SIMULATION OF MINIMUM ICE UNIT AND ITS EFFECT ON WATER PROPERTIES

The formation of a minimum ice unit (MIU) and ice crystal is simulated. The simulation indicates that an MIU is made up of 10 H2O molecules, and the MIU shows a four-hexagon cage structure. On the basis of simulation, we can calculate that 1 mol ice crystal contains 2 mol hydrogen bonds, and 16.67% hydrogen bonds should be broken during water fusion at 0°C. A total of 12.5% hydrogen bonds should be broken when 1 mol water is heated from 0°C to 100°C, and 70.83% hydrogen bonds should be broken when 1 mol water is vaporized into steam at 100°C. A total of 8.33% volume contract during water fusion at 0°C can also be calculated according to the MIU simulation in this paper.Minimum ice unit (MIU), simulation, hydrogen bonds, H2O molecules, water properties

Insight the effect of crystallinity of natural graphite on the electrochemical performance of reduced graphene oxide

The effects of the crystallinity of natural graphites on the electrochemical performance of the resulting reduced graphene oxides (RGOs) were systematically researched. Electrochemical measurements were first carried out to characterize the electrochemical performances of the RGOs. The results showed that the RGO prepared from flaky graphite (FG) hold the best electrochemical performance with the greatest specific capacitance, the smallest charge transfer resistance (Rct), the best capacitive behavior, and the lowest ions diffusion resistance in comparison with the other RGOs synthesized from natural lumpy graphite (LG) and amorphous graphite (AG) under the same conditions. Furthermore, XPS and Raman analysis were conducted to scientifically explain the phenomena. The results illustrated that RGO prepared from FG (FRGO) hold the highest reduction degree, the greatest size of the in-plane sp2 domains, and the fewest defects, leading FRGO to hold the best electrochemical performance. The crystallinity of natural graphite affected the microstructure of the resulting RGO by influencing its oxidation, exfoliation and chemical reduction process, and then indirectly controlled the electrochemical properties of the RGO. Keywords: Reduced graphene oxide, Natural graphite, Crystallinity, Electrochemical performanc

Correlation of Montmorillonite Sheet Thickness and Flame Retardant Behavior of a Chitosan–Montmorillonite Nanosheet Membrane Assembled on Flexible Polyurethane Foam

Polymer⁻clay membranes constructed via the layer-by-layer (LbL) assembly, with a nanobrick wall structure, are known to exhibit high flame retardancy. In this work, chitosan⁻montmorillonite nanosheet (CH⁻MMTNS) membranes with different thickness of MMTNS were constructed to suppress the flammability of flexible polyurethane (FPU) foam. It was found that a thinner MMTNS membrane was more efficient in terms of reducing the flammability of the FPU foam. This was because such MMTNS membrane could deposit cheek by jowl and form a dense CH⁻MMTNS membrane on the foam surface, thus greatly limiting the translation of heat, oxygen, and volatile gases. In contrast, a thicker MMTNS constructed a fragmentary CH⁻MMTNS membrane on the coated foam surface, due to its greater gravity and weaker electrostatic attraction of chitosan; thus, the flame retardancy of a thick MMTNS membrane was lower. Moreover, the finding of different deposition behaviors of MMTNS membranes with different thickness may suggest improvements for the application of clay with the LbL assembly technology

Driving force for the swelling of montmorillonite as affected by surface charge and exchangeable cations: A molecular dynamic study

Swelling of montmorillonite (MMT) is a nonnegligible factor in many industrial processes owing to its great ability to absorb water in interlayer space. It is not easy to determine whether the exchangeable cations or the MMT layers interacts much stronger with water molecules to provide the dominant driving force for the swelling of MMT. In this work, driving force for the swelling of montmorillonite as affected by surface charge and exchangeable cations has been investigated through molecular dynamics simulations (MDs). The adsorption energy between water molecules and MMT layers and between interlayer cations and water molecules was calculated to qualitatively characterize the driving force for the swelling of MMT, and higher negative adsorption energy means greater driving force. It is found that the adsorption energy between interlayer cations and water molecules are far higher than that between MMT layers and water molecules. Thus, it is the exchangeable cations that provide the dominant driving force for MMT to swell. Besides, it is observed that interlayer cations with stronger hydration ability (Mg > Ca > Na > K) have more negative adsorption energy to water molecules, which indicates that the stronger the hydration ability of exchangeable cations the greater contribution they make to the total driving force for the swelling of MMT. Keywords: Swelling, Montmorillonite, Surface charge, Exchangeable cations, Molecular dynamic simulation

Increasing the Fine Flaky Graphite Recovery in Flotation via a Combined MultipleTreatments Technique of Middlings

As the residual flaky graphite ores become miscellaneous and fine, a single treatment technique for the middlings from the flotation process of graphite ore cannot efficiently recover the valuable graphite in the multistage grinding-flotation technology. In the study, the existence form of graphite and relationship of graphite with the associated gangue minerals were estimated by optical microscope analysis. The results indicated that the fine flaky graphite particles embedded with gangue minerals like a honeycomb, making it difficult to be beneficiated using the typical flotation technique. A combination technique of individual process and concentrated returning for the treatment of middlings was used to increase the graphite recovery based on the co-existing relationship between graphite and gangue minerals in the middlings. The graphite recovery of the final concentrate upgraded from 51.81% to 91.14% at a fixed carbon (FC) content of 92.01% by a beneficiation process consisted of once coarse (94.41% passing 74 μm) and rougher, five stages regrinding and six stages cleaning. The proposed treatment technique for middlings is of great significance to increase the recovery of fine flaky graphite

