Recombination Rate Of Charge Carriers Research Articles

Effect of carbon nanotubes loading on the photocatalytic activity of zinc oxide/carbon nanotubes photocatalyst synthesized via a modified sol-gel method

Environmental crisis caused by constantly discharged of anthropogenic pollutants into the water bodies has been increasingly arousing the concern of public. Semiconductor metallic oxide such as zinc oxide with photocatalytic ability can serve as an auspicious alternative in tackling the issues mentioned. Nevertheless, massive recombination rate of photo-induced charge carriers, agglomeration and photocorrosion of zinc oxide often reduce its photocatalytic degradation performance. Therefore, this study aimed to elucidate the effect of carbon nanotubes loading on the photocatalytic activity of zinc oxide/carbon nanotubes photocatalyst that synthesized via a modified sol-gel method whereby the synthesis pathway excludes the necessity for organic additive and subsequence annealing treatment. Besides, the carbon nanotubes were added and ultrasonicated with precursor prior to the formation of zinc oxide which can enable the carbon nanotubes to serve as nucleation sites for the growth of zinc oxide. The zinc oxide was found to be attached on carbon nanotubes surface through the formation of zinc carboxylate group and morphologies of the zinc oxide/carbon nanotubes photocatalyst showed that the aggregation of zinc oxide was reduced in the presence of carbon nanotubes. The band gap energy of zinc oxide photocatalyst was slightly blue shifted after hybridized with carbon nanotubes. The zinc oxide/carbon nanotubes photocatalyst demonstrated greater photocatalytic activity than pure zinc oxide in degrading methylene blue under irradiation of sunlight and the photocatalytic activity of the zinc oxide/carbon nanotubes photocatalyst was increased with increasing carbon nanotubes loading. An optimum photocatalytic activity was obtained using zinc oxide/carbon nanotubes with 10 wt.% carbon nanotubes.

Pivotal roles of artificial oxygen vacancies in enhancing photocatalytic activity and selectivity on Bi2O2CO3 nanosheets

There is an increasing interest in bismuth carbonate (Bi2O2CO3, BOC) as a semiconductor photocatalyst. However, pure BOC strongly absorbs ultraviolet light, which drives a high recombination rate of charge carriers and thereby limits the overall photocatalysis efficiency. In this work, artificial oxygen vacancies (OV) were introduced into BOC (OV-BOC) to broaden the optical absorption range, increase the charge separation efficiency, and activate the reactants. The photocatalytic removal ratio of NO was increased significantly from 10.0% for pure BOC to 50.2% for OV-BOC because of the multiple roles played by the oxygen vacancies. These results imply that oxygen vacancies can facilitate the electron exchange between intermediates and the surface oxygen vacancies in OV-BOC, making them more easily destroyed by active radicals. In situ DRIFTS spectra in combination with electron spin resonance spectra and density functional theory calculations enabled unraveling of the conversion pathway for the photocatalytic NO oxidation on OV-BOC. It was found that oxygen vacancies could increase the production of active radicals and promote the transformation of NO into target products instead of toxic byproducts (NO2), thus the selectivity is significantly enhanced. This work provides a new strategy for enhancing photocatalytic activity and selectivity.

(Invited) Time Resolved Spectroscopy of Charge Carriers in TiO2 Anatase and Rutile Single Crystals. Effect of Oxygen Defects and Electrons/Holes Scavengers

In an effort to probe into the fundamentals of charge carriers dynamics relevant to photo-catalytic materials, we have performed femtosecond time resolved spectroscopy (TRS) on anatase and rutile single crystals in the gas phase as well as in aqueous environment. By studying the effect of pump fluence, differences in charge carrier recombination rates and nature between both crystals were observed. The time constants for carrier recombination are two orders of magnitude slower for anatase (101) when compared to those of rutile (110) single crystal. Bulk defects introduced by sample reduction via annealing in ultra-high vacuum resulted in faster recombination rates for both polymorphs. Both surfaces (fresh and reduced) probed by pump fluence dependence measurements revealed that the major recombination channel in fresh and reduced anatase and reduced rutile is the first-order Shockley–Reed mediated. The effect of a hole trapping agent (ethanol) and of electron trapping agents (Ag+ and Ce4+ cations) is investigated over TiO2(110) rutile single crystal. Ethanol adsorption resulted in increasing the transient absorption signal in the 700-950nm with a slight decrease of their lifetime. No change was seen in the 500nm region commonly attributed to the presence of holes. The decay of the 700-950 nm signal mainly composed of two components is considerably perturbed by the presence of Ag+ or Ce4+ cations, which may indicate its surface origin. Work in progress to extract kinetic information from the study of the concentration effect of these metal cations in both the “nominally” hole and electron transient absorption regions.

