Synthesis, characterization and multifunctional properties of plasmonic Ag-TiO2 nanocomposites

Photocatalytic degradation of Acid Red 18 by synthesized AgCoFe2O4@Ch/AC: Recyclable, environmentally friendly, chemically stable, and cost-effective magnetic nano hybrid catalyst

Chitosan (Ch) is a linear biodegradable natural carbohydrate polymer and the most appealing biopolymer, such as low-cost biodegradability, biocompatibility, hydrophilicity, and non-toxicity. In this case, Ch was utilized to synthesize AgCoFe2O4@Ch/Activated Carbon (AC) by the modified microwave-assisted co-precipitation method. The physical and chemical structure of magnetic nanocomposites was analyzed and characterized by Field Emission Scanning Electron Microscope (FESEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Energy Dispersive Spectroscopy (EDS), Diffuse Reflection Spectroscopy (DRS), Value stream mapping (VSM), Fourier transform spectroscopy (FTIR) and BET. The effects of various parameters on the removal of dye (Acid Red18), including catalyst dose, dye concentration, pH, and time were studied. Results showed that the highest removal efficiencies were 96.68 % and 84 % for the synthetic sample and actual wastewater, respectively, in optimal conditions (pH: 3, the initial dye concentration: 10 mgL-1, the catalyst dose: 0.14 gL-1, time: 50 min). Mineralization, according to the COD analysis, was 89.56 %. Photocatalytic degradation kinetics of Acid Red 18 followed pseudo-first order and Langmuir-Hinshelwood with constants of kc = 0.12 mg L-1 min-1 and KL-H = 0.115 Lmg-1. Synthesized photocatalytic AgCoFe2O4@Ch/AC showed high stability and after five recycling cycles was able to remove the pollutant with an efficiency of 85.6 %. So, the synthesized heterogenous magnetic nanocatalyst AgCoFe2O4@Ch/AC was easily recycled from aqueous solutions and it can be used in the removal of dyes from industries with high efficiency.

Preparation of core-shell structure Ag@TiO2 plasma photocatalysts and reduction of Cr(VI): Size dependent and LSPR effect

The poor light absorption and low carrier separation efficiency of Titanium dioxide (TiO2) limit its further application. The introduction of plasma metal Ag have the potential to solve these drawbacks owing to its plasma resonance effect. Thus core-shell structure Ag@TiO2 plasma photocatalysts was prepared by using facile reduction method in this work. More specifically, Ag@TiO2 composite catalysts with different Ag loading amounts were prepared in the presence of surfactant PVP. Ag@TiO2 demonstrates excellent light absorption performance and photoelectric separation efficiency compared with pure TiO2. As a result, it displays excellent performance of Cr(VI) reduction under visible light. The optimal composite catalysts Ag@TiO2-5P achieves exceptional visible-light-driven photocatalytic Cr(VI) reduction efficiency of 0.01416 min-1 that is 2.29 times greater than pure TiO2. To investigate the role of PVP, we also synthesized Ag@TiO2-5 without PVP. The experimental results show that although Ag@TiO2-5 Cr(VI) reduction performance is superior to pure TiO2, it significantly decreases compared with Ag@TiO2-5P. The results of TEM and optoelectronic testing show that agglomeration of Ag particles leads to a decrease in the photoelectric separation efficiency of Ag@TiO2-5. The smaller Ag particles provide more active sites and demonstrating a stronger overall local surface plasmon resonance (LSPR) effect. DMPO spin-trapping ESR spectra testing indicates that ∙O2- and ∙OH are the main reactive species. This research provides a potential strategy to prepare Ag-based plasma photocatalysts for environment protection.

ZnO based 0-3D diverse nano-architectures, films and coatings for biomedical applications

Thin-film nano-architecting is a promising approach that controls the properties of nanoscale surfaces to increase their interdisciplinary applications in a variety of fields. In this context, zinc oxide (ZnO)-based various nano-architectures (0-3D) such as quantum dots, nanorods/nanotubes, nanothin films, tetrapods, nanoflowers, hollow structures, etc. have been extensively researched by the scientific community in the past decade. Owing to its unique surface charge transport properties, optoelectronic properties and reported biomedical applications, ZnO has been considered as one of the most important futuristic bio-nanomaterials. This review is focused on the design/synthesis and engineering of 0-3D nano-architecture ZnO-based thin films and coatings with tunable characteristics for multifunctional biomedical applications. Although ZnO has been extensively researched, ZnO thin films composed of 0-3D nanoarchitectures with promising thin film device bio-nanotechnology applications have rarely been reviewed. The current review focuses on important details about the technologies used to make ZnO-based thin films, as well as the customization of properties related to bioactivities, characterization, and device fabrication for modern biomedical uses that are relevant. It features biosensing, tissue engineering/wound healing, antibacterial, antiviral, and anticancer activity, as well as biomedical diagnosis and therapy with an emphasis on a better understanding of the mechanisms of action. Eventually, key issues, experimental parameters and factors, open challenges, etc. in thin film device fabrications and applications, and future prospects will be discussed, followed by a summary and conclusion.

