Process Parameter Optimization for Cr (VI) Reduction Using Zero-Valent Iron Nanoparticles Via Response Surface Methodology

Synthesis and application of stabilized zero-valent iron nanoparticles for hexavalent chromium removal in saturated sand columns: experimental and modeling studies

Zero-valent iron nanoparticles (nZVI) modified with sodium dodecyl sulfate (SDS) as an anionic surfactant were successfully synthesized and applied to Cr (VI) removal. The prepared nanoparticles were characterized by field emission scanning electron microscope (FSEM), energy-dispersive spectrometry (EDS), and Fourier transform infrared spectrophotometer (FT-IR). Meanwhile, the surface charges of the stabilized nanoparticles were also determined. In this study, the kinetics of particle aggregation and sedimentation were investigated. It was found that the modified nanoparticles had great stabilization. Effects of pH, contact time, dosage of nanoparticles, and initial Cr(VI) concentrations on removal efficiency of the heavy metal ions were investigated and optimized. The maximum removal efficiency of Cr(VI) was obtained at pH 3.0 and 25 °C, at the value of 98.919 %. Cr(VI) removal occurred fast, and achieved equilibrium after 120 min. The maximum removal capacity reached up to 253.68 mg g−1 dry nanoparticles at a 300-mg L−1 Cr(VI)-containing sample. Kinetics study showed a rapid removal dynamics fitting pseudo-second-order kinetic model. The equilibrium data was nicely fit to the Freundlich model and indicates the adsorption of Cr(VI) was highly favorable. The obtained results indicated that nZVI modified by SDS could be used as an efficient alternative for removal of heavy metals with enhanced removal capacity and application stability.

Removal of Cr(VI) oxoanion from contaminated water using granular jujube stems as a porous adsorbent

This study was performed to investigate the latent potential of biomass gasifier waste material (BGWM) as an adsorbent for removal of Cr (VI) from aqueous solution. The present work also proposes an alternate use of gasifier refuge BGWM with great economic feasibility. The effects of initial pH, BGWM concentration, Cr(VI) concentration, temperature and contact time were investigated on the removal of Cr (VI) from aqueous solution. The maximum removal of Cr (VI) was found to be 99.67% at optimum condition of initial pH 2, contact time 80 min, initial Cr (VI) concentration 10 mg L−1, adsorbent dose 5 g L−1, agitation speed 120 rpm, and temperature 35°C. The adsorbent was characterised by SEM, EDX, XRD, BET and FTIR analysis to get important information about its effective application for Cr (VI) removal. The BET surface area of 165.287 m2 g−1 for BGWM was found comparable to that of commercial silica. Batch adsorption experiments showed that pseudo‐second‐order kinetics model and Langmuir isotherm model fitted the adsorption data very well. Thermodynamic parameters revealed the feasibility, spontaneity and endothermic nature of Cr (VI) adsorption onto BGWM. © 2015 American Institute of Chemical Engineers Environ Prog, 35: 95–102, 2016

Effects of physicochemical factors on Cr(VI) removal from leachate by zero-valent iron and α-Fe2O3 nanoparticles

Enhanced hexavalent chromium removal from aqueous solution using a sepiolite-stabilized zero-valent iron nanocomposite: Impact of operational parameters and artificial neural network modeling

