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The wetting and dewetting behaviors of Ag droplets on Mo(100), Mo(110), and Mo(111) surfaces were investigated over 1200-2000 K via molecular dynamics simulations. We used the diffusion energy barriers of Ag droplets on the three surfaces to analyze the phenomenon of different precursor films and adsorption layers on the different surfaces. Alloying enabled the Mo(111) surface better wettability in both Mo(110) and Mo(111) surfaces, where there were significant precursor films. We observed that the dewetting rate was the fastest on the surface with the densest adsorption layer. Simulations proved that the same molecular kinetic theory model was applicable to not only the wetting process but also the dewetting process on the same surface. We also provided evidence to support the fact that an increased temperature could reduce the time to reach equilibrium for the wetting and dewetting processes.

Random vapor nucleation leads to flooding condensation with degraded heat-transfer efficiency. Since an external electric field has a significant effect on manipulating droplets' motion, it is possible to be one of the effective methods to hinder flooding phenomena and improve the heat-transfer rate by applying the external electric field during condensation. However, the motion of nanodroplets is more sensitive to the electric field owing to the scale effect on the nanoscale. The effect of the electric field on growth has not explicitly been comprehended. This work studied the condensation processes on a nanodimpled surface under an electric field with various strengths and directions. The results showed that condensed droplets' growth under the electric field depends on the competition between the electric field force and solid-liquid interactions. Increased vertical electric field strength, the higher torsion by the electric field hindered the motion of vapor, decreased the collision frequency for water molecules with the cooled surface, and elongated the cluster when the electric field force dominates, thus deteriorating the condensation performance. While applying the horizontal electric field, the greater electric field strength leads to better condensation performance by the larger contacting area for heat exchange. A wetting transition induced by the electric field was observed when the electric field strength increased to a certain extent (

In this study, the wetting and dewetting behaviors of water nanodroplets containing various molecule numbers on nanopillar-arrayed surfaces in the presence or absence of an external electric field are investigated via molecular dynamics (MD) simulations, aiming to examine whether there is a scale effect. The results show that, in the absence of an electric field, nanodroplets on coexisting Cassie/Wenzel surfaces may be in the Cassie or the Wenzel state depending on their initial states, and apparent contact angles of the Cassie or Wenzel nanodroplets increase monotonously with increasing the droplet size. Energy analysis shows that on the same coexisting Cassie/Wenzel surface, when an electric field is imposed, a small nanodroplet possesses a lower energy barrier separating the Cassie state from the Wenzel state. Therefore, the small nanodroplet is easier to collapse into the Wenzel state. Moreover, the spontaneous Wenzel-to-Cassie dewetting transition is not observed for the nanodroplets after the removal of the electric field because the Wenzel state is a globally stable energetic state. With the same pillar geometry, both the wetting transition and the dewetting transition are significantly modified for liquids with higher intrinsic contact angles. The energy barrier of the wetting transition increases for both the large and small nanodroplets, meaning that the Cassie state becomes more robust. The energy curve shows that the Wenzel state of the large nanodroplet has higher energy so that the droplet can return to the Cassie state when removing the electric field. Intriguingly, although the small Wenzel nanodroplet has lower energy in the presence of the electric field, the dewetting transition still occurs. The increased solid-liquid interfacial tension when removing the electric field is responsible for this abnormal result. The wetting and dewetting transitions follow different energy pathways, leading to a hysteresis energy loop. There exists a critical water molecule number separating the unstable/stable Wenzel configurations, above which the Cassie state is energetically favorable and the dewetting transition can occur spontaneously after removing the electric field.

The anaerobic granulation technology has been successfully applied full-scale for treating high-strength recalcitrant acrylic acid wastewater. This mini-review highlighted the recalcitrance of acrylic acid and its biological degradation pathways. And then, the full-scale practices using anaerobic granulation technology for acrylic wastewater treatment were outlined. The granules are proposed to provide barriers for high-concentration acrylic acid to the embedded anaerobic microbes, maintaining its high degradation rate without apparent substrate inhibition. Based on this proposal, the prospects of applying anaerobic granulation technology to handle a wide range of high-strength recalcitrant wastewaters, to improve the current process performances, and to recover renewable resources were delineated. The anaerobic granulation for high-strength recalcitrant wastewater treatment is an emergent technology that can assist in fulfilling the appeals of the circular bioeconomy of modern society.

