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Photoactive TiO2 materials based on a C@TiO2 core-shell structure synthesized according to the bottom-up strategy using a spherical resin core were presented in relation to commercial TiO2 (P25) used as a reference material. The studied TiO2 materials were modified with Ag nanoparticles using two alternative methods: impregnation and precipitation. Depending on the deposition technique used, different distributions of the Ag modifier were achieved within the TiO2 structure. As confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements, the precipitation technique resulted in the formation of almost twice smaller, highly dispersed Ag nanoparticles compared to impregnation. Furthermore, the effect of the performed modification on the textural properties (low-temperature N2 adsorption) and surface composition (X-ray photoelectron spectroscopy) was determined. The phase composition of the TiO2 support as well as the dispersion of the Ag modifier significantly affected the energy gap determined from UV–Vis spectra and, consequently, their performance in the process photodegradation of 4-nitrophenol tested as a model molecule. In the case of the @TiO2 material modified with highly dispersed Ag, significantly higher photoactivity in the visible light range was observed than in the presence of analogous P25-based materials.

Zeitschrift für Naturforschung / B 76(5), 275-280 (2021). doi:10.1515/znb-2021-0031, Published by De Gruyter, Berlin

Inorganic chemistry 60(2), 919-929 (2021). doi:10.1021/acs.inorgchem.0c03041, Published by American Chemical Society, Washington, DC

Spherical mesoporous carbon (with a particle size in the range of 40–75 μm) was synthesized by nanoreplication of a hard silica template using sucrose as the carbon precursor. The mesoporous carbon...

The development of smart and sustainable photocatalysts is in high priority for the synthesis of H

Catalysis science & technology (2022). doi:10.1039/d2cy00050d, Published by RSC Publ., London

The development of smart and sustainable photocatalysts is in high priority for the synthesis of H2O2 because the global demand for H2O2 is sharply rising. Currently, the global market share for H2O2 is around 4 billion US$ and is expected to grow by about 5.2 billion US$ by 2026. Traditional synthesis of H2O2 via the anthraquinone method is associated with the generation of substantial chemical waste as well as the requirement of a high energy input. In this respect, the oxidative transformation of pure water is a sustainable solution to meet the global demand. In fact, several photocatalysts have been developed to achieve this chemistry. However, 97% of the water on our planet is seawater, and it contains 3.0-5.0% of salts. The presence of salts in water deactivates the existing photocatalysts, and therefore, the existing photocatalysts have rarely shown reactivity toward seawater. Considering this, a sustainable heterogeneous photocatalyst, derived from hydrolysis lignin, has been developed, showing an excellent reactivity toward generating H2O2 directly from seawater under air. In fact, in the presence of this catalyst, we have been able to achieve 4085 ?M of H2O2. Expediently, the catalyst has shown longer durability and can be recycled more than five times to generate H2O2 from seawater. Finally, full characterizations of this smart photocatalyst and a detailed mechanism have been proposed on the basis of the experimental evidence and multiscale/level calculations.

A wide series of copolymer materials with various contents of 4-vinyl-diisopropyl-phtalate ester (10–90 mol%), divinylbenzene (1–11 mol%) and styrene, as monomers, were obtained by radical copolymerization. In the last steps of the synthesis, diisopropyl ester functionalities were converted into the form of N-hydroxyphthalimide (NHPI) rings. The obtained materials with the NHPI groups immobilized in the copolymer structure were studied by various physicochemical techniques, including FT-IR, UV-Vis-DR, XPS, elemental analysis, and tested as catalysts in aerobic oxidation of p-methoxytoluene in the presence of Co(II) acetate co-catalyst. Conversion of the aromatic substrate was correlated with the NHPI content and cross-linking degree. The best catalytic performance (conversions higher than 23%) was achieved for the copolymer catalysts containing 60% and 30% of 4-vinyl-diisopropyl-phtalate ester. At too high concentrations of NHPI and DVB, some of the NHPI groups were transformed into inactive (C=O)-N=O species or not available due to embedding inside the copolymer structure. The mechanism of the process involving both NHPI centers, forming phthalimide N-oxyl (PINO) radicals, and Co(II) cations was discussed. Stability of the developed catalysts was also tested. The opening of imide rings took place during the catalytic process, resulting in the formation of carboxyl groups and the release of hydroxylamine molecules. The deactivated catalyst could be easily regenerated by repeating two last steps of closing imide ring.

