Bio-therapeutic Potential and Cytotoxicity Assessment of Pectin-Mediated Synthesized Nanostructured Cerium Oxide

In the present studies, renewable and nontoxic biopolymer, pectin, was extracted from Indian red pomelo fruit peels and used for the synthesis of cerium oxide nanoparticles (CeO₂-NPs) having bio-therapeutic potential. The structural information of extracted pectin was investigated by FTIR and NMR spectroscopic techniques. Physicochemical characteristics of this pectin suggested its application in the synthesis of metal oxide nanoparticles. Using this pectin as a template, CeO₂-NPs were synthesized by simple, one step and eco-friendly approach. The UV–Vis spectrum of synthesized CeO₂-NPs exhibited a characteristic absorption peak at wavelength 345 nm, which can be assigned to its intrinsic band gap (3.59 eV) absorption. Photoluminescence measurements of CeO₂-NPs revealed that the broad emission was composed of seven different bands. FTIR analysis ensured involvement of pectin in the formation and stabilization of CeO₂-NPs. FT-Raman spectra showed a sharp Raman active mode peak at 461.8 cm^?1 due to a symmetrical stretching mode of Ce–O vibration. DLS, FESEM, EDX, and XRD analysis showed that the CeO₂-NPs prepared were polydispersed, spherical shaped with a cubic fluorite structure and average particle size ≤40 nm. These CeO₂-NPs displayed broad spectrum antimicrobial activity, antioxidant potential, and non-cytotoxic nature.     

Au Nanoparticles Supported Nanoporous ZnO Sphere for Enhanced Photocatalytic Activity Under UV-Light Irradiation

Monodispersed 200 nm-sized ZnO spheres (SPs) with porous structure emanating from 8 nm zinc oxide nanoparticles (NPs) composing the SPs were synthesized by dissolving zinc acetate dihydrate in diethylene glycol at 160 °C. The prepared SPs were employed in fabricating the gold (Au) loaded ZnO (Au/ZnO SP) composite materials, exhibiting high photocatalytic activity in decomposing salicylic acid under UV-light irradiation. It is deduced that its high catalytic activity originates from the charge separation by transferring photoinduced electrons from the conduction band (CB) of ZnO to Au, since the CB level of ZnO (?0.5 V vs. NHE) is located more negative side than that of Au (+0.5 V vs. NHE). The evidence for the charge separation was provided by monitoring^.OH radical with bare ZnO SPs and Au/ZnO SP produced in the solution which readily react with 1,4-terephthalic acid (TA) inducing 2-hydroxy terephthalic acid (TAOH) that shows unique fluorescence peak at 426 nm.     

A Synergy of ZnO and ZnWO4 in Composite Nanostructures Deduced from Optical Properties and Photocatalysis

ZnO/ZnWO₄ composite rod-like nanoparticles were synthesized by low-temperature soft solution method at 95 °C with different reaction times (1–120 h), in the presence of non-ionic copolymer surfactant Pluronic F68. Obtained nanoparticles had diameters in the range around 10 nm and length of 30 nm. Optical properties such as reflection and room temperature photoluminescence of obtained samples showed strong dependence on their crystallinity and composition. Photocatalytic activity of ZnO/ZnWO₄ nanopowders was checked using photodegradation of selected dyes as model system. Obtained results were correlated with specific surface area, particle sizes, crystallinity and ZnO/ZnWO₄ ratio of the samples. As crystallinity of ZnWO₄ component in the ZnO/ZnWO₄ increase, photocatalytic activity also increases. The main findings can be explained by charge transfer reactions that follow light absorption by ZnO and ZnWO₄ in nanocomposite.     

Photocatalytic studies of silver doped ZnO nanoparticles synthesized by chemical precipitation method

Ag-doped ZnO nanoparticles (Zn_1?xAg_xO; where x = 0.00–0.05) were synthesized by chemical precipitation method. The synthesized products were characterized by X-ray diffraction, scanning electron microscope (SEM), transmission electron microscope (TEM) and UV–Vis spectrometer. The SEM and TEM micrographs revealed the agglomerated spherical-like morphology and the measurements show that the size of crystallites is in the range of 10–40 nm. Optical measurements indicated a red shift in the absorption band edge after Ag doping. The band gap values of as prepared undoped and doped with silver samples were found to decrease with increase in temperature from 300 to 800 °C. Photocatalytic activities of ZnO and Ag doped ZnO were evaluated by irradiating the sample solution to ultraviolet light by taking methylene blue as organic dye. The experiment demonstrated that the photo-degradation efficiency of 1 mol% Ag-doped ZnO was significantly higher than that of undoped and 2–5 mol% Ag doped ZnO under ultraviolet light irradiation.     

