Perovskite-type catalytic materials for environmental applications

Recent advances in perovskite-based Z-scheme and S-scheme heterojunctions for photocatalytic CO2 reduction

The dramatic rise in carbon dioxide levels in the atmosphere caused by the continuous use of carbon fuels continues to have a significant impact on environmental degradation and the disappearance of energy reserves. Past few years have seen a significant increase in the interest in photocatalytic carbon dioxide reduction because of its ability to lower CO2 releases from the burning of fossil fuels while also producing fuels and important chemical products. Because of their excellent catalytic efficiency, great uniformity, lengthy charge diffusion layers and texture flexibility that enable accurate band gap and band line optimization, perovskite-based nanomaterials are perhaps the most advantageous among the numerous semiconductors proficient in accelerating CO2 conversion under visible light. Firstly, a brief insight into photocatalytic CO2 conversion mechanism and structural features of perovskites are discussed. Further the classification and selection of perovskites for Z and S-scheme heterojunctions and their role in photocatalytic CO2 reduction analysed. The efficient modification and engineering of heterojunctions via co-catalyst loading, morphology control and vacancy introduction have been comprehensively reviewed. Third, the state-of-the-art achievements of perovskite-based Z-scheme and S-scheme heterojunctions are systematically summarized and discussed. Finally, the challenges, bottlenecks and future perspectives are discussed to provide a pathway for applying perovskite-based heterojunctions for solar-to-chemical energy conversion.

Soot Erased: Catalysts and Their Mechanistic Chemistry

Soot formation is an inevitable consequence of the combustion of carbonaceous fuels in environments rich in reducing agents. Efficient management of pollution in various contexts, such as industrial fires, vehicle engines, and similar applications, relies heavily on the subsequent oxidation of soot particles. Among the oxidizing agents employed for this purpose, oxygen, carbon dioxide, water vapor, and nitrogen dioxide have all demonstrated effectiveness. The scientific framework of this research can be elucidated through the following key aspects: (i) This review situates itself within the broader context of pollution management, emphasizing the importance of effective soot oxidation in reducing emissions and mitigating environmental impacts. (ii) The central research question of this study pertains to the identification and evaluation of catalysts for soot oxidation, with a specific emphasis on ceria-based catalysts. The formulation of this research question arises from the need to enhance our understanding of catalytic mechanisms and their application in environmental remediation. This question serves as the guiding principle that directs the research methodology. (iii) This review seeks to investigate the catalytic mechanisms involved in soot oxidation. (iv) This review highlights the efficacy of ceria-based catalysts as well as other types of catalysts in soot oxidation and elucidate the underlying mechanistic strategies. The significance of these findings is discussed in the context of pollution management and environmental sustainability. This study contributes to the advancement of knowledge in the field of catalysis and provides valuable insights for the development of effective strategies to combat air pollution, ultimately promoting a cleaner and healthier environment.

Research Progress on Photocatalytic CO2 Reduction Based on Perovskite Oxides

Photocatalytic CO2 reduction to valuable fuels is a promising way to alleviate anthropogenic CO2 emissions and energy crises. Perovskite oxides have attracted widespread attention as photocatalysts for CO2 reduction by virtue of their high catalytic activity, compositional flexibility, bandgap adjustability, and good stability. In this review, the basic theory of photocatalysis and the mechanism of CO2 reduction over perovskite oxide are first introduced. Then, perovskite oxides' structures, properties, and preparations are presented. In detail, the research progress on perovskite oxides for photocatalytic CO2 reduction is discussed from five aspects: as a photocatalyst in its own right, metal cation doping at A and B sites of perovskite oxides, anion doping at O sites of perovskite oxides and oxygen vacancies, loading cocatalyst on perovskite oxides, and constructing heterojunction with other semiconductors. Finally, the development prospects of perovskite oxides for photocatalytic CO2 reduction are put forward. This article should serve as a useful guide for creating perovskite oxide-based photocatalysts that are more effective and reasonable.

