29 research outputs found

    Synergetic Effect of MoS<sub>2</sub> and Graphene as Cocatalysts for Enhanced Photocatalytic H<sub>2</sub> Production Activity of TiO<sub>2</sub> Nanoparticles

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    The production of H<sub>2</sub> by photocatalytic water splitting has attracted a lot attention as a clean and renewable solar H<sub>2</sub> generation system. Despite tremendous efforts, the present great challenge in materials science is to develop highly active photocatalysts for splitting of water at low cost. Here we report a new composite material consisting of TiO<sub>2</sub> nanocrystals grown in the presence of a layered MoS<sub>2</sub>/graphene hybrid as a high-performance photocatalyst for H<sub>2</sub> evolution. This composite material was prepared by a two-step simple hydrothermal process using sodium molybdate, thiourea, and graphene oxide as precursors of the MoS<sub>2</sub>/graphene hybrid and tetrabutylorthotitanate as the titanium precursor. Even without a noble-metal cocatalyst, the TiO<sub>2</sub>/MoS<sub>2</sub>/graphene composite reaches a high H<sub>2</sub> production rate of 165.3 μmol h<sup>–1</sup> when the content of the MoS<sub>2</sub>/graphene cocatalyst is 0.5 wt % and the content of graphene in this cocatalyst is 5.0 wt %, and the apparent quantum efficiency reaches 9.7% at 365 nm. This unusual photocatalytic activity arises from the positive synergetic effect between the MoS<sub>2</sub> and graphene components in this hybrid cocatalyst, which serve as an electron collector and a source of active adsorption sites, respectively. This study presents an inexpensive photocatalyst for energy conversion to achieve highly efficient H<sub>2</sub> evolution without noble metals

    Amine-Functionalized Titanate Nanosheet-Assembled Yolk@Shell Microspheres for Efficient Cocatalyst-Free Visible-Light Photocatalytic CO<sub>2</sub> Reduction

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    Exploiting advanced semiconductor photocatalyst with superior activity and selectivity for the conversion of CO<sub>2</sub> into solar fuels and valuable chemicals is of worldwide interest. In this report, hierarchical amine-functionalized titanate nanosheets based yolk@shell microspheres were synthesized via one-pot organic amine mediated anhydrous alcoholysis of titanium­(IV) butoxide. The selected organic amine, diethylenetriamine, played multiple roles. First, it was essential for the crystallographic, morphological and textural control of the synthesized titanate nanoarchitectures. Second, it was crucial for the in situ functionalization of titanate nanosheets by concurrent interlayer intercalation and surface grafting, which gave rise to the strong visible-light absorption ability and high CO<sub>2</sub> adsorption capacity. As a consequence of the synergetic tuning in multilevel microstructures, an integrated engineering of the multifunctional modules of the titanate-based photocatalysts was achieved for efficient CO<sub>2</sub> reduction toward solar fuels

    A New Approach for Photocorrosion Inhibition of Ag<sub>2</sub>CO<sub>3</sub> Photocatalyst with Highly Visible-Light-Responsive Reactivity

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    A novel visible-light-responsive photocatalyst Ag<sub>2</sub>CO<sub>3</sub> was prepared by a facile precipitation reaction between NaHCO<sub>3</sub> and AgNO<sub>3</sub>. The as-prepared samples showed relatively high photocatalytic activity toward rhodamine B (RhB) degradation in aqueous solution. The observed photoreactivity on Ag<sub>2</sub>CO<sub>3</sub> was attributed to the synergetic effects of small band gap, great oxidation potential of photogenerated holes, and high separation efficiency of photogenerated electrons and holes. Nevertheless, Ag<sub>2</sub>CO<sub>3</sub> was unstable under visible light due to the photocorrosion resulting from metallic silver formation. The photocorrosion of Ag<sub>2</sub>CO<sub>3</sub> can be efficiently inhibited by adding AgNO<sub>3</sub> in the photocatalytic reaction system owing to the lower electrode potential of Ag/AgNO<sub>3</sub> than that of Ag/Ag<sub>2</sub>CO<sub>3</sub>. Our results shed new light on the photocatalytic activity as well as photocorrosion mechanism of silver-containing compounds and inhibit the method of photocorrosion

