A Promising Solid-State Synthesis of LiMn1- yFeyPO4 Cathode for Lithium-ion Batteries.

LiMn1-yFeyPO4 (LMFP) is a significant and cost-effective cathode material for Li-ion batteries, with a higher working voltage than LiFePO4 (LFP) and improved safety features compared to layered oxide cathodes. However, its commercial application faces challenges due to a need for a synthesis process to overcome the low Li-ion diffusion kinetics and complex phase transitions. Herein, a solid-state synthesis process using LFP and nano LiMn0.7Fe0.3PO4 (MF73) is proposed. The larger LFP acts as a structural framework fused with nano-MF73, preserving the morphology and high performance of LFP. These results demonstrate that the solid-state reaction occurs quickly, even at a low sintering temperature of 500 °C, and completes at 700 °C. However, contrary to the expectations, the larger LFP particles disappeared and fused into the nano-MF73 particles, revealing that Fe ions diffuse more easily than Mn ions in the olivine framework. This discovery provides valuable insights into understanding ion diffusion in LMFP. Notably, the obtained LMFP can still deliver an initial capacity of 142.3 mAh g-1, and the phase separation during the electrochemical process is significantly suppressed, resulting in good cycling stability (91.1% capacity retention after 300 cycles). These findings offer a promising approach for synthesizing LMFP with improved performance and stability.

Insight into the photocatalytic mechanism of the optimal x value in the BiOBrxI1-x, BiOClxI1-x and BiOClxBr1-x series varying with pollutant type.

It is known that bismuth oxyhalides (BiOX, X = Cl, Br, I) can easily form solid solutions like BiOBrxI1-x, BiOClxI1-x and BiOClxBr1-x (0 ≤ x ≤ 1) and exhibit composition-dependent photocatalytic performance. However, the reported results indicate that the optimal composition changes with pollutant type. That is to say, the specific x value with the best photocatalytic activity towards the degradation of a certain pollutant does not imply that it is an optimum x value for another pollutant. In order to explore the reason behind this, herein, three types of solid solutions with various x values were prepared in ethylene glycol/H2O (VEG : VH2O = 1) solution at room temperature, and their photocatalytic activity towards the degradation of bisphenol A (BPA), tetracycline (TC), malachite green (MG), methyl violet (MV) and rhodamine B (RhB) was assessed under visible-light illumination. Taking BiOBrxI1-x as an example, BiOBr0.5I0.5 exhibited the best degradation efficiency for BPA, MV and MG, whereas BiOBr0.95I0.05 possessed the best photocatalytic activity towards TC and RhB degradation. Detailed characterization suggests that light absorption and charge separation efficiency are not the main factors behind this difference. Given that direct oxidation of the holes was dominant in the degradation process, the oxidation ability of the solid solutions was correlated with the oxidation behavior of the pollutant. The prerequisite condition for degrading a certain pollutant is that the valence band potential of the solid solution should be more positive than the oxidation potential of the pollutant, and yet, too big a difference between these two potentials does not benefit rapid degradation.

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.

Transformation of phase and heterojunction type by using HAc-adsorbed Bi(NO3)3 as a Bi source.

Generally, preparing high-efficiency heterojunction photocatalysts via a facile room-temperature route is attractive from the perspective of energy and labor saving. Herein, by using dried and glacial acetic acid (HAc)-adsorbed bismuth nitrate, instead of Bi(NO3)3·5H2O, as a Bi source, a ß-Bi2O3/Bi5O7I heterojunction with well dispersed flowery hierarchical architecture was synthesized, which endows it with high surface area, open channels and good light harvest. More importantly, the change of the precursor achieved a successful transformation for both of phase and heterojunction type, i.e. from type-Ⅰ BiOI/[Bi6O5(OH)3](NO3)5·3H2O (labeled as BiOI/BBN) to Z-scheme ß-Bi2O3/Bi5O7I heterojunction. Since both ß-Bi2O3 and Bi5O7I are visible light responsive, ß-Bi2O3/Bi5O7I exhibited improved visible-light photocatalytic activity for the degradation of tetracycline (TC) and malachite green (MG) with apparent reactant rate (kapp) values about 10 and 11 times higher than those of BiOI/BBN. Besides, the presence of more oxygen vacancies also contributed to the enhancement in photocatalytic performance.

