Recent progress in magnetic polydopamine composites for pollutant removal in wastewater treatment

Various water pollution issues pose a significant threat to human water safety. Magnetic polydopamine composites (MPCs), which can be separated by magnetic fields after the adsorption process, exhibit outstanding adsorption capacity and heterogeneous catalytic properties, making them promising materials for water treatment applications. In particular, by modifying the polydopamine (PDA) coating, MPCs can acquire enhanced high reactivity, antibacterial properties, and biocompatibility. This also provides an attractive platform for further fabrication of hybrid materials with specific adsorption, catalytic, antibacterial, and water-oil separation capabilities. To systematically provide the background knowledge and recent research advances in MPCs, this paper presents a critical review of MPCs for water treatment in terms of both structure and mechanisms of effect in applications. Firstly, the impact of different PDA positions within the composite structure is investigated to summarize the optimization of properties contributed by PDA when acting as the shell, core, or bridge. The roles of various secondary modifications of magnetic materials by PDA in addressing water pollution problems are explored. It is anticipated that this work will be a stimulus for further research and development of magnetic composite materials with real-world application potential.

Mussel-inspired magnetic adsorbent MnO2/PDA@Fe3O4 for removing heavy metal ions contaminants in single and mixed systems

Heavy metal pollution has been a magnificent concern for a long period. A novel magnetic material, MnO₂/PDA@Fe₃O₄, was prepared in this paper. With the assistance of multiple characterization methods, it was confirmed that polydopamine coated the magnetic nucleus and acted as a dense intermediate layer for MnO₂ attachment. Having superior adsorption performance, MnO₂/PDA@Fe₃O₄ could remove heavy metal cations efficiently no matter in single or mixed systems. The maximum adsorption capacities calculated by the Langmuir model for Pb(II), Cu(II), and Cd(II) were 295.01 mg/g, 130.30 mg/g, and 115.16 mg/g, respectively. In mixed systems, the adsorbent showed obvious selectivity for Pb(II). And the variation of Cu(II) concentration was more responsible for Pb(II) adsorption than that of Cd(II). The kinetic and thermodynamic data revealed that the polluted ions immobilizations by MnO₂/PDA@Fe₃O₄ were chemisorption and were endothermic, entropy increase, spontaneous process. The presence of humic acid and coexisting ions induced only a very limited interference. In addition, MnO₂/PDA@Fe₃O₄ maintained excellent adsorption performance and stability after five cycles of adsorption and removed 98.33% Pb(II) and 71.24% Cu(II) from actual water, respectively. This study confirmed that the MnO₂/PDA@Fe₃O₄ had great potential and broad prospects to remediate the heavy metal contaminants in water.

Melanin-like nanoparticles: advances in surface modification and tumour photothermal therapy

Currently, tumor treatments are characterized by intelligence, diversity and personalization, but the therapeutic reagents used are often limited in clinical efficacy due to problems with water solubility, targeting, stability and multidrug resistance. To remedy these shortcomings, the application of multifunctional nanotechnology in the biomedical field has been widely studied. Synthetic melanin nanoparticles (MNPs) surfaces which contain highly reactive chemical groups such as carboxyl, hydroxyl and amine groups, can be used as a reaction platform on which to graft different functional components. In addition, MNPs easily adhere to substrate surface, and serve as a secondary reaction platform to modify it. The multifunctionality and intrinsic biocompatibility make melanin-like nanoparticles promising as a multifunctional and powerful nanoplatform for oncological applications. This paper first reviews the preparation methods, polymerization mechanisms and physicochemical properties of melanin including natural melanin and chemically synthesized melanin to guide scholars in MNP-based design. Then, recent advances in MNPs especially synthetic polydopamine (PDA) melanin for various medical oncological applications are systematically and thoroughly described, mainly focusing on bioimaging, photothermal therapy (PTT), and drug delivery for tumor therapy. Finally, based on the investigated literature, the current challenges and future directions for clinical translation are reasonably discussed, focusing on the innovative design of MNPs and further elucidation of pharmacokinetics. This paper is a timely and comprehensive and detailed study of the progress of MNPs in tumor therapy, especially PTT, and provides ideas for the design of personalized and customizable oncology nanomedicines to address the heterogeneity of the tumor microenvironment.

Degradation of methylene blue through Fenton-like reaction catalyzed by MoS2-doped sodium alginate/Fe hydrogel

In this study, a low-cost and high-performance MoS₂/sodium alginate (SA)/Fe (MSF) hydrogel catalyst was prepared. It was found that the MSF hydrogel could efficiently catalyze the degradation of methylene blue (MB) through the Fenton reaction without the addition of Fe²⁺. The reaction was initiated by Fe²⁺ which was derived from the cyclic redox reaction between MoS₂ and Fe³⁺ and produced large quantities of ·OH to degrade the MB. The effect of MoS₂ concentration, FeCl₃·6H₂O concentration, H₂O₂ dosage, solution pH, and light on the degradation was systematically studied. The MoS₂ concentration of 0.5 mg/ mL, FeCl₃·6H₂O concentration of 0.25 g/mL, 50 μL H₂O₂, and the pH of 4.0 were the optimized parameters. Moreover, it was found that the MB degraded faster under the infrared radiation. The MB removal rate reached as high as 98% within 15 min in the presence of a low concentration of H₂O₂ and the procedure could be repeated 5 times. The MSF hydrogel provided an effective and simple strategy for the sustainable degradation of organic pollutants in wastewater.

