Polydopamine/chitosan hydrogels-functionalized polyurethane foams in situ decorated with silver nanoparticles for water disinfection.

A new facile route to decorate polyurethane foams (PUF) with dense and uniform silver nanoparticles (AgNPs) to ensure efficient and long-term water disinfection is proposed. The antibacterial sponge was fabricated by sequential treatment with chitosan hydrogels grafting, polydopamine (PDA) coating, and finally in situ growth of AgNPs on the surface of substrate. The morphologies, chemical composition, crystalline nature, mechanical property, and swelling capacity of the composite were characterized. Its silver release behavior and bactericidal performances against Escherichia coli (E. coli) were evaluated. Results show that the composite demonstrated higher mechanical strength (compression strength, 51.34 kPa) and a rapid swelling rate with an equilibrium swelling ratio of 18.2 g/g. It possessed a higher loading amount of AgNPs (35.87 mg/g) than that of PUF@Ag (8.21 mg/g) and restricted the cumulative silver release of below 0.05% after 24-h immersion in water. Besides, it presented efficient bactericidal activity with complete reduction of E. coli with 10 min of contact time. The strong bactericidal action was probably governed by strengthening the contact between AgNPs immobilized on the substrate and bacteria cells. Furthermore, the composite demonstrated exceptional reusability for five cycles and exhibited a superior processing capacity in the flow test. Finally, the composite could effectively disinfect the natural water sample like a river in 30 min under real conditions.

Photocatalytically self-cleaning graphene oxide nanofiltration membranes reinforced with bismuth oxybromide for high-performance water purification.

Graphene oxide (GO) membranes have emerged as promising candidates for water purification applications, owing to their unique physicochemical attributes. Nevertheless, the trade-off between permeability and selectivity, coupled with their vulnerability to membrane fouling, poses significant challenges to their widespread industrial deployment. In this study, we introduce an innovative in-situ growth and layer-by-layer assembly technique for fabricating multilayer GO membranes reinforced with bismuth oxybromide (BiOBr) on commonly employed Nylon substrates. This method allows for the creation of two-dimensional lamellar membranes capable of photocatalytic self-cleaning and tunable nanochannel dimensions. The synthesized GO/BiOBr composite membranes exhibit remarkable water permeance rates (approximately 493.9 LMH/bar) and high molecular rejection efficiency (>99 % for Victoria Blue B and Congo Red dyes). Notably, these membranes showcase an enhanced photocatalytic self-cleaning performance upon exposure to visible light. Our work provides a viable route for the fabrication of functionalized GO-based nanofiltration membranes with BiOBr inclusions, offering a synergistic combination of high water permeability, modifiable nanochannels, and effective self-cleaning capabilities through photocatalysis.

Efficient adsorption of phosphorus by macroscopic MOF/chitosan composites and preliminary investigation of subsequent phosphorus recovery through electrochemically-driven struvite precipitation.

The proper management of phosphorus (P) from wastewater is crucial for sustainable development consideration. Herein, we developed a strategy which combines adsorption via tailored adsorbents and electrochemically-driven struvite precipitation (ESP) for P recovery. Novel polydopamine-modified Ce-MOF/chitosan composite beads (PDA@Ce-MOF-CS) were prepared by a facile in situ growth of Ce-MOF crystals incorporated natural polymers and PDA coating. The physicochemical properties of PDA@Ce-MOF-CS were characterized. Both batch and fixed-bed column experiments were conducted to evaluate its adsorption performances. Representatively, PDA@Ce-MOF-CS performed good selectivity for P removal and exhibited a maximum adsorption capacity of 161.13 mg P/g at pH 3 and 318 K. Meanwhile, the developed adsorbent showed great reusability after ten regeneration cycles as well as good adsorption stability. The dominant mechanism for efficient P adsorption included electrostatic attraction, surface precipitation and ligand exchange. Interestingly, PDA@Ce-MOF-CS exhibited a remarkable adsorption capacity of 92.86 mg P/g by treating real P-rich electroplating wastewater, and the desorbed P in the eluate could be effectively recovered and converted into a solid fertilizer as struvite via ESP. Overall, this work provided a new research direction for P recovery from wastewater as struvite by combined technologies with the help of macroscopic MOF architectures.

Calcium alginate gels-functionalized polyurethane foam decorated with silver nanoparticles as an antibacterial agent for point-of-use water disinfection.

