Diffusion Boundary Layer Research Articles

Ion transport facilitation through template based optimization of corrugation geometry over membrane surface

The resistance at the diffusion boundary layer limits ion transport through membrane (counter-ionic) in electro-electrodialysis (EED), which are addressed through novel design of flow promoter (spacer), but increased pressure drop in the flow channel and power consumption are major rudiments. This report investigates casting of template based micro molded membranes containing cylinder, square-pillar, and rectangular-pillar corrugations and their application in EED setup without spacer. Square-pillar showed higher ion transport relative to rectangular-pillar and cylinder, which was supported by increased surface area, and reduced boundary layer thickness. For height optimization of square pillar corrugation, corrugated membranes containing pillars of five different heights: 50, 75, 100, 125 and 150 μm were synthesized and tested for using EED setup, where 100 μm height showed better ion transport. Limited ion transport with corrugation height above 100 μm resulted lower concentration of NaOH requiring higher energy. Corrugated membrane with two different arrangements of square pillars: linear and staggered were tested keeping their height same (100 μm), where staggered arrangement showed better ion transport. Direction of applied current facing flat and corrugated performed differently in ion transport, and the latter performed better due to reduced boundary layer resistance. All EED experiments were conducted with industrial green liquor feed to obtain NaOH (mol·L−1) as product, where current density, flowrate and duration were kept unchanged. NaOH recovery, Current efficiency, and energy consumption estimates with each configuration was supported through velocity profiles obtained by solving equation of motion and continuity using COMSOL multiphysics software. Combine effect of turbulence creations due to corrugation, surface area increment and boundary layer thickness control the ion transport.

Evaluation by Means of Electrochemical Impedance Spectroscopy of the Transport of Phosphate Ions through a Heterogeneous Anion-Exchange Membrane at Different pH and Electrolyte Concentration

Electrodialysis is an innovative technique to reclaim phosphates from municipal wastewater. However, chemical reactions accompany the transport of these ions through ion-exchange membranes. The present study investigates the dependence of these phenomena on the initial pH and concentration of the phosphate-containing solution using a heterogeneous anion-exchange membrane. Linear sweep voltammetry, electrochemical impedance spectroscopy, and chronopotentiometry experiments were conducted for different phosphate-containing systems. For the most diluted solution, two limiting current densities (ilim) have been observed for pH 5 and 7.2, while only one ilim for pH 10, and correlated with the appearance of Gerischer arcs in EIS spectra. For pH 7.2, sub-arcs of Gerischer impedance were separated by a loop, indicating the involvement of the membrane functional groups. Increasing the phosphate concentration changed the system’s characteristics, reporting a single ilim. In the EIS spectra, the absence of Gerischer elements determined the attenuation of chemical reactions, followed by the development of a diffusion boundary layer, as indicated by the finite-length Warburg arcs. Chronopotentiometry clarified the mass transport mechanism responsible for distorting the diffusion boundary layer thickness at lower concentrations. The obtained results are expected to contribute to the phosphates recovery using electrodialysis in the most varied conditions of pH and concentration available in the environment.

Water motion and pH jointly impact the availability of dissolved inorganic carbon to macroalgae

The supply of dissolved inorganic carbon to seaweeds is a key factor regulating photosynthesis. Thinner diffusive boundary layers at the seaweed surface or greater seawater carbon dioxide (CO2) concentrations increase CO2 supply to the seaweed surface. This may benefit seaweeds by alleviating carbon limitation either via an increased supply of CO2 that is taken up by passive diffusion, or via the down-regulation of active carbon concentrating mechanisms (CCMs) that enable the utilization of the abundant ion bicarbonate (HCO3−). Laboratory experiments showed that a 5 times increase in water motion increases DIC uptake efficiency in both a non-CCM (Hymenena palmata, Rhodophyta) and CCM (Xiphophora gladiata, Phaeophyceae) seaweed. In a field survey, brown and green seaweeds with active-CCMs maintained their CCM activity under diverse conditions of water motion. Whereas red seaweeds exhibited flexible photosynthetic rates depending on CO2 availability, and species switched from a non-CCM strategy in wave-exposed sites to an active-CCM strategy in sheltered sites where mass transfer of CO2 would be reduced. 97–99% of the seaweed assemblages at both wave-sheltered and exposed sites consisted of active-CCM species. Variable sensitivities to external CO2 would drive different responses to increasing CO2 availability, although dominance of the CCM-strategy suggests this will have minimal impact within shallow seaweed assemblages.