Experimental investigation on the effects of DPF Cs-V-based non-precious metal catalysts and their coating forms on non-road diesel engine emission characteristics

Non-precious metal catalysts with good soot catalytic properties and a low cost have great potential for application in diesel particulate filters (DPF). In this study, we compared the effects of DPF supported by Cs₂V₄O₁₁ (Cs-V-based) non-precious metal catalysts and conventional Pt-Pd-based precious metal catalysts on the performance of a non-road diesel engine. Furthermore, the effects of on-wall coating and in-wall coating of Cs-V-based catalysts on DPF performance were also investigated. The results indicated that the particulate emissions from DPF with Cs-V-based catalysts were reduced slightly less than that with Pt-Pd-based catalysts; however, the particle number (PN) and particulate matter (PM) emissions were still reduced by 94.4% and 91.7%, respectively, meeting the non-road China IV limits under the non-road steady cycle (NRSC). In addition, CO, HC, and NO can also be slightly oxidized by the non-precious metal catalysts. On the other hand, the DPF with in-wall coating induced comparatively higher gaseous substances and particulate emissions and caused a higher exhaust back pressure (EBP), which was 9.6% higher than the on-wall coating under NRSC, negatively affecting engine performance. Additionally, the geometric mean diameter (GMD) for the DPF with in-wall coating was only 33.3 nm because of the large emission proportion of nuclear mode particles.

Investigation of Catalytic and Photocatalytic Degradation of Methyl Orange Using Doped LaMnO3 Compounds

LaMnO3 and 1% Pd-, Ag-, or Y-doped perovskite type nanomaterials were prepared by the sol-gel method, followed by heat treatment at a low temperature (600 °C for 6 h). The investigation through X-ray diffraction and FT-IR spectroscopy indicated that all samples were well crystallized, without secondary phases, and that the transition metal doping changed the crystal structure from the R-3c space group for the undoped LaMnO3 to the Pm-3m space group for the doped perovskite compounds. In this research paper, the efficiencies of the perovskite LaMnO3 materials for methyl orange removal were analyzed, wherein the effect of the doping ions and of the pH on the catalytic activity were studied together with a kinetic approach for the LaMnO3 materials at different values of the pH. Moreover, in the catalytic activity, it should be noted that a slightly better performance was obtained for the Ag-doped materials compared to the Y- and Pd-doped perovskite samples. The results presented for the perovskite LaMnO3 nanomaterials reinforce the interest in these multifunctional materials to be used in industrial applications; e.g., in water treatment.

Influence of the LaMn1−xFexO3 (x = 0–1) Composition on Catalytic Activities in the Reactions Involving Oxygen

Perovskite samples of the LaMn1−xFexO3 (x = 0–1) series were prepared by the Pechini method; their physicochemical properties were studied using XRD, HRTEM, XPS, and BET, and their catalytic activity was estimated in nitrous oxide decomposition and methane and CO oxidation reactions. In methane and CO oxidation reactions, all intermediate (0 < x < 1) samples of the series exhibited a lower catalytic activity normalized to the unit surface area as compared to the extreme terms, whereas in the nitrous oxide decomposition all intermediate samples were more active than extreme terms of the series. Different dependences of activities on the composition obtained in the study for the tested reactions involving the catalyst oxygen are caused by differences in the reaction mechanisms.

Advances in Designing Efficient La-Based Perovskites for the NOx Storage and Reduction Process

To overcome the inherent challenge of NOx reduction in the net oxidizing environment of diesel engine exhaust, the NOx storage and reduction (NSR) concept was proposed in 1995, soon developed and commercialized as a promising DeNOx technique over the past two decades. Years of practice suggest that it is a tailor-made technique for light-duty diesel vehicles, with the advantage of being space saving, cost effective, and efficient in NOx abatement; however, the over-reliance of NSR catalysts on high loadings of Pt has always been the bottleneck for its wide application. There remains fervent interest in searching for efficient, economical, and durable alternatives. To date, La-based perovskites are the most explored promising candidate, showing prominent structural and thermal stability and redox property. The perovskite-type oxide structure enables the coupling of redox and storage centers with homogeneous distribution, which maximizes the contact area for NOx spillover and contributes to efficient NOx storage and reduction. Moreover, the wide range of possible cationic substitutions in perovskite generates great flexibility, yielding various formulations with interesting features desirable for the NSR process. Herein, this review provides an overview of the features and performances of La-based perovskite in NO oxidation, NOx storage, and NOx reduction, and in this way comprehensively evaluates its potential to substitute Pt and further improve the DeNOx efficiency of the current NSR catalyst. The fundamental structure–property relationships are summarized and highlighted to instruct rational catalyst design. The critical research needs and essential aspects in catalyst design, including poisoner resistance and catalyst sustainability, are finally addressed to inspire the future development of perovskite material for practical application.

