Many natural substances contain calcium oxide (CaO), which is found in their basic structure. Due to its excellent structure and non-toxic properties, it is a potential element in the field of environmental management. The photocatalytic activity of bio-based catalyst synthesized from waste tomato stem (WTS) containing CaO (WTS-CaO) was examined in this study. This study is unique in that it uses a photocatalyst made from waste tomato stems to remove dye in a photocatalytic system. Characterizations of WTS-CaO were obtained using FTIR, XRF, SEM, and EDX analyses methods. In photocatalytic tests, the effects of light source, photocatalyst dosage, pH, and dye concentrations on dye removal efficiency was investigated at 90 min. In addition, the samples were subjected to sintering operations at temperatures of 900oC in order to examine the synthesis of CaO from waste tomato stem. Basic Red 2 (Safranin) which is a cationic dye was used in the photocatalytic experiments. The above parameters were determined to be optimal for photocatalytic studies done: 0.5 g/L catalyst dosage, 5 mg/L dye concentration, reuse of catalyst, amount of H2O2 and original solution pH under visible light.
Research Article
Preparation of bio-based adsorbent from waste tomato stem and used as photocatalyst for Basic Red 2 photocatalysis
https://doi.org/10.21203/rs.3.rs-1647278/v1
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Bio-based catalyst
waste tomato stem
calcium oxide
Basic Red 2
One of the world's critical problems is industrial pollution, which is created by a variety of uses. Water pollution is also a major issue. The amount of drinking water utilized and the water exposed to pollutions that are not suitable for the environment, clean water resources reach critical levels with the growing population (Donkadokula et al., 2020). Synthetic dyes with cationic, anionic, and nonionic classification consisting of water-soluble compounds are used very frequently, especially in the textile industry (Shindhal et al., 2021). These types of paints, which are resistant to high thermal environment, can stay in surface waters for a long time since they have high solubility in water (Benjelloun et al., 2021). Cationic dyes have teratogenic and carcinogenic effects on human cells and must be released into the environment without being discharged (Heidari et al., 2021). Many techniques such as membrane (Khoshnevisan et al., 2021), advanced oxidation process (Liu et al., 2021), electrocoagulation (Chanikya et al., 2021), adsorption (Prajapati et al., 2021) and photodegradation (Mousa et al., 2021) are used for the treatment of dye-containing wastewater. Traditional methods can only make organic compounds to another phase because to the high durability of dye compounds, resulting in secondary contamination (Keerthana et al., 2021).
Photocatalytic systems absorb photons and perform redox reactions, breaking complex organic molecules into smaller pieces, using semiconductor oxides or transition metal oxides (Ahuj et al., 2021). In photocatalytic systems, a variety of materials are used. Compounds like TiO2, ZnO, Ag2O and other semiconductors are the most popular. Also with their high oxidation power and resistance to photochemical corrosion, such compounds are chosen. (Cao et al., 2020; Yu et al., 2020; Li et al., 2021). Calcium oxide (CaO) has just been studied for its photoactivity. Due to their thermal stability, mechanical characteristics, and ease of recycling, calcium compounds like CaO have a wide range of uses. Moreover, CaO has the impact of improving the performance of the photocatalytic process in the synthesis of photocatalyst (Song et al., 2010; Nassar et al., 2021). CaO is formed naturally through the decarbonization of calcium carbonate (CaCO3) in the light of sun radiation. As a result of the thermochemical reaction, CaCO3 is broken down into CaO and CO2. CaCO3 calcination should be performed in a high concentration CO2 environment at temperatures greater than 900°C if it is desired to be synthesized in an experimental situation (Sun et al., 2020; Xu et al., 2021). The photocatalytic effect in photocatalytic processes involving photocatalysts made from tomato stems must be understood. After the photocatalysts have been adsorbed, the rays from the light source cause the production of holes and final electrons, which leads to the oxidativereducing reaction. •CO3−, as well as •O2−, plays an active role in tomato stem systems. •OH− causes the oxidation of H2O, which happens in electron-hole pairs as a result of excitation. •CO3− is formed when such radicals combine with carbonate and bicarbonate ions (Baláz et al., 2021). Natural calcium oxide or hydroxide materials are employed for a variety of applications due to their nanometric size, biocompatibility, and bioactive nature. The research's major aim is to inform pure nanocrystalline CaO in a green way and synthesize it with cutting-edge new research methods, so that it may be universally recognized by the scientific community around the world. The synthesis of photocatalysts for use in photocatalytic processes can be produced using a variety of ways. Catalysts created using the green synthesis approach are of particular interest because of their ecologically friendly properties and one-step synthesis process. For this purpose, biomaterials such as chicken egg shells are employed, which are mostly constituted of extremely tiny amounts of calcium carbonate and other organic compounds (Sinha et al., 2021; Chand et al., 2021).
