Kinetics, isotherm, and optimization of the hexavalent chromium removal from aqueous solution by a magnetic nanobiosorbent

Green low-cost synthesis of zero-valent iron nanoparticles from Palm Petiole Extract for Cr(VI) removal from water

One of the hottest research topics over the last decades was the valorization or/and recycling of agro-industrial wastes into different valuable liquid or solid products, which is considered a sustainable and low-cost approach. In this study, we developed zero-valent iron nanoparticles from Palm Petiole Extract (P-NZVI) using a green and straightforward approach. The as-synthesized P-NZVI was used to adsorb Cr(VI) in water. The physico-chemical characterizations of P-NZVI, including the particle size, crystalline structure, surface area, morphology, and functional groups, were investigated via several techniques such as UV-vis spectroscopy, SEM, TEM, XRD, FTIR, AFM, DLS, pHZPC measurement, and BET analysis. The adsorption performance of P-NZVI was studied under different operational parameters, including pollutant concentration, pH, temperature, and adsorbent mass. The adsorption rate was found to be 89.3% within 40 min, corresponding to the adsorption capacity of 44.47 mg/g under the following conditions: initial Cr(VI) concentration of 40 mg/L, pH 5, and a P-NZVI dosage of 1 g/L. It was found that the adsorption pattern follows the Langmuir and the pseudo-second-order kinetic models, indicating a combination of monolayer adsorption and chemisorption mechanisms. The thermodynamic study shows that the adsorption process is endothermic and spontaneous. The reusability of P-NZVI was carried out four times, showing a slight decrease from 89.3 to 87%. These findings highlight that P-NZVI's could be an effective green adsorbent for removing Cr(VI) or other types of toxic pollutants from water.

Modified Ordered Mesoporous Carbons for Cr(VI) Removal from Wastewater

The pristine CMK-3 carbon was ozonized and then chemically modified by the Zr and Fe compounds. The synthesized carbonaceous materials were characterized with physicochemical methods. The obtained carbons had a high specific surface area (ca. 800 m2 g-1) and an acidic surface. The Cr(VI) adsorption properties of the oxidized and Zr/Fe-modified carbon were studied. The highest static adsorption capacity towards Cr(VI) ions was evaluated for Zr/Fe-modified carbon (50.1 mg g-1) at pHeq = 5.8 after 240 min. The Elovich and Freundlich theoretical models were well fitted to the Cr(VI) adsorption kinetic and isotherm data on the Zr/Fe-modified CMK-3-type carbon. The leading Cr(VI) adsorption mechanism acting on the Zr/Fe-modified carbon was probably based on the redox reactions between Cr(VI) and the carbonaceous surface. Electrostatic attraction and surface complexation processes could also occur during Cr(VI) adsorption in the studied system. The effect of the competitive anions on the concentration level, such as in the galvanic wastewater for Cr(VI) adsorption onto chemically modified carbon, was negligible. The HCl and HNO3 media were insufficient for the Zr/Fe-modified carbon regeneration after Cr(VI) adsorption. The Zr/Fe-modified carbon was successfully applied for the efficient (>90%) Cr(VI) removal from the model galvanic wastewater.

Surface Engineering Design of Nano FeS@Stenotrophomonas sp. by Ultrasonic Chemical Method for Efficient U(VI) and Th(IV) Extraction

Nano-FeS has great potential for use in the management of radioactive contaminants. In this paper, we prepared a FeS@Stenotrophomonas sp. composite material by ultrasonic chemistry, and it showed excellent removal of uranium and thorium from the solution. Through optimization of the experimental conditions, it was found that the maximum adsorption capacities for uranium and thorium reached 481.9 and 407.5 mg/g for a composite made with a synthetic ratio of 1:1, pH 5 and 3.5, respectively, for U and Th, and sonication for 20 min. Compared with those of FeS or Stenotrophomonas alone, the removal capacity was greatly improved. The results of a mechanistic study indicated that efficient removal of the uranium and thorium was due to ion exchange, reduction, and microbial surface adsorption. FeS@Stenotrophomonas sp. could be applied to U(VI) and Th(IV) extraction for radioactive water.

