Sunlight-driven degradation of chlorpyrifos and imidacloprid using TiO₂/PHEMA nanocomposite: Synthesis, characterization, and photocatalytic performance

2.1. Materials

Titanium(IV) isopropoxide (Ti[OCH(CH₃)₂]₄, 99.99%), 2-hydroxyethyl methacrylate (HEMA) (CH₂=C(CH₃)COOCH₂CH₂OH, 99%), ammonium persulfate ((NH₄)₂S₂O₈, 98%), isopropyl alcohol ((CH₃)₂CHOH, ≥99.5%), glacial acetic acid (CH₃CO₂H, 99.7%), and hydrochloric acid (HCl, 37%) were purchased from Sigma-Aldrich and used as received without further purification. All solvents were of analytical grade. CPF (C₉H₁₁Cl₃NO₃PS, ≥98%) and IMD (C₉H₁₀ClN₅O₂, analytical standard, ≥98%) were obtained from Merck and used as model pollutants for photocatalytic degradation studies. All experiments involving CPF, IMD, and solvents were conducted in accordance with institutional safety protocols. Pesticide residues and solvent wastes were collected in designated containers and disposed of through the university’s hazardous waste management system.

2.2. Synthesis of TiO₂ NPs

TiO₂ NPs were synthesized via a modified solvothermal route adapted from established protocols (Ramakrishnan et al., 2020). In a typical preparation, 0.08 mol of Ti[OCH(CH₃)₂]₄ was dissolved in 100 mL of 1 M isopropanol and stirred on a hot plate at 70°C for 12 min to obtain a homogeneous solution. Subsequently, 12 mL of glacial acetic acid was introduced dropwise under continuous stirring, and the reaction mixture was maintained at the same temperature for an additional 3 h to promote controlled hydrolysis and condensation of the titanium precursor. The resulting sol was transferred into a 400 mL Teflon-lined stainless-steel autoclave and subjected to solvothermal treatment at 170°C for 7 h. After cooling to room temperature, the precipitate was collected by centrifugation, repeatedly washed with distilled water and ethanol to remove unreacted species and residual organics, and then dried at 60°C for 7 h. Finally, the dried powder was annealed at 450°C for 2 h in air to enhance crystallinity and phase stability of the TiO₂ NPs.

2.3. Synthesis of TiO₂/PHEMA NC

TiO₂/PHEMA NC was synthesized through a one-pot in situ radical polymerization method adapted from reported procedures (Erol et al., 2022). In a typical preparation, 100 mg of TiO₂ NPs were dispersed in 10 mL of 1.0 M hydrochloric acid containing 0.2 mL of 2-hydroxyethyl methacrylate (HEMA) monomer. The dispersion was sonicated for 25 min to achieve uniform distribution of TiO₂ within the monomeric solution. Subsequently, 5 mL of 1.0 M HCl solution containing 0.5 g of ammonium persulfate (APS) as a free-radical initiator (molar ratio 1:1 with respect to HEMA) was introduced dropwise under constant stirring. The mixture was maintained at 55°C with vigorous agitation for 4 h, allowing complete polymerization and simultaneous incorporation of TiO₂ into the poly(2-hydroxyethyl methacrylate) matrix. After the reaction, the obtained TiO₂/PHEMA NC was separated by filtration, thoroughly washed with ethanol and deionized water to remove unreacted monomers and initiator residues, and dried at 55°C for 12 h. The dried material was then finely ground using an agate mortar to obtain a homogeneous powder for subsequent characterization. For comparison, pure PHEMA was synthesized following the same protocol in the absence of TiO₂ NPs.

2.4. Characterization

Various analytical techniques were employed to investigate the physicochemical properties of the synthesized TiO₂ NPs and TiO₂/PHEMA NC. FTIR spectroscopy was performed using a Bruker Tensor II spectrometer (Bruker Corporation, Germany) to identify functional groups and confirm the successful polymerization of HEMA and its interaction with TiO₂. The crystalline structure and phase composition were analyzed by XRD using a PANalytical X’Pert PRO diffractometer (Malvern PANalytical, Netherlands) with CuKα radiation (λ = 0.15418 nm) (Salmi et al., 2024).

