Hydrolysis Precipitation Method Research Articles

Enhanced photocatalytic removal of indoor formaldehyde by ternary heterogeneous BiOCl/TiO2/sepiolite composite under solar and visible light

Mineral-based photocatalyst is a promising alternative to eliminate the volatile organic compounds (VOCs) air pollutants because of its low-cost and environmental-friendly merits. Herein, BiOCl/TiO2/sepiolite ternary heterogeneous photocatalyst was synthesized through a facile hydrolysis-precipitation method combining with the calcination crystallization procedure. The gaseous formaldehyde (HCHO) was employed as target pollutant to evaluate the photocatalytic activity of as-synthesized samples. The results indicated that BiOCl/TiO2/sepiolite composite performed much significantly higher adsorption and decomposition capacity for HCHO than pure TiO2, BiOCl and TiO2/BiOCl under solar and visible light. Based on the characterizations and density function theory (DFT) simulation results, the enhanced photocatalytic activity was mainly attributed to the synergistic effect between TiO2/BiOCl and sepiolite through the formation of ternary heterojunction. Such structure could lead to the higher adsorption capacity which can provide more reactive sites, and stronger light response ability as well as faster separation efficiency of photoinduced carriers forming more active radicals during the degradation process. Radical scavenger tests and ESR results indicated that photogenerated holes was the main active species in the reaction system. Overall, this study provides an insight into the design and synthesis of environment-friendly and high-effective heterogeneous composite for practical indoor formaldehyde removal.

Facile fabrication of heterogeneous TiO2/BiOCl composite with superior visible-light-driven performance towards Cr(VI) and tetracycline

Heavy metals and antibiotics are known for their difficulty of removal and enormous harmful intermediates released during degradation as well as the great threat to the health of human beings, which arouses urgent demand for highly efficient photocatalysts as solution. Thus, in this work, TiO2/BiOCl heterogeneous composite was synthesized via a facile and low-cost hydrolysis-precipitation method at room temperature without organic reagent. The characteristic results indicate anatase TiO2 nanoparticles with smaller grain size (around 15 nm) were uniformly dispersed on the surface of BiOCl nanosheets to form the heterogeneous structure. The hybrid catalyst exhibits higher photocatalytic performance for both Cr(VI) and tetracycline, and the synergistic degradation effect is demonstrated in the co-existent system. The superior photoactivity is mainly attributed to the excellent visible light capture capability and effective separation of photogenerated electron-holes pairs. Moreover, the main active radicals for Cr(VI) are photo-induced electrons (e−), and that for tetracycline are superoxide radical (•O2−) and holes (h+). Furthermore, the effect of mass ratio of TiO2 and BiOCl on the photocatalytic performance was discussed and a speculated degradation mechanism was also proposed. In summary, this work would provide significant meaningful guidance for the development of Ti-based composites in the field of wastewater treatment.

Ultrasonic‐Assisted Hydrolysis Precipitation Rapid Synthesis of Rod‐Like α‐Fe2O3 Nanostructures and Its Interfacial Electron Transfer Properties

AbstractUniform 3D rod‐like α‐Fe2O3 nanostructures are prepared by a simple ultrasonic‐assisted hydrolysis precipitation method. The obtained α‐Fe2O3 samples are characterized by X‐ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), and electrochemical workstation. These rod‐like α‐Fe2O3 nanostructures, with a mean diameter of about 38 nm, their ratios of length to diameter are about 5–8. The interfacial electron transfer properties of rod‐like α‐Fe2O3 nanostructures are verified. The current synthetic strategy provides a convenient, low‐cost, and nontoxic route to prepare 3D architectures of other semiconductors, and it is important for exploring oxide‐based nanostructures.

Synthesis of novel ternary heterogeneous BiOCl/TiO2/sepiolite composite with enhanced visible-light-induced photocatalytic activity towards tetracycline

