https://orcid.org/0009-0009-5552-8885
Abstract
Organic pollutants in water bodies pose a serious environmental problem, and photocatalytic technology is an efficient and environmentally friendly water treatment method. Titanium dioxide (TiO2) is a widely used photocatalyst, but it suffers from some drawbacks such as a narrow light response range, fast charge recombination, and low photocatalytic activity. To improve the photocatalytic performance of TiO2, this article reviews the preparation methods, performance evaluation, and applications of modified TiO2 photocatalysts. Firstly, the article introduces the effects of doping modification, semiconductor composite modification, and other modification methods on the structure and properties of TiO2 photocatalysts, as well as the common characterization techniques and activity test methods of photocatalysts. Secondly, the article discusses the effects and mechanisms of modified TiO2 photocatalysts on degrading dye, pesticide, and other organic pollutants in water bodies, as well as the influencing factors. Finally, the article summarizes the main achievements and advantages of modified TiO2 photocatalysts in degrading organic pollutants in water bodies, points out the existing problems and challenges, and prospects for the development direction and future of this field.
HIGHLIGHTS
Various techniques enhance titanium dioxide (TiO2) properties.
The study of the modified TiO2 photocatalytic mechanism.
Modified TiO2 excels in degrading organic pollutants.
In practical water treatment, modified TiO2 offers promising results and simultaneous challenges.
INTRODUCTION
Water is a precious resource on Earth, which is crucial for maintaining the ecological balance and ensuring the sustainable development of human society (Gavrilescu 2021). However, rapid industrialization, urbanization, and agricultural growth have led to an increasingly severe problem of organic pollutant contamination in water bodies, becoming one of the significant challenges in global environmental protection (Mushtaq et al. 2020). These organic pollutants in water primarily originate from industrial wastewater, agricultural runoff, urban sewage, and various human activities (Singh et al. 2020). Not only are these pollutants highly stable and difficult to degrade, but they may also pose threats to water quality and the ecosystem due to their potential toxicity, carcinogenicity, and mutagenicity (Ismail et al. 2019).
Therefore, there is an urgent need to explore efficient, economical, and environmentally friendly methods to remediate organic pollutants in water bodies. In recent years, photocatalytic technology has garnered considerable attention as an environmentally friendly approach to pollutant degradation (Subhiksha et al. 2022). This technology harnesses photocatalysts to generate highly active oxygen radicals, such as hydroxyl radicals (•OH) and superoxide radicals (
), under light irradiation (Acharya & Parida 2020). These radicals can oxidize and decompose organic pollutants in water, transforming them into harmless small molecules like carbon dioxide and water (Jiang et al. 2021). Among various photocatalysts, titanium dioxide (TiO2) has been extensively studied due to its advantages of low toxicity, high stability, affordability, and excellent chemical stability (Zhang et al. 2019; Turkten & Bekbolet 2020; Li et al. 2021a, 2021b).
However, TiO2 also suffers from some limitations, such as a narrow light absorption range, rapid electron-hole recombination rate, and low catalytic activity, which hinder the practical application of TiO2 photocatalysis (Jeon et al. 2020). To address these issues, researchers have focused on modifying TiO2 photocatalysts to enhance their photocatalytic performance (Arora et al. 2022). Modified TiO2 photocatalysts, achieved through the introduction of dopants, loading agents, or composites, can modulate TiO2's band structure, electronic transport properties, and surface characteristics, thereby effectively improving photocatalytic activity and selectivity (Chen et al. 2020).
It is worth noting that despite the existence of numerous review articles on TiO2 as a photocatalyst, this study stands out with its clear thematic focus and distinct motivation. The paper thoroughly discusses the performance of modified TiO2 photocatalysts, explores the underlying mechanisms of various modification methods, and discusses their efficiency in degrading organic pollutants in water. Additionally, special attention is given to the application of modified TiO2 photocatalysts in degrading diverse types of organic pollutants, highlighting their crucial value and promising prospects in treating organic water pollution.
Consequently, this paper aims to delve into the application of modified TiO2 photocatalysts in the degradation of organic pollutants in water bodies, exploring their potential in addressing water environmental issues. Through this research, we anticipate providing new insights and methods for treating organic pollutants in water bodies and promoting the widespread adoption and application of photocatalytic technology in practical scenarios.
