Environmental Photocatalysis

TiO 2 is an effective and well-known photocatalyst for water and air purification, but its practical applications in visible light-assisted chemical reactions are hindered mainly by its poor visible light absorption capacity. Nitrogen-doped TiO 2 (N-doped TiO 2) has attracted considerable attention as a photocatalyst, and rapid progress has been made in enhancing the photocatalytic efficiency of TiO 2 under visible light irradiation. N-doped TiO 2 exhibits broad absorption in the visible region, which can allow the utilization of a large part of the solar spectrum. This might be useful for environmental and energy applications, such as the photocatalytic degradation of organic pollutants, solar cells, sensors, and water splitting reactions. This review focuses on the major developments in the synthesis of N-doped TiO 2 and its possible applications in the photocatalytic degradation of organic pollutants and environmental remediation under visible light irradiation.

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.

Nano materials find wide applications due to their behavior at nano scale. The wide applications of nano materials demands the synthesis of material at nano scale. Researcher across the world are working of developing new materials and methods for synthesis and application of nano materials. Among all the methods biosynthesis of nano materials is finding much attention because of its simplicity, fastness, chemical free nature, nontoxicity, economical approach.In the present study the TiO2 nano particles are synthesized from titanium isopropoxide solution using neem leaves extract. The synthesized nanoparticles were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM) and particle size analyzer (PSA) and FTIR. The XRD peaks coincide with literature XRD pattern for cubic face centered titanium dioxideanatase phase (JCPDS No.21-1272). The TiO2 particles obtained are spherical in nature and were agglomerates of nanocrystallites. The average size of synthesized TiO2 nanocrystallites as calculated using Scherrer's Formula is 18 nm.

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.

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.

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.

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 (not omitting a plaidoyer for furthering research and development in this promising field), 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.
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

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.

Cerium oxide nanoparticles (CeO2 NPs) are a sought-after material in numerous fields due to their potential applications such as in catalysis, cancer therapy, photocatalytic degradation of pollutants, sensors, polishing agents. Green synthesis usually involves the production of CeO 2 assisted by organic extracts obtained from plants, leaves, flowers, bacteria, algae, food, fruits, etc. The phytochemicals present in the organic extracts adhere to the NPs and act as reducing and/or oxidizing agents and capping agents to stabilize the NPs, modify the particle size, morphology and band gap energy of the as-synthesized materials, which would be advantageous for numerous applications. This review focuses on the green extract-mediated synthesis of CeO 2 NPs and discusses the effects on CeO 2 NPs of various synthesis methods that have been reported. Several photocatalytic, antimicrobial, antioxidant and cytotoxicity applications have been evaluated, compared and discussed. Future prospects are also suggested.

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

This paper reports the synthesis of ZnS microspheres with cubic and hexagonal crystal phases using a solvothermal method. These materials were characterized by a range of techniques. The effects of Au and Ag-doping on ZnS were also examined. Hexagonal phase ZnO microspheres could be obtained by a CO oxidation process over the ZnS microspheres. The onset of CO oxidation occurred above 350 C, which was increased by Au and Ag doping. The synthesized materials were used for the photocatalytic degradation of mixed dyes {methylene blue (MB) þ methyl orange (MO) þ rhodamine B (RhB)}. The observed photocatalytic degradation rate over the photocatalysts was in the order, RhB < MB << MO. The photocatalytic degradation activity of the synthesized materials was observed in the order, Au-ZnS z Ag-ZnS << ZnS < ZnO. ZnO was ~6 times more efficient in the photocatalytic synthesis of 2-hydroxyterephthalic acid than the ZnS and metal-doped ZnS. These results further support the importance and wide applications of the synthesized ZnS, Ag-ZnS, Au-ZnS and ZnO microspheres.