Facet-Dependent Interfacial Charge Transfer in TiO2/Nitrogen-Doped Graphene Quantum Dots Heterojunctions for Visible-Light Driven Photocatalysis

Interfacial charge transfer is crucial in the efficient conversion of solar energy into fuels and electricity. In this paper, heterojunction composites were fabricated, comprised of anatase TiO2 with different percentages of exposed {101} and {001} facets and nitrogen-doped quantum dots (NGQDs) to enhance the transfer efficiency of photo-excited charge carriers. The photocatalytic performances of all samples were evaluated for RhB degradation under visible light irradiation, and the hybrid containing TiO2 with 56% {001} facets demonstrated the best photocatalytic activity. The excellent photoactivity of TiO2/NGQDs was owed to the synergistic effects of the following factors: (i) The unique chemical features of NGQDs endowed NGQDs with high electronic conductivities and provided its direct contact with the TiO2 surface via forming Ti–O–C chemical bonds. (ii) The co-exposed {101} and {001} facets were beneficial for the separation and transfer of charge carriers in anatase TiO2. (iii) The donor-acceptor interaction between NGQDs and electron-rich {101} facets of TiO2 could remarkably enhance the photocurrent, thus hindering the charge carriers recombination rate. Extensive characterization of their physiochemical properties further showed the synergistic effect of facet-manipulated electron-hole separation in TiO2 and donor-acceptor interaction in graphene quantum dots (GQDs)/TiO2 on photocatalytic activity.

CuO-decorated dual-phase TiO2 microspheres with enhanced activity for photocatalytic CO2 reduction in liquid–solid regime

Abstract Copper oxide (CuO)-decorated anatase and TiO2(B) dual-phase titania microsphere (CuO/TiO2(AB)) photocatalysts were synthesized using a facile two-step approach. The photocatalytic reduction of CO2 to form methyl formate (MF) in methanol was evaluated. The results indicated that the CuO-decorated dual-phase TiO2 microspheres displayed MF yield of 1800 μmol·g−1 under 4 h illumination, higher than other reference photocatalysts, due to its mixed-phase heterojunction structure and larger surface area, thus leading to an enhanced UV-light response, effective separation and low recombination rate of the photoinduced charge carriers. CuO/TiO2(AB) also showed good stability with the MF yield reproducibility greater than 90% in cyclic runs.

In-situ growth of Ag3PO4 on calcined Zn-Al layered double hydroxides for enhanced photocatalytic degradation of tetracycline under simulated solar light irradiation and toxicity assessment

The photocatalytic performance of Ag3PO4 is severely restricted by the photocorrosion and high charge carrier recombination rate. In order to overcome these defects, a novel Ag3PO4/calcined Zn-Al layered double hydroxides (APMO) heterostructure photocatalyst was fabricated via in-situ growth of Ag3PO4 particles on the surface of calcined Zn-Al layered double hydroxides (MMO). The crystal structures, morphologies, optical and photoelectrochemical properties of the as-synthesized samples were characterized using various techniques, and its photocatalytic activity for tetracycline (TC) degradation was evaluated under simulated solar light irradiation. Obviously, all the APMO composites demonstrated much higher photocatalytic performances for TC degradation than pure Ag3PO4. Especially, the APMO70 showed the highest photocatalytic activity, which was almost about 49.3 times as high as that of pure Ag3PO4, and the degradation efficiency was still above 89% after 5 cycles. The improved photocatalytic performance and stability of APMO were ascribed to the efficient charge transfer and strong interfacial contact between Ag3PO4 and MMO. The possible photocatalytic mechanisms involving the charge transfer pathway and reactive species generation during the process of TC degradation were also discussed. Finally, the aquatic toxicity of TC was assessed using Chlorella vulgaris (C. vulgaris) as an ecological indicator, and the result suggested that the as-prepared APMO composite can effectively diminish the aquatic toxicity of TC.

