In addressing the urgent need for treatment of refractory toxic dyes in industrial wastewater, the development of efficient photocatalytic water treatment technologies has emerged as a critical focus in environmental engineering. This study demonstrates a novel strategy for constructing oxygen vacancy (OV)-self-doped black TiO2 nanotube arrays (B-TNT-x) via sequential anodization and aluminothermic reduction, aiming to enhance visible-light-driven photocatalytic degradation of organic pollutants. The core innovation resides in the synergistic modulation of OVs to concurrently optimize electronic structure, charge carrier dynamics, and surface wettability, thereby overcoming the inherent limitations of conventional TiO2, including its broadband gap and poor visible-light responsivity.
The fabrication protocol comprises two critical stages: First, well-ordered TiO2 nanotube arrays are constructed via anodic oxidation with a titanium foil as the substrate. Subsequently, the prefabricated TiO2 nanotube arrays (TNT) undergo aluminothermic reduction within an alumina crucible packed with aluminum powder, introducing oxygen vacancies to yield defect-engineered TiO2 nanotube arrays.
Characterization reveals preferential accumulation of oxygen vacancies on the nanotube surface, inducing lattice reconstruction and increased surface roughness. FESEM analysis confirms that the wall thickness of B-TNT-450 reaches 15.33 nm, significantly exceeding that of pristine TNT (10.04 nm). Coupled with quantitative AFM characterization, this roughened surface morphology enhances hydrophilic surface wettability. HRTEM analysis identifies a 2-3 nm amorphous transition layer on B-TNT-450, indicating surface lattice distortion, while XRD confirms OV-induced low-angle shifting of the anatase (101) peak, evidencing lattice expansion attributable to O2- vacancy defects. XPS analysis detecting Ti3+ signatures and oxygen vacancies verifies the successful introduction of OV defects. UV-vis diffuse reflectance spectroscopy demonstrates that B-TNT-x extends light absorption into the visible and near-infrared regions. This phenomenon is ascribed to defect levels within the band gap introduced by oxygen vacancies, which reduce the maximum transition energy of valence electrons, thereby substantially broadening the catalyst's spectral response range. Complementary carrier behavior characterizations further confirm that defect-engineered B-TNT-x exhibits significantly suppressed photogenerated carrier recombination alongside enhanced migration and separation efficiencies. Photocatalytic performance is evaluated under visible-light irradiation. OV modification endows the photocatalyst with superhydrophilic surface properties, facilitating the formation of uniform water films and improving pollutant accessibility to active sites. In degradation experiments with methylene blue (MB) as a model pollutant, B-TNT-450 exhibits optimal performance, achieving 91.1% degradation efficiency with a reaction rate constant k = 0.013 83 min-1 per Langmuir-Hinshelwood kinetics, significantly outperforming unmodified TNT.
Mechanistically, OVs narrow the bandgap, mediating a two-step electron transition from the valence band to defect levels and subsequently to the conduction band, while concurrently functioning as charge separation centers to suppress carrier recombination. Furthermore, oxygen vacancies induce Ti3+ -rich Lewis acid sites, promoting superhydrophilic surface formation and enhancing hydroxyl adsorption capacity. This facilitates more uniform interfacial water film formation, thereby optimizing contact conditions between pollutants and TiO2 surface active sites to augment degradation efficiency. The emergent catalytic enhancement stems from the synergistic optimization of electronic structure and the hydrophilic surface achieved through oxygen vacancy engineering.
This work elucidates the dual regulatory role of oxygen vacancies in modulating electronic properties and surface wettability, establishing an innovative paradigm for defect engineering in photocatalytic materials. The integrated strategy combining structural, electronic, and interfacial modifications establishes a novel pathway for developing high-efficiency visible-light-responsive photocatalysts for advanced wastewater treatment.
Key words
photocatalytic degradation /
oxygen vacancies /
black TiO2 /
superhydrophilic surface /
surface modulation /
defect engineering
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References
[1] OU X X, DALY H, FAN X L, et al.High-Ionic-Strength Wastewater Treatment via Catalytic Wet Oxidation over a MnCeOx Catalyst[J]. ACS Catalysis, 2022, 12(13): 7598-7608.
[2] SHARMA N K, PHILIP L.Combined Biological and Photocatalytic Treatment of Real Coke Oven Wastewater[J]. Chemical Engineering Journal, 2016, 295: 20-28.
[3] SHANG K F, LI W F, WANG X J, et al.Degradation of P-Nitrophenol by DBD Plasma/Fe2+/Persulfate Oxidation Process[J]. Separation and Purification Technology, 2019, 218: 106-112.
[4] KOKLIOTI M A, SAUCEDO-OROZCO I, QUINTANA M, et al.Functionalized MoS2 Supported Core-Shell Ag@Au Nanoclusters for Managing Electronic Processes in Photocatalysis[J]. Materials Research Bulletin, 2019, 114: 112-120.
[5] LIN J Y, YE W Y, XIE M, et al.Environmental Impacts and Remediation of Dye-Containing Wastewater[J]. Nature Reviews Earth & Environment, 2023, 4: 785-803.
[6] CHONG M N, JIN B, CHOW C W K, et al. Recent Developments in Photocatalytic Water Treatment Technology: A Review[J]. Water Research, 2010, 44(10): 2997-3027.
