Band gap engineered TiO2 nanoparticles for visible light induced photoelectrochemical and photocatalytic studies

<div>Visible light-active TiO2 (m-TiO2) nanoparticles were obtained by an electron beam treatment of</div><div>commercial TiO2 (p-TiO2) nanoparticles. The m-TiO2 nanoparticles exhibited a distinct red-shift in the</div><div>UV-visible absorption spectrum and a much narrower band gap (2.85 eV) due to defects as confirmed by</div><div>diffuse reflectance spectroscopy (DRS), photoluminescence (PL), X-ray diffraction, Raman spectroscopy,</div><div>electron paramagnetic resonance, transmission electron microscopy, X-ray photoelectron spectroscopy</div><div>(XPS), electrochemical impedance spectroscopy (EIS) and linear scan voltammetry (LSV). The XPS</div><div>revealed changes in the surface states, composition, Ti4+ to Ti3+ ratio, and oxygen deficiencies in the m-</div><div>TiO2. The valence band XPS, DRS and PL results were carefully examined to understand the band gap</div><div>reduction of m-TiO2. The visible light-responsive enhanced photocatalytic activity of m-TiO2 was</div><div>demonstrated by degrading methylene blue and brilliant blue G. The EIS and LSV in the dark and under</div><div>visible light irradiation further support the visible light-induced photocatalytic activities of the m-TiO2</div><div>due to a decrease in electron transfer resistance and an increase in photocurrent. This study confirms</div><div>that m-TiO2 can be used effectively as a photocatalyst and photoelectrode material owing to its</div><div>enhanced visible light-induced photocatalytic activity.</div

Citrus essential oils: Extraction, authentication and application in food preservation

<p>Citrus EOs is an economic, eco-friendly and natural alternatives to chemical preservatives and other synthetic antioxidants, such as sodium nitrites, nitrates or benzoates, commonly utilized in food preservation. Citrus based EOs is obtained mainly from the peels of citrus fruits which are largely discarded as wastes and cause environmental problems. The extraction of citrus oils from the waste peels not only saves environment but can be used in various applications including food preservation. The present article presents elaborated viewpoints on the nature and chemical composition of different EOs present in main citrus varieties widely grown across the globe; extraction, characterization and authentication techniques/methods of the citrus EOs; and reviews the recent advances in the application of citrus EOs for the preservation of fruits, vegetables, meat, fish and processed food stuffs. The probable reaction mechanism of the EOs based thin films formation with biodegradable polymers is presented. Other formulation, <i>viz.</i>, EOs microencapsulation incorporating biodegradable polymers, nanoemulsion coatings, spray applications and antibacterial action mechanism of the active compounds present in the EOs have been elaborated. Extensive research is required on overcoming the challenges regarding allergies and obtaining safer dosage limits. Shift towards greener technologies indicate optimistic future towards safer utilization of citrus based EOs in food preservation.</p

Biogenic Synthesis, Photocatalytic, and Photoelectrochemical Performance of Ag–ZnO Nanocomposite

The development of coupled photoactive materials (metal/semiconductor) has resulted in significant advancements in heterogeneous visible light photocatalysis. This work reports the novel biogenic synthesis of visible light active <i>Ag</i>–ZnO nanocomposite for photocatalysis and photoelectrode using an electrochemically active biofilm (EAB). The results showed that the EAB functioned as a biogenic reducing tool for the reduction of Ag⁺, thereby eliminating the need for conventional reducing agents. The as-prepared <i>Ag</i>–ZnO nanocomposite was characterized by X-ray diffraction, transmission electron microscopy, diffuse reflectance spectroscopy, photoluminescence spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic experiments showed that the <i>Ag</i>–ZnO nanocomposite possessed excellent visible light photocatalytic activity for the degradation of methyl orange, methylene blue, and 4-nitrophenol. Electrochemical impedance spectroscopy and linear scan voltammetry under dark and visible light irradiation confirmed the enhanced visible light activity of the <i>Ag</i>–ZnO as photocatalyst and photoelectrode. These results suggest that Ag nanoparticles induced visible light photocatalytic degradation and enhanced the visible light activity of the photoelectrodes by minimizing the recombination of photogenerated electrons and holes, thereby extending the response of pure ZnO to visible light