    Enhanced Photoinduced-Stability and Photocatalytic Activity of CdS by Dual Amorphous Cocatalysts: Synergistic Effect of Ti(IV)-Hole Cocatalyst and Ni(II)-Electron Cocatalyst

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    CdS is one of the most well-known and important visible-light photocatalytic materials for water splitting to produce hydrogen energy. Owing to its serious photocorrosion property (poor photoinduced stability), however, CdS photocatalyst can unavoidably be oxidized to form S<sup>0</sup> by its photogenerated holes, causing an obviously decreased photocatalytic performance. In this study, to improve the photoinduced stability of CdS photocatalyst, amorphous TiO<sub>2</sub> (referred to as Ti­(IV)) as a hole cocatalyst was successfully loaded on the CdS surface to prepare Ti­(IV)/CdS photocatalysts. It was found that the resultant Ti­(IV)/CdS photocatalyst exhibited an obviously enhanced photocatalytic stability, namely, its deactivation rate clearly decreased from 37.9% to 13.5% after five cycles of photocatalytic reactions. However, its corresponding photocatalytic activity only showed a very limited increase (ca. 37.4%) compared with the naked CdS. To further improve its photocatalytic performance, the amorphous Ni­(II) as an electron cocatalyst was subsequently modified on the Ti­(IV)/CdS surface to prepare the dual amorphous-cocatalyst modified Ti­(IV)–Ni­(II)/CdS photocatalyst. In this case, the resultant Ti­(IV)–Ni­(II)/CdS photocatalyst not only exhibited a significantly improved photocatalytic activity and stability, but also could maintain the excellent photoinduced stability of CdS surface structure. Based on the experimental results, a synergistic effect of dual amorphous Ti­(IV)–Ni­(II) cocatalysts is proposed, namely, the amorphous Ti­(IV) works as a hole-cocatalyst to rapidly capture the photogenerated holes from CdS surface, causing the less oxidation of surface lattice S<sup>2–</sup> ions in CdS, while the amorphous Ni­(II) functions as an electron-cocatalyst to rapidly transfer the photogenerated electrons and then promote their following interfacial H<sub>2</sub>-evolution reaction. Compared with the traditional noble metal cocatalysts (such as Pt and RuO<sub>2</sub>), the present amorphous Ti­(IV) and Ni­(II) cocatalysts are apparently low-cost, nontoxic, and earth-abundant, which can widely be applied in the design and development of highly efficient photocatalytic materials

    Highly Active Mesoporous Ferrihydrite Supported Pt Catalyst for Formaldehyde Removal at Room Temperature

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    Ferrihydrite (Fh) supported Pt (Pt/Fh) catalyst was first prepared by combining microemulsion and NaBH<sub>4</sub> reduction methods and investigated for room-temperature removal of formaldehyde (HCHO). It was found that the order of addition of Pt precursor and ferrihydrite in the preparation process has an important effect on the microstructure and performance of the catalyst. Pt/Fh was shown to be an efficient catalyst for complete oxidation of HCHO at room temperature, featuring higher activity than magnetite supported Pt (Pt/Fe<sub>3</sub>O<sub>4</sub>). Pt/Fh and Pt/Fe<sub>3</sub>O<sub>4</sub> exhibited much higher catalytic activity than Pt supported over calcined Fh and TiO<sub>2</sub>. The abundance of surface hydroxyls, high Pt dispersion and excellent adsorption performance of Fh are responsible for superior catalytic activity and stability of the Pt/Fh catalyst. This work provides some indications into the design and fabrication of the cost-effective and environmentally benign catalysts with excellent adsorption and catalytic oxidation performances for HCHO removal at room temperature

    Direct Z‑Scheme TiO<sub>2</sub>/NiS Core–Shell Hybrid Nanofibers with Enhanced Photocatalytic H<sub>2</sub>‑Production Activity

