Enhanced photoelectrochemical water splitting using carbon cloth functionalized with ZnO nanostructures via polydopamine assisted electroless deposition

ZnO nanorods (ZnO-nr) have been widely studied as a promising nanomaterial for photoelectrochemical water splitting. However, almost all prior studies employed planar electrodes. Here, we investigated the performance of ZnO nanorods on a fibrous carbon cloth (CC) electrode, which offers a larger surface area for functionalization of photocatalysts. ZnO nanorods and Ni nanofilm were deposited on carbon cloth substrates for investigation as the photoanode and cathode of a photoelectrochemical water splitting setup, respectively. The use of polydopamine in the electroless deposition of ZnO ensured a uniform distribution of nanorods that were strongly adherent to the microfiber surface of the carbon cloth. Compared to ZnO nanorods grown on planar ITO/glass substrates, the CC-based ZnO photoanodes exhibited smaller onset potentials (1.1 VRHEvs. 1.8 VRHE), ∼40× larger dark faradaic currents at 1.23 VRHE and 5.5×-9× improvement in photoconversion efficiencies. Ni/CC cathodes were also found to exhibit a lower overpotential@10 mA cm-2 than Ni/Cu by 90 mV. The photocurrent obtained from the ZnO-nr/CC anode was highly stable across an hour and the peak current decreased by only 5% across 5 cycles of illumination, compared to 72% for the planar ZnO-nr/ITO anode. However, the response of the CC-based setups to changes in the illumination conditions was slower, taking hundreds of seconds to reach peak photocurrent, compared to tens of seconds for the planar electrodes. Using cyclic voltammetry, the double-layer capacitance of the electrodes was measured, and it was shown that the increased efficiency of the ZnO-nr/CC anode was due to a 2 order of magnitude increase in electrochemically active sites provided by the copious microfiber surface of the carbon cloth.

Palladium nanoparticles supported on ionic liquid and glucosamine-modified magnetic iron oxide as a catalyst in reduction reactions

A magnetic nanocomposite comprising imidazolium ionic liquid and glucosamine is successfully synthesized and used for stabilization of Pd nanoparticles. This new material, Fe₃O₄@SiO₂@IL/GA-Pd, is fully characterized and applied as a catalyst in the reduction of nitroaromatic compounds to desired amines at room temperature. Also, the reductive degradation of organic dyes such as methylene blue (MB), methyl orange (MO), and rhodamine B (RhB) is studied and compared with another previous publications. The survey of the stabilization of the palladium catalytic entities is described demonstrating the separation ability and recycling of them. In addition, TEM, XRD, and VSM analyses of the recycled catalyst confirmed its stability.

Facile synthesis of Fe3O4 nanoparticles/reduced graphene oxide sandwich composites for highly efficient microwave absorption

Component regulation and microstructure design are two effective strategies to adjust electromagnetic parameters and improve the microwave absorption performance of materials. In this study, a facile synthesis strategy consisting of ultrasonic dispersion, blast drying, and roasting is proposed to build a sandwich-like graphene-based absorbent, in which Fe₃O₄ nanoparticles with adjustable content are sandwiched uniformly between reduced graphene oxide nanosheets. The sandwich structure can form multiple interfaces, prevent the aggregation of nanoparticles, facilitate interface polarization, and endow the material with multiple electromagnetic loss mechanisms, which is very beneficial for impedance matching and microwave attenuation. Notably, the effective absorption bandwidth achieves 5.7 GHz, and the minimum reflection loss value is -49.9 dB. In addition, the synthesis process is simple and suitable for large-scale production and possible industrial applications. Thus, this facile route to fabricate sandwich-like graphene-based absorbents provides new ideas and approaches for designing new graphene-based nanocomposites.

