Fractionation data for cadmium in tobacco products, as obtained by sequential leaching of cadmium species with ICP-MS/MS analysis, and separately by X-ray absorption near edge structure (XANES) are presented here for the first time. The total amount of cadmium found in 3R4F cigarette cut tobacco was 1526 ± 42 μg kg−1, of which 5% was found in the smoke under ISO smoking conditions. XANES analysis showed that Cd in tobacco, cigarette smoke and ash was present in the + 2 oxidation state. Examination of the gas-particle partitioning of smoke cadmium suggests that Cd in mainstream smoke is best viewed as semi-volatile, existing in both particulate and gas phases. Sequential extraction of trapped tobacco smoke was carried out to get a deeper insight into the chemistry of cigarette smoke cadmium compounds. Consecutive extractions with ultrapure water, dilute (1%) nitric acid and 10% nitric acid led to extraction of a total amount of Cd which agreed with that obtained after microwave digestion of the whole sample, suggesting that cadmium was quantitatively leachable into aqueous/acidic solutions. Most Cd (~ 90% of the total Cd in the smoke condensate) was extracted into dilute nitric acid (likely as CdO, Cd(OH)2 and CdCO3) with a minor percentage (3%) extracted into water (likely as CdCl2) and in 10% nitric acid (likely as CdS). Extraction of trapped mainstream smoke with pentane, followed by ICP-MS/MS analysis, to examine the possible presence of organocadmium in 3R4F tobacco smoke, did not show the presence of organocadmium compounds above the method LOQ (2 μg kg−1), possibly due to their reactivity under the experimental conditions. The high selectivity with sufficient sensitivity achieved by ICP-MS/MS was invaluable to quantify Cd (at low μg kg−1levels) simultaneously with sulphur and chlorine in the tobacco smoke fractions of complex matrix. The cadmium chemistry in the smoke, identified in this study, is consistent with both relatively high lung absorption and DNA binding; both potentially important factors for disease progression in smokers.

Cigarette smoke is an aerosol containing a large number of chemicals, including toxicants. In recent years, a number of cigarette filter additives have been evaluated for their toxicant filtration properties. Screening is a useful tool to accelerate the testing and development of new filter additives and filtration mechanisms. The evaluation of a filter material screening technique based on the so-called InfraSORP technology is described. By comparing InfraSORP measurements with reference cigarette smoke experiments of potential cigarette filter materials like activated carbons and ion-exchange resin, an excellent correlation is demonstrated. This technique allows for a rapid screening of potential filter materials prior to testing any final candidates in cigarettes.

A series of copper manganese oxides doped with transition metal oxides were prepared by co-precipitation using copper acetate and manganese acetate as precursors, ammonium bicarbonate as precipitant, and metal nitrates as dopants. The catalysts were characterized by N2 adsorption-desorption, X-ray powder diffraction, temperature-programmed reduction, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The results showed that doping transition metal oxides into copper manganese oxides can modify the CO adsorption ability of the catalyst and thus affect the catalytic oxidation of CO.

It is with great pleasure that we dedicate this double issue of Adsorption Science & Technology to Professor K.S.W. Sing in honour of his 65th year of active work and research in the field of adsorption as well as to coincide with his 88th birthday. This special issue brings together a total of 13 invited academic and industrial contributions from his former doctoral students and colleagues. The papers come from all corners of the globe, including Argentina, Australia, Brazil, Egypt, Japan, Mexico, Portugal, Spain, U.S.A. and the U.K., emphasizing the overarching influence his work has spawned. The collection of articles provided in this issue recognizes his many contributions in the areas of physisorption, characterization of porous materials, discovery of novel materials and his influence on the field in general. Professor Sing was the founding editor of the journal Adsorption Science & Technology; however, he has been courteous enough not to use the journal for his own papers. Notwithstanding, his last two papers in the journal have been amongst the most cited ones (Sing and Williams 2004, 2005) in the journal’s history, paying tribute to the quality of his production. A showcase of his publication record until last year is described in detail in the “Biography” section, which is preceded by a short descriptive curriculum vitae that highlights the details of his most illustrious career. We have been very honoured to edit this special celebration issue and hope it becomes an inspiration to younger generations.

