UV Vis Diffuse Reflectance Spectra Research Articles

Tribocatalytic activity on Ba(Ti0.95Zr0.05)O3 surfaces: The role of oxygen vacancies and the aging effect

This study explores the potential of tribocatalysis, a resource-efficient degradation technique, using ferroelectric perovskite-type Ba(Ti0.95Zr0.05)O3 (BZT) with oxygen vacancies as a catalyst. The catalysts, synthesized via a standard solid-state method, were analyzed using XPS and EPR to confirm the presence of oxygen vacancies. Their electrical properties were evaluated through UV–vis diffuse reflectance spectra and Mott–Schottky plots. Freshly prepared BZT catalysts demonstrated a 92% degradation of Rhodamine B (RhB) within 20 h, achieving a reaction rate constant (K) of 0.114 h−1. However, aging significantly reduced RhB degradation, with de-aging failing to restore initial activity. The study attributes the catalyst's catalytic activity and aging issues to the oxygen vacancies, acting as shallow donor states. It also highlights the benefits of tribocatalysis due to electron accumulation at the surface from friction-generated contact, emphasizing the critical role of oxygen vacancies in catalytic degradation and long-term catalyst stability.

Hybrid collagen–cellulose–Fe3O4@TiO2 magnetic bio-sponges derived from animal skin waste and Kenaf fibers for wastewater remediation

Water pollution from synthetic dyes and oil spills has a significant impact on the environment and living species. Here, we developed a low-cost, environmentally friendly and easily biodegradable magnetic hybrid bio-sponge nanocomposite from renewable resources such as collagen and cellulose (Kenaf fibre cellulose–collagen, KFCC). We loaded it with magnetic bimetallic Fe3O4@TiO2 (BFT) NPs to produce a photocatalyst material (KFCC-BFT) for the treatment of colored wastewater as well as a sorbent for oil–water separation. The characterization of the bimetallic BFT NPs by XRD, HRTEM and VSM showed the deposition of TiO2 particles onto the surface of Fe3O4 with lattice interlayers spacing of 0.24 and 0.33 nm for Fe3O4 and TiO2, respectively with ferromagnetic property. The UV–vis diffuse reflectance spectra result indicated that the band gap energy of bio-sponges decreases with the increase of the bimetallic moiety. The photocatalytic efficiency of the as-prepared magnetic hybrid bio-sponge in the degradation of crystal violet dye was up to 91.2% under visible light conditions and 86.6% under direct sunlight exposure. Furthermore, the magnetic hybrid bio-sponge was used to separate motor oil from water (> 99%) and had a high oil sorption capacity of 46.1 g/g. Investigation of the recyclability and reusability performance for 9 cycles revealed that the bio-sponge had a high sorption capacity for up to 5 cycles. Our results suggest that the bio-polymer-supported BFT hybrid nanocomposite is a cost-effective and easily biodegradable photocatalyst and has great potential for real-field environmental remediation applications.

Thermal Polymerisation Synthesis of g-C3N4 for Photocatalytic Degradation of Rhodamine B Dye under Natural Sunlight

The photocatalytic performance of g-C3N4 materials prepared by different precursors for Rhodamine B (RhB) dye degradation was studied. Their crystal structure, morphologies, chemical compositions, functional groups, and optical and photoelectrochemical performances of prepared g-C3N4 were analysed and characterised using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-Vis diffuse reflectance spectra, photoluminescence, and electrochemical workstations. The degradation of RhB dye in the presence of visible light and sunlight was utilised to assess the photocatalytic efficiency of the g-C3N4 photocatalyst. The results of the photocatalytic comparison experiment showed that the g-C3N4 photocatalyst prepared with urea as a precursor (UCN) has the best photocatalytic performance, achieving 99.61% removal in 40 min. In addition, the photocatalyst UCN can completely degrade 10 mg/L RhB dye within 20 min under sunlight, demonstrating its potential for practical applications under natural sunlight conditions. After four cycles, the degradation rate remains above 99%, demonstrating excellent stability and reusability. Due to its lower average pore number, larger BET-specific surface area and volume of pores, UCN provides more activity spaces and facilitates the adsorption of pollutant molecules, thereby enhancing photocatalytic activity. It was established through the active substance trapping studies that the main reactive species involved in the photocatalytic degradation process of RhB dye is •O2−. This study showed that g-C3N4 synthesised with urea as the precursor has better photocatalytic performance in the degradation of RhB dye.

