Insight into the dynamic adsorption behavior of graphene oxide multichannel architecture toward contaminants

Graphene oxide(GO) channels exhibit unique mass transport behaviors due to their flexibility, controllable thinness and extraordinary physicochemical properties, enabling them to be widely used for adsorption and membrane separation. Nevertheless, the adsorption behavior of nanosized contaminants within the channels of GO membrane has not been fully discussed. In this study, we fabricated a GO membrane(PGn, where n represents the deposition cycles of GO) with multi channels via the crosslinking of GO and multibranched poly(ethyleneimine)(PEI). Phenol was used as molecular probe to determine the correlations between dynamic adsorption behavior and structural parameters of the multilevel GO/PEI membrane. PG8 shows higher adsorption capacities and affinity, which is predominantly attributed to the multichannel structure providing a large specific surface for phenol adsorption, enhancing the accessibility of active sites for phenol molecules and the transport of phenol. Density functional theory calculations demonstrate that the adsorption mechanism of phenol within GO channel is energetically oriented by hydrogen bonds, which is dominated by oxygen-containing groups compared to amino groups. Particularly, the interfaces which facilitate strong π-π interaction and hydrogen bonds maybe the most active regions. Moreover, the as-prepared PG8 membrane showed outstanding performance for other contaminants such as methyl orange and Cr(VI). It is anticipated that this study will have implications for design of GO-related environmental materials with enhanced efficiency.

Adsorption Behaviors of 4-Mercaptobenzoic Acid on Silver and Gold Films

The adsorption behaviors of 4-mercaptobenzoic acid on silver and gold nanoparticles were studied by surface-enhanced Raman scattering （SERS） and density functional theory. The silver and gold films by electrodeposition have the same excellent characteristics as SERS- active substrates. At the same, the SERS spectra indicate that 4-mercaptobenzoic acid molecules are adsorbed on the surfaces of gold nanoparticles through the S atom, and that the carboxyl group is far away from surface of gold nanoparticles, and that there is a certain angle between the plane of benzene ring and gold film. However, 4-mercaptobenzoic acid molecules are adsorbed on the surfaces of silver nanoparticles through the carboxyl group, and the S atom is far away from surface of silver nanoparticles, and there is also a certain angle between the plane of benzene ring and the surface of silver nanoparticles. Here it is demonstrated the calculated Raman frequencies are in good agreement with experimental values, and the calculated Raman frequencies are also helpful to infer the adsorption behaviors of 4- mereaptobenzoic acid molecules.

Photodegradation mechanism of two dyes: the influence of adsorption behavior on the novel TiO_2 particles

The relationship between adsorption behavior and photocatalytic mechanism of the two dyes was investigated. Adsorption isotherms showed that the adsorption of cationic pink FG was Langmuir type behavior, while the reactive brilliant red k-2G was Freundlich type behavior. The increasing pH favored the adsorption of FG but have little effect on the photodegradation. The increasing pH favored the adsorption and the photodegradation of k-2G. The presence of scavenger of h + vb and OH· radical potassium iodide inhibited the degradation of k-2G, free radicals scavenger tetranitromethane inhibited the photodegradation of FG. These results indicated that the photodegradation of FG mainly via free radicals in solution, and the photodegradation of k-2G was mainly on the catalysts surface or near the interface of solid and solution by react with h + vb and surface-bound OH·. The different effect of SO 2- 4, HCO - 3 on the adsorp tion and photodegradation of two dyes confirmed these results.

Adsorption behavior of Fe atoms on a naphthalocyanine monolayer on Ag(111) surface

Adsorption behavior of Fe atoms on a metal-free naphthalocyanine（H2Nc） monolayer on Ag（111） surface at room temperature has been investigated using scanning tunneling microscopy combined with density functional theory（DFT）based calculations. We found that the Fe atoms were adsorbed on the centers of H2Nc molecules and formed Fe–H2Nc complexes at low coverage. DFT calculations show that Fe sited in the center of the molecule is the most stable configuration, in good agreement with the experimental observations. After an Fe–H2Nc complex monolayer was formed, the extra Fe atoms self-assembled to Fe clusters of uniform size and adsorbed dispersively at the interstitial positions of Fe–H2Nc complex monolayer. Therefore, the H2Nc monolayer grown on Ag（111） could be a good template to grow dispersed magnetic metal atoms and clusters at room temperature for further investigation of their magnetism-related properties.

