Changzi Jin

Prussian blue/TiO2 nanocomposites as a heterogeneous photo-Fenton catalyst for degradation of organic pollutants in water

Nowadays, a lot of research focuses on accelerating FeII/FeIII redox cycles to increase the pseudo first-order rates of the Fenton reaction. Here, Prussian blue/titanium dioxide nanocomposites (PB/TiO2 NPs) were designed as heterogeneous photo-Fenton catalysts to increase the FeII recovery in degrading organic contaminants in water for the first time. The PB/TiO2 NPs were characterized by various analytical techniques to obtain the optimum ratio of PB and TiO2 for efficient degradation of organics. The performance of the catalysts was tested by following the removal of rhodamine B dye, salicylic acid, m-cresol, and isophorone under various conditions (pH, ratios of PB and TiO2, H2O2, and temperature). Formation of the intermediates of iron (FeII/FeIII) in the studied system using Mossbauer spectroscopy was explored for the first time and presents important insights into the relevant catalytic phenomena. The generation of ˙OH radicals in the reaction system was identified using electron paramagnetic resonance spectroscopic techniques. Results demonstrated that the developed PB/TiO2 NPs were stable and could degrade organic contaminants in water efficiently.

Ultrastable Hydroxyapatite/Titanium‐Dioxide‐Supported Gold Nanocatalyst with Strong Metal–Support Interaction for Carbon Monoxide Oxidation

Supported Au nanocatalysts have attracted intensive interest because of their unique catalytic properties. Their poor thermal stability, however, presents a major barrier to the practical applications. Here we report an ultrastable Au nanocatalyst by localizing the Au nanoparticles (NPs) in the interfacial regions between the TiO2 and hydroxyapatite. This unique configuration makes the Au NP surface partially encapsulated due to the strong metal-support interaction and partially exposed and accessible by the reaction molecules. The strong interaction helps stabilizing the Au NPs while the partially exposed Au NP surface provides the active sites for reactions. Such a catalyst not only demonstrated excellent sintering resistance with high activity after calcination at 800 °C but also showed excellent durability that outperforms a commercial three-way catalyst in a simulated practical testing, suggesting great potential for practical applications.

Visible-light-induced photocatalysis and peroxymonosulfate activation over ZnFe2O4 fine nanoparticles for degradation of Orange II

Refractory and non-biodegradable pollutants produced by industries have inevitably brought great threat to human life. Integrating several kinds of advanced oxidation processes (AOPs) into one system has been proposed to be an efficient strategy to remove such pollutants from the environment at low cost. In this study, magnetic zinc ferrite fine nanoparticles, firstly synthesized by a novel soft chemical solution process, showed super reactivity, good reusability and easy separation ability for visible-light-induced Orange II degradation in an integrated ZnFe2O4/PMS (peroxymonosulfate, 2KHSO5·KHSO4·K2SO4, OXONE) aqueous system. Powder X-ray diffraction, transmission electron microscopy, and 57Fe Mossbauer and X-ray photoelectron spectroscopy were employed to characterize the structure and morphology as well as recognize the physicochemical changes of the fine nanoparticles before and after the reaction. The generated oxidizing intermediates during the degradation process were detected by electron paramagnetic resonance spectroscopy and classic quenching experiments, which confirmed that both sulfate radical (SO4˙−) and hydroxyl radical (˙OH) co-existed in the degradation process. The systematic condition experiments further verified the dual functionality of the ZnFe2O4/PMS system, which actively acted as a photocatalyst and a PMS activator for dye molecule oxidation under visible light irradiation. This study proves that photocatalysis and PMS activation for remediation of organic pollutants in water can be easily integrated into one system by using zinc ferrite nanoparticles as an environmentally friendly catalyst.