Lead cyanamide PbNCN was synthesized by solid-state metathesis between PbCl2 and Na2NCN in a 1 : 1 molar ratio, and its structure was confirmed from Rietveld refinement of X-ray data. Electronic-structure calculations of HSE06 density-functional type reveal PbNCN to be an indirect semiconductor with a band gap of 2.4 eV, in remarkable quantitative agreement with the measured value. Mott-Schottky experiments demonstrate PbNCN to be a p-type semiconductor with a flat-band potential of 2.3 eV vs. the reversible hydrogen electrode (RHE) which is commonly used to estimate the value of the valence band edge position. Moreover, thin films of powderous PbNCN were assembled into a photoelectrode for photoelectrochemical water splitting. On the example of p-type PbNCN, this study provides the first experimental evidence that MNCN compounds can be applied as photocathodes for reductive reactions in photoelectrochemical cells.

Quaternary tantalum-based oxynitrides ATa(O,N)3, with electronic band gaps between 1.8 and 2.4 eV, are promising materials for photochemical water-splitting. The tailoring of their surface properties is a critical aspect to obtain efficient hole extraction. We report on the origin of improved photoelectrochemical (PEC) water oxidation by means of acidic treatment for this class of compounds on the example of cubic CaTaO2N particles. We address the effect of acidic treatment by using complementary physical characterization techniques, such as X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), 1H and 14N solid-state nuclear magnetic resonance (NMR) spectroscopy, electron microscopy and electronic band structure calculations at the density functional theory (DFT) level. In combination with photoelectrochemical measurements, solid-state NMR indicates that the restructured surface displays a meaningfully higher concentration of terminating OH groups. Subsequent deposition of a nickel borate (NiBi) catalyst on the acid-treated surface yields a higher percentual upsurge of photocurrent in comparison to pristine CaTaO2N. Our results highlight the application of solid-state NMR spectroscopy for understanding of the semiconductor-catalyst interface in photochemical devices.

A bottom-up strategy was used to construct SiO2@ZrO2 core-shell materials with amorphous or tetragonal structure of ZrO2 induced by calcination temperature. After etching of the SiO2 core with NaOH, @ZrO2 hollow spheres were formed as supports for different amounts of CuO (2.5–15.0 wt% of Cu). Significant differences in porosity and distribution of Cu2+ species were identified by X-ray diffraction, low-temperature N2 adsorption, UV-vis-DR and X-ray photoelectron spectroscopy. The Cu-containing catalysts based on tetragonal @ZrO2 exhibited higher surface areas and surface concentrations of finely dispersed Cu2+ compared to the series prepared using amorphous @ZrO2. Moreover, CuO particles deposited on the tetragonal ZrO2 shells appeared to be easier reducible during temperature-programmed reduction (TPR) measurements. Consequently, these catalysts were more active in the total oxidation of toluene, which mainly proceeded by the Mars-van Krevelen mechanism. Nevertheless, an analysis of correlation between the catalytic activity and reducibility for both studied catalyst series revealed that oxygen vacancies present on the surface of tetragonal ZrO2 clearly promote the reaction rate. The developed materials can be considered as useful for commercial application due to high selectivity to the combustion products (CO2 and H2O) and stable work even in a wide range of toluene concentrations and a moisture presence.

Metal-free nitrogen-doped carbon is considered as a green functional material, but the structural determination of the atomic positions of nitrogen remains challenging. We recently demonstrated that directly-excited solid state 15N NMR (ssNMR) spectroscopy is a powerful tool for the determination of such positions in N-doped carbon at natural 15N isotope abundance. Here we report a green chemistry approach for the synthesis of N-doped carbon using cellulose as a precursor, and a study of the catalytic properties and atomic structures of the related catalyst. N-doped carbon (NH3) was obtained by the oxidation of cellulose with HNO3 followed by ammonolysis at 800 °C. It had a N content of 6.5 wt% and a surface area of 557 m2 g-1, and 15N ssNMR spectroscopy provided evidence for graphitic nitrogen besides regular pyrrolic and pyridinic nitrogen. This structural determination allowed probing the role of graphitic nitrogen in electrocatalytic reactions, such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and nitrite reduction reaction. The N-doped carbon catalyst (NH3) showed higher electrocatalytic activities in the OER and HER under alkaline conditions and higher activity for nitrite reduction, as compared with a catalyst prepared by the carbonization of HNO3-treated cellulose in N2. The electrocatalytic selectivity for nitrite reduction of the N-doped carbon catalyst (NH3) was directly related to the graphitic nitrogen functions. Complementary structural analyses by means of 13C and 1H ssNMR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and low-temperature N2 adsorption were performed and provided support to the findings. The results show that directly-excited 15N ssNMR spectroscopy at natural 15N abundance is generally capable of providing information on N-doped carbon materials if relaxation properties are favorable. It is expected that this approach can be applied to a wide range of solids with an intermediate concentration of N atoms.

