Physical properties of the CNT:TiO2 thin films prepared by sol–gel dip coating

Uniform and highly adherent thin films of CNT:TiO₂ were synthesized by sol–gel dip coating method. Both TiO₂ and CNT:TiO₂ films showed very identical structural characteristics and no significant changes in the lattice values were observed. The crystalline size decreased from 20 nm for TiO₂ film to 17 nm for the 4%CNT:TiO₂ film. The film surface was very smooth and compact, as indicated by the roughness data obtained from AFM measurements; the root mean square (rms) average of the roughness was as low as 3 nm. The HRTEM showed that the CNTs are embedded in the matrix of TiO₂ indicating the formation of a composite. In Raman spectra the characteristic vibrations of the TiO₂ are identified, the increase in the FWHM of main anatase peak (144 cm^?1) in the case of the 4%CNT:TiO₂ film is interpreted as due to the incorporation of CNTs in the film. At the wavelength of 600 nm the refractive index of pure TiO₂ was 2.07 and the 4%CNT:TiO₂ showed a value of 2.29. The photoresponse curves showed typical features of charge trapping centers in the band gap of the films.     

Constructing direct Z-scheme photocatalysts with black N–TiO2-x/C and Cd0.5Zn0.5S for efficient H2 production

Black N doped TiO_2-x nanoparticles loaded on the carbon framework (N–TiO_2-x/C, NTC) were successfully fabricated by sol-gel method. In this work, the synthesized NTC material was combined with Cd_0.5Zn_0.5S (ZCS) short nanorods, forming a direct Z-scheme NTC/ZCS photocatalyst without using of electron mediator. The free radicals trapping experiment was also conducted through the degradation of RhB to determine photocatalytic mechanism. As a result, the 2% NTC/ZCS exhibited an optimal photocatalytic H₂ production rate which is up to 36.6 mmol/h/g and about 5.2 times higher than that of pristine ZCS nanorods. The apparent quantum efficiency (AQE) of the 2% NTC/ZCS hybrids at wavelength 420 nm was calculated to 51.2%. Moreover, long-term drying increases the close contact between NTC and ZCS, and this firm contact interface can promote charge transfer and improve photocatalytic stability of NTC/ZCS composite.     

The effects of Al2O3–TiO2 coating in a diesel engine on performance and emission of corn oil methyl ester

Today, as a result of increase in oil prices, limited fossil fuel resources, environmental consideration and global warming, the methyl ester fuels have been focused on alternative fuels. Methyl ester fuels can be used more efficiently in low heat rejection engines (LHR), in which the temperature of combustion chamber is increased by creating a thermal barrier. In this study, the piston, cylinder head, exhaust and inlet valves of a diesel engine were coated with the ceramic material Al₂O₃–TiO₂ by the plasma spray method. Thus, a thermal barrier was provided for the parts of the combustion chamber with these coatings. The effects of corn oil methyl ester that produced by the transesterification method, and No. D2 fuels’ performance and exhaust emissions’ rate were studied by using equal in every respect coated and uncoated engines. Tests were performed on the uncoated engine, and then repeated on the coated engine and the results were compared. A decrease in engine power and specific fuel consumption, as well as significant improvements in exhaust gas emissions (except NOx), were observed for all test fuels used in the coated engine compared with that of the uncoated engine.     

A durable and robust Fe–N–C electrocatalyst for oxygen reduction reactions by introducing Ti3C2–TiO2 as radical scavengers

Modern Fe–N–C electrocatalysts are promising as alternatives to expensive Pt-based catalysts for oxygen reduction reactions (ORR). Although the activity of this type of electrocatalyst have been improved over the years, their durability and longevity need critical enhancements for practical applications in fuel cells. Typically, the incomplete oxygen reduction inevitably generates reactive oxygen species, including ·OH and HO₂· radicals, which will fiercely attack the carbon support and directly damage active sites in Fe–N–C electrocatalysts. Herein, a durable and robust Fe–N–C@Ti₃C₂–TiO₂ electrocatalyst for high-efficiency ORR is synthesized, in which Ti₃C₂–TiO₂ could effectively scavenge ·OH radicals or decompose H₂O₂ molecules, and synergistically work with Fe–N–C catalysts to improve the durability. Consequently, the Fe–N–C@Ti₃C₂–TiO₂ electrocatalyst shows prominent ORR performance in both alkaline and acidic electrolytes, low H₂O₂ yield, and long-term stability. This work provides great prospects for the design of highly stable ORR electrocatalysts by introducing radical scavengers as an active defense to proactively eliminate H₂O₂ and its radicals.     

