Solutions In Binary Systems Research Articles

Feasibility of vanadium ion adsorption/desorption using nickel–aluminum complex hydroxides with different molar ratios

Herein, metal complex hydroxides containing nickel (Ni) and aluminum (Al) at different molar ratios (Ni:Al = 1:1 (NA11), 1:2 (NA12), 2:1 (NA21), 3:1 (NA31), and 4:1 (NA41)) were prepared. Scanning electron microscopy images, X-ray diffraction patterns, specific surface area, number of hydroxyl groups, and pHpzc were evaluated. Further, the adsorption capacity of vanadium ions was assessed, with NA21 showing a high potential to adsorb vanadium ions from the aqueous phase (177.5 mg/g). In addition, the effects of various factors, including pH, contact time, initial concentration, and temperature, on the adsorption of vanadium ions were demonstrated in this study using NA21. The optimal pH value for adsorbing vanadium ions was 5.0. Adsorption isotherms and kinetic data were fitted to a pseudo-second-order model (correlation coefficient: 0.958) and a Freundlich model (correlation coefficient: 0.930–0.982), respectively. This study elucidated that a part of the adsorption mechanism of vanadium was related to ion exchange and characteristics of NA21 surface. Moreover, NA21 showed capability to selectively adsorb vanadium ions from binary solution system containing chloride, nitrate, or sulfate ions. Vanadium ions adsorbed onto NA21 were more easily desorbed by a sodium hydroxide solution than a sodium sulfate solution. NA21 demonstrated consistent performance over at least three adsorption and desorption cycles under experimental conditions of this study. These findings provided valuable insights into the recovery of vanadium ions from aqueous media via adsorption/desorption treatment using NA21.

Deciphering the transfer mechanisms for CO2 absorption into binary blended solutions

A thorough understanding of the mechanisms involved in CO2 chemical absorption is crucial for the development of efficient CO2 capture technologies. Due to the insufficient insight into the interaction mechanism of different components in blended solutions, CO2 absorption reactions were often categorized as unidirectional transfer between absorption products. In this study, the CO2 absorption performance of binary blended solutions, including piperazine (PZ)/n-methyldiethanolamine (MDEA), ethanolamine (MEA)/MDEA, ammonia (NH3)/MDEA, PZ/potassium carbonate (K2CO3), and NH3/K2CO3, was investigated using a combination of experimental and computational methods. The CO2 absorption mechanisms of “competitive reaction”, “transfer reaction” and “parallel reaction” in the binary blended solution system were proposed. Kinetic experiments revealed that different blended solutions had varying impacts on the process of CO2 absorption. Among them, PZ/MDEA and MEA/MDEA solutions reduced the absorption rates by an average of 8% and 25%, respectively, compared to PZ or MEA component solutions. NH3/MDEA and PZ/K2CO3 solutions had absorption rates similar to those of single NH3/PZ component solutions. NH3/K2CO3 solutions, on the other hand, exhibited an average increase of 17% in absorption rates compared to NH3 solutions. Quantum mechanical (QM) methods were employed to evaluate of the absorption products and key processes in terms of kinetics and thermodynamics. Quantitative 13C NMR analyses were conducted to further investigate the interactions between components and the pathways of mass transport in blended solutions, which demonstrated proton transfer and CO2/-COO transfer between adsorption products. This study highlights an accurate description of the transfer mechanisms of various blended systems for the enhanced CO2 capture.

