Surface Modification of Hydrophobic Resin with Tricaprylmethylammonium Chloride for the Removal of Trace Hexavalent Chromium

Enhancing Uranium Removal with a Titanium-Incorporated Zirconium-Based Metal-Organic Framework

The urgent need to efficiently and rapidly decontaminate uranium contamination in aquatic environments underscores its significance for ecological preservation and environmental restoration. Herein, a series of titanium-doped zirconium-based metal-organic frameworks were meticulously synthesized through a stepwise process. The resultant hybrid bimetallic materials, denoted as NU-Zr-n%Ti, exhibited remarkable efficiency in eliminating uranium (U (VI)) from aqueous solution. Batch experiments were executed to comprehensively assess the adsorption capabilities of NU-Zr-n%Ti. Notably, the hybrid materials exhibited a substantial increase in adsorption capacity for U (VI) compared to the parent NU-1000 framework. Remarkably, the optimized NU-Zr-15%Ti displayed a noteworthy adsorption capacity (∼118 mg g-1) along with exceptionally rapid kinetics at pH 4.0, surpassing that of pristine NU-1000 by a factor of 10. This heightened selectivity for U (VI) persisted even when diverse ions exist. The dominant mechanisms driving this high adsorption capacity were identified as the robust electrostatic attraction between the negatively charged surface of NU-Zr-15%Ti and positively charged U (VI) species as well as surface complexation. Consequently, NU-Zr-15%Ti emerges as a promising contender for addressing uranium-laden wastewater treatment and disposal due to its favorable sequestration performance.

Polyacrylonitrile/Aminated Polymeric Nanosphere Nanofibers as Efficient Adsorbents for Cr(VI) Removal

In this work, polyacrylonitrile/aminated polymeric nanosphere (PAN/APN) nanofibers were prepared by electrospinning of monodispersed aminated polymeric nanospheres (APNs) for removal of Cr(VI) from aqueous solution. Characterization results showed that obtained PAN/APNs possessed nitrogen functionalization. Furthermore, the adsorption application results indicated that PAN/APN nanofibers exhibited a high adsorption capacity of 556 mg/g at 298 K for Cr(VI) removal. The kinetic data showed that the adsorption process fits the pseudo-second order. A thermodynamic study revealed that the adsorption of Cr(VI) was spontaneous and endothermic. The coexisting ions Na⁺, Ca²⁺, K⁺, Cl⁻, NO₃⁻ and PO₄³⁻ had little influence on Cr(VI) adsorption, while SO₄²⁻ in solution dramatically decreased the removal performance. In the investigation of the removal mechanism, relative results indicated that the adsorption behavior possibly involved electrostatic adsorption, redox reaction and chelation. PAN/APN nanofibers can detoxify Cr(VI) to Cr(III) and subsequently chelate Cr(III) on its surface. The unique structure and nitrogen functionalization of PAN/APN nanofibers make them novel and prospective candidates in heavy metal removal.

Optimized removal of hexavalent chromium from water using spent tea leaves treated with ascorbic acid

Spent tea leaves were functionalized with ascorbic acid to obtain treated tea waste (t-TW) to encourage the adsorption of hexavalent chromium from water. The adsorption removal of Cr(VI) was systematically investigated as a function of four experimental factors: pH (2–12), initial Cr(VI) concentration (1–100 mg L⁻¹), t-TW dosage (0–4 g L⁻¹), and temperature (10–50 °C) by following a statistical experimental design. A central composite rotatable experimental design based on a response surface methodology was used to establish an empirical model that assessed the individual and combined effects of factors on adsorptive removal of Cr(VI). The model was experimentally verified and statistically validated then used to predict optimal adsorption removal of Cr(VI) from water. At optimized conditions, ≥ 99% of 1 mg L⁻¹ Cr(VI) can be removed by 4 g L⁻¹ t-TW at a pH of 9. The adsorptive mechanism was assessed by conducting kinetics and equilibrium studies. The adsorption of Cr(VI) by t-TW followed a pseudo-second-order kinetics model (k₂ = 0.001 g mg⁻¹ h⁻¹) and could be described by Langmuir and Temkin isotherms, indicating monolayer adsorption and predominantly adsorbate-adsorbent interactions. The t-TW exhibited a competitive Cr(VI) adsorption capacity of 232.2 mg g⁻¹ compared with the other low-cost adsorbents. These results support the utilization of tea waste for the removal of hazardous metal contaminants from aqueous systems.