Backgrounds Cotton fabrics were modified on surface wettability for efficient oil/water separation. The modification adopted in previous literature are commonly complicated in steps, expensive in chemicals applied, and not environmentally begien in solvents used. Experiments This article applied a novel one-step modification protocol to modified cotton fabrics using tannic acid (TA) grafted via Michael addition/Schiff base reactions with long-chain alkylamines, including 1-tetradecylamine (TDA), 1-hexadecylamine (HDA), and 1-octadecylamine (ODA) with 14, 16 and 18 methyl groups, respectively, were applied in this study for cotton fabrics modification. The TA, an inexpensive natural polyphenol, was adopted for providing excess catechol groups for linking the cotton surface and the alkylamines. The grafting reactions via Michael addition/Schiff base reaction were performed at room temperature and pH 8.5 with catalysts CuSO4/H2O2 for significantly reducing the reaction time needed. Results The chemical analysis confirmed the modification of the cotton fabrics to possess hydrophobic surface, with contact angles for water droplets on the modified surface as 133.3o, 136.0o and 142.9° for TA-TDA, TA-HDA, and TA-ODA cotton fabrics, respectively; and diiodinemethane droplets on the modified surface being 56.0o, 58.8o and 59.3o, respectively. The modified cotton surface has intermediate dispersive component of surface energy (29.0–31.2 mJ/m2) and low polar component (4.2–6.2 mJ/m2), yielding high affinity to oil but low affinity to water. Parametric study revealed that the pH value and reaction time are the most important parameters for the alkylamine grafting reactions, while the reduction of catalyst amount used but still with sufficient modification on cotton fabrics can be achieved. The oil absorption tests with cotton fabrics contacting hexane (top)-water (bottom) layers revealed high hexane adsorption capacity: 0.96, 1.22, 1.25 g hexane/g cotton for TA-TDA, TA-HAD and TA-ODA cotton fabrics, respectively. The absorption tests with cotton fabrics contacting water first for 30 s then hexane for another 30 s had much lower absorption capability of hexane: 0.52, 0.85, 0.87 g hexane/g cotton for TA-TDA, TA-HAD and TA-ODA cotton fabrics, respectively, since water would penetrate the major pores for inhibiting further oil absorption.

This study provides a significant contribution to the development of multiple hydrogen-bonded supramolecular nanocarrier systems by demonstrating that controlling the hydrogen bond strength within supramolecular polymers represents a crucial factor to tailor the drug delivery performance and enhance the effectiveness of cancer therapy. Herein, we successfully developed two kinds of poly(ethylene glycol)-based telechelic polymers Cy-PEG and UrCy-PEG having self-constituted double and quadruple hydrogen-bonding cytosine (Cy) and ureido-cytosine (UrCy) end-capped groups, respectively, which directly assemble into spherical nanogels with a number of interesting physical characteristics in aqueous solutions. The UrCy-PEG nanogels containing quadruple hydrogen-bonded UrCy dimers exhibited excellent long-term structural stability in a serum-containing biological medium, whereas the double hydrogen-bonded Cy moieties could not maintain the structural integrity of the Cy-PEG nanogels. More importantly, after the drug encapsulation process, a series of in vitro experiments clearly confirmed that drug-loaded UrCy-PEG nanogels induced selective apoptotic cell death in cancer cells without causing significant cytotoxicity to healthy cells, while drug-loaded Cy-PEG nanogels exerted nonselective cytotoxicity toward both cancer and normal cells, indicating that increasing the strength of hydrogen bonds in nanogels plays a key role in enhancing the selective cellular uptake and cytotoxicity of drugs and the subsequent induction of apoptosis in cancer cells.

