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Hong Li, Ruben Canton‐Vitoria, [Yuto Urano](https://orcid.org/0009-0004-3646-2781), Sudhanshu Kumar Nayak, Eisuke Yamamoto, Makoto Kobayashi, [Ryo Kitaura](https://orcid.org/0000-0001-8108-109X), [Minoru Osada](https://orcid.org/0000-0002-6439-8068)

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[Covalent Functionalization of MXenes with Porphyrin for Visible‐Light Activation in Energy Conversion Nanodevices](https://mdr.nims.go.jp/datasets/a819a95d-7462-4715-932f-740645fe1656)

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Covalent Functionalization of MXenes with Porphyrin for Visible‐Light Activation in Energy Conversion NanodevicesRESEARCH ARTICLEwww.small-journal.comCovalent Functionalization of MXenes with Porphyrin forVisible-Light Activation in Energy Conversion NanodevicesHong Li, Ruben Canton-Vitoria,* Yuto Urano, Sudhanshu Kumar Nayak,Eisuke Yamamoto, Makoto Kobayashi, Ryo Kitaura, and Minoru Osada*MXenes such as Ti3C2 and Ti3CN are 2D materials characterized by thepresence of a Tx phase that passivates the reactive titanium surface.Modifying their chemical composition to anchor target molecules is of greatinterest for addressing key challenges, such as enhancing the conversion ofvisible light into electricity. In this study, a covalent functionalization strategyis developed to modify the Tx phase of Ti3C2 or Ti3CN with alkyl amines,followed by coupling with Zn-porphyrin. This process activates the opticalproperties of MXenes without causing any damage. X-ray photoelectronspectroscopy and infrared spectroscopy are pivotal in confirming the covalentfunctionalization, while thermogravimetric analysis, transmission electronmicroscopy, and additional techniques provided further insights intostructural and chemical features. Spectroelectrochemical investigations revealcarrier injection into MXenes under light illumination, potentially enhancingconductivity. Photodetectors fabricated from these films demonstrateresponsivities of 1.4–15.0 A W−1 and external quantum efficiencies rangingfrom 1300 to 2830% in the visible range, making them comparable towell-established hybrid 2D nanomaterials like MoS2 and WS2.1. IntroductionMXenes represent a rapidly emerging class of 2D materials.Ti3C2, the most widely studied MXene, consists of three atom-ically thin titanium layers interleaved with two atomically thincarbon layers, each plane exhibiting a hexagonal honeycombstructure. Ti3C2 exhibits metallic behavior, characterized by aH. Li, R. Canton-Vitoria, E. Yamamoto, M. Kobayashi, M. OsadaDepartment of Materials Chemistry & Institute of Materials and Systemsfor Sustainability (IMaSS)Nagoya UniversityNagoya 464–8601, JapanE-mail: rcanton@imass.nagoya-u.ac.jp;mosada@imass.nagoya-u.ac.jpR. Canton-VitoriaJoining andWeldingResearch InstituteOsakaUniversityOsaka 567-0047, JapanThe ORCID identification number(s) for the author(s) of this articlecan be found under https://doi.org/10.1002/smll.202503895© 2025 The Author(s). Small published by Wiley-VCH GmbH. This is anopen access article under the terms of the Creative Commons AttributionLicense, which permits use, distribution and reproduction in anymedium, provided the original work is properly cited.DOI: 10.1002/smll.202503895low recombination rate of photoactivatedelectron–hole (e−–h+) pairs[1] and excep-tional electrical conductivity of 2.4 × 106 Sm−1,[2,3] nearly twice that of graphene.[4,5]On the other hand, Ti3CN is semiconduct-ing, with a bandgap of 1.16 eV[6] and aconductivity of 2.5 × 105 S m−1, millionsof times greater[7,8] than that of MoSe2[9,10]or MoS2.[11] MXenes are also known fortheir excellent solubility and rich sur-face chemistry, making them applicableacross a wide range of fields, includingenergy storage[12,13] catalysis,[14,15] electro-magnetic interference shielding,[16,17]medicine,[18,19] and electronics.[20,21]Modification of the MXene surface is ofgreat interest, as it allows control over keyproperties. The Tx phase passivates the ti-tanium planes and is easily tunable, en-abling the presence of different functionalgroups such as─OH,─F,─S, or─N, whichenrich the chemistry and capabilities ofMXenes. Covalent functionalization offersthe advantage of creating a robust connection between 2D nano-materials and target components, enabling atomic-level contactbetween the two species. Unlike other 2D materials such asgraphene, where sp2 carbon must be converted to sp3 duringchemical modification,[22] the Tx phase of MXenes allows forcovalent functionalization without damaging the basal plane.However, the covalent modification of MXenes is limited to fiveY. Urano, S. K. Nayak, R. Kitaura, M. OsadaInternational Center for Materials NanoarchitectonicsNational Institute for Materials Science1-1 Namiki, Tsukuba 305-0044, JapanS. K. NayakUltrafast Photophysics and Photonics LaboratoryDepartment of PhysicsIndian Institute of Technology HyderabadTelangana, Kandi 502285, IndiaM. OsadaResearch Institute for Quantum and Chemical InnovationInstitutes of Innovation for Future SocietyNagoya UniversityNagoya 464–8601, JapanSmall 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (1 of 15)http://www.small-journal.commailto:rcanton@imass.nagoya-u.ac.jpmailto:mosada@imass.nagoya-u.ac.jphttps://doi.org/10.1002/smll.202503895http://creativecommons.org/licenses/by/4.0/http://crossmark.crossref.org/dialog/?doi=10.1002%2Fsmll.202503895&domain=pdf&date_stamp=2025-08-03www.advancedsciencenews.com www.small-journal.comFigure 1. Reaction route for MXene a3 and b3 hybrid materials.main reactions: phosphate,[23,24] carboxylate,[25,26] silane,[27,28] di-azonium salt,[29,30] and amination,[31] in addition to polymeriza-tion reactions.[32,33] While these approaches are well-established,a lack of simple characterization techniques that can definitivelyconfirm the formation of covalent bonds remains a challenge. In-deed, the new Ti─O bonds are difficult to distinguish from thosealready present in the Tx phase in techniques such as X-ray pho-toelectron spectroscopy (XPS), necessitating the use of more ad-vanced techniques as high-resolution transmission electron mi-croscopy (TEM). Only amination, a recently developed technique,has been shown to form a distinguishable Ti─N bond while pre-serving the surface of MXenes, therefore facilitating the use ofstraightforward characterization techniques.