Hydrothermal synthesis of hydroxyapatite-reduced graphene oxide (1D-2D) hybrids with enhanced selective adsorption properties for methyl orange and hexavalent chromium from aqueous solutions.

The presence of organic dye molecules and heavy metal ions in water causes ecological and public health problems. Therefore, remediation of water/wastewater contaminated with organic dye molecules and toxic metal ions is of importance. Herein, a reduced graphene oxide (RGO)-hydroxyapatite (Hat) (1D-2D) hybrid composite was fabricated through a hydrothermal process and applied for the adsorption of methyl orange (MO) and hexavalent chromium (Cr(VI)) from water. The as-fabricated RGO-Hat hybrids were characterized using FTIR, XRD, HR-TEM, SEM, XPS, EDAX, and TGA-DSC analytical techniques. The influencing parameters of adsorption performance, namely solution pH, contact time, and co-interfering ions, were explored to obtain the maximum adsorption capacity of contaminants from the solid-liquid interface. Batch studies revealed that MO and Cr(VI) adsorption followed the pseudo-second-order kinetic and the Langmuir isotherm models. The adsorption capacity was 49.14 and 45.24 mg g-1 for MO and Cr(VI), respectively. The adsorption of such ions over RGO-Hat hybrids was mainly driven by several uptake mechanisms viz, electrostatic force of attraction, π-π interactions, and hydrogen bonding. Thus, this study demonstrated that the RGO-Hat hybrid is a potential candidate for the treatment of MO and Cr(VI) from water.

Adsorptive performance of lanthanum encapsulated biopolymer chitosan-kaolin clay hybrid composite for the recovery of nitrate and phosphate from water.

Nitrate and phosphate are primary pollutants of water/wastewaters for eutrophication and methemoglobinemia diseases, harshly threatening the security of aquatic environments and human health as well as all living beings. The present work investigates the adsorption performance and mechanism of lanthanum encapsulated chitosan-kaolin clay (LCK) hybrid composite was prepared and utilized for the remediation of nitrate and phosphate from water. The fabricated LCK hybrid composite was characterized using XRD, SEM, BET, EDAX, TGA-DTA and FTIR analysis. The removal of nitrate and phosphate onto the LCK composite defined by pseudo-second-order kinetic model whereas the isotherms are described by Freundlich adsorption isotherm model and thermodynamic experiments showed spontaneous and exothermic nature of the adsorption process. Results also demonstrated that the LCK hybrid composite exhibited extremely high nitrate and phosphate adsorption capacity and stability which followed the mechanisms by ion exchange, complexation and electrostatic interactions. Adsorption-desorption experiments revealed that the LCK hybrid composite could be potentially reused with maintaining high adsorption efficiency. This study highlights the novel low-cost, eco-friendly and promising adsorbent for efficient denitrification and dephosphorization from water/ wastewater.

Synthesis and characterization of metal loaded chitosan-alginate biopolymeric hybrid beads for the efficient removal of phosphate and nitrate ions from aqueous solution.

The aim of this present scenario is to examine the removal performance and mechanism of phosphate and nitrate removal onto metal (Fe3+) loaded chitosan and alginate biopolymeric hybrid beads (Fe-CS-Alg) from aqueous solution. The batch adsorption experiments were accomplished via various operating parameters like pH, dosage, contact time, co-existing anions, and temperature. The equilibrium isotherm study was scrutinized by three different isotherm models like Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. The thermodynamic statics specifies that the spontaneous and endothermic nature of phosphate and nitrate adsorption. The proposed mechanism indicated that the removal of phosphate and nitrate ions was mainly governed by electrostatic interaction, complexation and ion exchange mechanism. Consequently, the adsorption mechanism was examined by studying the physicochemical characteristics of the beads and sorbate adsorbed beads using the FTIR, XRD, SEM and EDAX with mapping analysis and TGA analytical techniques. The performance of the Fe-CS-Alg beads in field condition was assessed with contaminated water sample taken from nearby an industrial area. Thus, the experimental outcomes clearly indicated that the developed biopolymeric hybrid beads could be utilized as the potential adsorbents for the removal of phosphate and nitrate ions from aqueous solution.

Removal of phosphate and nitrate ions from aqueous solution using La3+ incorporated chitosan biopolymeric matrix membrane.

The present investigation was carried out for the removal of phosphate and nitrate ions from aqueous solution using lanthanum incorporated chitosan membrane (La@CS) prepared by casting method. Systematic adsorption studies were performed by varying the influencing parameters like contact time, dosage, pH, interfering anions and temperature were optimized for the maximum phosphate and nitrate adsorption capacities. The adsorption equilibrium process was examined by Freundlich, Langmuir and Dubinin-Radushkevich isotherm models. The La@CS membrane showed an adsorption capacity of 76.6 and 62.6 mg/g for phosphate and nitrate ions respectively. Thermodynamic parameters such as ∆G°, ∆H° and ∆S° were calculated to understand the nature of adsorption. The synthesized La@CS membrane was characterized by FTIR, SEM, EDAX with mapping analysis, XRD, AFM, TGA-DSC and zero point charge analysis. The possible adsorption mechanism was found to be electrostatic attraction as well as by ion exchange between La@CS membrane and both anions like phosphate and nitrate. The experimental results clearly indicated that the prepared La@CS membrane could be utilized for the removal of phosphate and nitrate ions from aqueous solution.