Browsing by Author "Salaheldin, Taher A"

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    Silica-coated graphene compared to Si-CdSe/ZnS quantum dots: toxicity, emission stability, and role of silica in the uptake process for imaging purposes
    (Elsevier, 2022-05) ElZorkany, Heba ElSayed; Farroh, Khaled Yehia; El-Shorbagy, Haidan M; Elshoky, Hisham A; Youssef, Tareq; Salaheldin, Taher A; Sabet, Salwa
    Quantum dots (QDs) present a special type of nanocrystals (NCs) due to their unique optical and chemical properties. While cadmium- based QDs (Cd-QDs) have the most favorable physicochemical properties, their toxicity, instability in the aqueous phase, and loss of brightness at high temperature are some of the obstacles that prevent the wide use of Cd-QDs. Carbon-based QDs as graphene quantum dots (GQDs) represent a very promising biocompatible replacement. In the present work, we mainly focus on comparing the efficiency and uptake of GQDs and Cd-QDs for fluorescent imaging purposes and studying the. effect of growing silica shell on the emission and the uptake of QDs inside living human and bacterial cells. Graphene and CdSe/ZnS QDs were prepared and encapsulated in silica to increase their emission and uptake by living cells. Moreover, we studied their photostability and cytotoxicity. The Prepared G-Si QDs showed good emission inside the cytoplasmic portion of the liver hepatocellular carcinoma cell line (HepG2) and Bacillus subtilis (B. subtilis), but they revealed lower photoluminescence (PL) intensity compared to Si-CdSe/ZnS NCs although G-Si QDs are advantageous in other aspects, i.e. possess lower toxicity and higher stability with temperature variations.
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    Structure, magnetic and magnetocaloric properties of nano crystalline perovskite La0.8Ag0.2MnO3
    (ELSEVIER SCIENCE BV, 2019-06) AboZieda, Abd El-Rahman T.; Ghani, A. A; Ali, Ahmed I; Salaheldin, Taher A
    Nano crystalline La0.8Ag0.2MnO3 perovskite compound was prepared using sol-gel method. The synthesized nano compound was characterized using X-ray Diffraction (XRD) and High Resolution - Transmission Electron Microscope (HR-TEM). The magnetic and magnetocaloric properties were studied in a broad temperature range, and confirmed the presence of ferromagnetic-paramagnetic (FM-PM) transition around Curie temperature (T-C = 306 K). We reported a maximum magnetic entropy change vertical bar Delta S-M vertical bar(max) = 0.96 J/kg.K with relative cooling power (RCP) = 39.98 J/kg at magnetic field 2 T. Such results could be a significant practical application in magnetic refrigeration. The observed magnetic phase transition in the sample was testified a second order. The critical exponent analysis which define the magnetic transition revealed values 0.4025 for beta, 3.33 for delta and 0.93 for gamma. These values are closely related to those obtained by the mean field model. The second order magnetic phase transition is further confirmed by constructing a universal curve for variation of vertical bar Delta S-M vertical bar/vertical bar Delta S-max vertical bar vs rescaled temperature (theta) for various magnetic field values.
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    Synthesis, structural, magnetic and magnetocaloric properties of La0.8Sr0.2MnO3 nanoparticles
    (SPRINGER, 2019-04) Ali, Ahmed I; AboZied, Abd El-Rahman T; Ghani, AA; Salaheldin, Taher A
    In this work, we reported a detailed study on the synthesis, structural and magnetic properties of nanocrystalline La0.8Sr0.2MnO3. The synthesized nanoparticles were prepared using a sol-gel method and characterized using X-ray diffraction and high-resolution transmission electron microscope. The average particle size was found in the range from 40 to 45 nm. The magnetization versus temperature M(7) measurements as well as magnetization field dependence M(H) have been investigated using vibrating-sample magnetometer. The magnetization as a function of temperature M(7) indicated a broad second-order magnetic phase transition from ferromagnetic state to paramagnetic state in the Curie temperature region (320-340 K). The magnetocaloric effect of the sample has been estimated and presented a maximum magnetic entropy change vertical bar Delta S-M vertical bar(max) = 0.86 J kg(-1) K-1 with relative cooling power = 62.12 J kg(-1) at magnetic field (H) = 2T. Based on the result of magnetocaloric properties, the investigated sample could be considered as a good refrigerant material for near room temperature magnetic refrigeration.