TiO2 Nanocatalysts Research Articles

Synergistic effects of single/multi-walls carbon nanotubes in TiO2 and process optimization using response surface methodology for photo-catalytic H2 evolution

Nobel metals free MW/SW supported TiO2 nanocatalysts were prepared via wet impregnation assisted sol-gel method and tested for photocatalytic H2 evolution. The photoactivity of TiO2 mediated by MW/SW was considerably improved due to superior charges separation. More importantly, hydrogen production depends on wall numbers such as multiwall or single wall carbon nanotubes, works as electrons acceptor and promoted charges separation. The maximum H2 evolution rate of 11,060 ppm h−1g-cat−1 was achieved over MW/TiO2/SW, 1.24 folds higher than SW/TiO2 and 1.42 times higher than MW/TiO2 composites. This improved productivity was due to synergistic effects between SW/MW, which greatly promoted charge carriers separations and enables absorption of visible light. Besides, more H2 production with SW/TiO2 compared to MW/TiO2 was due to more trapping of electrons by single wall than using multi-walls. The activity of composite further enhanced with methanol as hole-scavenger, higher in order of methanol > ethanol > propanol due to presence of α-hydrogen atoms bonded with C-atoms. Response surface methodology (RSM) approach of full factorial design applied to investigate significance and influence of reaction time, loading of catalyst and methanol-water concentration on H2 yield. The interaction between parameters reveals that catalyst loading has more influence on H2 evolution compared to other factors. Therefore, this study provides a new approach for noble-metals free synthesis of composite with enhanced visible light H2 evolution and optimization of parameters for maximum photo-catalytic H2 production.

Heterogeneous Photocatalysis in Microreactors for Efficient Reduction of Nitrobenzene to Aniline: Mechanisms and Energy Efficiency

AbstractAniline was synthesized from nitrobenzene through photo‐induced reduction in microreactors under UV irradiation. Nitrobenzene solution and the nanofluid prepared by a TiO2 nanocatalyst, PEG‐400, and deionized water were mixed in a capillary microreactor. The effects of catalyst composition, residence time, and substrate concentration on the reaction performance were systematically investigated. The conversion of nitrobenzene and the yield of aniline reached high values under optimized conditions. The excellent reusability of the photocatalyst was realized for four runs. A mechanism was proposed for this photocatalytic reduction process based on reaction kinetics. Both photo‐induced electrons and •CO2− could reduce nitrobenzene to aniline. The photonic efficiency in the microreactor was still much higher than that obtained in batch reactors, which was mainly attributed to the much larger effective radiation area of the microreactor.

LED-activated immobilized Fe-Ce-N tri-doped TiO2 nanocatalyst on glass bed for photocatalytic degradation organic dye from aqueous solutions

Abstract The aim of this study was to evaluate the photocatalytic process efficiency of titanium dioxide (TiO2) nanoparticles doped with nitrogen (N), iron (Fe), and cerium (Ce) stabilized on a glass bed for the removal of organic dye from an aqueous medium in the presence of visible light. Synthesis of nanocatalysts was performed by sol–gel method. SEM, XRD, FTIR, DLS, AFM, and Zeta-potential analyses were used to identify and describe the properties of synthesized nanocatalysts. The effect of operating parameters, including pH, initial dye concentration, light intensity, contact time, and nanoparticle type on the removal efficiency was explored in a series of photocatalytic experiments. The results showed that doping TiO2 with N, Fe, and Ce resulted nanoparticles with different sizes and increased the photocatalytic activity as well as the surface charge of TiO2 nanoparticles. The Fe-N-Ce-TiO2 was found as the most efficient nanophotocatalyst among synthesized nanoparticles under both visible light and darkness. The experimental results showed that the removal of dyes in acidic pH was higher than that in neutral and alkaline pH. The complete removal of Direct Blue 15 dye under LED radiation could be achieved in optimal conditions of pH = 5.7, current intensity of 0.68 A (1000 lux), initial concentration of 25 mg/L, nanoparticle dose of 10 mg/cm 2 and 60 min of contact time. Findings of this study clearly demonstrated that the nanocatalytic process of Fe-Ce-N tri-doped TiO2 was highly effective in oxidizing dye pollutants in the visible light range, and the it could be very suitable for areas rich in sunlight for the oxidation of dye contaminants.

