Alexander M. Puziy

Highly stable performance of supercapacitors from phosphorus-enriched carbons

Phosphorus-rich microporous carbons (P-carbons) prepared by a simple H(3)PO(4) activation of three different carbon precursors exhibit enhanced supercapacitive performance in 1 M H(2)SO(4) when highly stable performance can be achieved at potentials larger than the theoretical decomposition potential of water. This ability of P-carbons greatly enhances the energy density of supercapacitors that are capable of delivering 16 Wh/kg compared to 5 Wh/kg for the commercial carbon. An intercept-free multiple linear regression model confirms the strongest influence of phosphorus on capacitance together with micropores 0.65-0.83 nm in width that are the most effective in forming the electric double layer.

Elucidation of the ion binding mechanism in heterogeneous carbon-composite adsorbents

Abstract A two-stage analysis of the mechanism of metal ion binding by a heterogeneous adsorbent was developed. In the first stage, a continuous proton affinity distribution was calculated from potentiometric titration data using the CONTIN method with a Langmuir kernel. Electrostatic effects were accounted for using a diffuse layer model. In the second stage, the parameters obtained from the continuous distribution function (i.e. the number of different types of surface sites, site densities and their protonation constants) were utilized in a discrete distribution to represent the adsorbent in surface complexation and double layer models using the GRFIT speciation code. This information on the surface groups was applied to metal ion potentiometric titration experiments to calculate the surface complexation equilibrium constants of the metal ions and hence elucidate the mechanism of ion binding to these sites. The proposed method was applied successfully to the adsorption of Sr and Cu ions on carbon-composite adsorbents, KAU-mod and SCN-mod. The continuous distribution method (CONTIN) revealed three types of surface sites within these carbon-composite adsorbents with pK values ranging between 3.5–4.1, 5.3–6.3 and 7.7–8.2. The analysis of the metal ion adsorption data using the GRFIT speciation code showed that only the first two surface sites were capable of forming surface complexes with the Sr ions, and that only the first site governed the adsorption of the Cu ions.

Functionalization of Carbon and Silica Gel by Phosphoric Acid

Functionalization of polymer-based carbon (SCS-3) and silica gel (SG60) by phosphoric acid at 800°C was investigated. It was shown that heat treatment of carbon and silica gel in the presence of phosphoric acid at 800°C provides a way of functionalizing materials with phosphorus-containing surface groups. Functionalization of the finished carbon occurs as a surface reaction while destruction of the silica gel structure was observed. Functionalization with phosphoric acid creates new acid surface groups — phosphorus-containing and oxygen-containing in the case of carbon and only phosphorus-containing in the case of silica gel. Enhancement of the amount of acid surface groups by functionalization improves the metal-ion binding properties of both carbon and silica gel.

Chapter 8 – Adsorption by Phosphorus-Containing Carbons

This chapter deals with the adsorption properties specific to phosphorus-containing carbons. The adsorption properties of these carbons are defined by their porous structure and the presence of polyphosphates bound to the carbon matrix. The adsorption properties imparted by polyphosphates to activated carbon include hydrophilicity, surface acidity, and the ability to adsorb cations. Surface phosphate groups are responsible for metal ion binding in aqueous solutions, especially at low levels of pH. Phosphorus-containing carbons exhibit enhanced electrochemical performance as anodes in lithium batteries and supercapacitors. In short, they have great potential in water treatment, the conditioning of engine fuel, and electrochemical energy storage devices.

Comparison of heterogeneous pore models QSDFT and 2D-NLDFT and computer programs ASiQwin and SAIEUS for calculation of pore size distribution

The pore size distributions (PSD) of selected carbons were calculated from their nitrogen adsorption isotherms using both the QSDFT model implemented in ASiQwin version 3.0 software (Quantachrome Instruments) and 2D-NLDFT model implemented in SAIEUS software (Micromeritics). The results showed that both the QSDFT and the 2D-NLDFT methods give similar PSDs despite the different methods for accounting for the heterogeneity of the carbon adsorbent. The characteristic features of the methods and software were discussed and possible improvements were proposed.

