A review on CaTiO3 photocatalyst: Activity enhancement methods and photocatalytic applications

Exploring the Role of Titanate Perovskites in the Oxidation of Amines via Photocatalysis

Considering that structural differences could affect the photocatalytic efficiency of titanate perovskites, cubic SrTiO3 (STO) and tetragonal CaTiO3 (CTO) were synthesised as models to elucidate the structure-activity relationship. STO and CTO materials were produced through hydrothermal approaches, adjusting parameters such as temperature and pressure to optimise material purity. Among the perovskite photocatalysts, two stand out for their exceptional photocatalytic capacity and crystalline purity: CaTiO3, prepared at 180 °C for 36 h, and SrTiO3, synthesised at 200 °C for 24 h. Notably, we explore the selective ability of these materials for the photocatalytic oxidative self-coupling of benzylamine (BZA) to produce N-benzylidenebenzylamine (BZI), with CaTiO3 emerging as the most efficient catalyst for this reaction. The CTO material prepared at 180 °C for 36 h (CTO180T-36) achieved a peak BZI production of 0.5 mM, with a total conversion of BZA after 7 h of irradiation. This study also emphasises the crucial role of reaction conditions and perovskite morphologies in fine-tuning photocatalytic performance. These findings highlight opportunities for developing efficient and selective photocatalytic processes, holding the compromise for applications in organic synthesis and sustainable green chemistry.

Influence of rapid heat treatment on the photocatalytic activity and stability of calcium titanates against a broad range of pollutants

Calcium titanate (CTO) photocatalysts were synthesized using a sol-gel method by adopting a cost-efficient, rapid calcination technique. The CTOs were characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, infrared spectroscopy, nitrogen adsorption, porosimetry measurements, scanning/transmission electron microscopy, and diffuse reflectance spectroscopy. Their photocatalytic activity was assessed through the photocatalytic degradation of phenol, oxalic acid, and chlorophenol under UV light exposure, using a commercial CTO as a reference. The stability of the samples was evaluated using compounds with -OH, -COOH, and -Cl functional groups. Characterization results showed that CTO composites containing anatase, rutile, and brookite titania were obtained. Increasing the calcination temperature led to various crystalline compositions, higher crystallinity, larger primary crystallite sizes, and smaller specific surface areas. The photocatalytic activity of all CTO/TiO2 composites was superior compared to the commercial CTO we used as a reference. The high photocatalytic activity of the best-performing composites was attributed to their higher specific surface areas and the synergistic effect between the crystal phases. A cost comparison was also made between our unique calcination technique and conventional calcination, and it was found that our method is approximately 35% more cost-effective, while retaining the photocatalytic activity.

Ultrasonic-assisted synthesis of CaCu3Ti4O12/reduced graphene oxide composites for enhanced photocatalytic degradation of pharmaceutical products: Ibuprofen and Ciprofloxacin

The objective of this research is to create a highly effective approach for eliminating pollutants from the environment through the process of photocatalytic degradation. The study centers around the production of composites consisting of CaCu3Ti4O12 (CCTO) and reduced graphene oxide (rGO) using an ultrasonic-assisted method, with a focus on their capacity to degrade ibuprofen (IBF) and ciprofloxacin (CIP) via photodegradation. The impact of rGO on the structure, morphology, and optical properties of CCTO was inspected using XRD, FTIR, Raman, FESEM, XPS, BET, and UV-Vis. Morphology characterization showed that rGO particles were dispersed within the CCTO matrix without any specific chemical interaction between CCTO and C in the rGO. The BET analysis revealed that with increasing the amount of rGO in the composite, the specific surface area significantly increased compared to the CCTO standalone. Besides, increasing rGO resulted in a reduction in the optical bandgap energy to around 2.09 eV, makes it highly promising photocatalyst for environmental applications. The photodegradation of IBF and CIP was monitored using visible light irradiation. The results revealed that both components were degraded above 97% after 60 min. The photocatalyst showed an excellent reusability performance with a slight decrease after five runs to 93% photodegradation efficiency.