MATERIALS AND METHODS
Preparation methods of modified TiO2 photocatalysts:
Doping modification method
). Superoxide radicals react with electrons and protons, forming hydrogen peroxide (H2O2), and hydrogen peroxide reacts with superoxide radicals, resulting in the formation of hydroxyl radicals (OH•), hydroxide ions (OH−), and molecular oxygen (O2) through a series of reactions. The visible light absorption by Bi/N-TiO2 and the effective charge carrier separation facilitated by bismuth species play a significant role in enhancing the photocatalytic activity of Bi/N-TiO2 for the degradation of 2,4-DCP. Bayan et al. (2020) conducted a study and found that co-doping TiO2 with zinc and fluorine ions induces the formation of oxygen vacancies on the catalyst surface. The presence of these vacancies enhances the generation of hydroxyl radicals (OH−) on the nanoparticle surface, which play a crucial role in the photocatalytic process. Additionally, zinc doping influences the formation of active species. Zinc ions (Zn2+) can trap electrons or holes, disrupting their stable configuration. Trapped electrons can react with oxygen molecules to produce superoxide radicals (
), while trapped holes can react with hydroxyl anions to form hydroxyl radicals (OH−). In the photocatalytic process, the model pollutant used is the organic azo-dye methylene blue (MB). The cationic functional groups of MB molecules initially adsorb onto the catalyst nanoparticle surface. Subsequently, the radical decomposition of MB takes place, leading to the opening of the central aromatic ring and the formation of intermediate degradation products. Finally, the photocatalytic decomposition culminates in the production of inorganic molecules such as CO2, 
, 
, and 
. These reactions occur under both UV and visible light irradiation. 
Mechanism for the degradation of 2,4-DCP by 10% Bi/N-TiO2 under visible light irradiation (Bagwasi et al. 2013).
Mechanism for the degradation of 2,4-DCP by 10% Bi/N-TiO2 under visible light irradiation (Bagwasi et al. 2013).
Semiconductor composite modification method
), which further convert to peroxyl radicals (·H2) and hydroxyl radicals (•OH), contributing to the oxidation degradation of organic pollutants. Organic pollutants are oxidatively degraded into inorganic small molecules, such as CO2 and H2O, achieving water purification. The study demonstrates that 0.2 wt% CQDs/LM-TiO2 composite material exhibits the highest photocatalytic activity, achieving a degradation rate of 91.04% for methyl orange within 24 min, which is significantly higher than pure TiO2 and LM-TiO2. This enhancement is attributed to CQDs' ability to enhance LM-TiO2's absorption in the visible light region, improve the separation efficiency of photo-generated charge carriers, and facilitate charge transfer at the heterojunction interface. Liu et al. (2019) conducted a study on the synthesis and characterization of Ag2O nanoparticle-decorated TiO2 nanofibers to enhance the photocatalytic decomposition of Rhodamine B (RhB) under visible light irradiation. The research findings indicate that the band alignment of the Ag2O/TiO2 composite at the heterojunction interfaces is responsible for the improved photocatalytic activity. Before Ag2O comes into contact with TiO2, the Fermi level of n-type TiO2 is slightly below the CB of TiO2, whereas the Fermi level of p-type Ag2O is slightly higher than the VB of Ag2O. When n-type TiO2 comes into contact with p-type Ag2O, their Fermi levels align together, forming a continuous new Fermi level. This alignment creates a p–n heterojunction at the interface, leading to a new band structure in the interface region. The different positions of the CB and the VB relative to the Fermi level in Ag2O and TiO2 cause electrons to the flow from Ag2O to TiO2 along the CB, while holes flow in the opposite direction from TiO2 to Ag2O along the VB. The realignment of the energy bands also generates a built-in electric field at the interface, directing from Ag2O to TiO2. Under visible light irradiation, Ag+ in Ag2O is partially reduced to AgO by photo-induced electrons, resulting in the formation of metallic Ag on the surface of both Ag2O and TiO2. This metallic Ag acts as an electron pool, facilitating the transfer of photoexcited electrons from the CB of p-type Ag2O to the CB of n-type TiO2. At the same time, the photo-generated holes are transferred from the VB of TiO2 to the VB of Ag2O. The presence of the built-in electric field further enhances the transfer and separation of charges. Electrons react with surface-adsorbed to produce superoxide radicals (
), while the holes exhibit strong oxidizing ability, directly oxidizing and decomposing RhB. Overall, the p–n heterojunction enhances charge transfer and separation, leading to increased photocatalytic activity. This phenomenon highlights the significance of band alignment in Ag2O/TiO2 composites, providing insights into the design and optimization of advanced photocatalytic materials. Figure 2 illustrates the photocatalytic mechanism of p-Ag2O/n-TiO2 nanofibers. 