Surface heterogeneity of carbon–silica adsorbents studied on the basis of the complex adsorption investigations

Abstract Silica-gel (SG) Si-60 was coated by pyrolytic coke using CVD from methylene chloride. The porous structure of carbon–silica adsorbents (carbosils) was analyzed on the basis of nitrogen adsorption isotherms at 77 K. It has been shown that carbosils are mesoporous adsorbents with complete absence of micropores. Total pore volume and surface area decrease during the carbon deposition on silica surface. Heterogeneity of surface of carbosil samples was estimated by adsorption energy distribution (AEDs) calculated from adsorption isotherms of nitrogen at 77 K and hexane, cyclohexane, benzene and chloroform adsorption isotherms at 473 and 483 K. AEDs were obtained by solving Adsorption Integral Equation with Hill-de Boer kernel function. N2 AEDs show that distribution of silica active surface sites responsible for N2 adsorption at 77 K is not altered during the carbon deposition. However, coke deposition leads to improving of polar–apolar surface composition, resulting in increase of adsorption of apolar (hexane) and decrease of adsorption of polar (chlorophorm) substances. The main changes observed in AEDs are connected with decreasing of silica accessible area at stable carbon structure during CVD of carbon.

Phosphoric Acid and Steam as Activation Agents for Carbonized Porous Polymer Surfaces

Carbon sorbents derived from the copolymer of 4,4′-bis(maleimidodiphenyl)methane and divinylbenzene are described. The influence of phosphoric acid treatment and the type of carrier gas used in the carbonization process were studied. Solid-phase extraction experiments were conducted to determine their impact on the sorption properties of these new sorbents. The recoveries and breakthrough volumes for phenolic compounds preconcentrated from water were studied.

Ethyl tert-butyl ether synthesis using carbon catalysts from lignocellulose

Porous structure, surface chemistry and catalytic properties of carbon catalysts with various acid groups in ethyl tert-butyl ether synthesis were studied. Carbon catalysts were obtained by phosphoric acid activation followed by sulphonation of lignocellulosic feedstocks of different origin. Porous structure of carbon catalysts was characterized by nitrogen adsorption. Surface chemistry was investigated by potentiometric titration. Carbon catalysts obtained from lignosulphonate and sucrose showed the highest catalytic activity in ethyl tert-butyl ether synthesis (reaction rate at 120℃ is 4.3–5.2 × 10−6 mol·g−1·s−1), is comparable to activity of Amberlyst-15 (5.0 ×10−6 mol·g−1·s−1). Calculated turnover frequency (TOF) of sulphonic groups (pKa = −2.5) equals 0.00116 s−1, polyphosphate groups (pKa = 1.9) 0.01019 s−1, strong carboxylic (pKa = 3.6) 0.00202 s−1 and 0 s−1 for weak carboxylic (pKa = 6) groups. The activity of acid groups with pKa lower than 3.6 is higher than the activity of sulphonic groups of Amberlyst-15 (TOF 0.00115 s−1).

Assessment of the structural evolution of polyimide-derived carbons obtained by phosphoric acid activation using Fourier transform infrared and Raman spectroscopy:

Two series of carbons obtained by carbonization of porous copolymer of 4,4′-bis(maleimidodiphenyl) methane (50 mol%) and divinylbenzene (50 mol%) with and without phosphoric acid (impregnation ratio 1.1) at temperatures 400–1000℃. The carbons were characterized using elemental analysis, nitrogen adsorption, potentiometric titration, Fourier transform infrared and Raman spectroscopy. It has been shown that phosphoric acid causes structural and chemical changes in polyimide copolymer as compared to thermally treated carbons. Structural changes: phosphoric acid promotes transformation of polyimide copolymer to carbon structure at lower temperatures as compared to thermally treated carbons. Phosphoric acid is responsible for formation of highly developed micro/mesoporous structure that is different from that of thermally treated carbons. Chemical changes: phosphoric acid causes elimination of hydrogen and nitrogen, introduction of phosphorus and oxygen as phosphate-like structure. Significant amount of phosphorus imparts acid properties to carbon.

PHOTOCATALYTIC AND PHOTOELECTROCHEMICAL CHARACTERISTICS OF MESOPOROUS TITANIUM DIOXIDE MICROSPHERES

It was established that the mesoporous microspheres with size of about 10 nm formed by anatase nanocrystals exhibit photocatalytic activity in the release of H2 from water–ethanol mixtures and in the gas-phase oxidation of benzene by atmospheric oxygen. They are also active during the generation of current in a photoelectrochemical cell exposed to UV light or in TiO2/CdS heterostructures exposed to visible light. It was shown that the efficiency of the photoprocesses involving the mesoporous microspheres significantly exceeds that of nonporous nanocrystalline Evonik P25 TiO2. Possible reasons for the enhanced photoactivity of the microspheres are discussed.