Removal of crystal violet from water using β-cyclodextrin functionalized biogenic zero-valent iron nanoadsorbents synthesized via aqueous root extracts of Ferula persica

Cr(VI) removal during cotransport of nano-iron-particles combined with iron sulfides in groundwater: Effects of D. vulgaris and S. putrefaciens

Iron-based materials such as nanoscale zerovalent iron (nZVI) are effective candidates to in situ remediate hexachromium (Cr(VI))-contaminated groundwater. The anaerobic bacteria could influence the remediation efficiency of Cr(VI) during its cotransport with nZVI in porous media. To address this issue, the present study investigated the adsorption and reduction of Cr(VI) during its cotransport with green tea (GT) modified nZVI (nZVI@GT) and iron sulfides (FeS and FeS2) in the presence of D. vulgaris or S. putrefaciens in water-saturated sand columns. Experimental results showed that the nZVI@GT preferred to heteroaggregate with FeS2 rather than FeS, forming nZVI@GT-FeS2 heteroaggregates. Although the presence of D. vulgaris further induced nZVI@GT-FeS2 heteroaggregates to form larger clusters, it pronouncedly improved the dissolution of FeS and FeS2 for more Cr(VI) reduction associated with lower Cr(VI) flux through sand. In contrast, S. putrefaciens could promote the dispersion of the heteroaggregates of nZVI@GT-FeS2 and the homoaggregates of nZVI@GT or FeS by adsorption on the extracellular polymeric substances, leading to the improved transport of Fe-based materials for a much higher Cr(VI) immobilization in sand media. Overall, our study provides the essential perspectives into a chem-biological remediation technique through the synergistic removal of Cr(VI) by nZVI@GT and FeS in contaminated groundwater. ENVIRONMENTAL IMPLICATION: The green-synthesized nano-zero-valent iron particles (nZVI@GT) using plant extracts (or iron sulfides) have been used for in situ remediation of Cr(VI) contaminated groundwater. Nevertheless, the removal of Cr(VI) (including Cr(VI) adsorption and Cr(III) generation) could be influenced by the anaerobic bacteria governing the transport of engineered nanoparticles in groundwater. This study aims to reveal the inherent mechanisms of D. vulgaris and S. putrefaciens governing the cotransport of nZVI@GT combined with FeS (or FeS2) to further influence the Cr(VI) removal in simulated complex groundwater media. Our findings provides a chemical and biological synergistic remediation strategy for nZVI@GT application in Cr(VI)-contaminated groundwater.

Remediation of oil-polluted soil using anionic and non-ionic composite biosurfactants

Petroleum hydrocarbons as pervasive pollutants pose a significant threat to soil ecology and human health. Surfactant washing as an established technique can effectively remediate soils contaminated by hydrocarbons. Biosurfactants, which combine the properties of surfactants and environmental compatibility, have attracted increasing interest. However, due to the high production cost of biosurfactants, their practical application is restricted. This study addressed these limitations by selecting two biosurfactants, β-cyclodextrin (C1) and sodium carboxymethyl cellulose (C2), and developed a promising cleaning agent formula through compounding and the addition of suitable additives. When the volume ratio of C1 to C2 was 8:2 and an 8 g/L mixture of sodium humate and sodium carbonate electrolyte was added, the surfactant system's surface tension reached a minimum, yielding optimal oil removal. The formation and synergistic behaviour of mixed micelles of surfactants were explained using ideal solution theory and the Rubingh model. By optimising the oil washing process parameters - normal temperature of 25 °C, pH 11, washing time of 2 h, solid-liquid ratio of 1:5, and oscillation frequency of 200 r/min - the oil removal rate achieved 76%. This cleaning agent, characterised by low production cost, straightforward application, environmental compatibility, and rapid, significant cleaning effect, shows potential for field-scale purification of petroleum-contaminated soil.

Green synthesis of nZVI-modified biochar significantly enhanced the removal of Cr(VI) from aqueous solution

Water contamination by hexavalent chromium (Cr(VI)) seriously jeopardizes human health, which is a pressing environmental concern. Biochar-loaded green-synthesized nZVI, as a green and environmentally friendly material, can efficiently reduce Cr(VI) to Cr(III) while removing Cr(VI) from water. Therefore, in this study, an efficient green-modified biochar material (TP-nZVI/BC) was successfully prepared using tea polyphenol (TP) and sludge biochar (BC) using a low-cost and environmentally friendly green synthesis method. The preparation conditions of TP-nZVI/BC were optimized using response surface methodology (RSM), revealing that the dosage of tea polyphenols plays a crucial role in the removal performance (R2 = 1271.09), followed by reaction time and temperature. The quadratic regression model proved accurate. The optimal preparation conditions are as follows: tea polyphenols (TP) dosage at 48 g/L, reaction temperature at 75 ℃, and a reaction time of 3 h. TP-nZVI/BC removed Cr(VI) from water at a rate 7.6 times greater than BC. The pseudo-second-order kinetic model (R2 = 0.987) accurately describes the adsorption process, suggesting that chemical adsorption predominantly controls the removal process. The adsorption of Cr(VI) by TP-nZVI/BC can be well described by the Langmuir model, and the maximum adsorption capacity reached 105.65 mg/g. FTIR and XPS analyses before and after adsorption demonstrate that nZVI plays a crucial role in the reduction process of Cr(VI), and the synergistic effects of surface adsorption, reduction, and co-precipitation enhance Cr(VI) removal. In summary, using green-modified biochar for Cr(VI) removal is a feasible and promising method with significant potential.