Enabling low molecular weight electrospinning through binary solutions of polymer blends

The formation of nanofibrous membranes via electrospinning is typically restricted to high molecular weight polymers in an appropriate solvent, correlated with the necessary formation of polymer chain entanglements that are needed to achieve successful production of electrospun fibers. The present work extends the electrospinning of low molecular weight polymers by investigating the electrospinning of a binary solution system consisting of two different low molecular weight polymers, using as a model system polycaprolactone (PCL) and gelatin in different ratios. The viscosities of the polymer solutions were characterized as a proxy for polymer chain entanglement and the resulting fibers were morphologically characterized by SEM imaging and further assessed water contact angle and molecular composition to determine the impact and homogeneity of the binary mixtures. We found that unitary solutions of either PCL or gelatin failed to generate proper fibers despite indications of chain entanglement. In contrast, binary solutions of low molecular weight PCL and gelatin generated different fiber quality and size distributions, depending on the ratio used, with direct correlations between fiber properties and the PCL:Gelatin ratio. It was discovered that the ratio of PCL to gelation was most predictive for successful fiber generation, with effective electrospinning occurring only for a define intermediate range of high blend ratios while both low and high blended binary solutions resulted in poor fiber production. Our study confirmed that this behavior was independent from absolute polymer concentration, indicating a unique interaction between these binary species which exists only under specific ratio concentrations and indicates promising new avenues to process low molecular weight polymers solutions.

Tailoring ethylenediamine functionalization on magnetic Zr-based metal-organic frameworks towards enhanced phosphate and tetracycline adsorption by synergy of Fe3O4 and amino functional groups

The development of efficient adsorbent for removing excessive nutrients (e.g. phosphorous – P) and antibiotics (e.g. tetracycline hydrochloride – TC) from livestock wastewater is necessary but challenging in practical application. In this study, magnetic Zr-based metal-organic frameworks (Fe3O4/UiO-66) with interfacial Fe-O-Zr bonds were synthesized and then modified with ethylenediamine (EDA) functional groups. The resultant optimized composite, namely Fe3O4/UiO-66-N2, showed promising removal of P and TC from both single and binary solution systems. It exhibited the maximum P and TC adsorption capacities of 90.0 mg P/g and 72.3 mg/g in the single component solution, respectively. In the binary solution with an initial P concentration of 5 mg P/L, the coexistence of TC posed a slight inhibition effect on the P adsorption over Fe3O4/UiO-66-N2. However, the TC adsorption was increased by raising the initial P concentration in solution from 5 mg P/L to 20 mg P/L. The Fe3O4 nanoparticles and EDA functional groups were suggested jointly improving the adsorption capacities of P and TC, with the synergy factors of 1.1 and 1.8, respectively. The effects of reaction time, water medium, initial pH and coexisting ions on the adsorption were investigated in detail. The mechanisms governing the adsorption of phosphate included electrostatic attraction, hydrogen bonding, ligand exchange and complexation. Those contributing to the adsorption of TC included Lewis acid-base interaction and π-π electron-donor-acceptor interaction, in addition to electrostatic attraction, hydrogen bonding and complexation. This work designed novel functionalized magnetic MOF composite adsorbents targeting at efficient and simultaneous removal of P and TC from water, under the synergistic effect of the Fe3O4 nanoparticles and surface functional groups.

Nitrogen-doped carbon nanotube catalytic membrane with peroxymonosulfate activation for the degradation of metronidazole and bisphenol A: Performance and mechanism comparison

As typical pharmaceuticals and personal care products (PPCPs), metronidazole (MNZ) and bisphenol A (BPA) normally presented in sewage effluent and surface water. The nitrogen-doped multi-walled carbon nanotube (NCNT) membrane was prepared and utilized as a peroxymonosulphate (PMS) catalyst to degrade MNZ and BPA. Within the NCNT membrane/PMS catalytic system, MNZ and BPA can be efficiently degraded, while different catalytic degradation mechanism exists related with their structure, adsorption properties and even PMS dosage. The optimal conditions for the degradation of MNZ and BPA were investigated. Quenching tests and electron paramagnetic resonance examination demonstrated that •OH radicals and 1O2 played roles in MNZ degradation, while surface-bound radicals and 1O2 dominated BPA degradation within the NCNT membrane catalytic PMS system. Electrochemical tests proved that an electron-transfer process between NCNT membrane and PMS during MNZ degradation, and the electron-transfer process was further verified with the degradation experiment in the binary-solute system (BPA and MNZ). PMS dosage had little influence on the degradation mechanism of MNZ and BPA.

