In this research, ZnO doped Ni was immobilized over activated carbon nanoparticles, and the prepared photocatalysts were characterized by FTIR, XRD, SEM, EDS, and BET analyses and used for the degradation of reactive red 120 (RR120) dye under LED light irradiation. The C/ZnO-Ni photocatalyst demonstrated a flower-like morphology with mesoporous features. The effect of the main parameters like Zn:Ni molar ratio, photocatalyst amount, carbon mesh size, solution pH, initial RR120 concentration, H2O2 and power of LED lamp was investigated to maximize the efficiency of RR120 degradation. The best photocatalytic RR120 degradation of 94.88% was observed under the optimum conditions in which Zn:Ni molar ratio, photocatalyst amount, carbon mesh size, solution pH, initial RR120 concentration, H2O2 and power of LED lamp were adjusted at 1:2, 50 mg, 270, 3, 5 ppm, 0.2 mL and 50 W, respectively. Kinetic studies confirmed the applicability of the Langmuir-Hinshelwood theory by which the dye concentration is a first-order function of time. The reusability study of the C/ZnO-Ni photocatalyst showed good stability of the photocatalyst after recycling 7 times under the optimum conditions.
Research Article
Activated carbon/ZnO-Ni nanoflower composite as an efficient photocatalyst for enhanced degradation of reactive red 120 dye under LED light
https://doi.org/10.21203/rs.3.rs-2472573/v1
This work is licensed under a CC BY 4.0 License
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Photocatalysis
Activatedcarbon/ZnO-Ni nanoparticles
Dye degradation
Advanced oxidation process
RR120 dye
LED light
In recent years, increasing the usage of mineral and organic materials as well as the population growth have had very destructive impacts on the quality of soil and water resources ( Tkaczyk et al. 2020). Surfactants, dyes and heavy metals are being widely utilized in our life, and their entry into the environment poses many risks to plants, human health and the environment (Palanisamy et al. 2020).Therefore, freshwater purification and quality water supply have become important global challenges (Areeb et al. 2021). So far, diverse methods such as surface adsorption, biological degradation and membrane-based separation have been employed to purify and remove organic compounds and dyes (Maleki and Esmaeili 2022; Hashimi et al. 2019). The utilized procedures have a lot of side costs and cannot destroy or remove all the toxic compounds in the water (Hameeda et al. 2020; Maleki et al. 2022a). As an efficient and environmentally friendly process, advanced oxidation process (AOP) has been considered as a worthwhile and key technology. This procedure is based on the production of highly active species such as hydroxyl radicals, which have the ability to highly oxidize dye molecules and lead to the destruction and removal of dye from water and wastewater and the mineralization of pollutants into CO2 and H2O (Bedia et al. 2019). By using strong oxidizing agents such as H2O2 or transition metal catalysts in aqueous media, the production of free radicals increases significantly (Maleki et al. 2022b). Photocatalytic processes are one of the most important classes of AOPs that have the ability to destroy and remove organic pollutants under light and are considered as a suitable, cost-effective and simple remediation technique (Maleki and Ashraf Talesh 2022a).
Photocatalysts are substances that increase the speed of chemical reactions when receiving light with suitable energy. Under irradiation, photocatalysts are excited by jumping electrons to a higher energy level and creating a hole with positive charge. The photo excited electron-holes have the potential of initiating redox reactions (Sydorchuk et al. 2021; Aziz et al. 2021). One of the most important surface reactions is the formation of hydroxyl radicals from oxidation of H2O molecule by photocatalysts (Maleki and Ashraf Talesh 2021; Vasiljevic et al. 2020). The surface and free hydroxyl radicals are highly reactive, thus they attack the adjacent organic molecules and decompose them into less harmful compounds (Lin et al. 2020). Till now, various metal oxides such as ZnO, TiO2, ZrO2, CuO, etc. have been employed as photocatalyst for wastewater treatment ( Hammouche et al. 2021; Hitkari et al. 2022; Kraidi et al. 2022). ZnO is still a proper candidate for the photocatalytic process as it is chemically stable, low-cost and available photocatalyst with high efficiency of photocatalytic degradation of organic pollutants. However, pure ZnO suffers from some shortages like wide band gap energy and high recombination rate of charge carriers (Karamian and Sharifnia 2018). In order to overcome these limitations, it is common to modify ZnO by metal and non-metal doping (Bisaria et al. 2021).
