Synergistic Bactericidal Effect of Zn2+ Ions and Reactive Oxygen Species Generated in Response to Either UV or X-ray Irradiation of Zn-Doped Plasma Electrolytic Oxidation TiO2 Coatings.

Zn-containing TiO2-based coatings with Na, Ca, Si, and K additives were obtained by plasma electrolytic oxidation (PEO) of Ti in order to achieve an effective and broad bactericidal protection without compromising biocompatibility. A protocol has been developed for cleaning the coating surface from electrolyte residues, ensuring the preservation of the microstructure and composition of the surface layer. Using high-resolution transmission electron microscopy, three characteristic microstructural zones in the PEO-Zn coating are well documented: zone 1 with a TiO2-based nanocrystalline structure, zone 2 with an amorphous structure, and zone 3 around pores with an amorphous-nanocrystalline structure. The excellent cytocompatibility of PEO-Zn samples was confirmed by three different methods: monitoring the proliferation of MC3T3-E1 cells, assessing the viability of sheep osteoblast cells using calcein-AM staining and fluorescence microscopy, and incubation with spheroids based on primary osteoblast cells and mouse embryonic fibroblast NIH3T3 cells. The PEO-Zn coatings absorb >60% of the incident light over the UV and Vis-NIR spectral ranges. After 24 h, the PEO-Zn coatings completely inactivate four types of strains: Gram-positive Staphylococcus aureus CSA154 and ATCC29213 and Gram-negative Escherichia coli K261 and U20, and also prevent E. coli U20 and K261 biofilm formation. The superior antibacterial activity is associated with the synergistic effect of Zn2+ ions in safe concentration and reactive oxygen species (ROS) generated in response to either UV irradiation or soft short-term X-ray irradiation. The X-ray irradiation-induced ROS formation by a PEO coating is reported for the first time. The enhanced bactericidal activity after X-ray irradiation compared to UV illumination is attributed to the more intense ROS generation in the first few hours. The results obtained significantly expand the possibilities of using PEO coatings on the surfaces of titanium implants.

Pulsed Laser Ablation of Oxygen deficiency Enriched Superlattice Vanadium Pentoxide (V2O5) Ultrathin Nextrode aiming for Flexible Binder-less Tandem Energy Harvesting Devices.

For the initial instance, oxygen deficiency-enriched vanadium pentoxide (O─V2O5@500) thin film electrodes are tuned by the Pulsed Laser Ablation technique. The O─V2O5@500 thin film electrode shows remarkable electrochemical performances confirming the greater potential window of -0.4 to 0.9 V versus Hg/HgO in an alkaline electrolyte; also, the O─V2O5@ 500 thin film electrode exhibits a noteworthy volumetric capacity of 167.7 mAh cm-3 (areal capacity of 73.3 µAh cm-2). Additionally, Density Functional Theory (DFT) theory calculations are carried out for oxygen-deficient V2O5. From the partial density of states (pDOS) and partial charge density analysis, it is clear that oxygen vacancy improves the electrical conductivity due to the higher degree of electron delocalization of V─O─V near the vacancy and enhances the redox properties due to the formation of in-gap states. Further, it is reported that a O─V2O5@ 500 ||PVA-KOH|| Bi2O3 A-650 thin film supercapbattery (TFSCB) device attains an exceptional discharge volumetric capacitance of 182.85 F cm-3 (equal volumetric capacity of 124.5 mAh cm-3). Furthermore, the TFSCB device exhibits an extraordinary maximum volumetric energy (power) density of 14.28 mWh cm-3 (1.66 W cm-3); TFSCB succeeds in supreme capacity retention of 86% with outstanding coulombic efficiency of 94.4% after 21 000 cycles.

Electrochromic Performance of Sputtered NbTi-Based Mixed Metal Oxide Thin Films with a Metallic Seed Layer.

An attempt has been made to promote the efficiency of the electrochromic (EC) windows to perform at a faster switching rate with good coloration and easy recyclability. In this work, ion-assisted pulsed DC unbalanced confocal magnetron sputtering is used to fabricate mixed metal oxide thin films of Nb and Ti (which are termed as NTO) for EC applications. Further, to increase the EC efficiency of this film, a very thin metallic seed layer is incorporated between the substrate and the film using the layer-by-layer (LBL) coating strategy. The film was prepared by two steps: (i) very thin metallic seed layer coating and (ii) mixed metal oxide NTO layer coating. The metal layer was made of a Nb metal, Ti metal, and NbTi mixed metal, which was coated with the substrate and NTO layer, resulting in three different films, namely, Nb-NTO, Ti-NTO, and NbTi-NTO. The EC properties of these three films were studied in 1 M LiClO4 dissolved in propylene carbonate and compared with the as-prepared NTO film. The results showed that the Nb-NTO film showed better EC properties, fast switching, better stability, and good recyclability. To check the stability, the film was subjected to prolonged cycling of 500 cycles with a harsh anodic and cathodic sweep at the scan rate of 100 mV s-1. The UV-Vis spectrum confirmed the Li+ trapping in the films after prolonged cycling. To detrap the ions from the host surface, galvanostatic detrapping is carried out called rejuvenation studies. The rejuvenation rate of films is studied at a constant current loading of ∼2 × 10-5 A cm-2. To check the commercialization of the EC window, we successfully fabricated the Nb-NTO device with a PEO-LiClO4-based polymer gel electrolyte.

