Effect of surface chemical composition on the surface potential and iso-electric point of silicon substrates modified with self-assembled monolayers

Kuo, Chung Yen; Chang, Hsun-Yun; Liu, Chi-Ping; Lee, Szu-Hsian; You, Yun-Wen; Shyue, Jing‐Jong

doi:10.1039/c0cp02615h

Cited by 35 publications

(27 citation statements)

References 25 publications

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“…In diatoms modified with APTES or AEAPTMS, the zeta potentials shifted to more positive values due to the presence of protonated amines (-NH + 3 ). As a result, isoelectric points (ieps) of pH 6.6 and 7.5 were observed for APTES and AEAPTMS-DE particles, respectively, in agreement with literature reports [41].…”

Section: Structural and Chemical Characterization Of Pristine And Modsupporting

confidence: 80%

“…An isoelectric point (iep) close to pH = 2 is indicated, which is quite similar to that of amorphous SiO 2 particles [40]. The zeta potential of MPTMS-DE particles did not change significantly in comparison with that of the pristine diatoms, despite the acidic nature of -SH groups form a negatively charged conjugate base on the diatom surface [41]. In diatoms modified with APTES or AEAPTMS, the zeta potentials shifted to more positive values due to the presence of protonated amines (-NH + 3 ).…”

Section: Structural and Chemical Characterization Of Pristine And Modmentioning

confidence: 69%

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Functionalized diatom silica microparticles for removal of mercury ions

Addai‐Mensah

Lošić

2012

Science and Technology of Advanced Materials

125

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Diatom silica microparticles were chemically modified with self-assembled monolayers of 3-mercaptopropyl-trimethoxysilane (MPTMS), 3-aminopropyl-trimethoxysilane (APTES) and n-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPTMS), and their application for the adsorption of mercury ions (Hg(II)) is demonstrated. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses revealed that the functional groups (-SH or -NH 2 ) were successfully grafted onto the diatom silica surface. The kinetics and efficiency of Hg(II) adsorption were markedly improved by the chemical functionalization of diatom microparticles. The relationship among the type of functional groups, pH and adsorption efficiency of mercury ions was established. The Hg(II) adsorption reached equilibrium within 60 min with maximum adsorption capacities of 185.2, 131.7 and 169.5 mg g −1 for particles functionalized with MPTMS, APTES and AEAPTMS, respectively. The adsorption behavior followed a pseudo-second-order reaction model and Langmuirian isotherm. These results show that mercapto-or amino-functionalized diatom microparticles are promising natural, cost-effective and environmentally benign adsorbents suitable for the removal of mercury ions from aqueous solutions.

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Section: Structural and Chemical Characterization Of Pristine And Modsupporting

confidence: 80%

Section: Structural and Chemical Characterization Of Pristine And Modmentioning

confidence: 69%

Functionalized diatom silica microparticles for removal of mercury ions

Addai‐Mensah

Lošić

2012

Science and Technology of Advanced Materials

125

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“…18 However, surface amine groups on gold, e.g., aminothiols, are unstable because these molecules can undergo chemical transformation, e.g., photoassisted oxidation of amine groups into nitroso groups and oxidation of thiol groups into sulfonate groups. 19−21 Furthermore, these surfaces are only stable up to 100°C.…”

Section: Introductionmentioning

confidence: 99%

Chemical Modifications of Silicon Surfaces for the Generation of a Tunable Surface Isoelectric Point

et al. 2014

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The aim of this work was to generate a tunable surface isoelectric point (sIEP), where the surface is modified with two molecules: a weak base (pyridine), carrying a pH dependent positive charge, and a derivative of a strong acid (sulfate), carrying a permanent negative charge in a physiologically relevant pH range. To this end, silicon surfaces were modified with 3-aminopropyltriethoxysilane. These amine-modified surfaces were subsequently derivatized into pyridine- or sulfate-modified surfaces. Then, the surface pKa of pyridine-modified surfaces was determined by a fluorescent nanoparticle adhesion assay (FNAA). Next, these values were used to calculate in which ratio the chemicals must be present in the reaction mixture to generate a mixed pyridine/sulfate-modified surface with a target sIEP. After preparing surfaces with a target sIEP, an FNAA with positively and negatively charged nanoparticles was used to verify the sIEP of the generated surfaces. The FNAA revealed that pyridine-modified surfaces had a pKa of 6.69 ± 0.18. When an sIEP was generated, negative nanoparticles bound to surfaces at pH values below the sIEP and positive nanoparticles bound at pH values above the sIEP. Furthermore, we found sIEP values of 5.97 ± 0.88 when we aimed for an sIEP of 6.2, and 7.12 ± 0.21 when we aimed for an sIEP of 7.1. Finally, the pH dependent binding and release of a negatively and positively charged (bio)polymer was investigated for a target sIEP of 7. A negatively charged polymer (poly(I:C)) was bound at a pH < sIEP and released at a pH > sIEP with a release efficiency of 85 ± 9% and a positively charged polymer (trimethyl chitosan) bound at a pH > sIEP and released at a pH < sIEP with a release efficiency of 72 ± 9%. In conclusion, we established a method for preparing modified silicon surfaces with a tunable sIEP, which can be used for pH-dependent binding and release of biomacromolecules.

