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Photocatalytic artificial fixation of N2 to NH3 occurs over NaYF4:Yb,Tm (NYF) upconversion nanoparticles (NPs) decorated carbon nitride nanotubes with nitrogen vacancies (NYF/NV-CNNTs) in water under near-infrared (NIR) light irradiation. NYF NPs with a particle size of ca. 20 nm were uniformly distributed on the surface of NV-CNNTs. The NYF/NV-CNNTs with 15 wt % NYF exhibited the highest NH3 production yield of 1.72 mmol L-1 gcat-1, corresponding to an apparent quantum efficiency of 0.50% under NIR light illumination, and about three times higher the activity of the bare CNNTs under UV-filtered solar light. 15N isotope-labeling NMR results confirm that the N source of ammonia originates from the photochemical N2 reduction. The spectroelectrochemical measurements reveal that NVs can greatly facilitate the photogenerated electron transfer without energy loss, while the presence of NYF NPs shifts both the deep trap state and the edge of conduction band toward a lower potential. Moreover, NYF NPs endow the photocatalyst with a NIR light absorption via the fluorescence resonance energy transfer process, and NVs have the ability to enhance the active sites for a stronger adsorption of N2 and decrease the surface quenching effect of NYF NPs, which thus can promote the energy migration within the heterojunctions. This work opens the way toward full solar spectrum photocatalysis for sustainable ammonia synthesis under aqueous system.

The diffuse reflectance spectroelectrochemistry (SE-DRS) and reversed double-beam photoacoustic spectroscopy (RDB-PAS) provide unique, complementary information on the density of electronic states (DOS) in the vicinity of the conduction band bottom. The measurements are performed under quite different conditions, representing the solid/liquid and solid/gas interfaces in SE-DRS and RDB-PAS, respectively. DOS profiles obtained from both types of measurements can be considered as unique "fingerprints" of the tested materials. The analysis of DOS profiles recorded for 16 different TiO2 samples confirms that both methods similarly describe the shapes of DOS profiles around the conduction band edges. The states characterized by energy higher than VBT (valence-band top) + E-g can be considered as electronic states within the conduction band. Recognition of the potential of the conduction band bottom allows one to classify the electronic states as deep or shallow electron traps or conduction band states, which play different roles in photocatalysis. The comparative analysis shows that both methods provide very useful information which can be used in understanding and predicting the photo(electro)catalytic reactivity of semiconductors.

Metal oxide-organic hybrid semiconductors exhibit specific properties depending not only on their composition but also on the synthesis procedure, and particularly on the functionalization method, determining the interaction between the two components. Surface adsorption is the most common way to prepare organic-modified metal oxides. Here a simple sol-gel route is described as an alternative, finely controlled strategy to synthesize titanium oxide-based materials containing organic molecules coordinated to the metal. The effect of the molecular structure of the ligands on the surface properties of the hybrids is studied using three enediols able to form charge transfer complexes: catechol, dopamine, and ascorbic acid. For each system, the process conditions driving the transition from the sol to chemical, physical, or particulate gels are explored. The structural, optical, and photoelectrochemical characterization of the amorphous hybrid materials shows analogies and differences related to the organic component. In particular, electron paramagnetic resonance (EPR) spectroscopy at room temperature reveals the presence of organic radical species with different evolution and stability, and photocurrent measurements prove the effective photosensitization of TiO

Metal oxide-organic hybrid semiconductors exhibit specific properties depending not only on their composition but also on the synthesis procedure, and particularly on the functionalization method, determining the interaction between the two components. Surface adsorption is the most common way to prepare organic-modified metal oxides. Here a simple sol–gel route is described as an alternative, finely controlled strategy to synthesize titanium oxide-based materials containing organic molecules coordinated to the metal. The effect of the molecular structure of the ligands on the surface properties of the hybrids is studied using three enediols able to form charge transfer complexes: catechol, dopamine, and ascorbic acid. For each system, the process conditions driving the transition from the sol to chemical, physical, or particulate gels are explored. The structural, optical, and photoelectrochemical characterization of the amorphous hybrid materials shows analogies and differences related to the organic component. In particular, electron paramagnetic resonance (EPR) spectroscopy at room temperature reveals the presence of organic radical species with different evolution and stability, and photocurrent measurements prove the effective photosensitization of TiO2 in the visible range induced by interfacial ligand-to-metal charge transfer.

Selective sulfoxide and sulfone production can be precisely controlled by choosing TiO2 polymorph and the reaction mode (catalysis versus photocatalysis).

