Experimental and computational study of photocatalytic degradation of volatile organic compounds in bitumen using sulfur-doped phenol-rich bio-oils

Abstract

Asphalt pavements are a significant source of volatile organic compounds (VOCs) emissions under solar radiation, accelerated asphalt aging and urban air pollution. Effective mechanisms are essential to reduce the environmental and health impacts of road infrastructure. In this study, a sustainable bio-based modification strategy is presented using sulfur-doped phenol-rich bio-oils derived from wood pellets (WPn) to suppress VOCs release from asphalt. In this process, tetrameric radical sulfur () reacts with the WPn to generate -WPn intermediates that capture VOCs molecules through a C–S cross-coupling pathway, forming stable VOCs--WPn adducts. The mechanism was validated experimentally using GC–MS, FT–IR, and UV–Vis spectroscopy, and supported by TD–DFT computational analysis. The UV–Vis absorption spectral of has been red-shifted to nearly 400 nm which potentially enhanced the ability of these VOCs compounds to absorb light at wavelength higher than 200 nm, thereby favoring the direct photodegradation of VOCs compounds. Also, the calculated activation energy barriers for the and VOCs reaction pathways were found to range between − 5.62 and − 25.86 kcal/mol, confirming the thermodynamic feasibility and suppression potential of VOCs emissions. This work highlights a practical and environmentally friendly approach for the development of cleaner and more resilient urban infrastructure.

Introduction

The inherent requirement for high temperatures throughout asphalt’s lifecycle, encompassing production, transportation, construction, and maintenance, leads to significant emissions of asphalt fume that is recognized as a primary source of VOCs^1,2. The complex chemical composition of bitumen emissions, comprising thousands of distinct compounds, ultimately coalesces into particulates exhibiting diverse toxicological profiles, thereby posing demonstrable risks to both human health and atmospheric equilibrium^3,4.

Furthermore, exposure to ultraviolet (UV) radiation significantly increases the emission of VOCs from bitumen-surfaced areas. Research indicates that UV-induced VOC emissions from bitumen harm human health and air quality, accelerating the aging and degradation of the bitumen itself^5–7. When exposed to solar radiation, continuous emissions from bitumen surfaces happen at ambient temperatures, indicating that these emissions are not restricted to high-temperature production processes^8,9.

In related efforts, extensive research has focused on the durability of aged bitumen, particularly concerning its chemical and physical properties, as well as the reduction of VOCs emissions^10,11. Modifiers show promise in delaying bitumen aging throughout the pavement’s service life^12,13. Furthermore, the majority of these agents pose environmental concerns owing to their toxic nature.

The prior research suggests that bio-modifiers can effectively enhance UV aging resistance when incorporated into bitumen or applied as a spray sealant^14,15. A variety of renewable bio-modifiers, sourced from either animal or vegetal origins, can function as rejuvenators. These include waste wood^16,17,waste vegetable cooking oil^18,19, sawdust²⁰, swine manure²¹, algae²², and waste vegetable oil²³.

Among these, wood pellet oil (WP) is a bio-oil modifier that demonstrates excellent aging resistance based on softening point and viscosity aging indices when incorporated into asphalt mixtures. This results in reduced binder viscosity and stiffening after aging, leading to lower moisture damage, extended service life, and improved resistance to rutting and stripping^24,25.

Besides bio-modifiers, the use of elemental sulfur as a modifier in asphalt pavements dates back to the 1970s^26–28. The growing interest in adding sulfur as an additive in bitumen mainly comes from its availability as a low-cost byproduct of the oil and gas industries. Furthermore, the use of elemental sulfur in bitumen mixtures has gained attention because it leads to improved mechanical characteristics and enhanced durability in sulfur-extended bitumen compared to conventional bitumen. Understanding its role is further complicated by the fact that sulfur, a naturally occurring element in bitumen, constitutes approximately 1 to 7% of its composition and is influenced by the predominant wavelength of ultraviolet (UV) radiation. When elemental sulfur (S₈) is subjected to UV radiation, it undergoes thermal scission of the S–S bonds within the sulfur ring, leading to the formation of an unstable radical () characterized by a linear arrangement of four sulfur atoms capable of accepting up to six electrons^29,30. Notably, elemental sulfur remains stable under UV irradiation; hence, it is anticipated that sulfur present in bitumen exacerbates oxidative aging by generating an increased number of free radicals. UV light can cleave sulfur, resulting in the formation of sulfur radicals that can initiate additional free-radical chain reactions, including polysulfide chain abstraction and cross-coupling with hydrocarbons^31,32. This reactivity, among other factors, can contribute to the observation that sulfur can gradually migrate to the surface of bitumen, forming “sulfur blooms” over time^33,34. Elemental sulfur also reacts with bitumen compounds, particularly under conditions of high temperatures and high sulfur concentrations^35,36. Beyond these interactions, free radicals generated by the sulfur could photocatalytically decompose VOCs and this process offers a promising strategy for mitigating air pollution stemming from bituminous materials within the built environment^37,38.

