Bioremoval of Hexavalent Chromium from Aqueous Solutions by the Brown Seaweed Dictyopteris polypodioides

Facile Synthesis of Fe(0)@Activated Carbon Material as an Active Adsorbent towards the Removal of Cr (VI) from Aqueous Media

A novel adsorbent substrate based on zero-valent iron in activated carbon (Fe(0)@AC) was introduced in this work, and was evaluated as a cheap adsorbent for the removal of Cr(VI) from aqueous solutions. The as-prepared Fe(0)@AC material was chemically prepared via NaBH4 reduction in the presence of ferric chloride as an iron source, followed by the addition of powdered activated carbon. The different physicochemical tools confirm the successful preparation of Fe(0) composite with activated carbon as a heterogeneous composite with heterogeneous morphology of the rock-shape structure, which could play a role in the metal adsorption application. Interestingly, the removal efficiency (RE) of Cr(VI) was increased from 52% to 84% due to the Fe(0)@AC adsorbent being changed from 0.2 to 0.4 g/100 mL. Following this, the increase rate was stabilized, and the RE reached 95% in the case of 0.8 g/100 mL from Fe(0)@AC adsorbent. This result could be due to the increase in the sorbent active sites with more contents from Fe(0)@AC. The adsorption model based on the Langmuir approach could successfully describe the experimental outcomes for Cr(VI) removal by Fe(0)@AC with the correlation coefficient of 0.977. To conclude, Fe(0)@AC heterogeneous material is an active adsorbent for Cr(VI) removal from aqueous solutions.

Structural and Adsorptive Characteristics of 2D Multilayer Nanoflakes of NiCo Phosphates for Chromium(VI) Removal: Experimental and Monte Carlo Simulations

Metal phosphates are efficient adsorbent materials for heavy elements present in industrial effluents because of their promising properties. Hexachromium ions are among the most dangerous contaminants owing to their harmful properties and non-degradability. Accordingly, the present work offers a simplified study of the preparation of bimetallic phosphate materials from nickel cobalt phosphate (NiCo-Ph) based on the sol-gel method in an equimolar ratio. Characterization of the bulk, crystal phase, texture profile, and nanosize of NiCo-Ph was carried out using various techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption isotherm measurements, field emission scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. In this regard, the adsorption performance of NiCo-Ph was exemplified through six batch experiments, elucidating the impacts of the sorbent dose, initial concentration of pollutants, sorption time, temperature, pH, and shaking rate. According to UV/vis spectrophotometry measurements and their related calculations of NiCo-Ph, the maximum removal efficiency (RE %) of 92% and adsorption capacity (q _m) of 37 mg/g were achieved at pH = 6, a dose of 5.0 g/L, 100 mg/L of [Cr(VI)], 300 rpm, adsorption time of 60 min, and 298 K. Monte Carlo simulations were also carried out to correlate the experimental data with theoretical calculations that provided a higher negative value (-911.62 kcal mol^-1) for the adsorption energy of Cr(VI) in acidic medium. The adsorbent NiCo-Ph prepared by this direct method is therefore recommended for the quantification of Cr(VI) under slightly acidic solutions and at room temperature, which can maintain its efficiency even up to six cycles.

Bioprocessing strategies for cost-effective simultaneous removal of chromium and malachite green by marine alga Enteromorpha intestinalis

A large number of industries use heavy metal cations to fix dyes in fabrication processes. Malachite green (MG) is used in many factories and in aquaculture production to treat parasites, and it has genotoxic and carcinogenic effects. Chromium is used to fix the dyes and it is a global toxic heavy metal. Face centered central composite design (FCCCD) has been used to determine the most significant factors for enhanced simultaneous removal of MG and chromium ions from aqueous solutions using marine green alga Enteromorpha intestinalis biomass collected from Jeddah beach. The dry biomass of E. intestinalis samples were also examined using SEM and FTIR before and after MG and chromium biosoptions. The predicted results indicated that 4.3 g/L E. intestinalis biomass was simultaneously removed 99.63% of MG and 93.38% of chromium from aqueous solution using a MG concentration of 7.97 mg/L, the chromium concentration of 192.45 mg/L, pH 9.92, the contact time was 38.5 min with an agitation of 200 rpm. FTIR and SEM proved the change in characteristics of algal biomass after treatments. The dry biomass of E. intestinalis has the capacity to remove MG and chromium from aquatic effluents in a feasible and efficient manner.

Removal of Cr(VI) by magnetic iron oxide nanoparticles synthesized from extracellular polymeric substances of chromium resistant acid-tolerant bacterium Lysinibacillus sphaericus RTA-01

BACKGROUND

Extracellular polymeric substances (EPS) from Cr(VI) resistant acid-tolerant biofilm forming bacterium (CrRAtBb) Lysinibacillus sphaericus RTA-01 was used for synthesis of magnetic iron oxide nanoparticles (MIONPs) in removal of Cr(VI).

METHODS

MIONPs synthesized in EPS matrix were characterized by UV-Vis, DLS, ATR-FTIR, XRD, FESEM, HRTEM and VSM. Primarily, the synthesis of MIONPs was established by the formation of black-colored precipitate through surface plasmon resonance (SPR) peak in between 330 and 450 nm.

RESULTS

The size of the spherical MIONPs with diameter range 13.75-106 nm was confirmed by DLS, XRD and FESEM analysis. HRTEM study confirmed the size of the MIONPs in the range of 10-65 nm. Moreover, the EDX and SAED confirmed the purity and polycrystalline nature of MIONPs. The ATR-FTIR peaks below 1000 cm-1 designated the synthesis of MIONPs. Also, the magnetic property of MIONPs was confirmed for separation from the aqueous solution. MIONPs were further checked for the adsorption of Cr(VI) with initial concentration range of 50-200 mg L-1. An adsorption isotherm and thermodynamic study were also carried out and the experimental data was best fitted in Langmuir isotherm model with maximum adsorption percent of 1052.63 mg g-1 of Cr(VI). Post interaction with Cr(VI), the surface characteristic of MIONPs in EPS matrix was evaluated by zeta potential, EDX, ATR-FTIR and XRD.

CONCLUSION

This study ascertained the adsorption of Cr(VI) over EPS stabilized MIONPs whereas the zeta potential and XRD analysis confirmed the presence of reduced Cr(IV) on the adsorbent surface.