Poly( m -phenylenediamine) functionalized Calotropis gigantea fiber for coupled adsorption reduction for Cr(VI)

Efficient removal of hexavalent chromium by nano-cerium-based adsorbent: The critical role of valence state and oxygen vacancy

Cerium-based adsorbents have been gradually used for the adsorption removal of highly toxic Cr(VI) from wastewater due to their low toxicity and wide working pH. However, the intrinsic properties of adsorbents contribute significantly to their adsorption performance, and the relationship between them needs to be clarified. Herein, series of nano-cerium based adsorbents (Ce@Cs) with different surface defects and Ce(III) content were prepared to explore their effects on the Cr(VI) adsorption capacity. Results showed that the optimal Ce@C performed well over a wide pH range of 2.0-12.0, and the calculated Cr(VI) adsorption capacity reached 302.43 mg/g at 45 ℃. Ce(III) and surface defects in cerium-based adsorbents exhibited an important influence on the Cr(VI) adsorption performance of Ce@Cs, and their contents showed a good positive correlation with the Cr adsorption capacity (R2 =0.988 and 0.827). A series of evidences confirmed that the generated Ce(III) and oxygen vacancies could provide more sufficient coordination number to promote Cr(VI) complexation with Ce@Cs and lower the impedance of Ce@Cs to improve the reduction of Cr(VI) to low-toxic Cr(III). This work provides new insights into the Cr(VI) adsorption using cerium-based adsorbents, which helps to improve their potential in the purification of Cr(VI)-containing wastewater.

Insights into the Applications of Natural Fibers to Metal Separation from Aqueous Solutions

There is a wide range of renewable materials with attractive prospects for the development of green technologies for the removal and recovery of metals from aqueous streams. A special category among them are natural fibers of biological origin, which combine remarkable biosorption properties with the adaptability of useful forms for cleanup and recycling purposes. To support the efficient exploitation of these advantages, this article reviews the current state of research on the potential and real applications of natural cellulosic and protein fibers as biosorbents for the sequestration of metals from aqueous solutions. The discussion on the scientific literature reports is made in sections that consider the classification and characterization of natural fibers and the analysis of performances of lignocellulosic biofibers and wool, silk, and human hair waste fibers to the metal uptake from diluted aqueous solutions. Finally, future research directions are recommended. Compared to other reviews, this work debates, systematizes, and correlates the available data on the metal biosorption on plant and protein biofibers, under non-competitive and competitive conditions, from synthetic, simulated, and real solutions, providing a deep insight into the biosorbents based on both types of eco-friendly fibers.

Evaluation of Adsorption Mechanism of Chromium(VI) Ion Using Ni-Al Type and Ni-Al-Zr Type Hydroxides

To evaluate the feasibility of nickel–aluminum (the Ni2+:Al3+ molar ratios of 1.0:1.0 and 1.0:2.0 are denoted as NA11 and NA12, respectively) and nickel–aluminum–zirconium type (the Ni2+:Al3+:Zr4+ molar ratios of 0.9:1.0:0.09 and 0.9:2.0:0.09 are denoted as NAZ1 and NAZ2, respectively) hydroxides for Cr(VI) removal from aqueous media, the adsorption capability and adsorption mechanism of Cr(VI) using the above-mentioned adsorbents were investigated in this study. The quantity of Cr(VI) adsorbed onto NA11, NA12, NAZ1, and NAZ2 was 25.5, 25.6, 24.1, and 24.6 mg g−1, respectively. However, the quantity of aluminum (base metal) released from NA11 (approximately 0.14 mg g−1) was higher than that from NAZ1 (approximately 1.0 µg g−1), indicating that NAZ1 was more suitable for Cr(VI) removal than NA11. In addition, the effects of pH, contact time, and temperature on the adsorption of Cr(VI) were evaluated. Moreover, to elucidate the adsorption mechanism of Cr(VI) using NA11 and NAZ1, the elemental distribution, X-ray photoelectron spectrometry spectra, and ion exchange capability were also determined. Cr(VI) adsorbed onto the NAZ1 surface was easily desorbed using a sodium hydroxide solution under our experimental conditions. The information regarding this study can be useful for removing Cr(VI) from aqueous media.