In this study, phenol-rich bio-oils have been employed, derived from wood-based biomass, in engineering durable asphalt with a high capacity for VOCs retention. The efficacy of these bio-oils in delaying the oxidative aging of asphalt is well-documented^39,40. It is hypothesized that integrating phenol-rich bio-oils into sulfur-extended asphalt offers a dual benefit. This combination is posited to not only inhibit sulfur crystallization within the bulk material and scavenge oxidizing radicals, but also to facilitate the formation of a phenol-sulfur assembly. The inherent radical nature of this assembly will promote the adsorption of VOCs. Consequently, a synergistic effect from combining elemental sulfur and phenolic bio-oils within the asphalt mixture has been illustrated, leading to the effective sequestration of VOCs within bituminous composites.

Synthesis and comprehensive characterization of the VOCs––WPn complexes were undertaken to acquire profound insights into its reactivity and unique structural attributes. Mass spectrometry, FT–IR, UV–Vis spectroscopy, and TD-DFT calculations (including energetic properties and UV–Vis spectra) were used to analyzed and investigate the degradation reactions of VOCs. The outcomes indicated a notable red shift in the UV–Vis absorption spectrum; these spectral peaks were attributed to the reaction between -WPn and VOC compounds, which led to degradation of the VOCs. The experimental data closely matched the theoretical predictions, thereby validating the proposed structural model. These findings highlight the potential of -WPn incorporation to promote efficient VOC degradation within the bituminous matrix, offering a promising strategy for enhancing the bitumen’s sustainability and long-term performance.

Computational methods

The inherent resistance of VOCs to direct UV or solar light degradation stems from their minimal UV–Vis absorption, primarily observed at wavelengths below 200 nm⁴¹. Consequently, a possible way to VOCs degradation lies in increasing their UV–Vis absorption³¹. The investigation detailed in this section centers on the potential reactions of with WPn, and their subsequent reactions with four designated VOCs (benzoic acid, benzofuran, dibenzo-thiophene, and 3-pentyl-thiophene) constitute the focus of this section. WPn compounds demonstrate reaction via a C–S cross-coupling, enabling swift integration into VOCs. This particular C–S cross-coupling reaction confers high UV–Vis absorption upon the product, attributable to the facile photodegradation of upon exposure to UV radiation at a wavelength (λ) of 400 nm.

To gain a deeper understanding of how sulfur-doped phenol-rich bio-oils react with VOCs, all computational analyses were performed using Time-Dependent Density Functional Theory (TD-DFT) calculations in Gaussian 09 software⁴². These calculations used the UCAM-B3LYP functional⁴³, combined with the standard Pople basis set, 6-311G**. The geometries were optimized for both the ground and transition states; afterward, the nature of these stationary points was confirmed through harmonic vibrational frequency calculations at the same level. The main goal of TD-DFT calculations is to thoroughly map the potential energy surface of reactions involving with WPn, as well as their reactions with VOCs, with reaction energetics calculated in kcal·mol⁻¹ through computations at the UCAM–B3LYP/6-311G** level of theory.

The degradation reactions of VOCs have been characterized and monitored by analyzing UV–Vis spectrum, which were generated via TD-DFT, as incorporated into the Gaussian 09 software suite. Visualization of the resultant UV–Vis spectra for the VOCs compounds was performed using the Xmgrace program⁴⁴.

Material and measurements

All experimental investigations were performed using analytical-grade materials to maintain high standards of purity and reliability. In particular, syringol (≥ 98%, analytical grade) were obtained from Sigma–Aldrich (Germany) and used without further purification. Elemental sulfur (S₈, ≥ 99.5%) and VOCs (benzoic acid, benzofuran, dibenzo-thiophene, and 3-pentyl-thiophene) of analytical grade were purchased from Merck (Germany). All solvents were of analytical grade and employed as received.