Phase transformation and heterojunction construction of bismuth oxyiodides by grinding-assisted calcination in the presence of thiourea and their photoactivity.

Bismuth-rich oxyhalides are promising photocatalysts due to their special layered structure and adjustable band gap energy. In this work, a series of bismuth oxyiodides were fabricated by grinding-assisted calcination in the presence of thiourea, where grinding-induced mechanical force could accelerate the decomposition reaction and thiourea could prohibit the crystal particles from growing due to coordination action. The combined effect of grinding and thiourea could decrease the temperature of phase transformation of bismuth oxyiodides. Among these, heterojunction Bi4O5I2/Bi5O7I containing uniform flower-like microspheres assembled by ultra-thin nanosheets exhibited the highest photocatalytic activity and favorable stability for the degradation of the antibiotic tetracycline under visible light irradiation. This work could provide a good reference for the design of bismuth-rich oxyhalide heterojunction for photocatalytic applications.

One-pot grinding method to BiO(HCOO)xI1-x solid solution with enhanced visible-light photocatalytic activity.

Considering that conventional hydrothermal route to prepare photocatalysts is energy-consumable and difficult to scale-up, herein, uniform bismuth oxide formate (BiOHCOO; BiOR) nanosheets were firstly prepared from solid-state chemical reaction by a facile room-temperature grinding method. Furthermore, since BiOR could only respond to UV light, thin-nanosheet-based flowerlike BiO(HCOO)xI1-x solid solutions were synthesized via a one-pot method by adding KI into the BiOR reaction mixture and continuously grinding for an additional duration. As compared with BiOR, the resulting solid solution with x = 0.57 possessed narrower band gap, optimal energy levels and higher surface areas, leading to much higher visible-light photocatalytic activity for multiple pollutants degradation including rhodamine B (RhB), malachite green (MG) and colorless bisphenol A (BPA). This work demonstrates an easily-handling and eco-friendly solid-state reaction route to solid solutions with excellent visible-light photocatalytic activity. Good photocatalytic performance was also confirmed by electrochemical techniques.

Milling-Induced Synthesis of BiOCl1-x Brx Solid Solution and Their Adsorptive and Photocatalytic Performance.

CH3 COO(BiO) (denoted as BiOAc) is one of the most easily obtained bismuth compounds and was for the first time proposed by our group as an effective UV light photocatalyst. Herein, BiOCl1- x Brx (x refers to the feeding atomic ratio) were obtained using a facile solid state milling and subsequent water washing. More importantly, all of the as-prepared BiOCl1- x Brx possessed better visible light photocatalytic activity to the corresponding ones obtained by previously reported solution route. Especially at an optimal x value of 0.5, the solid solution showed the highest photodegradation efficiency (~100%) for rhodamine B (RhB) with a concentration of 30 mg L-1 , whereas the degradation efficiency was only 63% over that obtained by solution route. Furthermore, the as-prepared BiOCl0.5 Br0.5 also exhibited excellent photodegradation activity for malachite green (MG). The superior photocatalytic performance of the as-prepared BiOCl0.5 Br0.5 could be attributed to its thinner sheetlike structures and highly exposed (001) facets, which enable effective separation of the photogenerated electrons and holes along the [001] direction. In addition, the as-prepared BiOCl0.5 Br0.5 revealed dramatic adsorption capacity for cationic dyes like MG, RhB and methylene violet (MV), as well as anion (Cr2 O7 )2- owing to electrostatic interaction between cationic dyes and negatively charged surface of BiOCl0.5 Br0.5 , and positively charged surface in K2 Cr2 O7 solution (pH ≈ 3).

One-Pot Strategy to Bi2S3/BiOCl Heterojunction with Enhanced Photocatalytic Activity.

