Preparation of zeolite hollow fibers for high-efficiency cadmium removal from waste water

Hierarchical hollow zeolite fiber in catalytic applications: A critical review

Zeolites have widely been studied because of the better performance as catalysts and supports. However, the zeolites with only micropores have drawbacks in reactivity and selectivity due to limitation of diffusivity. The hollow zeolite fibers (HZF) with hierarchical porosity however can overcome the problem. The HZF can be synthesized by such methods as incorporated substrate removal method, solid-solid transformation method, co-axial electrospinning technology, dry-wet spinning technology, and hollow fiber incorporation method. The unique hierarchical porous structure leads to the great improvement in the diffusion efficiency of reactants. The catalytic zeolite membrane fibers are the most commonly used as they have stronger catalyst stability and higher catalytic selectivity. The HZFs are suitable in catalytic applications such as selective catalysis, CO preferential oxidation, air purification and wastewater treatment. In order that the HZFs can be applied to industrial operations, more research work should be carried out, such as developments of self-assembly pure HZFs, catalytic substrate incorporated HZFs, HZFs with gradient multicomponent zeolites and HZFs with nanoscale diameters.

Preparation and Antibacterial Activity of Nano Copper Oxide- Loaded Zeolite 10X

Copper oxide nanosheet-loaded zeolite 10X nanocomposites (CuO-zeolite NCs) were successfully prepared by modifying zeolite 10X with CuSO₄ aqueous solution. The formation of copper oxide nanosheets on the surface of zeolite 10X was observed by SEM. The thickness of CuO nanosheets was about 30–40 nm, and the width ranged from 200 nm to 300 nm. The XRD patterns showed that the new diffraction peaks of copper oxide appeared at 35.6° and 38.8°. According to the XPS results, the Cu 2p_3/2 and Cu 2p_1/2 peaks in CuO-zeolite NC were centered at 934.1 eV and 953.8 eV, which could be attributed to Cu(II). The EDS analysis revealed that the energy spectra of calcium gradually decreased as the copper ion concentration increased during the preparation of CuO-zeolite NCs. Meanwhile, the energy spectra of copper increased gradually, and the highest content of copper in CuO-zeolite NCs reached 22.35 wt.%. The BET surface areas of zeolite 10X and CuO-zeolite NCs were 587 and 363 m²/g, respectively, based on the N₂ adsorption–desorption experiment. The antibacterial activities of CuO-zeolite NC were evaluated using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The antibacterial activities were related to both copper ion content in CuO-zeolite NCs and the particle size of copper oxide. The results showed that nano CuO-loaded zeolite 10X inhibited the activity of E. coli and S. aureus. CuO-zeolite NCs are expected to be further used in antifouling coating.

Preparation of Alumina-Sphere-Supported Potassium Chabazite Zeolite Membrane with Excellent Potassium Extraction Performance at Room Temperature

In this paper, a potassium chabazite (KCHA) zeolite membrane was prepared by coating KCHA zeolite on the surface of a porous alumina sphere. The performance of the KCHA zeolite membrane in extracting potassium from seawater and sea bittern at room temperature was studied in detail. The XRD results show that the prepared KCHA zeolite was a KCHA membrane. The EDS test indicated that the potassium content of the KCHA zeolite membrane reached a value of 18.33 wt.%. The morphology of the KCHA zeolite grown on the surface of the alumina sphere was similar to a sphere, and it had good symmetry. The potassium ion-exchange capacities of the KCHA zeolite membrane reached 32 mg/g in seawater and 77 mg/g in sea bittern at room temperature. Ion exchange between the ammonium ions and potassium ions in the KCHA zeolite membrane could be completed in a short time at room temperature. The KCHA zeolite membrane was proven to have good reusability in seawater and sea bittern. The selective ion-exchange mechanism of the KCHA zeolite membrane was controlled by a specific K⁺ ion memory.

State-of-the-Art Organic- and Inorganic-Based Hollow Fiber Membranes in Liquid and Gas Applications: Looking Back and Beyond

The aggravation of environmental problems such as water scarcity and air pollution has called upon the need for a sustainable solution globally. Membrane technology, owing to its simplicity, sustainability, and cost-effectiveness, has emerged as one of the favorable technologies for water and air purification. Among all of the membrane configurations, hollow fiber membranes hold promise due to their outstanding packing density and ease of module assembly. Herein, this review systematically outlines the fundamentals of hollow fiber membranes, which comprise the structural analyses and phase inversion mechanism. Furthermore, illustrations of the latest advances in the fabrication of organic, inorganic, and composite hollow fiber membranes are presented. Key findings on the utilization of hollow fiber membranes in microfiltration (MF), nanofiltration (NF), reverse osmosis (RO), forward osmosis (FO), pervaporation, gas and vapor separation, membrane distillation, and membrane contactor are also reported. Moreover, the applications in nuclear waste treatment and biomedical fields such as hemodialysis and drug delivery are emphasized. Subsequently, the emerging R&D areas, precisely on green fabrication and modification techniques as well as sustainable materials for hollow fiber membranes, are highlighted. Last but not least, this review offers invigorating perspectives on the future directions for the design of next-generation hollow fiber membranes for various applications. As such, the comprehensive and critical insights gained in this review are anticipated to provide a new research doorway to stimulate the future development and optimization of hollow fiber membranes.

