Surface Adsorption Properties Research Articles

Selective ammonia sensor based on copper oxide/reduced graphene oxide nanocomposite

Commercialization of a chemical sensor relies on the sensing performance, stability and selectivity for detecting gases at different environmental conditions. Here, we report ammonia sensors based on copper oxide (CuO) and reduced graphene oxide (rGO) nanocomposite with a hierarchical structure. The employed surfactant-free hydrothermal method for the sensing element synthesis is found to be efficient in yielding hierarchical nanoarchitectures. The synthesized CuO and rGO-CuO nanocomposite were characterized for structural, morphological, optical and surface adsorption properties. In order to understand the sensing properties, the printed sensors with pristine CuO and rGO-CuO composite were subjected to concentration, temperature and time-dependent ammonia sensing measurements. The rGO-CuO nanocomposite sensor showed an enhanced sensor response of 13 at room temperature (30 °C) and 30 at 300 °C, respectively which is a 10-fold increase as compared to pristine CuO based device. The selectivity experiments were carried out by exposing the sensor to ethanol, methanol, acetone, and ammonia. The sensor showed the highest response towards ammonia in comparison with other test gases. The observed sensing performance suggests the applicability of the present sensors to room temperature and elevated temperature operations.

Surface and protein adsorption properties of 316L stainless steel modified by polyvinyl alcohol and plasma-treated polyvinyl alcohol films

In this study, we investigated the surface and protein adsorption properties of 316L stainless steels coated with polyvinyl alcohol (PVA) and N2-plasma-modified PVA films. The water contact angle of the 316L stainless steel significantly decreased after the coating with the PVA film owing to the abundant hydrophilic functional groups formed on the surface of the PVA film. The signal of the hydrophilic functional groups of the PVA film became more significant after the N2 plasma modification, leading to a further decrease in the water contact angle of the PVA film. Electrochemical tests showed that the corrosion resistance of the 316L stainless steel improved by the coating of the PVA and N2-plasma-modified PVA films. Bicinchoninic-acid protein assay results showed that the 316L stainless steels coated with the PVA and N2-plasma-modified PVA films exhibited lower bovine serum albumin concentrations than that of the neat 316L stainless steel, indicating that the anticoagulant properties of the 316L stainless steel surface could be improved after the coating with the PVA and plasma-modified PVA films.

A highly selective and sensitive electrochemical sensor for tryptophan based on the excellent surface adsorption and electrochemical properties of PSS functionalized graphene

A new green method for the synthesis of poly(sodium 4-styrenesulfonate) functionalized graphene (PSS–graphene) in aqueous solution was realized by using graphene oxide nanosheets (GO) functionalized with PSS and ascorbic acid (AA) as an reducing agent. Various techniques, including Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and electrochemistry have been utilized to characterize the as-made nanocomposites. The PSS–graphene was used as a modifier to fabricate an electrochemical sensor of tryptophan (Trp). Due to the difference of the adsorption capacity of PSS–graphene for Trp and Tyr, as well as the different charge states of Trp and the other interfering substances, the sensor showed excellent selectivity for Trp. The synergistic amplification of the stronger enrichment and the enhanced electron transfer rate, the signal of Trp on the PSS–graphene modified electrode was about 100-fold enhanced compared to that of the bare GCE. The peak current of Trp is proportional to its concentration in a wide range from 0.04 to 10.0 µmol L−1 with detection limit of 0.02 µmol L−1. Further, the proposed sensor was applied for the detection of Trp in human serum samples. Favorable results revealed that this work provided a new design strategy and a valuable platform for highly selective and sensitive determination of Trp in complex samples.

