Sustainable Development of Magnetic Chitosan Core-Shell Network for the Removal of Organic Dyes from Aqueous Solutions.

The wide use of alizarin red S (ARS), a typical anthraquinone dye, has led to its continued accumulation in the aquatic environment, which causes mutagenic and carcinogenic effects on organisms. Therefore, this study focused on the removal of ARS dye by adsorption onto a magnetic chitosan core-shell network (MCN). The successful synthesis of the MCN was confirmed by ATR-FTIR, SEM, and EDX analysis. The influence of several parameters on the removal of ARS dye by the MCN revealed that the adsorption process reached equilibrium after 60 min, pH played a major role, and electrostatic interactions dominated for the ARS dye removal under acidic conditions. The adsorption data were described well by the Langmuir isotherm and a pseudo-second order kinetic model. In addition to the preferable adsorption of hydrophobic dissolved organic matter (DOM) fractions onto the MCN, the electrostatic repulsive forces between the previously adsorbed DOM onto MCN and ARS dye resulted in lower ARS dye removal. Furthermore, the MCN could easily be regenerated and reused for up to at least five cycles with more than 70% of its original efficiency. Most importantly, the spent MCN was pyrolytically converted into N-doped magnetic carbon and used as an adsorbent for various dyes, thus establishing a waste-free adsorption process.

Synthesis of magnetic chitosan biopolymeric spheres and their adsorption performances for PFOA and PFOS from aqueous environment.

Due to numerous applications and excellent environmental stability, long-chain perfluorinated chemicals (PFCs) are ubiquitous in water across the world and adversely affect the living organisms. Thus, this study focused on the mitigation of the most frequently used long-chain PFCs namely perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) from water using reduced graphene oxide modified zinc ferrite immobilized chitosan beads (rGO-ZF@CB) as an adsorbent. The results from the adsorption isotherm and kinetic studies revealed that the adsorption data fitted well to the Langmuir and the pseudo-second-order models. According to the Langmuir isotherm, the rGO-ZF@CB possessed the maximum adsorption capacity of 16.07 mg/g for PFOA and 21.64 mg/g for PFOS. Both the electrostatic attractions and hydrophobic interactions have driven the removal of PFOA and PFOS by prepared rGO-ZF@CB. Eventually, the rGO-ZF@CB could be considered as an efficient adsorbent for the effective removal of PFOA and PFOS molecules from the aqueous environment.

Magnetic kaolinite immobilized chitosan beads for the removal of Pb(II) and Cd(II) ions from an aqueous environment.

In recent decades, magnetic bead material has attracted considerable attention in water and wastewater purification. In this study, the potential of magnetic kaolinite immobilized in chitosan beads (MKa@CB) to remove Pb(II) and Cd(II) ions from an aqueous environment has been successfully investigated. The addition of magnetic kaolinite generates more active sites, whereas that of chitosan enhances the stability of synthesized bead materials, which enable them to effectively interact with the targeted contaminants. Various factors including agitation time, solution pH, and competitive ions were examined to optimize the removal efficiency of the MKa@CB. The adsorption kinetics and isotherm studies indicated that the adsorption fitted well to the pseudo-second-order kinetic model as well as to the Langmuir isotherm. The prepared adsorbent could be reused up to four cycles without any significant adsorption capacity loss. Thus, the synthesized MKa@4%CB can be a promising adsorbent in effectively removing Pb(II) and Cd(II) from water.

Enhanced photocatalytic response of ZnO embedded chitosan/ß-cyclodextrin towards the detoxification of Cr(VI) under visible light.

The present work focused on the assessment of heterogenous photocatalytic efficacy of ZnO@CS-ß-CD towards the degradation of hexavalent chromium under visible light illumination. The prepared ZnO@CS-ß-CD was extensively characterized using XRD, FTIR, SEM, EDX with mapping, TGA, DSC and UV/vis DRS techniques and the photoreduction of Cr(VI) to Cr(III) was confirmed by X-ray photoelectron spectroscopy. The DRS results revealed that the band gap of ZnO@CS-ß-CD was narrowed than ZnO from 3.23 to 2.01 eV. The photocatalyst hold excellent reusability up to seven cycles and the field trail results demonstrated for the practical application for the treatment of wastewater.

Surface-Induced Silica Scaling during Brackish Water Desalination: The Role of Surface Charge and Specific Chemical Groups.

Silica scaling of membranes used in reverse osmosis desalination processes is a severe problem, especially during the desalination of brackish groundwater due to high silica concentrations. This problem limits the water supply in inland arid and semiarid regions. Here, we investigated the influence of surface-exposed organic functional groups on silica precipitation and scaling. A test solution simulating the mineral content of brackish groundwater desalination brine at 75% recovery was used. The mass and chemical composition of the precipitated silica was monitored using a quartz crystal microbalance, X-ray photoelectron spectroscopy, and infrared spectroscopy, showing that surfaces with positively charged groups induced rapid silica precipitation, and the rate of silica precipitation followed the order -NH2 ∼ -N+(CH3)3 > -NH2/-COOH > -H2PO3 ∼ -OH > -COOH > -CH3. Force vs distance AFM measurements showed that the adhesion energy between a silica colloid glued to AFM cantilever and the studied surfaces increased as the surface charge changed from negative to positive. Thus, for the first time direct measurements of molecular forces and specific chemical groups that govern silica scaling during brackish water desalination is reported here. The influence of the different functional groups and the effect of the surface charge on silica precipitation that were found here can be used to design membranes that resist silica scaling in membrane-based desalination processes.

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.

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.

Calcium phosphate scaling during wastewater desalination on oligoamide surfaces mimicking reverse osmosis and nanofiltration membranes.

Desalinated domestic wastewater is an indispensable water resource in arid regions; however, its recovery can be limited by calcium phosphate scaling and fouling of the membrane. Here we investigated calcium phosphate mineralization on oligoamide surfaces that mimics reverse osmosis (RO) and nanofiltration (NF) membrane surfaces. We used a solution that simulates desalination of secondary treated domestic wastewater effluents for calcium phosphate mineralization experiments with oligoamide-coated gold surfaces. Attenuated total reflection-Fourier transform infrared spectroscopy and energy dispersive spectrometry showed that calcium phosphate and carbonate precipitated on RO mimetic surfaces. The rate of precipitation on oligoamide sensors was monitored by a quartz crystal microbalance, showing that scaling was more intense on the RO than the NF mimetic surface and that excessive carboxyl functional groups on both surfaces promoted scaling. Filtration experiments of similar solutions with commercial membranes showed that scaling was more intense on the RO membranes than on the NF membranes, which supported the results obtained with the oligoamide model surfaces. The results of this study can be implemented in developing RO and NF membranes to prevent calcium phosphate scaling and consequently lower water-treatment costs of domestic wastewater treatment.