In Situ Interfacial Engineering of CeO2 /Bi2 WO6 Heterojunction with Improved Photodegradation of Tetracycline and Organic Dyes: Mechanism Insight and Toxicity Assessment.

The construction of heterojunction photocatalysts is an auspicious approach for enhancing the photocatalytic performance of wastewater treatment. Here, a novel CeO2 /Bi2 WO6 heterojunction is synthesized using an in situ liquid-phase method. The optimal 15% CeO2 /Bi2 WO6 (CBW-15) is found to have the highest photocatalytic activity, achieving a degradation efficiency of 99.21% for tetracycline (TC), 98.43% for Rhodamine B (RhB), and 94.03% for methylene blue (MB). The TC removal rate remained at 95.38% even after five cycles. Through active species capture experiments, •O2 - , h+ , and •OH are the main active substances for TC, RhB, and MB, respectively. The possible degradation pathways for TC are analyzed using liquid chromatography-mass spectrometry (LC-MS). The photoinduced charge transfer and possible degradation mechanisms are proposed through experimentation and density functional theory (DFT) calculations. Toxicity assessment experiments show a significant reduction in toxicity during the TC degradation process. This study uncovers the mechanism of photocatalytic degradation in CeO2 /Bi2 WO6 and provides new insights into toxicity assessment.

Controlled synthesis and photocatalytic hydrogen evolution activities of cobalt carbides with different phase compositions.

Cobalt carbides are emerging as promising materials for various magnetic and catalytic applications. However, exploring dedicated cobalt carbides with optimal catalytic properties via adjusting phase compositions remains a significant challenge. Herein, three different cobalt carbides, CoxC (Co2C-Co3C), Co2C-Co, and Co3C, were successfully prepared using a facile one-pot green method. The phase compositions of cobalt carbides could be easily controlled by varying the cobalt-based precursors and carbon sources. More remarkably, three different cobalt carbides could serve as reduction cocatalysts decorated CdS for improved hydrogen production under visible light. Intriguingly, the obtained Co3C/CdS nanocomposite displayed the highest photocatalytic hydrogen evolution activity among the three composites and superior photocatalytic stability. This work provides a fundamental approach to tuning the photocatalytic properties of cobalt carbides for energy conversion fields.

Phase-controlled synthesis and magnetic properties of cubic and hexagonal CoO nanocrystals.

We report facile solution approaches for the phase-controlled synthesis of rock-salt cubic CoO (c-CoO) and wurtzite-type hexagonal CoO (h-CoO) nanocrystals. In the syntheses, the cobalt precursor cobalt (II) stearate is decomposed in 1-octadecene at 320 °C, and the crystalline phase of synthesized products depend critically on the amounts of H2O. While the presence of small amounts of H2O promotes the generation of c-CoO, h-CoO is obtained in the absence of H2O. The as-prepared c-CoO nanocrystals exhibit a multi-branched morphology with several short rods growing on the 〈100〉 direction interlaced together whereas the h-CoO nanocrystals show a multi-rod structure with several rods growing on the same base facet along the c-axis. The formation mechanisms are discussed on the basis of FTIR spectrometry data and color changes of the reaction mixture. Finally the magnetic properties of as-prepared CoO nanocrystals are measured and the results show that c-CoO nanocrystals are intrinsically antiferromagnetic with a Néel temperature of about 300 K but the antiferromagnetic ordering is not distinct for the h-CoO nanocrystals. Weak ferromagnetic contributions are also observed for both c-CoO and h-CoO nanocrystals with obvious magnetic hysteresis at 5 and 300 K. The uncompensated spins that can be induced by crystalline defects such as cation-vacancy may account for the observed weak ferromagnetism.

Seed-induced growth of flower-like Au-Ni-ZnO metal-semiconductor hybrid nanocrystals for photocatalytic applications.

