Green Synthesis of Metal-Doped ZnO Nanoparticles Using Bauhinia racemosa Lam. Extract and Evaluation of Their Photocatalysis and Biomedical Applications.

A fascinating problem in the fields of nanoscience and nanobiotechnology has recently emerged, and to tackle this, the production of metal oxide nanoparticles using plant extracts offers numerous benefits over traditional physicochemical methods. In the present investigation, ZnO nanoparticles were fabricated from Bauhinia racemosa Lam. (BR) leaves extract with various transition metal (TM) dopants (Ni, Mn, and Co). Plant leaves extract containing metal nitrate solutions were utilized as a precursor to synthesize the pristine and TM-doped ZnO nanoparticles. Structural, functional, optical, and surface properties of the fabricated samples were studied by using physicochemical and photoelectrochemical measurements. The organic pollutants tetracycline (TC), ampicillin (AMP), and amoxicillin (AMX) were used in the photocatalytic degradation assessment of the fabricated samples. Through X-ray diffraction (XRD) and transmission electron microscopy (TEM) investigation, the fabricated nanoparticles wurtzite crystal structure was verified. Moreover, Fourier transform infrared (FT-IR) analysis verified the existence of functional groups in the fabricated nanoparticles. The migration of electrons from the deep donor level and zinc interstitial to the Zn-defect and O-defect is related to the emission peaks seen at 468, 480, 534, and 450 nm in photoluminescence (PL) spectra. Co-ZnO nanoparticles demonstrated potent and excellent photocatalytic degradation performance for TC (91.09%), AMP (87.97%), and AMX (92.42%) antibiotics within 210, 180, and 150 min of visible light irradiation. Co-ZnO nanoparticles also demonstrated strong antimicrobial performance against Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Aspergillus flavus, Aspergillus niger, and Bacillus subtilis. Further investigation of in vitro cytotoxic potential against the A549 cell line (IC50 = 24 ± 0.5 µg/mL) utilizing MTT assay and the free radical scavenging performance of Co-ZnO nanoparticles estimated by DPPH assay utilizing l-ascorbic acid as a reference was also performed. Anti-inflammatory potential is also reviewed by comparing it with the standard drug Diclofenac, and the maximum activity was obtained for Ni-ZnO nanoparticles (IC50 = 72.4 µg/mL).

Enhancing air treatment through controlled fabrication of transition metal-doped titanium dioxide nanocomposites for photocatalytic toluene degradation.

Rapid industrial growth and urbanization have resulted in a significant rise in environmental pollution issues, particularly indoor air pollutants. As a result, it is crucial to design and develop technologies and/or catalysts that are not only cost-effective but also promising high performance and practical applicability. However, achieving this goal has been so far remained a challenging task. Herein, a series of transition metal M - TiO2 (M = W, Fe, Mn) nanocrystals was prepared for photocatalytic degradation of volatile organic compounds (VOCs), i.e., toluene. Of the nanocomposites tested, W-TiO2 showed significantly improved photocatalytic activity for VOC degradation under UV irradiation compared to the others. In particular, the optimized W dopant amount of 0.5 wt% resulted in the outstanding degradation performance of toluene (96%) for the obtained W-TiO2(0.5%) nanocomposite. Moreover, W-TiO2(0.5%) nanocomposite exhibited good stability for 32 h working under high toluene concentration (10 ppm) compared to the pristine TiO2. The current work demonstrates the potential usage of M - TiO2 nanocrystals, particularly W-TiO2(0.5%), as a promising photocatalyst for efficient VOCs degradation.

Theoretical design of transition metal-doped oxo-triarylmethyl as a disposable platform for adsorption of ibuprofen.

Emerging environmental contaminants have become a crucial environmental issue because of the highly toxic effluents emitted by factories. Ibuprofen (IBP), as a typical anti-inflammatory drug, is frequently detected in water sources. Therefore, its removal using various adsorbents has drawn great interest. Herein, the structural, electronic, energetic, and optical properties of pristine oxo-triarylmethyl (oxTAM) and transition metal-doped oxo-triarylmethyl (TM@oxTAM, TM = Sc, Ti, V, Cr, and Mn) for adsorption of the IBU drug were investigated using density functional theory (DFT) calculations implemented in Gaussian and VASP codes. Frontier molecular orbital (FMO), density of states (DOS), and electronic band structure results demonstrated that transition metal-doped oxTAM causes a significant reduction in the energy band gap (Eg) value of pristine oxTAM, with the highest decrease (30.14 %) in the case of Mn@oxTAM. It was found that transition metal doping onto oxTAM leads to an increase in the adsorption energies (1.20-2.64 eV) and charge density between transition metal and IBU. Natural bond orbital (NBO) analysis revealed that charge was effectively transferred from the IBU towards the transition metal, which was further analyzed by charge decomposition analysis (CDA). Furthermore, quantum theory of atoms in molecules (QTAIM), interaction region indicator (IRI), electron localization function (ELF), and radial distribution function (RDF) analyses revealed that the IBU is adsorbed on the Sc@oxTAM surface via covalent interactions, while electrostatic with partially covalent interactions are dominated in other IBU/TM@oxTAM complexes. The results suggest that TM doping on the oxTAM provides a new insight for developing photocatalyst-based covalent organic frameworks (COFs) to remove emerging pollutants in wastewater.

