ZnO TiO2 Research Articles

Design and synthesis of TiO2/ZnO nanocomposite with enhanced oxygen vacancy: Better photocatalytic removal of MB dye under visible light-driven condition

• TiO 2 /ZnO nanocomposite was synthesized by a facile hydrothermal route. • C. verum leaf extract was utilized as a bio-reducing and templating agent. • TiO 2 /ZnO (0.5mol) exhibited superior photocatalytic activity against MB dye removal. • TiO 2 /ZnO increases surface oxygen vacancy supressing recombination of e - -h + pair. • Excellent catalytic performance is owing to controlled surface oxygen vacancy and small particle size. Construction of capable, affordable, transition metal-based catalysts featuring photocatalytic behaviour is urgently required and important. Herein, for the first time we have synthesized an eco-friendly, capsule shaped ZnO nanoparticles (NPs) anchored upon TiO 2 nanoplates, by utilizing bio-active components available in Cinnamon verum leaf extract. The bio-active components, linalool and phytol served as a self-reducing and gapping agent that enrich the surface with oxygen vacancy without disrupting lattice arrangement. The XRD results confirms presence of wurtzite ZnO, anatase and rutile TiO 2 NPs. Anatase TiO 2 with ZnO supress the electron-hole pair recombination effect. The delayed luminescence behaviour is consistent with the UV-DRS results and suggests that the band gap of TiO 2 /ZnO has been widened. SEM with EDX results justifies that TiO 2 /ZnO nanocomposite mounted oxygen vacancy in a controlled phenomenon, which can boost the separation efficacy of photogenerated carriers and is in good agreement with the PL results. Under visible light irradiation for 60 minutes, TiO 2 /ZnO significantly improves photocatalytic degradation for aqueous organic dye pollutants. The k value of the TiO 2 /ZnO (0.5 mol) nanocomposite is 2.5x10 -2 mint -1 which is comparably higher. The unusual nanoarchitecture, high surface area, and wide band gap of TiO 2 /ZnO are primarily responsible for its noticeably improved photodegradation performance.

TiO2/ZnO double-layer broadband antireflective and down-shifting coatings for solar applications

Making full use of sunlight in solar cells requires reducing the reflection of light and minimizing spectral mismatch. Here, a TiO2/ZnO double-layer coating with both wider band antireflection and down-shifting performance was prepared. TiO2 sols and ZnO nanoparticles were synthesized via the sol-gel method and then successively coated on the surface of the Si substrate by dip-coating. Computational simulations were used to obtain the optimal refractive index and thickness of the coatings. In the experiments, the thicknesses of the TiO2 and ZnO coatings were adjusted by changing the lifting speed, and the refractive index of the TiO2 and ZnO coatings were adjusted by adding the porosity inducing agent and varying the concentration of the solution. The TiO2/ZnO coating reduces the reflectivity of the silicon substrate by 24.97% in the 400–1100 nm band, and the ZnO nanoparticles can convert light at approximately 345 nm–527 nm, reducing the spectral mismatch of the solar cell. The photocurrent of solar cells coated with TiO2/ZnO coatings was markedly improved, with an increase of 29% in the average photocurrent at 300–800 nm. Herein, TiO2/ZnO coatings have the potential to benefit the development of multifunctional coatings that are important for improving the efficiency of solar cells.

UV photodegradation of textile dyes using TiO2–ZnO supported on banana peel activated carbon

UV photodegradation of textile dyes using TiO2–ZnO supported on banana peel activated carbon

Influence of TiO2 and ZnO Nanoparticles on α-Synuclein and β-Amyloid Aggregation and Formation of Protein Fibrils