The combination of metal and semiconductor components in nanoscale to form a hybrid nanocrystal provides an important approach for achieving advanced functional materials with special optical, magnetic and photocatalytic functionalities. Here, a facile solution method is reported for the synthesis of Au-Ni-ZnO metal-semiconductor hybrid nanocrystals with a flower-like morphology and multifunctional properties. This synthetic strategy uses noble and magnetic metal Au@Ni nanocrystal seeds formed in situ to induce the heteroepitaxial growth of semiconducting ZnO nanopyramids onto the surface of metal cores. Evidence of epitaxial growth of ZnO{0001} facets on Ni {111} facets is observed on the heterojunction, even though there is a large lattice mismatch between the semiconducting and magnetic components. Adjustment of the amount of Au and Ni precursors can control the size and composition of the metal core, and consequently modify the surface plasmon resonance (SPR) and magnetic properties. Room-temperature superparamagnetic properties can be achieved by tuning the size of Ni core. The as-prepared Au-Ni-ZnO nanocrystals are strongly photocatalytic and can be separated and re-cycled by virtue of their magnetic properties. The simultaneous combination of plasmonic, semiconducting and magnetic components within a single hybrid nanocrystal furnishes it multifunctionalities that may find wide potential applications.

Synthesis and photocatalytic properties of multi-morphological AuCu3-ZnO hybrid nanocrystals.

Noble metal-semiconductor hybrid nanocrystals represent an important class of materials for many potential applications, especially for photocatalysis. The utilization of transition metals to form alloys with noble metals can not only reduce the preparation costs, but may also offer tunable optical and catalytic properties for a broader range of applications. In this study, we report on the solution synthesis of AuCu3-ZnO hybrid nanocrystals with three interesting morphologies, including urchin-like, flower-like and multipod-like nanocrystals. In the synthetic strategy, Au-Cu bimetallic alloy seeds formed in situ are used to induce the heteroepitaxial growth of ZnO nanocrystals on the surface of bimetallic alloy cores; thus different types of morphologies can be achieved by controlling the reaction conditions. Through high-resolution transmission electron microscopy observations, well-defined interfaces between ZnO and AuCu3 are observed, which indicate that ZnO has a (0001) orientation and prefers to grow on AuCu3 {111} facets. The as-prepared hybrid nanocrystals demonstrate morphology- and composition-dependent surface plasmon resonance (SPR) absorption bands. In addition, much higher photocatalytic efficiency than pure ZnO nanocrystals is observed for the hybrid nanocrystals in the degradation of methylene blue. In particular, the multipod-like AuCu3-ZnO hybrid nanocrystals show the highest catalytic performance, as well as more than three times higher photocurrent density than the pure ZnO sample. The reported synthetic strategy provides a facile route to the effective combination of a plasmonic alloy with semiconductor components at the nanoscale in a controlled manner.

Shape-related optical and catalytic properties of wurtzite-type CoO nanoplates and nanorods.

In this paper, we report the anisotropic optical and catalytic properties of wurtzite-type hexagonal CoO (h-CoO) nanocrystals, an unusual nanosized indirect semiconductor material. h-CoO nanoplates and nanorods with a divided morphology have been synthesized via facile solution methods. The employment of flash-heating and surfactant tri-n-octylphosphine favors the formation of plate-like morphology, whereas the utilization of cobalt stearate as a precursor is critical for the synthesis of nanorods. Structural analyses indicate that the basal plane of the nanoplates is (001) face and the growth direction of the nanorods is along the c axis. Moreover, the UV­vis absorption spectra, the corresponding energy gap and the catalytic properties are found to vary with the crystal shape and the dimensions of the as-prepared h-CoO nanocrystals. Furthermore, remarkable catalytic activities for H2 generation from the hydrolysis of alkaline NaBH4 solutions have been observed for the as-prepared h-CoO nanocrystals. The calculated Arrhenius activation energies show a decreasing trend with increasing extension degree along the <001> direction, which is in agreement with the variation of the charge-transfer energy gap. Finally the maximum hydrogen generation rate of the h-CoO nanoplates exceeds most of the reported values of transition metal or noble metal containing catalysts performing in the same reaction system, which makes them a low-cost alternative to commonly used noble metal catalysts in H2 generation from the hydrolysis of borohydrides, and might find potential applications in the field of green energy.

A new strategy to construct MOF-on-MOF derivatives for the removal of tetracycline hydrochloride from water by activation of peroxymonosulfate.