[31] However, the po-tential of diamines has not yet been fully exploited. The bifunc-tionality of diamines provides anchoring points for more com-plex functional groups, such as chromophores, enabling precisecontrol over MXenes’ optoelectronic properties.In its pure form, Ti3C2 and Ti3CN are not optically active.However, slight modifications, such as controlling the functionalgroups in the Tx layer with groups like ─OH or ─F, can open anindirect bandgap in Ti3C2 and tune that of Ti3CN.[1–3] Further-more, hybridization with target inorganic materials can activatetheir photoactive properties.[34] For example, Ti3C2 functional-ized with TiO2 has achieved responsivities of 202 A W−1 underUV irradiation, but its response is limited under visible light.[35]Other 2D materials, such as graphene, MoS2, or WS2, havealso improved their optical performance after functionalizationwith chromophores like porphyrin.[36] While light-conversionapplications,[37–40] like photocatalysis,[41–43] have been explored,the development of MXenes-based photosensors functionalizedwith photoactive molecules remains scarce. It is expected thatchromophores will activate the optical properties of MXenes bytransferring excitonic species and enhancing the number of car-riers. Then, the electron–hole pairs will have a lower recombina-tion ratio compared to materials with a direct bandgap. Hence,MXenes functionalized with chromophores might compete withother exceptional optically active 2D hybrids, such as transitionmetal dichalcogenides,[44,45] in the field of nanotechnology.In this study, we investigate the covalent functionalization ofTi3C2 and Ti3CN by introducing alkyl diamines to the Tx phase,which subsequently react with porphyrins via amidation to formphotoactive hybrid materials. The loading of organic species iscontrolled using techniques like the Kaiser test and thermogravi-metric analysis (TGA), while the covalent functionalization isconfirmed by X-ray photoelectron spectroscopy. Additionally, in-frared (IR) spectroscopy confirms the formation of amide bondsand ensures the complete removal of non-covalent species. X-raydiffraction (XRD) demonstrates layer-by-layer functionalization,and TEM reveals the atomic structure. Optical and electrochemi-cal studies show that charge carriers are introduced to Ti3C2 andTi3CN through electron and hole transfer events from the por-phyrins upon light irradiation, a key process explaining the ex-ceptional performance of the resulting photodevices across thefull visible spectrum.2. Results and Discussion2.1. Synthesis and CharacterizationTi3AlC2 and Ti3AlCN MAX phases were etched with ethane-1,2-diaminium difluoride salt mixed in HCl (12 m) for 12 h at60 °C. During this process, F− ions released from the nitro-gen salts attack the aluminum of Ti3AlC2 and Ti3AlCN. As aresult, the atomic Al layer undergoes oxidation, and hydrogenbubbles are observed. This etching process exposes an uncoor-dinated Ti layer, which can react with H2O molecules as well aswith Cl− or F−. Similar reactions have been observed in MAXphases and other molten salts like NH4F, LiF, or NaF.[46–48] How-ever, in this reaction, ethane-1,2-diaminium difluoride salt alsoreleases amines that can further react with Ti. After filtrationand pH-neutralization with trimethylamine, the surfaces of thelayered nanosheets Ti3C2Tx (a1) and Ti3CNTx (b1) contain pri-mary amines linked to the nanosheets, which are capable ofundergoing typical organic chemistry reactions. The presenceof the primary amines in Ti3C2Tx and Ti3CNTx was evidencedby the Kaiser test, showing loadings of 141 and 120 μmol g−1,Small 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (2 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 2. XPS spectra of Ti 2p for a) pristine Ti3AlCN and b) b2. c) N 1s (left) and C 1s (right) for pristine Ti3AlCN (bottom), b2 (middle) and b3 (top).d) Zn 2p for pristine Ti3AlCN b3.respectively. These Kaiser test values were notably high, consis-tent with other covalent functionalization techniques employedwith graphene.[49]One of the main goals in this study was to achieve the highestpossible amine loading to homogenize the Tx layer andminimizesecondary reactions in subsequent steps. Therefore, to increasethe level of free amines, a second reaction was performed withethylenediamine (EDA) at 75 °C, which served as both solventand reactant (Figure 1). Due to the greater stability of Ti-aminebonds compared to Ti─OH, Ti─F, or Ti─Cl bonds,[31,50] the sur-face of the Tx phase was exchanged to contain a larger numberof free amines, resulting in Ti3C2TNH2 (a2) and Ti3CNTNH2 (b2),with Kaiser test values of 370 and 307 μmol g‒1, respectively. Theamines on nanosheets a2 and b2 can react with the carboxylicacid group in target molecules, such as 5-(4-carboxyphenyl)-10,15,20-(triphenyl) porphyrin Zn2+ (ZnP), through amination.This reaction used N,N′-Dicyclohexylcarbodiimide (DCC) and4-Dimethylaminopyridine (DMAP) as coupling agents, yieldingthe hybrid materials Ti3C2TZnP (a3) and Ti3CNTZnP (b3). The firstevidence of functionalization came from the Kaiser test, whichshowed a decrease in amine loading from 370 and 307 μmol g‒1in a2 and b2 to 40 and 72 μmol g‒1 in a3 and b3, respectively (seeSection 4 Experimental Section).XPS proved indispensable for characterizing the bonding na-ture of the materials, revealing the formation of Ti‒N bonds fora2 and b2, and amide carbonyl groups for hybrid materials a3and b3 (Figure 2; Figure S1, Supporting Information). Initially,the Ti 2p spectra of Ti3AlCN can be deconvoluted into signa-tures at 462.55, 461.05, and 460.20 eV, corresponding to 2p1/2levels.[51,52] These signatures can be assigned to various bonds,including Ti‒N and Ti‒C, all appearing as doublets in the 2p3/2level, with binding energy separations of ≈5.65 eV, observed at456.80, 455.25, and 454.50 eV, respectively. However, we focus onthe signatures at 458.75 and 452.7 eV, which correspond to Ti‒Albonds.[53] In a2 and b2, the Ti‒Al bands significantly decrease,ensuring the chemical etching while new Ti‒N signatures appearat 460.45 and 454.75 eV, suggesting the successful formation ofa covalent bond between Ti and the amine (Figure 2a,b; FigureS1a,b, Supporting Information).