Eco-benign preparation of biosorbent using Momordica Charantia for the efficient removal of Cr(VI) ions from wastewater

Environmental pollution is the major issue of 21st century. The toxic industrial effluents are crucially damaging aquatic environment, in the form of heavy metals, dyes and acids. The heavy metals are toxic, carcinogenic, non-degradable and therefore must be removed to save natural environment and human health. Batch sorption efficiency of Momordica Charantia L. stem and root (MCS and MCR) was studied for Cr(VI) metal ions removal under controlled adsorption parameters. The adsorbed and residual concentration of Cr(VI) was determined by atomic absorption spectrophotometer (AAS). The adsorbent surface morphology was determined by FTIR, BET, SEM and elemental analysis by EDX. The Freundlich and Langmuir equilibrium isotherm and pseudo 1st and 2nd order kinetic models were studied to understand bio-sorption mechanism. The Freundlich isotherm and pseudo 2nd order kinetic was best fitted model for MCS and MCR bio-sorption process. The maximum Langmuir adsorption capacity (q max) was 312.50 and 400 (mg/g) for MCS and MCR respectively. The trend of removal efficiency (%) and metal uptake (q e) was in order as MCS > MCR. All data was statistically analyzed using mean values ± standard deviation (SD). In conclusion, MCS and MCR are suggested as excellent sorbents for the elimination of numerous contaminants from the wastewater.

A new organosilane passivation agent prepared at ambient temperatures to inhibit pyrite oxidation for acid mine drainage control

Acid mine drainage (AMD) is a significant environmental problem caused by the oxidation of pyrite and other metal sulfide ores. Organosilane passivation is an effective strategy to inhibit pyrite oxidation. However, synthetic organic silane passivation agents generally require temperatures of 50-80 °C, resulting in high energy consumption and high synthesis cost. In this study, a 3-aminopropyltrimethoxysilane -methyltrimethoxysilane (APS-MTMS) coatings was successfully prepared at ambient temperatures of 15-40 °C as a passivation agent to inhibit pyrite oxidation. Chemical leaching tests were used to study the inhibition performance of APS-MTMS for pyrite oxidation. The experimental results showed that the release of the total Fe from APS-MTMS-coated pyrite was 11.31 mg/L after chemical oxidation for 7 hours, and the passivation rate can reach 77.78%. The contact angle of the APS-MTMS-coated pyrite was significantly larger (140.4°) than that of the bare pyrite (58.8°), indicating that APS-MTMS prompted the formation of a superhydrophobic surface of pyrite, improving the oxidation resistance. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were applied to probe the interaction mechanism of APS-MTMS with pyrite. The results indicated that APS accelerated the Si-O-Si formation by amino protonation and enriched a crosslinked network of Si-O-Si and Fe-O-Si on the pyrite surface to prevent pyrite oxidation. This study provides a novel method for preparing organosilane passivation materials at ambient temperatures for AMD control.

Advances in biological methods for the sequestration of heavy metals from water bodies: A review

Pollution is a major concern of the modern era as it affects all the principal aspects of the environment, especially the hydrosphere. Pollution with heavy metals has unequivocally threatened aquatic bodies and organisms as these metals are persistent, non-biodegradable, and toxic. Heavy metals tend to accumulate in the environment and eventually in humans, which makes their efficient removal a topic of paramount importance. Treatment of metal-contaminated water can be done both via chemical and biological methods. Where remediation through conventional methods is expensive and generates a large amount of sludge, biological methods are favoured over older and prevalent chemical purification processes because they are cheaper and environment friendly. The present review attempts to summarise effective methods for the remediation of water contaminated with heavy metals. We concluded that in biological techniques, bio-sorption is among the most employed and successful mechanisms because of its high efficacy and eco-friendly nature.

