Photoluminescence Emission Spectroscopy Research Articles

Single ZnO Nanowire for Electrical and Optical NO2 Gas Sensing: Origin of Reversible and Irreversible Gas Effects Investigated by Photoluminescence Spectroscopy.

In this work, the gas sensing properties of a single ZnO nanowire (NW) are investigated, simultaneously in terms of photoluminescence (PL) and photocurrent (PC) response to NO2 gas, with the purpose of giving new insights on the gas sensing mechanism of a single 1D ZnO nanostructure. A single ZnO NW sensing device was fabricated, characterized, and compared with a sample made of bundles of ZnO NWs. UV near-band-edge PL emission spectroscopy was carried out at room temperature and by lowering the temperature down to 77 K, which allows detection of resolved PL peaks related to different excitonic transition regions. Surface effects were observed in PL maps, considering different nano and microstructures. Electrical and optical measurements were acquired at the same time during the NO2 gas exposure, allowing for the comparison of PL and PC response times and signal recovery. During NO2 gas desorption, irreversible behavior in the surface-related and donor-acceptor pair (DAP) regions is interpreted as the effect of an initial transient when electronic transfer from the gas molecules to the bulk occurs through the ZnO NW surface which acts as a channel. To the best of our knowledge, this is the first work which investigates the simultaneous PL optical and PC electrical response signals of a single ZnO NW to gas exposure.

A novel luminescent material with good luminescent thermal stability

In this study, we co-doped Mn4+ and Yb3+ into double perovskite K0.5La0.5SrMgWO6 to prepare a new phosphor. The structure and luminescent properties of the material were characterized by powder X-ray diffraction (XRD) and photoluminescence excitation (PLE) and emission (PL) spectroscopy. Under near-ultraviolet (n-UV) excitation, Mn4+- Yb3+ co-doped samples exhibited strong FR emission (600–800 nm) and Yb3+ near-infrared emission (900–1150 nm). Studied the energy transfer process from Mn4+ to Yb3+ in K0.5La0.5SrMgWO6: 1.5%Mn4+/1.5%Yb3+. In addition, K0.5La0.5SrMgWO6: 1.5%Mn4+/1.5%Yb3+ exhibits good thermal stability, maintaining a comprehensive fluorescence intensity of 98.37 % at 100 °C compared to 25 °C. These results indicate that the newly synthesized K0.5La0.5SrMgWO6: 1.5%Mn4+/1.5%Yb3+ phosphor has potential application prospects.

Band-gap tuning in Mn-doped Er2Ti2O7: Insight from the experimental and theoretical approach

We report the studies of electronic and optical properties of Er2Ti2−xMnxO7 (x = 0, 0.1, & 0.2) through combined theoretical insights from density functional theory (DFT) calculations and experimental approaches, including ultraviolet-visible absorption, photoluminescence emission spectroscopy, and Raman spectroscopy. For quantitatively correct optical bandgaps through DFT calculations, we considered the LDA-1/2 technique for the exchange-correlation interactions. The energy bandgap values obtained using theoretical formulations are in close accordance with the experimental results. The bandgap value obtained using the LDA-1/2 approach indicates the insulated ground state of the Er2Ti2−xMnxO7 (x = 0, 0.1, & 0.2) system. The band gap value obtained experimentally reduces from 3.82 eV to 2.45 eV as the level of Mn doping increases from 0 to 0.2. This reduction in the experimental band gap is attributed to the fact that inclusion of Mn atoms into the crystal lattice alters the electronic structure of the system. Substituting the Mn atom introduces additional electronic states within the band structure, leading to a modification of the band gap. Crystallographic data indicates that inclusion of Mn reduces the Ti-O bond length as in indicated in the table which reduces to 1.939(0) Å for x = 0.2 from 1.947(0) Å for x = 0. This results in the reduction of the extent of hybridization between O-2p and Ti-3d states, thereby reducing the band gap.

