Design of Zr-MOFs by Introducing Multiple Ligands for Efficient and Selective Capturing of Pb(II) from Aqueous Solutions

A versatile alginate aerogel with spatially separated sorption sites for simultaneously and collaboratively scavenging Pb(II) and tetracycline in wastewater: Insight into behavior and mechanisms in the mixture system

Alleviating combined pollution caused by heavy metals and antibiotics is of great significance for ecological sustainability and human health. It is still quite challenging to simultaneously and efficiently scavenge both pollutants due to their completely different physicochemical properties and the fierce competition between multi-pollutants faced by traditional adsorbents. In present work, a novel alginate-based aerogel microbead (GO/Fe3+-Ca2+-Alg) with specific sorption sites toward these two sorts of pollutants was fabricated via a 'multi-site coupling' strategy. It was found that multifarious sorption sites in the composite synergistically enhanced removal performance of Pb(II) and TC. The adsorption process of Pb(II) was better described by pseudo-second-order kinetics model (R2 = 0.968-0.989) and Langmuir isotherm model (R2 = 0.966-0.996). The maximum adsorption capacity of Pb(II) and TC in their individual systems was 268.04 and 1664.04 mg/g, respectively, superior to most reported sorption materials. Interestingly, in Pb(II)-TC binary system, Pb(II) capture was enhanced by co-existing TC and its adsorption capacity was positively correlated with concentration of co-existing TC, assigning to the formation of ternary complex (adsorbent-TC-Pb(II) or adsorbent-Pb(II)-TC). However, the removal of TC was enhanced with 10 mg/L Pb(II), and hindered with 20-80 mg/L Pb(II) because of the competition effect of Pb(II) and TC. Sequential adsorption as well as Zeta potential experiments were further performed to verify mutual interaction between Pb(II) and TC. More importantly, the as-designed material was applied in treatment of simulated aquaculture wastewater with removal rates above 80 %, showing its great potential for simultaneous and collaborative elimination of Pb(II) and TC in complex wastewater. This work provided unique insights into designing integrated adsorbents for wastewater bearing heavy metals and antibiotics.

Selective Trapping of In(III) Ions under σ-π* Bond Synergistic Effects by Modulating Lewis Basicity of Capture Sites on Nanofibers

Effectively selective recovery and separation of indium from alternative resources are of great environmental and economic significance. Although adsorption plays a critical role in this process, the design of highly selective capture sites remains a great challenge. Inspired by molecular orbital theory and hard and soft acids and bases theory (HSAB), we recognize that the nonequivalent orbital hybridization of In(III) ions renders them susceptible to deformation, exhibiting softer Lewis acidity. Herein, the thioacetamide-modified nanofiber (TAANF), with the O═C─NH─C═S as the capture sites, was prepared through an electrospinning technique combined with chemical modification. As expected, the O═C─NH─C═S exhibits softer Lewis basicity via modulated Lewis basicity of C═S by C═O, which better matches the Lewis acidity of In(III) ions to improve affinity. Adsorption studies showed that TAANF exhibited excellent properties for In(III) ions, especially in terms of selectivity; the selectivity coefficients range from 20 to 276 for K(I), Ca(II), Na(I), Mg(II), Mn(II), Zn(II), and Fe(II) ions in a multicomponent system. Furthermore, the capture mechanism indicates that In(III) ions not only can accept electrons from capture sites but also donate rich d2 orbit electrons to the π orbitals of capture sites, as demonstrated by XAFS, XPS, and DFT. This enables selective capture of In(III) ions by forming a stable six-membered ring under the synergistic effect of σ and feedback π bonds (σ-π*). Finally, this work provides a strategy to design highly selective capture sites and holds promise for recovering In(III) ions from alternative sources.

