Comparative study of antimicrobial and photocatalytic activity in titania encapsulated composite nanoparticles with different dopants

Abstract

The present study describes a relative comparison of antimicrobial and photocatalytic activity in titania encapsulated nickel ferrite nanoparticles with different dopants. The photocatalytic and antimicrobial activity in doped titania composite nanoparticles follows the sequence: W⁴⁺ doped > Nd³⁺ doped > Zn²⁺ doped > undoped titania. The maximum enhancement in tungsten doped titania is attributed to the greater inhibition of electron hole recombination process and decrease in band gap in titania. The ferrite magnetic nanoparticles encapsulated with the photocatalytic shell retain superparamagnetic characteristics and magnetic strength encouraging their potential application as removable antimicrobial photocatalytic composite nanoparticles. The combination of reverse micelle and hydrolysis method is recognised as a promising method for the synthesis of these composite nanoparticles.     

Weighting the influence of TiO2 anatase/brookite ratio in TiO2–Ag porous nanocomposites on visible photocatalytic performances

Nanocomposites based on TiO₂ aerogel and Ag nanoparticles have been successfully obtained through different synthesis methods and their specific surface areas have been determined by N₂ sorption (BET method). The photocatalytic potential for salicylic acid degradation has been evaluated. It was found that under visible light irradiation, all synthesized nanocomposites exhibit higher photocatalytic activity than the commercially available Aeroxide P25. By correlating the structural parameters with the photocatalytic performances, it has been found that the Ag nanoparticles and brookite phase presence alongside the anatase play important roles on the visible photocatalysts behavior. For the Ag containing samples with mixed anatase–brookite phases, it has been observed that the visible photocatalytic performance decreases with the increase in brookite crystalline phase content. On the other hand, the addition of Ag nanoparticles results, as expected, in a clear enhancement of the visible photocatalytic activity.     

Preparation,characterization and photocatalytic activities of holmium-doped titanium dioxide nanoparticles

Holmium-doped TiO₂ nanoparticles with high photocatalytic activities were prepared by sol–gel method and characterized by X-ray diffraction, transmission electron microscopy, ultraviolet–visible diffuse reflectance spectroscopy, and surface area measurement by nitrogen adsorption in this study. Experimental results indicated holmium doping could increase the surface area of TiO₂ nanoparticles, and inhibit the growth of crystalline size and the anatase-to-rutile phase transformation. The results of photodegrading methyl orange showed holmium doping improved the photocatalytic activity of TiO₂, and the reasons could be attributed to the synergetic effects of large surface areas, small crystallite size, lattice distortion and more charge imbalance of holmium-doped TiO₂. In our experiment, the optimal doped amount was 0.3 mol.% for the maximum photocatalytic degradation ratio when holmium-doped TiO₂ was calcined at 500 °C, and the optimal calcined temperature was 600 °C when the doped amount was 0.5 mol.%.     

Enhanced Photocatalytic Performances of CeO2/TiO2 Nanobelt Heterostructures

CeO₂/TiO₂ nanobelt heterostructures are synthesized via a cost‐effective hydrothermal method. The as‐prepared nanocomposites consist of CeO₂ nanoparticles assembled on the rough surface of TiO₂ nanobelts. In comparison with P25 TiO₂ colloids, surface‐coarsened TiO₂ nanobelts, and CeO₂ nanoparticles, the CeO₂/TiO₂ nanobelt heterostructures exhibit a markedly enhanced photocatalytic activity in the degradation of organic pollutants such as methyl orange (MO) under either UV or visible light irradiation. The enhanced photocatalytic performance is attributed to a novel capture–photodegradation–release mechanism. During the photocatalytic process, MO molecules are captured by CeO₂ nanoparticles, degraded by photogenerated free radicals, and then released to the solution. With its high degradation efficiency, broad active light wavelength, and good stability, the CeO₂/TiO₂ nanobelt heterostructures represent a new effective photocatalyst that is low‐cost, recyclable, and will have wide application in photodegradation of various organic pollutants. The new capture–photodegradation–release mechanism for improved photocatalysis properties is of importance in the rational design and synthesis of new photocatalysts.     