Precipitation behavior of calcium sulfate in leach solution of ion-adsorption rare earth ore after reverse osmosis

Ion-adsorption rare earth ore (IAREO) is a crucial source of mid-heavy rare earths elements (M-HRE). Reverse osmosis technology is a promising technique for the pre-concentration of the leach solution from in-situ leaching of IAREO. However, calcium sulfate scaling is inevitably formed in sulfate system, causing decreases in the flux and life time of membrane. Herein, to simulate the precipitation behavior of calcium sulfate in the leach solution of IAREO during reverse osmosis, a series of experiments was conducted in binary and quaternary supersaturated calcium sulfate solution systems. Experimental data show that the concentration of Ca2+ decreases with the increase of the concentration of Mg2+, and increases with the increase of the concentration of RE3+ in both binary and quaternary systems. Whereas, the influence of Al3+ on the concentration of Ca2+ is different. This variation of the Ca2+ concentration is explained by thermodynamic analysis. The difference of association concentration for Mg2+, Al3+ and RE3+ with SO42− in binary or quaternary system is the main reason. Finally, the influence and mechanisms of antiscalant on the precipitation behavior of calcium sulfate are discussed. X-ray diffraction (XRD), Zeta potential and scanning electron microscopy (SEM) analyses reveal that polyacrylic acid (PAA) effectively inhibits the crystal growth of calcium sulfate, and the precipitation time of calcium sulfate is prolonged, indicating that PPA is a potential inhibitor for calcium sulfate scaling during the process of reverse osmosis.

Experimental and molecular simulation analysis of the dissolution behavior of Musk ambrette in organic solvents

The solubility of Musk ambrette in i-propanol (IPA), i-butanol (IBA), n-heptane (HPT), n-hexane (HX), cyclohexane (CYH), methyl acetate (MAC), ethyl acetate (EAC), acetone (ACE), IPA + ACE at 278.15 K to 318.15 K was determined. The mole fraction solubility of Musk ambrette in pure IPA at the temperature of 298.15 K were found to be 0.9492 × 10-2 mol·mol−1. The difference is that the solubility of Musk ambrette in ACE reaches 0.2257 mol·mol−1, which is much higher than the solvent mentioned above. The strong intermolecular hydrogen bonding formed by IPA resulted in its lowest solvation capacity for Musk ambrette. In addition, to further investigate the solubility pattern of Musk ambrette, we used 8 models (Van’t Hoff, modified Apelblat, Buchowski-Ksiazczak, Yaws, NRTL, Wilson, Jouyban-Acree and Sun model) to fit and obtain a general equation for solubility versus temperature. These results yielded a large amount of statistically significant data. Comparisons revealed that the modified Apelblat and Yaws equation showed the least deviation in forecasting solubility variations with temperature. Meanwhile, we proved that the dissolution of Musk ambrette is a heat-absorbing entropy increasing process by Van't Hoff equation calculation. ΔsolGo for the 12 solvents is in the following order: ACE < MAC < EAC < w = 0.2007 < w = 0.4025 < w = 0.6076 < CYH < w = 0.8070 < HPT < HX < IBA < IPA. ΔsolGo is smaller the easier it dissolves, which is consistent with the law of dissolution. Secondly, we performed thermal analysis and X-ray diffraction tests on Musk ambrette crystals prepared in different solvents, which showed that none of the several systems investigated led to the creation of new crystalline forms or solvatoids, further confirming the suitability of the solvents. Besides, we discuss the correspondence between solubility and the HSP, π, α, β, and CED of the solvents and thus tentatively confirm the significant influence of the solvent properties on solubility. The principle of similarity and compatibility is satisfied for most of the solvents. In particular, the CED values of the larger solvents were not favorable for the solubilization of Musk ambrette. We also analyzed the molecular surface electrostatic potential of Musk ambrette by visualization techniques. Finally, IPA and ACE and their binary solution systems were analyzed by molecular dynamics simulations. The effect of solvent intermolecular interactions on the solubilization pattern was discussed. It was further confirmed that weak interactions of solvent molecules contribute more to the dissolution of Musk ambrette. These findings suggest that the prediction of solvent solubility can be initially achieved by molecular simulation techniques. Undoubtedly, this study will furnish a valuable information for the purification of Musk ambrette.