The average crystallite size (D) was calculated using the Debye–Scherrer equation, where K is the shape factor (0.9), β is the full width at half maximum (FWHM), and θ is the bragg angle. Morphological features and particle dispersion were examined by TEM using a JEOL JEM-2100 microscope (JEOL Ltd., Japan). Thermal stability and decomposition behavior were assessed via TGA using a Q500 analyzer (TA Instruments, USA) under a nitrogen atmosphere. UV–visible spectroscopy in the 200–800 nm range was carried out using a Shimadzu UV-2600 spectrophotometer (Shimadzu Corporation, Japan) to determine optical absorption and estimate the band gap energy.

2.5. Photocatalytic activity

The photocatalytic activity of the synthesized TiO₂ NPs and TiO₂/PHEMA NC was evaluated for the degradation of CPF and IMD under natural sunlight irradiation. Experiments were conducted in April 2025 in Jeddah, Saudi Arabia (21.49°N, 39.19°E) under clear-sky conditions, with an average solar irradiance of 650–780 W m⁻² (measured by a calibrated pyranometer, Kipp & Zonen) between 10:00 AM and 2:00 PM, and an ambient temperature ranging from 28–32°C. The spectral distribution was referenced against ASTM G-173 standard solar spectra, and photon flux was verified by potassium ferrioxalate actinometry, yielding ∼4.2 × 10⁻⁵ mol photons m⁻² s⁻¹ in the 300–400 nm region. Stock pesticide solutions of CPF and IMD were freshly prepared at a concentration of 5 mg L⁻¹ in a total volume of 200 mL. Aliquots were withdrawn from these stock solutions and used for each photocatalytic run. In a typical experiment, 5 mg of photocatalyst was dispersed in 10 mL of pesticide solution (5 mg L⁻¹, pH 10) and irradiated with sunlight for 10-90 min. Before light exposure, all suspensions were magnetically stirred in the dark for 20 min to establish adsorption–desorption equilibrium. Control experiments confirmed that no significant degradation occurred in the dark, indicating that pesticide removal was solely driven by photocatalysis.

The influence of operational parameters was systematically studied. The effect of pH was examined over the range 4–10 by adjusting the solution with 0.1 M HCl or NaOH, while maintaining an initial concentration of 5 mg L⁻¹, a catalyst dosage of 5 mg, and 90 min of irradiation. The role of initial pesticide concentration was assessed by varying levels between 5 and 15 mg L⁻¹ at pH 7 with 5 mg catalyst and 90 min irradiation. Catalyst loading was investigated by dispersing 20–50 mg in 10 mL of pesticide solution (5 mg L⁻², pH 10) and irradiating for 90 min.

At predetermined intervals, aliquots were collected, centrifuged to remove catalyst particles, and analyzed using a UV–Vis spectrophotometer at λ_max = 245 nm for CPF and 270 nm for IMD. The photocatalytic degradation efficiency (%) was calculated according to Eq. (2) (Salmi et al., 2023):

Where C₀ ​and C_t represent the initial concentration and the concentration at irradiation time t, respectively.

2.6. Reusability experiment

The reusability of the TiO₂/PHEMA NC photocatalyst was evaluated through consecutive degradation cycles of CPF and IMD under natural sunlight irradiation. After each photocatalytic run, the catalyst was recovered by centrifugation, washed thoroughly with deionized water and ethanol to remove residual pollutants, and dried at 60°C for 6 h before being reused in the subsequent cycle. This procedure was repeated for five consecutive runs under identical experimental conditions (5 mg L⁻¹ pesticide solution, 5 mg catalyst dosage, pH 10, and 90 min irradiation time). The degradation efficiency was calculated at the end of each cycle to assess the photocatalyst’s stability and recyclability.

