Photocatalytic water splitting Research Papers (original) (raw)

The possibility of producing bioethanol from the biomass of finger millet straw was studied. The effects of temperature, acid concentration, hydrolysis time, and substrate concentration were investigated. The result showed that a maximum... more

The possibility of producing bioethanol from the biomass of finger millet straw was studied. The effects of temperature, acid concentration, hydrolysis time, and substrate concentration were investigated. The result showed that a maximum sugar content of 79.04 and 82.01 %w/w was achieved using phenol-sulfuric acid and Fehling method, respectively, from hydrolysis of 10 % biomass concentration at 2 % sulfuric acid, 35 o C reaction temperature, and 4 days of hydrolysis time. The optimized hydrolyzate sample was fermented at optimized pH 6.0, 4 g/L yeast concentration, 32.5 o C reaction temperature, 4 days of fermentation time, and maximum of 7.28 %w/v of ethanol content was obtained using Pycnometer measurement. In general, the bioethanol achieved from FMS (7.28 %) at optimized conditions were highly promising and hence, it can be employed as an alternative lignocellulosic feedstock for bioethanol production rather than using food crops such as corn, sugarcane, etc.

Objective of this paper is to produce hydrogen which is an ideal fuel for the next generation because it is abundantly available in nature, energy efficient and clean. Wide varieties of technologies are available to produce hydrogen but... more

Objective of this paper is to produce hydrogen which is an ideal fuel for the next generation because it is abundantly available in nature, energy efficient and clean. Wide varieties of technologies are available to produce hydrogen but only few of them are considered environmental friendly. Solar water splitting via photo catalytic reaction is one of them which have attracted tremendous attention. In this paper we are working on hydrogen production via solar splitting. Photo catalytic water splitting is one of the promising technologies to produce pure and clean hydrogen. Since it is reasonable having low process cost and has a small reactor, it can be made for house hold application and hence has a huge market potential. Generation of hydrogen under visible irradiation is the main area of work. Based on the literature reported here, visible irradiation can be achieved by doping of TiO2 with metal or non-metal. We have used Fe doping to increase the efficiency. The result indicates that Fe doped sieves produce more hydrogen than the normal TiO2 coated sieve and the efficiency can be increased if we increase the number of doped sieves and surface area.

Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel... more

Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of the melem hydrazine precursor. Characterization revealed that in the C3N5 polymer, two s-heptazine units are bridged together with azo linkage, which constitutes an entirely new and different bonding fashion from g-C3N4 where three heptazine units are linked together with tertiary nitrogen. Extended conjugation due to overlap of azo nitrogens and increased electron density on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum resulting in bandgap reduction down to 1.76 eV. XRD, He-ion imaging, HR-TEM, EELS, PL, fluorescence lifetime imaging, Raman, FTIR, TGA, KPFM, XPS, NMR and EPR clearly show that the properties of C3N5 are distinct from pristine carbon nitride (g-C3N4). When used as an electron transport layer (ETL) in MAPbBr3 based halide perovskite solar cells, C3N5 outperformed g-C3N4, in particular generating an open circuit photovoltage as high as 1.3 V, while C3N5 blended with MAxFA1–xPb(I0.85Br0.15)3 perovskite active layer achieved a photoconversion efficiency (PCE) up to 16.7%. C3N5 was also shown to be an effective visible light sensitizer for TiO2 photoanodes in photoelectrochemical water splitting. Because of its electron-rich character, the C3N5 material displayed instantaneous adsorption of methylene blue from aqueous solution reaching complete equilibrium within 10 min, which is significantly faster than pristine g-C3N4 and other carbon based materials. C3N5 coupled with plasmonic silver nanocubes promotes plasmon-exciton coinduced surface catalytic reactions reaching completion at much low laser intensity (1.0 mW) than g-C3N4, which showed sluggish performance even at high laser power (10.0 mW). The relatively narrow bandgap and 2D structure of C3N5 make it an interesting air-stable and temperature-resistant semiconductor for optoelectronic applications while its electron-rich character and intrasheet cavity make it an attractive supramolecular adsorbent for environmental applications.

Pemaparan singkat mengenai prinsip dasar dari UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis DRS).

Hybrid nanocomposites of Cu 2 O−(R)TiO 2 , CuO−(R)TiO 2 , and Cu 3 TiO 4 −(R)TiO 2 (where R represents the rutile phase of TiO 2) nanopowders (NPs) were produced via solid state reaction followed by 20 h of ball milling; their... more

Hybrid nanocomposites of Cu 2 O−(R)TiO 2 , CuO−(R)TiO 2 , and Cu 3 TiO 4 −(R)TiO 2 (where R represents the rutile phase of TiO 2) nanopowders (NPs) were produced via solid state reaction followed by 20 h of ball milling; their photocatalytic activities were evaluated for methylene blue (MB) degradation under visible light intensity (∼65 mW/ cm 2) and compared to Degussa P25 under both ultraviolet (UV) and visible light irradiations. The highest MB degradation rate under the visible light irradiation was observed to be 0.271 ± 0.010 h −1 for Cu 2 O−(R)TiO 2 NPs, which was 2.5 times higher than that of P25, while under UV illumination both the Cu 2 O−(R)TiO 2 and Cu 3 TiO 4 − (R)TiO 2 NPs were slightly less active than that of the P25, and CuO−(R)TiO 2 was the least active among all. The solar energy conversion performance of the Cu x O−(R)TiO 2 NPs was observed to be controlled by the applied potentials. The highest stable cathodic photocurrent density (6.3 μA/cm 2) was observed for Cu 2 O−(R)TiO 2 NPs at a low negative bias voltage (−0.3 V vs Ag/AgCl, 3 M KCl) and under the solar simulator (AM 1.5G). This method to design multifunctional visible-light-active metal oxides is simple and scalable and has the potential to prepare other efficient photocatalysts for solar energy conversion.

This book details the chemistry of visible light-induced photocatalysis using different classes of nanocomposites. Starting with a general introduction and explanation of basic principles and mechanisms of (visible) light-induced... more

This book details the chemistry of visible light-induced photocatalysis using different classes of nanocomposites. Starting with a general introduction and explanation of basic principles and mechanisms of (visible) light-induced photocatalysis in the first two chapters, the following chapters detail the different types and classes of nanocomposites currently used in light-induced photocatalytic applications, including e.g. metal and mixed metal-oxide nanoparticles and –composites, nanoporous materials, polymeric and carbon-based nanocomposites. They explain the characteristics and importance of the different types of nanocomposites, as well as their synthesis and fabrication.In the end of the book an outlook on the unique applications of novel nanocomposites is offered, for example in water treatment and disinfection and removal of pollutants from wastewater, self-cleaning window panes based on photoactive materials, and many more. The book also addresses the challenges in present photocatalytic research, and therefore is a must-read for everybody interested in the developing field of nanocomposites and visible light-induced photocatalysis.

