► We used different ratios of alginate and k-carrageenan to obtain composite films. ► The composite films were cross-linked in two stages with CaCl2. ► The structures of the composite films were ...analysed by FTIR, XRD, DTG, TG and SEM. ► Cross-linked composite films show mechanical and swelling properties of hydrogels. ► The 1/3 alginate/k-carrageenan films are suitable for drug delivery applications.
The purpose of this work was to prepare an alginate/k-carrageenan composite film cross-linked with CaCl2 that could be used in biomedical applications. The influence of the alginate/carrageenan ratio on the composite films properties was studied in order to establish the optimal composition of the films. Several characterization methods such as: FTIR, XRD, TG/DTG, SEM were used, and the mechanical properties and the swelling behaviour of the obtained composite films were studied.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
MWCNT-CoFe2O4 nanocomposites were prepared in sequential synthesis steps by decorating CoFe2O4 nanoparticles on the surface of functionalized MWCNT. Initially, the CoFe2O4 nanoparticles were obtained ...by chemical precipitation and subsequently, the obtained CoFe2O4 nanoparticles were anchored on functionalized MWCNT through polymer wrapping. The thermal analysis approaches namely, evolved gas analysis (EGA) coupled with FT-IR spectra were involved in highlighting the sequential steps mechanism for obtaining MWCNT-CoFe2O4 nanocomposites. The composite formation was proved by X-ray Diffraction (XRD), Scanning Transmission Electron Microscopy (STEM), FT-IR spectroscopy, X-ray Photoelectron Spectroscopy (XPS). The influence of CoFe2O4 content on the magnetic and textural properties (surface area and porosity measurements) of the obtained nanocomposites was evidenced. Depicting the importance of thermal stability of nanomaterials in different industrial applications, the thermal behavior of MWCNT and CoFe2O4 was pointed out. Furthermore, the photocatalytic activity against organic pollutants such as Rhodamine B (RhB) and oxytetracicline (OTC) were evidenced. Additionally, it was evidenced that the MWCNTs acquired ferromagnetic behavior through spin polarized electron transfer from the CoFe2O4. The electron spin resonance spectroscopy (ESR) coupled with spin trapping technique was used to evidence the generation of reactive oxygen species (ROS). The obtained results suggest the efficient anchoring of CoFe2O4 on MWCNT through polymer linkage resulting in a thermal stable magnetic recoverable photocatalyst. The photocatalytic mechanism was discussed in terms spin polarized transitions and ROS generation. During the irradiation superoxide anion (O2-), hydroxyl (•OH) radical and nitroxide were detected.
•MWCNT-CoFe2O4 nanocomposites were prepared by polymer wrapping techniques.•The formation mechanism of CoFe2O4 on MWCNT was evidenced.•The MWCNT-CoFe2O4 nanocomposites are effective for RhB and OTC removal.•The photocatalysis mechanism is enhanced by the presence of cobalt ferrite.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Despite the rapid development of a wide variety of materials, zinc oxidic based compounds remain important multifunctional materials. Optimization of synthesis parameters is an essential step in ...controlling the morpho-structural properties of nanomaterials. For example, preparation of high purity ZnO without additional calcination stage as well as achieving reproducible larger batches is still a great challenge of our days. In this study we report a simple synthesis route for ZnO nanoparticles at room temperature, without any additives and without additional calcination stages using diisopropylamine (DIA) as precipitating agent. The study is focused on changing the molar ratio, the volume and the flow rate of the reactants. Depending on the pH evolution, the phase composition can be controlled to form zinc oxide, zinc hydroxide or layered zinc acetate. Pure zinc oxide phase was obtained at pH ~8 with DIA excess at least of 3 mole. The changes of the morpho-structural and optical properties of samples were investigated by X-Ray diffraction, infrared spectroscopy, scanning electron microscopy, mineralogical optic microscopy, optical and photoluminescence spectroscopy. A better understanding of the crystalline phases formation was achieved using theoretical calculation (DFT) with a good match of the results with the experimental ones. Luminescent studies showed that the emission of ZnO is in green spectral domain at ~548 nm due to V
O
→ VB transitions while the layered zinc acetate exhibits a much more complex blue emission at ~ 442 and 476 nm due to Zn
i
contributions. The luminescent mechanism was proposed, in order to explain the luminescent behavior of samples.