Phosphorylated chitosan-lignin composites for efficient removal of Pb(II) and Cu(II) from aqueous environments and sustainable upcycling of spent adsorbents

Efficient removal of Pb(II) and Cu(II) from wastewater is crucial for safeguarding environmental safety and public health. Biomass-based adsorbents with surface-specific functionality hold great promise for selective adsorption of metal cations. In this study, a novel phosphorylated chitosan-lignin (PCSL) composite is successfully synthesized via Mannich reaction. The PCSL exhibits remarkable selectivity in the adsorption of Pb(II) and Cu(II), as evidenced by Density Functional Theory (DFT) calculations. Furthermore, DFT analysis reveals that the incorporation of phosphate groups significantly enhances the chelation capacity of the adsorbent towards heavy metals. The PCSL demonstrates ultrafast adsorption capabilities for Pb(II) and Cu(II). Specifically, the adsorption processes reach equilibrium within 7 min and 5 min, respectively, with maximum adsorption capacities of 207.9 mg·g-1 for Pb(II) and 100.0 mg·g-1 for Cu(II). X-ray photoelectron spectroscopy analysis indicates that the adsorption mechanisms involve both chemical complexation and electrostatic attraction. Notably, the adsorbent can be recycled many times, and the spent Cu-PCSL, upon pyrolysis treatment, demonstrate remarkable catalytic activity in nitrate reduction reactions, with Faradaic efficiencies as high as 98.3 % and NH3 yield of 4.3 mg·h-1·mgcat.-1. This work not only advances the progression of biomass adsorbents but also demonstrates considerable industrial potential in mitigating water pollution and promoting sustainable development.

A novel fabrication of graphitic carbon nitride/chitosan composite modified with thiosemicarbazide for the effective static and dynamic adsorption of Pb2+ from aqueous media

In this work, graphitic carbon nitride (g-C3N4) prepared by thermal treatment, graphitic carbon nitride/chitosan (GCS), and graphitic carbon nitride/chitosan embedded thiosemicarbazide (TGCS) were developed as an effective solid adsorbent. The fabricated adsorbents were characterized by nitrogen adsorption, ATR-FTIR, TGA, XRD, ζ potential, SEM, and TEM, where TGCS composite had a higher surface area (536.79 m2/g), total pore volume (0.4152 cm3 /g), average pore size (3.09 nm), and pHPZC (6.4). TGCS revealed a Langmuir adsorption capacity of 329.61 mg/g for Pb2+ at an adsorbent dosage of 1.5 g/L, pH 5, 45 min of shaking, and 23 °C. The experimental results were applied well by pseudo-second-order kinetic and Langmuir isotherm. Through the first five adsorption-desorption cycles, only 12.2, 6.2, and 5.1 % decline in efficiency were noted for g-C3N4, GCS, and TGCS, respectively. Column adsorption capacity (qo, mg/g) was determined to be 132.24 mg/g at bed height 3 cm, flow rate of 80 mL/min, and 80 mg/L as initial Pb2+ concentration. Based on the lower reduced chi-square values (ꭓ2 × 10-4, 3.8810-12.9000) and the higher correlation coefficients (R2, 0.9917-0.9979), the Yoon-Nelson and Thomas models suggested an acceptable match for the breakthrough curve. Our findings suggested that TGCS had great adsorption capacity, strong selectivity, and quick kinetics, indicating its potential for water treatment applications.

Electrochemical Selective Removal of Oxyanions in a Ferrocene-Doped Metal-Organic Framework

Metal-organic frameworks (MOF) are a class of crystalline, porous materials possessing well-defined channels that have widespread applications across the sustainable landscape. Analogous to zeolites, these materials are well-suited for adsorption processes targeting environmental contaminants. Herein, a zirconium MOF, UiO-66, was functionalized with ferrocene for the selective removal of oxyanion contaminants, specifically NO3-, SO42-, and PO43-. Electrochemical oxidation of the embedded ferrocene pendants induces preferential adsorption of these oxyanions, even in the presence of Cl- in a 10-fold excess. Anion selectivity strongly favoring PO43- (Soxy/comp = 3.80) was observed following an adsorption trend of PO43- > SO42- > NO3- > (10-fold)Cl- in multi-ion solution mixtures. The underlying mechanisms responsible for ion selectivity were elucidated by performing ex situ X-ray photoelectron spectroscopy (XPS) on the heterogeneous electrode surface postadsorption and by calculating the electronic structure of various adsorption configurations. It was eventually shown that oxyanion selectivity stemmed from strong ion association with a positively charged pore interior due to the spatial distribution of charge by oxygen constituents. While ferrocenium provided the impetus for ion migration-diffusion, it was the formation of stable complexes with zirconium nodes that ultimately contributed to selective adsorption of oxyanions.

