Mixed Solution System Research Articles

A new thermodynamic model for predicting the 3-D phase equilibrium surface of gas hydrates considering the effect of salt concentration

An accurate understanding of the thermodynamic stability of gas hydrates in salt-bearing systems is of great significance for predicting the extent of hydrate accumulation and determining the hydrate decomposition domain. Therefore, this study proposes a thermodynamic model for predicting the temperature–pressure-salt concentration three-dimensional phase-equilibrium surface. The model considered the interaction of the electrolyte in a mixed salt solution system and non-spherical shaped hydrate crystal cavity. The modified van der Waals-Platteeuw (vdW-P) model and Benedict-Webb-Rubin-Starling (BWRS) equation of state were used to describe the hydrate phase. The Pitzer-Debye-Hückel equation and nonelectrolyte non random two liquid non random factor (N-NRTL-NRF) activity coefficient model were used to describe the fluid phase. The prediction results of the model agreed with the experimental data, and the absolute average relative deviation in temperature (AARD-T) under pure water conditions was only 0.08, and the AARD-T under electrolyte conditions did not exceed 0.15, which proved the accuracy and reliability of the model. The calculation results showed that when the mole fraction of chloride salt was greater than 0.02 and the pressure was higher than 20 MPa, chemical factors caused the p-T curves to translate. When the pressure was low, the temperature gradient along the direction of the salt concentration changed drastically, and the p-T curves no longer had translation characteristics. In comparison, under the same mole fraction, AlCl3 had a stronger inhibitory effect on the CH4 hydrate than the other chloride salts. The lnp-X-1/T three-dimensional surface of the CH4 hydrate exhibited good Clausius-Clapeyron linear behavior locally, and the surface had certain nonlinear characteristics. The degree of nonlinearity of the lnp-X-1/T three-dimensional surfaces of different types of chloride salts was different. A better inhibitory effect of the chloride salt electrolyte on the CH4 hydrate was associated with stronger nonlinearity between 1/T and lnp.

Phosphorylated porous phenolic resin for efficient extraction of low-concentration rare earth elements from tailing wastewater

Efficient extraction and recycling of rare earth elements (REEs) from low-concentration complex tailing wastewater is critical to meeting the growing industrial demands and optimizing resource utilization. In this work, three phosphorylated porous phenolic resins (PO-PPRs) were prepared via the phosphorylation of phenolic hydroxyl groups with POCl3, and employed to extract REE3+ from both simulated and practical low-concentration REE3+-containing aqueous solution. The PO-PPRs, characterized by hierarchical pore structures, exhibit high adsorption capacities for both light and heavy REE3+ ions over a broad pH working range from 3.0 to 7.0, along with fast adsorption kinetics (<30 min). And the maximum adsorption capacities of PO-PPRs for Nd3+, Dy3+ and Y3+ were found to be 104.1, 118.0 and 63.9 mg/g, respectively. Furthermore, the introduction of phosphonic groups significantly improves the REE3+ adsorption selectivity against various interfering metal ions such as Na+, K+, Ca2+, Mg2+, and Al3+. For instance, the Nd3+/Al3+ separation factor (S.F.) of 24 exceeded that of most commercial resins and reported materials. In a simulated mixed multi-element aqueous solution system containing Nd3+, Dy3+, Y3+, Al3+, Ca2+, Mg2+, Mn2+, K+ and Na+, PO-PPR-1 extracted 82.5% of total REE3+ while maintaining Al3+ adsorption efficiency of less than 13%. Moreover, the extraction efficiency of total REE3+ for PO-PPR-1 in pretreated practical wastewater from ion-adsorbed ores tailing reached 99.6%. Additionally, PO-PPRs demonstrated easy regeneration and excellent recycling performance after 5 consecutive adsorption–desorption cycles, confirming their promising application potential in low-concentration REEs extraction.