Nanoparticles of the Perovskite-Structure CaTiO3 System: The Synthesis, Characterization, and Evaluation of Its Photocatalytic Capacity to Degrade Emerging Pollutants

In this research work, the photocatalytic capacity shown by the nanoparticles of the CaTiO3 system was evaluated to degrade two pollutants of emerging concern, namely methyl orange (MO)-considered an organic contaminating substance of the textile industry that is non-biodegradable when dissolved in water-and levofloxacin (LVF), an antibiotic widely used in the treatment of infectious diseases that is released mostly to the environment in its original chemical form. The synthesis process used to obtain these powders was the polymeric precursor method (Pechini), at a temperature of 700 °C for 6 h. The characterization of the obtained oxide nanoparticles of interest revealed the presence of a majority perovskite-type phase with an orthorhombic Pbnm structure and a minority rutile-type TiO2 phase, with a P42/mnm structure and a primary particle size <100nm. The adsorption-desorption isotherms of the synthesized solids had H3-type hysteresis loops, characteristic of mesoporous solids, with a BET surface area of 10.01m2/g. The Raman and FTIR spectroscopy results made it possible to identify the characteristic vibrations of the synthesized system and the characteristic deformations of the perovskite structure, reiterating the results obtained from the XRD analysis. Furthermore, a bandgap energy of ~3.4eV and characteristic emissions in the violet (437 nm/2.8 eV) and orange (611 nm/2.03 eV) were determined for excitation lengths of 250 nm and 325 nm, respectively, showing that these systems have a strong emission in the visible light region and allowing their use in photocatalytic activity to be potentialized. The powders obtained were studied for their photocatalytic capacity to degrade methyl orange (MO) and levofloxacin (LVF), dissolved in water. To quantify the coloring concentration, UV-visible spectroscopy was used considering the variation in the intensity of the characteristic of the greatest absorption, which correlated with the change in the concentration of the contaminant in the solution. The results showed that after irradiation with ultraviolet light, the degradation of the contaminants MO and LVF was 79.4% and 98.1% with concentrations of 5 g/L and 10 g/L, respectively.

Engineering the Electronic Structure towards Visible Lights Photocatalysis of CaTiO3 Perovskites by Cation (La/Ce)-Anion (N/S) Co-Doping: A First-Principles Study

Cation-anion co-doping has proven to be an effective method of improving the photocatalytic performances of CaTiO3 perovskites. In this regard, (La/Ce-N/S) co-doped CaTiO3 models were investigated for the first time using first-principles calculations based on a supercell of 2 × 2 × 2 with La/Ce concentrations of 0.125, 0.25, and 0.375. The energy band structure, density of states, charge differential density, electron-hole effective masses, optical properties, and the water redox potential were calculated for various models. According to our results, (La-S)-doped CaTiO3 with a doping ratio of 0.25 (LCOS1-0.25) has superior photocatalytic hydrolysis properties due to the synergistic performances of its narrow band gap, fast carrier mobility, and superb ability to absorb visible light. Apart from the reduction of the band gap, the introduction of intermediate energy levels by La and Ce within the band gap also facilitates the transition of excited electrons from valence to the conduction band. Our calculations and findings provide theoretical insights and solid predictions for discovering CaTiO3 perovskites with excellent photocatalysis performances.

Influence of titanate photocatalyst in biohydrogen yield via photo fermentation from corn stover

The effects of three common titanate photocatalysts (TPC) on the photo fermentation biohydrogen production (PFHP) from corn stover were studied in this paper. Compared with CaTiO3 and BaTiO3, the experimental group with the addition of MgTiO3 showed stronger potential for PFHP, the maximum hydrogen yield of 344 mL (68.8 mL/g TS) was obtained at 3 g/L MgTiO3, increased by 48.3%. For CaTiO3, BaTiO3, the optimal amount of addition was 8 and 7 g/L, respectively, in which, the hydrogen yield was 308 and 288 mL (61.6 and 57.6 mL/g TS). TPC addition could shorten the delay period of hydrogen production lower the Oxidation-Reduction Potential (ORP) of fermentation broth, especially MgTiO3 addition, the delayed hydrogen production could be shortened by 33.2% compared with control group, and the ORP could reach the lowest value of -371 mV.

