This paper shows the use of membrane filters in adsorption of solution of tetracycline hydrochloride on graphene materials. The adsorption process was monitored at different wavelengths, different pH values at certain time intervals. The absorbances of the solutions were measured by UV-Vis spectrophotometry at two wavelengths (275 nm and 356 nm), and three pH values (pH 4, pH 7 and pH 10) every 90 minutes for 6 hours of monitoring, with constant stirring in an ultrasonic bath. The results showed decrease in absorbance at both wavelength and in all three pH values which proved the adsorption of tetracycline hydrochloride on GO and rGO. The largest decrease in absorbance was 98.1%. The most suitable pH value for adsorption was pH 4. This paper used a unique approach to filtration through membrane filters, which in the future could lead to the development of membrane filters based on graphene materials.

Hydrogen evolution reaction (HER) is one of the most important reactions in electrochemistry. This is not only because it is the simplest way to produce high purity hydrogen and the fact that it is the side reaction in many other technologies. HER actually shaped current electrochemistry because it was in focus of active research for so many years (and it still is). The number of catalysts investigated for HER is immense, and it is not possible to overview them all. In fact, it seems that the complexity of the field overcomes the complexity of HER. The aim of this review is to point out some of the latest developments in HER catalysis, current directions and some of the missing links between a single crystal, nanosized supported catalysts and recently emerging, single-atom catalysts for HER.

Graphene-based materials and their role in electrocatalysis related to hydrogen production have been intensively investigated by many authors, often justified through a low price of such materials. In this study we used single-step electrodeposition/graphene oxide reduction route to prepare Ni@reduced-graphene-oxide composites for electrochemical hydrogen evolution reaction (HER). As the precursors for reduced graphene oxide, two different home-made graphene oxides were used. When compared to pure electrodeposited Ni, composite catalysts show improved catalytic activity which depends on Ni electrodeposition time in a volcano-type fashion. Using electrochemically prepared graphene oxide, HER overvoltage needed to reach 10 mA cm −2 was reduced to only −97 mV, showing the improvement by roughly 200 mV when compared to pure electrodeposited Ni. It was concluded that structural disorder and surface oxidation of graphene-based materials are the key properties for reaching high HER activities of such prepared catalysts. Based on this observation, it was discussed whether it is economically justified to use high quality graphene oxide for the preparation of HER catalysts, as the price (production and commercial) of this material can be extremely high, often exceeding the price of platinum.

Abstract To contribute to the knowledge on the influence of synthesis procedure on the intercalation kinetics of lithium ions into phospho-olivines, LiFePO4/C composite samples (LFPC) were synthesized in two ways, the first one in a sol-gel procedure (SG), and the other in a solid-state reaction (SS). The X-ray diffractograms (XRD) of both samples overlapped with that of pure LiFePO4, taken from the crystallographic database. Scanning electron microscopy pictures indicated the high degree of interparticle sintering, which caused a considerable agglomerate growth. The results of potentiodynamic measurements in aqueous LiNO3 solution revealed that for SS sample, three times higher initial capacity from that of SG one, (amounting to 74 mAh g−1 at 5 mV s−1). However, capacity fade on rising scan rate is much more expressed for SS sample than for SG one. We suggest that a different degree of material utilization due to the incomplete coverage of olivine particles by carbon explains this difference. The technique of separation of diffusion and capacitance currents was applied in a kinetic analysis, but it was shown to be inappropriate. We suggest the inapplicability of classic CV theory to the intercalation system accompanied by phase transition. Instead, a model of ohmic resistance determination of process kinetics was considered. LFPC-SS sample delivers three times larger capacity in LiNO3, amounting to 74 mAh g−1 at 1 mV s−1.

The ability to tune charge storage properties of graphene oxide (GO) is of utmost importance for energy conversion applications. Here we show that electrochemical reduction of GO is highly sensitive to the cations present in the solution. GO is reduced at lower potential in alkali metal chloride solutions than in alkaline earth metal chlorides. During the reduction, capacitance of GO increases from 10 to 70 times. Maximum capacitances of reduced GO are between 65 and 130 F g-1, depending on the electrolyte and the presence of conductive additive. We propose that different interactions of cations with oxygen functional groups of GO during the reduction are responsible for the observed effect.

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.

Abstract Development of noble metal-free catalysts for hydrogen production is one of the cores of the sustainable energy economy. Here we present results of systematic analysis of catalytic activity of Ni-Mo alloy powders in alkaline media towards hydrogen evolution reaction (HER). Catalysts were prepared in a wide concentration range (from Ni0.2Mo0.8 to Ni0.9Mo0.1), and resulted with a volcano shaped activity-composition relationship, with maximum catalytic activity achieved for the powder with nominal composition Ni0.6Mo0.4. Improved HER activity is ascribed to reduced deactivation by hydride formation and adequate hydrogen-surface energetics on Ni-Mo catalysts. In the second part, we demonstrate a novel method for electrochemical formation of NiMo@rGO composites. Prepared composite electrodes show improved electrocatalytic activity compared to both pure Ni and Ni@rGO electrodes. Activity was observed to depend on the deposition time and is contributed by two factors: (i) formation of Ni-Mo system and (ii) formation of an interfacial region with rGO. We expect that the provided activity-composition relationship in combination with novel electrochemical NiMo-rGO composite formation procedure will provide a route for the development of new highly efficient noble metal-free HER electrocatalysts.

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

Eloksiranjem se postiÞe da su u svim korozijskim sredinama potencijali veæi, što znaèi da se stvara zaštitni film oksida. Oksidni sloj najstabilniji je u otopini sumporne kiseline, a najmanju zaštitnu ulogu pokazuje u 3 %-tnoj otopini HCl, 3 %-tnoj otopini NaCl i morskoj vodi. Poveæanjem debljine oksidnog sloja s 10 na 20 mikrometara ne postiÞe se poboljšanje zaštite od korozije izuzev u otopini NaOH. Eloksiranjem se smanjuju polarizacijski otpori prema sliènoj ovisnosti o korozijskoj sredini. Slièan i veæi zaštitni uèinak pokazuje eloksirani aluminij s debljinom sloja 20 mikrometara. Eloksiranjem se brzina korozije smanjuje za nekoliko desetaka puta, što potvrðuje da se eloksiranjem aluminij štiti od korozije. Vrijednosti su od 3,57 do 2699,00 mm a–1.