Hysteresis Index Research Articles

Adsorption and desorption of Cu, Zn, Pb, and Cd on surface sediments from a shallow lake, North China

The processes of adsorption and desorption of heavy metal ions on sediments is of great significance for water quality conservation. To investigate the adsorption and release characteristics of heavy metals on sediments from shallow lakes, an isothermal adsorption and desorption experiment of Cu2+, Zn2+, Pb2+, and Cd2+ on sediments from Baiyun Lake was carried out. Our results showed that sediments demonstrated a strong capacity of absorbing these heavy metal ions in a sorption system. The maximum sorption capacity for heavy metals on sediments followed the order Pb2+> Cd2+> Cu2+> Zn2+. The followed order of the maximum buffer capacities for heavy metals was Pb2+ > Cu2+ > Zn2+ > Cd2+. The Langmuir isotherms model can better fit the adsorption of Cu2+, whereas the Freundlich isotherm model for the adsorption of Zn2+, Pb2+, and Cd2+. In the maximum initial concentration treatment, Pb exhibited the highest desorption amount, followed by Cu and Zn, whereas the lowest amount of Cd was observed. The exponential and quadratic functions could describe the relationships of adsorption and desorption. In the maximum initial concentration treatment, the adsorption rates of these four heavy metals followed the order Pb2+ > Cd2+> Cu2+> Zn2+, whereas the desorption rates followed an opposite order. The hysteresis index (HI) values for Zn was smaller than 1, whereas the HI values for Cu and Cd were slightly larger than 1, suggesting slightly negative hysteresis processes. However, the HI value of Pb was larger than 1, indicating that Pb2+ was easily desorbed from sediments.

Enhancing quality of CsPbIBr<sub>2</sub> inorganic perovskite via cellulose acetate addition for high-performance perovskite solar cells

<sec>CsPbIBr<sub>2</sub> perovskite has been considered as a promising candidate for the light-harvesting material of perovskite solar cells (PSCs) due to its acceptable band gap and high stability. Nevertheless, the efficiency of CsPbIBr<sub>2</sub>-based PSC still lags behind that of its homologs and is far away from the theoretical value. This can be attributed to the poor quality of CsPbIBr<sub>2</sub> perovskite film. Therefore, it is highly desirable to improve the quality of CsPbIBr<sub>2</sub> perovskite film for enhancing the photovoltaic performance of CsPbIBr<sub>2</sub> PSCs. In this work, cellulose acetate (CA) is used as a polymer additive that is introduced into CsPbIBr<sub>2</sub> precursor solution for improving the quality of CsPbIBr<sub>2</sub> perovskite film via controlling crystallization process. The interaction between the C=O group of CA and Pb<sup>2+</sup> in the precursor solution and the enhanced viscosity of precursor solution induced by CA addition reduce the crystallization rate of CsPbIBr<sub>2</sub> perovskite. As a result, a compact CsPbIBr<sub>2</sub> perovskite film with high crystallinity, large grain size, and low density of defect is prepared. The remarkably improved quality of CsPbIBr<sub>2</sub> perovskite film upon CA addition can be attributed to the relatively slow crystallization rate. The slow crystallization rate allows the perovskite film to have enough time to form perfect perovskite crystal structure with large-size crystal grain and low density of defects. Furthermore, the oxygen functional groups of CA can passivate the undercoordinated Pb<sup>2+</sup>, which effectively suppresses the defects and traps induced by Pb<sup>2+</sup> in CsPbIBr<sub>2</sub> perovskite film.</sec> <sec>The stability of CsPbIBr<sub>2</sub> perovskite film is also greatly improved by CA addition. The added CA does not participate into the CsPbIBr<sub>2</sub> perovskite crystal but distributes at the grain boundaries and, or, interfaces area and forms a moisture barrier around perovskite grains, which obviously enhances the stability of CsPbIBr<sub>2</sub> perovskite film in the ambient air.</sec> <sec>The carbon-based CsPbIBr<sub>2</sub> perovskite solar cells with a configuration of FTO/TiO<sub>2</sub>/perovskite film/ carbon are fabricated by using the carbon layer as both the hole-transport layer and the back electrode. Under the illumination of 100 mW/cm<sup>2</sup>, the PSC based on CA-CsPbIBr<sub>2</sub> perovskite film delivers a high conversion efficiency of 7.52%, which is increased by 40% compared with the efficiency of the device based on the pure CsPbIBr<sub>2</sub> perovskite film. In addition, the PSC based on CA-CsPbIBr<sub>2</sub> perovskite film shows a hysteresis index (HI) of 7%, while the device based on pure CsPbIBr<sub>2</sub> film displays a higher HI of 22%. This result demonstrates that the CA addition can effectively suppress the hysteresis effect of inorganic PSCs. The stability of the PSC based on CA-CsPbIBr<sub>2</sub> perovskite film is investigated by tracking the variation of the efficiency with time in the ambient condition. The fabricated PSCs without any encapsulation are stored in the air. The photovoltaic performance is measured once a day. The efficiency of the PSC based on CA-CsPbIBr<sub>2</sub> perovskite remains more than 90% of its initial value after being stored in the air for 800 h, showing an excellent long-term stability. Therefore, this work provides a facile and effective method of improving the quality of CsPbIBr<sub>2</sub> perovskite films, which is expected to be helpful in developing high-efficiency and stable carbon-based inorganic PSCs.</sec>