The most common neurological disorders, i.e., Parkinson's disease (PD) and Alzheimer's disease (AD), are characterized by degeneration of cognitive functions due to the loss of neurons in the central nervous system. The aggregation of amyloid proteins is an important pathological feature of neurological disorders.The aggregation process involves a series of complex structural transitions from monomeric to the formation of fibrils. Despite its potential importance in understanding the pathobiology of PD and AD diseases, the details of the aggregation process are still unclear. Nanoparticles (NPs) absorbed by the human circulatory system can interact with amyloid proteins in the human brain and cause PD. In this work, we report the study of the interaction between TiO2 nanoparticles (TiO2-NPs) and ZnO nanoparticles (ZnO-NPs) on the aggregation kinetics of β-amyloid fragment 1-40 (βA) and α-synuclein protein using surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS). The characterizations of ZnO-NPs and TiO2-NPs were evaluated by X-ray diffraction (XRD) spectrum, atomic force microscopy (AFM), and UV-Vis spectroscopy. The interaction of nanoparticles with amyloid proteins was investigated by SERS. Our study showed that exposure of amyloid protein molecules to TiO2-NPs and ZnO-NPs after incubation at 37 °C caused morphological changes and stimulated aggregation and fibrillation. In addition, significant differences in the intensity and location of active Raman frequencies in the amide I domain were found. The principal component analysis (PCA) results show that the effect of NPs after incubation at 4 °C does not cause changes in βA structure.

Titanium Oxide and Zinc Oxide Nanoparticles in Combination with Cadmium Tolerant Bacillus pumilus Ameliorates the Cadmium Toxicity in Maize.

The efficiency of Cd-tolerant plant growth-promoting bacteria (PGPB), zinc oxide nanoparticles (ZnO NPs), and titanium dioxide nanoparticles (TiO2) in maize growing in Cd-rich conditions was tested in the current study. The best Cd-tolerant strain, Bacillus pumilus, exhibited plant growth stimulation in vivo and in vitro experiments. We determined the toxic concentrations (30 (ppm)) of both NPs for plant growth. B. pumilus, ZnO NPs (20 (ppm)), and TiO2 NPs (10 (ppm)) had a synergistic effect on plant growth promotion in Cd-contaminated soil (120 (ppm)) in a pot experiment. Both alone and in combination, these therapies reduced Cd toxicity, resulting in improved stress metabolism and defense responses. The combined treatments showed increased relative water content, photosynthetic pigments, proline, total sugars, and proteins and significantly reduced lipid peroxidation. Moreover, this combination increased the levels of minerals and antioxidants and reduced Cd bioaccumulation in shoots and roots by 40-60%. Our in silico pipeline presented a novel picture of the participation of ZnO-TiO2 protein interaction in both B. pumilus and maize. These findings provide fresh insights on the use of B. pumilus, ZnO, and TiO2 NPs, both separately and in combination, as a viable and environmentally benign strategy for reducing Cd stress in maize.

Pyro–catalytic co–pyrolysis of Delonix regia and butyl rubber tube: Kinetic modelling and thermodynamic insights

The target of the proposed work was to compute the kinetic modelling (KM) and thermodynamic insights (TI) for the pyro-catalytic co-pyrolysis (PCCP) of Delonix regia (DR) and Butyl rubber tube (BRT). For PCCP of DR and BRT (1:1 co-feed), three different types of catalysts were utilized: zeolite (Na–Y), noble metal on activated carbon (10 wt % Pt/C), and metal oxide (1:1 wt % TiO2–ZnO) catalysts of loading between 30 and 10 wt %. For computing KM and TI, several iso-conversional models such as Friedman (FM), Flynn–Wall– Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), Starink (STK), and Distributed Activation Energy Method (DAEM) were applied. At DR:BRT:Na-Y (1:1:10 wt %), the FWO model ascertained the lowest average values of activation energy Eα (kJ/mol) and pre-exponential factor A (s−1) as 180 and 5.95E+16, respectively whereas ΔH (kJ/mol) and ΔG (kJ/mol) as 175 and 180 for TI correspondingly.