This paper reports the preparation of calcium alginate gels-functionalized PUF decorated with AgNPs (CA/PUF@Ag) by in situ reduction of Ag+ ions to form AgNPs with weakly reducing glycerol in CA/PUF composite. The water-adsorbing capacity, chemical structure, crystalline nature, elemental composition and morphologies of the composite were characterized. The Ag release behavior of CA/PUF@Ag was investigated. The inhibition zone test, time-dependent co-culture assay, test tube test, and antibacterial filtration experiment with Escherichia coli as an indicator of bacterial contamination were conducted to explore the antimicrobial efficacy. Results indicated that the CA/PUF@Ag prepared at 0.25 % w/v of SA could absorb more water with a higher swelling ratio of 8.0 g/g than that of PUF@Ag (6.0 g/g), which was subsequently squeezed by minimal pressure stimuli. The CA/PUF@Ag had a larger initial AgNPs loading amount (8.48 mg/g), lower Ag release concentration (44.35 µg/L) and lower Ag release rate (0.27 %) after 14 days tests than those of PUF@Ag (7.93 mg/g, 80.87 µg/L and 0.60 % respectively). The CA/PUF@Ag was highly reusable because bacterial cells in the squeezed water recovered from the composite were completely inactivated over five cycles of operation, and exhibited good antibacterial efficacy as an antibacterial filter in a flow test.

Strong adsorption properties and mechanism of action with regard to tetracycline adsorption of double-network polyvinyl alcohol-copper alginate gel beads.

In the present study, glutaraldehyde was used as a hydrophobic modifier to crosslink polyvinyl alcohol (PVA), and copper ion was immobilized by sodium alginate (SA). Polyvinyl alcohol-copper alginate (PVA-CA) gel beads were prepared by a one-step process, and were used to adsorb and remove tetracycline (TC) from an aqueous solution. The beads were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) measurement, X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The adsorption experiment showed that the optimal pH value of the beads was 5, and that their adsorption met pseudo-second-order kinetic and Langmuir isothermal models. The adsorption thermodynamics experiment showed that the adsorption process was spontaneous and endothermic. Under optimal adsorption conditions, the maximum adsorption capacity for TC of the beads was 231.431 mg/g, which was much higher than that of a single copper alginate matrix. After 5 adsorption-desorption cycles, the adsorption capacity remained high. FTIR and X-ray photoelectron spectroscopy (XPS) revealed that the cation bonding bridge reaction was the main driving force behind the adsorption mechanism. Compared with other reported adsorption materials, the PVA-CA gel beads have high adsorption capacity, a simple preparation process, and excellent recovery performance.

Efficient Adsorption of Tetracycline from Aqueous Solutions by Modified Alginate Beads after the Removal of Cu(II) Ions.

This work dealt with a potential and effective method to reuse modified alginate beads after the removal of Cu(II) ions for efficient adsorption of tetracycline (TC) from aqueous solutions. The modified alginate beads were fabricated by a polyacrylamide (PAM) network interpenetrated in alginate-Ca2+ network (PAM/CA) decorated with polyethylene glycol as a pore-forming agent. The porous PAM/CA was characterized using scanning electron microscopy, Brunauer-Emmett-Teller, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis. The adsorption kinetics, isotherms, adsorption stability, and reusability studies of the adsorbent toward Cu(II) ions were scrutinized. The column performance of porous PAM/CA was tested with Cu(II)-containing electroplating wastewater. After Cu(II) adsorption, the Cu(II)-adsorbed PAM/CA (PAM/CA@Cu) was applied to remove TC from aqueous solutions without any regeneration process. The effects of pH, initial TC concentration, ionic strength, and coexisting ions on the adsorption were also discussed in detail. Compared with many reported adsorbents, the PAM/CA@Cu exhibited an excellent adsorption performance toward TC with a maximum adsorption capacity of 356.57 mg/g predicted by the Langmuir model at pH 5.0 and 30 °C with the absence of coexisting ions. The possible adsorption mechanism of TC onto the PAM/CA@Cu was revealed.

Interaction between tetracycline and microorganisms during wastewater treatment: A review.

Tetracycline (TC) is a commonly used human and veterinary antibiotic that is mostly discharged into wastewater in the form of the parent compounds. At present, wastewater treatment plants (WWTPs) use activated sludge processes that are not specifically designed to remove such pollutants. Considering the biological toxicity of TC in aquatic environment, the migration and fate of TC in the process of wastewater treatment deserve attention. This paper reviews the influence of TC on the functional bacteria in the sludge matrix and the development of tetracycline-resistant genes, and also discusses their adsorption removal rates, their adsorption kinetics and adsorption isotherm models, and infers their adsorption mechanism. In addition, the biodegradation of TC in the process of biological treatment is reviewed. Co-metabolism and the role of dominant bacteria in the degradation process are described, along with the formation of degradation byproducts and their toxicity. Furthermore, the current popular integrated coupling-system for TC degradation is also introduced. This paper systematically introduces the interaction between TC and activated sludge in WWTPs. The review concludes by providing directions to address research and knowledge gaps in TC removal from wastewater.