The polycondensation of resorcinol and formaldehyde in a water–ethanol mixture using the adapted Stöber method was used to obtain resol resins. An optimization of synthesis conditions and the use of an appropriate stabilizer (e.g., poly(vinyl alcohol)) resulted in spherical grains. The resins were carbonized in the temperature range of 600–1050 °C and then chemically activated in an aqueous HNO3 solution, gaseous ammonia, or by an oxidation–reduction cycle (soaking in a HNO3 solution followed by treatment with NH3). The obtained carbons were characterized by XRD, the low-temperature adsorption of nitrogen, SEM, TGA, and XPS in order to determine degree of graphitization, porosity, shape and size of particles, and surface composition, respectively. Finally, the materials were tested in phenol adsorption. The pseudo-second order model perfectly described the adsorption kinetics. A clear correlation between the micropore volume and the adsorption capacity was found. The content of graphite domains also had a positive effect on the adsorption properties. On the other hand, the presence of heteroatoms, especially oxygen groups, resulted in the clogging of the pores and a decrease in the amount of adsorbed phenol.

Valorization of lignin is still an open question and lignin has therefore remained an underutilized biomaterial. This situation is even more pronounced for hydrolysis lignin, which is characterized by a highly condensed and excessively cross-linked structure. We demonstrate the synthesis of photoactive lignin/Bi

Valorization of lignin is still an open question and lignin has therefore remained an underutilized biomaterial. This situation is even more pronounced for hydrolysis lignin, which is characterized by a highly condensed and excessively cross-linked structure. We report on photoactive lignin/Bi4O5Br2/BiOBr bio-inorganic composites consisting of a lignin substrate that is coated by Bi4O5Br2/BiOBr nanosheet photocatalysts. The structure of the hybrid material was investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy including energy dispersive X-ray (EDX) spectroscopy, and solid state 1H−13C nuclear magnetic resonance spectroscopy (1H−13C NMR). The material contains 18.9% of Bi4O5Br2/BiOBr and was found to be effective for the photocatalytic degradation of cationic methylene blue (MB) and zwitterionic rhodamine B (RhB) dyes under irradiation with 405 nm light. Lignin/Bi4O5Br2/BiOBr was able to decrease the dye concentration from 80 mg·L–1 to 12.3 mg·L–1 for RhB (85%) and from 80 mg·L–1 to 4.4 mg·L–1 for MB (95%). Complementary to the dye degradation, the lignin as a main component of the composite, was found to be efficient and rapid biosorbent for metal ions in aqueous solutions. The highest adsorption capacity was found after 2 hours of phases contact and reached 0.45 mmol·g–1 for Ni(II) ions (neutral media). The low cost, simplicity of the synthesis, good stability and ability to simultaneously photooxidize organic dyes and to adsorb metal ions, make the developed photoactive lignin/Bi4O5Br2/BiOBr composite a prospective material for textile wastewaters remediation

International audience; Dealuminated BEA zeolite (SiBEA) was chosen as a support of metal oxide(s) phase for catalytic combustion of volatile organic compounds (VOCs). Copper and/or manganese oxide(s) were deposited at various Cu/Mn molar ratios. Factors influencing the catalytic activity were found by chosen physicochemical methods, including XRD, XRF, low-temperature N2 adsorption, FT-IR, UV–Vis-DRS, STEM-EDX, XPS and H2-TPR. Depending on the chemical composition, CuO, (CuxMn3-x)1-δO4, Cu-doped Mn3O4 or Mn2O3 was formed as the dominant phase. The active phase particles were located mainly in the interparticle voids of the zeolite support. SiBEA gained Lewis acid sites after the introduction of the metal oxide phase, especially in the case of CuO deposition. The presence of copper in the catalytic system resulted in enhanced reducibility of the active phase, and in a consequence in high catalytic activity in the total oxidation of aromatic VOCs, which proceeds according to the Mars-van Krevelen mechanism. After the introduction of Mn, the co-existence of different valence forms was found due to the redox equilibrium: Cu2+ + Mn3+ = Cu+ + Mn4+. Definitely, the addition of Mn to Cu/SiBEA increased the number of available surface vacancies and had a beneficial effect on the catalytic performance.

