DRS Data Research Articles

Photoreduction of chromium (VI) by a composite of niobium (V) oxide impregnated with a Ti-based MOF

Herein, we report a novel composite material of Nb2O5@MIL–125 that exhibited enhanced photoreduction of hexavalent chromium. The composite material was fabricated through an impregnation approach, which comprised of a two-step hydrothermal synthesis. As-prepared Nb2O5 nanospheres exhibited very poor charge separation; MIL–125 (Ti) which is a Ti-based metal-organic framework was introduced into the lattice of the spheres to improve charge recombination rate. The synthesized material’s phase, crystallinity, textural and morphological studies were investigated utilizing XRD, Raman, TEM, SEM, and EDS, respectively. While the optical and photoelectrochemical behavior of the samples were obtained from UV–vis–DRS, PL, and EIS data. This data combined, illustrated the successful formation of a functional and effective heterointerface between Nb2O5 and MIL–125 (Ti). Ti introduced as the MOF in the lattice of Nb2O5 had an essential synergetic effect as the composite bearing the highest mole ratio of Ti showed higher effective photoreduction of hexavalent chromium. This was further complemented the PL and XPS data which highlighted the Nb–MIL–125 (2–3) composite to have excellent charge separation and rapid photoreduction of chromium.

Investigation of Structural, Optical and Electrical Transport Properties of Yttrium Doped La0.7Ca0.3MnO3 Perovskites

In the present study, bulk samples of yttrium doped La0.7−xYxCa0.3MnO3 (x = 0.3 and 0.4) are prepared through solid-state reaction route. The structural, optical and electrical transport properties have been explored through various analytical techniques. The x-ray diffraction (XRD) patterns affirm single phase and polycrystalline nature of the samples. Rietveld refinement analysis of the XRD data is used to determine the various structural parameters. It reveals that both the samples belong to orthorhombic crystal system with Pnma space group. Using Scherrer’s equation, a lower value of crystallite size is found in the higher concentration of yttrium doped sample. The band gap as determined from the UV–visible DRS data by employing the Tauc’s relation is found to enhance with the increase of yttrium concentration in La0.7Ca0.3MnO3. The low temperature resistivity measurements establish semiconducting nature of the samples over the temperature range of ~ 110–300 K. Moreover, the electrical resistivity data are interpreted within the variable range hopping (VRH) model to estimate the density of states at the Fermi level N(EF), mean hopping distance Rh(T) and hopping energy Eh(T). It is observed that the electrical quantities vary gradually with the change of Y content. The conduction mechanism in this system is governed in the framework of thermally activated small polaron hopping (SPH) model and accordingly various parameters namely Debye temperature (θD), activation energy (Ep) and optical phonon frequency (νph) are evaluated. The obtained results support a strong connection between structure and electrical behavior in our samples and can be elucidated on the basis of localization of charge carriers induced by the substituting ions.

Structure, optical and magnetic properties of a novel homometallic coordination polymers: Experimental and Computational studies

Single crystal of 1D homometallic coordination polymer involving cobalt metal ion and P2Mo5 Strandberg type polyoxometallate cluster (C6H10N2)2[Co(H2O)4P2Mo5O23].6H2O, is prepared in aqueous solution and characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance, fluorescence and magnetism. Single crystal X-ray diffraction analysis reveals that this compound crystallizes in the triclinic system with space group P ,bar{1}. The 3-(ammoniomethyl)pyridine C6H8N2 organic fragment is used merely as stabilizer for the promotion of topological structure. DRS data indicate that the synthesized material can be identified as a ferromagnetic semiconductor with optical bands gaps energy of 1.81 and 2.74 eV, respectively. The large value of refractive index observed in the visible region make the simple a promising candidate for visible optical communication devices and fluorescent emisson result provides that the complex belongs to a blue luminescent compounds. Moreover, magnetic measurements and electronic structure calculations show that P2Mo5 Strandberg polyoxoanion can be reported as a new class of ligand that is candidate to construct metal-inorganic framworks with long distance ferromagnetic superechange between Co(II) centers. The evidence from this study suggests that the syntesized polymer can become a great multifunctional material openning the door for the developpement of new coordination polymers based on Strandberg type polyxoxmetalate with potential applications.

