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T. DAVID WAITE 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2008 NANO Vol.3 No.5
Dithionite can be used to reduce Fe(II) and produce nanoscale zero-valent iron (nZVI) under conditions of high pH and in the absence of oxygen. The nZVI is coprecipitated with a sulfite hydrate in a thin platelet. The nanoparticles formed are not pure iron but this feature does not appear to affect their degradation performance under air or N2 gas conditions. The efficiency of trichloroethylene (TCE) degradation, when one is employing nanoparticles manufactured using dithionite (nZVIS2O4), is similar to if not slightly better than that of the more conventional borohydride procedure (nZVIBH4). The other advantages of the dithionite method are that (i) it uses a less expensive and widely available reducing agent, and (ii) there is no production of potentially explosive hydrogen gas. Oxidation of benzoic acid using the nZVIS2O4 particles results in different byproducts than those produced when nZVIBH4 particles are used. The low oxidant yield based on hydroxybenzoic acid generation is offset by the production of higher concentrations of phenol. The high concentration of phenol compared to hydroxybenzoic acids suggests that OH• addition is not the primary oxidation pathway when one is using the nZVIS2O4 particles. It is proposed that sulfate radicals () are produced as a result of hydroxyl radical attack on the sulfite matrix surrounding the nZVIS2O4 particles, with these radicals oxidizing benzoic acid via electron transfer reactions rather than addition reactions.
Adhesion of mussel foot proteins to different substrate surfaces
Lu, Qingye,Danner, Eric,Waite, J. Herbert,Israelachvili, Jacob N.,Zeng, Hongbo,Hwang, Dong Soo The Royal Society 2013 Journal of the Royal Society, Interface Vol.10 No.79
<P> Mussel foot proteins (mfps) have been investigated as a source of inspiration for the design of underwater coatings and adhesives. Recent analysis of various mfps by a surface forces apparatus (SFA) revealed that mfp-1 functions as a coating, whereas mfp-3 and mfp-5 resemble adhesive primers on mica surfaces. To further refine and elaborate the surface properties of mfps, the force-distance profiles of the interactions between thin mfp (i.e. mfp-1, mfp-3 or mfp-5) films and four different surface chemistries, namely mica, silicon dioxide, polymethylmethacrylate and polystyrene, were measured by an SFA. The results indicate that the adhesion was exquisitely dependent on the mfp tested, the substrate surface chemistry and the contact time. Such studies are essential for understanding the adhesive versatility of mfps and related/similar adhesion proteins, and for translating this versatility into a new generation of coatings and (including <I>in vivo</I> ) adhesive materials. </P>
폐쇄성 수면 무호흡 환자의 상하악 전방이동술 전후의 두부계측방사선 사진에서 산출한 기도직경, 상기도 공간의 기류저항과 호흡방해지수 변화와의 연관성
박광호,Park, Kwang-Ho,Waite, Peter D. 대한구강악안면외과학회 2001 대한구강악안면외과학회지 Vol.27 No.2
The purpose of this study cephalometrically evaluated changes in the posterior airway space for patients with obstructive sleep apnea syndrome(OSAS) before and after surgical advancement of the maxilla and mandible. The change in calculated airway resistance was correlated with the respiratory disturbance index(RDI). Twenty cephalometric radiographs were traced before and after surgery to determine the posterior airway area and calculate resistance. Polysomnograms of each patient were obtained before and after surgery. All patients had a decrease in calculated airflow resistance in the airway. The mean amount of resistance was 865.15 before surgery, decreasing to 192.65 after surgery (p<0.01). Eighty-five percent of the patients experienced improvement in their RDI. Reduction in the RDI appears to be due to an increase in the posterior airway space and decrease in flow resistance.
Advances in Surface Passivation of Nanoscale Zerovalent Iron: A Critical Review
Bae, Sungjun,Collins, Richard N.,Waite, T. David,Hanna, Khalil American Chemical Society 2018 Environmental science & technology Vol.52 No.21
<P>Nanoscale zerovalent iron (NZVI) is one of the most extensively studied nanomaterials in the fields of wastewater treatment and remediation of soil and groundwater. However, rapid oxidative transformations of NZVI can result in reduced NZVI reactivity. Indeed, the surface passivation of NZVI is considered one of the most challenging aspects in successfully applying NZVI to contaminant degradation. The oxidation of NZVI can lead to the formation of Fe<SUP>II</SUP>-bearing phases (e.g., Fe<SUP>II</SUP>O, Fe<SUP>II</SUP>(OH)<SUB>2</SUB>, Fe<SUP>II</SUP>Fe<SUP>III</SUP><SUB>2</SUB>O<SUB>4</SUB>) on the NZVI surface or complete oxidation to ferric (oxyhydr)oxides (e.g., Fe<SUP>III</SUP>OOH). This corrosion phenomenon is dependent upon various factors including the composition of NZVI itself, the type and concentration of aqueous species, reaction time and oxic/anoxic environments. As such, the coexistence of different Fe oxidation states on NZVI surfaces may also, in some instances, provide a unique reactive microenvironment to promote the adsorption of contaminants and their subsequent transformation via redox reactions. Thus, an understanding of passivation chemistry, and its related mechanisms, is essential not only for effective NZVI application but also for accurately assessing the positive and negative effects of NZVI surface passivation. The aim of this review is to discuss the nature of the passivation processes that occur and the passivation byproducts that form in various environments. In particular, the review presents: (i) the strengths and limitations of state-of-the-art techniques (e.g., electron microscopies and X-ray-based spectroscopies) to identify passivation byproducts; (ii) the passivation mechanisms proposed to occur in anoxic and oxic environments; and (iii) the effects arising from synthesis procedures and the presence of inorganics/organics on the nature of the passivation byproducts that form. In addition, several depassivation strategies that may assist in increasing and/or maintaining the reactivity of NZVI are considered, thereby enhancing the effectiveness of NZVI in contaminant degradation.</P> [FIG OMISSION]</BR>