Template-free synthesis of core—shell Fe₃O₄@MoS₂@mesoporous TiO₂ magnetic photocatalyst for wastewater treatment

Abstract

TiO₂ is the dominant and most widely researched photocatalyst for environmental remediation, however, the drawbacks, such as only responding to UV light (<5% of sunlight), low charge separation efficiency, and difficulties in recycling, have severely hindered its practical application. Herein, we synthesized magnetically separable Fe₃O₄@MoS₂@mesoporous TiO₂ (FMmT) photocatalysts via a simple, green, and template-free solvothermal method combined with ultrasonic hydrolysis. It is found that FMmT possesses a high specific surface area (55.09 m²·g⁻¹), enhanced visible-light responsiveness (∼521 nm), and remarkable photogenerated charge separation efficiency. In addition, the photocatalytic degradation efficiencies of FMmT for methylene blue (MB), rhodamine B (RhB), and tetracycline (TC) are 99.4%, 98.5%, and 89.3% within 300 min, respectively. The corresponding degradation rates are 4.5, 4.3, and 3.1 times higher than those of pure TiO₂ separately. Owing to the high saturation magnetization (43.1 A·m²·kg⁻¹), FMmT can achieve effective recycling with an applied magnetic field. The improved photocatalytic activity is closely related to the effective transport of photogenerated electrons by the active interlayer MoS₂ and the electron—hole separation caused by the MoS₂@TiO₂ heterojunction. Meanwhile, the excellent light-harvesting ability and abundant reactive sites of the mesoporous TiO₂ shell further boost the photocatalytic efficiency of FMmT. This work provides a new approach and some experimental basis for the design and performance improvement of magnetic photocatalysts by innovatively incorporating MoS₂ as the active interlayer and integrating it with a mesoporous shell.

Keywords

core—shell / MoS₂ / mesoporous TiO₂ / photocatalytic degradation / heterojunction / magnetic recycling

References

[1] Schneider J, Matsuoka M, Takeuchi M, et al. Understanding TiO₂ photocatalysis: Mechanisms and materials. Chem. Rev., 2014, 114(19): 9919.

[2] Li W, Elzatahry A, Aldhayan D, Zhao D. Core-shell structured titanium dioxide nanomaterials for solar energy utilization. Chem. Soc. Rev., 2018, 47(22): 8203.

[3] Kumaravel V, Mathew S, Bartlett J, Pillai SC. Photocatalytic hydrogen production using metal doped TiO₂: A review of recent advances. Appl. Catal. B, 2019, 244, 1021.

[4] Sun J, Zhang M, Wang ZF, et al. Synthesis of anatase TiO₂ with exposed {001} and {101} facets and photocatalytic activity. Rare Met., 2019, 38(4): 287.

[5] Hu MQ, Xing ZP, Cao Y, et al. Ti³⁺ self-doped mesoporous black TiO₂/SiO₂/g-C₃N₄ sheets heterojunctions as remarkable visible-lightdriven photocatalysts. Appl. Catal. B, 2018, 226, 499.

[6] Guo N, Zeng Y, Li HY, Xu XJ, Yu HW, Han XR. Novel mesoporous TiO₂@g-C₃N₄ hollow core@shell heterojunction with enhanced photocatalytic activity for water treatment and H₂ production under simulated sunlight. J. Hazard. Mater., 2018, 353, 80.

[7] Zeng XF, Wang JS, Zhao YN, Zhang WL, Wang MH. Construction of TiO₂-pillared multilayer graphene nanocomposites as efficient photocatalysts for ciprofloxacin degradation. Int. J. Miner. Metall. Mater., 2021, 28(3): 503.

[8] Wang DD, Han DL, Shi Z, et al. Optimized design of three-dimensional multi-shell Fe₃O₄/SiO₂/ZnO/ZnSe microspheres with type II heterostructure for photocatalytic applications. Appl. Catal. B, 2018, 227, 61.

