Experimental and DFT studies on highly selective separation of indium ions using silica gel/graphene oxide based ion-imprinted composites as a sorbent

A nanofiber with a p-π conjugated structure designed based on the Jahn-Teller effect for the removal of cupric tartrate from wastewater

Copper organic complexes with strong chemical stability and high solubility in water are difficult to eliminate with traditional adsorbents. In this work, a novel amidoxime nanofiber (AO-Nanofiber) with the p-π conjugated structure was fabricated through homogeneous chemical grafting coupled with electrospinning and applied to capture cupric tartrate (Cu-TA) from aqueous solutions. The adsorption capacity of Cu-TA by AO-Nanofiber was 198.4 mg/g at an equilibrium time of 40 min, and the adsorption performance remains basically unchanged after 10 times adsorption-desorption cycles. The capture mechanism of Cu-TA by AO-Nanofiber was jointly validated by experiments and characterization such as Fourier Transform Infrared Spectrometer (FT-IR), X-ray Photoelectron Spectroscopy (XPS), and Density functional theory (DFT) calculations. These results demonstrated that the lone pair of electrons of the N atom from the amino groups and the O atom from hydroxyl groups in the AO-Nanofiber is partially transferred to the 3d orbital of the Cu(II) ions in Cu-TA, leading to the Jahn-Teller distortion of the Cu-TA and the more stable structure of AO-Nanofiber@Cu-TA was generated.

Adsorption of Pd(II) ions by electrospun fibers with effective adsorption sites constructed by N, O atoms with a particular spatial configuration: Mechanism and practical applications

The separation and recovery of palladium from electronic waste (e-waste) are of great significance as they can alleviate environmental pollution and avoid resource loss. Herein, a novel nanofiber modified by 8-hydroxyquinoline (8-HQ-Nanofiber) with adsorption sites co-constructed by N and O atoms of hard bases was fabricated, which has good affinity properties for the Pd(II) ions belonging to soft acid in the leachate of e-waste. The adsorption mechanism of 8-HQ-Nanofiber for Pd(II) ions was revealed from the perspective of molecular level relied on a series of characterizations, such as FT-IR, ss-NMR, Zeta potential, XPS, BET, SEM and DFT. The adsorption of Pd(II) ions on 8-HQ-Nanofiber reached equilibrium within 30 min and the maximum uptake capacity was 281 mg/g at 318.15 K. The adsorption behavior of Pd(II) ions by 8-HQ-Nanofiber was described by the pseudo-second-order and Langmuir isotherm models. The 8-HQ-Nanofiber exhibited relatively good adsorption performance after 15 times of column adsorption. Finally, based on hard and soft acids and bases (HSAB) theory, a strategy to regulate the Lewis alkalinity of adsorption sites by specific spatial structures is proposed, which provides a new direction for the design of adsorption sites.

Computational and Experimental Investigation of the Selective Adsorption of Indium/Iron Ions by the Epigallocatechin Gallate Monomer

Selective recovery of indium has been widely studied to improve the resource efficiency of critical metals. However, the interaction and selective adsorption mechanism of indium/iron ions with tannin-based adsorbents is still unclear and hinders further optimization of their selective adsorption performance. In this study, the epigallocatechin gallate (EGCG) monomer, which is the key functional unit of persimmon tannin, was chosen to explore the ability and mechanism of selective separation/extraction of indium from indium-iron mixture solutions. The density functional theory calculation results indicated that the deprotonated EGCG was easier to combine with indium/iron cations than those of un-deprotonated EGCG. Moreover, the interaction of the EGCG-Fe(III) complex was dominated by chelation and electrostatic interaction, while that of the EGCG-In(III) complex was controlled by electrostatic interactions and aromatic ring stacking effects. Furthermore, the calculation of binding energy verified that EGCG exhibited a stronger affinity for Fe(III) than that for In(III) and preferentially adsorbed iron ions in acidic or neutral solutions. Further experimental results were consistent with the theoretical study, which showed that the Freundlich equilibrium isotherm fit the In(III) and Fe(III) adsorption behavior very well, and the Fe(III) adsorption processes followed a pseudo-second-order model. Thermodynamics data revealed that the adsorption of In(III) and Fe(III) onto EGCG was feasible, spontaneous, and endothermic. The adsorption rate of the EGCG monomer for Fe(III) in neutral solution (1:1 mixed solution, pH = 3.0) was 45.7%, 4.3 times that of In(III) (10.7%). This study provides an in-depth understanding of the relationship between the structure of EGCG and the selective adsorption capacity at the molecular level and provides theoretical guidance for further optimization of the selective adsorption performance of structurally similar tannin-based adsorbents.

Recovery, regeneration and sustainable management of spent adsorbents from wastewater treatment streams: A review

Adsorption is the most widely adopted, effective, and reliable treatment process for the removal of inorganic and organic contaminants from wastewater. One of the major issues with the adsorption-treatment process for the removal of contaminants from wastewater streams is the recovery and sustainable management of spent adsorbents. This review focuses on the effectiveness of emerging adsorbents and how the spent adsorbents could be recovered, regenerated, and further managed through reuse or safe disposal. The critical analysis of both conventional and emerging adsorbents on organic and inorganic contaminants in wastewater systems are evaluated. The various recovery and regeneration techniques of spent adsorbents including magnetic separation, filtration, thermal desorption and decomposition, chemical desorption, supercritical fluid desorption, advanced oxidation process and microbial assisted adsorbent regeneration are discussed in detail. The current challenges for the recovery and regeneration of adsorbents and the methodologies used for solving those problems are covered. The spent adsorbents are managed through regeneration for reuse (such as soil amendment, capacitor, catalyst/catalyst support) or safe disposal involving incineration and landfilling. Sustainable management of spent adsorbents, including processes involved in the recovery and regeneration of adsorbents for reuse, is examined in the context of resource recovery and circular economy. Finally, the review ends with the current drawbacks in the recovery and management of the spent adsorbents and the future directions for the economic and environmental feasibility of the system for industrial-scale application.

Activated carbon fiber modified with hyperbranched polyethylenimine and phytic acid for the effective adsorption and separation of In(iii)

The PA–HPEI–OACF constructed with PA, HPEI, and ACF displays excellent performance in the adsorption and separation of In(iii).