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To the best of our knowledge, we report for the first time the growth of brownmillerite Ca2Fe2O5 (CFO) single crystals under Argon (Ar) only ambience by optical floating zone (OFZ) technique and compare its structural and spectroscopic properties with CFO single crystals grown by OFZ method under air and oxygen (O2) atmospheres. Single-crystal X-ray diffraction confirms growth of Ca2Fe2O5 single crystals in all the atmospheres. Crystals grown in air and oxygen (O2) atmospheres show both metallic Fe0 and Fe3+states, whereas in Ar-grown crystals only Fe3+ oxidation state is observed. An enhancement in oxygen vacancies is also observed in Ar-grown crystals. Growth ambience is found to have a strong influence on cationic environment and binding energy of constituent elements, as is evident from the X-ray photoelectron spectroscopy of the Ca2Fe2O5 crystals. [ABSTRACT FROM AUTHOR]

Ideal sillenite type Bi12FeO20 (BFO) micron sized single crystals have been successfully grown via inexpensive hydrothermal method. The refined single crystal X-ray diffraction data reveals cubic Bi12FeO20 structure with single crystal parameters. Occurrence of rare Fe4+ state is identified via X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The lattice parameter (a) and corresponding molar volume (Vm) of Bi12FeO20 have been measured in the temperature range of 30–700 °C by the X-ray diffraction method. The thermal expansion coefficient (α) 3.93 × 10–5 K−1 was calculated from the measured values of the parameters. Electronic structure and density of states are investigated by first principle calculations. Photoelectrochemical measurements on single crystals with bandgap of 2 eV reveal significant photo response. The photoactivity of as grown crystals were further investigated by degrading organic effluents such as Methylene blue (MB) and Congo red (CR) under natural sunlight. BFO showed photodegradation efficiency about 74.23% and 32.10% for degrading MB and CR respectively. Interesting morphology and microstructure of pointed spearhead like BFO crystals provide a new insight in designing and synthesizing multifunctional single crystals. [ABSTRACT FROM AUTHOR]

This work reports the design and development of an efficient sillenite based visible light photoactive Bi 24 Ga 2 O 39 –TiO 2 (BGT) heterostructure. Structural and morphological studies based on X-ray diffraction (XRD) and high-resolution scanning electron microscopy (HRSEM) confirm the formation of combined phase as well the overall morphology of composite BGT. Additionally, X-ray photoelectron spectroscopy (XPS) results confirm the presence of Bi3+, Ga3+, Ti4+ & O2−. The composite exhibits a shift in the absorbance edge towards visible region of electromagnetic spectrum when compared to that of TiO 2. Suitable band edge positions in the composite facilitate the formation of type-1 heterojunction enhancing visible light photocatalytic property. The photocatalytic activity is evident from photo reduction of Cr (VI) (95% reduction in 180 min). The composite also plays an improved and effective role in the degradation of persistent drug ampicillin-cloxacillin (AMC) with a rate constant of 0.02 min−1. Photocatalytic experiments conducted at different pH values showed higher performance at lower pH ∼3. Trapping experiments performed on the sample confirm the role of holes as the main active species during photocatalysis. Appreciable recyclability of BGT composite was noted with respect to AMC drug degradation. • First report of Bi 24 Ga 2 O 39 - TiO 2 (BGT) composite for photo reduction of Cr (VI). • Enhanced photoreduction achieved up to 95% reduction in 180 min, without using any co-catalyst. • The BGT was utilized to degrade the ampicillin-cloxacillin drug with a rate constant of 0.02 min−1. • Photoactivity of BGT corroborated by efficient photocurrent density (∼1.91 μA/cm2). [ABSTRACT FROM AUTHOR]

Hydrogen evolution by overall water splitting has emerged as a potential method for green energy generation due to the introduction of highly efficient photocatalysts active under visible region of spectra. In the present work, we focus on a comparative study of the properties of Ga 1−x Zn x N 1−y O y oxynitride samples synthesized by two techniques and their effect on the sample properties. The samples were prepared by both traditional nitridation technique and solution combustion method. Room temperature photoluminescence studies revealed the introduction of additional energy levels above the valence band which in turns broadens the valence band and subsequently reduces the band gap. The band gap narrowing was further confirmed using diffuse reflectance spectroscopy and Valence band X-ray photoelectron spectroscopy (VB-XPS). It was also realized from VB XPS that the reduction of band gap in both the samples was due to upshift of valence band without affecting the conduction band. The presence of disorder activated modes in the samples was examined using temperature dependent Raman spectroscopy. In this work we corroborate the theoretical prediction reported by Al-Jassim et. al that the bandgap narrowing mechanism in ZnO rich solid solution and GaN rich solid solution is asymmetric and a significant bandgap reduction could be observed for ZnO rich solid solution than GaN rich. [ABSTRACT FROM AUTHOR]