Experimental and theoretical study for the sorption of Ni2+ and Cd2+ onto phosphoryl functionalized aluminum silicate composite

Phosphoryl functionalized Aluminum silicate (ASP) composite sorbent was synthesized using sol–gel technique and characterized with different techniques. The synthesized sorbent was tested for the sorption of Ni2+ and Cd2+ in aqueous solution at both single- and binary-solute systems under simulated conditions using batch technique. Batch experiments were executed as a function of pH, initial metal ion concentration and temperature. Structural and surface morphology of the synthesized sorbent were determined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The studied kinetic models suggested that the sorption of Ni2+ and Cd2+ onto ASP was found to follow the pseudo-second order and the Langmuir-Freundlich model was the best model to depict the sorption isotherms. The sorption equilibria of both ions were analyzed using two diverse statistical physics models (homogeneous and heterogeneous monolayer models). A Theoretical scrutiny of statistical physics calculations indicated that Ni2+ and Cd2+ sorption was multi-ionic where two sorption sites were involved but with a diverse contribution degree. The removal nature of Ni2+ and Cd2+ was endothermic and the calculated sorption amounts at saturation implied that Ni2+> Cd2+. Calculated interaction energies indicated the participation of physical forces in the sorption of both ions onto the synthesized sorbent surface and the variation of these sorption energies confirmed that both sorption sites participated in the removal of Ni2+ and Cd2+ but through different interactions type. Ions sorption capacity was increased with the temperature owing to increase in thermal agitation. This study reveals that phosphoryl functionalized aluminum silicate is an efficient sorbent that can be used for the sorption of Ni2+ and Cd2+ from aqueous solutions in both single- and binary -solute systems.

Study on the saltiness-enhancing mechanism of chicken-derived umami peptides by sensory evaluation and molecular docking to transmembrane channel-like protein 4 (TMC4)

The previously obtained chicken-derived umami peptides in the laboratory were evaluated for their saltiness-enhancing effect by sensory evaluation and S-curve, and the results revealed that peptides TPPKID, PKESEKPN, TEDWGR, LPLQDAH, NEFGYSNR, and LPLQD had significant saltiness-enhancing effects. In the binary solution system with salt, the ratio of the experimental detection threshold (129.17 mg/L) to the theoretical detection threshold (274.43 mg/L) of NEFGYSNR was 0.47, which had a synergistic saltiness-enhancing effect with salt. The model of transmembrane channel-like protein 4 (TMC4) channel protein was constructed by homology modeling, which had a 10-fold transmembrane structure and was well evaluated. Molecular docking and frontier molecular orbitals showed that the main active sites of TMC4 were Lys 471, Met 379, Cys 475, Gln 377, and Pro 380, and the main active sites of NEFGYSNR were Tyr, Ser and Asn. This study may provide a theoretical reference for low-sodium diets.

Designing Organic π-Conjugated Molecules for Crystalline Solid Solutions: Adamantane-Substituted Naphthalenes.

