Antimicrobial Colloidal Suspensions of Silver-Titania

Abstract

Titanium dioxide nanoparticles (TiO 2 Np) exhibiting properties of photocatalyst under ultraviolet light (UV) exposition related with destruction of some hazardous organic moieties. To enhance the antibacterial characteristics of this material in our works, we developed a new method of TiO 2 Np doping with silver nanoparticles (Ag 0 Np), whose biocidal properties are well defined. The obtained products, Ag 0 Np/TiO 2 Np, in the form of suspensions and powders were characterized from chemical, physical and antimicrobial activity point of view. In addition, a mechanism of Ag + ions reduction reaction to Ag 0 Np has been proposed. The developed method of the Ag 0 Np/TiO 2 Np synthesis consists of the in situ chemical deposition of the Ag 0 Np on the dispersed TiO 2 Np in the form of anatase, using aqueous solutions of poly(acrylic acid sodium salt) (PAS) and NaBH 4. The Ag 0 Np synthesis was carried out both in the presence and absence of TiO 2 Np. The chemical composition of Ag 0 Np/TiO 2 Np was assessed by atomic absorption spectrometrical method (AAS). The physical properties were evaluated as follows: crystallite structure and dimensions of nanopowders by X-ray diffraction method (XRD), UV-Vis absorption of colloidal suspensions and UV-Vis reflectance of nanopowders by spectrophotometrical method, grain size distribution of nanoparticles by dynamic light scattering method (DLS), stability of colloidal suspensions by zeta potential measurements, forms and shapes of Ag 0 Np and Ag 0 Np/TiO 2 Np by transmission electronic microscopy (TEM) and scanning electronic microscopy (SEM) respectively. The antimicrobial activity was tested by standard methods against some broad spectra of fungi and bacteria. In suspensions, the concentration of TiO 2 Np was 1 wt. % and the concentration of Ag 0 Np varied in the range of 0.005…0.15 wt. %. The Ag 0 Np suspensions and Ag 0 Np/TiO 2 Np suspensions were stable from the physical and chemical point of view. The physical characterization test results were in accordance, proving the achievement of colloidal solutions containing Ag 0 Np and TiO 2 Np spherical nanocrystallite with average diameters of 4.1 nm and 7.8 nm, respectively. The results of the biological tests showed the high fungistatic and antibacterial activities of both products in form of colloidal suspensions and powders. The developed "one pot method" is efficient, ecological and easy to be scaled-up. The obtained products have biological activity but it depends on the nature of the tested germs, lowering in the series: Gram negative bacteria, Gram positive bacteria and fungi. Also, a synergistic action was proved at destroying of Trichoderma viride fungus, which was not obtained either for Ag 0 Np or for TiO 2 Np, independently.

Historical textiles – a review of microbial deterioration analysis and disinfection methods

“…153,154 Antimicrobial activity is due to UV illumination of surfaces covered with titanium dioxide nanocomposites and depends on illumination time, surface area, light wavelength (the most effective is < 385 nm), and microorganisms (it has better bactericidal than fungicidal activity, and does not affect molds, such as conidia). 152,153,155 During irradiation, reactive forms of hydroxyl radicals and oxygen species are emitted, 156 which may adversely affect the degradation of cellulose and accelerate the fading of organic colorants, but on the other hand, may cause the destruction of biofilms and leaves no residue on the material. 157…”

Gendered Work, Skill, and Women's Labor Activism in Romanian Tobacco Factories from the 1920s to the 1960s

“…All the mechanics were male, categorized as "technical personnel" and considered skilled workers. 52 A "price notebook" drawn up by management, or-at least in the first half of the 1930s-by management and workers' representatives as part of the yearly negotiations for collective contracts, set day rates, piece rates, and other benefits. In 1930, at the Cluj Manufactory, 723 female workers and 131 male workers were paid through a combination of low fixed daily wages and piece rates reserved for unskilled workers.…”

“…25 A small fraction, less than one percent of the tobacco leaves used to produce cigarettes, were imported from Anatolia, Macedonia, and the United States. 26 Some Romanian tobacco leaf was exported to Czechoslovakia, Austria, Belgium, Sweden, and Germany-albeit in relatively small quantities compared to the exports of Bulgaria and Greece. 27 The tobacco products manufactured in Romania were destined exclusively for domestic consumption.…”

“…In the 1920s, female workers were tasked with either rolling allotted portions of tobacco for the hand-rolled luxury cigarettes or hand-packing an average of 140 kilograms of loose tobacco into seven thousand packages over the course of an eight hour shift, work that required strength, dexterity, and fast coordination between the workers on a team. 47 Despite beingclosely supervised by "control women" and workshop foremen, the women still exercised a degree of artisan-like control over the rhythm of work-as did the admittedly much more autonomous cigarreras in Sevilla. 48 In addition, female tobacco workers were employed in a factory that had a long history in Cluj and a long history of labor organizing-a 1911 strike and lockout was likely within living memory of at least one of the women who, in 1930, was reported to have been working at the factory since 1907.…”

“…In Romanian tobacco factories, women were almost exclusively put in the category of "manual execution personnel." 50 In other words, workers were considered unskilled or (de facto) semi-skilled (as in the case of women with "low level" supervisory positions in certain workshops). They were paid from a "workers' payment fund," rather than receiving "budget salaries"; the latter were reserved for white-collar workers and some of the factory's mechanics.…”