Titanium nitride nanoparticles for the efficient photocatalysis of bicarbonate into formate

Metallic nanoparticles can act as efficient photocatalysts thanks to the surface plasmons that they support, which are capable of harvesting light and generating hot carriers. Recently, titanium nitride (TiN) nanostructures have emerged as promising candidates for this application due to their much lower cost, and therefore greater sustainability, than structures made of noble metals, as well as their expected long-term thermal stability. In this work, we demonstrate that, under solar illumination, TiN nanoparticles, in combination with titanium dioxide (TiO2) nanostructures, can significantly increase the photocatalytic production of formate through the simultaneous photoreduction of bicarbonate and oxidation of glycerol. Importantly, we also show that TiN nanoparticles alone can provide an enhancement of the photocatalytic efficiently when compared to TiO2 nanocatalysts. Furthermore, by characterizing the morphology and material properties of the TiN nanoparticles after the reaction, we confirm that they remain stable under reaction conditions for extended periods of solar light exposure (8 hours). The results of this work advance our understanding of TiN nanoparticles as efficient photocatalysts and their use for the production of valuable chemicals.

Stabilization of Pd3−xIn1+x Polymorphs with Pd‐like Crystal Structure and their Superior Performance as Catalysts for Semi‐Hydrogenation of Alkynes

AbstractSelective hydrogenation (semi‐hydrogenation) reactions of alkynes rely on Pd‐based catalysts to provide the correct pathway to favour formation of double bonds and avoid full hydrogenation to single bonds. Here, we present the preparation and characterisation of “Pd3In”/TiO2 nanocatalysts, which show improved activity and selectivity compared to pure Pd catalysts, towards the liquid phase semi‐hydrogenation of 2‐methyl‐3‐butyn‐2‐ol (MBY) to 2‐methyl‐3‐buten‐2‐ol (MBE), a fundamental step in the preparation of pharmaceuticals, and other industrially produced substances, as well as a model reaction for the semi‐hydrogenation of alkynes. For both the supported and unsupported “Pd3In” alloys (later re‐defined as Pd3−xIn1+x), we stabilised two new cubic polymorphs with a Pd‐like structure, instead of the tetragonal structure as reported so far in the literature. The stabilisation of these new polymorphs was made possible by using a solution‐based synthesis and, thanks to the use of different solvents, the reaction was carried out at different temperatures and the Pd/In ratio could be tuned. The same synthetic approach was adapted to prepare two “Pd3In”/TiO2 catalysts by adding the TiO2 support to the reaction mixture, in a practical one‐step, one‐pot reaction. HREM and X‐Ray maps show that the cubic crystal structure of “Pd3In” is maintained when prepared in the presence of the support, however, the support seems to influence the Pd/In ratio.

Noble and Base-Metal Nanoparticles Supported on Mesoporous Metal Oxides: Efficient Catalysts for the Selective Hydrogenation of Levulinic Acid to γ-Valerolactone

The selective hydrogenation of levulinic acid, LA to γ-valerolactone, GVL in water and solvent-free systems using mesoporous TiO2, NiO and MnO2 metal oxides supported noble and base-metal nanoparticles was investigated. BET results showed that all the synthetized materials were mesoporous with type IV isotherms and type I hysteresis. The p-XRD peaks observed in the low angle region confirm the successful formation of the meso-structured materials, whereas the wide-angle diffraction patterns show that the crystalline structure of the pure nanocatalysts is maintained upon deposition of the metal. TPR results showed that the reduced supported nanocatalysts consist of metallic Ru, Pd, Cu and Cr, and the average particle sizes obtained from HRTEM were found to be of 2 to 6 nm in diameter. The as-synthetized reusable nanocatalysts were revealed to be highly efficient for the conversion of LA to GVL. The best performance with complete conversion of LA and > 95% GVL selectivity was obtained from the TiO2 and MnO2-based nanocatalysts when water was used as a solvent. The order of reactivity of the supported metal nanoparticles was established as: Pd ≈ Ru > Cu > Cr. With an activity, TOF of up to 277273 h−1/mol, the low cost copper-based nanocatalysts could be an alternative to the high cost noble metal-based catalysts.

