Photocatalysts

ABSTRACT In analogy to photocatalytic materials, the metal-organic framework MIL-53(Fe) showed up self-cleaning ability under light. In the presence of hydrogen peroxide and with exposure under UVA-VIS irradiation, organic impurities were decomposed completely without damage of MIL-53(Fe) structure. The method is efficient and environment-friendly such that all the free and confined 1,4-benzenedicarboxylic acid in the MOF were decomposed within 1 hour at room temperature. The MIL-53(Fe) samples before and after purification were fully analyzed by XRD, FTIR, FE-SEM and TGA measurements.

Zat pewarna baik alami maupun sintetik dari industri tekstil seperti industri batik adalah salah satu sumber pencemar air yang berbahaya. Zat pewarna ini dapat menurunkan kualitas air, sehingga konsentrasi zat pewarna dalam perairan harus sesuai dengan aturan yang berlaku. Beberapa metode yang dapat digunakan untuk menurunkan kadar zat pewarna di air limbah antara lain adsorpsi, fotodegradasi, dan ozonolisis. Naskah ini mengkaji perkembangan material berbasis MOF sebagai kandidat katalis dalam fotodegradasi zat pewarna dalam air limbah. Penggunaan material berbasis MOF untuk fotokatalis masih relatif baru namun memiliki potensi besar untuk degradasi air limbah. Material ini dapat dikembangkan dari mineral alam yang banyak tersedia di Indonesia. Kajian ini dilakukan melalui tinjauan pustaka dimana artikel-artikel yang digunakan sebagai literatur utama diperoleh dari jurnal internasional berbahasa Inggris dengan tahun terbit mulai tahun 2000. Berdasarkan hasil kajian, MOF dapat dijadikan sebagai kandidat fotokatalis dari berbagai zat pewarna seperti MB (metil biru), MO (metil orange), MV (metil violet), RhB (rhodamine biru), dll dengan hasil efisiensi degradasi yang bervariasi hingga 100%. Namun, penggunaan fotokatalis MOF dalam sampel air limbah nyata belum pernah dilaporkan. Selain itu, meskipun fotokatalis berbasis MOF dapat diperoleh dari berbagai metode seperti solvotermal (hidrotermal), larutan, dan/atau metode gel, kajian tentang produksi MOF yang ramah lingkungan skala massal tetap diperlukan.

Chalcogenides are narrow-band gap semiconductors that have been widely used as photocatalysts. These narrow-band gap materials allow more efficient absorption of over 40% of solar energy in the visible light range, which will eventually improve its photocatalytic properties. Under visible light irradiation, these materials generate electron and hole (e−/h+) pairs. Photo-generated e−/h+ pairs have been utilized to split water into hydrogen and oxygen and to remove and degrade industrial, pharmaceutical and agricultural organic/inorganic/biological pollutants that have been accumulated in the environment. In this perspective review, different types of chalcogenides, namely, binary, multinary (ternary and quaternary) and chalcogenide-based heterostructures are presented briefly. This perspective review also highlights the mechanisms involved and remarkable photocatalytic activity enhancement under visible light irradiation that has been widely researched such as the photocatalytic degradation of industrial pollutants and photocatalytic inactivation of bacteria. Lastly, future prospects for the use of chalcogenides as photocatalysts and chalcogenide-based heterostructures were discussed.

Photocatalysis using chalcogenide-based nanomaterials is a green technology that has been widely applied for environment remediation and energy production. Chalcogenide-based nanomaterials are visible-light responsive photocatalysts that have significant advantages including low cost, high efficiency, harmlessness, and stability.
This book deals with the different types of chalcogenide-based photocatalytic nanomaterials. This book will cover the fundamental concepts of photocatalytic reactions, mainly under visible light, involving chalcogenides for a range of energy and environment-related applications.
The book focuses on the nanostructure control, synthesis methods, activity enhancement strategies, environmental applications, and perspectives of chalcogenide-based nanomaterials. It offers guidelines for designing new chalcogenide-based nanoscale photocatalysts, at low cost and high efficiency, for the utilization of solar power in the areas of energy production and environment remediation.
Key Features
• Provides information on developing novel chalcogenide-based nanomaterials
• Outlines the fundamentals of chalcogenides-based photocatalysis
• Includes techniques for heterogeneous catalysis based on chalcogenide- based nanomaterials