The main aim of this study is to investigate the enhanced photocatalytic activity of ZnO nanoparticles by Ni doping and immobilizing on activated carbon nanoflowers for the degradation of Reactive Red 120 (RR120) dye under LED lamp. To the best of our knowledge, so far, no investigations have been carried out on the removal of RR120 with ZnO/Ni-doped catalysts immobilized on activated carbon nanoflower (C/ZnO-Ni). To this end, the photocatalyst was synthesized and characterized via XRD, FTIR, EDS, BET-BJH, and SEM techniques. It must be noted that the photocatalytic activity of Ni doped ZnO was compared with those of La and Cu doped ZnO. The photocatalytic performance of the C/ZnO-Ni was examined and optimized in terms of initial concentration of the dye, the power of the lamp, the catalyst dose, the effect of H2O2, and the effect of solution pH. Also, the kinetic study and reusability of the best photocatalyst were evaluated. Eventually, a plausible reaction pathway was suggested for the degradation of RR 120 dye during photocatalytic reaction.
Materials
Activated carbon, copper nitrate (Cu(NO3)2.3H2O), lanthanum nitrate (La (NO3)3.6H2O), nickel nitrate (Ni (NO3)2), zinc nitrate (Zn (NO3)2 6H2O), silver nitrate (AgNO3), urea (CH4N2O), Ethylenediaminetetraacetic acid (EDTA), hydrogen peroxide (H2O2 30%), Proxymonosulfate (H2SO5), nitric acid (HNO3) and sodium hydroxide (NaOH) from Merck were employed as the chemicals in this research. Also, the commercial RR120 (C44H30Cl2N14O20S6Na6, MW: 1469.98 gmol− 1) was purchased from sigma-aldrich. Figure 1 illustrates the molecular structure of the RR120. The main characteristics of RR120 dye are shown in Table 1.
|
Name |
RR120 |
|---|---|
|
Molecular formula |
C44H30Cl2N14O20S6 Na6 |
|
Molecular weight (gmol− 1) |
1469.98 gmol− 1 |
|
Color Index name |
Red |
|
Color Index number |
61951-82-4 |
|
λ max (nm) |
508 Nm |
|
Reactive group |
Azo group |
Preparation Of Photocatalyst
All the photocatalysts were synthesized by 80 wt.% activated carbon (C) (18 mm mesh). In the first stage, 0.8 g C, 0.46 g zinc nitrate and 0.49 g nickel nitrate with molar ratios of 1:1 were poured into a flask and 80 ml deionized water was added to it. Afterwards, the mixture was stirred at room temperature using a magnetic stirrer for 1 hour. Thereafter, the prepared specimen was transferred to an autoclave (130°C for 15 h) and then dried in an oven at 80°C for 12 h. The prepared specimen was transferred to a porcelain crucible and calcined again for 3 h in the oven at 300°C.The prepared sample was donated as C/ZnO-Ni. The other similar photocatalysts, C/ZnO-Cu, C/ZnO-N and C/ZnO-La, were synthesized by the same manner by substitution of nickel nitrate with coper nitrate, lanthanum nitrate, and urea, respectively.