Surface engineering of multifunctional nanostructured adsorbents for enhanced wastewater treatment: A review

Rapid urbanization and industrialization have significantly contributed to the contamination of the environment through the discharge of wastewater containing various pollutants. The development of high-performance surface functional nanostructured adsorbents is of wide interest for researchers. Therefore, we explore the significant advancements in this field, focusing on the efficiency of nanostructured materials, as well as their nanocomposites, for wastewater treatment applications. The crucial role of surface modification in enhancing the affinity of these nanostructured adsorbents towards targeted pollutants, addressing a key bottleneck in the utilization of nanomaterials for wastewater treatment, was specifically emphasized. In addition to highlighting the advantages of surface engineering in enhancing the efficiency of nanostructured adsorbents, this review also provides a comprehensive overview of the limitations and challenges associated with surface-modified nanostructured adsorbents, including high cost, low stability, poor scalability, and potential nanotoxicity. Addressing these limitations is essential for realizing the commercial viability of these state-of-the-art materials for large-scale wastewater treatment applications. This review also thoroughly discusses the potential scalability and environmental safety aspects of surface-modified nanostructured adsorbents, offering insights into their future prospects for wastewater treatment. It is believed that this review will contribute significantly to the existing body of knowledge in the field and provide valuable information for researchers and practitioners working in the area of environmental remediation and nanomaterials.

Enhanced production of withaferin A from the hairy root culture of Withania somnifera via synergistic effect of Methyl jasmonate and β-cyclodextrin

Due to low amounts of withanolides produced in some plants and high demand for various applications, their biotechnological production is widely researched. The effects of two explant types (i.e., leaf and stem from the in vitro seedlings of three genotypes of Withania somnifera) and four Rhizobium strains (i.e., LBA 9402, A4, ATCC 15834, and C58C1) to improve hairy root formation efficiency was studied. Furthermore, the combined effects of β-cyclodextrin (β-CD) and methyl jasmonate (MeJA) on withaferin A production after 48 h exposure time was examined. Four hairy roots having the maximum percentage of induced roots and mean number of induced roots to analyze their growth kinetics and identified G3/ATCC/LEAF culture having the maximum specific growth rate (μ = 0.036 day-1) and growth index (GI = 9.18), and the shortest doubling time (Td = 18.82 day) were selected. After 48 h exposure of G3/ATCC/LEAF culture to different elicitation conditions, maximum amounts of withaferin A were produced in samples co-treated with 0.5 mM β-CD + 100 μM MeJA (9.57 mg/g DW) and 5.0 mM β-CD + 100 μM MeJA (17.45 mg/g DW). These outcomes represented a 6.8-fold and 12.5-fold increase, respectively, compared to the control. Similarly, combined β-CD/MeJA elicitation increased gene expression levels of HMGR, SQS, SMT-1, and SDS/CYP710A involved in withanolides biosynthetic pathway, of which just SMT-1 had significant correlation with withaferin A production. These results demonstrated the superiority of G1-leaf explant and ATCC 15834 for hairy root induction, and revealed synergistic effect of MeJA and β-CD on withaferin A production.

Green synthesis of iron nanoparticles using mulberry leaf extract: characterization, identification of active biomolecules, and catalytic activity

The synthesis of iron-based nanoparticles (Fe NPs) using traditional preparation methods suffered from the disadvantages of high cost, environmental harm, and easy agglomeration. In this study, a novel eco-friendly method was proposed for the synthesis of iron nanomaterials (ML-Fe NPs): using antioxidant components extracted from mulberry leaf to reduce divalent iron (II). The preparation conditions of ML-Fe NPs were optimized by orthogonal tests. The prepared ML-Fe NPs exhibited an amorphous core-shell structure, displaying excellent dispersion and stability. During the synthesis process of ML-Fe NPs, the polyphenol molecules in mulberry leaf extract played a dominant role. A possible synthetic mechanism involving complexation, reduction, and encapsulation was proposed. Furthermore, the ML-Fe NPs were utilized to construct an ML-Fe NPs/peroxymonosulfate catalytic system for the degradation of Rhodamine B dye wastewater. The ML-Fe NPs demonstrated remarkable catalytic potential, achieving a 99% degradation efficiency for Rhodamine B within a span of 40 min.

Removal of water pollutants using plant-based nanoscale zero-valent iron: A review

Nanotechnology has been increasingly explored for the treatment of various waste streams. Among different nanoparticles, nanoscale zerovalent iron (nZVI) has been extensively investigated due to its high reactivity and strong reducing power. However, conventional methods for the synthesis of nZVI particles have several limitations and led to the green synthesis of nZVI using plant-based materials. Plant extracts contain various reducing agents that can be used for nZVI synthesis, eliminating the need for toxic chemicals, and reducing energy consumption. Additionally, each plant species used for nZVI synthesis results in unique physicochemical properties of the nanoparticles. This review paper provides an overview of plant-based nZVI particle synthesis, its characteristics, and its application for the removal of different classes of pollutants such as dyes, heavy metals, nutrients, and trace organic pollutants from water. The review shows that continued research on plant-based nZVI particles to fully understand its potential in wastewater treatment, especially for the removal of a wider variety of pollutants, and for improving sustainability and reducing the cost and environmental impact of the process, is necessary.

Dependency of Crystal Violet Dye Removal Behaviors onto Mesoporous V2O5-g-C3N4 Constructed by Simplistic Ultrasonic Method

This research examined the production of a V2O5-g-C3N4 nanocomposite to remove organic dyes from wastewater. To generate the V2O5-g-C3N4 nanocomposite, the sonication method was applied. The testing of V2O5-g-C3N4 with various dyes (basic fuchsin (BF), malachite green (MG), crystal violet (CV), Congo red (CR), and methyl orange (MO)) revealed that the nanocomposite has a high adsorption ability towards BF, MG, CV, and CR dyes in comparison with MO dye. It was established that the modification of pH influenced the removal of CV by the V2O5-g-C3N4 nanocomposite and that under optimal operating conditions, efficiency of 664.65 mg g−1 could be attained. The best models for CV adsorption onto the V2O5-g-C3N4 nanocomposite were found to be those based on pseudo-second-order adsorption kinetics and the Langmuir isotherm. According to the FTIR analysis results, the CV adsorption mechanism was connected to π–π interactions and the hydrogen bond.

