Data on energy-band-gap characteristics of composite nanoparticles obtained by modification of the amorphous potassium polytitanate in aqueous solutions of transition metal salts

Here we present the data on the energy-band-gap characteristics of composite nanoparticles produced by modification of the amorphous potassium polytitanate in aqueous solutions of different transition metal salts. Band gap characteristics are investigated using diffuse reflection spectra of the obtained powders. Calculated logarithmic derivative quantity of the Kubelka–Munk function reveals a presence of local maxima in the regions 0.5–1.5 eV and 1.6–3.0 eV which correspond to band gap values of the investigated materials. The values might be related to the constituents of the composite nanoparticles and intermediate products of their chemical interaction.


a b s t r a c t
Here we present the data on the energy-band-gap characteristics of composite nanoparticles produced by modification of the amorphous potassium polytitanate in aqueous solutions of different transition metal salts. Band gap characteristics are investigated using diffuse reflection spectra of the obtained powders. Calculated logarithmic derivative quantity of the Kubelka-Munk function reveals a presence of local maxima in the regions 0.5-1.5 eV and 1.6-3.0 eV which correspond to band gap values of the investigated materials. The values might be related to the constituents of the composite nanoparticles and intermediate pro-

Subject area
Materials science More specific subject area

Physical properties
Type of data Value of the data • The data reveals a complex configuration of electronic zones for the products obtained by soft chemistry methods such as modification of layered potassium polytitanate particles in aqueous solutions of transition metal salts. • This data attributes band gap values of the modified potassium polytitanates to the particular transition metal salt chosen for the modification. • The data can be applied to select the materials with optimal electron zones configuration for their application in different electronic devices.

Data
The dataset consists of energy-band-gap characteristics of the potassium polytitanate nanoparticles modified in the aqueous solutions of transition metal salts of organic acids including Cu(II), Fe(II), Co(II) oxalates, Zn formate, as well as Cr(II) and Ni(II) acetates at pH ¼5-6. The data are obtained using modified Kubelka-Munk spectral method which allows recognizing a presence of particles with different energy-band-gap characteristics.

Experimental design, materials and methods
The data on energy-band-gap characteristics are obtained using spectral method described in our previous work [1] and based on modified Kubelka-Munk approach [2,3]. This method allows obtaining configurations of electronic zones in the mixtures of particles, including nanoparticles, characterized with varied structure and composition such as amorphous and quasiamorphous objects. The following operations have been done to obtain the energy-band-gap datasets for the materials investigated. The so-called Tauc plots of {α(E) Á E} n ¼ f(E) have been constructed, where E is the photon energy and α(E) is the absorption coefficient replaced for optically dense systems by the Kubelka-Munk function F(E). The F(E) values is determined in accordance with [4,5] from the spectral dependence of diffuse reflection coefficient R(E) by the Eq. (1): Determining local maxima of a logarithmic derivative quantity defined as Δ(E)¼d{ln[F(E)E]}/dE allows reliable estimation of E g taking into account that the inclusion of the interband absorption at E ZE g must be accompanied by the appearance of the local maximum in Δ(E) corresponding to the conditions of E ¼E g . Discrepancies between E g estimations obtained using the traditional Tauc plot extrapolation method and the proposed approach do not exceed 0.02 eV. If a system consists of several kinds of particles, each type of particles characterized with similar electron structure can be described as related to the specific local maximum. The composite nanoparticles obtained by chemical modification of the amorphous particles of potassium polytitanate (PPT) in the aqueous solutions of copper, iron, nickel, zinc, chromium and cobalt salts of organic acids are investigated using the abovementioned experimental method.

Material preparation
The amorphous potassium polytitanate powder (trade-mark PPT-4, Nanocomposite Ltd., Russia), consisted of platy nanoparticles with a mean diameter of 273 7125 nm and a thickness of 5-15 nm was utilized in the experiments as raw material. The TiO 2 :K 2 O molar ratio of the powder corresponded to 4.05:1.00. The PPT powder was modified according to the following route [5][6][7]: 15 g of powder was put in a glass which then was filled with 100 ml of 10 À 3 M aqueous solution of the corresponding transition metal salts. The obtained suspension was stirred for 8 h and then the obtained product was separated by centrifugation and dried at 60°C for 4 h. The chemical composition of the prepared powders was determined in the oxide form using an energy-dispersive X-ray fluorescence spectrometer and reported in Table 1.
Further, modified PPT powders (PPTM) were compacted to density 2.2570.15 g/cm 3 in disks of 6 mm in diameter and 2.070.1 mm of thickness and used to investigate their optical reflection spectra.

Spectral data
The measured diffuse reflection spectra has been processed to obtain the Kubelka-Munk functions    method does not allow estimating the type of interband electron transition (direct or indirect); however, it allows assessing the data on energy-band-gap characteristics for the PPTM nanoparticles.
The Δ(E) plots for different PPTM possess two groups of peaks taking place in the obtained Δ(E) patterns. The 1st group is related to relatively high values of the photon energy and has higher intensity in comparison with another (patterns corresponding to the PPT modified with copper, nickel and zinc salts). The 2nd group appearing at lower photon energies might be characterized by higher intensity and has been observed for PPT modified with cobalt, iron and chromium salts. Taking into account that a presence of multiple maxima in each group of peaks could be explained by structural features of different particles as well as their size [8], the data on energy-band-gap characteristics of the investigated group of products allow a meaningful choice of the PPTM type for its specific application in photocatalysis, opto-electronics, photovoltaics and different semiconductor or solid-state electrolytes based electronic devices.