Mussel - Inspired biosorbent combined with graphene oxide for removal of organic pollutants from aqueous solutions

In this work, we develop a mussel-inspired biosorbent combined with graphene oxide for removal of organic dyes in water sources. The composite was prepared via self-polymerization of dopamine in weak alkaline solution containing graphene oxide at ambient condition. Morphological and structural studies revealed that polydopamine has gradually grown to cover the surface of graphene oxide flakes, partially reduced these flakes, and somehow form many grains (size around 20 nm) on the flakes instead of making very large aggregates as usual. The mass ratio between two components of the composite was also investigated to find the optimal one which provides enough surface area (20 m².g^-1) and maintain adhesive sites in order to ensure high-efficiency removal of organic molecules. The adsorption kinetics and isotherms of as-prepared adsorbent towards methylene blue were found to fit well with pseudo-first order kinetics model and Langmuir isotherm. The maximum adsorption capacity (q_m) and Langmuir constant (k_L) were estimated to be 270 mg.g^-1 and 0.49 L. mg^-1. The as-prepared bio-sorbent is very promising for remediation of water sources contaminated with cationic organic molecules and heavy metal ions.

Magnetic Response Combined with Bioactive Ion Therapy: A RONS-Scavenging Theranostic Nanoplatform for Thrombolysis and Renal Ischemia-Reperfusion Injury

Currently, the limited efficacy of antithrombotic treatments is attributed to the inadequacy of pure drugs and the low ability of drugs to target the thrombus site. More importantly, timely thrombolysis is essential to reduce the sequelae of cardiovascular disease, but ischemia-reperfusion injury (IRI) remains a major challenge that must be solved after blood flow recovery. Herein, a multifunctional therapeutic nanoparticle (NP) based on Fe₃O₄ and strontium ions encapsulated in mesoporous polydopamine was successfully constructed and then loaded with TNK-tPA (FeM@Sr-TNK NPs). The NPs (59.9 min) significantly prolonged the half-life of thrombolytic drugs, which was 3.04 times that of TNK (19.7 min), and they had good biological safety. The NPs were shown to pass through vascular models with different inner diameters, curvatures, and stenosis under magnetic targeting and to enable accurate diagnosis of thrombi by photoacoustic imaging. NPs combined with the magnetic hyperthermia technique were used to accelerate thrombolysis and quickly open blocked blood vessels. Then, renal IRI-induced functional metabolic disorder and tissue damage were evidently attenuated by scavenging toxic reactive oxygen and nitrogen species and through the protective effects of bioactive ion therapy, including reduced apoptosis, increased angiogenesis, and inhibited fibrosis. In brief, we constructed a multifunctional nanoplatform for integrating a "diagnosis-therapy-protection" approach to achieve comprehensive management from thrombus to renal IRI, promoting the advancement of related technologies.

Carbonized polydopamine layer-protected silicon substrates for light-addressable electrochemical sensing and imaging

The application of silicon (Si) substrate as photoelectrode in light-addressable electrochemistry (LAE) is severely limited due to its ease of surface oxidation. The resulted silicon oxide (SiO_x) layer is electronically insulating and blocks charge transfer between the electrode and electrolyte. Keeping the Si from being oxidized is a key challenge for its practical use as a semiconductor electrode. In this work, we find that by developing a thin layer of polydopamine film on the surface of Si substrate, followed by carbonization at 550 °C, the natural oxidation of Si substrate can be successfully forestalled. When applied as an electrode, it is further found that the carbonized polydopamine (cPDA) layer can also prevent anodic oxidation of Si. The cPDA layer-modified Si substrate exhibits good photoelectrochemical performance and great stability, with no obvious signal decrease under ambient environment over 32 h. Our work here provides a new modification strategy for anti-oxidation of Si substrate and it is promising in the application of light-addressable electrochemical sensing and imaging.

Improved Polydopamine Deposition in Amine-Functionalized Silica Aerogels for Enhanced UV Absorption

