Recent Advances in Graphene Based TiO2 Nanocomposites (GTiO2Ns) for Photocatalytic Degradation of Synthetic Dyes

Synthetic dyes are widely used in textile, paper, food, cosmetic, and pharmaceutical industries. During industrial processes, some of these dyes are released into the wastewater and their successive release into rivers and lakes produces serious environmental problems. TiO2 is one of the most widely studied and used photocatalysts for environmental remediation. However, it is mainly active under UV-light irradiation due to its band gap of 3.2 eV, while it shows low efficiency under the visible light spectrum. Regarding the exploration of TiO2 activation in the visible light region of the total solar spectrum, the incorporation of carbon nanomaterials, such as graphene, in order to form carbon-TiO2 composites is a promising area. Graphene, in fact, has a large surface area which makes it a good adsorbent for organic pollutants removal through the combination of electrostatic attraction and π-π interaction. Furthermore, it has a high electron mobility and therefore it reduces the electron-hole pair recombination, improving the photocatalytic activity of the semiconductor. In recent years, there was an increasing interest in the preparation of graphene-based TiO2 photocatalysts. The present short review describes the recent advances in TiO2 photocatalyst coupling with graphene materials with the aim of extending the light absorption of TiO2 from UV wavelengths into the visible region, focusing on recent progress in the design and applications in the photocatalytic degradation of synthetic dyes

Kinetic Model for Simultaneous Adsorption/Photodegradation Process of Alizarin Red S in Water Solution by Nano-TiO2 under Visible Light.

The simultaneous adsorption and visible light photodegradation of Alizarin Red S in water solutions were studied in real time mode by using nano-TiO2, such as Anatase and Aeroxide P-25, supported on polypropylene strips. Kinetic results of the overall process were compared with those obtained from separated steps of adsorption and photodegradation previously studied; kinetic advantages were evidenced with the simultaneous approach. From the study of different dye concentrations, a kinetic model has been proposed which describes the overall process. This model considered two consecutive processes: The adsorption of dye on TiO2 surface and its photodegradation. The obtained results were in good agreement with experimental data and can predict the profiles of free dye, dye adsorbed on TiO2 and photoproduct concentrations during the total process

Detrimental vs. beneficial influence of ions during solar (SODIS) and photo-Fenton disinfection of E. coli in water: (Bi)carbonate, chloride, nitrate and nitrite effects

In this work, we studied the effect of inorganic ions occurring in natural waters on E. coli inactivation by solar and photo-Fenton processes, two crucial methods for drinking water treatment in sunny or developing countries. HCO−, Cl−, SO −, NO−, NO− 3 423 2 and NH+4 were assessed at relevant concentrations for their inhibiting or facilitating role. The inactivation enhancement during solar disinfection (SODIS) was mainly attributed to the generation of HO• radicals produced during by excitation of NO−3 , NO−2 , while the HO• of photo-Fenton may be transformed into other radical species in presence of ions. Natural organic matter (NOM) was found to enhance both processes but also to hinder most of the enhancing ions, except for NO−2 ; modeling with the APEX software unveiled the inter-relations in the presence of NOM, and the possible inactivation activity by NO2 . The photo-Fenton inactivation was more significantly enhanced by ions than SODIS (besides the case of NO−3 , NO−2 ), but both processes were found robust enough

Kinetic Model for Photocatalytic Degradation of Alizarin Red-S by Polypropylene coated nano-TiO2

The aim of this study is optimize and clarify the total mechanism of adsorption/ visible-photodegradation of Alizarin Red S polypropylene coated nano-TiO2 Degussa P-25 and TiO2 Anatase as photocatalysts. The characterization of Alizarin Red S and its chemical interaction with TiO2 surface has been studied. The acid dissociation constants of Alizarin Red S are determined. Adsorption and photodegradation steps were simultaneously studied in order to propose a simple kinetic model which can describe the process in an adequate way. The results obtained from this kinetics model are in good agreement with experimental data

Graphene/TiO2 Nanocomposite for Efficient Visible-Light Photocatalysis: Synthesis, Characterization and Photocatalytic Applications.

