Zakiya Al-Azri - Academia.edu (original) (raw)

Papers by Zakiya Al-Azri

Research paper thumbnail of Noble Metal Modified TiO2 Photocatalysts for Solar Hydrogen Production: Roles of Metal Co-catalysts and Reaction Media

M/TiO2 (M = Pd, Pt or Au) photocatalysts demonstrate excellent activity for hydrogen (H2) product... more M/TiO2 (M = Pd, Pt or Au) photocatalysts demonstrate excellent activity for hydrogen (H2) production in alcohol-water mixtures under UV excitation. Their activity depends on two main factors: i) the metal co-catalyst (M) and ii) the reaction medium (alcohol sacrificial reagent). This thesis systematically evaluates the effect of metal co-catalyst type, co-catalyst metal loading, co-catalyst particle size and dispersion and also the effect of the sacrificial agent (alcohol type and concentration) on the activity of M/TiO2 photocatalysts for H2 production in alcohol-water mixtures under UV irradiation. A series of M/TiO2 photocatalysts with metal loading 0-4 wt.% were prepared by the deposition-precipitation with urea method, followed by calcination at 350 o C and/or H2 reduction at 500 o C using the commercial semiconductor photocatalyst, Degussa P25 TiO2 (85 wt.% anatase + 15 wt.% rutile) as the support. TEM analyses showed that the Pd and Pt co-catalysts were highly dispersed over the TiO2 support evidencing a strong metal-support interaction (MSI), with an average particle size of ~2 and 1.5 nm, respectively. For Au/TiO2, the MSI was weaker and the average metal nanoparticle size was larger (~5 nm) and the nanoparticles more spherical in shape. XPS, EXAFS and UV-Vis analyses confirmed the presence of predominantly zero valent metal nanoparticles on the surface of the photocatalysts. Photoluminescence data established that the metal co-catalysts effectively suppressed electron-hole pair (e-h +) recombination in TiO2 following UV photoexcitation. The noble metal co-catalysts also function as active centres for H2 evolution during alcohol photoreforming. In order to understand the effect of metal co-catalysts on hydrogen production, a series of metals were deposited on P25 TiO2. The amount of Pd, Pt and Au was varied, analyzed and tested in ethanol-water mixtures (80:20 volume ratio) under UV-fluxes comparable to that of sunlight (365 nm, 5-6 mW cm-2). The selection of P25 TiO2 as the support allowed meaningful comparison with the work of other groups. It was observed that optimal H2 production rates were achieved at metal loadings of 0.25-1 wt.% for Pd/TiO2 (40-45 mmol g-1 h-1); 0.5 wt.% for Pt/TiO2 catalysts (43 mmol g-1 h-1); and 1-2 wt.% for Au/TiO2 catalysts (32 mmol g-1 h-1). Higher metal loadings did not enhance the H2 rate confirming the existence of an optimal loading. At all metal loadings, the H2 production rates (in mmol g-1 h-1) for the M/TiO2 (M = Pd, Pt, Au) photocatalysts under UV excitation decreased in the order Pd/TiO2 > Pt/TiO2 > Au/TiO2 >> TiO2. Intrinsic properties of each metal such as dispersion, work function and the I dedicate this thesis to:

Research paper thumbnail of Metal particle size effects on the photocatalytic hydrogen ion reduction

Research paper thumbnail of Photocatalytic H2 Production from Ethanol–Water Mixtures Over Pt/TiO2 and Au/TiO2 Photocatalysts: A Comparative Study

Topics in Catalysis, 2013

Pt/TiO 2 (Pt loadings 0-4 wt%) and Au/TiO 2 (Au loadings 0-4 wt%) photocatalysts were synthesized... more Pt/TiO 2 (Pt loadings 0-4 wt%) and Au/TiO 2 (Au loadings 0-4 wt%) photocatalysts were synthesized, characterized and tested for H 2 production from ethanol-water mixtures (80 vol% ethanol, 20 vol% H 2 O) under UV excitation. Average metal nanoparticle sizes determined by TEM were 1-3 nm for Pt in the Pt/TiO 2 photocatalysts and 5-7 nm for Au in the Au/TiO 2 photocatalysts. Au/TiO 2 showed an intense localized surface plasmon resonance feature at *570 nm, typical for metallic Au nanoparticles of diameter *5 nm supported on TiO 2 . X-ray photoelectron spectroscopy and X-ray diffraction analyses established that Pt and Au were present in metallic form on the TiO 2 support. X-ray fluorescence revealed close accord between nominal and actual Pt and Au loadings. The Au/TiO 2 and Pt/TiO 2 photocatalysts both displayed very high activities for H 2 production under UV irradiation, with the Au/TiO 2 samples affording slightly superior rates of H 2 production at most metal loadings. The 2 wt% Au/TiO 2 and 1 wt% Pt/TiO 2 photocatalysts showed the highest H 2 production rates (32-34 mmol g -1 h -1 ). Photoluminescence studies confirmed that Pt and Au nanoparticles positively enhance the photocatalytic properties of P25 TiO 2 for H 2 production by acting as electron acceptors and thereby suppressing electron-hole pair recombination in TiO 2 .