Fourier-transform infrared (FTIR) spectra were recorded using a Shimadzu 8400 S spectrometer in the range of 4000–400 cm⁻¹, with samples prepared as potassium bromide (KBr) pellets. Ultraviolet–visible (UV–Vis) absorption spectra were measured on a Shimadzu UV-1650 spectrophotometer over the range of 200–800 nm. Mass spectrometric (MS) analyses were performed using an Agilent 5973 mass spectrometer under standard electron ionization (EI) conditions, unless otherwise specified.

For the synthesis of Benzoic acid–WP₃, a solution of 4-hydroxyphenylthiol and sulfur monochloride was prepared under continuous stirring, to which an aqueous solution of 4-mercaptobenzoic acid (1:1 molar ratio) was added dropwise at ambient temperature. After 5 min of additional stirring, pyridine (5 mL) was added, and the reaction mixture was stirred for another 2 h at room temperature. The resulting precipitate was isolated by vacuum filtration, washed twice with diethyl ether to remove residual impurities, and purified by recrystallization from a mixed solvent system of ethyl acetate and hexane.

The structure and purity of the obtained product were confirmed by FTIR, UV–Vis, and MS analyses. The characteristic absorption red shift (~ 200 nm) observed in UV–Vis spectroscopy after the C–S coupling reaction between WPn and VOCs confirmed the successful formation of the sulfur–phenolic hybrid structure.

Results and discussion

Computational results

The mechanistic pathways of these reactions were thoroughly investigated by employing a DFT-based model to determine ground state and transition structures. This computational approach utilized the UCAM-B3LYP method in conjunction with the 6–311G** basis set. Our primary investigation involved assessing the reactivity of with three bio-oils derived from wood pellets (WP). In this research, three WPn include syringol (C₈H₁₀O₃,(featuring a pair of electron-donating methoxy OCH₃ and catechol (C₆H₆O₂), which contains two electron-donating groups, OH and phenol (C₆H₅OH), for clarity, these bio-oil are labeled as WP1, WP2, and WP3, respectively (Fig. 1).

Fig. 1.

Optimized WPn structures at UCAM-B3LYP/6–311G** level of theory.

Upon the approach of the to WPn, the unpaired electron of reacts with a carbon atom on the phenol ring of WPn. This reaction result in the formation of a covalent C–S cross-coupling between the sulfur atom of and a carbon atom of WPn, thereby generating and leads to a more stable radical(Fig. 2). Also, Fig. 3 illustrates the final optimized geometries of the investigated complexes (), as determined by DFT calculations, which correspond to the most energetically stable configurations following full geometry optimization.

Fig. 2.

Optimized structures at UCAM-B3LYP/6–311G** level of theory.

Fig. 3.

Optimized structures at UCAM-B3LYP/6–311G** level of theory.

Figure 4 provides a comprehensive depiction of the potential energy surface, highlighting the most significant structures associated with the stationary points of the reaction and this figure depicts the reaction processes wherein

Fig. 4.

Schematic potential energy surface for the reaction among tetrameric sulfur radical (, wood pellets oil (WPn) and VOCs compounds.

To simplify within this study, R refers to reactants, TS to transition states, and P to products, each accompanied by a numerical identifier. By way of illustration, R₁, TS₁, and P₁ correspond to the reactants, transition states, and products of the reaction involving and WPn. Similarly, R₂, TS₂, and P₂ refer to the reactants, transition states, and products for the subsequent reaction with VOCs.

In this part, Table 1 summarizes the energetic results of the reaction between and WP1, WP2, and WP3, as indicating that the transition states for this reaction are located from − 1.04 to − 2.05 kcal mol^− 1 above the energy of the most stable reactants (R1). The potential energy barriers varied with WP1 demonstrating the smallest barrier and WP3 the largest. The generation of P1 proceeds with an energy release ranging from − 3.76 to − 6.37 kcal mol^− 1 as documented in Table 1.

Table 1.

The calculated reaction energies (in kcal.mol^− 1) at UCAM–B₃LYP/6-311G**.

