Dynamic adsorption of radon by activated carbon

The adsorption of radon on activated carbon has been used in or considered for a number of applications, including in situ decay beds, cyclic decontamination systems, and diffusive samplers. And although there are numerous measurements of the adsorption coefficients of specific activated carbons for radon, each of these applications depends on knowing, in addition to the adsorption coefficient for radon, the mass transfer factors describing its dynamic adsorption. Here we used a standard procedure in gas chromatography and chemical engineering, the spreading of a pulse as it passes through a bed of adsorbent, to determine these mass transfer factors. For this application, this procedure is developed further to correct the radon adsorption data for distortions caused by the decay of radon and by the presence of radon decay products in the detector. The results from eight activated carbons show a wide variation in the mass transfer coefficients for radon, which could affect significantly the suitability of adsorbents, as demonstrated here by the effect that mass transfer has on the performance of in situ decay beds.     

Impact of carbon nanotube morphology on phenanthrene adsorption

The present study examined the roles of the specific surface area (SSA), diameter, and length of carbon nanotubes (CNT) on the adsorption of phenanthrene (PNT) by analyzing the adsorption isotherms obtained with several single-walled carbon nanotubes (SWNT) and multiwalled carbon nanotubes (MWNT). At low equilibrium concentrations (e.g., 1?ppb), MWNTs with larger outer diameters exhibited higher PNT adsorption capacity on an SSA basis than those with smaller diameters. With increasing equilibrium concentration, adsorption on an SSA basis became independent of MWNT diameter, and the total surface area controlled maximum adsorption capacity. A similar analysis for the adsorption of naphthalene, a planar molecule with one less benzene ring but 20 times higher solubility than PNT, showed no correlation with respect to MWNT outer diameter. The results indicated that the surface curvature of MWNT was more important on the adsorption of PNT than on the adsorption of naphthalene. Specific surface area normalized isotherms did not show a correlation between PNT adsorption and lengths of SWNTs and MWNTs. Characterization results indicated that the morphology of CNTs plays an important role on the SSA and pore volume. Data from the manufacturer may not always represent the characteristics of CNTs in a particular batch. Therefore, accurate characterization of CNTs is critical to systematically examine the behavior of CNTs, such as adsorption and transport, in environmental systems.     

Mixed streams wastewater treatment using adsorption

Mixed samples prepared from known pure solutes are reported to have synergetic efforts with respect to single solute and multi-solute adsorption. Attempt is made to extend the theory of enhancement ratios to the mixed stream wastewater samples collected from dyes manufacturing industries. Synergetic effect of the multi-solutes as well as of mixture of adsorbents is observed for mixed streams of wastewater samples, containing a number of pollutants, on given inexpensive adsorbents. The Rathi Puranik model developed for single wastewater streams can be extended to the mixed stream wastewater samples using the rate of COD reduction prediction. The concept of average apparent enhancement factor is discussed.     

Enhanced adsorption of humic acids on ordered mesoporous carbon compared with microporous activated carbon

Humic acids are ubiquitous in surface and underground waters and may pose potential risk to human health when present in drinking water sources. In this study, ordered mesoporous carbon was synthesized by means of a hard template method and further characterized by X-ray diffraction, N2 adsorption, transition electron microscopy, elemental analysis, and zeta-potential measurement. Batch experiments were conducted to evaluate adsorption of two humic acids from coal and soil, respectively, on the synthesized carbon. For comparison, a commercial microporous activated carbon and nonporous graphite were included as additional adsorbents; moreover, phenol was adopted as a small probe adsorbate. Pore size distribution characterization showed that the synthesized carbon had ordered mesoporous structure, whereas the activated carbon was composed mainly of micropores with a much broader pore size distribution. Accordingly, adsorption of the two humic acids was substantially lower on the activated carbon than on the synthesized carbon, because of the size-exclusion effect. In contrast, the synthesized carbon and activated carbon showed comparable adsorption for phenol when the size-exclusion effect was not in operation. Additionally, we verified by size-exclusion chromatography studies that the synthesized carbon exhibited greater adsorption for the large humic acid fraction than the activated carbon. The pH dependence of adsorption on the three carbonaceous adsorbents was also compared between the two test humic acids. The findings highlight the potential of using ordered mesoporous carbon as a superior adsorbent for the removal of humic acids.     

