ZnO TiO2 Research Articles

Benchmarking Computational Alchemy for Carbide, Nitride, and Oxide Catalysts

AbstractKohn–Sham density functional theory (DFT)‐based searches for hypothetical catalysts are too computationally demanding for wide searches through diverse materials space. Here, the accuracy of computational alchemy schemes on carbides, nitrides, and oxides is assessed. With a single set of reference DFT calculations, computational alchemy approximates adsorbate binding energies (BEs) on a large number of hypothetical catalysts surfaces with negligible computational cost. Analogous to previous studies on metal alloys, computational alchemy predicts adsorbate BEs on rocksalt TiC(111), TiN(100), and TiO(100) materials, which have no bandgap, in close agreement with DFT results (with mean unsigned errors up to 0.33 eV). In contrast, it is found that semiconducting systems such as rutile TiO2(110), rutile SnO2(110), and rocksalt ZnO(100) can present more significant challenges. This work identifies these challenges being linked to the density of states at the Fermi level and by adding Pt dopants in the surface layer of TiO2, it is shown that computational alchemy can become more reliable with non‐transition metal systems. This remedy provides insight that promotes computational alchemy for broad searches for catalyst active sites through materials space beyond transition metal alloys.

Low-Temperature Co-Firing Ceramic Li2Zn3Ti4O12 Modified by Li2O–ZnO–B2O3 Eutectic Additive

Amaterial sintering at temperature 950°C for the technology of low-temperature co-firing ceramic used in the production of electronic components was developed in the system Li2O–ZnO–TiO2. The effect and method of synthesizing the eutectic sintering additive content in the system Li2O–ZnO–B2O3 on the compaction process and the dielectric properties of the obtained material were studied. The developed ceramic is characterized by the permittivity e = 17.7 and dielectric Q-factor 407 MHz.

Effect of metal oxide nanoparticles on the evolution of valuable gaseous products during pyrolysis of Turkish low-rank coal

In this study, TiO2 and ZnO nanoparticles were synthesized via solvothermal method and used as a catalyst for low-rank coal (LRC) pyrolysis to improve the gaseous product quality and yield. Effects of nanocatalysts on the yields of pyrolysis products distribution were discussed in details. Different reaction temperatures (400–700 °C) and catalyst to LRC ratios (1, 5, and 15% w/w) were examined. The optimum catalyst to LRC ratio was found as %1 by weight, while optimum pyrolysis temperature was determined as 700 °C. The gaseous products (hydrogen, methane, carbon dioxide, carbon monoxide and C2–C4 hydrocarbons) were characterized by micro gas chromatography (μGC) to understand the catalytic ability of TiO2 and ZnO nanoparticles while the pyrolytic oil (tar) was characterized by gas chromatography–mass spectroscopy (GC–MS) as well as Fourier-transform infrared spectroscopy (FT-IR). Through the thermogravimetric analysis method (TGA) weight loss was obtained in the samples.H-ZSM-5 as well-known pyrolysis catalysts was also used for the comparison purposes. The results showed that gaseous product yields were increased drastically in the presence of nano TiO2 and nano ZnO.

Synthesis of Zinc Oxide Supported on Titanium Dioxide for Photocatalytic Oxidative Desulfurization of Dibenzothiophene

Photocatalytic oxidative desulfurization (PODS) has received much attention due to low energy consumption and high efficiency, as well as simple and pollution-free operation. In this study, zinc oxide supported on titanium dioxide (ZnO/TiO2) catalysts were prepared via a simple electrochemical method. The presence of anatase phase TiO2 and wurtzite ZnO was confirmed by X-ray diffraction (XRD) analysis while band gap energies were determined by UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The photocatalytic activity was tested for desulfurization of 100 mg/L dibenzothiophene (DBT). The highest desulfurization rate (2.20 × 10-3 mM/min) was achieved using 1 g/L of 10 wt% ZnO/TiO2 after 2 hr under UV irradiation.

