Query: The effect of gold loading and particle size on photocatalytic hydrogen production from ethanol over Au/TiO 2 nanoparticles

Candidate papers:

abstract: Catalytic hydrogen production from renewables is a promising method for providing energy carriers in the near future. Photocatalysts capable of promoting this reaction are often composed of noble metal nanoparticles deposited on a semiconductor. The most promising semiconductor at present is TiO2. The successful design of these catalysts relies on a thorough understanding of the role of the noble metal particle size and the TiO2 polymorph. Here we demonstrate that Au particles in the size range 3 30 nm on TiO2 are very active in hydrogen production from ethanol. It was found that Au particles of similar size on anatase nanoparticles delivered a rate two orders of magnitude higher than that recorded for Au on rutile nanoparticles. Surprisingly, it was also found that Au particle size does not affect the photoreaction rate over the 3 12 nm range. The high hydrogen yield observed makes these catalysts promising materials for solar conversion.
author_names: Morag Murdoch

Geoffrey I N Waterhouse

Muhammad Amtiaz Nadeem

James B Metson

Mark A Keane

Russell F Howe

Jordi Llorca

Hicham Idriss
title: The effect of gold loading and particle size on photocatalytic hydrogen production from ethanol over Au/TiO2 nanoparticles.
venue: Nature chemistry
year: 2011

abstract: Metal/semiconductor interactions affect electron transfer rates and this is central to photocatalytic hydrogen ion reduction. While this interaction has been studied in great detail on metal oxide semiconductors, not much is known of Au particles on top of polymeric semiconductors. The effects of gold nanoparticle size and dispersion on top of g C3N4 were studied by core and valence level spectroscopy and transmission electron microscopy in addition to catalytic tests. The as prepared, non calcined catalysts displayed Au particles with uniform dimension (mean particle size 1.8 nm) and multiple electronic states: XPS Au 4f7/2 lines at 84.9 and 87.1 eV (each with a spin orbit splitting of 3.6 3.7 eV) These particles, which did not show localized surface plasmon resonance (LSPR) before the reaction, doubled in size after the reaction giving a pronounced LSPR at about 550 nm. The effect of the heating environment on these particles (in air or in H2) was further investigated. While heating in H2 gave Au nanoparticles of different shapes, heating under O2 gave exclusively spherical particles. Similar activity towards photocatalytic hydrogen ion reduction under UV excitation was seen in both cases, however. XPS Au 4f analyses indicated that an increase in deposition time, during catalyst preparation, resulted in an increase in the initial fraction of oxidized gold particles, which were easily reduced under hydrogen. The valence band region for Au/gC3N4 was further studied in an effort to compare it to what is already known for Au/metal oxide semiconductors. A shift of over 2 eV for the Au 5d doublets was noticed between reduced and oxidized gold particles with mean particle sizes between 2 and 6 nm, which is consistent with the final state effect. A narrow range of gold loading for optimal catalytic performance was seen, where it seems that a density of one Au particle per 10 x 10 nm2 is the most suitable. Particle size and shape had a minor effect on performance, which may indicate the absence of a plasmonic effect on the reaction rate.
author_names: Marine Caux

Herve Menard

Y M AlSalik

John T S Irvine

Hicham Idriss
title: Photo catalytic hydrogen production over Au/g C3N4: effect of gold particle dispersion and morphology.
venue: Physical chemistry chemical physics PCCP
year: 2019

abstract: Small plasmonic Au nanoparticles (NPs) decorated with TiO2 nanosheets were fabricated to improve the photocatalytic performance. The Au/TiO2 nanosheets with Au NPs of different sizes ranging from ~3 nm to 28 nm were prepared by using hydrothermally obtained TiO2 nanosheets as substrate via urea and light reduction method. During synthesis, the obtained Au NPs through urea reduction treatment in different calcination temperatures possessed smaller size ~3 13 nm) than those of the light reduction method ~28 nm) The introduced Au NPs were tightly loaded on the surface of TiO2 nanosheets through in situ growth reduction process of chloroauric acid. The emergence of smaller Au NPs promoted the photocatalytic performance over Au/TiO2 nanosheets. The as prepared Au/TiO2 nanosheets with small Au NP sizes of ~3 5 nm showed the highest photocatalytic rate of hydrogen production ~230 umol*h 1) under xenon lamp illumination, exceeding more than twice that of Au/TiO2 nanosheets with loading of larger Au NPs ~28 nm) The favorable constituents and combination of Au/TiO2 nanosheets provided large surface adsorptive sites for reactant adsorption, introduced plasmonic effects and formed Schottky barrier junction via surface plasmon resonance. The Schottky barrier height was lower due to the presence of smaller Au NPs, thereby enhancing the charge separation through the Schottky transfer hub to neighboring TiO2 nanosheets. The synergistic effect between the plasmonic hot carrier driven Au NPs and TiO2 nanosheets was discussed. The photocatalytic mechanism was also proposed for the fabrication of visible light restricted photocatalysts with smaller Au NPs.
author_names: Lei Cheng

