Surfactant-free Hydrothermal Route Research Articles

Construction of visible light-driven Eu-doped BiOBr hierarchical microflowers for ameliorated photocatalytic 2,4-dichlorophenol and pathogens decomposition with synchronized hexavalent chromium reduction

The presence of diverse environmental contaminants has posed unprecedented challenges to wastewater treatment. Herein, Eu-doped BiOBr hierarchical microflowers (Eu-BiOBr) were fabricated via a surfactant-free hydrothermal route as highly efficient photocatalysts for multipurpose wastewater remediation applications. Under visible light irradiation, the Eu-BiOBr products demonstrated meritorious photoactivity when exposed to the mixture solution of 2,4-dichlorophenol (2,4-DCP) and Cr(VI). Noticeably, 97.6% of 2,4-DCP was degraded after 80 min, and a complete Cr(VI) reduction was obtained within 60 min over the optimized 2 at% Eu-BiOBr. This was ascribed to Eu-doping efficiently accelerated charge separation and migration, thus proliferating more reactive species and enhancing photocatalytic performance. Moreover, the 2 at% Eu-BiOBr possessed good photoactivity after four successive runs, which confirmed its recyclability. Further, as an evaluation of electrical energy consumption, the 2 at% Eu-BiOBr was found to be more economical in decomposing both 2,4-DCP and Cr(VI). The reactive species scavenging tests validated that the hydroxyl radical played a major role for the photodegradation of 2,4-DCP whereas photogenerated electron served as predominant reactive species for Cr(VI) to be reduced to Cr(III). Additionally, the 2 at% Eu-BiOBr demonstrated much enhanced bactericidal activities against Escherichia coli and Bacillus cereus compared to pristine BiOBr. These results revealed that the Eu-BiOBr can be employed as visible light-driven photocatalytic and antibacterial candidates for practical applications in environmental cleanup.

Construction of Magnetic Z-Scheme P-Doped Biobr/CoFe<sub>2</sub>O<sub>4</sub> Nanocomposite for Expeditious Visible Light Photocatalytic Palm Oil Mill Effluent Degradation via the Assistance of IO<sub>4</sub><sup>-</sup> and S<sub>2</sub>O<sub>8</sub><sup>2-</sup>

P-BiOBr/CoFe2O4 nanocomposite was fabricated through a surfactant-free hydrothermal route and combined with electron acceptors (IO4- and S2O82-) for the first time to examine the palm oil mill effluent (POME) degradation and concurrently evaluated the biogas formation under visible light irradiation. The POME degradation efficiency reached 100% in 120 min over P-BiOBr/CoFe2O4/IO4-, which was much higher than the P-BiOBr/CoFe2O4/S2O82- (80.6%). Interestingly, the evaluation of the biogas production demonstrated that the P-BiOBr/CoFe2O4/IO4- photocatalysis generated greater amount of biogas (CH4 + CO2) compared to other systems. The great photocatalytic enhancement was due to the efficient charge carrier separation thanks to the Z-scheme heterojunction between P-BiOBr and CoFe2O4, and the electron trapping by IO4-. The hydroxyl radicals and photogenerated holes contributed majorly to POME degradation. Ultimately, the P-BiOBr/CoFe2O4 with IO4- and S2O82- assisting under visible light provided an effective and feasible method to degrade POME.

Template-free growth of copper-doped hydroxyapatite nanowhiskers and their use as uric acid electrochemical sensor

