In Situ Investigation of Electrochemically Mediated Surface-Initiated Atom Transfer Radical Polymerization by Electrochemical Surface Plasmon Resonance

Electrochemically mediated atom transfer radical polymerization (eATRP) initiates/controls the controlled/living ATRP chain propagation process by electrochemically generating (regenerating) the activator (lower-oxidation-state metal complex) from deactivator (higher-oxidation-state metal complex). Despite successful demonstrations in both of the homogeneous polymerization and heterogeneous systems (namely, surface-initiated ATRP, SI-ATRP), the eATRP process itself has never been in situ investigated, and important information regarding this process remains unrevealed. In this work, we report the first investigation of the electrochemically mediated SI-ATRP (eSI-ATRP) by rationally combining the electrochemical technique with real-time surface plasmon resonance (SPR). In the experiment, the potential of a SPR gold chip modified by the self-assembled monolayer of the ATRP initiator was controlled to electrochemically reduce the deactivator to activator to initiate the SI-ATRP, and the whole process was simultaneously monitored by SPR with a high time resolution of 0.1 s. It is found that it is feasible to electrochemically trigger/control the SI-ATRP and the polymerization rate is correlated to the potential applied to the gold chip. This work reveals important kinetic information for eSI-ATRP and offers a powerful platform for in situ investigation of such complicated processes

Simultaneous Transfer and Imaging of Latent Fingerprints Enabled by Interfacial Separation of Polydopamine Thin Film

Various approaches have been developed to visualize a latent fingerprint (LFP) for personal identification, but simultaneous transfer of a LFP for preservation has yet to be achieved. We herein report a novel strategy for simultaneous transfer and imaging of LFPs on a broad variety of substrates by using the interfacial separation of polydopamine (PDA) thin film, followed by electroless silver deposition. In this approach, a PDA thin film deposited on a polydimethylsiloxane (PDMS) flake is used to cover the substrate carrying LFPs and then gently peeled off. During this cover-separation process, PDA film is interfacially transferred from PDMS to the LFP ridges on the substrate in a spatially selective manner, leaving behind a complementary (negative) LFP pattern on the PDMS flake. Upon PDA-catalyzed electroless silver deposition, positive and negative LFP patterns are imaged on the original substrate and PDMS flake, respectively. This approach relies on the remarkably different adhesion energy of PDA on fingerprint sweat and PDMS and is applicable to fresh and aged LFPs on most nonporous substrates

Patterning of Metal Films on Arbitrary Substrates by Using Polydopamine as a UV-Sensitive Catalytic Layer for Electroless Deposition

Patterning metal films on various substrates is essentially important and yet challenging for developing a wide variety of innovative devices. We herein report a versatile approach to pattern metal (gold, silver, or copper) films on arbitrary substrates by using the bio-inspired polydopamine (PDA) thin film as a UV-sensitive adhesive layer for electroless deposition. The PDA film is able to be formed on virtually any solid surfaces under mild condition, and its rich catechol groups allow for electroless deposition of metal films with high adhesion stability. Upon UV irradiation, spatially selective oxidation of PDA film occurs and the local metal deposition is inhibited, thus facilitating successful patterning of metal films. Considering its versatility and simplicity, this strategy may demonstrate great applications in manufacturing various innovative devices

Improving the Mechanical Durability of Superhydrophobic Coating by Deposition on to a Mesh Structure

<p>Superhydrophobic surfaces (SHSs) require a combination of a rough nano- or microscale structured surface topography and a low surface energy. However, its superydrophobicity is easily lost, even under relatively mild mechanical abrasion, when the surface is mechanically weak. Here, we develop a method that significantly increases the mechanical durability of a superhydrophobic surface, by introducing a mesh layer beneath the superhydrophobic layer. The hardness, abrasion distance, flexibility and water-jet impact resistance all increase for the commercially available Ultra-ever Dry superhydrophobic coating. This is attributed to the increased mechanical durability offered by the mesh, whose construction not only increases the porosity of the SHS coating but acts as a third, larger structure, so that the superhydrophobic layer is now composed of a three-level hierarchical structure: the mesh, micropillars and nanoparticles.</p