The separation of simple minerals in the soil, microorganisms in the soil, and complicated substances into their simpler components and absorption into the body with the help of the plant's roots is called to as phytoremediation. The quality and development of the harvested product are known to be influenced by the soil content in tomato-growing regions. The kind of fertilizer that will aid in plant development, the content of irrigation water, and the minerals in soil components can all be easily absorbed by the agricultural product thanks to plant roots (Demirer, 2018; Chen et al., 2022). Ertürk (2021) researched tomato production using an aquatic system. She carried out his investigation with only irrigation water and two other additional materials that injected into the system to examine the influence of different supplemental materials in waterless agricultural production on growing farm products. The mineral content of tomato and tomato stem was determined using Inductively Coupled Plasma (ICP) analysis as a result of various agricultural crop production methodologies. Many distinct substances were discovered when the content of tomato stem (TS) was tested as part of the investigation. She came to the conclusion that the calcium (Ca) and phosphorus concentration of the tomato stem was higher in the eggshell experimental sets than in the other experimental sets. Quensafi et al. (2019) investigated the effect of soil characteristics on the production and growth of tomato plants irrigated with treated wastewater. Two different kinds of alkaline soils were employed in the experiment. The CaO content of two soil types was found to be 9.5 g/kg and 7.2 g/kg. The fresh weight and size of the fruits in the plants were reported to be higher as a result of the agricultural production in which the FS solid type was applied. CaO may inhibit fruit growth and limit its utilization in photosynthesis in soils with high CaO content, according to the researchers.
The aim of this study is to convert the CaCO3 in tomato stem wastes from harvested tomatoes to CaO (TS-CaO) using a one-step thermal technique and then use it to remove dye with a photocatalytic process. Both the environmentally friendly green synthesis of nanomaterials and the possibility of reusing waste material for other uses were assisted by the photocatalyst, which was created exclusively at high temperatures without the need of chemical catalysts. The amount of photocatalyst, dye concentration, solution pH value, and light source effects were all studied in photocatalytic experiments.
2.1. Preparation of waste tomato stem as photocatalyst with green synthesis
The remaining plant stems are collected after the tomatoes have been harvested. To purify the organic waste, soil, and dust on its surface, it is washed three times with distilled water in a bowl. First, the tomato stems were washed and dried in a 70oC oven for 2 h. The dried long stems were shredded to a specific size into the grinding machine, then powdered. Tomato stems were processed into powder and passed through a 35 mesh (500 µm) sieve before being placed in a ceramic pot. Finally, it was converted into ashes after being burned for 2 h at 900oC in a muffle furnace. The aim of sieving the powdered tomato stems before burning was to provide a uniform thermal process of the same size powdered particles.
2.2. Photocatalytic experiments using waste tomato stem as photocatalyst
Experiments were carried out to use tomato stems that had been subjected to high temperatures as a photocatalyst in the laboratory-established photocatalytic system. The photocatalysts were then stored in a desiccator until they were ready to use. Basic Red 2 (Safranin) cationic dye was used to make a synthetic dye solution for photocatalytic research. In photocatalytic studies, the effects of solution pH (6–12), photocatalyst dosage (0.5–1.5 g/L), light source, and dye concentrations (5–20 mg/L) were studied. The photocatalytic technique with WTS-CaO derived from waste tomato stem was used to explore dye removal in this study. In order to determine the best light source for photocatalytic tests, two different kinds of lamps were used separately. Under the settings defined in a preliminary investigation, six daylight lights (UVA, Philips TL8W Actinic BL) and six visible lamps (F8W/T5/54–768 light) were utilized. In the photocatalytic studies, a 500 mL aluminum-coated Pyrex photoreactor tube with an aluminum covering was used. An air pump with a flow rate of 150 mL/min was applied to ensure that ambient air was pumped to the reactor from the bottom, supporting photocatalytic oxidation and providing continuous mixing. Then, utilizing the most effective light source, photocatalytic tests on dye removal with WTS-CaO in the photocatalytic activity were carried out. Before dye removal measurements, all samples were centrifuged at 6000 rpm for 5 min. A UV–VIS spectrophotometer (HACH-DR3900) was used to evaluate dye removal effectiveness by measuring maximum photo-oxidation. The dye removal percentage was estimated using Eq. (1):
$$BR18 Dye Removal \left(\%\right): \frac{{C}_{i}-{C}_{e}}{{C}_{i}}*100$$
1
where Ci was the initial dye concentration and Ce was the dye concentration after defined reaction time t (min). Table 1 shows the chemical structure of Safranin dye.