In this paper, we describe the role of anatase and rutile crystal phases on diphenyl sulphide (Ph

We developed low-temperature (up to 200 °C) synthesis of TiO2 nanocomposites, which allows precise tuning of the anatase/rutile ratio. The materials were synthesized hydrothermally from strongly ac...

Hydrogen production by photocatalytic water splitting is one of the most promising sustainable routes to store solar energy in the form of chemical bonds. To obtain significant H

Hydrogen production by photocatalytic water splitting is one of the most promising sustainable routes to store solar energy in the form of chemical bonds. To obtain significant H2 evolution rates (HERs) a variety of defective TiO2 catalysts were synthesized by means of procedures generally requiring highly energy-consuming treatments, e.g. hydrogenation. Even if a complete understanding of the relationship between defects, electronic structure and catalytic active sites is far from being achieved, the band gap narrowing and Ti3+-self-doping have been considered essential to date. In most reports a metal co-catalyst (commonly Pt) and a sacrificial electron donor (such as methanol) are used to improve HERs. Here we report the synthesis of TiO2/C bulk heterostructures, obtained from a hybrid TiO2-based gel by simple heat treatments at 400 °C under different atmospheres. The electronic structure and properties of the grey or black gel-derived powders are deeply inspected by a combination of classical and less conventional techniques, in order to identify the origin of their photoresponsivity. The defective sites of these heterostructures, namely oxygen vacancies, graphitic carbon and unpaired electrons localized on the C matrix, result in a remarkable visible light activity in spite of the lack of band gap narrowing or Ti3+-self doping. The materials provide HER values ranging from about 0.15 to 0.40 mmol h−1 gcat−1, under both UV- and visible-light irradiation, employing glycerol as sacrificial agent and without any co-catalyst.

Tailored crystals of anatase TiO2 have been synthesized using a hydrothermal method with hydrofluoric acid and sodium fluoride as capping agents. Titanium dioxide in the form of sheets, tetragonal truncated bipyramids, cuboids and belts offer different exposed facets: {001}, {001}/{101}, {001}/{100} and {100}, respectively. The strongest oxygen adsorption was observed for crystals with exposed {001} facets. Adsorbed fluorides also improve oxygen adsorption. Our spectroelectrochemical (SE-DRS) measurements of density of electronic states (DOS) revealed that the energy of conduction band edge increases in the order: {101} generation) also depends on the exposed facets and increases in the order: cuboids, sheets, tetragonal truncated bipyramids, belts. Furthermore, fluoride ions drastically decrease the photocatalytic production of TAOH.

Synthetic procedures, including doping, sintering and surface coating, can noticeably affect the physicochemical properties of semiconductors. Introduced changes very often translate into photocatalytic and photoelectrochemical activity alterations. However, in this work we have focused on more subtle treatments, which result in lack of changes observed using XRD, UV-vis, porosimetry, TEM or SEM. We have subjected titanium dioxide (P25, UV100) to a treatment with reducing agents used in procedures of noble metal deposition (citrate, borohydride, and photoreduction), or surface decoration with small amounts of TiO2 by atomic layer deposition (ALD; 10 to 200 deposition cycles), which presumably should be neutral to its activity. Although the "classical" characterization methods did not show any differences between the original and treated samples, spectroelectrochemical (SE-DRS) determination of the density of states (DOS) and catechol adsorption tests revealed a significant influence of such treatments on the photocatalytic activity (photogeneration of HO radicals, water reduction, and herbicide degradation) and photoelectrochemical behaviour of the studied samples. We have shown that the applied slight surface modifications of titanium dioxide ("insignificant" at the first glance) may strongly affect the activity of this material. Such often overlooked effects must be taken into account during a comparative photoactivity analysis of various semiconductors, since an insignificant surface treatment may noticeably influence surface chemistry. We have also demonstrated that SE-DRS can be considered as a useful tool to study these effects, although it can be difficult to correlate a particular treatment with recorded changes in the density of states.