Green synthesis of zinc oxide nanoparticles using <Emphasis Type="Italic">Citrus sinensis</Emphasis> extract

This work addresses a low cost, non-toxic green synthesis of zinc oxide nanoparticles prepared using different amounts of Citrus sinensis extract. The zinc oxide nanoparticles presented the Zn–O bond at 618 cm^?1, a crystalline growth in a purely hexagonal wurtzite crystal structure, and different size and shape homogeneity depending on the amount of extract used. The band gap of the ZnO was at around 2.91 eV for all samples. The photocatalytic degradation studies were carried out using methylene blue with the zinc oxide nanoparticles under UV light; where sample M2 presented a degradation of around 83% at 120 min. These results presented a better degradation rate than commercially available zinc oxide nanoparticles.     

Mussel‐Inspired Immobilization of Catalysts for Microchemical Applications

Immobilization of photocatalytic TiO₂ nanoparticles inside PDMS‐based microreactors was successfully attempted by sequential mussel‐inspired surface engineering of microchannels by using CA‐PVP and commercially available TiO₂ nanoparticles, respectively. TiO₂‐immobilized microreactors accomplished continuous photocatalytic degradation of MB for up to 30 days without releasing TiO₂ nanoparticles from the surface of the microchannels, confirming the robustness of TiO₂‐immobilization in photocatalysis media. Regeneration of microreactors with diminished photocatalytic activities was also possible with simple strong acid treatment, enabling efficient cleaning of used microreactors.     

Preparation, characterization and application of TiO2 nanoparticles surface-modified by DDAT

DDAT(S-1-Dodecyl-S′-(α, α′-dimethyl-α″-acetic acid) trithiocarbonate) modified TiO₂ photocatalysts were prepared by hydrothermal treatment before TiO₂ crystallization. The adsorption of DDAT onto the surface of titania nanoparticles led the shifting of the onset wavelength of the optical absorption in the visible range corresponding to ligand-to-metal charge transfer transition within the surface-modified complex. The interaction of TiO₂ nanoparticles with DDAT was investigated by infrared spectra. The XRD indicated that the modification process could not influence the crystallite phase of TiO₂. The photocatalytic studies suggested that the DDAT modified TiO₂ photocatalysts showed enhanced photocatalytic efficiency of photodegradation of 2,4-dichlorophenol compared with the as-prepared TiO₂ under visible-light irradiation.     

Synthesis,structure and photocatalytic properties of nanoparticles from a carbon-containing composite based on silicon oxide modified with titanium dioxide

A pulsed plasmochemical method was used to obtain carbon-containing nanocomposites based on silicon oxide modified with titanium dioxide. The material contained a Si_xC_yO_z carrier with an average size of 50–150?nm and a shell of fine particles with an average size of 5–10?nm. The phase composition and morphology of the synthesized composites was studied by X-ray diffraction and transmission electron microscopy. The optical and photocatalytic properties of the nanoparticles from the carbon-based composite based on silicon oxide encapsulated in titanium dioxide were studied. The synthesized composite showed a high photocatalytic activity due to the decomposition of methylene blue under the influence of visible light in the wavelength range of 460–630?nm.     

Enhanced Photocatalytic Property of Reduced Graphene Oxide/TiO2 Nanobelt Surface Heterostructures Constructed by an In Situ Photochemical Reduction Method

A facile method is proposed to assemble graphene oxide (GO) on the surface of a TiO₂ nanobelt followed by an in situ photocatalytic reduction to form reduced graphene oxide (rGO)/TiO₂ nanobelt surface heterostructures. The special colloidal properties of GO and TiO₂ nanobelt are exploited as well as the photocatalytic properties of TiO₂. Using water–ethanol solvent mixtures, GO nanosheets are tightly wrapped around the surface of the TiO₂ nanobelts through an aggregation process and are then reduced in situ under UV‐light irradiation to form rGO/TiO₂ nanobelt surface heterostructures. The heterostructures enhance the separation of the photoinduced carriers, which results in a higher photocurrent due to the special electronic characteristics of rGO. Compared to TiO₂ nanobelts, the rGO/TiO₂ nanobelt surface heterostructures possess higher photocatalytic activity for the degradation of methyl orange and for the production of hydrogen from water, as well as excellent recyclability, with no loss of activity over five cycles.     