One-Pot Synthesis of Co/CoFe₂O₄ Nanoparticles Supported on N‑Doped Graphene for Efficient Bifunctional Oxygen Electrocatalysis

We herein report a facile strategy to synthesize transition metal/spinel oxide nanoparticles coupled with nitrogen-doped graphene (Co/CoFe₂O₄@N-graphene) as an efficient bifunctional electrocatalyst toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). This approach involves a spontaneous solution-polymerization of polydopamine (PDA) film on graphene oxide (GO) sheets in the presence of Fe³⁺ and Co²⁺ to form the Fe/Co-PDA-GO precursor, followed by pyrolysis at 800 °C in argon (Ar) atmosphere. During the calcination process, Co/CoFe₂O₄ nanoparticles are in situ formed via high-temperature solid state reaction and are further entrapped by the PDA-derived N-doped carbon layer. As-prepared Co/CoFe₂O₄@N-graphene exhibits highly efficient catalytic activity and excellent stability for both ORR and OER in alkaline solution. This work reports a facile synthetic approach to develop highly active electrocatalysts while offering great flexibility to tailor their components and morphologies and thus provides a useful route to the design and synthesis of a broad variety of electrocatalysts

Superoleophobic Textured Copper Surfaces Fabricated by Chemical Etching/Oxidation and Surface Fluorination

We report a convenient route to fabricate superoleophobic surfaces (abridged as SOS) on copper substrate by combining a two-step surface texturing process (first, the substrate is immersed in an aqueous solution of HNO₃ and cetyltrimethyl ammonium bromide, and then in an aqueous solution of NaOH and (NH₄)₂S₂O₈) and succeeding surface fluorination with 1H,1H,2H,2H-perfluorodecanethiol (PFDT) or 1-decanethiol. The surface morphologies and compositions were characterized by field emission scanning electron microscopy and X-ray diffraction, respectively. The results showed that spherical micro-pits (SMP) with diameter of 50–100 μm were formed in the first step of surface texturing; in the second step, Cu­(OH)₂ or/and CuO with structures of nanorods/microflowers/microballs were formed thereon. The surface wettability was further assessed by optical contact angle meter by using water (surface tension of 72.1 mN m^–1 at 20°C), rapeseed oil (35.7 mN m^–1 at 20°C), and hexadecane (25.7 mN m^–1 at 20°C) as probe liquids. The results showed that, as the surface tension decreasing, stricter choosing of surface structures and surface chemistry are required to obtain SOS. Specifically, for hexadecane, which records the lowest surface tension, the ideal surface structures are a combination of densely distributed SMP and nanorods, and the surface chemistry should be tuned by grafted with low-surface-energy molecules of PFDT. Moreover, the stability of the so-fabricated sample was tested and the results showed that, under the testing conditions, superhydrophobicity and superoleophobicity may be deteriorated after wear/humidity resistance test. Such deterioration may be due to the loss of outermost PFDT layer or/and the destruction of the above-mentioned ideal surface structures. For UV and oxidation resistance, the sample remained stable for a period of 10 days

Ru₂P Nanoparticle Decorated P/N-Doped Carbon Nanofibers on Carbon Cloth as a Robust Hierarchical Electrocatalyst with Platinum-Comparable Activity toward Hydrogen Evolution

It is desirable yet challenging to develop highly active and durable hydrogen evolution reaction (HER) electrocatalysts with Pt-comparable activity for future energy devices. In this work, we report Ru₂P nanoparticle decorated P/N dual-doped carbon nanofibers on carbon cloth (Ru₂P@PNC/CC-900) as a highly efficient and durable hierarchical HER electrocatalyst in both acidic and alkaline media. Electrochemical tests show that this Ru₂P@PNC/CC-900 possesses Pt-comparable HER activity to support 10 mA cm^–2 HER current density at low overpotential of 15 and 50 mV in acidic and alkaline condition, respectively. Density functional theory calculations reveal that coupling Ru₂P nanoparticles with heteroatom-doped carbon fibers leads to enhanced intrinsic HER activity. The integrative hierarchical architecture further endows high surface areas with good mechanical robustness to support abundant catalytically active sites and possesses excellent electrical conductivity and efficient access for mass transportation to facilitate the HER process

