<p>Three different carbons were prepared from rice husk by steam activation at 700 °C, H<sub>3</sub>PO<sub>4</sub>-activation followed by desilication or desilication followed by H<sub>3</sub>PO<sub>4</sub>-activation at 500 °C. Honeycomb monoliths were obtained by mixing of a carbon with montmorillonite followed by extrusion, curing, calcination and leaching by alkaline solution. Obtained blocks were compared in terms of their morphology and elemental composition using data of SEM/EDX-analysis. From low temperature nitrogen adsorption study results it follows that prepared monoliths are characterized by SBET up to 700 m<sup>2</sup>/g (V<sub>Σ</sub> = 0.79 cm<sup>3</sup>/g) and pore size distribution shows the maximum around 4 nm. Methylene blue number is as high as 250 mg/g.</p>
<p>Two different carbons, namely CAS-P-500 and CRH-P-500, were prepared from apricot stones and rice husk by H<sub>3</sub>PO<sub>4</sub>-activation at 500 °C and H<sub>3</sub>PO<sub>4</sub>/precursor (wt/wt) impregnation ratio of 2:1 followed by water washing and desilication by NaOH solution respectively. Elemental analyses of both samples using X-ray fluorescence spectroscopy and VARIO ELEMENTAR III elemental analyzer detected up to 1% of remained phosphorus and about 88% of carbon. SEM characterization and nitrogen adsorption data revealed that highly mesoporous materials were obtained. According to BJH scheme calculations, N<sub>2</sub> BET-surface area and pore volume for CAS-P-500 reached the values of 2030 m<sup>2</sup>/g and 1.64 cm<sup>3</sup>/g, while for CRH-P-500: 1690 m<sup>2</sup>/g and 1.95 cm<sup>3</sup>/g respectively. Activated carbons CAS-P-500 and CRH-P-500 were used as catalyst supports for the conversion of small amounts of benzene into cyclohexane to obtain cleaner gasoline. According to Euro-3 standards, gasoline should contain less than 1% of benzene, since the incomplete combustion of gasoline, which contains benzene, leads to formation of benzopyrene- a powerful carcinogen in exhaust gases. The activity of rhodium catalysts based on the CAS-P-500 and CRH-P-500 allow complete conversion of benzene into cyclohexane at 40 atm and 80 °C temperature and is comparable to those of based on conventional carbons: “Sibunit”, etc.</p>
The adsorption behavior of Au3+ ions on metal electrodes has been studied using an electrochemical quartz crystal microbalance combined with the cyclic voltammetry technique. The experiments were carried out for HAuCl4 using 0.1 mol·L-1 HCl (pH~1) as a background electrolyte solution. The kinetics of electroreduction of Au3+ ions on the rice husk based activated carbon and gold electrodes in chloride electrolytes by the cyclic voltammetry and the electrochemical quartz crystal microbalance with a variation of the scan rate in the range of 5‒50 mV·s-1 has been studied. The diffusion coefficient of Au3+ ions for the tested solution on gold and carbon electrodes was determined by the cyclic voltammetry method on the basis of the Randles-Ševčik equation. It is found that electroreduction of gold goes via the discharge of AuCl4- complexes to the formation of metallic gold with a current efficiency of 97‒99%. The scanning electron microscopic images of the gold adsorbed carbon surface was taken to see gold particles and their morphology. In SEM images, it is clearly seen that the surface of carbon has a relief structure and gold has grown in the form of clusters. The smallest gold nanoparticles that could be examined were 100‒250 nm in diameter on the surface of the c arbon electrode.
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