Construction of hierarchical TiO2 nanorod array/graphene/ZnO nanocomposites for high-performance photocatalysis

The photocatalytic performance of heterostructure photocatalysts is limited in practical use due to the charge accumulation at the interface and its low efficiency in utilizing solar energy during photocatalytic process. In this work, a ternary hierarchical TiO2 nanorod arrays/graphene/ZnO nanocomposite is prepared by using graphene sheets as bridge between TiO2 nanorod arrays (NRAs) and ZnO nanoparticles (NPs) via a facile combination of spin-coating and chemical vapor deposition techniques. The experimental study reveals that the graphene sheets provide a barrier-free access to transport photo-excited electrons from rutile TiO2 NRAs and ZnO NPs. In addition, there generates an interface scattering effect of visible light as the graphene sheets provide appreciable nucleation sites for ZnO NPs. This synergistic effect in the ternary nanocomposite gives rise to a largely enhanced photocurrent density and visible light-driven photocatalytic activity, which is 2.6 times higher than that of regular TiO2 NRAs/ZnO NPs heterostructure. It is expected that this hierarchical nanocomposite will be a promising candidate for applications in environmental remediation and energy fields.

Complex ZnO-TiO2 Core-Shell Flower-Like Architectures with Enhanced Photocatalytic Performance and Superhydrophilicity without UV Irradiation.

ZnO-TiO2 core-shell photocatalysts of a complex flower-like architecture were synthesized, using a well-controlled sol-gel coating reaction of presynthesized ZnO flower-like structures. The samples were characterized by X-ray diffraction, field emission scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, diffuse reflectance UV-vis and attenuated total reflectance-Fourier transform infrared spectroscopy, nitrogen adsorption-desorption measurements, and photoluminescence measurements. Well-defined, core-shell flowers with a wurtzite ZnO core and anatase TiO2 shells, with variable shell thickness, were acquired by appropriately adjusting the ZnO/Ti precursor mass feed ratio in the reaction. Moreover, hollow TiO2 flowers were obtained, and they retained their morphology following the etching of the ZnO core in an acidic solution. The photocatalytic performance of the core-shell and hollow semiconductors was evaluated via the decoloration of a methylene blue dye solution under UV-vis irradiation. The core-shell flowers exhibited a higher decoloration rate, when compared with bare ZnO flowers, TiO2 particles, and hollow TiO2 flowers, and the photoactivity was dependent on the TiO2 shell thickness. This was attributed to the efficient separation of the photogenerated holes and electrons at the ZnO-TiO2 interface. Moreover, the most photoactive core-shell catalyst exhibited excellent reusability and stability for at least three photocatalytic cycles and excellent superhydrophilicity without UV irradiation, which is due to the increased roughness of the flower-like structures.

ZnO nanoparticles implanted in TiO2 macrochannels as an effective direct Z-scheme heterojunction photocatalyst for degradation of RhB

A ZnO/TiO2 heterojunction photocatalyst based on ZnO nanoparticles embedded in the hierarchically structured TiO2 framework containing parallel macroporous channels and thin mesoporous walls has been synthesized by a common calcination treatment using zinc chloride and tetrabutyl titanate as the raw materials. The materials properties of the ZnO/TiO2 heterojunction photocatalysts have been carefully characterized with SEM/TEM, XRD, FTIR, XPS, BET analyses, UV–Vis absorption and photoluminescence spectroscopy. The photocatalytic performance for decomposition of Rhodamine B (RhB) under UV light irradiation has been systematically investigated in correlation with the materials structures. The apparent RhB degradation rate constant (k) has been determined to be 20.7 × 10−3 min−1 for the optimal hybrid photocatalyst with 5 wt% of ZnO loading, significantly higher that of pure TiO2 (12.2 × 10−3 min−1) and pure ZnO nanoparticles (5.7 × 10−3 min−1), respectively. Active species trapping experiments reveal that •OH and •O2− play the major roles in the photocatalytic reactions. The enhanced performance can be ascribed to the formation of a direct Z-scheme heterojunction structure between ZnO and TiO2 in contrast to the usual type-II heterojunction.

Hazy Al₂O₃-FTO Nanocomposites: A Comparative Study with FTO-Based Nanocomposites Integrating ZnO and S:TiO₂ Nanostructures.