Activated carbons with micropores for adsorption and filtration of the volatile constituents of mainstream cigarette smoke, together with mesopores for enhanced mass transport were prepared by a novel route. Treatment of coconut shell or other lignocellulosic precursors with aqueous NaOH, followed by thorough washing, charring and steam activation produced carbons with enhanced adsorption characteristics in smoking trials, compared with their microporous analogues. The mechanism of formation of these carbons is explained in terms of initial partial dissolution of the precursor in an aqueous alkali solution, followed by catalytic gasification of carbon in steam involving residual sodium.

Copper manganese oxides (CMOs) were synthesized using a co-precipitation method with different precursors and precipitants for carbon monoxide oxidation. The as-synthesized catalysts were characterized by powder X-ray diffraction (XRD), low temperature N2 sorption, Fourier transform-infrared spectroscopy (FT-IR), H2-temperature programmed reduction (H2-TPR), and thermal gravimetric analysis (TGA). Their catalytic activities for CO oxidation were tested by temperature programmed reaction. The results showed that the activity of CO oxidation strongly depended on the combination of precipitant and precursor anions, ranking in the order (Ac−+CO32−)>(NO3−+CO32−)>(Ac−+OH−)>(NO3−+OH−). The crystalline phase of copper manganese oxides obtained using strong electrolyte (OH−) as the precipitant were mainly spinel Cu1.5Mn1.5O4, while the catalysts prepared with weak electrolyte (CO32−) as the precipitant mostly comprised of MnCO3, Mn2O3 and CuO, and showed a much higher CO oxidation activity than that of the Cu1.5Mn1.5O4. Keeping the same precipitant while changing the precursor caused a change in the H2 consumption which influenced the CO oxidation activity. A suitable combination of precipitant and precursor resulted in the most efficient CO oxidation catalyst.

BACKGROUND:Cigarette smoking is a well recognized cause of diseases such as lung cancer, chronic obstructive pulmonary disease and cardiovascular disease. Of the more than 5000 identified species in cigarette smoke, at least 150 have toxicological activity. For example, formaldehyde and acetaldehyde have been assigned as Group 1 and Group 2B carcinogens by IARC, and hydrogen cyanide has been identified as a respiratory and cardiovascular toxicant. Active carbon has been shown to be an effective material for the physical adsorption of many of the smoke volatile species. However, physical adsorption of acetaldehyde, formaldehyde and also hydrogen cyanide from smoke is less effective using carbon. Alternative methods for the removal of these species from cigarette smoke are therefore of interest. A macroporous, polystyrene based ion-exchange resin (Diaion®CR20) with surface amine group functionality has been investigated for its ability to react with aldehydes and HCN in an aerosol stream, and thus selectively reduce the yields of these compounds (in particular formaldehyde) in mainstream cigarette smoke.RESULTS:Resin surface chemistry was characterized using vapour sorption, XPS, TOF-SIMS and 15N NMR. Diaion®CR20 was found to have structural characteristics indicating weak physisorption properties, but sufficient surface functionalities to selectively remove aldehydes and HCN from cigarette smoke. Using 60 mg of Diaion®CR20 in a cigarette cavity filter gave reductions in smoke formaldehyde greater than 50% (estimated to be equivalent to >80% of the formaldehyde present in the smoke vapour phase) independent of a range of flow rates. Substantial removal of HCN (>80%) and acetaldehyde (>60%) was also observed. The performance of Diaion®CR20 was found to be consistent over a test period of 6 months. The overall adsorption for the majority of smoke compounds measured appeared to follow a pseudo-first order approximation to second order kinetics.CONCLUSIONS:This study has shown that Diaion®CR20 is a highly selective and efficient adsorbent for formaldehyde, acetaldehyde and HCN in cigarette smoke. The reductions for these compounds were greater than those achieved using an active carbon. The results also demonstrate that chemisorption can be an effective mechanism for the removal of certain vapour phase toxicants from cigarette smoke.

