Insight into the sunlight-mediated photodegradation of active pharmaceuticals using ZnO-doped TiO₂/Carbon nanocomposite derived from leather waste

Abstract

Treatment of pharmaceutical wastewater is gaining importance due to health risks. In this study, carbon sourced from vegetable-tanned leather waste was utilized to develop an effective photocatalyst. ZnO incorporated TiO₂/carbon nanocomposites were synthesized via the sol–gel route by systematically changing the TiO₂:ZnO mass ratio. The nanocomposites exhibited a reduction in band gap energy values and particle size as ZnO content increased. The photocatalytic performance of the synthesized materials was tested for degrading sulfasalazine (SUZ) and losartan potassium (LP) under visible light and sunlight conditions. The ZnO@TiO₂/carbon (with a 1:0.075 mass ratio of TiO₂:ZnO) nanocomposite with a band gap energy of 3.23 eV demonstrated maximum degradation efficiencies of 97% and 96% for SUZ and LP, respectively, under sunlight illumination within 120 min. The photocatalytic degradation of SUZ was studied using radical scavengers and EPR spin-trap experiments. The findings indicate that superoxide (O₂^⋅−), holes from valence band (h_vb⁺) and adsorbed hydroxyl radicals (^⋅OH_ads) are the primary reactive species involved in the degradation of SUZ. Catalyst reuse was demonstrated up to three cycles. The photocatalytic performance was further evaluated in a synthetic wastewater matrix containing representative inorganic ions and natural organic matter, where the CTZ5 nanocomposite maintained appreciable degradation efficiency. ESI/MS based mechanistic studies identified 4-nitro-N-(2-pyridinyl)benzenesulfonamide and sulfapyridine as key intermediates. These findings highlight the nanocomposite’s strong potential for pharmaceutical wastewater treatment, thus contributing to environmental sustainability.

Keywords

Photocatalyst / Leather waste / Nanocomposite / Active pharmaceutical ingredients / Degradation pathway

References

[1] Vidaurre-Arbizu M, Pérez-Bou S, Zuazua-Ros A, Martín-Gómez C. From the leather industry to building sector: exploration of potential applications of discarded solid wastes. J Clean Prod, 2021, 291. 125960

[2] Chen H, Li M, Chattha SA, Zhang X, Peng B, Zhang C. A novel recycling technology for chrome shavings: efficient separation of chromium and collagen fibers based on swelling inhibition in alkali-acid processing<br>. Collagen Leather<br>, 2025, 7: 1.

[3] Lin H, Du Z, Xu L, Li C, Guan Y, Huang Y. Nitrogen-rich fibrous carbon enabling polysulfide conversion for lithium–sulfur batteries. Collagen Leather, 2025, 7: 26.

[4] Chatterjee K, Ashokkumar M, Gullapalli H, Gong Y, Vajtai R, Thanikaivelan P, Ajayan PM. Nitrogen-rich carbon nano-onions for oxygen reduction reaction. Carbon, 2018, 130: 645-651.

[5] Yi X, Luo D, Liu S, Chen Y, Guo J, Yan Q, Mao H. An environmentally benign chelative biosorbent for efficient adsorption remediation of tetracycline contamination. https://doi.org/10.1186/s42825-025-00230-9, 2025, 7: 42.

[6] Konikkara N, Kennedy LJ, Vijaya JJ. Preparation and characterization of hierarchical porous carbons derived from solid leather waste for supercapacitor applications. J Hazard Mater, 2016, 318: 173-185.

[7] Stejskal J, Ngwabebhoh FA, Sáha P, Prokeš J. Carbonized leather waste: a review and conductivity outlook. Polymers (Basel), 2023.

[8] Kaushal I, Saharan P, Kumar V, Sharma AK, Umar A. Superb sono-adsorption and energy storage potential of multifunctional Ag-Biochar composite. J Alloys Compd, 2019, 785: 240-249.