DFT investigation of SiO2 nanotube for adsorption of methyl- and propyl-paraben

A huge number of parabens, esters of p-hydroxybenzoic acid, are used in cosmetic and personal care products as preservative substances. Due to their detrimental effects on ecosystem and human health, taking precautionary measures to remove these compounds is an important task regarding the environmental issues. In this study, a silica (SiO2) nanotube has been selected as a novel sensor to adsorb the most common parabens which are methyl paraben and propyl paraben molecules. To this aim, density functional theory (DFT) calculations were used to evaluate the properties for investigated compounds. The calculated adsorption energies of the most stable configurations for methyl parban@SiO2 and propyl paraben@SiO2 complexes were found to be –0.238 and –0.242 eV, respectively. The electronic properties of nanotubes experienced dramatic changes in case of interactions with parabens, which led to declining the HOMO/LUMO energy gap of the nanotube to its original value. Such adsorption could also enhance the electrical conductivity of the nanotubes meaning that the utilized SiO2 nanotube could detect the existence of methyl and propyl parabens molecules in the environment. As a concluding remark, the investigated SiO2 nanotube could work as a possible sensor for hazardous paraben with the importance of environmental issues.

Morphology-Controlled Synthesis of α-Fe2O3 Nanocrystals Impregnated on g-C3N4-SO3H with Ultrafast Charge Separation for Photoreduction of Cr (VI) Under Visible Light

Surface functionalization and shape modifications are the key strategies being utilized to overcome the limitations of semiconductors in advanced oxidation processes (AOP). Herein, the uniform α-Fe₂O₃ nanocrystals (α-Fe₂O₃-NCs) were effectively synthesized via a simple solvothermal route. Meanwhile, the sulfonic acid functionalization (SAF) and the impregnation of α-Fe₂O₃-NCs on g-C₃N₄ (α-Fe₂O₃-NCs@CN-SAF) were achieved through complete solvent evaporation technique. The surface functionalization of the sulfonic acid group on g-C₃N₄ accelerates the faster migration of electrons to the surface owing to robust electronegativity. The incorporation of α-Fe₂O₃-NCs with CN-SAF significantly enhances the optoelectronic properties, ultrafast spatial charge separation, and rapid charge transportation. The α-Fe₂O₃-HPs@CN-SAF and α-Fe₂O₃-NPs@CN-SAF nanocomposites attained 97.41% and 93.64% of Cr (VI) photoreduction in 10 min, respectively. The photocatalytic efficiency of α-Fe₂O₃-NCs@CN-SAF nanocomposite is 2.4 and 2.1 times higher than that of pure g-C₃N₄ and α-Fe₂O₃, respectively. Besides, the XPS, PEC and recycling experiments confirm the excellent photo-induced charge separation via Z-scheme heterostructure and cyclic stability of α-Fe₂O₃-NCs@CN-SAF nanocomposites.

Laser-assisted preparation of Pd nanoparticles on carbon cloth for the degradation of environmental pollutants in aqueous medium

Laser ablation in liquid (LAL), one of the attractive methods for fabrication of nanoparticles, was used for the modification of carbon cloth (CC) by deposition of palladium nanoparticles (Pd NPs); a simple stirring method was deployed to deposit Pd NPs on the CC surface. Characterization techniques viz X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscope (SEM), energy-dispersive X-ray spectrometry (EDS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) were applied to study the surface of the ensuing samples which confirmed that LAL technique managed to fabricate and deposit the Pd NPs on the surface of CC. In addition, the catalytic prowess of the carbon cloth-Pd NPs (CC/Pd NPs) was investigated in the NaBH₄- or HCOOH-assisted reduction of assorted environmental pollutants in aqueous medium namely hexavalent chromium [Cr(VI)], 4-nitrophenol (4-NP), congo red (CR) and methylene blue (MB). The CC/Pd NPs system has advantages such as high stability/sustainability, high catalytic performance and easy reusability.

