A reusable mesoporous adsorbent for efficient treatment of hazardous triphenylmethane dye wastewater: RSM-CCD optimization and rapid microwave-assisted regeneration

In this research, mesoporous calcium aluminate nanostructures (meso-CaAl2O4) were synthesized using a citric acid-assisted sol–gel auto-combustion process as the potential adsorbent to eliminate toxic triphenylmethane dye malachite green (MG) from synthetic/real effluent. The surface morphology of meso-CaAl2O4 was highly porous with nanometric size and non-homogeneous surface. The specific surface area, total pore volume, and BJH pore diameter of meso-CaAl2O4 were 148.5 m2 g−1, 1.39 cm3 g−1, and 19 nm, respectively. The meso-CaAl2O4 also showed a very high heat resistance, due to losing only 7.95% of its weight up to 800 °C, which is mainly related to the moisture loss. The optimal adsorption conditions were obtained based on response surface methods (RSM)-central composite design (CCD) techniques. The Langmuir isotherm model was used for fitting the adsorption measurements, which presented 587.5 mg g–1 as the maximum adsorption capacity of the dye. The data obtained from the adsorption kinetics model were found to correspond to the pseudo-second-order model. Also, the thermodynamic parameters including enthalpy change (ΔH°), entropy change (ΔS°), and Gibbs free energy change (ΔG°) indicated that MG dye adsorption by the meso-CaAl2O4 was feasible, endothermic, and occurred spontaneously. Furthermore, the meso-CaAl2O4 was regenerated by microwave irradiation under 900 W at 6 min, and the MG dye removal efficiency was remained over 90% after the five cycles of microwave regeneration.

Molecular phylogeny of wood decay fungi of hardwood and their ability to produce laccase that correlates with triphenylmethane dye decolorization

Though Sri Lanka belongs to one of the 34 biodiversity hotspots of the world, its microfolora specially fungi are not well studied and underrepresented in the global literature. Here we report the fungal species diversity of decaying hardwood of a Sri Lankan dry zone forest for the first time. Decaying hardwoods were collected from historically important Dimbulagala forest reserve, Sri Lanka and fungi associated with these woods were isolated. Out of 35 fungal species identified using morphological and molecular methods, 11 species were first records in Sri Lanka. All the tested isolates were able to utilize wood as the sole carbon source and produced varying degrees of laccase. Isolates of Perenniporia tephropora, Coriolopsis caperata, Gymnopilus dilepis, Fusarium solani and Vanderbylia fraxinea were among the top six laccase producers. Except Fusarium solani, the rest of the isolates showed more than 70% decolorization of the of triphenylmethane dye and there was a significant positive correlation between laccase production and dye decolorization. To the best of our knowledge laccase production and dye decolorization ability of Vanderbylia fraxinea and Gymnopilus dilepis have never been reported in the fungal kingdom before. Perenniporia tephropora was isolated from one of the strongest decay resistant hardwood species, Ebony (Diospyros ebenum) also known as dark wood and V. fraxinea was isolated from another medicinally important hardwood Neem (Azadirachta indica). Findings of this study confirms that decaying hardwood of Sri Lanka provide unexplode a unique niche for discovering fungal species with biotechnological applications such as high laccase producers and dye decolorizers.

High performance adsorption of hazardous triphenylmethane dye-crystal violet onto calcinated waste mussel shells

Synthetic dyes are harmful to human beings, and the removal of colour from process or waste effluents is environmentally important. Crystal violet (CV) is a typical triphenylmethane dye, which is widely used in textile dyeing and paper printing industries. The present study shows that granulated and calcinated waste mussell shells (CWMS) can be used as a potential low-cost and locally available adsorbent for the removal of CV from aqueous solutions. The adsorption capacities of the CWMS for CV were investigated with respect to the effect of pH value, adsorbent dosage, contact time, initial dye concentration and temperature. Process variables were optimized, and a maximum dye adsorption of 482.0 mg/g was achieved at pH 6, 0.2 g/L adsorbent dosage, 220 min contact time and 25 °C for dye initial concentration of 100 mg/L. Adsorption kinetics and isotherms were followed by the pseudo-second order model and Freundlich isotherm models, respectively. Thermodynamic parameters demonstrated that adsorption of CV was spontaneous and endothermic in nature. The results indicated that the CWMS as a new adsorbent had the potential to serve in wastewater treatment applications, especially in the removal of CV from aqueous solutions.