Graphene oxide as an emerging sole adsorbent and photocatalyst: Chemistry of synthesis and tailoring properties for removal of emerging contaminants

Contaminants of emerging concern (CEC) contain a wide range of compounds, such as pharmaceutical waste, pesticides, herbicides, industrial chemicals, organic dyes, etc. Their presence in the surrounding has extensive and multifaceted effects on human health as they have the potential to persist in the environment, accumulate in biota, and disrupt ecosystems. In this regard, various remediation methods involving different kind of functional nanomaterials with unique properties have been developed. The functional nanomaterials can provide several mechanisms for water pollutant removal, such as adsorption, catalysis, and disinfection, in a single platform. Graphene oxide (GO) is a two-dimensional carbon-based material that has an extremely large surface area and a large number of active sites. Recent advances in synthesising GO have shown great progress in tailoring its various physiochemical, optical, surface, structural properties etc., making it better adsorbent and photocatalysts. In this review, sole adsorbent and standalone photocatalytic performances of GO for the removal of CEC have been discussed in light of tailoring its adsorption and photocatalytic properties through novel synthesis routes and optimizing synthesis parameters. This review also examines various models describing the structure of GO and its surface/structural modifications for improved adsorption and photocatalytic properties. The article provides valuable information for the production of efficient and cost-effective GO-based sole adsorbents and photocatalysts as compared to the traditional materials. Furthermore, future prospective and challenges for sole GO nanostructures to compete with traditional adsorbents and photocatalysts have been discussed providing interesting avenues for future research.

Ag decoration on Na2Ti3O7 nanowires for improved SERS and PHE performance

Na2Ti3O7 (NTO) is recognized as an authenticated promising photocatalyst and surface-enhanced Raman scattering (SERS) active material, although its performance is limited by its high carrier recombination rate, wide band gap and inadequate utilization of visible light. In this study, to solve these issues, sea urchin-shaped NTO nanowires directly grown on a substrate were fabricated, and then Ag nanoparticles were decorated on NTO nanowires using sputtering equipment. The as-prepared Ag-NTO substrates exhibited different morphologies and high SERS activity, which was confirmed by finite-difference time-domain (FDTD) simulations, showing that appropriate Ag decoration can bring more nanogaps and thus enhance the electromagnetic field (EM) contribution. We visualized the charge transfer (CT) mechanism in SERS and further investigated the catalytic hydrogen production process similarly induced by photogenerated CT. The optimal SERS substrate (Ag-NTO-3) was adopted to verify the photocatalytic hydrogen evolution (PHE) activity, and the hydrogen evolution rate of Ag-NTO-3 was 106.7 μmol h-1 (twice that of pristine NTO). Photoelectrochemical measurements and photoluminescence (PL) analysis were used to elucidate the potential enhancement mechanisms for the photocatalytic performance and CT process. This study can provide a valuable reference for performance and mechanism studies of SERS substrates and photocatalysts.

Highly efficient visible light active doped metal oxide photocatalyst and SERS substrate for water treatment

The development of efficient nanomaterials with promising optical and surface properties for multifunctional applications has always been a subject of novel research. In this work, the study of highly efficient TiO₂ nanorods (NRs) and Ta-doped TiO₂ NRs (Ta-TiO₂ NRs) synthesized by alkaline hydrothermal treatment followed by soaking treatment has been reported. NRs were investigated for their potential applications as recyclable/reproducible visible light active photocatalysts and surface-enhanced Raman scattering (SERS) substrates in wastewater treatment. NRs were characterized by various microscopic (scanning and transmission electron microscopy), spectroscopic (X-ray diffraction, X-ray photoelectron, UV-visible, photoluminescence, and Raman spectroscopy), and surface (Brunauer-Emmett-Teller) techniques. The NRs exhibited promising optical properties with a band gap of 2.95 eV (TiO₂ NRs) and 2.58 eV (Ta-TiO₂ NRs) showing excellent photo-degradation activities for methylene blue (MB) dye molecules under natural sunlight. Particularly, Ta-TiO₂ NRs showed enhanced response as visible light active photocatalysts in normal sunlight and also as SERS substrate attributed to the additional defects introduced by Ta doping. It could be explained by the combined effect of doping-induced enhanced visible light absorption and charge transfer (CT) properties of Ta-TiO₂ NRs. Furthermore, Ta-TiO₂ NRs were investigated for their long-term stability, reproducibility of the data, and recyclability in view of their potential applications in water treatment.