Adsorption Properties and Preparative Separation of Flavonoids from Rhizoma Smilacis Glabrae Using Macroporous Resins

Astilbin (AST), isoastilbin (ISO), and engeletin (ENG) are the main flavonoids in Rhizoma Smilacis Glabrae (RSG) and have many biological activities. In this study, the adsorption kinetics of AST, ISO, and ENG on HPD-300 resin was investigated and their adsorption processes conformed to a pseudo-second-order kinetics equation. The fitting curves of the intraparticle diffusion model showed three linear stages and did not pass through the origin, meaning the adsorption process of the three flavonoids was controlled by boundary layer diffusion and intraparticle diffusion. Their adsorption isotherms were also constructed and could be well-fitted by the Langmuir equation. A low temperature was favorable for their adsorption. The relative adsorption capacity of ENG was significantly higher than those of the other two compounds, indicating that the substitution pattern on ring B has an important impact on the adsorption of flavonoids with resin. The separation process was optimized by dynamic adsorption/desorption experiments. After separation, the purities of AST, ISO, and ENG increased from 5.55%, 1.22%, and 0.45% to 27.46%, 6.14%, and 2.27%, respectively, and all the recoveries exceeded 75%. After that, the three compounds were further separated by preparative HPLC and silica gel chromatography. In the final product, the purities of AST, ISO, and ENG could reach above 98%.

Floquet stability analyses of stratified oscillating boundary layers on adiabatic slopes

The presence of a no-slip, impermeable, adiabatic, sloped boundary in an otherwise quiescent, stably stratified, Boussinesq flow generates baroclinic vorticity within a diffusive boundary layer. Such conditions are typical of the oscillating boundary layers on adiabatic abyssal slopes, sloped lake bathymetry and sloped coastal bathymetry in the absence of high-wavenumber internal waves, mean flows, far-field turbulence on larger scales, and resonant tidal–bathymetric interaction. We investigate the linear stability of the oscillating flow within non-dimensional parameter space typical of the $M_2$ tide and hydraulically smooth, middle-latitude abyssal slopes through Floquet linear stability analysis. The flow dynamics depends on three non-dimensional variables: the Reynolds number for Stokes’ second problem, the Prandtl number, and a frequency ratio that accounts for the resonance conditions ( $C$ , criticality) of the buoyant restoring force and the tidal forcing. The Floquet analysis results suggest that oscillating laminar boundary layers on adiabatic abyssal slopes are increasingly unstable as Reynolds number, criticality parameter and/or spanwise disturbance wavenumber are increased. We also show that the two-dimensional Floquet linear instability necessarily generates three-dimensional baroclinic vorticity, which suggests that the evolution of the gravitational instabilities may be nonlinear as $t\rightarrow \infty$ .

Investigating the reactivity of TiOx and BDD anodes for electro-oxidation of organic pollutants by experimental and modeling approaches

The reactivity of two non-active anodes (BDD and TiOx) for the removal of organic pollutants from water was investigated and compared. A mathematical model for electro-oxidation of organic compounds was developed by considering (i) an analytical expression of the spatial distribution of •OH concentration at non-active anodes, (ii) mass transport through the diffusion boundary layer and (iii) both direct electron transfer and •OH-mediated oxidation for degradation of organic pollutants. The model was calibrated from experimental data using, for example, terephthalic acid as •OH probe molecule or ethanol as •OH quencher during paracetamol degradation. Calculation of the fraction of current ascribed to the different possible reactions as well as a sensitivity analysis allowed for highlighting the key mechanisms and limiting phenomena. Degradation of organics occurs almost exclusively through •OH-mediated oxidation under mass transport limitation and for sufficiently high reaction rate constants. Improvement of degradation kinetics strongly depends on mass transport enhancement of organic compounds to the reaction zone at the electrode surface. Competition between the mother molecule and degradation by-products for reaction with •OH did not significantly affect degradation kinetics under mass transport limitation. Direct electron transfer can potentially become important in presence of large amounts of •OH scavengers or for organic compounds that react slowly with •OH (k < 105 m3 mol−1 s−1). Results also showed that the implementation of a suitable •OH quenching experiment required the use of a concentration of ethanol of at least 100 mM for experiments performed at 5 mA cm−2 and with a concentration of target pollutant of 0.1 mM.

