Two-step Hydrothermal Treatment Research Articles

A bifunctional NiCo2S4/reduced graphene oxide@polyaniline nanocomposite as a highly-efficient electrode for glucose and rutin detection

A novel NiCo2S4/reduced graphene oxide@polyaniline (NiCo2S4/rGO@PANI) composite was synthesized by a facile two-step hydrothermal treatment and calcination, which was coupled with an in situ polymerization process.

Two-step hydrothermal synthesis of NiCo2S4/Co9S8 nanorods on nickel foam for high energy density asymmetric supercapacitors

It is still a huge challenge to obtain a high-energy-density asymmetric supercapacitors and develop an active electrode material with excellent electrochemical characteristics. Although NiCo2S4 has been considered as one of the promising positive electrode materials for asymmetric supercapacitors, the electrochemical performance of the NiCo2S4-based positive electrodes is still relatively low and cannot meet the demand in the devices. Herein, NiCo2S4/Co9S8 nanorods with a large capacitance are synthesized via a simple two-step hydrothermal treatment. A high-performance asymmetric supercapacitor operating at 1.6V is successfully assembled using the NiCo2S4/Co9S8 nanorods as positive electrode and activated carbon as negative electrode in 3M KOH aqueous electrolyte, which demonstrates a fairly high energy density of 49.6Whkg−1 at a power density of 123Wkg−1, an excellent capacitance of 0.91Fcm−2 (139.42Fg−1) at current density of 1mAcm−2 as well as a remarkable cycling stability due to the high physical strength, the large specific surface area, and the good conductivity for NiCo2S4/Co9S8 nanorods and the brilliant synergistic effect for NiCo2S4 and Co9S8 electrode materials. The as-prepared NiCo2S4/Co9S8 nanorods open up a new platform as positive electrode material for high-energy-density asymmetric supercapacitors in energy-storage.

Three-dimensional hierarchical anatase@rutile TiO2 nanotree array films decorated by silver nanoparticles as ultrasensitive recyclable surface-enhanced Raman scattering substrates

In this paper, we report a three-dimensional (3D) hierarchical nanostructure as a surface-enhanced Raman scattering (SERS) sensor by decorating Ag nanoparticles on a TiO2 nanotree (TNT) array film via a simple two-step hydrothermal treatment and a magnetron sputtering technique for the first time. The sensitivity, recyclability, and uniformity of the SERS-active substrates were investigated using Rhodamine 6G (R6G) as the probe molecule. A detection limit of 1.0 × 10−12 M R6G molecules and an enhancement factor of 5.29 × 105 were achieved on the 3D hierarchical TNT array film with 60 s Ag-sputtering. More importantly, the optimized TNT/Ag also exhibits excellent recyclability and uniformity. The relative standard deviation in the intensity of Raman vibration mode (1506 cm−1) was about 1.2%. Furthermore, the 3D hierarchical nanostructure was more efficient than the 1D nanostructure for SERS measurements. The excellent SERS performance is attributed to the formation of high-density hot spots for 3D nanostructure as well as the synergistic effects of electromagnetic and charge transfer. Moreover, the anatase@rutile mixed phase provides an additional charge transfer effect, which can lead to further enhancement of the Raman signal. The results show that the TNT/Ag nanostructure can be a promising candidate for SERS sensors.

Facile fabrication of flower-like CuCo2S4 on Ni foam for supercapacitor application

Electrochemical performance and production cost are the main concerns of electrode materials for the practical supercapacitor applications. Here we use a simple and universally applicable two-step hydrothermal treatment process to prepare the flower-like CuCo2S4 nanosheet arrays directly grown on Ni foam and employ it as binder-free and conductive-agent-free electrode for pseudocapacitors. The electrode at a current density of 5 mA cm−2 exhibits an ultrahigh capacitance of 908.9 F g−1 and at 30 mA cm−2 delivers an outstanding cycling stability with retaining 91.1% after 2000 cycles compared with its initial capacity. Furthermore, the assembled flower-like nanostructured CuCo2S4//active carbon asymmetric supercapacitor displays a specific capacitance of 93.5 F g−1 at 1 mA cm−2, an energy density of 29.2 Wh kg−1 at 127 W kg−1, as well as 126.39% capacitance retention through 2000 cycles at the high current density of 25 mA cm−2, suggesting the flower-like CuCo2S4 nanosheet arrays hold promise for practical application of high-performance supercapacitors.

