Agata Śliwak

Enhanced reduction of graphene oxide by high-pressure hydrothermal treatment

A high-pressure assisted hydrothermal treatment is proposed as a facile, green and efficient route for the reduction of aqueous dispersions of graphene oxide. Reactions were performed in an autoclave at mild temperature (180 °C) using only water and nitrogen or hydrogen gas. No further separation or purification of the reduced products was required. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis revealed that the application of high pressure significantly enhanced oxygen removal. The C/O atomic ratio of the graphene oxide sheets increased from 1.65 to 5.29 upon conventional hydrothermal treatment using autogenous pressure. Higher C/O ratios of 6.35 and 7.93 were obtained for graphene oxides that were reduced under high-pressure of nitrogen and hydrogen, respectively. Specifically, the use of high-pressure hydrogen improved the removal of oxygen double-bonded to carbon. The introduction of covalently bonded heteroatoms, which is commonly observed for the use of reductants such as hydrazine, was not detected. Furthermore, high-pressure reduction led to a better restoration of the sp2 conjugation than was obtained by conventional hydrothermal treatment, as determined by XPS and Raman spectroscopies. These findings illustrate the promise of high-pressure hydrothermal treatments for the eco-friendly mass production of reduced graphene oxide.

Carbon Nanofibers Grafted on Activated Carbon as an Electrode in High-Power Supercapacitors

A hybrid electrode material for high-power supercapacitors was fabricated by grafting carbon nanofibers (CNFs) onto the surface of powdered activated carbon (AC) through catalytic chemical vapor deposition (CCVD). A uniform thin layer of disentangled CNFs with a herringbone structure was deposited on the carbon surface through the decomposition of propane at 450 °C over an AC-supported nickel catalyst. CNF coating was controlled by the reaction time and the nickel content. The superior CNF/AC composite displays excellent electrochemical performance in a 0.5 mol L(-1) solution of K2 SO4 due to its unique structure. At a high scan rate (100 mV s(-1) ) and current loading (20 A g(-1) ), the capacitance values were three- and fourfold higher than those for classical AC/carbon black composites. Owing to this feature, a high energy of 10 Wh kg(-1) was obtained over a wide power range in neutral medium at a voltage of 0.8 V. The significant enhancement of charge propagation is attributed to the presence of herringbone CNFs, which facilitate the diffusion of ions in the electrode and play the role of electronic bridges between AC particles. An in situ coating of AC with short CNFs (below 200 nm) is a very attractive method for producing the next generation of carbon composite materials with a high power performance in supercapacitors working in neutral medium.

Guanidine, amitrole and imidazole as nitrogen dopants for the synthesis of N-graphenes

Three N-containing organic compounds – guanidine, amitrole (3-amino-1,2,4-triazole) and imidazole were selected and evaluated as new nitrogen dopants for the preparation of N-graphene. A graphene oxide aqueous dispersion was subjected to hydrothermal treatment at 180 °C for 8 h in the presence of the selected N-compounds. The nitrogen contents in the resultant N-graphenes were as high as 13.4 at%, which is among the highest reported for graphene materials. The X-ray photoelectron spectroscopy revealed that pyridinic nitrogen was predominant in all of the N-graphenes, accounting for up to 47% of the total nitrogen content. Deoxygenation of graphene oxide under hydrothermal conditions was also improved through the use of the N-compounds. Possible reaction mechanisms between graphene oxide and each N-compound are proposed.

Performance of Carbon Nanofiber and Activated Carbon Supported Nickel Catalysts for Liquid-Phase Hydrogenation of Cinnamaldehyde into Hydrocinnamaldehyde

The herringbone and platelet carbon nanofibers and the activated carbon were used as the supports of nickel catalyst for the selective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde (HALD). The hydrogenation of HALD and cinnamyl alcohol under the same experimental conditions was also performed to determine the susceptibility of the isolated and conjugated C=O and C=C bonds to hydrogenation. The catalytic activity and selectivity of the nickel supported on carbons of different structure were evaluated based on the determination of the rate constants of the hydrogenation reaction. The nickel particle size effect was found to be crucial for the catalyst performance.Graphical Abstract

Tailoring micro-mesoporosity in activated carbon fibers to enhance SO2 catalytic oxidation

Enhanced SO2 adsorption of activated carbon fibers is obtained by tailoring a specific micro-mesoporous structure in the fibers. This architecture is obtained via metal catalytic activation of the fibers with a novel precursor, cobalt naphthenate, which contrary to other precursors, also enhances spinnability and carbon fiber yield. In the SO2 oxidation, it is demonstrated that the combination of micropores and large mesopores is the main factor for an enhanced catalytic activity which is superior to that observed in other similar microporous activated carbon fibers. This provides an alternative way for the development of a new generation of catalytic material.

Precursors of volatile organic compounds emitted during phosphorite processing

Precursors of volatile organic compounds emitted during phosphorite processing The composition of solvent-soluble organic matter of phosphorite, which is a precursor of volatile organic compounds emitted by the fertilizer industry, was studied. A benzene-methanol mixture and chloroform were used for the extraction of free and bound bitumen from phosphorites, respectively. The separated bitumen fractions were characterized qualitatively by GC-MS and quantitatively by GC-FID. n-Alkanes, n-alkenes, fatty acids and isoprenoids were identified in the extracts. The main components were n-alkanes and n-alkenes, constituting over 80% of the total bitumen determined. An unexpected presence of n-alkenes only in the free bitumen fraction was found. The possible source of ill-smelling substances evolved during treatment of phosphorite with H2SO4 was discussed.