1819-796X (p-ISSN); 2541-1713 (e-ISSN)
94
Recent Progress of ZnO-Based Nanoparticle: Synthesizing Methods of Rare Earth Dopant and Applications
Nurlaela Rauf
Department of Physics, Hasanuddin University, Makassar 90245, Indonesia.
Correspondence email: n-rauf@fmipa.unhas.ac.id
DOI: https://doi.org/10.20527/flux.v20i1.16044 Submitted: 07 April 2023; Accepted: 30 April 2023
ABSTRACT−This review focus on the effect of doping rare earth metals on ZnO nanoparticles. ZnO is a semiconductor material with an average wide energy band gap of 3.2 eV. The doping is used to improve the properties of ZnO which strongly depend on their application. The concentration of doping and the process using sol-gel, hydrothermal and precipitation methods are affected in modifying the ZnO lattice parameters.
The doped application of ZnO nanoparticles as a semiconductor material has proven advantageous in enabling various photocatalytic, glucose biosensors, VOC detection sensors, antibacterial, biomedical, and optoelectronic spintronic, LED, NLO, and silicon solar cells. This review provided information for scientist in choosing the synthesizing methods of ZnO with desired properties and application in future.
KEYWORDS : application; hydrothermal; precipitation; sol-gel; ZnO nanoparticles
INTRODUCTION
ZnO or Zinc Oxide is an environmentally friendly semiconductor material with abundantly available in nature and wide range of applications (Ravichandran & Karthick, 2020a). Many researchers have developed nanostructured semiconductor materials because of their large surface area, small size, controllable shape, chemical composition and physiochemical stability (Nakarungsee et al., 2020). ZnO having a wide direct band gap (3.36 eV) and a large exciton binding energy 61 meV (Siddique et al., 2018) which enables applications in various electrical and optical fields. Nanostructured semiconductors are interest nowadays especially zinc oxide (ZnO) with a lot of attention among systematic researchers because of its photocatalytic ability, tuning the band gap, unique optical, magnetic and electronic properties (Anitha &
Muthukumaran, 2020). Wide application created nanoparticles, nanobelts, and other complex morphologies. Doping nanoscale designs can optimize performance. By changing ZnO lattice parameters, dopants increase material applicability. The dopan ion radius greatly affect the dopan’s ability to enter
the lattice of ion the crystal by creating distortion. The wide band gap of the zinc oxide semiconductor leads to have a good carrier density which the most promising magnetic semiconductors for optoelectronics, spintronics, and nanotechnology (Peña-Garcia, Guerra, Farias, et al., 2019). ZnO can absorb a large part of the solar spectrum, for changing the properties requires doping with appropriate methods (Priscilla et al., 2020).
Photocatalytic applications by absorbing electromagnetic radiation to speed reactions.
Sol-gel, coprecipitation, chemical bath deposition, hydrothermal, combustion, and doping ZnO nanoparticles at different concentrations can produce it. Morphological adjustment, particle size control, homogeneous particle preparation, and rare earth doping have been used to enhance pure ZnO's magnetic and photocatalytic properties. Cobalt has been studied. (Ravichandran & Karthick, 2020b) as dopants to improve the optoelectronic properties of semiconductors, including fuel cells, optical coatings, solid-state lasers, three-dimensional displays, sensors, platonic devices, high-tech applications like light-emitting diodes, piezoelectric
transducers and actuators, UV ultraviolet light emitters, photocatalysts, biosensors, biomedical applications, and dye-sensitive solar cell fabrication. (Sahu et al., 2020). ZnO nanoparticles doped with rare earth ions improve semiconductor nanoparticle optical properties, according to several studies. Rare earth metals trap electrons, preventing photo- generated electron-hole pair recombination.
(Anitha & Muthukumaran, 2020). Zinc is an inorganic material that can be synthesized. Its white crystalline powder is almost insoluble in water (Priscilla et al., 2020). This paper synthesizes in sol-gel, hydrothermal, and co- precipitation methods to test metal dopants (rare earth metals, noble metals, poor metals) and non-metals. This paper provides three methods with material reference from 2010 to recent to help produce specific function semiconductor material in the future.
METHODS
Many methods have been reported to produce ZnO; however, this review focuses on sol-gel methods, hydrothermal methods, and coprecipitation methods. The first step is to find a reference from sciencedirect.com, wiley, and sage by using keywords ZnO. Check the paper's objectives for metal and non-metal ZnO doping or co-doping. Select the 2010 paper and classify by doping: rare earth metals, noble metals, poor metals, and non-metals.