Background: The conversion of carbon dioxide into worthwhile chemicals through photo-catalysis has been a matter of attraction for the last four decades among the scientific community. However, the conversion rate has not yet been... more

Background: The conversion of carbon dioxide into worthwhile chemicals through photo-catalysis has been a matter of attraction for the last four decades among the scientific community. However, the conversion rate has not yet been achieved to the desired efficiency due to the inevitable barriers associated with the process making it as a Holy Grail. This presentation deals with the identification and critical evaluation of the hurdles that pulls back the photocatalytic processes on track and the recent advances in the scientific field that pertain to the photocatalytic conversion of carbon dioxide in the near future. Methods: We explored the content of more than 200 original research articles that are relevant to the desired topic and extracted the current knowledge on the so called photo-catalytic reduction of carbon dioxide. We have approached all the articles in a perspective way rather than a word to word recent advances in the field and found out the major limitations that have to be rectified. Results: The issues related to the state-of-the-art of carbon dioxide reduction are described in separate sections in detail. Mechanistic aspects should to be revisited with the help of advanced instrumentation facilities. Major problem associated is finding the appropriate material, hence efficient material should be engineered to overcome the high energy barrier associated with the reduction process. Product analysis as well as efficiency determination are highly susceptible to errors. It is very difficult to compare the work produced by any two labs between each other! Conclusion: There are so many hurdles associated invariably with the photocatalytic carbon dioxide reduction process which must be rectified in order to create an energy, sustainable society using direct sunlight as a primary energy source just as plants do. It could happen only by the collaborative research effort from various groups, irrespective of the implicit bias among the scientific community.

This paper examines photocatalytic hydrogen production as a clean energy solution to address challenges of climate change and environmental sustainability. Advantages and disadvantages of various hydrogen production methods, with a... more

This paper examines photocatalytic hydrogen production as a clean energy solution to address challenges of climate change and environmental sustainability. Advantages and disadvantages of various hydrogen production methods, with a particular emphasis on photocatalytic hydrogen production, are discussed in this paper. Social, environmental and economic aspects are taken into account while assessing selected production methods and types of photocatalysts. In the first part of this paper, various hydrogen production options are introduced and comparatively assessed. Then, solar-based hydrogen production options are examined in a more detailed manner along with a comparative performance assessment. Next, photocatalytic hydrogen production options are introduced, photocatalysis mechanisms and principles are discussed and the main groups of photocatalysts, namely titanium oxide, cadmium sulfide, zinc oxide/sulfide and other metal oxide-based photocatalyst groups, are introduced. After discussing recycling issues of photocatalysts, a comparative performance assessment is conducted based on hydrogen production processes (both per mass and surface area of photocatalysts), band gaps and quantum yields. The results show that among individual photocatalysts, on average, Au–CdS has the best performance when band gap, quantum yield and hydrogen production rates are considered. From this perspective, TiO 2 –ZnO has the poorest performance. Among the photocatalyst groups, cadmium sulfides have the best average performance, while other metal oxides show the poorest rankings, on average.

Heterogeneous photocatalysis is a promising technology especially for environmental remediation. Despite more than a decade of worldwide research in developing photocatalytic efficiency improving techniques, many questions regarding the... more

Heterogeneous photocatalysis is a promising technology especially for environmental remediation. Despite more than a decade of worldwide research in developing photocatalytic efficiency improving techniques, many questions regarding the large scale application of photocatalytic reactors still remain unanswered. Recently, improving the photocatalytic efficiency has gained scientific attention because it might lead to more economical and robust photocatalytic operation for environmental remediation. In this review, fundamental and comprehensive assessments of the photocatalytic concepts and their applications for environmental remediation are reviewed. The existing challenges and strategies to improve the photocatalytic efficiency are discussed. Further, recent developments and future research prospects on photocatalytic systems for environmental applications are also addressed.

The use of biomass to produce transportation and related fuels is of increasing interest. In the traditional approach of converting oils and fats to fuels, trans-esterification processes yield a very large coproduction of glycerol.... more

The use of biomass to produce transportation and related fuels is of increasing interest. In the traditional approach of converting oils and fats to fuels, trans-esterification processes yield a very large coproduction of glycerol. Initially, this coproduct was largely ignored and then considered as a useful feedstock for conversion to various chemicals. However, because of the intrinsic large production, any chemical feedstock role would consume only a fraction of the glycerol produced, so other options had to be considered. The reforming of glycerol was examined for syngas production, but more recently the use of photocatalytic decomposition to hydrogen (H 2) is of major concern and several approaches have been proposed. The subject of this review is this greener photocatalytic route, especially involving the use of solar energy and visible light. Several different catalyst designs are considered, together with a very wide range of secured rates of H 2 production spanning several orders of magnitude, depending on the catalytic system and the process conditions employed. H 2 production is especially high when used in glycerol-water mixtures.

A B S T R A C T Photocatalytic water-splitting technology by using nano-sized TiO 2 can produce low cost and environment-friendly hydrogen using renewable resource such as solar energy, which can fulfil the future requirements of energy.... more

A B S T R A C T Photocatalytic water-splitting technology by using nano-sized TiO 2 can produce low cost and environment-friendly hydrogen using renewable resource such as solar energy, which can fulfil the future requirements of energy. Nano-sized TiO 2 is highly efficient as a semiconductor photocatalyst possessing high surface area. The significant drawbacks of utilising TiO 2 as photocatalysts are reduced absorption capacity of visible radiation and fast recombination of photoexcited electron/hole (e − /h +) pair. Its activity is restricted to UV light, which is only ∼3–5% of the solar spectrum. This present review elucidates various aspects and the recent researches related to TiO 2 nano photocatalysis for the effective solar hydrogen generation via photocatalytic water splitting technology .

Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photo-catalytic activity of... more

Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photo-catalytic activity of nanostructured TiO 2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO 2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO 2 for photoelectrochemical water splitting. Arrays of rutile phase TiO 2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO 2 under visible light irradiation and transfer of holes to the aqueous electrolyte. CNFQD-sensitized TiO 2 nanorods exhibited a strong pho-toelectrochemical response up to 500 nm. Reuse experiments confirmed robustness and long term stability of the sample without exhausting the catalytic performance. The present work demonstrates a new pathway to sensitize TiO 2 to visible photons by the in situ formation of embedded heterojunctions with fluorine doped carbon nitride quantum dots.

