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...

The efficient coupling between light-harvesting absorbers and cocatalysts allowing for chemical transformation along multielectron pathways is of fundamental importance for the development of solar-fuel-producing photochemical systems. Herein we demonstrate that IrO x nanoparticles acting as efficient cocatalyst for water oxidation can be photoelectrochemically deposited from hexahydroxoiridate solutions into the porous structure of TiO 2 -PH (polyheptazine, "graphitic carbon nitride") hybrid photoanodes for water photooxidation. As compared to photoanodes loaded with IrO x by the conventional colloidal deposition method, hybrid photoanodes with photodeposited IrO x exhibit significantly enhanced dioxygen evolution under long-term irradiation with visible light (λ > 420 nm). Photocurrent transient measurements show that the undesired accumulation of holes in the TiO 2 -PH absorber is significantly reduced due to improved coupling between the absorber and the photodeposited cocatalyst. This decreases significantly the recombination rate, leads to more efficient dioxygen evolution, and improves the stability against photocorrosion. Photocurrent measurements under potentiodynamic conditions revealed that at low bias potentials (<0.6 V vs RHE) the photoconversion efficiency of hybrid photoanodes is limited by fast primary back electron transfer and by reduction of Ir(IV) to Ir(III). The performance and stability of hybrid photoanodes are also found to be drastically influenced by the solution chemistry (electrolyte composition and pH). The highest photoconversion efficiency was observed in sulfate-based electrolytes at pH ∼6.

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Benzene can be activated by visible light (λ > 455 nm) in the presence of TiO(2), which leads to formation of carbonaceous polymeric deposits on the titania surface. These photosynthesized surface-modified materials exhibit enhanced photoactivity in degradation of phenolic compounds, particularly under visible light irradiation.

Surface‐modified TiO2 photocatalysts were synthesized by a photosynthetic route involving visible‐light‐induced (λ>455 nm) activation of benzene and toluene at the surface of TiO2 leading to the formation of carbonaceous polymeric deposits. IR spectroscopic and photoelectrochemical experiments showed that the mechanism of the photosynthetic reactions involves intra‐bandgap surface states at TiO2 related to surface OH groups interacting with adsorbed aromatic molecules. The photosynthesized surface‐modified TiO2 materials exhibited enhanced activity, relative to pristine TiO2, in photocatalytic degradation (and complete mineralization) of 4‐chlorophenol. The improvement was pronounced particularly under visible‐light (λ>455 nm) irradiation with the relative initial photodegradation rate enhanced by a factor of four. The surface‐modified photocatalysts exhibited good stability under the operating conditions, and the optimum carbon content was approximately 0.5 wt %. Mechanistic studies showed that the enhanced visible‐light photodegradation of 4‐chlorophenol is due to modified surface‐adsorption properties that facilitate formation of a surface complex between titania and 4‐chlorophenol, rather than due to any sensitizing effect of the carbonaceous deposits. The study highlights the importance of considering the interaction between pollutant molecules and the photocatalyst surface in heterogeneous photocatalysis, and possibly opens up a route for photosynthesis of further surface‐modified photocatalysts with tuned surface properties.

improved by deposition of redox catalysts, which can effectively extract the photogenerated charge carriers, improve the rate of interfacial electron and/or hole transfers, and thus suppress undesired recombination processes. [2] In case of photocatalytic degradation of organic pollutants, this approach has been in particular motivated by the need to enhance the kinetics of dioxygen reduction by photogenerated electrons since this reaction represents typically the rate-limiting step in the photodegradation process. This has already been suggested by Gerischer and Heller in the 1990s, [3] and later confirmed by kinetic studies using transient absorption spectroscopy that have demonstrated that the reduction of dioxygen by photogenerated electrons occurs on a much longer timescale (microseconds) than, for example, the oxidation of alcohols by photogenerated holes (nanoseconds). [4] Indeed, significant enhancements of photocatalytic degradation rates have been, for example, demonstrated for TiO 2 photocatalysts modified by Pt, [3a,5] CuO x , and FeO x nanoparticles, [6] or even with isolated single Cu(II) and Fe(III) ions. [7] It is important to realize that a high degree of control over the loading, size, and surface catalytic properties of the redox catalyst particles is highly desirable in order to tune the resulting composites for optimum performance. [8] In this context, it is not surprising that mostly employed methods of preparation of photocatalytic composites have been impregnation [6a-d,9] and deposition precipitation, [3a,5,6e,f ] sinceIt is well established that the activity of photocatalysts can be improved by deposition of redox catalysts, which can effectively extract the photogenerated charge carriers, enhance the rate of interfacial reactions, and thus suppress undesired recombination processes. For optimum performance, a high degree of control over the loading, size, and surface catalytic properties of redox catalyst particles is desirable. Herein, a novel, highly controllable, and versatile method for preparation of TiO 2 catalyst composites is reported. It starts with the generation of "naked" (ligand-free) nanoparticles of CuO x or FeO x by pulsed laser ablation of metal oxide targets in water. In the next step, a nearly quantitative colloidal deposition of CuO x and FeO x nanoparticles onto anatase TiO 2 substrate is achieved by adjusting the pH in order to establish electrostatic attraction between the colloids and the substrate. The resulting TiO 2 -CuO x and TiO 2 -FeO x assemblies with optimum catalyst amount (≈0.5 wt%) exhibit photocatalytic rates in degradation of 2,4-dichlorophenoxyacetic acid enhanced by a factor of ≈1.5 as compared to pristine TiO 2 under simulated solar irradiation. The electrostatically directed assembly of TiO 2 with ligand-free catalyst nanoparticles generated by pulsed laser ablation is thus demonstrated as a viable tool for preparation of composites with enhanced photocatalytic performance. Photocatalytic CompositesThe ORCID identification number(s) for t...

Surface modification of heterogeneous photocatalysts with single-atom catalysts (SACs) represents an attractive approach towards enhancing the photocatalytic performance. However, our knowledge on the mechanism of photocatalysis enhancement at SAC-modified photocatalysts is still rather limited, which makes the rational design of high-performance photocatalysts based on SACs challenging. Herein, a series of photocatalysts for aerobic degradation of pollutants based on anatase TiO2 modified with various low-cost, non-noble SACs (vanadate, Cu and Fe ions) is reported. The most active SAC-modified photocatalysts outperform not only TiO2 modified with corresponding metal oxide nanoparticles, but also the state-of-the-art benchmark photocatalysts, such as platinized TiO2 or commercial P25 powders. A combination of in-situ EPR spectroscopy and theoretical calculations revealed that the best-performing photocatalysts modified with Cu(II) and vanadate SACs exhibit significant differences in the mechanism of activity enhancement, in particular with respect to the rate of catalysis of oxygen reduction. The superior performance of vanadate SAC-modified TiO2 is found to be related to the shallow character of the SAC-induced intragap states, which allows for both effective extraction of photogenerated electrons and fast catalytic turnover in reduction of dioxygen, and translates directly into diminished recombination. These results provide essential design guidelines for the development of efficient SAC-based photocatalysts.