Silica aerogels are interesting porous materials with extremely low density and high surface area, making them advantageous for a number of aerospace and catalysis applications. Here, we report the preparation of polydopamine (PDA)-functionalized silica aerogels using an in situ coating method, wherein the dopamine monomer was allowed to diffuse through the underlying structure of the gels in the absence of any external base and polymerize on the surface of the gel. The use of a siloxane precursor with an amine functionality decorates the silica backbone, allowing for a superior PDA coating, as evident in the darker color of PDA-coated amine-functionalized silica gels than PDA-coated silica-only gels and the X-ray photoelectron spectroscopy results. Furthermore, by varying the coating time, a series of aerogels with increasing optical absorption are prepared. Analyses using Brunauer-Emmett-Teller, scanning electron microscopy, and pycnometry show that the in situ PDA coating does not affect the inherent properties of the silica aerogels as opposed to PDA coatings deposited using an external base. Aerogels coated for 12 h and 24 h offer a surface area of 614 ± 35 and 658 ± 15 m²/g along with a porosity of 92.6 ± 0.9 and 92.4 ± 0.7%, respectively, properties similar to the native silica aerogels. PDA-coated aerogels have the potential to serve as UV ray mitigating materials due to the tortuosity of the underlying structure and the unique chemical properties of the PDA coating.

Stable Electrochemical Determination of Dopamine by a Fluorine-Terminated {001}-Exposed TiO2 Single Crystal Sensor

Photochemical oxidation is able to effectively regenerate the fouled electrode in electrochemical pollutant monitoring, while its regeneration capacity is limited by the surface-bound hydroxyl radical speciation with low activity and mobility, which is attributed to the dissociated water adsorption on hydrophilic metal oxides. In this work, fluorine-terminated {001}-exposed TiO₂ single crystals (F-TiO₂) are rationally designed to construct an Au-based electrochemical sensor (Au/F-TiO₂) for dopamine (DA) detection in different matrices. The Au/F-TiO₂ sensor exhibits an efficient and stable detection capacity in both environmental and biological samples. A superior photochemical regeneration capacity is obtained on the Au/F-TiO₂ electrode with much reduced matrix effects under UV irradiation. Spectral observation, crystallographic analysis, pollutant degradation performance, radical inhibition, and surface enhanced Raman scattering tests reveal that both the fluorine-terminated surface chemical features and the bulk-free radical speciation are mainly responsible for the superior photochemical regeneration capacity of the Au/F-TiO₂ electrode. Even for the real biological samples, a stable electrochemical DA detection is also achieved on the Au/F-TiO₂ sensor. Our work establishes a new approach to refine electrochemical sensors for stable monitoring and provides a robust photoactive electrode substrate with high efficiency and low cost for practical applications.

Highly Active Hydrogenation Catalysts Based on Pd Nanoparticles Dispersed along Hierarchical Porous Silica Covered with Polydopamine as Interfacial Glue

New catalysts based on Pd(0) nanoparticles (Pd NPs) on a bimodal porous silica of the UVM-7/polydopamine (PDA) support have been synthesized following two preparative strategies based on the sequential or joint incorporation of two components of the composite (Pd and PDA). We analyzed the role played by the PDA as ‘interfacial glue’ between the silica scaffold and the Pd NPs. The catalysts were tested for the hydrogenation of 4-nitrophenol using (NEt4)BH4 as the hydrogenating agent. In addition to the palladium content, the characterization of the catalysts at the micro and nanoscale has highlighted the importance of different parameters, such as the size and dispersion of the Pd NPs, as well as their accessibility to the substrate (greater or lesser depending on their entrapment level in the PDA) on the catalytic efficiency. Staged sequential synthesis has led to better catalytic results. The most active Pd(0) centers seem to be Pd NPs of less than 1 nm on the PDA surface. The efficiency of the catalysts obtained is superior to that of similar materials without PDA. A comprehensive comparison has been made with other catalysts based on Pd NPs in a wide variety of supports. The TOF values achieved are among the best described in the literature.

Photochemically Synthesized Ruthenium Nanoparticle-Decorated Carbon-Dot Nanochains: An Efficient Catalyst for Synergistic Redox Reactions

Ruthenium nanoparticle (NP)-decorated carbon dots (Ru/C-dots) were fabricated as a potential catalyst in the application of both oxidation and reduction. The photochemical method was used to synthesize Ru/C-dot nanohybrids. The as-prepared Ru/C-dots exhibited a core-shell-based nanochain structure, in which the spherical nature of C-dots further evolved to a layer structure to homogeneously encapsulate Ru NPs. Such Ru/C-dots have excellent catalytic properties, which were demonstrated in the oxidation of flavonoids and concomitantly reduction of inorganic complex and organic dyes, each yielding a high catalytic rate constant. We also proposed an appropriate catalytic mechanism for each reaction. Higher catalytic activity was achieved by the synergistic effect of the encapsulated Ru NPs and the C-dots layer. Further, this nanohybrid was successfully applied to inspect a real aqueous sample. We anticipated that Ru/C-dots nanohybrid may open up a broad platform for the design of efficient multifunctional catalysts.

