Acetylacetonate-modified TiO2 nanoparticles coated on the carbon felt as the negative electrode of vanadium redox flow battery for reducing HER and enhancing V3+/V2+ redox reactions

The occurrence of the hydrogen evolution reaction (HER) on the surface of the carbon-based negative electrode of the vanadium redox flow battery (VRFB) causes high charge transfer resistance (RCT) for the desired V3+/V2+ redox reaction leading to irreversible capacity loss. To this effect, we have synthesized acetylacetonate-modified TiO2 (SGTA) and unmodified TiO2 (SGT) coating colloidal solutions as electrocatalysts for enhanced V3+/V2+ redox reaction on the carbon-felt negative electrodes of VRFB. The SGTA particles exhibit significantly higher homogeneity with sizes of ≤15 nm, in comparison to the severely aggregated SGT particles with diameters of ∼23-75 nm in colloidal solution. When coated on the pristine carbon felt (P-CF), the surface morphology of the SGTA@CF electrode exhibits relatively dense, uniformly coated particles, in comparison to the sparse, non-even coating of aggregated particles on the SGT@CF electrode surface. Consequently, the charge transfer for V3+ → V2+ reduction reaction and charge storage capacity are determined to be in the order SGTA@CF > SGT@CF > P-CF, confirming that the competitive and irreversible HER was higher on the surface of non-evenly coated fibers and bare carbon felt, respectively.

Salicylic Acid-Modified Sm-TiO2 for Photoluminescence and Photocatalysis under Real Sunlight: Synergistic Effects between Ligand-to-Metal Charge Transfer (LMCT) and Sm3+ Dopant

A salicylic-acid (SA)-modified samarium-doped TiO2 complex (Sm-TiO2/SA) was synthesized via a sol-gel method followed by impregnation. A Raman Fourier transform IR and X-ray photoelectron spectroscopic study showed that SA (as an electron donor) forms a surface complex on the Sm-TiO2 surface through its phenolic/carboxylic functional groups. In the Sm-TiO2/SA complex, a ligand-to-metal charge transfer (LMCT) is active, inducing a marked red-shift in the absorption spectrum of TiO2, which extends to 550-600 nm. The synergetic effect between the LMCT process and the luminescent properties of the lanthanide ions (Sm3+) is discussed and supported by the photoluminescence spectra. Further photocatalytic experiments (under sunlight) and the study of the effect of different scavengers show the presence of competitive reactions between de-ethylation and cleavage of Rhodamine B (RhB) during its degradation. With the Sm-TiO2/SA complexes, the superoxide radical ion (O2 •-) is the main active species responsible for the N-de-ethylation pathway under sunlight irradiation. The cleavage of RhB by the hydroxyl radical (•OH) appears, instead, to dominate with the Sm-TiO2 photocatalysts.

Ab initio molecular dynamics of solvation effects and reactivity at the interface between water and ascorbic acid covered anatase TiO2 (101)

In this work, we present a detailed study of the interaction between ascorbic acid (L-asc) and anatase TiO2 (101) surface both in gas phase and in contact with water by using density functional theory and ab initio molecular dynamics simulations. In gas phase, L-asc strongly binds the TiO2 (101) surface as a dianion (L-asc2- ), adopting a bridging bidentate coordination mode (BB), with the two acid protons transferred to two surface 2-fold bridging oxygens (O2c). AIMD simulations show that the interaction between the organic ligand and the anatase surface is stable and comparable to the vacuum one despite the possible solvent effects and/or possible structural distortions of the ligand. In addition, during the AIMD simulations hydroxylation phenomena occur forming transient H3 O+ ions at the solid-liquid interface. For the first time, our results provide insight into the role of the ascorbic acid on the electronic properties of the TiO2 (101), the influence of the water environment on the ligand-surface interaction and the nature of the solid-liquid interface.