Photocatalytic degradation of MB over the samples under (a) visible light irradiation and (b) UV light irradiation (Zhao et al. 2020).
Photocatalytic degradation of MB over the samples under (a) visible light irradiation and (b) UV light irradiation (Zhao et al. 2020).
Concentration variation of MO vs. irradiation time in the presence of various catalysts under (a) UV irradiation and (b) visible-light irradiation (Wang & Zhou 2011).
Concentration variation of MO vs. irradiation time in the presence of various catalysts under (a) UV irradiation and (b) visible-light irradiation (Wang & Zhou 2011).
Degradation of different concentrations of 4-CP on TiO2 catalysts with different nanostructures (Song et al. 2021).
Degradation of different concentrations of 4-CP on TiO2 catalysts with different nanostructures (Song et al. 2021).
Other modification methods
Besides the two methods mentioned above, other ways to modify TiO2 include defect engineering, crystal facet engineering, carrier adsorption, and morphology control (Wang et al. 2023). Defect engineering alters the electronic structure and surface activity of TiO2 by introducing or adjusting lattice defects such as vacancies, interstitial atoms, or dislocations (Dong et al. 2018). Crystal facet engineering modifies the shape and lattice distortion of TiO2 by selecting different phases or facets, which affect its photocatalytic activity (Liu et al. 2014). Carrier adsorption enhances the photocatalytic efficiency of TiO2 by compositing or loading it with other materials such as graphene, carbon nanotubes (CNTs), and metal oxides to form heterojunctions or increase the specific surface area (Anucha et al. 2022). Morphology control improves its light absorption and carrier transport characteristics by controlling the morphology parameters such as particle size, shape, and porosity of TiO2 (Niu et al. 2018).
For ease of readability, a concise summary of other methods for modifying TiO2 is provided in Table 1.
Other modification methods
| Process types | Mechanization | Data sources |
|---|---|---|
| Defect engineering | Defect engineering in TiO2 involves using argon ion beam irradiation to create oxygen vacancies. These vacancies, formed by converting Ti4+ ions to Ti3+ and Ti2+ ions, enhance photocatalytic activity by reducing charge recombination and modifying surface properties and electronic states. | Qahtan et al. (2023) |
| TiO2 has defects like oxygen vacancies, Ti3+ defects, and grain boundaries. Oxygen vacancies trap electrons, reduce recombination, and improve charge separation. Ti3+ defects enhance visible light absorption due to their smaller bandgap than TiO2's Ti4+ states. | Li et al. (2022) | |
| Crystal facet engineering | Researchers have enhanced TiO2's photocatalytic performance by adjusting its crystal facets. Notably, the (101) surface of anatase TiO2 shows better activity than other facets due to its lower Schottky barrier height that aids efficient electron transfer. This approach also benefits TiO2 combined with Cr2O3, significantly raising CO2 conversion efficiency. | Fawzi et al. (2022) |
| Carrier adsorption | TiO2–ZnO/rGO materials have been modified using the hydrophobic compound hexamethyldisilane (HDMS) to enhance their properties. This modification increases the water contact angle to 103.6° by introducing aliphatic carbon groups. HDMS also prevents fouling and water absorption on the material's surface, leading to improved photocatalytic performance. These hydrophobic changes maintain catalytic activity by reducing unwanted water interactions, and significantly enhancing photocatalytic efficiency. | Fadillah et al. (2022) |
| Morphology control | Morphology control in photocatalytic materials hinges on particle size, quantum effects, and carrier migration. Smaller sizes amplify surface area, reactivity, and migration, but proximity to the electron's mean free path can heighten recombination. Nanomaterial morphology, structure, and surface properties also affect carrier migration, necessitating precise concentration or potential gradients. Advances in morphology-controlled synthesis show a link between morphology and photocatalytic traits. Diverse nanostructures, including 0D quantum dots, 1D rods, 2D sheets, and 3D spheres, have been investigated. | Liu et al. (2020) |
| Process types | Mechanization | Data sources |
|---|---|---|
| Defect engineering | Defect engineering in TiO2 involves using argon ion beam irradiation to create oxygen vacancies. These vacancies, formed by converting Ti4+ ions to Ti3+ and Ti2+ ions, enhance photocatalytic activity by reducing charge recombination and modifying surface properties and electronic states. | Qahtan et al. (2023) |