Manganese/Cobalt Bimetal Nanoparticles Encapsulated in Nitrogen-Rich Graphene Sheets for Efficient Oxygen Reduction Reaction Electrocatalysis

It is of vital importance to search for a nonprecious metal based sustainable and efficient oxygen reduction reaction (ORR) electrocatalyst for the next generation of energy conversion and storage technology. We herein report a hybrid bimetal material composed of MnO/Co nanoparticles encapsulated in nitrogen-rich graphene nanosheets (MnO/Co–N–G) as a high performance ORR catalyst in alkaline electrolyte. The MnO/Co–N–G catalyst is derived from Mn²⁺, Co²⁺ incorporated polydopamine (PDA) coated graphene oxide (GO) sheets via a carbonization process. The morphology, structure, and composition properties of as-prepared MnO/Co–N–G catalyst are systematically investigated. Electrochemical measurements show that the MnO/Co–N–G catalyst exhibits excellent ORR activity superior to commercial Pt/C, featuring higher limiting current density, better methanol resistance, and excellent long-term durability in alkaline solution. The bimetal nanoparticles are believed to be responsible for the impressive ORR activity of the catalyst

Mesoporous Hollow Nitrogen-Doped Carbon Nanospheres with Embedded MnFe₂O₄/Fe Hybrid Nanoparticles as Efficient Bifunctional Oxygen Electrocatalysts in Alkaline Media

Exploring sustainable and efficient electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is necessary for the development of fuel cells and metal–air batteries. Herein, we report a bimetal Fe/Mn–N–C material composed of spinel MnFe₂O₄/metallic Fe hybrid nanoparticles encapsulated in N-doped mesoporous hollow carbon nanospheres as an excellent bifunctional ORR/OER electrocatalyst in alkaline electrolyte. The Fe/Mn–N–C catalyst is synthesized via pyrolysis of bimetal ion-incorporated polydopamine nanospheres and shows impressive ORR electrocatalytic activity superior to Pt/C and good OER activity close to RuO₂ catalyst in alkaline environment. When tested in Zn–air battery, the Fe/Mn–N–C catalyst demonstrates excellent ultimate performance including power density, durability, and cycling. This work reports the bimetal Fe/Mn–N–C as a highly efficient bifunctional electrocatalyst and may afford useful insights into the design of sustainable transition-metal-based high-performance electrocatalysts

Polydopamine-Functionalization of Graphene Oxide to Enable Dual Signal Amplification for Sensitive Surface Plasmon Resonance Imaging Detection of Biomarker

Surface plasmon resonance imaging (SPRi) is one of the powerful tools for immunoassays with advantages of label-free, real-time, and high-throughput; however, it often suffers from limited sensitivity. Herein we report a dual signal amplification strategy utilizing polydopamine (PDA) functionalization of reduced graphene oxide (PDA-rGO) nanosheets for sensitive SPRi immunoassay in serum. The PDA-rGO nanosheet is synthesized by oxidative polymerization of dopamine in a gentle alkaline solution in the presence of graphene oxide (GO) sheets and then is antibody-conjugated via a spontaneous reaction between the protein and the PDA component. In the dual amplification mode, the first signal comes from capture of the antibody-conjugated PDA-rGO to form sandwiched immunocomplexes on the SPRi chip, followed by a PDA-induced spontaneous gold reductive deposition on PDA-rGO to further enhance the SPRi signal. The detection limit as low as 500 pg mL^–1 is achieved on a nonfouling SPRi chip with high specificity and a wide dynamic range for a model biomarker, carcinoembryonic antigen (CEA) in 10% human serum