Query: A review on H2 production through photocatalytic reactions using TiO2/ TiO2-assisted catalysts

Candidate papers:

abstract: Abstract Photocatalytic water splitting technology by using nano sized TiO2 can produce low cost and environment friendly hydrogen using renewable resource such as solar energy, which can fulfil the future requirements of energy. Nano sized TiO2 is highly efficient as a semiconductor photocatalyst possessing high surface area. The significant drawbacks of utilising TiO2 as photocatalysts are reduced absorption capacity of visible radiation and fast recombination of photoexcited electron/hole (e /h+ pair. Its activity is restricted to UV light, which is only ~3 5% of the solar spectrum. This present review elucidates various aspects and the recent researches related to TiO2 nano photocatalysis for the effective solar hydrogen generation via photocatalytic water splitting technology.
author_names: Rohini Singh

Suman Dutta
title: A review on H2 production through photocatalytic reactions using TiO2/TiO2 assisted catalysts
year: 2018

abstract: The production of carbon nanotubes (CNTs) is usually carried out either via catalytic decomposition of methane or by recrystallization of bio char species obtained by pyrolysis of solid wastes. Both techniques are generally executed at high temperatures and consume long time. Thus, these two methodologies are not considered to be economically feasible. This research work reports a facile and cost effective new route for the generation of CNTs via photocatalytic conversion of water to hydrogen. Specifically, water splitting photochemical reaction using a metal organic framework (Cr MIL 101) and TiO2 nanoparticles was demonstrated. The coupling of the aforementioned semiconductors, as novel matrices, to improve the photocatalytic reactivity toward hydrogen production in the presence of methanol, as a hole scavenger, under visible light was performed. The results revealed the high yield evolution of H2 showing a maximum purity of 99.3% with the in situ formation of carbon nanotubes over the surface of the Cr MIL 101/TiO2 binary system that was obtained by sonication. The use of this binary photocatalyst, however, as a physical mix could produce nano carbon species while simultaneously producing hydrogen rich syngas. The production of H2 gas that was simultaneously stored was noted when Cr MIL 101 was used individually as a photocatalyst. These data provide new advances in the field of water splitting by introducing promising candidate materials for the production of pure hydrogen as a clean fuel.
author_names: Rasha S Mohamed

Amal A Al Kahlawy

Ahmed M A El Naggar

Heba M Gobara
title: Innovative approach for the production of carbon nanotubes (CNTs) and carbon nanosheets through highly efficient photocatalytic water splitting into hydrogen using metal organic framework (MOF) nano TiO2 matrices as novel catalysts
year: 2020

abstract: Plasmonic nanostructures have played a key role in extending the activity of photocatalysts to the visible light spectrum, preventing the electron hole combination and providing with hot electrons to the photocatalysts, a crucial step towards efficient broadband photocatalysis. One plasmonic photocatalyst, Au/TiO2, is of a particular interest because it combines chemical stability, suitable electronic structure, and photoactivity for a wide range of catalytic reactions such as water splitting. In this review, we describe key mechanisms involving plasmonics to enhance photocatalytic properties leading to efficient water splitting such as production and transport of hot electrons through advanced analytical techniques used to probe the photoactivity of plasmonics in engineered Au/TiO2 devices. This work also discusses the emerging strategies to better design plasmonic photocatalysts and understand the underlying mechanisms behind the enhanced photoactivity of plasmon assisted catalysts.
author_names: Jehad Abed