The production of graphene in large quantities is an ongoing challenge for large-scale applications. A number of processes are used to produce graphene from graphene oxide but they need strong oxidizing and reducing agents [1]. However, graphene fabricated under these chemical conditions tends to have a certain number of structural defects, when compared to that produced from other techniques. For that purpose, top-down method such as the exfoliation of graphite powder in liquid phase by sonication is a very promising route due to its simplicity, its versatility and its low-cost [2]; besides, ultrasound treatment offers a suitable option to create high-quality graphene in great quantity. Graphene with the thickness of a single carbon atom owns unique physical and chemical properties including highly flexible structure, large surface area, high electrical and thermal conductivity and high chemical stability; also, in graphene, electrons have a linear relation between energy and momentum, so its band structure has no energy gap [3]. With these properties, graphene is an attractive material in applications that require a fast electron transfer, such as photocatalysis; it has been reported that graphene based semiconductor nanocomposites are considered as good photocatalyst for pollutant degradation [4]. Graphene is an ideal nanomaterial for doping TiO2 because the formation of Ti-O-C bonds extend the visible light absorption of TiO2. Moreover, electrons are easily transported from TiO2 to the graphene nano-sheets and the electron-hole recombination is significantly reduced; this is enhances the oxidative reactivity [5]. In this work, it was used an aqueous solution of a non-ionic surfactant, that acted like dispersing agent and as stabilizer to prevent layer stacking, for the direct exfoliation of graphite by sonication. The obtained graphene dispersion is characterized by X-Ray Diffraction (XRD), Dynamic Light Scattering (DLS) and UV-Visible spectroscopy, and it is used for the preparation of heterogeneous GR@TiO2 photocatalyst supported on polypropylene (PP). GR@TiO2 nanocomposites are used to treat water with environmental pollutants by photocatalytic

Band Gap Implications on Nano-TiO2 Surface Modification with Ascorbic Acid for Visible Light-Active Polypropylene Coated Photocatalyst

The effect of surface modification using ascorbic acid as a surface modifier of nano-TiO2 heterogeneous photocatalyst was studied. The preparation of supported photocatalyst was made by a specific paste containing ascorbic acid modified TiO2 nanoparticles used to cover Polypropylene as a support material. The obtained heterogeneous photocatalyst was thoroughly characterized (scanning electron microscope (SEM), RAMAN, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and Diffuse Reflectance Spectra (DRS) and successfully applied in the visible light photodegradation of Alizarin Red S in water solutions. In particular, this new supported TiO2 photocatalyst showed a change in the adsorption mechanism of dye with respect to that of only TiO2 due to the surface properties. In addition, an improvement of photocatalytic performances in the visible light photodegration was obtained, showing a strict correlation between efficiency and energy band gap values, evidencing the favorable surface modification of TiO2 nanoparticles

From TiO2 and Graphite to Graphene doped TiO2 for visible light photocatalytic degradation of refractory dye.