Integrated Approach for Hazardous Cr(VI) Removal: Reduction, Extraction, and Conversion into a Photoactive Composite, CuO/CuCr2O4

The present study reports on CuO-assisted reduction of Cr(VI) under ambient conditions using sodium borohydride and its complete removal. The confirmation of the reductive removal of Cr(VI) was assisted by powder X-ray diffraction, Fourier transform infrared, scanning electron microscopy, mic absorption spectro, UV-vis, and UV-vis-diffuse reflectance spectroscopy techniques. The analysis revealed that the process involved adsorption of dichromate ion on the surface of copper oxide, reduction of Cr(VI), and precipitation of Cr(III) as its hydroxide. Cr(VI) reduction capacity of CuO was found to be around 27.2 mmol/(g h). The residue collected showed promising reusability for 3 to 4 cycles, and the exhausted residue was finally converted into a black composite, CuO/CuCr₂O₄. The composite showed positive response for the photodegradation of methyl orange. Thus, the current protocol proposed a complete package of cost-effective reduction of Cr(VI) to Cr(III), precipitation into its hydroxide, and the conversion of the residue into a photoactive composite.

Novel functional fiber loaded with carbon dots for the deep removal of Cr(VI) by adsorption and photocatalytic reduction

A novel functional fiber (PAN-CDs) loaded with carbon dots (CDs) with excellent photoreduction and adsorption properties for Cr(VI) was prepared via an amidization reaction between the CDs' carboxyl groups and amine groups on polyacrylonitrile (PAN)-based ion exchange fibers, which could completely preserve the fluorescence properties of the CDs. The photoluminescence (PL), photocatalysis and adsorption properties of PAN-CDs were characterized and analyzed. The PAN-CDs possess high adsorption capacity (297.6 mg/g) and excellent kinetic behavior (attaining adsorption equilibrium in 30 min) for Cr(VI) adsorption. Furthermore, the residual Cr(VI) (approximately 3 mg/L) after adsorption could be removed completely by subsequent photoreduction by the PAN-CDs. The Cr-saturated PAN-CDs could be easily separated by filtering and regenerated, with no observable decay of removal efficiency after five regeneration cycles. In addition, due to the PL quenching action of Cr(VI), the PAN-CDs can also be used as sensor for quantitative detection of trace Cr(VI) in aqueous solution.

Preparation of a core-double shell chitosan-graphene oxide composite and investigation of Pb (II) absorption

The need for new and impactful materials to address the global problem of water pollution continues to be driving force in chemical research. This report presents the preparation of a core-double shell composite consisting of sand base substrate onto which sequential layers of chitosan and graphene oxide (GO) are deposited. The adsorption characteristics of this material for Pb (II) from aqueous solutions is investigated. Specifically, different initial lead concentrations are allowed to reach equilibrium with the chitosan-graphene oxide composites, after which the remaining abundance of lead in the aqueous phase is analyzed by atomic emission spectrometry. In many cases, the resulting equilibrium lead concentration of the treated water reached below the detection limit of the method used (<15 ppb) in less than three hours. Furthermore, the data from the adsorption experiments are plotted for comparison against two different isotherm models. This study suggests that the interaction between lead and the GO-chitosan composite more closely resembles characteristics anticipated by the Freundlich adsorption isotherm than that expected by Langmuir-like properties.

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).

An efficient and reusable quaternary ammonium fabric adsorbent prepared by radiation grafting for removal of Cr(VI) from wastewater

A novel quaternary ammonium polyethylene nonwoven fabric for removing chromium ions from water was prepared via radiation-induced grafting of glycidyl methacrylate and further modification with N,N'-dimethylethylenediamine. The structural and morphological characteristics of the adsorbent were analyzed using Fourier transform infrared spectroscopy (FTIR), thermogravimetry and differential thermogravimetry (TG/DTG), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The influences of several principal factors, including pH value, initial Cr(VI) concentration, contact time, and coexisting anions (including SO₄^2-, CO₃^2-, NO₃^-, PO₄^3-, and Cl^-), on adsorption performance were investigated via batch tests. The results showed that the optimum removal efficiency was 99.2% at pH 3 and the maximum adsorption quantity for Cr(VI) at 25 °C was 336 mg/g. The adsorption kinetic parameters were better fitted with the pseudo-second-order kinetic model, and the equilibrium data were described very well by the Freundlich isotherm model. Furthermore, the as-synthesized adsorbent exhibited excellent regeneration and recyclability while maintaining high adsorption performance after five adsorption/desorption cycles.

