Co-reporter:Lu Yang, Amer Hakki, Fazhou Wang, and Donald E Macphee
ACS Applied Materials & Interfaces May 24, 2017 Volume 9(Issue 20) pp:17034-17034
Publication Date(Web):May 5, 2017
DOI:10.1021/acsami.7b01989
The nitrate selectivity of TiO2 has important consequences for its efficiency as a NOx depollution photocatalyst. Most emphasis is typically given to photocatalyst activity, a measure of the rate at which NOx concentrations are reduced, but a reduction in NOx concentration (mainly NO + NO2) is not necessarily a reduction in atmospheric NO2 concentration because the catalytic process itself generates NO2. With NO2 being considerably more toxic than NO, more emphasis on nitrate selectivity, a measure of the NOx conversion to nitrate, and how to maximize it, should be given in engineering photocatalytic systems for improved urban air quality. This study, on the importance of adsorbed water in the photocatalytic oxidation of NOx, has identified important correlations which differentiate the role that water plays in the oxidation of NO and NO2. This observation is significant and offers insights into controlling nitrate selectivity on TiO2 and the potential for increased effectiveness in environmental photocatalyst applications.Keywords: adsorbed water; nitrate selectivity; NOx; supported TiO2; synthesis conditions;
Co-reporter:D.E. Macphee, A. Folli
Cement and Concrete Research 2016 Volume 85() pp:48-54
Publication Date(Web):July 2016
DOI:10.1016/j.cemconres.2016.03.007
Abstract
Concrete materials are ubiquitous in the developed world due to their versatility and cost-effectiveness as a construction material, but their great potential for increased functionality remains underdeveloped. As supports for photocatalysts, these structures offer viable solutions for the reduction of atmospheric pollutant concentrations, the source of which is often associated with urbanisation and the built infrastructure. This paper addresses (i) the photocatalytic mechanisms applicable to atmospheric depollution, (ii) the influence of doping, and (iii) the application of TiO2-based photocatalysts to concrete. Modifications to TiO2 will be discussed which can improve its activation in visible light and, in the treatment of NOx, improve catalytic selectivity towards nitrate rather than the more toxic NO2. The influence of the chemistry of cements on catalyst performance during both concrete placement and in service will also be addressed and some attention will be given to alternative strategies for introducing the photocatalyst to the concrete.
Co-reporter:Jonathan Z. Bloh, Andrea Folli and Donald E. Macphee
RSC Advances 2014 vol. 4(Issue 86) pp:45726-45734
Publication Date(Web):15 Sep 2014
DOI:10.1039/C4RA07916G
Titanium dioxide photocatalysis offers an excellent way to oxidise NOx to nitrate and thus reduce air pollution. However, unmodified titanium dioxide also releases a significant amount of the toxic intermediate nitrogen dioxide in the process, a problem that is rarely discussed in previous literature. Herein, we highlight this issue by presenting systematic data on the activity and selectivity of a number of commercial titania powders. The photocatalytic performance of a previously developed W/N-codoped titanium dioxide is also reported which, for the first time, offers a way to eliminate this problem as it exhibits an exceptionally high selectivity towards nitrate. The selectivity appears to be solely dependent on the tungsten content, a concentration of 4.8 at.% is sufficient to induce a very high selectivity. Furthermore, the high selectivity could also be replicated by a W/N-codoped sample derived from the industrial sulphate synthetic process. The increased selectivity comes at the expense of absolute activity, which is lower than in the reference titania samples. This raises the question of how to properly evaluate NOx abatement photocatalysts when there are two factors to consider, activity and selectivity. To resolve this, we propose to define a new figure of merit for the evaluation of NOx abatement photocatalysts by distilling total NOx removal and selectivity into one value, the DeNOx index. It is derived by assigning a toxicity value to both NO and NO2 and then expressing the change in total toxicity rather than the concentration change of the individual nitrogen oxides.
