Matt J. Chinn

An investigation of the porosity of carbons prepared by constant rate activation in air

Nutshell carbon was activated in air/N2 mixtures using controlled rate (CR) methods and the porosity characteristics compared with carbons activated conventionally in CO2 at 800 °C to the same degree of burn off. The advantages of CR activation in air include the use of lower temperatures and the avoidance of thermal runaway. It was also possible to prepare activated carbons with significant microporosity, showing that excessive external burn off was prevented. In the CR experiments, the rate of evolution of CO2 was controlled and constrained at a set level, either by altering the furnace temperature or the concentration of air in the activating gas. Although the highest micropore volumes (0.4 cm3 g−1) were obtained at 40% burn off with the conventional method, at 20% burn off, the CR method using air concentration to control CO2 evolution yielded carbons with similar micropore volumes (0.2 cm3 g−1) to those activated conventionally.

Oxygen-17 and deuterium NMR investigation into the adsorption of water on activated carbon

Magic‐angle spinning (MAS) 2H and 17O NMR spectra were obtained for water, following addition to an activated carbon. Shortly after addition two peaks are seen: a ‘free liquid’ resonance and a second broad resonance shifted to low frequency. The latter is attributed to water in the pores of the activated carbon. Over time, some intensity from the free water peak shifts into the lower frequency peak and a further decrease in the average chemical shift is seen. This is ascribed to gradual diffusion of water into the smaller pores with time. Comparisons between the 2H and 17O spectra are drawn with regard to the likely orientation of water molecules on the carbon surface in relation to the effects on chemical shifts by ring currents due to the graphene sheets. Spectra are presented for sealed samples spun at different MAS rates, and it is demonstrated that rates above 3 kHz induce loss of water from the pores, increasing the intensity of the free water peak. The implications of this centrifugation effect are discussed. Copyright

Modified mesoporous silicates for the adsorption and decomposition of toxic gases

New adsorbents based on MCM-41 have been developed for the adsorption and decomposition of HCN and CNCl. Adsorption of CNCl is provided by diaminoalkylsilane tethers bound to the surface. Reactivity towards HCN is provided by Cu2+ ions complexed by the diamines. Overall reactivity towards the two gases depends on the balance between free amine and Cu2+ concentrations. The performance of these adsorbents is superior to that of carbon-based adsorbents in which alkylamine and copper(II) salt are physisorbed on the carbon surface.

Preparation, Characterisation and Application of Metal-doped Carbons for Hydrogen Cyanide Removal

A novel method for the production of metal-doped activated carbons was developed. Evaluation of the materials produced showed that the metals were well dispersed throughout the carbon pore structure and had a high degree of accessibility. The filtration performance of these materials was assessed against HCN using inverse gas chromatography. The performance was affected both by the selection of metals and the conditions used in the production of the carbon. In-depth studies varying the synthesis parameters were performed with the aim of optimising the manufacturing process. Significant HCN adsorption capacity was developed which exceeded that of the current best available ASC-type carbons.

A Study of the Activation of Carbon Using Sample Controlled Thermal Analysis

A constant rate method involving the control of the concentration of evolved CO2 at a constant level was used to study the air activation of pure and copper-doped carbon prepared from sodium carboxymethylcellulose. Whereas under a linear heating regime, both types of carbon reacted suddenly and quickly with O2, under constant rate conditions this violent reaction was avoided and oxidation proceeded steadily at a lower temperature until complete burn off of the carbon was achieved. The catalytic effect of the copper on carbon gasification was noted with lower reaction temperatures for both linear heating (380°C compared to 500°C) and for the constant rate experiments (320°C compared to 400°C).

Comparison of new thermal and reactant gas blending methods for the controlled oxidation of carbon

Abstract Two approaches to sample controlled thermal analysis (SCTA) used preparatively were contrasted using the air activation of a nutshell derived carbon. The rate of reaction, corresponding to the level of evolved carbon dioxide, was monitored using a quadrupole mass spectrometer and controlled via software using a feedback loop. In the first approach, control of the rate was achieved via temperature under a constant concentration of oxygen in nitrogen, while in the second the reactant gas concentration (oxygen/nitrogen ratio) was changed while the furnace was held isothermally. Due to the exothermic nature of the carbon–oxygen reaction, temperature control of the activation process at high reaction rates was difficult and produced oscillatory behaviour, while good control of the process could be achieved using the gas concentration method at higher reaction rates. By using oxygen rather than the more usual CO 2 or H 2 O activation at 800–1000°C, the reaction takes place at 200–300°C with a consequent significant saving in energy costs.

Peroxydisulfate in MCM-48 silicas: powerful and clean materials for the removal of toxic gases

Sodium persulfate introduced into ordered MCM-48 silicas is described. The resulting materials are compared with existing activated carbon-based systems and MCM-48 containing transition metals such as Cu(II) and Cr(VI) for the decomposition of hydrogen cyanide and cyanogen. MCM-48 materials containing sodium persulfate alone improve on the protection offered by benchmark activated carbon systems and MCM-48 materials containing Cu(II) and Cr(VI), without the health risks associated with these metal ions.

Peroxides in ordered nanoporous silicas: clean alternatives to transition metal oxidants for the removal of toxic gases

Ordered nano-structured MCM-48 silica containing sodium peroxydisulfate is a novel, highly effective material for the decomposition of HCN under ambient conditions.

The adsorption and decomposition of cyanogen chloride by modified inorganic molecular sieves

Aluminosilicate and silicate porous solids have been evaluated as supports for triethylenediamine (TEDA) for the adsorption and decomposition of cyanogen chloride. A series of silica-gel supports has been used to study the effect of varying pore size. A series of faujasitic zeolites has been used to examine the effect of the cation exchange capacity of the support and the type of exchangeable cation. Results show that the activity of adsorbed TEDA towards cyanogen chloride appears to increase with increasing support pore diameter, and TEDA seems to be activated by basic adsorption sites on the support. Cesium-exchanged zeolite supports are particularly active. In general, zeolite supports appear to confer significantly higher activity to TEDA than traditional activated carbon supports. A series of mesoporous MCM-41 and AlMCM-41 supports has also been studied, but the activities of adsorbed TEDA are lower than expected. Significantly, the specific surface area of the inorganic supports does not seem to be a primary factor in controlling adsorbed TEDA activity.