Direct Z-scheme siloxene germanane nanosheet heterojunctions for broadband photodetection and ultrasensitive photoelectrochemical sensing

Abstract

Siloxene and germanane are two-dimensional (2D) direct-bandgap semiconductors that hold promise for a range of applications, including photocatalysis, electronics, and photodetectors (PDs). In this study, we explore a novel direct Z-scheme 2D-2D siloxene/germanane heterojunction fabricated via wet-mixing self-assembly. This heterojunction exhibits superior light absorption compared with the individual nanosheets. Notably, when employed as a photoelectrode material for photoelectrochemical (PEC) PDs, it shows a marked photoresponse across the 365-980 nm range, with a peak responsivity at 520 nm. Specifically, under 520 nm illumination, its responsivity surpasses those of siloxene and germanane nanosheets by factors of 221.3 and 3.7, respectively. Remarkably, even at zero bias, it achieves a high photoresponsivity of 3.75 μA W^-1 and a detectivity of 1.3 × 10⁸ Jones, demonstrating excellent self-powered performance. Owing to its exceptional light sensitivity at 520 nm, the Z-scheme heterojunction is particularly well suited for the PEC photodetection of tartrazine, offering an ultralow detection limit of 0.3 pM and a broad linear range from 1 pM to 1 μM in aqueous media. Overall, this research highlights the considerable potential of the siloxene/germanane heterojunction for advanced optoelectronic applications, including high-performance PDs and PEC sensors.

Keywords

Silicene / germanene / direct bandgap semiconductor / 2D Z-scheme heterojunction / PEC photodetector / PEC sensor

References

[1] Li X,Bi Y,Han J.Recent advances in 2D nanomaterials as photocatalysts for sustainable CO₂ reduction.Chem Eng J2026;542:178146

[2] Tang J,Wang T.A review of g-C₃N₄-based photocatalytic materials for photocatalytic CO₂ reduction.Carbon Neutral2024;3:557-83

[3] Yang Z,Ren J,Xue Y.2D/2D heterointerface engineering of Ni₂P/ZnIn₂S₄ photocatalysts for enhanced photocatalytic H₂ evolution.Mater Rep Energy2026;6:100401

[4] Wu R,Meng X.Competition between phonon-assisted and exciton photoluminescence modulated by temperature in WSe₂/graphene nanosheet heterostructures for flexible optoelectronic sensor devices.ACS Appl Nano Mater2024;7:16941-8

[5] Chen J,Cui D.Stacking independence and resonant interlayer excitation of monolayer WSe₂/MoSe₂ heterostructures for photocatalytic energy conversion.ACS Appl Nano Mater2020;3:1175-81

[6] Zhao F,Feng W.Germanium-based monoelemental and binary two-dimensional materials: theoretical and experimental investigations and promising applications.InfoMat2022;4:e12365

[7] Nakano H,Nakamura H.Preparation and structure of novel siloxene nanosheets.Chem Commun2005;23:2945-7

[8] Bianco E,Jiang S,Windl W.Stability and exfoliation of germanane: a germanium graphane analogue.ACS Nano2013;7:4414-21

[9] Jiang S,Cultrara ND.Covalently-controlled properties by design in group IV graphane analogues.Acc Chem Res2014;48:144-51

[10] Xiao M,Song H,Xiao B.Tunable band gaps and high carrier mobilities in germanene by Si doping in the presence of an external electric field: field effect transistors.Phys B Condens Matter2024;682:415859

[11] Madhushankar BN,Giousis T.Electronic properties of germanane field-effect transistors.2D Mater2017;4:021009

[12] Liu N,Xu K.Hydrogen terminated germanene for a robust self-powered flexible photoelectrochemical photodetector.Small2020;16:2000283

[13] Roy PK,Šturala J,Melle-Franco M.Hydrogen-terminated two-dimensional germanane/silicane alloys as self-powered photodetectors and sensors.ACS Appl Mater Interfaces2023;15:25693-703 PMCID:PMC10236439

[14] Zhang Q,Liu Z,Fu A.Germanene/MoS₂ heterostructure as promising anchoring and electrocatalyzing material for high performance lithium-sulfur batteries: a computational study.J Energy Storage2025;109:115205