Mesoporous nanoplate TiO2/reduced graphene oxide composites with enhanced lithium storage properties

Mesoporous nanomaterial has been extensively studied in high-performance anode materials, because of their large electrolyte–electrode contact area, small volume change, high safety and enhanced specific capacity during discharge/charge process. Herein, we use titanium trichloride as Ti-sources and adjust the pH of solvent to successfully prepare mesoporous nanoplate TiO2 on reduced graphene oxide (RGO) nanosheets via two-step hydrothermal treatment. Benefiting from the unique structure, as-prepared mesoporous nanoplate TiO2/RGO composites present high reversible capacity and strong cycling stability (high capacity of ∼200mAhg−1 at 1.2C after 300 cycles) as anode materials for Li ion batteries (LIBs).

Synergistic effects of electronic structure of WO3 nanorods with the dominant {001} exposed facets combined with silver size-dependent on the visible-light photocatalytic activity

Novel visible-light-driven plasmonic photocatalyst Ag/WO3-110 nanorods with the dominant {001} exposed facets were prepared via a two-step hydrothermal treatment and in-situ photoreduction reaction. The as-prepared samples were characterized by various analytical techniques, such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectroscopy, photoluminescence spectra and electrochemical impedance spectroscopy. The results illustrated that the intrinsic nature of charge separation on the {001} facets of WO3-110 nanorods as well as the surface plasmon resonance (SPR) effect of Ag nanoparticles (Ag NPs) can facilitate the charge transfer between Ag NPs and the {001} facets of WO3-110 nanorods. Moreover, the size of Ag NPs also plays an important role in the SPR effect and the photogenerated carrier separation. Those Ag NPs loaded on {001} facets of WO3 nanorods exhibit size-dependent photocatalytic activity for the MO and RhB degradation. Additionally, the underlying photocatalytic reaction mechanism was further investigated by the photoelectrochemical experiment and the controlled experiments using radical scavengers.

The effect of Ni doping concentration on the gas sensing properties of Ni doped SnO2

The Ni doped SnO2 has been prepared by two-step hydrothermal treatment and calcination, and characterized by XRD, TEM and Brunauer Emmett Teller N2 adsorption–desorption analysis. The results exhibit the Ni doped SnO2 is heterostructure composed of Ni-SnO2 on the surface of SnO2 nanoparticles, which are polycrystalline tetragonal with high specific surface area and average grain size of about 10nm. The sensors based on Ni doped SnO2 show very good gas sensing properties at low working temperature. The gas sensing properties of the Ni doped SnO2 are improved with low Ni-doping concentration (2–4mol%), but further increase of Ni-doping concentration results in deteriorated response by low conductivity. The sensor based on 2mol% Ni doped SnO2 and the sensor based on 4mol% Ni doped SnO2 show ultrahigh responses to n-butanol and formaldehyde, respectively, with good selectivity. These sensors could be promising candidates for selective detection of n-butanol and formaldehyde.

Photocatalytic reduction of carbon dioxide using iodine-doped titanium dioxide with high exposed {001} facets under visible light

Iodine-doped titanium dioxide nanosheets with high exposed {001} facets (IFTO) were synthesized by a two-step hydrothermal treatment followed by calcination at 350 °C.