Metal-free nitrogen-doped carbon is considered as a green functional material, but the structural determination of the atomic positions of nitrogen remains challenging. We recently demonstrated that directly-excited solid state 15N NMR (ssNMR) spectroscopy is a powerful tool for the determination of such positions in N-doped carbon at natural 15N isotope abundance. Here we report a green chemistry approach for the synthesis of N-doped carbon using cellulose as a precursor, and a study of the catalytic properties and atomic structures of the related catalyst. N-doped carbon (NH3) was obtained by the oxidation of cellulose with HNO3 followed by ammonolysis at 800 °C. It had a N content of 6.5 wt% and a surface area of 557 m2 g-1, and 15N ssNMR spectroscopy provided evidence for graphitic nitrogen besides regular pyrrolic and pyridinic nitrogen. This structural determination allowed probing the role of graphitic nitrogen in electrocatalytic reactions, such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and nitrite reduction reaction. The N-doped carbon catalyst (NH3) showed higher electrocatalytic activities in the OER and HER under alkaline conditions and higher activity for nitrite reduction, as compared with a catalyst prepared by the carbonization of HNO3-treated cellulose in N2. The electrocatalytic selectivity for nitrite reduction of the N-doped carbon catalyst (NH3) was directly related to the graphitic nitrogen functions. Complementary structural analyses by means of 13C and 1H ssNMR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and low-temperature N2 adsorption were performed and provided support to the findings. The results show that directly-excited 15N ssNMR spectroscopy at natural 15N abundance is generally capable of providing information on N-doped carbon materials if relaxation properties are favorable. It is expected that this approach can be applied to a wide range of solids with an intermediate concentration of N atoms.

A facile method of fabrication of ceramic monoliths assisted by 3D printing was developed for preparation of Co3O4-based catalysts of total oxidation of volatile organic compounds. The proposed approach was based on the production of a resin template, which was subsequently used at a casting step for the construction of corundum monolith. The walls of this material were additionally coated with a MFI zeolite layer providing the possibility of modification with a Co3O4 precursor using ion-exchange and impregnation techniques. The parent and Co3O4-modified monoliths with varying active phase content were characterized by SEM/EDS, XRD, XRF, XPS, UV–vis-DR and H2-TPR. Their catalytic performance in the toluene combustion was also tested. It was shown that the formation of Co3O4 spinel particles highly dispersed on the zeolite-coated monolith resulted in excellent catalytic activity measured by very high TOF values. Furthermore, stability tests confirmed that the obtained monolith catalysts can work for prolonged reaction time without noticeable changes in the toluene conversion and selectivity to CO2.

Valorization of lignin is still an open question and lignin has therefore remained an underutilized biomaterial. This situation is even more pronounced for hydrolysis lignin, which is characterized by a highly condensed and excessively cross-linked structure. We demonstrate the synthesis of photoactive lignin/Bi4O5Br2/BiOBr bio-inorganic composites consisting of a lignin substrate that is coated by semiconducting nanosheets. The XPS analysis reveals that growing these nanosheets on lignin instead on cellulose prevents the formation of Bi5+ ions at the surface region, yielding thus a modified heterojunction Bi4O5Br2/BiOBr. The material contains 18.9% of Bi4O5Br2/BiOBr and is effective for the photocatalytic degradation of cationic methylene blue (MB) and zwitterionic rhodamine B (RhB) dyes under light irradiation. Lignin/Bi4O5Br2/BiOBr decreases the dye concentration from 80 mg L−1 to 12.3 mg L−1 for RhB (85%) and from 80 mg L−1 to 4.4 mg L−1 for MB (95%). Complementary to the dye degradation, the lignin as a main component of the composite, was found to be efficient and rapid biosorbent for nickel, lead, and cobalt ions. The low cost, stability and ability to simultaneously photo-oxidize organic dyes and adsorb metal ions, make the photoactive lignin/Bi4O5Br2/BiOBr composite a prospective material for textile wastewaters remediation and metal ions recycling.

Mixed-anion inorganic compounds offer diverse functionalities as a function of the different physicochemical characteristics of the secondary anion. The quaternary metal oxynitrides, which originate from substituting oxygen anions (O2–) in a parent oxide by nitrogen (N3–), are encouraging candidates for photoelectrochemical (PEC) water splitting because of their suitable and adjustable narrow band gap and relative negative conduction band (CB) edge. Given the known photochemical activity of LaTiO2N, we investigated the paramagnetic counterpart NdTiO2+xN1–x. The electronic structure was explored both experimentally and theoretically at the density functional theory (DFT) level. A band gap (Eg) of 2.17 eV was determined by means of ultraviolet–visible (UV–vis) spectroscopy, and a relative negative flat band potential of −0.33 V vs reversible hydrogen electrode (RHE) was proposed via Mott–Schottky measurements. 14N solid state nuclear magnetic resonance (NMR) signals from NdTiO2+xN1–x could not be detected, which indicates that NdTiO2+xN1–x is berthollide, in contrast to other structurally related metal oxynitrides. Although the bare particle-based photoanode did not exhibit a noticeable photocurrent, Nb2O5 and CoOx overlayers were deposited to extract holes and activate NdTiO2+xN1–x. Multiple electrochemical methods were employed to understand the key features required for this metal oxynitride to fabricate photoanodes., The structural properties of the prospective metal oxynitride NdTiO2+xN1−x were experimentally and theoretically investigated. The band edge positions make the compound theoretically suitable for overall photochemical water splitting.