[9] Mian MM, Liu G. Recent progress in biochar-supported photocatalysts: synthesis, role of biochar, and applications. RSC Adv, 2018, 8: 14237-14248.

[10] Huang Q, Song S, Chen Z, Hu B, Chen J, Wang X. Biochar-based materials and their applications in removal of organic contaminants from wastewater: state-of-the-art review. Biochar, 2019, 1: 45-73.

[11] Khan AH, Aziz HA, Khan NA, Hasan MA, Ahmed S, Farooqi IH, Dhingra A, Vambol V, Changani F, Yousefi M, Islam S, Mozaffari N, Mahtab MS. Impact, disease outbreak and the eco-hazards associated with pharmaceutical residues: a critical review. Int J Environ Sci Technol, 2022, 19: 677-688.

[12] Chinnaiyan P, Thampi SG, Kumar M, Mini KM. Pharmaceutical products as emerging contaminant in water: relevance for developing nations and identification of critical compounds for Indian environment. Environ Monit Assess, 2018.

[13] Benoit L, Mir O, Vialard F, Berveiller P. Cancer during pregnancy: a review of preclinical and clinical transplacental transfer of anticancer agents. Cancers (Basel), 2021, 13: 1-19.

[14] Cardoso O, Porcher JM, Sanchez W. Factory-discharged pharmaceuticals could be a relevant source of aquatic environment contamination: review of evidence and need for knowledge. Chemosphere, 2014, 115: 20-30.

[15] Larsson DGJ, de Pedro C, Paxeus N. Effluent from drug manufactures contains extremely high levels of pharmaceuticals. J Hazard Mater, 2007, 148: 751-755.

[16] Shanmugam G, Sampath S, Selvaraj KK, Larsson DGJ, Ramaswamy BR. Non-steroidal anti-inflammatory drugs in Indian rivers. Environ Sci Pollut Res, 2014, 21: 921-931.

[17] Chinnaiyan P, Thampi SG, Ananthkumar M, Krishnaa ACB, Sasi M, Tejashwi L. Heterogeneous photo catalytic process using TiO₂ for removing Levetiracetam in water—a study. IOP Conf Ser Mater Sci Eng, 2020, 872. 012134

[18] Estrada-Arriaga EB, García-Sánchez L, Falcón-Rojas A. Experimental design approach for the removal of the antidiabetic drug, metformin at a high concentration by photocatalytic processes. Water Environ J, 2020, 35: 1-13.

[19] Phoon BL, Ong CC, Mohamed Saheed MS, Show PL, Chang JS, Ling TC, Lam SS, Juan JC. Conventional and emerging technologies for removal of antibiotics from wastewater. J Hazard Mater, 2020.

[20] Taoufik N, Boumya W, Janani FZ, Elhalil A, Mahjoubi FZ, Barka N. Removal of emerging pharmaceutical pollutants: a systematic mapping study review. J Environ Chem Eng, 2020.

[21] Benton O, Apollo S, Naidoo B, Ochieng A. Photodegradation of molasses wastewater using TiO₂–ZnO nanohybrid photocatalyst supported on activated carbon. Chem Eng Commun, 2016, 203: 1443-1454.

[22] Cao S, Song J, Li H, Wang K, Li Y, Li Y, Lu F, Liu B. Improving characteristics of biochar produced from collagen-containing solid wastes based on protease application in leather production. Waste Manage, 2020, 105: 531-539.

[23] Kutuzova A, Dontsova T, Kwapinski W. Application of TiO₂‐based photocatalysts to antibiotics degradation: cases of sulfamethoxazole, trimethoprim and ciprofloxacin. Catalysts, 2021.

[24] Mofokeng SJ, Kumar V, Kroon RE, Ntwaeaborwa OM. Structure and optical properties of Dy³⁺ activated sol-gel ZnO–TiO₂ nanocomposites. J Alloys Compd, 2017, 711: 121-131.