In this study, the novel ternary heterogeneous BiOCl/TiO2/sepiolite composite with enhanced visible-light-induced photocatalytic activity was synthesized via the hydrolysis precipitation method followed by a calcination crystallization process. The as-prepared samples were characterized by X-ray diffraction (XRD), UV–VIS diffused reflectance spectroscopy (DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL), respectively. Compared with bare BiOCl and TiO2, the ternary heterogeneous structure in BiOCl/TiO2/sepiolite significantly improved the visible-light-induced photocatalytic performance towards tetracycline (TC), and also contributed to the separation efficiency and recyclability of the photocatalyst. In addition, the influence of the mass ratio of BiOCl in the composites was also discussed, and the optimal mass ratio is identified as 50% (mBiOCl/(mTiO2 + mBiOCl). Furthermore, TC degradation by-products were further detected by HPLC-MS/MS, and a possible degradation pathway was proposed. Besides, ESR (Electron spin resonance) results indicated that the main active radical species were photo-induced holes (h+) and superoxide radical (O2−) in the TC degradation process. Hence, the enhanced photocatalytic activity of the prepared ternary composite was mainly attributed to the remarkable synergistic effect within the BiOCl/TiO2/sepiolite ternary heterogeneous system, resulting in the superior adsorption activity, the outstanding visible-light response performance and the efficient separation of the photogenerated electron-hole pairs. It is speculated that the novel ternary heterogeneous BiOCl/TiO2/sepiolite composite would have a broad application prospect in the field of wastewater treatment.

Theoretical calculation and experimental study of the electronic structure and catalysis of defected semiconductor

TiO2 photocatalysts with different types of oxygen vacancies were synthesized via a hydrolysis-precipitation method. The oxygen vacancies types, the charge carriers separation and the band structures of the photocatalysts were investigated by theoretical calculations and experimental characterizations. It is revealed that the energy level of oxygen vancancies with two trapped electrons is higher than that with one trapped electrons; the oxygen vancancies could act as charge carriers recombination centers. Therefore, TiO2 with two-electrons-trapped oxygen vancancies show enhanced visible-light photocatalytic activity, compared with the counterparts with one-electron-trapped oxygen vancancies. The photocatalyst with the lowest oxygen vacancies content shows the best photocatalytic activity under both UV and visible-light irradiation.

An Effective CuZn–SiO2 Bimetallic Catalyst Prepared by Hydrolysis Precipitation Method for the Hydrogenation of Methyl Acetate to Ethanol

A highly active CuZn–SiO2 catalyst with excellent stability in hydrogenation of methyl acetate (MA) was fabricated by the hydrolysis precipitation (HP) method. The HP method caused notable high dispersion of both copper and zinc species due to the strong interaction between metal species and silica support caused by the pseudo-homogeneous reaction during the mixing process. According to the linear correlation between the TOF (Cu+) and Zn/Cu ratio, the Cu+ was considered the predominant active site, and the Cu+ site derived from the strong interaction between copper and zinc species has higher activity than those Cu+ species generated from copper phyllosilicate. Compared to the CuZnO/Al2O3 and Cu–SiO2 catalysts, the Cu9Zn1–SiO2 catalyst displayed the highest catalytic activity on account of the high dispersion of active species and the enhanced ability of Cu+ species on ester adsorption by stronger Cu-ZnO interaction.

Synthesis of BiOCl/TiO 2 –zeolite composite with enhanced visible light photoactivity

Abstract The BiOCl/TiO2–zeolite composite was synthesized via a hydrolysis–precipitation method. The prepared samples were characterized by X-ray diffraction, thermogravimetric analysis, N2 adsorption–desorption, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV–vis diffused reflectance spectroscopy and photoluminescence. Using liquid rhodamine B and gaseous formaldehyde as the target pollutants, the visible light photoactivity of as received BiOCl/TiO2–zeolite composites was evaluated. Compared with bare BiOCl and TiO2, the composites exhibited considerably enhanced photoactivity for rhodamine B and gaseous formaldehyde. The enhancement should be attributed to the higher adsorption ability and the formation of effective BiOCl/TiO2 heterojunction in BiOCl/TiO2–zeolite composite. The influence of calcination temperatures on the photocatalytic performance of BiOCl/TiO2–zeolite composite was also investigated. The optimal calcination temperature is identified as 400 °C for liquid RhB decoloration due to the highest RhB adsorption capacity of composite. However, the composite calcined at 600 °C displayed the best gaseous formaldehyde degradation because of the high crystallinity of TiO2 and abundant (001) facets of BiOCl. This result further indicated that the enhanced photoactivity of BiOCl/TiO2–zeolite composite should be attributed to the coexistence of higher surface area and proper crystallinity. The BiOCl/TiO2–zeolite composite has broad application foreground in pollutants purification.