[15] Wu B,Veselý M.Functionalized germanane/SWCNT hybrid films as flexible anodes for lithium-ion batteries.Nanoscale Adv2021;3:4440-6

[16] Zhang X,Murugesan K.Two-dimensional siloxene: a promising silicon-based material with enhanced volume stability for Li-ion battery anode.Chem Eng J2026;532:174513

[17] Guo Q,Chen N.Few-layer siloxene as an electrode for superior high-rate zinc ion hybrid capacitors.ACS Energy Lett2021;6:1786-94

[18] Zhang E,Hong Y.Siloxene coupled graphene anode membrane with Zn-ion intercalation for all-solid-state Zn-ion hybrid supercapacitors.Chem Eng J2025;523:168578

[19] Huang Y,Zhong Z.A novel ratiometric biosensor based on germanene nanosheets for rapid and sensitive BRCA1 detection in differentiating T cells.Biosens Bioelectron2026;298:118411

[20] Song Z,Sturala J.Functionalized germanene-based nanomaterials for the detection of single nucleotide polymorphism.ACS Appl Nano Mater2021;4:5164-75

[21] Kovalska E,Luxa J.Edge-hydrogenated germanene by electrochemical decalcification-exfoliation of CaGe₂: germanene-enabled vapor sensor.ACS Nano2021;15:16709-18

[22] Ramachandran R,Zhao C,Wang F.2D siloxene sheets: a novel electrochemical sensor for selective dopamine detection.Appl Mater Today2020;18:100477

[23] Rosli NF,Sturala J,Webster RD.Siloxene, germanane, and methylgermanane: functionalized 2D materials of group 14 for electrochemical applications.Adv Funct Mater2020;30:1910186

[24] Giousis T,Miola M.Germanane and butyl-functionalized germanane as visible-light photocatalysts for the degradation of water pollutants.J Environ Chem Eng2023;11:109784

[25] Li S,Li D.Siloxene nanosheets: a metal-free semiconductor for water splitting.J Mater Chem A2016;4:15841-4

[26] Ng S,Vyskocil J.Two-dimensional functionalized germananes as photoelectrocatalysts.ACS Nano2021;15:11681-93

[27] Zhao F,Wang Y.Two-dimensional gersiloxenes with tunable bandgap for photocatalytic H₂ evolution and CO₂ photoreduction to CO.Nat Commun2020;11:1443 PMCID:PMC7081354

[28] Li M,Sakthivel T,Xu Z.Siloxene: an advanced metal-free catalyst for efficient photocatalytic reduction of aqueous Cr(VI) under visible light.Chem Eng J2021;421:129728

[29] Imagawa H,Itahara H.Photocatalytic NO removal over calcium-bridged siloxenes under ultraviolet and visible light irradiation.Dalton Trans2018;47:7070-6

[30] Luo J,Tong X.Colloidal quantum dots and two-dimensional material heterostructures for photodetector applications.Electron2024;2:e30

[31] Xiao J,Shi X.High-performance edge-contact monolayer molybdenum disulfide transistors.Research2025;8:0593 PMCID:PMC11739435

[32] Qiu D,Wang S.Recent advances in 2D superconductors.Adv Mater2021;33:2006124

[33] Wang Y,Wang Y.Broadband self-powered photoelectrochemical photodetector based on Te/Se heterostructure nanocomposites.Compos Commun2022;32:101175

[34] Li P,Liu Y.Unveiling the defect-accelerated charge transfer mechanism in ZnIn₂S₄/g-C₃N₄ Z-scheme heterojunctions for efficient solar fuel production.Carbon Neutral2026;5:e70139

[35] Tan X,Mohamed AR.Two-in-one redox photocatalysis: cooperative hydrogen evolution and benzaldehyde production via 2D MoS₂ cocatalyst-loaded hydrangea-like Zn₃In₂S₆.Mater Rep Energy2025;5:100374

[36] Lee J,Kwak BS.Atomic-scale structurally locked 1T/2H-MoS₂/ZnS Z-scheme heterojunctions for prolonged charge kinetics and dual-functional photocatalysis.Energy Environ Mater2026;e70493

[37] Yu H.Ripples in two-dimensional transition metal sulfides: formation mechanism, optoelectronic regulation, and application prospects.Battery Energy2026;5:e70108

