Phase Junction Research Articles

Comparative study of the effect of TiO2 support composition and Pt loading on the performance of Pt/TiO2 photocatalysts for catalytic photoreforming of cellulose

Herein, catalytic aqueous phase photoreforming of cellulose was carried out over Pt/m-TiO2 (i.e., mixed phase of anatase and rutile) and Pt/anatase catalysts to investigate the effect of the TiO2 support structure and Pt loading on the production of H2. The effect of the TiO2 support on the properties of the resulting Pt/TiO2 catalysts (such as actual Pt loading and BET surface area) was not significant. At low Pt loading of 0.16 wt.%, the TiO2 supports affected the sub-nanometre Pt structures which was confirmed by the diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterisation (using CO as the probe). Conversely, the effect of TiO2 supports on larger Pt particles (on 1 wt.% catalysts) was insignificant possibly due to the reduced effect of restructuration of bigger Pt particles on the TiO2 supports. With an increase in Pt loading from 0.16 wt% to 1.00 wt.%, the normalised H2 production rate (with respect to the actual supported Pt amount and specific surface area of the catalysts) showed a decreasing trend over the two types of the catalysts, i.e., from 10.6 to 1.4 μmol h−1 m−2 mgPt−1 for Pt/m-TiO2, and from 8.5 to 1.2 μmol h−1 m−2 mgPt−1 for Pt/anatase. Specifically, large Pt particle sizes reduced the CO2/H2 production from cellulose photoreforming over both Pt/m-TiO2 and Pt/anatase catalysts, indicting an important role played by Pt particle size in photoreforming. Interestingly, in this study, the m-TiO2 supported catalysts only showed the benefits of enhanced charge separation across the phase junction in producing H2 with small Pt particles (at sub-nanometre), whilst, when large Pt particles (at around 1–2 nm) were supported, such a benefit was not significant in cellulose photoreforming. The promoting effect of small, sub-nm particles is attributed to the better capture of photoelectrons from bulk TiO2 and better activity of H+ coupling on small Pt particle. Further fundamental study on such guest-host interactions is devised to optimise Pt/TiO2 catalysts for improving H2 production from photoreforming reactions.

Unraveling the Lattice Matching Effect in Surface Phase Junctions for Interfacial Charge Separation

Exquisite control over the interface structure is highly desired for the successful fabrication of a semiconductor heterojunction, which has been confirmed to effectively promote charge separation and transfer. However, the influences of the interface microstructure in the heterojunction on the charge separation and transfer efficiency are still unclear. Herein, taking the TiO2 heterophase junction (A/R) between anatase and rutile phases and the TiO2 homophase junction (Rs/R) between large rutile rodlike particles and small rutile nanoparticles (∼20 nm) as a prototypical model, it is found that the lattice match at the interface is a key factor determining the charge separation and transfer efficiency and the photocatalytic activity. As compared with A/R, the atomically smooth interface with a highly matched lattice in Rs/R leads to a less-defective and abrupt interface and provides a smooth interfacial charge separation and transfer path, leading to improved charge separation and transfer efficiency and a great enhancement in photocatalytic activity. This study provides a novel insight into optimizing the heterojunction structure by designing a highly matched lattice interface between two components.

Solar photocatalytic degradation of organic pollutants from indoor air using novel direct flame combustion based hollow nanocomposite of Pd/Anatase–Rutile TiO2 mixed phase and evaluation of the biocompatibility

The conventional methods (calcinations) are used to prepare diverse types of nanoparticles, however, to introduce specific properties for their applications, new strategy is required. Therefore, direct air flame combustion is a new technique utilized to synthesize novel nanoparticles instead of calcinations in the oven. In this work, the air flame combustion was used to prepare a new junction of anatase– rutile (A/R) mixed phase TiO2 deposited with palladium nanoparticles (Pd NPs). Herein, an A/R phase junction was obtained by flame combustion of carbon sphere templates. The novel nanocatalyst was characterized using XRD, SEM, TEM, UV–Vis light spectroscopy and SBET method for surface properties. It shows a higher performance during the photocatalytic degradation of formaldehyde gas pollutant under solar irradiation. The enhancement of catalytic activity was found to be 18-fold higher than the commercial TiO2-P25. The results of CO2 generated via the formaldehyde degradation by the novel nanophotocatalyst showed a high photocatalytic efficiency of 60%. Moreover, in the field application, it showed 75% formaldehyde removal when applied in the kitchen indoor air; it reveals also a wide array of antimicrobial activity. Therefore, this system will be more promising in various industrial applications.

