Sol-gel Synthesis and Characterization of Lithium and Cerium Codoped Perovskite

Perovskites are an important group of ceramic materials with a structural formula ABO3 and wide array of potential applications in electronics, superconductors, catalysis, etc. CaTiO3, by which the whole group was named for, is particularly significant due to its use in catalysis, but its photocatalytic activity is limited by a large band gap value (~3.5 eV). A possible solution is the substitution of A and B cations with foreign cations which causes the alteration of properties, including photocatalytic efficiency. The aim of this work was the sol-gel synthesis of lithium and cerium codoped CaTiO3, characterization of the prepared gel and ceramics obtained by its thermal treatment. Samples of codoped perovskite, Ca1-xLixCexTiO3, where x = 0, 0.01, 0.02, 0.03 and 0.04, were prepared and characterized using powder X–ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), differential thermal and thermo- gravimetric analysis (DTA-TGA), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Photocatalytic activity was evaluated through the study of methylene blue photocatalytic degradation. XRD analysis showed that the prepared samples consisted of calcium nitrate and titanium chelate. In accordance with the established thermal evolution path, all samples were thermally treated at 500 °C for 2 hours. Beside perovskite, Ca2Ti2O6 appeared as a secondary phase in all thermally treated samples. SEM analysis of thermally treated samples showed the presence of agglomerates of irregular morphology and the decrease of primary particles size with the increase of dopants concentration. The sample with x=0.04 showed an increased photocatalytic activity

Measurement and Control: Determination of the Semiconductors Band Gap by UV-Vis Diffuse Reflectance Spectroscopy

U radu je dan pregled pojmova i jednadžbi vezanih uz određivanje zabranjene zone metodom difuzne refleksijske spektroskopije i uporabu Taucova grafičkog prikaza. Kako bi se demonstrirao postupak i vrednovala sama metoda, primjenom metode određena je zabranjena zona komercijalnih uzoraka anatasa, rutila, cinkita i hematita. Na temelju eksperimentalno dobivenih vrijednosti širine zabranjene zone komentirana je točnost metode te osjetljivost pri razlikovanju poluvodiča s direktnim i indirektnim prijelazima. Pokazano je da Taucova metoda nije besprijekorna niti u pogledu točnosti niti razlikovanja indirektnih i direktnih elektronskih prijelaza u poluvodičkim materijalima, ali je vrlo praktičan način određivanja širine zabranjene zone poluvodiča budući da ne zahtijeva pretjerano skupu instrumentaciju a obrada eksperimentalnih podataka relativno je jednostavna. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.For the application of semiconductors, an important factor is the band gap, i.e., the minimum energy required for the transfer of electrons from the valence to the conduction band. One of the possible methods for band gap determination is diffuse reflectance spectroscopy and Tauc plot. In this paper, an overview of the terms and equations related to the said method is given, as well as its utilization in the determination of band gaps of commercial samples of various metal oxides. Thus, the procedure is demonstrated and evaluated through the determination of indirect and direct band gap values of anatase (TiO2), rutile (TiO2), zincite (ZnO), and hematite (Fe2O3). All samples were beforehand analysed and identified by X-ray powder diffraction on Shimadzu XRD 6000 diffractometer with CuKα radiation working in a step scan mode with steps of 0.02° and counting time of 0.6 s. It was determined that all samples are well crystallized with relatively large crystallite sizes. UV-Vis spectra of the samples, as well as barite, which was used as a reference, were obtained on the UV-Vis spectrometer with an integrating sphere in total reflectance mode. The UV-Vis DRS spectra were transformed to Kubelka-Munk function, after which Tauc plot was used for the determination of the indirect and direct band gap values of all samples. The obtained values for anatase were 3.20 eV for indirect transition and 3.41 eV for direct transition, and for rutile 3.00 eV for indirect transition and 3.11 eV for direct transition. The zincite sample showed an indirect band gap of 3.19 eV and direct band gap of 3.25 eV, while the obtained indirect band gap value for hematite was 1.96 eV and direct band gap value 2.15 eV. As may be seen, the method is not particularly useful when distinguishing direct from indirect semiconductors, since, for all samples, the curves in Tauc plot for both indirect and direct electron transitions possess a linear dependence region from which the band gap value is estimated. However, the obtained band gap values for all the studied semiconductors are in relatively good concordance with literature references. The method is perhaps most useful in monitoring the variation of band gap depending on the dopant content. Namely, the studied metal oxides are used in photocatalysis where the addition of dopants is expected to reduce the band gap to visible light area, and thus improve the photocatalytic activity of the semiconductor. It can be concluded that the Tauc method is not perfect in terms of accuracy and differentiation between indirect and direct electron transitions in semiconductors. Nevertheless, it is a very practical way of band gap assessment for semiconducting materials, because it requires no excessively expensive instrumentation, and the processing of experimental data is rather simple. This work is licensed under a Creative Commons Attribution 4.0 International License

