New Poly(β-Cyclodextrin)/Poly(Vinyl Alcohol) Electrospun Sub-Micrometric Fibers and their Potential Application for Wastewater Treatments

Dextrin-Based Adsorbents Synthesized via a Sustainable Approach for the Removal of Salicylic Acid from Water

Pharmaceuticals such as salicylic acid are commonly detected in wastewater and surface waters, increasing concern for possible harmful effects on humans and the environment. Their difficult removal via conventional treatments raised the need for improved strategies, among which the development of bioderived adsorbents gained interest because of their sustainability and circularity. In this work, biobased cross-linked adsorbents, synthesized via a sustainable approach from starch derivatives, namely beta-cyclodextrins and maltodextrins, were at first characterized via FTIR-ATR, TGA, SEM, and elemental analysis, showing hydrophilic granular morphologies endowed with specific interaction sites and thermal stabilities higher than 300 °C. Subsequently, adsorption tests were carried out, aiming to assess the capabilities of such polymers on the removal of salicylic acid, as a case study, from water. Batch tests showed rapid kinetics of adsorption with a removal of salicylic acid higher than 90% and a maximum adsorption capacity of 17 mg/g. Accordingly, continuous fixed bed adsorption tests confirmed the good interaction between the polymers and salicylic acid, while the recycling of the adsorbents was successfully performed up to four cycles of use.

ESI-IM-MS characterization of cyclodextrin complexes and their chemically cross-linked alpha (α-), beta (β-) and gamma (γ-) cyclodextrin particles as promising drug delivery materials with improved bioavailability

Cyclodextrins (CDs) are natural cyclic oligosaccharides with a relatively hydrophobic cavity and a hydrophilic outer surface. In this study, alpha (α-), beta (β-) and gamma (γ-) CD particles were prepared by directly using α-, β-, and γ-CDs as monomeric units and divinyl sulfone (DVS) as a crosslinker in a single-step via reverse micelle microemulsion crosslinking technique. Particles of p(α-CD), p(β-CD), and p(γ-CD) were perfectly spherical in sub- 10 µm size ranges. The prepared p(CD) particles at 1.0 mg/mL concentrations were found biocompatible with > 95 % cell viability against L929 fibroblasts. Furthermore, p(α-CD) and p(β-CD) particles were found non-hemolytic with < 2 % hemolysis ratios, whereas p(γ-CD) particles were found to be slightly hemolytic with its 2.1 ± 0.4 % hemolysis ratio at 1.0 mg/mL concentration. Furthermore, a toxic compound, Bisphenol A (BPA) and a highly antioxidant polyphenol, curcumin (CUR) complexation with α-, β-, and γ-CD molecules was investigated via Electrospray-Ion Mobility-Mass Spectrometry (ESI-IM-MS) and tandem mass spectrometry (MS/MS) analysis. It was determined that the most stable noncovalent complex was in the case of β-CD, but the complex stoichiometry was changed by the hydrophobic nature of the guest molecules. In addition, BPA and CUR were separately loaded into prepared p(CD) particles as active agents. The drug loading and release studies showed that p(CD) particles possess governable loading and releasing profiles.

Recent Advancements in Cyclodextrin-Based Adsorbents for the Removal of Hazardous Pollutants from Waters

Water is an essential substance for the survival on Earth of all living organisms. However, population growth has disturbed the natural phenomenon of living, due to industrial growth to meet ever expanding demands, and, hence, an exponential increase in environmental pollution has been reported in the last few decades. Moreover, water pollution has drawn major attention for its adverse effects on human health and the ecosystem. Various techniques have been used to treat wastewater, including biofiltration, activated sludge, membrane filtration, active oxidation process and adsorption. Among the mentioned, the last method is becoming very popular. Moreover, among the sorbents, those based on cyclodextrin have gained worldwide attention due to their excellent properties. This review article overviewed recent contributions related to the synthesis of Cyclodextrin (CD)-based adsorbents to treat wastewater, and their applications, especially for the removal of heavy metals, dyes, and organic pollutants (pharmaceuticals and endocrine disruptor chemicals). Furthermore, new adsorption trends and trials related to CD-based materials are also discussed regarding their regenerative potential. Finally, this review could be an inspiration for new research and could also anticipate future directions and challenges associated with CD-based adsorbents.

Sustainable Microbial and Heavy Metal Reduction in Water Purification Systems Based on PVA/IC Nanofiber Membrane Doped with PANI/GO

Effective and efficient removal of both heavy metal pollutants and bacterial contamination from fresh water is an open issue, especially in developing countries. In this work, a novel eco-friendly functional composite for water treatment application was investigated. The composite consisted of electrospun nanofiber membrane from blended polyvinyl alcohol (PVA)/iota carrageenan (IC) polymers doped with equal concentrations of graphene oxide (GO) nanoparticles and polyaniline (PANI). The effectiveness of this composite as a water purification fixed-bed filter was optimized in a batch system for the removal of cadmium (Cd⁺²) and lead (Pb⁺²) ions, and additionally characterized for its antimicrobial and antifungal properties and cytotoxicity effect. The fiber nanocomposite exhibited efficient antibacterial activity, with maximum adsorption capacity of about 459 mg g⁻¹ after 120 min for Cd⁺² and of about 486 mg g⁻¹ after 90 min for Pb⁺². The optimized conditions for removal of both metals were assessed by using a response surface methodology model. The resulting scores at 25 °C were 91.4% (Cd⁺²) removal at 117 min contact time for 89.5 mg L⁻¹ of initial concentration and 29.6 cm² membrane area, and 97.19% (Pb⁺²) removal at contact time 105 min for 83.2 mg L⁻¹ of initial concentration and 30.9 cm² nanofiber composite membrane. Adsorption kinetics and isotherm followed a pseudo-second-order model and Langmuir and Freundlich isotherm model, respectively. The prepared membrane appears to be promising for possible use in domestic water purification systems.