Photocatalysis and perovskite oxide-based materials: a remedy for a clean and sustainable future

The massive use of non-renewable energy resources by humankind to fulfill their energy demands is causing severe environmental issues. Photocatalysis is considered one of the potential solutions for a clean and sustainable future because of its cleanliness, inexhaustibility, efficiency, and cost-effectiveness. Significant efforts have been made to design highly proficient photocatalyst materials for various applications such as water pollutant degradation, water splitting, CO2 reduction, and nitrogen fixation. Perovskite photocatalyst materials are gained special attention due to their exceptional properties because of their flexibility in chemical composition, structure, bandgap, oxidation states, and valence states. The current review is focused on perovskite materials and their applications in photocatalysis. Special attention has been given to the structural, stoichiometric, and compositional flexibility of perovskite photocatalyst materials. The photocatalytic activity of perovskite materials in different photocatalysis applications is also discussed. Various mechanisms involved in photocatalysis application from wastewater treatment to hydrogen production are also provided. The key objective of this review is to encapsulate the role of perovskite materials in photocatalysis along with their fundamental properties to provide valuable insight for addressing future environmental challenges.

Perovskite Catalyst for In-Cylinder Coating to Reduce Raw Pollutant Emissions of Internal Combustion Engines

Aiming to achieve the highest combustion efficiency and less pollutant emission, a catalytic coating for cylinder walls in internal combustion engines was developed and tested under several conditions. The coating consists of a La0.8Sr0.2CoO3 (LSCO) catalyst on an aluminum-based ceramic support. Atomic force microscopy was applied to investigate the surface roughness of the LSCO coating, while in situ diffuse infrared Fourier transform spectroscopy was used to obtain the molecular understanding of adsorption and conversion. In addition, the influence of LSCO-coated substrates on the flame quenching distance was studied in a constant-volume combustion chamber. Investigations conclude that an LSCO coating leads to a reduction of flame quenching at low wall temperatures but a negligible effect at high temperatures. Finally, the influence of LSCO coatings on the in-cylinder wall-near gas composition was investigated using a fast gas sampling methodology with sample durations below 1 ms. Ion molecule reaction mass spectrometry and Fourier transform infrared spectroscopy revealed a significant reduction of hydrocarbons and carbon monoxide when LSCO coating was applied.

Effect of the Preparation Method of LaSrCoFeOx Perovskites on the Activity of N2O Decomposition

N2O remains a major greenhouse gas and contributor to global warming, therefore developing a catalyst that can decompose N2O at low temperatures is of global importance. We have investigated the use of LaSrCoFeOx perovskites for N2O decomposition and the effect of surface area, A and B site elements, Co–O bond strength, redox capabilities and oxygen mobility have been studied. It was found that by using a citric acid preparation method, perovskites with strong redox capabilities and weak Co–O bonds can be formed at relatively low calcination temperatures (550 °C) resulting in highly active catalysts. The enhanced activity is related to the presence of highly mobile oxygen species. Oxygen recombination on the catalyst surface is understood to be a prominent rate limiting step for N2O decomposition. Here the reduced strength of Co–O bonds and mobile lattice oxygen species suggest that the surface oxygen species have enhanced mobility, aiding recombination, and subsequent regeneration of the active sites. La0.75Sr0.25Co0.81Fe0.19Ox prepared by citric acid method converted 50% of the N2O in the feed (T50) at 448 °C.

Graphic Abstract

Selective catalytic reduction of NO by Fe-Mn nanocatalysts: effect of structure type

One of the most prominent features of selective catalytic reduction (SCR) of NO_x is using a well-structured catalyst to advance the reaction in a desirable condition. At the present work, various crystal structures of Fe-Mn nanocatalysts, FeMn₂O₄ spinel, FeMnO₃ perovskite and Fe₂O₃ (hematite)/Mn₂O₃ (bixbyite) nanocatalysts fabricated by co-precipitation method were evaluated for selective catalytic reduction of NO by NH₃ (NH₃-SCR). The studies specified that the crystal structure type had a high impact on structural properties and thereby the catalytic performance of the samples. The physicochemical characteristics of the nanocatalysts including molar ratio of metals, phase composition, crystallite size, particle size distribution, specific surface area, average pore diameter, pore volume, agglomeration degree, and amount and strength of the acidic site on the catalysts surfaces have been distinguished. From the catalytic activity evaluation, it was identified that the perovskite nanocatalyst had the best performance in NH₃-SCR reaction.

