Dependent Adsorption Research Articles

Effective and selective adsorption of organoarsenic acids from water over a Zr-based metal-organic framework

It is imperative to remove organicarsenic acids (OAAs) from water because they can convert into highly toxic inorganic arsenic compounds in natural environment via biotic and abiotic degradation routes. Herein, seven Zr-based metal-organic frameworks (Zr-MOFs) including DUT-67, UiO-66, UiO-67, MOF-808, MOF-808F, NU-1000, NU-1000B with various structures were screened for the adsorptive removal of representative OAAs including p-arsanilic acid (ASA) and roxarsone (ROX) in water media. Initial screening found that MOF-808 and MOF-808F have the largest adsorption capacities. Therefore, their adsorption behaviors including adsorption kinetics, isotherms, specificity and effects of pH were fully investigated. Remarkably, MOF-808F had the second largest maximum adsorption capacities of ASA (621.1 mg g−1) and ROX (709.2 mg g−1) among the reported MOF-based adsorbents. In addition, MOF-808F showed excellent selectivity and reusability and no observable drop of adsorption efficiency was found in the presence of equimolar competing ions (Cl−, OAc− or SO42−) or after three successive adsorptive runs. By contrast, MOF-808 had inferior adsorption specificity and reusability in spite of the very similar structure with MOF-808F. The structure-dependent adsorption performances can be explained by the distinct adsorptive mechanisms, which were revealed by zeta potential measurements, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculation etc. The dominant interaction between MOF-808 and ASA was coordination interactions, while ASA adsorption over MOF-808F was governed by the synergistic effect of π-π stacking, hydrogen bonding, and electrostatic interactions. This work no only presented an excellent adsorbent (MOF-808F) toward OAAs, but also revealed the structure dependent adsorption performances/mechanisms.

Factors affecting coupled degradation and time-dependent sorption processes of tebuconazole in mineral soil profiles

This laboratory degradation and adsorption study aimed to determine the tebuconazole degradation parameters for 6 profiles of Polish mineral soils and to find links between the tebuconazole degradation rate, its adsorption, soil microbial activity and other significant soil properties. The values of the adsorption distribution coefficient Kd, obtained in batch experiments after 96 h of shaking were in the range of 6.2–34.6 mL g−1. In both batch experiments and incubation experiments at 20 °C, the typical course of adsorption processes was observed, an initial rapid stage followed by a slow stage. In 3 of the 18 soils examined, adsorption was not reached within 51 days. The range of the half-life values was 201–433 days for the Ap horizon and up to 3904 days for subsoils, which were estimated using the two-site nonequilibrium adsorption model coupled with first-order degradation for dissolved and adsorbed pesticide. It was found that modeling the degradation of tebuconazole on the basis of the coefficients of microbial biomass activity for topsoil and two subsoils explained almost 96% of the variance of the estimated pore water degradation rate coefficients in examined soils. The degradation rate was also negatively correlated with the amount adsorbed in the time dependent adsorption sites. This fraction was the least available for soil microorganisms because it was strongly adsorbed in soil pores with a radius <2.5 nm, determined from the H2O desorption isotherm. The degradation rate was also affected by the ratio of the water content in soil during degradation experiments to the water content at field capacity. The results indicated that degradation occurred in the soil liquid phase only.

As(III) Removal from Aqueous Solution by Calcium Titanate Nanoparticles Prepared by the Sol Gel Method.

Arsenic (As) contamination of water is a serious problem in developing countries. In water streams, arsenic can be as As(V) and As(III), the latter being the most toxic species. In this work, an innovative adsorbent based on CaTiO3 nanoparticles (CTO) was prepared by the sol-gel technique for the removal of As(III) from aqueous solution. X-ray diffraction of the CTO nanoparticles powders confirmed the CTO phase. Transmission electron microscopy observations indicated an average particle size of 27 nm, while energy dispersive X-ray spectroscopy analysis showed the presence of Ca, Ti, and O in the expected stoichiometric amounts. The surface specific area measured by Brunauer, Emmett, and Teller (BET) isotherm was 43.9 m2/g, whereas the isoelectric point determined by Zeta Potential measurements was at pH 3.5. Batch adsorption experiments were used to study the effect of pH on the equilibrium adsorption of As(III), using an arsenite solution with 15 mg/L as initial concentration. The highest removal was achieved at pH 3, reaching an efficiency of up to 73%, determined by X-ray fluorescence from the residual As(III) in the solution. Time dependent adsorption experiments at different pHs exhibited a pseudo-second order kinetics with an equilibrium adsorption capacity of 11.12 mg/g at pH 3. Moreover, CTO nanoparticles were regenerated and evaluated for four cycles, decreasing their arsenic removal efficiency by 10% without affecting their chemical structure. X-ray photoelectron spectroscopy analysis of the CTO surface after removal experiments, showed that arsenic was present as As(III) and partially oxidized to As(V).

