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Altering the textural properties of activated carbons (ACs) via physicochemical techniques to increase their specific surface area and/or to manipulate their pore size is a common practice to enhance their adsorption capacity. Instead, this study proposes the utilization of the vacant sites remaining unoccupied after dye uptake saturation by removing the steric hindrance and same-charge repulsion phenomena via multilayer adsorption. Herein, it has been shown that the adsorption capacity of the fresh AC is a direct function of the dye molecular size. As the cross-sectional area of the dye molecule increases, the steric hindrance effect exerted on the neighboring adsorbed molecules increases, and the geometrical packing efficiency is constrained. Thus, ACs saturated with larger dye molecules render higher concentrations of vacant adsorption sites which can accommodate an additional layer of dye molecules on the exhausted adsorbent through interlayer attractive forces. The second layer adsorption capacity (60-200 mg·g-1) has been demonstrated to have a linear relationship with the uncovered surface area of the exhausted AC, which is, in turn, inversely proportional to the adsorbate molecular size. Unlike the second layer adsorption, the third layer adsorption is a direct function of the charge density of the second layer. [ABSTRACT FROM AUTHOR]

Abstract: Two types of activated carbons from tyre char (with or without sulphuric acid treatment) were produced via carbon dioxide activation with BET surface areas in the range 59–1118m2/g. Other characterisation tests include micropore and mesopore surface areas and volumes, pH, and elemental compositions, particularly heteroatoms such as nitrogen and sulphur. They were correlated to the adsorption capacity which were in the range of 0.45–0.71mmol/g (untreated) and 0.62–0.84mmol/g (acid-treated) for Acid Blue 25. In the case of larger-sized molecules like Acid Yellow 117, capacities were in the range of 0.23–0.42mmol/g (untreated) and 0.29–0.40mmol/g (acid-treated). Some tyre carbons exhibit a more superior performance than a microporous, commercial activated carbon (Calgon® F400). By modelling the dye adsorption equilibrium data, the Redlich–Peterson isotherm is adopted as it has the lowest SSE. Based on the surface coverage analysis, a novel molecular orientation modelling of adsorbed dyes has been proposed and correlated with surface area and surface charge. For the acid dyes used in this study, molecules were likely to be adsorbed by the mesopore areas. [Copyright &y& Elsevier]

Abstract: The disposal of waste tyre represents a serious concern in environmental management. Owing to the high carbon content of waste tyre rubber, it is feasible to convert waste tyres to a value-added product, i.e. activated carbon, for environmental applications. This study focuses on the effect of different activation conditions (e.g. temperature, holding time and acid treatment) on the porosity of activated carbons produced from tyre rubber. Experimental studies showed that nitric acid treatment to tyre chars is able to remove certain mineral contents such as Ca, K and Na, which affect the reactivity of gas–solid reactions in the subsequent physical activation process (CO2 as activating agent). Those acid-treated carbons developed high surface areas (over 1000m2/g) that were comparable to commercial products. They also posses high mesopore volume up to 0.855cc/g which has been shown favourable to the adsorption of larger-sized dye molecules. The Redlich–Peterson equilibrium isotherm model yielded the best-fit to experimental data for all three dyes using the non-linear error functions. [Copyright &y& Elsevier]

Minimum total amount of microwave treated date stone carbon (S S1 + S S2) for removal of Malachite Green using Langmuir-Freundlich model for different discharge concentrations, C2. [Display omitted] • High surface area carbon from microwaved waste date stone • High adsorption capacity of 98 mg/g for Malachite Green • Optimised two-stage batch adsorber design for minimum adsorbent use Microwave and thermal treatment methods have been applied in order to produce two derived active carbons using waste date pits/stones from a date syrup processing plant. The adsorption properties of the two products have been tested for the adsorption of the toxic Malachite Green dye, which is commonly applied in the textile and plastics industry. Equilibrium isotherms were determined by experiment and evaluated using six isotherm correlations. The optimum fitting correlation for the thermally treated product was the Langmuir-Freundlich isotherm and for the microwave product was the Redlich-Peterson. The surface areas of the thermal product and the microwave product were 669.3 m2/g and 1123 m2/g respectively; and maximum malachite green adsorption capacities were 58 mg/g and 98 mg/g respectively. A two-stage batch adsorber model has been developed to optimize the two-step adsorption process to adsorb malachite green and minimize the amount of adsorbent, and therefore adsorbent cost, used for both thermal treated and microwave treated date stones. The output applications include the minimum total adsorbent for designing various percentages dye removal based on various effluent discharge concentrations and various initial dye concentrations. [ABSTRACT FROM AUTHOR]