Synthesis of biphasic nanomaterials based on ZnO and SnO2: Application towards photocatalytic degradation of acid red dye

Zn2SnO4/SnO2 and ZnO/SnO2 biphasic nanocatalysts have been synthesized by a facile solvothermal method using ethylene glycol (EG) as solvent in three different ways maintaining the pH of the solution at either 3 or 9 followed by calcination at 700 °C. The nanocatalysts are characterized by different techniques to investigate their structure, composition, morphology and optical properties. The XRD results indicate the formation of pristine biphasic composites. The UV-absorbance and photoluminescence spectra confirms the formation of biphasic composites as well as presence of large number of defects in the prepared nanocatalysts. The biphasic nanocomposites possess better photocatalytic activity towards the degradation of Acid Red-183 (AR-183) dye than pristine SnO2 and ZnO nanoparticles. This is mainly due to better charge separation, minimal recombination rate of charge carriers and defect-riched structures of nanocatalysts.

Experimental and Computational Design of Highly Active Ce–ZrO2–GO Photocatalyst for Eosin Yellow Dye Degradation: The Role of Interface and Ce3+ Ion

As future photocatalyst require high activity and structural stability, the demand for high-performance photocatalyst that increases photocatalytic conversion efficiency is of significant interest. In this study, Ce–ZrO2–GO nanocomposite was fabricated by a co-precipitation technique and used for the photocatalytic degradation of eosin yellow (EY) dye under visible light irradiation. A hybrid DFT calculation was employed to analyse the electronic properties and the underlying mechanism of the observed photoactivity. The as-prepared Ce–ZrO2–GO (0.3% Ce) nanocomposite showed enhanced photodegradation of EY dye, which was about 15.98-fold higher than pure ZrO2. The enhanced performance of Ce–ZrO2–GO nanocomposite for EY dye degradation is due to the synergistic effect between the GO sheets and Ce–ZrO2. From the computational study, Ce ion could act as an electron mediator to capture the photoinduced electrons from ZrO2 to restrain the recombination rate of charge carriers. Testing with different scavengers showed that hydroxyl radicals play a major contribution to the degradation of EY dye with a pseudo first-order reaction kinetics. Total Organic Carbon analysis showed 76% mineralisation of EY dye over Ce–ZrO2–GO (0.3% Ce) nanocomposite, which is photostable and its efficiency remained almost the same after five cycles without any photocorrosion. The present study could offer an alternative approach to develop highly efficient photocatalysts for organic pollutant degradation using metal ion as a mediator to enhance charge migration, activity and structural stability of the nanocomposite. A series of Ce–ZrO2–GO nanocomposite were employed as a photocatalytic to degrade eosin yellow dye from wastewater. The present study offers an alternative approach to develop highly efficient photocatalysts for organic pollutant degradation using Ce ion as a mediator to enhance charge migration, activity and structural stability of the nanocomposite.

In-Situ Synthesis of Nb2O5/g-C3N4 Heterostructures as Highly Efficient Photocatalysts for Molecular H2 Evolution under Solar Illumination

This work focuses on the synthesis of heterostructures with compatible band positions and a favourable surface area for the efficient photocatalytic production of molecular hydrogen (H2). In particular, 3-dimensional Nb2O5/g-C3N4 heterostructures with suitable band positions and high surface area have been synthesized employing a hydrothermal method. The combination of a Nb2O5 with a low charge carrier recombination rate and a g-C3N4 exhibiting high visible light absorption resulted in remarkable photocatalytic activity under simulated solar irradiation in the presence of various hole scavengers (triethanolamine (TEOA) and methanol). The following aspects of the novel material have been studied systematically: the influence of different molar ratios of Nb2O5 to g-C3N4 on the heterostructure properties, the role of the employed hole scavengers, and the impact of the co-catalyst and the charge carrier densities affecting the band alignment. The separation/transfer efficiency of the photogenerated electron-hole pairs is found to increase significantly as compared to that of pure Nb2O5 and g-C3N4, respectively, with the highest molecular H2 production of 110 mmol/g·h being obtained for 10 wt % of g-C3N4 over Nb2O5 as compared with that of g-C3N4 (33.46 mmol/g·h) and Nb2O5 (41.20 mmol/g·h). This enhanced photocatalytic activity is attributed to a sufficient interfacial interaction thus favouring the fast photogeneration of electron-hole pairs at the Nb2O5/g-C3N4 interface through a direct Z-scheme.