Compounds	Reactant (R)	Transition states (TS)	Product (P)
-WP1	–1.56	–1.04	–3.76
-WP2	–2.68	–1.66	–5.93
-WP3	–3.44	–2.05	–6.37
VOCs Compounds+-WPn
Benzofuran --WP1	–7.74	–5.62	–10.44
Benzofuran --WP2	–11.71	–7.21	–15.33
Benzofuran --WP3	–13.52	–10.01	–18.24
Dibenzo-thiophene--WP1	–13.53	–11.72	–16.47
Dibenzo-thiophene--WP2	–16.64	–12.37	–17.33
Dibenzo-thiophene--WP3	–17.80	–13.15	–18.85
3-Pentylthiophene--WP1	–15.12	–17.36	–19.20
3-Pentylthiophene--WP2	–13.97	–16.13	–19.80
3-Pentylthiophene--WP3	–14.13	–15.99	–19.88
Benzoic acid --WP1	–19.03	–21.37	–23.52
Benzoic acid--WP2	–18.36	–19.95	–24.99
Benzoic acid--WP3	–21.26	–23.37	–25.86

Energy reaction of VOCs

We advanced the hypothesis that , functioning as a modifier for bitumen, augments the retention of VOCs within the bituminous composite. These radical intermediates are subsequently poised to couple with VOCs, ultimately constructing. The potency of compounds is ascribed to their ability to engage in C–S cross-coupling with VOCs, thereby facilitating the stabilization of VOCs within the bitumen matrix. This proposed mechanism has been rigorously verified by TD-DFT-based molecular modeling. Figure 4 illustrates the sequential reaction stages: after the initial formation of P₁ (), the subsequent reaction of P₁ with VOCs proceeds via a second transition state (TS₂), which precedes the generation of the final product, P₂ .

The TD-DFT calculations demonstrated that the activation energy barriers associated with the C–S coupling reactions between sulfur-doped phenol-rich bio-oils () and VOCs molecules are relatively low (between − 5.62 and − 25.86 kcal/mol). These low barriers imply that the reactions are thermodynamically feasible under the practical conditions encountered during asphalt production and service.

The computed energy values align well with real operating environments, suggesting that the predicted molecular interactions can indeed proceed in practice. This correlation reinforces the validity of the computational findings and highlights the potential of to effectively suppress VOCs emissions through feasible C–S cross-coupling and subsequent photodegradation processes.

Energy reaction of benzofuran

At this stage, a comparative assessment of the reaction energies for the radical reactions of with different VOCs becomes insightful. Qualified analysis, as presented in Table 1; Fig. 4, reveals that possesses the highest energy values. This enhanced reactivity of with benzofuran is directly linked to the presence of electron-donating substituents on the phenol ring. Crucially, the OCH₃ group, being a potent electron-donating substituent, effectively increase the electron density of . This enhancement results in a pronounced differentiation in reactivity, consequently accelerating the reaction between and benzofuran when contrasted with other WPn counterparts.

The reaction of with benzofuran is characterized by a reaction potential barrier within the range of −5.62 to −10.01 kcal mol⁻¹, proceeding through TS₂. The resultant product, P₂ (Benzofuran), is formed with an accompanying energy release of − 10.44 to − 18.24 kcal mol⁻¹, as comprehensively presented in Table 1 and depicted in Fig. 4.

Energy reaction of dibenzothiophen

The reactions between and dibenzothiophene proceed through transition states requiring energy input of − 11.72 and − 13.15 kcal mol⁻¹. The subsequent generation of is accompanied by an energy liberation of − 16.47 and − 18.85 kcal mol⁻¹ (refer to Table 1; Fig. 4). It is clear that the energy of this reaction will be an important factor in determining the efficacy of the degradation reaction of dibenzothiophen. Consequently, it is imperative to study the impact of introducing diverse electron-donating substituent groups into the WPn framework on these energy profiles; electron-donating groups in WPn lead to increased the reactivity with VOCs. From Table 1; Fig. 4, it is evident that the reaction energy for surpasses that of and .

Energy reaction of 3-pentylthiophene

The process was extended to encompass the reaction between and 3-pentyl-thiophene. Our calculations indicate that the potential energy barriers for TS₂) in this specific case span from − 17.36 to −15.99 kcal mol⁻¹. The generation of P2 ) proceeds with an associated energy liberation of − 19.20 to − 19.88 kcal mol⁻¹, which is comprehensively presented in Table 1. Table 1; Fig. 4 clearly illustrate that the P1 radical (from WP3) exhibits the highest calculated reaction energy for its reaction with VOCs among all WPn variants. This elevated energy is attributed to the electron-donating OCH₃ group in WP3, which the OCH₃ group intensifies the electron density within the , thereby heightening its propensity for reaction with 3-pentylthiophene. Such stabilization favors its reaction with 3-pentylthiophene, aligning with the observed highest reaction energy. In contrast, the reaction of with 3-pentylthiophene presents the lowest reaction energy, as summarized in Table 1; Fig. 4.

