Greta Patrinoiu

Polysaccharides Route: A New Green Strategy for Metal Oxides Synthesis

The present paper reviews some of the most important polysaccharide-based synthetic strategies of metal oxides, highlighting the polysaccharides multitasking abilities in the synthesis of nanosized oxide particles. The perspectives but also the unexplored areas of this new and promising green chemistry topic are also examined.

Tunable ZnO spheres with high anti-biofilm and antibacterial activity via a simple green hydrothermal route.

A family of distinct ZnO morphologies - hollow, compartmented, core-shell and full solid ZnO spheres, dispersed or interconnected - is obtained by a simple hydrothermal route, in the presence of the starch biopolymer. The zinc-carbonaceous precursors were characterized by infrared spectroscopy, thermal analysis and scanning electron microscopy, while the ZnO spheres, obtained after the thermal processing, were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV-VIS spectroscopy, photoluminescence measurements, antimicrobial, anti-biofilm and flow cytometry tests. The formation mechanism proposed for this versatile synthesis route is based on the gelling ability of amylose, one of the starch template constituents, responsible for the effective embedding of zinc cations into starch prior to its hydrothermal carbonization. The simple variation of the raw materials concentration dictates the type of ZnO spheres. The micro-sized ZnO spheres exhibit high antibacterial and anti-biofilm activity against Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa) reference and methicillin resistant clinical strains especially for Gram-negative biofilms (P. aeruginosa), demonstrating great potential for new ZnO anti-biofilm formulations.

Solid vs. hollow oxide spheres obtained by hydrothermal carbonization of various types of carbohydrates

Saccharide derived, self-templated carbonaceous spheres with embedded Zn (and Co) were obtained by a versatile one-pot hydrothermal synthesis and proved to be multipurpose precursors for full solid or hollow oxide spheres. Saccharide/Zn2+ ratios and saccharide type affect the morphology (size, shell thickness, surface roughness) of the oxide spheres.

Sustainable one-pot integration of ZnO nanoparticles into carbon spheres: manipulation of the morphological, optical and electrochemical properties.

ZnO-carbon composite spheres were synthesized via starch hydrothermal carbonization (HTC) in the presence of a soluble zinc salt (acetate), followed by thermal processing under an argon atmosphere. Besides sustainability, the one-pot procedure represents a scalable synthesis of tailored carbon-metal oxide spheres with a structurally-ordered carbon matrix obtained at a relatively low temperature (700 °C). The ability of zinc cations to develop different linkages with starchs hydrophilic functional groups and to act as external nucleators determines an increase in HTC yield; the effect is obvious even in the presence of small concentrations of zinc in the reaction medium (0.005 M), thus providing a way to improve the carbonization process efficiency. It is also shown that zinc content is the control vector of the spherical composites properties: a variation from 0.3 to 4.8 at% not only induces a variation in their size (200 nm-10 μm), interconnectivity (from disperse spheres to necklace-like aggregations), surface area and connected porosity (from micro- to mesoporosity), but also of their electrochemical and white light adsorption and emission features. Since the variation in zinc content is made by a simple adjustment of the raw material concentrations, the functionality of these carbon-based materials can be modulated in a straightforward manner.