Comments on“Adsorption behavior of heavy metal ions by carbon nanotubes grown on microsized Al_2O_3 particles”

Recently, Hsieh and Horng [1] published the paper entitled as above. In section 3 results and discussion, the authors mentioned the first and the second order kinetic models without any quotations. In fact these two kinetic models have been published [2-5]. In order to distinguish a kinetics model based on the ad- sorption capacity of a solid from the one based on the concentration of a solution, Lagergren＇s first-order rate equation has been called pseudo-first-order [6-7]. The Lagergren＇s equation has been widely cited, but there are far more mistakes made in the quotation and in the reference section of papers, including the title, the author＇s name, journal title, year of publishing, volume, and page number [3]. In addition, the second order kinetic expression for the adsorption systems of divalent metal ions using sphagnum moss peat has been reported by Ho [8].

ADSORPTION BEHAVIOR OF Pb(II) ON POTASSIUM HEXATITANATE WHISKER BY FAAS

Based on the advantage of high surface area and strong adsorption ability of potassium hexatitanate whisker, a method to determine trace Pb(II) content by combining solid phase extraction with Flame atomic absorption spectrometry (FAAS) was established. The adsorptive behavior of potassium hexatitanate whisker to Pb(II), primary influencing factors of adsorption and elution and effect of coexistence ions were investigated systemically. The optimal analytical conditions were discussed and examined. It was found that the adsorption rate of potassium hexatitanate whisker to Pb(II) was 100% at pH 4.0. Pb(II) could be eluted from potassium tetratitanate whisker with HCl (2mol/L) under boiling water for 30min. The detection limit was 5.75ng/mL, and relative standard deviation was 1.66% (n=9, CPb=2.0μg/mL).

Adsorption behavior of uranium on polyvinyl alcohol-g-amidoxime:Physicochemical properties, kinetic and thermodynamic aspects

Amidoxime-based adsorbents are widely studied as the main adsorbent in the recovery of uranium from seawater. However, the adsorption rate and loading capacity of such adsorbents should be further improved due to the economic viability consider- ation. In this paper, polyvinyl alcohol functionalized with amidoxime （PVA-g-AO） has been prepared as a new adsorbent for uranium （VI） adsorption from aqueous solution. The physicochemical properties of PVA-g-AO were investigated using infra- red spectroscopy （IR）, scanning electron microscope （SEM）, X-ray diffraction （XRD）, and X-ray photoelectron spectroscopy （XPS）. Results showed that the ligand monomers were successfully grafted onto the matrixes. The XRD and XPS analysis showed that uranium was adsorbed in metal ionic form rather than in crystal form. Uranyl （U （VI）） adsorption properties onto PVA-g-AO were evaluated. The adsorption of U （VI） by PVA-g-AO was fast, with an equilibrium time of less than 50 rnin. Additionally the maximum adsorption capacity reached 42.84 mg/g at pH 4.0.

Preliminary study of adsorption behavior of bovine serum albumin(BSA) protein and its effect on antibacterial and corrosion property of Ti-3Cu alloy

The adsorption behavior, antibacterial, and corrosion properties of a Ti-3 Cu alloy were studied in a phosphate-buffered saline solution containing 0, 1, 3, and 6 gL^(-1) bovine serum albumin protein at 37℃ and pH = 7.4(±0.2). The protein adsorption behavior was examined via cyclic voltammetry, secondary ions mass spectroscopy(SIMS), and angle-resolved X-ray photoelectron spectroscopy(ARXPS). The corrosion property was analyzed by the open circuit potential(OCP), potentiodynamic polarization(PD),and electrochemical impedance spectroscopy(EIS) examinations. The antibacterial test was conducted according to the GB/T 21510 China Standard. It was observed that the surface charge density(QA DS) was directly proportional to the amount of the adsorbed BSA protein, signifying that the protein adsorption was accompanied by the charge transfer, pointing to chemisorptions phenomena. BSA amino groups and other organic species were observed in the surface analysis examinations. It was shown that the formation of barrier complexes between the TiO_(2) oxide-layer and PBS solution resulted in decreasing the release of Cu-ions, which consequently reduced the antibacterial activity. On the other hand, these barrier complexes improved the corrosion resistance by increasing the charge transfer resistance and double-layer capacitance of the Ti-3 Cu alloy.