The goal of the work is to verify which properties of TiO2-based materials, influenced by small amounts of Fe, Co, Ga, Bi, W, Mo, V and Ni species used as modifiers, play the predominant role in changing the photoactivity of TiO2. Two groups of materials were studied: TiO2 synthesized in the presence of nanocrystalline metal oxide and dissolved metal ions (cations or oxyanions). Sols were calcined at 450, 600 or 900°C. Physicochemical properties of the materials were characterized by XRD, DRS, SEM, EPR, porosimetry and photocurrent measurements. The most detailed studies were focused on modifications by iron species. TiO2 doping was achieved for both Fe3+ and Fe2O3 modifiers after calcination at temperatures equal to or higher than 450 and 900°C, respectively. Morphology of the materials (phase composition, specific surface area, etc.) were influenced by iron species even if they were not introduced into the crystal lattice of TiO2. Comparison of activity of photocatalysts and elucidation of the role of various reactive oxygen species were based on photooxidation tests involving Azure B and terephthalic acid. In general, iron species improved photocatalytic activity, nevertheless, doping of the materials appeared detrimental. A particular improvement of the activity was achieved for composites with low iron contents (ca. 0.01%mol Fe:Ti). The studies revealed, that beside the widely discussed mechanisms (photo-Fenton processes, charge separation, photosensitization, etc.) iron species can indirectly influence the photocatalytic activity of TiO2 acting as phase-composition controllers (PCC) during the synthesis of this oxide, which determine morphology of the resulting photocatalyst. To support this hypothesis, several sets of other TiO2 materials were modified with Co, Ga, Bi, W, Mo, V and Ni species. We show, that the use of these modifiers in small amounts can influence indirectly the activity of photocatalysts regardless to the type of modifier. Therefore different photoactivity of the tested materials should be attributed to these modifier-induced structural and electronic changes of the photocatalysts rather than to any other function of dopants, including photosensitization, enhanced charge separation, catalytic activity, at which most of studies are focused.

Highly-active, surface-modified anatase TiO2 nanoparticles were successfully synthesized and characterized. The morphological and optical properties of the obtained (metallo)porphyrin@qTiO2 materials were evaluated using absorption and fluorescence spectroscopy, scanning electron microscopy (SEM) imaging, and dynamic light scattering (DLS). These hybrid nanoparticles efficiently generated reactive oxygen species (ROS) under blue-light irradiation (420 &plusmn, 20 nm) and possessed a unimodal size distribution of 20&ndash, 70 nm in diameter. The antimicrobial performance of the synthetized agents was examined against Gram-negative and Gram-positive bacteria. After a short-term incubation of microorganisms with nanomaterials (at 1 g/L) and irradiation with blue-light at a dose of 10 J/cm2, 2&ndash, 3 logs of Escherichia coli, and 3&ndash, 4 logs of Staphylococcus aureus were inactivated. A further decrease in bacteria viability was observed after potentiation photodynamic inactivation (PDI), either by H2O2 or KI, resulting in complete microorganism eradication even when using low material concentration (from 0.1 g/L). SEM analysis of bacteria morphology after each mode of PDI suggested different mechanisms of cellular disruption depending on the type of generated oxygen and/or iodide species. These data suggest that TiO2-based materials modified with sulfonated porphyrins are efficient photocatalysts that could be successfully used in biomedical strategies, most notably, photodynamic inactivation of microorganisms.

A visible light responsive heterojunction system composed of Fe2O3 nanorods (NF), reduced graphene oxide (rGO) and double oxide perovskites (LaSrFe2–nConO6, n = 1 (LSFC) and 0 (LSFF)) was rationally designed for an effective photoelectrochemical water splitting. The photoelectrodes were characterized in terms of structure, surface, physicochemical and functional properties with a focus on the electronic structure (e.g., the density of electronic states, band-edge, Fermi level positions), which was gauged from UPS, Kelvin probe (KP) and spectroelectrochemical (SE-DRS) measurements. The KP measurements not only revealed the successful and efficient contact of the materials with different work functions but also showed the drift direction of photogenerated charges. In the studied systems, the transparent, thin layer of rGO facilitates the hole transfer from NF (photoabsorber) to perovskites (electrocatalyst). The hydrogen conversion efficiency under visible and solar simulated irradiation for NF@rGO@LSFF reached remarkable values of 3.61 % and 1.13 % (STH), respectively.

In this study, the protocol of a single-step l-cysteine functionalized silver nanoparticle synthesis was described. Particle size distribution was determined. The crystallinity and chemical properties were investigated using XRD, HR-TEM, and XPS methods. Acute toxicity and irritant properties of obtained nanoparticles were studied using mice and rats as an animal model. The results showed that thanks to the applied protocol, it was possible to synthesize silver nanoparticles with narrow particle size distribution. Moreover, the concentration of final product was extremely high in comparison to other known methods. These nanoparticles showed neither irritant properties nor acute toxicity.

