# Characterization of Fabricated Gold-Doped ZnO Nanospheres and Their Use as a Photocatalyst in the Degradation of DR-31 Dye

Authors: Neha Verma; Vishal Jagota; Arnold C. Alguno; Alimuddin; Manik Rakhra; Pawan Kumar; Betty Nokobi Dugbakie
Journal: Journal of Nanomaterials
 (2022)

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## Abstract

Water contamination is a significant issue in the modern day, caused by the textile dying business, and it has a detrimental impact on living organisms. We report on the manufacture of gold-doped ZnO nanospheres using a simple heat treatment approach and the use of ZnO nanoparticles as photocatalysts for the degradation of methyl orange dye. To increase this degrading activity, Au was utilised as a modifier, and their temperature quenching effect was noticed. One of the most efficient electron grabbers in the conduction band is Au ion. The novelty of this recent research is that it has found that anatase to rutile phase transformation is promoted, and the highest transformation was achieved by using 1.0% of Au, which proves Au-doped ZnO-based nanoparticles are best for this degradation of dyes. The structural, morphological, optical, electrical, and photocatalytic characteristics of the synthesised nanocatalysts were determined. These nanoparticles have a grain size of 45-75 nm. Photocatalytic activity was investigated using UV-Vis spectra, and a significant absorption peak of about 482 nm was discovered. With increasing frequency, the dielectric constant and frequency of the produced nanoparticles drop. The kinetic analysis yields a rate constant of 0.0165 min-1 for nanosphere-like particles. At a concentration of 1% Au, the produced nanoparticles degrade the dye completely in 150 minutes when exposed to UV light.


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## Body

## 1. Introduction

Chemical synthesis has become increasingly important as the modern industry has progressed. The textile industry is one of the biggest consumers of chemicals on this list. The textile sector contributes to pollution of the environment and human health by using nonbiodegradable chemicals, which is why their eradication is a priority. Nowadays, the textile sector generates seven lakh tones of dyes every year, which often has a negative impact on the environment. Synthetic dyes are primarily employed in a variety of sectors, including food, leather, and textiles [1]. The photocatalytic destruction of organic pollutants in the presence of sunlight is a novel issue in the treatment of wastewater. ZnO nanoparticles might be a minimal, nontoxic, and stable photocatalyst for totally eliminating organic pollutants [2, 3]. While dye-contaminated water imparts color to the water, its nonbiodegradable nature poses a major threat to aquatic life. Dye poses a greater risk to human health and the environment. Researchers are working feverishly to protect the environment and human health. Advanced oxidation processes may be used in this clean-up. Among these activities, Au-doped ZnO as photocatalysts are critical for the UV-mediated destruction of hazardous compounds [4, 5]. The installation of dopants has garnered much attention. It has the potential to increase surface area and functionality. On the other hand, its electron-hole density and low surface area are the main roadblocks to its industrialisation. By forming a Schottky barrier that facilitates electron-hole separation, noble metals such as Pt, Ag, or Au improve the photocatalytic efficacy of ZnO [6, 7]. Several researchers have examined the doping of Zn with various doping elements such as Ce, In, Eu, and Sb to improve optoelectronic properties [8–11].Because of its potential to produce surface plasmon at a specific wavelength, Au is a promising nanoparticle for future improvements. A properly built Au-ZnO nanocomposite should promote hot electron injection between metallic nanoparticles and the ZnO conduction band, allowing this reaction to extend into the visible range [12, 13]. A synthetic dye called methyl orange (MO) has the chemical formula C14H14N3NaO3S. MO is a bright orange powder. Methyl orange sodium salt is the end product of this process. This dye can be dissolved in ethanol but only in very small amounts in water. It is utilised in a wide range of sectors, from textiles to printing on paper to plastic to food and leather [14, 15]. Methyl orange, on the other hand, is harmful to human health. It is therefore imperative to establish effective methods for dealing with health-related issues. Sedimentation and degradation by photocatalysis are only a few of the methods that have been employed [16, 17]. In the presence of a photocatalyst, one of the better strategies is photocatalytic degradation.Many scientists employ a gold salt solution to infuse metallic gold nanoparticles on ZnO surfaces, then use NaBH4, ascorbic acid, or glucose as a reducing agent to decrease Au3+ into metallic Ag nps [18, 19]. ZnO, a semiconductor from the II-VI family, is a significant dye decomposition catalyst (inorganic). According to [20], electrons in the conduction band react with O2, while holes in the valence band react with water. The radicals O2- and hydroxyl are produced. According to [21], azo dye was destroyed in 150 minutes by ZO films having Ag doped with ZO films.This quick reduction of gold cations, which hinders light penetration and lowers catalytic responsiveness, aids the formation of various agglomerates of metallic gold nanoparticles on the ZnO surface [9, 22]. The quenching impact of Au-doped ZnO nanoparticles was proven as a result of temperature change utilising a simple heat treatment approach (cool for 2 hrs.). Because of the reduction of Au3+, the activity of Au/ZnO decreased after heat treatment or hydrogen reduction. The use of an appropriate amount of Au3+ on the surface of ZnO as a photo-produced electron trap can help improve the effectiveness of the photocatalytic oxidation process. The synthesis of Au-doped ZnO nanoparticles and their effective photodegradation of methyl orange dye were shown to be quenched by temperature. In 150 minutes, UV irradiation with Au-ZnO nanoparticles causes practically complete photodegradation of the methyl orange dye.