[9] T. Tatarchuk, I. Mironyuk, V. Kotsyubynsky, A. Shyichuk, M. Myslin, and V. Boychuk, Structure, morphology and adsorption properties of titania shell immobilized onto cobalt ferrite nanoparticle core, J. Mol. Liq., 297(2020), art. No. 111757.

[10] Kumar A, Khan M, Fang LP, Lo IMC. Visible-light-driven N-TiO₂@SiO₂@Fe₃O₄ magnetic nanophotocatalysts: Synthesis, characterization, and photocatalytic degradation of PPCPs. J. Hazard. Mater., 2019, 370, 108.

[11] A.M. Chávez, R.R. Solís, and F.J. Beltrán, Magnetic graphene TiO₂-based photocatalyst for the removal of pollutants of emerging concern in water by simulated sunlight aided photocatalytic ozonation, Appl. Catal. B, 262(2020), art. No. 118275.

[12] Rahmah MI, Sabry RS, Aziz WJ. Preparation and photocatalytic property of Fe₂O₃/ZnO composites with superhydrophobicity. Int. J. Miner. Metall. Mater., 2021, 28(6): 1072.

[13] M.S. Abdel-Wahed, A.S. El-Kalliny, M.I. Badawy, M.S. Attia, and T.A. Gad-Allah, Core double-shell MnFe₂O₄@rGO@TiO₂ superparamagnetic photocatalyst for wastewater treatment under solar light, Chem. Eng. J., 382(2020), art. No. 122936.

[14] Zangeneh H, Zinatizadeh AA, Zinadini S, Feyzi M, Bahnemann DW. Preparation and characterization of a novel photocatalytic self-cleaning PES nanofiltration membrane by embedding a visible-driven photocatalyst boron doped-TiO₂-SiO₂/CoFe₂O₄ nanoparticles. Sep. Purif. Technol., 2019, 209, 764.

[15] Nguyen TB, Huang CP, Doong RA. Photocatalytic degradation of bisphenol A over a ZnFe₂O₄/TiO₂ nanocomposite under visible light. Sci. Total Environ., 2019, 646, 745.

[16] Sibi MG, Verma D, Kim J. Magnetic core—shell nanocatalysts: Promising versatile catalysts for organic and photocatalytic reactions. Catal. Rev., 2020, 62(2): 163.

[17] E. Mrotek, S. Dudziak, I. Malinowska, D. Pelczarski, Z. Ryżyńska, and A. Zielińska-Jurek, Improved degradation of etodolac in the presence of core—shell ZnFe₂O₄/SiO₂/TiO₂ magnetic photocatalyst, Sci. Total Environ., 724(2020), art. No. 138167.

[18] A. Pourzad, H.R. Sobhi, M. Behbahani, A. Esrafili, R.R. Kalantary, and M. Kermani, Efficient visible light-induced photocatalytic removal of paraquat using N-doped TiO₂@SiO₂@Fe₃O₄ nanocomposite, J. Mol. Liq., 299(2020), art. No. 112167.

[19] Dai ZC, Li DN, Chi L, et al. Preparation of porphyrin sensitized three layers magnetic nanocomposite Fe₃O₄@SiO₂@TiO₂ as an efficient photocatalyst. Mater. Lett., 2019, 241, 239.

[20] Aghamali A, Khosravi M, Hamishehkar H, Modirshahla N, Behnajady MA. Preparation of novel high performance recoverable and natural sunlight-driven nanocomposite photocatalyst of Fe₃O₄/C/TiO₂/N-CQDs. Mater. Sci. Semicond. Process., 2018, 87, 142.

[21] Wang WX, Xiao KJ, Zhu L, Yin YR, Wang ZM. Graphene oxide supported titanium dioxide & ferroferric oxide hybrid, a magnetically separable photocatalyst with enhanced photocatalytic activity for tetracycline hydrochloride degradation. RSC Adv., 2017, 7(34): 21287.