TiO2 Surface Engineering to Improve Nanostability: The Role of Interface Segregation

Nanoparticle stability against coarsening is one of the keys to allow better exploitation of the properties of nanoscale materials. The intrinsically high interfacial energies of nanoparticles constitute the driving force for coarsening, and therefore can serve as targets to design materials with improved thermal stability. In this study, we discuss the surface engineering of TiO2 nanocatalysts for artificial photosynthesis by exploiting the spontaneous segregation of Ba2+ ions to the interfaces of TiO2 nanocrystals. Ba2+ is a strong candidate for photoelectrocatalytic reduction of CO2 and its effects on interfacial energies lead to a remarkable increase in thermal stability. By using a systematic lixiviation method, we quantified the Ba2+ content located at both the surface and at grain boundary interfaces and combined with direct calorimetric measurements of surface energies and microstructural studies to demonstrate that Ba2+ excess quantities directly impact coarsening of TiO2 nanocatalysts by creatin...

Heterostructures of mesoporous TiO2 and SnO2 nanocatalyst for improved electrochemical oxidation ability of vitamin B6 in pharmaceutical tablets

The detection of water soluble vitamins using electrochemical method is widely established in pharmaceutical quality control laboratories, and especially the recent advances in hybrid heterostrucure nanomaterials has devoted to enhance the significant analytical parameters like sensitivity, selectivity and fast response time. Herein, we report the synthesis of a hybrid heterostructure comprising SnO2 nanoparticles supported mesoporous TiO2, and the obtained nanocomposite were fabricated over glassy carbon electrode (GCE) for the electrochemical oxidation of vitamin B6 in pharmaceutical tablets. The designed SnO2-TiO2/GC modified electrode exhibits well-defined oxidation peak with lowering over-potential and larger signal response compared to the pristine counterparts, and it is mainly due to the formation of abundant active surface layer offered by SnO2 cocatalyst, and thus significantly enhances the electrochemical surface area. Differential pulse voltammetry (DPV) measurements revealed a sharp increase in the anodic peak current upon addition of increasing concentration of vitamin B6. The analytical performance of the modified electrode displayed a wide linear range (0.1–31.4 µM), high selectivity, and excellent sensitivity (759.73 µA mM−1 cm−2) with low detection limit (35 nM). Thus, the resultant mesoporous hybrid nanocatalyst provides an efficient electrochemical platform for determination of various potential analytes.

Thumba methyl ester production using prepared novel TiO2 nano-catalyst in ultrasonic cavitation reactor

In this present research, the catalytic activity of the prepared TiO2 nanoparticles was evaluated towards the thumba methyl ester production by using it under ultrasonic cavitation reactor. TiO2 nanoparticles were prepared by ultrasonic assisted sol-gel method using titanium tetra-isopropoxide (TTIP) as precursor. The required parameter like ultrasonic irradiation time was varied from 10 to 60 min, power density from 10 W/L- 30 W/L, initial temperature from 5°C -20°C and water to TTIP weight ratio from 5-20 for sol-gel method. After completing all the experimental activity, it was found that the morphology of TiO2 nanoparticles largely depends on the factors such as ultrasonic irradiation time, power density, inlet temperature and water to TTIP ratio. The prepared TiO2 nanoparticles were useful for the thumba methyl ester production up to 92% conversion of triglycerides from thumba oil in ultrasonic cavitation reactor.

