Marin Kovacic

Solar-driven photocatalytic treatment of diclofenac using immobilized TiO2-based zeolite composites

The study is aimed at evaluating the potential of immobilized TiO2-based zeolite composite for solar-driven photocatalytic water treatment. In that purpose, TiO2-iron-exchanged zeolite (FeZ) composite was prepared using commercial Aeroxide TiO2 P25 and iron-exchanged zeolite of ZSM5 type, FeZ. The activity of TiO2-FeZ, immobilized on glass support, was evaluated under solar irradiation for removal of diclofenac (DCF) in water. TiO2-FeZ immobilized in a form of thin film was characterized for its morphology, structure, and composition using scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM/EDX). Diffuse reflectance spectroscopy (DRS) was used to determine potential changes in band gaps of prepared TiO2-FeZ in comparison to pure TiO2. The influence of pH, concentration of hydrogen peroxide, FeZ wt% within the composite, and photocatalyst dosage on DCF removal and conversion efficiency by solar/TiO2-FeZ/H2O2 process was investigated. TiO2-FeZ demonstrated higher photocatalytic activity than pure TiO2 under solar irradiation in acidic conditions and presence of H2O2.

Prediction of biodegradability of aromatics in water using QSAR modeling

The study was aimed at developing models for predicting the biodegradability of aromatic water pollutants. For that purpose, 36 single-benzene ring compounds, with different type, number and position of substituents, were used. The biodegradability was estimated according to the ratio of the biochemical (BOD5) and chemical (COD) oxygen demand values determined for parent compounds ((BOD5/COD)0), as well as for their reaction mixtures in half-life achieved by UV-C/H2O2 process ((BOD5/COD)t1/2). The models correlating biodegradability and molecular structure characteristics of studied pollutants were derived using quantitative structure-activity relationship (QSAR) principles and tools. Upon derivation of the models and calibration on the training and subsequent testing on the test set, 3- and 5-variable models were selected as the most predictive for (BOD5/COD)0 and (BOD5/COD)t1/2, respectively, according to the values of statistical parameters R2 and Q2. Hence, 3-variable model predicting (BOD5/COD)0 possessed R2=0.863 and Q2=0.799 for training set, and R2=0.710 for test set, while 5-variable model predicting (BOD5/COD)1/2 possessed R2=0.886 and Q2=0.788 for training set, and R2=0.564 for test set. The selected models are interpretable and transparent, reflecting key structural features that influence targeted biodegradability and can be correlated with the degradation mechanisms of studied compounds by UV-C/H2O2.

Comparative analysis of UV-C/H2O2 and UV-A/TiO2 processes for the degradation of diclofenac in water

The study investigates the treatment of diclofenac (DCF), a pharmaceutical included in the first watch list of the European Water Framework Directive as a new potential priority substance in water. Since the conventional wastewater treatment technologies do not efficiently remove DCF, advanced treatment technologies capable of its complete removal or destruction of its biological activity, need to be evaluated and eventually employed. For that purpose, typical representatives of photooxidative and photocatalytic advanced oxidation processes were applied. The effectiveness of UV-C/H2O2 and UV-A/TiO2 were compared regarding DCF conversion and mineralization kinetics, water quality parameters for assessing biodegradability and toxicity. In spite of similar biodegradability profiles, the obtained results indicate different DCF degradation pathways, which are reflected in different profiles of toxicity towards Vibrio fischeri. The observed DCF conversion and mineralization kinetics revealed the benefits of UV-C/H2O2 process. However, lower toxicity favored the application of photocatalytic over photooxidative treatment for DCF removal.

Reactivation and reuse of TiO2-SnS2 composite catalyst for solar-driven water treatment

One of the most important features of photocatalytic materials intended to be used for water treatment is their long-term stability. The study is focused on the application of thermal and chemical treatments for the reactivation of TiO2-SnS2 composite photocatalyst, prepared by hydrothermal synthesis and immobilized on the glass support using titania/silica binder. Such a catalytic system was applied in solar-driven treatment, solar/TiO2-SnS2/H2O2, for the purification of water contaminated with diclofenac (DCF). The effectiveness of studied reactivation methods for retaining TiO2-SnS2 activity in consecutive cycles was evaluated on basis of DCF removal and conversion, and TOC removal and mineralization of organic content. Besides these water quality parameters, biodegradability changes in DCF aqueous solution treated by solar/TiO2-SnS2/H2O2 process using simply reused (air-dried) and thermally and chemically reactivated composite photocatalyst through six consecutive cycles were monitored. It was established that both thermal and chemical reactivation retain TiO2-SnS2 activity in the second cycle of its reuse. However, both treatments caused the alteration in the TiO2-SnS2 morphology due to the partial transformation of visible-active SnS2 into non-active SnO2. Such alteration, repeated through consecutive reactivation and reuse, was reflected through gradual activity loss of TiO2-SnS2 composite in applied solar-driven water treatment.

