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In this study, chitosan was chemically modified with only diammonium phosphate (DAP) and DAP/EDTA (ethylenediaminetetraacetic acid) mixture for the removal of Pb(II) ions from aqueous solution. Modified chitosan forms were analyzed using thermo-gravimetric analyzer (TGA), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) to investigate the thermal degradation behavior, structural modifications, and the surface texture of the cross-linked chitosan adsorbents, respectively. The adsorption results were analyzed by well-known kinetic and isotherm models. The kinetics of metal adsorption followed the pseudo-second-order model. The maximum sorption capacities obtained from the Langmuir isotherm model were 126 mg/g for diammonium phosphate-modified Chitosan (DMC) and 137 mg/g for DAP/EDTA-modified chitosan (EDMC). The thermodynamic analysis showed that the metal removal process was endothermic in nature. [ABSTRACT FROM AUTHOR]

Multiwall carbon nanotubes (CNTs) and iron oxide impregnated carbon nanotubes (CNTs-iron oxide) were investigated for the adsorption of hazardous toluene and paraxylene (p-xylene) from aqueous solution. Pure CNTs were impregnated with iron oxides nanoparticles using wet impregnation technique. Various characterization techniques including thermogravimetric analysis, scanning electron microscopy, elemental dispersion spectroscopy, X-ray diffraction, and nitrogen adsorption analysis were used to study the thermal degradation, surface morphology, purity, and surface area of the materials. Batch adsorption experiments show that iron oxide impregnated CNTs have higher degree of removal of p-xylene (i.e., 90%) compared with toluene (i.e., 70%), for soaking time 2 h, with pollutant initial concentration 100 ppm, at pH 6 and shaking speed of 200 rpm at 25°C. Pseudo-second-order model provides better fitting for the toluene and p-xylene adsorption. Langmuir and Freundlich isotherm models demonstrate good fitting for the adsorption data of toluene and p-xylene. [ABSTRACT FROM AUTHOR]

The scarcity of water, especially in arid and semi-arid regions of the world is exerting great pressure on resources and establishing more need to provide good quality water for human and other consumptions. Water recovery/recycle/reuse has proven to be effective and successful in creating a new and reliable water supply. Accordingly, attention is being paid to the effective treatment of alternative sources of water (apart from fresh water) such as seawater, storm water, wastewater (e.g. treated sewage water), and industrial wastewater. In this review, the use of carbon nanotubes (CNTs), member of the fullerene structural family, is considered with special focus on the removal of heavy metals from water (lead, chromium, cadmium, arsenic, copper, zinc and nickel). A critical review into the adsorption behavior and use of the CNTs is given with attention being paid to the effects of surface modifications on the adsorption behavior and subsequent heavy metal removal. A review of the effect of a number of key variables including pH, CNTs dosage, time, ionic strength, temperature and surface charge are given. It will be demonstrated that, surface modification enhances positively the adsorption capacity of CNTs towards cadmium, chromium, lead, mercury, copper, zinc, cobalt and nickel as did the solution pH. CNTs have been proven to an excellent adsorbent for the removal of different heavy metals from water. However, most of the applications of CNTs are on lab scale in batch experiments. In spite of high costs, CNTs are expected to be a promising adsorbent in the future due to its high adsorption capacity compared to many traditional adsorbents. Researchers are also in quest of novel environment friendly techniques for the surface modification of CNTs to further improve their properties. Still, the feasibility of CNTs application in large scale treatment needs to be further studied. Effective techniques for regeneration/reuse of CNTs also need to be explored yet. One of the main hurdles that limit the applications of CNTs in large scale operation is the cost of CNTs. Future research works on developing a cost-effective way of CNT production and testing the toxicity of CNTs and CNT-related materials are recommended. [ABSTRACT FROM AUTHOR]