[25] Nguyen CH, Tran ML, Van Tran TT, Juang RS. Enhanced removal of various dyes from aqueous solutions by UV and simulated solar photocatalysis over TiO₂/ZnO/rGO composites. Sep Purif Technol, 2020.

[26] Shan R, Lu L, Gu J, Zhang Y, Yuan H. Photocatalytic degradation of methyl orange by Ag/TiO₂/biochar composite catalysts in aqueous solutions. Mater Sci Semicond Process, 2020, 114. 105088

[27] Rajput RB, Shaikh R, Sawant J, Kale RB. Recent developments in ZnO-based heterostructures as photoelectrocatalysts for wastewater treatment: a review. Environ Adv, 2022, 9. 100264

[28] Ali S, Ismail PM, Khan M, Dang A, Ali S, Zada A, Raziq F, Khan I, Khan MS, Ateeq M, Khan W, Bakhtiar SH, Ali H, Wu X, Shah MIA, Vinu A, Yi J, Xia P, Qiao L. Charge transfer in TiO₂-based photocatalysis: fundamental mechanisms to material strategies. Nanoscale, 2024, 16: 4352-4377.

[29] Pinzari F. Synthesis, photocatalytic and bio activity of ZnO–TiO₂ nanocomposites: a review study. Reactions, 2024, 5: 680-739.

[30] Khan ME. State-of-the-art developments in carbon-based metal nanocomposites as a catalyst: photocatalysis. Nanoscale Adv, 2021, 3: 1887-1900.

[31] Son BT. The development of biomass-derived carbon-based photocatalysts for the visible-light-driven photodegradation of pollutants: a comprehensive review. RSC Adv, 2021, 11: 30574-30596.

[32] Lu L, Shan R, Shi Y, Wang S, Yuan H. A novel TiO₂/biochar composite catalysts for photocatalytic degradation of methyl orange. Chemosphere, 2019, 222: 391-398.

[33] Xie X, Li S, Zhang H, Wang Z, Huang H. Promoting charge separation of biochar-based Zn–TiO₂/pBC in the presence of ZnO for efficient sulfamethoxazole photodegradation under visible light irradiation. Sci Total Environ, 2019, 659: 529-539.

[34] de Andrade JR, Vieira MGA, da Silva MGC, Wang S. Oxidative degradation of pharmaceutical losartan potassium with N-doped hierarchical porous carbon and peroxymonosulfate. Chem Eng J, 2020, 382. 122971

[35] Saravanan A, Kumar PS, Vo DVN, Yaashikaa PR, Karishma S, Jeevanantham S, Gayathri B, Bharathi VD. Photocatalysis for removal of environmental pollutants and fuel production: a review. Environ Chem Lett, 2021, 19: 441-463.

[36] Wei X, Zhang R, Zhang W, Yuan Y, Lai B. High-efficiency adsorption of tetracycline by the prepared waste collagen fiber-derived porous biochar. RSC Adv, 2019, 9: 39355-39366.

[37] Pérez-González M, Tomás SA, Morales-Luna M, Arvizu MA, Tellez-Cruz MM. Optical, structural, and morphological properties of photocatalytic TiO₂–ZnO thin films synthesized by the sol-gel process. Thin Solid Films, 2015, 594: 304-309.

[38] Pérez-González M, Tomás SA, Santoyo-Salazar J, Gallardo-Hernández S, Tellez-Cruz MM, Solorza-Feria O. Sol-gel synthesis of Ag-loaded TiO₂–ZnO thin films with enhanced photocatalytic activity. J Alloys Compd, 2019, 779: 908-917.

[39] Makuła P, Pacia M, Macyk W. How to correctly determine the band gap energy of modified semiconductor photocatalysts based on UV-Vis spectra. J Phys Chem Lett, 2018, 9: 6814-6817.

[40] Fan X, Hao H, Shen X, Chen F, Zhang J. Removal and degradation pathway study of sulfasalazine with Fenton-like reaction. J Hazard Mater, 2011, 190: 493-500.