Methane Activation on H-ZSM-5 Zeolite with Low Copper Loading. The Nature of Active Sites and Intermediates Identified with the Combination of Spectroscopic Methods.

Cu-modified zeolites have enormous potential as the catalysts facilitating the conversion of methane to methanol. It becomes important to investigate the active sites and the reaction mechanisms involved. In this paper, several spectroscopic methods such as UV-vis diffuse reflectance spectroscopy (UV-visDRS), pulse electron paramagnetic resonance (EPR), diffuse reflectance Fourier transform infrared spectroscopy, and solid-state (13C MAS) NMR have been employed to characterize the state of the Cu sites and the intermediates formed during the catalyst activation and methane-to-methanol transformation on Cu/H-ZSM-5 zeolite with low (0.10 wt %) Cu content. UV-vis DRS and EPR data imply the presence of two types of Cu2+ cations bound to the zeolite framework Si-O--Al sites (Z). One of them is a species of the type Z[Cu(II)O] or Z[Cu(II)(OH)] with extra-framework O- or OH- ligands. The other one refers to Z2Cu(II) species without extra-framework O-containing ligands. CW EPR studies reveal that the Z2Cu(II) species are the major part of the Cu(II) sites present in the zeolite. 1H HYSCORE and DRIFTS data are supportive of the formation of a molecular complex of methane and Z2Cu(II) species, with a strongly polarized C-H bond and a 3.3 Å separation between the hydrogen atom of methane and Cu. 13C MAS NMR provides evidence for the formation of both the surface methoxy intermediate and physisorbed methanol. It is suggested that experimentally identified Z[Cu(II)O] or Z[Cu(II)(OH)] are those sites that provide a homolytic cleavage of the methane C-H bond to yield surface bound methoxy species and/or methanol molecule, the possibility that has been recently justified with density functional theory ( Kulkarni et al. Catal. Sci. Technol. 2018 , 8 , 114 ). The comparison of the amount of the surface methoxy intermediates formed and the number of different Cu(II) sites present in the zeolite allowed us to conclude the involvement of Z2Cu(II) sites in methane C-H bond activation. The mechanism of methane activation on Z2Cu(II) sites has been proposed. It includes two steps: (1) the formation of the molecular complex of methane with Z2Cu(II); (2) heterolytic dissociation of the polarized C-H bond affording surface copper(II) hydride and methoxy species, both bound to zeolite framework Si-O--Al sites.

Investigation of structural, morphological and optical characteristics of Mn substituted Al-doped ZnO NPs: A Urbach energy and Kramers-Kronig study

Present work deals with the investigation of structural, morphological, elemental, chemical bonding and optical properties of simple sol-gel synthesized Al-doped ZnO and Mn-substituted Al-doped ZnO nanoparticles (NPs) using XRD, FE-SEM, EDAX, FT-IR and DRS techniques, respectively. A comprehensive evaluation of optical properties has also been done by Kramers-Kronig (KK) relations. The structural studies have revealed that the obtained patterns are mainly assigned to the hexagonal wurzite structure of the reference. The morphological investigations confirm the constitution of homogenous nanoscale particles with average grain sizes less than 40 nm for both samples. The optical band gap of the prepared samples is calculated using DRS data in two ways, Kubelka-Munk relation, and KK method. The band gap results show a red-shift with Mn-substitution in Al-doped ZnO. The disorderness (Urbach energy) of the samples is observed to be decreased with an increase in both band gap energy and crystallite size. Moreover, the optical parameters of the prepared samples such as refractive index, extinction coefficient and also dielectric constants are evaluated by applying KK relations on reflectivity curves.