Fatty Acid Quaternary Ammonium Surfactants Based on Renewable Resources as a Leveler for Copper Electroplating

AbstractA series of fatty acid quaternary ammonium surfactants (FAQAS 1 a–1 f) derived from renewable resource of fatty acid have been rationally designed and investigated as levelers applied in copper electroplating. Surface tension and contact angle indicated the FAQAS's surfactivity and wettability were closely related to the length of hydrophobic chains. FAQAS 1 a–1 f displayed the capability to inhibit the copper deposition in CV tests and their inhibiting abilities agreed with the order of their surfactivity and wettability. Compound 1 e showed the best inhibition capability, and was comprehensively tested by field‐emission scanning electron microscopy (FE‐SEM), X‐ray photoelectron spectroscopy (XPS) and other electrochemical measurements. The strong inhibition ability of compound 1 e on copper electrodeposition could be attributed to its fast and strong absorption of 1 e on the cathode surface. Moreover, galvanostatic measurements (GMs) indicated that compound 1 e not only cause polarization but also has stable synergistic effects with other additives to form a convection dependent competitive adsorption layer. In addition, through‐hole (TH) electroplating experiments verified that uniform TH could be obtained on copper electrodeposition using the bath containing compound 1 e. This work may shed some light on the pratical application of surfactants as effective leveler in acid copper electroplating.

Heat and mass transfer in activated carbon composites with artificial macro pores for heat pump applications

This paper presents a new simulation model for the heat and mass transfer in activated carbon compounds with new kind of artificial pores using methanol as a working fluid. The artificial pores are generated by blending polymer fibers to the activated carbon and binder mixture. In a subsequent sintering process, the polymer fibers are gasified, leaving additional pores that increase the overall mass transfer. Three measuring techniques are developed to determine the model parameters, including temperature and load dependent thermal conductivity, pressure and temperature dependent macroporous diffusivity and adsorption kinetics.

Investigating the Reaction and Transport Controlled Mechanism for the Sorption of Cr(III) and Mn(II) Ions onto Acid Activated Shale using Non-Linear Error Functions

Time dependent adsorption study on the sorption of Cr(III) and Mn(II) ions onto acid activated shale was conducted using batch adsorption techniques to investigate the effect of initial metal ion concentration on the process of adsorption. Experimental data obtained were fitted into different kinetic models to analyze the mechanism of adsorption in terms of reaction controlled and transport controlled mechanism. Some of the selected kinetic models include; Pseudo-first order, Pseudo-second order, Elovich, Film diffusion, Parabolic diffusion and Intra-particle diffusion model. From the result, it was observed based on the linear coefficient of determination (r2) that the experimental data fitted well into the various kinetic model tested. Application of non-linear error function such as error sum of square (SSE), root mean square error (RMSE) and residual average (RA) revealed that the rate limiting step for the adsorption of Cr3+ and Mn2+ ions on acid activated shale was chemical attachment (chemisorption) and the reaction mechanism follows the Pseudo-second order kinetic model.

Coverage dependent CO adsorption manners on seven MoP surfaces with DFT based thermodynamics method

CO interaction with MoP catalyst plays an important role in understanding the reaction mechanisms of syngas conversion into hydrocarbons and alcohols, which are promising feedstocks in industry. Herein, systematic ab initio computations were performed to identify the CO adsorption configurations and stable concentrations on different MoP surfaces at different conditions. Our investigations demonstrated that CO molecular adsorption is favored on MoP catalyst, and the saturation coverage ranges from 4/9 to 2 monolayers (ML) on different surfaces. With the atomistic thermodynamics method, the equilibrium phase diagrams were built to show the relationship of stable CO concentration with temperature and CO partial pressure on each surface. These results provide essential references for further converage dependent reaction mechanism studies.

