Research progress in self-oscillating polymer brushes.

Polymer brushes possess unique changes in physical and chemical properties when they are exposed to external stimuli and have a wide range of applications. Self-oscillating polymers are anchored on surfaces of certain materials and are coupled with some self-oscillating reactions (with the Belousov-Zhabotinsky (BZ) reaction as an example) to form self-oscillating polymer brushes. As an independent field of stimulus response functional surface research, the development of new intelligent bionic materials has good potential. This article reviews the oscillation mechanisms of self-oscillating polymer brushes and their classifications. First, the oscillation mechanisms of self-oscillating polymer brushes are introduced. Second, the research progress in self-oscillating polymers is discussed in terms of the type of self-oscillation reactions. Finally, possible future developments of self-oscillating polymer brushes are prospected.

Electrooxidation of Formamidine Disulfide Simultaneously Investigated by On-Line High Performance Liquid Chromatography and Cyclic Voltammetry.

The electro-oxidation of formamidine disulfide, an important sulfur-containing compound, was simultaneously investigated with on-line high-performance liquid chromatography and cyclic voltammetry. Using a home-made microporous sampler located at the electrode interface, the solution on the electrode surface was in situ sampled and analyzed. The electrochemical scanning was synchronously performed, which allowed the electro-oxidation products to be detected at a given potential. The main products on the surface of platinum electrode were found to be thiourea, formamidine sulfinic acid, cyanamide, and elemental sulfur. Forced convection arising from the sampling played an important role in the electrochemical oxidation. The extraction of electrode surface solution promoted the renewal of reactant and its intermediates, which induced the change of cyclic voltammetry curve. The forced convection also contributed to the redox peak current of the species on the cyclic voltammetry curves through the change of concentration of reactant and its intermediates. This technique can help to explore the reaction mechanism of complex electrochemical reactions.

Efficient immobilization of toxic heavy metals in multi-contaminated agricultural soils by amino-functionalized hydrochar: Performance, plant responses and immobilization mechanisms.

A novel amino-functionalized hydrochar material (referred to NH2-HCs) was prepared and used as the soil amendment to immobilize multi-contaminated soils for the first time. The results showed that the application of NH2-HCs significantly improved (P < 0.05) soil properties (i.e., pH value, cation exchange capacity and organic content). By introduction of NH2-HCs, the contaminated soil showed the highest value of 96.2%, 52.2% and 15.5% reductions in Cu, Pb and Cd bioavailable concentrations and the leaching toxicity of Cu, Pb and Cd were remarkably reduced by 98.1%, 31.3% and 30.4%, respectively. Most of exchangeable Cu, Pb and Cd reduced were transformed into its less available forms of oxidizable and residual fractions. Potential ecological risk assessment indicated that the element Cd accounted for the most of total risks in NH2-HCs amended soils. The mechanism study indicated that surface complexation, chemical chelating and cation-pi interaction of NH2-HCs played a vital role in the immobilization of heavy metals. Pot experiments further verified that the application of NH2-HCs significantly improved plant growth and reduced metal accumulations. The present study offered a novel approach to prepare amino-functionalized hydrochars with great potential as the green and alternative amendments for efficiently immobilizing heavy metals in multi-contaminated soil.

Pyrolysis kinetics and thermodynamic parameters of the hydrochars derived from co-hydrothermal carbonization of sawdust and sewage sludge using thermogravimetric analysis.

The thermal behavior of the hydrochars from co-hydrothermal carbonization (co-HTC) of sawdust (SD) and sewage sludge (SS) was investigated using thermogravimetric analysis. The comprehensive devolatilization index indicated that the devolatilization performance of SS was decreased by HTC, while it was significantly improved 7.38-23.69 times by co-HTC. The kinetic analysis showed that HTC of SS decreased the average activation energy from 308.96 and 314.78 kJ mol-1 to 220.86 and 221.27 kJ mol-1 by Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS), respectively, while it was increased from 182.37 to 207.06 kJ mol-1 and from 181.06 to 207.05 kJ mol-1 with the increasing proportion of SD from 25% to 75% during co-HTC, respectively. The thermodynamic parameters revealed that pyrolysis reactivity of the hydrochar derived from SD was improved by co-HTC of SD and SS. Kinetic and thermodynamic findings were useful for the design of pyrolysis process using hydrochar as solid fuel.

Light-Modulated Intermittent Wave Groups in a Diffusively Fed Reactive Gel.

Inspired by the biological growth that takes place in time-varying external fields such as light or temperature, we design an open reaction-diffusion system in order to investigate growth dynamics. The system is composed of the Belousov-Zhabotinsky (BZ) oscillatory reaction coupled with a copolymer gel consisting of NIPAAm and a photosensitive ruthenium catalyst. When subject to a unidirectional flow of the BZ reactants, the system displays groups of chemical waves whose structure depends upon the period and amplitude of illumination. Simulations of a modified six-variable Oregonator model exhibit all the complex wave groups found in our experiments. Studying this growth structure may aid in understanding the influence of periodic environmental variation on complex growth processes in living systems.

Experimental, numerical, and mechanistic analysis of the nonmonotonic relationship between oscillatory frequency and photointensity for the photosensitive Belousov-Zhabotinsky oscillator.

The oscillation frequency of a nonlinear reaction system acts as a key factor for interaction and superposition of spatiotemporal patterns. To control and design spatiotemporal patterns in oscillatory media, it is important to establish the dominant frequency-related mechanism and the effects of external forces and species concentrations on oscillatory frequency. In the Ru(bipy)3(2+)-catalyzed Belousov-Zhabotinsky oscillator, a nonmonotonic relationship exists between light intensity and oscillatory frequency (I-F relationship), which is composed of fast photopromotion and slow photoinhibition regions in the oscillation frequency curve. In this work, we identify the essential mechanistic step of the I-F relationship: the previously proposed photoreaction Ru(II)* + Ru(II) + BrO3(-) + 3H(+) → HBrO2 + 2Ru(III) + H2O, which has both effects of frequency-shortening and frequency-lengthening. The concentrations of species can shift the light intensity that produces the maximum frequency, which we simulate and explain with a mechanistic model. This result will benefit studies of pattern formation and biomimetic movement of oscillating polymer gels.