Gamma radiation-induced synthesis of novel PVA/Ag/CaTiO3 nanocomposite film for flexible optoelectronics

A flexible nanocomposite film based on polyvinyl alcohol (PVA), silver nanoparticles, and calcium titanate (CaTiO₃) was synthesized using gamma radiation induced-reduction. Temperature-dependent structural, optical, DC electrical conductivity, electric modulus, and dielectric properties of PVA/Ag/CaTiO₃ nanocomposite film were investigated. The XRD pattern proved the successful preparation of the nanocomposite film. Also, as the temperature increases, the average crystallite sizes of CaTiO₃ and Ag nanoparticles decrease from 19.8 to 9.7 nm and 25 to 14.8 nm, respectively. Further, the optical band gap increased from 5.75 to 5.84 eV with increasing temperature. The thermal stability is improved, and the semiconductor behavior for PVA/Ag/CaTiO₃ nanocomposite film is confirmed by thermal activation energy ΔE with values in the 0.11-0.8 eV range. Furthermore, the maximum barrier W_m value was found of 0.29 eV. PVA/Ag/CaTiO₃ nanocomposite film exhibits a semicircular arc originating from the material's grain boundary contributions for all temperatures. The optical, DC electrical conductivity, and dielectric properties of the PVA/Ag/CaTiO₃ nanocomposite film can be suitable for flexible electronic devices such as electronic chips, optoelectronics, and energy storage applications.

Recent advances in synthesis, structural properties, and regulation of nickel sulfide-based heterostructures for environmental water remediation: an insight review

Heterostructured nanomaterials exhibit pronounced potential in environmental science, including the water purification, pollutant monitoring, and environmental remediation. Especially, their application through advanced oxidation processes has been found capable and adaptable in waste water treatment. In semiconductor photocatalysts, metal sulfides are the leading materials. However, for further modifications, the progresses on specific materials need to be overviewed. Among metal sulfides, nickel sulfides are the emerging semiconductors due to relatively narrow band gaps, high thermal and chemical stability, and cost effectiveness. The aim of the present review is to conduct a thorough analysis and summary of recent progress in the application of nickel sulfide-based heterostructures in water decontamination. Initially, the review introduces the emerging needs of the materials for environment following the characteristics features of metal sulfides with emphasis on nickel sulfides. Subsequently, synthesis strategies and structural properties of nickel sulfide (NiS and NiS₂)-based photocatalysts are discussed. Herein, controlled synthesis procedures to influence their active structure, compositions, shape, and size for the enhanced photocatalytic performances are also considered. Furthermore, there is discussion on heterostructures formed by metal modification, metal oxides, and carbon hybridized nanocomposites. In the continuation, the modified characteristics are investigated which favors the photocatalytic processes for degradation of organic contaminations in water. The overall study highlights significant improvements in degradation efficiency of hetero-interfaced NiS and NiS₂ photocatalysts towards organics that are comparable to expensive noble-metal photocatalysts. Finally, we also added a little on prospects for future advancement of nickel sulfide-based photocatalysts for applications in sustainable environmental remediation.

A Porous Geopolymer Containing Ti-Bearing Blast Furnace Slag: Synthesis, Characterization, and Adsorption-Photodegradation Studies towards Methylene Blue Removal under Visible Light Condition

A porous geopolymer with adsorption and photocatalytic degradation functions was successfully developed by utilizing Ti-bearing blast furnace slag (TBBFS) as the raw material. The prepared porous geopolymers were characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, and Fourier transform infrared spectrum. Selective crystallization, water quenching, and natural cooling methods were employed to investigate the influences of these modifications on the applicability of TBBFS as a precursor for geopolymer synthesis. Water-quenched slag with amorphous content was prone to alkali dissolution, and the resulting geopolymer exhibited the highest adsorption capacity (97.18 mg/g) for methylene blue (MB) removal. Selective crystallization at 1400 °C generated a hybrid microstructure consisting of a non-cementitious CaTiO₃ crystallization phase and a cementitious amorphous fraction. The retention of CaTiO₃ in the final geopolymer enables a bifunctionality in adsorption-photodegradation. Particularly, the adsorption and photodegradation processes under various conditions were investigated. The superior removal efficiency for MB could be attributed to the synergistic effects between the geopolymer matrix and CaTiO₃, leading to an enhancement in the formation of hydroxyl radicals. The conversion of TBBFS into porous geopolymer offers an efficient and straightforward solution for slag utilization and dye removal.

