@article { ISI:000305419900012, title = {Gamma-Al2-xMxO3 +/- y (M = Ti4+ through Ga3+): potential pseudo-3D mesoporous materials with tunable acidity and electronic structure}, journal = {Journal of Materials Chemistry}, volume = {22}, number = {27}, year = {2012}, month = {APR}, pages = {13484-13493}, publisher = {ROYAL SOC CHEMISTRY}, type = {Article}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

A simple and highly efficient surfactant-free sol-gel process has been developed to obtain nanocrystalline mesoporous gamma-Al2O3 and metal ion incorporated mesoporous gamma-Al2O3 with general formula gamma-Al2-xMxO3 +/- y (where M = Ti4+ through Ga3+). Any one of the first row transition metal (TM) ions along with Ga3+ could be introduced into the gamma-Al2O3 framework in a direct one-pot synthesis process. The generality of the present synthesis recipe for metal ion incorporation in gamma-Al2O3 was demonstrated by preparation of an Al-Ga-M ternary oxide system with the metal ion composition of general formula Al9GaTM (TM = Ti4+ to Zn2+) and their characterization through various physicochemical and spectroscopic techniques. The mesoporous gamma-Al2-xMxO3 +/- y materials showed a BET surface area in the range of 200-400 m(2) g(-1) with a narrow pore size distribution. Wormhole mesoporosity makes the material pseudo-3D (p3D) with a small pore depth of few nm (\<10 nm). Metal ions in gamma-Al2O3 lead to changes in the acidity and electronic environment. XRD, TEM, and Al-27 MAS NMR studies demonstrate that the sol-gel process and the disordered mesoporous structure allow Ga and TM ions to be highly distributed and integrated in the gamma-Al2O3 framework. The efficacy of these materials in catalysis has been successfully evaluated for steam reforming of dimethylether: Ni, Cu and Zn containing Al9GaTM oxides showed high activity and stability. The smaller mesochannel depth (\<10 nm) and pseudo-3D characteristics that arise due to the wormhole-type disordered mesoporous framework of these alumina materials facilitate mass transport through them without any leaching of metal ions out of the lattice and pore blocking during the reaction, which makes them attractive in catalysis. This preparation method is versatile enough to be used for a reproducible synthesis of metal ion incorporated mesoporous gamma-Al2O3 by varying the metal content and their combinations, and it is expected that many other metal ions could be introduced into the lattice framework for a variety of applications by tuning acidity and electronic structure.

}, issn = {0959-9428}, doi = {10.1039/c2jm31184d}, author = {Mathew, Thomas and Sivaranjani, Kumarsrinivasan and Gnanakumar, Edwin S. and Yamada, Yusuke and Kobayashi, Tetsuhiko and Gopinath, Chinnakonda S.} } @article {47589, title = {Electronically integrated mesoporous Ag-TiO2 nanocomposite thin films for efficient solar hydrogen production in direct sunlight}, journal = {Energy Technology}, volume = {10}, year = {2021}, month = {AUG}, pages = {2100356}, type = {Article}, abstract = {

The synthesis of mesoporous TiO2 by a solution-based assembly process and Ag/TiO2 nanocomposites is provided. The efficacy of Ag/TiO2 nanocomposite as photocatalyst in thin-film form is demonstrated for solar hydrogen generation in sunlight. Integration of Ag with TiO2 dramatically enhanced the H-2 production: with 1 wt\% Ag on TiO2 (TiAg-1), the H-2 yield was observed to be 4.59 mmol h(-1) g(-1), which is 2.3 (30) times larger than 0.5 wt\% Ag on TiO2. TiAg-1 shows 4.3 times higher activity in film form compared with its powder counterpart. High photocatalytic efficiency is attributed to the surface plasmon resonance effect of Ag, electronic integration of Ag with TiO2, and subsequent valence band broadening, large distribution of Ag nanoparticles and abundant Ag-TiO2 Schottky junctions, and the later minimizes electron-hole recombination. Interparticle mesoporous network increases necking and the high surface area offers easy accessibility of the reactants to a large number of active sites.

}, keywords = {heterogeneous catalysis, heterojunctions, plasmon effect, Silver, solar energy conversion, Solar hydrogen}, issn = {2194-4288}, doi = {10.1002/ente.202100356}, author = {Mani, Sunesh S. and Rajendran, Sivaraj and Nalajala, Naresh and Mathew, Thomas and Gopinath, Chinnakonda S.} } @article {48980, title = {Facile one-pot synthesis of Cu x O/TiO2 photocatalysts by regulating Cu oxidation state for efficient solar H2 production}, journal = {ACS Applied Energy Materials }, volume = {7}, year = {2023}, month = {DEC }, pages = {104-116}, type = {Article}, abstract = {

Development of highly efficient CuxO/TiO2 photocatalysts by regulating the oxidation state of Cu exclusively in either single or mixed oxidation state(s) is desirable but difficult to achieve without employing any external reagents. The present work describes a one-pot synthesis strategy to obtain CuxO/TiO2 photocatalysts with Cu in +1 and/or +2 by using a suitable combination of ethylene diamine tetra acetic acid (EDTA) and ethylene diamine, carefully varying the Cu content, and heat treatment process. CuxO/TiO2 nanocomposite catalysts were characterized thoroughly by physicochemical methods. Textural analysis indicates a high dispersion of CuxO on porous TiO2 with p-n heterojunctions between them in CuxO/TiO2 catalysts. UV-visible spectral analysis suggests the presence of CuxO on TiO2 with significantly extended absorption from the UV to the visible region. X-ray photoelectron spectroscopy (XPS) analysis indicates a strong synergetic interaction between TiO2 and CuxO due to the comparable CB potential and p-n heterojunction at the interface among them. Photoelectrochemical studies demonstrate excellent charge-carrier separation efficiency, low charge-transfer resistance, and high double-layer capacitance with Cu2O/TiO2 photocatalysts. Photocatalytic efficacy of a CuxO/TiO2 nanocomposite in thin-film form has been demonstrated for solar hydrogen generation in sunlight. The incorporation of Cu+ in TiO2 largely improves the H-2 production, and all of the CuxO/TiO2 nanocomposites in thin-film form exhibited higher efficiency compared to their particulate/suspension counterpart. Among the composite catalysts, TiCu-1 in thin-film form, with Cu exclusively in +1 oxidation state, exhibited a high hydrogen production rate of 7.06 mmol/hg, which is 6 times higher than its suspension counterpart; also catalysts containing mixed Cu-oxidation states exhibited about 60-70\% activity as that of TiCu-1. The superior performance of Cu2O/TiO2 nanocomposites in thin-film form was due to their enhanced light harvesting ability, high mass transfer rate, and easy accessibility of the reactant species to the active sites.

}, keywords = {heterojunction, Photocatalysis, Solar hydrogen, thin film, titania}, issn = {2574-0962}, doi = {10.1021/acsaem.3c02272}, author = {Rajendran, Sivaraj and Mani, Sunesh S. and Nivedhitha, Thazhath R. and Asoka, Anantha Krishnan and Arun, Pushkaran S. and Mathew, Thomas and Gopinath, Chinnakonda S.} } @article {49419, title = {Bimetallic and plasmonic Ag and Cu integrated TiO2 thin films for enhanced solar hydrogen production in direct sunlight}, journal = {Energy Advances}, volume = {3}, year = {2024}, month = {APR}, pages = {829-840}, type = {Article}, abstract = {
Plasmonic metal nanoparticle-integrated mesoporous TiO2\ nanocomposites (Ag/TiO2, Cu/TiO2\ and Ag{\textendash}Cu/TiO2), prepared by a simple chemical reduction method, have been demonstrated to show superior activity in thin-film form for solar H2\ generation in sunlight. Integration of Ag + Cu on TiO2\ significantly enhances the solar H2\ production due to the combined SPR effect of both metal species and the possible synergistic interaction among Cu + Ag in Ag{\textendash}Cu/TiO2. TiAgCu-1 (0.75 wt\% Ag and 0.25 wt\% Cu on TiO2) showed the highest H2\ yield of 6.67 mmol h-1\ g-1\ and it is 43 times higher than that of bare TiO2. The thin-film form of TiAgCu-1 shows 5 times higher solar H2\ production than its powder counterpart. 1 wt\% of Ag or Cu on TiO2\ shows a H2\ yield of 4.6 or 2 mmol h-1\ g-1, respectively, which underscores the importance of combined or synergistic effects. The increase in solar H2\ generation in Ag{\textendash}Cu/TiO2\ is attributed to factors such as the SPR effect of Cu and Ag, and strong interaction between Ag and Cu. The high photocatalytic efficiency of the TiAgCu-1 thin film is attributed to the large dispersion of metallic species with relatively high Ag/Cu surface atomic ratio, enhanced light absorption, a heterogeneous distribution of Ag and Cu species, and high double layer capacitance. The inter particle mesoporous network increases the interfacial charge transfer and reduces the mass transfer limitations. The plausible photocatalytic reaction mechanism could involve the combination of direct electron transfer from metal (Cu/Ag) to TiO2\ as well as the significant field effect due to the Ag{\textendash}Cu alloy, which is expected to increase the electron excitation locally.
Plasmonic metal nanoparticle integrated mesoporous TiO2\ nanocomposites (Ag/TiO2, Cu/TiO2\ and Ag{\textendash}Cu/TiO2), prepared by a simple chemical reduction method, have been demonstrated to show superior activity in thin-film form for solar H2\ generation.