High hydrogen selectivity and anti-carbon ability by cracking of RP-3 jet fuel over Pt/ZrO2–TiO2–Al2O3 catalyst modified by MxOy (M = Ba,Sr and Ce) promoters

In order to improve the anti-carbon property and obtain higher H₂ yields, the promoters (BaO, SrO and CeO₂) were introduced into Pt/ZrO₂–TiO₂–Al₂O₃ catalyst. The activity of theses catalysts were investigated in the cracking reactions of RP-3 jet fuel under high temperature and high pressure conditions. The physicochemical characteristics of the catalysts were detected by Temperature programmed oxidation, Raman spectrum, N₂ adsorption–desorption, Transmission electron microscope, NH₃-temperature programmed desorption and NH₃-infrared spectroscopy techniques. It was found that the addition of BaO, SrO and CeO₂ promoted the well dispersion of Pt, stimulated the dehydrogenation reactions, and consequently higher hydrogen yields over modified catalysts were obtained. Moreover, the acid sites have been partially neutralized by these promoters, thus the total amount of acid sites as well as the Lewis acid sites decreased over the modified catalysts. The modified acidic properties inhibited the hydrogen transfer reactions and alkenes oligomerization reactions, resulting in the obvious decrease of carbon deposit. Therefore, the catalysts exhibited remarkable anti-carbon property after modifying by BaO, SrO and CeO₂. The valuable information in this work may be helpful to develop highly efficient catalysts for the advanced aircrafts.     

Design of functionalized double-metal MXenes (M2M’C2T2: M = Cr,Mo, M’ = Ti,V) for magnetic and catalytic applications

Two dimensional (2D) materials have demonstrated huge potential in wide applications ranging from nanodevices to energy storage. In this work, we propose a series of double-metal MXenes functionalized with various terminal atoms (M₂M’C₂T₂), including B, N, O, P and S, based on density-functional theory (DFT) calculation. We screen out a series of stable structures and study their magnetic and electronic properties. We find that the magnetism of M₂M’C₂T₂ can be regulated according to different transition metals and terminal atoms. The magnetic moments of Cr₂TiC₂T₂ and Cr₂VC₂T₂ (T = N, O or S) are mainly contributed by chromium, while those of Mo₂VC₂T₂ (T = N, O or S) are originated from vanadium. We also find that these monolayers are metal with spontaneous conductivity, which is favorable for the electrocatalysis. The Gibbs free energies for the adsorption of hydrogen atoms on Cr₂TiC₂S₂, Cr₂VC₂S₂ and Mo₂TiC₂P₂ are close to zero, indicating their high catalytic activity for hydrogen evolution reaction (HER). Our findings suggest that the functionalized double-metal MXenes are promising materials for magnetic nanodevices and electrocatalysts.     

A comparative study of Ni catalysts supported on Al2O3, MgO–CaO–Al2O3 and La2O3–Al2O3 for the dry reforming of ethane

CO₂ utilization through the activation of ethane, the second largest component of natural and shale gas, to produce syngas, has garnered significant attention in recent years. This work provides a comparative study of Ni catalysts supported on alumina, alumina modified with CaO and MgO, as well as alumina modified with La₂O₃ for the reaction of dry ethane reforming. The calcined, reduced and spent catalysts were characterized employing XRD, N₂ physisorption, H₂-TPR, CO₂-TPD, TEM, XPS and TPO. The modification of the alumina support with alkaline earth oxides (MgO and CaO) and lanthanide oxides (La₂O₃), as promoters, is found to improve the dispersion of Ni, enhance the catalyst's basicity and metal-support interaction, as well as influence the nature of carbon deposition. The Ni catalyst supported on modified alumina with La₂O₃ exhibits a relatively stable syngas yield during 8 h of operation, while H₂ and CO yields decrease substantially for Ni/Al₂O₃.     