Table 1. Chemical structure of Safranin dye (C20H19ClN4)
2.3. Characterization of WTS-CaO
It was determined using scanning electron microscopy (SEM) to determine the surface morphology of WTS-CaO. The maximum voltage and pressure applied to the X-ray source were 20 kV and 2.18e− 4 Pa, respectively. Energy dispersive X-ray spectroscopy (EDX) was designed to examine chemical composition on WTS-CaO surfaces. Fourier transform infrared (FTIR) spectra of WTS-CaO were examined through FTIR spectrometer. X-ray fluorescence (XRF) was used for the major components and minerals of the samples.
3.1. Characterization of WTS-CaO
The surface form of a photocatalyst is commonly recognized to have a significant impact on its photocatalytic activity. The surface morphology of the nanopowders formed from the tomato stem was investigated using SEM images in Fig. 1. It is observed that it consists of WTS-CaO hemispherical clusters of approximately the same size. These clusters are homogeneously distributed.
The FTIR spectra of WTS-CaO samples were recorded on a spectrophotometer over the range 4.000–400 cm− 1 using KBr pellets (Fig. 2). The peak at between 500 cm− 1 and 370 cm− 1 indicated the existence of Ca-O bond (Nadeem et al., 2022; Davoodbasha et al., 2021). Regions below 600 cm− 1 was attributed to the S-S stretching. The strong bands within 1100–1000 cm− 1 are due to the C–O group, which are characteristic peaks of polysaccharides. Symmetric stretching vibration of ionic carboxylic groups (–COO−) results a peak at 1409 cm− 1. 3700–2600 cm− 1, which could be attributed to the stretching vibration band of acidic OH groups. A peak indicating C-H stretch bonds was observed at 2987 cm− 1 in WTS-CaO (Alkanan et al., 2021; Gutha et al., 2015; Vorobyova et al., 2022).
The SEM-EDX results of WTS-CaO nanoparticle is shown in Fig. 3. The results of EDX shows the presence of peaks corresponding to C (8.88% w/w), O (45.27% w/w), Mg (1.63% w/w), Si (1.21% w/w), and Ca (43.02% w/w) according to the EDX spectra of WTS-CaO. The EDX peaks support the XRF result and indicate the purity of the synthesized WTS-CaO as catalyst.
The remaining tomato stems were collected and cleaned after harvesting the fruit. The elements in the contents of the two materials were determined by XRF analysis, both in the raw form and after the sintering process. XRF results are given in Table 2. According to the XFR results, no significant change was observed in the ratios of SiO2 and Fe2O3 compounds. A significant increase is observed in the amount of MgO after sintering. This increase indicates the formation of magnium oxide in the material due to the 900oC sintering of MgO. This can be explained by the conversion of Mg(OH)2 in the material to MgO with increasing temperature (Rani et al., 2020). The amount of SO3 in the raw tomato stem's composition increased after it was maintained at a high temperature, according to the findings. This condition could be caused by the conversion of sulfur-containing molecules (such as SO2) in the raw material's structure to SO3 at high temperatures (Moodley et al., 2022).
|
Materials |
Raw Tomato Stem (TS) |
WTS-CaO |
|---|---|---|
|
Element |
Dimension (%) |
Dimension (%) |
|
Na2O |
0.11 |
0.60 |
|
MgO |
1.55 |
7.65 |
|
P2O5 |
0.42 |
1.66 |
|
SiO2 |
0.35 |
0.39 |
|
SO3 |
0.85 |
2.66 |
|
Fe2O3 |
0.39 |
0.20 |
|
CaO |
26.94 |
67.93 |
As a result of XRF analysis of raw tomato stem (RTS), 26.94% CaO compounds were determined. After the tomato stem was burned in the muffle furnace at 900oC, the ratio of TS-CaO to CaO compound increased significantly to 67.93%. Gomez-Vazquez et al. (2021) conducted TGA analyses on calcium carbonate-containing materials at various temperatures. They discovered that protein denaturation occurred in the material at temperatures between 440°C and 485°C, while carbohydrates were degraded at temperatures between 553°C and 709°C, as a consequence of their research. They also reported that the endothermal transition, in which CO2 is released from CaCO3, occurs at a temperature of 709–792°C. When the temperature reaches 950°C, all of the CaCO3 in the shell is changed to CaO, according to the researchers. The highest removal efficiency was obtained at 900oC as a consequence of the experiments. In this case, as the temperature increases, all of the CaO in the tomato stem structure emerges.