Microbial photoelectrochemical cell for improved hydrogen evolution using nickel ferrite incorporated WO3 under visible light irradiation

The production of renewable and sustainable bioenergy has gained much more attention to contribute the society by reducing the impact of global warming. Additionally, biomass sources are highly desired due to its carbon-neutral property. In the current article, hydrogen evolution was studied by using a microbial electrolysis cell (MEC) system, composed of bio-photoelectrochemical cell (BPEC) and a microbial fuel cell (MFC). In this system, hydrogen generation was carried out under the illumination of visible light on BPEC photocathode and electrolysis voltage was supplied by MFC. The highest current density to be found as 0.74 A m−−2 with average rate of H2 evolution 1.46 ± 0.25 mL h−−1. The photogenerated electrons emitted from MFC anode were transported to the photocathode of BPEC by an external circuit. Further, the holes have the ability to capture few electrons generated from MFC anode under visible light irradiation. This kind of situation inhibits the recombination rate of charge carrier's, make it possible the availability of more electrons/holes for H2 production reactions. Additionally, it facilitates the leaving photogenerated electrons from MFC anode to contribute in the hydrogen generation reactions. It is firmed believed that the current study will provide an efficient strategy to rationally design a cost-competitive, ecofriendly and facile-fabrication for material and method for proficient hydrogen evolution.

Enhancement of photocatalytic hydrogen production of semiconductor by plasmonic silver nanocubes under visible light

A pivotal factor limiting the photocatalytic efficiency of water splitting is the high charge-carrier recombination rate in the photocatalyst. Here, we demonstrate this issue can be relieved by combining photocatalyst with a plasmonic metal. We introduced organic molecule capped silver nanocubes (Ag NCs) to Rh2−yCryO3/GaN:ZnO (host photocatalyst: GaN:ZnO, hydrogen production cocatalyst: Rh2−yCryO3) and showed that the Ag NCs improved the photocatalytic water splitting efficiency. Finite difference time domain simulations suggested this improvement can be ascribed to efficient photon scattering and intense local electric field by the localized surface plasmon resonance of Ag NCs. The Ag-Rh2−yCryO3/GaN:ZnO composite exhibited high photochemical stability due to the protection of Ag NCs by the organic surfactant.

2D/2D/2D heterojunction of Ti3C2 MXene/MoS2 nanosheets/TiO2 nanosheets with exposed (001) facets toward enhanced photocatalytic hydrogen production activity

Exposing the highly active facets and hybridizing the photocatalyst with appropriate cocatalysts with right placement have been regarded as a powerful approach to high performance photocatalysts. Herein, TiO2 nanosheets (NSs) are in situ grown on highly conductive Ti3C2 MXene and then MoS2 NSs are deposited on the (101) facets of TiO2 NSs with mainly exposed high-active (001) facets through a two-step hydrothermal method. And a unique 2D-2D-2D structure of Ti3C2@TiO2@MoS2 composite is achieved. With an optimized MoS2 loading amounts (15 wt%), the Ti3C2@TiO2@MoS2 composite shows a remarkable enhancement in the photocatalytic H2 evolution reaction compared with Ti3C2@TiO2 composite and TiO2 NS. It also shows good stability under the reaction condition. This arises from: (i) the in situ growth of TiO2 NSs construct strong interfacial contact with excellent electronic conductivity of Ti3C2, which facilitates the separation of carriers; (ii) the coexposed (101) and (001) facets can form a surface heterojunction within single TiO2 NS, which is beneficial for the transfer and separation of charge carriers; and (iii) the MoS2 NSs are deposited on the electrons-rich (101) facets of TiO2 NSs, which not only effectively reduces the charge carriers recombination rate by capturing photoelectrons, but also makes TiO2 NSs expose more highly active (001) facets to afford high-efficiency photogeneration of electron-hole pairs.

Facile synthesis of g-C3N4/CdWO4 with excellent photocatalytic performance for the degradation of Minocycline

A novel g-C3N4/CdWO4 composite was formed by hydrothermal process and utilized for the removal of Minocycline (MC) antibiotic under visible light exposure. The XRD patterns of synthesized sample reveal the pure crystalline structure and phase of g-C3N4/CdWO4. The SEM images of g-C3N4/CdWO4 showed regular short rod structure with diameter in the range of 20–60 nm. These images also showed that the g-C3N4/CdWO4 structure has well contacted surfaces which enhanced the interfacial transfer of charge as a result of which the performance of photocatalyst was improved. The energy dispersive spectroscopy (EDS) images of g-C3N4, CdWO4 and g-C3N4/CdWO4 conclude that there were no impurities in the synthesized samples. SEM and EDS results confirm the interface interaction develop between g-C3N4 and CdWO4 due to hybridization. The FTIR spectrum of composite showed that the composite formed had extensively conjugated system and the band gap energies calculated for CdWO4, g-C3N4 and g-C3N4/CdWO4 were 3.31 eV, 2.67 eV and 2.71 eV respectively. A remarkable drop in photoluminescence intensity of g-C3N4/CdWO4 was observed as compared to pure g-C3N4 and CdWO4 which led to lower recombination rate of photo-induced charge carriers and hence a higher photocatalytic performance for the degradation of minocycline under visible-light irradiation.