[38] Ding G,Zhang J,Chen L.Layered double hydroxides-based Z-scheme heterojunction for photocatalysis.EcoEnergy2024;2:22-44

[39] Yuan M,Mao S,Lin X.Construction Z-scheme heterostructure by WO₃ nanocubes embedded g-C₃N₄ nanosheets with n-π* electronic transition for enhanced visible light driven photocatalysis.J Photochem Photobiol A Chem2025;469:116581

[40] Zhu Q,Zhu Y,Yan W.In situ phase transition and Cu doping synergistically regulate perovskite Z-scheme heterojunction for photocatalytic CO₂ reduction.Energy Environ Mater2026;e70387

[41] Mandari KK.g-C₃N₄/MXene-based heterostructures: advanced catalysts for efficient and sustainable renewable energy production.Adv Ind Eng Chem2025;1:14

[42] Wang S,Liu Z,Wang L.Two-dimensional direct Z-scheme heterojunction photocatalysts for highly efficient energy conversion and chemical synthesis.ACS Nano2025;20:137-62

[43] Li Y.2D/2DZ-scheme WO₃/g-C₃N₄ heterojunctions for photocatalytic organic pollutant degradation and nitrogen fixation.Mater Adv2024;5:749-61

[44] Tuc Altaf C,Karagoz E,Demirci Sankir E.Self-powered photoelectrochemical photodetectors based on a CsPbBr₃/S-g-C₃N₄ heterojunction-sensitized 3D ZnO nanostructured thin film.ACS Appl Nano Mater2024;7:8186-96

[45] Xiao W,Huang W.Bismuth-based BiO Br_xI_1-x/Ti₃C₂ MXene schottky nanocomposites for Hg²⁺ photoelectrochemical sensors.ACS Appl Nano Mater2022;5:18168-77

[46] Qu J,Lan H.Space-confined growth of ultrathin P-type GeTe nanosheets for broadband photodetectors.Small2024;20:2309391

[47] Yang W,Xie L,Long M.A systematic study of switching, optoelectronics, and gas-sensitive properties of PCF-graphene-based nanodevices: insights from DFT study.Carbon Neutral2024;3:904-17

[48] Zeng W,Wu Z.Hierarchically converged defect engineering with 2-dimensional black phosphorus/MXene sequence for sensitive photoelectrochemical-electrostatic sensors.Research2025;8:0966 PMCID:PMC12550280

[49] Qin J,Zeng Y,Tang D.Recent advances in flexible sensors: from sensing materials to detection modes.TrAC Trends Anal Chem2024;181:118027

[50] Awasthi T,Joshi S.Advances in smart indicators and their integration with sensor systems for foodborne hazard monitoring.Food Control2026;183:111932

[51] Bhardwaj SK,Bhardwaj N.Recent advancements in nanomaterial based optical detection of food additives: a review.Analyst2023;148:5322-39

[52] Han J,Wei J.2D materials-based next-generation multidimensional photodetectors.Light Sci Appl2025;14:362 PMCID:PMC12514060

[53] Qiu Z.Nanostructure-based photoelectrochemical sensing platforms for biomedical applications.J Mater Chem B2020;8:2541-61

[54] Ali MA.Chemical synthesis of silicon nanosheets from layered calcium disilicide.J Phys Conf Ser2014;491:012009

[55] Hui X,Xia Q.Interface engineered Sb₂O₃/W₁₈O₄₉ heterostructure for enhanced visible-light-driven photocatalytic N₂ reduction.Chem Eng J2022;438:135485

[56] Jiang H,Wang D.Tunable type-I band alignment and electronic structure of GaSe/MoSi₂N₄ van der Waals heterostructure.Microstructures2025;5:2025009

[57] Sturala J,Matějková S.Exfoliation of Calcium germanide by alkyl halides.Chem Mater2019;31:10126-34

[58] Liu N,Lei Y.Germanene nanosheets: achieving superior sodium-ion storage via pseudointercalation reactions.Small Struct2021;2:2100041

[59] Chang C,Mu W.In situ fabrication of bismuth oxyiodide (Bi₇O₉I₃/Bi₅O₇I) n-n heterojunction for enhanced degradation of triclosan (TCS) under simulated solar light irradiation.Appl Catal B Environ2019;254:647-58