Adsorption behaviors of gas molecules on the surface of ZnO nanocrystals under UV irradiation

A UV-activated room temperature chemiresistive gas sensor based on ZnO nanocrystals film was fabricated. Its gas sensing properties under various conditions were also investigated in detail. The results shed new insight into the adsorption behaviors of gas molecules on the surface of ZnO nanocrystals under UV irradiation. The chemisorbed oxygen species(O^-2(ads)(hv)) induced by UV light govern the adsorption and desorption ways of other gas molecules on the surface of ZnO nanocrystals, which is dependent on the electron affinity of gas molecules. Gas molecules with higher electron affinity than oxygen molecules can be adsorbed on the surface by the competitive adsorption way, extracting electrons from the surface. Gas molecules with lower electron affinity than oxygen molecules are attracted by the adsorbed O^-2(ads)(hv)layer, releasing electrons to the surface. These processes can influence the gas sensing properties of the sensor. Our findings will pave the way for the fundamental understanding and design of UV-activated gas sensor in the future.

Tailoring the adsorption behavior of superoxide intermediates on nickel carbide enables high-rate Li-O_(2) batteries

Probing the relationship between the adsorption of superoxide species and the kinetics of Li-O_(2) chemistry is critical for designing superior oxygen electrodes for the Li-O_(2) battery,yet the modulation essence,especially at the atomic level,remains little understood.Herein,we reveal that the adsorption behaviors of superoxide species can be effectively regulated via a core-induced interfacial charge interaction,and we find that moderate adsorption strength can enable superior rate capability in a Li-O_(2) battery.More importantly,operando X-ray absorption near-edge structure and surface-enhanced Raman spectroscopy provide tools to monitor in situ the evolution of the superoxide intermediates and the electronic states of the catalyst's metal sites during the discharge and charge processes,and correlate these with the surface adsorption states.The concept of tuning adsorption behavior through interfacial charge engineering could open up new opportunities to further advance the development of the Li-O_(2) battery and beyond.

Insights into the effect of substrate adsorption behavior over hemelike Fe_(1)/AC single-atom catalyst

Unraveling the substrate adsorption structure–performance relationship is pivotal for heterogeneous carbon supported metal single-atom catalysts(M_(1)/C SACs).However,due to the complexity of the functional groups on carbon material surface,it is still a great challenge.Herein,inspired by structure of enzymes,we used activated carbon(AC),which has adjustable surface oxygen functional groups(OFGs),supported atomically dispersed Fe-N_(4) sites as heme-like catalyst.And based on a combination of scanning transmission electron microscopy(STEM),X-ray photoelectron spectroscopy(XPS),X-ray absorption spectroscopy(XAS),Mössbauer spectroscopy,Fourier transform infrared(FT-IR)characterizations,kinetics experiments and density functional theory(DFT)calculations,we revealed the effect of substrate adsorption behavior on AC support surface,that is,with the increase of carboxyl group in OFGs,the adsorbed 3,3',5,5'-tetramethylbenzidine(TMB)molecular increased,and consequently the substrate enriched on AC surface.Such carboxyl group as well as Fe-N_(4) active sites synergistically realized high-efficiency peroxidase-like activity,just like the heme.This work suggests that simultaneously constructing metal single-atom active sites and specific functional groups on carbon support surface may open an avenue for engineering metal-support synergistic catalysis in M_(1)/C SACs,which can further improve catalytic performance.

Construction of MnS/MoS_(2) heterostructure on two-dimensional MoS_(2) surface to regulate the reaction pathways for high-performance Li-O_(2) batteries

The inherent catalytic anisotropy of two-dimensional(2D) materials has limited the enhancement of LiO_(2) batteries(LOBs) performance due to the significantly different adsorption energies on 2D and edge surfaces.Tuning the adsorption strength in 2D materials to the reaction intermediates is essential for achieving high-performance LOBs.Herein,a MnS/MoS_(2) heterostructure is designed as a cathode catalyst by adjusting the adsorption behavior at the surface.Different from the toroidal-like discharge products on the MoS_(2) cathode,the MnS/MoS_(2) surface displays an improved adsorption energy to reaction species,thereby promoting the growth of the film-like discharge products.MnS can disturb the layer growth of MoS_(2),in which the stack edge plane features a strong interaction with the intermediates and limits the growth of the discharge products.Experimental and theoretical results confirm that the MnS/MoS_(2) heterostructure possesses improved electron transfer kinetics at the interface and plays an important role in the adsorption process for reaction species,which finally affects the morphology of Li_2O_(2),In consequence,the MnS/MoS_(2) heterostructure exhibits a high specific capacity of 11696.0 mA h g^(-1) and good cycle stability over 1800 h with a fixed specific capacity of 600 mA h g^(-1) at current density of100 mA g^(-1) This work provides a novel interfacial engineering strategy to enhance the performance of LOBs by tuning the adsorption properties of 2D materials.