[31] No significant changes in theTi 2p1/2 and 2p3/2 levels are observed when comparing b2 and b3with a3 or b3 (Figure S2, Supporting Information). The identicalspectra confirm that the Ti─N bond persists after the reaction,while the Ti─O band remains weak, indicating that no degrada-tion occurred during the reaction process.Next, the N 1s spectrum of Ti3AlCN shows negligible organicderivative signatures, with a peak at 393.45 eV correspondingto the graphenic nitrogen plane. The addition of amines in b2significantly increases the presence of NH and NH2 bonds at398.35 and 400.01 eV, respectively, confirming the incorpora-tion of EDA molecules (Figure 2c). Although direct evidence forSmall 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (3 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 3. IR spectra for a) Ti3AlC2 (gray), a1 (black), a2 (blue), a3 (red), EDA (purple), and ZnP (green), and b) Ti3AlCN (gray), b1 (black), b2 (blue),and b3 (red). Thermographs for c) Ti3AlC2 (gray), a1 (black), a2 (blue), a3 (red), and d) Ti3AlCN (gray), b1 (black), b2 (blue), and b3 (red).covalent functionalization between the amines and Ti3CN via ni-trogen is lacking, the low boiling point of EDA and the vacuumconditions of the XPS analysis (8 × 10−8 Torr) suggest sufficientinteraction between the amines and Ti3CN to prevent evapora-tion during the XPS analysis. For Ti3C2 in a2, a weak but dis-cernible band at 394.65 eV, similar to that observed in Ti3CN, ap-pears, supporting the formation of a new Ti−N covalent bond(Figure S1c, Supporting Information).[54] After the addition ofporphyrin in b3, new bands corresponding to amide (N─C═O)bonds were recorded at 401.23 eV, confirming the success of thecoupling reaction.[55] The C 1s spectra of hybrid materials a3 andb3 were also relevant (Figure 2c; Figure S1c, Supporting Infor-mation). First, pristine Ti3AlC2 exhibits signatures at 283.5 and279.9 eV, attributed to the presence of Ti─C─Ti and C─Ti─Nbonding, which persist in the spectra of a2 and b2.[54,56] Theseinteractions are highly predominant, masking signatures asso-ciated with organic species. However, the emergence of a newband at 286.95 eV suggests the presence of an N─C═O bond, fur-ther supporting the covalent linkage between the amines and theporphyrin. Finally, the Zn 2p1/2 and Zn 2p3/2 binding energies at1043.5 and 1020.3 eV, respectively, confirm the presence of ZnPin hybrid materials b3 and a3 (Figure 2d; Figure S1d, SupportingInformation).IR spectroscopy is highly useful for evaluating the organicmoi-eties within hybrid materials (Figure 3a,b). First, Ti3AlC2 andTi3AlCN MAX phases showed negligible characteristic IR signa-tures, whereas the nanosheets a1 and b1 exhibited themoieties at3455 and 3439 cm−1, associated with O─H and N─H vibrations,alongside the presence of C─H moieties at the 2700–3000 cm−1range. The C─H signatures were more pronounced in a2 andb2, as the O─H loading decreased in comparison with new alkylamines. Additionally, new bands at 1557 and 1554 cm−1, charac-teristic of EDA-like moieties, were observed. Hybrid materials a3and b3 are further characterized by the presence of amide sig-natures, at 1630 and 1572 cm−1 for a3 and 1632 and 1577 cm−1for b3, providing conclusive evidence for covalent linkage withZnP. The absence of the band at 1701 cm‒1, which correspondsto the carboxylic acid of pristine ZnP, confirms that the hybridmaterials a3 and b3 are free of non-covalent species.Raman spectroscopy was used to analyze the vibronic fea-tures of the MXene nanosheets of a1–3 and b1–3 (Figure S3a,b,Supporting Information). Initially, the MAX phases showed nopredominant peaks, whereas the nanosheets a1 and b1 exhib-ited similar signatures at 155, 259, 410, 608, 1338, 1592, 2976,3229, and 3320 cm−1. The peak at 155 cm−1 corresponds tothe doubly degenerated (Eg) mode for the in-plane surface Tivibrations,[57,58] while the peak at 608 cm−1 is associated withTi─C[50] and Ti─N[59] vibrations. In contrast, the peaks at 258 and410 cm−1 are related to the Tx layer,[60] suggesting the presenceof Ti─F, Ti─O[60] and Ti─N[7] bonds, and the peaks at 1338 and1592 cm−1 are indicative of a carbon pseudo-graphenic layer.[61,62]Finally, the bands between 2900 and 3400 cm−1 are attributed tothe alkyl chain of amines.[63,64] The intensity of the alkyl chainpeaks in a2 and b2, compared to the Eg mode, is higher than inSmall 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (4 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.coma1 and b1, indicating a greater content of amines. The variationsin intensity between the bands at 259–608 cm−1 in hybridmateri-als a3 and b3may be due to modifications of the Tx layer, such asthe transformation from amine to amide and basal functionaliza-tion with ZnP. The absence of shifts in the Eg mode (155 cm−1) orany other signatures in hybrid materials a3 or b3 suggests mini-mal impact on the vibrational structure of Ti3C2Tx and Ti3CNTxnanosheets.The XRD patterns of Ti3AlC2 and Ti3AlCN (Figure S3c,d, Sup-porting Information) show peaks at 9.54° and 9.59°, which shiftto lower angles in a2 and b2, reaching angles of 6.44° and 6.28°.This suggests an expansion of the interlayer spacing. Accordingto Bragg’s formula, the interlayer spacing increases from 9.26and 9.21 Å in Ti3AlC2 and Ti3AlCN to 13.71 and 13.62 Å in a2and b2, further expanding to 14.15 Å in both hybrid materials a3and b3. The slight increase in spacing of a3 and b3 indicates thatthe porphyrin skeleton is strongly attracted to the basal plane ofthe MXenes, maximizing the interaction between the 𝜋 orbitalsof the porphyrin, the d-orbitals of Zn, and the d-orbitals of Ti,both being perpendicular to the basal plane. This enhanced in-teraction is facilitated by the flexibility of the amines, allowingmore intimate contact compared to other covalent functionaliza-tion methods, such as those performed via diazonium salts, inwhich porphyrins interact perpendicularly with the basal planeof the MXene, thereby limiting 𝜋–d orbital hybridization.