Nitul S Rajput

Amine el Moutaouakil

Mustapha Jouiad
title: Recent Advances in the Design of Plasmonic Au/TiO2 Nanostructures for Enhanced Photocatalytic Water Splitting
venue: Nanomaterials
year: 2020

abstract: Abstract In this work we compare the performance of platinum and palladium co catalysts supported on Nb doped titania materials for the photo generation of hydrogen using methanol as sacrificial agent. Liquid and gas phase processes are considered. The catalysts physico chemical properties were characterized by a combination of X ray diffraction, UV vis and photoluminescence spectroscopies and transmission electron microscopy, and their photocatalytic performance assessed through the analysis of the optical properties, the measurement of the reaction rates and subsequent computation of the true quantum efficiency in both liquid and gas phase reactors. Using Pt and Pd containing catalysts having similar primary noble metal particle size we compare the two co catalysts performance in terms of the carbon containing product selectivity of the methanol photo transformation and the overall performance of the materials in the photon to chemical transformation as measured through the true quantum efficiency. The work shows that Pd displays competitive performance with respect to Pt under UV illumination but not under visible light. The physico chemical analysis of the solids and particularly the measurement of the charge carrier handling and recombination through photoluminescence at several wavelengths indicate the important role played by charge recombination upon UV illumination but also that other phenomena need to be considered under visible illumination to fully explain the photo catalytic evolution of hydrogen in noble metal containing catalysts.
author_names: Uriel Caudillo-Flores

Mario J Munoz-Batista

J A Cortes

Marcos Fernandez-Garcia

Anna Kubacka
title: UV and visible light driven H2 photo production using Nb doped TiO2: Comparing Pt and Pd co catalysts
year: 2017

abstract: Abstract The generation of hydrogen and oxygen from the photocatalytic water splitting reaction under visible light is a promisingly renewable and clean source for H2 fuel. The transition metal oxide semiconductors (e.g. TiO2, WO3, ZnO, and ZrO2) are have been widely used as photocatalysts for the hydrogen generation. Because of safety, low cost, chemical inertness, photostability and other characteristics (bandgap, corrosion resistance, thermal and environmental stability) TiO2 is considered as a most potential catalyst of the semiconductors being investigated and developed. However, the extensive applications of TiO2 are hampered by its inability to exploit the solar energy of visible region. Other demerits are lesser absorbance under visible light, and recombination of photogenerated electron hole pairs. In this review, we focus on the all the possible reactions taking place at the catalyst during photo induced H2 from water splitting reaction, which is green and promising technology. Various parameter affecting the photocatalytic water splitting reactions are also studied. Predominantly, this review is focussed on bandgap engineering of TiO2 such as the upward shift of valence band and downward shift of conduction bands by doping process to extend its light absorption property into the visible region. Furthermore, the recent advances in this direction including various new strategies of synthesis, multiple doping, hetero junction, functionalization, perspective and future opportunities of non metals doped TiO2 based nanostructured photocatalysts for various photocatalytic applications such as efficient hydrogen production, air purification and CO2 reduction to valuable chemicals have been discussed.
author_names: Shivaraj B Patil

Patil S Basavarajappa

Nagaraju Ganganagappa

M S Jyothi

Anjanapura V Raghu

Kakarla Raghava Reddy
title: Recent advances in non metals doped TiO2 nanostructured photocatalysts for visible light driven hydrogen production, CO2 reduction and air purification
venue: International Journal of Hydrogen Energy
year: 2019

