Review on the improvement of the photocatalytic and antibacterial activities of ZnO

Self-cleaning materials have gained considerable attention for both their unique properties and practical applications in energy and environmental areas. Recent examples of many TiO2-derived materials have been illustrated to understand the fundamental principles of self-cleaning hydrophilic and hydrophobic surfaces. Various models including those proposed by Wenzel, Cassie-Baxter and Miwa-Hashimoto are discussed to explain the mechanism of self-cleaning. Examples of semiconductor surfaces exhibiting the simultaneous occurrence of superhydrophilic and superhydrophobic domains on the same surface are illustrated, which can have various advanced applications in microfluidics, printing, photovoltaic, biomedical devices, anti-bacterial surfaces and water purification. Several strategies to improve the efficiency of photocatalytic self-cleaning property have been discussed including doping with metals and non-metals, formation of hetero-junctions between TiO2 and other low bandgap semiconductors, and fabrication of graphene based semiconductor nano-composites. Different mechanisms such as band-gap narrowing, formation of localized energy levels within the bandgap and formation of intrinsic defects such as oxygen vacancies have been suggested to account for the improved activity of doped TiO2 photocatalysts. Various preparation routes for developing efficient superhydrophilic–superhydrophobic patterns have been reviewed. In addition, reversible photo-controlled surfaces with tuneable hydrophilic/hydrophobic properties and its technological applications are discussed. Examples of antireflective surfaces exhibiting self-cleaning properties for the applications in solar cells and flat panel displays have also been provided. Discussion is provided on TiO2 based self-cleaning materials exhibiting hydrophilic and underwater superoleophobic properties and their utilities in water management, antifouling applications and separation of oil in water emulsions are discussed. In addition, ISO testing methods (ISO 27448: 2009, ISO 10678: 2010 and ISO 27447: 2009) for analysing self-cleaning activity and antibacterial action have also been discussed. Rapid photocatalytic self-cleaning testing methods using various photocatalytic activity indicator inks such as resazurin (Rz), basic blue 66 (BB66) and acid violet 7(AV7) for a broad range of materials such as commercial paints, tiles and glasses are also described. Various commercial products such as glass, tiles, fabrics, cement and paint materials developed based on the principle of photo-induced hydrophilic conversion of TiO2 surfaces have also been provided. The wide ranges of practical applications of self-cleaning photocatalytic materials suggest further development to improve their efficiency and utilities. It was concluded that a rational fabrication of multifunctional photocatalytic materials by integrating biological inspired structures with tunable wettability would be favorable to address a number of existing environmental concerns.

/pdf/self-cleaning-applications-of-tio2-by-photo-induced-4j922x6bm9.pdf

Self-Cleaning Applications of TiO2 by Photo-Induced Hydrophilicity and Photocatalysis

As an alternative to the gold standard TiO2 photocatalyst, the use of zinc oxide (ZnO) as a robust candidate for wastewater treatment is widespread due to its similarity in charge carrier dynamics upon bandgap excitation and the generation of reactive oxygen species in aqueous suspensions with TiO2. However, the large bandgap of ZnO, the massive charge carrier recombination, and the photoinduced corrosion–dissolution at extreme pH conditions, together with the formation of inert Zn(OH)2 during photocatalytic reactions act as barriers for its extensive applicability. To this end, research has been intensified to improve the performance of ZnO by tailoring its surface-bulk structure and by altering its photogenerated charge transfer pathways with an intention to inhibit the surface-bulk charge carrier recombination. For the first time, the several strategies, such as tailoring the intrinsic defects, surface modification with organic compounds, doping with foreign ions, noble metal deposition, heterostructuring with other semiconductors and modification with carbon nanostructures, which have been successfully employed to improve the photoactivity and stability of ZnO are critically reviewed. Such modifications enhance the charge separation and facilitate the generation of reactive oxygenated free radicals, and also the interaction with the pollutant molecules. The synthetic route to obtain hierarchical nanostructured morphologies and study their impact on the photocatalytic performance is explained by considering the morphological influence and the defect-rich chemistry of ZnO. Finally, the crystal facet engineering of polar and non-polar facets and their relevance in photocatalysis is outlined. It is with this intention that the present review directs the further design, tailoring and tuning of the physico-chemical and optoelectronic properties of ZnO for better applications, ranging from photocatalysis to photovoltaics.