Structural and Spectroscopic properties of Eu3+ doped SiO2–TiO2 nanoparticles for photonic applications

The Eu3+-doped TiO2 nanoparticles in sol gel silicate glasses of composition (80-x)SiO2 + 20TiO2 + 0.5xEu2O3, (SiTiEu) where x = 0.0 0.5, 1.5, 2.5 and 3.5 mol%, have been prepared by sol-gel technique. The glass samples were investigated by thermos-gravimetric analysis (TGA/DTA), ATR-FTIR, XRD, SEM, TEM, EDX, optical absorption and photoluminescence emission spectroscopy at room temperature (RT). The absorption wavelength of TiO2 doped sol-gel silicate glass were red shifted due to a reduction in band gap energy with increasing annealing temperatures. According to the TEM images, all of the particles were spherical and had an average diameter is around 10 nm. The visible spectra of the Eu3+ doped TiO2 nanoparticles in sol-gel silicate glasses displayed characteristic PL emission 5D0→7FJ (J = 0, 1, 2, 3, 4, 5) transitions of Eu3+ ions at 370 nm excitation. The anatase TiO2:1.5Eu3+ nanocomposite showed high photoluminescence emission at 370 nm excitation, which was attributed to the f-f transitions of Eu3+. The hypersensitive 5D0→7F2 transition was responsible for the major red emission. From the recorded spectra, radiative parameters and Judd-Ofelt (JO) intensity parameters were computed. The Eu3+ co-doped TiO2 nanoparticles in sol-gel silicate glasses displayed emissions mostly in the red regions realized from a CIE chromaticity diagram. The results suggested that materials may be used as an optical material of technological importance such as display devices and also for optical amplifier.

Fingerprinting Defects in Hexagonal Boron Nitride via Multi‐Phonon Excitation

AbstractSingle photon emitters in hexagonal boron nitride (hBN) have gathered a lot of attention due to their favorable emission properties and the manifold of possible applications. Despite extensive scientific effort, the exact atomic origin of these emitters has remained unknown thus far. Recently, several studies have tied the emission in the yellow spectral region to carbon‐related defects, but the exact atomic structure of the defects remains elusive. In this study, photoluminescence emission and excitation spectroscopy is performed on a large number of emitters within this region. By comparing the experimental data with theoretical predictions, the origin of yellow single photon emission in hexagonal boron nitride is determined. Knowledge of this atomic structure and its optical properties is crucial for the reliable implementation of these emitters in quantum technologies.

Carbon-related donor–acceptor pair transition in the infrared in h-BN

Experimental studies of intentionally doped impurities for the understanding of conductivity control in hexagonal boron nitride (h-BN) ultrawide bandgap (UWBG) semiconductor are limited but are highly desired for emerging applications of h-BN. We report synthesis by hydride vapor phase epitaxy and comparison photoluminescence (PL) emission spectroscopy studies of intentionally carbon (C)-doped and undoped h-BN semi-bulk crystals. In addition to the well-known C-related emission lines observed previously, a C-impurity-related transition near 1.31 eV consisting of multiple phonon replicas has been observed in C-doped h-BN at room temperature. Phonon replicas involved in the 1.31 eV emission have been identified using polarization resolve PL spectroscopy as the transverse acoustic (TA)/longitudinal acoustic (LA) and out-of-plane optical phonon (ZO) modes at the middle point, T, between the Γ- and K-points in the first Brillouin zone. Based on the agreement between the spectral peak position of the observed dominant emission line at 1.31 eV and the calculated energy-level separation between CB donor (carbon replacing boron) and Ci acceptor (carbon interstitial), the observed IR emission line can be decisively assigned to the donor–acceptor pair (DAP) transition involving the CB donor and Ci acceptor assisted by the intervalley (Κ → Μ) scattering processes. The results reinforce the perception that C impurities form deep-level centers and provided an improved understanding of C impurities in h-BN.

Efficient photocatalytic degradation of textile dye pollutants using thermally exfoliated graphitic carbon nitride (TE–g–C3N4)