In this study, we report the use of Al2O3 nanoparticles in combination with fluorine doped tin oxide (F:SnO2, aka FTO) thin films to form hazy Al2O3-FTO nanocomposites. In comparison to previously reported FTO-based nanocomposites integrating ZnO and sulfur doped TiO2 (S:TiO2) nanoparticles (i.e., ZnO-FTO and S:TiO2-FTO nanocomposites), the newly developed Al2O3-FTO nanocomposites show medium haze factor HT of about 30%, while they exhibit the least loss in total transmittance Ttot. In addition, Al2O3-FTO nanocomposites present a low fraction of large-sized nanoparticle agglomerates with equivalent radius req > 1 μm; effectively 90% of the nanoparticle agglomerates show req < 750 nm. The smaller feature size in Al2O3-FTO nanocomposites, as compared to ZnO-FTO and S:TiO2-FTO nanocomposites, makes them more suitable for applications that are sensitive to roughness and large-sized features. With the help of a simple optical model developed in this work, we have simulated the optical scattering by a single nanoparticle agglomerate characterized by bottom radius r0, top radius r1, and height h. It is found that r0 is the main factor affecting the HT(λ), which indicates that the haze factor of Al2O3-FTO and related FTO nanocomposites is mainly determined by the total surface coverage of all the nanoparticle agglomerates present.

Fabrication of TiO2/ZnO/Pt nanocomposite electrode with enhanced electrocatalytic activity for methanol oxidation

Platinum decorated heterogeneous catalysts for methanol oxidation reaction have crucial importance for the commercial sustainability of Direct Methanol Fuel Cells (DMFC). In this study, TiO2/ZnO/Pt nanocomposite film was fabricated as a promising electrocatalytic surface to enhance methanol oxidation in alkaline medium. Firstly, an TiO2/ZnO layer was prepared via DC sputtering followed by electrodeposition techniques on FTO electrode and then platinum nanoparticles were decorated onto the obtained nanocomposite film for the first time. The characterization of the developed transparent films was performed by using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cycling voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The XRD, FESEM and XPS results showed that metallic Pt nanoparticles were uniformly distributed onto the TiO2/ZnO film consisting of anatase TiO2 and wurtzite ZnO layers with a thickness of ca. 370 and 320 nm, respectively. Five cycles of deposition of ZnO and Pt nanoparticles showed best catalytic activity after optimization. The oxidation peak of 0.5 M methanol at TiO2/ZnO/Pt was located at −0.17 V and the corresponding peak current increased about 10- and 5-fold in comparison to FTO/Pt and FTO/TiO2/Pt electrodes, respectively.

A facile electrochemical–hydrothermal synthesis and characterization of zinc oxide hierarchical structure for dye sensitized solar cell applications

A facile hierarchical microstructured ZnO thin films consisting of microspheres and nanorods were deposited on zinc oxide–titanium oxide (ZnO–TiO2) seeded FTO substrate by applying a two-step chemical techniques. At first, ZnO microsphere was electrochemically deposited on ZnO–TiO2 seeded FTO substrate by varying the deposition potentials in the range of − 1.1 to − 1.3 V. Followed by, the nanorods were hydrothermally grown on the optimized ZnO microsphere (ZnO electrodeposited at − 1.3 V). SEM displays the ZnO microsphere and nanorod for films deposited by electrodeposition of − 1.3 and hydrothermal technique, respectively. The suppression of ZnO growth along the (0001) orientation is noticed due to electrostatic absorption of citrate ions. TEM images confirm the hexagonal structure of microstructures and nanorods oriented along the lateral and c-axis growth direction, respectively. The appearance of high-intensity XRD peaks, Raman E2 (high) mode and UV emission confirms the hierarchical structure possessing a higher crystalline nature with lesser atomic defects. The hierarchical structure has high dye absorption, light absorption and scattering ability. The efficiency (η) of dye sensitized solar cells (DSSCs) consisting microsphere and hierarchical structures is found to be 3.13 and 4.64%, respectively. The DSSC consisting of hierarchical structure has the higher charge transfer recombination resistance (Rrec) and electron lifetime (τr) than other DSSC.