Energy reaction of benzoic acid

For the reactions involving Benzoic acid, the processes are characterized by potential energy barriers ranging from − 21.37 to − 23.37 kcal mol⁻¹. These reactions also exhibit exothermic behavior, releasing reaction heats spanning − 23.52 to − 25.86 kcal mol⁻¹ (see Table 1).

The data reveal that WP3 possesses superior stability relative to WP1 and WP2. This observation stems from the strong electron-donating nature of the OCH₃ substituent in WP3, which this electron-donating substituent augments the electron density within . Consequently, this electronic effect facilitates a faster reaction between and benzoic acid compared to other WPn counterparts. In contrast, the lowest values for these energetic parameters are observed for Benzoic acid.

UV–Vis spectroscopy

VOCs compounds do not undergo a significant degradation by a direct UV or solar light due to low UV–Vis absorption which occurs in wavelength (λ = 200 nm). A potential approach to promote VOCs degradation lies in boosting their UV–Vis absorption. This enhanced absorption can be facilitated by the extensive cross-coupling functionalities present in bitumen molecules. WPn compounds demonstrate reaction via a C–S cross-coupling with , thereby enabling the rapid reaction of VOCs. This particular reaction confers high UV–Vis absorption upon the product, attributable to the facile photodegradation of upon exposure to UV radiation at a wavelength (λ) of 400 nm.

TD–UCAM–B₃LYP/6-311G** calculations of electronic absorption spectra were performed to corroborate experimental degradation observations. Figure 5, produced using the Xmgrace Program, illustrates the UV–Vis spectra obtained for VOCs and . These electronic absorption spectra span the 0–800 nm wavelength range.

Fig. 5.

Time-dependent DFT calculations to compute UV–Vis absorptions of four VOCs (Benzoic acid, Benzofuran, Dibenzo–thiophene and 3–Pentylthiophene).

The effects of on the UV–Vis spectra of VOCs in forthcoming sections have been examined, investigating outcomes across contexts characterized by the presence or absence of. To produce the UV–Vis spectra for our chemical compounds, we employed the Gaussian broadening function which this function incorporates the molar extinction coefficient (ε), a critical parameter that defines a compound’s light absorption capacity at a given wavelength (λ).

As depicted in Fig. 5, UCAM–B3LYP/6–311G** calculations forecast intense electronic transitions for the four VOCs within the 200–250 nm wavelength range. While the absorption spectra of the VOCs display a single absorption band, the observed UV–Vis absorption spectra for are centered around 400 nm. Consequently, a notable red shift of the absorption peaks from 200 nm to 400 nm is apparent when comparing the UV–Vis spectra of the VOCs with , concurrently with a decrease in peak intensity. As evidenced by the UV–Vis spectrum of in Fig. 5, the reactions between and VOCs compounds induce both a significant red shift and a concomitant decrease in the intensity of the maximum absorption peaks of the VOCs. This red shift effectively enhances the capacity of these compounds to absorb light at wavelengths greater than 200 nm, thereby considerably favoring their direct photodegradation. These results unequivocally demonstrate a notable modification in the UV–Vis absorption profile upon the transformation of VOCs into their degradation product . As substantiated by the calculated UV–Vis spectra depicted in Fig. 5, the maximum absorption peak intensity of the compounds is significantly diminished relative to that of the original VOCs.

Figure 5 graphically illustrates the profound influence of on the UV–Vis spectroscopic characteristics of VOCs. This observed spectrum indicates that the reaction between VOCs and actively initiates the degradation of the VOCs. Consequently, the incorporation of with VOCs demonstrably attenuates the sustainability of bitumen.

Experimental results of UV–Vis spectra

The UV–Vis spectrum of VOCs and was recorded at room temperature over the range of 200–800 nm (Fig. 6). All compounds display intense absorption bands in the short-wavelength UV region, corresponding predominantly to π→π* electronic transitions within the conjugated aromatic π-systems. Dibenzo-thiophene and 3-pentylthiophene exhibit absorption maxima between ~ 240–260 nm, reflecting the π-electron delocalization across the thiophene ring and, in the former, the extended fused aromatic framework. Benzoic acid displays the highest molar absorptivity (ε), with a λ_max near ~ 230 nm attributable to benzene ring π→π* transitions. Benzofuran shows relatively weaker absorption in this region, with maxima around ~ 225 nm, arising from the fused benzene–furan conjugation. The visible region spectra introduce a second, lower-intensity band for each compound within the 400–450 nm range. These features may arise in extended π-systems through intramolecular charge-transfer (ICT) processes, n→π* transitions, provides further evidence supporting the successful reaction with VOCs (Dibenzo-thiophene, 3-pentylthiophene, Benzoic acid, Benzofuran). This red shift indicates a change in the electronic environment of the chromophore, arising from the interaction between the organic compound and the moiety. Upon reaction, the conjugation and electron density distribution within the π-system is altered, resulting in a lower energy transition and, consequently, a shift of the absorption maximum toward longer wavelengths. Such red shifts are characteristic of strong intermolecular interactions that modify the delocalized electronic system.

