Advanced Photocatalytic Degradation of Dyes, Drugs, and Organic Pollutants via Carbon-Supported Nanoparticles

The rapid expansion of Industrial and pharmaceutical activities has significantly increased the discharge of organic pollutants, dyes, and drug residues into aquatic ecosystems, posing severe risks to both environmental and human health [1]. Dyes such as indigo carmine, rhodamine B, and methyl orange are widely used in textiles, cosmetics, and food processing, yet their high stability and resistance to biodegradation make their removal from wastewater challenging [2,3]. Similarly, pharmaceutical compounds including paracetamol, bisphenol A, and pesticides are frequently detected in water bodies, where they exhibit persistence and potential toxicity [4]. The accumulation of these pollutants necessitates the development of advanced and sustainable remediation strategies.

Among various approaches, photocatalysis has emerged as a green, cost-effective, and efficient technology for the degradation of organic contaminants [5]. Semiconductor-based photocatalysts, particularly TiO? and ZnO, are extensively studied due to their ability to absorb photons, generate electron–hole pairs, and produce reactive oxygen species (ROS) such as hydroxyl radicals and superoxide anions, which mineralize pollutants into harmless byproducts [6,7]. However, limitations such as the rapid recombination of photo-generated charges and restricted visible-light absorption significantly reduce their photocatalytic efficiency [8,9].

To overcome these challenges, the incorporation of carbon-based supports such as reduced graphene oxide (rGO), carbon nanotubes (CNTs), and activated carbon (AC) has proven to be highly effective [10]. Carbon supports provide a high surface area, excellent adsorption properties, and superior electrical conductivity, which enhance charge separation, prolong exciton lifetime, and facilitate electron transfer at the photocatalyst interface [11]. For example, TiO?/CNT and ZnO/graphene composites have shown enhanced degradation of dyes like methylene blue and methyl orange due to suppressed electron–hole recombination and efficient light harvesting [12,13]. Activated carbon-supported TiO? and ZnO photocatalysts further contribute through strong adsorption of pollutants and ease of separation, making them highly suitable for large-scale applications [14].In addition, ferrite–carbon composites and magnetic graphene-based materials enable magnetic recovery, improving reusability and environmental sustainability [15,16].

Microwave-assisted synthesis and activation methods have further improved the performance of carbon-supported photocatalysts by tailoring nanostructures, enhancing light absorption, and generating localized “hot spots” that accelerate degradation kinetics [17]. Such strategies have been successfully applied for the rapid degradation of dyes, pharmaceutical residues, and other hazardous organics, offering high mineralization efficiency and short reaction times [18].

Overall, carbon-supported photocatalytic systems demonstrate great potential for wastewater treatment due to their synergistic effects of adsorption and photocatalysis, high degradation efficiency toward dyes, drugs, and persistent pollutants, and excellent reusability. This study focuses on the design and evaluation of carbon-supported nanomaterials as advanced photocatalysts for environmental remediation, with particular emphasis on their role in the degradation of organic dyes and pharmaceutical pollutants under visible light irradiation.

Photocatalytic degradation of Dyes , Drugs and Organic pollutants:

2. Photocatalytic degradation of Dyes :

Photocatalytic degradation of dyes is an advanced oxidation process that utilizes light-activated catalysts to break down complex dye molecules into simpler, non-toxic compounds. This method is highly effective for removing persistent and hazardous dyes from wastewater, offering an eco-friendly alternative to conventional treatment methods.

2.1: Mechanism of Degradation:

Photocatalyst + hν → e_CB⁻ + h_VB⁺

O₂ + e^- → ⋅O₂^−?

h⁺ + H2O → ⋅OH + H⁺

Dye + ⋅OH/⋅O2− → intermediates → CO₂ + H₂O + inorganic ions

2.2: Malachite Green (MG):

