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PAPER View Article OnlineView Journal | View Issue

National Center for Nanoscience and Technology, Beijing 100190, China.

E-mail: hej@nanoctr.cn, gongjr@nanoctr.cn

† Electronic supplementary information (ESI) available: XRD pattern ofCF–WO3–Pt–CdS heterostructure (Fig. S1). UV–Vis diffuse reflectance spectra ofcarbon fibers, CF–WO3 and CF–WO3–Pt–CdS samples (Fig. S2). EIS Nyquistplots of as-prepared electrodes under visible irradiation (Fig. S3). SEM imageof CF–WO3–Pt–CdS after the photocatalytic O2 production (Fig. S4). Theadsorption of MB on as-prepared samples (Fig. S5). MB photodegradation ofas-prepared heterostructures (Fig. S6). See DOI: 10.1039/c3ce41826j‡ F. Wang and Y. Wang contributed equally to this work.

CrystEngCommThis journal is © The Royal Society of Chemistry 2014

Cite this: CrystEngComm, 2014, 16,

1389

Received 10th September 2013,Accepted 31st October 2013

DOI: 10.1039/c3ce41826j

www.rsc.org/crystengcomm

Pt nanoparticle and CdS quantum dot assistedWO3 nanowires grown on flexible carbon fibersfor efficient oxygen production†

Fengmei Wang,‡ Yajun Wang,‡ Xueying Zhan, Muhammad Safdar, Jianru Gong*and Jun He*

One-dimensional semiconductor nanomaterials are considered to be promising photocatalysts due to

their large surface-to-volume ratio and high charge separation efficiency. Here, a Pt nanoparticle and CdS

quantum dot (QD) co-decorated one-dimensional WO3 heterostructure was fabricated on flexible carbon

fibers for water oxidation via a facile method. WO3 nanowires (NWs), with their advantage of resilience

to photo-corrosion effects in aqueous solution, serve as the main photocatalyst; Pt nanoparticles and

CdS QDs act as the co-photocatalyst. It was found that the photocurrent density of this novel nanostructure

is about 5 times higher than that of pure WO3 under visible light irradiation. Significantly, the yield of

O2 after the 5.5 h reaction time with the assistance of AgNO3 reaches 1 μmol. This work not only provides

a conceptual blueprint for the design of a one dimensional heterostructure photocatalyst on flexible

substrate to ameliorate its recyclability but also offers an excellent alternative material for application in

renewable energy.

Introduction

Water splitting utilizing solar energy to generate hydrogen oroxygen has been considered as a promising and importantmethod in scientific communities. Fabrication of photocatalystswith high visible light photocatalytic activity is one of the keypoints for efficient solar water splitting.1–4 To date, there hasbeen much research5–8 reported based on semiconductors,especially TiO2,

9,10 ZnO11–13 and CdS14–16 for water splitting.Among various semiconductors, tungsten oxide (WO3), whichbelongs to the class of n-type semiconductors, has attractedmuch interest for use in electrochromic devices,17,18 as a gassensor19,20 and in supercapacitors21 due to its relatively narrowband gap (2.36–2.8 eV) and promising stable chemical andphysical properties.19,21,22 Recently, WO3 has gained great atten-tion as a promising visible light driven photocatalyst23,24

because of its resilience to photocorrosion effects in aqueoussolution,25 which promotes the performance of water oxidation

or pollutant degradation in water under daylight illumination,while at the same time maintaining a relatively long workinglifetime. Much systems research based on WO3 has been reported,such as WO3 nanostructures decorated with another semicon-ductor,24,26 graphene19 and noble metal deposition.27–29 Severaltypes of composite photocatalyst have been developed upto now. For example, Gong et al. introduced CdS clusters todecorate graphene nanosheets;14 Hsu et al. deposited Pt nano-particles on TiO2–In2O3.