• Enhanced degradation of persistent aqueous pollutants such as Bisphenol A (84%). • Photodegradation of Norfloxocin (82%) by visible light active BGO. • Regular pyramidal like growth of BGO micro crystal via hydrothermal synthesis. • Band gap variation achieved by adapting different synthesis routes. Among the numerous photocatalytic materials studied for potential application in degradation of organic effluents and antibiotic wastes, sillenite materials emerge as important candidates. In the present work, Ga based sillenite has been used to degrade aqueous persistent organic pollutants such as bisphenol (BPA) and Norfloxacin (NF) in presence of natural solar irradiation. Sillenite based oxides have exhibited various physico chemical applications due to their photocatalytic nature. Here, gallium based sillenite, Bi 24 Ga 2 O 39 , has been successfully synthesized through two different techniques, hydrothermal route (HY) and solid state reaction (SS) method. X-Ray Diffraction patterns and Rietveld refinement of same revealed the occurrence of sillenite single phase. Morphological investigation by Scanning Electron Microscopy revealed regular tetrahedral morphology of HY sample. X-ray photoelectron and Raman spectroscopy were performed to analyze the chemical composition and its environment. UV–Visible spectroscopy on sillenites was used to analyze and calculate the effective optical band gap energy ~2.55 eV (HY) and ~2.76 eV (SS) respectively. Photoelectrochemical measurements performed on the samples showed appreciable photocurrent response (~1.9 μA/cm2 for HY sample). The photoactivity of samples have been utilized for degradation of aqueous persistent organic pollutants, such as methylene blue, norfloxacin and bisphenol A in presence of visible light degrading upto 92%, 82% and 84% (HY) respectively. [ABSTRACT FROM AUTHOR]

Visible-light-driven hydrogen production is a promising pathway to realize efficient solar energy utilization. Here, Nd3+ incorporated ZnIn 2 S 4 (Nd-ZIS) was synthesized via facile one step hydrothermal method. Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS) confirm the successful incorporation of Nd3+ in ZnIn 2 S 4. Optical studies reveal the reduction of effective bandgap from 2.7 eV to 2.54 eV upon incorporation of Nd3+ with improved charge carrier life time of 3.12 ns. Electronic properties of ZIS and Nd-ZIS were investigated from first principle calculations. An attempt to improve photocatalytic activity of ZIS by modification with Nd3+ ions resulted in degradation of organic pollutant up to 98% under natural sunlight and decrease in life time of trap states up to a nominal value of 200 ms (as evident from photoelectrochemical measurements). The mechanism behind enhancement of photocatalytic activity of ZIS post Nd3+ integration has been proposed. Nd-ZIS was also utilized for water splitting activity exhibiting a considerable H 2 generation ∼3415 μmol g−1. To the best of our knowledge, activity of Nd3+ incorporated ZIS has been explored for the first time in present work. It is believed that an in-depth understanding of photoactivity of ZIS would be significantly important for designing materials with desired photocatalytic performance in future. Image 1 • Self-assembled hierarchical structures with improved photocatalytic activity. • Introduction of Nd3+ levels below the conduction band boosts carrier separation. • Multifunctional material with superior photoresponse. [ABSTRACT FROM AUTHOR]

Brownmillerite KBiFe 2 O 5 (KBFO) absorbs large part of the solar spectrum due to its smaller bandgap. This optical response has immense potential in photocatalytic applications. In this work, KBFO was successfully synthesized using citrate combustion method. X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) as well as Mössbauer spectroscopic studies, identify the valence state of Iron (Fe) as Fe3+. The strong magneto-dielectric coupling in KBFO was demonstrated by integrating both magnetization (M) and dielectric constant (ε) characteristics as a function of temperature. Magnetic and dielectric transitions were observed in close proximity in temperature range ∼780 K–760 K respectively. To the best of our knowledge, the photoelectrochemical properties of as developed KBFO were analyzed for the first time revealing a significant photoresponse with an average photocurrent density of 0.1 μA cm−2. The photocatalytic properties of KBFO were investigated by degrading organic effluent methylene blue (MB) under direct sunlight followed by a comparison with the photodegradation performance of perovskite BiFeO 3 (BFO). KBFO showed enhanced photocatalytic performance as compared to BFO due to its enhanced structural and optical properties. Image 1 • Multifunctional brownmillerite KBiFe 2 O 5 developed using citrate combustion method. • Strong magneto-dielectric coupling in KBiFe 2 O 5. • Photoelectrochemical properties of KBiFe 2 O 5 analyzed for first time and average current density found to be ∼0.1 μA/cm2 • Enhanced photodegradation efficiency of KBiFe 2 O 5 (E g = 1.67eV), over regular perovskite BiFeO 3 (Eg = 2.1 eV). [ABSTRACT FROM AUTHOR]