How Chemoresistive Sensors Can Learn from Heterogeneous Catalysis. Hints, Issues, and Perspectives

The connection between heterogeneous catalysis and chemoresistive sensors is emerging more and more clearly, as concerns the well-known case of supported noble metals nanoparticles. On the other hand, it appears that a clear connection has not been set up yet for metal oxide catalysts. In particular, the catalytic properties of several different oxides hold the promise for specifically designed gas sensors in terms of selectivity towards given classes of analytes. In this review, several well-known metal oxide catalysts will be considered by first exposing solidly established catalytic properties that emerge from related literature perusal. On this basis, existing gas-sensing applications will be discussed and related, when possible, with the obtained catalysis results. Then, further potential sensing applications will be proposed based on the affinity of the catalytic pathways and possible sensing pathways. It will appear that dialogue with heterogeneous catalysis may help workers in chemoresistive sensors to design new systems and to gain remarkable insight into the existing sensing properties, in particular by applying the approaches and techniques typical of catalysis. However, several divergence points will appear between metal oxide catalysis and gas-sensing. Nevertheless, it will be pointed out how such divergences just push to a closer exchange between the two fields by using the catalysis knowledge as a toolbox for investigating the sensing mechanisms.

A critical review on strategies for improving efficiency of BaTiO3-based photocatalysts for wastewater treatment

Barium titanate (BaTiO₃) photocatalysts with perovskite structures are promising candidates for the effective removal of hazardous organic pollutants from water/wastewater owing to several advantages, including low cost, non-toxicity, high stability, environmental friendliness, favorable band positions, high oxygen vacancies, multiple crystal phases, rapid migration of charge carriers at the surface, band bending, spontaneous polarization, and easy tailoring of the sizes and morphologies. However, this high dielectric/ferroelectric material is only active in UV light (band gap: 3.2 eV), which reduces the photocatalytic degradation performance. To make barium titanate more suitable for photocatalysis, the surfaces of the powders can be modified to broaden the absorption band. In this paper, various strategies for improving photocatalysis of barium titanate for removing organic pollutants (mostly dyes and drugs) from water/wastewater are critically reviewed. They include modifying the sizes and morphologies of the particles by varying the reaction times and synthesis temperatures, doping with metals/non-metals, loading with noble metal NPs (Ag and Au), and fabrication of heterojunction photocatalysts (conventional type II and Z-scheme). The current challenges and possible future directions of BaTiO₃-based materials are also discussed. This comprehensive review is expected to advance the design of highly efficient BaTiO₃-based materials for photocatalytic applications in water/wastewater treatment.

Nanostructured perovskite type gadolinium orthoferrite decorated RGO nanocomposite for the detection of nitrofurantoin in human urine and river water samples

Nitrofurantoin (NFT) is mainly used in humans for the treatment of urinary tract infections. NFT is used as feed additives in animals, due to its broad antimicrobial activity. However, it shows more side effects on human health and the environment. Therefore low-cost, portable, and rapid sensors are necessary for the detection of NFT in real samples. Herein, we successfully developed an electrochemical sensor using a glassy carbon electrode (GCE) modified with gadolinium orthoferrite (GdFeO₃) decorated on reduced graphene oxide (RGO) nanocomposite for the detection of NFT. The facile hydrothermal method was used to synthesis a novel GdFeO₃/RGO nanocomposite, the morphological and structural characterization was confirmed by the FESEM, HRTEM, EDX, XRD, Raman, and XPS techniques. The formation mechanism of GdFeO₃/RGO nanocomposite had been discussed. The effective intercalation of the nanostructured GdFeO₃ to the RGO sheets leads to the significant enhancement in physicochemical properties such as electrical conductivity, electro-active surface area, structural stability, and electrochemical activity, which was observed from the EIS and CV experimental results. The electrochemical studies established that the developed GdFeO₃/RGO sensor was highly sensitive and selective to NFT. Moreover, the GdFeO₃/RGO sensor exhibits good sensitivity of 4.1985 μA μM^-1 cm^-2, a low detection limit (LOD) of 0.0153 µM and a linear range from 0.001 to 249 µM for NFT detection under optimized experimental conditions. In addition, the investigation of storage time on the CV response of the GdFeO₃/RGO sensor indicates superior stability. Owing to these extraordinary analytical advantages, the as-fabricated sensor was applied to detect the NFT levels in human urine and river water samples with satisfactory results.