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    Photocatalytic water splitting to generate hydrogen (H<sub>2</sub>) is a sustainable approach for solving the current energy crisis. A novel TiO<sub>2</sub>/NiS core–shell nanohybrid was fabricated where few-layer NiS nanoplates were deposited on TiO<sub>2</sub> skeletons via electrospinning and hydrothermal methods. The NiS nanoplates with a thickness of ca. 28 nm stood vertically and uniformly upon the TiO<sub>2</sub> nanofibers, guaranteeing intimate contact for charge transfer. XPS analysis and DFT calculation imply that the electrons in NiS would transfer to TiO<sub>2</sub> upon hybridization, which creates a built-in electric field at the interfaces and thus facilitates the separation of useful electron and hole upon photoexcitation. <i>In-situ</i> XPS analysis directly proved that the photoexcited electrons in TiO<sub>2</sub> migrated to NiS under UV–visible light irradiation, suggesting that a direct Z-scheme heterojunction was formed in the NiS/TiO<sub>2</sub> hybrid. This direct Z-scheme mechanism greatly promotes the separation of useful electron–hole pairs and fosters efficient H<sub>2</sub> production. The hybrid nanofibers unveiled a high H<sub>2</sub>-production rate of 655 μmol h<sup>–1</sup> g<sup>–1</sup>, which was 14.6-fold of pristine TiO<sub>2</sub> nanofibers. Isotope (<sup>4</sup>D<sub>2</sub>O) tracer test confirmed that H<sub>2</sub> was produced from water, rather than from any H-containing contaminants. This work provides an alternative approach to rationally design and synthesize TiO<sub>2</sub>-based photocatalysts with direct Z-scheme pathways toward high-efficiency photogeneration of H<sub>2</sub>

    Microemulsion-Assisted Synthesis of Mesoporous Aluminum Oxyhydroxide Nanoflakes for Efficient Removal of Gaseous Formaldehyde

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    Mesoporous aluminum oxyhydroxides composed of nanoflakes were prepared via a water-in-oil microemulsion-assisted hydrothermal process at 50 °C using aluminum salts as precursors and ammonium hydroxide as a precipitating agent. The microstructure, morphology, and textural properties of the as-prepared materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption, and X-ray photoelectron spectroscopy (XPS) techniques. It is shown that the aluminum oxyhydroxide nanostructures studied are effective adsorbents for removal of formaldehyde (HCHO) at ambient temperature, due to the abundance of surface hydroxyl groups, large specific surface area, and suitable pore size. Also, the type of aluminum precursor was essential for the microstructure formation and adsorption performance of the resulting materials. Namely, the sample prepared from aluminum sulfate (Al-s) exhibited a relatively high HCHO adsorption capacity in the first run, while the samples obtained from aluminum nitrate (Al-n) and chloride (Al-c) exhibited high adsorption capacity and relatively stable recyclability. A combination of high surface area and strong surface affinity of the prepared aluminum oxyhydroxide make this material a promising HCHO adsorbent for indoor air purification

    Effects of Adsorbed F, OH, and Cl Ions on Formaldehyde Adsorption Performance and Mechanism of Anatase TiO<sub>2</sub> Nanosheets with Exposed {001} Facets

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    Formaldehyde (HCHO), as the main indoor air pollutant, is highly needed to be removed by adsorption or catalytic oxidation from the indoor air. Herein, the F<sup>–</sup>, OH<sup>–</sup>, and Cl<sup>–</sup>-modified anatase TiO<sub>2</sub> nanosheets (TNS) with exposed {001} facets were prepared by a simple hydrothermal and post-treatment method, and their HCHO adsorption performance and mechanism were investigated by the experimental analysis and theoretical simulations. Our results indicated that the adsorbed F<sup>–</sup>, OH<sup>–</sup>, and Cl<sup>–</sup> ions all could weaken the interaction between the HCHO and TNS surface, leading to the serious reduction of HCHO adsorption performance of TNS. However, different from F<sup>–</sup> and Cl<sup>–</sup> ions, OH<sup>–</sup> ion could induce the dissociative adsorption of HCHO by capturing one H atom from HCHO, resulting in the formation of one formyl group and one H<sub>2</sub>O-like group. This greatly reduced the total energy of the HCHO adsorption system. Thus, the adsorbed OH<sup>–</sup> ions could provide the additional active centers for HCHO adsorption. As a result, the NaOH-treated TNS showed the best HCHO adsorption performance mainly because its surface F<sup>–</sup> was replaced by OH<sup>–</sup>. This study will provide new insight into the design and fabrication of high performance adsorbents for removing indoor HCHO and, also, will enhance the understanding of the HCHO adsorption mechanism