/pdf/zinc-oxide-based-photocatalysis-tailoring-surface-bulk-xudspiii2k.pdf

Zinc oxide based photocatalysis: tailoring surface-bulk structure and related interfacial charge carrier dynamics for better environmental applications

Photocatalytic water treatment using nanocrystalline titanium dioxide (NTO) is a well-known advanced oxidation process (AOP) for environmental remediation. With the in situ generation of electron-hole pairs upon irradiation with light, NTO can mineralize a wide range of organic compounds into harmless end products such as carbon dioxide, water, and inorganic ions. Photocatalytic degradation kinetics of pollutants by NTO is a topic of debate and the mostly reporting Langmuir-Hinshelwood kinetics must accompanied with proper experimental evidences. Different NTO morphologies or surface treatments on NTO can increase the photocatalytic efficiency in degradation reactions. Wisely designed photocatalytic reactors can decrease energy consumption or can avoid post-separation stages in photocatalytic water treatment processes. Doping NTO with metals or non-metals can reduce the band gap of the doped catalyst, enabling light absorption in the visible region. Coupling NTO photocatalysis with other water-treatment technologies can be more beneficial, especially in large-scale treatments. This review describes recent developments in the field of photocatalytic water treatment using NTO.

/pdf/photocatalytic-water-treatment-by-titanium-dioxide-recent-2e04t4jvkf.pdf

Photocatalytic Water Treatment by Titanium Dioxide: Recent Updates

Two-dimensional (2D) materials have generated great interest in the past few years as a new toolbox for electronics. This family of materials includes, among others, metallic graphene, semiconducting transition metal dichalcogenides (such as MoS2), and insulating boron nitride. These materials and their heterostructures offer excellent mechanical flexibility, optical transparency, and favorable transport properties for realizing electronic, sensing, and optical systems on arbitrary surfaces. In this paper, we demonstrate a novel technology for constructing large-scale electronic systems based on graphene/molybdenum disulfide (MoS2) heterostructures grown by chemical vapor deposition. We have fabricated high-performance devices and circuits based on this heterostructure, where MoS2 is used as the transistor channel and graphene as contact electrodes and circuit interconnects. We provide a systematic comparison of the graphene/MoS2 heterojunction contact to more traditional MoS2-metal junctions, as well as a theoretical investigation, using density functional theory, of the origin of the Schottky barrier height. The tunability of the graphene work function with electrostatic doping significantly improves the ohmic contact to MoS2. These high-performance large-scale devices and circuits based on this 2D heterostructure pave the way for practical flexible transparent electronics.

/pdf/graphene-mos2-hybrid-technology-for-large-scale-two-3dg0f0mu9d.pdf

Graphene-MoS2 Hybrid Technology for Large-Scale Two-Dimensional Electronics

Synthesis of TiO2 nanoparticles by a combined sol–gel ball milling method and investigation of nanoparticle size effect on their photocatalytic activities

Stability and thermal conductivity of water-based carbon nanotube nanofluids

Morphology dependence of thermal and rheological properties of oil-based nanofluids of CuO nanostructures

The objective of this work is to investigate the effect of Ag nanoparticles on critical current of YBa2Cu3O7−δ (YBCO) superconductor. Ag nanoparticles with different particle sizes from 30 to 1000 nm were prepared through the chemical reduction of AgNO3 in an alcohol solution. Then, samples of YBCO superconductors were doped by 1 and 2 wt.% of Ag nanoparticles with different sizes. Samples were characterized with XRD, SEM and EDX measurements. Critical current measurements were performed using a standard four-probe technique at liquid nitrogen temperature. The results showed by increasing of Ag nanoparticles up to 700 nm the Jc increases, but decreases by further increase in Ag particles size. The critical current enhancement is attributed to the improved connectivity between the grain boundaries and better crystallization of the grains.

Mansoor Farbod

Papers

Synthesis of TiO2 nanoparticles by a combined sol–gel ball milling method and investigation of nanoparticle size effect on their photocatalytic activities

Stability and thermal conductivity of water-based carbon nanotube nanofluids

Morphology dependence of thermal and rheological properties of oil-based nanofluids of CuO nanostructures

Doping effect of Ag nanoparticles on critical current of YBa2Cu3O7−δ bulk superconductor

Effects of initial graphite particle size and shape on oxidation time in graphene oxide prepared by Hummers' method