In the removal of organic micro-pollutants from water, in addition to microporous there are mesoporous adsorbents that are increasingly gaining in importance. Mesoporous silica-based materials like MCM-41 have a high specific surface area and a large pore volume, properties that provide a high adsorption capacity towards pollutants. However, these materials have low hydrothermal stability which represents the main disadvantage in their wider usage in water treatments. Through the optimization of synthesis parameters and various post-synthetic modifications, better material characteristics may be achieved. Usually applied techniques for the material characterization are X-ray diffraction, N 2 -BET method, SEM, TEM and FTIR. The removal efficiency of water pollutants is determined by the MCM-41 structure, but also by the chemical structure of pollutants and in general depends on the pH and ionic strength of the treated water solutions.

In this study, modified sol-gel method was employed to synthesize the pure and Zr-doped titania catalysts. Brunauer-Emmett-Teller (BET) method was applied to determine porosity, X-ray diffraction (XRD) analysis was used to study crystal structure, scanning electron microscopy (SEM) was used to investigate morphology and Fourier transform infrared spectroscopy (FTIR) was used to examine surface properties/total acidity of the obtained catalysts samples. Photocatalytic activity was tested in the reaction of crystal violet (CV) dye decolourization/degradation under UV light irradiation. The effects of several photocatalysis operational parameters were considered, such as catalyst dosage, initial dye concentrations, duration of UV irradiation treatment, as well as catalysts calcination temperatures and dopant amounts. The obtained results indicated faster dye decolourization/degradation with the increase of the catalyst dosage and the decrease of initial CV concentrations. The Zr-doping affects photocatalytic properties, i.e. CV decolourization/degradation of the prepared catalytic materials. Thus, addition of 5 wt.% of ZrO 2 to titania increases photocatalytic effect for ∼15% and addition of 10 wt.% of ZrO 2 improves the photocatalytic efficiency of titania for nearly 30%.

Bentonite is mainly composed of clay minerals from smectite group, therefore it has a well developed and chemically active surface area and high cation exchange capacity. Moreover, an interlayer space of smectite has unusual hydration properties, which manifest as swelling of bentonite in water. These properties make bentonite as a commonly used raw material in chemistry and industry, and it is very important in environmental protection and water treatment as an effective sorbent of heavy metals. The results of X-ray diffraction, a cationic exchange capacity, specific surface area, acid-base properties of the surface and the swelling index showed that the bentonite sample contains mostly montmorillonite. The aim of this study was to test the efficacy of bentonite in the removal of Mn2+ from aqueous systems. The experimental results of Mn2+ adsorption on the bentonite were interpreted by Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms. The adsorption isotherm studies indicate that the adsorption of Mn2+ follows Langmuir isotherm very well. Theoretical monolayer saturation capacity according to Langmuir model was 12.41 mg/g. The removal of Mn2+ is achieved by ion exchange mechanism with naturally occurring cations in bentonite, as well as by forming the inner- and outer-sphere complexes with bentonite surface

Article Highlights• The efficiency of the solid deposits formation in the turbulent and laminar flow conditions of water is examined • The critical flow velocity is lower in the geothermal waters, and higher in drinking water • For different waters of approximately the same hardness, different critical flow velocities were obtained • There is a significant impact of colloidal state on the formation of microdisperse system • Mineralized waters contain colloidal matter and therefore have lower values of the critical flow velocity Abstract This paper deals with synchronised influences of hydromechanical and hydrochemical parameters on the formation of solid deposits in geothermal and other waters, which compose complex heterogeneous and micro-heterogeneous liquid-solid systems. The constituents of these waters in ionic, colloidal and micro-heterogeneous suspended liquid-solid states are responsible for the creation of carbonates, sulphates and other solid matters. In these processes, one cannot eliminate the influence of hydromechanical parameters with flow velocity and water flow criteria (laminar or turbulent flow) as vital factors. Experiments were conducted on the laboratory pilot installation with glass pipes of 2, 4, 6, 8 and 10 mm in diameter, respectively, and the flow was monitored by using a digital peristaltic pump with the flow rate of 2 ml/min to 5000 ml/min. The paper studies the impact of the linear flow velocity on the relative decrease of the initial water hardness in geothermal waters of Sijarinska Banja spa, Niška Banja spa and the estuary water of Medijana, Niš. From the obtained dependences, according to the linear regression model, for each diameter, critical values for linear velocities were determined, as an important parameter for the understanding of the synergism of the hydromechanical and hydrochemical parameters were determined.Keywords: microturbulence, microdispersion systems, water hardness, critical linear velocity, solid deposits.Geothermal, underground and other waters of high mineralization and high hardness comprise very complex composite heterogeneous systems playing a vital role in the energy efficiency, especially in dis-Correspondence: M.M. Purenović,

The preparation of γ-Al 2 O 3 catalyst support by the modified hydrothermal method and synthesis of KI/γ-Al 2 O 3 catalyst, as well as the investigations of their activities in the reaction of transesterification of sunflower oil were performed in this study. The effect of various process parameters on the transesterification reaction of sunflower oil with methanol and their impacts on the reaction conversions were examined. The γ-Al 2 O 3 support and KI/γ-Al 2 O 3 catalysts were characterized by BET, XRD and SEM methods. The physico-chemical properties (surface, textural, structural and morphological) of the catalyst were correlated with its catalytic efficiency. The obtained results implicate that textural and structural properties of the catalyst and also the catalyst activity in the reaction of transesterification essentially depend on textual and structural properties of the γ-Al 2 O 3 support. From the optimization of the process parameters, it was found that the optimal conditions for transesterification reaction are: molar ratio of methanol to oil 12:1; stirring speed 600 rpm; the reflux temperature of methanol; the reaction time 5h; the amount of catalyst in the reaction 3 wt.%.