| TiO2 has defects like oxygen vacancies, Ti3+ defects, and grain boundaries. Oxygen vacancies trap electrons, reduce recombination, and improve charge separation. Ti3+ defects enhance visible light absorption due to their smaller bandgap than TiO2's Ti4+ states. | Li et al. (2022) | |
| Crystal facet engineering | Researchers have enhanced TiO2's photocatalytic performance by adjusting its crystal facets. Notably, the (101) surface of anatase TiO2 shows better activity than other facets due to its lower Schottky barrier height that aids efficient electron transfer. This approach also benefits TiO2 combined with Cr2O3, significantly raising CO2 conversion efficiency. | Fawzi et al. (2022) |
| Carrier adsorption | TiO2–ZnO/rGO materials have been modified using the hydrophobic compound hexamethyldisilane (HDMS) to enhance their properties. This modification increases the water contact angle to 103.6° by introducing aliphatic carbon groups. HDMS also prevents fouling and water absorption on the material's surface, leading to improved photocatalytic performance. These hydrophobic changes maintain catalytic activity by reducing unwanted water interactions, and significantly enhancing photocatalytic efficiency. | Fadillah et al. (2022) |
| Morphology control | Morphology control in photocatalytic materials hinges on particle size, quantum effects, and carrier migration. Smaller sizes amplify surface area, reactivity, and migration, but proximity to the electron's mean free path can heighten recombination. Nanomaterial morphology, structure, and surface properties also affect carrier migration, necessitating precise concentration or potential gradients. Advances in morphology-controlled synthesis show a link between morphology and photocatalytic traits. Diverse nanostructures, including 0D quantum dots, 1D rods, 2D sheets, and 3D spheres, have been investigated. | Liu et al. (2020) |
Performance evaluation methods of photocatalysts
Modified TiO2 photocatalysts can be prepared by various methods, but their performance requires evaluation and analysis. Some of the common characterization methods for photocatalysts are X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis). These methods can provide information on the phase, morphology, composition, and band structure of photocatalysts. Some of the common photocatalytic activity test methods are the degradation of organic dyes, water splitting for hydrogen production, and photocatalytic reduction of carbon dioxide. These methods can indicate the efficiency and stability of photocatalysts under different reaction conditions. Some of the common photocatalytic activity evaluation indicators are reaction rate constant, quantum efficiency, and conversion rate. These indicators can quantitatively compare the merits and demerits of different photocatalysts (Cheng et al. 2016).
RESULTS
The application of modified TiO2 photocatalysts in the degradation of organic pollutants in water
Dye pollutants
Dye pollutants are a common type of organic pollutants in aquatic ecosystems. They have high chroma, strong stability, and low biodegradability, which pose serious threats to the water quality (Ma et al. 2021). Modified TiO2 photocatalysts are a novel class of eco-friendly catalysts. They can utilize visible light or ultraviolet light to generate electron-hole pairs, which produce powerful oxidative species such as hydroxyl radicals and superoxide radicals. These species can oxidize and degrade the organic pollutants in water, achieving water purification (Akhter et al. 2022).
Modified TiO2 photocatalysts have shown promising effects and mechanisms in degrading various types of dyes (Anucha et al. 2022). For instance, for azo dyes, modified TiO2 photocatalysts can break the azo bonds and benzene ring structures of dye molecules by different pathways, such as direct adsorption, charge transfer, and free radical attack, resulting in the loss of color and toxicity of the dye molecules (Zhang et al. 2021a, 2021b, 2021c). For aromatic amine dyes, modified TiO2 photocatalysts can cleave the aromatic amine structure by the free radical attack, hydroxyl substitution, etc., leading to the conversion of dye molecules into low-molecular-weight inorganic acids and water (Rauf et al. 2011). Different types of modified TiO2 photocatalysts also exhibit different performances in degrading various types of dyes. For example, modified TiO2 photocatalysts doped with metal or non-metal elements can enhance the light absorption ability and the separation efficiency of electron-hole pairs, thus improving the degradation efficiency (Basavarajappa et al. 2020). Modified TiO2 photocatalysts that composite with other semiconductor materials can form heterojunction structures, which can extend the light response range and improve the charge transfer ability, thus improving the degradation efficiency (Wang et al. 2021).