A recent update on green synthesized iron and iron oxide nanoparticles for environmental applications

Nanotechnology is considered the budding discipline in various fields of science and technology. In this review, the various synthesis methods of iron and iron oxide nanoparticles were summarised with more emphasis on green synthesis - a sustainable and eco-friendly method. The mechanism of green synthesis of these nanomaterials was reviewed in recent literature. The magnetic properties of these nanomaterials were briefed which makes them unique in the family of nanomaterials. An overview of various removal methods for the pollutants such as dye, heavy metals, and emerging contaminants using green synthesized iron and iron oxide nanoparticles is discussed. The mechanism of pollutant removal methods like Fenton-like degradation, photocatalytic degradation, and adsorption techniques was also detailed. The review is concluded with the challenges and possible future aspects of these nanomaterials for various environmental applications.

Mechanistic insights into sulfate and phosphate-mediated hexavalent chromium removal by tea polyphenols wrapped nano-zero-valent iron

Nano zero-valent iron via green synthesis (g-nZVI) has great potential in removing toxic hexavalent Cr(VI) from industrial wastewater. Sulfate and phosphate in wastewater can influence Cr(VI) removal by g-nZVI. In this study, the Cr(VI) removal kinetics by different g-nZVI materials were investigated with the existence of sulfate and/or phosphate, and the corresponding mechanisms were first revealed using multiple characterizations, including X-ray absorption near-edge spectra (XANES) and X-ray photoelectron spectroscopy (XPS). The results showed that Cr(OH)₃ was the dominant species initially formed on the surface of g-nZVI particles before transforming to Cr₂O₃ during the reaction of g-nZVI with Cr(VI). Sulfate in wastewater can promote the reduction from Cr(VI) to Cr(OH)₃ by g-nZVI, because sulfate triggers the release of Fe(II) and tea polyphenols (from tea extracts) from the g-nZVI surface due to the corrosion of Fe⁰ core, which is in line with an obvious increase in pseudo-second-order rate constant (k₂) and subtle change in Cr(VI) removal capacity (q_e). However, phosphate impedes the g-nZVI corrosion and inhibits q_e because of the inner-sphere complexation of phosphate onto g-nZVI decreasing the released Fe(II) for Cr₂O₃ production. When sulfate and phosphate coexisted in contaminated water, the inhibition effect of phosphate in Cr(VI) removal by g-nZVI was stronger than the promotion of sulfate. Accordingly, q_e value of g-nZVI declined from 93.4 mg g^-1 to 77.5 mg g^-1, while k₂ remained constant as the molar ratio of phosphate/sulfate increased from 0.1 to 10 in water. This study provides new insights into applying g-nZVI in efficient Cr(VI) removal from contaminated water with enrichment of sulphates and phosphates.

Fabrication of glutathione functionalized self-assembled magnetite nanochains for effective removal of crystal violet and phenol red dye from aqueous matrix

A novel fabrication of magnetite (Fe₃O₄) nanochains, surface functionalized with glutathione (GSH), has been attempted through a basic wet reduction method, coalesced with oxidative etching for the removal of crystal violet (CV) and phenol red (PR) from an aqueous solution. The structural and functional characterizations of GSH@Fe₃O₄ MNPs were performed using SEM-EDX, DLS, XRD, and FTIR. The nanochain-structured adsorbent was found to have an average size of 24 ± 1.29 nm and a zeta potential value of - 6.44 mV. The batch experiments showed that GSH@Fe₃O₄ MNPs have a brilliant removal efficiency of 97% and 79% for CV and PR dyes, respectively, within a period of 60 min. The influence of different operational parameters like adsorbent dosage, pH, temperature, reaction time, and initial dye concentration on the removal behaviour of the adsorbent was studied in detail. The adsorbate-adsorbent reaction was tested over isotherm models, and the reaction fitted well for Langmuir isotherm with an excellent q_max value of 1619.5 mg/g and 1316.16 mg/g for CV and PR dye, respectively. The experimental results were also validated using different reaction kinetics, and it was found that the pseudo-first-order model fits well for PR dye adsorption (R² = 0.91), while adsorption of CV dye was in best agreement with the pseudo-second-order kinetic model (R² = 0.98). Thermodynamic studies revealed that the adsorption reaction was spontaneous and endothermic in nature. Furthermore, GSH@Fe₃O₄ MNPs can be reused effectively up to 5 cycles of dye removal. Major mechanisms involved in the adsorption reaction were expected to be electrostatic attraction, hydrogen bonding, and π-interactions. The efficiency of GSH@Fe₃O₄ MNPs in real water samples suggested that it has a high potential for dye removal from complex aqueous systems and could be used as an effective alternative for remediation of dyes contaminated water.

Synergistic sorption performance of karaya gum crosslink poly(acrylamide-co-acrylonitrile) @ metal nanoparticle for organic pollutants

In this work, we tailor facile hydrogels nanocomposite (HNC) based on sustainable karaya gum for water treatment. Karaya gum crosslink poly(acrylamide-co-acrylonitrile) @ silver nanoparticle (KG-cl-P(AAm-co-AN)@AgNPs) HNC were made by an aqueous free radical in situ crosslink copolymerization of acrylamide (AAm) and acrylic acid (AA) in aqueous solution of KG-stabilized AgNPs. FTIR, XRD, DTA-TGA, SEM, and TEM were used to characterize HNC. The hydrogels' swelling, diffusion, and network characteristics were investigated. The removal efficiency of HNC was found to be 99% at pH 8 for a crystal violet (CV), dose of 0.02 g after 1 h. Dye adsorption by these hydrogels was also investigated in terms of isotherms, and kinetics. The dye's exceptionally high adsorption capacity on HNC for CV removal is explained by H-bonding interactions, as well as dipole-dipole and electrostatic interactions between anionic adsorbent and cationic dye molecules (Qmax, 1000 mg/g). The HNC can be regenerated with 0.1 M HCl and reused at least 10 times maintaining over 68% dye removal. The loading of AgNPs into the polymeric matrix of KG-cl-P(AAm-co-AN) significantly increases the removal percentage of CV dye from its aqueous solution, according to this study.

