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A new photocatalyst for CO2 reduction has been presented. The photocatalyst was prepared from a combination of a commercial P25 with a mesopore structure and carbon spheres with a microporous structure with high CO2 adsorption capacity. Then, the obtained hybrid TiO2-carbon sphere photocatalysts were deposited on a glass fiber fabric. The combined TiO2-carbon spheres/silica cloth photocatalysts showed higher efficiency in the two-electron CO2 reduction towards CO than in the eight-electron reaction to methane. The 0.5 g graphitic carbon spheres combined with 1 g of TiO2 P25 resulted in almost 100% selectivity to CO. From a practical point of view, this is promising as it economically eliminates the need to separate CO from the gas mixture after the reaction, which also contains CH4 and H2.

Three nanocrystalline samples of ZnO doped with MnO (with 20, 30, and 40 wt% of MnO in initial mixture) were synthesized by the wet chemical method. Previous X-ray diffraction study has found that they contained only hexagonal ZnO and cubic ZnMnO3 nanocrystals. DC magnetization study revealed a paramagnetic (PM) state above 50 K, the presence of mixed valence of Mn ions (Mn3+ and Mn4+) and an important role played by magnetic clusters influencing the behavior of the effective magnetic moment and effective interaction type. Low temperature results indicated a chain of magnetic transformation from PM to ferrimagnetic, to superparamagnetic and to blocked states. Electron spin resonance (ESR) provided additional information about magnetic relaxation of the spin clusters and possible location of separate Mn2+ and Mn4+ ions. Large magnetic inhomogeneity of our samples was evidenced, and it is the result of magnetic ions clustering, various valences of Mn ions, distribution of nanoparticle sizes, and competition of magnetic interactions.

This work aimed to obtain hybrid composites based on photoactive metal oxide and carbon having adsorption properties. The materials, composed of titanium dioxide or zinc oxide and spherical carbon, were obtained from resorcinol-formaldehyde resin, treated in a solvothermal reactor heated with microwaves and then subjected to carbonization, were received. The functional groups of pure carbon spheres (unsaturated stretching C=C, stretching C-OH and C-H bending vibrations), CS/ZnO and CS/TiO

A new approach to hydrogen production from water is described. This simple method is based on carbon dioxide-mediated water decomposition under UV radiation. The water contained dissolved sodium hydroxide, and the solution was saturated with gaseous carbon dioxide. During saturation, the pH decreased from about 11.5 to 7-8. The formed bicarbonate and carbonate ions acted as scavengers for hydroxyl radicals, preventing the recombination of hydroxyl and hydrogen radicals and prioritizing hydrogen gas formation. In the presented method, not yet reported in the literature, hydrogen production is combined with carbon dioxide. For the best system with alkaline water (0.2 m NaOH) saturated with CO

Zinc chloride and potassium oxalate are often applied as activating agents for carbon materials. In this work, we present the preparation of ZnO/carbon spheres composites using resorcinol-formaldehyde resin as a carbon source in a solvothermal reactor heated with microwaves. Zinc chloride as a zinc oxide source and potassium oxalate as an activating agent were applied. The effect of their addition and preparation conditions on the adsorption properties towards carbon dioxide at 0 °C and 25 °C were investigated. Additionally, for all tested sorbents, the CO

This study determines the effect of spent garnet as a replacement for natural sand in 3D-printed mortar at early ages. Five mixes with different spent garnet amounts were prepared (0%, 25%, 50%, 75% and 100% by volume). The ratio of binder to aggregate remained unchanged. In all mixes the water/binder ratio was assumed as a constant value of 0.375. Tests were performed to confirm the printability of the mix (a path quality test using a gantry robot with an extruder). Determinations of key buildability properties of the mix (green strength and Young’s Modulus) during uniaxial compressive strength at 15 min, 30 min and 45 min after adding water were conducted. A hydraulic press and the GOM ARAMIS precision image analysis system were used to conduct the study. The results showed that an increase in spent garnet content caused a decrease in green strength and Young’s Modulus (up to 69.91% and 80.37%, respectively). It was found that to maintain proper buildability, the recommended maximum replacement rate of natural sand with garnet is 50%. This research contributes new knowledge in terms of using recycled waste in the 3D printing technology of cementitious materials.