Competitive adsorption of sulfamethoxazole and bisphenol A on magnetic biochar: Mechanism and site energy distribution

Competitive adsorption and complementary adsorption between emerging pollutants has been observed in multiple studies. Investigation of the preference of pollutants for different types of adsorption sites can provide a supplementary perspective for understanding complementary adsorption. In this study, the simultaneous adsorption of two typical emerging pollutants, sulfamethoxazole (SMX) and bisphenol A (BPA), on magnetic biochar (MBC-1) was investigated. The results showed that the modification with ferric chloride optimized the surface properties of biochar (aromaticity, hydrophobicity, and oxygen-containing functional groups, etc.), and helped to remove SMX and BPA through various interactions. The equilibrium adsorption capacity of the two adsorbents was inhibited by competitive adsorption in the mixed solute systems, which was due to the same adsorption mechanism. When pH = 7, the SMX and BPA adsorption mainly involved pore filling, hydrophobic effect, π-π EDA, and hydrogen bonding. In addition, electrostatic force, surface coordination, and ion exchange have also been proven to be related to the adsorption of SMX and BPA. In the co-adsorption system, BPA's competitive advantage might be due to its superior hydrophobicity, charge property, and molecular diameter. In the competitive adsorption experiment, the total adsorption capacity (Qi) of the competitive solute exceeded the adsorption inhibition (△Qi) of the main solute, indicating that the two solutes occupied their preferred adsorption sites, which confirmed the complementary adsorption phenomenon. Complementary adsorption can be explained by the preference of SMX and BPA for different types of adsorption sites. BPA preferentially occupied high-energy sites in the co-adsorption system, such as π-π EDA interaction, ion exchange, and surface coordination. At the same time, SMX tended to be removed by hydrophobic interaction and hydrogen bonding.

Sorption Characteristics and Site Energy Distribution Theory of Typical Estrogens on Microplastics

Microplastics (MPs) and estrogens are high-profile emerging contaminants at present, and MPs might become the carrier of estrogens in the environment and induce combined pollution. To study the adsorption behavior of polyethylene (PE) microplastics to typical estrogens, the adsorption isothermal properties of the six estrogens[estrone (E1), 17α-estradiol (17α-E2), 17β-estradiol (17β-E2), estriol (E3), diethylstilbestrol (DES), and ethinylestradiol (17α-EE2)] in single-solute and mixed-solute systems were studied through batch equilibrium adsorption experiments, in which the PE microplastics before and after adsorption were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Then, the site energy distribution theory of the adsorption of six estrogens on PE microplastics was further analyzed based on the Freundlich model. The results showed that the adsorption process of selected estrogens with two concentrations (100 μg·L-1 and 1000 μg·L-1) on PE were more consistent with the pseudo-second order kinetic model. The increase in initial concentration reduced the equilibrium time of adsorption and increased the adsorbing capacity of estrogens on PE. In the single system (one estrogen) or mixed system (six estrogens) with different concentrations (10 μg·L-1-2000 μg·L-1), the Freundlich model showed the best fitting effect for the adsorption isotherm data (R2>0.94). The results of isothermal adsorption experiments and XPS and FTIR spectra showed that the adsorption of estrogens on PE in the two systems was heterogeneous adsorption, and hydrophobic distribution and van der Waals forces were the principal factors in the process of adsorption. The occurrence of C-O-C (in only the DES and 17α-EE2 systems) and O-C[FY=,1]O (in only the 17α-EE2 system) indicated that the adsorption of synthetic estrogens on PE was affected slightly by chemical bonding function, but no obvious effects were observed for natural estrogens. The results of site energy distribution analysis showed that, compared with the single system, the adsorption site energy of each estrogen shifted to the high-energy region in its entirety in the mixed system, and the site energy increased by 2.15%-40.98%. The energy change in DES was the most significant among all of the estrogens, indicating its competitive advantage in the mixed system. The above results of this study can provide some reference for the study of adsorption behavior, mechanism of action, and environmental risks under the coexisting condition of organic pollutants and MPs.

Down-conversion-induced delayed fluorescence via an inverted singlet-triplet channel

Inverted singlet-triplet molecules possessing a down-conversion process from the lowest excited triplet state (T1) to the lowest excited singlet state (S1) have recently roused much attention on account of potential merits in organic optoelectronics and photocatalysis. Nevertheless, investigations on inverted singlet-triplet molecules predominantly depend on the sophisticated ab initio calculations, while experimental attempts are extremely rare. In this work, we experimentally demonstrate the inverted singlet-triplet character of a heptazine derivative (HAP-3MF) which exhibits negative S1-T1 energy gaps (ΔEST) of −0.22 eV in toluene and −0.19 eV in acetonitrile based on meticulous photophysical investigations. To the best of our knowledge, this is the first time to directly obtain negative ΔEST based on fluorescence and phosphorescence spectra. Moreover, to better evaluate and reveal the photophysical features of extremely weak delayed emission in HAP-3MF, a mixed solution system of HAP-3MF:1,3-di(9H-carbazol-9-yl)benzene (mCP) in toluene at various molar ratios was subtly designed, and the energy transition mechanism involving a down-converted triplet-to-singlet channel was carefully elucidated.