Graphitic carbon nitride (g–C3N4), an organic photocatalyst was reported to have beneficial properties to be used in wastewater treatment applications. However, g–C3N4, in its bulk form was found to have poor photocatalytic degradation efficiency due to its inherent limitations such as poor specific surface area and fast electron–hole pair recombination rate. In this study, we have tuned the physiochemical properties of bulk g–C3N4 by direct thermal exfoliation (TE–g–C3N4) and examined their photocatalytic degradation efficiency against abundant textile dyes such as methylene blue (MB), methyl orange (MO), and rhodamine B (RhB). The degradation efficiencies for MB, MO, and RhB dyes are 92 ± 0.18%, 93 ± 0.31%, and 95 ± 0.4% respectively in 60 min of UV light irradiation. The degradation efficiency increased with an increase in the exfoliation temperature. The prepared catalysts were characterized using FTIR, XRD, FE-SEM, EDAX, BET, and UV-DRS. In BET analysis, TE–g–C3N4 samples showed improved surface area (48.20 m2/g) when compared to the bulk g–C3N4 (5.03 m2/g). Further, the TE–g–C3N4 had 2.98 times higher adsorption efficiency than the bulk ones. The free radicals scavenging studies revealed that the superoxide radicals played an important role in the photodegradation for dyes, when compared to the hydroxyl radical (.OH) and the photo-induced holes (h+), Photoluminescence (PL) emission and electrochemical impedance spectroscopy (EIS) spectra of TE–g–C3N4 indicated a lowered electron–hole pairs’ recombination rate and an increased photo-induced charge transfer respectively. Further, the TE–g–C3N4 were found to have excellent stability for up to 5 cycles with only a minor decrease in the activity from 92% to 86.2%. These findings proved that TE–g–C3N4 was an excellent photocatalyst for the removal and degradation of textile dyes from wastewater.

Water pollution remediation: Synthesis and characterization of poly(o‐methylaniline)/ZnO/rGO composite for photocatalytic degradation of dyes

AbstractWater pollution is growing at an alarming rate, particularly due to the colored wastewater released by the various industries into aquifers and fresh water sources, and in some extreme cases, they have reached the water table. Faisalabad, a city in Pakistan where there is an industrial cluster of textiles dyeing and manufacturers, water table has become undrinkable. The presence of hazardous dyes and chemicals imposes serious health issues on humans, animals, and plants. The treatment of such toxic dye effluents is crucial and could be done by efficient degradation methods such as photocatalysis. The current study presents synthesis of poly(o‐methylaniline)/zinc oxide/reduced graphene oxide nanocomposite (POMA/ZnO/rGO NC) using a chemical oxidative polymerization process and explores its properties as a photocatalyst by demonstrating degradation of three dyes. The composite was characterized using X‐ray diffraction (XRD), Fourier‐transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), photoluminescence emission spectroscopy (PL), Brunauer Emmett–Teller analysis (BET), and UV–visible spectroscopy (UV–visible). Further, the photocatalytic activity of POMA/ZnO/rGO NC was evaluated and compared by degrading the direct yellow 12 (DY 12), congo red (CR), and malachite green (MG) dyes in aqueous media under UV irradiation. The results indicated that after 110 min, POMA/ZnO/rGO composite degraded the dyes by 92% (DY 12), 86.1% (CR), and 82.1% (MG), respectively. Moreover, kinetic studies of the photocatalyst were also performed along with reusability test, total organic carbon, chemical oxygen demand, and degradation mechanism.

One-Step Dry Coating of Hybrid ZnO-WO3 Nanosheet Photoanodes for Photoelectrochemical Water Splitting with Composition-Dependent Performance.

In this study, the potential of zinc oxide (ZnO), tungsten oxide (WO3), and their composites (ZnO-WO3) as photoanodes for photoelectrochemical (PEC) water splitting was investigated. ZnO-WO3 nanocomposites (NCs) were deposited on fluorine-doped tin oxide substrates at room temperature using a one-step dry coating process, the nanoparticle deposition system, with no post-processes. Different compositions of ZnO-WO3 NCs were optimized to enhance the kinetics of the PEC water-splitting reaction. Surface morphology analysis revealed the transformation of microsized particle nanosheets (NS) powder into nanosized particle nanosheets (NS) across all photoanodes. The optical characteristics of ZnO-WO3 photoanodes were scrutinized using diffuse reflectance and photoluminescence emission spectroscopy. Of all the hybrid photoanodes tested, the photoanode containing 10 wt.% WO3 exhibited the lowest bandgap of 3.20 eV and the lowest emission intensity, indicating an enhanced separation of photogenerated carriers and solar energy capture. The photoelectrochemical results showed a 10% increase in the photocurrent with increasing WO3 content in ZnO-WO3 NCs, which is attributed to improved charge transfer kinetics and carrier segregation. The maximum photocurrent for a NC, i.e., 10 wt.% WO3, was recorded at 0.133 mA·cm-2 at 1.23V vs. a reversible hydrogen electrode (RHE). The observed improvement in photocurrent was nearly 22 times higher than pure WO3 nanosheets and 7.3 times more than that of pure ZnO nanosheets, indicating the composition-dependence of PEC performance, where the synergy requirement strongly relies on utilizing the optimal ZnO-WO3 ratio in the hybrid NCs.