This paper examines the synthesis of the ZnO/carbon spheres composites using resorcinol—formaldehyde resin as a carbon source and zinc nitrate as a zinc oxide source in a solvothermal reactor heated with microwaves. The influence of activation with potassium oxalate and modification with zinc nitrate on the physicochemical properties of the obtained materials and CO2 adsorption capacity was investigated. It was found that in the case of nonactivated material as well as activated materials, the presence of zinc oxide in the carbon matrix had no effect or slightly increased the values of CO2 adsorption capacity. Only for the material where the weight ratio of carbon:zinc was 2:1, the decrease of CO2 adsorption capacity was reported. Additionally, CO2 adsorption experiments on nonactivated carbon spheres and those activated with potassium oxalate with different amounts of zinc nitrate were carried out at 40 °C using thermobalance. The highest CO2 adsorption capacity at temperature 40 °C (2.08 mmol/g adsorbent) was achieved for the material after activation with potassium oxalate with the highest zinc nitrate content as ZnO precursor. Moreover, repeated adsorption/desorption cycle experiments revealed that the as-prepared carbon spheres were very good CO2 adsorbents, exhibiting excellent cyclic stability with a performance decay of less than 10% over up to 25 adsorption-desorption cycles.

A simple method of hydrogen production through the decomposition of water subjected to UV radiation is presented. Water contained dissolved sodium hydroxide and the solution was saturated with carbon dioxide gas. During saturation, the pH value dropped from about 11.5 to 7-8. The produced bicarbonate and carbonate ions acted as scavengers for hydroxyl radicals, preventing recombination of hydroxyl and hydrogen radicals, and giving priority to the formation of hydrogen gas.In the presented method, the production of hydrogen is combined with the utilization of carbon dioxide.

In this work, low-pressure synthesis of carbon spheres from resorcinol and formaldehyde using an autoclave is presented. The influence of reaction time and process temperature as well as the effect of potassium oxalate, an activator, on the morphology and CO2 adsorption properties was studied. The properties of materials produced at pressureless (atmospheric) conditions were compared with those synthesized under higher pressures. The results of this work show that enhanced pressure treatment is not necessary to produce high-quality carbon spheres, and the morphology and porosity of the spheres produced without an activation step at pressureless conditions are not significantly different from those obtained at higher pressures. In addition, CO2 uptake was not affected by elevated pressure synthesis. It was also demonstrated that addition of the activator (potassium oxalate) had much more effect on key properties than the applied pressure treatment. The use of potassium oxalate as an activator caused non-uniform size distribution of spherical particles. Simultaneously higher values of surface area and total pore volumes were reached. A pressure treatment of the carbon materials in the autoclave significantly enhanced the CO2 uptake at 25 &deg, C, but had no effect on it at 0 &deg, C.

ZnO nanoparticles doped with transition metal ions are intensively studied nanomaterials, due to their charges and the spins of electrons that provides new magnetic, optical and transport properties. They find a vast range of applications, ranging from optoelectronics to spintronics. In this context especially important is the room temperature ferromagnetism observed for ZnO doped nanomaterials, although this phenomenon is still a controversial and open topic in material science, mostly due to low reproducibility of results from samples prepared by different techniques. In the first part of this article a short review of papers using magnetometric methods to determine the magnetic characteristics of Co-doped ZnO nanomaterials is presented. Different models introduced to explain room temperature ferromagnetism (carrier mediated ferromagnetism, Co2+-oxygen vacancy pairs, blocked superparamagnetic clusters, Co2+-Zn interstitial pairs, heterogeneous distribution of magnetic ions) are examined and discussed. In the second part, magnetisation study of a new series of nCoO/(1-n)ZnO nanocomposites synthesized by hydrothermal method under higher than previously applied pressure will be described. The obtained experimental results will be analysed and information on magnetic systems responsible for the observed characteristics and the involved magnetic interactions will be deduced.