Behavior of N-Doped TiO2 and N-Doped ZnO in Photocatalytic Azo Dye Degradation under UV and Visible Light Irradiation: A Preliminary Investigation

N-doped TiO2 (N-TiO2) and N-doped ZnO (N-ZnO) were synthesized utilizing ammonia as a dopant source. The chemico-physical characteristics of synthesized samples were studied by Raman spectroscopy, X-ray diffraction, SEM analysis, N2 adsorption–desorption at −196 °C, and diffuse reflectance spectroscopy. Compared to undoped samples, the introduction of nitrogen in the semiconductor lattice resulted in a shift of band-gap energy to a lower value: 3.0 eV for N-ZnO and 2.35 eV for N-TiO2. The photocatalysts were tested for the degradation of Eriochrome Black T (EBT), which was selected as a model azo dye. Both N-doped semiconductors evidenced an improvement in photocatalytic activity under visible light irradiation (62% and 20% EBT discoloration for N-TiO2 and N-ZnO, respectively) in comparison with the undoped samples, which were inactive in the presence of visible light. Different behavior was observed under UV irradiation. Whereas N-TiO2 was more photoactive than commercial undoped TiO2, the introduction of nitrogen in ZnO wurtzite resulted in a drastic reduction in photocatalytic activity, with only 45% EBT discoloration compared to total color removal obtained with the commercial ZnO sample, suggesting intrinsic limitations for doping of this class of semiconductors.

Stimulated generation of photobiogas by morphologically tuned nanostructured ZnO and ZnO/TiO2

The photocatalytic degradation (PCD) of ethanol in an inert atmosphere on catalysis was explored in a lab-scale experiment. A morphologically tuned nanostructured controlled ZnO and ZnO/TiO2 nanocomposites were synthesized using a simple hydrothermal process under the control of several functionally capping agents marking a milestone in photocatalysis. It is possible that this could be modified to produce photobiogas out of organic dye pollution. The photocatalysts were characterized by the use of X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer, Emmett, and Teller (BET) surface area analyzer, Scanning electron microscope (SEM-EDX), and UV–Vis absorption spectroscopy. The photocatalytic activity of the ZnO and ZnO–TiO2 composite nanostructures was evaluated for the photodegradation of the Tartrazine (Tr) dye aqueous solution. Where the composite matrix exhibits higher photocatalytic activity than pure ZnO nanomaterials as a result of the synergistic interaction between ZnO and TiO2 particles. This is mainly due to its higher surface area than pure ZnO. Moreover, the photocatalytic activity of the tuned nanostructured materials is found to be enhanced by the effect of the capping agent and controlling the morphology. This increase is accompanied by a significant shift in surface shape and band gap energy. According to the findings, the designed morphologies of pure ZnO photocatalyst impacted the formation of photobiogas from the photocatalytic decomposition of ethanol as a model of organic pollutants in wastewater. However, when using composite ZnO/TiO2 photocatalysts, the rate of CH4 formation is significantly lower than when using ZnO photocatalysts alone. This may be attributed to the synergetic effect between ZnO and TiO2 particles which leads to a remarkable reduction in the newly formed band gap energy. This may result in a fast rate of recombination between the photogenerated charge carriers (e− and h+).

Antagonistic Skin Toxicity of Co-Exposure to Physical Sunscreen Ingredients Zinc Oxide and Titanium Dioxide Nanoparticles.

Being the main components of physical sunscreens, zinc oxide nanoparticles (ZnO NPs) and titanium dioxide nanoparticles (TiO2 NPs) are often used together in different brands of sunscreen products with different proportions. With the broad use of cosmetics containing these nanoparticles (NPs), concerns regarding their joint skin toxicity are becoming more and more prominent. In this study, the co-exposure of these two NPs in human-derived keratinocytes (HaCaT) and the in vitro reconstructed human epidermis (RHE) model EpiSkin was performed to verify their joint skin effect. The results showed that ZnO NPs significantly inhibited cell proliferation and caused deoxyribonucleic acid (DNA) damage in a dose-dependent manner to HaCaT cells, which could be rescued with co-exposure to TiO2 NPs. Further mechanism studies revealed that TiO2 NPs restricted the cellular uptake of both aggregated ZnO NPs and non-aggregated ZnO NPs and meanwhile decreased the dissociation of Zn2+ from ZnO NPs. The reduced intracellular Zn2+ ultimately made TiO2 NPs perform an antagonistic effect on the cytotoxicity caused by ZnO NPs. Furthermore, these joint skin effects induced by NP mixtures were validated on the epidermal model EpiSkin. Taken together, the results of the current research contribute new insights for understanding the dermal toxicity produced by co-exposure of different NPs and provide a valuable reference for the development of formulas for the secure application of ZnO NPs and TiO2 NPs in sunscreen products.