An open‐source automated workflow to delineate storm events and evaluate concentration‐discharge relationships

AbstractThe advent of in situ optical sensors that can collect sub‐daily measurements of nutrients and turbidity in flowing water bodies has yielded comparatively much larger water quality data sets than were previously available. With these newly available data sets, there has been increased interest in studying event‐based concentration‐discharge (c‐Q) relationships to infer the sources and pathways of various watershed constituents during storms. With water quality data sets increasingly growing in size and scope, the need to automate the processing and analyses of such data has become apparent. However, consensus on storm event delineation methods as they pertain to c‐Q analysis is currently lacking, and methodological details, including parameter values, are sometimes unreported in the literature. Here, we present an open‐source workflow using the programming language R that automates the processing of sub‐daily c‐Q data to analyze event‐based hysteresis patterns. Briefly, the workflow accepts a time series of concentration and discharge data, extracts stormflow from streamflow, delineates storm events and then evaluates c‐Q relationships using widely applied metrics like the hysteresis index (HI) and the flushing index (FI). We applied the workflow to three watersheds in the mid‐Atlantic United States, including a 0.4‐km2 agricultural watershed, a 150‐km2 urbanizing watershed and a 29 940‐km2 mixed land use river basin. Sub‐daily sensor‐based nutrient concentrations and discharge data were collected in each watershed. Using the small agricultural watershed as an example, we demonstrate the step‐by‐step application of the workflow. We then present results from the larger watersheds as a means for comparison and to illustrate the flexibility of the code. We believe that this rapid approach to event‐based c‐Q analysis will allow scientists and practitioners more time to focus on interpreting results, and promote greater scientific reproducibility. Likewise, we conclude this Scientific Briefing with suggested future improvements to the workflow to increase the automation of data analyses and reproducibility.

Band alignment and carrier recombination roles on the open circuit voltage of ETL‐passivated perovskite photovoltaics

Titanium dioxide (TiO2) is the most often utilised electron transport layer (ETL) in perovskite solar cells (PSCs). Owing to its inherent limitations such as low electron mobility, inadmissible charge accumulation and recombination, many efforts have been devoted to the surface alteration of TiO2 to enhance the performance of PSCs. However, the key mechanism of this improvement is still unclear. Here, we study the mesoporous TiO2 (ms-TiO2) ETL passivated by Nb2O5 and Ta2O5. The ETL modified PSCs show increased open-circuit voltage (VOC). Power conversion efficiency (PCE) of 18.70%, 20.71%, and 20.96% were obtained for the devices with ms-TiO2, ms-TiO2/Nb2O5 and ms-TiO2/Ta2O5 ETL. Furthermore, the hysteresis index (HI) of pristine ms-TiO2 (HI = 4.91%) based devices are much higher than the Nb2O5 (HI = 2.75%) and Ta2O5 (HI = 1.19%) based devices. Our characterization results reveal that the carrier recombination is the main factor in increasing the VOC rather than energy band alignment once we passivate the surface of the ETL. This work is helpful in providing new insights into the surface modification of the mesoscopic ETL.

Surface-Anchored Acetylcholine Regulates Band-Edge States and Suppresses Ion Migration in a 21%-Efficient Quadruple-Cation Perovskite Solar Cell.

