Understanding the Role of Silver Nanostructures and Graphene Oxide Applied as Surface Modification of TiO2 in Photocatalytic Transformations of Rhodamine B under UV and Vis Irradiation

This work is focused on photocatalytic properties of titanium dioxide thin coatings modified with silver nanostructures (AgNSs) and graphene oxide (GO) sheets which were analyzed in processes of chemical transformations of rhodamine B (RhB) under ultraviolet (UV) or visible light (Vis) irradiation, respectively. UV-Vis spectroscopy was applied to analyze the changes in the RhB spectrum during photocatalytic processes, revealing decolorization of RhB solution under UV irradiation while the same process coexisting with the transformation of RhB to rhodamine 110 was observed under Vis irradiation. The novelty of this study is the elaboration of a methodology for determining the parameters characterizing the processes occurring under the Vis irradiation, which enables the comparison of photocatalysts’ activity. For the first time, the method for quantification of rhodamine B transformation into rhodamine 110 in the presence of a semiconductor under visible light irradiation was proposed. Photocatalysts with various surface architectures were designed. TiO2 thin coatings were obtained by the sol-gel method. GO sheets were deposited on their surface using the dip-coating method. AgNSs were photogenerated on TiO2 or grown spontaneously on GO flakes. For characterization of obtained photocatalysts, scanning electron microscopy (SEM), X-ray diffraction (XRD) and diffuse-reflectance spectroscopy (DRS) techniques were applied. The results indicate that the surface architecture of prepared coatings does not affect the main reaction path but have an influence on the reaction rates and yields of observed processes

Ocena wpływu tlenku grafenu i nanostruktur srebra na aktywność fotokatalityczną powłok ditlenku tytanu

Dissertation thesis entitled "Assessment of the impact of graphene oxide and silver nanostructures on photocatalytic activity of titanium dioxide" is based on the study of titanium dioxide coatings modified with graphene oxide (GO) flakes and/or silver nanostructures (AgNS). Coatings were obtained by the sol-gel method combined with dip-coating technique. Graphene oxide was also deposited by dip-coating technique. Silver nanostructures were obtained by photocatalytic reduction. The study of photocatalytic properties was based on photocatalytic transformations of rhodamine B determined by UV-Vis spectrophotometric method. Changes of absorption spectrum caused by UV and Vis range were monitored separately. The theoretical part of the work describes the methods that are used to improve the photocatalytic activity of titanium dioxide. Separate chapters were assigned to silver nanostructures (AgNS) and graphene materials (G, i.e. graphene, graphene oxide and reduced graphene oxide). Moreover the synthesis of two-component (TiO2-AgNS and TiO2-G) and ternary (TiO2-G-AgNS) photocatalysts, their photocatalytic properties based on the degradation of contaminants and proposed electron flow mechanisms were analyzed. Furthermore The results of individual works questioning the effectiveness of the use of graphene materials in photocatalysis due to the lack of resistance of these materials to the action of reactive oxygen species were also discussed. The experimental part is divided into chapters including: 1) description and characteristics of titanium dioxide coatings and discussion of rhodamine B photocatalytic transformations in UV and Vis irradiation range, 2) modification of TiO2 coatings with AgNS having various sizes and numbers, and the impact of these parameters on the photocatalytic activity of a two-component system, 3) modification of TiO2 coatings with GO flakes with a certain degree of coverage and its dependence on the photocatalytic activity, 4) modification of TiO2 coatings with both GO flakes and AgNS forming 3 types of "architectures" differing in the method of preparation, including determining the impact of GO flakes on AgNS growth and determining the causes of AgNS growth on GO subsequently, ending with a comparison of photocatalytic properties of the obtained ternary systems, 5) analysis the stability of GO flakes deposited on TiO2 during irradiation. The summary refers to the mechanisms proposed in the literature and objectively evaluated the impact of TiO2 coating modifications on the photocatalytic activity of prepared systems in UV and Vis irradiation range. Coating morphology was examined using SEM. The crystallographic structure was determined using XRD. The value of the band gap of photocatalysts was determined by the DRS technique. The reasons of AgNS growth on GO were investigated by SEM, EDS and FT-IR techniques. The stability of GO flakes was determined by SEM techniques and Raman spectroscopy