The Photocatalytic Activity of CaTiO3 Derived from the Microwave-Melting Heating Process of Blast Furnace Slag

The extraction of titanium-bearing components in the form of CaTiO₃ is an efficient utilization of blast furnace slag. The photocatalytic performance of this obtained CaTiO₃ (MM-CaTiO₃) as a catalyst for methylene blue (MB) degradation was evaluated in this study. The analyses indicated that the MM-CaTiO₃ had a completed structure with a special length-diameter ratio. Furthermore, the oxygen vacancy was easier to generate on a MM-CaTiO₃(110) plane during the photocatalytic process, contributing to improving photocatalytic activity. Compared with traditional catalysts, MM-CaTiO₃ has a narrower optical band gap and visible-light responsive performance. The degradation experiments further confirmed that the photocatalytic degradation efficiency of pollutants by using MM-CaTiO₃ was 3.2 times that of pristine CaTiO₃ in optimized conditions. Combined with molecular simulation, the degradation mechanism clarified that acridine of MB molecular was stepwise destroyed by using MM-CaTiO₃ in short times, which is different from demethylation and methylenedioxy ring degradation by using TiO₂. This study provided a promising routine for using solid waste to obtain catalysts with excellent photocatalytic activity and was found to be in keeping with sustainable environmental development.

Nanoscale Iron Redistribution during Thermochemical Decomposition of CaTi1-x Fe x O3-δ Alters the Electrical Transport Pathway: Implications for Oxygen-Transport Membranes, Electrocatalysis, and Photocatalysis

Potential applications of the earth-abundant, low-cost, and non-critical perovskite CaTi_1-x Fe _x O_3-δ in electrocatalysis, photocatalysis, and oxygen-transport membranes have motivated research to tune its chemical composition and morphology. However, investigations on the decomposition mechanism(s) of CaTi_1-x Fe _x O_3-δ under thermochemically reducing conditions are limited, and direct evidence of the nano- and atomic-level decomposition process is not available in the literature. In this work, the phase evolution of CaTi_1-x Fe _x O_3-δ (x = 0-0.4) was investigated in a H₂-containing atmosphere after heat treatments up to 600 °C. The results show that CaTi_1-x Fe _x O_3-δ maintained a stable perovskite phase at low Fe contents while exhibiting a phase decomposition to Fe/Fe oxide nanoparticles as the Fe content increases. In CaTi_0.7Fe_0.3O_3-δ and CaTi_0.6Fe_0.4O_3-δ, the phase evolution to Fe/Fe oxide was greatly influenced by the temperature: Only temperatures of 300 °C and greater facilitated phase evolution. Fully coherent Fe-rich and Fe-depleted perovskite nanodomains were observed directly by atomic-resolution scanning transmission electron microscopy. Prior evidence for such nanodomain formation was not found, and it is thought to result from a near-surface Kirkendall-like phenomenon caused by Fe migration in the absence of Ca and Ti co-migration. Density functional theory simulations of Fe-doped bulk models reveal that Fe in an octahedral interstitial site is energetically more favorable than in a tetrahedral site. In addition to coherent nanodomains, agglomerated Fe/Fe oxide nanoparticles formed on the ceramic surface during decomposition, which altered the electrical transport mechanism. From temperature-dependent electrical conductivity measurements, it was found that heat treatment and phase decomposition change the transport mechanism from thermally activated p-type electronic conductivity through the perovskite to electronic conduction through the iron oxide formed by thermochemical decomposition. This understanding will be useful to those who are developing or employing this and similar earth-abundant functional perovskites for use under reducing conditions, at elevated temperatures, and when designing materials syntheses and processes.

