Synthesis of Y2O3: Eu Luminescent Phosphor with Increased Dispersion for Use in Medical Purposes

Photodynamic therapy (PDT) is a promising modern method for treatment of oncological, bacterial, fungal and viral diseases. However, its application is limited to diseases with superficial localization since the body tissues are not transparent for visible light. To address this problem and extend PDT application to abdominal diseases, an enhanced method of X-ray photodynamic therapy (XRPDT) is suggested, involving X-ray radiation easily penetrating the body tissues. The implementation of this approach requires the development of a pharmacological drug including a photosensitizer stimulated by visible light to yield active oxygen and a nanosized phosphor converting X-ray radiation into visible light with the wavelength required for the photosensitizer activation. This study is aimed at obtaining X-ray stimulated phosphors with nanosized particles suitable for XRPDT application. For this purpose, Y2O3:Eu phosphors were synthesized via hydrothermal processing of the corresponding mixed acetate followed by annealing. To prevent from the undesirable agglomeration of the particles in the course of hydrothermal synthesis and subsequent annealing, different techniques were used, including rapid thermal annealing (RTA), microwave annealing and addition of finely dispersed pyrogenic silica (aerosil) to the phosphor. The microwave annealing was carried out using a special installation including a resonance chamber for maintaining a standing wave of microwave radiation. The performed research allowed the determination of hydrothermal processing optimal duration affording the synthesis of phosphors with the highest luminescence brightness. The application of microwave annealing is found to provide phosphors with a more perfect crystal structure compared with RTA. The developed method of Y2O3:Eu phosphor synthesis involving pyrogenic silica addition to the autoclave allowed the preparation of samples with the amorphous structure and significantly reduced the particle size without a considerable decrease in the luminescence brightness. The particle size of the phosphor synthesized with aerosil addition is less than 100 nm that allows its implementation in pharmacological drugs for XRPDT.

Investigation on the Properties of Sustainable Reactive Powder Concrete by Utilization of Coir Pith Aggregates and Pyrogenic Silica

The present study investigates the properties of RPC developed using low cost eco-friendly materials such as pyrogenic silica (PS) and coir pith (CP) fine aggregates. This study investigates the effects of PS as silica fume replacement which is the main constituent for the production of reactive powder concrete which contained coir pith as a fine aggregate replacement instead of quartz sand up to 25%. The use of silica fume increases the particle packing density of RPC but increases the shrinkage phenomenon in RPC due to the minimum w/b ratio adopted. Therefore, in this research PS is used as a partial substitute for SF up to 30% and its effect on the mechanical and durability properties of coir pith containing RPC is studied. The test results showed that the mechanical strength values decreased with an increase in the addition of CP aggregate beyond 5% whereas the decrement in compressive strength was partially reduced when PS is used as silica fume replacement up to a maximum of 30%. The chloride penetration resistance was also improved with increasing PS substitution in RPC containing CP aggregates. The autogenous shrinkage and drying shrinkage were also significantly reduced due to the internal curing ability of the CP aggregates in combination with PS. The development of dense CSH gels from hydration is also evident from low CaO/ SiO2 ratio obtained from the EDS analysis. Hence the combination of PS with CP aggregates can reduce the shrinkage characteristics of RPC thereby providing eco-friendly sustainable concrete at low cost.

Synthesis and properties of nanocomposites based on zinc phosphate and fumed silica