[29,38]TGA was used to determine the loading of organic addendswithin all the functionalized materials (Figure 3c,d). The Ti3AlC2and Ti3AlCN MAX phases remained stable in the temperaturerange of 100–600 °C under a nitrogen atmosphere. Nanosheetsa1 and b1 showed a mass loss between 150 and 500 °C of 1.69%and 1.99%, respectively, which can be attributed to the degrada-tion of the organic and oxygen species in the Tx layer. The levelof functionalization increases in a2 and b2, with a mass loss of5.29% and 5.59%, respectively, which further rises to 9.84% and12.32% in hybridmaterials a3 and b3. These results indicate a rel-atively high degree of functionalization, with a value of one EDA-like functional group per 6.4 and 5.9 units of Ti3C2 or Ti3CN fora2 and b2, and one ZnP per 41.8 and 32.1 units of Ti3C2 or Ti3CNfor a3 and b3, respectively. Since a single ZnP covers ≈7 units ofa single face of Ti3C2 or Ti3CN, we can estimate a total surfacecoverage of 8.4% and 10.9% for a3 and b3, in the same order.The morphologies of the hybrid materials a3 and b3 wereexamined using TEM equipped with energy-dispersive spec-troscopy (EDS), as shown in Figures 4a–f and S4 (SupportingInformation), respectively. Both hybrid materials exhibited semi-transparent areas, suggesting the presence of aggregated single-or few-layered structures (Figure 4a; Figure S4a, Supporting In-formation). High-magnification images (Figure 4b; Figure S4b,Supporting Information) revealed a lattice structure resemblinggraphene, primarily composed of three stacked Ti planes—theheaviest element present—while N and C planes were essen-tially invisible. The exposed Ti surface showed no holes, ensur-ing a high-quality material. Fast Fourier Transform (FFT) anal-ysis revealed a hexagonal pattern consistent with a graphene-like lattice, characterized by a well-compact, zero-degree layeredstructure or a single layer (Figure 4c) and showing a Ti-Ti dis-tances of 2.7 Å. Notably, stains with a few nanometers squaredistributed around the sample were observed. These might cor-respond to areas enriched with amines or porphyrin,[65] a hy-pothesis further supported by the EDS mappings. The EDSmappings confirmed a relatively uniform distribution of ele-ments such as Ti, O, and Zn throughout the lattice of hybridmaterials a3 and b3 (Figure 4d–f; Figure S4c–e, SupportingInformation).SEM was further employed to analyze the morphologies ofa1, a2, a3 and b1, b2, b3 (Figures S5 and S6, Supporting Infor-mation). The MAX phases exhibited a uniform surface, whereasstacked layers became distinguishable after the etching processin a1 and b1, forming the typical accordion-like structure charac-teristic of MXenes. Additionally, all the materials (a1, a2, a3, andb1, b2, b3) showed a range of sizes, from 0.1 to 10 μm in length,with varying numbers of layers, from a few to multiple. Focus-ing on the most relevant changes in the EDS spectral mappings,the intensities of the Al K𝛼 peak in Ti3AlC2 and Ti3AlCN clearlydecreased in a1 and b1 (Figures S5e,f and S6e,f, Supporting Infor-mation). Spectral mappings of a2 and b2 revealed the presenceof N K𝛼, while those of hybrid materials a3 and b3 showed theZn K𝛼 peak, confirming the high N and Zn content throughoutthe flakes (Figures S5g,h and Figure S6g,h, Supporting Informa-tion). The EDS spectra (Figure 4g,h) further support these ob-servations. Specifically, Ti3AlC2 and Ti3AlCN exhibited an Al K𝛼peak at 1.48 keV, which was completely absent in a1 and b1, whilethe Ti K𝛼 peak at 4.50 keV remained. Light atoms, such as C K𝛼and N K𝛼, which contain peaks at 0.28 and 0.39 keV, respectively,are usually measured with low precision by EDX. Keeping thislimitation in mind, it is still valuable to observe the changes, asthey can provide qualitative information about each reaction car-ried out in the MXenes. For pristine materials, their signaturesare relatively small because the titanium plane shields the innerlayers. Nevertheless, both components are detected in a1 and b1,indicating the presence of amines on the surface, which becomemore pronounced in a2 and b2. Additionally, hybrid materials a3and b3 exhibited a new Zn K𝛼 peak at 1.03 keV, accompaniedby increased intensities of the C K𝛼 and O K𝛼 signatures, con-firming the presence of porphyrin. These results demonstratethat amines in a2 and b2 and Zn-porphyrin in a3 and b3 are ran-domly distributed across the entire surface of Ti3C2 and Ti3CN,respectively. Finally, atomic force microscopy (AFM) analysis ofisolated layers of a3 revealed a predominant population of layerswith a thickness of 1.5 nm, while those exceeding 5 nm were inthe minority. Since a single layer of Ti3C2 functionalized on bothsides is expected to have a thickness of 1.5 nm, this confirms thepresence of a large population of single layers (see Figure S5i–l,Supporting Information).2.2. Optical and Electronic PropertiesAt this stage, we can confidently confirm that the hybrid mate-rials are based on MXenes covalently functionalized with por-phyrin, ensuring significant preservation of the basal plane whileachieving substantial porphyrin loading. ZnP is a photoactivemolecule characterized by strong absorption and high quantumyield efficiency,[36,66] commonly transferring excitonic speciessuch as electrons to 2D materials like graphene,[22] therebyenhancing their optical performance. These studies are typi-cally performed in liquid media, where a covalent bond is cru-cial to ensure stable contact between the two species whileSmall 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (5 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 4. a,b) Low and high magnification TEM images of a hybrid material a3. c) FFT pattern of a hybrid material a3. d–f) EDS mappings of N, Zn, andTi core levels in the TEM image (a). g) EDS spectra of Ti3AlC2 (gray), a1 (black), a2 (blue), a3 (red). h) EDS spectra of Ti3AlCN (gray), b1 (black), b2(blue), and b3 (red).minimizing ZnP 𝜋–𝜋 interactions or aggregation. Therefore, ournext goal is to carefully analyze the optical and electronic prop-erties of the hybrid materials to understand the orbital interac-tions between the species and how the system responds to lightstimuli.Figure 5a,b displays the UV‒vis absorption spectra of the hy-brid materials a3 and b3. ZnP exhibited three peaks at 426.4,558.2, and 599.8 nm, corresponding to the Soret band and twoQ-bands of ZnP, respectively. In contrast, a2 and b2 show consis-tent absorption across the full spectrum. The spectra of a3 andb3 represent a superposition of both, with negligible changes inintensity or peak shifts.PL emission under equal optical concentrations (Figure 5c,d),meaning the same amount of excitonic species, showeddistinctive peaks at 607.0 and 660.5 nm for ZnP. These peaksare significantly quenched in a3 and b3, and variations in thespectral shape suggest that