The catalyst was made using a green synthesis approach, and the cationic azo dye Safranin were used in this work. Azo dyes are marked by the presence of chromophore (N = N) groups. This chromophore structure is known as an azo bond, and it is this component of the chromophore that gives the paint its color.
3.2. Results of the photocatalytic experiment using WTS-CaO
The process of photocatalytic degradation of nanomaterials by dye-containing pollutants involves the photocatalyst absorbing photons from the light source and then breaking the bonds between dye molecules in water with radicals created by nanoparticles. Experiments on the functional groups of WTS-CaO and the removal of dye with the action of a light source were carried out during the photocatalytic process. WTS-CaO was used in experiments to remove Safranin dye by a photocatalytic process. Variables such as dye concentration and pH value of the solution, photocatalyst dose, reuse of catalyst and light sources were investigated in the photocatalytic system. The samples were centrifuged and analyzed in a spectrophotometer after each set of experiments.
3.2.1 The effect of light source on the removal of Safranin dye with WTS-CaO in a photocatalytic system
The effect of the light source on the removal of dye using WTS-CaO in a photocatalytic system can be attributed to the light spectrum's domains. Depending on the type of light source, each has a different wavelength. Different wavelengths from the light source can activate the catalyst surface depending on the characteristics of the photocatalyst utilized (Baaloudj et al., 2021; Das et al., 2022). The aim of this study is to determine the most suitable light source for radical generation by the photons coming from the light source falling on the photocatalyst surface and stimulating the electrons in it. To investigate the effect of light intensity on dye degradation, researchers carried out experiments in the presence of UVA and visible light sources at 90 min. In the experiments that examined the impact of the light source, a sample was obtained from the system every 15 min and the color was measured. Light source studies were conducted using a dye concentration of 10 mg/L, a catalyst dose of 1 g/L, the original pH value, and a reaction time of 90 min. The lowest removal efficiency of Safranin dye was obtained in UVA compared to visible light, according to the test results (Fig. 4). Photocatalytic studies were continued under visible light source because the photodegradation efficiency of WTS-CaO under visible light source is higher than that of UVA.
In addition, in order to determine the negative effect of the light source on the structure of the dye, a photocatalytic experiment was conducted with the best efficiency, without the addition of catalyst. While the dye removal efficiency was 81.82% under visible light source, the dye removal efficiency was determined as 18.79% under the same conditions without the addition of catalyst. Visible light was chosen in the photocatalytic system because the dye removal efficiency was greatly increased by the addition of a catalyst.
3.2.2. Effect of pH on the removal of dye with WTS-CaO in a photocatalytic system
The effect of a photocatalyst called WTS-CaO on photodegradation was examined in this study by adjusting the pH of the solution. In addition, when a photocatalyst with a dye concentration of 10 mg/L was added to the solution, the ambient pH increased from 7 to 12. The reason for the increase in the pH value of the water with the addition of photocatalyst is that it raises the pH very quickly with the rapid release of basic ions such as Ca+ 2 (Jha et al., 2016). As a result, after adding the photocatalyst, different pH values of the solution were adjusted using 0.1 M NaOH and HCl in the photocatalytic studies. Photocatalytic experiments were carried out by adding 1 g/L photocatalyst to a solution containing 10 mg/L dye concentration for 90 min. The dye-containing water's pH was adjusted to 6.0, 8.0, 10.0, and 12.0. Figure 5 shows the results of changing the pH value. At the end of 90 min of dye removal experiment at pH 12, 82.15% dye removal efficiency was obtained. Similar results were obtained at other pH levels. There was no difference in photocatalytic degradation whether the pH of the solution was increased or decreased. Yang et al. (2022) investigated drug elimination using a photocatalytic method with they synthesized the nanomaterial. The photocatalytic studies revealed that tetracycline-hydrochloride (TH) had no effect on the photocatalytic process removal effectiveness with varying pH values, however the photocatalytic degradation efficiency of naproxen (NPX) altered with changing pH values. They explained this by stating that TH is not adsorbed on the nanomaterial surface and that the nanomaterial has a high NPX adsorption capability.