Malachite Green (MG) is a synthetic dye widely used in textile and dye industries due to its low cost and strong coloring ability, but it is highly toxic, carcinogenic, and banned in many countries. Direct discharge of MG-contaminated water causes severe environmental imbalance, health hazards to humans (liver, kidney, and skin damage), and reduced agricultural productivity. Traditional treatment methods such as adsorption, membrane filtration, electrocoagulation, ozonation, and biological treatments are often inefficient, costly, or generate toxic by-products. Photocatalytic degradation using semiconducting nanoparticles has emerged as an effective, eco-friendly solution, as it can completely mineralize MG into harmless products (CO? and H?O) under light irradiation without leaving residues. The process efficiency depends on factors like catalyst dosage, pH, dye concentration, irradiation time, and light source. Metal oxide nanoparticles such as TiO?, ZnO, CuO, Bi?O?, SnO?, CeO?, and Fe?O?, with tunable band gaps and morphologies (nanoparticles, nanotubes, nanosheets, etc.), have shown excellent photocatalytic performance under UV and visible light. These materials are low-cost, less toxic, reusable, and capable of degrading MG efficiently, making them promising candidates for wastewater treatment.

Table: 1 Malachite green dye degradation by various metal oxide nanoparticles, experimental condition, and its degradation efficiency:

Methylene Blue (MB) is a heterocyclic aromatic dye belonging to the thiazine class, widely used in textile, paper, and biological staining industries. It is highly soluble in water and exhibits strong absorption around 664 nm, giving it a deep blue color. Despite its industrial importance, MB is toxic, persistent, and non-biodegradable, leading to serious environmental hazards such as bioaccumulation and oxygen depletion in aquatic ecosystems. Therefore, the development of efficient photocatalytic methods using carbon-supported nanomaterials has gained attention to degrade MB into harmless end-products like CO? and H?O under visible or solar light.

Table:2 Methylene Blue dye degradation by various metal oxide nanoparticles, experimental condition, and its degradation efficiency:

Rhodamine B (RhB) is a xanthene-based cationic dye widely used in textile, paper, cosmetic, and biological staining industries. It exhibits intense fluorescence and high water solubility, with a maximum absorption around 554–556 nm. However, RhB is toxic, resistant to biodegradation, and has carcinogenic and mutagenic potential, making it a serious pollutant in aquatic environments. Due to its stability and environmental persistence, the removal of RhB from wastewater has become a critical challenge, and photocatalysis using carbon-supported nanocomposites has emerged as an efficient and sustainable method to degrade RhB into harmless by-products.

Table :3 Rhodamine B dye degradation by various metal oxide nanoparticles, experimental condition, and its degradation efficiency:

2.5 : Crystal violet dye:

Crystal Violet (CV), also known as Gentian Violet, is a synthetic cationic triphenylmethane dye extensively used in textile industries, paper printing, and as a biological stain. It exhibits strong absorption around 585–590 nm, giving a deep violet color. However, CV is highly toxic, mutagenic, and resistant to biodegradation, causing severe environmental risks when discharged into water bodies. Its persistence and carcinogenic nature make CV a priority pollutant, and thus the development of sustainable methods for its removal is essential. Among various approaches, photocatalysis using carbon-supported nanomaterials offers an effective, eco-friendly solution for degrading CV into harmless by-products under UV, visible, or solar irradiation.

Table : 4 Crystal Violet dye degradation by various metal oxide nanoparticles, experimental condition, and its degradation efficiency:

Congo Red (CR) is a benzidine-based anionic diazo dye widely used in textile, paper, leather, and printing industries. It exhibits high solubility in water and strong red coloration due to its extended conjugated azo bonds, with absorption maxima around 495–500 nm. Despite its industrial utility, Congo Red is known for its toxicity, carcinogenicity, and resistance to biodegradation, posing severe ecological and health risks when discharged into wastewater. Its molecular stability and complex aromatic structure make it challenging to remove by conventional treatment methods. Therefore, advanced treatment strategies such as photocatalysis using carbon-supported nanomaterials are increasingly investigated to achieve efficient and sustainable degradation of CR.

The photocatalytic efficiency of Congo Red degradation was strongly influenced by nanoparticle size and the role of carbon supports. In Fe–TiO?/activated carbon nanocomposites, TiO? crystals of ~15–25 nm were well-dispersed on porous carbon, as confirmed by XRD and TEM, which enhanced adsorption and reduced charge recombination. Radiation-synthesized SrO/AC showed quasi-spherical SrO nanoparticles of 20–30 nm anchored on activated carbon, with FTIR and UV–vis analyses confirming strong interaction between the phases, leading to ~90% degradation. Carbon dots (<10 nm), characterized by TEM, FTIR, and photoluminescence studies, provided abundant surface functional groups and excellent electron transfer, achieving up to 96% CR removal. Overall, characterization results highlight that smaller nanoparticles, high surface area, and carbon supports synergistically boost photocatalytic activity.