[41] Pérez-González M, Tomás SA, Santoyo-Salazar J, Morales-Luna M. Enhanced photocatalytic activity of TiO₂–ZnO thin films deposited by dc reactive magnetron sputtering. Ceram Int, 2017, 43: 8831-8838.

[42] Chen W, Kuang Q, Wang Q, Xie Z. Engineering a high energy surface of anatase TiO₂ crystals towards enhanced performance for energy conversion and environmental applications. RSC Adv, 2015, 5: 20396-20409.

[43] Yu Y, Ding Z, Zuo M, Jing C. Modulating high-index facets on anatase TiO₂. Eur J Inorg Chem, 2018, 2017: 683-693.

[44] Wang W-K, Gao M, Zhang X, Fujitsuka M, Majima T, Yu HQ. One-step synthesis of nonstoichiometric TiO₂ with designed (101) facets for enhanced photocatalytic H₂ evolution. Appl Catal B, 2016, 205: 165-172.

[45] Hessien MA, Sadek HEH, Taha MA, Khattab RM. Influence of ZnO and TiO₂ additions on structural, physical, and electrical properties of LaCo_0.3Mn_0.7O₃ perovskite. Sci Rep, 2025, 15: 1-19.

[46] Davis K, Yarbrough R, Froeschle M, White J. Band gap engineered zinc oxide nanostructures via a sol–gel synthesis of solvent driven shape-controlled crystal growth. RSC Adv, 2019, 9: 14638-14648.

[47] Clarke B, Ghandi K. The interplay of growth mechanism and properties of ZnO nanostructures for different applications. Small, 2023, 19: 1-20.

[48] Sanusi I, Almquist CB. ZnO/TiO₂ composite thin-film photocatalysts for gas-phase oxidation of ethanol. Catalysts, 2023, 13: 1-23.

[49] Kumari MLA, Devi LG, Maia G, Chen TW, Al-Zaqri N, Ali MA. Mechanochemical synthesis of ternary heterojunctions TiO₂(A)/TiO₂(R)/ZnO and TiO₂(A)/TiO₂(R)/SnO₂ for effective charge separation in semiconductor photocatalysis: a comparative study. Environ Res, 2022.

[50] Dhiman P, Rana G, Kumar A, Sharma G, Vo DVN, Naushad M. ZnO-based heterostructures as photocatalysts for hydrogen generation and depollution: a review. Environ Chem Lett, 2022, 20: 1047-1081.

[51] Zhang Y, Bo X, Zhu T, Zhao W, Cui Y, Chang J. Synthesis of TiO₂–ZnO n–n heterojunction with excellent visible light-driven photodegradation of tetracycline. Nanomaterials, 2024.

[52] Adormaa BB, Darkwah WK. Oxygen vacancies of the TiO₂ nano-based composite photocatalysts in visible light responsive photocatalysis. RSC Adv, 2018, 8: 33551-33563.

[53] Ma H, Hao B, Song W, Guo J, Li M, Zhang L. A high-efficiency TiO₂/ZnO nano-film with surface oxygen vacancies for dye degradation. Materials Basel, 2021.

[54] Abreu-Jaureguí C, Andronic L, Sepúlveda-Escribano A, Silvestre-Albero J. Improved photocatalytic performance of TiO₂/carbon photocatalysts: role of carbon additive. Environ Res, 2024, 251. 118672

[55] Kaviyarasu K, Geetha N, Kanimozhi K, Magdalane CM, Sivaranjani S, Ayeshamariam A, Kennedy J, Maaza M. In vitro cytotoxicity effect and antibacterial performance of human lung epithelial cells A549 activity of zinc oxide doped TiO₂ nanocrystals: investigation of bio-medical application by chemical method. Mater Sci Eng C Mater Biol Appl, 2017, 74: 325-333.

[56] Raval I, Shukla A, Gandhi VG, Dang KD, Nair NG, Nguyen VH. Interface-engineered Zn@TiO₂ and Ti@ZnO nanocomposites for advanced photocatalytic degradation of levofloxacin. Catalysts, 2026.