Ar/O2 plasma treatment of carbon nanotube membranes for enhanced removal of zinc from water and wastewater: A dynamic sorption-filtration process

In this study, pristine multi-walled carbon nanotubes (MWCNTs) were functionalized by using Ar/O2 plasma treatment technique, which enhanced adsorptive membrane filtration of zinc ions from water and wastewater. The XPS analysis showed that plasma treatment largely increased the surface oxygen groups content of MWCNTs from 2.78% to 6.79%. This change increased the surface negative charged, dispersion and adsorption properties of MWCNTs without causing any damages to the integrity of the nanotube pattern. Pressure-driven filtration of plasma-treated MWCNT (P-CNT) dispersion formed a stable layer inside the lumen of a hollow fiber membrane. The contact angle analysis demonstrated that after incorporation of P-CNT into the HF membrane increased membrane hydrophilicity. The P-CNT membrane effectively removed almost 100% of zinc from synthetic waters and approximately 80% of zinc from a wastewater effluent by surface complexation reaction. A follow-up regeneration study demonstrated that the adsorptive removal of zinc by the CNT membrane was reversible under selected conditions, thus making it possible to repeatedly use the membrane for long-term zinc filtration. This study suggests that HF membranes modified with P-CNTs possess superb adsorption properties for metal ions, allowing the operation of CNT membranes for water treatment.

Rubber Surface Change and Static Charging under Periodic Stress

Rubber materials play an important role in robotics, due to their sensing and actuating abilities, that are exploited in soft smart materials endowed with shape-adaptive and electroadhesive properties. The application of an electric field produces non-linear deformation that has been extensively modelled, but is not understood at the molecular level. The symmetric effect (the production of an electric field due to rubber deformation) was recently discovered and explained as follows: rubber surface chemical composition and adsorptive properties change during rubber deformation, allowing the surface to exchange charge with the atmosphere. The present work describes the complex surface morphology and microchemistry of tubing made from vulcanized natural rubber, showing that it is rough and made from two domain types: stiffer elevations containing Br or Al (depending on the sample used) and O, that rise above an elastic base that is exempt of elements other than C and H. The surface area fraction occupied by the elastic base is higher in the strained rubber than when it is relaxed. Electrostatic potential on rubber surfaces was measured as a function of the stretching frequency, using Kelvin electrodes and showing frequency-dependent potential variation. This is explained considering charge exchange between the atmosphere and rubber surface, mediated by water vapor adsorbed in the stretched rubber and trapped when it relaxes.

Effects of temperature and O partial pressure on the atomic structure of Al2O3 (0 0 0 1) surface

The first-principles calculation method was used to determine the effects of temperature and O partial pressure on the surface terminal of Al2O3 (0 0 0 1) by comparing the surface energy, surface adsorption energy, and surface atomic evaporation energy. Results showed that the surface energy of S_Al-Ter was lowest at vacuum and absolute zero. At room temperature (300 K) and in an Al-rich atmosphere, the surface energy and adsorption properties indicated that Al-Ter structure was most stable. The surface energy of O-Ter became the lowest at high temperatures and high O partial pressures; surface O atoms escaped easily at high temperatures, and the surface structure became unstable.

An alternative low-cost adsorbent for gold recovery from cyanide-leached liquors: Adsorption isotherm and kinetic studies

Pristine Macadamia nutshell-based activated carbons were chemically oxidized with different concentrations of H3PO4 and HNO3 to increase their surface adsorption properties and further explore if they could be an attractive alternative low-cost adsorbent for gold recovery from cyanide-leached liquors. The modified activated carbons were labeled MACN20, MACN40 and MACN55 to signify the materials prepared from 20%, 40% and 55% (v/v) HNO3, respectively. Similar nomenclature was followed for H3PO4-modified activated carbons. Brunauer-Emmet-Teller, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, elemental analysis and X-ray diffraction spectroscopy were used to characterize the prepared activated carbons. The physical properties were attained through determining attrition, ash content, volatile matter and moisture content of all the activated carbons. Various parameters that affect selective adsorption such as the effect of initial concentration, time, agitation speed, interfering species and the dose of the adsorbent were investigated. Optimal parameters for gold ion adsorption were as follows: solution pH, 10; contact time, 6 h; agitation speed, 150 r/min; sorbent amount, 4 g and initial concentration, 5.5 mg/L. The observed selectivity order was not the same for all the adsorbents, but the adsorption of gold was found to be mostly influenced in the presence of nickel and least influenced by copper. MACN55 was found to be the most efficient adsorbent with 74% of gold adsorption from a real-world sample and displayed a similar performance to coconut-based activated carbons.

