Increase In Surface Oxygen Content Research Articles

Effect of Electrolytic Plasma Polishing on Surface Properties of Titanium Alloy

Electrolytic plasma polishing (EPPo) is an advanced metal surface finishing technology with high quality and environmental protection that has broad application prospects in the biomedical field. However, the effect of EPPo on surface properties such as corrosion resistance and the wettability of biomedical titanium alloys remains to be investigated. This paper investigated the changes in surface roughness, surface morphology, microstructure, and chemical composition of Ti6Al4V alloy by EPPo and their effects on surface corrosion resistance, wettability, and residual stress. The results showed that Ra decreased from 0.3899 to 0.0577 μm after EPPo. The surface crystallinity was improved, and the average grain size increased from 251 nm to more than 800 nm. The oxidation behavior of EPPo leads to an increase in surface oxygen content and the formation of TiO2 and Al2O3 oxide layers. EPPo can significantly improve the corrosion resistance and wettability of titanium alloy in simulated body fluid and eliminate the residual stress on the sample surface. The surface properties are enhanced not only by the reduction in surface roughness but also by the formation of a denser oxide film on the surface, changes in the microstructure, an increase in surface free energy, and the annealing effect developed during EPPo. This study can provide guidance and references for applying EPPo to biomedical titanium alloy parts.

Adsorptive Structure and Mobility on Carbon Nanotube Exteriors Using Benzoic Acid as a Molecular Probe of Amphiphilic Water Contaminants.

Benzoic acid is the simplest aromatic carboxylic acid that is also a common water contaminant. Its structural and amphiphilic properties are shared by many other contaminants of concern. Based on a molecular dynamics study, this work reports the competitive adsorption of benzoic acid with water on the curved exteriors of carbon nanotubes of varying oxygen content. With the help of cylindrically approximated pair correlation functions, carboxyl-carboxyl associations were found to serve as an additional mechanism providing stability to the adsorbed benzoic acid on tube exteriors. These associations are secondary to the main aromatic-aromatic interactions during the adsorption process and therefore were not sufficient to establish the energy hierarchy at the adsorbed state with increase in surface oxygen content. The same mechanism was previously ascribed to the adsorption of the structurally similar but bulkier tannic acid. Both water and benzoic acid were organized into numerous mobility groups and a correspondence was established between species residence time and the average translation time taken to escape the tube vicinity. Vigorous exchange of water molecules among the first adsorption shell, the second adsorption shell, and the immediate vicinity radially outside was estimated to take place within a short time of about 10 ps.

Effect of activated carbon’s pore size distribution on oxygen induced heel build-up

Thermal desorption of volatile organic compounds (VOCs) from activated carbon (AC) is negatively impacted by oxygen. Oxygen reacts with the adsorbed VOCs, resulting in heel buildup in the porous structure of AC and reducing its adsorption capacity. This study investigated the contribution of physical properties of AC (specific surface area, micropore volume, and total pore volume) to this type of heel. Three different ACs with different micro/mesopore structures were tested through cyclic adsorption/desorption of 1,2,4-trimethylbenzene (TMB) using ultra-pure nitrogen (≤5 ppmv O2) as the purge gas during thermal desorption. Each set of experiments was repeated with dry air (21% O2) to evaluate the effect of O2 on heel build-up. Pore size distribution (PSD) analysis on the adsorbents cycled in dry air suggested a correlation between the amount of heel and the microporosity of adsorbents. Differential thermogravimetric (DTG) analysis was used to distinguish between the physically adsorbed and chemically formed heel. X-ray photoelectron spectroscopy (XPS) analysis showed a noticeable increase in surface oxygen content of the ACs desorbed in air. Finally, Boehm titration confirmed the presence of different surface oxygen functional groups on these adsorbents, suggesting oxidation reactions as the main mechanism of heel build-up.

Probing the Transformation of Boron Nitride Catalysts under Oxidative Dehydrogenation Conditions.

Hexagonal boron nitride (h-BN) and boron nitride nanotubes (BNNT) were recently reported as highly selective catalysts for the oxidative dehydrogenation (ODH) of alkanes to olefins in the gas phase. Previous studies revealed a substantial increase in surface oxygen content after exposure to ODH conditions (heating to ca. 500 °C under a flow of alkane and oxygen); however, the complexity of these materials has thus far precluded an in-depth understanding of the oxygenated surface species. In this contribution, we combine advanced NMR spectroscopy experiments with scanning electron microscopy and soft X-ray absorption spectroscopy to characterize the molecular structure of the oxygen functionalized phase that arises on h-BN and BNNT following catalytic testing for ODH of propane. The pristine BN materials are readily oxidized and hydrolyzed under ODH reaction conditions to yield a phase consisting of three-coordinate boron sites with variable numbers of hydroxyl and bridging oxide groups which is denoted B(OH) xO3- x (where x = 0-3). Evidence for this robust oxide phase revises previous literature hypotheses of hydroxylated BN edges as the active component on h-BN.