Sunlight driven photocatalytic degradation of RhB dye using composite of bismuth oxy-bromide kaolinite BiOBr@Kaol: Experimental and molecular dynamic simulation studies

This study reported the synthesis of a new eco-friendly photocatalyst nanocomposite based on kaolinite clay and bismuth oxybromide (BiOBr@Kaolinite) using a facile co-precipitation method in acidic medium. The prepared nanocomposite was characterized using several techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning microscopy electron (SEM), Transmission electron microscope (TEM), Energy-dispersive X-ray spectroscopy (EDX), UV–Vis diffuse reflectance spectra (DRS), and X-ray photoelectron spectroscopy (XPS). These techniques were used to determine the crystal phase, functional groups, morphology, elementary composition, chemical states, optical properties, and bad gap energy of as synthesized, respectively. The characterized materials were then applied for rapid photodegradation of Rhodamine B dye (RhB), indicating its effective use for the degradation of toxic organic pollutants under sunlight irradiation. The photocatalytic activity study showed that RhB dye (10 mg/L) was degraded within 30 min under sunlight irradiation. The degradation mechanism of RhB and the photocatalytic stability study of the nanocomposite BiOBr@0.4Kaol showed that, the high photocatalytic activity could be attributed to the charge transfer from kaolinite to BiOBr nanoparticles, which prevented the rapid recombination of the electron-hole pair induced during the photocatalytic process. Moreover, MD and DFT-D stimulations and adsorption calculations based on Monte Carlo were applied in this study. This study led to the development of an effective and environmentally friendly photocatalyst nanocomposite for the degradation of toxic organic pollutants in wastewater, highlighting its potential application in water treatment and depollution processes.

Co- and Ni-Doped TiO2 Nanoparticles Supported on Zeolite Y with Photocatalytic Properties.

Zeolite Y samples with microporous and hierarchical structures containing Ti-Ni and Ti-Co oxides were obtained as active photocatalysts. Different Ti amounts (5, 10% TiO2) were supported, followed by the loading of Ni or Co oxides (5%). X-ray diffraction evidenced the presence of TiO2 as an anatase. N2 adsorption-desorption results showed type IV isotherms for hierarchical zeolite Y samples, and a combination of type IV and I isotherms for zeolite Y samples. UV-Vis diffuse reflectance spectra showed a shift in the absorption band to visible with increasing Ti loading and especially after Co and Ni addition. A significant effect of the support was evidenced for Ti and its interaction with Co/Ni species. The zeolite Y support stabilized Ti in the 4+ oxidation state while hierarchical zeolite Y support favored the formation of Ti3+ species, Ni0 and Ni2+ and the oxidation of Co to 3+ oxidation state. Photocatalytic activity, under UV and visible light irradiation, was evaluated by the degradation of amoxicillin, used as a model test. The photocatalytic mechanism was investigated using ethanol, p-benzoquinone and KI as ·OH and ·O2- radicals and hole (h+) scavengers. The best results were obtained for the immobilized Ni-Ti species on the hierarchical zeolite Y support.