Physical and photoelectrochemical characterizations of SrWO<Subscript>4</Subscript> prepared by thermal decomposition. Application to the photo electro-oxidation of ibuprofen

We have reported the semi conducting and photoelectrochemical properties of SrWO₄ prepared by chemical route. The phase purity is confirmed by X-ray diffraction and the oxide is characterized by scanning electron microscopy, diffuse reflectance, and electrochemical impedance spectroscopy. SrWO₄ crystallizes in the scheelite structure with an average crystallite size of 378 ± 6 nm. The Raman spectrum gives an intense peak at 920 cm^?1 assigned to A _g mode while the infrared analysis confirms the hexagonal coordination of tungsten. The UV-visible spectroscopy shows an indirect optical transition at 2.60 eV. SrWO₄ exhibits n-type conduction by oxygen deficiency, confirmed by the chrono-amperometry and the intensity potential J(E) curve shows a small hysteresis. The Mott-Schottky plot gives electrons density of 5.72 × 10¹⁸ cm^?3 and a flat band potential of 0.27 V_SCE, indicating that the conduction band derives mainly from W⁶⁺: 6s orbital. The electrochemical impedance spectroscopy (EIS), measured in the range (1–10⁵ Hz), shows the predominance of the bulk contribution with a dark impedance of 38 kΩ cm². As application, the ibuprofen is degraded by electrocatalysis on SrWO₄ with a conversion rate of 42%. An improvement up to 77% has been obtained by electrophotocatalysis under UV light; the conversion follows a first order kinetic with a rate constant of 2.32 × 10^?4 min^?1.     

Calcination temperature-dependent morphology of photocatalytic ZnO nanoparticles prepared by an electrochemical–thermal method

ZnO nanoparticles (NPs) with tunable morphologies were synthesized by a hybrid electrochemical–thermal method at different calcination temperatures without the use of any surfactant or template. The NPs were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction, dynamic light scattering, thermogravimetry–differential thermal analysis, scanning electron microscope and N₂ gas adsorption–desorption studies. The FT-IR spectra of ZnO NPs showed a band at 450 cm^?1, a characteristic of ZnO, which remained fairly unchanged at calcination temperatures even above 300 °C, indicating complete conversion of the precursor to ZnO. The products were thermally stable above 300 °C. The ZnO NPs were present in a hexagonal wurtzite phase and the crystallinity of ZnO increased with an increasing calcination temperature. The ZnO NPs calcined at lower temperature were mesoporous in nature. The surface areas of ZnO NPs calcined at 300 and 400 °C were 51.10 and 40.60 m² g^?1, respectively, which are significantly larger than commercial ZnO nanopowder. Surface diffusion has been found to be the key mechanism of sintering during heating from 300 to 700 °C with the activation energy of sintering as 8.33 kJ mol^?1. The photocatalytic activity of ZnO NPs calcined at different temperatures evaluated by photocatalytic degradation of methylene blue under sunlight showed strong dependence on the surface area of ZnO NPs. The ZnO NPs with high surface area showed enhanced photocatalytic activity.     

Synthesis of cobalt-doped ZnO/rGO nanoparticles with visible-light photocatalytic activity through a cobalt-induced electrochemical method

ZnO is a semiconductor photocatalyst widely applied in photodegradation of organic pollutants and in photoelectric conversion. ZnO exhibits low photocatalytic activity due to poor absorption in the visible region. In this work, a novel cobalt-induced electrochemical growth method was developed to synthesize cobalt-doped ZnO/rGO nanoparticles in an aqueous solution at room temperature. Cobalt-doped ZnO/rGO nanoparticles exhibited wider visible-light absorption band ranging from 400 nm to 700 nm due to cobalt doping. The surface structure of ZnO formed by the cobalt-induced electrochemical method without other ions is suitable for photocatalytic reactions. The cobalt-doped ZnO/rGO nanoparticles were found to exhibit in photodegradation and photo-electrochemical measurements and exhibited enhanced photocatalytic activity under visible-light irradiation.     