Nanoscale 13(2), 869-877 (2021). doi:10.1039/D0NR06993K, Published by RSC Publ., Cambridge

Mixed-anion inorganic compounds offer diverse functionalities as a function of the different physicochemical characteristics of the secondary anion. The quaternary metal oxynitrides, which originate from substituting oxygen anions (O2–) in a parent oxide by nitrogen (N3–), are encouraging candidates for photoelectrochemical (PEC) water splitting owing to their suitable and adjustable narrow band gap and relative negative conduction band (CB) edge. Given the known photochemical activity of LaTiO2N, we investigated the paramagnetic counterpart NdTiO2N. The electronic structure was explored both experimentally and theoretically at the density-functional theory (DFT) level. A band gap (Eg) of 2.04 eV was determined by means of Ultraviolet-visible (UV-vis) spectroscopy, and a relative negative flat band potential of –0.33 V vs. reversible hydrogen electrode (RHE) was proposed via Mott–Schottky measurements. 14N solid state nuclear magnetic resonance (NMR) signals from NdTiO2N could not be detected,which indicates that NdTiO2N is berthollide, in contrast to other structurally related metal oxynitrides. Although the bare particle-based photoanode did not exhibit noticeable photocurrent, Nb2O5 and CoOx overlayers were deposited to extract holes and activate NdTiO2N. Multiple electrochemical methods were employed to understand the key features required for this metal oxynitride in order to fabricate photoanodes.

Bismuth(III) oxide-carbodiimide (Bi2O2NCN) has been recently discovered as a novel mixed-anion semiconductor, which is structurally related to bismuth oxides and oxysulfides. Given the structural versatility of these layered structures, we investigated the unexplored photochemical properties of the target compound for photoelectrochemical (PEC) water oxidation. Although Bi2O2NCN does not generate a noticeable photocurrent as a single photoabsorber, the fabrication of heterojunctions with the WO3 thin film electrode shows an upsurge of current density from 0.9 to 1.1 mA cm–2 at 1.23 V vs reversible hydrogen electrode (RHE) under 1 sun (AM 1.5G) illumination in phosphate electrolyte (pH 7.0). Mechanistic analysis and structural analysis using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (STEM EDX) indicate that Bi2O2NCN transforms during operating conditions in situ to a core–shell structure Bi2O2NCN/BiPO4. When compared to WO3/BiPO4, the in situ electrolyte-activated WO3/Bi2O2NCN photoanode shows a higher photocurrent density due to superior charge separation across the oxide/oxide-carbodiimide interface layer. Changing the electrolyte from phosphate to sulfate results in a lower photocurrent and shows that the electrolyte determines the surface chemistry and mediates the PEC activity of the metal oxide-carbodiimide. A similar trend could be observed for CuWO4 thin film photoanodes. These results show the potential of metal oxide-carbodiimides as relatively novel representatives of mixed-anion compounds and shed light on the importance of the control over the surface chemistry to enable the in situ activation., Phosphate electrolyte activates the metal oxide−Bi2O2NCN heterojunction.

Metal-free nitrogen-doped carbon is considered as a green functional material, but the structural determination of the atomic positions of nitrogen remains challenging. We recently demonstrated that directly-excited solid state 15N NMR (ssNMR) spectroscopy is a powerful tool for the determination of such positions in an N-doped carbon at natural 15N isotope abundance. Here we present a green chemistry approach to the synthesis of N-doped carbon using cellulose as precursor, and a study of the catalytic properties and atomic structures of the related catalyst. The N-doped carbon (NH3) was obtained by oxidation of cellulose with HNO3 followed by ammonolysis at 800°C. It had a N content of 6.5 wt.% and a surface area of 557 m2 g–1, and 15N ssNMR spectroscopy provided evidence for graphitic nitrogen besides of regular pyrrolic and pyridinic nitrogen. This structure determination enabled probing the role of graphitic nitrogen for electrocatalytic reactions, such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and nitrite reduction reaction. The N-doped carbon catalyst (NH3) had higher electrocatalytic activities in OER and HER under alkaline conditions and a higher activity for nitrite reduction, as compared with a catalyst prepared by carbonization of the HNO3-treated cellulose in N2. The electrocatalytic selectivity for nitrite reduction of the N-doped carbon catalyst (NH3) was directly related to the graphitic nitrogen functions. Complementary structural analysis by means of 13C and 1H ssNMR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and low-temperature N2 adsorption were preformed and provided support to the findings. The results show that directly-excited 15N ssNMR at natural 15N abundance is generally capable to provide information on N-doped carbon materials, and it is expected that the approach can be applied to a wide range of solids with an intermediate amount of N atoms.

