Effect of transition metal cations on the commensurate freezing of n-hexane confined in micropores of ZSM-5

Besides its importance concerning fundamental studies on gas adsorption in narrow pores, investigation of the commensurate freezing of a fluid within a zeolite is of practical importance in the application of zeolites in the processes of adsorption, separation and catalysis. In this work, the adsorption of n-hexane on HZSM-5 and its transition metal ion-exchanged modified forms was studied at 303 K by means of microcalorimetry. The thermal molar entropies changes of adsorption were calculated and thereby, the freezing-like behaviour of n-hexane inside the structure of the zeolite as a confinement media was noticed. This effect is governed by the attractive interactions between n-hexane molecules and the pore walls, and is influenced by the length of the pores and the nature of the charge-balancing cations. Among the investigated zeolites, a solid-like phase of n-hexane in the pores of zeolites with Fe(II) ions was the most similar to solid bulk n-hexane, while Cu(II) ions contributed to the lowest ordering of the obtained solid-like n-hexane phase

Quantifying acidity and basicity of oxides: a calorimetric approach

Given the great many applications of heterogeneous acid-base catalysis, the acidity and basicity of solid oxide catalysts (non-porous, such as ceria, zirconia or titania, or porous, such as zeolites) are considered crucial, among various characteristics which influence their performance. Namely, the concentration of acid/basic sites, their nature and their strengths are the most important parameters. Different methods are routinely being applied in the study of acidity/basicity, most often infrared spectroscopy and temperature programmed desorption. However, in terms of exact quantitative data on acidic/basic site strength distributions, a calorimetric method stands out as exceptional. It is designed to simultaneously record adsorption isotherms of basic (NH3) or acidic (SO2) probe molecules and the related thermal effects, via coupling of a calorimeter and a calibrated volumetric line equipped with pressure gauges. Microcalorimetric-volumetric measurements of adsorption yield several sets of results: the total number of sites (µmol/g), the concentration of irreversibly adsorbed probe molecules (number of “strong” sites, µmol/g), integral heats of adsorption (J/g) and differential heats of adsorption (kJ/mol), i.e. the distribution of strengths of the acid/basic sites. Examples of these unique results, which provide a fully quantitative image of acidity/basicity of oxide materials, unparalleled by any other technique, will be presented.X Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 26-27, 2022; Belgrad

Stimulacija zemljišne mikrobiološke aktivnosti sa klinoptilolitom - uticaj na rast biljke

Zeolites can mitigate ammonium losses to the environment by taking up the ions from sources such as farmyard manure and ammonium-bearing fertilizers. This ability can improve nitrogen fertilizing practice given that ammonium ions loaded onto zeolite are available for plant uptake. The main goal of this study was to assess the influence of zeolite (clinoptilolite) and ammonia-loaded clinoptilolite on growth and yield of red clover (Trifolium pratense L.), as well as their influence on the microbial dynamics in soil. Plants sown in pots were cut four times, and dry matter yield (DM) of each harvest was weighed. The number of culturable bacteria, moulds, ammonifiers, Azotobacter sp. and actinomycetes was determined at the beginning of the experiment, and after each harvest. Two control treatments (soil without fertilizer and soil supplemented with mineral fertilizer - CAN) were included in the study. The application of ammonia-loaded clinoptilolite positively and significantly affected the microbial activity and provided higher yields (from 4.9 g/pot in ammonia-loaded clinoptilolite treatment to 4.3 g/pot in soil with zeolite treatment). Our results suggest that the addition of clinoptilolite to organic fertilizers (manure, composts) could be recommended. The increase of microbial communities’ abundances and their activity represented the key benefit from clinoptilolite application.Zeoliti mogu ublažiti otpuštanje amonijaka u prirodu preko uzimanja jona iz izvora kao što su stajnjak i đubriva bogata amonijakom. Ova sposobnost može unaprediti đubrenje azotom preko zeolitom usvojenih amonijum jona koji bi tako postali dostupni za usvajanje biljkama. Cilj ovih ispitivanja je bio procena uticaja zeolita (klinoptilolita) i zeolita obogaćenog amonijakom na rast i prinos crvene deteline (Trifolium pratense L.), kao i na njihovu ulogu u mikrobiološkoj dinamici zemljišta. Biljke sejane u sudovima su košene četiri puta i meren je prinos suve materije (SM) svakog otkosa. Broj bakterija, plesni, amonifikatora, Azotobacter sp. i aktinomiceta je utvrđen na početku ogleda i nakon svakog košenja. U istraživanja su uključena dva kontrolna tretmana (zemljište bez đubriva i zemljište sa dodatim mineralnim đubrivom - KAN). Primena klinoptilolita obogaćenog sa amonijakom je pozitivno i značajno uticala na mikrobiološku aktivnost i povećala je prinos (od 4,9 g po sudu kod tretmana sa klinoptilolitom obogaćenim amonijakom do 4,3 g po sudu u zemljištu sa zemljištem i zeolitom zajedno). Naša istraživanja sugerišu da se može preporučiti dodavanje klinoptilolita organskim đubrivima (stajnjaku, kompostu). Ključna dobit od primene klinoptilolita bi se ogledala u povećanju zastupljenosti mikrobioloških zajednica i njihove aktivnosti

