Polymeric Precursor Method Research Articles

Synthesis and visible down- and up-conversion emissions from Yb3+/Ho3+/Tm3+ Co-Doped Y4Al2O9 (YAM) nanocrystalline particles

We studied Yb3+/Ho3+/Tm3+ co-doped Y4Al2O9 (YAM) crystalline phase prepared by a modified polymeric precursor method, involving pyrolytic treatment and a calcination at 1100 °C during 3 h. X-ray powder diffraction patterns and high-resolution transmission electron microscopy images revealed the formation of single monoclinic crystalline phase. The co-doped YAM phase presents an optical bandgap of 4.58 eV and high diffuse reflectance value in the visible region. Down- and up-conversions were observed and analyzed. Photoluminescence measurements showed three emission bands in the visible region: 471–486 nm (blue region), 536–548 nm (green region), and 638–665 (red region) from Tm3+ and Ho3+ ions. The CIE color coordinates of the up-conversion emissions under excitation at 980 nm were determined, demonstrating a yellowish emission color. Finally, the lifetimes of some Ho3+ and Tm3+ levels were determined, and an energy mechanism transfer is suggested for up-conversion processes.

Synthesis of rare earth containing single‐phase multicomponent metal carbides via liquid polymer precursor route

AbstractNovel high‐entropy carbide ceramics (HEC) containing rare earth metals, namely (Ti, Zr, Hf, Ta, La, Y)C, (Ti, Zr, Hf, Ta, Nb, La, Y)C, and (Ti, Zr, Hf, Ta, Nb, Mo, W, La)C were prepared with single‐phase structure by polymer precursor method. Controlled co‐hydrolysis and polycondensation of equiatomic metal‐containing monomers were conducted successively, followed by blending allyl‐functional novolac resin as carbon source, and the polymer precursors were obtained as clear viscous liquid solutions. The single‐phase formation possibility was theoretically analyzed from the aspects of size‐effect parameter δ of the designed compositions. All as‐obtained ceramics possessed single face‐centered‐cubic structure of metal carbides and high‐compositional uniformity from nanoscale to microscale. The (Ti, Zr, Hf, Ta, Nb, Mo, W, La)C ceramic powder pyrolyzed at 1800°C exhibited low‐oxygen impurity content of 1.2 wt%. Thus, multicomponent high‐entropy carbide nanoceramics with over five metal elements containing even rare earth element were firstly synthesized and characterized.

CeO2 and CeO2:Pr nanocrystalline powders prepared by the polymeric precursor method: Yellow and red pigments with tunable color

AbstractThe development of stable and reproducible inorganic pigments is noteworthy for industrial applications mainly considering more intense shades and low toxicity. Among the various candidates to substitute non‐hazardous red and yellow pigments, CeO2 and CeO2:Pr have been attracting attention because of their opacity and high‐temperature stability besides being environmental‐friendly and health‐friendly. In this study, nanostructured CeO2 and CeO2:Pr samples were synthesized using the polymeric precursor method and structural and optical characterizations were performed. Scanning electron microscopy reveals the morphology of CeO2 nanoparticles in which the particle size ranges from 22 to 28 nm as a function of the annealing temperature. Pr‐doping does not show influence on the particle size. XRD results show that CeO2 and CeO2:Pr samples crystallize in the cubic fluorite lattice with Fm3m space group. Raman spectra show the fluorite F2g mode, confirming the XRD results. With Pr‐doping and the annealing of the samples, two bands are observed between 550 and 600 cm−1, which are related to the defects in the fluorite structure associated with oxygen vacancies. XPS spectra reveal an increase in the ratio of Ce3+ ions depending on the annealing temperature and Pr‐doping. This increase is associated with the carbon removal from the lattice by annealing. This behavior causes a change in the hue of the powders as the annealing temperature increases. According to diffuse reflectance and colorimetric measurements, CeO2 shows a light‐yellow color due to the O 2p­Ce 4f transitions whose b* parameter mainly decreases with annealing, becoming almost white. The CeO2:Pr sample exhibits a red‐orange color because of the electronic transitions between 4f2 → 5d1 states of Pr3+. Upon annealing, L* and b* parameters decrease, resulting in a red‐brown shade. The charge compensation or charge transfer is responsible for the modification of the hue of these pigments.

