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A green reagent of ethylenediamine- N,N'-disuccinic acid (EDDS) was reported herein for reduction of graphene oxide (GO) with microwave assistance. The characteristics of EDDS reduced graphene oxide (ERG), and the tetracycline (TC) adsorption behavior of ERG was investigated. The results showed that the deoxygenation efficiency of GO strongly depended on the EDDS amount and the ERG can be successively obtained by recycled EDDS. The ERG obtained at EDDS/GO ratio of 5 (ERG5) exhibited a maximum capacity of 558.66 mg/g for TC adsorption, which is superior to GO and ERGs obtained at other EDDS/GO ratio. The adsorption reached equilibrium within 10 min, and the driving forces are likely the van der Waals forces, π-π electron-donor-acceptor (EDA) interaction and cation-π bonding between TC and the ERG surface. The adsorbent dose, pH, temperature, initial TC concentration, and ionic strength significantly affect the TC adsorption. The pseudo-second-order kinetics describes TC adsorption process very well, with correlation coefficients ( R ) greater than 0.99. The adsorption isotherm was best fitted by Freundlich equation, followed by Langmuir, Temkin, and Hill model equations. Analysis on adsorption thermodynamics shows that the adsorption is a spontaneous endothermic process. The ERG could be a cost-effective and promising sorbent for TC wastewater treatment due to its high-efficiency performance in real river water, medical wastewater, and municipal wastewater. [ABSTRACT FROM AUTHOR]

A role of rhamnolipid biosurfactant to enhance the biodegradation of hydrocarbons is known to be enhancing bacterial cell surface hydrophobicity (CSH) and adhesion of cells to hydrocarbons. Assumptions regarding the mechanism for rhamnolipid in changing CSH of Gram-negative bacteria are rhamnolipid-induced release of lipopolysaccharide (LPS) from the cell's outer membrane and adsorption/orientation of rhamnolipid on the cell surface. In this study, the relation between cell-wall LPS or rhamnolipid content and CSH of a Pseudomonas aeruginosa bacterium subjected to rhamnolipid treatment was investigated to add insights to the mechanism. Results showed that the initial CSH was determined by the type of substrate the cells grow on and the stage of growth. For glucose-grown cells with low initial CSH and high LPS content, rhamnolipid sorption in cell wall had no discernable effect on CSH. For cells grown on glycerol with medium initial CSH and low LPS content, rhamnolipid sorption increased CSH of exponential-phase cells but decreased that of stationary-phase cells. For hexadecane-grown cells with high initial CSH and high LPS content, rhamnolipid sorption decreased CSH of both exponential-phase and stationary-phase cells. The results indicated that CSH has a better correlation to the content of rhamnolipid in the cell wall than to the content of LPS in the presence of rhamnolipid treatment and that rhamnolipid adsorption may be an important mechanism for rhamnolipid to alter CSH of P. aeruginosa. [ABSTRACT FROM AUTHOR]

The effect of rhamnolipids (RL) on Cd adsorption by Penicillium simplicissimum ( P. simplicissimum) was studied. The maximum adsorption capacities of Cd were obtained at pH 6.0 for the intact P. simplicissimum and at pH 5.0 for the RL-pretreated P. simplicissimum, respectively. The adsorption equilibrium was reached after about 4 h. The experimental adsorption isotherms were in good agreement with the Langmuir model. The maximum adsorption capacities ( q) for the intact P. simplicissimum and for the RL-pretreated P. simplicissimum were 51.6 and 70.4 mg/g, respectively. The interactions between Cd and functional groups on the cell wall surface of the P. simplicissimum were identified by SEM, EDAX and FTIR analysis. It is indicated that carboxyl, amino and hydroxyl groups play major roles in the Cd adsorption. The results suggest that the RL-pretreated P. simplicissimum is a promising candidate for the removal of Cd from aqueous solutions. [ABSTRACT FROM AUTHOR]

Previously, adsorption feature of a dirhamnolipid biosurfactant on diverse microbial cells was studied and the effect of the adsorption on cell surface hydrophobicity was compared. In this paper, the adsorption behavior of a monorhamnolipid and a dirhamnolipid on cells of two Pseudomonas aeruginosa strains was investigated in order to further reveal the influence of biosurfactant structure and cell property on the adsorption and the relation between the adsorption and cell surface hydrophobicity. Experimental results showed that the adsorption capacity of all the cells to monorhamnolipid was much stronger than to dirhamnolipid, and the rhamnolipid-sourced P. aeruginosa cells, no matter grown on glucose or hexadecane, released extra dirhamnolipid when aqueous concentration of dirhamnolipid was too high. Length of surfactant alkyl chain as well as the type of carbon source used to cultivate the cell adsorbents had only minor influence on the adsorption. The adsorption was assumed to be driven by polar interaction between the rhamnolipid molecules and the cell surface chemical groups. The directional orientation of the rhamnolipid molecules with hydrophobic moiety extending to the environment may account for the rapid increase of cell surface hydrophobicity at low aqueous concentrations of the surfactant, while the stable or decreased cell hydrophobicity was probably the consequence of multiple surfactant layer formation or hemimicelle accumulation. [ABSTRACT FROM AUTHOR]