Enhanced Photocatalytic Oxidation of Isopropanol ... - ACS Publications

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Enhanced Photocatalytic Oxidation of Isopropanol by HKUST-1@TiO2 Core-shell Structure with Ultrathin Anatase Porous Shell: Toxic Intermediate Control Hongmei Wang, Tao Yu, Xin Tan, Huabin Zhang, Peng Li, Huimin Liu, Li Shi, Xiangli Li, and Jinhua Ye Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b01400 • Publication Date (Web): 01 Jul 2016 Downloaded from http://pubs.acs.org on July 5, 2016

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Industrial & Engineering Chemistry Research

Enhanced Photocatalytic Oxidation of Isopropanol by HKUST-1@TiO2 Core-shell Structure with Ultrathin Anatase Porous Shell: Toxic Intermediate Control †

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Hongmei Wang, Tao Yu, †

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Xin Tan, Huabin Zhang, Peng Li, Huimin Liu, Li Shi,

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Xiangli Li and Jinhua Ye

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School of Environmental Science and Engineering, Tianjin University, 92 Weijin Road, Nankai

District, Tianjin300072,China ‡

School of Chemical Engineering and Technology, Tianjin University, 92 Weijin Road, Nankai

District, Tianjin300072,China #

School of Science, Tibet University, Lhasa 850000, Tibet, China

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TU-NIMS Joint Research Center, School of Materials Science and Engineering, Tianjin

University, 92 Weijin Road, Nankai District, Tianjin 300072,China

ACS Paragon Plus Environment

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Environmental Remediation Materials Unit, International Center for Materials

Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Japan KEYWORDS: HKUST-1, TiO2, Photocatalytic oxidation, Isopropanol, Toxic intermediate control ABSTRACT: Poor adsorption of reactants and intermediates as well as low mineralization rate greatly restricts the application of common semiconductor photocatalyst TiO2 for air purification. A plausible solution would be to integrate Metal–organic frameworks (MOFs) materials with good gas adsorption property with traditional photocatalytic material TiO2 with exciton generation. A core-shell structured photocatalyst with functional MOFs HKUST-1(Cu3(BTC)2, BTC=1,3,5 benze-netricarboxylate) as core and porous ultrathin anatase film as shell was synthesized. The composite photocatalyst was characterised in detail and isopropanol degradation experiments were performed to evaluate the photocatalytic performances. The experimental results revealed that HKUST-1 can provide an especial pathway for photogenerated electrons migration and thus restrain the recombination of electrons and holes to increase the photocatalytic efficiency. Furthermore, the capture of reactants and intermediates was also enhanced due to the unique MOFs-TiO2 composite structure and the mineralization rate had been markedly enhanced. 1. INTRODUCTION The extensive uses of volatile organic compounds (VOCs) lead to air pollution1. And the air pollutants impact human health, comfort and productivity. Adsorption by activated carbon merely transfers pollutants from gaseous phase to the solid phase rather than decomposing them2. Thermal oxidation requires high temperatures for efficient operation3. Biofiltration is slow in


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speed and has no obvious effect. None of these techniques is decisively cost-effective for the gas stream with low concentration and large numbers of compounds species besides their inherent limitations4 as above. Photocatalysis can degrade a broad range of contaminants into innocuous final products such as CO2 and H2O without significant energy input5, so it shows great advantages in the application of air purification. TiO2 is considered to be one of the most promising photocatalyst for practical application because of its superior photocatalytic activity, chemical stability, low cost, and nontoxicity6, 7. But there are still some shortages for TiO2 to limit its applications as photocatalyst for air purification such as poor adsorption of reactants and intermediate products and low mineralization rate. The poor adsorption is one of the key factors which result in incomplete oxidation product—more toxic intermediate products. How to boost the complete degradation of VOCs into CO2 has easily become the main point of research efforts. It relies on that how to extend the residence time of reactants and intermediate products at active-site where more photo generated holes, which is important for the degradation process, can be accumulated. A plausible solution would be to integrate Metal–organic frameworks (MOFs) materials with good gas adsorption property with traditional photocatalytic material TiO2 with exciton generation. What’s more, this integrate can also promote photogenerated electrons transfer which can enhanced the photocatalytic activity. Metal–organic frameworks (MOFs) are an attractive class of porous coordination polymers consist of a metal center (or poly-nuclear metal cluster) linked through organic components by coordination bonds to form crystalline structures. The advantages such as high specific surface areas, tuneable structures and containing various chemical functionalities, make them attractive in many areas recently like photocatalysis8-10, selective gas sorption11-14, and electrical conductivity15-18. Studies of applications in photocatalytic decomposition of water and photocatalytic reduction of CO2