Performance evaluation of direct Z-scheme based modified titania composite for photocatalytic degradation of organic pollutants

Ceramic materials are widely used as a photocatalyst due to their low cost synthesis, photostability, suitable bandgap and excellent photodegradation properties. One such material is TiO2 however, it shows very low efficiency because it is only active in UV region (4 % of solar spectrum), have high holes-electrons recombination and low adsorption capacity. To address these limitations, highly active modified TiO2 based ceramic materials like Er2O3/TiO2, Molybdenum loaded TiO2 and TiO2/Er2O3 photocatalysts were synthesized by Sol-gel method. These synthesized photocatalysts were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence (PL) emission spectroscopy, UV–vis spectra, and Brunauer–Emmett–Teller (BET). The incorporation of Er2O3 into TiO2 and metal loading of molybdenum reduced the bandgap of TiO2 from 3.3 eV to 3.25 eV, 3.1 eV, and 3.09 eV for TiO2–Er2O3, Mo loaded TiO2 and Mo loaded TiO2–Er2O3, respectively. BET analysis revealed the enhancement of surface area by adding Er2O3 and Mo (from SBET = 39.9 m2/g to SBET = 67 m2/g) which is one of the crucial factors to increase the photocatalytic activity. The loading of molybdenum enhanced the immobilization of carriers that facilitated the photo-oxidation process and suppressed the electron-holes recombination (from 800 counts to 200 counts) as confirmed by the PL spectroscopy. The photocatalytic activity of these catalysts were evaluated by studying the photodegradation of Methylene blue (MB) under sunlight in standard conditions (1 sun, 1 atm). The synergistic effect of inclusion of Erbium Oxide and loading of molybdenum in titania-Erbium Oxide composite enhanced the photodegration efficiency from 13.2% to 75 %. The photocatalytic activities were in order of Mo@TiO2–Er2O3 > Mo@TiO2 > TiO2–Er2O3 > TiO2. These modifications also improved the conductivity of titania (σ = 4.43 × 10−4 Sm−1 to σ = 5.31 × 10−4 Sm−1) that was confirmed by Hall effect. These results supported the effectiveness of titania-modified composite for the degradation of industrial textile dye wastewater under sunlight and can be used for an optoelectronics applications.

Optical Properties of Heterostructured ZnO/NiO Nanocomposites Synthesized via Facile Precipitation Process

The semiconductor zinc oxide/nickel oxide (ZnO/NiO) heterostructured nanocomposites have been successfully synthesized via facile and eco-friendly homogeneous precipitation process with ethanol and water as solvents. The prepared nanocomposites were studied by means of structural and optical characteristics by using X-ray diffraction, ultraviolet visible absorption and photoluminescence emission spectro-scopies. The peaks in the XRD pattern attributed to the hexagonal wurtzite structure of ZnO and face-centered cubic structure of NiO, as a result the XRD analysis further confirmed that the solvents play a powerful role in size of the crystallite of the synthesized nanocomposites. Strong UV absorption may be seen in UV-vis absorbance spectra and samples of ZnO/NiO nanocomposite materials had greater energy gap (Eg) values than those of pure NiO and ZnO materials. The synthesized materials have demonstrated high photoluminescence emission in UV-blue region in the range of 241-498 nm, it might be a valuable source for future display applications. According to the aforementioned finding, the ZnO/NiO nanocomposites showed significant promise and were a viable material for optoelectronic devices.

Design and Synthesis of NTU-9/C3N4 Photocatalysts: Effects of NTU-9 Content and Composite Preparation Method.

