High Charge Separation Research Articles

A facile route to synthesize boron-doped g-C3N4 nanosheets with enhanced visible-light photocatalytic activity

The boron-doped g-C3N4 nanosheets (BCNNs) have been successfully synthesized via an ultra-rapid and environment-friendly microwave heating route. The reaction system is quite simple, using boric-acid-modified melamine as raw materials and carbon fibers as microwave absorbent, respectively. Based on the optical characterizations and calculation, the results show an abnormal phenomenon that the introduction of B element into g-C3N4 host leads to the increase in band gap. The enlarged band gap should be ascribed to the quantum confinement effect derived from the special nanosheets microstructure of the obtained BCNNs. For the visible-light photocatalytic experiment, 92.9% rhodamine B can be degraded at room temperature in just 30 min in the presence of BCNNs, and the photodegradation rate constant of BCNNs is 3.3 times that of the pure g-C3N4 (PCN). In comparison with the PCN, the enhanced photocatalytic activity of BCNNs can be attributed to the more satisfactory mesoporous structure, larger surface-to-volume ratio, and higher charge separation.

Three Birds, One‐Stone Strategy for Hybrid Microwave Synthesis of Ta and Sn Codoped Fe2O3@FeTaO4 Nanorods for Photo‐Electrochemical Water Oxidation

AbstractA “three birds, one stone” strategy is proposed to enhance the performance of hematite photoanode for photoelectrochemical water splitting. One‐pot hybrid microwave synthesis of Ta and Sn codoped Fe2O3@FeTaO4 core–shell nanorods on F:SnO2 substrate achieves three synergetic effects simultaneously: i) core–shell heterojunction formation to alleviate the significant electron–hole recombination; ii) preserved morphology of small‐diameter nanorods to provide a short hole diffusion distance; and iii) Ta and Sn codoping to enhance the electrical conductivity. These effects are not possible with conventional high temperature thermal synthesis in a furnace. As a result, core–shell Fe2O3@FeTaO4 electrode with FeOOH cocatalyst achieves a photocurrent density of 2.86 mA cm−2 at 1.23 VRHE under AM 1.5 G simulated sunlight (100 mW cm−2), which is ≈2.4 times higher than that of bare hematite (1.17 mA cm−2). In addition, the FeOOH/Fe2O3@FeTaO4 electrode exhibits a high surface charge separation efficiency of ≈85% and a modest bulk charge separation efficiency of ≈24%.

CdSe Quantum Dots/g-C3N4 Heterostructure for Efficient H2 Production under Visible Light Irradiation.

Novel photocatalysts -CdSe quantum dots (QDs)/g-C3N4- were successfully constructed. The structure, chemical composition, and optical properties of the prepared samples were investigated via a series of characterization techniques. The results indicated that CdSe QDs/g-C3N4 photocatalysts exhibited remarkably enhanced photocatalytic activity for visible-light-induced H2 evolution compared to pristine g-C3N4 and CdSe QDs and addition of 13.6 wt % CdSe QDs into the composite photocatalyst generated the highest H2 production rate. The enhanced photocatalytic performance of CdSe QDs/g-C3N4 can be attributed to the synergistic effects of excellent visible absorption and high charge separation efficiency from the heterostructure. This work could not only provide a facile method to fabricate semiconductor QDs-modified g-C3N4 photocatalysts but also contribute to the design for heterostructures.

A Specifically Exposed Cobalt Oxide/Carbon Nitride 2D Heterostructure for Carbon Dioxide Photoreduction

Photocatalytic reduction of CO2 provides an opportunity to reach carbon neutrality, by which CO2 emissions from fuel consumption can be converted back to fuels. The challenge is to explore materials with high charge separation efficiency and effective CO2 adsorption capacity to boost the photoreduction of CO2. Here we report that a 2D heterostructure comprised of Co3O4/2D g-C3N4 (COCN) can provide enhanced photocatalytic reduction of CO2 to CO, yielding a CO production rate of 419 μmol g–1 h–1 with a selectivity of 89.4%, which is 13.5 and 2.6 times higher than that of pure 2D g-C3N4 and Co3O4. The enhanced photocatalytic performance arises from (i) enhanced light absorption ability and charge separation efficiency originating from the unique 2D heterostructure connected through specifically exposed facet interfaces and (ii) favorable CO2 adsorption capacity. The study may provide insight for the establishment of a heterostructure-based photocatalytic system toward CO2 reduction.