[7] LIU C, KONG D S, HSU P C, et al.Rapid Water Disinfection Using Vertically Aligned MoS2 Nanofilms and Visible Light[J]. Nature Nanotechnology, 2016, 11: 1098-1104.
[8] WU H Y, INABA T, WANG Z M, et al.Photocatalytic TiO2@CS-Embedded Cellulose Nanofiber Mixed Matrix Membrane[J]. Applied Catalysis B: Environmental, 2020, 276: 119111.
[9] CHEN C, WANG B Y, XU J J, et al.Recent Advancement in Emerging MXene-Based Photocatalytic Membrane for Revolutionizing Wastewater Treatment[J]. Small, 2024, 20(37): 2311427.
[10] SONG K, MOHSENI M, TAGHIPOUR F.Application of Ultraviolet Light-Emitting Diodes (UV-LEDs) for Water Disinfection: A Review[J]. Water Research, 2016, 94: 341-349.
[11] SUBRAMANI A, JACANGELO J G.Emerging Desalination Technologies for Water Treatment: A Critical Review[J]. Water Research, 2015, 75: 164-187.
[12] SHEN J, SONG Z Q, QIAN X R, et al.A Review on Use of Fillers in Cellulosic Paper for Functional Applications[J]. Industrial & Engineering Chemistry Research, 2011, 50(2): 661-666.
[13] DONG H R, ZENG G M, TANG L, et al.An Overview on Limitations of TiO2-Based Particles for Photocatalytic Degradation of Organic Pollutants and the Corresponding Countermeasures[J]. Water Research, 2015, 79: 128-146.
[14] ESKANDARLOO H, ZAFERANI M, KIERULF A, et al.Shape-Controlled Fabrication of TiO2 Hollow Shells Toward Photocatalytic Application[J]. Applied Catalysis B: Environmental, 2018, 227: 519-529.
[15] GUO Q, ZHOU C Y, MA Z B, et al.Fundamentals of TiO2 Photocatalysis: Concepts, Mechanisms, and Challenges[J]. Advanced Materials, 2019, 31(50): 1901997.
[16] CAO H, LIU F Y, TAI Y T, et al.Promoting Photocatalytic Performance of TiO2 Nanomaterials by Structural and Electronic Modulation[J]. Chemical Engineering Journal, 2023, 466: 143219.
[17] WANG W K, MEI S B, JIANG H P, et al.Recent Advances in TiO2-Based S-Scheme Heterojunction Photocatalysts[J]. Chinese Journal of Catalysis, 2023, 55: 137-158.
[18] GAO J Q, SHEN Q Q, GUAN R F, et al.Oxygen Vacancy Self-Doped Black TiO2 Nanotube Arrays by Aluminothermic Reduction for Photocatalytic CO2 Reduction under Visible Light Illumination[J]. Journal of CO2 Utilization, 2020, 35: 205-215.
[19] GAO J Q, XUE J B, JIA S F, et al.Self-Doping Surface Oxygen Vacancy-Induced Lattice Strains for Enhancing Visible Light-Driven Photocatalytic H2 Evolution over Black TiO2[J]. ACS Applied Materials & Interfaces, 2021, 13(16): 18758-18771.
[20] WANG F H, ZHAO Q, LI H P, et al.Crystal Defect Engineering to Construct Oxygen Vacancies in MXene- Derived TiO2 Nanocomposites for Boosting Photocatalytic Degradation of 2, 4, 6-Trichlorophenol[J]. Chemical Engineering Journal, 2024, 481: 148855.
[21] ARUJA E.Displacement of X-Ray Reflexions[J]. Nature, 1944, 154: 53.
[22] DEMENTJEV A P, IVANOVA O P, VASILYEV L A, et al.Altered Layer as Sensitive Initial Chemical State Indicator[J]. Journal of Vacuum Science Technology A: Vacuum Surfaces and Films, 1994, 12(2): 423-427.
[23] SANJINÉS R, TANG H, BERGER H, et al. Electronic Structure of Anatase TiO2 Oxide[J]. Journal of Applied Physics, 1994, 75(6): 2945-2951.
[24] XIANG Q J, LV K L, YU J G.Pivotal Role of Fluorine in Enhanced Photocatalytic Activity of Anatase TiO2 Nanosheets with Dominant (001) Facets for the Photocatalytic Degradation of Acetone in Air[J]. Applied Catalysis B: Environmental, 2010, 96(3/4): 557-564.
[25] MOSES P R, WIER L M, LENNOX J C, et al.X-Ray Photoelectron Spectroscopy of Alkylaminesilanes Bound to Metal Oxide Electrodes[J]. Analytical Chemistry, 1978, 50(4): 576-585.
[26] KUZNETSOV M V, ZHURAVLEV J F, ZHILYAEV V A, et al.XPS Study of the Nitrides, Oxides and Oxynitrides of Titanium[J]. Journal of Electron Spectroscopy and Related Phenomena, 1992, 58(1/2): 1-9.
[27] SCHULZE P D, SHAFFER S L, HANCE R L, et al.Adsorption of Water on Rhenium Studied by XPS[J]. Journal of Vacuum Science Technology A: Vacuum Surfaces and Films, 1983, 1(1): 97-99.
Funding
Fundamental Research Program of Shanxi Province, China (202303021212270, 202203021212508)
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