Table :5 Congo Red dye degradation by various metal oxide nanoparticles, experimental condition, and its degradation efficiency :

Photocatalytic degradation of drugs is an efficient approach to eliminate pharmaceutical residues that persist in the environment and resist conventional treatments. Using light-driven catalysts, drug molecules are oxidized into harmless end products such as CO? and H?O, minimizing their ecological and health impacts.

3.1 : Ibuprofen:

Ibuprofen, a widely used nonsteroidal anti-inflammatory drug (NSAID), is one of the most frequently detected pharmaceutical contaminants in aquatic environments due to its extensive consumption and poor biodegradability. Its persistence raises serious environmental and health concerns, as it has been associated with toxicity toward aquatic organisms, endocrine disruption, and bioaccumulation. Kinetic studies of ibuprofen degradation reveal that its removal often follows pseudo-first-order reaction kinetics under photocatalytic processes. Ozonation and catalytic ozonation have been tested as efficient advanced oxidation methods, showing improved mineralization compared to conventional treatments. To enhance its removal, researchers have developed carbon-supported nanomaterials such as TiO?/activated carbon, Nb?O?/MWCNT, and plasmonic Au–Ag/C?N? composites, which provide large surface area, strong adsorption, and enhanced electron transfer. Characterization techniques such as SEM, TEM, XRD, BET, and UV–Vis spectroscopy confirm the structural and surface properties of these materials, ensuring high photocatalytic performance and effective ibuprofen degradation.

Table: 6 Ibuprofen drug degradation by various metal oxide nanoparticles, experimental condition, and its degradation efficiency:

Tetracycline is a broad-spectrum antibiotic extensively used in human and veterinary medicine, and is among the most frequently detected pharmaceutical pollutants in wastewater due to its incomplete metabolism and widespread use. Its persistence in the environment contributes to antibiotic resistance, ecological imbalance, and potential toxicity to aquatic organisms, including disruption of microbial communities. Adverse effects of tetracycline exposure include hepatotoxicity, gastrointestinal disturbance, and possible endocrine disruption. To monitor and optimize degradation, various characterization techniques such as X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM/SEM), Brunauer–Emmett–Teller (BET) surface analysis, Fourier-transform infrared spectroscopy (FTIR), and UV–Vis spectroscopy are employed, confirming the structural, surface, and optical properties of carbon-supported nanocomposites for efficient photocatalytic degradation.

Table: 7 Tetracycline drug degradation by various metal oxide nanoparticles, experimental condition, and its degradation efficiency.

3.3: Chloramphenicol :

Chloramphenicol is a broad-spectrum antibiotic widely used for bacterial infections but is considered a high-risk contaminant in the environment due to its persistence and potential to induce antibiotic resistance. Residues of chloramphenicol in aquatic systems are toxic to aquatic organisms and can cause serious health concerns in humans, including bone marrow suppression, aplastic anemia, and genotoxic effects. Its recalcitrant nature requires advanced treatment strategies such as photocatalysis and adsorption using carbon-supported nanocomposites. Characterization techniques such as X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM), Fourier-transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) surface analysis, Raman spectroscopy, and UV–Vis spectrophotometry are commonly employed to confirm morphology, surface area, crystallinity, and optical properties of these nanomaterials, ensuring their suitability for efficient degradation of chloramphenicol.

Table:8 Chloramphenicol drug degradation by various metal oxide nanoparticles, experimental condition, and its degradation efficiency:

3.4: Atenolol :

Atenolol is a widely prescribed β?-selective adrenergic receptor blocker used for the treatment of hypertension, angina pectoris, and cardiac arrhythmias. Due to its high consumption and poor biodegradability, atenolol has become one of the most frequently detected pharmaceutical contaminants in wastewater and surface waters. Its persistence poses environmental risks, including toxicity to aquatic organisms, interference with microbial metabolism, and potential bioaccumulation. Studies show that atenolol exposure can cause oxidative stress and disrupt aquatic ecosystems. To address this issue, advanced oxidation processes such as photocatalysis using carbon-supported nanomaterials have been investigated. Carbon materials such as graphene, activated carbon, and carbon nanotubes provide high surface area, enhanced electron transport, and adsorption sites that improve photocatalytic efficiency when coupled with TiO? or other semiconductors. Characterization of these composites typically involves X-ray diffraction (XRD) to confirm crystallinity, scanning and transmission electron microscopy (SEM/TEM) for morphology, Brunauer–Emmett–Teller (BET) surface analysis for porosity, Fourier-transform infrared spectroscopy (FTIR) for surface functional groups, and UV–Vis spectroscopy for optical activity. These techniques ensure the correlation between structural properties and photocatalytic performance in atenolol degradation.

