Zinc
oxide (ZnO) hollow spheres were prepared by the hydrothermal
method and encapsulated with fluorinated reduced graphene oxide (FRGO)
using a tetra-n-butylammonium bromide (TBAB) linker
to give an FRGO/ZnO composite. X-ray diffraction and microscopic studies
revealed their hexagonal-wurtzite structure, spherical morphology,
and size of the crystallite to be 26.7 nm. Diffuse reflectance UV–visible
spectroscopy showed an optical band gap and semiconductive nature
of the composite. Atomic force microscopy images show the surface
topography of FRGO-encapsulated ZnO hollow spheres. The photoluminescence
spectra depicted the electron–hole pair recombination order
to be ZnO > RGO/ZnO > FRGO/ZnO. The electrochemical impedance
spectroscopy
(EIS) demonstrates the increased charge-carrier mobility of the FRGO/ZnO
composite; the R
ct values of ZnO, RGO/ZnO,
and FRGO/ZnO were found to be 6.18 × 103, 4.07 ×
103, and 3.45 × 103 Ω, respectively.
All the three materials were employed as photocatalysts in the degradation
of methylene blue under UV-365 nm radiation and the results exposed
the higher photocatalytic activity of reduced fluorinated graphene
oxide/ZnO than RGO/ZnO and bare ZnO hollow spheres. The increased
photocatalytic activity of the composite is due to the enhanced vectorial
transport of charge carriers at the interface of the FRGO/ZnO composite
and suppression of charge-carrier recombination. The presence of fluorine
in the RGO sheet introduces additional defects and leverages heterogeneous
electron transport. In turn, mobility of light-generated charge carriers
is increased and results in suppression of their recombination, which
facilitates the photocatalytic process.
Hierarchically ordered, honeycomb-like nanoporous TiO2 electrodes are prepared by a simple electrochemical anodization process using ammonium fluoride dissolved in ethylene glycol as an electrolytic medium. Formation of hexagonally arranged nanopores along with the tubular structure and anatase crystalline phase of TiO2 is confirmed by field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) studies. Further, these nanoporous TiO2 electrodes are employed as a substrate for enzyme (horseradish peroxidase, HRP) immobilization in an attempt to enhance the electron transport across the semiconductor electrode-electrolyte interface. Two different strategies, namely, physical entrapment and covalent linking, are used for anchoring the enzyme. Various parameters such as conductivity, stability, enzyme loading, enzymatic activity, sensitivity, linear range, etc., are investigated by using electrochemical techniques. Structural and morphological analyses of enzyme-modified electrodes are carried out using spectroscopic (UV - vis) and microscopic (AFM) methods. In the case of physical entrapment, a simple drop casting method of HRP solution on the nanoporous TiO2 electrodes is used in contrast to chemical linking method where a monolayer of 3-aminopropyltrimethoxy silane (APTMS) is formed initially on TiO2 followed by HRP immobilization using an amide coupling reaction. Interestingly, both of these methods result in anchoring of HRP enzyme, but the amount of enzyme loading and the stability are found to be higher in the covalent linking method. Cyclic voltammetric studies reveal the formation of a well-defined reversible peak for HRP enzyme. Dependence of peak current with the scan rate suggests that HRP enzyme is immobilized and stable and that the overall electron transfer process is predominantly controlled by a diffusion process. Enzymatic activity of HRP is investigated by monitoring the reduction process of hydrogen peroxide by incremental addition using cyclic voltammetry and amperometry techniques, from which several kinetic parameters are determined.
Wattle (Acacia mearnsii) extract, a leather tanning agent which mainly composed of polyphenolic compounds was tried to degrade by photocatalytic degradation which is a hindrance to the conventional bio -treatment of tannery effluent. To serve the process a novel semiconductive mixed catalyst CdWO 4 -ZnO was prepared by simple hydrothermal method. The degradation reaction was carried with visible light source in neutral medium for three hours duration. The results depicted the better catalytic activity of CdWO 4 -ZnO (band gap 2.8 eV) in degrading the organics when compared to undoped ZnO (band gap 3.8eV) under visible light. The results also showed that the catalyst is appropriate at 36.8 weight percentage of CdWO 4 in ZnO. The catalyst morphological, optical characters and degradation of wattle were carefully analyzed.
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