Perfluorooctane sulfonate (PFOS) has drawn increasing attention due to its omnipresence and adverse health effects. We prepared a new adsorptive photocatalyst, Ga/TNTs@AC, based on activated carbon and TiO2, and tested the adsorption and subsequent solid-phase photodegradation of PFOS. Ga/TNTs@AC showed faster adsorption kinetics and higher affinity for PFOS than the parent AC, and could degrade 75.0% and mineralize 66.2% of pre-sorbed PFOS within 4-h UV irradiation. The efficient PFOS photodegradation also regenerates Ga/TNTs@AC, allowing for repeated uses without invoking chemical regenerants. The superior photoactivity is attributed to the oxygen vacancies, which not only suppressed recombination of the e−/h+ pairs, but also facilitated O2− generation. Both h+ and O2− played critical roles in the PFOS degradation, which starts with cleavage of the sulfonate group and converts it into PFOA that is then decarboxylated and defluorinated following the stepwise defluorination mechanism. Ga/TNTs@AC holds the potential for more cost-effective PFOS degradation.
Exploring the specific characteristics of pharmaceuticals and personal care products (PPCPs) via adsorption and degradation are scientific and practical significance to control their release to water matrix. In this work, a good adsorbent and ion-exchange material, i.e., titanate nanotubes (TNTs), was employed for adsorption of ciprofloxacin (CIP, a model PPCPs). The adsorption behaviors and mechanisms of CIP with different dissociated species by TNTs were studied through both experimental and theoretical calculations. The multilayered TNTs with high BET surface area (272.3 m2/g) and large pore volume (1.26 cm3/g) exhibited good adsorption property for CIP. The CIP species (i.e., CIP+, CIP±, CIP−) at various pH exhibited significantly different adsorption favorability. Adsorption kinetics and isotherms data revealed that TNTs offered the high uptake for CIP+ (Qmax = 464.47 μmol/g or 153.90 mg/g at pH 5) than CIP± and CIP−. Characterizations indicated the formation of Ti−O−N linkage between CIP molecules and TNTs after adsorption, suggesting the chemical interaction between CIP and TNTs. Density functional theory (DFT) calculations reveal variation on pH affects the protonation/deprotonation state of CIP, and then changes the distribution of molecular orbitals and the electrostatic potential (ESP) energy of CIP. ESP follows the trend as: CIP+ (180.57 kcal/mol) > CIP± (146.78 kcal/mol) > CIP− (12.30 kcal/mol), indicating the side of piperazine ring in CIP oriented to TNTs dominates the CIP adsorption. The integrated experimental and theoretical results, for the first time, suggest that ESP energy can serve as the indicator and predictor of adsorption ability for the PPCPs molecules with various speciation, and can help to deeply describe the adsorption mechanism of PPCPs. In addition, TNTs have great application for the removal of PPCPs through adsorption in practical wastewater treatment area.
Obtaining elastic properties of organic-rich shales through conventional geomechanical testing could be challenging due to availability of good quality core plugs and significant heterogeneous nature of the samples. In this regard, force spectroscopy methods, nanoindentation and atomic force microscopy (AFM) are two main powerful techniques to characterize elastic properties in nano/microscale. In this study, we investigate the applicability of these two methods on the same samples, by quantifying elastic modulus from the Bakken Shale. AFM provided us with modulus maps of higher resolution compared to the modulus maps from the nanoindentation that were created via geostatistical methods. Moreover, results from these methods were compared to demonstrate the advantages and shortcomings of each and discripancy in the outcome. To do so, multi-cluster deconvolution approach was adopted in the statistical analysis on the nanoindentation data, demonstrating 3 separate clusters and mechanical phases. AFM technique, similarly, distinguished three separate (mineral and organic) phases based on the corresponding modulus values, though with higher accuracy compared to nanoindentation and better distinction and less tolerance. It was found that nanoindentation, because it collects discrete datapoints that are farther apart from each other when thermal maturity is increased in the samples, would have difficulty to separate organic matter from intermediary phases. Overall, the range of modulus for each phase was larger in the data that was obtained by nanoindentation compared to the AFM which can be interpreted to the size of the tip and general higher resolution in the later one which is expected to probe a single particle rather than an aggregate of particles.