In this study, visible light-driven heterogeneous photocatalysts for hydrogen production are comparatively assessed based on technical, environmental, and cost criteria. The photocatalysis systems are compared with respect to their (i)... more

In this study, visible light-driven heterogeneous photocatalysts for hydrogen production are comparatively assessed based on technical, environmental, and cost criteria. The photocatalysis systems are compared with respect to their (i) rate of hydrogen generation per gram; (ii) rate of hydrogen generation per m2 of the specific surface area; and (iii) the band gap energy. The photocatalysis systems are also compared and discussed in terms of flammability, reactivity, and their impact on living systems' health. Furthermore, the costs of the required components of the photocatalysis systems are ranked. In addition to individual photocatalyst comparison, seven photocatalyst groups are ranked and compared. The results show that TiO2-C-362 and Ag0.03Mn0.40Cd0.60S show the highest in terms of µmol/h-gcat and µmol/h-m2cat, respectively, and TiO2-C-362 has the highest overall rankings. The Zn/In/S-based photocatalyst groups show the highest hydrogen production rate in terms of µmol/h-gcat and µmol/h-m2cat. Overall, Cd/S/Zn has the highest rankings when cost and health and environmental impact criteria are taken into account. Copyright © 2014 John Wiley & Sons, Ltd.

Bulk g‐C3N4 is an earth‐abundant, easily synthesizable, and exceptionally stable photocatalyst with an electronic bandgap of 2.7 eV. Herein, the concepts of P‐doping and size quantization are combined to synthesize highly fluorescent... more

Bulk g‐C3N4 is an earth‐abundant, easily synthesizable, and exceptionally stable photocatalyst with an electronic bandgap of 2.7 eV. Herein, the concepts of P‐doping and size quantization are combined to synthesize highly fluorescent P‐doped carbon nitride quantum dots (CNPQDs) with a bandgap of 2.1 eV. CNPQDs are hosted on anatase‐phase and rutile‐phase TiO2 nanotube array scaffolds, and examined as photoanodes for sunlight‐driven water‐splitting and as photocatalysts for surface catalytic reactions. Square‐shaped rutile phase TiO2 nanotube arrays (STNAs) decorated with CNPQDs (CNPQD‐STNA) generate 2.54 mA cm−2 photocurrent under AM1.5 G simulated sunlight. A champion hydrogen evolution rate of 22 µmol h−1 corresponds to a Faradaic efficiency of 93.2%. In conjunction with Ag nanoparticles (NPs), the CNPQD‐STNA hybrid is also found to be an excellent plexcitonic photocatalyst for the visible light‐driven transformation of 4‐nitrobenzenethiol (4‐NBT) to dimercaptoazobenzene (DMAB), producing reaction completion at a laser power of 1 mW (532 nm) while Ag NP/TNA and Ag NP/STNA photocatalysts cannot complete this transformation even at 10 mW laser power. The results point the way forward for photochemically robust, noble metal free, visible light harvesting photoacatalysts based on nanostructured heterojunctions of graphenic frameworks with TiO2.

Ag and CuO nanoparticles (NPs) synthesized on the surface of commercial TiO 2 (P25) by radiolytic reduction were characterized by diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), high-angle annular... more

Ag and CuO nanoparticles (NPs) synthesized on the surface of commercial TiO 2 (P25) by radiolytic reduction were characterized by diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). In the case of modification with silver and copper, results from HAADF-STEM, EDS, XPS, and XAS show that Ag@CuO nanoparticles (large silver cores decorated with small clusters of CuO) were obtained on TiO 2 −P25. The photocatalytic properties of bare and modified TiO 2 −P25 were studied for phenol photodegradation and for acetic acid oxidation under UV and visible irradiation. The mechanisms involved in photocatalysis were studied by time-resolved microwave conductivity (TRMC) and action spectra (AS). The electronic properties of the surface-modified TiO 2 −P25 were studied by TRMC to follow the charge-carrier dynamics. The modification with Ag nanoparticles or CuO nanoclusters induces an increase in the photocatalytic activity under both UV and visible light. The photocatalytic activity of Ag@CuO/P25 is higher under UV light but lower under visible light compared to the activity of CuO/P25 and Ag/P25. TRMC measurements show that surface modification of TiO 2 −P25 with Ag, CuO, and Ag@CuO nanoparticles plays a role in charge-carrier separation, increasing the activity under UV-light, and that Ag@CuO NPs are more efficient electron scavengers than Ag NPs and CuO nanoclusters. The localized surface plasmon resonance (LSPR) of Ag NPs and the narrow band gap of CuO induce an activity under visible light. The TRMC shows also responses under visible-light irradiation at different fixed wavelengths indicating that electrons are injected from Ag NPs in the conduction band (CB) of TiO 2 −P25. Moreover, under visible light, the photocatalytic activity of CuO/P25 is higher than that of plasmonic Ag/P25. CuO is able to activate TiO 2 −P25 in a wider range of wavelengths under visible-light irradiation, compared to the activation achieved by the presence of silver. The action spectra correlate with the absorption spectra for irradiation wavelengths in the range of 350−470 nm proving that decomposition of acetic acid is carried out by a photocatalytic mechanism.

The design, synthesis, and photoelectrochemical characterization of Co3(PO4)2, a hydrogen evolving catalyst modified with reduced graphene oxide (RGO), is reported. The 3D flowerlike Co3(PO4)2 heterojunction system, consisting of 3D... more

The design, synthesis, and photoelectrochemical characterization of Co3(PO4)2, a hydrogen evolving catalyst modified with reduced graphene oxide (RGO), is reported. The 3D flowerlike Co3(PO4)2 heterojunction system, consisting of 3D flowerlike Co3(PO4)2 and RGO sheets, was synthesized by a one-pot in situ photoassisted method under visible-light irradiation, which was achieved without the addition of surfactant or a structure-directing reagent. For the first time, Co3(PO4)2 is demonstrated to act as a hydrogen evolving catalyst rather than being used as an oxygen evolving photoanode. In particular, 3D flowerlike Co3(PO4)2 anchored to RGO nanosheets is shown to possess dramatically improved photocatalytic activity. This enhanced photoactivity is mainly due to the staggered type II heterojunction system, in which photoinduced electrons from 3D flowerlike Co3(PO4)2 transfer to the RGO sheets and result in decreased charge recombination, as evidenced by photoluminescence spectroscopy. The band gap of Co3(PO4)2 was calculated to be 2.35 eV by the Kubelka–Munk method. Again, the Co3(PO4)2 semiconductor displays n-type behavior, as observed from Mott–Schottky measurements. These RGO–
Co3(PO4)2 conjugates are active in the visible range of solar light for water splitting and textile dye degradation, and can be used towards the development of greener and cheaper photocatalysts by exploiting solar light.