Introduction of nitrogen defects into a graphitic carbon nitride framework by selenium vapor treatment for enhanced photocatalytic hydrogen production

Graphitic carbon nitride (g-C3N4) is a metal-free semiconductor photocatalyst that has attracted significant attention due to its promising application in photocatalytic hydrogen production. However, pristine g-C3N4 suffers from a high recombination rate of photo-generated charge carriers and also has a limited visible-light absorption range, resulting in low photocatalytic activity. Herein, we report on the preparation and testing of a g-C3N4 photocatalyst with tunable nitrogen defects that delivered improved photocatalytic activity. The nitrogen defects were gradually introduced into the g-C3N4 framework by a selenium vapor treatment of pure g-C3N4, which resulted in improved, stable catalytic activity for photocatalytic hydrogen production. Based on the experimental results and DFT calculations, we proposed that the enhanced photoactivity is attributed to the defect state (DS) formed by the nitrogen vacancy (VN) in the unit cell of g-C3N4 and a small widening of visible light absorption. This nitrogen-based photocatalyst with nitrogen deficiencies was found to deliver an average hydrogen generation rate of 1.16 mmol g−1 h−1 at room temperature (25 °C), which was 3.4 times greater than pristine g-C3N4. This process of introducing nitrogen defects into the graphitic carbon provides a promising way for enhancing the photocatalytic activity of g-C3N4-based materials for hydrogen production.

Electronic pump boosting photocatalytic hydrogen evolution over graphitic carbon nitride

The high rate of charge carrier recombination greatly limits the photocatalytic activity of graphitic carbon nitride (g-C3N4). In this contribution, body center cubic indium tin oxide nanoparticles (ITO NPs) as electronic pumps are directly formed on g-C3N4 via a facile one-pot method. The hydrogen production rate of Pt/ITO/g-C3N4 is 3.3 times as high as that of Pt/g-C3N4 under visible light (λ > 420 nm) irradiation. The excellent photocatalytic hydrogen evolution performance should be attributed to the close contact of well-dispersed ITO NPs with g-C3N4 in the prepared ITO/g-C3N4 and in situ formation of Pt onto ITO NPs, leading to accelerated photogenerated electron transfer from g-C3N4 to Pt through ITO pumps for hydrogen generation. In the present work, we successfully demonstrate a high-performance Pt/ITO/g-C3N4 system for visible light hydrogen evolution, and the essential role of ITO NPs as the electronic pumps for efficient photogenerated electron transfer could be informative for designing efficient systems for solar hydrogen generation.

Water-assisted prepared porous carbon nitride incorporated AgBr for highly efficient photocatalytic degradation of orange G under visible light

Carbon nitride is a commonly used photocatalyst for the degradation of organic dyes. However, the high rate of charge carrier recombination limit the photocatalytic activity. Here, a series of porous carbon nitride with AgBr nanoparticles (CN/AgBr) heterojunction are fabricated by thermal condensation of urea with the water and an in situ ion exchange approach. The porous structure of CN is beneficial to improve the photocatalytic performance and enhance the absorption of light energy, which is due to the multiple reflections of light within the macropores layered structure. And the incorporation of AgBr inhibit the charge carriers recombination due to the formation of heterojunction with CN. Furthermore, the photocatalytic activity of all samples are evaluated and display excellent activity in the degradation of orange G under visible light illumination. Among them, the CN/AgBr30 perform the most degradation efficiency, with a removal ratio of up to 92% within 10 min, which is attributed to efficient charge separation and transfer. At last, a photocatalytic mechanism is put forward and explained based on the ESR experiments, free radical and hole scavenging experiments and transient response photocurrent results.

Fabrication of interlayer β-CD/g-C3N4@MoS2 for highly enhanced photodegradation of glyphosate under simulated sunlight irradiation.

