S doped carbon for the photocatalytic degradation of pesticide

Materials Letters 263 (2020) 127271

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Fabrication of MoS2/ZnS embedded in N/S doped carbon for the photocatalytic degradation of pesticide Tansir Ahamad a,⇑, Mu Naushad a, Sameerah I. Al-Saeedi b, Sultanah Almotairi a, Saad M. Alshehri a a b

Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia Department of Chemistry, College of Science, Princess Nourah Bint Abdulrahman University, Riyadh, Saudi Arabia

a r t i c l e

i n f o

Article history: Received 10 October 2019 Received in revised form 26 December 2019 Accepted 27 December 2019 Available online 28 December 2019 Keywords: Hydrothermal MoS2 EPR Photocatalyst Dicofol

a b s t r a c t A highly efficient, recyclable mesoporous catalyst has been prepared via hydrothermal and post-calcination methods. The prepared nanocomposite (MoS2/ZnS@NSC) was characterized via several analytical techniques and used as a photocatalyst for the degradation of dicofol pesticide under visible irradiation. The results reveal that the fabricated nanocomposite show excellent catalytic activity due to the formation of active photogenerated species such as dOH, O2 and e which was supported by scavenger traping as well as EPR experiments and show excellent reusability for the treatment of pesticide in aqueous solution. Ó 2019 Published by Elsevier B.V.

1. Introduction Pesticides are the toxic compounds that used for killing or repealing the pests, including insects, rodents, fungi and unwanted plants (weeds). Because of the widespread use of the pesticides in agriculture and food production and theirconsumersare exposed to low levels of pesticide remains via their foods [1,2]. Long-term pesticide exposure has been linked to the development of several disease such as parkinsons; asthma; depression and anxiety; attention deficit and hyperactivity disorder (ADHD); and cancer, including leukaemia and non-Hodgkin’s lymphoma and more. According to World Health Organization and the UN Environment Programme reports every year about to 3 million farmers (agriculture workers) face severe poisoning from pesticides, and about 18,000 of whom die. Increasing pesticides application and improper wastewater disposal methods are of particular concern for the freshwater (surface and groundwater), coastal and marine environments. Therefore, the removal of polluted pesticides in aqueous environment has become a very important and challenging issue attracting attention of numerous scientists in recent years. Previously several techniques have been utilized for the degradation of pesticide residues such as photocatalysis, adsorption, Fenton process, hydrolysis, ionizing radiation, ultrasonic irradiation, and oxygen plasma treatment [3,4]. Among these ⇑ Corresponding author. E-mail address: [email protected] (T. Ahamad). https://doi.org/10.1016/j.matlet.2019.127271 0167-577X/Ó 2019 Published by Elsevier B.V.

technique, photocatalysis degradation of pesticide is one of the most suitable technique because it can be used in aquatic environment by oxidizing low concentrations of organic pollutants in water. Several photocatalyst such as TiO2, SnO2, SrTiO3, LaCoO3, BiVO4, Bi2WO6, ZnS and MoS2have been used for the degradation of organic pollutants. Among the semiconductor photocatalysts, Molybdenum disulfide (MoS2), due to the narrow band gap (1.9 eV) which could easily excite under visible light, has been extensively considered as the visible light responding photocatalyst and co-catalyst. However, highly recombination efficiency of electron-hole pair limited the wide application of MoS2 in photocatalysis, therefore other semiconductor can be used to increase the separation efficiency of the MoS2. Additionally, the MoS2 nanostructures easily aggregate and stack because of their high surface energy and interlayer van der Waals interaction, which limits the number of exposed active sites. On theother hand, zinc sulfide (ZnS) is a well-known semiconductor photocatalyst, with wide-band gap energy (3.2–4.4 eV) and can be produce heterojunctions with MoS2 to separate the photo-induced electrons and holes. Secondly, several studies revealed that, the support of the graphite carbon also increased the photocatalytic activates due to adsorption of pollutants on the surface. Nowadays, heteroatom such as N, B and S could tune electronic characteristics to accelerate the electron transport, offer more active sites and improve the photocatalytic activities. In the present study, we have fabricated a novel hetro-structure nanocomposite contains MoS2/ZnS nanoparticles embedded in N/S doped graphite carbon (MoS2/ZnS@NSC), and