Construction of efficient g-C3N4/NH2-UiO-66 (Zr) heterojunction photocatalysts for wastewater purification

• g-C 3 N 4 /NH 2 -UiO-66 (Zr) heterojunction photocatalysts were constructed. • The photocatalysts showed high-efficiency photocatalytic Cr (VI) removal activity. • Photocatalytic Cr (VI) and TC-HCl removal were synergistically promoted. Herein, g-C 3 N 4 /NH 2 -UiO-66 (Zr) heterojunction photocatalysts were successfully constructed by a solvothermal and in-situ deposition route. It presented high-efficiency photocatalytic hexavalent chromium (Cr (VI)) removal activity and promoted photocatalytic Cr (VI) reduction and tetracycline hydrochloride (TC-HCl) oxidation synergistically. The experimental and theoretical analysis confirmed that the photocatalytic removal efficiency of Cr (VI) by CU-20 wt.% forming heterojunction structure was 1.86 times that of pure NH 2 -UiO-66 (Zr) under visible light irradiation, and prepared photocatalysts exhibited significant stability and good repeatability. Simultaneously, the effects of different influencing factors such as the concentration of Cr (VI) and different pH values on the photocatalytic performance of CU-20 wt.% were clarified. Moreover, CU-20 wt.% could synergistically remove pollutants in the mixed solution system, and the efficiency of Cr (VI) reduction reached 100% within 90 min under visible light irradiation, and improved the efficiency of TC-HCl oxidation. A heterojunction structure constructed can effectively enhance the separation and transfer of carriers and synergistic effect, and furtherly improve the photocatalytic performance. This work proposes that photocatalysts with heterojunction structures would be effectively applied to wastewater purification.

An expedient in to the phase behaviour and scattering profile in PEO-PPO-PEO block copolymer mixed systems in aqueous solution

The present study aims to develop copolymeric micelles giving an account on the clouding behavior of two series of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers with varying molecular weight of PPO: one with moderate hydrophilicity i.e., 40 % PEO (L64, P84, P104) blended with very hydrophobic copolymers i.e., 10 % PEO (L61, L81, L101, L121). Marked changes in the solution behavior in our mixed copolymeric solution systems depicted the micellization and micelle growth/ transition along with the phase separation (2ϕ) which is well explained from cloud Point (CP) and solution relative viscosity (ηrel) study. The CP analysis showed the lower cloud point (LCP) and the conventional upper cloud point (UCP) i.e., two marvelous CP in the aqueous mixed Pluronics® system which motivated to explore the hypothesis of double cloud point. Such shifting phenomenon from LCP towards UCP demonstrated an increment in dynamic light scattering (DLS) intensity resulting in the obvious increment in the micellar dimensions i.e., hydrodynamic diameter (Dh) for the examined mixed copolymeric system. In addition, the small-angle neutron scattering (SANS) data were fitted to obtain the predictable parameters such as, hard sphere radius (Rhs), aggregation number (Nagg) and micellar morphology. Our findings corroborated the micellar transition from spherical to elongated ellipsoidal micelles with temperature ageing depicting a strong dependence on the amphiphilicity and concentration of the two BCPs in the mixed solution environment.

Large capacity and rapid rate of ion removal from synthetic municipal wastewater via CDI using chitosan-based nitrogen-doped porous carbon electrode

Capacitive deionization (CDI) technology has excelled in water treatment areas such as brackish water desalination, hard water softening and pollution ion removal. However, the poor performance of the electrodes used in CDI cell construction continues to limit its practical application. In this work, we used chitosan mixed with potassium hydroxide (KOH) and simply carbonized to synthesize porous carbon electrode materials (CTS-850) with excellent material and electrochemical performance, and achieve high adsorption capacity and fast adsorption rate in a variety of salt solutions. The material characterization of CTS-850 displayed super large specific surface area (>2300 cm3 g−1), pore volume and excellent nitrogen doping. Electrochemical characterization showed excellent specific capacitance, good conductivity and cycle performance. In CDI experiments, we explored the removal efficiency of electrodes carbonized under different temperatures in single and mixed solution systems, and the CTS-850 electrode had an ultra-high adsorption capacity of 47 mg g-1 and a fast adsorption rate of 6.7 mg g-1 min-1 in 15 mM synthetic municipal wastewater (～1750 mg L-1). In addition, we discussed the relationship between high adsorption capacity, fast adsorption rate and material properties. Our work is expected to provide guidance for the synthesis of higher performance CDI electrode materials.