excitonic species may be transferredfrom ZnP to Ti3C2 or Ti3CN. Moreover, the fluorescence quan-tum yield (𝜑f) of free ZnP, initially 3.1%, decreased to 1.3% and1.2% in a3 and b3, respectively. In short, the 𝜑f values were de-termined by comparing the linear slope of absorbance versus PLat different concentrations.To fully prove that PL quenching is related to the direct in-teraction with MXenes, fluorescence lifetime experiments wereperformed. Pristine ZnP exhibits a monoexponential decay witha lifetime of 1.75 ns, whereas materials a3 and b3 show a fasterdecay, better fitting a biexponentialmodel, with fast decay compo-nents of 0.30 and 0.26 ns, respectively (see inset in Figure S5c,d,Supporting Information). By employing Equations (1 and 2),we evaluated the quenching rate constant Ksq and the quan-tum yield qs of the singlet excited state, obtaining values of2.76 and 3.27 ns−1 and 83% and 85%, respectively. Therefore,these data confirm the photogenerated charge transfer from ZnPto MXenes.Ksq =1Tf− 1To(1)Small 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (6 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 5. UV‒vis spectra a) ZnP (green), a1 (black), a2 (blue), a3 (red), and b) ZnP (green), b1 (black), b2 (blue), b3 (red), and PL emission spectra(exc. 420 nm) of c) ZnP (green), a1 (black), a2 (blue) and a3 (red), and d) ZnP (green), b1 (black), b2 (blue), b3 (red) in dimethylacetamide. Lifetimes of(Inset c) ZnP (green), a3 (red), and IRF (gray), and (Inset d) ZnP (green), a3 (red), and IRF (gray). Cyclic voltammetry of e) ZnP (green), a2 (blue) anda3 (red), and f) ZnP (green), b2 (blue) and b3 (red). CV was performed in acetonitrile using tetrabutylammonium hexafluorophosphate (TBAPF6) 0.1 mas the electrolyte. The working, reference, and counter electrodes were glassy carbon, Pt-mesh, and Pt-wire, respectively, with a scan rate of 25 mV s‒1.qs (%) = 100 × Ksq × Tf (2)where Tf and To refer, in the same order, to the lifetime of thefast-decaying in a3 or b3 and free ZnP components.Cyclic voltammograms (CV) for a1, a2, a3 and b1, b2, b3 areshown in Figure 5e,f. The CV data provides valuable insights intothe oxidation and reduction potentials of the materials, identify-ing the regions where holes or electrons can be accommodated,respectively. All oxidative and reductive potentials are reportedversus ferrocene /ferrocenium (Fc/Fc+ = 0.0 V) redox couple andare summarized in Table S1 (Supporting Information). It is wellestablished that the first oxidative and reductive potentials are di-rectly correlated with the positions of the HOMO and LUMO,respectively, allowing a straightforward conversion from volts toSmall 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (7 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comelectron volts (eV), since the Fermi level of Fc/Fc+ correspondsto ‒4.8 eV on the vacuum energy scale (Equations S2 and S3,Supporting Information). For free ZnP, the first oxidative andreductive potentials were 0.58 and ‒1.55 V, respectively, corre-sponding to a bandgap (BG) of 2.13 eV. This BG value alignsclosely with the PL emission of porphyrin at 607 nm (2.05 eV).Additionally, applying the second reductive potential gives an en-ergy of 2.95 eV, which is related to the absorption of the Soretband of porphyrin at 426 nm (2.92 eV), consistent with reportsin the literature.[66] Ti3C2-based materials, such as a2 and a3,were metallic, but the addition of functionalities, such as nitro-gen derivatives, disrupts these properties, resulting in the open-ing of a bandgap.[67] This behavior has been widely reportedfor other 2D materials, including graphene,[68] MoS2,[69] WS2,[70]MoSe2,[71] and MXenes,[72,73] such as other Ti3C2 systems.[74]For a2, the first oxidation and reduction potentials were locatedat 0.05 and ‒1.02 V, respectively, corresponding to the conduc-tion band minimum (CBM) and valence band maximum (VBM),yielding a BG of 1.07 eV. Ti3CN has an indirect bandgap with a re-ported BG value of 1.16 eV,[7] which can also be tailored by the Txphase. b2, with an increased nitrogen content, exhibited slightlyhigher oxidation and reduction potentials at 0.32 and ‒1.15 V, re-spectively, yielding a BG of 1.43 eV. The cyclic voltammetry of a3and b3 does not reflect a simple superposition of the ZnP andMXene signatures, likely due to strong orbital overlap betweenthe ZnP and MXene. In fact, the ZnP signals appear smooth andare difficult to distinguish. However, the absence of significantshifts in the UV‒vis or PL spectra suggests minimal energeticvariation in the ZnP orbitals. For instance, the only discerniblepeak of ZnP in a3was located at 0.48 eV, which is 0.1 V lower thanthat of free porphyrin and within the margin of error (± 0.2 V).Regarding the nanosheets, the variations observed in a3 and b3,compared to a2 and b2, suggest an orbital rearrangement in theMXenes, primarily lowering the ground states. While a3 retainsa narrow bandgap of 1.43 eV, the BG of b3 expands to 2.14 eV.A vacuum energy diagram can be constructed, positioning theHOMO and LUMO of ZnP as well as the CBM and VBM of Ti3C2and Ti3CNwithin a3 and b3 (Figure S7, Supporting Information).Additionally, films of a3 and b3 were deposited on a goldsubstrate and analyzed using ultraviolet photoelectron spec-troscopy (UPS) and low-energy inverse photoelectron spec-troscopy (LEIPS), which further confirmed the positions of theCBM and VBM for Ti3C2 and Ti3CN (Figure S8, Supporting In-formation). When comparing UPS and LEIPS values by employ-ing Equations S4 and S5 (Supporting Information) with the ox-idative and reductive potentials obtained by CV, no shifts greaterthan 0.23 eV were observed (Figure S7, Supporting Information).Indeed, the agreement between these techniques increases thereliability of our findings. The orbital diagrams suggest a type-Ialignment for the hybrid material a3. For b3, a type-II alignmentwas initially observed, but the presence of trap states results intype-I alignment behavior instead. Inmore detail, trap states orig-inating from the pristine Ti3CN are expected to spread across theenergy levels, accommodating holes or electrons depending onwhether they lie above or below the Fermi level, respectively. TheUPS binding energy diagram displays a small but constant cur-rent up to the Fermi level, a trend also reflected in the valenceband energies and