## 2. Experimental Procedure

Nanoparticles of gold- (Au-) doped ZnO were created using a heat treatment method. These chemicals are all purchased from Sigma Aldrich, and they are triple-deionized water (TDW). In this process, dextrose is employed as fuel and 0.27 M zinc nitrate hexahydrate is dissolved in 15 ml triple-deionized water. Using a magnetic stirrer, the reaction is heated to 70°C and stirred continuously for 40 minutes. Au is used as a dopant at 1%. With and without quenching, doped ZnO nanoparticles have an impact on the temperature effect (direct cooling for 2 hrs before annealing). It was filtered and placed into a crucible in a muffle furnace at the temperature of 450°C after the stirring had been completed and the filtrate had been collected. It was crushed and annealed for an hour at 600°C after getting a spongy-like material for 10-12 minutes. Structural and morphological studies, optical and electrical properties, and photocatalytic properties of the synthesised nanoparticles were all carried out in great detail. Variations in the physical and chemical properties of ZnO nanoparticles made by a straightforward heat treatment procedure in different solvents are discussed.An X-ray Diffractometer (XRD) with X’Pert Pro analysis software and radiation sources ranging from 20 to 800 nm was used to determine the crystallinity of ZnO nanoparticles. The surface morphology was investigated using a JSM-6100 (JEOL) Field Emission Scanning Electron Microscope (FESEM). A Shimadzu device from Japan was used to examine the KBr pellets’ Fourier Transform Infrared Spectra (FTIR). For the KBr pellets analysed, this device provides information on both the organic and inorganic modes of the KBr pellets and their vibrational modes. With a Shimadzu UV-Vis 2600/2700 double beam spectrophotometer, we studied absorption and the optical band gap.


### 2.1. Methyl Orange Dye Photocatalytic Degradation

ZnO nanoparticles were put to the test against an orange dye using a custom-built photoreactor. A water-circulating jacket, an aperture for sample extraction, and a supply of oxygen were used to keep the temperature and heat dissipation constant during the photocatalytic experiment. UV radiation was created using a 125 W low-pressure mercury vapour lamp. The solution, which contained 20 ppm methyl orange color, required 150 ml of triple-deionized water. In the dye solution, ZnO nanoparticles were utilised as a photocatalyst. To maintain optimum photocatalyst homogeneity and sustain the absorption-desorption balance, the suspensions were ultrasonically homogenised in the dark for 30 minutes before UV irradiation. The photoreactor was placed atop a magnetic stirrer for the photocatalytic experiment. At 25-minute intervals, 3.0 ml of the solution was collected from the photoreactor and centrifuged at 3000 rpm to remove ZnO suspensions. Each sample’s UV-Vis spectrum was analysed between 2600 and 2700 nm to determine its UV-Vis spectrum (Shimadzu). The maximum wavelength of methyl orange is 482 nm. The photocatalytic degradation ratio was calculated using the equation:(1)Percentagephotodegradation=Ao−AAo×100,where Ao is the dye’s initial absorbance and A is the dye solution’s absorbance after UV light irradiation.