TiO2-SnS2 nanocomposites: solar-active photocatalytic materials for water treatment

The study is aimed at evaluating TiO2-SnS2 composites as effective solar-active photocatalysts for water treatment. Two strategies for the preparation of TiO2-SnS2 composites were examined: (i) in-situ chemical synthesis followed by immobilization on glass plates and (ii) binding of two components (TiO2 and SnS2) within the immobilization step. The as-prepared TiO2-SnS2 composites and their sole components (TiO2 or SnS2) were inspected for composition, crystallinity, and morphology using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) analyses. Diffuse reflectance spectroscopy (DRS) was used to determine band gaps of immobilized TiO2-SnS2 and to establish the changes in comparison to respective sole components. The activity of immobilized TiO2-SnS2 composites was tested for the removal of diclofenac (DCF) in aqueous solution under simulated solar irradiation and compared with that of single component photocatalysts. In situ chemical synthesis yielded materials of high crystallinity, while their morphology and composition strongly depended on synthesis conditions applied. TiO2-SnS2 composites exhibited higher activity toward DCF removal and conversion in comparison to their sole components at acidic pH, while only in situ synthesized TiO2-SnS2 composites showed higher activity at neutral pH.

Elucidating the Photocatalytic Behavior of TiO2-SnS2 Composites Based on Their Energy Band Structure

TiO2-SnS2 composite semiconducting photocatalysts with different building component ratios were prepared by hydrothermal synthesis (TiO2-SnS2-HT) and by immobilization of commercial TiO2 and SnS2 particles (TiO2-SnS2-COMM). The band gap values, which determine the catalysts’ photoactivity, were examined by diffuse reflectance spectroscopy and Kubelka–Munk transformations. The catalysts’ surface properties: specific surface area, charge and adsorption capacitance at the solid–solution interface were characterized using BET analysis, potentiometric titration and electrochemical impedance spectroscopy, respectively. The electronic band structure of TiO2-SnS2 photocatalyst, as the key property for the solar-driven photocatalysis, was deduced from the thermodynamic data and the semiconducting parameters (type of semiconductivity, concentration of the charge carriers, flat band potential) obtained by Mott–Schottky analysis. The photoactivity of both composites was studied in photocatalytic treatment of diclofenac (DCF) under simulated solar irradiation and was compared to the benchmark photocatalyst (TiO2 P25) activity. The influence of process parameters, such as pH, H2O2, and composite formulation on the effectiveness of DCF removal and conversion was investigated and discussed by employing response surface modeling (RSM) approach. The photocatalytic efficiency of both composite materials was discussed on the basis of the hetereojunction formation that facilitated the photoelectron transfer, promoting more efficient photocatalytic degradation of DCF.

Inovativna laboratorijska perilica namijenjena pranju viala

Čistoća laboratorijskog posuđa polovica je uspješne laboratorijske analize, ako parafraziramo poznatu poslovicu o čistoći i zdravlju. Nužno je osigurati zadovoljavajuću čistoću posuđa, no radi se o zahtjevnom i zamornom zadatku ako se radi o velikim količinama posuđa i k tomu minijaturnih dimenzija. Među takvo posuđe spadaju tzv. viale, malene bočice zapremnine najčešće 2 ml koje se upotrebljavaju za automatske dodavače uzoraka (engl. autosampler) u instrumentalnim kromatografskim metodama. Cijena pojedinačne viale bez čepa i silikonske septe je razmjerno mala, oko 1,20 kn prema web-katalogu tvrtke Sigma-Aldrich za pakiranje s 1000 komada viala.1 Zbog male pojedinačne cijene smatraju se potrošnim laboratorijskim materijalom.