Hybrid materials based on graphitic carbon nitride (g-C3N4) and NTU-9 metal-organic frameworks (MOF) were designed and prepared via solvothermal synthesis and calcination in air. The as-prepared photocatalysts were subsequently characterized using Brunauer-Emmett-Teller (BET) analysis, UV-Vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) emission spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The obtained NTU-9/C3N4 composites showed a greatly improved photocatalytic performance for the degradation of toluene in the gas phase under LED visible-light irradiation (λmax = 415 nm). The physicochemical properties and photocatalytic activities of the obtained NTU-9/C3N4 materials were tuned by varying the NTU-9 content (5-15 wt%) and preparation method of the composite materials. For composites prepared by calcination, the photocatalytic activity increased with decreasing NTU-9 content as a result of the formation of TiO2 from the MOFs. The best photocatalytic performance (65% of toluene was photodegraded after 60 min) was achieved by the NTU-9/C3N4 sample prepared via the solvothermal method and containing 15 wt% MOF, which can be attributed to the appropriate amount and stable combination of composite components, efficient charge separation, and enhanced visible-light absorption ability. The photocatalytic mechanisms of the prepared hybrid materials depending on the preparation method are also discussed.

Solar photocatalytic degradation of polyethylene terephthalate nanoplastics: Evaluation of the applicability of the TiO2/MIL-100(Fe) composite material

For the first time, TiO2/MIL-100(Fe) photocatalysts supported on perlite mineral particles prepared by the solvothermal/microwave methods and post-annealing technique were tested in the degradation of polyethylene terephthalate nanoplastics (PET NPs). Powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectroscopy, N2 physisorption, photoluminescence emission spectroscopy, photocurrent response, and electrochemical impedance spectroscopy were used to characterize the as-prepared materials. The response surface methodology approach was used to study the effects: pH of the NPs suspension and incorporated amount of MIL-100(Fe) on the TiO2/MIL-100(Fe) catalyst to optimize the photocatalytic degradation of the PET NPs under simulated solar light. The degradation of the PET NPs was evaluated by measuring turbidity and carbonyl index (FTIR) changes. The total organic carbon (TOC) in the solution during the degradation of the PET NPs was assessed to measure NPs oxidation into water-soluble degradation by-products. The active species involved in the photocatalytic degradation of PET NPs by the TiO2/MIL-100(Fe) composite was further examined based on trapping experiments. The use of 12.5 wt% TiO2/MIL-100(Fe) catalyst showed improved photocatalytic efficacy in the oxidation of PET NPs at pH 3 under simulated sunlight compared to bare TiO2. The increase in the carbonyl index (CI = 0.99), the reduction in the turbidity ratio (0.454), and the increase in the content of TOC released (3.00 mg/L) were possible with 12.5 wt% TiO2/MIL-100(Fe) material. In contrast, the PET NPs were slowly degraded by TiO2-based photocatalysis (CI = 0.96, turbidity ratio = 0.539, released TOC = 2.12 mg/L). The mesoporous TiO2/MIL-100(Fe) composites with high specific surface area, capacity to absorb visible light, and effective separation of photogenerated electron-hole charges clearly demonstrated the enhancement of the photocatalytic performance in the PET NPs degradation under simulated solar light.

Effect of Mn doping on the electronic and optical properties of Dy2Ti2O7: a combined spectroscopic and theoretical study

Electronic and optical studies on Dy2Ti2−Mn x O7 (x = 0.00, 0.05, 0.10, 0.15, & 0.20) have been presented through both, theoretical (density functional theory (DFT) calculations) and experimental (ultraviolet-visible absorption and photoluminescence emission spectroscopy) approaches. DFT calculations were employed considering the local density approximation (LDA) and LDA-1/2 for exchange-correlation interactions. Computed crystallographic parameters and energy band-gap using theoretical formulations are in good agreement with experimental results. The band-gap value obtained through the LDA-1/2 approach indicates insulated ground state of Dy2Ti2−x Mn x O7 (x = 0.00, 0.05, 0.10, 0.15, 0.20) system. Experimentally obtained band gap value reduces from 3.82 eV to 2.45 eV with increase in positive chemical pressure as x increases from 0 to 0.20. Reduction in band gap value is attributed to the fact that there exists a lack of hybridization between the O-2p orbital and Ti-3d orbital, which is well correlated with the crystallographic data. Jahn-Teller effect is likely to be responsible for the presence of a mixed state of Mn (explained using x-ray photoelectron spectroscopy results), resulting in the intermediate Mn state between the valence band and the conduction band with immediate inclusion of Mn at Ti site in Dy2Ti2−x Mn x O7 system.