We showcase herein organic crystalline solid solutions (CSSs) based on the simplest polycyclic aromatic hydrocarbon (PAH) scaffold, naphthalene, stabilized by dispersion forces induced by adamantane substitution. High thermal stability of the host and guest molecules synthesized by cross-coupling of dibromonaphthalene derivatives and 4-(1-adamantyl)phenyl boronic ester enabled formation of crystals by sublimation. We could generate binary monocrystalline solid solution systems proven by X-ray crystallography, the first system of designed CSSs stabilized exclusively via dispersion forces with structural evidence. These observations are additionally supported by lattice energy calculations and spectroscopic examinations. For the generation of CSSs, it is of utmost importance that the host and guest molecules have similar lattice energies and spatial compatibility. We anticipate that the thermostable organic CSS design demonstrated herein would be beneficial for functional materials and further investigation towards materials with unique properties.

ZIF-67 grows in chitosan-rGO hydrogel beads for efficient adsorption of tetracycline and norfloxacin

In this study, a novel hydrogel bead (rGO@ZIF-67@CS) was synthesized by integrating ZIF-67 into a chitosan and reduced graphene oxide (rGO) dual-network system. This hydrogel was designed for efficient removal of tetracycline (TC) and norfloxacin (NOR) in single- and binary-solute systems. The adsorption experiments revealed that TC and NOR can be effectively removed over a wide range of pH (4–8), achieving maximum adsorption capacities of 1685.26 mg·g−1 at pH = 4 for TC and 1890.32 mg·g−1 at pH = 5 for NOR. The pseudo-second-order kinetic and Langmuir models better fitted the kinetic and isotherm data of both antibiotics, indicating a homogeneous adsorption process dominated by monolayer chemisorption. Even after five adsorption–desorption cycles, the adsorption efficiency of the two antibiotics remained above 80 %. In the binary systems, rGO@ZIF-67@CS simultaneously removed 92.68 % of TC and 82.46 % of NOR. Additionally, in practical applications, the fixed-bed system treated 320 mL of the TC solution and 290 mL of the NOR solution. Microscopic characterization suggested that the adsorption mechanisms were likely attributed to pore filling, π-π stacking, hydrogen bond interactions, and complexation.

A systematic study of the competitive sorption of per- and polyfluoroalkyl substances (PFAS) on colloidal activated carbon

Treatment of environmental media contaminated with per- and polyfluoroalkyl substances (PFAS) is crucial to mitigate mounting health risks associated with exposure. Colloidal activated carbon (CAC) has shown promise in treating contaminated soils, but understanding the interaction among PFAS during sorption is necessary for optimal remediation. This study investigated the extent to which PFAS of varying chain lengths and functional groups compete for sorption to CAC. Batch tests were conducted with natural soil and spiked water, using CAC at 0.2% w/w to remove seven PFAS with individual starting concentrations up to 0.05 mmol L−1. PFAS sorption to CAC was evaluated in three systems: a composite mixture of all studied compounds, a binary-solute system, and a single-solute system. The sorption experiments exhibited strong PFAS affinity to CAC, with removal rates between 41% and 100%, and solid/liquid partition coefficients (Kd) between 10 and 104 L kg−1. Differences were noticed among the various spiking mixtures, based on perfluorocarbon chain length, functional group, and the starting PFAS concentrations. Competition effects were detected when PFAS were in a multi-solute system, with an average 10% drop in removal, which can evidently become more relevant at higher concentrations, due to the observed non-linearity of the sorption process. The PFAS most vulnerable to competition effects in multi-solute systems were the short-chain perfluoropentanoic acid (PFPeA) and perfluorobutane sulfonic acid (PFBS), with an up to 25% reduction in removal. In bi-solute systems, perfluorooctane sulfonamide (FOSA) dominated over its ionisable counterparts, i.e. perfluorooctane sulfonic acid (PFOS) and perfluorononanoic acid (PFNA), indicating the importance of hydrophobic effects or layer formation in the sorption process. These results underscore the importance of considering competition in PFAS sorption processes when designing and implementing remediation techniques for PFAS-contaminated media.