As populations grow, global energy consumption in the next 30 years is predicted to rise by nearly 50%. Nowadays and many years before, the most energy worldwide is provided by fossil fuel which leads to severe pollution and contributes... more

As populations grow, global energy consumption in the next 30 years is predicted to rise by nearly 50%. Nowadays and many years before, the most energy worldwide is provided by fossil fuel which leads to severe pollution and contributes to the greenhouse effect. Hydrogen is the most ideal alternative clean energy, but currently, there is no significant hydrogen production from renewable sources. Hence, there is an urgent need for the development of new photocatalysts which will allow a water splitting for hydrogen production. The photocatalytic water splitting using TiO2 offers a promising approach for clean, low-cost, and environmentally friendly production of hydrogen as a sustainable fuel. This paper reviews some recently used methods of synthesis such as hydrothermal, rapid breakdown anodization method, impregnation method, and sol-gel synthesis for the preparation of modified TiO2materials. These methods of synthesis provide the production of ultra-thin mesoporous TiO2 nanosheets, nanorods, and nanotubes as well as heterojunction structures. Some investigations show that introduction of Ti3+ atomic defects is beneficial for the photocatalytic water splitting for hydrogen generation. Some progress has been achieved by heterocoupling the two or more semiconductors. There is experimental evidence that in the presence of alcohol as a sacrificial agent, H2production rates decreased from a higher number of hydroxyl groups i.e. in order 3>2>1. The H2 generation is also larger when TiO2 is modified with the addition of small quantity of metal nanoparticles such as Pt, Pd, and Ni. One study has shown that the samples sensitised with Pt nanoparticles were superior to Pd and Ni modified TiO2, the other has shown that the co-catalyst activity followed the order Pd>Pt≈Au.

Layered double hydroxides (abbreviated as LDHs) are one of the nano-ordered layered compounds. The importance of layered compound is based on their ability to retain chemical species with electrical charges compatible to those of the... more

Layered double hydroxides (abbreviated as LDHs) are one of the nano-ordered layered compounds. The importance of layered compound is based on their ability to retain chemical species with electrical charges compatible to those of the layers. In this study we have reported the synthesis of nano-sized layered double hydroxide (LDH) by co-precipitation method using two different surfactants as cetyl trimethyl ammonium bromide (CTAB) and octadecyl trimethyl ammonium bromide (ODTMA) having different critical micelle concentration (CMC) /chain length and its comparative results on calcined surface modified LDH (CS-LDH). The structure of surface modified layered double hydroxide (CS-LDH) synthesized is unique and has important advantages to the photocatalytic activity. LDH has significant number of application due to their structural, chemical properties etc., these compounds can be used as catalyst, adsorbents, anion exchanger. The photocatalytic activity of prepared surface modified CS-LDH was tested on degradation of the methylene blue (MB) dye in an aqueous solution. The surface characteristics of LDH and CS-LDH were examined using Energy Dispersive X-ray (EDX), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and UV-Visible spectrophotometer for Photocatalytic activity under visible light using MB dye. It was observed that highly exfoliated and basal spacing in CS-LDH-ODTMA which enhanced photocatalytic activity (Approx. 60% degradation) than that of comparison to CS-LDH-CTAB (Approx. 32% degradation). Introduction Among the group of minerals referred to as 'Non-Silicate Oxides and Hydroxides' (Newman, 1987), the 'layered double hydroxides' (LDH) have many physical and chemical properties that are surprisingly similar to those of clay minerals. Their layered structure, wide chemical compositions (due to variable isomorphous substitution of metallic cations), variable layer charge density, ion-exchange properties, reactive interlayer space, swelling in water, and rheological and colloidal properties make LDH clay-like. But because of their anion-exchange properties, LDH were referred to as 'anionic clays' Layered double hydroxides (LDHs) are anionic clays also known as 'hydrotalcite-like' compound. The structure of hydrotalcite is related to that of brucite, Mg (OH)2 in which some of the Mg2+

Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward exploiting alternative energy resources such as solar energy. Here, we report the successful low-cost and easily... more

Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward exploiting alternative energy resources such as solar energy. Here, we report the successful low-cost and easily accessible synthesis of hybrid semiconductor@TiO 2 nanotube photocatalysts. In order to realize its maximum potential in harvesting photons in the visible-light range, TiO 2 nanotubes have been loaded with earth-abundant, low-band-gap fibrous red and black phosphorus (P). Scanning electron microscopy− and scanning transmission electron microscopy−energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photo-electron microscopy, and UV−vis measurements have been performed, substantiating the deposition of fibrous red and black P on top and inside the cavities of 100-μm-long electrochemically fabricated nano-tubes. The nanotubular morphology of titania and a vapor-transport technique are utilized to form heterojunctions of P and TiO 2. Compared to pristine anatase 3.2 eV TiO 2 nanotubes, the creation of heterojunctions in the hybrid material resulted in 1.5−2.1 eV photoelectrocatalysts. An enhanced photoelectrochemical water-splitting performance under visible light compared with the individual components resulted for the P@TiO 2 hybrids. This feature is due to synergistically improved charge separation in the heterojunction and more effective visible-light absorption. The electronic band structure and charge-carrier dynamics are investigated in detail using ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy to elucidate the charge-separation mechanism. A Fermi-level alignment in P@TiO 2 heterojunctions leads to a more reductive flat-band potential and a deeper valence band compared to pristine P and thus facilitates a better water-splitting performance. Our results demonstrate effective conversion efficiencies for the nanostructured hybrids, which may enable future applications in optoelectronic applications such as photodetectors, photovoltaics, photoelectrochemical catalysts, and sensors.

Nanostructured α-Fe2O3 thin film electrodes were deposited by aerosol-assisted chemical vapour deposition (AACVD) for photoelectrochemical (PEC) water splitting on conducting glass substrates using 0.1 M methanolic solution of Fe(acac)3.... more

Nanostructured α-Fe2O3 thin film electrodes were deposited
by aerosol-assisted chemical vapour deposition (AACVD) for
photoelectrochemical (PEC) water splitting on conducting
glass substrates using 0.1 M methanolic solution of Fe(acac)3.
The XRD analysis confirmed that the films are highly crystalline
α-Fe2O3 and free from other iron oxide phases. The
highly reproducible electrodes have an optical bandgap of
~2.15 eV and exhibit anodic photocurrent. The current–
voltage characterization of the electrodes reveals that the photocurrent
density strongly depended on the film morphology (SEM) analysis showed a change in the surface morphology
with the change in deposition temperature. The films deposited
at 450 °C have nanoporous structures which provide a
maximum electrode/electrolyte interface. The maximum photocurrent
density of 455 μA/cm2 was achieved at 0.25 V vs.
Ag/AgCl/3M KCl (~1.23 V vs. RHE) and the incident photon
to electron conversion efficiency (IPCE) was 23.6% at
350 nm for the electrode deposited at 450 °C.