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used for the photodegradation of dicofol pesticide under sunlight irradiation. 2. Experimental 2.1. Synthesis The polymeric bi-metal complex was used to prepare the nanocomposite. In a beaker 4.56 g diphenylthiourea was dissolved in formaldehyde aqueous solution (15 mL 10%) and the pH of the solution was mentioned 4 using dil HCl and heated at 80 °C for 60 min. After that to this solution 0.5 g of MoCl3 and 0.35 g of ZnCl2 was added and striped magnetically for 30 min. the resulting viscous polymeric bimetal complex then transferred into a 100 mL Teflon-line stainless steel autoclave and then the autoclave was put into the oven and heated at 180 °C for 24 h. The resulting hydrochar was collected and dried and then pyrolyzed in a tubular furnace at 800 °C under argon (99.9% purity) flow at 500 mL min 1 with a heating are 5 °C min 1 to get the MoS2/ZnS@NSC. 3. Results and discussion 3.1. Characterization of MoS2/ZnS@NSC MoS2/ZnS@NSC nanocomposite was fabricated via hydrothermal followed by calcination process und the presence of argon as Fig. SF-1. The FTIR spectra of the nanocomposite support the presence of the N and S in the graphite carbon due the appearance of the peak at around 3220, 1650, 1545, 1484 and 1032 cm 1 are related to O–H, C=S, C=C, C–N and C–O, respectively. The XRD spectra of the MoS2/ZnS@NSC show the peaks corresponding to MoS2, ZnS and graphite carbon. The diffraction peaks located at 2h = 33. 34°, 39.01° and 59° are due to (1 0 0), (1 0 3) and (1 1 0) planes of MoS2. Other peaks at 28.78°, 48.01°, and 56.58° are assigned to the (1 1 1), (2 0 0), and (3 1 1) crystal planes of wurtzite ZnS, respectively[5]. There is a noticeable broad peak at ~25.8° which

is ascribed to the (0 0 2) plane of graphite carbon. The doping of hetro-atoms and formation of the graphite carbon in the nanocomposite was also supported via Raman spectrum as shown in Fig. 1 (b), and two Raman bands are appeared at 1348 and 1586 cm 1 assigned to D and G bands respectively. The intensities ratio (ID/IG) is found to be 0.918 indicates the carbon matrix of MoS2/ZnS@NSC is rich of graphite structural. The porosity of the MoS2/ZnS@NSC was calculated using nitrogen isotherm by the BET and BJH methods as shown in Fig. 1(c), the results shows a very narrow range of pore diameter 15–20 nm and the surface area was found to be 678.21 m2g 1. The morphology of the nanocomposite was determined using the SEM and TEM. Fig. 1(d), show the SEM image and indicate that the ZnS and MoS2 nanoparticles are uniformly embedded into N/S doped carbon matrix. Fig. 1(e), TEM image revealed that the MoS2 nano-sheets grow and the ZnS nanoparticles are spherical in shape with average diameter 25 nm. The HRTEM image show the interplanar distance of 0.64 nm, and 0.19 nm which is in agreement with the (0 0 2) planes of hexagonal MoS2 and with (1 1 0) plane of wurtzite ZnS respectively. Fig. 2(a) show the XPS results show the presence of the C, N, O, S, Zn and Mo elements in the surface of MoS2/ZnS@NSC. Fig. 2(b) shows a high resolution C 1s XPS spectrum and deconvoluted in to four different peaks at 283.4, 284.3, 285.6 and 288.5 eV corresponding to C=C/C–C (sp2), C–C (sp3), C–O/C–N/C–S, and C=O/ C=S groups respectively [6]. The high resolution spectra of the N 1s split in to three peaks at 396.4, 398.3 and 400.2 eV corresponding to pyridinic, pyrrolic and quaternary N respectively, as shown in Fig. 2(c). In the high-resolution XPS spectra of S 2p as in Fig. 2(d), show two peaks assigned to S 2p1/2 and S 2p3/2 at ~161.5 and ~162.8 eV, respectively, and peak at 160.9 eV support the existence of S as S2 state [7]. The XPS spectra of Zn 2p also split in two peaks located at 1021.08 and 1044.02 eV attributed to Zn2P3/2 and Zn2P1/2, respectively as shown in Fig. 2(e). Fig. 1(f) show the high-resolution Mo 3d XPS spectrum and displayed two peaks at 228.8 and 232.4 eV, assigned to the Mo 3d5/2 and Mo 3d3/2 respectively.