Electrosorption of cadmium ions in aqueous solutions using a copper-gallate metal-organic framework

Recently, there is a recognized need for green technologies for the effective decontamination of toxic heavy metal ions in wastewater. This study demonstrates the electrochemically assisted uptake and release of cadmium ions (Cd²⁺) using a redox-active Cu-based metal-organic framework (MOF) electrode. Copper gallate (CuGA), which was synthesized in an aqueous solution, is a water-stable and cost-effective MOF adsorbent in which naturally abundant gallic acid is used as a linker. This work utilized copper within the CuGA structure as a redox center to attract Cd²⁺ by means of Cu²⁺/Cu⁺ reduction, exhibiting rapid uptake kinetics and a much higher capacity (>60 mg g^-1) compared to the case without electrochemical assistance (~15 mg g^-1). In addition, by applying an opposite overpotential to induce the re-oxidation of copper, the facile recovery of Cd²⁺ and the regeneration of the electrode were possible without regenerants. Physicochemical characterizations including XPS were conducted to investigate the chemical oxidation states and stability of the electrode after the effective electrosorption-regeneration process. This work presents the feasibility of a Cu-based MOF electrode as a reusable platform for the efficient removal of Cd²⁺, supporting the continued discovery and development of new Faradaic electrodes for electrochemical wastewater treatments.

Removal of Cd(II) using dithiocarboxyl cornstalk and the waste filtrate

A novel adsorbent, called dithiocarboxyl cornstalk (DTCS), was developed, and the effects of various parameters on the adsorption performance for Cd(II) with DTCS were investigated in this work. The results suggested that DTCS presented the efficient removal capacity for Cd(II) when the pH values, adsorption temperature, and oscillation rate were 3.0 to 6.0, 313 K, and 150 rpm, respectively. The adsorption kinetic data were more agreed with pseudo-second-order kinetic model, and the isotherm data could be characterized by Freundlich model. The thermodynamic data indicated the adsorption process was endothermic and spontaneous. The FTIR and SEM confirmed the chemisorption between Cd(II) and DTCS. Furthermore, to eliminate the secondary pollution, the waste filtrate generated in the preparation of DTCS was employed to remove Cd(II) through flocculation experiments. The results showed that the waste filtrate is a potential flocculant for the treatment of wastewater containing Cd(II).

Functionalized polyurethane sponge based on dopamine derivative for facile and instantaneous clean-up of cationic dyes in a large scale

Functionalized sponge adsorbent was prepared by a mussel-inspired strategy, which achieved successive modification of material and remained the properties of substrate. The dopamine derivative, DOPAm, was synthesized and adhered to polyurethane (PU) sponge before in situ polymerization with sodium p-styrenesulfonate. The adsorbent showed superior removal efficiency for cationic dyes (98.9 % for methylene blue (MB) at the concentration of 200 μmol/L); it took 1 s only for the adsorbent to adsorb the dyes by swelling and squeezing out the bulk solution simply. Meanwhile, the superior adsorption effect of the adsorbent could be maintained in a wide range of solution pH values from 1 to 13 at room temperature (293 K) in several repeat experiments, due to the slight influence of strong acid and alkali on polysulfonate. With unchanged other experimental conditions, the removal efficiency is still more than 90 % after reusing for 10 times at the different concentrations of MB dye solutions (50, 100, 200 μmol/L). For large-scale wastewater treatment, with the removal efficiency of 80.0 %, the adsorbent could purify 4.1 L wastewater containing MB dye (100 μmol/L) with the maximum flux of 22.2 L/(m³·s) without the assistance of any equipment except for a vacuum pump. Therefore, the adsorbent has great possibilities to be applied in high-efficient and convenient treatment of wastewater in a large scale.

Adsorption of Cadmium Ions from an Aqueous Solution on a Highly Stable Dopamine-Modified Magnetic Nano-Adsorbent

Magnetic nanomaterials were functionalized with dopamine hydrochloride as the functional reagent to afford a core-shell-type Fe₃O₄ modified with polydopamine (Fe₃O₄@PDA) composite, which was used for the adsorption of cadmium ions from an aqueous solution. In addition, the effects of environmental factors on the adsorption capacity were investigated. Furthermore, the adsorption kinetics, isotherm, and thermodynamics of the adsorbents were discussed. Results revealed that the adsorption of cadmium by Fe₃O₄@PDA reaches equilibrium within 120 min, and kinetic fitting data are consistent with the pseudo-second-order kinetics (R² > 0.999). The adsorption isotherm of Cd²⁺ on Fe₃O₄@PDA was in agreement with the Freundlich model, with the maximum adsorption capacity of 21.58 mg/g. The thermodynamic parameters revealed that adsorption is inherently endothermic and spontaneous. Results obtained from the adsorption-desorption cycles revealed that Fe₃O₄@PDA exhibits ultra-high adsorption stability and reusability. Furthermore, the adsorbents were easily separated from water under an enhanced external magnetic field after adsorption due to the introduction of an iron-based core. Hence, this study demonstrates a promising magnetic nano-adsorbent for the effective removal of cadmium from cadmium-containing wastewater.