Here, we develop a strategy to improve the visible-light-driven photocatalytic hydrogen evolution activity of g-C3N4 by compositing it with low-cost Ni(OH)2 nanoplatelets and inexpensive and earthabundant halloysite nanotubes. The... more

Here, we develop a strategy to improve the visible-light-driven photocatalytic hydrogen evolution activity of g-C3N4 by compositing it with low-cost Ni(OH)2 nanoplatelets and inexpensive and earthabundant
halloysite nanotubes. The Ni(OH)2@g-C3N4/halloysite nanocomposite photocatalysts with different amounts of Ni(OH)2 (0.5e10 wt%) were prepared, and a synergistic effect of Ni(OH)2 platelets and halloysite nanotubes on physicochemical properties and photocatalytic hydrogen evolution activity of g-C3N4 was investigated. As expected, the Ni(OH)2@g-C3N4/halloysite nanocomposite photocatalyst prepared with 1 wt% Ni(OH)2 exhibited the highest photocatalytic hydrogen evolution rate (18.42 mmol h1) which is much higher than that of g-C3N4 (0.43 mmol h1) and Ni(OH)2@g-C3N4 (9.12 mmol h1). Such enhancement in photocatalytic activity of Ni(OH)2@g-C3N4/halloysite nanocomposite photocatalyst is attributed to efficient transfer of photogenerated electrons from the g-C3N4 to Ni(OH)2 cocatalyst interface and trapping of photogenerated holes on the negatively charged surfaces of halloysite nanotubes. In addition, adsorption affinity of the water and methanol molecules was modeled using different surfaces of Ni(OH)2, halloysite-7Å, and g-C3N4 and it is found that combining the g-C3N4 with halloysite-7Å and Ni(OH)2 can significantly improve the adsorption of water and methanol molecules on the surface of the developed nanocomposite. This study offers a simple approach for developing an efficient and inexpensive nanocomposite for effective and applied photocatalytic water splitting methodology for hydrogen production and other possible optoelectronic and photocatalytic applications.

Simulations of the oxygen evolution reaction (OER) are essential for understanding the limitations of water splitting. Most research has focused so far on the OER at flat metal oxide surfaces. The structure sensitivity of the OER has,... more

Simulations of the oxygen evolution reaction (OER) are essential for understanding the limitations of water splitting. Most research has focused so far on the OER at flat metal oxide surfaces. The structure sensitivity of the OER has, however, recently been highlighted as a promising research direction. To probe the structure sensitivity, we investigate the OER at eleven hematite (Fe2O3) surfaces with density functional theory + Hubbard U (DFT + U) calculations. The results show that the O-O coupling (O-O bond formation via two adjacent terminal Os at dual site) OER mechanism at the (110) surface is competing with the mechanism of OOH formation at single site. We study the effects of surface orientation (110 vs. 104), active surface sites (bridge vs. terminal site), presence of surface steps and oxygen vacancy concentration on the OER and explore strategies to reduce the OER overpotential. It is found that the oxygen vacancy concentration is the most effective parameter in reducing the overpotential. In particular, an overpotential of as low as 0.47 V is obtained for the (110) surface with an oxygen vacancy concentration of 1.26 vacancies/nm 2 .

Nanostructured TiO 2 hollow spheres (THS) were prepared via a simple hydrothermal method with titanium butoxide, ethanol, urea, and ammonium sulphate. The effects of Ti/ethanol, and reflux temperature on the morphological properties of... more

Nanostructured TiO 2 hollow spheres (THS) were prepared via a simple hydrothermal method with titanium butoxide, ethanol, urea, and ammonium sulphate. The effects of Ti/ethanol, and reflux temperature on the morphological properties of the nanostructured THS were investigated. An impregnation method was subsequently employed to load metals such as Cu, Co, Cr, Ag, and Ni on the optimized THS, followed by calcination in H 2 /N 2 at 450 °C for 4 h. The morphological properties of the prepared samples were characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron mi-croscopy (TEM), and ultraviolet-visible spectroscopy (UV/vis). The SEM and TEM pictures showed that the Ti/ ethanol ratio of 1:10 resulted in the formation of uniform hollow spheres. The XRD spectre revealed that phase transformation took place as the reflux temperature was increased, with pure anatase TiO 2 hollow spheres being formed at 200 °C. The BET surface areas of the calcined photocatalysts were in the range of 80.6–116 m 2 /g −1. The UV/vis spectra of the photocatalysts showed that loading of transition metals reduced the band gap of the THS. The activities of the prepared catalysts were tested for hydrogen production via photocatalytic reforming of glycerol under solar irradiation. The improved hydrogen evolution from photocatalytic reforming of glycerol was attributed to: the high surface area which enhanced the adsorption of glycerol onto the surface of photo-catalysts; high crystallinity and the reduced band gap which improved the solar light harvesting; the hollow chamber within the TiO 2 spheres which produced multiple reflection of the light harvested, thus producing efficient electron/hole pair formation; and the detailed composition of the solids retarded the electron/hole recombination by trapping the electrons generated during the photo excitation of the photocatalysts, and thereby promoted their activity.

The sintering at 800 °C is found to induce the diffusion of Sn from the F-doped SnO2 (FTO) into the hematite lattice, enhancing the photoelectrochemical cell (PEC) properties of the hematite photoanodes, but this diffusion also has... more

The sintering at 800 °C is found to induce the diffusion of Sn from the F-doped SnO2 (FTO) into the hematite lattice, enhancing the photoelectrochemical cell (PEC) properties of the hematite photoanodes, but this diffusion also has detrimental effects on the conductivity of the FTO substrate. In the present research we examined the role of FTO deformation during the activation of hematite photoanodes synthesized on FTO substrates. The incorporation of Sn dopants from the FTO substrates in the hematite lattice was confirmed by X-ray photoelectron spectroscopy and was found to increase with sintering time. Further from the extended X-ray absorption fine structure analysis, it was found that the diffused Sn atoms affected the metal sites of the hematite lattice. Increased diffusion of Sn into the hematite lattice caused structural disordering of the FTO, but optimum sintering time compensated for the structural disordering and improved the ordering. Under high-temperature annealing at 800 °C, the FTO substrates underwent a stoichiometric change that directly affected their electrical conductivity; their resistivity was doubled after 20 min of sintering. Activation of hematite photoanodes by high-temperature sintering entails a kinetic competition between Sn dopant diffusion from the FTO substrate into the hematite and the resulting thermal deformation and conductivity loss in the FTO substrates.