One of the methods to modify TiO2 for photocatalytic applications is to dope it with silver nanoparticles (Ag/TiO2). Ag/TiO2 can enhance the photocatalytic activity of TiO2 by improving its light absorption, electron-hole separation, and affinity toward organic pollutants. For example, Zhao et al. (2020) significantly improved the catalytic efficiency of TiO2 under visible light by synergistically combining it with silver-covered carbon nanotubes (CA) to form a ternary structure called CNTs–Ag–TiO2 (CAT). The composite underwent comprehensive characterization using various techniques, including XRD, SEM, X-ray photoelectron spectroscopy, diffuse reflectance spectra, and photoluminescence spectra. The researchers studied the photocatalytic activity of CAT using MB as a model pollutant to investigate the influence of CA content in the composite on photocatalysis. As depicted in Figure 3, the incorporation of CA into TiO2 significantly enhanced its photocatalytic activity under both visible light and UV light. Notably, when the mass ratio of CA was 15%, the degradation rate of MB by CAT reached an impressive 80.8% under visible light within just 3 h, surpassing that of TiO2 alone by a remarkable 16.5 times. Similarly, under UV light, the degradation rate reached 99.2% within a mere 40 min, which was almost twice as fast as that of TiO2.
One type of modified TiO2 photocatalyst that is widely used is CNT-doped TiO2 (CNT/TiO2). CNTs form a composite structure with TiO2 that has close contact and provides a rapid electron transport channel. This reduces the recombination loss of electron-hole pairs and enhances the photocatalytic activity. Wang & Zhou (2011) conducted research to demonstrate the advantages of the composite photocatalyst CNTs/P-TiO2, prepared through the hydrothermal method, over pure TiO2. First, the CNTs/P-TiO2 photocatalyst exhibits a smaller crystalline size, leading to enhanced photocatalytic activity. Second, it boasts a larger surface area, providing abundant active sites for the adsorption and degradation of pollutants. Third, it exhibits stronger absorption in the visible range, enabling the effective utilization of visible light for photocatalysis. As depicted in Figure 4, the CNTs/P-TiO2 composite catalyst exhibits a synergistic effect in the photocatalytic degradation of methyl orange (MO) (a model organic pollutant). The combination of CNTs and phosphorus-doped TiO2 results in significantly higher photocatalytic activity compared to pure TiO2 and P25 (a commonly used commercial TiO2 photocatalyst) under both UV and visible light irradiation.
The degradation of dye pollutants by modified TiO2 photocatalysts depends on various factors. One of these factors is the pH value, which influences the ion balance and the surface charge state of water. These, in turn, affect the adsorption of dye molecules and modified TiO2 photocatalysts (Rafiq et al. 2021). Another factor is the temperature, which influences the reaction rate and the equilibrium constant. These, in turn, affect the degradation kinetics and thermodynamics. A third factor is the additives, which influence the properties and the reaction mechanism of the reaction medium. These, in turn, affect the degradation effect. Therefore, it is necessary to select appropriate modified TiO2 photocatalysts and optimize reaction parameters according to the specific water conditions and pollutant characteristics in practical applications, in order to achieve the optimal degradation effect (Han et al. 2009; Li et al. 2021a, 2021b).
Pesticide pollutants
One of the major sources of organic pollutants in aquatic ecosystems is pesticides, which pose serious threats to both environmental and human health (Gwenzi & Chaukura 2018). A promising technique for degrading pesticide contaminants is the use of modified TiO2 photocatalysts, which can harness solar or visible light to activate the modified TiO2 surface and generate reactive free radicals. These radicals can oxidize and decompose pesticide molecules into harmless or low-toxic substances (Pelaez et al. 2012). Modified TiO2 photocatalysts can be applied to various kinds of pesticides, such as herbicides and insecticides.