Kinetics and mechanism of CO2 gasification of coal catalyzed by Na2CO3, FeCO3 and Na2CO3–FeCO3

The purpose is to develop a mild catalytic CO₂-gasification technology that can promote CO₂ utilization and reduce cost in air separation systems with improving system efficiency and obtaining desirable gaseous products. In this study, the influence of Na, Fe and their composite catalysts on the structure and gasification reactivity of chars derived from pyrolysis of Powder River Basin (PRB) coal was investigated. The results showed that a strong positive synergistic effect between Na and Fe catalyst in the gasification process was observed, the catalytic activity of the added catalysts was in order of: 4% Na > 3% Na–1%Fe > 2% Na-2% Fe > 1% Na-3% Fe > 1% Na-2% Fe > 4% Fe > raw coal. The catalysts inhibited the growth of the aromatic ring structure and enriched the generation of O-containing functional groups. Compared to Fe, the Na-based catalyst could easily diffuse into inner pores of coal char, forming C–O–Na structure and thus increasing the gasification reactivity of chars. In addition, due to the formation of inert material between SiO₂ and Na, the catalytic activity of Na catalysts was significantly decrease at the late stage of char conversion. Comparatively, the Fe-based catalysts showed better stability life. Moreover, it was found that the activation energy for CO₂-gasification of PRB coal can be decreased by 50% due to the addition of Na catalyst.     

Accelerated transfer and separation of charge carriers during the photocatalytic production of hydrogen over Au/ZrO2–TiO2 structures by interfacial energy states

Energy states and surface plasmon resonance (SPR) play an important role in photocatalytic processes and power generation energy, for they improve the separation, transport, and mobility of charge carriers. The creation of Au/semiconductor heterostructures with different amounts of Au forms energy states that can modulate surface plasmon excitation, interfacial charge transport and photocatalytic activity to generate hydrogen. However, the Au loading effect on the interfacial charge transport and photocatalysis of plasmonic Au/semiconductors is unclear. For this reason, in this study, Au/ZrO₂–TiO₂ materials with different Au loadings were synthesized and evaluated in the photocatalytic production of hydrogen. The results confirmed boosted photoactivity with increased gold loading up to 5 wt.%, obtaining four times more hydrogen production than with the base material. The (photo) electrochemical measurements revealed that the Au inclusion provoked the adjustment of Fermi level values associated with the variation of surface energy states at the Au/ZrO₂–TiO₂ interface, which can be related to the modulation of SPR. This phenomenon can be explained by two simultaneous effects: i) the creation of energy states at the Au/ZrO₂–TiO₂ interface that modify the Fermi level to more negative potentials with respect to the base material, in order to have photogenerated electrons with higher reducing power to catalyze the hydrogen production; and ii) the Au metallic nanoparticles with SPR act as electronic reservoirs that extend the life time of photogenerated electron-hole pairs, thus enhancing the separation of charge carriers and the mobility of photogenerated electrons.     

Interaction between (La,Sr)MnO3 cathode and Ni–Mo–Cr metallic interconnect with suppressed chromium vaporization for solid oxide fuel cells

Interaction between (La_0.8Sr_0.2)_0.90MnO₃ (LSM) cathode and newly developed Ni–Mo–Cr metallic interconnect is investigated at 900 °C under operation conditions of solid oxide fuel cells (SOFCs). The results show that chromium deposition on the LSM cathodes in the presence of Ni–Mo–Cr interconnect is remarkably reduced as compared to that in the presence of a conventional Fe–Cr metallic interconnect (RA446). In contact with the Ni–Mo-Cr interconnect the overpotential, η, for the O₂ reduction reaction on LSM cathode decreased from 529 to 111 mV during the 1200 min current passage at 200 mA/cm². In contrast, η increased from 464 to 561 mV for the reaction in the presence of a RA446 interconnect. The decrease in η clearly indicates that chromium poisoning effect of the Ni–Mo–Cr interconnect is also significantly suppressed as compared to that with conventional Fe–Cr interconnect materials. The suppressed Cr deposition and poisoning effects observed on the LSM cathodes demonstrate promising potential of the Ni–Mo–Cr alloy as new interconnect materials with significant suppressed chromium vaporization and deposition for SOFCs.     

Solar photocatalytic removal of herbicides from real water by using sol–gel synthesized nanocrystalline TiO2: Operational parameters optimization and toxicity studies