Background Droplet impact on a superhydrophobic cylinder differs from that on a flat surface. After bouncing, once re-touch takes place, the contact time τc would increase, which is unfavorable for some applications. The increased τc may strongly depend on the Weber number and radius ratio, R*, of cylinder to droplet. Methods The impact is investigated via lattice Boltzmann method simulations. The particular emphasis is placed on re-touch rebound patterns and τc. Significant findings Rebound patterns and τc both strongly depend on a combined parameter, α=We/R*, characterizing the asymmetry of droplet spreading and retraction. As α increases, upward rebound and stretched breakup take place sequentially for the first bouncing, whereas rebound patterns change as intact re-touch rebound and separate re-touch rebound for the second bouncing. Increasing α enhances the asymmetry, which promotes the first rebound, thereby reducing τc regardless of rebound patterns. The enhanced asymmetry also accelerates rebound and thus reduces τc in the separate re-touch rebound regime, whereas it hinders rebound, leading to a significantly increased τc. The power-law correlations of τc vs α are developed for the first and second bouncing. Besides, a method is proposed to suppress or prevent the re-touch, which is proven to effectively reduce τc.

Enzymatic hydrolysis is the key step limiting the efficiency of the biorefinery of lignocellulosic biomass. Enzymes involved in enzymatic hydrolysis and their interactions with biomass should be comprehended to form the basis for looking for strategies to improve process efficiency. This article updates the contemporary research on the properties of key enzymes in the lignocellulose biorefinery and their interactions with biomass, adsorption, and hydrolysis. The advanced analytical techniques to track the interactions for exploiting mechanisms are discussed. The challenges and prospects for future research are outlined.

This study numerically investigates the effects of the Weber number (

Background The solid mediator Z-scheme heterojunctions are promising photocatalysts that have narrow band gaps to allow excitation of incorporated electrons under visible lights but with sufficient separation of the yielded electron hole-pairs and without suffering the reduction of their oxidization and reduction powers. Successful synthesis of mediator Z-scheme heterojunction acquires production of constituent semiconductors with desired Fermi levels and close contacts of the semiconductors with sandwiched metal mediator. Methods This mini-review discussed briefly the principles of photocatalyst and heterojunction photocatalysts, and then the current research and development studies on the way to design and synthesis of Z-scheme heterojunction were summarized. Significant findings Based on literature results, the perspectives to design and synthesis of a solid mediator Z-scheme for degrading specific pollutant were discussed and outlined. An illustrative example of design and synthesis of a novel Z-scheme photocatalyst, CuFe2O4/Cu/UiO66-NH2, with demonstration of its photodegradation performance of dye rhodamine 6 G, was presented at the end of the review.

The metal hexacyanoferrates with transition metal ions to replace ferric ions in the face center cubic structure of Prussian blue (PB) crystals are candidate adsorbents for radioactive cesium ions in waters. This study for the first time synthesized the shape stable poly(vinyl alcohol) (PVA) hydrogels with immobilized metal hexacynoferrate (PB analogue) that can be stored at dry and can efficiently adsorb cesium ions from waters after rewetting. A total of eight PB analogue particles in two families M3[Fe(III)(CN)6]2 (MFe(III)) or M4[Fe(II)(CN)6]2 (MFe(II)) with M=Zn, Ni, Cu, or Co were synthesized and were immobilized in the PVA hydrogels following boric acid and sulfate crosslinking. The produced PVA-PB analogue hydrogels are all stable in shape after dry and rewet, and the rewet hydrogels can adsorb cesium ions from waters at much higher rates. As predicted by the diffusion-reaction model, the apparent reaction constants for cesium ion adsorption are 4.2×10−4 1/s, 3.4×10−4 1/s, 3.9×10−4 1/s, 4.1×10−4 1/s, 4.1×10−4 1/s, 3.8×10−4 1/s, 1.1×10−3 1/s, and 9.6×10−4 1/s, for ZnFe(III), ZnFe(II), NiFe(III), NiFe(II), CuFe(III), CuFe(II), CoFe(III), and CoFe(II), respectively. The corresponding maximum adsorption capacities based on Langmuir isotherm model at 25 °C are 232.6 mg/g, 389.0 mg/g, 193.9 mg/g, 256.8 mg/g, 388.2 mg/g, 395.1 mg/g, 297.3 mg/g, and 391.2 mg/g, respectively. The use of PVA-CoFe(III) is the candidate for enhanced Cs removal from waters comparing the use of other PB analogues as adsorbent.