ZnO nanoparticles and poly(acrylic) acid-based polymer gel electrolyte for photo electrochemical cell

This work presents a photo electrochemical cell based on zinc oxide (ZnO) nanoparticles and poly(acrylic) acid (PAA) doped with sodium iodide (NaI) and iodine (I₂) polymer gel electrolyte. The ZnO powders were synthesized by sol–gel storage and sol–gel centrifugation. The ZnO powder synthesized via sol–gel centrifugation showed the optimal structural properties, with largest crystallite sizes of 58 nm, average particles size between 20 and 80 nm and indirect band gap energy of 3.20 eV. The highest conductivity [(8.0 ± 0.1) × 10^?2 S cm^?1] was obtained for PAA + 0.8 M NaI + 0.02 M I₂. This sample achieved the lowest activation energy (0.029 eV) and electrochemical stability at 1.6 V. The ZnO powder synthesized via sol–gel centrifugation and PAA + 0.8 M NaI + 0.02 M I₂ was fabricated as a Cu–ZnO/PAA + 0.8 M NaI + 0.02 M I₂/C-ITO photo electrochemical cell.     

Tuning the aspect ratio of hydrothermally grown ZnO by choice of precursor

Variable aspect ratio (length/diameter), one dimensional ZnO nanostructures are synthesized by reacting Zn²⁺ precursor derived from Zn·Ac₂, Zn·Cl₂ and Zn·(NO₃)₂ under hydrothermal treatment. The growth mechanism illustrating the formation of self-assembling from individual ZnO nanoparticles to rod-like form is explained briefly. XRD reveals that the ZnO obtained from various zinc salts are pure, wurtzite structure, with crystalline hexagonal phase. The qualitative analysis of ZnO formation and morphology of ZnO nanoparticles are estimated from FESEM and TEM micrographs. Strong UV absorption corresponding to the recombination of electron-hole pair is observed and the blue shift absorption obeys the size confinement effect. The extent of absorption relatively varies when the morphology is changed from nano-bundles to individual rod-like ZnO. When electrons are excited at wavelength of 240 nm, a strong near band edge (NBE) emission and surface defects emission are observed in the PL spectra. The broader emission situated in the blue-green region of the visible spectrum, originating from surface oxygen defects, is not observed in ZnO derived from Zn·Ac₂.     

Synthesis of ZnO/Cu2S core/shell nanorods and their enhanced photoelectric performance

In this work, two kinds of ZnO/Cu₂S core/shell nanorods (NRs) have been successfully synthesized from ZnO NRs for photoelectrochemical (PEC) water splitting by a versatile hydrothermal chemical conversion method (H-ZnO/Cu₂S core/shell NRs) and successive ionic layer adsorption and reaction method (S-ZnO/Cu₂S core/shell NRs), respectively. The photoelectrode is composed of a core/shell structure where the core portion is ZnO NRs and the shell portion is Cu₂S nanoparticles sequentially located on the surface. The ZnO NRs array provides a fast electron transport pathway due to its high electron mobility properties. The optical property of both two kinds of core/shell NRs was characterized, and enhanced absorption spectrum was discovered. Our PEC system produced very high photocurrent density and photoconversion efficiency under 1.5 AM irradiation for hydrogen generation. On the basis of a versatile chemical conversion process based on the ion-by-ion growth mechanism, H-ZnO/Cu₂S core/shell NRs exhibit a much higher photocatalytic activity than S-ZnO/Cu₂S core/shell NRs. The photocurrent density and photoconversion efficiency of H-ZnO/Cu₂S core/shell NRs are up to 20.12 mA cm^?2 at 0.85 V versus SCE and 12.81 % at 0.40 V versus SCE, respectively.     