## 2.1. Methyl Orange Dye Photocatalytic Degradation

ZnO nanoparticles were put to the test against an orange dye using a custom-built photoreactor. A water-circulating jacket, an aperture for sample extraction, and a supply of oxygen were used to keep the temperature and heat dissipation constant during the photocatalytic experiment. UV radiation was created using a 125 W low-pressure mercury vapour lamp. The solution, which contained 20 ppm methyl orange color, required 150 ml of triple-deionized water. In the dye solution, ZnO nanoparticles were utilised as a photocatalyst. To maintain optimum photocatalyst homogeneity and sustain the absorption-desorption balance, the suspensions were ultrasonically homogenised in the dark for 30 minutes before UV irradiation. The photoreactor was placed atop a magnetic stirrer for the photocatalytic experiment. At 25-minute intervals, 3.0 ml of the solution was collected from the photoreactor and centrifuged at 3000 rpm to remove ZnO suspensions. Each sample’s UV-Vis spectrum was analysed between 2600 and 2700 nm to determine its UV-Vis spectrum (Shimadzu). The maximum wavelength of methyl orange is 482 nm. The photocatalytic degradation ratio was calculated using the equation:(1)Percentagephotodegradation=Ao−AAo×100,where Ao is the dye’s initial absorbance and A is the dye solution’s absorbance after UV light irradiation.


## 3. Results and Discussions

### 3.1. Discussions and Outcomes

#### 3.1.1. Structural Consistency

The X-ray Diffraction (XRD) method was used to investigate the crystallinity of Au-doped ZnO nanoparticles. The XRD method was used to study Au-ZnO nanoparticles after they were exposed to temperature quenching. The XRD pattern of Au-ZnO is shown in Figure1. XRD patterns of Au-ZnO planes (100), (001), (002), (101), (102), (110), (103), and (112) at 2θ=31.89°, 34.42°, 36.23°, 47.54°, 56.69°, 62.95°, 68.0°, and 69.21°, respectively, reveal well-defined reflections in the hexagonal phase (201). The existence of the most pronounced peak demonstrates the material’s polycrystalline structure (101). Diffraction patterns measured closely match the typical card numbering method. Bragg’s formula was used to establish the distance between the lattices:
(2)nλ=2dsinθ,where d is interatomic spacing; θ is the incident angle, also known as the Bragg angle; and n is the reflection order and is the wavelength of the incident X-ray used.Figure 1
XRD spectra of Au-doped ZnO nanoparticles: (a) direct annealing; (b) with quenching effect of temperature.Crystal size was calculated using Scherrer’s formula:(3)D=kλβcosθ.These measured particles have been analysed from the ImageJ software, and it has been found that it lies in the nanoscale range, but the difference is that with quenching and without quenching, its nanoscale range is varying. The valuesD and K stand for crystal size, constant, full width half maximum, and Bragg’s angle, respectively. This yields the CuK1 radiation’s mean wavelength, full width half maximum, and Bragg’s angle, which is measured in radians. D’s computed value is displayed in Table 1. There is a 20-35 nm crystal size range that has been seen. There was no peak in the dopant used, which may have been due to a reduced dopant percentage. The peak’s maximum intensity shifts toward a larger diffraction angle as a result of temperature quenching. Oxygen deficiency during quenching may have resulted in a decrease in lattice properties. This might be due to this. This is because the crystals have grown in size. Quenching increases the (101) peak’s intensity, indicating that it prefers to be oriented along the c-axis.Table 1
Effect of temperature on different properties of Au-ZnO.
Effect of temperatureCrystallite size (XRD)Grain size (nm) (FESEM)Band gap (eV)Without quenching28.2340-453.046With quenching32.5355-603.024


