科研成果

Volatile organic compounds (VOCs) emitted from building and furnishing materials represent a major concern of indoor air quality, in particular in new buildings. We carried out multiweek nontargeted VOC measurements in 10 new apartments in Beijing, China, using online chemical ionization mass spectrometry. Dimethyl esters of succinic, glutaric, and adipic acids, which are rarely known for their presence in indoor air, were identified in three apartments. The identification was confirmed using authentic standards and by gas chromatography/mass spectrometry analysis. Despite varying concentrations, the three compounds exhibited largely consistent ratios across the three apartments and throughout the observation periods. The observed ratios resemble chemical composition of dibasic esters (DBE), which are a solvent mixture of the three compounds and have been used in the coating industry. A field “sniffing” experiment further confirms DBE emissions from the coatings of some wooden furniture in at least one apartment. The average airborne DBE concentrations in the three apartments were 41, 5, and 4 $μ$g/m3, respectively, exceeding the screening level of 1 $μ$g/m3 recommended by the Michigan Department of Environmental Quality, United States. In the context of fast-growing DBE usage, the current results suggest that DBE might be emerging indoor air pollutants and merit further investigation.

This study reports the different degradation mechanisms of carbamazepine (CBZ) and diclofenac (DCF) by single-atom Barium (Ba) embedded g-C3N4. Single-atom Ba is anchored onto g-C3N4 by forming ionic bond with triazine ring, thus greatly enhances the photocatalytic activity with an atom ratio of 1.78%. CBZ undergoes a typical photocatalysis mechanism, while DCF is degraded via a photosensitization-like process, which does not need band gap excitation of photocatalyst. By means of Density Functional Theory (DFT) calculation, the selectivity is found to be related with the different valence excitation modes of CBZ and DCF. Specifically, CBZ undergoes a local excitation, which does not obviously affect molecular configuration. In contrast, DCF undergoes a charge transfer excitation, which significantly changes the reactive sites distribution and facilitates photosensitization-like degradation. Due to the different degradation mechanism, the effects of pH, co-existed anions, and water matrix are also different. Since photosensitization-like mechanism does not rely on photo-generated holes mediated oxidation, the degradation efficient of DCF shows higher anti-interference capacity in real water.

Abstract In this paper, a difluoro-monobromo end group is designed and synthesized, which is then used to construct a novel polymer acceptor (named PY2F-T) yielding high-performance all-polymer solar cells with 15.22% efficiency. The fluorination strategy can increase the intramolecular charge transfer and interchain packing of the previous PY-T based acceptor, and significantly improve photon harvesting and charge mobility of the resulting polymer acceptor. In addition, detailed morphology investigations reveal that the PY2F-T-based blend shows smaller domain spacing and higher domain purity, which significantly suppress charge recombination as supported by time-resolved techniques. These polymer properties enable simultaneously enhanced JSC and FF of the PY2F-T-based devices, eventually delivering device efficiencies of over 15%, significantly outperforming that of the devices based on the non-fluorinated PY-T polymer (13%). More importantly, the PY2F-T-based active layers can be processed under ambient conditions and still achieve a 14.37% efficiency. They can also be processed using non-halogenated solvent o-xylene (no additive) and yield a decent performance of 13.05%. This work demonstrates the success of the fluorination strategy in the design of high-performance polymer acceptors, which provide guidelines for developing new all-PSCs with better efficiencies and stabilities for commercial applications.

Finding out the physical structure of neuronal circuits that governs neuronal responses is an important goal for brain research. With fast advances for large-scale recording techniques, identification of a neuronal circuit with multiple neurons and stages or layers becomes possible and highly demanding. Although methods for mapping the connection structure of circuits have been greatly developed in recent years, they are mostly limited to simple scenarios of a few neurons in a pairwise fashion; and dissecting dynamical circuits, particularly mapping out a complete functional circuit that converges to a single neuron, is still a challenging question. Here, we show that a recent method, termed spike-triggered non-negative matrix factorization (STNMF), can address these issues. By simulating different scenarios of spiking neural networks with various connections between neurons and stages, we demonstrate that STNMF is a persuasive method to dissect functional connections within a circuit. Using spiking activities recorded at neurons of the output layer, STNMF can obtain a complete circuit consisting of all cascade computational components of presynaptic neurons, as well as their spiking activities. For simulated simple and complex cells of the primary visual cortex, STNMF allows us to dissect the pathway of visual computation. Taken together, these results suggest that STNMF could provide a useful approach for investigating neuronal systems leveraging recorded functional neuronal activity.