[22] Bi JT, Huang X, Wang JK, et al. Oil-phase cyclic magnetic adsorption to synthesize Fe₃O₄@C@TiO₂-nanotube composites for simultaneous removal of Pb(II) and Rhodamine B. Chem. Eng. J., 2019, 366, 50.

[23] MirzaHedayat B, Noorisepehr M, Dehghanifard E, Esrafili A, Norozi R. Evaluation of photocatalytic degradation of 2,4-Dinitrophenol from synthetic wastewater using Fe₃O₄@SiO₂@TiO₂/rGO magnetic nanoparticles. J. Mol. Liq., 2018, 264, 571.

[24] Kumar A, Khan M, Zeng XK, Lo IMC. Development of g-C₃N₄/TiO₂/Fe₃O₄@SiO₂ heterojunction via sol—gel route: A magnetically recyclable direct contact Z-scheme nanophotocatalyst for enhanced photocatalytic removal of ibuprofen from real sewage effluent under visible light. Chem. Eng. J., 2018, 353, 645.

[25] Guo N, Li HY, Xu XJ, Yu HW. Hierarchical Fe₃O₄@MoS₂/Ag₃PO₄ magnetic nanocomposites: Enhanced and stable photocatalytic performance for water purification under visible light irradiation. Appl. Surf. Sci., 2016, 389, 227.

[26] Lu DZ, Fan HQ, Kondamareddy KK, et al. Highly efficient visible-light-induced photocatalytic production of hydrogen for magnetically retrievable Fe₃O₄@SiO₂@MoS₂/g-C₃N₄ hierarchical microspheres. ACS Sustainable Chem. Eng., 2018, 6(8): 9903.

[27] Sun YQ, Tan JB, Lin HH, et al. A facile strategy for the synthesis of ferroferric oxide/titanium dioxide/molybdenum disulfide heterostructures as a magnetically separable photocatalyst under visible-light. J. Colloid Interface Sci., 2018, 516, 138.

[28] Liu XF, Xing ZP, Zhang Y, et al. Fabrication of 3D flowerlike black N-TiO_2−x@MoS₂ for unprecedented-high visible-light-driven photocatalytic performance. Appl. Catal. B, 2017, 201, 119.

[29] Chen B, Meng YH, Sha JW, Zhong C, Hu WB, Zhao NQ. Preparation of MoS₂/TiO₂ based nanocomposites for photocatalysis and rechargeable batteries: Progress, challenges, and perspective. Nanoscale, 2018, 10(1): 34.

[30] Lyu JZ, Shao JW, Wang YH, et al. Construction of a porous core—shell homojunction for the photocatalytic degradation of antibiotics. Chem. Eng. J., 2019, 358, 614.

[31] H.L. Xiong, L.L. Wu, Y. Liu, et al., Controllable synthesis of mesoporous TiO₂ polymorphs with tunable crystal structure for enhanced photocatalytic H₂ production, Adv. Energy Mater., 9(2019), No. 31, art. No. 1901634.

[32] Tang HL, Ren Y, Wei SH, Liu G, Xu XX. Preparation of 3D ordered mesoporous anatase TiO₂ and their photocatalytic activity. Rare Met., 2019, 38(5): 453.

[33] Ma YW, Lu YF, Hai GT, et al. Bidentate carboxylate linked TiO₂ with NH₂-MIL-101(Fe) photocatalyst: A conjugation effect platform for high photocatalytic activity under visible light irradiation. Sci. Bull., 2020, 65(8): 658.

[34] Elkodous MA, El-Sayyad GS, Mohamed AE, et al. Layer-by-layer preparation and characterization of recyclable nanocomposite (Co_XNi_1−XFe₂O₄; X = 0.9/SiO₂/TiO₂). J. Mater. Sci. Mater. Electron., 2019, 30(9): 8312.

[35] F.P. Ran, Y.L. Zou, Y.X. Xu, X.Y. Liu, and H.X. Zhang, Fe₃O₄@MoS₂@PEI-facilitated enzyme tethering for efficient removal of persistent organic pollutants in water, Chem. Eng. J., 375(2019), art. No. 121947.