Indirect daylight oxidative degradation of polyethylene microplastics by a bio-waste modified TiO2-based material

Microplastics are recognized as an emerging critical issue for the environment. Here an innovative chemical approach for the treatment of microplastics is proposed, based on an oxidative process that does not require any direct energy source (irradiation or heat). Linear low-density polyethylene (LLDPE) was selected as target commodity polymer, due to its widespread use, chemical inertness and inefficient recycling. This route is based on a hybrid material coupling titanium oxide with a bio-waste, rosin, mainly constituted by abietic acid, through a simple sol-gel synthesis procedure. The ligand-to-metal charge transfer complexes formed between rosin and Ti4+ allow the generation of reactive oxygen species without UV irradiation for its activation. In agreement with theorical calculations, superoxide radical ions are stabilized at ambient conditions on the surface of the hybrid TiO2. Consequently, an impressive degradation of LLDPE is observed after 1 month exposure in a batch configuration under indirect daylight, as evidenced by the products revealed by gas chromatography-mass spectrometry analysis and by chemical and structural modifications of the polymer surface. In a context of waste exploitation, this innovative and sustainable approach represents a promising cost-effective strategy for the oxidative degradation of microplastics, without producing any toxic by-products.

Towards nanostructured red-ox active bio-interfaces: Bioinspired antibacterial hybrid melanin-CeO2 nanoparticles for radical homeostasis

Redox-active nano-biointerfaces are gaining weight in the field of regenerative medicine since they can act as enzymes in regulating physiological processes and enabling cell homeostasis, as well as the defense against pathogen aggression. In particular, cerium oxide nanoparticles (CeO2 NPs) stand as intriguing enzyme-mimicking nanoplatforms, owing to the reversible Ce+3/Ce+4 surface oxidation state. Moreover, surface functionalization leads to higher catalytic activity and selectivity, as well as more tunable enzyme-mimicking performances. Conjugation with melanin is an adequate strategy to boost and enrich CeO2 NPs biological features, because of melanin redox properties accounting for intrinsic antioxidant, antimicrobial and anti-inflammatory power. Herein, hybrid Melanin/CeO2 nanostructures were designed by simply coating the metal-oxide nanoparticles with melanin chains, obtained in-situ through ligand-to-metal charge transfer mechanism, according to a bioinspired approach. Obtained hybrid nanostructures underwent detailed physico-chemical characterization. Morphological and textural features were investigated through TEM, XRD and N2 physisorption. The nature of nanoparticle-melanin interaction was analyzed through FTIR, UV-vis and EPR spectroscopy. Melanin-coated hybrid nanostructures exhibited a relevant antioxidant activity, confirmed by a powerful quenching effect for DPPH radical, reaching 81 % inhibition at 33 μg/mL. A promising anti-inflammatory efficacy of the melanin-coated hybrid nanostructures was validated through a significant inhibition of BSA denaturation after 3 h. Meanwhile, the enzyme-mimicking activity was corroborated by a prolonged peroxidase activity after 8 h at 100 μg/mL and a relevant catalase-like action, by halving the H2O2 level in 30 min at 50 μg/mL. Antimicrobial assays attested that conjugation with melanin dramatically boosted CeO2 biocide activity against both Gram (-) and Gram (+) strains. Cytocompatibility tests demonstrated that the melanin coating not only enhanced the CeO2 nanostructures biomimicry, resulting in improved cell viability for human dermal fibroblast cells (HDFs), but mostly they proved that Melanin-CeO2 NPs were able to control the oxidative stress, modulating the production of nitrite and reactive oxygen species (ROS) levels in HDFs, under physiological conditions. Such remarkable outcomes make hybrid melanin-CeO2 nanozymes, promising redox-active interfaces for regenerative medicine.