Detection of the breakthrough of organic solvent vapors on an activated carbon adsorption column using a gas detecting reagent

A new adsorption device which is able to detect the breakthrough of organic solvent vapors was developed using a detecting reagent which is packed in a gas detector tube. The organic vapor which leaks from an activated carbon adsorption column reacts with the detecting reagent. The breakthrough is detected by the stain of the reagent. When the humidity of test air was zero, the reagent was stained sharply before the breakthrough was observed. However, in the case of using humid air, the color of the detecting reagent did not clearly change, even after the breakthrough had progressed considerably.     

活性炭对阿维菌素吸附效果的实验研究

目的评价体外不同条件下活性炭对阿维菌素的吸附效果。方法用人工胃液、人工肠液配制浓度为10、5和2.5 g/L的阿维菌素溶液,分别调至pH1.9和pH6.8,设活性炭干预组和对照组,于孵育10 min、30 min、1 h、2 h和4 h后离心,紫外可见分光光度法测上清液中阿维菌素浓度,计算阿维菌素随时间的残留率和活性炭对阿维菌素的吸附率。结果 (1)在人工胃液与肠液环境中,不同炭药比(活性炭与阿维菌素质量比)时活性炭对阿维菌素均具有良好的吸附作用,并且存在时间依赖性;各个检测时间点活性炭对阿维菌素的吸附率(Q)均随炭药比的增加而递增。(2)活性炭-阿维菌素复合物的稳定性较强,在胃肠排空时间内基本不发生解离现象。结论活性炭吸附阿维菌素效果良好,且与炭药比呈正相关。     

A passive diffusion 222Rn sampler based on activated carbon adsorption

A simple passive sampler for 222Rn with up to 24-hr integration times can be constructed by using a diffusion barrier to regulate the effective sampling rate of an ambient temperature activated carbon bed. The diffusion element serves to make sampler performance relatively independent of the properties of the type of carbon used. Satisfactory results are obtained if the total effective sample volume is kept well below the equivalent air volume of the activated carbon bed. The influence of various temperature and Rn profiles on the sampler's performance have been examined by experiment and by simulation. The amount of Rn adsorbed may be measured by gamma spectroscopy, by outgassing into an alpha scintillation flask, or by desorption into a liquid scintillator. In the latter case, a sensitivity of 0.2 pCi l-1 is obtainable for 24-hr exposures.     

从血透并发症谈血透设备的维护

血液透析是治疗肾功能衰竭最有效的方法，应用血液透析机挽救了成千上万人的生命。随着各血液净化中心规模的不断扩大，各类血透并发症时有发生。本文针对一些血透并发症对血液透析机及水处理系统的维护进行经验总结及探讨。     

The effect of moisture on the adsorption of chloroform by activated carbon

The effect of moisture on the ability of a granular activated carbon to adsorb chloroform vapor from a flowing airstream was studied under three test conditions: (1) chloroform and water vapor were introduced concurrently into a dry carbon bed; (2) dry chloroform was introduced into a humidified carbon bed; (3) humidified chloroform was introduced into a carbon bed at the same relative humidity. The criterion for bed performance was the time when the downstream chloroform concentration was 1% of that in the inlet stream. Chloroform concentration was essentially constant at 108 +/- 2 micrograms/cm3; relative humidities (RH) varied from 0 to 97%. No RH effect on the adsorption of chloroform by the carbon was observed in test (1); tests (2) and (3) showed monotonic decreases in chloroform adsorption for RH greater than 40%. These results indicated that, for a dry carbon bed, the 1% breakthrough time for chloroform adsorbed from atmospheres of RH from 13% to 95% was essentially the same as that when RH = 0%. For humidified carbon beds, no change in 1% breakthrough time for chloroform was observed until RH was greater than 40%.     