Development of polyaminated chitosan-zirconium(IV) complex bead adsorbent for highly efficient removal and recovery of phosphorus in aqueous solutions.

The aim of this work is to examine the adsorption performance and mechanism of phosphorus (P) onto polyethyene polyamine (PEPA) grafted chitosan-zirconium(IV) composite beads (CS-Zr-PEPA) from aqueous solutions. The morphology, functional groups, and surface area of the CS-Zr-PEPA beads were characterized by SEM, FTIR, and BET analysis. Batch adsorption experiments were conducted via different operating parameters such as solution pH, initial phosphate concentration, co-existing anions and temperature. The adsorption kinetics, equilibrium isotherms and adsorption stability of the adsorbent were scrutinized. In comparison with other CS-based beads, the CS-Zr-PEPA had a greater affinity towards P and exhibited a maximum adsorption capacity of 103.96 mg-P/g predicted by Langmuir mode. The reusability studies of CS-Zr-PEPA beads were carried out. The CS-Zr-PEPA beads exhibit preferable sequestration of P through specific interactions, as further demonstrated by studying physicochemical characteristics of the virgin beads and P-adsorbed beads using X-ray photoelectron spectroscopy (XPS). The column performance of CS-Zr-PEPA beads was tested with P-containing wastewater. Results indicated that the developed CS-Zr-PEPA composite beads could be utilized as a promising adsorbent for effective removal and recovery of P from water and wastewater.

Phosphorus removal and recovery from water with macroporous bead adsorbent constituted of alginate-Zr4+ and PNIPAM-interpenetrated networks.

Currently, there is a growing trend in employing natural biomaterials (e.g., alginate) to prepare a novel bead adsorbent for phosphorus (P) elimination. However, the utilization of alginate beads to remove and recover P from effluents possesses limitations associated with its physical characteristics such as a dense gel layer, poor mechanical strength and low stability. To overcome the limitations and improve the adsorption performances, we synthesized a novel alginate-derived bead constituted of PNIPAM network interpenetrated in alginate-Zr4+ network (PNIPAM/SA-Zr) decorated with polyethylene glycol as a pore-forming agent, and then investigated its ability to remove and recover P from effluents. The morphology, functional groups, surface area, and mechanical strength of the beads were evaluated by SEM, FTIR, BET, and swelling analysis. The adsorption of P was investigated by varying various factors. The adsorption kinetics, isotherms, and thermodynamics were studied. Particularly, the P-loaded beads exhibited a faster desorption rate under thermal stimulus, and remained good desorption efficiency and reusability within five consecutive cycles. Zeta-potential and XPS results revealed that the adsorption mechanisms were related to electrostatic interactions, ligand exchange, and the formation of inner-sphere complexes. The beads possessed favorable fixed-bed column operation performances for P removal and recovery from real wastewater.

[Phosphate Removal on Zirconium Alginate/Poly(N-isopropyl acrylamide) Hydrogel Beads with a Semi-interpenetrating Network].

Zirconium alginate/poly(N-isopropyl acrylamide) hydrogel beads with a semi-interpenetrating network (ZA/PNIPAM) were prepared by using the ionic crosslinking and radical polymerization method and investigated for phosphate removal from aqueous solutions. The effects on the adsorption performance of hydrogel beads, including initial pH, adsorbent dose, initial phosphate concentration, and co-existing anions, were evaluated systematically. Results showed that the ZA/PNIPAM could exhibit a maximum uptake capacity of phosphate at pH 2.The uptake capacity of the adsorbent increased with a decrease in the dose or an increase in the initial phosphate concentration. The presence of SO42- had a more negative effect on phosphate removal compared to Cl- and NO3-. The kinetics fitted a pseudo-second-order model and intraparticle diffusion model, suggesting the adsorption rate was mainly controlled by surface adsorption and diffusion into the interior of the hydrogel beads. The isotherm data could be described by the Freundlich model, indicating that the adsorption process was heterogeneous multilayer adsorption. The studies of FTIR, XPS, and zero point of charge with relevant adsorption data revealed that the phosphate adsorption mechanisms could be electrostatic attraction (physical adsorption) and ligand exchange reactions (chemical adsorption). After four cycles of regeneration, ZA/PNIPAM exhibited a stable uptake capacity, indicating favorable reusability.