Enhanced photoelectrocatalytic hydrogen production activity of SrTiO3–TiO2 hetero-nanoparticle modified TiO2 nanotube arrays

SrTiO3–TiO2 hetero-nanoparticle modified TiO2 nanotube arrays (ST–TiO2 NTAs) were constructed by following these steps: firstly, highly ordered TiO2 nanotube arrays (TiO2 NTAs) were synthesized directly on Ti foils through electrochemical oxidation, then SrTiO3–TiO2 nanoparticles were deposited on the TiO2 NTAs using two-step hydrothermal treatment. SrTiO3–TiO2 nanotube arrays (S–TiO2 NTAs) were also prepared by directly hydrothermal treatment of TiO2 NTAs for comparison. The photoelectrocatalytic hydrogen production activities of all the samples were evaluated by using ethylene glycol as a sacrificial reagent in water under a 300 W xenon arc lamp. The photoelectrocatalytic hydrogen production rate of TiO2 NTAs can be significantly improved by modifying SrTiO3–TiO2 hetero-nanoparticles and achieved a greatly promoted value of 314.9 μmol cm−2 h−1 which was 2.1 times higher than that of the unmodified TiO2 NTAs. Compared to S–TiO2 NTAs, ST–TiO2 NTAs showed a 32.8% increase in hydrogen production rate. Furthermore, SrTiO3–TiO2 hetero-nanoparticle modified TiO2 nanotube arrays exhibited excellent stability and was facile to be safely reused. The improvement of photocatalytic hydrogen production efficiency is attributed to the difference of the conduction band potential between TiO2 and SrTiO3 in SrTiO3–TiO2 hetero-nanoparticles, thereby boosting the transfer and separation of the photogenerated electron–hole pairs.

Carbon deposited TiO2-based nanosheets with enhanced adsorption ability and visible light photocatalytic activity

Carbon deposited TiO2-based nanosheets (C-TNS) photocatalysts were prepared by a two-step hydrothermal treatment of Degussa P25 titania using glucose as the carbon precursor. The microstructures, adsorption abilities, and visible light photocatalytic properties of the samples were investigated. Carbon deposition has significantly enhanced the visible light absorbing ability and dye molecules adsorption ability of TiO2-based nanosheets (TNS). The XPS result suggests that the deposited carbon mainly exists in the form of carbonaceous species, and carbon deposition results in the decrease of hydroxyl oxygen. When the glucose solution concentration is 2g/L, the obtained C-TNS possess the highest visible light photoactivity in degrading Rhodamine B (RhB), which is 12 times and 3 times of that of P25 and the pure TNS, respectively. The good reusability of C-TNS in the cyclic degradation experiments implies a potential application for dealing with organic pollutants. It is suggested that carbon deposition is a promising way to enhance the visible light photoactivity of TiO2-based nanosheets.

TiO2 nanobelts photocatalysts decorated with Bi2WO6 nanocrystals: Preparation and enhanced photocatalytic activity

In this paper, the controllable preparation of one-dimensional TiO2 nanobelts decorated with Bi2WO6 nanocrystals based on Ti foils was reported using two-step hydrothermal treatment method. X-ray photoelectron spectroscopy measurement results exhibited the binding energy changes of Ti and O elements, implying the strong adhesion of Bi2WO6 nanocrystals onto the surface of TiO2 nanobelts. The ultraviolet–visible (UV–vis) absorption spectra showed that the introduction of Bi2WO6 nanocrystals could induce the red-shift of absorption edge and exhibited a broad absorption band in the visible region, which extended the scope of absorption spectrum and help to improve the photocatalytic degradation efficiency. The photocatalytic experiment results revealed that Bi2WO6/TiO2 composites possess higher photocatalytic activities toward methyl orange than pure TiO2 nanobelts. The degradation efficiency of 90% after 5 cycles indicated that the as-prepared composite photocatalysts exhibited excellent long-time recyclable ability for the degradation of contaminants.

Preparation and electrochemical Li storage performance of MnO@C nanorods consisting of ultra small MnO nanocrystals

MnO, with low operation potential and cost, is very attractive among transition metal oxides as an anode material for Li ion batteries. In this work, hierarchical MnO@C nanorods, in which ultra-small MnO nanocrystals (generally <5 nm) were homogeneously dispersed in a carbon matrix and further coated with a well-proportioned carbon shell, were prepared through a two-step hydrothermal treatment and subsequent sintering at 600 °C, with a slow heating rate of 5 °C min−1. In contrast, when sintered at a higher temperature (800 °C) and a faster heating rate (10 °C min−1), the ultra-small MnO nanocrystals agglomerated into nanoparticles (30–80 nm) and partially lost the contact with the outer carbon shell. Profiting from the highly-dispersed ultra-small nanocrystals in the carbon matrix and the well-proportioned carbon shell, the carbon-coated MnO nanocrystals exhibited a reversible capacity of 481 mA h g−1 after 50 cycles at a current density of 200 mA g−1, which is higher than that of carbon-coated MnO nanoparticles. The results disclose the important roles of small particles and carbon shells in developing advanced anode materials for Li ion batteries.

