BELGRADE, SERBIA 2018 3rd International Meeting on Materials Science for Energy Related Applications held on September 25-26, 2018 at the University of Belgrade, Faculty of Physical Chemistry, Belgrade, Serbia is a satellite event of PHYSICAL CHEMISTRY 2018 14th International Conference on Fundamental and Applied Aspects of Physical Chemistry

The wide use of pesticides in modern agriculture and other areas results in an urgent need for their efficient removal from the environment. Adsorption of pesticides is one of the most commonly used strategies for this task. Here we analyze the adsorption of two organophosphorus pesticides, dimethoate (DMT) and chlorpyrifos (CPF), on graphene-based materials. The adsorption was found to be very sensitive to the structure of the adsorbents used. In particular, aliphatic DMT was found to prefer hydrophilic oxidized graphene surfaces. The CPF molecule, which contains an aromatic moiety, prefers adsorption on the surface of a graphene basal plane with high structural order and preserved π electron system. The toxicity of pesticide solutions is reduced after adsorption, suggesting that there is no oxidation of DMT and CPF to more toxic oxo forms. We emphasize that the combination of structural properties of adsorbents and adsorbates defines the adsorption of organophosphorus pesticides on graphene-based materials, while the specific surface area of adsorbents is not the major factor.

The increasing energy demands of modern society require a deep understanding of the properties of energy storage materials, as well as the tuning of their performance. We show that the capacitance of graphene oxide (GO) can be precisely tuned using a simple electrochemical reduction route. In situ resistance measurements, in combination with cyclic voltammetry measurements and Raman spectroscopy, have shown that upon reduction GO is irreversibly deoxygenated, which is further accompanied by structural ordering and an increase in electrical conductivity. The capacitance is maximized when the concentration of oxygen functional groups is properly balanced with the conductivity. Any further reduction and deoxygenation leads to a gradual loss of capacitance. The observed trend is independent of the preparation route and the exact chemical and structural properties of GO. It is proposed that an improvement in the capacitive properties of any GO can be achieved by optimization of its reduction conditions.

H2 production via water electrolysis plays an important role in hydrogen economy. Hence, novel cheap electrocatalysts for the hydrogen evolution reaction (HER) are constantly needed. Here, we describe a simple method for the preparation of composite catalysts for H2 evolution, consisting in simultaneous reduction of the graphene oxide film, and electrochemical deposition of Ni on its surface. The obtained composites (Ni@rGO), compared to pure electrodeposited Ni, show an improved electrocatalytic activity towards HER in alkaline media. We found that the activity of the Ni@rGO catalysts depends on the surface composition (Ni vs. C mole ratio) and on the level of structural disorder of the rGO support. We suggest that HER activity is improved via Hads spillover from the Ni particles to the rGO support, where quick recombination to molecular hydrogen is favored. A deeper insight into such a mechanism of H2 production was achieved by kinetic Monte-Carlo simulations. These simulations enabled the reproduction of experimentally observed trends under the assumption that the support can act as a Hads acceptor. We expect that the proposed procedure for the production of novel HER catalysts could be generalized and lead to the development of a new generation of HER catalysts by tailoring the catalyst/support interface.

1 Department of chemistry, Faculty of Science, Zmaja od Bosne 33-35, Sarajevo, Bosnia and Hercegovina 2 University of Belgrade Faculty of Physical Chemistry, Studentski trg 12-16, 11158 Belgrade, Serbia 3 Laboratory for Micro and Nanotechnology, Paul Scherrer Institute, Villigen, Switzerland. 4 Serbian Academy of Sciences and Arts, Knez Mihajlova 35, 11000 Belgrade, Serbia * E-mail: slavko@ffh.bg.ac.rs

Graphene synthesized by reduction of graphene oxide, depending on the degree of reduction, retains a certain amount of surface OH groups. Considering the surface OH groups/graphene layer system by means of density functional theory calculations, we evidenced the tendency of OH groups to cluster, resulting in enhanced system stability and no band gap opening. In the oxygen concentration range between 1.8 and 8.47 at%, with the addition of each new OH group, integral binding energy decreases, while differential binding energy shows the boost at even numbers of OH groups. Furthermore, we found that the clustering of OH groups over graphene basal plane plays a crucial role in enhancing the interactions with alkali metals. Namely, if alkali metal atoms interact with individual OH groups only, the interaction leads to an irreversible formation of MOH phase. When alkali atoms interact with clusters containing odd number of OH groups, a reversible transfer of an electron charge from the metal atom to the substrate takes place without OH removal. The strength of the interaction in general increases from Li to K. In an experimental investigation of a graphene sample which dominantly contains OH groups, we have shown that the trend in the specific interaction strength reflects to gravimetric capacitances measured in alkali metal chloride solutions. We propose that the charge stored in OH groups which interact with alkali metal cation and the π electronic system of the graphene basal plane presents the main part of its pseudocapacitance.

To make jewellery of gold, gold is alloyed with other metals. It is of great importance to accurately determine the total amount of pure gold in alloys used for making the jewellery and in jewellery made of gold, because it determines its value on the market. Several analytical methods are used for this purpose. This study was based on comparison of results of analysis of gold alloy for 14-carat jewellery obtained by non-destructive fluorescent analysis method and destructive cupellation method. The null hypothesis with 95 % confidence level on equivalence in measurement precision of perecnt by percent mass of gold in three very similar gold alloy samples in reproducibility conditions (three measurement series) for standard cupellation method and the method compared (validated), XRF method, has been confirmed. F-test did not confirm null hypothesis on precision equivalence for two mentioned analysis methods. There is a significant difference in variance values. However, the t-test was carried out, which verified the null hypothesis on equivalence between mean values of results achieved in two compared values. In order to confirm applicabilty of two methods ,Zscore was calculated giving values of less than 2, using statistical data from inter-laboratory program with 62 participating laboratories applying cupellation method, and 60 laboratories applying XRF method for analysis of gold alloy used in production of 14-carat jewellery. Article info Received: 06/12/2011 Accepted: 25/01/2012