Octopus tentacle-like molecular chains in magnetic flocculant enhances the removal of Cu(II) and malachite green in water

Preparation and application of composite magnetic flocculants for wastewater treatment: A review

Wastewater treatment plays a vital role in protecting natural environments. Among the various wastewater treatment methods, flocculation achieves effective wastewater treatment, owing to its high efficiency, convenience, and cost-effectiveness. Compared to traditional flocculants, Composite magnetic flocculants have attracted significant attention due to their distinctive "core-shell" structure, magnetic flocculation mechanism and high efficiency recovery. This promotes sustainable development in wastewater treatment, highlighting the significant prospects for its application and potential advancement. This review begins by discussing the raw materials and treatment methods of composite magnetic flocculants and presenting common materials and associated preparation techniques. By combining the advantages of organic and inorganic components, disparate raw materials give flocculants different properties and flocculation efficiency. Through the comprehensive analysis of the flocculation mechanism, the flocculation efficiency of various wastewater treatment targets was elucidated, and the exceptional performance in overcoming steric hindrance was introduced. Subsequently, recycling approaches were summarized to determine the advantages and disadvantages in terms of recovery efficiency, operational difficulty, and impact on particle structure. Based on the current developmental status, this review provides a prospective outlook on future exploration trends in composite magnetic flocculants, valuable references, and theoretical foundations for related research and engineering practices.

Core-Shell Magnetic Particles: Tailored Synthesis and Applications

Core-shell magnetic particles consisting of magnetic core and functional shells have aroused widespread attention in multidisciplinary fields spanning chemistry, materials science, physics, biomedicine, and bioengineering due to their distinctive magnetic properties, tunable interface features, and elaborately designed compositions. In recent decades, various surface engineering strategies have been developed to endow them desired properties (e.g., surface hydrophilicity, roughness, acidity, target recognition) for efficient applications in catalysis, optical modulation, environmental remediation, biomedicine, etc. Moreover, precise control over the shell structure features like thickness, porosity, crystallinity and compositions including metal oxides, carbon, silica, polymers, and metal-organic frameworks (MOFs) has been developed as the major method to exploit new functional materials. In this review, we highlight the synthesis methods, regulating strategies, interface engineering, and applications of core-shell magnetic particles over the past half-century. The fundamental methodologies for controllable synthesis of core-shell magnetic materials with diverse organic, inorganic, or hybrid compositions, surface morphology, and interface property are thoroughly elucidated and summarized. In addition, the influences of the synthesis conditions on the physicochemical properties (e.g., dispersibility, stability, stimulus-responsiveness, and surface functionality) are also discussed to provide constructive insight and guidelines for designing core-shell magnetic particles in specific applications. The brand-new concept of "core-shell assembly chemistry" holds great application potential in bioimaging, diagnosis, micro/nanorobots, and smart catalysis. Finally, the remaining challenges, future research directions and new applications for the core-shell magnetic particles are predicted and proposed.

Octopus-inspired flocculant for oily wastewater decontamination: Hydrophilic-hydrophobic convertibility and auto-separation characters

Unilateral hydrophobic flocculant and unsatisfactory floc separation constrained the efficacious purification of oil-containing wastewater. Illumined by the hunting behavior of mimic octopus, a biomimetic flocculant (CNSDA) with temperature-sensitive chains (color pouch) and hollow silica cores (mantle) was manufactured to derive hydrophilic-hydrophobic convertibility and auto-separation capabilities. Physical-chemical information of CNSDA was elucidated through characterization analysis. The flocculation behaviors of temperature-sensitive chains and hollow silica cores were evaluated by flocculation experiments. Results indicated that the configuration of CNSDA molecular chains varied from extension to constriction and revealed hydrophobicity as the temperature crossed 29.6 ℃. Compared with 20 ℃, the flocculation efficiencies rocketed at 40 ℃ by CNSDA, and excess flocculants were adsorbed by as-formed flocs through nonpolar interactions (the residual was low to 2.27 % at 160 mg/L). Concomitantly, the contracted molecular chains were contributed to generating dense flocs with low moisture content that flocked into large ones and expedited the solid-liquid separation process (60 % shorter than cationic polyacrylamide) with the auxiliary of low-density cores. The hydrophobic adsorption mechanism actuated by temperature-sensitive character was the decisive factor for high-efficiency flocculation. This study can provide meaningful references for the conception and exploitation of oily wastewater disposal agents.