30 Significantly, a three-componentheterostructure can greatly improve photocatalytic performanceby introducing a medium such as graphene and a noble metalwhich profoundly enhances carrier mobility.30–32 For example,Feng et al. have designed Fe2O3–rGO–BiV1−xMoxO4 compositeswhich can obtain a photocurrent density of ~1.97 mA cm−2.5

Compared with bulk photocatalysts, it is widely recognizedthat one-dimensional (1D) nanowires (NWs) grown on a sub-strate offer potential advantages in photoelectrochemical orphotocatalytic reactions due to their large surface-to-volumeratio, enhanced charge separation and migration properties.11

Moreover, NWs grown on substrates make it possible to recyclethe photocatalysts in contrast to conventional powder photo-catalysts.33 NW heterostructures by compositing with othermaterials6,10,11,34–36 can improve the photocurrent and H2 orO2 evolution efficiency owing to an enhanced light absorptionand charge separation efficiency. To date, many types of threecomponent NW semiconductor composite have been studied.11,32

However, to the best of our knowledge, there are few reportson WO3 NW based three-component heterostructure systems

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for the improvement of the photocatalytic performance ofWO3 NWs in water oxidation.

In this work, we present an example of a semiconductor–metal–semiconductor heterostructure system by chemically depos-iting CdS quantum dots (QDs) on Pt nanoparticles decoratedWO3 NWs grown on flexible carbon fibers (CF–WO3–Pt–CdS).For this new three-component system, WO3 NWs serve as themain photocatalyst while CdS QDs act as a co-catalyst, andphotogenerated electrons can be effectively separated and trans-ferred to the Pt nanoparticles to promote the overall chargeseparation efficiency. Meanwhile, the photogenerated holeson WO3 NWs will transfer to the valence band of CdS QDs,reducing the probability of photogenerated charge recombination.The holes will subsequently participate in the water oxidationto evolve O2. The photoelectrochemical measurement indicatesthat photocurrent density of this novel nanostructure is about5 times higher than that of pure WO3 under visible light irra-diation. Significantly, this system showed much better proper-ties of O2 evolution than pure WO3 NWs on carbon fibers. Theyield of O2 using WO3–Pt–CdS on carbon fibers (3 × 1.5 cm2)is about 1 μmol after a 5.5 h reaction time.

Experimental sectionPreparation of WO3–Pt–CdS heterostructures on flexiblecarbon fibers

The carbon fiber (CF) substrate was cleaned by sonication indeionized water, acetone, and ethanol respectively. WO3 NWs onCF were synthesized by a one-step high temperature (1000 °C)evaporation process via heating tungsten oxide powder as asource material in the furnace.25,37 After this evaporation depo-sition process, the color of the carbon fibers changed to gray.

Consequently, Pt decorated WO3 NWs were prepared by aphotodeposition (PD) method. In brief, carbon fibers with WO3

nanowires were soaked in a fixed concentration H2PtCl6·6H2Oaqueous solution, followed by absorption of the PtCl6

2− ionsunder stirring. Meanwhile, a 500 W xenon lamp irradiated thequartz tube to reduce the adsorbed Pt4+ to Pt nanoparticles.Finally, the carbon fiber substrate was washed with deionizedwater several times and dried at 60 °C.

Decoration of CdS QDs on WO3–Pt NWs was carried out usinga modified chemical bath deposition method (CBD) reported inprevious work.38 In a typical process, the as-prepared CF–WO3–Ptsample was incubated in an aqueous solution of 20 mMcadmium nitrate (Cd(NO3)2·4H2O) and 20 mM thioacetamideat 55 °C for 20 min with magnetic stirring. The CF–Pt–CdSand CF–WO3–CdS samples were prepared under the sameexperimental conditions.

Characterization

The morphologies and microstructures of the as-preparedsamples were examined with Hitachi S-4800 field-emissionscanning electron microscopy (FE-SEM), an X-ray energy dispersivespectrometer (EDS) and FEI Tecnai F20 transmission electronmicroscopy (TEM). The crystal structure of the product wascharacterized by X-ray diffraction (XRD, D/MAX-TTRIII(CBO)

1390 | CrystEngComm, 2014, 16, 1389–1394

diffractometer) using Cu-Kα radiation (λ = 1.5418 Å). Ramanspectra of the samples were obtained using an InVo-RENISHAWsystem. UV-vis diffuse reflectance spectra (DRS) were measuredby a UV–vis spectrometer (Lambda 750).

Photocurrent measurement

Photocurrent measurements were conducted in a typical three-electrode electrochemical system (CHI-650D) under visiblelight illumination (Xenon lamp, 139 mW cm−2, λ > 420 nm)with zero-bias versus a saturated calomel electrode (SCE). Thislamp supplied the visible light source in this system (λ > 420 nm).In this process, a sample of WO3–Pt–CdS nanostructuresserved as the working electrode and SCE acted as the referenceelectrode with a Pt counter electrode in 0.1 M Na2SO4 electrolyte.