Response Surface Methodology for Optimizing Zeolite Na-A Synthesis

A statistical technique for optimizing zeolite Na-A synthesis as a function of percent yield was investigated. A two-step hydrothermal treatment method assisted by microwave heating was applied on the extracted ion solution for zeolites synthesis. The optimization sequence included the application of an experimental design and the results obtained were fitted to a second order model. The resultant predicted data were used in creation of an optimal set of conditions. Box–Behnken design of response surface methodology of three factors with three levels was applied. The three factors which have been adopted were NaOH concentration (2, 4 and 6 M), microwave power level (10, 55 and 100 % of 800 W) and time of exposure to the irradiation (1, 3.5 and 6 min). With the application of the above experimental design three solid products, Na-A zeolite, sodalite octahydrate and gibbsite were formed. The three products were characterized by their X-ray diffraction images. It was found that the percent yield of Na-A zeolite would be optimized when the extracted Si ion concentration in the response optimizer was higher than 2,000 ppm and the base used in the extraction not more than 4 M. The optimum conditions to maximize the percent yield of zeolite Na-A were 3.8 M of NaOH, 2.5 min of time and 48.2 % W of microwave power level.

Growth of branched rutile TiO 2 nanorod arrays on F-doped tin oxide substrate

Branched rutile TiO 2 nanorod arrays were directly synthesized on the F-doped tin oxide (FTO) substrate through a two-step hydrothermal treatment by a seeding method with TiO 2-nanorods as seeds. The samples were characterized respectively by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and field-emission scanning electron microscopy (FESEM). Results showed that TiO 2 nanorods with nanobranches (TiO 2-NB) grew vertically on the FTO substrate. XRD and HRTEM results confirmed that the TiO 2-NB arrays were single-crystalline rutile. The optical properties of the samples were studied with a UV–vis spectrometer. The photocatalytic activity of the TiO 2-NB film is better than that of P25 particulate film. Direct electrical pathway and improved light-harvesting efficiency were crucial for the superior photocatalytic activity of the TiO 2-NB arrays.

A Mesoporous Sulfated Zirconia–Silica Material with High Hydrothermal Stability and Acid Catalytic Activity

Abstract A mesoporous sulfated zirconia–silica material with high hydrothermal stability was prepared by a two-step hydrothermal treatment process in a pH range of 1.65–3. This material still showed high surface area, large pore volume, and uniform structure after steam treatment at 800 °C for 5 h. In cumene cracking, the material exhibited relatively steady catalytic activity even after steam treatment at 600 °C for 2 h.

Unexpected phase transformation from VO2(R) to VO2(A) during hydrothermal treatment in the V2O5–H2C2O4–H2O system

Vanadium dioxide (VO2) was directly synthesized via the reduction of V2O5 with oxalic acid adopting two different types of hydrothermal processes in the temperature ranging from 180 to 260 °C. The products were characterized by X-ray diffraction, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). In all these processes, the VO2(B) phase was first formed at a relative lower temperature or the initial stage at higher temperature and then it transformed to the VO2(R) phase with the increase of temperature. The building-block-stacking mechanism was proposed to elucidate the transformation from VO2(B) nano-plates to snowflake-like VO2(R) powders. During this transformation, no trace of the VO2(A) phase was observed when one-step hydrothermal treatment method was used, whereas some part of the branches of the snowflake-like VO2(R) particles transformed to metastable VO2(A) nanofibers in the autoclave during cooling process when the two-step hydrothermal treatment method was conducted. The reason for this transformation can be contributed to the defects formed during the stacking process.

