Browsing by Author "Kibombo, Harrison S."
Now showing 1 - 13 of 13
Results Per Page
Sort Options
Item Competitive role of structural properties of titania–silica mixed oxides and a mechanistic study of the photocatalytic degradation of phenol(environmental, 2014) Rasalingam, Shivatharsiny; Kibombo, Harrison S.; Peng, Rui; Koodali, Ranjit T.TiO2–SiO2 mixed oxide materials were hydrothermally synthesized and the photocatalytic degradation of phenol under UV-irradiation was evaluated. We also demonstrated that varying the co-solvent, modulates the structural properties of the materials. In particular, the use of non-polar co-solvents such as toluene seemed to increase the crystallinity, surface area, and pore diameter while the crystallite size of titania seemed to change little. A comprehensive characterization using surface and bulk techniques evidenced the role of porosities, crystallinity, and Ti–O–Si linkages of the mixed oxides as significant factors that contribute to the degradation of phenol. The TiO2–SiO2 mixed oxide material prepared using only ethanol as the solvent showed 24% degradation of phenol after 120 min of irradiation whereas other mixed oxide materials degraded phenol more efficiently (57% to 100%) in the same duration of time. The higher photocatalytic activities of the mixed oxide materials prepared using non-polar solvents is attributed to a combination of factors that include higher Apparent Surface Coverages of Ti–O–Si heterolinkages, larger pore sizes, and most importantly higher crystallinities of the titania phase. Larger pore sizes enabled better transport of reactant molecules and products to and from the active sites (Ti–O–Si heterolinkages) and the higher crystallinities of the titania phase helped in minimizing the electron–hole recombination in these photocatalysts, and thus resulted in high degradation efficiencies.Item Cosolvent-Induced Gelation and the Hydrothermal Enhancement of the Crystallinity of Titania-Silica Mixed Oxides for the Photocatalytic Remediation of Organic Pollutants(The Journal of Physical Chemistry, 2011) Kibombo, Harrison S.; Zhao, Dan; Gonshorowski, Andra; Koppang, Miles D.; Koodali, Ranjit T.The photocatalytic activity of hydrothermally synthesized TiO2−SiO2 mixed oxides was examined in this study. Powder X-ray diffractometry, nitrogen adsorption, diffuse reflectance spectrometry, Raman, and UV−vis spectrometry demonstrated that the pore geometries and the nature of the crystal phase can be tailored by cosolvent-induced gelation (CIG) in the synthesis of mixed oxide materials. This body of work attempts to support the role of crystallinity enhanced by the hydrothermal synthesis (HTS) in establishing active sites pertinent to the advanced oxidation process (AOP) in TiO2−SiO2 mixed oxide materials.Item Effectively dispersed Europium Oxide dopants in TiO2 Aerogel supports for enhanced Photocatalytic Pollutant Degradation(Journal of Photochemistry and Photobiology A: Chemistry, 2013) Kibombo, Harrison S.; Weber, Amanda S.; Wu, Chia-Ming; Koodali, Ranjit T.The influence of supercritical drying and the europium oxide content on the physicochemical properties and the resultant photocatalytic activity of Eu-TiO2 aerogels for the degradation of salicylic acid were explored for the first time. It was demonstrated that the efficiencies might be influenced by a combination of factors such as enhanced adsorption, presence of trap states, and/or suppression of rutile phase formation. The well dispersed europium oxide dopants may act as trap states. A subsequent enhancement of charge separation avails electrons for oxygen attack to form superoxide ions, from which OH radicals can be generated, and are postulated to be primary contributors toward the degradation efficiencies in this study.Item Enhanced photocatalytic water splitting activity of carbon-modified TiO2 composite materials synthesized by a green synthetic approach(International Journal of Hydrogen Energy, 2012) Parayil, Sreenivasan Koliyat; Kibombo, Harrison S.; Wu, Chia-Ming; Peng, Rui; Koodali, Ranjit T.We report a green and facile approach for the preparation of carbon-modified (C-modified) TiO2 composite materials by hydrothermal synthesis followed by pyrolytic treatment. The resultant materials were characterized by powder X-ray diffraction (XRD), nitrogen physisorption studies, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM). The photocatalytic performances of these materials were evaluated by calculating the amount of hydrogen evolved from the decomposition of water under solar simulated irradiation conditions. An improvement was achieved from no H2 evolution at all with the bare TiO2, to an evolution of 0.21mLg−1h−1 from a composite material modified with an optimum carbon loading of 3.62%. These results suggested that the interaction of carbon with predominantly rutile form of TiO2 can promote shallow trapping of photogenerated electrons in the oxygen vacancies. This phenomenon consequently enhances the photocatalytic activity by minimizing charge carrier recombination, a characteristic demonstrated by fluorescence