We have studied the magnetic properties of nanocrystals of ZnO :MnO prepared by traditional wet chemistry method. The detailed structural and morphological characterization was performed. The results of systematic measurements of AC magnetic susceptibility as a function of temperature and frequency as well as DC magnetization are reported. We observed two different types of magnetic behavior depending on the concentration doping. For samples with low nominal content (up to 30 wt% of MnO), superparamagnetic behavior was observed. We attribute the observed superparamagnetism to the presence of nanosized ZnMnO 3 phase. For nanocrystals doped above nominal 60 wt% of MnO ferrimagnetism was detected with TC at around 42 K. This magnetic behavior we assign to the presence of nanosized Mn3O4 phase.

Carbon spheres were prepared by carbonisation of phenolic resin spheres obtained using a modified Stober method in a microwave assisted solvothermal reactor. Preparation process involved water–ethanol, ammonia water, resorcinol, potassium oxalate and formaldehyde. The mixture was stirred for 24 h at room temperature and then subjected to a pressure treatment, in which the solution was treated in a microwave assisted solvothermal reactor for 15 min at a pressure of 1–3 MPa. The proposed synthesis resulted in a material containing microporous carbon spheres having high surface area (from 1178 to 1648 m2/g), with diameters from 200 to 350 nm, total pore volume from 0.49 to 0.78 cm3/g, and high CO2 adsorption capacity from 3.86 to 5.03 mmol/g measured at 0.1 MPa and 25 °C. Taking into account the properties of the obtained material, it can be applied as a sorbent for CO2 capture.

The ZnO/ZnMn2O4 nanocomposite (ZnMn) was used as adsorbent for the removal of cationic dye Basic Yellow 28 (BY28) from aqueous solutions. The adsorbent was characterized by X-ray diffraction, scann...

The effect of an alkali treatment (potassium hydroxide) on the properties of a commercial activated carbon has been studied. The aim of the treatment was to improve the adsorption properties of the material toward carbon dioxide. In the result of the treatment, silica contained in the raw carbon was removed and the density of the material increased. The changes in the surface chemistry were observed as well. The treatment of the activated carbon with KOH resulted in a complete removal of carboxy and lactone groups and a decrease of the general content of the acidic groups (more significant than that of basic groups). Simultaneously, the surface concentration of hydroxyl groups increased. The alkali treatment of activated carbon resulted in an increase of carbon dioxide uptake of 14% (measured using a volumetric method at 0℃). The adsorption of carbon dioxide on activated carbon has a mixed (physicochemical) character and that two types of adsorption sites are present at the surface. The adsorption energy varies roughly from 25 to 60 kJ/mol.

In this work, production and characterization of carbon spheres from resorcinol and formaldehyde, using a microwave assisted solvothermal reactor, is presented. The influence of different experimental conditions, e.g., reaction time, pressure, and power, on the structure of the obtained materials, and carbon dioxide adsorption properties, was studied. Using the method described in this work, it is possible to significantly reduce the reaction time, to as low as 10 min, compared with widely described processes carried out in autoclaves, requiring several hours. Simultaneously, it was discovered that the application of higher reactor pressures, over 3 MPa, resulted in the destruction of spherical shape and the formation of graphitic layers. The importance of micropores below 0.4 nm, for adsorption of carbon dioxide, was also shown in this work. Microporous carbon spheres with efficient CO2 adsorption properties (nearly 7 mmol/g at 1 bar and 0 °C) were synthesized using this process.

Nanocrystalline samples of ZnO(Mn) were synthesized by hydrothermal method. The morphology of the samples was studied by HRTEM and SEM. X-ray diffraction was used to determine composition of the samples (ZnO and ZnMn2O4) and the mean crystalline size (from 16 to 99 nm). In this paper we report the experimental spectra of Raman scattering (from 100 to 1600 cm−1) with surface optical phonons (SOP) in range of 497–538 cm−1 as well as formation of new phases MnO, Mn3O4 and ZnMnO3. The phonon of registered phase's exhibit effects connected to phase concentration, while the SOP phonon mode exhibit significant confinement effect.