Photocatalytic decomposition of methylene blue on nanocrystalline titania prepared by different methods

Nanocrystalline particles of pure anatase titania were prepared by two different methods. One is the sol-gel method at ambient temperature using ultrasonication (TiO₂-SG-US) and conventional stirring method (TiO₂-SG-S) and the other by surfactant assisted hydrothermal synthesis (TiO₂-HT). More uniform distribution/dispersion of the nanoparticles (SEM), marginally higher surface area, better thermal stability and phase purity are some of the advantages of preparation of nanocrystalline titania by sol gel ultrasonication method and hydrothermal synthesis method. The behavior of anatase titania in photocatalytic decomposition of methylene blue in aqueous medium was studied as a function of the method of preparation and the crystallite size. The nanoparticles prepared by ultrasonication method were more effective than both, the sample prepared by conventional stirring method and commercial Degussa P-25. The higher photocatalytic activity of TiO₂-SG-US is attributed to the more uniform size of the particles as compared to TiO₂-SG-S samples. Both TEM and XRD data on TiO₂-HT samples reveal a uniform and nanocrystalline TiO₂ particles, which showed photocatalytic activity in both UV and visible region although brookite phase was also present.     

Substrate and Fe-doping effects on the hydrophilic properties of TiO2 thin films

Titanium dioxide films are known for their hydrophilic and photocatalytic characteristics. Increasing specific surface area and doping can enhance their photocatalytic activity and hydrophilicity. We report here results regarding the enhancement of the photocatalytic properties of titania by both controlling surface morphology and the anatase/rutile ratio. The samples were deposited on glass, indium tin oxide covered glass, and SrTiO₃ by sputtering and laser ablation techniques. Film structure and surface morphology were investigated by X-ray diffraction and atomic force microscopy. Film hydrophilicity was assessed from contact angle measurements during- and post-irradiation with UV light. The contact angle data are discussed in terms of the synergic effects of surface morphology, structure and composition of the films.     

Recent progress on magnetic iron oxide nanoparticles: synthesis,surface functional strategies and biomedical applications

Abstract

This review focuses on the recent development and various strategies in the preparation, microstructure, and magnetic properties of bare and surface functionalized iron oxide nanoparticles (IONPs); their corresponding biological application was also discussed. In order to implement the practical in vivo or in vitro applications, the IONPs must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of IONPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The new functionalized strategies, problems and major challenges, along with the current directions for the synthesis, surface functionalization and bioapplication of IONPs, are considered. Finally, some future trends and the prospects in these research areas are also discussed.     

Hydrothermal synthesis of surface-modified iron oxide nanoparticles

We synthesized surface-modified iron oxide nanoparticles in aqueous phase by heating an aqueous solution of iron sulfate (FeSO₄) at 473 K with a small amount of either n-decanoic acid (C₉H₁₉COOH) or n-decylamine (C₁₀H₂₁NH₂), which is not miscible with water at room temperature. Transmission electron microscopy showed that the addition of n-decanoic acid or decylamine changed the shape of the obtained nanoparticles. X-ray diffraction spectra revealed that the synthesized nanoparticles were in α-Fe₂O₃ or Fe₃O₄ phase while Fourier transform infrared spectroscopy and thermogravimetry indicated the existence of an organic layer on the surface of the nanoparticles. In the synthetic condition, decreased dielectric constant of water at higher temperature increased the solubility of n-decanoic acid or n-decylamine in water to promote the reaction between the surface of iron oxide nanoparticles and the organic reagents. After the synthesis, the used organic modifiers separated from the aqueous phase at room temperature, which may help the environmentally benign synthesis of surface-modified metal oxide nanoparticles.     

