Advances in Sorptive Removal of Hexavalent Chromium (Cr(VI)) in Aqueous Solutions Using Polymeric Materials

Surfactant-modified zein nanoparticles adsorbents for ultrafast and efficient removal of Cr(VI)

The adsorption and removal of heavy metal ions Cr(VI) is of great significance for human health and ecological environment. Here, an ultrafast and high efficient adsorbent for Cr(VI) was developed based on cetyltrimethylammonium bromide (CTAB)-modified zein nanoparticles (C-ZNPs). In comparison to pristine zein nanoparticles (ZNPs) (11.199 m2 g-1), the surfactant-modified C-ZNPs exhibited larger specific surface area (17.002 m2 g-1). Moreover, C-ZNPs had superior dispersion and more positive charge distribution, which contributed to the improvement for adsorption performance. The results showed that the saturated adsorption of Cr(VI) was reached up to 192.27 mg/g using the C-ZNPs nanosorbent at T = 298 K, pH = 4, t = 10s, and C0 = 125 mg/L. The removal rate was significantly faster than that reported natural polymer-based adsorbents. The experimental values were followed Freundich isothermal model and pseudo-second-order kinetic model, indicating that the adsorption occurred primarily through a multimolecular layer adsorption process, with a strong emphasis on chemisorption. Mechanistic investigations further revealed that the adsorption of Cr(VI) onto C-ZNPs was mediated by various interactions, including electrostatic attraction, complexation, and ion exchange. These findings provide insights into the efficient removal of Cr(VI) by C-ZNPs and suggest potential applications in water treatment and environmental remediation.

Remediation of chromium contaminated water and soil by nitrogen and iron doped biochars

Chromium (Cr) is a toxic and redox-sensitive contaminant that has accumulated in water and soil systems, becoming a serious issue worldwide. Producing novel remedial materials with enhanced removal efficiency from plentiful available sources is a pleasing aspect for Cr removal. This review explores valuable insights into the production of nitrogen doped biochar (N/BC), iron doped biochar (Fe/BC), and iron‑nitrogen doped biochar (Fe-N/BC) and their application for Cr (trivalent (Cr(III)) and hexavalent (Cr(VI)) removal. Specifically, this review focuses on conferring knowledge about producing environmentally friendly N and Fe doped BCs with enhanced surface functionalities, physicochemical properties, and holding capacities for removing Cr(VI) through adsorption and reduction. Affecting factors for Cr(VI) removal by N/BC, Fe/BC, and Fe-N/BC through reviewing the literature on the reaction system pH, mass transfer driving forces, effect of coexisting ions, BC production conditions, and redox potential are overviewed. Notably, isotherm and kinetic models and removal mechanisms of Cr(VI) by N/BC, Fe/BC, and Fe-N/BC with the assistance of characterization analyses, experimental results, and computational modeling methods are explored. Finally, the regeneration, cost evaluation, and environmental implications, as well as the real-world applications and environmental risks of N/BC, Fe/BC, and Fe-N/BC are discussed. This review shows that N and Fe doped BCs are remedial materials that can potentially remediate Cr(VI) contaminated water and soil.

Preparation and characterization of β-cyclodextrin capped magnetic nanoparticles anchored on cellulosic matrix for removal of cr(VI) from mimicked wastewater: Adsorption and kinetic studies

Hexavalent Chromium (Cr(VI)) is essential in many industrial processes. However, it finds its way into water bodies, posing health problems, including lung cancer and the inhibition of DNA and RNA in biological systems. Several chemical and traditional water purification methods have been developed in the past, but most are expensive, tedious and ineffective. This study aimed to prepare and characterize a low-cost hybrid adsorbent, β-Cyclodextrin capped magnetic nanoparticles anchored on a cellulosic matrix (CNC-Fe3O4NP-CD). The characterization techniques confirmed the integration of CNCs, Fe3O4NP and CD into the prepared CNC-Fe3O4NP-CD nanocomposite adsorbent. The adsorbent was employed in batch adsorption experiments by varying adsorption parameters, including solution pH, adsorbent dosage, initial Cr(VI) concentration, and contact time. From the findings, the nanocomposite adsorbent achieved a maximum Cr(VI) removal efficiency of 97.45%, while the pseudo-second-order kinetic model best fitted the experimental data with high linear regression coefficients (R2 > 0.98). The Elovich model indicated that the adsorption process was driven by chemisorption on heterogeneous surface sites, with initial sorption rates surpassing desorption rates. These findings established that CNC-Fe3O4NP-CD presents high efficiency for Cr(VI) removal under acidic pH, offering the potential for optimization and application in real-world wastewater treatment.