Dainan Zhang

Yulong Liao

Fei Li

Huaiwu Zhang

Quanjun Xiang
title: Constructing functionalized plasmonic gold/titanium dioxide nanosheets with small gold nanoparticles for efficient photocatalytic hydrogen evolution.
venue: Journal of colloid and interface science
year: 2019

abstract: Abstract Au nanoparticles of size ranging 2 6 nm were deposited over hexagonal CdS using three conventional metal deposition methods namely; deposition precipitation (DP) incipient wet impregnation (WI) photo deposition (PD) and a recently reported KI method by our group [1] The later involves reduction of Au3+ ions with iodide ions. XRD results confirmed the formation of CdS hexagonal phase from as prepared cubic phase at 600 degC under the N2 atmosphere. Transmission electron spectroscopy (TEM) diffused reflectance spectroscopy (DRS) X Ray fluorescence (XRF) ICP OES and photoreactions were conducted to study the effect of Au particle size, Au loading and Au plasmonic properties on H2 production activity. It was found that surface plasmon resonance (SPR) is directly linked to Au particle size. Among all four methods, 3 wt. Au deposited over hexagonal CdS by KI method with mean Au particle size of 4 nm showed highest performance for hydrogen production from water electrolyte mixture under visible light irradiation >420 nm and a flux of 35 mW/cm2) XPS results of Au/CdS prepared by KI method showed that Au is exclusively present in zero oxidation state before and after photocatalytic H2 production testes indicating the stable nature of Au/CdS catalyst. The H2 production activity of Au/CdS catalysts prepared by different metal deposition methods and H2 production mechanism in a water electrolyte is discussed in detail.
author_names: Imran Majeed

Muhammad Amtiaz Nadeem

Ejaz Hussain

Amin Badshah

Rubina Gilani

Muhammad Arif Nadeem
title: Effect of deposition method on metal loading and photocatalytic activity of Au/CdS for hydrogen production in water electrolyte mixture
year: 2017

abstract: Abstract This paper systematically compares the activity of Au/TiO 2 photocatalysts (Au loadings 0 10 wt. for H 2 production from ethanol water mixtures under UV excitation. Degussa P25 TiO 2 was used as the support phase. TEM analyses revealed that the average Au nanoparticle size at all loadings was 5 2 nm, with the Au nanoparticles preferentially located at the interfacial sites between TiO 2 crystallites. XRD, XRF, XPS, and UV Vis measurements established that metallic Au was the only gold species on the surface of the photocatalysts. The Au/TiO 2 photocatalysts showed an intense absorption maximum centred around 560 570 nm due to the localised surface plasmon resonance (LSPR) of the supported gold nanoparticles. Photoluminescence measurements revealed that gold nanoparticles effectively suppress electron hole pair recombination in TiO 2 even at low Au loadings. All of the Au/TiO 2 photocatalysts displayed high activity for H 2 production from ethanol water mixtures under UV irradiation, with the highest activities observed in the Au loading range 0.5 2 wt. (H 2 production rate 31 34 mmol g 1 h 1 In order to deconvolute the role of the P25 TiO 2 support in promoting H 2 production, anatase and rutile nanoparticles were isolated from P25 TiO 2 by selective chemical dissolution and then functionalised with gold nanoparticles (3 wt. loading, size 5 2 nm) The H 2 production activity of the resulting Au/anatase and Au/rutile photocatalysts was 22 and 10 mmol g 1 h 1 respectively, and substantially lower than the corresponding Au/P25 TiO 2 photocatalyst (32 mmol g 1 h 1 The data provide strong evidence that synergistic electron transfer between the TiO 2 polymorphs and supported Au nanoparticles is responsible for the high rates of H 2 production observed in the Au/P25 TiO 2 system. The interface between anatase and rutile crystallites, where gold nanoparticles preferentially deposit, is identified as a photocatalytic 'hot spot' for H 2 production. High Au loadings reduce the efficiency of such 'hot spots'
author_names: Vedran Jovic