Adsorption of Cationic Pollutants from Water by Cotton Rope Coated with Cyclodextrin Polymers

The contamination from perilous organic compounds (pesticide and dyes) in water generates a significant problem for the environment and humans. A modified textile was prepared by a coating of anionic cyclodextrin polymer, obtained from the cross-linking between citric acid and β-cyclodextrin in the presence of poly (vinyl alcohol), on the cotton cord for cationic pollutant removal from an aqueous solution. Its physicochemical properties were also characterized by gravimetry, titration, stereomicroscopy, SEM, TGA, ¹³C NMR, and ATR-FTIR. The CC2 system exhibited 79.2% coating yield, 1.12 mmol/g COOH groups, 91.3% paraquat (PQ) removal, 97.0% methylene blue (MB) removal, and 98.3% crystal violet (CV) removal for 25 mg/L of initial concentration. The kinetics was fitted to the pseudo-second-order model using 6 h of contact time. The isotherm was suitable for the Langmuir isotherm with a maximum adsorption of 26.9 mg/g (PQ), 23.7 mg/g (MB), and 30.3 mg/g (CV). After 120 h of contact time in water and 5% v/v of HCI in ethanol, the weight loss was 7.5% and 5.6%, respectively. Finally, the recyclability performance reached 84.8% (PQ), 95.2% (MB), and 96.9% (CV) after five reuses.

α-Hydroxy acids modified β-cyclodextrin capped iron nanocatalyst for rapid reduction of nitroaromatics: A sonochemical approach

This study reports a sonochemical approach for the synthesis and catalytic performance of zerovalent iron nanoparticles (nZVI) capped with two cyclodextrin (CD) crosslinked polymers derived from Lactic acid and Citric acid (CDLA and CDCA respectively). The polymers and the catalysts were characterized by NMR, FTIR, HRTEM, DLS, Zeta potential, FESEM, EDAX, VSM, XRD, XPS, TGA analysis. The catalysts proved to be sustainable and recyclable for rapid sonochemical reduction of nitroaromatics under ambient conditions. The isolated yield of the derivatives was found to be greater than 90%. The results suggest excellent dispersibility, stability, high iron content and smaller size of CDLA polymer capped nZVI compared to CDCA capped nZVI, leading to two-fold higher catalytic activity. The effect of various crucial catalysis parameters was investigated and optimized. The scope of the reaction was extended to other nitroaromatics under the optimized conditions. Being magnetically separable, the cost effective and non-toxic catalysts exhibited high recycling efficiency (~13 cycles), high turnover number (TON) and turnover frequency (TOF). The recyclable catalysts could be low-cost and sustainable options for organic transformation in water via sonochemical approach in aqueous medium.

Enhanced degradation of sulfamethoxazole by a modified nano zero-valent iron with a β-cyclodextrin polymer: Mechanism and toxicity evaluation

Rising concern about emerging and already persisting pollutants in water has urged the scientific community to develop novel remedial techniques. A new group of remediation methods is based on the modification of nanoscale zero-valent iron particles (nZVI), which are well known for treating volatile organic compounds and heavy metals. The properties of nZVI may be further enhanced by modifying their structure or surface using "green" polymers. Herein, nZVI was modified by a β-cyclodextrin polymer (β-CDP), which is considered an environmentally safe and inexpensive adsorbent of contaminants. This composite was used for the first time for the degradation of sulfamethoxazole (SMX). Coating by β-CDP not only enhanced the degradation of SMX (>95%, under 10 min) by the nanoparticles in a wide pH range (3-9) and enabled their efficient reusability (for three cycles) but also made the coated nZVI less toxic to the model bioindicator microalga Raphidocelis subcapitata. Moreover, degradation products of SMX were found to be less toxic to Escherichia coli bacteria and R. subcapitata microalga, contrary to the SMX antibiotic itself, indicating a simple and eco-friendly cleaning process. This research aims to further stimulate and develop novel remedial techniques based on nZVI, and provides a potential application in the degradation of antibiotics in a wide pH range. Moreover, the wealth of available cyclodextrin materials used for surface modification may open a way to discover more efficient and attractive composites for environmental applications.

Cyclodextrin modified green synthesized graphene oxide@iron nanoparticle composites for enhanced removal of oxytetracycline

The presence of residual antibiotics will lead to potential environmental risks. Here cyclodextrins (CDs) were successfully used to modify graphene-based iron nanoparticles (GO@Fe NPs) to enhance the absorption of oxytetracycline hydrochloride (OTC). The removal of OTC decreased in the order: γCD-GO@Fe NPs > βCD-GO@Fe NPs > αCD-GO@Fe NPs > GO@Fe NPs, with better performance than that of bare GO and Fe NPs. Characterization techniques were applied to better understand how CDs impact the structure of GO@Fe NPs and improve removal performance. Raman and X-ray diffraction analysis showed that GO acted as a carrier to support Fe NPs within the grafted cyclodextrin, where GO also participated in the removal process. Cyclodextrin modified GO@Fe NPs had relatively small particle sizes (15 nm), with a high surface area (61.7 m² · g^-1). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy suggested that cyclodextrin acted as both a stabilizing and capping agent during green synthesis, which could protect the reactivity of Fe NPs and simultaneously reduce aggregation. A potential synthesis mechanism of cyclodextrins modified composites was also proposed, and subsequent wastewater testing indicated that γCD-GO@Fe NPs had high potential for practical applications.

Removal of crystal violet from water by poly acrylonitrile-co-sodium methallyl sulfonate (AN69) and poly acrylic acid (PAA) synthetic membranes

The current investigation is focused on the removal of crystal violet (CV) from water by adsorption process (bach method). To achieve this purpose, specific membranes were prepared from poly acrylonitrile-co-sodium methallyl sulfonate (AN69) and poly acrylic acid (PAA) blends. The adsorption of CV onto AN69/PAA membranes was studied under various conditions: membrane composition, pH, contact time, initial concentration and temperature. To understand the effect of membrane morphology on adsorption process, scanning electronic microscopy (SEM) was employed to determine the features of section and membrane’s surface. From isotherm results, it was found that: the maximum adsorption capacity Q m was 1250 mg g−1, the Langmuir separation factor R L was lying between 0.33 and 0.76, the Freundlich intensity was higher than Unit (n = 1.25) and the adsorption process follows preferentially the Langmuir model (correlation constant R 2 = 0.99). The mechanism of adsorption is perfectly fitted by pseudo second order. The obtained results tend to confirm that the removal of dye molecules is due to the establishment of strong electrostatic interactions between cationic dye molecules and anionic membrane groups. The high adsorption capacity (1250 mg g−1) for the small dye molecules may open wide opportunities to apply these membranes in the removal of various hazardous pollutants commonly present in water.