Insights into the thermolytic transformation of lignocellulosic biomass waste to redox-active carbocatalyst: Durability of surface active sites

The thermolytic transformation of lignocellulosic spent coffee grounds to superior redox-active carbocatalyst (denoted as NBC) via nitrogen functionalization in a pyrolytic environment at various temperatures was investigated. The intrinsic (e.g. surface chemistry, degree of graphitization, etc.) and extrinsic (e.g. specific surface area, morphology, etc.) properties of the catalysts were systematically studied using various characterization techniques. The three main N configurations conducive to redox reactions, namely pyrrolic N, pyridinic N and graphitic N were present at different compositions in all the NBCs prepared at pyrolysis temperature ≥500 °C. The NBCs were used as peroxymonosulfate (PMS) activator for degrading bisphenol A. It was found that NBC-1000 (prepared at 1000 °C) has the highest catalytic performance (kapp = 0.072 min−1) due to the relatively higher specific surface area (438 m2 g−1), excellent degree of graphitization, and optimum N bonding configuration ratio. Based on the radical scavenger and electron paramagnetic resonance studies, the nonradical pathway involving 1O2 generation is identified as the prevailing pathway while the radical pathway involving SO4−and OH generation is the recessive pathway. Further investigation of the durability of surface active sites revealed that the active sites undergo N bonding configuration reconstruction and cannibalistic oxidation (increase in surface oxygen content) during PMS activation reaction. The graphitic N manifest greater catalytic activity and stability compared to pyridinic N and pyrrolic N under oxidizing environment. The results demonstrated that reaction optimization is critical to improve the durability of the catalyst. This study provides useful insights in converting lignocellulosic biomass waste into functional catalytic material, and the strategy to improve the durability of carbocatalysts for redox-based reactions.

Investigation of Antibacterial 1,8-Cineole-Derived Thin Films Formed via Plasma-Enhanced Chemical Vapor Deposition.

The need for low-fouling coatings for biomedical devices has prompted considerable interest in antibacterial compounds from natural and sustainable sources, such as essential oils. Herein, a tea tree oil-based precursor, 1,8-cineole, is used to fabricate antimicrobial films (denoted ppCin) by plasma-enhanced chemical vapor deposition. Film properties were comprehensively characterized using a variety of surface and bulk analytical tools, and the plasma gas phase is assessed using optical emission spectroscopy, which can be correlated to ppCin film properties. Notably, film wettability increases linearly with plasma pressure, yielding water contact angles ranging from ∼50° to ∼90°. X-ray photoelectron spectroscopy reveals less oxygen is incorporated at higher pressures, likely arising from the lower density of OH(g) species. Further, we utilized H2O(v) plasma surface modification of the ppCin films to improve wettability and find this results in a substantial increase in surface oxygen content. To elucidate the role of film wettability and antibacterial properties, both as-deposited and H2O(v) plasma-modified films were exposed to Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus using glass slides and hydrocarbon films deposited from 1,7-octadiene as positive controls. Overall, bacteria attach to a similar extent on all films, including controls, yet only essential oil-based films significantly prevent biofilm formation (4-7% coverage compared to ∼40% for controls).

Effect of aging on surface chemistry of rice husk‐derived biochar

Herein, we aimed to determine the physicochemical properties of biochar produced from rice husk at 350 and 550°C, to characterize changes in the biochar properties during aging and to identify the effect of aging time on these changes. To simulate different stages in the aging process, samples were incubated at a constant temperature in the dark and maintained at 60% water holding capacity for 100–300 d. The transformation and morphology of the biochar particles were monitored by diffuse‐reflectance Fourier transform infrared spectroscopy (DRIFTS), scanning electron microscopy (SEM) coupled with energy X‐ray dispersive spectroscopy, and X‐ray photoelectron spectroscopy (XPS). During aging, a layer formed on the surface and the content of easily oxidized substances increased with increased aging time. In addition, SEM indicated that oxidation occurred close to the biochar surface rather than in the biochar particle interior. Furthermore, the DRIFTS and XPS results indicated that the biochar surface produced at 550°C underwent decarboxylation and hydroxylation, while for the 350°C biochar, the increase in surface oxygen content was associated with the presence of hydroxyl moieties. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 410–417, 2018