    In Situ Fabrication of Ni–Mo Bimetal Sulfide Hybrid as an Efficient Electrocatalyst for Hydrogen Evolution over a Wide pH Range

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    Electrochemical water splitting to produce hydrogen bears a great commitment for future renewable energy conversion and storage. By employing an in situ chemical vapor deposition (CVD) process, we prepared a bimetal (Ni and Mo) sulfide-based hybrid nanowire (NiS<sub>2</sub>/MoS<sub>2</sub> HNW), which was composed of NiS<sub>2</sub> nanoparticles and MoS<sub>2</sub> nanoplates, and revealed that it is an efficient electrocatalyst for the hydrogen evolution reaction (HER) over a wide pH range due to the collective effects of rational morphological design and synergistic heterointerfaces. On a simple glassy carbon (GC) electrode, NiS<sub>2</sub>/MoS<sub>2</sub> HNW displays overpotentials at −10 mA cm<sup>–2</sup> catalytic current density (η<sub>10</sub>) of 204, 235, and 284 mV with small Tafel slopes of 65, 58, and 83 mV dec<sup>–1</sup> in alkaline, acidic, and neutral electrolyte, respectively, exhibiting pH-universal-efficient electrocatalytic HER performance, which is comparable to the recently reported state-of-the-art sulfide-based HER electrocatalysts. Theoretical calculations further confirm that the advantage of all-pH HER activity of NiS<sub>2</sub>/MoS<sub>2</sub> originates from the enhanced dissociation of H<sub>2</sub>O induced by the formation of lattice interfaces of NiS<sub>2</sub>–MoS<sub>2</sub> heterojunctions. This work can pave a valuable route for designing and fabricating inexpensive and high-performance electrocatalysts toward HER over a wide pH range

    Phenylamine-Functionalized rGO/TiO<sub>2</sub> Photocatalysts: Spatially Separated Adsorption Sites and Tunable Photocatalytic Selectivity

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    The preferential adsorption of targeted contaminants on a photocatalyst surface is highly required to realize its photocatalytic selective decomposition in a complex system. To realize the tunable preferential adsorption, altering the surface charge or polarity property of photocatalysts has widely been reported. However, it is quite difficult for a modified photocatalyst to realize the simultaneously preferential adsorption for both cationic and anionic dyes. In this study, to realize the selective adsorption for both cationic and anionic dyes on a photocatalyst surface, the negative reduced graphene oxide (rGO) nanosheets and positive phenylamine (PhNH<sub>2</sub>) molecules are successfully loaded on the TiO<sub>2</sub> surface (PhNH<sub>2</sub>/rGO-TiO<sub>2</sub>) with spatially separated adsorption sites, where the negative rGO and positive PhNH<sub>2</sub> molecules work as the preferential adsorption sites for cationic and anionic dyes, respectively. It was interesting to find that although all the TiO<sub>2</sub> samples (including the naked TiO<sub>2</sub>, PhNH<sub>2</sub>/TiO<sub>2</sub>, rGO-TiO<sub>2</sub>, and PhNH<sub>2</sub>/rGO-TiO<sub>2</sub>) clearly showed a better adsorption performance for cationic dyes than anionic dyes, only the PhNH<sub>2</sub>/rGO-TiO<sub>2</sub> with spatially separated adsorption-active sites exhibited an opposite photocatalytic selectivity, namely, the naked TiO<sub>2</sub>, PhNH<sub>2</sub>/TiO<sub>2</sub>, and rGO-TiO<sub>2</sub> showed a preferential decomposition for cationic dyes, while the resultant PhNH<sub>2</sub>/rGO-TiO<sub>2</sub> exhibited an excellently selective decomposition for anionic dyes. In addition, the resultant PhNH<sub>2</sub>/rGO-TiO<sub>2</sub> photocatalyst not only realizes the tunable photocatalytic selectivity but also can completely and sequentially decompose the opposite cationic and anionic dyes
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