Miray Bekbolet

An investigation of the photocatalytic efficiencies of TiO2 powders on the decolourisation of humic acids

Photocatalytic efficiencies of two commercial titania brands, Degussa P-25 and Hombikat UV-100 were discussed in relation to the degradation of humic acid in aqueous solutions. Decolourisation rate of humic acid (Colour436 ,m −1 ) for Degussa P-25 was found to be higher than the rate achieved by using Hombikat UV-100 specimen, both in terms of pseudo-first-order and Langmuir–Hinshelwood kinetics. The adsorption isotherms exhibited different trends and the application of the Freundlich adsorption model revealed KF values 0.549 for Degussa P-25, and 0.293 for Hombikat UV-100 indicating higher adsorption capacity of Degussa P-25 for humic acid under neutral pH conditions. This observation was also consistent with the intrinsic photocatalytic activities calculated as 0.196 m −1 min −1 m −2 for Degussa P-25 and 0.0269 m −1 min −1 m −2 for Hombikat UV-100. The higher surface area of Hombikat UV-100 did not render higher adsorption capacity values leading to higher degradation rates.

Inactivation of Escherichia coli by photocatalytic oxidation.

The inactivation of Escherichia coli (E.coli) was studied in presterilized surface water sample using titanium dioxide as the photocatalyst under irradiation of BLF Fluorescent lamps. Inactivation of E.coli (10(3) CFU/mL) was achieved in 60 min in the presence of 1.0 mg TiO2/mL. Photocatalytic inactivation data was evaluated in terms of first order rate equation N/N0 = e (-kIt). The reaction rate constant k, 1.22*10(-2)(mW min/cm2)-1 was calculated.

Photocatalytic and photoelectrocatalytic humic acid removal and selectivity of TiO2 coated photoanode

In this study, photocatalytic (PC) and photoelectrocatalytic (PEC) treatment methods were comparatively investigated as a possible means of removing humic acid (HA) following absorbance at 254 nm (UV(254)) and total organic carbon (TOC) analysis. The enhanced HA degradation rates were obtained in the PEC system over the conventional PC process under acidic, neutral and alkaline conditions. Preliminary and binary experiments were performed to determine the selectivity of the photoanode in terms of HA and chloride oxidation. TOC, chlorine and photocurrent parameters proved that HA was selectively removed before chlorine generation. The inhibitory effect of carbonate ions on the performance of photoanode was also studied under different pH values.

Sorption Studies of 2,4-D on Selected Soils

Adsorption/desorption characteristics of the herbicide 2,4-D on various types of soils were investigated. Batch equilibrium techniques were used in the laboratory experiments. Data were fitted to the linear and Freundlich sorption equations. K and Kf values ranged between 0.32–1.89 L- 1 mg and 2.6 × 10-3 – 7.4 mg kg- 1, respectively. Results showed that both for linear and Freundlich adsorption equations, for all soils, K and Kf were correlated to the organic matter content (r = 0.87 and r = 0.66, respectively). Adsorption was also positively correlated with silt and clay content of soils (r = 0.53) and negatively correlated with sand content.

Photocatalytic oxidation and subsequent adsorption characteristics of humic acids

Effect of TiO 2 photocatalyzed oxidation on the degradation and decolorization of humic acids was studied. The photocatalytic oxidation products were further investigated in terms of adsorptivity on activated carbon. With photocatalytic oxidation in a lab-scale batch reactor significant decolorization and a decrease in UV 280 and UV 254 took place. Simultaneously there was a decrease in TOC and COD. Parallel to this an evolution of BOD 5 was observed. Thus the BOD 5 /COD ratio increased with irradiation time and more biodegradable substances have been formed. A significant change in the structure of compounds in humic acid took place only after 3-4 hours of irradiation as determined by the decrease in COD/TOC ratio. Generally there was a slight decrease of adsorptivity after irradiation as concluded from the comparison of Freundlich isotherm constants for raw and irradiated humic acid. This decrease increased as the irradiation time increased. But for irradiation times to be used in practice in photocatalytic oxidation no significant change in adsorption is expected.

Photocatalytic and Photoelectrocatalytic Performance of 1% Pt Doped TiO2 for the Detoxification of Water

The degradation of formic acid (HCOOH), FA (a surrogate contaminant) using titanium dioxide (TiO2) and 1% Pt doped TiO2 electrodes, prepared by sol—gel methods, was investigated in a photoelectrocatalytic (PEC) system in order to determine the effect of Pt doping on the oxidation potential of TiO2. Pt doping shifts the position of band edge and therefore the direct and indirect oxidation potentials of TiO2 in PEC systems. As a result, the degradation of formic acid via the generation of hydrogen peroxide production on 1%Pt—TiO2 electrodes was much better than that on non-doped electrodes. The degradation of HCOOH was also examined with respect to the faradaic efficiency of this process. It was found that the 1%Pt—TiO2 photoanode had a 30% higher efficiency than that of non-doped TiO2 photoanodes.