Dislocation content of grain boundary phase junctions and its relation to grain boundary excess properties

We analyze the dislocation content of grain boundary (GB) phase junctions, i.e., line defects separating two different GB phases coexisting on the same GB plane. While regular GB disconnections have been characterized for a variety of interfaces, GB phase junctions formed by GBs with different structures and different numbers of excess atoms have not been previously studied. We apply a general Burgers circuit analysis to calculate the Burgers vectors b of junctions in two {\Sigma}5 Cu boundaries previously simulated with molecular dynamics. The Burgers vectors of these junctions cannot be described by the displacement shift complete (DSC) lattice alone. We show that, in general, the normal component of b is not equal to the difference in the GB excess volumes, but contains another contribution from the numbers of GB atoms per unit area {\Delta}N required to transform one GB phase into another. In the boundaries studied, the latter component dominates and even changes the sign of b. We derive expressions for the normal and tangential components of b in terms of the DSC lattice vectors and the non-DSC part due to {\Delta}N and additional GB excess properties, including excess volume and shears. These expressions provide a connection between GB phase transformations driven by the GB free energy difference and the motion of GB junctions under applied normal and shear stresses. The proposed analysis quantifies b and therefore makes it possible to calculate the elastic part of the energy of these defects, evaluate their contribution to the nucleation barrier during GB phase transformations, and treat elastic interactions with other defects.

Introduction of crystalline hexagonal-C3N4 into g-C3N4 with enhanced charge separation efficiency

Polymeric carbon nitride is a promising candidate for photocatalytic hydrogen evolution but mostly just shows moderate activity because of its inefficient charge separation and sluggish surface reaction kinetics. Phase-based heterostructures, especially crystal-phase heterostructures that are composed of identical compositions with different crystal phases, can endow nanomaterials with promising properties and efficient photocatalysis applications. In this study, a novel crystalline hexagonal-C3N4/g-C3N4 hetero-phase junction was synthesized using a direct in situ alkali salt template coupled with organic solvents strategy. High hydrophilicity was obtained because of the synergistic effect between alkali salt and organic solvents in the polycondensation process. The greatly increased separation and transfer efficiency of charge carriers and the improved proton absorption in the surface reaction of the photocatalyst were achieved by the constructed phase junctions between the crystalline hexagonal-C3N4 and amorphous g-C3N4 decorated with numerous hydrophilic groups. Thus, the carbon nitride hetero-phase junction exhibited dramatically enhanced photocatalytic performance in hydrogen evolution and excellent cycling stability under visible light irradiation. This work presents a novel insight into phase engineering based on carbon nitride materials with surface functional modification for an efficient photocatalytic activity.

Branching TiO2 nanowire arrays for enhanced ethanol sensing

Nanostructure modulation is effective to achieve high performance TiO2-based gas sensors. We herein report a wet-chemistry route to precipitate directly branched TiO2 nanowire arrays on alumina tubes for gas sensing applications. The optimized branched TiO2 nanowire array exhibits a response of 9.2 towards 100 ppm ethanol; whilst those of the pristine TiO2 nanowire array and the branched TiO2 nanowire powders randomly distributed are 5.1 and 3.1, respectively. The enhanced response is mainly contributed to the unique porous architecture and quasi-aligned nanostructure, which provide more active sites and also favor gas migration. Phase junctions between the backbone and the branch of the branched TiO2 nanowire arrays help the resistance modulation as a result of potential barriers. The facile precipitation of quasi-aligned arrays of branched TiO2 nanowires, which are in situ grown on ceramic tubes, thus provides a new economical synthetic route to TiO2-based sensors with excellent properties.

Copper-Doped ZnS with Internal Phase Junctions for Highly Selective CO Production from CO2 Photoreduction

ZnS is one of the promising earth-abundant catalysts for photoreduction reactions. The performance of ZnS in CO2 reduction is, however, limited because of its wide band gap, fast recombination of charge carriers, as well as low product selectivity due to the competing hydrogen evolution reaction (HER). Herein, Cu-doped ZnS containing abundant sphalerite and wurtzite phase (S–W) junctions is prepared and an enhanced photocatalytic activity with high selectivity in CO production is demonstrated. Both experimental and theoretical results reveal that Cu incorporation and the S–W phase junction enhance light absorption and promote photocatalytic activity. The presence of a Cu ion contributes to the CO generation and suppresses the competing HER by enhancing the bonding of the catalyst surface with •CO adsorbates. This work provides useful insights into the modification of CO2 reduction photocatalysts to realize high catalytic efficiency and product selectivity.