Constructing stable uranyl-copper(II) bimetallic organic frameworks using rigid thiophenedicarboxylic acid

By introducing Cu(II) ions as additional connecting nodes to construct stable heterometallic uranyl-organic frameworks (UOFs) with thiophene-2,5-dicarboxylic acid (H2TDC) and N-donor auxiliary ligands, three new uranyl complexes, namely, [Cu(phen)(UO2)(TDC)2] (1), [Cu(phen-NO2)2(UO2)(TDC)2]·3H2O (2), and [Cu(phen-NH2)(H2O)2(UO2)(TDC)2]·4H2O (3) (phen = 1,10-phenanthroline) have been successfully synthesized by hydrothermal reaction. Complex 1 exhibits a rare three-dimensional (3D) network structure of cds topology connected by UO2, Cu(phen), and TDC units. Both complexes 2 and 3 feature similar one-dimensional chain structures based on UO2, TDC, Cu(Phen-NO2)2 and UO2, TDC, Cu(phen-NH2)(H2O)2 respectively. The N-donor auxiliary ligands play a key role in determining their structural dimensionalities and bandgaps formation. Among the three uranyl complexes, phen with a smaller size than its derivatives, phen-NO2 and phen-NH2, was found to be favorable for constructing 3D UOFs. Moreover, complexes with both phen-NO2 and phen-NH2 showed varying degrees of redshift on optical spectra. The UV–Visible diffuse-reflectance spectra, analyzed with Tauc’s fitting in considering Urbach tailing, revealed an indirect bandgap of 2.94 eV, an indirect bandgap of 2.67 eV, and a direct bandgap of 2.45 eV for 1, 2 and 3, respectively. Moreover, thermogravimetric analyses indicate that 3D anhydrous uranyl complex 1 possessed a robust structure and excellent thermal stability above 250 ℃.

From Centrosymmetry to Noncentrosymmetry: Precise Structural Regulation and Characterization on ZnHPO3·2H2O Polymorphs.

Polymorphs of ZnHPO3·2H2O with centrosymmetry (Cmcm) and noncentrosymmetry (C2) structures were prepared by modified solution evaporation and seed-crystal-induced secondary nucleation methods. In Cmcm-ZnHPO3·2H2O, the zinc atoms are only octahedrally coordinated, while in C2-ZnHPO3·2H2O, they feature both tetrahedral and octahedral coordination. As a result, Cmcm-ZnHPO3·2H2O features a 2D layered structure with lattice water molecules located in the interlayer space, while C2-ZnHPO3·2H2O features a 3D electroneutral framework of tfa topology connected by Zn(1)O4, Zn(2)O6, and HPO3 units. The UV-visible diffuse reflectance spectra associated with Tauc's analyses give a direct bandgap of 4.24 and 4.33 eV for Cmcm-ZnHPO3·2H2O and C2-ZnHPO3·2H2O, respectively. Moreover, C2-ZnHPO3·2H2O exhibits a weak second harmonic generation (SHG) response and a moderate birefringence for phase matching, indicating its potential as a nonlinear optical material. Detailed dipole moment calculation and analysis confirmed that the SHG response mainly derived from the HPO3 pseudo-tetrahedra.

Highly Efficient Photo-Fenton Ag/Fe2O3/BiOI Z-Scheme Heterojunction for the Promoted Degradation of Tetracycline.

Novel Ag/Fe2O3/BiOI Z-scheme heterostructures are first fabricated through a facile hydrothermal method. The composition and properties of as-synthesized Ag/Fe2O3/BiOI nanocomposites are characterized by powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, UV-Vis diffuse reflectance spectra, etc. The Ag/Fe2O3/BiOI systems exhibit remarkable degradation performance for tetracycline (TC). In particular, the composite (Ag/Fe2O3/BiOI-2) shows the highest efficiency when the contents of Ag and α-Fe2O3 are 2 wt% and 15%, respectively. The effects of operating parameters, including the solution pH, H2O2 concentration, TC concentration, and catalyst concentration, on the degradation efficiency are investigated. The photo-Fenton mechanism is studied, and the results indicated that •O2- is the main active specie for TC degradation. The enhanced performance of Ag/Fe2O3/BiOI heterostructures may be ascribed to the synergic effect between photocatalysis and the Fenton reaction. The formation of Ag/Fe2O3/BiOI heterojunction is beneficial to the transfer and separation of charge carriers. The photo-generated electrons accelerate the Fe2+/Fe3+ cycle and create the reductive reaction of H2O2. This research reveals that the Ag/Fe2O3/BiOI composite possesses great potential in wastewater treatment.