Resveratrol Oligomers Inhibit Biofilm Formation of <i>Escherichia coli</i> O157:H7 and <i>Pseudomonas aeruginosa</i>

Biofilm formation is closely related to bacterial infection and is also a mechanism of antimicrobial resistance. Hence, the antibiofilm approach provides an alternative to an antibiotic strategy. In this study, the antibiofilm activities of resveratrol (<b>1</b>) and five of its oligomers, namely, ε-viniferin (<b>2</b>), suffruticosol A (<b>3</b>), suffruticosol B (<b>4</b>), vitisin A (<b>5</b>), and vitisin B (<b>6</b>), were investigated against enterohemorrhagic <i>Escherichia coli</i> O157:H7 and <i>Pseudomonas aeruginosa</i> PA14. Vitisin B (<b>6</b>), a stilbenoid tetramer, was found to inhibit biofilm formation by the two bacteria the most effectively and at 5 μg/mL inhibited <i>E. coli</i> O157:H7 biofilm formation by more than 90%

Effect of fruit juices and chloride ions on the corrosion behavior of orthodontic archwire

<p>Electrochemical and surface analytical study on the corrosion behavior of AISI 316L stainless steel orthodontic archwire in different fruit juices was carried out. The electrochemical parameters were measured after immersing the wires for approx. 24 h in artificial saliva (AS) containing different fruit juices and separately in fruit juices with 1% NaCl in AS. All the fruit juices used in this study increased the rate of corrosion process in AS in the presence or absence of salt. Addition of 1% NaCl to the AS, all experiments exhibited pitting. <i>Solanum lycopersicum</i> (Tomato) and <i>Durio zibethinus</i> (Amra) are rated as most detrimental to the surface followed by <i>Prunus domestica Linn</i>. (Plum) juice. SEM Micrographs of the specimens show formation of blisters onto the steel surface which are remnants of passive film.</p

Inhibition of Pseudomonas aeruginosa and Escherichia coli O157:H7 Biofilm Formation by Plant Metabolite ε‑Viniferin

Pathogenic biofilms are associated with persistent infection due to their high resistances to diverse antibiotics. Pseudomonas aeruginosa infects plants, animals, and humans and is a major cause of nosocomial diseases in patients with cystic fibrosis. In the present study, the antibiofilm abilities of 522 plant extracts against <i>P. aeruginosa</i> PA14 were examined. Three <i>Carex</i> plant extracts at a concentration of 200 μg/mL inhibited <i>P. aeruginosa</i> biofilm formation by >80% without affecting planktonic cell growth. In the most active extract of Carex pumila, resveratrol dimer ε-viniferin was one of the main antibiofilm compounds against <i>P. aeruginosa</i>. Interestingly, ε-viniferin at 10 μg/mL inhibited biofilm formation of enterohemorrhagic Escherichia coli O157:H7 by 98%. Although <i>Carex</i> extracts and <i>trans</i>-resveratrol are known to possess antimicrobial activity, this study is the first to report that <i>C. pumila</i> extract and ε-viniferin have antibiofilm activity against <i>P. aeruginosa</i> and <i>E. coli</i> O157:H7

Environmentally Sustainable Fabrication of Ag@<i>g‑</i>C₃N₄ Nanostructures and Their Multifunctional Efficacy as Antibacterial Agents and Photocatalysts

Noble-metal silver (Ag) nanoparticles (NPs) anchored/decorated onto polymeric graphitic carbon nitride (<i>g</i>-C₃N₄) as nanostructures (NSs) were prepared using modest and environment-friendly synthesis method with a developed-single-strain biofilm as a reducing implement. The as-fabricated NSs were characterized using standard characterization techniques. The nanosized and uniform AgNPs were well deposited onto the sheet-like matrix of <i>g</i>-C₃N₄ and exhibited good antimicrobial activity and superior photodegradation of dyes methylene blue (MB) and rhodamine B (RhB) dyes under visible-light illumination. The Ag@<i>g</i>-C₃N₄ NSs exhibited active and effective bactericidal performance and a survival test in counter to <i>Escherichia coli</i>, <i>Staphylococcus aureus</i>, and <i>Pseudomonas aeruginosa.</i> The as-fabricated NSs also exhibited superior visible-light photodegradation of MB and RhB in much less time as compared to other reports. Ag@<i>g</i>-C₃N₄ NSs (3 mM) showed superior photocatalytic measurements under visible-light irradiation: ∼100% MB degradation and ∼89% of RhB degradation in 210 and 250 min, respectively. The obtained results indicate that the AgNPs were well deposited onto the <i>g</i>-C₃N₄ structure, which decreases the charge recombination rate of photogenerated electrons and holes and extends the performance of pure <i>g</i>-C₃N₄ under visible light. In conclusion, the as-fabricated Ag@<i>g</i>-C₃N₄ NSs are keen nanostructured materials that can be applied as antimicrobial materials and visible-light-induced photocatalysts