abstract: Photocatalytic water splitting using semiconductor materials has attracted considerable interest due to its potential for clean production of H2 from water through the conversion of abundant solar energy into chemical energy. This article briefly analyzed the trend and progress in the research and development of visible light responsive photocatalysts for water splitting in the past few years. Particularly, metal sulfides and composite photocatalysts were discussed. This brief review article aims at facilitating a search of stable and efficient photocatalysts for water splitting, and revealing fundamental insight into the development of novel visible light adsorbing photocatalysts. Keyword: water splitting, visible light, hydrogen production, metal sulfide Hydrogen (H2) production using visible light photocatalyst for water splitting has attracted considerable attention due to the growing demand for environmentally friendly and sustainable energy sources. The number of journal articles on water splitting for H2 production dramatically increased over the past few years (Fig.1) highlighting the tremendous interests in photocatalytic water splitting as a means of producing renewable clean energy production with minimum carbon footprint. Since the early 1970s, intensive efforts have been directed toward research and development of various photocatalytic materials for water splitting for H2 production. Most traditional photocatalysts, such as TiO2 and ZnGa2O4, have relatively large band gaps and thus can capture only ultraviolet (UV) irradiation, which accounts for a small fraction of solar irradiation. To overcome this limitation, many types of visible light absorbing materials with narrower band gaps, such as mixed oxides, oxynitride, and metal sulfides, are developed as shown in Fig. 2. Until today, developing visible light photocatalysts remains the focus in this field. As shown in Fig. 1, the number of journal articles on visible light driven photocatalyst between 2006 and 2010 is almost 5 times the number of journal articles published between 1981 and 1985. It is also worth noting that before 2000, the publications on water splitting under UV irradiation outnumbered those under visible light. By contrast, after 2000, much more attention is being directed toward water splitting under visible light, especially in the past five years. Moreover, the number of journal articles on UV driven water splitting has declined over that past 5 years. This article compared the quantum yield (QY) and H2 productivity in different novel visible light adsorbing photocatalytic systems that were developed in the past few years. This article also examined the colloidal stability or durability, quantum efficiency, and potential environmental impacts between different studies, which laid groundwork toward developing and designing new rationale Fig. 1. The number of journal articles on water splitting published with years. VIS: visible light. UV: ultraviolet. NSTI Nanotech 2013, www.nsti.org, ISBN 978 1 4822 0586 2 Vol. 3, 2013 584 visible light responsive photocatalysts. 1. Visible light driven metal sulfide photocatalyst for water splitting Metal sulfides are attractive materials as candidates of visible light driven photocatalysts due to the narrow band gaps and negative valence band potentials. Despite the excellent visible light photocatalytic activity, they often exhibit poor photostability and undergo photocorrosion with prolonged light illumination. Yet the photocorrosion can be suppressed in the presence of sacrificial reagents. Many metal sulfide photocatalysts have been successful for H2 evolution in the presence of sacrificial reagents as demonstrated in Table 1. For instance, CdS is one of the most popular photocatalysts, 4 because of its appropriate band gap (2.4eV) and electronic structures (e.g. the conduction band is 0.9 eV in reference to NHE at PH=7, the valence band is +1.5 eV in reference to NHE at PH=7) Different photocatalysts led to dramatically different QYs for different systems (Table 1) In addition, it is actually challenging to quantitatively compare the H2 production efficiency and productivity due to the lack of a common measure or indicator. So, H2 productivity expressed with different units (i.e. mmol/h, mmol/mg/h, and mmol/m/h) were proposed and calculated in Table 1. Due to the availability of data or experimental details in the reference articles, we were able to obtain some of the H2 productivity quantities, which appeared to vary significantly with photocatalytic systems. Yan et al. reported that a quantum yield of 93% at 420 nm using the Pt PdS/CdS photocatalyst in the presence of the sacrificial reagent of Na2S and Na2SO3 which is the highest photocatalytic activity so far. Accordingly, its H2 productivity seems to be the highest. However, Graphene CdS and CdSeZnS/Zr/Ti/phosphate, if evaluated by the H2 production rate per unit photocatalyst mass, would apparently yield much greater H2 than Pt PdS/CdS. Thus, it is important develop holistic evaluation methods to access the H2 productivity for different photocatalytic systems. 