Graphitic carbon nitride (g-C3N4) has been considered to be a promising metal-free photocatalyst, although the high recombination rate of charge carriers and poor absorption of visible light have limited its applications. In order to overcome these problems, an interlayer composite photocatalyst that comprised β-cyclodextrin (β-CD), oxygen-doped C3N4 (O-C3N4) and molybdenum disulfide (MoS2) was successfully constructed for the highly enhanced photodegradation of glyphosate in this study. The structure and morphology, optical properties, and photoelectrochemical properties of the prepared photocatalyst were characterized via a series of characterization techniques. The average fluorescence lifetime of the composite photocatalyst was extended from 6.67 ns to 7.30 ns in comparison with that of g-C3N4, which indicated that the composite photocatalyst enhanced the absorption of visible light and also inhibited the recombination of electron–hole pairs. The mass ratio of MoS2 that corresponded to O-C3N4/MoS2-5 enabled the highest removal rate under simulated sunlight irradiation, which was almost twice that achieved using pure g-C3N4. Relative species scavenging experiments revealed that ·O2− was the main species during the process of photodegradation. Besides, a toxicity test indicated that glyphosate became less toxic or non-toxic after photodegradation. This study provided an effective, feasible and stable photocatalyst driven by simulated sunlight irradiation for the highly enhanced photodegradation of glyphosate.

Effect of monatomic and molecular ion irradiation on time resolved photoluminescence decay in GaN

Optical effects induced in silicon-doped wurtzite (0001) GaN epilayers by keV monatomic and molecular ion irradiation were experimentally investigated. Results were analyzed together with data on structure defect formation. In all the cases under consideration, an increase in the collision cascade density (the cases of molecular and heavy atomic ion bombardment) enhances the stable damage accumulation rate and, accordingly, intensifies quenching of luminescence. The processes of PL suppression were theoretically considered as an increase of surface recombination rate of nonequilibrium photo-excited charge carriers due to production of stable damage at the irradiated subsurface layer. It is shown that carrier diffusion determines PL decay time shortening in the shallow implantation cases studied.

Fabrication of novel 1D/2D V2O5/g-C3N4 composites as Z-scheme photocatalysts for CR degradation and Cr (VI) reduction under sunlight irradiation

Photocatalytic materials for environmental remediation of organic pollutants and heavy metals require not only a strong visible light response and high photocatalytic performance, but also the regeneration and reuse of catalysts. In this work, 1D/2D V2O5 nanorods/g-C3N4 nanosheets (VONRs/CNNs) composites were prepared by a facile impregnation method and employed in the degradation of a Congo red (CR) and reduction of Cr (VI) under sunlight irradiation. The as-prepared samples were studied by several characterization techniques including XRD, SEM, TEM, EDS, XPS, FTIR, UV–vis DRS and PL. Results revealed that the interface interaction between VONRs and CNNs was recognized via V2O5 nanorods loading on the surface of g-C3N4 nanosheets, improving the separation and transfer of photogenerated electron-hole pairs and restraining the recombination rate of charge carriers. As a result, the photocatalytic activity of the composites was enhanced in comparison with pure CNNs and VONRs. The photocatalytic efficiency of optimal composite (4-VONRs/CNNs) for the removal of CR (Cr (VI)) was about 9.33 (4.22) and 73.52 (19.2) times higher than that of pure CNNs and VONRs, respectively. Meanwhile, the 4-VONRs/CNNs exhibited good photocatalytic stability in recycling experiments. Such enormous enhancement in photocatalytic performance was predominantly ascribed to the efficient separation and transfer of photogenerated electron-hole pairs at the VONRs/CNNs interface imparted through the direct Z-scheme charge carrier migration mechanism. Moreover, the energy band structure and the quenching effects of different scavengers demonstrated that the electrons of CNNs and holes of VONRs with higher oxidizability and reducibility are the real participants in photocatalytic reactions.

Pronounced light trapping effect and enhanced photo-electrochemical property of type (II) aligned graphitic-C3N4 with embedded 1-D ZnO nanostructures

Graphitic carbon nitride (g-C3N4) with embedded 1D-ZnO nanostructures was prepared by simple two step thermal decomposition process. Photocatalyst exhibited higher optical absorption than pure ZnO due to π-π conjugations of C3N4, which thus allow greater adsorption on its surface. Conduction band (CB) edge of g-C3N4 being more negative than ZnO and Valence band (VB) of ZnO is more positive than VB of g-C3N4; this alignment of Type (II) resulted in transfer of excited electrons in g-C3N4 to the CB of ZnO. This charge transfer created the internal electrostatic potential, which aided in reducing the recombination rate of charge carriers. Finally, samples were tested for photo-electrochemical activity measured by generated photocurrent density with respect to voltage and time under illumination conditions.