It was hypothesized that activated carbons (ACs) prepared from hydrochar could be dispersed in solvents under certain conditions. The crude hydrochar formed by the hydrothermal carbonization (HTC) of glucose and was purified by dialysis. Dried dispersions of hydrochar were chemically activated with potassium bicarbonate (KHCO₃) at temperatures of 750–800 ​°C in N₂. The AC prepared from a freeze-dried dispersion of hydrochar could be dispersed in ethanol as 500 nm-sized colloids. It was noted that on regular drying of the hydrochar dispersions, macroscopically large, long, curved, and thin rods of hydrochar formed in the vials. The rods comprised colloidally-packed spherical particles. The rods may have formed from cracked and fractured colloidal coatings and detached from the wall of the vials. This conclusion was supported by analysing the structural features of the rods. The macroscopic shapes were retained on the chemical activation when the hydrochar precursor had been pyrolyzed in N₂ before activation. The ACs had specific surface areas of up to 1800 ​m²/g, and CO₂ uptake levels of up to 7.1 ​mmol/g at 0 ​°C and 101 ​kPa.

The agro-sector generates organic waste of various kinds, which potentially could be used to prepare functional materials, lessen environmental problems, and enhance circularity. In this context, the hypothesis that was put forward in this work is that prickly pear seed waste from the Tunisian agro-food industry could be used to prepare activated carbons. The prickly pear seed waste was first hydrothermally carbonized and the resulting hydrochar was activated in CO₂ at 800 °C. The yield of the hydrothermal carbonization process is of importance, and it was the highest at intermediate dwell times and temperatures, which was ascribed to the re-precipitation of hydrochar particles on the heat-treated biomass. The hydrochars and activated carbons were characterized with scanning electron microscopy, thermogravimetry, Raman spectroscopy, and N₂ and CO₂ adsorption/desorption analyses. The activated carbons had micro- (<2 nm) and mesopores (2–50 nm), and specific surface areas and total pore volumes of about 400 m^2 −1 and 0.21 cm³ g⁻¹. The study showed that the prickly pear seed waste could be effectively transformed into both hydrochars and activated carbons and that is advisable to optimize the hydrothermal process for the mass yield. A life cycle analysis was performed to assess the environmental impact of the production of typical activated carbons using the approach of this study. Further studies could be focused on enhancing the properties of the activated carbons by further optimization of the activation process.

Patterns of assembled colloidal particles can form on substrates due to solvent evaporation, and here we studied such phenomena in the drying of monodispersed colloidal hydrochar dispersions prepared by the hydrothermal carbonization of glucose and purified by dialysis. During the evaporation of water, line patterns or, in some cases, mud-like patterns formed. The line formation was investigated as a function of the pH of the dispersion, substrate shape, particle concentration, and concentration of sodium dodecylsulfate (SDS). The lines comprised dense assemblies of hydrochar particles. The line width increased with the successive evaporation of water. Sharper lines formed with the addition of SDS, which was ascribed to the effects of solubilization or moderated interactions. At greater particle concentrations, we also observed a continuous layer of colloidal particles between the lines. A mechanism for the line pattern formation derived from the literature on other colloids was proposed. Mud-like patterns formed on the substrate in concentrated samples without SDS addition and were put in the context of the formation of cracks in the drying of colloidal coatings. Hydrochars belong to carbon-rich colloids, which are of fundamental and technological importance. This research could be useful for in situ line printing within microfluidic devices, for example.

Carbon-rich colloids are of great fundamental and technological interest and in this thesis, I tested a range of hypotheses and studied aspects of small hydrochar-based colloids and their colloidal and material chemistry. Crude hydrochar dispersions were synthesized by hydrothermal carbonization of glucose and purified by dialysis. After the purification, stable and monodisperse dispersions of colloidal hydrochar particles in water were obtained. Evaporation of water from the colloidal hydrochar dispersion led to that the hydrochar particles deposited into repeated strip patterns on glass substrates, or underwent directed assembly into macroscopic rods or yarn-shaped objects at the glass-water-air interface.

In one study, we studied the strip patterns that comprised dense assemblies of hydrochar particles formed through directed assembly on the substrates during evaporation of water as a function of the sodium dodecylsulfate (SDS) addition, pH of the dispersion, geometry of the substrates, and concentration of the colloidal particle. The mechanisms were presented. In the published paper included in the thesis, the formation of the macroscopically large and assembled rods was studied during evaporation of water from the colloidal hydrochar dispersions. This assembly was studied along with the electrostatic stability of the dispersions at various pH and ion strengths and the redispersability of the assembled rods into the constituting colloidal particles. For matters of applications of the rod assemblies, pyrolysis and templating silicon carbide -tricopper silicide ((SiC-Cu₃Si) by reactive infiltration with a copper silicon alloy by reaction infiltration were introduced.

In two manuscripts, aspects of the dispersions of hydrochar particles were studied with means of KHCO₃ activation into activated carbons (ACs). In one study, hydrochar particles were activated, and then the ACs were dispersed in a solvent after physical grinding. The morphology, porosity, and CO₂ sorption properties, etc. of the activated carbons prepared by chemical activation were studied for freeze-dried hydrochar particles and the long bent yarn assemblies pretreated under different conditions. ACs of electrospun nanofibers of polyvinylpyrrolidone (PVP) and colloidal hydrochar were oxidized and chemically activated with KHCO₃ or K₂CO₃ and studied for the adsorption of CO₂.

Self-aggregated colloids can be used for the preparation of materials, and we studied long rod-like aggregates formed on the evaporation of water from dispersed particles of colloidal hydrochar. The monodispersed hydrochar particles (100–200 nm) were synthesized by the hydrothermal carbonization ofglucose and purified through dialysis. During the synthesis they formed colloidal dispersions which wereelectrostatically stable at intermediate to high pH and at low ion strengths. On the evaporation of water,macroscopically large rods formed from the dispersions at intermediate pH conditions. The rods formedat the solid-water interface orthogonally oriented with respect to the drying direction. Pyrolysis renderedthe rods highly porous without qualitatively affecting their shape. A Cu-Si alloy was reactively infiltratedinto the in-situ pyrolyzed hydrochars and composites of tricopper silicide (Cu3Si)-silicon carbide(SiC)/carbon formed. During this process, the Si atoms reacted with the C atoms, which in turned causedthe alloy to wet and further react with the carbon. The shape of the underlying carbon template wasmaintained during the reactions, and the formed composite preparation was subsequently calcined intoa Cu3Si-SiC-based replica of the rod-like assemblies of carbon-based colloidal particles. Transmission andscanning electron microscopy, and X-ray diffraction were used to study the shape, composition, andstructure of the formed solids. Further studies of materials prepared with reactive infiltration of alloysinto self-aggregated and carbon-based solids can be justified from a perspective of colloidal science, aswell as the explorative use of hydrochar prepared from real biomass, exploration of the compositionalspace in relation to the reactive infiltration, and applications of the materials in catalysis. 

Biomethane is a renewable fuel with a small environmental footprint. In its production, the removal of CO2 from the fermentation gas is critical. Pressure and vacuum swing adsorption (PSA and VSA) processes have certain advantages over other processes for the removal. Silicoaluminophosphate-56 (SAPO-56) has promising properties as an adsorbent for PSA- or VSA-based upgrading of raw biogas. It is typically synthesized by using N,N,N', N'-tetramethyl-1,6-hexanediamine (TMHD) as a structure directing agent (SDA). In this study, TMHD was partly replaced with three different low-cost templates: isopropylamine (IPA), dibutylamine, and tripropylamine. SAPO-56 was co-crystallized with mixtures of templating amines with up to a ratio of 30%:70% of TMHD:IPA. With using TMHD and IPA, small and defined crystals of SAPO-56 plus SAPO-47 formed instead of the large aggregates of SAPO-56 that formed when only TMHD was used. Solid-state 13C NMR spectroscopy was used to show that the IPA and TMHD had not been decomposed and that both molecules were included within the assynthesized crystals of SAPO-56. Synthetic composition diagrams were drawn with respect to the P2O5, SiO2, and Al2O3 compositions of the reaction mixtures and the formed crystalline SAPOs. In relation to these diagrams, the domains for stability of SAPO-56 were contrasted with those of SAPO-11, -17, -20, and -47. In particular, it was observed that SAPO-47 co-crystallized with SAPO-56 when a very large fraction of IPA was used under otherwise optimized conditions. As consistent with other studies, the SAPO-56 synthesized with dual SDAs had a very high uptake of CO2 at conditions relevant for PSA- or VSA-driven upgrading of raw biogas into methane.

Char obtained from biomass pyrolysis is an eco-friendly porous carbon, which has potential use as a material for electrodes in supercapacitors. For that application, a high microporous specific surface area (SSA) is desired, as it relates to the accessible surface for an applied electrolyte. Currently, the incomplete understanding of the relation between porosity development and production parameters hinders the production of tailor-made, bio-based pyrochars for use as electrodes. Additionally, there is a problem with the low reliability in assessing textual properties for bio-based pyrochars by gas adsorption. To address the aforementioned problems, beech wood cylinders of two different lengths, with and without pre-treatment with citric acid were pyrolysed at temperatures of 300-900 degrees C and analysed by gas adsorption. The pyrolyzed chars were characterised with adsorption with N-2 and CO2 to assess the influence of production parameters on the textual properties. The new approach in processing the gas adsorption data used in this study demonstrated the required consistency in assessing the micro- and mesoporosity. The SSA of the chars rose monotonically in the investigated range of pyrolysis temperatures. The pre-treatment with citric acid led to an enhanced SSA, and the length of the cylinders correlated with a reduced SSA. With pyrolysis at 900 degrees C, the micro-SSAs of samples with 10 mm increased by on average 717 +/- 32 m(2)/g. The trends among the investigated parameters and the textual properties were rationalized and provide a sound basis for further studies of tailor-made bio-based pyrochars as electrode materials in supercapacitors.

The oxygen reduction reaction (ORR) is central in carbon-neutral energy devices. While platinum group materials have shown high activities for ORR, their practical uses are hampered by concerns over deactivation, slow kinetics, exorbitant cost, and scarce nature reserve. The low cost yet high tunability of metal-organic frameworks (MOFs) provide a unique platform for tailoring their characteristic properties as new electrocatalysts. Herein, we report a new concept of design and present stable Zr-chain-based MOFs as efficient electrocatalysts for ORR. The strategy is based on using Zr-chains to promote high chemical and redox stability and, more importantly, tailor the immobilization and packing of redox active-sites at a density that is ideal to improve the reaction kinetics. The obtained new electrocatalyst, PCN-226, thereby shows high ORR activity. We further demonstrate PCN-226 as a promising electrode material for practical applications in rechargeable Zn-air batteries, with a high peak power density of 133 mW cm(-2). Being one of the very few electrocatalytic MOFs for ORR, this work provides a new concept by designing chain-based structures to enrich the diversity of efficient electrocatalysts and MOFs.

The effect of two process water (PW) recirculation strategies after hydrothermal carbonization (HTC) of brewers spent grains (BSG) is evaluated with the focus on the hydrochar characteristics. The HTC process has been carried out under different operating conditions, which are residence time between 2 and 4 h and temperature in the range of 200-220 degrees C. The composition of the hydrochars reveals that operating conditions have a more significant effect than PW recirculation. The composition of the liquid produced by HTC with PW recirculation is essentially controlled by the operating temperature, for instance, the total organic carbon (TOC) in the PW changes in the narrow range of 200-220 degrees C. A detailed analysis of PW also has been done. The main components of the liquid phase are lactic, formic, acetic, levulinic, and propionic acid as well as 5-hydroxymethylfurfural, that affect the surface structure of the hydrochars.

Global concerns regarding climate change and the energy crisis have stimulated, among other things, research on renewable and sustainable materials. In relation to that, hydrothermal carbonization of wet biomass has been shown to be a low-cost method for the production of hydrochars. Such hydrochars can be refined into materials that can be used in water purification, for CO2 capture, and in the energy sector. Here, we review the use of metal ions and particles to catalyze the formation of hydrochars and related hybrid materials. First, the effects of using silver, cobalt, tellurium, copper ions, and particles on the hydrothermal carbonization of simple sugars and biomass are discussed. Second, we discuss the structural effects of iron ions and particles on the hydrochars in conjunction with their catalytic effects on the carbonization. Among the catalysts, iron ions or oxides have low cost and allow magnetic features to be introduced in carbon-containing hybrid materials, which seems to be promising for commercial applications.