Design of Defect and Metallic Silver in Silver Phosphate Photocatalyst Using the Hydroxyapatite and Glucose

The defect and metallic silver (Ag) in silver phosphate (Ag3PO4) photocatalyst were successfully generated using hydroxyapatite (HA) and glucose. Two steps of synthesis were done in these experiments. Firstly, the Ag/HA powder was prepared by reacting AgNO3 and HA, followed by the addition of a glucose solution. Secondly, the suspension of Ag/HA was reacted with AgNO3 aqueous solution. The yellow product of Ag/Ag3PO4 photocatalyst was produced. The products were characterized using X-Ray Diffraction (XRD), Diffuse Reflectance Spectroscopy (DRS), Scanning Electron Microscope (SEM), Brunauer–Emmett–Teller (BET) and X-ray Photoelectron Spectroscopy (XPS). The decreased ratio of O/Ag and metallic Ag formation observed by the XPS was detected as the possible defect and Ag-doping in the photocatalyst. The enhanced photocatalytic activity might be caused by the oxygen vacancy and metallic Ag in Ag3PO4 that enables the separation of photo-generated electrons and holes.

Crystal Chemistry of the Microporous Zirconosilicate Na6Zr3[Si9O27], a Product of High-Temperature Transformation of Catapleiite, and Its Ag-Exchanged Form

The crystal structure of the Ag-exchanged form of the zirconosilicate with the simplified formula (Na6-2xCax▯x)Zr3[Si9O27] with x < 1 (the idealized formula Na6Zr3[Si9O27]), a product of thermal transformation of catapleiite, ideally Na2Zr[Si3O9]·2H2O, was studied using single crystal X-ray diffraction data. The crystal structure of Na6Zr3[Si9O27] is based on a heteropolyhedral framework built by nine-membered tetrahedral rings [Si9O27] and isolated [ZrO6] octahedra. This zirconosilicate demonstrates high exchange capacity to Ag (experiment with 1 M AgNO3 aqueous solution, 250 °C, 30 days). Its Ag-exchanged form with the simplified formula (Ag5Ca0.5)Zr3[Si9O27] is characterized by a significant distortion of the heteropolyhedral framework and strongly disordered arrangement of extra-framework cations (Ag) which results in the doubling of a parameter of the hexagonal unit cell [a = 23.3462(3), c = 10.10640(10) Å, V = 4770.45(13) Å3] and space group P63cm. Ag+ cations preferably occupy the sites that are close to the Na sites in Na6Zr3[Si9O27].

Adhesive systems used for sealing contaminated surfaces: a microleakage evaluation

The aim of this study was to compare two adhesive systems (OptiBond FL TM and OptiBond SOLO TM) used as a sole material for sealing pit and fissures on contaminated surfaces with respect to microleakage. After acid etching, 56 sound teeth were contaminated with 1 µl of plasma and randomly divided into 8 groups (n = 7). The adhesives were light activated under two conditions (Optilux VCL-403TM and VCL-500TM) for 30 s. Each specimen was exposed to one of the following aging treatments: thermal (4,000 X at 5-55°C for 60 s) plus load cycling (225,000 X with 83.3 N) or thermal plus load and pH cycling (mineralizing/demineralizing solutions). Then, they were immersed in a 50% AgNO3 aqueous solution, sectioned twice and had dye penetration measured through digitized images. ANOVA methods were used to assess the main effects of the factors as well as their interactions. The results indicated a significant difference between the adhesive systems (p < 0.05), suggesting that OptiBond FL TM has a better performance with respect to microleakage and could be used as a sealing material in accidentally moist or contaminated surfaces.