Influence of ammonium salts and temperature on the yield, morphology and chemical structure of hydrothermally carbonized saccharides

π-Conjugated Porous Polymer Nanosheets for Explosive Sensing: Investigation on the Role of H-Bonding

Nitroaromatic explosive sensing plays a critical role in ensuring public security and environmental protection. Herein, we report 2-pyridyl-thiazolothiazole (pyTTz) integrated blue-fluorescent π-conjugated porous polymer nanosheets, NTzCMP and TzCMP for selective sensing of picric acid (PA) among nitrophenol explosives. Acid-base interactions between PA and pyTTz of CMP lead to H-bonding interactions, where the hydroxy group of PA engaged in weak H-bonding interactions with pyridine and TTz of pyTTz moiety. This led to a strong fluorescence quenching of CMPs-such formation of ground state complex was supported by linear Stern-Volmer quenching plots, unaltered excited state lifetimes, and detailed FTIR analysis of PA exposed CMPs. Interestingly, both CMPs exhibited an excellent response to smaller analytes such as o-nitrotoluene compared to 2,4-dinitrotoluene. Both NTzCMP and TzCMP CMPs exhibited high KSV values of 9×103 and 2.1×103 M-1 for PA and the corresponding limit of detection values were found to be 0.46 and 1.6 ppm, respectively.

Koopmans' theorem for acidic protons

The famous Brønsted acidity, which is relevant in many areas of experimental and synthetic chemistry, but also in biochemistry and other areas, is investigated from a new perspective. Nuclear electronic orbital methods, which explicitly account for the quantum character of selected protons, are applied. The resulting orbital energies of the proton wavefunction are interpreted and related to enthalpies of deprotonation and acid strength in analogy to the Koopmans' theorem for electrons. For a set of organic acids, we observe a correlation which indicates the validity of such a NEO-Koopmans' approach and opens up new opportunities for the computational investigation of more complex acidic systems.

Lactic acid fermentation of food waste as storage method prior to biohydrogen production: Effect of storage temperature on biohydrogen potential and microbial communities

This study aims to investigate the impact of utilizing lactic acid fermentation (LAF) as storage method of food waste (FW) prior to dark fermentation (DF). LAF of FW was carried out in batches at six temperatures (4 °C, 10 °C, 23 °C, 35 °C, 45 °C, and 55 °C) for 15 days followed by biological hydrogen potential (BHP) tests. Different storage temperatures resulted in different metabolites distribution, with either lactate or ethanol being dominant (159.2 ± 20.6 mM and 234.4 ± 38.2 mM respectively), but no negative impact on BHP (averaging at 94.6 ± 25.1 mL/gVS). Maximum hydrogen production rate for stored FW improved by at least 57%. Microbial analysis showed dominance of lactic acid bacteria (LAB) namely Lactobacillus sp., Lactococcus sp., Weisella sp., Streptococcus sp. and Bacillus sp. after LAF. Clostridium sp. emerged after DF, co-existing with LAB. Coupling LAF as a storage method was demonstrated as a novel strategy of FW management for DF, for a wide range of temperatures.

Evolution of elemental nitrogen involved in the carbonization mechanism and product features from wet biowaste

Hydrothermal carbonization (HTC) represents elegant thermochemical conversion technology suitable for energy and resource recovery from wet biowaste, while the elemental nitrogen is bound to affect the HTC process and the properties of the products. In this review, the nitrogen fate during HTC of typical N-containing-biowaste were presented. The relationship between critical factors involved in HTC like N/O, N/C, N/H, solid ratio, initial N in feedstock, hydrothermal temperature and residence time and N content in hydrochar were systematic analyzed. The distribution and conversion of N species along with hydrothermal severity in hydrochar and liquid phase was discussed. Additionally, the chemical forms of nitrogen in hydrochar were elaborated coupled with the role of N element during hydrochar formation mechanism and the morphology features. Finally, the future challenges of nitrogen in biowaste involved in HTC about the formation and regulation mechanism of hydrochar were given, and perspectives of more accurate regulation of the physicochemical characteristics of hydrochar from biowaste based on the N evolution is expected.

Detection of Fe3+ and Hg2+ ions through photoluminescence quenching of carbon dots derived from urea and bitter tea oil residue

In this study, we prepared nitrogen-doped carbon dots (xNCDs) using hydrothermally-treated bitter tea oil residue with urea for the detection of metal ions by monitoring the photoluminescence quenching. The quantum yields of the xNCDs increased from approximately 3.85% (CDs) to 5.5% (3NCDs) and 7.2% (1NCDs), revealing that nitrogen doping effectively increases the fluorescence emission. The increased emission of the xNCDs can be attributed to radiative recombination resulting from the π-π* transition of the C=C or the n-π* transition between the C=O or N=O of sp³ units. Moreover, the CDs have abundant surface-attached phenolic and hydroxyl groups that coordinate with Fe³⁺ ions and quench the fluorescence. Conversely, Hg²⁺ ions preferentially adsorb on nitrogen-containing groups, such as amide-carbonyl groups (O=C-NH₂) and pyridinic and pyrrolic functionalities, on the surface of the NCDs owing to their strong affinity, quenching the substantial photoluminescence emissions. Our results suggest that bitter tea oil residue-derived carbon dots can be used to selectively detect metal ions, such as Fe³⁺ and Hg²⁺, by doping with nitrogen using urea as a nitrogen precursor.

Kinetic Study of Levulinic Acid from Spirulina platensis Residue

Microalgae have the potential to emerge as renewable feedstocks to replace fossil resources in producing biofuels and chemicals. Levulinic acid is one of the most promising substances which may serve as chemical building blocks. This work investigated the use of Spirulina platensis residue (solid residue after lipids extraction) to produce LA via acid hydrolysis reaction. In this study, Spirulina platensis residue was set to have a solid-liquid ratio of 5% (w/v). The effect of process parameters on the Spirulina platensis residue to levulinic acid hydrolysis reaction was observed at temperatures ranging from 140 to 180 °C under four acid concentrations, i.e., 0.25, 0.5, 0.8, and 1 M. A simplified kinetic model was also developed to describe the behavior of Spirulina platensis residue conversion to levulinic acid, based on the pseudo-homogeneous-irreversible-1^st order reaction. The results showed that the proposed model could capture the experimental data well. The reaction network also considered involvement of intermediate products namely glucose and 5-hydroxymethylfurfural. The results showed that Spirulina platensis residue, with acid catalysts, can be used to produce levulinic acid, and the kinetic model can provide useful information for understanding the Spirulina platensis residue to levulinic acid hydrolysis reaction.

Nitrogen-Containing Hydrochar: The Influence of Nitrogen-Containing Compounds on the Hydrochar Formation

Hydrothermal carbonization (HTC) of fructose and urea containing solutions was conducted at 180 °C to study the influence of nitrogen-containing compounds on conversion and product properties. The concentration of fructose was fixed, while the concentration of urea was gradually increased to study its influence on the formation of nitrogen-containing hydrochar (N-HC). The degradation of urea has an important influence on the HTC of fructose. The Maillard reaction (MR) promotes the formation of N-HC in acidic conditions. However, in alkaline conditions, MR promotes the formation of bio-oil at the expense of N-HC. Alkaline conditions reduce N-HC yield by catalyzing fragmentation reactions of fructose and by promoting the isomerization of fructose to glucose. The results showed that adjusting the concentration of nitrogen-containing compounds or the pH value of the reaction environment is important to force the reaction toward the formation of N-HC or N-bio-oil.