2. Water splitting for H2 production using composite photocatalysts Clearly, efficient photocatalytic water splitting systems require stable photocatalysts that have photocatalytic activity with repeated consecutive use. Most recently, many efforts have focused on the design of novel semiconductor materials and the optimization of chemical composition and microstructures to increase the photostability and quantum yield. For example, multicomponent sulfides, such as ZnIn2S4, 6 and (CuAg)xIn2xZn2(1 2x)S2 7, 8 have been studied as a new class of visible light driven photocatalysts for water splitting and H2 production. Zhang et al. recently developed a visible light responsive photocatalyst (Ru/(CuAg)0.15In0.3Zn1.4S2) and successfully achieved H2 evolution in the presence of KI as the sacrificial reagent. The study also examined the kinetics of photocatalytic generation of H2, stability and reusability of the catalyst over multiple cycles of H2 production and catalyst regeneration, which is not commonly reported elsewhere. The examination of stability and longevity of photocatalytic H2 production is important and necessary to quantitatively compare the actual H2 productivity from different photocatalytic systems. The photocatalyst reported by Zhang et al was well crystallized particles (30 50 nm in diameter) with high photocatalytic activity and broad visible light absorbance (from 400 nm up to 650 nm) The highest H2 production rate was approximately 190 6.5 mmol*h at the initial pH of 4 Fig. 2. The number of journal articles on different popular visible light responsive photocatalysts published from 2007 to 2012. NSTI Nanotech 2013, www.nsti.org, ISBN 978 1 4822 0586 2 Vol. 3, 2013 585 and 0.2 M KI as electron donor. The highest QY (QY under the wavelength of 420+ 5 nm) was 4.6 0.3% Although this QY does not seem to be stunning and even lower than those of some similar catalysts, such as Pt/CdS (QY 24% and (CuAg)0.15In0.3Zn1.4S2 (QY 7% the catalyst exhibited relatively good colloidal stability and was able to capture a wide spectrum of the solar irradiation (400 650 nm) Most importantly, this article provided systematic investigations on the longevity of the photocatalyst with consecutive reaction cycles. The study monitored the particle size distribution and metal ion release during the photocatalytic H2 production, which help understand why the H2 production rate decreased from 190 to 120 mmol*h with over different reaction cycles. It was experimentally observed that the photocatalyst particles underwent pronounced aggregation, which led to the increase in particle size; and a significant release of metal ions was observed during H2 production, which led to a loss of the catalyst mass and potential changes in the photocatalytic activity. Consequently, these processes may result in the decrease of photocatalytic activity and stability. 3. Conclusion Solar water splitting for H2 production is important to obtain clean energy in the future. Nowadays, there are many photocatalysts have been developed, and the focus is largely on the novel material synthesis and improvement of photocatalytic activity. In the future, it is necessary to take the stability and reusability of photocatalysts into consideration. In addition, applications of photocatalyst materials made of earth abundant elements would be more attractive and critical for energy sustainability. Table 1. Comparison of hydrogen evolution with different visible light responsive photocatalysts Catalyst Light source QY H2 Productivity Ref. mmol/h mmol/mg/h mmol/m/h Pt/CdS/TiO2 N.A. 20 54 0.68 N.A. 1 Pt PdS/CdS =420 nm 93 8770 29.23 N.A. 2 Pt/[In(OH)ySz]:Zn =420 nm 0.59 67 0.22 N.A. 12 PPy/CdS =430 nm N.A. 110 0.73 N.A. 13 Graphene CdS 420 nm 22.5 1120 556 N.A. 14 CdSeZnS/Zr/Ti/phosphate 420 nm 9.6 714 35.71 N.A. 15 CdS/TiO2 420 nm 43.4 402 N.A. N.A. 16 (Cd0.8Zn0.2)S =420 nm N.A. 302 3.02 N.A. 17
author_names: Yongsheng Chen

