RESUMEN
Solid materials with ultra-low thermal conductivity (κ) are of great interest in thermoelectrics for energy conversion or as thermal barrier coatings for thermal insulation. Many low-κ materials exhibit unique properties, such as weak or even insignificant dependence on temperature (T) for κ, i.e., an anomalous glass-like behavior. However, a comprehensive theoretical model elucidating the microscopic phonon mechanism responsible for the glass-like κ-T relationship is still absent. Herein, we take rare-earth tantalates (RE3TaO7) as examples to reexamine phonon thermal transport in defective crystals. By combining experimental studies and atomistic simulations up to 1800 K, we revealed that diffusion-like phonons related to inhomogeneous interatomic bonding contribute more than 70% to the total κ, overturning the conventional understanding that low-frequency phonons dominate heat transport. Furthermore, due to the bridging effects of interatomic bonding, the κ of high-entropy tantalates is not necessarily lower than that of medium-entropy materials, suggesting that attempts to reduce κ through high-entropy engineering are limited, at least in defective fluorite tantalates. The new physical mechanism of multimodal phonon thermal transport in defective structures demonstrated in this work provides a reference for the analysis of phonon transport and offers a new strategy to develop and design low-κ materials by regulating the inhomogeneity of interatomic bonding.
RESUMEN
The widespread use of biogas slurry could potentially raise the environmental risk of antibiotics. Dissolved organic matter (DOM), as the most active part of biogas slurry, was able to interact with antibiotics and play a crucial role in the structure and function of soil and aquatic ecosystems. The recent shifts in global climate patterns have garnered significant attention due to their substantial impact on temperature, thereby exerting a direct influence on the characteristics of DOM and subsequently on the environmental behavior of antibiotics. However, there is limited research concerning the impact of temperature on the binding of DOM and antibiotics. Thus, this study aimed to explore the temperature-dependent structural transformation and driving factors of biogas slurry-derived DOM (BSDOM). Additionally, the binding characteristics between BSDOM and the commonly used antibiotic norfloxacin (NOR) at different temperatures were studied by using multi spectroscopic methods and two-dimensional correlation spectroscopy (2D-COS) analysis. The results suggested that the temperature-dependent structural transformation of BSDOM was reversible, with a slight lag in the transition temperature under cooling (13 °C for heating and 17 °C for cooling). Heating promoted the conversion of protein-like to humic-like substances while cooling favored the decomposition of humic-like substances. BSDOM and NOR were static quenching, with oxygen-containing functional groups such as C-O and -OH playing an important role. Temperature influenced the order of binding, the activity of the protein fraction, and its associated functional groups. At temperatures of 25 °C and 40 °C, the fluorescent components were observed to exhibit consistent binding preferences, whereby the humic-like component demonstrated a greater affinity for NOR compared to the protein-like component. However, the functional group binding order exhibited an opposite trend. At 10 °C, a new protein-like component appeared and bound preferentially to NOR, when no C-O stretch corresponding to the amide was observed. The finding will contribute to a comprehensive understanding of the interaction mechanisms between DOM and antibiotics under climate change, as well as providing a theoretical basis to reduce the environmental risks of biogas slurry and antibiotics.