Synthesis of platinum-decorated iron vanadate nanorods with excellent sensing performance toward n-butylamine

The detection and monitoring of organic amines commonly found in food and medical industries (e.g. n-butylamine) has attracted increasing interests as they can induce adverse health effects to humans even at low concentrations. In this study, we have demonstrated the facile synthesis of platinum (Pt)-decorated iron vanadate (FeVO4) nanorods through a combined hydrothermal-polyol method, for highly sensitive and selective detection of toxic n-butylamine vapor with fast response/recovery time. The pure and Pt-decorated FeVO4 nanorods were successfully characterized using X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopes (TEM), X-ray photoelectron spectroscopy (XPS), and nitrogen (N2) adsorption-desorption isotherms. The as-synthesized FeVO4 nanorods were highly porous, exhibiting pore diameters in the range of 2–20nm, with a specific surface area of 21.4m2/g. Following surface modification, small platinum (Pt) nanoparticles with varying sizes of 2–5nm were uniformly loaded on the surface of these nanorods. The gas-sensing results reveal that the Pt-decorated FeVO4 nanorods exhibited three times higher response as well as three times faster response/recovery time, along with 5 times higher selectivity toward n-butylamine compared to the pure FeVO4 nanorods, under a relatively low optimum operating temperature of 240°C. The enhanced sensing performance of the Pt-decorated FeVO4 nanorods is attributed to a few factors, including: (i) the larger surface area exhibited by the Pt-decorated FeVO4 nanorods compared to the pure FeVO4 nanorods (∼1.5 times larger), which may provide more sites for the adsorption of both oxygen and gas molecules, (ii) the increase in surface oxygen content of the FeVO4 nanorods after the Pt modification (based on XPS analysis), which may lead to the formation of more oxygen ions to react with the n-butylamine gas during the sensing process to produce more electrons, thus leading to improved conductivity, and (iii) the electronic and chemical sensitization induced by the deposited Pt nanoparticles. These findings will develop the potential of metal vanadate nanocomposites as highly sensitive and selective gas-sensing materials for detecting organic amines.

Kinetics and Mechanism of Delignification of Switchgrass During Niobium Oxide Pretreatment

<abstract> Pretreatment is one of the most challenging and expensive steps in using biomass for fuel production. Hence, there is growing interest in exploring alternate pretreatment techniques. Recently it was suggested that biomass could be pretreated via solid acid catalysts. Hence, in this work, we used niobium oxide as a solid catalyst for pretreatment of switchgrass to understand the mechanism and kinetics of the delignification process. Alamo switchgrass was pretreated with 0.25 g g^-1 of niobium oxide at 60°C, 75°C, and 90°C for 20 to 120 min in a 150 mL batch reactor. Subsequently, switchgrass samples were characterized using scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and BET surface area analysis. SEM indicated that niobium oxide pretreatment was able to disrupt the external structure of switchgrass, which was corroborated by BET data. XPS of the pretreated surface indicated an increase in surface oxygen content, suggesting that niobium oxide was able to delignify switchgrass via oxidation. In addition, delignification of switchgrass ranged from 47.65% ±2.04% to 59.03% ±3.28% (60°C to 90°C). After enzymatic hydrolysis, a glucan conversion of 86.62% ±0.26% to 95.87% ±1.3% was also observed. Our results indicate that niobium oxide offers an effective and reusable pretreatment alternative to harsh chemicals that require significant downstream processing.

Dielectric barrier discharge atmospheric air plasma treatment of high amylose corn starch films

Atmospheric dielectric barrier discharge plasma is a novel non-thermal technology for food decontamination. The effects of dielectric barrier discharge plasma on the surface topography, thermal behavior, chemical composition and water vapor permeability of high amylose corn starch films have been examined. Plasma treatment significantly increased the surface roughness of the starch films. Thermal degradation profiles of all the starch films were similar, although a decrease in the maximum degradation temperature was observed after plasma treatment. X-ray photoelectron spectroscopy and Fourier transform Infrared spectra confirmed the increase in surface oxygen content and appearance of new O=C–O groups on the film surface after plasma treatment at 70 and 80 kV for 5 min. X-ray diffraction showed the A-type crystal structure which was not affected by plasma treatment. Surface hydrophilicity was also found higher after cold plasma treatment. Although, no significant change in the water vapor permeability was observed. The evaluation of plasma induced changes in the biodegradable polymers shows the compatibility of two environmentally-friendly strategies in food technology: cold plasma decontamination of food packaged with biodegradable materials.