Dual-emitting from Bi[formula omitted], Ln[formula omitted] (Ln [formula omitted] Eu, Sm) co-activated Ca[formula omitted]Sb[formula omitted]O[formula omitted] phosphor for optical temperature measurement

In this paper, a series of Ca(2−x−y) Sb2O7: xBi3+, yLn3+ (Ln = Eu, Sm) fluorescent powder samples were successfully obtained, which used the traditional high-temperature solid-phase synthesis method in the preparation process. Samples of Ca2Sb2O7: Bi3+, Ln3+ (Ln = Eu, Sm) fluorescent powder samples were structurally and optically characterized​ using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), photoluminescence excitation spectroscopy and emission spectroscopy, and fluorescence decay measurements. The results show that the prepared Ca(2−x−y) Sb2O7: xBi3+, yLn3+ (Ln = Eu, Sm) samples have an orthogonal spider web structure, which remains unchanged whether Bi3+ is single doped or Bi3+ is co-doped with Ln3+ (Ln = Eu, Sm). Under ultraviolet lamp (λex=340nm) irradiation, Bi3+ doped Ca2Sb2O7 powder shows a wide emission band centered at 435 nm, which is owing to the 3P1→1S0 transition of Bi3+ ion. Therefore, the effect of Bi3+ and Ln3+ (Ln = Eu, Sm) co-doped Ca2Sb2O7 samples on the luminescence intensity of the samples at different concentrations was studied. When the temperature was varied from 293 K to 483 K, the absolute temperature sensitivity (Sa) of doped Bi3+/Eu3+ and Bi3+/Sm3+ phosphors is 0.001K−1 (at 483 K) and 0.02K−1 (at 293 K), respectively, and the relative temperature sensitivity (Sr) is 1.03% K−1 (at 343 K) and 1.19% K−1 (at 293 K), respectively. These results demonstrate that Ca(2−x−y) Sb2O7: xBi3+, yLn3+(Ln = Eu, Sm) phosphors are prospective double emission thermal thermometers.

Mechanism insights into the enhanced photocatatlytic peroxydisulfate activation by Fe3O4/BiOI heterojunction

Combining various advanced oxidation processes has been considered as an emerging approach for degrading organic contaminants, which can overcome the deficiencies of a single one. In this study, the photocatalytic oxidation and persulfate-based oxidation were allied for degrading high-concentration Rhodamine B (RhB). To strengthen this alliance, Fe3O4/BiOI p-n heterojunctions were constructed by anchoring Fe3O4 nanoparticles onto flower-like BiOI. Various instrumental techniques, including X-ray diffractometer, field emission scanning electron microscope, transmission electron microscope, X-ray photoelectron spectrometer, photoluminescence emission spectroscopy, UV–Vis diffuse reflectance spectrometer, vibrating sample magnetometer and surface area analyzer were used to characterize these heterojunctions. 100 mg·L−1 RhB was utilized as the probing target to appraise the photocatalytic peroxydisulfate activation by Fe3O4/BiOI heterojunction under visible light illumination. The pseudo-first-order kinetic model could well describe the RhB degradation process. Finally, the mechanism on the photocatalytic peroxydisulfate activation over Fe3O4/BiOI heterojunction was proposed and discussed.

Enhanced Nanogenerator Performances of 1-D Al-Doped ZnO Nanorod Arrays through Ultrasonic Wave Systems

One-dimensional (1-D) well-aligned zinc oxide (ZnO) nanorods (NRs) without and with aluminum (Al) dopants were triumphantly grown on conductive indium–tin-oxide glass substrates through a simple chemical bath deposition at low temperature in this study. The designed devices are also called the AZO-0 and AZO-1 samples. After annealing in a vacuum state (10 min, 600 °C), the optical properties of the nanostructures were explored via photoluminescence emission spectroscopy. Field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and an X-ray diffraction spectrometer were used to investigate the surface nanostructures and crystalline properties of the NR arrays. It was seen that all nanostructures clearly showed a single-crystal property with hexagonal wurtzite shape and grew vertically on the substrate. The elemental content of the sample was checked by X-ray photoelectron spectroscopy and an energy-dispersive X-ray spectrometer. Additionally, nanogenerators (NGs) based on the 1-D AZO-0 and AZO-1 nanostructures were also fabricated and investigated. The copper tape was successfully utilized to combine nanostructures and electrodes for the NG device in an ultrasonic oscillator machine with a water chamber. As a result, it was found that the output power values of the AZO-1 NR NGs were higher than that of the AZO-0 NR NGs. The AZO-1 NRs revealed significantly superior conductive performance in NG devices and are promising candidates in future self-powered NG applications.