Self-Assembled Molecular Hybrids of CoS-DNA for Enhanced Water Oxidation with Low Cobalt Content.

Water oxidation in alkaline medium was efficiently catalyzed by the self-assembled molecular hybrids of CoS-DNA that had 20 times lower Co loading than the commonly used loading. The morphological outcome was directed by varying the molar ratio of metal precursor Co(Ac)2 and DNA and three different sets of CoS-DNA molecular hybrids, viz. CoS-DNA(0.036), CoS-DNA(0.06), and CoS-DNA(0.084) were prepared. These morphologically distinct hybrids had shown similar electrocatalytic behavior, because of the fact that they all contained the same cobalt content. The CoS-DNA(0.036), CoS-DNA(0.06), and CoS-DNA(0.084) required very low overpotentials of 350, 364, and 373 mV at a current density of 10 mA cm-2 (1 M KOH), respectively. The advantages of lower overpotential, lower Tafel slope (42.7 mV dec-1), high Faradaic efficiency (90.28%), high stability and reproducibility after all, with a lower cobalt loading, have certainly shown the worth of these molecular hybrids in large-scale water oxidation. Moreover, since DNA itself a good binder, CoS-DNA molecular hybrids were directly casted on substrate electrodes and used after drying. It also showed minimum intrinsic resistance as DNA is a good ionic and electronic conductor. Besides, the present method may also be extended for the preparation of other active electrocatalysts for water splitting.

Study of the Oxygen Evolution Reaction Catalytic Behavior of CoxNi1-xFe2O4 in Alkaline Medium.

Catalysts for the oxygen evolution reaction (OER) play an important role in the conversion of solar energy to fuel of earth-abundant water into H2 and O2 through splitting/electrolysis. Heterogeneous electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) exhibit catalytic activity that depends on the electronic properties, oxidation states, and local surface structure. Spinel ferrites (MFe2O4; M = Ni and Co) based materials have been attractive for the catalytic water oxidation due to their well-known stability in alkaline medium, easy synthesis, existence of metal cations with various oxidation states, low cost, and tunable properties by the desired metal substitution. To understand the better catalytic activity of MFe2O4 in detail the role of Ni and Co was studied through MxNi1-xFe2O4 (M = Co; 0 < x < 1), which was prepared by the sol-gel method. The results showed that bare NiFe2O4 has better catalytic activity (η = 381 mV at 10 mA cm-2 and Tafel slope of 46.4 mV dec-1) compared to Co-containing MxNi1-xFe2O4 (η = 450-470 mV at 10 mA cm-2 and Tafel slope of 50-73 mV dec-1) in alkaline medium, and the substitution of Co is found to suppress the catalytic activity of NiFe2O4. The degradation of catalytic activity with an increase in Co content was accounted for in further detailed investigations.

Biocompatibility evaluation of sputtered zirconium-based thin film metallic glass-coated steels.

Thin film metallic glasses comprised of Zr48Cu36Al8Ag8 (at.%) of approximately 1.5 µm and 3 µm in thickness were prepared using magnetron sputtering onto medical grade 316L stainless steel. Their structural and mechanical properties, in vitro corrosion, and antimicrobial activity were analyzed. The amorphous thin film metallic glasses consisted of a single glassy phase, with an absence of any detectable peaks corresponding to crystalline phases. Elemental composition close to the target alloy was noted from EDAX analysis of the thin film. The surface morphology of the film showed a smooth surface on scanning electron microscopy and atomic force microscopy. In vitro electrochemical corrosion studies indicated that the zirconium-based metallic glass could withstand body fluid, showing superior resistance to corrosion and electrochemical stability. Interactions between the coated surface and bacteria were investigated by agar diffusion, solution suspension, and wet interfacial contact methods. The results indicated a clear zone of inhibition against the growth of microorganisms such as Escherichia coli and Staphylococcus aureus, confirming the antimicrobial activity of the thin film metallic glasses. Cytotoxicity studies using L929 fibroblast cells showed these coatings to be noncytotoxic in nature.

Biosynthesis of calcium hydroxylapatite coating on sputtered Ti/TiN nano multilayers and their corrosion behavior in simulated body solution.

Titanium/titanium nitride (Ti/TiN) nanoscale multilayered films were deposited onto 316L stainless steel substrates by reactive magnetron sputtering using a Ti target. Coatings characterized by X-ray diffraction showed that the stack possesses centered cubic structure. The X-ray photoelectron spectroscopy survey spectra on the etched surfaces of the stack film on steel exhibited the characteristic Ti2p, N1s, and O1s peaks at the corresponding binding energies 454.5, 397.0, and 530.6 eV, respectively. Platelet adhesion experiments were carried out to examine the interaction between blood and the materials in vitro. The results indicated that the smoothness and lower isoelectric point contribute to better hemocompatibility of the Ti/TiN nanoscale multilayered coating. The biomediated synthesis of calcium hydroxylapatite (HA) was carried out on coated substrates using calcium-depositing bacteria. The observation of low corrosion current density (I(corr)) for the calcium HA-coated Ti/TiN specimens in simulated body fluid confirmed their highly resistive nature under the testing condition.