Anaerobic digestion (AD) is a potential bioprocess for waste biomass utilization and energy conservation. Various iron/carbon-based CMs (e.g., magnetite, biochar, granular activated carbon (GAC), graphite and zero valent iron (ZVI)) have been supplemented in anaerobic digestors to improve AD performance. Generally, the supplementation of CMs has shown to improve methane production, shorten lag phase and alleviate environmental stress because they could serve as electron conduits and promote direct interspecies electron transfer (DIET). However, the CMs dosage varied greatly in previous studies and CMs wash out remains a challenge for its application in full-scale plants. Future work is recommended to standardize the CMs dosage and recover/reuse the CMs. Moreover, additional evidence is required to verify the electrotrophs involved in DIET.

Denitrification reactions commonly remove nitrate and other reactive nitrogen (Nr) from wastewater. The C/N ratio indicates the sufficiency of organic carbons to drive heterotrophic denitrification; a low C/N ratio frequently leads to poor denitrification performance in wastewater treatment. This study proposed and tested a novel SharonDSR (denitrifying sulfide removal) process, with nitrite generated by the Sharon reactions and sulfide from sulfur-reducing reactions for promoting the following nitrite-based denitrification and denitrifying sulfide removal (DSR) process. The present reactor can remove nitrate at an efficiency of 97.7 %-93.5 % at an influent C/N ratio of 0.646-0.737 over a 96-d continuous-flow test. The microbial community study reveals the functional strains corresponding to individual groups of critical reactions. The stoichiometry analysis reveals the potential to apply the nitrite-based DSR process for Nr removal from ultra-low C/N (0.64) wastewaters, experimentally demonstrated in the present study with a C/N ratio of 0.16-0.39.

This article provides a perspective review on the use of modified cotton fabrics for oil–water separation. The principles of surface hydrophobicity of cotton fabrics are first described, from which the basis for producing superhydrophobic surfaces is presented. Then the preparation methods to convert hydrophilic cotton fabrics to hydrophobic fabrics are reviewed and discussed. Based on literature results the way to design novel preparation methods, the need to summarize testing protocols, and the comprehensive technoeconomic and sustainability analyses, are proposed. A demonstrative cotton fabrics test is used to reveal the significant role of conjugated fluid flows and surface interactions under different application scenarios for determining the separation efficiency of the oil–water mix.

As compared with silica aerogels, alumina aerogels have excellent high-temperature stability, and hence, are regarded as a promising candidate for high-temperature thermal insulation materials. However, heat transfer mechanisms for such materials remain insufficiently explored. In this study, based on real material microstructures, an analytical thermal conductivity model for alumina aerogel-fiber-opacifier composites is developed via a modified parallel-series equivalent electrical circuit approach. The model takes into account solid, gaseous, and solid-gas coupling heat conduction in aerogels, solid heat conduction in both fibers and opacifier particles, and radiation in aerogels, fibers, and opacifier particles. The model is validated by comparing its predictions with measured thermal conductivity data. The model predictions reveal that there are two kinds of solid-gas coupling heat transfer mechanisms, which occur in the corner regions between interconnected secondary particles and in the slit regions between adjacent chains, respectively. Because of this coupling, the contribution of gaseous heat conduction is comparable to that of solid heat conduction and radiation of aerogels, fibers, and opacifier particles, which is well supported by experimentally measured data of thermal conductivity. The model is also used to analyze effects of various parameters on the thermal insulation performance of the composites, such as diameters and volume fractious of both fibers and opacifier particles.

