Cr-doped Zinc Oxide Research Articles

Physicochemical and therapeutic studies of microwave-synthesized ZnO and Cr-doped ZnO nanoparticles for biomedical applications

Highly stable Zinc Oxide (ZnO) and Chromium (Cr) doped ZnO nanoparticles (NPs) are increasingly studied for biomedical applications due to their low toxicity, biodegradability, and affordability. In this paper, ZnO NPs and Cr doped ZnO NPs have been prepared by a microwave method. The prepared samples were studied with their physicochemical characteristics and successively investigated their impact on the antimicrobial, antioxidant, and biocompatibility properties. Correlations between physicochemical and biomedical properties were assessed. The NPs demonstrated strong, concentration-dependent antibacterial effects against E. coli and X. citri, with maximum inhibition zones of 15.53 mm (PZnO), 13.33 mm (CZnO), 13.56 mm (ZCr2), 14.03 mm (ZCr4), and 15.0 mm (ZCr6) for E. coli, and 13.73, 13.46, 14.50, 14.70, and 15.26 mm, respectively, for X. citri. They also showed significant antifungal activity against A. niger and R. stolonifer. Antioxidant activity, measured via DPPH radical scavenging, revealed inhibition rates of 58.52–92.27 % (PZnO), 56.27–90.65 % (CZnO), 51–85 % (ZCr2), 54–87 % (ZCr4), and 57.75–87.59 % (ZCr6). Hemolysis assays indicated biocompatibility, with hemolysis percentages below 5 % for all NPs at concentrations up to 500 µg/mL. These findings suggest that ZnO and Cr doped ZnO NPs are promising candidates for biomedical applications, offering antimicrobial and antioxidant properties with minimal toxicity to human erythrocytes.

Exploitation of green synthesized chromium doped zinc oxide nanorods (NRs) mediated by flower extract of Rhododendron arboreum for highly efficient photocatalytic degradation of cationic dyes Malachite green (MG) and Fuchsin basic (FB)

In this work, green method to synthesize chromium-doped zinc oxide (ZnO) nanorods (NRs) using an aqueous flower extract from Rhododendron arboretum is explored. Herein, chromium-doped ZnO NRs were prepared with different amount of chromium doping, varied as 2–10%. The green synthesized products underwent substantial analysis through X-ray diffraction (XRD), spectroscopic such as ultraviolet spectroscopy(UV-Vis) and scanning electron microscopy (SEM) methods. All samples were found to have hexagonal wurtzite ZnO, with average particle sizes of 52.41, 56.6, 54.44, 53.05, and 56.99 nm, respectively, for 2, 4, 6, 8, and 10% chromium doping in ZnO NRs. The Cr-doped ZnO NRs exhibited remarkable photocatalytic degradation activity of cationic dyes under UV-light, i.e., Malachite Green and Fuchsin Basic with degradation of 99.604 and 99.881%, respectively in 90 min. The reusability tests for these green synthesized Cr-doped ZnO NRs have also been carried out, showed 9–11 cycles with 85% of degradation efficiency. In addition, the Cr-doped ZnO NRs exhibited high selectivity for cationic dyes when experiments against mixture of dyes were performed. Photodegradation kinetics followed the pseudo-first-order model. The flower-extract-stabilized chromium-doped ZnO NRs demonstrated high photocatalytic activity toward malachite green and fuchsin basic dyes, potential material for pollution remediation.

Fabrication and Characterization of Acute Myocardial Infarction Myoglobin Biomarker Based on Chromium-Doped Zinc Oxide Nanoparticles.

