Károly Mogyorósi

Removal of 2-chlorophenol from water by adsorption combined with TiO2 photocatalysis

Abstract The results of a laboratory-scale study of an environmentally friendly water treatment method is presented, where the organic model pollutant 2-chlorophenol (2-CP) was first adsorbed and then removed by a direct photolytic or heterogeneous photocatalytic process. The adsorbent was an organically treated (with hexadecylpyridinium chloride) clay mineral (montmorillonite), and the photocatalyst was Degussa P25. The total organic carbon and total inorganic chloride contents were measured to monitor the mineralization process, while the degradation of 2-CP and the formation of intermediates were followed by HPLC. No negative effect of the suspended adsorbent was observed either in the direct photolytic process or in the heterogeneous photocatalytic degradation process. Although direct photolysis allows the highest degree of 2-CP removal, in this case the degradation of the organic pollutant is accompanied by destruction of the adsorbent. The removal of 2-CP through the combination of adsorption and heterogeneous photocatalysis was achieved in a reasonable acceptable time interval, and can therefore be suggested as an efficient, cost-effective and environment-friendly water treatment facility.

Photocatalytic H2 Production Using Pt-TiO2 in the Presence of Oxalic Acid: Influence of the Noble Metal Size and the Carrier Gas Flow Rate

The primary objective of the experiments was to investigate the differences in the photocatalytic performance when commercially available Aeroxide P25 TiO2 photocatalyst was deposited with differently sized Pt nanoparticles with identical platinum content (1 wt%). The noble metal deposition onto the TiO2 surface was achieved by in situ chemical reduction (CRIS) or by mixing chemically reduced Pt nanoparticle containing sols to the aqueous suspensions of the photocatalysts (sol-impregnated samples, CRSIM). Fine and low-scale control of the size of resulting Pt nanoparticles was obtained through variation of the trisodium citrate concentration during the syntheses. The reducing reagent was NaBH4. Photocatalytic activity of the samples and the reaction mechanism were examined during UV irradiation (λmax = 365 nm) in the presence of oxalic acid (50 mM) as a sacrificial hole scavenger component. The H2 evolution rates proved to be strongly dependent on the Pt particle size, as well as the irradiation time. A significant change of H2 formation rate during the oxalic acid transformation was observed which is unusual. It is probably regulated both by the decomposition rate of accumulated oxalic acid and the H+/H2 redox potential on the surface of the catalyst. The later potential is influenced by the concentration of the dissolved H2 gas in the reaction mixture.

Removal of organic pollutants in model water and thermal wastewater using clay minerals.

Water treatment method was developed for the removal of different anionic dyes such as methyl orange and indigo carmine, and also for thymol applying sodium bentonite and cationic surfactant - hexadecyltrimethylammonium bromide (HTAB) - or polyelectrolytes (polydiallyldimethylammonium chloride, poly-DADMAC and poly-amines). The removal efficiency of these model substrates was examined in model water using UV-Vis spectrophotometry, HPLC and TOC analysis. The clay mineral and HTAB were added in one step to the polluted model water in Jar-test experiments. The influence of the cation exchange capacity (CEC) of the applied clay mineral and the presence of polyaluminium chloride coagulant (BOPAC) were also tested for the water treatment process. The structures of the in situ produced and pre-prepared organoclay composites were compared by XRD analysis. The rapid formation of organoclay adsorbents provided very efficient removal of the dyes (65–90 % in 3–10 mg/L TOC0 range) with 200 mg/L sodium bentonite dose, however thymol was less efficiently separated. Adsorption efficiencies of the composites were compared at different levels of ion exchange such as at 40, 60 and 100 %. In the case of thymol, the elimination of inorganic carbon from the model water before the TOC analysis resulted in some loss of the analysed volatile compound therefore the HPLC analysis was found to be the most suitable tool for the evaluation of the process. This one-step adsorption method using in situ formed organoclay was better performing than the conventional process in which the montmorillonite-surfactant composite is pre-preapared and subsequently added to the polluted water. The purification performance of this method was also evaluated on raw and artificially polluted thermal wastewater samples containing added thymol.

