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1. Production and Modification of Hydrochar from Anaerobically Digested Cattail for Adsorbing Ammonium and Phosphorous in Wastewater

   https://doi.org/10.2166/wst.2021.378  

   Ghimire, s; Wang, l; Zhang, B; Xin, l; Shahbazi, A (October 2021, Water science technology)

   Rauch, W Liu (Ed.)

   Water contamination by nitrogen and phosphorus ions has a direct consequence of eutrophication to the ecosystem. The objective of this study is to investigate the production of hydrochars by acetic acid or sodium hydroxide assisted hydrothermal carbonization (HTC), various activation methods, and the potential of hydrochar as an adsorbent to remove NH4+-N and PO43--P from wastewater. The results showed that acetic acid or sodium hydroxide assisted HTC and activation with magnesium chloride or air could improve the surface properties of hydrochar. Acetic acid modification generated extensive oxygenated functional groups, while sodium hydroxide modification produced hydrochar with a high N/C ratio and surface aromaticity. Treating hydrochar with magnesium chloride could impregnate nano-magnesium particles on the hydrochar, thereby improving the ability to remove N and P. Air activation of hydrochar resulted in more oxygen containing functional groups. The NH4+-N and PO43--P adsorption capacities of these hydrochars ranged from 92.6 to 122.4mg/g and 1.6 to 15.8mg/g, respectively. The adsorption capacity of hydrochars in swine wastewater is similar to the results of artificial wastewater. The results suggested that Mg-nanoparticle dispersion and oxygen-containing functional groups played a major role in adsorption than ion exchange and physisorption. 

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2. Recent Progress on Emerging Applications of Hydrochar

   https://doi.org/10.3390/en15249340  

   Islam, Md Tahmid; Sultana, Al Ibtida; Chambers, Cadianne; Saha, Swarna; Saha, Nepu; Kirtania, Kawnish; Reza, M. Toufiq (December 2022, Energies)

   Hydrothermal carbonization (HTC) is a prominent thermochemical technology that can convert high-moisture waste into a valuable product (called hydrochar) at a relatively mild treatment condition (180–260 °C and 2–10 MPa). With rapidly growing research on HTC and hydrochar in recent years, review articles addressing the current and future direction of this research are scarce. Hence, this article aims to review various emerging applications of hydrochars, e.g., from solid fuel to soil amendment, from electron storage to hydrogen storage, from dye adsorption, toxin adsorption, heavy metal adsorption to nutrient recovery, and from carbon capture to carbon sequestration, etc. This article further provides an insight in the hydrochar’s working mechanism for various applications and how the applications can be improved through chemical modification of the hydrochar. Finally, new perspectives with appropriate recommendations have been made to further unveil potential applications and its improvement through hydrochar and its modified version. 

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3. Effect of Hydrothermal Carbonization on Fuel and Combustion Properties of Shrimp Shell Waste

   https://doi.org/10.3390/en16145534  

   Saha, Swarna; Islam, Md Tahmid; Calhoun, Joshua; Reza, Toufiq (July 2023, Energies)

   Shrimp shell is a popularly consumed seafood around the globe which generates a substantial quantity of solid wet waste. Hydrothermal carbonization (HTC) could be a viable pathway to convert wet shrimp shell waste into energy-dense hydrochar. The present study aims to assess the fuel properties, physicochemical attributes, and combustion properties of shrimp shell hydrochar generated with a wide range of HTC temperatures (110–290 °C). Results showed that a rise in carbonization rate results in a decline in mass yield to as low as 25.7% with the increase in HTC temperature. Thermogravimetric analysis indicates shrimp shell hydrochars to be more thermally stable than raw dried feedstock. Results from the bomb calorimeter report a maximum HHV of 27.9 MJ/kg for SS-290, showing a 13% increase in energy densification compared to raw shrimp shell. The slagging and fouling indices determined for the hydrochars further assisted in addressing the concern regarding increasing ash content changing from 17.0% to 36.6%. Lower ratings of the slagging index, fouling index, alkali index, and chlorine content for hydrochars at higher temperature indicate the reduced probability of reactor fouling during combustion. The findings of the analysis demonstrate that HTC is a promising approach for transforming shrimp shell waste into a potential fuel replacement. 

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4. Soybean-derived blue photoluminescent carbon dots

   https://doi.org/10.3762/bjnano.11.48  

   Wang, Shanshan; Sun, Wei; Yang, Dong-sheng; Yang, Fuqian (January 2020, Beilstein Journal of Nanotechnology)

   Biomass-derived carbon dots (CDs) are biocompatible and have potential for a variety of applications, including bioimaging and biosensing. In this work, we use ground soybean residuals to synthesize carbon nanoparticles by hydrothermal carbonization (HTC), annealing at high temperature, and laser ablation (LA) in a NH 4 OH solution. The carbon nanoparticles synthesized with the HTC process (HTC-CDs) exhibit photoluminescent characteristics with strong blue emission. The annealing of the HTC-processed carbon particles in the range of 250 to 850 °C causes a loss of the photoluminescent characteristics of the CDs without any significant change in the microstructure (amorphous structure) of the carbon particles. The LA processing of the annealed HTC-processed carbon particles introduces nitrogen-containing surface-functional groups and leads to the recovery of the photoluminescent features that are different from those of the HTC-CDs and dependent on the fraction of nitrogen in the surface-functional groups. The photoluminescence of both the HTC-CDs and LA-CDs is largely due to the presence of N-containing surface-functional groups. The quantum yield of the LA-CDs is more constant than that of the HTC-CDs under continuous UV excitation and does not exhibit a significant reduction after 150 min of excitation. The methods used in this work provide a simple and green strategy to introduce N-surface-functional groups to carbon nanoparticles made from biomass and biowaste and to produce stable photoluminescent CDs with excellent water-wettability. 

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5. Nitrogen-induced shift of photoluminescence from green to blue emission for xylose-derived carbon dots

   https://doi.org/10.1088/2632-959X/aba771  

   Wang, Shanshan; Yang, Dong-Sheng; Yang, Fuqian (August 2020, Nano Express)

   Abstract The discovery of carbon dots opens a new avenue to the applications of nanomaterials in biosensing and bioimaging. In this work, we develop simple methods to prepare carbon nanoparticles from xylose and to tune the photoluminescence (PL) characteristics of the xylose-derived carbon nanoparticles via the combination of three different processes: hydrothermal carbonization (HTC), annealing at 850 °C and laser ablation (LA) in a NH₄OH solution. The HTC-synthesized carbon dots (CDs) exhibit green emission under the 365 nm UV excitation, the annealing of the HTC-synthesized CDs leads to complete loss of the PL characteristics, and the LA processing of the annealed carbon nanoparticles recovers the PL characteristics with blue shift in comparison to the HTC-synthesized CDs under the same UV excitation. the PL characteristics of the HTC-CDs and the LA-CDs are dependent on theπ-π* transition of C-containing surface-functional groups andπ-π* and n-π* transitions of N-containing surface-functional groups, respectively, which are responsible for the difference in the PL characteristics between the HTC-synthesized CDs and the LA-processed CDs. The approaches demonstrated in this work provide a viable method to introduce and tune surface-functional groups on the surface of carbon nanoparticles. 

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