The nanopowders of (ZnO)1–x(Al2O3)x, where x ranges from 0 to 0.7, were obtained by two chemical methods: the co-precipitation/calcination and hydrothermal synthesis. The first assessment of structural and optical properties of the obtained nanopowders was undertaken by the SEM, XRD, Raman and far-infrared spectroscopy, which was followed by the photoluminescence spectroscopy at room temperature. The obtained far-infrared reflectivity spectra were analyzed using the fitting procedure. The dielectric function of ZnO–Al2O3 nanopowders was modeled by the Maxwell-Garnet formula under the assumption that the nanopowders are a mixture of homogenous spherical inclusions in air. The combined plasmon-LO phonon modes (CPPM) were observed in the far-infrared reflection spectra. The photoluminescence spectra contain emissions related to the presence of ZnO, ZnAl2O4, and AlOOH phases in the nanomaterial, which is in agreement with the results obtained by other experiments.

Nanocrystaline samples of ZnO(Fe) were synthesized by traditional wet chemical method followed by calcinations. Samples were characterized by X-ray diffraction to determine composition of the samples (ZnO, ZnFe 2 O 4 and Fe 2 O 3 ) and the mean crystalline size (from 8 to 51 nm). In this paper we report the experimental spectra of Raman scattering (from 200 to 1600 cm −1 ) with surface optical phonons (SOP) in range of 500–550 cm −1 . The phonon of registered phase’s exhibit effects connected to phase concentration, while the SOP phonon mode exhibit significant confinement effect.

Magnetic properties of the nCoO/(1-n)ZnO (n = 0.4, 0.50, 0.60 and 0.70) nanocomposites obtained by using traditional wet chemical synthesis method followed by calcination at 600∘C were investigated by dc magnetometry and magnetic resonance spectroscopy. XRD measurements revealed the presence of only two phases: ZnO (hexagonal nanocrystals with sizes in 64–300 nm range) and spinel phase Co3O4 (spheroidal nanocrystals with sizes in 14–21 nm range). Magnetic dc susceptibility measurements in 2–300 K range revealed dominating paramagnetic behavior in the whole temperature range and the presence of a strong temperature-independent component. With exception of n = 0.70 sample, no behavior connected with the expected phase transition to antiferromagnetic phase in Co3O4 and superparamagnetism was registered. Experimental results could be consistently explained by assuming that the most of high-spin Co2+ ions are involved in formation of antiferromagnetic pairs or clusters. Low intensity electron paramagnetic resonance spectra registered at RT were attributed to two different magnetic components – one involving paramagnetic Co2+ ions at Zn2+ sites in ZnO and the other due to Co2+ in Co3O4 phase or more probably the superparamagnetic resonance of Co3O4 nanoparticles. The former component dominates in nanocomposites with small concentration of cobalt, the latter in highly Co concentrated samples.

Zinc oxide (ZnO) nanocrystals containing Fe2O3 have been synthesized by the calcination method. Ferromagnetic resonance (FMR) and dc magnetization measurements of 0.40(Fe2O3)/0.60(ZnO) nanocomposite have been carried out in the 4–300 K range to study the magnetic properties of agglomerated magnetic zinc ferrite ZnFe2O4 (ZFO) nanoparticles with an average crystallite size of 12 nm. Temperature dependence of the resonance field, linewidth, and the integrated intensity calculated from FMR spectra have been determined to obtain the value of the uniaxial anisotropy field and to establish the ranges of different relaxation types. Magnetization measurements in ZFC and FC modes as well as the study of hysteresis loops allowed calculating different magnetic characteristics—blocking/freezing temperature, magnetic moment, anisotropy constant, and anisotropy field. The observed magnetic properties of 0.40(Fe2O3)/0.60(ZnO) nanocomposite were explained based on the core-shell model of ZFO nanoparticles. From comparison of FMR and dc magnetization measurements, the temperature ranges of magnetic phases existing in ZFO nanoparticles in 0.40Fe2O3/0.60ZnO nanocomposite are proposed.