Immobilization of crystallized photocatalysts on ceramic paper by titanium(IV) ethoxide and photocatalytic decomposition of phenol

A simple method of persistent immobilization was developed for the fixing of highly efficient precrystallized (or even doped) titania (TiO2) based photocatalysts. TiO2 nanoparticles (Aeroxide P25 and VLP7000) were immobilized on the surface of Al2O3-based ceramic paper. For the immobilization, a titanium alkoxide (Ti(OEt)4) was applied as a fixing agent. This type of immobilization resulted in a photocatalytically active surface, which was used in fixed-bed flow reactors through the application of different forms of artificial or solar irradiation to activate the TiO2. To verify the stability, the decomposition of phenol was repeatedly measured on the same TiO2-covered ceramic paper; the photocatalytic performance proved to remain constant throughout five 2-h cycles. The potential for application on an industrial scale was demonstrated by a pilot-plant-scale flow reactor. The developed immobilization method is a simple technique that can be used to investigate the long-term efficiency of novel TiO2 samples, or can be applied in real air/water treatments.

Preparation and photooxidation properties of metal oxide semiconductors incorporated in layer silicates

Various metal oxide semiconductor nanoparticles (TiO2, ZnO, SnO2) were stabilized in the interlamellar space of clay minerals with a layered structure. In the first step, metal oxide/hydroxide nanosol particles were prepared by acidic hydrolysis, and the incorporation of the nanoparticles was next carried out between the layer silicates by a heterocoagulation method. Metal oxide semiconductor/layer silicate composites with large specific surface areas (a s > B ET=122–251 m2> g-1>) were prepared with (TiO2) and without calcination at 400 °C (ZnO, SnO2). The structure of these composites was characterized by X-ray diffraction measurements and their photocatalytic properties were determined in aqueous solutions, using salicylic acid as a test molecule.

Visible light driven photocatalytic elimination of organic- and microbial pollution by rutile-phase titanium dioxides: new insights on the dynamic relationship between morpho-structural parameters and photocatalytic performance

The characteristic properties and the resulted photocatalytic efficiencies of rutile-phase titanium dioxides were investigated in the present study. A series of rutile with different primary particle sizes (5.2–290 nm) were produced by a sol–gel method followed by calcination and were characterized by XRD, DRS, TEM, XPS, EPR, IR and N2 adsorption. Their photocatalytic efficiencies were determined in the decomposition of phenol, and in the inactivation of E. coli bacteria under visible light irradiation. The results were compared with the photocatalytic performance of commercial Aldrich rutile and Aeroxide P25 powders. Of the non-commercial products, the TiO2 with the smallest particle size displayed the highest efficiency, while the surface-normalized photocatalytic performance was significantly higher for the larger rutile particles. This can be explained by the red shift of light absorption at higher calcination temperatures. Although Aldrich rutile and the corresponding laboratory-made photocatalyst exhibited similar structural features (e.g. particle size, specific surface area, morphology and light absorption), the latter proved to be less efficient despite its Ti3+ content (while Aldrich rutile contains only Ti4+). The main reason for the much higher photocatalytic performance was the presence of Ti–O–O– entities on the surface of Aldrich rutile. On the basis of these results, in the case of rutile-phase titanium dioxide, the presence of Ti–O–O– entities was more beneficial, than the presence of Ti3+ and low-binding-energy oxygen (which indicates defects) in relation with the photocatalytic performance under visible light irradiation.

Exciton dynamics of GaSe nanoparticle aggregates

Time-resolved and static spectroscopic results on GaSe nanoparticle aggregates are presented to elucidate the exciton relaxation and diffusion dynamics. These results are obtained in room-temperature TOP/TOPO solutions at various concentrations. The aggregate absorption spectra are interpreted in terms of electrostatic coupling and covalent interactions between particles. The spectra at various concentrations may then be interpreted in terms of aggregate distributions calculated from a simple equilibrium model. These distributions are used to interpret concentration-dependent emission anisotropy kinetics and time-dependent emission spectral shifts. The emission spectra are reconstructed from the static emission spectra and decay kinetics obtained at a range of wavelengths. The results indicate that the aggregate z axis persistence length is about 9 particles. The results also show that the one-dimensional exciton diffusion coefficient is excitation wavelength dependent and has a value of about 2 x 10(-5) cm(2)/s following 406 nm excitation. Although exciton diffusion results in very little energy relaxation, subsequent hopping of trapped electron/hole pairs occurs by a Forster mechanism and strongly red shifts the emission spectrum.