Song et al. (2021) focused on developing a highly efficient photoelectrocatalyst for the degradation of organic pollutants using a TiO2 catalyst. Their research demonstrated the synthesis of TiO2 nanocones, which exhibited superior performance and durability compared to other TiO2 catalysts. As depicted in Figure 5, the nanocone catalyst showcased enhanced degradation performance for a specific organic pollutant, 4-chlorophenol (4-CP), achieving a degradation efficiency of 99% and a mineralization efficiency of over 55% at a concentration of 20 ppm. The apparent rate constant for the nanocone catalyst was found to be 5.05 h−1 g−1 m2, which is significantly higher than that of nanorod and aggregated particle catalysts. The improved performance of the nanocone catalyst is attributed to its unique conical morphology, which enables the efficient separation and transfer of photo-generated charges, leading to enhanced photoelectrocatalytic (PEC) activity. Additionally, computational fluid dynamics simulations suggest that the three-dimensional conical structure facilitates mass transfer, further enhancing PEC performance. This research underscores the significance of nanometer-scale morphology tuning in photoelectrocatalysts for improved charge transfer and mass transportation, ultimately enhancing the PEC performance in the degradation of persistent pollutants. Anirudhan et al. (2020) developed a magnetic TiO2 embedded molecularly imprinted polymer (mTiO2-MIP) nanocomposite for the efficient degradation of diuron under visible light. Diuron, an environmental priority pollutant commonly found in water bodies due to pesticide overuse, served as the target compound for degradation. The primary objective of the study was to create a photocatalyst capable of effectively degrading diuron using visible light. The mTiO2-MIP photocatalyst was synthesized by molecular imprinting on mTiO2 using 3-thiophene acetic acid and 3-thiophene carboxaldehyde, forming a conducting layer of MIP. Various characterization techniques, including Fourier-transform infrared spectroscopy (FT-IR), XRD, SEM, TEM, vibrating sample magnetometer (VSM), UV–vis, diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry, and photoluminescence spectroscopy, were employed to analyze the nanocomposite. The MIP layer in the nanocomposite enhanced the catalyst's selectivity and acted as a photosensitizer. The study revealed that the mTiO2-MIP photocatalyst exhibited superior photocatalytic degradation of diuron compared to mTiO2 under visible light. The combination of magnetism and molecular imprinting technology with TiO2 offered a novel and efficient approach for diuron degradation under visible light. In conclusion, the utilization of TiO2, particularly in the form of the mTiO2-MIP nanocomposite, proved to be effective in degrading pesticides like diuron under visible light conditions. The findings highlight the potential of this photocatalytic system for environmental remediation applications.
The degradation of pesticide pollutants by modified TiO2 photocatalysts depends on various factors, such as pH, temperature, and additives. pH affects the surface charge of modified TiO2 and the ionization degree of pesticide molecules, which influences their adsorption and reaction rate (Singh et al. 2023). Temperature determines the activity and stability of modified TiO2 photocatalysts. The photocatalytic effect will decrease if the temperature is too high or too low. Additives can alter the structure, morphology, specific surface area, band structure, etc., of modified TiO2 photocatalysts, which can enhance or reduce their photocatalytic activity. Therefore, it is necessary to choose appropriate modified TiO2 photocatalysts and optimal reaction conditions according to the types of pesticide pollutants and water quality conditions to achieve the best degradation effect in practical applications.
Other organic pollutants
Modified TiO2 is a photocatalyst that can degrade various organic pollutants in water, such as dyes, pesticides, phenols, benzenes, and surfactants. These pollutants are resistant to natural degradation and pose serious threats to water quality and ecology. Modified TiO2 can utilize visible light or ultraviolet light to generate electron-hole pairs, which then produce reactive oxygen species (ROS), such as hydroxyl radicals (•OH) and superoxide radicals (
). These ROS have high oxidative potential and can react with organic pollutants, transforming them into carbon dioxide and water and thus achieving water purification.