Efficacy of biomaterial based photocatalytic composite in treating dye pollutants

A biomaterial based photocatalytic composite, hydroxyapatite–TiO2–ZnO (HAp-TiO2–ZnO) has been developed following a solid-state combustion method while its efficacy was investigated through the photodegradation of (i) aquatic solution of synthetic dye, methylene blue (MB); and (ii) real textile dye effluent. The degradation profile was explored considering several factors, e.g.: (i) initial dye concentration; (ii) illumination span; (iii) dose of photocatalyst; and (iv) pH of targeted dye solution. The photodegradation was performed in both indoor and outdoor environment using halogen lamp (500 W) and sunlight respectively. Observed photodegradation revealed that though the photocatalytic composite effectively decomposed methylene blue at various extents under different experimental conditions but a dose of 0.5g photocatalyst/100 mL substrate solution (10×10-6 M methylene blue solution at pH 4) expedited optimal degradation (~ 97%) at 2 hours’ time interval. On the other hand though it was possible to degrade the textile effluent to some extent by illuminating through halogen lamp and sunlight but the success rate did not exceed 50%.Bangladesh J. Sci. Ind. Res.53(2), 139-144, 2018

Predictable Particle Engineering: Programming the Energy Level, Carrier Generation, and Conductivity of Core-Shell Particles.

Core-shell structures are of particular interest in the development of advanced composite materials as they can efficiently bring different components together at nanoscale. The advantage of this structure greatly relies on the crucial design of both core and shell, thus achieving an intercomponent synergistic effect. In this report, we show that decorating semiconductor nanocrystals with a boronate polymer shell can easily achieve programmable core-shell interactions. Taking ZnO and anatase TiO2 nanocrystals as inner core examples, the effective core-shell interactions can narrow the band gap of semiconductor nanocrystals, change the HOMO and LUMO levels of boronate polymer shell, and significantly improve the carrier density of core-shell particles. The hole mobility of core-shell particles can be improved by almost 9 orders of magnitude in comparison with net boronate polymer, while the conductivity of core-shell particles is at most 30-fold of nanocrystals. The particle engineering strategy is based on two driving forces: catechol-surface binding and B-N dative bonding and having a high ability to control and predict the shell thickness. Also, this approach is applicable to various inorganic nanoparticles with different components, sizes, and shapes.

CO 2 hydrogenation to methanol over CuO–ZnO–TiO2–ZrO2: a comparison of catalysts prepared by sol–gel, solid-state reaction and solution-combustion

Three CuO–ZnO–TiO2–ZrO2 catalysts with the same composition were prepared through sol–gel, solid-state reaction, and solution-combustion methods and characterized by X-ray diffraction (XRD), N2 adsorption, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction with H2 (H2-TPR), reactive N2O adsorption, and adsorption of H2 and CO2 followed by temperature-programmed desorption (H2-TPD, CO2-TPD) techniques. Their catalytic performances for CO2 hydrogenation to methanol were tested in a fixed-bed reactor under the conditions of 200–280 °C, 3 MPa, and SV = 2400 mL gcat−1 h−1. The results indicated that the texture, structure, reducibility, and adsorption capacity for reactants of the CuO–ZnO–TiO2–ZrO2 catalyst were affected noticeably by preparation methods and the catalyst prepared by sol–gel method exhibited the highest CO2 conversion and methanol selectivity, which reached to 17.0% and 44.0%, respectively. The highest activity of the CuO–ZnO–TiO2–ZrO2 catalyst prepared by sol–gel method was attributed to the largest metallic Cu surface area and adsorption capacity for H2.

Hydrothermal synthesis of mesoporous TiO2–ZnO nanocomposite for photocatalytic degradation of methylene blue under UV and visible light

Mesoporous ZnO–TiO2 was synthesized successfully by a one-step hydrothermal procedure using titanium sulfate and Zinc nitrate hexahydrate as precursors, and Pluronic P123 as a template. The prepared ZnO–TiO2 materials were heat treated at 400, 600, 800 and 1000 °C to remove the template and increase the degree of crystallization. Field emission scanning electron microscopy, wide angle X-ray diffraction, Fourier transformed infrared spectroscopy, transmission electron microscopy and N2 adsorption–desorption experiments were used to characterize the synthesized powders. Comparison photocatalytic investigations for the prepared materials and commercially available P25 were carried out under identical UV and visible light to understand the effect of the achieved phases and surface area on photocatalytic rate constant and percentage degradation. Results show that the sample which was heat treated at 800 °C (S-800) presents a very high performance under visible light and around 60% of the methylene blue (MB) solution can be degraded by this catalyst in spite of its low surface area. The high efficiency of this sample under visible light can be related to its high degree of crystallinity, formation of anatase and titanium–zinc oxide phases and interfacial coupling between ZnO and TiO2 nanoparticles.

