Surfactant‐Modified Hydrophilic Nanostructured Porous Silicon for the Photosensitized Formation of Singlet Oxygen in Water

Abstract

Porous silicon (porSi), which contains luminescent Si nanocrystal assemblies, is a promising semiconductor material for the photosensitized formation of singlet oxygen, 1 O 2 , for biological applications. However, because as-prepared luminescent Si nanocrystals are H-terminated and therefore hydrophobic, the first step to create a prototype of Si nanocrystalbased photosensitizer should be a modification of the Si nanocrystal surface with the aim to make it hydrophilic and able to work in a biological ambient. Such surface modification by surfactants should not, however, result in a decrease of the nanocrystals' durability that may, in principle, take place because of surfactant-induced weakening of surface tension and the consequent increase of interaction with H 2 O molecules. Surfactants should not also decrease the ability of the nanocrystals to transfer the excitation energy to acceptors (first of all molecular oxygen) on their surface. These rather contradictory tasks have been largely solved in the present work by use of nonionic surfactants physically adsorbed on the porSi surface.One of the strategic objectives of nanotechnology is the development of new materials of nanometer size that have entirely new physical properties, and, therefore, new functionality. Over the last decade, tailoring of material characteristics by size control has been demonstrated for many types of semiconductors. Optical and electronic properties of semiconductor nanocrystals can be simply engineered by changing their size and composition. When electrons and holes are squeezed into a dimension that approaches a critical size, quantum-confinement effects become apparent. This effect can be seen experimentally as a widening of the semiconductor nanocrystal bandgap.[1]

A hybrid Si@FeSiy/SiOx anode structure for high performance lithium-ion batteries via ammonia-assisted one-pot synthesis

“…Perrine et al 34 report that a clean and fresh Si surface could be terminated with H + and NH 2À groups while fresh Si was exposed to ammonia in an ultrahigh vacuum chamber at room temperature. In addition, Chirvony et al 35 show that H-terminated Si particles can react with H 2 O, forming terminal hydroxides, into which H 2 O can further penetrate and the Si-Si bonds are inserted by oxygen, forming silicon oxide. That Si particles terminated weakly with H + may be possible in the hybrid structures aer 20 and 40 h of milling, due to the decomposition of NH 3 and the generation of a fresh surface of Si during milling.…”

Surfactant-assisted growth of anodic nanoporous niobium oxide with a grained surface

“…Surfactants are well-known additives that can control the pore depth and morphology during the anodization of silicon [21][22][23]. For example, cationic surfactant was reported to have been readily absorbed in the oxidized porous silicon with a hydrophobic Hterminated surface, which can lead to an increase in the depth of straight pore channels [21,23].…”

Physical adsorption vs. chemical binding of undecylenic acid on porous silicon surface: a comparative study of differently functionalized materials

“…For time, surface modification of PSi has been a widely accepted method for making the material hydrophilic and enabling its functioning in water ambient. Using this approach, we attempted to create a prototype of the PSi based photosensitizer that would be miscible with water and work in aqueous ambient without considerable decay of its luminescence [1]. The two methods were used: (1) the physical adsorption of undecylenic acid UD at PSi surface and (2) the chemical binding of the same molecules through opening of their C=C bonds, interaction with surface Si-H groups and formation of the Si-C bonds.…”