Novel Rh(Pd)-Cu(Ni) supported catalysts for oxy-steam reforming of methanol

Monometallic copper, nickel and bimetallic Pd(Rh)-Cu(Ni) catalysts supported on a binary oxide containing various content of ZrO2 and Al2O3 were prepared by impregnation method. Their physicochemical and catalytic properties in oxy-steam reforming of methanol reaction (OSRM) were extensively investigated. Selecting an optimal composition of the catalyst for the OSRM process was the main goal of this work. The influence of zirconia content on the reactivity and physicochemical properties of supported copper catalysts in OSRM was also studied. The reactivity measurements showed that the supported copper catalyst was more active than the nickel catalyst. The catalytic measurements showed that the catalyst properties depend on their surface composition, acidity and adsorption properties. High selectivity of supported copper catalyst with composition 20%Cu/ZrO2·Al2O3 (Zr:Al = 1:2) towards carbon dioxide and hydrogen was confirmed. In addition, the promotion effect of palladium and rhodium on the activity of monometallic supported copper and nickel catalysts in OSRM was confirmed. The most active system in the OSRM process was 0.5%Rh-20%Cu/ZrO2·Al2O3.

Research on the sustainable efficacy of g-MoS2 decorated biochar nanocomposites for removing tetracycline hydrochloride from antibiotic-polluted aqueous solution

Antibiotic concentrations in surface waters far exceed the pollution limit due to the abuse of pharmaceuticals, resulting in an urgent need for an approach with potential efficiency, sustainability and eco-friendliness to remove antibiotic pollutants. A novel biochar-based nanomaterial was synthesized by hydrothermal synthesis and was investigated for its removal potential for tetracycline hydrochloride (TC) from both artificial and real wastewater. The associative facilitation between biochar and g-MoS2 nanosheets was proposed, revealing the favorable surface structures and adsorption properties of the composite. The related adsorption kinetics, isotherms and thermodynamics were studied by several models with adsorption experimental data, turning out that biochar decorated by g-MoS2 exhibited optimum TC removal with adsorption capacity up to 249.45 mg/g at 298 K. The adsorption behavior of TC molecules on g-MoS2-BC can be interpreted well by three-step process, and it is dominated by several mechanisms containing pore-filling, electrostatic force, hydrogen bond and π-π interaction. In addition, the cost-effective g-MoS2-BC nanocomposites demonstrated excellent adsorption and recycling performance in TC-contaminated river water, which might provide the underlying insights needed to guide the design of promising approach for contaminant removal on a large scale in practical application.

Effect of metal in Schiff bases of chitosan adsorbed on glassy carbon electrode in the inhibition of sphingomyelinase C toxin

This study was conducted to assess the catalytic electrode surface adsorption and capture properties of different metal chitosan derivatives in aqueous phosphate buffer solution (pH = 7.3). Early, recent work showed that the response of Iron chitosan complex with R = -CH3 on the periphery, over blood red cells in presence of sphingomyelinase C was protected. The effect of others substituent (R = -Br, -Cl, -F, NO2, -OCH3, -H) on the periphery of the Schiff base ligand did not show correlation with the oxidation of sphingomyelinase C and its biological response. For this reason, various adsorbed metal (M = Fe of recent work, Cu, Ni and Co) complexes of chitosan and Schiff bases on glassy carbon electrode for the oxidation of sphingomyelinase C were investigated and compared, each one with -CH3 group on the periphery of the Schiff base. UV–Vis and IR-TF spectroscopies, electrochemistry and microscopy assay were performed; then, the metal effect underlying. For the Schiff base, cobalt and copper complexes did not proved to be a remarkable cellular protector in presence of the enzyme, but the nickel complex showed to be a cellular protector at short time, this conclusion help to proposal a reaction mechanism for the electrochemical and biological studies.