Efficient removal of hexavalent chromium from water by an adsorption–reduction mechanism with sandwiched nanocomposites

Hexavalent chromium Cr(vi), one of the most toxic contaminants, is released in the environment due to various anthropogenic activities. This study presents a novel sandwiched nanocomposite synthesized using graphene oxide (GO), manganese dioxide (MnO₂) nanowires, iron oxide (Fe₃O₄) nanoparticles and polypyrrole (PPy) to remove hexavalent chromium ion Cr(vi) from water by an adsorption–reduction mechanism. In the sandwiched nanocomposites, GO provided enough surface area, functional groups, and hydrophilic surface for efficient absorption. Fe₃O₄ nanoparticles with excellent magnetic properties make it easy to separate and recover from water. Under acidic conditions, MnO₂ nanowires act as both template and oxidant to initiate the polymerization of pyrrole monomers on its freshly activated surface to obtain GO/MnO₂/Fe₃O₄/PPy (designated as GMFP) nanocomposite. GMFP could effectively adsorb Cr(vi) through electrostatic attraction, and the adsorbed Cr(vi) ions were partly reduced to trivalent chromium Cr(iii) (62%), resulting in the efficient adsorption and high removal of Cr(vi) from water. Hexavalent chromium adsorption by GMFP is strongly pH dependent and the adsorption kinetics followed the pseudo-second-order model. The Langmuir isothermal model described the adsorption isotherm data well and the maximum adsorption capacity was up to 374.53 mg g⁻¹ at pH 2.0. These experimental results suggested that GMFP had great potential as an economic and efficient adsorbent of hexavalent chromium from wastewater, which has huge application potential.

A sandwiched nanocomposite has been developed to remove hexavalent chromium ion Cr(vi) from water by an adsorption–reduction mechanism.

Surface-Functionalized Porous Lignin for Fast and Efficient Lead Removal from Aqueous Solution

The development of ecofriendly sorbents for fast and efficient removal of heavy metals from aqueous media still remains a significant challenge. Here, we report that this task can be addressed by creating a porous naturally occurring polymer, as illustrated by functionalizing lignin with large numbers of mesopores and functional groups. We show that surface-functionalized porous lignin (SFPL), obtained by a two-step process, has a large surface area of 22.3 m2/g, 12 times that of lignin, and a high density of dithiocarbamate groups (2.8 mmol/g). SFPL was found to exhibit an excellent adsorption performance toward lead ions dissolved in water. For example, 99% of the lead ions from 50 mL of a solution containing 20 mg/L lead ions was removed in just 30 min by 0.01 g of SFPL. The saturated adsorption capacity of SFPL for lead ions was found to be 188 mg/g, which is 13 times that of the original lignin and 7 times that of activated carbon. The adsorption process is endothermic and involves intraparticle diffusion and chemical adsorption between lead ions and the functional groups of SFPL. The cost effectiveness and environmental friendliness of SFPL make it a promising material for removing lead and other heavy metals from wastewater.

Structure regulation of silica nanotubes and their adsorption behaviors for heavy metal ions: pH effect, kinetics, isotherms and mechanism

Silica nanotubes (SNTs) with controlled nanotubular structure were synthesized via an electrospinning and calcination process. In this regard, SNTs were found to be ideal adsorbents for Pb(II) removal with a higher adsorption capacity, and surface modification of the SNTs by sym-diphenylcarbazide (SD-SNTs) markedly enhanced the adsorption ability due to the chelating interaction between imino groups and Pb(II). The pH effect, kinetics, isotherms and adsorption mechanism of SNTs and SD-SNTs on Pb(II) adsorption were investigated and discussed detailedly. The adsorption capacity for Pb(II) removal was found to be significantly improved with the decrease of pH value. The Langmuir adsorption model agreed well with the experimental data. As for kinetic study, the adsorption onto SNTs and SD-SNTs could be fitted to pseudo-first-order and pseudo-second-order model, respectively. In addition, the as-prepared SNTs and SD-SNTs also exhibit high adsorption ability for Cd(II) and Co(II). The experimental results demonstrate that the SNTs and SD-SNTs are potential adsorbents and can be used effectively for the treatment of heavy-metal-ions-containing wastewater.

Integrated lignin-mediated adsorption-release process and electrochemical reduction for the removal of trace Cr(vi)

Hexavalent chromium Cr(vi) is extremely toxic and is classified as a human carcinogen, even at trace concentrations.