Bio-inspired construction of melanin-like polydopamine-coated CeO2 as a high-performance visible-light-driven photocatalyst for hydrogen production

In recent years, cerium oxide has been the most widely studied photocatalyst due to its unique properties.

A Facile Path to Graphene-Wrapped Polydopamine-Entwined Silicon Nanoparticles with High Electrochemical Performance

Graphene-coated silicon nanoparticles with polydopamine buffers have been designed and successfully fabricated as anodes for lithium ion batteries, where the polydopamine was grown on the silicon nanoparticles and then coated with graphene layers. The expansion cavities for silicon nanoparticles during charging and discharging process are provided by the polydopamine buffer layers. The outermost graphene coating layers not only keep the pulverized silicon particles together without disintegration, but also improve the electric conductivity of silicon nanoparticles. Silicon nanoparticles of an industrial product level with different size distributions and oxidation layers were used in this work. High electrochemical performances with specific capacities of 1100 mAh g^-1 were achieved by the designed silicon composites with polydopamine and graphene after 550 cycles at a current rate of 200 mA g^-1 .

Good practices for reporting the photocatalytic evaluation of a visible-light active semiconductor: Bi2O3, a case study

The use of dyes to evaluate visible-light photocatalysts requires a proper determination of the contribution from the competing processes: adsorption, sensitization, photobleaching and degradation.

Simple Preparation of Porous Carbon-Supported Ruthenium: Propitious Catalytic Activity in the Reduction of Ferrocyanate(III) and a Cationic Dye

The present study involves the synthesis, characterization, and catalytic application of ruthenium nanoparticles (Ru NPs) supported on plastic-derived carbons (PDCs) synthesized from plastic wastes (soft drink bottles) as an alternative carbon source. PDCs have been further activated with CO₂ and characterized by various analytical techniques. The catalytic activity of Ru@PDC for the reduction of potassium hexacyanoferrate(III), (K₃[Fe(CN)₆]), and new fuchsin (NF) dye by NaBH₄ was performed under mild conditions. The PDCs had spherical morphology with an average size of 0.5 μm, and the Ru NP (5 ± 0.2 nm) loading (4.01 wt %) into the PDC provided high catalytic performance for catalytic reduction of ferrocyanate(III) and NF dye. This catalyst can be recycled more than six times with only a minor loss of its catalytic activity. In addition, the stability and reusability of the Ru@PDC catalyst are also discussed.

Mussel-inspired graphene oxide nanosheet-enwrapped Ti scaffolds with drug-encapsulated gelatin microspheres for bone regeneration

Graphene oxide (GO) attracts considerable attention for biomedical applications owing to its unique nanostructure and remarkable physicochemical characteristics. However, it is challenging to uniformly deposit GO on chemically inert Ti scaffolds, which have good biocompatibility and wide applications in bone engineering. In this study, a GO-functionalized Ti porous scaffold (GO/Ti scaffold) was prepared by depositing GO onto polydopamine (PDA) modified Ti scaffolds. The mussel-inspired PDA modification facilitated the interaction between GO and Ti surfaces, leading to a uniform coverage of GO on Ti scaffolds. BMP2 and vancomycin (Van) were separately encapsulated into gelatin microspheres (GelMS). Then, drug-containing GelMS were assembled on GO/Ti scaffolds and anchored by the functional groups of GO. The modified scaffold independently delivered multiple biomolecules with different physiochemical properties, without interfering with each other. Thus, the GO/Ti scaffold has the dual functions of inducing bone regeneration and preventing bacterial infection. In summary, this mussel-inspired GO/Ti hybrid scaffold combined the good mechanical properties of Ti scaffolds and the advantages of GO nanosheets. GO nanosheets with their unique nanostructure and functional groups, together with GelMS on Ti scaffolds, are suitable carriers for drug delivery and provide adhesive sites for cell adhesion and create nanostructured environments for bone regeneration.