Efficient removal of oil pollutant via simultaneous adsorption and photocatalysis using La–N–TiO2–cellulose/SiO2 difunctional aerogel composite

Nano-TiO2 photocatalysts doped with La–N(La–N–TiO2) were prepared by solgel method. The La–N–TiO2 was loaded on the cellulose/SiO2 composite aerogel (La–N–TiO2–CSA). La–N–TiO2–CSA had both oil absorption and oil degradation functions under the sun. The static state water contact angle is up to 148° close to superhydrophobic surface. An apparent decomposition rate of oil is 92%, which is much higher than 26% of pure TiO2. Under the visible light irradiation, the photocurrent density has increased by 50%. Characterization results show that LaONO3 was uniformly distributed in TiO2 crystal. Compared with pure TiO2, the UV–Vis DRS data showed the absorption band of La–N–TiO2 had extended to 441 nm. The La increased the valence band position and N lowered the conduction band position, which reduced the band gap of TiO2 from 3.59 to 2.81 eV. The formation of LaONO3 reduced carrier transfer resistance, and the migration rate and electron–hole separation efficiency were improved. The possible oil decomposition pathways were proposed.

Photocatalytic Performances and Antibacterial Activities of Nano-Zno Derived By Cetrimide-Based Co-Precipitation Method by Varying Solvents

In this work, zinc oxide nanoparticles have been synthesized by cost-effective and based on the efficient cetrimide and varying solvents are using the method of co-precipitation annealing at 350 C. The resultant powder samples were characterized well by means of XRD, SEM, FT-IR, PL and UV-visible DRS spectroscopy. Among them, XRD exhibits ZnO has the structure of hexagonal wurtzite with a preferred orientation of 101 planes. It is noted in ZnO represented in SEM images have different solvents and cetrimide has a strong influence on the morphology of ZnO nanostructures that are to be sized are 50nm, 70nm, 90nm 100nm. It confirms that the changes in the band-gap from UV-vis DRS data. The presence of Zn-O confirms various functional groups decomposed in the sample from FTIR data. The PL study states that the emission band available at approximately 410nm and checks the recombination level shows low, further, it correlates with good photocatalytic properties. The sunlight measured by Lux meter and dye degradation studies is done by a simple aeration photocatalytic technique represents 95% degradations and under UV light is 85%. Besides, the scavengers of the responsive species of during the degradation were additionally examined for photocatalytic mechanism. An antibacterial activity is enhanced significantly, which is based on the attribution of Nano features of ZnO nanostructures for p. aeruginosa bacteria. Thus, this study paved the way for potential applications of photocatalytic and antibacterial activities.

Advanced photocatalytic performance of novel BiOBr/BiOI/cellulose composites for the removal of organic pollutant

An environmental friendly BiOBr/BiOI/cellulose composite was successfully prepared via the facile in situ synthesis method using pulp board as the cellulose source in TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation. The obtained samples were characterized by the SEM, XRD, FT-IR, BET, XPS, UV–Vis DRS, TOC, HPLC, EPR, PL and EIS. The results suggested that there was a remarkable compatibility between BiOBr/BiOI and cellulose. The BiOBr/BiOI/cellulose composite exhibited extensively photocatalytic degradation activity and recycling properties under visible light irradiation. The photocatalytic activity of resultant samples was determined sufficiently through decomposition of rhodamine B (RhB), fluorescein dye (FL) and colorless antibiotic tetracycline hydrochloride (TC). DRS and PL analysis data indicated that the enhanced light harvesting ability and higher separation efficiency of photogenerated electron–hole pairs contributes to the excellent photocatalytic activity. On the basis of the experimental results and estimated energy band positions, the mechanism of enhanced photocatalytic activity was proposed. Moreover, the portable photocatalysts were easily recycled and reused, showing potential applications for environmental purification.