WTS-CaO has a weak adsorption capacity on the surface of the photocatalyst in adsorption experiments, according to preliminary studies done within the scope of the study. Safranin dye removal efficiency of 1 g WTS-CaO/L in 1 h reaction time was found to be 1.2% in adsorption tests. The fact that pH has no effect on photocatalytic efficiency and is almost unaffected by pH can be explained by the fact that Safranin dye is absorbed by the photocatalyst despite of ambient pH. In this study, it was decided to use the pH value of the solution containing the dye solution after adding the photocatalyst (pH 12) because changing the pH value had no impact on photocatalytic studies.
3.2.3. Effect of WTS-CaO dosage on the removal of Safranin dye in a photocatalytic system
Photocatalytic studies with various photocatalyst dosages were carried out to investigate the effect of WTS-CaO dosage on decolorization. Several photocatalyst doses were added to the solution with an initial concentration of Safranin dye of 10 mg/L and a pH of 12 under the visible lights. The dosages of WTS-CaO photocatalyst applied were 0.25, 0.5, 1.0, and 1.5 g/L. During the photocatalytic studies, the intensity of the light source was kept constant. In photocatalytic degradation, the effect of photocatalyst dosage on dye removal efficiency is shown in Fig. 6.
The removal efficiency values of 0.25, 0.5 and 1.0 g/L photocatalyst dosages were determined to be 62.87%, 84.71%, and 82.15%, respectively, when the effect of WTS-CaO dosage on the photocatalytic system was evaluated. It was discovered that the dye removal efficiency gradually increased as the amount of photocatalyst increased. However, the results of the dye removal efficiency of the catalysts in the amount of 0.5 g/L and 1 g/L are very close to each other. Therefore, a smaller amount of catalyst was considered suitable for this study. The Safranin dye removal efficiency decreased below 57.26% when the amount of WTS-CaO was raised to 2 g/L. At the maximum dosages, the photodegradation effect is the severe. This can be explained by the fact that adding more photocatalyst to the dyed water causes turbidity, which prevents photons from the light source from reflecting onto the photocatalyst surface (Nadeem et al., 2021). In the research published by Ernawati et al. (2021), they viewed the decreasing pollutant removal effectiveness with increasing catalyst amount as turbidity caused by the high amount of photocatalyst in the solution, and thus irradiation limits the penetration depth. It was determined that the highest Safranin removal efficiency was obtained with the amount of 0.5 g/L photocatalyst in the amount experiments of the photocatalyst synthesized from the tomato stem, and it was determined to be used in the experiments of the initial dye concentration.
3.2.4. Effect of Safranin concentrations on the removal of dye with WTS-CaO in a photocatalytic system
The dye concentration dissolved in the water is one of the most important criteria impacting the wastewater treatment technology. The effect of initial solution concentration on Safranin dye in a photocatalytic system using WTS-CaO was investigated in this study. The varied initial of Safranin dye removal efficiency of photocatalyst with increasing and decreasing initial concentration was found in photocatalytic experimental results at end of 90 min. Initial dye concentrations of 5, 10, and 20 mg/L were derived from stock dye solutions. The effects of the initial dye concentration was investigated by adding 0.5 g/L photocatalyst to the dye solutions at the optimum dosage. During the photocatalytic studies, the intensity of the light source was kept constant and not changed. Figure 7 illustrates the obtained results.
The dye removal effectiveness declined with rising dye concentrations, according to the experimental results of changing Safranin dye concentrations. The dye removal efficiency for dye concentrations of 5, 10, and 20 mg/L was 97.14%, 84.71%, and 69.43%, respectively. It was reported that using photocatalysts with increasing initial dye concentrations had a damaging effect on dye degradation, and dye removal efficiency gradually decreased. The reason for the decrease in the dye removal efficiency with increasing initial dye concentration can be explained by the constant amount of photocatalyst in the system, the increased competition between the active sites of WTS-CaO and the dye molecules, and the reduced photocatalyst excitation with the limited photon presence with increasing dye concentration (Sugashini et al., 2022).