Comparison of toluene adsorption among granular activated carbon and different types of activated carbon fibers (ACFs)

Activated carbon fiber (ACF) has been demonstrated to be a good adsorbent for the removal of organic vapors in air. Some ACF has a comparable or larger surface area and higher adsorption capacity when compared with granular activated carbon (GAC) commonly used in respiratory protection devices. ACF is an attractive alternative adsorbent to GAC because of its ease of handling, light weight, and decreasing cost. ACF may offer the potential for short-term respiratory protection for first responders and emergency personnel. This study compares the critical bed depths and adsorption capacities for toluene among GAC and ACF of different forms and surface areas. GAC and ACF in cloth (ACFC) and felt (ACFF) forms were challenged in stainless steel chambers with a constant concentration of 500 ppm toluene via conditioned air at 25°C, 50% RH, and constant airflow (7 L/min). Breakthrough data were obtained for each adsorbent using gas chromatography with flame ionization detector. Surface areas of each adsorbent were determined using a physisorption analyzer. Results showed that the critical bed depth of GAC is 275% higher than the average of ACFC but is 55% lower than the average of ACFF. Adsorption capacity of GAC (with a nominal surface area of 1800 m(2)/g) at 50% breakthrough is 25% higher than the average of ACF with surface area of 1000 m(2)/g, while the rest of ACF with surface area of 1500 m(2)/g and higher have 40% higher adsorption capacities than GAC. ACFC with higher surface area has the smallest critical bed depth and highest adsorption capacity, which makes it a good adsorbent for thinner and lighter respirators. We concluded that ACF has great potential for application in respiratory protection considering its higher adsorption capacity and lower critical bed depth in addition to its advantages over GAC, particularly for ACF with higher surface area.     

Mucosal delivery of antigens using adsorption to bacterial spores

The development of new-generation vaccines has followed a number of strategic avenues including the use of live recombinant bacteria. Of these, the use of genetically engineered bacterial spores has been shown to offer promise as both a mucosal as well as a heat-stable vaccine delivery system. Spores of the genus Bacillus are currently in widespread use as probiotics enabling a case to be made for their safety. In this work we have discovered that the negatively charged and hydrophobic surface layer of spores provides a suitable platform for adsorption of protein antigens. Binding can be promoted under conditions of low pH and requires a potent combination of electrostatic and hydrophobic interactions between spore and immunogen. Using appropriately adsorbed spores we have shown that mice immunised mucosally can be protected against challenge with tetanus toxin, Clostridium perfringens alpha toxin and could survive challenge with anthrax toxin. In some cases protection is actually greater than using a recombinant vaccine. Remarkably, killed or inactivated spores appear equally effective as live spores. The spore appears to present a bound antigen in its native conformation promoting a cellular (T_h1-biased) response coupled with a strong antibody response. Spores then, should be considered as mucosal adjuvants, most similar to particulate adjuvants, by enhancing responses against soluble antigens. The broad spectrum of immune responses elicited coupled with the attendant benefits of safety suggest that spore adsorption could be appropriate for improving the immunogenicity of some vaccines as well as the delivery of biotherapeutic molecules.     

血透临床工程师对血透机的日常管理及维护保养

血液透析简称为血透,它是指通过某种方式将人体内部的血液引流到人体外部透析器中,在对流、弥散作用下,不仅要让人体内的电解质达到正常水平,还需要让人体能够维持酸碱平衡,最终达到清除人体内代谢废物的目的。随着我国科技的不断发展,我国的医疗技术设备也有很大提升,人们开始意识到医疗设备的重要性。该文主要研究的是血透临床工程师对血透机的日常管理及维护保养。     

The effect of moisture on the adsorption of xenon by activated carbon.

The following procedure was used to determine the effect of moisture on the adsorption of xenon from air onto activated carbon: A known amount of water is added to a sample of dried activated carbon and allowed to equilibrate. This activated carbon is then split between two cylindrical beds placed in a temperature controlled water bath, and air is passed through the beds sequentially. Because the beds contain pre-moistened activated carbon from the same sample, the first bed acts as a buffer, maintaining a constant humidity in the second. The mean holdup time of a pulse of 133Xe injected into the second bed is used to determine the adsorption coefficient for xenon under these conditions. Measurements were made for three carbons activated to 35, 40, and 59%, respectively, at temperatures of 25 degrees C and 55 degrees C. The effect of moisture on the same activated carbon at these two temperatures shows an affine relationship that could be helpful in extending these results to other temperatures. At low moisture uptakes, a plot of the log(adsorption coefficient) vs. moisture uptake gives a straight line.