Photocatalytic Process
A certain amount of RR 120 dye was poured into a beaker containing 100 ml deionized water over a magnetic stirrer. The initial concentration of dye was measured by a spectrometer (Spectronic 20D, Mylton Roy, USA) at a wavelength of 508 nm. Then, a specific amount of catalyst was added to the solution in darkness and the concentration of dye was measured by after 2 h being in darkness. Next, the reactor was exposed to LED light and at specific time intervals the concentration of dye was measured to obtain the photocatalytic activity. In this study, different mesh sizes of AC (500(25µ), 270(53µ), 60(250µ), 35(500µ), 18(1mm) and 14(1.40mm) micrometers) were used and compared to find the best mesh size. In addition, the effect of ZnO: Ni ratio (1:1, 1:0, 2:1, 1:2 and 0:1) was investigated. The effects of H2O2(0, 0.2, 0.4, 0.5, 1 and 2 mL), solution pH (3, 5, 7, 9 and 11), and initial dye concentration (5, 10, 15, 20 ppm) on the degradation of RR120werestudied.The efficiency of RR120 removal was acquired by applying Eq. (1).
1where X is the efficiency of RR120 removal, C0 and C are the concentration of RR120 dye at times 0 and t under visible light irradiation, respectively. The laboratory procedure of photocatalytic degradation of RR120 are depicted schematically in Fig. 2.
Photocatalysts Characterization Methods
To characterize the crystalline structure, activated carbon, ZnO and C/ZnO-Ni samples were studied by XRD analyis (1.5405 A° = λ XRD-PHILIPS PW 1800). Surface morphology of the photocatalysts was evaluated by SEM (LEO 1455 VP) method. EDS test was employed for elemental assessments and also their distribution on the surface of the heterogeneous catalyst(VERTEX 70, Germany). The textural properties and specific surface area were determined by applying the BET test (Microtrac Bel Corp- model Belsorp mini II, Japan, Quanta Chrome). The surface functional groups of the photocatalysts were investigated by FTIR analysis (Bruker Vector 22). Diffuse reflectance spectroscopy (DRS) of the samples was recorded from 200–800 using a Jasco V-670 spectrophotometer at room temperature.
Characterization of nanocatalysts
XRD
Crystalline structure of pure activated carbon and C/ZnO-Ni photocatalysts was discovered by XRD analysis (Fig. 3). As exhibited, there are similar peaks in the structure of pure activated carbon and C/ZnO-Ni photocatalysts, revealing that both nanoparticles have similar crystalline phases. In the XRD pattern of pure activated carbon, three peaks located at 2θ = 20°, 25°, 30° and 2θ = 40°, 50° are confirmations of the presence of amorphous carbon. These peaks show that the carbon rings are arranged irregularly. Also, in Fig. 3, the peaks observed at 32 − 12° demonstrate carbon plates possessing high amounts of oxygen (Zhang et al. 2021; Deng et al. 2020). The main polycrystalline peaks of ZnO were observed at 31.7, 34.4, 47.5, 56.5, 62.8 and 68.3°. C/ZnO-Ni 1:2 composites exhibited new peaks at 2θ = 24.44°, which is related to the presence of Ni on pure activated carbon nanoparticles. The Scherrer equation that relates the diffraction width (β) and the crystallite grain mean particle sizes of activated carbon and C/ZnO-Ni photocatalysts 18 and 26 nm can be calculated by Eq. 1 (Maleki and Ashraf Talesh 2022b):
2where D is the mean particle size, K = 0.9 is the shape characteristic of the catalyst, λ is the X-ray wavelength (for Cu kα = 1.54 A°), and β is the Bragg diffraction angle.
FT-IR
To determine the functional groups of the synthesized nanoparticles, the FTIR spectra of AC and C/ZnO-Ni photocatalysts is shown in Fig. 4. The band observed at 1043 cm− 1 is related to vibration of C-O bond (Kang et al. 2010). The peaks in the range of 2500–3500 cm− 1 are related to the OH stretching vibration in both photocatalysts. The peak at 480 cm− 1 is due to the vibration of the Zn-O functional group (Raizada et al. 2014). The peak at 1384 cm− 1 is related to C-H, and the peaks at 1007 to 1350 cm− 1are attributed to the C-Zn bond of unsaturated groups and halide on the surface of activated carbon after modification. The peak of 1238 cm− 1 indicates the presence of a metal. FT-IR results clearly confirmed that acidic functional groups on the surface of photocatalysts were grown by modification, which can lead to the change of catalysts activity (Murugesan et al. 2021).
