TiO2-coated nanostructures for dye photo-degradation in water

TiO2-MoS2-PMMA Nanocomposites for an Efficient Water Remediation

An improvement of water supply and sanitation and better management of water resources, especially in terms of water reuse, is one of the priorities of the European Green Deal. In this context, it is crucial to find new strategies to recycle wastewater efficiently in a low-cost and eco-friendly manner. The immobilization of inorganic nanomaterials on polymeric matrices has been drawing a lot of attention in recent years due to the extraordinary properties characterizing the as-obtained nanocomposites. The hybrid materials, indeed, combine the properties of the polymers, such as flexibility, low cost, mechanical stability, high durability, and ease of availability, with the properties of the inorganic counterpart. In particular, if the inorganic fillers are nanostructured photocatalysts, the materials will be able to utilize the energy delivered by light to catalyze chemical reactions for efficient wastewater treatment. Additionally, with the anchoring of the nanomaterials to the polymers, the dispersion of the nanomaterials in the environment is prevented, thus overcoming one of the main limits that impede the application of nanostructured photocatalysts on a large scale. In this work, we will present nanocomposites made of polymers, i.e., polymethyl methacrylate (PMMA), and photocatalytic semiconductors, i.e., TiO2 nanoparticles (Evonik). MoS2 nanoflakes were also added as co-catalysts to improve the photocatalytic performance of the TiO2. The hybrid materials were prepared using the sonication and solution casting method. The nanocomposites were deeply characterized, and their remarkable photocatalytic abilities were evaluated by the degradation of two common water pollutants: methyl orange and diclofenac. The relevance of the obtained results will be discussed, opening the route for the application of these materials in photocatalysis and especially for novel wastewater remediation.

Titanium Dioxide Nanoparticles: Effects on Development and Male Reproductive System

Titanium dioxide nanoparticles (TiO₂-NPs) are used intensively. Thanks to their extremely small size (1-100 nm), TiO₂-NPs are more absorbable by living organisms; consequently, they can cross the circulatory system and then be distributed in various organs including the reproductive organs. We have evaluated the possible toxic effect of TiO₂-NPs on embryonic development and the male reproductive system using Danio rerio as an organism model. TiO₂-NPs (P25, Degussa) were tested at concentrations of 1 mg/L, 2 mg/L, and 4 mg/L. TiO₂-NPs did not interfere with the embryonic development of Danio rerio, however, in the male gonads the TiO₂-NPs caused an alteration of the morphological/structural organization. The immunofluorescence investigation showed positivity for biomarkers of oxidative stress and sex hormone binding globulin (SHBG), both confirmed by the results of qRT-PCR. In addition, an increased expression of the gene responsible for the conversion of testosterone to dihydrotestosterone was found. Since Leydig cells are mainly involved in this activity, an increase in gene activity can be explained by the ability of TiO₂-NPs to act as endocrine disruptors, and, therefore, with androgenic activity.

A C2N/ZnSe heterostructure with type-II band alignment and excellent photocatalytic water splitting performance

A type-II C₂N/ZnSe heterostructure with strong light-absorption ability, high carrier mobility and low exciton binding energy, exhibits excellent photocatalytic water splitting performance

Fabrication of Ultra-High Aspect Ratio (>420:1) Al2O3 Nanotube Arraysby Sidewall TransferMetal Assistant Chemical Etching

We report a robust, sidewall transfer metal assistant chemical etching scheme for fabricating Al2O3 nanotube arrays with an ultra-high aspect ratio. Electron beam lithography followed by low-temperature Au metal assisted chemical etching (MacEtch) is used to pattern high resolution, high aspect ratio, and vertical silicon nanostructures, used as a template. This template is subsequently transferred by an atomic layer deposition of the Al2O3 layer, followed by an annealing process, anisotropic dry etching of the Al2O3 layer, and a sacrificial silicon template. The process and characterization of the Al2O3 nanotube arrays are discussed in detail. Vertical Al2O3 nanotube arrays with line widths as small as 50 nm, heights of up to 21 μm, and aspect ratios up to 420:1 are fabricated on top of a silicon substrate. More importantly, such a sidewall transfer MacEtch approach is compatible with well-established silicon planar processes, and has the benefits of having a fully controllable linewidth and height, high reproducibility, and flexible design, making it attractive for a broad range of practical applications.