Effect of Preparation Methods on Phosphate Adsorption by Iron-Titanium Binary Oxide: Coprecipitation and Physical Mixing

To investigate the effect of preparation methods on surface characteristics and adsorption properties of the formed metal composite oxides, two kinds of iron-titanium binary oxides were synthesized by a coprecipitation method or a physical mixing method and were denoted as CFe-Ti and MFe-Ti, respectively. The prepared CFe-Ti and MFe-Ti were systematically characterized using SEM, XRD, BET, and FTIR techniques. Their phosphate adsorption behaviors were also studied via batch adsorption experiments. Compared with pure FeOOH and TiO2, CFe-Ti exhibited a looser nanostructure with more pore and surface hydroxyls. Moreover, the CFe-Ti had a high maximal phosphorus adsorption capacity of 40.6 mg·g-1, which is about 1.5 times and 2.4 times as high as that of pure FeOOH (27.2 mg·g-1) and TiO2 (16.7 mg·g-1), respectively. This suggests that an obvious synergistic effect is present in the CFe-Ti system. However, the morphology and structure of MFe-Ti were not significantly different from those of pure FeOOH and TiO2. The maximal adsorption capacity of MFe-Ti was 22.7 mg·g-1, which is obviously lower than that of CFe-Ti and even lower than that of pure FeOOH. Evidently, there is no synergistic effect in the MFe-Ti system. In addition, phosphate adsorption mechanisms at the surface of CFe-Ti and MFe-Ti were the same as those of their component oxides, and chemical adsorption occurred at the surface of the oxides through the formation of inner-sphere complexes. Therefore, the surface characteristics and adsorption properties of the metal composite oxides were closely related to their preparation methods. The coprecipitation method was a simpler and more economical way than the physical mixing method to fabricate a highly effective iron-titanium binary oxide for phosphate adsorption.

In2O3 nanofibers surface modified by low-temperature RF plasma and their gas sensing properties

Hierarchical structure In2O3 nanofibers were synthesized by traditional electrospinning technology. Then, In2O3 nanofibers were treated 30 min by using low-temperature RF oxygen plasma and hydrogen plasma, respectively. The morphology, structure, composition and element content of the In2O3 nanofibers modified by oxygen plasma and hydrogen plasma were characterized and analyzed by XRD, SEM, BET and XPS. After modification by plasma, the morphology, structure and element contents of the In2O3 nanofibers were significantly changed. Gas sensors were fabricated based on In2O3 nanofibers modified by oxygen plasma and hydrogen plasma, respectively. Gas sensing properties of modified In2O3 sensors were investigated by a static test system to a variety of VOC gases in the concentration range of 0.3–500 ppm. The test result shows that In2O3 gas sensor modified by oxygen plasma exhibits excellent acetone sensing properties, It indicates that surface adsorption properties of In2O3 nanofibers can be improved by surface modification technology using low-temperature RF plasma, so as to improve the gas sensing properties of sensors.

Synthesis and Characterization of Co3O4-MnxCo3-xO4 Core-Shell Nanoparticles

ABSTRACTThe mixed-valence oxide Co3O4 nanoparticles, having the normal spinel structure, possess large surface area, active-site surface adsorption properties, and fast ion diffusivities. Consequently, they are widely used in lithium-ion batteries, as well as for gas sensing and heterogeneous catalysis applications. In our research, we use a two-step method to synthesize Co3O4–based core-shell nanoparticles (CSNs). Cobalt oxide (Co3O4) nanoparticles were successfully synthesized using a wet synthesis method employing KOH and cobalt acetate. Manganese was incorporated into the Co3O4 structure to synthesize inverted Co3O4@MnxCo3-xO4 CSNs using a hydrothermal method. By adjustment of pH value, we obtained two different morphologies of CSNs, one resulting in pseudo-spherical and octahedron-shaped nanoparticles (PS type) whereas the second type predominantly have a nanoplate (NP type) morphology. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS) have been performed in order to determine the morphological and structural properties of our CSNs, whereas the magnetic properties have been characterized using a superconducting quantum interference device (SQUID) magnetometer. XRD and TEM results show that the CSNs have the same spinel crystal structure throughout the core and shell with an average particle size of ∼19.8 nm. Our Co3O4 nanoparticles, as measured prior to CSN formation, are shown to be antiferromagnetic (AFM) in nature as shown by the magnetization data. Our SQUID data indicate that the core-shell nanoparticles have both AFM (due to the Co3O4 core) and ferrimagnetic properties (of the shell) with a coercivity field of 300 Oe and 150 Oe at 5 K for the PS and NP samples, respectively. The magnetization vs temperature data show a spin order-disorder transition at ∼33 K and a superparamagnetic blocking temperature of ∼90 K for both batches.

