Tetramethylphosphonium-smectite (TMP-clay) and tetramethylammonium-smectite (TMA-clay), were prepared and characterized as adsorbents for a series of aromatic and chlorinated hydrocarbons. The sorption of benzene, alkylbenzenes, and carbon tetrachloride as vapors and as solutes from water was studied to evaluate the effect of water on adsorption efficiency. Adsorption of organic vapors depended on the N2 BET surface area. TMA-clay was a slightly better adsorbent than TMP-clay, due to its somewhat higher surface area. The Langumir isotherms obtained indicated that adsorption occurred predominantly in the interlayer micropores, apparently on mineral surfaces between onium ions. Adsorption efficiency of both organo-clays decreased, compared to vapor sorptions, in presence of water. Lower sorption was apparently due to shrinkage of the interlayer pore or cavity sizes by hydration of interlayer TMA and TMP cations. Although sorption efficiencies of both organo-clays was reduced in presence of bulk water, the extent of reduction was much less for TMP-clay. Thus, TMP-clay was a better adsorbent than TMA-clay in presence of water, despite its lower surface area, in direct contrast to vapor sorption. The Langumir isotherms indicated interlayer sorption of benzene, alkylbenzenes and carbon tetrachloride from water by TMP-clay. The absence of Langumir isotherms for toluene, ethylbenzene and p-xylene uptake from water by TMA-clay indicated that these bulkier solutes were not adsorbed in the interlayers. These results indicate that hydration of TMA cations causes shrinkage of the interlayer pores to dimensions that exclude these solutes. The lower degree of hydration of TMP cations enables TMP-clay to maintain interlayer pores large enough to accommodate the bulkier alkylbenzenes.

Toxic pharmaceutical pollutants, such as nicotine, represent a significant threat to natural water sources due to their continuous discharge. To address this issue, clay minerals and their composites have demonstrated exceptional adsorptive and remedial capabilities for wastewater purification. This research focused on developing green clay-polymeric adsorbents for the efficient removal of pharmaceutical pollutants from industrial wastewater. The synthesis involves creating halloysite nanotube–polythiophene nanocomposites through a green and cost-effective method using vapour polymerization and a solvent-free, ball-milled technique for the adsorptive removal of nicotine from wastewater. The investigation evaluates the impacts of preparation, modification and environmental conditions on the adsorptive performance of these clay-based nanocomposites compared to pure polythiophene. The polymerization process was evaluated by varying the vapour polymerization holding time for a fixed amount of oxidant (FeCl3) and halloysite nanotube (HNT) to investigate the impacts of monomer vapour exposure time on the polymerization of nanocomposites. Following the characterization of the synthesized adsorbents using various methods, the study investigated the impacts of various parameters (e.g. adsorbent dosage, pH and contact time) on the adsorption capabilities of the materials on a laboratory scale. The results revealed that the incorporation of HNT improved the adsorbing performance of nanocomposites. The pH, absorbent concentration and contact time directly affect nicotine adsorption. Significantly, halloysite–polythiophene 3 with a 2 h polymerization duration demonstrated the maximum adsorption efficacy of 78.94% at pH 10 after a 24 h contact time. The environmentally friendly halloysite-based nanocomposite shows promising potential as an effective adsorbent for pharmaceutical pollutant (nicotine) removal from aquatic environments.

An important application of clay is as a solid adsorbent for industrial dyes. The aim of the present work was to carry out an experimental—theoretical study of the adsorption of dye mixtures, namely malachite green (MG) and Congo red (CR), by bentonite. Adsorption studies were conducted after evaluation of the impact of several parameters, including pH, adsorbate dose, and contact time, on the removal of MG and CR. The pH of the dye solution is strongly affected by the chemistry of both the dye molecules and of the adsorbent in an aqueous solution. Where both dye molecules exist in solution, the optimum pH was found to be 8.2 in order to achieve the maximum adsorption of both MG and CR. Preliminary studies showed that 60 min of contact time is sufficient to reach adsorption equilibrium. The adsorption studies were carried out using 1.0 g samples of bentonite. The amount of dye adsorbed was found by application of classical least squares to the synthetic dye mixtures. Data from equilibrium adsorption on bentonite were analyzed by Freundlich, Langmuir, Redlich-Peterson, and Temkin isotherm equations using regression analysis for non-linear forms of those equations. For binary-mixture analysis, isotherm parameters were determined from single-component adsorption studies and the theoretical amount of dye adsorbed was calculated using an extended Langmuir isotherm. Non-linear error analysis showed that the Temkin and Redlich-Peterson isotherms gave the best fits to the equilibrium data for adsorptive removal of MG and CR by bentonite.

The flavonoid naringin is the main source of the undesirable bitter taste in some citrus juices. In commercial debittering processes, the naringin is adsorbed on non-ionic polymeric resins. Organo-clays (OCs), which have been used as sorbents for organic pollutants, could also have affinity for the naringin molecule, and thus potentially could serve as a debittering agent. The objective of the present study was to characterize the sorption capacity of a prepared OC to evaluate its ability to remove naringin from aqueous solutions, investigating the effect of adsorbent dose, initial concentration of naringin, temperature, contact time, and pH. The OC was prepared by the intercalation of cationic surfactant hexadecyltrimethylammonium bromide in a Mexican bentonite. The host clay and the OC were characterized by X-ray diffraction, Fourier-transform infrared, and nitrogen gas adsorption. The OC showed a surface area of 9.3 m2 g-1, 11.35 nm average pore diameter, and a basal spacing, d001, of 2.01 nm. The adsorbent removed naringin at the rate of 60-72% at 25°C and pH 3. The sorption capacity increased with pH and temperature. Experimental data were well fitted by both Langmuir and Freundlich adsorption models. Most of the sorption took place during the first 10 min and the equilibrium time was reached within 720 min. The rate of sorption was adjusted to pseudo second-order kinetics.