### 3.2. Surface Morphology

FESEM images of Au-ZnO nanoparticles generated under the quenching effect of temperature are shown in Figure2. In the case of direct annealing, the surface was rather rough, and the grain size was not uniform [35]. However, as quenching time increased, surface roughness reduced. As seen in Figure 2(b), doped ZnO nanoparticles (quenching) create almost equally dispersed nanoparticles of various forms, the majority of which are spherical in shape with an average diameter of 45–75 nm (Table 1). Thus, it has been shown that the quenching impact of temperature improves the quality of doped nanoparticles. These findings suggest that quenching makes nanoparticles more homogeneous. It has a high volume-to-surface ratio, which is helpful for photodegradation of dyes.Figure 2
FESEM images of Au-ZnO nanoparticles: (a) direct annealing; (b) with quenching effect of temperature.
(a)(b)


### 3.3. Optical Properties

The compositional features of Au-ZnO nanoparticles were studied using infrared Fourier transformation spectroscopy. Figure3 displays the FTIR spectra of quenched and unquenched ZnO nanoparticles. (a) A large band of doped ZnO nanoparticles can be seen at 3479 cm-1, while another strong band at 481 cm-1 reveals the stretching mode of ZnO. This indicates the presence of ZnO in the combination. The COO- group can be found between 1250 and 1750 cm-1.Figure 3
FTIR spectra of Au-ZnO nanoparticles: (a) direct annealing; (b) with quenching effect of temperature.ZnO nanoparticle absorbance spectra range from 200 to 800 nm at room temperature, according to a UV-visible spectrophotometer (varies between 1 and 1.4). (b) Ultraviolet/visible spectra provide information on nanomaterial excitonic and transition characteristics. It is necessary to compare how many photons travel through and how many strikes a sample in order to determine its transmittance [23]. Because of the size difference, the UV absorption peak moves from 407 nm to 410 nm [24]. Au-ZnO nanoparticles’ UV absorption intensity is greater than the temperature’s quenching impact, even if they are heated directly. The optical band gap of the synthesised ZnO nanoparticles may be calculated using the absorbance spectra shown in Figures 4(a) and 4(b):
(4)Eg=1240λ,where λ is the maximum wavelength of the well-defined absorbance peak.Figure 4
Absorbance spectra of Au-ZnO nanoparticles: (a) direct annealing; (b) with quenching effect of temperature.The reduction in band gap might be caused by a variety of variables, including structural parameter, carrier concentration, grain size, and impurity presence, or it could be caused by the elimination of oxygen vacancies [25, 26]. The optical band gap is reported to be between 3.00 and 3.20 eV (Table 1), with a greater band gap seen in the case of direct thermal annealing [27]. This is considered to have a higher conductivity in the case of quenched nanoparticles.


### 3.4. Electrical Properties

Measurements of capacitance and dielectric constant may be used to determine the nature of the nanoparticles created [28]. The fluctuation of capacitance and dielectric constant with frequency is shown in Figures 5(a) and 5(b), and it is discovered that high frequencies have a low capacitance value. Additionally, it has been reported that higher capacitance values are seen in the case of Au-ZnO nanoparticles generated by the quenching effect of temperatures in the range of 2-10 μF. A high capacitance value is the outcome of interface states that are in equilibrium with the ac signal in order to accurately follow it [29]. Due to their electrical characteristics, these produced materials are advantageous for fabricating charge storage devices. The formula may be used to get the value of the dielectric constant:
(5)C=€0€rAd,where C represents capacitance, €0 represents the dielectric constant, A is the area of the round pellet, and d represents its thickness. The dielectric constant falls with frequency, as seen in Figures 6(a) and 6(b). This frequency-dependent fluctuation is caused by the charge transport relaxation time [30].Figure 5
Capacitance versus frequency; dielectric constant versus frequency of Au-ZnO nanoparticles: (a) direct annealing.Figure 6
Capacitance versus frequency; dielectric constant versus frequency of Au-ZnO nanoparticles: (b) with quenching effect of temperature.