Wan-Ting Chen

Dongxiao Sun-Waterhouse

Mark G Blackford

Hicham Idriss

Geoffrey I N Waterhouse
title: Effect of gold loading and TiO2 support composition on the activity of Au/TiO2 photocatalysts for H2 production from ethanol water mixtures
year: 2013

abstract: Abstract Au and/or Ni nanoparticles were synthesized by radiolysis on TiO 2 (commercial P25) at various composition (metal content) The modified photocatalysts were characterized by High Resolution Transmission Microscopy (HRTEM) Energy Dispersive X ray Spectroscopy (EDS) UV vis Diffuse Reflectance Spectroscopy (DRS) and X ray Photoelectron Spectroscopy (XPS) The charge carrier mobility was studied by Time Resolved Microwave Conductivity (TRMC) The photocatalytic activities were tested under UV vis irradiation using polychromatic and monochromatic light (action spectrum analysis of apparent quantum efficiency) Surface modified TiO 2 with Au and Ni nanoparticles showed high photocatalytic activity for hydrogen evolution from aqueous methanol solution. The enhanced hydrogen evolution rate was obtained for TiO 2 co modified with Au and Ni, where synergetic effect of the two metals was revealed. A very small amount of gold associated to nickel (atomic ratio Ni:Au 5:1 with a total optimized metal loading of 0.5 at% can induce a significant increase in H 2 formation.
author_names: Ana Laura Luna

Ekaterina Novoseltceva

Essyllt Louarn

Patricia Beaunier

Ewa Kowalska

Bunsho Ohtani

Miguel A Valenzuela

Hynd Remita

Christophe Colbeau-Justin
title: Synergetic effect of Ni and Au nanoparticles synthesized on titania particles for efficient photocatalytic hydrogen production
year: 2016

abstract: Abstract Photo catalytic hydrogen production has been studied on Au supported CdS catalysts under visible light irradiation in order to understand the effect of Au particle size as well as the reaction medium properties. Au nanoparticles of size about 2 5 nm were deposited over hexagonal CdS particles using a new simple method involving reduction of Au 3+ ions with iodide ions. Within the investigated range of Au (between 1 and 5 wt. fresh particles with mean size of 4 nm and XPS Au4f/Cd3d surface ratio of 0.07 showed the highest performance (ca. 1 molecule of H 2 /Au atom s 1 under visible light irradiation >420 nm and a flux of 35 mW/cm 2 The highest hydrogen production rate was obtained from water (92% ethanol (8% in an electrolyte medium (Na 2 S Na 2 SO 3 TEM studies of fresh and used catalysts showed that Au particle size increases (almost 5 fold) with increasing photo irradiation time due to photo agglomeration effect yet no sign of deactivation was observed. A mechanism for hydrogen production from ethanol water electrolyte mixture is presented and discussed.
author_names: Imran Majeed

Muhammad Amtiaz Nadeem

Maher Al-oufi

Muhammad Arif Nadeem

Geoffrey I N Waterhouse

Amin Badshah

James B Metson

Hicham Idriss
title: On the role of metal particle size and surface coverage for photo catalytic hydrogen production: A case study of the Au/CdS system
year: 2016

abstract: Solar hydrogen production from renewables such as ethanol and water is potentially a key means of fuel generation either for direct combustion or to power fuel cells. To achieve this few methods are possible among them are those involving photocatalytic processes on semiconductor materials due to the simplicity of the concept and its technical feasibility. However, no materials have been found, to date, that can be used for this process. Among the most promising photo catalysts are those composed of TiO2 based material in presence of a transition metal such as Au or Pd because of the simplicity of their structure and the present industrial knowledge. Gold catalysts with finite nanoparticle size have been found to be very active for specific reactions in dark conditions such as CO oxidation Yet, their potential as active materials for photoreactions has only received sporadic attention and considerable work is needed because the size of Au, the size of the TiO2 particulate support and the nature of TiO2 can each, in turn, influence the photo reaction rate. The rate of H2 production from water is so far very small to be used as a model system for materials study. Alcohol are known however to act as hole scavengers and when used in the appropriate environment (i.e. in presence of only traces of O2 as in the liquid phase) can be used in a systematic way to test for materials properties and help the design of the better photo catalysts. We have opted for ethanol as an alternative feedstock to methanol for two main reasons. Firstly, ethanol is produced from renewable sources and secondly it is a realistic prototype for larger molecules as it has a carbon carbon bond and thus serves as a prototype for larger organic compounds. In this work we are focusing on the effect of TiO2 polymorphs and size while keeping the Au particle size constant in order to extract information on the reaction rate. In addition we compare the effect of the polymorph of TiO2: Anatase and rutile separately and together.
author_names: Muhammad Amtiaz Nadeem