In-situ formation of Ag nanoparticles in the MAO coating during the processing of cp-Ti

Silver nanoparticle (Ag-NP) containing antibacterial micro-arc oxidation (MAO) coatings have already been synthesized over titanium-based materials via the MAO process employed in silver acetate (AgC₂H₃O₂) containing electrolyte. However, the way of incorporation and in-situ formation of Ag-NPs within the MAO coating have not been documented yet. Present work was initiated to reveal the mechanism of Ag-NP formation within the MAO coatings. Thus, the structure of the MAO coating fabricated on commercial purity titanium in the AgC₂H₃O₂-containing electrolyte was investigated by electron microscopy techniques. To this end, the cross-sectional high-resolution electron microscopy studies were carried out on lamella cut out with the focused ion beam technique, and these investigations were backed by X-ray photoelectron spectroscopy measurements of chemical composition on the surface of the MAO coating. These studies revealed that Ag is dispersed in the form of nanoparticles throughout the coating and that a higher density was confirmed closer to the micro-pores.

Surface functionalization of bamboo leave mediated synthesized SiO2 nanoparticles: Study of adsorption mechanism, isotherms and enhanced adsorption capacity for removal of Cr (VI) from aqueous solution

Green synthesis of nanoparticles (NPs) provides economic and environmental benefits as an alternative to chemical or physical methods. Furthermore, the surface properties of such NPs can be modulated by means of the functionalization with different groups making them suitable for various advanced functional applications including water pollutants removal using adsorption technique. In the present work, an eco-friendly synthesis route for nano-adsorbent SiO₂ NPs and subsequent surface modifications for enhanced adsorption capacity in removal of Cr(VI) ions from aqueous solution are reported. The green synthesis of SiO₂ NPs was carried out using simple bamboo leaves followed by surface modification with amine (A-SiO₂) and carboxylic (C-SiO₂) functional groups with aim to study the effect of functionalization on adsorption capacity. These nano-adsorbents were characterized by FTIR, SEM, XPS, BET, and zeta potential. and adsorption of Cr(VI) was studied at varying parameters i.e. NPs mass, contact time, and solution pH. The investigation shows interesting results revealing the importance of interactions between the surface functional groups on SiO₂ NPs and Cr(VI) species as well as experimental conditions for the choice of surface modifier to achieve a maximum adsorption capacity. The adsorption mechanism has been studied using Langmuir, Freundlich and Temkin adsorption isotherms. The maximum adsorption capacity has been achieved in the case of A-SiO₂ NPs which was found to 174 mg/g and much higher than that of SiO₂ and C-SiO₂ NPs attributed to the selective adsorption and pH conditions. Additionally, A-SiO₂ NPs exhibit excellent recyclability indicating their suitability for promising and long term potential applications. This study provides a novel, simple and cost-effective synthesis/surface engineering technology for producing high performance recyclable nano-adsorbents for adsorptive removal of Cr(VI).

Recent Advances on Metal Oxide Based Nano-Photocatalysts as Potential Antibacterial and Antiviral Agents

Photocatalysis, a unique process that occurs in the presence of light radiation, can potentially be utilized to control environmental pollution, and improve the health of society. Photocatalytic removal, or disinfection, of chemical and biological species has been known for decades; however, its extension to indoor environments in public places has always been challenging. Many efforts have been made in this direction in the last two–three years since the COVID-19 pandemic started. Furthermore, the development of efficient photocatalytic nanomaterials through modifications to improve their photoactivity under ambient conditions for fighting with such a pandemic situation is a high research priority. In recent years, several metal oxides-based nano-photocatalysts have been designed to work efficiently in outdoor and indoor environments for the photocatalytic disinfection of biological species. The present review briefly discusses the advances made in the last two to three years for photocatalytic viral and bacterial disinfections. Moreover, emphasis has been given to the tailoring of such nano-photocatalysts in disinfecting surfaces, air, and water to stop viral/bacterial infection in the indoor environment. The role of such nano-photocatalysts in the photocatalytic disinfection of COVID-19 has also been highlighted with their future applicability in controlling such pandemics.