Photocatalytic oxygen evolution from water

Photocatalytic water oxidation experiments were conducted ina 500 mL cylinder quartz reactor at ambient temperature. A300 W xenon research lamp with a 420 nm cutoff filter (the lightintensity was 100 mW cm−2) was used as a visible light source.In a typical O2 evolution experiment, the WO3–Pt–CdS sample(3 × 1.5 cm2) with 12 mg photocatalyst on it was placed on thebottom of the reactor containing 80 mL mixed aqueous solu-tion with 0.05 M AgNO3. Before irradiation, the system wasplaced under vacuum for about 30 mins to remove the air insideand to ensure that the system was under anaerobic conditions.A specific volume of gas was intermittently sampled and ana-lyzed by gas chromatography (GC-14C, Shimadzu, Japan, TCD,argon as a carrier gas and a 5 Å molecular sieve column). Abase-line was recorded for each test before exposure to thexenon lamp.

Results and discussionSynthesis and structural analysis

Fig. 1a represents the scheme of the preparation process of theCF–WO3–Pt–CdS sample. The morphologies and elemental mapsof the WO3, WO3–Pt, and WO3–Pt–CdS NWs on the carbon fibersare displayed in Fig. 1(b–e). Fig. 1b shows a low-magnificationSEM image of WO3 NWs on carbon fibers, demonstrating ahighly uniform and quasi-aligned hierarchical structure. Thedensity of the NWs on CFs was high and the NWs nearlycovered the whole fiber in the inset of Fig. 1b. After photo-deposition of the Pt nanoparticles, the morphologies revealedin Fig. 1c were lightly changed. Due to the electron-chargedcharacteristics of the WO3 NWs under the visible light irradia-tion, Pt nanoparticles were selectively deposited on thesurfaces of the WO3 NWs.30 Fig. 1d displays the morphologyof Pt nanoparticles decorated WO3 NWs after reacting withCd(NO3)2·4H2O) and thioacetamide solution in the chemicalbath deposition process. Distinctly, the nanoparticles depositedon the WO3–Pt NWs, indicating the formation of CdS QDs. Thecorresponding EDS image (Fig. 1e) of the CF–WO3–Pt–CdS sam-ple confirmed the existence of the elements C, W, O, S, Cd, Pt(note that the C signal originates from the carbon fiber).

This journal is © The Royal Society of Chemistry 2014

Fig. 1 (a) Scheme of the preparation process of the CF–WO3–Pt–CdSsample, SEM images of (b) CF–WO3 nanowires, (c) CF–WO3–Pt,(d) CF–WO3–Pt–CdS, and (e) EDS of CF–WO3–Pt–CdS. The insets in(b, c, d) show the whole carbon fiber morphologies correspondingly,(CVD – chemical vapor deposition; PD – photodeposition; CBD – chemicalbath deposition).

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Fig. 2 displays the Raman spectra of WO3–Pt–CdS nano-wires on flexible CFs. The bands centered at 808 cm−1 and706 cm−1 are attributed to W–O stretching. In addition, O–W–Ostretching was revealed at the band centered at 273 cm−1.25

Evidently, the peaks of the as-prepared WO3–Pt–CdS nano-structures on CFs at 306 cm−1 and 604 cm−1 are related to thelongitudinal optical phonon mode (LO) type confined vibrationsof CdS lattice confirming the formation and existence of theCdS QDs.32,39 In addition, the phase purity and crystal structureof the as-prepared sample was consistent with XRD spectra(Fig. S1†). No characteristic diffraction peaks of Pt can be

Fig. 2 Raman spectra of CF–WO3, CF–WO3–Pt, and CF–WO3–Pt–CdSsamples.

This journal is © The Royal Society of Chemistry 2014

observed on these patterns because of the low Pt loadingamounts and relatively low diffraction intensity.

