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Members of the Quantum Gap Association recently published a manuscript illustrating the results of a study conducted between collaborating laboratories in national institutes in Belgrade, Lisbon, and Stockholm. This is the second part of two-part research relating to the means of manipulation of titanium dioxide semiconductor’s physicochemical properties and its likely future photocatalytic usage. 

  • K. Batalović, J. Radaković, N. Bundaleski, Z. Rakočević, I. Pašti, N. V. Skorodumovaand C. M. Rangel, "Origin of photocatalytic activity enhancement in Pd/Pt-deposited anatase N-TiO2 – experimental insights and DFT study of the (001) surface", Phys. Chem. Chem. Phys., 2020, vol 22, pp. 18536-18547

The study addressed the subject of potential acceleration of photocatalytic reaction by adjustment of nano-sized titanium dioxide semiconductor‘s surface with doping of TiO2 crystal lattice and deposing atoms that modify the behavior of its charge carriers. Why are charge carriers important in semiconductors – you can read in detail in the best book ever written on topics of solid-state physics, Solid State Physics by Neil W. Ashcroft and David Mermin. The significance of controlled surface adjustments is even greater when the material in question has an impending role in photocatalytic reaction, given that induced adjustments are responsible for the tuning of inherent physicochemical properties, such as the width of semiconductor’s bandgap

To fine-tune the width of nano-sized titanium dioxide’s bandgap, noble metals palladium (Pd) and/or platinum (Pt) are deposited on the surface of this material, which was previously doped with nitrogen (N); thus the collaborative study initiated with the synthesis of enriched titanium dioxide. To control the concentration of dopants and attempt the single-atom deposition, the semiconductor was doped under strict and very precise experimental conditions. The synthesis of TiO2 and doping with nitrogen, palladium, and platinum atoms were performed in Portugal’s National Laboratory for Energy and Geology (LNEG) by guest researchers from Serbian Institute for nuclear sciences “Vinča”. Further experiments, necessary to test the outcome of induced modifications, were performed in collaboration with experimentalists from the same Serbian institute and Centre of Physics and Technological Research from Portugal. To understand the origins of improvements occurring as a result of the used synthesis approach, the experiments were followed by the first principles computational analysis performed in collaboration between the Faculty of physical chemistry from Belgrade, Institute “Vinča”, and a research group from Swedish Uppsala University. Computational simulations of photochemical properties based on quantum chemistry enabled precise interpretation of effects noble metals Pt and Pd, and N induced upon adsorption on the surface of TiO2.

This synergetic study revealed the benefits of post-adsorptive effects of noble metals upon semiconductors fitting for photocatalytic reactions. We will not exhibit the results of this study, as they can be found on the link of the Physical Chemistry Chemical Physics journal. However, some of the attention-grabbing terms relating to the scope of the research and mentioned within this text will be explained in short and presented further down.

Like human defects, those of crystals come in a seemingly endless variety, many dreary and depressing, and a few fascinating.

Neil W. Ashcroft & N. David Mermin in Solid State Physics

Adsorption – the process of bonding of atoms, ions, or molecules to a surface of a material

Photoreaction – chemical reaction involving absorption of electromagnetic radiation by one or more reactants 

Photocatalysis – acceleration of chemical reaction induced by adding photocatalyst

Photocatalyst – chemical which absorbs light and provides energy to reactants in order to make the reaction occur; photocatalysts are essentially semiconductors

Titanium dioxide – TiO2; titanium(IV)oxide is a naturally occurring oxide of titanium. Due to its stability and affordability, this material has several active applications – like paint, sunscreen, and food coloring (E171) – it is also a wide-gap semiconductor, which in anatase crystal arrangement exhibits noteworthy photocatalytic activity. However, to be an all-inclusive semiconductor accepted as a photocatalyst, it is essential to reduce the width of its bandgap and address all of the disruptions caused by the recombination of charge carriers, which are the basis of modern electronics, as explained by rules of quantum physics. 

Given the significance of TiO2 positive sides, modification and regulation of physicochemical properties of this material are the dominant research point in studies concerning photocatalysis. Emerging aspects and fresh research perspectives regarding this semiconductor are constantly growing, thus the number of research groups addressing the issues of inconsistencies and deficiencies is increasing.

Photo by Science in HD on Unsplash