Constructing CdIn2S4/ZnS type-I band alignment heterojunctions by decorating CdIn2S4 on ZnS microspheres for efficient photocatalytic H2 evolution

In this study, a series of promising binary hybrid heterojunction CdIn2S4/ZnS (CIS/ZnS) were constructed via a facile hydrothermal method. Credible characterization methods including powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectra (DRS) were carried out to investigate the physicochemical properties the as-obtained photocatalysts. Photocatalytic water splitting for hydrogen evolution was performed to evaluate the photocatalytic activity of the photocatalyst. The results indicate that the light-harvesting ability could be markedly enhanced by decorating CdIn2S4 on ZnS microspheres. Compared with the pristine CdIn2S4 and ZnS, the hybrid photocatalysts present more efficient photocatalytic hydrogen production performance. Among composite photocatalysts, the 5% CIS/ZnS sample manifests the highest photocatalytic hydrogen production rate of 10.80 mmol g−1 h−1, which is 2.6 and 5.4 times higher than that of ZnS and CdIn2S4, respectively. Moreover, a type-I band alignment mechanism was prudently put forward to interpret the photocatalytic hydrogen generation activity. The boosted photocatalytic hydrogen evolution activities of CIS/ZnS can be attributed to the enhanced light-harvesting ability, efficient separation and transfer of the photo-induced charge carriers, and inhibition of electrons and holes recombination of binary hybrid CIS/ZnS photocatalysts.

Photoelectrochemical aptasensing of tetracycline enabled by efficient photoanode: Integrating high visible light-harvesting Bi2S3 and metal-free g-C3N4 into Z-scheme heterojunction

The development of a reliable method for detecting tetracycline (TC) in fish is essential to ensure the safety of aquatic products and human health. Herein, a photoelectrochemical (PEC) aptasensor was fabricated for the efficient detection of TC based on a designed efficient photoanode with a novel high light-harvesting heterojunction of bismuth sulfide/graphitic carbon nitride (Bi2S3/g-C3N4) as a photoactive material. The Bi2S3/g-C3N4 exhibited enhanced photocurrent due to its increased light capture capability, high carrier density and especially low electron-hole recombination efficiency enabled by the Z-scheme electron transfer, which was verified by the UV–vis diffuse reflectance spectrum, Mott–Schottky plot, and electron spin resonance spectroscopy. Under optimal experimental conditions, the fabricated aptasensor had the advantages of a wide linear range of 0.01–10 nM, a low detection limit of 3 pM and good selectivity and reproducibility. When the aptasensor was applied to determine TC in fish, the results were in good agreement with the UPLC-MS/MS method, indicating the reliability of the PEC aptasensing method for detecting TC in real samples.

Template-Free Synthesis of Two New Luminescent One-Dimensional High-Nuclearity Silver Polyclusters

The metallophilic properties, spherical configuration, and flexible coordination of silver ions make them prone to create various coordination modes and structural features. Therefore, with the increase of the complexities of self-assembly, the effect of various synthetic conditions in the final structure of silver compounds becomes diverse and attractive. In this study, two new silver polyclusters, 16- and 21-nuclearity, protected by multiple ligands including alkynyl, trifluoroacetate, and diphenylphosphinate, were synthesized and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, and Fourier transform infrared (FTIR) spectroscopy. The optical properties and thermal stability of the polyclusters were studied by solid-state ultraviolet-visible (UV-vis) absorption and solid UV-vis diffuse reflectance spectra and gravimetric analysis, respectively. The formation of the two polyclusters can be fine-controlled by simply adjusting the stoichiometric ratio of diphenylphosphinate ligands to silver precursors under the same synthetic condition, leading to the different coordination modes between ligands and Ag centers. This work shows a facile and template-free method to synthesize and control the silver polycluster assembly, encouraging further development of new polyclusters with the potential for various applications.