Graphical Abstract
The pH evolution during the precipitation affects the morphology of the samples (layered, rounded aggregates). The blue or green luminescent emission is due to the presence of interstitial zinc (Zn
i
) and oxygen vacancies (V
o
) in layered zinc acetate or ZnO structures.
Highlights
ZnO, Zn(OH)
2
and Zn
5
(OH)
8
(Ac)
2
∙4H
2
O were prepared by precipitation.
Preparative parameters were optimized for larger batches of ZnO.
The phase purity and structural parameters are affected by pH evolution.
Triangular, rounded, tetragonal bipyramid and lamellar structures were obtained.
Blue and green luminescence peaked at 442 and 550 nm is due to Zn
i
and V
o
defects.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this study we present our first attempts to obtain silicate apatite phosphors by precipitation with NaOH under microwave conditions. Y and La precursors fired at different temperatures ...(800 °C÷1400 °C) led to phosphors with hexagonal apatite structure belonging to the space group P63/m and with crystallites size up to 105 nm. The structure and chemical composition of samples were evaluated based on FTIR, XRD and ICP-OES while the morphology, surface state and porosity were revealed using SEM and BET investigations. The impact of the firing temperature on the purity phase, crystalline order degree, crystallites size and luminescent properties of the apatite phosphors are discussed. It was found that the nature of rare earth (Y3+ or La3+) same as the incorporation degree of activator (Tb3+) is responsible for the apatites green - turquoise emission. ICP-OES measurements show that the Tb3+ amount incorporated in the apatite lattice increase with firing temperature and is lower in La-phosphors compared with Y-phosphors. The 5D4–7F5 transition observed in the green spectral domain was dominant in Y- phosphors while 5D3-7F6,5,4 transitions from blue spectral region was dominant in La-phosphors. The chromatic coordinates shifts from green to turquoise with firing temperature and depends on the excitation radiation, indicating the applicative potential of these phosphors in display screens for solid-state lighting applications.
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•First attempts to prepare Ca2RE7.88Tb0.12(SiO4)6O2 under microwave conditions.•Incorporation degree of activator (Tb3+) increase with firing temperature.•Morpho-structure, surface state and porosity depend on synthesis conditions.•Green emission was obtained for Y-phosphors and turquoise for La-phosphors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
La
10−x
Bi
x
(SiO
4
)
6
O
3
ceramics (x = 0; 0.1; 0.15; 0.2; 0.3) were obtained from precursors prepared by gel combustion using
l
-aspartic acid as fuel. This study presents the effect of Bi
3+
...doping level and sintering temperature on the morpho-structural and electrical properties of apatites. Processes involved in the apatite formation same as crystallization temperature were examined through TGA. The XRD patterns have showed that all samples adopt the apatite structure and crystallize in the hexagonal space group P-3(147). Samples crystallite size varies between ~ 58 and ~ 118 nm depending on the Bi
3+
doping level and the sintering temperature. In order to explain the conduction in apatite, the preferential position of Bi
3+
in lattice and the occupancy factors of O5, O6 were calculated by Rietveld refinement. ICP-OES and XPS measurements give the bismuth amount accommodated in apatite lattice and its oxidation states. The morphology, homogeneity and compactness of the ceramics at different Bi doping level were examined through SEM. The relative density of the material is enhanced by the sintering temperature up to 1500 °C, reaching 91.63% for sample doped with 1.5% Bi. Through EIS investigations, the conductivities at 500 °C, for sample doped with 1.5% Bi, are: 9.22 × 10
−5
Scm
−1
(sintered at 1400 °C) and 1.02 × 10
−3
Scm
−1
(sintered at 1500 °C), respectively, values which are higher than that of un-doped apatite (6.46 × 10
−5
Scm
−1
).