Visible light proven Si doped TiO2 Nanocatalyst for the Photodegradation of Organic dye

Abstract In the present work, such nanomaterial has been synthesized using titanium oxide as a base material and using Si as a dopant material. The structural, surface morphological and textural characterization for the synthesized pure TiO2 and Si doped TiO2 (STO) nanomaterial were characterized using X-ray diffraction studies (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM). The porous nature and absorption nature the nanomaterial was analysed using Braunner Emmet teller studies (BET) and Ultra-violet diffuse reflectance spectroscopy (UV-DRS) studies. The compositional ratio of the nanomaterial was explained with Energy dispersive studies (EDS). On comparing both the nanomaterial, sharp crystalline peaks supporting the formation of TiO2 in anatase form and on comparison shift in peaks with blend nature shows the presence of dopant Si along with TiO2 nanomaterial. The photocatalytic run were performed using pyrex reactor and the parameters responsible were examined. Catalyst dose, period of contact, pH and initial dye concentration were optimized and a final run was performed. L-H kinetic studies, carried out to find the pathway and rate of the photodegradation reaction. Finally regeneration studies were studied to elucidate the cost effectiveness and economical value of the photocatalyst synthesized. The Band gap reduction which helps in the shift of electrons from valence band to conduction band enables the photocatalytic activity in the visible light region.

Controlling Self-Assembly of Cellulose Nanocrystal to Synergistically Regulate (001) Reactive Facets and Hierarchical Pore Structure of Anatase Nano-TiO2 for High Photocatalytic Activity

As one of the most efficient and environmentally benign strategies to treat organic dye pollution, TiO2 photocatalytic technology has attracted increasing and wide interests in environmental governance, for which dominantly exposed (001) facets and high porosity are of great importance for catalytic performance. To date, however, how to synergistically regulate the dominant growth of (001) facets and the formation of hierarchical pore structures still remains challenging. Here, we report a limited growth strategy mediated by the self-assembly of cellulose nanocrystal (CNC) to prepare anatase TiO2 nanocatalyst with dominantly exposed (001) reactive facets. Notably, crystal growth in the confined space of layered CNC structures favors exposing (001) facets, and the easy removal of the soft biotemplate facilitates creating hierarchical pores. Furthermore, the (001) facet percentage, pore size, and porosity can be easily modulated by controlling the CNC concentration. After introducing an up-conversion quantu...

Degradation of paraquat from contaminated water using green TiO2 nanoparticles synthesized from Coffea arabica L. in photocatalytic process.

The TiO2 nanoparticles synthesized from the extract of Coffea arabica L. (or TiO2/C) were used to remove paraquat from contaminated water in heterogeneous photocatalysis process. In this work, the sol-gel process using Coffea arabica L. as the solvent chemical were performed to obtain the TiO2 nano-catalyst. The value of pHpzc of TiO2/C was 2.9 which caused a highly acidic surface of catalyst. The paraquat is effectively removed in alkaline medium due to the adsorption ability of paraquat on the surface of TiO2/C. The paraquat degradation followed the pseudo-first-order model with the apparent rate constants of 5.84 × 10-2, 4.08 × 10-2, and 2.28 × 10-2 min-1 for TiO2/C, TiO2, and without TiO2, respectively, under the presence of ultraviolet (UV) and H2O2. The combined TiO2/C with UV and H2O2 was the most efficient process, exhibiting a maximum 66.3% degradation of 50 mg/L over 90 min at pH 10.

A co-relation study of efficient photocatalytic reduction of aromatic nitriles and band energies of Cu loaded elongated TiO2 nanocatalysts

Abstract Photoreduction of nitroaromatics into amines with TiO2 (P25) via greener method has attracted a great deal of interest. Generally, this reaction is feasible as the reduction potential of nitro groups (-0.5 eV) lies below the conduction band (-0.85 eV vs. NHE) of TiO2. However, functional groups such as nitrile (-CN), azido (-N3), aceto (-CH3CO), etc. are generally not photoreduced by conventional P25 due to their unfavorable reduction potential relative to titania. This report demonstrates efficient photocatalytic reduction of aromatic nitriles by tuning the band energies of Cu-TiO2 nanostructures of different morphologies. The band energetics were determined by optical and electrochemical studies which revealed that Cu loaded titania nanotubes (Cu-TNT) possess more negative conduction band gap (-2.7 eV vs. vacuum) energy as compared to LUMO level of benzonitrile (-2.82 eV). This factor has probably facilitated better reduction efficiency of benzonitrile (> 90%) and its derivatives with Cu-TNT in comparison to almost no reactivity with Cu-P25 under similar conditions. In addition to suitable conduction band position of Cu-TNT, presence of anatase phase and higher surface area (204 m2/g) might have enhanced the reaction rate.