[36] D.D. Wang, J.H. Yang, X.Y. Li, et al, Effect of thickness and microstructure of TiO₂ shell on photocatalytic performance of magnetic separable Fe₃O₄/SiO₂/mTiO₂ core—shell composites, Phys. Status Solidi A, 214(2017), No. 3, art. No. 1600665.

[37] Guo BJ, Yu K, Fu H, et al. Firework-shaped TiO₂ microspheres embedded with few-layer MoS₂ as an anode material for excellent performance lithium-ion batteries. J. Mater. Chem. A, 2015, 3(12): 6392.

[38] Li W, Liu MB, Feng SS, et al. Template-free synthesis of uniform magnetic mesoporous TiO₂ nanospindles for highly selective enrichment of phosphopeptides. Mater. Horiz., 2014, 1(4): 439.

[39] Yu YQ, Yan L, Cheng JM, Jing CY. Mechanistic insights into TiO₂ thickness in Fe₃O₄@TiO_2—GO composites for enrofloxacin photodegradation. Chem. Eng. J., 2017, 325, 647.

[40] Liu YP, Li YH, Peng F, et al. 2H- and 1T- mixed phase few-layer MoS₂ as a superior to Pt co-catalyst coated on TiO₂ nanorod arrays for photocatalytic hydrogen evolution. Appl. Catal. B, 2019, 241, 236.

[41] Fortes AD, Suard E, Knight KS. Negative linear compressibility and massive anisotropic thermal expansion in methanol monohydrate. Science, 2011, 331(6018): 742.

[42] Z.Z. Li, H.Z. Li, S.J. Wang, F. Yang, and W. Zhou, Mesoporous black TiO₂/MoS₂/Cu₂S hierarchical tandem heterojunctions toward optimized photothermal-photocatalytic fuel production, Chem. Eng. J., 427(2022), art. No. 131830.

[43] Guo L, Yang Z, Marcus K, et al. MoS₂/TiO₂ heterostructures as nonmetal plasmonic photocatalysts for highly efficient hydrogen evolution. Energy Environ. Sci., 2018, 11(1): 106.

[44] D.C. Nguyen, T.L.L. Doan, S. Prabhakaran, et al., Hierarchical Co and Nb dual-doped MoS₂ nanosheets shelled micro-TiO₂ hollow spheres as effective multifunctional electrocatalysts for HER, OER, and ORR, Nano Energy, 82(2021), art. No. 105750.

[45] Wang DD, Yang JH, Li XY, Zhai HJ, Lang JH, Song H. Preparation of magnetic Fe₃O₄@SiO₂@mTiO_2—Au spheres with well-designed microstructure and superior photocatalytic activity. J. Mater. Sci., 2016, 51(21): 9602.

[46] Peng B, Meng XW, Tang FQ, Ren XL, Chen D, Ren J. General synthesis and optical properties of monodisperse multifunctional metal-ion-doped TiO₂ hollow particles. J. Phys. Chem. C, 2009, 113(47): 20240.

[47] Jin J, Yu JG, Guo DP, Cui C, Ho W. A hierarchical Z-scheme CdS—WO₃ photocatalyst with enhanced CO₂ reduction activity. Small, 2015, 11(39): 5262.

[48] Jiang ZF, Wan WM, Wei W, et al. Gentle way to build reduced titanium dioxide nanodots integrated with graphite-like carbon spheres: From DFT calculation to experimental measurement. Appl. Catal. B, 2017, 204, 283.

[49] X. Bai, Y.L. Ji, M.Y. She, et al., Oxygen vacancy mediated charge transfer expediting over GQDs/TiO₂ for enhancing photocatalytic removal of Cr (VI) and RhB synchronously, J. Alloys Compd., 891(2022), art. No. 161872.

[50] Zhang Y, Yuan JS, Zhao L, et al. Boosting exciton dissociation and charge transfer in P-doped 2D porous g-C₃N₄ for enhanced H₂ production and molecular oxygen activation. Ceram. Int., 2022, 48(3): 4031.