Bi2S3/BiOCl (denoted as BS-BC) heterojunction photocatalyst has been reported to be able to increase light absorption, promote charge separation and consequently enhance photocatalytic efficiency in comparison with single BiOCl. However, the heterojunction was usually prepared by a two-step method, i.e., BiOCl was firstly prepared and then to BS-BC heterojunction through an ion exchange strategy. In this work, BS-BC was prepared by a one-pot room temperature route, where Bi(NO3)3 dissolved in aqueous urea solution could homogeneously react with a mixture solution of NaCl and thiacetamide (TAA) to form BS-BC heterojunction. The urea could prohibit the hydrolysis of Bi(NO3)3 and accelerate the decomposition of TAA to release S2-, and as a consequence, the heterojunction photocatalyst with small size and large interfacial area could be prepared in several hours. The resulted heterojunction exhibited better visible-light photocatalytic activity for RhB degradation than individual BiOCl or that prepared by a two-step route due to close contact between Bi2S3 and BiOCl, modified band structures and effective interfacial charge transfer.

Synthesis of Unique Flowerlike Bi2 O2 (OH)(NO3 ) Hierarchical Microstructures with High Surface Area and Superior Photocatalytic Performance.

Unique flowerlike Bi2 O2 (OH)(NO3 ) (denoted as BION) hierarchical microstructures assembled by ultrathin nanosheets were hydrothermally synthesized from incomplete hydrolysis of anhydrous bismuth nitrate (Bi(NO3 )3 ) after adsorption of glacial acetic acid (HAc). The structure, composition, and optical properties of the products were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis spectroscopy, etc. The as-prepared flowerlike BION possessed an ultra-high surface area and thus exhibited exceptional photocatalytic activity for rhodamine B (RhB) degradation under UV light irradiation with an efficiency of about 17; 6 and 2.5 times higher than spherical, aggregated sheet-like BION and P25 TiO2 , respectively, and also superior to the reported sheet-like BION. It also showed good photocatalytic activity for crystal violet (CV) degradation. This work opens new routes for the rational design and synthesis of nontoxic basic bismuth nitrates with a facile synthetic approach, controllable morphology, and excellent photoreactivity.

A facile and rapid room-temperature route to hierarchical bismuth oxyhalide solid solutions with composition-dependent photocatalytic activity.

The unique nanosheet-based flower-like BiOCl1-xBrx (x=0-1) hierarchical solid solutions have been prepared by the reaction of Bi2O3 and KCl/KBr in mixed solution of glacial acetic acid (HAc) and H2O in dozens of minutes under ambient conditions. During the preparation process, the intermediate bismuth oxide acetate (CH3COOBiO) plays a key role in the formation of BiOCl1-xBrx solid solutions in such a short time. The as-prepared hierarchical BiOCl1-xBrx solid solutions possess high specific surface areas and modified band structures, which exhibit enhanced photocatalytic activity for Rhodamine B (RhB) degradation in comparison with pure BiOCl and BiOBr under visible light irradiation, with the activity reaching the maximum at x=0.5. The photodegradation efficiency of the BiOCl0.5Br0.5 solid solution is twice and 12times higher than P25 TiO2 under UV and visible light irradiation, respectively.

A completely controlled sphere-to-bilayer micellar transition: the molecular mechanism and application on the growth of nanosheets.

The combination of a simple modification of the sample addition method to generate a sort of continuously accumulated external stimulation with only minute increments in amplitude and the introduction of probe molecules (herein aniline) within the micelle allow the direct continuous in situ spectroscopic monitoring of possible micellar transitions. In this way, a sphere-to-ellipsoid and further an ellipsoid-to-bilayer micellar transition of sodium dodecyl sulfate (SDS) induced by camphor sulfuric acid (CSA) is observed to experience four stages in the time sequence: (i) the accumulated protons released from CSA in the hydration layer of the micelle stimulate the rearrangement of SDS micelles; (ii) the micelles transform into ellipsoidal shapes as evidenced by the characteristic chemical shift anisotropy and the corresponding molecular dynamic properties from probe molecules; (iii) further protonation of aniline induces the micelle to turn into lamellar structures; (iv) aniline is freed from the micelle while leaving the SDS bilayers undistorted. Moreover, polyaniline nanosheets incorporating SDS bilayers in sandwich structures, which can display excellent capacitive behavior at relatively high current densities for the fabricated supercapacitors, are prepared from the aniline oriented by the bending energy of the SDS bilayers.

