Enhanced removal performance of zero-valent iron towards heavy metal ions by assembling Fe-tannin coating

Green synthesized Zn-based mono and bi-metallic nanoparticles for improved micronutrient delivery: A futuristic study in hydroponic crop culture system

Hydroponic farming is gaining importance due to the rapid expansion of cities worldwide. However, the significance of nano-enabled nutrient delivery in hydroponic crop culture is still poorly understood. Therefore, ZnO monometallic and Zn-Cu bimetallic nanoparticles (MNP and BNP) were innovatively synthesized through green routes using alcoholic leaf extract (ALE) 1-10 % (w/v) of Chrysalidocarpus lutescens due to its enriched phytochemical profile, prolific radical scavenging efficiency, and reasonably high IC50 values. The structural uniformity and batch-wise yield of MNP and BNP were optimized following response surface methodology. The uniqueness of C. lutescens-derived phytochemicals facilitated the production of anisotropic and crystalline MNP and BNP. It was revealed that structural uniformity and yields were most significant at pH 9 with 3 % ALE for both MNP (Yield/batch -20.54 ± 0.15 g) and BNP (Yield/batch - 18.37 ± 0.30 g). Both nanoparticles were hexagonal 30-85 nm nanocrystals, stable at alkaline pH (∼9) with uniform pore volume, surface area, and surface charge. The hydroponic compatibility of the MNP and BNP were compared with non-nanoscale Zn and Cu by cultivating Cicer arietinum with different doses of MNP, BNP, and other treatments. Among all doses, 250 and 500 mg L-1 doses of MNP and BNP significantly augmented C. arietinum germination by ∼40-45 % and plumule growth by ∼18-22 % and enhanced chlorophyll stability while reducing oxidative stress in the seedlings. The MNP and BNP were ecologically safe for microorganisms (Rhizobium sp. and Salmonella typhi) and were viable within 250 mg L-1 to 2000 mg L-1 of MNP and BNP doses. Overall, the study reveals that the green synthetic routes using C. lutescens phytoextract led to significant yield of productive, biocompatible, and organically rich Zn and Cu-based MNP and BNP that can be easily pursued and sustainably applied in hydroponics or other agriculture platforms.

Efficient adsorption of chloroquine phosphate by a novel sodium alginate/tannic acid double-network hydrogel in a wide pH range

In this work, a novel double-network composite hydrogel (SA/TA), composed of sodium alginate (SA) and tannic acid (TA), was designed and fabricated by a successive cross-linking method using Ti(IV) and Ca(II) as crosslinkers. SA/TA exhibited reinforced mechanical strength and anti-swelling properties because of the double-network structure. SA/TA was used as an adsorbent for removal of a popular antiviral drug, chloroquine phosphate (CQ), in water. The adsorption performance of SA/TA was systematically investigated, to study various effects including those of TA mass content, solution pH, adsorption time, and initial CQ concentration. Adsorption was also examined in presence of inorganic and organic coexisting substances commonly found in wastewater, and under different actual water samples. Batch experimental results indicated that SA/TA could maintain higher and more stable CQ uptakes within a wide solution pH range from 3.0 to 10.0, compared to its precursor, SA hydrogel, owing to the addition of TA-Ti(IV) coordination network. The maximum experimental CQ uptake exhibited by the 1:1 (by wt) SA/TA (SA/TA2) was as high as 0.699 mmol/g at the initial pH of 9.0. A high concentration of coexisting NaCl evidently reduced the CQ uptakes of SA/TA2 due to the electrostatic shielding effect, moreover, divalent cations including Ca(II) and Mg(II) also inhibited the adsorption of CQ due to competitive adsorption. However, humic acid had little effect on this adsorption. Considering the apparent adsorption performance, the aforementioned effects of various factors and the spectroscopic characterizations, multi-interactions are suggested for adsorption including chelation, electrostatic interactions, π-π electron donor-acceptor interaction and hydrogen bonding. SA/TA showed a slight loss in adsorption capacity toward CQ and sustained physicochemical structural stability, even after six adsorption-desorption cycles. In addition to CQ, SA/TA could be efficiently used for adsorption of two other antivirus drugs, namely, hydroxychloroquine sulfate and oseltamivir phosphate. This work provides an effective strategy for the design and fabrication of novel adsorbents that can effectively adsorb antiviral drugs over a wide pH range.