The surging demand for energy and staggering pollutants in the environment have geared the scientific community to explore sustainable pathways that are economically feasible and environmentally compelling. In this context, harnessing solar energy using semiconductor materials to generate charge pairs to drive photoredox reactions has been envisioned as a futuristic approach. Numerous inorganic crystals with promising nanoregime properties investigated in the past decade have yet to demonstrate practical application due to limited photon absorption and sluggish charge separation kinetics. Twodimensional semiconductors with tunable optical and electronic properties and quasi-resistance-free lateral charge transfer mechanisms have shown great promise in photocatalysis. Polymeric graphitic carbon nitride (g-C 3 N 4) is among the most promising candidates due to fine-tuned band edges and the feasibility of optimizing the optical properties via materials genomics. Constructing a two-dimensional (2D)/2D van der Waals (vdW) heterojunction by allies of 2D carbon nitride sheets and other 2D semiconductors has demonstrated enhanced charge separation with improved visible photon absorption, and the performance is not restricted by the lattice matching of constituting materials. With the advent of new 2D semiconductors over the recent past, the 2D/2D heterojunction assemblies are gaining momentum to design high performance photocatalysts for numerous applications. This review aims to highlight recent advancements and key understanding in carbon nitride based 2D/2D heterojunctions and their applications in photocatalysis, including small molecules activation, conversion, and degradations. We conclude with a forward-looking perspective discussing the key challenges and opportunity areas for future research.

Being the partial differential equations along with the Lorentz law the Maxwell's equation laid the foundation for classical electromagnetism, classical optics, and electric circuits. The equations provide a mathematical model for electric, optical, and radio technologies, such as power generation, electric motors, wireless communication, lenses, radar etc. Maxwell's equations describe how electric and magnetic fields are generated by charges, currents, and changes of the fields.[note 1] One important consequence of the equations is that they demonstrate how fluctuating electric and magnetic fields propagate at a constant speed (c) in the vacuum, the "speed of light". Known as electromagnetic radiation, these waves may occur at various wavelengths to produce a spectrum from radio waves to γ-rays. The equations are named after the physicist and mathematician James Clerk Maxwell, who between 1861 and 1862 published an early form of the equations that included the Lorentz force law. He also first used the equations to propose that light is an electromagnetic phenomenon.

A research team led by Prof. Wu Zhengyan from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences (CAS) has recently introduced a high-efficiency Z-scheme photocatalyst to deal with contaminants in water. [35]
These results indicate carbonyl elimination mechanisms involving electronically and vibrationally excited species. [34]
Researchers at the University of Southampton have transformed optical fibers into photocatalytic microreactors that convert water into hydrogen fuel using solar energy. [33]

Photocatalysis has been carefully studied in
the last 25 years, thanks to their versatility
in the utilization as a pollutant degradation
process, due to stricter regulations, that are
􀁗􀁋􀁈􀀃 􀁕􀁈􀃀􀁈􀁆􀁗􀁌􀁒􀁑􀀃 􀁒􀁉􀀃 􀁖􀁒􀁆􀁌􀁈􀁗􀁜􀂶􀁖􀀃 􀁓􀁕􀁈􀁒􀁆􀁆􀁘􀁓􀁄􀁗􀁌􀁒􀁑􀀃 􀁒􀁉􀀃
maintaining its environment free of pollutants.
The photocatalysis process is based on the
transfer of charge through the interface
between the semiconductor and the polluted
watery solution. In the interface of these two
components the resultant is a redistribution that
􀁖􀁌􀁊􀁑􀁌􀂿􀁆􀁄􀁑􀁗􀁏􀁜􀀃􀁈􀁛􀁗􀁈􀁑􀁇􀁖􀀃􀁌􀁑􀀃􀁅􀁒􀁗􀁋􀀃􀁖􀁌􀁇􀁈􀁖􀀑􀀃􀀷􀁋􀁈􀀃􀁓􀁕􀁈􀁖􀁈􀁑􀁆􀁈􀀃
of semiconductor is needed in photocatalysis,
in which the conductivity increases with
temperature, but it is less than in metals. One of
the most outstanding aspects is the generation
of electron-hole pair, being this the principle
on which photocatalysis is based, since through
this model the absorption of photons and the
distribution of different electronic states in the
surface is explained. Thanks to this phenomenon
the degradation of organic molecules, colorants,
and metals such as cadmium, nickel, mercury,
copper, chromium, among others, is possible.