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Red light (600–800 nm) plays an important role in the photosynthesis process of plants, therefore the development of red-light emitting phosphors for plant growth LED devices is of real interest from ...scientific and technological point of view. In this study, different compositions of niobate perovskites with the general formula LixMg2Nb0.992−yVyMn0.008O6 (x = 1–5, y = 0–0.25) were prepared by solid-state reaction. The influence of the lattice composition over the luminescent properties of phosphors was studied following two research directions. The first direction implies changes in the charge balance of the perovskite by varying the Li+ amount in the host lattice, while the second strategy produces lattice deformation through incorporation of various amounts of V5+at Nb5+ sites. The crystal structure, chemical composition, optical band gap, oxidation state of doping ions and luminescence properties of the samples are studied in detail. Under 483 nm excitation the photoluminescence spectra exhibit intense red emissions ascribed to the 2E→4A2 transition in Mn4+. It has been found that the addition of V5+ in Li4Mg2Nb0.992Mn0.008O6, intensifies the red emission even more with percentages up to 32 %.
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•LixMg2Nb0.992−yVyMn0.008O6, (x = 1÷5, y = 0÷0.25) samples were prepared by solid state reaction.•The phase purity and structural parameters are affected by the amount of Li+ and V5+.•Depending on the composition, Mn4+, Mn2+ and V4+ were identifies affecting luminescence.•Red luminescence is peaked at ∼658 due to 2E→ 4A2 transition in Mn4+.•Addition of 25 % mole of V5+ in perovskite with x = 4 increases the red emission with 32 %.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Silicates with apatite structure have become one of the most promising candidates for solid-state lighting applications. Herein we report the synthesis of pure apatite Ca
2
Y
7.76
Ce
0.12
Tb
0.12
...(SiO
4
)
6
O
2
phosphors with enhanced luminescence via a simple precipitation method. The aim of this study is to optimize the precipitation reaction through pH control and TEOS amount. In this respect, different types of precursors were prepared by precipitation between yttrium–calcium–cerium–terbium nitrates and NaOH at various pH. The extremely complex decomposition processes of precursors are discussed based on thermogravimetric analysis. The structure, morphology, surface state and porosity of both precursors and phosphors were investigated based on FTIR, XRD, SEM and BET. It was found that the crystallinity degree of the precursors decreases from 36% to 5% with the increase of pH from 7 to 11. After the thermal treatment, the phosphors become pore-less and well crystallized with crystallite sizes up to 106 nm. The phase composition of the phosphors strongly depends on the pH during the precipitation. Synthesis performed with 40% excess of TEOS at pH 11 led to phosphors with pure apatite structure and enhanced luminescence. Under excitation with 365 nm the apatite phosphors exhibits a broad emission band in the range of 350–480 nm, due to transitions in Ce
3+
and narrow lines in range of 480–650 nm specific for transitions in Tb
3+
.
Highlights
Gel precursors are prepared by precipitation at different pH for synthesis of apatite phosphors.
pH affects the morpho-structure and surface state of both precursors and phosphors.
Pure apatite with crystallites size of 66.5 nm was obtained at pH 11.
Effect of pH on Ce
3+
and Tb
3+
emission intensities was discussed in detail.
Apatites show blue, white-turquoise or greenish colour depending on excitation.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Different types of gel precursors were obtained via microwave-assisted precipitation, gel-combustion, sol–gel, and Pechini methods in order to prepare Ca
2
Y
7.76
Ce
0.12
Tb
0.12
(SiO
4
)
6
O
2
...phosphors with apatite structure. The processes involved during the thermal treatment of precursors were revealed by TGA– FT-IR coupling. ICP-OES reveals that the incorporation degree of dopants (Ce
3+
, Tb
3+
) in silicate lattice are close to theoretical values while Ca
2+
and Y
3+
values shows differences depending on the synthesis route. The phosphors composition, morphology, structure, and optical characteristics are revealed by SEM, XRD, FTIR, and luminescent investigations. Pure hexagonal apatite with crystallite size of 76.5 nm was identified in sample prepared by gel-combustion, while cubic-Y
2
O
3
and monoclinic-Y
2
SiO
5
, as secondary phases, were found in precipitated samples. The purity phase was enhanced by increasing the TEOS amount during precipitation. As a result of the Ce
3+
incorporation into different symmetry sites, the excitation spectra are dominated either by 321 or 360 nm band. Turquoise emission of apatites is shifted toward blue region by increasing the excitation wavelength from 231 to 360 nm.
