Recently, one-dimensional (1D) ZnO nanomaterials (NMs) have been extensively studied because both their functional properties and highly controllable morphology make them important building blocks for understanding nanoscale phenomena and realizing nanoscale devices. Compared with high temperature (>450 degrees C) vapor phase methods, solution-based synthesis methods can be conducted at low temperatures (25-200 degrees C) allowing for compatibility with many organic substrate materials and offer additional advantages such as straightforward processing, low cost, and ease of scale up. Although there exist several review articles in the literature regarding the synthesis and applications of 1D ZnO NMs, those focusing on solution-based synthesis methods are lacking. Thus, this review focuses mainly on 1D ZnO NMs synthesized by solution-based processing. Firstly, 1D ZnO non-patterned, nanoparticle-seeded synthesis and its associated solution growth kinetics are discussed. Next, synthesis of vertically-aligned ZnO nanorod arrays with controlled pattern and density on various substrates is reviewed. Finally, important applications of 1D ZnO NMs are highlighted including sensors, field emission devices, photodetectors, optical switches, and solar cells.

In this communication, we reported for the first time an ultrasensitive nanostructrued sensor that can detect 50 ppt of NH 3 gas in air. Specifically, nanograins of a p-type conductive polymer, polyaniline (PANI), are enchased on an electrospun n-type semiconductive TiO 2 fiber surface. The resistance of the p-n heterojunctions combining with the bulk resistance of PANI nanograins can function as electric current switches when NH 3 gas is absorbed by PANI nanoparticles. As a result, the sensor sensitivity can be significantly improved. The sensor fabricated in this work is 1000 times more sensitive than the best PANI sensor reported in the literature.* To whom the correspondence should be addressed, yulin.deng@ chbe.gatech.edu (Y. Deng).

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ZnO nanorods were synthesized via a solution synthesis method with temperatures ranging from 55 to 85 °C. The nanorods have a hexagonal cross-section length of 200−300 nm. Powder X-ray diffraction analysis showed the nanorods are single crystal materials. Using inductively coupled plasma technique, the Zn2+ concentration in solution was analyzed and the lengths of the nanorods were obtained from a SEM micrograph with ImageJ software. The concentration of Zn2+ could be described with a first-order reaction mechanism. Nanorod length analysis showed that lower temperature was beneficial to nanorod growth and high temperature resulted in a competition between nucleation and nanorod growth. With some reasonable assumptions, the correlation between the concentration of zinc ions and the length of nanorods was developed. The simple kinetics model developed in this paper agrees with the experimental results very well for low-temperature reaction, at which the nucleation could be ignored. However, at high temperature, due to the competition of nucleation with the particle growth, the experimental results deviate from the model prediction.