Sol-Gel-Syntheses and Structural as well as Electrical Characterizations of Anatase- and Rutile-Type Solid Solutions in the System IrO2 -TiO2

This paper describes solid solutions in the quasibinary oxide system iridium-titanium IrO₂ -TiO₂ with rutile and anatase crystal structures. Based on X-ray diffraction evaluations using Rietveld refinements, changes of lattice parameters were determined within the composition series of 0-100 mol % iridium. These changes prove the existence of a complete solid solution series in the rutile structure type. The solubility limit for iridium in the anatase lattice was found to be 6.0(8) mol % iridium for the underlying sol-gel process. In addition, iridium is a promoter for the conversion from anatase to rutile type. Furthermore, the X-ray diffraction results of a calcination temperature series for the composition with 5 mol % iridium are shown, which confirm the findings of the composition series and allow conclusions on the phase segregation behavior. The results are complemented by 2-point conductivity measurements at different pressures in a piston press to investigate the question of the conductivity mechanism.

Tetracycline Removal through the Synergy of Catalysis and Photocatalysis by Novel NaYF4:Yb,Tm@TiO2-Acetylacetone Hybrid Core-Shell Structures

Novel hybrid core-shell structures, in which up-converting (UC) NaYF₄:Yb,Tm core converts near-infrared (NIR) to visible (Vis) light via multiphoton up-conversion processes, while anatase TiO₂-acetylacetonate (TiO₂-Acac) shell ensures absorption of the Vis light through direct injection of excited electrons from the highest-occupied-molecular-orbital (HOMO) of Acac into the TiO₂ conduction band (CB), were successfully synthesized by a two-step wet chemical route. Synthesized NaYF₄:Yb,Tm@TiO₂-Acac powders were characterized by X-ray powder diffraction, thermogravimetric analysis, scanning and transmission electron microscopy, diffuse-reflectance spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence emission measurement. Tetracycline, as a model drug, was used to investigate the photocatalytic efficiencies of the core-shell structures under irradiation of reduced power Vis and NIR spectra. It was shown that the removal of tetracycline is accompanied by the formation of intermediates, which formed immediately after bringing the drug into contact with the novel hybrid core-shell structures. As a result, ~80% of tetracycline is removed from the solution after 6 h.

Extrinsic Point Defects in TiO2-Acetylacetone Charge-Transfer Complex and Their Effects on Optical and Photochemical Properties

TiO₂-based visible-light-sensitive nanomaterials are widely studied for photocatalytic applications under UV-Vis radiation. Among the mechanisms of visible-light sensitization, extrinsic oxygen vacancies have been introduced into TiO₂ and charge-transfer complexes (CTCs) have been formed between chelating ligands, such as acetylacetone, and nanocrystalline TiO₂ (TiO₂-ACAC). However, the influence of extrinsic oxygen vacancies on the photocatalytic performance of TiO₂-based CTCs is unknown. In this work, surface/bulk extrinsic oxygen vacancies were introduced into TiO₂-ACAC through calcination at 270 °C under static air, argon, and hydrogen atmospheres. TiO₂-ACAC CTCs were characterized by X-ray powder diffraction, thermogravimetric analysis, diffuse-reflectance spectroscopy, photoluminescence, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy techniques. The correlation between EPR-spin trapping and tetracycline (TC) photodegradation, using scavengers, highlighted the key role of the superoxide radical in TC degradation by TiO₂-ACAC CTCs under low-power visible-light radiation. The increased extrinsic oxygen vacancies concentration was not beneficial for the photocatalytic performance of TiO₂ CTCs, since bulk extrinsic oxygen vacancies additionally act as recombination centers. In fact, the TiO₂-ACAC CTC with the lowest extrinsic oxygen vacancies concentration exhibited the highest photocatalytic performance for TC degradation due to an adequate distribution of extrinsic bulk oxygen vacancies, which led to the trapped electrons undergoing repeated hopping, reducing the recombination rates and improving the efficiency in superoxide radicals production. Our findings indicated that TiO₂-ACAC CTCs are able to degrade pollutants via interactions with electronic holes and principally superoxide radicals and also, provided fundamental information about the influence of surface/bulk extrinsic oxygen vacancies on the photocatalytic performance, lattice parameters, and optical and photochemical properties of TiO₂-based CTCs.

