P.J.M. Carrott

Low-Cost Adsorbents: Growing Approach to Wastewater Treatment—a Review

Industrial, agricultural, and domestic activities of humans have affected the environmental system, resulting in drastic problems such as global warming and the generation of wastewater containing high levels of pollutants. As water of good quality is a precious commodity and available in limited amounts, it has become highly imperative to treat wastewater for removal of pollutants. In addition, the rapid modernization of society has also led to the generation of huge amount of materials of little value that have no fruitful use. Such materials are generally considered as waste, and their disposal is a problem. Also, there are some materials that are available in nature that have little or no use. The utilization of all such materials as low-cost adsorbents for the treatment of wastewater may make them of some value. An effort has been made to give a brief idea of an approach to wastewater treatment, particularly discussing and highlighting in brief the low-cost alternative adsorbents with a view to utilizing these waste/low-cost materials.

Adsorption of nitrogen by porous and non-porous carbons

Abstract Nitrogen isotherms have been determined at 77 K on a number of carbon blacks and microporous carbons. Application of the Dubinin-Radushkevich (DR) method has shown that linear plots are given by both nonporous and microporous samples. The range of linearity is considerably reduced by increasing the micropore size, while graphitisation of nonporous carbon leads to the formation of two distinct linear regions. Application of the α s method provides strong evidence for two stages of micropore filling: 1. (a) a primary process involving enhanced adsorbate-adsorbent interactions 2. (b) a secondary process which is the result of cooperative effects associated with the filling of wider micropores.

Preparation of activated carbon fibres from acrylic textile fibres

Abstract Acrylic textile fibres have been used to prepare activated carbon fibres (ACF). Characterisation by means of elemental analysis, XRD, SEM and low temperature nitrogen adsorption show that the properties of the acrylic ACF compare favourably with those of non-textile PAN, Kevlar and Nomex ACF. A particularly interesting, and never previously reported, feature was observed with fibres activated at 900°C. It was found, with one fibre in particular, that over a very limited range of burn-off between 40 and 50% the micropore volume tripled, the mean pore width suddenly increased, the mean stack height, Lc, suddenly decreased and the reactivity decreased by more than a half. The observed changes suggest a change in the mechanism of activation from one involving principally gasification of amorphous or more reactive carbon at low burn-off to one involving principally attack of individual crystallites and their reorganisation at higher burn-off.

Influence of preparation conditions in the textural and chemical properties of activated carbons from a novel biomass precursor: The coffee endocarp

In this work a novel biomass precursor for the production of activated carbons (AC) was studied. The lignocellulosic material used as precursor is the coffee bean endocarp, which constitutes an industrial residue from the Portuguese coffee industry. Activation by carbon dioxide and potassium hydroxide produces activated carbons with small external areas and pore volumes up to 0.22 and 0.43cm3g(-1), respectively, for CO2 and KOH activation. All the ACs produced are very basic in nature with point of zero charge higher than 8. SEM/EDX studies indicate the presence of K, O, Ca and Si. By FTIR it was possible to identify the formation on the ACs surface of several functional groups, namely phenol, alcohol, quinone, lactone, pyrone and ether as well as SiH groups. The tailoring of the porous and chemical structure of the activated carbons produced is possible by selecting the appropriate production conditions.

Adsorption of volatile organic compounds onto activated carbon cloths derived from a novel regenerated cellulosic precursor

Activated carbon cloths (ACC) were prepared from lyocell, a novel regenerated cellulose nanofibre fabric, by phosphoric acid activation in inert atmosphere at two different final thermal treatment temperatures (864 and 963 degrees C). Benzene, toluene and n-hexane isotherms at 298 and 273K were measured in order to gain insight into the porous structure of the ACC and to evaluate their performance for the removal of volatile organic compounds (VOCs). The Dubinin-Radushkevich equation was employed to evaluate textural parameters of the ACC. The textural characteristics of the ACC were compared with those previously determined from nitrogen (77K) and carbon dioxide (273K) adsorption data. The samples were essentially microporous. The textural parameters calculated from the hydrocarbon isotherms were in good agreement with those evaluated from nitrogen isotherms for the ACC with the wider microporosity. Additionally, the Freundlich model provided a good description of the experimental isotherms for the three volatile organic compounds. The ACC obtained at the higher temperature exhibited a larger adsorption capacity. The ACC were also electrically conductive and showed potential for regeneration by the Joule effect, as determined from macroscopic electrical measurements before and after n-hexane adsorption.