Preparation of Nb2O5-decorated hierarchical porous ZnO microspheres with enhanced photocatalytic degradation of palm oil mill effluent

In the present work, Nb2O5-decorated hierarchical porous ZnO microspheres (ZnO/Nb2O5) were successfully prepared through a facile surfactant-free method. The as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectroscopy and Brunauer–Emmett–Teller surface area analyses. Under UV light irradiation, the ZnO/Nb2O5 composites degraded palm oil mill effluent (POME) efficiently and demonstrated much higher photocatalytic activity compared to those of pure ZnO and Nb2O5. The enhanced photocatalytic degradation performance of ZnO/Nb2O5 composites was attributed to the high charge separation efficiency and hydroxyl radical generation ability as verified by the photoluminescence spectra. Phytotoxicity test upon the POME degradation over ZnO/Nb2O5 photocatalysis considerably decreased through the measurement of radicle lengths of Vigna radiata. Moreover, the ZnO/Nb2O5 composites were reused several times without appreciable loss of activity. This work revealed that the as-prepared ZnO/Nb2O5 composites have great potential for practical applications in the field of wastewater treatment.

A true oxygen-linked heptazine based polymer for efficient hydrogen evolution

O-doped/functional g-CN polymers are promising materials which have been reported to modify inherent electronic structure and light harvest ability of the g-C3N4 based photocatalysts. However, the doping position and concentration of hetero atom remains ill-defined although enhanced photocatalytic activity of modified g-CN photocatalysts has been reported. Herein, a facile two step procedure to synthesize heptazine polymer with defined O-atom position in polymer structure is presented. Cyameluric acid, a member of cyamelurine family upon polycondensation under inert atmosphere ensures the insertion of O-atom at bridge position between heptazine units in growing polymer. The developed polymer OLHP (oxygen linked heptazine polymer) attains high hydrogen production efficiency likely due to high O-content and efficient charge separation evident from PL spectra compared to g-CN. This heptazine based precursor design also eliminates the possibility of presence of triazine based moiety defects in g-C3N4 polymers.

A nanostructured CuWO4/Mn3O4 with p/n heterojunction as photoanode toward enhanced water oxidation

In this paper, we report a novel photoanode fabricated by spin-coating n-type CuWO4 nano-ovoids on the surface of fluorine-doped tin oxide (FTO) glass and then modified with p-type Mn3O4 nanospheres using a deposition-annealing method. A novel nanocomposite (CuWO4/Mn3O4) with p/n heterojunction formed on the surface of FTO glass. The characterazation results of the nanocomposite indicate that the two moieties of the nanocomposite intimately contact with each other. The photoelectrochemical tests of the prepared CuWO4/Mn3O4 photoanode reveal that the electrode can produce larger anodic photocurrent and show enhanced incident photon-to-current efficiency (IPCE) than the bare CuWO4 photoanode does. Moreover, the PEC tandem cell assembled by using the CuWO4/Mn3O4 electrode as photoanode and Pt plate as counter electrode demonstrates enhanced photocatalytic activity and stability for photoeletrochemical (PEC) water splitting. The amount of hydrogen and oxygen, collected from the counter chamber and the photoanode chamber, separately, reached to 5.0 μmol and 2.3 μmol, respectively, under 2 h simulated sunlight irradiation at 1.20V vs. RHE bias without any sacrificial agent. The remarkable performance of the nanocomposite anode owe to the formed heterojunction structure in the nanocomposite, leading to high photoexcited charge transfer and separation.

High-Performance Photocatalytic Hydrogen Production and Degradation of Levofloxacin by Wide Spectrum-Responsive Ag/Fe3O4 Bridged SrTiO3/g-C3N4 Plasmonic Nanojunctions: Joint Effect of Ag and Fe3O4.