Optical and quantitative detection of cobalt ion using graphitic carbon nitride-based chemosensor for hydrometallurgy of waste lithium-ion batteries

A hydrometallurgy is one of the most important techniques for recycling waste LIBs, where identifying the exact composition of the metal-leached solution is critical in controlling the metal extraction efficiency and the stoichiometry of the regenerated product. In this study, we report a simple and selective optical detection of high-concentrated Co2+ using a graphitic carbon nitride (g–CN)–based fluorescent chemosensor. g-CN is prepared by molten salt synthesis using dicyandiamide (DCDA) and LiI/KI. The mass ratio of LiI/KI to DCDA modifies the resulting g-CN (CNI) in terms of in-plane molecular distances of base sites including cyano functional groups (─CN) and fluorescent emission wavelength via nucleophilic substitution. The fluorescent sensing performance of CNIs is evaluated through photoluminescence (PL) emission spectroscopy in a broad Co2+ concentration range (10−4–100 M). The correlation between the surface exposure of hidden nitrogen pots (base sites) and PL intensity change is achieved where the linear relationship between the PL quenching and the logarithm of Co2+ concentration in the analyte solution is well established with the regression of 0.9959. This study will provide the design principle of the chemosensor suitable for the fast and accurate optical detection of Co2+ present in a broad concentration range for hydrometallurgy for the recycling of waste LIBs.

Oxygen-deficient low band gap black zirconia nanoparticle synthesis and tailoring its band gap/photoluminescence via silver doping

This study focuses on the non-aqueous sol-gel synthesis of zirconia nanopowder and explores the tunability of its band gap, absorption, and photoluminescence. Multiple characterization techniques were used to examine the impact of oxygen vacancies (color centers) and silver doping on changes in the structural and optical properties of zirconia. XRD results confirmed the rare black-colored pure tetragonal zirconia and monoclinic-tetragonal mixed zirconia products. The UV–Vis analysis provided insights about the absorbance and confirmed the extraordinarily high absorbance over the entire visible spectrum of electromagnetic radiation and also ascertained the defect level that governed the low band gap of the synthesized black zirconia powders. With increasing the doping concentration, the photoluminescence emission spectroscopy stimulated at an excitation wavelength of 250 nm revealed a rising luminescence peak at 422 nm (2.94eV). The distinctive stretching modes of zirconia powder samples were validated by FTIR investigations. The FESEM was used to study the microstructure's morphology, and the EDX spectrum was used to analyze the samples' elemental composition. The high-bandgap white samples with strong PL emission (blue) can be used to create high-quality wLEDs, whereas the low-bandgap black zirconia may prove to be an outstanding solar light absorption material.

Kinetic analysis of p-rGO/n-TiO2 nanocomposite generated by hydrothermal technique for simultaneous photocatalytic water splitting and degradation of methylene blue dye.

In this study, the nanocomposites of reduced graphene oxide/TiO2 (rGO/TiO2 with different percentages) have been synthesized using a modified Hummers' method followed by hydrothermal treatment. The morphology and bonding structure of the prepared samples have been characterized by Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS). The photo-characteristic aspects of the prepared samples have been indicated by photoluminescence (PL) emission spectroscopy and ultraviolet-visible diffuse reflection spectroscopy (DRS). The photocatalytic performance of rGO/TiO2 demonstrated that it is an effective photocatalyst for methylene blue (MB) dye decomposition through illumination by a mercury lamp. Within 60 min of continuous irradiation, the nanocomposite-induced MB decomposition reached a rate of over 99%. Different MB concentrations and optimal percent loadings in catalysts have been investigated. Furthermore, the results showed that as the amount of catalyst increased, the decomposition of MB enhanced. Finally, the loading percentage of rGO with TiO2 has been studied, and an empirical equation relating the reaction rate constant until the mass of the photocatalyst and dye concentration has been proposed. The results showed that the prepared nanocomposites had good photocatalytic activity toward water splitting and photo-decomposition of MB.