Co-doped ZnO nanoparticles synthesized by an adapted sol–gel method: effects on the structural,optical, photocatalytic and antibacterial properties

Pure and Co-doped ZnO nanoparticles were synthesized with different cobalt levels (1–10 mol%) via adapted sol–gel method using water as solvent and characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy and photoacoustic absorption spectroscopy. The results showed that all the samples have hexagonal wurtzite structure, with no evidence of any secondary phases until 10 mol% of the dopant. The average crystallite size of the samples was in the range of 25–50 nm, do not showing significant differences with the increase of the dopant level. However, the band gap energy of the nanoparticles decreases from 2.98 eV (pure ZnO) to 1.95 eV (10 mol% of Co). The photocatalytic activity of the samples was evaluated on the removal of methylene blue under visible light irradiation, which revealed an efficiency reduction by Co-doping ZnO. The antibacterial property was carried out indicating activity of the prepared samples against gram-positive bacteria.     

Green Synthesized Iron Oxide Nanoparticles Effect on Fermentative Hydrogen Production by Clostridium acetobutylicum

A green synthesis of iron oxide nanoparticles (FeNPs) was developed using Murraya koenigii leaf extract as reducing and stabilizing agent. UV–vis spectra show that the absorption band centred at a wavelength of 277 nm which corresponds to the surface plasmon resonances of synthesized FeNPs. Fourier transform infrared spectroscopy spectrum exhibits that the characteristic band at 580 cm^?1 is assigned to Fe–O of γ-Fe₂O₃. Transmission electron microscopy image confirms that the spherical with irregular shaped aggregates and average size of nanoparticles was found to be ～59 nm. The effect of synthesized FeNPs on fermentative hydrogen production was evaluated from glucose by Clostridium acetobutylicum NCIM 2337. The hydrogen yield in control experiment was obtained as 1.74?±?0.08 mol H₂/mol glucose whereas the highest hydrogen yield in FeNPs supplemented experiment was achieved as 2.33?±?0.09 mol H₂/mol glucose at 175 mg/L of FeNPs. In addition, the hydrogen content and hydrogen production rate were also increased from 34?±?0.8 to 52?±?0.8 % and 23 to 25.3 mL/h, respectively. The effect of FeNPs was compared with supplementation of FeSO₄ on fermentative process. The supplementation of FeNPs enhanced the hydrogen production in comparison with control and FeSO₄. The supplementation of FeNPs led to the change of the metabolic pathway towards high hydrogen production due to the enhancement of ferredoxin activity. The fermentation type was shifted from butyrate to acetate/butyrate fermentation type at the addition of FeNPs.     

Synthesis and Characterization of CeO2 Nanoparticles via Solution Combustion Method for Photocatalytic and Antibacterial Activity Studies

CeO₂ nanoparticles have been proven to be competent photocatalysts for environmental applications because of their strong redox ability, nontoxicity, long-term stability, and low cost. We have synthesized CeO₂ nanoparticles via solution combustion method using ceric ammonium nitrate as an oxidizer and ethylenediaminetetraacetic acid (EDTA) as fuel at 450 °C. These nanoparticles exhibit good photocatalytic degradation and antibacterial activity. The obtained product was characterized by various techniques. X-ray diffraction data confirms a cerianite structure: a cubic phase CeO₂ having crystallite size of 35 nm. The infrared spectrum shows a strong band below 700 cm⁻¹ due to the Ce−O−Ce stretching vibrations. The UV/Vis spectrum shows maximum absorption at 302 nm. The photoluminescence spectrum shows characteristic peaks of CeO₂ nanoparticles. Scanning electron microscopy (SEM) images clearly show the presence of a porous network with a lot of voids. From transmission electron microscopy (TEM) images, it is clear that the particles are almost spherical, and the average size of the nanoparticles is found to be 42 nm. CeO₂ nanoparticles exhibit photocatalytic activity against trypan blue at pH 10 in UV light, and the reaction follows pseudo first-order kinetics. Finally, CeO₂ nanoparticles also reduce Cr^VI to Cr^III and show antibacterial activity against Pseudomonas aeruginosa.     