Investigating the Performance and Stability of Fe3O4/Bi2MoO6/g-C3N4 Magnetic Photocatalysts for the Photodegradation of Sulfonamide Antibiotics under Visible Light Irradiation

In this study, an Fe3O4/Bi2MoO6/g-C3N4 magnetic composite photocatalyst was synthesized for the visible-light-driven photocatalytic degradation of sulfonamide antibiotics, specifically sulfamerazine (SM1). Characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), photoluminescence spectroscopy (PL), UV-vis diffuse reflectance spectra (UV-vis), and the use of a vibrating sample magnetometer (VSM), were employed to analyze the fabricated samples. The composite exhibited efficient visible-light absorption and charge separation, with optimal photocatalytic performance achieved at a pH value of 9.0. The study reveals the importance of solution pH in the degradation process and the potential applicability of the composite for efficient magnetic separation and recycling in photocatalytic processes. The Fe3O4/Bi2MoO6/g-C3N4 magnetic composite photocatalyst demonstrated exceptional stability and recyclability, maintaining a high degradation efficiency of over 87% after five consecutive cycles. An XRD analysis conducted after the cycling tests confirmed that the composite’s composition and chemical structure remained unchanged, further supporting its chemical stability. This investigation offers valuable insights into the photocatalytic degradation of sulfonamide antibiotics using magnetic composite photocatalysts and highlights the potential of the Fe3O4/Bi2MoO6/g-C3N4 composite for practical applications in environmental remediation.

Cuprous oxide core-shell heterostructure facilely encapsulated by cadmium metal organic frameworks for enhanced photocatalytic hydrogen generation

Light absorption and separation of photo-generated electrons and holes are important to photocatalytic hydrogen evolution of a photocatalyst. Herein, a special metal organic framework (MOFs) was fabricated by encapsulating of 2-methylimidazole and cadmium nitrate on the silica coated cuprous oxide (Cu2O/SiO2/CdIF). The structure, morphology, composition, and valence state of the obtained materials were analyzed. It was demonstrated that the core-shell Cu2O/SiO2/CdIF heterostructure was achieved. Also, the photocatalytic activity and stability of H2 generation over the Cu2O/SiO2/CdIF nanocomposite were investigated. Interestingly, the Cu2O/SiO2/CdIF nanocomposite exhibited high activity which was hardly changed after five recycles. By means of Raman spectra, solid diffuse reflection UV–vis spectra, photoelectric response, and interfacial resistance, it was shown that higher light absorption, efficient charge separation and strong synergistic effect among the components in the heterostructure were responsible to the enhanced performance in the Cu2O/SiO2/CdIF nanocomposite.

Low-temperature synthesis, characterization and photocatalytic properties of lanthanum vanadate LaVO4

In this study, we have successfully prepared tetragonal lanthanum vanadate LaVO4 nanoparticles by a facile co-precipitation method at room temperature. The obtained materials were characterized using different structural and micro-structural techniques such as the characterization by X-ray diffraction (XRD), UV–Vis diffuse reflectance spectrum (DRS), transmission electron microscopy (TEM), and Raman spectrometry. The obtained structure is crystallized in single tetragonal phase with pin-like nanostructure. A main optical transition with bandgap energy of 3.26 eV is evidenced, and the average lifetime of charges carriers was found to be 1 ns Furthermore, the photoluminescence occurs in the visible light range. The photocatalytic activity was evaluated by the photocatalytic degradation of methylene blue (MB) with initial concentration of 10 mg L−1. The result indicates that LaVO4 particles showed a best photocatalytic activity of 98.2% degradation for methylene blue solution after irradiation of 90 min under visible light. Furthermore, the photocatalytic mechanism and reusability were studied.