Additive Manufacturing of Intertwined Electrode Pairs ‐ Guided Mass Transport with Gyroids

Electrochemical flow reactors facilitate the storage of renewable energies and the carbon‐neutral production of platform chemicals. To maximize the reactor efficiency, unhindered mass transport in the flow channel and high surface electrodes is required. However, state‐of‐the‐art reactors are limited by the conventional parallel plate designs. Herein, 3D intertwined electrode pairs are presented, based on triply periodic minimal surfaces that facilitate mass transport and provide high surface areas. Three gyroid designs with outer dimensions of 20 × 40 × 70 mm are manufactured from stainless steel via selective laser melting and implemented into a conventional flow cell. By design, the electrodes are rendered porous through the targeted control of the energy density during fabrication. Mass transport characterization by use of the fast ferri‐/ferrocyanide redox reaction demonstrates that smaller unit cells and thus shorter interelectrode distances achieve significantly increased current densities. Moreover, the addition of convective channels formed by second‐level gyroid structures removes diffusion boundary layers by promoting convective flow in electrode vicinity. The convective flow enhancement of the microscale channels even surpasses the effect of the unit cell size reduction, demonstrating importance of mass transport control. The integrated electrode design holds great potential for efficient next‐generation electrochemical flow reactors.

An impact of Richardson number on mixed convective flow of nanoparticles with heat and mass transfer

The problems of mixed convection viscoelastic fluid flow and heat transfer past a permeable stretching sheet are investigated considering the suction/injection, radiation and thermo-diffusion effects and thermophoresis. The fluid under consideration is water-based and consists of three distinct shaped nanoparticles with the claim of superior heat transmission. The dimensional equation that models the aforesaid transport phenomenon was non-dimensionalized, parameterized, and solved analytically using appropriate similarity variables. Both the heat and concentration analyses are considered in this boundary layer problem. The analyses of viscoelasticity, suction/injection, and boundary effects, which affect the fluid flow, are studied. Graphs are used to determine and present the behaviour of physical parameters such as Lewis, Prandtl, Dufour and Soret numbers influencing temperature and concentration field. The results revealed the existence of multiple solutions for higher Prandtl number values. The dynamic, thermal, and diffusive boundary layer domains are substantially improved as values rise. This study has importance in extrusion processing, dyeing of metals, etc., in engineering applications where the heat transfer of the fluid is controlled.

Identifying Characteristic Frequencies in the Electrochemical Impedance of Ion-Exchange Membrane Systems.

In this study, the characteristic frequencies of the electrochemical impedance of ion-exchange membrane systems constituted by the membrane and two diffusion boundary layers adjacent to the membrane were investigated. Approximations of the impedance of the Randles equivalent electric circuit in multiple frequency ranges were considered, and the characteristic frequencies of the zeros and poles of orders ½ and 1 were derived. The characteristic geometric frequencies, those associated with the interfacial charge transfer and the diffusive transport processes, as well as those associated with the transitions between processes, were identified by means of analytical expressions.

Granulation of Bismuth Oxide by Alginate for Efficient Removal of Iodide in Water.

The granulation of bismuth oxide (BO) by alginate (Alg) and the iodide adsorption efficacy of Alg–BO for different initial iodide concentrations and contact time values were examined. The optimal conditions for Alg–BO granulation were identified by controlling the weight ratio between Alg and BO. According to the batch iodide adsorption experiment, the Alg:BO weight ratio of 1:20 was appropriate, as it yielded a uniform spherical shape. According to iodide adsorption isotherm experiments and isotherm model fitting, the maximum sorption capacity (qm) was calculated to be 111.8 mg/g based on the Langmuir isotherm, and this value did not plateau even at an initial iodide concentration of 1000 mg/L. Furthermore, iodide adsorption by Alg–BO occurred as monolayer adsorption by the chemical interaction and precipitation between bismuth and iodide, followed by physical multilayer adsorption at a very high concentration of iodide in solution. The iodide adsorption over time was fitted using the intraparticle diffusion model. The results indicated that iodide adsorption was proceeded by boundary layer diffusion during 480 min and reached the plateau from 1440 min to 5760 min by intraparticle diffusion. According to the images obtained using cross-section scanning electron microscopy assisted by energy-dispersive spectroscopy, the adsorbed iodide interacted with the BO in Alg–BO through Bi–O–I complexation. This research shows that Alg–BO is a promising iodide adsorbent owing to its high adsorption capacity, stability, convenience, and ability to prevent secondary pollution.