[57] Stefańska KS, Kubiaka A, Piasecki A, Goscianska J, Nowaczyk G, Jurga S, Jesionowski T. TiO₂–ZnO binary oxide systems: comprehensive characterization and tests of photocatalytic activity. Materials, 2018, 11: 1-19.

[58] Kubiak A, Siwińska-Ciesielczyk K, Bielan Z, Zielińska-Jurek A, Jesionowski T. Synthesis of highly crystalline photocatalysts based on TiO₂ and ZnO for the degradation of organic impurities under visible-light irradiation. Adsorption, 2019, 25: 309-325.

[59] Izhar NI, Mohd Hir ZA, Rafaie HA, Daud S. Influence of ZnO content on activated carbon/ZnO for enhanced acetaminophen removal under very low light intensity: kinetics, operational variables, and radical trapping response. Kuwait J Sci, 2025, 52. 100391

[60] Zahoor S, Muhammad S, Kashif M, Shahzad N, Liu Y, Celik C, Ambreen N, Ali A, Wu H, Azizi S. Advances in mesoporous nanomaterials for photocatalytic degradation of pollutants : fundamentals, material classifications, challenges and future prospects. Coord Chem Rev, 2025.

[61] Yan B, Zheng J, Wang F, Zhao L, Zhang Q, Xu W, He S. Review on porous carbon materials engineered by ZnO templates: design, synthesis and capacitance performance. Mater Des, 2021.

[62] Tsai MT, Chang YY, Huang HL, Hsu JT, Chen YC, Wu AYJ. Characterization and antibacterial performance of bioactive Ti–Zn–O coatings deposited on titanium implants. Thin Solid Films, 2013, 528: 143-150.

[63] Ullah H, Khan KA, Khan WU. ZnO/TiO₂ nanocomposite synthesized by sol gel from highly soluble single source molecular precursor. Chin J Chem Phys, 2014, 27: 548-554.

[64] Ghamarpoor R, Fallah A, Jamshidi M. A review of synthesis methods, modifications, and mechanisms of ZnO/TiO₂-based photocatalysts for photodegradation of contaminants. ACS Omega, 2024, 9: 25457-25492.

[65] Huang Z, Jia S, Wei J. A visible light active, carbon–nitrogen–sulfur co-doped TiO₂/g-C₃N₄ Z-scheme heterojunction as an effective photocatalyst to remove dye pollutants. RSC Adv, 2021, 11: 16747-16754.

[66] Rajput RB, Mane RS, Jamble SN, Jha N, Kale RB. N-doped carbon/TiO₂ composites with enhanced photocatalytic performance for the removal of organic pollutants. J Phys Chem Solids, 2024.

[67] Rasouli K, Rasouli J, Mohtaram MS, Sabbaghi S, Kamyab H, Moradi H, Chelliapan S. Biomass-derived activated carbon nanocomposites for cleaner production: a review on aspects of photocatalytic pollutant degradation. J Clean Prod, 2023, 419. 138181

[68] Low J, Yu J, Jaroniec M, Wageh S, Al-Ghamdi AA. Heterojunction photocatalysts. Adv Mater, 2017.

[69] Prasannalakshmi P, Shanmugam N. Fabrication of TiO₂/ZnO nanocomposites for solar energy driven photocatalysis. Mater Sci Semicond Process, 2017, 61: 114-124.

[70] Zhang X, Chen H, Liu S, Zhang B, Zhu H, Chen H, Wen B, Chen L. Preparation of TiO₂-graphitized carbon composite photocatalyst and their degradation properties for tetracycline antibiotics. J Mol Struct, 2022, 1270. 133897

[71] Sapinska D, Adamek E, Masternak E, Zielińska-Danch W, Baran W. Influence of pH on the kinetics and products of photocatalytic degradation of sulfonamides in aqueous solutions. Toxics, 2022, 10: 655.