Synthesis of functionalized α -Fe2O3 nanoparticles: Characterization and applications

In this study, EDTA functionalized α -Fe2O3 (Ferric Oxide) NPs were synthesized via chemical and green synthetic methods. FTIR spectra confirmed the functionalization of NPs with EDTA. X-ray diffraction confirmed the formation ‘α’ form of Fe2O3. UV–Vis diffuse reflectance spectra were applied to study the band gap of the NPs and was determined as 2.75 eV. MB and MG dyes were used as model dyes to study the adsorption and photocatalytic properties of NPs under visible and ultraviolet light radiation respectively. FESEM and HRTEM methods are used to study the morphology of the synthesized nanoparticles. Surface functionalization played a significant role in understanding the adsorption of dyes onto the surface of the photocatalyst. The crystallite size of chemical synthesized and green synthesized α- Fe2O3 was found to be 12 nm and 9 nm respectively. Maximum degradation efficiency of 58% and 86% was obtained for the degradation of MB and MG respectively and 85.9% of corrosion inhibition efficiency was also achieved. The results proved that functionalization of nanoparticles will lead enhancement of the following mediated synthesized EDTA functionalized α -Fe2O3 is a promising material to use for different application. Hence, green synthesized NPs are expected to offer significant insight into their multifunctional applications.

Enhancement of visible light photocatalytic pharmaceutical degradation and hydrogen evolution of Bi5O7Br by in situ disorder engineering

In order to simultaneously solve the problems of the poor light absorption capacity and high recombination rate of photogenerated carriers, Bi5O7Br photocatalyst with abundant ordered/disordered structures (O/D-Bi5O7Br) was prepared through a simple in situ disorder engineering. The prepared samples were characterized by XRD, TEM, HRTEM, SAED, XPS, UV-Vis diffuse reflectance spectra (DRS), and the activity was evaluated by photocatalytic degradation of tetracycline hydrochloride (TC) and hydrogen evolution under visible light irradiation. Results revealed that the ordered/disordered structure not only enhances the light absorption ability, uplifts conduction band position, facilitates the transfer and separation of photogenerated carriers, but also offers abundant unsaturated atoms as active sites for the photocatalytic process. Therefore, O/D-Bi5O7Br exhibits a high hydrogen evolution rate of 38.12 μmol/(g·h) and superior TC degradation rate of 86% within 135 min.

Two New Aluminoborates with 3D Porous-Layered Frameworks.

Two new aluminoborates, NaKCs[AlB7O13(OH)]·H2O (1) and K4Na5[AlB7O13(OH)]3·5H2O (2), have been hydro(solvo)thermally made with mixed alkali metal cationic templates. Both 1 and 2 crystallize in the monoclinic space group P21/n and contain similar units of [B7O13(OH)]6- cluster and AlO4 tetrahedra. The [B7O13(OH)]6- cluster is composed of three classical B3O3 rings by vertex sharing, of which two of them connect with AlO4 tetrahedra to constitute monolayers, and one provides an O atom as a bridging unit to link two oppositely orientated monolayers by Al-O bonds to form 3D porous-layered frameworks with 8-MR channels. UV-Vis diffuse reflectance spectra indicate that both 1 and 2 exhibit short deep-UV cutoff edges below 190 nm, revealing that they have potential applications in deep-UV regions.

Enhanced Photocatalytic Coupling of Benzylamine to N-Benzylidene Benzylamine over the Organic-Inorganic Composites F70-TiO2 Based on Fullerenes Derivatives and TiO2.

