Current Organic Chemistry - Volume 19, Issue 6, 2015

Converting solar energy directly into chemical energy by means of artificial photosynthesis provides a flexible option for energy storage and transportation. The material’s structure and morphology, wisely tailored via a nanochemistry approach, could lead to desirable photocatalytic performances. The smallest dimension structures, one-dimensional nanostructures which could be utilized for efficient electrons and optical excitations transmit, are expected to play an important role in photocatalytic organic synthesis, a typical example of artificial photosynthesis. In this review, we describe current progresses in photocatalytic organic synthesis research, including photocatalytic selective oxidation of alcohols, nitroaromatic compounds reductions, and reduction of CO2 to renewable fuels, with centered on profits of one-dimensional morphology. The possible research directions are presented along with typical instances of some current advances in this area, which involves co-catalysts, light-absorbers as well as charge transport units of one-dimensional nanostructures.

Low-dimensional nanocarbon materials and metal/metal oxide (hydroxide) or semiconductors have been world-widely investigated due to their distinct physical and chemical properties for potential applications in environmental remediation. Three-dimensional (3D) hierarchical nanocomposites can be facilely constructed by using different low-dimensional nanomaterials as building blocks, thus leading to the full utilization or even synergistic effect of all the component materials with multifunctional properties. Herein, an overview is presented on the design and construction of hierarchically organized nanocomposites derived from low-dimensional nanocarbons (i.e. one-dimensional (1D) carbon nanotubes (CNTs), two-dimensional (2D) graphene, and 3D aerogels) and metal, metal oxide (hydroxide) or semiconductors (i.e. 0D nanoparticles (NPs), 1D nanorods, nanowires, nanotubes or nanofibers, 2D flakes), and their potential applications for efficient removal of organic pollutants through adsorption or catalytic reactions.

Research towards the establishment of photoelectrocatalytic oxidation of organics as an advanced oxidation method for the degradation of organic pollutants (sometimes coupled with the production of hydrogen or electric energy) is reviewed. Apart from the principles and the historical background of the method, special emphasis is given to its applicability under visible light illumination. To that direction, the photoanode materials that show visible light activity are reviewed. These can be classified as single component semiconductors, bi-component semiconductors and modified TiO2-materials. The latter include non-metal-doped (e.g. C-, N-, S-doped) as well as metal-decorated (e.g. Pt-, Au-, Ag-decorated) TiO2 oxide powders or nanotubes. Studies aimed at testing the activity of these materials towards model organic compounds oxidation as well as actual pollutants are presented. The potential of the method, especially for air treatment and for simultaneous energy and/or hydrogen production is emphasized.

Nowadays, the environmental pollutions are great threats to the health of humans and the sustainable development of the world. A wide variety of harmful organic pollutants are leading to the disruption of ecosystems as well as illness in the human body. The design and synthesis of cost-effective, reusable and efficient photocatalysts for organics degradation are highly desired. Biomass-inspiring method is a novel and effective strategy to obtain efficient photocatalysts with controlled morphology, unique structure, compositional utilization, and functional specificity. In this paper, a brief introduction of biomass-inspired functional photocatalysts is given first, followed by an explanation of the oxidation process of semiconductor photocatalysts for degradation of organics. Three typical type organic pollutants--dyes, phenols and volatile organic compounds as well as their degradation process are presented. Afterwards, we highlight the synthesis and applications of some representative biomass-inspired semiconductor photocatalysts derived from nature, ranging from nanoscale, microscale, mesoscale to marcoscale, by using biomolecules, microorganism, animals and plants as templates. Examples of the fabrication of active photocatalysts through self-doping biogenic elements (e.g., I, N, P, S,C) derived from biomass templates are also provided. At last, we point out some challenges for the large-scale commercial applications of biomass-inspired photocatalysts and summarize some advantageous prototypes derived from nature for future design of promising photocatalysts or photocatalystic systems.

This review is focused on studies related to the elimination of organic pollutants present in aqueous systems by titanium dioxide photocatalyst under visible light illumination. The titanium dioxide semi-conductor has emerged as a very promising technology for the oxidation and mineralization of aqueous organic pollutants because of its properties such as high stability, low cost and non-toxicity. This photocatalytic process has also been used for the oxidation of organic pollutants present in air and soil besides water, in addition to the production of electricity and hydrogen in photoelectrochemical cells fed with organic wastes which renders benefits to the environment. This work covers different approaches reported in the literature for the degradation of aqueous organic pollutants by heterogeneous titanium dioxide photocatalysis. With attention given to influencing parameters, such as catalyst preparation, modification, loading and phase, pH, annealing temperature, bias potential application and inorganic ions. Such parameters are paramount to the photoactivity of this semiconductor, particularly under visible light radiation; conditions of which are imperative for viable technological green application of the phenomena.

Ionic liquids are an environmentally friendly media and have been utilized in many research fields. Ionic liquids have many advantageous properties as follows: (1) Vapor pressure is extremely low for many ionic liquids; (2) Thermal and chemical stability are very high; (3) Excellent solubility in both inorganic and organic chemicals; (4) Polarity and phase behavior are changeable; (5) Excellent electrochemical properties; (6) Low melting point. Many ionic liquids are liquid at temperature as low as -60 °C. This property is useful to utilize in the cold climates; (7) Designable functional groups. Due to the excellent physical and chemical properties, ionic liquids can be utilized as novel and promising materials in renewable energy generation and energy storage processes. For example, ionic liquids can be utilized as novel electrolytes in solar cells, including dye-sensitized solar cells, quantum dotorganic solar cells, polymer solar cells, and thin films solar cells. Ionic liquids electrolytes have good thermal stability and high conductivity compared to conventional electrolytes. In addition, ionic liquids can be utilized in energy storage processes. Ionic liquids are excellent electrolytes for batteries, including Li-ion battery, Li battery, Li-oxygen battery, Li-air battery, Li-sulfur battery, Al-ion battery, Alair battery, Na secondary battery, and Na-ion batteries. Moreover, ionic liquids can be utilized as electrolyte additives in batteries, such as Li-ion battery and lead acid battery, to improve the efficiency of the original electrolytes. The recent development of utilizing ionic liquids as electrolytes in solar cells and batteries, as well as electrolyte additives in batteries, is introduced in this review.