SEM
The morphology, pores, ups and downs, bumps, holes, and surface changes of pure activated carbon and C/ZnO-Ni photocatalysts were assessed through SEM analysis as shown in Fig. 5. From Fig. 5 (a and b), it is clearly seen that the activated carbon has a porous structure with wrinkled surface which is favorable for immobilization of photocatalyst nanoparticles. After the introduction of ZnO-Ni, as shown in Fig. 5 (c and d), the composite exhibits a nanoflower morphology. The C/ZnO-Ni particles have the particles diameter less than 100 nm.
EDS
The surface elemental composition of the pure activated carbon and C/ZnO-Ni photocatalysts was identified by EDS analysis. The results are displayed inFig. 6. According to Fig. 6(a), pure activated carbon nanoparticles contain C, O, K, Ca and Mg with the atomic composition of 93.99 and 5.48, 0.39, 0.08 and 0.06%, respectively. The EDS profile of the C/ZnO-Ni indicates the presence of new peaks of Zn and Ni with the atomic composition of 0.19 and 0.2%. The non-stochiometric ratio of Zn: Ni is attributed to the limited accuracy of the EDS instrument. The atomic composition of O increased from 5.48 up to 8.90% by introduction of ZnO-Ni, confirming the presence of ZnO over the surface of activated carbon.
Bet Surface Area
The surface features of the pure activated carbon and C/ZnO-Ni photocatalysts, such as specific surface area, pore diameter and pore volume were specified by BET analysis. Based on Table 2, the BET specific surface area of pure activated carbon and C/ZnO-Ni photocatalysts are 288.32 and 303.95m2/g, respectively. Langmuir specific surface area also confirms the increased surface area after immobilization of ZnO-Ni nanoparticles. This means that the ZnO-Ni has a porous structure. The average pore diameter of pure activated carbon and C/ZnO-Ni photocatalysts are 2.3184 and 2.4194 nm, respectively, confirming that both photocatalysts have mesoporous structures. Moreover, the total pore volume of pure activated carbon and C/ZnO-Ni photocatalysts are0.1671 and 0.1838 cm3/g, respectively, revealing the high pore volume of these photocatalysts which is a desire feature for catalytic processes (Zhang et al. 2021; Murugesan et al. 2021). The high specific surface area and pore volume demonstrate that the C/ZnO-Ni has suitable physical properties for dye degradation.
|
Feature |
Activated carbon |
C/ZnO-Ni |
|---|---|---|
|
Vm (cm3(STP) g− 1) |
66.242 |
69.834 |
|
as,BET (m2.g− 1) |
288.32 |
303.95 |
|
as,Lang (m2.g− 1) |
426.38 |
469.91 |
|
Total pore volume(cm3.g− 1) |
0.1671 |
0.1838 |
|
Mean pore diameter (nm) |
2.3184 |
2.4194 |
Uv-vis Drs
The UV-vis absorption spectra of activated carbon and C/ZnO-Ni is shown in Fig. 7 (a). As is evident in this figure, the absorption spectrum of activated carbon nanoparticles changes with the incorporation of ZnO-Ni. The band gap of photocatalysts can be determined by Eq. 3 (Swat et al. 2017):
3where α is the absorption coefficient (cm− 1), 
is the photon energy (eV), A is the constant of the equation, and Eg is the energy of the band gap (Shan et al. 2020). By plotting (𝛼h𝑣)2 in terms of h𝑣 and with the assistance of linear extrapolation, band gap values can be determined. It can be seen in Fig. 7 (b) that with the incorporation of ZnO-Ni into activated carbon, the band gap decreased from 3.34 to 2.86 eV. ZnO and Ni create an extra energy level between the band energies of the parent activated carbon, leading to limiting the overall band gap. By diminishing the band gap, the C/ZnO-Ni is expected to exhibit higher photocatalytic activity than pure activated carbon (Vasile et al. 2001).