Preparation, Absorption Spectra, and Luminescence Properties of Er2O3- and Yb2O3-Doped Oxyfluoride Glasses in the CaF2–SiO2–B2O3–Bi2O3–TiO2–ZnO–Y2O3 System

Preparation, Absorption Spectra, and Luminescence Properties of Er2O3- and Yb2O3-Doped Oxyfluoride Glasses in the CaF2–SiO2–B2O3–Bi2O3–TiO2–ZnO–Y2O3 System

A novel self-cleaning functional composite coating with extraordinary anti-corrosion performance in high pressure CO2 conditions

This study demonstrates an alternative method for fabricating a novel integrated anticorrosion self-cleaning functional coating using the GO nanosheets with the TiO2–ZnO heterostructure to effectively induce charge separation and to accomplish photoinduced hydrophilic conversion. Through ultraviolet light (UV) irradiation, the PFDTMS-modified filler transformed from hydrophobic to hydrophilic, while the fluorine groups on the surface of the filler still existed. Research of EIS shows that the impedance at 0.01 Hz of 20% F/T-Z-G Polyurea coating was about 1 × 103 times higher than polyurea coatings, after 24 h of immersion in 2.8 MPa, 110 °C pure CO2 and NaCl solution. The results demonstrate that F/T-Z improves the dispersion of GO and make the polyurea matrix denser, inhibiting the diffusion of corrosive medium. Additionally, the GO and fluorine groups strengthen the shielding performance of the coating. Moreover, the TiO2–ZnO heterojunction traps H2O molecules to form hydroxyl radicals (OH•). Simultaneously, Fe2+ and Fe3+ combine with OH• to form Fe3O4, and the passivation film was formed on the surface of steel. It is believed that this hydrophilic-hydrophobic integrated functional coating will be an excellent candidate for technological applications, such as anticorrosion, self-cleaning materials and composite coatings.

Evaluation of Effects of Titanium Dioxide and Zinc Oxide Nanoparticles on Baker’s Yeast (Saccharomyces cerevisiae) Glutathione Reductase Activities

The glutathione reductase (GR) of baker's yeast (Saccharomyces cerevisiae) was exposed to titanium dioxide nanoparticles (TiO2 NPs) and zinc oxide nanoparticles (ZnO NPs) at concentrations of 0, 25, 50, 100, 250, and 500mg/L (ppm) in vitro. According to the calculations, the effect of 25, 50, 100, 250, and 500mg/L TiO2 NPs on GR enzyme activities resulted in percentage changes of - 3.12; - 0.87; - 2.12; - 2.12, and - 1.50, respectively. Percentage changes in GR enzyme activities with the effect of 25, 50, 100, 250, and 500mg/L ZnO NPs were calculated as - 2.01; + 1.88; + 0.38; - 2.51, and + 0.75, respectively. It can be deduced from this research that the change in concentrations of TiO2 NPs and ZnO NPs has no statistically significant effect on GR enzyme activities in comparison with the control groups (p > 0.05, N = 3).

Photocatalytic degradation of methyl orange on ZnO–TiO2/SO42− heterojunction composites

ZnO–TiO2/SO42− (ZTOS) heterojunction composites were prepared by an inorganic precipitation-peptization method. It is found that the molar ratios of Zn : Ti have obvious influence on the ultraviolet (UV) light absorption and morphology of ZTOS. The results of photocatalytic characterizations indicate that the degradation rate of methyl orange on ZTOS (90.34%) is significantly higher than that of on the pure TiO2 (43.58%). In addition, the ZTOS can holds 97% photocatalytic activity after cyclic stability measurements. The remarkable improved performance obtained on ZTOS is attributed to the stronger UV light absorption, large specific surface area and effective charges separation caused by the heterojunction structure of ZnO–TiO2. Furthermore, the active species for the decomposition of methyl orange on ZTOS are proposed to be the photo-generated holes and radicals of ·O2−, ·OH and SO4−· formed during photo-induced reactions.