A zeolite-montmorillonite (zeolite-Mt) nano-adsorbent was prepared by calcination at 600°C. The synthesized nano-adsorbent was tested for removal of a toxic and cationic dye (crystal violet) from water, and it was characterized by various techniques. The effects of variables such as pH, temperature, adsorbent dosage and initial dye concentration on the removal efficiency of the dye were investigated by response surface methodology (RSM). Experimental conditions were optimized by RSM to achieve the maximum dye removal efficiency. Optimum conditions for maximum removal of dye were obtained at pH 9, temperature of 25°C, adsorbent dosage of 2 g L−1 and initial dye concentration of 40 mg L−1. Under these conditions, the maximum removal efficiency obtained was 99.9%. Various isotherms were applied to study adsorption equilibrium, and of these, the Freundlich isotherm provided the best fit. In addition, the fractal-like integrated kinetic Langmuir model was the most appropriate among several kinetic models. The thermodynamic parameters were also determined. The zeolite-Mt prepared under optimum conditions displayed a greater adsorption capacity than activated carbon (manufactured by Merck) and than various other adsorbents.

A dairy cow model was established to measure the transmission of aflatoxin M1 (AFM1) into milk. Four Ayrshire mid-lactation dairy cows (ranging 590 – 650 kg body weight and averaging 4.5 years of age) were used in a crossover experimental design in which each cow acted as its own control and was subjected to four dietary treatments administered as six 12-day feeding periods followed by a 7-day washout period. Periods I – VI comprised a 7 d of adaptation followed by 5 d of sampling. Period VII was a 7-d washout with sampling in the final two days. From each morning's milking, yield was recorded and sampled for AFM1 analysis by HPLC. Treatments included a negative control, contamination with AFB1 (5 µg of AFB1/kg feed), AFB1 + Mycosorb® (MTB) 10 g/cow/d, and AFB1 + MTB 50 g/cow/d. In response to the negative control, AFM1 concentrations in milk remained below the limit of detection (<5 ng/kg), whereas cows fed the AFB1-contaminated feed had milk AFM1 concentrations ranging from 110 to 230 ng/kg. At the end of the washout period, AFM1 was again undetectable. The dairy cow model was also used to test the efficacy of the yeast-cell-wall-based mycotoxin binder Mycosorb® (MTB) in reducing secretion of AFM1 into milk by cows fed the same AFB1-contaminated diet. When supplemented at 50 g/head/day, MTB significantly reduced (P < 0.05) AFM1 secretion into milk with no adverse effects on milk production. The dairy cow model is a sensitive tool for measuring aflatoxin transmission to milk and mycotoxin binder efficacy at 5 µg of AFB1/kg feed. As it is common for on-farm AFB1 concentrations to exceed 5 µg/kg, more research may be warranted to determine the effectiveness of the model at higher AFB1 concentrations.

The diffusion equation is used to model and analyze sorption, a process used in the purification or separation of fluids. For the diffusion inside a spherical porous solid immersed in a limited-volume and well-stirred fluid, Ruthven [5], Crank [3] and, for the analogous flow of heat, Carslaw and Jaeger [2] give an eigenfunction expansion solution to the diffusion equation that provides accurate long-time solutions when only a few terms are used. However, to obtain the same accuracy for short-time solutions the number of eigenfunction terms required increases exponentially. An alternative error function solution of Carman and Haul [1] is accurate for sufficiently short times but not for long times. Although their solution is well quoted [3, 4, 6], Carman and Haul do not provide a derivation in their paper. This paper provides a full derivation of the short-time solution of Carman and Haul that uses only the first term of a negative exponential series in the Laplace domain. It is shown that the accuracy and range of the short-time result is improved by the inclusion of additional terms of the negative exponential series. An analysis of short-time and long-time resultsis presented, together with recommendations as to their use.

Fungi may develop in stored grains following field inoculation. In the course oftheir development fungi utilize plant nutrients, contributing to a reduction in their content. This reduction is obviously related to the degree of fungi development, but may become relevant in extreme cases. During the process of host colonization fungi may also produce toxins that are harmful for humans and animals. This occurs mainly under specific conditions of plant stress, such as those produced by adverse weather conditions, for instance drought has been shown to prompt aflatoxin production in peanuts. Differences in mycotoxin production are also related to plant genotype. Aflatoxin B1 produced by Aspergillus flavus is the most carcinogenic natural substance known. It is frequently charged with the reduction in performance of domestic birds, even when its concentration in the feed is very low. Approaches to eliminate mycotoxins from contaminated grains are not always worthwhile in practical and economical terms. Strategies used to reduce mycotoxin levels in cereal grains include the dilution of infected with healthier grains or the addition of adsorbents to the feeds. Several compounds such as activated charcoal, aluminosilicates and processed cell wall of Saccharomyces sp. (esterified glucomannan) have shown to be effective as mycotoxin adsorbents in poultry feeds. Adsorbent effectiveness has been reported with in vitro and in vivo techniques; however, it is still very difficult to quantify their benefits in commercial operations.