Earth-abundant and nano-micro composite catalysts of Fe3O4@reduced graphene oxide for green and economical mesoscopic photovoltaic devices with high efficiencies up to 9%

The ideal liquid–solid heterogeneous electrocatalysis should have not only high catalytic activity but also free electron transport. However, preparing a single catalyst that simultaneously possesses both advantages has proven to be challenging. Herein, we prepared nano–micro composite catalysts (NMCCs) composed of highly dispersed Fe3O4 nanoparticles fixed on reduced graphene oxide (RGO) sheets (namely Fe3O4@RGO-NMCC) as the counter electrode (CE) in dye-sensitized solar cells (DSCs). Compared with the Fe3O4 or RGO CE, the Fe3O4@RGO-NMCC CE exhibited improved activity and reversibility for the catalytic reduction of triiodide ions (I3−) to iodide ions (I−). Notably, DSCs using rigid and flexible Fe3O4@RGO-NMCC CEs achieved high PCEs up to 9% and 8% on fluorine-doped tin oxide (FTO)/glass substrates and flexible polymer substrates, respectively. These values are, to our knowledge, some of the highest reported efficiencies for DSCs based on a flexible Pt-free CE. We ascribed the superior catalytic performance of Fe3O4@RGO-NMCC to faster electron hopping between Fe2+ and Fe3+ and free electron transport by broad RGO sheets. Finally, Fe3O4@RGO-NMCC exhibited good stability in the practical application of DSCs because Fe3O4 nanoparticles were chemically bonded to the surface of RGO. Our work here will be of great interest for fundamental research and practical applications of Fe3O4 in lithium batteries, splitting water and magnetic fields.

Magnetic iron oxide nanoparticles coated by hierarchically structured silica: a highly stable nanocomposite system and ideal catalyst support

A well-defined core–shell nanocomposite with magnetic iron oxide nanoparticles coated by a hierarchically structured silica shell has been synthesized through a sol–gel process and pseudomorphic transformation. The prepared materials were characterized by means of transmission electron microscopy, small and wide angle X-ray diffraction, Mossbauer spectroscopy and N2 physical adsorption–desorption. It has been shown that the core–shell nanocomposite possesses a magnetic core in the form of Fe3O4 or γ-Fe2O3 and a unique hierarchically structured silica shell consisting of an inner nonporous shell and outer shell with hierarchical pores. As a result, this nanocomposite exhibits high stability (acid resistance) and a large surface area (447 m2 g−1), which will be especially suitable for use as catalyst supports. To demonstrate this point, a functional catalyst consisting of small Pt nanoparticles well-dispersed on the porous surface of the magnetic core–shell nanocomposite was fabricated. In the hydrogenation of nitrobenzene and 2-nitrochlorobenzene to the corresponding aniline compounds, the hierarchically porous catalyst showed superior performances to its counterpart with a monomodal porous structure. In addition, the used catalyst could be separated conveniently from the reaction system with an external magnetic field. Subsequent recycling tests further confirmed the outstanding reusability and regeneration ability of the composite catalyst.

Classical strong metal–support interactions between gold nanoparticles and titanium dioxide

The classical strong metal–support interaction between TiO2 and IB metals was demonstrated. Supported metal catalysts play a central role in the modern chemical industry but often exhibit poor on-stream stability. The strong metal–support interaction (SMSI) offers a route to control the structural properties of supported metals and, hence, their reactivity and stability. Conventional wisdom holds that supported Au cannot manifest a classical SMSI, which is characterized by reversible metal encapsulation by the support upon high-temperature redox treatments. We demonstrate a classical SMSI for Au/TiO2, evidenced by suppression of CO adsorption, electron transfer from TiO2 to Au nanoparticles, and gold encapsulation by a TiOx overlayer following high-temperature reduction (reversed by subsequent oxidation), akin to that observed for titania-supported platinum group metals. In the SMSI state, Au/TiO2 exhibits markedly improved stability toward CO oxidation. The SMSI extends to Au supported over other reducible oxides (Fe3O4 and CeO2) and other group IB metals (Cu and Ag) over titania. This discovery highlights the general nature of the classical SMSI and unlocks the development of thermochemically stable IB metal catalysts.