A fluorine-doped, chlorine-intercalated carbon nitride (CNF-Cl) photocatalyst has been synthesized for simultaneous improvements in light harvesting capability along with suppression of charge recombination in bulk g-C 3 N 4. The... more

A fluorine-doped, chlorine-intercalated carbon nitride (CNF-Cl) photocatalyst has been synthesized for simultaneous improvements in light harvesting capability along with suppression of charge recombination in bulk g-C 3 N 4. The formation of heterojunctions of these CNF-Cl nanosheets with low bandgap, earth abundant bismuth oxyiodide (BiOI) was achieved, and the synthesized heterojunctions were tested as active photoanodes in photoelectrochemical water splitting experiments. BiOI/CNF-Cl heterojunctions exhibited extended light harvesting with a band-edge of 680 nm and generated photocurrent densities approaching 1.3 mA cm −2 under AM1.5 G one sun illumination. Scanning Kelvin probe force microscopy under optical bias showed a surface potential of 207 mV for the 50% BiOI/CNF-Cl nanocomposite, while pristine CNF-Cl and BiOI had surface photopotential values of 83 mV and 98 mV, respectively, which in turn, provided direct evidence of superior charge separation in the heterojunction blends. Enhanced charge carrier separation and improved light harvesting capability in BiOI/CNF-Cl hybrids were found to be the dominant factors in increased photocurrent, compared to the pristine constituent materials. Supplementary material for this article is available online

A B S T R A C T With rising energy consumption in the world and the negative environmental and human health impacts of fossil fuels, the demand for renewable energy sources is increasing. The energy generated by renewable energy sources... more

A B S T R A C T With rising energy consumption in the world and the negative environmental and human health impacts of fossil fuels, the demand for renewable energy sources is increasing. The energy generated by renewable energy sources can be stored either in a chemical (water splitting) or an electrochemical (battery or supercapacitor) form, that are two distinct processes. Here, we introduce an integrated solar-powered system for both electrochemical energy storage and water electrolysis. A nickel-cobalt-iron layered double hydroxide (Ni-Co-Fe LDH) was successfully synthesized on nickel foam as a substrate using a fast, one-step electrodeposition approach. The Ni-Co-Fe LDH exhibited excellent electrochemical properties both as an active electrode material in supercapacitors, and as a catalyst in the oxygen evolution reaction (OER). When employed as the positive electrode in a supercapacitor, along with activated carbon as the negative electrode in an asymmetric configuration, the ultrathin and porous Ni-Co-Fe LDH nanoplatelets delivered an ultrahigh specific energy of 57.5 W h kg −1 with an outstanding specific power of 37.9 kW kg −1 and an excellent cycle life. As an OER electrocatalyst, Ni-Co-Fe LDH exhibited superior electrocatalytic performances with a very low overpotential of 0.207 V versus a reference hydrogen electrode (RHE) at 10.0 mA cm −2 , and a small Tafel slope of 31 mV dec −1. The superior energy storage and catalytic OER properties of the Ni-Co-Fe LDH nanoplatelet array can be attributed to both the synergistic effects among the metal species and the unique mesoporous structure of the LDH that provides facilitated charge/ion diffusion pathways and more available active sites.

A set of titanium dioxide and gold-modified titanium dioxide samples were prepared by flame spray pyrolysis (FP) and characterized by BET, XRD, HRTEM and UV–vis reflectance analysis. Their photocatalytic activity in hydrogen production in... more

A set of titanium dioxide and gold-modified titanium dioxide samples were prepared by flame spray pyrolysis (FP) and characterized by BET, XRD, HRTEM and UV–vis reflectance analysis. Their photocatalytic activity in hydrogen production in water suspension, either from water photosplitting or from methanol photoreforming, was tested in an expressly set up, closed recirculation laboratory scale photoreactor and compared to those of commercial TiO2 samples, including Degussa P25, pure rutile and pure anatase. The rate of hydrogen evolution (rH2) increased with increasing the anatase content, pure anatase being the most active photocatalyst. Surface area and crystallinity, both key properties of photocatalysts, can be tuned up by properly setting FP operation parameters, including the selection of the organic solvent/fuel. In particular, FP-made TiO2 prepared from a xylene solution showed more active than P25. Finally, rH2 increased by one order of magnitude in water photosplitting and ...

Photocatalytic activity of a-MnO 2 nanorod synthesized through a low temperature (90 8 C) single step precipitation route in the absence of surfactant and template is reported. Dependence of precipitation time on morphology of the... more

Photocatalytic activity of a-MnO 2 nanorod synthesized through a low temperature (90 8 C) single step precipitation route in the absence of surfactant and template is reported. Dependence of precipitation time on morphology of the synthesized a-MnO 2 has been investigated and the photocatalyst has been tested for the degradation of organic cationic and anionic dyes. Detailed study on the degradation of Rhodamine B (RhB) has been carried out. The lower precipitation time (of 6 h) is found to be ideal for the synthesis of the photocatalyst. The mechanism of RhB photodegradation under visible light using a-MnO 2 nanorods has been established through mass spectra analysis. The intermediate products during degradation exhibits de-ethylation and mineralisation steps. Experimental results suggest that both super oxide and hydroxyl radicals are the main active species in the process. Total organic carbon (TOC) analysis of treated RhB reveals complete mineralisation. The photodegradation efficiency of a-MnO 2 for cationic and anionic dyes are found to be 95–100 % under visible light irradiation. The excellent photocatalytic activity of a-MnO 2 can be correlated with its 1-D morphology of high aspect ratio and low photoluminescence intensity. The complete dye dis-coloration within 10 min and total mineralisation of RhB in 25 min is quite significant especially under visible light irradiation and has never been reported earlier.

In this paper, quasi-solid-state dye-sensitized solar cell has been constructed based on natural photo-sensitizers extracted from the bracts of Bougainvillea spectabilis and the leaves of Euphorbia cotinifolia using acidified (0.1 M HCl)... more

In this paper, quasi-solid-state dye-sensitized solar cell has been constructed based on natural photo-sensitizers extracted from the bracts of Bougainvillea spectabilis and the leaves of Euphorbia cotinifolia using acidified (0.1 M HCl) distilled water and ethanol separately. The absorption spectra of the extracts were performed in the spectral range from 395 to 750 nm. The cells were assembled using commercial TiO 2 powder film and PEDOT coated FTO glasses as working and counter electrodes , respectively, and also the quasi-solid electrolyte sandwiched in between. The Photovoltaic parameters such as short circuit current density (J sc), open circuit voltage (V oc), fill factor (FF), and overall conversion efficiency (g) for the as-prepared DSSC were determined under 100 mW/ cm 2 illuminations. The highest open circuit voltage (V oc = 0.549 V) and short circuit current density (J sc = 0.592 mA/cm 2) were obtained from the DSSCs assembled by natural dye extracted with the acidified ethanol of Bougainvillea spectabilis bracts and the leaves of Euphorbia cotinifolia, respectively. The highest power conversation efficiency (g) of the as-prepared DSSC assembled with natural dye extracted from Bougainvillea spectabilis bracts using acidified ethanol as extracting solvent was 0.175 %. The use of Bougainvillea spectabilis and Euphorbia cotinifolia pigments as natural sensitizers along with the use of quasi-solid electrolyte and PEDOT coated FTO counter electrodes could be a possible alternative for the production of low-cost and environment friendly DSSCs.