Self-sensitized photodegradation and adsorption of aqueous malachite green dye using one-dimensional titanium oxide nanofilaments

Truly one-dimensional titanium oxide nanofilaments with a lepidocrocite structure (1DLs) were explored in the adsorption and photocatalytic degradation of aqueous malachite green (MG), a toxic polluting dye. Decolorization is monitored by ultraviolet-visible spectroscopy, and mineralization is confirmed by total organic carbon analysis. The 1DL/MG flocs are characterized by scanning electron microscopy and X-ray diffraction. 1DLs, a colloidal nanomaterial, exhibit flocculating behavior while demonstrating high affinity for MG, with a maximum uptake of >680 mg/g rapidly via ion exchange. Additionally, 1DLs decolorize MG under visible light only, unlike most available titania products, via a self-sensitization effect. MG is decolorized by 1DLs by >70% in 30 min under 1 sun exposure of visible light. Counterintuitively, dye adsorption increases as the normalized concentration by mass of 1DL decreases. Demonstrating high adsorption capacity and dye mineralization supports the use of 1DLs in water treatment and self-sensitization for photoelectrochemical devices, like solar cells.

Synthesis of chitosan-based grafting magnetic flocculants for flocculation of kaolin suspensions

A series of novel chitosan-based magnetic flocculants FS@CTS-P(AM-DMC) was prepared by molecular structure control. The characterization results showed that FS@CTS-P(AM-DMC) had a uniform size of about 21.46 nm, featuring a typical core-shell structure, and the average coating layer thickness of CTS-P(AM-DMC) was about 5.03 nm. FS@CTS-P(AM-DMC) exhibited excellent flocculation performance for kaolin suspension, achieved 92.54% turbidity removal efficiency under dosage of 150 mg/L, pH 7.0, even at high turbidity (2000 NTU) with a removal efficiency of 96.96%. The flocculation mechanism was revealed to be dominated by charge neutralization under acidic and neutral conditions, while adsorption and bridging effects play an important role in alkaline environments. The properties of magnetic aggregates during flocculation, breakage, and regeneration were studied at different pH levels and dosages. In the process of magnetophoretic, magnetic particles collide and adsorb with kaolin particles continuously due to magnetic and electrostatic attraction, transform into magnetic chain clusters, and then further form three-dimensional network magnetic aggregates that can capture free kaolin particles and other chain clusters. Particle image velocimetry confirmed the formation of eddy current of magnetic flocs and experienced three stages: acceleration, stabilization, and deceleration.

Magnetic coagulation and flocculation of kaolin suspension using Fe3O4 with plant polyphenol self-assembled flocculants

In this work, magnetic flocculant (Fe3O4@PP) was synthesized using plant polyphenol (PP) as a shaping ligand via in situ self-assembly. Characterization results revealed that Fe3O4@PP exhibited uniform particle size and excellent dispersibility with PP coating amount of 16.4 %. Experimental results suggested that Fe3O4@PP showed excellent turbidity removal efficiency in a wide pH range (3.0-10) and initial turbidity range (50-2000 NTU). Under the optimal conditions, Fe3O4@PP achieved 95.2 % of turbidity removal for simulated kaolin suspension and 96.9 % for actual wastewater. Fe3O4@PP exhibited excellent recycling and reusability properties, with high recycling efficiency of 93.3 % even after the fifth cycle. Microscopic observation revealed the formation process of magnetic flocs, involving particle aggregation, chain and cluster formation, and dense network aggregate formation. The structural characteristics and size of magnetic flocs were found to be significantly influenced by the combined effects of magnetic force, electric charge, van der Waals force, and functional groups on the surface of PP. The extended Deryaguin-Landau-Verwey-Overbeek models indicated that magnetic interactions were the primary mechanism for magnetic flocculation, accompanied by charge neutralization, adsorption bridging, sweeping, and net trapping.