A comparative study of the photocatalytic activity of two different TiO₂ catalysts in solar photocatalytic oxidation, mineralization and detoxification of waters containing herbicides 2,4-dichlorophenoxyacetic acid (2,4-D), bentazon and toxic intermediates was performed in a pilot plant scale photoreactor. Commercial TiO₂ (Degussa P25) and TiO₂ synthesized by citrate sol–gel method (ECT-1023t) were selected as photocatalysts. The optimal basic operational parameters to eliminate these herbicides and toxic intermediates were established for both catalysts at laboratory scale. ECT-1023t showed better photocatalytic activity than the commercial Degussa P25 at solar pilot plant scale with both herbicides in real water at natural pH (6.8–7.8) without any additive. The toxicity of the treated solutions was evaluated using the Microtox test based on the inhibition of bioluminescence of the bacteria Vibrio fischeri. The toxic effect of the main intermediate of 2,4-D, the 2,4-dichlorophenol (2,4-DCP), was higher than the parental herbicide. Acute toxicity of 2,4-D and intermediates (2,4-DCP) was reduced during the photocatalytic treatment by using ECT-1023t as photocatalyst. Longer times were necessary to obtain similar results when using P25 as photocatalyst. No inhibitory growth effect of the herbicide bentazon and its photoproducts on Vibrio fischeri bacteria bioluminescence was observed for either photocatalyst in any of the irradiated samples collected at predetermined times using an initial concentration of 0.1325 mM of the herbicide.     

One-pot synthesis of Cu–TiO2/CuO nanocomposite: Application to photocatalysis for enhanced H2 production,dye degradation & detoxification of Cr (VI)

Photocatalytic hydrogen production under the visible spectrum of solar light is an important topic of research. To achieve the targeted visible light hydrogen production and improve the charge carrier utilization, bandgap engineering and surface modification of the photocatalyst plays a vital role. Present work reports the one-pot synthesis of Cu–TiO₂/CuO nanocomposite photocatalyst using green surfactant -aided -ultrasonication method. The materials characterization data reveals the TiO₂ particle size of 20–25 nm and the existence of copper in the lattice as well as in the surface of anatase TiO₂. This is expected to facilitate better optical and surface properties. The optimized photocatalyst shows enhanced H₂ production rate of 10,453 μmol h⁻¹ g⁻¹ of the catalyst which is 21 fold higher than pure TiO₂ nanoparticles. The photocatalyst was tested for degradation of methylene blue dye (90% in 4 h) in aqueous solution and photocatalytic reduction of toxic Cr⁶⁺ ions (55% in 4 h) in aqueous solution. A plausible mechanistic pathway is also proposed.     

Synthesis,characterization and investigation of the electrochemical hydrogen storage properties of CuO–CeO2 nanocomposites synthesized by green method

Pure CuO–CeO₂ nanocomposites were synthesized by simple thermal decomposition method in presence of various Cu salts as a copper source and fructose as a green capping agent. In this study, the effect of various parameters such as the type of copper sources, temperature and time of reaction on the morphology and the particles size were studied. The products were characterized via X-ray diffraction (XRD) pattern, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), N2 adsorption (BET), vibrating sample magnetometer (VSM), and infrared spectrum (FT-IR). The optical property of the nanocomposite was examined via UV–vis (DRS) spectroscopy and the band gap was calculated to 3 eV. Also, the hydrogen storage capacity of CuO–CeO₂ nanocomposites and CeO₂ nanoparticles were investigated via chronopotentiometry method for the first time. The discharge capacity of CeO₂ nanoparticles and CuO–CeO₂ nanocomposites in 1 mA current and 20 cycles obtained 2150 and 2450 mAh/g, respectively.     

Sustainable and selective hydrogen production by steam reforming of bio-based ethylene glycol: Design and development of Ni–Cu/mixed metal oxides using M (CeO2, La2O3, ZrO2)–MgO mixed oxides

Hydrogen (H₂) production in a clean and green manner via renewable sources is at present of great interest. Ethylene glycol, a bio-based feedstock, offers a sustainable route for high purity H₂ production. In the current investigation, MgO based mixed metal oxides containing CeO₂, La₂O₃ and ZrO₂ were synthesized and used to support 20 wt% Ni–Cu (1:1). The impacts of altering support characteristics on catalytic behavior have been studied and compared in H₂ synthesis via ethylene glycol steam reforming (SR), employing various characterization techniques such as XRD, SEM, EDX, TEM, H₂-TPR, H₂-TPD, TG-DSC and BET. Further, high resolution XPS studies were performed to explore the valence states and effectiveness of surface engineering of the catalysts. Assessment of the efficacy of catalysts was done via several parameters such as reactant conversion, H₂ concentration and long-term stability. All the synthesized materials produced encouraging results with high H₂ yield and conversion under the said operating conditions [T- 623 to 773 K; GHSV - 3120 to 6240 h^?1; P - 0.1 MPa; S/C - 3 to 7.5 mol/mol]. Amongst the three catalysts, Ni–Cu/La₂O₃–MgO and Ni–Cu/CeO₂–MgO exhibited superior behavior for high H₂ production. Ni–Cu/La₂O₃–MgO was better in comparison to Ni–Cu/CeO₂–MgO in terms of reactant conversion whereas Ni–Cu/CeO₂–MgO showed highest H₂ concentration (98 mol %) and improved stability along with absence of carbon deposition owing to its high mobile oxygen vacancies in its lattice. The highly active cubic CeO₂ species and its long-term durability (up to 8 cycles) owing to its exceptional redox property further justified its efficacy. The optimized process showed that at T = 773 K, GHSV = 3120 h^?1, S/C = 4.5 mol/mol for Ni–Cu/La₂O₃–MgO and Ni–Cu/CeO₂–MgO and at T = 773 K, GHSV = 3120 h^?1, S/C = 6 mol/mol and for Ni–Cu/ZrO₂–MgO, maximum H₂ concentration was obtained. At the end, reaction pathway followed by the catalysts was proposed.     