CeO2 thin film supported on TiO2 porous ceramics

The work demonstrates an easy and simple method for obtaining a TiO2 porous ceramic coated with a CeO2 thin film (COTF) on the surface. Replica technique used a 30 PPI polyurethane sponge and TiO2 ceramic suspension. Dip coating technique was used to coat the material surface and cerium polymeric resin synthesis was obtained by polymeric precursors method. Thermal analysis indicated a thermostable material from 500 °C. X-ray diffraction analysis of calcined CeO2, at 600 to 900 °C, resulted in monophasic and crystalline with a fluorite type cubic structure. Scanning electron microscopy made it possible to monitor COTF formation and growth from islands shape to a more homogenous form over 10 depositions.

Structural characterization, morphology, optical and colorimetric properties of NiWO4 crystals synthesized by the co-precipitation and polymeric precursor methods

In this paper, nickel tungstate (NiWO4) crystals were synthesized by the co-precipitation and polymeric precursor methods, followed by heat treatment at 1073 K for 4 h and 2 h, respectively. Their structure, morphology, optical and colorimetric behavior were characterized by different techniques. X-ray diffraction, Rietveld refinement and Fourier transform-infrared spectroscopy proved that these NiWO4 crystals present a wolframite-type monoclinic structure, space group (P2/c) and seven infrared-active (4Au and 3Bu) modes from 400 to 1,200 cm−1. A software of three-dimensional visualization for electronic and structural analysis using the Rietveld refinement analysis as input data was employed for modeling the cluster coordination and electron density mapping of the NiWO4 crystals. These data indicate that their lattice is composed of distorted octahedral [NiO6]/[WO6] clusters and inhomogeneous distribution of electronic charges between both clusters. Field emission scanning electron microscopy images were performed to observe the shape and average size of the crystals. Additionally, we investigated the optical band gap values and colorimetric properties through of ultraviolet–visible spectroscopy and colorimetry measures, respectively. Finally, our colorimeter data showed that the NiWO4 crystals obtained can be used as inorganic colored pigments, possibly in the ceramics industry.

Smart waste management of waste cooking oil for large scale high quality biodiesel production using Sr-Ti mixed metal oxide as solid catalyst: Optimization and E-metrics studies

Biodiesel was prepared at laboratory scale via transesterification reaction from waste cooking oil using Sr-Ti mixed metal oxide as a heterogeneous base catalyst. The solid base catalyst was synthesized by polymer precursor method. The most efficient active phase of catalyst was explored by varying the Sr/Ti atomic ratio in mixed metals oxides. The synthesized catalyst underwent for TGA, Powder XRD, SEM, EDX, FT-IR, XPS, and BET surface area analysis to assess its physicochemical characteristics. Additionally, basicity which has been observed as the most process governing factor was also evaluated through Hammett indicator-benzoic acid titration method. The Sr-Ti mixed metals oxide with 4:1 was observed with highest catalytic activity for methanolysis reaction. Its potency was facilitated by fairly acquired BET surface area (43.6 m2/g) and basic strength (2.89 mmol/g). The appreciable values of both the parameters imparted the high catalytic activity in Sr-Ti mixed metals oxide with atomic ratio 4:1. Onward, transesterification reaction was optimized for the maximum FAME conversion through RSM using CCD. The confirmatory tests showed the consistency with the conclusions drawn from RSM study regarding optimized values of concerned process variables. Transesterification reaction turned out 98% FAME conversion exerting catalyst dose (1.0 wt%), methanol to oil molar ratio (11:1), and reaction time (80 min) at reaction temperature (65 °C) and agitation speed (600 rpm) featured by RSM study. The closeness in optimized value of anticipated and confirmatory results perceived the efficiency of CCD and approving its potency as successful tool to estimate the highest FAME conversion. Next, a pseudo-first-order kinetic model of transesterification reaction was established. In addition to this, the thermodynamic functions were also computed through Eyring plot dictating the non-spontaneity and endergonic nature of transesterification reaction. The Environment-factor (E-factor) and Turn Over Frequency (TOF) were enumerated and they approved the prepared Sr-Ti mixed metals oxide as an efficient and sustainable catalyst for biodiesel production through transesterification. Finally, all the important fuel properties of prepared biodiesel from waste cooking oil was discerned within the range laid by ASTM D-6751 standards for biodiesel which coined the compatibility of prepared methyl ester with CI engines as a substitute of diesel fuel.

