Browsing by Author "Akhavan, B"

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    Development of negatively charged particulate surfaces through a dry plasma-assisted approach
    (Royal Society of Chemistry, 2015-01-15) Akhavan, B; Jarvis, K; Majewski, PJ
    A dry two-step plasma process is introduced for the fabrication of particulate surfaces showing negative charges over a wide range of pH. Plasma polymerized thiophene (PPT) was initially deposited onto silica particles using an inductively coupled plasma polymerization reactor fitted with a rotating barrel. Sulfur-functionalized particles were further chemically modified through an oxidative air or water plasma treatment. Wide ranges of plasma specific energies (0.06–2.4 kJ cm−3) and treatment times (5–60 minutes) were employed to manipulate the surface chemistry, hydrophobicity and surface charge of the silica particles. Surface chemistry of the modified silica particles was studied using X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectroscopy (ToF-SIMS). Changes in hydrophobicity and surface charge of the modified particles were quantified via Washburn capillary rise measurements and electrokinetic analysis, respectively. Plasma treatment of PPT coated particles resulted in homogenous formation of –SOx(H) functionalities such as sulfonate (SO3−), sulfonic acid (SO3H), and sulfate (SO42−) on surfaces. Such changes in surface chemistry significantly decreased the zeta potential and isoelectric point of the particles as well as their degree of hydrophobicity. In comparison to air plasma, water plasma was found to be a better candidate for the treatment of PPT coated particles as it produced surfaces with lower zeta potentials and isoelectric points. Our introduced solvent-free approach is applicable for the modification of almost any other particles regardless of their shape and surface chemistry. Such surface engineered particles could be utilized as protein detectors/adsorbents, solid-state catalysts, and heavy metal removal agents. © Royal Society of Chemistry 2017
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    Development of oxidized sulfur polymer films through a combination of plasma polymerization and oxidative plasma treatment
    (Americal Chemial Society, 2014-01-29) Akhavan, B; Jarvis, K; Majewski, PJ
    A novel two-step process consisting of plasma polymerization and oxidative plasma treatment is introduced in this article for the first time for the fabrication of −SOx(H)-functionalized surfaces. Plasma-polymerized thiophene (PPT) was initially deposited onto silicon wafers and subsequently SOx(H)-functionalized using air or oxygen plasma. The effectiveness of both air and oxygen plasma treatments in introducing sulfur–oxygen groups into the PPT film was investigated as the plasma input specific energy and treatment time were varied. The surface chemistries of untreated and treated PPT coatings were analyzed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS), whereas spectroscopic ellipsometry was used to evaluate the film thickness and ablation rate. Surface chemistry analyses revealed that high concentrations of −SOx(H) functionalities were generated on the surface upon either air or oxygen plasma treatment. It was found that, at low plasma input energies, the oxidation process was dominant whereas, at higher energies, ablation of the film became more pronounced. The combination of thiophene plasma polymerization and air/oxygen plasma treatment was found to be a successful approach to the fabrication of −SOx(H)-functionalized surfaces. © 2014, American Chemical Society.
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    Plasma polymer-functionalized silica particles for heavy metals remova
    (American Chemical Society, 2015-01-20) Akhavan, B; Jarvis, K; Majewski, PJ
    Highly negatively charged particles were fabricated via an innovative plasma-assisted approach for the removal of heavy metal ions. Thiophene plasma polymerization was used to deposit sulfur-rich films onto silica particles followed by the introduction of oxidized sulfur functionalities, such as sulfonate and sulfonic acid, via water–plasma treatments. Surface chemistry analyses were conducted by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. Electrokinetic measurements quantified the zeta potentials and isoelectric points (IEPs) of modified particles and indicated significant decreases of zeta potentials and IEPs upon plasma modification of particles. Plasma polymerized thiophene-coated particles treated with water plasma for 10 min exhibited an IEP of less than 3.5. The effectiveness of developed surfaces in the adsorption of heavy metal ions was demonstrated through copper (Cu) and zinc (Zn) removal experiments. The removal of metal ions was examined through changing initial pH of solution, removal time, and mass of particles. Increasing the water plasma treatment time to 20 min significantly increased the metal removal efficiency (MRE) of modified particles, whereas further increasing the plasma treatment time reduced the MRE due to the influence of an ablation mechanism. The developed particulate surfaces were capable of removing more than 96.7% of both Cu and Zn ions in 1 h. The combination of plasma polymerization and oxidative plasma treatment is an effective method for the fabrication of new adsorbents for the removal of heavy metals. © 2015 American Chemical Society
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    Plasma polymerization of sulfur-rich and water-stable coatings on silica particles
    (Elsevier, 2015-02-25) Akhavan, B; Jarvis, K; Majewski, PJ
    The plasma polymerization of thiophene has been applied to develop sulfur-rich coatings on silica particles. A range of plasma input energies (0.06–2.4 kJ ⋅ cm− 3) and deposition times (2–30 min) were applied in the plasma polymerization process. The surface chemistry of plasma polymerized thiophene (PPT)-coated particles was evaluated via X-ray photoelectron spectroscopy (XPS), while the distribution of sulfur-containing groups was studied by time of flight secondary ion mass spectroscopy (ToF-SIMS). Washburn capillary rise measurements quantified the hydrophobicity of uncoated and PPT-coated particles. The stability of PPT-coated particles in water was evaluated for immersion durations of 5 min to 24 h. Surface chemistry analyses showed a rapid and homogenous formation of sulfur-rich PPT layers on particles at a low plasma input energy of 0.06 kJ ⋅ cm− 3. ToF-SIMS results suggested the formation of high density thiol functionalities on surfaces. PPT coatings demonstrated high stability in water, which was attributed to their highly hydrophobic character. The deposition rate of PPT on particles and planar surfaces has also been compared in this investigation. It has been shown that the plasma polymerization of a monomer on a 2-D surface produces significantly thicker coatings in comparison to a 3-D surface. The plasma polymerization of thiophene via a rotating reactor was found to be an effective method for the fabrication of sulfur-rich coatings on particulate surfaces. © 2017 Elsevier B.V.