High-Throughput Computational Screening of Cubic Perovskites for Solid Oxide Fuel Cell Cathodes

It is a present-day challenge to design and develop oxygen-permeable solid oxide fuel cell (SOFC) electrode and electrolyte materials that operate at low temperatures. Herein, by performing high-throughput density functional theory calculations, oxygen vacancy formation energy, E_vac, data for a pool of all-inorganic ABO₃ and A^I_0.5A^II_0.5BO₃ cubic perovskites is generated. Using E_vac data of perovskites, the area-specific resistance (ASR) data, which is related to both oxygen reduction reaction activity and selective oxygen ion conductivity of materials, is calculated. Screening a total of 270 chemical compositions, 31 perovskites are identified as candidates with properties that are between those of state-of-the-art SOFC cathode and oxygen permeation components. In addition, an intuitive approach to estimate E_vac and ASR data of complex perovskites by using solely the easy-to-access data of simple perovskites is shown, which is expected to boost future explorations in the perovskite material search space for genuinely diverse energy applications.

Perovskite Oxide-Based Materials for Photocatalytic and Photoelectrocatalytic Treatment of Water

Meeting the global challenge of water availability necessitates diversification from traditional water treatment methods to other complementary methods, such as photocatalysis and photoelectrocatalysis (PEC), for a more robust solution. Materials play very important roles in the development of these newer methods. Thus, the quest and applications of a myriad of materials are ongoing areas of water research. Perovskite and perovskite-related materials, which have been largely explored in the energy sectors, are potential materials in water treatment technologies. In this review, attention is paid to the recent progress in the application of perovskite materials in photocatalytic and photoelectrocatalytic degradation of organic pollutants in water. Water treatment applications of lanthanum, ferrite, titanate, and tantalum (and others)-based perovskites are discussed. The chemical nature and different synthetic routes of perovskites or perovskite composites are presented as fundamental to applications.

Effects of A-site composition of perovskite (Sr1-x Ba x ZrO3) oxides on H atom adsorption, migration, and reaction

Hydrogen (H) atomic migration over a metal oxide is an important surface process in various catalytic reactions. Control of the interaction between H atoms and the oxide surfaces is therefore important for better catalytic performance. For this investigation, we evaluated the adsorption energies of the H atoms over perovskite-type oxides (Sr1-x Ba x ZrO3; 0.00 ≤ x ≤ 0.50) using DFT (Density Functional Theory) calculations, then clarified the effects of cation-substitution in the A-site of perovskite oxides on H atom adsorption, migration, and reaction. Results indicated local distortion at the oxide surface as a key factor governing H atom adsorption. Subtle Ba2+ substitution for Sr2+ sites provoked local distortion at the Sr1-x Ba x ZrO3 oxide surface, which led to a decrement in the H atom adsorption energy. Furthermore, the effect of Sr2+/Ba2+ ratio on the H atoms' reactivities was examined experimentally using a catalytic reaction, which was promoted by activated surface H atoms. Results show that the surface H atoms activated by the substitution of Sr2+ sites with a small amount of Ba2+ (x = 0.125) contributed to enhancement of ammonia synthesis rate in an electric field, which showed good agreement with predictions made using DFT calculations.