A MOF-on-MOF composite derivative material named ZIF-67@Ce-MOF-600 was designed and synthesized. The preparation of ZIF-67@Ce-MOF-600 was optimized from the aspects of the ratio of metal and ligand, heat-treatment temperature. It was demonstrated by XRD, FT-IR, SEM-EDS and TEM. The optimum conditions for the activation of PMS by ZIF-67@Ce-MOF-600 for the degradation of tetracycline (TC) were investigated by adjusting the catalyst dosage, TC, pH, peoxymonosulfate (PMS) concentration, and different kinds of water, co-existing anions and pollution. Under optimal conditions (20 mg catalysts and 50 mg PMS added) in 100 mL of tetracyclines (TC) solvent (20 mg TC/L), the removal rate could reach up to 99.2% and after five cycles was 70.5%. The EPR results indicated the presence of free radicals and non-free radical, among which free radicals intended to play a major role in the degradation process. Its possible degradation pathways and attack sites were analyzed by liquid-phase mass spectrometry and DFT analysis.

Fast one-pot synthesis of a Se-rich MnCdSe solid solution for highly efficient cocatalyst-free photocatalytic H2 evolution.

Designing high-efficiency and stable metal selenides for visible-light-induced photocatalytic H2 production has been challenging. Here, a novel class of Se-rich MnCdSe solid solution with a tunable band structure is fabricated through a fast one-pot strategy. In the absence of any cocatalysts, the optimal MnCdSe nanocrystals exhibit a much higher visible-light-driven H2 evolution activity (2582 µmol g-1 h-1) than the pristine CdSe (30 µmol g-1 h-1), and achieve an apparent quantum yield (AQY) of 7.5% at 420 nm. This work opens a new gateway to explore metal selenide-based solid solutions for photocatalytic applications.

Porous CoxP nanosheets decorated Mn0.35Cd0.65S nanoparticles for highly enhanced noble-metal-free photocatalytic H2 generation.

Incorporating 2D transition-metal phosphides into visible-light-driven semiconductors is fascinating for advancing novel photocatalysts. In this paper, porous CoxP nanosheets prepared by phosphating Co(OH)2 nanosheets are coupled with Mn0.35Cd0.65S nanoparticles for significantly boosted photocatalytic H2 evolution performance. The optimal CoxP/Mn0.35Cd0.65S hybrids show an excellent visible-light H2 production rate of 7188.9 µmol g-1h-1 upon visible light with an apparent quantum yield (AQY) of 18.9% at 420 nm. The H2 production rate of the 5% CoxP/Mn0.35Cd0.65S sample is about 257 times bare CdS and even 18 times higher than pristine Mn0.35Cd0.65S. This dramatic photocatalytic H2 generation activity is mainly ascribed to the efficient charge transfer and abundant active sites by introducing the porous CoxP nanosheets. The photocatalytic mechanism of the CoxP/Mn0.35Cd0.65S composites is investigated by the photoluminescence (PL), time-resolved photoluminescence (TRPL), electrochemical, and photoelectrochemical (PEC) tests. This work presents a viable strategy to design a 2D/0D hybrid system containing porous cobalt phosphides nanosheets and MnCdS solid solutions for noble-metal-free photocatalytic application.

Efficient degradation of Bisphenol A by dielectric barrier discharge non-thermal plasma: Performance, degradation pathways and mechanistic consideration.

The discharge of recalcitrant and persistent organic pollutants into the environment and subsequent adverse impacts on the ecosystem has aroused a great concern all over the world. In this study, dielectric barrier discharge (DBD) non-thermal plasma was employed to eliminate bisphenol A (BPA). The influences of several vital experimental parameters, including discharge voltage, initial pH of solution, and rate of water flow on degradation of BPA, were explored in detail. In addition, the real wastewater from pharmaceutical factory was utilized to test the oxidation performance of DBD system. 96.8% chemical oxygen demand removal was achieved using DBD system. Radical quenching experiment as well as electron paramagnetic resonance test demonstrated that •OH was the main reactive oxygen species for the degradation of BPA. Moreover, eight major BPA degradation intermediates were identified by UPLC-MS. Ultimately, based on the UPLC-MS test results, a possible degradation pathway of BPA was proposed.

Composition-dependent activity of ZnxCd1-xSe solid solution coupled with Ni2P nanosheets for visible-light-driven photocatalytic H2 generation.