Mechanochemical synthesis of Cd-doped ZnO nanoparticles

Istraživano je koliki se udio kadmija može ugraditi u kristalnu rešetku cinkita mehanokemijskom sintezom. Kao prekursori su korišteni metalni kloridi i natrijev karbonat dok je natrijev klorid korišten kao razrjeđivač. Nakon mehanokemijske sinteze uzorci su termički obrađeni pri 600 °C u trajanju 2 sata kako bi se iz ZnCO3 dobio ZnO. Pripremljeni uzorci ispitani su rendgenskom difrakcijom praha (XRD), infracrvenom spektroskopijom s Fourierovom transformacijom tehnikom prigušene totalne refleksije (FTIR-ATR), UV-Vis difuznom refleksijskom spektroskopijom (DRS), elektronskim pretražnim mikroskopom (SEM) i energetski razlučujućom rendgenskom spektroskopijom (EDS). Fotokatalitička učinkovitost vrednovana je na temelju procesa razgradnje organske boje metilenskog plavila (MB), praćenog UV-VIS spektroskopijom. Rezultati su pokazali da je mehanokemijskom sintezom iz korištenih prekursora u rešetku cinkita moguće ugraditi do 2 % kadmija, te da se pri većim udjelima kadmija osim cinkita pojavljuju i druge faze poput kadmijeva oksida i kadmijeva karbonata. Dopiranjem cinkita kadmijem dovodi do pojave većih kristalita ZnO. Dopiranjem kadmijem ne postižu se veće promjene u morfologiji, energiji zabranjene zone niti fotokatalitičkoj aktivnosti ZnO.The limit of zincite crystal lattice doping with cadmium in the course of mechanochemical synthesis has been investigated. Metal chlorides and sodium carbonate were used as precursors and sodium chloride as diluent. After mechanochemical synthesis samples were thermally treated at 600 °C for 2 h, in order to enable transformation of ZnCO3 to ZnO. The prepared samples were characterized by X-ray diffraction (XRD), Attenuated total reflectance Fourier-transformed infrared spectroscopy (FTIR-ATR), UV–Vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Photocatalytic efficiency has been evaluated through methylene blue (MB) dye degradation process via UV-Vis spectroscopy. The results showed that limit of Zn replacement with Cd in ZnO crystal lattice via mechanochemical synthesis with precursors used is only 2 %. In a presence of larger share of Cd, cadmium oxide or carbonate phases appears. It was noted that doping with Cd impair ZnO nanocrystallinity. No significant differences of ZnO band-gap, morphology and photocatalytic activity with doping were observed

Kinetic characterization of MenD enzyme in the reaction of bicatalytical synthesis of 6-cyano-4-oxohexanoic acid

U ovom radu je provedena biokatalitička reakcija 1,4-karboligacije akrilonitrila i α-ketoglutarata uz dekarboksilazu MenD. Ispitan je utjecaj kofaktora magnezija i tiamin difosfata na početnu reakcijsku brzinu. Kinetika enzima je mjerena metodom početnih brzina, te je opisana dvosupstratnom Michaelis Menteničinom kinetikom. Postavljen je matematički model procesa u kotlastom reaktoru. Provedbom reakcije u kotlastom reaktoru uz 100 %-tni suvišak α-ketoglutarata, postignuta je potpuna konverzija akrilonitrila.Biocatalytical reaction of 1,4-addition of α-ketoglutarate and acrylonitrile catalyzed by decarboxylase MenD was carried out. The influence of cofactors magnesium and tiamin diphosphate on the initial reaction rate was tested. Kinetics of the enzyme was measured by the initial reaction rate method and was described by double substrate Michaelis-Menten kinetics. Mathematical model of the process in batch reactor was set. While preforming the reaction in a batch reactor with the α-ketoglutarate excess of 100%, complete conversion of acrylonitrile was achieved