Effect of the Ce3+ concentration on laser-sintered YAG ceramics for white LEDs applications

This paper describes the laser sintering and luminescence properties of Y3Al5O12 (YAG) phosphors doped with different concentrations of Ce3+ and synthesized using the polymeric precursor method. The ceramics were sintered by a new laser sintering technique in which a CO2 laser is employed as the heating source. The resultant ceramics exhibited a homogeneous microstructure with narrow grain size distribution and high relative density. The introduction of Ce3+ ions led to luminescence quenching at a concentration above 0.5 mol% and a redshift of the emission spectrum band with increasing cerium concentration. The excitation spectrum showed two characteristic bands centered at 340 nm and 460 nm and a relative change in their intensity by change the Ce3+ concentration. The presence of a single valence (Ce3+) of cerium was determined by X-ray absorption near edge structure measurements.

Fotocatálise do Corante Azul de Metileno por Sistemas como SrSnO 3, BaSrSnO3 e CaSrSnO3

Com a grande preocupação da população com os problemas ambientais, têm surgido métodos mais efiazes para o tratamento de eflentes. Nesse contexto, surge o estudo sobre a aplicação dos materiais cerâmicos, por exibir propriedades fotocatalíticas como uma alternativa para a descontaminação de corantes em águas residuais. Este trabalho, reportam-se dados da degradação fotocatalítica do corante Azul de Metileno após a adição do catalisador SnSrO 3 (antes e após a adição de 0,1% Ba e 0,1% Ca). Para tal, amostras foram sintetizados pelo método do Precursor Polimérico, calcinadas à: 500, 800 e 1000 ºC/4 horas e caracterizadas por DRX, UV-VIS e fotocatálise.

Efeito do Substituinte Sr na Transição de Fase do PT: Correlação Teórica e Experimental das Propriedades Eletrônicas e Estruturais

A transição de fase dos compostos PT, PST e ST, sintetizados pelo Método dos Precursores Poliméricos, foram estudados através da correlação teórica e experimental empregando DFT, utilizando o pacote computacional CRYSTAL14. Os modelos foram construídos em uma supercela 1x1x2 utilizando dados do refiamento de Rietveld. Os resultados foram interpretados em termos de Estrutura de Bandas, Densidade de Estados, evolução estrutural e valor de gap. Nestes modelos, foram possíveis a identifiação e a compreensão da transição de fase e redução na relação c/a concluindo que os modelos sofrem transição de fase conforme aumenta-se a concentração de substituinte Sr na matriz do PT.

Influência do Método de Síntese e do Tratamento Térmico na Fotoluminescência de Nanocompósitos de Céria Dopada com Gadolínio/Zircônia

Neste trabalho, os nanocompósitos de interesse foram preparados, utilizando-se o Método dos Precursores Poliméricos, por meio do qual se prepararam os citratos de céria dopados com 10, 15 e 20% de gadolínio, e encapsularam-se com 3% em mol de ZrO2, em diferentes temperaturas. Para a caracterização dos materiais obtidos, utilizaram-se as técnicas de Difração de Raios X e Emissão Fotoluminescente. Verifiou-se que a alta concentração do dopante ocasiona tanto a melhoria na emissão, pela adição de defeitos, quanto a diminuição, pelo quenching da emissão. O aumento na temperatura de tratamento térmico também reduz a emissão, uma vez que diminui a quantidade de defeitos.

