Changseok Han

Photoinactivation of Escherichia coli by sulfur-doped and nitrogen-fluorine-codoped TiO2 nanoparticles under solar simulated light and visible light irradiation.

Titanium dioxide (TiO2) is one of the most widely used photocatalysts for the degradation of organic contaminants in water and air. Visible light (VL) activated sulfur-doped TiO2 (S-TiO2) and nitrogen-fluorine-codoped TiO2 (N-F-TiO2) were synthesized by sol-gel methods and characterized. Their photoinactivation performance was tested against Escherichia coli under solar simulated light (SSL) and VL irradiation with comparison to commercially available TiO2. Undoped Degussa-Evonik P-25 (P-25) and Sigma-TiO2 showed the highest photocatalytic activity toward E. coli inactivation under SSL irradiation, while S-TiO2 showed a moderate toxicity. After VL irradiation, Sigma-TiO2 showed higher photoinactivation, whereas S-TiO2 and P-25 showed moderate toxicity. Oxidative stress to E. coli occurred via formation of hydroxyl radicals leading to lipid peroxidation as the primary mechanism of bacterial inactivation. Various other biological models, including human keratinocytes (HaCaT), zebrafish liver cells (ZFL), and zebrafish embryos were also used to study the toxicity of TiO2 NPs. In conclusion, N-F-TiO2 did not show any toxicity based on the assay results from all the biological models used in this study, whereas S-TiO2 was toxic to zebrafish embryos under all the test conditions. These findings also demonstrate that the tested TiO2 nanoparticles do not show any adverse effects in HaCaT and ZFL cells.

Synthesis, characterization and photocatalytic evaluation of visible light activated C-doped TiO2 nanoparticles

We have demonstrated heterogeneous photocatalytic degradation of microcystin-LR (MC-LR) by visible light activated carbon doped TiO(2) (C-TiO(2)) nanoparticles, synthesized by a modified sol-gel route based on the self-assembly technique exploiting oleic acid as a pore directing agent and carbon source. The C-TiO(2) nanoparticles crystallize in anatase phase despite the low calcination temperature of 350 °C and exhibit a highly porous structure that can be optimized by tuning the concentration of the oleic acid surfactant. The carbon modified nanomaterials exhibited enhanced absorption in the broad visible light region together with an apparent red shift in the optical absorption edge by 0.5 eV (2.69 eV), compared to the 3.18 eV of reference anatase TiO(2). Carbon species were identified by x-ray photoelectron spectroscopy analysis through the formation of both Ti-C and C-O bonds, indicative of substitution of carbon for oxygen atoms and the formation of carbonates, respectively. Electron paramagnetic resonance spectroscopy revealed the formation of two carbon related paramagnetic centers in C-TiO(2), whose intensity was markedly enhanced under visible light illumination, pointing to the formation of localized states within the anatase band gap, following carbon doping. The photocatalytic activity of C-TiO(2) nanomaterials was evaluated for the degradation of MC-LR at pH 3.0 under visible light (λ > 420 nm) irradiation. The doped materials showed a higher MC-LR degradation rate than reference TiO(2), behavior that is attributed to the incorporation of carbon into the titania lattice.

Oxidative esterification via photocatalytic C–H activation

Direct oxidative esterification of alcohol via photocatalytic C–H activation has been developed using VO@g-C3N4 catalyst; an expeditious esterification of alcohols occurs under neutral conditions using visible light as the source of energy.

An innovative zinc oxide-coated zeolite adsorbent for removal of humic acid

Zinc oxide (ZnO)-coated zeolite adsorbents were developed by both nitric acid modification and Zn(NO3)2·6H2O functionalization of zeolite 4A. The developed adsorbents were used for the removal of humic acid (HA) from aqueous solutions. The synthesized materials were characterized by porosimetry analysis, scanning electron microscopy, X-Ray diffraction analysis, and high resolution transmission electron microscopy. The maximum adsorption capacity of the adsorbents at 21±1°C was about 60mgCg(-1). The results showed that the positive charge density of ZnO-coated zeolite adsorbents was proportional to the amount of ZnO coated on zeolite and thus, ZnO-coated zeolite adsorbents exhibited a greater affinity for negatively charged ions. Furthermore, the adsorption capacity of ZnO-coated zeolite adsorbents increased markedly after acid modification. Adsorption experiments demonstrated ZnO-coated zeolite adsorbents possessed high adsorption capacity to remove HA from aqueous solutions mainly due to strong electrostatic interactions between negative functional groups of HA and the positive charges of ZnO-coated zeolite adsorbents.

Nanodiamond–TiO2 composites for photocatalytic degradation of microcystin-LA in aqueous solutions under simulated solar light

Titanium dioxide (TiO2) has been under intensive investigation for photocatalytic degradation of cyanobacterial toxins. In order to develop more efficient photocatalysts, TiO2 and oxidized nanodiamonds (NDox) were combined as a composite catalyst (NDox–TiO2), which was tested in the photocatalytic oxidation of microcystin-LA (MC-LA), a cyanotoxin frequently found in freshwater. NDox–TiO2 and neat TiO2 photocatalysts were prepared by a liquid phase deposition method. A wide variety of analytical techniques, including physical adsorption of nitrogen, X-ray diffraction (XRD), UV-Vis and IR diffuse reflectance spectroscopies (DRUV-Vis and DRIFT), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were used to characterize the materials. The performance of the photocatalysts was studied under both simulated solar and visible light. The kinetic results show remarkable efficiency for the NDox–TiO2 composite under simulated solar light irradiation with a synergistic factor of more than 15 relative to neat TiO2, while negligible photocatalytic activity was observed for the degradation of MC-LA when NDox–TiO2 was used under visible light illumination due to the wide band gap of the composite material. The photocatalytic efficiency of NDox–TiO2 was ascribed to the good dispersion of both phases in the composite material, facilitating the possible electronic interaction at the heterojunction interface between NDox and TiO2.