TiO2 nanoflower photocatalysts: Synthesis, modifications and applications in wastewater treatment for removal of emerging organic pollutants

Titanium dioxide (TiO₂) has been considered as one of the most promising photocatalysts nanomaterials and is being used in a variety of fields of energy and environment under sunlight irradiation via photocatalysis. Highly efficient photocatalytic materials require the design of the proper structure with excellent morphology, interfacial structures, optical and surface properties, etc. Which are the key points to realize effective light-harvesting for photocatalytic applications. Hierarchical TiO₂ based nanoflower structures (i.e., 3D nanostructures) possess such characteristics and have attracted much attention in recent years. The uniqueness of TiO₂ nanoflowers (NFs) with a coarse texture and arranged structures demonstrates higher photocatalytic activity. This review deals with the hydrothermal synthesis of 3D TiO₂ NFs and effect of shape/size as well as various key synthesis parameters to improve their optoelectronic and photocatalytic properties. Furthermore, to improve their photocatalytic properties, various strategies such as doping engineering and heterojunction/nanocomposite formation with other functional nanomaterials have been discussed followed by their potential applications in photocatalytic degradation of various emerging pollutants discharged into the wastewater from various sources. Importance of such 3D nanoarchitecutres and future research in other fields of current interest in environments are discussed.

Photocatalytic TiO2 nanomaterials as potential antimicrobial and antiviral agents: Scope against blocking the SARS-COV-2 spread

The whole world is struggling with current coronavirus pandemic that shows urgent need to develop novel technologies, medical innovations or innovative materials for controlling SARS-CoV-2 infection. The mode of infection of SARS-CoV-2 is still not well known and seems to spread through surface, air, and water. Therefore, the whole surrounding environment needs to be disinfected with continuous function. For that purpose, materials with excellent antiviral properties, cost effective, environmental friendly and practically applicable should be researched. Titanium dioxide (TiO₂) under ultraviolet light produces strong oxidative effect and is utilized as photocatalytic disinfectant in biomedical field. TiO₂ based photocatalysts are effective antimicrobial/antiviral agents under ambient conditions with potential to be used even in indoor environment for inactivation of bacteria/viruses. Interestingly, recent studies highlight the effective disinfection of SARS-CoV-2 using TiO₂ photocatalysts. Here, scope of TiO₂ photocatalysts as emerging disinfectant against SARS-CoV-2 infection has been discussed in view of their excellent antibacterial and antiviral activities against various bacteria and viruses (e.g. H1N1, MNV, HSV, NDV, HCoV etc.). The current state of development of TiO₂ based nano-photocatalysts as disinfectant shows their potential to combat with SARS-CoV-2 viral infection and are promising for any other such variants or viruses, bacteria in future studies.

Optical limiting applications of resonating plasmonic Au nanoparticles in a dielectric glass medium

Plasmonic nanostructures exhibiting high optical nonlinearities are widely used in the rapidly growing modern nanotechnology of nonlinear optics including biomedical applications due to their tunable plasmonic behavior. In this work, we investigate the nonlinear optical properties of uniformly distributed Au nanoparticles (NPs) embedded in pre-synthesized sodium-zinc borate glass by the well-known ion-exchange technique for optical limiting (OL) applications. Various techniques such as optical absorption spectroscopy, x-ray photoelectron spectroscopy, Transmission Electron Microscope (TEM), Photoluminescence, Time of Flight secondary mass spectroscopy and the Z scan technique were used for the characterization of these NPs. TEM confirmed spherically shaped Au NPs with varying sizes of up to 16 nm, in agreement with optical absorption spectroscopy. Nonlinear optical (NLO) properties of these Au NPs were investigated by using an open as well as close aperture Z scan technique which exhibited enhanced optical nonlinearities. The two-photon absorption (2PA) coefficients demonstrated an increasing trend while the OL threshold values demonstrated a decreasing trend as a function of heat treatment. The improved 2PA coefficients and decreased OL threshold values endorsed the Au NPs containing glasses as contending materials for the fabrication of promising optical limiters for the protection of eyes and other sensitive instruments from laser induced damages.

Bacteria Detection: From Powerful SERS to Its Advanced Compatible Techniques

The rapid, highly sensitive, and accurate detection of bacteria is the focus of various fields, especially food safety and public health. Surface-enhanced Raman spectroscopy (SERS), with the advantages of being fast, sensitive, and nondestructive, can be used to directly obtain molecular fingerprint information, as well as for the on-line qualitative analysis of multicomponent samples. It has therefore become an effective technique for bacterial detection. Within this progress report, advances in the detection of bacteria using SERS and other compatible techniques are discussed in order to summarize its development in recent years. First, the enhancement principle and mechanism of SERS technology are briefly overviewed. The second part is devoted to a label-free strategy for the detection of bacterial cells and bacterial metabolites. In this section, important considerations that must be made to improve bacterial SERS signals are discussed. Then, the label-based SERS strategy involves the design strategy of SERS tags, the immunomagnetic separation of SERS tags, and the capture of bacteria from solution and dye-labeled SERS primers. In the third part, several novel SERS compatible technologies and applications in clinical and food safety are introduced. In the final part, the results achieved are summarized and future perspectives are proposed.