The application of zerovalent iron nanoparticles in diverse organic transformations has garnered significant attention over the past decade, primarily due to the high natural availability, low toxicity, and cost-effectiveness of iron metal. The core of zerovalent iron nanoparticles, composed of zerovalent iron, acts as a reducing agent for contaminants, while its outer iron oxide shell offers active sites for chemisorption and facilitates electrostatic interactions with heavy metals. Advances in synthetic methodologies for producing Fe nanoparticles and their stabilization using various support materials have played a pivotal role in enhancing their utility in catalysis. This review consolidates understanding of the nanoscale zerovalent iron structure, its synthesis techniques, removal mechanisms, practical applications for heavy metals such as cadmium (Cd), copper (Cu), and lead (Pb), as well as the challenges associated with its use. This review explores the catalytic properties of zerovalent iron (nZVI) nanoparticles and their critical role in environmental remediation and catalysis. It highlights the factors influencing their performance, including chemical composition, size, surface properties, and the presence of stabilizing agents. The document emphasizes the importance of advanced characterization techniques such as TEM, SEM, and SAXS for understanding particle morphology and structural properties. Challenges such as agglomeration, rapid oxidation, and environmental concerns are addressed, alongside strategies to enhance their efficiency. This comprehensive discussion underscores the significance of nZVI in academic research and industrial applications, providing insights into both their potential and limitations. Additionally, it provides insights into potential future directions for advancing iron nanoparticle-mediated reduction reactions. HIGHLIGHTS The review comprehensively discusses the application of nanomaterials for the removal of highly toxic hexavalent chromium from aqueous environments. The parameters include pH, initial concentration, contact time, nanomaterial dosage, and temperature, which affect Cr (VI) removal. Cr (VI) removal using nanomaterials involves interconnected mechanisms such as adsorption, electrostatic attraction under acidic conditions, reductive transformation to Cr (III), and subsequent complexation or surface precipitation of Cr (III) on the nanomaterial surfaces. Emphasis is placed on the regeneration potential of nanomaterials to enhance sustainability in practical applications. GRAPHICAL ABSTRACT

The current study deals with Cr(VI) removal by nanotitania under fluorescent light and dark conditions. The equilibrium removal capacities, 85.85 and 59.4 mg of Cr(VI) g−1 of nanoparticle were noted for nanotitania interacted under light and dark conditions, respectively, at optimized conditions (pH: 7.0, contact time: 30 min, initial Cr(VI) concentration: 20 mg l−1, nanoparticle dosage: 0.1 g l−1). Under both the conditions, the equilibrium removal data fitted well with the Langmuir isotherm model. The nanotitania followed a second-order kinetics under light condition whereas a pseudo-second-order kinetics was observed under dark condition. The surface characterization of nanotitania was carried out by zeta potential measurement and transmission electron microscope (TEM). Fourier transform infrared (FT-IR) studies carried out under light and dark conditions indicate the interaction of surface functional groups to Cr(VI). Cr(VI) removal study carried out in the Cr(VI)–Cr(III) mixture showed a decrease in Cr(VI) removal capacity with increase in Cr(III) concentration. A 92% regeneration of nanoparticle was observed indicating efficient reusability of the system. The applicability of the nanotitania in Cr(VI) contaminated water was studied by spiking Cr(VI) in natural water matrices like ground water and lake water.

Tannery industries’ effluent contains a high concentration of Cr (VI) which has the potential to affect the environment and public health. Therefore, this study aimed to investigate the optimization of Cr (VI) adsorption by activated carbon (AC) derived from Eichhornia crassipes from an aqueous solution. The adsorbent was activated with dilute sulfuric acid followed by thermal activation. AC was characterized using proximate analysis, SEM, FTIR, X-ray diffraction, and the BET method. The Cr (VI) removal optimization process was performed using a central composite design under the response surface methodology. The proximate analysis showed that the moisture content, volatile matter, ash content, and fixed carbon of the activated carbon were 5.6%, 18.2%, 14.4%, and 61.8% respectively. The surface areas of the Eichhornia crassipes before activation, after activation, and after adsorption were 60.6 g/m2, 794.2 g/m2, and 412.6 g/m2 respectively. A highly porous structure with heterogeneous and irregular shapes was observed in the SEM micrograph. In the FTIR analysis, different peaks are indicated with various functional groups. The intensity of XRD peaks decreased as 2 theta values increased, which indicates the presence of an amorphous carbon arrangement. The point of zero charge (pHpzc) of the activated carbon was found to be 5.20. A maximum Cr (VI) removal of 98.4% was achieved at pH 5, contact time 90 min, adsorbent dose 2 g, and initial Cr (VI) concentration of 2.25 mg/L. Statistically significant interactions (P < 0.05) were observed between the initial Cr (VI) concentration and adsorbent dose as well as the initial Cr (VI) concentration and contact time. Langmuir adsorption isotherm fitted the experimental data best, with an R2 value of 0.99. The separation constant (RL) indicates that the adsorption process is favorable. The kinetic experimental data were best fitted with the pseudo-second-order model with an R2 value of 0.99 whereas the adsorption rate is controlled by intraparticle and extragranular diffusion processes. Generally, the AC has the potential to be a strong adsorbent candidate for wastewater treatment at the industrial level.

