Highly efficient rutile TiO₂photocatalysts with single Cu(ii) and Fe(iii) surface catalytic sites

Abstract

Highly active photocatalysts were obtained by impregnation of nanocrystalline rutile TiO 2 powders with small amounts of Cu(II) and Fe(III) ions, resulting in the enhancement of initial rates of photocatalytic degradation of 4-chlorophenol in water by the factor of 7 and 4, compared to pristine rutile, respectively. Detailed structural analysis by EPR and X-ray absorption spectroscopy (EXAFS) revealed that Cu(II) and Fe(III) are present as single species at the rutile surface. The mechanism of the photoactivity enhancement was elucidated by a combination of DFT calculations and detailed experimental mechanistic studies including photoluminescence measurements, photocatalytic experiments using scavengers, OH radical detection, and photopotential transient measurements. The results demonstrate that the single Cu(II) and Fe(III) ions act as effective cocatalytic sites, enhancing the charge separation, catalyzing "dark" redox reactions at the interface, improving thus the normally very low quantum yields of UV light-activated TiO 2 photocatalysts. The exact mechanism of the photoactivity enhancement differs depending on the nature of the cocatalyst. Cu(II)decorated samples exhibit fast transfer of photogenerated electrons to Cu(II/I) sites, followed by enhanced catalysis of dioxygen reduction, resulting in improved charge separation and higher photocatalytic degradation rates. At Fe(III)-modified rutile the rate of dioxygen reduction is not improved and the photocatalytic enhancement is attributed to higher production of highly oxidizing hydroxyl radicals produced by alternative oxygen reduction pathways opened by the presence of catalytic Fe(III/II) sites. Importantly, it was demonstrated that excessive heat treatment (at 450 °C) of photocatalysts leads to loss of activity due to migration of Cu(II) and Fe(III) ions from TiO 2 surface to the bulk, accompanied by formation of oxygen vacancies. The demonstrated variety of mechanisms of photoactivity enhancement at single site catalyst-modified photocatalysts holds promise for developing further tailored single-site-modified photocatalysts for various applications. 19calculations that have the surface exposed to vacuum. Furthermore, the oxygen atom of the cluster forms a short bond of 1.79 Å with a fivefold coordinated titanium atom of the surface, closing a TiO 6 octahedra. Figure 10. (a) DOS of the TiO 2 (R)-Cu system, spin-up channel only, aligned to the DOS of the ideal TiO 2 (R) surface. (b) The spin up channel DOS of the final relaxed electron polaron system for the TiO 2 (R)-Cu system. Cu contribution shown. The zero of the x-axis is fitted to the VBM for both plots.The electronic structure of TiO 2 (R)-Cu is shown in Figure 10a. The Cu atom has a significant presence on the CBE. This is primarily due to the Cu d-states. Further, we compare the position of the decorated rutile TiO 2 surface to the bare rutile surface, by comparison and alignment of the electrostatic potential in the vacuum region. 61 When the alignment is taken into action, the Cu-state is margi...

Recent Developments in Accelerated Antibacterial Inactivation on 2D Cu-Titania Surfaces under Indoor Visible Light

“…These studies have shown a drastic enhancement of the bacterial inactivation kinetics of E. coli when Cu was added to binary-oxides in percentages from 0.01% (decoration) up to 1% (doping) [119,127,173]. A variety of TiO2-Cu preparations and the evaluation of their activity for diverse applications is an area of current interest [129][130][131]174]. The relevance of TiO2-Cu catalysts and photocatalysts addressing the issue of bacterial inactivation is reflected in the increasing number of studies focusing on the antibacterial effects of TiO2-Cu and TiO2/Cu in the form of 2D-coatings, suspensions, spheres, alloys, and decorated binary Next, we address the issue of the MRSA bacterial inactivation kinetics and relate the inactivation time to the applied light intensity.…”

“…These studies have shown a drastic enhancement of the bacterial inactivation kinetics of E. coli when Cu was added to binary-oxides in percentages from 0.01% (decoration) up to 1% (doping) [119,127,173]. A variety of TiO 2 -Cu preparations and the evaluation of their activity for diverse applications is an area of current interest [129][130][131]174].…”

Accelerated Antibacterial Inactivation on 2D Cu-Titania Surfaces: Latest Developments and Critical Issues

“…The relevance of the TiO 2 -Cu catalysts and photocatalysts addressing the issue of bacterial inactivation is reflected in the increasing number of studies focusing on the antibacterial effects of TiO 2 -Cu and TiO 2 /Cu in the form of 2D-coatings, suspensions, spheres, alloys, and doped binary oxides [169][170][171][172][173][174][175].…”

FeOOH and Fe2O3 co-grafted TiO2 photocatalysts for bisphenol A degradation in water

“…To improve the photocatalytic activity of TiO 2 , modification of TiO 2 with transition metals such as inexpensive Fe(III) species has been widely studied. There are three main approaches to modifying TiO 2 with Fe(III): (1) doping of Fe(III) into the TiO 2 lattice to narrow the band gap or to introduce intraband impurity states for enhanced visible light activity [4][5][6]; (2) loading crystalline iron oxide (Fe 2 O 3 ) or iron oxyhydroxide (FeOOH) onto the TiO 2 surface and forming heterojunctions at the interface between Fe 2 O 3 and TiO 2 or between FeOOH and TiO 2 to enhance charge transfer between the two types of crystals [7][8][9][10]; (3) grafting highly dispersed Fe(III) ions or nanoclusters onto the TiO 2 surface to induce interfacial charge transfer (IFCT) from TiO 2 valence band (VB) to the Fe(III) states [11][12][13][14][15].…”

“…Different from doping, the grafting method uses a relatively low temperature and thus the Fe(III) locates on the surface rather than in the lattice of TiO 2 . The much lower amount of Fe used in grafting typically leads to the formation of isolated ions or clusters of Fe(III) species (iron oxide [14,15] or oxyhydroxide [11,13]). The IFCT from TiO 2 VB to Fe(III), because of the higher redox potential of Fe(III)/Fe(II) (0.77 V vs SHE) than the TiO 2 CB (~ 0V vs SHE), is the main reason for enhanced charge separation and visible light activity [11].…”