22Z-Scheme CdS/Pt-N-TiO 2 and CdS/Pt-N,FTiO 2 nanocatalysts were synthesized using a sol-gel impregnation method and evaluated for their photocatalytic H 2 /O 2 production via overall water splitting, with no extrernal electron or hole... more

22Z-Scheme CdS/Pt-N-TiO 2 and CdS/Pt-N,FTiO 2 nanocatalysts were synthesized using a sol-gel impregnation method and evaluated for their photocatalytic H 2 /O 2 production via overall water splitting, with no extrernal electron or hole acceptors. The 0.5CdS/Pt-N-TiO 2 material achieved a photocatlytic production of 639 μmol/g/h of H 2 in tandem with 319 μmol/g/h of O 2. The photocatalytic H 2 /O 2 production data show that N-incorporation in the TiO 2 lattice boosts overall water splitting, while F-incorporation inhibits the catalytic performance. Quantitative monitoring of the photogenerated Ti 3+-surface and Ti 3+-lattice electrons, as well as of the pho-togenerated holes (h +) by Electron Parmagnetic Resonce spectrsocopy, show that CdS/Pt-N-TiO 2 achieves enhanced e − /h + photogeneration due to intraband states generated by N-dopping, facilitating the flow of electrons via Pt to the valence band of CdS. The leaching of Cd 2+ ions' due to phootocorrosion of the CdS quantum dots, was montiored in-situ using Anodic StrippingVoltammtery (ASV). The Cd 2+ leaching data reveal a severe inhibition of CdS photocorrosion ofN-dopped catalysts, CdS/Pt-N-TiO 2. This reveals a dual beneficial role of N-atoms: [i] boosting the visible light photocactivity, and [ii] inhibiting CdS photocorrosoion. A consistent Z-scheme reaction mechanism is proposed for the catalytic H 2 /O 2 production by CdS/Pt-N-TiO 2 and CdS/Pt-N-F-TiO 2 heterojunctions, taking into account the photoinduced e − /h + dynamics as well as the interfacial {CdS} /{Pt-N/F-TiO 2 } chemistry.

Single step hydrothermal synthesis of CdS/Oxide (Oxide = ZnO, Al2O3) was demonstrated and examines their photocatalytic activity in presence of graphene oxide (GO). CdS/Al2O3/GO and CdS/ZnO/GO both exhibits enhanced photocatalytic... more

Single step hydrothermal synthesis of CdS/Oxide (Oxide = ZnO, Al2O3) was demonstrated and examines their photocatalytic activity in presence of graphene oxide (GO). CdS/Al2O3/GO and CdS/ZnO/GO both exhibits enhanced photocatalytic activity for hydrogen generation with apparent quantum yields (AQY) of 14% and 30% respectively. Moreover, CdS/Oxide/GO displayed efficient photodegradation of organic dye; ~90% for CdS/Al2O3/GO and ~99% for CdS/ZnO/GO within 60 min of time interval. Superior photocatalytic properties are attributed to the enhanced surface area and effective separation of photoinduced charge carriers due to the presence of graphene oxide. The present study highlights the potential application of graphene based materials in the field of energy conversion and environment remediation.

Cu 2 O is a promising earth-abundant semiconductor photocathode for sunlight-driven water splitting. Characterization results are presented to show how the photocurrent density (J ph), onset potential (E onset), band edges, carrier... more

Cu 2 O is a promising earth-abundant semiconductor photocathode for sunlight-driven water splitting. Characterization results are presented to show how the photocurrent density (J ph), onset potential (E onset), band edges, carrier density (N A), and interfacial charge transfer resistance (R ct) are affected by the morphology and method used to deposit Cu 2 O on a copper foil. Mesoscopic and planar morphologies exhibit large differences in the values of N A and R ct. However, these differences are not observed to translate to other photocatalytic properties of Cu 2 O. Mesoscopic and planar morphologies exhibit similar bandgap (e.g.) and flat band potential (E fb) values of 1.93 ± 0.04 eV and 0.48 ± 0.06 eV respectively. E onset of 0.48 ± 0.04 eV obtained for these systems is close to the E fb indicating negligible water reduction overpotential. Electrochemically deposited planar Cu 2 O provides the highest photocurrent density of 5.0 mA cm −2 at 0 V vs reversible hydrogen electrode (RHE) of all the morphologies studied. The photocurrent densities observed in this study are among the highest reported values for bare Cu 2 O photocathodes.

Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34-xFexO6-δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow... more

Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34-xFexO6-δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6-δ (BCNFCo), exhibited an optical absorption edge at ~ 800 nm, p-type conduction and a distinct photoresponse upto 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskite and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm-2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ~ 88%.

We report a record 100% photon-to-hydrogen production efficiency, under visible light illumination, for the photocatalytic water-splitting reduction half-reaction. This result was accomplished by utilization of nanoparticle-based... more

We report a record 100% photon-to-hydrogen production efficiency, under visible light illumination, for the photocatalytic water-splitting reduction half-reaction. This result was accomplished by utilization of nanoparticle-based photocatalysts, composed of Pt-tipped CdSe@CdS rods, with a hydroxyl anion−radical redox couple operating as a shuttle to relay the holes. The implications of such record efficiency for the prospects of realizing practical over all water splitting and solar-to-fuel energy conversion are discussed.

In this study, a self-organized nanotubular titanium dioxide (TiO2) array was successfully produced by anodizing pure titanium in a mixture of glycerol, distilled water (8% vol.), and ammonium fluoride using a dual electrode system. The... more

In this study, a self-organized nanotubular titanium dioxide (TiO2) array was successfully produced by anodizing pure titanium in a mixture of glycerol, distilled water (8% vol.), and ammonium fluoride using a dual electrode system. The size control and distribution of the nanopores were performed in a DC voltage range varying from 30 V to 60 V. The diameter of TiO2 nanopores varies from 59 to 128 nm depending on the anodizing voltage. Energy-dispersive X-ray spectroscopy (EDX) analysis reveals that the as-prepared films are essentially composed of TiO2. According to the X-ray diffraction (XRD) and Raman spectroscopy analysis, the nanotubular arrays of TiO2 annealed at 600°C for 2 hours are composed of a phase mixture of anatase and rutile. Mott-Schottky analysis showed that the TiO2 nanotubes are consistent with an n-type semiconductor with a donor density of about 1017 cm-3. Preliminary results on the photocatalytic degradation of a pharmaceutical pollutant showed that the TiO2 na...