Studies on photocatalytic performance and photodegradation kinetics of zinc oxide nanoparticles prepared by microwave-assisted sol–gel technique using ethylene glycol

ZnO nanoparticles with an average particle size of 27 nm were fabricated using a microwave-assisted sol–gel method in the presence of ethylene glycol. The nanoparticles were characterized by X-ray diffraction, Monshi’s equation, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. The band gap energy of the nanoparticles was measured to be 3.27 eV by UV–Vis absorption and reflection spectroscopy. Photocatalytic activity of the synthesized nanoparticles was assessed by degrading nitrophenol in aqueous solution under UV-C irradiation. The effects of initial nitrophenol concentration, amount of photocatalyst, and of pH on the photodegradation process were investigated. Degradation samples were analyzed by UV–Vis spectroscopy. Nitrophenol was removed by 98 % within 240 min. The degradation kinetics were studied and fitted well to pseudo-first-order and Langmuir–Hinshelwood models.     

Improved efficiency of dye-sensitized solar cells by design of a proper double layer photoanode electrodes composed of Cr-doped TiO2 transparent and light scattering layers

A new strategy for enhancing the efficiency of TiO₂ dye-sensitized solar cells (DSSCs) by design of a new double layer film doped with Cr ions, with various morphologies, is reported. X-ray diffraction and field emission scanning electron microscope (FE-SEM) analyses revealed that the synthesized nanoparticles had uniform and nanometer grains with different phase compositions and average crystallite size in the range of 10–12 nm depending upon Cr atomic percentage. UV–vis absorption showed that Cr introduction enhanced the visible light absorption of TiO₂ nanoparticles by shifting the absorption onset to visible light region. Furthermore, the band gap energy of nanoparticles decreased with an increase in dopant concentration due to reduction of particle size. It was found that, 3 at.% Cr-doped TiO₂ DSSC in the form of a double-layer film composed of TiO₂ nanoparticles, as the under-layer, and mixtures of nano- and micro-particles with weight ratio of 80:20, as the over-layer, (i.e., CT3/NM3 solar cell) had the highest power conversion efficiency of 7.02 %, short current density of 17.32 mA/cm² and open circuit voltage of 674 mV. This can be related to achievement of a balance among the electron injection, light scattering effect and dye sensitization parameters. Optimization of light scattering effect of photoanode electrode led to improve the photovoltaic performance of CT3/NM3 double-layer solar cell and was demonstrated by diffuse reflectance spectroscopy. The presented strategy would open up new insight into fabrication of low-cost TiO₂ DSSCs with high power conversion efficiency.     

Preparation and Optoelectronic Property of a SnO2/CdS Nanocomposite Based on the Flowerlike Clusters of SnO2 Nanorods

A SnO₂/CdS nanocomposite based on the flowerlike clusters of SnO₂ nanorods was prepared and characterized with x-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and EDX analysis. The SEM and TEM images show the nanocomposite is composed of CdS nanoparticles and flowerlike clusters of SnO₂ nanorods. The UV–vis spectrum of the nanocomposite displays a new absorption band in the region of 350 to 530 nm, compared with that of the flowerlike clusters of SnO₂ nanorods. The measurement of optoelectronic property indicates that the photoresponse of the composite is extended into the visible region and the incident photon-to-current conversion efficiency (IPCE) of the composite is up to 6.5 in the range of 400 to 440 nm. These phenomena ought to be ascribed to the special nanostructure of the SnO₂/CdS composite obtained.     

Facile synthesis of nanostructured Ni-Co/ZnO material: An efficient and inexpensive catalyst for Heck reactions under ligand-free conditions

