Joanna Sreńscek-Nazzal

Photocatalytic hydrogen generation over alkali niobates in the presence of organic compounds

Photocatalytic hydrogen generation over alkali niobates in the presence of organic compounds The photocatalytic efficiency of alkali niobate-based compounds (Li, Na, K) for hydrogen generation has been investigated. The systematic study showed that the highest photocatalytic activity was observed in the case of Na/Nb2O5 catalyst which contained sodium niobate (NaNbO3) phase and that the most efficient electron donor for hydrogen generation was formic acid. In addition, the effect of organic donor (HCOOH) concentration on the amount of the evolved hydrogen was studied.

Effect of CeO2 and Sb2O3 on the phase transformation and optical properties of photostable titanium dioxide

In the present work, the effect of individual additives calculated as molar fractions of Sb2O3 and CeO2 (xSb2O3 range: 0.03–0.08 %, xCeO2 range: 0.05–0.14 %), on the phase composition, phase transformation, and optical properties of photostable rutile titanium dioxide was studied using selective leaching method, ICP-AES technique, XRD method, spectrophotometric analysis and SBET measurements. The starting material was hydrated titanium dioxide. It was observed that the addition of Sb2O3 to TiO2 did not influence the anatase-rutile phase transformation, but increasing the CeO2 addition caused a decrease in the rutilization degree. Thus, CeO2 acted as an inhibitor of the TiO2 phase transformation. Sb2O3 addition to TiO2 presumably caused the formation of a co-phase of Sb with Ti. Cerium formed a separate phase, CeO2, and reacted partly with titanium, probably creating co-phase, Ce0.8Ti0.2O2. Comparing the colour of modified rutile titanium dioxide according to the type of the additive introduced, it was found that TiO2 with CeO2 had higher brightness but lower white tone values when compared with TiO2 modified with Sb2O3. The relative lightening power and grey tone of the modified TiO2 were higher in TiO2 modified with Sb2O3. The values of the photocatalytic activity measured in all TiO2 samples modified either with Sb2O3 or CeO2 were very similar and varied around the value of 21.

An analysis of the effect of the additional activation process on the formation of the porous structure and pore size distribution of the commercial activated carbon WG-12

The paper presents the results of research into the effects of the additional activation process of the commercial activated carbon WG-12 with KOH, ZnCl2, KOH/ZnCl2 and K2CO3 as activating agents on the formation of the porous structure and the adsorptive properties of that material. The numerical analyses were carried out on the basis of the isotherms of nitrogen adsorption with the use of the method based on the Brunauer-Emmett-Teller, the Dubinin-Radushkevich equations, the non-local and the quenched solid density functional theories as well as the LBET method with the unique fast multivariate procedure of porous structure identification and the new LBET class adsorption models. Also, the research in question yielded information regarding the usefulness of the said methods of carbonaceous adsorbent porous structure description for practical technological applications and scientific research, as well as the possibilities to make practical use of the research results.

Surface characteristics of KOH-treated commercial carbons applied for CO2 adsorption:

The effect of an alkali treatment (potassium hydroxide) on the properties of a commercial activated carbon has been studied. The aim of the treatment was to improve the adsorption properties of the material toward carbon dioxide. In the result of the treatment, silica contained in the raw carbon was removed and the density of the material increased. The changes in the surface chemistry were observed as well. The treatment of the activated carbon with KOH resulted in a complete removal of carboxy and lactone groups and a decrease of the general content of the acidic groups (more significant than that of basic groups). Simultaneously, the surface concentration of hydroxyl groups increased. The alkali treatment of activated carbon resulted in an increase of carbon dioxide uptake of 14% (measured using a volumetric method at 0℃). The adsorption of carbon dioxide on activated carbon has a mixed (physicochemical) character and that two types of adsorption sites are present at the surface. The adsorption energy varies roughly from 25 to 60 kJ/mol.

The Increase of the Micoporosity and CO2 Adsorption Capacity of the Commercial Activated Carbon CWZ-22 by KOH Treatment

The chemical modification of CWZ-22—commercial activated carbon (AC) with KOH‐ to enhance CO2 adsorption was examined. The effect of different impregnation ratios KOH:CWZ-22 from 1 to 4 was studied. The ACs were characterized by CO2 and N2 sorption, Fourier transform infrared (FTIR), SEM, and XRD methods. The impregnation of CWZ-22 with KOH highly effectively increased the porosity, specific surface area, and pore volume of ACs. The specific surface area of KOH:CWZ-22 = 4 increased to 1299 m2/g as compared with pristine, which is equal to 856 m2/g. The total pore volume raised from 0.51 to 0.77 cm3/g. The chemical modification of CWZ-22 increased the CO2 adsorption capacity up to 38%. The Sips model described very good CO2 adsorption on KOH:CWZ-22 = 4 and pristine sample. The surface of both ACs was homogenous. The values of isosteric heats of adsorption indicated on physisorption.