Modification of the Optical and Electronic Properties of TiO2 By N Anion-Doping for Augmentation of the Visible Light Assisted Photocatalytic Performance

In this work, a nitrogen-doped anatase TiO2 nanocrystal is prepared by a modified sol-gel preparation method using the nonionic surfactant (polyoxyethylene sorbitan monooleate) as a structural controller and a soft template. The as-prepared samples are characterized by X-ray diffraction, Raman spectroscopy, UVVis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy techniques. Then the photocatalytic activity of these samples is assessed by the photocatalytic oxidation of phenol under visible light irradiation. The phenol concentration is measured using a UV-Vis spectrometer. Experimental results show that N-doping leads to an excellent visible light photocatalytic activity of the TiO2 nanocatalyst. Furthermore, the formation energy and electronic structure of pure and N-doped anatase TiO2 are described by density functional theory (DFT) calculations. It is found that N-doping narrowed the band gap of bare TiO2, which leads to an excellent visible light photocatalytic activity of N–TiO2 nanocatalysts. Therefore, the prepared N–TiO2 photocatalyst is expected to find the use in organic pollutant degradation under solar light illumination.

Application of Potassium Ion Impregnated Titanium Dioxide as Nanocatalyst for Transesterification of Linseed Oil

The current work comprises the investigation of biodiesel production from linseed oil using TiO2 and a potassium L-tartrate monobasic (C4H5KO6)-modified TiO2 nanocatalyst. Different amounts of C4H5...

Comparing Photocatalytic Degradation of Gaseous Ethylbenzene Using N-doped and Pure TiO2 Nano-Catalysts Coated on Glass Beads under Both UV and Visible Light Irradiation

Volatile Organic Compounds (VOCs) are within the main industrial air pollutants whose release into the atmosphere is harmful to the ecosystem and human health. Gas-phase photocatalytic degradation of ethylbenzene, an aromatic VOC emitted from various sources, has been investigated in this study using TiO2 nanoparticle-coated glass beads in an annular photoreactor. To use visible light irradiation, TiO2 nanoparticles were doped by nitrogen using urea. The results showed that nitrogen doping significantly increased the removal efficiency of ethylbenzene under visible light irradiation compared with the pure TiO2, so that the removal efficiencies between 75–100% could be yielded for the initial ethylbenzene concentrations up to 0.13 g/m3 under visible light which could be useful for improving indoor air quality. The UV irradiated reactor needed less residence time and much higher removal efficiencies could be yielded at high initial concentrations. When the residence time under UV irradiation was one third of the same under visible light, the removal efficiency was more than 80% for the inlet concentrations up to 0.6 g/m3, whereas the removal efficiency under visible light was about 25% at this inlet concentration. Langmuir-Hinshelwood kinetic model could be well fitted to the photocatalytic reaction in both irradiation systems.

Visible-Light-Induced Photocatalytic Degradation of PAH-Contaminated Soil and Their Pathways by Fe-Doped TiO2 Nanocatalyst

The aim of the present study was to establish the photocatalytic efficiency of Fe-doped TiO2 nanocatalysts toward polycyclic aromatic hydrocarbons (PAHs), which were phenanthrene, anthracene, and fluoranthene, contaminated soil under visible irradiation. The morphology, phase, and particle size of the prepared nanocatalyst have been studied as a first mention in literature. The photoresponse of the TiO2 extends from UV region to the visible region was proved by the diffuse reflectance spectrophotometry (DRS). The surface area is greatly increased though the Fe-doped TiO2 compared with the bare TiO2. The pH value of the media showed the beneficial to PAH absorption on the Fe-doped TiO2 under the alkaline condition due to the surface catalyst possesses much negative charge, which is increase in percentage of PAH degradation. Based on GC-MS study, the mechanism of photoactivity of the selected PAHs involves hydroxylation, ring opening, and rearrangement reactions. The main intermediates of PAH photodegradation were found to be 9-octadecanoic acid, heptadecane, octadecane, cyclohexane (1-hexadecylheptadecyl), and 15-hydroxypentadecanoic acid.