Synthesis of Bi nanowire networks and their superior photocatalytic activity for Cr(vi) reduction.

Interconnected Bi nanowire networks were synthesized for the first time via a solvothermal route by using ethylene glycol (EG) as both a solvent and a reducing agent, and citric acid (CA) as a stabilizing agent at a molar ratio of CA/Bi(3+) = 5. Among various reaction conditions including the temperature, reaction time and precursor concentration, the molar ratio of CA/Bi(3+) was the dominant experimental parameter to influence the morphology and structures of the Bi crystals. Highly dispersed Bi microspheres and network-like Bi thick wires were obtained if the molar ratio of CA/Bi(3+) was changed to 2.5 and 10, respectively. As compared to other additives including trisodium citrate, cetyltrimethylammonium bromide (CTAB) and oxalic acid, good solubility of CA in EG together with its coordination effect played a crucial role in the formation of network-like Bi nanowires. The Bi nanowire networks exhibited excellent photocatalytic performance for Cr(vi) reduction. Cr(vi) was completely reduced to less toxic Cr(iii) after 8 min and 55 min of UV and visible-light irradiation, respectively.

Nucleation of polyaniline nano-/macrotubes from anilinium composed micelles.

A mechanistic study on the nucleation of polyaniline nanotubes (PANI-NT) through template-free method is explored by in situ solution-state (1)H NMR experiments via a careful analysis of the spectral evolution of the major species in the course of the reaction. Before polymerization, aniline and salicylic acid have assembled into loosely packed micelles due to electrostatic interactions and the proton exchange reaction between aniline and anilinium. A three-stage polymerization with a formation, accumulation of aniline dimers, as well as a generation of phenazine-like oligomers is observed, which can be attributed to the monomer transformation from neutral aniline molecules to anilinium cations and the significantly lowered pH in the reaction. Strong π-π stacking interactions from the phenazine-like oligomers facilitate the intermolecular aggregation which initiates the formation of PANI-NT. At first, such aggregates, locating at the outermost layer of anilinium composed micelles, shield in situ formed protons from releasing into the aqueous bulk but into the micelle instead. Due to the continuously increased charge in the micelle, a sphere-to-rod structural transition occurs which leads the oligomer aggregates to be sheathed at the exterior of the rod. Further consumption of anilinium in the micelle leaves the internal cavity while the fusion between the micelles elongates the length of the tubes. Our work demonstrates that (i) loosely packed anilinium composed micelles, highly mobile monomers within the micelle, and efficient blockage of the proton-releasing to the aqueous bulk are three key factors for the generation of tubular structures; and (ii) dynamic NMR line shape analysis provides a new perspective for resolving the formation profile of nanostructured polymers.

[Preparation, characterization and photocatalysis of Bi2WO6 nanocrystals].

In the present study, bismuth tungstate (Bi2WO6) nanocrystals were prepared by the hydrothermal method using bismuth nitrate (Bi(NO3)3 x 5H2O) and sodium tungstate (Na2WO4 x 2H2O) as raw materials at 150 degrees C for 24 h. The powder X-ray diffraction (XRD) pattern shows that the Bi2WO6 nanocrystals belong to the orthorhombic phase with calculated lattice constants a = 5.457 angstroms, b = 16.435 angstroms and c = 5.438 angstroms. The X-ray photoelectron spectra (XPS) indicate that the obtained Bi2WO6 was pure. The photocatalytic activity of the nanocrystal prepared by using water, N, N-dimethyl formamide (DMF) and ethylene glycol (EG) as the solvent respectively were studied for the degradation of rhodamine B under visible light irradiation. The results show that Bi2WO6 sample obtained in EG has the best photocatalytic activity mainly owing to good dispersion, small particle size and broader spectrum response for visible light. In addition, the influence of pH and surfactant on the Bi2WO6 photocatalytic activity was also studied. The results show that Bi2WO6 sample has better photocatalytic activity when prepared at 150 degrees C and pH 1.0 with sodium dodecylsulfate (SDS) as the surfactant. The photoluminescence (PL) spectra of the prepared Bi2WO6 reveal that the recombination of photo-generated electrons and holes was inhibited over Bi2WO6 prepared with SDS and thus its photocatalytic ability was enhanced.