Development and validation of the DGT technique using the novel cryogel for measuring dissolved Hg(II) in the estuary

The complex seawater matrix has significantly influenced the determination of estuarine dissolved Hg(II), hindering its monitoring and risk assessment in maricultural areas. In this work, SiO2-SH-DGT assembled by the sulfhydryl-modified silica cryogel (SiO2-SH cryogel) as the novel binding phase was developed to tackle this problem. The uniform dispersion of the cryogel into binding gel was advantageous for achieving remarkable and comparable capacity, which endowed the estimated diffusion coefficient (D) to be 1.39–3.08 times of the existing research. The SiO2-SH-DGT performance was independent of pH (3–9), ionic strength (10–800 mM), fulvic acid at low content, and seawater matrix (Na+, K+, Ca2+, Cl−), but the high content of Mg2+ did interfere with the Hg(II) accumulation, which manifested as competitive adsorption and diffusion. Therefore, the calibrated model was established by calibrating accumulated mass (M′) and diffusion coefficient (D′) based on the Mg2+ concentration, its high accuracy was further verified in the lab. Finally, SiO2-SH-DGT was deployed in the three typical aquaculture areas in Beibu Gulf, field trials achieved the actual Hg(II) level to be 1.52–5.38 ng/L with consideration of the diffusion boundary layer. The finding could provide new thought and technical support for metal pollution monitoring in estuary maricultural areas.

Assessment of Conductive Sites on Carbon Fiber Reinforced Polymer Plastics' Surfaces Using Electrochemical Methods

The components of automobile bodies have been manufactured primarily from steel since cars were first made. With the goal of energy savings, light-weighting is being adopted by substituting steel with a variety of light metals and composite materials. A DOE sponsored project in collaboration with PPG and Ford studied the use of automotive closure panels comprising an inner carbon fiber reinforced polymer (CFRP) sheet and an outer aluminum alloy (AA) sheet. The ends of closure panels are sealed with hem flange joints. A major concern is the formation of a galvanic cell within the joint wherein CFRP is the cathode that will accelerate the corrosion of the AA sheet. Various combinations of AA6xxx alloys with CFRP having two different orientations of carbon fiber, i.e., random and twill, are studied in this work. CFRP can only exert a galvanic driving force on a coupled AA panel by electrical connection at cut edges where sheared carbon fibers are exposed, or if carbon fibers are exposed on the CFRP panel surface by lack of coverage of the insulating epoxy matrix. It is believed that processing and curing variables lead to varied epoxy cover on the surfaces of CFRP. Electrochemical measurements such as the measurement of oxygen reduction limiting current density during cathodic polarization show that as-fabricated surfaces of CFRP panels exhibit some extent of electrochemical activity, indicating some lack of coverage of C fibers. It is of interest to characterize the epoxy cover on the CFRP surfaces in terms of the nature of the active sites (e.g., whether C fibers are totally uncovered or covered by a very thin layer of epoxy) and the density and distribution of the sites. A technique was developed to identify the exact locations of active sites on both random and twill CFRP by electrodeposition of small amounts of Cu. If the amount of deposited copper is small, the deposits indicate the location and number of the active sites on the CFRP surface. These deposits were also analyzed by serial sectioning using Focused Ion Beam/Scanning Electron Microscope. High resolution images of the deposit/epoxy interfaces provide a description of the nature of the defective/conductive regions on CFRP surfaces. Rotating disk electrode experiments were also performed to determine the oxygen reduction reaction (ORR) limiting current densities of CFRP at different electrode rotation rates i.e., different diffusion boundary layer thicknesses. These aspects are related to the overall mass transport in the electrolyte, which provides a deeper understanding of the kinetics on CFRP and the nature of active sites behaving as microelectrodes. The observations from the copper electrodeposition study and rotating disk electrode experiments will be correlated and the role of CFRP as a cathode contributing to the corrosion of AA in the galvanic couple will be presented.This work was supported by the U.S. Department of Energy through award DE-EE0007760, in collaboration with PPG Industries and Ford Motor Company.