Bimetallic Pd@Ni-mesoporous TiO2 nanocatalyst for highly improved and selective hydrogenation of carbonyl compounds under UV light radiation

Bimetallic Pd@Ni nanostructure exhibited enhanced co-catalytic activity for the selective hydrogenation of benzaldehyde compare to their monometallic counterparts. Impregnation of these mono/bimetallic nanostructures on mesoporous TiO2 leads to several surface modifications. The bimetallic PNT-3 (Pd3@Ni1/mTiO2) exhibited large surface area (212m2g−1), and low recombination rate of the charge carriers (e−-h+). The hydrogenation reaction was analyzed under controlled experiments. It was observed that under UV-light irradiations and saturated hydrogen atmosphere the bimetallic PNT-3 photocatalyst display higher rate constant k=5.31×10−1h−1 owing to reduction in the barrier height which leads to efficiently transfer of electron at bimetallic/mTiO2 interface.

Photocatalytic degradation of azo dye acid orange 7 using different light sources over Fe3+-doped TiO2 nanocatalysts

Abstract The photocatalytic degradation of a model azo dye acid orange 7 (AO7) by Fe3+-doped TiO2 nanocatalyst has been studied under UV, Visible ( λ >400 nm) and solar light irradiation. The role of hydrogen peroxide to enhance the catalyst’s efficiency was examined. The reaction pathway of complete mineralization was investigated by monitoring the temporal evolution of reaction intermediates and low molecular weight organic acids (LMWOA) as final products in solution. These LMWOAs are oxidized eventually to inorganic ions such a nitrate, sulfate, oxalate etc, which are confirmed using GC–MS, UV–Vis and Ion Chromatographic analyses. The optimized conditions of photocatalytic degradation were obtained for degradation under different light source. The Fe 3 + -doped TiO2 showed high dye degradation efficiency under both UV (100%), visible (100%) and solar light (90%) which distinguishes Fe 3 + -doped TiO2 from materials in literature that are only efficient in particular light source for dye degradation. Furthermore, the Fe 3 + doped titania photocatalysts are stable and can maintain performance up to 6 recycle use. Reaction kinetics for UV and solar light induced degradation followed first order reaction whereas visible light degradation followed a zero-order reaction.

Efficient Photocatalytic Reduction of CO2 Present in Seawater into Methanol over Cu/C-Co-Doped TiO2 Nanocatalyst Under UV and Natural Sunlight

Photocatalytic reduction of CO2 in seawater into chemical fuel, methanol (CH3OH), was achieved over Cu/C-co-doped TiO2 nanoparticles under UV and natural sunlight. Photocatalysts with different Cu loadings (0, 0.5, 1, 3, 5, and 7 wt%) were synthesized by the sol–gel method and were characterized by XRD, SEM, UV–Vis, FTIR, and XPS. Co-doping with C and Cu into TiO2 remarkably promoted the photocatalytic production of CH3OH. This improvement was attributed to lowering of bandgap energy, specific catalytic effect of Cu for CH3OH formation, and the minimization of photo-generated carrier recombination. Co-doped TiO2 with 3.0 wt% Cu was found to be the most active catalyst, giving a maximum methanol yield rate of 577 μmol g-cat−1 h−1 under illumination of UV light, which is 5.3-fold higher than the production rate over C-TiO2 and 7.4 times the amount produced using Degussa P25 TiO2. Under natural sunlight, the maximum rate of the photocatalytic production of CH3OH using 3.0 wt% Cu/C-TiO2 was found to be 188 μmol g-cat−1 h−1, which is 2.24 times higher than that of C-TiO2, whereas, no CH3OH was observed for P25.