The design of high-efficient MOFs for selective Ag(I) capture: DFT calculations and practical applications

Recovering silver from wastewater not only significantly reduces environmental harm but also meets the growing demand for silver in modern industry. Here, a novel metal-organic framework adsorbent (MOF-RD) using rhodanine derivatives as linkers is introduced for the efficient and selective capture of silver ions in real wastewater. The adsorption of MOF-RD followed pseudo-second-order and Sips models, and thermodynamic investigations revealed the process to be endothermic. MOF-RD demonstrated a remarkable adsorption capacity of 707.2 mg·g-1 for Ag(I) at pH 5 and 318 K. The interaction between silver ions and MOF-RD was mainly electrostatic attraction and coordination, with coordination primarily occurring at the CO and CS sites within the rhodanine motif. The practical applicability of MOF-RD for selective adsorption of Ag(I) was validated in actual wastewater with high-concentration competing metal ions. Furthermore, after 10 adsorption-desorption cycle experiments, MOF-RD still retained a strong regenerative capability. The results reveal the good potential of MOF-RD as an adsorbent for selectively recovering Ag(I) from industrial wastewater. Additionally, the strategies and methods adopted in this article also provide new perspectives and technical paths for the separation and recovery of other metal ions in wastewater.

Recyclable Fe3O4@UiO-66-PDA core-shell nanomaterials for extensive metal ion adsorption: Batch experiments and theoretical analysis

With the ever-increasing challenge of heavy metal pollution, the imperative for developing highly efficient adsorbents has become apparent to remove metal ions from wastewater completely. In this study, we introduce a novel magnetic core-shell adsorbent, Fe3O4@UiO-66-PDA. It features a polydopamine (PDA) modified zirconium-based metal-organic framework (UiO-66) synthesized through a simple solvothermal method. The adsorbent boasts a unique core-shell architecture with a high specific surface area, abundant micropores, and remarkable thermal stability. The adsorption capabilities of six metal ions (Fe3+, Mn2+, Pb2+, Cu2+, Hg2+, and Cd2+) were systematically investigated, guided by the theory of hard and soft acids and bases. Among these, three representative metal ions (Fe3+, Pb2+, and Hg2+) were scrutinized in detail. The activated Fe3O4@UiO-66-PDA exhibited exceptional adsorption capacities for these metal ions, achieving impressive values of 97.99 mg/g, 121.42 mg/g, and 130.72 mg/g, respectively, at pH 5.0. Moreover, the adsorbent demonstrated efficient recovery from aqueous solution using an external magnet, maintaining robust adsorption efficiency (>80%) and stability even after six cycles. To delve deeper into the optimized adsorption of Hg2+, density functional theory (DFT) analysis was employed, revealing an adsorption energy of -2.61 eV for Hg2+. This notable adsorption capacity was primarily attributed to electron interactions and coordination effects. This study offers valuable insights into metal ion adsorption facilitated, by magnetic metal-organic framework (MOF) materials.