Tin(ii) oxide carbodiimide is a novel prospective semiconductor material with a band gap of 2.1 eV and lies chemically between metal oxides and metal carbodiimides. We report on the photochemical properties of this oxide carbodiimide and apply the material to form a heterojunction with CuWO

Nd modified TiO2 photocatalysts containing 0.15–1.5 wt.% of Nd (wt.% Nd determined by XRF) as well as parent TiO2 were investigated for the photocatalytic oxidation of CH3OH. The photocatalysts were prepared by the common sol-gel method followed by thermal treatment. The textural, structural and electronic properties of all synthesized photocatalysts were characterized by nitrogen physisorption, powder X-ray diffraction, X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, Raman spectrometry, DR UV–vis spectroscopy, electron paramagnetic resonance spectroscopy and photoelectrochemical measurements. It was revealed that all materials show comparable band gap energy and phase composition. However, the addition of different amounts of Nd in the range of 0.15–1.5 wt.% significantly affected the TiO2 crystallite size, the specific surface area, the amount of surface O species and subsequently also the photocurrent response. The positive role of neodymium was proved at its very low loading, i.e. for Nd/TiO2 with 0.15 wt.% Nd which exhibited the highest photocatalytic activity. The photocatalytic activity was promoted by both increasing crystallite size of TiO2 and decreasing amount of surface O species.

CuWO4 is a photoanode candidate in neutral pH, and manganese-based oxygen evolution reaction electrocatalysts are of high interest due to their low price and low toxicity. Considering the unexplored chemistry of transition-metal carbodiimides/cyanamides for the PEC water oxidation, we investigated MnNCN as an electrocatalyst for CuWO4 under AM 1.5G illumination in potassium phosphate electrolyte (pH 7). Surface functionalization of CuWO4 photoanodes with MnNCN increased the photocurrent from 22 to 30 μA cm-2 at 1.23 V vs RHE. Complementary structural analysis by means of XRD and XPS revealed that MnNCN forms a core-shell structure MnNCN@MnPO x in phosphate electrolyte and mimics a manganese phosphate electrocatalyst. As such, the surface chemistry of MnNCN significantly differs from previous studies on the cobalt analogue (CoNCN). A separately prepared MnNCN electrode developed a small but detectable photocurrent due to photogenerated holes inside the semiconducting carbodiimide core of the MnNCN@MnPO x structure.

Copper-containing mixed metal oxides were studied as catalysts for selective catalytic oxidation of ammonia. The performed research shows a high correlation between Cu amount and catalyst efficiency, especially dinitrogen selectivity. Copper species, mainly in the form of highly dispersed CuO oxides, were found to be responsible for high N2 selectivity, which decreased with increasing Cu loading and the formation of CuO bulk-like species. The addition of cerium seemed to have an effect on material’s catalytic activity and N2 selectivity. The increase in selectivity towards N2 of Ce-impregnated materials was attributed to the formation of copper-cerium redox couples on the material’s surface. The catalytic tests performed under different NH3/O2 molar ratios revealed that the developed materials exhibit high catalytic activity in a wide range of ammonia concentrations and oxygen contents.

Bearing in mind the need to develop optimal transition metal oxide-based catalysts for the combustion of volatile organic compounds (VOCs), yolk-shell materials were proposed. The constructed composites contained catalytically active Co3O4 nanoparticles, protected against aggregation and highly dispersed in a shell made of porous SiO2, forming a specific type of nanoreactor. The bottom-up synthesis started with obtaining spherical poly(styrene-co-acrylic acid) copolymer (PS30) cores, which were then covered with the SiO2 layer. The Co3O4 active phase was deposited by impregnation using the PS30@SiO2 composite as well as hollow SiO2 spheres with the removed copolymer core. Structure (XRD), morphology (SEM), chemical composition (XRF), state of the active phase (UV-Vis-DR and XPS) and reducibility (H2-TPR) of the obtained catalysts were studied. It was proven that the introduction of Co3O4 nanoparticles into the empty SiO2 spheres resulted in their loose distribution, which facilitated the access of reagents to active sites and, on the other hand, promoted the involvement of lattice oxygen in the catalytic process. As a result, the catalysts obtained in this way showed a very high activity in the combustion of toluene, which significantly exceeded that achieved over a standard silica gel supported Co3O4 catalyst.