In-situ growth of TiO2 phase junction nanorods with Ti3+ and oxygen vacancies to enhance photocatalytic activity

The titanium dioxide phase junction nanorods with Ti3+ and oxygen vacancies (Ov) were successfully prepared by in-situ growth method and vacuum freeze-drying, which was used for photocatalytic removal of gas phase mercury. Experimental results and characterization data indicate that the phase junction, Ti3+ and Ov synergistically promote photogenerated electron-hole separation and transfer efficiency and photocatalytic activity. The efficiency of the most efficient sample reaches 63.77 %, which is about 3.6 times that of commercial P25. Finally, we proposed the reaction mechanism that the phase junction, Ti3 + and Ov in TiO2 nanorods form an effective charge transport channel. This work provides new ideas for the effective utilization of solar energy and the design of photocatalysts.

Oriented titania nanotube biphase junction arrays on water splitting

Photocatalyst with phase junction is of great importance to achieve high charge separation and transfer efficiency on solar energy utilization. Herein, an oriented anatase/rutile biphase junction based on TiO2 nanotube arrays are facile prepared by novel oriented thermal annealing method. Its phase distribution and proportion can be tuned by adjusting heat radiation direction and time, respectively. Light absorption spectroscopy and photoelectrochemical measurements reveal that the oriented phase junction is crucial for charge transfer and separation. The sample containing with 34.4% rutile phase has the highest incident photon-to-current efficiency and charge separation efficiency, and achieves ca. 2.2 and 4.7 folds photocurrent density enhancement compared to pristine anatase and rutile phase TiO2 arrays, respectively. The photocurrent density of oriented biphase junction arrays (0.458 mA·cm−2 at 1.23 V vs RHE) is also significantly higher than random phase junction sample or previous reported result. This work demonstrates that the great potential of oriented biphase junction arrays can be applied in efficient charge separation and transfer on solar energy conversion.

A review on the preparation, microstructure, and photocatalytic performance of Bi2O3 in polymorphs.

In recent years, the semiconductor bismuth oxide (Bi2O3) has attracted increasing attention as a potential visible-light-driven photocatalyst due to its simple composition, relatively narrow bandgap (2.2-2.8 eV), and high oxidation ability with deep valence band levels. Owing to the symmetry of its unit cell, Bi2O3 exists in more than one crystal form and exhibits phase-dependent photocatalytic properties. However, the phase-selective synthesis of Bi2O3 is a complex process, and its phase transformation usually occurs in a wide temperature range. Therefore, the development of Bi2O3 phases with a controllable microstructure and good photocatalytic properties is a great challenge. Hundreds of articles have been reported on the phase-selective synthesis and photocatalytic performance of Bi2O3. However, an interacting and critical review has rarely been reported, and thus it is essential to fill the gap in the literature. In this review, the phase-dependent photocatalytic performance of Bi2O3 is presented in detail. The phase-selective synthesis and temperature-dependent phase stability of highly active Bi2O3 are explored. The phase junction in Bi2O3 is reviewed, and the future perspective with an outlook on contemporary challenges is provided finally.

Green preparation of porous hierarchical TiO2(B)/anatase phase junction for effective photocatalytic degradation of antibiotics.

In this study, porous hierarchical bronze/anatase phase junction TiO2 assembled by ultrathin two-dimensional nanosheets was prepared by a novel, green and simple deep eutectic solvent-regulated strategy. Due to its structural features, the TiO2 sample exhibited enhanced photocatalytic activities for multiple kinds of antibiotics, including ofloxacin, ciprofloxacin and chloramphenicol.

Phase junction-confined single-atom TiO2–Pt1–CeO2 for multiplying catalytic oxidation efficiency

The phase junction confinement within the TiO2–Pt1–CeO2 ensemble leads to 5 times higher CO oxidation efficiency under 300 K.