The as-prepared WO3–Pt–CdS nanostructures on CFs werefurther characterized by TEM and high resolution TEM (HRTEM).Fig. 3a and b show the low-magnification TEM images of a singleWO3 NW and a decorated WO3 NW with Pt and CdS nano-particles. Fig. 3b shows that CdS QDs with sizes ranging from10 to 25 nm are on the surface of the WO3 nanowire. Mean-while, Pt nanoparticles, some of them agglomerated togetherwith quite small sizes, are deposited on the surface of theWO3 NWs. In order to observe the crystalline lattice region,HRTEM images of pure WO3 NWs and WO3–Pt–CdS nano-structures are displayed in Fig. 3c and d. Three sets of parallellattice fringes with a spacing of 0.38 nm, 0.20 nm and 0.33 nmwere obtained, corresponding to the (002) plane of monoclinicWO3,

25 the (200) plane of Pt nanoparticles27 and the (002) planeof CdS QDs,38 respectively. The selected-area electron diffrac-tion (SAED) pattern in Fig. 3c indicates that WO3 NWs aresingle crystalline with a growth direction of [002]. Additionally,the HRTEM image also reveals a distinguished and coherent inter-face between WO3 NWs, Pt nanoparticles and CdS QDs, demon-strating the formation of semiconductor–metal–semiconductorheterostructures. From the above analysis, a WO3–Pt–CdS nano-structure has been successfully fabricated on the CFs. Theoptical properties of samples are studied using UV-Vis diffusereflectance spectra (shown in Fig. S2†). In contrast to pureWO3 NWs on CFs, WO3–Pt–CdS nanostructures exhibit a signifi-cant enhancement in light absorption intensity and a red-shiftof absorption edge due to the presence of CdS QDs. This fact,coupled with the above characterization, indicates our specialWO3–Pt–CdS heterostructures have a broader light absorption dueto their novel interfaces of semiconductor–metal–semiconductorheterostructures. The interface can facilitate the charge sepa-ration and transfer, which gives rise to a synergetic effect toenhance the O2 production performance.

Fig. 3 (a) A low-magnification TEM image of a typical WO3 nanowire,(b) Pt nanoparticle and CdS QD decorated WO3 NWs. High resolutiontransmission electron microscopy (HRTEM) images of (c) WO3 NWs(inset is the corresponding SAED pattern of a WO3 NW) and(d) CF–WO3–Pt–CdS sample.

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Photocatalytic properties on flexible carbon fibers

To better understand the role of the WO3 NWs, Pt nano-particles and CdS QDs, photoelectrochemical (PEC) measure-ments were performed. Photoresponses of different sampleelectrodes with visible light switching on and off are depictedin Fig. 4, which generally are used to evaluate the electronicinteraction among WO3, Pt nanoparticles, and CdS QDs. Asshown in Fig. 4a, prompt and reversible photocurrent responsesare achieved for each on–off cycle when the as-preparedCF–WO3–Pt–CdS sample serves as a working electrode. The“vertical” change between the on and off cycles indicates thatthe separation rate of photogenerated electron–hole pairs increaseddue to the heterostructure built between these three compo-nents.5 In contrast, the photocurrent of the CF–WO3 sampleshows a relatively slow response as shown in Fig. 4a. Under thesame conditions, the photocurrent density of CF–WO3–Pt–CdSis about five times higher, while that of CF–WO3–Pt electrodeis about two times higher than that of pristine CF–WO3 asshown in Fig. 4a. The significant enhancement of photocurrentdensity originates from the charge separation occurring inCF–WO3–Pt and CF–WO3–Pt–CdS samples. It is worthy ofnote that the photocurrent density of CF–WO3–Pt–CdS ishigher than that of the CF–WO3–CdS and CF–Pt–CdS elec-trodes. Therefore, the deposition of Pt nanoparticles on thesurface of the WO3 NWs improves the photogeneratedelectron–hole separation on the interface of the WO3 NWsbecause of the different conduction band alignment and Fermilevel of WO3 and Pt nanoparticles. In our system, it is sug-gested that Pt nanoparticles can separate and collect thephotogenerated electrons, leaving holes in the WO3 NWs andconsequently reducing the recombination rate of the photo-generated electrons and holes. After the chemical depositionof CdS QDs, CF–WO3–Pt NWs reveal further enhancementin photocurrent generation, demonstrating that chargeseparation is further improved and a pronounced chargeseparation occurs at the WO3/CdS, CdS/Pt interfaces of theWO3–Pt–CdS NWs. Therefore, this hybrid WO3–Pt–CdS nano-structure effectively promotes the overall charge separationefficiency. Furthermore, it is noteworthy that the photocurrentof the CF–WO3–Pt–CdS electrode maintains relative stability

Fig. 4 (a) Photocurrent response of the different sample electrodes toon–off cycles of visible light (λ > 420 nm) illumination; (b) transientphotocurrent response of the electrodes with CF–WO3, CF–WO3–Pt,CF–WO3–Pt–CdS, CF–Pt–WO3 and CF–WO3–CdS nanostructures undervisible light (λ > 420 nm) irradiation.