COPPER ADSORPTION ONTO POMEGRANATE PEEL ACTIVATED CARBON AS A NEW ADSORBENT

Pomegranate peel-based activated carbon was prepared using phosphoric acid impregnation for removing copper ions from aqueous solutions. The activated carbon sample was characterized using N2 adsorption–desorption isotherms, SEM, FTIR, and Boehm titration. Batch adsorption experiments were performed as a function of initial pH, contact time, initial ion concentration and temperature. The metal adsorption was found pH dependent, with maximum adsorption occurring at an initial pH of 5.4. Langmuir, Freundlich and Temkin isotherms were used to analyze the equilibrium data at different temperatures. The Freundlich isotherm was considered to be the best model for representing Cu(II) adsorption data. The kinetic studies were analyzed using pseudo-first order, pseudo-second order and intraparticle diffusion models, with good fitting to the pseudo-second-order model. The adsorption behavior of the binary solution system Cu(II)-Cd(II) showed that the adsorbent has higher selectivity towards copper ions than cadmium ions.

Kinetic and isotherm of competitive adsorption cadmium and lead onto Saccharomyces cerevisiae autoclaved cells.

Heavy metal pollution has been regarded as a significant public health hazard during the industrialization, which also have exhibited various types of toxicological manifestations. Moreover, due to the high cost and toxic by-products, some conventional remediation methods were limited to heavy metals pollution control. In this work, autoclaved Saccharomyces cerevisiae was used as a biosorbent for the removal of Cd2+ and Pb2+ from single and binary ions aqueous solution system. The kinetics and isotherm of Cd2+ and Pb2+ were studied in different ion systems. The results showed that the competitive adsorption ability of S. cerevisiae to Pb2+ was stronger than that to Cd2+ in binary ions solution. To all the single ion solution of Cd2+ or Pb2+ and binary ions solution of Cd2+-Pb2+, there always existed that the adsorption of metal ions on S. cerevisiae fitted well with pseudo-second-order kinetic model and Langmuir isotherms model. The adsorption quantity qt in different solutions followed the sequence as qt (Cd2+-Pb2+) > qt (Pb2+-single) > qt (Pb2+-binary) > qt (Cd2+-single) > qt (Cd2+-binary). The autoclaved S. cerevisiae used in this research was one kind of rapid and favourable biosorbent for Pb2+ and Cd2+. In Pb2+ and Cd2+-containing solutions, sites competition and jointed toxicity of Pb2+ and Cd2+ on S. cerevisiae cells were the key to the total adsorption effect, and further researches were necessary in the next work. Thus, the current research presented that the autoclaved S. cerevisiae could be applied as an effective biosorbent for heavy metal adsorption from water environment and the design of eco-friendly technologies for the treatment of waste liquor.

The adsorption and reduction of anionic Cr(VI) in groundwater by novel iron carbide loaded on N-doped carbon nanotubes: Effects of Fe-confinement

Confining reactive nanoparticles (e.g., zero-valent iron) in nano-capsules prevents their aggregation and preserves their reactivity. However, confined Fe-based materials are ineffective in removing anionic contaminants, and the mechanisms are unclear. In this study, at different pyrolysis temperatures, novel iron carbide (Fe3C) loaded N-doped carbon nanotubes (MU-CNTs/Fe) were prepared, in which Fe was loaded onto CNTs as unconfined Fe prepared at 700 °C (U7) or confined Fe prepared at 800–900 °C (U8 and U9, respectively). When tested for their ability to remove Cr(VI) oxyanions, unconfined Fe showed higher adsorption, reduction, and reusability than confined Fe. Moreover, the selective adsorption of Cr(VI) using U7 was demonstrated in a binary solution system with coexisting anions and complicated groundwater. The key mechanism of the enhanced Cr(VI) removal by unconfined Fe was its considerably enhanced reductive precipitation mediated by surface adsorbed and dissolved Fe2+, accounting for 40.8 % of the overall Cr(VI) removal. This study proposes a novel strategy for modulating the transformation of nonconfinement to confinement of nanoparticles based on the pyrolysis temperature and provides new insights into the mechanisms of iron confinement on the removal of metal oxyanions from groundwater.