PROPERTIES AND THERMODYNAMICS OF ADSORPTION OF BENZOIC ACID ONTO XAD-4 AND A WATER-COMPATIBLE HYPERCROSSLINKED ADSORBENT

The adsorption behavior of benzoic acid onto a water-compatible hypercrosslinked polymeric adsorbent NJ-8 wascompared with that onto macroporous Amberlite XAN-4. This paper focuses on the static equilibrium adsorption behaviors,the adsorption thermodynamics and the column dynamic adsorption profiles. Five isotherm models are used to fit the results.This shows that the Freundlich equation can give a perfect fit. The specific surface area of NJ-8 is about as high as that ofAmberlite XAD-4, but the adsorbing capacity for benzoic acid on NJ-8 is about 14.9%-64.8% higher than that on AmberliteXAD-4, which is attributed to its microporous mechanism and partial polarity. The negative values of the adsorptionenthalpy are indicative of an exothermic process. Both enthalpy and free energy changes of adsorption manifest a physicalsorption process. The negative values of the adsorption entropy indicate that adsorption is well consistent with the restrictedmobilities and the configurations of the adsorbed molecules on the surface of the studied adsorbents with superficialheterogeneity. Both adsorbents were used in mini-column experiments to demonstrate the higher breakthrough adsorbing capacity of the hypercrosslinked polymeric adsorbent NJ-8 to benzoic acid, as compared with that of Amberlite XAD-4.

Adsorption of D113 Resin for Dysprosium(Ⅲ)

The adsorption behavior and mechanism of D ll 3 resin for Dy（lII） was investigated by using the method of resin adsorption. Experimental results show that the optimum medium pH of adsorption of D 113 resin for Dy^3- is pH=6.00 in the HAc-NaAc medium. The static adsorption capacity of D113 resin for Dy3. is 292.7 mg·g^-1. The optimum eluant is 0.5 mol,L-~ HC1. The adsorption rate constant is k298=6.8× 10-6s^-1. The apparent activation energy of D113 resin for Dy（Ⅲ） is 14.79 kJ·mol^-1. The adsorption behavior of D113 resin for Dy（Ⅲ） obeys the Freundlich isotherm. The adsorption parameters of thermodynamic are AH=14.48 kJ·mol^-1,△S=54.69 J·mol^-1,K^-1, △G= 1.82 kJ·mol^-1.The adsorption mechanism of Dll3 resin for Dy^3- was confirmed by chemical analysis and IR spectra.

Impedance Characterization of Adsorption Process of Calmodulin on Au Substrate and its Combination with Ca^(2+)

In this paper, the adsorption process of calmodulin (CaM) on Au substrate was first investigated with electrochemical impedance spectroscopy (EIS) method. The result reveals that the adsorption of the protein-calmodulin contains two steps, i.e., one short quick step followed by a slow one. The complexation of calmodulin with Ca2+ was also first probed using EIS technique, in which the complexation of CaM with Ca2+ could be reflected by the change of apparent membrane capacitance(Capp) clearly. In all above measurements, a redox couple Fe(CN)63-/ Fe(CN)64- was used as probing-pin to reflect all the changes occurring in the above process. Our work suggests that some biological processes of CaM could be studied using EIS method conveniently.

Adsorption characteristics of copper in rivers contaminated by acid mine drainage from copper mine

In this paper, the partitioning of copper between surfacial sediments and overlaying water in Dawu-Le An River, which was contaminated by acid mine drainage resulted from mining activities,was studied by field investigation and acid dissolution experiment.Simulated adsorption experiments were carried out to study the adsorption of copper on amorphous iron oxyhydroxide and ore tailing particles.The results showed that it was the binding of copper onto the surface of amorphous Fe/Al oxyhydroxides and ore tailing particles that regulated the concentrations of dissolved Cu at downstream of Dawu River and its inlet into Le An River.A significant part of adsorbed copper was likely to be associated with amorphous Fe/Al oxyhydroxides coated on the surface of ore tailing particles. A simplified surface complexation model can be used to describe the adsorption behavior in the river.