A novel technology for vanadium and chromium recovery from V-Cr-bearing reducing slag

Wastewater produced in the process of vanadium extraction from vanadium slag is treated by reduction and neutralization which produces a V-Cr-bearing reducing slag. The recovery of vanadium and chromium from this slag was investigated by a comprehensive route including sulfuric acid leaching, selective oxidation of low valent vanadium and hydrolysis precipitation of vanadium and chromium. Under the most suitable conditions including a leaching time of 4h, sulfuric acid addition of 74wt% and leaching temperature of 90°C, the leaching of vanadium and chromium reached 90.9% and 97.8%, respectively. The vanadium of low valent in leach solution was selectively oxidized by manganese dioxide with the oxidation of 96.9%, while Cr(III) was not oxidized. The hydrolysis precipitation method was used to separate and recover V(V) and Cr(III), and the recovery of vanadium and chromium reached 98.3% and 99.1%, respectively. The overall vanadium and chromium recovery was 86.5% and 96.9%, respectively.

Honeycomb-like micro-mesoporous structure TiO2/sepiolite composite for combined chemisorption and photocatalytic elimination of formaldehyde

Structured hybrid materials based on the combination adsorbent-photocatalyst have large surface area, an average pore diameter, good dispersion and strong adsorptivity, showing promising performance for environmental applications. In this study, honeycomb-like micro-mesoporous structure TiO2/sepiolite composites were fabricated using TiCl4 and modified sepiolite (MS) nanofibers as the precursors by a hydrolysis-precipitation method. The effect of the textural, morphological and structural properties of TiO2/sepiolite composites on the adsorption and photocatalytic degradation of formaldehyde (HCHO) in gas phase was analyzed. The results indicate that thermal treatment at 550 °C and TiO2/MS weight ratios of 1/2 ensure an optimum combination of textural, optical and HCHO adsorption and photocatalytic properties. At ambient temperature, the optimal catalyst (relative humidity of 45%, and HCHO initial concentration of 6.56 mg/m3) could efficiently decompose HCHO into CO2 and H2O, and still showed a good performance even after 4 cycles under UV irradiation. The excellent performance of the TiO2/sepiolite is primarily ascribed to the synergistic effect between the adsorbability of sepiolite nanofibers and the catalytic ability of TiO2 nanoparticles.

Preparation and Properties of Yb:YAG and Nd:YAG Nanocrystals

Yb:YAG and Nd:YAG nanocrystals were synthesized by a ultrasound-microwave-assisted alkoxide hydrolysis precipitation method. The effect of reaction parameters including the microwave radiation power, microwave radiation time and calcination temperature on the composition of the products was investigated. The Yb:YAG and Nd:YAG nanocrystals were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectrum. The results show that the pure phase Yb:YAG and Nd:YAG nanocrystals can be obtained at microwave radiation power of 385 W, microwave radiation time of 30 min and calcination temperature of 1100 °C. The cooperative luminescent intensities of the Yb:YAG and Nd:YAG nanocrystals reach the maximum at the calcination temperature of 1100 °C.

Design and Synthesis of TiO₂ Hollow Spheres with Spatially Separated Dual Cocatalysts for Efficient Photocatalytic Hydrogen Production.

TiO2 hollow spheres modified with spatially separated Ag species and RuO2 cocatalysts have been prepared via an alkoxide hydrolysis–precipitation method and a facile impregnation method. High-resolution transmission electron microscopy studies indicate that Ag species and RuO2 co-located on the inner and outer surface of TiO2 hollow spheres, respectively. The resultant catalysts show significantly enhanced activity in photocatalytic hydrogen production under simulated sunlight attributed to spatially separated Ag species and RuO2 cocatalysts on TiO2 hollow spheres, which results in the efficient separation and transportation of photogenerated charge carriers.

Efficient tuning of surface copper species of Cu/SiO2 catalyst for hydrogenation of dimethyl oxalate to ethylene glycol

The chemoselective synthesis of ethylene glycol (EG) from the hydrogenation of dimethyl oxalate (DMO) derived from syngas is an attractive technology in the modern chemical industry. This work reported a novel hydrolysis precipitation (HP) method to efficiently tune the active copper species of Cu/SiO2 catalysts for DMO hydrogenation. Characterization techniques such as N2 physical adsorption, X-ray diffraction, H2 temperature programmed reduction, N2O titration, Fourier-transform infrared spectra, transmission electron microscopy, and X-ray photoelectron spectroscopy were employed to reveal the origin of the catalytic performances. Compared to the ammonia evaporation (AE) method, the HP method presented remarkable higher dispersion of copper species and large ratio of Cu+/(Cu++Cu0) on the catalyst surface, resulting in a superior catalytic performance in the hydrogenation of DMO to EG. Moreover, the amount of Cu0 and Cu+ sites on catalyst surface is dramatically affected by copper loading, and the catalyst with 30% copper showed the highest catalytic activity with a space time yield of 1.74gEG/(gcat·h) at 463K. Meanwhile, the positive correlation between Cu+ surface area and space time yield of EG suggests that the amount Cu+ is the key factor for hydrogenation of DMO to EG on the as-prepared Cu/SiO2 catalyst. The formation of more Cu+ species in the catalyst would enhance the activation of CO group in DMO and significantly improve the catalytic performances in DMO hydrogenation.