Room-temperature synthesis of self-assembled Sb2S3 films and nanorings via a two-phase approach.

The freestanding Sb(2)S(3) films were easily synthesized at the interface of water and toluene at room temperature, where Na(2)S and (C(2)H(5)OCS(2))(3)Sb (xanthate, O-ethyldithiocarbonate) acted as sulfur and antimony source, respectively. After 3 h of aging, the Sb(2)S(3) films with a flat surface toward organic side and rough surface toward aqueous side were assembled by sheaflike Sb(2)S(3) nanowires. The Sb(2)S(3) nanorings formed by end-to-end connection of the bundled nanowires appeared in the water layer when the reaction time reached 24 h. The Sb(2)S(3) nanorings showed higher photocatalytic activity for methyl orange degradation under visible light than the Sb(2)S(3) films owing to broader spectrum response and better aqueous dispersion.

Growth of copper sulfide dendrites and nanowires from elemental sulfur on TEM Cu grids under ambient conditions.

Copper sulfide dendrites and subsequent uniform nanowires up to tens of micrometers long can be grown on carbon-coated transmission electron microscopy (TEM) Cu grids from elemental sulfur at room temperature under ambient conditions without any solvent and surfactants. TEM and high-resolution TEM studies demonstrated the morphology evolution of Cu2S from dendrites into ultra-long nanowires with increasing ageing time. The sulfur species influenced significantly the growth rate of Cu2S dendrites and nanowires, but the final morphology remained the same. The native oxide on the surface of Cu grids played a critical role in the formation of Cu2S dendrites and nanowires. The crystal structures and phase purity of Cu2S samples were confirmed by x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDX). A solid-liquid-solid growth model may be considered a potential mechanism in Cu2S morphology evolution on the basis of the experimental results. Most importantly, the present study provides a simple and environmentally friendly route for the growth of one-dimensional (1D) Cu2S on Cu substrate.

Decorating graphene oxide with CuO nanoparticles in a water-isopropanol system.

A facile chemical procedure capable of aligning CuO nanoparticles on graphene oxide (GO) in a water-isopropanol system has been described. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations indicate that the exfoliated GO sheets are decorated randomly by spindly or spherical CuO nanoparticle aggregates, forming well-ordered CuO:GO nanocomposites. A formation mechanism of these interesting nanocomposites is proposed as intercalation and adsorption of Cu2+ ions onto the GO sheets, followed by the nucleation and growth of the CuO crystallites, which in return resulted in the exfoliation of GO sheets. Moreover, the obtained nanocomposites exhibit a high catalytic activity for the thermal decomposition of ammonium perchlorate (AP), due to the concerted effect of CuO and GO.

Graphene oxide--MnO2 nanocomposites for supercapacitors.

A composite of graphene oxide supported by needle-like MnO(2) nanocrystals (GO-MnO(2) nanocomposites) has been fabricated through a simple soft chemical route in a water-isopropyl alcohol system. The formation mechanism of these intriguing nanocomposites investigated by transmission electron microscopy and Raman and ultraviolet-visible absorption spectroscopy is proposed as intercalation and adsorption of manganese ions onto the GO sheets, followed by the nucleation and growth of the crystal species in a double solvent system via dissolution-crystallization and oriented attachment mechanisms, which in turn results in the exfoliation of GO sheets. Interestingly, it was found that the electrochemical performance of as-prepared nanocomposites could be enhanced by the chemical interaction between GO and MnO(2). This method provides a facile and straightforward approach to deposit MnO(2) nanoparticles onto the graphene oxide sheets (single layer of graphite oxide) and may be readily extended to the preparation of other classes of hybrids based on GO sheets for technological applications.