[60] Hu K,Zhou Z,Guan X.Direct Z-scheme photocatalytic systems based on vdW heterostructures for water splitting and CO₂ reduction: fundamentals and recent advances.Microstructures2024;4:2024021

[61] Kong XY,Chai S,Mohamed AR.Oxygen vacancy induced Bi₂WO₆ for the realization of photocatalytic CO₂ reduction over the full solar spectrum: from the UV to the NIR region.Chem Commun2016;52:14242-5

[62] Lu Y,Huang T.Oxygen vacancy-dependent photocatalytic activity of well-defined Bi₂Sn₂O_7-x hollow nanocubes for NO_x removal.Environ Sci Nano2021;8:1927-33

[63] Ni H,Hu Y.Two-dimensional SnSe/GeSe van der Waals heterostructure with strain-tunable electronic and optical properties.J Phys Chem Solids2019;131:223-9

[64] Ma J,Yin Z.“One stone four birds” design atom co-sharing BiOBr/Bi₂S₃ S-scheme heterojunction photothermal synergistic enhanced full-spectrum photocatalytic activity.Appl Catal B Environ Energy2024;344:123601

[65] Cultrara ND,Arguilla MQ.Synthesis of 1T, 2H, and 6R germanane polytypes.Chem Mater2018;30:1335-43

[66] Ren X,Huang Z.Environmentally robust black phosphorus nanosheets in solution: application for self-powered photodetector.Adv Funct Mater2017;27:1606834

[67] Wang B,Tang P.Graphene-like tungsten sulphide nanosheets prepared by hydrothermal intercalation/exfoliation route and its application for photodetector.Fullerenes Nanotubes Carbon Nanostruct2019;27:928-33

[68] Xie Z,Huang W.Ultrathin 2D nonlayered tellurium nanosheets: facile liquid-phase exfoliation, characterization, and photoresponse with high performance and enhanced stability.Adv Funct Mater2018;28:1705833

[69] Huang H,Li Z.Two-dimensional bismuth nanosheets as prospective photo-detector with tunable optoelectronic performance.Nanotechnology2018;29:235201

[70] Fan T,Huang W,Zhang H.Two-dimensional non-layered selenium nanoflakes: facile fabrications and applications for self-powered photo-detector.Nanotechnology2019;30:114002

[71] Li Z,Guo Z.High-performance photo-electrochemical photodetector based on liquid-exfoliated few-layered InSe nanosheets with enhanced stability.Adv Funct Mater2017;28:1705237

[72] Qiao H,Wang B,Qi X.Novel tin disulfide/graphene photoelectrochemical photodetector based on solid-state electrolytes and its performances.J Mater Sci Mater Electron2019;30:3208-13

[73] Ren X,Huang Z.Investigating the photocurrent generation and optoelectronic responsivity of WS₂-TiO₂ heterostructure.Opt Commun2018;406:118-23

[74] Lan C,Yin Y,Wang S.Synthesis of single-crystalline GeS nanoribbons for high sensitivity visible-light photodetectors.J Mater Chem C2015;3:8074-9

[75] Li Y,Lin H.Efficient visible-light induced H₂ evolution from T-Cd_xZn_1-xS/defective MoS₂ nano-hybrid with both bulk twinning homojunctions and interfacial heterostructures.Appl Catal B Environ2020;267:118702

[76] Li X,Deng F.Advances in Z-scheme and S-scheme heterojunctions for photocatalytic and photoelectrocatalytic H₂O₂ production.Chin Chem Lett2025;36:111418

[77] Chen X,Zhang Q.Z-scheme Bi₂O₃/CuBi₂O₄ heterojunction enabled sensitive photoelectrochemical detection of aflatoxin B1 for health care, the environment, and food.Biosens Bioelectron2022;214:114523

[78] Jin H,Ma X,Wei W.Enhancement of photocatalytic activity of a two-dimensional GeH/graphene heterobilayer under visible light.RSC Adv2015;5:52264-8

[79] Louafi W,Rezouali K,Lounis S.Electronic structure and elastic response of WSe₂/MoS₂ van der Waals heterostructures: effects of stacking.Comput Mater Sci2026;264:114485