We synthesize copper-doped hydroxyapatite (Cu HAp) bioceramic nanowhiskers (aspect ratio ˃ 85) by a surfactant-free hydrothermal route. The detailed structural and compositional characterizations confirm the existence of catalytic multivalent Cu 1+ /Cu 2+ dopant ions and secondary β TCP phase. The dopant-induced oxygen vacancies promote active sites on the mesoporous surface (specific area ~ 60.4 m 2 /g) for electrochemical applications. The electrochemical studies of the fabricated Cu HAp FTO revealed good response, sensitivity and stability towards uric acid (lowest stable detection limit ~0.5 μM) in the lower and higher concentration regimes respectively. Thus, our fabricated Cu HAp shows surface-dependent electrochemical activities and non-enzymatic selective response to uric acid. Novel nanowhisker shaped mesoporous copper-doped hydroxyapatite has been employed for catalytic activity and sensing. Three electrode-based non-enzymatic electrochemical sensing of uric acid has been studied by voltammetry and amperometry. Multivalent dopant-induced oxygen vacancies and presence of secondary phase regulates the active sites on the whisker surface. • Copper-doped hydroxyapatite synthesis by surfactant-free hydrothermal route. • Novel mesoporous nanowhisker-shaped morphology of high specific surface area. • Multivalent doping induced oxygen vacancies promote active sites on surface. • Stable eco-friendly non-enzymatic electrochemical sensor of uric acid. • Good sensitivity, selectivity, fast response and reproducibility is achieved.

Interface coupling of 1T-phase dominated MoS nanosheets with nitrogen-doped graphene towards enhanced hydrogen evolution reaction

• 1T-MoS x nanosheets vertically grown on N-doped graphene via interface coupling strategy. • Mo–N coupling hetero-interface promotes 2H-to-1T phase transition of MoS x. • Interface structure and phase composition optimized by tuning N-doped graphene content. • Enhanced hydrogen evolution reaction activity and excellent cycling stability achieved. Herein, a three-dimensional network hetero-structure comprising 1T-phase dominated MoS x nanosheets vertically grown on nitrogen-doped reduced graphene oxide (MoS x /N-rGO) was constructed through a surfactant-free hydrothermal route and applied to hydrogen evolution reaction (HER). We demonstrate that N species in graphene lattices play a vital role for the interface coupling between MoS x and N-rGO via Mo–N bonds, thereby promoting the 2H-to-1T phase transition of MoS x . By adjusting N-rGO content, the 1T-phase concentration of MoS x can reach 81.7% and the corresponding surface structure is optimized. The excellent synergistic effect dependent on robust hetero-interface can increase basal plane/edge active sites and accelerate electron/proton reaction kinetics. Consequently, MoS x /N-rGO exhibits enhanced HER activity with a low onset potential of 100 mV, notably small Tafel slope of 38 mV dec −1 and excellent cycling stability.

Hydrothermal synthesis of Zn-doped α-Fe2O3 nanocubes for selective detection of triethylamine

With the growing attention on environment protection, gas sensors fabricated with metal oxide semiconductor (MOS) have stimulated increasing research interest because of their capability for fast detection of various harmful gases. Here, Zn-doped α-Fe2O3 nanocubes (ZFO NCs) with about 300–500 nm in edge length were successfully prepared via a surfactant-free hydrothermal route and their gas sensing properties were investigated by using as bare α-Fe2O3 NCs as reference. It was found that as applied as active materials for detecting volatile organic compounds (VOCs), the obtained ZFO NCs showed some impressively improved triethylamine (TEA) sensing performances, especially of better selectivity and higher sensitivity. The response (Ra/Rg) of the best ZFO sensor (ZFO-5) to 100 ppm TEA was as high as 64.3, and its selectivity coefficient (STEA/Ammonia) was 6.50, both of which were well above that of the pure α-Fe2O3 sensor. Besides, the ZFO-5 sensor also shows good stability and repeatability. The gas sensitive mechanism of the ZFO NCs was discussed.

Z-scheme heterojunction nanocomposite fabricated by decorating magnetic MnFe2O4 nanoparticles on BiOBr nanosheets for enhanced visible light photocatalytic degradation of 2,4-dichlorophenoxyacetic acid and Rhodamine B