Nanocrystalline samples of ZnO(Mn) were characterized by X-ray diffraction to determine composition of the samples (ZnO, Mn3O4, ZnMn2O4 and ZnMnO3) and the mean crystalline size (between 9 and 13 nm for ZnMnO3 phases, from 24 to 47 nm for Mn3O4 phases and above 100 nm for ZnO and ZnMn2O4 phases). In this paper we report the experimental spectra of Raman scattering (from 200 to 1600 cm−1) with surface optical phonons (SOP) in range of 520–575 cm−1. The phonon of registered phases exhibits effects connected to phase concentration, while the SOP phonon mode exhibits significant confinement effect.

The aim of the present work is to study the magnetic properties of nanocrystals of ZnO(Co) prepared by two methods of synthesis. We used the microwave assisted hydrothermal synthesis and traditional wet chemistry method followed by calcination. The detailed structural characterization was performed by means of X-ray diffraction and micro-Raman spectroscopy measurements. The magnetic properties were studied by means of AC susceptibility χ. All samples demonstrated Curie–Weiss behavior at higher temperatures. For calcination process, the negative values of the Curie–Weiss θ temperature were observed indicating the predominance of antiferromagnetic interactions. For samples prepared by hydrothermal synthesis, we observed the breakdown of predominance of antiferromagnetic interactions.

On Raman scattering spectra of nanocrystaline samples ZnO(Co) prepared by use of the microwave assisted hydrothermal synthesis, surface optical phonons (SOP) where observed in the range of 519 - 572 cm-1. The mean crystalline size (33 - 300 nm) as well as the phase composition of obtained samples (ZnO, ZnCo2O4) where determinate with X - ray diffraction measurements. These measurements aloud us to study the change of SOP modes position with crystalline size and how change in concentration of doping element CoO influence the change of SOP modes intensity.

Nanocrystalline 0.95MnO/0.05ZnO sample has been prepared by coprecipitation and calcination processes. X-ray diffraction showed the presence of Mn 3 O 4 nanocrystallites with an average size of 43 nm. Magnetic properties of the 0.95MnO/0.05ZnO sample have been investigated by dc magnetization and magnetic resonances (electron paramagnetic resonance (EPR), ferromagnetic resonance (FMR)) methods. The magnetization study has shown the presence of dominating Mn 3 O 4 paramagnetic and ferrimagnetic (below 46 K) phases. The blocking temperature determined from magnetization measurements was 41 K. An FMR study has shown the evidence of the spread of nanoparticles sizes. An EPR signal from paramagnetic phase of Mn 3 O 4 was observed at temperatures above 45 K and from defects/spurious phases in the low temperature range ( T

Currently, wide-gap ZnO nanoparticles bear important potential application in electro-optical devices, transparent ultraviolet protection films, and spintronic devices. We have studied the magnetic properties of nanocrystals of ZnO(Fe, Co, Mn) prepared by two methods of synthesis. We have used the microwave assisted hydrothermal synthesis and traditional wet chemistry method followed by calcination. The detailed structural characterization was performed by means of X-ray diffraction and micro-Raman spectroscopy measurements. The morphology of the samples was studied by means of SEM and TEM microscopy. The results of systematic measurements of AC magnetic susceptibility as a function of temperature and frequency as well as SQUID magnetization are presented. The SQUID magnetization measurements revealed a clear bifurcation of the FC and ZFC plots. Such behavior suggested superparamagnetic behavior above the blocking temperature. The dynamic magnetic measurements were performed at small AC magnetic field with amplitude not exceeding 5 Oe and different frequency values (from 7 Hz to 9970 Hz). For ZnO(Fe) and ZnO(Mn), the AC susceptibility maxima has been found for in-phase susceptibility Re(χ) and for out of phase susceptibility Im(χ). We analyzed the observed frequency dependence of the peak temperature in the AC susceptibility curve using the empirical parameter Φ that is a quantitative measure of the frequency shift and is given by the relative shift of the peak temperature per decade shift in frequency, as well as Vogel- Fulcher law. We observed two different types of magnetic behavior, spin-glasslike behavior or superparamagnetic behavior, depending on the synthesis process. For ZnO(Co) nanocrystalline samples high temperature Curie-Weiss behavior in AC magnetic susceptibility was observed. We observed that the determined negative values of the Curie- Weiss temperature θ depend strongly on the nominal content of cobalt oxide. It was shown that for calcination method the values of θ increase with the increase of magnetic ion content indicating enhancement of predominance of antiferromagnetic interactions. For hydrothermal method the opposite effect was observed indicating the breakdown of predominance of aniferromagnetic coupling with the increase of nominal magnetic ion content. This paper gives an in-depth discussion of the structural and magnetic properties of ZnO nanocrystals in addition to the technological issues such as different methods of wet chemical synthesis.