3.2.5. Reuse of catalyst for Safranin dye removal with WTS-CaO
Studies on the re-use of catalysts were also performed and are discussed in this paper. The photocatalytic process with 0.5 g/L catalyst in a 100 mL volume of solution with an initial concentration of 10 mg/L at the original pH value was terminated at the conclusion of the 1.5 h reaction time. The catalyst was then rinsed with distile water, filtered, and dried in an oven at 60oC overnight. In the next cycle, the dried catalyst was employed under the same conditions. After centrifuging the samples from the reuse tests, color measurements were conducted with a spectrophotometer. The results of the reuse of adsorbents are given in Fig. 8. The removal efficiency of the catalyst used after the first cycle was determined as 84.71%. After the second cycle, the dye removal efficiency decreased to about 81.31%, and the dye removal efficiency decreased to 69.95% after the third cycle. After the fourth and fifth reuse cycles, the dye removal efficiencies were measured as 40.56% and 32.49%, respectively.
In conclusion, WTS-CaO nano-photocatalyst was successfully made with waste tomato stem using a simple thermal approach. The green synthesis method is based on the principle of obtaining ash from waste tomato stems only with high temperature and organic material. according to the characterization results, a photocatalyst that produces hydroxyl in water was produced by the conversion of all calcium carbonate in the organic material into calcium oxide under high temperature (900oC). The main purpose of this study is to use the organic-based photocatalyst. In the studies of the light source, the visible light provided the highest dye removal efficiency. It was observed that the photocatalytic activity did not change with changing of pH values. Considering the results of the effect of the amount of photocatalyst on the photocatalytic system, the removal efficiency increases with increasing amount of photocatalyst. However, it was determined that the removal efficiency of Safranin dye decreased abruptly due to the turbidity of water containing dye in the highest amount of photocatalyst. Therefore, the optimum amount of WTS-CaO was determined as 0.5 g/L. Finally, it was determined that the dye removal efficiency decreased gradually with the increasing initial concentration in the effect of the initial dye concentration on the photocatalytic activity.
This study is promising that the photocatalyst synthesized from waste tomato stem can be used as a new and promising treatment material with the photocatalytic effect. It is suggested that this photocatalyst produced by green synthesis should be developed and researches should continue.
- Ahuja, P., Ujjain, S. K., Kanojia, R., & Attri, P. (2021). Transition metal oxides and their composites for photocatalytic dye degradation. Journal of Composites Science, 5(3), 82.
- Alkanan, Z. T., Al-Hilphy, A. R., Altemimi, A. B., Mandal, R., & Pratap-Singh, A. (2021). Comparison of quality characteristics of tomato paste produced under ohmic-vacuum combination heating and conventional heating. Applied Food Research, 1(2), 100014.
- Baaloudj, O., Assadi, A. A., Azizi, M., Kenfoud, H., Trari, M., Amrane, A., ... & Nasrallah, N. (2021). Synthesis and characterization of ZnBi2O4 nanoparticles: photocatalytic performance for antibiotic removal under different light sources. Applied Sciences, 11(9), 3975.
- Baláž, M., Boldyreva, E. V., Rybin, D., Pavlović, S., Rodríguez-Padrón, D., Mudrinić, T., &
- Benjelloun, M., Miyah, Y., Evrendilek, G. A., Zerrouq, F., & Lairini, S. (2021). Recent advances in adsorption kinetic models: their application to dye types. Arabian Journal of Chemistry, 14(4), 103031.
- Cao, Y. Q., Zi, T. Q., Zhao, X. R., Liu, C., Ren, Q., Fang, J. B., ... & Li, A. D. (2020). Enhanced visible light photocatalytic activity of Fe2O3 modified TiO2 prepared by atomic layer deposition. Scientific Reports, 10(1), 1-10.
- Chand, K., Jiao, C., Lakhan, M. N., Shah, A. H., Kumar, V., Fouad, D. E., ... & Cao, D. (2021). Green synthesis, characterization and photocatalytic activity of silver nanoparticles synthesized with Nigella Sativa seed extract. Chemical Physics Letters, 763, 138218.
- Chanikya, P., Nidheesh, P. V., Babu, D. S., Gopinath, A., & Kumar, M. S. (2021). Treatment of dyeing wastewater by combined sulfate radical based electrochemical advanced oxidation and electrocoagulation processes. Separation and Purification Technology, 254, 117570.