quenching of the TiO2 emission.Item Exploration of Room Temperature Synthesis of Palladium containing cubic MCM-48 Mesoporous Material(Microporous and mesoporous materials, 2014) Kibombo, Harrison S.; Balasanthiran, Vagulejan; Peng, Rui; Koodali, Ranjit T.Pd-MCM-48 mesoporous materials were synthesized by a modified Stöber synthesis method in 4h at room temperature. Pd nanoparticles were prepared by using Na2[PdCl4] and Pd(acac)2 as Pd precursors, and their influence in the preparation of the cubic MCM-48 mesoporous phase was investigated. In addition, Pd(0) nanoparticles was prepared separately and added to the synthesis gel. The influence of varying the Pd precursor, solvent media, the time of addition of Pd precursor, and the concentration of NaBH4 reducing agent used for preparation of Pd(0) and its effect for the formation of the cubic phase were investigated. These resultant materials were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–Visible spectroscopy, nitrogen physisorption, and CO-Pulse titration. Reusability studies assessing a material prepared using Pd(0)-DMAP encapsulated nanoparticles that were reduced with 0.1N NaBH4 i.e. 3%Pd-MCM-48-D-N01 indicate that the yields for the hydrogenation of trans-cinnamic acid are greater than 95% even after 8 catalytic cycles, and at which the cubic phase was maintained under our experimental conditions.Item Facile template free method for textural property modulation that enhances adsorption and photocatalytic activity of aperiodic titania supported silica materials(Applied Catalysis B: Environmental, 2013) Kibombo, Harrison S.; Rasalingam, Shivatharsiny; Koodali, Ranjit T.A series of aperiodic titania–silica photocatalysts were prepared in ethanolic solutions of co-solvents such as ethyl acetate (EtOAc), acetonitrile (ACN), acetone (ACT), and N,N′-dimethylformamide (DMF) using a combination of sol–gel chemistry and mild hydrothermal conditions. Extensive structural characterization emerged critical in demonstrating that the incorporation of such polar aprotic solvents is a viable approach for the enhancement and modulation of textural properties such as surface areas and pore sizes without the use of expensive templates. These studies revealed that the dark adsorption capacities of Rhodamine B (RhB) dye were dependent on the pore volume, and had minimal role on the photocatalytic degradation of the dye molecules. However, photocatalysts with large pore diameters exhibited improved initial degradation rates, suggesting that the sizes of the pores through which organics can diffuse in and out of the mesostructure are vital for their effective photocatalytic degradation under visible light irradiation. This work provides an insight into the use of facile preparation methods for the design of photocatalysts of desired porosities that are optimal for application in areas such as persistent organic pollutant remediation in waste water management.Item Heterogeneous Photocatalytic Remediation of Phenol by Platinized Titania-Silica Mixed Oxides under Solar-Simulated Conditions(The Journal of Physical Chemistry, 2011) Kibombo, Harrison S.; Koodali, Ranjit T.Aperiodic mesoporous TiO2–SiO2 mixed oxide materials were platinized by the incorporation of Pt0 by three different methods to understand the role of Pt on the photocatalytic activity of phenol under solar simulated conditions. The physicochemical properties of the resultant photocatalysts were examined by powder X-ray diffractometry, nitrogen adsorption, diffuse reflectance spectroscopy, and transmission electron microscopy. These characterization techniques illustrated the enhanced morphological properties of the mesostructure such as the presence of highly crystalline anatase TiO2, large pore geometries, and active Ti–O–Si linkages, respectively. CO chemisorption analysis and TEM images accentuated the role of small Pt crystallite sizes in the development of photocatalysts with high degradation efficiencies.Item Influence of Ti–O–Si hetero-linkages in the photocatalytic degradation of Rhodamine B(Catalysis communications, 2013) Rasalingam, Shivatharsiny; Kibombo, Harrison S.; Wu, Chia-Ming; Baltrusaitis, Jonas; Koodali, Ranjit T.The influence of Ti–O–Si hetero-linkages in the degradation of Rhodamine B (RhB) dye over TiO2–SiO2 xerogels is exemplified by XPS analysis. We demonstrate a relationship between the percentage surface content of Ti–O–Si and the rate of photocatalytic degradation of RhB. Our detailed surface investigation revealed that the overall degradation of RhB is enhanced due to the high surface percentage content of Ti–O–Si species, high crystallinity of titania phase, and its effective dispersion on a high surface area porous silica support.Item Investigation of the role of platinum oxide for the degradation of phenol under simulated solar irradiation(pplied catalysis B: environmental, 2013) Kibombo, Harrison S.; Wu, Chia-Ming; Peng, Rui; Baltrusaitis, Jonas; Koodali, Ranjit T.We demonstrate that a desired oxidation state can be achieved by synthetic colloidal methods and the choice of characterization technique