John C Crittenden

J Huang

Daisuke Minakata

Peng Wang

Guangshan Zhang

Wen Zhang
title: Water Splitting for H2 Production using Visible light responsive Photocatalysts
year: 2013

abstract: The photoassisted catalytic reaction, conventionally known as photocatalysis, is expanding into the field of energy and environmental applications. It is widely known that the discovery of TiO2 assisted photochemical reactions has led to several unique applications, such as degradation of pollutants in water and air, hydrogen production through water splitting, fuel conversion, cancer treatment, antibacterial activity, self cleaning glasses, and concrete. These multifaceted applications of this phenomenon can be enriched and expanded further if this process is equipped with more tools and functions. The term "photoassisted" catalytic reactions clearly emphasizes that photons are required to activate the catalyst; this can be transcended even into the dark if electrons are stored in the material for the later use to continue the catalytic reactions in the absence of light. This can be achieved by equipping the photocatalyst with an electron storage material to overcome current limitations in photoassisted catalytic reactions. In this context, this article sheds lights on the materials and mechanisms of photocatalytic reactions under light and dark conditions. The manifestation of such systems could be an unparalleled technology in the near future that could influence all spheres of the catalytic sciences.
author_names: Mohan Sakar

Chinh-Chien Nguyen

Manh-Hiep Vu

Trong-On Do
title: Materials and Mechanisms of Photo Assisted Chemical Reactions under Light and Dark Conditions: Can Day Night Photocatalysis Be Achieved?
venue: ChemSusChem
year: 2018

abstract: The photo assisted catalytic reaction, conventionally known as photocatalysis, is blooming into the field of energy and environmental applications. It is widely known that the discovery of TiO2 assited photochemical reactions has led to achieve several unique applications such as degradation of pollutants in water and air, hydrogen production through water splitting, fuel conversion, cancer treatment, anti bacterial activity, self cleaning glasses and concrete, etc. These multifaceted applications of this phenomenon can be enriched and expanded further if this process is equipped with more tools and functions. The term 'photo' assisted catalytic reactions clearly emphasizes that the photons are required to activate the catalyst, where this can be transcended even into dark if the electrons are stored in the material for the later use to continue the catalytic reactions in the absence of light. This can be achieved by equipping the photocatalyst with a so called electron storage material as to break the present limitations in 'photo' assisted catalytic reactions. In this context, this perspective article sheds lights on the materials and mechanism of the materials that perform photocatalytic reactions under light and dark conditions. The manifestation of such material systems could be an unparalleled technology in near future that would possibly make foot prints in all the sphere of the catalytic sciences.
author_names: Chinh-Chien Nguyen

Manh-Hiep Vu

Trong-On Do
title: A Perspective Review on the Materials and Mechanisms of Photo Assisted Chemical Reactions under Light and Dark: Can it be called as Day Night Photocatalysis?

abstract: Abstract The production of H2 via photocatalytic water splitting reaction has attracted a great attention as a clean and renewable energy for next generation. Despite tremendous efforts, the present challenge for materials scientist is to develop highly active photo catalysts for splitting of water at low cost. This article reports the synthesis of TiO2 reduced graphene oxide hybrid nanomaterials through ionothermal method using functionalized ionic liquid for the enhanced hydrogen generation via water splitting reaction. The structural and morphological properties of the samples were investigated by XRD, Raman spectroscopy, TG DTA, UV vis spectroscopy and TEM. A substantial increase of H2 evolution was observed for TiO2 reduced graphene oxide hybrid nanomaterials. This is due to the high migration efficiency of photo induced electrons and the inhibition of charge carrier recombination due to the electronic interaction between TiO2 and reduced graphene oxide. i.e, reduced graphene oxide acts as an electron acceptor which effectively hinders the electron hole pair recombination of TiO2.
author_names: Ganganagappa Nagaraju

Krishnappa Manjunath

Sujoy Sarkar

E Gunter

Sergio Ribeiro Teixeira

Jairton Dupont
title: TiO2 RGO hybrid nanomaterials for enhanced water splitting reaction
year: 2015