Synthesis and characterisation of ZnO synthesized by glycine-nitrate combustion process

One of the ways to get rid of toxic organic compounds that industries release into natural waters is photocatalysis of the decomposition of organic compounds on the surface of heterogenous photocatalysts such as zinc oxide. Zinc oxide is a semiconductor that interacts with UV and near-UV visible light by generating electron-hole pairs which decompose organic molecules. Therefore it is useful to explore different ways of synthesizing zinc oxide and to test quality and quantity of organic decomposition photocatalysis so as to enable the commercial use of the material. Zinc oxide is also a respectable material for use as a photoelectrocatalyst in water oxidation, for example, which can be useful for generating oxygen while using natural sunlight - a clean and abundant energy source. In this project nanocrystalline zinc oxide was synthesized by glycin-nitrate combustion process and the powder was annealed on temperatures of 400 °C and 500 °C. Obtained particles where characterized in detail using X-ray powder diffraction (XRPD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, field emission scanning microscopy (FESEM), photoluminescence spectroscopy (PL) and diffuse reflectance spectroscopy (DRS). The results show that obtained samples are nanocrystalline wurtzite zinc oxide, with particle diameters of 33 nm (annealed at 400 °C) ad 48 nm (annealed at 500 °C). Both samples show significant amount of various crystal defects. Zinc oxide band gap of the samples are determined to be lower than the band gap of the bulk zinc oxide. Photoelectrocatalytic properties were investigated via electrochemical methods: linear voltammetry (LV), chronoamperometry (CA) and impedance spectroscopy (EIS). The results show that material is photostable and reactive to the light. Water oxidation is enhanced by exposing to sunlight. Finally, photocatalytic properties are tested with determining kinetic parameters of phenole and methyl blue decomposition. Zinc oxide nanoparticles are efficient photocatalysts, although sample annealed at 500 °C shows better properties than sample annealed at 400 °C

Structural, morphological and optical characteristics of ZnO particles synthesized in the presence of surfactants CTAB and Pluronic F-127