Immature persimmon residue as a novel biosorbent for efficient removal of Pb(II) and Cr(VI) from wastewater: Performance and mechanisms

Owing to the powerful affinity of tannin toward heavy metal ions, it is frequently immobilized on adsorbents to enhance their adsorption properties. However, natural adsorbents containing tannin have been overlooked owing to its water solubility. Herein, a novel natural adsorbent based on the immature persimmon residue (IPR) with soluble tannin removed was fabricated to eliminate Pb(II) and Cr(VI) in aquatic environments. The insoluble tannin in IPR endowed it with prosperous properties for eliminating Pb(II) and Cr(VI), and the IPR achieved maximum Pb(II) and Cr(VI) adsorption quantities of 68.79 mg/g and 139.40 mg/g, respectively. Kinetics and isothermal adsorption analysis demonstrated that the removal behavior was controlled by monolayer chemical adsorption. Moreover, the IPR exhibited satisfactory Pb(II) and Cr(VI) removal efficiencies even in the presence of multiple coexisting ions and showed promising regeneration potential after undergoing five consecutive cycles. Additionally, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) analysis unveiled that the elimination mechanisms were primarily electrostatic attraction, chelation and reduction. Overall, the IPR, as a tannin-containing biosorbent, was verified to possess substantial potential for heavy metal removal, which can provide new insights into the development of novel natural adsorbents from the perspective of waste resource utilization.

Schiff base MOFs and their derivatives for sequestration and degradation of pollutants: present and future

Removal of contaminants via adsorption and catalysis have received a significant interest as energy and money-saving solutions for treating the world's wastewater. Metal-organic frameworks (MOFs), a newly discovered class of porous crystalline materials, have demonstrated tremendous promise in the removal and destruction of contaminants for water purification. In order to improve the interactions of MOFs with the target pollutants for their selective removal and degradation, the Schiff base functionalities emerged as promising active sites. Through pre- and post-synthetic alterations, Schiff base functionalities are integrated into the pore cages of MOF adsorbent materials. To understand the adsorptive/catalytic mechanism, potential interactions between the Schiff base sites and the target pollutants are discussed. Based on cutting-edge techniques for their synthesis, this paper examines current developments in the creation of Schiff base-functionalized MOFs as innovative materials for adsorptive removal and catalytic degradation of contaminants for water remediation.

Adsorption of methyl orange from aqueous solution with lignin-modified metal-organic frameworks: Selective adsorption and high adsorption capacity

The lignin-based metal-organic framework (UIO-g-NL) was prepared by a Schiff base reaction of aminated lignin and the zirconium cluster-based MOF (UIO-66-NH2) as an adsorbent of methyl orange (MO). The results showed that UIO-g-NL maintained the original crystal structure and aminated lignin was successfully introduced after functionalization. UIO-g-NL selectively adsorbed MO from a mixed solution 50 mg/L MO and 50 mg/L methylene blue (MB), with an adsorption efficiency of nearly 100%. In a mixed solution 250 mg/L MB and 250 mg/L MO, UIO-g-NL adsorbed both dyes with 1120.70 mg/g for MB and 961.54 mg/g for MO. Hydrogen bonding, π-π and NH-π interactions, and electrostatic attraction contribute to the MO adsorption by UIO-g-NL. In the MO/MB mixture, MO adsorption by UIO-g-NL follows the pseudo-second-order kinetic and Freundlich isotherm models, which is an endothermic, spontaneous, and feasible adsorption process. Furthermore, the MO adsorption efficiency of UIO-g-NL remained high (>90%) after six re-use cycles.

Lignin-modified metal-organic framework as an effective adsorbent for the removal of methyl orange