## 3.1. Discussions and Outcomes

### 3.1.1. Structural Consistency

The X-ray Diffraction (XRD) method was used to investigate the crystallinity of Au-doped ZnO nanoparticles. The XRD method was used to study Au-ZnO nanoparticles after they were exposed to temperature quenching. The XRD pattern of Au-ZnO is shown in Figure1. XRD patterns of Au-ZnO planes (100), (001), (002), (101), (102), (110), (103), and (112) at 2θ=31.89°, 34.42°, 36.23°, 47.54°, 56.69°, 62.95°, 68.0°, and 69.21°, respectively, reveal well-defined reflections in the hexagonal phase (201). The existence of the most pronounced peak demonstrates the material’s polycrystalline structure (101). Diffraction patterns measured closely match the typical card numbering method. Bragg’s formula was used to establish the distance between the lattices:
(2)nλ=2dsinθ,where d is interatomic spacing; θ is the incident angle, also known as the Bragg angle; and n is the reflection order and is the wavelength of the incident X-ray used.Figure 1
XRD spectra of Au-doped ZnO nanoparticles: (a) direct annealing; (b) with quenching effect of temperature.Crystal size was calculated using Scherrer’s formula:(3)D=kλβcosθ.These measured particles have been analysed from the ImageJ software, and it has been found that it lies in the nanoscale range, but the difference is that with quenching and without quenching, its nanoscale range is varying. The valuesD and K stand for crystal size, constant, full width half maximum, and Bragg’s angle, respectively. This yields the CuK1 radiation’s mean wavelength, full width half maximum, and Bragg’s angle, which is measured in radians. D’s computed value is displayed in Table 1. There is a 20-35 nm crystal size range that has been seen. There was no peak in the dopant used, which may have been due to a reduced dopant percentage. The peak’s maximum intensity shifts toward a larger diffraction angle as a result of temperature quenching. Oxygen deficiency during quenching may have resulted in a decrease in lattice properties. This might be due to this. This is because the crystals have grown in size. Quenching increases the (101) peak’s intensity, indicating that it prefers to be oriented along the c-axis.Table 1
Effect of temperature on different properties of Au-ZnO.
Effect of temperatureCrystallite size (XRD)Grain size (nm) (FESEM)Band gap (eV)Without quenching28.2340-453.046With quenching32.5355-603.024


## 3.1.1. Structural Consistency

The X-ray Diffraction (XRD) method was used to investigate the crystallinity of Au-doped ZnO nanoparticles. The XRD method was used to study Au-ZnO nanoparticles after they were exposed to temperature quenching. The XRD pattern of Au-ZnO is shown in Figure1. XRD patterns of Au-ZnO planes (100), (001), (002), (101), (102), (110), (103), and (112) at 2θ=31.89°, 34.42°, 36.23°, 47.54°, 56.69°, 62.95°, 68.0°, and 69.21°, respectively, reveal well-defined reflections in the hexagonal phase (201). The existence of the most pronounced peak demonstrates the material’s polycrystalline structure (101). Diffraction patterns measured closely match the typical card numbering method. Bragg’s formula was used to establish the distance between the lattices:
(2)nλ=2dsinθ,where d is interatomic spacing; θ is the incident angle, also known as the Bragg angle; and n is the reflection order and is the wavelength of the incident X-ray used.Figure 1
XRD spectra of Au-doped ZnO nanoparticles: (a) direct annealing; (b) with quenching effect of temperature.Crystal size was calculated using Scherrer’s formula:(3)D=kλβcosθ.These measured particles have been analysed from the ImageJ software, and it has been found that it lies in the nanoscale range, but the difference is that with quenching and without quenching, its nanoscale range is varying. The valuesD and K stand for crystal size, constant, full width half maximum, and Bragg’s angle, respectively. This yields the CuK1 radiation’s mean wavelength, full width half maximum, and Bragg’s angle, which is measured in radians. D’s computed value is displayed in Table 1. There is a 20-35 nm crystal size range that has been seen. There was no peak in the dopant used, which may have been due to a reduced dopant percentage. The peak’s maximum intensity shifts toward a larger diffraction angle as a result of temperature quenching. Oxygen deficiency during quenching may have resulted in a decrease in lattice properties. This might be due to this. This is because the crystals have grown in size. Quenching increases the (101) peak’s intensity, indicating that it prefers to be oriented along the c-axis.Table 1
Effect of temperature on different properties of Au-ZnO.
Effect of temperatureCrystallite size (XRD)Grain size (nm) (FESEM)Band gap (eV)Without quenching28.2340-453.046With quenching32.5355-603.024