Optical nanosensors for biofilm detection in the food industry: principles, applications and challenges

Biofilms are the universal lifestyle of bacteria enclosed in extracellular polymeric substances (EPS) on the contact surfaces of food processing facilities. The EPS-encapsulated foodborne bacterial pathogens are the main food contaminant sources, posing a serious threat to human health. The microcrystalline, sophisticated and dynamic biofilms necessitate the development of conventional microscopic imaging and spectral technology. Nanosensors, which can transfer the biochemical information into optical signals, have recently emerged for biofilm optical detection with high sensitivity and high spatial resolution at nanoscale scopes. Therefore, the aim of this review is to clarify the main detection scope in biofilms and the detection principles of optical nanosensors arousing Raman enhancement, fluoresce conversion and color change. The difficulties and challenges of biofilm characterization including the secretion and variation of main biochemical components are first discussed, the details about the principles and application examples of bioassays targeting foodborne pathogens based on optical nanosensors are then summarized. Finally, the challenges and future trends in developing optical nanosensors are also highlighted. The current review indicates that optical nanosensors have taken the challenges of detecting biofilm in complex food samples, including the characterization of biofilm formation mechanism, identification of microbial metabolic activities, diagnosis of potential food pathogens and sanitation monitoring of food processing equipment. Numerous in-depth explorations and various trials have proven that the bioassays based on multifunctional optical nanosensors are promising to ensure and promote food safety and quality. However, there still remains a daunting challenge to structure reproducible, biocompatible and applicable nano-sensors for biofilm characterization, identification, and imaging.

Detect, remove and re-use: Sensing and degradation pesticides via 3D tilted ZMRs/Ag arrays

The objective of this study was to design a versatile and reusable pesticide detection surface-enhanced Raman scattering (SERS) substrate in combination with SERS enhancement and self-cleaning properties. In this paper, we present an inexpensive way to synthesize three-dimensional tilted ZnO micron rods with an Ag hierarchical structure (ZMRs/Ag arrays). Although expensive materials and complex methods were not used, the detection limit of thiram residue was 10^-11 M, with a quantitative relationship (R² = 0.9929) between the thiram concentration and the intensity of the SERS peaks. Additionally, the substrates exhibited fast and efficient photocatalytic activity for the degradation of adsorbed thiram, and the degradation rate in 30 min was close 100 % under visible-light irradiation. The enhancement and photocatalytic mechanism of this substrate were meticulously analyzed in detail. Furthermore, the residues of several mixed pesticides (e.g., thiram and methamidophos compounds) in various juices (such as grape, pear, orange, apple, and cherry juices) were quickly detected using ZMRs/Ag substrates. The main advantages of this substrate are recyclability, stability, selectivity, handiness, and cost-eff ;ectiveness. The substrate can prevent single-use problems associated with conventional SERS substrates and can be applied in pesticide residue and food security.

Thermally induced structural metamorphosis of ZnO:Rb nanostructures for antibacterial impacts

In this work, we report on the synthesis of pure and Rb doped ZnO (ZnO:Rb) nanoparticles by a simple combustion technique followed by thermal treatment in an open-air atmosphere. The prepared samples were characterized using UV-vis spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), photoluminescence, Raman spectroscopy and scanning electron microscopy. The wurtzite hexagonal phase structure of ZnO and a secondary phase of Rb₂ZnO₂ was observed after doping ZnO with Rb. FTIR and DSC confirmed the functional groups and the thermal stability of the ZnO samples. Field emission scanning electron microscope showed an irregular shaped agglomerated morphology for the ZnO:Rb samples. The chemical states of the undoped and Rb doped samples were identified using X-ray photoelectron spectroscopy for both pure and ZnO:Rb samples. In addition, ZnO:Rb samples exhibit good antimicrobial activities against Bacillus subtilis with a change in antibacterial behaviour as compared to pure ZnO structures indicating their multifunctional applications.

Photocatalytic degradation of dye by Ag/TiO2 nanoparticles prepared with different sol-gel crystallization in the presence of effluent organic matter