Due to its optical and electrical properties, low toxicity, chemical and physical stability, as well as inexpensiveness, zinc oxide (ZnO) based materials have a great potential to be used as photoelectrode in photo(electro)catalysis. Photo(electro)catalytic activity of ZnO materials can be improved by modification of particles morphology and surface topology. In this work, the influence of two different surfactants: cetyltrimethylammonium bromide (CTAB) and Pluronic F-127, on the crystal structure, morphology, optical and photo(electro)catalytic properties of ZnO particles, were examined. ZnO powders were synthesized by microwave processing of a precipitate which was previously prepared by "drop by drop" method in the presence of the surfactants. The crystal structure and phase purity of the ZnO particles were determined by X-ray diffraction and Raman spectroscopy. The effects of the surfactants on ZnO particles morphology were examined by the field emission scanning electron microscopy (FE-SEM). The optical properties were studied using UV-Vis diffuse reflectance and photoluminescence spectroscopy. Photocatalytic activity was examined via decolorization of methylene blue under direct sunlight irradiation. It was found that synthesized ZnO powders have a significant photocatalytic activity. Electrochemical properties were studied using linear sweep voltammetry and impedance spectroscopy in Na2SO4 electrolyte. ZnO powder synthesized in the presence of CTAB (ZnO/CTAB) showed the most significant reduction of potential and the fastest kinetic of oxygen evolution

Micro/mesoporous aluminosilicate materials via dual templating, Part 1: synthesis and characterization

In a quest for optimal synthesis procedure of hierarchically porous zeolite by dual template method, a series of materials was prepared starting from zeolite yielding precursor with an addition of surfactant as a mesoporogen. Characterization of the obtained materials showed that all samples possess micro and mesoporous structures, which ratio depends on the amount of surfactant present in the reaction mixture. However, in the most of the samples separation of phases occurred, and crystalline zeolite phase along amorphous MCM-41 like phase were detected, except for the sample obtained from the modified precursor, where only crystalline zeolite phase was obtained, with a specific and unusual morphology. Adsorption isotherm of that sample resembles the isotherms obtained for post synthesis modified samples

The extraction of antioxidative compounds from rusks enriched with millet flour (Panicum miliaceum L.)

Two different ways of extracting antioxidative compounds (including soluble polyphenols) from rusks made from wheat flour with added millet (Panicum miliaceum L.) were compared, i.e., solvent extraction and in vitro digestion. Wheat flour was replaced by millet flour in amounts of 10, 20 or 30 wt. % (per dry mass). Solvent extraction was realized using a mixture of ethanol and water in different percentages, with or without the addition of formic acid. The total content of phenolic compounds (TPC) was determined using Folin-Ciocalteu reagent, while the antioxidative capacity was measured by the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay. The efficiency of solvent extraction was enhanced by the addition of formic acid. The addition of millet flour in amounts up to 20 % enhanced the antioxidative properties. It was shown that in vitro digestion was more efficient in the extraction of antioxidative compounds, in comparison with solvent extraction

Enhanced photo(electro)catalytic properties of ZnO particles synthesized by CTAB-assisted microwave processing

ZnO/CTAB powder was prepared by microwave processing of a precipitate with the aid of cetyltrimethylammonium bromide (CTAB). The effects of CTAB on the crystal structure, morphology, optical and photo(electro)catalytic properties of ZnO particles were studied. The results showed that CTAB did not influenced crystal structure or phase purity of ZnO. However, even low concentration of CTAB vary particles morphology; cone-like particles were prepared by processing without CTAB, while a mixture of spheroidal and plate-like ZnO particles were produced when 0.001 M CTAB was used. It was found that synthesized ZnO powders have 0.10 eV lower band gap energy then bulk ZnO (3.37 eV). A high photocatalytic activity for decolorization of methylene blue water solution was established after 2 h of sunlight irradiation; efficiency was 100 and 67% for ZnO/CTAB and ZnO, respectively. Electrochemical test showed faster oxygen evolution kinetics when ZnO/CTAB was used as anode material. Enhanced photo(electro)catalytic activities of ZnO/CTAB particles are attributed to better absorption of visible light due to both, larger dimensions and surface sensitization by CTAB

CTAB- and pluronic F-127-assisted microwave processing of ZnO particles with modified morphology and optical properties

