Papers by Keyword: Photocatalytic Activity

Abstract: This work demonstrates the successful preparation of two types of photocatalytically active nanostructured materials from an industrial waste product – Sal Ammonia Skimming – using hydrochloric acid as a leaching medium. The whole production process was developed to prepare valuable ZnO nanomaterials in both fibrous and powdered forms. This involved a sequence of hydrometallurgical processing, needle-less electrospinning, and conventional calcination of recycled environmentally polluting industrial waste. The morphologies and phase composition of the resulting ZnO powder and ZnO fibers were analyzed using SEM, EDS, and XRD analyses. The impact of the morphology of the prepared nanomaterials on the photocatalytic efficiency of the ZnO-based photocatalyst – powder versus ZnO nanofibers – was evaluated through decolorization experiments of the commonly used methylene blue dye in batch mode. Methylene blue was chosen as a model substance for toxic industrial pollutants. A 25 W UVA lamp with an emission maximum at 365 nm was used as a light source. Removal efficiencies were carefully tested and compared for different nanomaterial morphologies and preparation conditions. The most photocatalytically active ZnO-based nanomaterial was the electrospun nanofibrous one calcined at 600 °C for 1 h. This material achieved 100 % removal of a 10⁻⁵ mol/L methylene blue dye from the solution within 700 minutes at an increased catalyst-to-dye ratio of 500 mg/50 ml. Based on the obtained results, it can be stated that the prepared materials exhibit high photocatalytic activity under UV light irradiation and have a potential for photocatalytic water remediation applications.

Abstract: Nanostructured titanium dioxide (TiO₂) was synthesized via a hydrothermal method to enhance photocatalytic degradation of organic and pharmaceutical contaminants in wastewater. Characterization techniques confirmed the formation of anatase-phase TiO₂ with a tetragonal structure, spherical morphology, and an average crystallite size of 29 nm. The material exhibited a band gap of 3.1 eV. The TiO₂ solution has proven to be very effective in accelerating the breakdown of pharmaceutical and organic contaminants in wastewater, as evidenced by several methods, including high-performance liquid chromatography (HPLC) and Gas chromatography (GC). Photocatalytic performance was evaluated under varying catalyst concentrations and pH levels. Optimal degradation efficiency (72%) was achieved at pH 10, demonstrating TiO₂'s potential as an effective photocatalyst for wastewater treatment.

Abstract: In this study, zinc dross (ZD) was used as precursor to prepare hematite/zinc oxide (Fe₂O₃/ZnO) nanocomposites with bacterial cellulose (BC) as catalyst support to prevent agglomeration of the obtained Fe₂O₃/ZnO. pH during the dissolution process of ZD was varied at 4.2 and 5.5 (namely ZD4 and ZD5, respectively) to know the effect of pH on the formation of Fe₂O₃/ZnO/BC. As comparison, Fe₂O₃/ZnO from its pure precursor was also prepared with the same pH and Zn concentration of ZD4 and ZD5 (namely ZF4 and ZF5, respectively). Atomic absorption spectroscopy (AAS) results showed that Zn and Fe content in ZD4 sample (42,059 and 8,615 ppm, respectively) are higher than Zn and Fe content in ZD5 sample (25,554 and 2,204 ppm, respectively). X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) results of all samples confirmed the successful synthesis and deposition of Fe₂O₃/ZnO on BC. Scanning electron microscope (SEM) results revealed that the average particle size of Fe₂O₃/ZnO/BC samples at pH 5.5 (341 nm for ZD5 and 385 nm for ZF5 samples respectively) are slightly smaller than samples at pH 4.2 (418 nm for ZD4 and 426 nm for ZF4 samples respectively). Photocatalytic activities results showed that Fe₂O₃/ZnO/BC samples at pH 5.5 (45.7% for ZD5 and 57.9% for ZF5 samples respectively) have slightly higher activity than samples at pH 4.2 (38.1% for ZD4 and 41.9% for ZF4 samples respectively). These findings demonstrate the potential use of ZD and suggest that dissolution of ZD at pH 5.5 led to smaller particles size and higher photocatalytic activity than pH 4.2.

