Recyclable Capture and Destruction of Aqueous Micropollutants Using the Molecule-Specific Cavity of Cyclodextrin Polymer Coupled with KMnO4 Oxidation

Bioavailability for organic chemical bioaccumulation follows the power law

Despite the importance of bioavailability for organic chemical bioaccumulation by terrestrial and benthic invertebrates, the principles of bioavailability for organic chemical bioaccumulation remain poorly understood. Here we use large-scale databases with contrasting geographic, compound and organism coverage (from 925 sites, 446 compounds and 184 invertebrate species), and report that bioavailability for organic chemical bioaccumulation follows the power law. It represents that the internal concentration of organic chemicals is the composite power function of the lipid fraction of invertebrates, bulk site concentration of compounds, and organic carbon content of soils/sediments. This law directly links environmental exposures and body burdens of organic chemicals in contaminated sites, and provides a method for enabling case-specific risk assessments of a vast number of organic chemicals and contaminated sites. Our findings may pave the way for translating bioavailability knowledge into risk-oriented regulation of organic chemicals and contaminated sites.

An integrated approach using ozone nanobubble and cyclodextrin inclusion complexation to enhance the removal of micropollutants

Ozone (O₃) has been widely used for the elimination of recalcitrant micropollutants in aqueous environments, due to its strong oxidation ability. However, the utilization efficiency of O₃ is constrained by its low solubility and short half-life during the treatment process. Herein, an integrated approach, using nanobubble technology and micro-environmental chemistry within cyclodextrin inclusion cavities, was studied in order to enhance the reactivity of ozonisation. Compared with traditional macrobubble aeration with O₃ in water, nanobubble aeration achieved 1.7 times higher solubility of O_3, and increased the mass transfer coefficient 4.7 times. Moreover, the addition of hydroxypropyl-β-cyclodextrin (HPβCD) further increased the stability of O₃ through formation of an inclusion complex in its molecule-specific cavity. At a HPβCD:O₃ molar ratio of 10:1, the lifespan of O₃ reached 18 times longer than in a HPβCD-free O₃ solution. Such approach accelerated the removal efficiency of the model micropollutant, 4-chlorophenol by 6.9 times, compared with conventional macrobubble ozonation. Examination of the HPβCD inclusion complex by UV-visible spectroscopy and Nuclear Magnetic Resonance analyses revealed that both O₃ and 4-chlorophenol entered the HPβCD cavity, and Benesi-Hildebrand plots indicated a 1:1 stoichiometry of the host and guest compounds. Additionally, molecular docking simulations were conducted in order to confirm the formation of a ternary complex of HPβCD:4-chlorophenol:O₃ and to determine the optimal inclusion mode. With these results, our study highlights the viability of the proposed integrated approach to enhance the ozonation of organic micropollutants.

Efficient photoelectrocatalytic performance of beta-cyclodextrin/graphene composite and effect of Cl− in water: degradation for bromophenol blue as a case study

Photoelectrocatalytic technology has proven to be an efficient way of degrading organic contaminants, including dyes. Graphene (GR) -based catalysts have been frequently used in photoelectrocatalysis, due to their excellent catalytic performances. In this work, the GR/beta-cyclodextrin (GR/β-CD) composite was prepared and used for a widely used triphenylmethane dye (bromophenol blue, BPB) photoelectrocatalytic degradation. The results indicated that the degradation of the prepared GR/β-CD composite for BPB was effective with the combination of external bias voltage and simulated sunlight irradiation. Under optimum conditions, the BPB (10 mg L⁻¹) was completely eliminated by GR/β-CD composite within 120 min. ˙O₂⁻ played a prominent role in the BPB photoelectrocatalytic degradation. The time required for the removal of BPB in water to reach 100% can be reduced to 30 min with the presence of Cl⁻, owing to the generation of ˙Cl. Moreover, the toxicity of the degraded system with Cl⁻, predicted by the QSAR (Quantitative Structure–Activity Relationship) model in ECOSAR (Ecological Structure–Activity Relationships) program, was weaker than that without Cl⁻. The prepared GR/β-CD composite revealed great advantages in photoelectrocatalytic degradation of organic pollutants due to its metal-free, low cost, simplicity, and efficient performance. This work provided new insight into the efficient and safe degradation of organic pollutants in wastewaters.