A simple, efficient and economically viable method for the Heck reaction has been accomplished in the absence of phosphine ligand. The Heck reaction was performed using nanostructured Ni-Co/ZnO material as a heterogeneous catalyst in a DMF/H₂O solvent system and in the presence of K₂CO₃, at 120 °C. The Ni-Co/ZnO nanostructures were prepared by the facile reduction-impregnation method. The structural and morphological properties of Ni-Co/ZnO nanostructure were investigated using various physico-chemical characterization techniques. Structural studies displayed the formation of hexagonal (wurtzite) ZnO. Electron microscopy imaging showed the presence of agglomerated clusters of Ni-Co nanoparticles over the surfaces of elliptical, flower bud-like and irregularly shaped sub-micron sized particle bundles of ZnO. The elemental composition analysis (EDX) confirmed the loading of Ni and Co nanoparticles over the nanocrystalline ZnO. The surface chemical state analysis of Ni-Co/ZnO material validated that Ni nanostructure exists in Ni²⁺ and Ni³⁺ species, whereas, Co nanostructure exists in Co²⁺ and Co³⁺ species. UV–Vis diffuse reflectance spectroscopy displays red shift in the light absorption edge of Ni-Co/ZnO catalyst compared to pure ZnO. The as-prepared Ni-Co bimetallic supported ZnO nanostructure showed better catalytic activity and stability for the Heck reactions under phosphine ligand-free conditions. Ni-Co/ZnO catalyzed Heck reactions afforded the corresponding cross-coupled products with moderate to good yields (up to 92%). Ni-Co/ZnO catalyst could be reused for five successive runs without significant loss of catalytic activity.     

Combustion synthesis of calcium doped ZnO nanoparticles for the photocatalytic degradation of methylene blue dye

ZnO nanoparticles are one of the prominent photocatalysts for environmental applications due to its high redox ability, nontoxic and higher stability. This report explains the synthesis of ZnO nanoparticles by a simple solution combustion method using zinc nitrate hexahydrate as an oxidizing agent and incense stick powder as fuel at 400 °C. Several techniques were adopted for the characterization of the obtained product. X-ray diffraction (XRD) pattern shows that a lower concentration of fuel gives pure ZnO and a higher concentration of fuel results in calcium doped ZnO with a cubic phase having a crystallite size of 32–28 nm. UV–vis spectrum shows that as the fuel concentration increases, band gap decreases and reaches to 3.33 eV for 3 g of fuel. Spongy networks with many pores wereobserved in the scanning electron microscope (SEM) and transmission electron microscope (TEM) images showed the average particle size of Ca doped ZnO NPs is about 20 nm. Pure and Ca doped ZnO nanoparticles were examined for photocatalytic degradation of methylene blue (MB) dye under UV light irradiation. The results prove that Ca doped ZnO nanoparticles show good photocatalytic activity.     

The electronic spectrum of (−)-s-(ps)-2,5,3',6'-tetrahydro[2.2]paracyclophane-2-carboxylic acid

A new, efficient route was used in the synthesis of [2,2]paracyclophane-2-carboxylic acid. The chiral acid was then resolved and the Birch reduction performed yielding one enantiomer of tetrahydro[2,2]paracyclophane-2-carboxylic acid. The UV spectrum of tetrahydro[2,2]paracyclophane-2-carboxylic acid in isopentane shows one absorption at 206 nm (?_max=5271). There are three bands observed in the CD spectrum in isopentane at 236 nm ([θ] = 1.8 × 10⁴), 201 nm ([θ]=-16×10⁴) and a positive band indicated below 180 nm but not observed, in ethanol the CD spectrum exhibits a band at 205 nm ([θ]= 1.5×10⁴) and the UV spectrum shows a band at 208 nm (?_max=5915). The bands were assigned and possible reasons for the occurrence of a π→π^* transition at unexpectedly long wavelengths are discussed.     

Structures and optical properties of Zn1?x Ni x O nanoparticles by coprecipitation method

Nanocrystals of undoped and nickel-doped zinc oxide (Zn_1?x Ni _x O, where x?=?0.00?C0.05) were synthesized by the coprecipitation method. Crystalline size, morphology, and optical absorption of prepared samples were determined by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and UV?Cvisible spectrometer. XRD and SEM studies revealed that Ni-doped ZnO crystallized in hexagonal wurtzite structure. Doping of ZnO with Ni²⁺ was intended to enhance the surface defects of ZnO. The incorporation of Ni²⁺ in place of Zn²⁺ provoked an increase in the size of nanocrystals as compared to undoped ZnO. Crystalline size of nanocrystals varied from 10 to 40?nm as the calcination temperature increased. Enhancement in the optical absorption of Ni-doped ZnO indicated that it can be used as an efficient photocatalyst under visible light irradiation. Optical absorption measurements indicated a red shift in the absorption band edge upon Ni doping. The band gap value of prepared undoped and Ni-doped ZnO nanoparticles decreased as annealing temperature was increased up to 800?°C.