3.1. UV–Vis spectroscopy and band gap analysis

The optical absorption spectra of TiO₂ NPs and the TiO₂/PHEMA NC display well-defined edges in the near-UV region, characteristic of intrinsic band-to-band transitions in TiO₂. For pristine NPs, the absorption onset occurs around 348 nm, whereas incorporation of PHEMA results in a slight bathochromic shift to 358 nm (Fig. 1a, Table 1). This redshift indicates that the polymer matrix modifies the local electronic environment of TiO₂, likely through interfacial interactions between hydroxyl or carbonyl groups of PHEMA and surface Ti sites. Such interactions can introduce shallow defect states, promote interfacial charge transfer, and reduce agglomeration, thereby extending the absorption profile marginally into the visible region (Rahimli and Musayeva 2025). The optical band gap energy (Eg) was estimated by plotting (αhν)² versus photon energy (Tauc plot) and extrapolating the linear region (Johannes et al., 2020). Tauc plot analysis corroborates this observation, revealing a bandgap energy of ∼2.65 eV for the TiO₂/PHEMA NC, which is significantly lower than that of pristine TiO₂ NPs (Fig. 1b). This narrowing of the bandgap can be attributed to defect-mediated electronic states and enhanced polymer–semiconductor coupling, which reduce the excitation threshold for electron–hole generation. In comparison, bulk anatase TiO₂ typically exhibits a bandgap of ∼3.2 eV, and sol–gel or hydrothermally derived NPs generally fall within the range of 3.1–3.3 eV (Shejale et al., 2021). The observed reduction, therefore highlights the effectiveness of PHEMA incorporation in tailoring the optical properties of TiO₂, enabling improved utilization of solar light for photocatalytic processes.

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Fig. 1.

UV–Vis absorption spectra of bandgap energy of (a) TiO₂ NPs and (b) TiO₂/PHEMA NC.

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3.2. FTIR analysis

The FTIR spectra of PHEMA, TiO₂ NPs, and TiO₂/PHEMA NC confirm the structural features of each component and their effective integration in the NC (Fig. 2). For PHEMA, the broad absorption band at 3444 cm⁻¹ corresponds to O–H stretching vibrations, while the peak at 2924 cm⁻¹ is due to aliphatic C–H stretching (Makreski et al., 2018; Boral et al., 2021). The band at 1614 cm⁻¹ is attributed to skeletal vibrations of C=C bonds, likely originating from residual vinyl groups or the polymer backbone (Nahas et al., 2025). Additional peaks at 1345 cm⁻¹ and 1079 cm⁻¹ are assigned to C–H bending and C–O–C stretching of ester groups, respectively (Ma et al., 2016, Toledo et al., 2018, Zhang and Sun 2020), whereas the band at 623 cm⁻¹ corresponds to C–H out-of-plane bending. In the spectrum of TiO₂ NPs, the broad signal near 3444 cm⁻¹ indicates surface hydroxyl groups and adsorbed water, while the peak at 1459 cm⁻¹ corresponds to C–H bending vibrations (Gopanna et al., 2019). The characteristic Ti–O–Ti stretching modes are observed at 623, 549, and 438 cm⁻¹, confirming the formation of TiO₂ (Moradi et al., 2021, Qutub et al., 2022). In the TiO₂/PHEMA NC spectrum, the coexistence of polymeric features (3444, 1614, 1079 cm⁻¹) alongside TiO₂ lattice vibrations (623, 549, 438 cm⁻¹) demonstrates successful incorporation of TiO₂ into the PHEMA matrix. The retention and slight shifts of these bands suggest interfacial interactions, such as hydrogen bonding between PHEMA functional groups and TiO₂ surface hydroxyls, confirming the formation of a stable hybrid NC.

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Fig. 2.

FT-IR spectra of PHEMA, TiO₂ NPs, and TiO₂/PHEMA NC.