Photocatalytic Activity of MoS2 Nanoflower-Modified CaTiO3 Composites for Degradation of RhB under Visible Light

Nanoflower-like MoS₂ deposited on the surface of rectangular CaTiO₃(CTO) was designed and synthesized via a simple template-free strategy. Through SEM, TEM, and other characterization methods, the MoS₂ nanoflowers were confirmed to be well deposited on the surface of CTO. LED was used as the visible light source, and rhodamine B (RhB) in an aqueous solution was used as the model pollutant to assess the photodegradation activity of the samples. The results showed that the MoS₂/CaTiO₃(MCTO) composite significantly improved the photocatalytic degradation of rhodamine B (RhB) in water, compared with a single CTO, and with the MCTO-2 composite photocatalysts, 97% degradation of RhB was achieved in 180 min, and its photocatalytic activity was about 5.17 times higher than that of the bare CTO. The main reasons for enhancing photocatalytic performance are the strong interaction between the nanoflower-like MoS₂ and rectangular CTO, which can lead to the effective separation of electron transfer and photoexcited electron-hole pairs in MCTO composites. This work provides a new notion for researching an effective method of recycling catalytic materials.

Application of perovskite oxides and their composites for degrading organic pollutants from wastewater using advanced oxidation processes: Review of the recent progress

In the recent years, perovskite oxides are gaining an increasing amount of attention owing to their unique traits such as tunable electronic structures, flexible composition, and eco-friendly properties. In contrast, their catalytic performance is not satisfactory, which hinders real wastewater remediation. To overcome this shortcoming, various strategies are developed to design new perovskite oxide-based materials to enhance their catalytic activities in advanced oxidation process (AOPs). This review article is to provide overview of basic principle and different methods of AOPs, while the strategies to design novel perovskite oxide-based composites for enhancing the catalytic activities in AOPs have been highlighted. Moreover, the recent progress of their synthesis and applications in wastewater remediation (pertaining to the period 2016-2022) was described, and the related mechanisms were thoroughly discussed. This review article helps scientists to have a clear outlook on the selection and design of new effective perovskite oxide-based materials for the application of AOPs. At the end of the review, perspective on the challenges and future research directions are discussed.

Synthesis, Properties and Photocatalytic Activity of CaTiO3-Based Ceramics Doped with Lanthanum

The aim of this work is to study the effect of lanthanum doping on the phase formation processes in ceramics based on CaTiO3, as well as to evaluate the effectiveness of the ceramics as photocatalysts for the decomposition of the organic dye Rhodamine B. The methods used were scanning electron microscopy to evaluate the morphological features of the synthesized ceramics, X-ray diffraction to determine the phase composition and structural parameters, and UV-Vis spectroscopy to determine the optical properties of the ceramics. During the experiments it was found that an increase in the lanthanum dopant concentration from 0.05 to 0.25 mol leads to the formation of the orthorhombic phase La0.3Ca0.7TiO3 and the displacement from the ceramic structure of the impurity phase TiO2, which presence is typical for the synthesized ceramics by solid-phase synthesis. On the basis of the data of the X-ray phase analysis the dynamics of phase transformations depending on concentration of lanthanum was established: CaTiO3/TiO2 → CaTiO3/La2TiO5 → CaTiO3/La0.3Ca0.7TiO3 → La0.3Ca0.7TiO3. During the determination of photocatalytic activity it was found that the formation of La0.3Ca0.7TiO3 phase leads to an increase in the decomposition rate as well as the degree of mineralization.

Photocatalytic Reduction of Carbon Dioxide on TiO2 Heterojunction Photocatalysts-A Review

The photocatalytic reduction of carbon dioxide to renewable fuel or other valuable chemicals using solar energy is attracting the interest of researchers because of its great potential to offer a clean fuel alternative and solve global warming problems. Unfortunately, the efficiency of CO₂ photocatalytic reduction remains not very high due to the fast recombination of photogenerated electron–hole and small light utilization. Consequently, tremendous efforts have been made to solve these problems, and one possible solution is the use of heterojunction photocatalysts. This review begins with the fundamental aspects of CO₂ photocatalytic reduction and the fundamental principles of various heterojunction photocatalysts. In the following part, we discuss using TiO₂ heterojunction photocatalysts with other semiconductors, such as C₃N₄, CeO₂, CuO, CdS, MoS₂, GaP, CaTiO₃ and FeTiO₃. Finally, a concise summary and presentation of perspectives in the field of heterojunction photocatalysts are provided. The review covers references in the years 2011–2021.