The Effect Of Operating Parameters On The Photocatalytic Degradation Of Rr120
Effect of ZnO doping with Ni, La, Cu and N on the photo-degradation of RR120
The effect of doping ZnO with Ni, La, Cu and Non the photocatalytic degradation of RR120 was investigated and the results are shown in Fig. 8(a). This study was carried out under experimental conditions of 30 min duration in the dark, solution pH7, 5 ppm initial concentration of RR120, 30 mg catalyst (C/ZnO, C/ZnO-Ni, C/ZnO-La, C/ZnO-Cu and C/ZnO-N),activated carbon mesh size of 18 (1 mm), 1 mL H2O2 under a 30W LED lamp for 115 min. It is clear that C/ZnO-Ni photocatalyst has higher removal efficiency than other prepared catalysts. The different photocatalysts exhibited photocatalytic activity in the descent order of C/ZnO-Ni > C/ZnO-N > C/ZnO-Cu > C/ZnO > C/ZnO-La.BET analysis revealed that incorporating ZnO-Ni on activated carbon increased the specific surface area and pore size, which reflects the desired porosity of ZnO-Ni. Besides, C/ZnO-Ni showed modified light absorption ability, thus increasing photocatalytic activity. C/ZnO-Ni was chosen as the best photocatalyst among other competitors to be investigated in the ongoing experiments.
Effect Of Activated Carbon Mesh Size On The Photo-degradation Of Rr120
The impact of activated carbon mesh size (500 (25 µm), 270 (53 µm), 60 (250 µm), 35 (500 µm), 18 (1 mm) and 14 (1.4 mm)) on the removal efficiency of RR120was studied and the obtained results are shown in Fig. 8(b). The other experimental conditions were the same as the previous step. The mesh size was. It can be seen that mesh size 270 has shown the highest performance of RR120 dye removal during 105 min of light irradiation. The reason for this can be attributed to the higher porosity of the mesh 270 catalyst. However, with higher porosity, more active sites are available, and the ability of photocatalysts to produce active species increases. In catalysts with higher mesh, due to the destruction of holes, the specific surface area and active sites of nanoparticles available for dye absorption are considerably reduced. On the other hand, in catalysts with a smaller mesh size, smaller holes are formed, which do not have a significant ability to absorb dye due to their smaller pore diameter (Sobana et al. 2013; Jafari et al. 2017). The next experiments were done by activated carbon mesh size of 270.
Effect Of Zn:ni Molar Ratio On The Photo-degradation Of Rr120
The effect of Zn:Ni ratio of 0:1, 1:0, 1:1, 1:2 and 2:1 on the efficiency of RR120 degradation was studied under the experimental conditions of solution pH 7, initial dye concentration of 5 ppm, C/ZnO-Ni catalyst amount of 30 mg with carbon mesh size of 270, H2O2amount of 1mL under irradiation of 30W LED lamp. The results are displayed in Fig. 9 (a). The highest removal rate is related to the catalyst with Zn:Ni molar ratio of 1:2. The lowest photocatalytic activity belongs to Zn:Ni ratio of 0:1, showing that NiO is not a favorable photocatalyst under these conditions for the degradation of RR120. When Zn: Ni molar ratio is 1:1, one can say that the concentration of dopant is less than its optimum concentration. Under high Zn:Ni molar ratio of 2:1, the overloading of Ni diminishes the photocatalytic activity due to the shade effect and accumulation over catalyst surface (Vasile et al. 2019). It should be noted that C/ZnO-Ni means the optimal catalyst (C/ZnO-Ni 1:2) in the next experiments.