Tannic acid modified microscale zero valent iron (TA-mZVI) with enhanced anti-passivation capability for Cr(VI) removal

The removal of Cr(VI) from aqueous solutions using microscale zerovalent iron (mZVI) shows promising potential. However, the surface passivation of mZVI particles hinders its widespread application. In this study, we prepared tannic acid (TA) modified mZVI composite (TA-mZVI) by a simple sonication method. The introduction of TA allowing TA-mZVI composite to adsorb Cr(VI) rapidly under electrostatic forces attraction, guarantying TA-mZVI exhibited remarkable Cr(VI) removal capacity with a maximum adsorption capacity of 106.1 mg⋅g-1. At an initial pH of 3, it achieved a rapid removal efficiency of 96.2% within just 5 min, which was 7.7 times higher than that of mZVI. Various characterizations, including XPS and CV analysis, indicated that the formation of TA-Fe complexes accelerates electron transfer. In addition, TA endows functional groups to TA-mZVI, raising the dispersion and stability and serves as a protective layer hindering passivation. Further mechanistic analysis revealed that Cr(VI) removal by TA-mZVI followed an adsorption-reduction-precipitation mechanism, with TA mitigating the surface passivation of mZVI and facilitating the reduction of most Cr(VI) to Cr(III). Batch cyclic experiments revealed that TA-mZVI exhibited satisfactory performance, maintaining over 85% Cr(VI) removal even after five cycles and minimally affected by various coexisting ions. With notable advantages in cost-effectiveness, ease-synthesis and recovery, this work provides a great promise for developing efficient reactive adsorbent for addressing Cr(VI) contamination in aqueous solutions.

Exploring adsorption capacity and mechanisms involved in cadmium removal from aqueous solutions by biochar derived from euhalophyte

Biochar has shown potential as a sorbent for reducing Cd levels in water. Euhalophytes, which thrive in saline-alkali soils containing high concentrations of metal ions and anions, present an intriguing opportunity for producing biochar with inherent metal adsorption properties. This study focused on biochar derived from the euhalophyte Salicornia europaea and aimed to investigate its Cd adsorption capacity through adsorption kinetics and isotherm experiments. The results demonstrated that S. europaea biochar exhibited a high specific surface area, substantial base cation content, and a low negative surface charge, making it a highly effective adsorbent for Cd. The adsorption data fit well with the Langmuir isotherm model, revealing a maximum adsorption capacity of 108.54 mg g-1 at 25 °C. The adsorption process involved both surface adsorption and intraparticle diffusion. The Cd adsorption mechanism on the biochar encompassed precipitation, ion exchange, functional group complexation, and cation-π interactions. Notably, the precipitation of Cd2+ with CO32- in the biochar played a dominant role, accounting for 73.7% of the overall removal mechanism. These findings underscore the potential of euhalophytes such as S. europaea as a promising solution for remediating Cd contamination in aquatic environments.

Selective removal of Cr(VI) by tannic acid and polyethyleneimine modified zero-valent iron particles with air stability

In this study, a new composite adsorbent for Cr(VI) removal was developed by immobilizing polyethyleneimine (PEI) on the surface of zero-valent iron (ZVI) particles with tannic acid (TA) as a stabilizer. The adsorbent (denoted as Fe-TA-PEI-10) was easy to prepare and regenerate, requiring no conditions for storage. It was found to be particularly effective for Cr(VI) removal from wastewater via reduction and adsorption. Electrochemical analysis revealed that TA significantly reduced the electron transfer resistance of Fe-TA-PEI-10 and reduced the highly toxic Cr(VI)to the less toxic Cr(III). In addition, PEI endowed amino groups to Fe-TA-PEI-10, raising the zero charge point (pH_pzc) of Fe-TA-PEI-10 (pH_pzc= 7.80), allowing it to adsorb Cr(VI) from the solution rapidly under electrostatic forces and chelating effects. The adsorption process was consistent with the pseudo-first-order model (R² >0.99) and the Langmuir isotherm model (R² >0.99), and the maximum adsorption capacity could reach 161.6 mg/g. In particular, this study presented for the first time that TA-modified Fe(0) had excellent stability in the air, and the adsorbent showed no decrease in performance for Cr(VI) removal even after exposure to the air for 30 days. When tested with a simulated electroplating rinsing wastewater, the Fe-TA-PEI-10 showed very high selectivity for Cr(VI) removal. The mechanism of Cr(VI) removal with Fe-TA-PEI-10 was found to be based on adsorption and reduction. This work provided a new scheme for developing efficient and long-lasting reactive adsorbent for Cr(VI) removal.