Iron oxides nanostructures have a wide range of applications in different fields. Properties of nanostructures depend on their size, morphology and chemical composition. The precipitation method is one of the most known and advantageous techniques for the synthesis of metal oxide nanoparticles. To investigate the effect of precursor on properties of iron oxide nanostructures, iron oxide has been synthesized using precipitation method with iron (III) acetate, iron (III) chloride and iron (III) nitrate as the iron precursor. The products were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM). Hematite Nanorods were obtained using acetate precursor with uniform shape and lack of agglomeration. Chloride and nitrate precursors were led to the formation of Wuestite and magnetite phase, respectively. In the case of using chloride and nitrate precursors, nanoparticles existed with bulk structures. FTIR spectra of all samples showed strong absorption peaks of Fe-O bond vibration at 400-600 cm-1. This study provides good insights into the synthesis of engineered iron oxide nanostructure with desired properties for different applications.

Tungsten, silver and tungsten/silver co-doped titania nanopowders were synthesised via an aqueous sol–gel method. The size distribution and zeta potential of the starting sols were determined via photon correlation spectroscopy (PCS). The dried gels were thermally treated at two different temperatures, and the occurrence of amorphous phase was assessed using the combined Rietveld–RIR X-ray powder diffraction method. A systematic study of the optical properties of the powders was made with diffuse reflectance spectroscopy (DRS), and the energy band gaps were calculated using the differential reflectance method; while their morphology was investigated using electron microscopy analysis (TEM). The photocatalytic activity of the samples was assessed in liquid–solid phase, under UVA-light and visible-light irradiation, monitoring the degradation of an organic dye. The influence of the phase composition, optical properties, dimensions, and specific surface area of the powders on the photocatalytic activity was thoroughly discussed.

Dear Colleagues and Researchers,

It gives me immense pleasure to introduce you the prestigious Journal of Saudi Chemical Society (JSCS). This is the official publication of the Saudi Chemical Society in collaboration with Elsevier.

I’m extremely delighted to invite you to submit a research article, review article or both for the special issue of the Journal of Saudi Chemical Society on the subject of “Nanomaterials as Photocatalysts” for which I will be the Guest Editor.
http://www.journals.elsevier.com/journal-of-saudi-chemical-society/call-for-papers/
http://www.journals.elsevier.com/journal-of-saudi-chemical-society/call-for-papers/special-issue-on-nanomaterials-as-photocatalysts/

This forthcoming special issue is devoted for articles related to the design and synthesis of novel nanomaterials for photocatalysis with special focus on visible light-induced photocatalysis. Therefore, on behalf of JSCS, I request you to submit your research and/or review articles that cover a wide range of recent advancements in the topic related to the title of the special issue. Articles related to the nanostructure photocatalyst for environmental remediation can also be submitted.

I hereby invite prospective authors to submit their research articles, review article or both that have not been previously published, and are not being considered for publication elsewhere. Topics of interests include, but not limited to the following areas:
Nanomaterials for photocatalysis

Nanomaterials for visible light photocatalysis

Nanomaterials for environmental remediation through photocatalysis

Nanomaterials for CO2 reduction/oxidation via photocatalysis

Nanomaterials for water purification through photocatalysis

All the articles will be reviewed following the regular reviewing procedure of the Journal of Saudi Chemical Society. Submission to the Journal of Saudi Chemical Society will proceed totally online at the website http://www.ees.elsevier.com/jscs/default.asp. Please follow the guide for authors (http://www.elsevier.com/journals/journal-of-saudi-chemical-society/1319-6103/ guide-for-authors) to prepare your article. The scientific quality of articles which clearly falls within the scope of the issue will be the only criteria for manuscript acceptance.

The Journal of Saudi Chemical Society is an English language, peer-reviewed scholarly publication in the area of chemistry. The journal publishes original research articles, reviews and short reports. The JSCS is issued by the Saudi Chemical Society and is published by King Saud University in collaboration with Elsevier and is edited by an international group of eminent researchers.

The deadline for manuscript submission is the February 28, 2015, with an intended publication date of July 30, 2015. Your contribution will be highly appreciated.

With thanks
--
Mohammad Mansoob Khan, Ph.D.
Research Professor &
Guest Editor of the Special Issue
School of Chemical Engineering
Yeungnam University
Geongbuk 712-749, Gyeongsan-si
Republic of Korea
Phone: 0082-10-5175-0707 (Cell)
Email: mmansoobkhan@yahoo.com
URL: http://works.bepress.com/mmansoob_khan/

Chalcogenide-Based Nanomaterials as Photocatalysts deals with the different types of chalcogenide-based photocatalytic reactions, covering the fundamental concepts of photocatalytic reactions involving chalcogenides for a range of energy and environmental applications. Sections focus on nanostructure control, synthesis methods, activity enhancement strategies, environmental applications, and perspectives of chalcogenide-based nanomaterials. The book offers guidelines for designing new chalcogenide-based nanoscale photocatalysts at low cost and high efficiency for efficient utilization of solar energy in the areas of energy production and environment remediation.