CV. Additionally, TEM images (Figure 4b)highlight nanometric regions with varied functionalization, sug-gesting the presence of areas that may still exhibit characteris-tics of the pristine material. These regions are likely responsiblefor creating a few, but significant trap states within the material.This analysis provides a critical foundation for interpreting the re-sults discussed in the subsequent spectroelectrochemical (SEC)experiments.SEC assays were performed to further confirm the effect oflight on the electronic states of ZnP, Ti3C2, and Ti3CN. The ab-sorption spectra of free porphyrin exhibit a similar trend un-der different potentials when compared to a3 and b3, suggest-ing limited interaction between the different species (FigureS9, Supporting Information). Interestingly, the PL emission offree porphyrin decreases under positive or negative voltage,whereas it increases in a3 and b3 (Figure 6). In the absenceof applied potential, the photogenerated holes and electrons offree porphyrin recombine effectively, without significant inter-actions with external species, resulting in strong PL emission(Figure S10a, Supporting Information). For hybrid materials a3and b3, the photoexcited electrons in the LUMO of porphyrincan transfer to the CBM of MXenes, while the photogener-ated holes in the HOMO of porphyrin transfer to the VBM ofMXenes, consistent with a type-I alignment in both materials(Figure 7a).Under positive voltage, the Fermi level of the system is low-ered, quenching the PL emission of free ZnP by transferring elec-trons to the surrounding environment (Figure S10b, SupportingInformation). In the hybrid materials, lowering the Fermi leveldepletes electrons associated with the VBM and/or trap states ofMXenes in a3 and b3, resulting in a reduction of hole-electronrecombination events between the HOMO of ZnP and Ti3C2 orTi3CN (Figure 7b). Conversely, under negative voltages, the Fermilevel is elevated. For free ZnP, this leads to PL quenching due tohole transfer to the environment (Figure S10c, Supporting In-formation). However, in a3 and b3, the trap states and CBM ofTi3C2 or Ti3CN become enriched with electrons, preventing re-combination of the electrons in the LUMO of porphyrin with theexcited states of MXenes (Figure 7c). It should be mentioned thatthe voltage-dependent behavior observed in free porphyrin alsoinfluences ZnP within a3 and b3. However, the interactions be-tween MXenes and ZnP predominate due to the covalent link-age, ensuring consistent and close interaction between the twospecies. In summary, UV‒vis, PL, CV, UPS, and LEIPS providein-depth information about the band structure of thesematerials,suggesting a type-I behavior alignment in both a3 and b3. Whiledirect evidence of energy transfer between ZnP and MXenesremains inconclusive, the SEC experiments confirm electronand hole transfer from porphyrin to Ti3C2 and Ti3CN within a3and b3.2.3. Photo-Device ApplicationsSo far, we have demonstrated the covalent functionalization reac-tion between ZnP and MXenes in a two-step process. This func-tionalization occurs on the basal plane, layer-by-layer, enhanc-ing the interaction between both components. We then investi-gated the optical and electronic interaction of ZnPwith Ti3C2 andTi3CN, which results in a type-I band alignment. In this configu-ration, ZnP facilitates the transfer of holes and electrons, therebySmall 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (8 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 6. PL emission intensity under crescent voltages from 0 to 2 V for a) free ZnP, c) a3, and e) b3, and decrescent from 0 to ‒2 V for b) free ZnP, d)a3, and f) b3, in DMAc by employing 0.1 m of TBAPF6.Small 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (9 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 7. Carrier transfer process from ZnP to a3 or b3 under a) 0 V, b) positive, and c) negative voltage.enhancing the carriers of the hybrid materials. The next logicalstep is to explore an application where the new properties of a3and b3materials are relevant. To this end, we can develop photo-sensors based on ultrathin layers and analyze the photo-response(Equation S6, Supporting Information), responsivity (EquationS7, Supporting Information), external quantum efficiency (Equa-tion S8, Supporting Information), specific detectivity (EquationS9, Supporting Information), and superficial conductivity (Equa-tion S10, Supporting Information).Regarding device fabrication, the spontaneous assemblytechnique[75] outperforms Langmuir-Blodgett[76] or single-droplet.[77] The optimal conditions are described in theSupporting Information. It should be noted that when filmsbased on pristine materials (a2 or b2) undergo functionaliza-tion, only the first layer of the nanofilm can be decorated withporphyrin, leaving the inner layers unaffected. This limitationcompromises one of the key advantages of covalent functional-ization, namely, layer-by-layer functionalization. Therefore, thedevices were constructed directly with a3 and b3. On the otherhand, an accurate comparison between pristine and functional-ized materials requires evaluating the same device before andafter functionalization, which is not feasible in this study. Toaddress this limitation, several devices of 50 pairs of electrodes,each with the same dimensions (50 μm channel width and100 μm length), were fabricated for a2, b2, a3, and b3. All devicesexhibited similar thicknesses, proximately 5 nm, and comparablequality, with 99.20% surface coverage, as evaluated using opticalmicroscopy, AFM, and SEM (Figure 8). Devices constructed witha3 achieved dark currents of 1.7 μA (8.4 nS sq‒1), while thosewith b3 reached 9.0 μA (45 nS sq‒1). In contrast, devices basedon a2 and b2 demonstrated consistently poor performance, withcurrents in the fA range, as illustrated in Figure S11 (SupportingInformation).Next, the optical activity of devices based on a3 and b3 wasevaluated under various light sources, including UV-B (254 nm;4.8 eV), UV-A (365 nm; 3.41 eV), blue (442 nm; 2.81 eV), green(532 nm; 2.34 eV), red (593 nm; 2.10 eV), and white light, withincident powers of 0.9, 40, 10, 13, 6 and 31 mW cm‒2, respec-tively. While pronounced photo-responses were observed fromUV-A to red wavelengths for a3 and b3 (Figure 9a; Figure S12,Supporting Information), a2 and b2 showed no optical perfor-mance (Figure S13, Supporting Information). Moreover, hybridmaterials a3 and b3 demonstratedminimal drift over several lightpulses (3 min), ensuring high system stability for extended peri-ods up to 4 h. Although instrument limitations prevented pre-cise measurement, the photo-response times and recovery timeswere estimated to be below 1 s. As illustrated in Figure 9a, the ro-bust photo-response, with on-off ratios superior to 25-fold, high-lights the potential of these materials as efficient photosensors.For comparison purposes, Figure 9b shows the normalized pho-toresponse against the incident light power, clearly demonstrat-ing enhanced performance in the visible region.Further insights were obtained through responsivity and spe-cific detectivity measurements (Figure 9c,d). Porphyrin-basedMXenes exhibited a significant improvement in the visible re-gion compared to pristine materials (Figure 9; Figures S12 andS13, Supporting Information). The responsivity and specific de-tectivity values for a3 and b3 ranged from 1.40 to 15.0 A W‒1 and3.0–23.0 × 1010 Jones under any wavelength within the visiblerange. Material a3 exhibited equal responsivity and specific de-tectivity under UV-A and red light, with values of 3.50 AW‒1 and9.4 × 1010 Jones, respectively, which are close to those for greenand blue light. For material b3, red light showed the best perfor-mance, reaching values of 15.0 A W‒1 and 23.0 × 1010 Jones. No-tably, b3 under blue and red irradiation surpassed the responsiv-ity and specific detectivity values of UV-A by ≈20% and 30%, re-spectively. The strong light response observed in our instrumentmay result from a combination of factors, making it difficult topinpoint a single cause. Nonetheless, we have analyzed the dataand propose a plausible hypothesis, which should be consideredas an interpretation rather than a conclusive fact. Focusing onhybrid material b3, the highest responsivity was observed underred light (2.10 eV), close to the Ti3CN bandgap within b3, pre-viously calculated as 2.14 eV, likely enhanced by the Q band ofporphyrin at 599 nm (2.08 eV). The second-highest responsivityoccurred in the blue region, which aligns with the absorption ofSmall 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (10 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 8. a) Optical microscope image of electrodes employed for a2, b2, a3, and b3. b) Optical microscope showing the channel of a3 or b3-basednanodevices. c) SEM of a scratched area for evaluating the quality of a representative film for a3 or b3. d) AFM of a representative film for a3 or b3.e) Nanofilm mapping coverage evaluated from Figure 8d, and calculated by Image J. f) AFM of a scratched area for evaluating the thickness of arepresentative film for a3 or b3.Figure 9. a) Performance of a3 devices under different light-wavelength irradiation, b) photo-response at 1 mW cm−2, c) responsivity, d) specific detec-tivity, and e) EQE of a3 (black) and b3 (red) based devices under different wavelength excitation and bias voltage of 5 V.Small 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (11 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comFigure 10. Comparison of the responsivity and EQE[35,66,78–98] of a3 and b3 with other 2D hybrid materials. The yellow area represents studies with onlyresponsivity data. The red rectangles represent work in this study. The black dots indicate covalent functionalization studies. The blue dots correspondto non-covalent functionalization with organic molecules. The green dots represent studies related to MXenes.the Soret band of porphyrin, followed by UV-A (3.41 eV), poten-tially attributed to a direct transition from the VBM of Ti3CN tothe LUMO+1 of porphyrin, calculated at 3.28 eV. The response at2.34 eV in the green region might be influenced by the Q bandabsorption at 558 nm (2.23 eV). In contrast, the lack of sensitivityto UV-B is likely due to its high energy, which does not corre-spond to any plausible transitions in the system. Although ad-ditional mechanisms may contribute, it is clear that porphyrinplays a crucial role in enhancing the photoactivity of these hybridmaterials.The quantum efficiency of a3 and b3 (Figure 9e) is also an im-portant parameter in photosensors, with values of 1300% and2830% under a bias voltage of 5 V, which is approximately oneorder of magnitude larger than the average of previous studieson MXene-based materials.[78] This indicates that each incidentphoton on the hybrid materials a3 and b3 is capable of generat-ing multiple charge carriers (holes and electrons), highlightingthe high performance of the device. Moreover, the elevated quan-tum efficiency and responsivity indicate that electrons and holestransferred from porphyrin to MXenes are not self-annihilatedbut instead disperse around the basal plane, contributing as ex-citonic carriers.Finally, we compared the best responsivity, quantum effi-ciency (Figure 10), and photo-response (Figure S14, Support-ing Information) of a3 or b3 devices with those reported inthe literature.[35,44,66,78–98] Among MXene-based materials, a3or b3 devices occupy a privileged position, surpassed only byTiO2/MXene[35] and ReS2-Ti3C2.[82] Most functionalized Ti3C2or Ti3CN focus on UV-A and UV-B regions, leaving the visi-ble range either unexplored or inactive, with rejection ratios ex-ceeding three orders of magnitude.[78] In this context, the perfor-mance of a3 and b3 remains peerless. We then evaluated our re-sults against well-established 2D material-based photodetectors,particularly those targeting visible light, such as TMDs. CovalentSmall 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (12 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.comwww.advancedsciencenews.com www.small-journal.comfunctionalization techniques in this field are scarce, withonly a few examples involving PCBM,[79] porphyrin,[99–102] andpyrene.