Mussel-inspired construction of thermo-responsive double-hydrophilic diblock copolymers-decorated reduced graphene oxide as effective catalyst supports for highly dispersed superfine Pd nanoparticles

Well-dispersed ultrafine palladium nanoparticles supported by reduced graphene oxide functionalized with catechol-terminated thermo-responsive block copolymer (PdNPs@BPrGO) were successfully constructed for highly efficient heterogeneous catalytic reduction. We first synthesized a novel temperature-responsive episulfide-containing double-hydrophilic diblock copolymer, poly(poly(ethylene glycol) methyl ether methacrylate-co-2,3-epithiopropyl methacrylate)-block-poly(N-isopropylacrylamide) (P(PEGMA-co-ETMA)-b-PNIPAM), through a reversible addition-fragmentation chain transfer (RAFT) polymerization utilizing a chain-transfer agent with a catechol unit as the end group. The obtained block copolymers can be facilely anchored to the surface of GO via mussel-inspired chemistry. The PdNPs were loaded on GO decorated with block copolymer brushes (BPrGO) as a support via the in situ reduction of palladium precursors with the episulfide ligands of the block copolymer as a stabilizer. The resulting PdNPs@BPrGO nanohybrid catalyst had good water dispersibility and stability. Furthermore, a low dosage of PdNPs@BPrGO catalyst exhibited excellent catalytic performance in the reduction of methylene blue and nitrophenols. The performance was attributed to the ability of PdNPs@BPrGO to facilitate the diffusion of reactants compared to PdNPs@GO without polymer modification. PdNPs@BPrGO also possessed an interesting temperature-responsive catalytic property due to the reversible "coil-to-globule" phase transition behaviour of PNIPAM blocks onto the surface of catalyst. The PdNPs@BPrGO catalyst was successfully recovered and reused five times without any detectible loss in catalytic activity, demonstrating its great potential in a wide range of industrial catalytic applications.

Electrocatalytic enhancement of platinum and palladium metal on polydopamine reduced graphene oxide support for alcohol oxidation

The objective of our work is to improve low-temperature fuel cell catalysts by increasing the surface area to augment the efficiency of catalytic reactions. Reduced graphene oxide (rGO) supports were prepared by adding N-containing derivatives of polydopamine (PDA) and loading of Pt and Pt-based metal alloy nanoparticles were accomplished for catalyst preparation. To study the effects of surface modification on catalyst activity, the GO surfaces modified by addition of PDA (PDA-rGO) were richer in oxygen- and nitrogen-containing functional groups, which reduced the number of graphene defects. Reduction of metals (M = Pt, Pd, Pt_xPd_y where x and y = 1-3) by NaBH₄ produced M/GO (metal on GO) and M/PDA-rGO (metal on PDA-rGO) catalysts. Examination of morphology and chemical composition confirmed that the existence of particle size on M/PDA-rGO catalysts was smaller than that on M/GO catalysts in agreement with calculated electrochemically active surface areas (ECSA). Electrochemical analysis was conducted to evaluate the catalyst activity and stability. The prepared catalysts had significantly greater surface areas as a result of association between the metal nanoparticles and the oxygen and nitrogen functional groups on the rGO supports. The catalysts also exhibited lower onset potentials and greater current intensities, I_f/I_b values, and long-term stabilities for methanol and ethanol oxidation compared with those of commercial PtRu/C. Moreover, the diameter of the Nyquist plot of the catalysts on PDA-rGO were smaller than that of the catalysts M/GO. The results suggest that variation of the Pt_xPd_y atomic ratio on carbon nanocomposites is an encouraging means of enhancing electrocatalytic performance in direct alcohol fuel cell applications.