Preparation and characterization of (100 − x) TiO2 + (x)ZnO nanocomposites for dye-sensitized solar cells using Beta vulgaris and Syzygium cumini natural dye extract

The present paper attempts to report the preparation of TiO2–ZnO nanocomposite photoanode materials for dye-sensitized solar cells (DSSC) and analyse the efficiency of DSSC with natural dyes. The structural and optical characteristics of the composites were studied by transmission electron microscopy, X-ray diffraction, field effective scanning electron microscopy, energy dispersive spectrometry, photoluminescence and absorption spectroscopy. The synthesized nanocomposites formed on FTO substrates are applied as photoanode in a dye-sensitized solar cell (DSC). The natural dyes extracted from Beta vulgaris (Beetroot) and Syzygium cumini (black plum) were used in the fabrication of DSSC. The solar cells’ photovoltaic performance in terms of short-circuit current, open circuit voltage, fill factor and energy conversion efficiency was tested with photocurrent density–voltage measurements. The evolution of the solar cells parameters is explored as a function of the photoanode and type of dye used in DSSC fabrication.The obtained results show that the efficiency of DSSC significantly changes with the addition of ZnO to TiO2, while the Beta vulgaris dye has evidently shown higher photo sensitized performance compared to Syzygium cumini in the preparation of DSSC.

Designing biomimetic porous celery: TiO2/ZnO nanocomposite for enhanced CO2 photoreduction

The nanostructured heterojunction photocatalysts are considered promising in photocatalytic reduction in the carbon dioxide. Herein, we demonstrate a simple sol–gel and hydrolysis process to design nanostructured TiO2/ZnO heterojunction, by using the biological template celery stalk. The nanostructured photocatalyst consists of anatase TiO2 and wurtzite ZnO nanoparticles. A well-connected heterojunction, with uniformly distributed nanoparticles, on the pores and folds of celery stems, is obtained. The enhanced specific surface area of 55.5 m2/g is achieved. The crystal structure, morphology and surface composition are investigated by electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. Furthermore, we demonstrate the photocatalytic performance of as-synthesized nanostructure TiO2/ZnO heterojunction. The photocatalytic yield, of CO2 reduction into CH4, exhibits a five times increase, from 0.55 to 2.56 µmol h−1 g−1, for the nanocomposite as compared to the pure TiO2. This enhanced performance corresponds to the efficient charge transfer and hindrance in the recombination of electron–hole pairs due to the optimum band positions of ZnO and TiO2. This study demonstrates the potential of using biotemplates to design efficient photocatalysts to convert CO2 into useful solar fuels.

Effect of calcination temperature on the microstructure and electronic properties of TiO2–ZnO nanocomposites and implications on photocatalytic activity

TiO2–ZnO nanocomposites with a constant Ti:Zn molar ratio of 1:0.1 were prepared via sol–gel process followed by calcination at 300, 400, 500, 600, and 700 °C. The structural and compositional characterizations of these nanocomposites were performed through XRD, FTIR, SEM, and EDAX. Bandgap was measured using DRS. Photocatalytic performance of the nanocomposites was evaluated by decolorization of methyl orange dye under UV and visible irradiation with and without aeration. The results showed that increase in calcination temperature resulted in nanocomposites with well-defined morphology. Although the particle size increased with increase in calcination temperature, the crystallinity of the particles also increased, resulting in enhanced photocatalytic activity. A temperature-dependent anatase-to-rutile phase transformation was observed in TiO2–ZnO nanocomposite beyond 600 °C. The calcination temperature influenced both dye adsorption on the nanocomposites and also dye decolorization by photocatalysis. Even when present at low molar concentration, ZnO in the nanocomposite caused sufficient decrease in bandgap (2.6 eV) at temperatures as low as 400 °C, such that visible irradiation could cause dye decolorization. However, the best decolorization performance was observed in the presence of the nanocomposite calcined at 600 °C. Aerated systems showed better performance in all cases. Desorption of the dye remaining adsorbed on the nanocomposite at the end of the photocatalytic reaction, confirmed that adsorption accounted for only 6.6 and 3% of dye removal in the nanocomposites calcined at 600 °C with UV and visible irradiation, respectively. However, in other systems, ignoring adsorption may cause significant overestimation in photocatalytic loss of dye from the system.

