Interaction of La3+- and Ce3+-exchanged hectorites with oligomeric hydroxy-Al cations results in the formation of cross-linked hectorites possessing moderately high surface areas (~ 220–280 m2/g) and high thermal stability. The basal spacings of these products were generally in the range 17.0–18.0 A, the exact d(001) value depending on the age of the hydroxy-Al oligomeric solution and on the pH of the starting hectorite dispersion. Interaction of Li- or Ce-fluorhectorite with hydroxy-Al oligocations produced the corresponding cross-linked fluorhectorites, which showed markedly higher basal spacings (18.2–20.0 Å for air-dried samples), surface areas (~300–380 m2/g), and thermal stability, as compared with those of the cross-linked hectorites. The cross-linking agent applied in the synthesis of the hydroxy-Al hectorite and fluorhectorite products consisted of a solution of hydroxy-Al oligomers aged for periods of 7 to 27 days. A constant ratio of 2.0 mmole Al/g of smectite was used in all preparations. The high basal spacings and porosity of the newly synthesized products are consistent with a structure similar to that previously proposed for cross-linked hydroxy-Al montmorillonite.

By ion exchanging expandable clay minerals with large, cationic oxyaluminum polymers, “pillars” were introduced that permanently prop open the clay layers. On the basis of thermal, infrared spectroscopic, adsorption, and X-ray powder diffraction (XRD) analysis, the interlayering of commercial sodium bentonite with aluminum chlorohydroxide, [Al13O4(OH)24(H2O)12]+7, polymers appears to have produced an expanded clay with a surface area of 200–300 m2/g. The pillared product contained both Brönsted and Lewis acid sites. XRD and differential scanning calorimetry measurements indicated that the micropore structure of this interlayered clay is stable to 540°C. Between 540° and 760°C, the pillared clay collapsed with a corresponding decrease in surface area (to 55 m2/g) and catalytic cracking activity for a Kuwait gas oil having a 260°-426°C boiling range.

Radiocarbon (14C) analysis of carbon dioxide (CO2) can be extremely useful in carbon cycle studies because it provides unique information that can infer the age and source of this greenhouse gas. Cartridges containing the CO2-adsorbing zeolite molecular sieve are small and highly portable, which makes them more suitable for field campaigns in remote locations compared to some other CO2 collection methods. However, sampling with molecular sieve cartridges usually requires additional equipment, such as an infrared gas analyser, which can reduce portability and pose limitations due to power demands. In addition, 14C analysis of CO2 is increasingly being used in field experiments which require high numbers of replicate CO2 collections, placing extra pressure on an expensive and cumbersome collection apparatus. We therefore designed and built a molecular sieve CO2 sampling kit that utilizes a small, low power CO2 sensor. We demonstrate the reliability of the new kit for the collection of CO2 samples for 14C analysis in a series of laboratory and field tests. This inexpensive sampling kit is small, light-weight, highly portable, and has low power demands, making it particularly useful for field campaigns in remote and inaccessible locations.

We developed a passive sampler for time-integrated collection and radiocarbon (14C) analysis of soil respiration, a major flux in the global C cycle. It consists of a permanent access well that controls the CO2 uptake rate and an exchangeable molecular sieve CO2 trap. We tested how access well dimensions and environmental conditions affect collected CO2, and optimized cleaning procedures to minimize 14CO2 memory. We also deployed two generations of the sampler in Arctic tundra for up to two years, collecting CO2 over periods of 3 days–2 months, while monitoring soil temperature, volumetric water content, and CO2 concentration. The sampler collects CO2 at a rate proportional to the length of a silicone tubing inlet (7–26 µg CO2-C day-1·m Si-1). With constant sampler dimensions in the field, CO2 recovery is best explained by soil temperature. We retrieved 0.1–5.3 mg C from the 1st and 0.6–13 mg C from the 2nd generation samplers, equivalent to uptake rates of 2–215 (n=17) and 10–247 µg CO2-C day-1 (n=20), respectively. The method blank is 8 ± 6 µg C (mean ± sd, n=8), with a radiocarbon content (fraction modern) ranging from 0.5875–0.6013 (n=2). The sampler enables more continuous investigations of soil C emission sources and is suitable for Arctic environments.

Radiocarbon (14C) analysis of carbon dioxide (CO2) provides unique information on the age, turnover and source of this important greenhouse gas, raising the prospect of novel scientific investigations into a range of natural and anthropogenic processes. To achieve these measurements, cartridges containing zeolite molecular sieves are a reliable and convenient method for collecting CO2 samples. At the NERC Radiocarbon Facility (East Kilbride) we have been refining our molecular sieve methods for over twenty years to achieve high-quality, reproducible and precise measurements. At the same time, we have been developing novel field sampling methods to expand the possibilities in collecting gas from the atmosphere, soil respiration and aquatic environments. Here, we present our latest improvements to cartridge design and procedures. We provide the results of tests used to verify the methods using known 14C content standards, demonstrating reliability for sample volumes of 3 mL CO2 (STP; 1.6 mg C) collected in cartridges that had been prepared at least three months earlier. We also report the results of quality assurance standards processed over the last two years, with results for 22 out of 23 international 14C standards being within measurement uncertainty of consensus values. We describe our latest automated procedures for the preparation of cartridges prior to use.

The authors have developed an active absorption system combining a molecular sieve with a pressure gradient as a way to overcome the shortcomings of the phosphoric acid solution displacement method. Taking advantage of the pressure gradient produced between the inside and outside of a bottle, as water moves through it, CO2 in the atmosphere can actively be absorbed onto a molecular sieve in its pathway. A comparative study showed that the technique was in agreement with the phosphoric acid displacement method, within error. We applied the new method to collect not only atmospheric CO2 samples, but also CO2 samples from soil respiration to verify its utility. Simple yet practical, our method is well suited to extended collection times in a variety of environments, and capable of providing relatively large amounts of carbon for high-precision accelerator mass spectrometry (AMS) 14C analyses of atmospheric samples.

Converting biomass to charcoal produces physical and chemical changes greatly increasing environmental recalcitrance, leading to great interest in the potential of this carbon form as a long-term sequestration strategy for climate change mitigation. Uncertainty remains, however, over the timescale of charcoal’s environmental stability, with estimates varying from decadal to millennial scales. Uncertainty also remains over charcoal’s effect on other aspects of carbon biogeochemical cycling and allied nutrient cycles such as nitrogen. Radiocarbon is a powerful tool to investigate charcoal mineralization due to its sensitivity; here we report the results of a study using 14C-dead charcoal (pMC=0.137±0.002) in organic-rich soil (pMC=99.76±0.46), assessing charcoal degradation over 55 days of incubation. Using this method, we discriminated between decomposition of indigenous soil organic matter (SOM) and charcoal by microorganisms. SOM was the major source of carbon respired from the soil, but there was also a contribution from charcoal carbon mineralization. This contribution was 2.1 and 1.1% on days 27 and 55, respectively. We also observed a negative priming effect due to charcoal additions to soil, where SOM mineralization was repressed by up to 14.1%, presumably arising from physico-chemical interactions between soil and charcoal.