Preparation and photocatalytic activity of TiO 2 powders from titanium citrate complex using two-step hydrothermal treatments

White, almost carbon-free TiO 2 powders were prepared from a titanium citrate complex ((NH 4) 4[Ti 2(C 6H 4O 7) 2(O 2) 2]·4H 2O) using a two-step hydrothermal treatment. The product yield, carbon contamination, and crystalline phase of TiO 2 depended on both the temperature and pH value for each treatment. Titanium was precipitated as a solid phase (H 2Ti 2O 5·H 2O) using the first hydrothermal treatment in the basic condition (pH = 12) at temperatures less than 150 °C. Then white rutile or anatase powder was crystallized using the second hydrothermal treatment at 200 °C. By changing the pH condition of the second hydrothermal treatment, rutile and anatase were synthesized selectively. The photocatalytic decomposition activity of obtained rutile powder for gaseous 2-propanol under visible light was increased by Cu-grafting.

Fabrication and magnetic property of α-Fe 2O 3 nanoparticles/TiO 2 nanowires hybrid structure

α-Fe 2O 3 nanoparticles/TiO 2 nanowires hybrid structure is fabricated by two-step hydrothermal treatment. TiO 2 nanowires are prepared by heating of titanate nanowires, which are obtained by hydrothermal treatment of TiO 2 powder and further repeated HCl treatment. α-Fe 2O 3 nanoparticles are deposited on the surface of TiO 2 nanowires by hydrothermal treatment in Fe(NO 3) 3 solution. The HRTEM images confirm the junctions between α-Fe 2O 3 nanoparticles and TiO 2 nanowires. The formation of hybrid structures has significant influence on the magnetic properties of α-Fe 2O 3. The Morin transition temperature of α-Fe 2O 3 nanoparticles/TiO 2 nanowires hybrid structure is 190 K, which is determined by the sharp peak in the differential ZFC curve. Whereas there is no observable Morin transition for the corresponding isolated α-Fe 2O 3 nanoparticles with similar average particles size of ca. 20 nm.

Synthesis and visible-light photocatalytic activity of Bi-doped TiO 2 nanobelts

Bi-doped anatase TiO 2 nanobelts were synthesized from layer-structural titanate nanobelts using two-step hydrothermal treatment approach. X-ray diffraction (XRD) patterns and transmission electron microscopic (TEM) images show that the doping of Bi 3+ cations does not change the crystal structure and morphology of TiO 2 nanobelts. The energy-dispersive X-ray (EDX) and inductively coupled plasma-mass spectrometry (ICP-MS) analytic results suggest that the doping cations mainly exist near the surface of the TiO 2 nanobelts. The ultraviolet-visible (UV–vis) absorption spectra show that the absorption edge for the samples with Bi 3+ has red shift as compared with that of undoped TiO 2 nanobelts, and correspondingly, the photocatalytic degradation of methylene blue under visible-light illumination is enhanced with the increase of Bi-doping content.

Alkaline pre-treatment of rice hulls for hydrothermal production of acetic acid

To solve the blockage caused by silica during the hydrothermal conversion of rice hulls into acetic acid in a continuous-flow reactor, the removal of silica from rice hulls and the retainment of organics by alkaline extraction were carried out in a range of pH values from 5 to 12 and temperatures from 30 to 85 °C. It was found that the efficiency of silica removal and organics retainment strongly depended on the pH value but was less influenced by the reaction temperature. Based on the individual behaviour of holocellulose, lignin, silica and extracts during the alkaline extraction, a two-step low-temperature pre-treatment for removing silica but retaining organics was proposed. Water washing was firstly performed to recovery a portion of lignin and extracts, and then alkaline extraction was operated to remove silica in the rice hulls. 92.1% silica was removed and 73.4% organics retained after the two-step low-temperature pre-treatment. The retained organics was treated by a two-step hydrothermal treatment and an acetic acid yield of 20.8%, similar to that from non-extracted rice hulls, was achieved. The obtained silica could be expected to be used as fine raw materials for the production of silicon-based products.