Probing polydopamine adhesion to protein and polymer films: microscopic and spectroscopic evaluation

Polydopamine has been found to be a biocompatible polymer capable of supporting cell growth and attachment, and to have antibacterial and antifouling properties. Together with its ease of manufacture and application, it ought to make an ideal biomaterial and function well as a coating for implants. In this paper, atomic force microscope was used to measure the adhesive forces between polymer-, protein- or polydopamine-coated surfaces and a silicon nitride or polydopamine-functionalised probes. Surfaces were further characterised by contact angle goniometry, and solutions by circular dichroism. Polydopamine was further characterised with infrared spectroscopy and Raman spectroscopy. It was found that polydopamine functionalisation of the atomic force microscope probe significantly reduced adhesion to all tested surfaces. For example, adhesion to mica fell from 0.27 ± 0.7 to 0.05 ± 0.01 nN nm-1. The results suggest that polydopamine coatings are suitable to be used for a variety of biomedical applications.

The green synthesis of ultrafine palladium–phosphorus alloyed nanoparticles anchored on polydopamine functionalized graphene used as an excellent electrocatalyst for ethanol oxidation

A new catalyst, consisting of ultrafine Pd–P alloyed nanoparticles (NPs) anchored on polydopamine functionalized graphene (Pd–P/PDA-GS), was fabricated by a green, facile and surfactant free method for ethanol electrocatalytic oxidation reaction (EOR).

Surface-Engineered Polydopamine Particles as an Efficient Support for Catalytic Applications

Mussel-inspired polydopamine (PDA) particles with the size of ∼270 nm are used as a support of palladium (Pd) nanoparticles (NPs) for catalyst preparation. The surface morphology of the PDA particle has been modified via corrosion of CF₃COOH. Surface chemistry of the obtained PDA particle has been engineered by the formation of a carboxylic acid-terminated alkanethiol monolayer. The obtained self-assembled monolayer-modified PDA (SAM-PDA) particles are used to load Pd NPs by simply adding H₂PdCl₄ solution to a suspension of SAM-PDA particles at room temperature. Transmission electron microscopy, energy-dispersive X-ray mapping, dynamic light scattering, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis, and Fourier transform infrared are used to characterize the catalyst and to investigate the process. Uniform Pd NPs (2-3 nm) have been well-dispersed on the SAM-PDA particles via controllable surface engineering. Surface charges and interactions with a metal ion are regulated by the monolayer of carboxylic acids. The surface chemistry of PDA particles has been finely engineered for efficient loading of noble metal NPs. The obtained Pd/SAM-PDA catalyst has shown greatly increased activity and good reusability compared with Pd/PDA in the reduction of 4-nitrophenol (4-NP) by sodium borohydride or H₂. The kinetic data of 4-NP hydrogenation catalyzed by Pd/SAM-PDA are fitted to a Langmuir-Hinshelwood (L-H) model, and the calculated apparent activation energy of this process is 40.77 kJ mol^-1.

Preparation of raspberry-like γ-Fe2O3/crackled nitrogen-doped carbon capsules and their application as supports to improve catalytic activity

In this manuscript, we have introduced a novel method to improve the catalytic activity of metal nanoparticles via optimizing the support structure. To this end, raspberry-like γ-Fe₂O₃/crackled nitrogen-doped carbon (CNC) capsules were prepared by a two-step method. Compared with traditional magnetic capsules, in γ-Fe₂O₃/CNC capsules, the γ-Fe₂O₃ nanoparticles were embedded in a CNC shell; therefore, they neither occupied the anchoring sites for metal nanoparticles nor came into contact with them, which was beneficial for increasing the metal nanoparticle loading. Numerous tiny cracks appeared on the porous CNC shell, which effectively improved the mass diffusion and transport in catalytic reactions. Additionally, the coordination interaction could be generated between the precursor metal ions and doped-nitrogen atoms in the capsule shell. With the help of these structural merits, γ-Fe₂O₃/CNC capsules were ideal supports for Pd nanoparticles, because they were beneficial for improving the Pd loading, reducing the nanoparticle size, increasing their dispersity and maximizing the catalytic performance of Pd nanoparticles anchored on the inner shell surface. As expected, γ-Fe₂O₃/CNC@Pd catalysts exhibited a dramatically enhanced catalytic activity towards hydrophilic 4-nitrophenol and hydrophobic nitrobenzene. The reaction rate constant k was compared with recent work and the corresponding reference samples. Moreover, they could be easily recycled by using a magnet and reused without an obvious loss of catalytic activity.