Engineering highly active Cd1−xZnxS nanopopcorns via zinc blende/wurtzite phase junctions for enhanced photocatalytic H2 evolution without a co-catalyst

Cd1−xZnxS nanopopcorns with ZB/WZ phase junctions for effectively enhanced visible-light photocatalytic H2 evolution without a co-catalyst.

Time-Enhanced Performance of Oxide Thermoelectric Modules Based on a Hybrid p-n Junction.

The present challenge with all-oxide thermoelectric modules is their poor durability at high temperatures caused by the instability of the metal-oxide interfaces at the hot side. This work explains a new module concept based on a hybrid p–n junction, fabricated in one step by spark plasma co-sintering of Ca3Co4–xO9+δ (CCO, p-type) and CaMnO3−δ/CaMn2O4 (CMO, n-type). Different module (unicouple) designs were studied to obtain a thorough understanding of the role of the in situ formed hybrid p–n junction of Ca3CoMnO6 (CCMO, p-type) and Co-oxide rich phases (p-type) at the p–n junction (>700 °C) in the module performance. A time-enhanced performance of the modules attributed to this p–n junction formation was observed due to the unique electrical properties of the hybrid p–n junction being sufficiently conductive at high temperatures (>700 °C) and nonconductive at moderate and low temperatures. The alteration of module design resulted in a variation of the power density from 12.4 (3.1) to 28.9 mW/cm2 (7.2 mW) at ΔT ∼ 650 °C after 2 days of isothermal hold (900 °C hot side). This new concept provides a facile method for the fabrication of easily processable, cheap, and high-performance high-temperature modules.

Fracture and damage model of composite ceramics

It is of great significance to study the damage and fracture mechanism of trigonometrically symmetric eutectic multiphase ceramics with excellent mechanical properties at room temperature and high temperature. According to the microstructure characteristics of inner triangular symmetric eutectic in multiphase ceramics, a two-scale cell model containing triangular symmetric eutectic was established. The fracture stress of cohesive bond in eutectic was calculated by considering the conditions of cohesive bond fracture at interface phase and fiber junction. The damage variable was introduced and combined with cohesive bond fracture stress to establish the microcosmic damage fracture stress model of eutectic Based on the Dugdale Barenblatt model, the damage localization band model is established by introducing the micro damage fracture stress as the residual strength. It is found that with the increase of fiber volume fraction, the strong confinement of interface phase is destroyed, the residual strength decreases and the length of damage localization band increases with the increase of fiber volume fraction. Reducing the damage degree and selecting the appropriate fiber volume content can increase the fracture stress of eutectic, and then reduce the length of damage localization band, increase the threshold value of crack instability propagation, and enhance the material strength.

Phase-Junction Electrocatalysts towards Enhanced Hydrogen Evolution Reaction in Alkaline Media.

To ensure sustainable hydrogen production by water electrolysis, robust, earth-abundant, and high-efficient electrocatalysts are required. Constructing a hybrid system could lead to further improvement in electrocatalytic activity. Interface engineering in composite catalysts is thus critical to determine the performance, and the phase-junction interface should improve the catalytic activity. Here, we show that nickel diphosphide phase junction (c-NiP2 /m-NiP2 ) is an effective electrocatalyst for hydrogen production in alkaline media. The overpotential (at 10 mA cm-2 ) for NiP2 -650 (c/m) in alkaline media could be significantly reduced by 26 % and 96 % compared with c-NiP2 and m-NiP2 , respectively. The enhancement of catalytic activity should be attributed to the strong water dissociation ability and the rearrangement of electrons around the phase junction, which markedly improved the Volmer step and benefited the reduction process of adsorbed protons.

Phase‐Junction Electrocatalysts towards Enhanced Hydrogen Evolution Reaction in Alkaline Media

AbstractTo ensure sustainable hydrogen production by water electrolysis, robust, earth‐abundant, and high‐efficient electrocatalysts are required. Constructing a hybrid system could lead to further improvement in electrocatalytic activity. Interface engineering in composite catalysts is thus critical to determine the performance, and the phase‐junction interface should improve the catalytic activity. Here, we show that nickel diphosphide phase junction (c‐NiP2/m‐NiP2) is an effective electrocatalyst for hydrogen production in alkaline media. The overpotential (at 10 mA cm−2) for NiP2‐650 (c/m) in alkaline media could be significantly reduced by 26 % and 96 % compared with c‐NiP2 and m‐NiP2, respectively. The enhancement of catalytic activity should be attributed to the strong water dissociation ability and the rearrangement of electrons around the phase junction, which markedly improved the Volmer step and benefited the reduction process of adsorbed protons.