Selective detection of Cu2+ using nitrogen-doped carbon dots derived from humic acid and urea based on specific inner filter effect

A new kind of nitrogen-doped carbon dots (N-CDs) was synthesized via a simple hydrothermal strategy using humic acid as the carbon source and urea as the nitrogen source. The fluorescence intensity of as-prepared N-CDs was quenched significantly in presence of Cu²⁺ based on a specific inner filter effect, which could be utilized to construct a selective sensor for monitoring Cu²⁺ in aqueous samples. The sensor exhibited good linearity over the range of 0.1-2 μM, and high sensitivity with a detection limit of 25 nM. Under the optimal conditions, there was no significant interference by other metal ions such as Cd²⁺, Al³⁺, Cr³⁺, Fe³⁺, Pb²⁺, Na⁺, Ni⁺, Fe²⁺, Ba²⁺, Ca²⁺, Co²⁺, Mg²⁺, As³⁺, K⁺, Zn²⁺ for Cu²⁺ detecting except Hg²⁺.The interference of Hg²⁺ can be masked by addition of sodium chloride. The experimental results demonstrated that the prepared N-CDs owned strong fluorescence, high monodispersity, good stability and good water solubility, and the constructed sensor had many advances and great application prospect in environmental field.

A Short Review on Recent Advances of Hydrogel-Based Adsorbents for Heavy Metal Ions

The growth of industry fulfills our necessity and promotes economic development. However, pollutants from such industries pollute water bodies which pose a high risk for living organisms. Thus, researchers have been urged to develop an efficient method to remove toxic heavy metal ions from water bodies. The adsorption method shows promising results for the removal of heavy metal ions and is easy to operate on a large scale, thus can be applied to practical applications. Numerous adsorbents were developed and reported, among them hydrogels, which attract great attention because of the reusability, ease of preparation, and handling. Hydrogels are generally prepared by the cross-linking of polymers that result in a three-dimensional structure, showing high porosity and high functionality. They are hydrophilic in nature because of the functional groups, and are non-toxic. Thus, this review provides various methods of hydrogel adsorbents preparation and summarizes recent progress in the use of hydrogel adsorbents for the removal of heavy metal ions. Further, the mechanism involved in the removal of heavy metal ions is briefly discussed. The most recent studies about the adsorption method for the treatment of heavy metal ions contaminated water are presented.

Cyclodextrin-based adsorbents for the removal of pollutants from wastewater: a review

Water is a vital substance that constitutes biological structures and sustains life. However, water pollution is currently among the major environmental challenges and has attracted increasing study attention. How to handle contaminated water now mainly focuses on removing or reducing the pollutants from the wastewater. Cyclodextrin derivatives, possessing external hydrophilic and internal hydrophobic properties, have been recognized as new-generation adsorbents to exert positive effects on water pollution treatment. This article outlines recent contributions of cyclodextrin-based adsorbents on wastewater treatment, highlighting different adsorption mechanisms of cyclodextrin-based adsorbents under different influencing factors. The crosslinked and immobilized cyclodextrin-based adsorbents all displayed outstanding adsorption capacities. Particularly, according to specific pollutants including metal ions, organic chemicals, pesticides, and drugs in wastewater, this article has classified and organized various cyclodextrin-based adsorbents into tables, which could pave an intuitive shortcut for designing and developing efficient cyclodextrin-based adsorbents for targeted wastewater pollutants. Besides, this article specially discusses cost-effectiveness and regeneration performance of current cyclodextrin-based adsorbents. Finally, the challenges and future directions of cyclodextrin-based adsorbents are prospected in this article, which may shed substantial light on practical industrial applications of cyclodextrin-based adsorbents.

Spherical Bi2WO6/Bi2S3/MoS2 n-p Heterojunction with Excellent Visible-Light Photocatalytic Reduction Cr(VI) Activity

Exploiting excellent photocatalytic activity and stable heterostructure composites are of critical importance for environmental sustainability. The spherical Bi₂WO₆/Bi₂S₃/MoS₂ n-p heterojunction is first prepared via an in situ hydrothermal method using Bi₂WO₆, Na₂MoO₄·2H₂O, and CH₄N₂S, in which the intermediate phase Bi₂S₃ is formed due to chemical coupling interaction of Bi₂WO₆ and CH₄N₂S. Scanning electron microscopy indicates that the compactness of the sample can be easily adjusted by changing the contents of S and Mo sources in the solution. The results of ultraviolet–visible (UV–vis) diffuse reflectance spectra, photoluminescence, transient photocurrent response, and electrochemical impedance spectra indicate that the formation of heterojunctions contributes to enhancing visible-light utilization and promoting photogenerated carrier separation and transfer. The composite material is used as a catalyst for the visible light photocatalytic reduction of Cr(VI). Remarkably, the optimal Bi₂WO₆/Bi₂S₃/MoS₂ n-p heterojunction achieves the greatest Cr(VI) reduction rate of 100% within 75 min (λ > 420 nm, pH = 2); this rate is considerably better than the Cr(VI) reduction rate of pure Bi₂WO₆. The recycling experiment also reveals that the photocatalytic performance of the n-p heterojunction toward Cr(VI) is still maintained at 80% after three cycles, indicating that the n-p heterojunction has excellent structural stability. The capture experiment proves that the main active species in the system are electrons. The reasonable mechanism of Bi₂WO₆/Bi₂S₃/MoS₂ photocatalytic reduction Cr(VI) is proposed. Our work provides new research ideas for the design of ternary heterojunction composites and new strategies for the development of photocatalysts for wastewater treatment.