Organic/inorganic nanohybrid materials are a new type of functional materials that have attracted great interest in the last decades, due to their exceptional optical, electrical, mechanical, thermal and catalytic properties. The present study reports a modified sol gel method, so-called "in-surface oxidation of Ti 3+ ions", for the synthesis of carbon nanotube/titania (CNT/TiO 2) nanohybrids. The CNT/TiO 2 nanohybrid material was synthesized with different volumes of TiCl 3 as the titanium source. To analyze their morphology, textural, surface crystallographic and optical properties the materials were characterized by Scanning and Transmission Electron Microscopy (SEM and TEM), X-ray Diffraction (XRD), Fourier Transformed Infrared (FT-IR), Energy-Dispersive X-ray analysis (EDX), X-ray Photoelectron Spectroscopy (XPS), Raman, BET and UV-Vis Diffuse Reflectance Spectroscopy (UV-DRS). The morphological, physico-chemical and textural aspects to account for the results are exhibited. Interestingly, the TiO 2 nanoparticles are well dispersed on CNT surface of the nanohybrid. More interestingly, doping of nitrogen atoms in CNT during the Ti 3+ oxidation step increases the nucleation sites on CNT surface. The quality of the TiO 2 coating depends on various reaction conditions such as temperature and TiCl 3 concentration. The photocatalytic performance of the photocatalysts was tested by degradation of methyl orange. The experimental results indicate that the CO -Ti, N-Ti-O and TiC bonding between CNT and TiO 2 in the nanohybrid material promoted a good photogenerated charge separation, thus greatly improving the photo-catalytic activity of the nanohybrid photocatalyst, when compared to pure TiO 2 .

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.

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.

Developing efficient visible-light-driven (VLD) photocatalysts for environmental decontamination has drawn significant attention in recent years. Herein, we have reported a novel heterostructure of multiwalled carbon nanotubes (MWCNTs) coated with BiOI nanosheets as an efficient VLD photocatalyst, which was prepared via a simple solvothermal method. The morphology and structure were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (DRS), and specific surface area measurements. The results showed that BiOI nanosheets were well deposited on MWCNTs. The MWCNTs/BiOI composites exhibited remarkably enhanced photocatalytic activity for the degradation of rhodamine B (RhB), methyl orange (MO), and para-chlorophenol (4-CP) under visible-light, compared with pure BiOI. When the MWCNTs content is 3 wt %, the MWCNTs/BiOI composite (3%M-Bi) achieves the highest activity, which is even higher than that of a mechanical mixture (3 wt % MWCNTs + 97 wt % BiOI). The superior photocatalytic activity is predominantly due to the strong coupling interface between MWCNTs and BiOI, which significantly promotes the efficient electron-hole separation. The photo-induced holes (h +) and superoxide radicals (O 2 −) mainly contribute to the photocatalytic degradation of RhB over 3%M-Bi. Therefore, the MWCNTs/BiOI composite is expected to be an efficient VLD photocatalyst for environmental purification.

Hydroxyapatite (Ca 10 (PO 4) 6 (OH) 2 , HAp) is a calcium phosphate employed both in biomedicine and for environmental remediation. It is known that HAp can also be photocatalytic under UV light, probably due to oxygen deficiencies, but the mechanism is unclear, and reported optical band gap energies vary greatly. For the first time we propose the mechanisms and precise kinds of vacancies which may cause the photocatalytic activity of HAp, and compare these theoretical data with our measured data on both samples of marine origin and commercial HAp powders. Density functional theory (DFT) (from first principles calculations and Density of States (DOS) modelling) was used to calculate the optical band gap energy (E g) created by various possible oxygen vacancies in the HAp lattice: O from PO 4 , O from OH, the loss of an entire OH group, or the simultaneous loss of O from PO 4 and an entire OH group. The modelled values match the measured values very closely, suggesting that in non-photocatalytic HAp, if any vacancies exist, they are O atoms from the OH group, resulting in a band gap of ∼5 eV in the UVC region (not present in solar light at the Earth's surface). However, in photocatalytic HAp, reduction from the combustion of an organic component at 1000 • C led to oxygen deficiency in the phosphate groups, probably in the O15 position, giving an E g of ∼3.45 eV, in the UVA region (present in sunlight). Heating HAp with no organic component to 1200 • C also led to vacancies, of both an entire OH group and oxygen from PO 4 groups, which led to an intermediate E g value of ∼4 eV, on the boundary of the UVA-UVB regions. Absorption peaks were also predicted in the visible-light region with some types of vacancy.