X-ray photoelectron spectroscopic investigations of Cu2O nanoparticles

Cuprous oxide nanoparticles of five different sizes were obtained by electrochemical as well as chemical routes. Various capping agents were used to passivate the nanoparticles. X-ray diffraction studies show formation of single phased, cubic Cu₂O nanoparticles. X-ray photoelectron spectroscopic studies indicate formation of CuO phase on the surface of Cu₂O nanoparticles for uncapped as well as for those, capped by tetraoctylammonium bromide. On the other hand polyacrylamide and polyvinyl pyrrolidone capped samples did not show presence of CuO. X-ray photoelectron spectroscopy also indicates formation of a Cu²⁺ complex with the capping material on the surface of Cu₂O nanoparticles. The results were discussed in terms of capability of passivation of various additives.     

Solar photocatalytically active,engineered silver nanoparticle synthesis using aqueous extract of mesocarp of Cocos nucifera (Red Spicata Dwarf)

ABSTRACT

Silver nanoparticles synthesised using aqueous extract of Cocos nucifera (CN) mesocarp were evaluated for their photocatalytic activity under solar irradiation. The silver nanoparticles were synthesised by a green method of harnessing bioactive phytocomponents from the mesocarp of Cocos nucifera. Large-scale application of this process necessitates the manoeuvering of the process parameters for increasing the conversion of silver ions to nanoparticles. Process parameters influencing the morphological characteristics of silver nanoparticles such as precursor salt concentration and pH of the synthesis mixture were studied. The crystalline nanoparticles were characterised using UV-vis spectroscopy, XRD, FTIR, SEM and EDX analysis. CN extract and 5 mM silver nitrate solution at a ratio of 1:4 (v/v) in the synthesis mixture was found to be the optimum. Alkaline initial pH of the synthesis mixture was found to favour the synthesis of smaller sized monodispersed silver nanoparticles. Solar energy was harnessed for the photocatalytic degradation of Malachite green dye using silver nanoparticles obtained through the green synthesis method. Overall process aims at utilisation of naturally available resource for the synthesis of silver nanoparticles as well as the degradation of dyes using these nanoparticles, making it useful in the treatment of wastewater.     

Antibacterial and photocatalytic activity of ZnO nanoparticles from Zn(OH)2 dehydrated by azeotropic distillation,freeze drying,and ethanol washing

In this study, the antibacterial and photocatalytic activities of a series of ZnO nanoparticles (NPs) produced using different dehydration methods on as-prepared zinc hydroxide precipitates (Zn(OH)₂) have been investigated. Oven drying, azeotropic distillation, freeze drying, and ethanol washing methods were compared for their ability to yield non-agglomerated powders after precipitation synthesis. β-Zn(OH)₂ single phase was observed after ethanol washing, oven drying, and freeze drying procedures, while azeotropic distillation transformed β-Zn(OH)₂ into ZnO before calcination. Nanosized powders with high surface areas were produced via sublimation during the freeze drying process, and by replacement of hydroxyl groups on the precipitate surface with butoxy groups during azeotropic distillation. Both the photocatalytic degradation of Rhodamine B and the antibacterial activity against the pathogens Escherichia coli and Staphylococcus aureus were enhanced for dehydration methods that increased the surface area of ZnO NPs, suggesting that both photocatalytic and antibacterial behaviors were governed by similar mechanisms.     

Study on crystallinity and morphology controlling of titania using acrylamide gel method and their photocatalytic properties

In this study, polyacrylamide gel method was used for preparation of pure and mixed phase TiO₂ nanoparticles. The influence of synthesis conditions on the physicochemical properties of products was investigated. It was found that the type of acid, which was used for acidifying the precursor solution together with calcination temperature can affect the phase structure, crystalline size, morphology and thereby photocatalytic activity of obtained TiO₂ nanoparticles. Different trends were observed during the phase transformation, particle growth, shift in energy of band gap with the change in tensile strain to compressive strain of the prepared TiO₂ nanomaterial. X-ray diffraction (XRD) showed that prepared nanocrystals, which were calcined at 450 °C have pure anatase and anatase–rutile mixed structures. The prepared samples having crystallite size between 5 nm and 60 nm were observed at different calcination temperatures. In addition, the photocatalytic activities of the prepared samples were evaluated by monitoring the degradation of Cresol Red (CR). The results show that the photocatalyst (TEC_I), exhibits the highest photocatalytic efficiency where 94.7% of CR can be decomposed after UV exposure for 75 min.     