Síntese de Condutores Protônicos de Cerato de Estrôncio (SrCeO 3) pelo Método dos Precursores Poliméricos para Uso em Células a Combustíveis

O crescente aumento tecnológico traz consigo a necessidade de se produzir novos materiais que atendam tal evolução de maneira sustentável. Nesse sentido, o estudo de perovskitas de cerato de estrôncio SrCeO3 torna-se de grande relevância, visto que estes materiais possuem propriedade de condução protônica e são bastante utilizadas como eletrólito sólido para células a combustíveis de óxido sólido, as quais são muito importantes para a geração de energia com baixas ou nenhuma emissões de poluentes, por meio de combustíveis renováveis. Logo, o presente trabalho visou sintetizar o SrCeO3 pelo método do precursor polimérico dopado e não dopado e caracterizá-los estruturalmente.

Sol-gel synthesis and electrochemical properties of wolframite FeNbO4

In the current effort, illustrate a different case FeNbO4 with wolframite structure. FeNbO4 was prepared by sol-gel polymeric precursor method in prospect of estimated prominent specific capacity. One cause is owing to the reduction of both Fe and Nb. The electrochemical lithium insertion/extraction studies on wolframite FeNbO4 were conducted with a rate of C/10 in the potential window of 1.0-3.8V. Ex-situ XRD procedure was used to identify the Structural changes all the way through insertion/extraction of Lithium. The details of synthesis and lithium insertion mechanism in FeNbO4 will be discussed.

NiWO4 powders prepared via polymeric precursor method for application as ceramic luminescent pigments

NiWO4 was prepared using the polymeric precursor method and studied in terms of physical and chemical properties to verify its stability for industrial applications as pigments. The characterization was accomplished using thermal analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) and UV–Vis spectroscopies, colorimetric coordinates, and Raman spectra. Increasing the temperature, successive exothermic reactions were observed and they are related with thermal decomposition of the organic compound. The stability was reached at ~700 °C. The material is verified to become completely free of second phase at ~800 °C. The end NiWO4 powders showed an intense charge transfer (CT)-related tail centered in the ultraviolet region, resulting in a yellow product. In addition, the powders exhibited broad excitation band and broad deep blue–green emission band, which were enhanced with increasing powders’ crystallinity.

Interface excess on Li2O-doped γ-Al2O3 nanoparticles

One of the attempts to improve γ-alumina catalytic performance lies in the use of additives that prone to segregate on its interfaces. The catalytic activity depends on the acidity or basicity of the doping oxides. Li2O is one of these oxides that when is loaded on γ-alumina surface decreases the number of Lewis acid sites. However, little is known about the Li2O distribution in the γ-alumina structure and interfaces. Thus, a detailed study of the lithium oxide distribution in the nanostructure of γ-alumina is the aim of this study. Nanometric powders were synthesized by the polymeric precursor method. The nanopowders were doped with Li+ ions (0.1, 0.5, 1, 3, 5, and 10 mol%) followed by calcination at 650 °C and 750 °C for 15 h. The powders were characterized by XRD, XRF, FTIR-DRIFT, BET specific surface area (SSA) and helium pycnometry. The surface excess due to the lithium oxide segregation was determined by the selective lixiviation method which has proved to be effective in quantifying surface excess of segregated ions at oxide interfaces. The crystallite sizes of the nanopowders varied from 3.3 nm to 9.2 nm, while their SSA were between 82.0 m2/g to 119.9 m2/g. The chemical analyses suggest that the lithium segregates in the γ-alumina interfaces at 650 °C, but it volatilizes from the surface after calcination at 750 °C.