Fig. 6.

The UV–Vis spectrum of VOCs and .

Experimental results of FT–IR spectra

The FTIR spectrum of benzoic acid––WP₃ (Fig. 7) exhibits a broad absorption band in the range 3300–2500 cm⁻¹, attributable to hydrogen-bonding interactions between the carboxylic acid moiety and the hydroxyl group of WP₃. A strong, well-defined band at 1710 cm⁻¹ corresponds to the C = O stretching vibration of the carboxyl group, consistent with characteristic absorptions observed for VOCs. Additional absorption bands were observed at 1334, 1174, and 1022 cm⁻¹, assigned to C–S, C–O, and C–C stretching vibrations, respectively. Distinct peaks in the 600–400 cm⁻¹ region, corresponding to S–S stretching modes, provide evidence for the successful formation of the Benzoic acid––WP₃ complex. Aromatic C = C stretching vibrations were detected in the 1600–1400 cm⁻¹ range, while C–H stretching absorptions were observed between 2900 and 2700 cm⁻¹.

Fig. 7.

The FTIR spectrum of Benzoic acid--WP3.

Experimental results of mass spectra

Mass spectrometric analysis provided further confirmation of the molecular structure of benzoic acid––WP₃. The spectrum (Fig. 8) displayed a weak molecular ion peak at m/z 355, consistent with the calculated molecular mass of the target compound. The fragmentation profile was characteristic of aromatic tetrasulfide frameworks, with sequential cleavage of S–S, Ph–S, and [M–Sₙ]⁺ bonds. A dominant fragment at m/z 279 was assigned to the concurrent loss of H₂O and CO₂ ([M–63]⁺), a well-established dissociation pathway in molecules bearing both carboxylic acid and phenolic functionalities. Additional peaks at m/z 218, 167, 149, and 122 arose from progressive disruption of phenyl–S and S–S linkages. Distinct diagnostic signals at m/z 105, 91, and 77 corresponded to the phenylthiol cation (C₆H₅S⁺), the tropylium ion (C₇H₇⁺), and the benzene cation (C₆H₆⁺), respectively, thereby reinforcing the proposed structural assignment.

Fig. 8.

Mass spectrum of the Benzoic acid--WP3 complex.

Conclusion

This study investigates the photocatalytic activity and C–S cross-coupling affinity of and WPₙ with volatile organic compounds (VOCs) in the bitumen matrix. Both experimental and computational approaches were employed to explore the molecular interactions between and VOCs. Experimental validation using GC–MS, FT–IR, and UV–Vis spectroscopy, supported by TD–DFT calculations, confirmed the successful formation of VOCs––WPₙ complexes and their photodegradation behavior. A pronounced red shift in the UV–Vis absorption band, from approximately 200 nm to nearly 400 nm, was observed following the C–S coupling reaction between –WPₙ and VOCs. This shift enhances the complex’s ability to absorb near-UV and visible light, increasing photoexcitation efficiency and promoting photodegradation of VOCs molecules. Consequently, VOCs are transformed into more stable, less volatile sulfur-containing species within the asphalt matrix. Theoretical findings, with activation energy barriers ranging from − 5.62 to − 25.86 kcal/mol, indicate that the –WPn interactions with VOCs effectively hinder emission of these compounds through thermodynamically favorable reaction pathways.

The results indicate that , as cost-effective, reusable, and easily manageable bio-modifiers, efficiently drive C–S cross-coupling reactions with VOCs in asphalt systems. These findings suggest substantial potential for reducing material costs, mitigating asphalt aging, and decreasing atmospheric VOCs emissions.

Author contributions

Razieh Sadat Neyband: Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Mohammad Almasi: Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.

Funding

No Funding.

Data availability

All data generated or analyzed during this study are included in this article.

Declarations

Competing interests

The authors declare no competing interests.