Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

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Dye-Sensitized Solar Cells

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Recent developments have greatly improved the sensitivity of optical sensors based on metal nanoparticle arrays and single nanoparticles. We introduce the localized surface plasmon resonance (LSPR) sensor and describe how its exquisite sensitivity to size, shape and environment can be harnessed to detect molecular binding events and changes in molecular conformation. We then describe recent progress in three areas representing the most significant challenges: pushing sensitivity towards the single-molecule detection limit, combining LSPR with complementary molecular identification techniques such as surface-enhanced Raman spectroscopy, and practical development of sensors and instrumentation for routine use and high-throughput detection. This review highlights several exceptionally promising research directions and discusses how diverse applications of plasmonic nanoparticles can be integrated in the near future.

Biosensing with plasmonic nanosensors

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

Designing advanced nonprecious metal electrocatalysts to reduce overpotential and accelerate hydrogen evolution reaction (HER) has attracted considerable attention. However, improving the sluggish kinetics for electrocatalytic HER in alkaline media is still a great challenge. Herein, we found that amorphous NiO nanoclusters directly grown on nickel foam (NiO/NF) as a bifunctional HER catalyst demonstrated an ultrahigh electrocatalytic activity in alkaline environment. Such excellent HER performance of NiO/NF might mainly originate from the exposed interfaces of metallic Ni and amorphous NiO. The coordinatively unsaturated amorphous NiO domain is propitious to the adsorption of water molecule and the successive cleavage of HO–H bond, while the neighboring metallic Ni domain is beneficial to the adsorption of resulting Hads intermediate and recombination into hydrogen molecules, thus expediting the HER toward lower overpotential. These findings may open a window to the design and preparation of earth-abundant, low-cost metal oxide/metal electrocatalysts with desirable HER activities.

Enhanced electrocatalytic hydrogen evolution activity of nickel foam by low-temperature-oxidation

Zeolite membranes have gained much attention in recent years, due to their potential application in various fields such as catalysis, gas separation, pervaporation, etc. [1–4]. There are many reports on the synthesis, characterization and applications of zeolite membranes [1–4], but literatures about the formation mechanism of zeolite membrane are fewer [5–7]. To prepare zeolite membranes, many methods have been developed, including hydrothermal crystallization [8], vapor phase synthesis [9], and microwave heating [10, 11]. It was reported that microwave heating and crystal seeding could help the formation and improve the performance of zeolite membranes [10]. It was proposed that the formation of zeolite membranes included the following three stages: sol or gel adhesion on the substrate to form the gel layer, the nucleation and crystallization stage, and the dissolving stage [10, 12, 13]. However, there are few reports on the direct observation of these stages, especially under microwave radiation. In this report, by using scanning electron microscopy (SEM), the formation stages of zeolite NaA membrane in microwave radiation environment were observed and confirmed with the results from X-ray diffraction (XRD) and gas permeation measurements. The disk shaped substrates (30 mm in diameter, 3 mm in thickness) used were porous α-Al2O3 made by casting, with pore radius of 0.3–0.5 μm and ca. 50% porosity. The precursor of the gel was prepared by mixing sodium hydroxide, sodium aluminate, water glass and water, and aging for 24 h with vigorous stirring. The final molar composition of the gel was 3Na2O: Al2O3: 2SiO2: 200H2O. After one face of the substrates was rubbed with zeolite NaA crystals as seeds, the substrates were put vertically in Teflon vessels containing 120 ml gel. Then the vessels were transferred into a microwave oven, heated up to 90 ◦C within 1 min, and reacted for a range of specified times. After the reaction, the membranes were vigorously ultrasonically vibrated in water for 10 min to remove the species physically absorbed on the substrates, washed by de-ionized water to pH = 7.0 and dried at 150 ◦C for 3 h. The membranes were characterized by scanning electron microscopy (SEM) on a JEM-1200E scanning electron microscope and Xray diffraction (XRD) using Cu Kα (λ = 0.154 nm) radiation operating at 40 kV and 100 mA on a Rigaku D max /b powder diffractometer. The integrity of the membrane was evaluated with gas permeation tests.

Characterization of the formation of NaA zeolite membrane under microwave radiation

ZnSe photocatalytic films made of $$ \left\{ {000 1} \right\} $$
 -ended microdisks and $$ \left\{ {2\overline{1} \overline{1} 0} \right\} $$
 -ended nanobelts have been successfully synthesized via a solvothermal route followed by annealing in Ar atmosphere. Zn foils are used as both the Zn source and the substrate, Se powder as the Se source, and ethylenediamine (en) as the solvent. Lower temperature and Se concentration prefers the formation of $$ \left\{ {000 1} \right\} $$
 -faceted ZnSe microdisks, while higher temperature and Se concentration leads to the formation of $$ \left\{ {2\overline{1} \overline{1} 0} \right\} $$
 -faceted ZnSe nanobelts. Photoluminescence spectra show that both samples exhibit a visible-light emission, and ZnSe microdisks have more defects than ZnSe nanobelts. ZnSe microdisks have a superior photocatalytic activity over ZnSe nanobelts in the degradation of rhodamine B under visible light. The higher photocatalytic activity of ZnSe microdisks is attributed to larger amount of $$ \left\{ {000 1} \right\} $$
 facets and defects in the ZnSe microdisks.

Synthesis of ZnSe microdisks and nanobelts and their visible-light photocatalytic properties

Polymer electrolyte membrane fuel cells (PEMFCs) are energy conversion devices that produce electricity from a supply of fuel, such as hydrogen. One of the major challenges in achieving efficient energy conversion is the development of cost-effective materials that can act as electrocatalysts for PEMFCs. In this letter, we demonstrate that, instead of conventional noble metals, such as platinum, chromium nitride nanocrystals of fcc structure exhibit attractive catalytic activity for PEMFCs. Device testing indicates good stability of nitride nanocrystals in low temperature fuel cell operational environment.

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Proton exchange membrane fuel cells with chromium nitride nanocrystals as electrocatalysts

CdSe and CdSe/CdS core/shell nanoparticles were prepared by a one-pot synthesis process. The CdSe/CdS core/shell nanoparticles showed red-shift absorption and emission spectra compared to the CdSe core. An optimal reaction time for CdS to form on the CdSe nanoparticles was evaluated and the highest photoluminescence yield of approximately equal to 20% was observed for the core/shell nanoparticles. Using nanosecond laser spectroscopy, the photoluminescence of CdSe nanoparticle was investigated and found to exhibit a monoexponential decay with a lifetime of 52.2 ns, while the photoluminescence of CdSe/CdS core/shell nanoparticles demonstrated biexponential decay characterised by a fast component around 25 ns and a slow component around 100 ns. The Stokes shift, photoluminescence yield, and lifetimes were correlated and attributed to the stress in the interface induced by the lattice mismatch of CdSe and CdS. The red-shift of the absorption and emission spectra of CdSe/CdS nanoparticles was discussed with the concepts of the quantum confinement and electronic confinement effects.

Xiaobo Chen

Papers

Enhanced electrocatalytic hydrogen evolution activity of nickel foam by low-temperature-oxidation

Characterization of the formation of NaA zeolite membrane under microwave radiation

Synthesis of ZnSe microdisks and nanobelts and their visible-light photocatalytic properties

Proton exchange membrane fuel cells with chromium nitride nanocrystals as electrocatalysts

Spectroscopic investigation of II–VI core-shell nanoparticles: CdSe/CdS