The aim of the work was to synthesize nanocomposites based on pyrogenic silica and zinc phosphate by a simple method without using a large amount of solvent and to study the characteristics and properties of the obtained materials. The dual systems of zinc phosphate/pyrogenic silica with the different ratio of components were synthesized via mechanical grinding in a porcelain drum ball mill of fumed silica (Orysyl A-380), zinc acetate (Zn(CH3COO)2·2H2O) and phosphoric acid with distilled water, followed by air-drying in an oven at 125 °C (2 h) and calcination in a muffle oven at 450 °C for 2 h. The zinc phosphate content was 0.1, 0.2, and 0.3 mmol per 1 g of SiO2. The control sample (ZP-K) was synthesized by thermal treatment of the precipitate, formed after mixing on a magnetic stirrer an aqueous solution of zinc acetate with the addition dropwise of phosphoric acid, without the use of SiO2. X-ray diffraction studies of the nanocomposites confirmed the formation of the crystalline phase of Zn3(PO4)2·4H2O (orthorhombic modification) both in the silica-containing and control ZP-K samples after air drying at 125 °C, while heat treatment at 450 °C leaded to the formation of the anhydrous monoclinic Zn3(PO4)2 phase. The content of the zinc phosphate in the dual composites was 0.1, 0.2, and 0.3 mmol per 1 g of SiO2. The IR spectra of the nanocomposites indicated the presence of absorption bands in the range of 3760-3600 cm-1, which were attributed to the unequal structural ‒OH groups of silicon and phosphorus atoms. It was found that the presence of zinc phosphate on the SiO2 surface does not cause the chemical interaction with silica during heat treatment of composites in air even at 900-1000 °C. It was shown that the ability of Zn3(PO4)2/SiO2 composites to adsorb water vapor decreases with increasing amount of modifying compound. The effect of the obtained phosphorus-containing nanocomposite on the thermal stability of an alkyd polymer matrix was considered.

HDPE/SILICA COMPOSITES- PART I: PREPARATION AND CHARACTERIZATION OF METHYLSILANE AND OCTYLSILANE-MODIFIED SILICAS

This paper reports the main results concerning the synthesis and characterization of methylsilane and octylsilane-modified silicas. The modification of the silicas with these groups aims to make the silica surface hydrophobic and thus compatible with high-density polyethylene (HDPE) in HDPE/silica composites. In the present work, two types of silica were organofunctionalized: a pyrogenic silica and a silica gel. The silicas were characterized by a series of complementary techniques with the objective of investigating the nature of the surface species and their textural and morphological characteristics. The SEM images showed that the modification of the silicas with organosilanes has been not resulted in changes on the morphology and on the size of silica particles. In relation to the texture properties, determined by N2 adsorption-desorption porosimetry, the silica modification resulted in a decrease of the specific area (SBET) and the mean pore volume, a behavior attributed to the partial coverage of the adsorption sites by the organosilane molecules. The TGA analysis showed that both the methylsilane groups and the octylsilane groups on the surface of silica and silica gel are thermally stable up to 200 ° C, which enables the organofunctionalized silicas in terms of thermal stability, for the process of preparing the composites by extrusion. The results of applying these organofunctionalized silicas in the development of HDPE/silica composites will be presented in a subsequent article, part II of this research.

HDPE/SILICA COMPOSITES-PART II: EFFECT OF SILICA PARTICLE SIZE AND SILICA MODIFICATION ON THE THERMAL AND MECHANICAL PROPERTIES

In this work, the effect of silica particle size and organosilane type used in the silica organofunctionalization on the thermal and mechanical properties of high-density polyethylene (HDPE)/silica composites were evaluated. HDPE/silica composites were prepared by the extrusion method using two types of silica: fumed silica, with nanometric particle size and silica gel, micrometric, modified with organosilanes containing methyl or octyl functional groups. Silicas were added to the HDPE at 1% v/v concentration. The addition of the silicas to the HDPE did not influence the melt (Tm) and the crystallization (Tc) temperatures of the resulting composites but influenced its crystallinity. The mechanical property of Izod impact strength, the dynamicmechanical rheological test (DMTA) and the surface contact angle analysis showed improvements in relation to pure HDPE when used methyl-modified pyrogenic silica as filler. This result suggests that the surface modification of pyrogenic silica with methylsilane groups results in a stronger interaction of this silica with the HDPE matrix. This effect was not observed for micron-sized silica gel, where modification with organosilanes was not sufficient to guarantee interfacial interaction with the HDPE matrix.