A first-principles study of electronic structure and photocatalytic performance of two-dimensional van der Waals MTe2–As (M = Mo,W) heterostructures

To efficiently produce green energy and to overcome energy crises and environmental issues, photocatalytic water splitting has become the core heart of recent research. Fabricating heterostructures with type-II band alignment can enhance the photocatalytic activity. By first-principles computations, we study Mo(W)Te₂–As van der Waals (vdW) heterostructures as promising photocatalysts for overall water splitting. The bandgap, band edge position and optical properties can be modified by biaxial strain. With appropriate compressive strain of 2% and 3%, the WTe₂–As heterostructures show transition from type-I to type-II band alignment, which could slow down electron-hole pair recombination. Compared with Mo(W)Te₂ and As monolayers, the band edge of Mo(W)Te₂–As heterostructures is on favorable positions for straddling the water redox potentials. Moreover, Mo(W)Te₂–As heterostructures fascinatingly show strong absorption peaks in both visible and near ultra-violet region, making them promising candidates for overall water splitting photocatalysts.     

Oxidative steam reforming of ethanol over Ni/Al2O3 catalysts promoted by CeO2, ZrO2 and CeO2–ZrO2

Oxidative steam reforming of ethanol at low oxygen to ethanol ratios was investigated over nickel catalysts on Al₂O₃ supports that were either unpromoted or promoted with CeO₂, ZrO₂ and CeO₂–ZrO₂. The promoted catalysts showed greater activity and a higher hydrogen yield than the unpromoted catalyst. The characterization of the Ni-based catalysts promoted with CeO₂ and/or ZrO₂ showed that the variations induced in the Al₂O₃ by the addition of CeO₂ and/or ZrO₂ alter the catalyst's properties by enhancing Ni dispersion and reducing Ni particle size. The promoters, especially CeO₂–ZrO₂, improved catalytic activity by increasing the H₂ yield and the CO₂/CO and the H₂/CO values while decreasing coke formation. This results from the addition of ZrO₂ into CeO₂. This promoter highlights the advantages of oxygen storage capacity and of mobile oxygen vacancies that increase the number of surface oxygen species. The addition of oxygen facilitates the reaction by regenerating the surface oxygenation of the promoters and by oxidizing surface carbon species and carbon-containing products.     

Enhanced electrochemical performance and stability of (La,Sr)MnO3–(Gd,Ce)O2 oxygen electrodes of solid oxide electrolysis cells by palladium infiltration

Palladium-impregnated or infiltrated La_0.8Sr_0.2MnO₃–Gd_0.2Ce_0.8O_1.9 (LSM-GDC) composites are studied as the oxygen electrodes (anodes) for the hydrogen production in solid oxide electrolysis cells (SOECs). The incorporation of small amount of Pd nanoparticles leads to a substantial increase in the electrocatalytic activity and stability of the LSM-GDC oxygen electrodes. The electrode polarization resistance (R_E) at 800 °C on a 0.2 mg cm⁻² Pd-infiltrated LSM-GDC electrode is 0.13 Ω cm², significantly smaller than 0.42 Ω cm² for the reaction on the pure LSM-GDC electrodes. The overpotential loss is also substantially reduced after the Pd infiltration; at an anodic overpotential 50 mV and 800 °C, the current increases from 0.15 A cm⁻² for the pure LSM-GDC anode to 0.47 A cm⁻² on a 0.3 mg cm⁻² Pd-infiltrated LSM-GDC. The infiltrated Pd nanoparticles enhance the stability of the LSM-GDC oxygen electrodes and are most effective in the promotion of the diffusion, exchange and combination processes of oxygen species on the surface of LSM-GDC particles, leading to the increase in the oxygen evolution reaction rate.