Sophorolipid modification enables high reactivity and electron selectivity of nanoscale zerovalent iron toward hexavalent chromium

Nanoscale zero-valent iron is considered to be a promising nanostructure for environmental remediation, while increasing the electron selectivity of nanoscale zerovalent iron (nZVI) during target contaminant removal is still a challenge (electron selectivity, defined as the percentage of electrons transferred to the target contaminants over the number of electrons donated by nZVI). In this study, the strategy for increasing the reactivity and electron selectivity of nZVI via sophorolipid (SL-nZVI) modification was proposed. The results showed that the removal efficiency and electron selectivity of SL-nZVI toward Cr(VI) was 99.99% and 56.30%, which was higher than that of nZVI (61.16%, 25.91%). Meanwhile, the particles were well characterized and the mechanism for enhanced reactivity and electron selectivity was investigated. Specially, both the morphology and BET specific surface area characterization suggested that stability against aggregation was higher in SL-nZVI nanoparticles than in nZVI. Besides, X-ray photoelectron spectroscopy (XPS), Tafel polarization curves, and Electrochemical impedance spectroscopy also indicated that the introduction of sophorolipid successfully prevent the nanoparticles from oxidation and benefit the electron transferring. In addition, a water contact angle test revealed that SL-nZVI nanoparticles were less hydrophilic (contact angle = 34.8°) than nZVI (contact angle = 23.9°). Therefore, in terms of reactivity, sophorolipid modification inhibited the aggregation of the nanoparticles and enhanced the electrical conductivity. For electron selectivity, the introduction of sophorolipid not only benefited Cr(VI) adsorption and the electron transfer from Fe⁰ to the surface-adsorbed Cr(VI) that followed but also reduced the possibility of side reactions between Fe⁰ and H₂O. This study demonstrates that the introduction of sophorolipid is an effective strategy for developing a highly efficient nZVI-based nanocomposite system and highlights the potential role of sophorolipid in improving the electron selectivity of nZVI.

Facile preparation of activated carbon supported nano zero-valent iron for Cd(Ⅱ) removal in aqueous environment

Activated carbon-supported nano-zero-valent iron (nZVI@AC) is considered to be one of the most promising materials for in-situ remediation of pollutants in aqueous environment, while liquid phase reduction (LPR) is one of the most commonly used preparation methods for nZVI@AC. However, the complex operation and the requirement of various agents limit the practical application of the traditional liquid-phase reduction (TLPR). In this study, an improved liquid phase reduction method (ILPR) was proposed, which was characterized by solid-state dosing of reducing agents. Compared with TLPR, ILPR simplified the preparation process, while there was no requirement of polyethylene glycol and ethanol. When the Cd(II) removal efficiency was used as the evaluation index, the preferred parameters of ILPR were as follows: AC/FeSO₄·7H₂O mass ratio was 15:1; NaBH₄ dosage was 8 g; ultrasonic time was 1 h; stirring time was 20 min. Moreover, the Cd(II) removal efficiency of nZVI@AC prepared by ILPR (nZVI@AC-I) was greater than 92.00%, which was superior to that of nZVI@AC prepared by TLPR (nZVI@AC-T). The characterization results showed that the pore parameters, surface functional groups and iron contents of nZVI@AC-I and nZVI@AC-T were basically the same. However, the distribution of iron-containing particles on the surface of nZVI@AC-I was more uniform. Furthermore, the Fe⁰ in nZVI@AC-I had a smaller particle size and a higher content. Overall, this study provided a promising approach for nZVI@AC preparation.