Phosphorene has attracted intense interest due to its unexpected high carrier mobility and distinguished anisotropic optoelectronic and electronic properties. In this work, we unraveled strain engineered phosphorene as a photocatalyst in... more

Phosphorene has attracted intense interest due to its unexpected high carrier mobility and distinguished anisotropic optoelectronic and electronic properties. In this work, we unraveled strain engineered phosphorene as a photocatalyst in the application of water splitting hydrogen production based on density functional theory calculations. Lattice dynamic calculations demonstrated the stability for such kind of artificial materials under different strains. The phosphorene lattice is unstable under compression strains and could be crashed, whereas phosphorene lattice shows very good stability under tensile strains. Further guarantee of the stability of phosphorene in liquid water is studied by ab initio molecular dynamics simulations. Tunable band gap from 1.54 eV at ambient condition to 1.82 eV under tensile strains for phosphorene is evaluated using parameter-free hybrid functional calculations. Appropriate band gaps and band edge alignments at certain pH demonstrate the potential application of phosphorene as a sufficiently efficient photocatalyst for visible light water splitting. We found that the strained phosphorene exhibits significantly improved photocatalytic properties under visible-light irradiation by calculating optical absorption spectra. Negative splitting energy of absorbed H2O indicates the water splitting on phosphorene is energy favorable both without and with strains.

There are still gaps in the field of reference electrode that is needed to assist electrolysis in high temperature electrolytes (e.g. molten hydroxides) for H2 gas production. This research aims to fill the gaps by preparing Ni/Ni(OH)2... more

There are still gaps in the field of reference electrode that is needed to assist electrolysis in high temperature electrolytes (e.g. molten hydroxides) for H2 gas production. This research aims to fill the gaps by preparing Ni/Ni(OH)2 reference electrode and more importantly testing its effectiveness against important performance factors including; ion conducting membrane (e.g. mullite tubes), internal electrolyte composition, working temperature and electrochemical control (e.g. potential scan rate). Then, this reference electrode was used to study the electrocatalytic activity various cheaper working electrode materials including; stainless steel (St.st), Ni, Mo and Ag in comparison with Pt by the means of chronoamperometry and voltammetry. The effect of introducing steam into electrolyte (eutectic mixture of NaOH and KOH) on the electrocatalytic activity of these working electrodes was also studied. It was observed that the potential of hydrogen evolution with different working electrodes followed an order as; Pt > Ni > St. st > Ag > Mo (positive to negative). The performance of each working electrode was confirmed through chronoamperometry for hydrogen evolution at a constant potential of −0.7 V. It was also found in cyclic voltammetry and confirmed by chronoamperometry that the introduction of steam was apparent as increasing the current density at cathodic limit for hydrogen evolution. This study could help to develop non-precious metal electrodes for the production of hydrogen fuel. In future, there will be a potential in the threshold concentration of steam for H2 gas production.

Supply of pure drinking water and air is a perquisite for sustaining of civilization and in this respect the clays are found to have significant importance as a semiconductor support material due to their layered morphology, chemical as... more

Supply of pure drinking water and air is a perquisite for sustaining of civilization and in this respect the clays are found to have significant importance as a semiconductor support material due to their layered morphology, chemical as well as mechanical stability, cation exchange capacity, non-toxic nature, low cost and availability. In spite of availability of technique very few studies have been done on the effect of clay structure on photocatalytic efficiency of semiconductor/clay nanocomposites. The TiO 2 /clay nano-composites were synthesized from different clays having textural differences (1:1 and 2:1); by a simple and time as well as cost effective method under microwave conditions. Formation of anatase TiO 2 nanoparticles on surface of different clays was achieved at 180 C within 10 min of time. Phase composition, particle morphology, specific surface area, chemical bonding, etc. of those samples were characterized by using XRD, TEM, FESEM, FTIR and nitrogen gas adsorption-desorption (BET) methods. Formation of TiO 2 nanoparticles on clay surface were confirmed by monitoring peaks of anatase TiO 2 with crystallite size 10e20 nm in X-Ray diffraction pattern of TiO 2 /Clay nanocomposites. The TiO 2 /clay nanocomposites exhibited high surface area and uniform pore distribution compared to pure clays and TiO 2 (Degussa P25, Germany). The photocatalytic activities of the nanocomposites were found to be depended on clay texture as well as optical characteristics apart from their surface area. The 2:1 clay (bentonite, kunipia-F) was observed to act as better support for TiO 2 in comparison with 1:1 clay (kaolin); regarding its photo-catalytic degradation of methylene blue (MB) and volatile organic compound (VOC) such as chlorobenzene (CB) due to their different texture and optical properties. TiO 2 / bentonite nanocomposite has high optical absorbance under UV spectrum. It also showed surface area of 112 m 2 /g with high photocatalytic activity with a rate constant 0.02886 and 0.0460 min À1 for MB and CB degradations respectively. It had also been found that, the photocatalytic activity of the TiO 2 /bentonite nanocomposites were 8 and 5 times higher for MB and CB degradation respectively in compare with Degussa P25.

We report the fabrication of 3D hierarchical hetero-nanostructures composed of thin α-Fe 2 O 3 nanoflakes branched on TiO 2 nanotubes. The novel α-Fe 2 O 3 /TiO 2 hierarchical nanostructures, synthesized on FTO through a multi-step... more

We report the fabrication of 3D hierarchical hetero-nanostructures composed of thin α-Fe 2 O 3 nanoflakes branched on TiO 2 nanotubes. The novel α-Fe 2 O 3 /TiO 2 hierarchical nanostructures, synthesized on FTO through a multi-step hydrothermal process, exhibit enhanced performances in photo-electrochemical water splitting and in the photocatalytic degradation of an organic dye, with respect to pure TiO 2 nano-tubes. An enhanced separation of photogenerated charge carriers is here proposed as the main factor for the observed photo-activities: electrons photogenerated in TiO 2 are efficiently collected at FTO, while holes are transferred to the α-Fe 2 O 3 nanobranches that serve as charge mediators to the electrolyte. The morphology of α-Fe 2 O 3 that varies from ultrathin nanoflakes to nanorod/nanofiber structures depending on the Fe precursor concentration was shown to have a significant impact on the photo-induced activity of the α-Fe 2 O 3 /TiO 2 composites. In particular, it is shown that for an optimized photo-electrochemical structure, a combination of critical factors should be achieved such as (i) TiO 2 light absorption and photo-activation vs. α-Fe 2 O 3-induced shadowing effect and (ii) the availability of free TiO 2 surface vs. α-Fe 2 O 3-coated surface. Finally, theoretical analysis, based on DFT calculations, confirmed the optical properties experimentally determined for the α-Fe 2 O 3 /TiO 2 hierarchical nanostructures. We anticipate that this new multi-step hydrothermal process can be a blueprint for the design and development of other hierarchical heterogeneous metal oxide electrodes suitable for photo-electrochemical applications.