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after four on–off light cycles. Fig. 4b also demonstrates thephotoresponse of CF–WO3–Pt–CdS photoelectrode to be thefastest among the as-prepared photoelectrodes.

EIS Nyquist plots are a powerful method to investigate theinterface charge separation efficiency. The arc sizes of theNyquist plots reflect the separation efficiency of the photo-generated electron–hole pairs.40,41 In addition, the intermediatefrequency response is due to the charge transport and transferat the sample and the electrode interface. The smaller the arcsize, the quicker the charge transport. EIS Nyquist plots of theas-prepared samples under light irradiation (Fig. S3†) revealthat the CF–WO3–Pt–CdS sample has a smaller arc radius,i.e. a higher charge separation efficiency than that of CF–WO3,CF–WO3–Pt, CF–WO3–Pt–CdS and CF–Pt–CdS. These resultssuggest both WO3 NWs and Pt nanoparticles play very vital rolesin improving the carrier separation efficiency. Noteworthily,as shown in Fig. 5a, it is obvious that the charge separationefficiency of the CF–WO3–Pt–CdS sample is highest amongthese three as-prepared samples. Meanwhile, Fig. 5b showsEIS Nyquist plots of CF–WO3–Pt–CdS samples with and withoutlight irradiation, indicating that an effective and fast electron–hole separation occurred under visible light irradiation. Corre-spondingly, Bode plots in Fig. 5c also reflect the efficient electronlifetime in CF–WO3, CF–WO3–Pt, CF–WO3–Pt–CdS samples,respectively. The lifetime (te) can be determined by using thefollowing eqn (1), where the fmax is the frequency at which thelow frequency peak appears in the Bode plot.42,43 The te (1.54 s)found in the cell of the CF–WO3–Pt–CdS working electrode wasfound to be longer than that of the other working electrodes(CF–WO3 and CF–WO3–Pt) (0.16 s). Therefore, the electroncombination was greatly reduced and the electron lifetime

Fig. 5 EIS Nyquist plots of (a) the CF–WO3 (black), CF–WO3–Pt (red),and CF–WO3–Pt–CdS (blue) electrodes under visible irradiation (λ > 420 nm)and (b) the CF–WO3–Pt–CdS electrode with (red) and without (black)visible light; corresponding Bode phase plots of (c) the CF–WO3 (black),CF–WO3–Pt (red) and CF–WO3–Pt–CdS (blue) electrodes under visiblelight and (d) the CF–WO3–Pt–CdS electrode with (red) and without(black) visible light irradiation.

This journal is © The Royal Society of Chemistry 2014

Fig. 7 Schematic for the photocatalytic water oxidation mechanism ofWO3–Pt–CdS nanostructures on flexible carbon fibers.

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increased concurrently. In addition, the Bode plots of theCF–WO3–Pt–CdS sample under dark and visible light irradi-ation are shown in Fig. 5d. Upon irradiation, a much moreprolonged te is obtained (1.54 s) compared to that found inthe dark (0.16 s), which means there is a longer electron life-time under light radiation.

tfe 1

2 max

(1)

The Pt nanoparticle and CdS QD assisted WO3 NWs onflexible carbon fibers were tested for photocatalytic O2 genera-tion in the presence of AgNO3 as a sacrificial electron scavenger.The results of photocatalytic O2 evolution under visible lightirradiation (λ > 420 nm) are demonstrated in Fig. 6. Comparedwith pure WO3 NWs, WO3–Pt, WO3–CdS and Pt–CdS hybridphotocatalysts grown on CFs, apparently continuous O2 produc-tion was observed when the WO3–Pt–CdS hybrid photocatalyston CFs was exposed to visible light with an average rate of0.2 μmol h−1 from 12 mg of nanowire heterostructures. Here,Pt nanoparticles and CdS QDs serve as cocatalysts, which areessential in this three-component system, to generate O2 fromwater. On average, under light illumination, nearly constantO2 evolution by this system was observed for at least 2.5 h.Profoundly, the yield of O2 after a 5.5 reaction time reached1 μmol. As shown in Fig. 6b, the O2 yield of CF–WO3–Pt–CdSafter 5.5 h is significantly higher than other samples, whichindicates that all the components in this system are indis-pensable for achieving a high photocatalytic efficiency. Moreimportantly, this system also showed good stability after lightirradiation as can be seen from the post irradiation SEMimage (Fig. S4†).