Effect Of Hoon The Photo-degradation Of Rr120
Owing to the strong electrophilic nature, H2O2 is a powerful oxidizing agent that can accelerate photocatalytic dye degradation process. Herein, the photocatalytic activity of C/ZnO-Ni was investigated for RR120 degradation by using different amounts of H2O2(0, 0.2, 0.4, 0.5, 1 and 2 mL), initial dye concentration of 5 ppm, catalyst amount of 30 mg with carbon mesh size of 270 under irradiation of 30 W LED lamp. The obtained results are depicted in Fig. 9(b). As illustrated, H2O2 has a positive effect on the RR120degradation. H2O2involves in surface charge transfer process by receiving conduction band electrons and formation of •OH. The •OH species the take part in the RR120 degradation process and enhance the efficiency of photocatalytic activity. As can be seen, the best photocatalytic activity was found when the amount of H2O2 was adjusted at 0.2 mL. Further increment of H2O2 led to diminishing photocatalytic activity which is due to suppression of the dye degradation in the original pathway. Therefore, with an excessive increase of H2O2 concentration, the photocatalytic efficiency decreases (Valarmathi and Gogate 2012; Sathishkumar et al. 2013). Based on the results, the optimal amount of H2O2 occurred at 0.2 ml. For the next experiments, the amount of H2O2 was fixed at 0.2 mL.
Effect Of Ph On The Photo-degradation Of Rr120
To assess the influence of pH on the photocatalytic degradation of RR120, the solution pH was increased from 3 up to 11. The experimental conditions were initial dye concentration of 30 ppm, C/ZnO-Ni amount of 5 mg with carbon mesh size of 270, H2O2amount of 0.2 mL under irradiating a 30 W LED lamp. The obtained results are depicted in Fig. 10 (a). As can be seen, the efficiency of RR120 degradation gradually decreases with the raising solution pH. The effect of solution pH on the photocatalytic activity strongly depends on the zeta potential of the photocatalyst. It can be concluded that in an acidic environment, due to the presence of H+ ions, the surface of the photocatalyst becomes positively charged while the RR120 molecules are negatively charged and, therefore, an electrostatic bond is established between the photocatalyst and dye, which improves the decomposition efficiency. At higher pH values, due to the presence of hydroxyl ions, the adsorbent becomes negatively charged and establishes electrostatic repulsion with the dye, which is intrinsically negatively charged, and the removal efficiency decreases (Fikiru et al. 2018; Run et al. 2010; Alkan et al. 2005).
Effect Of Initial Rr120 Concentration On The Photo-degradation Of Rr120
The impact of initial RR120 concentration on the photocatalytic activity of C/ZnO-Ni was investigated and the results are indicated in Fig. 10 (b). The degradation rate depends on the possibility of generating OH radicals on the photocatalyst surface to trigger the photocatalytic reactions (Konstantinou and Albanis et al. 2004). The results reveal that the highest photocatalytic activity was obtained where the initial concentration of RR120 was 5 ppm. One can say the accumulation of RR120 over the photocatalyst surface leads to blockage of surface active, thus decreasing photocatalytic activity (Fikiru et al. 2018). Besides, increasing dye concentration leads to turbidity of the solution, and therefore the light absorption by photocatalyst particles decreases. It worth to note that a proportion of light photons can be absorbed by dye molecules and this restrict the light absorption by photocatalyst surface to excite charge carriers. All these phenomena reduce the productivity of hydroxyl radicals. Moreover, increasing the initial RR120 concentration leads to the formation of more amounts of intermediaries, which makes the reaction mechanism more complicated (Soltani and Shams Khoramabadi 2015).
Effect Of The Amount Of C/zno-ni Photocatalyst On The Photo-degradation Of Rr120
Figure 11 (a) depicts the effect of C/ZnO-Ni photocatalyst amount on the RR120 degradation. Under darkness condition, the efficiency of RR120 removal was improved by raising the amount of photocatalyst from 10 to 70 mg. In such situation, photocatalyst particles act as adsorbent. BET analysis confirmed the porosity feature of the C/ZnO-Ni nanoparticles. Under light illumination, raising the catalyst amount from 10 to 50 mg increased the photocatalytic degradation of RR120. This is attributed to the enhanced the number of surface active sites which participate in the photocatalytic reactions. Nevertheless, further increasing the amount of photocatalyst up to 70 mg resulted in declining the photocatalytic activity. This is due to the accumulation of suspended particles which leads to the light scattering and reducing light penetration to the internal parts of the photoreactor (Noorimotlagh et al. 2018).