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“…Thiol groups on MPTMS would be expected to interact more weakly with the mildly acidic hydroxyl groups on the silica surface than the amine groups on APTMS. 21 Nitrogen adsorption-desorption isotherms are all of type IV (Supporting Information), indicating mesoporous structures. 22 Table 2 shows surface area, pore volume and pore size data for the catalysts studied.…”

Section: Catalytic Activitymentioning

confidence: 99%

Environmentally Benign Bifunctional Solid Acid and Base Catalysts

Elmekawy

Shiju

Rothenberg

et al. 2014

Ind. Eng. Chem. Res.

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ABSTRACT:Solid bi-functional acid-base catalysts were prepared in two ways on an amorphous silica support: 1) by grafting mercaptopropyl units (followed by oxidation to propylsulfonic acid) and aminopropyl groups to the silica surface (NH 2 -SiO 2 -SO 3 H), and 2) by grafting only aminopropyl groups and then partially neutralising with phosphotungstic acid, relying on the H 2 PW 12 O 40 -ion for surface acidity (NH 2 -SiO 2 -NH 3 + [H 2 PW 12 O 40 -], denoted as NH 2 -SiO 2 -PTA).Surface acidity and basicity were characterised by adsorption calorimetry, using SO 2 as a probe for surface basicity and NH 3 for surface acidity. Catalytic activities were compared in a two-stage cascade: an acid-catalysed deacetalisation followed directly by a base-catalysed Henry reaction. Overall, the NH 2 -SiO 2 -SO 3 H catalysts showed higher concentrations and strengths of both acid and base sites, and higher activities than NH 2 -SiO 2 -PTA. Both catalysts showed evidence of cooperative acid-base catalysis. Importantly, the bi-functional catalysts exhibited catalytic advantage over physical mixtures of singly functionalised catalysts. 3 INTRODUCTIONMany liquid phase processes in fine chemicals synthesis require acid or base catalysts. Conventionally, homogeneous acids and bases dissolved in the reaction mixtures are used. In most cases, replacing these with solid acids and bases brings substantial environmental benefit by reducing waste and simplifying product separation. 1-3Almost inevitably, however, solid acids and bases are less active than their homogeneous counterparts. Despite this, one case where they might be able to offer particular advantage is where both acid and base catalysis is required, either in sequential steps or through a cooperative catalytic mechanism. A difficulty associated with preparation of the aminopropyl/propylsulfonic acid bi-functional catalysts (NH 2 -SiO 2 -SO 3 H) is that the acid group is grafted to the silica using (3-mercaptopropyl)trimethoxysilane (MPTMS) and an oxidation step is required to convert the thiol (-SH) to sulfonic acid (-SO 3 H). The two main routes reported are based on hydrogen peroxide/sulfuric acid, and on nitric acid (as both oxidant and acidifier). 11,12 The method used must be chosen to effectively oxidise thiol 12 but with minimal reaction with the base groups. Nitric acid has been shown to be the more effective reagent under these conditions 13 so nitric acid is used as the oxidant in the work reported here.An amorphous silica gel has been used as the catalyst support, rather than the ordered SBA-15 silica used in our previous work. Silica gel does not exhibit the friability and low bulk density of SBA-15 14-16 while the surface properties and stability are similar, and it can be functionalised in the same way. The silica gel used here has been chosen to have an average pore diameter similar to that of SBA-15. The tandem deacetalisation-Henry reaction shown in Scheme 2 has been used. The first step is the acid-catalysed deacetalisation of benzaldehyde dimethyl acetal i...

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Effect of surface chemical composition on the surface potential and iso-electric point of silicon substrates modified with self-assembled monolayers

Cited by 35 publications

References 25 publications

Functionalized diatom silica microparticles for removal of mercury ions

Functionalized diatom silica microparticles for removal of mercury ions

Chemical Modifications of Silicon Surfaces for the Generation of a Tunable Surface Isoelectric Point

Environmentally Benign Bifunctional Solid Acid and Base Catalysts

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