Novel oxymagnesite/green rust nanohybrids for selective removal and slow release of phosphate in water

The new paradigm in wastewater treatment demands to change traditional pollutants removal into resource recovery, especially for non-renewable P resources, effectively recovering phosphate from wastewater and reutilizing it as a nutrient is crucial to P sustainable utilization and P-related pollution control. The nanomaterial-based adsorption technology for P recovery from wastewater is becoming a research hotspot due to its high efficiency and selectivity. Herein, to recover aqueous phosphate, we developed novel oxymagnesite/green rust (OMGR) nanohybrids by a one-pot hydrothermal method. Green rust nanoparticles dispersed on the highly reactive oxymagnesite (MgO2MgCO3) nanosheets could achieve efficient recovery and reuse of P. The volume ratio of water to ethylene glycol played an important role in the preparation of OMGR. The OMGR possessed an excellent selectivity of phosphate removal in the presence of multi-anions and wide pH adaptability in 4.0–10.0. The formation of MgP nanocrystals and the inner-sphere FeOP complexes via ligand exchange contributed to the selective removal of P by OMGR, and the removal capacity reached 141 mg P.g−1. The process of phosphate removal by OMGR was spontaneously endothermic and controlled by the intraparticle and boundary layer diffusion. Most importantly, the high bioavailable P (127 mg.g−1) of P-loaded OMGR had a persistent release behavior regulated by dissolution and diffusion, indicating that the P-loaded OMGR can act as a slow-release P-fertilizer. The findings provide a green and eco-friendly approach to realizing P resource recovery and reuse for phosphate-containing wastewaters.

Fast arsenate As(V) adsorption and removal from water using aluminium Al(III) fixed on Kapok fibres

Arsenic (As) is among the most dangerous metalloids and is harmful to human wellbeing. In this laboratory study, Al(III)-modified kapok fibres (Al-Kapok) were used to remove As(V) from water. The sorbent was characterised using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX). Batch experiments were performed to observe the performance of Al-Kapok in the removal of As(V) and to examine the effects of pH, temperature, adsorbent dose, and coexisting ions on the adsorption process. The surface of the sorbent changed after aluminium modification, and the results of the batch experiments showed that the adsorption of As(V) occurred mainly via endothermic-spontaneous chemisorption at the solution and solid interface of Al-Kapok. The As(V) removal efficiency was approximately 76%–84%, and it was slightly affected at pH levels below 8.0. Further study showed that the maximum adsorption capacity of Al-Kapok for As(V) was 118 μg/g at 30 °C and pH 6, and notable adverse effects were caused by the presence of SO42−and PO43−. It was also found that the boundary layer and film diffusion contributed more to As(V) adsorption. After five adsorption/desorption cycles, regeneration recovered approximately 92% of the adsorption capacity of Al-Kapok used. Overall, Al-Kapok appears to be a suitable adsorbent material for the purification of As-contaminated water.

Modelling and analysis of an endothermic reacting counter-current flow

We study the endothermic reaction and flow of a granular solid reactant, where energy for the reaction is provided by a counter-current flow of hot gases through the porous reactant bed. Research into reacting flows typically focusses on exothermic combustion processes. However, endothermic processes are common in the metallurgy industry, including the production of cement, silicon and rutile titanium dioxide. Several common features are observed in experimental and numerical studies of these processes, including critical temperatures of the reactant at which the chemical reaction begins, and regions of the reactor with uniform reactant temperature. Motivated specifically by the processes in a silicon furnace, we analyse a model of endothermic, reacting counter-current flow using the method of matched asymptotic expansions. Assuming the Péclet number in the solid is large, we explore the full range of values for the dimensionless inter-phase heat-transfer rate, finding six distinguished limits. In all limits, we find a diffusive boundary layer in which there is a fast chemical reaction rate due to the high temperatures, analogous to exothermic flame fronts. Outside this region, the counter-current flow is crucial to the chemical processes. For intermediate values of the heat-transfer rate, we find the same qualitative properties as those observed across the metallurgy industry, and we quantify the dependence of these properties on the flow rate and heat-transfer rate. In the limit of large heat-transfer coefficient, we derive the single-temperature limit, in which the solution structure is dependent on the direction of net heat flux through the domain.