Highly photoresponsive semiconductor photocatalysis for energy and environmental applications require judicious choice and optimization of semiconductor interfaces for wide spectral capabilities. This work aims at rational designing of highly active SrTiO3/g-C3N4 junctions bridged with Ag/Fe3O4 nanoparticles for utilizing Z-scheme transfer and surface plasmon resonance effect of Ag augmented by iron oxide. The SrTiO3/(Ag/Fe3O4)/g-C3N4 (SFC) catalyst was employed for photocatalytic hydrogen production and photodegradation of levofloxacin (LFC; 20 mg/L) under UV, visible, near infra-red, and natural solar light exhibiting high performance. Under visible light (<780 nm), SFC-3 sample (30 wt % g-C3N4 and 3% Ag/Fe3O4) shows a H2 evolution of 2008 μmol g-1 h-1 which is ∼14 times that of bare g-C3N4. In addition, 99.3% removal of LFC was degraded in 90 min under visible light with retention of activity under sun. The inherent topological properties, complete, higher charge separation, and reduced recombination allowed this catalyst for a high photocatalytic response which was proved by UV-diffuse reflectance spectroscopy, photoluminescence, electrochemical impedance spectroscopy, and photocurrent response measurements. Scavenging experiments and electron spin resonance analysis reveal that the mechanism shifts from a dual charge transfer in case of binary junction to essential Z-scheme with incorporation of Ag/Fe3O4. Both •O2- and •OH are main active radicals in visible light, whereas •O2- majorly participate under UV. The synergistic effect of SrTiO3, g-C3N4, and plasmon resonance of Ag/Fe3O4 not only improves light response and reduce recombination but also enhances the redox-ability of charge carriers. A H2 production mechanism and LFC degradation pathway (degradation, defluorination, and hydrolysis) has been predicted. This work paves a way for development of photocatalysts working in practical conditions for pollution and energy issues.

Mixed-Phase MOF-Derived Titanium Dioxide for Photocatalytic Hydrogen Evolution: The Impact of the Templated Morphology

Herein, we explored a simple metal–organic framework (MOF)-mediated synthesis for the controlled preparation of pure and mixed-phase titania (TiO2) nanoparticles. Scanning electron microscopy images revealed that the MOF-derived TiO2 retains the MOF crystal shape, and through powder X-ray diffraction and X-ray photoelectron spectroscopy, it is demonstrated that the crystal template is composed of nanosized TiO2 rutile and anatase particles. The presence of both TiO2 rutile and anatase phases in the crystal template enhances the interactions between them, thus suppressing the electron–hole recombination. This has an impact on the photocatalytic reduction of water because templated MOF-derived TiO2 outperforms the commercial (P25 Degussa), titanium isopropoxide-derived and nontemplated MOF-derived TiO2. Our study demonstrates that the morphologically induced high charge separation efficiency afforded by using MOF crystals as precursors can lead to the generation of catalytically more active materials that c...

Lateral Polymer Photodetectors Using Silver Nanoparticles Promoted PffBT4T-2OD:PC61BM Composite

The fabrication of lateral polymer photodetectors (L-PPDs) is rarely reported in literature. Unlike vertical photodiode or phototransistor, it would be much more difficult to experimentally improve all of the performance metrics in lateral structure under long channel without compromising any of them. The performance metrics include charge separation, photomultiplication, trapped-charge relaxation, dark current, fast response and so on. In this research, L-PPDs with comparable performance to photodiodes were developed, and the photodetectors have the structure of quartz/Ag-NPs (1 nm)/ PMMA (30 nm)/PffBT4T-2OD:PC61BM (D/A ratio = 1:1.2; 140 nm)/Ag–Ag electrodes. A phase control of BHJ allows effective electrons to be trapped under high PCBM ratio, which simultaneously gives high charge separation and photomultiplication (gain = 161.5 at a current density of 73 mA/cm2). Moreover, photogenerated electrons trapped in active layer can be neutralized by photoinduced holes stored in Ag-NPs, resulting in an obvio...