Recent Advances in Endocrine Disrupting Compounds Degradation through Metal Oxide-Based Nanomaterials

Endocrine Disrupting Compounds (EDCs) comprise a class of natural or synthetic molecules and groups of substances which are considered as emerging contaminants due to their toxicity and danger for the ecosystems, including human health. Nowadays, the presence of EDCs in water and wastewater has become a global problem, which is challenging the scientific community to address the development and application of effective strategies for their removal from the environment. Particularly, catalytic and photocatalytic degradation processes employing nanostructured materials based on metal oxides, mainly acting through the generation of reactive oxygen species, are widely explored to eradicate EDCs from water. In this review, we report the recent advances described by the major publications in recent years and focused on the degradation processes of several classes of EDCs, such as plastic components and additives, agricultural chemicals, pharmaceuticals, and personal care products, which were realized by using novel metal oxide-based nanomaterials. A variety of doped, hybrid, composite and heterostructured semiconductors were reported, whose performances are influenced by their chemical, structural as well as morphological features. Along with photocatalysis, alternative heterogeneous advanced oxidation processes are in development, and their combination may be a promising way toward industrial scale application.

Interfacial Charge Transfer Complexes in TiO2-Enediol Hybrids Synthesized by Sol-Gel

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.

Site-specific halloysite functionalization by polydopamine: A new synthetic route for potential near infrared-activated delivery system

Halloysite nanotubes (HNTs) represent a versatile core structure for the design of functional nanosystems of biomedical interest. However, the development of selective methodologies for the site-controlled functionalization of the nanotubes at specific sites is not an easy task. This study aims to accomplish a procedure for the site-selective/specific, "pin-point", functionalization of HNTs with polydopamine (HNTs@PDA). This goal was achieved, at pH 6.5, by exploiting the basicity of ZnO nanoparticles anchored on the HNTs external surface (HNTs@ZnO) to induce a punctual polydopamine polymerization and coating. The morphology and the chemical composition of the nanomaterial was demonstrated by several techniques. Turbidimetric analysis showed that PDA coating affected the aqueous stability of HNTs@PDA compared to both HNTs@ZnO and HNTs. Notably, hyperthermia studies revealed that the nanomaterial induced a local thermic rise, up to 50 °C, under near-infrared (NIR) irradiation. Furthermore, secondary functionalization of HNTs@PDA by selective grafting of biotin onto the PDA coating followed by avidin binding was also accomplished.

Characterization of anthropogenic organic matter and its interaction with direct yellow 27 in wastewater: Experimental results and perspectives of resource recovery

The concept of natural organic matter of anthropogenic origin is introduced and its characteristics and interaction with chemical pollutants are investigated by adopting several distinct analytic methodologies. Scanning electron microscopy indicates that the used sample of anthropogenic organic matter (AOM) has an amphiphilic nature, which allows its supramolecular organization in water. Fourier transform infrared spectroscopy, in turn, gives a clear indication about the presence of polysaccharide markers, lipidic and amidic fractions, and suggests the absence of free organic acid. AOM sample and AOM mixed with dye sample were examined by the three-dimensional excitation-emission matrix fluorescence spectra and the nuclear magnetic resonance mono-dimensional spectra. The results highlighted the interactions occurring between the AOM and the reactive dye, selected as a representative chemical pollutant. Electron Spin Resonance confirms that the used AOM is able to completely include the dye in its structure. Overall, the obtained results indicate that the fate, transport, and toxicity of pollutants in the environment can be drastically influenced by the presence of AOM.

The Influence of Nd and Sm on the Structure and Properties of Sol-Gel-Derived TiO2 Powders

TiO₂ nanopowders modified by Nd and Sm were prepared using the sol-gel technique. It was found by XRD analysis that the samples containing Sm are amorphous up to 300 °C, while those with Nd preserve a mixed organic-inorganic amorphous structure at higher temperatures (400 °C). The TiO₂ (rutile) was not detected up to 700 °C in the presence of both modified oxides. TiO₂ (anatase) crystals found at about 400 °C in the Sm-modified sample exhibited an average crystallite size of about 25-30 nm, while doping with Nd resulted in particles of a lower size-5-10 nm. It was established by DTA that organic decomposition is accompanied by significant weight loss occurring in the temperature range 240-350 °C. Photocatalytic tests showed that the samples heated at 500 °C possess photocatalytic activity under UV irradiation toward Malachite green organic dye. Selected compositions exhibited good antimicrobial activity against E. coli K12 and B. subtilis.