Investigation of Photoluminescence and Optoelectronics Properties of Transition Metal-Doped ZnO Thin Films.

Thin films of zinc oxide (ZnO) doped with transition metals have recently gained significant attention due to their potential applications in a wide range of optoelectronic devices. This study focuses on ZnO thin films doped with the transition metals Co, Fe, and Zr, exploring various aspects of their structural, morphological, optical, electrical, and photoluminescence properties. The thin films were produced using RF and DC co-sputtering techniques. The X-ray diffraction (XRD) analysis revealed that all the doped ZnO thin films exhibited a stable wurtzite crystal structure, showcasing a higher structural stability compared to the undoped ZnO, while the atomic force microscopy (AFM) imaging highlighted a distinctive granular arrangement. Energy-dispersive X-ray spectroscopy was employed to confirm the presence of transition metals in the thin films, and Fourier-transform infrared spectroscopy (FTIR) was utilized to investigate the presence of chemical bonding. The optical characterizations indicated that doping induced changes in the optical properties of the thin films. Specifically, the doped ZnO thin film's bandgap experienced a significant reduction, decreasing from 3.34 to 3.30 eV. The photoluminescence (PL) analysis revealed distinguishable emission peaks within the optical spectrum, attributed to electronic transitions occurring between different bands or between a band and an impurity. Furthermore, the introduction of these transition metals resulted in decreased resistivity and increased conductivity, indicating their positive influence on the electrical conductivity of the thin films. This suggests potential applications in solar cells and light-emitting devices.

Transition metal-doped germanium oxide nanozyme with enhanced enzyme-like activity for rapid detection of pesticide residues in water samples.

Designing highly active nanozymes for bioanalysis and environmental sensing remains a challenge. In this study, transition metal, palladium (Pd) and iron (Fe), doped germanium oxide (GeO2) nanozyme was designed and optimized. Compared with the pristine GeO2 nanozyme, the transition metal doped GeO2 nanozyme have lower Michaelis-Menten constants and higher catalytic activity, indicating that the Pd and Fe doped GeO2 nanozyme not only enhance their affinity for the substrate but also improve its catalytic activity. In addition, a colorimetric sensor based on the GeO2@Pd-H2O2-TMB system was constructed for the visual detection of simazine in water samples due to the good affinity between TMB and simazine. This sensor has good selectivity and sensitivity with a detection limit of 6.21 µM because of the highest catalytic performance of GeO2@Pd nanozyme. This study broadens the application of nanozymes in environmental field and other nanozymes can also be enhanced in activity by simple transition metal doping.

Design of Novel Transition-Metal-Doped C6N2 with High-Efficiency Polysulfide Anchoring and Catalytic Performances toward Application in Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are highly expected because of their high theoretical specific capacity and energy density. However, its application still faces challenges, including the shuttle effect affecting the sulfur reduction reaction, the high decomposition energy barrier of Li2S during charging, the volume change of sulfur, and the poor conductivity during charging and discharging. Here, combined with density functional theory and particle swarm optimization algorithm for the nitrogen carbide monolayer structural search (CmN8-m, m = 1-8), the surprising discovery is that a single metal-atom-doped C6N2 monolayer could effectively accelerate the conversion of lithium polysulfide and anchor lithium polysulfide during discharging and decrease the decomposition energy barrier of Li2S during charging. This "anchoring and catalyzing" mechanism effectively reduces the shuttle effect and greatly improves the reaction kinetics. Among a series of metal atoms, Cr is the best doping element, and it exhibits suitable adsorption energy for polysulfides and the lowest decomposition energy barrier for Li2S. This work opens up a new way for the development of transition-metal-doped carbon-nitrogen materials with an excellent catalytic activity for lithium polysulfide as cathode materials for Li-S batteries.