Self-sacrificing template synthesis of CdS quantum dots/Cd-Hap composite photocatalysts for excellent H2 production under visible light

Well dispersive CdS quantum dots (QDs) were successfully in-situ grown on cadmium hydroxyapatite (Cd5(PO4)3OH, Cd-Hap) assembled rods through a self-sacrificing hydrothermal method. No any nocuous organic ligands were used in such self-sacrificing route, allowing for a green approach to prepare CdS QDs with clean surfaces and enough active sites. The deposition of CdS QDs onto Cd-Hap surfaces led to a dramatically enhanced performance in H2 production under visible light irradiation as compared to bulk CdS nanoparticles. The optimal CdS QDs/Cd-Hap composite displayed a H2 evolution rate of 14.1 μmol h−1 without using any noble metal cocatalyst, which was about 4.2 times higher than that of pristine CdS. The apparent quantum efficiency for CdS QDs/Cd-Hap composite was up to 18%. It was also found that CdS QDs/Cd-Hap composite can continuously generate H2 from water in the presence of electron donors for more than 125 h. The enhanced photocatalytic performance of CdS QDs/Cd-Hap composites could be attributed to the high charge separation efficiency resulting from the efficient capture of photoinduced electrons by oxygen vacancies in Cd-Hap rods and the quantum confinement effect of CdS QDs with strong redox capacity as well as the increased active sites.

Hierarchically porous BiOBr/ZnAl1.8Fe0.2O4 and its excellent adsorption and photocatalysis activity

Herein, we reported an efficient and green approach to synthesize a novel 2D BiOBr/ZnAl1.8Fe0.2O4 heterojunction photocatalysts by using tissue paper as template. The as-prepared sample was composed of microfibers interspersed with each other to form 2D structure, and each microfiber was assembled by BiOBr microspheres and ZnAl1.8Fe0.2O4 nanoparticles derived from layered double hydroxides precursors. The obtained samples exhibited both high adsorption capacity and superior photocatalytic activity in removal of antibiotics and anionic dyes from water. The maximum adsorption capacities of BiOBr/ZnAl1.8Fe0.2O4 towards Congo Red (CR) and Doxycycline (DC) were 210.5 and 227.4 mg g−1, respectively, and the pseudo-second order kinetic model describes the adsorption process well. The as-synthesized samples also exhibited superior photocatalytic activity toward low concentration of CR and DC under simulated sunlight irradiation thanks to its high charge separation ratio, hierarchically porous morphology and synergic adsorption-photocatalysis effect.

Three-Dimensional Bicontinuous BiVO4/ZnO Photoanodes for High Solar Water-Splitting Performance at Low Bias Potential.

A photoanode capable of high-efficiency water oxidation at low bias potential is essential for its practical application for photocathode-coupled tandem systems. To address this issue, a photoanode with low turn-on voltage for water oxidation and high charge separation efficiency at low bias potential is essential. In this study, we demonstrate the photoanode of the BiVO4/ZnO three-dimensional (3D) bicontinuous (BC) structure. ZnO has a relatively cathodic flat-band potential, which leads to low turn-on potential; the BiVO4/ZnO 3D BC photoanode shows an onset potential of 0.09 V versus the reversible hydrogen electrode ( VRHE). Moreover, we achieve remarkably high charge separation efficiency at low bias potential (78% at 0.6 VRHE); this is attributed to the application of thin-film BiVO4 shells by high light-scattering properties of the 3D BC structure. As a result, the BiVO4/ZnO 3D BC photoanode generates a high water oxidation photocurrent of up to 3.4 ± 0.2 mA cm-2 (with CoPi catalyst coating). This photocurrent value is reproducible, and the photocurrent-to-O2 conversion efficiency is over 90%. To the best of our knowledge, this is the highest value among the values of the photocurrent at 0.6 VRHE in previous BiVO4-based heterojunction photoanodes.

Design and fabrication of an α-Fe2O3/TiO2/Si 3D hierarchical photoanode for improved photoelectrochemical water splitting

Ordered hierarchical structured films are considered promising photoanodes for high-performance water-splitting because of their large surface area for light absorption and excellent charge transfer process. In this paper, a novel hierarchical structured photoanode based on growing TiO2 on a Si nanowire substrate and coupling with Fe2O3 nanothorns was designed and fabricated via a simple method to obtain photoelectrochemical (PEC) properties. The Fe2O3/TiO2/Si nanowire arrays (NWs) were characterized in detail using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–vis spectra. The 3D Fe2O3/TiO2/Si hierarchical photoanode exhibited a photocurrent density of 3.5 mA cm−2 at a bias potential of 1.23 V (vs. RHE), which is approximately 87.5 times higher than that of the Si nanowire array (NW) photoanode. The measurement results showed that the improved PEC performance could be attributed to the synergistic effect of the large surface area, low charge transfer resistance, and high charge separation in the hierarchical structure.