Butterfly cluster like lamellar BiOBr/TiO2 nanocomposite for enhanced sunlight photocatalytic mineralization of aqueous ciprofloxacin

The present study for the first time reports facile in-situ room temperature synthesis of butterfly cluster like lamellar BiOBr deposited over TiO2 nanoparticles for photocatalytic breakdown of ciprofloxacin (CIP). The butterfly cluster arrangement of BiOBr resulted in an increase in surface area from 124.6 to 160.797 m2·g−1 and subsequently increased incident light absorption by the composite photocatalyst. The XRD indicated the existence of TiO2 as spherical ≈10–15 nm diameter particles with [101] preferential growth planes of anatase phase while the lamellar BiOBr showing growth along [110] and [102] preferential planes that were also confirmed by the HR-TEM images. DRS data implicated 2.76 eV as the energy band gap of the synthesized nanocomposite while PL spectroscopic analysis predicted it to be 2.81 eV. XPS measurements examined the chemical oxidation states of the constituents among the nanocomposite samples. The lameller structure of BiOBr in 15%BiOBr/TiO2 acts as a manifold promoting both visible light (λ > 420 nm) and direct sunlight catalytic degradation of 25 mg·L−1 aqueous CIP up to 92.5% and 100%, respectively within 150 min. The rate constant values suggested that the visible light photocatalysis of CIP with 15%BiOBr/TiO2 was 5.2 and 9.4 times faster compared to pristine TiO2 and BiOBr, respectively. The free radical scavenging study demonstrated that although photogenerated superoxide ions and holes contribute to the overall photocatalytic activity, yet, hydroxyl radicals predominantly control the CIP oxidation. The synthesized nanocomposite was re-used up to five cycles and retained 82.98% efficiency even after 5th use cycle showing a decline of only 12%. The catalyst stability and easy recovery adds to its reusability and value of the photocatalytic process.

Catalytic performance of Cu/hydroxyapatite catalysts in CO preferential oxidation in H2-rich stream

Abstract A series of Cu/HAP catalysts was prepared by impregnation and characterised by TEM, BET, DRS, XPS, H2-TPR, XRD, TEM and FTIR techniques. H2-TPR and DRS data revealed that at low concentration ( The activity of the reduced samples in COTOX and COPROX processes revealed remarkable differences when the Cu content was increased from 0.8 to 14.8%. For instance, analysing the TOF values calculated for the two processes and the characterisation data, it was concluded that the catalysts with low Cu loadings (0.8% and 3.6%) were the most active ones and their sites involved in the CO oxidation reaction were almost similar. The addition of CO2 and water seemed to affect the performances of the two catalysts via different pathways. Indeed, in contrast to the Cu(4)/HAP, the Cu(1)/HAP catalyst became more selective in the presence of CO2 and water. Moreover, under these realistic COPROX conditions, the latter was 6.6 times more active than the former. A correlation with the characterisation data showed that the most efficient species consisted of those presenting strong interaction with the HAP support. By contrast, the sites exhibiting high concentration of Cu lattice imperfections showed a relatively low activity.

Influence of USY zeolite recrystallization on physicochemical properties and catalytic performance of NiMo/USY-Al2O3 hydrocracking catalysts

The effect of ultrastable zeolite Y recrystallization on the properties of NiMo/USY-Al2O3 hydrocracking catalyst has been studied. The mesoporosity, being introduced as the result of zeolite Y recrystallization, is mainly preserved at the subsequent steps of NiMo catalysts preparation. The total concentration of Brønsted acid sites in the catalysts varies proportionally to that for the corresponding zeolites used for preparation. It is observed that the higher the recrystallization degree the lower the concentration of strong Brønsted acid sites in the catalysts. UV–vis DRS, HRTEM and XPS data suggest that the state of supported Ni and Mo is similar for the catalysts prepared with parent and recrystallized zeolites. The catalysts based on recrystallized zeolites have significantly higher activity in hexadecane hydrocracking as compared to the catalyst obtained using parent zeolite. This effect is rationalized in terms of the improved accessibility of zeolite acid sites after recrystallization. Moreover, the mesoporosity introduced by zeolite Y recrystallization has a positive effect on the selectivity of NiMo/USY-Al2O3 hydrocracking catalyst.