Although incorporating multiple halogen (bromine) anions and alkali (rubidium) cations can improve the open-circuit voltage (Voc ) of perovskite solar cells (PSCs), severe voltage loss and poor stability have remained pivotal limitations to their further commercialization. In this study, acetylcholine (ACh+ ) is anchored to the surface of a quadruple-cation perovskite to provide additional electron states near the valence band maximum of the perovskite surface, thereby enhancing the band alignment and minimizing the Voc loss significantly. Moreover, the quaternary ammonium and carbonyl units of ACh+ passivate the antisite and vacancy defects of the organic/inorganic hybrid perovskite. Because of strong interactions between ACh+ and the perovskite, the formation of lead clusters and the migration of halogen anions in the perovskite film are suppressed. As a result, the device prepared with ACh+ post-treatment delivers a power conversion efficiency (PCE) (21.56%) and a value of Voc (1.21V) that are much higher than those of the pristine device, along with a twofold decrease in the hysteresis index. After storage for 720 h in humid air, the device subjected to ACh+ treatment maintained 70% of its initial PCE. Thus, post-treatment with ACh+ appears to be a useful strategy for preparing efficient and stable PSCs.

Fluvial sediment export from pristine forested headwater catchments in the Congo Basin

Studies on sediment export from tropical forest watersheds are scarce. Of the assessments that do exist, most are of larger rivers or are model-based and lack validation with measured data. Understanding the mechanisms of sediment export dynamics in forested headwaters is important for assessing downstream effects and as a baseline for net impacts of land-use change. To that end, we quantified annual total suspended sediment (TSS) yields in forested headwater catchments of two major forest types in central Africa (tropical lowland forest and subtropical Miombo woodland) and analyzed turbidity-discharge hysteresis over one hydrological year. We measured TSS yields of 0.24 ± 0.09 t ha−1 yr−1 in the Miombo woodland and 0.25 ± 0.05 t ha−1 yr−1 in the lowland forest catchment. The Miombo woodland experienced similar TSS yields as the lowland forest despite a shorter, five-month, rainy season and lower annual precipitation. In the Miombo forest, sparser vegetation cover, seasonal fires that remove understory vegetation and high rainfall intensity during the rainy season therefore resulted in similar TSS yields. As a result of these differences in vegetation and rainfall, approximately 68% of TSS was exported during storm events in the Miombo woodland and 30% in the lowland forest. Both sites showed mainly clockwise hysteresis (positive hysteresis index) patterns of sediment export. In the Miombo woodland, the hysteresis index (i.e., the magnitude and direction of hysteresis) increased with the ongoing rainy season, indicating source limitation already after one month of rain. In the lowland forest, the predominant clockwise hysteresis was more likely caused by the increasing contribution of baseflow during the falling limb of an event, whereas during the rising limb there is a quick flushing of surface material available in the forest. These findings based on hysteresis analysis were further supported by C:N ratio and δ13C analyses of particulate organic matter (POM). POM C:N ratios increased and δ13C signatures decreased with increased discharge in the lowland forest, indicating the mobilization of topsoil sediments during rain events. In contrast, the Miombo exhibited no shifts in C:N ratios nor in the δ13C signature. Despite the pristine nature of these forests and their assumed negligible sediment yields, our results demonstrate that erosion is a significant loss process in tropical forests and call for future research to examine its role in forest functioning and biogeochemical cycling.

Seismic performance improvement of existing RCFs using external PT-PBSPC frame sub-structures: Experimental verification and numerical investigation

A novel external sub-structure is developed for the seismic performance improvement of existing frame buildings, namely, post-tensioned precast bolt-connected steel-plate reinforced concrete frame (PT-PBSPC frame). The mechanism and design of the sub-structure are introduced, and the pseudo-static experiments are conducted based on 4 scaled frames to verify the technique details (e.g., precast or monolithic, with or without prestress) as well as the macro responses (e.g., failure patterns, hysteresis curves, strain developments, self-centering capacities). The simulation model verified by the experiments is given, and the numerical elements and materials are compared to indicate the distinct varying tendency as well as the necessary detail selection. The parametric study is also performed to extend experimental work and to further discuss the different controlling parameters. Generally, the experiments prove the equivalent-performance to the monolithic specimen as well as the high-efficiency of the external precast-assembly operation. Superior functions of prestressed tendons are verified in view of hysteresis behaviors and indices analyses (e.g., peak capacity improvements and residual deformation reductions). The simulations supplement with the test data, recommend the main factors for the passive control design, and provide the model base for the further performance explorations and technique applications of the PT-PBSPC frame in the earthquake-prone areas.