Novel eco-friendly method to prepare Ti/RuO2–IrO2 anodes by using polyvinyl alcohol as the solvent

Electrochemical oxidation processes are promising solutions for wastewater treatment due to their high efficiency, effortless control, and versatility. Mixed metal oxides anodes are particularly attractive due to their low cost and specific catalytic properties. Here, we report the synthesis of a new Ti/RuO2-IrO2 anode fabricated through an innovative eco-friendly methodology using polyvinyl alcohol (PVA) as the solvent. Comparative anodes were also prepared by the conventional method of polymeric precursors. For both methods, anodes were calcined at 300, 400, and 500 °C. X-ray diffraction data confirmed the formation of RuO2 and IrO2 in the rutile-type structure for all conditions. Moreover, compared to conventional polymeric precursor method, PVA-made anode obtained at 300 °C presented increased voltammetric charge (210%), besides reduced charge-transfer resistance (1.8-fold lower). Electrochemical degradation of the Reactive Blue 21 dye showed that the PVA-made Ti/RuO2-IrO2 anode has the highest degradation efficiency, and its kinetic rate constant is until 2 times greater than the conventional anode. Besides, due to rougher and more compact surfaces, the better adhesion of the film observed for the PVA-made anodes, the accelerated service lifetime of the anode was prolonged 4.3-fold.

RuO2–IrO2 solid state micro-liquid film pH sensor based on polymeric precursor method

The glass-type electrodes based pH sensors suffer from the weakness of fragility and poor stability in acid/alkali solution. To overcome these disadvantages, a novel solid-state pH sensor based on a RuO2–IrO2 H+ sensitive electrode via a polymeric precursor method was developed in this paper. The electrochemical performance of pH sensor was tested in different conditions. The experimental results showed that the sensitivity of the pH sensor could reach a high level of 52.0 mV/pH in a wide pH range of 2 ∼ 10. Furthermore, the response of pH sensor was fast and the response time remained less than 2.2 s even under varying pH conditions. The experiment was repeated three times during a period of time, the potential difference of pH sensor was between ±0.3 mV and ±0.9 mV in different pH value solutions, demonstrating its good stability, repeatability, recyclability and small potential drift. The negligible interference of Li+, Na+, K+, Ca2+, Mg2+, to the proposed pH sensor was also proven experimentally.

Rare-earth-free zinc aluminium borate white phosphors for LED lighting

A novel family of rare-earth-free white phosphors was synthesized by the polymeric precursor method, based on the trapping of molecular emitters in a zinc aluminium borate matrix, resulting in an intense and easily tuneable photoluminescence.

Defect dipole-induced high piezoelectric response and low activation energy of amphoteric Yb3+ and Dy3+ co-doped 0.5BaTi0.8Zr0.2O3-0.5Ba0.7Ca0.3TiO3 lead-free ceramics

Co-doping of piezoelectric ceramics by amphoteric rare earth ions has resulted in synergistic improvement of their electrical properties. In this study, Yb3+ and Dy3+ co-doped lead-free 0.5BaTi0.8Zr0.2O3-0.5Ba0.7Ca0.3TiO3 nanoparticles and ceramics were prepared. The synthetic process of the nanoparticles by a modified Pechini polymeric precursor method was studied by FT-IR, TG-DSC, HRTEM, XRD, and Raman spectroscopy. The densified (>96%) ceramics were obtained by sintering the as-synthesised nanoparticles at 1220 °C, and the influence of Yb content (x) on the phase structure, permittivity, ferroelectricity, piezoelectricity, and thermophysical performances was studied. Initially, for low x, Yb3+ occupied A sites in the perovskite structure as donor dopants, resulting in improved ferroelectric and piezoelectric properties and decreased domain switching activation energy with few oxygen vacancies; while the electrical properties deteriorated as x increased further. The relationships of the defect dipole-induced electrical properties or/and activation energy with internal stress, structure distortions, and impurity phase were deduced. The optimum piezoelectric coefficient (d33* = 683 p.m./V) with the lowest domain switching activation energy (Ea = 0.233 eV) was determined at x = 0.60 mol%, indicating that the ceramics were suitable for practical applications.