Bioinspired antibacterial PVA/Melanin-TiO2 hybrid nanoparticles: the role of poly-vinyl-alcohol on their self-assembly and biocide activity

Hybrid Melanin-TiO₂ nanoparticles are promising bioinspired antibacterial agents for biomedical coatings and food-packaging fields. However, due to a very low colloidal stability, they showed a high tendency to self-aggregate and rapidly precipitate, making not easy their use in aqueous medium to produce homogeneous antimicrobial coatings or nanocomposites. A valid strategy to improve their dispersion is the combination with a hydrophilic water-soluble polymer such as poly-vinyl-alcohol (PVA), which is a good choice to improve the colloidal stability of nanoparticles and to modulate their agglomeration. In this work, we propose an in-situ synthetic approach based on the hydrothermal route, by which the hybrid Melanin-TiO₂ nanoparticles were prepared starting from the inorganic and organic precursors in the presence of PVA. Combined approach of TEM, XRD, TG/DSC, EPR and DLS techniques allows for assessing the PVA role in the formation of hybrids and on their morphological features as well as colloidal stability and aqueous dispersion. Antibacterial tests demonstrated the biocide activity of PVA/Melanin-TiO₂ nanoparticles against Escherichia coli bacterial cultures, which resulted partially influenced by the PVA content. This study provides key information on the mutual influence of organic/inorganic components on the functional properties of the final hybrid nanocomposites, contributing to define a much more far-reaching implementation in the synthesis of bioinspired polymer-based nanocomposites.

The Influence of Calcination Temperature on Photocatalytic Activity of TiO2-Acetylacetone Charge Transfer Complex towards Degradation of NOx under Visible Light

The improvement of photocatalytic activity of TiO2-based nanomaterials is widely investigated due to the tentative of their industrialization as environmental photocatalysts and their inherently low solar spectrum sensitivity and rapid recombination of charge carriers. Coupling of oxygen-based bidentate diketone to nanocrystalline TiO2 represents a potential alternative for improving the holdbacks. Formation of TiO2-acetylacetone charge transfer complex (CTC) by sol-gel route results in a hybrid semiconductor material with photodegradation activity against toxic NOx gas. In this research, the influence of the chelating agent acetylacetone (ACAC) content on the CTC photocatalytic efficiency under visible light was evaluated. A high content of ACAC in the CTC is not a decisive factor for efficiency of photocatalytic reactions. In fact, the highest efficiency for NOx degradation (close to 100%, during 1 h of visible light exposure) was reported for the material calcined in air at 300 °C with the content of strongly bonded acetylacetone not higher than 3 wt.%. Higher calcination temperature (400 °C) left TiO2 almost completely depleted in ACAC, while at the highest applied temperature (550 °C) a portion of anatase was transformed into rutile and the sample is free of ACAC. The analyses pointed out that superoxide anion radical (O2−) plays an active role in photo-oxidation of NOx. Our findings indicate that this CTC has both high visible light spectral sensitivity and photocatalytic efficiency.