The ability of two very different active carbons, a polymer-derived carbon (with ultramicropores and supermicropores, and a large volume of "transport" pores) and a coconut shell-derived carbon (predominantly ultramicroporous), to reduce the levels of volatile toxicants in cigarette smoke has been measured and compared. The polymer-derived carbon was found to be approximately twice as effective in removing the majority of measured smoke vapour-phase toxicants compared to the coconut shell-derived carbon in three different cigarette formats and with two different smoking regimes. Single-component dynamic breakthrough experiments were conducted with benzene, acrylonitrile and 2-butanone at 298 K for beds of each carbon under dry (0% RH) and wet (60% RH) conditions. Longer breakthrough times were found with the polymer-derived carbon, and breakthrough times recorded under wet conditions were found to be up to 20% shorter than those obtained under dry conditions. Correlations between micropore volume, dynamic adsorption volume and filter bed breakthrough time have been demonstrated.

The main requirements for the adsorption of cigarette smoke vapours using active carbons and the methods currently being used to characterise and select carbons for this application are reviewed. Emphasis is placed on the total volume of smoke, the pulsed characteristics and relatively short challenge times, the compounds in the smoke and the environment in which adsorption takes place. Using experimental data, the types of carbons most suitable for cigarette filter application are considered, as are the adsorption kinetics required to meet this challenge. The concept of carbon ageing and the effects of water within the smoke are also reviewed.

The use of active carbons for the removal of toxic organic compounds, for example from air or smoke, is of significant interest. In this paper, the equilibrium and dynamic adsorption characteristics of two active carbons are explored; one microporous coconut based and the other micro-mesoporous derived from a synthetic resin. Benzene, acetaldehyde and acrylonitrile were chosen as the probe toxicant vapours and adsorption was measured at a temperature of 298 K. The nitrogen equilibrium data (at 77 K), analysed using the BET, Dubinin-Radushkevich equations and DFT models, showed a higher overall adsorption capacity, more supermicroporosity and a higher proportion of pores wider than 2 nm for the synthetic resin based material. A micropore distribution biased toward the ultramicropore width-range was observed for the nutshell material. As a consequence, the characteristic adsorption energies in micropores are higher for the nutshell material than the resin based carbon. The effect of these different pore size characteristics on the adsorption kinetics, obtained by fitting the data to the linear driving force (LDF) model, is that the resulting adsorption rate constants are higher across much of the relative pressure range ( p / p s ) studied for the resin based carbon compared to the nutshell material. Significantly, the wider pores of the resin-based carbon result in higher rates of adsorption in the micropore filling domain. When evaluated under dynamic conditions in cigarette smoke, improved toxicant removal was observed using the resin based carbon.

The adsorption and desorption of ethyl acetate on a coconut-based activated carbon has been studied using static and flow adsorption methods at different temperatures from 295 K to 325 K. The adsorbed state of ethyl acetate was studied using nitrogen adsorption at 77 K after the pre-adsorption of ethyl acetate. The adsorption isotherms of ethyl acetate were of Type I in the IUPAC classification, suggesting micropore filling by ethyl acetate molecules. The micropore volume of the activated carbon as evaluated from ethyl acetate adsorption using the liquid density of ethyl acetate agreed well with that from nitrogen adsorption. Nitrogen adsorption after pre-adsorption of ethyl acetate indicated considerably packed molecular states of ethyl acetate molecules within the micropores. Thus, ethyl acetate molecules can migrate to the deeper parts of micropores in the case of static adsorption measurements. However, the specific surface area evaluated from ethyl acetate adsorption was nearly 40% smaller than that from nitrogen adsorption under the assumption of an isotropic structure. The assumption of a highly orientated adsorption structure for ethyl acetate molecules on the pore wall led to a good correlation even as far as the surface area was concerned. In addition, 26 kJ/mol of the excess stabilization energy determined from the temperature dependence of the ethyl acetate adsorption isotherm supports the favourable molecular alignment of ethyl acetate molecules which increases the molecule–pore wall interactions.

The pore size, distribution and volume of activated carbon are extremely important for maximizing adsorption of vapours formed during cigarette smoking. Increasing micropore volume leads to an increase in the removal efficiency. Because of the relatively high flow rates encountered during the smoking process, mesopores appear to be beneficial as transport pores especially in cases where the micropore volume is relatively low and thus the most accessible micropore sites may be rapidly saturated. Film diffusion limitations seem to be present at the very high space velocities encountered in a filter under the conditions of cigarette smoking. The removal efficiency from smoke is approximately inversely proportional to the vapour pressure of the constituents.