Adsorption-photocatalysis synergistic removal of contaminants under antibiotic and Cr(VI) coexistence environment using non-metal g-C3N4 based nanomaterial obtained by supramolecular self-assembly method

Due to the rapid development of modern industry, the coexistence of antibiotics and inorganic heavy metals pollutants in wastewater has become a universal phenomenon. Therefore, developing efficient and eco-friendly photocatalyst for mixed pollutants degradation is significant. In this work, a well-designed phosphorus and sulfur co-doped g-C3N4 with feeble N vacancies catalyst (P/S-g-C3Nx) was fabricated by supramolecular self-assembly method, and was applied to remove berberine hydrochloride (BH) and Cr(VI) simultaneously with the synergy of adsorption-photocatalysis. A series of experiments was conducted to unveil the synergistic mechanism. The kinetic models indicated that the adsorption of P/S-g-C3Nx improved the BH removal process by accelerating the photo-degradation, because the adsorption rate > surface degradation rate > bulk degradation rate. Besides, the photo-degradation process improved the BH removal rate by regenerating the adsorption sites of P/S-g-C3Nx. Moreover, from the experiments in BH-Cr(VI) mixed solution system, the existence of BH also enhanced the surface adsorption of Cr(VI) in P/S-g-C3Nx sample, and the reduction rate of Cr(VI) was also promoted with the existence of BH. Overall, the results of this investigation suggest that the adsorption-photocatalysis synergy method is an efficient way to eliminate organic pollutant and Cr(VI) simultaneously.

Gold imprinted adsorption based on eugenol

Synthesis of Ionic Imprinted Polymer (IIP)-Au have been carried out using polyeugenoxy acetate (PA) as the base polymer. IIP is formed through the transfer of a basic polymer with a metal template which is then crosslinked with ethylene glycol dimethacrylate (EGDMA) and the release of the metal template using acid. Non Imprinted Polymers are also synthesized for use as a comparison. Polymerization of up to IIP and NIP was carried out using infrared spectrophotometers and SEM-EDX. IIP and NIP are used to determine the rate and capacity of adsorption through kinetics and adsorption isotherms studies. Adsorption selectivity tests were carried out on a mixed metal solution system Au(III)/Cd(II), Au(III)/Pb(II), and Au(III)/Fe(III). The amount of adsorbed metal ions is calculated based on the remaining metal ions in the solution measured using atomic absorption spectroscopy. The results of the adsorption of Au(III) metal ions in IIP and NIP followed the second-order pseudo and isotherm followed Langmuir. adsorption capacity in IIP-PA is (28,305 mg/g), and NIP-PA adsorption capacity is (45,080 mg/g). IIP adsorption selectivity is greater than NIP in binary solutions in the order of Au(III)/Cd (II)> Au(III)/Pb(II)> Au(III)/Fe(III).

Amino-functionalized mesoporous silica-magnetic graphene oxide nanocomposites as water-dispersible adsorbents for the removal of the oxytetracycline antibiotic from aqueous solutions: adsorption performance, effects of coexisting ions, and natural organic matter.

The amino-functionalized mesoporous silica-magnetic graphene oxide nanocomposite (A-mGO-Si) was synthesized and used for oxytetracycline (OTC) removal from water. Various factors like the effects of initial concentration, contact time, and influence of pH were investigated. Selective adsorption experiments in connection with coexisting ions and dissolved organic matter (DOM) were also investigated. In this study, humic acid (HA) and tannic acid (TA) were representative of both hydrophobic and hydrophilic DOM, respectively. Results indicated that A-mGO-Si had an adsorption ability for OTC that was relatively greater than that of virgin magnetic graphene oxide (mGO), graphene oxide (GO), Fe3O4 particles, and SBA-15 mesoporous silica and also showed a better uptake removal capacity for OTC at low initial concentration in comparison with the other adsorbents. The adsorption behavior of OTC onto A-mGO-Si could be described by the pseudo-second-order kinetic model and the Freundlich isotherm model. The electrostatic interaction has no influence on the OTC absorbed when the OTC is in an aqueous medium in its zwitterion form (3.22 < pH < 7.46). At high pH, the weak π-π EDA interactions and hydrogen bonding may manifest themselves, hence causing a lower adsorption capacity. The main adsorption mechanisms were plausibly activated by H-bonding, and π-π EDA interactions, while the electrostatic interaction (cation-π interaction) might be the minor adsorption mechanism. Addition of individually exogenous ions (Na+, Mg2+, NO-, and CO32-) resulted in a decrease of OTC adsorption due to the emergence of a competitive effect. Considering the presence of HA and TA in mixed solute systems, the DOM was likely to form a stronger interaction system with mGO-Si, thereby resulting in an adsorption level which was more competitive in the process at low aqueous phase concentration of OTC. In contrast to the high aqueous phase, the coexistence of DOM could promote OTC adsorption. The phenomenon may reflect the result that a surface complexation mechanism could achieve in adsorptions.