In this study, novel Z-scheme BiOBr/MnFe2O4 nanocomposites were successfully fabricated using a simple and surfactant-free hydrothermal synthetic route. The physicochemical and optical characteristics of the photocatalysts were analyzed by various instruments. The obtained BiOBr/MnFe2O4 nanocomposites significantly accelerated the photodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D) and Rhodamine B (RhB) when compared with other analyzed photocatalysts under visible light irradiation. Among all samples, the BiOBr/MnFe2O4-10 nanocomposite exhibited the best photocatalytic performance. The improved photoactivity was ascribed to the formation of Z-scheme heterojunction between BiOBr and MnFe2O4, thereby resulting in efficient separation of charge carriers. Photoelectrochemical and photoluminescence analyses were carried out to validate this conclusion. Furthermore, the BiOBr/MnFe2O4 nanocomposite can be easily separated and recycled without significant loss of photoactivity after five consecutive uses. The intermediate products produced during the photodegradation of 2,4-D were also detected. Radical quenching experiments revealed that the hydroxyl radicals played critical roles in the photodegradation reactions. Finally, a possible photocatalytic enhancement mechanism of BiOBr/MnFe2O4 nanocomposites was proposed.

A three-dimensional porous CoSnS@CNT nanoarchitecture as a highly efficient bifunctional catalyst for boosted OER performance and photocatalytic degradation.

It is urgent and significant to develop competent, inexpensive transition metal-based catalysts with multifunctional catalytic properties for wide applications. To meet this requirement, herein, for the first time, we present a novel bifunctional CoSnS@CNT hybrid via a simple one-pot surfactant-free hydrothermal method. The CoSnS@CNT hybrid has a unique three-dimensional (3D) porous nanoarchitecture, which is constructed by ultrathin CoSnS homogenously and compactly anchored on a highly conductive CNT skeleton. The porous nanoarchitecture of CoSnS@CNT provides abundant catalytic sites and facilitates ion diffusion, and the CNT skeleton accelerates electron transfer. Benefitting from these merits, the CoSnS@CNT hybrid acted as a bifunctional catalyst with boosted electrocatalytic and photocatalytic performance, where it delivered a tremendous oxygen evolution reaction (OER) performance with a low overpotential of 330 mV at a current density of 10 mA cm-2 and excellent outstanding stability. Moreover, it showed 91.72% photocatalytic degradation for Rhodamine B dye, which is 2-times higher than that of bare CoSnS. This study presents a systematic approach to judiciously design nanostructures and simply synthesize non-noble metal-based bifunctional catalysts with boosted electrocatalytic and photocatalytic activities.

Effect of various technological parameters on particle morphology and uniformity of α-Ni(OH)2 synthesized via surfactant-free hydrothermal route

Hierarchical microspheres of α-Ni(OH)2, uniform in size and shape, have been synthesized through a facile surfactant-free hydrothermal route. Experimental parameters such as reaction time, temperature and reactant concentration were systematically optimized to produce monodispersed particles. SEM analysis confirmed that the particles synthesized from a recipe containing 2.65 × 10−2 mol. L−1 nickel chloride and 5.6 × 10−1 mol. L−1 urea aged at 85 °C for 2 hours were uniform in size and morphology. HR-TEM results showed that the hierarchical microspheres are made up of thin sheet-like units. The crystal structure of the α-Ni(OH)2 microspheres was investigated by XRD which showed (003) as the preferred orientation plane having 7.369 Å interplanar spacing and crystallite size of 21 nm. The intercalation of CO3 −2 and OCN− species was revealed by FT-IR spectroscopy. The average activation energy (41.23 KJ mol−1) for thermal-induced transformation reaction was determined based on the TG/DTA data recorded at three heating rates. The present green and facile route could be extended to synthesize monodispersed systems of other metal compounds.

Ultra thin NiO nanosheets for high performance hydrogen gas sensor device

Unstacked two dimensional (2-D) NiO nanosheets are synthesized via easy surfactant-free hydrothermal chemical route. NiO sensor is investigated for high performance and selective hydrogen (H2) gas sensing properties. Structural analysis is carried out using XRD pattern. The morphology of NiO is confirmed by using FESEM and TEM micrographs. Atomic state and elemental composition are analyzed by recording XPS and EDS spectra respectively. NiO sensor exhibited a high gas response of 191% for 150 ppm H2 concentration at 250 °C operating temperature with response time 150 s. The lowest H2 detection is observed at the concentration of 10 ppm having the gas response of 22%. The H2 response of NiO sensor was tested at different operating temperatures as well as gas concentrations. The dynamic gas response and sensor stability were recorded and analyzed. The sensing mechanism of NiO sensor was discussed.