Abstract: rGO/Fe₃O₄ nanocomposites were prepared through the solid-state technique by adjusting FeCl₂ and FeCl₃ volumes (1, 2, 3, 4, and 5 ml). The structural, chemical, morphological, and optical properties of the nanocomposites were investigated using XRD, FTIR, SEM, and UV-Vis Spectroscopy. The synthesized rGO/Fe₃O₄ nanocomposite was deposited on an FTO substrate through drop coating to fabricate a CE plate, which was then tested using a solar simulator with FTO/TiO₂ serving as the photoanode. The XRD patterns of the rGO/Fe₃O₄ nanocomposite showed consistency with COD data number 3000327. Calculations using Debye's Scherrer equation demonstrated that Fe₃O₄ crystal size diminished as Fe₃O₄ concentration increased. The FTIR analysis confirmed the existence of C=C and Fe-O bonds, characteristic of rGO and Fe₃O₄ particles' functional groups. As FeCl₂ and FeCl₃ concentrations increased from 1 ml to 5 ml, the band gap energy of the rGO/Fe₃O₄ nanocomposite expanded from 3.14 eV to 3.39 eV. This band gap energy expansion correlated with improved DSSC solar cell performance, with efficiency increasing from 0.003% (RF1) to 0.097% (RF5), suggesting catalytic activity supporting electrolyte regeneration in DSSC solar cells.

Abstract: Utilising an uncomplicated, environmentally friendly strategy to synthesise nanoparticles presents a prospective substitute for dangerous chemical and expensive physical techniques. Therefore, this study was initiated with the objectives of synthesising Co₃O₄ nanoparticles using a facile green route and evaluating their magnetic properties and photocatalytic activities. Spherical Co₃O₄ nanoparticles with dimensions ranging from 8 to 32 nm were successfully produced using garlic extract. Magnetic analysis revealed weak ferromagnetism at low temperatures, with a coercive field of 14×10^-4 T. This low-temperature weak ferromagnetism may be attributed to uncompensated surface spins that form a short-range ordered cluster of spins. However, inside the sample, an antiferromagnetic exchange interaction occurs between non-magnetic tetrahedral Co²⁺ ions and magnetic octahedral Co³⁺ ions. Consequently, an exchange bias field of approximately 8.76 ×10^-4 T was observed. Above the Néel temperature, the thermal energy overcomes the antiferromagnetic ordering, resulting in paramagnetic behaviour at room temperature. Furthermore, the photocatalytic activity of the green synthesised Co₃O₄ nanoparticles demonstrated 55% degradation of methyl orange (MO) dye within 90 minutes. However, more efficient degradation (63% degradation within 90 minutes) of MO was achieved in the presence of a small amount of NaBH₄, which typically functions as a source of electrons to enhance the degradation rate. The photocatalytic (dye degradation) activity of these green synthesised room temperature paramagnetic Co₃O₄ nanoparticles could be applicable for water purification processes.

Abstract: In this study, zinc oxide (ZnO) and copper-doped zinc oxide nanoparticles (Cu-ZnO NPs) were synthesized using a green method that employed Rosmarinus officinalis leaf extract as a reducing agent. Copper was incorporated as a dopant at concentrations of 3% and 5%. Zinc acetate dihydrate and copper acetate served as the precursors and dopants, respectively. The synthesized samples were characterized utilizing a range of techniques, including XRD, SEM, EDX, Raman spectroscopy, UV-visible spectroscopy, and PL spectroscopy. XRD and Raman spectroscopy analyses validated the effective incorporation of Cu²⁺ ions into the ZnO wurtzite structure. SEM analysis indicated that the nanoparticles displayed a spherical morphology, while EDX analysis confirmed the presence of zinc (Zn), copper (Cu), and oxygen (O), thereby validating the sample's purity. UV-visible spectra revealed a reduction in the optical band gap with increasing Cu concentration. Photoluminescence peaks observed at 383 nm and 565 nm were ascribed to electron transitions from deep donor levels, particularly from Zn interstitials to Zn and oxygen vacancies. The 5% Cu-doped ZnO NPs demonstrated the highest photocatalytic activity, achieving 90% degradation of Rhodamine B (RhB) dye under UV irradiation in 135 minutes. They also exhibited significant antibacterial activity, particularly against Gram-positive bacteria (Staphylococcus aureus) compared to Gram-negative bacteria (Escherichia coli).