## 3.2. Surface Morphology

FESEM images of Au-ZnO nanoparticles generated under the quenching effect of temperature are shown in Figure2. In the case of direct annealing, the surface was rather rough, and the grain size was not uniform [35]. However, as quenching time increased, surface roughness reduced. As seen in Figure 2(b), doped ZnO nanoparticles (quenching) create almost equally dispersed nanoparticles of various forms, the majority of which are spherical in shape with an average diameter of 45–75 nm (Table 1). Thus, it has been shown that the quenching impact of temperature improves the quality of doped nanoparticles. These findings suggest that quenching makes nanoparticles more homogeneous. It has a high volume-to-surface ratio, which is helpful for photodegradation of dyes.Figure 2
FESEM images of Au-ZnO nanoparticles: (a) direct annealing; (b) with quenching effect of temperature.
(a)(b)


## 3.3. Optical Properties

The compositional features of Au-ZnO nanoparticles were studied using infrared Fourier transformation spectroscopy. Figure3 displays the FTIR spectra of quenched and unquenched ZnO nanoparticles. (a) A large band of doped ZnO nanoparticles can be seen at 3479 cm-1, while another strong band at 481 cm-1 reveals the stretching mode of ZnO. This indicates the presence of ZnO in the combination. The COO- group can be found between 1250 and 1750 cm-1.Figure 3
FTIR spectra of Au-ZnO nanoparticles: (a) direct annealing; (b) with quenching effect of temperature.ZnO nanoparticle absorbance spectra range from 200 to 800 nm at room temperature, according to a UV-visible spectrophotometer (varies between 1 and 1.4). (b) Ultraviolet/visible spectra provide information on nanomaterial excitonic and transition characteristics. It is necessary to compare how many photons travel through and how many strikes a sample in order to determine its transmittance [23]. Because of the size difference, the UV absorption peak moves from 407 nm to 410 nm [24]. Au-ZnO nanoparticles’ UV absorption intensity is greater than the temperature’s quenching impact, even if they are heated directly. The optical band gap of the synthesised ZnO nanoparticles may be calculated using the absorbance spectra shown in Figures 4(a) and 4(b):
(4)Eg=1240λ,where λ is the maximum wavelength of the well-defined absorbance peak.Figure 4
Absorbance spectra of Au-ZnO nanoparticles: (a) direct annealing; (b) with quenching effect of temperature.The reduction in band gap might be caused by a variety of variables, including structural parameter, carrier concentration, grain size, and impurity presence, or it could be caused by the elimination of oxygen vacancies [25, 26]. The optical band gap is reported to be between 3.00 and 3.20 eV (Table 1), with a greater band gap seen in the case of direct thermal annealing [27]. This is considered to have a higher conductivity in the case of quenched nanoparticles.