TiO₂ nanoparticle-doped Ag (Ag/TNPs) have good photocatalytic properties based on localized surface plasmon resonance (LSPR) effect. The effluent organic matter (EfOM) can be easily activated by photo-excitation to promote pollutant photodegradation, but excessive EfOM has an inactive effect. Herein, the purpose of this paper is to investigate the changes of photocatalytic performance by Ag/TNPs in the presence of EfOM. Three Ag/TNPs made by condensation crystallization or rotary evaporation crystallization using the sol-gel method were conducted in photocatalytic degradation of methyl orange (MO). The Ag/TNPs crystallized by condensation had greater separation rate of photogenerated electron-hole pairs and photocatalytic degradation of MO with high load rates of binding Ag and TiO₂ than those formed by rotary evaporation crystallization. Indeed, EfOM could be excited to produce the active substances under illumination resulting in the promotion of MO degradation. However, contrary to previous speculation, no additive effect of MO photodegradation was observed with the addition both of EfOM and Ag/TNPs at different pH values (5~9) and ion strength (0~0.4 mol L^-1). It can be explained that the EfOM changed the morphology and active sites in Ag/TNPs' surface. Meanwhile, EfOM could be consumed and degraded by Ag/TNP photocatalysis leading to the concentration of free radicals to decrease. This study revealed a nonsynergistic effect between nanomaterial and EfOM for photocatalysis. EfOM would have a negative effect on photocatalytic degradation of organic compounds by Ag/TNPs in the aquatic environment. Graphical abstract .

TiCaPCON-Supported Pt- and Fe-Based Nanoparticles and Related Antibacterial Activity

A rapid increase in the number of antibiotic-resistant bacteria urgently requires the development of new more effective yet safe materials to fight infection. Herein, we uncovered the contribution of different metal nanoparticles (NPs) (Pt, Fe, and their combination) homogeneously distributed over the surface of nanostructured TiCaPCON films in the total antibacterial activity toward eight types of clinically isolated bacterial strains (Escherichia coli K261, Klebsiella pneumoniae B1079k/17-3, Acinetobacter baumannii B1280A/17, Staphylococcus aureus no. 839, Staphylococcus epidermidis i5189-1, Enterococcus faecium Ya-235: VanA, E. faecium I-237: VanA, and E. coli U20) taking into account various factors that can affect bacterial mechanisms: surface chemistry and phase composition, wettability, ion release, generation of reactive oxygen species (ROS), potential difference and polarity change between NPs and the surrounding matrix, formation of microgalvanic couples on the sample surfaces, and contribution of a passive oxide layer, formed on the surface of films, to general kinetics of the NP dissolution. The results indicated that metal ion implantation and subsequent annealing significantly changed the chemistry of the TiCaPCON film surface. This, in turn, greatly affected the shedding of ions, ROS formation, potential difference between film components, and antibacterial activity. The presence of NPs was critical for ROS generation under UV or daylight irradiation. By eliminating the potential contribution of ions and ROS, we have shown that bacteria can be killed using direct microgalvanic interactions. The possibility of charge redistribution at the interfaces between Pt NPs and TiO₂ (anatase and rutile), TiC, TiN, and TiCN components was demonstrated using density functional theory calculations. The TiCaPCON-supported Pt and Fe NPs were not toxic for lymphocytes and had no effect on the ability of lymphocytes to activate in response to a mitogen. This study provides new insights into understanding and designing of antibacterial yet biologically safe surfaces.

Investigation of silver nanoparticles on titanium surface created by ion implantation technology

Objectives: Using dental Ti implants has become a well-accepted and used method for replacing missing dentition. It has become evident that in many cases peri-implant inflammation develops. The objective was to create and evaluate the antibacterial effect of silver nanoparticle (Ag-NP) coated Ti surfaces that can help to prevent such processes if applied on the surface of dental implants.

Methods: Annealing I, Ag ion implantation by the beam of an Electron Cyclotron Resonance Ion Source (ECRIS), Ag Physical Vapor Deposition (PVD), Annealing II procedures were used, respectively, to create a safely anchored Ag-NP layer on 1x1 cm² Grade 2 titanium samples. The antibacterial effect was evaluated by culturing Staphylococcus aureus (ATCC 29213) on the surfaces of the samples for 8 hours, and comparing the results to that of glass as control and of pure titanium samples. Alamar Blue assay was carried out to check cytotoxicity.

Results: It was proved that silver nanoparticles were present on the treated surfaces. The average diameter of the particles was 58 nm, with a 25 nm deviation and Gaussian distribution, the the filling factor was 25%. Antibacterial evaluation revealed that the nanoparticle covered samples had an antibacterial effect of 64.6% that was statistically significant. Tests also proved that the nanoparticles are safely anchored to the titanium surface and are not cytotoxic.

Conclusion: Creating a silver nanoparticle layer can be an option to add antibacterial features to the implant surface and to help in the prevention of peri-implant inflammatory processes. Recent studies demonstrated that silver nanoparticles can induce pathology in mammal cells, thus safe fixation of the particles is essential to prevent them from getting into the circulation.