A photocatalytic water oxidation mechanism is proposed inFig. 7. When decorated with Pt nanoparticles and CdS QDs toform a heterostructure, the band structure of WO3 is reconfigured.Since the Conduction Band (CB) position of WO3 (0.74 V vs.NHE)44,45 is lower than that of CdS (−0.52 V vs. NHE),39 theexcited electron on the CB of CdS would transfer to that ofWO3, leaving holes in CdS under light illumination. Pt nano-particles can function as electron collectors in the compositeand inhibit the charge recombination by accepting the

Fig. 6 (a) Visible-light-driven photocatalytic O2 production usingWO3–Pt–CdS, WO3, WO3–Pt, WO3–CdS and Pt–CdS hybrid photocatalystson flexible carbon fibers; (b) comparison of the photocatalyticO2-production activity after 5.5 h under visible light irradiation(λ > 420 nm) over CF–WO3–Pt–CdS, CF–WO3, CF–WO3–Pt, CF–WO3–CdSand CF–Pt–CdS samples.

This journal is © The Royal Society of Chemistry 2014

photoexcited electrons from WO3 NWs or CdS QDs. Mean-while, photoexcited holes on the Valence Band (VB) of WO3

transfer to that of CdS, leading to higher electron–hole separa-tion efficiency. Photoexcited holes will participate in wateroxidation because the position of O2/H2O (1.23 V vs. NHE)46 islower than the valence band of WO3 (3.44 V vs. NHE) andCdS (1.88 V vs. NHE). Therefore, the reconfigured band energystructure provides an increased amount of photogeneratedholes for participation in water oxidation. At the same time,the free electrons generated were consumed by Ag+ in theaqueous solution in this reaction system.

To further study the photocatalytic properties of this three-component system, degradation experiments using methyleneblue (MB) as an indicator dye under visible light irradiationwere also studied. Before switching on the light, the absorp-tion process was traced by withdrawing the solution in thegiven time interval (Fig. S5†). After absorption equilibrium,the MB degradation performance of the as-prepared sampleswas investigated and the results are illustrated in Fig. S6.†As can be seen in Fig. S6,† the apparent rate constant k41,47 ofpure WO3 NWs, WO3–Pt NWs, and WO3–Pt–CdS nanostruc-tures on flexible CFs are 0.0066 min−1, 0.0073 min−1, and0.0087 min−1, respectively. WO3–Pt–CdS nanostructures fabri-cated on carbon fibers show the best photocatalytic perfor-mance in MB degradation, indicating the advantage of thissystem. The possible schematic mechanism for the enhance-ment of photocatalytic activity of WO3–Pt–CdS nanostructureson flexible carbon fibers is shown in the insert of Fig. S6.†

Conclusions

Pt nanoparticles and CdS QDs assisted WO3 NWs grown onflexible carbon fibers were synthesized via a facile three-stepmethod. WO3 NWs, with the advantage of resilience to photo-corrosion effects in aqueous solution, serve as the mainphotocatalyst and the CdS QDs act as the co-photocatalyst.With the introduction of Pt nanoparticles on the WO3–CdSheterostructure, the photogenerated electrons can be effectivelyseparated and transferred to the Pt nanoparticle to promotethe overall charge separation efficiency. The photocurrentdensity of the WO3–Pt–CdS nanostructure is about 5 timeshigher than that of pure WO3 NWs. The results of the photo-catalytic O2 production and MB degradation reveal that thephotocatalytic activity of WO3 nanowires on flexible carbon

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fibers is obviously enhanced after the deposition of Pt andCdS nanoparticles. Significantly, the yield of O2 was 1 μmol after5.5 h reaction time under visible light irradiation (λ > 420 nm),which is the first implementation on flexible carbon fibers.As is known to us, the conventional powder photocatalysts arehard to separate from solution, which hinders the practicalapplication of photocatalysis. By comparison, this three-componentphotocatalytic system on flexible carbon fibers serves as a newblueprint to ameliorate the recyclability of photocatalysts inaqueous solution because it is easy to remove from the aqueoussolution directly. Noteworthily, the introduction of the noblemetal nanoparticles into the traditional binary semiconductorcomposites provides a new strategy to design new visible-light-driven photocatalytic water splitting for H2 or O2 evolution.

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