Microwave Assisted Preparation of YAG and Yb:YAG Transparent Ceramic Nanopowders for Laser Crystal

YAG and Yb:YAG transparent ceramic nanopowders for laser crystal were synthesized by microwave-assisted alkoxide hydrolysis precipitation method. The YAG and Yb:YAG nanopowders were characterized by differential thermal analysis and thermo gravimetric analysis (DTA-TG), infrared spectrum (IR), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and photoluminescence (PL) spectrum. The results show that the crystallizing temperature of the precursor of YAG and Yb:YAG is about 930 °C. The pure phase YAG and Yb:YAG nanopowders can be obtained at microwave radiation power of 385 W, microwave radiation time of 30 min and sintering temperature of 1100 °C. The average particle size of YAG is about 120 nm. Yb:YAG is uniform sphere and the average sizes is about 100 nm. The intensity of luminescence of Yb:YAG nanopowders decreased with the increasing of microware time. The maximum luminous intensity of the Yb:YAG nanopowders can be obtained when the microwave radiation is 30 min.

N-doped mesoporous TiO2 nanoparticles synthesized by using biological renewable nanocrystalline cellulose as template for the degradation of pollutants under visible and sun light

Yellow-colored N-doped mesoporous TiO2 photocatalyst (TiO2-NT) with visible-light response was prepared by a hydrolysis–precipitation method at different urea contents with the use of nanocrystalline cellulose (NCC) as template. The photocatalytic activity was investigated through the degradation of phenol, nitrobenzene, and methyl orange (MO) under artificial visible and sun light irradiation. X-ray photoelectron spectroscopy (XPS), UV–Vis diffuse spectroscopy (DRS), X-ray diffraction (XRD), thermogravimetry–differential thermal analysis (TG/DSC), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and N2 adsorption–desorption isotherms were used for catalyst characterization. The results showed that NCC-templated TiO2 with a suitable N-doping content (TiO2-NT) exhibited higher activity under visible and sun light irradiation than N-doped TiO2 synthesized without NCC template (TiO2-N). Affected by the hydroxyl groups of NCC macromolecule and the Ti precursor, the growth and aggregation of TiO2 precursor before calcination were inhibited. The NCC template led to high dispersion, small grain size, and high specific surface area of TiO2-NT. Nitrogen doping was proposed to adjust band gap and electrical properties of TiO2 by establishing acceptor defect. N-doped TiO2 with the intrinsic donor defect of oxygen vacancy and the nitrogen-to-oxygen acceptor defect could be excited by visible irradiation for efficient pollutant degradation.

Synthesis and photocatalytic activity of mesoporous TiO2 nanoparticle using biological renewable resource of un-modified lignin as a template

Mesoporous TiO2 was synthesized by a hydrolysis precipitation method with the utilization of the biological renewable resource of lignin as template and TiCl4 as reactant. The photocatalytic activity of TiO2 was investigated by the degradation of phenol under UV light irradiation. The microstructure, crystallinity, powder characteristic, and chemical bonding of the catalyst were analyzed. The 500 °C-calcined TiO2 had average crystallite size of about 11.1 nm and a mesoporous structure with specific area of 165.8 m2/g and pore volume of 0.312 cm3/g. The results showed that TiO2 synthesized with lignin template exhibited high photocatalytic activity, which can be attributed to the electronegativity and the network skeleton of lignin to uniformly distribute the TiO2 precursor for forming TiO2 mesoporous particles. The mechanism for the improved photodegradation of the lignin-assisted TiO2 was proposed.