Synchronous removal of oxytetracycline and Cr(Ⅵ) in Fenton-like photocatalysis process driven by MnFe2O4/g-C3N4: Performance and mechanisms

Complex wastewater has more complicated toxicity and potential harm to organisms, and synchronous REDOX of complex pollutants in wastewater has always been a bottleneck in the development of advanced oxidation technology. Herein, a Fenton-like photocatalytic system (MnFe2O4/g-C3N4 heterojunction composites) was established to simultaneously remove oxytetracycline (OTC) and Cr(Ⅵ) in this study. The MnFe2O4/g-C3N4 heterojunction composites exhibited outstanding catalytic performances for OTC and Cr(Ⅵ) removal, and more than 90% of OTC and nearly 100% of Cr(Ⅵ) were simultaneously removed within 1 min photocatalysis. The photo-generared electrons and holes played significant roles in Cr(Ⅵ) reduction and OTC degradation, respectively. Moreover, the heterojunction formed between g-C3N4 and MnFe2O4 effectively accelerated the separation and migration of photogenerated carriers. The OTC degradation was mainly initiated by cracking of benzene rings, degradation of substituents, and removal of groups such as -OH, -NH2, -CH3, and -CONH2, resulting in generation of small molecular substances; Cr(Ⅲ) was the main reduction product of Cr(Ⅵ). Meanwhile, the MnFe2O4/g-C3N4 heterojunction composites also exhibited excellent stability and reusability in removal of OTC and Cr(Ⅵ).

N-Phenyl acrylamide-incorporated porous silica-bound graphene oxide sheets with excellent removal capacity for Cr(iii) and Cr(vi) from wastewater

The sophisticatedly altered Hummer's and sol-gel procedures were applied for the synthesis of graphene oxides and porous silica monolith particles respectively. The Fischer esterification protocol was used for coupling silica monoliths with graphene oxides. A N-phenyl acrylamide-incorporated porous polymer was synthesized at the surface of composites via reversible addition fragmentation chain transfer polymerization. The composition was confirmed by Fourier transform infra-red spectroscopy, FE-SEM, X-ray diffraction, zeta potential (zeta pH), Brunauer-Emmett-Teller (BET/BJH) analysis, and EDAX analysis. The resulting polymer-bound composite efficiently removed Cr(vi) and Cr(iii) from waste water. Adsorption parameters such as contact time, pH effect, temperature, and adsorbent and adsorbate concentration were optimized for the optimal output of the composite. The kinetic and equilibrium models were applied to the adsorption of Cr(vi) and Cr(iii) at the adsorbent surface. The maximum adsorption capacity (qe) of Cr(vi) and Cr(iii) was found to be 298.507 mg g-1 and 401.874 mg g-1, respectively, using the same initial concentration of Cr(vi) and Cr(iii) [10-60 ppm]. The adsorption data of both states of the Cr-metal followed the pseudo 2nd-order kinetic model with regression values of 0.996 ∼ Cr(vi) and 0.999 ∼ Cr(iii) at ambient temperature. Similarly, the adsorption data of Cr(vi) best fit into the Langmuir adsorption isotherm (R2 = 0.972) while that of Cr(iii) followed the Freundlich model (R2 = 0.983).

Silk/Polyamidoamine Membranes for Removing Chromium VI from Water

Polyamidoamine hydrogels prepared by the radical post-polymerization of α,ω-bisacrylamide-terminated M-AGM oligomers, in turn obtained by the polyaddition of 4-aminobutylguanidine with N,N'-methylenebisacrylamide, were reinforced with raw silk fibers, which can establish covalent bonds with the polyamidoamine matrix via reaction of the amine groups in the lysine residues with the acrylamide terminals of the M-AGM oligomer. Silk/M-AGM membranes were prepared by impregnating silk mats with M-AGM aqueous solutions and subsequent crosslinking by UV irradiation. The guanidine pendants of the M-AGM units imparted the ability to form strong but reversible interactions with oxyanions, including the highly toxic chromate ions. The potential of the silk/M-AGM membranes to purify Cr(VI)-contaminated water down to the drinkability level, that is, below 50 ppb, was tested by performing sorption experiments both in static (Cr(VI) concentration 20-2.5 ppm) and flow conditions (Cr(VI) concentration 10-1 ppm). After static sorption experiments, the Cr(VI)-loaded silk/M-AGM membranes could easily be regenerated via treatment with a 1 M sodium hydroxide solution. Dynamic tests performed using two stacked membranes and a 1 ppm Cr(VI) aqueous solution reduced Cr(VI) concentration down to 4 ppb. Remarkably, the use of renewable sources, the environmentally friendly preparation process, and the goal achieved meet eco-design requirements.