Antibacterial properties of doped nanoparticles

Nanoparticles have high potential as antibacterial agents, owing to their ability to produce reactive oxygen species (ROS). Recent studies have indicated that this ROS generation is highly affected by the modification of band structure by the introduction of various dopant materials into them. Thus, doped nanoparticles have been extensively studied in the recent literature. The types of dopants, synthesis techniques, and experimental parameters have been found to affect the overall electronic structure of the material, leading to varied antibacterial efficiency. This review summarizes some of the prominent dopant nanomaterials, various methods of synthesizing doped nanoparticles used against bacterial cells, and the main factors involved in it. Despite the extensive research on the mechanism of the antibacterial action, it is still poorly understood mainly due to the inherent complexities and dynamics in cell membranes. Some of the major proposed mechanisms of action of each kind of dopant nanomaterial have also been reported in this work, focusing on the bacterial cell structure.

Highly visible-light-responsive Cu2O/rGO decorated with Fe3O4@SiO2 nanoparticles as a magnetically recyclable photocatalyst

The rhombic dodecahedral cuprous oxide-reduced graphene oxide/core-shell Fe₃O₄@SiO₂ composites (denoted as rCu₂O-rGO/Fe₃O₄@SiO₂) are successfully synthesized facilely via a wet-chemical route. The resulting rCu₂O-rGO/Fe₃O₄@SiO₂ combines the unique structure of Cu₂O, electronic characteristics of reduced graphene oxide (rGO) and magnetic property of Fe₃O₄@SiO₂ to be an effective and recoverable photocatalyst for the degradation of methyl orange (MO). The obtained results show that rCu₂O-rGO/Fe₃O₄@SiO₂ is capable of completely degrading MO in the presence of a very low catalyst concentration (0.125 g l^-1) within a short time (60 min) under visible light compared to the reported catalysts. The observations may be due to the distinctive interfacial structures of rhombic dodecahedral Cu₂O nanoparticles connected to rGO sheets that can enhance the separation of photogenerated electron-hole pairs, stabilize the Cu₂O and increase MO adsorption, as evidenced by a variety of spectroscopic analyses (transmission electron microscopy, x-ray photoelectron spectroscopy and photoluminescence). More importantly, these efficient photocatalysts can easily be recovered under a magnetic field and remain highly photoactive towards the degradation of MO after cyclic tests, and may be promising photocatalysts for practical applications in the solar-energy purification of wastewater.

Mechanisms of the enhanced antibacterial effect of Ag-TiO2 coatings

It has been demonstrated that Ag-TiO₂ nanocomposite coatings with excellent antimicrobial activity and biocompatibility have the potential to reduce infection problems. However, the mechanism of the synergistic effect of Ag-TiO₂ coatings on antibacterial efficiency is still not well understood. In this study, five types of Ag-TiO₂ nanocomposited coatings with different TiO₂ contents were prepared on a titanium substratum. Leaching tests indicated that the incorporation of TiO₂ nanoparticles into an Ag matrix significantly promoted Ag ion release. Surface energy measurements showed that the addition of TiO₂ nanoparticles also significantly increased the electron donor surface energy of the coatings. Bacterial adhesion assays with Escherichia coli and Staphylococcus aureus demonstrated that the number of adhered bacteria decreased with increasing electron donor surface energy. The increased Ag ion release rate and the increased electron donor surface energy contributed to an enhanced antibacterial efficiency of the coatings.

Improved electrochemical properties of morphology-controlled titania/titanate nanostructures prepared by in-situ hydrothermal surface modification of self-source Ti substrate for high-performance supercapacitors

Ti substrate surface is modified into two-dimensional (2D) TiO₂ nanoplatelet or one-dimensional (1D) nanorod/nanofiber (or a mixture of both) structure in a controlled manner via a simple KOH-based hydrothermal technique. Depending on the KOH concentration, different types of TiO₂ nanostructures (2D platelets, 1D nanorods/nanofibers and a 2D+1D mixed sample) are fabricated directly onto the Ti substrate surface. The novelty of this technique is the in-situ modification of the self-source Ti surface into titania nanostructures, and its direct use as the electrochemical microelectrode without any modifications. This leads to considerable improvement in the interfacial properties between metallic Ti and semiconducting TiO₂. Since interfacial states/defects have profound effect on charge transport properties of electronic/electrochemical devices, therefore this near-defect-free interfacial property of Ti-TiO₂ microelectrode has shown high supercapacitive performances for superior charge-storage devices. Additionally, by hydrothermally tuning the morphology of titania nanostructures, the electrochemical properties of the electrodes are also tuned. A Ti-TiO₂ electrode comprising of a mixture of 2D-platelet+1D-nanorod structure reveals very high specific capacitance values (~7.4 mF.cm⁻²) due to the unique mixed morphology which manifests higher active sites (hence, higher utilization of the active materials) in terms of greater roughness at the 2D-platelet structures and higher surface-to-volume-ratio in the 1D-nanorod structures.