Titania photonic crystal photocatalysts functionalized by graphene oxide nanocolloids

Photonic crystal-assisted semiconductor photocatalysis has been attracting significant attention as an advanced photon management approach that combines light harvesting with the macro/mesoporous structured materials properties permitting enhanced mass transport and high adsorption. In this work, surface functionalization of well-ordered photonic band gap engineered TiO2 inverse opal films fabricated by the convective evaporation-induced co-assembly method was performed by graphene oxide nanocolloids (nanoGO). The loading of GO nanosheets was determined by the films’ macropore size, with minimal effects on their long range periodicity and photonic properties. While nanoGO deposition reduced mesoporosity of the nanocrystalline titania walls, their surface functionality was greatly improved by the abundant oxygen groups of the GO nanosheets leading to increased pollutant adsorption. Slow photon amplification in the aqueous phase methylene blue photodegradation was identified for the unmodified TiO2 photonic films under both UV–vis and Vis illumination upon spectral overlap of the low energy edge of the inverse opal stop band (in water) with the dye electronic absorption, due to (red) slow photons localized in the titania skeleton that distinctly accelerated dye photodegradation kinetics. The photocatalytic efficiency was further improved for the nanoGO functionalized TiO2 inverse opal films via the synergetic action of interfacial electron transfer from TiO2 to the GO nanosheets. Under UV–vis light, the functionalized photonic films outperformed benchmark mesoporous Aeroxide® P25 TiO2 films where nanoGO modification, despite the enhanced dye adsorption, resulted in adverse effects in photocatalytic degradation due to pore clogging. Combination of the exceptional structural and photonic properties of TiO2 inverse opals with the high adsorption capacity and charge separation afforded by GO nanocolloids is proposed as a promising modification route for the development of efficient photocatalytic films.

Fabrication of nanocomposite photocatalyst CuBi2O4/Bi3ClO4 for removal of acid brown 14 as water pollutant under visible light irradiation.

In the present study, CuBi2O4/Bi3ClO4 nanocomposites have been fabricated via an improved Pechini sol-gel process using the mixtures of various gelling agents and polybasic acids. This work shows that by controlling the reaction conditions such as kind of polybasic acids, gelling agents, pH and mole ratio of polybasic acid to total metals, the CuBi2O4/Bi3ClO4 nanocomposites with ultrafine sphere-like, irregular polyhedral-like, plate-like and cubic-like morphologies were prepared. The phase, elemental composition, morphology and optical characteristics of as-synthesized CuBi2O4/Bi3ClO4 nanostructures were analyzed utilizing UV-Vis, FESEM, TEM, HRTEM, FT-IR, XRD, TOC and EDS techniques. Furthermore, the CuBi2O4/Bi3ClO4 nanocomposites exhibited excellent TOC removal (75%) and photocatalytic activity (92%) to photodegradation of acid brown 14 azo dye as water pollutants under visible light irradiation. The excellent degradation activity of CuBi2O4/Bi3ClO4 photocatalyst can be attributed to the strong visible light absorption, high charge separation efficiency, fine particle size distribution and proper band gap of the nanocomposite. In addition, the reliable photocatalytic mechanism was discussed on the basis of the radical trapping study, which revealed the h+ and O2- radicals were the prevailing active species in the photocatalytic process.

Remarkable enhancement on photoelectrochemical water splitting derived from well-crystallized Bi2WO6 and Co(OH)x with tunable oxidation state

Bismuth tungsten oxide (Bi2WO6) has been extensively utilized as a promising photocatalyst for water splitting and contaminant degradation. However, its applications as the photoanodes for photoelectrochemical (PEC) water splitting have been greatly restricted owing to the intrinsically poor charge transport and sluggish oxygen evolution reaction (OER) kinetics. Herein, we demonstrated that the PEC performances of Bi2WO6 photoanodes could be remarkably enhanced by the well-crystallized construction, which could achieve the favorable conductivity for the bulk charge transport. More importantly, amorphous Co(OH)x nanofilms with optimized oxidation state were decorated on Bi2WO6 photoanode by a facile impregnation method, an unprecedented photocurrent density of 0.94 mA/cm2 and a high surface charge separation efficiency of 98% at 1.23 VRHE has been achieved, more than 58-fold enhanced OER activity compared with traditional Bi2WO6 sample. These results demonstrated that the appropriate crystal construction and cocatalyst decoration with tunable oxidation state could serve as an effective strategy toward developing high-efficiency PEC water splitting systems.