Computational Evaluation of Mg–Salen Compounds as Subsurface Fluid Tracers: Molecular Dynamics Simulations in Toluene–Water Mixtures and Clay Mineral Nanopores

Molecular tracers that can be selectively placed underground and uniquely identified at the surface using simple on-site spectroscopic methods would significantly enhance subsurface fluid monitoring capabilities. To ensure their widespread utility, the solubility of these tracers must be easily tuned to oil- or water-wet conditions as well as reducing or eliminating their propensity to adsorb onto subsurface rock and/or mineral phases. In this work, molecular dynamics simulations were used to investigate the relative solubilities and mineral surface adsorption properties of three candidate tracer compounds comprising Mg–salen derivatives of varying degrees of hydrophilic character. Simulations in water–toluene liquid mixtures indicate that the partitioning of each Mg–salen compound relative to the interface is strongly influenced by the degree of hydrophobicity of the compound. Simulations of these complexes in fluid-filled mineral nanopores containing neutral (kaolinite) and negatively charged (montmoril...

Controlled Hydrodeoxygenation of Phenolic Components in Pyrolysis Bio-oil to Arenes

Hydrodeoxygenation of phenolic components in pyrolysis bio-oil is considered to be a potential strategy for producing renewable aromatic chemicals. The key issue of this process is the establishment of an effective catalytic system that can cleave the CAr–O bonds without affecting the aromatic structure. To achieve this goal, an efficient heterogeneous catalyst with solid acid support (WOx/ZrO2) and active metal (Ru) was prepared in this study. The Ru–WOx/ZrO2 catalyst can effectively convert model phenolic compounds into aromatic hydrocarbons. For a mixed phenolic sample, the conversion to and selectivity for arenes were all around 90%. The good selectivity was proved to be strongly related to the surface adsorption and acid properties of the catalyst as well as the reaction pathway. Moreover, the hydrodeoxygenation of a pretreated bio-oil was also conducted and presented a satisfactory yield of arenes at 240 °C with 1 MPa of H2 reacted for 5 h. The depolymerization of high-molecular-weight phenolic olig...

Green synthesis and influence of calcined temperature on the formation of novel porous diatomite microspheres for efficient adsorption of dyes

The novel porous diatomite microspheres were prepared by spray drying and subsequent calcination. Effects of calcined temperatures on the microstructure, specific surface area and adsorption properties of the microspheres were investigated systematically. Results showed that the porous microspheres exhibited spherical characteristic with both macropore and mesoporous features. The phases of the microspheres kept amorphous at 800 °C and crystallized into crystobalite at 1000 °C. The microspheres after calcined at 600 °C showed removal efficiency of 95.6% with the dosage of 20 g/L under the starting concentration of 100 mg/L. The adsorption process of methylene blue onto microspheres followed the pseudo-second-order kinetic model and Langmuir equation. The dye solutions could be easily filtrated by the microsphere layers and became colorless. It suggested that the porous diatomite microspheres had potential application in dyeing wastewater filtration and adsorption treatment.

Biomass Potential of Virgin and Calcined Tapioca (Cassava Starch) for the Removal of Sr(II) and Cs(I) from Aqueous Solutions.