Thermal treatments of activated carbon fibres using a microwave furnace

Abstract Thermal treatment of activated carbon fibres (ACF) in a flow of N2 gas has been carried out using a microwave device operating at 2450 MHz and with a power input of 1000 W, instead of a conventional furnace, and the samples were analysed by means of low temperature N2 adsorption, elemental analysis and determination of points of zero charge. The results show that microwave treatment for periods between 5 and 30 min affects the porosity of the ACF, causing a reduction in micropore volume and micropore size. More importantly, the results also show that microwave treatment is a very effective method for modifying the surface chemistry of the ACF. During microwave treatment surface groups are completely eliminated, whereas oxygen and nitrogen atoms bonded within the pseudo-graphitic layer planes are retained. On re-exposure to air the surface groups only reform to a very limited extent and as a result very basic carbons, with points of zero charge approximately equal to 11, are readily obtained.

INFLUENCE OF SURFACE IONIZATION ON THE ADSORPTION OF AQUEOUS ZINC SPECIES BY ACTIVATED CARBONS

A surface ionization and adsorption model is used to simulate the adsorption of zinc species from aqueous solutions of varying pH on a number of different activated carbons and the results compared with experimental data. In all cases good agreement is obtained between theory and experiment. It is shown that for most of the carbons the uptake of zinc is due to adsorption of Zn2+ ions on ionized acid sites, the calculated equilibrium constants being of the order of 106–107. On the other hand, one of the carbons used (NORIT AZO) contains virtually no acid sites, but a high concentration of strong basic sites, and the uptake of zinc in this case appears to be due to adsorption of a negatively charged hydroxy complex on protonated basic sites, the estimated equilibrium constant being 108.

Cellulose: A review as natural, modified and activated carbon adsorbent

Cellulose is a biodegradable, renewable, non-meltable polymer which is insoluble in most solvents due to hydrogen bonding and crystallinity. Natural cellulose shows lower adsorption capacity as compared to modified cellulose and its capacity can be enhanced by modification usually by chemicals. This review focuses on the utilization of cellulose as an adsorbent in natural/modified form or as a precursor for activated carbon (AC) for adsorbing substances from water. The literature revealed that cellulose can be a promising precursor for production of activated carbon with appreciable surface area (∼1300m(2)g(-1)) and total pore volume (∼0.6cm(3)g(-1)) and the surface area and pore volume varies with the cellulose content. Finally, the purpose of review is to report a few controversies and unresolved questions concerning the preparation/properties of ACs from cellulose and to make aware to readers that there is still considerable scope for future development, characterization and utilization of ACs from cellulose.

Phenol removal onto novel activated carbons made from lignocellulosic precursors: influence of surface properties.

The adsorption of phenol from dilute aqueous solutions onto new activated carbons (AC) was studied. The novel activated carbon was produced from lignocellulosic (LC) precursors of rapeseed and kenaf. Samples oxidised with nitric acid in liquid phase were also studied. The results have shown the significant potential of rapeseed and kenaf for the activated carbon production. The activated carbons produced by carbon dioxide activation were mainly microporous with BET apparent surface area up to 1350 m(2)g(-1) and pore volume 0.5 cm(3)g(-1). The effects of concentration (0.1-2 mM) and pH (3-13) were studied. The phenol adsorption isotherms at 25 degrees C followed the Freundlich model with maximum adsorption capacities of approximately 80 and 50 mg g(-1) for the pristine and oxidised activated carbons, respectively. The influence of pH on the adsorption has two trends for pH below and above 10. It was possible to conclude that when phenol is predominantly in the molecular form the most probable mechanism is based on the pi-pi dispersion interaction between the phenol aromatic ring and the delocalised pi electrons present in the activated carbon aromatic structure. When phenolate is the major component the electrostatic repulsion that occurs at high pH values is the most important aspect of the adsorption mechanism.

Evolution of micropore structure of activated charcoal cloth

Abstract A series of microporous charcoal cloths of burn-offs between 20 and 92% have been prepared and studied by means of nitrogen, isobutene, methanol, and water adsorption isotherm measurements. The results indicate that at a level of burn-off of about 50%, the polarity of the surface falls to a minimum while the micropore volume, when expressed in terms of the same initial weight of carbon, reaches a maximum. At higher levels of burn-off both pore widening and pore narrowing occur. In addition, significant shrinkage of the carbon structure occurs at all stages of burn-off. The results are discussed in terms of a simple model, and it is concluded that densification of the carbon structure during activation exerts a significant influence on the evolution of the micropore structure.