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Fig. 2. (a) A wide XPS spectra for MoS2/ZnS@NSC (b) C 1s, (c) N 1s and (d) S 2p (e) Zn 2p (f) Mo 3d.

3.2. Photocatalytic activity Photocatalytic activity was evaluated against dicofol under visible light irradiation, and the results are presented in Fig. 3(a). Blank experiments (without light or catalyst) reveal that no discrete

photoactivity was observed over the prepared catalysts. It can be seen that the maximum characteristic absorption peak of dicofol is significantly reduced due to the 84.5% degradation. Fig. 3(b), show the the kinetics of photocatalytic degradation of dicofol and the reaction constant is found to be 0.16 min 1. The stability and

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reusability of MoS2/ZnS@NSC catalyst was carried out via five cycles and the results show the excellent catalytic activities remains about to 77.2% after five cycles as shown in Fig. 3(d). To estimate the active photogenerated active spices such as free radical, electron and hole scavenger traping experiments were performed by adding TBA (scavenger for dOH), BQ (scavengers for O2 ), AgNO3 (scavenger for e ) and FA (scavengers for both h+ and dOH) into the photocatalytic solution, respectively [8]. As shown in Fig. 3 (d), revealed that the degradation was carried out via free radical (dOH), peroxo (O2 ) and electron (e ), on the other hand, no noticeable effect was observed with holes. Additionally the EPR technique also support the formation of the free radical (dOH) with DMPO under the irradiation of light, as shown in Fig. 3(e), the intensity was increased with increasing the time of irradiation and support the degradation of dicofol [9]. The degradation mechanism with the intermediates (m/z) is given in supporting information. The proposed schematic band structure and charge-transfer process of the MoS2/ZnS@NSC photocatalyst in our system are illustrated in Fig. 3(f).

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors extend their sincere appreciation to the Deanship of Scientific Research at King Saud University for funding this Research Group (RG-1438-026). This work was also funded by the Deanship of Scientific Research at Princess Nourah Bint Abdulrahman University through the Fast-track Research Funding Program. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.127271.

4. Conclusion

References

In this study, a novel photocatalyst MoS2/ZnS@NSC was fabricated successfully and used for the degradation of dicofol pesticides. The analytical analysis results support the fabrication of nanocomposites in its pure form and the photocatalytic results support the degradation of pesticides via e- and free radical active species. The reusability results support the stability of the catalyst and its can be used visible-light-driven photocatalyst with high efficiency in dealing with pesticides pollution in the water.

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CRediT authorship contribution statement Tansir Ahamad: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing - original draft, Writing - review & editing. Mu Naushad: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Resources, Software, Supervision, Validation, Visualization, Writing - original draft, Writing - review & editing. Sameerah I. Al-Saeedi: Formal analysis, Funding acquisition, Investigation, Methodology, Writing - review & editing. Sultanah Almotairi: Formal analysis, Funding acquisition, Investigation, Methodology, Writing - review & editing. Saad M. Alshehri: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Resources, Software, Writing - review & editing.