First-principles exploration of oxygen vacancy impact on electronic and optical properties of ABO3-δ (A = La, Sr; B = Cr, Mn) perovskites

ABO3-δ perovskites are utilized in many applications including optical gas sensing for energy systems. Understanding the opto-electronic properties allows rational selection of the perovskite-based sensors from a diverse family of ABO3-δ perovskites, associated with the choices of A and B cations and range of oxygen concentrations. Herein, we assess the impact of oxygen vacancies on the electronic structure and optical response of pristine and oxygen-vacant ABO3-δ (A = La, Sr; B = Cr, Mn) perovskites via first-principles calculations. The endothermic formation energy for oxygen vacancies shows that the generation of ABO3-δ defect structures is thermodynamically possible. LaCrO3 and LaMnO3 have direct and indirect ground-state band gaps, respectively, whereas SrCrO3 and SrMnO3 are metallic. In the presence of an oxygen mono-vacancy, however, the band gap decreases in LaCrO3-δ and vanishes in LaMnO3-δ. In contrast to the decrease in the band gaps, the oxygen vacancies in ABO3-δ are found to increase optical absorption in the visible to near-infrared wavelength regime, and thus lower the onset energy of absorption compared with the pristine materials. Our assessments emphasize the role of the oxygen vacancy, or other possible oxygen non-stoichiometry defects, in perovskite oxides with respect to the opto-electronic performance parameters that are of interest for optical gas sensors for energy generation process environments.

Fe-Doped g-C3N4: High-Performance Photocatalysts in Rhodamine B Decomposition

Herein, Fe-doped C3N4 high-performance photocatalysts, synthesized by a facile and cost effective heat stirring method, were investigated systematically using powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface area measurement, X-ray photoelectron (XPS), UV-Vis diffusion reflectance (DRS) and photoluminescence (PL) spectroscopy. The results showed that Fe ions incorporated into a g-C3N4 nanosheet in both +3 and +2 oxidation states and in interstitial configuration. Absorption edge shifted slightly toward the red light along with an increase of absorbance in the wavelength range of 430-570 nm. Specific surface area increased with the incorporation of Fe into g-C3N4 lattice, reaching the highest value at the sample doped with 7 mol% Fe (FeCN7). A sharp decrease in PL intensity with increasing Fe content is an indirect evidence showing that electron-hole pair recombination rate decreased. Interestingly, Fe-doped g-C3N4 nanosheets present a superior photocatalytic activity compared to pure g-C3N4 in decomposing RhB solution. FeCN7 sample exhibits the highest photocatalytic efficiency, decomposing almost completely RhB 10 ppm solution after 30 min of xenon lamp illumination with a reaction rate approximately ten times greater than that of pure g-C3N4 nanosheet. This is in an agreement with the BET measurement and photoluminescence result which shows that FeCN7 possesses the largest specific surface area and low electron-hole recombination rate. The mechanism of photocatalytic enhancement is mainly explained through the charge transfer processes related to Fe2+/Fe3+ impurity in g-C3N4 crystal lattice.

Review on Sensing Applications of Perovskite Nanomaterials

Recently, perovskite-based nanomaterials are utilized in diverse sustainable applications. Their unique structural characteristics allow researchers to explore functionalities towards diverse directions, such as solar cells, light emitting devices, transistors, sensors, etc. Many perovskite nanomaterial-based devices have been demonstrated with extraordinary sensing performance to various chemical and biological species in both solid and solution states. In particular, perovskite nanomaterials are capable of detecting small molecules such as O2, NO2, CO2, etc. This review elaborates the sensing applications of those perovskite materials with diverse cations, dopants and composites. Moreover, the underlying mechanisms and electron transport properties, which are important for understanding those sensor performances, will be discussed. Their synthetic tactics, structural information, modifications and real time sensing applications are provided to promote such perovskite nanomaterials-based molecular designs. Lastly, we summarize the perspectives and provide feasible guidelines for future developing of novel perovskite nanostructure-based chemo- and biosensors with real time demonstration.

Photocatalytic degradation of methylene blue dye in aqueous solution by MnTiO3 nanoparticles under sunlight irradiation

Nanophotocatalyst MnTiO3 powders were synthesized by sol-gel technique and characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), as well as their thermal behavior has been studied by differential thermal and thermogravimetric analyses (DTA/TGA). Powders morphology was analyzed by means of Transmission electron microscopy (TEM). Effect of various process parameters like amount of photocatalyst, dye concentration, solution pH and irradiation time on the extent of removal of dye were studied in detail. The photo-degradation was relatively higher using lower amount (0.005 g) of semiconductor, reached rate of 75% and 70% after 240 min for mixed MnTiO3/TiO2 and pure MnTiO3 nanocatalysts. The kinetic model of photocatalytic degradation of MB follows pseudo-first-order kinetic with a high correlation coefficient values (R2 > 0.95). These results underline the use of effective, low-cost and easily available MnTiO3 photocatalyst for the decomposition of pollutants to water under natural sunlight.