Highlights
Ce–Tb-doped silicate apatite phosphors were prepared using four different synthesis routes.
The thermal decomposition of gel precursors was evaluated based on TG-FTIR.
Pure apatite with crystallites size of 76.5 nm was obtained using gel-combustion.
Structure and luminescence of apatites was improved using 50 mol% excess of TEOS in precipitation.
Excitation spectra are dominated by 321 or 360 nm band depending on phase purity.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Inorganic luminescent materials comprise a wide range of compounds showing a large area of applications in sensing, imaging, drug delivery or optical-electrical displays. In this study, various ...luminescent zinc hydroxy-carbonate compounds were prepared by precipitation using different precipitating agents such as LiOH, NH
3
, Na
2
CO
3
and (NH
4
)
2
CO
3
. The morpho-structure and optical properties of samples are investigated by X-Ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), adsorption and porosity measurements (BET), optical (UV–Vis) and photoluminescence (PL) spectroscopy. The phase composition, morphology and porosity of zinc hydroxide (ZH) and zinc hydroxy-carbonates (ZHC) strongly depends on the evolution of pH and availability of different ionic species during the precipitation. The spherical particles of zinc hydroxy-carbonate compounds with sizes ranging between 5 and 20 nm, exhibits strong tendency to form layered or spongy aggregates. BET investigations show that the porosity is distributed either at the surface (ZH) or in the depth of the particles (ZHC) and the specific surface area of samples varies between 15 m
2
/g. and 55 m
2
/g. The effect of various amounts of Cu
2+
on optical properties of samples is also discussed. Luminescent studies confirm that interaction with Cu
2+
leads first to enhancement and then to quenching of the purple–blue emission of samples while, the energy band gap decreases due to the apparition of new acceptor–donor levels in the optical band gap. A mechanism is proposed to explain the luminescent behavior of the samples.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•Y2SiO5:Ce was prepared by combustion using aspartic or glutamic acid as fuels.•Combustion process occurs differently depending on the fuels amount.•Single phase X2-Y2SiO5 phosphors were obtained in ...fuel rich conditions.•PL measurements indicate that aspartic acid is a better fuel than glutamic.•Optimal preparative conditions were established for synthesis of Y2SiO5:Ce.
Cerium activated yttrium silicate (Y2SiO5:Ce) phosphors were prepared by combustion, using yttrium–cerium nitrate as oxidizer, aspartic or glutamic acid as fuel and TEOS as source of silicon. In this study, aspartic and glutamic acid are used for the first time for the synthesis of Y2SiO5:Ce phosphors. The fuels molar amount was varied from 0.5mol to 1.5mol in order to reveal the thermal behavior of intermediary products (gels and ashes) same as the structural and luminescent characteristics of final products (phosphors). According to thermal analysis correlated with FTIR and XPS investigations, the combustion process occurs differently depending on the fuel amount; unreacted nitrate compounds have been identified in fuel lean conditions and carbonate based compounds along with organic residue in rich fuel conditions. The conversion to well crystallized silicates was revealed by changes of FTIR vibration bands and confirmed by XRD measurements. Based on luminescent spectra, aspartic acid is a better fuel than glutamic acid. A positive effect on the luminescence have been observed for samples fired in air due to complete remove of organic residue. The best luminescence was obtained for combustions with 0.75mol aspartic acid and 1.25mol glutamic respectively, fired at 1400°C for 4h in air atmosphere.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