Research paper thumbnail of Noble Metal Modified TiO2 Photocatalysts for Solar Hydrogen Production: Roles of Metal Co-catalysts and Reaction Media

M/TiO2 (M = Pd, Pt or Au) photocatalysts demonstrate excellent activity for hydrogen (H2) product... more M/TiO2 (M = Pd, Pt or Au) photocatalysts demonstrate excellent activity for hydrogen (H2) production in alcohol-water mixtures under UV excitation. Their activity depends on two main factors: i) the metal co-catalyst (M) and ii) the reaction medium (alcohol sacrificial reagent). This thesis systematically evaluates the effect of metal co-catalyst type, co-catalyst metal loading, co-catalyst particle size and dispersion and also the effect of the sacrificial agent (alcohol type and concentration) on the activity of M/TiO2 photocatalysts for H2 production in alcohol-water mixtures under UV irradiation. A series of M/TiO2 photocatalysts with metal loading 0-4 wt.% were prepared by the deposition-precipitation with urea method, followed by calcination at 350 o C and/or H2 reduction at 500 o C using the commercial semiconductor photocatalyst, Degussa P25 TiO2 (85 wt.% anatase + 15 wt.% rutile) as the support. TEM analyses showed that the Pd and Pt co-catalysts were highly dispersed over the TiO2 support evidencing a strong metal-support interaction (MSI), with an average particle size of ~2 and 1.5 nm, respectively. For Au/TiO2, the MSI was weaker and the average metal nanoparticle size was larger (~5 nm) and the nanoparticles more spherical in shape. XPS, EXAFS and UV-Vis analyses confirmed the presence of predominantly zero valent metal nanoparticles on the surface of the photocatalysts. Photoluminescence data established that the metal co-catalysts effectively suppressed electron-hole pair (e-h +) recombination in TiO2 following UV photoexcitation. The noble metal co-catalysts also function as active centres for H2 evolution during alcohol photoreforming. In order to understand the effect of metal co-catalysts on hydrogen production, a series of metals were deposited on P25 TiO2. The amount of Pd, Pt and Au was varied, analyzed and tested in ethanol-water mixtures (80:20 volume ratio) under UV-fluxes comparable to that of sunlight (365 nm, 5-6 mW cm-2). The selection of P25 TiO2 as the support allowed meaningful comparison with the work of other groups. It was observed that optimal H2 production rates were achieved at metal loadings of 0.25-1 wt.% for Pd/TiO2 (40-45 mmol g-1 h-1); 0.5 wt.% for Pt/TiO2 catalysts (43 mmol g-1 h-1); and 1-2 wt.% for Au/TiO2 catalysts (32 mmol g-1 h-1). Higher metal loadings did not enhance the H2 rate confirming the existence of an optimal loading. At all metal loadings, the H2 production rates (in mmol g-1 h-1) for the M/TiO2 (M = Pd, Pt, Au) photocatalysts under UV excitation decreased in the order Pd/TiO2 > Pt/TiO2 > Au/TiO2 >> TiO2. Intrinsic properties of each metal such as dispersion, work function and the I dedicate this thesis to:

Research paper thumbnail of Metal particle size effects on the photocatalytic hydrogen ion reduction

Research paper thumbnail of Photocatalytic H2 Production from Ethanol–Water Mixtures Over Pt/TiO2 and Au/TiO2 Photocatalysts: A Comparative Study

Topics in Catalysis, 2013

Pt/TiO 2 (Pt loadings 0-4 wt%) and Au/TiO 2 (Au loadings 0-4 wt%) photocatalysts were synthesized... more Pt/TiO 2 (Pt loadings 0-4 wt%) and Au/TiO 2 (Au loadings 0-4 wt%) photocatalysts were synthesized, characterized and tested for H 2 production from ethanol-water mixtures (80 vol% ethanol, 20 vol% H 2 O) under UV excitation. Average metal nanoparticle sizes determined by TEM were 1-3 nm for Pt in the Pt/TiO 2 photocatalysts and 5-7 nm for Au in the Au/TiO 2 photocatalysts. Au/TiO 2 showed an intense localized surface plasmon resonance feature at *570 nm, typical for metallic Au nanoparticles of diameter *5 nm supported on TiO 2 . X-ray photoelectron spectroscopy and X-ray diffraction analyses established that Pt and Au were present in metallic form on the TiO 2 support. X-ray fluorescence revealed close accord between nominal and actual Pt and Au loadings. The Au/TiO 2 and Pt/TiO 2 photocatalysts both displayed very high activities for H 2 production under UV irradiation, with the Au/TiO 2 samples affording slightly superior rates of H 2 production at most metal loadings. The 2 wt% Au/TiO 2 and 1 wt% Pt/TiO 2 photocatalysts showed the highest H 2 production rates (32-34 mmol g -1 h -1 ). Photoluminescence studies confirmed that Pt and Au nanoparticles positively enhance the photocatalytic properties of P25 TiO 2 for H 2 production by acting as electron acceptors and thereby suppressing electron-hole pair recombination in TiO 2 .