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3.3. XRD analysis

The XRD analysis provides clear insight into the structural features of the prepared materials (Fig. 3). Neat PHEMA exhibits a broad diffraction peak at 2θ ≈ 13.82°, confirming its amorphous nature (Alamgir et al., 2021a). In contrast, TiO₂ NPs display sharp reflections at 2θ = 25.3°, 37.9°, 38.6°, 48.1°, 54.0°, 55.2°, 62.8°, 68.9°, and 75.2°, indexed to the (101), (004), (112), (200), (105), (211), (204), (116), and (215) planes of the anatase phase (JCPDS 01-073-1764), respectively. Additional peaks at 27.6°, 36.2°, 41.4°, 44.3°, 57.0°, 70.1°, and 76.9° correspond to the (110), (101), (111), (210), (220), (112), and (202) planes of the rutile phase, respectively (JCPDS 01-088-1172), confirming the coexistence of anatase and rutile polymorphs. The TiO₂/PHEMA NC retains these crystalline reflections alongside the amorphous halo of the polymer, though with reduced intensities, indicating effective encapsulation and uniform dispersion of TiO₂ crystallites within the PHEMA matrix. For crystallite size determination, the most intense anatase (101) reflection at 2θ = 25.3° was employed, using a shape factor (K) of 0.9 and β corrected for instrumental broadening. Crystallite size calculations using the Scherrer equation revealed an average size of ∼34 nm for pure TiO₂, which slightly decreased to ∼32.9 nm in the composite, suggesting that the polymer phase restricts crystal growth and suppresses agglomeration (Bokuniaeva and Vorokh 2019). Importantly, the coexistence of anatase and rutile phases is advantageous, as their heterojunctions promote efficient charge separation and electron transfer, enhancing photocatalytic efficiency. Simultaneously, the amorphous PHEMA network enhances NP stability and homogeneity, resulting in a structurally robust hybrid material with synergistic properties.

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Fig. 3.

XRD pattern of PHEMA, TiO₂ NPs and TiO₂/PHEMA NC.

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3.4. TGA analysis

TGA evaluated the thermal stability of TiO₂ NPs and TiO₂/PHEMA NC in the range of 25–800°C (Fig. 4). Pure TiO₂ NPs exhibited excellent stability, showing only minor weight losses of 3.3% between 50–200°C, attributed to the evaporation of physically adsorbed moisture and surface hydroxyl groups (Lothenbach et al., 2016), and an additional 3.9% loss up to 800°C, likely due to the gradual removal of residual organic species or lattice oxygen release. In contrast, the TiO₂/PHEMA NC demonstrated a more pronounced multi-step degradation profile. An initial weight loss of 8.5% in the 50–160°C range corresponds to the removal of physically bound water and low-molecular-weight volatiles entrapped in the polymer network. The significant degradation, amounting to ∼33.9% between 200–800°C, is attributed to the thermal decomposition of the PHEMA matrix, involving chain scission, depolymerization, and oxidative degradation of the organic backbone (Carboué et al., 2022). Compared with neat TiO₂, the higher weight loss of the NC reflects the presence of the organic polymer fraction, while the residual weight at 800°C confirms the stable inorganic TiO₂ framework. These results highlight the superior thermal stability of TiO₂ NPs and the typical polymer-degradation behavior of PHEMA, and confirm the successful incorporation of TiO₂ into the polymer matrix.

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Fig. 4.

TGA analysis of TiO₂ NPs and TiO₂/PHEMA NC.