Metal selenide semiconductors have been rarely used for photocatalytic water splitting because of their poor stability and severe photocorrosion properties. Hence, designing stable metal selenides with suitable bandgap energies has considerable practical significance in photocatalytic H2 evolution. In this work, a novel series of ZnxCd1-xSe (x = 0 âˆ¼ 1) with tunable band structure were fabricated through a simple solvothermal method. Impressively, the ZnSe exhibited a maximum H2 production rate of 1056 µmol g-1h-1, which was higher than that of CdSe and ZnxCd1-xSe solid solutions. Such visible-light photoactivity for water reduction to H2 was attained even after 6 cycling photocatalytic experiments. Moreover, the two-dimensional (2D) Ni2P nanosheets act as a high-efficiency cocatalyst integrated with ZnxCd1-xSe semiconductor to boost photocatalytic H2 generation performance. The optimal 8% Ni2P/ZnSe composites displayed excellent cycling stability and superior photocatalytic H2 evolution performance (4336 µmol g-1h-1), which was about 4.1 times that of pure ZnSe under visible light irradiation. Photoelectrochemical (PEC), photoluminescence (PL), and time-resolved photoluminescence (TRPL) measurements reveal that the improved photoactivity Ni2P/ZnSe photocatalysts were ascribed to the effective separation and migration of photoinduced carriers. The present work paves a pathway to explore the fabrication of ZnxCd1-xSe solid solutions and the hybridization of 2D transition metal phosphides nanosheets toward photocatalytic applications.

Insights into the role of dual reaction sites for single Ni atom Fenton-like catalyst towards degradation of various organic contaminants.

The trade-off of Fenton-like catalysts in activity and stability remains a challenge in practical remediation applications. In this work, we successfully synthesized an efficient and stable catalyst comprised of single nickel (Ni) atoms dispersed on N-doped porous carbon (named Ni-SAs@CN) through a simple micropore confinement strategy. The catalyst exhibited outstanding catalytic performance with 25.8 min-1 turnover frequency for peroxymonosulfate (PMS) activation toward degradation of various organic pollutants (e.g., antibiotics, dyes, and plasticizers) in a wide pH range (4.5-10.8). Electron paramagnetic resonance and in situ Raman analyses demonstrated that both radical (including SO4•- and •OH) and Ni-PMS* dominated nonradical (via electron transfer) pathways played pivotal role in the decomposition of organics. The X-ray adsorption fine structure analysis and computational pieces of evidence demonstrate that the atomically dispersed NiN4 coordination is the intrinsic catalytic site for PMS activation. Meanwhile, pyrrolic N acts as a functional site to anchor target contaminants to the surface region for oxidation. In this process which is benefited from the dual active sites, the target contaminants were degraded via combined radical and nonradical pathways, which significantly boost the overall oxidation and mineralization kinetics.

Ferroelectricity and Schottky Heterojunction Engineering in AgNbO3: A Simultaneous Way of Boosting Piezo-photocatalytic Activity.

As an efficient and economical way of dealing with organic pollutants, piezo-photocatalysis has attracted great interest. In this work, we demonstrated that ferroelectricity and Schottky heterojunction engineering could significantly enhance the piezo-photocatalytic activity of AgNbO3. The poled 20 mol % K+ doped AgNbO3 disclosed its superior piezo-photocatalytic activity of 0.131 min-1 for 10 mg·L-1 RhB, which is 7.8 times of the pristine one under the condition of illumination only. The designed piezo-photocatalyst also exhibited good piezo-photocatalytic stability after four cycles. These merits are attributed to the built-in electric field associated with the large spontaneous polarization and low coercive field originated from the stable ferroelectric state after ferroelectricity engineering, plus with the electron trapper effect of the in situ precipitated metal Ag particles. Our work not only provides a promising piezo-photocatalyst for degrading organic contaminants but also paves a good way for developing high piezo-photocatalytic activity catalysts.

NiO Nanosheets Coupled With CdS Nanorods as 2D/1D Heterojunction for Improved Photocatalytic Hydrogen Evolution.