Highly sensitive determination of Tenofovir in pharmaceutical formulations and patients urine : comparative electroanalytical studies using different sensing methods

This paper discusses the electrochemical behavior of antiviral drug Tenofovir (TFV) and its possible applicability towards electroanalytical determination with diverse detection strategies using square-wave voltammetry. Namely, oxidation processes were investigated using glassy carbon electrode with graphene oxide surface modification (GO/GCE), while the reduction processes, related to the studied analyte, were analyzed at a renewable silver amalgam electrode (Hg(Ag)FE). Scanning electron microscopy imaging confirmed the successful deposition of GO at the electrode surface. Catalytic properties of graphene oxide were exposed while being compared with those of bare GCE. The resultant modification of GCE with GO enhanced the electroactive surface area by 50% in comparison to the bare one. At both electrodes, i.e., GO/GCE and Hg(Ag)FE, the TFV response was used to examine and optimize the influence of square-wave excitation parameters, i.e., square wave frequency, step potential and amplitude, and supporting electrolyte composition and its pH. Broad selectivity studies were performed with miscellaneous interfering agents influence, including ascorbic acid, selected saccharides and aminoacids, metal ions, non-opioid analgesic metamizole, non-steroidal anti-inflammatory drug omeprazole, and several drugs used along with TFV treatment. The linear concentration range for TFV determination at GO/GCE and Hg(Ag)FE was found to be 0.3–30.0 µmol L(–1) and 0.5–7.0 µmol L(–1), respectively. The lowest LOD was calculated for GO/GCE and was equal to 48.6 nmol L(–1). The developed procedure was used to detect TFV in pharmaceutical formulations and patient urine samples and has referenced utilization in HPLC studies

ZnFe2O4/TiO2 composites with type-I heterojunction for photocatalytic reduction of CO2

The composites of ZnFe2O4 (ZFO) with TiO2 (anatase, rutile) were synthesized and tested towards the photocatalytic reduction of CO2 to CO in the gas phase. ZFO was obtained through the precipitation from zinc and iron nitrates(V) precursors, followed by hydrothermal treatment, and its physicochemical properties were examined using XRD, FT-IR, XPS, SEM-EDS, and XRF techniques. ZFO was simply ground in the agate mortar with one of the TiO2 polymorphs, forming ZFO/anatase and ZFO/rutile. Spectroelectrochemical (SE-DRS), surface photovoltage (SPV), transient photocurrent and diffuse reflectance UV–vis spectroscopy (DRS) measurements were applied to understand the fate of photogenerated electrons and holes. The results point to the type-I heterojunction that is formed in the case of all ZFO/TiO2 systems. This type of band alignment is responsible for boosted photoactivity of the composites compared to the components used separately. The results confirm that the selection of anatase favours reaching higher yields of CO production, which is attributed rather to better electron mobility within anatase compared to rutile than to preferential, reducing properties of the rutile’s conduction band

Analytical performance of clay paste electrode and graphene paste electrode-comparative study

The analytical performance of the clay paste electrode and graphene paste electrode was compared using square wave voltammetry (SWV) and cyclic voltammetry (CV). The comparison was made on the basis of a paracetamol (PA) determination on both working electrodes. The influence of pH and SWV parameters was investigated. The linear concentration ranges were found to be 6.0 × 10−7–3.0 × 10−5 and 2.0 × 10−6–8.0 × 10−5 mol L−1 for clay paste electrode (ClPE) and graphene paste electrode (GrPE), respectively. The detection and quantification limits were calculated as 1.4 × 10−7 and 4.7 ×10−7 mol L−1 for ClPE and 3.7 × 10−7 and 1.2 × 10−6 mol L−1 for GrPE, respectively. Developed methods were successfully applied to pharmaceutical formulations analyses. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to characterize ClPE and GrPE surfaces. Clay composition was examined with wavelength dispersive X-ray (WDXRF)