Graphene oxide loaded fibrous matrixes of polyether block amide (PEBA) elastomer as an adsorbent for removal of cationic dye from wastewater

Novel highly porous nanoparticle materials are increasingly being applied in adsorption processes, but they need to be supported by robust matrixes to maintain their functionality. We present a study of hosting graphene oxide (GO) particles on polyether block amide (PEBA) melt electrospun fibers and applying such composite matrix to the adsorption of the cationic dye (crystal violet) from water. Various amounts of GO (from 0.5 to 2.0%) were mixed into pure PEBA and electrospun by melt electrospinning obtaining micro fibrous matrixes. These were characterized for morphology (SEM), chemical composition (FTIR), crystallinity (XRD), and wetting behavior (WCA). The increasing amount of GO adversely affected fiber diameter (reduced from 13.18 to 4.38 μm), while the hydrophilic properties (Water contact angle decrease from 109 to 76°) and overall dye adsorption was increased. Efficient adsorption has been demonstrated, reaching approximately 100 % removal efficiency using a 2% GO composite matrix at a dose of 40 mg/l and pH of 10. Further increase of GO concentration in polymer is not feasible due to instability in the electrospinning process.

Synthesis of montmorillonite-supported nano-zero-valent iron via green tea extract: Enhanced transport and application for hexavalent chromium removal from water and soil

The nano-zero-valent iron composite (nZVI@TP-Mont) was successfully prepared using a low-cost and environmental-friendly green synthesis via tea leaves extract (tea polyphenols, TPs) and the montmorillonite (Mont). The batch and column experiments and characterization were conducted to investigate the transport behavior and Cr(VI) remediation by nZVI@TP-Mont in water/soil. Due to its particular surface characteristics and morphology (i.e., the Fe⁰ core wrapped by TPs, the doped sulfur, and interlayer structure), the nZVI@TP-Mont composite showed a great removal capacity of Cr(VI) and sufficient mobility under different soil conditions. We opine the increase in the Cr(VI) reduction of nZVI@TP-Mont was attributed to the tethering of Fe₂O₃ on the surface of Fe⁰ core by the support of Mont interlayer, especially the TP-coverage around nZVI@TP-Mont surface unwrapped, thereby increasing the regenerated reactive Fe²⁺ and the exposed reaction sites of Fe⁰ cores to Cr(VI). The increased transportability of nZVI@TP-Mont slightly depends on the heterogeneous soil properties (i.e., ionic strength, sand/soil ratio, and pH). The two-site kinetic attachment model fitting results suggest Cr(VI)/Cr(III) speciation associated with the agglomerated nZVI@TP-Mont were efficiently immobilized in soil. Therefore, this study would benefit the efficient application of the green-synthesized nZVI@TP-Mont in in-situ remediation of soils contaminated by Cr(VI).

Preparation of Sepiolite Nanofibers Supported Zero Valent Iron Composite Material for Catalytic Removal of Tetracycline in Aqueous Solution

The heavy use of antibiotics in medicine, stock farming and agriculture production has led to their gradual accumulation in environmental media, which poses a serious threat to ecological environment and human safety. As an efficient and promising catalyst for the degradation of antibiotics, nanoscale zero valent iron (nZVI) has attracted increasing attention in recent years. In this study, sepiolite nanofiber supported zero valent iron (nZVI/SEP) composite was prepared via a facile and environmentally friendly method. The nZVI particles (with size of 20–60 nm) were dispersed evenly on the surface of sepiolite nanofibers, and the catalytic performance for the removal of tetracycline hydrochloride (TC-HCl) in aqueous system was investigated. The effect of nZVI loading amount, catalyst dosage, H₂O₂ concentration and pH on the removal efficiency of TC-HCl were studied. It was revealed that the sepiolite supporter effectively inhibited the agglomeration of nZVI particles and increased the contact area between contaminant and the active sites, resulting in the higher catalytic performance than pure nZVI material. The TC-HCl removal efficiency of nZVI/SEP composite was up to 92.67% when TC-HCl concentration of 20 mg/L, catalyst dosage of 1.0 g/L, H₂O₂ concentration of 1.0 mM, pH value of 7. Therefore, the nZVI/SEP composites possess high catalytic activity for TC-HCl removal and have great application prospects in antibiotic wastewater treatment.

[Recent developments of pesticide adsorbents based on cyclodextrins]

The invention and application of pesticides have greatly increased the yield of crops, greatly contributing to ensuring people's basic livelihoods and gradually improving their livelihoods to a well-off level. However, foods, water sources, and soil, containing high levels of pesticide residues, result in increasingly serious pollution. Pesticide residues usually have the characteristics of micro toxicity, difficult biodegradation, and bioaccumulation, and thus pose serious threat to living organisms and ecosystems. In recent years, pesticide pollution has earned worldwide focus. Thus, methods for the efficient detection of trace pesticides and reduction of the harm caused by pesticide pollution are urgently required. Researchers have used catalysis, electrochemistry, membrane separation, adsorption, and other methods to enrich pesticides from complex matrices. Among these, adsorbents have attracted much attention owing to their advantages of simple operation steps, rapid treatment process, and low amounts of organic solvents required. Research on adsorption materials has always been a very active field, and is also the key to the success of separation and enrichment of pesticides from complex matrices. Development of adsorbents with the advantages of simple synthesis, environment-friendliness, high stability, and strong reusability is of great significance. There has been some progress in the field of pesticide adsorption using supramolecular compounds. Cyclodextrin is a macrocyclic compound with a cavity after crown ether, which can form inclusion complexes via host guest interactions as the main body. Cyclodextrin can also be modified by etherification, esterification, oxidation, and other chemical reactions to improve its adsorption performance. Pesticides can be classified into organic and inorganic substances. One of the most widely used inorganic fungicides is the Bordeaux solution, whose main component is Cu²⁺. Organic fungicides, insecticides, herbicides, and plant growth regulators are basically organic molecules, whose hydroxyl and carboxyl groups can form complexes with Cu²⁺. As a matrix, cyclodextrin not only increases the surface area of the materials, but also provides the binding sites of hydroxyl and carboxyl groups, which guarantees efficient enrichment of Cu²⁺. Organic pesticides with high polarity, high electron density, and strong hydrophobicity could be better adsorbed. In this paper, the application of cyclodextrin-based adsorbents in pesticide adsorption was reviewed, and on this basis, reference to future development directions and application prospects were provided. The adsorption capacity of individual pesticide adsorbents based on cyclodextrin, as reviewed in this paper, is not high enough. Therefore, improving the adsorption capacity is currently a major research target. Some of the above-mentioned adsorbents have unclear degradation mechanisms and can easily cause secondary pollution. Therefore, the development of environment-friendly pesticide adsorbents that are easy to regenerate is a promising research direction for the future. After adsorption, some detection methods are used to determine whether the pesticide residues are up to the standard; however, the detection instruments are expensive. Therefore, the development of a combined detection mechanism that can reduce workload and cost is a promising research direction. Finally, the development of smart cyclodextrin-based adsorbents is also an efficient and rapid method to reduce the cost of detecting residual pesticide concentrations and the risk of pesticide pollution. For example, intelligent materials, whose color changes can be observed by the naked eye, not only adsorb pesticides, but also respond according to the concentration of residual pesticides.