[45] Our devices demonstrated superior performance inresponsivity. In terms of dark-to-light current ratio (photo-response), only PCBM-MoS2 andMoS2-ZnP outperform a3 or b3.In a broader context, when including non-covalent systems andinorganic species such as nanoparticles, a3 or b3 devices exhibitaverage performance in responsivity and EQE. Nevertheless, bycovalently functionalizing optically inactive Ti3C2 and Ti3CNwithporphyrins, we have developed highly effective photodetectors ca-pable of covering the entire visible spectrum, rivaling the bestresults reported in the literature.3. ConclusionIn conclusion, the Tx phase of MXenes was modified to carryalkyl amines, enabling straightforward functionalization withporphyrin. The flexibility of the alkyl amines facilitates close elec-tronic interaction between the aromatic porphyrin skeleton andthe MXenes’ basal plane. This process allowed for large function-alization loading, as confirmed by the Kaiser test and TGA, withXPS and IR providing definitive evidence of covalent functional-ization.A type-I band alignment was observed between ZnP and Ti3C2or Ti3CN, while SEC experiments suggest efficient hole andelectron transfer events under light irradiation, increasing thenumber of carriers on the surface of MXenes. Unlike other 2Dmaterials, such as graphene, basal functionalization of MXenesdoes not introduce defects; instead, it stabilizes the Ti layers,enabling high-quality nanodevices.[20] Photodetectors based onthese nanofilms showed significant improvements in currentand photo-response after functionalization, especially under visi-ble light, demonstrating performance on par with the most ad-vanced MXene-based devices.[20,34] Specifically, the maximumvalues of responsivity and external quantum efficiency reached10.35 A W‒1 and 2440%, respectively. This work highlightsthe potential of chromophore-functionalized MXenes for light-related nanodevice applications, distinguishing them from other2D materials.4. Experimental SectionSynthesis of MXenes Nanosheets: In a 25 mL vial containing 5 mL ofethylenediamine (EDA), 3.7 g of ammonium fluoride (NH4F) was slowlyadded under stirring, forming a white solid as NH3 bubbles were released.Then, 5 mL of HCl (35%) was slowly added, followed by 500 mg of Ti3AlC2or Ti3AlCN. The reaction was kept under stirring at 60 °C for Ti3AlC2 or atreflux temperature for Ti3AlCN under a nitrogen atmosphere. During theetching process, bubbles were observed due to the production of hydrogengas. After stirring for 1 day with occasional sonication, the solution was fil-tered using PTFE membranes with a pore size of 0.2 μm and sequentiallywashed with water, N-Methyl-2-Pyrrolidone (NMP), and methanol, result-ing in a black solid.Next, the solid was tip-sonicated for 1 h in DMSO using a BransonDigital Sonifier SFX 550 set to 70% amplitude. The solid was obtainedafter filtering the original solutions of Ti3AlC2 or Ti3AlCN, respectively,using PTFE membranes with a pore size of 0.2 μm and sequentiallywashing with water, trimethylamine, N-Methyl-2-Pyrrolidone (NMP), andmethanol. The product was tip-sonication for 1 h in ethylenediaminete-traacetic acid (EDTA) solution, which was prepared by dissolving EDTA inNaOH solution with pH = 12. The solid products a1 and b1 were obtainedafter the same filtration washing process.The materials a1 or b1 were immersed in 20 mL of EDA for 1 day at70 °C for a1 or 100 °C for b1 under a nitrogen atmosphere. The productsa2 and b2 were obtained after filtration by employing PTFE membraneswith a pore size of 0.2 μm and washing with water and acetone.Synthesis of ZnP-MXenes a3 and b3: A mixture of 20 mg DCC, 20 mgDMAP, 10 mg ZnP (which was 5-(4-carboxyphenyl)-10,15,20-(triphenyl)porphyrin Zn2+), and 20 mg of a2 or b2 was dispersed in 10 mL of drypyridine. The reaction mixture was stirred at 40 °C for 5 days with occa-sional sonication, while small amounts of DCC were added periodically.After this period, the reaction mixture was filtered using PTFE membraneswith a pore size of 0.2 μm and washed with 30 mL of water and 30 mL ofacetone. The hybrid materials a3 and b3 were then collected as a solid.Fabrication of Photodevice: A 1 × 1 cm2 SiO2/Si (90 nm) substrate wascleaned with acetone and covered with a metal mask featuring 50 pairsof electrodes with channel areas of 500 × 50 μm2 square hollow pattern.Ti/Au electrodes (5/50 nm) were deposited on the surface using electronbeam evaporation. Next, 250 μL of a solution of a2, a3, or b2, b3 in DMSO(4 g L‒1) was added to a 40 mL vessel containing the vertically placedsubstrate, deep in ≈30 mL of water. Then, 7 mL of a mixture of ethanoland water (v/v = 1:1.5) was carefully dropped onto the water’s surface.After several seconds, a nanofilm based on a2, a3 or b2, b3 was formedat the water interface and deposited onto the substrate by removing thewater.Supporting InformationSupporting Information is available from the Wiley Online Library or fromthe author.AcknowledgementsH.L. and R.C.V. contributed equally to this work. This work was funded bythe Grant-in-Aid for Scientific Research KAKENHI (21H05015, 22H01907,23K17956), Japan Society for the Promotion of Science (JSPS), De-sign & Engineering by Joint Inverse Innovation for Materials Architec-ture (DEJI2MA), MEXT and the joint usage/research program of IMaSS,Nagoya University. H.L. acknowledges the support of the Innovation forChinese Scholarship Council (CSC) (202106060068).Conflict of InterestThe authors declare no conflict of interest.Data Availability StatementThe data that support the findings of this study are available in thesupplementary material of this article.Keywords2D Materials, covalent functionalization, light conversion, MXenes,photosensorsReceived: March 27, 2025Revised: June 26, 2025Published online: August 4, 2025[1] S.Mathew,M. Ramachandra, S. Devi K R, D. Pinheiro, S.Manickam,C. H. Pang, S. H. Sonawane,Mater. Today Sustain. 2023, 24, 100568.Small 2025, 21, e03895 © 2025 The Author(s). Small published by Wiley-VCH GmbHe03895 (13 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. 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Small published by Wiley-VCH GmbHe03895 (15 of 15) 16136829, 2025, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smll.202503895 by National Institute For, Wiley Online Library on [23/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.small-journal.com Covalent Functionalization of MXenes with Porphyrin for Visible-Light Activation in Energy Conversion Nanodevices 1. Introduction 2. Results and Discussion 2.1. Synthesis and Characterization 2.2. Optical and Electronic Properties 2.3. Photo-Device Applications 3. Conclusion 4. Experimental Section Supporting Information Acknowledgements Conflict of Interest Data Availability Statement Keywords  2025-09-06T01:59:09+0530 Preflight Ticket Signature