[Study on the preparation and spectral characteristics of Bi2S3 nanoribbons].

In the present study, bismuth sulfide (Bi2S3) nanoribbons were prepared by the hydrothermal method using bismuth nitrate (Bi(NO3)3 x 5H2O), thioacetamide (C2H5NS) and nitrilotriacetic acid (C6H9NO6) as raw materials at 180 degrees C for 12 h. The reaction time was largely reduced and the route has been unreported. The constituent, structure and morphology of the products were characterized by XRD, XPS and TEM, respectively. The powder X-ray diffraction (XRD) pattern shows that the Bi2S3 crystals belong to the orthorhombic phase (JCPDS:17-320) with calculated lattice constants a = 1.1106 nm, b = 1.0993 nm and c = 0.3892 nm, which are consistent with the reported values (a = 1.1149 nm, b = 1.1304 nm and c = 0.3981 nm). Transmission electron microscopic (TEM) studies reveal that the appearance of as-prepared Bi2S3 is nanoribbon-like with the typical width of about 100 nm; and the high-resolution transmission electron microscope (HRTEM) image shows that the crystal grows along the y axis. The quantification of X-ray photoelectron spectra (XPS) analysis peaks gives an atomic ratio of 2 : 3 for Bi : S, which is consistent with the given formula of Bi2S3. Furthermore, the Raman and UV-Vis spectra of the product were also studied. Compared with bulk Bi2S3 (236 cm(-1)), the Raman absorption band of the Bi2S3 nanoribbons (195 cm(-1)) red-shifts 41 cm(-1), which is because of the surface effect of nanomaterials. Furthermore, the product has absorption at the wavelength of about 450 nm in the UV-Vis region. The direct bang gap energy (Eg) was estimated to be about 1.58 eV(Eg of the bulk Bi2S3 is 1.3 eV), which indicates that the product has potential application in the optical and electrical areas.

[Study on the preparation and spectral characteristics of CeO2 nanocrystallines].

Ceria (CeO2) nanoparticles were prepared by precipitation method using cerium nitrate (Ce(NO3)3 x 6H2O) and ammonia (25 Wt%) as raw materials under the reaction for 3 h and ageing for 9 h at 80 degrees C without any surfactants and further calcination. The powder X-ray diffraction (XRD) pattern shows the as-prepared CeO2 crystals belong to the cubic phase and are well crystallized. Transmission electron microscopic (TEM) studies reveal that the appearance of as-prepared CeO2 is hexagonal, which is proposed to be the projection of polyhedral shape. The regular fringes spacing of 0.31 nm is in agreement with the d value of (111) lattice planes of cubic phase CeO2 from high-magnification TEM image. Reaction conditions such as the concentration of precipitant, reaction temperature and ageing duration exert important influence on the purity and morphology of the product. Ce(OH)3 was detected when the reaction was processed at lower pH (< 9) or with ageing duration less than 8 h at 80 degrees C. The size of polyhedral ceria nanoparticles increased with longer ageing time (> 15 h). If the reaction went on at a temperature lower than 40 degrees C, a large quantity of rodlike Ce(OH)3 was produced according to TEM observation. Raman spectra of CeO2 nanocrystallines exhibit a Raman shift at 465 cm(-1), corresponding to a F2g Raman band from the space group Fm3m of a cubic fluorite structure, while the Raman shift at about 600 cm(-1) may be attributed to the second Raman vibration mode of O2- vacancy due to Ce3+ impurity. Photoluminescence spectrum of CeO2 shows an emission at 465 nm at room temperature, which may be explained by charge transition from the 4f band to the valence band of CeO2.