Table : 9 Atenolol drug degradation by various metal oxide nanoparticles, experimental condition, and its degradation efficiency :

Photocatalytic degradation of organic pollutants is a sustainable treatment method that employs light-activated catalysts to decompose harmful organic compounds. This process effectively converts toxic and persistent pollutants into environmentally benign substances, helping to reduce water and soil contamination.

4.1: Pesticides:

Pesticides are widely applied in agriculture to control pests and improve crop yields, but their excessive and uncontrolled use has resulted in persistent contamination of soil and aquatic ecosystems. Many pesticides are recalcitrant, non-biodegradable, and toxic, leading to bioaccumulation, endocrine disruption, genotoxicity, and ecological imbalance. Atrazine, chlorpyrifos, and organophosphates are commonly detected in water sources and are associated with risks to aquatic organisms and human health. Traditional wastewater treatments are often inefficient in removing such pollutants. To overcome this, carbon-supported metal oxide nanocomposites (graphene oxide, activated carbon, carbon nitride, etc.) have been developed for photocatalytic degradation. Carbon provides a large surface area, excellent adsorption capacity, and enhanced electron transfer, which minimizes recombination of photogenerated electron–hole pairs. Characterization techniques such as XRD (crystallinity), SEM/TEM (morphology), BET (surface area/porosity), FTIR (functional groups), Raman, and UV–Vis (optical properties) are commonly employed to confirm structural and surface properties, ensuring high performance in pesticide degradation.

Table : 10 Pesticide degradation by various metal oxide nanoparticles, experimental condition, and its degradation:

 Parabens are synthetic esters of p-hydroxybenzoic acid widely used as preservatives in cosmetics, pharmaceuticals, and personal care products because of their low cost, antimicrobial activity, and chemical stability. Common examples include methylparaben, ethylparaben, and propylparaben. However, their frequent detection in water bodies has raised environmental and health concerns, as parabens exhibit endocrine-disrupting activity, potential carcinogenicity, and aquatic toxicity. They mainly originate from cosmetic industry effluents and domestic wastewater. Characterization of photocatalysts used for paraben degradation typically involves XRD (crystal structure), SEM/TEM (morphology), BET (surface area), FTIR (functional groups), and UV–Vis spectroscopy (optical properties), confirming structural features for efficient photocatalytic performance.

Table:11 Paraben degradation by various metal oxide nanoparticles, experimental condition, and its degradation:

4.3 : Polycyclic Aromatic Hydrocarbons (PAHs) :

Polycyclic aromatic hydrocarbons (PAHs) are a large class of organic pollutants consisting of fused aromatic rings that are produced mainly by incomplete combustion of fossil fuels, biomass, and industrial processes. They are widely detected in air, water, and sediments due to their hydrophobic and persistent nature. PAHs such as naphthalene, phenanthrene, pyrene, and benzo[a]pyrene are toxic, mutagenic, and carcinogenic, posing serious threats to ecosystems and human health through bioaccumulation and long-term exposure. Conventional treatment methods are often inefficient because of their chemical stability and low solubility. Photocatalytic degradation has emerged as a promising strategy for PAH removal, where light-excited semiconductors generate reactive oxygen species (ROS) that mineralize PAHs into less harmful products. Carbon-supported nanoparticles (e.g., TiO?-graphene, biochar/g-C?N? composites) are particularly attractive due to their high adsorption capacity, enhanced charge separation, and extended visible-light response. Characterization of such composites typically involves XRD (crystalline phases), SEM/TEM (morphology), BET (surface area), FTIR/XPS (surface chemistry), and UV–Vis DRS (band gap), which together explain their improved photocatalytic activity.

Table 12: PAHs degradation by various metal oxide nanoparticles, experimental condition, and its degradation: