In this work, the influence of (NH4)(2)SO4 and (NH4)(2)HPO4 as well as temperature is examined on the hydrothermal carbonization of glucose, fructose and sucrose. Increasing the temperature from 160 to 220 degrees C increased the yield of hydrothermal carbon for each saccharide for the (NH4)(2)SO4 solution, whereas (NH4)(2)HPO4 produced a yield that was independent of temperature. The addition of (NH4)(2)SO4 increased the yield obtained at 220 degrees C by 4.27, 7.03 and 2.01 wt% for glucose, fructose and sucrose over the baseline salt free solution, respectively. (NH4)(2)SO4 also increased the quantity of acid produced and the average size of the hydrothermal carbon spheres. Conversely, (NH4)(2)HPO4 produced carbon structures consisting of interlocked spherical shapes and produced almost no acidic products. XPS analysis revealed that (NH4)(2)SO4 incorporated nitrogen and sulfur into the hydrothermal structure, while (NH4)(2)HPO4 only allowed nitrogen to be incorporated. It was assessed that NH4(+) enhances the production of hydrothermal carbon, except in the presence of PO43-, which prevents the reaction from effectively forming hydrothermal carbon and organic acids. [GRAPHICS] .

Humic acids (HAs) represent an economic and environmental challenge in water treatment, as they have the propensity to foul membranes and create toxic byproducts when interacting with chlorine. To overcome this, HAs were submitted to hydrothermal carbonization to convert them into an easy to remove, valuable carbon material. The result was a carbonaceous material which was easy to filter/dewater compared to HAs with a char yield of 49 +/- 1.8 wt %, and with 46.6 1.4 wt % ending up in the water phase, 2.2 +/- 0.2 wt % in the tar, and the rest in the gaseous fraction. The molecular weight distribution of the organic matter in the water pre-and post-HTC indicated that the structure was broken into several different fragments with a lower molecular weight than that initially present. Physicochemical analysis of the material via elemental analysis, X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and solid-state nuclear magnetic resonance indicated that under hydrothermal carbonization, the aromatic structure of HAs condensed. Carboxylic acids groups were also lost from the surface of HAs, with ether and alcohols increasing because of their loss. The morphology of the obtained material had an amorphous macrostructure consisting of many smaller light lamellar carbon fragments. Finally, the hydrothermal treatment increased the surface area from 0.4 to 103.0 m(2) g(-1).The porosity is located in the mesoporous range of 10-80 nm with a maximum peak at 50 nm.

Hydrothermal carbons have been shown to have controllable surface functionalization through various post-treatment techniques, which indicates these materials may be tuned for specific applications. For this reason, Near Edge X-ray Absorption Fine Structure (NEXAFS) studies have been conducted on a series of nitrogen doped and non-doped heat treated and activated hydrothermal carbons to further understand the changes in surface functionality with treatment. The NEXAFS carbon K-edge spectrum of the non-doped samples displayed a loss of oxygen functionalities (C=O and C-OH) as well as the furan ring structure with increasing temperature, while C=C bonds from graphitic groups increased. This effect was amplified further upon the addition of phosphoric acid (H3PO4) during activation. The doped hydrothermal carbons displayed similar functionality to the non-doped, although the effect of both heat treatment and activation was diminished. The nitrogen K-edge displayed characteristic peaks for pyridine and imines/amides, with pyrroles located under the broad ionization step. This work represents the first time a series of heat treated and activated hydrothermal carbons have been examined via NEXAFS spectroscopy. Additionally, difference analysis has been applied to the NEXAFS spectra to obtain a deeper understanding in the changes in surface functionality, a previously unused technique for these materials. 

Step potential electrochemical spectroscopy (SPECS) has been applied to nitrogen-doped and non-doped hydrothermal carbons that have been activated or heat-treated at a range of temperatures. The highest surface area achieved was 422 m(2).g(-1) under heat-treatment at 600 degrees C, and 2275 m(2).g(-1) using H3PO4 chemical activation at 800 degrees C. The heat-treated series reported a maximum capacitance of 84 F.g(-1) at 10 mV.s(-1), whereas the activated series had a maximum capacitance of 306 F.g(-1) at 10 mV.s(-1) . SPECS analysis revealed that pseudo-capacitance for the hydrothermal carbon doped with nitrogen was interlinked with the degree of oxygen functionality, and that decreasing the oxygen content of the surface increased the pseudo-capacitance contribution from nitrogen. Pseudo-capacitance also increased with activation from the incorporation of phosphate groups; however, the nitrogen-doped hydrothermal carbons displayed minimal double-layer capacitance (60.6 F.g(-1) at 10 mV.s(-1)) despite having reasonable surface areas (1500-1600 m(2).g(-1)).

Activated carbon forms an important step in the treatment of waste water in water treatment facilities. These facilities produce a range of underutilized sludge materials, which can be synthesized into activated carbon, reducing the amount of disposed sludge. Other waste materials high in organic matter, such as horse manure, are also ideal contenders for activated carbon upgrading. This study compares the hydrothermal carbonization followed by activation of sewage sludge and horse manure. Chemical activation was conducted using KOH and H₃PO₄, with physicochemical properties and adsorption of multiple contaminants being tested. Yield and inorganic content varied considerably, with KOH activated materials producing lower yields with higher inorganic content. A maximum surface area of 1363 m²g^-1 and 343 m²g^-1 was achieved for the horse manure and sewage sludge, respectively. Horse manure activated carbons displayed a high affinity for all adsorbates, other than arsenic, which was associated with high carbon content, carbon-oxygen functional groups and low mineral content.

Purpose:

The material properties of carbons from hydrothermal carbonization (HTC), typically referred to as hydrochars, are crucial for hydrochar use in adsorption-related applications. More knowledge is needed on how HTC temperature is altering material properties of different wet low-cost materials and how it is affecting adsorption of contaminants. Studies systematically comparing different feedstocks and carbonization temperatures are needed, because comparisons between available studies are obstructed by the differences in reaction conditions and analysis techniques. 

Methods: In this study, hydrochars were prepared at 180℃, 220℃, and 260℃ from fiber sludge and biosludge from a paper mill, digested sewage sludge, and horse manure. Surface properties of the raw materials and chars were characterized and the adsorption capacity of methylene blue was studied. 

Results: The most substantial change, i.e., a decrease in the oxygen-functionalities of cellulose-rich materials (horse manure and fiber sludge), was caused by degradation of cellulose, while digested sludge types (biosludge and sewage sludge) seemed not to change substantially with the HTC temperature. Adsorption capacities varied between 9.0 and 68 mg g-1 char, being highest for biosludge treated at 220℃. Adsorption dropped drastically at the highest HTC temperature (260℃), which may be due to the decrease in oxygen-containing functionalities. Also substantial differences were seen between different feedstock materials. 

Conclusions: These results suggest that adsorption properties can be tailored both by selection of HTC temperature and feedstock.