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3.5. TEM analysis

The TEM analysis provides detailed insight into the morphology and size distribution of the synthesized materials. For the pristine TiO₂ NPs (Fig. 5a), the images reveal quasi-spherical particles with a relatively uniform distribution and an average size of ∼14.2 nm, forming loosely aggregated clusters. In contrast, the TiO₂/PHEMA NC (Fig. 5b) exhibits NPs embedded within a lower-contrast amorphous matrix corresponding to the PHEMA phase. The incorporation of the polymer results in a slight reduction of the mean particle size to ∼13.5 nm, along with a more diffuse morphology and diminished interparticle agglomeration, highlighting the role of PHEMA in restricting particle growth and stabilizing dispersion. The smaller particle size in the composite can be attributed to the polymer chains acting as a confining medium, limiting crystal coalescence during synthesis and subsequent thermal treatment (Tan et al., 2016, Mohammed et al., 2025). It should also be noted that while TEM provides direct visualization of particle diameters, XRD analysis reflects the coherent scattering domain size, which may differ due to microstrain, lattice defects, or instrumental factors. Nonetheless, the average particle sizes obtained from TEM align closely with the Scherrer-derived crystallite sizes (∼34 nm for TiO₂ and ∼32.9 nm for TiO₂/PHEMA NC), thereby confirming the nanoscale dimensions of the materials and supporting the conclusion that the polymer matrix effectively moderates crystallite growth and maintains the structural integrity of the TiO₂ phase.

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Fig. 5.

TEM micrographs of (a) TiO₂ NPs and (b) TiO₂/PHEMA NC.

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3.6. Degradation of CPF and IMD

The time-dependent photocatalytic degradation profiles of CPF and IMD (Figs. 6a-b) demonstrate a clear correlation between irradiation duration and removal efficiency. In both cases, a steady decline in the characteristic absorption peaks with prolonged exposure confirms the progressive mineralization of the pesticides. UV–visible spectrophotometric analysis identified the maximum absorption wavelength (λ_max) of CPF at 289 nm and IMD at 271 nm, which were used to monitor their degradation (Akbari Shorgoli and Shokri 2017, Adanan et al., 2025). For TiO₂ NPs, degradation followed a gradual pathway, reaching 81% for CPF and 83.5% for IMD after 90 min. In contrast, the TiO₂/PHEMA NC achieved markedly higher efficiencies, 95.6% for CPF and 97.3% for IMD, within the same irradiation period. The sharper decline observed during the initial 40–50 min reflects rapid generation of reactive oxygen species and effective electron–hole separation facilitated by the composite structure. Kinetic analysis was performed using the pseudo-first-order model expressed as (Khairnar and Shrivastava 2019):

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Fig. 6.

UV–Vis spectra and photocatalytic degradation of (a) CPF and (b) IMD using TiO₂ NPs and TiO₂/PHEMA NC; First-order kinetic plot of ln⁡(A0/At ) versus time of (c) TiO₂ NPs, and (d) TiO₂/PHEMA NC.

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Where C₀ and Cₜ represent the initial and residual concentrations of the pesticide at irradiation time t, and k is the apparent rate constant.

Kinetic analysis further confirmed the enhanced photocatalytic performance of the TiO₂/PHEMA NC. The apparent rate constants for CPF (0.0336 min⁻¹) and IMD (0.0377 min⁻¹) were nearly double those of pristine TiO₂ (0.0190 and 0.0194 min⁻¹, respectively), demonstrating significantly accelerated degradation dynamics under sunlight (Fig. 6c and d, Table 2). The consistently higher k values of the NC indicate improved charge-separation efficiency and stronger responsiveness to solar irradiation compared with unmodified TiO₂. The enhanced activity of the NC can be attributed to several synergistic effects: the PHEMA matrix improves NP dispersion and suppresses agglomeration, increases photon absorption through a slight redshift in the absorption edge, and establishes interfacial charge-transfer pathways that minimize electron–hole recombination (Tiwari and Dhoble 2016). These effects were confirmed by characterization, where TEM revealed improved dispersion and reduced aggregation, UV–Vis analysis demonstrated an extended absorption edge; FTIR indicated interfacial interactions between PHEMA functional groups and TiO₂ surface sites, and XRD showed restricted crystallite growth. These combined structural and electronic modifications imparted by the polymer support result in enhanced photon utilization, prolonged carrier lifetimes, and a higher density of active surface sites, thereby enabling the TiO₂/PHEMA NC to achieve significantly greater pesticide mineralization efficiency under identical irradiation conditions. A comparative evaluation (Table 3) further confirms that the TiO₂/PHEMA NC achieves superior degradation efficiency under sunlight, outperforming pristine TiO₂, and demonstrating strong potential as an effective photocatalyst for pesticide removal.