Lake waters often act as important methane sources for global greenhouse gas emission, but it would be more complex as lakes are regulated by rivers. In this study, seasonal variations of dissolved and emitted methane in the Poyang Lake, the largest freshwater lake in China, are investigated based on a specially designed monitoring. As a typical subtropical linking-to-river lake, the Poyang shows characteristics of the "lake" in wet season and the "river" in dry season alternatively over a year. Consequently, CH(4)flux from the Poyang Lake to the Yangtze River closes to the highest in January due to concentrated dissolved CH(4)and "river" effects in dry season, while CH(4)flux to the atmosphere falls to the lowest in July because of intensified CH(4)oxidization and diluted dissolved CH(4)as well as "lake" effects in wet season. Overall, CH(4)fluxes from Poyang Lake to the atmosphere and to the Yangtze River were 19 and 0.35 Gg CH(4)yr(-1), respectively. The Three Gorges Dam, the world's largest dam in the Yangtze River, would further intensify this pattern, enhancing the transformation between "lake phase" and "river phase". This study also provides the paradigm for CH(4)budget from other large lakes in similar situations around the world.

China is one of the diversity centers of gymnosperms. Nearly one-fifth (195 species) of gymnosperms are located in China, but 69 species are threatened. To date, the conservation status of gymnosperms, especially threatened gymnosperms in China, remains largely unknown, which seriously restricts the comprehensive protection of gymnosperms. Understanding the distribution pattern of species richness and exploring the relationships between species richness and environmental factors are key steps for their protection. In this study, we first constructed a database for the 69 threatened species of gymnosperms with 13 270 distribution records. It is found that 31 of the grid cells (50 × 50 km) cover all threatened gymnosperm species in China, and the grid cells of threatened gymnosperms are mainly distributed in the southern area of the Yellow River, with a distribution center in the Western Sichuan Plateau. Then, we evaluated the conservation status of threatened gymnosperms, and the results indicate that 9 (13%) threatened gymnosperms are distributed outside of nature reserves. Therefore, there are still conservation gaps in the protection of threatened gymnosperms in China. We should give more attention to unprotected threatened gymnosperms and conduct taxonomic studies on the species without detailed distribution records. Finally, conservation priority areas and priority conservation levels of threatened gymnosperms in China were proposed. The Western Sichuan Plateau is the most important conservation priority area of threatened gymnosperms. This study will shed light on plant protection and forest management in China.

Short- and medium-chain chlorinated paraffins (SCCPs and MCCPs, respectively) have raised environmental concern due to their potential for persistence, long-range transport, bioaccumulation, and toxicity. However, little is known about the production, use, and environmental emissions of SCCPs and MCCPs in China, the world’s largest producer and consumer. In this study, we estimated the amounts of SCCPs and MCCPs produced and used in China in 2018–2019 based on a nationwide survey and measurements of concentrations in products, from which we estimated the environmental emissions of SCCPs and MCCPs in China. Our results show that 225.2 and 236.4 metric kilotons (kt) of SCCPs and 428.5 and 450.2 kt of MCCPs were used in China in 2018 and 2019, respectively, with poly(vinyl chloride) (PVC) products dominating SCCP and MCCP usage. Moreover, a total of 3.9 and 4.2 kt SCCPs and 3.8 and 4.1 kt MCCPs were emitted into China’s environment in 2018 and 2019, respectively. Although less MCCPs are released into the air relative to SCCPs, their level exceeds the emission of SCCPs into soil. Finally, detailed mass balance calculation indicates that, although emissions from the use of PVC products dominate SCCP and MCCP inputs into the air, emissions from the use of polyurethane foam adhesives are more closely related to input into surface waters for SCCPs and MCCPs. For input into soil, the main emission sources are the use of polyurethane foam adhesives (for SCCPs) and rubber products (for MCCPs). This study provides a preliminary overview of the distributions of SCCPs and MCCPs in products and insight into the mass balance of SCCPs and MCCPs from their production and use to emission in China. This assessment also provides an important foundation for better understanding the environmental risks and fates associated with SCCPs and MCCPs in China and around the world.