Application and modeling of pressure-concentration double-driven diffusion dialysis

Diffusion dialysis (DD) is an ion exchange membrane separation process driven by concentration differences. DD is simple to operate and has excellent stability, low energy consumption, and a low installation cost. To overcome the limitations of the traditional DD process, such as low processing capacity and serious water osmosis, the authors propose a pressure-concentration double-driven (PCDD) DD process. This novel DD is double driven because the concentration difference is the main mass transfer force, and the pressure difference is the assistant mass transfer force. The common FeSO4/H2SO4 mixed solution system is used to investigate the PCDD DD process. Our first area of interest is the operating parameters' effects (the pressure difference as well as the initial H2SO4 and FeSO4 concentrations in feed) on the PCDD DD process performance. Results show that the high pressure difference can significantly promote the increment of the H+ dialysis coefficient from 0.0012 to 0.0039 m/h and the Fe2+ dialysis coefficient from 1.25 × 10−5 to 5.95 × 10−5 m/h. Pressure differences in high value can also change the direction of water osmosis (from the dialysate to diffusate). All these are employed to maintain the separation factor in an acceptable range (∼65). Moreover, the increment of the initial FeSO4 concentration in the feed can improve the H+ dialysis coefficient and reduce the Fe2+ dialysis coefficient to increase the separation factor further. However, increasing the initial H2SO4 concentration in the feed is not a commonly accepted method to improve the PCDD DD process performance. A mathematical model based on non-equilibrium thermodynamics is established to quantify the PCDD DD mass transfer process. Notably, the fitting results of the calculated fluxes based on the model and the experimental fluxes are very satisfactory. The research presented here indicates that the PCDD DD process can increase the DD's processing capacity, maintain a good separation effect, and inhibit the water osmosis simultaneously.

Foaming in aqueous solutions of mixtures of a zwitterionic and a cationic surfactant in presence of an electrolyte

This paper reports the foamability and the stability of foams of aqueous solutions of mixed systems of a zwitterionic surfactant (i.e. N-Dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate) and a cationic surfactant (i.e. cetyltrimethylammonium bromide) in the presence of NaCl. The synergism between the surfactants was examined by measuring the surface tension for various compositions of the surfactants and the salt. The interaction occurring between the surfactant molecules adsorbed at the air–water interface influenced the monolayer properties. The mixed surfactant system produced a significant decrease in surface tension as compared to the single surfactant systems. In the presence of salt, the surface tension reduction was larger. The interaction among the surfactant molecules at the air–water interface and the same in the mixed micelles was quantified by the respective interaction parameters. The blender test was used to investigate the foamability and foam stability. The foamability studies showed synergistic behavior inasmuch as higher foam volumes were generated in the mixed surfactant systems as compared to the single surfactant systems. The addition of salt had a remarkable effect on the foaming properties of the mixed surfactant systems. It increased the stability of foams significantly. The synergism between the surfactant molecules had a notable influence on the zeta potential at the air–water interface.