Vitamin C mediates the activation of green tea extract to modify nanozero-valent iron composites: Enhanced transport in heterogeneous porous media and the removal of hexavalent chromium

Both green tea (GT) extract and vitamin C (VC) were used for the reduction of Fe³⁺ to Fe⁰ using a green synthesis method. Modified nanozero-valent iron (GT-nZVI@VC nanocomposites) was successfully obtained and characterized as α-Fe⁰-iron oxide/VC by multiple analytical methods. The GT-nZVI@VC nanocomposites showed better transportability than nZVI, in that transport behavior was slightly dependent on various ratios of sand/soil in water-saturated heterogeneous porous media. Breakthrough curves of GT-nZVI@VC nanocomposites in paddy soil exhibited "blocking effects" and were well described using a first-order straining coefficient (k₂) on site 2 obtained from a two-site kinetic attachment model. In particular, GT-nZVI@VC (VC/Fe = 0.6) showed higher Cr(VI) removal (especially reducibility) in both paddy soil and water compared to that of nZVI and VC. It is likely that the synergistic effects of VC (ascorbic acid) and tea polyphenols can increase the released free electrons into solution, favoring the high reduction of Cr(VI) into Cr(III) (i.e., FeOCr₂O₃, Cr(OH)₃ and Cr₂O₃), where Cr(III) is prone to be immobilized by the nanocomposites in soil. This research highlights that VC can mediate the activation of GT extract to successfully modify nZVI, which could be beneficial for efficient transport in subsurface and remediation of Cr(VI)-contaminated soil and underground water.

Zero Valent Iron Nanoparticle-Loaded Nanobentonite Intercalated Carboxymethyl Chitosan for Efficient Removal of Both Anionic and Cationic Dyes

A zero valent iron-loaded nano-bentonite intercalated carboxymethyl chitosan (nZVI@nBent-CMC) composite was fabricated and characterized by FT-IR, TEM, TEM-EDX, XRD, BET surface area, and zeta potential measurements. The as-fabricated nZVI@nBent-CMC composite exhibited excellent removal efficiency for both anionic Congo red (CR) dye and cationic crystal violet (CV) dye. The maximum uptake capacities of CR and CV onto the nZVI@nBent-CMC composite were found to be 884.95 and 505.05 mg/g, respectively. The adsorption process of both dyes well fitted with the Langmuir isotherm model and pseudo-second order kinetic model. Thermodynamic data clarified that the adsorptions of both CR and CV onto the nZVI@nBent-CMC composite are spontaneous processes. Moreover, the adsorption of CR onto the nZVI@nBent-CMC composite was found to be an exothermic process while that of CV is an endothermic process. The nZVI@nBent-CMC composite also exhibited excellent reusability for both studied dyes without noticeable loss in the removal efficiency, suggesting its validity to remove both anionic and cationic dyes from wastewater.

Complexation of an Azo Dye by Cyclodextrins: A Potential Strategy for Water Purification

The chemistry of the host-guest complex formation has received much attention as a highly efficient approach for use to develop economical adsorbents for water purification. In the present study, the synthesis of three β-cyclodextrin (β-CD) inclusion complexes with the oil orange SS (OOSS) azo dye as a guest molecule and their potential applications in water purification are described. The complexes were synthesized by the coprecipitation method and characterized by Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). FTIR and thermal analyses confirmed the encapsulation of OOSS dye within the hydrophobic cavity of β-CD. The encapsulation of hydrophobic dye inside the β-CD cavity was mainly due to the hydrophobic-hydrophobic interaction. The results showed that the stability of the OOSS dye had been improved after the complexation. The effect of three different compositions of the host-guest complexes was analyzed. The present study demonstrated that the hydrophobic dye could be removed from aqueous solution via inclusion complex formation. Thus, it can play a significant role in removing the highly toxic OOSS dye from the industrial effluent.

Green synthesis of hydrophilic activated carbon supported sulfide nZVI for enhanced Pb(II) scavenging from water: Characterization, kinetics, isotherms and mechanisms

For green synthesis of nZVI with low aggregation and high antioxidation, green tea extracts were explored as reductant during the synthesis with modification by hydrophilic porous activated carbon (HPAC) and sulfidation technology. Characterization results identified the effective preparation of porous activated carbon (PAC) with microporous and mesoporous characteristics, and the successful loading of S-nZVI nanoparticles on S-nZVI@HPAC. Moreover, HPAC was identified to have a higher degree of hydrophilicity surface compared to PAC, while the S-nZVI with an atomic ratio of S/Fe (0.16) further improved the hydrophilic performance of S-nZVI@HPAC. Batch adsorption revealed that the S-nZVI@HPAC possessed a pH-dependent adsorption performance with a fast kinetic equilibrium within 120 min and an outstanding Pb(II) binding of 295.30 mg/g at pH = 5.0 and 50 °C. Thermodynamic results exhibited positive ΔH° and ΔS°, clearly indicative of the endothermic property of Pb(II) uptake onto S-nZVI@HPAC with an increase in randomness, while the negative ΔG° uncovered a favorable and spontaneous process. Furthermore, the S-nZVI@HPAC was believed to enhance the Pb(II) uptake via the synergistic effects of electrostatic attraction, chemical precipitation, complexation and reduction. The results of this work highlighted the hydrophilic porous activated carbon supported sulfide nZVI for efficient remediation of Pb(II) contaminated water.

