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Particles of iron oxide (Fe3O4 ; 20–40 nm) were embedded within activated carbons during the activation of hydrothermally carbonized (HTC) biomasses in a flow of CO2. Four different HTC biomass samples (horse manure, grass cuttings, beer production waste, and biosludge) were used as precursors for the activated carbons. Nanoparticles of iron oxide formed from iron catalyst included in the HTC biomasses. After systematic optimization, the activated carbons had specific surface areas of about 800 m2g1. The pore size distributions of the activated carbons depended strongly on the degree of carbonization of the precursors. Activated carbons prepared from highly carbonized precursors had mainly micropores, whereas those prepared from less carbonized precursors contained mainly mesopores. Given the strong magnetism of the activated carbon–nano-Fe3O4 composites, they could be particularly useful for water purification.

Activated carbons were produced by chemical activation of hydrothermally carbonized (HTC) beer waste, with phosphoric acid as the activation agent. The activation was optimized within a full factorial design, using the outcome of 19 different experiments. Four different parameters (concentration of the acid, activation time, activation temperature, flow rate) were analyzed with respect to their influence on the median pore size. The concentration of H3PO4 had a strong positive effect on the median pore size. The specific surface areas of these activated carbons were ∼1000 m2/g, which compared well commercially available activated carbons. The activated carbons had mostly large pores with a size of ∼4 nm, and a significant amount of acid surface groups. Scanning electron microscopy (SEM) revealed that the morphology of the HTC beer waste changed significantly after the chemical activation. The capacity to adsorb methylene blue from aqueous solutions was 341 mg/g, for one of the activated carbons at pH 7. A Langmuir model described the uptake of the dye quite well, which suggested a homogeneous adsorption of Methylene Blue (MB).

Activated carbons (ACs) are actively researched as electrode materials for supercapacitors and there is a significant interest to produce ACs from sustainable and low cost precursors. In this study, various ACs were prepared from hydrothermally carbonized sugars by KOH activation. Both the hydrothermal carbonization and activation processes were optimized to tailor the properties (e.g. textural properties, chemical composition, N-doping, electrical conductivity) of the ACs. For instance, the BrunauerEmmett-Teller (BET) surface areas (S BET ) were tuned in the range of 800-3000 m 2 g À1 with associated variation in the extent of microporosity and pore size distributions (PSDs). The ACs were evaluated electrochemically as materials for supercapacitor electrodes in a symmetrical two-electrode cell using an aqueous electrolyte. The relationship between the electrochemical, textural, electrical, and physicochemical properties were analyzed systematically to understand the key factors determining the electrochemical performance. A high specific capacitance (C m ) of $260 F g À1 was achieved at a moderately high S BET of $1300 m 2 g À1, which was equivalent to a C m /S BET of 20 mF cm À2, for an optimal AC prepared from hydrothermally carbonized glucose. The very high surface-specific capacitance highlights that the specific surface area is certainly not the sole limiting parameter for effective electrode materials.

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