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China-US team develops inkjet-printing assisted method for high-throughput generation of catalyst libraries
19 October 2012
|Inkjet printing assisted cooperative-assembly (IJP-A) synthesis uses stabilized “inks”, a specially modified color management system, and multidimensional group testing rapidly to identify optimal catalysts. Credit: ACS, Liu et al. Click to enlarge.|
A team from Zhejiang University (China) and the University of California, Santa Barbara have developed an inkjet printing assisted cooperative-assembly technique for ultrafast explorations in combinatorial chemistry. The system can precisely synthesize up to eight-component meso-structured metal oxides catalysts at a rate of 1,000,000 formulations per hour.
The method can also be applied to explore most multiple-component metal oxides, metal sulfides, metal nitrides, and metal complexes for functional materials and establish composition-structure−property relationships. The technique should have immediate practical implications and advantages for addressing biology, energy, and environment challenges, the team suggests in a paper published in the ACS journal Nano Letters.
In the paper, they describe the system and its application to identify rapidly an inexpensive and efficient quaternary catalyst for photocatalytic hydrogen evolution.
Heterogeneous catalysis is of vital importance in our society and constitutes a cornerstone of life from biological processes to the large-scale production of bulk chemicals. A promising candidate family for heterogeneous catalysis is that of the mesoporous metal oxides (MMOs). The MMOs possess high internal surface areas, variable pore sizes, and designable pore networking that can be used for the support of a wide variety of active sites and supported catalyst species, as well as the reactant/product residence time control that is required for the creation of highly selective and high-yield catalysts. Because of the sensitivity of catalytic performance to catalyst structural, electronic, and compositional variables, catalyst design and optimization is a formidable challenge.
We believe that developing an improved high-yield synthetic route to produce multi-component mesoporous metal oxides (MMMOs) integrated with an efficient screening strategy would greatly enable the design and discovery of high-performance solid-state catalysts.
...Among the synthesis techniques, inkjet printing has been widely and actively used for the high-throughput nano-fabrication of materials. However, only a few inorganic materials can be inkjet printed, due to the dissimilar condensation kinetics and chemistry of the precursors of metal species leading to difficulty in preparing inkjet-printable precursors. In addition, redox reactions and phase transformations, including bulk crystallization, can limit the stability of complexes at elevated temperatures.—Liu et al.
The team used a nanoparticle sol−gel cooperative-assembly system to formulate the inorganic precursor inks for inkjet printing assisted cooperative-assembly (IJP-A) synthesis. The ink system consists of an amphoteric nonaqueous solvent, metal species, and block-copolymers to optimize the performance of the ink. By using traditional nonaqueous solvents and complexing ligands such as acids to control growth and condensation kinetics, the team found that ink solutions can form stable colloidal nanoparticles that are mono-dispersed in size for most common metal precursors.
The colloidal nanoparticles serve as building blocks and can be cooperatively assembled with each other, with elemental inorganic species, and with appropriate co-solvents, block copolymers, or surfactants to form the desired meso-structured library.
With a selection of metal species stabilized in the ink system, a large number of compounds can be easily and reproducibly obtained by inkjet printing.
Block-copolymers...co-assembled with metal ions and nanoparticles are used as structure-directing agents (SDA), as binders to template a variety of high surface area mesoporous structures of metal oxides (2−50 nm) and also to formulate a high quality “ink” solution. Over 25 different single-element formulations of colloidal nanoparticles, and/or a large number of composition combinations of these elements, can be made into colloidal ink. This ink formulation is a major breakthrough that makes it possible to meet the stringent requirements for the IJP-A technique.—Liu et al.
They also input a series of CMYK (cyan, magenta, yellow, black) color images into the color-management software for printing the compositional variation of the libraries. The color-management system includes an “Absolute Colorimetric” profile to create a one-to-one output between the “percent value” of each color in an image and the “printing volume” of each ink and a “Multichannel Combiner” to extend the printable space. This printing process is programmed and reproducible.
They also developed a “Multichannel Combiner” function to merge two CMYK images (C1M1Y1K1 + C2M2Y2K2) into a new image (C′M′Y′K′) that does not have any overlaps with its precursor inks. By doing so, they were able to double the capability of the IJP-A system to eight metal components. In principle, the number of components that can be synthesized is equal to the number of channels of the printer head.
To accelerate the discovery process of the optimal catalyst, they proposed a multi-dimensional group testing strategy, achieving a 25,000-fold reduction in the number of performance validation experiments over an exhaustive one-by-one search.
Xiaonao Liu, Yi Shen, Ruoting Yang, Shihui Zou, Xiulei Ji, Lei Shi, Yichi Zhang, Deyu Liu, Liping Xiao, Xiaoming Zheng, Song Li, Jie Fan, and Galen D. Stucky (2012) Inkjet Printing Assisted Synthesis of Multicomponent Mesoporous Metal Oxides for Ultrafast Catalyst Exploration. Nano Letters doi: 10.1021/nl302992q
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