Ultrasensitive detection of UO2 2+ based on dopamine-functionalized MoOx quantum dots

Uranium is an important nuclear fuel and the risk of human exposure to uranium increases as increasing amounts of uranium-containing waste enter the environment due to the rapid growth of nuclear power. Therefore, rapid, sensitive, and portable uranium detection is a promising approach to effectively control and monitor uranium contamination. To achieve this goal, abundant oxygen- and nitrogen-containing groups were introduced to molybdenum oxide quantum dot (MoO_x QDs) surfaces with dopamine (DA) modification. Due to the excellent coordination ability of oxygen- and nitrogen-containing groups with uranium, the obtained DA-functionalized MoO_x QDs (DA-MoOx QDs) showed a strong binding affinity for uranium and sensitivity was increased nearly 1000-fold compared with MoO_x QDs alone. The limit of detection was 3.85 nM, which is higher than most of the reported nanomaterials. Moreover, the DA-MoOx QD-based method showed high selectivity and uranium could be clearly detected under masking with ethylenediaminetetraacetic acid even when the concentration of other metal ions was 100-fold higher than that of uranium, showing a very promising method for uranium contamination control and monitoring.

Skeleton Engineering of Homocoupled Conjugated Microporous Polymers for Highly Efficient Uranium Capture via Synergistic Coordination

Developing efficient adsorbents for uranium enrichment is of great significance for resource sustainability and environmental safety. This study presents a facile and adaptable post-synthetic strategy to prepare highly efficient uranium adsorbents via engineering the π-conjugated skeletons of homocoupled conjugated microporous polymers (HCMPs). Taking advantage of the diyne units in the π-conjugated skeletons, bis-amidoxime uranophiles, one of the state-of-the-art ligands of uranyl ions, were introduced to the frameworks of HCMPs. The functionalized HCMPs preserved the interconnected 3D microporous networks and rigid conjugated skeletons with abundant bis-amidoxime ligands uniformly distributed in the pore channels. Such structural advantages of the adsorbents afforded very fast adsorption kinetics within 15 min to reach the equilibrium and high capacity of uranium (450 mg/g). Moreover, DFT calculation suggests a synergistic coordination as the most energetically favored coordination mode of the uranyl/bis-amidoxime complexes. This study contributes new insights into the underlying mechanism responsible for the highly efficient adsorption ability of the bis-amidoxime-functionalized HCMPs toward uranium. Meanwhile, the synthetic methodology established here could be extended to task-specific design and skeleton engineering of more functional HCMPs for broadened applications.

Preparation of Magnetic CuFe2O4@Ag@ZIF-8 Nanocomposites with Highly Catalytic Activity Based on Cellulose Nanocrystals

A facile approach was successfully developed for synthesis of cellulose nanocrystals (CNC)-supported magnetic CuFe2O4@Ag@ZIF-8 nanospheres which consist of a paramagnetic CuFe2O4@Ag core and porous ZIF-8 shell. The CuFe2O4 nanoparticles (NPs) were first prepared in the presence of CNC and dispersant. Ag NPs were then deposited on the CuFe2O4/CNC composites via an in situ reduction directed by dopamine polymerization (PDA). The CuFe2O4/CNC@Ag@ZIF-8 nanocomposite was characterized by TEM, FTIR, XRD, N2 adsorption-desorption isotherms, VSM, and XPS. Catalytic studies showed that the CuFe2O4/CNC@Ag@ZIF-8 catalyst had much higher catalytic activity than CuFe2O4@Ag catalyst with the rate constant of 0.64 min-1. Because of the integration of ZIF-8 with CuFe2O4/CNC@Ag that combines the advantaged of each component, the nanocomposites were demonstrated to have an enhanced catalytic activity in heterogeneous catalysis. Therefore, these results demonstrate a new method for the fabrication of CNC-supported magnetic core-shell catalysts, which display great potential for application in biocatalysis and environmental chemistry.