- Chen, L., Beiyuan, J., Hu, W., Zhang, Z., Duan, C., Cui, Q., ... & Fang, L. (2022). Phytoremediation of potentially toxic elements (PTEs) contaminated soils using alfalfa (Medicago sativa L.): A comprehensive review. Chemosphere, 133577.
- Cheng, G., Wan, J., Li, Q., Sun, L., Zhang, Y., Li, Z., ... & Fu, J. (2022). Degradation of Reactive Brilliant Red X-3B by Photo-Fenton-like Process: Effects of Water Chemistry Factors and Degradation Mechanism. Water, 14(3), 380.
- Das, S., & Ahn, Y. H. (2022). Synthesis and application of CdS nanorods for LED-based photocatalytic degradation of tetracycline antibiotic. Chemosphere, 291, 132870.
- Davoodbasha, M., Pugazhendhi, A., Kim, J. W., Lee, S. Y., & Nooruddin, T. (2021). Biodiesel production through transesterification of Chlorella vulgaris: Synthesis and characterization of CaO nanocatalyst. Fuel, 300, 121018.
- Demirer, T. (2018). A research on the determination of productivity levels of tomato grown areas. African Journal of Agricultural Research, 13(50), 2808-2817.
- Donkadokula, N. Y., Kola, A. K., Naz, I., & Saroj, D. (2020). A review on advanced physico-chemical and biological textile dye wastewater treatment techniques. Reviews in environmental science and bio/technology, 19(3), 543-560.
- Ernawati, L., Yusariarta, A. W., Laksono, A. D., Wahyuono, R. A., Widiyandari, H., Rebeka, R., & Sitompul, V. (2021). Kinetic Studies of Methylene Blue Degradation using CaTiO3 Photocatalyst from Chicken Eggshells. In Journal of Physics: Conference Series (Vol. 1726, No. 1, p. 012017). IOP Publishing.
- Ertürk, H. (2021). Growth of tomato plantlets in soilless culture, enriched with egg shell waste and algae.
- Gutha, Y., Munagapati, V. S., Naushad, M., & Abburi, K. (2015). Removal of Ni (II) from aqueous solution by Lycopersicum esculentum (Tomato) leaf powder as a low-cost biosorbent. Desalination and Water Treatment, 54(1), 200-208.
- Heidari, Z., Pelalak, R., Malekshah, R. E., Pishnamazi, M., Marjani, A., Sarkar, S. M., & Shirazian, S. (2021). Molecular modeling investigation on mechanism of cationic dyes removal from aqueous solutions by mesoporous materials. Journal of Molecular Liquids, 329, 115485.
- Jha, P., & Singh, K. (2016). Effect of MgO on bioactivity, hardness, structural and optical properties of SiO2–K2O–CaO–MgO glasses. Ceramics International, 42(1), 436-444.
- Keerthana, S. P., Yuvakkumar, R., Kumar, P. S., Ravi, G., Vo, D. V. N., & Velauthapillai, D. (2021). Influence of tin (Sn) doping on Co3O4 for enhanced photocatalytic dye degradation. Chemosphere, 277, 130325.
- Khoshnevisan, S., & Bazgir, S. (2021). Treatment of dye wastewater by direct contact membrane distillation using superhydrophobic nanofibrous high-impact polystyrene membranes. International Journal of Environmental Science and Technology, 18(6), 1513-1528.
- Li, Z., Zhang, Z., Dong, Z., Wu, Y., Liu, J., Cheng, Z., ... & Liu, Y. (2021). Synthesis of MoS2/Pg-C3N4 nanocomposites with enhanced visible-light photocatalytic activity for the removal of uranium (VI). Journal of Solid State Chemistry, 302, 122305.
- Liu, L., Chen, Z., Zhang, J., Shan, D., Wu, Y., Bai, L., & Wang, B. (2021). Treatment of industrial dye wastewater and pharmaceutical residue wastewater by advanced oxidation processes and its combination with nanocatalysts: A review. Journal of Water Process Engineering, 42, 102122.
- Luong, T. H., Nguyen, T. H., Nguyen, B. V., Nguyen, N. K., Nguyen, T. Q., & Dang, G. H. (2022). Efficient degradation of methyl orange and methylene blue in aqueous solution using a novel Fenton-like catalyst of CuCo-ZIFs. Green Processing and Synthesis, 11(1), 71-83.