In this article, we describe the fabrication and characterization of a sensor for acute myocardial infarction that detects myoglobin biomarkers using chromium (Cr)-doped zinc oxide (ZnO) nanoparticles (NPs). Pure and Cr-doped ZnO NPs (13 × 1017, 20 × 1017, and 32 × 1017 atoms/cm3 in the solid phase) were synthesized by a facile low-temperature sol-gel method. Synthesized NPs were examined for structure and morphological analysis using various techniques to confirm the successful formation of ZnO NPs. Zeta potential was measured in LB media at a negative value and increased with doping. XPS spectra confirmed the presence of oxygen deficiency in the synthesized material. To fabricate the sensor, synthesized NPs were screen-printed over a pre-fabricated gold-coated working electrode for electrochemical detection of myoglobin (Mb). Cr-doped ZnO NPs doped with 13 × 1017 Cr atomic/cm3 revealed the highest sensitivity of ~37.97 μA.cm−2nM−1 and limit of detection (LOD) of 0.15 nM for Mb with a response time of ≤10 ms. The interference study was carried out with cytochrome c (Cyt-c) due to its resemblance with Mb and human serum albumin (HSA) abundance in the blood and displayed distinct oxidation potential and current values for Mb. Cr-doped ZnO NP-based Mb biosensors showed 3 times higher sensitivity as compared to pure ZnO NP-based sensors.

Promising Cr-Doped ZnO Nanorods for Photocatalytic Degradation Facing Pollution

Chromium (Cr)-doped zinc oxide (ZnO) nanorods with wurtzite hexagonal structure were prepared through a thermal decomposition technique. The concentration effect of the Cr doping on the structural, morphological, and optical properties of the ZnO nanorods was established by correlating various measurements: transmission electron microscopy (TEM), photoluminescence (PL), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and several UV-visible studies. The obtained nanorods were investigated as photocatalysts for the photodegradation process of methyl orange (MO), under UV-vis light illumination. Different weights and time intervals were studied. A 99.8% photodegradation of MO was obtained after 100 min in the presence of 1 wt.% Cr III acetate hydroxide and zinc acetate dehydrate “ZnO-Cr1”. The kinetic rate constant of the reaction was found to be equal to 4.451 × 10−2 min−1 via a pseudo-first order rate model. Scavenger radicals demonstrated the domination of OH• radicals by those of O2•− superoxide species during the photodegradation. The interstitial oxygen site Oi is proposed to play a key role in the generation of holes in the valence band under visible irradiation. The ZnO-Cr1 photocatalyst displayed good cycling stability and reusability.

Structural, linear and non-linear optical properties of Cr-doped ZnO thin film for optoelectronics applications

Abstract In this work, optical properties of undoped zinc oxide (ZnO) and chromium (Cr) doped ZnO prepared at different concentrations of Cr (2, 3, and 5 wt.%) on glass substrates by a spray pyrolysis method are reported. The structural properties investigated by X-ray diffraction revealed the hexagonal wurtzite structure, noting that the crystallite size of the films decreases with increasing Cr content. The optical characterization of the samples was carried out using spectral transmittance. The refractive index, energy gap, and extinction coefficient of pure and Cr-doped ZnO thin films have been calculated. The single oscillator model of Wemple–DiDomenico was used to study the dispersion of the refractive index. The oscillator parameters, the single oscillator energy, the dispersion energy, and the static refractive index were determined. The linear optical susceptibility and non-linear optical susceptibility were also studied and discussed. These promising results achieved by Cr-doping of ZnO exhibited an important behavior for technological applications in electronic, optoelectronic devices and non-linear optical applications.

Fabrication of pulsed laser-deposited Cr-doped zinc oxide thin films: structural, morphological, and optical studies

High-quality c-axis-oriented Cr-doped ZnO thin films were grown on 100-μm-thick Si (100) wafer substrate by Pulsed Laser Deposition (PLD) technique. The PLD is a versatile technique for growing thin films and a wide range of materials. The structural analyses confirm the wurtzite structure of synthesized samples and are preferentially oriented along c-axis perpendicular to substrate the surface. The intensity of defect-induced mode frequency for Cr-doped ZnO film increased due to the formation of highly crystalline films. In Raman spectra, E2 (high) mode shows redshift owing to optical phonon confinement induced by uncertainty in photon wave vectors i.e., downshift of Raman peaks. Cr-doped ZnO thin film consists of nanorod-shaped grains of different sizes. Each rod possesses width in a range of 85–93 nm and length upto several hundred nanometres. The decrease in peak intensity of Cr-doped ZnO film photoluminescence (PL) spectrum is attributed to a fall in the electron–hole recombination process. In visible region of PL spectra, green light emission peak at about 567 nm was associated with defects in ZnO. It is observed after doping root mean square (RMS) roughness increases with which means the surfaces becomes rough and grain size increases.