Eddy et al. (2021) conducted a study on the photocatalytic degradation of phenol using silica-modified TiO2 as a composite photocatalyst. Phenol, a hazardous organic pollutant commonly found in industrial wastewater, poses significant risks to environmental and human health, making its removal crucial. In their research, they incorporated silica extracted from natural resources, such as beach sand, into the composite. The photocatalytic activity and characterization of the TiO2/Si2 composite were extensively investigated. Various techniques, including XRD, FT-IR, SEM, and particle size analysis, were employed to thoroughly characterize the composite. The study revealed that the composite exhibited high crystallinity and significantly improved photocatalytic activity compared to commercial TiO2. Under UV irradiation, the optimized composite achieved a remarkable phenol degradation rate of 96.05% within 120 min, surpassing commercial TiO2 by 3.5 times. The findings suggest that silica-modified TiO2 holds great potential as an effective photocatalyst for phenol degradation in wastewater treatment applications.
In a study conducted by Murgolo et al., SWCNTs-TiO2 nanoparticles were utilized for the photodegradation of various organic pollutants, including pharmaceuticals such as warfarin, mefenamic acid, metoprolol, and carbamazepine. The degradation rates of these pollutants were found to be comparable to those achieved with Degussa P25 TiO2, a widely used photocatalyst. However, it was observed that the TiO2 loading in the SWCNT–TiO2 system was lower compared to Degussa P25 TiO2. Moreover, when the photodegradation was performed in real wastewater samples, the efficiency of both catalysts decreased. In another study, multi-walled CNTs (MWCNTs) were combined with TiO2 for the degradation of tetracycline antibiotic (TCL). The resulting MWCNT–TiO2 nanocomposite exhibited the efficient degradation of TCL in both deionized water and real wastewater samples. The complete removal of TCL at concentrations up to 10 mg/dm3 was achieved within 100 min of irradiation. While the efficiency decreased for higher TCL concentrations, low concentrations were still removed even after 10 min of irradiation. Additionally, the MWCNT–TiO2 nanocomposite showed improved efficiency in reducing chemical oxygen demand (COD) and total organic carbon (TOC) in real wastewater samples compared to bare TiO2. In summary, SWCNT–TiO2 nanocomposites have demonstrated the effective degradation of organic pollutants, including pharmaceuticals. Their photocatalytic activity has been compared to traditional TiO2 photocatalysts and has shown similar or improved efficiency in the removal of various organic pollutants, especially at lower concentrations (Krakowiak et al. 2021).
CONCLUSIONS
This paper systematically investigates the application of modified TiO2 photocatalysts in the degradation of organic pollutants in water. Due to their environmentally friendly and high-efficiency characteristics, modified TiO2 photocatalysts have gained significant attention as a promising water purification technology. By utilizing visible or ultraviolet light to generate active oxygen radicals, such as hydroxyl radicals and superoxide radicals, these catalysts can oxidize and degrade organic pollutants in water, effectively improving the water environment. The study first introduces different modification methods, including doping modification and semiconductor composite modification, and discusses their impacts on catalyst performance. The results demonstrate that modification is an effective approach to enhancing photocatalyst performance, increasing light absorption and electron-hole pair separation efficiency, and significantly improving the degradation efficiency of organic pollutants. Furthermore, this paper focuses on the application of modified TiO2 photocatalysts in the degradation of dyes, pesticides, and other organic pollutants. The research results show that these catalysts exhibit excellent degradation efficiency for different types of organic pollutants. Concerning dye pollutants, modified TiO2 catalysts can effectively break the chemical bonds of dye molecules, transforming them into harmless low-molecular-weight inorganic substances. For pesticide pollutants, modified TiO2 catalysts can efficiently oxidize and degrade pesticide molecules, thereby effectively removing pollutants and purifying water environments. Lastly, this paper explores the factors affecting the degradation efficiency of modified TiO2 photocatalysts. Factors such as pH, temperature, and additives significantly influence the surface charge of the catalyst and the adsorption and reaction rates of pollutants. Therefore, optimizing reaction parameters can further enhance the degradation efficiency in practical applications. Consequently, for specific water quality conditions and pollutant characteristics, selecting appropriate modified catalysts and optimal reaction conditions are essential to achieve the best degradation results. In conclusion, modified TiO2 photocatalysts show tremendous potential and prospects in water treatment. This paper provides valuable references and guidance for in-depth research in this field, aiming to improve and optimize photocatalysis technology, enhance water purification efficiency, and promote environmentally friendly water treatment projects. Future research can further expand the application of modified TiO2 photocatalysts in the treatment of different organic pollutants, advancing the practical implementation of this technology and making greater contributions to safeguarding water environments and maintaining ecological balance.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.
%20cropped.png?versionId=5945)