Photocatalysis of Cr- and Fe-Doped CeO2 Nanoparticles to Selective Oxidation of 5-Hydroxymethylfurfural.

Oxygen vacancies (Vo) present in CeO2 nanoparticles (NPs) can effectively boost their photocatalytic activity under ultraviolet (UV) light. To improve photocatalytic performance, Cr- and Fe-doped CeO2 NPs with increased Vo were prepared using a simple method of doping Cr and Fe ions into CeO2 NPs, which was confirmed by an in-depth analysis of the structural and electronic changes. Through photocatalytic degradation (PCD) experiments with 5-hydroxymethylfurfural (HMF), we found that the PCD rates of the two doped CeO2 NPs were faster than that of the CeO2 NPs. In addition, the conversion of HMF to 2,5-furandicarboxylic acid (FDCA) using the doped CeO2 NPs occurred only through the mechanism of the selective oxidation to 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), exhibiting better efficiency than using CeO2 NPs.

DFT-based investigation of different properties for transition metal-doped germanium TMGen (TM = Ru, Rh; n = 1-20) clusters.

The geometries and energetic, electronic, and magnetic features of transition metal-doped germanium (TMGen with TM = Ru, Rh; n = 1-20) clusters are systematically studied by means of first principle computations on the basis of the density functional theory (DFT) approach. The doping TM atom largely participates to strengthen the Gen cluster stability by increasing the binding energies. A good stability is obtained for RuGe12, RhGe12, and RhGe14 clusters. The various explored isomers of TMGen clusters possess a total spin magnetic moment going from 0 to 2µB, except for RhGe2 with 3µB. These results open nice perspectives of these good candidate clusters for applications in nanoelectronics and nanotechnologies.

Novel quantification of formation trend and reaction efficiency of hydroxyl radicals for investigating photocatalytic mechanism of Fe-doped TiO2 during UV and visible light-induced degradation of acid orange 7.

A detailed mechanistic investigation of the hydroxyl radical (•OH) formation and organic pollutant degradation over transition metal-doped and undoped TiO2 photocatalysts was performed by the quantitative measurement of •OH and the identification of intermediate products under various experimental conditions. The Fe-doped TiO2 as a typical subject was prepared, characterized and used to degrade an azo dye Acid Orange 7 (AO7). It is indicated that the enhanced photocatalytic activity of Fe-doped TiO2 for AO7 degradation was attributed to the increase in surface area, the facilitated charge transfer via Fe-dopant, and a red shift of absorbable wavelength, maintaining a great formation of •OH under visible irradiation. The oxidation of H2O by holes was estimated as the major pathway of •OH formation rather than the reduction of dissolved O2 by electrons, and their formation trends reached to approximately 75% and 25%, respectively. Meanwhile the synergistic effect of Fe-dopant produced nearly 10% of extra •OH by visible light photoactivation. The intermediate products and pathways of AO7 degradation varied greatly with different photocatalysts and conditions of the process, involving several reaction mechanisms such as the azo bond cleaving, naphthalene oxidation, desulfonation, and hydroxylated products generation. Through the quantification of •OH-reacted efficiency we proposed, a stoichiometry of •OH affecting overall reaction mechanisms in the TiO2-assisted photodegradation of AO7 was further established. This study can provide new insights on how to better clarify the variation regularity of organic pollutant degradation from different treatments of the •OH-based advanced oxidation processes.

Determining the Catalytic Activity of Transition Metal-Doped TiO2 Nanoparticles Using Surface Spectroscopic Analysis.

The modified TiO2 nanoparticles (NPs) to enhance their catalytic activities by doping them with the five transition metals (Cr, Mn, Fe, Co, and Ni) have been investigated using various surface analysis techniques such as scanning electron microscopy (SEM), Raman spectroscopy, scanning transmission X-ray microscopy (STXM), and high-resolution photoemission spectroscopy (HRPES). To compare catalytic activities of these transition metal-doped TiO2 nanoparticles (TM-TiO2) with those of TiO2 NPs, we monitored their performances in the catalytic oxidation of 2-aminothiophenol (2-ATP) by using HRPES and on the oxidation of 2-ATP in aqueous solution by taking electrochemistry (EC) measurements. As a result, we clearly investigate that the increased defect structures induced by the doped transition metal are closely correlated with the enhancement of catalytic activities of TiO2 NPs and confirm that Fe- and Co-doped TiO2 NPs can act as efficient catalysts.