}, doi = {https://doi.org/10.1039/d4ya00056k}, author = {Mani, Sunesh S. and Rajendran, Sivaraj and Arun, Pushkaran S. and Vijaykumar, Aparna and Mathew, Thomas and Gopinath, Chinnakonda S.} } @article {49446, title = {Multifunctional NiO/Ti3+{\textendash}TiO2 for concurrent water reduction and glycerol oxidation to value added products by sunlight driven photocatalysis}, journal = {Journal of Materials Chemistry A}, year = {2024}, month = {SEP}, type = {Article}, abstract = {

The present work describes the synthesis of bifunctional-mesoporous-self-doped Ti3+\ containing NiO/TiO2\ photocatalysts for concurrent utilization of e-\ and h+\ to produce H2\ and value-added products (VAPs), respectively, from aqueous glycerol. UV-vis diffuse reflectance results and band gap analysis revealed an improved light absorption due to integration of Ni2+\ with Ti3+/TiO2. Various electrochemical, PL and TRPL spectral analyses demonstrate p{\textendash}n heterojunction formation between NiO and Ti3+{\textendash}TiO2, which enhances charge separation and helps in achieving improved activity. HRTEM analysis of NiO/Ti3+{\textendash}TiO2\ nanocomposites revealed that NiO is highly dispersed on TiO2\ with interfacial heterojunctions between them. XPS results demonstrate the partial reduction of Ti4+\ to Ti3+\ and Ni{\textendash}Ti synergetic interaction in NiO/TiO2\ to form NiO/Ti3+{\textendash}TiO2\ nanocomposites. EXAFS studies show that the Ni{\textendash}O bond distance is similar to that of NiTiO3\ suggesting electronic integration of components of the photocatalyst by forming a Ni2+{\textendash}O{\textendash}Ti3+/Ti4+\ lattice network. Ni2+/Ti3+{\textendash}TiO2\ nanocomposites as a bifunctional photocatalyst exhibited significantly enhanced activity in H2\ production and conversion of glycerol to VAPs, namely, glycolaldehyde, 1,3-dihydroxyacetone, and formic acid; formation of these products highlights not only oxidation, but also C{\textendash}C cleavage of glycerol. The NiO/Ti3+{\textendash}TiO2\ photocatalysts fabricated in thin film form displayed higher photocatalytic efficiency than their powder counterpart. Among NiO/Ti3+{\textendash}TiO2\ nanocomposites NiT-3 exhibits the highest H2\ yield at 15.62 mmol h-1\ g-1, which is 38 times higher than that of bare TiO2. The enhanced photocatalytic activity is ascribed to the high charge carrier density, the synergistic interaction between Ni2+\ and Ti3+{\textendash}TiO2, formation of a p{\textendash}n heterojunction at the interface between NiO and Ti3+{\textendash}TiO2\ and effective utilization of charge carriers for redox reactions.

}, doi = {https://doi.org/10.1039/D4TA06910B}, author = {Rajendran, Sivaraj and Saju, Simi and Mani, Sunesh S. and Asoka, Anantha Krishnan and Saha, Arindam and Arun, Pushkaran S. and Ghosh, Biplab and Mathew, Thomas and Gopinath, Chinnakonda S.} } @article {49440, title = {Review on the recent advances in the design and structure{\textendash}activity relationship of TiO2-based photocatalysts for solar hydrogen production}, journal = {Energy Advances}, volume = {3}, year = {2024}, month = {JUN}, type = {Article}, abstract = {

The major issues that determine the efficiency of photocatalyst composite materials for solar hydrogen production, with or without a sacrificial agent, are efficient visible light harvesting properties, efficient separation of charge carriers and their utilization of redox sites, and stability. Thus, significant efforts have been devoted in the past few decades to modify the above characteristics by integrating constituent components of composites using different approaches. In the present review, we aim to summarize the recent advances, predominantly, in the area of TiO2-based photocatalyst composites for solar hydrogen production. Firstly, we present the recent progress in material integration aspects by discussing the integration of TiO2 with different categories of materials, including noble/3d metals, metal oxides/sulphides/selenides, other low bandgap semiconductors, C-based materials, and dye sensitizers. Furthermore, we discuss how material integration helps in tailoring the electronic and optical properties for activity tuning in solar H2 production. Subsequently, critical changes in the physico-chemical and electronic properties of composites with respect to their preparation methods, morphology, crystallographic facets, particle size, dopant, calcination temperature, and structure{\textendash}activity relationship to solar hydrogen production are addressed in detail. Moreover, we discuss the importance of fabricating a photocatalyst in a thin film form and performing solar hydrogen production in different reactor set-ups for enhancing its photocatalytic performance, while addressing device scalability. Despite the significant advancements made in this field, solar-to-hydrogen conversion efficiency still needs to be improved to realise the practical application of solar hydrogen production. In this case, the direct conversion of water to hydrogen via overall water splitting and renewable H2 production from wastewater or biomass components by employing suitable photocatalysts are some possible ways to improve the energy efficiency, and continuous research in the above directions is highly desirable.

}, doi = {10.1039/D4YA00249K}, author = {Mani, Sunesh S. and Rajendran, Sivaraj and Mathew, Thomas and Gopinath, Chinnakonda} }