Development of a predictive kinetic model with statistically analyzed parameters for Donnan Dialysis process

Donnan Dialysis (DD) utilizes ion exchange membranes that allow the selective transport of target ions from a feed solution to a concentrated receiver solution. The kinetics of DD involves boundary layer diffusion (BLD), diffusional membrane transport (MD), and a mixed regime where both mechanisms are active. The objective of the research was to develop an automated computational model that can predict nitrate, bicarbonate, and sulfate concentration profiles and transport mechanisms in DD processes. Experiments were conducted in a batch dialyzer in sole- and multi-component feed solutions and NaCl receiver solutions.Training of the model included numerical extraction of the BLD and MD coefficients from the experimental data; determination of the statistically significant parameters that affect the DD transport; development of correlations between these parameters and the kinetic coefficients; and mapping of the ratio between the boundary layer resistance and the membrane resistance to determine the transport mechanism.The predictive model, included the kinetic equations, i.e., the Nernst-Planck formulation, mass balances, and electro-neutrality, the correlations, and the mapping of the transport mechanism. The model was verified by the experimental data used for the model training and validated by independent datasets. Very good fits between the predicted and experimental concentration profiles were obtained, and the ability to determine the transport mechanism was demonstrated.

Polyvinyl Chloride Microplastics Leach Phthalates into the Aquatic Environment over Decades.

Phthalic acid esters (phthalates) have been detected everywhere in the environment, but data on leaching kinetics and the governing mass transfer process into aqueous systems remain largely unknown. In this study, we experimentally determined time-dependent leaching curves for three phthalates di(2-ethylhexyl) phthalate, di(2-ethylhexyl) terephthalate, and diisononyl phthalate from polyvinyl chloride (PVC) microplastics and thereby enabled a better understanding of their leaching kinetics. This is essential for exposure assessment and to predict microplastic-bound environmental concentrations of phthalates. Leaching curves were analyzed using models for intraparticle diffusion (IPD) and aqueous boundary layer diffusion (ABLD). We show that ABLD is the governing diffusion process for the continuous leaching of phthalates because phthalates are very hydrophobic (partitioning coefficients between PVC and water log KPVC/W were higher than 8.6), slowing down the diffusion through the ABL. Also, the diffusion coefficient in the polymer DPVC is relatively high (∼8 × 10–14 m2 s–1) and thus enhances IPD. Desorption half-lives of the studied PVC microplastics are greater than 500 years but can be strongly influenced by environmental factors. By combining leaching experiments and modeling, our results reveal that PVC microplastics are a long-term source of phthalates in the environment.

Magnetized vermiculite loaded with waste polishing powder to recover phosphorus in waste water

In view of the phosphorus pollution in water bodies and the shortage of phosphate rock resources, the preparation of cheap, accessible and easy-to-recycle adsorbents for the recovery of phosphorus in sewage has attracted much attention. In this study, waste rare earth polishing powder (WP) was doped with magnetized vermiculite (Mev) at a mass ratio of 1:1 through acid leaching and advection precipitation method to prepare the magnetic Mev-WP composite material for adsorbing and recovering phosphorus in the water. The results show that Mev-WP is easy to be separated from water by an external magnetic field and the main reason why Mev-WP specificity can adsorb phosphorus is that the rare earth elements of La and Ce in the polishing powder are loaded on the flake magnetized vermiculite in the form of La (OH)3 and Ce(OH)3. The phosphorus adsorption process of Mev-WP is an endothermic mono-layer chemical adsorption that includes boundary layer diffusion and internal diffusion, of which the boundary layer diffusion is the rate-limiting step, which can complete rapid adsorption within 30 min. Except for HCO3− ions, other coexisting anions in the water have no significant effect on adsorption, but the adsorption capacity is greatly affected by pH. At pH 11 to 3, the material is a stable and environmentally-friendly adsorbent, and with the decrease of pH, the adsorption capacity increases significantly. When the pH is 3, at 25 °C, the adsorption capacity can reach up to 63.79 mg/g. The phosphorus adsorption mechanism of Mev-WP is electrostatic attraction and ligand exchange between -OH on La-OH and Ce-OH and phosphate groups in the water to generate La-O-P and Ce-O-P coordination complexes to remove phosphorus. After 5 times desorption and recycling, the phosphorus recovery rate of the material reaches 65 %, and the deep phosphorus removal verification in urban sewage is effective. Studies have shown that Mev-WP is a promising specific phosphorus recovery agent.