Investigations on the ZnO- and Cr-doped ZnO powders

Among the metal–oxide nanoparticles, pure and doped zinc oxide (ZnO) has been widely studied due to their potential applications, such as electrical, thermal and optical materials. In this context, samples of undoped ZnO and Cr-doped ZnO powders were prepared using a solution-combustion route. The formation of the combustion products was confirmed by X-ray diffraction analysis. The samples were well characterized using the Fourier transform infrared spectroscopy and scanning electron microscopy techniques. In the sample, photoluminescence studies showed that ZnO could be excited at 267 nm, while an ultraviolet emission centred at $${\sim }383\,\hbox {nm}$$ was exhibited. Antibacterial-activity testing was carried out using the disc-diffusion method.

Structural and optical properties of Cr-doped ZnO thin films

In the present work, chromium (Cr)-doped zinc oxide (ZnO) thin films were prepared on silicon and glass substrates by using the sol–gel spin-coating technique. The influence of chromium doping on the structural and optical properties of zinc oxide films was investigated. The X-ray diffraction results reveal that the films are polycrystalline in nature with hexagonal wurtzite structure. The absence of secondary diffraction peaks other than those for zinc oxide suggests that the chromium ions successfully replaced zinc (Zn) ions and were incorporated into the crystal-lattice positions. The average grain size and the strain arising due to the introduction of chromium ions in the lattice were obtained by using Williamson–Hall analysis. The surface morphology of the films was observed by field emission scanning electron microscopy. The Raman spectra of the films show a peak at 434 cm−1 corresponding to E2 (high) mode of crystalline zinc oxide wurtzite structure, and the intensity of this mode decreases with increase in chromium doping. The films are highly transparent (∼90%) in the visible region, which reduces with chromium doping.

Phase analysis in Zn1− x Cr x O through charge density

Cr-doped zinc oxide Zn1− x Cr x O powder samples are synthesized by a standard high-temperature solid-state reaction technique with x = 0.00, 0.04, and 0.08. The powders are analyzed for the electron densities using X-ray diffraction. The electron densities of observed wurtzite phase ZnO as well as the spinel phase ZnCr2O4 are mapped and analyzed for Cr doping concentration. The charge density study reveals that the Cr atom is added in the lattice as Cr3+ rather than Cr2+.

Performance of Cr-doped ZnO for acetone sensing

Zinc oxide (ZnO) doped with chromium (Cr) was synthesized by reactive co-sputtering for gas sensing applications. The effect of varying the contents of Cr (from 1 to 4at%) on the ZnO gas sensor response was studied. X-ray diffraction analysis reveals the high orientation of c-axis of the prepared films. The optimum operating temperature of the undoped ZnO was 400°C and shifted to 300°C for the Cr-doped ZnO under the acetone vapour. The 1% Cr doping ZnO gas sensor was most sensitive for the acetone vapour. The ability of the 1% Cr-doped ZnO to produce repeatable results under different acetone vapour concentrations was tested. The timing properties of the doped Cr ZnO gas sensor were 70 and 95s for the rise and recovery time respectively.

First-principles study of doping effect on the phase transition of zinc oxide with transition metal doped

Zinc oxide (ZnO) is a promising material for its wide application in solid-state devices. With the pressure raised from an ambient condition, ZnO transforms from fourfold wurtzite (B4) to sixfold coordinated rocksalt (B1) structure. Doping is an efficient approach to improve the structures and properties of materials. Here we use density-functional theory (DFT) to study doped ZnO and find that the transition pressure from B4 phase to B1 phase of ZnO always decreases with different types of transition metal (V, Cr, Mn, Fe, Co, or Ni) doped, but the phase transition path is not affected by doping. This is consistent with the available experimental results for Mn-doped ZnO and Co-doped ZnO. Doping in ZnO causes the lattice distortion, which leads to the decrease of the bulk modulus and accelerates the phase transition. Mn-doped ZnO shows the strongest magnetic moment due to its half filled d orbital. For V-doped ZnO and Cr-doped ZnO, the magnetism is enhanced by phase transition from B4 to B1. But for Mn-doped ZnO, Fe-doped ZnO, Co-doped ZnO, and Ni-doped ZnO, B1 phase shows weaker magnetic moment than B4 phase. These results can be explained by the amount of charge transferred from the doped atom to O atom. Our results provide a theoretical basis for the doping approach to change the structures and properties of ZnO.