Recent advances in nano-technology and nano-additives can give enhanced properties to natural hydraulic lime (NHL), creating a multifunctional material. We have prepared a novel nanocomposite, made of a commercial mortar with 1 wt% and 5 wt% added titania nanoparticles (NPs). These TiO2 NPs are themselves doped with 1 mol% silver, to give the material enhanced photocatalytic and antimicrobial properties. The Ag-doped TiO2 NPs were made from a simple, costs effective, aqueous green nanosynthesis process, and the end material only contains 0.01–0.05% Ag. As this mortar is intended to both combat atmospheric pollution, and create more durable/lower maintenance building façades (plastering and finishing) by limiting attack from microorganisms and pollutants, its photocatalytic anti-pollution activity under solar and visible (no UV) light for nitrous oxide (NOx) and volatile organic compound (VOC) removal was studied. The addition of dopants did not significantly alter the physical properties or curing of the mortar, while it showed excellent photocatalytic activity under sunlight, The mortars with only 1 and 5 wt% additives degraded 10.6% and 21% NOx after 45 mins, respectively, comparing well to a value of 50% for a pure TiO2/Ag+ sample. They also degraded VOCs under visible light, of the kind used for lighting inside buildings, with no UV component. As the NPs are contained in the whole of the mortar layer, not just as a coating, if the surface is chipped or damaged this mortar will not loose its photocatalytic capabilities.

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 h
1) which is much higher than that of g-C3N4 (0.43 mmol h
1) and Ni(OH)2@g-C3N4 (9.12 mmol h
1). 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.

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.

Emerging pollutants like metronidazole (MNZ) affect the removal efficiency of conventional activated sludge (CAS) based wastewater treatment plants and can escape traditional treatment facilities. Advanced oxidation processes (AOPs) and membrane filtration could complement the existing processes to completely eliminate pollutants of emerging concern in wastewaters. This work investigated the application of photochemical processes for treating a synthetic wastewater effluent from CAS treatment and membrane filtration of the biological effluents after CAS experiments with MNZ, caffeine (CAF) and ibuprofen (IBU). Photochemical experiments were conducted in a batch photochemical reactor. The influence of different chemical species such as H 2 O 2 , Fe(II), K 2 S 2 O 8 and TiO 2 and of pH value in the system were studied in terms of TOC removal and MNZ degradation. The application of UV/K 2 S 2 O 8 /Fe(II) resulted in 78 % TOC removal in the effluent. Complete degradation of MNZ was observed after 30 min of treatment in the following experiments: UV/H 2 O 2 /Fe(II) at pH 3 and UV/K 2 S 2 O 8. Moreover, the effluents were treated by means of a membrane bioreactor (MBR). Polycarbonate track-etch membranes of 50 and 100 nm pore size were used. The results obtained showed that the carbon removal by the MBR was comparable with the conventional biological treatment. Rejection of MNZ depends on the presence/absence of other emerging contaminants in the wastewater effluents.

Synthesized cerium oxide nanoparticles (S-CeO 2 NPs) and 1%, 5% and 10% zirconium doped CeO 2 (Zr-doped CeO 2) NPs were fabricated using aqueous leaf extract of Pometia pinnata. The synthesized NPs were characterized using standard techniques which confirmed successful synthesis of NPs with particle size ranging from 12 to 23 nm and band gap energy of 2.54-2.66 eV. Photoantioxidant activities showed enhanced activities under visible light irradiation in comparison to the dark condition in the dose-dependent study. Biofilm inhibition studies showed ~ 73% biofilm inhibition of Staphylococcus aureus at 512 µg/mL for S-CeO 2 , whereas 10% Zr-doped CeO 2 NPs showed biofilm inhibition of 52.7%. The bactericidal tests showed killing properties at 1024 µg/mL of S-CeO 2 NPs and at 512 µg/mL of 1% Zr-doped CeO 2. Reduced bactericidal activities were observed for 5% and 10% Zr-doped CeO 2. These studies showed that the fabricated NPs have both good photoantioxidant and antibacterial properties.