Synthesis and investigation of SnS<Subscript>2</Subscript>/RGO nanocomposites with different GO concentrations: structure and optical properties,photocatalytic performance

In this study, we report the synthesis of tin disulfide/reduced graphrene oxide (SnS₂/RGO) nanocomposites by a simple one-step hydrothermal method. In order to investigate the effect of RGO on the structure and optical properties and photocatalytic activity of the products a series of nanocomposites was prepared with different concentrations of GO. The samples were examined using X-ray diffraction, field emission scanning electron microscopy (FESEM), Raman spectroscopy, UV–Vis spectroscopy and photoluminescence techniques. The results confirmed the growth of SnS₂ with the hexagonal phase. FESEM analysis showed that the hexagonal tin disulfide nanoplates are uniformly dispersed on the surface of the graphene oxide sheets. The optical examination of SnS₂ and SnS₂/RGO nanocomposites indicated that the band gaps of all nanocomposites are greater than that of SnS₂ due to the quantum confinement effect. The photocatalytic activity of the SnS₂/RGO nanocomposites was investigated for degradation of the acid orange 7 dye under visible light. It was observed that all nanocomposites have a higher photocatalytic activity for the degradation in comparison with pure SnS₂. The optimum concentration of GO in SnS₂/RGO nanocomposite for achieving the highest photocatalytic efficiency (81%) was determined as 2 mg ml^?1 during 180 min.     

Laser synthesized TiO2-based nanoparticles and their efficiency in the photocatalytic degradation of linear carboxylic acids

Abstract

Titanium dioxide nanoparticles were synthesized by laser pyrolysis, their surface and electronic properties were modified by gold and/or nitrogen. These materials were characterized by different techniques like X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). Time resolved conductivity (TRMC) was used to study the charge separation of electron/hole pairs. Altogether (XPS, EPR, TRMC), the physicochemical characterizations are well correlated with chemical photoactivity of the different samples. Their photocatalytic activity was evaluated for the degradation of linear carboxylic acids (C2-C3) under UV and visible illumination. The decomposition rate of acids was measured, it shows that the modification with gold increases the photoactivity while the presence of nitrogen slows down the process. Such observations are in good agreement with evolution of TRMC signals. A degradation pathway has been determined by identification of intermediate products by chromatography and EPR, results show different intermediate species. In particular EPR confirms the presence of NO^2? paramagnetic centers and shows two novel N centered paramagnetic centers. A decrease of the degradation rate is observed with increase of carboxylic acid chain length.     

1D sub 10 nm nanofabrication of ultrahydrophobic Ag@TiO2 nanowires and their photocatalytic,UV shielding and antibacterial properties

Here we report the synthesis of 1D TiO₂ sub 10 nm nanowires through one pot hydrothermal method in an alkaline NaOH medium at 95 °C for 36 h. Further, these TiO₂ nanowires were embellished with silver (Ag) using polyvinylpyrrolidone (PVP) and ethylene glycol (EG) based solvothermal route at 160 °C for 4 h. With Ag decoration the photocatalytic activity was enhanced and the complete photooxidation of Methylene Blue (MB) was achieved in 35 min under optimized conditions. Super- and ultra-hydrophobic coating on cotton fabric exhibited a consistent antibacterial activity with enhanced UV-blocking property. Enhanced multifunctional properties observed were primarily attributed to the formation of Ag decorated 1D sub 10 nm TiO₂ nanowires heterojunctions achieved using facile chemical route. Hence, such multiple functionalities make the 1D sub 10 nm TiO₂ nanowires good candidate for industrial and domestic wastewater treatment.