Co-reporter:Jonathan Z. Bloh ; Andrea Folli
The Journal of Physical Chemistry C 2014 Volume 118(Issue 36) pp:21281-21292
Publication Date(Web):August 22, 2014
DOI:10.1021/jp507264g
For a systematic study of the material, samples of W/N-codoped titania with different concentrations of the dopants were prepared. The physicochemical properties and in particular their band structure were subsequently evaluated experimentally to elucidate the effect of W-doping, N-doping, and W/N-codoping on the band structure of TiO2. For this purpose, a combined approach of optical spectroscopy and electrochemical impedance spectroscopy was chosen. The doped samples featured both a reduced band gap and a positively shifted conduction band edge. Both conduction band edge and band gap followed a linear dependence on the nitrogen content. They also demonstrate visible light absorption capability, which is associated with interstitial nitrogen doping. Tungsten doping did not influence the band structure of TiO2 directly. It did, however, facilitate nitrogen uptake and stabilize it at higher temperatures. These higher nitrogen doping levels then in turn reduced the band gap and lowered the conduction band edge. Codoping with tungsten therefore offers an excellent way to precisely adjust the nitrogen content and correspondingly the conduction band position of titanium dioxide.
Co-reporter:Andrea Folli, Claus Pade, Tommy Bæk Hansen, Tiziana De Marco, Donald E. Macphee
Cement and Concrete Research 2012 Volume 42(Issue 3) pp:539-548
Publication Date(Web):March 2012
DOI:10.1016/j.cemconres.2011.12.001
The present work offers a general overview about application of titanium dioxide (or titania), TiO2, photocatalysis to concrete technology in relation to enhanced aesthetic durability and depollution properties achieved by implementing TiO2 into cement. Chemistry of degradation of Rhodamine B (RhB), a red dye used to assess self-cleaning performances of concretes containing TiO2, as well as oxidation of nitrogen oxides (NOx), gaseous atmospheric pollutants responsible for acid rains and photochemical smog, is investigated using two commercial titania samples in cement and mortar specimens: a microsized, m-TiO2 (average particle size 153.7 nm ± 48.1 nm) and a nanosized, n-TiO2 (average particle size 18.4 nm ± 5.0 nm). Experimental data on photocatalytic performances measured for the two samples are discussed in relation to photocatalyst properties and influence of the chemical environment of cement on titania particles. Impacts on applications in construction concrete are also discussed.
Co-reporter:Ellis M. Gartner, Donald E. Macphee
Cement and Concrete Research 2011 Volume 41(Issue 7) pp:736-749
Publication Date(Web):July 2011
DOI:10.1016/j.cemconres.2011.03.006
The drive towards sustainability in construction is shaping our attitudes towards alternatives to Portland cement. Although the cement and concrete industry is essentially sustainable with respect to raw materials supply, and concrete manufacture actually gives relatively low CO2 emissions per unit volume compared to most competitive construction materials, the current focus on climate change has led to concerns about cement industry-generated CO2. Thus, there is interest in developing alternative cements with lower associated CO2 emissions. This paper seeks to provide a context for innovative development through a review of what is meant by a hydraulic cementitious binder, identification of key physico-chemical properties of successful binders and how novel systems generally rely on similar factors. Concepts such as reactivity, availability of reactive species and physico-chemical drivers for the formation of cementitious systems are discussed as a basis for introducing and reviewing recent developments in the search for ever more environmentally sustainable cements.
Co-reporter:I. Garcia-Lodeiro, A. Palomo, A. Fernández-Jiménez, D.E. Macphee
Cement and Concrete Research 2011 Volume 41(Issue 9) pp:923-931
Publication Date(Web):September 2011
DOI:10.1016/j.cemconres.2011.05.006
Sodium aluminosilicate hydrate (N-A-S-H) gel, the main reaction product of the alkali-activated aluminosilicates, differs of the aluminium-modified calcium silicate hydrate (C-A-S-H) gel of PC pastes. Increasing the level of SCM to reduce PC content of binders are being considered to address reduction in CO2 emissions, activation of the additional SCM content by alkali activation represents a possible environmentally sustainable solution. Therefore, mixtures of C-A-S-H and N-A-S-H gels might be anticipated and the present study assesses the compatibility relationships between them.Compositional diagrams are provided to indicate phase compositional ranges and the phase assemblages obtained under equilibrium conditions. In calcium-rich formulations (pH in excess of 12), C-A-S-H and C2ASH8 form as stable phases. However, in the lime poor part of the diagram an amorphous gel (N,C)-A-S-H precipitates but its stability is dependent on system pH and available Ca. (N,C)-A-S-H gels are de-stabilised by Ca to give C-A-S-H gels in suitable systems.