Development of advanced materials for cleaner energy generation through fuel cells

The use of fuel cells in the transportation sector holds promise as a sustainable option for the generation of cleaner energy along with cumulative lesser GHG emissions.

Ab-initio prediction of structure stability, electromagnetic, optical and thermoelectric behavior of orthorhombic LaXO3 (X= Cr, Mn, Fe): For device application

In this paper, theoretical calculations for electronic band structure, the density of states, the optical and thermoelectric response of orthorhombic LaXO₃ (X = Cr, Mn, Fe) compounds are calculated. The Full Potential Linearized Augmented Plane Wave plus local orbital (FP-LAPW + lo) method is used in the context of density functional theory. Band gaps of three compounds are determined using Wu Cohen Generalized Gradient approximation with additional U potential (WC-GGA + U). Ferromagnetism is observed due to strong p-d hybridization and is justified by observed magnetic moments across individual atoms and at interstitial regions, and exchange constants are also reported. Optical properties are explained by calculating real and imaginary parts of the dielectric function, refractive index (n), extinction coefficient (k), reflection coefficient (R), the absorption coefficient (α), and energy loss spectrum (L). High value of dielectric constant, very small reflectivity and lower energy loss factor in, visible to ultraviolet region favours them for optoelectronic devices. We also computed the thermoelectric properties, including Seebeck coefficient, thermal and electrical conductivity and power factor as a function of temperature by combining results from DFT and Boltzmann transport theory. The phonon dispersion curve shows the stability of the current structures.

Catalytic Enhancement of CO Oxidation on LaFeO3 Regulated by Ruddlesden-Popper Stacking Faults

The influence of planar defects, in the form of stacking faults, within perovskite oxides on catalytic activity has received little attention because controlling stacking-fault densities presents a major synthetic challenge. Furthermore, stacking faults in ceramics are not thought to appreciably impact surface chemistry, which partly explains why their direct effect on catalysis is generally ignored. Here, we show that Ruddlesden-Popper (RP) stacking faults in otherwise stoichiometric LaFeO₃ can be broadly controlled by modulating the ceramic synthesis route. Electronic structure calculations along with electron microscopy and spectroscopy show that energetically favorable RP faults occur both near the surface and in bunches and enhance CO oxidation kinetics. Density functional theory (DFT) + U shows that subsurface RP faults strengthen the adsorption and co-adsorption of CO, O, and O₂, which could lower the apparent activation energy of CO oxidation on faulted catalysts compared to that on their pristine counterparts. Our work suggests that planar defects should be considered a new and useful feature in hierarchal nanoscale design of future catalysts.

Electronic Percolation Threshold of Self-Standing Ag-LaCoO3 Porous Electrodes for Practical Applications

Perovskite LaCoO3 materials have various applications, from selective permeable membranes and gas sensing devices to water splitting applications. However, the intrinsic electrical resistivity of the perovskite limits the applicative potential. To overcome that, Ag powder was used with LaCoO3 to obtain porous composite electrodes with enhanced conductivities. For that, a series of composite Ag-LaCoO3 powders were prepared into pellets and pre-sintered at various temperatures up to 1000 ∘C. Their structural properties and morphology were investigated by X-ray diffraction and scanning electron microscopy. The electronic transport of compacted specimens was studied by impedance spectroscopy. The results indicate that the presence of Ag acts as pre-sintering additive to obtain porous electrodes, with porosity values as high as 40% at 50 vol. % Ag. Moreover, the overall electrical resistivity of the composite electrodes varied well over four orders of magnitude. The results are discussed within the generalized Bruggeman theory for effective media comprising arbitrarily shaped metallic and semiconducting inclusions.

Rare earth double perovskites: a fertile soil in the field of perovskite oxides

This review summarizes the compositions, syntheses, and applications of rare earth A₂B′B′′O₆ double perovskites.