Valery V. Lunin’s research while affiliated with Lomonosov Moscow State University and other places

Porous oxide materials are widely used in environmental catalysis owing to their outstanding properties such as high specific surface area, enhanced mass transport and diffusion, and accessibility of active sites. Oxides of metals with variable oxidation state such as ceria and double oxides based on ceria also provide high oxygen storage capacity which is important in a huge number of oxidation processes. The outstanding progress in the development of hierarchically organized porous oxide catalysts relates to the use of template synthetic methods. Single and mixed oxides with enhanced porous structure can serve both as supports for the catalysts of different nature and active components for catalytic oxidation of volatile organic compounds, soot particles and other environmentally dangerous components of exhaust gases, in hydrocarbons reforming, water gas shift reaction and photocatalytic transformations. This review highlights the recent progress in synthetic strategies using different types of templates (artificial and biological, hard and soft), including combined ones, in the preparation of single and mixed oxide catalysts based on ceria, and provides examples of their application in the main areas of environmental catalysis.

The temperature dependence of the solubility product of copper (II) oxalate CuC2O4 was determined in the range 20–45 °C from the results of precipitation potentiometric titration of aqueous Cu²⁺ solution with oxalate solution. The titration was performed with a copper indicator electrode. Based on the obtained values of the solubility product, the formation enthalpy and entropy of solid copper oxalate have been found.

Lithium and complex lithium greases were modified by few-layer graphene nanoflakes. Tribological tests demonstrate improvement of the lubricating characteristics, e.g. increase of the welding load and decrease of the wear scar diameter after the modification. XPS method showed occurrence tribochemical reaction between lithium 12-hydroxystearate molecules and graphene nanoflakes surface during exploitation of the grease. It was shown that graphene nanoflakes are corrosion-inactive in lubricating compositions and compatible with modern additive packages.

Cylindrical and conical carbon nanotubes were used as catalysts for the conversion of C3–C4 secondary aliphatic alcohols. The effect of the oxidative and reductive treatment of carbon nanotubes on the catalytic activity, selectivity and the conversion of propan-2-ol and butan-2-ol related to the structure of carbon matrix was revealed.

N-doped nanocarbons are promising materials for metal-free and supported catalysts. Three types of N-doped carbon nanotubes (N-CNTs) were synthesized by chemical vapor deposition (CVD), by oxidation of the CVD produced N-CNTs with nitric acid, and by post-doping of oxidized undoped CNTs with ammonia. Cobalt catalysts with 20[Formula: see text]wt.% loading supported on N-CNTs were tested in the Fischer–Tropsch synthesis. Oxidized N-CNTs containing pyridone groups demonstrated the best stabilization of cobalt nanoparticles. The catalyst on this support showed the highest selectivity towards [Formula: see text] hydrocarbons. The performance of the catalyst supported on CVD N-CNTs was the worst because of the large variation in cobalt particle size and low reduction degree. The catalysts supported on post-doped CNTs demonstrated the best activity, but high methane selectivity because of the low Co particle size ([Formula: see text][Formula: see text]nm).

Supercritical antisolvent (SAS) precipitation technique, although being versatile and ecologically friendly, suffers from the lack of convenient methods for necessary thermodynamic parameters measurement. Recently we have proposed a method for solubility measurement in binary fluids based on an online hyphenation of supercritical antisolvent method and supercritical fluid chromatography (SAS-SFC). In this paper, we demonstrate the applicability of this method to the investigation of both selective precipitation from solution and particle size tuning in SAS using lower dicarboxylic acids as model objects. Measured solubility values adequately reflect selective crystallization from solution. SAS precipitation was observed only for those components, which concentration was above solubility in CO2-solvent mixture as predicted by SAS-SFC method. Also, concentration dependences of particle size plotted in supersaturation coordinates instead of direct concentration in initial solution give additional insight into crystallization behaviour in SAS.

The template pyrolysis synthesis, as a bottom-up approach, and oxidation, as a top-down approach, were combined to produce pristine and nitrogen doped carbon dots. Varying the precursor type, synthesis temperature and oxidation time the color of carbon dots was tuned from green to orange because of the bandgap changes and formation of interband states. TEM, Raman, and XPS data revealed the graphene core of carbon dots with the shell of carboxyl and hydroxyl functionalities. The bulk and surface N-doping of the carbon dots affected their photoluminescence in a different way because of the opposite effect on the π-electron system: the core modification led to a blue shift, while the surface amination resulted in a red shift. A blue shift was also observed for the undoped dots with increasing the synthesis temperature, while more prolonged oxidation led to a red shift. Excitation with different wavelengths revealed the inhomogeneity of photoluminescence sites in nitrogen-doped carbon dots.

The aim of the research is to choose the most efficient adsorbent for two-stage ozone-sorption purification of groundwater containing both trichloroethylene (TCE) and tetrachloroethylene (PCE) between three carbon sorbents produced in Russia (AUT-M, CAUSORB-221, and AG-3). Sorption isotherms of TCE and PCE on AUT-M and CAUSORB-221 at 296 K were fitted by the Freundlich equation. The better TCE and PCE sorption ability of AUT-M in comparison with CAUSORB – 221 and AG-3 was demonstrated. The optimum parameters for ozonation and sorption stages of groundwater purification from TCE and PCE are elucidated using laboratory and pilot-plant scales. Prolonged test of this technology for purification of ground demonstrated that the higher achievable efficiency of destruction with ozone is 94% for TCE and 38% for PCE. Ozonation-sorption treatment of groundwater allows one to achieve TCE and PCE removal efficiency of 96-97% and 92-94% correspondingly. The most efficient carbon sorbent is microporous carbon fiber AUT-M. Using this sorbent, TCE and PCE concentrations in treated water decrease below the MPC level (5 μg/L) adopted in Russia. It is concluded that the combination of ozonation with sorption of residual contaminants by carbon sorbents is a promising way for the purification of waters containing chlorinated contaminants.

Mesoporous graphene nanoflakes (GNFs) of different thickness with a specific surface area of 660–1720 m2/g were produced by the template synthesis via hexane pyrolysis over MgO. The structure and morphology of GNFs were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and low-temperature N2 physisorption. The electrochemical performance of GNF-based supercapacitors was tested in ionic liquid electrolyte (1.2 M N+Et4TFSI− in CH3CN) by cyclic voltammetry and galvanostatic charge – discharge measurements. The assembled symmetric supercapacitors with a wide voltage window of 3 V delivered specific capacitance of 112 F/g at 5 mV/s and 105 F/g at 0.5 A/g with a high rate capability of ~81% at a current density of 15 A/g. The energy density reached 32.8 Wh/kg corresponding to the power density of 0.7 kW/kg. Furthermore, even at a high power density of 19.9 kW/kg, GNFs still showed an energy density of 24.3 Wh/kg, which made them promising for application in supercapacitors.