An environmentally-friendly chitosan-lysozyme biocomposite for the effective removal of dyes and heavy metals from aqueous solutions.

Developing efficient and cost-effective adsorbents for removing heavy metals and dyes from water streams is of utmost importance as prolonged human and animals consumption might lead to adverse health effects. In the present study, an environmentally-friendly bio-composite of a polysaccharide with a protein was prepared, by conjugating chitosan to lysozyme using glutaraldehyde as a crosslinker. We investigated the utility of this chitosan-lysozyme biocomposite (CLC) as an adsorbent for the removal of methyl orange (MO) dye and hexavalent chromium (Cr(VI)) ions from aqueous solutions. CLC showed excellent removal of MO and Cr(VI) along with concurrent removal of other heavy metals such as Cd(II) and Ni(II) ions from aqueous mixtures. The maximum adsorption capacities of CLC for MO and Cr(VI) were as high as 435 and 216 mg g-1, respectively. This study demonstrates the potential use of conjugated biopolymers such as chitosan and lysozyme for water treatment applications.

Laser-Induced Graphene by Multiple Lasing: Toward Electronics on Cloth, Paper, and Food.

A simple and facile method for obtaining patterned graphene under ambient conditions on the surface of diverse materials ranging from renewable precursors such as food, cloth, paper, and cardboard to high-performance polymers like Kevlar or even on natural coal would be highly desirable. Here, we report a method of using multiple pulsed-laser scribing to convert a wide range of substrates into laser-induced graphene (LIG). With the increased versatility of the multiple lase process, highly conductive patterns can be achieved on the surface of a diverse number of substrates in ambient atmosphere. The use of a defocus method results in multiple lases in a single pass of the laser, further simplifying the procedure. This method can be implemented without increasing processing times when compared with laser induction of graphene on polyimide (Kapton) substrates as previously reported. In fact, any carbon precursor that can be converted into amorphous carbon can be converted into graphene using this multiple lase method. This may be a generally applicable technique for forming graphene on diverse substrates in applications such as flexible or even biodegradable and edible electronics.

Hexavalent chromium ion and methyl orange dye uptake via a silk protein sericin-chitosan conjugate.

Sericin, a protein waste product of the silk industry, was crosslinked with chitosan, and a chitosan-sericin conjugate (CS) was prepared, characterized and used to remove hexavalent chromium (Cr(vi)) ions and methyl orange (MO) dye from aqueous solutions. The CS was shown to effectively remove Cr(vi) ions and MO dye at maximum adsorption capacities (Langmuir) of 139 mg g-1 for Cr(vi) ions and 385 mg g-1 for MO dye. Moreover, the adsorption of both Cr(vi) ions and MO dye was highly pH dependent and varied under different experimental conditions. Cr(vi) ion and MO dye uptake by the CS was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry analysis. Additionally, XPS analysis of the Cr(vi)-loaded CS revealed that Cr(vi) was reduced to the less toxic Cr(iii). The CS was shown not only to be highly amenable to regeneration, but also to be able to effectively remove MO dye and Cr(vi) ions from a binary mixture.

Mechanism of the Hydrolysis of Endosulfan Isomers.

The objective of this study was to elucidate the mechanism of abiotic hydrolysis of ES isomers, i.e., Endosulfan-1 (ES-1) and Endosulfan-2 (ES-2), using a combination of experiments and density functional theory (DFT) calculations. Hydrolysis of both ES-1 and ES-2 resulted in the formation of Endosulfan Alcohol (ES-A). The rate of hydrolysis was first order in all cases and increased with both pH and temperature. Rate expressions describing the hydrolysis rates of ES-1 and ES-2 as a function of pH and temperature were obtained and validated with independent data sets. DFT calculations were performed using three functionals (M06-2X, B3LYP, and MPW1K) and both IEFPCM-UFF and SMD to introduce solvent effects. The geometry optimization of molecules ES-1 and ES-2 showed that the free energy of ES-1 was larger, and therefore, ES-2 was the more thermodynamically stable isomer. DFT calculations also supported a hydrolysis mechanism involving two successive attacks by OH- ions on C-O bonds resulting in the attachment of OH- and the elimination of SO3- from the ES molecule, but only the first attack was rate limiting. Calculations with all functionals and solvent effect combinations supported the experimentally observed result of faster hydrolysis of ES-2 than of ES-1. The MPW1K functional along with IEFPCM-UFF for solvent effect simulated the free energy of activation to be the closest for both ES-1 and ES-2 with less than 3% error with respect to the values computed from the experimental observations. The kinetic rate expression for ES hydrolysis derived on the basis of the proposed mechanism was identical to the rate expression derived from experiments. It was deduced that the hydrolysis rates of both ES isomers may vary over 3 orders of magnitude depending on the prevalent pH and temperature.

Impact of the composition of the bacterial population and additional carbon source on the pathway and kinetics of degradation of endosulfan isomers.

Abiotic and bacterial degradation is presented for the two isomers α- and ß- of the organochlorine pesticide endosulfan, denoted as ES-1 and ES-2, respectively. Biodegradation studies were conducted with two indigenous species Pseudomonas putida (P. putida) and Rhodococcus sp. Both ES isomers rapidly hydrolyzed in water at pH ≥ 7 but the hydrolysis was inhibited in the presence of biomass. The pesticide partitioned onto the biomass making it unavailable for abiotic hydrolytic reaction. Spontaneous temperature dependent abiotic conversion of ES-2 to ES-1 was reported in the presence of dual air-water phases but was not observed in the abiotic aqueous phase. Biodegradation experiments with pure isomers showed a small amount of interconversion (∼5%) in either direction and ruled out any preferential interconversion of the ES-2 isomer to ES-1 or vice versa. Both the species were shown to degrade ES-2 at a higher rate compared to ES-1 which may lead to enrichment of ES-1 in agricultural fields in short-term following application of the pesticide. P. putida degraded both the ES isomers through oxidative and hydrolytic pathways while the Rhodococcus sp. used only the hydrolytic pathway. Since ES-S (product of the oxidative pathway) is orders of magnitude more toxic than the parent isomers, the short term toxicity of a field following the application of the pesticide may increase if the composition of the indigenous bacterial population is such that the oxidative pathway is preferred over the hydrolytic one. The presence of an additional carbon source increased the rates of degradation of both the isomers but the enhancement was greater for the degradation rate of ES-2 than ES-1.