Anti-biofilm activities of quercetin and tannic acid against <i>Staphylococcus aureus</i>

<div><p> <i>Staphylococcus aureus</i> is a leading cause of nosocomial infections because of its resistance to diverse antibiotics. The formation of a biofilm is one of the mechanisms of drug resistance in <i>S. aureus</i>. The anti-biofilm abilities of 498 plant extracts against <i>S. aureus</i> were examined. Seventy-two plant extracts belonging to 59 genera and 38 families were found to significantly inhibit the formation of biofilms of <i>S. aureus</i> without affecting the growth of planktonic cells. The most active extract, from <i>Alnus japonica</i>, inhibited the formation of biofilms by three <i>S. aureus</i> strains by >70% at 20 μg ml⁻¹. Transcriptional analyses showed that extract of <i>A. japonica</i> repressed the intercellular adhesion genes <i>icaA</i> and <i>icaD</i> most markedly. Quercetin and tannic acid are major anti-biofilm compounds in the extract of <i>A. japonica</i>. Additionally, the extract of <i>A. japonica</i> and its component compound quercetin, reduced hemolysis by <i>S. aureus</i>. This phenomenon was not observed in the treatment with tannic acid. This study suggests that various plant extracts, such as quercetin and tannic acid, could be used to inhibit the formation of recalcitrant biofilms of <i>S. aureus</i>.</p> </div

Defect-Induced Band Gap Narrowed CeO₂ Nanostructures for Visible Light Activities

This work reports an electron beam irradiation (30 kGy and 90 kGy) approach to narrow the band gap of the pristine CeO₂ nanostructure (p-CeO₂) to enhance their visible light activity through defect engineering. This was confirmed by diffuse reflectance spectroscopy, photoluminescence, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller, electrochemical impedance spectroscopy, and linear scan voltammetry. XPS revealed changes in the surface states, composition, Ce⁴⁺ to Ce³⁺ ratio, and other defects in the modified CeO₂ nanostructures (m-CeO₂). The m-CeO₂ exhibits excellent photocatalytic activities by degrading 4-nitrophenol and methylene blue in the presence of visible light (λ > 400 nm) compared to the p-CeO₂. The optical, photocatalytic, and photoelectrochemical studies and proposed mechanism further support the enhanced visible light photocatalytic activities of the m-CeO₂. This study confirmed that defect-induced band gap engineered m-CeO₂ could be used effectively as photocatalyst and photoelectrodes owing to their enhanced visible light photocatalytic activities

Enhanced Thermal Stability under DC Electrical Conductivity Retention and Visible Light Activity of Ag/TiO₂@Polyaniline Nanocomposite Film

The development of organic–inorganic photoactive materials has resulted in significant advancements in heterogeneous visible light photocatalysis. This paper reports the synthesis of visible light-active Ag/TiO₂@Pani nanocomposite film via a simple biogenic–chemical route. Electrically conducting Ag/TiO₂@Pani nanocomposites were prepared by incorporating Ag/TiO₂ in <i>N</i>-methyl-2-pyrrolidone solution of polyaniline (Pani), followed by the preparation of Ag/TiO₂@Pani nanocomposite film using solution casting technique. The synthesized Ag/TiO₂@Pani nanocomposite was confirmed by UV–visible spectroscopy, photoluminescence spectroscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The Ag/TiO₂@Pani nanocomposite film showed superior activity towards the photodegradation of methylene blue under visible light compared to Pani film, even after repeated use. Studies on the thermoelectrical behavior by DC electrical conductivity retention under cyclic aging techniques showed that the Ag/TiO₂@Pani nanocomposite film possessed a high combination of electrical conductivity and thermal stability. Because of its better thermoelectric performance and photodegradation properties, such materials might be a suitable advancement in the field of smart materials in near future