Zr-Doped TiO2 Electron Transport Layer for Reduced Hysteresis and Highly Efficient Perovskite Solar Cells

Zr-doped TiO2 electron transport layer for reduced hysteresis and highly efficient perovskite solar cells Chirag Saharan, Pawan S Rana* Department of Physics, Deenbandhu Chhotu Ram University of Science and Technology, Murthal, Sonepat, India, 131039 drpawansrana.phy@dcrustm.orgLarge number of defects in compact TiO2 (c-TiO2) layer hinders the power conversion efficiency (PCE) of hybrid perovskite solar cells (PSCs). Metal doping in c-TiO2 layer has been recognized as a successful approach for boosting the PCE of PSCs. In this work, different amount of Zr is added in c-TiO2 layer and its impact on the photovoltaic properties of methylammonium lead iodide (MAPbI3)-based PSCs is studied. Incorporation of Zr enhanced the charge carrier collection at TiO2/perovskite interface as well as conductivity of TiO2 layer. It is observed that Zr-doping has reduced the dark current significantly by suppressing the leakage path. Consequently, the PSCs with optimal Zr-doping (10 vol%) displays open-circuit voltage (V OC) of 1.076 V, short-circuit current density (J SC) of 23.57 mA cm-2, and PCE of 18.16% under one-sun illumination. From our fundamental study, we confirm that Zr doping in TiO2 is highly beneficial to reduce the hysteresis index (HI) as low as 6.8% in comparison to pristine TiO2 with large HI of 17.9% and it reduces the trap-state density as well as non-geminated recombination losses. Together, our findings will pave the way for engineering the energy level of electron transport layer and fabrication of highly efficient PSCs. Key Words: Hybrid perovskite solar cells; Zr-doping; band alignment, trap-state density, non-geminated recombination losses

In Situ Management of Ions Migration to Control Hysteresis Effect for Planar Heterojunction Perovskite Solar Cells

AbstractAs one of the most promising photovoltaic materials, the efficiency of inorganic–organic hybrid halide perovskite solar cells (PSCs) has reached 25.5% in 2020. However, the stability and hysteresis remain primary challenges before it can become a commercial photovoltaic technology. Therefore, those issues have drawn significant attention for photovoltaic applications. In this work, a study of the PSCs hysteresis improvement is presented based on a combination of first‐principles simulations, scanning electron microscopy images, and time‐dependent photocurrent measurements. It indicates the hysteresis led by the ion migration and accumulation is mainly localized at the two interfaces: one is between electron transport layer and active layer, and the other is between active layer and hole transport layer. Considering the massive defects at the grain boundaries (GBs), they lower the potential barriers significantly. The defect density at GBs is therefore reduced via the in situ passivation of PbI2 crystals. The hysteresis index is decreased from 22.43% down to 1.04%, and results in an improvement in efficiency from 17.12% up to 20.10%. Following the understanding of defect‐induced hysteresis, an approach to improve the hysteresis is provided, which can be integrated into the fabrication process and widely applied to enhance the performance of PSCs.

Strong but reversible sorption on polar microplastics enhanced earthworm bioaccumulation of associated organic compounds

Sorption/desorption of two organic compounds (OCs), phenanthrene (PHE), and 1-nitronaphthalene (1-Nnap) on three polar and one nonpolar polypropylene (PP) microplastics (MPs) and earthworm bioaccumulation of MP associated PHE were systematically studied. Poly-butylene succinate (PBS) with the lowest glass transition temperature (Tg) showed the highest sorption toward PHE and 1-Nnap (Kd: 25,639 ± 276 and 1673 ± 28.8 L kg−1, respectively), while polylactic acid (PLA) with the highest Tg showed the least sorption (182 ± 5 and near 0), confirming that hydrophobic partition was the main driving force of sorption. However, polar interactions also contributed to the preferential sorption of 1-Nnap on polar poly-hydroxyalkanoates (PHA). Moreover, small particle size favored the sorption of MPs and simulated weathering enhanced sorption on MPs with medium/high Tg. As for desorption, slight hysteresis was observed in most cases with near-zero hysteresis index (HI), and PHE generally had higher HI than 1-Nnap. The simulated digestive solution could further promote the desorption of PHE. The PHE concentrations in earthworms with the presence of 5% PBS or PP MPs in soil were 1.50–2.35 or 1.59–1.75 times that of the control without MPs; and PBS MPs with the smallest particle size showed the greatest enhancement. The results of this study confirmed that polar MPs could strongly but reversibly sorb both polar and nonpolar OCs and hence promote the bioaccumulation of OCs to soil organisms.