LFER and the Effect of Temperature on Oxyanion Adsorption by Goethite

A linear relationship between the Gibbs free energy, ΔGr,H+, of the aqueous complex deprotonation reaction, and the Gibbs free energy, ΔGr,ads, of bidentate surface complexation reaction of oxyanions was derived from modelling of temperature dependent batch equilibrium adsorption experiments. As exemplified in this study, this relationship may be exploited to predict temperature-dependent adsorption behavior of oxyanions not yet known such as pertechnetate.

Highly efficient adsorption of benzothiophene from model fuel on a metal-organic framework modified with dodeca-tungstophosphoric acid

Reduction of sulfur-containing compounds from fossil fuel is vital. This work reports on the adsorptive removal of benzothiophene (BT) from liquid fuel using a highly porous metal-organic framework based on a bicomponent zirconium(IV) benzene-tricarboxylate Zr(BTC), and its post-synthetically modified hybrid form with dodeca-tungstophosphoric acid (HPW/Zr(BTC). The HPW loading for the high-performing hybrid adsorbents was 0.5–2.0 wt/wt of W/Zr. Temperature and concentration dependent BT adsorption data were in good agreement with the non-linear Langmuir model combined with a van’t Hoff description of the heat of adsorption. The maximum predicted adsorption capacities were estimated to be 290 and 238 mg.g−1 for HPW(1.5)/Zr(BTC) and Zr(BTC) comparable to the contemporary reported adsorbents. The adsorption kinetics followed a pseudo-second order model, which was related to the low concentration of BT used for these studies. Although the highly porous Zr(BTC) had good adsorptive sites, its adsorption capacity was enhanced by incorporation of HPW, this was attributed to availability of added acid sites for adherence of basic BT. The adsorption findings were further corroborated with DFT calculations, which showed favorable BT adsorption with calculated binding energies of −140.2 and −47.3 kJ.mol−1 for HPW(1.5)/Zr(BTC) and Zr(BTC), respectively. Much of adsorption sites were retained after regeneration of adsorbents.

An extended standard blocking filtration law for exploring membrane pore internal fouling due to rate-determining adsorption

Membrane internal fouling due to foulant adsorption onto the pore walls is a critical aspect of fouling. The classical “standard blocking law” for internal fouling simplistically assumes instantaneous adsorption such that the adsorbed amount grows linearly with the filtered liquid volume, which is inadequate to describe realistic internal fouling with varied adsorption rates. In this study, an extended standard blocking law for scenarios involving time dependent adsorption is proposed and yields an expression of the form dR/dV ∼ RN (where R is filtration resistance and V is filtrate volume). Two ultimate scenarios of the law, i.e. the 1st-kind for sufficiently fast adsorption with the characteristic exponent N ≈ 1.5 (similar to the classical standard blocking) and the 2nd-kind for sufficiently slow adsorption with N ≈ 2.5 are experimentally verified via microfiltration of model polysaccharide (alginate) solutions using hydrophobic and hydrophilic membranes. Transition between the 1st-kind and 2nd-kind laws is related to the rates of adsorption versus filtrational mass transfer. The extended law provides an improved tool to evaluate internal fouling, particularly that associated with adsorption of hydrophilic matter (such as polysaccharides) into hydrophilic membranes.

Nanopore characterization of mine roof shales by SANS, nitrogen adsorption, and mercury intrusion: Impact on water adsorption/retention behavior

