Non-crosslinked systems modulate the gel behavior and structural properties of chitosan/silica composite aerogels.

The aim of this study was to achieve rapid gelation of chitosan (CS) and silica (SA) without crosslinking agent, the relationship between process parameters and the composite aerogels properties were also explored. By varying the composition ratio of the system (from SA:CS = 1:1 to 5:1), the system gelation time was reduced by >12 times, and the drying shrinkage of the composite aerogel reached a minimum of 7.6 %. During the two recombination processes, chitosan rapidly formed aqueous colloid secondary structure under the influence of ethanol. This phenomenon reduced the stability of the system and allowed silica to form a two-phase composite hydrogel. Because the network gap between the fibers was used as a limiting medium for gel growth. In addition, the chitosan/silica composite aerogels exhibited a mesoporous structure with low density (0.1144 g/cm3), and the thermal conductivity was 0.028 W/(m·K) at 30 °C. The trimethylchlorosilane made the composite aerogel have good hydrophobicity with water contact angle as 134.7°, and the adsorption capacity of carbon tetrachloride could reach >10 times of its own weight. This study provides an eco-friendly and high-efficiency method for preparing aerogels, which has potential applications in the fields of thermal insulation, oil-water separation, etc.

Self-standing 2D/2D Co3O4@FeOOH nanosheet arrays as promising catalysts for the oxygen evolution reaction.

The rational design of a highly efficient oxygen evolution reaction (OER) is crucial for the practical applications of water electrolysis. Herein, a hybrid Co3O4@FeOOH/NF electrode was fabricated by loading FeOOH sheets on the surface of Co3O4 nanosheet arrays via a newly developed chemical deposition protocol. The decoration of FeOOH on Co3O4 nanosheet arrays not only endows a strong electronic interaction between the two components but also offers sufficient active sites for the OER process. Benefitting from these advantages, Co3O4@FeOOH/NF exhibited outstanding OER activity in terms of a low overpotential of 209 mV at 10 mA cm-2 and a low Tafel slope of 48.9 mV dec-1. Moreover, nearly steady state operation current and negligible change in the phase and morphology of the catalyst also indicate remarkable stability. This work may provide an important guide for the design of high-performance electrocatalysts for energy conversion applications.

Ultra-light polylactic acid/combination composite foam: A fully biodegradable flame retardant material.

In this study, low-density polylactic acid (PLA) flame retardant foams were prepared using lignin fiber (LF), ammonium polyphosphate (APP), resorcinol bis(diphenyl phosphate) (RDP) and SiO2 aerogel. LF, RDP and SiO2 aerogel alone did not improved the flame retardancy of PLA composites; however, APP alone required a higher addition of amount to achieve a better flame retardancy. The synergistic effect between the four can improve the flame retardancy of PLA at a lower addition level. The intumescent flame retardant system composed of LF/APP/RDP/SiO2 aerogel can not only form a dense carbon layer on the surface of the material when burning to improve the flame retardant performance, but also improve the thermal stability of PLA, increase the degradation temperature and reduce the thermal weight loss rate. The final PLA flame retardant foam (density: 0.022 g/cm3) prepared by supercritical foaming can reach V-0 rating in UL-94 vertical combustion test, and the limiting oxygen index (LOI) can reach 30.5 %.

Suspended particle effects on ClO2/ultraviolet light combined disinfection of effluent.

The concentration of suspended solids of effluent often varies in a wide range, therefore the dose of ultraviolet light (UV) in disinfection process needs to be adjusted to meet the disinfection criterion at a high frequency, and the desired disinfection effect is difficult to be ensured. The particles size and particle-associated fecal coliform (F.C.) contribution, and their influence on UV disinfection were investigated when ClO2 and UV combined disinfection process was used. The results showed that suspended solids content had a major impact on UV disinfection efficiency, especially the large particle size fraction. Particles (D>10 microm) associated F. C. were difficult to be disinfected and were the main part of the tailings of F.C. inactivation curve. Pre-ClO2 oxidation could reduce the number of particles in effluent, and make large particles decrease to small ones. Therefore, the influence of particles on UV disinfection could be reduced after pre-ClO2 oxidation, and the resistance ability to particle loadings of combined process was enhanced. Moreover, the combined process has a lot of advantages, such as low toxicity, low operational/maintenance costs; it is also convenient to be established in the existing wastewater plant or the new planned one.