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 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.

Polypyrrole nanofiber/Zn-Fe layered double hydroxide (Ppy NF/Zn-Fe LDH) was synthesized as nanocomposite of enhanced adsorption and photocatalytic properties. The formation of the composite was confirmed by XRD, FT-IR, HSEM, HRTEM, BET surface area and UV-vis spectrophotometer. Ppy NF/Zn-Fe LDH composite exhibits clear enhancing in the specific surface area and obvious reducing in the band gap energy (from 2.8 eV for Zn-Fe LDH to 2.31 eV for the composite). This was reflected in a considerable improvement in the adsorption capacity and photocatalytic removal of safranin dye. The adsorption capacity was enhanced by about 22% higher than Ppy NF and by 31% higher than Zn-Fe LDH. The photocatalytic removal was improved by 41.6% higher than Ppy NF and by about 54% higher than Zn-Fe LDH. The adsorption of safranin dye by the composite is chemisorption adsorption and occurs in a multilayer form. The complete photocatalytic removal of 5 mg/L of safranin dye can be achieved after 120 min illumination time using 0.05 g of the composite as photocatalyst and the best results can be obtained at neutral to alkaline conditions. Realistic application of the composite for the removal of dye from raw water samples revealed the applicability of the product for the purification of tap water, groundwater, and sewage water. Moreover, it can be used for six cycles of safranin dye removal from water. The photocatalytic degradation process appears to be controlled by the created hydroxyl radicals and formed photogenerated holes as the dominant active oxidizing radicals.

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.

Though there are many advantages for the TiO2 compared to other
semiconductor photocatalysts, its band gap of 3.2 eV restrains application to the UV-region of the electromagnetic
spectrum (
≤
387.5 nm). As a result, development of visible-light active titanium dioxide
is one of the key challenges in the field of semiconductor photocatalysis. In this review, advances in
the strategies for the visible light activation, origin of visible-light activity, and electronic structure of
various visible-light active TiO2 photocatalysts are discussed in detail. It has also been shown that if
appropriate models are used, the theoretical insights can successfully be employed to develop novel
catalysts to enhance the photocatalytic performance in the visible region. Recent developments in theory
and experiments in visible-light induced water splitting, degradation of environmental pollutants,
water and air purification and antibacterial applications are also reviewed. Various strategies to identify
appropriate dopants for improved visible-light absorption and electron–hole separation to enhance the
photocatalytic activity are discussed in detail, and a number of recommendations are also presented.

applications in energy and environmental areas. Recent examples of many TiO2-derived materials have
been illustrated to understand the fundamental principles of self-cleaning hydrophilic and hydrophobic
surfaces. Various models including those proposed by Wenzel, Cassie-Baxter and Miwa-Hashimoto are
discussed to explain the mechanism of self-cleaning. Examples of semiconductor surfaces exhibiting
the simultaneous occurrence of superhydrophilic and superhydrophobic domains on the same surface
are illustrated, which can have various advanced applications in microfluidics, printing, photovoltaic,
biomedical devices, anti-bacterial surfaces and water purification.
Several strategies to improve the efficiency of photocatalytic self-cleaning property have been discussed
including doping with metals and non-metals, formation of hetero-junctions between TiO2 and
other low bandgap semiconductors, and fabrication of graphene based semiconductor nano-composites.
Different mechanisms such as band-gap narrowing, formation of localized energy levels within the
bandgap and formation of intrinsic defects such as oxygen vacancies have been suggested to account
for the improved activity of doped TiO2 photocatalysts. Various preparation routes for developing
efficient superhydrophilic–superhydrophobic patterns have been reviewed. In addition, reversible photocontrolled
surfaces with tuneable hydrophilic/hydrophobic properties and its technological applications
are discussed. Examples of antireflective surfaces exhibiting self-cleaning properties for the applications
in solar cells and flat panel displays have also been provided. Discussion is provided on TiO2 based selfcleaning
materials exhibiting hydrophilic and underwater superoleophobic properties and their utilities
in water management, antifouling applications and separation of oil in water emulsions are discussed.
In addition, ISO testing methods (ISO 27448: 2009, ISO 10678: 2010 and ISO 27447: 2009) for analysing
self-cleaning activity and antibacterial action have also been discussed. Rapid photocatalytic self-cleaning
testing methods using various photocatalytic activity indicator inks such as resazurin (Rz), basic blue 66
(BB66) and acid violet 7(AV7) for a broad range of materials such as commercial paints, tiles and glasses
are also described. Various commercial products such as glass, tiles, fabrics, cement and paint materials
developed based on the principle of photo-induced hydrophilic conversion of TiO2 surfaces have
also been provided. The wide ranges of practical applications of self-cleaning photocatalytic materials
suggest further development to improve their efficiency and utilities. It was concluded that a rational
fabrication of multifunctional photocatalytic materials by integrating biological inspired structures with
tunable wettability would be favorable to address a number of existing environmental concerns