The organic-inorganic composites F70-TiO2, based on fullerene with carboxyl group derivatives and TiO2 semiconductor, have been designed and constructed to become an optical-functional photocatalyst via the facile sol-gel method. The composite photocatalyst obtained shows excellent photocatalytic activity for the high-efficiency conversion of benzylamine (BA) to N-benzylidene benzylamine (NBBA) with air pressure at a normal temperature under visible light irradiation. By optimizing the composition, the composites with the 1:15 mass ratio of F70 and TiO2, denoted as F70-TiO2(1:15), demonstrated the highest reaction efficiency for benzylamine (>98% conversion) to N-benzylidene benzylamine (>93% selectivity) in this study. However, pure TiO2 and fullerene derivatives (F70) exhibit decreased conversion (56.3% and 89.7%, respectively) and selectivity (83.8% and 86.0%, respectively). The UV-vis diffuse reflectance spectra (DRS) and Mott-Schottky experiment's results indicate that the introduction of fullerene derivatives into anatase TiO2 would greatly broaden the visible light response range and adjust the energy band positions of the composites, enhancing the sunlight utilization and promoting the photogenerated charge (e--h+) separation and transfer. Specifically, a series of results on the in situ EPR tests and the photo-electrophysical experiment indicate that the separated charges from the hybrid could effectively activate benzylamine and O2 to accelerate the formation of active intermediates, and then couple with free BA molecules to form the desired production of N-BBA. The effective combination, on a molecular scale, between fullerene and titanium dioxide has provided a profound understanding of the photocatalysis mechanism. This work elaborates and makes clear the relationship between the structure and the performance of functional photocatalysts.

Facile preparation of CuBi2O4/TiO2 hetero-systems employed for simulated solar-light selective oxidation of 4-methoxybenzyl alcohol model compound

The selective photocatalytic oxidation of organic substances is today considered one of the green techniques to synthesize important starting materials in different technological applications. This work reports an efficient, simple and cheap strategy for the synthesis of a new photocatalytic CuBi2O4-TiO2 (CBO/TiO2) heterosystem at room temperature. The prepared powders were characterized by X-ray diffraction (XRD), UV–Vis diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. The photocatalytic activity was evaluated by performing a probe reaction, namely the partial oxidation of 4-methoxybenzyl alcohol (4-MBA) to 4-methoxybenzaldehyde (4-MBAld) in aqueous solution under irradiation of simulated sunlight. The CBO/TiO2 coupled systems showed a higher photoactivity than the single photocatalysts reaching a selectivity of 45% towards 4‑methoxy-benzaldehyde with an alcohol conversion of 77% after 4 h of irradiation. Furthermore, although a high alcohol conversion was achieved, the selectivity towards 4-MBAld was significant, unlike what has been reported in the literature for many heterogeneous photocatalytic reactions whose selectivity generally decreases significantly with the increasing conversion of the starting alcohol molecule. The improved photocatalytic activity could be attributed to the partial coverage of the TiO2 surface by CBO which reduces the subsequent oxidation of the formed aldehyde.

Defects characteristic investigation of bismuth ferrite nanocrystallites through positron annihilation and supportive methods

Phase pure bismuth ferrite (BFO) nanocrystallites were synthesized by sol-gel method. The variation in the time of calcination at 600 °C is used as the parameter to vary the sizes of the nanocrystallites. X-ray diffraction and electron microscopic studies revealed the formation of BFO nanocrystallites of well-defined sizes and morphology. The elemental stoichiometric compositions of the samples were verified using energy dispersive analysis of X-rays and further by X-ray photoelectron spectroscopy. The UV–visible diffuse reflectance spectra showed strong absorption at the wavelength ∼556 nm (2.23 eV) for BFO nanocrystallites of dimensions 20 nm. For nanocrystallites of sizes smaller than this limit, the band gap energies showed remarkable increase due to the onset of quantum confinement effects. The band gap energies showed increase at larger crystallites sizes as well, indicating defects formation due to oxygen deficiencies. Positron annihilation spectroscopy is used to characterize and monitor the defects. The formation of Bi3+-O2- divacancies significantly altered the positron annihilation characteristics at larger crystallite sizes.