Surface optical phonons (SOP) were observed in the range of 496–572 cm−1 on Raman scattering spectra of nanocrystalline samples of ZnO(Co) prepared by use of the microwave assisted hydrothermal synthesis and traditional wet chemistry method followed by calcinations. The phase composition of the samples (ZnO, Co3O4, ZnCo2O4) and the mean crystalline size (14–300 nm) were determined using X-ray diffraction measurements. The SOP phonon mode exhibit significant size confinement effect, while the phonons of registered phases exhibit effects connected to phase concentration.

Fine particles n(MnO)/(1 − n)ZnO (n = 0.05 to 0.95) were prepared by wet chemistry method. According to X-ray diffraction analysis the obtained samples with n = 0.95, 0.90, 0.80, 0.70, 0.60 contained Mn3O4 and ZnMn2O4 phases, while samples with n = 0.05, 0.10, 0.20, 0.30, 0.40 and 0.50 contained ZnMnO3 and ZnO phases. The mean crystalline size of ZnMnO3 varied from 8 to 13 nm. The magnetic resonance investigations have been carried out at room temperature. Slightly asymmetric, broad and intense magnetic resonance line is recorded for all samples. The magnetic resonance spectra parameters showed marked differences depending on the composition index n. This could be explained by the variation of the magnetic susceptibility and a much slower evolution of spin relaxation, associated with the interaction of crystal field and superexchange interactions. Taking into account the values of magnetic resonance parameters, the investigated samples could be divided into two groups: these with the composition index n 0.50. A detailed discussion of the magnetic properties of different phases in the n(MnO)/(1−n)ZnO system is presented.

The aim of the present work is to study the magnetic properties of ZnO(Fe) nanocrystalline samples prepared by two methods of synthesis. We have used the microwave assisted hydrothermal synthesis and traditional wet chemistry method followed by calcination. The detailed structural characterization was performed by means of X-ray diffraction and micro-Raman spectroscopy measurements. The dynamic magnetic properties were studied by means of AC susceptibility χ . The measurements were performed at small AC magnetic field with amplitude not exceeding 5 Oe and different frequency values (from 7 Hz to 9970 Hz). The AC susceptibility maxima have been found for in-phase susceptibility Re ( χ ) and for out of phase susceptibility Im ( χ ). We analyzed the observed frequency dependence of the peak temperature in the AC susceptibility curve using the empirical parameter Φ that is a quantitative measure of the frequency shift and is given by the relative shift of the peak temperature per decade shift in frequency, as well as Vogel–Fulcher law.

Nanocrystaline samples of ZnO(Fe) were synthesized by wet chemical method. Samples were characterized by X-ray diffraction to determine composition of the samples (ZnO, Fe 2 O 3 , ZnFe 2 O 4 ) and the mean crystalline size (8–52 nm). In this paper we report the experimental spectra of Raman scattering. Main characteristics of experimental Raman spectrum in 200–1600 cm −1 spectral region are: sharp peak at 436 cm −1 and broad two-phonon structure at ∼1150 cm −1 , typical for ZnO; broad structure below 700 cm −1 that has different position and shape in case of ZnFe 2 O 4 or Fe 2 O 3 nanoparticles. Low-frequency Raman modes were measured and assigned according to confined acoustic vibrations of spherical nanoparticles. Frequencies of these vibrational modes were analyzed in elastic continuum approximation, which considers nanoparticle as homogeneous elastic sphere.