Kinetic characterization of MenD enzyme in the reaction of bicatalytical synthesis of 6-cyano-4-oxohexanoic acid

U ovom radu je provedena biokatalitička reakcija 1,4-karboligacije akrilonitrila i α-ketoglutarata uz dekarboksilazu MenD. Ispitan je utjecaj kofaktora magnezija i tiamin difosfata na početnu reakcijsku brzinu. Kinetika enzima je mjerena metodom početnih brzina, te je opisana dvosupstratnom Michaelis Menteničinom kinetikom. Postavljen je matematički model procesa u kotlastom reaktoru. Provedbom reakcije u kotlastom reaktoru uz 100 %-tni suvišak α-ketoglutarata, postignuta je potpuna konverzija akrilonitrila.Biocatalytical reaction of 1,4-addition of α-ketoglutarate and acrylonitrile catalyzed by decarboxylase MenD was carried out. The influence of cofactors magnesium and tiamin diphosphate on the initial reaction rate was tested. Kinetics of the enzyme was measured by the initial reaction rate method and was described by double substrate Michaelis-Menten kinetics. Mathematical model of the process in batch reactor was set. While preforming the reaction in a batch reactor with the α-ketoglutarate excess of 100%, complete conversion of acrylonitrile was achieved

Mechanochemical synthesis of Cd-doped ZnO nanoparticles

Istraživano je koliki se udio kadmija može ugraditi u kristalnu rešetku cinkita mehanokemijskom sintezom. Kao prekursori su korišteni metalni kloridi i natrijev karbonat dok je natrijev klorid korišten kao razrjeđivač. Nakon mehanokemijske sinteze uzorci su termički obrađeni pri 600 °C u trajanju 2 sata kako bi se iz ZnCO3 dobio ZnO. Pripremljeni uzorci ispitani su rendgenskom difrakcijom praha (XRD), infracrvenom spektroskopijom s Fourierovom transformacijom tehnikom prigušene totalne refleksije (FTIR-ATR), UV-Vis difuznom refleksijskom spektroskopijom (DRS), elektronskim pretražnim mikroskopom (SEM) i energetski razlučujućom rendgenskom spektroskopijom (EDS). Fotokatalitička učinkovitost vrednovana je na temelju procesa razgradnje organske boje metilenskog plavila (MB), praćenog UV-VIS spektroskopijom. Rezultati su pokazali da je mehanokemijskom sintezom iz korištenih prekursora u rešetku cinkita moguće ugraditi do 2 % kadmija, te da se pri većim udjelima kadmija osim cinkita pojavljuju i druge faze poput kadmijeva oksida i kadmijeva karbonata. Dopiranjem cinkita kadmijem dovodi do pojave većih kristalita ZnO. Dopiranjem kadmijem ne postižu se veće promjene u morfologiji, energiji zabranjene zone niti fotokatalitičkoj aktivnosti ZnO.The limit of zincite crystal lattice doping with cadmium in the course of mechanochemical synthesis has been investigated. Metal chlorides and sodium carbonate were used as precursors and sodium chloride as diluent. After mechanochemical synthesis samples were thermally treated at 600 °C for 2 h, in order to enable transformation of ZnCO3 to ZnO. The prepared samples were characterized by X-ray diffraction (XRD), Attenuated total reflectance Fourier-transformed infrared spectroscopy (FTIR-ATR), UV–Vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Photocatalytic efficiency has been evaluated through methylene blue (MB) dye degradation process via UV-Vis spectroscopy. The results showed that limit of Zn replacement with Cd in ZnO crystal lattice via mechanochemical synthesis with precursors used is only 2 %. In a presence of larger share of Cd, cadmium oxide or carbonate phases appears. It was noted that doping with Cd impair ZnO nanocrystallinity. No significant differences of ZnO band-gap, morphology and photocatalytic activity with doping were observed