Building triple shelled ZnO hollow microspheres decorated TiO2 nanotree to boost light harvesting and reduced charges recombination in dye sensitized solar cell

It is well known that the microstructure of photoanode materials has direct influence on light harvesting and charges recombination in dye sensitized solar cells (DSSC). However, design of photoanode materials for efficient light harvesting and electron transport is still in challenge. Therefore, we developed a hierarchical microstructure of multi shelled ZnO hollow microspheres (MS ZnO HMS) decorated TiO2 nanotree (NT) for DSSCs application with aim to take advantages of enhanced light scattering and enlarged specific area offered by MS ZnO HMS and reduced charges recombination provide by TiO2 NT. The morphology, microstructure and crystalline of ZnO HMS and TiO2 NT have been characterized by SEM, TEM and XRD, confirming the successful building of MS ZnO HMS decorated TiO2 NT. I–V tests show that significant enhancement of short-circuit current density (Jsc) can be achieved by controlling shell numbers of MS ZnO HMS and combining MS ZnO HMS with TiO2 NT. As a result, the triple shelled ZnO HMS (TS ZnO HMS) decorated TiO2 NT (TS ZnO HMS/TiO2 NT) improve the power conversion efficiency (PCE) to 7.40%, which is 138% and 40% higher than DSSCs based on TiO2 NT (3.11%) and TS ZnO HMS (5.27%). IPCE, OCVD and EIS measurements indicate that the combination of TS ZnO HMS with TiO2 NT contribute to the improvement of light harvesting efficiency and prolonging of electron lifetime.

Study of the Interaction of Ti-Zn as a Mixed Oxide at Different pH Values Synthesized by the Sol-Gel Method and Its Antibacterial Properties.

TiO2, ZnO, and their combination (TiO2–ZnO) at different molar ratios and pH values (Ti–Zn A and B 3:1, 1:1, and 1:3) via the sol–gel method were characterized by SEM, XRD, UV-Vis, and FT-IR. Moreover, antibacterial tests of the nanoparticles were conducted against Escherichia coli (E. coli), Salmonella paratyphi (S. paratyphi), Staphylococcus aureus (S. aureus), and Listeria monocytogenes (L. monocytogenes). The indirect bandgap of the Ti–Zn binary oxide synthesized in the basic process at molar ratios of 3:1, 1:1, and 1:3 exhibited a higher eV (3.31, 3.30, and 3.19 eV, respectively) compared to pure TiO2 (3.2 eV) and synthesized in the acid process (3.22, 3.29, and 3.19 eV at same molar ratio, respectively); in addition, the results of the indirect bandgap were interesting due to a difference found by other authors. Moreover, the sol–gel method promoted the formation of a spherical, semi-sphere, and semi-hexagonal shape (TiO2, Ti–Zn 1:1, and Ti–Zn 1:3) with a size ≤ 150 nm synthesized during the acid process, with a crystallite size of ~71, ~12, ~34, and ~21 nm, respectively, while ZnO NPs developed a hexagonal and large size (200–800 nm) under the same synthesis process (acid). Samples were classified as TiO2 anatase phase (basic synthesis); however, the presented changes developed in the rutile phase (24% rutile phase) at an acid pH during the synthesis process. Moreover, Ti–Zn maintained the anatase phase even with a molar ratio of 1:3. The most interesting assessment was the antibacterial test; the Ti–Zn A (1:3) demonstrated a bacteriostatic effect compared with all treatments except ZnO, which showed a similar effect in dark conditions, and only Gram-positive bacteria were susceptible (Listeria monocytogenes > Staphylococcus aureus). Therefore, the Ti–Zn characteristic suggests that the results have potential in treating wastewater as well as in pharmaceutical (as drug carriers) and medical applications.