Geoff Waterhouse

Jordi Llorca Pique

J M R Muir

Hicham Idriss
title: Ethanol photoreaction to Hydrogen over Au/TiO(2) catalysts: Effect of Au particle size and TiO(2) bulk structure
year: 2011

abstract: The catalytic activity of Pd core porous SiO2 shell catalysts (Pd@SiO2) with different Pd particle size was evaluated for the direct synthesis of hydrogen peroxide from hydrogen and oxygen. In the synthesis of palladium nanoparticles, the Pd particle size increased with the decrease of the ratio of polyvinylpyrrolidone (PVP) to Pd. Among the prepared Pd@SiO2 catalysts, Pd@SiO2_PVP2 (Pd loading 1.02 wt% PVP to Pd precursor molar ratio 2) had the largest Pd particle size (4.2 nm) and showed the highest hydrogen peroxide production rate (330 mmol H2O2/gPd*h) The production rate of hydrogen peroxide decreased along with the decrease in Pd particle size. As the Pd nanoparticles became smaller, energetic sites (defects, edges, and corners) where the O O bond is dissociated and the formation of water is promoted were more exposed on the surface. Thus, fewer energetic sites on the Pd surface are favored for synthesizing hydrogen peroxide, which was the major reason for Pd@SiO2_PVP2 being the most active among the prepared Pd@SiO2 catalysts.Graphical Abstract
author_names: Seongmin Kim

Dae Won Lee

Kwan Young Lee

EunAe Cho
title: Effect of Pd Particle Size on the Direct Synthesis of Hydrogen Peroxide from Hydrogen and Oxygen over Pd Core Porous SiO2 Shell Catalysts
venue: Catalysis Letters
year: 2014

abstract: Abstract Low cost semiconductor photocatalysts that can efficiently harvest solar energy and generate H 2 from water or biofuels will be critical to future hydrogen economies. Here, we evaluate the performance of low cost Ni/TiO 2 photocatalysts (Ni loadings 0 4 wt. for H 2 production from ethanol water mixtures (0 100 vol. EtOH) under UV excitation. Ni(II) was deposited on P25 TiO 2 by the complex precipitation method, followed by H 2 reduction at 500 degC for 2 h to obtain Ni/TiO 2 photocatalysts. TGA, TEM, XRD, Ni 2p XPS, Ni L edge NEXAFS, Ni K edge EXAFS, UV Vis and photoluminescence measurements confirmed that Ni 0 was the dominant nickel species on the surface of the Ni/TiO 2 photocatalysts, with the Ni particle size ~1 2 nm. The photocatalytic activity of Ni/TiO 2 photocatalysts was highly dependent on the Ni loading, with the optimal Ni loading being 0.5 wt. which afforded a H 2 production rate of 11.6 mmol g 1 h 1 (or 0.258 mmol m 2 h 1 at an EtOH:H 2 O volume ratio of 10:90 and a UV flux comparable to that in sunlight. High H 2 production rates were achieved over a wide range of EtOH:H 2 O concentrations, with a 95:5 volume ratio affording the highest rate (24.3 mmol g 1 h 1 The 0.5 wt. Ni/TiO 2 photocatalyst displayed superior photocatalytic activity to a 2 wt. Au/TiO 2 reference photocatalyst at low ethanol concentrations (1 15 vol. which is attributed to the high co catalyst dispersion achieved in the Ni/TiO 2 system. Results suggest that Ni/TiO 2 photocatalysts are promising alternatives to M/TiO 2 (M Pd, Pt or Au) photocatalysts for solar H 2 production from biofuels.
author_names: Wan-Ting Chen

Andrew Chan

Dongxiao Sun-Waterhouse

Toshihiro Moriga

Hicham Idriss

Geoffrey I N Waterhouse
title: Ni/TiO2: A promising low cost photocatalytic system for solar H2 production from ethanol water mixtures
year: 2015