Impedance spectroscopy of undoped and Cr-doped ZnO gas sensors under different oxygen concentrations

Thin films of undoped and chromium (Cr)-doped zinc oxide (ZnO) were synthesized by RF reactive co-sputtering for oxygen gas sensing applications. The prepared films showed a highly c-axis oriented phase with a dominant (0 0 2) peak appeared at a Bragg angle of around 34.13 °, which was lower than that of the standard reference of ZnO powder (34.42 °). The peak shifted to a slightly higher angle with Cr doping. The operating temperature of the ZnO gas sensor was around 350 °C, which shifted to around 250 °C with Cr-doping. The response of the sensor to oxygen gas was enhanced by doping ZnO with 1 at.% Cr. Impedance spectroscopy analysis showed that the resistance due to grain boundaries significantly contributed to the characteristics of the gas sensor.

Intrinsic ferromagnetic properties in Cr-doped ZnO diluted magnetic semiconductors

The Cr-doped zinc oxide (Zn 1− x Cr x O, 0≤ x≤0.08) diluted magnetic semiconductors have been synthesized successfully by the sol–gel method. Investigations on magnetic, optical and structural properties of the produced samples have been done. Energy dispersive spectroscopy (EDS) shows the existence of Cr ion in the Cr-doped ZnO. The results of X-ray diffraction (XRD), the transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) indicate that the Cr ions are at least partially substitutionally incorporated into the crystal lattice of ZnO. The produced samples show good high- T c (Curie temperature) ferromagnetism (FM) in Cr-doped ZnO nanoparticles with Cr concentration of less than 5 at%. The results of photoluminescence (PL) further testify that FM is an intrinsic property of the Cr-doped ZnO nanoparticles. And the occurrence of FM should mainly contribute to the Cr doping.

Comment on “Effect of annealing temperature on structure, magnetic properties and optical characteristics in Zn 0.97Cr 0.03O nanoparticles” by Liu et al., [Appl. Surf. Sci. 256 (2010) 3559

The authors of a recent paper (Appl. Surf. Sci. 256 (2010) 3559) studied the effect of annealing temperature on structural, magnetic and optical properties in Cr-doped zinc oxide (Zn 0.97Cr 0.03O) nanoparticles synthesized by sol–gel method. The authors have verified that Cr ions, in 3+ valence state, substitute the Zn ions in the ZnO lattice. They concluded that the ferromagnetism observed in the samples is an intrinsic property of the Cr-doped ZnO. However, we noticed an unusual point in this article. The Cr 2p XPS spectrum shown by them is against the general trend of the 2p XPS spectra of the transition metals. In this light, we re-measured the high-resolution 2p XPS spectrum of Cr for a 3% Cr-doped ZnO sample that is entirely different than theirs. The spectrum presented by them therefore demands proper interpretations or it might mislead the researchers in this developing field.

Effect of annealing temperature on structure, magnetic properties and optical characteristics in Zn 0.97Cr 0.03O nanoparticles

The Cr-doped zinc oxide (Zn 0.97Cr 0.03O) nanoparticles were successfully synthesized by sol–gel method. The relationship between the annealing temperature (400 °C, 450 °C, 500 °C and 600 °C) and the structure, magnetic properties and the optical characteristics of the produced samples was studied. The results indicate that Cr (Cr 3+) ions at least partially substitute Zn (Zn 2+) ions successfully. Energy dispersive spectroscopy (EDS) measurement showed the existence of Cr ion in the Cr-doped ZnO. The samples sintered in air under the temperature of 450 °C had single wurtzite ZnO structure with prominent ferromagnetism at room temperature, while in samples sintered in air at 500 °C, a second phase-ZnCr 2O 4 was observed and the samples were not saturated in the field of 10000 Oe. This indicated that they were mixtures of ferromagnetic materials and paramagnetic materials. Compared with the results of the photoluminescence (PL) spectra, it was reasonably concluded that the ferromagnetism observed in the studied samples was originated from the doping of Cr in the lattice of ZnO crystallites.