A novel reusable, high-compressible cotton regenerated cellulose/chitosan composite aerogel (RC/CSCA) was prepared using N-methylmorpholine-N-oxide (NMMO) as the green cellulose solvent, and ...glutaraldehyde (GA) as the crosslinking agent. The regenerated cellulose obtained from cotton pulp could chemically crosslink with chitosan and GA, to form a stable 3D porous structure. The GA played an essential role in preventing shrinkage and preserving the deformation recovery ability of RC/CSCA. Due to the ultralow density (13.92 mg/cm3), thermal stability (above 300 °C), and high porosity (97.36 %), the positively charged RC/CSCA can be used as a novel biocomposite adsorbent for effective and selective removal of toxic anionic dyes from wastewater, showing an excellent adsorption capacity, environmental adaptability, and recyclability. The maximal adsorption capacity and removal efficiency of RC/CSCA for methyl orange (MO) was 742.68 mg/g and 95.83 %.
Display omitted
•A novel porous regenerated cellulose/chitosan composite aerogel was prepared.•The stability of composite aerogel was enhanced by the potentiation of chemical crosslinking.•The aerogel shows selective adsorption of anionic dyes when coexisting with cationic dyes.•FTIR revealed the selective adsorption mechanism mainly via electrostatic interaction.
NH3, SO2, NOx and the inorganic ions of PM2.5 in winter 2009, 2014 and 2016 were examined to investigate the change in NH3 and aerosol chemistry in Beijing, China. NH3 concentrations showed an ...increase by 59% on average, in contrast to the decrease of SO2 by 63% from winter 2009 to 2016. The mean mass ratio of NH3/NHx was 0.83 ± 0.12 in 2016, which is higher than those obtained in 2009 and 2014, implying more NHx remaining as free NH3 in 2016 winter. Our findings suggest that vehicles exhaust emissions are an important NH3 source in urban central atmosphere of Beijing in winter. Despite the observed NOx presenting declining trends from 2014 to 2016, nitrate concentrations even exhibited a significant increasing trend, which may be largely attributable to high NH3 levels. An in-depth analysis of measured NH3 and aerosol species in a heavy pollution episode in December 2016, combined with the acidity predicted by ISORROPIA II model demonstrated abundant NH3 most of the time in air, where NH3 is not only a precursor for NH4+ but also effect the neutralization of SO42− and NO3− in PM2.5. With high RH and low photochemical activity, elevated NO3− concentration was attributed to an enhanced heterogeneous conversion of NOx to HNO3 to form NH4NO3 in pollution transport stage. The decrease in NOx from high level and the increase in NH3, with peaks of SO42− occurring were observed in pollution cumulative stage. The aqueous-phase oxidation of SO2 by NO2 to sulfate might play an important role with high pH values. Our results suggested that the simultaneous control of NH3 emissions in conjunction with SO2 and NOx emissions would be more effective in reducing particulate matter PM2.5 formation.
Display omitted
•NH3 and the chemistry components of PM2.5 change significantly from 2009 to 2016.•Vehicles exhaust is an important contributor to NH3 in central Beijing in winter.•Increasing nitrate trend may be largely attributable to high NH3 levels.
Plant height is an important and valuable agronomic trait associated with yield and resistance to abiotic and biotic stresses. Dwarfism has positive effects on plant development and field management, ...especially for tall monocotyledon banana (
spp.). However, several key genes and their regulation mechanism of controlling plant height during banana development are unclear. In the present study, the popular cultivar 'Brazilian banana' ('BX') and its dwarf mutant ('RK') were selected to identify plant height-related genes by comparing the phenotypic and transcriptomic data. Banana seedlings with 3-4 leaves were planted in the greenhouse and field. We found that the third and fourth weeks are the key period of plant height development of the selected cultivars. A total of 4563 and 10507 differentially expressed genes (DEGs) were identified in the third and fourth weeks, respectively. Twenty modules were produced by the weighted gene co-expression network analysis (WGCNA). Eight modules were positively correlated with the plant height, and twelve other modules were negatively correlated. Combining with the analysis of DEGs and WGCNA, 13 genes in the signaling pathway of gibberellic acid (GA) and 7 genes in the signaling pathway of indole acetic acid (IAA) were identified. Hub genes related to plant height development were obtained in light of the significantly different expression levels (|log2FC| ≥ 1) at the critical stages. Moreover, GA3 treatment significantly induced the transcription expressions of the selected candidate genes, suggesting that GA signaling could play a key role in plant height development of banana. It provides an important gene resource for the regulation mechanism of banana plant development and assisted breeding of ideal plant architecture.
This study investigated the English writing anxiety experienced by preservice English as second/foreign language teachers in Hong Kong, and its impact on their written corrective feedback (WCF). A ...total of 34 highly proficient preservice teachers responded to the Second Language Writing Anxiety Inventory (Cheng, 2004), which measured writing anxiety in three dimensions (i.e., cognitive, somatic and avoidance anxiety). Ten were selected to provide WCF to a sample student writing and receive an individual interview immediately afterwards. Over half of the 34 participants were found suffering from moderate or high levels of writing anxiety, especially in the cognitive dimension. Compared to their less apprehensive peers who adopted more indirect feedback, highly anxious student teachers had a clear preference to direct and comprehensive feedback. Their WCF practices were found affected by five factors, including their conception of English writing, concerns of teacher professional credibility and work ethics, concerns of student cognition and motivation, confidence in students’ ability, and their feedback experience as students and student teacher during teaching practicum. These factors were synthesized into a grounded-theory model of four internal forces that drive student teachers towards either a focus-on-form, direct, comprehensive approach to WCF or a broad-based, indirect and selective approach. Suggestions were made for further research.