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.

This present work focuses on the photocatalytic activity of Fe(III) salt-impregnated TiO2 catalysts for studying
the effect of anion on the photocatalytic activity of the salt-impregnated catalysts. The salt-impregnated TiO2
photocatalyst samples prepared using FeCl3, Fe(NO3)3, and Fe2(SO4)3 were characterized by X-ray diffraction
(XRD), UV-vis diffuse reflectance spectrophotometry (DRS), Fourier transform infrared absorption
spectrophotometry (FT-IR), and surface area measurement by N2 adsorption. Fe(III) ion impregnation of
TiO2 with different salts is observed to influence photocatalytic degradation of acetophenone. Fe(III) salt
anions were observed to influence the initial rate of degradation. For example, the initial rate of degradation
of acetophenone decreases with an increase in percentage of Fe(III) ions in the case of the catalysts prepared
using ferric nitrate and ferric chloride salts. However, the initial rate of degradation was observed to increase
with ferric sulfate impregnated catalysts. The final percentage degradation of acetophenone was found to
increase continuously with an increase in Fe(III) ion concentration, irrespective of the anion. These observations
have been discussed in terms of influence of the presence of Fe(III) ions on the recombination of the electron
and holes generated during UV irradiation of TiO2. Similarly, the effect of anion has been discussed in terms
of radical-scavenging ability of chloride and radical-generating ability of sulfate anions.

We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C 3 N 5 is a low-band-gap (E g = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C 3 N 5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C 3 N 5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm 2 V −1 s −1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm 2 V −1 s −1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J−V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C 3 N 5 in CdS-MHP. C 3 N 5 , with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core−shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.

Calcium phosphate based materials of natural origin with photocatalytic properties were produced. Bones of Atlantic cod fish were treated in appropriate solutions (either Ca-or Ti-containing salts) and successively annealed. Results showed multiphasic materials (hydroxyapatite, b-tricalcium phosphate and anatase titania) with excellent photocatalytic performance under both UV and visible light, with an anatase concentration of only about 2 mol%. Results with such a low amount of anatase have never been reported before for a calcium phosphate-based material; this is attributed to the presence of anatase being mainly on the surface. Single-phase hydroxyapatite (Ca 10 (PO 4) 6 (OH) 2 or HAp) also showed some photocatalytic properties and antibacterial activity.

It is highly desired to develop an efficient large surface area CoCrFeO4-based beads sun-light driven photocatalysts with excellent recycling features for degrading high-concentration dyes. Herein, a novel CoCrFeO4 oxide nanoparticles have customarily been synthesized by the
combination of three metals (Co, Cr and Fe) via co-precipitation method in aqueous solution and then millimeter-scale CoCrFeO4 oxide chitosan-composite beads (CoCrFeO4-CB) were prepared by incorporating the CoCrFeO4 in chitosan polymer in basic medium, which makes the
adsorbent easier to separate. The number of optimized nanocomposite beads used for the removal of high-concentration dyes displays 5-time photoactivity enhancement under sun-light irradiation compared to pristine CoCrFeO4. Based on the fluorescence spectra related to theformed •OH amounts, temperature-programmed desorption and electrochemical results, it is deduced that the unprecedented photocatalytic activities are mainly attributed to the large surface
area, and enhanced charge separation from the chitosan as well as its promotion effects on O2 activation. Influencing factors that effect the photocatalytic efficiency of dyes, such as catalyst dose, dyes concentration, time, and the light source was also studied. More importantly, after five catalytic cycles, no evident deactivation was observed, suggesting the satisfactory stability of the investigated photocatalyst. Also, large numbers of superoxides radicals form which is the main active species participate in the degradation of acid black were analyzed using a radical trapping experiment. It is expected that our work could render navigated information for steering toward the design and applications of the CoCrFeO4-based photocatalyst with sun-light
utilization for environmental remediation.