Chemical Constituents and Uses of Calotropis Procera and Calotropis Gigantea – A Review (Part I – The Plants as Material and Energy Resources)

The traditional and current use of Calotropis procera and C. gigantea, two soft-wooded, xerophytic shrubs of the family Apocynaceae, are reviewed against the background of the plants' chemical constituents and their biological properties. The focus is on the usage of the plants for building materials, natural pesticides, animal feed and bioremediative purposes.

Synthesis of core-shell UiO-66-poly(m-phenylenediamine) composites for removal of hexavalent chromium

The present research developed a direct in situ heterogeneous method to synthesize UiO-66-poly(m-phenylenediamine) core-shell nanostructures by inducing assembly of m-phenylenediamine radical on UiO-66 surfaces. The strong interaction between negative charged UiO-66 and positive radical from the oxidation of monomer is the major driving force. The produced UiO-66-poly(m-phenylenediamine) composites exhibited a distinct core-shell morphology with controllable surface features. The UiO-66₁-PmPD_0.5 showed a uniform PmPD shell with a thickness of 40-60 nm and the nanocomposite exhibited a high specific surface area of 319.77 m² g^-1. Moreover, the Cr(VI) adsorption amount of the polymeric shell in the nanocomposites can reach as high as 745 mg g^-1, far beyond the performance of the original PmPD. The adsorption tends to be equilibrium within 300 min. This research opens a hopeful window for facile and large-scale fabrication of core-shell nanostructures with controllable core-shell configuration, exhibiting high prospect in heavy metal removal from water.

Reusable and removable PmPD/PVA membrane for effective Cr(vi) adsorption and reduction

The PmPD/PVA membranes with facile reusability for and highly effective removal of Cr(vi).

Facile Functionalization of Natural Peach Gum Polysaccharide with Multiple Amine Groups for Highly Efficient Removal of Toxic Hexavalent Chromium (Cr(VI)) Ions from Water

The development of low-cost adsorbent with excellent adsorption property remains a big challenge. Herein, the functionalization of natural peach gum polysaccharide (PGP) with multiple amine groups for the removal of toxic Cr(VI) ions from water was studied. The obtained PGP-NH₂ gel exhibited high-removal efficiency (>99.5%) toward Cr(VI) ions, especially with relatively low initial concentration of Cr(VI) ions (≤250 mg/L). The influences of pH, ionic strength, contact time, initial concentration, and temperature on the adsorption of Cr(VI) ions were systematically investigated. The PGP-NH₂ gel showed rapid adsorption rate and could reach adsorption equilibrium within about 40 min. The Cr(VI) ion uptake process could be described by pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity of PGP-NH₂ gel could reach 188.32 mg/g. Thermodynamic investigation results indicated the spontaneous and exothermic characteristic of the uptake process. Moreover, the PGP-NH₂ gel also exhibited favorable reusability, and 135.52 mg/g of adsorption capacity was retained even after being reused for five times. Considering its low cost and superior uptake property, the PGP-NH₂ gel holds a great promise for employing as an adsorbent to treat Cr(VI) ion-containing wastewater.

Adsorption of Hexavalent Chromium by Eucalyptus camaldulensis bark/maghemite Nano Composite

In the present study, Eucalyptus camaldulensis bark/maghemite composite (ECMC) was used for potential application as a low-cost adsorbent for the removal of Cr(VI) from aqueous solution. The structural characterization, morphology and elemental analysis of ECMC were performed by Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray (EDX) and X-ray Diffraction (XRD). The effects of various independent parameters, contact time, initial Cr(VI) concentration, temperature, pH, and adsorption were investigated. It was found that the adsorption capacity of ECMC increases with increasing Cr(VI) concentration and temperature. The optimum pH was found to be 2 for the removal of Cr(VI) by ECMC. The adsorption capacity was found to be 70.1 mg/g with 0.1 g ECMC at pH 2 and 30 °C. Additionally, 10 and 50 mg/L Cr(VI) were removed from 100 mL aqueous solution by 0.1 g ECMC with 99 % and 93.46 % removal efficiencies, respectively. Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Jovanovic, Smith, Koble Korringen, Vieth-Sladek and Sips Isotherm Models were applied to the experimental data to understand the adsorption mechanism better. The Freundlich Isotherm Model described the adsorption process better (R2 = 0.991) among the other isotherms studied.