Stability, aggregation, and sedimentation behaviors of typical nano metal oxide particles in aqueous environment

The wide use of nano metal oxide particles (NMOPs) brings about their inevitable release into the water environment, affecting the environment and human health. Therefore, the stability, aggregation, and sedimentation process of four typical NMOPs (ZnO NPs, CeO2 NPs, TiO2 NPs, and CuO NPs) were investigated in artificial water and real municipal sewage to reveal their complicated behavior. Results showed that NMOPs aggregated at the pH of zero-charge point, and their hydrodynamic diameters and aggregation rates could reach the maximum values. The hydrodynamic diameters and aggregation rates of ZnO NPs, CeO2 NPs, TiO2 NPs, and CuO NPs at the zero-charge point were 617, 1760, 870, 1502 nm, and 31.7, 1158.1, 48.3, 115.7 nm/min, respectively. In addition, the dissolution of NMOPs led to the sedimentation rates under acidic conditions being much lower than those under neutral and alkaline conditions. The aggregation and sedimentation performance of NMOPs were affected by not only pH but also ionic strength (IS) and species. The aggregation rates of NMOPs increased with the increase of IS (0–10 mM), and the maximum aggregation rate of CeO2 NPs was 470.1 nm/min (pH = 7 and CaCl2 = 10 mM). According to Coulomb's law, divalent cations (Mg2+, Ca2+) were more competitively adsorbed on the surface of NMOPs than monovalent cations (K+, Na+), which increased the zeta potential and aggregation rate of NMOPs. Furthermore, the NMOPs were easier to aggregate in municipal sewage because of the homogeneous aggregation between nanoparticles and heterogeneous aggregation with natural colloids. The total interaction energy between NMOPs was calculated by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theoretical formula, which was consistent with the experimental results.

Q-switched fiber laser using a polysulfone membrane enhanced with biosynthesized zinc oxide and titanium dioxide nanoparticles for use as saturable absorber

We presented the polysulfone membrane enhanced with zinc oxide and titanium dioxide (Psf membrane ZnO TiO2) saturable absorber (SA) to induce passively Q-switched erbium-doped fiber laser (EDFL). The Psf membrane ZnO TiO2 was synthesized by the phase inversion technique. To obtain the Psf membrane ZnO TiO2 as a SA, the SA was deposited on the fiber ferrule through a simple exfoliation technique. The modulation depth of the Psf membrane ZnO TiO2 SA was 1.06%, with a saturation intensity of 0.0006 MW cm−2. Stable Q-switched pulses were generated at 1572 nm with a threshold pump power of 59.80 mW after inserting the prepared Psf membrane ZnO TiO2 into the EDFL ring cavity. As the pump power ranges from 59.80 mW to 165.50 mW, the repetition rate increases from 13.05 to 22.61 kHz, while the pulse duration decreases from 76.60 to 44.23 µs. When the pump power reaches a maximum power of 165.50 mW, the corresponding pulse energy and optical signal-to-noise ratio are 19.00 nJ and 61.27 dB, respectively. To our best knowledge, this is the first research utilizing Psf membrane ZnO TiO2 as SA to generate Q-switched pulses. Our research work addresses a new reference for the generation of pulsed laser using Psf membrane ZnO TiO2 and discovers that it has numerous applications in nonlinear optics and ultrafast laser technology, which significantly broadens the barrier of materials for the ultrafast laser techniques.

Density Functional Theory Study and Photocatalytic Activity of ZnO/N-Doped TiO2 Heterojunctions

The beneficial effects on ZnO and TiO2 photocatalytic activity resulting from a suitable combination of doping and heterojunctions were proposed and investigated by a synergistic experimental and theoretical study. In detail, the ZnO/N-doped TiO2 heterojunction was synthesized and tested in the photocatalytic degradation of atrazine under UV and visible light. Wide-angle X-ray diffraction (WAXD) analysis reveals the presence of both ZnO and TiO2 crystalline phases in the heterojunction. UV–vis DRS analysis shows that the simultaneous presence of ZnO and N-doped TiO2 in the heterojunction results in a slight increase in the band gap value in the UV region , while the shoulder in the visible region typically of bare N-doped TiO2 is preserved. On the basis of these experimental observations, density functional theory (DFT) calculations were carried out to model both the N-doped TiO2 structure and to rationalize the experimental decrease in the band gap energy. The DFT modeling of band alignment of the ZnO/N-doped TiO2 heterojunction allowed us to define the “minimal band gap” (MBG), corresponding to the interface gap, which resulted in smaller band gap energy than the two separate semiconductor band gaps. Furthermore, the DFT modeling of the electronic structure of N-doped TiO2 predicted the existence of additional energy levels between the TiO2 valence and conduction bands, which allowed us to justify the activity of the heterojunction under visible light irradiation. Photocatalytic tests showed that the ZnO/N-doped TiO2 heterojunction performance was better than that of both N-doped TiO2 and ZnO alone, allowing us to achieve almost complete atrazine degradation under UV light irradiation, whereas 24% of atrazine degradation was achieved after 180 min of visible light irradiation. Finally, the photocatalytic results achieved by using scavenger molecules for reactive oxygen species showed that ·OH and ·O2– are both reactive species in atrazine photocatalytic degradation under UV irradiation, while ·OH is responsible for the photocatalytic processes under visible irradiation. DFT modeling, validated by these results, finally allowed us to define a model of the band alignment and photogenerated charge-transfer mechanism for the ZnO/N-doped TiO2 heterojunction.