Nano-engineered Adsorbent for the Removal of Dyes from Water: A Review

Background:

The huge quantity of wastewater, containing poisonous and hazardous dyes, is released by various industries which pollute water in direct and indirect ways. Most of the dyes are a dangerous class of water contaminants which have affected the environment drastically. Some dyes such as congo red, rhodamine B, methylene blue, methyl violet, and crystal violet are a serious threat to human beings.

Remediation Method:

Numerous methods are available for the removal of dyes from water. Adsorption, being a superior and eco-friendly technique, has advantage of eliminating organic dyes because of the availability of materials as adsorbents. The inexpensive nanomaterials are a more attractive choice for remediation of various dyes due to their unique properties and offer an adequate pathway to adsorb any organic dye from water to overcome its hazardous effects on human health.

Results:

In this review, we have discussed the latest literature related to various types of synthesis, characterization and uses as adsorbent for highly adsorptive removal capacity of nanoparticles for organic dyes.

Conclusion:

Adsorption technology provides an attractive pathway for further research and improvement in more efficient nanoparticles, with higher adsorption capacity, for numerous dyes to eliminate the dyes discharged from various industries and thus reduce the contamination of water. Therefore, nanocomposites may contribute to future prospective water treatment process.

A review on novel composites of MWCNTs mediated semiconducting materials as photocatalysts in water treatment

Many technologies were explored to eliminate the harmful pollutants entering water systems and to minimize their impact on environment. In general, photo-catalysis is one of the sustainable techniques with wider applications and semiconductors in particular were efficiently utilized in the photocatalytic degradation of pollutants. Semiconducting materials, such as TiO₂, ZnO, BiO, CdS, and Ag₃PO₄ are frequently used as photo-catalysts due to their suggestible band gap and structural properties. The generation of reactive oxygen species such as hydroxyl and superoxide radicals is the crucial factor in degradation of pollutant molecules. The rapid recombination of photo-generated electron-hole pairs impacts on the efficacy of semiconductors as photo-catalysts. The integration of properties of multi-walled carbon nanotubes (MWCNTs) with semiconductors is considered as imperative alternative strategy to boast the photocatalytic efficiency. The combinative merits of composites of MWCNTs and various semiconductor materials give new vista for water treatment and environmental protection. This review describes the scope of different types of MWCNT and semiconductor composites as photo-catalysts and their structure-property relationships in oxidative degradation and mineralization of organic pollutants, in particular.

Polymeric platform for the growth of chemically anchored ZnO nanostructures by ALD

The synthesis of hybrid nano-composites in which an inorganic layer is grown on a polymeric surface via chemical bonds, is a challenging goal for many applications from photocatalysis, to sensing and optoelectronics.

Preparation of Ti species coating hydrotalcite by chemical vapor deposition for photodegradation of azo dye

TiO₂ in anatase crystal phase is a very effective catalyst in the photocatalytic oxidation of organic compounds in water. To improve its photocatalytic activity, the Ti-coating MgAl hydrotalcite (Ti-MgAl-LDH) was prepared by chemical vapor deposition (CVD) method. Response surface method (RSM) was employed to evaluate the effect of Ti species coating parameters on the photocatalytic activity, which was found to be affected by the furnace temperature, N₂ flow rate and influx time of precursor gas. Application of RSM successfully increased the photocatalytic efficiency of the Ti-MgAl-LDH in methylene blue photodegradation under UV irradiation, leading to improved economy of the process. According to the results from X-ray diffraction, scanning electron microscopy, Brunner-Emmet-Teller and Barrett-Joyner-Hallender, thermogravimetric and differential thermal analysis, UV-vis diffuse reflectance spectra analyses, the Ti species (TiO₂ or/and Ti⁴⁺) were successfully coated on the MgAl-LDH matrix. The Ti species on the surface of the Ti-MgAl-LDH lead to a higher photocatalytic performance than commercial TiO₂-P25. The results suggested that CVD method provided a new approach for the industrial preparation of Ti-coating MgAl-LDH material with good photocatalytic performances.