Dissolution Behavior of Sodium Phosphate in a Na3PO4–Na2WO4–NaOH Solution System

Sodium hydroxide autoclaving is the main method for smelting scheelite in China. In this method, sodium phosphate is added as an additive to realize the highly efficient decomposition of scheelite, and a crude sodium tungstate solution containing sodium phosphate and sodium hydroxide is obtained. In the subsequent process of ion exchange, phosphorus ions in the solution compete with the resin adsorption of tungstate, which reduces the adsorption capacity of the resin and endangers the purity of the subsequent sodium tungstate solution. To remove the phosphorus from crude sodium tungstate solution, a chemical purification method is usually adopted. The principle of the chemical purification method is to use chemical reagents to react with impurities to form precipitates to achieve the purpose of impurity removal. Because of the advantages of simple industrial implementation and high impurity removal efficiency, it has been widely used in phosphorus removal from crude sodium tungstate solution. However, in the process of phosphate removal in a crude sodium phosphate solution, the chemical purification method has some disadvantages. First, the additional cost of chemical reagents is required, and other metal impurities from chemical reagents would be introduced to crude sodium tungstate solution. Second, phosphate impurity removed by the chemical precipitation method is usually sedimented in other forms but sodium phosphate, which makes the phosphate resource unable to be recycled for tungsten smelting. Therefore, a novel phosphorus removal method needs to be developed. The dissolution behavior of sodium phosphate in a Na3PO4–Na2WO4–NaOH system was investigated in this paper. The results showed that in binary or ternary solution systems of sodium phosphate, sodium tungstate, and sodium hydroxide, the common-ion effect and salt effect exist simultaneously. The common-ion effect decreases the solubility of sodium phosphate, while the salt effect increases the solubility of sodium phosphate. Increasing the concentration of sodium hydroxide or sodium tungstate and lowering the temperature of the solution can greatly reduce the phosphorus concentration in crude sodium tungstate solution, making the crude sodium tungstate solution meet industrial requirements of ion exchange. The results of the study lay a theoretical foundation for the development of new phosphorus removal methods.

Kinetics of Adsorption Competition of Pb-Cu and Pb-Methylene Blue in Aqueous Solution using Silica Gels from Coal Fly Ash

The present study investigates the removal of Pb2+ using silica gel (SG) in the presence of the Cu2+ (Pb-Cu) and methylene blue (Pb-MB) ion competitor. These pollutants are toxic and harmful to the ecosystem. The presence of the multicomponent pollutants causes more complications to remove from the water system. The adsorptions were examined in a batch system under certain experimental conditions (pH solution system and contact time). Meanwhile, the FTIR spectrophotometer determines the differences adsorption interaction in silica functional groups before and after adsorption. The results showed that the silanol group of silica gel acted as an adsorption site. In the single systems, the adsorption capacity of silica gel follows the order MB &gt; Cu2+ &gt; Pb2+ of around 84.03; 64.81; and 56.88 mg.L−1, respectively. The kinetic adsorptions of both single and binary systems were best fitted to pseudo-second-order models. In the binary solution systems, both adsorption capacity and adsorption rate of each component decreased compared to the single system. The results indicated that the cationic competitors influenced the Pb2+ adsorption, or vice versa, depending on the amount of charge and adsorption affinity.

Investigation of intermolecular interactions in organic solutions by combining two-dimensional correlation Raman spectroscopy and DFT simulation: Example of methanol and Chloralkane