In this work, the transient supercooling performance of thermoelectric coolers is numerically investigated via a three-dimensional, multiphysics, and transient model. The particular focus is placed on how to increase the holding time of supercooling state to meet some specific cooling requirements. A new concept of effective cooling temperature line is proposed to evaluate the supercooling performance. On the basis of this concept, the frequently used holding time of supercooling state is replaced by an effective holding time, teff-hold. As a reference baseline, the transient supercooling performance is first evaluated under a single current pulse and the largest teff-hold is determined by searching for the optimal pulse width and amplitude. Subsequently, the supercooling performance and the effective holding time are evaluated under a continuous double current pulse whose shape can be characterized by the pulse width (τ1) and amplitude (P1) of the first pulse, the pulse width (τ2) and amplitude (P2) of the second pulse, and the initial current (Iini,2) of the second pulse. The results show that among the five parameters Iini,2 is the most dominant parameter to achieve a larger teff-hold. Only when Iini,2 is higher than the initial current of the first pulse, employing a double pulse can yield a larger teff-hold than employing the optimal single pulse. The results also demonstrate that with a proper Iini,2 the value of teff-hold can be further prolonged by optimizing τ1, τ2, P1, and P2, and the largest teff-hold for the optimal double pulse is increased by 59.8%, as compared with that of the optimal single pulse. Finally, the principles for selecting parameters of a double current pulse are discussed.

Efficient droplet shedding from surfaces is fundamentally interesting and important due to its promising potential in numerous applications, such as anti-erosion, anti-icing, and self-cleaning. In this work, the bouncing dynamics of the head-on impact of two nanodroplets on superhydrophobic surfaces are investigated through molecular dynamics simulations. Three bouncing patterns, including regular-coalescence-bouncing, coalescence-hole-bouncing, and ring-bouncing, are identified at a wide range of impacting Weber numbers. For three bouncing patterns, the time evolutions of the spreading factors and the vertical velocity components are employed to analyze the particular dynamic behaviors and elucidate the underlying physics. As a counter-intuitive bouncing pattern, the ring-bouncing that two impact nanodroplets coalesce, spread, and then leave the surface in a ring shape without retracting exhibits a remarkable reduction in contact time by up to 60%. Considering four typical states for the ring-bouncing pattern, the comparison of the velocity distribution within the droplet clearly reveals that the ring-shaped droplet reshapes interfaces, which leads to a special hydrodynamics distribution. As a result, the internal flows at the inner and outer edges along the opposite direction collide with each other, leading to a sudden increase in the upward velocity. Combining the largely decreased contact area between solid and liquid with the small surface adhesion, the ring-shaped droplet rapidly bounces off the surface at the maximum spreading state. Finally, it is significantly highlighted that the ring-bouncing pattern offers a new avenue to break the contact time limit for efficient droplet shedding.

An increasing attention has been paid to the secure and sustainable management of agricultural wastes, especially lignocellulosic biomass. Nanobubble water (NBW) contains 10

This work investigates the retraction and bouncing dynamics of an impacting low-viscosity nanodroplet on superhydrophobic surfaces via molecular dynamics simulations, aiming to reveal the scaling laws of retraction and bouncing velocities and to establish the relationship between them. The retraction velocity, Vre, is found to scale as Vre ∼ Dmax/ τc,n, where Dmax is the maximum spreading diameter, τc,n = ( D0/ V0) We1/2 Oh1/3 is the inertial-capillary-viscous time, and We and Oh are the Weber number and Ohnesorge number, respectively. The bouncing stems from the collision of the retracting rim at the center of the nanodroplet, leading to the bouncing velocity scaling as the retraction velocity. Combining the relationship of Vre ∼ Dmax/ τc,n with the scaling law of Dmax ∼ We1/2 Oh1/3 D0 yields both the retraction and bouncing velocities scaling as the impact velocity, indicating that both the retraction and bouncing velocities of low-viscosity nanodroplets on a superhydrophobic surface depend merely on the impact velocity. An energy analysis shows that the proportion of the surface energy at the maximum spreading state ( Es,max) to the initial kinetic energy ( Ek,ini) follows Es,max/ Ek,ini ∼ Oh2/3, whereas the proportion of the bouncing kinetic energy ( Ek,b) to the surface energy at the maximum spreading state follows Ek,b/ Es,max ∼ Oh−2/3, leading to constant Ek,b/ Ek,ini and also constant restitution coefficient for low-viscosity nanodroplets impacting superhydrophobic surfaces.