A modular synthesis concept to prepare a library of mainly amorphous porous carbons has been developed. The carbons show – while keeping the textural properties nearly unchanged - systematically varied features such as the content of nitrogen, oxygen, iron and graphitic species, respectively. These individual features and the cross-relations between them were characterized with respect to applications of the carbons as reactants or catalysts in different test reactions, namely the temperature-programmed oxidation (TPO), the oxidation of sulphurous acid (OSA), the electrochemical oxygen reduction reaction (ORR) and the oxidative dehydrogenation of ethylbenzene (ODH), respectively. The carbon materials show striking similarities in terms of catalytic activity in TPO, OSA and ORR, respectively. The influence of individual nitrogen species and graphitic species on the catalytic behaviour was analyzed in detail. Pyrrole-like nitrogen species are obviously beneficial for the activation of molecular oxygen in different test reactions while pyridine-like species do not affect the catalytic behaviour. Graphitic species do not significantly influence the catalytic activity of otherwise amorphous carbons. For ODH, it was shown that nitrogen functionalities enhance the overall catalyst deactivation by catalysing the destruction of active sites.

We investigated CuWO4 as a promising photoanode and its surface functionalization with Ag2NCN. The composite photoanode displays a synergetic effect between its constituents during photoelectrochemical (PEC) water oxidation. After placing Ag2NCN particles on the CuWO4 thin film, the photocurrent density increases from 15 to 45 μA cm–2 at 1.23 V vs reversible hydrogen electrode (RHE) in phosphate buffer electrolyte at pH 7 under simulated AM1.5 G illumination. The different positions of the band edges of CuWO4 and Ag2NCN favor charge carrier separation at their interface. Upon illumination, photogenerated electrons of both semiconductors are transferred to the conduction band and can migrate to the counterelectrode. The higher position of the conduction band edge of Ag2NCN allows its electrons to be injected into the conduction band of CuWO4. Simultaneously, holes from the cyanamide are blocked, because the valence band edge position of CuWO4 is positioned lower than for Ag2NCN. This results in more effici...

Sunlight can be used to split water into hydrogen and oxygen by means of a photoelectrochemical (PEC) cell. Oxide nanostructures in heterojunction geometry, consisting of anisotropic WO3 nanostructures coated with a second narrower bandgap semiconductor, such as α-Fe2O3, have emerged as prospective photoanodes. We report on the integration of monodisperse CoPd nanocrystals (NCs) with α-Fe2O3 and WO3/α-Fe2O3 heterojunction semiconductor nanostructures for PEC water oxidation. Depositing CoPd NCs on the surface of hematite leads to more stable photocurrents in comparison to the bare electrode, which indicates improved electron-hole separation at the semiconductor-electrolyte interface. Altering the surface of WO3/α-Fe2O3 photoanodes with CoPd NCs induces a cathodic shift of the onset potential and increases photocurrent density from 0.15 to 0.5 mA cm-2 during water oxidation at 1.23 V vs. RHE under AM 1.5 G illumination (pH 7).

ACS applied materials & interfaces 12(26), 29173-29180 (2020). doi:10.1021/acsami.0c03975, Published by American Chemical Society, Washington, DC

Tin(II) oxide carbodiimide is a novel prospective semiconductor material with a band gap of 2.1 eV and lies chemically between metal oxides and metal carbodiimides. We report on the photochemical properties of this oxide carbodiimide and apply the material to form a heterojunction with CuWO4 thin films for photoelectrochemical (PEC) water oxidation. Mott–Schottky experiments reveal that the title compound is an n-type semiconductor with a flat-band potential of −0.03 V and, as such, the position of the valence band edge would be suitable for photochemical water oxidation. Sn2O(NCN) increases the photocurrent of CuWO4 thin films from 32 μA cm−2 to 59 μA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) in 0.1 M phosphate buffer (pH 7.0) under backlight AM 1.5G illumination. This upsurge in photocurrent originates in a synergistic effect between the oxide and oxide carbodiimide, because the heterojunction photoanode displays a higher current density than the sum of its individual components. Structural analysis by powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) reveals that Sn2O(NCN) forms a core–shell structure Sn2O(NCN)@SnPOx during the PEC water oxidation in phosphate buffer. The electrochemical activation is similar to the behavior of Mn(NCN) but different from Co(NCN).