## 3.4. Electrical Properties

Measurements of capacitance and dielectric constant may be used to determine the nature of the nanoparticles created [28]. The fluctuation of capacitance and dielectric constant with frequency is shown in Figures 5(a) and 5(b), and it is discovered that high frequencies have a low capacitance value. Additionally, it has been reported that higher capacitance values are seen in the case of Au-ZnO nanoparticles generated by the quenching effect of temperatures in the range of 2-10 μF. A high capacitance value is the outcome of interface states that are in equilibrium with the ac signal in order to accurately follow it [29]. Due to their electrical characteristics, these produced materials are advantageous for fabricating charge storage devices. The formula may be used to get the value of the dielectric constant:
(5)C=€0€rAd,where C represents capacitance, €0 represents the dielectric constant, A is the area of the round pellet, and d represents its thickness. The dielectric constant falls with frequency, as seen in Figures 6(a) and 6(b). This frequency-dependent fluctuation is caused by the charge transport relaxation time [30].Figure 5
Capacitance versus frequency; dielectric constant versus frequency of Au-ZnO nanoparticles: (a) direct annealing.Figure 6
Capacitance versus frequency; dielectric constant versus frequency of Au-ZnO nanoparticles: (b) with quenching effect of temperature.


## 4. Photocatalytic Application

The photocatalytic application used Au-doped ZnO nanoparticles with methyl orange as the target dye. Using UV light, photocatalytic degradation was performed. At regular time intervals of 200-750 nm, methyl orange dye absorbance spectra are shown in Figure7. Au-ZnO-induced breakdown of methyl orange was 99.0% during 10 hours of exposure to sunlight [31]. Methyl orange dye is broken down by doped ZnO nanoparticles, as seen by a gradual decline in absorbance intensity. The photocatalytic activity of Au ions, which operate as an efficient scavenger and trap electrons in the conduction band, is mostly due to the fluctuation in the shape of nanoparticles during quenching. Photocatalysis relies heavily on ZnO’s capacity to suck up dye molecules [32, 33].Figure 7
Absorption spectra for the photocatalytic degradation of methyl orange: (a) without temperature quenching and (b) with temperature quenching effect.
(a)(b)Figure8 depicts the photodegradation of methyl orange dye as a function of time and relative concentration in the presence of UV light. On Au-doped ZnO nanoparticles (photocatalyst), we employed both direct annealing (without quenching) and temperature-induced quenching to conduct this photocatalytic degradation experiment [34, 35]. In the presence of Au-ZnO, methyl orange dye fades completely within 150 minutes. Increased UV irradiation of methyl orange dye suspension for 150 minutes leads to a drop in the dye solution’s A/A0 value. In this experiment, ZnO was coupled with an Au nanoparticle as a dopant and photocatalyst (Figure 8(a)). The percent decline of photocatalytic degradation with and without the temperature quenching effect is shown in Figure 8(b). The % degradation of methyl orange dye as a function of irradiation time is shown in Figure 8(b). After 150 minutes of UV irradiation in the presence of Au modifier ZnO nanoparticles, dye degradation is complete (125 W). [36, 37]. The percent decline of photocatalytic degradation with and without the temperature quenching effect is shown in Figure 8(b). The % degradation of methyl orange dye as a function of irradiation time is shown in Figure 8(b). After 150 minutes of UV irradiation in the presence of Au modifier ZnO nanoparticles, dye degradation is complete (125 W) [38].Figure 8
Time of ageing ofA/Ao for MO dye with Au-doped ZnO nanoparticles (min): (a) no quenching; (b) quenching with temperature.
(a)(b)