Effect Of Sacrificial Agents On The Photo-degradation Of Rr120
Sacrificial agents are substances that promote the catalytic activity by scarify themselves. Persulfate, H2O2, AgNO3 and EDTA were used as sacrificial agents. The photocatalytic experiments were carried out by 50 mg C/ZnO-Ni with the carbon mesh size of 270, solution pH of 3, initial RR120 concentration of 5 ppm under irradiation of 50 W LED light. The results are shown inFig. 11 (b). After 120 min, the observed photocatalytic degradation of RR120 was in the order of H2O2 > persulfate > EDTA > AgNO3. The addition of H2O2 caused the highest efficiency of RR120 degradation which is due to the formation of hydroxyl radical (Liu et al. 2019).
Effect Of The Lamp Power On The Photo-degradation Of Rr120
The effect of lamp power on the photocatalytic process is shown in Fig. 12. Increasing the power of lamp from 9 to 50 W resulted in the improvement of the photocatalytic process, which is ascribed to the development of light absorption efficiency and generation of more active sites by C/ZnO-Ni catalyst. In the other words, the rate of photocatalytic process is higher when the flux of absorbed photons increases (Liu et al. 2019; Noorimotlagh et al. 2020).
The best photocatalytic RR120 degradation of 94.88% was obtained under the optimum conditions in which the initial RR120 conditions, solution pH, H2O2 amount, C/ZnO-Ni amount, carbon mesh size and power of LED lamp were adjusted at 5 ppm, 3, 0.2 mL, 50 mg, 270 and 50 W, respectively.
Comparison Of The C/zno-ni Performance With Other Similar Photocatalysts
A literature review of the research background demonstrates that few studies have been done on the removal of RR 120 dye using LED light. To the best of our knowledge, the simultaneous use of activated carbon/zinc oxide doped with nickel and LED lamp for the removal of RR120 is reported for the first time in this study. In general, UV light is more efficient than sunlight. However, LED lamp is an energy saving, available and cheap light source. Table 3compares the results obtained in this work with those obtained by similar photocatalysts for the degradation of RR120.
|
Catalyst type |
Removal time (min) |
Removal efficiency (%) |
Light source |
Lamp (W) |
Ref. |
|---|---|---|---|---|---|
|
CdS/SiO2-porphyrins |
30 |
67 |
Sun |
- |
(Krishnakumar et al. 2020) |
|
Pb – ZnO |
150 |
96 |
UV |
- |
(Gnanamozhi et al. 2020) |
|
TiO2/UV system |
90 |
100 |
UV |
- |
(Cho and Zoh 2007) |
|
Ag-ZnO |
60 |
100 |
UV |
125 |
(Chankhanittha et al. 2021) |
|
20 |
100 |
Sun |
- |
||
|
ZnO/BaTiO3/C |
4800 |
93.67 |
UVA |
36 |
(Ong et al. 2019) |
|
CoFe2O4/TiO2 |
60 |
- |
Tungsten halogen |
150 |
(Jafari et al. 217) |
|
Zr-Ag-ZnO |
30 |
79.9 |
UVA |
- |
(Subash et al. 2013a) |
|
Ce–Ag–ZnO |
30 |
95.5 |
UVA |
- |
(Subash et al. 2013b) |
|
BC/g-C3N4 |
3600 |
98 |
LED |
36 |
(Zheng et al. 2019) |
|
Ni-ZnO |
60 |
90 |
UV |
- |
(Gnanamozhi et al. 2020) |
|
C/ZnO-Ni |
115 |
94.88 |
LED |
50 |
Present study |
Kinetic Analysis
The process of RR120 removal was scrutinized under light illumination for 105 min and in darkness for 30 min by C/ZnO-Ni nanoparticles. In the absence of light, the surface absorption process was dominant, while under LED light irradiation, the photocatalytic process played a substantial role. To study the kinetic aspect of RR120 degradation by C/ZnO-Ni, the RR120 concentration was evaluated at specific time intervals in the presence of different sacrificial agents. As can be seen from Fig. 13, the kinetics of photocatalytic reactions follows the Langmuir-Hinshelwood (L-H) theory. The L-H model suggests a first-order kinetic equation (Eq. 2) for such heterogeneous catalytic reactions (Peng et al. 2020).