[72] Qudsieh IY, Ali MA, Maafa IM. Effect of water matrix on photocatalytic degradation of organic pollutants in water: a literature review. Rev Chem Eng, 2025, 41: 539-573.

[73] Petala A, Arvaniti OS, Travlou G, Mantzavinos D, Frontistis Z. Solar light induced photocatalytic removal of sulfamethoxazole from water and wastewater using BiOCl photocatalyst. J Environ Sci Health A Tox Hazard Subst Environ Eng, 2021, 56: 963-972.

[74] Yang J, Luo X. Ag-doped TiO₂ immobilized cellulose-derived carbon beads: one-pot preparation, photocatalytic degradation performance and mechanism of ceftriaxone sodium. Appl Surf Sci, 2021.

[75] Brook S. The absolute energy positions of conduction and valence bands of selected semiconducting minerals. Am Mineral, 2000, 85: 543-556.

[76] Mohapatra L, Cheon D, Yoo SH. Carbon-based nanomaterials for catalytic wastewater treatment: a review. Molecules, 2023, 28: 1805.

[77] Hoffmann MR, Martin ST, Choi W, Bahnemannt DW. Environmental applications of semiconductor photocatalysis. Chem Rev, 1995, 95: 69-96.

[78] Nosaka Y, Nosaka AY. Generation and detection of reactive oxygen species in photocatalysis. Chem Rev, 2017.

[79] Thoben C, Hartner NT, Hitzemann M, Raddatz CR, Eckermann M, Belder D, Zimmermann S. Regarding the influence of additives and additional plasma-induced chemical ionization on adduct formation in ESI/IMS/MS. J Am Soc Mass Spectrom, 2023, 34: 857-868.

[80] Omrani N, Nezamzadeh-Ejhieh A. Focus on scavengers’ effects and GC-MASS analysis of photodegradation intermediates of sulfasalazine by Cu₂O/CdS nanocomposite. Sep Purif Technol, 2020, 235. 116228

[81] Qiu P, Chen H, Jiang F. Cobalt modified mesoporous graphitic carbon nitride with enhanced visible-light photocatalytic activity. RSC Adv, 2014, 4: 39969-39977.

[82] Tshangana C, Mubiayi MP, Kuvarega A, Mamba B, Muleja AA. Peracetic acid-graphene oxide quantum dots oxidation process for effective sulfasalazine degradation and staphylococcus aureus inactivation. SSRN Electron J, 2022.

[83] Zhuang X, Li X, Yang Y, Wang N, Shang Y, Zhou Z, Li J, Wang H. Enhanced sulfamerazine removal via adsorption-photocatalysis using Bi₂O₃–TiO₂/PAC ternary nanoparticles. Water, 2020.

[84] Pant B, Pant HR, Barakat NAM, Park M, Jeon K, Choi Y, Kim HY. Carbon nanofibers decorated with binary semiconductor (TiO₂/ZnO) nanocomposites for the effective removal of organic pollutants and the enhancement of antibacterial activities. Ceram Int, 2013, 39: 7029-7035.

[85] Yan XJ, Tang Y, Ma C, Liu Y, Xu J. Deactivation and regeneration of photocatalysts: a review. Desalin Water Treat, 2018, 124: 160-176.

[86] Mokhtari S, Faghihian H, Mirmohammadi M. A core/shell TiO₂ magnetized molecularly imprinted photocatalyst (MMIP@TiO₂): synthesis and its photodegradation activity towards sulfasalazine. Environ Sci Pollut Res, 2023, 30: 13624-13638.

[87] Rezaei M, Nezamzadeh-Ejhieha A. The ZnO–NiO nano-composite: a brief characterization, kinetic and thermodynamic study and study the Arrhenius model on the sulfasalazine photodegradation. Int J Hydrog Energy, 2020, 45: 24749-24764.

Funding

Department of Science and Technology, Ministry of Science and Technology, India(DST/TMD (EWO)/OWUIS-2018/RS-01)

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