Moisture-induced reduction in the strength of shales is one of the primary mechanisms of roof degradation affecting the stability and safety of underground coal mines. The underlying mechanisms of nanoscale matrix-water interactions remains unclear. Thus, an improved understanding of the nanopore structure, and dependent water adsorption and retention behavior of shale is key in defining strength degradation due to seasonal variations in humidity and temperature in underground coal mines. We use small-angle neutron scattering (SANS), low-pressure N2 adsorption (LPNA), and high-pressure mercury intrusion porosimetry (MIP) to characterize the nanopore structure of a fireclay (7F) and four coal mine roof shales (6R, 5A, 6F, H6) from the Illinois basin. The results show that overall distributions of pore volume obtained from SANS, LPNA and MIP techniques agree well between methods and over a wide range of pore size from ~1 nm to ~100 nm. Mercury porosities for the five ordered (7F, 6R, 5A, 6F, H6) samples (7.3%, 7.8%, 8.3%, 12.3%, 4.6%) are higher than the respective N2 porosities (5.0%, 6.3%, 3.8%, 8.2%, 2.5%), as attributed to the dilation of mesopores and compression of the grain skeleton induced by high pressure intrusion of mercury. The SANS porosities for samples 7F, 6R, 5A, 6F (4.0%, 6.2%, 4.1%, 8.8%) are in good agreement with their N2 porosities. Among all tested samples, H6 shale exhibits a relatively high SANS porosity (8.0%) but the lowest N2 (2.5%) and mercury porosities (4.6%). This is attributed to the interlayer micro-pore spaces within montmorillonite, which is detected by SANS but not by the two fluid penetration methods due to the inaccessibility of N2 molecules and mercury. Based on LPNA, larger micropores (1.5–2 nm) and mesopores (2–50 nm) predominantly contribute to the total porosity (~77.8%–87.6%) for the five tested samples.The water adsorption isotherms are measured by dynamic vapor sorption (DVS) and water retention curves are calculated based on the characterized pore size distribution (PSD) by LPNA and MIP techniques. Pore structures of the five studied samples evidently exert a strong influence on their water adsorption and retention behaviors. Water adsorption capacity correlates positively with total porosity/specific surface area (SSA), with a large proportion of micro/meso-pores resulting in the strong water retention capacity with matric suction reaching ~100–150 MPa for liquid saturation < 3%. Among the studied fireclay/shales, samples with higher retention capacity tend to adsorb more water. Thus, nanopore structure and its impact on water adsorption and retention behavior exert the key controls on shale-water interaction and its implication on strength reduction of roof shales in underground coal mines.

Concentration dependent adsorption of aromatic organic compounds by SWCNTs: Quantum-mechanical descriptors for nano-toxicological studies of biomolecules and agrochemicals

For evaluating the environmental risk associated using carbon nanotubes (CNTs), a successful prediction is desired for the adsorption of organic compounds (OCs) by CNTs at different adsorbate concentrations. This is most often achieved through poly-parameter linear solvation energy relationships (LSERs) based on solvatochromic descriptors. This study examines the real predictivity of the existing LSERs for predicting the adsorption of OCs by single-walled CNTs (SWCNTs) while comparing it with that of the models developed in the present work using quantum-mechanical descriptors. The real predictivity of the quantum-mechanical models and existing LSERs is compared using state-of-the-art statistical procedures employing an external prediction set of compounds not used in the model development. The quantum-mechanically computed mean polarizability, but originating from the interactions between electrons of parallel spin, is found to play an essential role in the adsorption of OCs by SWCNTs. Besides the solvatochromic descriptors (McGowan volume and molar excess refractivity), the instantaneous inter-electronic interactions, captured through electron-correlation based quantum-mechanical descriptors, are found to significantly affect the adsorption at varying adsorbate concentration. The models developed using a combination of quantum-mechanical and solvatochromic descriptors are found to be quite reliable. The models proposed were further employed to predict the adsorption of agrochemicals such as insecticides, pesticides, herbicides, as well as adsorption of endocrine disruptors and biomolecules such as nucleobases and steroid hormones. These are predicted to be strongly adsorbed by SWCNTs with Progesterone and Guanine exhibiting maximal interaction with the SWCNTs among biomolecules. The quantum-mechanical descriptors proposed in this work can be used for the risk assessment of SWCNTs in systems where adsorption is the primary process.