Core-shell structured TiO2@In2O3 for highly active visible-light photocatalysis

Core-shell structured TiO2@In2O3 with high visible-light photocatalytic activity have been successfully fabricated by solvothermal method. The as-obtained products were characterized by field transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV–visible diffuse reflectance spectra (UV–vis DRS). Structural characterizations demonstrated that the In2O3 layers were comprised of nanocrystallites ca. 14 nm in size and displayed rough surfaces. The UV–vis DRS data showed that In2O3 greatly expanded the visible light absorption band edge of TiO2. The results revealed that the obtained TiO2@In2O3 with core-shell structure showed enhancement of the visible-light photocatalytic activity to degrade methyl orange (MO) comparing with the pure TiO2 and In2O3 products.

Strain induced optical properties of perovskite LaFeO3

Tuning the properties of perovskite metal oxide by varying the crystal structure leads to many functional applications. Here strain induced by an external matrix like reduced graphene oxide (RGO) in the crystal structure of LaFeO3 (LFO) and its related optical properties are investigated. X-ray diffraction technique is used to find the strain in the crystal structure of graphene-LFO (GL) composite. The band gap and band tailing energy of the composites are determined by applying modified Kubelka–Munk function on UV–Vis DRS data. The steady-state fluorescence emission spectra of the samples show a monotonic decrease with increase in concentration of RGO. GL composites show enhanced photocatalytic degradation of RhodamineB (RhB) dye under solar spectrum irradiation. Variations in lifetime, fluorescence intensity and photocatalytic activity of GL composites are explained in terms of intermediate bands produced by RGO and associated radiation-less transitions of photoexcited electrons. RGO induced strain and tuning the optical properties of perovskites can provide a pathway to engineer new multifunctional materials in optoelectronic applications.

Novel catalyst based on mono- and di-vanadium substituted Keggin polyoxometalate incorporated in poly(acrylic acid-co-acrylamide) polymer for the oxidation of sulfides

Composite materials based on [PVxW12-xO40](3+x)− with x = 1 or 2 (PVW and PV2W respectively), included in poly(acrylic acid-co-acrylamide) gel (PAACA), were synthesized. The samples were characterized by different techniques such as FT-IR, 31P MAS-NMR, 51V-NMR, XRD, DTA-TGA, UV–vis DRS, and the acidic properties were estimated by means of potentiometric titration with n-butylamine. Samples containing 10, 20 and 30% (w/w) of polyoxotungstovanadate (POTV) were prepared by inclusion of the POTV in the polymer during its synthesis. According to Fourier transform infra-red and magic angle spinning-nuclear magnetic resonance studies, the predominat anion present in the samples is [PVxW12-xO40](3+x)−, and there is no evidence of its decomposition during the synthesis of hybrid materials and the drying step. According to XRD results, these anions are greatly dispersed in the PAACA or present as amorphous phases.UV–vis DRS data reveal that the samples synthesized using POTV with two vanadium atoms (PAACA-PV2W) exhibit lower values of absorption edge energy than those prepared using PVW (PAACA-PVW), which correlates with a higher oxidizing capacity.The potentiometric titration shows strong acid sites of the hybrid materials, and their number increases with the number of vanadium atoms and with the amount of POTV incorporated in the PAACA grid.The hybrid materials prepared by inclusion of POTV during the polymer synthesis exhibit appropriate physicochemical features to catalyze the oxidation of diphenyl sulfide (DPS) to its sulfone employing acetonitrile as solvent H2O2 as a green oxidant. The samples with 30% w/w of POVT, which show higher catalytic performance, are suitable for the DPS oxidation and can be reused without remarkable drop of their catalytic activity. Furthermore, they show high activity as a catalyst in the oxidation reaction of 4,4´-diamino diphenyl sulfide to the corresponding sulfone (dapsone) used for malaria treatment.