Surfactant-Free Synthesis of Single-Crystalline Bi4Ti3O12 Nanosheets with Excellent Visible-Light Photocatalytic Activity

Single-crystalline Bi4Ti3O12 nanosheets with a thickness less than 10 nm and a lateral size larger than 20 μm have successfully synthesized via a surfactant-free hydrothermal route by employing K2Ti6O13 nanofibers prepared in advance as titanium sources. The as-prepared samples were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and selected area electron diffraction, respectively. The results revealed that the single-crystalline Bi4Ti3O12 nanosheets are dominated with (010) facets. In general, the slow exfoliation of TiO6 octahedron lamella and the fast combination of the subnitrate radicals with the Bi3+ ions situated in (010) planes induce the crystallization of the single-crystalline Bi4Ti3O12 nanosheets. In addition, the as-prepared single-crystalline Bi4Ti3O12 nanosheets propose a narrowed gap of ca. 2.41 eV and after modified by Pt-quantum-dots exhibit excellent visible-light photocatalytic activity. It is believed that the surfactant-free in the hydrothermal system induce more amount of surface state responsible for the narrowed gap and the excellent visible-light photocatalytic activity.

Mono-crystalline SnTe with micro-octahedroncharacteristic: One-pot facile synthesis and comprehensive crystallographic evidence

AbstractIn recent years, topological crystalline insulators have attracted increased attention due to practical demands of tunable electronic, spin electronic and thermoelectric devices. As an important topological crystalline insulator, mono-crystalline SnTe octahedra with {111} dominated surfaces, were successfully synthesized on a large scale via a surfactant-free hydrothermal synthesis route in this work. Important controlling factors for phase and morphology, i.e. reaction temperature, reactant concentration and stoichiometric ratio, are discussed in detail. The results indicated that high temperature is favorable for forming pure phase, and excessive Sn suppresses the appearance of SnTe with octahedral morphology. Lower reactant concentration is beneficial to preparing uniform SnTe octahedra via the selective growth mechanism. Crystallographic characteristics of the SnTe octahedra were investigated using focused ion beam, electron backscattered diffraction and transmission electron microscopy analysis. The hexagonal-like micro-plate (cut from an octahedron) was confirmed as mono-crystalline by the corresponding three Euler angle maps, the Kikuchi diffraction pattern and selected-area diffraction. It can be further deduced from the multiple experimental results that surfaces of octahedral SnTe are dominated by {111} crystallographic planes and the average size is 1–3 μm. Controllable mono-crystalline octahedra would effectively promote the development of topological crystalline insulators and their micro devices.

Preparation of novel flower-like BiVO4/Bi2Ti2O7/Fe3O4 for simultaneous removal of tetracycline and Cu2+: Adsorption and photocatalytic mechanisms

To improve the visible light utilization and adsorption capacity for combined pollutants (Tetracycline and Cu2+), novel flower-like BiVO4/Bi2Ti2O7/Fe3O4 composite has been successfully synthesized for the first time via a simple two-step process, surfactant-free hydrothermal route and solvothermal method. The crystal structures, chemical compositions, morphologies, optical and photocatalytic properties of the as-prepared samples were characterized by the techniques of XRD, XPS, SEM, HRTEM, BET, UV–vis DRS, and Photocurrent tests (PT). The synthetic sample with 4:1:20 (S5) mass ratio of BiVO4/Bi2Ti2O7/Fe3O4 possessed the highest adsorption capacity and photocatalytic performance simultaneously in all of the as-prepared composites. Adsorption experiment (model 1 and model 2) suggested that there was not only competitive adsorption but also synergistic adsorption mechanisms between Cu2+ and TC. Compared to pure BiVO4, and BiVO4/Bi2Ti2O7, BiVO4/Bi2Ti2O7/Fe3O4 displayed more superior photodegradation efficiency with 97.22% removal of TC (10 mg/L) in 60 min, where the optimal conditions were catalyst dosage 1.00 g/L and initial pH at 6.0. In addition, radical trapping experiments revealed that the photo-induced active species superoxide radical (O2−) and holes (h+) were the predominant active species in the photocatalytic system. These features demonstrate that the BiVO4/Bi2Ti2O7/Fe3O4 has great application potential for combined pollutants’ removal from water.