Photocatalytic H2 Evolution Using Different Commercial TiO2 Catalysts Deposited with Finely Size-Tailored Au Nanoparticles: Critical Dependence on Au Particle Size

One weight percent of differently sized Au nanoparticles were deposited on two commercially available TiO2 photocatalysts: Aeroxide P25 and Kronos Vlp7000. The primary objective was to investigate the influence of the noble metal particle size and the deposition method on the photocatalytic activity. The developed synthesis method involves a simple approach for the preparation of finely-tuned Au particles through variation of the concentration of the stabilizing agent. Au was deposited on the TiO2 surface by photo- or chemical reduction, using trisodium citrate as a size-tailoring agent. The Au-TiO2 composites were synthetized by in situ reduction or by mixing the titania suspension with a previously prepared gold sol. The H2 production activities of the samples were studied in aqueous TiO2 suspensions irradiated with near-UV light in the absence of dissolved O2, with oxalic acid or methanol as the sacrificial agent. The H2 evolution rates proved to be strongly dependent on Au particle size: the highest H2 production rate was achieved when the Au particles measured ~6 nm.

Investigating ABCB1-Mediated Drug-Drug Interactions: Considerations for In vitro and In vivo Assay Design

BACKGROUND ABCB1 is a key ABC efflux transporter modulating the pharmacokinetics of a large percentage of drugs. ABCB1 is also a site of transporter mediated drug-drug interactions (tDDI). It is the transporter most frequently tested for tDDIs both in vitro and in the clinic. OBJECTIVE Understanding the limitations of various in vitro and in vivo models, therefore, is crucial. In this review we cover regulatory aspects of ABCB1 mediated drug transport as well as inhibition and the available models and methods. We also discuss protein structure and mechanistic aspects of transport as ABCB1 displays complex kinetics that involves multiple binding sites, potentiation of transport and probe-dependent IC50 values. RESULTS Permeability of drugs both passive and mediated by transporters is also a covariate that modulates apparent kinetic values. Levels of expression as well as lipid composition of the expression system used in in vitro studies have also been acknowledged as determinates of transporter activity. ABCB1-mediated clinical tDDIs are often complex as multiple transporters as well as metabolic enzymes may play a role. This complexity often masks the role of ABCB1 in tDDIs. CONCLUSION It is expected that utilization of in vitro data will further increase with the refinement of simulations. It is also anticipated that transporter humanized preclinical models have a significant impact and utility.

Comparison of UV-and UV/VUV-induced photolytic and heterogeneous photocatalytic degradation of phenol, with particular emphasis on the intermediates

Abstract The application of UV photolysis (254 nm), UV/VUV photolysis (254/185 nm) and heterogeneous photocatalysis (TiO2, 254 nm) for the decomposition of phenol has been investigated and compared. For the experiments, the same experimental apparatus, with the same energy consumption has been used. The experimental results suggest that, beside the direct photolysis, HO• has important role in UV/VUV, while HO2• /O2•- in UV photolysis. In the presence of TiO2 the direct UV photolysis is completely suppressed because of the competitive light absorption between TiO2 particles and phenol. In UV or UV/VUV irradiated solutions, the total organic carbon (TOC) concentration decreases after the complete decomposition of phenol while, in the presence of TiO2 TOC and phenol concentration are found to decrease in parallel. In all cases the same aromatic (1,2- and 1,4- dihydroxybenzene) and aliphatic intermediates (maleic, tartaric and oxalic acid) are formed, their formation and decomposition were also systematically investigated and compared.