Chemical communications : ChemComm 56(86), 13193-13196 (2020). doi:10.1039/D0CC04894A, Published by The Royal Society of Chemistry, Cambridge

Nanoscale 12(5), 3121-3128 (2020). doi:10.1039/C9NR09818F, Published by RSC Publ., Cambridge

A nanowire photoanode SrTaO2N, a semiconductor suitable for overall water-splitting with a band gap of 2.3 eV, was coated with functional overlayers to yield a core–shell structure while maintainin...

Iron was deposited on MCM-41 using template ion-exchange (TIE) method. Solutions of FeCl2 and [Fe3(OAc)6O(H2O)3]NO3 were used as precursors of deposited iron species. It was shown that deposition of significant amount of iron, in some cases above 10 wt.% in recalculation to Fe2O3, on MCM-41 or Ti-MCM-41 resulted only in a relatively small decrease of the specific surface area and porosity of the mesoporous silica supports. Moreover, in case of iron acetate oligocations deposition, the formation of iron oxide micro-rods outside of the MCM-41 structure was found. Such effect was not observed when a solution of FeCl2 was used for iron deposition. MCM-41 and Ti-MCM-41 modified with iron by TIE method were found to be active catalysts for the process of the selective oxidation NH3 to N2 (NH3-SCO). In this process, the catalysts effectively operated in the high-temperature range with a very high selectivity to dinitrogen (above 90% at 550 °C). Some differences in catalytic performance, related to type of the mesoporous support as well as iron loading and precursor used for deposited iron species, were observed.

A synthesis of metal oxide modified clays based on the hydrogel template assisted route was proposed. This novel method was verified by an intercalation of poly(acrylic acid) (PAA) into the interlayer space of montmorillonite (MT) using the in situ polymerization technique. The obtained hydrogel/clay composite with a MT/PAA mass ratio close to 1.0 exhibited an expanded layered structure and an excellent adsorption capacity for transition metal cations. These features were exploited to the modification of MT-PAA material with various amounts of Fe3+ cations by deposition at controlled pH = 2.5. The introduced Fe species favored the hydrogel burning, therefore in a subsequent step the organic template could be easily removed by calcination under oxidizing conditions at temperature protecting the clay against deep dehydroxylation. A gradual delamination of MT with an increase in the Fe content was observed after thermal treatment. This effect resulted in opening of the MT structure, manifested by a relatively high surface area and a large porosity. XRD, TEM, UV–Vis-DRS and XPS measurements exhibited that the formed α-Fe2O3 nanoparticles were highly dispersed on the exfoliated clay, which comprised a framework stabilizing the nanophase.

Cobalt mixed oxide with cesium promoter was deposited on different ceramic open-cell foams (Al2O3 + SiO2, ZrO2 and SiO2 + Al2O3 + C-graphite, Lanik Ltd., Czech Republic) by wet impregnation method. The catalysts were tested for N2O decomposition and characterized by AAS, XRD, TPR-H2, FTIR, Raman, XPS, SEM and nitrogen adsorption. The same impregnation procedure resulted in different amounts of deposited Co3O4-Cs on each support and different dispersion of Co3O4 and Cs on the surface. The Al2O3+SiO2 (Al-Si) based ceramic foam was recognized as the most suitable support. The difference in the catalytic activity of unsupported Co3O4-Cs and Co-Cs/Al-Si could be explained in terms of different dispersion levels of individual components on the support, leading to changes in the Cs/Co surface molar ratio of atoms in close contact and subsequent changes in reducibility. Direct correlation of specific rate constant for N2O decomposition and surface Cs/Co molar ratio was found.

A capacitive sensor based on S-{12-[1-(pyridin-4-ylmethyl)-1H-1,2,3-triazol-4-yl]dodecyl} ethanethioate (FT), a compound with a functional group exhibiting selective affinity towards Cr(VI) ions, was developed. FT was mixed with shorter-chain thiol-decanethiol (DT), to obtain an Au electrode surface well covered by a thiol monolayer. The composition and high quality of self-assembled monolayers (SAMs) were crucial factors influencing the performance of the capacitive sensor. In this work, SAMs formed from FT and DT mixtures with different compositions were studied. For physicochemical characterization of SAMs X-ray photoelectron spectroscopy (XPS), contact angle measurements as well as atomic force microscopy (AFM) were used. Cyclic voltammetry was employed to estimate an electrode surface coverage. Based on the obtained results, the composition of thiol layer providing the best parameters for capacitive sensing of chromium(VI) was chosen. Moreover, the analytical performance of sensor was verified.