Combining sediment fingerprinting and hydro-sedimentary monitoring to assess suspended sediment provenance in a mid-mountainous Mediterranean catchment

Soil erosion and sediment transport are controlled by complex factors promoting variable responses in catchment's erosion rates and sediment yields. To mitigate eventual negative effects derived from altered fluxes, integrated catchment management plans should assess the sediment cascade from upstream erosive processes, sediment mobilization through hillslopes and within the channel, up to downstream sediment yields. This study links hydro-sedimentary dynamics with sediment fingerprinting source ascription in a mid-mountainous Mediterranean catchment during five hydrological years (2013–2018). Soil colour parameters and fallout radionuclides were used as tracers to predict dominant suspended sediment sources using (i) a Bayesian mixing model (MixSIAR) and (ii) an End Member Mixing Analysis (EMMA). MixSIAR suggested that crops were the dominant source in most of the collected samples. EMMA showed similar results, clustering all except one sediment samples close to the crop and channel bank signatures. In addition, a quantitative hysteresis index was calculated and floods were clustered in function of their hydro-sedimentary characteristics. Despite different patterns were associated to each of the four identified clusters (e.g. different sediment loads and maximum suspended sediment concentrations), correlation between sediment origin and hydro-sedimentary variables was not significant due to the little seasonal variation in source type ascription.

Effect of watershed disturbance and river-tributary confluences on watershed sedimentation dynamics in the Western Allegheny Plateau

Harmful algal blooms (HABs) have increased in the Ohio River Basin over the past decade. Fine sediment dynamics are now recognized to play an important role in the proliferation and toxicity of HABs. As a result, the fate of sediment at confluences of tributaries and regulated river systems may be important zones for sediment retention and burial. The objective of this study was to improve understanding of watershed sediment loading dynamics and backwater inundation impacts on sedimentation within confluence watersheds. The study site selected for this work was the Fourpole Creek watershed in the Western Allegheny Plateau ecoregion of Appalachia, which is a mixed-use watershed with predominantly forested and urban landcover with a backwater floodplain wetland at the confluence with the Ohio River. Approximately 16 months of high-frequency (15-minute) turbidity data was used as a surrogate for total suspended solids at upstream and downstream nodes of the backwater confluence feature. Continuous sediment yield estimates suggested an annual sediment yield of 82 t/km2 and was found to be higher than sediment yields reported elsewhere in Appalachian watersheds without mining disturbances. A modified sediment rating curve using both seasonal and annual regression approaches were found to underpredict sediment yield by 29% and 80%, respectively. A hysteresis-based source unmixing method and hysteresis index were used to quantify sediment source and flow pathways during events and suggested high variability in sediment source contributions both seasonally and within-seasons, suggesting three likely sediment sources in the watershed including in-channel/gully erosion, resuspension of recently deposited sediment in the fluvial network, and erosion of subsurface macropores from forested uplands. Upstream-downstream monitoring of the confluence floodplain suggested 34% of the annual sediment inputs were retained during the continuously monitored 2019 calendar year. Our results suggest that confluence floodplains play an important role in intercepting and storing sediment inputs. Efforts to limit downstream sediment loads should ensure the function of confluence floodplains is maintained or enhanced when considering watershed management strategies in these landscapes.

Effect of SnO2 Colloidal Dispersion Solution Concentration on the Quality of Perovskite Layer of Solar Cells

The electron transport layer (ETL) is critical to carrier extraction for perovskite solar cells (PSCs). Moreover, the morphology and surface condition of the ETL could influence the topography of the perovskite layer. ZnO, TiO2, and SnO2 were widely investigated as ETL materials. However, TiO2 requires a sintering process under high temperature and ZnO has the trouble of chemical instability. SnO2 possesses the advantages of low-temperature fabrication and high conductivity, which is critical to the performance of PSCs prepared under low temperature. Here, we optimized the morphology and property of SnO2 by modulating the concentration of a SnO2 colloidal dispersion solution. When adjusting the concentration of SnO2 colloidal dispersion solution to 5 wt.% (in water), SnO2 film indicated better performance and the perovskite film has a large grain size and smooth surface. Based on high efficiency (16.82%), the device keeps a low hysteresis index (0.23).

