Shape-Tunable Hollow Silica Nanomaterials Based on a Soft- Templating Method and Their Application as a Drug Carrier Jiao Chen, † Xu Wu, † Xiaodong Hou, † Xingguang Su, ‡ Qianli Chu, † Nenny Fahruddin, † and Julia Xiaojun Zhao* ,† † Department of Chemistry, University of North Dakota, Grand Forks, North Dakota 58202, United States ‡ Department of Analytical Chemistry, College of Chemistry, Jilin University, Changchun 130012, P. R. China ABSTRACT: A one-step soft-templating method for synthesizing shape-tunable hollow silica nanomaterials was developed in a reliable and highly reproducible way. For the first time, both nonspherical and spherical shapes with hollow interiors, including nanowire, nanospheres, and nanotadpole, were successfully obtained by simply changing the solvent. Poly(vinylpyrrolidone) (PVP)-water droplets were used as soft templates for the formation of hollow structures, while three different solvents, including 1-propanol, 1-pentanol, and ethanol, led to the designed shapes. It was found that the solvent, the formation of PVP-water droplets, the amount of ammonia, and the reaction time had great effects on the morphology of synthesized hollow nanomaterials. The effect of various factors on the morphology was systematically studied to propose a growth mechanism. The obtained hollow silica nanomaterials showed excellent reproducibility and great potential for a large-scale synthesis. Finally, the application of the developed hollow silica nanomaterials was demonstrated using the hollow spherical silica nanoparticles. Its drug-carrying ability was studied. The results could be extended for doping various target molecules into the hollow structures for a broad range of applications. KEYWORDS: hollow silica nanomaterials, soft-templating, shape-tunable, PVP, solvent, drug carrier 1. INTRODUCTION Hollow silica nanomaterials (HSNs) have attracted noticeable attention because of their excellent biocompatibility, easy surface functionalization accessibility, good chemical inertness, and thermal stability. 1-8 They have been used in diverse fields including drug delivery, sensing, catalysis, and large biomo- lecular release. 9-11 The approaches for synthesizing HSNs can be broadly divided into two categories: hard templating 12-16 and soft templating. 17-19 The hard-templating method normally needs a layer of the desired materials coated on the surface of the template core, followed by the selective removal of the template. This approach has been widely used and proven to be effective for the synthesis of hollow nanomaterials with controllable shell thickness. However, tedious and complicated procedures are usually required, which are sometimes expensive and unsuitable for large-scale synthesis. Many efforts have been devoted to developing self-templating methods. In the soft-templating method, no additional templates are needed, and therefore it may have the advantage of a simple synthetic process and better scalability. For example, Wang and Zeng applied a novel microemulsion system to synthesize hollow silica nanoparticles, in which 1-dodecanethiol served as an oil phase in the “oil-in-water” emulsion and a soft template for the hollow interior. Moreover, the central space of the SiO 2 spheres was tunable by varying the amount of DDT. 20 On the other hand, the HSNs obtained by soft-templating methods are mostly spherical in morphology. The preparation of well-defined hollow nonspherical nanomaterials with tunable sizes and morphologies by hard-templating methods generally introduces additional challenges because of the difficulties in forming a uniform coating around high-curvature surfaces and the deficiency of appropriate nonspherical templates. There- fore, the ability to tune the structure, size, and morphology of the synthesized nanomaterials is an important goal in current material synthesis and device fabrication. 21,22 Recently, Chen et al. developed a method to synthesize silica nanotubes based on the thermolysis of silicon tetraacetate with the assistance of both hard and soft templates. 23 Wu et al. found that rodlike hollow silica particles could be obtained by using a surfactant mixture composed of zwitterionic and anionic surfactants as the templates with the assistance of a constructure-directing agent. 24 These nonspherical new members expand the versatility of the hollow nanomaterials family and bring some novel properties, functions, and potential applications. How- ever, the preparation of nonspherical nanomaterials generally requires strict reaction conditions in addition to high cost and Received: November 2, 2013 Accepted: December 3, 2014 Published: December 3, 2014 Research Article www.acsami.org © 2014 American Chemical Society 21921 dx.doi.org/10.1021/am507642t | ACS Appl. Mater. Interfaces 2014, 6, 21921-21930