Adsorption of trichlorphon on phyllosilicate minerals:Effect of low-molecular-weight organic acids

The use of trichlorphon in large quantities causes a large number of organic pollutants to enter water, sediments, and soils. Phyllosilicate minerals are considered effective adsorbents for organic pollutants. However, the adsorption behavior of organic pollutants on soil minerals affected by low-molecular-weight organic acids(LMWOAs) is not fully understood. In this study, the effect of LMWOAs on the adsorption behavior of trichlorphon on phyllosilicate minerals was investigated using a combination of adsorption measurements and molecular spectroscopic techniques(attenuated total reflection-Fourier transform infrared spectroscopy(ATR-FTIR) and X-ray photoelectron spectroscopy(XPS)). The adsorption of trichlorphon onto kaolinite(KAO) and montmorillonite(MON) was suppressed by increasing pH, indicating that electrostatic interaction played a key role in adsorption, especially at low pH. In the presence of citric acid(CA), there was an obvious promotion of trichlorphon adsorption on KAO and MON. In the presence of oxalic acid(OA), the adsorption of trichlorphon on KAO was promoted, whereas the adsorption on MON was inhibited, especially at pH 4.0. The presence of CA and OA increased the adsorption by increasing the exposure of hydrophobic sites of KAO and MON. The results from ATR-FTIR and XPS also indicated that the hydrophobic Si–O sites of phyllosilicate minerals were the preferred adsorption sites for trichlorphon in the presence of CA and OA, probably driven by the hydrophobic effect. However, the weak effect of OA on MON caused an increase in the electrostatic repulsion between MON and trichlorphon molecules, thus inhibiting adsorption. This study is significant for a deeper understanding of self-purification of soil and sediment systems in the presence of organic pollutants.

Simulation of transport mechanism of radium isotopes in aquifer on the southern coast of Laizhou Bay

Naturally occurring radium(^(223)Ra,^(224)Ra,^(226)Ra,and^(228)Ra)isotopes have been widely applied as geochemical tracers in marine environments,especially when estimating the submarine groundwater discharge(SGD).In this sense,the influencing factors and transport mechanism of radium isotope activity in aquifers can be key information for SGD estimation.This work evaluates the adsorption/desorption behavior of^(224)Ra and^(226)Ra in the solid-liquid phase through a leaching experiment and analysis of field data.The results suggested that radium isotope activity was positively correlated with salinity and grain size,in the case of abundant sediments.Through ion analysis,we found that the ions(Na^(+),Ca^(2+),Mg^(2+),and Ba^(2+))exchanged with radium isotopes in the process of transport.A 1-D reactive transport model was established to simulate the transport process of radium isotope in aquifers.The model successfully simulated the variation of radium isotope desorption activity with salinity and was subsequently verified in the field.This study contributes to the understanding of the geochemical behavior of radium isotopes in aquifers and provides guidance for selecting a suitable groundwater endmember in SGD estimation.

Synergistic depression mechanism of zinc sulfate and sodium dimethyl dithiocarbamate on sphalerite in Pb−Zn flotation system

The depression mechanism of zinc sulfate(ZnSO4)and sodium dimethyl dithiocarbamate(DMDC)as the combined depressant on sphalerite was investigated by micro-flotation experiments,ion complexing tests,contact angle tests and X-ray photoelectron spectroscopy(XPS)analysis.The micro-flotation tests revealed that ZnSO4+DMDC had a better selective depression effect on sphalerite than using single ZnSO4 or DMDC.Ion complexing tests confirmed that DMDC had a strong complexing capacity with lead ions or hydroxy complexes.Contact angle tests illustrated that ZnSO4+DMDC makes the sphalerite surface more hydrophilic than ZnSO4 or DMDC.XPS analysis indicated that the combined depressant could prevent collector adsorbing on the Pb-activated sphalerite surface by a competitive adsorption method,while the combined depressant and collector were co-adsorbed on galena surface.

Insight into mineral flotation fundamentals through the DFT method

Flotation is a complex process that occurs in solid-liquid-gas multiphase systems,and its main factors include the minerals,separation medium,as well as various flotation reagents.The study of mineral properties and interactions with other components such as reagents and water lays the basic theoretical foundation for flotation.Density functional theory(DFT) calculations can qualitatively evaluate the exchange of matter and energy between the mineral system and the surroundings and quantitatively characterize these behaviors,which greatly expands the breadth and depth of flotation studies.This review systematically summarizes the advances of flotation research based on DFT studies,including the study of mineral crystal chemistry represented by the theory of lattice defects,mineral surface hydration such as hydrophilicity and hydrophobicity,surface regulation mechanism,and collecting mechanism based on surface adsorption theory.More significantly,it systematically elaborates different types of collectors according to their characteristics and emphatically explains the mechanism of some typical collectors in detail.