Make a table based on doping type after reading the abstract, discussion, and conclusion, then it shown on Table 1.
RESULTANDDISCUSSION Dopants
ZnO doped with rare earth metals
Rare earth-containing inorganic phosphorus material has been considered for luminescence efficiency and photophysical properties in high-functioning luminescence devices, display devices, solid-state lighting, and sensor applications in recent decades.
(Singh et al., 2020), in their research of Gd ion- doped CaLa2ZnO5 samples prepared by the sol-gel combustion method at an optimum concentration of 0.045 mol Gd3+ ion and Gd3+
ion occupied a distorted site in the LaO8 polyhedra in CaLa2ZnO5 host. From the SEM results, the particles containing pores and the XRD results, Gd3+, can be easily combined in the CaLa2ZnO5 lattice because of their similar ionic radii, respectively 0.93 Å and 1.032 Å. The crystal size of the Scherrer equation is in the range of 38.08-43.69 nm. The incorporation of small amounts of rare-earth ions does not cause significant changes in structure. The ferromagnetic and photocatalytic properties of Gd-doped pure ZnO (Yakout, 2018) confirmed the structure of the single-phase ZnO wurtzite and the effective incorporation of ions into the ZnO host lattice and an optical bandgap of 3.22 eV and implantation of Gd based double dopants causing a redshift between 0.01-0.29 eV with magnetization saturation 0.0133 emu/g and coercivity 85 Oe. Sol-gel and precipitation at 8000C for 10 hours synthesized luminescent dopants. (Guckan et al, 2020) at a concentration of 0.1% exerted an effect on the β-dose linearity extended from 1 Gy to 0.2 Gy, from the PL spectrum showing green emission associated with defects when the excitation wavelength was 350 nm, two sharp peaks at 579 and 615 nm are related to the Eu and when the calcination temperature is increased. After 1000 C, the porous structure appears at this peak. XRD shows pure hexagonal wurtzite structure. Effect of Eu (Vinoditha et al., 2019) on the third-order nonlinear response (TRO) of ZnO nanoparticles was also investigated by the Hydrothermal Facile technique, using Saponim as a capping agent and showing good crystallinity with the hexagonal wurtzite crystal structure where the lattice parameter increases with an Eu concentration of 1 at%, 3 at% and 5 at% calculated using the WH plot.
Local defect states below the conduction band reduced the energy gap with increased Eu doping concentrations. As well as morphological and luminescence studies (Suganthi & Chandra Bose, 2012) with the same 5 at% Eu dopant concentration showed Eu at the Zn site with a strong peak at 436 cm- 1 and an unchanged absorption peak at 373 nm. Additionally, Er (Vinoditha et al., 2020)
Table 1. Dopant rare earth metals Dopa
nt
Precursors Synthesis Conditions
Concentration Synthesis (Molar Ratio)
Meth ods
Properties and
applications
Reference
Eu zinc sulfate, Europium (III) nitrate
pentahydrate, polyethyleneimin e, ammonium hydroxide
Calcination at 800, 900, 1000, 1100 and 12000C for 2, 4, 6, 8, 10 and
24 h
at 0.1% Sol-
gel
hexagonal wurtzite structure g(D) of 1.04, dose range: 1 Gy to 0.2 kGy
(Guckan et al., 2020)
Gd Ca (NO3)2∙4H2O, La(NO3)3∙6H2O, Zn(NO3)2∙6H2O, citric acid, and Gd(NO3)3∙6H2O
Reaction at 500 rpm for 1 h, heated at 110°C Dried at 500°C for 120 min
Annealed at 10000C for 6 h
CaLa2ZnO5: Gd (CLZ1- CLZ6)
Sol- gel
crystallite size: 38.08–
43.69nm λexc = 227 nm
(Singh et al., 2020)
Y and Cu
zinc acetate dehydrate, yttrium (III) acetate monohydrate, copper acetate monohydrate, N,N dimethyl- formamide (DMF)
Reaction at 60oC for 2 h
evaporated and dried for 2 h annealed at 500oC for 4 h
Zn.96-xY.04CuxO (x = 0, 0.05, 0.10 and 0.15)
Sol- gel
Hexagonal wurtzite structure, crystallite size (D): 15.9 – 23.9 nm oxygen percentage:
57.88% to 64.53%
optoelectroni c device as transparent electrode
(Ananda n et al., 2014)
Nd and V
Zinc nitrate hexahydrate, neodymium nitrate hexahydrate ammonium metavanadate, citric acid, hexamethylenetet ramine,
Terephthalic acid, isopropyl alcohol.