Photocatalytic degradation of phenazopyridine contaminant in soil with direct solar light

ABSTRACTPhotocatalytic degradation of waste pharmaceutics, with solar radiation, is described here as a feasible method to purify pre-contaminated soils. Phenazopyridine has been used as a model soil contaminant. Two different nano-size powders have been first examined as catalysts, namely commercial TiO2 (anatase) and commercial ZnO. As the ZnO showed higher catalytic efficiency, the study was then focused on it. The commercial ZnO powder was then compared with lab-prepared ZnO powder, and the latter shows relatively higher efficiency. The ZnO was used in two different ways. In one way, dry ZnO catalyst powder was spread onto the soil, while in the other way the ZnO was sprayed onto the soil surface by a wet spray method. The spray technique shows slightly higher efficiency, in addition to being easier to apply at future large scale. Depending on conditions and type of photocatalyst used, up to 90% contaminant removal can be achieved in 30 min. In case of photocatalysis experiments, the reacted contaminant molecules undergo complete degradation with no detectable side reaction organic products. Possible evaporation or escape of organic contaminant, or other possibly resulting organics, is ruled out by a series of control experiments. Photodegradation process takes place only at the catalytic sites on the soil surface, where contaminant molecules that diffuse from the soil bulk are completely degraded. Other useful organisms inside the soil are not affected as they are kept away from catalyst sites. A plausible mechanism is proposed for the degradation process.

Chemical Synthesis and Characterization of ZnO–TiO2 Semiconductor Nanocomposites: Tentative Mechanism of Particle Formation

The compounds of ZnO–TiO2 can combine the characteristics of the individual oxides which has allowed them to be used as photocatalysts in general, photodegradants in the degradation of dyes, photocatalytic oxidation of NOx, antimicrobial, among other applications. In this study, ZnO–TiO2 semiconductor nanocomposites were synthesized in a controlled way at low temperature. These samples of ZnO–TiO2 were characterized using thermal analysis (TDA/TGA), IR and UV–Vis absorption spectroscopies, X-ray diffraction, and scanning electron microscopy. The primary particles showed a nanometric size (< 100 nm) and spheroidal morphology. All samples presented zincite as the main crystalline phase. When Ti4+ was added, the peaks of the diffractograms shifted slightly with respect to pure ZnO. This indicates the formation of a solid solution. Zn2TiO4 was observed in doped ZnO samples treated at 700 °C. The UV–Vis absorption spectra showed a band in the range between 350 and 425 nm, with a maximum around 375 nm (3.31 eV). With the addition of Ti4+, the nanocomposites showed a better absorbance in the visible range. Considering the nature of the synthesis process used, a mechanism was proposed to explanation of the formation of Nanocomposites.

Flexible Ultraviolet and Ambient Light Sensor Based on a Nanomaterial Network Fabricated Using Selective and Localized Wet Chemical Reactions.

We report ZnO nanowire- and TiO2 nanotube-based light sensors on flexible polymer substrates fabricated by localized hydrothermal synthesis and liquid phase deposition (LPD). This method realized simple and cost-effective in situ synthesis and integration of one-dimensional ZnO and TiO2 nanomaterials. The fabricated sensor devices with ZnO nanowires and TiO2 nanotubes show very high sensitivity and quick response to the ultraviolet (UV) and ambient light, respectively. In addition, our direct synthesis and integration method result in mechanical robustness under external loading such as static and cyclic bending because of the strong bonding between the nanomaterial and the electrode. By controlling the reaction time of the LPD process, the Ti/Zn ratio could be simply modulated and the spectral sensitivity to the light in the UV to visible range could be controlled.