Advanced oxidation of a commercially important nonionic surfactant: Investigation of degradation products and toxicity

The evolution of degradation products and changes in acute toxicity during advanced oxidation of the nonionic surfactant nonylphenol decaethoxylate (NP-10) with the H2O2/UV-C and photo-Fenton processes were investigated. H2O2/UV-C and photo-Fenton processes ensured complete removal of NP-10, which was accompanied by the generation of polyethylene glycols with 3-8 ethoxy units. Formation of aldehydes and low carbon carboxylic acids was evidenced. According to the acute toxicity tests carried out with Vibrio fischeri, degradation products being more inhibitory than the original NP-10 solution were formed after the H2O2/UV-C process, whereas the photo-Fenton process appeared to be toxicologically safer since acute toxicity did not increase relative to the original NP-10 solution after treatment. Temporal evolution of the acute toxicity was strongly correlated with the identified carboxylic acids being formed during the application of H2O2/UV-C and photo-Fenton processes.

Photocatalytic degradation of natural organic matter: Kinetic considerations and light intensity dependence

The current study was conducted to investigate the photocatalytic degradation kinetics of humic acid at different light intensities using commercial TiO2 powders. The pseudo first order kinetic model and Langmuir-Hinshelwood (L-H) rate equation in modified forms were used to compare the photocatalytic activ- ities of TiO2 materials as a function of light intensity. Under constant irradiation conditions, the pseudo first order reaction rates as well as L-H rates were found to be decreasing in the following trend; Degussa P-25, Millennium PC-500 and Millennium PC-100. The pseudo first order rate constants showed the same decreas- ing trend as the pseudo first order reaction rates while L-H rate constants exhibited a light intensity related change in the ordering of the photocatalysts. At the lowest light intensity, L-H rate constants decreased as follows: Millennium PC-500 > Millennium PC-100 > Degussa P-25. However, increasing the light intensity changed the order to; Millennium PC-100 > Millennium PC-500 > Degussa P-25 revealing the significance of the L-H adsorption constant. Under constant irradiation conditions, ionic strength dependent changes in the structure of humic acid did not alter degradation efficiency trend of the photocatalyst specimens and they were ordered such as; Degussa P-25 > Millennium PC-500 > Hombikat UV-100 > Millennium PC-100 > Merck. The results presented in this research also confirmed the effectiveness of Degussa P-25 as a photo- catalyst for the degradation of humic acid.

Sequential Oxidation of Humic Acids by Ozonation and Photocatalysis

In this study, humic acids, the natural polymerized organic compounds which are responsible for the formation of disinfection by-products such as haloacetic acids and trihalomethanes upon chlorination, are oxidized in a sequential system incorporating ozonation and photocatalysis. Titanium dioxide is used as photocatalyst in the photocatalytic oxidation phase. Humic acid degradation kinetics is evaluated both for ozonation and photocatalysis. The Freundlich adsorption model is used for defining the adsorption characteristics of humic acid solutions on the photocatalyst after the ozonation step. The Langmuir-Hinshelwood model is also studied for explaining the adsorptive and photocatalytic removal of humic acids.

A Comparative Approach to the Application of a Physico‐Chemical and Advanced Oxidation Combined System to Natural Water Samples

Abstract Natural organic matter removal (NOM) efficiencies of samples from three major drinking water sources (Elmali, Omerli, and Buyukcekmece) of Istanbul were compared using different treatment systems. Enhanced coagulation as a physico‐chemical method was applied using ferric chloride and aluminum sulphate as the coagulating agents. Moreover, the application of enhanced coagulation in combination with photocatalytic oxidation using TiO2 was investigated. The efficiency of NOM removal relevant to each treatment step was assessed through DOC removal, UV254 removal, and fluorescence measurements. Irrespective of the treatment applied as enhanced coagulation, photocatalytic oxidation or their combinations, the highest removal efficiency was determined for Elmali followed by Omerli and Buyukcekmece samples both in terms of DOC and UV254. Enhanced alum coagulation leads to significant variation in DOC removals as 44%, 28% and 26% for Elmali, Omerli, and Buyukcekmece water samples, respectively. Upon application of ferric chloride as the coagulant, the DOC removals achieved were found to be slightly higher as compared to alum. Moreover, the combined treatment incorporating photocatalytic oxidation subsequent to alum coagulation leads to 36%, 37%, and 50% of DOC removal for Omerli, Buyukcekmece, and Elmali respectively. The improvement of removal efficiencies in combined treatment systems were scrutinized with an emphasis on induced water properties as supported by the specific fluorescence intensities of the samples.