Thermodynamics, Kinetics and Isotherms Studies for Sorption of Direct and Disperse Dyes onto Eco-friendly Pre-treated Cellulose Acetate Fabric using Ultraviolet Irradiation

Introduction: Owing to the restoration of hydroxyl groups, cellulose acetate fibers can be dyed with direct dyes. There are some drawbacks in the conventional deacetylation process of cellulose acetate from environmental point of view. Methods: This process involves high temperature, alkalinity and large volume of effluent. The goal of this work is to improve the dyeing properties of cellulose acetate fabric using an eco-friendly treatment process. In this paper, cellulose acetate fabric was treated with ultraviolet light (UVB) at an air pressure of 1 atm to improve dyeability. Then, the untreated and UV treated fabrics were dyed with direct and disperse dyes. UV treated cellulose acetate fabric showed higher dye adsorption compare to that of untreated cellulose acetate fabric. Five adsorption isotherm models including sold solution, Langmuir, Freundlich, Temkin and BET were applied to determine the adsorption behavior. At all temperatures studied, experimental data were better fitted with the Freundlich and Nernst models for direct and disperse dyes respectively. Thermodynamic parameters such as change in free energy (ΔG0), the enthalpy (ΔH0), and the entropy (ΔS0) were also evaluated. Results: The calculated thermodynamic values showed that the adsorption of these dyes onto the cellulose acetate fabric was a physical adsorption process and endothermic in nature. These data also implied that the adsorption of direct dye onto cellulose acetate fabric was spontaneous at the experimental temperature range and adsorption of disperse dyes can be spontaneous at higher temperatures. Moreover, the ΔG0 values for the adsorption of disperse dyes onto the UV-treated fabrics were less than those for untreated fabrics suggesting that UV treated fabrics require less external energy. Conclusion: Among the kinetic models studied, it was found that the pseudo second-order kinetic model was the best model to describe the dye sorption process on the UV treated and untreated cellulose acetate fabrics. The UV treatment led to an improvement in the boundary layer diffusion effect.

Ciliary flows in corals ventilate target areas of high photosynthetic oxygen production

Most tropical corals live in symbiosis with Symbiodiniaceae algae whose photosynthetic production of oxygen (O2) may lead to excess O2 in the diffusive boundary layer (DBL) above the coral surface. When flow is low, cilia-induced mixing of the coral DBL is vital to remove excess O2 and prevent oxidative stress that may lead to coral bleaching and mortality. Here, we combined particle image velocimetry using O2-sensitive nanoparticles (sensPIV) with chlorophyll (Chla)-sensitive hyperspectral imaging to visualize the microscale distribution and dynamics of ciliary flows and O2 in the coral DBL in relation to the distribution of Symbiodiniaceae Chla in the tissue of the reef building coral, Porites lutea. Curiously, we found an inverse relation between O2 in the DBL and Chla in the underlying tissue, with patches of high O2 in the DBL above low Chla in the underlying tissue surrounding the polyp mouth areas and pockets of low O2 concentrations in the DBL above high Chla in the coenosarc tissue connecting neighboring polyps. The spatial segregation of Chla and O2 is related to ciliary-induced flows, causing a lateral redistribution of O2 in the DBL. In a 2D transport-reaction model of the coral DBL, we show that the enhanced O2 transport allocates parts of the O2 surplus to areas containing less chla, which minimizes oxidative stress. Cilary flows thus confer a spatially complex mass transfer in the coral DBL, which may play an important role in mitigating oxidative stress and bleaching in corals.