Zinc aluminate and cerium-doped zinc aluminate nanoparticles are synthesised by co-precipitation method. Ammonium hydroxide is used as a precipitating agent. The synthesised compounds are char-acterised by powder X-ray diffraction (XRD), Fourier transform Infrared spectroscopy (FT-IR), Ultraviolet diffuse reflectance spectroscopy (UV-DRS), Thermogravimetric analysis (TGA), Scanning electron mi-croscopy (SEM) and Surface area measurements. The photocatalytic activity of zinc aluminate and cerium doped zinc aluminate nanoparticles are studied under the UV light and visible light taking methylene blue as a model pollutant. The amount of catalyst, concentration of dye solution and time are optimised under UV-light. Degradation of methylene blue under the UV-light is found to be 99% in 20 min with 10 mg of cerium doped catalyst. Compared to visible light degradation, the degradation of dye under UV-light is higher. Cerium doping in zinc aluminate (ZnAl 2 O 4 :Ce 3þ) increased the photocatalytic activity of zinc aluminate.

A series of titania–transition metal and titania–rare earth element mixtures, with the stoichiometry Ti1−xMxO2, where M=Ce, Eu, La, Nb, W, Y, and x ranging from 0 to 0.05 atoms per formula unit, were prepared via solid-state reaction of the precursor oxides. The products of the synthesis were thermally treated in air and two maximum temperatures (900 and 1000 °C) were reached.

The addition of transition metal and rare earth ions to the TiO2 structure modified the anatase-to-rutile phase transition temperature, depending on the valence state of the ions added. Transition metals entered the titania structure, but essentially no solid solution between the rare earth elements and TiO2 was detected.

The photocatalytic activity of the powders was assessed in liquid–solid and gas–solid phases, under UVA and visible-light irradiation, monitoring the degradation of an organic dye and isopropanol, respectively. The results were explained by taking into account the relative amounts of anatase and rutile in the samples, the specific surface area of the powders, and their optical properties.

Metal oxides are of great technological importance in environmental remediation and electronics because of their capability to generate charge carriers when stimulated with required amount of energy. The promising arrangement of electronic structure, light absorption properties, and charge transport characteristics of most of the metal oxides has made possible its application as photocatalyst. In this article definition of metal oxides as photocatalyst, structural characteristics, requirements of the photocatalyst, classification of photocatalysts and the mechanism of the photocatalytic process 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 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...

Graphitic carbon nitride (g-C 3 N 4) usually exhibits weak photocatalytic activity for CO 2 reduction and pollutant degradation. Herein, the visible-light activities of g-C 3 N 4 nanosheets are successfully improved by co-modifying SnO 2 and Ag, with ∼10-time and ∼8-time improvement respectively for CO 2 conversion and 2,4-di-chlorophenol (2,4-DCP) degradation as compared to the pure g-C 3 N 4. Mainly based on the transient-state surface photovoltage responses, transient-state photoluminescence spectra and electrochemical analyses, it is confirmed that the improved photoactivities are attributed to the synergistic effect of the prolonged charge lifetime and the provided catalytic function by modifying SnO 2 and Ag, respectively. In addition, the synergistic effect is also feasible by replacing Ag with Au. This work will provide an effective strategy for designing high-activity g-C 3 N 4 based photocatalysts.

Ag-SnO2 nanocomposites (1 mM and 3 mM) were synthesized in water at room temperature using an electrochemically active biofilm. The resulting nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, diffuse reflectance spectroscopy, photoluminescence spectroscopy and X-ray photoelectron spectroscopy. The Ag-SnO2 nanocomposites exhibited enhanced photocatalytic activity under visible light irradiation for the degradation of methyl orange, methylene blue, 4-nitrophenol and 2-chlorophenol compared with pure SnO2 nanostructures. Photoelectrochemical measurements, such as electrochemical impedance spectroscopy, linear scan voltammetry and differential pulse voltammetry in the dark and under visible light irradiation, further supported the visible light activity of the Ag-SnO2 nanocomposites. These results showed that the Ag nanoparticles induced visible light activity and facilitated efficient charge separation in the Ag-SnO2 nanocomposites, thereby improving the photocatalytic and photoelectrochemical performance.