Graphene/BiVO4/TiO2 nanocomposite: tuning band gap energies for superior photocatalytic activity under visible light

A facile, ultrasonic wave-assisted one pot hydrothermal method has been developed to fabricate reduced graphene oxide/bismuth vanadate/titanium oxide (RGO/BiVO4/TiO2) ternary nanocomposites. By utilizing graphene oxide (GO) as multifunctional structure, RGO/BiVO4/TiO2 (GBT) with diverse percentage composition possessing varying band gap energies is obtained. XRD and Raman spectroscopy evince formation of tetragonal and monoclinic phases of BiVO4. The band gap energies of the components of the composite were determined by applying modified Kubelka–Munk function on UV–Vis DRS data. Tuning of band gap energy of the BiVO4 and TiO2 were simultaneously achieved by modifying the concentrations of GO and TiO2 during synthesis. The GBT exhibited enhanced photocatalytic degradation of methylene blue (MB) under visible light irradiation. The relative photocatalytic activity rates of the composites in GBT series are in agreement with the photoluminescence data. The mechanism behind the activity suggests GO acting as an electron trapper and TiO2 behaving as an efficient mediating co-catalyst. The band gap energy tuning led to reduction in time needed for complete MB degradation from 40 min with RGO/BiVO4 to 10 min with the ternary composite GBT. It is expected that the work would encourage new vistas to engineer different combinations of graphene based ternary composites which might lead to potential applications guided by band gap tuning.

Visible light driven LaFeO3 nano sphere/RGO composite photocatalysts for efficient water decomposition reaction

Abstract RGO loaded on LaFeO3 nano sphere (GLFO) has been designed with greater stability in order to promote the photocatalytic activity towards water splitting by tuning the optical band gap of LFO and reducing the e− and h+ recombination process. To alleviate the charge recombination, an effective strategy is to employ reduced graphene oxide (RGO) as a charge sink, separator and transporter. Gel combustion method has been adopted to prepare LFO nano sphere and through ultrasonication LFO spheres was fabricated on RGO surface. The synthesized nano structured materials are characterized by powder X-ray diffraction (PXD), UV–vis diffuse reflectance spectra (UV–vis DRS), transmission electron microscopy (TEM/HRTEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. UV–vis DRS data revealed that the nanocomposites are visible light absorbing semiconductors with band gap ranging from ∼2.1–1.96 eV. When tested the photocatalyst towards hydrogen production under visible light, the rate of GLFO increases more than two fold than neat LFO. So as a case study, the GLFO photocatalyst can contribute a remarkable outcome in the photocatalytic field. Formation mechanism, structural, optical and electronic properties of LaFeO3 nanosphere/RGO composite is discussed and correlated with photocatalyic activity.

Simultaneous assessment of key properties of arid soil by combined PXRF and Vis–NIR data

SummaryArid soil is common worldwide and has unique properties that often limit agronomic productivity, specifically, salinity expressed as soluble salts and large amounts of calcium carbonate and gypsum. Currently, the most common methods for evaluating these properties in soil are laboratory‐based techniques such as titration, gasometry and electrical conductivity. In this research, we used two proximal sensors (portable X‐ray fluorescence (PXRF) and visible near‐infrared diffuse reflectance spectroscopy (Vis–NIR DRS)) to scan a diverse set (n = 116) of samples from arid soil in Spain. Then, samples were processed by standard laboratory procedures and the two datasets were compared with advanced statistical techniques. The latter included penalized spline regression (PSR), support vector regression (SVR) and random forest (RF) analysis, which were applied to Vis–NIR DRS data, PXRF data and PXRF and Vis–NIR DRS data, respectively. Independent validation (30% of the data) of the calibration equations showed that PSR + RF predicted gypsum with a ratio of performance to interquartile distance (RPIQ) of 5.90 and residual prediction deviation (RPD) of 4.60, electrical conductivity (1:5 soil : water) with RPIQ of 3.14 and RPD of 2.10, Ca content with RPIQ of 2.92 and RPD of 2.07 and calcium carbonate equivalent with RPIQ of 2.13 and RPD of 1.74. The combined PXRF and Vis–NIR DRS approach was superior to those that use data from a single proximal sensor, enabling the prediction of several properties from two simple, rapid, non‐destructive scans.