Fabrication of dandelion clock-inspired preparation of core-shell TiO2@MoS2 composites for unprecedented high visible light-driven photocatalytic performance

Phase junction construction and surface modification are two practical engineering strategies toward efficient photocatalysis. In the present work, core-shell TiO2@MoS2 heterojunction composites were directly constructed via one-step hydrothermal method. The prepared catalysts are characterized by X-ray diffraction, Raman spectroscopy, Scanning electron microscopy, Transmission electron microscopy, and N2 adsorption–desorption studies to know the structural, morphological, and textural properties. The optical absorption and prevention of electron–hole recombination process was studied by UV–Vis diffuse reflectance spectra (DRS) and photoluminescence analysis. The photocatalytic degradation experiment was carried out using methyl orange (MO) and 4-nitrophenol (4-NP) for all the catalysts under visible light irradiation. The results reveal that MoS2@TiO2 heterojunction catalyst shows excellent photocatalytic activity toward 4-NP such as high removal efficiency (96%), high apparent constant (0.0242 min−1), and long-term stability. The enhancement in the photodegradation is due to dandelion clock heterostructures of MoS2@TiO2 possess high specific surface area (103.5 m2/g), specific pores (11.8 nm). The photoelectrochemical results suggest that MoS2@TiO2 catalyst exhibits the high photoresponse than compared with pure MoS2 and TiO2 catalysts, respectively.

Nitrogen-doped mixed-phase TiO2 with controllable phase junction as superior visible-light photocatalyst for selective oxidation of cyclohexane

Nitrogen-doped anatase/rutile mixed-phase TiO2 photocatalysts with carbonaceous species were successfully fabricated by pyrolyzing MIL-125 (Ti) and P25 composite as the precursor, and subsequently doping nitrogen into the pyrolysis product using urea as the dopant in a sealed reactor. Through varying the addition amount of P25 in the precursor, the ratios of anatase/rutile phases in the photocatalysts were conveniently adjusted. The photocatalysts showed excellent photocatalytic cyclohexane oxidation performances under visible light irradiation. The yield of the KA oil (cyclohexanol and cyclohexanone) reached 112.44 μmol after 5 h illumination for the photocatalyst with the optimal anatase/rutile ratio (N-TiO2-3), which was 5.66 and 39.87 times that of N-TiO2-0 (nitrogen-doped anatase TiO2) and N-P25 (nitrogen-doped P25), respectively. In the meantime, the selectivity toward cyclohexanone could reach 100%. The influences of pyrolysis temperature and atmosphere on the microstructure of catalysts and resulting catalytic performances for cyclohexane oxidation were also investigated. The improved photocatalytic properties were attributed to the combined effects of the high visible-light absorption caused by nitrogen doping, valid separation of photogenerated electron-hole pairs derived from the mixed-phase junction, unique auxiliary function of carbonaceous species and porous structure. A possible photocatalytic mechanism was proposed according to the active species determined by trapping experiments.

FAPbI3 perovskite thin film having α/δ phase junction and its light harvesting performance in solar cell

In this study, FAPbI3 perovskite thin films having α/δ phase junction have been prepared by the two-step solution method at short annealing time. In first stage, the structural, morphological and optical properties of the PbI2 and FAPbI3 films have been investigated. The XRD, SEM and UV–Visible analyses have shown that the FAPbI3 film quality has improved with increasing annealing temperature and the film annealed at 170 °C have bandgap of 1.49 eV and high covering capability with average grain size of ~ 61 nm. The transition from PbI2 to FAPbI3 form has enhanced with increasing annealing temperature. Moreover, the α/δ phase junction form crystalline depend annealing temperature has been observed in FAPbI3 films and the α/δ phase junction has enhanced with increasing annealing temperature. In second stage, performance of the FAPbI3 films have been investigated as active layer in solar cell having structure of Glass/ITOPEDOT:PSS(~ 50 nm)/FAPbI3(~ 400 nm)/PC61BM(~ 70 nm)/Al(~ 100 nm). The best solar cell has performance parameters; Jsc is 18.12 mA/cm2, Voc is 0.74 V, FF is 59% and PCE is 7.91%. The results showed that presence of dominant δ phase in FAPbI3-based solar cells has caused S-sharped J–V character.