4where C0 and Ct are the RR120 concentrations (mg/L) at times 0 and t, respectively. kapp and tare the apparent rate constant (min− 1) and reaction time (min), respectively. Figure 13 reveals the linear relationship between the RR120 concentration and the irradiation time. The slope indicates the rate constant of the reaction (kapp) and is a criterion of the photocatalytic activity (Pang et al. 2021). The highest value of the reaction rate constant (0.019) was acquired by using H2O2, while the lowest reaction constant (0.0077) was obtained by AgNO3. The obtained rate constants alongside the determination coefficients are summarized in Table 4.
|
Sacrificial agent |
kapp (min− 1) |
R2 |
|---|---|---|
|
AgNO3 |
0.0077 |
0.9359 |
|
Persulfate |
0.0099 |
0.9148 |
|
EDTA |
0.012 |
0.9174 |
|
H2O2 |
0.019 |
0.9594 |
Reusability Of C/zno-ni Photocatalyst
The stability of the prepared C/ZnO-Ni nanoparticles was investigated at the optimum operational conditions for 7 runs (Fig. 14). For each run, the C/ZnO-Ni nanoparticles were filtrated and rinsed with methanol and water mixture and dried at 110°C for 90 min to eliminate any moisture or contaminants before being employed again for the next run. The photocatalytic activity decreased from 94.88% up to 78.34% after 7 times recycling. It can be said that the synthesized C/ZnO-Ni nanoparticles are a favorable photocatalyst for the photocatalytic wastewater treatment.
In this research, the photocatalytic performance of ZnO-Ni immobilized on activated carbon was investigated for the removal of RR120 dye. The photocatalyst was synthesized and characterized by SEM, BET, FTIR, XRD and EDS analyses. The characterization methods exhibited that ZnO and Ni were incorporated well on the activated carbon surface. Also, adding ZnO doped Ni to activated carbon enhanced the specific surface area and porosity of the photocatalyst from 288.32 to 303.95 m2/g. The best photocatalytic performance of 94.88% was obtained under the optimal conditions of initial RR120 concentration of 5ppm, solution pH of 3, H2O2 amount of 0.2 mL, C/ZnO-Ni catalyst amount of 50 mg, carbon mesh size of 270 and irradiation time of 115 min under 50 W LED lamp. Kinetic studies confirmed the conformity of L-H theory for RR120 degradation by C/ZnO-Ni and different sacrificial agents of persulfate, H2O2, AgNO3, EDETA. The results showed that the kinetics of photocatalytic RR120 follows pseudo-first-order model, and the highest rate constant and determination coefficient belonged to a situation that H2O2 was as a sacrificial agent. The addition of H2O2resulted in the efficient removal and reduction of photogenerated electron-hole pairs recombination, and the degradation efficiency was greatly improved by the addition of H2O2 compared to other sacrificial agents. Furthermore, the results of assessing the reusability of nanoparticles in optimal conditions demonstrated that after 7 consecutive runs, the photocatalytic performance decreases by only 14.3%. This study showed that C/ZnO-Ni can be applied as a promising photocatalyst for the degradation of RR120.
Ethics approval and consent to participate
Not applicable.
Consent for publication
All authors read and approved the final manuscript. All authors are fully aware of this manuscript and have permission to submit the manuscript for possible publication.
Availability of data and materials
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
Competing interests
The authors have no conflict of interest with each other.
Authors' contributions
All authors contributed to the study conception and design. Kousar Norozi: Data curation, Writing - original draft, Visualization, Investigation. Mohsen Mansouri: Supervision, Writing- review & editing. Elham Karamian: Writing- & editing. Basir Maleki: Conceptualization, Methodology, Writing - review & editing.
Funding
No funding was obtained for this study.
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