Competitive transport processes of chloride, sodium, potassium, and ammonium in fen peat

There is sparse information on reactive solute transport in peat; yet, with increasing development of peatland dominated landscapes, purposeful and accidental contaminant releases will occur, so it is important to assess their mobility. Previous experiments with peat have only evaluated single-component solutions, such that no information exists on solute transport of potentially competitively adsorbing ions to the peat matrix. Additionally, recent studies suggest chloride (Cl-) might not be conservative in peat, as assumed by many past peat solute transport studies. Based on measured and modelled adsorption isotherms, this study illustrates concentration dependent adsorption of Cl- to peat occurred in equilibrium adsorption batch (EAB) experiments, which could be described with a Sips isotherm. However, Cl- adsorption was insignificant for low concentrations (<500 mg L−1) as used in breakthrough curve experiments (BTC). We found that competitive adsorption of Na+, K+, and NH4+ transport could be observed in EAB and BTC, depending on the dissolved ion species present. Na+ followed a Langmuir isotherm, K+ a linear isotherm within the tested concentration range (~10 – 1500 mg L−1), while the results for NH4+ are inconclusive due to potential microbial degradation. Only Na+ showed clear evidence of competitive behaviour, with an order of magnitude decrease in maximum adsorption capacity in the presence of NH4+ (0.22 to 0.02 mol kg-1), which was confirmed by the BTC data where the Na+ retardation coefficient differed between the experiments with different cations. Thus, solute mobility in peatlands is affected by competitive adsorption.

Activity and Stability Relationship for Anion Doped CoSxSe2-X Dichalcogenides for the Hydrogen Evolution Reaction

As an ideal clean energy carrier, hydrogen can be produced through polymer electrolyte membrane (PEM) electrolysis by generating H2 from H2O. However, noble platinum group metals (PGM) remain the most common electrocatalysts for hydrogen evolution reaction (HER). The expense and scarcity of these catalytic materials obstruct the wide-spread adoption of electrochemical fuel generation technologies 1. Sulfur based transition metal dichalcogenides (TMDs) have emerged as a promising alternative to PGM HER electrocatalysts as they are abundant, inexpensive, and exhibit a low HER overpotential in acidic environment 2,3. Here we present a systemic assessment of the compositional dependent HER activity and stability for Co-based mixed chalcogen, CoSxSe2-x, pyrite TMDs. We observe a decrease in HER activity from the single chalcogen TMDs, CoS2 and CoSe2, to mixed chalcogen TMDs, as shown in Figure 1. This observed compositional trend in HER activity can be explained by the unique combination of compositional dependent hydrogen adsorption free energy (ΔGHad) and bulk resistivity/conductivity of the pyrite TMD. With near thermoneutral ΔGHad, the highest resistivity among the compositions was observed. The following increase in Se content leads to the decrease in HER activity due to a steady movement away from optimal ΔGHad. As the composition approaches CoSe2, however, it is observed that HER activity again increases at higher Se contents, with CoSe2 exhibiting similar activity to CoS2. This highlights the convolution of ΔGHad and material conductivity in determining the HER activity. Furthermore, through stability tests under constant potential HER electrolysis, as shown in Figure 2, Se-rich Co-based pyrite TMDs are found to be more durable than S-rich samples. Therefore, with an HER activity matching that of CoS2, but with a dramatic improvement in stability, CoSe2 breaks away from the traditional inverse activity/stability relationship and represents a promising material for non-PGM HER electrocatalysis in acidic based PEM electrolyzers. Wang, J. et al. Mater. 28, (2016) 215-230.Chhowalla, H. et al. Nature Chemistry 5, (2013) 263-275.Jaramillo, T. et al. Science 317, (2007) 100-102. Figure 1

A New Synthesis Approach for Carbon Nitrides: Poly(triazine imide) and Its Photocatalytic Properties.

Poly(triazine imide) (PTI) is a material belonging to the group of carbon nitrides and has shown to have competitive properties compared to melon or g-C3N4, especially in photocatalysis. As most of the carbon nitrides, PTI is usually synthesized by thermal or hydrothermal approaches. We present and discuss an alternative synthesis for PTI which exhibits a pH-dependent solubility in aqueous solutions. This synthesis is based on the formation of radicals during electrolysis of an aqueous melamine solution, coupling of resulting melamine radicals and the final formation of PTI. We applied different characterization techniques to identify PTI as the product of this reaction and report the first liquid state NMR experiments on a triazine-based carbon nitride. We show that PTI has a relatively high specific surface area and a pH-dependent adsorption of charged molecules. This tunable adsorption has a significant influence on the photocatalytic properties of PTI, which we investigated in dye degradation experiments.