Self-assembly of graphene oxide/PEDOT:PSS nanocomposite as a novel adsorbent for uranium immobilization from wastewater

In recent years, water pollution caused by radionuclides has become a rising concern, among which uranium is a representative class of actinide element. Since hexavalent uranium, i.e. U(VI), is biologically hazardous with high migration, it's essential to develop efficient adsorbents to minimize the impact on the environment. Towards this end, we have synthesized a novel material (GO/PEDOT:PSS) by direct assembling graphene oxide (GO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) through a facile ball milling method, which shows impressing performance for the immobilization of U(VI). On the basis of the batch experiments, GO/PEDOT:PSS exhibits ionic strength-independent sorption edges and temperature-promoted sorption isotherms, revealing an inner-sphere complexation with endothermic nature. The sorption kinetics can be illustrated by the pseudo-second-order model, yielding a rate constant of 1.09. × 10^-2 g mg^-1∙min^-1, while the sorption isotherms are in coincidence with the Langmuir model, according to which the maximum sorption capacity is measured to be 384.51 mg g^-1 at pH 4.5 under 298 K, indicating a monolayer sorption mechanism. In the light of the FT-IR and XPS investigations, the surface carboxyl/sulfonate group is responsible to the chelation of U(VI), indicating that the enhanced sorption capacity may be ascribed to the PSS moiety. These findings can greatly contribute to the design strategy for developing highly efficient adsorbents in the field of radioactive wastewater treatment.

Recent Trends in Mussel-Inspired Catechol-Containing Polymers (A Review)

Syntheses and applications of mussel-inspired polymeric materials have gained a foothold in research in recent years. Mussel-inspired chemistry coupled to Michael addition and Schiff’s base reactions was the key success for this intensive research. Unequivocally, The basic building brick of these materials is catechol-containing moiety, namely, 3,4-dihydroxyphenyl-L-alanine (L-DOPA or DOPA) and dopamine (DA). These catechol-based units within the chemical structure of the material ensure chiefly its adhesive characteristic to adherends of different natures. The newly-made catechol-bearing polymeric materials exhibit unique features, implying their importance in several uses and applications. Technology advent is being advantaged with these holdfast mussel protein-like materials. This review sheds light into the recent advances of such mussel-inspired materials for their adhesion capacity to several substrata of different natures, and for their applications mainly in antifouling coatings and nanoparticles technology.

Amidoxime-modified chitosan for pigment red 224 enrichment through reversible assembly

An amidoxime-modified chitosan, featuring favorable porosity and super-lipophilic properties, was successfully prepared for pigment red 224 enrichment.

Metal-Free Photoinduced Electron Transfer-Atom Transfer Radical Polymerization Integrated with Bioinspired Polydopamine Chemistry as a Green Strategy for Surface Engineering of Magnetic Nanoparticles

Developing green and efficient technologies for surface modification of magnetic nanoparticles (MNPs) is of crucial importance for their biomedical and environmental applications. This study reports, for the first time, a novel strategy by integrating metal-free photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) with the bioinspired polydopamine (PDA) chemistry for controlled architecture of functional polymer brushes from MNPs. Conformal PDA encapsulation layers were initially generated on the surfaces of MNPs, which served as the protective shells while providing an ideal platform for tethering 2-bromo-2-phenylacetic acid (BPA), a highly efficient initiator. Metal-free PET-ATRP technique was then employed for controlled architecture of poly(glycidyl methacrylate) (PGMA) brushes from the core-shell MNPs by using diverse organic dyes as photoredox catalysts. Impacts of light sources (including UV and visible lights), photoredox catalysts, and polymerization time on the composition and morphology of the PGMA brushes were investigated. Moreover, the versatility of the PGMA-functionalized core-shell MNPs was demonstrated by covalent attachment of ethylenediamine (EDA), a model functional molecule, which afforded the MNPs with improved hydrophilicity, dispersibility, and superior binding ability to uranyl ions. The green methodology by integrating metal-free PET-ATRP with facile PDA chemistry would provide better opportunities for surface modification of MNPs and miscellaneous nanomaterials for biomedical and electronic applications.

Performance and Mechanism of Uranium Adsorption from Seawater to Poly(dopamine)-Inspired Sorbents

Developing facile and robust technologies for effective enrichment of uranium from seawater is of great significance for resource sustainability and environmental safety. By exploiting mussel-inspired polydopamine (PDA) chemistry, diverse types of PDA-functionalized sorbents including magnetic nanoparticle (MNP), ordered mesoporous carbon (OMC), and glass fiber carpet (GFC) were synthesized. The PDA functional layers with abundant catechol and amine/imine groups provided an excellent platform for binding to uranium. Due to the distinctive structure of PDA, the sorbents exhibited multistage kinetics which was simultaneously controlled by chemisorption and intralayer diffusion. Applying the diverse PDA-modified sorbents for enrichment of low concentration (parts per billion) uranium in laboratory-prepared solutions and unpurified seawater was fully evaluated under different scenarios: that is, by batch adsorption for MNP and OMC and by selective filtration for GFC. Moreover, high-resolution X-ray photoelectron spectroscopic and extended X-ray absorption fine structure studies were performed for probing the underlying coordination mechanism between PDA and U(VI). The catechol hydroxyls of PDA were identified as the main bidentate ligands to coordinate U(VI) at the equatorial plane. This study assessed the potential of versatile PDA chemistry for development of efficient uranium sorbents and provided new insights into the interaction mechanism between PDA and uranium.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Glass surface modification via Cu(0)-mediated living radical polymerization of fluorinated and non-fluorinated acrylates

The glass surface was modified via Cu(0)-mediated living radical polymerization of butyl acrylate and trifluoroethyl methacrylate by using the grafting from and grafting to methodologies.