Abstract: Zinc oxide (ZnO) thin films have attracted considerable attention due to their versatile applications in optoelectronic devices, transparent electrodes and surface acoustic wave devices. In particular, their photocatalytic properties make them interesting for wastewater treatment. In this study, we investigate the influence of substrate and film thickness on the structure and photocatalytic activity of ZnO thin films prepared by atomic layer deposition (ALD). The photocatalytic activity of ZnO films on Si, glass, Al, and porous Al substrates was investigated under UV irradiation, focusing on the decomposition of methylene blue (MB) as a model for an organic pollutant. To understand the mechanism of photodegradation, detailed information on the morphology of the nanostructured ZnO surface and the surface chemistry was obtained by scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). We have shown that the photocatalytic activity depends on ZnO film thickness and that it reaches saturation at a film thickness of about 20 nm, independent of the substrate. Furthermore, we compared the photocatalytic activity of ZnO films on flat substrates and porous aluminum (prepared by electrochemical anodization) at an optimal film thickness of 20 nm. Our results show that the ZnO thin film on porous aluminum has a significantly higher photocatalytic activity. After 300 minutes of UV lamp exposure, the ZnO thin film deposited on flat aluminum demonstrated the least photocatalytic activity, leading to a reduction of approximately 35% in the concentration of the MB solution. In contrast, the ZnO film coated on a porous anodic aluminum substrate exhibited the highest photocatalytic efficiency, with a reduction in the MB solution concentration by approximately 85%.

Abstract: Photocatalytic technology is one of the promising technologies for wastewater treatment. Herein, zinc oxide/multi-walled carbon nanotubes (ZnO/CNTs) photocatalyst was successfully prepared by hydrothermal method with combining in-situ synthesis technology. The micro-morphology, crystalline structure, surface chemical elements, and optical properties were characterized by SEM, TEM, XRD, FTIR, UV-Vis, and DRS technologies. The ZnO/CNTs photo-catalyst exhibited enhancement photo activity for degradation of organic pollutants under simulated light irradiation. Specifically, the photo-catalytic activity of the ZnO/CNTs catalysts improved with the rise of CNTs content in the composites. Investigation on the photo-degradation mechanism verified that the presence of CNTs in the catalyst not only optimized the band structure of ZnO semiconductor but also contributed to the transfer of photo-generated electrons and reducing the recombination of electron-hole pairs due to its excellent conductivity. Moreover, the active radical groups such as superoxide radical (O-2), hole (h⁺), and hydroxyl radical (·OH) played the dominated role for the pollutants degradation under the simulated sunlight irradiation. In addition, ZCT20 catalysts and light irradiation had synergistic effects on antibacterial activity, whose antibacterial rates against E. coli and S. aureus were up to 99.96% and 99.94%, respectively. Investigation on antibacterial mechanisms revealed that the existence of ROS and the continuous release of Zn²⁺ played an important role for improving the antibacterial activity of the ZCT20 catalyst under the simulated sunlight irradiation.

Abstract: Mixed oxide of titanium dioxide was synthesized by adding SnO₂ and CeO₂ through a precipitation method for the degradation of methylene blue (MB) under visible light. The as-prepared was dried and calcined at various temperatures, i.e. 450-750 °C. The calcined products were characterized by XRD, DRUV, and FTIR. The effect of calcination temperature was studied on the photodegradation of MB under visible light. The photocatalytic activity showed that calcined photocatalytic at 650 °C shows the lowest bandgap energy and the highest photocatalytic activity in the decomposition of methylene blue under visible light.

Abstract: This paper reports on the successful synthesis of fine nanoparticles of nickel-substituted lithium-iron ferrites of composition Li_0.5-x/2Ni_xFe_2.5-x/2O₄ (0.2≤ x ≤1.0) by the sol-gel autocombustion method. It has been found that the alternating current (AC) and direct current (DC) conductivity is preferably tuned due to its dependence on temperature and nickel doping. Analysis of the Arrhenius dependences also confirms the appearance of more than one conduction mechanism upon substitution. The predominance of one type of conductivity over another depends on the concentration of the substituting element. Measurement of the magnetic properties has shown that the substitution of Ni²⁺ can significantly change the saturation and residual magnetization. Samples of composition Li_0.4Ni_0.2Fe_2.4O₄ have the highest saturation magnetization (84.08 emu/g), residual magnetization (15.85 emu/g), and the lowest coercive force (0.18 kOe). All the obtained results indicate a significant effect of the substitution of Ni²⁺ ions on the structure and properties of Li_0.5-x/2Ni_xFe_2.5-x/2O₄ ferrite nanoparticles.Photocatalytic properties have been obtained by the degradation of Methylene Blue dye under illumination with a halogen lamp. It is shown that an increase in the content of nickel ions leads to a change in the type of conductivity: from n-type (unsubstituted lithium pentaferrite) to p-type (with substitution x = 0.8 and higher). These systems are characterized by hopping conduction realized by octa-positions according to the mechanisms Fe³⁺+e^-↔Fe²⁺, and Ni³⁺↔Ni²⁺+h⁺. The predominance of one or another mechanism depends on the content of nickel ions. The optical band gap ranges from 1.4 to 2.25 eV. Samples with nickel content x = 0.4 and x = 0.8 have shown the best degradation ability, which is 97% within 160 min for Methylene Blue.