In this study, we prepared novel adsorbents containing virgin and calcined tapioca products for removing strontium (Sr(II)) and cesium (Cs(I)) from aqueous solutions. The characteristics of tapioca, along with its capacity to adsorb Sr(II) and Cs(I), were evaluated. Multiple tapioca products were prepared and tested. The adsorbent prepared by boiling the tapioca followed by calcination at 300°C (BTP300) was the most effective. In addition, adsorption was affected by the adsorbent's surface properties. The Sr(II) and Cs(I) adsorbed onto BTP300 could be recovered through desorption by hydrochloric acid at different concentrations, which indicates that BTP300 can be used several times for adsorption/desorption. The results of this study suggest that BTP300, which was produced from tapioca biomass, can remove Sr(II) and Cs(I) from aqueous solutions.

Foams Stabilized by β-Lactoglobulin Amyloid Fibrils: Effect of pH.

β-Lactoglobulin fibrils could serve as a surface-active component and form adsorption layers at the air/water interface. In this study, the physical parameters related to the surface adsorption, foaming, and surface properties of β-lactoglobulin fibrils as a function of pH (2-8) were investigated. Results showed that an increase of pH from 2 to 5 led to a rise of the viscoelastic modulus of the surface adsorption layer and half-life time (t1/2) of foams, but it decreased foamability. When the pH was close to its isoelectric point (5.2), fibrils had the lowest electrostatic repulsion and entangled at the air/water interface resulting in a tightly packaged adsorption layer around bubbles to prevent coalescence and coarsening. When the pH (7-8) was higher than the pI of fibrils, the negatively charged β-lactoglobulin fibrils possessed good foamability (∼80%) and high foam stability (t1/2 ≈ 8 h) simultaneously even at low concentration (1 mg/mL). It demonstrated that β-lactoglobulin fibrils with negative charges presented a good foaming behavior and could be a potential new foaming agent in the food industry.

Surface and Protein Adsorption Properties of 316L Stainless Steel Modified with Polycaprolactone Film.

The surface and protein adsorption properties of 316L stainless steel (316L SS) modified with polycaprolactone (PCL) films are systematically investigated. The wettability of the PCL films was comparable to that of bare 316L SS because the rough surface morphology of the PCL films counteracts their hydrophobicity. Surface modification with PCL film significantly improves the corrosion resistance of the 316L SS because PCL is insulating in nature. A coating of PCL film effectively reduces the amount of adhered bovine serum albumin (BSA) on the surface of 316L SS in a bicinchoninic acid protein assay. PCL is both biodegradable and biocompatible, suggesting the potential for the surface modification of implants used in human bodies; in these applications, excellent corrosion resistance and anticoagulant properties are necessary.

Synthesis of Cr3+-doped TiO2 nanoparticles: characterization and evaluation of their visible photocatalytic performance and stability

ABSTRACTCr3+-doped TiO2 nanoparticles (Ti-Cr) were synthesized by microwave-assisted sol-gel method. The Ti-Cr catalyst was characterized by X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, N2 adsorption-desorption analysis, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy (XPS) and zetametry. The anatase mesoporous Ti-Cr material exhibited a specific surface area of 54.5 m2/g. XPS analysis confirmed the proper substitution of Ti4+ cations by Cr3+ cations in the TiO2 matrix. The particle size was of average size of 17 nm for the undoped TiO2 but only 9.5 nm for Ti-Cr. The Cr atoms promoted the formation of hydroxyl radicals and modified the surface adsorptive properties of TiO2 due to the increase in surface acidity of the material. The photocatalytic evaluation demonstrated that the Ti-Cr catalyst completely degraded (4-chloro-2-methylphenoxy) acetic acid under visible light irradiation, while undoped TiO2 and P25 allowed 45.7% and 31.1%, respectively. The rate of degradation remained 52% after three cycles of catalyst reuse. The higher visible light photocatalytic activity of Ti-Cr was attributed to the beneficial effect of Cr3+ ions on the TiO2 surface creating defects within the TiO2 crystal lattice, which can act as charge-trapping sites, reducing the electron−hole recombination process.