Application of the immobilized enzyme on magnetic graphene oxide nano-carrier as a versatile bi-functional tool for efficient removal of dye from water

Herein, we report bi-functional applications of a novel immobilized enzyme on the modified magnetic graphene oxide (GO) for effective removal of dyes from water. The amine functionalized GO nano-carrier was covalently attached to a model enzyme (PersiManXyn1). The enzyme assays showed that the specific activities of the free and immobilized enzyme were 856.05 and 1141.1 µmolmin^-1mg^-1, respectively. While the free enzyme showed only 5% of its maximum activity, the immobilized PersiManXyn1 preserved more than 35% of its activity, at 90 °C. After four weeks storage, the free enzyme has been deactivated, but the immobilized enzyme retained 54% of its initial activity. The immobilized PersiManXyn1 was proficiently applied for dye removal from water using two strategies. While only pristine nano-carrier and free enzyme showed no considerable catalytic ability, the immobilized PersiManXyn1 could catalytically reduce the concentrated dye solutions within 150 s with superior reusability (94% dye removal after 15^th cycle). Proficient treatment of a real textile effluent by the immobilized PersiManXyn1 approved its practical applications in the water remediation.

Application of cellulose nanocrystals prepared from agricultural wastes for synthesis of starch-based hydrogel nanocomposites: Efficient and selective nanoadsorbent for removal of cationic dyes from water

A novel and bio-based hydrogel nanocomposite were developed using reinforcement of starch grafted copolymers of 2-acrylamido-2methyl propane sulfonate and acrylic acid (starch-g-(AMPS-co-AA)) hydrogel with magnetite-functionalized cellulose nanocrystals (MCNCs). The MCNCs-hydrogel was utilized as a proficient and environmentally benign nanoadsorbent for removal of cationic dyes with great capacity and selectivity. Sugar-beet pulp (SBP) was exploited for CNCs production through acid hydrolysis of enzymatic-mediated SBP. Fe₃O₄ nanoparticles were anchored on CNCs to synthesize MCNCs as the nanofiller of MCNCs/starch-g-(AMPS-co-AA) hydrogel. The synthesis of CNCs, MCNCs and hydrogel nanocomposite were confirmed using FESEM, FTIR, VSM and TGA analyses. Hydrogel nanocomposite showed excellent and reusable capacity for specific adsorption of cationic dyes. The effects of nanoadsorbent dosage, time, pH, dye initial concentration, and temperature on the adsorption were scrutinized for two model cationic dyes (crystal violet (CV) and methylene blue (MB). Adsorption capacities for CV and MB were 2500.0 mg/g and 1428.6 mg/g, respectively.

Cyclodextrin-Based Synthesis and Host-Guest Chemistry of Plasmonic Nanogap Particles with Strong, Quantitative, and Highly Multiplexable Surface-Enhanced Raman Scattering Signals

We developed a synthetic strategy to form cyclodextrin-based intrananogap particles (CIPs) with a well-defined ∼1 nm interior gap in a high yield (∼97%), and were able to incorporate 10 different Raman dyes inside the gap using the cyclodextrin-based host-guest chemistry, leading to strong, reproducible, and highly multiplexable surface-enhanced Raman scattering (SERS) signals. The average SERS enhancement factor (EF) for CIPs was 3.0 × 10⁹ with a very narrow distribution of the EFs that range from 9.5 × 10⁸ to 9.5 × 10⁹ for ∼95% of the measured particles. Remarkably, 10 different Raman dyes can be loaded within the nanogap of CIPs, and 6 different Raman dye-loaded CIPs with little spectral overlaps were distinctly detected for cancer cell imaging applications with a single excitation source. Our synthetic strategy provides new platforms in precisely forming plasmonic nanogap structures with all key features for widespread use of SERS including strong signal intensity, reliability in quantification of signal and multiplexing capability.

Proficient dye removal from water using biogenic silver nanoparticles prepared through solid-state synthetic route

An environmentally benign, one-pot and highly scalable method was presented to produce biogenic silver nanoparticles (Ag NPs) using the solid-state synthetic route. Four plant-derived candidate bio-reductants (i.e., Datura stramonium, Papaver orientale, Mentha piperita, and Cannabis sativa) were investigated to compare the efficiency of solid-state route and typical solution method. M. piperita was selected as the best plant resource to produce totally pure and uniform Ag NPs (average diameter of 15 nm) without any aggregation. The purity and size of biogenic Ag NPs, were tailored by adjusting the M. piperita leaf powder/silver nitrate weight ratio and temperature. The as-synthesized Ag NPs were effectively utilized as an eco-friendly nanoadsorbent in water remediation to remove a model dye (i.e., crystal violet). The key factors affecting on the sorption process (i.e., nanoadsorbent dosage, temperature, pH, dye initial concentration, and shaking time) were investigated. The pseudo-second-order kinetic model was well fitted to the sorption process and at the optimum sorption conditions, based on the Langmuir model, the adsorption capacity was found to be 704.7 mg/g. The current, cost effective and feasible method could be considered as an applicable strategy to produce green, reusable and proficient Ag NPs as nanoadsorbents for removal of dyes from contaminated water.