The present situation reveals the dependence on fossil fuels, which is seriously accountable for two major impediments: (i) global warming due to increasing atmospheric carbon dioxide (CO2) and (ii) the alarming consumption of energy assets. The reduction of green CO2 in terms of producing solar fuels would be an expedient accomplishment to resolve both problems, simultaneously. The review classifies different categories of photocatalysts applied in foregoing photocatalytic CO2 conversion processes with detailed information concerning operating conditions, preparation techniques and physical properties of catalysts, radiation sources, and selectivity. The categories are concentrated on metal oxides, sulfides, phosphides, and p-type and nonmetal oxide semiconductors. In addition, their modification by doping co-metals, noble metals, transition metals and non-metals for visible light response is emphasized. Besides, for harnessing solar fuel, the recent prospect and advancement of novel sensitized catalysts by dye elements, phthalocyanines and quantum dots (QDs) are also highlighted in this review. This technology needs more efficient solar active catalysts to increase production rates as well as selectivity. The recent scenario indicates that massive prospects and opportunities still exist in this area for further investigation on catalyst selection. This journal is © the Partner Organisations 2014.

http://pubs.rsc.org/en/Content/ArticleLanding/2014/RA/c4ra01769b

Cerium oxide nanoparticles (CeO 2 NPs) were fabricated and grown on graphene sheets using a facile, low cost hydrothermal approach and subsequently characterized using different standard characterization techniques. X-ray photoelectron spectroscopy and electron paramagnetic resonance revealed the changes in surface states, composition, changes in Ce 4+ to Ce 3+ ratio, and other defects. Transmission electron microscopy (TEM) and high resolution TEM revealed that the fabricated CeO 2 NPs to be spherical with particle size of ~10–12 nm. Combination of defects in CeO 2 NPs with optimal amount of two-dimensional graphene sheets had a significant effect on the properties of the resulting hybrid CeO 2-Graphene nanostructures, such as improved optical, photocatalytic, and photocapacitive performance. The excellent photocatalytic degradation performances were examined by monitoring their ability to degrade Congo red ~94.5% and methylene blue dye ~98% under visible light irradiation. The photoelectrode performance had a maximum photocapacitance of 177.54 Fg −1 and exhibited regular capacitive behavior. Therefore, the Ce 3+-ion, surface-oxygen-vacancies, and defects-induced behavior can be attributed to the suppression of the recombination of photo-generated electron–hole pairs due to the rapid charge transfer between the CeO 2 NPs and graphene sheets. These findings will have a profound effect on the use of CeO2-Graphene nanostructures for future energy and environment-related applications.



Visible light-induced photocatalysis using harmless, sustainable, and inexhaustible solar energy is used widely in water purification to remove toxic organic pollutants, such as harmful organic dyes, herbicides, and pesticides 1. Since the innovation of water splitting under UV light irradiation by Honda and Fujishima 1, 2 , semiconductor photocatalytic technology using solar energy has been studied widely to understand the purification of polluted water, production of renewable hydrogen energy from water splitting, and the removal of harmful microorganisms 2, 3. The TiO 2 semiconductor is one of the most widespread photocatalysts owing to its low cost, non-toxicity, relatively high chemical stability, and strong oxidizing power 4–9. On the other hand, the wide band gap (3.2 eV) of TiO 2 , which means that it can only utilize ultraviolet light that makes up about 4% of solar energy, and low quantum efficiency limits its use in large scale applied applications 3, 10. To resolve these drawbacks of TiO 2 , considerable efforts have been made to improve its photocatalytic ability and to extend its light-response range, such as doping 11, 12 , and cocatalyst loading 13. Nevertheless, there are still many problems to solve and it is urgent and critical to develop an efficient, sustainable, and stable photocatalyst that is driven by visible light 14–17 , which accounts for approximately 45% of solar energy 18. Over the past few years, considerable efforts have been made towards the development of highly effective and robust photocatalysts for the oxidative degradation of organic dyes to harmless end-products, such as CO 2 , and H 2 O 11, 18. Nanosized metal oxides (TiO 2 , SnO 2 , CeO 2 , and WO 3) and their composites with carbon based materials have been reported to have electronic properties with excellent