Although production of solar fuels from water or carbon dioxide seems still too expensive to compete with fossil fuels, application of photocatalysis for synthesis of valuable organic chemicals may appear an interesting approach. The use of a photocatalyst and light as the energy source can be considered as a green, sustainable alternative for other methods of fine chemicals production. In this chapter we review approaches to synthesize organic compounds in heterogeneous photocatalytic systems. The described reactions can be divided into three main groups due to their mechanisms: (1) reactions of organic substrates with photocatalytically activated small molecules; (2) a direct photocatalytic activation of one organic substrate; and (3) reactions involving a direct activation of two organic molecules. The understanding of plausible mechanisms of the photocatalytic reactions and properties of photocatalytic systems favoring the desired reaction should facilitate the design of new photocatalysts and convenient conditions to synthesize new specific chemicals.

The information on the electronic structure of nano- and microstructured semiconductors is crucial for their applications in photovoltaics, optoelectronics and photocatalysis. The distribution of intra-bandgap electronic states is one of the most relevant parameters which may be tuned in order to provide desired properties of a photoactive material. We propose the use of a modified spectroelectrochemical method for the characterisation of vacant electronic states distributed close to the edge of the titanium dioxide conduction band. These additional levels localized within the bandgap were semi-quantitatively characterized for several samples made of different polymorphs (or their blends) of TiO2. The applicability of the method for the determination of deep and shallow electron traps was confirmed. A quantitative analysis of the latter was also conducted for the selected samples. The presented approach provides also the information on the stability of electronic states, which is crucial for numerous practical applications.

Anatase-brookite TiO2 photocatalysts were prepared by the sol-gel process controlled within reverse micelles and processing by pressurized hot solvents–water/methanol/water (TiO2(M)) and water/ethanol/water (TiO2(E)), as an unconventional alternative to common calcination. The main goal of this work was to prepare anatase-brookite mixtures by processing by two different alcohols (methanol and ethanol) and evaluate the influence of the alcohol on the photocatalytic activity. Prepared photocatalysts were characterized by organic elemental analysis, nitrogen physisorption, XRD, UV–vis, photoelectrochemical and spectroelectrochemical measurements and XPS. The prepared photocatalysts efficiency was tested on the photocatalytic reduction of carbon dioxide and compared with commercial TiO2 Evonik P25. Both prepared nanocomposites were more efficient towards methane production but Evonik P25 was the most efficient towards hydrogen generated through water splitting. The higher performance of anatase-brookite mixture towards methane production can be explained by (i) a higher photocatalytic activity of brookite than rutile; (ii) a large surface area of anatase-brookite composites enabling better carbon dioxide adsorption; (iii) the photoinduced electron transfer from the brookite conduction band to the anatase conduction band. On the other hand, a higher production of hydrogen in the presence of Evonik P25 is caused by a better charge separation in anatase-rutile than anatase-brookite phase compositions. TiO2(M) appeared more active than TiO2(E) in the photocatalytic reduction of carbon dioxide due to a lower density of defects created in the crystal lattice.

Utilization of visible light by photosensitization of semiconductor photocatalysts via surface attachment of small colorless organic pollutants (COP) is an effective way to stimulate their photocatalytic degradation. Herein, by means of the spectroscopic, photoelectrochemical, spectroelectrochemical, and photocatalytic studies combined with the DFT+D molecular modeling, we show how disubstituted benzene derivatives, like catechol (CAT), salicylic acid (SAL), phthalic acid (PTA), and terephthalic acid (TPA), can tune the photocatalytic properties of rutile nanorods with the dominant (110) termination. We elucidated in a systematic way the COP ligand-binding configurations, the alignment of energy levels, and the charge-transfer pathways from the organic admolecules to the titania substrate. The pDOS structures of the COP@r-TiO2(110) assemblies were interpreted in terms of electronic interactions between the titania photocatalyst and the COP adspecies. It was shown that the appearance of additional states w...

A group of selected hexafluorometallates $([AIF_{6]^{3-}}]), [TiF_{6}]^{2-}, and [SiF_{6}]^{2-})$ has been adsorbed at the surface of titanium dioxide. Such modification influenced the electronic and chemical properties of $TiO_{2}$ , as well as its photoactivity. The modification with $[TiF_{6}]^{2-}]$ inhibited the e fficiency of OH• production but enhanced the generation of photocurrent and singlet oxygen. The results of modifications with $[ZrF_{6}]^{2-}$ were the opposite-generation of $^{1}\textrm{O}_{2}$ was not observed in this case and photocurrents were lower; however, due to a better OH• production, degradation of herbicides was faster.