2D a-Fe2O3 doped Ti3C2 MXene composite with enhanced visible light photocatalytic activity for degradation of Rhodamine B

a-Fe2O3/Ti3C2 MXene composite was synthesized using uniform 2D a-Fe2O3 nanosheets and layered Ti3C2 MXene via a facile ultrasonic assisted self-assembly method. The microstructures of as-prepared a-Fe2O3/Ti3C2 MXene composite were characterized and analyzed by X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (UV–vis DRS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Photocatalytic activity of a-Fe2O3/Ti3C2 MXene composite was evaluated for the degradation of Rhodamine B (RhB) under visible light irradiation. The results indicated that 2D a-Fe2O3 nanosheets were well dispersed and anchored on the surface of layered Ti3C2 MXene to form numerous heterostructure interfaces, which can achieve strong visible light absorption and high charge separation efficiency. Due to the synergy effect, a-Fe2O3/Ti3C2 MXene composite had excellent photocatalytic activity and recycling stability. And a possible charge transfer mechanism on the intimate interfaces between a-Fe2O3 and Ti3C2 is also proposed.

Facile Green Synthesis of BiOBr Nanostructures with Superior Visible-Light-Driven Photocatalytic Activity.

Novel green bismuth oxybromide (BiOBr-G) nanoflowers were successfully synthesized via facile hydrolysis route using an Azadirachta indica (Neem plant) leaf extract and concurrently, without the leaf extract (BiOBr-C). The Azadirachta indica leaf extract was employed as a sensitizer and stabilizer for BiOBr-G, which significantly expanded the optical window and boosted the formation of photogenerated charge carriers and transfer over the BiOBr-G surface. The photocatalytic performance of both samples was investigated for the degradation of methyl orange (MO) and phenol (Ph) under the irradiation of visible light. The leaf extract mediated BiOBr-G photocatalyst displayed significantly higher photocatalytic activity when compared to BiOBr-C for the degradation of both pollutants. The degradation rate of MO and Ph by BiOBr-G was found to be nearly 23% and 16% more when compared to BiOBr-C under visible light irradiation, respectively. The substantial increase in the photocatalytic performance of BiOBr-G was ascribed to the multiple synergistic effects between the efficient solar energy harvesting, narrower band gap, high specific surface area, porosity, and effective charge separation. Furthermore, BiOBr-G displayed high stability for five cycles of photocatalytic activity, which endows its practical application as a green photocatalyst in the long run.

Highly dispersed and noble metal-free MPX (M = Ni, Co, Fe) coupled with g-C3N4 nanosheets as 0D/2D photocatalysts for hydrogen evolution

Developing high-efficiency and low-cost photocatalysts by avoiding expensive noble metals is a great challenge. Here, highly dispersed metal (M = Ni, Co, Fe) phosphides modified g-C3N4 nanosheets (CNNS) were prepared through in situ precipitation and solid/gas-phase phosphorization. The results confirmed that metal phosphides (MPX) nanoparticles with high dispersion were well loaded on CNNS surface. The property well reveals the transfer path of photogenerated charges and the origin of high charge separation efficiency in photocatalytic reaction, thus yielding a remarkable catalytic activity. The apparent quantum efficiency (AQY) based on the NiPX/CNNS-900 is up to 6.61% at 400 nm while the H2 evolution rate boosts to 4068.84 μmol·g−1·h−1, which is 50 times higher than that of pristine CNNS. The mechanism could be attributed to the highly dispersed MPX nanoparticles on the surface of CNNS, which acted as effective active sites to promote the separation and migration of photogenerated charges, leading to greatly increase in H2 production. This study is beneficial to further develop the high-efficient, low cost and environmentally-friendly CNNS-based photocatalytic materials for H2 production.