Fabrication of SrTiO3/g-C3N4 heterostructures for visible light-induced photocatalysis

We investigated a new method for the preparation of visible light-activated heterostructured photocatalysts made up of SrTiO3 (STO) and g-C3N4 (CN). The photocatalysts were synthesized by the polymeric precursor method to obtain STO, which was further thermally treated at 550 °C for 2 h in presence of melamine at different proportions for CN formation. The SrTiO3/g-C3N4 heterostructures were termed as STOCN-Mel88%, STOCN-Mel92%, STOCN-Mel95%, STOCN-Mel97% and STOCN-Mel99% indicating the use of melamine at 88%, 92%, 95%, 97% or 99%. The SrTiO3/g-C3N4 heterostructures were characterized for their crystalline structure, optical properties, thermal stability, morphology and surface composition, and photocatalytic potential, which was evaluated by photodegradation of methylene blue dye and amiloride under visible light. The melamine content exhibited a strong influence on the formation of CN, as well as on the bulk structure, surface and photocatalytic properties of the SrTiO3/g-C3N4 heterostructures. The heterostructures were catalytically active under visible light due to their reduced band gap energy. The presence of oxygen vacancies in the STO phase associated with the CN phase improved the photogenerated electron-hole charge separation in the SrTiO3/g-C3N4 catalysts. The synthesis described here is efficient in obtaining visible light-activated photocatalysts that are applicable to photocatalytic processes under solar light.

Studies on fast and green biodiesel production from an indigenous nonedible Indian feedstock using single phase strontium titanate catalyst

Strontium titanate was synthesized by polymer precursor method and its catalytic activity as heterogeneous basic catalyst was tested in transesterification reaction for high-quality biodiesel production form Madhuca indica oil. The synthesized strontium titanate was characterized by powder X-ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM) attached with Energy Dispersive X-ray Spectroscopy (EDS), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR). Surface area and basicity were also determined using Brunauer-Emmett-Teller (BET)surface area analyzer and Hammett indicator method. The structural characterizations of catalyst enunciated the single perovskite phase formation of well-assorted strontium titanate nanospheres. The transesterification reaction was optimized using one variable at a time (OVAT) and Response Surface Methodology (RSM) using Box Behnkehn Design (BBD) to comprehend the linear effect and interactive effect of process variables on biodiesel production. The optimized reaction condition through OVAT was obtained as: catalyst dose (1.3 wt%), methanol to oil molar ratio (18:1), reaction temperature (65 °C), reaction time (120 min), and agitation speed (600 rpm) while RSM predicted the highest methyl ester conversion at optimum catalyst dose (1.19 wt%), methanol to oil molar ratio (21.5:1), reaction temperature (71 °C), and reaction time (97.7 min). The confirmatory experiment noticed the highest 98% FAME conversion at following reaction conditions catalyst dose (1.2 wt%), methanol to oil molar ratio (22:1), reaction temperature (65 °C), and reaction time (100 min). Confirmatory experiment showed its close agreement with the predicted values from RSM instead OVAT. According to RSM, catalyst dose, reaction temperature, reaction time, and methanol to oil molar ratio were influencing process parameters for transesterification in descending order of their strength. Furthermore, a pseudo-first-order kinetic model was established with the activation energy (Ea) of 65.95 kJ mol−1. The Environmental Factor (E-factor) and Turn Over Frequency (TOF) were also determined and demonstrated the prepared catalyst as a sustainable and potential heterogeneous base catalyst. The physicochemical properties of produced biodiesel were evaluated to check its compatibility with conventional diesel fuel.