Controlled synthesis of micro/nanoscale Mg-MOF-74 materials and their adsorption property

Micro/nanoscale Mg-MOF-74 materials with different morphologies and sizes have been fabricated in the presence of polyvinylpyrrolidone (PVP) by adjusting the amount of aqueous ammonia and reaction temperature. The obtained samples were characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and it was found that the Mg-MOF-74 particles show morphology and size dependent adsorption properties. The selectivity factors of the Mg-MOF-74 particles at 273 K were calculated based on the experimental single-component isotherms by ideal adsorbed solution theory (IAST). The results indicate that the Mg-MOF-74 particles have intrinsic high selectivity for adsorption of CO2 over CH4 and N2.

Hybrid Materials: Flexible Modulation of CO‐Release Using Various Nuclearity of Metal Carbonyl Clusters on Graphene Oxide for Stroke Remediation (Adv. Healthcare Mater. 5/2018)

A facile CO-release material for in-situ vasodilation as a treatment for stroke-related vascular diseases is developed by K.V. Kong, L.D. Liao and co-workers in article number 1701113. Utilizing the size dependent adsorption properties of ruthenium carbonyl clusters (Ru-CO) onto graphene oxide (GO), the rate and amount of formation of the CO release-active RuII(CO)2 species can be modulated by a simple mixing procedure. Further modulation of thermal and CO release properties can be achieved via a hybridization of medium- and high- nuclearity of Ru-CO clusters that can provide photo-thermal response for in-situ CO release in a cortical photo-thrombotic ischemia rat model.

Tuning the magnetic properties of hydrogenated bilayer graphene and graphene/h-BN heterostructures by compressive pressures

We investigated the electronic structure and magnetic properties of hydrogenated bilayer graphene and graphene/h-BN heterostructure as a function of applied uniaxial compression normal to the interface plane using van der Waals density functional theory. The H atoms preferred a cluster formation was found in the hydrogenated bilayer graphene and graphene/h-BN systems with a non-magnetic ground state. With increasing external pressure, the equivalence of two sublattices in graphene was broken because of the interaction between graphene and the underlying layer and the site dependent adsorption energy difference was greatly enhanced with the applied pressure. This resulted in a transition from an NM ground state to a ferromagnetic in hydrogenated bilayer graphene and graphene/h-BN heterostructure. Thus, we propose that the magnetic property can be manipulated by external pressure and that hydrogenated systems can be utilized for potential spintronics applications at low H concentrations.

PH dependent CO adsorption and roughness-induced selectivity of CO2 electroreduction on gold surfaces

Gold belongs to the category of metal electrocatalysts for CO2 reduction reaction (CO2RR) producing CO as a major product due to its inability to bind CO. In this work, we found that when the interfacial pH becomes alkaline, CO, the major product of CO2RR, interacts with gold surfaces to produce minor products like formate and methanol. The course of product formation and CO adsorption on gold was explored by their oxidative voltammetric responses obtained immediately after CO2RR in the forward cathodic scan and SECM studies provided more insights into the effect of interfacial pH on product selectivity. The electrode roughness was found to change the interfacial pH gradients as a result of microheterogeneity of surfaces. The roughness of gold surface was systematically changed from smoothened surface to nanoporous (highly rough) surface. NMR spectroscopic analysis pointed to the presence of methanol and formate being formed on nanoporous Au (np- Au) in significant amounts. Formate production was found increasing as a result of changes in the interfacial pH.

Additive Induced Formation of Ultrathin Sodium Chloride Needle Crystals.

A multitude of ultrathin crystal needles are formed during the evaporation of saturated aqueous NaCl solution droplets in the presence of amide containing additives. The needles are as small as 300 nm wide and 100–1000 μm in length. Heating experiments, X-ray diffraction, and energy dispersive X-ray spectroscopy showed that the needles are cubic sodium chloride crystals with the needle length direction pointing toward [100]. This shape, not expected for the 43̅m point group symmetry of NaCl, has been explained using a model, based on tip formation by initial morphological instability followed by time dependent adsorption of additive molecules blocking the growth of the needle side faces. The latter also suppresses side branch formation, which normally occurs for dendrite growth.