In situ solid-state fabrication of hybrid AgCl/AgI/AgIO3 with improved UV-to-visible photocatalytic performance

The AgCl/AgI/AgIO₃ composites were synthesized through a one-pot room-temperature in situ solid-state approach with the feature of convenient and eco-friendly. The as-prepared composites exhibit superior photocatalytic performance than pure AgIO₃ for the degradation of methyl orange (MO) under both UV and visible light irradiation. The photodegradation rate toward MO of the AgCl/AgI/AgIO₃ photocatalyst can reach 100% after 12 min irradiation under UV light, or 85.4% after 50 min irradiation under visible light, being significantly higher than AgCl, AgI, AgIO₃ and AgI/AgIO₃. In addition, the AgCl/AgI/AgIO₃ photocatalyst possesses strong photooxidation ability for the degradation of rhodamine B (RhB), methylene blue (MB), phenol, bisphenol A (BPA) and tetracycline hydrochloride under visible light irradiation. The reactive species capture experiments confirmed that the h⁺ and •O²⁻ play an essential role during the photocatalytic process under UV light or visible light irradiation. The enhanced effect may be beneficial from the enhanced light adsorption in full spectrum and increased separation efficiency of photogenerated hole-electron pairs, which can be ascribed to the synergistic effect among AgCl, AgI and AgIO₃ nanoplates in AgCl/AgI/AgIO₃ composites.

Novel synthesis of ZnO/PMMA nanocomposites for photocatalytic applications

The incorporation of nanostructured photocatalysts in polymers is a strategic way to obtain novel water purification systems. This approach takes the advantages of: (1) the presence of nanostructured photocatalyst; (2) the flexibility of polymer; (3) the immobilization of photocatalyst, that avoids the recovery of the nanoparticles after the water treatment. Here we present ZnO-polymer nanocomposites with high photocatalytic performance and stability. Poly (methyl methacrylate) (PMMA) powders were coated with a thin layer of ZnO (80 nm thick) by atomic layer deposition at low temperature (80 °C). Then the method of sonication and solution casting was performed so to obtain the ZnO/PMMA nanocomposites. A complete morphological, structural, and chemical characterization was made by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses. The remarkable photocatalytic efficiency of the nanocomposites was demonstrated by the degradation of methylene blue (MB) dye and phenol in aqueous solution under UV light irradiation. The composites also resulted reusable and stable, since they maintained an unmodified photo-activity after several MB discoloration runs. Thus, these results demonstrate that the proposed ZnO/PMMA nanocomposite is a promising candidate for photocatalytic applications and, in particular, for novel water treatment.

Optical and photocatalytic properties of TiO2 nanoplumes

Here we report the photocatalytic efficiency of hydrogenated TiO₂ nanoplumes studied by measuring dye degradation in water. Nanoplumes were synthesized by peroxide etching of Ti films with different thicknesses. Structural characterization was carried out by scanning electron microscopy and transmission electron microscopy. We investigated in detail the optical properties of the synthesized material and related them to the efficiency of UV photodegradation of methylene blue dye. The obtained results show that TiO₂ nanoplumes act as an effective antireflective layer increasing the UV photocatalytic yield of the film.

Synthesis of stable core–shell structured TiO2@Fe3O4 based on carbon derived from yeast with an enhanced photocatalytic ability

By using yeast as the carbon source, stable core–shell structured TiO₂@Fe₃O₄ based on carbon (TiO₂@Fe₃O₄-carbon) was obtained.

Single-crystal TiO2 nanowires by seed assisted thermal oxidation of Ti foil: synthesis and photocatalytic properties

TiO₂ nanowires growth was investigated varying the synthesis parameters. Nanowires demonstrated improved photocatalytic activity, especially when treated in forming gas.