Graphene production is an ongoing challenge for large-scale applications. Many processes are used to produce graphene 1. Top-down method such as the exfoliation of graphite powder in liquid phase by sonication is a promising route to create high quality graphene in great quantity due to its simplicity, its versatility and its low-cost 2. Graphene with the thickness of a single carbon atom owns unique physical and chemical properties like large surface area, highly flexible structure, high electrical and thermal conductivity and high chemical stability 3. With these properties, graphene is an attractive material in applications that require a fast electron transfer, such as photocatalysis. In fact, graphene based semiconductor nanocomposites are considered as good photocatalyst for pollutant degradation 4. Graphene is an ideal nanomaterial for doping TiO2 because the formation of Ti-O-C bonds extend the visible light absorption of TiO2. Furthermore, electrons are easily transported from TiO2 to graphene nano-sheets and the electron-hole recombination is reduced; this is enhances the oxidative reactivity 5. In this work, graphene doped TiO2 nanocomposite was used as photocatalytic materials for the Alizarin Red S degradation in water solutions. Graphene dispersions were prepared by liquid-phase exfoliation of graphite in the presence of a non-ionic surfactant, Triton X-100. The obtained graphene dispersion was characterized by X-Ray Diffraction, Dynamic Light Scattering and UV-Visible spectroscopy and was subsequently used for the preparation of graphene doped-TiO2 photocatalyst. Graphene doped-TiO2 nanocomposites showed higher adsorption of Alizarin Red S on the catalyst surface and higher photocatalytic activity for its degradation under visible light irradiation, respect to those obtained with pure TiO2 6. References: 1) Dimiev, A. M.; Tour, J. M. ACS Nano, 2014, 8, 3060 - 3068. 2) Samorì, P. et al. Chemical Society Reviews, 2014, 43, 381 - 398. 3) Geim, A.K.; Novoselov, K. S. Nature Materials, 2007, 6, 183 - 191. 4) Khalid, N. R.; Hong, Z. et al. Current Applied Physics, 2013, 13, 659 - 663. 5) Li, F.; Cheng, H. M. et al. Advanced Functional Materials, 2011, 21, 1717 - 1722. 6) Giovannetti, R.; D’ Amato, C. A. et al. Scientific Reports, 2015, 5, 17801

Environmental Remediation by Light Driven Advanced Oxidation Processes: Pollutant Degradation and Bacterial Disinfection

This PhD thesis in Chemical Science started in November 2015 at the School of Advanced Studies of University of Camerino. The research activity described in this PhD thesis was carried out at University of Camerino in the School of Science and Technology (Dr. Rita Giovannetti’s Research Group) and at École Polytechnique Fédérale de Lausanne in the Institut des Sciences et Ingénierie Chimiques (Prof. César Pulgarin’s Research Group). In this PhD thesis, after a “GENERAL INTRODUCTION” about the aim of the PhD project, are reported an INTRODUCTION regarding environmental and water pollution and Advanced Oxidation Processes, in Chapter 1, and two successive Sections. In Section 1, entitled “GRAPHENE BASED TiO2 NANOCOMPOSITES FOR PHOTOCATALYTIC DEGRADATION OF SYNTHETIC DYES”, are present three Chapters. After a general introduction in Chapter 2 on TiO2 and Graphene-TiO2 photocatalysis, in Chapter 3 and Chapter 4 are reported all obtained results. In particular, in Chapter 3 is reported the first work regarding the preparation and optimization of a new heterogeneous photocatalyst constituted by TiO2 and graphene prepared by exfoliation of graphite, with a special attention into preparation and characterization of graphene dispersion. The new graphene-TiO2 photocatalyst was used for the photodegradation of Alizarin Red S solution under visible light irradiation. Meanwhile, in Chapter 4 is reported the second work regarding the preparation, optimization and characterization of a new heterogeneous photocatalyst constituted by TiO2 and reduced graphene oxide prepared by thermal reduction of graphene oxide, with a special attention into preparation and characterization of reduced graphene oxide dispersion. As in the case of Chapter 3, the new reduced graphene oxide-TiO2 photocatalyst was used for the photodegradation of Alizarin Red S solution under visible light irradiation. In Section 2, entitled “SOLAR DISINFECTION AND PHOTO-FENTON PROCESSES FOR BACTERIA INACTIVATION IN WATER”, are present two Chapters. After a general introduction in Chapter 5 on Solar Disinfection and Photo-Fenton treatments for water depuration, in Chapter 6 are reported all obtained results. In particular, the effect of the presence of various inorganic ions, which individually or in combination with each other can act as scavenger of OH radicals or can produce additional OH radicals or other active radical species on inactivation of Escherichia Coli with Solar Disinfection and Photo-Fenton processes is discussed in detail. Results of this PhD thesis are published and/or submitted for publication in scientific international journals and presented as Congress communications

Environmental Remediation by Light Driven Advanced Oxidation Processes: Pollutant Degradation and Bacterial Disinfection