Zinc oxide-based materials have a great potential to be applied as photocatalysts in the processes of removal of organic and biological pollutants from drinking and wastewaters. A major drawback of ZnO as visible-light absorber is a band energy gap of 3.37 eV, which restricts the material to absorb UV light only. This drawback can be overcame by modifying the optical absorption properties of zinc oxide particles. Different approaches have been applied to modify the visible light photocatalytic activity of ZnO materials: (1) metal and nonmetal ion doping, (2) hydrogenation, (3) the incorporation of crystalline defects in the form of vacancies and interstitials, (4) the modification of particles morphology and surface topology, etc. In this study we investigated the influence of different surfactants on the morphology, optical properties and functionality of ZnO particles. Two different surfactants were employed during microwave processing of ZnO particles, cetyltrimethylammonium bromide (CTAB) as cationic and Pluronic F-127 as non-ionic one. The crystal structure and phase purity of the ZnO particles were determined by X-ray diffraction and Raman spectroscopy. Effects of the surfactants on particles morphology and texture properties were observed with field emission scanning electron microscopy (FE–SEM) and nitrogen adsorption–desorption isotherm, respectively. The optical properties were studied using UV–Vis diffuse reflectance and photoluminescence (PL) spectroscopy. Functionality of ZnO particles was studied due to their photocatalytic and electrochemical activities. Photocatalytic activity was examined via decolorization of methylene blue under direct sunlight irradiation. Electrochemical behavior of the ZnO samples as anode material was evaluated by linear sweep voltammetry in Na2SO4 electrolyte; the oxygen evolution kinetics were determined and compared

Adsorpcija nikotina iz vodenih rastvora na različitim vrstama zeolita

The plant alkaloid, nicotine, is a strongly toxic heterocyclic compound: the lethal dose for an adult human being (40-60 mg) is importantly lower in comparison with the other known poisons such as arsenic or strychni­ne. Cigarettes represent "the most toxic and addictive form of nicotine". Besides the negative effects of nicotine on public health produced by self-administration, recently another potentially very dangerous effect has been recognized: because of its miscibility with water, nicotine can be found in industrial wastewaters, and consequently, in groundwater. Therefore, the problem of nicotine removal from aqueous solutions has became an interesting topic. In this work, the removal of nicotine has been probed by adsorption on solid materials. Adsorption of nicotine on different zeolites (clinoptilolite, ZSM-5 and beta zeolite) and on activated carbon was investigated from aqueous solutions, at 298 K. The obtained results are presented as adsorption isotherms: the amount of adsorbed nicotine as a function of equilibrium concentration. These data were obtained from the residual amount of nicotine in the aqueous phase, by the use of UV spectroscopy. The highest amounts of adsorbed nicotine was found for activated carbon and p zeolite (~ mmol·g-1). The attempt to modify the adsorption properties of ZSM-5 zeolite has been also done: ZSM-5 was modified by ion-exchange with VIII group metal (Cu2+ and Fe3+). In addition, the adsorption of nicotine on ZSM-5 zeolite with different Si/Al ratios has been done. It has been noticed that ion-exchange did not improve the adsorption possibilities, while the adsorption was importantly lower in the case of higher silicon content in ZMS-5 structure. 13C NMR spectra were collected for suspensions formed of solid adsorbent and aqueous solution of nicotine; in this way, the part of nicotine molecule which is most probably connected with the adsorbent was recognized.U ovom radu ispitivana je adsorpcija nikotina iz vodenih rastvora na različitim zeolitima (klinoptilolitu, ZSM-5 i beta zeolitu) kao i na aktivnom uglju visoke specifične površine; na 298K. Dobijeni rezultati prikazani su u formi adsorpcionih izotermi: količina adsorbovanog nikotina u funkciji od ravnotežnih koncentracija nikotina. Ovi podaci dobijeni su iz određivanja količine nikotina preostale u vodenoj fazi, metodom UV spektroskopije. Najveće količine adsorbovanog nikotina utvrđene su na aktivnom uglju i beta zeolitu (~ mmol/g). Iz 13C NMR spektara snimljenih iz suspenzije: čvrsti adsorbent-vodeni rastvor nikotina, utvrđen je atom ugljenika preko koga se molekul nikotina najverovatnije vezuje sa površinama zeolita