O₂˙⁻ played a crucial role in the photoelectrocatalytic degradation of BPB by the prepared GR/β-CD. Cl⁻ marginally promoted the degradation of BPB and chlorinated intermediates were generated.

The classification and application of cyclodextrin polymers: a review

After introducing the concept of cyclodextrin polymers, their classification and applications have been summarized.

Maleic Anhydride Cross-Linked β-Cyclodextrin-Conjugated Magnetic Nanoadsorbent: An Ecofriendly Approach for Simultaneous Adsorption of Hydrophilic and Hydrophobic Dyes

A magnetic nanoadsorbent with a cross-linked β-Cyclodextrin maleic anhydride polymer capable of simultaneous removal of hydrophilic and hydrophobic dyes was developed with high efficacy and desorption/recycling efficiency. The effect of various parameters (concentration, adsorbent dosage, contact time, pH, and temperature) was evaluated to assess the optimum adsorption conditions. The superparamagnetic nanoadsorbent (SPNA) could be easily separated by magnetic decantation and showed maximum removal of malachite green with 97.2% adsorption efficiency. Studies on simultaneous adsorption of dyes from a mixture were performed and the adsorption capacity was calculated. Interestingly, the phenomenon of competitive adsorption was observed. The adsorption process can be fitted well into the Langmuir isotherm model and follows pseudo-second-order kinetics. SPNA could be effectively regenerated and recycled at least five times without any significant loss in removal efficiency. SPNA could be an ideal adsorbent for water remediation because of excellent dye removal efficiency in addition to chemical stability, ease of synthesis, and better reusability.

Cyclodextrin-enhanced 1,4-dioxane treatment kinetics with TCE and 1,1,1-TCA using aqueous ozone

Enhanced reactivity of aqueous ozone (O₃) with hydroxypropyl-β-cyclodextrin (HPβCD) and its impact on relative reactivity of O₃ with contaminants were evaluated herein. Oxidation kinetics of 1,4-dioxane, trichloroethylene (TCE), and 1,1,1-trichloroethane (TCA) using O₃ in single and multiple contaminant systems, with and without HPβCD, were quantified. 1,4-Dioxane decay rate constants for O₃ in the presence of HPβCD increased compared to those without HPβCD. Density functional theory molecular modeling confirmed that formation of ternary complexes with HPβCD, O₃, and contaminant increased reactivity by increasing reactant proximity and through additional reactivity within the HPβCD cavity. In the presence of chlorinated co-contaminants, the oxidation rate constant of 1,4-dioxane was enhanced. Use of HPβCD enabled O₃ reactivity within the HPβCD cavity and enhanced 1,4-dioxane treatment rates without inhibition in the presence of TCE, TCA, and radical scavengers including NaCl and bicarbonate. Micro-environmental chemistry within HPβCD inclusion cavities mediated contaminant oxidation reactions with increased reaction specificity.

Cu2O@β-cyclodextrin as a synergistic catalyst for hydroxyl radical generation and molecular recognitive destruction of aromatic pollutants at neutral pH

Wastewater systems contain a large number of compounds, such as anthropogenic aromatic pollutants and natural organic matter (NOM), and usually have pH higher than 4. Fenton-like reaction is the most widespread method for removal of organic pollutants, but their reactivity with H₂O₂ may be inhibited by NOM due to the competition of hydroxyl radicals and chelating agents. In this work, Cu₂O@β-cyclodextrin was developed to achieve the collaboration between molecular recognition and Fenton-like catalysis to destruct aromatic pollutants at neutral pH. In Cu₂O@β-CD, covalent CuOC bond was topotaxially converted from CuCl assisted by β-CD at room temperature. Covalently linked β-CD could keep humic acid from interfering catalytic performance of Cu₂O surfaces and inhibit the leaching of copper. A higher catalytic ability was observed for Cu₂O@β-CD with rate constant 0.0331 min^-1 than Cu₂O (0.0064 min^-1) at neutral pH. A mechanism of synergistic catalysis was proposed on the basis of Cu⁺, β-CD and phenoxo-Cu²⁺ complexes in the Cu₂O@β-CD/BPA/H₂O₂ system. The strategy of coupling molecular recognition into Fenton-like reaction provides an efficient and promising approach to the destruction of aromatic pollutants at neutral pH.