This PhD thesis in Chemical Science started in November 2015 at the School of Advanced Studies of University of Camerino. The research activity described in this PhD thesis was carried out at University of Camerino in the School of Science and Technology (Dr. Rita Giovannetti’s Research Group) and at École Polytechnique Fédérale de Lausanne in the Institut des Sciences et Ingénierie Chimiques (Prof. César Pulgarin’s Research Group). In this PhD thesis, after a “GENERAL INTRODUCTION” about the aim of the PhD project, are reported an INTRODUCTION regarding environmental and water pollution and Advanced Oxidation Processes, in Chapter 1, and two successive Sections. In Section 1, entitled “GRAPHENE BASED TiO2 NANOCOMPOSITES FOR PHOTOCATALYTIC DEGRADATION OF SYNTHETIC DYES”, are present three Chapters. After a general introduction in Chapter 2 on TiO2 and Graphene-TiO2 photocatalysis, in Chapter 3 and Chapter 4 are reported all obtained results. In particular, in Chapter 3 is reported the first work regarding the preparation and optimization of a new heterogeneous photocatalyst constituted by TiO2 and graphene prepared by exfoliation of graphite, with a special attention into preparation and characterization of graphene dispersion. The new graphene-TiO2 photocatalyst was used for the photodegradation of Alizarin Red S solution under visible light irradiation. Meanwhile, in Chapter 4 is reported the second work regarding the preparation, optimization and characterization of a new heterogeneous photocatalyst constituted by TiO2 and reduced graphene oxide prepared by thermal reduction of graphene oxide, with a special attention into preparation and characterization of reduced graphene oxide dispersion. As in the case of Chapter 3, the new reduced graphene oxide-TiO2 photocatalyst was used for the photodegradation of Alizarin Red S solution under visible light irradiation. In Section 2, entitled “SOLAR DISINFECTION AND PHOTO-FENTON PROCESSES FOR BACTERIA INACTIVATION IN WATER”, are present two Chapters. After a general introduction in Chapter 5 on Solar Disinfection and Photo-Fenton treatments for water depuration, in Chapter 6 are reported all obtained results. In particular, the effect of the presence of various inorganic ions, which individually or in combination with each other can act as scavenger of OH radicals or can produce additional OH radicals or other active radical species on inactivation of Escherichia Coli with Solar Disinfection and Photo-Fenton processes is discussed in detail. Results of this PhD thesis are published and/or submitted for publication in scientific international journals and presented as Congress communications

Equilibrium and kinetic aspects in photoactivity of Polypropilene coated Nano-TiO2

Water pollution has always been a major problem to the environment; the discharge of pollutants into water bodies is illegally and it is a source of organic compounds in wastewater . These pollutants are resistant to the biological and phisical treatments and in particular, dyes are the first pollutant species identified due to their obvious color and they are undesirable in water, even in very small amounts. The treatment of these dyes effluents is highly desired for the preservation of the environment. Heterogeneous photocatalysis has attracted considerable attention and the most used photocatalyst is TiO2 which show advantages such as chemical and biological resistance, low price, expensive recycling and recovery of the photocatalyst [2]. The aim of present work is the study and the use of two commercial types of TiO2 such as Anatase and Degussa P-25 supported on Polypropylene (PP) strips using Visible light in the photodegradation of two reference dyes, Methylorange and Alizarin Red S, in acid, basic and neutral conditions. The optimization of TiO2 pastes preparation using two commercial TiO2 has been performed and a low-cost dip-coating procedure was developed. Scan Electron Microscopy and Atomic Force Microscopy were used in order to obtain morphological information of TiO2 on support material. Equilibrium and kinetic aspects in the adsorption and photodegradation of Methylorange and Alizarin Red S are described using Polypropylene-TiO2 films in the Visible/TiO2/air reactor showing efficient dyes degradation. [1] C. Guillard, H. Lachheb, A. Houas, M. Ksibi, E. Elaloui, J. Herrmann, Journal of Photochemistry and Photobiology, 158 (2003) 27–36. [2] D. S. Bhatkhande, V. G. Pangarkar and A. ACM Beenackers, Journal of chemical technology and biotechnology, 77 (2001) 102