Reaction with vigorous stirring at room
temperature, ultrasonication of ambient condition for 2 h, heated at 48 h at 700C.
dried at 900C for 14 h
calcined at 5000C for 4 h
Nd: 4 mol%
and V: 1 mol%, Nd_V_Z (Nd:
2-6 mol%, V 1 mol%)
Sol- gel
Hexagonal wurtzite structure, crystallite size: 19.9 – 35.8 nm photocatalyts , the
abatement of organic pollutants
(Alam et al., 2019)
Y and Co
Zinc nitrate, cobalt nitrate, yttrium nitrate and citric acid
reaction at 80°C dried at 150°C for 10 h
heated at 500°C for 4 h
Zn0.92Co0.04Yo0. 04O
Sol- gel
hexagonal wurtzite structure Particle size:
11.2 nm
(Bhakta
&
Chakrab arti, 2019) Zn0.96Co0.04O hexagonal
wurtzite structure
Particle size:
20.51 nm Spintronic Ce
and Li
Zinc acetate 97ehydrate (Zn(CH3COO)2.2 H2O), 2-
methoxyethanol, MEA, cerium nitrat, lhitum asetat
Reaction at 60 °C for 1 h
dried at 80 °C for 10 min
annealed at 500
°C for 1 h
(Ce= 0.1 at.%) and (Li= 5, 10, 15 and 20 at.%)
Sol- gel
hexagonal wurtzite structures crystallite size: 15.7 – 19.8 nm --- ---
(Chelouc he et al.., 2017)
Gd, Mn
Zinc nitrate, gadolinium nitrate, manganese chloride, and sodium hydroxide
Solution stirred for 10 min Heated at 120 °C for 24 h
dried at 80 °C for 12 h
3 at % hydr
other mal
monodispers e and closely hexagonal shaped Particle size:
42 – 48 nm Bandgap:
3.25 – 3.30 eV ferromagneti c material
(Poornap rakash et al., 2017)
into the ZnO host matrix associated with surfactant (Oleylamine) showed a bandgap shrinkage, decreased MBE emission intensity with increased dopant concentration due to the formation of surface defects under the edge of the conduction band, which was investigated using UV-vis spectroscopy.
To obtain the desired nanocrystalline phase and increase the void of ZnO nanoparticles with Gd3+ dopants (Das et al., 2017) were also carried out where samples were sintered at 4000C and 6000C for 2 hours with the result that there was no impure phase in the ZnO nanostructures. Void oxygen and room temperature ferromagnetic content in a 5% sample were described with a blank- assisted magnetic polaron assisted. The correct selection and concentration of dopant atoms in a co-doped system are essential in achieving high dielectric constants in the ZnO nanosystem. On the other hand, the addition of Mn (Poornaprakash et al., 2017) also entered the replacement ion hexagonal lattice without changing its internal structure with an average size of 42-48 nm, monodisperse, hexagonal morphology, and a redshift from the absorption edge confirming a decreased optical bandgap. Not only that, the use of the
addition of rare earth metals dopant, namely Cerium (Vakili et al., 2019), in overcoming difficulties associated with accessing water resources, processing, and recycling is effective at 1% molar percentage and efficiency increases to 51.56% under the light. UV and 32.45% under visible light, increasing the influent to 3000 mg/L results in a decrease in efficiency of up to 21.9% under UV light and 10.12% under visible light and an increase in exposure time.
Mixed phase photoluminescence at Tb3+
with a dopant concentration of 0.025% by sol- gel technique (Mhlongo et al., 2019), emitted at 585 nm when excited at 374 nm, was associated with a defect centre in the ZnO phase. It then shows emission peaks at 545, 590, and 623 nm associated with the 4f from Tb3+ at an annealing temperature of 10000C. The annealing period can be increased to 5.4 hours to increase luminescence and cooling. Yttrium- doped ZnO thin film heterojunction diode on p-Si substrate annealed at 600°C has a flash voltage of 2.61 V and an ideality factor of 1.89.
ZnO's donor electrons shift the Fermi energy level toward the conduction band, increasing hetero diode interest. (S. K. Sharma et al., 2018).