Preparation and characterization of PEG/PVDF composite membranes and effects of solvents on its pervaporation performance in heptane desulfurization

Polyethylene glycol/polyvinylidene fluoride (PEG/PVDF) composite membranes were prepared using different water–organic solvent mixtures and the composite membranes obtained were characterized by Fourier transform infrared spectroscopy (FTIR-ATR), scanning electron microscopy, wide-angle X-ray diffraction (WAXD), and X photoelectron spectroscopy (XPS). Pervaporation (PV) experiments were conducted to characterize the sulfur removal properties of the PEG/PVDF composite membranes using a feed mixture of heptane and ethyl thioether with a sulfur concentration of 300 ng/μL over the temperature range of 65–80°C. All membranes investigated in this work showed proper PV performance and the E-PEG exhibited the highest PV flux and the highest sulfur enrichment factor of 5.17 at 65°C. The correlation of membrane crystallinity and surface oxygen content with PV performance was established. A decrease in membrane crystallinity or an increase in surface oxygen content greatly improved the membrane desulfurization property which was due to a decrease in mass transport resistance and an increase in sorption at membrane surface respectively. Finally, suggestions on the establishment of mass transfer model in PV process were made based on the results of the WAXD, FTIR-ATR, XPS studies and PV experiments.

Modulating calcium phosphate formation using CO 2 laser engineering of a polymeric material

The use of simulated body fluid (SBF) is widely used as a screening technique to assess the ability of materials to promote calcium phosphate formation. This paper details the use of CO 2 laser surface treatment of nylon® 6,6 to modulate calcium phosphate formation following immersion in SBF for 14 days. Through white light interferometry (WLI) it was determined that the laser surface processing gave rise to maximum Ra and Sa parameters of 1.3 and 4.4 μm, respectively. The use of X-ray photoelectron spectroscopy (XPS) enabled a maximum increase in surface oxygen content of 5.6%at. to be identified. The laser-induced surface modifications gave rise to a modulation in the wettability characteristics such that the contact angle, θ, decreased for the whole area processed samples, as expected, and increased for the patterned samples. The increase in θ can be attributed to a transition in wetting nature to a mixed-state wetting regime. It was seen for all samples that calcium phosphate formed on each surface following 14 days. The largest increase in mass, Δg, owed to calcium phosphate formation, was brought about by the whole area processed sample irradiated with a fluence of 51 J cm − 2 . No correlation between the calcium phosphate formation and the laser patterned surface properties was determined due to the likely affect of the mixed-state wetting regime. Strong correlations between θ, the surface energy parameters and the calcium phosphate formation for the whole area processed samples allow one to realize the potential for this surface treatment technique in predicting the bone forming ability of laser processed materials.

On the predominant mechanisms active during the high–power diode–laser modification of the wettability characteristics of an SiO2/Al2O3–based ceramic material

