In this study, the phototransformation of low-density polyethylene (LDPE), and polyvinyl chloride (PVC) was promoted in porous sulfur polymer nanocomposite under sunlight. In order to investigate the potential photo catalytic effects of   porous sulfur polymer the effects of some operational conditions on the photoremoval yields of during the transforLDPE and PVC were studied. 99% and 96% for LDPE and PVC yields was at a PB concentration of 3 mg/l, at LDPE and PVC concentrations of 400 mg/l a a nanocomposite size and surface area of 10 micron and 0,098 m2/m,respectively, at 40 Oc temperature a a pH of 5.00 at a sun ligth power of 50 W/m2. The FTIR analysis showed that the -SSH sulfanes groups porous sulfur polymers disappeared at 909 cm−1 at So / PB mass ratios of 20:40 to 30: 60 and to 60:120. TGA analysis showed the thermal stability of the porous sulfur polymer nanocomposites. XRD analysis showed that the persitance of the nanocomposite with the presence of pure salt at 2θ=31°, 46°, 56°, and 66° after treatment. 

Microplastics generated from the degradation of plastics in the environment due to sunlight, air, moisture, and heat [1,2]. They can contain som toxic  compounds which can threaten the ecocystem.  Flora and fauna can be exposed to the aforementioned pollutants and they can be ingested and eaten due to their minimized size liken nanometer and micrometer.

 [3,4]. This toxicity of some microplastics can cause inhibitions to the aquatic and terrestrial Organisms. The presence of microplastics in wastewater was investigated by a lot of recent studies The main source providing the disturbances and emissions of these pollutants was the surface runoffs [5-7]. On the other hand, the concentrations of some personal care products containing fragments increased. Some microplatics cannot be treated in conventional treatment plants and some microplastics can be released to the rivers and and to the oceans [8-10].  The existing technologies used in the wastewater treatment plants (coagulation, filtration, and advanced oxidation processes) cannot removed effectively and large volumes of   wastewaters containing microplastics was discharged to the receiving water bodies. In last decades a lot of microplastic removal processes was developed for microplastic removal like adsorption, magnetic extraction, membrane filtration, coagulation and photodegradation [11-13]. Among these processes, photodegradation is a promising process to degrade the   microplastics under UV ligth. Under this ligth, the electrons in the   the nanocomposites activated and generated electron-hole pairs resulting in    reactive oxidizing species (ROS).  These species can then break down   the microplastics into harmless byproducts, such as carbon dioxide and water. 

 Polymeric materials such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and polyvinyl chloride (PVC) are common materials under study due to their widespread use, particularly in the  packaging industry,  which contributes  to  microplastic pollution  in  the World[14-17]. The biodegradability of   microplastic-based materials like polyurethanes (PU), polylactic acid (PLA), nylon, polycarbonates, and were studied [18-20]. Microplastics are decomposed through photodegradation and possible biodegradation, [21-24]. The physicochemical properties of polymers depend on environmental conditions such as weather conditions, temperature, irradiation and pH values. Microplastics in aqueous bodies are a potential threat to aquatic species and they were considered an emerging contaminant. They are not degraded, and they can adhere to animals when they enter the food chain. On the other hand, they can adsorb some harmful pollutants.

Sulfur polymers have numerous applications like optoelectronic, superhydrophobic materials, and photochemical materials, biopolymers and proton-conducting electrolytes. The porous sulfur-containing polymers can be used to adsorpt the heavy metals. On the other hand, the photoactive properties of sulfur-containing polymers were reported. The porous sulfur-containing polymers was used for removing organic contaminants from pharmaceuticals, personal care products, and endocrine disruptors. 

In this study low-density polyethylene (LDPE), and polyvinyl chloride (PVC) microplastics was choosen to remediate them with porous sulfur-containing polymer using   1,3-diisopropenylbenzene via photodegradation. The effects of some operational parameters like concentration of pollutants and nanocomposite, surface area of nanocomposite, temperature, pH and light intensity on the  photodegradation yields of LDPE and PVC was studied. 

Production of porous sulfur-containing polymer nanocomposite

Elemental sulfur was heated under 190–210 °C in a magnetic stirring. Once completely molten then certain amount of 1,3-diisopropenylbenzene (PB) was added. So / PB mass ratio was varied from 20:40 to 30: 60 and to 60:120. The component was stirred, the still-liquid pre-polymer was transferred in a silicone cap. Te mixture was blended and it was maintained at 160 °C for 6 h. 