Co-reporter:Andrea Folli, Steven B. Campbell, James A. Anderson, Donald E. Macphee
Journal of Photochemistry and Photobiology A: Chemistry 2011 220(2–3) pp: 85-93
Publication Date(Web):
DOI:10.1016/j.jphotochem.2011.03.017
Co-reporter:Donald E. Macphee;Daniel Rosenberg
Journal of Solid State Electrochemistry 2011 Volume 15( Issue 1) pp:99-103
Publication Date(Web):2011 January
DOI:10.1007/s10008-010-1062-4
The use of photocatalysts in the remediation of contaminated water is now well established in the scientific literature, the most common photocatalyst being nano-dimensional particulate titanium dioxide. The generation of charge and charge transfer mechanisms on titanium dioxide are also well described, but this paper addresses the use of tungsten oxide and discusses its potential in water remediation when supported as a photoelectrocatalytic electrode. A photoelectrocatalytic cell is described and its performance in the context of the band structure of tungsten oxide is discussed.
Co-reporter:I. García Lodeiro, A. Fernández-Jimenez, A. Palomo, D.E Macphee
Cement and Concrete Research 2010 Volume 40(Issue 1) pp:27-32
Publication Date(Web):January 2010
DOI:10.1016/j.cemconres.2009.08.004
Reducing Portland cement content in cementitious binders offers a means to address the adverse environmental impacts of Portland cement manufacture. This paper investigates the impacts on hydration product chemistry of partially replacing Portland cement with alkali-activated aluminosilicates. Here, short-term effects of soluble alkali and aluminium, likely to be available in an alkali-activated system, on the structure of synthetic C-S-H gels are assessed. .C-S-H gels (synthesized at pH values of over 13) were mixed with different concentrations of aluminium nitrate and sodium hydroxide. The gels were characterized by FTIR, TEM/EDX and XRD 72 h later. The results showed that both alkali and aluminium increased the degree of silicate polymerisation in the C-S-H gels and precipitated a crystalline calcium aluminosilicate phase.
Co-reporter:Suwimol Asavapisit, Donald E. Macphee
Cement and Concrete Research 2007 Volume 37(Issue 5) pp:776-780
Publication Date(Web):May 2007
DOI:10.1016/j.cemconres.2007.02.003
Abstract
This research investigated the immobilization potential of alkali-activated lime–rice husk ash (RHA) for synthetic Cr(OH)3, Fe(OH)3, Zn(OH)2 and zinc cyanide plating sludge. The binder consists of hydrated lime and RHA at a weight ratio of 45:55. Waterglass (Na2SiO3) with SiO2/Na2O ≈ 3 and anhydrous sodium carbonate (Na2CO3) were used as alkali activator between 0 and 8 wt.% of the binder. Results showed that Zn(OH)2 addition causes a considerable strength development in control and sodium silicate-activated samples but only after 14 days. Similar observations were found for the sample loaded with 10 wt.% plating sludge but this only occurred after 28 days. A possible explanation for these phenomena is that the initial formation of calcium zincate, which has a set retarding effect, inhibits early strength development. At later ages, calcium zincate dissolves and Zn is taken up in the formation of C–S–Z–H solid solutions leading to strength development. These phenomena were not observed from the sodium carbonate-activated lime–RHA matrices. In these, it is believed that zinc/calcium carbonates readily form inhibiting calcium zincate and C–S–Z–H formation. Despite this, carbonate-containing mixes with up to 30 wt.% plating sludge gave a 14-day strength and Cr concentration in TCLP leachate that meet the regulatory limit for landfilling.