Restricted accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Lawrence J. 2002On the predominant mechanisms active during the high–power diode–laser modification of the wettability characteristics of an SiO2/Al2O3–based ceramic materialProc. R. Soc. Lond. A.4582445–2463http://doi.org/10.1098/rspa.2002.0984SectionRestricted accessOn the predominant mechanisms active during the high–power diode–laser modification of the wettability characteristics of an SiO2/Al2O3–based ceramic material J. Lawrence J. Lawrence Manufacturing Engineering Division, School of Mechanical and Production Engineering, Nanyang Technological University (NTU), Nanyang Avenue, Singapore 639798 () Google Scholar Find this author on PubMed Search for more papers by this author J. Lawrence J. Lawrence Manufacturing Engineering Division, School of Mechanical and Production Engineering, Nanyang Technological University (NTU), Nanyang Avenue, Singapore 639798 () Google Scholar Find this author on PubMed Search for more papers by this author Published:08 October 2002https://doi.org/10.1098/rspa.2002.0984AbstractThe mechanisms responsible for modifications to the wettability characteristics of an SiO2/Al2O3–based ceramic material in terms of a test–liquid set, comprising human blood, human blood plasma, glycerol and 4–octonol, after high–power diode–laser (HPDL) treatment, have been elucidated. Changes in the contact angle, θ, and hence the wettability characteristics of the SiO2/Al2O3–based ceramic, were attributed primarily to modifications to the surface roughness of the ceramic resulting from HPDL interaction, which accordingly effected reductions in θ, and to the increase in the surface oxygen content of the ceramic after HPDL treatment, since an increase in surface oxygen content intrinsically brings about a decrease in θ (and vice versa) and the increase in the polar component of the surface energy, γPsv, due to the HPDL–induced surface melting and resolidification, which consequently created a partly vitrified microstructure that was seen to augment the wetting action. However, the degree of influence exerted by each mechanism was found to differ markedly. Isolation of each of these mechanisms permitted the magnitude of their influence to be determined qualitatively. Surface energy, by way of microstructural changes, was found to be by far the most predominant element governing the wetting characteristics of the SiO2/Al2O3–based ceramic. To a much lesser extent, surface oxygen content, by way of process gas, was also seen to influence changes in the wettability characteristics of the SiO2/Al2O3–based ceramic, while surface roughness was found to play a minor role in inducing changes in the wettability characteristics. Previous ArticleNext Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsCited by Lawrence J, Waugh D and Liang H (2014) Predominant and Generic Parameters Governing the Wettability Characteristics of Selected Laser-Modified Engineering Materials Laser Surface Modification and Adhesion, 10.1002/9781118831670.ch8, (289-335) Hao L and Lawrence J (2006) Effects of Nd:YAG laser treatment on the wettability characteristics of a zirconia-based bioceramic, Optics and Lasers in Engineering, 10.1016/j.optlaseng.2005.08.001, 44:8, (803-814), Online publication date: 1-Aug-2006. Hao L, Lawrence J and Chian K (2005) Osteoblast cell adhesion on a laser modified zirconia based bioceramic, Journal of Materials Science: Materials in Medicine, 10.1007/s10856-005-2608-3, 16:8, (719-726), Online publication date: 1-Aug-2005. Hao L, Lawrence J, Phua Y, Chian K, Lim G and Zheng H (2005) Enhanced human osteoblast cell adhesion and proliferation on 316 LS stainless steel by means of CO2 laser surface treatment, Journal of Biomedical Materials Research Part B: Applied Biomaterials, 10.1002/jbm.b.30194, 73B:1, (148-156), Online publication date: 1-Apr-2005. Lawrence J (2004) Wetting and bonding characteristics of selected liquid metals with a high–power diode–laser–treated alumina bioceramic, Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 460:2046, (1723-1735), Online publication date: 8-Jun-2004. Hao L and Lawrence J (2005) On the role of laser-induced microstructures in influencing the surface energy of magnesia partially stabilized zirconia bioceramic, Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 10.1243/095440504772830219, 218:1, (59-76), Online publication date: 1-Jan-2004. Lawrence J and Hao L (2004) Bonding characteristics of selected liquid-metals with a CO2 laser treated magnesia partially stabilised zirconia bioceramic PICALO 2004: 1st Pacific International Conference on Laser Materials Processing, Micro, Nano and Ultrafast Fabrication, 10.2351/1.5056122, 978-0-912035-76-5, (708) Hao L, Lawrence J, Lim G and Zheng H (2004) Examination of CO2 laser-induced rapid solidification structures on magnesia partially stabilised zirconia and the effects thereof on wettability characteristics, Optics and Lasers in Engineering, 10.1016/j.optlaseng.2003.10.002, 42:3, (355-374), Online publication date: 1-Sep-2004. Hao L and Lawrence J (2003) Effects of CO2 laser irradiation on the wettability and human skin fibroblast cell response of magnesia partially stabilised zirconia, Materials Science and Engineering: C, 10.1016/S0928-4931(03)00056-0, 23:5, (627-639), Online publication date: 1-Oct-2003. This Issue08 October 2002Volume 458Issue 2026 Article InformationDOI:https://doi.org/10.1098/rspa.2002.0984Published by:Royal SocietyPrint ISSN:1364-5021Online ISSN:1471-2946History: Published online08/10/2002Published in print08/10/2002 License: Citations and impact Keywordswettabilitysurface energymeltinghigh–power diode laser (HPDL)vitrification

The effect of the thermal stability of some synthetic MnO 2 samples on their electrochemical and catalytic activity

The effect of heat treatment of five synthetic MnO 2 samples of various crystalline modifications on their O/Mn ratio, electrochemical activity (depolarising capacity), initial rate of catalytic decomposition of H 2O 2 and BET surface area has been investigated. Because of its high thermal stability, the depolarising capacity of β-MnO 2 does not undergo much change even up to 500°C of calcination. Similarly, α and γ-MnO 2 samples exhibit an appreciable depolarising capacity up to 400°C of calcination. On the other hand, like its thermal stability, the depolarising capacity of δ-MnO 2 steadily decreases from 110 to 500°C. The rate of decomposition of H 2O 2 shows two maxima; one at 200°C and the other at 500–600°C: the former is attributed to the increase in surface oxygen content during dehydroxylation, the latter is attributed to the presence of a favourable Mn 3+-Mn 4+ couple at the transition temperature. The BET surface areas of all the samples show a gradual decrease from 200 to 600°C.