Characterization of porous sulfur-containing polymer nanocomposite

To characterization of porous sulfur-containing polymer, nitrogen adsorption/desorption isotherms were acquired at 79 K using a surface area analyzer (NOVA).  Scanning Electron Microscopy (SEM) imaging and Energy-Dispersive X-ray Spectroscopy (EDS) were performed using an FEI Inspect F system with an operational acceleration voltage of 10–20 kV. Fourier transformed infrared (FTIR) spectra were recorded using a Bruker Tensor 27 instrument over the wavenumber range of 500 to 4000 cm−1. Powder X-ray difraction patterns were performed by Panalytical X’Pert PRO MPD equipped PIXcel detector. Cu Kα radiation was utilized, and data were collected over a range of 5–70° using loose powder samples on thin Mylar flm within aluminium well plates. Termogravimetric analysis (TGA) (was conducted under an inert atmosphere on a TA Instruments TGA 5500. Heating was carried out at a heating rate of 10 ºC min−1, from room temperature to 600 °C. 

Analytical Measurements 

LDPE and PVC were analyzed by a gas chromatograph with a flame ionization detector using a TRACE GC gas chromatograph. It was provided with a 30 m × 0.32 mm Rtx-1 column.

Photocatalytic studies

Photocatalytic experiments were carried out in a laboratory scale reactor made of quartz with a volüme of 3 l. The photorector was a vertical tubular reactor, and the treated solution was circulated by a peristaltic pump operating with a speed of 20 l h−1. The loop contained also a sampling port and was fed with air at a rate of (2,0 cm3 s−1).

Results and Discussion 

 FTIR analysis results 

Te extent of PB mass ration (60 and 120) indicates the consumption of double bonds during the crosslinking process (Figure 1). The -SSH sulfanes groups also in porous sulfur polymers disappeared at 909 cm−1 band in the FTIR spectra at So / PB mass ratios of 20:40 to 30: 60 and to 60:120 (Figure 1). As a result, of polymerization the peaks associated with sulpfur monomer exhibited maximal peaks at 698 cm−1 band in the FTIR spectra (Figure 1). This showed the presence that C-S bond formation. The exhibited the peaks relevant to sulfur comonomer units which has an appearance at 690 cm−1 band in the FTIR spectra,illustrating the  C-S bonds 

Figure 1: FTIR analysis results of PB nanocomposite at different S/ PB ratios

TGA analysis results

 In order to detect the thermal stability of porous sulfur polymers (PB), TGA analysis were performed. Figure 2 illustrates TGA thermograms of porous sulfur polymers at different percentages of varying weight percentages of sulfur and PB. Te graph depicts that the degradation of pure sulfur commences at approximately 190 °C, with complete weight loss (100%) observed around 283 °C. However, the PB exhibited a higher decomposition temperature than pure sulfur. Additionally, the PB had a residue at 600 °C, and this residual content increased with a rise in pollutant content within the composition.

Figure 2: TGA analysis results

XRD analysis results

XRD patterns for pure sulfur and porous sulfur polymer nanocomposite after water treatment are presented in Figure 3. In the case of pure sulpfur, characteristic difraction peaks were discernible at 2θ=23°, 27°, 28°, 53°, and 56°. However, these peaks were absent following the copolymerization reaction in polymers containing over 60% PB content. This absence suggests 

a transformation from crystalline monoclinic sulfur to a highly cross-linked amorphous copolymer structure. Te difraction peaks originating from pure salt (at 2θ=31°, 46°, 56°, and 66°) remained observable in PB afer water treatment. This persistence indicates the presence of residual table salt even afer the water washing treatment. 

Figure 3: XRD analysis results

SEM analysis results

SEM images of raw PB with a So to PB mass ratio of 20:40 before treatment indicated the pesence of a non-porous surface (Figure 4a). The SEM image indicates homogenous disturbances of salt and sulfur in the PS nanocomposite. Afer treatment, these salts were dissolved and a porous structure was generated (Figure 4b). The non homogenous structure of pore can be increased with salt. Figure 4c showed that the pores sizes increased. This increases the surface contour of the porurs media for increase the adsorption process at the beginning of photodegradation. [29-30].

a (magnification : 5µm)	B (magnification : 5µm)	C (magnification : 500 µm)

Figure 4: SEM image of porous sulfur polymers at a So / PB mass ratio of 20:40 in raw PB (a), treated PB (b), treated PB(c)