Three-year lifetime and regeneration of superoxide radicals on the surface of hybrid TiO2 materials exposed to air

The generation and stabilization of reactive oxygen species (ROS), including the superoxide radical anion (O₂^-), have a huge potential in environmental remediation and industrial chemical processes, but they still remain a challenge. Here, we elucidate the formation, stability and reactivity of superoxide radicals spontaneously produced on the surface of a hybrid TiO₂-acetylacetonate material exposed to air. EPR spectra reveal an exceptional lifetime (up to three years, in air at room temperature) of the adsorbed O₂^-, which can also be easily regenerated after its decay. The performances of this material in the degradation of organic pollutants in aqueous solution without any light irradiation indicate a heterogeneous catalytic mechanism, mediated by superoxide radicals, with a synergistic homogeneous action of hydroxyl radicals (OH), which are released in solution, as detected by the EPR spin trapping method. The regeneration ability of the adsorbed superoxide radicals by simple exposure to air counteracts the partial instability in aqueous environment of the organic component of the hybrid structure allowing the catalyst reuse. These structural and functional features joined to the simple preparation route open a new perspective in the field of advanced oxidation processes for hybrid TiO₂ materials.

Insights into mechanisms of UV/ferrate oxidation for degradation of phenolic pollutants: Role of superoxide radicals

In this study, the performances and mechanisms of UV/ferrate(VI) oxidation were investigated comprehensively using 2,4-dichlorophenol (2,4-DCP) as a probe compound. UV/ferrate(VI) oxidation could efficiently degrade 2,4-DCP and its oxidation ability outperformed conventional UV-based advanced oxidation processes. Moreover, the degradation process of 2,4-DCP followed the pseudo-first order kinetics. In the absence of phosphate buffer, the rate constant of 2,4-DCP degradation increased from 9.4 × 10^-3 to 2.4 × 10^-2 min^-1 when pH value was increased from 3.0 to 6.0. However, the degradation was significantly inhibited by phosphate buffer at an identical pH due to the complexation of phosphate with the ferrate(VI) decay products. HCO₃^- appreciably accelerated the degradation of 2,4-DCP, while Cl^- showed a negligible effect on the degradation. For the first time, combining with the results of chemical probe method, competitive kinetic experiment, electron spin resonance spectra and radical quenching studies, superoxide radicals were demonstrated as the dominant reactive species responsible for the degradation. On the basis of the intermediates detected by LC-MS/MS analysis, a pathway for 2,4-DCP degradation was proposed. This study provides a novel approach for contaminant removal using UV/ferrate(VI) oxidation and sheds new insights into the oxidation mechanisms.

Photocatalytic hydrogen evolution by co-catalyst-free TiO2/C bulk heterostructures synthesized under mild conditions

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.

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

Solar radiation is becoming increasingly appreciated because of its influence on living matter and the feasibility of its application for a variety of purposes. It is an available and everlasting natural source of energy, rapidly gaining ground as a supplement and alternative to the nonrenewable energy feedstock. Actually, an increasing interest is involved in the development of efficient materials as the core of photocatalytic and photothermal processes, allowing solar energy harvesting and conversion for many technological applications, including hydrogen production, CO2 reduction, pollutants degradation, as well as organic syntheses. Particularly, photosensitive nanostructured hybrid materials synthesized coupling inorganic semiconductors with organic compounds, and polymers or carbon-based materials are attracting ever-growing research attention since their peculiar properties overcome several limitations of photocatalytic semiconductors through different approaches, including dye or charge transfer complex sensitization and heterostructures formation. The aim of this review was to describe the most promising recent advances in the field of hybrid nanostructured materials for sunlight capture and solar energy exploitation by photocatalytic processes. Beside diverse materials based on metal oxide semiconductors, emerging photoactive systems, such as metal-organic frameworks (MOFs) and hybrid perovskites, were discussed. Finally, future research opportunities and challenges associated with the design and development of highly efficient and cost-effective photosensitive nanomaterials for technological claims were outlined.