### 4.1. Degradation by Photocatalysis Kinetics of Methyl Orange Dye with and without Temperature Quenching

The kinetics of Au-ZnO nanoparticles (photocatalyst) for methyl orange degradation were investigated using the Langmuir-Hinshelwood kinetic model [32]:
(6)lnC0C=kt,where C0 is methyl orange dye concentration and methyl orange dye concentration at irradiation time “t,” respectively. K stands for “pseudo-first-order rate constant.”The linear connection between irradiation duration is seen in Figure9. Half-life, linear regression coefficients (R), R2, and rate constant are summarized in Table 2. The photodegradation rate constant K for MO dye is determined by the slope of the line passing through the origin. Using MO dye, K was found to have a maximum value of 0.01667 cm-1. Methyl orange dye degraded rapidly within 150 minutes. Apparently, both doping and the quenching effect of temperature are to blame for MO dye’s rapid degradation. Figure 10 shows the doped ZnO nanoparticles after 150 minutes of UV irradiation with and without quenching conditions.Figure 9
MO dye pseudo-first-order kinetics with ZnO photocatalysts.Table 2
Kinetic data for methyl orange dye photodegradation in the presence of doped ZnO nanoparticles as photocatalysts.
Effect of temperatureRate constant (min-1)T1/2 (min)RR2Without quenching0.0151746.74910.994750.9797With quenching0.0166742.77840.871510.7521Figure 10
Doped ZnO nanoparticles after 150 minutes of UV irradiation.


### 4.2. Outcome of the Result

(i)
Herein, the gold-doped ZnO sample has been synthesised by using a simple heat treatment approach(ii)
This doping element is very seldom studied(iii)
Their effect with and without quenching on the photodegradation of dyes has been found(iv)
The best catalytic activity has been found with quenching(v)
At a concentration of 1% Au, the produced nanoparticles degrade the dye completely in 150 minutes when exposed to UV light


## 4.1. Degradation by Photocatalysis Kinetics of Methyl Orange Dye with and without Temperature Quenching

The kinetics of Au-ZnO nanoparticles (photocatalyst) for methyl orange degradation were investigated using the Langmuir-Hinshelwood kinetic model [32]:
(6)lnC0C=kt,where C0 is methyl orange dye concentration and methyl orange dye concentration at irradiation time “t,” respectively. K stands for “pseudo-first-order rate constant.”The linear connection between irradiation duration is seen in Figure9. Half-life, linear regression coefficients (R), R2, and rate constant are summarized in Table 2. The photodegradation rate constant K for MO dye is determined by the slope of the line passing through the origin. Using MO dye, K was found to have a maximum value of 0.01667 cm-1. Methyl orange dye degraded rapidly within 150 minutes. Apparently, both doping and the quenching effect of temperature are to blame for MO dye’s rapid degradation. Figure 10 shows the doped ZnO nanoparticles after 150 minutes of UV irradiation with and without quenching conditions.Figure 9
MO dye pseudo-first-order kinetics with ZnO photocatalysts.Table 2
Kinetic data for methyl orange dye photodegradation in the presence of doped ZnO nanoparticles as photocatalysts.
Effect of temperatureRate constant (min-1)T1/2 (min)RR2Without quenching0.0151746.74910.994750.9797With quenching0.0166742.77840.871510.7521Figure 10
Doped ZnO nanoparticles after 150 minutes of UV irradiation.


## 4.2. Outcome of the Result

(i)
Herein, the gold-doped ZnO sample has been synthesised by using a simple heat treatment approach(ii)
This doping element is very seldom studied(iii)
Their effect with and without quenching on the photodegradation of dyes has been found(iv)
The best catalytic activity has been found with quenching(v)
At a concentration of 1% Au, the produced nanoparticles degrade the dye completely in 150 minutes when exposed to UV light


## 5. Conclusions

Utilising dextrose as fuel, Au-doped ZnO nanoparticles were generated utilising a simple heat treatment process to analyse methyl orange dye photodegradation. Ceramic-based nanoparticles generated by temperature doping and quenching have remarkable optical characteristics and are very crystalline, as can be seen from the findings. Charge storage devices may benefit from Au-electrical ZnO’s characteristics. These findings suggest that the quenching effect of temperature has excellent photocatalytic qualities. The degradation of Au-doped ZnO nanoparticles was found to be finished in 150 minutes, with a rate constant of 0.01659 cm-1. –OH radical breakdown is impacted by the dye solution, as well. Ultrasonic irradiation was utilised to enhance these radicals. This is, to the best of our knowledge, the quickest rate of decrease.



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