Mechanochemical synthesis of Cd-doped ZnO nanoparticles

Istraživano je koliki se udio kadmija može ugraditi u kristalnu rešetku cinkita mehanokemijskom sintezom. Kao prekursori su korišteni metalni kloridi i natrijev karbonat dok je natrijev klorid korišten kao razrjeđivač. Nakon mehanokemijske sinteze uzorci su termički obrađeni pri 600 °C u trajanju 2 sata kako bi se iz ZnCO3 dobio ZnO. Pripremljeni uzorci ispitani su rendgenskom difrakcijom praha (XRD), infracrvenom spektroskopijom s Fourierovom transformacijom tehnikom prigušene totalne refleksije (FTIR-ATR), UV-Vis difuznom refleksijskom spektroskopijom (DRS), elektronskim pretražnim mikroskopom (SEM) i energetski razlučujućom rendgenskom spektroskopijom (EDS). Fotokatalitička učinkovitost vrednovana je na temelju procesa razgradnje organske boje metilenskog plavila (MB), praćenog UV-VIS spektroskopijom. Rezultati su pokazali da je mehanokemijskom sintezom iz korištenih prekursora u rešetku cinkita moguće ugraditi do 2 % kadmija, te da se pri većim udjelima kadmija osim cinkita pojavljuju i druge faze poput kadmijeva oksida i kadmijeva karbonata. Dopiranjem cinkita kadmijem dovodi do pojave većih kristalita ZnO. Dopiranjem kadmijem ne postižu se veće promjene u morfologiji, energiji zabranjene zone niti fotokatalitičkoj aktivnosti ZnO.The limit of zincite crystal lattice doping with cadmium in the course of mechanochemical synthesis has been investigated. Metal chlorides and sodium carbonate were used as precursors and sodium chloride as diluent. After mechanochemical synthesis samples were thermally treated at 600 °C for 2 h, in order to enable transformation of ZnCO3 to ZnO. The prepared samples were characterized by X-ray diffraction (XRD), Attenuated total reflectance Fourier-transformed infrared spectroscopy (FTIR-ATR), UV–Vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Photocatalytic efficiency has been evaluated through methylene blue (MB) dye degradation process via UV-Vis spectroscopy. The results showed that limit of Zn replacement with Cd in ZnO crystal lattice via mechanochemical synthesis with precursors used is only 2 %. In a presence of larger share of Cd, cadmium oxide or carbonate phases appears. It was noted that doping with Cd impair ZnO nanocrystallinity. No significant differences of ZnO band-gap, morphology and photocatalytic activity with doping were observed

Kinetic characterization of MenD enzyme in the reaction of bicatalytical synthesis of 6-cyano-4-oxohexanoic acid

U ovom radu je provedena biokatalitička reakcija 1,4-karboligacije akrilonitrila i α-ketoglutarata uz dekarboksilazu MenD. Ispitan je utjecaj kofaktora magnezija i tiamin difosfata na početnu reakcijsku brzinu. Kinetika enzima je mjerena metodom početnih brzina, te je opisana dvosupstratnom Michaelis Menteničinom kinetikom. Postavljen je matematički model procesa u kotlastom reaktoru. Provedbom reakcije u kotlastom reaktoru uz 100 %-tni suvišak α-ketoglutarata, postignuta je potpuna konverzija akrilonitrila.Biocatalytical reaction of 1,4-addition of α-ketoglutarate and acrylonitrile catalyzed by decarboxylase MenD was carried out. The influence of cofactors magnesium and tiamin diphosphate on the initial reaction rate was tested. Kinetics of the enzyme was measured by the initial reaction rate method and was described by double substrate Michaelis-Menten kinetics. Mathematical model of the process in batch reactor was set. While preforming the reaction in a batch reactor with the α-ketoglutarate excess of 100%, complete conversion of acrylonitrile was achieved