Applications
In using the type of doping material shown in Figure 1, the concentration of doping on ZnO and different methods significantly influence the results of the material obtained and its application. As a rare earth metal, the effect of Eu doping with Saponin capping agent by hydrothermal method showed that with increasing doping, grain size and bandgap energy decreased to 18 nm and 2.94 eV at 5% Eu and showed assertive saturated absorption behaviour and was possible in applications NLO (Vinoditha et al., 2020).
Photonic device manufacturing may benefit from nonlinear parameter quantification. Eu dopant at 5% exhibits assertive saturation absorption with carrier depletion in the ground state, and the thermo-optical effect causes self- focusing. Nonlinear optical enhancements
helped NLO applications like optical switching, memory management, and optical data storage. (Vinoditha et al.., 2019). Another study using Eu's dopant (Suganthi & Chandra Bose, 2012) using the hydrothermal method revealed that the doping concentration is controlled to produce different morphologies.
The results obtained with 1% doping showed that the particle size of 33 nm increased with increasing doping and showed superior Luminescent properties. High-thermal stability and antibacterial polymer composites can control bacterial growth and extend food shelf life. According to antibacterial reports, co-precipitation by co-doping 4% Cu into Zn- La-O increases crystal size and oxygen vacancy density, increasing ROS values and killing pathogenic microorganisms. (Anitha &
Muthukumaran, 2020).
(a) (b)
Figure 1. Schematic diagram application of ZnO a) Photocatalyst, b) Sensing NH3
The ZnO hydrothermal method can be used for optical sensing with 1% Al doping (Agarwal et al., 2020). Defects that trap electrons reduce electron concentration and shrink the bandgap, improving UV emission and Al doping. With the sol-gel method, the synthesis of the IDE nanostructured biosensor device successfully detected different versions of DNA (Gherab et al., 2020). With the same method, the sensor based on Mg 3% ZnO showed a competitive response at a working temperature of 300 C. in detecting low ethanol (Jaballah et al., 2020). Thus, the sol-gel method holds promise for developing a cost-effective,
non-enzymatic electrochemical glucose biosensor with good features, practical application with high accuracy and precision at 97% glucose concentration in human blood serum with the addition of 10 times 0.1M NaOH at pH 13 (Mahmoud et al., 2019).
Photocatalysts use photons to break down organic pollutants using ZnO doping. Sunlight photo-induced ZnO fills the e- of the valence band (VB) and empties the conduction band (CB). Photo-induction produces electron-hole pairs (e-/h+) that migrate to the ZnO surface and are seen in redox reactions, where h+
creates hydroxyl radicals with water and
hydroxide ions. Instead, e- reacts with oxygen to produce superoxide radical anions and hydrogen peroxide. Hydrogen peroxide and superoxide radicals form hydroxyl radicals (Boon et al., 2018). The resulting hydroxyl radicals are potent oxidizing agents that will attack the adsorbed pollutants on the ZnO surface to produce fast intermediates.
Moreover, these intermediates will eventually be converted into CO2, H2O compounds, and mineral acids. The addition of doping generally increases the degradation efficiency significantly. Al films as ZnO dopants deposited onto glass substrates by simple sol- gel immersion showed good photocatalytic efficiency due to charge entrapment by Al dopants, increased surface area due to size reduction, grain, and AZO thin film bandgap narrowing. 81% transmission. Increased grain boundary density increases optical scattering and transmission, and doping concentration decreases the optical band gap from 3.44 to 3.06eV (Islam et al., 2019). On the other hand, in a study conducted (Gherab et al., 2020) at Al 3 at %, Used for IDE biosensor devices to detect DNA applications with good stiffness for long- term use, photocatalyst applications, ceramic materials (Wang et al., 2020). In photocatalysts, power depends on the ability of the material to generate electrons and holes by light irradiation (Narjis et al., 2020). Ti is a metal at a concentration of 0.09, resulting in better light absorption to produce polymer solar cells (PSC) with higher power conversion efficiency (R. N. Chauhan, 2019).
CONCLUSIONS
ZnO is a semiconductor with a 3.2 eV energy bandgap. Doping ZnO improves its properties for use in various fields.
Hydrothermal and precipitation affect ZnO nanoparticle doping of rare earth metals, metals, noble metals, poor metals, and non- metals with the sol-gel method. Doping concentration, type, and process affect ZnO lattice parameters. Doped ZnO nanoparticles as semiconductors enable photocatalytic, glucose biosensors, VOC detection sensors, antibacterial, biomedical, optoelectronic,
spintronic, LED, NLO, and silicon solar cell applications.
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