Herein, lignin-modified metal-organic frameworks (NH2-UIO@L) are prepared using a one-step synthesis as sorbents for the removal of organic dyes from water. The introduction of lignin improved the adsorption sites. NH2-UIO@L2 adsorption of MO conforms to Langmuir model, and the adsorption capacity of NH2-UIO@L2 on MO was 214.13 mg·L-1 with an adsorption efficiency up to 99.28 %, which was significantly higher than values for other adsorbents. Due to hydrogen bonds, π-π interactions and electrostatic interactions, MO was effectively removed by NH2-UIO@L2 and its adsorption efficiency is maintained at 90.55 % after six cycles. The adsorption kinetics showed that the NH2-UIO@L2 adsorption of MO was chemical adsorption and controlled by intraparticle diffusion and external mass transfer. Further, the adsorption performance of NH2-UIO@L2 on MO and MB in mixed MO/MB solution was investigated. The adsorption capacity of NH2-UIO@L2 in mixed MO/MB solution was 207.04 mg·L-1 for MO and 243.31 mg·L-1 for MB; the adsorption of NH2-UIO@L2 on MO followed the Dubinin-Radushkevich and pseudo-second-order models, and the adsorption on MB followed the Temkin and pseudo-second-order models. Hydrogen bonds, π-π interactions, and pore filling are all implicated in the removal of MO and MB. In particular, the electrostatic attraction between MB and MO improves the adsorption efficiency of NH2-UIO@L2 on MB. NH2-UIO@L2 has good reusability, maintaining an adsorption efficiency of 97.66 % for MO and up to 99.15 % for MB after six cycles. Its simple preparation and superior adsorption suggest that NH2-UIO@L2 has considerable potential to remove organic dyes from wastewater.

Synthesis of Highly Efficient and Recyclable Bimetallic Cox-Fe1-x-MOF for the Synthesis of Xanthan and Removal of Toxic Pb2+ and Cd2+ Ions

Mono-(Fe) and bimetallic Cox-Fe1-x-MOF with different Co and Fe contents was successfully synthesized by the solvothermal method. The structural properties of the prepared samples were characterized by X-ray diffraction, transmission electron microscopy (TEM), Brunauer-Emmett-Teller specific surface area, and Fourier transform infrared spectroscopy. The results revealed the successful formation of mono and mixed Cox-Fe1-x-MOF. Also, the results of TEM displayed that the particle structure of Cox-Fe1-x-MOF changed to octahedral after the addition of cobalt. The surface acidity results illustrated that the samples showed both Lewis and Brønsted acid sites, and Cox-Fe1-x-MOF possessed more surface acidity than Fe-MOF. The catalytic performance of the prepared samples was tested by synthesis of 14-phenyl-14H-dibenzo [a, j] xanthene (xanthene), and bimetallic Cox-Fe1-x-MOF showed higher activity compared to monometallic Fe-MOF. The sample with Co0.50-Fe0.50-MOF gave the highest yield of xanthene with 90.2%. In addition, the prepared samples were used for removal of Pb2+ and Cd2+ ions from the aqueous solution. The sample with Co0.50-Fe0.50-MOF showed the highest removal efficiency compared with mono- and other bimetallic samples. The results illustrated that the addition of Co to Fe enhanced the structural properties, acidity, and catalytic performance of the prepared samples due to the synergistic effect between Fe and Co ions. According to the obtained results, the prepared samples showed great potentials for the synthesis of pharmacologically active compounds and environmental protection.

Tuning the Dual Active Sites of Functionalized UiO-66 for Selective Adsorption of Yb(III)

The recovery of rare earth elements (REEs) from discharged electronic devices or mineral waste water is highly essential but still facing challenges. In this work, two amino-functionalized carboxyl-UiO-66 (UiO-66-COOH-TETA and UiO-66-(COOH)₂-ED) prepared via the postmodification method were employed as the adsorbents for Yb(III) capture. The experimental results revealed their superior adsorption capacities of 161.5 and 202.6 mg/g, respectively. Meanwhile, their adsorption processes can be described by the pseudo-second-order kinetic model and Langmuir model. Effects of initial pH and temperature on adsorptions were systematically evaluated, affording an optimal operating condition (i.e., pH of 5.5-6, T of 65 °C, t of 10 h). Moreover, the fabricated materials exhibited great reusability after five adsorption-regeneration cycles. UiO-66-COOH-TETA demonstrated good separation selectivity for Yb(III) over light REEs (i.e., 3.98 of Yb/Ce, 3.51 of Yb/Nd). Based on the density functional theory calculations and characterization analysis (XPS, Zeta, mapping, and IR), the adsorption mechanisms were mainly attributed to significant electrostatic attraction and strong surface complexation between N and O sites and Yb(III).