- Luque, R. (2021). State-of-the-art of eggshell waste in materials science: recent advances in Mousa, H. M., Alenezi, J. F., Mohamed, I. M., Yasin, A. S., Hashem, A. F. M., & Abdal-hay, A. (2021). Synthesis of TiO2@ ZnO heterojunction for dye photodegradation and wastewater treatment. Journal of Alloys and Compounds, 886, 161169.
- Nadeem, F., Bhatti, I. A., Ashar, A., Yousaf, M., Iqbal, M., Mohsin, M., ... & Alwadai, N. (2021). Eco-benign biodiesel production from waste cooking oil using eggshell derived MMCaO catalyst and condition optimization using RSM approach. Arabian Journal of Chemistry, 14(8), 103263.
- Nadeem, F., Bhatti, I. A., Ashar, A., Yousaf, M., Iqbal, M., Mohsin, M., ... & Alwadai, N. (2021). Eco-benign biodiesel production from waste cooking oil using eggshell derived MM-CaO catalyst and condition optimization using RSM approach. Arabian Journal of Chemistry, 14(8), 103263.
- Nassar, A. M., & Alotaibi, N. F. (2021). Eggshell recycling for fabrication of Pd@ CaO, characterization and high-performance solar photocatalytic activity. Environmental Science and Pollution Research, 28(3), 3515-3523.
- Ouansafi, S., Abdelilah, F., Kabine, M., Maaghloud, H., Bellali, F., & El Bouqdaoui, K. (2019). The effects of soil proprieties on the yield and the growth of tomato plants and fruits irrigated by treated wastewater. AIMS Agriculture and Food, 4(4), 921-938.
- Prajapati, A. K., & Mondal, M. K. (2021). Novel green strategy for CuO–ZnO–C nanocomposites fabrication using marigold (Tagetes spp.) flower petals extract with and without CTAB treatment for adsorption of Cr(VI) and Congo red dye. Journal of Environmental Management, 290, 112615.
- Shindhal, T., Rakholiya, P., Varjani, S., Pandey, A., Ngo, H. H., Guo, W., ... & Taherzadeh, M. J. (2021). A critical review on advances in the practices and perspectives for the treatment of dye industry wastewater. Bioengineered, 12(1), 70-87.
- Sinha, S., Aman, A. K., Singh, R. K., Kr, N., & Shivani, K. (2021). Calcium oxide (CaO) nanomaterial (Kukutanda twak Bhasma) from egg shell: Green synthesis, physical properties and antimicrobial behaviour. Materials Today: Proceedings, 43, 3414-3419.
- Song, L., & Zhang, S. (2010). A simple mechanical mixing method for preparation of visible-light-sensitive NiO–CaO composite photocatalysts with high photocatalytic activity. Journal of Hazardous Materials, 174(1-3), 563-566.
- Sugashini, S., Gomathi, T., Devi, R. A., Sudha, P. N., Rambabu, K., & Banat, F. (2022). Nanochitosan/carboxymethyl cellulose/TiO2 biocomposite for visible-light-induced photocatalytic degradation of crystal violet dye. Environmental Research, 204, 112047.
- Sun, H., Li, Y., Yan, X., Wang, Z., & Liu, W. (2020). CaO/CaCO3 thermochemical heat storage performance of CaO-based micrometre-sized tubular composite. Energy Conversion and Management, 222, 113222.
- Vorobyova, V., Skiba, M., & Vasyliev, G. (2022). Extraction of phenolic compounds from tomato pomace using choline chloride–based deep eutectic solvents. Journal of Food Measurement and Characterization, 16(2), 1087-1104.
- Xu, T. X., Tian, X. K., Khosa, A. A., Yan, J., Ye, Q., & Zhao, C. Y. (2021). Reaction performance of CaCO3/CaO thermochemical energy storage with TiO2 dopant and experimental study in a fixed-bed reactor. Energy, 236, 121451.
- Yang, H., Wang, W., Wu, X., Siddique, M. S., Su, Z., Liu, M., & Yu, W. (2022). Reducing ROS generation and accelerating the photocatalytic degradation rate of PPCPs at neutral pH by doping Fe-NC to g-C3N4. Applied Catalysis B: Environmental, 301, 120790.
- Yu, Y., Yao, B., He, Y., Cao, B., Ma, W., & Chang, L. (2020). Oxygen defect-rich In-doped ZnO nanostructure for enhanced visible light photocatalytic activity. Materials Chemistry and Physics, 244, 122672.