Spatially heterogeneous invasion of toxic plant mediated by herbivory.

Spatially homogeneous (ODE) and reaction-diffusion models for plant-herbivore interactions with toxin-determined functional response are analyzed. The models include two plant species that have different levels of toxicity. The plant species with a higher level of toxicity is assumed to be less preferred by the herbivore and to have a relatively lower intrinsic growth rate than the less toxic plant species. Two of the equilibrium points of the system representing significant ecological interests are E1, in which only the less toxic plant is present, and E2, in which the more toxic plant and herbivore coexist while the less toxic plant has gone to extinction. Under certain conditions it is shown that, for the spatially homogeneous system all solutions will converge to the equilibrium E2, whereas for the reaction-diffusion model there exist traveling wave solutions connecting E1 and E2.

Dynamics of an SIS reaction-diffusion epidemic model for disease transmission.

Recently an SIS epidemic reaction-diffusion model with Neumann (or no-flux) boundary condition has been proposed and studied by several authors to understand the dynamics of disease transmission in a spatially heterogeneous environment in which the individuals are subject to a random movement. Many important and interesting properties have been obtained: such as the role of diffusion coefficients in defining the reproductive number; the global stability of disease-free equilibrium; the existence and uniqueness of a positive endemic steady; global stability of endemic steady for some particular cases; and the asymptotical profiles of the endemic steady states as the diffusion coefficient for susceptible individuals is sufficiently small. In this research we will study two modified SIS diffusion models with the Dirichlet boundary condition that reflects a hostile environment in the boundary. The reproductive number is defined which plays an essential role in determining whether the disease will extinct or persist. We have showed that the disease will die out when the reproductive number is less than one and that the endemic equilibrium occurs when the reproductive number is exceeds one. Partial result on the global stability of the endemic equilibrium is also obtained.

Theoretical investigation on the reaction of adhesion unit dopa in mussel with electrolyzing seawater.

Adhesive proteins secreted by the marine mussel could bind strongly to all kinds of surfaces, for instance, ship hulls and petroleum pipelines. Studies indicated that there was an unusual amino acid 3,4-dihydroxy-l-phenylanine (dopa), which was the crucial super adhesive unit in the proteins. The technology of electrolyzing seawater was employed to generate HOCl solution to hinder the adhesion. However, the detailed anti-fouling mechanism of HOCl solution remained unknown to be fully explained. Herein, we theoretically reported a study of single molecular (dopa) reaction under the HOCl solution environment, which would be helpful to reveal the anti-fouling mechanism through electrolyzing seawater. By using the density functional theory (DFT) quantum mechanics procedure, we theoretically studied the reaction mechanism of the adhesive unit dopa in mussel with electrolyzing seawater. Two possible pathways (1 and 2) were obtained (Fig. 6). The transition state for each pathway was determined, the intrinsic reaction coordinate (IRC) was analyzed and the mechanism had been confirmed. The calculations indicated dopa tended to have electrophonic attacking substitution reaction to generate 3-chlorine-4,5-dihydroxyphenylalanine (dopa-Cl) with different pathways, which hindered the formulation of conjuncted dopa-dopa and thus the stickiness among mussel adhesive proteins reduced. The transition states computation showed that pathway (1) had one transition state (TS1-1) with an activation energy of 102.22 kJ mol(-1), while pathway (2) had two transition states (TS2-1, TS2-2) with activation energies of 191.98 kJ mol(-1) and 42.00 kJ mol(-1) respectively and one intermediate (IM2-1). Rate constant value of pathway (1) was much bigger than that of pathway (2) regardless of high or low temperature, which meant that in the reaction process, pathway (1) was the favorable reaction step; but as the temperature rose, the competitiveness of pathway (2) gradually increased. After the theoretical calculation, we found that it was Cl(+) played an important and direct role in the dopa's modification.

Weakly coupled traveling waves for a model of growth and competition in a flow reactor.

For a reaction-diffusion model of microbial flow reactor with two competing populations, we show the coexistence of weakly coupled traveling wave solutions in the sense that one organism undergoes a population growth while another organism remains in a very low population density in the first half interval of the space line; the population densities then exchange the position in the next half interval. This type of traveling wave can occur only if the input nutrient slightly exceeds the maximum carrying capacity for these two populations. This means, lacking an adequate nutrient, two competing organisms will manage to survive in a more economical way.