A luminescent cerium metal–organic framework for the turn-on sensing of ascorbic acid

Based on a simple redox reaction, the cerium metal–organic framework (ZJU-136-Ce) exhibits highly sensitive and selective turn-on sensing of AA.

Stabilization of nanosized titanium dioxide by cyclodextrin polymers and its photocatalytic effect on the degradation of wastewater pollutants

Advanced oxidation processes (AOPs) are considered highly competitive water treatment technologies for the removal of organic pollutants. Among AOP techniques, photocatalysis has recently been the most widely studied. Our aims were to investigate how the dispersion of nanosized titanium dioxide (nanoTiO₂) applied in photodegradation-based procedures can be stabilized with cyclodextrins in order to obtain a new, more efficient photocatalyst for the purification of waters polluted by xenobiotics applying UV irradiation. During our work, on the one hand, we studied the behavior and stability of nanoTiO₂ in cyclodextrin solutions. On the other hand, we used various monomer and polymer cyclodextrin derivatives, and assessed the options for nanoTiO₂ stabilization in the presence of various salts and tap water on the basis of turbidity tests. The physical stability of nanoTiO₂ dispersions is diminished in the presence of the salts found in tap water (and occurring also in surface waters and ground water) and they are precipitated immediately. This colloidal instability can be improved by cyclodextrin derivatives. Based on the results of our studies we have selected carboxymethyl β-cyclodextrin polymer (CMBCD-P) for stabilization of nanoTiO₂ dispersions. The photocatalytic degradation of methylene blue and ibuprofen as model organic pollutants in various media (distilled water, NaCl solution and tap water) has been studied using nanoTiO₂ as catalyst stabilized by CMBCD-P. CMBCD-P itself showed a catalytic effect on the UV degradation of methylene blue. In addition to enhancing the colloid stability of nanoTiO₂ CMBCD-P showed also synergistic effects in catalyzing the photodecomposition process of the dye. On the other hand, ibuprofen as a model pharmaceutical, a pollutant of emerging concern (EP), was protected by CMBCD-P against the photocatalytic degradation showing that inclusion complex formation can result in opposite effects depending on the structure of the host–guest complex.

High Adsorption of Sulfamethoxazole by an Amine-Modified Polystyrene-Divinylbenzene Resin and Its Mechanistic Insight

Sulfamethoxazole (SMZ) adsorption by a series of amine-modified polystyrene-divinylbenzene resins (PSA/B/C/D) was investigated. All resins showed a similar pH dependent adsorption of SMZ but their capacities were linearly related with the contents of primary amines (-NH2) rather than secondary amines (-NH-). Mechanisms of SMZ adsorption by PSA (highest -NH2 content) were discussed as an example. Due to comparable pKa, H-bonding interactions of -NH2(0) with SMZ(0) (regular H-bond) and SMZ(-) (negative charge-assisted H-bond, (-)CAHB) successively contributed most adsorption (pH 4-9). At weakly acidic pH, -NH2(0) was partially protonated and electrostatic attraction between -NH3(+) and SMZ(-) occurred concurrently, but could be hindered by increased loading of SMZ(0). Hydrophobic/ π-π interactions were not major mechanisms as phenanthrene and nitrobenzenes had little effect on SMZ adsorption. At alkaline pH, where SMZ(-) and -NH2(0) prevailed, adsorption was accompanied by the stoichiometric (∼1.0) proton exchange with water, leading to OH(-) release and the formation of (-)CAHB [SO2N(-)···H···NH2]. The interaction and SMZ spatial distribution in the resin-phase were further confirmed by FTIR and Raman spectra. SMZ was uniformly adsorbed on external and interior surfaces. SMZ adsorption by PSA had low-interference from other coexistent matter, but high stability after multiple regenerations. The findings will guide new adsorbent designs for selectively removing target organics.