3.7. Effect of various parameters on photocatalytic activity

3.7.1. Effect of pH

The effect of pH on the photocatalytic performance of the TiO₂/PHEMA NC toward CPF and IMD (Fig. 7). Both pesticides displayed enhanced degradation efficiencies as the pH increased from acidic to alkaline conditions. At pH 4, degradation was relatively low (58% for CPF and 61.3% for IMD) due to limited hydroxyl radical generation and weaker adsorption on the catalyst surface. Efficiency increased steadily with alkalinity, reaching 89.1% (CPF) and 92.1% (IMD) at pH 8 and peaking at 96.7% and 99.1%, respectively, at pH 10. The improvement is attributed to the higher availability of OH⁻ ions, which facilitate •OH radical formation and accelerate photocatalytic oxidation (Nekooie et al., 2021). A slight decline beyond pH 10 (95.1% for CPF and 94.0% for IMD at pH 12) suggests that excess OH⁻ may act as radical scavengers, reducing activity. Notably, IMD consistently degraded more efficiently than CPF across the entire pH range, indicating greater susceptibility to photocatalytic attack. These findings confirm that alkaline conditions, particularly pH 10, are optimal for maximizing the photocatalytic efficiency of the TiO₂/PHEMA NC.

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Fig. 7.

Effect of pH on the photodegradation efficiency of CPF and IMD using TiO₂/PHEMA NC.

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3.7.2. Effect of CPF and IMD initial concentration

The influence of initial pesticide concentration on the photocatalytic efficiency of the TiO₂/PHEMA NC (Fig. 8). At 5 mg L⁻¹, degradation reached 96.7% for CPF and 98.1% for IMD, demonstrating the high activity of the NC under dilute conditions. Increasing the concentration to 10 and 15 mg L⁻¹ led to progressive declines in efficiency, reaching 86% and 75.7% for CPF and 91% and 80.7% for IMD, respectively. This decrease is attributed to the saturation of active surface sites and reduced photon penetration at higher pollutant loads, which limit the generation of reactive oxygen species (Farahbakhsh et al., 2022). The consistently higher degradation of IMD compared to CPF suggests a greater susceptibility of IMD to photocatalytic oxidation, likely due to its molecular structure. These results confirm that the NC is highly effective at low-to-moderate concentrations, but efficiency decreases at higher pollutant levels due to kinetic and optical constraints.

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Fig. 8.

Influence of initial concentration on CPF and IMD degradation by TiO₂/PHEMA NC.

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3.7.3. The effect of photocatalyst dose

The effect of catalyst dosage on the photocatalytic degradation of CPF and IMD using the TiO₂/PHEMA NC has been shown in Fig. 9. At a catalyst mass of 20 mg, degradation efficiencies were relatively low, with 72.7% for CPF and 75.7% for IMD, reflecting the limited number of available active sites for pollutant adsorption and radical generation. Increasing the mass to 30 and 40 mg significantly enhanced degradation, achieving 78.1% and 91.2% for CPF and 87.6% and 96.6% for IMD, respectively, due to the greater surface area and higher density of active sites, which facilitated more efficient light absorption and the formation of reactive oxygen species. The maximum efficiency was obtained at 50 mg, with 95.7% CPF and 98.1% IMD degradation, indicating that beyond this dosage, the catalyst provides sufficient active surface to ensure nearly complete removal of the pesticides. These results demonstrate that photocatalytic efficiency strongly depends on catalyst loading, with optimal performance achieved when the mass provides sufficient active sites without introducing significant light scattering or shielding effects.

