Search

Novel mesoporous carbon-silica composites were prepared from vinasse, a by-product from ethanol production, as the carbon source, and sodium silicate (Na2SiO3) and potassium silicate (K2SiO3) as low-cost silica source alternatives to tetraethyl orthosilicate (TEOS). The composites were characterized for their surface area and porous properties using nitrogen adsorption-desorption porosimetry. The composites possessed a high mesopore volume (45-77%) with moderate specific surface areas (343-656 m2/g) and pore size of 3.12-5.58 nm. The adsorption behaviour of carbon-silica composites for the removal of four silk dyes (Green 41, Blue 32, Dark red 34 and Dark gold brown 35) from aqueous solution was investigated and compared with a commercial activated carbon. The effects of adsorption time, dye concentration, pH and temperature were analyzed. The dye adsorption kinetics of all four dyes followed the pseudo-second order kinetic model, suggesting chemisorption as the dominant mechanism. Moreover, the intraparticle diffusion model showed that both internal diffusion and external diffusion were rate-limiting. The maximum adsorption capacities for all dyes were found at pH - 2. The equilibrium data for silk dyes adsorption were best described by the Langmuir equation, thus indicating monolayer adsorption. Thermodynamic parameters indicated that the dye adsorption was an endothermic process (ΔH > 0). The negative values of free energy (ΔG) confirmed that dye adsorption was spontaneous at the investigated temperatures (303-323 K). For all dyes, the maximum adsorption capacities of carbon-silica composites were comparable to the commercial activated carbon. The combination of vinasse with low-cost silica sources is a promising approach to produce inexpensive carbon-silica composites for application as adsorbents for dye removal from aqueous waste solutions generated during silk manufacture and dyeing. [ABSTRACT FROM AUTHOR]

In this study, hydrolyzed Dipterocarpus alatus leaves (HDL), waste from biodiesel production, were used as precursor to prepare activated carbon. The HDL residue was treated with 30 wt% ZnCl2 (raw material:ZnCl2 solution = 1:2 by weight) for 1 to 24 h followed by carbonization at 500 °C for 1 h in N2 atmosphere. The highest specific surface area of 497 m² g -1 was obtained with 12 h treatment. The physicochemical properties of the optimum carbon were investigated by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, proximate analysis, bulk density and pH, and the potential of the activated carbon for methylene blue (MB) adsorption was tested under various contact times and initial dye concentrations. Adsorption equilibrium was reached within 50 min. The adsorption of MB onto the HDL-derived activated carbon followed pseudo-second order kinetics through chemisorption, with intra-particle diffusion as the significant controlling step. The Langmuir isotherm provided a better fit of the adsorption equilibrium than the Freundlich isotherm, with a maximum monolayer adsorption capacity of 338.86 mg g-1 . The activated carbon prepared from Dipterocarpus alatus leaves residue exhibited good adsorption uptake for MB and therefore presents an attractive and effective adsorbent for cationic dyes. [ABSTRACT FROM AUTHOR]

This study examines the treatment of bagasse fly ash (BFA), a solid waste generated from boilers in the sugar industry, using acid (HCl, H2SO4 and HNO3) treatment and carbonization under N2 atmosphere. The obtained adsorbents were characterized for their porous properties including BET surface area, total pore volume and average pore size. The treated fly ash with the highest surface area (TFA) was studied in detail for its physicochemical properties and the adsorption of methylene blue (MB) dye from aqueous solutions, and was compared with untreated BFA and a commercial activated carbon (CAC). The physicochemical characterization indicated that BFA and TFA represent adsorbents with low and moderate surface area (26 and 239 m2/g, respectively) with functional groups on their surface, while CAC has a high surface area (1130 m2/g) with weak surface functional groups. For all three adsorbents, the MB adsorption equilibrium was attained within 90 min and the kinetic data were best described by pseudo-second order and intra-particle diffusion kinetic models. The adsorption isotherms followed the Langmuir equation with a maximum MB adsorption capacity of 27.2, 39.0 and 42.1 mg/g for BFA, TFA and CAC, respectively. The comparable adsorption capacities of TFA and CAC suggest that the MB adsorption involves both surface area and surface functional groups on the adsorbents. Thus, this study demonstrates that BFA, a low cost solid waste, can be converted by simple treatment into an effective adsorbent for MB removal from aqueous solution with performance comparable to that of high surface area CAC. [ABSTRACT FROM AUTHOR]