitated as A-HA, a high TOC concentration remains in the liquid, which is shown to be mainly organic acids. Therefore, we also evaluated the HTC and HTH liquids for anaerobic biomethane production, and found that compared to the original cow manure digestate, the HTH liquids increased methane yield by 110.3 to 158.6%, a significant enhancement relative to the 17.2% increase seen with HTC liquid. The strong reduction in organic acids during biogas production from HTH liquid indicates the potential for converting soluble byproducts into methane, while maintaining high A-HAs levels in the solid product. Highlights: Hydrothermal humification of the digestate feedstock created about 37.5 wt% artificial humic acids in both solid and liquid phases. Increasing the alkaline content of the reaction media significantly decreased the aromatic content in the process liquid while increasing the concentration of organic acids and sugars. There was little to no gas production observed in the HTH process at higher alkaline contents, indicating carbon preservation in the liquid and solid phases. Anaerobic processing of the hydrothermal humification (HTH) process liquid resulted in a 158.6% increase in methane production compared to the primary biomass. The organic acid concentrations decreased after the anaerobic fermentation, while the main HTH product, artificial humic acids, remained nearly unchanged. [ABSTRACT FROM AUTHOR]

The potassium salt of polyheptazine imide (K–PHI) is a promising photocatalyst for various chemical reactions. From powder X–ray diffraction data an idealized structural model of K–PHI has been derived. Using atomic coordinates of this model we defined an energetically optimized K–PHI structure, in which the K ions are present in the pore and between the PHI–planes. The distance between the anion framework and K+ resembles a frustrated Lewis pair-like structure, which we denote as frustrated Coulomb pair that results in an interesting adsorption environment for otherwise non-adsorbing, non-polar gas molecules. We demonstrate that even helium (He) gas molecules, which are known to have the lowest boiling point and the lowest intermolecular interactions, can be adsorbed in this polarized environment with an adsorption energy of − 4.6 kJ mol−1 per He atom. The interaction between He atoms and K–PHI is partially originating from charge transfer, as disclosed by our energy decomposition analysis based on absolutely localized molecular orbitals. Due to very small charge transfer interactions, He gas adsorption saturates at 8 at%, which however can be subject to further improvement by cation variation. [ABSTRACT FROM AUTHOR]

High-performance thermally insulating materials from renewable resources are needed to improve the energy efficiency of buildings. Traditional fossil-fuel-derived insulation materials such as expanded polystyrene and polyurethane have thermal conductivities that are too high for retrofitting or for building new, surface-efficient passive houses. Tailored materials such as aerogels and vacuum insulating panels are fragile and susceptible to perforation. Here, we show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fire-retardant and strong anisotropic foams that perform better than traditional polymer-based insulating materials. The foams are ultralight, show excellent combustion resistance and exhibit a thermal conductivity of 15 mW m−1 K−1, which is about half that of expanded polystyrene. At 30 °C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale engineering is a promising strategy for producing foams with excellent properties using cellulose and other renewable nanosized fibrous materials. [ABSTRACT FROM AUTHOR]

Soil amendment with hydrochar produced by hydrothermal carbonization of biomass is suggested as a simple, cheap, and effective method for increasing soil C. We traced C derived from corn silage hydrochar (δC of −13 ‰) added to 'coarse' and 'fine' textured soils (δC of −27 ‰ for native soil C (SOC)) over two cropping seasons. Respiration rates increased in both soils ( p < 0.001) following hydrochar addition, and most of this extra respiration was derived from hydrochar C. Dissolved losses accounted for ~5 % of added hydrochar C ( p < 0.001). After 1 year, 33 ± 8 % of the added hydrochar C was lost from both soils. Decomposition rates for the roughly two thirds of hydrochar that remained were very low, with half-life for less estimated at 19 years. In addition, hydrochar-amended soils preserved 15 ± 4 % more native SOC compared to controls (negative priming). Hydrochar negatively affected plant height ( p < 0.01) and biomass ( p < 0.05) in the first but not the second crop grown on both soils. Our results confirm previous laboratory studies showing that initially, hydrochar decomposes rapidly and limits plant growth. However, the negative priming effect and persistence of added hydrochar C after 1 year highlight its soil C sequestration potential, at least on decadal timescales. [ABSTRACT FROM AUTHOR]

The production of hydrogen from water using a catalyst and solar energy is an ideal future energy source, independent of fossil reserves. For an economical use of water and solar energy, catalysts that are sufficiently efficient, stable, inexpensive and capable of harvesting light are required. Here, we show that an abundant material, polymeric carbon nitride, can produce hydrogen from water under visible-light irradiation in the presence of a sacrificial donor. Contrary to other conducting polymer semiconductors, carbon nitride is chemically and thermally stable and does not rely on complicated device manufacturing. The results represent an important first step towards photosynthesis in general where artificial conjugated polymer semiconductors can be used as energy transducers. [ABSTRACT FROM AUTHOR]