A novel approach for the preparation of phase-tunable TiO2 nanocomposite crystals with superior visible-light-driven photocatalytic activity

Abstract A series of novel TiO2 nanocomposite crystals with superior visible-light-driven photocatalytic activity were successfully prepared using a soft chemical solution process involving direct reaction of aqueous H2O2 with a 2-ethoxyethanol solution of tetraisopropyl titanate before calcination of the resulting peroxo-titanium complexes at 500 °C for 4 h. The synthesized TiO2 samples are composed of anatase and rutile phases, and the ratio of rutile could be continuously tuned from 0 to 96% by altering the 2-ethoxyethanol volume. There are clear red-shifts in the UV-Vis absorption spectra and apparent band gap narrowing for the synthesized TiO2 in comparison with Evonik P-25. The synthesized TiO2 samples are found to be much more efficient for methylene blue degradation under visible-light irradiation. The optimized sample (2-ethoxyethanol: 5 ml; rutile in bulk: 46%) exhibits 5-fold higher adsorption capacity and 3-fold higher photocatalytic activity than those of Evonik P-25 (λ ≥ 400 nm). Characterizations including X-ray diffraction and Raman spectroscopy reveal that the surface of the optimized TiO2 sample only contains a small quantity of rutile. It is concluded that the surface phase composition and distribution of the TiO2 nanocomposite crystals are essential to their greatly enhanced photocatalytic activities and strong adsorption capacities. In addition, the concentration of defects existing in the synthesized TiO2 is also regarded to account for these enhanced properties.

Bridging Dealumination and Desilication for the Synthesis of Hierarchical MFI Zeolites

The rational design of zeolite-based catalysts calls for flexible tailoring of porosity and acidity beyond micropore dimension. To date, dealumination has been applied extensively as an industrial technology for the tailoring of zeolite in micropore dimension, whereas desilication has separately shown its potentials in the creation of mesoporosities. The free coupling of dealumination with desilication will bridge the tailoring at micro/mesopore dimensions; however, such coupling has been prevailingly confirmed as an impossible mission. In this work, a consecutive dealumination-desilication process enables the introduction of uniform intracrystalline mesopores (4-6 nm) into the microporous Al-rich zeolites. The decisive impacts of steaming step have been firstly discovered. These findings revitalize the functions of dealumination in porosity tailoring, and stimulate the pursuit of new methods for the tailoring of industrially relevant Al-rich zeolites.

One-step synthesis of nanorod-aggregated functional hierarchical iron-containing MFI zeolite microspheres

Novel hierarchical iron-containing MFI zeolite microspheres composed of oriented-assembled nanorods were prepared through a one-step hydrothermal crystallization without a mesoporous template agent. This is the first report on constructing functional hierarchical zeolite microspheres with aggregated MFI nanorods and well-dispersed α-Fe2O3 nanoparticles by adding glucose into the synthetic system. The obtained samples were characterized by powder XRD, N2 physical adsorption–desorption, FT-IR spectroscopy, UV-vis spectroscopy, XPS spectroscopy and Mossbauer spectroscopy. The results show that the microspheres possess uniform diameters from 4 to 5 μm, a hierarchical porous structure, a high surface area (502 m2 g−1), and well-dispersed ultrafine α-Fe2O3 nanoparticles. More importantly, the microspheres have been shown to have an excellent catalytic performance for the photocatalytic degradation of phenol. Thus, this synthesis method opens up routes for the in situ preparation of other functional porous materials with unique nanostructures.

Zinc-modulated Fe-Co Prussian blue analogues with well-controlled morphologies for the efficient sorption of cesium

Prussian blue analogues (PBAs) with tunable compositions and morphologies have demonstrated great potential in many applications. We successfully synthesized a series of KFexZn1−x[Co(CN)6] (FexZn1−x–Co) PBAs with well-controlled compositions and morphologies and used them as adsorbents for the removal of Cs+ ions. The increase of Zn : Fe ratio had a significant influence on the final morphology and improved the sorption capacity for Cs. X-ray diffraction and X-ray absorption fine structure spectra were used to confirm that the Cs+ ions were inserted into the crystal channels rather than simply adsorbed on the surface of the PBAs. Based on the quantitative correlation between the concentration of ions released from the PBAs and the Cs+ ions adsorbed, the mechanism of Cs+ sorption in the FexZn1−x–Co PBAs was studied and a Zn2+-modulated Cs+ sorption model, which illustrated the difference in sorption behavior between the FexZn1−x–Co PBAs, was proposed and confirmed by FTIR spectra, extended X-ray absorption fine structure spectra and 57Fe Mossbauer spectra. The results indicated that the FexZn1−x–Co PBAs are excellent candidates for the removal of radioactive 137Cs from nuclear waste.