Sediment transport dynamics in small agricultural catchments in a cold climate: A case study from Norway

Increased nutrient and soil losses from agricultural areas into water bodies constitute a global problem. Phosphorus is one of the main nutrients causing eutrophication in surface waters. In arable land, phosphorus losses are closely linked to sediment losses. Therefore, a better understanding of the sediment-runoff processes in agricultural areas is a key to reduce the eutrophication impacts and to implement mitigation measures. The objectives of this study were to identify dominant sediment runoff processes in cultivated grain-dominated catchments in a cold climate. We assessed continuous high-resolution turbidity data, temporal and spatial catchment properties and agricultural management data to describe and get a better understanding of the cause-relationship of sediment transfer in two small agricultural dominated catchments in southern Norway. The concentration-discharge pattern, index of connectivity and agricultural activities were considered with the wider aim to establish a link between field and catchment scale. The results showed that the dominant concentration-discharge pattern was a clockwise concentration-discharge (c-q) hysteresis in both catchments indicating that areas close to or in the stream gave the highest contribution to turbidity. The main driver for turbidity was discharge, though soil water storage capacity, rain intensity and former discharge events also played a role. Intensity of soil tillage and index of connectivity (likelihood of water and particles to be transported to the stream) impacted the c-q hysteresis index. Little vegetation cover and high intensity of soil tillage led to a high hysteresis index, which indicates a quick increase in turbidity following increased discharge. Other links between agricultural management and in stream data were difficult to interpret. The findings of this study provide information about discharge, field operations and vegetational status as drivers for turbidity and about the spatial distribution of sediment sources in two agricultural catchments in a cold climate. The understanding of sediment runoff processes is important, when implementing management actions to combat agricultural emissions to water most efficiently.

Decoupling the effects of defects on efficiency and stability through phosphonates in stable halide perovskite solar cells

Summary Understanding defects is of paramount importance for the development of stable halide perovskite solar cells (PSCs). However, isolating their distinctive effects on device efficiency and stability is currently a challenge. We report that adding the organic molecule 3-phosphonopropionic acid (H3pp) to the halide perovskite results in unchanged overall optoelectronic performance while having a tremendous effect on device stability. We obtained PSCs with ∼21% efficiency that retain ∼100% of the initial efficiency after 1,000 h at the maximum power point under simulated AM1.5G illumination. The strong interaction between the perovskite and the H3pp molecule through two types of hydrogen bonds (H…I and O…H) leads to shallow point defect passivation that has a significant effect on device stability but not on the non-radiative recombination and device efficiency. We expect that our work will have important implications for the current understanding and advancement of operational PSCs.

Comparison of adsorption behaviors of selected endocrine-disrupting compounds in soil.

Bisphenol-A (BPA), 17α-ethinylestradiol (EE2), and 4-nonylphenol (4NP) are endocrine-disrupting chemicals (EDCs) that are useful models for studying the potential fate and transport of EDCs in soil and water environments. Two alluvial soils with contrasting physicochemical properties were used as adsorbents for this study. The Zook soil material had more organic matter and clay than the sandy loam Hanlon soil material. Batch equilibrium experiments were performed to generate adsorption isotherms, to determine the adsorption parameters, and to assess desorption hysteresis. Adsorption of BPA to both soils followed an L-type isotherm, and 4NP adsorbed to both Hanlon and Zook soils exhibited S-shape isotherms. EE2 adsorbed to the Zook soil also followed an S-shaped isotherm, but EE2 adsorbed to the Hanlon soil showed an H-type isotherm. Overall, the Sips model fit the data well, with standard errors of prediction generally ≤6%. The adsorption affinity (KLF ) values were highest for 4NP, and BPA had the lowest hysteresis indices. The data suggest that BPA was most likely adsorbed by soil organic matter via hydrogen bonding involving its two phenolic groups. In contrast, isotherm shape, model affinity indices, lack of desorption, and molecular-scale characteristics led us to infer that 4NP was adsorbed largely by the retention of molecular clusters, perhaps in clay nanopores. Finally, the adsorption of EE2 exhibited different isotherm shapes for the two soils as well as intermediate affinity and desorption indices, suggesting that EE2 molecules could be retained both by soil organic matter and by clay.