Designing low-cost, environment friendly, and highly active photocatalysts for water splitting is a promising path toward relieving energy issues. Herein, one-dimensional (1D) cadmium sulfide (CdS) nanorods are uniformly anchored onto two-dimensional (2D) NiO nanosheets to achieve enhanced photocatalytic hydrogen evolution. The optimized 2D/1D NiO/CdS photocatalyst exhibits a remarkable boosted hydrogen generation rate of 1,300 µmol h-1 g-1 under visible light, which is more than eight times higher than that of CdS nanorods. Moreover, the resultant 5% NiO/CdS composite displays excellent stability over four cycles for photocatalytic hydrogen production. The significantly enhanced photocatalytic activity of the 2D/1D NiO/CdS heterojunction can be attributed to the efficient separation of photogenerated charge carriers driven from the formation of p-n NiO/CdS heterojunction. This study paves a new way to develop 2D p-type NiO nanosheets-decorated n-type semiconductor photocatalysts for photocatalytic applications.

Enhanced catalytic activation of photo-Fenton process by Cu0·5Mn0·5Fe2O4 for effective removal of organic contaminants.

In this study, Cu0·5Mn0·5Fe2O4 nanoparticles were synthesized through a facile coprecipitation process, evaluated as highly efficient photo-Fenton catalyst for removal of bisphenol A (BPA). Benefit for its larger surface area and unique chemical composition, the Cu0·5Mn0·5Fe2O4 catalyst exhibited superior catalytic activity toward the degradation of BPA, with a rate constant values ranging from 0.247 to 1.090 min-1 based on different operating parameters (catalyst load, initial solution pH, H2O2 concentration and reaction temperature). Importantly, an excellent BPA removal efficiency exceeding 95.2% were obtained after eight successive runs of photo-Fenton process. Electron paramagnetic resonance (EPR) spectroscopy and radical scavenger experiments demonstrated that the hydroxyl radical was the dominant radical in degradation of BPA. A possible BPA degradation pathway was proposed according to the detected intermediates by GC-MS and HPLC. In brief, this work is expected to provide a new heterogeneous photo-Fenton catalyst for the organic pollutants removal from wastewater.

Sub-5 nm Ultra-Fine FeP Nanodots as Efficient Co-Catalysts Modified Porous g-C3N4 for Precious-Metal-Free Photocatalytic Hydrogen Evolution under Visible Light.

Sub-5 nm ultra-fine iron phosphide (FeP) nano-dots-modified porous graphitic carbon nitride (g-C3N4) heterojunction nanostructures are successfully prepared through the gas-phase phosphorization of Fe3O4/g-C3N4 nanocomposites. The incorporation of zero-dimensional (0D) ultra-small FeP nanodots co-catalysts not only effectively facilitate charge separation but also serve as reaction active sites for hydrogen (H2) evolution. Herein, the strongly coupled FeP/g-C3N4 hybrid systems are employed as precious-metal-free photocatalysts for H2 production under visible-light irradiation. The optimized FeP/g-C3N4 sample displays a maximum H2 evolution rate of 177.9 µmol h-1 g-1 with the apparent quantum yield of 1.57% at 420 nm. Furthermore, the mechanism of photocatalytic H2 evolution using 0D/2D FeP/g-C3N4 heterojunction interfaces is systematically corroborated by steady-state photoluminescence (PL), time-resolved PL spectroscopy, and photoelectrochemical results. Additionally, an increased donor density in FeP/g-C3N4 is evidenced from the Mott-Schottky analysis in comparison with that of parent g-C3N4, signifying the enhancement of electrical conductivity and charge transport owing to the emerging role of FeP. The density functional theory calculations reveal that the FeP/g-C3N4 hybrids could act as a promising catalyst for the H2 evolution reaction. Overall, this work not only paves a new path in the engineering of monodispersed FeP-decorated g-C3N4 0D/2D robust nanoarchitectures but also elucidates potential insights for the utilization of noble-metal-free FeP nanodots as remarkable co-catalysts for superior photocatalytic H2 evolution.

Hierarchical ZnIn2 S4 /MoSe2 Nanoarchitectures for Efficient Noble-Metal-Free Photocatalytic Hydrogen Evolution under Visible Light.