Application of Central Composite Design approach for removal of chromium (VI) from aqueous solution using weakly anionic resin: Modeling, optimization, and study of interactive variables

Removal of Cr(VI) from synthetic aqueous solutions by filamentous green algae Spirogyra porticalis

The response surface methodology involving the five‐level central composite design (CCD) was employed to model and optimize the Cr(VI) immobilization process in a Cr‐spiked soil using starch‐stabilized zerovalent iron nanoparticles (ZVIn). ZVIn were synthesized via a borohydride reduction method and characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). All Cr(VI) immobilization experiments were conducted in a batch system. The variables for the CCD optimization were the ZVIn dosage (% w/w), reaction time (min), and initial Cr(VI) concentration in soil (mg/kg). The predicted response values by the second‐order polynomial model were found to be in good agreement with experimental values (R2 = 0.968 and adj‐R2 = 0.940). The optimization result showed that the Cr(VI) immobilization efficiency presented the maximal result (90.63%) at the following optimal conditions: ZVIn dosage of 1.5% w/w, reaction time of 60 min, and an initial Cr(VI) concentration of 400 mg/kg.

Application of phytogenic zerovalent iron nanoparticles in the adsorption of hexavalent chromium

Zero-valent iron nanoparticles embedded into reduced graphene oxide-alginate beads for efficient chromium (VI) removal

The tannery industry inevitably generates toxic and catastrophic wastewater, which results in a huge threat to public health and water resources. Therefore, this work aimed to synthesize parthenium hysterophorus-based biochar–Fe3O4 composite for removal of Cr(VI) from tannery wastewater under 34 full factorial experimental designs of the Box–Behnken, which was analyzed using response surface methodology under four independent factors of pH (3, 6, and 9), initial Cr(VI) concentrations (40, 70, and 100 mg/L), contact times (30, 60, and 90 min), and adsorbent doses (20, 60, and 100 mg/100 mL). This composite adsorbent was described by a high BET surface area of 237.4 m2/g, XRD prominent peaks, SEM morphology corroborate and FTIR multifunctionalities of O–H at 3296 cm−1, the vibration of ketone C–OH at 1240 cm−1, and the vibration of C–O–C at 1147 cm−1 and Fe–O stretching at 542 cm−1. The maximum Cr(IV) removal efficiency of 91.8% was recorded at an initial Cr(VI) concentration of 40 mg/L, pH of 3, adsorbent dose of 100 mg/100 mL, and a contact time of 90 min, whereas the minimum Cr(VI) removal of 17.3% was observed at an initial Cr(VI) concentration of 100 mg/L, 20 mg/100 mL of adsorbent dose, pH of 9, and contact time of 30 min. The concentration of Cr(VI) in real wastewater was determined to be 85.13 mg/L and its remediation was found to be 81.8%. Langmuir’s model was the best fit with experimental data at R2 0.99 and qmax 400 mg/g, showing that the adsorption process was homogenous and monolayer. In conclusion, the adsorption results were encouraging, and biochar–Fe3O4 appears to be a potential candidate for Cr removal from wastewater.