Photocatalytic cellulosic electrospun fibers for the degradation of potent cyanobacteria toxin microcystin-LR

Non-woven, high surface area photocatalytic cellulosic electrospun fibers were fabricated for solar-light-driven water treatment purposes and tested for photocatalytic decomposition of the potent cyanobacteria toxin microcystin-LR (MC-LR). Electrospun fibers of cellulose acetate were converted to succinylated cellulose and then loaded with titania nanoparticles using a simple solution based technique. It was found that the type of titania nanoparticle (visible light activated or UV light activated), the surface area of the fiber mat, and loading solution pH all have an effect on the distribution of titania along the fibers. The titania coverage and surface area of the fiber mats were found to correlate well with the degree of MC-LR degradation under both visible and solar light irradiation. The difference in titania coverage, determined using X-ray photoelectron microscopy (XPS), was two to three times smaller in the lower surface area samples. These photocatalytic electrospun fibers could be advantageously used for drinking water and wastewater treatment applications using solar light as a renewable source of energy.

Monitoring of 2-butanone using a Ag–Cu bimetallic alloy nanoscale electrochemical sensor

Spherical shaped silver–copper alloy nanoparticles of 10–15 nm size were synthesized by an aqueous polymer solution method. The synthesized nanoscale Ag–Cu alloy was characterized by UV-Visible spectroscopy, X-ray diffraction spectroscopy, transmission electron microscopy (TEM), high resolution TEM, and energy dispersive spectroscopy. The XRD pattern showed high crystallinity and phase formation of the nanoparticles. The bimetallic alloy nanoparticles were coated over a well-polished glassy carbon electrode and the designed sensor was applied for the detection of a highly carcinogenic carbonyl compound, 2-butanone. Electrochemical studies revealed that PEI used as a capping agent also enhances the sensing of the modified electrode for the recognition of 2-butanone. The sensor developed from Ag–Cu (1 : 1) alloy nanoparticles showed the best sensing properties for the detection of 2-butanone as evidenced by electrochemical impedance spectroscopy and a 0.1 μM detection limit.

Phosphate removal using modified Bayoxide® E33 adsorption media

The adsorption of phosphate onto modified Bayoxide® E33 (E33) and underlying mechanisms were comparatively investigated by batch kinetics, sorption isotherms, rapid small-scale column tests, and material characterization. Synthesis of modified E33 was conducted by the addition of manganese and silver nanoparticles on the surface of the goethite (α-FeOOH)-based E33. Upon successful adsorbent synthesis, the materials were characterized using SEM, TEM, XRD, EDX, HR-TEM, and BET surface area analysis. The adsorption kinetics is described by a fast initial adsorption stage followed by a slow adsorption stage, complying with pseudo second-order kinetics and Elovich kinetics. Sorption isotherms revealed that the equilibrium capacity of one of the modified adsorbents (E33/AgII) exceeded that of unmodified E33 likely due to its increased BET surface area. Column experiments confirmed the results for adsorption kinetics and equilibrium of phosphate sorption onto E33 and modified E33. This suggests that media modification has the potential to improve phosphate removal properties.

Long afterglow green phosphors functionalized with Fe-N doped TiO2 for the photocatalytic removal of emerging contaminants

Long Afterglow Green Phosphors Functionalized with Fe-N Doped TiO2 for the Photocatalytic Removal of Emerging Contaminants Olga Sacco , Vincenzo Vaiano, Changseok Han, Diana Sannino, Dionysios D. Dionysiou, Paolo Ciambelli Department of Industrial Engineering, University of Salerno, Via Giovanni Paolo II 132, 84084 Fisciano (SA), Italy. Environmental Engineering and Science Program, Department of Biomedical, Chemical and Environmental Engineering, University of Cincinnati, Cincinnati, OH 10 45221-0012, USA vvaiano@unisa.it

CHAPTER 5:The Green Synthesis and Environmental Applications of Nanomaterials

This chapter summarizes the use of green chemistry on the synthesis of nanomaterials as well as their environmental applications. Green routes for the synthesis of nanomaterials are discussed, including those using nontoxic solvents and natural template materials, such as ionic liquid, leaf and tea extract, natural cellulose, sucrose, starch, and plant leaves. Such methods could decrease the use of hazardous chemicals in chemical processes and reduce or eliminate undesirable products during the synthesis process. The employment of micro-organisms for the green synthesis of nanoparticles is also described. In addition, the use of nanomaterials as photocatalysts, Fentons catalysts, and disinfectants is reported for environmental remediation including the degradation of organic contaminants and the inactivation of pathogenic micro-organisms in water. Finally, the importance of immobilization of nanomaterials onto substrates for their sustainable application to environmental remediation, in particular, contaminated water and wastewater treatment is presented.