Event and seasonal hydrologic connectivity patterns in an agricultural headwater catchment

Abstract. Connectivity of the hillslope and the stream is a non-stationary and non-linear phenomenon dependent on many controls. The objective of this study is to identify these controls by examining the spatial and temporal patterns of the similarity between shallow groundwater and soil moisture dynamics and streamflow dynamics in the Hydrological Open Air Laboratory (HOAL), a small (66 ha) agricultural headwater catchment in Lower Austria. We investigate the responses to 53 precipitation events and the seasonal dynamics of streamflow, groundwater and soil moisture over 2 years. The similarity, in terms of Spearman correlation coefficient, hysteresis index and peak-to-peak time, of groundwater to streamflow shows a clear spatial organization, which is best correlated with topographic position index, topographic wetness index and depth to the groundwater table. The similarity is greatest in the riparian zone and diminishes further away from the stream where the groundwater table is deeper. Soil moisture dynamics show high similarity to streamflow but no clear spatial pattern. This is reflected in a low correlation of the similarity with site characteristics. However, the similarity increases with increasing catchment wetness and rainfall duration. Groundwater connectivity to the stream on the seasonal scale is higher than that on the event scale, indicating that groundwater contributes more to the baseflow than to event runoff.

High-Efficiency, Low-Hysteresis Planar Perovskite Solar Cells by Inserting the NaBr Interlayer.

With great research potential, the perovskite solar cells (PSCs) have been well developed in recent years, but there are still some urgent issues like efficiency and hysteresis defects that severely limit their commercialization. Interface modification is a significant measure to reduce defects and promote performance. In the article, an easy and effective strategy of modifying the electron transport layer (ETL) with NaBr is proposed to improve efficiency and reduce hysteresis. The charge carrier dynamics can be greatly optimized by diffusing NaBr on the ETL. The efficiency of the NaBr coated device can achieve 21.16%, which is extremely higher than the control one and shows low hysteresis behavior with a hysteresis index reduced from 0.135 to 0.025. The results indicate that the NaBr modification provides a novel strategy for preparing PSCs with high efficiency and low hysteresis.

Understanding the CO2 adsorption hysteresis under low pressure: An example from the Antrim Shale in the Michigan Basin: Preliminary observations

The gas adsorption hysteresis effects have strong implications for the characterization of the micropore structure, which is one of the most important properties of shales. This study describes one of the first investigations of low-pressure CO2 adsorption hysteresis illustrated on the Antrim Shale samples, Michigan Basin. A total of 23 samples were characterized by using a combination of X-Ray diffraction (XRD), Rock-Eval pyrolysis, scanning electron microscope (SEM) imaging and CO2 adsorption. The partial least linear regression (PLS) was employed to study the influence of rock composition on the micropore structures and hysteresis index (HI). The results showed that the micropore parameters (surface area and volume) are positively correlated to the amount of organic matter and clay minerals, and have a negative correlation to non-clay minerals. In the Antrim Shale samples, the CO2 adsorption hysteresis seen under low pressure appears to be controlled mainly by the pore network effect caused by the presence of ink-bottle shaped pores, rather than by the swelling of clays and organic matter.

Effects of supergene geochemical processes on desorption and bioavailability of polycyclic aromatic hydrocarbons in soil of karst area

ABSTRACT Supergene geochemical processes (SGPs) occur ubiquitously in the Earth´s surface, but their effects on the fate and bioavailability of polycyclic aromatic hydrocarbons (PAHs) in soil remain unclear. Study selected phenanthrene and pyrene as representative PAHs and yellow soil (YS) and limestone soil (LS) of karst area in southwest China, to investigate the effects of SGPs on the desorption and bioavailability of PAHs. Two soils were subjected to repeated freeze-thawing and long-term storage for SGPs. The hysteresis index values of pollutants increased with increase cycles of freeze-thawing and storage time. Under the SGPs, the phenanthrene fast desorption fraction of YS and LS decreased by 22.01% and 24.79%, respectively, and that of pyrene were by 23.81% and 28.12%, respectively. The desorption fraction of 24 hours was a better proxy of the fraction of bioavailability than that of 6 hours. The desorption rate of PAHs was negatively correlated with the hydrophobicity of PAHs.