Recent Progress with In Situ Characterization of Interfacial Structures under a Solid-Gas Atmosphere by HP-STM and AP-XPS

: Surface science is an interdisciplinary field involving various subjects such as physics, chemistry, materials, biology and so on, and it plays an increasingly momentous role in both fundamental research and industrial applications. Despite the encouraging progress in characterizing surface/interface nanostructures with atomic and orbital precision under ultra-high-vacuum (UHV) conditions, investigating in situ reactions/processes occurring at the surface/interface under operando conditions becomes a crucial challenge in the field of surface catalysis and surface electrochemistry. Promoted by such pressing demands, high-pressure scanning tunneling microscopy (HP-STM) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS), for example, have been designed to conduct measurements under operando conditions on the basis of conventional scanning tunneling microscopy (STM) and photoemission spectroscopy, which are proving to become powerful techniques to study various heterogeneous catalytic reactions on the surface. This report reviews the development of HP-STM and AP-XPS facilities and the application of HP-STM and AP-XPS on fine investigations of heterogeneous catalytic reactions via evolutions of both surface morphology and electronic structures, including dehydrogenation, CO oxidation on metal-based substrates, and so on. In the end, a perspective is also given regarding the combination of in situ X-ray photoelectron spectroscopy (XPS) and STM towards the identification of the structure-performance relationship.

Synergistic Effect of Photocatalytic Degradation of Hexabromocyclododecane in Water by UV/TiO2/persulfate

In this work, the elimination of hexabromocyclododecane (HBCD) is explored by using photodegradation of the UV/TiO2 system, the UV/potassium persulfate (KPS) system, and the homo/heterogeneous UV/TiO2/KPS system. The experimental results show that the dosages of TiO2 and potassium persulfate have optimum values to increase the degradation degree. HBCD can be almost completely degraded and 74.3% of the total bromine content is achieved in the UV/TiO2/KPS homo/heterogeneous photocatalysis, much more than in the UV/persulfate system and the UV/TiO2 system. Roles of radicals SO4•− and OH• in the photocatalysis systems are discussed based on experimental measurements. The high yield of the concentration of bromide ions and decreased pH value indicates that synergistic effects exist in the UV/TiO2/KPS homo/heterogeneous photocatalysis, which can mineralize HBCD into inorganic small molecules like carboxylic acids, CO2 and H2O, thus much less intermediates are formed. The possible pathways of degradation of HBCD in the UV/TiO2/KPS system were also analyzed by GC/MS. This work will have practical application potential in the fields of pollution control and environmental management.

Solar light efficient photocatalytic activity degradation of emergent contaminants by coated TiO2 nanoparticles

The photocatalytic degradation of different emergent contaminants in aqueous solutions has been studied by using oligomer-coated TiO₂ nanoparticles under solar light irradiation.

Replacing Nitrogen by Sulfur: From Structurally Disordered Eumelanins to Regioregular Thiomelanin Polymers

The oxidative polymerization of 5,6-dihydroxybenzothiophene (DHBT), the sulfur analog of the key eumelanin building block 5,6-dihydroxyindole (DHI), was investigated to probe the role of nitrogen in eumelanin build-up and properties. Unlike DHI, which gives a typical black insoluble eumelanin polymer on oxidation, DHBT is converted to a grayish amorphous solid (referred to as thiomelanin) with visible absorption and electron paramagnetic resonance properties different from those of DHI melanin. Mass spectrometry experiments revealed gradational mixtures of oligomers up to the decamer level. Quite unexpectedly, nuclear magnetic resonance (NMR) analysis of the early oligomer fractions indicated linear, 4-, and 7-linked structures in marked contrast with DHI, which gives highly complex mixtures of partially degraded oligomers. Density functional theory (DFT) calculations supported the tendency of DHBT to couple via the 4- and 7-positions. These results uncover the role of nitrogen as a major determinant of the structural diversity generated by the polymerization of DHI, and point to replacement by sulfur as a viable entry to regioregular eumelanin-type materials for potential applications for surface functionalization by dip coating.

Electronic properties of TiO2-based materials characterized by high Ti3+ self-doping and low recombination rate of electron–hole pairs

Ti³⁺ self-doped black titania is obtained by a simple annealing in air without harsh conditions nor external reducing agents.

Sustainable hydrogen production from electroplating wastewater over a solar light responsive photocatalyst

An environmentally friendly and sustainable photocatalytic hydrogen production system was successfully developed using EDTA in the wastewater as the photo-excited hole scavenger and a solar light responsive material as the photocatalyst.