Influences of the mixed LiCl-CaCl2 liquid desiccant solution on a membrane-based dehumidification system: Parametric analysis and mixing ratio selection

The membrane-based liquid desiccant dehumidification system has high energy efficiency without the traditional liquid system carry-over problem. The performance of such a system strongly depends on solution's temperature and concentration, which have direct relationship to the solution surface vapour pressure. Compared with the pure liquid desiccant solution, the mixed liquid desiccant solution has lower surface vapour pressure, better system performance and lower material cost. In this paper, the performance of a flat-plate membrane-based liquid desiccant dehumidification system with the mixed solution (LiCl and CaCl2) is investigated through theoretical and experimental approaches. A mathematical model is established to predict the system performance, while the electrolyte non-random two-liquid (NRTL) method is applied to calculate the mixed solution properties. The influences of the solution mixing ratio, temperature Tsol and concentration Csol are evaluated, and it is found that the regeneration heat Qreg can be dramatically reduced by either applying a high concentration solution or increasing CaCl2 content in the mixed solution. Compared with the pure LiCl solution system, the mixed solution system COP can be improved up to 30.23% by increasing CaCl2 content for a 30% concentration solution. The optimum mixing ratio varies with the solution concentration. For the mixed LiCl-CaCl2 solution, the system highest COPs appear at the mixing ratios of 3:1, 2:1 and 1:1 for 20%, 30% and 40% concentrations respectively.

Nonionic surfactant enhanced biodegradation of m-xylene by mixed bacteria and its application in biotrickling filter

ABSTRACTIn this study, m-xylene biodegradation was examined in bacteria-water mixed solution and biotrickling filter (BTF) systems amended with the nonionic surfactant Tween 80. The mixed bacteria were obtained from the activated sludge of a coking plant through a multisubstrate acclimatization process. High-throughput sequencing analysis revealed that Rhodanobacter sp. was the dominant species among the mixed bacteria. In the bacteria-water mixed solution, the bacterial density increased with increasing Tween 80 concentration. Hence, Tween 80 could be utilized as substrate by the mixed bacteria. Tween 80, with concentrations of 50–100 mg L−1, could enhance the bioavailability of m-xylene and consequently improve the degradation efficiency of m-xylene. However, further increasing the initial concentration of Tween 80 would decrease the degradation efficiency of m-xylene. At concentrations exceeding 100 mg L−1, Tween 80 was preferentially degraded by the mixed bacteria over m-xylene. In BTF systems, when the m-xylene inlet concentration was 1200 mg m−3 and the empty bed residence time was 20 sec, the removal efficiency and elimination capacity of BTF1 with Tween 80 addition were at most 20% and 24% higher than those of BTF2 without Tween 80 addition. Overall, the integrated application of the mixed bacteria and surfactant was demonstrated to be a highly effective strategy for m-xylene waste gas treatment.Implications: The integrated application of mixed bacteria and surfactant was demonstrated to be a promising approach for the highly efficient removal of m-xylene. Surfactant can activate mixed bacteria to degrade m-xylene by increasing its bioavailability. Besides, surfactant can be utilized as carbon source by the mixed bacteria so that the growth of mixed bacteria can be promoted. It is expected that the integrated application of both technologies will become more common in future chemical industry.

Symbiosis mechanism of iron and manganese oxides in oxic aqueous systems

Iron and manganese oxides are ubiquitous in soils and sediments, and their formation and conversion processes affect the migration and transformation of heavy metals and organic pollutants. Mn2+ was found to affect the formation of iron oxides from Fe2+ oxidation. However, little attention has been paid to the oxidation process at the initial stage and generation of manganese oxides in the reaction system of Fe2+aq and Mn2+aq. This work investigated the formation process and mechanism of iron and manganese oxides in a mixed solution system of Fe2+aq and Mn2+aq under oxic condition. The effect of pH (5.0–9.0) on the reaction process and products was further studied. The results indicated that Fe2+aq was oxidized to goethite and lepidocrocite, and Mn2+ adsorbed on the surface of iron oxides was catalytically oxidized to poorly crystalline manganese oxides by dissolved O2 in a mixed solution of Fe2+aq and Mn2+aq. Compared with the absence of Mn2+aq, the presence of Mn2+aq caused no obvious changes in the species of iron oxides, but significantly increased the oxidation rate of Fe2+aq. Formation of manganese oxides on the surface decreased the crystallinity of the iron oxides. The increase of pH enhanced the oxidation of Fe2+aq and Mn2+aq and formation of lepidocrocite. This work expands our understanding of the interactions and geochemical processes of Fe2+aq and Mn2+aq.

Polymeric Ion Pumps: Using an Oscillating Stimulus To Drive Solute Transport in Reactive Membranes.