abstract: The production of chemical fuels by using sunlight is an attractive and sustainable solution to the global energy and environmental problems. Photocatalytic water splitting is a promising route to capture, convert, and store solar energy in the simplest chemical compound (H2) [1] Since the initial report of a photoelectrochemical cell using Pt TiO2 electrodes for hydrogen evolution by Fujishima and Honda in 1972, considerable studies have been focused on the development of highly efficient and stable photocatalyst powder systems, and especially on using earth abundant semiconductors and co factors for water splitting. In practice, the achievement of the conversion of solar energy into hydrogen necessitates the spatial integration of semiconductors and co catalysts to form surface junctions, so as to optimize the capture of light and to promote charge separation and surface catalytic kinetics. The construction of effective surface junctions is therefore of vital importance, and not only strongly depends on the properties, such as crystal structure, band structure, and electron affinity, of both semiconductors and catalysts but also on the interface between the two materials. In photocatalysis, an ohmic contact between photocatalysts and cocatalysts can allow the prompt migration of light induced charge, thus resulting in an efficient photocatalytic reaction. Recently, we found that graphitic carbon nitride (g CN) a polymeric melon semiconductor with a layered structure analogous to graphite, meets the essential requirements as a sustainable solar energy transducer for water redox catalysis; these requirements include being abundant, highly stable, and responsive to visible light. g CN is indeed a new type of visible light photocatalyst that contains no metals, and has a suitable electronic structure (Eg 2.7 eV, conduction band at 0.8 V and valence band at 1.9 V vs. RHE) covering the water splitting potentials. An improvement in the efficiency of H2 production has been demonstrated by the introduction of nanohierarchical structures into g CN. It is noted that, like many other photocatalysts, g CN alone shows very poor electrocatalytic activities for water splitting and relies on surface co catalysts to activate its photocatalytic functions. The co catalyst cooperates with the light harvester to facilitate the charge separation and increases the lifetime of the photogenerated electron/hole pair, while lowering activation barriers for H2 or O2 evolution. Thus, the use of a co catalyst leads to an increase in overall photocatalytic performance, including activity, selectivity, and stability. Generally, the efficiency of a given photocatalytic system is dependent on the ability of the co catalysts to support reductive and/or oxidative catalysis. In particular, the structural characteristics and intrinsic catalytic properties of a co catalyst are important. However, the study of the structural and electronic compatibility between g CN and co catalysts has been limited so far. The co catalysts used are mainly platinum group metals or their oxides, which are scarce and expensive. Photocatalytic/catalytic systems based on abundantly available materials are certainly desirable for large scale hydrogen production for future energy production based on water and sunlight. Among various hydrogen evolution reaction (HER) catalysts, molybdenum sulfur complexes have received a lot of attention. MoS2 was found to be a good electrocatalyst for H2 evolution, and the HER activity stemmed from the sulfur edges of the MoS2 crystal layers. [10] When grown on graphene sheets, nanostructured MoS2 exhibited excellent HER activity owing to the high exposure of the edges and the strong electronic coupling to the underlying planar support. Incomplete cubane [Mo3S4] clusters and amorphous MoS2 are also proven HER catalysts. Some of these HER catalysts have been used in photocatalytic H2 production and they exhibited a remarkable promoting effect. MoS2 has a similar structure to graphite; it has a layered crystal structure consisting of S Mo S "sandwiches" held together by van der Waals force. The fact that g CN and MoS2 have analogous layered structures should minimize the lattice mismatch and facilitate the planar growth of MoS2 slabs over the g CN surface, thus constructing an organic inorganic hybrid with graphene like thin layered heterojunctions (Scheme 1a) Such a distinct nanoscale structure has some advantages. It can increase the accessible area around the planar interface of the MoS2 and g CN layers and diminish the barriers for electron transport through the co catalyst, thus facilitating fast electron transfer across the interface by the electron tunneling effect. Also, thin layers can lessen the light blocking effect of the co catalyst, thus improving the light utilization by g CN. Importantly, the intrinsic band structures Y. Hou, J. Zhang, G. Zhang, Y. Zhu, Prof. X. Wang Research Institute of Photocatalysis, College of Chemistry and Chemical Engineering, Fuzhou University Fuzhou 350002 (China) E mail: xcwang@fzu.edu.cn
author_names: Yidong Hou

Anders B Laursen

Jinshui Zhang

Guigang Zhang

Yongsheng Zhu

Xinchen Wang

Soren Dahl

Ib Chorkendorff
title: Layered nanojunctions for hydrogen evolution catalysis.
venue: Angewandte Chemie
year: 2013