Natural Alginate as a Graphene Precursor and Template in the Synthesis of Nanoparticulate Ceria/Graphene Water Oxidation Photocatalysts

Visible-Light Photocatalysts and Their Perspectives for Building Photocatalytic Membrane Reactors for Various Liquid Phase Chemical Conversions

Photocatalytic organic synthesis/conversions and water treatment under visible light are a challenging task to use renewable energy in chemical transformations. In this review a brief overview on the mainly employed visible light photocatalysts and a discussion on the problems and advantages of Vis-light versus UV-light irradiation is reported. Visible light photocatalysts in the photocatalytic conversion of CO2, conversion of acetophenone to phenylethanol, hydrogenation of nitro compounds, oxidation of cyclohexane, synthesis of vanillin and phenol, as well as hydrogen production and water treatment are discussed. Some applications of these photocatalysts in photocatalytic membrane reactors (PMRs) for carrying out organic synthesis, conversion and/or degradation of organic pollutants are reported. The described cases show that PMRs represent a promising green technology that could shift on applications of industrial interest using visible light (from Sun) active photocatalysts.

A Mechanistic Approach on Oxygen Vacancy-Engineered CeO2 Nanosheets Concocts over an Oyster Shell Manifesting Robust Photocatalytic Activity toward Water Oxidation

Lethargic kinetics is the foremost bottleneck of the photocatalytic water oxidation reaction. Hence, in this respect, the CeO₂ coral reef made up of nanosheets is studied focusing on the oxygen vacancy that affects the water oxidation reaction. First, CeO₂ was prepared in an oyster shell/crucible with the presence/absence of urea by a simple calcination technique to tune the oxygen vacancy. More oxygen vacancy was detected in CeO₂ prepared from urea and oyster shell, which is evidenced from Raman and PL analyses. Further, the oyster shell-treated sample was found to be of nanosheet type with numerous pores as observed via TEM analysis. The theoretical approach was adopted to expose the role of oxygen vacancies and the fate of scavenging agents in the water oxidation mechanism. It was observed that an oxygen vacancy plays a vital role in minimizing the activation energy hump and opposes the reverse reaction. The apparent conversion efficiency of 7.1% is calculated for the oxygen evolution reaction. Oxygen vacancy, quantum confinement effect, and charge separation efficiency are mainly responsible for the better photocatalyzed water oxidation reaction and hydroxyl radical production. This investigation will help in providing valuable information toward designing cost-effective oxygen vacancy-oriented nanosheet systems and the importance of vacancy in the water-splitting reaction.

Quality Improvement of Few-Layers Defective Graphene from Biomass and Application for H2 Generation

Pyrolysis of filmogenic natural polymers gives rise to the formation of films of few-layers defective, undoped, and doped graphenes with low electrical conductivity (3000 to 5000 Ω/sq). For the sake of valorization of biomass wastes, it would be of interest to decrease the density of structural defects in order to increase the conductivity of the resulting few-layers graphene samples. In the present study, analytical and spectroscopic evidence is provided showing that by performing the pyrolysis at the optimal temperature (1100 °C), under a low percentage of H₂, a significant decrease in the density of defects related to the presence of residual oxygen can be achieved. This improvement in the quality of the resulting few-layers defective graphene is reflected in a decrease by a factor of about 3 or 5 for alginic acid and chitosan, respectively, of the electrical resistance. Under optimal conditions, few-layers defective graphene films with a resistance of 1000 Ω /sq were achieved. The electrode made of high-quality graphene prepared at 1100 °C under Ar/H₂ achieved a H₂ production of 3.62 µmol with a positive applied bias of 1.1 V under LED illumination for 16 h.

The mechanism of photocatalytic CO2 reduction by graphene-supported Cu2O probed by sacrificial electron donors

Cu₂O nanoparticles (5 nm) adsorbed on defective graphene (Cu₂O/G, 1.74 wt%) is an efficient photocatalyst for CO₂ methanation in the presence of electron donors.

Enhanced visible light harnessing and oxygen vacancy promoted N, S co-doped CeO2 nanoparticle: a challenging photocatalyst for Cr(vi) reduction

Enhanced photocatalytic activity of N-, S-doped ceria nanoparticles towards Cr(vi) reduction under visible light irradiation.

Direct preparation of high quality graphene on dielectric substrates

Recent advances in the field of the direct growth of graphene on dielectric substrates are described.

High catalytic activity of oriented 2.0.0 copper(I) oxide grown on graphene film

Metal oxide nanoparticles supported on graphene exhibit high catalytic activity for oxidation, reduction and coupling reactions. Here we show that pyrolysis at 900 °C under inert atmosphere of copper(II) nitrate embedded in chitosan films affords 1.1.1 facet-oriented copper nanoplatelets supported on few-layered graphene. Oriented (1.1.1) copper nanoplatelets on graphene undergo spontaneous oxidation to render oriented (2.0.0) copper(I) oxide nanoplatelets on few-layered graphene. These films containing oriented copper(I) oxide exhibit as catalyst turnover numbers that can be three orders of magnitude higher for the Ullmann-type coupling, dehydrogenative coupling of dimethylphenylsilane with n-butanol and C–N cross-coupling than those of analogous unoriented graphene-supported copper(I) oxide nanoplatelets.

Supported metal nanoparticles have been widely used as heterogeneous catalysts. Here, the authors report the synthesis of (1.1.1) copper on few layer graphene which oxidize to orientated (2.0.0) copper(I) oxide nanoplatelets which display high catalytic activity for a number of organic coupling reactions.

Graphene-Based Photocatalysts for Solar-Fuel Generation

The production of solar fuel through photocatalytic water splitting and CO2 reduction using photocatalysts has attracted considerable attention owing to the global energy shortage and growing environmental problems. During the past few years, many studies have demonstrated that graphene can markedly enhance the efficiency of photocatalysts for solar-fuel generation because of its unique 2D conjugated structure and electronic properties. Herein we summarize the recent advances in the application of graphene-based photocatalysts for solar-fuel production, including CO2 reduction to hydrocarbon fuel and water splitting to H2. A brief overview of the fundamental principles for splitting of water and reduction of CO2 is given. The different roles of graphene in these graphene-based photocatalysts for improving photocatalytic performance are discussed. Finally, the perspectives on the challenges and opportunities for future research in this promising area are also presented.

Graphene-based photocatalysts for oxygen evolution from water

Recent achievements of GR-based photocatalysts for oxygen evolution from water are summarized with perspectives on major challenges and opportunities.

Copper nanoparticles supported on doped graphenes as catalyst for the dehydrogenative coupling of silanes and alcohols

Copper nanoparticles (NPs) supported on a series of undoped and doped graphene materials (Gs) have been obtained by pyrolysis of alginate or chitosan biopolymers, modified or not with boric acid, containing Cu(2+) ions at 900 °C under inert atmosphere. The resulting Cu-G materials containing about 17 wt % Cu NPs (from 10 to 200 nm) exhibit high catalytic activity for the dehydrogenative coupling of silanes with alcohols. The optimal material consisting on Cu-(B)G is more efficient than Cu NPs on other carbon supports.