[51] Yu SQ, Han B, Lou YC, Liu Z, Qian GD, Wang ZY. Rational design and fabrication of TiO₂ nano heterostructure with multi-junctions for efficient photocatalysis. Int. J. Hydrogen Energy, 2020, 45(53): 28640.

[52] Liu L, Jiao SL, Peng YT, Zhou W. A green design for lubrication: Multifunctional system containing Fe₃O₄@MoS₂ nanohybrid. ACS Sustainable Chem. Eng., 2018, 6(6): 7372.

[53] Y.F. Zhao, R. Wu, H. Yu, et al., Magnetic solid-phase extraction of sulfonamide antibiotics in water and animal-derived food samples using core—shell magnetite and molybdenum disulfide nanocomposite adsorbent, J. Chromatogr. A, 1610(2020), art. No. 460543.

[54] Y.X. Wang, L. Rao, P.F. Wang, Z.Y. Shi, and L.X. Zhang, Photocatalytic activity of N-TiO₂/O-doped N vacancy g-C₃N₄ and the intermediates toxicity evaluation under tetracycline hydrochloride and Cr(VI) coexistence environment, Appl. Catal. B, 262(2020), art. No. 118308.

[55] A. Krishnan, P.V. Vishwanathan, A.C. Mohan, R. Panchami, S. Viswanath, and A.V. Krishnan, Tuning of photocatalytic performance of CeO_2—Fe₂O₃ composite by Sn-doping for the effective degradation of methlene blue (MB) and methyl orange (MO) dyes, Surf. Interfaces, 22(2021), art. No. 100808.

[56] M. Rafieezadeh and A.H. Kianfar, Synthesis and characterization of the magnetic submicrocube Fe₃O₄/TiO₂/CuO as a reusable photocatalyst for the degradation of dyes under sunlight irradiation, Environ. Technol. Innov., 23(2021), art. No. 101756.

[57] Raza A, Shen HL, Haidry AA, Cui SS. Hydrothermal synthesis of Fe₃O₄/TiO₂/g-C₃N₄: Advanced photocatalytic application. Appl. Surf. Sci., 2019, 488, 887.

[58] Shao N, Wang JN, Wang DD, Corvini P. Preparation of three-dimensional Ag₃PO₄/TiO₂@MoS₂ for enhanced visible-light photocatalytic activity and anti-photocorrosion. Appl. Catal. B, 2017, 203, 964.

[59] Ou W, Pan JQ, Liu YY, et al. Two-dimensional ultrathin MoS₂-modified black Ti^3+—TiO₂ nanotubes for enhanced photocatalytic water splitting hydrogen production. J. Energy Chem., 2020, 43, 188.

[60] Wang FL, Wang YF, Feng YP, et al. Novel ternary photocatalyst of single atom-dispersed silver and carbon quantum dots co-loaded with ultrathin g-C₃N₄ for broad spectrum photocatalytic degradation of naproxen. Appl. Catal. B, 2018, 221, 510.

[61] Bai Y, Ye LQ, Chen T, et al. Facet-dependent photocatalytic N₂ fixation of bismuth-rich Bi₅O₇I nanosheets. ACS Appl. Mater. Interfaces, 2016, 8(41): 27661.

[62] Liu CY, Zhang YH, Dong F, et al. Chlorine intercalation in graphitic carbon nitride for efficient photocatalysis. Appl. Catal. B, 2017, 203, 465.

[63] Zhou Z, Gao JX, Zhang GS, et al. Optimizing graphene—TiO₂ interface properties via Fermi level modulation for photocatalytic degradation of volatile organic compounds. Ceram. Int., 2020, 46(5): 5887.

[64] Ma JZ, Wang CX, He H. Enhanced photocatalytic oxidation of NO over g-C₃N_4—TiO₂ under UV and visible light. Appl. Catal. B, 2016, 184, 28.