Co-reporter:Donald E. Macphee, Stephanie J. Barnett
Cement and Concrete Research 2004 Volume 34(Issue 9) pp:1591-1598
Publication Date(Web):September 2004
DOI:10.1016/j.cemconres.2004.02.022
Abstract
The thaumasite form of sulfate attack (TSA) has received considerable research attention since its discovery in several motorway bridge foundations in the UK in 1998. Its significance as a deterioration mechanism in concrete, leading to the fluidisation of the matrix in extreme cases, is now acknowledged. Despite the continuing uncertainties that exist with regard to mechanisms for thaumasite formation, there is now reasonable agreement on conditions that favour TSA, and, as with all deleterious reactions affecting concrete structures, there is a desire to be able to anticipate the likelihood of occurrence so that such problems can be ‘designed out’ in the formulation stage. Inevitably, this points to the development of suitable models and the generation of reliable data. It is towards this latter goal that this paper is focused. Building on our previous studies, which reported on the means of fixing intermediate compositions in the ettringite–thaumasite solid solution series, this paper describes the treatment of solubility data, which can be utilised in phase development and solubility models involving this system.
Co-reporter:H.W Chandler, D.E Macphee
Cement and Concrete Research 2003 Volume 33(Issue 2) pp:265-270
Publication Date(Web):February 2003
DOI:10.1016/S0008-8846(02)01024-4
Abstract
This paper presents a simple mathematical model of the flow behaviour of fresh cement pastes and mortars based on a soil mechanics approach. A soil mechanics model can mimic many of the features of the pastes rheological behaviour indicating that physical, as well as chemical, factors might control many of these.
Specifically, we have developed a simple mathematical model of the evolution of the packing of the clinker or sand grains and its effect on the flow of the paste or mortar. This not only incorporates the role of the pore water but also copes with the large deformations typical of the mixing and placement of mortars. This model is used here to simulate small cyclic deformations with a large drift accumulating in one direction, and is able to capture both the liquefaction and locking phenomena seen in practice when mortars are vibrated.
Co-reporter:S.J. Barnett, D.E. Macphee, N.J. Crammond
Cement and Concrete Composites 2003 Volume 25(Issue 8) pp:851-855
Publication Date(Web):December 2003
DOI:10.1016/S0958-9465(03)00116-1
Solid solutions between thaumasite and the related phase ettringite were prepared and characterised by X-ray diffraction and infrared spectroscopy. A miscibility gap in the solid solution is identified and defined. Crystallographically, the miscibility gap is identified as a gap in the unit cell dimensions of the solid phases formed between c≅20.95 (10.475) and c≅21.3 Å. A combination of quantitative X-ray powder diffraction and infrared spectroscopy enabled us to define the miscibility gap in terms of Al:Si ratio. Ettringite can accept the replacement of 1/2 its Al by Si, while thaumasite tolerates little or no Al in its structure.
Co-reporter:S.J Barnett, D.E Macphee, E.E Lachowski, N.J Crammond
Cement and Concrete Research 2002 Volume 32(Issue 5) pp:719-730
Publication Date(Web):May 2002
DOI:10.1016/S0008-8846(01)00750-5
Abstract
Solid solutions between thaumasite and ettringite were prepared by methods analogous to those well established for the preparation of thaumasite and ettringite. The extent of immiscibility in this system is investigated by varying the Al:Si and SO42−:CO32− ratios in reactant mixtures. The solids produced were analysed by quantitative X-ray diffraction, with Rietveld refinement also providing accurate unit cell dimensions, energy-dispersive X-ray analysis and infrared spectroscopy. The compositional and unit cell variations in the solid solution are discussed. A wide variety of solid solution compositions were produced with both the thaumasite and ettringite structures, but all preparations were considerably diluted by secondary amorphous products.
