Engineering Nitrogen‐Doped Carbon Quantum Dots: Tailoring Optical and Chemical Properties through Selection of Nitrogen Precursors

The process of N‐doping is frequently employed to enhance the properties of carbon quantum dots. However, the precise requirements for nitrogen precursors in producing high‐quality N‐doped carbon quantum dots (NCQDs) remain undefined. This research systematically examines the influence of various nitrogen dopants on the morphology, optical features, and band structure of NCQDs. The dots are synthesized using an efficient, eco‐ friendly, and rapid continuous hydrothermal flow technique. This method offers unparalleled control over synthesis and doping, while also eliminating convention‐related issues. Citric acid is used as the carbon source, and urea, trizma base, beta‐alanine, L‐arginine, and EDTA are used as nitrogen sources. Notably, urea and trizma produced NCQDs with excitation‐independent fluorescence, high quantum yields (up to 40%), and uniform dots with narrow particle size distributions. Density functional theory (DFT) and time‐dependent DFT modelling established that defects and substituents within the graphitic structure have a more significant impact on the NCQDs’ electronic structure than nitrogen‐containing functional groups. Importantly, for the first time, this work demonstrates that the conventional approach of modelling single‐layer structures is insufficient, but two layers suffice for replicating experimental data. This study, therefore, provides essential guidance on the selection of nitrogen precursors for NCQD customization for diverse applications

Hydrothermal carbonization and pyrolysis in wetland engineering:Carbon sequestration, phosphorus recovery, and structural characterization of willow-based chars with X-ray μ-computed tomography

Willows from engineered wetland systems (EWS) offer a sustainable approach to wastewater treatment and biomass production. Our study assesses their potential for nutrient recovery and carbon sequestration using slow pyrolysis (600 °C) and hydrothermal carbonization (250 °C). Here, we propose EWS-pyrochars as a ready-to integrate opportunity for soil amendment, as they exhibit a predominant CO2 release and the absence of harmful compounds in pyrolysis-chromatograms, indicating higher stability than hydrochars. Using sequential P-extractions, we observed a high bioavailability in the willow-woodchips and a significant P-retention in EWS-chars—up to 92 % in pyrochars and near-complete retention in hydrochars, along with a higher labile-P fraction of 21 % in hydrochars than 5 % in pyrochars. Utilizing X-ray-based techniques, Raman spectroscopy, scanning electron microscopy, and gas physisorption, we characterized the EWS-chars' structures. We revealed innovative 3D-visualizations, which transcend previous literature by providing insights into the chars' internal porosity and quantifying, for the first time, their carbonaceous structural thickness via a meshing algorithm and the mean Feret diameter. EWS-pyrochars exhibit remarkable aromaticity with a higher concentration of overall sp2 C-atoms at 63 % vs. 43 % in hydrochars. Moreover, unlike hydrochars, which depict occluded porosity, EWS-pyrochars exhibited 92 % water storage-like pores. Although hydrochars indicated lower carbonization and thermal stability than pyrochars, their higher carbon retention (55 vs. 41 % in pyrochar) suggest superior annual benefits—on a 10 ha EWS scale—of 80-tons of carbon sequestration and 334 kg of phosphorus recovery versus 60-tons of carbon and 298 kg of phosphorus with pyrochars. Our findings suggest innovative materials for resource recovery, advancing the engineered wetland systems field, shifting their traditional use, and opening the opportunity for future integration into biorefineries.</p

Iodine Migration and Degradation of Perovskite Solar Cells Enhanced by Metallic Electrodes

We monitored the evolution in time of pinhole-free structures based on FTO/TiO₂/CH₃NH₃PbI_2.6Cl_0.4 layers, with and without spiro-OMeTAD and counter electrodes (Ag, Mo/Ag, and Au), aged at 24 °C in a dark nitrogen atmosphere. In the absence of electrodes, no degradation occurs. While devices with Au show only a 10% drop in power conversion efficiency, remaining stable after a further overheating at 70 °C, >90% is lost when using Ag, with the process being slower for Mo/Ag. We demonstrate that iodine is dislocated by the electric field between the electrodes, and this is an intrinsic cause for electromigration of I^– from the perovskite until it reaches the anode. The iodine exhaustion in the perovskite layer is produced when using Ag electrodes, and AgI is formed. We hypothesize that in the presence of Au the iodine migration is limited due to the buildup of I^– negative space charge accumulated at the perovskite–OMeTAD interface