Preparation and Photocatalytic Activity of Sepiolite/Flower-Like BiOCl Nanocomposites

Sepiolite/flower- like BiOCl nanocomposites as photocatalyst have been successfully prepared by hydrolysis precipitation method. And the influence of temperature, pH and Bi(NO3)3concentration on the unique morphology of the nanocomposites was investigated. Moreover, the photocatalytic activity of these nanocomposites was examined for the degradation of rhodamine B. The results show that the flower-like BiOCl is uniformly dispersed on the sepiolite and this nanocomposites exhibit a photocatalytic efficiency of 14.29%-16.67% higher than that of pure BiOCl nanosheets for the degradation of rhodamine B, and the catalyst has an excellent cycling stability.

Effects of Calcination Condition on Photocatalytic Properties of Nano-TiO$lt;inf$gt;2$lt;/inf$gt;/Opal Composite and Its Mechanism

Nanocrystalline TiO2 particles immobilized on opal by a hydrolysis precipitation method are used as a novel catalyst in photocatalysis. Effects of crystalline and size, BET specific surface area and porous properties on the photoactivity were investigated by characterizing samples obtained under various calcination temperatures and periods. Results reveal that there is still no evidence of rutile phase in XRD patterns when the calcination temperature increases to 800℃. This indicates that the opal support impedes the phase transformation. The photocatalytic reactivity of this nano-TiO2/opal composite catalyst was evaluated by degrading Rhodamine B (RhB) under ultraviolet light. The sam- ple calcined at 600℃ for 2 h exhibits the smaller crystalline size and larger specific surface area with a concomitant higher activity of 97.24% for RhB degradation by 4 h irradiation under 250 W Hg lamp.

Research of Nano-TiO<sub>2</sub> Composites on Malachite Green Decolorizing Effect

A supporting body of diatomite-based porous ceramics was prepared by a solid-phase sintering process and low-temperature calcination process. nanoTiO2 membrane was loaded on the carrier by the hydrolysis precipitation method and using TiCl4 as the precursor. The influences of various parameters such as the initial concentration of malachite green, the amount of composites, and the initial pH had been investigated. Under the same test conditions, the decolorizing rate of malachite green was higher when the initial concentration was 6 mg/L, the composites dosage was 5 g/L, and the initial pH was 8 respectively. The influence mechanism of the initial concentration of malachite green, the amount of composites, and the initial pH for malachite green was discussed.

N, S co-doped-TiO2/fly ash beads composite material and visible light photocatalytic activity

Using TiCl4 as the titanium source, urea as the precipitating agent, nano-TiO2/fly ash beads composite materials were prepared by hydrolysis-precipitation method. Using (NH2)2CO and (NH2)2SC as the N and S source respectively, N and S co-doped TiO2/fly ash beads composite materials were prepared by grinding them together according to a certain proportion and calcined at 500°C for 2h. The composite materials were characterized by SEM, EDS, XPS, and UV–vis spectrophotometer methods. The UV–vis absorption spectra results show that the absorption edge of un-doped composites is 390nm while that of doped composites red-shifts to 500nm. The photocatalytic activity of composite materials was evaluated by degradation of methyl orange under visible light irradiation (halogen lamp, 250W). The results showed that after irradiation for 1h, degradation rate of N, S co-doped-TiO2/fly ash beads composite material can reach 65%, while the degradation rate of un-doped sample and P25 were just 10% and 6%, respectively. The composite material also showed excellent recycling properties.

A comparison of N‐doped TiO2 photocatalysts preparation methods and studies on their catalytic activity

AbstractBackgroundN‐doped TiO2 can narrow the TiO2 forbidden band and thereby increase its catalytic activity under visible light. In this work, three methods (the sol–gel method (SG), the tetrabutyl titanate hydrolysis precipitation method TN', and the H2O2‐modified method (TNH)) were used to prepare N‐doped TiO2 photocatalysts. The Reactive Red‐Violet dye (KN‐R) was used as the target pollutant. The catalytic activities of the photocatalysts prepared via the three methods were compared and studied.ResultsThe structures and optoelectronic properties of these catalysts were characterized by various means. The results demonstrated that the N‐doped TiO2 catalyst synthesized using the TNH method exhibited the most efficient catalytic activity under visible light and produced a degradation rate of 90% for the Reactive Red‐Violet dye. The N‐doped TiO2 prepared using the SG method exhibited the lowest catalytic activity under both UV and visible light. The kinetics of photocatalysis degradation for KN‐R by N‐doped TiO2 prepared by TNH method was studied and found to be zero order due to the good adsorption effect between KN‐R and TiO2.ConclusionThe N‐doped TiO2 prepared by TNH method showed good photocatalytic activity in the case of degrading dye under both UV and visible light. © 2013 Society of Chemical Industry