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Fig. 9.

Effect of photocatalyst amount for degradation of CPF and IMD using TiO₂/PHEMA NC.

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3.8. Reusability results

The recycling performance of the TiO₂/PHEMA NC has been shown in Fig. 10a. The photocatalyst maintained high degradation efficiencies for both CPF and IMD over five successive runs, with only a marginal decline observed. In the fifth run of the first cycle, efficiency decreased for CPF from 95.68% to 92.02%, while IMD degradation declined from 97.36% to 93.01%. The slight reduction in activity may be attributed to partial surface fouling by intermediate products or minor catalyst loss during recovery steps. Nevertheless, the photocatalyst consistently retained more than 92% efficiency even after the fifth cycle, demonstrating excellent stability, structural robustness, and reusability. These results confirm that the TiO₂/PHEMA NC is a durable and reliable photocatalyst for the repeated degradation of a pesticide under solar irradiation. XRD analysis before and after five photocatalytic cycles (Fig. 10b) further supports this conclusion. The fresh TiO₂/PHEMA NC displayed reflections of both anatase and rutile phases. However, after repeated use, the anatase peaks remained dominant while the weaker rutile signals at 27.6° and 36.2° were no longer detected. This suggests a gradual suppression of the rutile contribution, possibly due to preferential surface modification or structural reorganization under irradiation (Adanan et al., 2025). Notably, the persistence of the anatase framework without new phases or amorphization demonstrates that the NC retains its essential crystalline integrity, which aligns with its sustained photocatalytic performance across multiple cycles.

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Fig. 10.

(a) Reusability of TiO₂/PHEMA NC for CPF and IMD degradation over five cycles. (b) XRD patterns before and after cycling.

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3.9. Mechanism of photocatalytic activity

The photocatalytic degradation of CPF and IMD using TiO₂ NPs and TiO₂/PHEMA NC under sunlight irradiation can be rationalized based on the fundamental semiconductor photocatalysis pathway, as schematically illustrated in Fig. 11. Upon exposure to solar photons with energy equal to or greater than the band gap of TiO₂ (3.2 eV for pristine TiO₂, reduced to ∼2.6 eV for TiO₂/PHEMA NC), electrons (e⁻) in the valence band (VB) are excited to the conduction band (CB), leaving behind positively charged holes (h⁺) (Eq. 4):

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Fig. 11.

Proposed photocatalytic degradation mechanism of CPF and IMD over TiO₂/PHEMA NC under sunlight irradiation.

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In the TiO₂/PHEMA NC, interfacial interactions between PHEMA functional groups and TiO₂ surface sites facilitate more efficient separation of these charge carriers, reducing recombination losses. The photoexcited electrons can migrate to the TiO₂ surface and react with dissolved molecular oxygen to form superoxide radicals ($O_2^{•-}$) (Eq. 5), which may undergo subsequent protonation and transformation into hydroperoxyl radicals (•HO₂) and eventually hydroxyl radicals (•OH) (Nekooie et al., 2021) (Eqs. 6-8):

Meanwhile, photogenerated holes (h⁺) in the VB can directly oxidize water molecules or surface hydroxyl groups to produce additional hydroxyl radicals (Eq. 9):

These radicals (•OH, •O₂⁻) are highly oxidative and non-selectively attack CPF and IMD molecules, initiating oxidative degradation via successive dechlorination, dealkylation, ring-opening, and eventual mineralization into CO₂, H₂O, and other innocuous species (Adanan et al., 2025).

The enhanced photocatalytic performance of the TiO₂/PHEMA NC arises from synergistic effects: (i) extended light absorption due to bandgap narrowing, (ii) efficient charge separation at the TiO₂–PHEMA interface via HOMO–LUMO alignment, and (iii) improved surface reactivity and dispersion, as evidenced by TEM, FTIR, and UV-Vis analyses.