Dual Functional Ta-Doped Electrospun TiO2 Nanofibers with Enhanced Photocatalysis and SERS Detection for Organic Compounds

There is a growing interest in multifunctional nanomaterials for the detection as well as degradation of organic contaminants in the water. In this work, we report on the development of dual functional TiO₂ nanofibers (TNF) with different tantalum (Ta) doping (1-10 mol %) by a simple electrospinning technique. As-prepared TNF show mesoporous dominant structure, which are favorable for photocatalytic activity due to the presence of catalytic spots. Ta doping decreases the crystalline size within TiO₂ matrix because of the incorporation of Ta⁵⁺ ions and restricts the phase transformation from anatase to rutile. Ta doping slightly enhances the visible light absorption because of the Ti³⁺ defects sites created upon Ta⁵⁺ doping. The effect of Ta doping within TiO₂ matrix was systematically studied for the degradation of methylene blue (MB) dye under ultraviolet (UV) and solar light irradiation. The 5% Ta-doped TNF were found to be optimal and showed 5.1 and 2.2 times higher photocatalytic activity as compared to TNF under UV and solar light irradiation, respectively. The effect of Ta doping for the detection of MB molecules was also studied by surface enhanced Raman scattering (SERS). It was observed that 5% Ta-doped TNF exhibit higher photocatalytic activity and enhanced SERS signals of adsorbed MB molecules as compared to the TNF. The enhanced photocatalytic and SERS activities can be explained as combined effects of enhanced visible light absorption, lower crystalline size, and slightly higher surface area. The observed results show that Ta doping induces new energy levels below the conduction band of TiO₂ because of Ti³⁺ defects, which inhibit the photogenerated charge recombination acting as electron traps and promote charge transfer mechanism acting as an intermediate state for TiO₂ to MB molecule electron transfer, and are mainly responsible for the enhanced photocatalytic and SERS activities, respectively.

Three-dimensional plasmonic Ag/TiO2 nanocomposite architectures on flexible substrates for visible-light photocatalytic activity

In this study, a periodic three-dimensional (3D) Ag/TiO₂ nanocomposite architecture of nanowires was fabricated on a flexible substrate to enhance the plasmonic photocatalytic activity of the composite. Layer-by-layer nanofabrication based on nanoimprint lithography, vertical e-beam evaporation, nanotransfer, and nanowelding was applied in a new method to create different 3D Ag/TiO₂ nanocomposite architectures. The fabricated samples were characterized by scanning electron microscopy, transmission electron microscopy, focused ion-beam imaging, X-ray photoelectron spectrometry, and UV–visible spectroscopy. The experiment indicated that the 3D nanocomposite architectures could effectively enhance photocatalytic activity in the degradation of methylene blue solution under visible light irradiation. We believe that our method is efficient and stable, which could be applied to various fields, including photocatalysis, solar energy conversion, and biotechnology.

Surface Sensitive Techniques for Advanced Characterization of Luminescent Materials

The important role of surface sensitive characterization techniques such as Auger electron spectroscopy (AES), X-ray photo electron spectroscopy (XPS), time of flight scanning ion mass spectrometry (TOF-SIMS) and High resolution transmission electron microscopy (HRTEM) for the characterization of different phosphor materials is discussed in this short review by giving selective examples from previous obtained results. AES is used to monitor surface reactions during electron bombardment and also to determine the elemental composition of the surfaces of the materials, while XPS and TOF-SIMS are used for determining the surface chemical composition and valence state of the dopants. The role of XPS to determine the presence of defects in the phosphor matrix is also stated with the different examples. The role of HRTEM in combination with Energy dispersive spectroscopy (EDS) for nanoparticle characterization is also pointed out.

Role of silver doping on the defects related photoluminescence and antibacterial behaviour of zinc oxide nanoparticles

The Ag doped ZnO (ZnO:Ag) NPs with a hexagonal wurtzite structure were synthesized by a solution combustion method. X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) were used to study the defects, local electronic and atomic structures before and after Ag doping. XPS and XANES studies confirmed the deficiency of concentration of defects in ZnO after Ag doping. The photoluminescence study showed the deep level emission in the orange-red region in addition to the band to band emission. It was also found that the defect related emission of ZnO was decreased with an increasing in Ag concentration. The antibacterial behaviour of ZnO and ZnO:Ag NPs was studied against the gram positive and gram negative bacteria. The role of Ag doping and defects in the ZnO NPs were discussed for the observed antibacterial and photoluminescence behaviour.

A new strategy for effective distance regulation of the surface plasmon assisted coupling reaction of p-nitrothiophenol to p,p′-dimercaptoazobenzene

Plasmon assisted reactions on a metal surface occur through a different mechanism compared to traditional reaction conditions.