Milan Momčilović

Synthesis and characterization of resorcinol formaldehyde carbon cryogel as efficient sorbent for imidacloprid removal

AbstractCarbon cryogel (CC) has been prepared through sol gel polycondensation of resorcinol with formaldehyde in basic aqueous solution followed by freeze-drying and carbonization. Porous properties of CC analyzed by gravimetric McBain method confirmed the expected surface area and degree of mesoporosity. Obtained powdered material was used for the removal of pesticide imidacloprid from aqueous solutions under regular batch adsorption procedure. A set of several isotherm models including Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, Brouers–Sotolongo, Redlich–Peterson, Sips, Toth, Jovanovic, Hurkins–Jura, Halsey and Radke–Prausnitz model was used for nonlinear fitting of equilibrium data. Several models fitted with quite high correlation coefficients. Bangham and Elovich model fitted suitably for kinetic study indicating that pesticide diffusion into carbons pores is important step which dictates the process rate. Suitability of kinetic models decreased with the increase in adsorbent dosage. Imidac...

The acid–base, morphological and structural properties of new biosorbent obtained by oxidative hydrothermal treatment of peat

Samples of natural peat (NP) were hydrothermally treated at different temperatures in oxidative and acidic aqueous medium to tailor their acid–base, adsorption, morphological and other properties. The obtained materials were thoroughly characterized by SEM, XRD and FTIR techniques, followed by determination of pHpzc, examination of adsorption characteristics and the extent of organic matter leaching in water. Acid–base characteristics of these materials were examined by potentiometric and conductometric titration of corresponding aqueous suspensions. Experimental potentiometric data were interpreted using ProtoFit software (NEM, non-electrostatic model) which provided pKa values and concentrations of surface sites which are compared with corresponding values obtained by conductometric titration method. There are two main types of surface groups (carboxylic and phenolic) that are dominant in the materials and determine their acid–base behavior in the aqueous medium. Temperature during oxidative hydrothermal treatment has no significant effect on the total number of surface groups, but influences the ratio of carboxylic and phenol-type groups. Hence, acid–base properties of peat can be tailored, which is useful in designing and improving adsorptive characteristics of peat for the preferential removal of certain pollutants from water.

n-hydrocarbons conversions over metal-modified solid acid catalysts

The quality of a straight-run fuel oil can be improved if saturated n-hydrocarbons of low octane number are converted to their branched counterparts. Poor reactivity of traditional catalysts in isomerization reactions imposed the need for the development of new catalysts among which noble metal promoted acid catalysts, liquid and/or solid acid catalysts take a prominent place. Sulfated zirconia and metal promoted sulfated zirconia exhibit high activity for the isomerization of light alkanes at low temperatures. The present paper highlights the original results which indicate that the modification of sulfated zirconia by incorporation of metals (platinum and rhenium) significantly affects catalytic performances in n-hydrocarbon conversion reactions. Favourable activity/selectivity of the promoted sulfated zirconia depends on the crystal phase composition, critical crystallites sizes, platinum dispersion, total acidity and type of acidity. Attention is also paid to the recently developed solid acid catalysts used in other conversion reactions of hydrocarbons.