is crucial for determining the physicochemical properties that influence the photocatalytic activities. XPS studies showed that PtO2 was realized in this study, and the resultant crystalline PtO2–TiO2 prepared by subsequent hydrothermal treatment demonstrated activity for phenol degradation under simulated solar light irradiation. Preformed platinum based TiO2 ensures control over the oxidation state and the crystallite size of titania. The role of Ptox in the form of stable Pt4+ is elucidated as a mild recombination center, whereas the crystallite size of Pt in surfactant free Pt0–TiO2 appears to be the overriding factor for attaining enhanced photocatalytic performance.Item Naphthalene derivatized TiO2–carbon hybrid materials for efficient photocatalytic splitting of water(Catalysis today, 2013) Parayil, Sreenivasan Koliyat; Kibombo, Harrison S.; Koodali, Ranjit T.We report a facile approach for the synthesis of TiO2–Carbon (C) hybrid formed by a ligand-to-metal charge transfer (LMCT) complexation between a small organic molecule precursor, 2,3-dihydroxynaphthalene (DN) and TiO2 nanomaterial. The resultant photocatalysts were characterized by powder X-ray diffraction (XRD), surface area and porosity analysis, Raman spectroscopy, diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and by X-ray photoelectron spectroscopy (XPS). Carbonization by N2 pyrolysis at 800°C altered the physical properties of the TiO2 as evidenced by the increase in the surface area of TiO2 from 6.5m2g−1 to 12.5m2g−1 and fluorescence quenching of TiO2 emission. The photocatalytic performances of these TiO2–C hybrid materials were evaluated by calculating the amount of hydrogen evolved from the decomposition of water under solar simulated illumination. A marked improvement was observed from ∼0 to 2.6 μmol/gTiO2/h evolved from the bare TiO2-0 and TiO2–C-240 composites, respectively. These results suggested that anchoring of C onto the TiO2 surface can harness effective transfer of electrons through the TiO2–C hetero junction, and promote the photocatalytic performance of TiO2.Item Synthesis of mixed phase anatase-TiO2(B) by a simple wet chemical method(Materials Letters, 2013) Parayil, Sreenivasan Koliyat; Kibombo, Harrison S.; Wu, Chia-Ming; Koodali, Ranjit T.A photoactive mixed phase, anatase-TiO2(B) was synthesized from a mixture of trititanate nanotube and urea at relatively mild conditions. This material exhibited enhanced photocatalytic hydrogen generation under simulated solar irradiation. The enhancement was credited to the presence of mixed phases of anatase and TiO2(B) that minimized charge-carrier recombination. The results validate the superior performance of anatase-TiO2(B) compared to anatase or TiO2(B) alone. Such mixed phase materials may also be applicable for solar assisted degradation of persistent organic pollutants and solar energy conversion devices.Item Synthesis-Dependent Oxidation State of Platinum on TiO2 and Their Influences on the Solar Simulated Photocatalytic Hydrogen Production from Water(The Journal of Physical Chemistry, 2013) Parayil, Sreenivasan Koliyat; Kibombo, Harrison S.; Baltrusaitis, Jonas; Koodali, Ranjit T.Platinized TiO2 photocatalysts of different compositions of Pt0 and PtO2 were prepared by modifying the synthesis procedures. The physicochemical properties of the composite materials were characterized by X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. Energy dispersive X-ray spectroscopy measurements confirmed the presence of Pt species existing as PtO2 and/or mixtures of Pt0 and PtO2. The composite material, Pt–TiO2–2%H, contained a high amount of metallic Pt0 and PtO2 in close proximity with TiO2 that promoted an enhanced photocatalytic hydrogen evolution activity under simulated solar light irradiation. Although Pt–TiO2–2%C and Pt–TiO2–2%T consisted of similar compositions of PtO2, these oxidized platinum species seem to appear further apart from TiO2 in Pt–TiO2–2%C than Pt–TiO2–2%T. This caused dramatic variation in their optical behaviors such as strong fluorescence quenching and lower photocatalytic hydrogen evolution activity in the former photocatalyst. A photocatalyst prepared by the conventional photodeposition method was also prepared, characterized, and its photocatalytic activity assessed. This work provides an opportunity to understand the role of PtO2 for photocatalytic production of hydrogen from platinized TiO2 composites and the importance of heterojunctions in such photocatalysts for solar energy conversion.Item Versatility of heterogeneous photocatalysis: synthetic methodologies epitomizing the role of silica support in TiO2 based mixed oxides(Catalysis Science & Technology, 2012) Kibombo, Harrison S.; Peng, Rui; Rasalingam, Shivatharsiny; Koodali, Ranjit T.Heterogeneous photocatalysis continues to be an active area of research with focus on developing catalytic systems that can degrade toxic pollutants in the gas and aqueous phase, and split water to generate hydrogen and oxygen. In this review, the incorporation of silica phases in titanium dioxide based photocatalysts is reviewed.