About this Research Topic:

Photocatalysis is a chemical reaction that takes place in presence of a photocatalyst and a suitable light. In other words, it is a reaction that uses light to generate a pair of excited electron and positive hole to induce redox reactions, as the first step, with both positive and negative Gibbs-energy change.

A photocatalyst is a material that harvests light to bring it to higher energy level and provides such energy to a reacting substance to make a chemical reaction to take place. Multi-anion photocatalysts contain two or more anion-forming elements and exhibit unprecedented photocatalytic, optoelectronic and physicochemical properties compared with homo-anion counterparts. For example, N,S co-doped TiO2 has been reported for enhanced visible light induced photocatalytic activities for energy and environment related applications.

Photocatalysis promises a solution to challenges associated with the intermittent nature of sunlight that is considered as renewable and ultimate energy source to power and energy related activities on the Earth. Other examples are water splitting, hydrogen production, water treatment and disinfection, removal of pollutants from contaminated water and air, photocatalytic tiles, photocatalytic paints, self-cleaning window panels based on photoactive materials and many more. Hence, there is a need to understand the fundamental concepts of photocatalysis in a simple way of using multi-anion photocatalysts.

This research topic will provide a complete overview to photocatalysis combining the theoretical and fundamental concepts of photocatalysis from synthesis of novel photocatalysts, reaction engineering, and exploring several important applications of photocatalysis. Most importantly, this research topic will mainly focus on multi-anion photocatalysts for environmental remediation, energy production, conversion etc. The objectives include: 1. All the latest information about multi-anion photocatalyst materials will be compiled and readers will be benefited. 2. Fundamental and advanced understanding of multi-anion photocatalysts materials will be collected. 3. Use of multi-anion photocatalyst materials in energy conversion and environmental remediation will be focused.

This research topic will provide vast and extensive information about the multi-anion compounds as novel photocatalysts. All the latest developments in this field will be invited, evaluated and compiled. This research topic will be a valuable collection that will stimulate the interest of target audience as researchers and students in designing advanced nanostructured materials for wastewater treatment, energy production and conversion, environmental remediation etc. using multi-anion photocatalysts. We welcome submissions of Original Research, Review, Mini-review and Prospective from the following aspects:

• Recently developed multi-anion photocatalyst materials that assist in energy production and conversion, environmental remediation, etc.
• Fundamental understanding of controlled synthesis of multi-anion photocatalyst materials.
• Basics and mechanism of energy production and conversion, environmental remediation, etc.

Keywords: Multi-Anion Photocatalysts; Photocatalysts; Photocatalysis; Energy Conversion; Environmental Remediation

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This paper reports a simple, biogenic and green approach to obtain narrow band gap and visible light-active TiO 2 nanoparticles. Commercial white TiO 2 (w-TiO 2) was treated in the cathode chamber of a Microbial Fuel Cell (MFC), which produced modified light gray TiO 2 (g-TiO 2) nanoparticles. The DRS, PL, XRD, EPR, HR-TEM, and XPS were performed to understand the band gap decline of g-TiO 2. The optical study revealed a significant decrease in the band gap of the g-TiO 2 (E g = 2.80 eV) compared to the w-TiO 2 (E g = 3.10 eV). The XPS revealed variations in the surface states, composition, Ti 4+ to Ti 3+ ratio, and oxygen vacancies in the g-TiO 2. The Ti 3+ and oxygen vacancy-induced enhanced visible light photocatalytic activity of g-TiO 2 was confirmed by degrading different model dyes. The enhanced photoelectrochemical response under visible light irradiation further supported the improved performance of the g-TiO 2 owing to a decrease in the electron transfer resistance and an increase in charge transfer rate. During the TiO 2 treatment process, electricity generation in MFC was also observed, which was ~0.3979 V corresponding to a power density of 70.39 mW/m 2. This study confirms narrow band gap TiO 2 can be easily obtained and used effectively as photocatalysts and photoelectrode material.