Synthesis of Fluorinated Graphene/CoAl-Layered Double Hydroxide Composites as Electrode Materials for Supercapacitors

CoAl-layered double hydroxide/fluorinated graphene (CoAl-LDH/FGN) composites were fabricated via a two-step hydrothermal method. The synthesized CoAl-LDH/FGN composites have been characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and electrochemical measurements. The results indicated that the fluorinated carbon with various configuration forms were grafted onto the framework of graphene, and the C–F bond configuration and fluorine content could be tuned by the fluorination time. Most of semi-ionic C–F bonds were formed at an appropriate fluorination time and, then, converted into fluorine rich surface groups (such as CF₂, CF₃, etc.) which were electrochemically inactive as the fluorination time prolonged. Moreover, the CoAl-LDH/FGN composites prepared at the optimal fluorination time exhibited the highest specific capacitance (1222 F/g at 1 A/g), the best rate capability, and the most stable capacitance retention, which offered great promise as electrode materials for supercapacitors

High-Toughness Poly(lactic Acid)/Starch Blends Prepared through Reactive Blending Plasticization and Compatibilization

In this study, poly(lactic acid) (PLA)/starch blends were prepared through reactive melt blending by using PLA and starch as raw materials and vegetable oil polyols, polyethylene glycol (PEG), and citric acid (CA) as additives. The effects of CA and PEG on the toughness of PLA/starch blends were analyzed using a mechanical performance test, scanning electron microscope analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, X-ray diffraction, rheological analysis, and hydrophilicity test. Results showed that the elongation at break and impact strength of the PLA/premixed starch (PSt)/PEG/CA blend were 140.51% and 3.56 kJ·m−2, which were 13.4 and 1.8 times higher than those of pure PLA, respectively. The essence of the improvement in the toughness of the PLA/PSt/PEG/CA blend was the esterification reaction among CA, PEG, and starch. During the melt-blending process, the CA with abundant carboxyl groups reacted in the amorphous region of the starch. The shape and crystal form of the starch did not change, but the surface activity of the starch improved and consequently increased the adhesion between starch and PLA. As a plasticizer for PLA and starch, PEG effectively enhanced the mobility of the molecular chains. After PEG was dispersed, it participated in the esterification reaction of CA and starch at the interface and formed a branched/crosslinked copolymer that was embedded in the interface of PLA and starch. This copolymer further improved the compatibility of the PLA/starch blends. PEGs with small molecules and CA were used as compatibilizers to reduce the effect on PLA biodegradability. The esterification reaction on the starch surface improved the compatibilization and toughness of the PLA/starch blend materials and broadens their application prospects in the fields of medicine and high-fill packaging

Adsorption of dodecylamine hydrochloride on graphene oxide in water

Cationic surfactants in water are difficult to be degraded, leading to serious water pollution. In this work, graphene oxide (GO) was used as an adsorbent for removing Dodecylamine Hydrochloride (DACl), a representative cationic surfactant. X-ray diffraction (XRD), FT-IR spectroscopy and atomic force microscope (AFM) were used to characterize the prepared GO. The adsorption of DACl on GO have been investigated through measurements of adsorption capacity, zeta potential, FTIR, and X-ray photoelectron spectroscopy (XPS). The experimental results have shown that the adsorption kinetics could be described as a rate-limiting pseudo second-order process, and the adsorption isotherm agreed well with the Freundlich model. GO was a good adsorbent for DACl removal, compared with coal fly ash and powdered activated carbon. The adsorption process was endothermic, and could be attributed to electrostatic interaction and hydrogen bonding between DACl and GO. Keywords: Graphene oxide, Dodecylamine hydrochloride, Adsorption isotherm, Adsorption mechanism

Model-based assessment of estrogen removal by nitrifying activated sludge

© 2018 Elsevier Ltd Complete removal of estrogens such as estrone (E1), estradiol (E2), estriol (E3) and ethinylestradiol (EE2) in wastewater treatment is essential since their release and accumulation in natural water bodies are giving rise to environment and health issues. To improve our understanding towards the estrogen bioremediation process, a mathematical model was proposed for describing estrogen removal by nitrifying activated sludge. Four pathways were involved in the developed model: i) biosorption by activated sludge flocs; ii) cometabolic biodegradation linked to ammonia oxidizing bacteria (AOB) growth; iii) non-growth biodegradation by AOB; and iv) biodegradation by heterotrophic bacteria (HB). The degradation kinetics was implemented into activated sludge model (ASM) framework with consideration of interactions between substrate update and microorganism growth as well as endogenous respiration. The model was calibrated and validated by fitting model predictions against two sets of batch experimental data under different conditions. The model could satisfactorily capture all the dynamics of nitrogen, organic matters (COD), and estrogens. Modeling results suggest that for E1, E2 and EE2, AOB-linked biodegradation is dominant over biodegradation by HB at all investigated COD dosing levels. However, for E3, the increase of COD dosage triggers a shift of dominant pathway from AOB biodegradation to HB biodegradation. Adsorption becomes the main contributor to estrogen removal at high biomass concentrations