A forest of SiO2 nanowires covered by a TiO2 thin film for an efficient photocatalytic water treatment

Disordered TiO₂/SiO₂ nanowires possess enhanced photocatalytic activity due to the synergy of morphology and light trapping properties of the NW forest.

Recent advances in the synthesis and application of photocatalytic metal–metal oxide core–shell nanoparticles for environmental remediation and their recycling process

Metal–metal oxide core–shell nanoparticles have received enormous research attention owing to their fascinating physicochemical properties and extensive applications. In this review we have discussed the challenges and recent advances in their synthesis and application.

Effect of Pt Nanoparticles on the Photocatalytic Activity of ZnO Nanofibers

For this study, we originally realized ZnO nanofibers (∼50 nm in mean radius) mixed with Pt nanoparticles (∼30 nm in mean radius), prepared by pulsed laser ablation in liquid, and investigated their photocatalytic performance. The material was synthesized by the simple electrospinning method coupled with subsequent thermal treatments. Methylene blue was employed as a representative dye pollutant to evaluate the photocatalytic activity of the nanofibers. It was found that the Pt-ZnO fibers exhibit a photodegradation reaction rate that is ∼40 % higher than the one obtained for reference ZnO fibers. These encouraging results demonstrate that Pt-ZnO nanofibers can be fruitfully applied for environmental applications.

Surface Properties and Photocatalytic Activities of the Colloidal ZnS:Mn Nanocrystals Prepared at Various pH Conditions

Water-dispersible ZnS:Mn nanocrystals (NC) were synthesized by capping the surface with mercaptoacetic acid (MAA) molecules at three different pH conditions. The obtained ZnS:Mn-MAA NC products were physically and optically characterized by corresponding spectroscopic methods. The UV-Visible absorption spectra and PL emission spectra showed broad peaks at 310 and 590 nm, respectively. The average particle sizes measured from the HR-TEM images were 5 nm, which were also supported by the Debye-Scherrer calculations using the X-ray diffraction (XRD) data. Moreover, the surface charges and the degrees of aggregation of the ZnS:Mn-MAA NCs were determined by electrophoretic and hydrodynamic light scattering methods, indicating formation of agglomerates in water with various sizes (50–440 nm) and different surface charge values accordingly the preparation conditions of the NCs (−7.59 to −24.98 mV). Finally, the relative photocatalytic activities of the ZnS:Mn-MAA NCs were evaluated by measuring the degradation rate of methylene blue (MB) molecule in a pseudo first-order reaction condition under the UV-visible light irradiation. As a result, the ZnS:Mn-MAA NC prepared at the pH 7 showed the best photo-degradation efficiency of the MB molecule with the first-order rate constant (k_obs) of 2.0 × 10⁻³·min⁻¹.

Controllable synthesis porous Ag2CO3 nanorods for efficient photocatalysis

The novel porous Ag2CO3 nanorods were facilely synthesized via a one-pot aqueous solution reaction at room temperature. The crystalline phase and size distribution of the nanorods were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. In addition, the porous feature of nanorods was confirmed by transmission electron microscopy (TEM) and nitrogen adsorption-desorption. The morphology and size of the Ag2CO3 crystal can be regulated via the choice of dispersing agents and adding approaches of reactants. Photocatalytic results show that the porous Ag2CO3 nanorods exhibit excellent photodegradation of rhodamine B (RhB) under visible-light irradiation, particularly the photoactivity performance and stability can be further improved in the presence of sodium bicarbonate (NaHCO3). It is indicated that NaHCO3 can prevent effectively the photocorrosion and promote the probability of electron-hole separation.

Low temperature sputtered TiO2 nano sheaths on electrospun PES fibers as high porosity photoactive material

Low temperature approach based on combining electrospinning and reactive sputtering processes to realise a porous mesh of PES fibers wrapped by TiO₂ nano-sheaths, active under UV illumination.