AbstractApproximately 40% of the Tibetan Plateau (TP) is underlain by continuous permafrost, yet its impact on fluvial water and sediment dynamics remains poorly investigated. Here we show that water and sediment dynamics in the permafrost-dominated Tuotuohe basin on the TP are driven by air temperature and permafrost thaw, based on 33-year daily in-situ observations (1985-2017). Air temperature regulates the seasonal patterns of discharge and suspended sediment concentration (SSC) by controlling the changes in active contributing drainage area (ACDA, the unfrozen erodible landscape that contributes hydrogeomorphic processes within a catchment) and governing multiple thermal processes such as glacier-snow melt and permafrost thaw. Rainstorms determine the short-lived fluvial extreme events by intensifying slope processes and channel erosion and likely also by enhancing thaw slumps. Furthermore, the SSCs at equal levels of discharges are lower in autumn (September-October) than in spring (May-June) and summer (July-August). This reduced sediment availability in autumn can possibly be attributed to the increased supra-permafrost groundwater runoff and the reduced surface runoff and erosion. Due to rapid climate warming, the ACDA has increased significantly from 1985 to 2017, implying expanding landscapes for hydrogeomorphic processes. As a result, the fluvial water and sediment fluxes have substantially increased. In a warmer and wetter future for the TP, the fluvial sediment fluxes of similar permafrost-underlain basins will continue to increase with expanding erodible landscapes and intensifying thermal and pluvial-driven geomorphic processes. Thus, permafrost thaw should be considered as an important driver of past and future water and sediment changes for the TP.This article is protected by copyright. All rights reserved.
China's resistance to Japanese aggression escalated into a full-scale war in 1937. The continuously deteriorating situation stimulated the rise of Chinese nationalism in the diaspora communities worldwide. The Japanese invasion of China, accompanied by the emergence of the National Salvation Movement (NSM) in Southeast Asia, provided the overseas Chinese with a rare opportunity to re-examine their ‘Chineseness’, as well as their relationships with the colonial states and the increasingly self-aware indigenous populations. This research problematises traditional approaches that tend to regard the NSM as primarily driven by Chinese patriotism. Juxtaposing Malaya and Java at the same historical moment, the article argues that the emergence of the NSM was more than just a natural result of the rising Chinese nationalism. Local politics and the shifting political orientations of overseas Chinese communities also profoundly shaped how the NSM played out in different colonial states.
Background Mangrove ecosystems are vulnerable due to the exotic Spartina alterniflora (S. alterniflora) invasion in China. However, little is known about mangrove sediment microbial community assembly processes and interactions under S. alterniflora invasion. Here, we investigated the assembly processes and co-occurrence networks of the archaeal and bacterial communities under S. alterniflora invasion along the coastlines of Fujian province, southeast China. Results Assembly of overall archaeal and bacterial communities was driven predominantly by stochastic processes, and the relative role of stochasticity was stronger for bacteria than archaea. Co-occurrence network analyses showed that the network structure of bacteria was more complex than that of the archaea. The keystone taxa often had low relative abundances (conditionally rare taxa), suggesting low abundance taxa may significantly contribute to network stability. Moreover, S. alterniflora invasion increased bacterial and archaeal drift process (part of stochastic processes), and improved archaeal network complexity and stability, but decreased the network complexity and stability of bacteria. This could be attributed to S. alterniflora invasion influenced microbial communities diversity and dispersal ability, as well as soil environmental conditions. Conclusions This study fills a gap in the community assembly and co-occurrence patterns of both archaea and bacteria in mangrove ecosystem under S. alterniflora invasion. Thereby provides new insights of the plant invasion on mangrove microbial biogeographic distribution and co-occurrence network patterns.
To investigate the capability of pi-pi stacking motifs to enable spin-spin coupling, we designed and synthesized three pairs of regio-isomers featuring two radical moieties joined by a [2.2]paracyclophane (CP) unit. By fusing indeno units to CP, two partially stacked fluorene radicals are covalently linked, exhibiting evident antiferromagnetic (AFM) coupling regardless of the orientation of two spins. Remarkably, while possessing high diradical indices of 0.8 and 0.9, the two molecules demonstrate good air stability by virtue of their singlet ground state. Single crystals help unravel the structural basis of their AFM coupling behaviors. When two radical centers are arranged at the pseudometa-positions around CP, the face-to-face stacked phenylene rings intrinsically confer orbital interactions that promote AFM coupling. On the other hand, if two radicals are directed in the pseudopara-orientation, significant orbital overlapping is observed between the radical centers (i.e., C9 of fluorene) and the aromatic carbons laid on the side, rendering AFM coupling between the two spins. In contrast, when two fluorene radicals are tethered to CP via C9 through a single C-C bond, ferromagnetic (FM) coupling is manifested by both diradical isomers featuring pseudometa- and pseudopara-connectivity. With minimal spin distributed on CP and thus limited contribution from pi-pi stacking, their spin-spin coupling properties are more similar to a pair of nitroxide diradical analogues, in which the two spins are dominantly coupled via through-space interactions. From these results, important conclusions are elucidated such as that although through-space interactions may confer FM coupling, with weakened strength shown by PAH radicals due to their lower polarity, face-to-face stacked p-frameworks tend to induce AFM coupling, because favorable orbital interactions are readily achieved by PAH systems hosting delocalized spins that are capable of adopting varied stacking motifs.