The development of membranes that separate molecules on the basis of chemical factors, rather than physical factors, is one promising approach to meeting the demand for membranes that are more selective. In this study, the design of multifunctional, pH-responsive membranes that selectively pump a target solute is detailed. The membranes consist of two functional components: a gate layer made from an amine-functionalized copolymer and a reactive matrix lined by iminodiacetic acid groups that bind divalent cations reversibly. These two chemistries exhibit concurrent changes in the cation binding affinity and gate permeability in response to the pH value of the surrounding solution such that when the membranes are exposed to an oscillating pH, the combination drives a facilitated transport mechanism that pumps ions. In mixed solute systems, calcium permeated through the membrane four times faster than sucrose in the presence of an oscillating pH even though the solutes possess similar hydrodynamic sizes and permeated through the membrane at the same rate when the pH value was constant. The development of polymeric ion pumps was guided by a model that provided several critical insights. First, the solute binding capacity and thickness of the membrane define the asymptotic limit for enhanced selectivity. Second, the maximum enhancement in selectivity is realized in the limit of infinitely rapid oscillations. The multifunctional membranes discussed here provide a platform for the development of processes that can fractionate molecules of similar size but varying chemistry.

Strong enrichment of atmospherically relevant organic ions at the aqueous interface: the role of ion pairing and cooperative effects.

Surface affinity, orientation and ion pairing are investigated in mixed and single solute systems of aqueous sodium hexanoate and hexylammonium chloride. The surface sensitive X-ray photoelectron spectroscopy technique has been used to acquire the experimental results, while the computational data have been calculated using molecular dynamics simulations. By comparing the single solute solutions with the mixed one, we observe a non-linear surface enrichment and reorientation of the organic ions with their alkyl chains pointing out of the aqueous surface. We ascribe this effect to ion paring between the charged functional groups on the respective organic ion and hydrophobic expulsion of the alkyl chains from the surface in combination with van der Waals interactions between the alkyl chains. These cooperative effects lead to a substantial surface enrichment of organic ions, with consequences for aerosol surface properties.

Effect of pickling process on removal of oxide layer on the surface of ferritic stainless steel

ABSTRACTOxide layer formed on stainless steel surface can result in a decrease in surface quality. Thus, it must be removed. In this paper, we investigated the effect of different pickling processes on removal of the oxide layer. Ferritic stainless steel was used as raw material. After it received annealing treatment, the components and structure of the oxide layer formed on its surface were studied. Then, the annealed stainless steel was pickled in hydrochloric acid solution system and mixed acid solution system, respectively. Results are as follows. The oxide layer on stainless steel surface has a thickness of 15–35 μm. With increase in hydrochloric acid concentration in hydrochloric acid pickling solution, the weight loss rate of stainless steel increases and is always greater than that in mixed acid pickling system. In addition, the surface of the stainless steel pickled in hydrochloric acid is smoother than that pickled in mixed acid. Furthermore, compared with channels in the oxide layer created during mixed acid pickling, those created during hydrochloric acid pickling are more, leading to shorter removal time. These results are important for increasing the pickling efficiency and improving the surface quality of stainless steel.

Adsorption characteristics of phenol and heavy metals on biochar from Hizikia fusiformis

The objective of the present study is to evaluate the absorption efficacy of H. fusiformis biochar (HFB) for the removal of phenol and heavy metals from single and mixed solute systems of these species under different experimental conditions. The effects of contact time, pH change, initial phenol concentration, and heavy metal concentration on the adsorption capacity of HFB were investigated. The kinetics and equilibrium models of sorption of the components of the single and mixed solute systems on HFB were also studied. The experimental data were fitted to kinetic and equilibrium models. The batch experiments revealed that 360 min of contact time was sufficient to achieve equilibrium for the adsorption of both phenol and heavy metals. The adsorption of phenol and nickel by HFB followed the pseudo-second-order kinetic model, which was quite adequate for describing the adsorption mechanism. The equilibrium data for the adsorption of phenol and heavy metals fit well to the Langmuir model with regression coefficients of R 2 > 0.819. The maximum Langmuir adsorption capacities were 10.39, 12.13, 22.25, 2.24, 2.89, and 22.03 mg/g for phenol, Ni2+, Zn2+, Cu2+, Pb2+, and Cd2+, respectively. Moreover, HFB exhibited optimal sorption under slightly acidic conditions at pH 6. The HFB used in the present study exhibited higher adsorption capacity for the removal of phenol and heavy metals from aqueous solutions compared to documented sorbents. These results demonstrate that HFB is potentially useful for alleviating the harmful effects of phenol and heavy metal in wastewater treatment systems.