Effects of nanocomposite concentration

The PB nanocomposite concentration was increased from 1 mg/l up to 5 mg/l with a S/PB ratio of 20:40 to detect the the optimal nnocomposite dose for maximal LDPE and   PVC photodegradation yields. The photocatalytic activity of LDPE and PVC enhanced when the PB concentration was increased from 1 mg/l to 2 and 3 mg/l (Table 1). The yields reached from 70% - 72% to 84% and 88% and to 99% and 96% for LDPE and PVC at a PB concentration of 3 mg/l. Further increase of PB nanocomposite concentration showed sligthly   lowest photocatalytic activity. The LDPE and PVC yields decreased to 84% and 81% at 5 mg/l PB nanocomposite concentration. The photodegradation yields of LDPE and PVC pollutants are influenced by the active site and the photoabsorption of the catalyst used. Adequate loading of PB nanocomposite increases the generation rate of electron/hole pairs for enhancing the photodegradation of LDPE and PVC microplastics. High dose of the PB lowered the light penetration and reduces the photodegradation percentages of polutants. At high PB nanocomposite concentration the surface area decreased while the size of the nanocomposite increased [31-33]. 

Table 1: Effect of nanocomposite concentration on the photodegradation yields

Effect of LDPE and PVC concentrations

The effect of initial pollutant concentration on the photocatalytic degradation is illustrated in Table 2. It was observed that the phodegradation efficiency as a function increasing pollutant concentration. At 50, 100, 200 and 400 mg/l LDPE and PVC concentrations the yields recorded between 98-99% and 95-96%, respectively for LDPE and PVC.  When the pollutant concentrations were incresed to 500 and 700 mg/ irradiation was not adequate to complete the degradation of the pollutants. The yields of pollutants decreased to 85-89% and to 79-75% for LDPE and PVC [34,35].

Table 2: Effect of pollutant concentration on the photodegradation yields

Effect of surface area 

The PB nanocomposite surface area significantly affects the pollutant removal efficiencies during the photodegradation during photocatalysis. The   activity of PB depends on on the holes and electron during activation of PB nanocomposite. Small particle sized PB nanocomposite (10 nm) sizes translate to reduced distance tranferring the electrons and holes during photocatalysis ending with high LDPE and PVC photodegradation yields (99% and 96%) (Table 3). PB Nanocomposites with a size 40 nm the PB exhibited high photodegradation yields (98% and 95%). 

In this study negligible weight losses were observed for PB nanocomposite resulting in, surface area effect of photodegradation yields was not significant. 

Table 3: Effect of nanocomposite size and surface on the photodegradation yield

Effect of temperature 

The temperature was increased from 20 oC up to 25, 30 and 40 Oc. At 20 oc the PLDE and PVC yields was accounted as 94% and 97%, respectively. As the temperature was increased to 40 Oc the LDPE and PVC yields reached to a maximum (99% and 97%) (Table 4). Generally, at high temperatures like 80°C, there is ecombination of charge carriers, ending with inhibition of photodegradation. As the temperature was increased to 40°C the photocatalytic activity increased since the kinetic energy for the reactive species elevated [36]. 

Table 4:  Effect of temperature on the photodegradation yields

Effect of pH

The formation of reactive oxidizing species by photocatalyst depends to pH. The pH influences the electrical double-layer charge at the solid electrolyte interface, affecting the formation of the electron–hole pairs on the surface of the photocatalyst [32-34]. Variation in pH modifies the potentials of catalytic processes. The surface of PB nanocomposite is positively charged at pH= 5 and negatively charged in apH of 8 (Table 5). LDPE and PVC exhibited crystalline structure and exhibited high photodegradation yields at pH=5. 

Table 5: Effect of pH on the photodegradation yields

Effect of sun ligth

The wavelength and intensity of sunligth affect significantly the the photodegradation of   LDPE and PVC. The sun light is stronger than visible light because its waves are shorter than those of visible light.  Therefore, it has higher efficiency in the photo degradation of microplastics. The number of photons available for activating the catalyst surface was relevant with sun intensity. The lower the intensity, the lower the activation energy; as a result,

low photodegradation efficiency is observed. With an increase in intensity, more active sites are activated increasing the interactions between the catalyst and the adsorbed substrate on its surface, hence higher degradation rates are attained.  In this study it was found that the photodegradation yields of LDPE and PVC were   maximum at a sun ligth intensity of 50 W/ m2 compared to 20 W/m2 (Table 6) 

Table 6: Effect of sun power on the photodegradation yields

In this study two microplastics namely low-density polyethylene (LDPE), and polyvinyl chloride (PVC) was photodegraded by porous sulfur polymer nanocomposite under optimized conditions. High photodegradation yields as high as 99% and 97% was detected for LPDE and PVC, respectively. This nano composited can be suggested to the photo removal of other microplastics degraded with difficulty at short times.