Here, we proposed a universal approach to solve a seesaw relationship between thermal effect control and conversion efficiency in strong exothermic acetylene hydrogenation by constructing Pd‐based ...single atom alloy (SAA), in which Cu was chosen as host atom and heat transfer agent. Lower desorption energy of *C2H4 intermediate on isolated Pd atoms greatly improved ethylene selectivity. Notably, this excellent performance was well maintained, even at extremely low space velocity, implying the thermal effect was effectively controlled. On one hand, the heat generation rate over single active site was largely decreased. On another hand, host Cu atoms with proper continuity degree endowed the SAA with attractive lattice heat capacity and phonon scattering rate, which ensured the instant heat transfer from Pd atoms to the surroundings. The optimized performance (conversion 90.7% and selectivity 95.8%) was stably operated for 270 h under GHSV = 2400 h−1.
Cellulose-based carbon aerogels as biodegradable and renewable biomass materials have presented potential applications in oil/water separation. Herein, a novel carbon aerogel composed of natural ...microfibrils/regenerated cellulose (NM/RCA) was directly prepared by economical hardwood pulp as raw material using a novel co-solvent composed of deep eutectic solvent (DES) and N-methyl morpholine-N-oxide monohydrate (NMMO·H2O). In addition, the morphology and structure of the filiform natural microfibers could be remained after carbonized at 400 ℃, which resulted in a low density (8–10 mg cm−3), high specific surface area (768.89 m2 g−1) and high sorption capability. In addition, the aerogel exhibited high compressibility, outstanding elasticity, excellent fatigue resistance, and recyclability (80.5% height recovery after repeating 100 cycles at the strain of 80%). Due to the morphology and composition of the carbonized microfiber surface, the superhydrophobic materials with a water contact angle of 151.5°, could sorb various oils and organic solvents with 65–133 times its own weight and maintain 91.9% sorption capacity after 25 cycles. In addition, the aerogels could achieve the continuous separation of carbon tetrachloride (CCl4) from water with a high flux rate of 11,718.8 L m−2 h−1. Therefore, our prepared NM/RCA aerogels are anticipated to have broad potential applications in oil purification and contaminant remediation.
Display omitted
•Natural microfibrils/regenerated cellulose carbon aerogels are fabricated.•The natural cellulose fibers are fixed by lamellar regenerated cellulose.•The excellent sorption capacity of NM/RCA for oil is up to 65.4–131 g g−1.•NM/RCA shows high separation efficiency of oil/water mixture ≥ 99.94%.
In this study, a corrugated constrained groove pressing (CCGP) technology based on a semicircle groove was proposed, improving the uniformity of strain accumulation in deformed metal sheets through ...staggered groove pressing. First, 6061-O aluminum alloy was processed at room temperature via conventional CCGP (Conv-CCGP) and 90° cross CCGP (Cross-CCGP). The effects of strain route and deformation pass on the microstructure evolution of the CCGPed alloy were investigated and correlated with mechanical properties. Changes in the mechanical properties of the CCGPed alloy at room temperature measured via tensile in different directions and hardness tests were studied. Results showed that the strength and hardness of the CCGPed sheet in both routes were considerably improved, but ductility was decreased. Cross-CCGP can effectively alleviate the anisotropy of the deformed sheet and achieve optimal strength in roll direction (RD) and transverse direction (TD) at two passes. Yield strength (YS) and ultimate tensile strength (UTS) along RD were increased by 190.2% and 15.5% relative to the initial alloy, reaching 119 MPa and 134 MPa, respectively. Along TD, YS and UTS were increased by 255.0% and 36.0%, reaching 142 MPa and 151 MPa, respectively. Characterization techniques, including electron backscatter diffraction and high-resolution transmission electron microscopy, were used to establish comprehensive models of dynamic recovery-based substructure evolution and dynamic recrystallization-dominated grain refinement. Meanwhile, the integrated microstructural changes and theoretical calculations identified dislocation strengthening and local grain refinement as the major contributors to the strengthening of the CCGPed alloy. In addition, tensile fracture surface analysis showed that the CCGPed alloy still underwent plastic fracture, but the fracture mode shifted from tension fracture into shear fracture.
•A CCGP technology to uniform strain by staggered groove pressing was proposed.•CCGPed sheets show significant improvement in microhardness, YS and UTS.•Combined models of substructure evolution and grain refinement were developed.•Dislocations and local grain refinement on enhancement of strength were discussed.•The tensile fracture mechanisms of the CCGPed alloy were analyzed.
There are few studies on lead's effect on bone mineral density (BMD) in childhood. In this study, we examined the association between lead exposure and BMD among 13,951 children and adolescents aged ...8-19 years from NHANES 1999-2006 and 2011-2018. The whole blood lead levels (BLLs) were used as lead exposure biomarkers, and total BMD, subtotal BMD, lumbar spine BMD and limb BMD were used as outcome variables. The survey weighted multivariable generalized additive models (GAMs) with smoothing terms were used to explore the association between blood lead levels and BMDs, adjusted for age, sex, race/ethnicity, height, weight, family-income-to-poverty ratio and blood cadmium. Subgroup analyses stratified by sex and bony sites were further performed. We found an N-shaped curve association between BLLs and total BMD, subtotal BMD and limb BMD for males and females, whereas the association between BLLs and lumbar spine BMD was only significantly negative for females. The findings suggested that lead exposure had different effects on BMD of different bony sites (highly cortical or trabecular regions) in childhood and adolescence and had different effects on the same bone among different ages population and/or at different levels.
PDF