Titanium dioxide (TiO2) is well established as one of the most common photocatalysts used for many environmental, anti-pollution and antibacterial applications. However, in this work, novel photocatalytic TiO2 nanopowders were modified with additions of 1 mol% copper, zinc or copper + zinc (with various Cu: Zn ratios). These were prepared via a green sol–gel route and thermally treated at 450 ºC. For the first time, a direct comparison of the effects of these two modifying agents was performed, both as single and co-substitution. The compounds were thoroughly characterised by means of advanced X-ray diffraction (Whole Powder Pattern Modelling, WPPM) and spectroscopic methods (Raman and UV–vis). For functional properties, the photocatalytic activity in the gas-solid phase (nitrous oxides (NOx) and isopropanol degradation (VOCs)) was tested under UV and visible light, and antibacterial activity against Gram positive and Gram negative bacterial strains was also investigated. Neither copper nor zinc entered into the TiO 2 structure, but nucleated as oxides at the surface of titania nanoparticles, thus creating a nano-heterojunction between the semiconductor materials; this also retarded the anatase-to-rutile phase transition. When comparing and contrasting their functional properties, it was found that Zn modification gave greater photocatalytic activity than that with Cu. On the contrary, for antibacterial activity, copper was shown to be a better additive. Co-modification with both metals did not improve the antibacterial behaviour, but did lead to an increase in photocatalytic activity in some cases.

Describes different types of nanocomposites, such as metal nanocomposites and mixed metal-oxide nanoparticles, nanoporous nanocomposite materials, polymer and carbon-based nanocomposites
Offers a concisely structured and systematic overview for newcomers to a developing field
Provides the fundamentals as well as an outlook on applications, future perspectives and challenges

Reduced graphene oxide sheets (RGO) with different number of graphene layers were used as platforms for TiO 2 nanoparticles deposited using hydrothermal process. The nanomaterials were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), photoluminescence spectroscopy (PL) and diffuse reflectance UV–vis spectroscopy (DR-UV-vis). The photocatalytic activity of the nanocomposites was investigated in a model reaction of phenol decomposition under visible light irradiation. Here, the influence of graphene thickness on its photoactivity was explored. It was found that the highest photocatalytic activity was observed for the catalyst composed of single layer graphene and decreased when a number of graphene layers was higher. This might be related to the surface and electronic properties of reduced graphene oxide arising from different number of graphene layers and its interaction with titanium dioxide: (i) higher interfacial area of TiO 2-RGO with lower thickness of RGO, which could influence in enhanced transferring of photoinduced electron–hole pairs between TiO 2 and RGO, hence improving their separation ; (ii) variations in excitations lifetime relating to the diverse surface quality and density of trap sites of reduced graphene oxide; (iii) higher charge carriers mobility in 1-layer RGO compared to 2-and few-layers.

Photocatalysis offers a promising route to address the challenges of future energy production and anthropogenic environmental pollution. Here we demonstrated the synthesis of a high activity Ag/TiO 2 photocatalyst through a two-step, sol-gel and mechanothermal decomposition method employing a silver acetate precursor. Bulk and surface characterization revealed the formation of dispersed metallic silver nanoparticles (∼9 nm diameter) decorating anatase crystallites (∼14 nm) which stabilized a significant concentration of Ti 3+ surface species. Synergy between silver and titania enhanced the pho-tophysical properties, narrowing the band gap and suppressing charge-carrier recombination. Ag/TiO 2 exhibited good visible light activity and excellent stability over 3 cycles for the aqueous phase photocat-alytic degradation of methyl orange dye (38 mol/h/g cat), and excellent hydrogen production from water splitting (910 mol/h/g cat).

A B S T R A C T ZnO microstructures decorated with Ag nanoparticles photocatalysts synthesized using a simple sol-gel method at different Ag content. The prepared photocatalysts were then characterized by XRD, FESEM, EDX and TEM shows that the ZnO microstructures successfully decorated with Ag nanoparticles and influenced the catalytic photodegradation performance of methelyne blue dye under UV light irradiation. The effect of different Ag content on the structural, surface morphology and catalytic photodegradation of Ag nanoparticles decorated microstructures ZnO were analyzed. The results show that there is a trend of increasing photocatalytic activity with Ag content of between 2.33–63.31 at.% where the highest photodegradation efficiency 87.74% and pho-todegradation rate constant, k of 0.032 min −1 for degradation of methelyne blue with 60 min of irradiation. The enhancement of the photocatalysis activity with increasing Ag content can be explained by the increase in the electron-hole pair lifetimes due to electrons promoted to the conduction band are trapped in the Ag nano-particles which acted as electron sinks.