Evaluating bioavailability of organic pollutants in soils by sequential ultrasonic extraction procedure

Under current retrospective risk assessment framework, the total concentrations of organic pollutants in soils have been employed as the standard for over 30 years. The total concentrations reflect the overall accumulation in soils but tend to be overly conservative for assessing the ecological risks, where the bioavailability plays an important role. In this study, the bioavailability of organic pollutants in soils was evaluated using a stepwise and tiered classification method, namely the sequential ultrasonic extraction procedure (SEUP). The water-soluble and acid-soluble fractions extracted by the SEUP were the bioavailable fractions. The reliability and environmental relevance of the speciation method were examined with representative organic pollutants using the root uptake methods and the semipermeable membrane devices (SPMDs). The plant uptake amounts corrected with weight were highly correlated with the bioavailable fractions (R(2) > 0.75). The amounts of the bioavailable fractions were negatively correlated with the logKow values (R(2) ranging from 0.71 to 0.77) of the organic pollutants and the contents of soil organic matter (R(2) ranging from 0.68 to 0.96). As a refinement of the current risk assessment framework, the SUEP that has proved to be a reliable and convenient is thus highly recommended for evaluating the bioavailability of organic pollutants in soils.

A pH-responsive and magnetically separable dynamic system for efficient removal of highly dilute antibiotics in water

In order to control the antibiotic-related crisis and reduce the negative impacts on the environment and human health, it is urgent to develop effective technologies to eliminate residual antibiotics in water. Herein, we successfully fabricated a novel, pH-responsive and magnetically separable dynamic system for micropollutant adsorption and oxidation degradation in graphene oxide (GO)/nanoscale zero-valent iron (nZVI) composite with macroscopic structure. The pH-responsive self-assembly behavior of GO/nZVI composite was explored. The macroscopic structure of GO/nZVI composite serves as an excellent adsorbent for antibiotic removal in water. The adsorption process is fast and highly efficient even in high salty and humic acid containing water under acid to neutral conditions. After removal antibiotics, GO/nZVI composite is conveniently separated by magnetic system and put into alkaline solution (pH > 9) for adsorbent regeneration. Interestingly, it is found that at pH > 9, GO/nZVI composite disassembles partly upon increasing pH values, leading to the elution of antibiotics for efficient antibiotics degradation by ozonization. More importantly, this pH-responsive GO/nZVI system exhibits high removal efficiency, high stability, reusability and easily separation, making it a promising method for treatment of water with micropollutants.

Effective adsorption of phenolic pollutants from water using β-cyclodextrin polymer functionalized Fe3O4 magnetic nanoparticles

β-Cyclodextrin polymer functionalized magnetic nanoparticles possess adsorption properties favorable for the purpose of removing phenolic pollutants.

Hyper-crosslinked β-cyclodextrin porous polymer: an adsorption-facilitated molecular catalyst support for transformation of water-soluble aromatic molecules

A hyper-crosslinked β-cyclodextrin porous polymer (BnCD-HCPP) was designed and synthesized facilely by β-cyclodextrin benzylation and subsequent crosslinking for efficient adsorption and catalysis.

A hyper-crosslinked β-cyclodextrin porous polymer (BnCD-HCPP) was designed and synthesized facilely by β-cyclodextrin benzylation and subsequent crosslinking via a Friedel–Crafts alkylation route. The BnCD-HCPP shows an extremely high BET surface area, large pore volume, and high thermal stability, making it a highly efficient adsorbent for removal of aromatic pollutants from water. The adsorption efficiency in terms of distribution coefficient, defined as the ratio of adsorption capacity to equilibrium adsorbate concentration, ranged from 10³ to 10⁶ mL g^–1 within a concentration of 0–100 ppm, one order of magnitude higher than that of other β-cyclodextrin-based adsorbents reported previously. The molar percentage of adsorbate to β-cyclodextrin exceeded 300%, suggesting that the adsorption occurred not only in the cyclodextrin cavities via a 1 : 1 complexation, but also in the nanopores of the BnCD-HCPP created during the hyper-crosslinking. The BnCD-HCPP can be further functionalized by incorporation of gold nanoparticles for catalytic transformation of adsorbed phenolic compounds such as 4-nitrophenol to 4-aminophenol.