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using composite materials combined MOFs with TiO2 have been reported and it is proved that photoexcited electrons can be effectively transferred from the semiconductor to the MOF19-23. But there are few reports about the application of this kind of material in photocatalytic degradation of VOCs. In this paper, a typical MOFs, HKUST-1(Cu3(BTC)2, BTC= benzene-1,3,5-tricarboxylate), was chosen as support because it has a better selective adsorption of the intermediates and it can restrain the recombination of electrons and holes by transferring electrons away from TiO2, in addition, its stability is much better than many other MOFs materials and its 3D structure remains relatively stable24-26 during the processes of the composite material preparation and photocatalytic degradation. A core-shell structured constructed by depositing ultrathin porous layer of anatase on HKUST-1 to boost the complete degradation of VOCs into CO2 by TiO2. Isopropanol (IPA), a kind of typical VOCs, has been well studied before and the process of its photocatalytic degradation was well known. Acetone is the main intermediate product which is not wished to be seen in the application of air purification because it is more toxic than IPA itself. So we selected IPA as the target reactant to explore the impact of HKUST-1@TiO2 core-shell structure on the process of photocatalytic degradation of VOCs. We speculate that the degradation rate of IPA can be increased significantly and the production of CO2 can be enhanced. The introduction of innovative materials MOFs can be a new idea of designing composite materials for promoting the application of photocatalysis technique for VOCs air pollution in semi-hermetic systems and hermetic systems if the speculation is proper.


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2. MATERIAL AND METHODS 2.1. Synthesis of HKUST-1. In a standard synthesis, Cu(NO3)2·3H2O (Wako Pure Chemical Industries Ltd) was dissolved in 15 mL distilled water, 1.5 g of polyvinyl pyrrolidone ( PVP, M.W. = 29000, Sigma-Aldrich) was dissolved in 15 mL ethanol and stirred for 15 min, and 1,3,5-H3BTC(2.0mmol, 0.42g, Wako Pure Chemical Industries Ltd) was dissolved in the solution for 15 min, then the solution of Cu(NO3)2·3H2O was slowly added to the solution of 1,3,5-H3BTC. The mixture was stirred for 1 h. The mixture was transferred into a 50 mL teflon-lined stainless steel autoclave and kept at 120°C for 12 h in oven to yield HKUST-1 crystals. 2.2. Synthesis of HKUST-1@TiO2. HKUST-1crystals (25 mg) were dispersed in 50 mL ethanol. Then it was mixed with 250 µL of tetrabutyl titanate (Sigma-Aldrich). The dispersion was stirred at room temperature for 20 min, and then mixed with 3.5 mL of water and 105 µL of HF. The mixture was stirredat room temperature for another 20 min, then moved to a 100 mL Teflon autoclave liner and heated at 180 °C for 12 h. The resulting particles were isolated by centrifugation and washed with ethanol three times. Finally, the obtained powder was dried at 80 °C in vacuum. Pure TiO2 were prepared by the same synthetic method just without HKUST-1. 2.3. Characterization. X-ray Diffraction（XRD）patterns of the catalysts were recorded using powder X-ray diffraction (RINT-2000; Rigaku Corp., Japan) with Cu Kα radiation. The specific surface areas were determined with a surface area analyzer (BEL Sorp-II mini, BEL Japan Co., Japan) by the


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Brunauer-Emmett-Teller (BET) method. The diffuse reflectance spectra of the samples were recorded on a UV-visible spectrophotometer (UV-2600PC; Shimadzu Corp., Japan) with barium sulfate as the reference. Samples for transmission electron microscopy (TEM) analysis were prepared by drying a drop of nanocrystal dispersion in absolute ethanol on amorphous carbon– coated copper grids. High–resolution TEM (HRTEM) characterization was performed with a JEM-2100F (Japan) operated at 150 kV. SEM images were taken on a FEI Sirion 200 fieldemission scanning electron microscopy operated at 5 kV. The concentrations of various metals were measured with SII nano technology Inc. model SPS3520UV-DD (ICP-OES) after dissolving the samples in sulfuric acid. The samples were fused with K2S2O7. The melt was dissolved in sulfuric acid. SII nano technology Inc. model SPS3520UV-DD. 2.4. Photocurrent Test. The films were made by spin coating method. 2.5 mg sample was dispersed in 2.5 mL ethanol, and the dispersion was dropped to FTO conducting glass (1 cm×2 cm) which was rotated at 1500 rpm for 15 s by using spin coater. After depositing by spin coating, the film was dried at 60℃ for 8 h in vacuum to evaporate the solvent and remove organic residuals. The film was then inserted into a tube furnace and annealed in Ar at 150℃ for 1 h.

The photocurrent developed by irradiating the photoanode was performed with a CHI electrochemical analyzer (ALS/CH model 650A) using a standard three-electrode mode with 0.5M Na2SO4 solution as the electrolyte. Sample films were used as working electrodes; a Pt sheet served as counter-electrode. An Ag/AgCl (saturated KCl) electrode (RE-1C; BAS Inc.) served as the reference electrode. A 500W Xe lamp (Optical ModuleX, Ushio Inc.) with filter


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(400 nm

Enhanced Photocatalytic Oxidation of Isopropanol ... - ACS Publications

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