Alex O. Ibhadon

Ultrasound‐ and Microwave‐Assisted Preparation of Lead‐Free Palladium Catalysts: Effects on the Kinetics of Diphenylacetylene Semi‐Hydrogenation

The effect of environmentally benign enabling technologies such as ultrasound and microwaves on the preparation of the lead‐free Pd catalyst has been studied. A one‐pot method of the catalyst preparation using ultrasound‐assisted dispersion of palladium acetate in the presence of the surfactant/capping agent and boehmite support produced the catalyst containing Pd nanoparticles and reduced the number of pores larger than 4 nm in the boehmite support. This catalyst demonstrated higher activity and selectivity. The comparison of kinetic parameters for diphenylacetylene hydrogenation showed that the catalyst obtained by using the one‐pot method was seven times as active as a commercial Lindlar catalyst and selectivity towards Z‐stilbene was high. Our work also illustrated that highly selective Pd/boehmite catalysts can be prepared through ultrasound‐assisted dispersion and microwave‐assisted reduction in water under hydrogen pressure without any surfactant.

Ultrasound-assisted selective hydrogenation of C-5 acetylene alcohols with Lindlar catalysts

The selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY) was performed in the presence of Lindlar catalyst, comparing conventional stirring with sonication at different frequencies of 40, 380 and 850 kHz. Under conventional stirring, the reaction rates were limited by intrinsic kinetics, while in the case of sonication, the reaction rates were 50-90% slower. However, the apparent reaction rates were found to be significantly frequency dependent with the highest rate observed at 40 kHz. The original and the recovered catalysts after the hydrogenation reaction were compared using bulk elemental analysis, powder X-ray diffraction and scanning and transmission electron microscopy coupled with energy-dispersive X-ray analysis. The studies showed that sonication led to the frequency-dependent fracturing of polycrystalline support particles with the highest impact caused by 40 kHz sonication, while monocrystals were undamaged. In contrast, the leaching of Pd/Pb particles did not depend on the frequency, which suggests that sonication removed only loosely-bound catalyst particles.

Photocatalytic degradation of ketorolac tromethamine (KTC) using Ag-doped ZnO microplates

In this study, Ag-doped ZnO microplates were prepared via precipitation technique and further characterized by FESEM, EDS, XRD, FTIR, TGA, XPS, UV-DRS and RT-PL techniques. The outcomes indicated that Ag+ ions were well incorporated into ZnO lattice leading to the absorption of ZnO in visible region as well as effective charge separation. The photocatalytic experiments exhibited that Ag-doped ZnO microplates show higher catalytic activity (91%) than bare ZnO (71%) for the degradation of KTC drug under solar illumination. The photocatalytic degradation of KTC drug over Ag-doped ZnO microplates obeyed pseudo first-order kinetics model. Also, the role of active species was examined by the addition of several scavengers in the photocatalytic degradation system. The results indicated that h+, ·OHs, 1O2 and ·OH were considered as prime reactive species in photocatalytic degradation process.

Fabrication of novel carbon quantum dots modified bismuth oxide (α-Bi2O3/C-dots): Material properties and catalytic applications

The present work reports the facile and the template free sonochemical synthesis of a novel catalyst, α-Bi2O3/C-dots, for the degradation of indigo carmine (IC) dye, its simulated dyebath effluent and levofloxacin under visible light catalysis. The compositional, structural, optical and morphological analysis of α-Bi2O3/C-dots was studied using analytical, spectroscopic and microscopic techniques. X-ray diffraction (XRD) results confirmed the presence of a monoclinic phase of α-Bi2O3 in the nanocomposite and crystallite size of 28.75 nm. Photoluminescence (PL) and UV-vis diffuse reflectance spectra (UV-DRS) studies showed good optical properties and a band gap of 2.49 eV. The synthesized photocatalyst showed superior visible-light driven photocatalytic activity for the degradation of indigo carmine dye (86% dye degradation in 120 min) compared to pure α-Bi2O3 (57%). α-Bi2O3/C-dots also exhibited 79% degradation of antibiotic drug levofloxacin within 120 min, under optimized conditions of pH, catalyst dose and initial dye concentration. Scavenger studies revealed that hydroxyl radicals and electrons played predominant roles in the photocatalytic degradation of IC dye. With respect to total organic carbon (TOC) analysis, 68.8% total organic carbon reduction of the IC dye (10 mg/L) was observed under the same experimental conditions. The catalytic efficiency of C-dots in the photocatalytic process is explained by proposing a degradation mechanism.

Solar light driven photocatalytic degradation of levofloxacin using TiO2/carbon-dot nanocomposites

This paper reports the synthesis of TiO2 quantum dots, carbon dots (C-dots), and TiO2/C-dots using facile sol–gel and hydrothermal methods. The synthesized quantum dots were further characterized in detail to understand their crystalline, structural, morphological, thermal and optical properties using various spectroscopic and analytical techniques. The characterization results confirmed that the prepared photocatalysts exhibited high crystallinity, purity and excellent optical properties. The morphological results indicated that the C-dots were uniformly distributed over the TiO2 quantum dots and nanocomposites have an average size of 12 nm. Furthermore, the prepared sample, i.e. TiO2/C-dots, was efficiently employed as a potential heterogeneous photocatalyst for solar light driven photocatalytic degradation of a fluoroquinolone antibiotic drug levofloxacin. To optimize the photocatalytic degradation experiments, various catalyst dose-dependent, pH-dependent, and initial drug-concentration dependent experiments were carried out. The photocatalytic experiments revealed almost complete photocatalytic degradation of levofloxacin (10 mg L−1) within 90 minutes of solar light illumination using the TiO2/C-dots under optimum conditions, whereas bare TiO2 showed only 66.5% degradation of the drug. Different commercial photocatalysts such as TiO2 PC-50 and TiO2 PC-500 were also used for comparing the photocatalytic efficiency of the synthesized photocatalyst. Furthermore, the stability of the photocatalyst was studied by performing recyclability experiments up to 5 cycles using the TiO2/C-dots, indicating that the nanocomposites could be reused without any significant loss. The TOC results indicated the simultaneous 53.4% mineralization and photocatalytic degradation of levofloxacin under optimized conditions. The enhanced photocatalytic activity of the nanocomposites was attributed to the presence of the C-dots in the system, which provided more active sites for the drug molecules and also restricted the recombination of charge carriers. The role of active radical species in the photocatalytic degradation of levofloxacin was also investigated. A photocatalytic degradation mechanism and pathway were also proposed.