Methanol (MeOH)-Dichloromethane (CH2Cl2) and methanol-Chloroform (CHCl3) binary solution systems under the different circumstances were studied using Raman spectroscopy combined with density functional theory (DFT) and two-dimensional correlation spectroscopy (2DCRS). Weak HBs interactions exist in the binary solutions, which can be reflected by the vibration of CH bond (in CH2Cl2 or CHCl3) and CO bond (in MeOH). We explore the influence of mole fractions and temperature of these two vibration modes and perform 2DCRS analysis to reveal the changes intermolecular interactions. The results showed that the Raman spectra of CH vibration of Chloralkane has a frequency shift as the molar fraction of methanol changes both in MeOHCH2Cl2 and MeOHCHCl3 binary solution. In MeOHCH2Cl2, both the bending and stretching vibration of CH move towards higher wavenumber as the MeOH mole fraction increases, but the bending vibration moved towards higher wavenumber and the stretching vibration moved towards lower wavenumber in MeOHCHCl3. This phenomenon is mainly due to the variation of intermolecular HBs and is affected by the vibrational coupling between different chemical bonds. The 2DCRS has a higher resolution, can be used to distinguish the weak peaks masked in one-dimensional spectra, showed that there is a correlation between the chemical bonds of MeOH and CH2Cl2, which proves the existence of HBs, and MeOH is more sensitive to the change of circumstance. The Raman intensity of CH2Cl2 increased more obvious than that of MeOH during the heating process in MeOHCH2Cl2 binary solution, and the full width at half maximum (FWHM) of the Raman peak in the solid phase changed more unregular than that in the liquid phase. Finally, the DFT simulation was used to optimize the geometrical structure under three modes, and vibration analysis and interaction energy calculation were performed. The HBs energies obtained in the three coordination modes are 9.68 kcal/mol, 5.04 kcal/mol and 11.31 kcal/mol, respectively, and the simulated vibration modes and Raman spectra are matched well with the experimental results.

Cobalt-gadolinium modified biochar as an adsorbent for antibiotics in single and binary systems

In this work, fresh biochar modified with cobalt (Co) and rare earth element gadolinium (Gd) was prepared for ciprofloxacin (CIP) and tetracycline (TC) removal in single- and binary-solute systems. Co- and Gd-modified biochar (MBC), possessing a sponge-like structure, was found to be efficient in CIP and TC removal in both systems. The BET surface area and pore volume of MBC were 370.3737 m2/g and 0.1991 cm3/g, respectively. Both TC and CIP sorption kinetic data in regard to MBC were fitted with a pseudo-second-order model. Adsorption of CIP onto MBC was consistent with the Langmuir model, while TC adsorption was consistent with the Freundlich model. The adsorption capacity of MBC was 44.44 mg/g for CIP and 119.05 mg/g for TC. Although the adsorption capacity decreased in the competitive system, it still reached 31.15 and 117.65 mg/g, respectively. Therefore, MBC might yield a great promise to treat complex antibiotic wastewater.

Microanalysis of Single Poly(N-isopropylacrylamide) Droplet Produced by an Optical Tweezer in Water: Isotacticity Dependence of Growth and Chemical Structure of the Droplet.

Thermoresponsive phase separation mechanisms of aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions were investigated using an optical tweezer combined with a Raman microspectroscope. A near-infrared laser beam (λ = 1064 nm) was focused into the solution to produce and trap a single polymer microdroplet under an optical microscope. The laser beam played two important roles: The first role is to locally heat the solution to induce phase separation in which numerous polymer microdroplets are generated around the focus, while the second one is to collect these microdroplets. Eventually, a single polymer droplet was stably produced and trapped at the focus. Our method enabled us to perform two types of microanalysis for the droplet. Analysis I is real-time monitoring the growth of the polymer droplets by which we can determine the growth rate of droplets. Analysis II is Raman microspectroscopy to reveal chemical components of the droplets. By means of these two analyses, we revealed important phase separation mechanisms in terms of stereoregularity (isotacticity) dependence. From analysis I, we show that droplet growth is governed by the Ostwald ripening mechanism and the growth is accelerated by increasing the isotacticity. From analysis II, we show that the gelation is promoted in the droplet (physical gel formation) with increasing isotacticity. Our technique should be a versatile tool to explore liquid-liquid phase separation mechanisms for various binary solution systems.