A highly efficient visible-light-driven photocatalyst is urgently necessary for photocatalytic hydrogen generation through water splitting. Herein, ZnIn2 S4 hierarchical architectures assembled as ultrathin nanosheets were synthesized by a facile one-pot polyol approach. Subsequently, the two-dimensional-network-like MoSe2 was successfully hybridized with ZnIn2 S4 by taking advantage of their analogous intrinsic layered morphologies. The noble-metal-free ZnIn2 S4 /MoSe2 heterostructures show enhanced photocatalytic H2 evolution compared to pure ZnIn2 S4 . It is noteworthy that the optimum nanocomposite of ZnIn2 S4 /2 % MoSe2 photocatalyst displays a high H2 generation rate of 2228 µmol g-1 h-1 and an apparent quantum yield (AQY) of 21.39 % at 420 nm. This study presents an unprecedented ZnIn2 S4 /MoSe2 metal-sulfide-metal-selenide hybrid system for H2 evolution. Importantly, the present efficient hybridization strategy reveals the potential of hierarchical nanoarchitectures for a multitude of energy storage and solar energy conversion applications.

Controllable synthesis of Cu-Ni core-shell nanoparticles and nanowires with tunable magnetic properties.

Cu seeds were used to direct the epitaxial growth of Ni shell to form Cu-Ni core-shell cubes, tetrahexahedrons and nanowires. The controllable epitaxial growth of Ni shells on Cu cores provided selectively exposed surfaces and morphologies as well as tunable magnetic properties.

Colloidal synthesis of Cu-ZnO and Cu@CuNi-ZnO hybrid nanocrystals with controlled morphologies and multifunctional properties.

Metal-semiconductor hybrid nanocrystals have received extensive attention owing to their multiple functionalities which can find wide technological applications. The utilization of low-cost non-noble metals to construct novel metal-semiconductor hybrid nanocrystals is important and meaningful for their large-scale applications. In this study, a facile solution approach is developed for the synthesis of Cu-ZnO hybrid nanocrystals with well-controlled morphologies, including nanomultipods, core-shell nanoparticles, nanopyramids and core-shell nanowires. In the synthetic strategy, Cu nanocrystals formed in situ serve as seeds for the heterogeneous nucleation and growth of ZnO, and it eventually forms various Cu-ZnO hetero-nanostructures under different reaction conditions. These hybrid nanocrystals possess well-defined and stable heterostructure junctions. The ultraviolet-visible-near infrared spectra reveal morphology-dependent surface plasmon resonance absorption of Cu and the band gap absorption of ZnO. Furthermore, we construct a novel Cu@CuNi-ZnO ternary hetero-nanostructure by incorporating the magnetic metal Ni into the pre-synthesized colloidal Cu nanocrystals. Such hybrid nanocrystals possess a magnetic Cu-Ni intermediate layer between the ZnO shell and the Cu core, and exhibit ferromagnetic/superparamagnetic properties which expand their functionalities. Finally, enhanced photocatalytic activities are observed in the as-prepared non-noble metal-ZnO hybrid nanocrystals. This study not only provides an economical way to prepare high-quality morphology-controlled Cu-ZnO hybrid nanocrystals for potential applications in the fields of photocatalysis and photovoltaic devices, but also opens up new opportunities in designing ternary non-noble metal-semiconductor hybrid nanocrystals with multifunctionalities.

Electrostatic Assembly of Sandwich-like Ag-C@ZnO-C@Ag-C Hybrid Hollow Microspheres with Excellent High-Rate Lithium Storage Properties.

Herein, we introduce a facile electrostatic attraction approach to produce zinc-silver citrate hollow microspheres, followed by thermal heating treatment in argon to ingeniously synthesize sandwich-like Ag-C@ZnO-C@Ag-C hybrid hollow microspheres. The 3D carbon conductive framework in the hybrids derives from the in situ carbonation of carboxylate acid groups in zinc-silver citrate hollow microspheres during heating treatment, and the continuous and homogeneous Ag nanoparticles on the outer and inner surfaces of hybrid hollow microspheres endow the shells with the sandwiched configuration (Ag-C@ZnO-C@Ag-C). When applied as the anode materials for lithium ion batteries, the fabricated hybrid hollow microspheres with sandwich-like shells reveal a very large reversible capacity of 1670 mAh g(-1) after 200 cycles at a current density of 0.2 A g(-1). Even at the very large current densities of 1.6 and 10.0 A g(-1), the high specific capacities of about 1063 and 526 mAh g(-1) can be retained, respectively. The greatly enhanced electrochemical properties of Ag-C@ZnO-C@Ag-C hybrid microspheres are attributed to their special structural features such as the hollow structures, the sandwich-like shells, and the nanometer-sized building blocks.