Facile synthesis of superparamagnetic β-CD-MnFe2O4 as a peroxymonosulfate activator for efficient removal of 2,4- dichlorophenol: structure, performance, and mechanism

In this study, superparamagnetic β-CD-MnFe₂O₄ with a large surface area was synthesized via a facile co-precipitation method, with β-cyclodextrin (β-CD) acting as a coating agent. The as-prepared β-CD-MnFe₂O₄ exhibited better catalytic performance than bare MnFe₂O₄ in terms of activating peroxymonosulfate (PMS) to degrade 2,4-dichlorophenol (2,4-DCP) over a broad pH range of 5-11. Electron spin resonance spectroscopy (ESR) and free radical quenching experiments indicate that various active species (SO₄^-/OH/O₂^-/¹O₂) are generated in the β-CD-MnFe₂O₄/PMS system and that pollutants trapped in the cyclodextrin cavity are quickly degraded. Various reaction parameters of the β-CD-MnFe₂O₄/PMS system and the stability of β-CD-MnFe₂O₄ were also investigated. The results indicate that β-CD-MnFe₂O₄ is promising for use in water purification owing to its excellent magnetic separation and recovery properties and good resistance to humic acid (HA).

Sustainable Synthesis of Nanoscale Zerovalent Iron Particles for Environmental Remediation

Nanoscale zerovalent iron (nZVI) particles represent an important material for diverse environmental applications because of their exceptional electron-donating properties, which can be exploited for applications such as reduction, catalysis, adsorption, and degradation of a broad range of pollutants. The synthesis and assembly of nZVI by using biological and natural sustainable resources is an attractive option for alleviating environmental contamination worldwide. In this Review, various green synthesis pathways for generating nZVI particles are summarized and compared with conventional chemical and physical methods. In addition to describing the latest environmentally benign methods for the synthesis of nZVI, their properties and interactions with diverse biomolecules are discussed, especially in the context of environmental remediation and catalysis. Future prospects in the field are also considered.

Synthesis and adsorption behavior of hydroxypropyl-β-cyclodextrin-polyurethane magnetic nanoconjugates for crystal and methyl violet dyes removal from aqueous solutions

In this study, hydroxypropyl-β-cyclodextrin (HPβCD), HPβCD-conjugated magnetic nanoparticles (HPMN) and HPβCD-conjugated magnetic nanoparticles with polyurethane networks (HPMNPU) were synthesized and used as adsorbents for the removal of crystal violet (CV) and methyl violet (MV) dyes from aqueous solutions. Magnetic nanocomposites were characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The results of characterization analyses indicated that HPβCD was successfully modified with magnetic nanoparticles and polyurethane networks. In this work, a novel definitive screening design (DSD) was initially used to investigate the adsorption and elimination of dye impurities. This method allows a drastic reduction in the number of experiments needed to investigate those systems characterized by a large number of variables. The effects of nine quantitative parameters were investigated: initial dye concentration, adsorbent dose, contact time, temperature, pH, ionic strength, HMDI/HP ratio, MN/HP ratio, and stirrer speed. Analysis of a DSD model revealed that only four variables, namely, adsorbent dose, contact time, initial dye concentration and HMDI/HP ratio were statistically significant. Compared with HPMN, HPMNPU nanocomposites showed better adsorption performance for the removal of CV and MV from aqueous solutions. The maximum adsorption capacity values of HPMNPU were approximately 1269 mg g-1 and 1667 mg g-1 for CV and MV, respectively. This study showed that HPMNPU adsorbents exhibited high adsorption performance for the removal of CV and MV from water and could be promising adsorbent materials for the efficient removal of cationic dyes from wastewaters.

Microwave-accelerated sorption of cationic dyes onto green marine algal biomass

Monolithic algal green powder (MAGP) was fabricated based on the marine green macroalga Enteromorpha flexuosa. It was scrutinized by using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared (FT-IR), point of zero charge (PH_PZC), and Brunauer-Emmett-Teller (BET) surface area. The ability of Enteromorpha flexuosa to capture both crystal violet (CV) and methylene blue (MB) from aqueous solutions was evaluated. The influence of variable conditional parameters on CV dye and MB dye batch sorption was investigated. Results showed that percentage removal of 90.3% and 93.4% were obtained under optimum conditions of variables for CV and MB, respectively. Effect of microwave radiation on dye sorption was also appraised. Processing the sorption under microwave irradiation (microwave-enforced sorption, MES) increases mass transfer and a contact time as low as 1 min is sufficient under optimized conditions (exposure time and power) reaching the equilibrium. The reusability of MAGP sorbent was achieved for four cycles of sorption/desorption by using 0.5 M HCl. The ability of MAGP for cationic dyes removal from spiked tap water and petrochemical plant discharge wastewater samples was successfully registered. Ultimately, the displayed data showed a superior and excellent ability of algal powder to be exploited as a green, harmless, and effective sorbent for cationic dye removal.

Synthesis of a novel 3,5-diacrylamidobenzoic acid based hyper-cross-linked resin for the efficient adsorption of Congo Red and Rhodamine B

A novel hyper cross-linked, 3,5-diacrylamidobenzoic acid based resin (APEADA) has been synthesized for the highly efficient removal of Congo red (CR) and Rhodamine B (RhB) from aqueous solution. The synthesized resin was extensively characterized by FT-IR, FESEM, PXRD, EDX, BET analysis, TGA and solid state ¹³C (CP-MAS) NMR. APEADA exhibits thermal stability (≈ 200 °C) and a considerable surface area (64.78 m² g^-1), as suggested by Thermogravimetric Analysis (TGA) and Brunauer-Emmett-Teller (BET) analysis, respectively. The experimental data of dyes adsorption onto resin was examined by a variety of isotherm models wherein Langmuir and Temkin models were found to be the best fit for explaining the adsorption of both RhB (R² = 0.9899) and CR (R² = 0.9919). The resin can efficiently remove CR (92.03%) at pH 8.14 and moderately adsorb RhB (45.3%) at pH 5.01 and exhibits maximum adsorption capacity (Q_max) for CR (280.0 mg g^-1) and RhB (23.28 mg g^-1) at 318.6 K. The thermodynamic analysis of the data revealed that the adsorption processes were exothermic and spontaneous. Moreover, APEADA showed efficient removal efficiency (80.13%) for dyes in simulated effluents which warrants its utility and effectiveness in industrial waste water treatment.