Solar-Light-Driven Improved Photocatalytic Performance of Hierarchical ZnIn2S4 Architectures.

In the quest for developing novel narrow band gap semiconductor materials, the research in metal chalcogenides has gained a strong attraction. In the present investigation, a surfactant-free hydrothermal route has been followed to design hierarchical self-assembled flower-like ZnIn2S4 structures through control over precursor concentration and hydrothermal processing parameters. Uniform hexagonal marigold flower-like ZnIn2S4 architectures (∼4 μm) were formed with self-assembly of petals (thickness ∼8–12 nm) forming rose-like structures and finally forming marigold flowers in 24 h duration. The hierarchical ZnIn2S4 flower structure has been used as photocatalysts for the degradation of dye and chlorinated phenols. Photodegradation demonstrates that the high surface area from the porous flower architecture (∼72 m2/g) with an enhanced visible light absorption giving low band gap energy (2.15 eV) is responsible for higher photocatalytic performance. Complete degradation of the organic pollutants has been observed within 90 min in the presence of natural sunlight. To understand the participating reactive species contributing to degradation, scavenger studies were performed for deducing the plausible photocatalytic degradation pathways. This study might open new insights into the design of novel hierarchical structures.

One-step preparation of zirconia coated silica microspheres and modification with d-fructose 1, 6-bisphosphate as stationary phase for hydrophilic interaction chromatography

In this study, ZrO2 layer coated silica microspheres (ZrO2/SiO2) were successfully prepared by a facile one-step surfactant-free hydrothermal route under low pH condition. The synthesized ZrO2/SiO2 material was then modified with d-fructose 1, 6-bisphosphate (FDP) to improve the chromatographic separation property of the material. Fused-silica capillary columns were prepared with the modified material for evaluation. Phenolic, nucleobases and alkaloids compounds in hydrophilic interaction chromatographic (HILIC) mode showed symmetrical peaks. The FDP-ZrO2/SiO2 stationary phase showed better performance than ZrO2/SiO2 packing material and demonstrated great potential for application in HILIC mode.

Textured SnSe micro-sheets: One-pot facile synthesis and comprehensive understanding on the growth mechanism

Preferential aligned SnSe micro-sheets were successfully synthesized via a surfactant-free hydrothermal synthesis route. The Lotgering factor F and the intensity ratio of (400) to (111) for SnSe Micro-sheets prepared by the optimized process is 0.64, 9.85, respectively, which verify the obvious textured characteristic of micro-sheets. The micro-sheets with uniform composition are polycrystallines with an orthorhombic crystal structure, show the preferential aligned morphology assembled by a great deal of nano-particles according to observation and analysis from the electron diffraction pattern, the lattice fringe, the Energy-dispersive spectroscopy and the transmission electron microscopy (TEM) images. Through deep observation from high-resolution transmission electron microscopy, an arc pattern verifies the textured characteristic of the SnSe sheet. The preferential aligned growth mechanism can be understood by researching effect of reaction temperature, alkali concentration on phase, preferred orientation and morphology. A proper temperature can control textured degree via adjusting effective diffusion, rotation of nano-crystal and fluid movement. Increasing alkali concentration enhances the surface adsorption stability of chalcogenides, and decreases new nucleation site in the (011) face, and helps the dis-matched nano-crystal re-dissolute, which results in formation of square-like textured micro-sheets. A proposed growth mechanism of textured SnSe micro-sheets with two growth models (the lateral growth model and the vertical growth model) is provided, and the two growth models control textured characteristic of micro-sheets, which can be adjusted by change of reaction temperature and alkali concentration.