Synthesis, Crystal Growth, Characterization, and Theoretical Studies of 3-(4-fluorophenyl)-1-(4-methylphenyl)prop-2-en-1-one

Single crystals of 3-(4-fluorophenyl)-1-(4-methylphenyl)prop-2-en-1-one (FMPP) have been grown by mixed solvent system ethanol and chloroform 2:1 (v/v) at room temperature. Single crystal X–ray diffraction reveals that FMPP belongs to monoclinic system with four molecules in the unit cell. The structure and the crystallinity of the material were further confirmed by FT-IR, FT-Raman, and powder X–ray diffraction analyses. The band gap energy is estimated by Kubelka–Munk algorithm using DRS data. Theoretical calculations were performed to derive the optimized geometry and the first-order molecular hyperpolarizability (β) values. The as-grown crystal is further characterized by GC-Mass, SEM, and thermal analyses.

Excellent sun-light-driven photocatalytic activity by aurivillius layered perovskites, Bi₅-xLaxTi₃FeO₁₅ (x = 1, 2).

Aurivillius phase layered perovskites, Bi5-xLaxTi3FeO15 (x = 1, 2) are synthesized by solid-state reaction. The compounds are characterized by powder X-ray diffraction (PXD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), UV-vis diffuse reflectance (UV-vis DRS), and photoluminescence (PL) spectroscopy. UV-vis DRS data revealed that the compounds are visible light absorbing semiconductors with band gaps ranging from ∼2.0-2.7 eV. Photocatalytic activity studies by Rhodamine B (RhB) degradation under sun-light irradiation showed that these layered oxides are very efficient photocatalysts in mild acidic medium. Scavenger test studies demonstrated that the photogenerated holes and superoxide radicals (O2(•-)) are the active species responsible for RhB degradation over the Aurivillius layered perovskites. Comparison of PL intensity, dye adsorption and ζ-potential suggested that a slow e(-)-h(+) recombination and effective dye adsorption are crucial for the degradation process over these photocatalysts. Moreover, relative positioning of the valence and conduction band edges of the semiconductors, O2/O2(•-), (•)OH/H2O potential and HOMO-LUMO levels of RhB appears to be responsible for making the degradation hole-specific. Photocatalytic cycle tests indicated high stability of the catalysts in the reaction medium without any observable loss of activity. This work shows great potential in developing novel photocatalysts with layered structures for sun-light-driven oxidation and degradation processes largely driven by holes and without any intervention of hydroxyl radicals, which is one of the most common reactive oxygen species (ROS) in many advanced oxidation processes.

English

A novel and simple chemical route was used for the deposition of ZnO thin film from aqueous solution of zinc–ammonia complex, integrating the merits of successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition methods. ZnO thin films on glass substrates were deposited with the precursor of zinc– ammonia complex. Characterization techniques of XRD, SEM, EDAX and DRS are used to characterize ZnO thin films. X-ray diffraction study show that the film prepared in this work exhibits good crystallinity with the hexagonal wurtzite crystalline structure and the preferential orientation along (0 0 2) plane, with a texture coefficient value of ~2.56, average crystallite size of 28.92 nm and with lattice constants a = b = 3.257 A, c = 5.215 A. EDAX spectrum indicates that the film consists of zinc and oxygen elements. The optical band gap energy of the thin films is calculated from optical absorption spectrometry using DRS data and the value was found to be direct allowed transition ~3.22 eV.