Recommended by Franca Morazzoni This paper reviews recent investigations of the influence of dopants on the optical properties of TiO 2 polymorphs. The common undoped polymorphs of TiO 2 are discussed and compared. The results of recent doping efforts are tabulated, and discussed in the context of doping by elements of the same chemical group. Dopant effects on the band gap and photocatalytic activity are interpreted with reference to a simple qualitative picture of the TiO 2 electronic structure, which is supported with first-principles calculations.

CdS-Graphene nanocomposite for visible light-driven photocatalytic degradation of organic model dye pollutants. a b s t r a c t This paper reports cadmium sulphide nanoparticles-(CdS NPs)-graphene nanocomposite (CdS-Graphene), prepared by a simple method, in which CdS NPs were anchored/decorated successfully onto graphene sheets. The as-synthesized nanocomposite was characterized using standard characterization techniques. A combination of CdS NPs with the optimal amount of two-dimensional graphene sheets had a profound influence on the properties of the resulting hybrid nanocomposite, such as enhanced optical, photocat-alytic, and photo-electronic properties. The photocatalytic degradation ability of the CdS-Graphene nanocomposite was evaluated by degrading different types of dyes in the dark and under visible light irradiation. Furthermore, the photoelectrode performance of the nanocomposite was evaluated by different electrochemical techniques. The results showed that the CdS-Graphene nanocomposite can serve as an efficient visible-light-driven photocatalyst as well as photoelectrochemical performance for optoelec-tronic applications. The significantly enhanced photocatalytic and photoelectrochemical performance of the CdS-Graphene nanocomposite was attributed to the synergistic effects of the enhanced light absorption behaviour and high electron conductivity of the CdS NPs and graphene sheets, which facilitates charge separation and lengthens the lifetime of photogenerated electron–hole pairs by reducing the recombination rate. The as-synthesized narrow band gap CdS-Graphene nanocomposite can be used for wide range of visible light-induced photocatalytic and photoelectrochemical based applications.

This work reports an electron beam irradiation (30 kGy and 90 kGy) approach to narrow the band gap of the pristine CeO2 nanostructure (p-CeO2) to enhance their visible light activity through defect engineering. This was confirmed by diffuse reflectance spectroscopy, photoluminescence, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller, electrochemical impedance spectroscopy, and linear scan voltammetry. XPS revealed changes in the surface states, composition, Ce4+ to Ce3+ ratio, and other defects in the modified CeO2 nanostructures (m-CeO2). The m-CeO2 exhibits excellent photocatalytic activities by degrading 4-nitrophenol and methylene blue in the presence of visible light (λ > 400 nm) compared to the p-CeO2. The optical, photocatalytic, and photoelectrochemical studies and proposed mechanism further support the enhanced visible light photocatalytic activities of the m-CeO2. This study confirmed that defect-induced band gap engineered m-CeO2 could be used effectively as photocatalyst and photoelectrodes owing to their enhanced visible light photocatalytic activities.

Photocatalysis can be used in water remediation, by which, toxic pollutants are removed from the water and converted into harmless products. In this study, silver niobate and 1% to 10% La-doped silver niobates were synthesized by the sol-gel method. FESEM studies showed that the morphology of the photocatalysts changed from prism-like to small cube-like particles with increasing La-doping. Also, the EDX mapping confirms the presence of Ag, Nb, and La within the silver niobate and La-doped silver niobates. XRD analysis verified the presence of AgNbO3 and AgNb3O8 in the samples. Furthermore, results from the Tauc plots showed that Ladoping resulted in a slight decrease in band gap energy as compared to the silver niobate. The photocatalytic properties of the silver niobate and La-doped silver niobates were investigated for the photocatalytic degradation of methylene blue and Rhodamine B dyes. It was shown from the experiment that La-doping can improve the photocatalytic performance of the silver niobate.