Preparation and characterization of MnIn-layered double hydroxides (LDHs), extension of the synthesis to fabricate MnM(III)-LDHs (M = Al, Sc, Cr, Fe, Ga), and the comparison of their photocatalytic and catalytic activities in the oxidation of hydroquinone

The preparation of a new member of the hydrotalcite supergroup, i.e., MnIn-LDHs with Mn:In molar ratios from 5:2 to 8:2 was developed for the first time, by using the co-precipitation technique. The effect of the presence of air, N2 or H2 was systematically tested. The physico-chemical properties of the solids were characterized in detail. The application of reductive atmosphere proved to be vital for achieving phase-pure products. While the thermal behavior of the LDHs with different Mn:In molar ratios were largely similar, the increasing Mn:In ratio resulted in decreasing direct optical band gaps from 4.06 to 3.14 eV. By using the optimized conditions found for MnIn-LDHs, Mn4M(III)-LDHs were also prepared with M = Al, Sc, Cr, Fe, Ga. The catalytic performance of the various Mn(II)-based LDHs were tested under dark and UV–Vis-illuminated conditions for the transformation of hydroquinone in acetonitrile medium. The photocatalytic mechanism over MnIn-LDHs was studied by radical trapping tests, indicating the photogenerated holes play an important role in the decomposition of hydroquinone and even benzoquinone. The incorporation of Sc(III), Cr(III) and Fe(III) resulted in catalysts with outstanding performance both with and without illumination; under these conditions several metal oxides/semiconductors (like BiVO4, Bi2WO6, SrTiO3, Bi2O3, SnO2, WO3, In2O3, ZnO and Degussa P25 TiO2) and even the nonmetallic g-C3N4 proved to be inactive. The largest photocatalytic contributions were measured for the Mn4Cr- and Mn4In-LDHs. The selectivity and yield of the benzoquinone formation was found to be the largest in the case of the Mn4Al-, Mn4Fe- and Mn4In-LDHs using UV–Vis light source.

Preparation and characterization of N-doped ZnO and N-doped TiO2 beads for photocatalytic degradation of phenol and ammonia

N-doped ZnO beads (NZB) and N-doped TiO2 beads (NTB) were synthesized via a modified sol–gel technique utilizing chitosan (CS)/polyvinyl alcohol (PVA) hydrogel beads as basic support for photocatalyst. Urea was used as a source of nitrogen in the preparation of N-doped ZnO beads, while ammonium acetate, CH3COONH4, was used as a nitrogen source in the production of N-doped TiO2 beads. The characteristics of synthesized beads were identified by scanning electron microscope (SEM), X-ray photoelectron spectroscopy analysis (XPS), X-ray diffraction (XRD), N2 adsorption–desorption isotherms, BET surface area, Fourier transform infrared (FT-IR) measurements, and diffuse reflectance spectroscopy (DRS) studies. The use of the nitrogen doping method for photocatalyst was performed to adjust the bandgap and electrical properties of ZnO and TiO2 by establishing acceptor defects. NZB and NTB with the intrinsic donor defect of oxygen vacancy and the nitrogen-to-oxygen acceptor defect could be activated by a less-energy UV consumption for efficient pollutant degradation. The results indicated that the as-synthesized NZB achieved much higher degradation activity than NTB, commercial ZnO, and TiO2 in the decomposition of a binary mixture composed of ammonia and phenol under UV light irradiation.