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

Waste plastic filter modified with polyaniline and polypyrrole nanoparticles for hexavalent chromium removal

Chromium (Cr) is a toxic heavy metal for environmental compartments and human health. In this study, waste polypropylene hollow filters (PPF) with an optimal pore size of 5 μm were amino-functionalized with an optimized amount of polyaniline (PANI) and polypyrrole (PPy) as an adsorbent for removing Cr (VI). The adsorbent was characterized by scanning electron microscope, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and the Brunauer-Emmett-Teller method, showing the successful polymerization of co-polymer on the surface of PPF and increasing the surface area up to 15.08 m² g^-1. A Box-Behnken design was applied by a quadratic model with 99.15% accuracy, revealing a significant impact of the initial concentration of Cr (VI) on the removal efficiency. Dynamic adsorption was conducted in a continuous and semi-continuous system with over 99% removal efficiency for various initial concentrations of Cr(VI). The fitted data showed that the adsorption process followed the pseudo-second-order kinetics and Langmuir isotherm models at the optimum pH of 2 with the predicted maximum adsorption capacity of 510.9 mg g^-1 of PANI+PPy, which was significantly higher than some reported adsorbents. The effect of coexisting cations (Cu²⁺, Ni²⁺, and Zn²⁺) and anions (SO₄^2-, Cl^- and NO₃^-) on the removal efficiency revealed selective adsorption of Cr(VI) by the adsorbent. The produced adsorbent was capable of removing 76.6% of Cr(VI) from real electroplating wastewater. Regeneration of the adsorbent was performed by NaOH 1 mol L^-1 up to three cycles with a 20% reduction in adsorption performance. All data showed that PPF@PANI+PPy was a promising adsorbent for Cr(VI) removal from aqueous solutions and real-world wastewater.

Hexavalent chromium adsorption on virgin, biochar, and chemically modified carbons prepared from Phanera vahlii fruit biomass: equilibrium, kinetics, and thermodynamics approach

A novel biosorbent Phanera vahlii fruit biomass (PVF) and its biochar and chemically modified forms were studied for the elimination of Cr(VI) from synthetic solutions. Biosorbents were characterized through BET, FTIR, FESEM, EDX, and TGA technique. The parameters influencing biosorption were optimized and found as pH 2.0, temperature 303 K, initial metal concentration 500 mg/L, and biosorbent dosage 0.5 g/L. The ideal contact time was 180 min for all biosorbents. Freundlich isotherm was found to have good correlation with investigational data, which indicated that biosorption takes place in multiple layer style. Langmuir adsorption isotherm yielded the highest biosorption capacity (Q_o) to be 159.1, 225.1, 244.1, and 278.5 mg/g for Phanera vahlii fruit biomass, Phanera vahlii biochar, Phanera vahlii phosphoric acid activated carbon, and Phanera vahlii zinc chloride activated carbon, respectively. Experimental data had good correlation with pseudo-second-order kinetic model fitted. Thermodynamic studies indicated the biosorption process to be spontaneous, stable, and endothermic. Thus, it was concluded that Phanera vahlii fruit biomass and the derived activated carbons are promising biosorbents for adsorption of chromium from aqueous solutions. Graphical abstract.

Holographic Performance of Azo-Carbazole Dye-Doped UP Resin Films Using a Dyeing Process

For the practical application of dynamic holography using updatable dyed materials, optical transparency and an enlarged sample size with a uniform dispersion of the dye and no air bubbles are crucial. The holographic films were prepared by applying a dyeing method comprising application, curing, dyeing, and washing to an unsaturated polyester (UP) resin film. The unsaturated polyester (UP) resin film with high optical transparency was dyed with a 3-[(4-cyanophenyl)azo]-9H-carbazole-9-ethanol (CACzE) (azo-carbazole) dye via the surfactant, polyoxyethylene (5) docosyl ether, in an aqueous solution. The amount of dye uptake obtained via the dyeing process ranged from 0.49 to 6.75 wt.%. The dye concentration in the UP resin was proportional to the dye concentration in the aqueous solution and the immersion time. The UP resin film with 3.65 wt.% dye exhibited the optical diffraction property η₁ of 0.23% with a response time τ of 5.9 s and a decay time of 3.6 s. The spectroscopic evaluation of the UP resin film crosslinking reaction and the dyeing state in the UP resin film are discussed. Furthermore, as an example of its functionality, the dynamic holographic properties of the dye-doped UP resin film are discussed.