Anatase-type TiO 2 nanotube arrays (TiO 2-NTAs) were grown on Ti foil by anodic oxidation in CH 3 COOH/NH 4 F solutions followed by thermal treatment. The surface of TiO 2-NTAs was further decorated by palladium and silver metal clusters through a chemical-reduction method and its photocatalytic activity was tested by investigating the degradation of p-nitrophenol (PNP) in aqueous solution under visible-light irradiation and electrical polarization. The effects of preparation variables both on microstructural properties of samples and photocatalytic activity were examined by using the 3D response surface and the 2D contour plots. The experimental investigations carried out by using XRD, SEM, HRTEM, EDS, XRF, ICP-AES, XPS, DRS, and PL, demonstrated a strong relation between the phase structure and the photocatalytic activity of TiO 2-NTAs. Titania nanotubes grown in acetic acid solution and thermally post-treated have stable anatase crystal structure, to a point that by performing annealing at 800 • C for 3 h, only the 35% of anatase transforms into rutile. Finally, it was shown that the TiO 2-NTAs decorated with Pd(0.72 wt%) and Ag(1.26 wt%) particles show higher photocatalytic activity compared with nanotubes modified with single metal particles. It is believed that the high photoactivity of TiO 2 nanotubes decorated with Pd–Ag heterostructures is due to the prolonged lifetimes of photogenerated electron–hole pairs. The possible mechanism for the enhanced photocatalytic activity is discussed in detail.

Chalcogenides are narrow-band gap semiconductors that have been widely used as photocatalysts. These narrow-band gap materials allow more efficient absorption of over 40% of solar energy in the visible light range, which will eventually improve its photocatalytic properties. Under visible light irradiation, these materials generate electron and hole (e À /h +) pairs. Photo-generated e À /h + pairs have been utilized to split water into hydrogen and oxygen and to remove and degrade industrial, pharmaceutical and agricultural organic/inorganic/biological pollutants that have been accumulated in the environment. In this perspective review, different types of chalcogenides, namely, binary, multinary (ternary and quaternary) and chalcogenide-based heterostructures are presented briefly. This perspective review also highlights the mechanisms involved and remarkable photocatalytic activity enhancement under visible light irradiation that has been widely researched such as the photocatalytic degradation of industrial pollutants and photocatalytic inactivation of bacteria. Lastly, future prospects for the use of chalcogenides as photocatalysts and chalcogenide-based heterostructures were discussed.

Bacterial and dye pollution are major problems with wastewater treatment. An increasing number of photo-catalysts are being used in industry to kill bacterial and reduce pollution. In the present study, highly stable SnO 2-doped nanocomposites have been prepared successively by a hydrothermal method. The synthesized na-nocomposite was characterized using a range of techniques, such as X-ray diffraction, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy and electron probe micro analysis, ultraviolet visible spectroscopy, Fourier transform infrared spectroscopy, and high resolution transmission electron microscopy (HR-TEM). The nanocomposites showed significant dose-dependent bactericidal activity in the disc diffusion assay and cell viability test. The S-GO-SnO 2 200 μg/mL produced a cell viability of 184.3 ± 11.71 and 172.3 ± 3.05 × 10 6 CFU/mL for E. coli and P. graminis, respectively. The S-GO-SnO 2 showed significant pho-tocatalytic degradation against MB in 120 min. The photocatalyst S-GO-SnO 2 showed 159 and 161 × 10 6 CFU/ mL at 150 min in E. coli and P. graminis, respectively. The cells treated with photocatalytic SnO 2-doped nano-composites showed 50% cell death. HR-TEM revealed 50% cell growth inhibition by bacterial damage. This photocatalytic SnO 2-doped nanocomposite is a good candidate for treating industrial wastewater treatment contaminated with dyes and bacteria.

A highly efficient, recyclable and magnetically separable core-shell structured CuZnO@Fe3O4microspherewrapped with reduced graphene oxide (rGO@CuZnO@Fe3O4) photocatalyst has been developed and usedfor the photoreduction of carbon dioxide with water to produce methanol under visible light irradiation.Owing to the synergistic effect of the components and to the presence of a thin Fe2O3layer on Fe3O4,rGO@CuZnO@Fe3O44 exhibited higher catalytic activity as compared to the other possible combinationssuch as CuZnO@Fe3O42 and GO@CuZnO@Fe3O43 microspheres. The yield of methanol in case of using2 and 3 as photocatalyst was found to be 858 and 1749 mol g−1cat, respectively. However, the yieldwas increased to 2656 mol g−1cat when rGO@CuZnO@Fe3O44 was used as photocatalyst under sim-ilar experimental conditions. This superior photocatalytic activity of 4 was assumed to be due to therestoration of the sp2hybridized aromatic system in rGO, which facilitated the movement of electronsand resulted in better charge separation. The synthesized heterogeneous photocatalyst could readily berecovered by external magnet and successfully reused for six subsequent cycles without significant lossin the product yield.