Surfactant-free hydrothermal synthesis of CePO4 microbundles assembled by aligned nanorods

In this research, CePO4 microbundles composed of aligned nanorods have been successfully synthesized through a facile surfactant-free hydrothermal route. The whole synthetic process was rather simple and green. And different synthetic parameters including the aging time and acidic strength were investigated such to understand the formation of the novel hierarchical microarchitectures. It was found that the hydrothermal time, as well as the acidic strength of the precursor media played a key role in mediating the assembly of one-dimensional micrcobundles from initially formed nanorods. Based on a series of experimental observations, a ‘precipitation-growth’ mechanism is proposed to describe the growth of the unique microstructures.

Lanthanide-doped Sr2ScF7 nanocrystals: controllable hydrothermal synthesis, the growth mechanism and tunable up/down conversion luminescence properties

Sr2ScF7 micro/nanocrystals with various morphologies were firstly synthesized via a one-step surfactant-free hydrothermal route. Sr2ScF7:Yb3+/Er3+/Tm3+ phosphors show tunable RGB and white emissions.

Hydrothermal synthesis of novel flower-like BiVO4/Bi2Ti2O7 with superior photocatalytic activity toward tetracycline removal

A novel flower-like BiVO4 and BiVO4/Bi2Ti2O7 heterojunction photocatalyst was firstly synthesized by surfactant-free hydrothermal route, which is very convenient, rapid, controllable and environmentally friendly. The crystal structures, chemical composition, morphology, optical and photo-catalytic property of the as-prepared samples were characterized by the techniques of XRD, XPS, SEM, HRTEM, BET, UV–vis DRS, and PL. The BiVO4/Bi2Ti2O7 heterojunction photocatalyst exhibited higher photocatalytic activity than pure BiVO4 and Bi2Ti2O7 for the degradation of tetracycline (TC) under xenon lamp irradiation. The enhanced photocatalytic activities of BiVO4/Bi2Ti2O7 composites were either related to the particular structural features or the mass ratios of BiVO4 and Bi2Ti2O7 in the composites. The possible photocatalytic mechanism of the BiVO4/Bi2Ti2O7 composite has been speculated by detecting reactive species based on free radicals trapping experiments. The preliminary removal pathways of tetracycline was proposed on the basis of the identified intermediates using LC-TOF/MS.

Hydrothermal synthesis of phosphate-doped BiVO4 with exposed (010) facets and enhanced sunlight-driven photocatalytic properties

Phosphate-doped monoclinic BiVO4 (mBiVO4) single-crystalline sheets with exposed (010) facets were synthesized by a surfactant-free hydrothermal route for the first time. The results indicate that the appropriate addition of PO4 oxoanion has significant influence on the crystal growth of mBiVO4 along (010) facets, as well as morphology of the products. The sheet-like mBiVO4 doped with 5% PO4 oxoanion possesses the highest intensity ratio of I(040)/I(121), and exhibits the best sunlight-driven photocatalytic performance for methylene blue degradation. The exposed (010) facets of the PO4-doped mBiVO4 which is in favor of increasing the separation of photogenerated electron-hole pairs plays a leading role on the enhanced photocatalytic activity of 5% PO4-doped mBiVO4.

The self-assembly mechanism of CaWO4@CaWO4:Dy3+ core/shell microspheres via a simple surfactant-free hydrothermal route

In this work, we reported the fabrication and characterization of CaWO4@CaWO4:Dy3+ core/shell microspheres via a facile hydrothermal method without organic surfactant. The samples were characterized by XRD, SEM, EDS and photoluminescence. These core/shell microspheres were constructed by nanoparticles through a self-assembly way without any organic surfactant or template. The solid and hollow microspheres prepared through positive and reverse precipitation respectively were used as the precursor. The reduction of the surface energy and high temperature in the hydrothermal process provided the kinetics and thermodynamics motion of the self-assembly course respectively. The direct doped CaWO4:Dy3+ and CaWO4@CaWO4:Dy3+ (core–shell) microspheres show characteristic emission of Dy3+. The luminescent intensity of the core/shell phosphor was enhanced with respect to the direct doped one of the same doping concentration. The possible mechanism was also proposed.