2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

Semiconductor-based Photocatalytic Hydrogen Generation

Here, we present a review of the antibacterial effects of silver nanomaterials, including proposed antibacterial mechanisms and possible toxicity to higher organisms. For purpose of this review, silver nanomaterials include silver nanoparticles, stabilized silver salts, silver–dendrimer, polymer and metal oxide composites, and silver-impregnated zeolite and activated carbon materials. While there is some evidence that silver nanoparticles can directly damage bacteria cell membranes, silver nanomaterials appear to exert bacteriocidal activity predominantly through release of silver ions followed (individually or in combination) by increased membrane permeability, loss of the proton motive force, inducing de-energization of the cells and efflux of phosphate, leakage of cellular content, and disruption DNA replication. Eukaryotic cells could be similarly impacted by most of these mechanisms and, indeed, a small but growing body of literature supports this concern. Most antimicrobial studies are performed in simple aquatic media or cell culture media without proper characterization of silver nanomaterial stability (aggregation, dissolution, and re-precipitation). Silver nanoparticle stability is governed by particle size, shape, and capping agents as well as solution pH, ionic strength, specific ions and ligands, and organic macromolecules—all of which influence silver nanoparticle stability and bioavailability. Although none of the studies reviewed definitively proved any immediate impacts to human health or the environment by a silver nanomaterial containing product, the entirety of the science reviewed suggests some caution and further research are warranted given the already widespread and rapidly growing use of silver nanomaterials.

https://link.springer.com/content/pdf/10.1007%2Fs11051-010-9900-y.pdf

A review of the antibacterial effects of silver nanomaterials and potential implications for human health and the environment

Recent achievements in the construction of surfaces with special wettabilities, such as superhydrophobicity, superhydrophilicity, superoleophobicity, superoleophilicity, superamphiphilicity, superamphiphobicity, superhydrophobicity/superoleophilicity, and reversible switching between superhydrophobicity and superhydrophilicity, are presented. Particular attention is paid to superhydrophobic surfaces created via various methods and surfaces with reversible superhydrophobicity and superhydrophilicity that are driven by various kinds of external stimuli. The control of the surface micro-/nanostructure and the chemical composition is critical for these special properties. These surfaces with controllable wettability are of great importance for both fundamental research and practical applications.

Design and Creation of Superwetting/Antiwetting Surfaces

Heavy metal removal from water/wastewater by nanosized metal oxides: a review.

Hierarchical micropapillae and nanofolds are known to exist on the petals' surfaces of red roses. These micro- and nanostructures provide a sufficient roughness for superhydrophobicity and yet at the same time a high adhesive force with water. A water droplet on the surface of the petal appears spherical in shape, which cannot roll off even when the petal is turned upside down. We define this phenomenon as the “petal effect” as compared with the popular “lotus effect”. Artificial fabrication of biomimic polymer films, with well-defined nanoembossed structures obtained by duplicating the petal's surface, indicates that the superhydrophobic surface and the adhesive petal are in Cassie impregnating wetting state.

Petal Effect: A Superhydrophobic State with High Adhesive Force

A hexagonal-close-packed (hcp), hierarchical amorphous TiO2 nanocolumn array was fabricated by pulsed laser deposition (PLD) using a PS colloidal monolayer as a template under a high pressure (6.7 Pa) of background oxygen gas. The formation mechanism was investigated, and a model of multidirection glancing deposition was proposed to explain the formation process. This strategy can be extended to the fabrication of similar structures using different materials. Interestingly, this nanostructured array could be transferred to almost any substrate, avoiding restriction of substrate types in fabrication of nanocolumn arrays, which is helpful in the design and creation of nanodevices on various desired substrates. This hierarchical nanocolumn array exhibits excellent superamphiphilicity with both water and oil contact angles of 0 degrees, without further UV irradiation. More importantly, the amorphous TiO2 nanocolumn array demonstrates better performance in photocatalytic activity than an anatase nanocolumn array due to its large surface area and special microstructures, suggesting that the surface area of the TiO2 is preferable to its crystal structure for enhancing photocatalytic activity. The combination of superamphiphilicity and photocatalytic activity gives the surface an excellent self-cleaning effect.

Hexagonal-close-packed, hierarchical amorphous TiO2 nanocolumn arrays: transferability, enhanced photocatalytic activity, and superamphiphilicity without UV irradiation.

Superhydrophobic bionic surfaces with hierarchical micro/nano structures were synthesized by decorating single-walled or multiwalled carbon nanotubes (CNTs) on monolayer polystyrene colloidal crystals using a wet chemical self-assembly technique and subsequent surface treatment with a low surface-energy material of fluoroalkylsilane. The bionic surfaces are based on the regularly ordered colloidal crystals, and thus the surfaces have a uniform superhydrophobic property on the whole surface. Moreover, the wettability of the bionic surface can be well controlled by changing the distribution density of CNTs or the size of polystyrene microspheres. The morphologies of the synthesized bionic surfaces bear much resemblance to natural lotus leaves, and the wettability exhibited remarkable superhydrophobicity with a water contact angle of about 165° and a sliding angle of 5°.

Superhydrophobic Bionic Surfaces with Hierarchical Microsphere/SWCNT Composite Arrays

Besides the traditional lithographical techniques to fabricate the ordered mciro/nanostructured arrays, the route of the monolayer colloidal crystal template is a recently promising, alternative process for the synthesis of the micro/nanostructures with different designed morphologies. By this strategy, two-dimensional ordered arrays, e.g., nanoparticle arrays, pore arrays, nanoring arrays, nanobowl arrays, hollow sphere arrays, etc., even one-dimensional nanostructures of ordered nanorod/nanopillar/nanowire arrays, etc., could be prepared. Recent progress in this area is reviewed, including synthesis strategies and morphology-dependent properties of the micro/nanostructured arrays such as optical properties, wettability, surface-enhanced Raman scattering, and photonic bandgap.

Ordered Micro/Nanostructured Arrays Based on the Monolayer Colloidal Crystals†

We present a facile synthetic route to a silver bowl-like array film with hierarchical structures on glass substrate using the colloidal monolayer as a template. In these special hierarchical structures, microstructures were provided by a colloidal template of polystyrene latex spheres and nanostructures resulting from the thermal decomposition of silver acetate. These structures were chemically modified with 1-hexadecanethiol, and a corresponding self-assembled monolayer (SAM) was formed on their surfaces. Due to the lotus leaf-like morphology with hierarchical micro/nanostructures, the film displayed an extraordinary superhydrophobicity after chemical modification. Water contact angle and sliding angle were 169° and 3° (the weight of water droplets:  3 mg), respectively. Additionally, its optical property has also been investigated. This structure could be used in microfluidic devices, optical devices, and biological science.

Yue Li

Papers

Hexagonal-close-packed, hierarchical amorphous TiO2 nanocolumn arrays: transferability, enhanced photocatalytic activity, and superamphiphilicity without UV irradiation.

Superhydrophobic Bionic Surfaces with Hierarchical Microsphere/SWCNT Composite Arrays

Ordered Micro/Nanostructured Arrays Based on the Monolayer Colloidal Crystals†

Silver Hierarchical Bowl-Like Array: Synthesis, Superhydrophobicity, and Optical Properties

Superhydrophobicity of 2D ZnO ordered pore arrays formed by solution-dipping template method.